Entire MnDOT Pavement Design Manual

MnDOT Pavement Design Manual, Jun 20, 2017

MNDOT PAVEMENT DESIGN MANUAL

Chapter 1 – Introduction

MnDOT Pavement Engineer Date


Contents Introduction ........................................................................................................................................................ 1

100 - Scope .......................................................................................................................................................... 2

110 - Process for Review and Acceptance ..................................................................................................... 3


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Introduction

This manual contains standards and guidelines used for pavement design and related subjects. A list of topics that are within the scope of this manual is shown in Section 100 - Scope.

This manual will be maintained by the MnDOT Pavement Design Unit (Office of Materials and Road Research) and will be available on the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/manual.html. The manual will be updated annually with additional updates as required.

Updates, revisions and additions to this manual will be made available for review prior to being signed and approved. The procedure for review and approval is contained in Section 110 – Process for Review and Acceptance.

Note: All references to “specifications” refer to the most current version of the MnDOT Standard Specifications for Construction.

http://www.dot.state.mn.us/materials/pvmtdesign/manual.html


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100 - Scope

The scope of this manual includes the following subjects:

1. Collection and evaluation of data that is required for the design of pavements.

2. Designing pavements and specifying materials, which includes the determination of thickness and types of materials for pavement surfacing, base, subbase, and any prepared soil.

3. Construction and materials requirements that are typically specified in the project’s Materials Design Recommendation (MDR). This includes such things as use of subsurface drains, use of geotextiles, PCC pavement joint design, and pavement specifications.

4. The pavement-type selection process, including the identification of alternate designs, the development of a life-cycle cost analysis (LCCA), and alternate bidding.

5. The process for developing a Materials Design Recommendation (MDR) and Pavement Design Memorandum (PDM).


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110 - Process for Review and Acceptance

1. Draft updates, revisions and additions will be distributed to the following entities for review and comment:

• All MnDOT Materials Engineer Organization (MEO) and Soils Engineer Organization (SEO) members.

• Any MnDOT Unit with expertise in the subject. • Pavement industry representatives, including: the Concrete Paving Association

of Minnesota (CPAM) and the Minnesota Asphalt Pavement Association (MAPA).

• The Minnesota Division office of the Federal Highway Administration (FHWA).

• Anyone who has stated a desire to be included in the reviewing process.

2. Comments will be addressed and changes will be considered.

3. The final draft must be approved by the FHWA before continuing to the final step.

4. The revised manual will be considered to be in effect when it has been signed by the MnDOT Pavement Engineer and placed on the MnDOT Pavement Design website.

MnDOT Pavement Design Manual, Aug 14, 2017

MNDOT PAVEMENT DESIGN MANUAL Chapter 2 – Investigation



Contents Introduction ........................................................................................................................... 1

200 – Falling-Weight Deflectometer (FWD) .................................................................... 2

210 - Friction Testing ........................................................................................................ 13

220 - Borings ...................................................................................................................... 14

230 - Cores .......................................................................................................................... 30

240 - Ground Penetrating Radar (GPR) ......................................................................... 32

250 - Traffic Data .............................................................................................................. 34

260 - Roadway Construction History ............................................................................. 36

270 - Visual Condition Assessment ................................................................................ 38

280 – Pavement Management System ............................................................................ 42

299 - Chapter 2 Appendix ................................................................................................ 51


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Introduction

This chapter contains standards and recommendations for performing an investigation to assess the condition of an existing roadway to determine the project design parameters.


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200 – Falling-Weight Deflectometer (FWD)

The falling-weight deflectometer (FWD) is a device used to evaluate pavement and pavement layer stiffness. It is a trailer-mounted (or truck-mounted) device that operates by dropping a weight on to the pavement and measuring the resulting pavement deflection at various points away from the load. Various computations may be performed on the deflection data to evaluate the pavement’s integrity, its overall stiffness, and the stiffness of its constituent layers. FWD may also be used to evaluate PCC joint load transfer.

MnDOT FWD sensor spacing and drop sequences are shown in the chapter appendix (Section 299.5 – FWD testing).

FWD testing, that is intended to be analyzed with the TONN2010 or ELMOD programs, is normally performed in the summer and early autumn months when the pavement is unaffected by frost or thaw-weakening. In the northern districts (D1, D2, D3, D4) testing is normally performed from June 1st to October 15th. In the southern districts (Metro, D6, D7, D8) testing is normally performed June 1st to November 1st.

Photo 200.1 – FWD in the process of testing.


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FWD testing of PCC joint load transfer is preferred to be performed in the fall with temperatures <70 °F. Testing should not be performed when there evidence of joint “locked-up.” Joint “lock-up” is when heat expansion of the pavement slabs cause the pavement joints to narrow to a degree that there is a high amount of aggregate interlock that isn’t always present.

Typically, MnDOT districts will be asked to file requests for FWD testing the winter before the testing season so that the operators can be most efficiently scheduled. However, testing may be requested at any time.

MnDOT districts may request FWD testing by sending a completed non-destructive testing request form to the Non-Destructive Testing Supervisor. The form and the Non-Destructive Testing Supervisor’s contact information are available on the FWD page of the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/fwd.html.

Several options are available to analyze FWD data depending on purpose. These options include:

• TONN2010 method (evaluation of HMA pavements) • ELMOD back-calculation(evaluation of HMA and PCC pavement layer moduli) • Load Transfer Efficiency (evaluation of PCC pavement joints)

Explanations of these analysis options and their use are contained in the following sections.

http://www.dot.state.mn.us/materials/pvmtdesign/fwd.html


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1. TONN2010 method (evaluation of HMA pavements)

TONN2010 is the product of research project “Allowable Axle Loads on Pavements” (Final Report #2011-02) performed by Peter Bly, Derek Tompkins, Lev Khazanovich of the University of Minnesota which was further refined in research project “Implementing TONN2010” (Final Report # 2014RIC16) by W. James Wilde of Minnesota State University, Mankato

TONN2010 is a program that, using falling-weight deflectometer data (FWD), calculates the load carrying capacity of HMA roadways and the moduli of the road’s HMA, aggregate base and subgrade layers. The TONN2010 analysis uses many the models and standards that MnPAVE-Flexible uses and is conceptually similar to MnPAVE-Flexible but backwards (i.e. MnPAVE-flexible is used to determine the pavement section necessary to carry a load and TONN2010 determines the load that a pavement section can carry).

After entering the necessary inputs and starting TONN2010, the analysis begins by determining the moduli of the constituent pavement layers. TONN2010 doesn’t perform a full back-calculation process to accomplish this but instead interpolates the moduli from previously performed back-calculation basins contained in the “backdefl.txt” file. Next TONN2010 adjusts the moduli of the HMA layer to reflect what it would be at a standard temperature of 72°F.

After the moduli are calculated and the HMA modulus is adjusted, the critical pavement responses (strains and deflections) are computed using the layered elastic program MnLAYER (Khazanovich and Wang 2010). The responses are computed for five seasons (with the pavement moduli adjusted to reflect the season). After the critical responses are determined for each season, the damage analysis is performed using the 20-year design ESALs. Damage analysis for TONN2010 involves: 1) AC fatigue cracking damage analysis; 2) subgrade rutting damage analysis, 3) base shear failure analysis, and 4) base deformation analysis. This analysis is very similar to how MnPAVE-Flexible analyzes pavement designs and it uses the same models.

TONN2010 reports the calculated moduli of each of the layers (with the HMA layer moduli adjusted to a standard 72°F), the subgrade R-value (which is calculated from the subgrade moduli), and TONN2010 load capacity in tons (which is based on whichever damage criteria that results in the lowest rating).


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A. Installing TONN2010

The TONN2010 program is available on the MnDOT Pavement Design website on the “Software” page located at the following link http://www.dot.state.mn.us/materials/pvmtdesign/software.html. This link contains an installation program that will create a “C:\TONN2010” directory and place the “backdefl.txt” and “tonn2020.dll” files in it. The TONN2010 Excel spreadsheet may be renamed, copied, or moved to any directory.

If the install program won’t run on your computer, follow the link to “install TONN2010 components manually” on the “Software” page of the MnDOT Pavement Design website. This will open a webpage that will provide directions and links to install the program manually.

B. FWD Data

The TONN2010 spreadsheet is made to process FWD data from Dynatest FWDs with 9 or 10 geophones. It is designed to read Access (.mdb) data files made by the FWD or Excel FWD data files that are made by the MnDOT pavement design unit from Dynatest FWD data files. The program will automatically convert Metric (SI) data into English units.

C. Analyzing FWD data with TONN2010

FWD data, from either an Access file or a MnDOT FWD Excel data file can be loaded into TONN2010 and analyzed. If FWD data is already loaded into TONN2010, it can be re-analyzed without having to reload the data.

(1) If not already done, install TON2010; follow the steps in the installation section.

(2) If the data has not already been loaded, then load the FWD data

- Click on the “Get FWD Data” and the “Get FWD Data Form” will appear. - Click on either “Load Access (mdb.) Data” or “Load ‘TONN’ Excel (.xls*) Data File.” - Navigate to the FWD data file with the browse form that will appear. Click open.

- A drop-down box will appear on the “‘get FWD Data Form”. With this drop-down,

select which of the FWD drops to use (FWDs collect data from several drops at each test location at different weights). The standard is to use the last drop that rounds to 9,000lbs (e.g., if drop 1 is 9,234, drop 2 is 9,456 and drop 3 is 12,056, select drop 2).

http://www.dot.state.mn.us/materials/pvmtdesign/software.html


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(3) Fill-in inputs

- Previous day’s max and min temp

The MnDOT Non-destructive Testing Supervisor normally fills this in before sending out the FWD Excel data file and so it should load with the FWD data. If it’s not present, use a weather website (such as Weather Underground) to look up the weather history for the day before the FWD testing occurred (the test date is given at the top of TONN2010). Input the previous day’s minimum and maximum temperature so that the average temperature may be calculated.

- HMA Thickness

Fill in cell A11 and the click on ‘fill’ box next to it to fill in the HMA thickness column (column E). The program actually reads the HMA thickness in column E where the HMA thickness for individual test locations may be edited. NOTE: TONN2010 can only analyze HMA thicknesses from 2 to 12 inches. HMA Thickness of less than 2 inches will not be read and the analysis will stop. HMA Thicknesses greater than 12 inches will be analyzes as 12 inches.

- Base Thickness

This is the material below what is considered HMA and above what is considered as subgrade. In general it should be the thickness of everything between the HMA and above the subgrade (see discussion section). Fill in cell A14 and the click on ‘fill’ box next to it to fill in the Base Thickness column (column H). The program actually reads the Base Thickness in column H where the thickness for individual test locations may be edited. NOTE: TONN2010 can only analyze base thicknesses from 3 to 48 inches. Base thicknesses less than 3 inches will not be read and the program will stop analyses. Base thicknesses greater than 48 inches will be analyzed as 48 inches.


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- Design ESALs The standard is to use the roads predicted 20-year accumulated flexible ESALs. Fill in cell A17 and the click on ‘fill’ box next to it to fill in the ESAL column (column I). The Design ESALs in Column I may be edited for individual test locations.

- County

Select the county where the FWD testing occurred from the drop-down box.

(4) Run TONN2010

Click on the “Run TONN2010” box. Calculation will stop and a message will appear if any required inputs are absent.

(5) Wait

Calculating takes 1-2 seconds per test location so it may take a while to calculate all the data. A message saying “Calculating TONN2010, Please wait” will appear during calculation which will disappear when calculation is completed.

(6) View results

Results are shown for each test location for the TONN2010 Capacity in Tons, the HMA moduli adjusted to 72°F, the base and subgrade moduli, and the subgrade moduli shown as R-value. The TONN2010 capacities 85th percentile (85% of readings are greater) value is normally reported as the final value. For all other values, the average is used. NOTE: An outlier criterion is used to highlight data that may be considered as an outlier. Since the TONN2010 rating is reported as the 85th percentile, this is useful to highlight unusually weak spots. Where the average is reported, the highlighted values should be deleted to prevent skewing the average.


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D. After the TONN2010 analysis has been completed.

(1) Make KML file. TONN2010 can produce a KML file of the results that may be viewed using Google Earth.

- Click on the “Make KML File” box. - A box will appear asking “value to plot” which is the value that will appear with the test

location on the finished map. Choose either the TONN Rating or the R-value then click “select and continue.”

- With the browse form that will appear, navigate to a location to save the KML file,

enter a file name, and click save. A file with the selected filename and the .kml extension will be written to the selected location.

- A message announcing that the KML file was “Successfully Converted” will appear.

Click ‘OK” to close the message. - The KML file can be introduced to Google Earth by either

• Open Google Earth and then find the KML file using the file menu. • Open Google Earth and then drag the KML file into the Google Earth window. • Right-click on the KML file and then choose “open with” and the select Google

Earth.

NOTE: Creating the KML file requires accurate GPS locations recorded during FWD testing. Any data points with missing coordinates cannot be mapped.

(2) Overlay Design. TONN2010 has the capability to estimate the thickness of a HMA overlay necessary for the roadway to be rated as a 10-ton road by TONN2010.

- Click on the “Begin Overlay Design” button. - The “Overlay Design” sheet will appear. - The user may choose the desired ton-rating and percentile of the roadway after

application of the overlay but MnDOT standard is a 10-tons at 85th percentile (i.e. 85% of the individual test points are equal to or greater than 10 tons).


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- The roadway may be split into up-to five segments. A separate overlay design will be

performed for each segment. Use the two charts to decide where to divide the roadway based on existing pavement strength, pavement layer thicknesses and ESALs.

- Click on the “Run Overlay Module”. - The estimated overlay thickness will be calculated and displayed. A calculated overlay

thickness of more than 5 inches will display only as “>5”.

(3) Estimate Number of ESALs for 10-ton Rating. If the TONN2010 analysis has been completed and the ESALs are the same for all locations, then TONN2010 can estimate the number of ESALs that could be used in the analysis to result in a 10-ton rating. This is referred to as an estimate because only two of the distresses that are used to calculate the ton-rating are sensitive to traffic, if the ton-rating of a location or locations is the result of a non-traffic sensitive distress then the calculation cannot be exact. Please, check the estimate by performing the TONN2010 analysis using the estimated ESALs.

- Click the “Estimate Number of ESALs for 10 ton Rating” button. - A reminder about the need to have the TONN2010 analysis completed and ESALs the

same for all points will appear. Click ‘OK’ to continue. - Wait for TONN2010 to calculate. - The calculated estimate will appear in as a message box. Click ‘OK’ to close the box. - Check the estimate by entering it as the number of design ESALs and clicking the

“RUN TONN2010” Button.


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E. TONN2010 Discussion

This program can only analyze a 3-layer pavement with HMA, base, and subgrade. Judgment must be used to determine which layer an existing material should be attributed to. A general rule would be to include bound materials with HMA, any aggregate base (e.g. CL 5, CL 5Q, or CL 6) and sub-base (e.g. CL 3, CL 4, Select Granular Material, and Granular Material) with base, and the material that the R-value should represent with subgrade.

The procedure that determines the layer moduli is dependent on having accurate thickness data. It is especially sensitive to the HMA thickness and it should be within an inch or two of the actual thickness. It is much less sensitive to inaccuracies in the base thickness but it should still be accurate to within a few inches.

The program can only analyze 20 different segments. A new pavement segment occurs anytime there is a change in HMA thickness, base thickness, or design ESALs. If there are more than 20 an error will be reported and the analysis will stop.

This program performs a process to calculate layer moduli that is similar to back-calculation and has some of its properties and limitations.

• Subgrade moduli are the most stable values of the calculated moduli and least sensitive to inputs.

• HMA moduli are the second most stable values. If the program has accurate thickness

values and the FWD was able to collect accurate data then this value should be also be accurate. HMA moduli are sensitive to having accurate HMA thickness and may be affected by pavement that is difficult for the FWD to collect good data from (e.g. cracked, material problems).

• Base is the least stable of the layers and the hardest to determine the moduli. This layer is

sandwiched between two other layers and tends to “take-up the slack” of the calculation of their moduli. This layer’s moduli often have a very high standard deviation and the calculated moduli may be affected by a portion of the moduli of an adjacent layer being attributed to it. Values tend to be more stable with newer HMA and accurate layer thicknesses.


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2. ELMOD back-calculation (analysis of HMA and PCC pavement)

ELMOD is a commercially available FWD back-calculation program designed to calculate the elastic moduli of pavement layers from FWD pavement deflection data. The MnDOT Pavement Design Unit (Office of Materials and Road Research) has licensed copies of this program and can perform the analysis if requested. It may be used to analyze deflection data collected from HMA or PCC pavements. But it isn’t recommended to design pavements using soil moduli derived from testing PCC pavements because the back-calculated moduli are often much greater than the actual moduli.

MnDOT Pavement Design Unit personnel will perform FWD testing required for ELMOD back-calculation. Tests are usually taken every 1/10 of a mile in the outside wheel path (the same as used for the TONN method). Additionally, any data that has been previously collected for the TONN method can usually be analyzed with ELMOD.

ELMOD requires accurate information on the number and thickness of the layers in the pavement section which must be provided by the analysis requester. The ELMOD analysis will be performed by MnDOT Pavement Design Unit personnel and the results will be e-mailed to the requester as an Excel spreadsheet.

3. Load Transfer Efficiency (evaluation of PCC pavement joints) Load transfer efficiency (LTE) is the measure of how well a load is distributed across a PCC joint or crack. It is provided by a combination of the pavement’s base, aggregate interlock, and any dowel bars. It is an important property of PCC pavements because poor load transfer creates high slab stresses, which contributes to faulting, pumping, and corner breaks. LTE is measured by dropping the FWD weight on one side of a joint (or crack), then recording the subsequent pavement deflections at the location of the weight’s impact and on the un-loaded side of the joint (see Figure 200.3). The ratio of the unloaded slab’s deflection to the loaded slab’s deflection multiplied by 100 is reported as the load transfer efficiency (LTE). Table 200.3, based on AASHTO guidance, is used to categorize LTE results. Care should be taken when applying this table to pavements with relatively small deflections; it may classify pavements as having “Poor” LTE, but the joints may have low differential deflections and may perform well. The data collected for LTE analysis may also be analyzed to detect potential voids under the PCC.

Table 200.3 – LTE Categories LTE Condition

70% or greater Good 50% to 70% Marginal

Less than 50% Poor


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MnDOT Pavement Design Unit (Office of Materials and Road Research) personnel will perform the FWD testing required to calculate LTE. The standard testing frequency is to test a minimum of 10 joints per mile and a minimum of 30 joints per project (unless a different frequency or the testing of cracks is requested). The standard test location is to load the leave-slab at the outside wheel path. MnDOT Pavement Design Unit personnel will perform the LTE analysis, and the pavement deflections and the calculated LTE will be e-mailed to the requester as an Excel spreadsheet.

Loaded Slab Deflection

# 1

Slab position prior to loading

Slab position with load applied

FWD Load Deflection Sensor Slab position prior to

loading

# 10

Slab position with load applied

Deflection Sensor

Unloaded Slab Deflection

Direction of Traffic

Figure 200.3 – Diagram of LTE testing.

Leave Slab

Approach Slab


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210 - Friction Testing

The MnDOT Office of Materials and Road Research operates one Dynatest pavement friction tester. This device indicates pavement friction by measuring the force that prevents a non-turning (i.e. locked-up) tire from sliding on the pavement’s surface. This is an important parameter because inadequate friction may lead to more occurrences of skid-related accidents. It may also be an important parameter when evaluating materials and construction practices. The Pavement Friction Tester is a two-wheeled trailer towed by a pick-up truck. It conforms to ASTM E-274 “Standard Test Method for Skid Resistance of Paved Surfaces Using a Full-Scale Tire” specifications. MnDOT’s pavement friction tester has one smooth tire and one ribbed tire and can perform testing with either one. Ribbed tires are considered to be less sensitive to pavement macrotexture and water film depth than smooth tires and to be more sensitive to pavement microtexture. During testing, the device is driven at a constant speed of 40 mph. When a test is taken, pumps are activated that spray water in front of the test wheel. The brakes on the test wheel are then activated and the horizontal and vertical forces acting on the wheel are measured. This data is used to calculate the Friction Number (FN). Friction testing may be performed whenever pavement temperatures are warm enough that the water sprayed during testing won’t freeze and become a hazard. MnDOT districts may request friction testing by sending a completed non-destructive testing request form to the MnDOT Non-Destructive Testing Supervisor. The form and the Non-Destructive Testing Supervisor’s contact information are available on the friction page of the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/friction.html.

The test results will be e-mailed to the requester. Contact the MnDOT Pavement Design Unit (Office of Materials and Road Research) to discuss the results.

http://www.dot.state.mn.us/materials/pvmtdesign/friction.html


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220 - Borings

Borings are taken for foundation surveys, to evaluate aggregate and borrow sources, and to survey the soils of the road alignment. Borings required for a foundation survey are usually performed by the MnDOT Foundation Unit (Office of Materials and Road Research) or consultant. Other borings are taken by district personnel or district-contracted consultants. District personnel typically limit their boring depths to less than 15 feet to avoid creating an “environmental well” which requires special licensing to fill.

1. Types of borings A. Undisturbed samples, defined as intact specimens of material that are minimally altered from

their in situ condition, are required to test for those properties that are controlled by the overall material mass, such as strength and permeability. Undisturbed soil samples and rock cores required for foundation design are usually obtained by the MnDOT Foundations Unit (Office of Materials and Road Research).

B. Disturbed samples (Auger Borings), defined as samples that are broken up and/or

remolded, that can be used for determining properties that are controlled by the individual components of the material such as the grain-size distribution and Atterberg limits. District or district-contracted consultants typically collect disturbed samples.

Disturbed samples are obtained using augers having a minimum diameter of 3.75 inches and in accordance with AASHTO T 203 – “Standard Specification for Soil Investigation and Sampling by Auger Borings.” The augers are rotated and advanced into the soil the desired distance. They are then withdrawn without rotating (i.e., pulled dead) from the hole and the soil is removed for examination and testing or samples may also simply be obtained from the auger cuttings.

2. Types of boring surveys A. Foundation survey

Data for the design of bridges, large culverts (i.e., culverts having a cross-section of more than 80 square feet), retaining walls, special roadway embankment designs on soft, compressible soils, and buildings are obtained from a Foundation Survey. Notify the MnDOT Foundations Unit (Office of Materials and Road Research) of the need to perform a Foundation Survey. The MnDOT Foundations Unit is responsible for scheduling these surveys and will provide all drilling and sampling, laboratory testing, and foundation recommendations. In addition, the


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MnDOT Foundations Unit will provide piezometer and/or slope inclinometer installations where detailed stability analyses need to be performed. The District Materials/Soils Engineer may be involved in reading the piezometers and slope inclinometers and performing other data gathering to assist the MnDOT Foundations Unit.

Small culverts, defined as those with a cross-section of less than 80 square feet in size, may be investigated by the district. A minimum of three borings should be planned on a section along the culvert alignment in these situations or as specified by the District Materials/Soils Engineer. The borings should be extended to provide field identification and groundwater information to at least 5 feet below the proposed culvert bottom.

B. Borrow source survey

Potential borrow sources should be explored by sufficient borings to determine the quantity and quality of borrow materials and the level of the ground water table. Borings should be extended 3 feet past the depth of planned excavation and spaced on a 100-foot grid pattern, or closer in the case of non-uniform deposits. Typically, disturbed samples are collected but the MnDOT Foundations Unit (Office of Materials and Road Research) may be contacted to obtain undisturbed samples if accurate shrink/swell factors are desired.

Field-identify the materials in each boring (see Section 220.5 – field-identification) on at least one sample from each major material in the survey area, perform a soils classification (see Section 220.3.A – soils classification), and if the material is granular, also perform a mechanical analysis (see Section 220.3.B – mechanical analysis).

C. Aggregate source survey

Proposed aggregate sources should be explored with a number of borings sufficient to determine the quantity and quality of aggregate available. Use an 8 to 12-inch diameter auger in order to have a sufficient diameter to retrieve a representative sample of the potential aggregate source material. These borings are usually spaced on a 100-foot grid pattern; although the grid should have closer spacing in erratic deposits and may be less frequent in uniform areas.

A representative sample of the granular material should be taken from each hole for each substantial change in the appearance of the material, along with at least one sample for each 10 feet of penetration. Field-identify all materials (see Section 220.5 – field-identification) and perform a mechanical analysis on each sample (see Section 220.3.B – mechanical analysis). Samples from auger-bored holes deeper than 40 feet are not considered reliable because of the disturbance and displacement of materials as they rise on the auger.


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D. Soils survey

A soils survey is the sampling and testing of subsurface soils to identify and characterize the existing soil, rock, groundwater, aggregate base/subbase, and pavement conditions. The soil sampling typically consists of disturbed borings (augers) and occasionally test-pits or hand augers.

The primary purpose of a soil survey is to discover subsurface materials and conditions that may affect construction or may negatively affect roadway performance and should be addressed in design. This includes discovering the limits of poor foundation soils (soils that contain peat, marl, >5% organic material by weight) or areas of wet conditions (any area where the soils are described as “wet” in the boring logs). These materials often require removal and replacement with a suitable material or constructing a drainage system. A soils survey will also help to identify any frost susceptible soils (silt) that may be addressed with the design thickness of the aggregate base, subbase, and engineered soil. Additionally, a soil survey will help establish the suitability of material for re-use as embankment and establish the stability of any slopes.

Borings should be deep enough to develop the engineering data required for analysis and should penetrate major soil horizons, frost depth, and frost-susceptible materials. Borings should be taken to a depth of at least 5 feet below the proposed bottom of subcut and at least 5 feet below existing ground in fill sections. At least one boring in each fill section should extend to a depth equal to the height of the proposed fill.

The extent of the soils survey and testing performed on the recovered material is dependent on the scope of the project. The following section describes the minimum boring intervals on a road alignment and the tests to be performed. However, additional borings may be required for slopes or to establish the limits of swamps or other areas of wet or poor foundation soils. Wet areas or poor foundation soils may be indicated by localized poor pavement performance, nearby standing water or vegetation associated with wet conditions (e.g. tamarack, cattails or rushes).

(1) New construction/reconstruction

Take auger borings approximately every 100 feet along the proposed alignment (the District Materials/Soils Engineer may extend the interval to 200 feet if the subsurface materials are uniform). On divided highways the borings on the two roadways may be staggered.

Field-identify the materials in each boring (see Section 220.5 – field-identification). Perform a soils classification (see Section 220.3.A – soil classification) on at least one sample from each major material encountered in the survey area and perform a mechanical analysis (see Section 220.3.B – mechanical analysis) on at least one sample of each major granular material per mile.


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The boring interval must be adjusted if the following conditions are encountered:

Bedrock. Boring intervals must be decreased and additional borings taken on a cross-section when there is evidence of bedrock. The number of borings required depends on the anticipated rock variability and length of cut. When there is evidence of bedrock above the proposed bottom of subcut, rock coring will be required. Requests for geological work, geophysical work, and/or rock coring should be made through the MnDOT Geology Unit (Office of Materials and Road Research), with copy to the MnDOT Foundations Unit (Office of Materials & Road Research). District-contracted consultants are required to perform this work as per contract. Swamp areas. These are areas of poor foundation soils and/or wet conditions that are often associated with a swamp or swampy areas. Boring intervals must be decreased and additional borings taken on a cross-section to determine the extent and composition of swamp areas. Poor foundation soils contain peat, marl, >5% organic material by weight, or other soils as directed by the District Materials/Soils Engineer. Wet conditions are any area where the soils are described as “wet” in the boring logs. A minimum of three borings are required for each cross-section when relatively uniform swamp bottoms are encountered. These borings are taken at the centerline and on each side of the roadway, typically, halfway between the shoulder P.I. and the toe of the slope. At least one boring should extend 15 feet below the apparent swamp bottom to provide adequate evidence against a false bottom. In swamp areas with variable non-uniform bottoms the boring strategy should be modified to include additional borings. In cases of widening existing embankments constructed on previously consolidated soft ground, attention to borings in proposed toe areas is advised to ensure that the widened embankment is not unstable. Resistance soundings, which consist of advancing the augers without sampling and recording the level where resistance is felt (assumed bottom of swamp), may be used to supplement boring information. District-contracted consultants are required to perform this work as per contract. Scheduling of work in swampy areas is important. It may be easier to access the site during winter months when the swampy area is frozen. If it is determined that soil boring of the swamp will result in injury to persons or damage to adjacent facilities, or if a floated embankment is desired, the MnDOT Foundations Unit (Office of Materials and Road Research) should be contacted to obtain undisturbed samples, install piezometers, and/or perform stability studies. Deep or side-hill cuts. Care should be taken in determining the soil and water conditions present whenever deep or side-hill cuts of ≥ 30 feet deep are proposed. In such areas, boring intervals must be reduced, and borings must be taken along the centerline as well as the edge of the roadway. Where general instability could create a problem, borings should


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be placed on sections perpendicular to the centerline on the uphill side of the cut. Where buildings or structures are located adjacent to the crest of slope, the MnDOT Foundations Unit (Office of Materials and Road Research) should be notified so that undisturbed sampling, piezometer installation, and/or stability studies can be performed.

(2) Full-depth reclamation (FDR), stabilized full-depth reclamation (SFDR), rubblization, and

crack and seat

Take an auger boring approximately every ½ mile. Field-identify (see Section 220.5 – field identification) the materials in each boring. Perform a soils classification (see Section 220.3.A – soils identification) on at least one sample from each major material in the survey area and perform a mechanical analysis (see Section 220.3.B – mechanical analysis) on at least one sample of each major granular material per mile. A larger auger diameter or removal of pavement sections may be necessary to recover samples of granular material that contain over-size material.

Subgrade corrections. Additional borings may be required to establish the limits of any identified subgrade corrections. Subgrade corrections are areas that are identified to correct specific unstable conditions in the subgrade of an existing road (e.g., frost heaves, subgrade failures, and settlements). A sufficient number of borings should be taken to determine the depth and limits of the area required for repair. At a minimum, one boring must be taken within the repair area to establish the depth and one boring from beyond each side of the repair to establish limits.

(3) HMA or PCC Overlays

Borings are only needed to establish the limits of any subgrade corrections (see the previous section, Section 220.2.D (2)).

3. Soil tests

The following section discusses many of the tests that can be performed by the district or the Office of Materials & Road Research on soil samples obtained for input into the design process. Reference is made to the Grading and Base Manual (http://www.dot.state.mn.us/materials/gbmanual.html) and/or MnDOT Lab Manual (,http://www.dot.state.mn.us/materials/labmanual.html) for detailed descriptions of the tests. All testing of undisturbed samples to determine engineering properties (including R-value) is performed by the MnDOT Office of Materials & Road Research.

A. Soil classification

Classify soil samples using the triaxial chart according to the MnDOT Grading and Base Manual Section 5-692.603.d and the MnDOT Lab Manual Section 1302 – Particle Size Analysis of Soil.

http://www.dot.state.mn.us/materials/gbmanual.html

http://www.dot.state.mn.us/materials/labmanual.html


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The AASHTO Soils Classification System (see Section 299.1 - AASHTO Soils Classification) and the Unified Soils Classification System (see Section 299.2 - Unified Soils Classification) are two other common classification systems. A correlation between these two classification systems with soil classification according to the triaxial chart is shown in Table 299.3.

B. Mechanical analysis

A mechanical analysis consists of a sieve analysis of a sample’s coarser portion and a hydrometer analysis of its fine-grained portion. This analysis is used to classify the soil and may determine the suitability of the soil for an engineering application. The method for performing sieve analysis is in the MnDOT Grading and Base Manual Section 5-692.215 and the MnDOT Lab Manual Section 1200. This test is based on AASHTO T 27. The procedure for performing the hydrometer test is in MnDOT Lab Manual Section 1302. This test is based on AASHTO T 88.


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C. R-value

The R-value (resistance value) test is a materials stiffness test. The R-value is calculated from the ratio of an applied vertical pressure to the developed lateral pressure and is a measure of the materials resistance to plastic flow. Values could range from 0 to 100, where 0 is the resistance of water and 100 is the resistance of steel. It is performed in the laboratory on material recovered from borings. Specific instruction on the method normally used by the MnDOT can be found in the MnDOT Lab Manual Section 1307. The R-value test is performed to define a soil’s stiffness for pavement design. R-values tests are often not performed because projects frequently have historical R-values or because R-values may be estimated with the FWD (see Section 200 – Falling-Weight Deflectometer (FWD)). However, if there are no historical R-value data and the FWD cannot be used (the FWD must perform tests on HMA for R-value testing) then the soil’s stiffness must be determined by R-value tests. The sampling rate for R-value testing varies according to soil type and is shown in Table 220.1.

Table 220.1 - R-value Sampling Frequency Guidelines Major Soil Texture*

Recommended Minimum Sampling Rate

Minimum Number of Total Samples

Sands 0 (assume a value of 70) ** 0** Clays, Clay Loams 1 every 2 miles 3

Sandy Loams (non-plastic to slightly

plastic) 3 per mile 5

Silt Loams 3 per mile 5 Silty Clay Loams 3 per mile 5

Sandy Loams (Plastic) 3 per mile 5 Sandy Clay Loams 3 per mile 5

* Major soil texture refers to a soil texture significant enough in areal extent to economically justify a change in pavement design.

** If the percentage passing the No. 200 (75 μm) sieve exceeds 15%, then sample and select a Design R-value in the same manner as for clay, clay loams. This means that a sufficient number of gradation checks of the sand areas will have to be made to determine if Stabilometer tests are required.

Note: Samples should be representative of the upper 5 feet of the proposed road grade as much as possible.


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D. Soil fertility

Soil fertility tests are run by the MnDOT Office of Materials & Road Research on soils to determine acceptability for topsoil and planting soil and which fertilizer to use. The types of tests run are gradation, pH and organic content, phosphorus, potassium and soluble salts. Use the following sampling rates

• Where the topsoil is to be removed and replaced to provide a growing medium, samples

should be taken at the rate of one per mile from the full depth of the topsoil to be removed. Additional samples are required if there is a major change in soil type.

• If the topsoil is not being replaced, samples should be taken from all horizons that will be exposed and provide a growing medium. In this case, the sampling rate must be one per mile.

E. Organic content

The organic content of a soil sample is determined by using AASHTO T 267. AASHTO T 194 must be used if the suitability of the soil for growth is desired.

F. Moisture

The moisture content of a soil sample is most commonly determined by either the oven or the calcium carbide gas pressure (speedy moisture) method. These methods are presented in the MnDOT Grading and Base Manual Section 5-692.250. They are based on AASHTO T 217 (speedy moisture) and T 265 (drying oven).

G. In situ strength

The in situ strength of aggregate or granular layers may be tested using a Dynamic Cone Penetrometer (DCP). This test is performed by dropping a standard weight to drive a pointed tip into the material being tested and counting the number of blows per inch of penetration. This test is frequently performed in a core hole. Specific instruction on the method used by MnDOT can be found in the MnDOT Grading and Base Manual Section 5-692.255.

H. Atterberg Limits

Atterberg Limits are used to determine the plasticity index (PI) of soil which is necessary to classify the soil. The plasticity index is determined according to the MnDOT Lab Manual Chapters 1303 and 1304.


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4. Sample sizes

Minimum sample size required for various tests are given in Table 220.2.

Table 220.2 - Required Sample Sizes. Test Size

Mechanical analysis of granular material 20-30 lb. Mechanical analysis for cohesive material 10 lb.

Mechanical analysis and moisture-density for cohesive material 25-30 lb.

Fertility 10 lb. R-value determination 60 lb.

pH for soil 1 lb. in clean plastic or glass container

5. Field identification

Identification of soil types in the field, which is typically limited to an estimate of texture, plasticity, and color, is normally done without the benefit of major equipment, supplies, or time. It is necessary for a general assessment of sites during field reconnaissance activities and during the initial phases of more detailed work, such as the investigation of an emergency remediation or a planned geotechnical or pavement survey. It may, in some instances, be the only effort ever expended towards identifying the encountered soils, but in most cases it will serve as an aid in assigning more detailed laboratory tests.

With increased experience, field personnel should become more competent and skilled in accurately classifying the encountered soils based solely on field techniques. Regardless of experience level, however, laboratory testing must be performed to validate and sharpen the field technician's ability. Perform soil field identification according to the following sections of the MnDOT Grading and Base Manual • Section 5-692.603.e – Field Determination of Texture • Section 5-692.603.f – Feel and Appearance of Soil Mass • Section 5-692.604 – Secondary Classifiers • Section 5-692.605 – Organic Soils


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6. Format for boring survey notes

Visual observations, the sequence of materials encountered in the borings, and the results of field tests must be carefully and accurately recorded. Most organizations use a paper or electronic "boring log," "record of subsurface exploration," or some similarly titled form for this purpose. MnDOT strongly recommends that each District Soils Engineer keep such data in a uniform, organized, and retrievable manner.

The record of each boring in the “boring log” should be capable of standing alone, complete with all of the following information, entered in the order given:

• Project identification and number • Boring location, typically by roadway station and offset left or right of centerline • Method of drilling and sampling (e.g., flight augers with grab samples) • Date of start and completion • Names of drill crew members • Surface elevation • Depth of materials encountered and description (see the MnDOT Geotechnical

Manual Section 5.4.2) at http://www.dot.state.mn.us/materials/geotmanual.html • Sample locations • Ground water information when encountered and at recorded times after drilling • Other pertinent information and/or general observations

The accuracy of the recorded information is important because it becomes the basis for subsequent design recommendations. For example, the level of silt seams may impact frost design, wet or saturated layers may impact dewatering or drainage requirements, and shear planes or other discontinuities may impact slope stability.

An example of a field log can be found in Figure 3-2 of the MnDOT Geotechnical Manual.

7. Abbreviations

Standard terms and abbreviations are desirable, both for saving time when describing soil samples and for ease of interpretation of field notes, profiles, etc., by others. The following terms and abbreviations (see Table 220.3) are approved by MnDOT for use in describing samples and preparing field notes.

http://www.dot.state.mn.us/materials/geotmanual.html


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Table 220.3 – Approved terms and abbreviations

Heading/Location Terms Abbv.

Trunk Highway ................................ TH Station ............................................ Sta Reference Point .............................. RP Offset .............................................. OS Left .................................................. LT Right ................................................ RT Centerline ....................................... C/L Plus ................................................. + Northbound .................................... NB Southbound .................................... SB Eastbound ....................................... EB Westbound ..................................... WB Feet ................................................. FT Tenths ............................................. Tenths kilometers ....................................... km meters ............................................. m millimeters ...................................... mm Months ........................................... Mo Matls Engr's Name .......................... MEngr Crew's Name ................................... Crew Individual Letters A thru Z. . (Upper Case) Numbers 0 thru 9 ............................ 0,1,2,3,4,5,6,7,8,9 Ramp ............................................... Ramp Loop ................................................ Loop Frontage Road ................................ FR Service Drive ................................... SrDr Source Name/Number .................... Srce Mainline .......................................... ML Shoulder.......................................... SHLD State Project No .............................. SP Control Section ............................... CS County Road ................................... CR County State Aid Highway .............. CSAH Soils Engr's Name ............................ SEngr Section ............................................ Sec Township ........................................ Twp Range .............................................. Rng Decimal Point .................................. . One-quarter .................................... 1/4 One-half .......................................... 1/2 Three-quarters ................................ 3/4 Plus/Minus ...................................... +/- Approximate ................................... Approx

Question Mark ................................ ? Inplace ............................................ Inp Surfacing Terms Concrete ......................................... CONC Bituminous ...................................... BIT Aggregate ....................................... AGG Bit Treated Base .............................. BTB


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Material Terms Gravel ............................................. G Sand ................................................ S Sand and Gravel .............................. S&G Loamy Sand..................................... LS Loamy Sand and Gravel .................. LS&G Sandy Loam..................................... SL Loam ............................................... L Silt ................................................... Si Silt Loam ......................................... SiL Silty Clay Loam ................................ SiCL Clay Loam ....................................... CL Sandy Clay Loam ............................. SCL Clay ................................................. C Silty Clay .......................................... SiC Sandy Clay ....................................... SC Boulder Terms Limestone ....................................... Lmst Sandstone ....................................... Sst Dolostone ....................................... Dolo Shale ............................................... Shale Boulder (over 3") ............................ Bldr Moisture Terms dry ................................................... dry damp ............................................... damp moist ............................................... moist wet .................................................. wet saturated ........................................ sat Color & Shade Terms black ................................................ blk brown ............................................. brn grey ................................................. gry yellow ............................................. yel tan ................................................... tan blue ................................................. blu white ............................................... wht green ............................................... grn red .................................................. red orange ............................................. orng dark ................................................. dk light ................................................. lt

Textural Terms Very Fine ......................................... VF Fine ................................................. F Coarse ............................................. Cr Plasticity Terms slightly plastic ................................. slpl nonplastic ....................................... nonpl plastic .............................................. pl highly plastic. ................................. hpl Consistency Terms Very soft ......................................... Vsoft soft .................................................. soft firm ................................................. firm stiff .................................................. stiff Very stiff ......................................... Vstiff hard ................................................ hard Very hard. ...................................... Vhard Compactness Terms Very loose ...................................... Vloose loose ............................................... loose medium dense ................................ meddense dense .............................................. dense Very dense ..................................... Vdense Water Condition Terms water level ...................................... H2O Flowing Artesian ............................ FlArt perched water ................................ perch Peat Classification Terms Peat ................................................. peat spongy ............................................ spongy fiberous peat .................................. fpeat semi fiberous peat .......................... sfpeat well decomposed peat ................... wdpeat partially decomposed peat ............. pdpeat


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Organic Content Terms non organic ..................................... nonorg slightly organic ................................ slorg organic ............................................ org highly organic ................................. horg Descriptors Deteriorated ................................... Det Stripped .......................................... Strpd Sound .............................................. Snd Unsound ......................................... UnSnd weathered ...................................... wx Bedrock ........................................... bedrock debris .............................................. debris chips ................................................ chips seams .............................................. seams layers .............................................. layers marbled .......................................... mrbl mottled .......................................... mtld fill .................................................... fill cut .................................................. cut fat ................................................... fat frozen .............................................. frzn ice lenses ........................................ icelns ice .................................................. ice topsoil ............................................. ts slope dressing ................................. sd wood ............................................... wood woody ............................................ woody roots ............................................... roots shells ............................................... shells Iron Oxide Stained .......................... IOS till .................................................... till

Miscellaneous with ................................................. w/ without ........................................... w/o variable ........................................... var natural ............................................ nat Not Applicable ................................ N/A and .................................................. & or .................................................... or to..................................................... to included .......................................... inc Gas Smell ........................................ GasSm Road Tar .......................................... RdTar sample ............................................ smpl Soil ID .............................................. SID R-value ............................................ RVal Gradation ........................................ Grad Fertility ............................................ Fert Extraction ........................................ Xtract at ..................................................... @ Time Of Drilling .............................. TOD hour ............................................... hr no return. ........................................ noret poor return ..................................... prret fluid ................................................ fluid REFUSAL ......................................... REFUSAL Equipment Auger Truck ..................................... AT Hand Auger ..................................... HA 50# Sounding Hammer ................... 50SH 20# Sounding Hammer ................... 20SH Portable Auger ................................ PA Dynamic Cone Penetrometer ......... DCP Other comments: - no periods - keep UPPER & lower case letters


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8. Soils profile or cross-section

A soils profile or cross-section will help to visualize the physical relationship between the existing soil or pavement conditions and the new roadway. This diagram is a profile or cross-section of the information obtained during the performed surveys. It should be drawn to scale, such as 1 inch equals 5 to 10 feet vertically and 1 inch equals 20 to 100 feet horizontally, depending on the detail and complexity of the project. The following information should be included:

• Project identification • Existing and proposed grades, and/or existing ground lines • Boring locations, including station and offset • Existing pavement and subgrade conditions, including interpreted stratigraphy • Ground water • Pertinent test results

A soils profile or cross-section must be submitted as part of the MDR on projects where there is significant soils work. For projects that do not typically require extensive soils information, such as overlays, a soils profile is not necessary.

Figure 220.1 is an example of a properly prepared soils profile.


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Figure 220.1 - Example soils profile


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9. Sealing or backfilling borings A. Environmental wells

All borings meeting the legal definition of an environmental well will be drilled and sealed in accordance with Minnesota Department of Health regulations. Boreholes conducted for a boring survey or to monitor groundwater that are 15 feet or more in depth meet the definition of an environmental well. Environmental wells will be bored and sealed only by personnel licensed and equipped to do so legally.

The MnDOT Foundations Unit (Office of Materials and Road Research) may be contacted regarding any questions concerning environmental wells.

B. Non-environmental wells All borings not meeting the definition of an “environmental well” shall be backfilled with the drill cuttings, on-site soils, or imported material, with a texture and permeability similar to materials encountered in the boreholes. Imported backfill materials shall have a lower permeability than material encountered. The borehole shall be completely filled from the bottom or cave-in depth to the original ground surface. Tamping or compacting the backfill material shall be performed as necessary to minimize voids or backfill subsidence. Backfilling must be performed after completion of the borehole.

Note: Borings must not be permitted in known or suspected contaminated areas regardless of boring depth or groundwater elevation. If contamination of any type is noted while drilling, work must be stopped and the next level supervisor contacted immediately for further instructions.


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230 - Cores

This section discusses pavement cores collected to evaluate existing pavement. Cores collected for construction inspection/acceptance are not within the scope of this manual.

1. PCC

Coring existing PCC pavement is most often performed when there are special concerns, such as poor pavement materials, to determine the nature and extent of cracking, or to determine the suitability of the existing PCC pavement for recycling as PCC aggregate. Generally, coring is not required for new/reconstruction or unbonded overlay projects.

PCC pavement cores may be taken on or off a crack or joint. A core taken off a crack or joint will provide the pavement thickness and may be used for materials analysis. A core taken on a joint or a crack may show joint or crack deterioration that is not visible from the surface and may be useful in determining a cause of PCC deterioration.

Contact the MnDOT Concrete Engineering Unit (Office of Materials and Road Research) to discuss the use and location of any PCC coring.

2. HMA

HMA pavement coring may be performed to establish the thickness of the pavement and its condition. The cores may be collected from locations off-cracks, to establish HMA pavement thickness and pavement condition, or on-cracks in the HMA pavement, to establish the depth and condition of the crack. In addition to coring, GPR testing (see Section 240 - GPR) may be performed to establish a continuous record of HMA pavement thickness.

A. Off-crack cores

Cores taken off-cracks in intact HMA pavement are necessary to establish the pavement thickness. This is important for pavement thickness design, FWD data analysis, GPR data analysis, and for calculating removal quantities. In addition to indicating pavement thickness, these cores can also show the general condition of the HMA, including the presence of stripped or debonded layers Collect these cores from the middle of the lane and try to be at least 6 feet away from any crack.


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B. On-crack cores

Cores taken on-cracks are used to establish the depth and condition of the crack. This may be useful to assess the overall pavement condition, establish the depth of milling, and the degree of pre-overlay repair.

Core possible top-down cracks (typically occurring in the wheel-path) to determine their depth. Milling depth may be adjusted to completely remove this distress. Other types of cracks may be cored to determine if milling will reveal hidden deterioration. Often HMA pavement cracks exhibit stripping and are wider near the bottom of the pavement. These cracks may need to be repaired after milling or they may possibly make the roadway a poor candidate for certain types of rehabilitation techniques.

Collect on-crack cores in the vicinity of off-crack cores so that they may be compared.

C. The minimum recommended coring interval and the recommended use of GPR for different project types is shown the following table.

Table 230.1 – Minimum HMA Pavement Coring Intervals & for Use of GPR

Off-crack Cores On-crack Cores GPR New/Reconstruction 1 per mile** 0 No

FDR/SFDR 1 per mile* 0 Yes

CIR 1 per mile* 1 per mile Yes

PCC Overlay 1 per mile* 1 per mile Yes

HMA Overlay 1 per mile 1 per mile No

* Increase coring to two per mile if no GPR data will be collected.

** Not necessary if there is sufficient data from boring logs to develop a HMA pavement removal quantity.


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240 - Ground Penetrating Radar (GPR)

GPR is a non-destructive testing tool used to map the subsurface conditions. GPR works by emitting radar waves from an antenna of a type and frequency that are able to penetrate the ground and into subsurface layers. They are reflected back and give indications when the waves encounter an interface of materials with differing electrical properties. GPR antennas may be either “air-launched” or “ground-coupled” depending on the application.

1. Types of antennas A. Air-launched antennas are mounted so that they do not come into contact with the ground.

They are typically on a vehicle and can collect data at highway speeds depending on the application. Typically, GPR can image to a depth of three to five feet depending on the frequency of the antenna being used and the properties of the materials but ambient electrical interference, the presence of water, or dense/highly conductive material will tend to obscure the image.

Although sampling density may be limited in high-speed data collection, these antennas work well for determining the thickness of pavement and (in most cases) aggregate base layers. The GPR data may also indicate stripping in the HMA pavement. They are less effective for imaging PCC pavements when PCC is installed over electrically similar base materials.

B. Ground-coupled antennas are operated on or very near the surface and are often dragged across the ground manually. Higher sampling density can be obtained due to the slower speed of the antenna over the surface. Ground-coupled antennas are normally used for locating subsurface objects. The depth and clarity of the image depends on the frequency of the antenna used and materials encountered. There are various antennas available with different frequencies that can image different depths and resolutions. Subsurface water and dense/highly conductive materials tend to obscure the imaging; however, ground-coupled antennas are much less susceptible to ambient noise. These antennae work well to determine layer thicknesses and interfaces, locate steel in PCC pavements and bridges, and locate buried structures or subsurface voids.

2. Use of GPR

It is recommended to use GPR to determine the HMA pavement thickness for full-depth reclamation (FDR), stabilized full-depth reclamation (SFDR), cold in-place recycling (CIR) and whitetopping projects (see Table 230.1). For these types of projects, the thickness of the existing pavement is critical and unlike coring, GPR images the pavement thickness continuously and can


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produce thickness data of the pavement (and potentially the base layer) as needed - up to the GPR’s maximum sampling density.

HMA cores are necessary to refine and improve the accuracy/precision (calibrate) of the interpreted GPR data. Provide the core locations to the GPR operators so that they can run the radar directly over those core locations. The GPR data will then be calibrated using those cores. If no cores were collected prior to GPR data collection, or more information is needed, collect cores from locations based on the GPR data, such as thin/thick sections or areas with unusual readings. The GPR operator and analyst should be provided with any pavement section data.

3. Collecting GPR Data

Contract a consultant to collect and analyze GPR data to determine pavement and/or base depth. Use the “Consultant GPR Scope of Work” document, located on the MnDOT Pavement Design website, to develop the scope of work when using a consultant.

The preparation of the scope is crucial and is dictated by the type of survey desired – depth(s) of target(s), size(s) of target(s). Shallow, highly-detailed surveys are required for smaller defects (cracks, voids) and these typically are best handled by a high-frequency, ground-coupled antenna.

When setting up the scope of services it is important to consider the type and level of detail required in the interpreted results. Data interpretation time is the main cost-driver in a consultant GPR contract. Carefully consider the needs for your specific project

If a consultant cannot be contracted because of time or some other constraint, the MnDOT Office of Materials and Road Research has the necessary equipment and is capable of performing the testing and analysis on a case-by-case basis.

The MnDOT Research Unit (Office of Materials and Road Research) has a variety of GPR antennas that may be useful to determine layer thicknesses & interfaces, locate steel in PCC pavement or indicate the location of buried structures. They may also be used to indicate the existence of subsurface voids or other anomalies. Contact the MnDOT Research Unit to discuss the feasibility of GPR testing for a particular application and to request testing.


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250 - Traffic Data

1. A signed traffic forecast is required for all projects that will construct more than ½ mile of pavement in the DL≥20 pavement design categories (see Chapter 7 – Pavement-type Selection for pavement design categories). To obtain a signed traffic forecast, contact the District Traffic Forecaster or the Office of Transportation System Management – Traffic Forecasting Section.

2. Projects that will construct less than a ½ mile of pavement in the DL>20 pavement design categories or that will construct pavement in the DL<20 pavement design categories (see Chapter 7) do not need a signed traffic forecast, but should have a traffic forecast developed using the most up-to-date copy of the “ESAL FORECASTING TOOL,” available on the pavement design website http://www.dot.state.mn.us/materials/pvmtdesign/software.html.

3. The following table summarizes the traffic data requirements:

Table 250.1 – Traffic Data Requirements

Pavement Design Category Length Traffic Data

DL≥20 > ½ mile Signed Forecast

DL≥20 < ½ mile Estimate with ESAL Forecasting Tool

DL<20 All Estimate with ESAL Forecasting Tool

4. The “ESAL FORECASTING TOOL” is an Excel spreadsheet that contains data collected from

Vehicle Classification (VC) sites on state roads in Minnesota. This historic data is used to estimate current traffic and future accumulated ESALs. To use the “ESAL FORECASTING TOOL” A. Click on the “enable” box on the orange bar if it appears near the top of the spreadsheet.

B. Enter the “Base Year” in cell B4.

C. Left-click on the orange “FIND SITES” button at the upper-right of the spreadsheet.

Clicking this button opens a form to select the appropriate VC site.



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D. Fill in the “ROUTE #” text button; do not include the route designation (e.g., MN, US, I).

E. Left-click on the down-arrow of the drop-down list. This will open a drop-down list of the available VC sites for the previously entered route #, and the reference points (RPs) of the limits that the data directly applies. Choose the VC site that most closely applies to the segment that the forecast is being performed for. A map of the VC sites is located on the “MAP” tab of the spreadsheet to aid in selecting VC sites.

F. Left-click on the “CLOSE FORM” button.

G. Use the average (design lane) ESALs or the (two-way) HCADT that appear in row 17 of the

spreadsheet. The AADT Growth Rate may be used to approximate the HCADT growth rate.


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260 - Roadway Construction History

Roadway Construction History includes the year, project number, limits, width, and depth of all pavement construction activities in a road’s history. This information is useful in evaluating the type and thickness of the pavement layers and their suitability for use with the proposed project. It is required data in all Pavement Design Memoranda (PDM) and Materials Design Recommendations (MDR) for pavement projects. The format for reporting is contained in the PDM and MDR templates. The following are suggested sources to get Roadway Construction History information.

1. The highway pavement management application (HPMA) includes past construction activities, pavement thickness, and project identification number (S.P.). Follow steps 1-9 but skip steps 7, 7A and 7B of Section 280.1 to view this data.

2. The construction project log contains an index of historic construction and maintenance of

mainline state roads. The construction history of each control section is indexed by district then county. It is available at http://www.dot.state.mn.us/roadway/data/const-projlog-bydistrict.html Clicking on a control section number will open up a webpage that contains construction and maintenance history for the entire control section. Note the year, project number, type, thickness, and remarks of activities that occurred within the project limits. Maintenance activities are not required to be included in the roadway construction history of the MDR/PDM.

3. View the historical project plans to confirm and supplement the data in the construction project log or the roadway history file. Historical project plans are available for viewing on the MnDOT electronic document management system (EDMS) at the following links*:

- internal

http://edms/cyberdocs/Libraries/Default_Library/Groups/MNDOT_USERS/frameset.asp

- external http://dotapp7.dot.state.mn.us/cyberdocs_guest/Libraries/Default_Library/Groups/GUESTS/frameset.asp

* Contact the district if the plans are not available on EDMS.

http://www.dot.state.mn.us/roadway/data/const-projlog-bydistrict.html



http://dotapp7.dot.state.mn.us/cyberdocs_guest/Libraries/Default_Library/Groups/GUESTS/frameset.asp

http://dotapp7.dot.state.mn.us/cyberdocs_guest/Libraries/Default_Library/Groups/GUESTS/frameset.asp


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Select “Road and Bridge Plans and Construction Contracts” from the left side of the page (see Figure 250.1). When the search form opens, enter a State Project No. and click on “Perform Search” near the top of the form. The search will show a list of files available for viewing. Any pop-up blocker may need to be disabled.

Click here to perform the search.

Figure 250.1 – The Internal EDMS Search Screen


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270 - Visual Condition Assessment

A visual condition assessment is an evaluation of the condition and distresses apparent at the pavement surface. It is an effective method of choosing which types of rehabilitation options are reasonable for a roadway and determining repair strategies. A visual condition assessment is required as part of the project’s MDR and PDM. The following tables list common distresses that may affect a project and should be included in the MDR/PDM. Additional information and standards are available in the Distress Identification Manual for the LTPP (4th Revised Edition), available at https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03031/03031.pdf

Table 270.1 HMA Pavements Distress Type Description

Fatigue Cracking (Alligator Cracking)

A series of interconnected cracks with a pattern that resembles an alligator’s skin or chicken wire. Typically, the result of fatigue failure caused by excessive loading or weak pavement structure. Generally, assumed to initiate at the bottom of the pavement.

Block Cracking Interconnected cracks with a rectangular pattern. Cracks range from 1’ to 10’ apart. Associated with aged pavements and “dry” HMA mixes.

Edge Cracking Cracks along the edge of a HMA pavement. Often the result of poor drainage and/or lack of support.

Longitudinal Cracking (wheel path)

Cracks predominately parallel to the road’s center-line and located in a wheel path. Typically, a load related distress that initiates at the pavement’s surface.

Longitudinal Cracking (non-wheel path)

Cracks predominately parallel to the road’s center-line and located outside the wheel paths. Generally, not a load related distress but may be caused by a lack of stability in the road structure.

Reflective Cracking Cracks in HMA overlays that are initiated by joints or cracks in the existing HMA or PCC pavement.

Transverse Cracking Cracks perpendicular to the road’s centerline. Typically, caused by temperature induced stresses. These cracks may degrade and ‘cup’ (i.e. the area around the crack depresses) which is a significant cause of pavement roughness.

Patch/Patch Deterioration

Area where the initial pavement has been replaced or additional material has been applied.

https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03031/03031.pdf

https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03031/03031.pdf


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Table 270.1 HMA Pavements (continued) Distress Type Description

Rutting A longitudinal depression of a wheel path. Rutting is a load induced distress caused by excessive loading or an insufficient or unstable pavement structure.

Shoving Longitudinal displacement of an area of the pavements surface. Generally seen in areas of braking or accelerating vehicles. Caused by unstable HMA pavement that may be the result of the HMA mix having too high asphalt content, too much fine aggregates, or too much smooth or rounded aggregates.

Bleeding Excess asphalt binder on the pavement surface. May be caused by too much binder used in the HMA mix, surface treatment, or tack coat.

Polished Aggregate Smooth, slippery surface caused by traffic wearing away the surface binder and polishing off the sharp edges of HMA’s coarse aggregate. Polishing is seen with soft aggregates.

Raveling Rough, pitted surface caused by the dislodging of aggregate and binder. May be caused by mix segregation, low mix density, stripping (i.e. removal of binder by moisture), and aging of the asphalt binder.

Lane-to-Shoulder Drop off

Settlement of the shoulder lower than the traveled lane.

Pumping Seeping or pumping of water and fine aggregate from beneath the pavement through pavement cracks. Caused by water collecting under the pavement through cracks or a high water table and unable to drain away.

Table 270.2 PCC Pavements Distress Type Description

Corner Breaks A crack from a transverse joint to a longitudinal joint (or edge of pavement) within half a slab’s length of a slab’s corner. Caused by load repetitions and exacerbated by slab loss of support, poor load transfer, and curling stresses.

Durability Cracking (‘D’ Cracking)

A series of closely spaced cracks parallel to a joint. Caused by aggregates with poor freeze-thaw properties.

Longitudinal Cracking Cracks parallel to the road’s centerline. May be caused by, late sawing of longitudinal joints, ground movements, or curling and traffic stresses.

Transverse Cracking Cracks perpendicular to the road’s centerline. At mid-slab, it is generally a load induced distress but closer to the joints it may indicate late sawing of the transverse joints.


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Table 270.2 PCC Pavements (continued) Distress Type Description

Joint Seal Damage Loss of the ability of a joint seal to keep water and incompressible material from entering a sealed joint.

Joint Spalling Cracking, breaking or chipping of the edge of a joint or crack. May be caused by, high traffic, misaligned dowel bars, poor PCC properties, or the joint was sawed too early.

Map Cracking/Scaling Map cracking is a series of hairline cracks in the very surface of the PCC pavement that may result in the loss of material from the pavement surface (scaling). May be caused by over-finishing or deicing chemicals but may also indicate alkali-silicate reaction (ASR).

Polished Aggregates Smooth, slippery surface caused by traffic wearing away the surface mortar and polishing off the sharp edges of the PCC’s coarse aggregate. Polishing is seen with soft aggregates.

Blowups Lifting and shattering of PCC pavement at a joint or crack. The result of insufficient room for the thermal expansion of the PCC pavement.

Faulting A difference in the height of adjacent PCC slabs at a joint or crack. Typically the approach slab (the slab where traffic approaches the joint) is higher than the leave slab. Faulting may be prevented/minimized by having good slab load transfer and stable, non-erodible support.

Punchouts (CRCP) Spalling, breaking-up, or faulting of an area of CRCP pavement that is enclosed by two transverse cracks, a longitudinal crack and the edge of pavement. Associated with too little steel reinforcement or corrosion of the steel reinforcement.

Lane-to-Shoulder Drop off/Separation

Difference in elevation of the shoulder and the outside of the PCC mainline or a widening of this joint. Usually caused by settling of the shoulder.

Patch/Patch Deterioration

Area where the initial pavement has been replaced or additional material has been applied.

Pumping Seeping or pumping of water and fine aggregate from beneath the pavement through pavement cracks. Caused by water collecting under the pavement through cracks or a high water table and unable to drain away.


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Table 270.3 Special Areas Distress Type Description

Frost Heaves/Boils Frost heaves are areas where the pavement has been pushed-up higher than the surrounding pavement by frost lenses during freezing temperatures. Frost boils are areas of pavement distress caused by trapped water in thawing pavement during melting temperatures. These areas are usually only apparent seasonally and will need to be reported by personnel familiar with the road’s condition in the winter, such as maintenance personnel.

Subgrade Failures They may often be identified as isolated areas of alligator cracking (HMA) or panels with crescent-shaped cracks (PCC) with a depression or deformation of the pavement’s surface.


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280 – Pavement Management System

The highway pavement management application (HPMA) is MnDOT’s pavement management system software, which contains a database of roadway properties, performance, and history. It also is used to analyze pavement performance and develop various funding scenarios based on pavement decision trees and performance prediction models. For more information and the availability of the program, contact the MnDOT Pavement Management Unit (Office of Materials and Road Research) or visit their website at http://www.dot.state.mn.us/materials/pvmtmgmt.html. Additional information about pavement distresses and how they are reported in the HPMA is contained in the MnDOT Distress Identification Manual. It is available at the following link https://www.dot.state.mn.us/materials/manuals/pvmtmgmt/Distress_Manual.pdf 1. The HPMA is often useful for designing pavements because it contains a description of the

present pavement, past construction, pavement performance indicators and pavement distresses. Much of this data is required to be included in MDRs and PDMs.

A means to view this data for a project can be found in HPMA by following these steps:

STEP 1. Open HPMA.

STEP 2. Left-click on “Section” (see Figure 280.1).

STEP 3. Left-click on “View Section Data” (see Figure 280.1).

STEP 4. Left-click on “View Data” (see Figure 280.1).

http://www.dot.state.mn.us/materials/pvmtmgmt.html

https://www.dot.state.mn.us/materials/manuals/pvmtmgmt/Distress_Manual.pdf


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Figure 280.1 – View of HPMA for steps 2, 3 & 4

Step 2 – Left-click here.



Note: View Type is “Table View”.


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STEP 5. Left-click on the appropriate road segment (see Figure 280.2).

STEP 6. View the roadway section by left-clicking on “Section Details” (see Figure 280.2); this brings up the “Section Data” screen.

STEP 7. In the “Section Data” screen, left-clicking on “Performance” (see Figure 280.3) will

display performance and distress data.

STEP 7A. Predicted future performance indicators of the current pavement and any selected rehabilitation may be viewed by left-clicking “Plot” in the index models area (see Figure 280.4).

STEP 7B. Predicted performance indicators of a future activity may be viewed by using the following steps (see Figure 280.5):

1. Checking the “Include future activity” check box 2. Choosing an activity 3. Selecting a year for the activity 4. Refreshing the graph display

STEP 8. In the “Section Data” screen, left-clicking on “History” (see Figure 280.3) will show

past construction activities and condition indexes.

STEP 9. In the “Section Data” screen, left-clicking on “View Data” (see Figure 280.3) will show past construction activities, pavement thickness, and project identification number (S.P.).

Step 5 – Left-click on appropriate road segment.

Step 6 – Left-click here to open “Section Data”.

Figure 280.2 – View of HPMA for steps 5 & 6


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Step 7 – Left-click here for performance and distress data.

Step 8– Left-click here for construction history and past performance.

Step 9– Left-click for past projects.

Figure 280.3 – View of “Section Data” screen for step 7, 8 & 9


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Figure 280.4 – View of “Section Performance Data” screen

Step7A– Left-click here to plot performance.

Pavement Distresses. Performance Indexes.


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Figure 280.5 – View of the “Index Performance” screen

Step7B-1 – Check this box.

Step7B-2 – Select an activity here.

Step7B-3 – Select a year for the activity to occur.

Step7B-4 – Left-click to refresh the graph display.


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2. HPMA reports the performance of the roadway using several indices which may be viewed by following steps 1-6 of Section 280.1 and as shown on figure 280.4. The following is a brief explanation of the indices that are required to be reported in MDRs and PDMs. A. IRI: International Roughness Index

IRI is a ride or roughness index that is calculated from the pavement profile (using a quarter-car mathematical model) that is reported in inches/mile. IRI is the index that is used in MnDOT ride specifications (specification 2399) to measure the ride of newly constructed pavements.

B. RQI: Ride Quality Index

The RQI is MnDOT’s ride or roughness index. It uses a 0.0 – 5.0 rating scale, the higher the value, the smoother the road. It is a conversion of IRI based on the perception of ride of a panel of volunteers.

Most new construction projects have an initial RQI slightly over 4.0. The minimum RQI value used in the HPMA decision model to trigger rehabilitation is 2.5. This does not mean the road is un-drivable at this level but rather that it has deteriorated to a point where most people feel it is uncomfortable to drive and it is in need of major rehabilitation.

The following table contains the descriptive names for RQI categories.

Table 280.1 - Ride Quality Index (RQI) Performance Categories

Descriptive Category RQI Range Very Good 5.0 – 4.1

Good 4.0 – 3.1 Fair 3.0 – 2.1 Poor 2.0 – 1.1

Very Poor 1.0 – 0.0

C. SR: Surface Rating

The SR is MnDOT’s crack and surface distress index. It uses a 0.0 – 4.0 rating scale with a SR of 4.0 representing a brand new road with no distresses. As the type, amount and severity of the various distresses increase, the SR decreases. The pavement distresses that make up the SR are determined by trained raters from the MnDOT Pavement Management Unit (Office of Materials and Road Research) using the criteria contained in the MnDOT Distress Identification Manual.


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D. PQI: The Pavement Quality Index

The PQI is MnDOT’s overall pavement condition index. It combines the RQI and SR to give an overall performance indicator and ranges from 0.0 to about 4.5.

𝑃𝑃𝑄𝑄𝐼𝐼 = �𝑅𝑅𝑄𝑄𝐼𝐼 ∗ 𝑆𝑆𝑅𝑅

3. Pavement distresses are included in the HPMA data. Pavement distresses are collected by the pavement management van and rated according to the MnDOT Distress Identification Manual. Pavement distress data may be viewed by following steps 1-6 of Section 280.1 and as shown on figure 280.4. The following tables give descriptions of the distresses and their abbreviations.

4.

Table 280.1 - HMA Pavement Distresses Name Abbreviation Description

Transverse Crack

TRAN Cracks predominantly perpendicular to the pavement centerline.

Longitudinal Crack

LONG Cracks predominantly parallel to the pavement centerline.

Multiple Cracking MULT

A pattern of cracks dividing the pavement into approximately rectangular blocks. The size of the blocks ranges from 6 inches to approximately 3 feet across. This type of distress normally covers the entire pavement surface.

Alligator Cracking ALLI

A series of interconnected cracks forming many-sided, sharp-angled pieces, six inches or less in size typically located in the wheel paths or where traffic loads are concentrated.

Rutting RUTS A longitudinal surface depression located in the wheel path. It may also have associated transverse displacement.

Raveling & Weathering RAVL

Wearing away of the pavement surface in hot mix asphalt concrete caused by the dislodging of aggregate particles and/or the loss of the asphalt binder. Raveling generally occurs in the wheel paths and weathering in the non-traffic areas.

Patching PTCH

A portion of the pavement surface, 1 foot or greater in width, and in either wheelpath. If the patch is full width of the lane being surveyed it must be less than 50 feet in length. If not, it is considered to be an overlay.

Longitudinal Joint Cracking LJNT Cracks predominantly along the pavement centerline,

lane division lines or the lane to shoulder division.


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Table 280.2 - PCC Pavement Distresses Name Abbreviation Description

Transverse Joint Spall TJSP

Cracking, breaking, chipping or fraying along the transverse joint or edge of a slab. Joints that have bituminous patches are also considered as spalled.

Faulted Joints FLJT A difference in elevation of at least 0.25 inches across a transverse joint.

Cracked Panels CRCK

A panel or slab with cracks resulting in the panel being divided into three or less pieces. The cracks must be at least 2 feet long for the slab to be counted as cracked.

Broken Panels BROK A panel or slab with cracks resulting in the panel being divided into four or more pieces. The cracks must be at least 2 feet long for the slab to be counted as broken.

Faulted Panels FLPN A difference in elevation of at least 0.25 inches across a transverse crack within a slab.

Overlayed Panels

OVRL Panel with a HMA overlay.

Patched Panels P5SF

A portion of the pavement surface, at least 5 sq.ft., that has been removed and replaced or had additional material applied and is in a deteriorated condition. A deteriorated condition is defined as any bituminous patch or a concrete patch showing deficiencies such as spalling or raveling at the edges or within the patch.

Durability Cracking (D-

cracking) DCRK

A series of closely spaced, crescent shaped, hairline cracks that appears in a concrete slab adjacent and roughly parallel to transverse cracks and joints, longitudinal joints and free edges of slabs. Dark coloring often exists around the cracking pattern and surrounding area.

Longitudinal Joint Spall

LJSP Cracking, breaking, chipping or fraying along the longitudinal joint or edge of a slab. Joints that have bituminous patches are also considered as spalled.


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299 - Chapter 2 Appendix

1. AASHTO Soils Classification

In 1928, the Bureau of Public Roads introduced a classification system with eight soil groups, designated A-1 through A-8, to be used for assessing the suitability of road subgrade materials. Major revisions to the system, most recently in 1987, have resulted in the chart shown in Table 299.1. This system is based on the proportion of grain diameters falling between sieve Nos. 10, 40, and 200 (2.0mm, 0.425mm, and 75 μm) as well as the soil’s plasticity. It is a quick, rational method for categorizing both undisturbed natural soil and fill in terms of its performance as a subgrade material. The system has been found to be applicable in areas with vastly different soil types and origins. In addition to the seven classifications shown in Table 299.1, an eighth classification, Group A-8, has been added to include highly organic soils (peat or muck). Soils in this classification are identified visually rather than by gradation and Atterberg limits.


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Table 299.1 - AASHTO Classification of soils and soil-aggregate mixtures (from AASHTO M 145-91)

CLASSIFICATION OF SOILS AND SOIL-AGGREGATE MIXTURES General Classification Granular Materials (35% or less passing No. 200 (75µm) sieve) Silt-Clay Materials (More than 35% No.

200 (75µm) sieve)

Group Classification

A-1 A-3* A-2 A-4 A-5 A-6 A-7

A-1-a A-1-b A-2-4 A-2-5 A-2-6 A-2-7 A-7-5 A-7-6

Sieve Analysis:

Percent passing:

No. 10 (2mm) 50 max. --- --- --- --- --- --- --- --- ---

No. 40 (425µm) 30 max. 50 max. 51 min. --- --- --- --- --- --- --- ---

No. 200 (75µm) 15 max. 25 max. 10 max. 35

max. 35 max. 35 max. 35 max. 36 min. 36 min. 36 min. 36 min.

Characteristics of fraction passing No. (40No. 425µm) sieve:

Liquid Limit --- --- 40 max. 41 min. 40 max. 41 min. 40

max. 41 min. 40 max. 41 min.

Plasticity Index 6 max. N.P. 10 max. 10 max. 11 min. 11 min. 10

max. 10

max. 11

min. 11 min**

Usual Types of Significant Constituent

Materials

Stone Fragments Gravel and Sand

Fine Sand Silty or Clayey Gravel and Sand Silty Soils Clayey Soils

General Rating as Subgrade Excellent to Good Fair to Poor

*The placing of A-3 before A-2 is necessary in the “left to right elimination process” and does not indicate the superiority of A-3 over A-2.

**The plasticity index of A-7-5 is equal to or less than the liquid limit minus 30. The plasticity index of the A-7-6 subgroup is greater than the liquid limit minus 30.

There are three broad types under which the AASHTO groups and subgroups are divided. These are "granular" (A-1, A-3, and A-2), "silt-clay" (A-4 through A-7), and “highly organic” (A-8) materials. The transitional group, A-2, includes soils which exhibit the characteristics of both granular and silt-clay soils, making subdivision of the group necessary for adequate identification of material properties. A more detailed discussion of the AASHTO groups is included in Section 5-692.606 of the MnDOT Grading and Base Manual.

The engineering considerations for granular and silt-clay soils are significantly different. The following discussion highlights major differences between these two types.

A. Granular. Granular materials include mixtures of rock fragments ranging from fine to coarse grained. Granular materials may include a non-plastic to slightly plastic soil binder, but are limited to 35 percent or less of the soil passing the No. 200 (75 μm) sieve. MnDOT's


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Specification 3149 limits granular backfill to no more than 20 percent passing the No. 200 (75 μm) sieve. Granular materials generally provide the most desirable subgrade.

It is possible, however, that some granular materials near the silt-clay boundary may have characteristics unsuitable for roadways in the presence of water. This is because capillarity (or a chemical affinity for water) may induce a volume change or softening of the material. In addition, frost heave becomes a concern in materials with high silt contents. Therefore, the elevation of the ground water table should be carefully considered when the subgrade is composed of these transitional soils

B. Silt-clay. Silt-clay materials are soils having more than 35 percent passing the No. 200 (75 μm) sieve. The behavior of these soils is dominated by the fines in the soil mass. Silt-clay materials (A-4 through A-7) can provide suitable road subgrades when their shortcomings are accounted for by proper design or construction practices. Subgrades classified as A-6 or A-7 usually dictate a thickened pavement section and strictly maintained grading tolerances. A-7 materials are generally considered the poorest performers with regard to roadway construction.

Determining the AASHTO classification of a soil is a two-step process. First, the soil is categorized into one of the eight major “A” groups using the gradation limits set in Table 299.1. Generally, the lower-numbered soils to the left of the chart are more preferable subgrade materials than those on the right. However, this is not always true: A-3 materials usually out-perform A-2 materials. A subdivision of some of the major groups is necessary to account for varying characteristics, e.g., A-2-6 and A-2-7. These classifications can be checked graphically using Figure 299.1.


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Figure 299.1 - Relationship between liquid limit and plasticity index for silt-clay groups (from AASHTO M 145-91)

Two examples of obtaining the proper classification of a soil using the AASHTO system (Table 299.1) are given below:

Example 1. What is the classification of a soil sample with 75% passing the No. 10 (2.0 mm) sieve, 55% passing the No. 40 (0.425 mm) sieve, and 12% passing the No. 200 (75 μm) sieve, a liquid limit of 20, and a plasticity index of 4?

Start at the left of Table 299.1 and move to the right. The soil is granular because 35% or less passes the No. 200 (75 μm) sieve. The soil is not an A-1-a because 50% or more passes the No. 10 (2.0mm) sieve, not an A-1-b because 50% or more passes the No. 40 (0.425 mm) sieve and not an A-3 because 10% or more passes the No. 200 (75 μm) sieve. However, it meets all of the requirements of an A-2-4 because 35% or less passes the No. 200 (75 μm) sieve, its liquid limit is 40 or less, and its plasticity index is 10 or less. The soil should be classified as an A-2-4.

Example 2. What is the classification of a soil sample with 100% passing the Nos. 10 and 40 (2.0 mm and 0.425 mm) sieves, 72% passing the No. 200 (75 μm) sieve, a liquid limit of 45, and a plasticity index of 25?

Start at the left of Table 299.1 and move to the right. The soil is a silt-clay because 36% or more passes the No. 200 (75 μm) sieve. The soil is not an A-4 because its liquid limit is 40 or more, not an A-5 because its plasticity index is 10 or more, and not an A-6 because its liquid limit is 40 or more. However, it meets all of the requirements of an A-7 because 36% or more passes the No. 200 (75 μm) sieve, its liquid limit is 41 or more, and its plasticity index is 11 or


55

more. Furthermore, the soil should be classified as an A-7-6 because its plasticity index (25) is larger than its liquid limit minus 30 (15).

The subgrade quality of silt-clay soils can vary from poor to good within each major group. Therefore, a group index (G.I.) is added to the group symbol found in Table 299.1 to indicate the plastic properties of the fines passing the No. 200 (75 μm) sieve. Calculation of this group index is the second and final part of the AASHTO classification. Generally, the higher the value of the group index for a given group classification the poorer the performance as a subgrade material. Therefore, a group index of zero (0) indicates a “good” subgrade material and a group index of 20 or more indicates a “poor” subgrade material.

The formula used to compute the group index is

G.I. = (F - 35) [0.2 + 0.005 (LL - 40)] + 0.01 (F - 15) (PI - 10) Eq. 299.1

where

G.I. = group index, reported as a positive whole number or zero

F = percentage passing the No. 200 (75 μm) sieve, expressed as a whole number (This percentage is based only on the material passing the 3.0 inch (75 mm) sieve)

LL = liquid limit

PI = plasticity index

Note that only the second term, which accounts for the effect of the plasticity index, is used for the group classifications of A-2-6 and A-2-7.

The group index is added in parenthesis after the group symbol, i.e., A-4(5) or A-7-5(17), etc. Two examples are given below:

Example 1. What is the complete classification of an A-7-5 with 80% passing the No. 200 (75 μm) sieve, a liquid limit of 90, and a plasticity index of 50?

The G.I. = (80 - 35) [0.2 + 0.005 (90 - 40)]

+ 0.01 (80 -15) (50 - 10) = 46.

Therefore, the complete classification is A-7-5(46).


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Example 2. What is the complete classification of an A-2-7 with 30% passing the No. 200 (75 μm) sieve, a liquid limit of 50, and a plasticity index of 30?

Using only the second term in Equation 299.1, the G.I. = 0.01 (30 - 15) (30 - 10) = 3.

Therefore, the complete classification is A-2-7(3).

The influence of fine content, plasticity, and liquid limit on group index is shown graphically in AASHTO M145-91.

The following descriptions provide profiles of each of the groups within the AASHTO classification system shown in Table 299.1:

Group A-1 includes well-graded gravel through fine sand with little or no non-plastic binder. Subgroup A-1-a includes stone fragments and gravel, with or without fines. Subgroup A-1-b includes predominantly coarse sand with or without fines. When properly placed and compacted, these materials perform well as road subgrades, as they are free draining and possess ample strength when properly placed.

Group A-2 consists of transitional granular materials, all of which have less than 35 percent fines. Subgroups A-2-4 and A-2-5 have fines that are silty (non-plastic). Subgroups A-2-6 and A-2-7 have fines that are similar to A-6 or A-7 soils; that is, the fines are more plastic. A-2 soils, usually having group indices up to four, may range from good to fair as road subgrade. Frost susceptibility begins to be a problem in the A-2 soils, especially where the water table is in proximity to the zone of yearly frost depth.

Group A-3 is mostly poorly graded fine sand with few fines. Typical examples include blow sand, some beach sands, or poorly graded stream or river sand with minimal gravel content. A-3 soils are relatively free draining and possess desirable strength characteristics, but they may be somewhat difficult to compact due to their uniformity.

Group A-4 soils are non-plastic to moderately plastic silts. Sand and gravel contents can range up to 64 percent. Group indices usually range up to eight, with lower values indicative of higher gravel and/or sand contents. Again, where drainage is poor and free water is available to the silty subgrade, frost heave should be considered as a significant factor affecting the desirability of this material.

Group A-5 soils are similar in grain-size distribution to A-4 soils, but have higher liquid limits, indicative of diatomaceous or micaceous soils. The elastic nature of these soils, especially in the absence of sand, causes group indices to be higher than the A-4 soils, perhaps as high as 12. Frost considerations are, again, a significant factor affecting usage of these soils as road subgrade.

Group A-6 soils are clays, usually plastic with 75 percent or more passing the No. 200 (75 μm) sieve. With increasing sand content, up to 64 percent, the group index may be held low; but


57

the group index can range up to 16 if the soil is devoid of sand. Usually, significant changes of volume will occur between dry and wet states. These materials may compact sufficiently at proper moisture content, but they will generally require a thicker pavement section to provide a non-yielding road surface. Frost considerations are usually outweighed by their affinity for water and the resulting volume changes and strength reductions that can result.

Group A-7 soils may be very elastic and plastic, subject to very high volume change with variations in moisture content. Strength can be low to high, but all A-7 soils are quite impermeable. A-7 soils are only utilized as road subgrade where nothing else is available.

Group A-8 soils are highly organic peats or mucks. These soils are highly undesirable for road subgrades and generally require removal.

2. Unified Soils Classification

Another classification system used widely is the Unified Soil Classification System (USCS). The present system, modified by the U.S. Army Corps of Engineers and the Bureau of Reclamation, was introduced during World War II by Casagrande of Harvard University to assist engineers in the design and construction of airfields. As with the AASHTO system, the USCS utilizes grain-size distribution and plasticity characteristics to classify soils. The USCS, however, categorizes soils into one of 15 major soil groups that additionally account for the shape of the grain-size distribution curve.

Table 299.2 shows the USCS classification system along with the criteria for associating the group symbol, such as "CL," with the soil. In this chart, D60 refers to the diameter of the soil particles where 60 percent of the sample would be finer. Similarly, D10 relates to the maximum diameter of the finest 10 percent of soil, by weight.


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Table 299.2 - Unified Soil Classification System chart (after U.S. Army Corps of Engineers, Waterways Experiment Station, TM 3-357, 1953)


59

The plasticity chart shown in the lower right-hand portion of Table 299.2 is a graphical representation of the USCS based solely on the plastic and liquid limits (MnDOT’s Geotechnical Manual Section 4.8.1) of the material passing the No. 40 (0.425mm) sieve. Clays will plot above the "A-line" and silts below. The chart further divides the clays and silts into low (less than 50) and high liquid limits.

Two examples of using Table 299.2 to obtain the soil's proper Unified Classification are:

Example 1. What is the classification of a soil sample with 88% passing the No. 4 (4.76mm) sieve, 38% passing the No. 200 (75 μm) sieve, a liquid limit of 15, and a plastic limit of 4?

Initially, it is determined that the soil is coarse grained because more than half (62%) is retained on the No. 200 (75 μm) sieve. It is then determined to be a sand because more than half of the 62% that is retained on the No. 200 (75 μm) sieve passes the No. 4 (4.76mm) sieve. Since there is more than 12% passing the No. 200 (75 μm) sieve, the soil is a sand with fines. The intersection of the liquid limit (15) and plasticity index (15 - 4 = 11) is above the "A line" on the plasticity chart. Therefore, the soil is an SC.

Example 2. What is the classification of a soil sample with 77% passing the No. 200 (75 μm) sieve, a liquid limit of 44, and a plastic limit of 18?

Initially, it is determined that the soil is fine grained because more than half (77%) passes the No. 200 (75 μm) sieve. The intersection of the liquid limit (44) and plasticity index (44 - 18 = 26) indicates a classification of CL.

3. Correlation of classification systems

The triangular textural, AASHTO and USCS classification systems all associate pertinent engineering properties with identifiable soil groupings. However, each system defines soil groups in a slightly different manner. For example, the triangular textural and AASHTO classification systems distinguish gravel from sand at the No. 10 (2.0 mm) sieve, whereas the USCS uses a break at the No. 4 (4.76 mm) sieve. The same coarse-grained soil could, therefore, have different percentages of gravel and sand in the triangular textural and USCS classification systems.

Because of such differences, a direct correlation of these soil classifications cannot be made. However, it is possible to make a general comparison as shown in Table 299.3


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Table 299.3 - Approximate Equivalent Classifications. MnDOT Triangular Textural AASHTO (Group Index) Unified (USCS)

Gravel A-1-a(0) GW, GP

Sand A-1-b(0) SW, SP

Coarse Sand A-1-a, A-1-b(0) SW, SP

Fine Sand A-1-b, A-3(0) SW, SP

Loamy Sand A-2-4, A-2-5(0) SM, SC

Sandy Loam

Slightly Plastic A-2-4, A-2-6, A-2-7(0) SM, SC

Plastic A-4(0-4) SM, SC

Loam A-4(0-4) ML, OL, MH, OH

Silt Loam A-4(0-4) ML, OL, MH, OH

Silt A-4 ML, OL, MH, OH

Sandy Clay Loam A-6, A-5(0-16) SC, SM

Clay Loam A-6(0-16) ML, OL, CL, MH, OH, CH

Silty Clay Loam A-6, A-5(0-16) ML, OL, CL, MH, OH, CH

Sandy Clay A-7, A-7-6(0-20+) SC, SM

Silty Clay A-7, A-7-5(0-20+) OL, CL, OH, CH

Clay A-7(0-20+) CL, CH, OH, OL

4. Volume and weight relationships

Soil is comprised of a mixture of soil solids, water, and air. The relative proportion of each of these constituents determines many of the properties of the soil. A soil block diagram, with symbols for each of its volume and mass components, is shown in Figure 299.3.


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Figure 299.3 - Volume and weight relationships for soil

The moisture content is the ratio of the weight of water to that of the dry soil solids, expressed as a percent. It is determined as follows:

w WwWs

* 100= Eq. 299.2

where:

w = moisture content (%)

Ws = dry weight of solids (gm)

Ww = weight of water (gm)


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Table 299.4 - Typical Moisture Contents* Material Moisture Content, w (%)

Gravel 2-10 Sand 5-15 Silts 5-40 Clays 10-50 (or more)

Organic (Peat) > 50 * Terzaghi, K. and Peck, R. B., “Soil Mechanics in Engineering

Practice”

The porosity is the ratio of the volume of voids to the total volume and may be expressed as either a percent or decimal. It is determined as follows:

n V

v

V= Eq. 299.3

where:

n = porosity

Vv = volume of voids (cm3)

V = total volume, (cm3)

The degree of saturation is the ratio of the volume of water to the total volume of voids, expressed as a percent. It is determined as follows:

S V

x 100 w

V= Eq. 299.4

where:

S = saturation (%)

Vw = volume of water (cm3)


The void ratio is the ratio of volume of voids to volume of solids and may be expressed as a percent or decimal. It is determined as follows:

e V

x 100 v

sV= Eq. 299.5

where:

e = void ratio


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Vs = volume of solids (cm3)

The density, or unit weight, of the soil mass is further divided into moist density and dry density. Moist density is the weight of water and soil solids divided by the volume of the soil mass. Dry density is the weight of only the soil solids divided by the volume of the soil mass. These values are determined using the following formulas:

Vm

W W

w s

V=

+ Eq. 299.6

or

Yd

Y

m

1 +w

100

= Eq. 299.7

where:

Ym = moist density (pcf or (kg/m3))

Yd = dry density (pcf or (kg/m3))

Ws = weight of solids (lb. or (kg))

Ww = weight of water (lb. or (kg))

w = moisture content (%)

V = total volume (ft3 or (m3))


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Table 299.5 Typical Dry Densities* Soil lb/ft3

Gravel and Sand 120 – 140 (1,900 – 2,250) Silts and Clay 90 – 110 (1,450 – 1,750)

Peat ~ 20 (300) * Terzaghi, K. and Peck, R. B., “Soil Mechanics in Engineering Practice”

The density of the soil mass affects the strength of the soil. Generally, the strength of a soil increases as its dry density increases. Also the potential for the soil to take on water at later times is decreased by higher densities. This is due to the decreased presence of air space in the soil mass.

The in situ moisture content of a soil is often used, along with the soil classification, to determine the suitability of the material as a subgrade. Generally, as the moisture content of a soil increases its strength decreases and the potential for deformation and instability increases. For example, if the natural moisture content is near the liquid limit then the soil will quickly be disturbed by earth moving equipment and is unlikely to be suitable subgrade material. On the other hand, a natural moisture content below the plastic limit indicates a relatively firm material that could provide a suitable subgrade, provided that additional moisture is not added. The moisture content of a soil should be expected to vary seasonally.

5. FWD testing A. MnDOT uses Dynatest FWDs that are each equipped with 10 pavement deflection sensors.

One of the 10 sensors is located on a bracket behind the load plate and is used for PCC joint transfer testing. The following sensor positions (in distance to the center of the load plate are used):

Table 299.6 – FWD Sensor Positions

Sensor # 1 2 3 4 5 6 7 8 9 10*

Distance 0

mm 203.2 mm

304.8 mm

457.2 mm

609.6 mm

914.4 mm

1219 mm

1524 mm

1829 mm

-305 mm

* This sensor is placed in a bracket behind the load plate.


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B. For FWD testing that will be analyzed with the TONN program or the ELMOD program, the following drop sequence is recorded: • 2 drops at 9,000 pounds. • 2 drops at 12,000 pounds.

C. For FWD testing of PCC joint load transfer, the following drop sequence is recorded:

• 2 drops at 9,000 pounds. • 2 drops at 12,000 pounds. • 2 drops at 15,000 pounds.

D. MnDOT standard FWD test locations are every tenth of a mile in the outside wheelpath.



Chapter 3 – Pavement Subsurface




300 - Definitions ................................................................................................................................................ 1

310 - Aggregate Base and Subbase .................................................................................................................. 3

320 - Below the Subbase ................................................................................................................................... 5

330 - Compaction ............................................................................................................................................ 13

340 - Shrinkage Calculation ............................................................................................................................ 16

350 - Infiltration ............................................................................................................................................... 19

360 - Culvert Backfill Treatments .................................................................................................................. 21

370 - Subsurface Drainage .............................................................................................................................. 21

380 - Frost Effects ........................................................................................................................................... 38


1

Introduction

Pavement subsurface includes the base, subbase, engineered soil and embankment. The pavement structural design and minimum pavement sections are contained in Chapter 4 - HMA and Chapter 5 - PCC. This chapter contains requirements and guidance for the design of the pavement subsurface to address concerns such as weak or unstable soils, differential frost heave, and subsurface moisture.

300 - Definitions

This section contains several definitions of pavement subsurface components that are used in this chapter. Examples of these terms are illustrated in Figure 300.1.

Figure 300. 1 – Example of new rural pavement sections

Drain

Aggregate Base

Grading Grade

Topsoil or Slope Dressing

Paved Shoulder Agg. Surfacing Paved

Shoulder Mainline Pavement

Top of Subgrade

Natural Ground Level (After Removing Topsoil)

Select Grading Material

Subbase

Embankment (Fill) Section Excavation (Cut) Section

Existing Soil

Embankment

Granular Material

Subgrade Excavation


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Aggregate Base is the layer of aggregate placed below the HMA or PCC pavement. Typically, it is made of a layer of class 5 or class 6 dense-graded aggregates (Specification 3138.2E), but it may also contain a drainable layer. This layer provides; a construction platform for paving, a portion of the pavement structure, a filter layer, and resistance to differential frost heave. This layer also is resistant to the effects of moisture such as; maintaining strength when saturated, resistant to moisture damage, and will not draw water up through capillary action (important for frost resistance). Class 5 and class 6 aggregate base also provide some limited drainage capability. It drains better than non-granular soils, but its drainage capability is much less than designated drainable materials. Grading Grade is defined by the MnDOT Standard Specifications for Construction as the bottom of the aggregate base. Subbase is the layer of granular material below the aggregate base. Typically, it is select granular or granular (Specification 3149.2B), but it may also contain layers of class 3 or class 4 aggregates (Specification 3138.2E). Subbase provides resistance to differential frost heave, improved moisture properties as compared to non-granular soils and may provide part of the pavement structure. Subbase must have drains below its outside edges unless it is daylighted to the in-slope. Top of Subgrade is the surface of material immediately beneath the granular material. If there is no granular material, then the top of subgrade is the grading grade. Engineered Soil is often referred to as “subcut”, “compaction subcut”, or “uniformity subcut”. It is the layer of select grading material (Specification 2105.1A6) immediately beneath the subbase. This layer provides a uniform, compacted layer for the pavement structure and improves resistance to differential frost heave as compared to the existing soil. Select Grading Materials are all mineral soils found in the Triaxial Chart in the Grading and Base Manual, excluding silt. Silt is defined as soils containing 80% or more silt-sized particles. Marl and organic soils are also excluded (Specification 2105.1A.6).


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310 - Aggregate Base and Subbase

This chapter only applies to the materials and specifications of aggregate base and subbase; for thickness and structural requirements see Chapter 4 - HMA or Chapter 5 - PCC.

1. Aggregate base

Specify the following materials to be used as aggregate base.

A. Dense-graded aggregate base (Specification 3138)

• Class 5 –This material is the most commonly used and is applicable in most situations. • Class 5Q – This material may be used whenever class 5 may be specified. It is a special

gradation that is intended to be more convenient to produce when the source aggregate is quarried.

• Class 6 – This material is generally regarded as a somewhat higher quality material than class 5 because it has fewer fines (improves drainage), more crushed material (improves stability), and a stricter requirement for aggregate properties.

B. Drainable bases (Specification 3136) - There are two types of drainable bases: open graded aggregate base (OGAB) and drainable stable base (DSB).

• OGAB may only be specified with PCC pavements and it must be accompanied by edge-drains. Its use is limited to PCC pavements because its excellent drainability comes at the expense of its stability. The minimum layer thickness is 4.0 inches (see Figure 500.1) and must be placed on dense-graded aggregate base to prevent intrusion of fine materials into the OGAB. The typical installation of OGAB is shown in MnDOT Standard Plan Sheet 5-297.432.

• DSB is a more stable material than OGAB. DSB has less drainability than OGAB but it is still very drainable. It may be used where dense-graded aggregate base is used, but a drainage path must be provided. The drainage path may be provided by either edge-drains or by daylighting the layer to the in-slope.


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2. Subbase

The following materials are suitable for use as pavement subbase: (1) Select granular material (Specification 3149.2B.2): This is the most commonly specified

material. (2) Select granular material (super sand) (Specification 3149.2B.3): This is select granular

material with stricter gradation requirements for material passing the No. 40 and No. 200 sieves, which are intended to improve this materials drainage and frost performance as compare to select granular material. Specifying this material is dependent on its availability, cost, and district preference or experience.

(3) Select granular material – modified: Select granular material with the specifications

modified by Special Provision or plan note may be specified due to district preference or experience.

(4) Class 3 or class 4 aggregate (Specification 3138): For the design of pavements, these

materials have a greater structural contribution than the same thickness of select granular. These materials are specified at the discretion of the District Materials/Soils Engineer (see Chapter 4 - HMA).

A. Drains

If the subbase is placed in an excavation of non-granular soil (percent passing ratio [No. 200 (75 μm)/1 inch (25 mm)] sieve > 20)) that is not daylighted, then provide longitudinal subcut drains on each side of the subbase (see Section 370 – Subsurface Design).


5

320 - Below the Subbase

Any construction beneath the aggregate base and subbase is at the discretion of the District Materials/Soils Engineer. This section contains subgrade treatments and corrections commonly used on MnDOT projects.

1. Subgrade preparation/engineered soil

The existing soil is normally prepared with the following:

A. Subgrade preparation (Specification 2112) consists of shaping, mixing, and compacting the top 6.0 inches of existing soil before placing the next layer.

B. Engineered soil is often referred to as a “subcut”, “compaction subcut”, or “uniformity

subcut”. This is a layer of select grading material (Specification 2105.1A6) immediately beneath the subbase. Typically, this layer is constructed by excavating the existing soil to the depth of the engineered soil layer, removing any silt or unsuitable material from the excavated soil, then blending, backfilling, and compacting the excavated soil (specified as select grading material) into the excavation. The source of the select grading material for the backfill does not need to be from the excavation but if it meets materials specifications it may be used. This provides a uniform, compacted layer for the pavement structure and improves resistance to differential frost heave as compared to the existing, undisturbed soil. Engineered soil is typically specified from 1 to 4 feet deep, depending on district preference and experience.

2. Special treatments

A. Swamp areas

Swamps are areas where poor foundation soils and/or wet materials are excavated and replaced with a suitable backfill or a floated embankment is used. Poor foundation soils contain >5% organic material by weight, peat, marl, or other soils. Wet material is any material where the soils are described as “wet” in the boring logs. Suitable backfill is typically either granular material or plastic material (select grading material).

Determine the depth and limits of required excavation by using soil borings (see Section 220 - Borings). The MnDOT Foundations Unit (Office of Materials and Road Research) may also be contacted for recommendations.


6

(1) Excavation and backfill. In this method, swamp materials are excavated and replaced with suitable backfill. For fills of intermediate height (5 to 20 feet), the typical section shown in Figure 320.1 should be used as a guide. a. In general, swamp materials should be excavated outward (from the road centerline)

and down from the point of intersection of the proposed side slopes and roadway surface (P.I.) to a depth of about two thirds the swamp thickness. From that point, the swamp materials should be excavated on a slope of 1(V) to ½(H) outward and up to the existing grade and in and down to the bottom of the swamp.

b. For shallow fills of less than about 5 feet, a floated embankment may be used; or the

excavation may be made on a steeper slope of 1(V) to ½(H), but must extend outward and all of the way down to the bottom of the swamp.

c. For high fills of more than about 20 feet in height, where more excavation is required to

maintain stability, the typical section (1(V) to 1½(H) slope), or even flatter, should be maintained and extend outward and all the way down to the swamp bottom. These fills must be designed by a geotechnical engineer.

d. Poor foundation soils may be disposed of outside the completed toe of the roadway

embankment. In general, disposal areas for swamp materials should have 1(V) to 10(H) or flatter slopes, unless otherwise specified by the MnDOT Foundations Unit (Office of Materials and Road Research).

e. Backfill material should consist of either granular or select grading. If the excavation is performed underwater, the excavation should be backfilled with granular material to a level at least two feet higher than the local water level. If the excavation is performed in the dry (due to natural causes or the water having been removed from the excavation by sumps and pumping) it may be backfilled with either select grading or granular soils. However, granular soils are generally the preferred swamp backfill material.


7

Figure 320.1 - Typical swamp sections


8

f. Caution should be exercised if sumps and surface pumping are used, as such methods may decrease overall stability and result in flowing material or slides and damage to adjacent structures. In some swamp excavations it may be necessary to maintain the natural water level, even by pumping in water, to keep the sides of the excavation stable or to minimize possible settlement of adjacent structures.

g. The proximity of adjacent structures to the excavation should be a carefully considered. The damage that would result from flowing material or slides should be addressed. Installation and monitoring of settlement plates, hub lines, or other instrumentation may be necessary, and should be coordinated with the MnDOT Foundations Unit (Office of Materials and Road Research).

(2) Floated embankment. In the placement of a floated embankment, existing trees, brush, and other surface vegetation is clear cut with only minimal disturbance to the existing vegetative mat. The embankment is placed directly over the existing swamp, proceeding from the toes in toward the road centerline, with the slope width, including berms, exceeding twice the depth of the swamp. Typically, this method requires less fill material because the swamp material is not removed. Placement of geosynthetics (geotextiles or geogrids) between the swamp and placed embankment materials is recommended in order to minimize ruts, expedite work, increase allowable stresses on the swamp subgrade and to allow the floated embankment to act as a cohesive whole. It should be noted that the use of geosynthetics will not eliminate settlement, but will tend to make it more uniform.

It may also be desirable to use light weight fill (e.g., geofoam, wood chips, shredded tires, etc.) for floating the embankment.

Note: The use of geosynthetics for earth reinforcement (MnDOT Specification 3733, type VI), or the use of light weight fill, should be coordinated with and studied by the MnDOT Foundations Unit (Office of Materials and Road Research).

(3) Embankment widening on weak soils. The placement of additional fill adjacent to an existing roadway may be accomplished by either excavation and backfill or use of a floated embankment. In either case, particularly if excavation and backfill is used, the stability of the old road core should be considered. Figure 320.2 depicts embankment widening over weak soils. This type of work should be studied and coordinated with the MnDOT Foundations Unit and/or MnDOT Pavement Design Unit (Office of Materials and Road Research).


9

Figure 320.2 – Cross-section of an embankment over an existing roadway in swamp area


10

B. Subgrade correction

Subgrade Corrections are used to eliminate specific unstable conditions in the subgrade of an existing road (e.g., frost heaves and subgrade failures). These areas may be visually apparent and may appear as weak areas in Falling-Weight Deflectometer (FWD) data (see Section 200 - Falling-Weight Deflectometer (FWD)). Take borings to identify if poor/wet foundation soils are present and to determine the depth and limits of the subgrade correction (see Section 220.2.D.(2) - Subgrade corrections).

Remove any poor/wet foundation soils and backfill with uniform soils. Poor foundation soils contain peat, marl, >5% organic material by weight, or other soils as directed by the District Materials/Soils Engineer. Wet materials are any soils that are described as “wet” in the boring logs. Backfill is typically either granular material or select grading material (if the excavation is dry). Wet areas may be drained with subsurface drains or by daylighting the granular material to the ditch.

C. Shadow treatment

Differential heave may occur at the limits of the shadow cast by an overhead bridge. In locations where this may occur, excavate 2 feet deeper than the subbase and backfill with granular material. This treatment should extend for at least 150 feet, plus tapers, on either side of the bridge.

D. Rock excavation (1) Preliminary designs for rock excavation must be based on MnDOT's Road Design

Manual, Section 4-6.02. Final designs should be established only after completion of a detailed geological investigation.

(2) Roadway excavations require the determination of the rock excavation method

(mechanical or explosive) and transitions into and out of rock sections. Both transverse and longitudinal transitions should be provided in the design to minimize differential cracking. (Generally, rock designs provide for 6.0 inches of paid overbreak below the bottom of the rock subcut).


11

3. Embankments A. Any embankment in the road core must be either select grading or granular material. Non-

structural grading materials (Specification 2105.1A8) may be used as embankment outside the road core (as described in the standard specifications).

The road core (2105.1A1) is defined as the area below the grading grade to the bottom of the excavation and between the following:

• For embankment heights ≤ 30 ft., from the grading grade point of intersections (P.I.s) with a

1(V) to 1(H) slope and • For embankment heights > 30 ft., from the grading grade point of intersections (P.I.s) with a

1(V) to 1½(H) slope.

B. Slope preparation. Embankments which are to be widened and have in-slopes steeper than 1(V) to 4(H) require that the slopes be flattened to this slope, or flatter; or that steps (benches) be cut into the slope (See MnDOT's Specification 2105.3C). The material used for the embankment widening should substantially match the existing embankment material in terms of textural classification, color, moisture and performance characteristics.

C. Controlled rate/surcharge. Compressible silts, clays, and organic deposits may be improved

by surcharging. A surcharge is applied in controlled lifts to the area to be treated and allowed to remain while the foundation soils consolidate sufficiently to increase their strength or reduce compressibility. After sufficient time for the required compression has occurred, either the surcharge is removed or additional fill may be placed. Surcharging has proven to be a relatively inexpensive method of treating deep compressible deposits.

D. Monitoring of embankment settlements and movements is done through the installation of

settlement plates, hub lines, control points or other instrumentation. Installation and location of settlement plates on, and hub lines and control points outside of, the embankment should be coordinated with the MnDOT Foundations Unit (Office of Materials and Road Research).


12

4. Transitions

Transitions between different materials and depths should be tapered to avoid differential movement (e.g., frost heaving) of the pavement. The following transitions should be provided:

A. When connecting new surfacing, cut vertically to the bottom of the existing aggregate base (or to the bottom of the new aggregate base, whichever is deeper) then diagonally at a 1(V) to 1(H) slope to the bottom of the recommended subgrade excavation.

B. When connecting to existing roadways at the termini of proposed new construction, cut vertically to the bottom of the existing aggregate base (or to the bottom of the new aggregate base, whichever is deeper); then at a 1(V) to 20(H) taper to the bottom of the recommended subgrade excavation.

C. When matching into existing crossroads, cut vertically to the bottom of the existing surfacing

(or to the bottom of the new surfacing design, whichever is deeper) then at a 1(V) to 4(H) slope to the bottom of the recommended subgrade excavation.

D. Provide 1(V) to 20(H) tapers when transitioning between subsurface layer depths. Tapers

between non-granular and granular must should be constructed so that the granular soil overlays the plastic soil.

5. Topsoil removal Provide a depth of existing topsoil to be removed and reused in areas that will be disturbed by construction.


13

330 - Compaction

Compaction is the process of increasing the density of aggregate or soil by reducing its air voids using mechanical means, such as rolling or tamping. It is carried out to improve the material’s engineering properties such as load-bearing capacity, stability, stiffness, volume change characteristics, and resistance to settlement and frost damage. The inspection of compaction activities and their results is necessary to ensure that the materials compaction is sufficient.

Specify, in the MDR, the appropriate method of compaction testing of aggregates and embankment. In most instances more than one method is available and which method to specify will be based on district experience/preference and available resources.

1. Aggregate A. Specified density (Specification 2211.3.D.2.a)

Specified density is used only for virgin aggregate base material. The specified density method compares the density of the compacted material to a reference value determined in the laboratory from a proctor test.

B. Quality compaction (Specification 2211.3.D.2.b)

Quality compaction is the compaction of each lift until there is no further evidence of consolidation. It is the default compaction requirement for aggregate surfacing.

C. Penetration index (Specification 2211.3.D.2.c)

Penetration index (PI) is the default method of compaction testing for aggregate base. The penetration index method is based on testing the compacted material with a dynamic cone penetrometer (DCP). A DCP consists of two 5/8 inch shafts coupled near mid-point. The lower shaft contains an anvil and a pointed tip which is driven into the ground by dropping a sliding hammer contained on the upper shaft onto the anvil. The amount that the shaft penetrates into the soil (recorded in millimeters) per blow is known as the DCP penetration index (DPI). The allowable DPI for different materials and moisture contents is given in Table 2211-3 of the MnDOT Standard Specifications for Construction.


14

2. Embankment (soils and granular materials) A. Compaction testing not required

Mechanical compaction is not required on portions of the embankment that are constructed with predominantly stone or rock fragments or placed in conjunction with topsoil covering or roadside grading. Compaction testing should not be used on waste materials or non-rock material (topsoil, etc.) utilized for incidental drainage or landscaping outside the roadbed embankment. However, it is the responsibility of the project field inspector to approve that the placed material is a compact mass that is acceptably consolidated.

B. Specified density (Specification 2105.3.F.1 )

Specified density is used for embankment material that doesn’t meet the definition of granular. The Specified density method compares the density of the compacted material to a reference value determined from a proctor test. The requirement for the percentage of the reference density for the existing material is found in specification 2105.3.F.1.

C. Quality compaction (Specification 2105.3.F.2)

Quality compaction is the compaction of each lift until there is no further evidence of consolidation.

D. Penetration index (Specification 2105.3.F.3)

The Penetration index (PI) is used when the material that is being compacted meets the definition of granular.

The penetration index method is based on testing the compacted material with a dynamic cone penetrometer (DCP). A DCP consists of two 5/8 inch shafts coupled near mid-point. The lower shaft contains an anvil and a pointed tip which is driven into the ground by dropping a sliding hammer contained on the upper shaft onto the anvil. The amount that the shaft penetrates into the soil (recorded in millimeters) per blow is known as the DCP Penetration Index (DPI). The allowable DPI for different materials and different moisture contents is given in Table 2105-6 of the MnDOT standard specifications for Construction.

E. Test rolling (Specification 2111)

Test rolling is an evaluation of a subgrade or subbase with a heavy roller to evaluate the adequacy of the roadbed construction relative to uniformity and consistency of the subgrade support in terms of strength, stiffness, stability, density and moisture content. The test roller will detect weak/unstable subgrade areas due to inadequate compaction (both in terms of moisture content and density), and/or unstable soils to a depth of about 5 feet. The failed areas will require corrective measures. These measures may include removing the


15

unstable/unsuitable soils, reducing the moisture content by aeration, or the re-compaction of the soil.

Test rolling in accordance with MnDOT 2111 is not, generally, recommended for the following situations.

(1) Embankments or backfills thinner than 30.0 inches. Test rolling these shallow areas probably will not pass the 2111 requirements.

(2) Roadbed construction where shallow underground utilities are present. (3) Roadway segments with numerous, closely spaced, shallow, underground structure

(culvert, storm sewers, other utilities, etc.). In all situations where test rolling is used, shallow structures must be protected against damage from the test roller. Structures should have at least 30.0 inches of soil cover prior to testing the subgrade. This depth may require the temporary increase in soil cover over the structure (construction of a blister).

(4) Roadway segments with relatively closely spaced bridge overpasses. (5) Areas where geo-synthetics are placed within the upper 5 feet of the embankment.

F. Proof rolling (special provision)

Proof rolling is a method, similar to test rolling, to evaluate the adequacy of subgrade compaction. The weight of the testing equipment (a loaded truck) is substantially lower with proof rolling and therefor the depth that is being tested is less. Contact the MnDOT Grading and Base Unit (Office of Materials and Road Research) for available Proof Rolling Special Provisions.


16

340 - Shrinkage Calculation

Provide soil shrink/swell factors if the project uses Specification 2105 for excavation and embankment. Shrinkage factors are not required when Specification 2106 is used for excavation and embankment. In this instance, the contractor is responsible for their own shrinkage calculations.

Shrink/swell factors are determined by locating the material source and then estimating their volume change from their undisturbed condition to their reworked and compacted condition (although, MnDOT, typically, does not specify the borrow sources to use for a project). This change is referred to as the shrink (if the compacted density is greater than the in situ density) or swell (if the compacted density is less than the in situ density) of the material. The factor is particularly important when haul distances are long.

A shrinkage factor of 100 percent means that a material will occupy the same volume when placed and compacted in the roadway as it did in the ground prior to excavation. A factor greater than 100 means that the natural material will shrink and more borrow or excavation material will be needed to build the planned embankment. A factor less than 100 percent indicates that the natural material will swell (i.e., its density at the borrow source is greater than its expected density in the roadway embankment).

One complication to be considered when determining shrinkage factors is the consolidation of the underlying foundation soils during construction. This consolidation can induce roadbed settlement in tilled fields, which would have a dramatic effect on the amount of fill needed on the project. The shrinkage factor is therefore the sum of the compaction factor plus other factors. If varying conditions are encountered, more than one shrinkage factor may be required.

The preferred method to determine the shrinkage/swell factor is to obtain undisturbed soil samples from the borrow pit and measure their in situ density and moisture content. These undisturbed soil samples may be taken either at the surface or in shallow excavations. In the case of non-granular soils, MnDOT Foundation Unit (Office of Materials and Road Research) drill rigs can obtain undisturbed thin-wall tube samples at depth. Densities of deep granular soils are most commonly estimated from N60 values (the SPT N value corrected for field procedures).

The existing density values should be compared against the Proctor density/moisture curves to arrive at a compaction factor. Although MnDOT's specifications may call for 95 or 100 percent of AASHTO T99 (Method C) density, the as-built density may be greater than the specification density. Investigation 183, “Application of AASHO Road Test results to Design of Flexible Pavements in Minnesota”, concluded that non-granular fills are generally placed about 3 percent above specification density, while granular fills are generally about 4 percent higher.


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After the compaction factor is calculated, it should be adjusted for foundation consolidation to arrive at an estimated shrinkage factor (Shrinkage Factor = Compaction Factor plus other factors).

Shrinkage factors have, in the past, included the disposal of unsuitable material: this practice is misleading and should be discontinued. A separate calculation should be made to determine the amount of unsuitable materials (primarily organic soils) that cannot be utilized on the job. Likewise, estimates of swamp shrinkage should be made separately due to complicating factors such as vertical subsidence and lateral compression. Guidance in this area may be obtained from the MnDOT Foundations Unit (Office of Materials and Road Research).

The MnDOT Geology Unit (Office of Materials and Road Research) should be contacted for an estimate of swell when rock cuts are being considered. Generally, rock shrinkage factors will be less than 100 percent.

It may not be necessary to make an estimate of the shrinkage factor for particularly small projects where exploratory resources are not available. In these situations, it is acceptable to use prior experience and outside sources to estimate factors. One such source of existing engineering properties of Minnesota soils is the Natural Resources Conservation Service’s Web Soil Survey available at http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm.

Another source of published shrinkage factors is an MHD study performed by W.W. Dreveskracht. A regression analysis of some 70 compaction versus depth of excavation calculations resulted in the values presented in Table 340.1.

Table 340.1 - Compaction vs Depth

Depth Feet Compaction

(Shrinkage) Factor 1 122 2 116 5 108

10 102 15 98 20 96 25 94 30 92

The values given are compaction factors only and do not include other factors, such as equipment shrinkage, which must be considered to arrive at an estimated shrinkage factor.

http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm


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An additional adjustment may be made to account for accidental loss or waste during hauling. This adjustment should change the final factor by no more than five percent.

Lastly, past MnDOT experience indicates that field conditions (e.g., depth, overburden and material type) impact the shrinkage or swell as shown in Table 340.2.

.

Table 340.2 - Approximate Shrinkage Factors

Material Shrinkage Factor (%) Rock

Sandstone 90 - 100 Limestone, granite,

basalt, etc. 70 - 90

Shale 90 - 110 Soil

Deep cuts and high fills 100 - 130 Normal cuts and fills 130 - 140

Ditch cuts and shallow fills

135 - 150

Shoulder grading 140 - 150 Light shoulder grading 150 – 165

Swamp Backfill Removing small

amount of topsoil 130

5 ft. below natural ground

135

10 ft. below natural ground

140

15 to 20 ft. below natural ground, irregular bottom

145

About 30 ft. below natural ground, very

irregular bottom 150


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350 - Infiltration

Infiltration of water into the ground is a practice used to reduce the amount of water that would normally drain as a surface flow. However, water can be damaging to pavement structures and areas used for infiltration should be limited to areas where the water will not degrade the pavement. Follow these guidelines for the location of infiltration with regard to pavement sections.

On state highways, no water should be introduced into any area that may be a source of water for the base, subbase, or existing soil above the groundwater table.

• In rural cross-sections, this area extends from shoulder PI to PI and downward and outward at 1(V) to 2 (H) slopes (see Figure 350.1) to the top of the groundwater table.

• For urban cross-sections, the width of this area is 12 feet beyond the back-side of the curb to the depth of the base and subbase, and from the back of the curb down to the top of the groundwater table (see Figure 350.2). Infiltration may be allowed within 1 foot of the back of the curb if an impermeable barrier is used to protect the base, subbase, and existing soil (see Figure 350.2).

Non-highway pavements, such as sidewalks, driveways, parking lots, utility roads, and some low-speed low-volume city streets may be designed to allow infiltration under their structure. A minimum of 6.0 inches of aggregate material should be placed under the pavement and above the depth of any infiltration. This will act to drain the pavement material and keep moisture from being introduced to the pavement from below. Although, the minimum aggregate depth is not sufficient to reduce frost heaving and will have a minimal effect on loss of pavement section strength from saturation.

Note: These guidelines only address concerns related to the pavement section. There may be additional considerations related to slope stability, maintenance, and other factors that must be addressed.


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Figure 350.1 - Rural roadway section

Base & Subbase C L

Existing Soil No Infiltration Area (Between Dotted Lines) No Infiltration Area (Between Dotted Lines)

1 to 2 (V:H) Slope

Groundwater Table

Figure 350.2 - Urban roadway section

Base & Subbase (hatched)

12 in

No Barrier With Impermeable Barrier 12 ft

No Infiltration Area (Between Dotted Lines)

Impermeable Barrier

1 to 2 (V:H) Slope

Groundwater Table

Existing Soil


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360 - Culvert and Storm Drain Bedding and Backfill

This section covers the bedding and backfill treatments of culverts, storm drains, and concrete box culverts with less than a 20-foot deep excavation. Treatments for excavations greater than 20 feet must be designed by a registered Geotechnical Engineer. For the purposes of this manual, culverts are defined as structures that are open on each end to convey surface water under a highway, railroad or embankment. Since culverts are open on each end, air is generally allowed to flow through, resulting in frozen ground conditions in the area immediately surrounding the culvert. For this reason culverts generally have more rigorous bedding and backfill requirements than storm drains. Per MnDOT Standard Specification 2501, entrance culvert designs are reviewed on a case-by-case basis. Only use the bedding details shown in this section if specifically requested by the District Hydraulics or Materials Engineer. Storm drain is defined as part of the drainage system that receives runoff from one or more inlets and conveys the runoff through a closed-conduit to a discharge point. Since free air flow through the system is generally limited, storm drain typically does not experience the same freezing conditions as culverts, and has lesser requirements for bedding and backfill. The following details and recommendations for bedding pipes and box culverts are based upon successful past practice. However, the District Materials and/or Soils Engineer is free to use engineering judgement to modify them to suit the unique conditions (frost depth, material properties, etc.), or construction requirements that may exist at a particular site. 1. Bedding and backfill of rigid pipe culverts

Rigid pipe culverts are made from reinforced concrete and should be bedded as shown in Figure 360.1.

Rigid centerline pipe culverts (culverts that cross the roadway centerline) will generally be designed with special backfill treatment and granular backfill tapers as shown below (Figures 360.2 - 360.4) to help to reduce the differential heave at the roadway surface caused by frost penetration into the soil around the pipe, particularly if the in situ soils are non-granular. These treatments are in addition to using the aforementioned bedding detail (Figure 360.1). Hence, for rigid pipe culverts the project Materials Design Recommendation (MDR) should specify which


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backfill treatment and frost depth to use, any modifications to the standard backfill treatment, and whether to use a plastic soils cap (refer to Figure 360.15).

A. Backfill treatments for rigid centerline pipe culverts

The treatments are shown below and are available as electronic dgn files on the MnDOT Design Standards Unit website under “Design Details”. ( PDF of same drawings , says dgn on projectwise http://ihub/designsupport/standards/design.html)

Treatment # 1 - Applies to all rigid culverts with granular existing soil (Figure 360.2). Treatment # 2 - Applies to rigid culverts with existing non-granular soils where the frost

depth* is above the center of the pipe (Figure 360.3). Treatment # 3 - Applies to rigid culverts with existing non-granular soils where the frost

depth* is below the center of the pipe (Figure 360.4). *Districts have developed standard frost depth for the specification of culvert treatments.

The notes in Figure 360.1 include provisions for allowing coarse filter aggregate beneath the pipe when installing in wet conditions.

Figures 360.5 through 360.7 provide additional information and details regarding the lateral and longitudinal extent of the culvert treatments. The area noted as "Zone A" depicts the slopes and details in the immediate vicinity of the pipe. “Zone B” depicts the details further away from the pipe. The sketches shown portray the taper slopes and details for rigid centerline culvert treatment #2, treatments 1 & 3 and those for flexible pipes are similar, but vary slightly. These sketches are shown for general reference and are not intended to be included in the roadway plans.

Refer to the MnDOT Drainage Manual for information regarding maximum & minimum fill height for culverts and storm drains. The MnDOT Drainage Manual is available at the following link http://www.dot.state.mn.us/bridge/hydraulics/drainagemanual.html.

B. Geotextile

A geotextile (MnDOT Standard Specification 3733, type V) is often specified for use below the aggregate bedding for separation and stabilization if the existing soils are soft and/or unstable. If a geotextile is required it should be included in the MDR.

http://ihub/designsupport/standards/design.html

http://www.dot.state.mn.us/bridge/hydraulics/drainagemanual.html


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Figure 360.1 – Rigid pipe culvert bedding


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Figure 360.3 – Treatment # 2: rigid culverts with existing non-granular soils where the frost depth is above the center of the pipe.

Figure 360.2 – Treatment # 1: rigid culverts with existing granular soil.


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Figure 360.5 – Longitudinal section view

Figure 360.4 – Treatment #3: rigid culverts with non-granular existing soils where the frost depth is below the center of the pipe.


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Figure 360.6 – Cross section view

Figure 360.7 – Isometric view


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2. Bedding and backfill of rigid pipe storm drain

The main purpose for bedding and backfilling storm drain with granular materials is to provide for good compaction and support around the pipe, as shown in Figure 360.8.

Granular backfill above storm drain may result in a granular block wholly within the frost zone of plastic soils, which can cause frost heave. In addition, on urban highways with numerous small diameter shallow storm drain lines crossing at close intervals, backfilling with granular materials becomes quite costly and may create construction difficulties. Therefore, it is recommended that all storm drain be backfilled with the same or similar material found in the excavation that meets "Selected Grading Material" as defined under MnDOT Standard Specification 2105.1.A.6 unless otherwise recommended by the District Materials and/or Soils Engineer. The Select Grading Material may be either plastic or granular soil as long as it meets 2105.1.A.6 and is free of clods, stones over 3 inches, sod and roots.

Figure 360.8 – Rigid pipe storm drain bedding


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Do not use the culvert backfill treatments shown above for closed-end storm drainage systems. However, they may be used on open-end (i.e. outlet apron) storm drain pipe located under roadway pavements if recommended by the District Materials and/or Soils Engineer. If a special granular backfill is required, consider using a treatment type similar to those shown above (Figures 360.2-360.4).

3. Bedding and backfill of flexible pipe culverts Flexible pipe culverts include those made from high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), or metal and should be bedded as shown in Figure 360.9. Refer to chapter 2 of the MnDOT Drainage Manual for information regarding restrictions on pipe material types. Similar to rigid pipe culverts, centerline flexible pipe culverts may also need to be constructed with special backfill treatments and granular backfill tapers to help to reduce the differential heave at the roadway surface caused by frost penetration into the soil around the pipe, particularly if the in situ soils are non-granular. These treatments are in addition to using the aforementioned bedding detail (Figure 360.9). Hence, for flexible pipe culverts the project MDR should specify which backfill treatment and frost depth to use, any modifications to the standard backfill treatment, and whether to use a plastic soils cap.

A. There are three different backfill treatments for flexible pipe culverts. The treatments are shown below and are available as electronic dgn files on the MnDOT Design Standards Unit website under “Design Details”.

Treatment # 1 - Applies to all flexible culverts with granular existing soil (Figure 360.10). Treatment # 2 - Applies to flexible culverts with existing non-granular soils where the frost

depth* is above the center of the pipe (Figure 360.11). Treatment # 3 - Applies to flexible culverts with existing non-granular soils where the frost

depth* is below the center of the pipe (Figure 360.12).

*Districts have developed standard frost depth for the specification of culvert treatments. The notes in Figure 360.9 include provisions for allowing coarse filter aggregate beneath the pipe when installing in wet conditions. Details regarding the lateral and longitudinal extent of culvert treatments are similar to those for rigid culverts as shown in Figures 360.5 through 360.7. These sketches are shown for general reference and are not intended to be included in the roadway plans.


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Figure 360.9 – Flexible pipe culvert bedding


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Figure 360.11 – Treatment # 2: flexible pipe culverts with existing non-granular soils where the frost depth is above the center of the pipe.

Figure 360.10 – Treatment # 1: flexible pipe culverts with existing granular soil.


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Trench width tables for the various types of flexible pipe are included in the electronic dgn files on the MnDOT Design Standards Unit website under “Design Details” and are also published in the MnDOT Drainage Manual. In general, they are equal to or wider than the trench width required for rigid pipe.

Refer to the MnDOT Drainage Manual for information regarding maximum & minimum fill height for flexible culverts and storm drains.

B. Geotextile

If the existing soils are soft and/or unstable consider requiring a geotextile (MnDOT Standard Specification 3733, type V) below the aggregate bedding for separation and stabilization. If a geotextile is required include it in the MDR.

Figure 360.12 – Treatment #3: flexible Culverts with non-granular existing soils where the frost depth is below the center of the pipe.


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4. Bedding and backfill of flexible storm drain

The main purpose for bedding and backfilling storm drain with granular materials is to provide for good compaction and support around the pipe, as shown in Figure 360.13.

Figure 360.13 – Flexible pipe storm drain bedding


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Similar to rigid storm drain, backfilling a flexible storm drain with granular material within the frost zone and within plastic soils, may cause a frost heave. Therefore, it is recommended to backfill with the same or similar material found in the excavation that meets Selected Grading Material as defined under Specification 2105.1.A.6, unless modified by the District Materials and/or Soils Engineer. The Select Grading Material may be either plastic or granular soil as long as it meets 2105.1.A.6, and is free of clods, stones over 3 inches for metal pipes (1” for material within 2 ft. of plastic pipe), sod and roots.

Do not use the culvert backfill treatments shown above for closed-ended storm drainage systems. However, they may be used on open-end (i.e. outlet apron) storm drain pipe located under roadway pavements, if recommended by the District Materials and/or Soils Engineer. If a special granular backfill is required, consider using a treatment type similar to those shown above (Figures 360.2-360.4).

5. Bedding and backfill of concrete box culverts

Bed concrete box culverts in accordance with Figure 360.14. Include in the MDR the depth at which the 1:20 taper begins. Similar to pipe culverts, one may use coarse aggregate bedding to bed culverts in wet locations.

Figure 360.14 – Box culvert bedding and treatment


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6. Plastic soils cap at the end of drainage structures

Erosion and piping may occur in the granular bedding and/or the backfill of drainage structures on either the inlet or outlet ends, although, the problem is generally more prevalent at the inlet. Scour is generally less of a problem when flare-type aprons are provided for the structure.

Large pipe and precast box culverts normally have concrete aprons and drop walls to protect the bedding from erosion. However, this may not be sufficient to prevent erosion around the structure, especially with flooding conditions and granular embankments.

To alleviate this potential problem, a plastic soil cap as shown in Figure 360.15 should be recommended in the MDR when erosion of a pipe or box culvert is a concern or for any other structures identified by the District Hydraulics Engineer. The end treatment normally will only be required at the inlet end of the structure; however, when deemed necessary it may also be used at the outlet end. The end treatment may be recommended for use with either granular embankments or plastic soil embankments when granular backfill treatments are provided.

Figure 360.15 – Plastic soil cap treatment at culverts


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370 - Subsurface Drainage

Excess subsurface water has a detrimental effect on both HMA and PCC pavements and the lower pavement layers. It reduces the strength of the aggregate base, subbase, and soil which may cause pavement cracking or rutting, deterioration of existing pavement cracks and joints, and promotes frost heave. To address the problem of subsurface water, base and subbase layers may be daylighted to the ditch or subsurface drains may be installed. The following discuss alternatives for removing subsurface water. 1. Subsurface drain types and design guidelines

MnDOT uses several types of drains to remove water from pavement structures. The following is a list of these types, including recommendations for their use.

A. Subcut drains (specification 2502.3.f) Subcut sections are at high risk for collecting potentially damaging subsurface water because these sections may create a “bathtub” by extending relatively permeable material below the natural, less permeable grade. Subcut drains are designed to remove the water from this “bathtub”. They are typically a longitudinal perforated pipe located in the bottom of each of the outer-most corners of granular backfilled subcuts (see MnDOT Standard Plan 5-297.430 and 5-297.433). The use of subcut drains is recommended for most situations.

B. Edge-drains Edge-drains are installed along each side of the mainline pavement and are intended to drain a portion of the pavement structure. There are two types of edge-drains, pavement edge-drain type (specification 2502.3.g) and permeable aggregate base type (Specification 2502.3.e).

(1) Pavement edge-drain type drains (Specification 2502.3.g) Pavement edge-drains type drains may be installed during the construction of a new pavement structure or (more typically) retrofitted into an existing pavement structure. These drains consist of a perforated pipe, wrapped in a geotextile fabric, which is placed in the bottom of a trench filled with fine filter aggregate (Specification 3149.2.J.2) (see MnDOT Standard Plan 5-297.432). They are used to collect and discharge water infiltrating into the pavement system from rain, snow melt, and spring-thaw seepage.


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While these drains are effective in mitigating water that infiltrates through the pavement surface, they are located too high in the structure to be able to correct groundwater problems. The MnDOT Geology Unit (Office of Materials and Road Research) should be contacted to address any groundwater concerns.

Pavement edge-drain type (Specification 2502.3.g) is recommended to be used in these situations:

With rubblized or crack and seat projects. With unbonded PCC overlay (UBOL) projects that use a geotextile fabric as an

interlayer (if the fabric cannot be drained by a daylighted aggregate base layer). When PCC or HMA full-depth pavements on plastic soils receive rehabilitation work of

any magnitude. In any areas where the pavement has a history of pumping.

(2) Permeable aggregate base (PAB) type drains (specification 2502.3.e)

Permeable aggregate base (PAB) type drains consist of a perforated pipe, not-wrapped in a geotextile fabric, which is placed in the bottom of a trench filled with permeable aggregate (see MnDOT Standard Plan 5-297.431 & 5-297.432). This type of drain provides a relative high-rate of flow and is required when a pavement is constructed with a highly permeable drainage layers such as:

• Open-graded aggregate base (OGAB) • Drainable stable base (DSB) • Permeable asphalt stabilized stress relief course (PASSRC) • Permeable asphalt stabilized base (PASB)

2. Discharge pipe and headwall

Subsurface drains are drained by 4.0 inch non-perforated, rigid thermoplastic (TP) discharge pipes and connections at specified intervals. Precast concrete headwalls with rodent screens are provided at each discharge pipe to protect its ends.

Discharge pipes should be daylighted to the ditch through headwalls or tied into the storm sewer system at distances no greater than 500 feet, although this distance should be no greater than 300 feet where pavement grades are less than 0.2 percent. MnDOT Standard Plan 5-297.433 illustrates the typical drain design.


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3. Pavement widening drainage system Permeable aggregate base (PAB) is a recommended option for designs that involve the widening of narrow pavements to facilitate the drainage of any water trapped in the existing pavement by the widening. The drainage system is shown in MnDOT Standard Plan 5-297.432. The type of PAB material (OGAB, PASB) used for this widened section is optional.

Where PAB is used under a widened section on the high side of a superelevated roadway, two drain options are available:

• Move the drain from the outside edge of PAB to the inside edge (next to existing pavement). • Eliminate the PAB in these areas and substitute either class 5 base or, as appropriate, deep-

strength bituminous or concrete.

The standard pavement edge-drain (3-inch diameter) is used with the PAB widening design and not the PAB drain (4-inch diameter) because they are less expensive and will provide adequate drainage for the widened section.

4. Interceptor drains (mini weeps) Interceptor drains are incorporated into unbonded concrete pavement overlay designs to collect water from the existing PCC joints and major cracks. These drains typically connect into a standard permeable base drain for discharge.

The design concept is shown in MnDOT Standard Plan 5-297.432.

5. Subsurface drain maintenance Proper maintenance of subsurface drain systems is critical to the performance of pavement systems, with the lateral outlet pipes being the primary area of concern. Vegetation growth, roadside slope debris, and topsoil are notorious for obstructing and plugging these outlet pipes. If the drain system becomes blocked it can severely harm the pavement structure by reversing its normal function and allowing more water to build up than would normally exist in the pavement. Therefore, inspection, cleaning, and repairing of the subsurface drains and lateral outlets should be regularly scheduled every two years or less to avoid damage. A simple mandrel can be used to check the discharge pipes and connections, which are the locations where most problems occur. The use of 2-inch diameter video equipment for inspection of the edge-drain system after, and even during, construction is recommended (The MnDOT Geology Unit has access to such cameras should they be needed). Note: Drainage systems should not be incorporated into the pavement system unless

a commitment to regularly inspect and maintain them has been made by the district.


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380 - Frost Effects

This section discusses frost heaving, thaw weakening, and estimating frost depth.

1. Detrimental effects of frost A. Frost heaving

Frost heaving is caused by frost lenses growing in a frost susceptible soil. Frost lenses begin as ice crystalizing within the larger soil voids. As freezing temperatures continue and advance deeper into the soil, water may remain unfrozen in the soil’s pore structure despite freezing temperatures. This unfrozen water, augmented by any source of unfrozen water from below, is transported upwards by capillary rise, to crystalize and add to the mass of the frost lenses. As the frost lenses grow, the overlying soil and pavement will heave up, potentially resulting in pavement roughness and cracking. The frost lenses will grow until the water source is used up, or until temperatures are low enough to freeze the capillary water, in which case a secondary layer of frost lenses may form at a lower depth. The frost heaving process is diagramed in Figure 370.1.

Three conditions are necessary for frost lenses to form and cause frost heave. These are:

• Freezing temperatures • Water • Frost susceptible soil – Any material with more than 3% material finer than 0.02 mm is

considered to be likely frost susceptible (see Figure 370.2).

Removal of any of these conditions will eliminate or minimize frost heaving. If these conditions occur uniformly, heaving will occur uniformly which normally is not detrimental to pavement performance. However, if these conditions are non-uniform, heaving will also be non-uniform which will cause pavement roughness and possible cracking.


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B. Thaw weakening

Freezing Air Temperatures

Unfrozen Layer (Water source)

Frozen Layer Ice Lenses Ice Lenses

Capillary Rise

Deepest Advance of Freezing Temperatures.

Mixture of Water (in the soil pore structure) and Ice.

Figure 370.1 - Diagram of Frost Heaving

Figure 370.2 - Frost susceptibility of various soil types tested by the Corps of Engineers, 1950-1970 (from FHWA-TS-80-224, "Highway Subdrainage Design," August 1980).


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Thaw weakening occurs during spring melting when ice contained in the pavement subsurface melts. Because thawing typically proceeds from the top down, this water is trapped by the remaining frozen soil beneath. The increase in moisture from this trapped water reduces the stiffness of the pavement subsurface layers and more fatigue will occur to the pavement structure than during normal conditions.

2. To reduce frost effects A. Replace frost-susceptible material with frost resistant material

Frost susceptible soils have pore sizes that promote capillary rise which facilitates the growth of frost lenses. Therefore, the degree of a soil’s frost susceptibility is related to the amount of fines that it contains. Materials with less than 10% finer than no. 200 (75 µm) sieve are considered to be frost resistant and will likely experience little frost heaving. Materials with greater amounts of fines are considered frost susceptible to some degree with soils containing silts regarded as the most frost susceptible. Clays also contain fine material but their permeability may be so low as to inhibit capillary rise and the growth of frost lenses.

Generally, it is impractical and not-cost effective to replace all of the pavement structure with frost resistant material. MnDOT’s standard pavement structure requirements are a compromise between cost and anticipated benefits. For new HMA pavements on non-granular soils, MnDOT requires a minimum total pavement structure of 30.0 inches for roads with less than 7 million 20-year BESALs and 36.0 inches for roads with more than 7 million 20-year BESALs. This thickness includes pavement, base, and subbase. This depth is approximately one-half the average frost depth for Minnesota overall. Higher trafficked roads require thicker frost resistant because the increase in reliability and performance are considered worth the expense. For new PCC pavements on non-granular soils, MnDOT requires a minimum of 4.0 inches of base on 12.0 inches of subbase.

B. Provide good roadway drainage

Water in the pavement subsurface is a necessary condition for both frost heaving and thaw weakening and minimizing it will minimize both frost effects. Provide surface drainage and seal any cracks or joints to keep surface water from entering the pavement subsurface. Use aggregate and granular materials under the pavement and provide a path for these layers to drain. The drainage path may include drains or daylighting the layer, which is extending the width of a pavement layer to near the in-slopes (only covered by topsoil) so that the layer may directly drain to the ditch.


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C. Uniform soil

Uniform soil will tend to heave uniformly which typically isn’t detrimental to a pavement.

D. Match materials and use transitions

Uniform frost heave is typically not a problem but any abrupt differences in heave will be experienced as a bump or roughness. It is important to match the thickness and materials of adjacent sections and to use appropriate transitions when differences are necessary.

4. More information on frost

Consult the Army Corps of Engineers’ Engineering Manual (EM 1110-3-138), “Pavement Design for Seasonal Frost Conditions” at http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-3-138.pdf

http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-3-138.pdf

http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-3-138.pdf



Chapter 4 – HMA (Hot-Mix Asphalt)




400 – New/Reconstructed HMA Pavements................................................................................................ 2

410 - Reclamation/Recycling of Existing HMA Pavement ......................................................................... 4

420 – Rubblization and Crack and Seat ........................................................................................................ 11

430 - Pavement Design using MnPAVE-Flexible ...................................................................................... 14

440 - HMA Overlay of Existing Pavement .................................................................................................. 30

450 - Materials and Specifications ................................................................................................................. 34


1

Introduction

For this manual, HMA refers to hot-mix asphalt or warm-mix asphalt layers of a pavement structure. HMA pavement may be constructed on new aggregate base, recycled material used as aggregate base, such as full-depth reclamation (FDR), or placed as an overlay on existing pavement. Other asphalt containing materials such as cold in-place recycling (CIR) or stabilized full-depth reclamation (SFDR) is considered as stabilized aggregate base material. Surface treatments, such as seal coats or microsurfacing, are considered as surface treatments and not pavement.

This chapter contains directions for designing HMA pavement on mainline highways, determining the HMA specification required for a Materials Design Recommendation (MDR), and evaluating existing pavement with regard to rehabilitation with a HMA overlay. The process for pavement-type selection is contained in Chapter 7 – Pavement-Type Selection.


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400 – New/Reconstructed HMA Pavements

This section contains directions to design pavements for projects that include the complete removal of the existing pavement or construction on a new alignment.

New/reconstructed HMA pavements are built on aggregate base and granular subbase. The base and subgrade provide a portion of the pavement’s structure, a solid working platform for construction and improved engineering properties as compared to native, non-granular soils; such as higher strength, less reduction in strength during spring thaw, lower frost susceptibility, and improved drainage.

Use the following standards to design new/reconstructed HMA pavements:

1. Projects that involve working the existing soil must comply with Figure 400.1 and its notes.

2. Projects that do not involve working the existing soil must comply with the following:

A. These projects must have existing soil, subbase, and/or aggregate base material in good condition, suitable to perform as a portion of the pavement structure and to remain in the pavement section. The designer must evaluate the existing materials and determine what material will remain and what treatment, if any, will be required.

B. These projects do not need to comply with all of the requirements shown in Figure 400.1. However, a minimum of 4.0 inches of HMA (a 5.0-inch HMA minimum may be used on urban sections) on a minimum of 6.0 inches of aggregate base must be used.

3. Design the pavement using MnPAVE-Flexible according to Section 430 – Pavement Design Using MnPAVE-Flexible.

4. Specify the mix type, ride specification, lift thicknesses, and compaction requirement using Section 450 – Materials and Specification.

5. Any construction beneath the typical shown in Figure 400.1 is at the discretion of the District Materials/Soils Engineer. For guidance regarding the pavement subsurface design see Chapter 3 - Pavement Subsurface.

6. For guidance on pavement cross sections consult the MnDOT Road Design Manual (Chapter 4 –Cross Sections and Chapter 7 – Pavement Design).


3

Figure 400.1 – Pavement design standards for new/reconstructed HMA pavement for projects that involve working the existing soil.

NOTE 1 For non-granular soils, the minimum pavement structure (i.e. pavement, aggregate base, and subbase) thickness required is:

• 30.0 inches for 20-year BESALs ≤ 7 million • 36.0 inches for 20-year BESALs > 7 million

NOTE 2 Any construction beneath the typicals shown above shall be at the discretion of the District Materials/Soils Engineer.

• For non-granular soils use select granular. Class 3 or class 4 can be substituted for a portion of the select granular material at the discretion of the District Materials/Soils Engineer.

• For granular soils (percent passing ratio

[no. 200 (75 μm)/1.0 inch (25 mm)] sieve ≤ 20), mix and compact the upper 12.0 inches (minimum) of the existing granular soils.

HMA Pavement

Aggregate Base

Granular Subbase

Soil

• 4.0-inch minimum thickness • 5-inch HMA minimum may be used on

urban sections

• 6.0-inch minimum thickness

Layer

Notes

See Note 1

See Note 2


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410 - Reclamation/Recycling of HMA Pavement

Reclamation/Recycling of HMA pavement includes processes that grind the existing HMA pavement and re-use it in the new pavement section. This includes full-depth reclamation (FDR), stabilized full-depth reclamation (SFDR), cold in-place recycling (CIR), and cold central plant recycling (CCPR). For more information see the Basic Asphalt Recycling Manual from the FHWA and the Asphalt Recycling and Reclaiming Association at the following link http://www.cdrecycling.org/assets/concrete-recycling/1-124-barm1.pdf.

If the existing HMA material is removed from the roadway and then re-used as base, then use Section 400 – New/Reconstructed HMA Pavements. 1. Pavement condition assessment

Assess current pavement condition and existing materials.

A. Examine existing pavement to determine whether there are weak subgrade or base areas. B. Use Ground Penetrating Radar (GPR), to ascertain pavement and base thicknesses. C. Take cores samples for calibration purposes of the GPR and for evaluation of the HMA. The

total number of cores should equal at least one per quarter mile. D. Analyze cores to discern the uniformity of gradation, crushing, and condition. Evaluate the

sample’s gradation and crushing along discontinuities by slicing the core, performing a burn extraction and analyzing the sample for crushing and gradation by depth of core.

E. Sample the base and subgrade at each core location and determine:

(1) Base thickness, gradation, crushing and strength (perform DCP testing through base,

subbase and subgrade). (2) Subbase thickness and gradation (3) Subgrade attributes:

Establish the soil samples classification according to the triaxial chart and the soil’s strength attributes (R-value or other). Consider repairing the subgrade where it is weak, as

http://www.cdrecycling.org/assets/concrete-recycling/1-124-barm1.pdf


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reclamation projects do not improve a weak subgrade; establish that the condition of the subgrade is adequate and requires, at the most, minimal repairs. Areas that require subgrade repair may be visually apparent (see Section 270), may appear as weak areas in FWD data (see Section 200), or may appear as areas of wet or poor foundation souls in a soils survey (see Section 220.1.D).

F. Consider cement soil stabilization for weak areas. It can be cost effective, if an entire HMA

section is being reclaimed. Soil stabilization will aid in the long term performance by not only providing a stable platform for the longevity of the project, but it will also increase compaction efforts during construction.

As an alternative to cement stabilization, the designer should consider the use of a fabric separator or a geogrid.

2. Reclamation selection

Use Table 410.1 and the following as a guide to rehabilitation selection.

A. CIR may be preferred for thicker existing HMA (≥ 7 inches) and there are no underlying distresses.

B. Consider CIR for an existing HMA overlay on a jointed concrete (BOC).

C. FDR and SFDR are preferred for thinner (< 7 inches) HMA sections.

D. Consider SFDR if it is desirable to strengthen the base without raising the grade as much as a FDR.

E. Consider cold central plant recycling (CCPR) for projects that involve stabilizing the subgrade. The CCPR process involves; removing all of the existing HMA, strengthening the subgrade, placing cold central plant mix and then paving new HMA.


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Table 410.1 - Rehabilitation Selection Guideline

Rehabilitation Recommendation

Distress CIR SFDR Soil Stabilization

Raveling

Potholes

Rutting

Corrugations

Shoving

Fatigue Cracking

Block Cracking

Longitudinal Cracking

Transverse Cracking

Reflective Cracking

Swells/Bumps/Sags

Sags

Depressions

Poor Ride Quality

Weak Subgrade

3. In-depth design

This section contains general reclamation guidelines for CIR, SFDR and FDR.

The three most important design attributes for CIR, SFDR and FDR to consider are:

• Crushing % (aim for a minimum of 20%). • Gradation (aim for a minimum of 40% retained on the No. 4 (4.76mm) sieve and a

maximum of 10% retained on the No. 200 (75 μm) sieve). • Having a firm platform to compact against.


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A. Full-depth reclamation (FDR) design

FDR involves using a reclaiming machine to crush and blend-together the existing HMA pavement and aggregate. The blended material is moved as necessary to allow it to be compacted in 6-inch lifts. After compaction and shaping, it will then act as base for new HMA pavement. Therefore, staging should be considered during design.

As per above, the minimum goal should be to meet a gradation with a minimum of 40% retained on the No. 4 (4.76mm) sieve and a maximum of 10% retained on the No. 200 (75 μm) sieve. Excess crushing over 20% may be substituted for a deficiency in No. 4 (4.76mm) sieve gradation.

Do not over-mill the HMA, as often the existing HMA will provide needed crushing and rock for the reclaimed material. Consider correcting the grade after reclamation. Reclaiming first will provide good rock and crushing percentages for the reclaimed material. Excess reclaimed material may be used on shoulders and gravel roads to stabilize them. If the reclaimed material is expected to be deficient in crushing or gradation, provide additional rock placed in front of the reclaimer. One hundred percent crushed chip seal rock (FA -3 per MnDOT specification 3127) works well for this purpose. (Note that older HMA may be a very sandy mix and may not provide the needed rock or crushing).

Establish a reclaiming depth of at least 1 inch deeper than the HMA pavement. This will allow the teeth of the reclaiming machine to pass through the HMA and to be cooled by the aggregate layer. Alternatively, aggregate may be placed on top of the existing HMA to cool the teeth but is not preferred.

It is preferred to establish a reclaiming depth that will provide a blend of 50% HMA and 50% aggregate; however, use caution as that design provides less structure to compact against and there is greater potential to incorporate dirty (i.e. excess fine material) base, subbase, and subgrade into the final product. Therefore, deeper depths of reclamation are not recommended, unless a thick clean base, subbase and strong subgrade is present.

Consider compaction aids comprised of calcium chloride or other salt materials, which will aid in compaction and may provide some strength. However, note that when saturated, compaction aids will perform similar to reclaimed material without compaction aids during the spring thaw period.

(1) Reclaiming Depth • Only existing HMA and sound aggregate should be included in the reclaiming section. • The maximum depth that typical reclaiming machines can reclaim is 18 inches but a

depth of 12 inches is typically used. Note: stay as far above weak soils as possible because bearing capacity is needed for compaction.


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• If there is a definite change in the pavement section, design for multiple milling depths, added aggregate, or reclaiming depths within the project.

B. Stabilized full-depth reclamation (SFDR) design

SFDR is FDR that has had a stabilizing agent added. After the roadway has been reclaimed, a second pass of the reclaiming machine is made to apply and blend-in a stabilizer. The stabilizer is typically asphalt emulsion or foamed asphalt. This layer will then be shaped, compacted, and allowed to cure before being paved with new HMA pavement.

As with FDR, design SFDR with adequate rock and crushing and a good platform to compact against (see above).

It is recommended to use either an emulsion derived from PG 58-28 or foamed asphalt meeting PG 49-34.

An SFDR mix design is recommended to determine the method (foaming or emulsion), bituminous type and amount of additives needed. See the “Mix Design Criteria for SFDR” in the Grading and Base Manual Section 5-692.290.

(1) Reclaiming depth

Establish a reclaiming depth of 1 inch deeper than the HMA pavement. This will allow the teeth of the reclaiming machine to pass through the HMA and to be cooled by the aggregate layer. A greater amount of aggregate is not preferred for SFDR because the required emulsion percentage is increased and there is greater potential to incorporate dirty base, subbase, and subgrade into the final product.

a. Only existing HMA and sound aggregate should be included in the reclaiming section.

b. If there is a definite change in the pavement section, design for multiple milling depths, added aggregate or reclaiming depths for the project.

(2) Stabilization depth

The maximum stabilization depth is 6 inches, and the typical minimum depth is 4 inches. Design the stabilization depth to meet the design needs of the pavement.

C. Cold in-place recycling (CIR) design

CIR is produced by grinding HMA and adding an emulsion or foamed asphalt in one process. It is less expensive than SFDR but does not fix a weak base. This layer will then be shaped, compacted, and allowed to cure before being paved with new a new HMA pavement or a surface treatment.


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As with (S)FDR, design CIR to have adequate rock, % crushing and a good platform to compact against. Assess changes in gradation of the HMA throughout the cores during design.

A CIR mix design is recommended to determine the method (foaming or emulsion), bituminous type and amount of additives needed. See the “Mix Design Criteria for SFDR” in the Grading and Base Manual Section 5-692.291.

A benefit of using a CIR layer is that it retards reflective cracking. Reflective cracking may be further retarded by reducing the thickness of the existing cracked pavement (by milling).

It is recommended to use either an emulsion derived from PG 58-28 or foamed asphalt meeting PG 49-34.

(1) CIR grinding and stabilization depth. a. Only existing HMA should be included in the reclaiming section.

b. The recommended thickness for a CIR layer is 3 to 4 inches.

c. Except for BOC, ensure there is a minimum of 6 inches of aggregate base (or an

equivalent in other materials) for support of the CIR train.

d. Typically, leave at least the bottom two inches of existing HMA undisturbed if it is produced over existing HMA. Design to just above the top surface of a bituminous overlay for BOC pavements.

D. Cold central plant recycling (CCPR)

CCPR is a method where asphalt millings are processed with asphalt then placed back onto a pavement surface. It is most applicable where all the pavement surface is removed to the subgrade, the subgrade is then stabilized and the CCPR material is placed directly onto the stabilized soil, which is topped with HMA.

A mix design is recommended to determine the bituminous type and amount of additives needed. See the Mix Design Criteria for CIR in the Grading and Base Manual Section 5-692.291.

For more information and/or assistance on FDR, SFDR or CIR, contact the Reclamation - Grading and Base Unit of the Office of Materials & Road Research at http://www.dot.state.mn.us/materials/gbacontacts.html

http://www.dot.state.mn.us/materials/gbacontacts.html


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4. Pavement Design A. Design the pavement thickness of FDR, SFDR, and CIR using MnPAVE-Flexible according

to Section 430 - Pavement Design Using MnPAVE-Flexible. Use the following minimum HMA pavement thicknesses for the pavement designs.

• FDR - The minimum HMA pavement thickness is 4.0 inches (a 5-inch HMA minimum

may be used on urban sections).

• SFDR - A minimum HMA pavement thickness of 2.0 inches may be used if placed on a minimum of 6.0 inches of SFDR.

• CIR - The minimum HMA pavement thickness is 2.0 inches, but a seal coat may be acceptable for shoulders not normally used for traffic.

B. Specify the HMA mix type, ride specification, lift thicknesses, and compaction requirement

using Section 450 - Materials and Specification.


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420 – Rubblization and Crack and Seat

Rubblization and crack and seat are two methods used to process existing PCC pavement to prevent reflective cracking and allow the fractured PCC to serve as a base for new HMA pavement.

1. Rubblization (2231 Pavement Breaking Special Provision (S-108))

Rubblization is intended to reduce the existing PCC modulus and obliterate the existing PCC joints in order to prevent reflective cracking of the HMA pavement and allow the rubblized PCC to act as new base. Rubblization involves breaking the existing PCC slab into pieces (3.0 inches maximum at surface and 9.0 inches maximum at the bottom of pavement), compacting the rubblized material, and paving an HMA pavement.

A. Evaluation and pre-HMA paving repairs.

(1) Rubblization projects require a minimum average R-value of 17 or a minimum of 1 foot of granular material under the existing PCC pavement. The R-value may be determined by performing laboratory tests on samples obtained from borings (see Section 220 - Borings) or from FWD testing an existing HMA shoulder, if it was constructed with the mainline and it is not heavily cracked.

(2) Establish the material and condition of the existing subgrade with borings (see Section 220 - Borings). Roadways with wet subgrades are poor rubblization candidates. However, wet subgrades may be remedied by installing subsurface drains a year prior to rubblization.

(3) Before rubblization, remove any existing HMA overlay.

(4) Before rubblization, repair spot areas of poor subgrade support or bad PCC joints with

full -depth HMA.

(5) When edge-drains do not exist, install edge-drains prior to rubblization or remove the shoulders and daylight the base and subbase so that water may drain.


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B. Design the HMA pavement

(1) Use a minimum HMA pavement thickness of 4.0 inches.

(2) A layer of permeable asphalt stabilized base (PASB) or permeable asphalt stress relief course (PASSRC) (specification 2363) is recommended as the first layer of HMA to reduce or delay any reflective cracking. This layer does not contribute towards the minimum HMA requirement.

(3) The pavement must be designed using MnPAVE-Flexible according to Section 430 - Pavement Design Using MnPAVE-Flexible.

(4) Specify the mix type, ride specification, lift thicknesses, and compaction requirement using

Section 450 - Materials and Specification.

2. Crack and seat (2231 Pavement Cracking Special Provision (S-107) and 2231 Pavement Seating in Special Provision (S-109))

The crack and seat process involves cracking the existing PCC pavement into 3 to 4-foot pieces, firmly seating the pieces, then paving a HMA pavement. The intention is to reduce the size of the PCC pieces to minimize movements at existing cracks and joints. This will minimize the frequency and severity of reflective cracking. It is an especially useful technique when moving or rocking panels have been identified.

C. Evaluation and pre-HMA paving repairs.

(1) Establish the material and condition of the existing subgrade with borings (see Section 220 - Borings). Roadways with wet subgrades are poor crack and seat candidates. However, wet subgrades may be remedied by installing subsurface drains a year prior to performing the crack and seat.

(2) Remove any existing HMA overlay of the PCC pavement before crack and seating. (3) Repair spot areas of poor subgrade support or bad joints and patch the pavement with full

depth HMA.

(5) When edge-drains do not exist, install edge-drains prior to crack and seating or remove the shoulders and daylight the base and subbase so that any water that gets into the PCC has a way to drain.


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D. Design the HMA pavement.

(1) Use a minimum HMA pavement thickness of 4.0 inches. (2) A layer of permeable asphalt stabilized base (PASB) or permeable asphalt stress relief

course (PASSRC) (specification 2363) is recommended as the first layer of HMA to reduce or delay any reflective cracking. This layer does not contribute towards the minimum HMA requirement.

(3) For crack and seat projects that use a PASB or PASSRC layer use a design life of 20 years. Otherwise, use the HPMA program to predict the performance of the crack and seat project(see Section 280 – Pavement Management System, steps 1-7B for directions) in order to determine when a rehabilitation activity will occur. The number of years until a rehabilitation activity occurs is the design life. Table 440.2 or experience may be used to determine the design life if it clearly demonstrates that a different value than derived from the HPMA program should be used.

(4) Specify the mix type, ride specification, lift thicknesses, and compaction requirement using Section 450 - Materials and Specification.


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430 - Pavement Design using MnPAVE-Flexible

MnPAVE-Flexible is a mechanistic-empirical (M-E) pavement thickness design program for HMA pavements. It calculates the stresses and strains in the roadway from traffic loading and material properties for the pavement layers. Then the calculated stresses and strains are used with empirically derived equations to predict fatigue cracking (bottom-up) and rutting in the roadway. The final output is the reliability that the pavement structure will successfully meet fatigue and rutting requirements when evaluated with a Monte Carlo simulation.

MnPAVE-Flexible is a computer program that combines known empirical relationships with a representation of the mechanics from layered elastic theory used in modeling flexible pavement behavior. The mechanistic portions of the program calculate the tensile strain at the bottom of the asphalt layer, the compressive strain at the top of the soil, and the maximum principal stress 6.0 inches from the top of the aggregate base layer (or at the bottom of the base if it is 6.0 inches or thinner).

MnPAVE-Flexible consists of three input modules: climate, traffic, and structure; and three design levels: basic, intermediate, and advanced. The level is selected based on the amount and quality of information known about the material properties and traffic data. In the basic mode, only a general knowledge of the materials and traffic data are required. The intermediate level corresponds to the amount of data currently required for MnDOT projects. The advanced level requires the determination of modulus values for all materials over the expected operating range of moisture and temperature.

MnPAVE-Flexible simulates traffic loads on a pavement using a layered elastic analysis (LEA) called WESLEA. It is a five-layer analysis program written in 1987 by Frans Van Cauwelaert at the Catholic Superior Industrial Institute Department of Civil Engineering in Belgium and modified in 1989 by Don R. Alexander at the U.S. Army Engineer Waterways Experiment Station in Vicksburg, Mississippi. All layers are assumed to be isotropic (same properties in all directions) and infinite in the horizontal direction. The fifth and final layer is assumed to be semi-infinite in the vertical direction. Material inputs include layer thickness, modulus, Poisson’s ratio, and an index indicating the degree of slip between layers. MnPAVE-Flexible assumes zero slip at all layer interfaces. All stresses and strains are considered to be within the elastic range of the material (no permanent deformation). Other inputs include load and evaluation locations. Loads are characterized as being circular and are expressed in terms of pressure and radius. The LEA program calculates normal and shear stress, normal strain, and displacement at specified locations.

Output includes the expected life of the pavement, which is calculated using a damage factor based on Miner's Hypothesis. Reliability is estimated using Monte Carlo simulation. There is also a batch


15

section for testing a range of layer thicknesses. In Research Mode (accessible from the "View" menu in the main MnPAVE-Flexible window), output includes various pavement responses for each season. Note: DO NOT design projects in research mode!

1. Installing MnPAVE-Flexible Note: An IT professional may be required for installation, if you do not have

administrator rights.

The installation file can be downloaded from the MnPAVE-Flexible website at: http://www.dot.state.mn.us/app/mnpave .

A. Left-click on “Download MnPAVE Flexible” and follow the prompts and instructions to start the MnPAVE Setup Wizard:

B. Use the MnPAVE Setup Wizard to determine the location that MnPAVE files and folders will use and install MnPAVE-Flexible.

• The executable MnPAVE.exe and Help files will be placed in “Program Files\MnDOT\MnPAVE” unless a different location is specified.

• A MnPAVE folder will be added to the Windows Start Menu, unless a different folder is specified.

C. Finish. At this point there will be a MnPAVE icon on the desktop and in the Windows Start menu under the folder name specified in Step F.

2. Using MnPAVE-Flexible

A. Starting the program.

The program can be started by double-clicking on the MnPAVE icon on the desktop or selecting MnPAVE from the Windows Start, select programs, then selecting the folder name specified in Step F of Section 430.1 (the default is MnPAVE).

B. Main Control Panel.

MnPAVE-Flexible initially opens to the Main Control Panel (shown in Figure 430.1). The Main Control Panel contains 5 input modules, a toolbar and a quick access bar that contain several utilities. MnPAVE-Flexible designs are performed by completing the modules in order from left to right. A module will not become available for input until the preceding module has sufficient inputs.

http://www.dot.state.mn.us/app/mnpave


16

Figure 430.1 – MnPAVE-Flexible Main Control Panel

Toolbar

Input Modules

Quick Access Bar


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C. Opening and saving a file.

MnPAVE-Flexible will automatically open to a new project. It is recommended to begin a design by saving the new project. MnPAVE-Flexible saves project files to an .mpv file format that is unique to MnPAVE-Flexible. A filename that includes the SP number is recommended.

The following commands can be used to open and save MnPAVE-Flexible files.

(1) The current file can be saved by clicking on , located on the quick access bar or by selecting "Save" from the "File" menu of the toolbar.

(2) Changes can be saved as a new file name by selecting "Save As" from the "File" menu.

(3) A new MnPAVE-Flexible file can be opened by clicking on the icon or by selecting "New" from the "File" menu on the toolbar.

(4) An existing MnPAVE-Flexible file can be opened by clicking on the icon or by selecting "Open" from the file menu. A recently saved file can also be selected from the list at the bottom of the "File" menu of the toolbar.


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D. Project Information Module The Project Information Module is a form for entering information necessary to identify a MnPAVE-Flexible project. MnDOT district, county, city, highway, construction type, design engineer, and project notes are entered in this module. This data will be retained with the saved MnPAVE-Flexible file and it will appear on the final design printout.

Identifying the county of the project in the Project Information Module will also locate the project in the Climate Module. This may be the easiest and most convenient method to locate the project in the Climate Module. MnPAVE-Flexible will identify the location of the climate data as the center of the county. The Climate Module will still need to be accessed before proceeding to the next module will be allowed.

In the notes section,

- For full-depth reclamation (FDR), stabilized full-depth reclamation (SFDR), or cold-in-place recycling (CIR) projects, identify the existing pavement layers and any milling used in the pavement design.

- Identify any assumptions that were used for the pavement design.

E. Climate Input Module Figure 430.2 - Project Information Module


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The Climate Input Module is where the project location is specified so that MnPAVE-Flexible can determine the local climate. The Climate Input Module contains a set of coordinates and a Minnesota map and is shown in Figure 430.3. If the longitude and latitude are known, those coordinates can be directly inputted into the module. Otherwise, left click on the map at the project location.

Coordinates may be entered here.

Or click on the Project location.

Figure 430.3 - Climate Module


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F. Traffic Module

This module is where traffic data and design life is entered.

(1) Select “Lifetime” and enter the 20-year flexible ESALs (BESALs) which can be found on the project traffic forecast. MnPAVE-Flexible also requires an ESAL annual growth rate which may also be found on the traffic forecast, although 2% is provided as a reasonable default.

(2) Specify the design period length as “20” years.

In some windows, such as this one, the initial view shows only the details necessary for a basic pavement design. To view more details click this button.

Figure 430.4 - Traffic Module


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G. Structure Module

In the Structure Module, the layers of the pavement structure are identified, by up to five layers. The user defines the layer thicknesses and materials and may specify some material properties. MnPAVE-Flexible assigns material properties to the layers based on the user-defined materials and then creates a model of the pavement structure.

As a rule for MnPAVE-Flexible, use average values for all material inputs. MnPAVE-Flexible methodology is based on the expectation that any inputs are average and procedures are included to account for variability in the materials. Outliers may be removed prior to determining the averages but no reliability factor should be applied.

(1) The HMA Mix Properties Form (see Figure 430.5) opens when the Structure Input

Module is initially accessed. This form may also be accessed on the “select sub-type” section of the Structure Module at a later time. This input screen is where the HMA binder grade is specified. If “show details” is chosen, the percent binder content and gradation may be specified. If there are layers (or in MnPAVE-Flexible “lifts”) of HMA with differing binder grades, binder content, or gradation then the properties of each layer may be specified here for up to three “lifts.”

a. The HMA Mix Properties Form is where the expected traffic speed is specified. This is

an important input for MnPAVE-Flexible. HMA is a viscoelastic material and is sensitive to the rate of loading. HMA behaves much stiffer with shorter loading (i.e., faster traffic). Conversely, the slower traffic moves, the more time it has to load the HMA and the more it behaves as a liquid. The standard is to specify the posted speed limit as the expected speed.

b. When this form is completed, click “OK” to continue to the Structure Input Module.


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(2) The Structure Input Module (see Figure 430.6) opens to the Basic Inputs tab. Here the layer thicknesses and material types are defined. In the edit structure area, the structure may be defined by up to 5 layers but may be as few as 3. a. The top layer is always HMA. You may click on the HMA layer in the “Select Subtype”

area to edit the HMA Mix Properties form (See the previous section).

b. Aggregate/granular layers. Aggregate base (AggBase), subbase, rubblized portland cement pavement (RPCC), SFDR, and CIR may be selected as layers in the edit structure area. Aggregate base (AggBase) and subbase will need to be further defined in the “select subtype” area (on the right). FDR is available as a subtype of aggregate base.

The pavement structure may only include two aggregate/granular layers. These include layers defined as AggBase, Subbase, RPCC, SFDR, and CIR. If the pavement structure includes more than two aggregate/granular layers then “Multi-Layer” may be selected as a subtype of an aggregate base or subbase layer. Within the “Multiple Aggregate Layers” form, the layer can be defined by up-to three layers of different aggregate/granular

Figure 430.5 – HMA Mix Properties Form

Appears when the “Show Details” button is clicked.


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materials and MnPAVE-Flexible will combine their properties into one composite layer. When performing a CIR pavement design, include the thickness of any remaining existing HMA with the thickness of the CIR layer. For example, 6 inches of existing HMA will have the top 4 inches recycled as CIR and 2 inches of existing HMA will remain undisturbed. Define this in the pavement structure as one 6-inch layer of CIR.

c. Define the next to bottom layer as engineered soil and the bottom layer as undisturbed soil.

Engineered soil represents soil that has been blended and re-compacted. Its thickness is normally the depth of any subcut that is backfilled with select grading material or the depth of any subgrade preparation (see Chapter 3 – Pavement Subsurface). If the project will not disturb the existing soil, the roadway soil is assumed to have been previously engineered or has been in place long enough to behave as an engineered soil; and the engineered soil layer is specifies as being 12.0 inches thick.


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Basic Tab

Edit Structure Area

Select Subtype Area

Intermediate Tab

Figure 430.6 – Structure Input Module – Basic Tab


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i. Choose a soil type by clicking on the soil layers in the select subtype area.

ii. The intermediate tab of the Structure Input Module allows you to enter strength parameters for aggregate, subbase, and engineered soil.

iii. If DCP testing has been performed on the in-place material, the DCP index may be

entered for an aggregate or subbase layer by checking the layer checkbox and entering the value. Do not check the check box without entering a value.

iv. If the soil has a known R-value, enter this number by checking the layer checkbox

and entering the value. Use the average R-value of any testing. The engineered soil is always the second to the last layer.

v. MnPAVE–Flexible always applies ½ the engineered soils R-value to the

undisturbed soil which must always be the bottom layer.

Aggregate and subbase DCP index may be entered here.

Engineered soil R-value may be entered here.

Figure 430.7 – Structure Module – Intermediate Tab


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D. Output Module

The Output Module (see Figure 430.10) is where the reliability and life expectancy of the pavement structure is shown. MnPAVE–Flexible models the effect of traffic and climate on the proposed pavement structure while taking in account variations in layer strengths and thicknesses. Note: All final designs must meet reliability requirements when using the Monte Carlo simulation.

(1) The following describes the three different ways that MnPAVE-Flexible models variations and reliability:

a. The quickest way to model the thickness and strength of the layers is to use a 70%

confidence level. This accounts for variations in the pavement structure and reliability by simply reducing the strength and thickness of the pavement layers. MnPAVE-Flexible is able to calculate the estimated years to failure, for fatigue and rutting, almost immediately using this method. The estimated life shown on the left side of the Output module is determined with this method.

Allowable stress is also calculated using this method. The allowable stress is the maximum stress allowed in the aggregate base layer due to a single heavy load event. A warning will appear immediately if the allowable stress criteria are not met. The allowable stress warning will indicate the minimum HMA thickness required to meet the allowable stress criteria.

b. Quick reliability is an estimate of a Monte Carlo simulation. c. The Monte Carlo simulation is the slowest calculation of the three methods. The time

for running this process ranges from less than one minute to a few minutes. The Monte Carlo simulation calculates the life of the pavement many times over. Each time, it varies the pavement layers’ strengths and thicknesses based on their averages and variances. The reported reliability is the percentage of these calculated lives that met or exceeded the required design life.


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(2) Upon opening the Output module an “Allowable Stress Warning” may appear, see Figure 430.8. This warning appears if the pavement structure has less than 3” of aggregate base material and consequently the stress in the aggregate layer cannot be calculated. If the pavement structure is intended to have less than 3” of aggregate base then disable the warning by clicking “Yes” and continue with the design output.

(3) Upon opening the Output module an “Allowable Stress Results” message may appear, see

Figure 430.9. This message appears when the allowable stress from a heavy, one-time load is calculated to exceed allowable stress in the base and indicates that the pavement structure must be improved. Clicking the “Adjust Layer 1 to Meet Requirements” button will close the message and add the minimum amount of thickness to the top layer so that allowable stress requirements are met. Otherwise, click “Close” and manually add pavement structure so that the requirements will be met.

Figure 430.8 – Allowable Stress Warning

Figure 430.9 – Allowable Stress Results


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(4) When the Output Module opens, it immediately calculates the estimated pavement life using a 70% confidence level. The “thickness goal seek” button can be used to optimize the layer thicknesses so that the lowest estimated life (fatigue or rutting) equals the design life. The user has the option to choose the layer to be optimized.

When “thickness goal seek” is used for non-HMA layers, the HMA layer will be adjusted for fatigue first (if necessary), and then the selected layer thickness will be adjusted. This is because adjusting underlying layers has a relatively small effect on fatigue life and may result in very thick layers.

The user may also manually change the thickness of the pavement layers. After any changes, the recalculate button must be clicked to recalculate the estimated lives with the new thicknesses.

(5) The Quick Reliability simulation may be initiated prior to the Monte Carlo simulation to further refine the trial pavement design.

(6) The final pavement design must meet the minimum reliability requirements of the Monte Carlo simulation for rutting and fatigue. According to the Monte Carlo simulation the final pavement design must have a reliability of

• ≥85% for less than 1 million flexible ESALs • ≥90 % for 1 million to 15 million flexible ESALs • >95% for more than 15 million flexible ESALs

(7) Whenever possible, the fatigue and rutting years should be within 5 years of each other to optimize the HMA and granular material thicknesses.

• Fatigue life is largely an effect of HMA thickness. • Rutting life is largely an effect of granular material thickness.

(8) Report the final pavement design.

I. Reports

A summary report can be saved as PDF file by clicking on the PDF icon on the quick access bar or by selecting "PDF Design Summary" from the "File" menu.

A screen shot of the output window can be saved by clicking on the camera icon on the quick access bar. Most other windows have a camera icon that can be clicked to print a screen shot.


29

Recalculate: Click this button after adjusting any layer thicknesses to recalculate the Estimated Life.

Estimated Life: Base on 70% confidence.

Adjust Materials: Layer thicknesses may be adjusted here.

Thickness Goal Seek: Adjusts the selected layer thickness to provide a 20-year Estimated Life.

Quick Reliability: An estimate of the Monte Carlo Simulation.

Monte Carlo Simulation: The reliability of the pavement structure.

Figure 430.10 – Output Module


30

440 - HMA Overlay of Existing Pavement

HMA overlays are placed on existing, intact HMA or PCC pavement that has not been processed (e.g., FDR, CIR, or rubblization). Typically, HMA overlays are less than 5.0 inches thick.

The performance of an HMA overlay is dependent on the condition of the existing pavement. Existing cracks, especially transverse thermal cracks, will reflect through the new HMA overlay which commonly limits the life of HMA overlays. Additionally, frost heaves, subgrade failures, severe stripping, or rutting of the aggregate base layer may also limit the performance of any HMA overlay if not repaired. If the roadway has considerable distresses that will limit the life of an HMA overlay, then consider other rehabilitation techniques. Existing PCC pavements that exhibit movement (i.e., rocking) are not recommended for a HMA overlay. Instead, to eliminate any movement, use the crack and seat or rubblization processes (see Section 420 – Rubblization and Crack and Seat).

Use this section to design HMA overlays of intact HMA or PCC pavements.

1. Use of milling

HMA pavements are often milled prior to placement of a HMA overlay. Leave a sufficient thickness of existing HMA to support any traffic or construction activities until the HMA overlay is placed. Milling is used for the following reasons: A. Milling will help restore the profile of the existing pavement’s surface, remove patching and

sealing materials that may bleed through the overlay, and remove surface distresses that otherwise might have reflected through the overlay. Typically, milling more than 2.0 inches is not necessary to attain these benefits.

B. Milling may be used to flatten any bumps or dips in the existing HMA. C. Milling may be used to remove any stripped or debonded layers in the existing HMA. If the

debonded or stripped layers are too deep to be removed, adjust the milling depth to leave a sufficient thickness of existing HMA to support any traffic or construction activities until the HMA overlay is placed.

D. Milling may also be used to lower the existing road surface profile to lessen the grade raise due

to placing an overlay.


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2. Establishing cross-slope

A proper pavement cross-slope (.02 feet/feet) may be constructed by either of these methods.

A. Mill the existing HMA pavement at its existing cross-slope and pave the HMA overlay with

variable thickness to produce the proper pavement cross-slope. B. Mill the existing HMA pavement at the proper pavement cross-slope and pave the HMA

overlay at one consistent thickness.

3. HMA overlay design life and thickness A. The design life of an HMA overlay is the number of years until a rehabilitation activity will

occur. Use the HPMA program to predict the performance of the HMA overlay (see Section 280 – Pavement Management System, steps 1-7B for directions) to determine when a rehabilitation activity will occur; unless Table 440.1 or Table 440.2, or experience, clearly demonstrates that a different value should be used.

B. For HMA roads that have a seasonal load restriction of less than 10 tons, the thickness of the

HMA overlay necessary to remove the restriction may be calculated using the TONN program and Falling Weight Deflectometer (FWD) data. See Section 200 - Falling-Weight Deflectometer (FWD) for guidance in getting and processing FWD data.

4. Background of Tables 440.1 and 440.2

Tables 440.1 and Table 440.2 are the result of a survey, originally performed in 1993, of the District Materials Engineers and Central Office Pavement Engineers. Averages and standard deviations of the survey were calculated and outliers (more than 2 standard deviations away from the average) were eliminated. The averages and standard deviations were recalculated. The tables basically consist of these averages and standard deviations, with very minor modifications for uniformity.

These tables were compared to the historical performance of HMA overlays using MnDOT’s pavement management system to verify that the design life averages and ranges in these tables are still applicable;. It was determined that the design lives and ranges contained in the tables are reasonable and remain applicable.


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Table 440.1 - Design lives of HMA overlays of existing HMA

MEDIUM (2-4") OVERLAY

20 Year Flexible ESALS

HIGH MED LOW

Sur

face

Con

ditio

n GOOD LIFE 10 12 14

RANGE 2 2 3

FAIR LIFE 8 10 12

RANGE 2 2 2

POOR LIFE 7 8 10

RANGE 2 2 2

THICK (≥4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio


RANGE 2 2 3

FAIR LIFE 11 13 15

RANGE 2 2 3

POOR LIFE 9 11 13

RANGE 2 2 2

MILL & MEDIUM (2-4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio


RANGE 3 3 3

FAIR LIFE 9 11 13

RANGE 3 3 3

POOR LIFE 8 10 12

RANGE 3 3 3

MILL & THICK (≥4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio


RANGE 2 2 3

FAIR LIFE 12 14 17

RANGE 2 2 3

POOR LIFE 11 13 16

RANGE 2 2 3

Surface Condition Key

GOOD - Minimal Stripping & No Rutting

FAIR - Severe Transverse Cracking Or Minimal Rutting Or Some Stripping

POOR - Severe Rutting Severe Stripping Or Severe Multiple Cracking

TRAFFIC 20 Year Flexible ESALS

HIGH >5M MED 1-5M LOW <1M


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Table 440.2 - Design lives of HMA overlays of existing PCC

MEDIUM (2-4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio

n GOOD LIFE 8 10 12

RANGE 2 2 2

FAIR LIFE 6 8 10

RANGE 2 2 2

POOR LIFE 5 6 8

RANGE 2 2 2

THICK (≥4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio


RANGE 2 2 2

FAIR LIFE 10 12 13

RANGE 2 2 2

POOR LIFE 8 10 12

RANGE 2 2 2

MILL & MEDIUM (2-4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio

n GOOD LIFE 9 11 13

RANGE 2 2 3

FAIR LIFE 7 9 11

RANGE 2 2 3

POOR LIFE 6 8 9

RANGE 2 2 3

MILL & THICK (≥4") OVERLAY


HIGH MED LOW

Sur

face

Con

ditio


RANGE 2 3 4

FAIR LIFE 11 13 15

RANGE 2 3 4

POOR LIFE 9 11 13

RANGE 2 3 4

Surface Condition Key

GOOD - Minimal Stripping & No Rutting

FAIR - Severe Transverse Cracking Or Minimal Rutting Or Some Stripping

POOR - Severe Rutting Severe Stripping Or Severe Multiple Cracking

TRAFFIC 20 Year Flexible ESALS

HIGH >5M MED 1-5M LOW <1M


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450 - Materials and Specifications

Use this section to help determine HMA materials (provided with a Mixture Designation Code) and other specifications that are included in a Materials Design Recommendation (MDR). For more information and/or assistance on HMA materials, contact the MnDOT Bituminous Engineering Unit (Office of Materials and Road Research) or visit their website at http://www.dot.state.mn.us/materials/bituminouscontacts%20new.html.

1. Mixture Designation Code

The Mixture Designation Codes are used to specify HMA mixes and a Mixture Designation Code for each HMA mix on a project must be included in the project’s MDR. There may be several different HMA mixes designated on a single project, although, judgment should be used to minimize the total number of different HMA mixes. Typically, it is not economic to specify another bituminous mixture for less than 2,000 tons. Examples of areas that may have different mixes on a project include; mainline wearing course, non-wearing course, shoulders, temporary pavements, local roads, multi-use trails, and others.

A. The Mixture Designation Code uses the following format: • 1st two letters are the mix design procedure – SP (Superpave gyratory mix design) or SM

(stone matrix). • 2nd two letters are the course – WE (wear course) or NW (non-wear course). • 5th letter is the maximum aggregate size – A through D. • 6th digit is the design traffic level – 2 through 6. • 7th and 8th digits are the design air voids – 40 (4.0% for wear course) or 30 (3.0 for non-wear

course and Low-Volume Non-Trunk Highway Wear Course). • Last letter is the asphalt binder grade – A, B, C, E, F, H, I, L or M.

http://www.dot.state.mn.us/materials/bituminouscontacts%20new.html


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B. Begin with Table 450.1 to determine the proper Mixture Designation Code(s).

Table 450.1 - Mixture Designation Mixture Course Code Format

Non-wear (4.0 inches below pavement surface)** SPNW (1)*(2)*30(3)* Wear (top 4.0 inches of pavement)** SPWE (1)*(2)*40(3)* Shoulder Wear & Low-Volume Non-Trunk Highway Wear

SPWE (1)*(2)*30(3)*

Stone Matrix Asphalt (SMA) >30 million ESALs SMWEE640H * Select (1) Aggregate size, (2) Traffic Level and (3) Asphalt Binder Grade as shown below * * The wearing course may be reduced to 3.0 inches for non-trunk highways with traffic

levels <3 million ESALs. (1) Aggregate size.

Table 450.2 - Aggregate Size and Recommended Minimum Lift Thickness Code Letter

Maximum Aggregate Size, Superpave (mm)

Nominal Maximum Aggregate Size

Minimum Lift Thickness

A SP 9.5 1/2 inch 1.5 inch B SP 12.5 3/4 inch 2.0 inches C SP 19.0 1 inch 3.0 inches D SP 4.75 3/8 inch 0.75 inch

Typically, aggregate size A or B is specified in asphalt paving mixtures. Aggregate size A provides a finer, tighter pavement surface and tighter longitudinal joints. Aggregate size B is coarser. Lift thickness should be considered when selecting aggregate size. Aggregate size A may be specified for the final lift only with aggregate size B used for all underlying lifts. However, aggregate size A may be placed on all lifts, too. With the approval of the Engineer, the Contractor may supply a gradation with a smaller maximum aggregate size than that specified (i.e. A instead of B).


36

(2) Design traffic level.

Table 450.3 - Traffic Level Traffic Level 20-year Design ESALs

2 <1 million

AADT < 2,230

3 1 - <3 million

AADT >2,300 to <6,000 4 3-<10 million 5 10-≤30 million 6 > 30 million

Note 1: For slow traffic consider designating a higher traffic level. Contact the MnDOT Bituminous Engineer for guidance.

Note 2: SMA (Stone Mastic Asphalt) is a premium stone on stone mix

intended only for the highest traffic volume facilities. Contact the MnDOT Bituminous Engineer for guidance regarding SMA.

(3) Asphalt binder grade letter

The asphalt binder grade letter is used to identify the PG Binder Grade. The MnDOT PG binder grades follow AASHTO M332 (MSCR). The standard MSCR PG grades for Minnesota are PG58, followed by the traffic loading designation and then the minimum pavement design temperature. For example: PG58S-XX, PG58H-XX, PG58V-XX, and PG58E-XX. The traffic loading designations are S (standard), H (high), V (very high) and E (extremely high). The asphalt binder grade letter and the PG grade (with and without MSRC designation) are shown in Table 450.4 and the recommended asphalt binder grades for typical applications are shown in Table 450.5 and Table 450.6.

Specify MSCR PG binder grades in all MDR’s. Since, at the present time, there is a transition to MSCR PG binder grades Table 450.4 shows both MSCR PG grading and the equivalent PG grade. To use MSCR PG binder grading it is necessary for the MDR to contain instructions to include special provisions for (2360) Plant Mixed Asphalt Pavement (MSCR) and (3151) Bituminous Material (MSCR) in the contract documents. Special provisions are available in the “Boiler Plate” on the MnDOT Special Provision website http://www.dot.state.mn.us/pre-letting/prov/pdf/SP2016.pdf.

http://www.dot.state.mn.us/pre-letting/prov/pdf/SP2016.pdf


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Table 450.5 - Recommended Asphalt Binder Grade for Mainline

Type of Construction <3 million 20-year ESALs

3 -10 million 20-year ESALs

>10 million 20-year ESALs

Overlay, wear course (Top 4.0 inches)3 B (PG 58S-28) B (PG 58S-28)1 E (PG 58H-28)1

New Construction,2

Wear course (Top 4.0 inches)3 C (PG 58H-34) C (PG 58H-34)1 F (PG 58V-34)1

All non-wear course3 B (PG 58S-28) 1. Selecting a higher PG will provide increased resistance to rutting. Contact the MnDOT

Bituminous Engineer for guidance.

2. New construction includes: reconstruction, rubblization, CIR, full-depth reclamation (FDR), and stabilized full-depth reclamation (SFDR).

3. The wearing course may be reduced to 3.0 inches for non-trunk highways with traffic levels <3 million ESALs.

Table 450.4 - PG Asphalt Binder Grade Letters Letter MSCR PG Grade Equivalent PG Grade

A PG 52S-34 B PG 58S-28 PG 58-28 C PG 58H-34 PG 58-34, PG 58-34(PMB) E PG 58H-28 PG 64-28, PG 64-28(PMB) F PG 58V-34 PG 64-34, PG 64-34(PMB) H PG 58V-28 PG 70-28, PG 70-28(PMB) I PG 58E-34 PG 70-34 L PG 64S-22 M PG 49S-34


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Table 450.6 - Recommended Binder Grade for Shoulders

Traffic Allowed Traffic Prohibited Next to Concrete

Mainline and Concrete Curb and Gutter

Generally, the same binder grade as mainline, but not

to exceed PG 58H-xx.

B (PG 58S-28) or A (PG 52S-34)

B (PG 58S-28) or E (PG 58H-28)

Asphalt binder grade notes:

a. Use SMA on the final wearing surface only (top 1.5” – 2” lift). Specify a minimum PG 70-28 (H) for SMA mixtures. Contact the MnDOT Bituminous Engineer for guidance.

b. With the agreement of the MnDOT Bituminous Engineer, the designer may allow, by Special Provision, the Contractor’s option to use PG 64S-22 on overlay construction when both of the following conditions are met:

• Overlay thickness of 3.0 inches or less and • Average in-place crack/joint spacing of 30-feet or less.

The Special Provision will limit the allowable RAP usage to 15% for mixtures specifying PG 64S-22.

c. For temporary construction (2 years or less) consider using PGS-22 when PG 58H-28 or PG 58V-34 is otherwise recommended.

d. For special or unique design considerations contact the MnDOT Bituminous Engineer.


39

2. HMA compaction designation

MnDOT Standard Specifications for Construction specification 2360 designates the HMA compaction method as the Maximum Density Method (2360.3.D1) but Ordinary Compaction (2360.3.D2) may also be specified.

A. Maximum density is tested by cutting cores from the completed pavement and determining their bulk density in a laboratory. This is the standard and should always be specified for mainline pavement (unless the total HMA quantity is less than 500 tons).

B. Ordinary compaction uses a control strip to determine the rolling pattern for compaction of the HMA pavement. This is typically designated for small areas or areas that will be difficult to collect cores from. Designate ordinary compaction for the following:

• Layers identified in the typical sections with a minimum planned thickness less than 1½ in. • Thin lift leveling. • Wedging layers. • Patching layers. • Driveways. • Areas the Contractor cannot compact with standard highway construction equipment and

practices. • Bike paths, walking paths, and other similar non-traffic paving areas.

3. HMA lift thickness The MDR designates the thickness of the individual lifts that will be used to construct the HMA pavement. The following items should be considered when establishing the lift thicknesses:

• The recommended minimum lift thickness for each aggregate size is shown in Table 450.2.

• Improved density is the greatest benefit of specifying thicker lifts. • Improved ride is the greatest benefit of paving more lifts (see the following section on

specifying smoothness). However, the ride improvement from 2 to 3 lifts is less than the improvement from 1 to 2 lifts.


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4. Smoothness

The MDR designates the ride equation or percent ride improvement to apply to HMA paving on the project. Use the following guidelines to determine which ride equation or percent ride improvement is appropriate. Consult the MnDOT Bituminous Engineer for other construction types not covered.

A. For the following construction types, use Equation HMA-A:

• New construction with a minimum of 3 lifts. • Overlay with a minimum of 3 lifts and lift thicknesses of at least 1.5 inches. • Construction with a minimum of 3 lifts, with curb and gutter and at least 8 feet separating

the traffic lane from the curb and gutter (i.e. a shoulder at least 8-feet wide). B. For the following construction types use Equation HMA-B:

• New construction with 2 lifts. • Construction with a minimum of 3 lifts, with curb and gutter adjacent to at least one driving

lane. • 2-lift overlays with 1.5 inch minimum lift thickness. • Winter-carry-over, wearing course on 2 lifts. • FDR or SFDR with 2 lifts. • Cold-in-place recycled pavements with 2 lifts. • Two lifts over concrete pavement.

C. For single-lift overlay construction on bituminous choose either Equation HMA-C or Percent Ride Improvement. Percent Ride Improvement is used only on single lift overlay projects that do not include milling (See Note 1 below for single-lift overlay on concrete). The Percent Ride Improvement provision compares the smoothness of the roadway before any construction activities have taken place to the smoothness of the roadway after construction activities are finished. Incentive/disincentive is determined by the percent ride improvement. Percent Ride Improvement is intended to be used in situations where the existing roadway is in poor condition. Data from pilot projects show that the rougher the road segment to begin with the greater the relative improvement possible. For instance, a road segment with a starting smoothness of 150 in/mile is more likely to be reduced to a smoothness of 75 in/mile than a road segment starting at 75 in/mile is to be reduced to a Smoothness of 37.5 in/mile. Contact the Special Provisions Unit to insert the Percent Ride Improvement in a Contract.


41

For the following construction types, use Percent Ride Improvement (1) (2): • Single-lift bituminous over bituminous (BOB) overlays on a roadway surface with an overall

Ride Quality Index (RQI) < 2.8 (MRI greater than 120 in/mi)*.

For the following construction types, use Equation HMA- C (1):

• Single lift bituminous over bituminous (BOB) overlays on a roadway surface with an overall

RQI > 2.8 (MRI 120 in/mi or less)*.

* This information is available in the District’s Pavement Management Condition Rating Reports.

Note 1: Table 2399-2 of the MnDOT Standard Specification excludes smoothness testing of

single-lift overlays on concrete, but requires evaluation of “Areas of Localized Roughness” (ALR) and the 10-foot straightedge. However, there may be unique situations on single-lift BOC construction where a smoothness evaluation requirement is appropriate. Consult the MnDOT Bituminous Engineer for guidance in those considerations.

Note 2: The original smoothness and final smoothness values should be obtained by calendar date

as close to one another as possible. Do not run the original smoothness in one year and the final smoothness in a different year (i.e. carryover projects).

The following “typical” smoothness values and the equivalent RQI are given for a perspective of various pavement smoothness numbers:

Table 450.6 Typical Smoothness Values

MRI RQI New pavement (3-lifts) 37 in/mile 4.1 New pavement (2-lifts) 47 in/mile 3.9 New pavement (1-lift) 60 in/mile 3.6

Aged pavement (10 years) 110 in/mile 2.9 Aged pavement (20 years) 150 in/mile 2.5

Table 2399-2 of the MnDOT Standard Specifications lists pavement surfaces that are excluded from smoothness testing but subject to evaluation of “Areas of Localized Roughness” (ALR) and the 10-foot straightedge 2360.3E (Surface Requirements). There may be other instances where you feel the ride specification is not appropriate on a project. In those instances make note in the Special Provisions that ride will be verified by MnDOT Standard Specification 2360.3E.


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4. Longitudinal joint enhancements Specify any longitudinal joint enhancements in the MDR for inclusion in a project. These products are intended to improve the long-term performance of longitudinal “cold” joints in HMA paving that are often the source of early pavement distress. The following joint enhancements are available for inclusion in projects and their specifications can be found on the MnDOT Bituminous Engineering website at http://www.dot.state.mn.us/materials/bituminousdesignpage.html A. Fog Sealing: This consists of treating the longitudinal construction joint with a light

application of bituminous material to seal the surface. This treatment is recommended for use on newly constructed HMA longitudinal joints and can also be used to maintain an existing longitudinal joint. The fog seal must be applied before permanent pavement markings are placed or before re-striping of an existing pavement.

B. Joint Adhesive: This is a thick, rubberized asphalt material applied to the vertical face of the cold joint before the adjacent lane is placed. The material is designed to provide a better bond between HMA passes and produce a better, more durable longitudinal joint that minimizes the potential for water infiltration.

C. Joint Stabilization: This consists of applying a fog seal over the longitudinal construction joint of a Hot Mixed Asphalt (HMA) Pavement with a light application of bituminous material, composed of petroleum oils and resins emulsified in water, as shown in the plans.

http://www.dot.state.mn.us/materials/bituminousdesignpage.html

MnDOT Pavement Design Manual, Dec 3, 2015


Chapter 5 – PCC (Portland Cement Concrete)




500 - New/Reconstructed PCC Pavements .................................................................................................. 2

510 - PCC Overlay of Existing HMA - Whitetopping ................................................................................. 5

520 - Unbonded PCC Overlay of Existing PCC – UBOL ........................................................................ 13

530 - PCC Joint Design ................................................................................................................................... 21

540 - PCC Thickness Design using MnPAVE-Rigid ................................................................................. 26

550 - Whitetopping Thickness Design using BCOA-ME ......................................................................... 29

560 - PCC Standard Plans and Plates ............................................................................................................ 35


1

Introduction

This chapter contains directions for designing portland cement concrete (PCC) mainline pavements and evaluating existing pavement with regard to rehabilitation with a PCC overlay. The process for deciding which pavement type to use on a project is described in Chapter 7 – Pavement-Type Selection.


2

500 - New/Reconstructed PCC Pavements

This section contains directions for the design of new/reconstructed PCC pavements which are projects that include the complete removal of the existing pavement or construction on a new alignment.

These pavements are built on aggregate base and granular subbase. The base and subbase layers provide a solid working-platform for construction of the PCC pavement and improved engineering properties as compared to native, non-granular soils; such as higher strength, less reduction in strength during spring thaw, lower frost susceptibility, and improved drainage. Base layers may also be constructed of drainable materials, which require either edge drains or daylighting the drainable layer to the ditches.

Use the following standards to design new/reconstructed PCC pavements:

1. Projects that involve working the existing soil must follow Figure 500.1 and its notes. 2. Projects that do not involve working the existing soil the subgrade must meet the following:

A. These projects must have existing soil, subbase, and/or aggregate base material in good condition, suitable as a platform for construction and to remain as part of the pavement section. The designer must evaluate the existing materials and determine what material will remain and what treatment, if any, will be required.

B. These projects do not need to meet all of the requirements shown in Figure 500.1. However, the minimum thickness for the PCC is 6.0 inches and the PCC must be constructed on a minimum of 4.0 inches of drainable or aggregate base (either new or existing). The aggregate base may be class 5, class 5Q or class 6.

3. If open graded aggregate base (OGAB) is used then edge-drains must be provided for its drainage. If drainable stable base (DSB) is used then it must be daylighted to the ditch or edge-drains must be provided for its drainage.

4. The PCC pavement thickness must be designed with the MnPAVE-Rigid program according to Section 540 – PCC Thickness Design Using MnPAVE-Rigid.

5. Use Section 530 – Joint Design to determine joint spacing, joint designations, dowel, and tie bar

requirements.


3

6. For guidance on pavement cross sections consult the Road Design Manual (Chapter 4 –Cross-Sections and Chapter 7 – Pavement Design).

7. Any construction beneath the typical shown in Figure 500.1 is at the discretion of the District Materials/Soils Engineer. For more guidance see Chapter 3 – Pavement Subsurface.


4

Figure 500.1 – Pavement design standards for New PCC Pavement for projects that involve working the existing Soil.

• When using aggregate base: o For non-granular existing soils use a

minimum of 12.0 inches of select granular materials.

o For granular soils (percent passing ratio

[no. 200 (75 μm)/1.0 inch (25 mm)] sieve ≤ 20), mix and compact the upper 12.0 inches (minimum) of the existing granular soils.

• When using a drainable base, place it on a

minimum of 4.0 inches of aggregate base (class 5, class 5Q or class 6).

PCC Pavement

Drainable or Aggregate Base

Granular Subbase

Existing Soil

6.0-inch minimum thickness

• 4.0-inch minimum thickness aggregate base (class 5, Class 5Q, Class 6).

• Or 4.0 inches of drainable base (OGAB or DSB).

Layer

Notes

Any construction beneath the granular subbase shall be at the discretion of the District Materials/Soils Engineer.


5

510 - PCC Overlay of Existing HMA - Whitetopping

MnDOT uses two procedures to design PCC overlays of existing HMA. One procedure uses the BCOA-ME (bonded concrete overlay of asphalt – mechanistic-empirical) program to design bonded PCC overlays of existing HMA. MnDOT uses PCC thicknesses ranging between 4.0 and 6.0 inches with this program. The relatively thin design thickness is made possible by taking advantage of a bond between the new PCC overlay and the existing HMA pavement. All designs with this procedure use a 20-year design life.

The second procedure uses the MnPAVE-Rigid program to design PCC overlays of existing HMA with PCC thicknesses 6.0 inches and greater. This program does not consider any bonding with the existing HMA. Designs with this procedure use a 35-year design life or may be used with a 20-year design life when using the BCOA-ME program wouldn’t be appropriate.

The following steps outline the data collection and design process (including the design of construction details) for whitetopping.

1. Survey of existing HMA pavement. Collect the following data to evaluate the suitability of the existing HMA for use with a bonded PCC overlay:

A. Perform a visual condition assessment of the existing HMA Surface and note:

• The amount of fatigue cracking. • The frequency of thermal cracks, their condition and widths. • Any areas that may not provide uniform support such as widenings within the travel lane,

cracked or uneven pavement edges, frost heaves, or subgrade failures. • The depth of rutting. • Any local distresses that may need to be repaired prior to placing the PCC overlay. • Areas of patching or evidence of maintenance activities. • The condition of the existing shoulders.

B. Collect project ride, surface rating, and rut depth information from the pavement management system (see Section 280 – Pavement Management System).


6

C. Collect HMA pavement cores away from cracks and on (or near) cracks in the existing HMA (see Section 230 - Cores) to determine the pavement thickness and the subsurface condition of the cracks.

D. Contact area maintenance personnel to determine if there are any areas of high maintenance,

frost heaves or other areas of concern.

2. Design the PCC overlay Use Table 510.1 to determine which design program to use, either BCOA-ME (Section 550 - Whitetopping Thickness Design Using BCOA M-E) or MnPAVE – Rigid (Section 540 - PCC Thickness Design Using MnPAVE-Rigid). Design the PCC overlay with the appropriate program.

Table 510.1 – Program to Use for Whitetopping Design

Program Design Life BCOA-ME

Candidate*

MnPAVE-Rigid

Candidate** Min. PCC Thickness

BCOA-ME 20 4.0 Inches MnPAVE-Rigid 20 6.0 Inches MnPAVE-Rigid 35 6.0 Inches

* Candidate for BCOA-ME design

• The existing pavement has uniform support conditions with only localized weak areas that must be repaired prior to placing the PCC overlay.

• The primary distresses in the existing HMA pavement are surface distresses. • Thermal cracks in the HMA pavement are predominately non-deteriorated thermal

cracks. Deteriorated thermal cracks will require repair prior to placing the PCC overlay. • There is a sufficient existing HMA thickness so that after any proposed milling;

o 85% of the cores are 4.0 inches or thicker. o Any individual core must be a minimum of 3.0 inches thick. Any areas with less than

3.0 inches of HMA may be treated by removing the existing HMA pavement and constructing a 6.0-inch (minimum) PCC section.


7

** Candidate for MnPAVE-Rigid design • The existing HMA pavement has significant structural deterioration and areas of

uneven support conditions. • Existing HMA overlay of PCC Pavement. • The existing pavement exhibits evidence of significant foundation movement due to

settlements, frost heave, swelling soils, etc. • The existing HMA has been widened, or will require widening, within the area of the

driving lane. • The HMA pavement that will remain after any milling exhibits stripping and/or

debonded layers. • HMA pavements with predominately deteriorated thermal cracks that will require repair

prior to placing the PCC overlay. • There is an insufficient existing HMA thickness so that after any proposed milling:

o More than 15% of the cores are less than 4.0 inches thick. o There are individual cores less than 3.0 inches thick. However, any areas of less than

3.0 inches of HMA may be treated by removing the existing HMA pavement and constructing a 6.0-inch (minimum) PCC section.

3. Milling and pre-overlay repairs of the existing HMA pavement.

• Mill HMA pavements that exhibit shoving and/or rutting prior to placing the PCC overlay. The milling depth should be at least one half inch below the rutting and shoving.

• The existing HMA pavement may be milled to reduce the rise in pavement grade caused by the placement of the PCC overlay.

• If the PCC overlay is thinner than 5.0 inches then the surface of the existing HMA pavement must always be milled prior to placing the PCC overlay.

• When milling, avoid leaving a thin layer of existing bituminous that may debond. Adjust the milling depth to leave at least one half inch of thickness of an existing lift.

• Provide for full-depth patching (including foundation repair) of any areas of subgrade failure or bottom-up cracking (alligator cracking).

• Subgrade repair and full-depth patch any area that exhibits differential frost heave • Patch or fill depressions (potholes). • Patch or fill cracks that are wide, deteriorated cracks.


8

4. Design joints according to Section 530 – Joint Design.

5. PCC overlays wider than the existing mainline pavement (PCC Overlay 6.0 inches and thicker).

A. When the PCC overlay is wider than the existing HMA pavement and the outside edge of

the existing pavement is not under the new driving lane (as marked), follow the details of Figure 510.2.

Figure 510.2 - PCC overlay wider than the existing HMA pavement and the outside edge of the existing pavement is not under the new driving lane (PCC overlay 6.0 inches or thicker).

Topsoil

Shoulder Driving Lane

Aggregate base Existing HMA pavement

New PCC overlay

A

B C

B C

Tie bar

NOTES:

A. This area may be compacted aggregate base or a material that will provide equal or better support.

B. If the PCC overlay extends 2 feet, or less, beyond the existing HMA Pavement, then no tie bar is required.

C. If the PCC overlay extends more than 2 feet beyond the existing HMA Pavement, then saw a joint in the PCC overlay at the extent of the existing HMA Pavement and include a tie bar.

Shoulder PI


9

B. When the PCC overlay is wider than the existing HMA pavement and the outside edge of the existing pavement is under the new driving lane (as marked), follow the details of Figure 510.3.

Figure 510.3 - PCC overlay wider than the existing HMA pavement and the outside edge of the existing pavement is under the new driving lane (PCC overlay 6.0 inches or thicker).

6. PCC overlay wider than existing mainline pavement (PCC overlay less than 6.0 inches thick) A. When the PCC overlay is wider than the existing pavement and the outside edge of the

existing pavement not under the new driving lane (as marked) follow the details of Figure 510.4.

B. PCC overlays that are wider than the existing HMA pavement and the outside edge of the

existing pavement is under the driving lane (as marked) are poor candidates for a PCC overlay designed with BCOA-ME (i.e. <6.0 inches thick) and should be designed with MnPAVE-Rigid (see Section 540 - PCC Thickness Design Using MnPAVE-Rigid).

NOTES:

A. This area must be HMA or PCC.

B. If the PCC overlay extends 2 feet, or less, beyond the existing HMA Pavement, then no tie bar is required.

C. If the PCC overlay extends more than 2 feet beyond the existing HMA Pavement, then include a tie bar but do not saw a joint (because it would be in the driving lane).

Topsoil

Driving lane


New PCC overlay

A

B C

B C

Tie bar

Shoulder Shoulder PI


10

7. Reinforcing steel

For pavements 6.0 inches or greater in thickness, place tie bars over any changes in underlying support that are more than 2 feet from the edge of the PCC overlay. If this location is in the driving lane, place the tie bars but do not cut a joint.

Do not include reinforcing steel in PCC overlays that are less than 6.0 inches thick, unless using the configuration of Figure 510.4.

Figure 510.4 - PCC overlay wider than the existing pavement and the outside edge of the existing pavement is not under the new driving lane (PCC overlay Less than 6.0 inches thick).

Topsoil

Shoulder Driving lane


New PCC overlay

A

B

C

NOTES:

A. This area may be compacted aggregate base or a material that will provide equal or better support.

B. Widening must be a minimum of 1.5 feet wide.

C. Provide a 36.0-inch long, No. 4 or No. 5 tie bar by stapling it to the surface of the existing HMA; saw a joint in the PCC overlay at the extent of the existing HMA Pavement.

6.0 inches min.

Shoulder PI

Tie bar


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8. Transitions

Transitions between whitetopping and adjacent pavement are areas of high stresses. A thickened section in this area is recommended to prevent future distresses. Figure 510.5 and Figure 510.6 show the typical transition details for HMA and PCC pavements. Figure 510.7 shows the typical transition for paving on grade or full depth repair sections.

9. Additional information

An additional source of information on whitetopping is the “Guide to Concrete Overlays, Third Edition” (ACPA publication TB021.03P) available at http://www.cptechcenter.org/technical-library/documents/Overlays_3rd_edition.pdf

Existing HMA pavement

New PCC overlay

Existing aggregate base

Approximately 6 feet Approximately 6 feet

PCC thickness (H) inches PCC thickness (H +3.0) inches

Saw cut

Figure 510.5 - Transition from whitetopping to adjoining HMA pavement.

http://www.cptechcenter.org/technical-library/documents/Overlays_3rd_edition.pdf



12

Existing HMA

New PCC overlay


20’ Taper

Refer to Figure 510.8

12 or 15’ To match project joint spacing

C2H-D joint C2H joint

Refer to Standard Plate No. 1150


Existing PCC

Center of Panel

Figure 510.6 - Transition from whitetopping to existing PCC pavement.

Figure 510.7 - Transition from whitetopping to New PCC.

Existing HMA pavement

New PCC overlay


20’ Taper

New PCC pavement

New aggregate base

New subbase


C2H-D joint C2H-D joint

12 or 15’ To match project joint spacing

C2H joint Center of

Panel


13

Figure 510.8 – Supplemental steel reinforcement

3- #4 Bars @ 2’ C-C

3- #4 Bars @ 2’ C-C

1’ 1’

13 -

14’ t

ypic

al

6”

13 -

15’ t

ypic

al

Equa

lly sp

aced

C/L

6”

16 -

#6 B

ars

16 -

#6 B

ars

Equa

lly sp

aced

Dowel bar assembly (see Standard Plate 1103)

C1U or C2H joint cut perpendicular to C/L at end of transition taper

C1D-D or C2H-D C1D-D or C2H-D

L1TU

or L

1TH

12 or 15’ To match the project joint spacing

Note: All supplemental steel must be epoxy coated and comply with MnDOT spec. 3301.

Center of Panel


14

520 - Unbonded PCC Overlay of Existing PCC – UBOL

Unbonded PCC overlays are used to rehabilitate distressed PCC pavements. They are constructed by placing a new PCC overlay on an interlayer that separates the new overlay from the existing pavement. The interlayer may be made of permeable asphalt stabilized stress relief course (PASSRC), new or existing HMA, or a geotextile that is designed for this purpose. The interlayer is intended to prevent a bond developing between the existing pavement and the new PCC overlay and, in the case of PASSRC and geotextile, to also provide drainage.

The following steps outline the data collection and design process (including the design of construction details) for unbonded concrete overlays of existing PCC pavement.

1. Document the condition of the existing PCC pavement and shoulders. Unbonded PCC overlays may be used to rehabilitate most existing PCC pavements. Collect the data required by this section to help design the PCC overlay and to determine the necessary pre-overlay repairs. A. Core the pavement to determine the thickness of the existing PCC pavement and shoulders. B. Determine the height of faulting from the MnDOT pavement management system data or

field measurements. C. Visually examine the pavement for any Distress-cracking (D-cracking) or alkali-silica reaction

(ASR). D. Visually examine the pavement to determine the number and extent of slabs that are:

• Shattered • Rocking • Moving • Heaving • Settling

E. If the unbonded overlay will require widening beyond the existing PCC roadway, evaluate the existing shoulders to determine if they are stable enough to support the widening or need to be repaired or replaced.


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2. Pre-overlay repairs In the design procedures, pre-overlay repair refers to minor repairs and milling of an existing asphalt overlay. One major advantage of an unbonded overlay is the amount of repair to the existing pavement prior to overlay is minimized. Unbonded overlays are not intended to bridge localized areas of non-uniform support but locations of unstable support or movement should be repaired. The following tables (Table 520.1 and 520.2) should be reviewed and repaired prior to placement of the overlay:

A. Existing jointed concrete pavements (JPCP and JRCP)

Most of the serious deterioration in existing jointed plain concrete pavement (JPCP) and jointed reinforced concrete pavement (JRCP) that requires pre-overlay repair occurs at joints and cracks. The following table (Table 520.1) describes common distresses and recommended repair for these types of pavements.


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TABLE 520.1 – Recommended Pre-Overlay Repairs of Existing Distresses in JPCP

Distress Type Repair

Working crack No repair is needed for non-spalled cracks.

Spalling Remove loose material & patch with HMA or PCC.

Faulting < 0.25 inches

No repair of the joint or crack for faulting will be necessary.

Use 1.0 inch of PASSRC or standard HMA as the interlayer. Fabric may also be used.

Faulting > 0.25 inches

Use 1.5 inches of PASSRC or standard HMA as the interlayer instead of using fabric or remove the faulting with grinding/milling and use fabric.

Pumping/free water

Use PASSRC as the interlayer; install interceptor drains and/or edge drains.

PCC Durability (D-cracking and ASR problems)

Remove loose pieces of concrete pavement and patch with a HMA or PCC before placing the interlayer.

Rocking or unstable slab with high deflection or pumping problems

Repair the subbase and/or subgrade if soft or eroded material is responsible for the loss of support.

Replace the pavement with full-depth PCC or HMA.

Badly shattered slab with working cracks

Repair the subbase and/or subgrade if it is soft or eroded.

Replace the pavement with full-depth PCC or HMA.

Settlement Level-up with HMA or PCC.

Severe Frost Heave Subgrade correction and full-depth PCC or HMA replacement.


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B. Existing continuously reinforced concrete pavement (CRCP) The most serious distresses in CRCP that require repair are punch-outs and ruptured steel. The following table describes common distresses and recommended repair for this type of pavement.

TABLE 520.2 – Recommended Pre-Overlay Repairs of Existing Distresses in CRCP

Distress Type Repair

Punch-out, blowups, high severity D-cracking

Full-depth PCC removal (repair area should extend at least 18.0 inches beyond the area of distress).

Excavate and re-compact the subbase and subgrade.

Replace full-depth with concrete.

Deteriorated or working Transverse cracks with ruptured steel and construction joints with high-severity spall

Repair full-depth with PCC or HMA.

Saw joints in the existing PCC every 100 feet to sever the steel reinforcement.

3. Interlayer design

A. PASSRC – permeable asphalt stabilized stress relief course PASSRC is an open-graded HMA that prevents the PCC overlay from bonding to the existing PCC and provides drainage. Provide edge-drains when using PASSRC. Details for PASSRC with edge drains are shown in Standard Plan 5-297.432. The typical design thickness of PASSRC is 1.0 inch. This may be increased to 1.5 inches if faulting greater than 0.25 inch is present. NOTE: Perform any crown corrections with the PCC overlay rather than the interlayer to prevent difficulties with anchoring dowel bar baskets. Other corrections may require adjustments to the interlayer.


18

B. Non-woven geotextile fabric A specially designed geotextile fabric may be used as an interlayer. This fabric provides drainage and prevents the PCC overlay from bonding to the existing PCC. Geotextile fabric is an acceptable alternate for most candidate PCC pavements. However, the use of geotextile fabric is not advised if joint faulting is greater than 0.25 inch because of concerns that the overlay may “lock onto” the fault which will cause a stress concentration. Geotextile fabric requires drainage, either by daylighting (shown in Figure 520.1 & Figure 520.2), or edge drains (replace the PASSRC layer with a geotextile interlayer in Standard Plan 5-297.432).

Figure 520.1 - Geotextile interlayer with daylighting detail for HMA or aggregate shoulders.

C B


Existing PCC

PCC Overlay 6” min.

Geotextile fabric interlayer

Existing shoulder

Topsoil

NOTES:

A. If this area will be under the driving lane (as marked) then this area must be HMA or PCC; otherwise, this area may be compacted aggregate base material or material with equal or better support.

B. If the PCC overlay will extend more than 2 feet beyond the existing PCC then include tie bars.

C. If the PCC Overlay will extend more than 2 feet past the outside edge of the existing PCC and the outside edge of the existing PCC won’t be under the driving lane; saw a longitudinal joint in the PCC overlay at the outside edge of the existing PCC.

6”-12” Shoulder PI

C

B

A


19

Figure 520.2 - Geotextile interlayer with daylighting detail for PCC shoulders.

C. New HMA

New HMA may be used as an interlayer. It will prevent the PCC overlay from bonding to the existing PCC but it will not provide drainage.

The typical design thickness is 1.0 inch but should be increased to 1.5 inches if faulting greater than 0.25 inches is present.

NOTE: Perform any crown corrections with the PCC overlay rather than the interlayer to prevent difficulties with anchoring dowel bar baskets. Other corrections may require adjustments the interlayer.

D. Existing HMA overlay over PCC Pavement An existing HMA overlay may be used as all or part of the interlayer. If badly deteriorated, it should be removed and replaced with some other interlayer. Otherwise, it should be milled to provide a smooth surface profile and to establish the cross-slope on which to build the overlay.

4. Transitions

Transition from an unbonded overlay to on-grade pavements should be in accordance with Figure 520.3 or Figure 520.4.


Existing PCC

PCC overlay

Geotextile fabric interlayer

Existing shoulder

PCC shoulder

Topsoil Aggregate shouldering

Extend the geotextile fabric 6” to 12” beyond the PCC shoulder


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5. Thickness design

Design unbonded PCC overlays of existing PCC pavements using the MnPAVE-Rigid program according to Section 540 - PCC Thickness Design Using MnPAVE-Rigid. Use 20-year and 35-year design lives as required by Chapter 7 – Pavement-Type Selection.

6. Additional information

An additional source of information on unbonded overlays of PCC Pavements is the “Guide to Concrete Overlays, Third Edition” (ACPA publication TB021.03P) available at http://www.cptechcenter.org/technical-library/documents/Overlays_3rd_edition.pdf

Existing PCC pavement


20’ Taper

New aggregate base

New subbase Refer to Figure 510.8

12 or 15’ to match project joint spacing

Center of Panel C1U joint C2H-D joint

C1U-D joint

Unbonded PCC overlay On-grade PCC

PASSRC


20’ Taper

Aggregate base (or HMA non-wearing course)

12 or 15’ to match project joint spacing

Center of Panel C1U joint C1U-D joint C1U-D joint

Unbonded overlay On-grade PCC

PASB 4.0”

New aggregate base

PASSRC


7.5” Existing PCC pavement

Figure 520.3 Transition from an unbonded overlay to an on-grade pavement.

Figure 520.4 Transition from an unbonded overlay to an on-grade pavement.



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530 - PCC Joint Design

1. Joint spacing, dowel bars, and tie bars Joint spacing and dowel bars in concrete pavements must comply with Table 530.1. In any case, longitudinal joints must not be placed near the wheel paths (such joints lead to increased degradation and decreased service life).

The required number of dowel bars in a 12-foot lane is defined as either a “Full -Set” or “Wheel Path.” A “Full-Set” is 11 dowel bars spaced 1 foot apart (on center) and shown in MnDOT Standard Plate 1103. “Wheel Path” is 3 dowels in each wheel path for a total of 6 dowels per 12-foot lane. For the placement of “Wheel Path” dowels with a “Full-Set” basket, see Figure 530.1.

Table 530.1 – PCC Joint Spacing/Dowel Bars PCC

Thickness Joint Spacing Dowel Bars All Longitudinal

Joints Longitudinal (Panel Width)

Transverse (Panel Length)

Size Number (Per 12’ Lane)

≥ 10 ½ inches

12’ – 14’ 15’ 1 ½” dia. Dowels

Full-Set (11 dowels)

No. 5 tie bars (36” long)

8-10 inches 12’ – 14’ 15’ 1 ¼” dia. Dowels

Full-Set (11 dowels)***


7 & 7.5 inches

12’ – 14’ 15’ 1” dia. Dowels



6 & 6.5 inches *

12’ – 14’ 12’ 1” dia. Dowels



6 & 6.5 inches *

6’ – 8’ 6’ Un-Doweled No. 4 tie bars (30” long)**

4 -5.5 inches 6’ – 8’ 6’ Un-Doweled See Figure 510.4**

* 6.0 & 6.5-inch overlays may have either 12’-14’x 12’ or 6’-8’x6’ panels. Contact the MnDOT Pavement Design and Concrete Engineers to determine the best option.

** Do not include tie bars on pavements less than 6.0 inches thick, unless using the arrangement of Figure 510.4.

*** Use Wheel Path (6 dowels) dowels bars for UBOL or whitetopping.


22

2. Joint designation Specify in the Materials Design Recommendation (MDR), the typical contraction (transverse) and longitudinal joints on a project. A. Contraction joints

Use the following steps to determine the joint designation of the contraction joints. Contact the MnDOT Concrete Unit (Office of Materials and Road Research) if varying from the recommendations. STEP 1. Use Table 530.1 to determine if the contraction joints will or will not include

dowel bars. STEP 2. Use Table 530.2 to determine, based on joint sealing recommendations, which

joint references may be designated. STEP 3. Using the determinations of the previous steps, designate the PCC contraction

joints as one of the joint references in Table 530.3 (based on MnDOT Standard Plan 5-297.221).

BASKET

Do Not Install Dowel Bars

Figure 530.1- "Wheel Path" dowels in a "Full-Set" basket


23

Table 530.2 – Concrete Joint Sealing Guidelines

Type of Construction * Speed Limit Base Material Joint

Reference All Roadways, excluding

ramps and loops ≤ 45 mph

All C2H

C2H-D PCC Overlay on Existing HMA (Whitetopping) < 6” thick

> 45 mph

Existing HMA

New Construction

> 45 mph

All C1U

C1U-D

Unbonded PCC Overlay of Existing PCC (UBOL)

PCC Overlay on Existing HMA (Whitetopping) ≥ 6” thick

Ramps and Loops All

* For future concrete pavement rehabilitation (CPR) projects, follow the same recommended practices as original construction. Contact the MnDOT Concrete Unit with questions.

Table 530.3 – Contraction Joint Reference, Detail & Sealer Spec. Table (MnDOT Standard Plan 5-297.221)

Joint Reference Joint Sealant Material & Spec. Joint Width Without Dowels With Dowels

C1U C1U - D Unsealed 1/8 inch

C2H C2H - D Hot Pour – 3725 1/8 inch

C3P C3P - D Preformed Elastomeric - 3721 3/8 inch

C4S C4S - D Silicone - 3722 3/8 inch

C5H C5H - D Hot Pour – 3725 3/8 inch


24

B. Longitudinal joints Use the following steps to determine the joint designation of the longitudinal joints. Contact the MnDOT Concrete Unit (Office of Materials and Road Research) if varying from the recommendations. STEP 1. Determine the type of longitudinal joint

• L1 – A paved construction joint (i.e. the PCC on each side of the joint is placed

concurrently). • L2 – Tied/keyed construction joint (i.e. PCC on one side of the joint is placed

with a keyway formed in it and/or tie bars; the abutting pavement is placed later).

• L3 – Butted Construction Joint (i.e. PCC is simply placed against previously placed PCC).

STEP 2. Determine if the joints should be tied

(1) Tied joints

• L1 and L2 joints are generally recommended to be tied. (2) Untied joints

• When a roadway is 5 or more lanes wide, include a L3 joint so that no more than 4 lanes are tied together.

• Pavements less than 6.0 inches thick, unless using the arrangement of Figure 510.4.

• L3 joints don’t have the option to include tie bars.

STEP 3. Determine if a keyway (with tie bars) should be included.

• A keyway (intended to improve load transfer across the joint) may be specified for L2 joints of PCC pavement 7.0 inches or thicker.

• Keyways are not provided for shoulder joints.

STEP 4. Determine if the joints must be sealed.

• Do not seal L2 or L3 joints. • Seal L1 joints if the contraction joints will be sealed.


25

STEP 5. Designate the PCC longitudinal joints as one of the joint references in the Table

530.4 (based on MnDOT Standard Plan 5-297.221) using the determinations of the previous steps.

Table 530.4 – Longitudinal Joint Reference, Detail & Sealer Spec. Table (MnDOT Standard Plan 5-297.221)

Joint Reference

Joint Sealant Material & Spec. Joint Width Without

Tie Bars

With Tie Bars

With Keyway with Tie

Bars

L1U L1TU Unsealed 1/8 inch

L1H L1TH Hot Pour –3725 1/8 inch

L2TU L2KTU Unsealed

L2TH L2KTH Hot Pour – 3725 3/8 inch

L3U Unsealed

L3H Hot Pour – 3725 3/8 inch


26

540 - PCC Thickness Design using MnPAVE-Rigid

MnPAVE-Rigid is a PCC pavement design program which uses transverse cracking as the controlling distress. It is based on the MEPDG version 1.1, a mechanistic-empirical design procedure which accounts for the effects of traffic loading and environment. MnPAVE-Rigid was locally calibrated for Minnesota pavements through: 1) the use of local climate data and weigh-in-motion traffic data; 2) the incorporation of previously conducted calibrations of the MEPDG for Minnesota pavements; 3) the inclusion of advanced analysis features included in MnPAVE-Rigid’s flexible design counterpart, MnPAVE-Flexible. 1. This section provides standards for the design of PCC pavements using the MnPAVE-Rigid

program. The MnPAVE-Rigid program may be used for the pavement design of the following:

• New/reconstructed PCC pavements on aggregate base, including full-depth reclamation (FDR). New/reconstructed PCC Pavements on aggregate base that involve working the subgrade must also meet the standards shown in Figure 500.1 and its notes.

• Unbonded PCC overlays of existing PCC. • PCC overlays on existing HMA, or on a composite pavement of HMA on PCC, with a design

life of 35 years. A 20-year design life may be used if the project wasn’t determined to be a candidate for design with BCOA-ME.

Figure 540.1 - View of MnPAVE-Rigid


27

2. Follow the steps below to perform PCC pavement design using MnPAVE–Rigid. It can be obtained from the Software page of the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/software.html. STEP 1. Open the program. It should open to the “Main” tab which is where design inputs are

entered and the thickness calculated. STEP 2. For a new project, begin by entering a short, identifiable name into the “Project name”

text box. This will be the name of the data file that saves the user’s inputs. An existing data file can be loaded by clicking on the “Load from *.txt file” button.

STEP 3. Enter any notes into the “Project Notes” text box. STEP 4. Enter the design life into the “Design Life, Years” text box. This will be either 20 or

35. STEP 5. Choose the project’s district from the “Climate (by district)” drop-down list. STEP 6. Enter the “Initial, HCADT.” This value is the base year “HCADT: two-way” (Heavy

Commercial Average Daily Traffic) that is found on the project’s traffic forecast. STEP 7. Enter the “Linear yearly growth (%).” This value is the “GROWTH/YR” for the

“HCADT: two-way” that is found on the project’s traffic forecast. STEP 8. The default “Axle load spectra” is “MnDOT WIM Average” which is appropriate for

most situations.

“MnDOT WIM Heavy” may be selected from the “Axle load spectra” drop-down list if a traffic forecast shows that more than 70% of the HCADT is 5 axle + trucks and twin trailers. Use “MnDOT WIM Heavy” if the following formula is true.

⌊(5𝐴𝐴𝐴𝐴 + 𝑇𝑇𝑇𝑇𝑇𝑇)% + (5𝐴𝐴𝐴𝐴 + 𝑇𝑇𝑇𝑇𝑇𝑇 𝑀𝑀𝐴𝐴𝐴𝐴)% + (5𝐴𝐴𝐴𝐴 + 𝑇𝑇𝑇𝑇𝑇𝑇 𝑂𝑂𝑇𝑇𝑂𝑂)%⌋

𝑂𝑂𝐻𝐻𝐴𝐴𝐻𝐻𝑇𝑇%> .70



28

STEP 9. For “Widened outer lane,” if any the following conditions are met, select “yes”:

• The outside lane will be paved at least 1 foot past the marked edgeline. • The outside lane will be paved at the same time as the concrete shoulder and the

joint between them will include tie bars (i.e. a concrete shoulder with a tied L1 joint).

• The outside lane will include an integral curb and gutter.

If none of these conditions are met, select “No.” STEP 10. For “Shoulder type”:

• If the outside lane will be paved separately from a concrete shoulder or a curb and gutter, and the joint between them will include tie bars (i.e. a concrete shoulder with a tied L2 joint) then select “tied PCC.”

• Otherwise, select “HMA, Untied PCC, or Aggregate.” STEP 11. Set the “Joint spacing” to either 12 or 15 feet. The joint spacing with regard to the

calculated thickness must meet the requirements of Section 530. Note: Select 12 feet if 6X6 foot panels are intended to be used.

STEP 12. Left-click on the “Run” button to calculate the pavement thickness. If all inputs

haven’t been completed then an error box will appear that requests the completion of all the inputs.

STEP 13. Use the following rounding procedure to determine the Design Thickness.

• Round-down 0.01 to 0.19 to the nearest inch (X.01 to X.19 = X.0) • Round 0.20 to 0.69 to the nearest ½ inch (X.20 to X.69 = X.5) • Round-up 0.70 to 0.99 to the next inch (X.70 to X.99 = X+1.0)

STEP 14. Make sure that the joint spacing is appropriate for the design thickness according to

Section 530. Run the program again after making any adjustments to the joint spacing. NOTE: If PCC pavement designs with both 12 and 15-foot joint spacings are

both applicable, the design with the 15-foot spacing is generally preferred.


29

550 - Whitetopping Thickness Design using BCOA-ME

Use this section to design whitetopping with a 20-year design life if the project was determined to be a candidate for BCOA-ME design according to Section 510.1.B. Otherwise, design whitetopping pavement using MnPAVE-Rigid (see Section 540 - PCC Thickness Design Using MnPAVE-Rigid).

A. Use the BCOA-ME program according to the following directions.

STEP 1. Load the BCOA-ME. The program is available as a webpage at http://www.engineering.pitt.edu/Sub-Sites/Faculty-Subsites/J_Vandenbossche/BCOA-ME/BCOA-ME-Design-Guide/. The program is available only as a webpage and an internet connection is required for its use.

STEP 2. Enter the latitude, longitude and elevation of the project.

Left-clicking on the “Geographic Information” button will open the Geographic Information webpage which will provide help with getting this information. The Geographic Information webpage provides two options for getting the latitude, longitude and elevation.

Option 1 opens an external website that will provide the required information for any city or address. Left-clicking on the “Open Webpage” button opens the veloroutes.org website. Alternatively, Google Earth may also be used. After using the website to determine the latitude, longitude and elevation return to the Geographic Information webpage. Return to BCOA-ME by either left-clicking the “Cancel” button or using your browser’s back button. The latitude, longitude and elevation must then be manually entered into the appropriate boxes. Option 2 provides a drop-down list of cities with available information. Choose the appropriate city and then Left-click the “submit” button. The “submit” button will return you to BCOA-ME and automatically fill the latitude, longitude and elevation boxes. Only use option 2 if the project is located near one of the available cities.

http://www.engineering.pitt.edu/Sub-Sites/Faculty-Subsites/J_Vandenbossche/BCOA-ME/BCOA-ME-Design-Guide/

http://www.engineering.pitt.edu/Sub-Sites/Faculty-Subsites/J_Vandenbossche/BCOA-ME/BCOA-ME-Design-Guide/


30

STEP 3. Enter the Design Lane ESALs. Do not use the “ESALs Calculator” button. If the pavement design will be constructed or is a possible alternate bidding project then use the 20-year Rigid ESALs from the project’s traffic forecast. Otherwise, the average 20-year Rigid ESALs from the ESAL Forecasting Tool are acceptable (see Section 250 – Traffic Data).

STEP 4. Leave the Maximum Allowable Percent Slabs Cracked at “25” and the Desired Reliability against Slab Cracking at “85.”

Figure 550.1 – View of BCOA-ME


31

STEP 5. Set the AMDAT Region ID to “1” using the drop-down box. STEP 6. Enter the Sunshine Zone using the drop-down box. To determine the correct value,

left-click on the blue label that says “Map of Sunshine Zone.” Find the correct value using the map then left-click on the “back” button or anywhere on the map to return to the BCOA-ME. The value is not automatically sent to the BCOA-ME and the value must be manually selected with the drop-down box. For Minnesota the value will always be either “4” or “5.”

STEP 7. Enter the Post-Milling HMA Thickness in inches. This is the Design Existing HMA

Thickness minus the proposed milling depth. The Design Existing HMA Thickness is the 85% percentile thickness of the HMA cores (85% with that thickness or greater).

STEP 8. Choose a HMA Fatigue condition, either Adequate or Marginal. Adequate is defined

as 0-8% fatigue cracking and Marginal is defined as 8-20% fatigue cracking. Clicking on the “Example of Fatigue Cracking” button opens a webpage with visual examples of both conditions. Return to BCOA-ME by either left-clicking the “Back” button or using your browser’s back button.

STEP 9. Enter the Modulus of Subgrade Reaction, k-value. This value represents the

composite support of the subgrade and any in-place base material. Compute this value by using the “k-value Calculator” button. Clicking this button opens your internet browser to the American Concrete Pavement Association’s (ACPA) k-value calculator website at http://apps.acpa.org/applibrary/KValue/. Guidance for its use is shown in Figure 550.2. Calculating the k-value does not automatically place the value in the BCOA-ME and the value must manually be entered.

STEP 10. Select either the “Yes” or “No” button to indicate if transverse cracks are present.

The design process includes a check to determine if there is the potential for reflective cracking to occur. This does not affect the design thickness but indicates whether preemptive measures should be taken prior to placing the overlay to prevent reflective cracking into the overlay.

STEP 11. Enter the “Average 28-day Flexural Strength” as 650. STEP 12. Enter the “Estimated PCC Elastic Modulus” as 4,000,000. Don’t use the “Epcc

Calculator” button. STEP 13. Enter a “Coefficient of Thermal Expansion” of 5.0. Don’t use the “CTE Calculator”

button.

http://apps.acpa.org/applibrary/KValue/


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STEP 14. Select the “Fiber type” as “No Fibers” with the drop-down box. STEP 15. Select a “Joint Spacing” of “6 x 6” with the drop-down box. STEP 16. Left-click on the “Calculate Design” button to calculate the design. Warning, the

program will not automatically recalculate the design when changes are made to the inputs and the “Calculate Design” button must be clicked again.


33

Figure 550.2 - ACPA k-value Calculator

1.Click on the calculator.

2. Select “Resistance Value (R-Value)” and enter the mean R-value.

3 click “Calculate. Resilient Modulus”

4. Choose Layer Type. Typically the selected material will be “unstabilized (granular) subbase.” (Repeat for each layer.)

5. Use a Resilient Modulus of 27,000 for aggregate base or 15,000 for select granular.

6. Enter the layer thickness.

7. To define another layer repeat 4-6.

8. Click the “Calculate” button to compute the composite k-value.


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B. Results

The program displays the calculated PCC overlay thickness, which is the exact, un-rounded value and also displays the design PCC overlay thickness which is the rounded final value. Do not report a design PCC overlay thickness of less than 4.0 inches; report it as 4.0 inches..

C. Printing and saving results

Right-click anywhere on the BCOA-ME and select “Print preview” from the drop-down menu. Make sure that preview looks acceptable. Typically, setting the print size to “shrink to fit” will provide the best appearance for the BCOA-ME; however, superfluous information will be on a second page and only the first page will require printing. Either select a printer to print a physical copy or, if equipped, select “Adobe PDF” to create an Adobe PDF file.


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560 - PCC Standard Plans and Plates

In the MDR, provide the MnDOT Standard Plans and Plates for PCC pavement to include as a reference in the project plans. 1. Access to MnDOT Standard Plans and Plates:

The MnDOT Standard Plans are available at the following link: http://standardplans.dot.state.mn.us/

The MnDOT Standard Plates are available at the following link: http://standardplates.dot.state.mn.us/

2. These are commonly used or referred to standard plans/plates in PCC paving plans:

• Any of the Standard Plans in the 200 series (5-297.2xx) • Standard Plan 5-296.616 – Rumble Strips for Concrete • Standard Plate 1070x - Reinforced Panel over Culverts • Standard Plate 1103x - Typical Dowel Bar Assembly • Standard Plate 1141x - Pavement Keyway for Keyed Joint Construction • Standard Plate 1150x - Construction of Header Joints • Standard Plate 1210x – Concrete Pavement Adjacent to Railway Crossing

http://standardplans.dot.state.mn.us/

http://standardplates.dot.state.mn.us/

MnDOT Pavement Design Manual, Jul15, 2015


Chapter 6 – Ramps, Shoulders, Turn Lanes & Miscellaneous Pavements




600 – Ramps and Loops ................................................................................................................................... 1

610 - Shoulders ................................................................................................................................................... 2

620 - Widening Existing Lanes and Adding Lanes ....................................................................................... 4

630 - Turn Lanes ................................................................................................................................................ 5

640 - Temporary Median Crossovers .............................................................................................................. 6

650 - Parking Lots and Driveways .................................................................................................................. 7

660 - Roundabouts ............................................................................................................................................ 8

670 - Shared-Use Paths ..................................................................................................................................... 8


1

Introduction

This chapter contains standards and guidance for the pavement design of non-mainline pavements. Often the design of these pavements will require a degree of engineering judgment and may follow district preference/experience.

600 – Ramps and Loops

Ramps and loops are short roads which allow vehicles to enter or exit a grade separated highway. Ramp pavements are constructed of HMA or PCC. Use the following to design ramp pavements.

1. HMA

HMA is a suitable material for ramps for most applications, including for both HMA and PCC mainlines. Existing HMA ramps may be rehabilitated with the same methods as used for mainline pavements (e.g. overlays, full-depth reclamation (FDR), stabilized full-depth reclamation (SFDR), and cold-in-place recycling (CIR)).

The pavement must meet the pavement design requirements of Chapter 4 – HMA.

2. PCC

PCC is a suitable material for ramps and loops. Existing PCC ramps may be rehabilitated with the same methods as used for mainline PCC pavements.

The pavement must meet the pavement design requirements of Chapter 5 – PCC. Consider matching the PCC thickness of the ramps to the mainline or cross-road.


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610 - Shoulders

Shoulders are pavement (HMA/PCC) or aggregate that extends past the marked traffic lanes and is not intended for use as a travel lane. In specially designated areas shoulders may be used by buses to bypass traffic.

Shoulder material is dictated by the mainline pavement material, the amount and type of vehicle use on the shoulder, the condition and type of any existing shoulders, and the results of any required LCCA.

See the Roadway Design Manual - Chapter 4 – Cross Sections for more information on shoulder widths and cross-sections.

1. Materials A. Aggregate surfacing

(1) Aggregate shoulders

Aggregate is a relatively inexpensive material that may be used to construct shoulders, however, aggregate requires re-grading and may not perform well under high traffic or heavy loads. Because of these limitations, aggregate shoulders are typically used on low-volume, rural roads in which the shoulders are not subject to repetitive loads. Typically, the top 3.0 inches of aggregate shoulders are constructed of class 1 or class 2 aggregate surfacing and may contain recycled material (depending on district preference/experience) placed on the same aggregate base material as mainline.

(2) Aggregate shouldering with paved shoulder In addition to any paved shoulder (HMA/PCC), a 1.5-foot wide strip of aggregate (class 1, class 2, or recycled HMA millings) is provided to “round” the intersection of the shoulder and the inslope. This is considered a useable part of the shoulder.

B. HMA

HMA may be used to construct shoulders for either HMA or PCC mainline pavements.

(1) When mainline rehabilitation projects increase the elevation of the mainline pavement, the elevation of the shoulders must be raised to match the mainline. To achieve this, HMA


3

shoulders are typically either overlaid or rehabilitated by reclaiming the existing HMA, placing aggregate base as required, and paving a new HMA shoulder.

(2) HMA shoulders are classified as either “thin” (<4.0 inches) or “thick” (≥4.0 inches). Shoulders classified as “thin,” are expected to be rehabilitated by being removed and replaced. “Thick” HMA shoulders are expected to be rehabilitated with an overlay or a mill and overlay. The difference in expected rehabilitation activities will affect any LCCA performed on the road.

(3) New HMA shoulders are typically constructed 3.0 or 4.0 inches thick and placed on the same aggregate base as the mainline. If the HMA shoulder is designated as a bus-only shoulder then the thickness should be structurally designed according to Chapter 4 – HMA. The subsurface layers should match the mainline pavement to maintain the continuity of drainage and to prevent any differential heaving between mainline and the shoulders.

C. PCC

PCC is suitable shoulder material for PCC mainline pavements. Besides acting as a durable, low-maintenance shoulder material, a tied PCC shoulder provides structural benefits to mainline PCC pavements (that have full lane-width panels) which may result in a thinner required mainline PCC thickness.

Minimum thickness

• PCC shoulders that are placed as whitetopping (PCC overlay of existing HMA) have a minimum required thickness of 4.0 inches (same as whitetopping). See Section 510 – PCC Overlay of Existing PCC - Whitetopping for the pavement design of whitetopping.

• For a tied PCC shoulder, the PCC shoulder thickness must meet the following

o No thinner than 5.0 inches.

o No thinner than ½ the mainline PCC thickness plus 2.0 inches. This allows the tie-bars to be placed mid-depth in the mainline pavement and provide 2.0 inches of cover for the tie bars.

• If the PCC shoulder is designated as a bus-only shoulder then include dowel bars and

design the thickness according to Chapter 5 - PCC.

• For other circumstances, PCC shoulders have a minimum required thickness of 4.0 inches.


4

620 - Widening Existing Lanes and Adding Lanes

This section discusses permanent additions to an existing pavement such as widening, or adding/extending turn lanes. In general, to minimize differential movement relative to adjacent existing pavements, additions are designed to match the thickness and materials of adjacent pavements as much as practical.

1. Mainline widening and adding through lanes

Pavements that carry through-traffic must meet the structural requirements of Chapter 4 - HMA or Chapter 5 - PCC. However, the pavement section should be designed to match the adjacent existing section rather than following Figure 400.1 or Figure 500.1. Any of these pavement segments that are more than a ½ mile long must have a signed traffic forecast. Contact the MnDOT Concrete Engineering Unit (Office of Materials and Road Research) to discuss the suitability of tying a new concrete lane to an existing concrete lane.

2. Other additions

Typically, traffic data is not available to design pavement additions, such as adding (or extending) turn lanes or auxiliary lanes. These sections are recommended to match the adjacent existing pavements and have at a minimum:

• 4.0 inches of HMA pavement on aggregate base and subbase that matches the mainline structure.

• 5.0 inches of PCC pavement on aggregate base and subbase that matches the mainline structure.

3. Pavement widening drainage system

Permeable aggregate base (PAB) is a recommended option for designs that involve the widening of narrow pavements so as to perpetuate the drainage of any water trapped in the existing pavement by the widening. The drainage system is shown in MnDOT Standard Plan 5-297.432. The type of PAB material (drainable stable base (DSB), open-graded aggregate base (OGAB), and permeable asphalt stabilized base (PASB)) used for this widened section is optional.


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630 - Turn Lanes

If the turn lanes are expected to carry a high amount of heavy commercial truck traffic, then the turn lane should be designed to meet the structural requirements of Chapter 4 - HMA or Chapter 5 - PCC. Contact the MnDOT Concrete Engineering Unit (Office of Materials and Road Research) to discuss the suitability of tying a new concrete lane to an existing concrete lane.

At a minimum, turn lanes must meet the following requirements:

• 4.0 inches of HMA pavement on aggregate base and subbase that matches the mainline structure.

• 5.0 inches of PCC pavement on aggregate base and subbase that matches the mainline structure.


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640 - Temporary Median Crossovers

Temporary median crossovers are HMA pavements that are installed before a project on a divided highway to allow traffic to be diverted from one set of lanes, across the median, to the other set of lanes and are removed at the completion of the project.

At a minimum provide 4.0 inches of HMA with 6.0 inches of aggregate base. It is recommended to construct the entire embankment required for the crossover from granular material.

Note: It is recommended to complete construction of temporary median crossovers 60 days prior to receiving traffic or construct them the previous season if possible.


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650 - Parking Lots and Driveways

Use this section to design the pavement section of parking lots and driveways. Evaluation and treatments below these sections are at the discretion of the District Materials/Soils Engineer.

1. HMA

• For parking lots or driveways that are ordinarily loaded with passenger cars, the minimum pavement section is 3.0 inches of HMA and 6.0 inches of aggregate base.

• For parking lots or driveways that accommodate heavy trucks, the minimum pavement section is 4.0 inches of HMA and 12.0 inches of aggregate base.

• If a large number of heavy trucks are expected then design the pavement thickness according to Chapter 4 – HMA.

• Mix Designation o For parking lots or driveways that are ordinarily loaded with passenger cars, specify a mix

designated as SPWEB330A, SPWEB330B or SPWEB330C. o For parking lots or driveways that accommodate heavy trucks, specify a mix designated as

SPWEB440F.

2. PCC

• For parking lots the minimum pavement section is 5.0 inches of PCC on 12.0 inches of aggregate base.

• For driveways the minimum pavement section is 4.0 of PCC on aggregate base. o Joints will be sealed, un-doweled, and should not be more than 6 feet apart. For doweled

joints, follow Table 530.1 – PCC Joint Design.

• If a very large number of heavy trucks are expected, then design the pavement according to Chapter 5 – PCC.


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660 - Roundabouts

Roundabouts have the same pavement design requirements as mainline pavements; see Chapters 4- HMA or Chapter 5-PCC. A separate traffic forecast must be developed for just the roundabout to be used for the pavement design.

Because of the turning-movements and slow speeds experienced in a roundabout, it is recommended to increase the high temperature of the asphalt PG by one grade.

Contact the MnDOT Concrete Engineering Unit (Office of Materials and Road Research) to discuss details for PCC truck aprons and PCC roundabouts.

670 - Shared-Use Paths

A shared-use path is typically located on exclusive right-of-way, with no fixed objects in the pathway and minimal cross flow by motor vehicles. Portions of a shared-use path may be within the road right-of-way but physically separated from the roadway by a barrier or landscaping. Users typically include bicyclists, in-line skaters, wheelchair users (both non-motorized and motorized) and pedestrians.

Subgrade and surfacing recommendations for shared-use paths should be provided by or reviewed by the District Materials/Soils Engineer, and included in the project’s Materials Design Recommendation (MDR). Shared-Use Paths may be paved with PCC or HMA. For HMA, it is recommended to specify a SPWEA230B bituminous mixture for the shared-use path surfacing. This mix includes a PG 58-28 binder; however, specifying a PG 52-34 or PG 58-34 binder is acceptable. Guidelines for the design of the Pavement Structure of shared-use paths are contained in Section 5-5.0 of The MnDOT Bikeway Facility Design Manual. http://www.dot.state.mn.us/bike/pdfs/manual/Chapter5.pdf

http://www.dot.state.mn.us/bike/pdfs/manual/Chapter5.pdf



Chapter 7 – Pavement-Type Selection



Contents Introduction ........................................................................................................................... 1

700 - Steps to Perform Pavement-Type Selection ........................................................... 3

710 - Pavement Design Categories ..................................................................................... 4

720 - Determination of Which LCCA Process to Follow .............................................. 6

730 - Formal LCCA Process ............................................................................................... 8

740 - District LCCA Process ............................................................................................ 12

750 - Alternate Bidding ..................................................................................................... 16

760 - LCCA Formulas and Standards ............................................................................. 18

770 - LCCA Maintenance Activities................................................................................ 23


1

Introduction

Scope This chapter contains the process to determine the pavement-type of MnDOT projects.

Background MnDOT has had separate procedures to determine the pavement-type of new pavement projects (last documented in Technical Memorandum 10-04-MAT-01), rehabilitation projects (last documented in Technical Memorandum 09-12-MAT-03) and to determine the pavement-type through alternate bidding. This chapter replaces those procedures.

In addition, this chapter implements Minnesota State Statute 174.185. This legislation requires a life-cycle cost analysis (LCCA) to be performed for all pavement projects in the reconditioning (RD), resurfacing (RS), and road repair (RX) funding categories. The LCCA is required to compare competing paving materials using equal design lives and equal comparison periods. If the chosen alternate does not have the lowest life-cycle-cost, then the justification is required to be documented.

Overview Pavement-type selection determines a project’s pavement-type by using a LCCA or alternate bidding.

LCCA is used to calculate the low-cost alternate, among alternates with equal benefits, by comparing each alternate’s combined initial and future costs. The value of future costs and benefits is converted into a present cost using a process called discounting. Discounting represents the time value of money given its ability to earn interest (i.e. a dollar today is worth more than a dollar tomorrow); this means the later a future cost occurs, the lower the value of its present cost. Initial cost is an estimate of an alternate’s construction costs. The initial cost shouldn’t include all construction costs, but it does need to include all costs that differ between the alternates.

Pavement-type selection requires following one of two LCCA processes, either Formal LCCA or District LCCA. The Formal LCCA process is performed to determine the low-cost alternate and to evaluate if the project is a good candidate for alternate bidding. Good candidates for alternate bidding are projects with competitive alternates that are both likely to attract bidders, which are typically projects that involve pavements with long design lives (20 years or greater). The District LCCA process is used only to determine the low-cost alternate.


2

Since the Formal LCCA is used to evaluate projects for alternate bidding costs must be calculated in the same manner as alternate bidding, by accounting for the length of the project, variations in pavement design and width, and variations in shoulder design and width that occur over the project’s length. This involves calculating costs for multiple segments of pavement and summing the costs together to determine a total cost for each alternate.

The District LCCA process is used only to determine the low-cost alternate. The District LCCA process is simpler and not every variation in pavement design and pavement width is included in the LCCA.

Both LCCA processes use standard schedules of future activities to calculate future costs. The standard schedules specify when and what future activities will occur and the quantities needed to develop their cost. A 50-year schedule of future activities is provided for most pavement-types and design lives, which is a sufficient period to ensure that a major rehabilitation activity will occur in the schedule. Some pavement-types with short design lives (less than 20 years) only have 35-year schedules provided. These pavement-types will require multiple rehabilitations, and perhaps reconstruction, in a 50-year period and these activities are too uncertain to predict with accuracy. So that all schedules may be compared, a 35-year schedule is provided for all pavement-types and design lives.

The standard schedules of future costs were developed by the MnDOT Pavement Design Engineer and are based on preventive and rehabilitation activities as they are currently performed. Data for developing the standard schedules came from pavement management system (PMS) data and quantities from MnDOT projects. In addition, judgment and accepted MnDOT standards were used to supplement the available data when it was not sufficient. Draft schedules were distributed for review and comment to the District Materials/Soils Engineers as well as representatives of the HMA and PCC pavement industries.

User, supplemental, and other noneconomic costs are not formally evaluated by the LCCA processes or alternate bidding; however, these costs may be used to help determine applicable alternates for the LCCA processes and may be used as justification (on a case-by-case basis) for an exception to the LCCA processes or for the use of alternate bidding.

At the completion of the LCCA processes either, the low-cost alternate is selected; a different alternate is selected if an exception is granted, or the project continues to alternate bidding.

Projects in the Formal LCCA process may have their pavement-types selected using the alternate bidding process. Plans for alternate bidding projects contain two pavement-type alternates and contractors choose the alternate on which they will bid. The low-cost bidder is determined after considering the initial construction cost (the contractor’s bid) and the bid adjustment factor, which is the difference in the discounted future costs between the alternates and is added to the alternate with the greater discounted future costs.


3

700 - Steps to Perform Pavement-Type Selection

The pavement-type selection process begins with pavement designs that were proposed during the project planning or the project scoping processes. The proposed designs and the directions given in this chapter are used to select the pavement-type.

Begin the pavement-type selection with the following steps.

STEP 1. Identify the “unique pavement designs” that were proposed in the project selection or project scoping processes.

One or more pavement design may have been proposed over the length of the project. Each of these pavement designs (not necessarily contiguous) that are consistent in pavement structure, thickness, width, material, and design life is defined as a “unique pavement design.”

For example, project scoping may only propose one pavement design, such as a 4.0-inch overlay for the length of the project, and therefore the project would have only one “unique pavement design.” Project scoping of another project may propose a 4.0-inch overlay for the majority of the project but also proposes reconstruction at multiple locations. The overlay would be one “unique pavement design”, and the reconstruction design would be a second “unique pavement design” (if the reconstruction design is the same for all locations).

STEP 2. Categorize each “unique pavement design” using Section 710 - Pavement Design Categories.

STEP 3. Determine which LCCA process to follow using Section 720 - Determination of

Which LCCA Process to Follow.

STEP 4. Follow either the Formal LCCA process, Section 730 - Formal LCCA Process, or the District LCCA process, Section 740 - District LCCA Process, as determined by Section 720 - Determination of Which LCCA Process to Follow.

STEP 5. Continue to the alternate bidding process, Section 750 - Alternate Bidding, if it was

determined to do so by the Formal LCCA process.

STEP 6. 12-18 months prior to the project letting, review any previously prepared LCCA for the project, and update the LCCA if changes to costs or to the project may change the outcome.


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710 - Pavement Design Categories

Use the following descriptions, or Flowchart 710.1, to categorize each “unique pavement design” that was proposed by the project planning or project scoping processes. Reference Chapters 4 HMA & 5 – PCC to determine design lives. After categorizing all of the project’s “unique pavement designs”, continue to Section 720 - Determination of Which LCCA Process to Follow.

1. DL ≥ 20 (Design Life of 20 years or greater)

This category includes pavement with a design life of 20 or more years.

Examples include:

• New/reconstructed HMA • New/reconstructed PCC • Full-depth reclamation (FDR) • Stabilized full-depth reclamation (SFDR) • Rubblization of PCC • Cold-in-place recycling (CIR) • PCC overlays (whitetopping or unbonded overlay) • Other

This category does not include HMA overlays 5.0 inches thick or less. For the purpose of choosing a LCCA process all HMA overlays 5.0 inches or less but greater than 2.0 inches in thickness are included in the DL<20 category.

2. DL < 20 (Design Life less than 20 years) This category includes pavement designs that have a design life less than 20 years and are thicker than 2.0 inches. For the purpose of choosing a LCCA process, all HMA overlays 5.0 inches or less but greater than 2.0 inches in thickness are included in this category regardless of design life.

3. ≤ 2” Maintenance

This category includes new pavements ≤ 2.0 inches thick. These projects are considered to be maintenance activities with no opportunity to develop an alternate pavement type.


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Does the pavement design have a design life of less than 20 years?

Categorize the next unique pavement design.

Does the pavement design have a design life of 20 or more years?

Is the design an overlay ≤ 2.0 inches?

The pavement design is categorized as DL < 20.

The pavement design is categorized as ≤ 2” Maintenance.

START With first unique pavement

design

The pavement design is categorized as DL ≥ 20.

Is the pavement design a HMA overlay >2.0 inches and ≤5.0 inches thick?

The pavement design is categorized as DL < 20.

Have all the unique pavement designs been categorized?

YES

NO

NO

NO

NO

YES

YES

Continue to Section 720.

Flowchart 710. 1 – Categorizing “unique pavement designs”

YES

YES


6

720 - Determination of Which LCCA Process to Follow

Use the following tables, or Flowchart 720.1, and the pavement design categories determined in Section 710 - Pavement Design Categories to determine which LCCA process to follow.

Table 720.1 – Follow Formal LCCA

OR

Projects that have 60,000 or more contiguous sq. yds.(1) of pavement in the DL≥ 20 Category.

Any project that the district wants to evaluate as a potential alternate bidding candidate.

Table 720.2 – Follow District LCCA

OR

Projects that have more than 7,500 sq. yds. but less than 60,000 contiguous sq. yds.(1) of pavement in the DL≥ 20 Category.

Projects that have 60,000 or more sq. yds.(1) of pavement in the DL<20 Category.

AND Does not meet the requirements to follow the Formal LCCA process.

Table 720.3 - No LCCA Required

Any projects that does not meet the requirements to follow the Formal LCCA process or District LCCA process. The designer should select the proposed pavement design.

(1) The pavement area is calculated using only the 12-foot wide travel lane of the mainline

pavement and doesn’t include shoulders, ramps, parking lanes, turn lanes, or auxiliary lanes.


7

Flowchart 720.1 – Determining which LCCA process to follow

(1) The pavement area is calculated using only the 12-foot wide travel lane of the mainline pavement and doesn’t include shoulders, ramps, parking lanes, turn lanes, or auxiliary lanes.

Does the project include 60,000 or more contiguous sq. yds.(1) of pavement in the DL ≥ 20 Category?

The project requires a Formal LCCA. Continue to Section 730.

Does the district want to evaluate the project for Alternate Bidding?

Does the project include 60,000 or more sq. yds.(1) of pavement area in the DL<20 Category?

Does the project include more than 7,500 sq. yds. but less than 60,000 contiguous sq. yds.(1) of pavement area in the DL ≥ 20 Category?

The project requires a District LCCA. Continue to Section 740.

No LCCA Required. Select the proposed pavement design.

START

NO

NO

The project requires a Formal LCCA. Continue to Section 730.

The project requires a District LCCA. Continue to Section 740.

The project does not meet the requirements to perform a Formal or District LCCA

YES

YES

YES

YES

NO

NO


8

730 - Formal LCCA Process

Follow this section if Section 720 - Determination of Which LCCA Process to Follow determined that a Formal LCCA is required.

STEP 1. Develop pavement designs for the required alternates for each “unique pavement design” that meets either of the following criteria (A or B below). Chapter 9 - Construction and Rehabilitation Alternates may be consulted to determine appropriate alternates.

Criteria A. For each “unique pavement design” in the DL≥ 20 Category, develop pavement designs for the required alternates in Table 730.1.

Table 730.1 - Required Alternates for DL≥20 Category

Alternate Number 1 2 3

Pavement Material HMA PCC PCC

Design Life 20 Years 20 Years 35 Years


9

Criteria B. For each “unique pavement design” in the DL< 20 Category that is greater than 7,500 sq.yds(1), develop pavement designs for the required alternates in Table 730.2

Table 730.2 - Required Alternates for DL<20 Category

Alternate Number

1 2 3

Pavement Material

As Proposed in Scoping or Project Development(2) HMA PCC

Design Life

For the Pavement Design Proposed in

Scoping or Project Development(2)

20 Years 20 Years

(1) The pavement area is calculated using only the 12-foot wide travel lane of the mainline

pavement and doesn’t include shoulders, ramps, parking lanes, turn lanes, or auxiliary lanes. (2) The design life and pavement material of the pavement design proposed in scoping or

project development process. Chapters 4 HMA and 5 - PCC may be consulted to determine design life.

STEP 2. Perform a LCCA to calculate the net present cost of each alternate.

A. Get the most current version of the “Initial cost spreadsheet” and the “LCCA

standard spreadsheet” from the Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/lcca.html The website contains a version of the “Initial cost spreadsheet” and the “LCCA standard spreadsheet” for each district. These spreadsheets contain item prices specific to each district and are updated annually. In addition to annually updating the prices, the spreadsheets may be updated to improve usability or correct errors.

B. Calculate initial cost for each pavement design Use the “Initial cost spreadsheet” to calculate the initial cost of constructing a representative mile of each pavement design. The initial cost must include the cost of constructing the pavement section between the shoulder points of intersection (PI). This includes the cost of the mainline and shoulder pavements, base, subbase, and engineered soil. Additional costs may also be included that reflect the difference in

http://www.dot.state.mn.us/materials/pvmtdesign/lcca.html


10

construction of the alternates, such as; different grade raises between alternates, traffic detour or no detour, constructing under traffic, or A+B contracting.

The “Initial cost spreadsheet” contains the most common item costs to estimate the construction cost but if a necessary item cost is not provided contact the MnDOT Pavement Design Engineer.

C. Perform LCCA(s) using the “LCCA standard spreadsheet” This spreadsheet follows the LCCA standards in Section 760 – LCCA Formulas and Standards and Section 770 – LCCA Maintenance Activities. 1. Perform a LCCA for alternates developed from Table 730.1 and a separate

LCCA for alternates developed from Table 730.2. 2. For each LCCA:

• Use a 50-year analysis period for alternates developed from Table 730.1. • Use a 35-year analysis period for alternates developed from Table 730.2.

3. The “LCCA standard spreadsheet” automates the calculation of future costs using the user’s inputs, Section 760 – LCCA Formulas and Standards and Section 770 – LCCA Maintenance Activities, and the “District Standard Prices.” For each segment, the user enters an initial cost developed from the “Initial cost spreadsheet” and completes an input form with data related to that alternate’s pavement design, pavement section geometry, and segment length. When the data in the input form is accepted, the Net Present Cost of that segment of the alternate are automatically calculated.

4. The “LCCA standard spreadsheet” spreadsheet will calculate the net present cost

of each alternate by summing the individual net present costs of each segment of the alternate.

STEP 3. Send the completed LCCA to the MnDOT Pavement Design Engineer for review and

changes. When the LCCA is to the satisfaction of the MnDOT Pavement Design Engineer continue to Step 4.

STEP 4. If the Net Present Cost of a HMA and a PCC option are within 10% of each other then

continue to Section 750 – Alternate Bidding, otherwise continue to Step 5.


11

STEP 5. Select the low cost alternate

The alternate with the least Net Present Cost is the low-cost option and must be selected unless the district is granted an exception. The reason for the exception must be documented in an exception form and is considered granted when it is signed by the MnDOT Pavement Engineer. The exception form is available on the Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html. Reasons for an exception may include;

• The low-cost alternate isn’t physically constructible • Construction would cause unreasonable user delay or user hardship (e.g. construction

would require unacceptable closures, long detours, or an extended construction period)

• Performance would be unacceptable • Other supplemental costs or noneconomic factors (see Table 960.1)

STEP 6. Based on the selected pavement alternate, prepare and distribute a Materials Design

Recommendation (MDR) in accordance with Section 810 - Materials Design Recommendation (MDR). Attach the LCCA and any exceptions to the MDR.

http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html


12

740 - District LCCA Process

Follow this section if Section 720 - Determination of Which LCCA Process to Follow indicated that a District LCCA is required.

STEP 1. For each “unique pavement design” that meets either of the following criteria (A or B below), develop the required alternate pavement designs. Chapter 9 - Construction and Rehabilitation Alternates may be consulted to determine appropriate alternates that meet the requirements of the tables.

Criteria A. For each “unique pavement design” in the DL<20 Category, that has a pavement area of 60,000 or more sq. yds (1), develop pavement designs for the alternates required in Table 740.1. Consult Chapter 9 - Construction and Rehabilitation Alternates for appropriate pavement alternates that may provide the requirements of Table 740.1.

If the project contains a total pavement area greater than 60,000 sq. yds (1) in the DL<20 Category, but no individual “unique pavement design” has an area greater than 60,000 sq. yds (1), develop pavement designs for alternates of the longest design in the DL<20 Category.

Table 740.1 - Required Alternates for DL<20 Category

Alternate Number

1 2 3

Pavement Material

As Proposed in Scoping or Project Development(2) HMA PCC

Design Life

For the Pavement Design Proposed in

Scoping or Project Development(2)

20 Years 20 Years


(2) The design life and pavement material of the pavement design proposed in scoping or project development process. Chapters 4 –HMA and 5 - PCC may be consulted to determine design life.


13

Criteria B. For each “unique pavement design”, DL≥ 20 Category, that is greater than 7,500 sq. yds. but has a pavement area less than 60,000 sq. yds. (1), develop pavement designs for the alternates in Table 740.2. Consult Chapter 9- Construction and Rehabilitation Alternates for appropriate pavement alternates that may provide the requirements of Table 740.2.

Table 740.2 – Required Alternates for DL≥ 20 Category

Alternate Number 1 2 3

Pavement Material HMA PCC PCC

Design Life 20 Years 20 Years 35 Years


STEP 2. Perform a LCCA to calculate the net present cost of each alternate. A. Get the most current version of the “Initial cost spreadsheet” and the “LCCA

standard spreadsheet” from the Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/lcca.html The website contains a version of the “Initial cost spreadsheet” and the “LCCA standard spreadsheet” for each district. These spreadsheets contain item prices specific to each district and are updated annually. In addition to annually updating the prices, the spreadsheets may be updated to improve usability or correct errors.

B. Calculate initial cost for each pavement design Use the “Initial cost spreadsheet” to calculate the initial cost of constructing a representative mile of each pavement design. The initial cost must include the cost of constructing the pavement section between the shoulder points of intersection (PI). This includes the cost of the mainline and shoulder pavements, base, subbase, and engineered soil. Additional costs may also be included that reflect the difference in construction of the alternates, such as; different grade raises between alternates, traffic detour or no detour, constructing under traffic, or A+B contracting.

The “Initial cost spreadsheet” contains the most common item costs to estimate the construction cost but if a necessary item cost is not provided contact the MnDOT Pavement Design Engineer.

http://www.dot.state.mn.us/materials/pvmtdesign/lcca.html


14

C. Perform LCCA(s) using the “LCCA standard spreadsheet” This spreadsheet follows the LCCA standards in Section 760 – LCCA Formulas and Standards and Section 770 – LCCA Maintenance Activities. 1. Perform a LCCA for alternates developed from Table 740.1 and a separate

LCCA for alternates developed from Table 740.2. 2. For each LCCA:

• Use a 35-year analysis period for alternates developed from Table 740.1. • Use a 50-year analysis period for alternates developed from Table 740.2.

3. The “LCCA standard spreadsheet” automates the calculation of future costs using the user’s inputs, Section 760 – LCCA Formulas and Standards and Section 770 – LCCA Maintenance Activities, and the “District Standard Prices.” For each segment, the user enters an initial cost developed from the “Initial cost spreadsheet” and completes an input form with data related to that alternate’s pavement design, pavement section geometry, and segment length. When the data in the input form is accepted, the Net Present Cost of that segment of the alternate are automatically calculated.

4. The “LCCA standard spreadsheet” spreadsheet will calculate the net present cost

of each alternate by summing the individual net present costs of each segment of the alternate.


15

STEP 3. Select the low cost alternate

The alternate with the least Net Present Cost is the low-cost option and must be selected unless the district is granted an exception. The reason for the exception must be documented in an exception form and is considered granted when it is signed by the District Engineer. The exception form is available on the Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html. Reasons for an exception may include;

• The low-cost alternate isn’t physically constructible • Construction would cause unreasonable user delay or user hardship (e.g. construction

would require unacceptable closures, long detours, or an extended construction period)

• Performance would be unacceptable • Other supplemental costs or noneconomic factors (see Table 960.1)

STEP 4. Based on the selected pavement alternate, prepare and distribute a Materials Design

Recommendation (MDR) in accordance with Section 810 - Materials Design Recommendation (MDR). Attach the LCCA and any exceptions to the MDR.



16

750 - Alternate Bidding

Follow this section if Section 730 - Formal LCCA Process indicated that the Net Present Cost of one HMA and one PCC option are within 10% of each other.

1. Determine if the project is a good candidate for alternate bidding

Having alternates with Net Present Costs within 10% of each other is indicative of a good project for alternate bid but there are also other concerns to evaluate to determine if a project is a good candidate. A good project is a project where both pavement types are constructible, will provide acceptable performance and will have competitive bidders. Below are examples of reasons that a project will not be a good candidate.

• An alternate isn’t physically constructible • An alternate’s construction would cause unreasonable user delay or user hardship (e.g.

construction would require unacceptable closures, long detours, or an extended construction period)

• The performance of an alternate would not be unacceptable • It’s unlikely that there will be competitive bidders for both alternates • Other supplemental costs or noneconomic factors (see Table 960.1)

If a project is believed to not be a good candidate for alternate bidding then the district (with the guidance MnDOT Pavement Design Engineer) may request an exception to using the alternate bidding process. The exception is granted when it is signed by the MnDOT Pavement Engineer. This exception may also serve as an exception to choosing the low-cost option. The exception form is located on the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html.

2. Documentation A. If an exception to following the Alternate Bidding process has been granted

Based on the selected pavement alternate, prepare and distribute a Materials Design Recommendation (MDR) in accordance with Section 810 - Materials Design Recommendation (MDR). Attach the LCCA and any exceptions to the MDR.

B. Good candidate for Alternate Bidding

Prepare a Pavement Design Memorandum (PDM) in accordance with Section 800 - Pavement Design Memorandum (PDM). The PDM details the pavement alternates, how they were developed and which pavement alternates will be used for alternate bidding. Attach



17

the LCCA to the PDM and submit it to the MnDOT Pavement Design Engineer. The MnDOT Pavement Design Engineer will review the PDM and attachments and may request that the district make changes. After any changes are made, the MnDOT Pavement Design Engineer will distribute the PDM to representatives of the Concrete Paving Association of Minnesota (CPAM) and Minnesota Asphalt Pavement Association (MAPA) for a comment period of two weeks. After the comment period, the MnDOT Pavement Design Engineer will address any comments and sign the PDM.

When the PDM is signed, the MDR may be developed using the paving alternates for alternate bidding. Prepare and distribute the MDR in accordance with Section 810 - Materials Design Recommendation (MDR). Attach the LCCA to the MDR and continue to the next section, Section 750. C - Alternate bidding process.

C. Alternate bidding process STEP 1. Design the project plans with the HMA and PCC alternates that were developed in

the Formal LCCA process. Attempt to have the same pavement widths and profile grade between the alternates.

STEP 2. The MnDOT Pavement Design Engineer develops the project bid adjustment

factor(s) as follows:

A. For the alternate designs presented in the final plans, perform an LCCA of all costs other than initial costs using the approach described in Section 730 - Formal LCCA Process.

B. The bid adjustment factor for an alternate is calculated as the difference between

its net present cost and the net present cost of the alternate with the lowest net present cost. The alternate with the lowest net present cost always has a bid adjustment factor of $0.00 which doesn’t need to be reported.

C. Calculate the bid adjustment factor on the alternates as presented in the final

plans. D. Develop the bid adjustment factor within 6 months of the project bid.

STEP 3. Letting and awarding for alternate bidding

The project will be advertised for bids with the bid adjustment factor(s) and plans that include the pavement alternates. Bidders may bid on either pavement alternate. The low-cost bidder will be determined after adding the appropriate bid adjustment factor to each bid.


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760 - LCCA Formulas and Standards

LCCA compares pavement alternates by calculating the net present cost for each alternate. The net present cost is the initial cost plus the discounted cost of future activities minus the cost of any discounted remaining service life (RSL) value.

1. Discount rate (r)

The discount rate is equal to the average of the 5 most recent years’ real interest rate of a 30-year treasury bonds as published each year by the federal Office of Management & Budget (OMB). Each year’s discount rate will be determined by the MnDOT Office of Investment & Management and distributed by July 1st.

2. Remaining service life (RSL) value

The Remaining service life value is the residual value of an improvement when its service life extends beyond the end of the analysis period. The RSL value is calculated as the cost of the last rehabilitation or reconstruction activity multiplied by the ratio of the number of years of the activity’s service life that are remaining at the end of the analysis period over the service life of the activity. The RSL value is included in the LCCA as negative cost. A remaining service life value will not be calculated for maintenance activities (e.g. surface or crack treatments, shoulder joint sealing, and shoulder fog sealing).

3. District standard prices

This is a list of each district’s item costs which are used to estimate initial and future costs. It will be updated annually by the MnDOT Pavement Design Engineer by July 1st of each year. The values will be based on each district’s bid prices from the March 1st of the previous year to April 30th of the current year. The proposed price list will be made available for review by the district, CPAM, and MAPA prior to being accepted.


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5. Formulas

A. Remaining service life (RSL)

𝑅𝑅𝑅𝑅𝑅𝑅 = 𝐶𝐶𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴 × 𝑁𝑁𝑅𝑅𝐿𝐿𝑁𝑁𝑆𝑆𝐿𝐿

RSL = Remaining service life value

C Last Activity = Cost of the last rehabilitation or reconstruction activity. This activity may include reconstruction or a rehabilitation activity such as a CPR or an overlay. This would not include maintenance activities such as surface treatments or crack treatments, shoulder joint sealing, or shoulder fog sealing.

NSL = Service life of the last activity in years.

NRL = Unused service life, in years, of the last activity at the end of the Analysis Period.


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B. Present cost of each activity

𝑃𝑃𝐶𝐶𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴 = 𝐶𝐶𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴 × �1

(1 + 𝑟𝑟)�𝑁𝑁𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴

PC Activity = Present cost of an activity (or RSL)

C Activity = Cost of an activity (or RSL)

N Activity = Number of years after construction that an activity is scheduled to take place

r = Discount rate, decimal form (Section 760.1)


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C. Net present cost of an alternate (for one segment)

∑[𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑁𝑁𝐴𝐴 = 𝐶𝐶𝐼𝐼𝐼𝐼𝐴𝐴𝐿𝐿𝐴𝐴𝐿𝐿𝐼𝐼 + ∑𝑃𝑃𝐶𝐶𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴

𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴 = Net present cost of an alternate (for one segment)

𝑃𝑃𝐶𝐶𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴𝐿𝐿𝐴𝐴 R = Present cost of activities (or RSL)

C Initial = Initial cost of construction

Note: Do not include an initial cost (C Initial) when calculating the bid adjustment factor for alternate bidding.

5) Net present cost of an alternate (for an entire project with multiple segments)

[𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑃𝑃𝑅𝑅𝑃𝑃𝑃𝑃𝑆𝑆𝑃𝑃𝐴𝐴 = ∑[𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑁𝑁𝐴𝐴

[𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑃𝑃𝑅𝑅𝑃𝑃𝑃𝑃𝑆𝑆𝑃𝑃𝐴𝐴 = Net present cost of an alternate for the entire project when the project has multiple segments.

[𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑁𝑁𝐴𝐴 = Net present cost of an alternate for an individual segment.


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D. Bid adjustment factor for an alternate

𝐵𝐵𝐵𝐵𝐵𝐵𝐴𝐴𝐿𝐿𝐴𝐴𝑆𝑆𝑅𝑅𝑁𝑁𝐴𝐴𝐴𝐴𝑆𝑆 = [𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑃𝑃𝑅𝑅𝑃𝑃𝑃𝑃𝑆𝑆𝑃𝑃𝐴𝐴 − 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 [𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑃𝑃𝑅𝑅𝑃𝑃𝑃𝑃𝑆𝑆𝑃𝑃𝐴𝐴

𝐵𝐵𝐵𝐵𝐵𝐵𝐴𝐴𝐿𝐿𝐴𝐴𝑆𝑆𝑅𝑅𝑁𝑁𝐴𝐴𝐴𝐴𝑆𝑆 R = Bid adjustment factor for an alternate.

[𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑃𝑃𝑅𝑅𝑃𝑃𝑃𝑃𝑆𝑆𝑃𝑃𝐴𝐴 R = The net present cost of the alternate (for all segments)

𝑅𝑅𝑙𝑙𝐿𝐿𝑙𝑙𝑙𝑙 [𝑁𝑁𝑃𝑃𝐶𝐶𝐴𝐴𝐿𝐿𝐴𝐴]𝑃𝑃𝑅𝑅𝑃𝑃𝑃𝑃𝑆𝑆𝑃𝑃𝐴𝐴 R = The net present cost of the alternate with the lowest net present cost


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770 - LCCA Maintenance Activities

This section contains the schedules and quantities that are used by the “MnLCCA” spreadsheet for performing LCCA’s and determining bid adjustment factors for use in alternate bidding.

1. The following Maintenance and Rehabilitation Schedules are presented in this section

• Table 770.1 - PCC with 12’ or 15’ joint spacing - design life = 20 years • Table 770.2 - PCC with 12’ or 15’ joint spacing - design life = 35 years • Table 770.3 - PCC with 6’ X 6’ joint spacing - design life = 20 years PCC thickness = 5.5

inches or greater • Table 770.4 - PCC with 6’ X 6’ joint spacing - design life = 20 years PCC thickness = 5.0

inches or less • Table 770.5 - PCC with 6’ X 6’ joint spacing - design life = 35 years • Table 770.6 - New HMA pavement over aggregate base, FDR, SFDR, CIR, or rubblized PCC

- design life = 20 years • Table 770.7 - HMA Overlay - design life (DL) = 13 to 17 years • Table 770.8 - HMA Overlay - design life (DL) >17 years

2. Use the following definitions:

• Thin HMA Shoulders – are less than 4.0 inches in thickness • Thick HMA Shoulders – are 4.0 inches or greater in thickness


24

PCC Table 770.1 - PCC with 12’ or 15’ Joint Spacing

Design Life = 20 years

35 Year Analysis Period 50 Year Analysis Period Pavement Age Treatment Treatment

0 Initial Construction Initial Construction 20 1st CPR 1st CPR

35 End of Analysis Period (No Remaining Service Life)

Remove & Replace (PCC with 20-year Design Life)

50 End of Analysis Period (5/20 Remaining Service Life)

Pavement Preservation Rehabilitation Quantities

12’ or 15’ Long Panels Age Treatment Mainline Quantity Shoulder Treatment

20

Type BA Repair 1% Surface Area Thin Bit Shoulders: Remove & Replace Thick Bit Shoulders: 1.5” Mill & Overlay

Type B3 Repair 2% Transverse & Longitudinal Joints

Type CD-HV Repair 7% Transverse Joints Type CX Repair 6% Surface Area Surface Grind 68% Surface Area

35 Remove & Replace (PCC with 20-year

Design Life) 100% 100%

50 End of Analysis Period 25% Remaining Service Life [5/20]


25

Table 770.2 - PCC with 12’ or 15’ Joint Spacing Design Life = 35 years

35 Year Analysis Period 50 Year Analysis Period

Pavement Age Treatment Treatment 0 Initial Construction Initial Construction

20 1st CPR 1st CPR

35 End of Analysis Period (No Remaining Service Life) 2nd CPR



12’ or 15’ Long Panels Age Treatment Mainline Quantity Shoulder Treatment

20

Type BA Repair 1% Surface Area Thin Bit Shoulders: Remove & Replace Thick Bit Shoulders: 1.5” Mill & Overlay



35

Type B3 Repair 2% Transverse & Longitudinal Joints Thin Shoulders: Fog Seal

Thick Shoulders: Fog Seal


50 End of Analysis Period No Remaining Service Life


26

Table 770.3 - PCC with 6’ X 6’Joint Spacing Design Life = 20 years

PCC thickness = 5.5 inches or Greater


6’ x 6’panels Age Treatment Mainline Quantity Shoulder Treatment

20

A2 Repair 10% Transverse & Longitudinal Joints

Thin Bit Shoulders: Remove & Replace

Thick Bit Shoulders: 1.5” Mill

& Overlay

CX Repair 15% Surface Area

Surface Grind 50% Surface Area

35 Replace with PCC Design Life = 20 years 100 % 100 %





Remove & Replace (PCC with a 20-year Design Life)



27

Table 770.4 - PCC with 6’ X 6’Joint Spacing Design Life = 20 years

PCC thickness = 5.0” or Less


6’ x 6’panels Age Treatment Mainline Quantity Shoulder Treatment

20 A2 Repair 10% Transverse &

Longitudinal Joints Fog Seal 100 % CX Repair 25% Surface Area Surface Grind 100% Surface Area

30 Replace with PCC Design Life = 35 years 100 % 100 %




30 Remove & Replace (PCC with a 35-year Design Life)

Remove & Replace (PCC with a 35-year Design Life)




28

Table 770.5 - PCC with 6’ X 6’ Joint Spacing Design Life = 35 years

35 Year Analysis Period 50 Year Analysis Period

Pavement Age Treatment Treatment 0 Initial Construction Initial Construction

20 1st CPR 1st CPR

35 End of Analysis Period (no remaining service life) 2nd CPR

50 End of Analysis Period (No Remaining Service

Life)


6’ x 6’ panels Age Treatment Mainline Quantity Shoulder Treatment

20

Type A2 Repair 5% Transverse & Longitudinal Joints

Thin Bit Shoulders: Remove & Replace Thick Bit Shoulders: 1.5” Mill & Overlay


Type CX Repair 5% Surface Area Surface Grind 23% Surface Area

35

Type A2 Repair 10% Transverse & Longitudinal Joints Thin Shoulders: Fog Seal

Thick Shoulders: Fog Seal


Type CX Repair 8% Surface Area Surface Grind 68% Surface Area



29

HMA

Table 770.6 - New HMA Pavement over Aggregate Base, FDR, SFDR, CIR, or Rubblized PCC

Design Life = 20 years

35 Year Analysis Period 50 Year Analysis Period Pavement

Age Treatment Treatment

0 Initial Construction Initial Construction 8 Crack Treatment Crack Treatment

12 Surface Treatment (1) (2) Surface Treatment (1) (2) 20 Mill & Overlay (1st Overlay) Mill & Overlay (1st Overlay) 23 Crack Treatment Crack Treatment 27 Surface Treatment (2) Surface Treatment (2)


37 Mill & Overlay (2nd Overlay) 40 Crack Treatment 44 Surface Treatment


(1) Delete when ultra-thin bonded wearing course is used

(2) Eliminate chip seal and fog seal when 20 year BESALs are >7 million


30


Rural Section

Age Treatment Mainline Quantity Shoulder Treatment Shoulder Quantity

8 Crack Treatment 16% Mainline Length

12 Chip Seal (1) (2) 31% Mainline Length Fog

Seal (1) (2) 31% Shoulder Length

Microsurfacing (1) (2) 9% Mainline Length Fog Seal (1) (2) 9% Shoulder Length

20 Mill: Top lift + ½” Overlay: Mill thickness +1.5” 100% Mainline Area 1.5”

Overlay 100% Shoulder Area


27 Chip Seal (1) (2) 31% Mainline Length Fog Seal (1) (2) 31% Shoulder Length

37 Mill: 2” Overlay: 3.5” 100% Mainline Area 1.5”



44 Chip Seal (1) (2) 31% Mainline Length Fog Seal (1) (2) 31% Shoulder Length

50 End of Analysis Period 4/17 Remaining Service Life (1) Delete when ultra-thin bonded wearing course is used



31

Urban Section Age Treatment Mainline Quantity Shoulder

Treatment Shoulder Quantity


12 Chip Seal (1) (2) 31% Mainline Length Fog Seal (1) (2) 31% Shoulder Length Microsurfacing (1) (2) 9% Mainline Length Fog Seal(1) (2) 9% Shoulder Length

20 Mill & Overlay: 3” 100% Mainline Area

1.5” Mill & Overlay

100% Thick Shoulder Area

Remove & Replace 100% Thin Shoulder Area

23 Crack Treatment 32% Mainline Length 27 Chip Seal (1) (2) 31% Mainline Length Fog Seal (1) (2) 31% Shoulder Length

37 Mill & Overlay: 3.5” 100% Mainline Area



Remove & Replace 100% Thin Shoulder Area

40 Crack Treatment 32% Mainline Length 44 Chip Seal (1) (2) 31% Mainline Length Fog Seal (1) (2) 31% Shoulder Length


(1) Delete when ultra-thin bonded wearing course is used



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Table 770.7 - HMA Overlay

Design Life (DL) = 13 to 17 years

Pavement Age Treatment 0 Initial Construction (1st Overlay) 3 Crack Treatment 7 Chip Seal*

DL Mill & Overlay (2nd Overlay) DL +3 Crack Treatment DL +7 Chip Seal*

2*DL -1 Mill & Overlay (3rd Overlay) 2*DL +2 Crack Treatment (1) 2*DL +6 Chip Seal* (2)

35 End of Analysis Period

(Remaining Life of Last Overlay = [(3*DL-38)/(DL-2)]

* Eliminate chip seal and fog seal when 20 year BESALs are >7 million (1) Do not use when DL = 17 (2) Do not use when DL = 15, 16, 17


33


Rural Section


3 Crack Treatment 32% Mainline Length 7 Chip Seal * 31% Mainline Length Fog Seal* 31% Shoulder Length

DL Mill: 2” Overlay: 3.5” 100% Mainline Area 1.5”


DL + 3 Crack Treatment 32% Mainline Length DL + 7 Chip Seal * 31% Mainline Length Fog Seal* 31% Shoulder Length

2*DL-1 Mill: 2” Overlay: 3.5” 100% Mainline Area 1.5”


2*DL+2 Crack Treatment (1) 32% Mainline Length 2*DL+6 Chip Seal * (2) 31% Mainline Length Fog Seal* 31% Shoulder Length

35 End of Analysis Period Remaining Service Life = [(3*DL-38)/(DL-2)])

Urban Section



DL Mill & Overlay: 3.5” 100% Mainline Area



Remove & Replace

100% Thin Shoulder Area


2*DL-1 Mill & Overlay: 4” 100% Mainline Area

2” Mill & Overlay


Remove & Replace


2*DL+2 Crack Treatment (1) 32% Mainline Length 2*DL+6 Chip Seal * (2) 31% Mainline Length Fog Seal* 31% Shoulder Length


* Eliminate chip seal and fog seal when 20 year BESALs are >7 million

(1) Do not use when DL = 17 (2) Do not use when DL = 15, 16, 17


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Table 770.8 - HMA Overlay Design Life (DL) >17 years

Pavement Age Treatment

0 Initial Construction (1st Overlay) 3 Crack Treatment 7 Chip Seal*

DL Mill & Overlay (2nd Overlay) DL +3 Crack Treatment DL +7 Chip Seal*

35 End of Analysis Period

(Remaining Life of Last Overlay = [(2*DL-36)/(DL-1)]


Rural Section



DL Mill: 2” Overlay: 3.5” 100% Mainline Area 1.5”



35 End of Analysis Period Remaining service life = [(2*DL-36)/(DL-1)]

Urban Section



DL Mill & Overlay: 3.5” 100% Mainline Area

2” Mill & Overlay


Remove & Replace


DL+3 Crack Treatment 32% Mainline Length DL+7 Chip Seal * 31% Mainline Length Fog Seal* 31% Shoulder Length

35 End of Analysis Period Remaining Service Life = [(2*DL-36)/(DL-1)]

* Eliminate chip seal and fog seal when 20 year BESALs are >7 million



Chapter 8 – Documentation




800 - Pavement Design Memorandum (PDM) ............................................................................................. 2

810 - Materials Design Recommendation (MDR) ........................................................................................ 3

820 - PDM Template Instructions .................................................................................................................. 6

830 - MDR Template Instructions ................................................................................................................ 29


1

Introduction

There are two documents that may be required to provide for a pavement project. A Pavement Design Memorandum (PDM) is required when the Formal LCCA process is followed. This document enables the MnDOT Pavement Design Engineer to review and approve the pavement design. A Materials Design Recommendation (MDR) is required for all projects that include grading or pavement. It is used to document and communicate pavement and geotechnical design recommendations to the project designers. This chapter describes the content, development, review and approval processes of these two documents.


2

800 - Pavement Design Memorandum (PDM)

A PDM is required when the Formal LCCA process is followed so that the pavement design can be reviewed and approved by the MnDOT Pavement Design Engineer. A PDM is written to document the alternate pavement designs that were considered, the information required for the pavement designs’ development, and the project’s LCCA. See Chapter 7 – Pavement-Type Selection to determine if the project will follow the Formal LCCA process and, therefore, will require the completion of a PDM.

1. Format

The PDM template must be used for all PDMs. The template is available on the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html and directions for completing it are in Section 820 – PDM Template Instructions.

2. Distribution and Review

A. The draft PDM is sent to the MnDOT Pavement Design Engineer.

B. The MnDOT Pavement Design Engineer reviews the PDM and attachments and may request any necessary changes to be made.

C. If the project will proceed to alternate bidding, the MnDOT Pavement Design Engineer will distribute the PDM to the FHWA Pavements, Materials and Construction Engineer and representatives of the Concrete Paving Association of Minnesota (CPAM) and Minnesota Asphalt Pavement Association (MAPA). The associations will have a comment period of two weeks and the MnDOT Pavement Design Engineer will address any comments.

D. The MnDOT Pavement Design Engineer will sign the finalized PDM and the project may proceed with the pavement designs described in the PDM.



3

810 - Materials Design Recommendation (MDR)

The MDR provides pavement and geotechnical design recommendations for MnDOT projects to the project designer. This includes recommendations for layer thickness, materials, treatments, and specifications necessary to design the project. Note: Only the pavement designs that will be used in the project plans need to be included

in the MDR. 1. Format

A template for formatting the MDR is available on the MnDOT Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html. The template format is required for projects that will use Alternate Bidding. See Section 830 - MDR Template Instructions for directions for using this template.

2. Distribution and Review

A. Complete a draft MDR. B. Complete a MDR routing sheet for the draft MDR. The MDR routing sheet template is

available on the MnDOT pavement design website. C. Distribute the MDR and MDR routing sheet to the distribution list shown in Table 810.1.

The method of distribution of the MDR, MDR routing sheet, and supporting documents vary by district preference and may be accomplished by e-mailing copies of the files, ProjectWise links, or electronic data management system (EDMS) links. These methods are all acceptable for review; however, the MDR, MDR routing sheet, and supporting material, must be archived in the MnDOT EDMS and should be placed there as early as possible.

D. Provide for a review period of two weeks.

E. Review comments, finalize, and archive the MDR.



4

Table 810.1 – Distribution List for Project MDRs

Materials & Road Research, Maplewood MnDOT Pavement Engineer Pavement projects. MnDOT Pavement Design Engineer

Pavement projects.

MnDOT Bituminous Engineer

Projects that include HMA pavement.

MnDOT Concrete Engineer Projects that include PCC pavement. MnDOT Grading and Base Engineer

Projects that include any work to a roadway’s subgrade, base, or include aggregate shoulders.

MnDOT Pavement Preservation Engineer

Projects that include FDR, SFDR, CIR or any HMA pavement preservation.

MnDOT Foundations Engineer

Projects that include fills of cuts deeper than 30’.

MnDOT Geology Projects that include rock cuts. Central Office, St. Paul

MnDOT Special Provisions Engineer

Final MDR only

MnDOT Design Support Engineer

Final MDR only

The District This is the district’s preference, but would typically include the Soils Engineer, Materials Engineer, Design Engineer, Project Engineer, and others.

District decision

FHWA

FHWA Area Engineer* * Note: Must be a copy of

the file(s), cannot be ProjectWise or EDMS links.

Projects on the National Highway System that are a Project of Corporate Interest (POCI), Project of Division Interest PODI, or as requested. A list of PODI projects are available on the Pavement Design website at http://www.dot.state.mn.us/materials/pvmtdesign/docs/index.html Or contact the appropriate FHWA Area Engineer

FHWA Pavements, Materials and Construction Engineer

Projects on the Interstate System



5

Use the following to find the appropriate FHWA Area Engineer and contact information http://www.fhwa.dot.gov/mndiv/staff/districts.cfm

http://www.fhwa.dot.gov/mndiv/staff/districts.cfm


6

820 - PDM Template Instructions

This section contains directions for completing the template for PDMs.

Note: Delete any tables or rows within tables that do not apply to the project.


7

Office Memorandum TO: Recipient's Name MnDOT Pavement Design Engineer FROM: Sender's Name Author’s Title DATE: Month, Day, Year SUBJECT: PAVEMENT DESIGN MEMORANDUM

SP # The Project’s SP Number. Highway # The number(s) of the State Highway(s) within the project limits Project Limits Text Description of the Project Limits RP XXX+00.XXXX to RP XXX+00.XXXX Length of Project XX.XXX Miles Funding Category e.g. RC (Reconstruction), RD (Reconditioning), MC (Major Construction) Programmed Letting Date XX/XX/XXXX

Date

MnDOT Pavement Design Engineer


8

Project Information Project Scope

Type of Work General project description e.g. mainline reconstruction and overlay ramps.(may be found in scoping)

Benefit The expected improvement the project will provide; be specific (i.e. the amount of ride improvement, or amount of life extension).

LCCA Process Formal Alternate Bid Yes or No (see Chapter 7) HMA Overlay Design Life

If this project includes a HMA Overlay, the design life of the HMA Overlay

Pavement Design Segments This is a list of project segments that require separate pavement designs.

Segment # Highway #

From RP

To RP

Design Type

1 PCC or HMA Overlay, Reconstruction, FDR,SFDR, etc.

2


9

Existing Facility This is a description of the existing road and its general geometry. Scoping documents and the Pavement Management System (see Section 280) may be useful in completing this section.

Highway Multiple segments may be required to describe the existing road. Include a copy for each segment.

From From RP To To RP

Number of Lanes No. of lanes, if it’s divided, and description of any median. Mainline Pavement

Type HMA or PCC. For PCC include the joint spacing, # of dowels, thickness etc.

Mainline Pavement Width Width in feet.

Shoulder Type HMA, PCC, aggregate, any curb and gutter. Shoulder Width Width in feet of each shoulder. Seasonal Load

Restriction The posted seasonal load restriction in tons; 10 tons if there is no posted restriction.

Speed Limit The posted speed limit. Roadway Construction History See Section 260 for guidance on obtaining this information. If this material is extensive, it may be placed as an appendix to this document. The following are examples of two sections of a project.

RP 123.789 to RP 126.987 - MN 23 to 3rd Street Year SP Activity Width Depth 1989 2309-001 Minor CPR/ Patching 30’ 1954 2309-123 CPR 1945 2309-789 HMA Shoulders 6’ 2.5” 1945 2309-789 Doweled PCC 30’ 8” 1945 2309-789 Aggregate Base 30’ 6’


10

RP 126.987 to RP 129.102 – 3rd Street to E Limits Franklin

Year SP Activity Width Depth 1989 2309-01 HMA Overlay 24’ 4.5” 1989 2309-01 HMA Milling 24’ 3” 1973 2309-12 HMA Overlay 24’ 4” 1951 2309-111 Chip Seal 24’ 1950 2309-22 Spot Patching 24’ 1945 2309-789 Doweled PCC with Aggregate Base 30’ 8”

Roadway Condition

Pavement Distresses A general description of the visible distresses. For guidance see Section 270.

Areas of Concern Any areas that may need repair or special treatment, such as frost heaves or subgrade failure. For guidance see Section 270.

Attach photos or diagrams as needed. Pavement Performance Data This section documents the Pavement Performance Data for the road within the project limits. Pavement Performance Data is available from Pavement Management System (see Section 280).

Year: Year that the data was collected

Segment Description Dir. From RP To RP RQI SR PQI IRI (in/mile)

I, D, U

R-Value/FWD Data This section reports the R-value from either FWD data or laboratory testing (or both). Use this table to document FWD data using the TONN method, see Section 200. Any FWD (TONN Analysis) and Laboratory R-Values must be attached in the appendix.


11

FWD Data

Date: Date of Testing

Reported Capacity

Overlay Thickness R-Value

Mean Std. Dev.

Use this table to document any Laboratory R-values, see Section 220.

Laboratory R-Values

Count Mean Minimum Maximum Std. Dev. # of tests

Comments: Any notes, comments, or concerns about the collected data. Core/GPR This section reports the HMA thickness (and condition) collected from coring or GPR see Sections 230 & 240. Date: Date that the data was collected on.

Segment: Segment #

Location Count Average Minimum Maximum Std. Dev.

Mainline, shoulder, turn-lanes, etc

Provide the location of any photos of the cores and of any GPR report. These may be attached, in EDMS, or ProjectWise. Comments: Any notes, comments, or concerns about the collected data.


12

Traffic A signed MnDOT traffic forecast is required for all PDMs. See Section 250.

Traffic Forecast #: Traffic Forecast Date:

Hwy From RP To RP

Base Year

2-way Design Lane

HCADT

2-way HCADT Growth/

Year

20 Yr. Design Lane

Cumulative BESAL’s

20 Yr. Design Lane

Cumulative CESAL’s

35 Yr. Design Lane


Life-Cycle Cost Analysis (LCCA) This section contains the results of the LCCA analysis according to Chapter 7.

Alternate #1 Alternate #2 Alternate #3 Description Design Life

Project Net Present Cost % of Low Cost

Selected Exception: Does the district request an exception to either selecting the low-cost option or to following the alternate bidding process? See Chapter 7. Any exception form should be attached.


13

Pavement Recommendations This section contains the recommended pavement design(s) for the Pavement Design Segments (listed on the second page of the memo). If the project will follow the Alternate Bidding process then there will be HMA and PCC options for those segments that will be included in Alternate Bidding (see Chapter 7 – Pavement-Type Selection).


14

NEW HMA

Segment # Highway # From RP To RP Design Type

# TH # ###.### ###.### New HMA

Mainline

Pavement Thickness (inches) Lifts Mix Design/

Material Spec. Compaction Testing Width (ft.)

Wear Sec. 400 ---- ---- --- ---- Scoping

Non-Wear Sec. 400 ---- ---- --- ---- Scoping

Smoothness --- Notes

Mainline Subsurface

Thickness (inches)


Base Sec. 400 Sec. 400 & 310 --- ---

Subbase Sec. 400 Sec. 400 & 310 --- ---

Eng. Soil Sec. 320 Sec. 320 --- --- Subgrade Prep. Sec. 320 --- ---

Notes

HMA Shoulders Thickness (inches) Lifts Mix Design/

Material Spec. Compaction Testing

Width (ft.)

Lt Rt

HMA Sec. 610 --- --- --- --- Scope Scope

Aggregate Surfacing Sec. 610 Sec. 610 --- --- 610 610

Shoulder Agg. Base

As Needed Match Agg.

Base --- ---

Notes

Aggregate Shoulders Thickness Material Spec. Compaction

Testing Width

Lt Rt

Aggregate Surfacing Sec. 610 Sec. 610 --- --- Scope Scope

Added Aggregate Base


Base --- ---

Notes


15

X.X” Engineered Soil

Cross-Section from RP XXX to RP XXX

X.X” Sub-base

X.X” Class X

X.X” HMA Wearing Course

X.X” YYYYYYY

X.X ft XX.X ft XX.X ft X.X ft

X.X” YYYYYYY

X.X” HMA Non-Wearing Course



X.X” Sub-base

X.X” Class X


X.X” YYYYYYY


X.X” YYYYYYY



16

FDR/SFDR/CIR


# TH # ###.### ###.### FDR,SFDR or CIR

Existing Mainline

Pavement Depth

(inches) Material Note Width (ft.)

Existing HMA Sec.230, 240, 260 HMA Sec. 260

Existing Aggregate

Sec.230, 240, 260

Sec.230, 240, 260

Notes

Mainline

Pavement Depth

(inches) Lifts Material Spec. Width (ft.)

Milling Sec. 410 --- #.# Added

Aggregate Sec. 410 Sec. 410 --- #.#

Reclaim/ Recycle Sec. 410 Sec. 410 --- #.#

Stabilize Sec. 410 Sec. 410 --- #.#

Notes

Mainline Pavement

Thickness (inches) Lifts Mix Design/


Wear Sec. 400 --- Sec. 450 --- --- Scoping

Non-Wear Sec. 400 --- Sec. 450 --- --- Scoping

Smoothness --- Notes

HMA Shoulders



Width (ft.)

Lt Rt

HMA Sec. 610 --- Sec. 450 --- --- Scope Scope


Shoulder Agg. Base As Needed Match Agg.

Base --- ---

Notes


17


Testing Width (ft.)

Lt Rt


Added Aggregate

Base As Needed Match Agg.

Base --- ---

Notes

X.X” Existing Aggregate


X.X” YYYYYYY

X.X” YYYYYYY X.X” FDR

X.X” SFDR

X.X” New HMA Overlay


X.X” YYYYYYY X.X” YYYYYYY


18

Rubblize/Crack & Seat


# TH # ###.### ###.### Rubblize/Crack & Seat

Mainline

Pavement Depth


Existing HMA Sec. 230, 240, 260 HMA Sec. 260

Existing PCC Sec. 260 PCC Sec. 260 Existing

Aggregate Sec. 230, 240, 260 HMA

Notes

Mainline

Pavement Depth


Mill HMA Sec. 410 --- #.# Rubblize/

Crack & Seat Special Provision # and if any edits are required, Sec. 420

Subsurface Drains Type of drain & outlets and its specification, Sec. 420

Notes

Mainline Pavement




Non-Wear Sec. 420 --- Sec. 450 --- --- Scoping

Smoothness Sec. 450 Notes


19

HMA Shoulders



Width (ft.)

Lt Rt




Base --- ---

Notes


Testing Width

Lt Rt


Added Aggregate


Base --- ---

Notes


X.X” YYYYYYY

X.X” YYYYYYY

4” Perf. PE Pipe



X.X” Rubblized PCC



20

HMA Overlay


# TH # ###.### ###.### HMA Overlay

Mainline

Pavement Depth




Aggregate Sec. 230, 240, 260

Notes

Mainline

Pavement Depth


Mill HMA Sec. 440 --- #.# Notes

Mainline Pavement


Material Spec. Compaction Testing Width (ft)



HMA Shoulders



Width (ft.)

Lt Rt




Base --- ---

Notes


21


Testing Width

Lt Rt


Added Aggregate


Base --- ---

Notes

X.X” ExistingPave.


X.X” Class X




X.X” Sub-base Mill X.X” Existing HMA



X.X” Sub-base

X.X” Class X

X.X” HMA Overlay

X.X” YYYYYYY


X.X” YYYYYYY

Mill X.X” Existing HMA X.X” Existing Pave.


22

NEW PCC


# TH # ###.### ###.### New PCC

Mainline

Pavement Thickness (inches)

Joint Spacing (ft.)

Dowel Arrangement

Dowel Size Sealant Width (ft.)

PCC Sec. 500 Sec. 530 Sec. 530 530 Sec. 530 Scoping

Notes Mainline

Subsurface Thickness (inches) Lifts Material Spec. Compaction

Testing Width (ft.)

Base Sec. 500 Sec. 500 & 310 --- ---

Subbase Sec. 500 Sec. 500 & 310 --- ---

Eng. Soil Sec. 320 Sec. 320 --- --- Subgrade

Prep. Sec. 320 --- ---

Subsurface Drains Type of Drain & outlets, Sec. 500

Notes ---

HMA Shoulders



Width (ft.)

Lt Rt




Base --- ---

Notes


23


Testing Width

Lt Rt


Added Aggregate


Base --- ---

Notes

PCC

Shoulders Thickness Material Spec. Compaction Testing

Width

Lt Rt PCC Sec. 610 Scope Scope



Base --- ---

Notes


24

X.X” YYYY

YYY Joint YYY Joint YYYY Joint


X.X” YYYYYYY

X.X” YYYYYYY

X.X” Class X 4” Perf. PE Pipe

X.X” New PCC

XX.X ft X.X ft X.X ft XX.X ft


X.X” Sub-base



X.X” Sub-base

X.X” Class X

X.X” New PCC

X.X” YYYYYYY


X.X” YYYYYYY YYYY Joint YYYY Joint


25

Whitetopping


# TH # ###.### ###.### Whitetopping

Mainline

Pavement Depth


Mill HMA Sec. 510 Sec. 510 #.# Notes

Mainline Pavement

Thickness (inches)

Joint Spacing (ft.)

Dowel Arrangement


PCC Overlay Sec. 500 Sec. 530 Sec. 530 530 Sec. 530 Scoping Notes

HMA Shoulders



Width (ft.)

Lt Rt




Base --- ---

Notes


Testing Width

Lt Rt


Added Aggregate


Base --- ---

Notes


26

PCC


Width




Base --- ---

Notes


X.X” YYYYYYY

X.X” YYYYYYY X.X” New PCC Overlay


X.X” Existing HMA



27

UBOL


# TH # ###.### ###.### Unbonded Overlay

Mainline

Pavement Depth


Mill HMA Sec. 520 --- #.# Notes

Mainline Pavement

Thickness (inches)

Joint Spacing (ft.)

Dowel Arrangement



Mainline Subsurface

Thickness (inches) Lifts Material Spec. Compaction

Testing Width (ft.)

Interlayer Sec. 520 Sec. 520 --- --- Subsurface

Drains Type of drain & outlets, Sec. 520

Notes

HMA Shoulders



Width (ft.)

Lt Rt




Base --- --

Notes


Testing Width

Lt Rt


Added Aggregate


Base --- ---

Notes


28

PCC Shoulders Thickness Material Spec. Compaction

Testing Width




Base --- ---

Notes

Attachments: Attach or provide a link to the location of the following:

Printouts of the pavement design programs’ output for each pavement design.

Signed Traffic Forecast Summaries.

Soil Borings and Cores (or link)

The LCCA and any supporting calculations.

Any LCCA or Alternate Bidding Exceptions.

Any GPR, Geotechnical, or other reports.


X.X” YYYYYYY

X.X” YYYYYYY

X.X” Interlayer 4” Perf. PE Pipe

X.X” New PCC Overlay



X.X” Existing PCC


29

830 - MDR Template Instructions

This section contains directions for completing the template for MDR.

Note: Delete any tables or rows within tables that do not apply to the project.


30

Office Memorandum TO: Recipient's Name Recipient’s Title FROM: Sender's Name Author’s Title DATE: Month, Day, Year SUBJECT: MATERIALS DESIGN RECOMMENDATION

SP # The Project’s SP Number. Highway # The number(s) of the State Highway(s) within the project limits Project Limits Text Description of the Project Limits RP XXX+00.XXXX to RP XXX+00.XXXX Length of Project XX.XXX Miles Funding Category e.g. RC (Reconstruction), RD (Reconditioning), MC (Major Construction) Programmed Letting Date XX/XX/XXXX Pavement Design Memorandum Yes/No


31

Project Information Project Scope

Type of Work General project description e.g. mainline reconstruction and overlay ramps.(may be found in scoping)

Benefit The expected improvement the project will provide; be specific (i.e. the amount of ride improvement, or amount of life extension).

LCCA Process Formal or District (see Chapter 7) Alternate Bid Yes or No (see Chapter 7) HMA Overlay Design Life If this project includes a HMA Overlay, the design life of the HMA Overlay

Pavement Design Segments This is a list of project segments that require separate pavement designs.

Segment # Highway #

From RP

To RP

Design Type

1 PCC or HMA Overlay, Reconstruction, FDR,SFDR, etc.

2


32

Existing Facility This is a description of the existing road and its general geometry. Scoping documents and Pavement Management System (see Section 280) may be useful in completing this section.

Highway Multiple segments may be required to describe the existing road. Include a copy for each segment.

From From RP To To RP

Number of Lanes No. of lanes, if it’s divided, and description of any median. Mainline Pavement

Type HMA or PCC. For PCC include the joint spacing, # of dowels, thickness etc.

Mainline Pavement Width Width in feet.

Shoulder Type HMA, PCC, aggregate, any curb and gutter. Shoulder Width Width in feet of each shoulder. Seasonal Load

Restriction The posted seasonal load restriction in tons; 10 tons if there is no posted restriction.

Speed Limit The posted speed limit. Roadway Construction History See Section 260 in Chapter 2 for guidance on obtaining this information. If this material is extensive, it may be placed as an appendix to this document. The following are examples of two sections of a project.

RP 123.789 to RP 126.987 - MN 23 to 3rd Street Year SP Activity Width Depth 1989 2309-001 Minor CPR/ Patching 30’ 1954 2309-123 CPR 1945 2309-789 HMA Shoulders 6’ 2.5” 1945 2309-789 Doweled PCC 30’ 8” 1945 2309-789 Aggregate Base 30’ 6’


33

RP 126.987 to RP 129.102 – 3rd Street to E Limits Franklin

Year SP Activity Width Depth 1989 2309-01 HMA Overlay 24’ 4.5” 1989 2309-01 HMA Milling 24’ 3” 1973 2309-12 HMA Overlay 24’ 4” 1951 2309-111 Chip Seal 24’ 1950 2309-22 Spot Patching 24’ 1945 2309-789 Doweled PCC with Aggregate Base 30’ 8”

Roadway Condition

Pavement Distresses A general description of the visible distresses. For guidance see Section 270.

Areas of Concern Any areas that may need repair or special treatment, such as frost heaves or subgrade failure. For guidance see Section 270.

Attach photos or diagrams as needed. Pavement Performance Data This section documents the Pavement Performance Data for the road within the project limits. Pavement Performance Data is available from Pavement Management System (see Section 280).

Year: Year that the data was collected

Segment Description Dir. From RP To RP RQI SR PQI IRI (in/mile)

I, D, U

R-Value/FWD Data Projects must develop an R-value from either FWD data or laboratory testing (or both). Use this table to document FWD data using the TONN Method, see Section 200. Any FWD (TONN Analysis) and Laboratory R-Values must be attached in the appendix.


34

FWD Data

Date: Date of Testing

Reported Capacity

Overlay Thickness R-Value

Mean Std. Dev.

Use this table to document any Laboratory R-values, see section 220.

Laboratory R-Values

Count Mean Minimum Maximum Std. Dev. # of tests

Comments: Any notes, comments, or concerns about the collected data. Core/GPR This section reports the HMA thickness (and condition) collected from coring or GPR see Sections 230 & 240. Date: Date that the data was collected on.

Segment: Segment #

Location Count Average Minimum Maximum Std. Dev.

Mainline, shoulder, turn-lanes, etc

Provide the location of any photos of the cores and of any GPR report. These may be attached, in EDMS, or ProjectWise. Comments: Any notes, comments, or concerns about the collected data.


35

Traffic See Section 250.

Traffic Forecast #: Traffic Forecast Date:

Hwy From RP To RP

Base Year

2-way Design Lane

HCADT

2-way HCADT Growth/

Year

20 Yr. Design Lane Cumulative

BESAL’s

20 Yr. Design Lane


35 Yr. Design Lane


Life-Cycle Cost Analysis (LCCA) This section contains the results of the LCCA analysis according to Chapter 7.

Alternate #1 Alternate #2 Alternate #3 Description Design Life

Project Net Present Cost % of Low Cost

Selected Exception: Does the district request an exception to either selecting the low-cost option or to following the alternate bidding process? See Chapter 7. Any exception form should be attached.


36

Pavement Recommendations This section contains the recommended pavement design(s) for the Pavement Design Segments (listed on the second page of the memo). Note: The table columns that have the heading “spec.” are intended to contain the

number of the appropriate construction specification or special provision, or indicate that a plan note will be provided.


37

NEW HMA


# TH # ###.### ###.### New HMA

Mainline

Pavement Thickness (inches) Lifts Mix Design/


Wear Sec. 400 Sec. 450 Sec. 450

Spec, SP, or Plan Note

Sec. 450 Scoping

Non-Wear Sec. 400 Sec. 450 Sec. 450


Sec. 450 Scoping


Mainline Subsurface


Testing Width (ft.)

Base Sec. 400 Sec. 400 & 310


Sec. 330

Subbase Sec. 400 Sec. 400 & 310


Sec. 330

Eng. Soil Sec. 320 Sec. 320


Sec. 330

Subgrade Prep. Sec. 320


Sec. 330

Notes


38

HMA Shoulders Thickness (inches) Lifts Mix Design/


Width (ft.)

Lt Rt

HMA Sec. 610 Sec. 450 Sec. 450


Sec. 450 Scope Scope

Aggregate Surfacing Sec. 610 Sec. 610


Sec. 330 610 610

Shoulder Agg. Base


Base


Match Agg. Base

Notes


Testing Width

Lt Rt




Added Aggregate Base


Base


Match Agg. Base

Notes



X.X” Subbase

X.X” Class X

X.X” New HMA Wearing Couse

X.X” YYYYYYY


X.X” YYYYYYY

X.X” New HMA Non-Wearing Couse


39

Misc. Pavement Recommendations and Instructions to Designers

Provide any other necessary instructions to the project designer for the design and construction of this pavement segment that were not provided in the previous tables.



X.X” Sub-base

X.X” Class X


X.X” YYYYYYY


X.X” YYYYYYY



40

FDR/SFDR/CIR


# TH # ###.### ###.### FDR,SFDR or CIR

Existing Mainline

Pavement Depth


Existing HMA Sec. 230,240, 260 HMA Sec. 260

Existing Aggregate

Sec. 230,240, 260

Sec. 230, 240, 260

Notes

Mainline

Pavement Depth


Milling Sec. 410 Sec. 410 #.# Added

Aggregate Sec. 410 Sec. 410 Sec. 410 #.#

Reclaim/ Recycle Sec. 410 Sec. 410 Sec. 410 #.#

Stabilize Sec. 410 Sec. 410 Sec. 410 #.#

Notes

Mainline Pavement





Sec. 450 Scoping



Sec. 450 Scoping



41

HMA Shoulders



Width (ft.)

Lt Rt






Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes


Testing Width

Lt Rt




Added Aggregate


Base


Match Agg. Base

Notes



X.X” Existing Aggregate


X.X” YYYYYYY

X.X” YYYYYYY X.X” FDR

X.X” SFDR





42

Rubblize/Crack & Seat


# TH # ###.### ###.### Rubblize/Crack & Seat

Mainline

Pavement Depth





Notes

Mainline

Pavement Depth


Mill HMA Sec. 410 Sec. 410 #.# Rubblize/

Crack & Seat Special Provision # and if any edits are required, Sec. 420

Subsurface Drains Type of drain & outlets and its specification, Sec. 420 & 370

Notes

Mainline Pavement





Sec. 450 Scoping



Sec. 450 Scoping



43

HMA Shoulders



Width (ft.)

Lt Rt






Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes


Testing Width

Lt Rt




Added Aggregate


Base


Match Agg. Base

Notes


X.X” YYYYYYY

X.X” YYYYYYY

4” Perf. PE Pipe



X.X” Rubblized PCC



44




45

HMA Overlay


# TH # ###.### ###.### HMA Overlay

Mainline

Pavement Depth





Notes

Mainline

Pavement Depth



Mainline Pavement


Material Spec. Compaction Testing Width (ft)



Sec. 450 Scoping


HMA Shoulders



Width (ft.)

Lt Rt






Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes


46


Testing Width

Lt Rt




Added Aggregate


Base


Match Agg. Base

Notes

X.X” ExistingPave.


X.X” Class X X.X” New HMA Overlay



X.X” Subbase



X.X” Sub-base

X.X” Class X

X.X” HMA Overlay

X.X” YYYYYYY


X.X” YYYYYYY

Mill X.X” Existing HMA X.X” Existing Pave.


47




48

NEW PCC


# TH # ###.### ###.### New PCC

Mainline

Pavement Thickness (inches)

Joint Spacing (ft.)

Dowel Arrangement


PCC Sec. 500 Sec. 530 Sec. 530 530 Sec. 530 Scoping Notes

Mainline Subsurface


Testing Width (ft.)

Base Sec. 500 Sec. 500 & 310


Sec. 330

Subbase Sec. 500 Sec. 500 & 310


Sec. 330

Eng. Soil Sec. 320 Sec. 320


Sec. 330

Subgrade Prep. Sec. 320


Sec. 330

Subsurface Drains Type of drain & outlets and its specification, sec. 500 & 370

Notes

HMA Shoulders



Width (ft.)

Lt Rt






Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes


49


Testing Width

Lt Rt




Added Aggregate


Base


Match Agg. Base

Notes

PCC


Width




Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes

PCC Joint Designation (MnDOT Standard Plan 5-297.221)

Joint Type Sealant Spec. Contraction Joint Sec. 530 Sec. 530 Longitudinal Joint Sec. 530 Sec. 530

Outside Shoulder Joint Sec. 530 Sec. 530 XXXXXXX Joint Sec. 530 Sec. 530


50


Provide a list of the PCC paving standard plans and plates that the designer must include in the project plans (see Section 550). Provide any other necessary instructions to the project designer for the design and construction of this pavement segment that were not provided in the previous tables.

X.X” YYYY



X.X” YYYYYYY

X.X” YYYYYYY

X.X” Class X 4” Perf. PE Pipe

X.X” New PCC

XX.X ft X.X ft X.X ft XX.X ft


X.X” Subbase



X.X” Sub-base

X.X” Class X

X.X” New PCC

X.X” YYYYYYY


X.X” YYYYYYY YYYY Joint YYYY Joint


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Whitetopping


# TH # ###.### ###.### Whitetopping

Mainline

Pavement Depth



Mainline Pavement

Thickness (inches)

Joint Spacing (ft.)

Dowel Arrangement



HMA Shoulders



Width (ft)

Lt Rt

HMA Sec. 610 No. and

Thickness, Sec. 450

Sec. 450





Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes


Testing Width

Lt Rt




Added Aggregate


Base


Match Agg. Base

Notes


52

PCC Shoulders Thickness Material Spec. Compaction

Testing Width




Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes



Outside Shoulder Joint Sec. 530 Sec. 530

XXXXXXX Joint Sec. 530 Sec. 530





X.X” YYYYYYY

X.X” YYYYYYY X.X” New PCC Overlay


X.X” Existing HMA



53

UBOL


# TH # ###.### ###.### Unbonded Overlay

Mainline

Pavement Depth



Mainline Pavement

Thickness (inches)

Joint Spacing (ft.)

Dowel Arrangement



Mainline Subsurface


Testing Width (ft.)

Interlayer Sec. 520 Sec. 520 520 Sec. 450 Scoping Subsurface

Drains Type of drain & outlets and its specification, Sec. 520 & 370

Notes

HMA Shoulders



Width (ft)

Lt Rt






Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes


54


Testing Width

Lt Rt




Added Aggregate


Base


Match Agg. Base

Notes

PCC


Width




Sec. 330 610 610


Base

Match Agg. Base

Match Agg. Base

Notes



Outside Shoulder Joint Sec. 530 Sec. 530

XXXXXXX Joint Sec. 530 Sec. 530


55





X.X” YYYYYYY

X.X” YYYYYYY

X.X” Interlayer 4” Perf. PE Pipe

X.X” New PCC Overlay



X.X” Existing PCC


56

Use of Paver Mounted Thermal Profile (PMTP) and Intelligent Compaction (IC) Methods

Paver Mounted Thermal Profiling (PMTP) is the process of continuously monitoring and recording the location and temperature of the asphalt mat immediately behind the paver screed during placement operations. This identifies any thermal segregation in the uncompacted asphalt which may affect the pavement’s performance and durability.

Intelligent Compaction (IC) refers to the compaction of road materials, such as soil, aggregate base, or asphalt, using self-propelled rollers integrated with a position monitoring system and an onboard documentation system that can display real-time, color coded maps of roller location, number of passes, roller speeds, amplitudes and vibration frequencies of the roller drum. Some systems are also equipped with drum vibration instrumentation, infrared temperature sensors, and/or automatic feedback control. The onboard documentation system on these rollers also displays real-time, color-coded maps of stiffness response or pavement surface temperatures, or both. This improves monitoring and recording of the compaction process to ensure that the material is properly and uniformly compacted.

The PMTP and IC methods are recommended for use when the following project/site conditions are met:

1. The technology can be used with the following specifications:

Table 830.1 - Use of Intelligent Compaction and Thermal Profiling

Technology Specification

Intelligent Compaction (IC)—SP 2016 Quality Management Special

2215 (SFDR), 2331 (CIR), 23531, 2360, 2365

Paver Mounted Thermal Profile (PMTP) Method—SP 2016 Quality

Management 2360, 2365

1 IC is recommended for use on 2353, only when used in conjunction with 2360 (i.e., when IC is already being used with 2360).

2. Net lane miles are greater than or equal to 4. Note: These technologies can be used on smaller projects. It is anticipated that the recommended lane miles will decrease with time as more contractors are equipped with these systems.


57

3. Cellular coverage, to allow for automatic transfer of data to the cloud, at least one time per day. Areas with intermittent locations of limited to no cellular coverage are allowed within the project limits, since the systems can store data until adequate data cellular coverage is available.

4. Adequate global navigation satellite system (GNSS) coverage through the project limits is required for recording of the real-time, spatial location of equipment. Table 830.2 lists the required accuracies.

Table 830.2 – Required GNSS Accuracy Technology Accuracy

Intelligent Compaction (IC) Method— SP 2016 Quality Management Special ± 2 in (50 mm) in the X and Y Direction

Paver Mounted Thermal Profile (PMTP) Method —

SP 2016 Quality Management ± 4 feet (1.2 m) in the X and Y Direction

Removals

Any needed directions to the designer to provide for the removal of existing materials.

Geotechnical Recommendations Special Treatments

Swamp areas, shadow treatments, rock excavation, or subgrade corrections: For any of these areas specify:

The depth of the correction/treatment and its limits (Section 320.2) The backfill material and its specification (Section 320.2) Compaction testing (Section 330) Any tapers or transitions in materials (Section 320.4)

Embankment

If there will be any additional embankment construction specify the:

Embankment material, its specification, and any plan note or special provision edits to modify the material (Section 320.3)

Compaction testing (Section 330)


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Application of any surcharge (Section 320.3.c) Monitoring equipment (Section 320.3.d)

Topsoil

If construction activities will disturb any topsoil, provide the depth of topsoil to be stripped and reused.

Borrow Shrinkage Factor

If there will be a quantity of borrow using specification 2105 then develop a borrow shrinkage factor (Section 340).

Culverts

Frost depth and soil-type: Provide an estimated frost depth and soil-type (plastic or granular). This information is used to select the correct culvert backfill treatment (Section 360.1).

Fabric: Specify if any geotextile fabric, and type, (Section 360.2) should be included in the culvert backfill treatment.

Plastic Soil Cap: Specify if a plastic soil cap treatment (Section 360.3) is required for any culverts.

Modifications: Give full instructions, and specify the materials, of any modifications to the standard culvert backfill treatment drawings (Figures 360.1-4).

Plan Notes

Provide the text to any notes to be included in the project plans.

Edits or Additions to Special Provisions Provide any changes or text that is intended to be added to any special provisions.

Attachments: Attach or provide a link to the location of the following:

Printouts of the pavement design programs’ output for each pavement design.

Signed traffic forecast summaries.

Soil borings and cores (or link).

The LCCA and any supporting calculations.

Any LCCA or alternate bidding exceptions.


59

Any GPR, geotechnical, or other reports.

MnDOT Pavement Design Manual, July 15, 2015


Chapter 9 – Construction and Rehabilitation Alternates




900 – Existing Pavement-Types ...................................................................................................................... 2

910 – Rehabilitation with HMA Overlay (>2 inches) .................................................................................. 3

920 – Rehabilitation with PCC Overlay ......................................................................................................... 5

930 – Rehabilitation with FDR/SFDR/CIR ............................................................................................... 10

940 – Rehabilitation with Rubblization/Crack & Seat ............................................................................... 13

950 – New/Reconstruction ............................................................................................................................ 15

960 – Noneconomic Factors .......................................................................................................................... 16


1

Introduction

This chapter contains alternates to consider for new construction/reconstruction or rehabilitation of existing pavements. It is intended to be used to develop the pavement alternates required by Pavement-Type Selection (see Chapter 7 – Pavement-Type Selection) and may be used as an aid to the scoping process.

Process

STEP 1. Find the existing pavement-type and the possible rehabilitation alternates in Table 900.1.

STEP 2. Use the tables in Sections 910-950 to determine which alternates are applicable.

Additionally, consult Table 960.1 for noneconomic factors.


2

900 – Existing Pavement-Types

Table 900.1 – Existing Pavement-Types and Possible Rehabilitation Alternates

Existing Pavement-type Description Possible

Rehabilitation*

HMA on Aggregate Base

HMA pavement, including any HMA overlays, placed on several inches of aggregate base.

• HMA overlay (>2 inches) • PCC overlay • FDR/SFDR/CIR • New/Reconstruction

Full-Depth HMA on Subgrade

HMA pavement, including any HMA overlays, placed on sub-grade.

• HMA overlay (>2 inches) • PCC overlay • FDR/SFDR/CIR • New

HMA on PCC HMA pavement placed on previously constructed PCC Pavement.

• HMA overlay(>2 inches) • PCC overlay • CIR • Rubblization • Crack and Seat • New/Reconstruction

PCC on Aggregate Base or Subgrade

PCC pavement placed on either aggregate base or subgrade.

• HMA overlay (>2 inches) • PCC overlay • Rubblization • Crack and Seat • New/Reconstruction

PCC on HMA PCC pavement placed on previously constructed HMA Pavement.

• HMA overlay (>2 inches) • PCC overlay • FDR/SFDR • New/Reconstruction

PCC on PCC PCC pavement placed on previously constructed PCC Pavement.

• HMA overlay (>2 inches) • PCC overlay • Rubblization • Crack and Seat • New/Reconstruction

* This list includes typical, available rehabilitation alternates. It is not intended to exclude any alternates that may be available for a project.


3

910 – Rehabilitation with HMA Overlay (>2 inches)

Table 910.1 - HMA Overlay on Existing HMA Manual Location Section 460.

Description

Paving >2” of HMA on an existing HMA pavement’s surface. It is intended to improve ride, reduce surface distress, may improve pavement structure, and preserve the existing pavement. Existing HMA may be milled prior to the HMA overlay to remove surface distresses and to reduce the road’s profile.

Design Life Typically, MnDOT projects use a design life of 13-19 years depending on existing pavement condition, traffic, and HMA overlay thickness.

Good Candidate • Structurally sound pavement that needs only minor improvements. • Projects in which a limited design life is acceptable.

Poor Candidate

• Pavements that exhibit structural problems such as: o Deforming or rutting subsurface layers. o Large amounts of bottom-up fatigue cracking. o Subgrade failures and/or seasonal heaving issues.

• Pavements with a large amount of surface distress (rutting, cracking, and poor ride) that will not be sufficiently improved by an HMA overlay.

• Projects in which a long design life is desired..

Pros

• May add structure. • Improves ride and reduces surface distresses. • Relatively inexpensive. • Short construction period. • Reduces short-term maintenance.

Cons • Limited ability to improve structure and function. • May raise road profile. • Limited design life.


4

Table 910.2 - HMA Overlay on Existing PCC Manual Location Section 460.

Description

Paving >2” of HMA on an existing PCC pavement’s surface. It is intended to improve ride, reduce surface distress, may improve pavement structure, and preserve the existing pavement. Any existing HMA may be milled prior to the HMA overlay to remove surface distresses and to reduce the road’s profile.


Good Candidate • Structurally sound pavement that needs only minor improvements. • Projects in which a limited design life is acceptable.

Poor Candidate

• Pavements with rocking or moving panels. • Pavements on subgrades with seasonal heaving issues. • Pavements with large amounts of cracked or shattered panels. • Projects in which a limited design life is unacceptable.

Pros

• May add structure. • Improves ride and reduces surface distresses. • Relatively inexpensive. • Short construction period. • Reduce short-term maintenance.

Cons

• Limited ability to improve structure and function. • Limited design life. • Joints and cracks in the existing PCC will reflect through the HMA overlay. • May induce PCC blow-ups. • The HMA overlay may spall at severe existing PCC joints or cracks. • Probable reflective cracking over joints and cracks in the concrete. • Raises in the pavement profile.


5

920 – Rehabilitation with PCC Overlay

PCC overlays may be used to rehabilitate existing HMA and existing PCC pavements. PCC overlays of HMA pavements, or whitetopping, may be designed using two different procedures. One procedure, using the BCOA-ME, requires a durable bond between the PCC overlay and the existing HMA. The other whitetopping design procedure, using MnPAVE-Rigid, doesn’t consider a bond and may be used on more deteriorated HMA pavement than the bonded design. PCC overlays of existing PCC pavement, or UBOL, use an interlayer to prevent the bonding of the PCC overlay to the existing PCC pavement.


6

Table 920.1 – Bonded PCC Overlay of Existing HMA – Designed using BCOA-ME

Manual Location Section 510.

Description

This type of design counts on the bond between the PCC overlay and the existing HMA to ensure that they behave as a single monolithic pavement layer. BCOA thicknesses typically range from 4.0” to 6.0”. The surface of the existing HMA may be milled to remove surface distresses and to reduce or eliminate increases in the profile of the overlaid pavement. Any existing PCC overlay may be removed, the existing HMA prepared, and replaced with a new PCC overlay.

Design Life 20 years

Good Candidate

• The existing HMA pavement has stable support conditions with only localized weak areas that may be repaired prior to placing the PCC overlay.

• The primary distresses in the existing HMA pavement are surface distresses. • Thermal cracks in the HMA pavement are predominately non-deteriorated

thermal cracks. Deteriorated thermal cracks will require repair prior to placing the PCC overlay.

• There is a sufficient existing HMA thickness so that after any proposed milling:

o 85% of the cores are 4.0” or thicker. o Any individual core must be a minimum of 3.0” thick. Any

areas of less than 3.0” of HMA may be treated by removing the existing HMA pavement and constructing a 6.0” (minimum) PCC section.

Poor Candidate

• The existing HMA pavement has significant structural deterioration and areas of uneven support conditions.

• Existing HMA overlay of PCC Pavement. • The existing pavement exhibits differential frost movements. • The existing HMA has been widened, or will require widening, within the

area of the driving lane. • The HMA pavement that will remain after any milling exhibits stripping

and/or debonded layers. • HMA pavements with predominately deteriorated thermal cracks that will

require repair prior to placing the PCC overlay. • There is an insufficient existing HMA thickness so that after any proposed

milling:

o More than 15% of the cores are less than 4.0” thick. o There are individual cores less than 3.0” thick. However, any

areas of less than 3.0” of HMA may be treated by removing


7

the existing HMA pavement and constructing a 6.0” (minimum) PCC section.

Pros • Adds structure. • Improves ride and reduces surface distresses. • Relatively inexpensive.

Cons

• Requires a sufficient thickness of sound HMA pavement. • Requires stable support. • May require a rise in road profile. • Existing active cracks in the HMA may reflect through to the PCC overlay.


8

Table 920.2 – Non-Bonded PCC Overlay of Existing HMA – Designed using MnPAVE-Rigid

Manual Location Section 510.

Description

This design-method does not require a bond between the PCC Overlay and the existing HMA. The minimum thickness is 6.0”. Any existing HMA may be milled prior to the HMA overlay to remove surface distresses and to reduce the road’s profile. Any existing PCC overlay may be removed, the existing HMA prepared, and replaced with a new PCC overlay.

Design Life 20 or 35 years

Good Candidate • The existing pavement has stable support conditions or will require only localized repairs.

Poor Candidate • Poorly draining roads that will not provide stable support for the PCC

overlay. • The existing pavement exhibits differential frost movements.

Pros • Adds structure. • Improves ride and reduces surface distresses. • May be used on most existing HMA pavements.

Cons • More expensive than a bonded PCC overlay. • May require a raise in road profile. • Existing active cracks in the HMA may reflect through to the PCC overlay.


9

Table 920.3 – Unbonded PCC Overlay of Existing PCC - “UBOL” Manual Location Section 520.

Description A PCC overlay that uses a “bond-breaker” to separate it from existing PCC pavement. The minimum pavement thickness is 6.0 inches.

Design Life 20 or 35 years

Good Candidate • The existing pavement has stable support conditions or will require only

localized repairs. • The roadway has room to permit a significant raise in road profile.

Poor Candidate

• Significant areas that will require repair prior to placing the PCC overlay. • Existing pavement has rocking or moving panels. • The existing pavement exhibits differential frost movements. • Roadways with a significant number of bridges requiring profile adjustments.

Pros

• Improves ride and pavement distress. • May be used on most existing PCC pavements. • May be used on faulted pavements or pavements with material related

distresses. • Significantly streamlined construction as compared to reconstruction.

Cons • Requires stable support conditions. • Will require a significant raise in road profile.


10

930 – Rehabilitation with FDR/SFDR/CIR

Note: MnPAVE-Flexible must be used to design theses options.

Table 930.1 – Full-Depth Reclamation (FDR) Manual Location Section 420.

Description

FDR involves using a reclaiming machine to crush and blend-together existing HMA pavement and aggregate. The blended material is moved as necessary to allow it to be compacted in 6-inch lifts. After compaction and shaping, it will then act as base for new HMA pavement.


Good Candidate

• A roadway with few or no subgrade problems. • The pavement has sufficient existing aggregate base to cool the reclaimer

teeth and to reclaim with existing HMA. HMA may be milled or aggregate added to the pavement surface prior to reclaiming to help meet this proportion.

• A roadway that has room to permit a significant raise in road profile.

Poor Candidate • A roadway that requires a large amount of subgrade repair. • The roadway does not have room to permit a significant raise in road profile. • The pavement exhibits differential frost movements.

Pros • Typically, less expensive than reconstruction. • Rehabilitates pavements that are structurally and functionally unsound. • Removes all pavement distresses and pavement material problems.

Cons

• Not intended to repair subgrade problems (however, localized areas can be addressed during design and construction).

• Requires sufficient thickness existing aggregate. • Will require a significant raise in road profile.


11

Table 930.2 – Stabilized Full-Depth Reclamation (SFDR) Manual Location Section 420.

Description

SFDR is FDR that has had a stabilizing agent added. After the roadway has been reclaimed, a second pass of the reclaiming machine is made to apply and blend-in a stabilizer. The stabilizer is typically emulsified asphalt with additives or foamed asphalt cement. This layer will then be compacted, shaped, and allowed to cure before being paved with new HMA pavement.


Good Candidate • A roadway with few or no subgrade problems. • An HMA pavement with at least 3 inches of existing aggregate base.

Poor Candidate • A roadway that requires a large amount of subgrade repair. • A pavement without aggregate base. • The pavement exhibits differential frost movements.

Pros

• Rehabilitates pavements that are structurally and functionally unsound. • Uses thinner HMA as compared to FDR. • Will require less of a raise in road profile than FDR. • Requires less in-place aggregate than FDR. • Typically, less expensive than reconstruction. • Removes all pavement distresses and pavement material problems.

Cons

• Not intended to repair subgrade problems (however, localized areas can be addressed during design and construction).

• Requires some existing aggregate. • Stabilization adds to the cost as compared to FDR.


12

Table 930.3 – Cold In-place Recycling (CIR) Manual Location Section 420.

Description

CIR involves milling a portion of the existing HMA, mixing the milled material with emulsified asphalt and additives, and paving the roadway with the milled/emulsified mix. These activities are all performed in one pass of a CIR ‘train’. The paved CIR material is then compacted and, after a suitable curing time, it is paved with HMA pavement.


Good Candidate • A roadway with few or no subgrade problems. • Will support the CIR train.

Poor Candidate • A roadway that requires a large amount of subgrade repair. • Support for the heavy CIR train cannot be provided during construction. • The pavement exhibits differential frost movements.

Pros • CIR layer may retard reflective cracking. • Removes surface distresses.

Cons • Will not repair subgrade problems. • Retains the distresses and any materials problems of material that is left

remaining.


13

940 – Rehabilitation with Rubblization/Crack & Seat

Table 940.1 – Rubblization Manual Location Section 430.

Description

Rubblization is intended to reduce the existing PCC modulus in order to prevent reflective cracking of the new HMA pavement and allow it to act as new base. Rubblization involves breaking the existing PCC slab into pieces (3.0 inches maximum at surface and 9.0 inches maximum at the bottom of pavement), compacting the rubblized material, and paving an HMA pavement.


Good Candidate • Subgrade with an average R-Value of at least 17 or at least 12 inches of

granular material. • Room to permit a raise in road profile.

Poor Candidate

• The pavement exhibits differential frost movements. • Subgrade with an R-Value of less than 17 and less than 12 inches of granular

material. • Rise in road profile not permissible.

Pros

• Less expensive than reconstruction. • Removes surface distresses and allows the existing PCC pavement to act as

base for a new HMA pavement. • Rubblized PCC is stronger than aggregate base.

Cons • Requires a solid subgrade that doesn’t require subgrade repairs. • Significant rise in road profile. • Edge-drains must be installed prior to rubblization.


14

Table 940.2 – Crack and Seat Manual Location Section 430.

Description

The Crack & Seat process involves cracking the existing PCC pavement into 3 to 4-foot pieces, firmly seating the pieces, and paving HMA pavement. The intention is to reduce the size of the PCC pieces to minimize movements at existing cracks and joints. This will minimize the frequency and severity of reflective cracking. It is an especially useful technique when moving or rocking panels have been identified.


Good Candidate • Roadway with a good subgrade that does not require extensive repairs. • Room to permit a raise in road profile.

Poor Candidate

• Saturated subgrade which cannot be addressed through edge drain installation.

• The pavement exhibits differential frost movements. • Rise in road profile not permissible.

Pros

• Less expensive than reconstruction. • Removes surface distresses and allows the existing PCC pavement to act as

base for a new HMA pavement. • Cracked PCC is stronger than aggregate base.

Cons • Requires a solid subgrade that doesn’t require subgrade repairs. • Significant rise in road profile. • Edge-drains need to be installed prior to Crack and Seat.


15

950 – New/Reconstruction

Table 950.1 – New/Reconstruction Manual Location Section 400 (HMA) or Section 500 (PCC).

Description Removal of any existing pavement and construction of new pavement placed on new or existing base and subbase.

Design Life 20 or 35 (PCC only) years.

Good Candidate

• New alignment. • Structurally and functionally unsound pavement. • Requires changes in geometry. • Requires widespread subgrade repairs. • Doesn’t have room to permit a rise in the road profile.

Poor Candidate • Projects in which less expensive options are available.

Pros

• Subgrade repairs may be performed and subsurface drainage installed. • Geometric problems may be addressed. • Pavement subsurface may be constructed with frost resistant materials. • Removes previous distresses and poor materials. • Controls final road profile. • Long design life. • Provide a sound platform for future rehabilitations.

Cons • Typically, the most expensive alternate. • Generally, a longer construction period than other alternates. • Construction operations are susceptible to elements.


16

960 – Noneconomic Factors

Table 960.1 – Noneconomic Factors to Consider When Evaluating Pavement Alternates

Technical Other • Roadway geometrics (e.g., varying lane widths,

presence of vertical curves, longitudinal grades).

• Continuity of adjacent pavements and lanes. • Characteristics of subgrade soils. • Traffic during construction. • Future needs on geometric or capacity changes. • Safety considerations, such as delineating the

contrast between pavement and shoulder.

• Availability of local materials and experience.

• Conservation of materials and energy. • Local government preferences or local

politics. • Stimulation of competition among paving

materials suppliers. • Noise issues due to work-zone construction

or tire-pavement friction. • Experimental materials or design concepts. • Maintenance experience and equipment. • Industry capability to perform the required

work. • Sustainability, such as through energy

efficiency, emissions reduction, and resource conservation.

Documents

Entire MnDOT Pavement Design Manual