STRUCTURAL ANALYSIS OF 1 PERVIOUS CONCRETE PAVEMENT.pdf

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STRUCTURAL ANALYSIS OF PERVIOUS CONCRETE PAVEMENT12

Mary Vancura (corresponding)

Graduate Research Assistant

University of Minnesota

Department of Civil Engineering500 Pillsbury Drive S.E.Minneapolis, MN 55455

Phone: 612-597-3431E-mail: [email protected]

Kevin MacDonald

Vice President of Engineering ServicesCemstone Products Co.

2025 Centre Pointe Blvd #300Mendota Heights, MN 55120


Lev Khazanovich

Associate Professor

University of Minnesota

Department of Civil Engineering500 Pillsbury Drive S.E.Minneapolis, MN 55455


3Paper resubmitted 15 November 2010 in consideration for4

Transportation Research Board 90th Annual Meeting,523-27 January 20116

78

Words: 3,9159Figures: 810

Tables: 611Photographs: 012

Total Word Count: 7,4151314

TRB 2011 Annual Meeting Paper revised from original submittal


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Vancura, MacDonald, and Khazanovich 1

STRUCTURAL ANALYSIS OF PERVIOUS CONCRETE PAVEMENT12

Abstract34

Pervious concrete pavement must perform as both a stormwater management tool and a5

pavement. While much of the research has focused on pervious concretes porosity and6 permeability, presently, there are few guidelines for structural analysis and design of pervious7concrete pavement. In this paper, stiffness and fatigue analyses were completed for an existing8

pervious concrete pavement using Westergaards theory of a medium-thick plate on a Winkler9foundation. The stiffness evaluation compared the responses of pervious and conventional10

concrete pavements to falling weight deflectometer (FWD) stresses and to models created in11ISLAB2005. It was found that although pervious concrete has a lower modulus of elasticity than12

conventional concrete pavement, Westergaards model adequately describes the behavior of13pervious pavements. Additionally, a fatigue analysis of pervious concrete was completed using14

the StreetPave fatigue model.15



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INTRODUCTION1Pervious concrete has a network of interconnected voids that allow liquid to pass through2

the concrete matrix. These voids are typically 15%-35% of the concretes total volume (1). The3voids are maintained through placement and compaction because of gap-graded coarse aggregate4

and a viscous cement paste that prevents the separation of paste and aggregates. Fine aggregate5

is typically omitted from pervious concrete because it increases the paste volume, which causes a6 decrease in the interconnected void volume.7In the United States, pervious concrete is primarily used as a stormwater infiltration tool8

that is disguised as pavement in parking lots, patios, sidewalks, and low volume roads. To these9ends, pervious concrete is a dual-purpose building material that typically must satisfy10

specifications both as a stormwater management tool and as a pavement, and its design requires a11balance of permeability and strength.12

Much of the pervious concrete research has focused on its role as a stormwater13management tool while the structural behavior of pervious pavement has received much less14

attention. In a survey of 22 pervious concrete pavements throughout the state of Minnesota,15including driveways, sidewalks, low-volume roads, parking lots, and residential alleys, many16

exhibited good structural performance. However, sections showed signs of premature structural17 distress in the form of both top down and bottom up structural cracks from very few heavy load18

repetitions.19One of the unknowns in the structural analysis of pervious concrete pavement is if20

Westergaards model of a plate on a Winkler foundation, the model traditionally used for21analysis of conventional rigid pavements, is a model that adequately describes its behavior.22

Furthermore, it is not clear if the empirical components of existing pavement analysis and design23tools need to be calibrated for pervious concrete separately from conventional concrete24

pavement.25This paper examined these unknowns. This was accomplished by comprehensive analysis26

of falling weight deflectometer (FWD) data collected at MnROAD, the Minnesota Department27of Transportations (MnDOT) pavement testing facility and finite element modeling using28

ISLAB2005. Additionally, a fatigue analysis was completed of pervious concrete pavement29using the StreetPave fatigue model. The details of this analysis are presented below.30

31BACKGROUND32

33

MnROAD Pavement Testing Facility34

MnDOT operates a pavement testing facility in Albertville, MN. The purpose of the35facility is to build and instrument innovative pavement sections and monitor their behavior. One36

component of the facility is a low-volume road with approximately twenty-four, 500-foot long37pavement test sectionsreferred to as cellsthat are loaded multiple times each day by an 8038

kip, 5-axle, 18 wheel semi truck and trailer. The low-volume loop pavements include39conventional asphalt and concrete pavements, rehabilitation pavements, and most recently,40

pervious concrete pavements.4142

Pervious and Conventional Concrete Pavements43The structural behavior of two pervious concrete pavement cells and three conventional44

concrete pavement cells with similar thicknesses and base and subgrade materials were45considered for this study. The pervious concrete pavements occupying MnROAD low volume46



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road Cells 85 and 89 were constructed in 2008 and were originally designed as 7-inches of1pervious Portland cement concrete (PCC) over 12 in. of CA-15, a MnDOT-specified base2

material (Table 1). Cell 85 rests on a sand subgrade, and Cell 89 rests on a clay subgrade.3Beneath the subgrade in both cells, a plastic barrier, geotextile fabric, and transverse drains were4

installed. According to construction records, the CA-15 base material showed instability during5

construction so railroad ballast was used to stabilize the subgrade in the top four inches, joints6 were cut at 10 ft spacing, and no steel dowels or tie bars were included in the pavements (2).7The conventional concrete pavements analyzed for this report occupied Cells 36, 38, and8

40 on the low volume road and were built in 1993. Cell 36 consists of a 6.5-inch Portland9cement concrete (PCC) pavement over 5-inches of granular base over a sand subgrade. Cell 3810

is a 6.5-inch PCC pavement over 5 inches of granular base over a clay subgrade. Cell 40 is a116.3-inch to 7.6-inch PCC pavement over 5-inches of granular base over a clay subgrade. Cells12

36, 38, and 40 were chosen for analysis because they had similar section thickness and base and13subgrade materials as the pervious concrete in Cells 85 and 89.14

15TABLE 1 Percent by mass passing square sieve openings for MnDOT designated CA-1516

coarse aggregate (3).17 AggregateDesignation

50 mm(2 in)

37.5 mm(1.5 in.)

31.5 mm(1.25 in.)

25 mm(1 in.)

19 mm(3/4 in.)

16 mm(5/8 in.)

12.5 mm(1/2 in)

9.5 mm(3/8 in.)

4.75mm

(#4)

CA-15 100 95-100 35-65 5-25 0-7

18

Data acquired from MnROAD1920

FWD21In general, FWD tests are performed on most of the MnROAD pavement cells multiple22

times each year to test the structural response of pavements. Specifically, FWD tests were23performed on multiple locations of the conventional and pervious concrete pavements in Cells24

36, 38, 40, 85, and 89 at least five times between March 2009 and November 2009.2526

Modulus of Rupture27MnDOT also acquired modulus of rupture (MR) data from the pervious concrete28

pavements in Cells 85 and 89. The MR data was determined by third point beam bending tests29according to ASTM C 78 at 3, 7, and 28 days. The test beams were cast in molds with concrete30

obtained from the concrete trucks that delivered the concrete for the construction of Cells 85 and3189. The average MR values of the pervious concretes in Cells 85 and 89 are shown in Table 2.32

3334



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TABLE 2 Average modulus of rupture values of pervious concrete in Cells 85 and 8912

85 Driving Lane 89 Driving Lane

Day MR (psi) Day MR (psi)

3 295 3 330

7 320 7 39028 330 28 440

85 Passing Lane 89 Passing Lane

Day MR (psi) Day MR (psi)

3 440 3 435

7 450 7 430

28 490 28 490

3

STRUCTURAL ANALYSIS OF PERVIOUS CONCRETE PAVEMENTS45

The behavior of conventional rigid pavements is modeled using Westergaards theory of6a medium-thick plate resting on a Winkler foundation (4). It is currently not clear if this model7

accurately predicts the behavior of pervious concrete pavement. The applicability of8Westergaards model to pervious concrete was evaluated by comparing the behavior of9

conventional and pervious concrete pavements exposed to similar stresses, temperature, and10moisture conditions. The stresses were imparted by FWD tests performed on the pavements.11

12Backcalculating Subgrade Modulus and Modulus of Elasticity of Conventional and13

Pervious Concrete Pavements1415

FWD16

Deflections of the conventional and pervious concrete pavements measured by the FWD17tests were used to backcalculate the subgrade modulus and modulus of elasticity of the18pavements using Westergaards model parameters. FWD sensors were located at the prescribed19

intervals of 0, 8, 12, 18, 24, 36, and 60 inches from the center of load. The FWD load varied20from 5,500 to 15,000 lbs with three typical loads6,000, 9,000, and 12,000 lbsdropped at21

multiple pre-defined locations across the pavement surfaces. The load was dropped onto a plate22with a radius equal to 5.9 inches. The sensors measured deflections caused by the imparted load,23

and the deflections were used to back-calculate the dynamic subgrade modulus (kd) using the24AREA method. Subsequently, equations of Kirchhoffs plate theory were used to determine the25

modulus of elasticity (E) of the concrete.2627

AREA method28The AREA method is a tool for estimating kdof concrete pavements based on FWD29

deflection data and is discussed in detail in (5). It estimates the area of a deflected basin by30utilizing the trapezoidal rule for deflections measured by 4 or 7 sensor locations. The response31

of the deflection basin to an applied load is used to calculate the dynamic subgrade modulus,32which, in turn, is used to estimate the modulus of elasticity (E) of the concrete layer.33

34



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To begin calculating kdof conventional and pervious concrete pavements in Cells 36, 38,140, 85, and 89, A7 was calculated with FWD deflection data from seven sensors and the A72

equation (Equation 1). The A4 equation, which uses deflection data from four sensors, was used3to verify A7 calculations and is indicated by Equation 2 (5). Both the A4 and A7 methods are4

based on Westergaards theory and both can be used for backcalculation. The 1993 American5

Association of State Highway and Transportation Officials (AASHTO) Guide for Design of6 Pavement Structures uses the A4 method to calculate kd. The 1998AASHTO Guide for Design7of Pavement Structures, 4

thEd, Supplementuses the A7 method to calculate kd. Moving8

forward, it will be important that the method used for the calibration of a design procedure for9pervious concrete pavements is used for future evaluation procedures of pervious pavements to10

ensure consistency.1112

1. Deflections at seven sensors were measured and inserted into the A7 equation.1314

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16dris the measured deflection at the sensor located a radial distance r from the location of the17

applied load.1819

2. For the A7 sensor configuration, the radius of relative stiffness (l)was estimated with20

Equation 3 and the prescribed coefficients shown in Table 3, line 1. For the A4 sensor21configuration, Equation 2 was substituted for the A7 term in Equation 3, and the coefficients22

from Table 3, line 2 were used.23

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TABLE 3 Coefficients for the AREA calculation of radius of relative stiffness () (4)26

AREA x1 x2 x3 x4

A7 60 289.708 -0.698 2.566

A4 36 1812.279 -2.559 4.387

27

3. The subgrade dynamic modulus (kd) was estimated at each sensor location with Equation 4.28Equation 4 utilizes a non-dimensional deflection coefficient (dr

*), the magnitude of the applied29

load in (P) in lbs, the radius of relative stiffness (l), and the FWD deflection data measured at a30

radial distance r from the location of applied load (dr). dr*was calculated using Equation 5. The31

dr*coefficients, a, b, and care listed in Table 4.32

33



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TABLE 4 a, b, and ccoefficients for Equation 5 (4).3Sensor location at rinches from applied

load

a b c

0 0.12450 0.14707 0.07565

8 0.12323 0.46911 0.07209

12 0.12188 0.79432 0.07074

18 0.11933 1.38363 0.06909

24 0.11634 2.06115 0.06775

36 0.10960 3.62187 0.06568

60 0.09521 7.41241 0.06255

44. The values of land kdwere used to calculate the pavements flexural stiffness (D). Equation5

6 is an alternative equation for the radius of relative stiffness from Equation 3, and was solved6

for D.78

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94. Once D was determined, plate mechanics were employed to solve for the pervious concretes10modulus of elasticity (E). For a Kirchhoff plate, Equation 7 represents a plates flexural stiffness11

and includes E (4). Equation 7 was rearranged to solve for E:1213

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h = thickness of the plate (in.)15

= Poissons Ratio1617

5. To solve for E with known parameters, Equation 6 was substituted into Equation 7:1819

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20FWD deflection profiles

21

The deflection profiles generated by FWD tests on the pervious concrete pavements22resembled those of the conventional pavements. An example of deflection profiles from a23

pervious concrete pavement (Cell 85) and a conventional concrete pavement (Cell 36) is shown24in Figure 1. The pervious concrete pavements consistently deflected more than the conventional25

concrete pavements under similar loads.26



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1FIGURE 1 An example of the FWD deflection basin profiles from a pervious concrete2

pavement (Cell 85) and a conventional concrete pavement (Cell 36).34

Determination of a Typical Pervious Concrete Modulus of Elasticity5The average and range of E values were determined from FWD tests and the AREA6

method for the pervious concrete pavements in cells 85 and 89 and conventional concrete7pavements in Cells 36, 38, and 40. These values are shown in Table 5.8

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TABLE 5 Average and range of E for the pervious concrete pavements in MnROAD Cells185 and 89 and for conventional concrete pavements in MnROAD Cells 36, 38, and 40.2

Cell Number/lane Rigid Pavement Type Average E

(psi)

Range of E (psi)

85 Driving Pervious 2,090,000 1.47E+06 to

2.87E+0685 Passing Pervious 2,850,000 1.58E+06 to

7.03E+06

89 Driving Pervious 2,680,000 1.75E+06 to4.08E+06

89 Passing Pervious 2,830,000 1.38E+06 to6.94E+06

36 Driving Conventional 8,190,000 6.80+06 to9.04E+06

36 Passing Conventional 5,380,000 4.4E+06 to5.96E+06

38 Driving Conventional 6,150,000 5.01E+06 to7.75E+06

38 Passing Conventional 4,520,000 3.99E+06 to5.71E+06

40 Driving Conventional 6,560,000 5.30E+06 to

7.93E+06

40 Passing Conventional 7,280,000 5.40E+06 to

9.47E+06

3

From the FWD tests and AREA method calculations, it was shown that the E of pervious4concrete pavement in cells 85 and 89 was less than the E of conventional concrete pavements in5

Cells 36, 38, and 40. Additionally, it was decided to assume an E of 2,500,000 psi for future6pervious concrete pavement analysis when more representative E values are not available.7

8Sensitivity of Modulus of Elasticity to Load9

One indication that pervious concrete pavements can be analyzed with conventional10concrete pavement theory is to compare the E of pervious concrete pavement backcalculated11

from FWD deflections that were induced by varying loads. Since Westergaards pavement12model is linear, backcalculated E values for pervious concrete pavements on a given day should13

be consistent for low, medium, and high loads. Figure 2 shows that the backcalculated E values14for pervious concrete in Cell 85 driving lane are similar on a given date for varying loads.15

Similar plots were produced for all pervious concrete pavement cells. While this does not prove16

anything about pervious concrete, it does not contradict the linear theory of Westergaards17model.18

19



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1FIGURE 2 Backcalculated modulus of elasticity values for a pervious concrete pavement2

(Cell 85 driving lane) for low, medium, and high load levels.34

Verifying kdand E with ISLAB20055

Another way to verify that Westergaards theory could be applied to pervious concrete6pavement behavior was to input the kdand E values generated from a particular FWD load case7

into ISLAB2005 (6), a finite element-based pavement design software, and compare the8ISLAB2005 deflection predictions with the FWD sensor deflections. ISLAB2005 relies on9

principles of Westergaards theory to generate its output, so if the ISLAB2005 and FWD sensor10deflections were similar, this would also signify that pervious concrete pavement behavior could11

be predicted by Westergaards theory.12To simulate interior loading of an infinite slab in ISLAB2005, the pervious and13

conventional concrete pavements were modeled as 24 ft by 24 ft sections with a load at the14center. ISLAB2005 accepted inputs for pavement thickness, exact load and pressure, and15

average kdand E values as determined by deflections from one FWD test and either the A4 or A716AREA method. ISLAB2005 output the deflections at 0, 8, 12, 28, 24, 36, and 60 inches from the17

center of the load. These deflections were compared to the deflections registered by the sensors18during the FWD test.19

A graphical example of the data output from one of these comparisons is displayed in20Figure 3. This example represents the typical relationship observed between FWD deflections21

and ISLAB2005-generated deflections with A4 and A7-calculated kdand E values.22

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STRUCTURAL ANALYSIS OF 1 PERVIOUS CONCRETE PAVEMENT.pdf