study on the variation of mixing temperature and compaction temperature of bituminous concrete

8/12/2019 study on the variation of mixing temperature and compaction temperature of bituminous concrete

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Chapter 1

1.1IntroductionFlexible pavements are those, which on the whole have low or negligible flexural strength and

are rather flexible in their structural action under the loads. The flexible pavement layers reflect

the deformation of the lower layers on to the surface of the layer. Thus if the lower layer of the

pavement or soil subgrade is undulated, the flexible pavement surface also gets undulated. A

typical flexible pavement consist of four components.

Bituminous concrete or Asphalt Concrete is a composite material commonly used in construction

projects such as road surfaces, parking lots, and airports. Asphalt concrete consists

of asphalt (used as a binder) mixed with mineral aggregate and then laid down in layers and

compacted. Asphalt concrete was refined and enhanced to its current state by Belgian inventor

and U.S. immigrant Edward de Smedt.It is increasingly being used as the core of embankment

dams.

It is commonly called simply asphalt, blacktop, or paving (particularly in North America). The

terms "asphalt (or asphaltic) concrete", "bituminous asphalt concrete", and "bituminous mixture"

are typically used only in engineering and construction documents and literature. The

abbreviation "AC" is sometimes used for "asphalt concrete" but can also denote "asphalt content"

or "asphalt cement", referring to the liquid asphalt portion of a bituminous mixture.

Asphalt concrete pavements are often called just "asphalt" by laypersons who tend to associate

the term "concrete" with Portland cement concrete only. The engineering definition of concrete

is any composite material composed of mineral aggregate glued together with a binder, whether

that binder is Portland cement, asphalt or even epoxy.

The aim of this project is to study the variation of mixing temperature & compaction temperature

of bituminous concrete mix.


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Chapter 2

Flexible Pavement

2.1 Cross Section Of Flexible Pavement

Surface Course ( Wearing Course)

Surface course of the pavement structure engineered to accommodate and distribute traffic loads,

provide skid resistance, minimize disintegrating effects of climate, reduce tire/pavement noise,

improve surface drainage, and minimize infiltration of surface water into the underlying base,

sub base and subgrade. Sometimes referred to as the surface layer, the surface course may be

composed of a single layer, constructed in one or more lifts of the same material, or multiple

layers of different materials. (See fig.1.2)

Surface course


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Base Course

The base course is the layer of material immediately beneath the surface of binder course and it

provides additional load distribution and contributes to the sub-surface drainage It may be

composed of crushed stone, crushed slag, and other untreated or stabilized materials.

Sub-Base Course

The sub-base course is the layer of material beneath the base course and the primary functions

are to provide structural support, improve drainage, and reduce the intrusion of fines from the

sub-grade in the pavement structure If the base course is open graded, then the sub-base course

with more fines can serve as a filler between sub-grade and the base course A sub-base course is

not always needed or used. For example, a pavement constructed over a high quality, stiff sub-

grade may not need the additional features offered by a sub-base course. In such situations, sub-

base course may not be provided.

Sub Grade

The top soil or sub-grade is a layer of natural soil prepared to receive the stresses from the layers

above. It is essential that at no time soil sub-grade is overstressed. It should be compacted to the

desirable density, near the optimum moisture content.

2.2Bituminous ConcreteBituminous concrete orAsphalt Concreteis a composite material commonly used in

construction projects such as road surfaces, parking lots, and airports. Asphalt concrete consists

of asphalt (used as a binder) mixed with mineral aggregate and then laid down in layers and

compacted. Asphalt concrete was refined and enhanced to its current state by Belgian inventor

and U.S. immigrant Edward de Smedt.

It is increasingly being used as the core of embankmentdams.

It is commonly called simply asphalt, blacktop, or paving(particularly in North America). The

terms "asphalt (or asphaltic) concrete", "bituminous asphalt concrete", and "bituminous mixture"

are typically used only in engineering and construction documents and literature. The

abbreviation "AC" is sometimes used for "asphalt concrete" but can also denote "asphalt content"

or "asphalt cement", referring to the liquid asphalt portion of a bituminous mixture.

Asphalt concrete pavements are often called just "asphalt" by laypersons who tend to associate

the term "concrete" with Portland cement concrete only. The engineering definition of concrete

is any composite material composed of mineral aggregate glued together with a binder, whether

that binder is Portland cement, asphalt or even epoxy.


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Chapter 3

Types of Mixes

In the mixing process, the aggregates are first blended, heated, and dried. Then the aggregates

and the asphalt binder are heated to the mixing temperature. All the equipment used for mixing

are heated to the mixing temperature. Subsequently, the aggregate and the binder are mixed. For

this process, the asphalt binder should be fluid enough for uniformmixing. There are two typesof mixes

1. Hot Mix2. Cold Mix

3.1 Hot Mix

Hot Mix Asphalt is produced by heating the asphalt binder to decrease its viscosity, and drying

the aggregate to remove moisture from it prior to mixing.

Mixing is generally performed with the aggregate at about 300 F (roughly 150 C) for virgin

asphalt and 330 F (166 C) for polymer modified asphalt, and the asphalt cement at 200 F

(95 C).

Paving and compaction must be performed while the asphalt is sufficiently hot. In many

countries paving is restricted to summer months because in winter the compacted base will cool

the asphalt too much before it is able to be packed to the required density. HMAC is the form of

asphalt concrete most commonly used on high traffic pavements such as those on major

highways, racetracks and airfields.

Superpave, short for "superior performing asphalt pavement," is a pavement system designed to

provide longer lasting roadways. Key components of the system are careful selection of binders

and aggregates, volumetric proportioning of ingredients, and evaluation of the finished product.

Hot mix asphalt concrete (commonly abbreviated as HMA) is produced by adding either zeolites,

waxes, asphalt emulsions, or sometimes even water to the asphalt binder prior to mixing. This

allows significantly lower mixing and laying temperatures and results in lower consumption of

fossil fuels, thus releasing less carbon dioxide, aerosols and vapors. Not only are working

conditions improved, but the lower laying-temperature also leads to more rapid availability of the

surface for use, which is important for construction sites with critical time schedules. The usage

of these additives in hot mixed asphalt (above) may afford easier compaction and allow cold

weather paving or longer hauls.

3.2 Cold Mix


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Cold mix asphalt concrete is produced by emulsifying the asphalt in water with (essentially) soap

prior to mixing with the aggregate. While in its emulsified state the asphalt is less viscous and

the mixture is easy to work and compact. The emulsion will break after enough water evaporates

and the cold mix will, ideally, take on the properties of cold HMAC. Cold mix is commonly used

as a patching material and on lesser trafficked service roads.

3.3 Types of Temperature3.3.1 Mixing Temperature

It is the temperature of the asphalt at which it mixed together with the aggregates.

3.3.2 Compaction Temperature

It is the temperature at which the mixture of asphalt & aggregates is compacted using a roller.


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Chapter 4

Distress in Flexible Pavement

4.1Bleeding4.1.1 Description

A film of asphalt binder on the pavement surface. It usually creates a shiny, glass-like

reflecting surface (as in the first photo) that can become quite sticky. Sometimes referred to

as flushing.

4.1.2 Problem

Loss of skid resistance when wet

4.1.3 Possible Causes

Bleeding occurs when asphalt binder fills the aggregate voids during hot weather and

then expands onto the pavement surface. Since bleeding is not reversible during cold

weather, asphalt binder will accumulate on the pavement surface over time. This can be

caused by one or a combination of the following: Excessive asphalt binder in the HMA

(either due to mix design or manufacturing) Excessive application of asphalt binder

during BST application (as in the above figures) Low HMA air void content (e.g., not

enough room for the asphalt to expand into during hot weather)

4.1.4 Repair

The following repair measures may eliminate or reduce the asphalt binder film on the

pavements surface but may not correct the underlying problem that caused the bleeding:

Minor bleeding can often be corrected by applying coarse sand to blot up the excess asphaltbinder. Major bleeding can be corrected by cutting off excess asphalt with a motor grader

or removing it with a heater planer. If the resulting surface is excessively rough,

resurfacing may be necessary (APAI, no date given).


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Bleeding as a result of overasphalting

4.2 Block Cracking

4.2.1 Description

Interconnected cracks that divide the pavement up into rectangular pieces. Blocks range in

size from approximately 0.1 m2 (1 ft2) to 9 m2 (100 ft2). Larger blocks are generally

classified as longitudinal and transverse cracking. Block cracking normally occurs over alarge portion of pavement area but sometimes will occur only in non-traffic areas.

4.2.2 Problem

Allows moisture infiltration, roughness.


HMA shrinkage and daily temperature cycling. Typically caused by an inability of asphalt

binder to expand and contract with temperature cycles because of: Asphalt binder aging Poor

choice of asphalt binder in the mix design .

4.1.2 Repair

Strategies depend upon the severity and extent of the block cracking: Low severity cracks ( 1/2 inch wide and cracks with raveled edges).

Block cracking on a low volume pavement


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4.3 Raveling

4.3.1 Description

The progressive disintegration of an HMA layer from the surface downward as a result of

the dislodgement of aggregate particles.

4.3.2 Problem

Loose debris on the pavement, roughness, water collecting in the raveled locations resulting

in vehicle hydroplaning, loss of skid resistance.


Several including:

Loss of bond between aggregate particles and the asphalt binder as a result of:

A dust coating on the aggregate particles that forces the asphalt binder to bond with the dust

rather than the aggregate Segregation. If fine particles are missing from the aggregate matrix,

then the asphalt binder is only able to bind the remaining coarse particles at their relatively

few contact points.

Inadequate compaction during construction. High density is required to develop sufficientcohesion within the HMA. The third figure above shows a road suffering from raveling due

to inadequate compaction caused by cold weather paving.

Mechanical dislodging by certain types of traffic (studded tires, snowplow blades or tracked

vehicles). The first and fourth figures above show raveling most likely caused by snow

plows.

4.3.4 Repair

A raveled pavement should be investigated to determine the root cause of failure. Repair

strategies generally fall into one of two categories: Small, localized areas of raveling.


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Remove the raveled pavement and patch. Large raveled areas indicative of general HMA

failure. Remove the damaged pavement and overlay.

Raveling due to low density

4.4 Rutting4.4.1 Description

Surface depression in the wheelpath. Pavement uplift (shearing) may occur along the sides of

the rut. Ruts are particularly evident after a rain when they are filled with water. There are

two basic types of rutting: mix rutting and subgrade rutting. Mix rutting occurs when the

subgrade does not rut yet the pavement surface exhibits wheelpath depressions as a result of

compaction/mix design problems. Subgrade rutting occurs when the subgrade exhibits

wheelpath depressions due to loading. In this case, the pavement settles into the subgrade ruts

causing surface depressions in the wheelpath.

4.4.2 ProblemRuts filled with water can cause vehicle hydroplaning, can be hazardous because ruts tend

to pull a vehicle towards the rut path as it is steered across the rut.


Permanent deformation in any of a pavements layers or subgrade usually caused by

consolidation or lateral movement of the materials due to traffic loading. Specific causes of

rutting can be:


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Insufficient compaction of HMA layers during construction. If it is not compacted

enough initially, HMA pavement may continue to densify under traffic loads.

Subgrade rutting (e.g., as a result of inadequate pavement structure)

Improper mix design or manufacture (e.g., excessively high asphalt content, excessive

mineral filler, insufficient amount of angular aggregate particles)

Ruts caused by studded tire wear present the same problem as the ruts described here, but

they are actually a result of mechanical dislodging due to wear and not pavement

deformation.

4.4.4 Repair

A heavily rutted pavement should be investigated to determine the root cause of failure (e.g.

insufficient compaction, subgrade rutting, poor mix design or studded tire wear). Slight ruts

(< 1/3 inch deep) can generally be left untreated. Pavement with deeper ruts should be

leveled and overlayed.

Severe mix rutting


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Chapter 5

Methodology

5.1 Materials Used

5.1.1 Aggregates

Aggregates are inert granular materials such as sand, gravel, or crushed stone that, along with

water and portland cement, are an essential ingredient in concrete. For a good concrete mix,

aggregates need to be clean, hard, strong particles free of absorbed chemicals or coatings of

clay and other fine materials that could cause the deterioration of concrete. Aggregates,

which account for 60 to 75 percent of the total volume of concrete, are divided into two

distinct categories-fine and coarse. Fine aggregates generally consist of natural sand or

crushed stone with most particles passing through a 3/8-inch (9.5-mm) sieve. Coarse

aggregates are any particles greater than 0.19 inch (4.75 mm), but generally range between

3/8 and 1.5 inches (9.5 mm to 37.5 mm) in diameter. Gravels constitute the majority of

coarse aggregate used in concrete with crushed stone making up most of the remainder.

5.1.2 Filler

Fillers are particles added to material (plastics, composite material, concrete) to lower the

consumption of more expensive binder material or to better some properties of the mixtured

material. Worldwide more than 53 million tons of fillers with a total sum of approximatelyEUR16 billion are used every year in different application areas, such as paper, plastics,

rubber, paints, coatings, adhesives and sealants. As such, fillers, produced by more than 700

companies, rank among the world's major raw materials and are contained in a variety of

goods for daily consumer needs.

5.1.3 Bitumen

Bitumen is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may

be found in natural deposits or may be a refined product; it is a substance classed as a pitch.

Until the 20th century, the term asphaltumwas also used.The primary use of

asphalt/bitumen is in road construction, where it is used as the glue or binder mixed

with aggregate particles to create asphalt concrete. Its other main uses are for bituminous

waterproofing products, including production of roofing felt and for sealing flat roofs.


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The terms asphaltand bitumenare often used interchangeably to mean both natural and

manufactured forms of the substance. In American English, asphalt (or asphalt cement) is the

carefully refined residue from the distillation process of selected crude oils. Outside the

United States, the product is often called bitumen. Geological terminology often prefers the

term bitumen. Common usage often refers to various forms of asphalt/bitumen as "tar", such

as at the La Brea Tar Pits. Another term, mostly archaic, refers to asphalt/bitumen as "pitch".

5.2Tests On Materials5.2.1Aggregate Impact TestIt has been designed to evaluate the toughness or the resistance of the stone aggregates to

breaking down under repeated application of impact.

5.2.2Los Angeles Abrasion Test

It is done to find the percentage wear due to the relative rubbing action between the

aggregates and steel balls used as abrasive charge.

5.2.3Aggregate Crushing Value Test

It is done to find the strength of coarse aggregates or the resistance to crushing of the coarse

aggregates under the applied load.

5.2.4 Penetration TestIt is conducted to classify the bitumen into different grades.

5.3Mix PreparationFor the purpose of mix preparation following methods are used-

5.3.1 Hveem Method


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The basic concepts of the Hveem mix design method were originally developed by Francis

Hveem when he was a Resident Engineer for the California Division of Highways in the late

1920s and 1930s.

The Hveem mix design method consists of three basic steps:

1. Aggregate selection. Different agencies/owners specify different methods of aggregate

acceptance. Typically, a battery of aggregate physical test is run periodically on each

particular aggregate source. Then, for each mix design, gradation and size requirements

are checked. Normally, aggregate from more than one source is required to meet

gradation requirements.

2. Asphalt binder selection. HDOT uses the the Superpave PG System. Hawai'i's common

asphalt binder grade is a PG 64-16.

3.

Optimum asphalt binder content determination. In the Hveem method, this step can

be broken up into 5 substeps:

o Prepare multiple initial samples, each at a different asphalt binder content. For

instance, one sample each might be made at 4.5, 5.0, 5.5, 6.0, 6.5 and 7 percent

asphalt by dry weight for a total of six samples.

o Compact these trial mixes in the California Kneading Compactor (see Figures 1

and 2). This compactor is specific to the Hveem mix design method.

o

Test the samples for stability and cohesion using the Hveem stabilometer and

cohesiometer. These tests are specific to the Hveem mix design method. Passing

values of stability and cohesion depend upon the mix class being evaluated.

Typically, all samples pass the cohesion test and three or four pass the stability

test.

o Determine the density and other volumetric properties of the samples.

o Select the optimum asphalt binder content. The asphalt binder content

corresponding to 4 percent air voids is selected as long as this binder content

passes stability and cohesion requirements.


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HDOT's California Kneading Compactor.


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Chapter 6

Marshall Method Of Mix Design

The basic concepts of the Marshall mix design method were originally developed by Bruce

Marshall of the Mississippi Highway Department around 1939 and then refined by the U.S.Army. Currently, the Marshall method is used in some capacity by about 38 states. The

Marshall method seeks to select the asphalt binder content at a desired density that satisfies

minimum stability and range of flow values.

6.1 Marshall Mix Design Procedure

The Marshall mix design method consists of 6 basic steps:

1. Aggregate selection.

2. Asphalt binder selection.

3. Sample preparation (including compaction).

4. Stability determination using the Hveem Stabilometer.

5. Density and voids calculations.

6. Optimum asphalt binder content selection.

6.1.1 Aggregate Selection

Although Hveem did not specifically develop an aggregate evaluation and selection

procedure, one is included here because it is integral to any mix design. A

typical aggregate evaluation for use with either the Hveem or Marshall mix design methods

includes three basic steps:

1. Determine aggregate physical properties. This consists of running various tests to

determine properties such as:o Toughness and abrasion

o Durability and soundness

o Cleanliness and deleterious materials

o Particle shape and surface texture


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2. Determine other aggregate descriptive physical properties. If the aggregate is

acceptable according to step #1, additional tests are run to fully characterize

the aggregate. These tests determine:

o Gradation and size

o Specific gravity and absorption

3.

Perform blending calculations to achieve the mix design aggregate gradation. Often,

aggregates from more than one source or stockpile are used to obtain the

final aggregate gradation used in a mix design. Trial blends of these different gradations

are usually calculated until an acceptable final mix design gradation is achieved. Typical

considerations for a trial blend include:

o All gradation specifications must be met. Typical specifications will require the

percent retained by weight on particular sieve sizes to be within a certain band.

o

The gradation should not be too close to the FHWAs 0.45 power maximum

density curve. If it is, then the VMA is likely to be too low. Gradation should

deviate from the FHWAs 0.45 power maximum density curve, especially on the

2.36 mm (No. 8) sieve.

Asphalt Binder Evaluation

The Marshall test does not have a common generic asphalt binder selection and evaluation

procedure. Each specifying entity uses their own method with modifications to determine the

appropriate binder and, if any, modifiers. Binder evaluation can be based on local

experience, previous performance or a set procedure. The most common procedure is

the Superpave PG binder system. Once the binder is selected, several preliminary tests are

run to determine the asphalt binders temperature-viscosity relationship.

Sample Preparation

The Marshall method, like other mix design methods, uses several trial aggregate-

asphalt binder blends (typically 5 blends with 3 samples each for a total of 15 specimens),

each with a different asphalt binder content. Then, by evaluating each trial blends

performance, an optimum asphalt binder content can be selected. In order for this concept to

work, the trial blends must contain a range of asphalt contents both above and below the

optimum asphalt content. Therefore, the first step in sample preparation is to estimate an


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optimum asphalt content. Trial blend asphalt contents are then determined from this

estimate.

Optimum Asphalt Binder Content Estimate

The Marshall mix design method can use any suitable method for estimatingoptimum asphalt content and usually relies on local procedures or experience.

Sample Asphalt Binder Contents

Based on the results of the optimum asphalt binder content estimate, samples are typically

prepared at 0.5 percent by weight of mix increments, with at least two samples above the

estimated asphalt binder content and two below.

Compaction with the Marshall Hammer

Each sample is then heated to the anticipated compaction temperature and compacted with a

Marshall hammer, a device that applies pressure to a sample through a tamper foot (Figure

1). Some hammers are automatic and some are hand operated. Key parameters of the

compactor are:

Sample size = 102 mm (4-inch) diameter cylinder 64 mm (2.5 inches) in height

(corrections can be made for different sample heights)

Tamper foot = Flat and circular with a diameter of 98.4 mm (3.875 inches) corresponding

to an area of 76 cm2(11.8 in

2).

Compaction pressure = Specified as a 457.2 mm (18 inches) free fall drop distance of a

hammer assembly with a 4536 g (10 lb.) sliding weight.

Number of blows = Typically 35, 50 or 75 on each side depending upon anticipated

traffic loading.

Simulation method = The tamper foot strikes the sample on the top and covers almost the

entire sample top area. After a specified number of blows, the sample is turned over and

the procedure repeated.


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Marshall drop hammers.

The standard Marshall method sample preparation procedure is contained in:

AASHTO T 245: Resistance to Plastic Flow of Bituminous Mixtures Using the Marshall

Apparatus

The Marshall Stability and Flow Test

The Marshall stability and flow test provides the performance prediction measure for the

Marshall mix design method. The stability portion of the test measures the maximum load

supported by the test specimen at a loading rate of 50.8 mm/minute (2 inches/minute).

Basically, the load is increased until it reaches a maximum then when the load just begins to

decrease, the loading is stopped and the maximum load is recorded.

During the loading, an attached dial gauge measures the specimens plastic flow as a result of

the loading (figure below). The flow value is recorded in 0.25 mm (0.01 inch) increments at

the same time the maximum load is recorded.


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Marshall stability testing apparatus

Typical Marshall design stability and flow criteria are shown in Table 1.

Mix Criteria

Light Traffic

(< 104ESALs)

Medium Traffic

(104

106ESALs)

Heavy Traffic

(> 106ESALs)

Min. Max. Min. Max. Min. Max.

Compaction

(number of blows on each end

of the sample)

35 50 75

Stability (minimum)2224 N

(500 lbs.)

3336 N

(750 lbs.)

6672 N

(1500 lbs.)

Flow (0.25 mm (0.01 inch)) 8 20 8 18 8 16


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Percent Air Voids 3 5 3 5 3 5

Table: Typical Marshall Design Criteria (from Asphalt Institute, 1979)

One standard Marshall mix design procedure is:

AASHTO T 245: Resistance to Plastic Flow of Bituminous Mixtures Using Marshall

Apparatus

Density and Voids Analysis

All mix design methods use density and voids to determine basic HMA physical

characteristics. Two different measures of densities are typically taken:

1.

Bulk specific gravity (Gmb).2. Theoretical maximum specific gravity (TMD, Gmm).

These densities are then used to calculate the volumetric parameters of the HMA. Measured

void expressions are usually:

Air voids (Va), sometimes expressed as voids in the total mix (VTM)

Voids in the mineral aggregate (VMA)

Voids filled with asphalt (VFA)

Generally, these values must meet local or State criteria.

Nominal Maximum

Particle Size Minimum VMA (percent)

(mm) (U.S.)

63 2.5 inch 11

50 2.0 inch 11.5

37.5 1.5 inch 12

25.0 1.0 inch 13

19.0 0.75 inch 14


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12.5 0.5 inch 15

9.5 0.375 inch 16

4.75 No. 4 sieve 18

2.36 No. 8 sieve 21

1.18 No. 16 sieve 23.5

Table :Typical Marshall Minimum VMA

(from Asphalt Institute, 1979])

Selection of Optimum Asphalt Binder Content

The optimum asphalt binder content is finally selected based on the combined results of

Marshall stability and flow, density analysis and void analysis (Figure

3). Optimum asphalt binder content can be arrived at in the following procedure (Roberts et

al., 1996):

1. Plot the following graphs:

o Asphalt binder content vs. density. Density will generally increase with

increasing asphalt content, reach a maximum, then decrease. Peak density usually

occurs at a higher asphalt binder content than peak stability.

o

Asphalt binder content vs. Marshall stability. This should follow one of twotrends:

o * Stability increases with increasing asphalt binder content, reaches a peak, then

decreases.

o * Stability decreases with increasing asphalt binder content and does not show a

peak. This curve is common for some recycled HMA mixtures.

o Asphalt binder content vs. flow.

o Asphalt binder content vs. air voids. Percent air voids should decrease with

increasing asphalt binder content.

o Asphalt binder content vs. VMA. Percent VMA should decrease with

increasing asphalt binder content, reach a minimum, then increase.

o Asphalt binder content vs. VFA. Percent VFA increases with

increasing asphalt binder content.


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2. Determine the asphalt binder content that corresponds to the specifications median air

void content (typically this is 4 percent). This is the optimum asphalt binder content.

3. Determine properties at this optimum asphalt binder content by referring to the

plots. Compare each of these values against specification values and if all are within

specification, then the preceding optimum asphalt binder content is

satisfactory. Otherwise, if any of these properties is outside the specification range the

mixture should be redesigned.

Plot: Asphalt binder content vs measured values

Documents

study on the variation of mixing temperature and compaction temperature of bituminous concrete