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Evaluating the Performance of Asphalt Concrete Mixtures 71
The design compaction level and the design air void content also affect the fatigue resistance
of HMA. HMA fatigue resistance increases with increasing compactive effort. Mixtures that are
produced with greater compaction energy have improved performance in fatigue. For constant
in-place air void content, fatigue resistance improves with increasing design air void content.
This effect may at first seem counterintuitive, but for constant in-place air void content, increasing
the design air void content mostly has the effect of increasing the compaction effort during
construction. Because mixtures with very high air void content will be difficult to compact to an
acceptably low in-place air void content and because mixtures with design air void contents that
are too low may exhibit poor rut resistance, design air void contents are controlled within a narrow
range for HMA mixtures, typically 4.0 ± 0.5% for surface course mixtures.
Durability
Design VMA and in-place air void content have a major effect on the durability of HMA
mixtures. Mixture durability improves as VBE increases. For a constant design air void content,
VBE increases with increasing VMA. All else being equal, smaller NMAS mixtures have higher
VMA and, therefore, have improved durability compared to larger NMAS mixtures. The dura-
bility of dense-graded mixtures can be improved by increasing the design VMA (within limits)
as discussed in Chapter 8. SMA mixtures have even greater durability due to their even higher
design VMA.
In-place air void content has a major effect on the durability of HMA. Mixture permeability
increases with increasing in-place air void content. As permeability increases, binder age hardening
and moisture infiltration increase, making the pavement less durable and more susceptible to
moisture damage. Proper field compaction is therefore essential to producing durable pavements.
Laboratory Testing
Several laboratory tests have been developed to evaluate the performance of HMA. Tests have
been developed to assess the resistance of HMA to rutting, fatigue cracking, thermal cracking,
and moisture sensitivity. Additionally, laboratory-conditioning procedures have been developed
to simulate the effects of short-term aging that occurs during construction and long-term aging
that occurs during the service life of the pavement. Although numerous laboratory performance
tests have been developed, only a few have been standardized and are routinely used for evaluation
of HMA.
Rut Resistance Testing and HMA Mix Design
Several laboratory tests are available for evaluating the rutting resistance of HMA. These
include tests that measure engineering properties, such as modulus or permanent deformation,
and proof tests, such as the Asphalt Pavement Analyzer or Hamburg Wheel-track Test. Some
specifying agencies and mixture designers have developed a level of confidence in specific tests
and criteria for their local mixtures and pavements. In recent years, a major effort was undertaken
to develop a rutting performance test and associated criteria that could be applied universally
to HMA mixtures throughout the United States. The resulting device is the asphalt mixture
performance tester (AMPT), previously called the simple performance test (SPT) system; because
of its anticipated high level of future support by specifying agencies, this device is one recommended
in this manual to measure rut resistance. Rut resistance can be evaluated in the AMPT using the
dynamic modulus test, the flow number test, or the flow time test. Use of the dynamic modulus
test to evaluate rut resistance was developed in conjunction with the MEPDG and is discussed
in detail in NCHRP Report 580: Simple Performance Tests for Permanent Deformation of Hot Mix
Asphalt--Volume 1: The E* Specification Criteria Program. Use of both the flow number test and
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72 A Manual for Design of Hot Mix Asphalt with Commentary
flow time test to evaluate rut resistance during the mix design process are discussed in this
manual. Four other tests are recommended in this manual as candidates for performance tests
for the evaluation of rut resistance:
· The repeated shear at constant height (RSCH) test performed with the Superpave shear tester
(SST).
· The high-temperature indirect tension (IDT) strength test.
· The asphalt pavement analyzer (APA).
· The Hamburg Wheel-track Test.
These six tests for evaluating rut resistance are discussed below. Specific information on using
these tests in the mix design process are given in Chapter 8.
The Asphalt Mixture Performance Tester
Figure 6-1 shows the AMPT. It is a relatively small, computer-controlled test machine that can
perform various tests on HMA over a temperature range of 4 to 60°C. The machine is available in
the United States from several manufacturers who have demonstrated compliance with a detailed
equipment specification prepared as part of National Cooperative Highway Research Program
(NCHRP) Project 9-29 and contained in NCHRP Report 513: Simple Performance Tester for
Superpave Mix Design: First Article Development and Evaluation. Two of the tests that can be
performed in the AMPT have been related to the rutting performance of HMA. These are the
dynamic modulus and the flow number tests. Ruggedness testing with the AMPT has demonstrated
that it can control both of these tests with sufficient accuracy for use in specification testing. An
interlaboratory study to establish precision statements for the dynamic modulus and flow number
tests will be completed in the Fall of 2010. As this manual was being finalized, procedures for
Figure 6-1. Photograph of a simple performance
test system.
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Evaluating the Performance of Asphalt Concrete Mixtures 73
these tests were available in an AASHTO Provisional Standard, TP 79: Determining the Dynamic
Modulus and Flow Number for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance
Tester (AMPT). A National Highway Institute (NHI) training course on the AMPT was also
being planned.
Dynamic Modulus Test--in the dynamic modulus test, an HMA specimen is subjected to a
sinusoidal compressive load. The resulting stress and strain are recorded and used to calculate
the dynamic modulus and phase angle for the mixture. The dynamic modulus is abbreviated E*
(pronounced E-star; E for elastic modulus, and * for dynamic). E* is the peak stress in the test
divided by the peak strain and represents the overall stiffness of the mixture. The phase angle is
the amount that the strain lags the stress and is a measure of the elasticity of the mixture. The lower
the phase angle, the more elastic the response. The stresses and strains in the dynamic modulus
test are intentionally kept small to keep the response of the HMA in the linear range.
Dynamic modulus testing can be conducted at different temperatures and loading frequencies
to evaluate the effect of temperature and traffic speed on the mixture stiffness. E* data from
different temperatures and loading rates can be combined into a master curve that describes the
mixture stiffness for any combination of temperature and loading rate. A dynamic modulus
master curve is the primary HMA materials input needed for the design of HMA pavements
using the MEPDG. AASHTO TP 79-09, Determining the Dynamic Modulus and Flow Num-
ber for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT),
which was developed in NCHRP Project 9-29, is the standard test method for obtaining
dynamic modulus measurements on HMA with the AMPT. AASHTO PP 61-09, Developing
Dynamic Modulus Master Curves for Hot Mix Asphalt (HMA) Using the Asphalt Mixture
Performance Tester (AMPT), also developed in NCHRP Project 9-29, is the recommended
practice for developing dynamic modulus master curves for pavement structural design using
the AMPT.
Criteria for using the dynamic modulus to judge the rutting resistance of an HMA mixture
for a specific pavement can be obtained from the E* AMPT Specification Criteria Program
developed in NCHRP Project 9-19 and described in NCHRP Report 580. This software uses the
calibrated rutting model included in the MEPDG to determine project-specific testing conditions
and dynamic modulus criteria to limit rutting to a specified level. The MEPDG is discussed in
more detail later in this chapter. The E* AMPT Specification Criteria Program requires the user
to enter information about the specific pavement, including HMA layer thicknesses, design traffic
level, design traffic speed, environmental conditions at the project site, and the allowable rut
depth in each HMA layer. The software then returns, for each HMA layer, the recommended
testing conditions (temperature and frequency), and the minimum E* that the mixture must
have to limit rutting to the specified level. Specifying agencies choosing to use dynamic modulus
as the measure of rutting resistance can use this software to establish E* values and testing
conditions based on the location of the mixture in the pavement (i.e., surface, intermediate or base),
traffic level, and temperature conditions.
Flow Number Test--the flow number is an alternative to the dynamic modulus test for
evaluating rutting resistance. In this test, a sample of the HMA mixture at high temperature
is subjected to a repeated compressive stress pulse. This repeated loading produces perma-
nent strain in the specimen, which is recorded by the AMPT for each load cycle. Figure 6-2
is an example of a permanent strain curve that results from a flow number test. The point in
the permanent strain curve where the rate of accumulation of permanent strain reaches a
minimum value has been defined as the flow number. The flow number has been related to
the rutting resistance of HMA. As the flow number increases, rutting resistance also increases.
AASHTO TP 79-09 includes the standard test method for using the AMPT to obtain the flow
number of HMA.
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74 A Manual for Design of Hot Mix Asphalt with Commentary
5.0 Permanent Strain Permanent Strain Rate 0.0050
4.5 0.0045
Permanent Strain Rate, % per Cycle
4.0 0.0040
3.5 0.0035
Permanent Strain, %
3.0 0.0030
2.5 0.0025
2.0 0.0020
Flow Number = Minimum
1.5 Permanent Strain Rate 0.0015
1.0 0.0010
0.5 0.0005
0.0 0.0000
0 1000 2000 3000 4000 5000 6000
Load Cycle
Figure 6-2. Typical data from the flow number test.
Flow Time Test--the flow time test differs from the flow number test in that a constant rather
than a repeated load is applied to the specimen and the total deformation is monitored. Thus, the
flow time test is simply a static creep test and the flow time is defined as the loading time required
to initiate tertiary creep, which is the point at which the rate of deformation begins to increase.
The flow time test was envisioned as a simpler alternative to the flow number test.
AMPT Specimens--The AMPT requires a test specimen that is 100 mm (4.0 in) in diameter
by 150 mm (6.0 in) high. The specimen is sawed and cored from the middle of a 150 mm in
diameter by 175-mm-high gyratory-compacted specimen. Figure 6-3 shows a completed AMPT
test specimen and the original gyratory-compacted specimen from which the test specimen
was cut. AASHTO PP 60-09, Preparation of Cylindrical Performance Test Specimens Using the
Figure 6-3. Photograph of an AMPT test specimen.
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Evaluating the Performance of Asphalt Concrete Mixtures 75
Superpave Gyratory Compactor (SGC), also developed in NCHRP Project 9-29, is the recommended
procedure for preparing AMPT specimens.
There are three reasons for using smaller test specimens obtained from larger gyratory specimens
in the AMPT:
1. To obtain an appropriate aspect ratio for the test specimens. Research performed during NCHRP
Project 9-19 found that a minimum specimen diameter of 100 mm with a height-to-diameter
ratio of 1.5 was needed.
2. To eliminate areas of the gyratory specimens with high air void content. Gyratory-compacted
specimens typically have high air void content near the ends and around the circumference
of the specimen.
3. To obtain relatively smooth, parallel ends for testing, which helps ensure proper stress
distribution within the specimen during loading.
The air void content of the AMPT specimen will have a major effect on the properties
measured in the AMPT. AMPT specimens used to evaluate rutting resistance should be pre-
pared to the expected average field air void content at the time of construction, not the
design air void content. Mixtures should be short-term oven aged for 4 hours at 135°C in
accordance with the procedure for Short-Term Conditioning for Mixture Mechanical Prop-
erty Testing in AASHTO R 30. A reasonable air void tolerance for AMPT specimens is ±0.5%.
The AMPT specimen will have a lower air void content than the larger gyratory specimen
from which it is produced. AASHTO PP 60-09 contains a procedure for achieving the target
air void content for AMPT specimens.
The number of replicates to be tested depends on the repeatability of the test and the desired
accuracy of the resulting data. Based on current estimates of coefficients of variation for the
dynamic modulus and flow number tests of 13 and 20%, respectively, it is recommended that
two replicate specimens be used for dynamic modulus testing and four replicate specimens for
flow number testing. These numbers of replicates will result in coefficients of variation for the
mean values of dynamic modulus and flow number of approximately 10%.
Other Laboratory Tests for Rut Resistance
Other laboratory tests are available for evaluating the rutting resistance of HMA. Those most
often used are the Superpave Shear Tester (SST), the High-Temperature Indirect Tensile Test (IDT),
the Asphalt Pavement Analyzer (APA), and the Hamburg Wheel-Track Test.
Repeated Shear at Constant Height (RSCH) Test. This is one of several tests that can be
performed with the SST. The RSCH test is designed to evaluate the rutting resistance of HMA
by applying repeated shear loading to an HMA specimen at high temperatures. The test has been
standardized as AASHTO T 320. The RSCH test is performed on 150-mm-diameter specimens
that are 38 to 50 mm thick, depending on the nominal maximum aggregate size. The test specimens
are glued to loading platens and subjected to repeated direct shear loading while the vertical load
is varied to maintain the specimen at a constant height. In September 1997, during the Superpave
implementation effort, the Mixtures Expert Task Group established preliminary guidelines for
using the RSCH test to evaluate the rutting resistance of HMA. In the standard performance
test--discussed in detail in Chapter 8 of this manual--the RSCH test is performed at the maximum,
7-day average pavement temperature found 20 mm below the pavement surface, as given in
LTPPBind Version 3.0. The SST, a relatively expensive device, is available in few laboratories in
the United States. Figure 6-4 is a photograph of an SST. The RSCH test is not recommended for
routine evaluation of the rut resistance of HMA mixtures in the laboratory--the other tests
discussed in this chapter are generally easier to perform and less expensive to conduct and so
more widely used than the RSCH test. For those laboratories that have an SST device, specific
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76 A Manual for Design of Hot Mix Asphalt with Commentary
Figure 6-4. Photograph of the SST.
recommendations for using it to evaluate mixture rut resistance during the mix design process
are given in Chapter 8.
The High-Temperature IDT Strength Test. This test was developed as a quick and inexpensive
procedure for evaluating rut resistance using equipment currently available in many HMA
design and quality assurance laboratories. Christensen, Bonaquist, and Jack reported an excellent
relationship between rutting resistance and the indirect tensile strength at high temperature in
a 2000 publication. Additional work confirming these results was reported in 2004 by Zaniewski
and Srinivasan. The test is conducted on standard gyratory specimens produced for mixture
design or quality assurance with the indirect tensile strength equipment used in AASHTO T 283.
Specimens should be compacted to the design gyration level. When testing specimens as part of
mixture design, the mixture should be short-term oven aged for 4 hours at 135°C in accordance
with the procedure for Short-Term Conditioning for Mixture Mechanical Property Testing in
AASHTO R 30. When testing quality assurance specimens from plant production, the short-
term aging is not required. The testing temperature is 10°C less than the 50% reliability, 7-day
average maximum pavement temperature obtained from LTPPBind Version 3.0.
The Asphalt Pavement Analyzer and Hamburg Wheel-Track Test. The APA (see Figure 6-5)
and the Hamburg Wheel-Track tests are proof tests for rutting resistance that are used by some
specifying agencies. Both tests attempt to simulate the effect of traffic loading by rolling a small
loaded wheel over an HMA specimen at high temperature. In the APA, the load is applied through
Figure 6-5. Photo- a rubber hose that can be inflated to a specified pressure. In Hamburg Wheel-Track testing, the
graph of the asphalt load is applied through a steel wheel. Conditioned air is used for temperature control in the APA,
pavement analyzer. while Hamburg Wheel-Track testing uses water to control the temperature of the test specimen.
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Evaluating the Performance of Asphalt Concrete Mixtures 77
The Hamburg Wheel-Track test can be used to assess both rutting resistance and moisture
sensitivity. Originally, these tests were performed on rectangular specimens; however, in recent
years the equipment has been modified to use 150-mm-diameter gyratory-compacted specimens.
The standard test method for the APA is AASHTO TP 63-09; the standard test method for
Hamburg Wheel-Track testing is AASHTO T 324.
Agencies that specify these tests have established criteria for rutting resistance based on the
deformation or impression depth after a specified number of load cycles. For example, for high
traffic levels, the Georgia Department of Transportation specifies a maximum deformation of 5 mm
in the APA after 8,000 cycles at a test temperature of 64°C. The Texas Department of Transporta-
tion specifies the minimum number of wheel passes in the Hamburg Wheel-Track test to reach
an impression depth of 12.5 mm when tested at a temperature determined by the performance
grade of the asphalt binder. These values are >10,000 for mixes produced with PG 64-XX binder,
>15,000 for mixes produced with PG 70-XX binder, and >20,000 for mixes produced with
PG 76-XX binder. Additional information on the use of the APA and Hamburg Wheel-Track
testing as performance tests for use in the mix design process is given in Chapter 8.
Fatigue Testing
The only standard test method available for fatigue testing of HMA is the flexural fatigue test,
AASHTO T 321. In this test a beam sample, 380 mm long by 63 mm wide by 50 mm high, is
subjected to strain-controlled, repeated four-point bending. The beam samples are prepared
using either a kneading or rolling wheel compaction; there are no AASHTO standards for either
of these methods of laboratory compaction. Figure 6-6 shows a device for flexural fatigue testing.
The number of laboratories in the United States that can fabricate and test flexural fatigue spec-
imens is limited.
During a flexural fatigue test, the beam is damaged by the repeated flexing. This damage results
in a decrease in the modulus of the beam. The beam is considered failed when the modulus
decreases to 50% of its initial value. The number of loading cycles applied to the beam can range
Figure 6-6. Photograph of flexural fatigue apparatus.
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78 A Manual for Design of Hot Mix Asphalt with Commentary
1000
Initial Strain, in/in
100
10
1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10
Cycles to Failure
Figure 6-7. Typical S-N diagram for HMA.
from 1,000 to 10,000,000 or more. The results of fatigue tests are presented in the form of S-N
diagrams, which are simply plots of the applied strain and the corresponding number of cycles
to failure. Figure 6-7 presents a typical S-N diagram for HMA generated from laboratory test
data. The point where the fatigue life becomes indefinite is called the fatigue endurance limit.
Because of its extreme importance in the structural design of perpetual pavements, research is
in progress to better define the endurance limit for HMA.
Generating an S-N curve for HMA requires testing several beams at different strain levels.
Due to the high variability of fatigue testing, each strain level requires testing a number of
replicate specimens. Because of the high level of effort required to generate S-N curves for HMA,
fatigue testing is rarely performed in practice. Instead, relationships between mixture compositional
factors and fatigue life that have been developed from databases of tests on a number of mixtures
are used. These relationships show that the most important mixture design factor affecting the
fatigue life of HMA is the effective volumetric binder content of the mixture, VBE. By controlling
VBE, the mixture design process controls the fatigue life of the mixture. As discussed previously,
VBE, is controlled in the design method described in this manual by controlling both the VMA
and the design air void content.
Thermal Cracking
The MEPDG can predict the amount of thermal cracking that will occur in an asphalt pavement.
To perform this analysis, information on the creep and strength properties of the HMA at low
temperatures are needed. These properties are measured using the Indirect Tensile Tester (IDT),
AASHTO T 322. Low-temperature tests on HMA require an expensive environmental chamber
and the capacity to impose high loads on the test specimens. Figure 6-8 shows a specimen
being tested in the IDT. Only a few laboratories in the United States have IDT equipment for
low-temperature testing.
AASHTO T 322 involves preparing nine IDT test specimens and performing creep and strength
tests on three specimens each at temperatures of 0, -10, and -20°C. The results of the creep tests
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Evaluating the Performance of Asphalt Concrete Mixtures 79
Figure 6-8. Photograph of
specimen in the IDT.
are used to generate a compliance master curve for the mixture, which governs the buildup of
thermal stresses in the pavement. The potential for thermal fracture depends on the magnitude
of the estimated thermal stress relative to the tensile strength of the mixture.
IDT test specimens are 150 mm in diameter by 38 mm thick. They are formed by sawing the
test specimen from the middle of a gyratory-compacted specimen. Sawed ends are needed to
attach the deformation measuring equipment. IDT testing is usually conducted on specimens
compacted to the anticipated in-place air void content and exposed to long-term oven aging in
accordance with AASHTO R 30.
Because the resistance to thermal cracking is almost completely governed by the properties of
the binder, IDT testing is usually only performed when the binder cannot be tested using the
bending beam rheometer and direct tension device. When modifiers are added to the mixture rather
than the binder, it may be necessary to conduct IDT testing to evaluate the low temperature
properties of the resulting mixtures.
Moisture Sensitivity Testing
Two tests have received acceptance in the United States to evaluate the moisture sensitiv-
ity of HMA: the Lottman procedure (AASHTO T 283) and the Hamburg Wheel-Track test
(AASHTO T 324). In many cases, the two tests provide different results, likely because they
simulate different moisture damage processes. Recent efforts to improve moisture sensitivity
testing using the Environmental Conditioning System (ECS) developed during the Strategic
Highway Research Program have not yet resulted in a standard test method used by state agencies
in the routine design of HMA.
In AASHTO T 283, six laboratory specimens are prepared to an air void content of 7.0 ± 0.5%,
then divided into two subsets with approximately equal average air void contents. The tensile
strength of one subset is measured dry. The tensile strength of the second subset is measured
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80 A Manual for Design of Hot Mix Asphalt with Commentary
20
18
16 Stripping Slope
14
Rut Depth, mm
12
10
8
Creep Slope
6
4
2
Stripping Inflection Point
0
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Number of Passes
Figure 6-9. Typical rut depth versus wheel pass curve from AASHTO T 324.
after conditioning by vacuum saturation followed by a freeze-thaw cycle and a warm water soak.
The ratio of the average tensile strength of the conditioned to unconditioned subsets and a visual
assessment of stripping is used to measure moisture sensitivity. A mixture is considered to have
an acceptable level of moisture sensitivity if the tensile strength ratio is equal to or greater than
80% and there is no visual evidence of stripping in the conditioned test specimens.
Since the Hamburg Wheel-Track test (AASHTO T 324) tests HMA submerged in water, it can
also be used to evaluate the resistance of a mixture to moisture damage. Moisture sensitivity
is evaluated by computing the stripping inflection point, which is defined as the intersection
of the slopes from the creep and stripping portions of the rut depth versus wheel pass curve as
shown in Figure 6-9. The recommended air void content of laboratory-prepared specimens for
AASHTO T 324 is 7.0 ± 2.0%.
Criteria for evaluating moisture sensitivity based on AASHTO T 324 place a minimum limit on
the stripping inflection point. For example, Aschenbrener et al. suggested for Colorado conditions
that mixtures with good performance with respect to moisture damage (life of 10 to 15 years)
should have a stripping inflection point greater than 14,000 passes.
Short- and Long-Term Oven Conditioning
When conducting performance tests on HMA, it is important to simulate the effects of
(1) short-term aging that occurs during plant mixing and construction and (2) long-term aging
that occurs during the service life of the pavement. During production and laydown, some of the
binder is absorbed into the aggregate, decreasing the effective binder content, and the binder is
aged by the high temperatures that occur in the overall construction process. Further oxidative
aging of the binder occurs during the service life of the pavement. During the Strategic Highway
Research Program, procedures for short-term and long-term conditioning of mixtures were
developed. These were subsequently standardized in AASHTO R 30.
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Evaluating the Performance of Asphalt Concrete Mixtures 81
The short-term conditioning procedure consists of conditioning loose mixture in a forced
draft oven at 135°C for 4 hours. The mixture is evenly spread in a pan to a thickness between
25 and 50 mm and stirred every hour.
In the long-term conditioning procedure, test specimens prepared from loose mix that was
previously short-term conditioned as described above are further conditioned in a forced draft
oven before testing. The temperature for this conditioning is 85°C for a period of 120 hours
Because rutting is a distress that occurs early in the life of a pavement, performance testing to
assess rutting resistance should be conducted on specimens that have been short-term conditioned.
Fatigue and thermal cracking tests should be performed on specimens that have been long-term
conditioned. AASHTO T 283 has a different conditioning procedure of 16 hours in a forced draft
oven at 60°C.
Evaluating the Need for Performance Testing
It is neither practical nor necessary to perform the full suite of performance tests discussed
above when designing HMA using conventional materials, including most modified binders.
The test methods for fatigue and thermal cracking require a high level of effort and complex
equipment, and substantial research has shown that resistance to these forms of distress can be
controlled by controlling the effective binder content of the mixture and the low temperature
binder grade, respectively. Rutting resistance is somewhat more difficult to control since several
compositional factors affect rutting resistance, and if these act in the same direction, the resulting
HMA may exhibit poor performance. Fortunately, tests for rutting resistance using the AMPT
are relatively easy to perform and criteria differentiating various levels of performance are
available. There is general agreement in the industry that testing the specific combinations of
binder, aggregate, and additives used in an HMA mixture is the only way to assess the potential
for moisture sensitivity.
Table 6-4 summarizes the performance testing recommended in this manual for HMA
made from conventional materials, including most modified binders. It is recommended that
all mixtures be evaluated for moisture sensitivity using AASHTO T 283. Equipment for this test
is widely available. Rutting resistance should be evaluated for mixtures designed for traffic levels
greater than 3 million ESALs. Rutting resistance can be evaluated using either the dynamic
modulus test in conjunction with the E* AMPT Specification Criteria Program, or the flow
number test and the criteria given in Chapter 8. Performance testing is not recommended for
fatigue cracking when the mixture design criteria given in Chapters 8 and 10 or 11 are met.
Performance testing for thermal cracking is not recommended when binders are selected using
the Performance Grading system.
For HMA made with non-conventional materials, performance tests for rutting, fatigue
cracking, thermal cracking, and moisture sensitivity should be performed and compared to
results from mixtures made with conventional materials. Non-conventional materials might
include recycled materials such as ground glass, ground tire rubber, ground or shredded plastic
Table 6-4. Recommended performance tests for HMA made with
conventional materials including most modified binders.
Design Traffic Levels for Which
Property Recommended Test Property Should be Evaluated
Moisture Sensitivity AASHTO T 283 All
Permanent Deformation Flow Number or Dynamic 3 Million ESAL and greater
Modulus, AASHTO TP 79-09
Fatigue Cracking None NA
Thermal Cracking None NA
