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CHAPTER 1
Introduction and Research Approach
Problem Statement and Research Scope of Study
Objectives
Research was conducted to document the ability of aggregate
Hot-mix asphalt (HMA) mixtures are complex materials tests identified in NCHRP Project 4-19 to predict in-service
composed of mineral aggregates and asphalt binder. Because performance of HMA pavements. Relationships between aggre-
about 95 percent by weight of the HMA mixture is aggregate, gate properties and HMA pavement performance were evalu-
the coarse and fine aggregate properties influence pavement ated in full-scale accelerated loading conditions. Individual
performance significantly. Studies have shown that HMA aggregate tests, as well as combinations of tests that related to
pavement rutting and stripping can be directly related to HMA performance, were identified. Recommendations for use
improper selection and use of aggregates (1). in HMA aggregate selection and mixture design procedures
Tests and associated criteria used by highway agencies to have been provided. Specifically, a practical set of performance-
select aggregate for HMA mixtures are empirical. Often, they related aggregate tests has been recommended for inclusion
have not been related to pavement performance directly. in HMA mixture design systems. Future research to determine
Aggregate tests that provide clearer relationships with per- the ruggedness, precision, and bias of the test methods has
formance will provide better means for evaluating and select- been suggested.
ing aggregates.
The completed NCHRP Project 4-19, "Aggregate Tests
Research Approach
Related to Asphalt Concrete Performance in Pavements," rec-
ommended a set of performance-related aggregate tests for The research was performed in two phases. Phase I
evaluating aggregates for use in HMA pavements. Pavement included review of NCHRP Report 405 and other relevant lit-
performance indicators assumed to be related to these labora- erature and the development of a research plan. Phase II
tory aggregate tests were permanent deformation because of included execution of the research plan established in Phase
traffic loading (both with and without stripping), fatigue crack- I and preparation of the final project report.
ing, and surface defects (e.g., raveling, popouts, and potholes). Relating results of the aggregate tests shown in Table 1 to
The performance relationships were developed based on labo- the HMA distresses of rutting, moisture susceptibility, and
ratory tests with the Superpave Shear Tester (SST) and the Geor- fatigue served as the basis for the validation experiments.
gia Loaded Wheel Tester (GLWT); however, these relationships The research was conducted according to the plan, shown in
were not validated with prototype-scale traffic tests; the NCHRP Figure 1, which involved aggregate testing, identification of
4-19 researchers recommended additional research as shown in HMA mixture designs, and HMA mixture testing using accel-
Table 1. The objective of the current research was to use accel- erated pavement tests. The accelerated testing was completed
erated pavement testing techniques to perform the rutting, in three series, each relating to one of three HMA distresses
fatigue, and moisture susceptibility validation experiments noted above.
identified in NCHRP Project 4-19.Analysis was directed toward
developing a descriptive ranking of each aggregate test indicat-
Aggregate Testing
ing how well it related to HMA performance. Also, appropriate
tests for given combinations of climatic conditions, materials, Aggregates were characterized using tests listed in Table 2.
and traffic loads have been suggested. These include the tests identified in NCHRP Project 4-19,
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Table 1. Validation experiments recommended by Kandhal
and Parker [1].
Experiment Validation Experiment Performance
Uncompacted Void Content of Coarse Aggregate and
Rutting and
1 Flat or Elongated Particles (2:1 ratio) in Coarse
Fatigue
Aggregate
Rutting and
2 Uncompacted Void Content of Fine Aggregate Fatigue
Moisture
3 Methylene Blue Test of Fine Aggregate
Susceptibility
Particle Size Analysis and Methylene Blue of p0.075
4 Rutting
Material
Durability/
5 Micro-Deval and Magnesium Sulfate Soundness Tests
Toughness
Coarse Aggregates: Dolomite, Limestone,
Gravel, Granite, Traprock
Step 1:
Fine Aggregates: Two Natural Sands,
Selection and Collection of Materials Crushed Gravel Sand, Granite, Traprock
Coarse Aggregate Tests:
Uncompacted Void Content, Flat or
Elongated Particles, Micro-Deval, LA
Abrasion, Percent Fractured, Soundness,
Step 2: Deleterious Material
Aggregate Tests and HMA Mixture Fine Aggregate Tests:
Designs Fine Aggregate Angularity, Methylene Blue,
D60, D10, Sand Equivalent, Micro-Deval,
Soundness
HMA Mixture Designs:
Step 3:
Ndesign = 100, Nmax = 160
Accelerated Pavement Tests
Step 3a: Rutting performance evaluated by
INDOT/Purdue APT, dry condition, 50°C test
Rutting Tests temperature
Step 3b: Moisture susceptibility performance
evaluated by INDOT/Purdue APT, wet
Moisture Susceptibility Tests condition, 46°C test temperature
Step 3c: Fatigue performance evaluated by
INDOT/Purdue APT, dry condition, 10°C
Fatigue Tests
HMA plant stockpile aggregates evaluated
for gradation, flat or elongated, uncompacted
void content of fine aggregate, methylene
Step 4: blue value, D60, D10
Aggregate Test Evaluations Aggregate from plant mixtures and test
section cores evaluated for gradation, flat or
elongated, uncompacted void content of fine
aggregate
Step 5:
Statistical analysis, data interpretation,
Analysis and Report Preparation conclusions and recommendations
Figure 1. Research work flowchart.
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Table 2. Aggregate characterization tests.
Recommended
by Kandhal and Superpave
Test Method Parker Requirement Additional Test
Sieve Analysis for Determining
Gradation and Size (AASHTO T11 & X X
T27)
Uncompacted Void Content of Coarse
Aggregate, Method A (AASHTO X
TP56)
Uncompacted Void Content of Coarse
Aggregate, Method B (AASHTO X
TP56)
Flat or Elongated Particles in Coarse
X (2:1) X (5:1) X (3:1)
Aggregate (ASTM D4791)
Flat and Elongated Particles in Coarse
X (3:1, 5:1)
Aggregate (ASTM D4791)
Uncompacted Void Content of Fine
X X
Aggregate, Method A (ASTM C1252)
Uncompacted Void Content of Fine
X
Aggregate, Method B (ASTM C1252)
Virginia Test Method for
Determining Percent Voids in Fine X
Aggregates (VTM5)
Methylene Blue Test for Fine
X
Aggregate (AASHTO TP57)
Particle Size Analysis of p0.075
Materials for Determining D60, D30, X
and D10 Sizes
Methylene Blue Test for p0.075
X
Material (AASHTO TP57)
Micro-Deval Test (AASHTO TP58) X
Magnesium Sulfate Soundness Test
X
(AASHTO T104)
Clay Content by Sand Equivalent
X
(AASHTO T176)
Clay Lumps and Friable Particle
X
(AASHTO T112)
Percent Fractured Particles in Coarse
Aggregate (ASTM D5821) X
Los Angeles Abrasion Test (ASTM
X
C96)
Specific Gravity and Absorption of
X
Aggregate (AASHTO T84 and T85)
the aggregate tests specified by Superpave criteria, Uncom- performance were studied by constructing and testing 11 test
pacted Void Content of Coarse Aggregate, Method B sections in the Accelerated Pavement Tester (APT). Five of the
(AASHTO TP 56), and Virginia Test Method for Determin- test sections were coarse-graded HMA mixtures with grada-
ing Percent Voids in Fine Aggregates (VTM5) tests. tions plotting below the maximum density line (MDL). The
other six sections were fine-graded HMA mixtures with gra-
dations plotting along or above the MDL.
Accelerated Testing Experiments
Rutting Experiment
Moisture Susceptibility Experiment
The rutting experiment design is shown in Table 3. Coarse
aggregate, fine aggregate, and particles smaller than the 0.075- Five fine-graded HMA mixtures were used to investigate rela-
mm sieve (p0.075) were evaluated for their effect on HMA tionships between moisture susceptibility and fine aggregate
rutting performance. For coarse-graded mixtures, a natural properties as shown in Table 4. Performance as affected by mois-
sand was used in combination with various coarse aggregates. ture damage was assessed by the amount of rutting observed in
For fine-graded mixtures, an uncrushed gravel was used as the the HMA mixtures. The AASHTO T 283 test was also per-
coarse aggregate in combination with various fine aggregates. formed on cores extracted from the APT test lanes before accel-
The effects of coarse and fine aggregate on HMA mixture erated pavement testing. Stripping after traffic was also noted
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Table 3. Rutting experiment design.
Aggregate Aggregate
Performance Test
Category Mix Coarse Fine
CA-1 Dolomite (IN)
Coarse Aggregate Test
CA-2 Limestone (IN)
Methods Evaluation
(Coarse-graded CA-3 Granite (NC) Natural Sand A (IN)
CA-4 Gravel (IN)
Mixtures)
CA-5 Traprock (VA)
FA-1 Dolomite (IN)
FA-2 Granite (NC)
Fine Aggregate Test
FA-3 Traprock (VA)
Methods Evaluation Gravel (IN)
FA-4 Crushed Gravel Sand (IN)
(Fine-graded Mixtures)
FA-5 Natural Sand A (IN)
FA-6 Natural Sand B (OH)
Table 4. Moisture susceptibility experiment design.
Aggregate Performance Aggregate
Test Category Mix Coarse Fine
FAM-1 Granite (NC)
Fine Aggregate Test FAM-2 Traprock (VA)
Methods Evaluation FAM-3 Dolomite (IN) Crushed Gravel Sand (IN)
(Fine-graded Mixtures) FAM-4 Natural Sand A (IN)
FAM-5 Natural Sand B (OH)
visually.After construction and before testing, water was pooled descriptive ranking indicating how well each test related to
on the test lanes for 2 days with the pavement heating system performance. Subsequently, multivariable regression analyses
turned on. During APT testing, the test sections were kept wet were conducted to investigate whether a single test or a com-
by adding water to the pavement surface. bination of aggregate tests best predicted HMA performance.
This process provided a rational basis for recommending
aggregate tests related to HMA performance.
Fatigue Experiment
The relative effect of traffic was determined through analysis
Relationships between fatigue cracking and coarse and fine of the APT test results. For example, APT traffic repetitions and
aggregate properties were evaluated through the construction rutting at different levels of one or more material characteristics
and testing of six APT sections as indicated in Table 5. These (e.g., fine aggregate angularity) were plotted. An example of
mixtures were selected from the 11 mixtures used in the rutting these relationships is shown in Figure 2. Alternatively, a level of
experiment based on performance. Fatigue performance was distress could be selected (e.g., 10-mm rut depth) at which to
characterized by percent fatigue cracking in the wheel path. compare the effect of the aggregate characteristic on perform-
ance. Figure 3 shows a relationship for FAA and a 10-mm rut
depth distress level. This type of analysis was used to determine
Analysis Methods
the aggregate characteristic's sensitivity to traffic level and also
Experiments were designed to test the hypotheses that provide a method of developing traffic-related input for regres-
there are relationships between aggregate tests (properties) sion analysis targeted at determining the performance of HMA
and HMA performance when full-scale accelerated loading is pavements at different traffic levels with the individual or mul-
applied. Analysis of variance (ANOVA) was used to develop a tiple aggregate properties as input factors.
Table 5. Fatigue experiment design.
Aggregate Performance Aggregate
Test Category Coarse Fine
Coarse Aggregate Test CA-2 (Limestone)
Methods Evaluation CA-3 (Uncrushed Gravel) Natural Sand A (IN)
(Coarse-graded Mixtures) CA-4 (Granite)
Fine Aggregate Test FA-1 (Natural Sand A)
Methods Evaluation Uncrushed Gravel (IN) FA-3 (Natural Sand B)
(Fine-graded Mixtures) FA-4 (Granite)
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25
FAA = 39, N10 = 1000
6000
20 FAA = 43, N10 = 2450
Load Repetitions to 10mm Rut
FAA = 47, N10 = 5000 5000
Rut Depth (mm)
15
4000
Depth
10 3000
2000
5
1000
0 0
0 1000 2000 3000 4000 5000 6000 35 40 45 50
Load Repetitions (N) FAA
Figure 2. Effect of FAA on rut depth. Figure 3. Effect of UVA on traffic.
