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3 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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4 Table 1. Validation experiments recommended by Kandhal and Parker . 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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5 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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6 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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7 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.