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4 Research Approach step, methods were categorized into direct and indirect. Direct methods were defined as those wherein particle characteris- A comprehensive literature review was conducted during tics (shape, texture, and angularity) are measured, described this study. The literature search focused on aggregate particle qualitatively, and possibly quantified through direct measure- characteristics that are likely to influence pavement perform- ment of individual particles. In indirect methods, particle ance (summarized in Appendix B). The literature search also characteristics are lumped together as geometric irregularities covered image analysis methods for characterizing aggregate and determined based on measurements of bulk properties. In shape properties (summarized in Appendix C), and test pro- the second step, methods that share the same analysis concept cedures currently used in the United States and other countries were grouped together to ensure that the selected candidate and those proposed as part of recent research for measuring methods represent different analysis concepts. In the third these characteristics (summarized in Appendix D). The research step, tests were selected from each group based on practicality, also included critical evaluation of all available test methods labor requirements, cost, repeatability, versatility, and field based on the published literature, identification of test methods applicability for further evaluation. Some of the currently for experimental evaluation, conduct of statistically designed used test methods were included in the intensive evaluation experiments to evaluate test methods, rank and recommenda- tion of test methods for measuring aggregate characteristics, for comparison. and development of a methodology for classification of aggre- The following test methods were considered for further gates based on shape. experimental evaluation: Uncompacted Void Content of Fine Aggregates (AASHTO T 304), Uncompacted Void Content of Coarse Aggregates (AASHTO TP56), Compacted Aggregate Evaluation of Test Methods Resistance (CAR), Percentage of Fractured Particles in Coarse Information gathered from the literature was used (1) to Aggregate (ASTM D 5821), Flat and Elongated Coarse Aggre- conduct a comparative analysis of the available test methods gates (ASTM D 4791), Multiple Ratio Shape Analysis (MRA), and (2) to select test methods that will be subjected to inten- VDG-40 Videograder, Buffalo Wire Works PSSDA, Camsizer, sive experimental evaluation in this study. The advantages WipShape, Aggregate Imaging System (AIMS), University of and disadvantages of all test methods were summarized. Three Illinois Aggregate Image Analyzer (UIAIA), and Laser-Based steps were used to select test methods (Figure 1). In the first Scanning Analysis System (LASS). All Test Methods Step 1: Divide methods into direct and Direct Indirect indirect. Step 2: Divide D-1 D-2 D-3 I-1 I-2 I-3 methods based on analysis concepts. Step 3: Select methods based on practicality, cost, labor requirements, and field D-2-a D-3-a I-1-a I-2-a I-3-a applicability. Further Evaluation Figure 1. Approach for preliminary evaluation, screening, and prioritization of test methods.