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13 Aggregate Gradation Specification ) determined that the mance. New innovations in aggregate testing were also exam- restricted zone was a redundant requirement when used in con- ined, especially those related to aggregate shape, angularity, junction with the other aggregate and volumetric properties and texture. specified in AASHTO M323. Pooled Fund Study 176, "Vali- dation of SHRP Asphalt Mixture Specifications Using Accel- erated Testing," examined the effects of VMA, fine aggregate 1.3 SCOPE angularity (FAA), and gradation on the performance (pri- To accomplish the research objectives, five tasks were con- marily rutting) of HMA. Finally NCHRP Project 4-30, "Test ducted; their descriptions are as follows: Methods for Characterizing Aggregate Shape, Texture, and Angularity," was recently awarded. It is expected that this · Task 1--State of the Practice: In Task 1, a literature study will provide new methods to more accurately measure search and review was conducted to determine the cur- the aforementioned properties with improved precision. rent state of the practice on the evaluation and valida- Evaluation of aggregate properties has been included in tion of the Superpave aggregate criteria and the state of some field and accelerated performance studies. The LTPP the art on the development of promising new methods Program documents the construction and tracks the perfor- of aggregate characterization. The results from Task 1 mance of numerous HMA pavements. Some of the HMA are presented in Chapter 2. The influence of aggregate pavements in the Specific Pavement Studies (SPS) were crushing operations is also discussed in Chapter 2. designed with the Superpave methodology. The SPS-1, -5, and, · Task 2--Survey of Ongoing Research: In Task 2, a sur- particularly, -9 sections provide limited data relating aggregate vey was conducted to identify the preliminary findings properties to performance. Three test tracks--the MnRoad, of ongoing research related to aggregate properties. The WesTrack, and the NCAT Test Track--include Superpave- results from Task 2 are presented in Chapter 2 in con- designed HMA. The NCAT Test Track has a number of dif- junction with the results from the literature review. ferent aggregate sources and gradations represented by the test · Task 3--Survey of Agency Specifications: A survey was sections. Accelerated testing related to aggregate properties conducted of state aggregate specifications for aggregate has also been conducted by the FHWA's Accelerated Load- used in the production of HMA. The survey provides ing Facility (ALF) and the Indiana Department of Transporta- insights into the widespread adoption of the Superpave tion (DOT)Purdue University APT Facility. method and into the aggregate tests that agencies ques- Based upon performance histories of locally available mate- tion. The survey results are summarized in Chapter 3; see rials or research projects conducted to address concerns relat- also the Appendix. ing to the aggregate specifications included in AASHTO · Task 4--Review Performance Data from Field Test Sec- M323, numerous agencies have modified their aggregate tions and Full-Scale Accelerated Testing: Results from specifications for Superpave-designed HMA. Often times this field test sections and accelerated test sites were reviewed experience is not shared with other agencies that are using to gather performance relationships for aggregate prop- similar materials. A consensus among the states, based on their erties. As expected, there are complex interactions when experiences, may indicate the need to alter aggregate test pro- aggregate properties are altered. These interactions tend cedures or specifications on a national basis. to dilute any correlations that may exist; however, trends were identified. The results from the performance review 1.2 OBJECTIVE are summarized in Chapter 4. Specific experiments are also discussed in relationship to specific test methods in The objective of this study (NCHRP Project 9-35) was to Chapter 2. review the technical literature and ongoing research to identify · Task 5--Final Report: The final report was prepared the consensus, source, or other aggregate properties that sig- to document all of the research conducted in Tasks 1 nificantly impact HMA performance. The review also exam- through 4. Chapters 5 and 6 present (1) future work sug- ined the effect of production and crushing operations on gested for validating new aggregate shape and texture aggregate properties. The review concentrated on the effect parameters based on image analysis and evaluation of of aggregate properties on HMA designed using the Super- the CAR test and (2) a summary of the conclusions of pave methodology, HMA construction, and HMA perfor- NCHRP Project 9-35.