Precision of AASHTO TP62-07 for use in mechanistic-empirical pavement design guide for flexible pavements

In the Mechanistic-Empirical Pavement Design Guide (MEPDG), one of the most important material inputs for designing flexible pavements is the dynamic modulus (E^*). Currently, AASHTO has provided a provisional test specification for measuring the E^* of hot-mix asphalt mixtures, AASHTO TP62-07 [Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt (HMA)]. Under AASHTO TP62-07, recommendations are provided for sample preparation-compaction, measurement system, testing conditions-procedures, and calculations. Unfortunately, information regarding the general precision of the test method does not exist. With many different test machines capable of conducting AASHTO TP62-07 and the importance of E ^* in flexible pavement design, an understanding of the general precision of the test method and its influence on the MEPDG is needed. This paper describes the results of a round-robin study conducted to address the need for a precision-type statement for AASHTO TP62-07. Seven laboratories, all having equipment compliant with the specifications in AASHTO TP62-07, were asked to laboratory age, compact, prepare, and test six HMA test specimens according to the provisions in AASHTO TP62-07. A statistical analysis was conducted on the test data in a precision statement environment. On the basis of the test results, an initial precision statement for AASHTO TP62-07 was generated and presented. The test results for the seven different laboratories were also used as inputs in the MEPDG to evaluate the relative differences in predicted pavement distresses. Results from the precision evaluation were used to recommend modifications to AASHTO TP62-07 to promote greater precision in different testing laboratories and the results were reevaluated in the MEPDG.