University of California Pavement Research Center

Caltrans has adopted mechanistic-empirical (ME) methods for flexible pavement design, and is using performance-related construction specifications on some projects for hot mix asphalt. Performance-related specifications are used to help ensure that as-built materials meet the performance requirements assumed in ME pavement structural designs. PRS pose new challenges for materials producers and contractors who have never had to relate volumetric mix design parameters to achievement of mechanistic parameters for fatigue life and rutting resistance based on results from performance-related laboratory tests. The objective of this project is to provide guidance to mix designers and contractors to support their decision making regarding changes to mix designs to achieve PRS requirements. The guidance presented in this report was initially developed based on past experience. To validate the guidance and demonstrate its usage, a production mix approved by the California Department of Transportation was selected as the starting point for a set of adjustments applied to the mix and measurement of the effects of each adjustment on mechanistic performance indicators. A total of three sets of adjustments were evaluated, which resulted in a total of four mixes including the baseline. The mechanistic performance parameters evaluated in this study include stiffness, fatigue resistance, and rutting resistance. In addition to direct comparison of laboratory test results, mechanistic-empirical simulations were conducted to evaluate the laboratory mix performance results on predicted pavement performance when the mix was used as a pavement surface layer. The initial mix design guidance was found to be generally consistent with the laboratory test results for the example mix albeit with some minor exceptions. The mix design guidance was then revised based on findings from this study. It is recommended that the revised guidance be used and more data collected to make further improvements.