Implementation of Asphalt-Rubber Mixes into the Mechanistic Empirical Pavement Design Guide

The Mechanistic-Empirical Pavement Design Guide (MEPDG) developed by the National Cooperative Highway Research Program (NCHRP) utilizes material properties to predict distresses in pavement structures. This new MEPDG is in the process of replacing the traditional pavement design based on the AASHTO 1993 Design Guide. The Arizona Department of Transportation (ADOT) uses Asphalt- Rubber (AR) mixes state-wide. These mixes include both gap and open gradation designs. However, the national calibration process that was undertaken for the MEPDG did not include asphalt-rubber mixes. Because of their unique characteristics, this paper addresses steps and efforts undertaken in a recent study to implement these AR mixes into the MEPDG. There were several issues and limitations identified pertaining to the implementation of AR mixes in the MEPDG. Short and long term recommendations were provided. An important outcome includes a modified Dynamic Modulus predictive equation for AR mixes that is expected to be used in a future implementation of AR mixes in MEPDG.