Comparison of asphalt rubber and conventional mixture properties: Considerations for mechanistic-empirical pavement design guide implementation

In 1999 the Arizona Department of Transportation (ADOT) started outlining and developing a long-range pavement research program. This research program was established in cooperation with Arizona State University (ASU) and had the ultimate goal of implementing the Mechanistic-Empirical Pavement Design Guide (MEPDG) for Arizona. Since ADOT uses asphalt rubber (AR) mixes for new and rehabilitation pavement designs, an integral part of the MEPDG calibration effort must include AR mixtures, which were not included in the MEPDG's development. The objective of this study was to perform a comparison between AR properties and those of the conventional dense graded asphalt mixtures typically used for MEPDG development, calibration, and validation. Another important task was to evaluate how these mixes could be implemented into the MEPDG in the short term and to make recommendations on how to use them in future designs. A total of 23 AR mixtures were available for analysis from a joint ADOT-ASU database. The database contains several engineering properties of AR mixes and binders. These data were used to compare properties, select MEPDG input parameters, generate design analysis for permanent deformation and fatigue cracking, run case studies to predict performance, and compare results with field performance data. Several issues were identified pertaining to the implementation of AR mixes in the MEPDG, and recommendations were provided.