The main objective of this study is to assess the sensitivity of assumed binder grade on performance prediction of RAP mixtures. This is achieved by utilizing the Mechanistic-Empirical Design Guide (MEPDG) Version 1.0 software to predict the performance of a flexible pavement structure with a RAP modified hot mix asphalt (HMA) layer. Different design runs are conducted using the three hierarchical levels of analysis in the MEPDG software. Runs were done for three climactic regions while changing HMA layer properties and keeping all the unbound layer properties and traffic input held constant. Comparison of the predicted performance of the various runs reveals important findings regarding the extent and manner that the HMA inputs affect pavement distresses and performance at the three levels of analysis. The assumed performance grade (PG) grade for reclaimed asphalt pavement (RAP) mixtures has only a small effect for Level 1 analysis. However, for the conditions and parameters examined in this study, the effect becomes significant for Level 2 and/or Level 3 analysis. Performance prediction using Level 1 inputs is the least conservative for the structure and mixtures examined in this study. The difference in predictions between Level 2 and Level 3 becomes more prominent as the difference between the assumed high and low temperature PG grade of RAP mixtures increases. The relative ranking in performance among the mixtures is consistent for all input levels and conditions tested. When using the MEPDG, selection of analysis level and assumed PG grade for the RAP mixtures is critical for performance prediction and estimation of pavement life at failure. Conducting the numerous MEPDG software runs in this study also enabled the identification of critical and sensitive factors that need to be considered when incorporating RAP mixtures in pavement design using the Version 1.0 software.
Abstract