Determination of in-place hot-mix asphalt layer modulus for rehabilitation projects by a mechanistic-empirical procedure

This paper summarizes the findings of a project that evaluated the procedures proposed by the Mechanistic-Emphical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. A total of 33 cores were extracted from nine sites in Virginia to measure their dynamic moduli in the lab. Falling weight deflectometer (FWD) testing and visual pavement rating were performed at the sites, and the resilient modulus was measured in the laboratory. Selected cores were tested for their bulk densities and then for their dynamic moduli. The cores were broken down and tested for their maximum theoretical specific gravity. Finally, an ignition test was performed to find the percentage of binder and to reclaim the aggregate for gradation analysis. Volumetric properties were then calculated and used as input for the Witczak dynamic modulus prediction equations to find what the MEPDG calls the undamaged master curve of the HMA layer. The FWD data, resilient modulus data, and pavement rating were used to find the damaged master curve of the HMA layer as suggested for Input Levels 1, 2, and 3, respectively. It was found that the resilient modulus data needed for a Level 2 type of analysis (as proposed in Chapter 2 of the MEPDG) does not represent the entire HMA layer thickness, and therefore it was recommended that this analysis should not be performed. The use of Level 1 data is recommended because FWD testing appears to be the only procedure investigated that can measure the overall condition of the entire HMA layer.