A Study of Superpave Design Gyrations for High Traffic Surface Mixtures

The methodology of the research that was used to evaluate the comparative results of surface mixes with a nominal maximum aggregate size of 12.5mm is presented in this paper. Also presented are the recommended Ndes values for C-level and D-level mixes, which are designed to handle traffic levels of 3-30 Million and greater than 30 Million ESALs, respectively. In order to determine the amount of asphalt that was present, asphalt concrete mixes were fabricated utilizing the Superpave design process at Ndes levels of 50, 75, 100, and 125 gyrations. Using the Asphalt Mixture Performance Tester instrument, we were able to determine the dynamic modulus (E*) at the design asphalt content for a number of different gyration levels. The E* data and related binder properties were used as input in the AASHTO Darwin-ME software to anticipate the rutting and fatigue performance of the mixtures. This was accomplished by assuming a model pavement section and appropriate traffic levels. In order to determine which Ndes are most appropriate, relative performance indicators for rutting and fatigue have been developed and plotted against asphalt content. The Ndes value of 85 gyrations was found to be ideal for both surface mixes after extensive research.