Determination of volumetric criteria for designing hard asphalt mixture

Abstract The current mix design method that is established based on the volumetric properties works well for conventional hot-mixed asphalt (HMA), but does not satisfy the design of hard HMAs. Hard HMAs refer to the mixtures designed using hard asphalt binder whose penetration is less than the conventional one (70#). Increasing asphalt content is regarded to be an effective way to design hard HMAs and keeps them away from thermal cracking problem. Therefore, this research explored the suitable volumetric criteria for designing hard HMAs. The principle of establishing the volumetric criteria is to ensure hard HMAs can achieve the equivalent performance as conventional ones. Eleven groups of AC16 containing three penetration grades of asphalt binders (70#, 50#, and 30#) were designed, and the volumetric properties, uniaxial penetration shear test (UPST), low-temperature bending test (LTBT) and four-point bending test (4PBT) were then conducted. Based on experiment data, two key volumetric criteria of AFT and VMA are established for hard HMAs. It can be seen that when the ranges of AFT maintain within the 10–11.2 µm and 12.9–13.4 µm, respectively, the 50# and 30# hard HMAs can reach the equivalent high- and low- temperature performance as 70# conventional HMAs. Correspondingly, the ranges of criteria in VMA for 50# and 30# hard HMAs need to maintain within 15.6–17.5% and 17.6–19.5%, respectively. Overall, a higher value of volumetric criteria is required for designing hard HMA compared with conventional one. In addition, the results of 4PBT indicate that hard HMAs can also exhibit good fatigue resistance when they are designed within these criteria.