Design and evaluation of gap-graded asphalt rubber mixtures

This paper describes the evaluation of the design and performance of gap-graded asphalt rubber mixtures (GGAR) under laboratory conditions with one type of asphalt binder, three crumb rubbers, and four gap-graded gradations of one aggregate type. The resulting mixture samples were tested and evaluated for their high-temperature performance and fatigue resistance and their performance was compared with that of conventional Stone Matrix Asphalt mixtures (SMA). For mixture design, GGAR can have mineral filler content less than that of SMA and have the volume of air voids larger than typical values for an SMA. As a result, the optimum asphalt content is also larger than that of SMA. The laboratory testing results indicate that GGAR performs as well as SMA with respect to high-temperature and has better fatigue resistance than a conventional SMA. More field tests should be carried out on GGAR in various environmental conditions to determine its optimum manufacture and long term performance.