Development of Preliminary Balanced Mix Design Method for Stone Matrix Asphalt

Since the volumetric-based Superpave mix design methods were implemented in the early 2000s, many roads have been reported to suffer from surface cracking due to insufficient binder or rutting because of excessive binder oil. To improve the mix durability and performance, the balanced mix design (BMD) methods for hot mix asphalt (HMA) have been adopted by state highway agencies. However, most of the research studies related to BMD focused on the dense-graded HMAs, and unconventional and innovative paving materials, such as the stone matrix asphalt (SMA) were not sufficiently investigated during the development of the BMD methods. SMA is a gap-graded HMA that is designed to maximize deformation resistance and durability by using a structural basis of stone-on-stone contacts. Due to the structural and ingredient difference in SMA and conventional HMA, the design concepts for the two types of mixtures are different, and additional tests are needed in the SMA mix design. Therefore, it is necessary to incorporate the design concept in the balanced mix design methods. In this proposed study, the investigators aim to develop a preliminary BMD method for SMA mixes through systematic laboratory testing. The performance of SMA with different designs will be evaluated and compared with the counterpart conventional HMA. The performance testing methods and their performance threshold limits that are suitable for SMA mix design will also be identified in this research.