Design and Performance of Mixes for Use as Ultrathin Overlay

Friction loss is one of the most critical issues faced by agencies responsible for maintaining and preserving pavement structures. Various methods are used for surface treatments, including seal coats, slurry seals, and ultrathin asphalt concrete overlays. Ultrathin overlays have increased in popularity due to their lack of noise and improved ride quality, as well as their reduced overall cost due to the reduced layer thickness. This study had two major objectives: (1) to determine the best aggregate structure for use as an ultrathin overlay; and (2) to evaluate the volumetric-based criterion that is currently used to determine the optimum binder content for mixes used in ultrathin overlays. The performance of different mix types was evaluated using laboratory techniques including the traditional and modified Hamburg wheel tracking method and the three-wheel polishing device. Of the six potential gradations or aggregate structures that could be used as an ultrathin overlay, three were found to be suitable based on the performance tests. The optimum binder content, as defined by the volumetric criterion, was also generally the optimum based on performance tests conducted in the laboratory.