Granular overlays have been used by the Washington State Department of Transportation (WSDOT) for about 30 years. Since the mid-1980's and along with the full implementation of the WSDOT Pavement Management System (WSPMS), WSDOT has been interested in examining the performance of granular overlays. It is felt by WSDOT that the performance of this rehabilitation treatment is better than one might reasonably expect. Further, past practice in Washington State occasionally required that the preexisting surfacing (often several bituminous surface treatment (BST) layers) be scarified prior to placement of the crushed rock layer. As will be shown in this report, this practice is not supported by this research.
This study examined granular overlays by using three different techniques. First, previous research on the behavior of confined crushed rock layers was studied. Through these studies, information was sought concerning the stiffness that have been found in crushed rock layers, what can be done to improve the crushed rock layer, and the problems that have been encountered in working with confined crushed rock layers. Next, the usable life of the granular overlay was compared with that of other types of pavement resurfacing, including asphalt concrete (AC) overlays and BST. Finally, the granular overlays were tested to determine their properties and to measure the effect of different designs on their performance.