Granular Overlays on Low-Volume Roads in Washington State: Structural and Performance Characteristics

Abstract

The granular overlay system is an alternative type of overlay for rehabilitating mostly low-volume, rural pavements. The overlay consists of a layer of densely compacted, crushed stone overlaid by a generally thin surface layer (either a bituminous surface treatment or asphalt concrete). The Washington State Department of Transportation continues to be interested in these roadways because performance has been better than expected with rehabilitation survival lives doubling from 7 to 14 years with the addition of granular overlays. Previous attempts to backcalculate layer moduli and understand the structural characteristics of granular overlays were limited because of uncertainties associated with layer thicknesses. With known layer thicknesses obtained from four sites, backcalculation of granular overlay pavements was possible. These moduli along with straightforward performance information are used to characterize granular overlays.