Performance-Based Design Method for Gradation and Plasticity of Granular Road Surface Materials

Abstract

Granular-surfaced roads frequently experience severe surface damage and degradation, which adversely affects traffic safety and significantly increases maintenance costs. The importance of the gradation and plasticity of granular-surfaced road materials have long been recognized. However, very few studies have focused on quantifying the effects of gradation and plasticity on the resulting mechanical performance of granular roadways. In this study, laboratory tests and statistical analyses were conducted to quantify the effects of variations in gradation and plasticity on the mechanical performance of granular road surface materials. A performance-based design method was developed using Fuller’s model to replace the commonly used arbitrary gradation band specifications. To validate the performance of the proposed method, field test sections were constructed then tested through a seasonal freeze–thaw period. Compared with existing gradation band specifications, the laboratory and field test results demonstrated that the proposed method is more closely tied to performance and can be used to develop specifications with more precise targets. To help secondary roads agencies implement the method while also recycling existing surface materials, a gradation optimization program was developed to determine the mixing ratios of existing roadway aggregate and two to three new quarry materials to come closest to the theoretical gradation for optimum performance. A complete set of testing, design, and construction procedures is also recommended to provide more cost-effective solutions to building or reconstructing granular-surfaced roads.