Evaluation of Coarse- and Fine-Graded Superpave Mixtures under Accelerated Pavement Testing

Abstract

Initial Superpave^® implementation guidelines encouraged mix designers to develop coarse gradations for higher-traffic-level mixtures, as this was thought to produce a more robust aggregate structure. Consequently, many agencies have specified the use of a coarse-graded asphalt mixture on high-volume facilities. However, target density can be difficult to obtain while compacting coarse-graded mixtures, and control of volumetric properties is harder to maintain than it is for fine-graded mixtures. The Florida Department of Transportation (FDOT) conducted an experiment to assess the rutting performance of coarse- and fine-graded Superpave mixtures under accelerated pavement testing (APT). Both mixtures consisted of aggregate from the same source and were made with virgin binder meeting the requirements of performance grade 67-22. Both mixtures contained the same effective binder content and were designed for 10 million to 30 million equivalent single axle loads, according to the standard Superpave mix design methodology. During placement of these mixtures, all standard FDOT density requirements and acceptance criteria were applicable. The subsequent investigation showed that under similarly controlled conditions, the fine-graded mixture performed slightly better than the coarse-graded mixture in terms of rutting resistance. This paper describes the testing program, data collection efforts, and subsequent analysis and findings and focuses primarily on rutting as generated and observed under APT.