Book Description

Unexpected performance of coarse-graded and crushed stone mixtures when compared to fine-graded and partially crushed gravel mixtures at WesTrack led to an examination of consensus aggregate properties for all mixtures used. These properties did not explain the differences in performance, but an analysis of mixture sensitivity to asphalt content and percent passing the 0.075 mm sieve did highlight the potential for substantial changes in volumetrics in terms of air voids for coarse-graded Superpave mixtures. The rutting performance of both coarse and fine-graded mixtures was sensitive to asphalt content, with coarse-graded mixtures highly sensitive to decreases in asphalt content and both types of mixtures sensitive to increases in asphalt content. Increased variability in aggregate gradation for the coarse-graded mixture coupled with this sensitivity may explain the unexpected performance. Based on these results, a sensitivity analysis was recommended for inclusion in the Superpave mix design process. Rutting performance models also indicated that volumetrics and aggregate properties related to gradation significantly contribute to performance.