Effect of aggregate gradation on the cracking performance of wearing course mixtures

Cracking is one of the main failure mechanisms of asphalt pavements. This study investigates the effects of aggregate gradation on the cracking performance of hot mix asphalt (HMA) mixtures at two stages, i.e., the cracking initiation and cracking propagation stages. Based on the continuous maximum density (CMD) of aggregate gradation and the dominant aggregate size range (DASR) model, a novel cracking performance index-designated the gradations-based cracking resistance index (GCI)-was developed to easily evaluate the cracking resistance of wearing course mixtures. This simple index was applied to comparatively investigate cracking resistance in a variety of dense-, coarse-, and fine-graded mixtures with 12.5-mm nominal maximum particle size. Seven blends of different aggregate gradations were developed using the conventional Marshall mix design method. This study employed the notched semi-circular bending test to evaluate the cracking resistance of the HMA mixtures. The experiments demonstrated a strong relationship between GCI and cracking resistance at the cracking initiation stage. In addition, cracking resistance was observed to increase with increasing GCI value. These findings indicate that the novel index has potential applications for evaluating the cracking performance of wearing course mixtures.