Failure mechanism analysis of asphalt–aggregate systems subjected to direct shear loading

In order to investigate the mechanical behavior of asphalt–aggregate systems subjected to direct shear loading and reveal the shear failure mechanism, four groups of direct shear tests were conducted on composite specimens under different experimental conditions with a self-manufactured direct shear test apparatus at 25 °C. Comparative studies were conducted to evaluate the effects of stone surface treatment, asphalt film thickness and loading rate on the shear mechanical behavior of asphalt–aggregate specimens. Results showed that two kinds of the complete stress–displacement curves, including the general single-peak curve and the first-known double-peak curve, were clearly observed for each condition. In addition, the internal failure mechanisms were analyzed based on qualitative and quantitative methods. It can be concluded that the potential failure modes of the direct shear test include adhesive failure at the asphalt–aggregate interface and cohesive failure within the asphalt film. The research results enhance understanding of the shear mechanical behavior and failure mechanism of asphalt mixture, and also provide a reference for the interfacial failure.