Effect of Asphalt Film Thickness on Asphalt–Aggregate Adhesion under Aging

The occurrence of cracking, loosening, and other distresses in asphalt pavements is closely related to the failure of asphalt–aggregate adhesion. Studying the effect of asphalt film thickness on asphalt–aggregate adhesion can facilitate an understanding of the mechanism of disease in asphalt pavements. To study the impact of asphalt film thickness on asphalt–aggregate adhesion, this study tested and evaluated the adhesion between asphalt and aggregates at different asphalt film thicknesses from a macromechanical perspective via pullout tests. In addition, based on the surface energy theory, the effects of different film thicknesses on the adhesion of asphalt–aggregate were analyzed from a surface mechanics perspective. Further, the aggregates were subjected to surface property testing to further investigate the differences between the surface mechanics and the macromechanics results. The results showed that for an asphalt film thickness of 400 μm, the failure energy density (FED) and cohesive work (WA) of the asphalt exhibited the same trend, and certain properties of asphalt influenced its adhesion to the aggregate. For an asphalt film thickness of 25 μm, the FED and the asphalt adhesion work (Was) exhibited the same trend, and the combined effect of the asphalt and slag properties influenced the adhesion of asphalt to steel slag. Moreover, with decreasing asphalt film thickness, the adhesion between asphalt and aggregates was reduced owing to the influencing factors of the asphalt, which can effectively reduce the influence of the aging effect on adhesion.