Generation and evolution mechanisms of pavement asphalt aging based on variations in surface structure and micromechanical characteristics with AFM

Asphalt aging is more serious at the pavement surface due to the exposed environment, which can cause to the variations of surface characteristics. However, the surface characteristics were lost in reshaping the asphalt sample when applying the traditional aging method. It is still unclear about the generation and evolution mechanisms of pavement asphalt aging. In this study, asphalt was aged using self-developed test equipment that took all factors, including heat, ultraviolet radiation and water, into consideration. Then the surface structure and mechanical properties were explored with an optical microscope and atomic force microscopy. The results show that two characteristic regions appear at the surface of samples after aging. The mechanical properties of the two regions were measured using AFM force curve measurements. We found that the adhesion ability of the aged film was much less than that of virgin asphalt, whereas the hardness and modulus of the aged film were significantly greater. However, the adhesion ability, hardness and modulus of the valley area were similar to unaged asphalt binder. Finally, we presented the possible generation and evolution mechanisms on the aging of the asphalt binder.