Nano surface evolution properties of crumb rubber modified asphalt due to aging and adhesion failure mechanism

To investigate the impact of thermal-oxidative aging and thermal-oxidative-water (TOW) aging on the multiscale bonding behavior between asphalt and aggregate, this study utilized atomic force microscopy (AFM) to explore the micromorphology, nanosurface roughness, and surface energy of base asphalt (BA) and crumb rubber modified asphalt (CRMA). Simultaneously, the pull-off test was conducted to assess the bonding strength between asphalt and aggregate. The results revealed that, with aging progression, BA exhibited an increase in black and white beelike structures in terms of average area and maximum length, while the total area and quantity decreased. In contrast, CRMA showed a relatively uniform black-and-white speckle structure in its microscale morphology before and after aging, without the presence of beelike structures. The roughness parameters of asphalt increased with aging, and the presence of moisture intensified this trend. The addition of crumb rubber (CR) reduced the height difference between the peri- and perpetua-phase, resulting in lower roughness for CRMA compared to BA. The surface energy and pull-off strength of both BA and CRMA decreased with aging, with CRMA exhibiting a smaller reduction compared to BA. Specifically, the pull-off strength of BA with aggregate decreased by 10.80%, 42.48%, and 67.08%, while CRMA exhibited reductions of 6.08%, 35.04%, and 52.96% in pull-off strength with aggregate. Sensitivity analysis demonstrated a negative correlation between asphalt surface roughness and macroscopic pull-off strength, while surface energy exhibited a positive correlation with macroscopic pull-off strength.