Analysis of asphalt microscopic and force curves under water-temperature coupling with AFM

Asphalt, as a crucial material in road construction, is affected by external environmental factors, among which water and temperature are the primary causes of water damage to asphalt pavements. Different hydro-thermal environments can cause varying types of damage to asphalt or the asphalt-aggregate interface. To analyze the micro-performance changes of different types of asphalt under various hydro-thermal environments, this study conducts tests on PG64-22 matrix asphalt, PG76-22 SBS-modified asphalt and PG82-34 high viscosity asphalt under different hydro-thermal coupling and freeze-thaw cycle conditions using Atomic Force Microscopy (AFM). The analysis is based on the obtained micro-morphology images and mechanical properties, exploring the impact mechanisms of different hydro-thermal environments on various asphalts. Results show that under different hydro-thermal conditions, the three asphalts exhibit different morphological changes: the asphalt surface's “bee-shaped structure” is gradually destroyed after hydro-thermal coupling, while a “disappearance-reappearance” phenomenon is observed under freeze-thaw cycles. Moreover, the roughness of the two modified asphalts shows a different trend from that of the matrix asphalt, indicating that the modifier alters the micro-structure of asphalt to some extent. Under hydro-thermal coupling, the adhesion force of the three asphalts decreases linearly, with matrix asphalt decreasing by 89.2% after 3 hours, SBS modified asphalt by 63.1%, and high-viscosity asphalt by 23.9%, showing that high-viscosity asphalt has better waterproof and heat-resistant performance. During freeze-thaw cycles, the adhesion force between the asphalt and the tip shows varying degrees of recovery. Additionally, there are differences in adhesion force across different areas of the asphalt surface, which tend to diminish with hydro-thermal coupling or freeze-thaw cycles. These results indicate that hydro-thermal coupling and freeze-thaw cycles have different mechanisms of damage to the internal structure of asphalt, providing important data for understanding the damage mechanisms in depth.