Microstructural evolution and micromechanical properties of asphalt due to chloride salt erosion: Insights from atomic force microscopy

To explore the impact of chloride salt erosion on the microstructure and micromechanical properties of asphalt, this study utilizes the atomic force microscopy (AFM) to examine the evolution of micromorphology, surface roughness, adhesion, and Young's modulus of asphalt in dry conditions, under various chloride salt concentrations, and after different erosion times. The results indicate significant changes in the microtopography of the asphalt surface due to chloride salt erosion, characterized by the reorganization of nanoscale protrusions and white spots. This results in a decrease in their quantity and total area, while the average area increased, demonstrating a trend of phase dispersion and aggregation. Erosion increased the surface roughness of the asphalt and significantly altered its mechanical properties. Specifically, with an increase in chloride salt concentration, the average roughness (R-a) of asphalt, after one day of erosion relative to its dry state, increased by 7.99 %, 33.06 %, and 52.55 %, respectively. As the erosion time was extended, at a 2.5 % chloride salt concentration, the growth rate of R-a reached 33.06 %, 54.68 %, and 67.22 %, respectively. A declining trend in nano adhesion was observed, indicating internal structural damage and reduced durability, while Young's modulus significantly increased, suggesting a densification of the asphalt matrix and enhanced rigidity.