Analysis of nanoscale evolution features of microstructure of asphalt based on atomic force microscopy

Abstract

To reveal the microstructural evolution of asphalt at the nanoscale, this study utilizes an atomic force microscope (AFM) to observe the surface morphology of asphalt and employs roughness theory for its quantitative assessment. The effects of asphalt type, aging state, immersion time, chloride salt concentration, and modifiers on beelike structures and roughness were comprehensively considered. The results demonstrated that the area and number of beelike structures, as well as the roughness, varied with different asphalt types. After aging, the surface morphology of the asphalt became rougher, leading to an increase in surface roughness, while both the number and area of the beelike structures in the asphalt showed a decreasing trend. With increasing immersion time, water penetrated into the asphalt and interacted with its components, disrupting the colloidal structure under dry conditions and causing microstructural damage and peeling. Consequently, distinct nanoscale protrusions and white spots appeared on the asphalt surface. Moreover, the total area of beelike structures decreased, and the roughness parameters increased with an increase in chloride salt concentration. Compared to matrix asphalt, the beelike structures in crumb rubber (CR) modified asphalt disperse into finer, speckled black-and-white patterns. The styrene–butadiene–styrene (SBS) modifier forms a stable three-dimensional spatial network structure within the asphalt, diminishing the difference between beelike and non-beelike structures. In the original state, the average roughness (Ra) and root mean square roughness (Rq) of PJ90/CR are 63.0% and 74.0% lower than those of PJ90, respectively. Meanwhile, the Ra and Rq of PJ90/SBS are 42.7% and 46.9% lower than those of PJ90, respectively.