Investigation of microscale aging behavior of asphalt binders using atomic force microscopy

Atomic force microscopy (AFM) has the capacity to distinguish among different phases at high resolution, and it is widely used in obtaining topography and mechanical property maps for asphalt binders. This study investigated the effects of long-term aging on both SBS-modified asphalt and base asphalt using AFM. In describing the study findings, this paper introduces two new indices used to quantify changes in the microstructures of asphalt, namely, the percentage of elliptical bee structures and surface roughness. In addition, the Derjaguin-Muller-Toporov modulus and adhesive force were measured to quantify the mechanical properties of the micro-phases. Finally, to evaluate the influence of aging on composite phase properties, a parallel model from the field of composite materials was introduced and applied. The results indicate that aging significantly affected the microstructures and mechanical behavior of micro-phases of asphalt binders. Aging also had a significant influence on the microstructures of the asphalt, especially in the bee structures. The percentage of bee structures increased or decreased after aging depending on the asphalt binder type, while surface roughness always decreased. Aging also increased the composite modulus of the micro-phases and decreased the composite adhesion of the micro-phases. These findings are in agreement with the macroscale aging behavior of asphalt binders.