Microstructural, Surface Energy, and Thermal Behavior Changes of Virgin and Aged Bitumen after Fusion

Abstract

To investigate the effects of aging on the microstructure, mechanical behavior, and thermal performance of bitumen surfaces, this study utilizes atomic force microscopy (AFM) for a qualitative and quantitative assessment of the surface morphology, roughness, and surface energy evolution at the microscopic scale during the fusion process of both virgin and aged bitumen. The formation mechanism of beelike structures is also analyzed. Additionally, the thermal stability of bitumen is evaluated through thermogravimetric (TG) and derivative thermogravimetry (DTG) curves. Results revealed substantial differences in polarity and structure between asphaltene and surrounding bitumen molecules, leading to ineffective dissolution and dispersion of asphaltene in surrounding bitumen molecules, ultimately forming distinct striped beelike structures. With an increase in the content of virgin bitumen, the quantity and total area of beelike structures significantly increase, whereas their size and average area decrease. Aging induces the migration and alteration of bitumen internal components, resulting in the aggregation, dispersion, and fusion of biomass on the microsurface, thereby increasing surface roughness and decreasing surface energy. With the introduction of virgin bitumen and rejuvenators, bitumen surface roughness markedly decreases, whereas surface energy exhibits an increasing trend. This suggests that the microstructural properties of rejuvenated bitumen are effectively restored, with high fusion homogeneity between virgin and aged bitumen. Thermal analysis results indicate that the characteristic temperature and residual weight of rejuvenated bitumen are lower than aged bitumen, approaching the virgin bitumen. Specifically, the residual weight for virgin bitumen, aged bitumen, and rejuvenated bitumen are 17.23%, 22.03%, and 17.65%, respectively. This suggests that the introduction of rejuvenators increases the content of light components in bitumen, leading to a lower thermal decomposition temperature due to the volatilization of light components during heat treatment.