Effect of fraction changes driven by asphalt binder aging on the surface energy of asphalt binder

The differential effects of fraction changes on the surface energy of asphalt binder during aging remain unclear, which constitutes a key theoretical deficiency hindering targeted anti-aging and rejuvenation of asphalt binder. In this study, an asphalt binder reconstitution method was adopted to isolate the effects of fraction variations on asphalt binder performance, and the interference of this reconstitution method on the evaluation indicators was determined. The contact angle method and surface energy theory were employed to elucidate the influence of fraction changes on asphalt binder surface energy during aging. Meanwhile, Fourier-transform infrared spectroscopy, gel permeation chromatography, and 1H nuclear magnetic resonance spectroscopy were utilized to reveal the mechanisms through which changes in key fractions govern surface energy variations. The results indicate that, in the comparison of performance indicators before and after asphalt binder reconstitution, the surface energy, oxygen-containing functional group indices, and weight-average molecular weight were only slightly affected by reconstitution, and thus could serve as performance indicators for further analysis. Qualitative changes in maltenes and asphaltenes respectively dominate the increases in sulfoxide and carbonyl groups during asphalt binder aging. Quantitative changes in fractions dominate the increase in hydroxyl groups during aging through the rising proportion of asphaltenes possessing high hydroxyl content. Furthermore, qualitative changes in maltenes lead to a decrease, whereas those in asphaltenes lead to an increase in the weight-average molecular weight of the asphalt binder. The decline in surface energy during asphalt binder aging is predominantly governed by qualitative changes in asphaltenes, which deteriorate the surface energy by elevating the carbonyl index. This study reveals, for the first time, the effects of fraction changes on asphalt binder surface energy during aging and the associated key mechanisms, thereby offering a theoretical basis for targeted anti-aging and rejuvenation strategies for asphalt binder.