Insight into the oxidative aging behavior of asphalt using experiment-derived average molecular models and quantum chemistry calculations

The aging phenomenon of asphalt, primarily driven by the oxidation of its internal components, leads to irreversible degradation of pavement performance. In this study, the aging behavior of asphalt is examined through the experimental development of average molecular models, subsequently applied to quantum chemistry (QC) calculations. The average molecular models are able to provide a representation of the chemical components, as derived from two distinct crude sources, based on the improved Brown-Ladner (B-L) method. Comprehensive QC calculations included molecular polarity analysis, electrostatic potential (ESP) analysis, frontier molecular orbital (FMO) theory analysis, binding energy and weak interactions analysis, are performed to gain a multifaceted understanding of aging behaviors and mechanisms. The results reveal a significant increase in the polarity of asphaltenes and resins, accompanied by a reduction in the uniformity of charge distribution owing to aging. As aging progresses, the orbital energy gaps of both asphaltenes and resins generally decrease, with a more pronounced reduction observed in resins, indicating enhanced chemical reactivity after aging. Furthermore, the binding energies between molecular dimers significantly increase after long-term aging. Specifically, the formation of intermolecular hydrogen bonds under the influence of polar functional groups leads to an increase in electrostatic interactions. This ultimately manifests as diminished cracking resistance of asphalt binder at the macroscopic scale. Overall, this study demonstrates the effectiveness of integrating experimentally derived average molecular models with QC calculations to unravel the intrinsic mechanisms underlying asphalt aging.