Aging and Antiaging Mechanisms of Nano-ZnO–Modified Asphalt under Various Aging Conditions

Abstract Natural solar radiation, high temperatures, and precipitation act synergistically to induce progressive aging in road asphalt. The incorporation of nano-ZnO has been shown to enhance the asphalt’s resistance to aging. Thus, this study aims to investigate the aging behavior of the rheological properties of asphalt under various aging conditions and to elucidate the antiaging mechanisms of nano-ZnO–modified asphalt at both the microscopic and molecular levels. Experimental investigations, including temperature sweep tests, multiple stress creep recovery tests, and aging characterization techniques such as Fourier transform infrared spectroscopy, gel permeation chromatography, and thin layer chromatography–flame ionization detection, were conducted on nano-ZnO–modified asphalt following thermal oxidative and environmental aging. Rheological test results demonstrated that nano-ZnO enhanced the high-temperature rutting resistance of asphalt and decreased the rheology-based aging indices. Furthermore, 4% by weight was identified as the optimal dosage; it increased the rutting factor of the modified asphalt by 23.7% compared to the base asphalt and exhibited superior antiaging performance. At the microscopic level, a dosage of 4% nano-ZnO effectively inhibited the formation of carbonyl and, particularly, sulfoxide functional groups induced by aging, and retarded the aggregation of small molecules into large molecules. In addition, ultraviolet (UV)-visible absorption tests indicated that nano-ZnO oxide exhibits strong absorption characteristics for ultraviolet light. Furthermore, molecular dynamics (MD) simulations were used to analyze changes in interaction energy, mean square displacement, and radial distribution functions (RDF) of the four major asphalt components before and after aging. MD simulations demonstrated a significant binding energy between nano-ZnO and asphaltenes. This preferential binding mechanism inhibits asphaltene self-aggregation, leading to a 29.1% reduction in the aging-induced RDF peak. These findings provide a scientific basis for understanding the antiaging mechanisms of nano-ZnO–modified asphalt and support its practical engineering applications.