Evolution and Mechanism of Asphalt–Aggregate Interfacial Behavior Induced by Asphalt Ultraviolet Aging: From Microscale Adhesion to Macroscale Mechanical Response

The deterioration of asphalt physicochemical properties under ultraviolet (UV) aging affects the microscale and macroscale characteristics of the asphalt–aggregate interface. To reveal the evolution and underlying mechanisms of these characteristics, this study investigated the microscale adhesion and macroscale mechanical response of the asphalt–aggregate interface induced by UV aging of asphalt. First, the variations in the chemical composition, surface morphology, and surface mechanical properties of base asphalt (BA) and high-viscosity asphalt (HVA) under UV aging were elucidated using Fourier-transform infrared spectroscopy (FTIR), asphalt four-component analysis, and atomic force microscopy (AFM). Subsequently, the microscale interfacial work of adhesion was quantified by AFM measurements and surface free energy theory, whereas the macroscale viscoelastic and tensile responses under dynamic shear and uniaxial tensile loading were assessed using an improved frequency sweep test with aggregate substrates and pull-off tests, respectively. Finally, the intrinsic linkages among the microscale properties of asphalt, the microscale interfacial adhesion, and the macroscale mechanical response were examined using Pearson correlation analysis. The results indicated that, with increasing UV aging severity, the resin and asphaltene contents and the carbonyl, sulfoxide, and aromatic functional groups in both BA and HVA increased, whereas the butadiene index of HVA declined. Concurrently, the surface roughness and modulus of both asphalts rose, whereas their surface adhesive force diminished. The microscale interfacial work of adhesion and the macroscale pull-off strength were correspondingly reduced, and the failure mode transitioned from cohesive to adhesive. Under dynamic shear loading, the BA–aggregate interface exhibited enhanced elasticity and diminished viscosity owing to the increase of polar components, whereas the HVA–aggregate interface displayed the opposite trend as a result of the degradation of its elastomeric polymer network. Furthermore, Pearson correlation analysis confirmed that the UV-induced changes in the chemical composition, surface morphology, and mechanical properties of the asphalt reduced the microscale interfacial work of adhesion, thereby impairing the macroscale viscoelastic and tensile performance. These findings deepen the mechanistic understanding of UV-induced asphalt–aggregate interfacial degradation.