Effects of Blending Temperature and Time on Interfacial Diffusion Behavior and Fatigue Response of Virgin-Aged Asphalt Binders.

To elucidate the diffusion behavior between virgin and aged asphalt binders and its relationship with fatigue performance, a concentric-circle blending system with a well-defined initial interface was constructed. By varying the blending temperature and time, the interfacial blending process was characterized from the perspectives of macroscopic performance, component migration, and molecular motion using dynamic shear rheometry, linear amplitude sweep, thin-layer chromatography with flame ionization detection, fluorescence microscopy, and molecular dynamics simulations. The results showed that thermal exposure produced a continuous interfacial transition region between the virgin and aged asphalt binders. Fatigue life generally increased as the sampling position shifted from the aged-binder side toward the virgin-binder side. At 5% strain, increasing the blending temperature from 135 to 165 °C increased the interfacial fatigue life by 173.8%, while extending the blending time from 15 to 60 min increased the fatigue life by 96.6%. The SARA fractions and fluorescence morphology results indicated that thermal exposure promoted component migration and redistribution on both sides of the interface, causing the initially distinct interface to gradually evolve into a continuous transition region. Molecular simulations further demonstrated that increasing temperature significantly enhanced the molecular mobility of all components and expanded the spatial overlap between the virgin and aged asphalt binders in the interfacial region. These results indicate that an increased extent of diffusion corresponds to an increase in fatigue life within the interfacial region and that the blending state between virgin and aged asphalt binders is an important factor affecting the local fatigue performance of recycled asphalt binder.