Rheological Behavior and Coupled Mechanisms of Naphthenic Oil and Desulfurized Rubber Powder in Asphalt Binders

The combined utilization of desulfurized rubber powder (DRP) and naphthenic oil (NO) offers a promising strategy to enhance the performance and sustainability of asphalt binders for high-reclaimed asphalt pavement (RAP) applications. This study investigates the rheological behavior and coupled mechanisms of DRP and NO across a wide dosage range. The rheological tests were conducted to evaluate high-temperature, low-temperature, and fatigue performance. Spectroscopic and microscopic analyses, together with molecular dynamics simulations, were employed to explore interfacial interactions and structural evolution. Results reveal that DRP dominates the high-temperature rheological behavior by promoting the formation and densification of nano-colloidal particle networks. In contrast, NO governs low-temperature and fatigue performance by enhancing molecular mobility and stress relaxation. NO also exerts a softening and lubricating effect at the DRP–asphalt interface, facilitating interfacial fusion. However, at high DRP contents, dense nano-structures restrict NO diffusion and lead to localized aggregation, weakening its beneficial effects. These findings provide a mechanistic understanding of the coupled roles of DRP and NO in asphalt binder modification and offer guidance for optimizing formulations tailored for high-RAP mixtures.