Examining the impact of nano-titanium dioxide on the adhesion and failure behavior of asphalt mixtures in acid rain conditions

This study investigates the combined effects of nano-TiO₂ modification and environmental pH conditions on the performance of asphalt mixtures, with a particular focus on moisture susceptibility, fatigue resistance, low-temperature cracking, and surface free energy (SFE) characteristics. Nano-TiO₂ was incorporated into the asphalt binder at a fixed dosage of 5% by weight of binder, selected based on previous optimization studies reported in the literature. The results indicate that nano-TiO₂ modification significantly improves the overall performance of asphalt mixtures. Specifically, fatigue life increased by approximately 45% under dry conditions compared to the control mixture. However, under acidic exposure (pH 4), both modified and unmodified mixtures exhibited a reduction in fatigue performance, although the nano-TiO₂ modified mixtures consistently showed higher fatigue resistance than the control samples across all environmental conditions. Similarly, improvements in moisture resistance and fracture performance were observed in modified mixtures, although the magnitude of improvement was influenced by environmental pH. SFE analysis further revealed that nano-TiO₂ enhances both cohesive and adhesive energy components of the binder, while acidic conditions reduce surface polarity and weaken interfacial interactions. Overall, the findings demonstrate that nano-TiO₂ modification improves the intrinsic durability of asphalt mixtures; however, environmental acidity plays a critical role in governing the extent of performance improvement. These results highlight the importance of considering environmental exposure conditions when evaluating the long-term behavior of nanomodified asphalt systems.