Mechanistic elucidation of dual-scale reinforcement in rock–Nano TiO ₂ modified asphalt for enhanced durability and performance balance

Abstract While traditional Rock Asphalt (RA) provides high-temperature stiffness and rutting resistance, its application in cold climates is limited due to low-temperature brittleness and high thermal susceptibility. This study explores the mechanistic basis of a novel composite modification combining RA and Nano-Titanium Dioxide (Nano-TiO 2 ), termed Rock Composite Asphalt (RCA), aiming to improve low-temperature performance without compromising high-temperature properties. Six asphalt binders (Base, SBS, BRA, RCA-1, RCA-2, RCA-3) and their corresponding AC-13 mixtures were investigated. Rheological, microstructural, and conventional performance tests—including Dynamic Shear Rheometer (DSR), low-temperature bending, and fatigue analysis—were employed to elucidate the interaction mechanisms. Results indicate that the optimal RCA formulation (20% RA + 1.0% Nano-TiO 2 , RCA-2) achieves a synergistic enhancement: Nano-TiO 2 particles interact with RA components to modify the binder microstructure, reducing crystallization at low temperatures and improving ductility, while the RA matrix maintains high-temperature stiffness. The modified binder exhibited a 5 °C ductility increase of ~31% and a 45% improvement in Penetration Index (PI), reflecting enhanced thermal adaptability. Correspondingly, the RCA-2 mixture demonstrated superior dynamic stability ( 2.16 times higher than BRA ) and fatigue life ( 2.88 times higher k value ), attributed to the refined binder-aggregate interface and mitigated microcrack propagation. This study provides mechanistic insights into how nanomaterial-assisted RA modification can overcome the traditional performance trade-off, offering a viable strategy for durable asphalt pavements in regions with high temperature variations and heavy traffic.