Modified recycled aggregate in asphalt mixtures: an evaluation of interfacial adhesion and pavement performance

To address water damage in asphalt pavements using recycled concrete aggregates, this study evaluated single and composite modifications with silane coupling agents and nano-silica. Both methods improved aggregate physical–mechanical properties, achieving a minimum water absorption of 2.79%, density of 2.42 g/cm³, crush value of 17.6% and Los Angeles abrasion value of 22.96%. The chemical elements (C, O, Si and Ca) and diffraction peak positions (0.33, 0.30 and 0.29 nm) remained unchanged after modification, indicating that the modification mechanisms of the single and composite approaches are consistent. Composite modification using nano-silica combined with two different types of silane coupling agents increased the Marshall modulus index by 40.53% and 32.49%, the low-temperature splitting strength by 5.76% and 22.83%, and the freeze‒thaw splitting strength ratio by 14.72% and 7.58%, respectively. The composite-modified asphalt mixture exhibited the slowest rates of mass loss and density change under multiple freeze‒thaw cycles and withstood more than four cycles, demonstrating significantly enhanced freeze‒thaw durability. This study confirms that composite modification technology is superior to single modification. The core advantage lies in the synergistic effect of nano-silica and silane coupling agents, which comprehensively improves water damage resistance and freeze‒thaw durability without altering the underlying modification mechanism.