Performance evaluation of recycled asphalt using dual-activated kaolin via wet grinding and KH550

Recycled asphalt faces limitations in widespread application due to poor rheological properties and insufficient aging resistance. As a soft clay mineral, kaolin can improve aging resistance of asphalt when combined with silane coupling agent (KH550), while its effectiveness remains limited with unclear anti-aging mechanisms. This study developed a mechano-chemically treated kaolin (MTK) via an innovative dual activation technology combining wet grinding and KH550 modification to improve the comprehensive properties of recycled asphalt. The particle size distribution, infrared spectra, mineral composition and micromorphology of original kaolin (ORK), conventionally treated kaolin (CTK) and MTK were characterized. Then the rheological properties and surface energy of recycled asphalt modified with ORK, CTK and MTK (ORA, CRA, and MRA) were investigated. And their aging resistance and mechanisms were also systematically explored. The results indicate that mechano-chemically activation reduces the average particle size of kaolin by 97 % to 0.90 μm, while simultaneously decreasing crystallinity and inducing structural defects on the surface. This process exposes more active sites, indicating a significant enhancement in both surface activity and dispersibility of MTK. Compared with ORA, MRA exhibits an increased surface energy of 14.11 mJ/m² along with a significantly higher proportion of dispersive components. Under all three aging methods, aged MRA reveals the lowest fatigue factor and the glass transition temperature, representing superior fatigue resistance and low-temperature performance. Incorporating MTK substantially declines the carbonyl index, sulfoxide index and surface roughness of aged recycled asphalt. MRA with MTK retains the highest aromatic hydrogen atom (H A ) content after short-term, long-term and UV aging, reaching 10.62 %, 9.22 % and 9.45 %, respectively, indicating that MTK effectively suppresses the substitution reaction and chain-extension kinetics during aging process, thereby significantly retarding the aging progression of recycled asphalt.