Effect of RAP surface modification on mechanical properties of stable crushed gravel with mineral admixture

To address the key bottleneck of weakened bonding at the interface between inorganic binder and aggregate caused by the surface asphalt film on reclaimed asphalt pavement (RAP) coarse aggregate, a method using mineral admixture slurry for RAP interface modification is proposed. Through compaction, unconfined compressive strength, splitting strength, and drying shrinkage tests, the effects of different RAP contents (12%, 28%, 44%, 59%) on the mechanical properties of recycled mixtures before and after modification were systematically studied, and a comprehensive evaluation was conducted in combination with function fitting ( R 2 ≥ 0.94) and life cycle carbon emission accounting. The results show that interface modification reduces the optimum moisture content of the P component (modified RAP) by 1.10%∼7.20% compared with the unmodified NP component (unmodified RAP), significantly improving compaction properties; the compressive strength of the P component changes in a quadratic parabolic pattern with the increase of RAP content ( R 2 ≥ 0.94), reaching a 28-day compressive strength of 6.5 MPa at 28% content, which is 25.0% higher than that of fully crushed stone mixture, while the NP component shows a quadratic decreasing function ( R 2 ≥ 0.98); the 28-day splitting tensile strength of the P component increases by 94.1% compared with the 7-day strength, and the 60-day drying shrinkage microstrain is reduced by 67.1% compared with cement- stabilized crushed stone; carbon emission accounting shows that when the RAP content is 28%, the carbon emissions per unit volume of mixture are reduced by 54.3% compared with cement-stabilized crushed stone. Interface modification technology effectively achieves the synergistic optimization of “strength improvement-crack resistance enhancement-carbon reduction” for RAP recycled mixtures, providing a theoretical basis for the high-value utilization of RAP in semi-rigid bases.