Enhancing the performance of recycled rigid pavement coarse aggregate by mechanical–chemical synergistic treatment for lower-layer airport pavement concrete

To promote high-value reuse of decommissioned rigid pavements, a synergistic treatment for recycled rigid pavement coarse aggregate was developed and its suitability for airport pavement lower-layer concrete was evaluated. The treatment combined mechanical grinding with sodium silicate impregnation. A two-way factorial experiment was used to determine the optimum treatment parameters. Concrete containing untreated or treated recycled aggregate (RA) was then assessed for workability, mechanical performance and salt–frost (S–F) resistance at different RA replacement ratios (R_r), and the interlayer treatment for dual-layer concrete was optimised. The optimum treatment was found to be 20 min grinding followed by impregnation in a 10 wt% sodium silicate solution. Compared with the untreated aggregate, the crushing value and flat-and-elongated particle content decreased by 20.9% and 27.5%, respectively. At R_r = 50%, the treated concrete still satisfied airport pavement performance requirements and showed markedly improved S–F resistance. The suitable interlayer condition for the tested system was 20–25 mm RA broadcast at 16–24 kg/m² with a casting interval below 1.5 h. An illustrative direct cost comparison indicated a 14.8% reduction in total assessed cost for the treated concrete. The results support a practical route for high-value reuse of decommissioned rigid pavements in sustainable airport construction.