Enhancing pervious concrete with recycled brick–concrete aggregates through composite modification under freeze–thaw and sulfate conditions

The utilization of recycled brick-concrete aggregate (RBCA) from demolition waste in pervious concrete offers environmental and economic benefits, but its poor quality limits application. This study investigated three composite modification methods—sodium silicate-silane (SS), pozzolanic slurry (PS), and combined pozzolanic slurry-sodium silicate-silane (PS-SS)—to improve RBCA. Modified aggregates were used to prepare recycled aggregate pervious concrete (RAPC), and the effects of long-term freeze–thaw cycles and sulfate attack on mass loss, strength, fracture behavior, and permeability were evaluated. Microstructural evolution of the interfacial transition zone (ITZ) was also analyzed to reveal damage and enhancement mechanisms. Results showed that unmodified RAPC experienced severe degradation after 160 freeze–thaw cycles, with mass, fracture toughness, and permeability losses significantly greater than natural aggregate concrete (NAC). Aggregate modification effectively reduced mass and strength losses by 20–45 %, with PS-SS showing the best freeze–thaw resistance. Under sulfate attack, RAPC exhibited initial mass and strength increases due to expansive reaction products, followed by accelerated deterioration. Modified RAPC demonstrated lower mass loss, reduced strength degradation, and smaller permeability increases than untreated RAPC. Among the three methods, PS-SS provided the greatest improvement, reducing compressive strength loss by 44.8 % and permeability loss by 27.0 % compared with untreated RAPC. Microstructural analysis confirmed that modifications reduced RA water absorption and enhanced ITZ hydration, resulting in fewer pores and cracks. Overall, all three methods improved the durability of RAPC, with the PS-SS method achieving the most significant enhancement against freeze–thaw and sulfate erosion, supporting its potential for sustainable pavement applications.