Roadway runoff purification by pervious concrete incorporating recycled brick–concrete aggregates: performance and mechanisms

Roadway runoff is a major source of urban non-point pollution, transporting suspended solids, nutrients, organic matter and heavy metals that threaten receiving waters. Recycled aggregate pervious concrete (RAPC) offers a multifunctional pavement solution by coupling runoff purification with construction and demolition (C&D) waste recycling. However, a quantitative and mechanism-based understanding of how recycled aggregates and pore-scale structure jointly govern long-term purification remains limited. In this study, the pollutant removal performance and mechanisms of RAPC were systematically investigated using (i) batch adsorption and kinetic tests on recycled aggregates and (ii) long-term dynamic rainfall simulations on pervious concrete, representing pavement service-like hydraulic loading. The purification behaviors of total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), Zn²⁺ and Pb²⁺ were evaluated for mixtures with different recycled-aggregate contents and surface modification strategies. Results show that incorporating recycled aggregates significantly enhances the long-term pollutant retention capacity relative to natural-aggregate pervious concrete, with pronounced removal of 10–100 μm TSS and improved removal of nutrients, organics and heavy metals. Adsorption kinetics of recycled aggregates are well described by a pseudo-second-order model, whereas dynamic breakthrough under rainfall loading is well captured by the BDST model. CT/Avizo-based microstructural analyses indicate that increased pore specific surface area and ion-enriched cementitious interfaces jointly control adsorption and retention. Moreover, pore specific surface area exhibits a strong linear correlation with pollutant uptake capacity. Overall, this work provides a quantitative structure–performance framework for designing RAPC pavements with improved roadway-runoff purification.