Exploring the efficacy of travertine pervious concrete pavement: A novel approach for urban runoff heavy metal mitigation

To reduce the dependence on natural aggregates and to improve the utilization of solid waste, travertine waste cutting stone pieces were used as aggregate to produce travertine pervious concrete (TPC). This paper focuses on the effect of various factors, including contact time, travertine replacement rate, cement amount used, contact area and competitive adsorption on the removal of Cd2+, Cu2+ and Pb2+ by TPC and travertine under the rapid method and immersion method. The results showed that the contact time between TPC and heavy metal solution directly affects the adsorption capacity. The removal rates of Cd2+, Cu2+ and Pb2+ (95.28–100.00 %) with the immersion method are greatly higher than that under the rapid method (only 12.38–27.45 %). Encased in cement paste, travertine aggregates in pervious concrete can only remove 1.52–4.80 % of heavy metal ions. As the main adsorbent for heavy metal ions, the cement paste reported in this study can remove almost all heavy metal ions in the solution under the long-term leaching tests. Furthermore, the travertine itself with porosity and high CaO also has a higher ability to remove heavy metals and its removal capacity was also directly affected by the contact area. Under the influence of ternary competitive mechanism, the adsorption capacity of TPC is Pb2+ > Cd2+ > Cu2+. Finally, a laboratory-scale TPC pavement (TPCP) with a rainfall system was built. The 72.17–96.23 % urban runoff could be removed by TPCP in one hour, and the removal rates of TPCP for Cd2+, Cu2+ and Pb2+ all exceeded 96.0 % within 30 minutes, demonstrating environmental friendliness.