Utilizing heat-mechanical synergistic treatment for separating concrete waste into high-quality recycled aggregate, active recycled powder and new concrete

Abstract

Previous literatures highlighted that it is sustainable to reutilize concrete waste as recycled building materials, but a high value-added recycling approach is urgently needed. Therefore, this work investigated the feasibility of using heat-mechanical synergistic treatment at 600–800 °C for separating concrete waste into high-quality recycled aggregate (HRA) and active recycled powder (ARP). The HRA had much lower adhered mortar content and water absorption than ordinary recycled aggregate (ORA); the ARP contained active calcium silicate and calcium oxide, and 800 °C-separated ARP had greater reactivity than 600 °C-separated ARP. Incorporating HRA and intermixing ARP both decreased the compressive strength. However, the HRA blended concrete had greater compressive strength than ORA blended concrete, and the compressive strength of concrete with 100% 800 °C-separated HRA was 14.6% larger than that of concrete with 100% ORA; besides, the concrete with 800 °C-separated ARP had higher compressive strength than the concrete with 600 °C-separated ARP. Although the addition of HRA or ARP raised the transport properties of concrete, HRA blended concrete had lower transport properties than ORA blended concrete, and the concrete with 800 °C-separated ARP had lower transport properties than concrete with 600 °C-separated ARP. At 100% replacement ratio, the capillary absorption coefficient and chloride migration coefficient of concrete with 800 °C-separated HRA were 11.1% and 22.6% lower than those of concrete with 100% ORA. Higher heat temperature can induce extra damage in HRA but elevate the ARP reactivity, and the heat-mechanical synergistic treatment can be adjusted for optimization according to the actual requirement.