Enhancing the performance of waste-derived super-sulfated with carbonated recycled concrete fines for cemented paste backfill applications

This study investigates the performance enhancement of super-sulfated cement (SSC) derived from arsenic-containing bio-oxidation waste (BW) through the incorporation of carbonated recycled concrete fines (CRCF). The findings revealed that the addition of 5wt% CRCF yields optimal performance, with compressive strengths reaching approximately 1.83, 12.59, and 42.81 MPa at 1, 3, and 28 d, respectively. These values represented significant increases of 408.3%, 10.0%, and 14.3% compared to the reference sample. The improvement was attributed to the synergistic effects of ultrafine CRCF particles acting as fillers and nucleation sites, as well as the high reactivity of silica gels, which promoted the formation of additional hydration gels. Microstructural analysis confirmed that CRCF addition refined pore structure, and enhanced the stiffness of C–S–H gels. Furthermore, CRCF served as a net CO₂ sink, sequestering 0.268 kg CO₂ per kilogram of CRCF and thereby reducing the carbon footprint of SSC. In addition, the feasibility of applying CRCF-modified SSC in cemented paste backfill (CPB) is highlighted, given the high cement-related carbon footprint of conventional CPB. When 5wt% CRCF-modified SSC was employed in CPB, its 3-d compressive strength attained over 70% of that of ordinary Portland cement (OPC), while the 28-d strength was comparable to that of OPC. The proposed binder thus provides a sustainable pathway for BW valorization, combining waste utilization, carbon sequestration, and improved engineering performance.