Binder derived from industrial solid waste: a low-carbon attempt for deep soil mixing pile

This study develops a solid waste–based binder (SWB) as a sustainable alternative to ordinary Portland cement (OPC) for deep soil mixing (DSM) applications. The binder was formulated using steel slag (SS), mineral slag (MS), two desulfurisation by-products (DP-1 and DP-2), and a reduced amount of OPC. The optimal composition, determined by way of response surface methodology, was MS:SS:DP-1:DP-2:OPC = 40:20:15:5:20. The SWB-stabilised silt achieved unconfined compressive strengths (UCS) of 1.99 MPa at 7 days and 3.21 MPa at 28 days, with notable synergistic effects between MS and SS. A predictive model for 28-day UCS incorporating moisture and binder content was established. Hydration reactions produced cementitious gels with minimal heavy metal leaching. Full-scale DSM pile tests showed that SWB-treated piles (60 and 70 kg/m) reached bearing capacities of 220 and 260 kN, outperforming OPC-treated piles (160 kN at 60 kg/m), and exhibited higher quality indices. SWB-treated piles reduce total carbon dioxide emissions by more than 70% and binder material costs by over 60% compared with OPC, yielding a more than three-fold improvement in carbon efficiency. As a sustainable binder with technical, environmental, and economic viability, SWB directly contributes to UN SDG 11 by improving urban infrastructure in climate resilience and resource efficiency.