Effect of blast furnace slag substitution for cement in carbon-reduced and low-cost solidified/stabilized cementitious materials

The development of low-carbon cementitious materials involves the selection of the appropriate raw materials and the transformation of the hydration mechanism. In this study, low-carbon and low-cost cementitious materials were prepared using municipal solid waste incineration fly ash (MSWI FA), blast furnace slag (BFS), and desulfurization gypsum (DFG) as raw materials to reduce clinker usage. Results showed that the compressive strength of K5 (mass ratio of BFS: DFG: MSWI FA = 7:1:2) after 360 d of curing was 41.49MPa, with a low leaching concentration of heavy metal residues that meet groundwater Class II standards, a dioxin content of only 25 ngTEG/kg, and a stable pH value ranging between 11 and 11.5. Microscopic analysis revealed a continuous decrease in the Ca/Si atomic ratios of K4 (mass ratio of BFS: DFG: MSWI FA: P·I 42.5 = 42:10:20:28) and K5, i.e., 1.18–1.54 and 1.04–1.23, respectively, with the increase in the hydration age. The highest Al/Si atomic ratio of K5, i.e., 0.26–0.31, was observed with the strongest conversion trend of calcium–silicate–hydrate gel into calcium–aluminum–silicate–hydrate gel, and the network structure of sodium–(calcium)–aluminum–silicate–hydrate gel zeolite-like phase was generated. The water-to-binder (WTB) mass ratio of 0.35 was determined to be more suitable for the K4 and K5 systems and resulted in a 56.83% and 90.82% reduction in half-life t∂ compared with the WTB ratio of 0.5, respectively. Notably, the value of the reaction velocity constant K in the induction period was 10 times that of K1, and the autocatalytic reaction controlled the value of N to <1. The X-ray absorption near-edge structure indicated that Zn solidification produced Zn2SiO4 with a small solubility product. The production of 1 t of K5 emitted only 10.83kg/t of CO2, which was 40 times less than that of K1. Overall, K5 provides the highest economic benefit at 40.08 USD/t, and the clinker-free cementitious system with multisolid waste synergy has significant advantages in terms of solidifying harmful substances, reducing carbon emissions, and lowering costs.