Unlocking the Synergy of Carbonation and Hydration: A Novel Curing Strategy for High-Performance MgO–SiO ₂ Treated Sediments

To address the disposal and resource recovery challenges of dredged sediment, this study developed MgO–SiO2 system utilizing solid waste-derived light-burned magnesia (LBM) and silica fume (SF) under carbonation-hydration curing. The effects of this synergistic approach on material properties were systematically investigated by adjusting the LBM/SF ratio and precarbonation time. The results indicated that this strategy effectively enhanced material strength and optimized microstructure. Specifically, specimens with an LBM/SF ratio of 6:4 and a precarbonation time of 0.5 h (6M4S0.5C) exhibited a 38% increase in 28 day strength compared to the hydration system. Microstructural analysis revealed that hydrated magnesium carbonates (HMCs) formed during moderate precarbonation served as structural skeleton, retaining the reactive Mg2+ and alkaline environment for subsequent reactions. This promoted the formation of hydrated magnesium silicate (M–S–H) gel and its interweaving, constructing a “gel-crystal” composite network that optimized pore structure and enhanced macroscopic strength. Based on thermogravimetric analysis data, a strength prediction model was further established using the mass loss ratio of the reaction products, achieving a quantitative correlation between multiphase composition and macroscopic properties. Sustainability assessments indicated that, compared to the ordinary Portland cement (OPC) system, 6M4S0.5C reduced CO2 emissions by 41.8% and lowered the sustainability index (CO2 emissions required to achieve 1 MPa of strength) by 40.5%. The research provided a theoretical foundation and technical approach for the low-carbon resource utilization of dredged sediment.