Regulation of ettringite and synergistic solidification in a multi-solid-waste cementitious composite incorporating highly reactive magnesium slag

To enable the resource utilization of magnesium slag, this study develops a ternary all-solid-waste cementitious system composed of highly reactive granular magnesium slag (TDMS-ps), circulating fluidized bed fly ash (CFBFA), and desulfurized gypsum (DG), with an emphasis on how DG dosage regulates hydration and performance. Hydration reaction, product assemblage, and pore-structure characteristics were characterized by isothermal calorimetry in conjunction with XRD and MIP. The results show that increasing DG markedly alters the heat-release kinetics, manifested by a shortened induction period and an advanced main exothermic peak. An optimum DG content of 12% was identified: compared with MFDG0, MFDG12 achieved a 28d compressive strength of 44.1 MPa, corresponding to an increase of 91.7%, and a 47.67% reduction in 180 d drying shrinkage. Microstructural evidence further indicates that DG promotes ettringite (AFt) formation and refines the pore structure, which is beneficial for strength development and drying-shrinkage mitigation. Overall, this study elucidates the regulatory role of DG dosage on the reaction progress and performance evolution of a magnesium-slag-based ternary solid-waste system, providing a practical reference for the valorization of magnesium slag. • Achieved high-value utilization of highly reactive granular magnesium slag (TDMS-ps). • Demonstrated TDMS-ps with self-cementing properties and sustained alkaline activation capability. • Identified TDMS-ps as the key factor in the alkaline–sulfate synergistic activation mechanism. • Enhanced β-C2S reactivity in TDMS-ps by optimizing desulfurized gypsum (DG) incorporation.