Effect of gypsum on tobermoritization in a monticellite-OPC-alkali model system

Monticellite (CaMgSiO 4 ), a common mineral phase in high-magnesium metallurgical solid waste, exhibits extremely low hydration reactivity, which restricts its resource utilization in the field of building materials. Sulfates can promote the cleavage of Si-O bonds and provide crystalline nucleation sites, rendering them applicable to the C-M-S-H system. Taking this as a model system, this paper systematically investigates the effect of gypsum on tobermorite formation in the monticellite-OPC-alkali system under autoclaving conditions, and explores its hydration process and mechanism. Characterization methods such as XRD, FTIR, TG-DTG and SEM-EDS were employed to analyze and deeply explore the microscopic hydration mechanism. The results show that within the investigated range, the addition of gypsum improves the compressive strength and dry density of the specimens. The maximum values of 6.5 MPa and 1832.9 kg/m 3 are achieved at a gypsum dosage of 4 wt% and an autoclaving duration of 12 h. Gypsum not only promotes the dissolution of monticellite but also acts like a regulator for crystal growth, facilitating the transformation of metastable amorphous intermediate phases (such as C-S-H gel) into highly crystalline and structurally dense platy tobermorite. As a model-system study, this work provides a theoretical basis for the research on the activation of magnesium-containing silicate minerals, thereby offering a reference for the resource utilization of high-magnesium industrial solid wastes in autoclaved building materials.