Utilization of carbonated alkaline solid wastes in ordinary Portland cement-metakaolin-limestone ternary mixture: Underlying the role of low grade-sustainable calcium carbonate sources

Alkaline solid wastes are widely generated as by-products annually from construction demolition, steel making, and metal refining industries. Consequently, there is high pressure on their disposal and environmental protection. Carbonation treatment of alkaline solid wastes provides a potential way to valorize CO₂ and produce low-grade artificial limestone particles. This study investigates the utilization of carbonated alkaline wastes, including recycled cement fines, steel slag, iron recycled steel slag, and magnesium slag in green ternary cement (limestone-metakaolin-cement system) production. The detailed characterization of carbonated alkaline solid wastes and the performance of metakaolin-cement based ternary systems were evaluated. The reaction mechanism of carbonated alkaline wastes in metakaokin-cement based binder is proposed. The results indicated carbonated alkaline solid waste powder containing relatively low calcite (14.4%–50.38%) and negative surface charges. In addition, the amount of reactive Si at Q₃ and Q₄ were observed. The precipitated calcite on the surface of particles resulted in the deterioration of the workability of ternary mixtures compared to natural limestone. However, the equivalent amount of CO₃-AFm phases produced by precipitated calcium carbonate and additional hydrates from the reaction of amorphous silica in carbonated alkaline solid wastes contributed to a comparable mechanical performance (49.5 MPa–50.82 MPa) and compact microstructure of ternary binders. Carbonated alkaline solid wastes can be a sustainable component to replace natural limestone in green ternary cement production.