Effect of Carbonation Degree on Mineral Composition, Microstructure, and Cementitious Properties of BOF Slag

This study explores the utilization of steel slag in the cement industry through direct aqueous carbonation. The carbonation process produces nano-sized CaCO₃ particles as the main product. Increasing the carbonation degree leads to larger particle size and higher crystallinity of CaCO₃. The distribution of BOF slag particle sizes changes, and the specific surface area significantly increases. Optimal carbonation time of 5 min exhibits the highest hydration activity, with a carbonation degree of 15.17% and a CO₂ uptake rate of 5.16%. When 30% cement content is replaced with carbonated BOF slag, the mortars' compressive strength increases by 58.5%, 23.0%, and 14.0% at 3 days, 7 days, and 28 days, respectively, compared to non-carbonated BOF slag. Carbonation treatment has a stronger influence on early hydration activity. After hydration, more C–S–H and AFt are present, improving the compactness and mechanical properties of the composite cementitious material.