Soundness of steel slag as building materials: A review

Poor soundness is a major issue limiting the use of steel slag as a building material. This paper identifies f-CaO, f-MgO, the RO phase, and sulfur as the primary components causing soundness problems in steel slag and analyzes their interactions. The paper reviews standard soundness evaluation methods, including f-CaO and f-MgO content measurements, immersion expansion ratio, autoclave chalked ratio, autoclave expansion ratio, and boiling methods, and compares regulations across different applications. Potential techniques to mitigate soundness issues are introduced, with heat-stewing and reconstruction recommended for initial control in steel mills. Steel slag with low f-MgO can be treated using acidification. Combining grinding with carbonation and acidification is suggested for optimal results, while controlling the level of grinding. Carbonation is an effective and energy-efficient process to eliminate f-CaO and f-MgO. Direct preparation of carbonated steel slag construction materials is advised to capture CO₂ as well.