Volume Stabilization of Steel Slag for Low-Carbon Construction Materials: Mechanisms, Treatment Technologies, and Engineering Application Pathways

Steel slag (SS), a major industrial solid waste generated during steelmaking, has considerable cementitious potential and high hardness for use in low-carbon construction materials. However, its widespread utilization is limited by poor volume stability arising from the delayed hydration and expansion of free CaO (f-CaO) and free MgO (f-MgO). This review systematically examines the formation mechanisms of these expansive phases and evaluates four stabilization technologies, including surface modification, high-temperature modification, acid treatment, and carbonation, with respect to their reaction mechanisms, technical advantages, limitations, and engineering applicability. The performance of stabilized SS in cementitious matrices and as construction aggregates is also assessed, together with the corresponding application scenarios. Carbonation is a promising route because it can simultaneously reduce reactive expansive phases and mineralize CO2. However, its stabilization efficiency depends strongly on slag characteristics, reaction conditions, and achievable carbonation depth. Major barriers to industrial application include reliance on single-modification strategies, limited engineering-scale validation, and the lack of unified standards for evaluating volume stability. Future research should focus on synergistic composite technologies, particularly flue-gas carbonation coupled with microbial mineralization, and standardized multi-indicator evaluation frameworks to promote the large-scale, high-value, and low-carbon utilization of SS.