Accelerated carbonation of steel slag: A review of methods, mechanisms and influencing factors

The disposal of steel slag in landfills not only squanders precious landfill resources but also results in significant environmental contamination. Steel slag can be used to replace cement and natural aggregates in concrete. Nonetheless, utilizing untreated steel slag directly presents a substantial hazard to the structural characteristics and durability of concrete. To avoid this problem, study on accelerated carbonation of steel slag as construction materials has been extensively conducted. This review paper begins by introducing the classification and physicochemical properties of steel slag; it then describes the typical approaches of steel slag carbonation, including direct carbonation (dry carbonation, wet carbonation) and indirect carbonation (pH-swing, microbial carbonation), along with their processes and carbonation mechanisms. Furthermore, based on the reviewed literature, the influences of various reaction parameters such as reaction time, liquid-to-solid ratio, temperature, additives, CO2 concentration, pressure, pH on carbonation effectiveness are analyzed. Also, the impact of carbonated steel slag on the micro-pore structure, stability, workability, and mechanical properties of concrete is discussed. Finally, the challenges and future work of using carbonated steel slag as construction materials are provided.