Quantitative analysis and phase assemblage of basic oxygen furnace slag hydration

Basic oxygen furnace (BOF) slag from steelmaking could be applied as a binder in building materials, reducing the CO₂ footprint and solid waste, which is relevant for industrial waste management and circular economy. However, its use is mostly restricted because its hydraulic activity is poorly understood. The BOF slag was hydrated in this study, and its reaction products were systematically characterized using XRD, QXRD, and SEM/EDX-based phase mapping. Internal consistency checks of the data were performed between the analytical techniques. The results revealed that the composition of the amorphous hydration products could be identified and quantified, and the main hydration products were hydrogarnets and C-S-H gel. An extended milling process significantly improved the reactivity, and all the major slag phases, including wüstite, participated in the reaction. Brownmillerite formed hydrogarnets during the first 7 days of hydration. The new hydration products contributed to the immobilization of vanadium and chromium. Particle size played an important role in the amount of C₂S reacting, the composition of the hydrogarnets and C-S-H gel, their proportions, and the immobilization capacity. Based on the findings, an overall hydration reaction was developed.