A Novel “Two-Step” γ → α′L → β Phase Transformation Method for Dicalcium Silicate in AOD Slag for Improving Hydration Activity

Regulating the phase transformation of γ  →  β in dicalcium silicate (C 2 S) can effectively improve the hydration activity and recycling rate of AOD slag; however, the evolution law for γ  →  β in C 2 S has not been extensively investigated. In this study, a novel “two-step” γ  →  α ′ L  →  β phase transformation method in C 2 S was designed based on the study of the pure C 2 S phase at a nonequilibrium state in the low- and middle-temperature ranges. The “two-step” method can be used to realize the transformation from needle-like nanostructured γ -C 2 S grains to lamellar-structured β -C 2 S grains, exhibiting the trend of interlaminar peeling accompanied by expansion of the particle volume and leading to the appearance of macroscopic lamellar cracking in β -C 2 S particles. In addition, the β -C 2 S mass fraction in AOD slag treated by water cooling at 680 °C reaches a maximum value of 47.5 wt pct, while the treated AOD slag presents abundant holes and defects, which can effectively enlarge the hydration contact area.