A Novel "Two-Step" gamma -> alpha '(L) -> beta Phase Transformation Method for Dicalcium Silicate in AOD Slag for Improving Hydration Activity

Regulating the phase transformation of gamma -> beta in dicalcium silicate (C2S) can effectively improve the hydration activity and recycling rate of AOD slag; however, the evolution law for gamma -> beta in C2S has not been extensively investigated. In this study, a novel "two-step" gamma -> alpha '(L) -> beta phase transformation method in C2S was designed based on the study of the pure C2S 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 gamma-C2S grains to lamellar-structured beta-C2S grains, exhibiting the trend of interlaminar peeling accompanied by expansion of the particle volume and leading to the appearance of macroscopic lamellar cracking in beta-C2S particles. In addition, the beta-C2S mass fraction in AOD slag treated by water cooling at 680 degrees 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.