In-situ observations of tricalcium silicate formation in modified electric arc furnace slag under different temperature regimes

Electric Arc Furnace (EAF) steelmaking slag is a significant byproduct generated during EAF steelmaking and utilizing EAF slag for cement clinker production potentially offers both economic and environmental benefits. The formation of tricalcium silicate (C₃S - 3CaO∙SiO₂) in EAF slag, the principal hydration phase in Portland cement clinker, plays a critical role in enabling the utilization of EAF slag for cement production. In this study, we conducted in-situ observations of C₃S formation and slag crystallization in modified EAF slags under varying temperature regimes. The results indicated that rapid cooling from 1600 °C to room temperature at a cooling rate of -1500 K/min °C led to the formation of a layered structure consisting of dicalcium silicate (C₂S) and a calcium ferrite (CF) based slag. The process of C₃S crystal growth was observed under both isothermal and non-isothermal conditions. Under isothermal condition with low degree of undercooling, the C₃S crystals predominantly formed equiaxed shapes, whereas higher undercooling levels promoted the development of dendrites C₃S. The growth of C₃S crystals is accompanied by the transformation of C₂S via the reaction: C₂S (s) + CaO (l) → C₃S (s). Extending the holding time at 1600 °C enhanced C₃S nucleation, resulting in a higher C₃S content in the slag.