Transformation of tricalcium silicate crystalline forms in steel slag under cooling processes and mechanisms for enhancing hydration activity

As a metallurgical bulk solid waste, stockpiled steel slag risks land occupation, as well as soil and groundwater pollution. Its low-activity T₁-C₃S (Ca₃SiO₅) changes to high-activity M₃-C₃S boosted hydration activity and reduces harmful releases <i>via</i> lattice solidification, thereby meeting environmental and industrial needs. To fit "green" metallurgical processes, we achieved T₁-C₃S-to-M₃-C₃S transformation in steel slag by optimizing cooling parameters and preparing and characterizing pure-phase C₃S and studying cooling-induced crystal forms. Meanwhile, first-principles calculations explored the reactivity-electronic structure relationship of C₃S polymorphs. Results indicated increased cooling rate weakened pure-phase C₃S lattice amplitude, and water cooling at the synthesis temperature led to relatively high T₁-C₃S mass fraction. For steel slag under a specific water-cooling temperature, MgO solid solution effectively promoted the conversion of T₁-C₃S to M₃-C₃S to maximize M₃-C₃S content. Also, rapid cooling accelerated steel slag particle cracking, significantly increased pore parameters, and optimized compatibility with construction material feedstock. We optimized the cooling process to achieve T₁-C₃S-to-M₃-C₃S transformation in steel slag, mitigated solid waste secondary pollution, clarified mechanisms, and supported steel slag high-value utilization and upgrading of metallurgical green processes.