Microstructure and hydration of interstitial in clinkers produced over molten steel

Scalable electrical production of clinker is possible under reducing conditions, and the reactivity of C₃A produced in such conditions has only been superficially described. We examined electric clinkers made over molten steel with a range of fineness and compared them against commercial clinkers. Using x-ray diffraction, calorimetry, and backscattered electron microscopy/image analysis, we investigated the roles of morphology, crystal structure, and phase interaction. Shortage of Fe³⁺ ions in the interstitial in electric clinkers makes its C₃A more reactive like white cements and synthetic systems. In the presence of ferric oxides, ferrite is formed and the concentration of dissolved Fe³⁺ ions in C₃A increases. The kinetics of C₃A hydration are hindered both by the ferrite phases intermixing with the C₃A phase, hence acting as a physical barrier for dissolution, and by Fe³⁺ ions dissolving in C₃A, thereby reducing its intrinsic reactivity. Although this higher reactivity of C₃A requires more gypsum to ensure proper sulfation, this can be managed by controlling fineness and blending with supplementary cementitious materials.