Insight into discrepancies in hydration reactivity of ferrite phase in Portland cement clinker and synthetics

The ferrite phase (4CaO center dot Al2O3 center dot Fe2O3 or C4AF), as one of the cardinal mineral phases intrinsic to Portland cement (PC) clinker, is conventionally ascribed a subdued hydration reactivity within the PC clinker system. However, the separately synthesized pure ferrite phase often shows robust hydration performance, leading to a long-standing academic discourse regarding its hydration reactivity. Elucidating the differences in the hydration reactivity of the ferrite phase assumes paramount significance, contributing to attain an optimal performance in high ferrite PC. The principal objective of this study resides in unraveling the intrinsic distinctions in the hydration reactivity among ferrite phases subject to diverse synthesis conditions. The outcomes show that the pure ferrite phase surpasses its counterparts extracted from cement clinker (both from laboratory synthesized and industrial clinker) in terms of hydration reactivity. Notably, the pure ferrite phase can be successfully synthesized at 1350 degrees C, a temperature below the customary sintering threshold for PC clinker (typically at 1450 degrees C). This divergence of synthesized temperature contributes to the partial dissociation of the ferrite phase and a consequent reduction in its Al/Fe ratio. Furthermore, the diminished hydration reactivity of the ferrite phase can also be attributed to the transition of [Al/FeO4] tetrahedral configurations to [Al/FeO6] octahedral arrangements within the crystal structure, which is confirmed by density functional theory simulations. This work provides a new perspective on the reactivity of ferrite phase, which contribute new guidance for the development of PC clinker with high hydration reactivity of ferrite phase.