Interaction of water vapour with anhydrous cement minerals

Abstract

The prehydration of industrial cements (CEM I 52·5 R and API Oilwell Class G) and pure cement clinker minerals (C₃S, cubic C₃A, orthorhombic C₃A, C₄AF) has been studied at 60 and 85% relative humidity using in situ X-ray diffraction (XRD), calorimetry, environmental scanning electron microscopy and X-ray photoelectron spectroscopy. This combination of techniques identifies the key components involved in the surface prehydration process. Prehydration of cement leads to dramatic retardation of hydration. in situ XRD shows the retardation of portlandite formation after prehydration, supporting the calorimetry results. X-ray photoelectron spectroscopy and ESEM investigations show surface modification after prehydration for C₃S, C₃A and doped C₃A (4%Na₂O). Prehydration of cement leads to modification of the surface area and surface charge, which can strongly influence the reactivity of bulk cements. This is relevant to the quality of cement during storage.