Effects of pre-hydration on hydraulic properties on Portland cement and synthetic clinker phases

The ageing of cements (CEM I 52,5 R and API Oilwell Class G) and also the pure cement clinker minerals (C3S, pure C3A, Na2O-doped C3A, C4AF and calcium sulphate hemihydrate) has been studied at 60% and 85% RH using in-situ XRD, calorimetry, ESEM, XPS and FTIR-ATR. This combination of techniques has identified the key components involved in the surface pre-hydration process. Pre-hydration of cement leads to retardation of hydration. In-situ XRD shows the retardation of Portlandite formation after prehydration, which explains the heat development seen via calorimetry. XPS and ESEM investigations show surface modification after prehydration for C3S, C3A and doped C3A (4% Na2O). Pre-hydration of cement leads to modification of the surface area and surface charge, which can strongly influence the reactivity of bulk cements and their interaction with admixtures. This is relevant to the quality of cement during storage.