Diffraction-enhanced Computed Tomography of Cement Pastes: 3D Imaging of the Nucleation Processes

The properties of cementitious materials are related to the microstructure of their binder matrix, which forms by a sequence of dissolution-precipitation reactions converting the clinker phases into hydrates, among which the main hydration product is calcium silicate hydrate (C-S-H). Here, we monitor non-invasively the evolution of the cement paste microstructure during hydration by synchrotron X-ray diffraction-enhanced computed micro-tomography (XRD-CT). This innovative technique yields phase-resolved images of the hydrating cement paste at different stages, which are combined to map the sites where dissolution and precipitation processes occur. The results indicate that the nucleation mechanism of C-S-H changes when cement hydrates in the presence of poly-carboxylate ether (PCE) superplasticizers, which are commonly used to control the paste rheology. The observed change is essential to understand the development of the cement microstructure and to provide a direct link between the reaction kinetics and the physico-mechanical properties of the system.