Direct Imaging of Nucleation Mechanisms by Synchrotron Diffraction Micro-Tomography: Superplasticizer-Induced Change of C–S–H Nucleation in Cement

The properties of cementitious materials are related to the microstructure of their binder matrix, which develops, during cement hydration, by a sequence of dissolution–precipitation reactions. Here, microstructural development is monitored during hydration by synchrotron X-ray diffraction-enhanced computed microtomography (XRD-CT). This innovative, noninvasive technique yields images of the crystallographic phases present in the hydrating cement paste at different stages, which are combined to map the sites where dissolution and precipitation occur. The results indicate that the nucleation mechanism of the main hydration product (a calcium-silicate hydrate commonly referred to as C–S–H) changes in the presence of polycarboxylate ether (PCE) superplasticizers. 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 physicomechanical properties of the system.