Examining microstructural evolution of Portland cements by in-situ synchrotron micro-tomography

The application of synchrotron radiation X-ray computed micro-tomography (SR X-μCT) as a non-invasive approach to the microstructural investigation of Portland cement binders during hydration is presented. The two- and three-dimensional µm-scale imaging of undisturbed samples at hydration ages from ~1.5 h to 3 days is used to obtain a direct visualization of the spatial and temporal relationships between different cement paste components. The microstructural evolution of two cementitious systems during the early stages of hydration is successfully monitored from the comparison of tomographic slices and volumes, clearly showing the progressive growth of hydration phases; the changes in the amount of porosity and unreacted clinker are also quantified. Some critical issues related to the experimental setup and data processing are addressed and discussed as well. Furthermore, a simple procedure to estimate the mean X-ray absorption coefficient of cement pastes from X-ray radiographs is illustrated. The results confirm the potentialities of synchrotron-based X-ray computed micro-tomography for the three-dimensional investigation of µm-scale modifications in hydrating cement pastes with an adequate time resolution, thus providing a real in-situ monitoring of the microstructural evolution of such complex materials.