Elucidation of cement hydration mechanisms by time-lapse X-ray computed micro-tomography and direct validation of a continuous hydration model

The hydration process and the associated microstructural evolution of cement paste are complicated and need accurate numerical models to elucidate their complex mechanisms. Most existing models rely on idealised initial microstructures and thus have not been directly and faithfully validated by experiments. Here, time-lapse X-ray computed micro-tomography (mu XCT) was first used to follow the hydration process from 1 to 28 days in two Portland cement paste specimens with water-to-cement ratios of 0.4 and 0.6, respectively. The evolution of microstructure, porosity and hydration degree was tracked at 2.7 mu m voxel resolution and statistically analyzed for each specimen by processing 7 successive 3D mu XCT scans. For each specimen, the day 1 mu XCT image was then segmented and used as the initial image-based microstructure for our recently developed continuous hydration model to simulate the hydration process. The simulated evolution of microstructure, porosity and hydration degree was found in good agreement with the time-lapse mu XCT data. This study represents the first-time direct experimental validation of a hydration model for cement paste, and demonstrates the powerful synergy between mu XCT tests and image-based modelling in elucidating the full hydration process.