4D in situ monitoring of the setting of α plaster using synchrotron X-ray tomography with high spatial and temporal resolution

This paper is dedicated to the in situ follow up of the setting of an alpha plaster using synchrotron X-ray tomography, with a high spatial resolution, down to 0.3 mu m (0.16 mu m voxel size), and a high time resolution with a scan every 30 s. This combination of spatial and time resolution is amongst the best reported in the literature so far and is of particular interest for the study of moderately rapid transformation of the microstructure at a small scale. It enables to characterize both the dissolution of hemihydrate particles and the precipitation of gypsum crystals. A dissolution rate for the hemihydrate particles is determined, in good coherence with previous work on beta plaster using lab X-ray tomograph. A thickening of gypsum crystals with hydration time is also noted. A quantitative analysis of hydration is performed through the calculation of a microstructural degree of reaction from the X-ray tomography volumes, after peak deconvolution of the gray value histogram at different hydration times.