Ptychographic X-ray computed tomography analysis of cement pastes

Abstract

Ptychographic X-ray computed tomography provides 3D electron mass density and attenuationcoefficient distributions of unaltered cement pastes with an isotropic resolution below 100 nm. Thisimaging technique allows quantitatively distinguishing between different components with very similarabsorption contrast.Samples were measured at the cSAXS beamline: i) a neat Portland Cement (PC); ii) a PC-CC blend:80 wt% of PC and 20 wt% of CaCO3, and iii) a PC-FA blend: 70 wt% of PC and 30 wt% of fly ash. Themain aim of this study is to have a better insight of the microstructure of theamorphous/nanocrystalline gels with submicrometer spatial resolution. It is worth noting that it ispossible to determine the gel mass density and water content within the attained 3D resolution (about100 nm). Here, we focused on the spatial distribution of the different components and in the variation of theelectron density values which are very related to the mass density values. Special attention is paid tothe density values of the amorphous (or nanocrystalline) components. The electron and mass densityvalues of the C-S-H gel for three pastes are thoroughly analyzed. The density values range from 2.05-2.10 g·cm-3 for high density C-S-H gel for neat PC and PC-CC pastes to 1.80 g.cm-3 for low densityC-S-H gel in PC-FA paste. The density value of poorly crystalline iron-siliceous hydrogarnetcomponent, d=2.52 g·cm-3, has also been determined.A summary of our ongoing research focused on the analyses of cement pastes by synchrotron PXCTis reported and discussed