X-ray near-field ptychographic nanoimaging of cement pastes

The hydration processes of Portland cements (PC) and blends are complicated as there are many components with great heterogeneity at different length scales. Thus, 3D nanoimaging techniques with high spatial resolution and scanning large fields of view are needed. Here, synchrotron X-ray near-field ptychographic tomography is used to investigate four pastes within 0.2 mm thick capillaries: PC with CaCl₂, PC hydration enhanced by C-S-H nucleation seeding, PC partly substituted with metakaolin, and PC partly substituted with metakaolin and limestone. Data analysis emphasis has been placed on the characterization of amorphous components: (i) C-S-H and C-A-S-H gels; (ii) iron aluminium siliceous hydrogarnets; (iii) metakaolin; and (iv) aluminium carboaluminate, AFm-like. Synchrotron ptychotomography yields electron density and absorption coefficient tomograms and the resulting bivariate plots are instrumental for characterising these amorphous components. The attained spatial resolution, ∼220 nm, with very good contrast allowed us to determine nanofeatures including mass densities and spatial distributions of amorphous components. For instance, the C-S-H gel mass density differences between the two type of accelerated pastes are detailed.