Characterization of water sorption cycle in the cement microstructure of controlled oxide composition

This thesis investigates the water vapour sorption behaviour of samples with maximized calcium-silicate-hydrate (C-S-H) content. Primarily, the role of heterogeneous and homogeneous cavitation has been studied during the drying of cementitious materials. Classical nucleation theory has been used to investigate the parameters affecting cavitation pressures. The volume balance analysis showed that homogeneous cavitation should occur in the gel pores of the inner product of the C-S-H. The results also indicate that it is crucial to consider the role of cavitation when using desorption isotherms for determining the pore size distribution. Further, the effect of the hydration temperature on the microstructure of the samples has been investigated by analysing their water desorption behaviour. The amount of capillary and gel water content determined using water desorption isotherms were found to be in good agreement with the mass balance calculations. These mass balance calculations have been carried out by using multiple characterization techniques including X-ray diffraction (XRD), thermogravimetric analysis (TGA), proton nuclear magnetic resonance relaxometry (1H NMR), and scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX). Thereafter, the water vapour desorption behaviour of the C-S-H samples synthesized using three different techniques has been compared. The first technique involved preparing a single-phase C-S-H using double decomposition and dropwise precipitation. The Gibbs Energy Minimization Software (GEMS) has been used to simulate the relationship between the calcium to silica (Ca/Si) ratio of synthetic C-S-H and the pH, as alkalis are introduced. In the second technique, the reactive belite binder has been hydrated to produce samples with maximized C-S-H content and the Ca/Si ratio has been varied using supplementary cementitious materials. The third technique involved mixing white cement with silica fume so that the content of C-S-H is maximized at the expense of portlandite. Finally, the moisture absorption behaviour of the samples has been investigated using static as well as dynamic tests. Disjoining pressure-based concept of excess surface work has been used to explain the absorption behaviour. The sorption isotherms of Mobil Composition of Matter No. 41 (MCM-41) have been used to study the role of surface interactions on water sorption. The sorption behaviour of isopropanol as an adsorptive has also been discussed