Abstract
1H nuclear magnetic resonance (NMR) relaxometry is used to characterise cement paste microstructure from the stand point of the pore water. Attention focuses primarily on pore-water interactions and the morphology of calcium-silicate-hydrate (C-S-H), the active phase of cement paste. The method is non-destructive and non-invasive. NMR allows the quantitative separation of water by confinement. The first pore-type resolved sorption isotherm of any cementitious material is measured. This provides insight into water location during drying and wetting. The C-S-H interlayer and gel pore sizes are estimated based on T2 relaxation times (0.94 ± 0.04 and 3.1±0.2nm) and amplitudes of relaxation components during drying (1.5 ± 0.3 and 4.5 ±1.6 nm). The specific surface areas are also evaluated. The evolution of nanoscale porosity for underwater cured white cement pastes, with and without silica fume addition, are determined during hydration and as a function of temperature in the range 10°C to 60°C. The C-S-H density and chemical composition are evaluated using NMR supported by X-ray diffraction and thermogravimetric analysis. The calculated C-S-H ‘solid’ density and composition, excluding gel pore water, in never-dried 28 days old white cement paste are 2.64 ± 0.03 g/cm3 and Ca1.53±0.02(Si0.960. 01,Al0.04±0.01)03.51±0.02(H2O)1.92±0.05. The C-S-H ‘bulk’ density, including gel pore water, is 1. 90±0.02 g/cm3. Increase of curing temperature does not alter the Ca/(Si+Al) ratio. However, a significant decrease in C-S-H water content and increase in density is observed and attributed to the fewer locally stacked C-S-H layers. NMR relaxation activation energies are estimated. Insight into the mechanism of water-isopropanol exchange, used for arresting cement hydration, is provided. NMR shows that the exchange occurs in a selective manner with no C-S-H interlayer water alteration. The connectivity of the C-S-H interlayer and gel pores with interhydrate-capillary pores is evidenced.