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H NMR has been used to characterise white Portland cement paste incorporating 10 wt.% of silica fume. Samples were measured sealed throughout the hydration without sample drying. Paste compositions and C-S-H characteristics are calculated based on H NMR signal intensities and relaxation analysis. The results are compared with a similar study of plain white cement paste. While the presence of silica fume has little influence on C-S-H densities, the chemical composition is impacted. After 28 days of sealed hydration, the Ca/(Si + Al) ratio of the C-S-H is 1.33 and the H2O(Si + Al) ratio is 1.10 when 10% of silica fume is added to the white cement. A densification of the C-S-H with time is observed. There are no major changes in capillary, C-S-H gel and interlayer pore sizes for the paste containing silica fume compared to the plain white cement paste. However, the gel/interlayer water ratio increases in the silica fume blend.

The nanoscale morphology of, and pore water interactions in, calcium silicate hydrate (C-S-H), the active component of cement, remain uncertain. H nuclear magnetic resonance (NMR) can fully characterize the nanoporosity of C-S-H in as-prepared material without the need for damaging sample drying. We use NMR to follow the density of C-S-H in sealed cured pastes as a function of degree of hydration (α) and water to cement ratio. We show clear evidence for C-S-H densification. The C-S-H "solid" density, exclusive of gel pore water, slightly decreases from ρ = 2.73 g/cm at α ≈ 0.4 to 2.65 g/cmat α ≈ 0.9 due to an increase in the number of layers in the nanocrystalline aggregates. In the same range, the C-S-H "bulk" density, including gel water, increases from around 1.8 to 2.1 g/cm. The increase corresponds to a transition from growth of low-density product containing gel pores to higher density product devoid of gel pores. We update Powers' classical model from 1947. In contrast to the single "hydrate" of Powers, NMR differentiates between C-S-H and calcium hydroxide and separates out the interlayer water within the C-S-H. It shows a clear nonlinearity in the growth of the different fractions with α. © 2012 American Chemical Society.