Influence of silica fume on the microstructure of cement pastes: New insights from 1H NMR relaxometry

1H 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 1H 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.