Analytical Electron Microscopy of Cement Pastes: III, Pastes Hydrated for Long Times

Abstract

Analyses of 131 particles of C‐S‐H in several mature tricalcium silicate pastes hydrated for 1 to 30 years gave a mean Ca/Si ratio of 1.46 with a range of 1.2 to 1.8. Similar analyses of 152 particles in mature cement pastes hydrated for 2 to 3 years gave a mean Ca/ Si ratio of 1.53 with a range of 1.0 to 2.8. Taken together with similar, previously published data for younger pastes, these findings indicate that the mean Ca/Si ratio does not change significantly after 1 day in tricalcium silicate pastes but decreases significantly with time in cement pastes; after several years, the mean Ca/Si ratios are similar in the two cases, despite the presence of other components in the C‐S‐H formed from cement. For the C‐S‐H of cement pastes, the mean Al/(Ca plus; Mg) and Fe/(Caplus;Mg) ratios increase with time but the mean S/(Caplus;Mg) ratio decreases. The composition of the AFm phase does not change greatly after 28 days.