Variation in the Composition of C-S-H Gel in Portland Cement Pastes Cured at Various Temperatures

Variation in the composition of C-S-H gel, the main hydration product of portland cement, cured at various temperatures, was studied using scanning electron microscopy with energy dispersive X-ray spectroscopy. Samples of two cement pastes were cured isothermally under water at 10°, 30°, and 60°C for one year. For the inner-product C-S-H gel of both cement pastes, increased curing temperature decreased the Ca/Si and Al/Ca ratios, but increased the S/Ca ratio. The Al/S and (Al + Fe)/S ratios decreased with increased curing temperature. Sulfur, probably in the form of sulfate ions, could be sorbed by the C-S-H gel at higher temperatures.