Chemical Composition of C-S-H Gel Formed in the Hydration of Calcium Silicate Pastes

The chemical and physical compositions of C-S-H formed in paste hydration of C₃S cured at 4°, 25°, and 65°C and of C₂S and a C₃S/C₂S blend cured at 25°C were studied using quantitative X-ray diffraction analysis (QXDA), extraction, and thermal effluent gas analysis (TEGA) to determine the free CH content. The amount of CH determined by extraction is greater than or equal to that determined by QXDA. The difference between the two results increased with the H₂O surface area of the paste, indicating the existence of adsorbed CH in the form of Ca²⁺ and (OH)^? ions which cannot be measured by QXDA and suggesting that the extraction method is better for estimating the composition of C-S-H.