Quantitative Analysis of Reaction Degree of Fly Ash–Cement Composite Cementitious Materials

The reaction degree of fly ash–cement composite cementitious material under hydrothermal conditions was studied by measuring the loss on ignition, acid-insoluble residua, calcium oxide, silicon oxide, and effective calcium content of hardened paste. The main crystal hydration product of tobermorite in hardened paste was quantified by QXRD. The effects of quicklime (CaO) content, the fineness of raw materials, and the reaction temperature were discussed. The results show that increasing the quicklime content is beneficial to improving the reaction degree, and the calcium to silica ratio of reaction products is between 1.47 and 1.89. The hydrothermal reaction activity of fly ash is higher than that of ground quartz sand, and the particle fineness of raw material has an obvious influence on the reaction degree. When coarse sand is used, the calcium to silica ratio of reaction products is 3.42, indicating that hydrated calcium silicate gel is the main product. The reaction degree increases with the increase of reaction temperature, and the transformation from tobermorite to xonotlite occurs at 210 °C. The results of QXRD show that there is approximately a positive linear correlation between the tobermorite content and the reaction degree (or acid-insoluble residua).