INFLUENCE OF FLUORIDE ION ON THE HYDRATION IN CEMENT PASTE CONTAINING RETARDER

Abstract

Retarders（ex. Sucrose）are used to control the hydration of cement in concrete. The effect of retarder may change in low-temperature calcined cement containing fluoride, but there is no research about this point. In this study, authors investigated the influence of fluoride addition on the hydration, the specific surface area of the solid phase, and the amount of adsorbed retarder in cement paste containing retarder. Sucrose, sodium gluconate, dextrin, and K₃PO₄ were used as the retarder. The hydration of cement with sucrose was less retarded in cement paste with KF, i.e. the effect of sucrose was weakened by KF addition. In contrast, the hydration of cement with sodium gluconate, dextrin, or K₃PO₄ was more retarded in cement paste with KF, i.e. the effect was enhanced by KF addition. Since the specific surface area and the amounts of adsorbed organic retarders increased with KF addition, it is supposed that some types of fine particles were generated by KF addition and retarders adsorbed to the particles. It is supposed that the sucrose’s preferential adsorption to the particles decreased the amount of adsorbed sucrose on cement particles and caused the decrease in the effect of sucrose on the hydration. In contrast, the increase in the effect of sodium gluconate, dextrin, and K₃PO₄ cannot be explained by the preferential adsorption. It is supposed that the increase in the effect relates to the synergy between the effect of these three retarders and the effect of fluoride precipitation on cement particles.