Working mechanism of superplasticizer in cement paste with fluoride ion

Abstract

Low-temperature calcination for cement manufacturing by the addition of fluoride compounds has been researched by many investigators. Although it is possible that fluoride ions elute to the suspension after calcination, there are very few studies about the influence of fluoride ion on the fluidity of cement paste with superplasticizer. This paper describes the influence of fluoride ions on the adsorption mechanism of polycarboxylate based superplasticizer in cement paste. When the amount of KF was increased, the viscosity of the cement paste with superplasticizer and the amount of adsorbed superplasticizer increased. The fluidity with the polycarboxylate based superplasticizer containing more functional groups was more susceptive to KF addition and the amount of adsorbed superplasticizer was larger for the polycarboxylate based superplasticizer containing more functional groups. The specific surface area increased with KF addition. In the case of no KF addition, the hydration of alite was retarded by the addition of polycarboxylate based superplasticizer. In contrast, in the case of KF addition, the hydration of alite was not retarded by the addition of superplasticizer. It is supposed that some types of fine particles were generated by KF addition and the fine particles deprived the cement particles of superplasticizer.