Influence of Sulfate lon on Adsorption Characteristics and Steric Hindrance Effects of Polycarboxylate-Based Superplasticizers.

Abstract

We discussed the influence of sulfate ion on the fluidizing mechanism of polycarboxylate-based superplasticizers (PC) in cement paste by considering adsorption characteristics of PC and steric hindrance effects. The fluidity, amount of adsorbed PC on cement particles and sulfate ion concentration in aqueous phase were measured using cement paste with some dosages of PC and alkali sulfate. The fluidity of cement paste decreased with increasing alkali sulfate. Clear correlation between the amount of PC adsorbed and the fluidity did not obtain. The fluidity decreased linearly with increasing sulfate ion concentration. We had showed that sulfate ion reduced the thickness of adsorbed PC and steric hindrance effects. The results of this study suggested that sulfate ion reduced the fluidity of cement paste mainly because of reducing steric hindrance effects with any dosage of PC.