Effects of sulfates on adsorption-dispersing polycarboxylate behaviour with different carboxylic densities

Abstract

The adsorption behaviour and dispersing capability of structurally different polycarboxylate superplasticisers (PCEs), with various carboxylic densities, was investigated in the presence of sulfates. The effect of sulfates on the early cement hydration evolution in the presence of PCEs with different carboxylic densities was also analysed. It was found that a higher proportion of carboxylate groups in the PCE backbone contributed to more intense adsorption of PCE onto cement grains, which contributed to lower sensitivity to the competitive adsorption of sulfate ions and hence produced higher resistance to the negative impacts of sulfates on fluidity and zeta potential. The addition of sulfates partially eliminated the retardation effect of PCE on cement hydration and boosted the nucleation of hydrates with increased cumulative hydration heat and higher heat evolution peak in the acceleration period. A higher concentration of sulfates led to a greater acceleration effect on cement hydration. However, PCEs with higher carboxylic density showed enhanced resistance to the impacts of sulfates on cement hydration.