Compatibility between polycarboxylate-based admixtures and blended-cement pastes

Abstract

Compatibility between three structurally different PCEs and four commercial cements: one non-blended cement and three blended cements, was studied by adsorption, zeta potential, rheological and calorimetric methods.

According to the adsorption curve results, the higher the percentage of carboxylates groups in the admixture, the more intensely it is adsorbed on cement pastes. Moreover, admixtures were shown to be adsorbed by the additions as well, being most effectively adsorbed in limestone.

From the rheological point of view, the optimum carboxylate group/ester group ratio for the admixtures used in the present study was found to range from 0.7 to 1.2. The fluidizing effect of the admixtures on cement pastes is conditioned by the presence of mineral additions. Despite the low adsorption rates of the admixtures in slag-blended cements, the inclusion of PCEs generated the steepest declines in the rheological parameters.

The delay of admixtures on cement hydration intensifies with rising PCE dosage. This admixture-mediated retarding effect was also observed to vary depending on the nature of the addition, and was most intense in slag-blended cement.