2002

Effect of an adimixture based on polycarboxylates on the rheology and setting time of cement portand pastes

AUTHORS

Francisca Puertas, Mª del Mar Alonso, Tomás Vázquez
Instituto de Ciencias de la Construcción Eduardo Torroja (CSIC)

ABSTRACT

The effect of the dosage of a superplasticizer admixture based on polycarboxylateS on the setting times and rheological properties in CEM I 42.5 R and CEM III/B 32.5 N cement pastes have been studied.

When the admixture dosage increases a lengthening of the beginning of the setting time is produced. A lineal relationship exists among that beginning setting time and the admixture dosage. Mathematical equations that describes the process for both cements have been determined, so that it is possible to predict the beginning of the setting time in cement pastes containing an admixture based in polycarboxylates, depending on their dosage.

The results obtained through the minislump tests coincides with the evolution of the value of the rheological parameters (yield stress and plastic viscosity). The flowability effect of the superplasticizer admixture based on polycarboxylates is much marked in CEM III/B cement pastes that in CEM I pastes. Likewise, the best dosage from the point of view of flowability for both cements, is located between the 0.3 and 0.5%. Higher contents of admixtures don't produces substantial modifications in the rheological properties.