Effect of Comb type Superplasticizers on hydration kinetics of Industrial Portland cements

摘要

Comb type Superplasticizers are widely used in concrete formulations because of their efficiency to improve initial workability of concrete without water addition and to lengthen workability retention over time. Their dispersing effect is linked to the adsorption of polymer on cement grain surfaces which leads to steric repulsion effect. However, their use in concrete is often associated to a delay on cement hydration kinetic, which can cause in some cases significant undesired retardation of concrete setting time. In this paper, the study about the effect of two commercial polycarboxylate ether (PCE) superplasticizers on the hydration kinetic of several Ordinary Portland cements is presented. The cements differ mainly by their alkaline level and their tricalcium aluminate amount, while the superplasticizers differ by the type of their backbone. The investigation is focused on the delay induced by superplasticizers on acceleration period, obtained thanks to calorimetric measurements on cement paste. Results showed first that for both PCE superplasticizers, the delay obtained at similar dosage changes in function of the chemistry composition of cement. Nevertheless, these variations are different in function of the PCE superplasticizer used. With one PCE superplasticizer, the behaviour is explained by the fact that the delay induced is correlated to the initial adsorption of the superplasticizer for most of cements, while with the other PCE superplasticizer, it appears that the delay induced is correlated to the quantity of superplasticizer remaining in solution.