Study on the effect of VMA admixture for concrete cured under different conditions on air permeability and sorptivity

Abstract

• Application of VMA resulted in a decrease in compressive strength of concrete in most cases. • VMA resulted in an increase in sorptivity with increasing admixture dosage regardless of the specimen curing applied. • The effect of VMA application on concrete air permeability is negative in most cases. • The use of the plasticiser cause an elongation of initial setting time resulting from retardation of hydration processes. • In general, the same kinds of hydration products were identified in all the hardened samples after long time of hydration. The main goal of this research was to determine the effect of viscosity modifying agent admixture and specimen curing conditions on air permeability, sorptivity and mechanical properties of concrete and determining the effect of the admixture on the intensity of early cement hydration and the phase composition of the hardened cement paste. Used admixtures decreases 28 day compressive strength and the reduction depends on the kind of cement and curing conditions. VMA admixture did not significantly affect the sorptivity of the CEM I series, while in the case of the CEM III series, the sorptivity increased with increasing admixture dosage. The effect of VMA application on concrete permeability is negative in most cases and is most evident in the specimens tested after drying at 65 °C. The rate of heat release during hydration and the related parameters depend primarily on the type of cement, and in the case of admixtures, the use of plasticiser has a much greater effect than VMA. In general, the same kinds of hydration products were identified in all the hardened samples after long time of hydration. The quantitative composition of hardened cement paste depends mainly on the kind of cement used. It was found that the presence of admixtures had a greater impact on the quantitative composition of the cement paste in the case of samples made with CEM I.