EFFECT OF LIMESTONE ON THE CEMENT PASTE HYDRATION IN THE PRESENCE OF POLYCARBOXYLATE SUPERPLASTICISER

The addition of certain ingredients in conventional concrete is essential for improving rheological properties of this construction material. The effect of limestone and superplasticisers on the hydration kinetics of self-compacting concrete (SCC) was investigated on cement paste scale. These additives interact mostly with cement paste, since aggregates are considered to be inert materials. The understanding of the effect of these mineral and chemical additives on the hydration kinetics of cement paste is the key to design a self-compacting concrete with great properties. Four CEM I 52.5 N Portland Cements, limestone (LS) and one type of superplasticiser (SP) were used in this research. The hydration kinetics were evaluated by monitoring the storage modulus growth and different coefficients of a self-acceleration kinetics equation were used to depict the effect of different concentrations of SP with and without the optimum concentration of limestone (30%) on the hydration kinetics of cement pastes. It was observed that the rate of hydration increased with the increase in SP concentration depending on the cement used. The addition of limestone in the superplasticised cement paste significantly retarded the hydration kinetics for all four cements. The rheological behaviour of self-compacting cement paste was found to be very sensitive to the chemical and physical properties of the cements used.