ABSTRACT
Abstract The efficiency of superplasticizer was determinated by measuring the viscosity of cement pastes and the amount of free superplasticizer in cement pastes. Three phases of superplasticizer in cement pastes were distinguished; free, adsorbed on cement particles and absorbed into hydration products. The viscosity of cement paste correlated with the amount of the superplasticizer adsorbed on cement. The superplasticizer absorbed into hydration products was found only in the pastes where superplasticizer was added simultaneously with water. The absorbed superplasticizer did not have any effect on the viscosity of cement paste. The amount of the absorbed superplasticizer depended on the dosage of the admixture and also on the specific surface area of tricalcium alumínate in cement. When superplasticizer was added simultaneously with water white foam was formed on the surface of the cement paste. This foam was identified mainly as ettringite. Also, a synthetic ettringite was prepared in the presence of superplasticizer. There was a clear limit in the content of the superplasticizer bound by the ettringite. Below the mole ratio one between sulphonate and ettringite all superplasticizer was practically bound into ettringite but it appears to be impossible to bind more than one mole of sulphonate to a mole of ettringite. Keywords: Absorption, addition time, adsorption, cement paste, superplasticizer, viscosity,
1 Introduction
It is widely agreed that the water reduction effect of the superplasticizer is caused by improved dispersion of the cement grains in the mixing water. The flocculation of
cement particles is decreased or prevented, and the water otherwise immobilized within the floes is added to that in which the particles can move [1].
