Influence of alkali sulphates on the rheological properties of tricalcium silicate pastes.

Using simultaneously the dynamic mode rheometry and the conduction calorimetry it has been possible to specify the effect of electrolytes on the rheological properties of tricalcium silicate pastes. The effect of Na2SO4 and K2SO4 on the mechanical and chemical evolutions of tricalcium silicate pastes was studied and compared with NaOH, KOH and gypsum effects. For alkali hydroxydes a decrease in the moduli of the paste, i.e. a negative effect of electrolytes on the mechanical properties of the paste, is observed for a given quantity of hydrates formed. This negative intrinsic effect can be linked to other studies on the nature of the forces responsible for setting. For alkali sulphates an increase in the moduli of the paste is observed for a given hydration rate for concentration lower than 0.3 M but for higher concentration there is a negative effect. As this negative effect is absent with calcium sulphate, it can be attributed to the only presence of alkaline ions.