Impacts of Phosphoric Acid and Phosphates on Hydration Kinetics of Portland Cement

The impacts of phosphoric acid and phosphates on the hydration kinetics of Portland cement were investigated via monitoring isothermal heat evolution of cement hydration,the measurement of Zeta potential and the elemental concentrations in the aqueous phase of the hydrating cement pastes.The results indicate that phosphoric acid and phosphates can prolong the induction period of cement hydration,and decrease the hydration rate during the acceleration period.The impacts of phosphoric acid and phosphates on the hydration kinetics of portland cement could be due to the formation of the precipitates covering the surface of the hydrating cement grains,which reduced the dissolution rate of cement phases and affected the nucleation process of hydrates.The Zeta potential measurement and aqueous ion concentration tests of cement pastes exhibited the formation of the precipitate covered on cement surface.