The effect of the addition of fly ash on the hydration of cement

The effect on the hydration of cements of a 30% replacement by fly ash has been studied by a combination of techniques including calorimetry, thermogravimetry (accompanied by DTA and DTG), X-ray diffractometry and electron microscopy.The development of microstructure has been studied during the hydration of the neat and fly ash cements.The progress of the reaction has been monitored using calorimetry and X-ray diffraction.By relating these results, the effect of the fly ash on the hydration of major cement components can be deduced.In fly ash cement pastes a noticeable change in the amount of calcium hydroxide and the strength occurs after 7 days hydration at 20 °C.The pozzolanic reaction is accelerated as C3S content in the cement is increased.The decrease in calcium hydroxide content followed dissolution of the fly ash surface, and the reaction augments the compressive strength.The increase of the hydration temperature has advanced and enhanced hydration of all the cement components and has a particularly strong effect on the pozzolanic reaction.