Study on the Chemical Activation of Fly Ash in Fly Ash Blended Portland Cement System

Comparative study was carried out on the effect of three chemical activators with different anions on the activation of fly ash in fly ash-Portland cement clinker system by means of physical property test and XRD analysis.Results show that addition of these three chemical activators in an appropriate dosage promotes the activation of fly ash significantly.The optimum dosage is NaOH 0.5% at which the increase of 3 d and 28 d compressive strength of the cement mortar is 6.8% and 7.7% respectively,and Na2SO4 3.0% at which the increase of 3 d compressive strength is 18.2%,and Na3PO4·12H2O 2.0% at which the increase of 28 d compressive strength is 17.7%.XRD analysis reveals that addition of the chemical activators causes reduction of the intensity of the diffraction peaks responsible for quartz in fly ash and Ca(OH)2 in hardened cement paste,which suggests that the reaction between Ca(OH)2 originated from the hydration of cement and the acidic oxides originated from fly ash is enhanced,thus accelerating the evolution of the potential reactivity of fly ash.