Study on the Composite Activation of Fly Ash in Cement Clinker-fly Ash System

The effectiveness of activation on fly ash in cement clinker-fly ash system by the composite addition of CaO,Na2SO4 and alum was studied by means of cement mortar test.Meanwhile the composition and the microstructure of the hardened cement paste were characterized by XRD analysis and SEM observation.The results showed that the activity of fly ash is properly developed by addition of CaO-Na2SO4-alum composite activator,reduction of the early strength of fly ash being decreased and fly ash cement made of 42.5 Portland cement clinker and 50% fly ash giving strength property which meets the requirement of PF 42.5 fly ash cement by finely grinding and composite activation.XRD analysis shows that addition of CaO-Na2SO4-alum composite activator has caused the reduction of XRD intensity of quartz and Ca(OH)2,suggesting that the reaction between Ca(OH)2 released from the hydration of Portland cement clinker and acidic oxides in fly ash is promoted,hence the activation of fly ash being accelerated,while SEM observation shows that the surface of the fly ash particles in hardened cement paste with addition of CaO-Na2SO4-alum composite activator is severely attacked and a denser microstructure of hardened cement paste.