Chemistry and mineralogy of some Indian fly ashes

摘要

Amongst the factors governing pozzolanic reactivity of fly ash, chemical composition and mineralogy of individual grains are of considerable importance. Electron dispersive x-ray (EDX) analysis on the other hand provides a promising tool to investigate chemistry of individual grains for both amorphous and crystalline phases. The paper reports the results of analysis of fly ashes from three sources. It was observed that the finer particles ( < 45μm) in high-calcium fly ash were rich in Ca, Al, S and Si whereas coarse particles ( >75 μm) were of Fe and Si and corresponding glass and minerals. No such difference was observed in low-calcium fly ash. The fly ash particles consist of layers of glassy phase of different chemical composition. Alumino silicate type of glass in low-calcium fly ash and both alumino silicate and calcium aluminate type of glass in high-calcium fly ash were observed. XRD analysis showed formation of ettringite on hydration of high-calcium fly ash. The relationship between glass quality and chemical composition is discussed.