Usage of  Fly ash based cement and concrete has become increasingly popular with the recognition that in addition to strength, other properties such as impermeability ,elastic modulus and resistance to corrosion are critical parameters for long term durability and low life cycle cost.

The abundant availability of fly ash as a byproduct from coal fired thermal power plants has led researchers to focus on the factors responsible for the pozzolanacity of the fly ash as also the means for enhancing its reactivity .

The comparative reactivity of Class-C and    Class – F fly ashes has been studied and reported by researchers in great detail.

However very few studies relate to the relation between the amorphous glassy phase contents and the reactivity of low lime class-F fly ashes.

An attempt has been made to correlate the chemical, mineralogical and microstructural  characteristics of the Low lime Class-F fly ashes from different sources with its reactivity as a pozzolana.

 Hydration studies have been carried out to assess the pozzolanacity of the Low Lime     Class – F fly ashes of different sources, using a method evolved at the authors laboratory which monitors the kinetics of hydration of the blended cement pastes ( made with 20% Fly ash under study )  and neat OPC pastes  at different ages of hydration .

Based on the studies the authors rate the pozzolanacity of the different fly ashes  and  conclude that the differences in the  amorphous contents of the fly ashes result in a variability in the  nature and content of the combined water (TGA/DTA),Mineralogy(XRD)and Microstructure of the hydrated blended cement pastes indicating a difference in the stoichiometry of the  CSH phases formed by the different fly ashes . The article was published at 5th ISCC Shanghai 2002

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