Fly ash as an assemblage of model Ca–Mg–Na-aluminosilicate glasses

Model Ca–Mg–Na-aluminosilicate glasses based on compositions found in a calcareous fly ash were synthesised and their reactivity assessed in NaOH solution and in Portland cement paste. It was found that the reactivity followed the same trend in both systems and that the reaction of the glasses in pastes was very similar to that of the components of similar composition in the real fly ash. This finding indicates that the reactivity of glass in cement can be directly linked to the chemical composition of the glass. Further, when the reactivity of the glasses was normalized to their surface area, it was found that there exists a strong correlation with the NBO/T, the ratio of non-bridging oxygens and tetrahedral ions in the glass.