A comprehensive analysis of hydration kinetics and compressive strength development of fly ash-Portland cement binders

Utilizing fly ash (FA) to partially replace Portland cement (PC) in formulating sustainable cementitious binders can significantly mitigate environmental impacts associated with PC manufacturing and improper disposal of FAs. The main objective of this research is to employ a cost-efficient and simple method to assess the reactivity of FAs in PC. This is intended to enhance the replacement level of FAs in PC, without scarifying its performance. In this study, 10 FAs—each with unique chemical composition and molecular structure—are used to substitute two PCs at 10-to-50%mass replacement levels. Hydration kinetics and compressive strength of [PC + FA] binders are investigated. Equilibrium phase assemblages obtained from thermodynamic simulations were used to estimate the volume fraction of hydrates formed in [PC + FA] binders. The correlation between compressive strength of [PC + FA] binders and their volume fraction of hydrates is explored and employed to determine the degree of reaction of FA. The number of constraints derived from the topological constraint theory are used to represent the reactivity of FAs. Outcomes indicate that FAs with low value of number of constraints tend to show, resulting in enhanced hydration heat release and improved compressive strength. This improvement occurs irrespective of PC composition and replacement level of FA. The reactivity of FA ranges from 3 % to 29 % at 3 days.