A study on high strength concrete with fly ash

In the coming years, the use of high-strength concrete is estimated to increase rapidly, with a substantial impact on the economy and the development of sustainable concrete technology. The use of fly ash (FA) as a partial replacement of Portland cement in high strength concrete is a most important topic because the use of FA not only benefits the economy, environmental aspects but also improves the properties of the concrete.In this study, the properties of high strength concrete (HSC) with FA was compared to HSC without FA. Workability, compressive strength, autogenous shrinkage, temperature rise, chloride penetration, and carbonation resistance were tested on nine HSC mixtures. The test results reveal that using FA in HSC mixture significantly enhances many properties when compared to mixtures containing only silica fume (SF) or mixtures with the combination of both SF and ground granulated blast furnace slag (GGBS). Its viscosity decreased while solid volume concentration increased, particularly in the ternary binder mixtures containing 20% FA and 10% SF. Combining 20% FA with 7% SF in the HSC reduces the peak temperature measured by the semi-adiabatic temperature rise test, and is equivalent to the HSC mixture with 20% FA or mixture with combined 30% GGBS and 7% SF. Concrete mixtures comprising 20% FA and SF show slightly lower 28-day compressive strength than the SF-only mixture, but their 91-day compressive strengths are equivalent to those of the SF-only mixtures. Due to the improved microstructures, all HSC mixtures perform well in terms of carbonation and rapid chloride permeability, particularly the ternary binder mixtures. The effects of FA on HSC properties were further investigated using WPD, SEM, XRD, and SP dosage to reveal the mechanical characteristics. Although 30% GGBS showed better performance compared to 20% FA in term of compressive strength, utilizing FA in HSC improved concrete performance in terms of viscosity, autogenous shrinkage, heat generation, and rapid chloride permeability as well as cost-effectiveness.