Performance of sustainable concretes containing very high volume Class-F fly ash and ground granulated blast furnace slag

Abstract

In recent years, with the aim of lowering the environmental impact of concrete, the partial replacement of cement in concrete with fly ash (FA) and ground granulated blast furnace slag (GGBS) has received significant attention. This paper presents the first experimental study on the properties of concrete containing ternary binders with high volume Class-F FA and GGBS partially replacing cement up to 90%. A total of 15 batches of concrete were manufactured with binary and ternary binders based on FA, GGBS, and cement. Experimental tests were performed to establish the density, workability, compressive strength, elastic modulus, flexural strength, splitting tensile strength, and water absorption of different mixes. The results indicate that the compressive strength of concrete containing FA decreases significantly with an increase in the FA content from 50% to 90%. The concretes containing GGBS at up to 90% cement replacement exhibit a similar compressive strength to that of conventional concrete after 28 days. It is found that ternary mixes with a 70% replacement ratio and relative FA to GGBS ratio (Ψ) of 1:2, and those with a 50% replacement ratio and Ψ of 1:1 develop a similar 28- and 90-day compressive strength to that of conventional concrete. A further increase in the replacement ratio and Ψ results in a decrease in the compressive strength. The results also show that GGBS mixes develop a slightly higher 28-day elastic modulus than that of conventional concrete mix. Although the elastic modulus of FA and the majority of the ternary mixes is lower than that of conventional concrete, ternary mixes with 70% (Ψ of 1:2) and 50% (Ψ of 1:1) replacement ratios develop a similar elastic modulus to that of conventional concrete. It is observed that an increase in the FA and GGBS content, respectively, results in a significant increase and moderate decrease in the water absorption of concrete. All ternary mixes with up to 90% cement replacement exhibit lower water absorption than conventional concrete mix. These highly promising findings suggest that the technology used in this study can provide an attractive avenue for high volume use of FA and GGBS in concrete with the possibility of significantly reducing its environmental impact.