Effect of ground granulated blast furnace slag on strength and shrinkage properties of fly ash-based geopolymers

The work aims to study the influence of ground granulated blast furnace slag in the composition of the binder on the strength and shrinkage of geopolymer concrete based on class F fly ash.Three mixtures were produced, differing in the proportion of ground granulated blast furnace slag replacing fly ash -10%, 30%, and 50%.A mixture was made using Portland cement with the same binder consumption as geopolymer mixtures.The water-cement ratio in all mixtures was 0.55.The concrete with 30% slag showed the greatest strength.The compressive strength of this concrete was 34% higher than the concrete with Portland cement.All mixtures of geopolymer mortars have a higher shrinkage value than a mortar containing Portland cement.The shrinkage strain of the geopolymer mortar decreases with increasing fly ash content.Thus, a mixture containing 90% fly ash has a shrinkage of 65% less than a mixture with 50% fly ash, which is associated with the microaggregate filling effect of fly ash.The lowest weight loss was shown by specimens with 50% fly ash and 50% slag because, with increasing ground granulated blast furnace slag content, more water is consumed to form CSH and CASH gels.Of the three mixtures with the addition of slag, the mixture with 10% slag has the greatest weight loss.The same mixture has less shrinkage among the three mixtures with the addition of slag.This suggests that a larger mass loss does not directly lead to higher drying shrinkage.