Influence of Fly Ashes on the Drying Shrinkage of Superplasticized Concretes in the Presence of SRA

Abstract

This paper describes how concretes with portland cement in the presence of fly ash or beneficiated fly ash (BFA) all at a slump of about 240 mm (9.4 in.) were made. Fly ash or BFA was used as a mineral addition replacing 20% of portland cement in both plain and superplasticized concretes with or without shrinkage-reducing admixtures (SRA). The 28-day compressive strength of the superplasticized and plain concretes without mineral addition were higher than those of the corresponding concretes with fly ash and lower than that with BFA. Drying shrinkage of specimens exposed to a dry environment with relative humidity of 50% up to 4 months was measured. In the presence of fly ash the drying shrinkage decreased by about 15% with respect to the corresponding plain concretes without fly ash. In the presence of a superplasticizer and/or a SRA there was further reduction in dry shrinkage of fly ash mixtures. The drying shrinkage of concretes, where portland cement was replaced by BFA was lower than that of the corresponding concretes with fly ash. Even in the presence of superplasticizer and/or SRA a further reduction of drying shrinkage of BFA concretes was found. In fly ash or BFA concrete mixtures, and more significantly in the presence of superplasticizer and/or SRA, the cracking in restrained slabs was reduced in terms of both the number and the width of cracks.