Analysis of shrinkage reducing admixtures on drying shrinkage of concrete

Synopsis: The objective of this research was to verify the feasibility of reducing the drying shrinkage of concrete made with portland pozzolan cement. Major variables included slump, shrinkage-reducing admixture brand, admixture dosages and specimen dimensions. Tests were carried out on 132 prism specimens and shrinkage strains were measured up to 360 days of drying. Also compressive strength, splitting strength and static modulus of elasticity were determined. Based on the results obtained, it was concluded that all of the five brand admixtures evaluated reduce drying shrinkage. One of the experimental admixtures exhibited the best behavior and reduced up to 45% of the average free shrinkage of concrete at 360 days of drying. Results were compared with drying strain predictions of ACI, CEB, B3, GL, Sakata and Sakata 2001 models. It was concluded that in general all the analyzed shrinkage models do not adequately represent the observed shrinkage behavior of concretes made with portland pozzolan cement and shrinkage-reducing admixtures. Therefore, two prediction models to estimate drying shrinkage strains were developed based on the ACI drying-time function, and Sakata's ultimate shrinkage strain. One of these models is for use at a design level when no information about a particular shrinkage reducing admixture is known, and the other is applicable to concrete made with a particular admixture brand.