Compatibility of Shrinkage-Reducing and Air-Entraining Admixtures

The compatibility of two shrinkage-reducing admixtures (SRAs) with two air-entraining admixtures (AEAs)--one surfactant-based and one foaming polymer-based--was examined based on freezing-and-thawing durability, scaling resistance, and air-void characteristics of hardened concrete. SRA dosages of 0, 0.5, 1.0, and 2.0% by weight of cement were used. Test results show that interactions between admixtures can reduce air-void stability, contributing to lowered freezing-and-thawing durability and scaling resistance. Without an SRA, concrete mixtures containing either AEA exhibited good freezing-and-thawing durability and scaling resistance. With an SRA, mixtures containing the surfactant-based AEA performed well, while those containing the polymer-based AEA did not. Mixtures containing higher dosages of SRA, regardless of AEA, experienced a greater loss in air content in concrete between the plastic and hardened conditions. Mixtures with an increased air-void spacing factor experienced decreased durability, with the greatest decrease observed in those with air-void spacing factors greater than 0.008 in. (0.20 mm). Keywords: admixtures; air-void analysis; freezing-and-thawing durability; scaling resistance; shrinkage.