The Effect of Superplasticizer Addition on the Properties of Calcium Sulfoaluminate Mortars

Practical use of calcium sulfoaluminate cements (CSAs) is dependent on their compatibility with admixtures. The following paper presents research into the effects of three different superplasticizers (SPs) (polycarboxylate ethers, modified polycarboxylates, and polynaphthalene sulfonate), and the effect of a w/c ratio in a range of 0.45–0.35 in mortars containing superplasticizer on the chosen mortar properties. The conducted tests related to consistency, initial setting time, hydration heat, flexural and compressive strength, early shrinkage (first 20 h), and drying shrinkage. The results indicate that the superplasticizer type has significant effect on the properties of CSA mortars. All superplasticizers prolonged the initial setting and induction phase of hydration in relation to CSA mortar which did not contain superplasticizer by up to 109%; however, their effect on compressive and flexural strength, drying shrinkage, and early shrinkage was dependent on the type of superplasticizer involved. Polycarboxylate ether SP provided the best results for mortar properties, as it did not affect compressive strength significantly, but reduced plastic shrinkage. Polynapthalene-based SP decreased strength and increased shrinkage more than other superplasticizers, making it the least compatible. Decreasing the w/c ratio for mortar containing superplasticizer allowed us to mitigate some of the issues, as mortars with SP1 in a low w/c ratio exhibited higher compressive and flexural strength by, respectively, 41% and 80% in the case of a w/c ratio of 0.35, and lower shrinkage.