Cement and Superplasticizer Combinations: Compatibility and Robustness

This study highlights the notion of robustness of combinations of cements and superplasticizers. Tests done with various cements and different families of superplasticizers showed that although a combination of a cement and a superplasticizer could be compatible, it is not necessarily robust. Sometimes a little variation in the dosage of the admixture could lead to detrimental side effects, such as segregation, excessive set retardation, or excess air content in the concrete. Results showed that the chemical composition of the cement is critical to ensure good compatibility and adequate robustness of various combinations of cements and superplasticizers. The chemical nature of the superplasticizer also plays a role in the behavior of such combinations. The C₃A content, the soluble (alkali) sulphate content, and the fineness of the cement, which influence the adsorption rate of the superplasticizers on the cement particles, are among the key factors that control the compatibility and the robustness of cement-superplasticizer combinations, especially for polysulfonated admixtures. Based on the results of this study, a rough prediction of the compatibility and robustness of cements and superplasticizers could be made by analyzing the chemical composition of the cement and the chemical nature of the superplasticizer.