Effect of Polycarboxylate Superplasticizer in Ordinary Portland Cement and Sulfate Resistant Cement

Abstract

Polycarboxylate superplasticizers (PCE) are the most widely used admixtures in today’s cementitious construction materials. The molecular structure has a decisive influence on the effectiveness of PCE, which also can be tailored to serve in a different cementitious system. The current study investigates the influence of the backbone charge density of PCE on the rheology, hydration kinetics, and adsorption behavior of ordinary Portland cement (OPC) and sulfate-resistant cement (SRC). The results indicate that regardless of the PCE type, OPC requires a higher amount of PCE to be adsorbed to induce changing of rheological parameters and hydration kinetics. Regardless of the cement type, the PCE with a higher charge density exhibits higher adsorption behavior, corresponding to lower viscosity measurement. Compared to OPC, SRC is more sensitive to the introduction of both PCEs and has a lower saturation dosage, indicating that SRC generally provides better workability properties regardless of the PCE. In this paper, rheology, adsorption isotherms, and calorimetry are employed to relate the backbone charge density and dosage of polycarboxylate superplasticizers to their performance in ordinary Portland cement and sulfate-resistant cement. The effect of the polycarboxylate superplasticizer on the rheology and retarding phenomenon of cement paste and the effectiveness of the two types of cement were investigated. The study shows that the adsorption capacity of polycarboxylate superplasticizer molecules increases with backbone charge density, therefore decreasing the yield stress and plastic viscosity of cement paste up to saturation dosage. It was also shown that the polycarboxylate superplasticizer molecules with high charge delayed the setting time of the cement paste compared to the low charge. More polycarboxylate superplasticizers are required in ordinary Portland cement to achieve saturation dosage. In addition, the same yield stress can be achieved by introducing less polycarboxylate superplasticizer in sulfate-resistant cement compared to ordinary Portland cement. This study provides a theoretical basis for the application of sulfate-resistant cement in construction.