Effects of the chemical structure on the properties of polycarboxylate-type superplasticizer

Based on the analysis of the chemical structure of polycarboxylate-type superplasticizers with polyoxyethylene (PEO) side chains, the dispersing properties for cement particles were investigated. Analyzed characteristics were the PEO side chain length, the degree of backbone polymerization, the composition of functional groups such as carboxylic and sulfonic groups, and the purity of polymers. Their relative effectiveness as dispersants was evaluated in cement paste by measuring paste flow, plastic viscosity, and shear yield stress at different water/cement ratios (w/c). Although the effects of chemical structure on the paste fluidity were not significant at high w/c, they became significant at w/c below 25%. Polymers with longer PEO side chains, lower degrees of backbone polymerization, and higher contents of sulfonic groups showed higher dispersing power. Higher concentrations of ionic functional groups in the aqueous phase delayed the setting of cement paste. (C) 2000 Elsevier Science Ltd. All rights reserved.