Effects of polycarboxylate superplasticizers with different molecular structure on the hydration behavior of cement paste

Abstract

Effects of polycarboxylate (PCE) superplasticizers with different densities of carboxylate groups, functional group contents, molecular weight, and side chain polymerization degrees on the hydration behavior of Portland cement were investigated in this study. The experiments were conducted by using semi-adiabatic calorimeters equipped with a temperature measurement system. The water cement ratio (W/C) was 0.4, and the PCE dosage used was 0.3%. Besides, the Total Organic Carbon (TOC) experiments were taken to further study the delaying mechanism of different PCE on cement hydration. The ability to delay hydration increased in PCEs with high densities of carboxylate groups, short side chains, and high molecular weight and the copolymerization of methyl acrylate (MA) monomers decreased the heat flow peak. Nevertheless, the main hydration temperature peak and the maximum elevated temperature decreased when the density of the carboxylate groups increased. Moreover, PCEs with only a moderate molecular weight had the lowest hydration degree. The main hydration peak decreased but appeared in advance when the amount of MA monomers copolymerized with PCEs was increased; the hydration degree also decreased. PCEs only polymerized by methyl allyl polyethenoxy ether (TPEG400) macromonomer had a hydration degree of 69.46%. Absorption amount results indicate that PCEs affect the hydration of cement paste by absorbing PCEs on the surface of cement particles or encapsulating some cement particles to restrain cement hydration. PCEs grafted with MA hydrolyzed to carboxylic and hydroxyl groups, which can both restrain the hydration of cement paste.