Effect of Molecular Structure of Polycarboxylate Water Reducers on Hydration of Cement

A series of polycarboxylate water reducers (PCs) with different molecular structures were synthesized in aqueous system. The molecular structure of PCs was characterized by a gel permeation chromatography. The effect of molecular structure on the dispersibility and dispersion stability of PCs was discussed. The effect of molecular structure of PCs on the hydration of cement was also analyzed via the methods of hydration heat and electrical resistivity. The results show that the PCs with a shorter polyethylene oxide (PEO) side chain exhibit a higher dispersion stability. The PCs showed the higher dispersibility and dispersion stability at the same time when the density of PEO side chain was 1:3, which was correlated to the molecular mass distribution of PCs. The presence of PCs shortened the earlier induction period and prolonged the induction period of hydration of cement, showing that the PCs had a retarding effect on the hydration of cement. This effect was strengthened for the PCs with a shorter PEO side chain and a moderate density of PEO side chain, which was related to the adsorption behavior of PCs. In this case, the retarding effect was also slightly strengthened with the decreased molecular mass. Similarly, the presence of PCs prolonged the ion solution balance period of hydration in the curve of electrical resistivity, and this lengthening effect was more obvious for the PCs with a shorter PEO side chain and a moderate density of PEO side chain, which was similar to the effect of molecular structure on the induction period of hydration in the curve of heat evolution.