Influence of PCE on Rheological and Hydration Performances of Cement Paste

The addition of polycarboxylate superplasticizers (PCE) can alter the microstructure of dispersion system, and hence improve the fluidity of cement paste. In this paper, adsorption isotherms of PCE as well as the rheological and the hydration properties of cement paste have been systematically investigated. Cement hydration property was analyzed by isothermal calorimetry, differential thermal analysis (DTA), and thermogravimetric analysis (TG). The pore structures were investigated by mercury intrusion porosimetry (MIP) and dynamic water vapor sorption (DWVS). The microstructure and composition characteristics of hydration products were investigated by scanning electron microscopy (SEM) equipped with secondary electron imaging (SEI), backscattered electron imaging (BSE), and energy dispersive X-ray spectrometer (EDS). The results indicate that a higher PCE dosage leads to an increase of fluidity and a decrease of apparent viscosity as well as yield stress of fresh cement paste, owing to the disassembled flocculation and the released water from flocculation. The adsorption of PCE shows a double-layer adsorption behavior. The first adsorbed layer of PCE attributes to the zeta potential and the fluidity of cement paste, while the second adsorbed layer makes no contribution to these properties. The hydration degree of the cement paste is hindered by the addition of PCE at 1 day, but promoted at 3 days, while the promotion of hydration process almost vanishes at 28 days. The addition of PCE decreases the size of hydration products in hardened cement paste and changes the composition of hydrated calcium silicate (C-S-H) gel. The decreased porosity as well as average pore size due to good dispersion capability of PCE significantly improves the concrete performance.