Effects of PCEs with various carboxylic densities and functional groups on the fluidity and hydration performances of cement paste

Abstract

In this research, effects of polycarboxylate superplasticizers (PCEs) with various carboxylic densities and functional groups on the adsorption behavior, dispersing performance as well as hydration characteristics of cement paste were systematically investigated. PCEs with different architectures were synthesized through substituting acrylic groups with sulfonic groups, ester groups, acylamino group, and changing the molar ratio between HPEG and acrylic groups in the PCE backbones under free radical solution polymerization. The molecular structures of different PCEs were characterized by size exclusion chromatography (SEC). The adsorption isotherms and the dispersing properties of different molecular PCEs were measured by total organic carbon measurement (TOC), mini-slump cone and shear rheometer, respectively. Cement hydration characteristics in the function of various molecular PCEs were investigated through X-ray diffraction (XRD), differential thermal analysis-thermogravimetric analysis (DTA-TG) as well as isothermal calorimetry. Results show that carboxylic density and the functional groups in PCE molecules significantly influence the adsorption behavior and the dispersing performance of PCEs. The increase in carboxylic density and integrating sulfonic groups into PCE backbone can enhance the adsorption capability of PCEs onto cement grain surface, which hence generate higher initial dispersing property. PCEs with higher carboxylic density hinder the cement hydration during the induction period, but promote the maximum hydration degree during the acceleration period. Integrating sulfonic group into PCEs backbone significantly promotes the cement hydration, while integrating amide groups or ester groups into the backbone of PCEs depresses the cement hydration process. The variation in cement hydration caused by the addition of different molecular PCEs is almost diminished at 28 d.