Adsorption and Dispersing Capability of Polycarboxylate Superplasticizers with Various Functional Groups

Abstract:

A series of polycarboxylate superplasticizers (PCEs) with different functional groups were synthesized through free radical polymerization. The adsorption behavior as well as dispersing capability of these PCEs was investigated. In addition, the effects of these PCEs on cement hydration process were systematically studied through isothermal calarimetry and Xray diffraction(XRD). The results show that PCE with acylamino groups most significantly depresses the dispersing capability due to highly decreased adsorption amount on cement particles, while PCEs with ester function groups rarely influence the dispersing capability. PCEs with sulfonic groups exhibit enhanced adsorption behavior. The introduction of ester groups or AMPS into PCE backbones remarkably hinders the induction period of cement paste, in comparison with reference PCE (P(PEG1AA4)) (the molar ratio of side chains to negative ions is 1:4), while the introduction of sulfonic groups into PCE molecules improves the maximum hydration heat evolution rate at acceleration period. At early ages, PCEs inplanted with sufonic groups, acylamino groups, or ester groups promotes the hydration process in comparison with reference PCEs (P(PEG1AA4)). However, at 28 days, cement paste added with reference PCE (P(PEG1AA4)) exceeds that with other PCEs in cement hydration degree.