Preparation and Mechanism Study of Slow-Release Polycarboxylate Superplasticizers

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Title: Preparation and Mechanism Study of Slow-Release Polycarboxylate Superplasticizers

Author(s): Jinzhi Liu, Jiaping Liu, Yong Yang, Dongliang Zhou, and Qianping Ran

Publication: Special Publication

Volume: 302

Issue:

Appears on pages(s): 243-252

Keywords: polycarboxylate; slow-release; zeta potential; adsorption; dispersability retention

Date: 6/1/2015

Abstract:
Slump loss of fresh concrete was a common issue in engineering construction, especially under high temperature and long distance transportation conditions. Therefore, slow-release polycarboxylate superplasticizers (PCEs) have been widely used to reduce the slump loss in various engineering projects. In this study, three kinds of PCEs with different proportions of hydroxyl ester groups (HEG) were synthesized and characterized by 1H-NMR and Gel Permeation Chromatography (GPC). The effects of the HEG content on dispersion retention, adsorption kinetics and zeta potential of fresh cement suspensions were systematically investigated to figure out the mechanism. For PCEs with the same molar ratio of carboxyl group and reactive polyether, the dispersion retention ability of PCEs is improved with the increasing of HEG ratio. HEG in PCEs can be slowly converted to carboxyl groups in the alkaline environment of cement suspension, which could enhance the adsorption of PCE molecules onto the surface of cement particles. Despite major of the initially adsorbed-PCE molecules might have been embedded in hydration products, free PCE molecules with released carboxyl groups in the solution can continuously adsorb onto the surface of cement particles and play a role in dispersion. This explains why slow-release PCEs have a dispersion retention effect on cement particles within a certain time.