Effect of Amphoteric Comb-Like Copolymer Dispersant on Dispersibility and Dispersibility Retention of Cement Pastes

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Title: Effect of Amphoteric Comb-Like Copolymer Dispersant on Dispersibility and Dispersibility Retention of Cement Pastes

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

Publication: Special Publication

Volume: 288

Issue:

Appears on pages(s): 1-12

Keywords: adsorption; amphoteric comb-like copolymer; dispersion; dispersibility retention; early hydration; mechanism.

Date: 9/14/2012

Abstract:
Polycarboxylate superplasticizers have revolutionized concrete technology in the past years. Their Comb-like structure consisting of a polyelectrolyte backbone and nonionic poly (ethylene oxide)-based “teeth”side chains offers a huge opportunity to polymer design. However, to our knowledge, almost all polycarboxylate belong to anionic copolymers. In this study, amphoteric comb-like copolymers (PAMP) with different molar ratio of anionic to cationic group in main chain were synthesized and characterized. The effects of molar ratio of anionic to cationic group in main chain on dispersion, dispers¬ibility retention, adsorption behavior and early hydration behavior in fresh cement suspen¬sions were investigated systematically to elucidate their mechanisms. The moderate incor¬poration of cationic group into comb-like copolymers improved the dispersion ability. However, when the content of cationic group was further increased, as the adsorbed amount of PAMP was increased, the dispersibility became worse. The fluidity retention for PAMP was enhanced with increasing cationic content in main chain. Besides, there is a negative correlation between the dispersibility retention ratio and copolymer concentration in solu¬tion. The adsorption sites, adsorption conformation and early hydration behavior should be together considered to explain its dispersion and the dispersibility retention of cement pastes with amphoteric copolymers. Besides, there exists an optimal balance between the molar ratios of anionic to cationic groups in backbone of comb-like copolymers.