Effect of Alkali Sulfate on the Rheological Behavior of Cement Paste Containing a Superplasticizer

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Title: Effect of Alkali Sulfate on the Rheological Behavior of Cement Paste Containing a Superplasticizer

Author(s): T. Nawa, H. Uchi, and Y. Fukaya

Publication: Special Publication

Volume: 119

Issue:

Appears on pages(s): 405-424

Keywords: adsorption; alkalies; cement pastes; flocculating; hydration; plasticizers; rheology; sulfates; viscosity; zeta potential; Materials Research

Date: 9/1/1989

Abstract:
The influence of alkali sulfate on the viscosity of cement paste containing a superplasticizer was studied by using rotational viscometer. The mechanism of the action of superplasticizer on the fluidity of cement paste was also investigated. A larger amount of superplasticizer was rapidly adsorbed onto C3A and C4AF compared to that on C3S and C2S. The presence of alkali sulfate inhibited the adsorption of superplasticizer on C3A and C4AF, thus permitting increased adsorption on C3S and C2S. The reduction of viscosity of cement paste by superplasticizer is dependent mainly on its adsorption onto C3S and C2S. Therefore, an increase in alkali sulfate leads to an increase in the adsorption of superplasticizer on C3S and C2S, and results in reduced viscosity of cement paste. Excessive amount of alkali sulfate, however, compressed the electric double layer, providing an increase in viscosity of cement paste. Based on the results, it was concluded that there was an optimum alkali sulfate level with respect to the fluidity of cement paste containing the superplasticizer.