The Electrostatic Potential of Highly Filled Cement Suspensions Containing Various Superplasticizers

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Title: The Electrostatic Potential of Highly Filled Cement Suspensions Containing Various Superplasticizers

Author(s): 0. Blask and D. Honert

Publication: Special Publication

Volume: 217

Issue:

Appears on pages(s): 87-103

Keywords: adding time; cement paste; dispersive force; electrostatic repulsion; mixing energy; rheology; superplasticizer; zeta potential

Date: 9/1/2003

Abstract:
One of the most challenging tasks in cement chemistry is to understand exactly how superplasticizers work and why they occasionally fail. The higher fluidity of superplasticized concrete is considered to be caused by an increased dispersive force. This dispersive force can be increased in two ways, either by electrostatic repulsion or by steric repulsion. The way in which dispersive forces are increased depends on the kind of superplasticizer used. It is' commonly known that sulfonate-based admixtures increase electrostatic repulsion while polycarboxylate-based admixtures increase steric repulsion. This paper analyses the influence of various superplasticizers, mixing energy and adding time of superplasticizer on the electrostatic potential of different cement pastes. The electrostatic potential has been observed by measuring the zeta-potential of cement pastes using the electro kinetic sonic amplitude method (ESA). Additionally, suspensions of cement and silica have been used to study the dispersing mechanisms of different superplasticizers. The results lead to a better understanding of the way sulfonateand polycarboxylate-based admixtures work.