The Role of Adsorption Energy in the Sulfate-Polycarboxylate Competition


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Title: The Role of Adsorption Energy in the Sulfate-Polycarboxylate Competition

Author(s): R.J. Flatt, J. Zimmermann, C. Hampel, C. Kurz, I. Schober, L. Frunz, C. Plassard, and E. Lesniewska

Publication: Special Publication

Volume: 262


Appears on pages(s): 153-164

Keywords: adsorption energy; atomic force microscopy; sulfate; superplasticizers.

Date: 10/1/2009

The interaction between sulfates and polycarboxylate polymers has become a subject of much discussion and occasional concern over the past years. Laboratory studies have shown that sulfates may prevent some polycarboxylate polymers from adsorbing, which causes a reduction in flow properties of cementitious materials. This seems to have led to the belief that this phenomenon is generally true for all polycarboxylates. In fact, it depends very much on the detailed polymer structure. Examples of this will be shown both with flow examples on paste, and experiments by atomic forces microscopy that illustrate in a very convincing way that this competition does not always turn to the advantage of sulfate ions. Furthermore, it is discussed how the outcome of this competition is governed by variations in the adsorption energy of the polymers.