Title: Effects of Superplasticizers in Highly Alkaline Model Suspensions Containing Silica Fume

Author(s): R.J. Flatt, Y.F. Houst, P. Bowen, H. Hofmann, J. Widmer, U. Sulser, U. Maeder and T.A. Burge

Publication: Symposium Paper

Volume: 178

Issue:

Appears on pages(s): 911-930

Keywords: admixtures; adsorption; rheology; silica fume; superplasticizers.

DOI: 10.14359/6015

Date: 6/1/1998

Abstract:
The behavior of superplasticizers has been studied in highly alkaline suspensions of magnesium hydroxide and silica fume, which can be considered as good model system for cementitious systems containing silica fume. Rheology showed that as superplasticizer dosage is increased, suspensions pass from behaving as Bingham fluids to Newtonian fluids. Beyond a critical concentration large dispersed particles sediment due to the absence of yield stress. The critical concentrations required to obtain Newtonian fluids has allowed to elucidate the dependence between adsorption and dispersion. Indeed, dispersion appears to be only linked to adsorbed polymers and can therefore be attributed either to electrostatic or steric repulsion mechanisms. On the other hand, superplasticizer requirement increases with silica fume fraction in particular with the less ionic polymer. This indicates important electrostatic interactions with the surface in the process of adsorption.