Electrostatic repulsion between particles in cement suspensions: Domain of validity of linearized Poisson–Boltzmann equation for nonideal electrolytes

Abstract

To understand the dispersion of cement particles by superplasticizers, proper quantification of the possible mechanisms involved (electrostatic, steric, and depletion forces) is required. This is an important objective to help understand the origin of unexpected incompatibilities between some cement and superplasticizer combinations and more generally predict the rheological behavior. The relative importance of the electrostatic interaction with respect to steric hindrance is currently under much debate. The debate centered on this topic has not fully explored how the nonideal electrolyte found in cement suspensions effects the simplified Debye–Hückel approximation for evaluation of electrostatic repulsion. In this article, the nonideality of the cement aqueous phase—suspension electrolyte—has been taken into account based on solubility equilibria of the possible ionic species present in typical cement suspensions. By replacing the normally assumed symmetric electrolyte (1:1, 2:2, or 3:3) with a noninteger symmetric electrolyte, the simple Debye–Hückel approach has been shown to remain valid for negative potentials down to around 30 mV. Significant deviations are found for positive potentials greater than 10 mV.