The role of steric repulsive force in the dispersion of cement particles in fresh paste prepared with organic admixture

The existence of the steric repulsive force has never yet been determined, though the improved dispersibility of solid particles in concrete by adding the organic admixture is considered to be primarily caused by the dispersion of solid particles by the electrostatic repulsive force based on the formation of an electric double layer made of the admixture adsorbing to the surface of solid particles and the increase of the surface potential, and by the steric repulsive force based on the interaction between the adsorption layers of admixture. The authors proved for the first time the existence of the steric repulsive force acting on the surface of cement particles adsorbing the organic admixture by measuring the interactive force between surface of cement clinker adsorbing the admixture with an atomic force microscope, and measuring the zeta potential of fresh cement paste under actual water-to-cement ratio by electrokinetic sonic amplitude method. It is also clarified that the rate of contribution of electrostatic and steric repulsive force to the dispersion of cement and hydrated cement particles differs by the kind of organic admixture. Copyright (C) 1997 Elsevier Science Ltd.