Working mechanisms of water reducers and superplasticizers

Abstract The yield stress of cement suspensions depends on the balance between attractive and repulsive interparticle forces on the one hand and shear forces on the other hand. The effect of superplasticizers on yield stress comes from introducing a repulsive interparticle force that reduces the overall attractive force between cement particles, and consequently the yield stress. Early-generation superplasticizers were believed to disperse by inducing electrostatic repulsion, but because of their high ionic strength, cement suspensions can hardly be stabilized by electrostatic repulsion. The data presented here suggest that it is rather steric repulsion that must be considered at full surface coverage. Polycarboxylate ether or PCE superplasticizers are broadly accepted to act through steric hindrance. Here we describe the role of the molecular structure in the dispersive effect under conditions of full and incomplete surface coverage.