Effect of non-ionic auxiliary dispersants on the rheological properties of mortars and concretes of low water-to-cement ratio

Abstract

A high plastic viscosity can be very disadvantageous for the processing of concrete as it often entails a sticky and honey-like consistency. This is especially the case for concretes prepared at low water content and a large amount of fine supplementary cementitious materials (e.g. silica fume). Unfortunately, most of the common polycarboxylate (PCE) superplasticizers cannot effectively reduce the plastic viscosity of such highly particle loaded systems, even though they exhibit strong dispersing capability and can produce high spread flow or slump. In this study, it is demonstrated that non-ionic molecules like diethylene glycol or 2-methyl-2,4-pentane diol can reduce the plastic viscosity when admixed with a PCE superplasticizer. The effect of those auxiliary dispersants on the rheological parameters was investigated by spread flow, flow line and V-funnel tests using mortar and concrete prepared from Portland-limestone cements exhibiting low w/c ratios (0.26 and 0.35, respectively). Moreover, the impact of such non-ionic molecules on the strength development of mortar specimens was tested. Mechanistic investigations revealed that the co-dispersants increase the amount of the liquid phase and hence the thickness of the lubricating layer around the particles. As a result, interparticle friction is reduced and a less sticky material with a higher speed of flow is obtained.