Influence of the type of viscosity-modifying admixtures and metakaolin on the rheology of grouts

Abstract

The Viscosity-modifying admixtures (VMAs) contribute to the control of the rheology of grouts and are used to enhance plastic viscosity, cohesion, stability, and resistance to bleeding of cement-based systems.  This paper reports the results of an investigation on the effect of type of VMAs, namely two types of diutan gums and a welan gum and metakaolin (MTK), plus a superplasticiser, on the rheology behaviour of cement grouts.  All mixes were made with polycarboxylic superplasticiser at 0.6% and 0.9%.  The dosages of VMAs were 0.05%, and 0.10%, with a fixed water-to-binder ratio of 0.40.  The investigated fresh properties of the grouts included the mini-slump flow, plate cohesion, and rheology parameters: namely yield value and plastic viscosity.  The rheological parameters were obtained using a vane viscometer.  Control grouts (with and without superplasticiser and VMA) were also tested and compared to mixes containing VMAs.  The results indicated that the incorporation of MTK reduced the fluidity and increased the plate cohesion and yield stress, and plastic viscosity due to the higher surface area of MTK.  The diutan gum grouts improved the grout fresh properties and rheology compared to the welan gum grouts.