Impact of a viscosity-modifying admixture on the properties of lime mortars

Viscosity-modifying admixtures are frequently used in mortars to improve their fresh state properties, especially in pre-mixed products, with consequences for their hardened properties. However, the knowledge on the influence of these admixtures on lime-based materials is still incipient. In this context, this paper intends to analyse the impact of a viscosity-modifying admixture (VMA) in the fresh and hardened state properties of aerial lime mortars. In the fresh state, the VMA led to a thickening of the lime suspension, which translated into a progressive increase in torque, plastic viscosity and yield stress (after an initial decrease) with increasing dosage. At the same time, it increased air content, which made the mortars easier to handle, and increased the bleeding rate, but the amount of bleed water was lower. In the hardened state, the VMA did not improve mechanical strength owing to a porosity increase (based on a rise in large pores).