Investigating the Working Mechanisms of Viscosity-Modifying Admixtures through Rheological and Water Transport Properties

Viscosity modifying admixtures (VMAs) show great potential in achieving the desired rheological properties for 3D concrete printing. In addition to rheology, water transport properties are critically important; due to the absence of formwork, freshly printed components with high exposed surface areas are susceptible to excessive water loss. In this study, the effect of VMAs (i.e., attapulgite/palygorskite nanoclay and diutan gum) on the water transport properties of cement pastes were investigated. Bleeding, water retention under suction pressure, and evaporation under airflow were measured. The nanoclay was found to reduce bleeding but had no effect on water retention or evaporation. The diutan gum was found to reduce bleeding, improve water retention, and decrease evaporation loss. The potential working mechanisms of nanoclay and diutan gum are discussed and tied to observations of the rheological and water transport properties of the modified pastes.