Rheology Control and 3D Concrete Printing with Fly ash-based Aqueous Nano-silica Enhanced Alkali-activated Binders

Abstract Efficient alkali-activated binder pastes of slag and fly ash-based aqueous nano-silica (FABANS) that provide enhanced strength are used for developing extrusion-based 3D printing applications. The binder pastes of slag made with FABANS are not suitable for printing due to low yield stress and insufficient thixotropy. Rheology control for enhancing the yield stress and thixotropic buildup is evaluated using bentonite clay and carboxymethyl cellulose (CMC). There is a synergistic enhancement in yield stress and thixotropic buildup provided by the combined use of bentonite and CMC that provides improved printability and buildability. Very rapid increase in yield stress with excess clay content in the presence of CMC, however, produces choking of flow and printability loss. The proportion of CMC and clay that provides the required thixotropic buildup for buildability is established. Printability and buildability of concrete mixture made with binder paste of FABANS with the proportion of rheology modifiers is demonstrated.