Rheology-Control and 3D Concrete Printing with Fly Ash-Based Aqueous Nano-Silica Enhanced Alkali-Activated Binders (2024-05)¶

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 printable concretes. The binder pastes of slag made with FABANS are not suitable for printing due to low yield stress and insufficient thixotropic buildup. 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. Excess CMC results in a Maxwell-type behavior causing shape instability due to continuous relaxation under stress. 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.