Insights into material design, extrusion rheology, and properties of 3D-printable alkali-activated fly ash-based binders

Material design of alkali activated fly ash-based binders for extrusion-based 3D printing, the rheological responses that are influential in ensuring printability, and the properties of such binders are discussed in this paper. Fly ash is supplemented with fine limestone, slag, or portland cement to provide adequate microstructural packing required for printability. The alkaline activators help reduce the yield stress and enhance the cohesiveness of the mixtures. Based on the measured shear yield stress at different times and concurrent printing of a filament, the printability window and yield stress bounds for printability, applicable for the chosen printing parameters, are established. This approach could be used for mixture qualification for extrusion-based printing. The Benbow-Bridgwater model is implemented on extrusion rheology results of pastes to determine the extrusion yield stress and wall slip shear stress, which are useful process-related parameters. It is shown that these parameters can also be related to shear and extensional rheological properties of alkali-activated pastes, thus ensuring a much-needed link between parameters related to material design and the process of extrusion. Mechanical properties and pore structure similar to those of conventionally cast mixtures are achieved.