The development of a fly ash-based geopolymer for extrusion-based 3D printing, along with a printability prediction method

This paper presents insights into the design and development of a geopolymer consisting of fly ash and ground granulated blast furnace slag (GGBFS) usable for extrusion-based 3D printing. It also reports on factors influencing the printability of the geopolymer, such as the amount of GGBFS, the solids content, mixing time, and activator ratio. Besides measuring the setting behaviour, the yield stress, and the ultrasonic velocity, we also conducted a modified flow spread test to investigate the geopolymer’s early physical material properties. We also used analytical methods (SEM, XRD, and TG) to explain its physical behaviour. We introduced an adjusted test for the flow spread (VFS test), which gives information about the thixotropic behaviour depending on the shear stress and the opentime for printing. By comparing the derivatives of the yield stress curve with printing tests on an XYZ gantry printer and analysis of the yield stress measurement’s transition point, we also present a unique method that allows researchers to assess the printability of the geopolymer solely on one small-scale laboratory tests without requiring printing tests on a physical 3D printer.