Buildability of Geopolymer Concrete for 3D Printing with Microwave Heating

Abstract

A novel application of microwave heating was investigated to attain on-demand setting of concrete for the improvement in buildability of 3D printable geopolymer concrete. An integrated microwave heating facility at the nozzle head was replicated using laboratory experiments to understand its effect on the structural build-up of printed filaments. Different microwave heating durations of 5, 10 and 20 s were studied, and the fresh and hardened properties were compared with control specimen (without microwaving). At optimised heating, the interlayer bond strength was found to be increased by 127% and 122% at 7 and 28 days respectively. Furthermore, structural recovery of material after extrusion that governs its buildability, showed a tremendous improvement at optimum heating period. Control specimens could only recover up to 32% of the initial viscosity, whereas addition of microwave heating for 10 s enhanced the viscosity recovery to more than 70%. Effect of microwave heating on cement based concrete 3D printing was also studied to assess the robustness of this technique. Outcomes from this study proposes a novel approach of applying microwave heating to construction 3D printing to achieve “set-on-demand” printable concrete. This study provides a starting point to develop new generation of print head to combat issues faced by current 3D printing practices.