Halloysite reinforced 3D-printable geopolymers

This study investigates the role of halloysite nanotube as a mineral-based thixotropic admixture to 3D printable geopolymer mortar. The first part of this paper focuses on the fundamental characterization of the thermal evolution of halloysite at 30-1000 degrees C. In the second part, we show how the calcination and concentration of halloysite influence the fresh and hardened properties of 3D-printable geopolymer mortar. It was found that regardless of thermal treatment, using only 1-2 wt% halloysite can significantly increase the rheological prop-erties and buildability of the mortars without compromising their mechanical strength. However, the setting time of geopolymer only accelerated when highly reactive dehydroxylated halloysite was used. Compared with mold-cast specimens, the mechanical properties of 3D-printed specimens were lower at early ages due to their higher surface dehydration; however, the gap became closer over time.