PVA fiber reinforced red mud-based geopolymer for 3D printing: Printability, mechanical properties and microanalysis

Red mud-based geopolymers are an efficient alternative to resolve the high cement consumption in 3D printed concrete (3DPC). From a materials perspective, good printability and mechanical properties are critical to adopting red mud-based geopolymers in 3DPC. In this study, we selected bauxite tailings-red mud and blast furnace slag to prepare geopolymers. Polyvinyl alcohol (PVA) fibers with 0, 0.3 %, 0.6 %, 0.9 %, and 1.2 % volume fractions were used to reinforce 3D printed red mud-based geopolymers. To evaluate the influence of PVA fiber on the printability and mechanical properties of 3D printed red mud-based geopolymer. We tested the workability, extrudability, structural build-up ability, shape stability, and mechanical properties of the red mud-based geopolymer containing different volume fraction PVA fibers, and a microstructural analysis was performed to reveal the interface bond between the fibers and the geopolymer matrix. The results showed that adding PVA fibers impaired the workability of the red mud-based geopolymer mortar. The red mud-based geopolymer mortar showed a more than threefold increase in extrusion pressure compared to the control mixture (P0) when adding 1.2 % vol fiber. For all other mixtures, the increase was less than twice that of the control mixture. The PVA fiber had a significant positive impact on the structural build-up ability and shape stability of the 3D printable red mud-based geopolymer. In addition, PVA fibers promoted the bending strength of the hardened geopolymer specimens better than the compression strength, and the geopolymer gel on the fibers indicated the good interfacial bonding ability of the PVA fiber. This study demonstrates the feasibility of 3D printed red mud-based geopolymer and the reinforcement of 3D printed red mud-based geopolymer by PVA fibers, providing a material perspective to increase the range of red mud applications in 3D printed concrete.