Concrete gyroid: an additive manufacturing (AM) method to 3D print gyroid geometries with a cementitious material

The gyroid is a triply periodic minimal surface (TPMS) that efficiently distributes stress under compressive loading in all Cartesian orientations. Despite the gyroid’s geometric ability to evenly distribute load, it has yet to be more broadly introduced to concrete additive manufacturing (AM) due to the difficulty of printing steep, doubly curved overhangs with a cementitious material. Consequently, the employment of the gyroid TPMS in AM has been limited to small and nano-scale applications. However, for doubly curved 3D printed concrete (3DPC) structures, the feasibility of the print is determined by the relationship between geometry, tool path design, and the mechanical and rheological properties of the concrete material being extruded. Using a 6-axis robotic arm with an accelerator-injection extruder as an end-effector, this research examines the fabrication limitations to construct a 3DPC gyroid. The methods of this paper will present: (1) a parametric method to digitally model a gyroid TPMS through non-uniform rational basis spline (NURBS) surfaces followed by (2) a series of geometric density studies for robotic fabrication, which informed the design of (3) a continuous tool path. Using these findings, (4) several samples were printed to test the overhang limits of the 3DPC gyroid samples. Finally, one of the overhang samples was prepared for a series of compression tests, which demonstrated that the 3DPC gyroid structure could support over 1000 kilonewtons. Though large variability was observed in the performance of three gyroid samples tested, the research demonstrates that steep overhangs can be printed in concrete for gyroid-based structures.