Material-informed Formwork Geometry: The effects of cross-sectional variation and patterns on the strength of 3D printed eggshell formworks

Fused deposition modelling (FDM) 3D printing of formworks for concrete has the potential to increase geometric freedom in concrete construction. However, one major limitation of FDM printed formworks is that they are fragile and often cannot support the hydrostatic pressure exerted by the concrete. The research project 'Eggshell' combines robotic 3D printing of formwork with the casting of a fast-hardening concrete to reduce hydrostatic pressure to a minimum. Eggshell can be used to fabricate architectural-scale building components; however, knowledge of the influence formwork geometry has on the hydrostatic pressure resistance is still sparse, resulting in unexpected breakages of the formwork. This paper presents an empirical study into the breakage behaviour of FDM printed formworks when subjected to hydrostatic pressure. Firstly, the study aims to give a first insight into the breakage behaviour of formworks with a constant cross-section by casting a self-compacting concrete into the formwork until breakage. Then, we investigate if three-dimensional patterning of the formwork can have a beneficial effect on the breakage behaviour. Finally, the preliminary results are validated through the fabrication of two full-scale columns. The empirical results point towards the fact that sharp corners in formworks are weaker compared to rounded corners. Although the presented results are still preliminary, they mark an important step in the development of reliable design and fabrication strategies using 3D printed formworks