Additive Thermoplastic Formwork for Freeform Concrete Columns

The degree of geometric complexity a concrete element can assume is directly linked to our ability to fabricate its formwork. Additive manufacturing allows fabrication of freeform formwork and expands the design possibilities for concrete elements. In particular, fused deposition modeling (FDM) 3D printing of thermoplastic is a useful method of formwork fabrication due to the lightweight properties of the resulting formwork and the accessibility of FDM 3D printing technology. The research in this area is in early stages of development, including several existing efforts examining the 3D printing of a single material for formwork— including two medium-scale projects using PLA and PVA. However, the performance of 3D printed formwork and its geometric complexity varies, depending on the material used for 3D printing the formwork. To expand the existing research, this paper reviews the opportunities and challenges of using 3D printed thermoplastic formwork for fabricating custom concrete elements using multiple thermoplastic materials. This research cross-references and investigates PLA, PVA, PETG, and the combination of PLA-PVA as formwork material, through the design and fabrication of nonstandard structural concrete columns. The formwork was produced using robotic pellet extrusion and filament-based 3D printing. A series of case studies showcase the increased geometric freedom achievable in formwork when 3D printing with multiple materials. They investigate the potential variations in fabrication methods and their print characteristics when using different 3D printing technologies and printing materials. Additionally, the research compares speed, cost, geometric freedom, and surface resolution.