Large-Scale 3D Printing of a Shell Structure Reinforced by the Flow-Based Pultrusion Process (2024-09)¶

Concrete and mortar elements are well-known for their inherent brittle fracture and low tensile strength. They require reinforcement to be used in the AEC (Architecture, Engineering, and Construction) industry. Within the additive manufacturing domain, ensuring the durability of printed structures hinges on addressing the critical issue of reinforcement. This research presents a case study of a specific reinforcement process for 3D printing known as Flow-Based Pultrusion (FBP, Caron et al., 2021), emphasizing its applications in designing and printing a shell structure. The FBP method involves the pulling of numerous continuous fiber rovings by a fresh mortar with fast structuration. The resulting material, as an Anisotropic Concrete, exhibits unidirectional reinforcement (Demont et al., 2022, 2021). Coupled with 3D printing, this approach enables the design and fabrication of optimized geometries wherein the material is strategically placed, and reinforcement is oriented accordingly. The mechanical properties of this composite material are significantly influenced by the reinforcement ratio, the impregnation quality, the fiber properties, and the mortar’s mechanical features. In this study, a custom mortar is designed and printed. For the reinforcement process, long carbon fiber from Teijin is used: 800 Tex Tenax HTS40. First of all, different ratio of fiber is printed as shown on table 1, to perform 4 points bendind test. A small path is printed, and samples are extracted at hardened state from this printed object. Samples were cut to be 160 mm long, 25 mm width and 20 mm height. The 4-point bending test (100 mm between supports and 80 mm between the two loads application) shown interesting results: all fibers specimens break in shear, and symptomatic diagonal cracks are visible. Ductility on this material is observable for all fibers specimens, but only the 6 fibers specimen show multi-cracking. Finally, the next phase of this research focus on print a large-scale shell structure. This shell is designed and optimized to minimize the mass of the structure through an anisotropic mechanical failure criterion: Trai-Wu. This Failure criterion, the different load case (with eccentric loads for not compressive only structure) and the optimization process will be presented during the oral presentation, figure 1A shows the different optimized geometries. And figure 1B shows the reinforced printed shell.