Interlayer reinforcement of 3D printed concrete by the in-process deposition of U-nails

3D concrete printing has tremendous potential for construction manufacturing; however, weak interface bonding between adjacent layers remains a well-known issue that affects the mechanical properties of printed structures. The layers introduce anisotropy and reduce the capacity to resist tensile and shear loads. Reinforcements, inserted perpendicular to the printed layers to traverse the interfaces, can improve these limitations, but the insertion of reinforcements is difficult to achieve in practice, and there are few published studies exploring appropriate methods. This study presents a promising approach using U-shaped nails inserted into concrete during the printing process. The bridging effect and dowel action of the applied U-nails are visualised and analysed to elucidate the toughness improvement. The ultimate tensile strength and shear strength of 3D printed concrete are significantly increased by 145.0% and 220.0%, respectively. U-nails with a filament thickness of 2-2.5 mm are recommended to yield optimal improvement in the interlayer strength.

Automated summary

Inserting U-shaped nails into concrete during the 3D printing process improves the weak interface bonding between adjacent layers, significantly increasing the tensile and shear strength of 3D printed concrete. This method has great potential and benefits of reducing anisotropy, providing a new approach to enhance the mechanical properties of printed structures.