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.

3D混凝土打印在建筑制造方面具有巨大潜力；然而，相邻层之间的弱界面结合仍然是一个众所周知的问题，它会影响印刷结构的机械性能。这些层引入了各向异性并降低了抵抗拉伸和剪切载荷的能力。与印刷层垂直插入以穿过界面的钢筋可以改善这些限制，但在实践中很难实现钢筋的插入，并且很少有已发表的研究探索适当的方法。这项研究提出了一种在打印过程中使用 U 形钉插入混凝土的有前途的方法。对应用的 U 形钉的桥接效应和销钉作用进行可视化和分析，以阐明韧性的提高。3D打印混凝土的极限抗拉强度和抗剪强度分别显着提高了145.0%和220.0%。建议使用 2-2.5 毫米细丝厚度的 U 形钉，以优化层间强度。