Underperformed interfacial bond and anisotropic properties are often observed in three-dimensional-printed concrete, where the printing pattern is unidirectional. Such issues could be potentially alleviated by replicating microstructures of natural materials or applying different architectures, where printed layers are arranged into unique and unconventional patterns. Furthermore, the quest to develop printing methods for highly complex or self-support concrete architecture could benefit from these nature-inspired patterns. In this work, the influences of different architectural arrangements of layers on mechanical properties of hardened concrete on compressive and flexural strengths are investigated. Specifically, unidirectional (0°), cross-ply (0°/90°), quasi-isotropic (0°/ ± 45°/90°), and helicoidal patterns (with pitch angles of 10°, 20°, and 30°) are used to create unidirectional, bidirectional, and multidirectional layers in printed objects without and with 0.75% by volume of 6 mm-long steel fibers. The experimental results demonstrate considerable improvements in the flexural strengths of nontraditional specimens without steel fibers over the unidirectional control with a few exceptions. Among investigated patterns, the quasi-isotropic demonstrates significant influences in both compressive and flexural responses of printed concrete samples without steel fibers. The addition of steel fibers leads to noticeable improvement on both compressive and flexural strengths of samples in any pattern compared with their counterparts without fibers. Besides, the inclusion of steel fibers into unconventional layups (cross-ply, quasi-isotropic, and helicoidal patterns) leads to the alleviation of directional dependence of mechanical properties, which is a limitation of the unidirectional samples with fibers. Of all helicoidal patterns, the one with a 10°-angle layup is shown to be more beneficial to the flexural strength enhancement and damage resistance in bending. X-ray microcomputed tomography measurements are performed to visualize the direction and distribution of fibers.

中文翻译：

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打印图案对三维打印纤维增强混凝土力学性能的影响

在三维打印混凝土中经常观察到表现不佳的界面粘合和各向异性特性，其中打印图案是单向的。通过复制天然材料的微观结构或应用不同的架构，这些问题可能会得到缓解，其中印刷层被排列成独特且非常规的图案。此外，为高度复杂或自支撑混凝土建筑开发打印方法的探索可以从这些受自然启发的模式中受益。在这项工作中，研究了层的不同结构布置对硬化混凝土的抗压强度和抗弯强度力学性能的影响。具体来说，单向 (0°)、交叉层 (0°/90°)、准各向同性 (0°/ ± 45°/90°) 和螺旋图案（螺距角为 10°、20°、和 30°) 用于在打印对象中创建单向、双向和多向层，不包含和包含 0.75% 的 6 毫米长钢纤维。实验结果表明，除了少数例外，与单向控制相比，没有钢纤维的非传统试样的抗弯强度有相当大的改进。在调查的模式中，准各向同性对不含钢纤维的打印混凝土样品的压缩和弯曲响应都有显着影响。与没有纤维的对应物相比，添加钢纤维可以显着改善任何图案的样品的抗压强度和抗弯强度。此外，将钢纤维纳入非常规叠层（正交层、准各向同性、和螺旋图案）导致减轻机械性能的方向依赖性，这是单向纤维样品的局限性。在所有螺旋图案中，具有 10° 角叠层的螺旋图案被证明更有利于弯曲强度的提高和弯曲时的抗损伤性。执行 X 射线微计算机断层扫描测量以可视化纤维的方向和分布。