Three-dimensional (3D) concrete printing technology has been considered promising, attracting extensive attention in the engineering field. Multiwalled carbon nanotubes (MWCNTs) have been used as an additive to reinforce the cement-based material. However, the research on the 3D printed MWCNT-reinforced high-strength concrete is rare. This research is to study the mechanical properties and pore structure of MWCNT-reinforced reactive powder concrete (RPC) for 3D printing. In this research, the workability of the printed RPC mixture with MWCNTs was first tested to pass the criteria of 3D printing. Then, the enhancement effect of MWCNTs on the printed RPC was tested by mechanical properties after hardening. Meanwhile, strength–displacement curves were recorded. In addition, the pore structures of printed RPC were observed and analyzed by X-ray computed tomography (CT) images. The results show that 0.05 wt% MWCNTs have no effect on the workability of the printable RPC slurry. MWCNTs could enhance the mechanical properties of the printed RPC by filling the flaws inside the samples, increasing the viscosity of the RPC slurry and forming bridges between cracks. Besides, 0.05 wt% MWCNTs may cause the failure mode of the printed RPC from brittle failure to ductile failure. In addition, MWCNTs significantly reduced the porosity of the printed RPC by decreasing pores with a volume over 0.01 mm³. As CT images show, the interlayer zone (IZ) of the 3D printed RPC sample is prone to pores, and a higher volume fraction is evident. In particular, within the volume of IZs, the minimum volume fraction at the IZ of 3D printed RPC appears on sample with MWCNTs.

中文翻译：

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材料挤压制备三维打印用多层碳纳米管增强活性粉末混凝土的力学性能和孔结构

三维（3D）混凝土打印技术被认为是有前途的，在工程领域引起了广泛的关注。多壁碳纳米管 (MWCNT) 已被用作增强水泥基材料的添加剂。然而，关于 3D 打印多壁碳纳米管增强高强混凝土的研究却很少。本研究旨在研究用于 3D 打印的 MWCNT 增强反应性粉末混凝土 (RPC) 的力学性能和孔隙结构。在这项研究中，首先测试了打印的 RPC 混合物与 MWCNTs 的可加工性，以通过 3D 打印的标准。然后，通过硬化后的力学性能测试 MWCNTs 对印刷 RPC 的增强效果。同时，记录强度-位移曲线。此外，通过 X 射线计算机断层扫描 (CT) 图像观察和分析印刷的 RPC 的孔结构。结果表明，0.05 wt% MWCNTs 对可印刷 RPC 浆料的可加工性没有影响。多壁碳纳米管可以通过填充样品内部的缺陷、增加 RPC 浆料的粘度和在裂缝之间形成桥梁来增强印刷 RPC 的机械性能。此外，0.05 wt%的MWCNTs可能会导致印刷RPC的失效模式从脆性失效转变为延性失效。此外，MWCNTs 通过减少体积超过 0.01 mm 的孔隙显着降低了印刷 RPC 的孔隙率 增加 RPC 浆料的粘度并在裂缝之间形成桥梁。此外，0.05 wt%的MWCNTs可能会导致印刷RPC的失效模式从脆性失效转变为延性失效。此外，MWCNTs 通过减少体积超过 0.01 mm 的孔隙显着降低了印刷 RPC 的孔隙率 增加 RPC 浆料的粘度并在裂缝之间形成桥梁。此外，0.05 wt%的MWCNTs可能会导致印刷RPC的失效模式从脆性失效转变为延性失效。此外，MWCNTs 通过减少体积超过 0.01 mm 的孔隙显着降低了印刷 RPC 的孔隙率³ . 如 CT 图像所示，3D 打印 RPC 样品的层间区 (IZ) 容易出现孔隙，并且明显具有较高的体积分数。特别是，在 IZ 的体积内，3D 打印 RPC 的 IZ 处的最小体积分数出现在具有 MWCNT 的样品上。