To enhance the safety and functionality requirements of engineering structures, carbon nanotubes are used to improve the performance of concrete. However, their high cost limits their large-scale application. In this study, industrial multi-walled carbon nanotubes (IMWCNT) were employed to ultra-high performance concrete (UHPC) to achieve a balance between nanomodification and economy. The effects of different IMWCNT contents on the flowability, mechanical properties, and water resistance of UHPC were investigated. Moreover, the hydration products, microstructure, and fiber–matrix interface characteristics of UHPC specimens were analyzed using thermogravimetric analysis and scanning electron microscopy. The incorporation of appropriate amounts of IMWCNTs could effectively improve the mechanical properties and crack resistance of UHPC and partly prevent the infiltration of water into the matrix. Adding 0.1 wt% IMWCNTs resulted in optimal mechanical properties, and the flexural/compressive strengths of fiberless UHPC mortar and fibrous UHPC (2 vol% steel fibers) were increased by 6.7/5.2 % and 8.5/11.3 %, respectively. Microstructural analysis of the samples showed that uniformly dispersed IMWCNTs can enhance cement hydration and bridge the cracks at the microscale and nanoscale. In addition, incorporating an appropriate amount of IMWCNTs in UHPC reduced the porosity of its fiber–matrix interface and optimized steel fiber distribution in the matrix. Cost-benefit analyses results showed that although the addition of IMWCNTs increases the manufacturing cost of fibrous UHPC, their addition in moderate amounts (0.1 wt%) does not adversely affect the economic index due to the improvement in mechanical properties.

中文翻译：

---

工业多壁碳纳米管对超高性能混凝土力学性能和微观结构的影响


为了提高工程结构的安全性和功能性要求，碳纳米管用于提高混凝土的性能。然而，它们的高成本限制了它们的大规模应用。在这项研究中，将工业多壁碳纳米管 （IMWCNT） 用于超高性能混凝土 （UHPC），以实现纳米改性和经济性之间的平衡。研究了不同 IMWCNT 含量对 UHPC 流动性、力学性能和耐水性的影响。此外，使用热重分析和扫描电子显微镜分析了 UHPC 样品的水化产物、微观结构和纤维-基体界面特性。掺入适量的 IMWCNTs 可以有效改善 UHPC 的力学性能和抗裂性，并在一定程度上防止水渗入基体。添加 0.1 wt% IMWCNTs 可实现最佳力学性能，无纤维 UHPC 砂浆和纤维 UHPC （2 vol% 钢纤维） 的弯曲/压缩强度分别提高了 6.7/5.2 % 和 8.5/11.3 %。样品的微观结构分析表明，均匀分散的 IMWCNTs 可以增强水泥水化并在微观尺度和纳米尺度上弥合裂缝。此外，在 UHPC 中掺入适量的 IMWCNT 可降低其纤维-基体界面的孔隙率并优化钢纤维在基体中的分布。成本效益分析结果表明，尽管 IMWCNT 的添加增加了纤维 UHPC 的制造成本，但适量添加 （0.1 wt%） 不会由于机械性能的改善而对经济指数产生不利影响。