Research on the mechanical properties of steel fibers reinforced carbon nanotubes concrete

Introducing steel fibers (SFs) into carbon nanotubes (CNTs) concrete can fully exert the synergistic effect of SFs and CNTs in both micro and macro, alleviating the high brittleness of CNTs concrete while enhancing its mechanical properties. In this study, the mechanical behavior of CNTs concrete reinforced with hooked-end steel fiber (HSF) and milled steel fiber (MSF) with respective volume fractions of 1.0%, 1.5%, and 2.0% were examined regarding compressive (cubic and axial), splitting tensile and flexural strengths at 28 days. Meanwhile, Digital Image Correlation (DIC) was used to quantify the crack propagation on specimen surface under varied flexural loads. The results confirmed CNTs' ability to improve the compressive, splitting tensile and flexural strength of plain concrete, but the inability to refine brittle failure. Include SFs further enhanced CNTs concrete’s strength and reduced its brittleness. In terms of fiber type, HSF-reinforced CNTs concrete outperformed MSF-reinforced in compressive, splitting tensile strength, and reducing the brittleness of CNTs concrete, whereas surrendered the latter in flexural strength. Crack propagation observed by DIC demonstrated the reinforced specimens’ good ductility due to the ability of SFs to restrict crack propagation and improve deforms of the whole specimen. Additionally, Scanning Electron Microscope (SEM) observation of CNTs-compacted concrete microstructure revealed the excellent synergistic effect of CNTs and SFs in bonding with cement matrix. Macroscopically, CNTs and SFs together could improve the mechanical properties and ductility of cement materials, and even structure durability.