Influence of carbon nanotube on properties of concrete: A review

Carbon nanotube (CNT) has been increasingly used in concrete due to its good mechanical properties and electrical conductivity. Scholars around the world have carried out in-depth researches on carbon nanotube concrete (CNTC). Notably, they have proved that CNTs can play a variety of roles in concrete, such as bridging matrix cracks, filling internal pores and promoting cement hydration reaction. Based on these studies, different dispersion modes of CNTs are compared and the workability of CNTC is analyzed in this paper. At the same time, mechanical properties of CNTC including compressive strength, tensile strength, flexural strength and dynamic performance against impact are systematically reviewed. The durability of CNTC is also reviewed including chloride penetration resistance, carbonation resistance, sulfate resistance, impermeability, high temperature resistance and freezing-thawing resistance. In addition, the application of CNTs as conductive filler in concrete and analysis of the microscopic mechanism of CNTC are also summarized. The results show that the addition of CNTs will generally reduce the workability of concrete, but the pre-dispersed liquid CNTs relatively increase the liquidity. CNTs with OH group and nickeling have an outstanding enhancement on mechanical properties. COOH functionalized and shorter CNTs significantly improve the dynamic impact resistance of ultra-high-performance concrete. CNTs optimize internal pore structure and enhance interface transition zone (ITZ) to improve durability. At the same time, CNTC also shows good quality maintenance at high temperature, and its internal structure changes into a new form at 600 ℃. As self-sensing concrete, CNTC has good strain sensitivity and can be used to detect structures. In general, CNTC is a new building material with good application prospects. The review aims to help scholars systematically understand the action behavior of CNTs in concrete and may further promote the application of CNTC in practical projects.