Spalling mechanism of carbon nanotube concrete at elevated temperature

Abstract Carbon nanotube concrete (CNTC) has attracted wide research interests due to its excellent mechanical properties and thermostability. Mechanical properties of CNTC at ambient temperature were widely studied by researchers, but the behavior of material at elevated temperatures still requires further study. For cement-based materials, spalling can occur under fire attack and cause structural failure. Up till now, the effect of carbon nanotubes (CNTs) on the spalling mechanism of concrete at elevated temperature is still unclear. In the current study, the spalling response of CNTC with different water cement ratios and various contents of CNTs at elevated temperature are experimentally investigated. The mechanism of CNTs inhibit spalling during the heating process is discussed. The concrete samples with lower water cement ratio (w/c) show stronger spalling sensitivity than those with higher w/c at elevated temperature. The experimental results show that when the w/c of the sample is 0.42 and the content of CNTs is 0.1 wt%, the effect of inhibiting spalling is the best. The spalling probability of the sample is the smallest, which is 20%. The tensile strength of CNTs and the bond strength between CNTs and concrete matrix increase the total energy required for crack propagation, which can effectively reduce the formation and propagation of cracks. The effects of crack bridging and porosity increasing in concrete matrix caused by CNTs are benefit to prevent spalling, while filling pores may reduce the spalling resistance of CNTC. In addition, the uniaxial compression test of CNTC with different contents under 140 days curing was carried out to study the aging effect of CNTs on the strength of concrete. The mechanism of pore wall crack propagation between compression and spalling failure of CNTC is investigated.