Mechanism of MWCNT on the performance of concrete from the perspective of thermal stability

Carbon nanotubes (CNT) demonstrate enormous potential for application in concrete due to their nanoscale size and highly crystalline structure. However, their comprehensive performance post fire conditions requires systematic research. CNT dispersions were prepared and mixed with concrete and heated to 200–800 °C, followed by water spray cooling. The effect of CNT on mechanical properties such as compressive strength, stress-strain, elastic modulus and compressive toughness was investigated in comparison with plain concrete. Additionally, a series of indoor experiments including thermal analysis (TG-DTG), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), Raman spectra (RS), and X-ray diffraction (XRD) were conducted to reveal the enhancement mechanism of CNT on the thermal stability of concrete. The experimental results demonstrate that CNT significantly enhance the high-temperature resistance of concrete. Within the range of 25–800 °C, the compressive strength, elastic modulus, and compressive toughness of concrete increased by 5.29–65.19 %, 19.92–168 % and 16.54–20.56 %, respectively. This is attributed to the stable structure of CNT at high temperatures and the fact that the elevated temperature favors the activation of CNT, which enhances its interaction with hydration products and plays a villain in the formation of the pore network. Furthermore, through a comprehensive analysis of existing research and experimental results, an empirical constitutive model for the stress-strain relationship of CNT reinforced concrete exposed to high temperatures has been proposed, which aligns well with the experimental results.