Evaluation of microstructure and mechanical performance of CNT-reinforced cementitious composites at elevated temperatures

Experimental studies are carried out to examine the microstructure and mechanical performance of carbon nanotube (CNT) reinforced cementitious composites at elevated temperatures (25 °C, 200 °C, 400 °C and 600 °C). Two different contents (0.1% and 0.2% by weight of cement) of CNT are added to cement paste. X-ray powder diffraction (XRD) results show that CNT does not improve or impede the hydration of cement minerals at room temperature, while at higher temperatures the further hydration process caused by high-pressure steam is impeded by CNT. The morphology observed by scanning electron microscopy (SEM) indicates that the bridging effect of CNT can be maintained below 400 °C, while CNT is mostly spalled with the matrix on the walls of pores and gaps at 600 °C. The residual flexural and compressive strength are measured. The reinforcing effect of CNT is most obvious at 400 °C, which is due to the potential of CNT as channels for releasing high-pressure steam.