Investigating the effect of carbon nanotube on early age hydration of cementitious composites with isothermal calorimetry and Fourier transform infrared spectroscopy

The effects of a range of carbon nanotube (CNT) additions (0.1-0.5% by weight of cement) on the early hydration processes (0-24h) of cementitious composites were investigated by isothermal calorimetry, Fourier transform infrared spectroscopy (FTIR), X-Ray powder diffraction (XRD) analysis and scanning electron microscope (SEM) observation. The addition of CNT can improve the rate of hydration heat of cementitious composites. However, 0.1 wt% CNT obviously decreased the total cumulative hydration heat of cementitious composites. Additionally, the peaks corresponding to V4SiO44- vibrations were shifted from 496 cm(-1) to higher frequencies (534 cm(-1), 534 cm(-1) and 546 cm(-1)) at 24h due to the inclusion of CNT (0.1%, 0.3% and 0.5%). It is hypothesized that CNT with high surface energy can improve the energy of cementitious composites and increase the polymerization of C-S-H. According to the XRD test, CNT didn't affect the types of cement hydration products, but can reduce the orientation index of calcium hydroxide crystal. The microstructure observations demonstrated that CNT can also change the morphologies of hydration products and modify the microstructure of cementitious composites. Such behaviors could be associated with the case that CNT can increase the polymerization degree of C-S-H which was verified by the isothermal calorimetry and FTIR test.