Properties improvement of multiwall carbon nanotubes-reinforced cement-based composites:

Multiwall carbon nanotubes with extraordinary mechanical properties have been widely used as effective nano-reinforcer of cement-based composites. In this research, multiwall carbon nanotubes were dispersed uniformly in aqueous solution using N,N-dimethylformamide as dispersant with ultrasonication. The structure and micromorphology of multiwall carbon nanotubes were characterized via X-ray photoelectron spectroscopy and transmission electron microscopy. The effect of N,N-dimethylformamide on multiwall carbon nanotubes dispersion was better than that of previous dispersants. The multiwall carbon nanotubes/cement composites with different multiwall carbon nanotubes contents were prepared and the mechanical performances of multiwall carbon nanotubes/cement composites were researched. Results showed that the flexural strength growth rate of multiwall carbon nanotubes/cement composites was 21.7% and the compressive strength growth rate of the multiwall carbon nanotubes/cement composites was 2.9% incorporating with 0.04 wt% multiwall carbon nanotubes at 28 days. The ratio of compressive strength to flexural strength of decline rate of multiwall carbon nanotubes/cement composites was 15.9% with 0.04 wt% multiwall carbon nanotubes at 28 days. The isothermal calorimetry (TAM Air) showed that multiwall carbon nanotubes could accelerate the hydration reaction. The X-ray diffraction and thermal gravity analysis (TG/DTG) suggested that multiwall carbon nanotubes could improve the hydration process and increase the number of hydration products. The mercury intrusion porosimetry revealed the porosity of multiwall carbon nanotubes/cement composites was decreased. There is an effect of multiwall carbon nanotubes on inhibiting the extension of cracks and promoting the degree of compactibility of the cement-based composites. The micromorphology of multiwall carbon nanotubes/cement composites was observed through scanning electron microscope.