Effect of Dispersity of Multi-walled Carbon Nanotubes on Compression Strength of Cement

Multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) have widely been used to reinforce the cement or to monitor the safety of concrete through its electrical properties. As carbon nanotubes have the property of easy aggregation, its dispersions in cement and concrete play a decisive role in enhancement and conductivity. In this paper, the dispersity of MWCNTs in water and in cement paste, as well as its effect on the compressive strength of composition with MWCNTs and cement are investigated, using ultrasonic dispersion and three kinds of surface active agents Polycarboxylate Superplasticizer (Ad), Poly Vinyl Pyrrolidone (PVP) and washing powder (WP). The dispersity of MWCNTs in water, which is shown in numeral photo is analyzed by observation while cement paste is analyzed by scanning electron microscope (SEM). The results show that MWCNTs is easy to agglomerate both in water and in cement paste and exhibits poor reinforce ability if single Ad is used as advisable surface active agent, even though librated by ultrasonic. Assisted by ultrasonic, PVP and WP can promote dispersions of MWCNTs both in water and cement paste obviously. Therefore the PVP increases the compressive strength. The WP decreases the strength evidently because more air bubbles were brought inside the cement paste and the dimension of hole was heightened, the density of hardened cement then lowers remarkably.