Mechanical properties and microstructure of multi-walled carbon nanotube-reinforced cement paste

Carbon nanotubes (CNTs) have great potential to improve the strength and toughness of traditional cement-based building materials. After effective dispersion in water with a surfactant, followed by separation using a centrifuge, multi-walled carbon nanotubes (MWCNTs) can be stored stably for over three months. Our study focused on the microstructure and compressive strength of Portland cement reinforced with MWCNTs. As the proportion of added MWCNTs was increased from 0% to 0.2% by weight of cement, the mechanical properties of the cement paste correspondingly improved. With the addition of 0.1 wt% MWCNT, the 7-day and 28-day compressive strengths increased by 22% and 15%, respectively. The cement paste flexural strength was also improved by addition of MWCNTs. Scanning electron microscopy (SEM) analysis showed that the carbon nanotubes were well dispersed in the cement hydration products. Debonding, bridging, and mesh filling were also observed by SEM. Pressured-mercury testing was used to measure pore distribution in the MWCNT-reinforced cement pastes, and it was found that the pore size distribution tilted in favor of gel pores, pores that have a positive influence on mechanical strength. (C) 2014 Elsevier Ltd. All rights reserved.