Effect of multi-walled carbon nanotubes (MWCNTs) on the strength development of cementitious materials

The proposed study aimed to investigate the potential use of pristine multi-walled carbon nanotubes (MWCNTs) as nano reinforcement in enhancing mechanical properties of hybrid MWCNT/silica fume cement composites. Dispersion of MWCNTs was facilitated utilizing very fine particles of silica fume which also helped in an improved interfacial bond between MWCNTs and the cement matrix. The MWCNTs dispersion within the hardened cement matrix was qualitatively assessed by Field Emission Scanning Electron Microscope (FESEM) analysis. It was also observed that addition of MWCNTs accelerated the hydration process. The test results showed an increment in compressive strength by 12.4% and reduction in autogenous shrinkage by 8.5% for hybrid MWCNT/silica fume cement composites containing 0.01% MWCNTs (by wt. of binder). However, higher additions (greater than 0.03%) of MWCNTs appeared to have adverse effects on specimens. It was found that properly dispersed MWCNTs filled the fine pores in the cement matrix by providing an additional nucleation site for the formation of calcium silicate hydrate (C-S-H) that results in a denser microstructure, which in turn enhanced the strengths and limited the autogenous shrinkage. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.