Mechanical and microstructural properties of cement pastes containing carbon nanotubes and carbon nanotube-silica core-shell structures, exposed to elevated temperature

This study aims to investigate the effects of carbon nanotubes and carbon nanotube-silica core-shell structures, on the behaviour of cement pastes exposed to high temperature (300, 450 and 600 degrees C). Pristine multi-walled carbon nanotubes (MWCNTs) were coated with a solid nanosilica (NS) shell, to form a core-shell nanostructure (MWCNT/NS). The cement pastes were incorporated with three different nanomaterial contents equal to 0.125, 0.25 and 0.5 wt.-% of cement. The results demonstrate that incorporation of an optimum amount (0.125 wt.-%) of MWCNT/NSs, is much more beneficial than the incorporation of MWCNTs, for improving the properties of unheated and heated cement pastes. Silica shell improves the binding ability between cement matrices and nanotubes, which is reflected in specimens' compressive strength retention, as well as in decreased micro cracking. However, exceeding the optimum amount of MWCNTs and MWCNT/NSs can lead to an agglomeration of nanomaterial, thus decreasing the thermal resistance of cement pastes.