Title: The effect of carbon nano- and microfibers on microcrack formation

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Publication: CIA

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Date: 2/28/2011

Abstract:
The effect of incorporation of Multiwalled Carbon Nanotubes (MWCNT) and Carbon Micro Fibers (CMF) on crack formation and crack propagation of cement-based matrixes was studied. Cement pastes were produced using a vacuum mixer and had constant water to binder ratio of 0.5. The MWCNTs were either untreated or surface-functionalized. The functionalized MWCNTs included incorporation of active COOH groups. Internal tensional forces were introduced by repeated freeze-thaw cycles. Strain gauges were used to follow internal damage of the specimens, while the crack formation was studied by Scanning Electron Microscopy using resin impregnated and polished samples. The results showed that at an equal number of cycles an average crack width reached 1-2 μm in the case of the specimens without fibers and with MWCNTs. In the case of the specimens containing CMF no microcracks were observed. The application of the CMFs restricted formation of microcracks already at very early stage. The mechanical testing of the CMFs specimens showed also significant increase of the flexural strength in comparison with the reference mortar specimens as well as these incorporating MWCNTs.