Preparation and microstructural properties study on cement composites reinforced with multi-walled carbon nanotubes

In this research, multi-walled carbon nanotubes were used to delay the propagation and growth of cracks in cement mortar on the nanoscale. To improve the dispersion of multi-walled carbon nanotubes in the cement mix a polycarboxylate superplasticizer was used. The mechanical strength of multi-walled carbon nanotubes-cement nanocomposites mix containing 0.1-2% nanotubes by weight (wt) and 0.5% superplasticizer by (wt) was measured and compared with that of cement prepared without multi-walled carbon nanotubes. It was found that the tensile strength of the specimens increased about 70% up to 0.3%, multi-walled carbon nanotubes. With further increase in multi-walled carbon nanotubes, a decrease in tensile strength was observed. Field-emission scanning electron microscopy used to observe the fracture surface of specimens containing 0.3wt% nanotubes indicated that the multi-walled carbon nanotubes were well dispersed and there were no agglomerates visible in the matrix. Field-emission scanning electron microscopy observation also revealed good bonding between the multi-walled carbon nanotubes and the surrounding cement matrix. In addition, X-ray diffraction data showed the multi-walled carbon nanotubes accelerated the dissolution and growth of the calcium silicate hydrate hydration products compared with the control cement mortar. Mercury intrusion porosimetry test results showed that chemical species could not penetrate the specimens containing 0.1wt% and 0.3wt% multi-walled carbon nanotubes as easy as other specimens. Thermogravimetric analysis results indicated that the cement hydration was enhanced in the presence of the multi-walled carbon nanotubes.