Aspect ratio effect of multi-walled carbon nanotubes and carbon fibers on high-performance cement mortar matrices

Formulation of high-performance cement mortar matrices reinforced with varying aspect ratios of carbon nanotubes and carbon fibers have been devised. Investigations on comparative effect of varying aspect ratios of carbon nanotubes and carbon fibers, with varying loads at two different water to cement ratios (w/c) of 0.45 and 0.50 in cement mortar matrices, were studied for the fracture response of the composites in crack initiation and propagation phases. The experiments concluded that an optimum addition of carbon nanotubes results in substantial improvements in terms of fracture properties. However, in case of carbon fibers, optimum increase in flexural strength was attained for carbon fibers having 12 mm length with 0.45 w/c, with the inclusion percentage of 0.15 by weight of cement indicating the increase in flexural strength up to 62.47%, followed by carbon fibers of 6 mm length at 0.45 w/c with the increase of 41.02%. Research also provides novelty for selection of optimum formulations among different aspect ratios. The field emission scanning electron microscopy evidenced a uniform level of tubes/fibers dispersion, the effective reinforcing effect by the tubes/fibers on the host matrix by providing the fracture mechanics phenomena of crack initiation, crack suppression, crack bridging and fiber–matrix debonding.