Performance Evaluation of MWCNTs Reinforced Cement Mortar Composites using Natural and Commercial Surfactants

An efficient and promising approach for effectively dispersing multi-walled carbon nanotubes (MWCNTs) in cementitious composites has been investigated. The naturally occurring organic extracts from species of indigenously known 'Keekar' trees scattered along tropical and sub-tropical regions; is found as an exceptional replacement to the non-natural commercial surfactants. In the initial phase of investigation, ideal surfactant's content required for efficient dispersion of MWCNTs in solution was determined using ultraviolet spectroscopy. The experimental investigations were then extended to five different cement composite formulations containing 0.0, 0.025, 0.05, 0.08 and 0.10% MWCNTs by weight of cement. It was observed that the natural surfactant produced efficient dispersion at much reduced cost (approx. 14%) compared with the commercial alternate. The estimated weight efficiency factor phi was found 6.5 times higher for the proposed sustainable replacement to the conventional along with remarkable increase of 23% in modulus of rupture on 0.08 wt% addition of MWCNTs. Besides strength enhancement, the dispersed MWCNTs also improved the first crack and ultimate fracture toughness by 51.5% and 35.9%, respectively. The field emission scanning electron microscopy of the cryofractured samples revealed efficient dispersion of MWCNTs in the matrix leading to the phenomenon of effective crack bridging and crack branching in the composite matrix. Furthermore, the proposed scheme significantly reduced the early age volumetric shrinkage by 39%.