Effect of dual-modified CNTs on strength and chloride resistance of cementitious systems

This study is undertaken to explore, first, the dispersibility of dual-modified carbon nanotubes (CNTs) by way of non-covalent modification. Various non-ionic and ionic surfactants were employed and mutually combined with varying relative proportions. Then, the best few combinations from the dispersion test were used further for producing mortar mixtures reinforced with CNTs. These samples were later assessed for their mechanical strength and chloride resistance. A suite of morphological, thermal and microstructural characterisations was carried out to understand the underlying mechanisms. The results show that, compared with the single modification, the dispersibility of CNT could be improved more significantly by way of the dual modification. In particular, 70-90% of non-ionic surfactant, in proportion to the total surfactant addition, imparted the best dispersibility to CNTs in an aqueous solution. In addition, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry and scanning electron microscopy outputs reveal that the enhanced dispersion of CNTs by dual modification promoted the hydration process and the ensuing microstructure evolution of mortar specimens. Together, these offset the strength reduction imparted by entrained pores when introducing chemical surfactants and, more importantly, empowered the chloride resistance of CNT-reinforced mortars.