Dispersion Of Carbon Nanotubes And The Durability Of Carbon Nanotubes Reinforced Cement-based Composites

As their excellent mechanical, electrical properties, carbon nanotubes become one of the most promising nano-materials. Carbon nanotubes reinforced cement-based composites are becoming more and more, but the works are mainly focused on the mechanical and electrical properties of cement-based composites, and the researches of their durable performances are rare. This paper studies four aspects such as the dispersion of carbon nanotubes, chloride permeability resistance, sulfate attack resistance, autogenous shrinkage of carbon nanotubes reinforced cement-based composites. By the microscopic test techniques, mechanisms of carbon nanotubes improving durability performances are analyzed. Main research works are as follow.Several surfactants were used individually and combinatorially to disperse the carbon nanotubes in aqueous solution with ultrasonic treatment. By measuring the UV-visible absorbency, combining static observation and centrifugal separation, the dispersion of carbon nanotubes in aqueous solution was studied. The results show that polyvinylpyrrolidone (PVP) has the best dispersion effect on carbon nanotubes when using one surfactant and polyvinylpyrrolidone with methyl cellulose have the best dispersion effect on carbon nanotubes when using two surfactants. The dispersion and mechanism of carbon nanotubes in aqueous solution were investigated by measuring the UV-visible absorbency, adsorption isotherm, surface tension and zeta potential of carbon nanotubes suspensions. The results show that the optimum concentration ratio of PVP to MWNTs is 5:1.The adsorption isotherm shows a two-step adsorption platform, and the isotherm reaches the saturation plateau at PVP concentration of 0.5g/L. The surface tension of MWNTs suspensions decreases from 60.86mN/m to 50.76mN/m, and the zeta potential of MWNTs suspensions increases from-15.6m V to-7.8mV.The chloride permeability resistance and sulfate attack resistance are tested according to Chinese Standard GB/T50082-2009. The autogenous shrinkage testing method is same as the one brought forward by An Mingzhe. The results show that MWNTs can reduce chloride ion diffusion coefficient, improve the resistance to sulfate erosion, and reduce the early-age autogenous shrinkage of cement-based composite materials. When MWNTs content is 0.10wt.%, the chloride ion diffusion coefficient reaches the minimum value of 1.43×10-12m2/s which falls by 39.7% compared with reference sample; The corrosion resistant coefficient of K120 is larger than 1.0; When MWNTs content is 0.15wt.%, the autogenous shrinkage reaches the minimum value, which falls by 28% compared with reference sample in 7 days age.The microscopic testing results show that MWNTs can fill micro holes of cement-based materials to improve the compactness of cement. When erosion failures happen in hardened cement, MWNTs effectively prevent the formation and development of cracks by playing the "bridge" role. MWNTs can promote the hydration of cement, and increase the generation of hydrated calcium silicate. They can also refine the aperture, lower the porosity, and improve the microstructure of cement-bases composite materials greatly.