Piezoresistive Properties And Conductive Mechanism Of High Dispersion Carbon Nanotube-cement Based Composites

It is no doubt that the most widely used building material is cement, which is soimportance to society and economy and be a focus of building material. As an importantmember of nanomaterial, carbon nanotube is a1D material processing outstandingmechanical, thermal, optical and electrical properties. High performance andmultifunctional composite material prepared by compounding carbon nanotube andcement has received intense research publicity. Furthermore, as a life cycle detectionsensor of civil engineering structures’ health, the electrical conductivity of cementmatrix can be improved by the use of carbon nanotubes. In my graduation thesis, I focuson the preparation of carbon nanotube-cement based composites with a low cost andhigh efficiency dispersion of carbon nanotubes. Change of the carbon nanotubeaggregates under the action of ultrasonic has been systematic study, as well as thedistribution of carbon nanotubes in the cement matrix. The structure of carbon nanotubeconductive nework and some factors which may affect the resistance of the compositehave been analysed.Carbon nanotube agglomerates will be broken into small clusters in the ultrasoniccavitation. And the cluster size decreases with the increase of ultrasonic time. Thecarbon nanotubes will be reaggregated in ethanol when the cluster size is less than1μm.By control the ultrasonic time and add cement powder while ultrasonic, the carbonnanotubes dispersed in ethanol be suppressed to reaggregate. The composite with highcarbon nanotubes dispersion efficiency can be prepared by mix the pretreated powderwith water after removing the solvent. the bending strength can be increased by14.23%for the composite with0.01%carbon nanotube.By testing the resistance of the composites under different humidity, temperature,and in the salt solution or the action of forces of change, results show that theconductivity change comes mainly from the change of joint resistance between carbonnanotubes and conductive network structure. As a porous material, the deformationunder stress of hardened cement is not linear. In less than5MPa loading,, the resistancedecreases with the increase of the force when the content of carbon nanotube is0.2%and increases for0.5%. The resistance increases with the increase of stress decreaseslinearly when the stress is5-10MPa.Based on the electrical properties of composite, the results show the relationshipbetween the electrical conductivity of composites and the content of carbon nanotubesobey the percolation theory. The conductivity of composite with increased by nearly2orders of magnitude than that of pure cement then the content of carbon nanotubes is0.1%, as the conductive network formation, compose of4.92×10-5S/m increased to 1.59×10-3S/m. The microstructure of composite indicates that the carbon nanotubesdispersed uniformly in the matrix, and the lower percolation threshold of0.095%isobtained. Through the analysis on the composite conductive network, results show thatthe critical index near the percolation threshold decreases with the increase of thecontent of carbon nanotubes, the conductivity of composites growth slowly withbackbone density decreasing. The piezoresistive property of composite is related to theloading method and the conductive network. Changes of conductive network can beresponse to the deformed of cement matrix’s microstructure well.