Study On Electrical Conductivity And Piezoresistive Properties Of Carbon Nanotube Cement Mortar Composites

The unique structure of carbon nanotubes makes them have excellent electrical properties.Adding well dispersed carbon nanotubes into cement-based materials can effectively improve their conductivity.At the same time,the incorporation of carbon nanotubes can make the cement-based materials produce easily observed resistance changes under pressure.The observation results can be used for long-term in-situ health monitoring of the structure.At present,the research on the conductivity and piezoresistance of carbon nanotube cement-based materials mostly focuses on the case that carbon nanotube is a single size.In this paper,four different sizes of carbon nanotube are selected to make carbon nanotube cement mortar samples.The factors that affect the conductivity and piezoresistance of the composites were studied,and the mechanism of conductivity was verified and explained by micro and micro experiments.The main work is as follows(1)The influence of different amount and size of carbon nanotubes on the electrical conductivity of cement mortar was studied.The relationship between the polarization time and the resistivity was tested.According to the test results,the effect of polarization effect on the measured resistivity was minimized by electrifying for 1 min before the test.When the content of carbon nanotubes is 0.1%(0.1wt%)of cement,the conductivity of carbon nanotubes cementbased materials increases suddenly,which is 137.3% higher than that of the samples without carbon nanotubes.After that,when the content continues to increase,the conductivity does not continue to increase,but slightly decreases.The results show that the conductivity of cement mortar with MWT is the shortest when the MWT content is 0.1%.(2)The change of electrical conductivity of carbon nanotube cement mortar under different factors was studied.Both humidity and temperature increase the conductivity of carbon nanotube cement mortar.Humidity and temperature increase the conductivity of cement mortar with higher content of carbon nanotube,and increase the conductivity of cement mortar with smaller length diameter ratio.With the change of temperature,the increase of conductivity is small when the temperature rises at first(15 ?-30 ?),and larger when the temperature rises at last(30 ?-50 ?).With the increase of humidity,the increase speed of conductivity is small at first,and larger at last.(3)The results show that the porosity of samples decreases and the conductivity of charged ions in pore solution decreases.Carbon nanotubes with high content(0.2wt%)and smaller aspect ratio have better pore refinement effect on cement mortar samples,but the change of porosity is small,and the most probable pore size is far less than the critical pore size,and the conductivity of conductive ions in pore solution is weaker.(4)The piezoresistive properties of carbon nanotube cement mortar were studied.Under uniaxial compression,the addition of carbon nanotubes can improve the piezoresistive properties of cement mortar,in which 0.075wt% of carbon nanotubes can improve the piezoresistive properties of cement mortar the most,and the carbon nanotubes with the largest aspect ratio can improve the piezoresistive properties of cement mortar the most.