Research On The Influence Of Multiphysics On The Piezoresistive Effect Of Carbon Nanotube Concrete Structure

Concrete bridges are in a service state where factors such as temperature,humidity and load are constantly changing.Factors such as physical fields and material components affect and restrict the development of intelligent concrete.Scholars at home and abroad have conducted a lot of research on the electrical properties of carbon nanotube cement-based composites.Due to the many influencing factors,the form and degree of influence of various physical fields are also quite different.At present,the attention and depth of research on this issue is not enough,and the theory of piezoresistive effect is not yet perfect.Therefore,it is necessary to study the influence of multiphysics on the piezoresistive effect of carbon nanotube concrete members.The research purpose of this paper is:to carry out the multi physical field influence test of the piezoresistive effect of carbon nanotube concrete and the piezoresistive test of carbon nanotube concrete members(beams);combined with the percolation theory,effective medium theory,field emission theory,based on the tunnel effect theory and current density model,to establish the theoretical model of the piezoresistive effect of carbon nanotube concrete;to reveal the influence of various physical fields on carbon nanotube concrete The mechanism and characteristics of piezoresistive effect.The main contents and achievements of this paper are as follows(1)The conductive and piezoresistive properties of carbon nanotube cement-based composites were studied.The conductive and piezoresistive mechanisms were analyzed.The effects of physical field and material composition on the conductive properties of carbon nanotube cement-based composites were explained.Main conclusions:the main influencing factors of piezoresistive effect of carbon nanotube concrete include physical field and material composition.The influence of physical field includes voltage,stress/strain,temperature and humidity,and the influence of material composition includes morphology,content,water cement ratio,admixture and admixture of carbon nanotubes.(2)Through the dispersion test of carbon nanotubes,the scheme of efficient preparation of carbon nanotube suspension is determined,and the influence of multi physical fields(stress,humidity,temperature and voltage)on the electrical properties of carbon nanotube concrete is studied by orthogonal test.Main conclusions:when the mixing ratio of SDBS and CNTs is 2:1,the CNTs suspension has the best dispersion after40min ultrasonic treatment,and the absorbance can reach 1.90A;with the increase of humidity,the stress sensitivity first increases,then decreases,and then increases;with the increase of temperature,the stress sensitivity first increases and then decreases;the sensitivity of a voltage of 1V is significantly higher than other voltage levels,but the piezoresistive response is susceptible to interference from other factors.(3)Experimental study on piezoresistive effect of carbon nanotube reinforced concrete beams is carried out to analyze the influence of reinforcement amount,loading rate and test voltage on piezoresistive effect of carbon nanotube reinforced concrete structures(beams).The main conclusions are as follows:under different load levels,the single reinforced concrete beam has good piezoresistive effect and good stability;the effect of different loading rates on piezoresistive response is not obvious;under different voltages,the initial resistivity decreases gradually with the increase of voltage,the variation amplitude of resistivity also decreases gradually,and the noise of piezoresistive response curve increases obviously.(4)Based on the theory of tunnel conduction,the theoretical model of piezoresistive effect of carbon nanotube concrete is established.Based on the analysis results of piezoresistive test of carbon nanotube concrete,the physical fields of temperature,humidity and voltage of the theoretical model are calibrated.The main conclusions are as follows:after the correction of humidity on piezoresistive model,the theoretical value is consistent with the change law of interpolation curve;the theoretical value of resistivity change fraction at different temperatures is different from the experimental value,but the overall change law tends to be consistent,and the correlation coefficient R~2 of the two is up to 0.825;the resistivity change fraction changes in a quadratic parabola with the increase of voltage,and the resistivity change fraction decreases with the increase of voltage at 20V The correlation coefficient R~2 between theoretical value and experimental value can reach 0.997.In this paper,the experiment and theory are combined to reveal the influence of various physical fields on the piezoresistive effect of carbon nanotube concrete,which provides a certain basis for carbon nanotube concrete to play its excellent function scientifically and reasonably in the field of engineering intelligent monitoring.