The Research Of Pressure-Sensitive And High Temperature Mechanical Properties Of Carbon Nanotubes Reinforced Cement-based Composites

The 21st century,the cement-based composite material are developing in the direction of high performance,high strength,high toughness,high durability,high resistance to crack and multifunctional/intelligent.Because of the shortcomings of traditional structural health monitoring systems using embedded or additional strain sensors in engineering applications,new cement-based sensors have emerged.Compared with traditional sensors,these new sensors have the advantages of low cost,good durability,large sensing volume,and no reduction in structural mechanical properties.Carbon nanotubes(CNTs)have excellent mechanical,electrical,thermal,optical and electromagnetic properties.Composites with cement-based materials can realize the complementary advantages of component materials.They can not only improve the mechanical properties of cement-based materials such as strength,elasticity and toughness,but also endow cement-based materials with excellent electrical,thermal,electromagnetic and other functional properties.Among them,carbon nanotubes cement matrix composites(CNT/CC)has a broad application prospect in the future intelligent building,health monitoring,disaster prevention and mitigation and other fields due to its good pressure sensitivity,enhancement and high temperature resistance.In order to give full play to the excellent performance of CNT and overcome the agglomeration phenomenon of CNT in cement-based materials.This paper first studies the dispersibility of CNTs.The different surfactants,polyvinylpyrrolidone(PVP),gum Arabic(GA)and sodium dodecyl sulfate(SDS),are used individually to prepare Multi-walled carbon nanotubes(MWCNTs)suspension to compare the dispersion and stability of MWCNTs in the aqueous system by static observation method and transmission electron microscope(TEM)observation.CNT/CC are made from different surfactants,and their working properties and mechanical properties are compared.The electrical properties and pressure-sensitive properties are studied by four-electrode method.The optimal surfactant is determined to prepare piezoelectric CNT/CC,which mainly study the effect of MWCNTs content on the working performance,mechanical properties and pres sure-sensitive properties of CNT/CC,and compare the effects of different loading amplitudes and loading rates on the stress and strain sensing characteristics of CNT/CC under cyclic loading.The microscopic analysis of the conductive mechanism of MWCNTs on cement-based materials.In addition,the high temperature mechanical properties of CNT/CC are also discussed.The research results are as follows:(1)The results show that each surfactants can uniformly disperse MWCNTs,which is compared with MWCNTs suspension without surfactants.PVP has the best dispersion effect on MWCNTs.Its suspension can maintain the stability for a long time.Compare the fluidity,mechanical properties and pressure-sensitive properties of CNT/CC with different surfactants.The results show that CNT/CC that is prepared by using PVP can maintain a good fluidity,macro-mechanical properties,electrical properties and pressure-sensitive properties.(2)It is determined that PVP is used to prepare piezoelectric CNT/CC.The fluidity of CNT/CC decreased gradually with the increase of MWCNTs content.The compressive strength of CNT/CC specimens first increase and then decrease with the increase of MWCNTs content.The addition of appropriate MWCNTs has significant enhanced effects on the compressive strength of CNT/CC.(3)When the MWCNTs content is 0.05?0.10wt.%,the conductivity of CNT/CC changed significantly.MWCNTs with low content are easy to obtain good dispersion.It is easy to conduct to the mutual contact of conductive polymer of MWCNTs and form the conductive network in the cement matrix.When the content of MWCNTs is 0.10wt.%,CNT/CC has good pressure-sensitive property.Combined with SEM observation,MWCNTs uniformly dispersed in cement matrix which overlap each other to form a good conductive network.(4)CNT/CC have stable repeatability in response to strain under different loading amplitudes.The pressure-sensitive property of CNT/CC increase with the stress amplitude increase.Under the condition of the same loading amplitude,the pressure-sensitive performance of CNT/CC is improved with the increase of loading rate.(5)After 800?,the relative residual flexural strength and compressive strength of CNT/CC are about 30?35%and 45?50%,respectively.However,the contorl specimens are spalling.Observed by SEM,MWCNTs still play a bridging role in cement matrix and provide a good channel for the release of the high-temperature after 800?.To a certain extent,it alleviates the deterioration of high temperature property of cement-based composites.It is a good cement-based material with high temperature resistance.