Piezoelectric Properties Of Carbon Nanotube Cement Based Materials

Carbon nanotubes(CNTs)were mixed into cement to produce cement-based composites with good piezoelectric properties.The electrical conductivity of CNTs cement-based composites will change when subjected to external pressure.Compared with other materials,CNTs cement-based materials have the advantages of good compatibility with concrete structure,corrosion resistance,high conductivity and good mechanical properties.CNTs cement-based materials are made into sensors and embedded in the key nodes of the main body of the structure to detect the change of stress inside the structure.In this paper,the piezoelectric properties of cement-based carbon nanotubes(CNTs)were studied,and three groups of experiments were carried out to provide some references for the application of CNTs cement-based composites in structural health monitoring.The conclusions are as follows:(1)CNTs can rapidly promote cement hydration in the early stage of cement hydration(within 1h).The higher the concentration of CNTs added,the faster the early stage of hydration and the higher the degree of hydration.(2)In the process of one-way loading or unloading of the same specimen with the addition of CNTs,the resistivity change rate of the specimen basically showed a linear relationship with the absolute strain.With the increase of the number of CNTs added,the resistance change range of the specimen showed a trend of increasing first and then decreasing,which was mainly determined by the mechanism of infiltration electrical conductivity.(3)The main reasons for the initial resistivity drift are the polarization effect and the hysteresis of CNT displacement recovery.The water-binder ratio will affect the dispersion degree of CNT and thus the drift degree.Adding GA can reduce the drift degree,and it basically decreases with the increase of GA content.(4)When Ga and CNT conduct electricity together,the piezoelectric sensitivity of the composite material will be greatly improved.The optimal combination of piezoelectric performance of the composite material is:water-binder ratio 0.35,CNC content 0%,graphene content 0.05%,CNTs content 0.1%.The influence of various factors on piezoelectric performance of the specimen is from large to small:water-binder ratio>CNTs content>GA content>CNC content.(5)The addition of PVA fiber and quartz sand can increase the mechanical properties of CNT composites,but both will reduce the sensitivity of CNT composites.The experiment found that the addition of 50%quartz sand and 0.8%or 1%PVA fiber has little interference on the sensitivity of CNTs composites.