The Mechanical-electrical-sensitive Properties Of Carbon Fiber Reinforced Cement-based Composites

In the construction industry,cement is an important basic raw material,which is widely used in various construction projects as a cementitious material.With the advancement of science and technology and the development of society,ordinary cement-based composite materials can no longer meet people’s higher requirements,therefore,building structures are gradually developing in the direction of intelligence,automation and informatization.Therefore,using Portland cement as the matrix,carbon fiber cement-based composites were prepared,which improved the electrical properties of the materials and their sensitivity to humidity,temperature and force deformation on the basis of ensuring or even improving the mechanical properties of the materials,so as to realize the intelligent monitoring of building structures.The specific research content is as follows:(1)Using the method of electrical theory analysis and AC impedance test,we explored the equivalent circuit model of carbon fiber cement-based composite material during electrical performance test and determined the test conditions of cement bulk resistance,that is,when the test frequency was 300kHz,the result measured by LCR instrument was only the bulk resistance of cement blocks.At the same time,the AC impedance analysis of the cement blocks under different working conditions ensures the stability of the circuit model.(2)The influence of water-cement ratio and carbon fiber content on compressive strength and flexural strength of materials was studied.The results show that the increase of the watercement ratio weakens the mechanical properties of the material,and the addition of a certain amount of carbon fiber can improve the mechanical properties of the material,but the influence of carbon fiber on the mechanical properties depends on the dispersion effect of carbon fiber.At the same time,combined with the results of scanning electron microscopy test,the internal microstructure and carbon fiber dispersion of different proportions of the test block were observed,and the influence mechanism of strength was studied and analyzed.(3)The influencing factors of the electrical properties of carbon fiber cementitious composites were discussed a theoretical prediction model of resistance on time was established,and the influence mechanism of curing time,curing conditions,water-cement ratio and carbon fiber content on electrical properties was clarified.The results show that with the curing time,the internal structure of the cement test block gradually compacts with the hydration reaction,and the resistance first increases and then tends to stabilize.Compared with laboratory curing conditions,the test block curing environment is rich in water vapor and the test block resistance is small under standard curing conditions.At the same time,the larger the water-cement ratio,the more water contained in the test block,and the better the conductivity.In addition,carbon fiber can improve the conductivity of the material,in order to ensure the dispersion effect of carbon fiber,the resistance of the blocks gradually decreases with the increase of carbon fiber content,but when the carbon fiber increases to 0.20%,the carbon fiber conductive network is quite complete,and the resistance is no longer reduced.(4)The sensitive properties of carbon fiber cementitious composites were studied,including moisture sensitivity,temperature sensitivity and pressure sensitivity.The resistance changes of cement blocks under different moisture content,different temperatures and different loads were tested and studied,and it was found that the resistance had good perception of moisture content,temperature and load.At the same time,the test block is cyclically loaded in the elastic stage,the resistance change rate and load change show a good correlation,and increasing the cyclic load rate can improve the stability of the resistance change rate,and the pressure sensitivity is also related to the ratio of the material.When the water-cement ratio is 0.48 and the carbon fiber content is 0.20%,the pressure sensitivity of the material is the best.