Research On Mechano-electric Smart Properties Of Carbon Fiber Reinforced Concrete And Plain Concrete And Its Application

Concrete is used in civil structures on a large scale. Serious damage, even sudden breakage of concrete structures has happened because of steel corrosion, environmental erosion and man-made factors. So it is an important strategy to develop a healthy monitoring and self-adaptive control system for concrete structures, especially, for some crsis infrastructures. This study will provide a theoretical and experimental basis for the performance of smart concrete structures, which can realize multifunction, such as loading, sensing and actuating. The study is also one of the important fields in smart materials and systems.In the dissertation, the study on carbon fiber reinforced concrete (CFRC) and plain concrete has been reviewed. Then mechano-electric effect of CFRC and plain concrete, its mechanisms , the interaction among mechano-electric effect, piezoresistivity and seebeck effect, the electrical circuit model of concrete based on mechano-electric effect, electromagnetic emission of concrete, the mathematical model of mechano-electric effect are investigated. Also the converse effect of mechano-electric effect of CFRC and plain concrete, that is, electromechanical effect, and the interaction between electromechanical effect and electrothermal effect of CFRC are examined. At last, the application of mechano-electric effect on smart concrete structures is discussed. The following conclusions can be obtained:(1) The stress induced electrical current increases with stress increasing, and decreases with stress decreasing. The sensitivity of CFRC and plain concrete depends on their component, loading condition and the method of measurement. The study on mechano-electric effect of hardened cement paste provides a new method to make smart concrete structures.(2) An electric double layer(EDL) model is brought forward. According to this model, mechano-electric effect is related to the electrokinetic phenomenon of solid/liquid interface EDL in concrete. Experiments on ionic polarization effect are done to prove the micro mechanism.(3) An electrical circuit model based on mechano-electric effect is supposed. Using this model, the principle of measurement is described.(4) The relationship between electric emission pluse and the propagation of cracks in concrete under quasi-static loading is exhibited. Then a model on electromagnetic emission relying on the extent of cracks is put forward. Using this model, the amplitude of electrical field and magnetic field, the largest frequency are estimated. An understanding of electrical emission of concrete may lead toHipractical application such as nondestructive testing of concrete.(S)According to nonequilibrium thermodynamics, a mathematical model on the relationship between strain gradient and electric potential gradient is presented.(6) The electrically induced strain is observed in both CFRC and plain oncrete. Compared with plain concrete, CFRC demonstrates more sensitive to the outward electric field. That is, CFRC can produce the same strain as plain cement paste with smaller voltage.(7)The influence of mechano-electric effect of CFRC on piezoresistivity can be ignored. However, when both temperature gradient and compressive stress exist, the interaction between mechano-electric effect and Seebeck effect is obvious. So methods are suggested to remove the coupling effect. Similarly, electromechanical effect of CFRC can affect electrothermal effect and vice versa.(8) Smart concrete structure based on mechano-electric effect of CFRC and plain concrete is developed. By means of mechano-electric effect, a concrete beam can sense stress. It can sense impact taking advantage of electric emission.