Study On Electrical Resistance Tomographic Of Carbon Fiber Reinforced Concrete Structure

This paper, study on Electrical Resistance Tomographic (ERT) of Carbon Fiber Reinforced Concrete (CFRC) structure, is sponsored by the National Natural Science Foundation of China (No. 50238040).ERT method has many advantages, such as non-intrusion, online property, no-radioactivity, simpleness, inexpensiveness, portability, fast respond, result understandability and having mass of information of the result. This technology has been applied on physic, earth reconnoiter and hydrology. So far, no usage of ERT of concrete structure monitoring has been reported yet, because the resistivity of is very hight and not steatbale. CFRC, which is a kind of cement containing a small amount of short carbon fibers and has the properity of conductivity and pressure sensitivity, make it possible to monitor the CFRC structure by ERT method.This paper put forward a new method of monitoring CFRC structure by ERT technology. ERT aims to reconstruct the conducting ( or dielectric) properties of an object from measurements of the electrical signals measured from all possible sensing electrodes while an exciting current or voltage is exerted to the object throught a pair of sensing electrodes mounted on the sufface of it. Therefore, the spatial gradients of electrical conductivity, which are a function of damage or strain gradients, can be measured.The correlative matters about the applications of ERT of CFRC structure monitoring are studied, and the main innovatory work are listed as follow:1. A new projection method of ERT is put forward in this paper. Compare to other ERT projection methods, all measurements of voltages are token the potential of the lower one of the pair of exciting electrodes potential as the same referent potential, and the voltages sampled from all the sensing electrodes (the voltage of referent electrode is 0V) are stored one by one according to the electrodes number in this method, which predigest the measure system, and achieve a maturity projection record of excited voltage and responed voltages with a compact storage stucture.2. A numerical projection method used for complex resistivity distribution is proposed and designed. The author constructs parameterized hole-models and develops computer aided modeling software and ANSYS programs auto-generating software. Thus many functions of projection can be realized in ANSYS system automaticly, such as building the FEM model for complex resistivity distribution, changing loads, solving and recording data of projection, which resolves many important and difficult problems involved in using numerical projection method in ANSYS system, such as large mumbers of interactive manual operation, a long period of projection and high probability of making mistakes etc.3. An image reconstructed algorithm called Contour Line Regulate (CLR) metdod based on physics model is put forward. In this method, all the unknown resisitivities of the elements in an area carved by contour lines are regarded as one unknown quantity, which would reduce the counts of unknown quantities and converted the ill-posed invert problem to a well one in the projection. In another projection, an alternant reducing method of the counts of unknown quantities is adopted because the contour lines are changed. This dynamic reducing method allows the counts of element great to the counts of independent datum, and a high resolution image is availabled. Compared to non-back projection reconstructed methods, the principle of this algorithm is simple. Jacobi matrix and Hessian matrix are not necessary and no regularization method is need in this algorithm. It has the advantages of high speed and steady. Compared to back projection reconstructed methods, because the CLR method is an iterative algorithm, it has high precision.4. An ERT system of CFRC structure is developed. This paper does a full and detailed research on ERT. Based on researches of basic principles and pivotal theory, the author builds up a set of ERT system for CFRC structure monitoring for the first time. The system includes following modules: hardware and software system of ERT projection measurement, configurement module of ERT system, definition module of ERT projection model and ERT reconstruction model, ERT image reconstructed module and image processing module, etc. This system provides a whole set of independent hardware and software platform for the further research on ERT of CFRC structure.5. The paper studies ERT technology of structures with different section shapes and ununiform electrodes arrangement. Recently ERT research groups generally do many reseach on ERT system with certain section shapes and uniform electrodes arrangement. Take physical reconnaissance of the globe for example, the earth is the research object. Its section shapes is semi-infinite space and ERT electrodes are equal spaced. The object of industry flow monitoring is pipes. Its section shape is circle and the electrodes are arranged uniformly.The paper researches the ERT system of structures with various section shapes, such as square, bar-shape and several heteromorphous section shapes, and ERT simulation is carried out for the structure with heteromorphous section shapes and ununiform electrode arrangement. The research results show that the ERT images of structures with all section shapes are satisfactory and appropriate ERT electrodes arrangement can enhance partial tomography resolution. Furthermore the feasibility of monitoring CFRC structure by ERT technology and the validity of the research are validated by experimentations.