Study of Corrosion Detection of Rebar Embedded in Concrete by Modified AC Impedance Method
|School||Harbin Institute of Technology|
|Course||Disaster Prevention and Mitigation and Protection Engineering|
|Keywords||RC bridges corrosion detecting AC impedance method equivalent circuit|
Bridge, the important and key element in transportation system, plays an important role in smoothly and healthy traffic system and the national economy. For now, most of bridges in China are RC bridges and built in the 1960s~1970s. However, due to poor bridge management and element aging of the bridge, corrosion of steel in concrete is so serious that it had induced more and more bridge failure and fatal accidents in China. Certainly, the same events have also been found in all over the world. It has been proven that we can greatly improve the safety and durability of the bridges and prolong their service lives if the corrosion is detected in its early stage and some effective prevention solutions are systematically executed before the corrosion is getting worse. In this thesis, a modified concrete-surface-based AC impedance method is studied by use of the equivalent circuit method, and it is figured out how several factors affect the detected apparent impedance.Firstly, impedance at the interface of the rebar and concrete is discussed. Based on AC impedance method, the equivalent circuit of the impedance at the interface is set up. Meanwhile, with the use of the equivalent circuit and its impedance spectrum, the relationship between characteristics of the impedance spectrum and the parameters of the equivalent circuit is obtained and analyzed. Also, the Cole-Cole model is applied to simulate the interface impedance. It is proved that with the proper dereferencing, Cole-Cole model can be effectively used to estimate the interface impedance and its corresponding characteristics.Secondly, with the set up of the coordinate system and the knowledge of electrical science, expression of potential at point in the concrete is obtained. According to the relationship between the impendence and the potential, it is proved that the main influencing factors for the detected apparent impedance include: the interface impendence, the distance between electrodes, the embedded depth of the rebar and the resistivity of the concrete.Thirdly, an equivalent circuit for the apparent impedance is built considering the interface impendence, the distance between electrodes, the embedded depth of the rebar and the resistivity of the concrete, and its expression is got.Lastly, serial spectrums with different the above parameters are obtained based on frequency scanning method in the software platform of MATLAB. How these factors influence the impedance spectrum and some advices for practical use concluded from above research are given at the end of this thesis.