Estimation of the level of corrosion in reinforced steel by using FMCW radar

In countries like Turkey, which are geologically young and located on active fault lines, earthquakes are a major natural threat. The tragic results of the most recent earthquake in our country on February 6, 2023 have once again shown how much this threat should be considered and how urgent steps should be taken against earthquakes. With today's studies and technology, it is not possible to predict or know when an earthquake will occur, how severe and destructive it will be. However, it is possible to perform risk analyses of existing buildings or to reduce the destructive effects of earthquakes in advance and to minimize loss of life and property. From this perspective, it is essential to perform durability and risk checks of building stocks before earthquakes. In order to perform the tests of these structures, which number in the millions and do not comply with earthquake regulations, and which must be constantly checked for changes in corrosion levels at certain intervals even if they comply with regulations, in a short time, at low cost and with minimal need for manpower, the estimation of corrosion levels in iron reinforcements with FMCW radar is proposed in this study.The most commonly used method is currently the coring technique, which is a destructive method. This technique pushes for alternative searches due to the length of analysis processes, damage to columns and high human demand. The proposed study is a highly preferable non-destructive testing method in terms of eliminating these disadvantages. In the thesis study, it was aimed to determine the presence of corrosion on the iron in a cylindrical concrete mold by taking real measurements with FMCW radar. For this purpose, the phase difference change was observed with the MATLAB narrowed scenario and then the results were obtained in the simulation environment. In real life, FMCW radar scans were taken between 2.3-2.6 GHz from the irons in the concrete cylindrical mold and the data were evaluated. While the electromagnetic wave moves in the material, the physical and chemical properties of the environments affect the amplitude and phase of the advancing wave. Inferences are made by looking at this information from the wave's progress between layers. According to the expected results, the increase in the corrosion level in the iron in the concrete will cause a phase change. According to the simulation results obtained, a phase difference of 6 degrees occurred at 2.45 GHz level in the presence of 1 mm corrosion with a corrosion level of 0 mm thickness, i.e. without corrosion. According to the narrowed MATLAB scenario, a phase difference approximately 8 degrees, was observed between the phase degree formed in the 1 mm corroded plate at 2.43 GHz levels and the corroded plate. According to the FMCW measurements taken on real iron, a phase difference of 28 degrees occurred between clean iron and corroded iron. Then, when the irons were placed in a cylindrical concrete mold and FMCW scanning was performed, corrosion detection was achieved between clean iron and corroded iron a phase difference of approximately 5° occurred at 2.4 GHz levels, but no significant result was obtained for iron with medium level corrosion. As a result, the presence of corrosion was determined accurately with FMCW radar, but the reliability of the mathematical models obtained for corrosion grading needs to be increased.