Non-destructive testing system design for corrosion detection in reinforced concrete structures

Assessing the residual life and durability of structures in the construction industry is a major concern, not only in dangerous earthquake situations but also under normal conditions. Our country is located on many active fault lines and hundreds of thousands of building stocks on these fault lines were not risk-assessed long before the current earthquake regulations and are estimated to be "unsafe" according to the latest earthquake regulations of 2018. It is very important to determine the risk status of such a large number of buildings quickly and economically. From this perspective, the use of nondestructive methods instead of destructive methods such as stripping in the earthquake performance analysis of structures, especially in the determination of reinforcement number and corrosion in reinforced concrete structures, will provide significant advantages in terms of time and economy. When the literature on the related field of study is examined, it is understood that the destructive and non-destructive methods in use for the necessary detection and control of building reinforcements have problems such as high cost, long time losses, and high margin of error. For these reasons, there is a need for an alternative solution that works with an acceptable margin of error, produces fast results, and is more economical. The non-destructive testing device planned to be part of the decision support mechanisms to be used in building inspections is a ground penetrating radar (GPR) system based on the use of frequency modulated continuous wave (FMCW) method, which is a mature technology and offers uniqueness in corrosion measurement. In this direction, a prototype FMCW Radar has been designed and implemented with software components. Simulations were carried out in different scenarios on the simulation environment. Then, measurements were taken using both corroded and clean cylindrical metal materials to verify the corrosion detection capability of the device. Since this study involves the realisation of a prototype FMCW Radar system, the measurements taken with the device are preliminary measurements. The data sets obtained from the FMCW Radar were analysed with algorithms using digital signal processing techniques. As a result of the analyses, voltage losses of 0.24 V between the maximum amplitude points and 0.309 V in the working region were observed in the measurements taken from the highly corroded target and the clean target. The frequency shift between the maximum amplitude points was calculated as 117 MHz. As a result of the examination of the response signals in terms of phase shift, it was observed that there was a total phase difference of 52 degrees between +21 and -31 degrees. The scanning measurements showed that the location of the iron material in the scanning area could be determined, and that there was an intensity difference between the measurement results of highly corroded iron and clean iron material. The analyses revealed the presence of amplitude distortion, intensity difference, frequency shift and phase shift in the response signals of the target objects due to corrosion.