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This paper presents a study on the feasibility of using electrical resistance tomography (ERT) for detecting cracks in concrete. Our previous studies have demonstrated that cracks in concrete can be detected with ERT in cylindrical geometries. In this work, the main focus is on investigating the capability of ERT for crack detection and characterization in more realistic geometries in which the sensor array is attached to one planar surface of concrete. The feasibility of ERT in crack detection is tested with: 1) concrete slabs containing plastic plates; and 2) beams with real cracks generated by three-point bending. The results with slabs demonstrate the ability of ERT to distinguish between crack-like defects with different depths and to detect laminar defects. The results with beams verify that the method is also feasible in the case of real cracks.
Keywords: crack detection; electrical resistance tomography; imaging; nondestructive testing.
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INTRODUCTION
Cracking and deterioration of concrete are the dominant factors reducing the service life of concrete structures. Although the cracking phenomena may occur due to a variety of reasons, the underlying cause of any cracking is the relatively low tensile strength of concrete. Cracking occurs when the tensile stresses exceed the tensile strength of the material because of external loads or intrinsic volumetric instability caused by moisture, chemical, and/or thermal effects. Severe cracking is frequently a concern because such cracks provide an easy access for harmful agents, which may lead to corrosion of the reinforcing steel, thus reducing the structural capacity of the concrete (TRB 2006).
In addition to conventional destructive evaluation, a number of nondestructive testing (NDT) techniques have been developed with the aim of easy and reliable evaluation of the concrete structures (Wiggenhauser 2008). To detect cracks, acoustic emission and ultrasonic (Maji and Shah 1998, Sakata and Ohtsu 1995), impact echo (Sansalone and Carino 1989), ground-penetrating radar (Louizi et al. 2002, Rhim 2001), and infrared thermography (Sakagami and Kubo 2002) methods have been used. Over the last two decades, there has been a growing interest in using electrical methods for NDT of concrete. Various parameters, such as concrete humidity (Hunkeler 1997, McCarter and Garvin 1989) and chloride distributions (Loche et al. 2005, McCarter et al. 2001), affect the electrical properties (resistivity) of...