Electrical Resistance Tomography imaging of concrete

Abstract

Cracking and deterioration of concrete are the leading causes of a premature failing of reinforced concrete structures. To assess the condition of concrete, a variety of destructive and non-destructive testing methods have been developed. From these two methods, the non-destructive testing (NDT) is a more favorable (albeit more challenging) option since the tested target is left undamaged. The NDT modalities include acoustic, electromagnetic and radiation based techniques. In this thesis, the feasibility of electrical resistance tomography (ERT) for NDT of concrete is studied. In ERT, electric currents are injected into the target through electrodes that are are attached to the boundary of the target. The resulting voltages between the electrodes are measured and this boundary voltage data is then used to reconstruct the internal conductivity distribution of the target. The reconstruction of the internal conductivity distribution of concrete is expected to provide valuable information about the condition of the structure so that appropriate repairs can be taken in time. The difficulty in ERT, as is in any other diffuse tomography modality, is that the problem has a nature of an ill-posed inverse problem. This implies that the solutions of the problem are unstable and nonunique in the classical sense. As a consequence, extra attention must be directed to the mathematical modeling of the measurements as well as to the reconstruction methods. Furthermore, concrete is strongly heterogeneous material composed of cement matrix, aggregate and different chemical compounds that create a challenging target for electrical modalities. Previous studies have shown that ERT is a potential tool for NDT of concrete, but the quality of the reconstruction was not yet sufficient for practical applications. In this thesis, especially localizing reinforcing bars and crack identification are considered. To meet those aims, novel computational methods for the image reconstruction are developed. For the crack identification and localizing reinforcing bars, a novel adaptive meshing approach was developed. In the new approach cracks and reinforcing bars are modeled as internal structures. The results show that by employing accurate mathematical models and statistical inversion techniques based on the Bayesian framework, ERT can become an applicable tool for practical NDT of concrete.

Finite Element Method Applied in Electromagnetic NDTE: A Review

“…The third problem is the complexity of any in-situ measurements, involving uncertainties higher than those associated with laboratory setting. These issues are discussed by [118], in the context of eddy current defectoscopy, and by Karhun et al [110], who applied ERT to detection of internal defects in concrete structures. The numerical solution of the inverse problem is usually not unique, and it is sensitive to modelling errors and a measurement noise.…”

“…Kahunen et al [110] applied ERT to 3D imaging of concrete. They used an in-house software for both the forward and inverse analysis.…”

Non-destructive evaluation of concrete using a capacitive imaging technique: Preliminary modelling and experiments

“…which is valid for Electrical Resistance Tomography (ERT) applications [21,32,33] and potential drop methods [34,35].…”

“…The resolution of GPR system is limited to 100mm for commercial systems due owing to the wavelength used [17,18] which is not really suitable for the majority of artifacts of interest in structural assessment. Other electromagnetic techniques, such as electrical resistance measurement [19], impedance spectroscopy [20] and electrical resistance tomography [21] are reported to be used for inspection and evaluation of concrete structures, but they all require a perfect electrical contact between the electrode and the target surface.…”

Embedded-based Instrumentation System for Electrical Resistivity Measurement on Conductive Concrete using Four-Electrode Method

“…Moreover, it can be equipped with a set of greater numbers of electrodes in order to develop a electrical resistivitybased tomography instrumentation system. Potential applications of Electrical Resistance Tomography (ERT) in the construction industry are include measurement of the thickness of the concrete cover on top of reinforcement bars location provided by ERT could be utilized in diagnosing the corrosion rate of reinforcement bars 2 . The other researches that have been carried-out 3,4 , show that electrical resistivity measurement can be applied to determine crackings on reinforced concrete structures and also to evaluate the corrosion of reinforcing steel.…”