Study on Detection Limit of Buried Defects in Concrete Structures by Using Infrared Thermography

Abstract

In Japan it happens that concrete parts suddenly collapse to create obstacles to the traffic in tunnels, on highways and bridges. Thus, the safety issue has become a serious social problem. Therefore, the detection of hidden defects in concrete building constructions in order to prevent an accidental damage is the important application area for nondestructive testing (NDT) techniques. Until now, the inspection is typically performed by using a hammer that is subjective and takes too much time. Infrared thermography is a promising NDT technique that might help in the fast detection of invisible (hidden) defects. Transient, or active, thermal NDT requires external thermal stimulation of the objects under test by warming up or cooling down the object surface. However, low-power and long heating is significantly affected by environmental conditions. Recent Japanese research in this area has been rather qualitative, i.e. without putting the accent on evaluating parameters of hidden defects. In this study, the experimental results are modeled and processed by using the thermal NDT software package developed at the Tomsk Institute of Introscopy. This has allowed not only optimizing test parameters but also obtaining reasonable estimates of defect parameters for air-filled voids and inclusions in concrete. It is shown that MRTD values measured by ourselves for the first time are of a little help while evaluating detection limit.

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“…Current SHM systems almost adopt Non-Destructive Testing (NDT) techniques, which can be divided into two types: on-demand type and in situ. The on-demand NDT techniques are based on instrumentation brought to the measurement site on-demand, including X-ray, infrared thermography, laser scanning and microwave radar [ 2 , 3 , 4 , 5 ]. However, these techniques cannot measure the physical quantities of concrete directly and the measured results are not real-time.…”

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