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.
Proven non-destructive tests have been widely used to detect invisible flaws. However, those methods are not remote sensing and cannot be applied in a severe environment. A thermal technique using the infrared radiometer is useful to detect the flaw, as is allows for remote sensing. In this paper, an abnormal radiation temperature distribution of the test piece was measured to detect the internal flaw by the infrared radiometer. The detection limit of the flaws was obtained experimentally and analysed numerically by means of analysis of the conductive heat flow around the flaw. The thermal image method represents thermal and detection behaviour of surface and internal flaws using the infrared radiometer. ' .
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