In Japan it happens that building parts made of concrete 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 defects under test by warming up or cooling down the defect 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 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 experimented by us are of a little help while evaluating detection limits.

Date Published: 1 April 2003
PDF: 6 pages
Proc. SPIE 5073, Thermosense XXV, (1 April 2003); doi: 10.1117/12.487450

Published in SPIE Proceedings Vol. 5073:
Thermosense XXV
K. Elliott Cramer; Xavier P. Maldague, Editor(s)