<title>Thermographic NDT of building envelopes utilizing in-door heating systems</title>

The deterioration of concrete structures due to drastic changes in environment or due to poor workmanship has become very serious in Japan recently. In particular, since buildings are finished with render or tile on their facades in order to improve durability and appearance in many cases, the number of accidents resulting in injury or death caused by the fall of these finishing materials in increasing continuously. As a method of detecting delaminations of finishing materials, the thermographic survey using thermal imager is widely used because of the advantages of easiness, rate of data sampling and safeness. However, since this method is based on the difference of surface temperature between delaminated areas and sound areas generated by solar radiation, the method cannot be used under cloudy weather. It is a big difference between the construction field and other fields like metals, ceramics and plastics, which can do artificial heating or cooling easily. In order to improve the applicability and limitations of the method, a study was carried out. In ths study, instead of exposing an external wall to the sun, a method of heating the rear side of the wall by using the indoor heating system of the building was discussed and tested. As a result, it was proved that below-surface defects of building facades could be located without solar radiation by controlling the room temperature appropriately. This paper outlines the procedure and results of the study.