The deficiency inside concrete stuctures which induces deterioration of concrete strutures is a serious problem all over the world. In many cases, the deficiencies are hidden inside the concrete structures, and it is inpossible to observe the deficiencies with unaided eyes. The usual detection was performed by destructive testing methods. But destructive testing methods decrease the structures, and so are not good measurement. For not to destroy the structures, however, research concerned with the development of non-destructive testing of concrete has nearly all taken place during the past 46 years . But the applied infrared thermography to detect the deterioration of concrete strutures was only 23 years. Infrared thermography has been found capable of detecting delamination because there is a difference in the surface temperature of sound and delaminated concrete structures under heated conditions. This article describes the fundamental experiment of detectiong the cavities inside concrete structures with infrared thermography
