Maintenance and non-destructive inspection of concrete structures in Japan

Japan has been producing a large amount of concrete structures throughout our country since 1950's. The important structures such as Shinkansen, Highways etc. have been used for more than 35 years, and it is now becoming an important problem to maintain the existing concrete structures. The normal maintenance method is to inspect the structures periodically, and when the degree of deterioration exceeds certain limit, repair or retrofitting of the structures is performed. To inspect existing concrete structures, visual inspection is the easiest and the most fundamental method. But this method may not be applicable for inspecting defects that does not appear on the surface of concrete. For such defects, non-destructive inspection (NDI) is the only method that can be applied. This paper explains briefly the background of the problem, how the maintenance of concrete structures are being done, and introduces some new applications of NDI techniques in Japan.