Practical image measurement of crack width for real concrete structure

Crack width is an important data in the inspection and diagnosis for the safety management of concrete structures. Usually the crack width measurement is done manually by specialists using crack scale. However, it takes a long time and lacks the objectivity for quantitative analysis. Therefore, the importance of image processing for visual inspection has been increasing in civil and construction engineering. Recently, many methods for the crack width measurement have been proposed. We have already tried to measure crack width utilizing image processing. However, these methods concentrated only on the application to test specimens. In this paper, we proposes an improved image measurement method of crack width for the application to real concrete structures. Our method attached crack scale on the concrete surface in the image acquisition. Crack width is measured by the brightness of crack scale areas on the image with sub-pixel order accuracy. In the real world, the lighting condition is different in various environments. For its difference, this paper clarifies the efficient condition of our method for the practical use. The validity of the proposed technique is investigated through experiments with images of a real concrete surface.