Practical image measurement of crack width for real concrete structure

Crack width is an important data item in inspection and diagnosis for the safety management of concrete structures. Usually the crack width measurement is performed manually by specialists using a crack scale. However, it takes a long time and lacks the objectivity needed for quantitative analysis. Therefore, the importance of image processing for visual inspection has been increasing in civil and construction engineering. Recently, many methods for crack width measurement have been proposed. We have already tried to measure crack width utilizing image processing. However, these methods have concentrated only on the application to test specimens. In this paper, we propose an improved image measurement method for crack width determination, intended for application to real concrete structures. In our method, a crack scale is applied to the concrete surface for image acquisition. The crack width is measured by the brightness of the crack scale areas on the image with sub-pixel order accuracy. In the real world, the lighting conditions differ in various environments. To deal with such differences, this paper clarifies the conditions of effectiveness of our method for practical use. The validity of the proposed technique is investigated by experiments with images of a real concrete surface. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(10): 1–12, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10151