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In Situ Photographic Survey of Crack Propagation in Flexible Pavements

Traditionally, methods for measurement of cracks in roads are manual and subjective, which in turn means time-consuming and inaccurate. Generally, crack length and position data show accuracy of about one meter, which is insufficient when studying crack development of single cracks. Automatic methods exist, but their resolution is not high enough to study propagation of hairline cracks. The objective of this study is to develop and evaluate a new method for detection of hairline cracks using digital photographs. Yearly from 1998 to 2002, crack data have been collected on two in-service road objects, and the crack propagation has been studied. Cracks were extracted using digital image processing. Seasonal effects, such as healing, are also investigated. The rate of crack propagation shows high variations between different years, although the shape of the crack pattern obtained at different measurements is similar. Some crack segments visible in 1999 and 2000 disappear in 2001 and return at the same positions in 2002. The method is mainly suitable  for research purposes on limited areas.