Surface crack detection by flash thermography on concrete surface

Abstract

. The follow-up actions and the corresponding severity index on different building defects are listed in Table 1. Therefore, the range of crack width of interest in this study is from 0.15 mm to 1 mm. A cement panel with major cracks with widths of 0.5-1 mm and micro-cracks having widths of 0.1-0.5 mm are inspected and the results are presented. Moreover, this paper provides a comparison of the effectiveness of two traditional crack detection techniques, Sobel and Canny, and one proposed method, the sheared image subtraction method, and the results are also presented. Cracking may impair the durability of concrete by allowing immigration of external aggressive agents; therefore, crack monitoring is always a vital part in building pathology. This study proposes to apply short-duration pulsed thermography - flash thermography (FT) - for surface crack detection. This method allows full-field and non-contact qualitative observation of thermal radiation from an object surface and is highly accepted in the aerospace industry. It is superior to the common practice of surface crack detection - visual inspection. The overall inspection time is reduced and hence maintenance costs lowered. During inspection, the inspected surface is excited with a heat-pulse of short duration (~3 ms). Surface cracking is detected based on the difference in heat emission between cracks and intact region. The results show that FT can detect surface cracks with 0.5 mm to 1 mm crack width successfully but micro-cracks (0.1 mm-0.5 mm) can only be detected by adding water with FT. In addition, this study also compared the performances of traditional Sobel and Canny edge detectors and a proposed shear image subtraction method, for crack detection. The results show that the sheared image subtraction method is significantly more effective than the other two edge detection techniques in identifying cracks.