Application of flash thermography for crack identification in concrete materials

Deterioration of concrete materials is always initiated with the formation of cracks. Therefore, monitoring crack formation and their propagation is crucial in concrete durability assessment. This paper proposes to apply short-duration pulsed thermography - flash thermography (FT) - for surface crack detection. It allows fill-field and non-contact qualitative observation of thermal radiation from the object surface and is widely accepted in the aerospace industry. It is superior to the common practice of surface crack detection - visual inspection - since overall inspection time is saved and the maintenance costs are lowered. FT can be employed to detect and monitor a large number of cracks at the same time with just a flash time. A surface crack is detected based on the difference in light and IR radiation reflections between the cracks and intact region. The surface cracks, with widths ranging from 0.04 mm to 0.6 mm, are inspected and the results show that FT can detect surface cracks with widths larger than 0.32 mm successfully without further image processing. First-derivative processing has been applied and finer cracks of widths ranging from 0.04 mm to 0.1 mm can be observed.