Subsurface defect detection in concretes by active infrared thermography

This paper presents observations from an active infrared thermography (IRT) experiment about structural monitoring by taking advantage from solar irradiance as a clean and renewable source of energy for thermal excitation. This contributes to reduction of carbon emissions associated with maintenance of existing concrete infrastructure and ensuring their extended life, and safe operation. The models in these observations were five concrete slabs made from a typical mix used for bridge construction in the UK, with simulated subsurface void (representing the defect) at depths of 5 to 25 mm (5mm increment) at the centre of slabs, and one slab without simulated defect. This study was conducted during a sunny afternoon. A sequence of IR images was collected for each slab (six sequences in total), and these sequences were used to calculate the average thermal contrast on surface of the slabs and evaluate its variation with depth of subsurface defect. Finally, the trend of thermal contrast is compared with the trend of thermal contrast from excitation by IR heater to highlight the limitations and future research needs for subsurface damage detection using solar irradiance.

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