Steel detection in reinforced concrete wall by microwave infrared thermography

This paper presents a NDT by infrared thermography with a microwave excitation system. The advantages of such stimulation lie in the volumetric absorption of incoming waves which lead to a greater sounded depth. The device generating the microwaves was made of a commercial magnetron 800 W at 2.45 GHz associated with a pyramidal horn antenna. This method was applied to detect the steel reinforcements (deformed bar 12 mm of diameter placing at every 10 cm) in a concrete specimen (1 m x 1m x 6.5 cm) with a concrete cover of 3.8 cm. The specimen was heated with an average power of 600 W for 5 min. An infrared camera was placed on the same side as the stimulated surface and thermograms were recorded at regular intervals. The whole assembly was placed in a protective enclosure against high frequency electromagnetic fields. The method based on a contrast algorithm was used to analyze the thermogram series. The result shows a higher temperature rise in front of the steel reinforcement areas. The effect of microwave caused an increase in moderate temperature does not lead to alteration of inspected concrete. Crown Copyright 2013 Published by Elsevier Ltd. All rights reserved.