Steel fibres were able to be identified in concrete and visually represented with the aid of two differing non-destructive test methods. Induction thermography and microwave thermography were employed in this project, which was completed in 2014 and approved by the regional government of Upper Bavaria. Both methods were able to provide evidence of the distribution and orientation of steel fibres in concrete and mortar. Both methods succeeded in detecting the fibres by means of a high-resolution infrared camera within approximately 10 seconds of the commencement of thermal excitation. Steel fibres were detected up to a depth of 2.5 cm from the surface using induction thermography. They could be identified up to a depth of 1.5 cm with the microwave thermography method. With induction thermography, evidence could also be provided of fibres in fresh concrete. This means that this technology is not only suitable for assuring the quality specified for steel fibre reinforced concrete components in the precast industry but for in-situ concrete applications as well. It could be shown that this testing technology has need of only a very short excitation time on conveyor belts, thus making high throughput possible.
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