15 April 2011 Combined NDT methods for characterization of subsurface cracks in concrete
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One of the most frequent problems in concrete structures is corrosion of metal reinforcement. It occurs when the steel reinforcement is exposed to environmental agents. The corrosion products occupy greater volume than the steel consumed, leading to internal expansion stresses. When the stresses exceed concrete strength, eventually lead to corrosion-induced cracking beneath the surface. These cracks do not show any visual sign until they break the surface, exposing the structure to more accelerated deterioration. In order to develop a methodology for sub-surface damage characterization, a combination of non destructive testing (NDT) techniques was applied. Thermography is specialized in subsurface damage identification due to anomalies that inhomogeneities impose on the temperature field. Additionally, ultrasonic surface waves are constrained near the surface and therefore, are ideal for characterization of near-surface damage. In this study, an infrared camera scans the specimen in order to indicate the position of potential damage. For cases of small cracks, the specimens are allowed to cool and the cooling-off curve is monitored for more precise results. Consequently, ultrasonic sensors are placed on the specified part of the surface in order to make a more detailed assessment for the depth of the crack. Although there is no visual sign of damage, surface waves are influenced in terms of velocity and attenuation. The combination of the NDT techniques seems promising for real structures assessment.
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E. Z. Kordatos, E. Z. Kordatos, M. Strantza, M. Strantza, D. V. Soulioti, D. V. Soulioti, T. E. Matikas, T. E. Matikas, D. G. Aggelis, D. G. Aggelis, } "Combined NDT methods for characterization of subsurface cracks in concrete", Proc. SPIE 7982, Smart Sensor Phenomena, Technology, Networks, and Systems 2011, 79820W (15 April 2011); doi: 10.1117/12.881025; https://doi.org/10.1117/12.881025

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