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International audience; This research paper presents the application of the microwave infrared thermography (MIRT) technique for the purpose of detecting and characterizing defects in the carbon-fiber-reinforced polymer (CFRP) composite reinforcement of concrete specimens. Initially, a numerical model was constructed, which consisted of a broadband pyramidal horn antenna and the specimen. The present study investigated the application of a 360 W power system that operated at a frequency of 2.4 GHz, specifically focusing on two different operational modes: continuous and modulated. The specimen being examined consisted of a solid concrete slab that was coated with an adhesive layer, which was then overlaid with a layer of CFRP. Within the adhesive layer, at the interface between the concrete and CFRP, there was a defect in the form of an air gap. The study examined three distinct scenarios: a sample without any defects, a sample with a defect positioned at the center, and a sample with a defect positioned outside the center. The subsequent stage of the investigation incorporated experimental verification of the numerical modeling results. The experiment involved the utilization of two concrete specimens reinforced using CFRP, one without any defects and the other with a defect. Numerical modeling was used in this study to analyze the phenomenon of microwave heating in complex structures. The objective was to evaluate the selected antenna geometry and determine the optimal experimental configuration. Subsequently, these findings were experimentally validated. The observations conducted during the heating phase were particularly noteworthy, as they differed from previous studies that only performed observation of the sample after the heating phase. The results show that MIRT has the potential to be utilized as a method for identifying defects in concrete structures that are reinforced with CFRP.

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CCBY; International audience; This paper presents two infrared thermography methods with CO2 Laser excitation and microwave excitation applied to defect detection in CFRP. The tests were conducted with two specimens, one with defect, and another one without defect. On two concrete plates 40 cm× 40 cm× 4.5 cmwere reinforced by CFRP; the defects were made by the absence of adhesive on an area10 cm× 10 cm. The specimens were heated by microwave, generated by a commercial magnetron of 2.45 GHz and guided by a pyramidal horn antenna, with a power of 360 W within 150 s. Another series of the tests was conducted with CO2 Laser, wavelength 10.6 μm, by heating the samples with a power of 300 W within 40 s. An infrared camera sensitive to medium waves in range of 3 - 5 μm, with a detector of 320 × 256 matrix detector in InSb (Indium Antimonide), was used to record the thermograms. As a result, the CO2 Laser excitation is better for the delamination detection in CFRP. This study opens interesting perspectives for inspecting other types of defects in materials sciences; the microwave excitation is suitable for the deep defects in the materials whereas the CO2 Laser excitation is better for the defects near the surface of the materials.

This paper presents a NDT by infrared thermography with excitation CO2 Laser, wavelength of 10.6 μm. This excitation is the controllable heating beam, confirmed by a preliminary test on a wooden plate 1.2 m x 0.9 m x 1 cm. As the first practice, this method is applied to detecting the defect in CFRP heated by the Laser 300 W during 40 s. Two samples 40 cm x 40 cm x 4.5 cm are prepared, one with defect, another one without defect. The laser beam passes through the lens of a deviation device, and heats the samples placed at a determinate position and area. As a result, the absence of adhesive can be detected. This method displays prominently its application as NDT with the composite materials. This work gives a good perspective to characterize the laser beam, which is very useful for the next detection campaigns., {"references":["Ch. Maierhofer, A. Brink, M. Röllig, H. Wiggenhauser, \"Transient thermography for structural investigation of concrete and composites in the near surface region,\" Infrared Physics & Technology, vol. 43, pp. 271-278, 2002.","Jeff R. Brown, H. R. Hamilton, \"Quantitative infrared thermography inspection for FRP applied to concrete using single pixel analysis,\" Construction and Building Materials, 2010.","Akbar Darabi, Xavier Maldague, \"Neural network based defect detection and depth estimation in TNDE,\" NDT & E International, vol. 35, pp. 165-175, 2002.","C. Ibarra-Castanedo, F. Galmiche, A. Darabi, M. Pilla, M. Klein, A. Ziadi, S. Vallerand, J.-F. Pelletier, X. Maldague, \"Thermographic nondestructive evaluation: overview of recent progress,\" in SPIESociety of Photo-Optical Instrumentation Engineers, Procedures Thermosense XXV, 2003.","Hernán D. Benítez, Humberto Loaiza,Eduardo Caicedo,Clemente Ibarra- Castanedo,AbdelHakim Bendada,Xavier Maldague, \"Defect characterization in infrared non-destructive testing with learning machines,\" NDT & E International, vol. 42, pp. 630-643, 2009.","M. R. Clark, D. M. McCann, M. C. Forde, \"Application of infrared thermography to the non-destructive testing of concrete and masonry bridges,\" NDT & E International, vol. 36, pp. 265-275, 2003.","XAVIER P.V. MALDAGUE, Theory and Practice of Infrared Technology for Nondestructive Testing. Canada, 2001.","Manyong Choi, Kisoo Kang, Jeonghak Park, Wontae Kim, Koungsuk Kim, \"Quantitative determination of a subsurface defect of reference specimen by lock-in infrared thermography,\" NDT & E International, vol. 41, pp. 119-124, 2008.","S. Vallerand, X. Maldague \"Defect characterization in pulsed thermography: a statistical method compared with Kohonen and Perceptron neural networks,\" NDT & E International, vol. 33, pp. 307- 315, 2000. [10] U. Galietti, D. Palumbo, G. Calia and F. Ancona, \"New data analysis to evaluate defects in composite materials using microwaves thermography,\" presented at the 11th International Conference on Quantitative InfraRed Thermography, University of Naples Federico II, Naples, Italy, 2012. [11] Hongjoon Kim, Kyungyoung Jhang, Minjea Shin, Jaeyeol Kim \"A noncontact NDE method using a laser generated focused-Lamb wave with enhanced defect-detection ability and spatial resolution,\" NDT & E International, vol. 39, pp. 312-319, 2006. [12] J. Schlichting, Ch. Maierhofer, M. Kreutzbruck, \"Crack sizing by laser excited thermography,\" NDT & E International, vol. 45, pp. 133-140, 2012. [13] S. E. Burrows, S. Dixon, S.G. Pickering, T. Li, D.P. Almond, \"Thermographic detection of surface breaking defects using a scanning laser source,\" NDT & E International, vol. 44, pp. 589-596, 2011. [14] Teng Li, Darryl P. Almond, D.Andrew S. Rees, \"Crack imaging by scanning pulsed laser spot thermography,\" NDT & E International, vol. 44, pp. 216-225, 2011. [15] L. De Lorenzis and J. G. Teng, \"Near-surface mounted FRP reinforcement: An emerging technique for strengthening structures,\" Composites Part B: Engineering, vol. 38, pp. 119-143, 2007. [16] M. J. Chajes, et al., \"Durability of concrete beams externally reinforced with composite fabrics,\" Construction and Building Materials, vol. 9, pp. 141-148, 1995"]}

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