Detection of cracks in concrete strengthened with CFRP systems using infra-red thermography

Bond defects due to the development of cracks in concrete strengthened externally with CFRP can degrade the integrity of the composite system. Previous studies have addressed this issue by using different non-destructive testing (NDT) methods, and most have attempted to determine a reliable method to detect cracks and recognize their properties. Infrared thermography (IRT) has emerged as an effective method to detect the propagation of cracks and determine their width in the substrate structure of the composite system. This paper presents the findings of an investigation of CFRP-concrete samples containing various kinds of artificial and loading cracks at the concrete surface. Different types of FRP fabrics and laminate combinations were used in the design. Active IRT was adopted for the thermal observation. Thermal pulses were applied with different angles to enhance crack measurement. The results show that the technique is capable of detecting the location and width of cracks quite adequately. Moreover, the location of the external heating and interval pulse has a considerable effect on crack detection. However, the results show that it is not possible to determine crack depth by using pulsed IRT.