Bond defect detection using PTT IRT in concrete structures strengthened with different CFRP systems

In the context of increased use of carbon fibre reinforced polymer (CFRP) to strengthen concrete structures, the bonding conditions between CFRP and existing structures are crucial. Recently, infrared thermography (IR) non-destructive testing (NDT) has emerged as a technique for bond detection. This paper reports in detail the detection of different unbond, debonding and delamination areas within the bond zone between single- and multi-layer CFRP and concrete structures. Pulse thermography (PTT) was chosen for the IR tests. Pulse intervals of 1 s, 3 s, and 5 s were used as thermal loading to all specimens and halogen lamps were positioned at different distances from the investigated surfaces. Each IR test involved the analysis of 600 IR images. Thermal responses were recorded to detect and study defect characterizations. The paper recommends the minimum thermal input to generate well-recognized bond defect detection, and the results show that the maximum thermal signal is proportional to the number of CFRP layers.