Multisource ultrasound-excited thermography for detecting concrete microcracks in hydraulic structures

Hydraulic concrete structures often suffer from cracking that could lead to engineering accidents. Thus, it is important to identify emerging concrete cracks so that the premonitory danger of the components can be comprehensively evaluated, and the disaster management level can be advanced to the initial stage of the hazard. This study investigated the use of ultrasound-excited thermography to detect surface microcracks in concrete engineering components. A detection system and method for the synergistic excitation of multiple excitation sources were developed, and self-adaptive pressure-loading sleeves containing back shafts made of glass fibre-reinforced nylon were developed to exert pressure on the transducers. Eighteen groups of in-situ experiments were conducted on important parts of the key component using a combination of 28-kHz and 40-kHz-transducers with a power of 100 W. The results demonstrate that ultrasound-excited thermography with the synergistic excitation of multiple excitation sources can be applied to detect surface cracks in approximately semi-infinite reinforced concrete members in-situ. The radius of the current investigation of cracks stimulated by one 100-W transducer pressed by the self-adaptive sleeve in reinforced concrete members is as far as 300 mm. The minimum widths of the detected cracks are 0.03 mm.