Hybrid elastic-wave CT with impact acoustics for single-side measurement in concrete structures

For maintenance of infrastructures, advanced inspection techniques applicable to diagnosis and prognosis are increasingly in great demands. Elastic-wave computed tomography (CT) is one of the techniques that have been extensively applied to the inspection of concrete structures. This conventional technique requires inputs being recorded and hence limits the number of inputs and relevant examined ray paths in acknowledging that the number of sensor is limited and sensor installation is time-consuming in the field. To tackle this difficulty, we presented a hybrid CT method by introducing the concept of acoustic emission (AE) localization to the conventional elastic wave CT, enabling simultaneous identification of both elastic-wave velocity distributions and input locations. With this hybrid method, the velocity distribution can be constructed with no input information required, implying a saving in number of sensor and in sensor installing time. It also implies that inputs can be performed arbitrary times at arbitrary locations for yielding sufficient examined path rays even with a limited number of receiving sensors. In this study, we applied this technique to the single-side tomography of surface waves excited by mechanical impacts. The feasibility of this hybrid CT method was illustrated on a 1.5 × 1.5 × 0.3 m concrete specimen and on a cracked concrete wall in field. Also, its superior efficiency and resolution was shown.