Lateral Damage Identification in RC Slabs by Several Tomographic Approaches with Rainy Induced Elastic Waves

Abstract

It is generally recognized that preventive and proactive maintenance works are necessary for such important infrastructure as bridges and tunnels. For reinforced concrete (RC) members, essential issues include establishing a maintenance system with the appropriate measures prior to the extensive damage and failure.As a result of budgetary restrictions, preventive and proactive maintenance of infrastructure are desired, and thus inspections by non-destructive testing (NDT) methods providing early damage information must be applied. In terms of the damage assessment and estimation of repair and retrofit recovery in concrete structures, in addition to current NDT, innovative methods must be established.The authors are thus studying tomography techniques based on elastic waves and acoustic emission (AE) to visualize three dimensional internal defects in concrete. In AE tomography, past reports can be found in literatures [1] and [2]; however, as they did not consider diversion of wave propagation paths (hereafter referred to as ray paths), few successful results can be obtained. In consideration of the diversion of the ray paths, the basic analytical procedure and the applicability of these techniques have already been reported as elastic-wave tomography [3] and AE tomography [4] by authors.Through the tomography technique, internal conditions are obtained using elastic wave parameters such as amplitudes and elastic wave velocities. This technique has been developed in the field of seismology and geophysics [5] to [7] as well as ultrasonic [8] to [10]. In this study, elastic wave velocity and attenuation rate are [11] used as the parameter. In elastic wave tomography, both the location of the excitation and the excitation time are known, whereas they are unknown for AE tomography. Specifically, the tomography can evaluate the elastic wave velocity Efficient inspection techniques for ageing infrastructures are in great demand. In this study, rainy induced acoustic activity, which has so far been treated as a nuisance event for acoustic monitoring, is ambitiously utilized to identify damages of reinforced concrete (RC) slabs. Specifically, in-situ acoustic emission (AE) measurements of RC bridge slabs are conducted for a week. First, internal damages of the slabs are evaluated by both of AE activity and elastic wave velocity by means of AE monitoring and AE tomography. As for some representative locations showing each different damage estimated by the AE activity and the velocity, core samples are retrieved for the verification. In addition, AE activity induced by rain droplets in a short period of minutes are identified by an AE source location algorithm followed by computation on attenuation rate distribution. Through the evaluations, it was found that the distribution of AE sources induced by precipitation could reflect internal damage of RC slabs i.e., dense areas of source locations imply the intact or minor damage, while sparse areas of source locations suggest serious damage of RC decks. With this finding, the p...

Fast Tomography: A greedy, heuristic, mesh size–independent methodology for local velocity reconstruction for AE waves in distance decaying environment in semi real-time

“…Tomographic technique with AE is becoming a popular tool to study damage in many real-life structures. 27,28 Ohtsu et al 9 have congregated all recent development in ray tracing methodologies for tomographic reconstruction of AE waves. The standard process is briefly described through the following equations.…”