Severe deterioration in aging infrastructures, especially in concrete structures, is currently becoming a critical issue world-wide. Since the preventive and proactive maintenance of infrastructures are necessary for repair before approaching to the final phase as the appearance of large-scale deterioration, efficient non-destructive testing (NDT) is imperative for the damage evaluation of infrastructures. In this concern, we have developed acoustic emission (AE) tomography technique as the promising NDT AE tomography can estimate distributions of elastic-wave velocities and attenuation-rates nondestructively inside reinforced concrete (RC) members. These distributions are to be readily associated with the degradation. In this study, AE sensors and accelerometers were employed to measure AE activities in steel-plate RC slabs. In order to examine monitoring areas in comparison with those of AE sensors, AE activities were detected by the accelerometers attached to heads of anchor-bolts, which were applied as temporary fixing tools to install reinforcing steel-plates at the bottom of RC slab. In the case of deteriorated structures, the secondary AE activity is generated from existing defects induced by traffic loads. Consequently, AE tomography analysis was carried out from the arrival times and the amplitudes of the secondary AE activities. It is found that damaged areas evaluated by one-side access AE tomography from the distributions of elastic-wave velocities and signal attenuations are in remarkable agreement with locations of internal cracks observed from on-site core-drilled samples.
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