RC bridge deck replacement will be taking more than half of budget in intensive renovation program of road investment in Japan. Prolong life-time measures such as improvement of the materials and effective repair methods to sustain a long life span are thus studying rigorously. Those countermeasures are implemented when the damage or deterioration becomes remarkable as to be observed by naked eyes, and therefore these activities can be regarded as a corrective maintenance activity, contrary to proactive maintenance. As for the proactive maintenance overall health evaluation for the infrastructures even in the early damage/ deterioration stage would be vital. Acoustic emission is an elastic wave generated due to cracks occurrence, growth and nucleation, and these AEs are referred to as primary AE activity while the emissions due to existent cracks’ reversible motion induced by internal stress distributions are referred to as secondary AE activity. In general the further deterioration proceeds, the more intensive AE activity are obtained. While as for the elastic wave velocities within the objective, smaller velocities imply more deteriorated condition than that of large velocities. Accordingly, it can be appeared that small velocity with remarkable AE occurrence could suggest serious deterioration condition; however careful examinations of AE activity in combination with wave velocity in seriously fatigue-damage RC deck questions this fact, e.g., serious damage areas, assumed both from elastic wave velocity and developed cracks on the surface, generates less emissions than of miner damage. This study details those findings with on-site AE monitoring and AE tomography results.

More than 30 years have passed since the steel plate bonding technique was applied for the first time to reinforced concrete (RC) slabs of road bridges in Japan as a strengthening measure against fatigue damage. Debonding of the steel plates as well as damage in concrete are often found as a dull sound during hammer tests. Efforts are being made for more frequent inspections; however, visual observation has a limitation in detecting damage in the concrete of the repaired slabs which are covered with steel plates at the bottom. Although the presence and extent of debonding can be roughly known from the change in sound during hammer tests, there are no decisive methods to detect or evaluate the internal damage of the concrete. The purpose of this study is to establish a method to evaluate damage in concrete of steel plate-bonded RC slabs on road bridges in service, with the focus placed on the temporary set anchors in the repaired slabs which had been used to hold the steel plates until settlement of adhesive agent for secure bonding. The proposed technique utilizes the anchor bolts as ultrasonic probes.