Damage evaluation of an internal concrete in steel-plate bonded slabs with anchor-bolts

Re-deterioration is currently found in reinforced concrete (RC) slabs of highways, which were retrofitted with steel-plates. However, the presence of asphalt pavement and steel-plates covering the top and bottom surfaces of the slabs makes it extremely difficult to determine internal damage of concrete. The damage could significantly affect the load carrying capacity and the durability of the whole structure. In this study, a novel technique for proper inspection and evaluation is proposed, by applying the temporary anchors left on the steel-plates bonded as sensing probes. An impact is driven by hammering the head of anchor bolt, which is employed as a sensing probe to detect elastic waves through RC slabs. By focusing on the characteristic frequency band of the Rayleigh waves, the arrival time and the associated velocity are to be evaluated. An inspection was carried out on an existing bridge in service for the verification of the sensing technique. It is found that the anchor-bolt sensing technique proposed is applicable to evaluation of internal damage of concrete slabs retrofitted with steel-plates.