Damage Evaluation for Concrete Bridge Deck by Means of Stress Wave Techniques

Different from postfailure maintenance in many perspectives, preventive maintenance of civil engineering structures is another highly crucial measure, not only for achieving efficient distribution of limited budget over existent aging infrastructures but also for maximizing their service lifespans. In the context of road bridges, their functional failure often causes serious impact on safety and logistics, which could turn out to be detrimental to the social economy. To appropriately maintain a huge number of aging infrastructures, a strategic maintenance program, facilitating both the global- and local-diagnosis approaches, that is effective in assessing early damage is of high demand. In this study, fatigue damage of concrete bridge decks, which is a common form of deterioration among bridges, was examined by sensitive nondestructive testing methods utilizing propagation of stress waves. Specifically, the fatigue damage process of concrete decks due to repeated traffic loads is visualized by means of active and passive elastic wave techniques, namely the elastic wave tomography and acoustic emission techniques. In the experiment, a full-scale concrete deck was subjected to repeatedly moving wheel load, to induce fatigue damage to the concrete. At three stages of after initial loading, after 10,000 passage and after 20,000 passages of 150-kN wheel loading, the fatigue test was suspended temporarily, and elastic waves were transmitted into the concrete to inspect interior structure with elastic waves' velocity. Applying static load with gradual increment in magnitude, acoustic emission testing was then conducted to extract characteristic acoustic emission (AE) parameters with regard to the intrinsic damage. Promising elastic wave parameters for quantifying the damage, which have been identified through experimental studies, were later verified using in situ deck specimens hewed out from an actual bridge. These experiments showed that by using sparsely arrayed AE sensors for measurement, followed by extracting AE frequency features, global investigation of the integrity of bridge decks could be carried out. Once the area of interest was identified through analysis of AE data, detailed information such as cross-sectional damage could be visualized by employing ultrasonic testing and tomographic reconstruction procedure.