Evolution of Fatigue Damage in Wheel-Loading Tests Evaluated by 3D Elastic-Wave Tomography

Abstract

Currently, for proper maintenance of infrastructures, preventive and proactive measures for prognosis of infrastructures are preferable in comparison with reactive/corrective maintenances of structures that are highly deteriorated. This is so because vast sums are generally necessary for recovering the performance of the highly damaged structures. Therefore, prognostic maintenance must be conducted to establish economic and efficient management systems for the existing concrete infrastructures to complete their designed service life and to even extend them. Severe deterioration of aging infrastructures is currently a critical issue. In particular, the damage and deterioration of concrete slabs in bridges and highways are regarded as a critical issue worldwide. These components are often so fatigue-damaged under conditions of heavy traffic that repair and retrofit work definitely require regulating the traffic, thereby severely disrupting their function for the users. Consequently, preventive and proactive maintenances of concrete slabs that are in service are being urgently demanded for establishing the prognosis for civil engineering. To decide the maintenance systems based on the prognosis of concrete slabs, evolution of the fatigue damage and internal defects should be evaluated properly, if possible, visually. In this respect, Acoustic Emission (AE) tomography and elastic-wave tomography is under investigation and development as innovative nondestructive testing (NDT) methods. By determining the three-dimensional velocity distribution inside a slab via the above methods, the damaged or deteriorated areas are identified. Until now, regulated on-site visual inspections are only performed for the slab components of in-service infrastructures. However, the recent methods can predict the internal defects before the deteriorations physically emerge on the surface. Therefore, inspection methods to identify internal defects in concrete are to be readily implemented prior to the repair works. In the present work, a comparative study is performed during the internal progress of the fatigue damage induced by wheel-loading to identify the damaged area quantitatively via elastic-wave tomography, followed by a comparison with resultant surface crack conditions. The results show a good agreement between the predicted low-velocity zones and the damaged areas estimated by crack distributions, displacements, and strains. In particular, at locations where cracks are intensely observed, the velocities decrease below 3400 m/s. Furthermore, the areas with velocities below 2700 m/s are also observed in the slab corresponding to the attainment of the fatigue limit.