Application of Elastic-Wave Tomography to Repair Inspection in Deteriorated Concrete Structures

Abstract

Currently, it is highly important to establish economical and efficient management systems for existing concrete infrastructures, in order to fulfil their service design lives and even to extend them. Severe deterioration in aging infrastructure is currently found to be a critical issue. For repairing deteriorated and damaged structures, large budgets are necessary, but budgetary restrictions are often imposed. As a result, preventive and proactive maintenance of infrastructure is desired, and inspections by non-destructive testing (NDT) methods must be applied. In terms of damage assessment and estimation of repair and retrofit recovery in concrete structures, in addition to current NDT, innovative methods must be established. For crack repair methods applied to the existing structures, inspection techniques to assess repair installations have not yet been practically developed. There are many reports that improper repair efforts have resulted in re-deterioration. Although epoxy injection and patch repair methods are widely implemented to refill internal cracks from the concrete surface, it is found in most cases that internal defects remain unknown and potentially could lead to the re-deterioration. Therefore, inspection methods to visualize internal defects in concrete must be readily implemented as a countermeasure for repair works. In the present study, the evaluation of repair effectiveness was performed in a reinforced concrete (RC) pier and a concrete wall in an existing structure. As an innovative NDT method, elastic-wave tomography is applied to evaluate three-dimensional (3D) velocity distribution before and after the repair. Penetration of the repair material and the increase in velocity due to the repair effect are visually and quantitatively identified. Additionally, a 3D tomography technique for one-side access is newly proposed, using drill-hammring to generate an elastic wave. Accordingly, the internal quality of concrete after patch repair is successfully visualized by the elastic wave velocity distribution.