Evaluation of non-destructive techniques for inspection of post- tensioned concrete bridges

Reinforced concrete bridges with post-tensioned (PT) cables are particularly critical structures, as the degradation of the tendons is not fully detectable through conventional investigation methods and/or through visual inspections, due to the intrinsic nature of the structural typology. In fact, PT cables are encased in plastic or metal ducts which aim at protecting them from corrosion, but at the same time hide them making it impossible to evaluate their condition by visual inspection alone. Deterioration conditions of PT systems are broadly categorized into strand defects and grout defects. The deteriorated conditions of PT systems usually lead to a loss of prestressing force, with impacts on the bridge management in the form of reduced load capacity and structural safety, need for expensive rehabilitation interventions, and traffic disruption. Modern inspection guidelines have identified non-destructive (ND) methods suitable for evaluating the conditions of the tendons and the grout. Moreover, ND technologies used in other industries may have potential for PT bridge assessments. The present contribution aims at presenting a simple procedure to rank the non-destructive (ND) methods, that are currently used for investigating the deterioration of tendons and grout, through a series of metrics formulated to evaluate the various technologies under four different aspects, namely accuracy of measurement, ease of use, cost, and impact on the operation of the bridge. The goal is to provide the bridge owners with a decision tool that can assist them in the selection of the optimal ND technology for the evaluation of a particular strand or grout defect.