Assessment of Inspection Procedures for Pre-stressed Concrete Bridges with Post-tensioned Cables

The management of existing pre-stressed concrete bridges, with post-tensioned cables, is a current and complex issue, both from administrative and technical points of view. It should aim at maintaining the efficiency of the road networks, and especially at guaranteeing the safety of the road users.

Existing post-tensioned concrete bridges are often aged structures, subjected to degradation phenomena and to heavy traffic loads. Moreover, the realization process of post-tensioned concrete beams, consisting in difficult phases, has often led to conditions that accelerate the degradation of cables during the service life. The presence of voids in the ducts, mainly due to imperfect grout injections, in addition to the presence of chlorides and hydrogen, could activate dangerous localized corrosion phenomena and lead to a high reduction of the safety level. Highway managers are therefore asked to carefully evaluate the state of conservation of these bridges, with a consequent significant economic impact, given the large number of beams that must be inspected. In this article, the experimental campaign carried out to assess reliable and quick procedures for the inspection of pre-stressed concrete bridges with post-tensioned cables, is presented and discussed. Laboratory and in-situ tests were performed to investigate and calibrate traditional and innovative systems able to perform the different required phases: the identification of the cable positions, the localization and quantification of defects, and the evaluation of the residual pre-stressing level.