Condition assessment and service life prediction of a marine concrete structure: an interesting case study

摘要

On the windward side of an existing box girder bridge exposed to aerosol and incidentally spray chloride profiles were determined at an age of 18 and 32 years as to obtain data on the development of chloride ingress over time and to predict the time to onset of reinforcement corrosion. According to the chloride contents determined at the level of the reinforcing steel for an age of 18 years corrosion was likely to be present, however neither visual inspections nor large scale potential mapping revealed any spots suspect of corrosion. Chloride profiling performed at an age of 32 years indicated that chloride ingress was much slower than was anticipated. A full probabilistic approach was adopted to predict the development of chloride ingress over time and onset of reinforcement corrosion using updated values for the so-called ageing factor and the critical chloride content. However, the results obtained with these predictions proved to be far more pessimistic than is shown by the actual condition of the bridge. As a consequence it was decided not to rely anymore on predictions based on numerical models using probabilistic calculations but in contrast to adopt a pragmatic engineering approach using common sense as a basis.