Precast pre-tensioned concrete bridge construction became common in New Zealand in the 1950s and a large number of pre-tensioned concrete bridges were constructed between 1953 and 1980.
These bridges do not meet today’s durability requirements and many are at risk of chloride-induced pre-tensioned reinforcement corrosion.
This deterioration can be difficult to detect in visual inspections and has immediate structural implications, so prediction or early detection of at-risk structures is critical for bridges to achieve their required service lives.
This report presents an assessment of the New Zealand pre-tensioned concrete bridge stock and identifies bridges at risk of pre-tensioned reinforcement corrosion.
Construction eras based on evolving construction practices are identified, and examples of typical beam types used in each era are presented.
The exposure classification of each pre-tensioned concrete bridge on the state highway network was remotely estimated using a Google Earth-based tool developed for the purpose. A sample of 30 bridges was selected for inspection, and chloride profiles and concrete cover depth surveys were obtained from each structure.
This data was used in diffusion models to predict the remaining service life before initiation of chloride-induced reinforcement corrosion for each bridge, and the results were then applied to other similar bridges in New Zealand.