THE WORLD'S FIRST HYBRID CORROSION PROTECTION SYSTEMS FOR PRESTRESSED CONCRETE BRIDGES

摘要

The Kyle of Tongue Bridge in Sutherland, Northern Scotland opened in 1970, has an overall span of 184m consisting of 18 approximately equal spans and carries a single lane dual carriageway. Prestressed concrete beams form the deck, with reinforced concrete pilecaps supported on steel piles. The bridge was patch repaired in 1989 due to chloride induced corrosion. However, inspections from 1999 onwards reported on-going corrosion and structural deterioration. A refurbishment contract was let in 2011 to extend the service life of the structure for a 30 year period by providing corrosion arrest and prevention. The Tiwai Point Bridge in Invercargill, Southland, New Zealand opened in 1969, has an overall span of 486m consisting of 27 approximately equal spans and carries a single lane dual carriageway. It is comprised of prestressed and post-tensioned concrete beams forming the deck, with reinforced concrete pilecaps supported on prestressed concrete piles. The superstructure was replaced in 2009-2010 due to severe corrosion to the reinforcement. Hybrid cathodic protection systems were developed and implemented for both structures. For Kyle of Tongue, hybrid cathodic protection was used to arrest existing corrosion activity to the prestressed concrete beams of the superstructure and extend their service life for a 30 year period by providing corrosion arrest and prevention. For Tiwai Point Bridge, a trial hybrid cathodic protection system was developed to provide corrosion prevention to the prestressed concrete piles within the tidal zone with a targeted service life of 50 years. Hybrid electrochemical treatment provides an attractive alternative to other corrosion protection treatments as it combines the power to arrest the corrosion activity with the simplicity and low maintenance requirements of galvanic technologies. It offers a temporary energising phase to arrest corrosion followed by a permanent galvanic mode phase which is particularly beneficial for prestressed concrete structures in order to reduce hydrogen embrittlement risk. This paper provides a summary of the performance of such hybrid electrochemical systems and how they can be advantageously utilised on prestressed concrete structures to extend their service life.