Service life extension of state highway 16 bridges – New Zealand’s first hybrid corrosion protection application

Abstract

State Highway 16 (SH16) is an existing motorway of significant strategic importance connecting central Auckland to the city's western suburbs and beyond. It carries, on average, some 90,000 vehicles per day, and runs through an environmentally sensitive coastal marine reserve. Two highway bridges, namely Whau River Bridge and Causeway Bridge are currently being refurbished due to extensive chloride contamination as a result of exposure to a tidal marine environment and exhibit surface cracking, spalling and reinforcement corrosion. A hybrid corrosion protection system has been selected as the preferred corrosion management solution to arrest corrosion and to ensure a residual service life of 50 years. The hybrid corrosion protection (HCP) system comprises discrete zinc anodes which were installed on both the reinforced and pre-stressed concrete piles from the Lowest Astronomical Tide (LAT) level, up to the soffit of the crossbeams. The anodes operate in two phases, initially energised using low voltage DC power to arrest ongoing corrosion and thereafter in galvanic mode to provide corrosion prevention for the residual service life. HCP minimised physical works on site, negated the requirement for extensive replacement of chloride contaminated concrete, allowed work to take place accommodating incoming and outgoing tides and offers protection against chloride induced corrosion to the substructures. This is the first HCP system designed and installed in New Zealand, and it is believed to be the first of its kind for pre-stressed concrete in tidal water in the world.