Service life extension of SH16 bridges – New Zealand's first hybrid corrosion protection

Abstract

State Highway 16 (SH16) is a motorway of significant strategic importance, connecting central Auckland to the city's western suburbs and beyond. It carries an average of 90 000 vehicles per day and runs through an environmentally sensitive coastal marine reserve. Two bridges on the route – Whau River Bridge and Causeway Bridge – were rehabilitated due to extensive chloride contamination as a result of exposure to the marine environment. This paper offers a holistic review of the inspection, durability assessment and design processes, and discusses construction, operation and maintenance details. The durability assessment considered deterioration mathematical modelling with regard to service life extensions of 25 and 50 years. A hybrid corrosion protection (HCP) system was selected as the preferred corrosion management solution. The system operates in two phases, initially energised using low-voltage direct current power to arrest ongoing corrosion and thereafter in galvanic mode to provide corrosion prevention. A structural health monitoring system was also designed and installed to offer long-term performance monitoring. The HCP system minimised physical works on site, negated the requirement for extensive replacement of chloride-contaminated concrete, allowed work to take place around the natural tide cycles and offers long-term protection. This is the first HCP system designed and installed in New Zealand and is believed to be the first of its kind for prestressed concrete in tidal waters.