Award of Excellence: Transportation Category
Silver Jubilee Bridge Remediation
Widnes, Cheshire, United Kingdom
Submitted by Mott MacDonald, Ltd.
Halton Borough Council
Widnes, Cheshire, UK
Mott MacDonald, Ltd.
Altrincham, Cheshire, UK
Rudheath, Cheshire, UK
The Silver Jubilee Bridge offers the only river crossing between the two Liverpool tunnels and bridge crossings in Warrington, 20 miles (32 km) upstream. The bridge also crosses the Manchester Ship Canal, providing sufficient headroom for shipping. It forms part of the major highway route in northwest England, carrying over 90,000 vehicles per day on four lanes.
Since the mid-1960s, the highways in this part of England have been subjected to chloride-based deicing salts during the winter months. Chlorides have penetrated the concrete cover, and levels at the reinforcement commonly exceed 2% by mass of cement, which is more than sufficient to initiate and sustain corrosion.
Any closure for repairs would result in a diversion of at least 40 miles (64 km) and even partial closures result in heavy congestion to the local road network. Therefore, a remediation strategy rather than reconstruction plan was developed to prevent any traffic disruptions and subsequent detrimental effects to the local economy.
A lightweight, prefabricated bolt-on “cassette” cathodic protection system was identified as the most suitable solution. The system was originally developed for use on harbor structures in Norway and consisted of mixed-metal oxide-coated titanium (MMOTi) ribbon anodes in a glass-fiber foam-filled fiber-reinforced polymer (FRP) tray which are mounted to the underside of the bridge deck using sleeved bolts.
To test its suitability, the cassettes were installed on a 200 ft (60 m) trial area on the soffit of the deck. The trial area was energized in October 2008 and protected over 600 square yards (520 square meters). The section was monitored over a period of 1 year and showed excellent results, demonstrating that the remaining suspended deck could be protected using this system.