Highways Agency

The Project

The Dunheved Bridge at Launceston carries the A30 dual carriageway over the river Tamar. It is actually a pair of bridges, as there are separate bridge decks for each carriageway. It was first constructed when the Launceston Bypass was built in 1975.

Since then the concrete decks had been adversely affected by internal chemical reactions. These resulted in the formation of a “gel” which expanded inside the concrete. This resulted in spalling, delamination and cracking of the concrete, together with corrosion of the reinforcing bars and prestressing cables, and meant that substantial repairs were necessary.

The existing concrete decks were replaced with new steel and concrete composite ones. The concrete elements are now protected with a waterproofing system to prevent future ingress of water and the consequences described earlier. The steel elements were fabricated from weathering steel that will eliminate the need for future ongoing maintenance painting of the structure, thereby minimising future traffic delays and disruption.

The decision to replace the decks completely followed a cost benefit analysis of the various options proposed. Remedial works to the existing decks would have been time consuming and extremely disruptive to traffic. Although a new bridge was slightly more expensive, it will result in a much longer life of the structure and the works caused minimal delays to the road user, as the new decks were built ‘off-line’ and then slid into place.

Work began in Jan 06 and was completed in Spring 07.