Nene Bridge was constructed over the River Nene in the 1970s and has become iconic for its ‘v’ shaped pier. It is a major traffic route and provides access to vehicles travelling from the A1 to A47 highways, as well as pedestrians and cyclists going between the north and south of the city.
As part of a major repair programme being carried out by contractor
Recent inspections revealed signs of structural distress to the bearings and cracking to the saddles of the piers. Traditional bearing replacement methods were not possible.
The ornate design of the piers did not allow space on top of the piers for jacks to be positioned beneath the superstructure, raising it to then replace the bearings. In addition, jacking points were not provided within the box girders.
Designers at Skanska considered options for replacing the bearings and strengthening the piers while at the same time remaining sympathetic to the appearance of the original piers.
This led them to develop the solution of encasing the piers in reinforced concrete jackets to strengthen them and also to provide jacking platforms for the superstructure lifted to enable the bearings to be replaced. For this solution to work, the concrete used in the jackets needed to be strong enough to strengthen the piers and to carry the jacking loads; self-compacting, to flow around the dense reinforcement; and lightweight, to minimise the additional load on the foundations.
Aggregate Industries suggested the use of Lytacrete, a concrete mix using the lightweight secondary aggregate Lytag. The company says that it can effectively reduce the dead load by around 25% over normal weight control while offering the same level of structural performance. Aggregate Industries is supplying its solution to the project over the next 12 months.
Throughout the project, Lytacrete has been placed around the piers. Owing to its high strength and self-compacting nature, the mixture needed to be free-flowing to ensure it could be placed around the complex and congested steel reinforcement. As a result, Aggregate Industries says the solution has proved ideal for strengthening the pier as well as maintaining its ‘v’ shaped design.
“Lytacrete has performed well on the Nene Bridge bearings project, successfully flowing around the complex steel reinforcement to form the unique geometry required,” said Dan Wood, site manager for Skanska Infrastructure Services.