Lightweight concrete solution for Nene Bridge
Key role for Aggregate Industries’ Lytacrete concrete in structural refurbishment of iconic bridge piers
CONSTRUCTED over the river Nene in the 1970s, Nene Bridge, in Peterborough, is an iconic, award-winning structure noted for its V-shaped piers. As a major traffic route, it provides access to vehicles travelling from the A1 to the A47, as well as pedestrians and cyclists going between the north and south of the city.
The bridge is currently undergoing extensive structural refurbishment work, including pier reinforcement and bearing replacement, as part of a repair programme being carried out by Skanska.
Recent inspections of the bridge revealed signs of structural distress to the bearings and cracking to the saddles of the piers. Traditional methods of replacing the bearings were not possible because the ornate architectural design of the original piers did not allow space on top of the piers for jacks to be positioned beneath the superstructure. In addition, jacking points were not provided within the box girders.
As such, the designers at Skanska considered various options for replacing the bearings and strengthening the piers, whilst 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 the piers and also to provide jacking platforms for the superstructure to be lifted to allow the bearings to be replaced.
For this solution to work, the concrete used in the jackets would need to be strong enough to strengthen the piers and to carry the jacking loads, self-compacting enough to flow around the congested steel reinforcement, and lightweight enough to minimize the additional load on the foundations.
As the first bridge repair of its kind in the UK to deploy this method, Aggregate Industries suggested the use of Lytacrete, a high-strength, free-flowing, self-compacting concrete mix using the company’s innovative lightweight secondary aggregate Lytag, which can effectively reduce the dead load by approximately 25% over normal weight control, while offering the same level of structural performance.
This solution proved ideal for strengthening the piers as well as maintaining their unique V-shaped design, and the Lytacrete concrete can also withstand jacking of the bridge deck in order to replace the bearings – a core process of the refurbishment.
Simon Wycherley, general manager at Aggregate Industries, commented: ‘We’re incredibly proud to be involved in the repair works of Nene Bridge, the first project of its kind to use our Lytacrete solution in this way. Coupled with our on-site technical expertise, we hope our innovative concrete solution ensures this iconic structure lasts the test of time.’
Dan Wood, site manager for Skanska Infrastructure Services, added: ‘Lytacrete has performed well on the Nene Bridge bearings project, successfully flowing around the complex steel reinforcement to form the unique geometry required. I would like to thank Aggregate Industries for taking on board feedback and working with Skanska to refine the mix design to suit the bridge’s unique requirements.’