Aggregate Industries plays pivotal role in Nene Bridge refurbishment

Nene Bridge is an award-winning structure with an iconic ‘v’ shaped pier, which was constructed over the River Nene in the 1970s. It is a major traffic route, providing access to vehicles travelling from the A1 to the A47, as well as being used by pedestrians and cyclists going between the north and south of the city. The extensive refurbishment includes reinforcing the bridge piers and replacing bearings, as part of a programme that is being carried out by Skanska.

Signs of structural distress and cracking to the saddles of the piers were revealed in recent inspections of the bridge. Due to the ornate architectural design of the original piers, traditional methods of replacing bearings were not possible, as there was no space on top of the piers for jacks to be positioned beneath the superstructure replacing the bearings. Additionally, jacking points were not provided within the box girders.

Designers at Skanska therefore considered various options for replacing the bearings and strengthening the piers, whilst also remaining sympathetic to the appearance of the original piers. This led to the solution of encasing the piers in reinforced concrete jackets. These would both strengthen the piers and provide jacking platforms for the superstructure, lifted to enable the bearings to be replaced. In order for this solution to work, it was important for the concrete used in the jackets to be strong enough to strengthen the piers and carry the jacking loads. The concrete also needed to be self-compacting to flow around the dense reinforcement and lightweight, in order to minimise the additional load on the foundations.

This would be the first bridge repair of its kind in the UK to use this method. Aggregate Industries suggested the use of Lytacrete, a concrete mix that uses the innovative lightweight secondary aggregate, Lytag. This can effectively reduce the dead load by approximately 25% over normal weight control, while offering the same level of structural performance.

Lytacrete was placed around the piers meaning that, with its high strength and self-compacting nature, it also needed to be free flowing. This would ensure that it could be placed around the complex and congested steel reinforcement. Consequently, the solution strengthened the pier and maintained its unique ‘v’ shaped design. The concrete is also able to withstand the jacking of the deck of the bridge to replace the bearings, which is a core process of the refurbishment.

Over the next year, Aggregate Industries will ensure, with its robust delivery framework, that all concrete arrives on time and to the exact specifications, ensuring the concrete is available to surround, rebar, and form the required shape.

“We are 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,” said Simon Wycherley, General Manager at Aggregate Industries. “Coupled with our onsite technical expertise, we hope our innovative concrete solution ensures this iconic structure lasts the test of time.”

“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. “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.”

Read the article online at: https://www.worldcement.com/europe-cis/14012019/aggregate-industries-plays-pivotal-role-in-nene-bridge-refurbishment/