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Weight watcher

Lightweight concrete helped the project team for the Blackfriars Station redevelopment deliver efficiently and successfully. NCE reports.

A bespoke concrete solution has helped engineers overcome a complex engineering challenge on the Blackfriars Station redevelopment project in London.

The redevelopment is part of the £6bn Thameslink Programme.

The project, managed by Network Rail and headed by Balfour Beatty Civil Engineering Major Projects division, will deliver the first station to span the River Thames.

Once rebuilt, the new Blackfriars station will allow trains to run more frequently across the heart of the capital.

New station entrance

Due for completion in spring 2012, the project is meeting several design and engineering challenges, not least the task of creating a new pavilion entrance to the new South Bank station entrance above an existing underground car park.

“Lightweight aggregate enables the creation of a material that can be 25% to 40% lighter than the structural concrete made with traditional aggregate”

The entrance was designed as a suspended slab cantilevered off a ring beam on 300mm diameter, 15m long reinforced concrete micropiles.

Lead design engineer Jacobs specified that the load placed over the car park roof could not be heavier than the existing concrete slab, and must weigh no more than 1,600 kg/m3.

Using concrete made with traditional aggregate to achieve the required strength would have needed a concrete slab weighing approximately 2,400 kg/m3.

A solution was therefore needed to enable the level of strength required and the specified weight limit to be achieved.

Making concrete using materials firm Lytag’s lightweight aggregate (LWA) helped the project team produce a slab with the required lightness and strength.

Secondary aggregate

LWA is a secondary aggregate that is approximately half the weight of traditional aggregate but which can deliver the same levels of structural integrity when used as a concreting aggregate.

Its use to make structural concrete enables the creation of a material that can be 25% to 40% lighter than that made with traditional aggregate.

As a secondary material, the use of Lytag LWA has also contributed to the project’s environmental credentials.

Made by sintering pulverised fuel ash, its use diverts a material that may otherwise be sent to landfill as well as reducing demand on quarried aggregate.

In this particular project Lytag, Balfour Beatty Civil Engineering and Kilnbridge Construction created a mix
of Lytag lightweight coarse and fine aggregates, which enabled the concrete to meet the strength requirements for the roof while weighing just 1,400 kg/m3.

Using LWA avoided the need for additional, costly reinforcement.

Largest solar bridge

With Blackfriars Station set to become the world’s largest solar bridge - solar panels are being installed above the new station platforms - minimising the project’s environmental impact was a priority.

Bespoke solutions such as this will help the concrete industry play a key role in the development of cost efficient infrastructure.

As more projects come forward through the National Infrastructure Plan, the Blackfriars Station redevelopment shows that there are effective quick wins.


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