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Birmingham tunnel logistics call for self-compacting concrete

When VolkerLaser needed to reinstate concrete walls at three tunnels in Birmingham it turned to Cemex and its self-compacting concrete.

Earlier this year, VolkerLaser began work demolishing and reinstating a number of concrete walls in three Birmingham tunnels – Lancaster, St. Chad’s and Queensway.

The firm placed and compacted concrete as normal where possible, but when it came to reinstating walls within a few inches of the tunnel, roofing access became a problem.

Vibrating compaction equipment such as a poker could not be brought in and only one face was exposed.

“We carry out lots of tests to make sure the concrete has the right consistency and the right compressive strength for the job”

Richard Kershaw, Cemex

Cemex was employed to develop a bespoke mix of concrete that could meet the challenges of the project.

“We have developed self-compacting concrete for a number of years under our Evolution brand,” says Cemex national technical manager Richard Kershaw.

“The client needed to place the concrete in a difficult-to-access place, and it had to be self-compacting as we couldn’t get a poker in place.”

Over 600 m of concrete in 18 months

Cemex developed Evolution Structural for the Birmingham tunnel jobs. It is a self-levelling and self-compacting concrete that flows and compacts without any external vibration, and could also be poured from a single point if need be.

“It was created at our central lab in Southam and delivered to site from our plant in Aston, Birmingham,” Mr Kershaw explains. “We carry out lots of tests to make sure the concrete has the right consistency and the right compressive strength for the job.”

“We are definitely seeing a move towards self-compacting in a lot of different markets”

Richard Kershaw, Cemex

Cemex carried out the work with Evolution Structural in July and August 2013, and supplied the more conventional concrete for the rest of the tunnel in the 16 months leading up to that. In total, the company supplied more than 600 cu m of material over the two phases of the contract.

The three tunnels all carry major road arteries for Birmingham, so traffic management and logistics were an issue.

“To overcome this and help manage traffic flows more effectively, all of our work was carried out at night,” Mr Kershaw says.

“This also helped with the heat, which can be a factor when considering the logistics of a project. It was obviously very hot this summer, but by carrying the work out at night when it was cooler it didn’t really have an effect.”

Shift towards self-compacting concrete

Contractors are increasingly requesting self-compacting concretes over more traditional concrete products, with the trend evident throughout Europe.

“We are definitely seeing a move towards self-compacting in a lot of different markets,” Mr Kershaw says.

“The market is moving towards higher-consistence concrete and we’re providing a lot less at the S2 or S3 slump-test level. Most of it is S4 or higher now, as it’s easier to place.”

Much of this is down to the weight of the concrete and the fact that pours are getting larger and more complex.

“The pours are getting much bigger now, so this requires specialised technology”

Richard Kershaw, Cemex

“It’s heavy to move but it’s still placed in the traditional method. If it can flow when pumped, it’s better,” Mr Kershaw says.

“The pours are also just getting much bigger now. You often see slab pours of 200 to 250 cu m, so this requires specialised technology.

“Speed of construction is also really important on these big projects, so if the concrete is self-compacting and compacts quicker then that’s another advantage.”

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