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London Power Tunnels sees record pour of cement-free concrete

11 May 23 National Grid and its contractor Hochtief-Murphy Joint Venture (HMJV) have completed what is said to be the world’s largest ever continuous pour of Wagners’ Earth Friendly Concrete on the £1bn London Power Tunnels project.

Capital Concrete supplied 736 cubic metres (736,000 litres) of cement-free concrete for the base of the 55-metre deep tunnel drive shaft at National Grid’s Hurst substation in south London.

The single continuous pour took 11 hours to complete.

Wagners’ Earth Friendly Concrete uses a binder of ground granulated blast furnace slag and fly ash geopolymer concrete system, chemically activated using industrial waste products instead of cement. This mix is said to reduce carbon by around 64%, saving an estimated 111kg of CO2 per cubic metre poured in comparison to concrete which would have traditionally been used.

National Grid said that the use of Earth Friendly Concrete was driven by a team of young engineers on the project and supported by HMJV’s consultants at Aecom, Mott MacDonald and WSP following several trials at different London Power Tunnels sites.

The at Hurst substation site was needed to infill the base of the 55-metre deep tunnel shaft to its permanent level, following completion of 9.2km of tunnelling over two tunnel drives from Hurst to Eltham and Crayford.

National Grid project director Onur Aydemir said: “We are always looking for new ways to innovate and to now be using this carbon saving cement-free alternative to conventional concrete at scale and on site is exciting. This world record-breaking pour also offers the opportunity to evaluate the technology ahead of future possible rollout across our network in England and Wales, demonstrating our ambition to achieve net zero construction across all our projects by 2025/26.”

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Hochtief-Murphy Joint Venture technical lead Raj Kundan said: “At HMJV, in conjunction with our supply chain family, we strive to advance innovative and cutting-edge solutions – and the incredible work the team have done on the project in the trialling and large-scale use of Earth Friendly Concrete in temporary as well as permanent applications is a great example of that.

“Completing the largest ever continuous cement free concrete pour is testament to the ingenuity and collaboration of all involved working as part of this Project 13 Enterprise scheme, and shows how a client, contractor and the supply chain can work together to help take a major step moving the industry forward in reducing carbon emissions.”

Wagners is an Australian company that has a licence agreement in the UK with London-based Capital Concrete, co-owned by Brett and Breedon, to which it supplies off-the-shelf chemicals for mixing EFC on site.

Andy Izod, UK regional manager for Wagners, said: “This is the largest continuous EFC pour that has ever been undertaken and to do it on Earth Day, the 22nd of April, is quite fitting. We hope that other major clients will follow National Grid’s example in helping us to decarbonize the construction sector.”

Capital Concrete managing director Luke Smith said: “We have been supplying Earth Friendly Concrete since January 2020 as a low carbon, high performance alternative to standard, cement-based concrete. We are delighted that the Capital Concrete team could work together with Hochtief-Murphy to provide the technical expertise and focus on customer service to deliver the biggest EFC pour globally to date over an 11-hour period for the London Power Tunnels project.”

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