Record breaking use of cement-free concrete at London Power Tunnels


The world’s largest continuous pour of cement-free concrete has been achieved during a £1 billion project to rewire London.

736m3, or 736,000 litres (enough to fill around two 25m swimming pools) of more sustainable, cement-free concrete was poured to fill the base of the 55m deep tunnel drive shaft at National Grid’s Hurst Substation in South London.

National Grid and contractor HOCHTIEF-MURPHY Joint Venture have extensively tested Earth Friendly Concrete prior to use on the £1bn London Power Tunnels project. The low-carbon cement saved an estimated 82 tonnes of CO2, the equivalent emissions of driving a petrol car around the world 18 times.

The cement free solution was developed by Wagners and supplied by Capital Concrete and uses a binder of ground granulated blast furnace slag and fly ash geopolymer concrete system chemically activated using industrial waste products instead of cement. The concrete reduces carbon by around 64 per cent saving an estimated 111kg of CO2 per cubic metre poured in comparison to concrete which would have traditionally been used.

The use of Earth Friendly Concrete was driven forward by a team of young engineers on the project and supported by HMJV’s engineering experts and AECOM, Mott MacDonald and WSP, following several trials at different London Power Tunnels sites.

The record-breaking pour on Earth Day (22 April) at National Grid’s Hurst substation site was needed to infill the base of the 55m deep tunnel shaft to its permanent level, following the successful completion of 9.2km of tunnelling over 2 tunnel drives from Hurst to Eltham and Crayford.

Elsewhere on the London Power Tunnels project, there are several measures in place to reduce the environmental impact of construction and keep National Grid on track to achieve net zero carbon construction in the UK by 2025/26. These include:

Optimisation of designs and construction methodologies of the tunnel and shafts network by HMJV saving approximately 50,000 tonnes of CO2, leading to a 30 per cent reduction against baseline.

99.98 per cent of project waste being diverted away from landfill, a 21 per cent reduction against the carbon reduction pre-project baseline for shafts, tunnels and headhouses, equivalent to 25,250 tonnes of CO2.

A new 400kV substation at the heart of the project in Bengeworth Road, Lambeth will be built using SF6 free gas insulated switchgear technology in a UK first.

“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,” Onur Aydemir, National Grid project director, said. “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.”

Raj Kundan, technical lead for HOCHTIEF-MURPHY Joint Venture 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.”

Andy Izod, UK regional manager for Wagners said: “We are delighted that National Grid and HOCHTIEF-MURPHY Joint Venture have chosen to use Earth Friendly Concrete (EFC) at their LPT project as by using an ultra-low carbon concrete for this application they have saved an estimated 82 tonnes of CO2, which is roughly the equivalent of driving a new car 18 times around the world.

“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 decarbonise the construction sector.”

Luke Smith, managing director of Capital Concrete 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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