In total, 736m3 of 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. The cement free solution, developed by Wagners and supplied by Capital Concrete, uses a binder of ground granulated blast furnace slag and fly ash geopolymer concrete chemically activated using industrial waste products instead of cement. The concrete is said to reduce carbon by around 64 per cent, saving an estimated 111kg of CO2 per cubic metre poured compared to concrete which would have traditionally been used.
In a statement, 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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The use of Earth Friendly Concrete was driven by a team of young engineers on the project and supported by National Grid contractor HOCHTIEF-MURPHY Joint Venture (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 tunnel shaft to its permanent level, following the completion of 9.2km of tunnelling over two tunnel drives from Hurst to Eltham and Crayford.
Raj Kundan, technical lead for HMJV said: “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.”
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