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Northern Line Extension Nine Elms to Battersea
Our work focused on finding ultra-low carbon alternatives to Portland cement, which is traditionally used in concrete.
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Going further on London’s Northern Line

Mott MacDonald was lead designer for FLO, the joint venture between Ferrovial Agroman and Laing O’Rourke delivering the Northern Line extension (NLE), a 3.2km addition to the London Underground network.

Client
Ferrovial-Laing O'Rourke Joint Venture
Expertise
Advisory, oversight, peer review
More than 80%
CO2 equivalent content reduction

Opportunity

The NLE project consisted of two new subterranean stations – one at the iconic former power station at Battersea and another to the east, at Nine Elms – and two ventilation shafts in Kennington, as well as bored and sprayed concrete lining (SCL) tunnels and spheroidal graphite iron (SGI) turnouts. Overall, about 50,000m3 of concrete was needed to build the line and stations.

Solution

With cement manufacture a major source of greenhouse gas emissions, our work focused on finding ultra-low carbon alternatives to Portland cement, which is traditionally used in concrete. The cementitious product in concrete can account for as much as 50% of total emissions over the lifetime of a building, bridge or tunnel. Adding industrial waste products such as fly ash and ground granulated blast-furnace slag (GGBS) is a tried and trusted way of significantly reducing the carbon footprint of concrete.

Outcome

Portland cement (CEM I) typically generates 913kg of CO2 for each tonne of finished product. By contrast, cementitious materials made using limestone, fly ash or GGBS (CEM II), generate between 615 and 859kg of CO2, depending on the amount added. GGBS typically replaces about 50% of the Portland cement component in concrete, and sometimes up to 70%. We went much further on the NLE, raising the proportion to 95% for the secant piling concrete, reducing the CO2 equivalent content compared with the CEM II mix by more than 80%.

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