“96% of the concrete poured in situ on the eastern section of London’s new ‘super sewer’ is low-carbon!” Pierre-Édouard Denis, Materials Engineer at VINCI Construction Grands Projets

“London’s new ‘super-sewer’, the Thames Tideway Tunnel, measuring 25 km long and 7.2 metres in diameter, is designed to clean up the Thames and lastingly improve the river’s water quality. VINCI Construction won the contract to build the 10 km eastern section of the tunnel, awarded by Tideway Ltd.

For this headline project, our teams felt it was the obvious choice to implement low-carbon construction solutions, in line with our targets to use 90% low-carbon concrete by 2030 and meet our client’s goals to reduce the programme’s overall carbon footprint by 8%. To achieve those goals, we set in motion a strategy that consisted in both curbing the amount of concrete and reinforcement used and shrinking the carbon footprint of our concrete.

First of all, we assessed the carbon footprint of the types of concrete that would be used by charting them on the EXEGY® matrix. This decision-making tool is useful for choosing the best concrete based on its technical properties and its CO₂ emissions.

Consequently, three main low-carbon concrete formulas were poured at the worksite: one containing 73% blast-furnace slag, so far reducing the carbon footprint by 150 tonnes of CO₂ equivalent for 6,000 cu. metres of concrete; a second with 50% slag, which has saved 130 tonnes of CO₂ equivalent for 1,500 cu. metres of concrete to date; and a third using local marine sand, saving 1,350 tonnes of CO₂ equivalent for 45,000 cu. metres of concrete. Other “ultra-low-carbon” formulations containing between 80% and 90% slag have also been developed with the concrete manufacturer Hanson.

These efforts have produced outstanding results, as around 96% of the concrete used for the permanent structures, excluding tunnel segments, is low-carbon!

I’m extremely proud of this collective success and its coherence. This project is not only virtuous in its intention – to reduce pollution of the Thames – but also in its construction methods, in particular by incorporating EXEGY® low-carbon concrete.”