The Thames Tideway Tunnel is a “super-sewer”, measuring 7.2 metres in diameter, that will run 25 km through London. Most of the tunnel is being built under the banks of the Thames, at a depth of between 30 and 65 metres. The purpose of the structure is to intercept sewage spills and clean up the river.
Project
Thames Tideway Tunnel infrastructure for London’s sewer and stormwater network
Project owner
Tideway Ltd.
Project management
CVB joint venture: Costain / VINCI Construction Grands Projets / Bachy Soletanche
RMC partner involved in the project
Hanson
Time frame
2017 to 2025
VINCI Construction is building the tunnel’s eastern section, which stretches along 10 km
Six construction sites have been set up, comprising six deep shafts, offshore structures and structures connected to the existing system. Along the entire eastern section, VINCI Construction made a point of incorporating low-carbon construction solutions, both to meet its target of using 90% low-carbon concrete at its sites by 2030 and to comply with the goals set by the project owner, Tideway Ltd., to reduce its carbon footprint. In places where low-carbon concretes could not be used for technical reasons, reducing the thickness of the tunnels’ secondary lining saved 11,000 cu. metres of concrete.
More than 150,000 cu. metres of concrete were poured in situ on this project, including 70,000 cu. metres of low-carbon concrete.
Three low-carbon concrete formulas were used on the worksite:
- – One concrete formula containing 73% blast-furnace slag (initially 67%), which has saved 150 tonnes of CO2 equivalent for the 6,000 cu. metres of concrete poured to date;
- – A second containing 50% slag (initially 40%), which has saved 46 tonnes of CO2 equivalent for the 450 cu. metres of concrete poured to date;
- – A third using local marine sand, reducing the carbon footprint by 1,350 tonnes of CO2 equivalent for the 45,000 cu. metres of concrete to be poured.
Other “ultra-low-carbon” formulations containing blast-furnace slag have been developed with the concrete manufacturer Hanson.
Innovative design solutions to reduce the carbon footprint of the tunnels’ secondary lining
On these parts of the structure, the setting time after pouring the concrete was only 12 hours before the formwork would be removed. Given these technical restrictions, low-carbon concrete made by increasing the amount of ground slag could not be used, as its early-age strength requirements did not comply with production cycles.
To reduce the carbon footprint of this part of the structure, design was optimised to reduce the thickness and therefore the amount of concrete used. For these tunnels, consortium teams used a C50/60 concrete reinforced with steel fibres. The formula has a carbon footprint of 366 kg of CO2 equivalent per cu. metre.
The decreased thickness of the tunnel lining resulted in the following:
- – A reduction from 250 mm to 180 mm for the Greenwich Connection Tunnel (GRECT), reducing the amount of concrete used by around 5,000 cu. metres, i.e. approximately 19% of the total volume;
- – A reduction from 300 mm to 240 mm for the Main Tunnel D (MNTLD), reducing the amount of concrete used by around 6,000 cu. metres, i.e. approximately 27% of the total volume.
These optimisations saved 4,500 tonnes of CO2 equivalent and £1.6 million.
70,000
Volume of EXEGY® concrete in cu. metres
4,500
Tonnes saved for the secondary lining (less concrete used)
1,350
Local sand for the lining
1,600
Tonnes of CO2e saved by using low-carbon concrete*
* Based on the minimum value of traditional concrete for each strength class.
