Having produced 220 000 m3 of concrete for London’s largest sewer upgrade scheme by Thames Water, the final pour and dismantle of Cemex’s Lee Tunnel concrete plant have taken place. The new 4 mile long tunnel, which cost £635 million, will handle 39 million t of sewage a year.
Cemex has worked with joint venture MVB, Morgan Sindall, Vinci Construction Grands Projets and Bachy Soletanche to provide a number of bespoke concrete mix designs, from mix design to delivery and placement.
“This is one of the most complicated infrastructure projects of recent years. Even before work began on site in autumn 2010 we had to look at every eventuality with the concrete and how performance might be affected. We carried out trial mixes at our National Technical Centre and on site reviewing amongst others, cement designation and content, maximum aggregate size and admixture combinations. We had to be sure the mixes would be usable and retain consistence even when they had been skipped down the shaft or pumped onto the concrete train,” explains Richard Kershaw, National Technical Manager, Cemex UK Readymix.
Starting with the diaphragm walls of the outer shaft, the concrete used was a C50/60 grade mix incorporating 70% ground granulated blast furnace slag as a cement replacement. Within this outer shaft the main inner lining was cast as a 750 mm thick concrete cylinder. The outstanding aspect was a 29-hour continuous pour. A total of 11 000 m3 was pumped using a C50/60 36% GGBS cement replacement mix reinforced with more that 500 t of steel fibre.
Within the tunnel, Cemex worked with MVB to develop a solution to the scheme’s requirements for the secondary lining. The primary lining was a precast system, but the secondary lining consisted of a 300 mm thick steel fibre reinforced lining, cast in-situ within two 30.6 m shutters, reducing the previously bored 7.8 m internal diameter to 7.2 m. The lining was built along the complete 7 km tunnel.
For this part of the project, following months of trials, the team developed a concrete that would retain consistence for up to six hours, contained Dramix 5D steel fibres at 40 kg/m3, develop early compressive strength and flow for 15m without any segregation.
“Lee Tunnel was a challenging project in which the design and technology of the concrete was pushed to the limit. The concrete was essential to help build an exceptional structure needed by the people of London,” concludes Richard.
Adapted from press release by Rebecca Bowden
Read the article online at: https://www.worldcement.com/europe-cis/15122015/cemex-lee-tunnel-project-completed-180/