Thames Tideway, Deptford
Product: Euromix Concrete, Bespoke Mix Design
Client: Thames Tideway Deptford
Main contractor: Slipform Engineering
Location: River Thames, London
Date of completion: 2019
The challenge:
150-year-old and was built for a population less than half its current size. The result of this is that every year, millions of tonnes of raw sewage spills, untreated, into the River Thames, creating an environmental and health hazard. To solve this problem, the Thames Tideway Project is constructing a new 25km ‘Super Sewer’ under the River Thames to intercept the waste and clean up the river for the good of London’s residents and wildlife. As part of this huge project, concrete was required by Slipform Engineering for the construction of the Thames Tideway secondary lining walls at the Deptford Shaft, a 17.050m diameter, 39.180m deep shaft with walls of varying thicknesses from 900mm to 2500mm. A vortex tube surrounding the walls also included in the works.
The solution:
Working alongside Slipform Engineering technical team we developed a mix design and then the slipform Engineering team carried out extensive testing on setting times and consistency to ensure that the concrete mix was suitable for the challenge of 24 hour pouring in the various wall thicknesses simultaneously. During these pre-construction trials, the concrete setting time was tested on the concrete mixes containing various levels of retarder. Additional trials also had to be conducted on mixes from the back-up concrete batching plant to ensure that they maintained the same consistency and setting times.
Euromix / Tarmac and Slipform Engineering then produced full technical reports for approval by Tideway for use of the developed mix design on their projects. The Tideway specification originally did not allow for the use of 100% marine aggregates due to concerns on the chloride content, therefore Tarmac had to develop a full STP for the control of chloride content in the 100% marine sand to gain Thames Tideway’s approval to allow its use. This STP then required Tarmac to sample and monitor the chloride content at the plant.
The base mix developed was suitable for the majority of the slipform works with a setting time of approx. 3.5-5.5 hours depending on exact consistency and ambient weather conditions. Retarded concrete mixes were only planned to be utilised if the setting time of the concrete becomes too fast for the works progression due to heat generation from the 2500mm thick wall cast below.
Results and benefits
As planned, concrete was pumped down the shaft to slipform level using the Camfaud Mobile pump fleet, in the following pour sequence:
- Pour 1 – 960m3 for 110 hours of continuous concrete
- Pour 2 – 557m3 for 50 hours of continuous concrete
- Pour 3 – 536m3 for 50 hours of continuous concrete
- Pour 4 – 245m3 for 30 hours of continuous concrete
Work progressed at an average slipform rate of 200mm lifting per hour. Throughout the pour, the concrete setting time was under constant surveillance by the Slipform Engineering supervisor and rig driver and they then advised out plant batcher when any changes to the mix being delivered to site was required.
A perfect slipform finish was achieved with no remedial works required to the walls formed. There were no concrete plant breakdowns or delays to the slipform progress during the pour. Concrete heat generation was maintained within the specification limits and all strength test samples passed without issue. The client and contractor were delighted with the way the concrete performed on site, the efficient way it was supplied throughout the pour and the finish achieved.
