DC4 Grout

 

Structural, sulphate-resisting grout for sewer upgrade 

Northern Outfall Sewer Upgrade - East London

 

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Client

Thames Water

Contractor

Mcallister Group

Location type

Large sewer tunnel

Completion

September 2025

Project

Structural, sulphate-resisting grout for major sewer upgrade
When engineers needed a structural, sulphate resisting grout to install this sewer tunnel lining on part of the Northern Outfall Sewer in East London, they asked Pozament to come up with the solution.

The Challenge

This project was part of a major upgrade to the Northern Outfall Sewer (NOS) in East London which serves over 4 million people, running from Wick Lane, near Stratford to the Beckton Sewage Treatment Works, the ​largest in Europe. The investment was intended to improve the resilience of the waste water network and help it to cope with future demands. As well as being a vital part of London’s waste water network, the NOS also has an important role in the transport network, with the underbridge supporting major roads and railways. This particular section consisted of eight, 2.7m wide tunnels, originally built in the 1860’s that supported the A118 Stratford High Street, a busy dual carriageway used by over 40,000 vehicles per day. An initial survey in 2020 raised concerns over the structural integrity of the underbridge structure, showing the existing sewer soffit had weakened over time.

Our Solution

The engineer’s solution involved installing glass reinforced plastic (GRP) linings within the existing sewer tunnels. Specialist contractor McAllister Group was employed to install the GRP liners which would then be back-filled with strengthening the underbridge and the sewer barrels. Pozament were approached to supply a suitable structural grout to fill the void between the new GRP tunnel lining and the existing tunnel wall. The chosen grout would need to deliver the flowing consistency needed to fully fill the voids and the structural performance needed to support the underbridge, the carriageway and the vehicles that use it. The client specification also needed to be sulphate resistant to Design Class 4. Although the tunnel had been cleaned before the work started this would ensure that the grout was not affected by any remaining contaminants.

Results and Benefits

Work was scheduled to be carried out on each sewer barrel individually and completed by September 2025.  As planned 15,000 bags of Pozament DC4 Grout were supplied over the course of the project as required by the contractor, around 300 tonnes in total. In line with the client’s requirements the grout was supplied in plastic weatherproof bags which were durable enough to cope with the conditions on site. In each tunnel, the lining section was put into place then sealed at both ends with formwork. The grout was then pumped in to fill the void. The high flow characteristics of the grout allowed it to be quickly pumped into place, enabling penetration and void filling with no bleed or shrinkage. All Pozament grouts are quality assured and are tested and packaged in accordance with BS EN ISO 9001. Pozament’s range of specialist grouts, mortars, cements and water stops are relied on by civil engineers to tackle the most challenging problems. For more details visit: pozament.com. 
 
"Selecting the right materials was a key part of the successful delivery of this project. The Pozament grout used on this project, delivered the consistent flow performance needed to help us to work efficiently, along with the structural performance and sulphate resistance required by the specification. Our engineers were happy with the way it performed on site and would use it again on future projects" Freddie, Fowler, Assistant Project Manager, McAllister. 
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