Keeping disruption to a minimum is a major issue when deciding how best to carry out carriageway repairs. So, when Southampton City Council needed to stabilise concrete slabs on an approach to the city’s docks last month, it wanted a solution that would complete the job quickly and allow the road to remain open.

By injecting Geobear’s expanding geopolymer under the slabs, both these requirements were met.

‘About 1,500 lorries use this road in a 24-hour period, so it’s not the sort of thing you can shut down,’ says Vic Collier, Colas’ site manager for the Millbrook Roundabout project. ‘If we’d had to rip out all the slabs, we’d have been looking at between eight and 11 months, and that’s without reconstruction of kerbs and a roundabout.’

With a sub base mixture of stone and crushed concrete, plus an inconsistent thickness of concrete slabs, some movement was detected at the site. So, the city council, with Colas and consultant, Halcrow, brought in geopolymer resin injection specialists Geobear (formerly Uretek) to fill the voids under the roadway and stabilise the slabs, without the need for excavations.

The geopolymer material is ideal for road use, as it functions best where there is a high load expected in one direction and very little in the other. It is also lightweight, adding little burden to distressed subgrades, while the process is unaffected by temperatures ranging from 00 C to 1000 C, allowing work in colder seasons.

The application method involves injecting expanding geopolymer material through a series of small-diameter holes, drilled at one to 1.5m centres. These holes are small enough to cause no slab breakout at the base of the concrete and no overall slab weakening. Once injected, the material expands up to 30 times its volume, providing a strong vertical lift if needed, and compressive strength of up to 10,000 kPa.

Importantly, the process is controllable, due in part to the material’s rapid curing time, but also to its all-in-one process that lifts without pumping the slab. The process both consolidates the ground and lifts the slab to tolerances of +/- 5mm, monitored by laser level. This precision makes it possible to stabilise only, without any lift.

Over a five-week period at the Millbrook Roundabout project in Southampton, the company completed repairs to 8,500m2 of carriageway, with minimal disruption. The road remained open throughout, and there were no delays to traffic. ‘We’ve taken seven months off the job, and the port authority hasn’t had one complaint about how we’ve done it,’ says Collier.

During the work, very little equipment was required on the road – a hose from the self-contained truck, a laser level and a drill. It allows a fast clear up, so a team can work between rush hours.

*This article was originally written for Surveyor magazine and describes in detail our work on the Southampton Docks approach.