Home » Projects » A55 J35 – J34 Westbound Pavement Slab Stabilisation


Blue indicates slabs needing stabilisation

A GPR survey carried out in advance of planned resurfacing works highlighted voiding below concrete pavement slabs on this section of the A55. The slabs lay beneath a 40mm thick layer of asphalt that was due to be planed off prior resurfacing.

The resurfacing was scheduled to be carried out over two-weekend road closures to minimise disruption to commuters and local residents. However, the extent of the voiding and suspected slab condition was such that NMWTRA, (North & Mid Wales Trunk Road Agency) the ultimate client, needed to remedy the issue, as this was essential in prolonging the life of the soon to be laid new asphalt surface.


Customer alternatives

A clear option to the client was to resurface the existing area without addressing the voids. However, the client correctly identified that in leaving voids the asset life of the surface would be reduced massively. The likelihood would be that the surface would require a replacement within five years. In addressing filling the voids and stabilising the slab, the client could be assured that the surface life would extend beyond 20 years.

In terms of the stabilisation works, one option was the breakout and replace/stitch repair however, there were 171 slabs identified upon planing out with voiding and/or in poor condition. With it being possible to replace a maximum of 4 slabs per shift this wasn’t a viable option to NMWTRA with only 10 shifts available to complete the work. Whilst some slabs ultimately had to be replaced such was their condition a quicker solution needed to be found.


Why Geobear

One of the key concerns for NMWTRA was to minimise disruption to the local community in terms of congestion, delays on the A55. The importance in the speed of delivery of works was one of a number of important factors for the client to consider. 

Injection whilst monitoring using laser

The speed of delivery and minimising disruption was essential. Geobear can work in a small footprint area of the carriageway at any one time with minimal plant and labour. This, therefore, allows site traffic and other trades (concrete repair contractors) to pass by with their equipment to work in other areas of the 2.5 km long section of the dual carriageway.

It was also a condition of the contract that the work was to be undertaken at night with one lane of the carriageway being opened to commuters during the day. They, therefore, needed a solution that not only stabilised the pavement but also allowed the treated slabs to be trafficked by cars and HGVs within a relatively short period of time following treatment. 

Geobear’s geopolymer material ticked all the boxes as the injected geopolymer cures within minutes of injection to 95% of its final working strength.

Slab replacement was only being undertaken in lane 1 which was under permanent closure for the duration of the project, due the time necessary for the newly laid concrete to cure.

Meanwhile, Geobear were able to work in both lanes 1 & 2 for the full duration of the night closure with zero impact on commuters. 

A further benefit to using Geobear is that fact that the weather does not hinder the ability to deliver projects. During the on-site works, there was heavy rainfall on a number of nights which slowed some other works down. This had no detrimental impact on Geobear’s work as the specialist geopolymer selected for the scheme is hydro insensitive and actually works to displace water from beneath the slab and sealing it so it can not return.

Geobear solution

Geobear stabilised 130 of the 171 compromised 6 x 4metre slabs during 9 night closures with 2 teams of 3 technicians and 2 injection units; on average 16 slabs were treated each shift.

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