Managing a Highways Asset – the Process Explained

From the traveller routes in the Iron Age to the Roman Empire’s Watling Road, Britain like the rest of the world has relied heavily on its road network.

Although today, the necessity is not to advance the movement of troops but to maintain the availability to move goods and people safely. The UK Highways Network consists of many types of road, the critical routes being the motorways and trunk roads. Behind the scenes, the management of this 260,000 mile network is through central and local authorities and their appointed agents.

The vast proportion of our network is made up of flexible roads, with under 10% being concrete. Under normal circumstances, the design life of a flexible surface is 10-15 years and concrete much longer than that. However there are issues that will cause the roads to become unstable during their life and they will require unscheduled maintenance.

Managing these assets is a monumental task for Highways England. Every year each flexible road is subjected to a number of network-wide surveys. One being a Traffic Speed Deflectometer (TSD) survey to flag any issues with the structural condition of the asset. Another survey is the TRACS condition survey which identifies issues from the surface. These surveys are conducted by the HE appointed surveyors and the results are fed into the central HAPMS (Highways England Pavement Management System). All road sections can be assigned a category between 1-4; any area of the road with a 3 requires investigation and 4 indicates more immediate action with a likely requirement for remedial work. 

Once this network-wide data has been captured, asset managers can then break the network down into manageable schemes. They will first assess whether a scheme will require further analysis of data and additional survey information from coring, a slower speed deflectograph or a falling weight deflectometer. Together with visual inspections, the asset manager is able to determine the cause of a problem and consider potential solutions.

There are typically three types of issue that an asset manager would see on a flexible pavement; fretting and surface defects where the surface breaks up, pavement structural issues which results in more pronounced cracking across a surface or more infrequent longitudinal profile issues where entire sections of road have dropped. 

Similarly, our concrete roads are inspected annually to determine their fitness for purpose. The challenges with concrete slabs differ slightly as surface failure is not as prevalent. Problematic slabs are more likely to rock when trafficked, sink or break-up. Although well under 10% of the network is concrete, these problems are often encountered by asset managers.

On many schemes, the remedial process is straightforward, minor resurfacing might be required to rectify surface problems, but where pavement structural issues or concrete rocking is present, a more comprehensive solution can be required. 

Where an asset has a structural issue the solution requires a design with a robust, long term plan in mind. The options in both cases are considered primarily in accordance with safety and road availability requirements; asset managers need to find solutions that minimise downtime of the asset and avoid full closure. Consideration is also given to the nature of the problem, in many cases the structural issues that see cracking surfaces and sinking slabs are a result of weakening of the sub-foundation or soils beneath. This could be caused by years of compression by vehicles, water ingress, environmental factors or poorly made ground on construction.

There are two main options to stabilise a slab, cementitious grouting or geopolymer injection. Both solutions achieve the same goal, stabilising the ground beneath the asset, however, the method and process are quite different. Cementitious grouting is the traditional method whereby cement-based material is pumped into the sub base to set and stabilise the road. The cementitious solution requires lengthy closures and set-up and the curing time of the material means a road can not be trafficked for a number of days whilst it cures. Furthermore, major plant equipment needs mobilising and the relative carbon footprint is high.

With a geopolymer solution, expansive material is injected into the area that needs to be stabilised. All the plant and equipment is contained within one unit and there is no set-up time. A two-component material is pumped through drilled 16mm holes to the required depth and it expands to fill voids and compact the existing soil or foundation base. With one injection unit, the time to completely stabilise the foundation of a concrete slab can be undertaken in less than an hour.

Time plays an important role in choosing a solution, Highways England needs to return an asset to use with minimal disruption. Geobear can stabilise complete sections overnight, or using single lane closures. Crucially, the geopolymer cures within 15 minutes, meaning assets can be used almost immediately after Geobear complete stabilisation works. Because there is no excavation and the time on site is limited the exposure to construction risks are hugely reduced.

As no major plant is required or excavation needed the carbon footprint is also a lot lower than other methods, a recent study by KSL compared geopolymer on a project with cementitious solutions and found a significant reduction in carbon emitted through the geopolymer process. The conclusion indicated that in comparable situations geopolymer always provides less environmental damage. 

Historically, Britain’s roads were designed and engineered by the Romans. Following a period of expansion in the medieval era, it wasn’t until the advent of road vehicles in the 20th century that major developments occurred. Similarly, in today’s era, more frequent and heavier traffic is impacting the asset life of our ageing roads and modern solutions are required to remediate the problems safely, whilst minimising delay.