Roads are at the core of our national transport system. One third of all traffic and two-thirds of all freight use the Strategic Road Network. It is the backbone of the country’s economy and a lifeline for communities everywhere, big and small.
The state and structural integrity of the roads is therefore integral to the smooth running of the country. It is why Highways England is embarking on an extensive programme of maintenance and repair as part of its second Road Investment Strategy, prioritising safety, customer satisfaction and sustainability.
A brief history of concrete
The design and construction processes for concrete roads were derived from those developed to construct airfield pavements, particularly during the Second World War. But it wasn’t until the 1970s and the first oil crisis that concrete roads in the UK became more common. The shortage of oil led to rationing, including of bitumen, produced from the refining of petroleum and used widely for road surfaces.
Concrete roads rapidly expanded during the 1980s, supported by a breakthrough in concrete design in 1987, when the Transport and Road Research Laboratory (TRRL, and now known as TRL) published Research Report 87 (RR87) design guidance for concrete pavements. The document looked at different construction methodologies, analysed their performance in terms of design, thickness and types of foundations used. The research proved that the performance of concrete roads was particularly sensitive to the strength of the foundation underneath.
To achieve the best performance, RR87 advised that concrete foundations should be constructed with an equivalent foundation modulus of 270 megapascals (MPa) or above, which can only be achieved by using a cement stabilised subbase. This is a stiffer, more uniform material and reduces the risk of cracking and early slab failure. After the publication of RR87, the industry switched from granular foundation design to cement stabilised foundation design.
Today, about 4% of the national road network or 172 miles in England is made of concrete. Many concrete roads have now exceeded their design life, particularly the older concrete pavements built before RR87. They are deteriorating quickly and showing multiple defects, from minor cracking to severe spalling. Repair and maintenance work is required urgently.
Pursuing the circular economy
Working within a limited budget, the challenge is to make the most of what we already have. One of the infrastructure industry’s priorities is to improve sustainable practices, and one sure-fire way to do this is to follow the circular economy philosophy.
Principles of the circular economy dictate that we should reduce waste and pollution by limiting our reliance on natural, finite resources and instead maintain, recycle and reuse the waste materials we already have in circulation.
In the context of concrete roads, the asset is in its highest value state in-situ and priority should be given to extending the service life in the first instance. Life extension works – such as crack repairs, concrete bay replacements, full and partial depth repairs, joint sealing and surface grinding – can achieve great results, prolonging the life of concrete roads by several years.
Concrete is manufactured from aggregate, cement and water and is 100% recyclable. Once a surface is broken down, any steel reinforcement can be removed and recycled, and the concrete re-used as an aggregate in the production of new concrete products or as a granular aggregate material – a process that seamlessly turns a waste product into a valuable resource.
Despite many advantages, concrete road pavements are disliked by many drivers because of the noise they make, which comes from the interaction between the tyres and the surface of the road.
Research in 2017 from independent watchdog Transport Focus reflected motorists’ discontent with our concrete roads, with driving on these surfaces commonly described as a stressful, noisy experience. Compared with the much smoother, quieter journeys on asphalt, this poses a huge challenge for Highways England to solve going forward.
The texture of pavement surfaces can be categorised as either positive or negative. Surfaces with a positive surface texture tend to create more noise, whereas those with a negative surface texture absorb it. Early on in concrete road construction, the texture created through the application of brushed finishes on the road surfaces presented a series of transverse ridges that reflected the tyre noise back into the environment and vehicle. Joints between the concrete slabs further added to the noise and discomfort when driving over them.
However, these challenges can be mitigated through the application of surface treatments, such as diamond grinding and grooving, which has been applied already to some sections of the road network. One of the most promising evolutions of this approach currently being explored is Next Generation Concrete Surface (NGCS).
NGCS involves grinding a thin layer off the surface of the concrete and then introducing longitudinal grooves – that is, in the direction. The grinding process smoothens the surface by removing irregularities, while the introduction of the grooves improves noise characteristics by introducing a negative surface texture and also achieves the required surface friction.
Creating a lasting digital legacy
Asset management is now widely recognised as a critical component in looking after and prolonging the design life of infrastructure. In the maintenance of concrete pavements, this could be a game-changer. It all comes down to selecting the best investments to retain and protect assets at the right time. This means understanding your asset, its condition and how it is performing and deteriorating. Armed with this knowledge, you can apply effective maintenance interventions at an appropriate time to extend the life of the asset. It also delays the moment when an asset falls into disrepair, when more time-consuming and costly repairs or replacement measures are required.
If we want to build durable roads with the lowest whole-life cost, lowest whole-life carbon footprint and the lowest impact on drivers and roadside neighbours, we need to look at the whole life-cycle of assets, taking into account the total cost of a product or service over its lifetime.
Reliable data is key to this. Today, information on the state of our roads is gathered via network-level surveys and investigations at project level.
Pooling this information together has been a blind spot for the industry thus far. By improving the collection, management and use of this data, we can more accurately inform future maintenance and repair works. The right budget decisions would then be targeted at the optimum time to intervene.
Mott MacDonald software offers a user-friendly platform to store and access information on asset management, helping clients to confidently handle and manage their data. Platforms such as Moata can bring individual pieces of information on the network together so that all stakeholders can easily visualise them and make informed decisions. It gives everyone a birds-eye view of the network, the quality and age of concrete pavements and any defects that are forming.
Once a project is completed, we hand over the legacy of knowledge and data to the client, so they can use it for ongoing performance assessments and maintenance strategies in a targeted manner.
We are also working to develop Machine Learning (ML) algorithms to automatically review survey data captured by multi-function survey vehicles. Our ambition is to automatically take the captured images and compare them against a comprehensive database of concrete road defects. The algorithm will then draw from this database and learn to identify every individual issue and prescribe relevant treatments for each. By using ML, we can quickly do initial sifts of survey data and make robust decisions about maintenance needs more quickly and efficiently than before.
Our knowledge and expertise enable us to continually develop new and better ways to maintain, construct and monitor the performance of pavements.
One step ahead
Our historical involvement and knowledge of the road network gives us an appreciation of the challenges our clients face, as well as the context as to why pavements perform the way they do, and where we need to focus improvements in future.
We work collaboratively with many supply-chain partners, contractors, product manufacturers, material suppliers and other stakeholders, which gives us a holistic insight into the industry. Thanks to this collaborative approach and our positive industry relationships, we always include the contractor early in conversations about safety in design, ensuring we manage all issues early on. Starting the communication process in good time ensures a smoother delivery of the projects on the ground.
We can be a one-stop shop for all engineering, consultancy, environmental and project management services. This approach offers greater project efficiencies and ensures better communication and collaboration across disciplines.
This holistic oversight across the industry also enables us to keep our fingers on the pulse of the testing and introduction of new technologies, so we can always be prepared to stay ahead of the game.
Kieran Kelly, Principal pavement engineer at Mott MacDonald, is one of the guest speakers at this year’s Highways UK. He is contributing to a panel discussion on ‘Loving concrete – concrete is forever (if you look after it)’ at 2:40pm UK time on 4 November. You can watch it live by registering here.