From Risk to Reward – The Sustainable Road Ahead
In 2016, FM Conway made a decision to push forward with new thinking that could reshape the future of road surfacing. At the heart of that choice was our commitment to sustainability and material circularity, principles that underpin everything we do.
We had long recognised the potential of Recycled Asphalt Pavement (RAP), a material created by reclaiming and reprocessing old road surfaces, to deliver both environmental and performance benefits.
The industry was cautious, but we were determined to challenge that thinking, and with the backing of Transport for London (TfL), we laid the UK’s first 50 per cent RAP surface course mix on the A1 Mill Hill Interchange. The aim was simple – to prove that sustainability and innovation are not at odds with quality and resilience.
It worked. Nearly a decade on, the results show that our circular economy approach is not only possible but essential, delivering a surface that outperforms virgin materials and setting a new benchmark for the industry’s sustainable future.
We want to see the use of high RAP content become standard practice across the industry. With its use proven to be safe and reliable, we have a real chance to boost the sector’s contribution to sustainability goals.
Breaking down barriers
At the time of the Mill Hill trial, using high levels of RAP in base and binder courses was already becoming more accepted, with 50 per cent content mixes relatively common. But when it came to surface courses, the topmost layer directly exposed to traffic and the elements, industry guidance capped RAP content at just 10 per cent. The perceived trade-offs on issues like skid resistance and longevity had kept usage low.
We wanted to prove that high levels of RAP were not only safe and durable, they were the most sustainable option. By reusing asphalt, aggregates and planings, we can conserve natural resources and reduce carbon emissions, thereby contributing to the UK’s net zero goals.
The trial in action
The A1 Mill Hill Interchange was chosen for the trial, a high speed, high volume section of strategic network in north London. Working closely with TfL engineers, we developed a 50 per cent RAP surface course mix tailored for the location. This mix used carefully selected reclaimed materials and was designed to meet stringent requirements for stiffness, texture depth, skid resistance and rutting performance.
Two lanes were laid using the high RAP mix and one control lane with conventional, virgin material. From day one, we put in place a programme of long-term monitoring, knowing that the true value of the trial would come from how these materials performed under years of stress.
In 2024, TfL commissioned an independent supplier to extract 18 core samples from across all three lanes. The results speak for themselves.
The results today
The results from the trial were extremely positive. Not only did we see equal performance between the RAP and virgin materials, but in some cases, the recycled mix outperformed its counterpart.
The most visible and critical damage on heavily trafficked roads is rutting, the permanent deformation of the road where wheel paths are caused by repetitive use. In this area, we saw the RAP mixture do better than the virgin mix, with 1.2mm of rutting versus 1.6mm. The 25 per cent reduction in rutting proves durability and improved resistance to reshaping under the weight of many vehicles.
The virgin mix was significantly stiffer too, achieving 3,033MPa compared with 4,488MPa for the RAP mix. That means even after almost a decade, the RAP is far less prone to cracking, showing its enhanced performance and endurance for the long term.
These are not marginal wins. They are significant signs that sustainable materials, when carefully selected and applied, can outperform traditional mixes.
Beyond the trial
The success of the Mill Hill trial opened the door to further innovation. Already, we’ve increased RAP content to 92 per cent, setting a new standard for surfacing at Elmfield Way in Westminster. We’ve pushed the boundaries in the last decade with the help of our partners like TfL, Westminster City Council and National Highways, and we’re looking to continue our work in this area, increasing the amount of recycled materials in the strategic road network.
But progress in this area requires more than just improved materials and processes, it takes a mindset shift. It takes partnerships built on trust, like the one we have forged with TfL, and a willingness to take calculated risks backed by rigorous evidence. We worked with Lukash Manandhar, Principal Engineer at Transport for London on the project who said it best:
“Early collaboration with FM Conway was key to the results we see today, helping to shift perceptions of RAP being both durable, and equally as important, reliable.
“The joint trial paved the way for another successful scheme on the A40 in west London, and we’ll continue to work closely with FM Conway to reduce carbon usage in our projects.”
The need for innovation
The road ahead isn’t without its additional challenges and we recognise that recycling isn’t the only answer to our sustainability concerns. We will need to think about resilience more broadly although materials re-use can and should be a part of that. Climate change especially is introducing more extreme weather patterns. The Met Office recently published a report that found the UK is breaking heat and rainfall records more frequently as the climate warms. This has an impact on our roads, increasing the risk of cracking and potholes forming.
The use of battery electric vehicles, which is becoming more widespread, is also a looming issue. These cars are heavier than their petrol and diesel counterparts, putting yet more pressure on our roads and making them more susceptible to damage.
These stressors demand a more durable, more resilient road network. Fortunately, RAP has proven it can help us deliver under these conditions, with its blend of aged and rejuvenated binder offering improved resistance to cracking and breakage. However, it isn’t a silver bullet, we need to continue innovating in a range of areas to address the issues ahead.
Thinking ahead
With the Department for Transport predicting a 22 per cent rise in all highways traffic in England and Wales between 2025 and 2060, we know we need to boost the durability of our roads. Trying to stick to the same approach just won’t deliver the sustainability or the quality required of our future network.
Pushing the envelope on recycling didn’t just help us do better – it showed us how to think differently and encouraged innovation. We can use that mindset to drive the changes needed to develop the next generation of materials and techniques.
The A1 Mill Hill trial began as, just that, a trial. But today, it stands as a blueprint for future ready infrastructure showing that with the right ingredients, collaborative partners, technical excellence, and bold thinking, comes sustainability in road surfacing that no longer comes with compromise.
The evidence is in. RAP works. And with every project that embraces circularity, we move closer to a road network that’s not only stronger, but built to endure the demands of tomorrow.
Article by Mark Flint, Technical Director at FM Conway.
