Construct - Issue 51

“…in 2016, it was the first time we’d used 50% recycled asphalt on such a major route, and it proved it could handle heavy traffic.”

The results of our work with TfL validate what we’ve known all along: that RAP can deliver better results than virgin mixes in some areas.

Both materials showed comparable results for water sensitivity/resistance and bonding strength with the underlying layer. The real difference came to light when evaluating rut resistance and stiffness. RAP materials rutted much less, only 1.2mm versus 1.6mm for traditional materials – a 25% reduction. What’s more, the stiffness of the traditional material was much higher at 4,488MPa compared to 3,033MPa for the RAP mix. So, despite a decade of use, the RAP sections were much less prone to rutting and cracking – proving excellent performance and durability. FM Conway worked with Lukash Manandhar, Principal Engineer at Transport for London, who says of the project: “The A1 Mill Hill trial was a milestone for us and the industry too – challenging perceptions of high proportions of RAP in a way that had not been done before. It was the first time we’d used 50% recycled asphalt on such a major route, and it proved it could handle heavy traffic. What made the difference was the early collaboration with FM Conway. Working closely from the start meant we could show that RAP isn’t just durable but reliable too. The success here gave us the confidence to do the same on the A40 in west London. We’re committed to reducing our carbon usage as we work towards net zero, so we’ll keep building on the results from this trial to cut emissions even further in future projects.”

The results show that sustainable road construction is far from a compromise; it’s the future. Since the pioneering work done in 2016, there has been wider adoption of sustainable materials in the highways sector. In 2024, FM Conway laid a new road surface for Westminster City Council using 92% recycled content, currently the highest percentage for any project in the UK. “The use of high levels of recycled asphalt has grown significantly, but there’s still a long way to go to making it standard practice,” says Mark Flint, technical director at FM Conway. “The results of our work with TfL validate what we’ve known all along: that RAP can deliver better results than virgin mixes in some areas. The important thing now is to look at how we can incorporate high-recycled asphalt into specifications by default.” The trial highlighted the importance of close collaboration between contractors and client teams. Mark adds: “The highways industry faces some big challenges over the next few years, not least getting to net zero carbon. We need new thinking, but progress can only happen if the industry works together to hit common goals. That’s why trials like this are so important, and it’s why we wanted to share the outcome of our work – so that we can collectively build on success.”

FACTS Client

Transport for London (TfL) Divisions • Aggregates and Asphalt • Surfacing

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