TfL in successful pioneering trial with recycled asphalt

Fifty percent recycled asphalt pavement mix on busy A1 at Mill Hill paves way for wider adoption

TRANSPORT for London (TfL) has become one of the first highway authorities in the UK to successfully run a trial that mixed 50% reclaimed asphalt pavement (RAP) into the top layer of new road surfaces – an approach that reduced both construction waste and the need to import new raw materials, and helped to reduce carbon emissions. The trial ran for nine years from 2016.

Carried out with supplier FM Conway, the trial monitored the performance and durability of RAP in road surfaces on the A1 at Mill Hill, a key strategic road into and out of London. It found that the material can endure frequent, heavy traffic and matches the performance of traditional asphalt in terms of quality, texture, safety, and maintenance.

Alongside intensive monitoring, laboratory testing on the material’s structural behaviour and response to force and load showed it maintained its firmness and integrity over the trial period, which are indicators of its durability.

This challenged the industry standards of the time, which involved restricting the use of RAP in the top layer of roads to just 10%, and shifted a long-standing industry perception that the use of recycled content belonged in the lower layers of roads, as it was believed that it could not match the durability or performance of fresh material mixes.

Building on the success of the pilot, TfL has carried out further trials on A40 Westway and promotes high-RAP asphalt as an option in future highways works on its network. As an early adopter, TfL is well positioned to share findings, guidance, and outcomes to support wider industry learning and innovation, to encourage broader implementation of 50% RAP mixture proportion.

Increased adoption will not only reduce carbon and cost throughout the project, but also increase national investment in the infrastructure and technologies needed to process and separate RAP effectively. The trial contributes to TfL’s wider sustainability goal to decarbonize its operations and supply chain in order to help London become a net-zero-carbon city by 2030.

Isabel Coman, TfL’s director of engineering and asset strategy, said: ‘We are committed to reducing carbon emissions across our assets and infrastructure to help us meet our net-zero targets. By trialling a higher proportion of recycled asphalt on the A1 at Mill Hill, we’ve become one of the first authorities in the UK to successfully incorporate 50% RAP in the top layer of one of our major roads and proved its ability to withstand heavy traffic loading.

‘This trial demonstrates our commitment to sustainability and gives a strong signal to the supply chain that we are seeking innovative solutions to reduce the embedded carbon in our major construction materials. We hope this encourages other highway authorities to conduct similar trials and continue to drive improvements in sustainability, reliability, and durability across the sector.’

FM Conway’s technical director, Mark Flint, said: ‘The use of high levels of recycled asphalt has grown significantly but there’s still a long way to go to make it standard practice. The results of our work with TfL validate what we’ve known all along: that RAP can deliver comparable results to mixes made entirely with virgin materials. The trial has proven that sustainability and innovation advances can be made without compromising the quality and durability of our roads. Partnerships built on trust, like the one we have forged with TfL, are key to continuing this progress.’

TfL now incorporates recycled asphalt where feasible and works closely with supply chain partners at the project level to identify and implement opportunities for increasing RAP usage wherever applicable.