TfL Pioneers Use of 50% Recycled Asphalt in Top-Layer Road Surfacing

Transport for London (TfL) has taken a significant step forward in sustainable highway construction by becoming one of the first UK highway authorities to successfully complete a long-term trial using 50% Reclaimed Asphalt Pavement (RAP) in the top layer of a road surface.

The landmark trial, undertaken in collaboration with long-standing partner FM Conway, ran from 2016 over a nine-year period and focused on a critical stretch of the A1 at Mill Hill – a strategic arterial route serving traffic in and out of the capital. The initiative aimed to challenge the prevailing industry standard, which had traditionally limited RAP usage in surface courses to just 10%.

Challenging Industry Norms

Comprehensive on-site monitoring, supported by rigorous laboratory testing, confirmed that the high RAP asphalt not only matched the performance of conventional materials but also demonstrated resilience under heavy and frequent traffic conditions. The findings mark a shift in industry perception, illustrating that recycled content is capable of delivering equivalent – if not superior – performance in terms of surface texture, safety, and structural integrity.

Historically, RAP was reserved for base and binder courses due to concerns over its durability in surface applications. This trial directly counters those assumptions, providing compelling evidence that high RAP mixtures can uphold the structural demands of major roadways.

Scaling Innovation Across the Network

Buoyed by the trial’s success, TfL has extended the application of high RAP materials to other key locations, including the A40 Westway, and is actively promoting the use of 50% RAP mixes as a standard option for future surfacing works.

As an early adopter of this technology, TfL is not only driving innovation within its own network but also encouraging wider uptake across the highways sector by sharing results, technical insights, and best practices with other authorities and industry stakeholders.

Increased implementation of high RAP asphalt is expected to bring multiple benefits – notably reducing construction waste, cutting the demand for virgin aggregates, and significantly lowering carbon emissions associated with material production and transport.

A Strategic Step Towards Net Zero

The initiative forms a crucial component of TfL’s broader strategy to decarbonise its infrastructure and supply chain operations as London strives to 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.”

Supply Chain Partnerships Drive Progress

FM Conway’s Technical Director, Mark Flint, praised the collaborative approach, stating:

“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. 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.”

TfL continues to incorporate RAP wherever feasible and works closely with its supply chain to maximise recycled content. In parallel, the authority is also advancing decarbonisation strategies for other high-impact materials such as concrete and steel.

TfL has joined other major infrastructure clients in endorsing the Construction Leadership Council’s Five Client Carbon Commitments, further reinforcing its leadership role in fostering low-carbon innovation across the construction and transport sectors.