This ICE Carbon Champions case study highlights the asphalt alternative that could help National Highways to hit its net zero targets.
National Highways, which manages England’s strategic road network, has challenged the highways sector to cut the carbon footprint of asphalt – one of the key components of road construction and maintenance.
A trial on the A30 in Devon has shown that replacing a percentage of the carbon-intensive binder in the asphalt with a bio-based alternative can reduce its greenhouse gas emissions by 20%.
National Highways’ net zero strategy
National Highways aims to achieve net zero greenhouse gas emissions for construction and maintenance activities by 2040. A key part of hitting this target is the decarbonisation of asphalt production and installation.
Asphalt is one of the most widely used materials in the building and maintenance of major roads, but it’s a significant contributor to the carbon footprint of those processes.
National Highways estimates that 77,300tCO2e of greenhouse gases were emitted from using asphalt on the UK’s roads in 2020.
Roadmap for decarbonising asphalt
In 2022, National Highways published Net zero highways: our zero-carbon roadmap for concrete, steel and asphalt. This document identified a range of measures to decarbonise asphalt production and installation by 2040. These included:
- maximising the durability of roads;
- adopting lower-carbon fuels to produce asphalt;
- making more use of asphalt produced at lower temperatures;
- using a high percentage of reclaimed asphalt in new road materials; and
- reducing the embodied carbon of bitumen.
Bitumen is a key component of traditional asphalt, acting as a binder. Because bitumen is made from crude oil, the embodied emissions associated with its production contribute significantly to asphalt’s carbon footprint, sometimes accounting for more than a quarter of its total greenhouse gas emissions.
Enter bio-based binders
Bio-based binders, also known as a biogenic or bio-binders, are an emerging technology with the potential to cut these emissions significantly by replacing some of the bitumen.
Bio-binders are produced from a natural material that absorbs and stores carbon dioxide throughout its life.
The carbon dioxide is ‘locked’ into the bio-binder, which prevents its return to the atmosphere, even when the asphalt is recycled. In effect, this transforms the road into a carbon sink.
Incorporating such binders can reduce the embodied carbon footprint of bitumen by up to 250kgCO2e/t.
Trial of bio-binders on the A30
National Highways wanted to understand more about the benefits of bio-binders and their potential role in achieving its net zero targets. It commissioned AtkinsRéalis to conduct a research project called Future asphalt surface course linking to NH net zero.
The work, undertaken in collaboration with Heidelberg Materials, included laying two trial sections of asphalt on the A30 Cutteridge to Alphington scheme, west of Exeter, in February 2023.
This was the first time that polymer-modified binders, such as and including bio-binder, had been laid on the strategic road network in its surface course materials.
The trial was designed to enable National Highways to evaluate and understand the technology’s performance.
Two binders containing biogenic material were tested: Nynas’s Nypol RE and Shell’s Bitumen CarbonSink.
A control section of surface was also laid using conventional binder, to compare the long-term performance of the trial materials with that of traditional bitumen-based asphalt.
Results – carbon savings and durability
The trial bio-binders delivered a potential carbon footprint saving calculated at 13.75kgCO2e/t, relative to the control section. This equals a 20% reduction over lifecycle stages A1 (raw material extraction and processing) to A3 (manufacturing).
Based on the total production of 1,200t of bio-asphalt, it’s estimated that the A30 Cutteridge to Alphington scheme delivered a potential saving of 16.5tCO2e.
Heidelberg Materials and the University of Nottingham are conducting a comprehensive performance assessment of the materials. Laboratory testing to date has shown that they achieve or exceed the required performance standards.
After being in situ for more than 18 months, the materials on the A30 showed similar performance to that of the traditional asphalt in the control section.
Follow-on projects
In light of the successful A30 trial, biogenic asphalt has been laid on two further sections of the strategic road network as part of the project.
In these trials – on the A2 in June 2024 and the A34 in July – biogenic binders have been used with other lower-carbon technologies:
- warm mix asphalt, which is produced at lower temperatures than traditional hot mix asphalt; and
- the inclusion of up to 30% reclaimed asphalt in the mix.
Heidelberg Materials installed these sections and their performance is being evaluated by AtkinsRéalis in collaboration with the University of Nottingham.
Assessing the potential
The A30 trial was a chance to assess the performance of low-carbon bio-binders under real-world traffic. Monitoring will continue, so that the researchers can assess the whole-life benefits of bio-binders and understand how this technology can help National Highways to hit its net zero targets.
The trial has also advanced the technology readiness level of future specifications and wider applications in the sector.
The trials on the A2 and A34 have shown that it’s possible, through several decarbonisation methods, to further reduce carbon impacts and promote more recycling to support the circular economy.
Name of project:
Innovative bio-binder trials on the strategic road network
Project team members:
- Professor Gordon Airey, University of Nottingham
- Callam Brough, Shell Construction and Road
- Dennis Day, Nynas
- Paul Edwards, National Highways
- Adrian Hadley, Heidelberg Materials
- Donna James, AtkinsRéalis
- Umesh Parajuli, National Highways
- Tony Parry, AtkinsRéalis
- Matthew Wayman, National Highways
- Dr Michael Wright, AtkinsRéalis
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