National Highways extends PMB bio-binder trials on the strategic road network

by Adrian Tatum

National Highways has extended its trials of bio-binders to include warm mix asphalt
(WMA) and recycled content to provide a circular, lower carbon, Clause 942 thin
surface course solution that will help it meet its net zero objectives.

Heidelberg Materials has used its CarbonLock asphalt containing polymer modified
bitumen (PMB) bio-binders, produced as both hot mix and warm mix asphalts, and
containing up to 30 per cent reclaimed asphalt (RA) to test the feasibility of various
configurations.

Bio-binders contain natural biogenic material, which absorbs and stores CO2
throughout its life, which is then ‘locked’ within bio-binders and not released back into
the atmosphere, even when the asphalt is recycled. In addition, the PMB binder used
in the trials is expected to enhance durability and further extend the life of the asphalt,
reducing the frequency of maintenance interventions.

The latest trials on the A2 near Canterbury, Kent, and A34 near Newbury, follow the
success of last year’s trial on the A30 in Devon and extensive lab-based testing at the
University of Nottingham in conjunction with AtkinsRéalis Jacobs Joint Venture (JV).
On the A2, four sections, each comprising of a 45mm surface course and varying from
700 to 1,000 lane metres in length, were carried out as part of the National Highways
– A2 Kingston Scheme. They are:

a control section using conventional WMA with a standard PMB;
CarbonLock PMB asphalt produced as hot mix asphalt;
CarbonLock PMB asphalt produced as WMA; and
CarbonLock PMB asphalt containing 20% RA produced as WMA.
2/3. The A34 trials, carried out as part of the National Highways – A34 SB South I sley to Beedon Scheme, replicated these and also added a fifth trial section: CarbonLock PMB asphalt containing 30% RA produced as WMA. Adrian Hadley, Technical Head (Asphalt and Aggregate) at Heidelberg Materials UK, said: “We are increasingly working with our clients to reduce the carbon impact of road maintenance and construction projects, helping them meet their net zero
ambitions.
“These further trials with National Highways are another example of this and move us another step forward.
“In the A34 trial we also reused the old planed out road surface to supply the RA in the 20 per cent and 30 per cent trials, making it a truly circular solution.” The A2 trials used over 1,500 tonnes – and the A34 around 500 tonnes – of
CarbonLock asphalt, reducing the carbon emissions associated with the asphalt by
around 26 per cent.
The work was coordinated by AtkinsRéalis Jacobs JV as part of the National
Highways research project Future Asphalt Surface Course Linking to NH Net Zero
under SPaTS 2. The trial sections are undergoing extensive laboratory testing and are
being closely monitored to see how they compare with ‘standard’ PMB asphalt used in
the control sections in terms of performance and whole-life carbon reduction.
Umesh Parajuli, Senior Advisor (Pavements) in the Safety Engineering and Standards
Division, National Highways, said: “National Highways is committed to trialling
innovative lower carbon asphalt solutions to help meet our 2040 net zero carbon
deadline for construction and maintenance activities on the SRN.
“The performance of the CarbonLock asphalt laid on the A30 has been excellent and now the second phase of the trial is looking at using bio-binders in conjunction with other low carbon innovations such as WMA and RA as well.
“We hope these trials will help to bring innovative low carbon asphalt solutions using bio-binders into our specification.”
Michael Wright, Technical Director at AtkinsRéalis, added: “It is critical for the industry to explore and test innovative solutions which contribute to the UK’s Net Zero commitments. The extension of this trial is testament to success of extensive
collaboration across the supply chain and academia, in partnership with National
Highways.