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.
The latest trials on the A2 near Canterbury (pictured below) and A34 near Newbury follow last year’s trial on the A30 in Devon and extensive lab-based testing at the University of Nottingham in conjunction with a AtkinsRéalis Jacobs Joint Venture (JV).
Heidelberg Materials used its CarbonLock asphalt containing (PMB) bio-binders and containing up to 30% reclaimed asphalt (RA) in the trials to test the feasibility of various configurations.
On the A2, four sections of 45mm surface course varying from 700 to 1,000 lane metres in length were laid as part of the National Highways – A2 Kingston Scheme.
The trial sections are:
- a control section using conventional WMA with a standard polymer modified bitumen (PMB);
- CarbonLock PMB asphalt produced as hot mix asphalt;
- CarbonLock PMB asphalt produced as WMA;
- CarbonLock PMB asphalt containing 20% RA produced as WMA.
The A34 trial, carried out as part of the National Highways – A34 SB South Isley to Beedon Scheme, deployed the same asphalt sections but also included 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: ‘In the A34 trial we also reused the old planed out road surface to supply the RA in the 20% and 30% trials, making it a truly circular solution.’
The A2 trials used over 1,500 tonnes of CarbonLock asphalt and the A34 around 500 tonnes, reducing the carbon emissions associated with the asphalt by around 26%.
The trial sections are undergoing extensive laboratory testing and 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 National Highways’ Safety Engineering and Standards Division, said: ‘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.’
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.
The work was co-ordinated by AtkinsRéalis Jacobs JV as part of the National Highways research project Future Asphalt Surface Course Linking to NH Net Zero under SPaTS 2.
Michael Wright, technical director at AtkinsRéalis, added: ‘The extension of this trial is a testament to the success of extensive collaboration across the supply chain and academia, in partnership with National Highways.’
