Heidelberg Materials has supplied its CarbonLock asphalt containing polymer modified bitumen (PMB) bio-binders, produced as both hot mix and warm mix asphalts, and containing up to 30% reclaimed asphalt 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 and A34 near Newbury, follow a trial last year on a stretch of the A30 near Exeter 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 National Highways’ A2 Kingston Scheme. They are:
- a control section using conventional warm mix asphalt (WMA) with a standard polymer modified bitumen (PMB)
- CarbonLock PMB asphalt produced as hot mix asphalt
- CarbonLock PMB asphalt produced as WMA, and
- CarbonLock PMB asphalt containing 20% reclaimed asphalt produced as WMA.
The A34 trials, carried out as part of the A34 SB South Isley to Beedon Scheme, replicated these and also added a fifth trial section: CarbonLock PMB asphalt containing 30% reclaimed asphalt 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 reclaimed asphalt in the 20% and 30% trials, making it a truly circular solution.”
The A2 trials used more than 1,500 tonnes, and the A34 around 500 tonnes, of CarbonLock asphalt, reducing the carbon emissions associated with the asphalt by around 26%.
The work was coordinated by AtkinsRéalis Jacobs JV as part of a National Highways research project. The trial sections are undergoing laboratory testing and are being 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.”
