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New aggregates help decarbonise roads



Last month [March] Durham County Council became the first road authority to use a carbon negative aggregate called ACLA in an asphalt mix. ACLA, which is created by sequestering carbon into the aggregate material, is produced by Low Carbon Materials, which officially launched it in March too.


According to Low Carbon Materials, by replacing between 5 and 7% of an asphalt mix with ACLA, a net zero asphalt could be produced. That could be good news for councils with demanding net zero deadlines on the horizon.


The asphalt containing the ACLA was used in the binder course of Elvet Hill, a road in Durham. The mix, which also contained some recycled asphalt planings (RAP), was produced by Tynedale Roadstone and laid by Rainton Construction, which are both part of the MGL Group.


This is a project on home turf for Low Carbon Materials, which was originally called Sphera. Co-founded by Dr Natasha Boulding, Dr Phil Buckley and Scott Bush, it is a spin-off from Durham University


Low Carbon Materials has been working with Skanska and Tarmac to develop ACLA, funded by National Highways’ Accelerating Low Carbon Innovation Programme. The plan is that initial trials will lead to using the aggregate on the Strategic Road Network as part of the £507m A4228 improvement project in Cambridgeshire.


By working with the Innovation Programme, Low Carbon Materials should get help in meeting standards and regulations, something that all new materials and technologies come across. As we know at Thermal Road Repairs, this can take some time, effort and investment.


Low Carbon Materials has not provided information on how ACLA is made. Other companies, such as Blue Planet, combine carbon dioxide produced from manufacturing process with waste that contains calcium such as demolition concrete, cement kiln dust or slag.


Low Carbon Materials has already developed a carbon negative aggregate for use in concrete called OSTO. It is made from waste destined for incineration, such as waste plastic and won the company a finalist’s place on Prince William’s Earthshot Prize in 2022.


According to Low Carbon Materials, 1 tonne of ACLA has permanently removed 750kg carbon from the atmosphere. The embodied carbon of standard asphalt mixes ranges from 30 to 70kg of carbon per tonne.


Assuming that Durham Council’s stretch of road performs as expected, and that the production of ACLA could be ramped up, this technology has the potential to make a difference to carbon emissions from road construction. There’s no silver bullet to decarbonising our roads – we need to attack this on multiple fronts.


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Thermal Road Repairs: Decarbonising the asphalt repair industry

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