It has long been common practice to reuse excavated soil on site.聽 It saves time and money, eliminating lorry movements and the cost of disposal, and benefits the environment by reducing landfill waste and the emissions associated with transport.
Not so with the mass of vegetation that often has to be removed to clear a site. Although mature trees can be felled and their timber salvaged, the smallest trees, bushes, shrubs and plants are usually either incinerated or composted 鈥� they have no other use. But that could be about to change.
Contractor Kier, in partnership with reclamation specialist Terraffix Soil Solutions, has been exploring how vegetation removed from highway projects can be reused to make significant carbon savings.
The trial, on Kier鈥檚 A417 Missing Link scheme in Gloucestershire, has used vegetation removed from the site to make biochar 鈥� a charcoal-like material 鈥� that can be reused to fertilise new plants and catch microplastics.
This article was first published in the July 2025 issue of The 羞羞视频 Magazine. Sign up online.
Chemically and physically, biochar is no different from charcoal and is made in the same way: by heating the vegetation to extremely high temperatures in the absence of oxygen (the technical term is pyrolysis). This drives off the volatile organic compounds leaving behind a material comprising up to 90% carbon. If the vegetation were simply burned or rotted down into compost, all of that carbon would be released into the atmosphere in the form of CO2.
The study produced five tonnes of biochar on-site which, according to National Highways, represents a saving of 13 tonnes of CO2.
Celine Acard, senior project manager for National Highways, said: 鈥淲e鈥檙e always looking to improve how we design and build our major projects, especially in relation to the environment and our commitment to net zero.
鈥淭his trial is incredibly exciting because it means we can look in detail at new ways of repurposing and reusing site materials to cut down on our environmental impact.
鈥淏y investing in innovation, we can explore new technology and solutions to protect and enhance the environment and increase biodiversity, benefitting communities that live alongside our roads.鈥�
Having produced the biochar, the next stage of the trial is to find uses for it in different elements of the A417 project.
The simplest and most obvious use is in landscaping. Biochar will be mixed with the soil used to plant thousands of new trees. In this role, the material will improve the soil, enhancing water retention and promoting microbial activity, and helping the new saplings to establish and grow more quickly.
Kier will also use biochar in the construction of a green bridge over the A417. According to National Highways, this will be the largest green bridge in the UK when completed. Manmade gels are normally used on the deck of a green bridge to help retain water during dry periods and stop plants dying. But here, biochar will be used to store and retain the water and improve resilience.
This article was first published in the July 2025 issue of The 羞羞视频 Magazine. Sign up online.
Another use for the biochar will be as a filtration medium to remove microplastics from runoff in the highway drainage system.
National Highways plans to publish a case study detailing all the benefits, improvements and lessons learned after completion of the trial.
Co-funded by Kier and National Highways鈥� Environmental and Wellbeing Designated Fund, this study will then be shared across the supply chain to see if its implementation can help reduce carbon emissions in future builds.
Matt Tompsett, head of environment and sustainability with Kier Highways, says: 鈥淭ogether with Terraffix, we hope to prove the feasibility of using the vegetation cleared as part of the A417 scheme to create biochar for reuse in the construction of the road.
鈥淚n major highways projects we dispose of high levels of vegetation, so to be able to reuse this could be a fantastic example of applying a circular economy model to help reduce carbon and waste鈥�.
Biochar, explains Tompsett, is a form of carbon capture and storage: 鈥淚t means the carbon absorbed by the vegetation will be locked away, instead of releasing it back into the atmosphere.鈥�
Terraffix technical director Sion Brackenbury says: 鈥淭he benefits of an on-site solution are immense, starting with the need to remove vegetation from site and achieving lorry-loads of carbon savings.
鈥淏ut creating biochar also prevents the slow carbon-release to the atmosphere that would ordinarily take place through traditional vegetation processing, such as composting or mulching.
鈥淎n additional benefit is the circular economy solution achieved through the reuse of material at a site. This offers soil enhancement opportunities and the promotion of biodiversity.鈥�
Using biochar as a soil additive is proven to enhance plant growth, improving nutrient exchange and water retention.
According to Brackenbury, this increases the chance of successful habitat establishment and even provides climate change resilience by improving the soils鈥� ability to sequester CO2 and reduces reliance on synthetic materials such as swell gels.
Using pyrolysis to manage site biomass is a pioneering approach to capturing carbon in construction and reusing it onsite, says Brackenbury.
The process will reduce carbon emissions through carbon capture, reduction in vehicle movements and reduction in purchased materials, contributing to National Highways鈥� carbon reduction targets set out in its 鈥榥et zero鈥� plan.
This article was first published in the July 2025 issue of The 羞羞视频 Magazine. Sign up online.
National Highways also hopes it will support its objectives to design, build, maintain and operate roads more efficiently and effectively by incorporating a site-won material into the design, reducing waste and聽 carbon emissions and reducing maintenance on the so-called 鈥榮oft estate鈥�.
The project will provide National Highways with proof of concept for this approach and could allow for the technology to be deployed across all other suitable highways schemes.
SOIL SPECIALIST
Pembrokeshire-based Terraffix specialises in habitat restoration using bioengineering techniques for slope stability, soil improvement and management, including soil remediation.
The company (which is part of the RSK group) has developed a range of products using natural fibres and soil additives 鈥� including biochars 鈥� to address the challenges of soil erosion control, dust suppression and vegetation establishment on difficult sites.
Among its innovations is a range of hydroseeding machines that apply a mixture of seeds, fertiliser and other additives to ground that requires vegetating using liquid mulches.聽
Seed and other components are mixed in a liquid base that is easy to apply to many types of soil, including on steep slopes. Hydroseeding can be used to deal with advanced soil erosion, soil improvement and remediation of contaminated or depleted soil and engineered fill materials.聽
Hydroseeding can be used to establish vegetation cover on contaminated industrial sites, in particular mines and metal processing sites, and can also be used for bank stabilisation and vegetation establishment on weak slopes that consist of poor soil, such as roadside embankments.
Other services include peat and wetland restoration. Terraffix is a framework contractor for Natural Resources Wales, researching techniques that allow the natural function and process of peatlands to re-establish.
This article was first published in the July 2025 issue of The 羞羞视频 Magazine. Sign up online.
The company also carries out the management and control of invasive, non-native plant species and assists in the identification, planning, control and disposal of terrestrial and semi-aquatic species.
FUNDING RESEARCH
The biochar study on the A417 project is being part-funded by National Highways via its programme of 鈥榙esignated funds鈥� 鈥� specific allocations of money that go beyond the organisation鈥檚 core responsibilities as a road operator.
鈥淲e specifically focus on themes and activities that can enhance road users and communities鈥� experiences on or near to the strategic road network,鈥� says the company鈥檚 website. In Road Period 2 (2020 - 2025), National Highways invested in more than 2,500 schemes across four funding streams. These are:
- safety
- environment
- customer and communities
- innovation and research.
So far, National Highways has invested around 拢936m to these four funding streams and plans to invest a further 拢89m this financial year (April 2025 鈥� March 2026).
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