As part of a £282 million (~$381 million) project, the National Center for Composites (NCC, Bristol, UK) and construction company Skansa (Stockholm, Sweden) are testing an ‘industry first’ low-carbon concrete with basalt fiber reinforcement, designed to reduce congestion for motorists on the M42 Junction 6 national highways, a temporary haul road for construction vehicles and a well-known bottleneck in the Midlands. While aiming to reduce carbon emissions – a combination that would reduce the carbon footprint by more than 50% – the project also serves to improve the structural performance of reinforced concrete and improve productivity, safety and costs.
The trial, conducted by Skanska, in partnership with the NCC and funded by National Highways (NH), compares traditional reinforced concrete to low-carbon concrete reinforced with basalt fibers.
The production of cement, a key ingredient in concrete, currently accounts for around 7% of global CO2 emissions. In the UK, this figure is below 1.5% thanks to innovation and investment in efficient plant, fuel switching and the use of low carbon cement substitutes which are by-products of other industries.
Macadam (Solihull, UK), a member of the project’s supply chain, provided two types of concrete for the trial: a mix comprising a conventional mixed cementitious material and an alternative low-carbon mix incorporating a cementitious material activated by an alkali (AACM) instead of cement.
“Made in a conventional concrete plant located near the project and installed in exactly the same way as traditional materials, this new sustainable product offers a carbon footprint that is up to 80% lower than that of standard CEM I concrete”, says Robert Gossling, commercial engineering manager for Tarmac. “We hope this demonstration will help accelerate the development of innovative low-carbon materials.”
Photo credit: The NCC
Basalt Technologies UK Ltd. (London, UK) supplied the basalt fiber reinforcement. “Basalt is a lightweight composite material that consumes 62% less CO2 than steel during its manufacture”, explains Malcolm Newton, director of Basalt Technologies. “It includes an inert non-metallic material that does not corrode, making it more durable than steel. Basalt fiber reinforcement is also up to four to five times lighter than steel, making it safer to handle, repair and transport with fewer truck movements.
Field and laboratory testing will be carried out over the next few months following the start of the trial, which started in early December 2021. Four reinforced concrete slabs have been poured at the site of Junction 6 of the M42 in the part of a temporary transport road which will be heavily used by construction vehicles and will be monitored throughout the duration of the works. The tiles include:
- Slab A: Conventional concrete + metal reinforcement
- Slab B: Low-carbon concrete + metal reinforcement
- Slab C: Conventional concrete + basalt reinforcement
- Slab D: Low-carbon concrete + basalt reinforcement
The team is now monitoring the slabs in situ. Full-size test slabs were sent to a specialist laboratory for bending and shear testing. All collected test results will provide knowledge about the curing process, ease of construction, safety benefits, functional properties and structural behavior of different combinations of concrete and reinforcement. This will provide insight into the future use of more sustainable materials in construction.
The test will also provide a better understanding of the impact of the use of these materials upstream of the Eurocode 2 standards revision project, which will include the use of composites in the design of concrete structures. This is currently under development.
“This project, its learnings and test results, are key to understanding the impact of low carbon concrete and advanced composite reinforcement systems to reduce embodied carbon for the construction industry,” adds Carys Holloway, Technology Program Manager, NCC. “I look forward to seeing the expected ease of planing basalt fiber reinforced slabs for recycling and the potential this has for end of life. [EOL] scenarios.
The Skanska and NCC team will also work with HS2 to further research and develop this innovative low carbon solution. Work to upgrade the M42 junction is expected to be completed in 2024-2025.
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