A trial into the use of low carbon reinforced concrete 12 months ago has yielded sufficiently positive results that the new material is set to be used more widely.
Preparing the basalt rebar on the initial trailOver the past year Skanska, alongside the National Composites Centre, Tarmac, Basalt Technologies and National Highways, has carried out a trial on a low carbon reinforced concrete – made with no cement and no steel.
The trial was carried out at Skanska’s £282m M42 junction 6 project for National Highways. Cement-free concrete with basalt fibre reinforcement was used on a temporary haul road for construction vehicles. Analysis, now published, shows no loss of resilience or product performance.
Tarmac provided two types of concrete for the trial: a mix comprising conventional blended cementitious material and a low carbon alternative mix incorporating an alkali activated cementitious material (AACM) in place of the cement.
This AACM concrete was mixed at a conventional concreteplant close to the project and installed in the same way as traditional materials. The reinforcement steel replacement was of Bastech, a basalt fibre reinforced polymer rebar.
This is five times lighter and twice as strong as steelrebar and is naturally resistant to corrosion, alkalis and acids. The AACM concrete delivers a carbon footprint up to 80% lower than a standard CEM I concrete, it is claimed, while the basalt rebar averages 60% less than steel.The trial involved the construction of four concreteslabs on temporary haul roads on the M42 junction 6 highways improvement scheme.
The slabs were laid in December 2021 and were made up of:
Slab A – conventional concrete + steelreinforcement
Slab B low carbon concrete + steelreinforcement
Slab C – conventional concrete + basalt reinforcement
Slab D– low carbon concrete + basalt reinforcementThe road was used by construction vehicles throughout the trial period, with in-situ and laboratory tests carried out over a number of months. Full scale specialist lab tests involved bending and shear testing of the four types of slabs.
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