Tarmac trials ultra low-carbon concrete on HS2 project

Tarmac has successfully trialled the use of ultra low-carbon concrete on part of the HS2 route in the Chilterns.

The manufacturer worked with the Align consortium – a joint venture between Bouygues Travaux Publics, VolkerFitzpatrick and Sir Robert McAlpine – which is delivering the central section of Phase One of HS2. The project used up to 90 per cent ground-granulated blast-furnace slag (GGBS) to reduce carbon emissions.

The low carbon concrete was used for the floor slab and parts of the walls for a pre-cast factory which will supply components for a new viaduct on the project

The mixes, designed to Align concrete specification, exceeded expectations in both fresh and hardened properties, and showed that the new concrete can be produced in normal concrete plants and placed via mixer truck and by skip with tremie pipe.

Recent research by a number of concrete manufacturers has shown that low carbon alternatives can replace common Portland cement in a number of areas, significantly reducing carbon emissions from the material.

The tarmac concrete combined the very high GGBS with an alkali activated cementitious material conforming to BS EN197, which is the standard for cementitious materials allowed to be used in ready mixed concrete.

The footprint covers all aspects of the concrete production and supply with no carbon off-setting applied, delivering an actual footprint of 133kg/square metre CO2e. This represents a saving of 220 tonnes CO2e for every 1,000 square metres produced.

Tarmac head of commercial engineering solutions Robert Gossling said: “Against the backdrop of the climate emergency, this project underlines the clear benefits which can be unlocked when clients and contractors collaborate, in this case engaging to help understand and accelerate the adoption of this new low-carbon concrete solution.

“Together we’ve shown this new concrete is fit for purpose in slabs and walls, with good repeatability and works with standard production and construction methods. This product is a great step along the industry zero-carbon route map, and the demonstration will help accelerate adoption of this new concrete.”

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