Sustainable Construction

Tarmac and Align trial innovative low carbon concrete


“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.”

Robert Gossling, head of commercial engineering solutions, Tarmac

As a key partner to Align, the joint venture delivering the Central 1 (C1) section of HS2 Phase One, we announced in February 2022 that we had demonstrated an innovative new low carbon concrete solution. Together, we have a common goal of working towards net zero carbon construction and this new concrete, which is only recently available following extensive laboratory design, offers the potential to help achieve this objective.

Align was quick to provide applications for early demonstration and testing at full scale using one of three Tarmac concrete batch plants at a Chalfont Lane construction site in Hertfordshire.

A structural slab forming part of the new viaduct pre-cast factory and a vertical wall were poured. 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.

The new low carbon concrete has a carbon footprint following industry BSI PAS2050 calculation rules that gives a 62% reduction in CO2e per cubic metre of concrete, compared to a standard CEM I concrete, meeting the same specification in the same raw materials.

The footprint covers all aspects of the concrete production and supply with no carbon off-setting applied, delivering an actual footprint of 133kg/m3 CO2e. This represents a saving of 220 tonnes CO2e for every 1000m3 produced.

This has demonstrated the potential to use very high ground slag (GGBS) contents in excess of 90%, as an alkali-activated cementitious material conforming to BS EN197, the standard for cementitious materials allowed to be used in ready mixed concrete, to significantly reduce carbon emissions, whilst still producing a quality finish and allowing normal construction and demoulding times.

Robert Gossling, our head of commercial engineering solutions, said: “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.”

Daniel Altier, project director for Align, said: “It is a strategic imperative for Align, reflecting the priorities of our JV partners and in line with HS2 commitments, to reduce carbon emissions by 50%, to look for opportunities to improve our carbon footprint. The early results of this trial are very encouraging and highlight the benefits to be gained through close collaboration with our supply chain partners.”

We will continue to collaborate with Align by expanding the trial on other available areas of the C1 project and on development of low carbon concrete solutions.

We are proud to be currently providing concrete for the construction of the Central 1 section of HS2 Phase One that is being delivered by Align. This includes a 21.6-kilometre section of high-speed rail infrastructure incorporating a 3.37-kilometre viaduct across the Colne Valley, a 16.04-kilometre twin-bored tunnel, and five vent shafts handling both intervention and tunnel ventilation facilities.