As architects and specifiers face growing pressure to reduce embodied carbon, attention is turning to the materials that make up some of a building’s most carbon-intensive elements. Concrete remains fundamental to modern construction, but the cement it contains is responsible for a significant proportion of its embodied carbon. As a result, identifying practical ways to lower cement-related emissions is becoming an important consideration during the specification process.
Traditional supplementary cementitious materials (SCMs), including GGBS and fly ash, have helped reduce concrete’s carbon impact for many years. However, supply constraints are prompting the industry to seek alternative solutions. One material attracting significant interest is calcined clay, a locally sourced SCM that can help deliver meaningful carbon reductions while maintaining performance and buildability.
Most of concrete’s embodied carbon is associated with Portland cement production. Calcined clay works by partially replacing cement within the mix, reducing carbon emissions while maintaining the strength and durability demanded by modern structures. Produced by heating aluminium-silicate clays at controlled temperatures, the material develops pozzolanic properties that contribute to the concrete’s overall performance.
PRODUCED FROM BY-PRODUCTS
What makes calcined clay particularly relevant to the UK market is its availability. The material can be produced from by-products generated by the domestic clay brick manufacturing industry, creating a local, circular solution that helps reduce waste while strengthening supply chain resilience. For specifiers increasingly considering material provenance and whole-life carbon performance, this presents an attractive opportunity.
As with any emerging construction material, widespread adoption depends on confidence. Sustainability benefits alone are rarely enough to secure specification. New materials must demonstrate that they can be designed, supplied and installed using established construction methods while delivering reliable performance throughout the building lifecycle. Extensive testing across the industry has therefore focused not only on carbon reduction but also on strength development, durability and practical on-site performance.
One of the most significant demonstrations of calcined clay’s potential can be found at Brent Cross in North London. Working alongside developer Related Argent, structural engineers Whitby Wood and Fairhurst, and principal contractor Midgard, Capital Concrete supplied what is believed to be the UK’s first structural residential application of calcined clay concrete, including the country’s first calcined clay suspended slab.
The project team sought opportunities to reduce embodied carbon while ensuring that any alternative concrete solution would perform identically to conventional mixes. To support the specification process, detailed technical information, embodied carbon assessments and performance testing data were provided. Additional early-age strength testing helped build confidence among stakeholders and demonstrated compliance with project requirements. The final mix incorporated calcined clay supplied by LKAB Minerals, produced from a by-product of UK clay brick manufacturing. By replacing 30% of the cement content, the concrete achieved a reported 10% reduction in embodied carbon compared with previous mixes used on the development.
Perhaps most importantly, the material integrated seamlessly into the construction process. It was manufactured using conventional batching methods, delivered through established supply chains and placed, pumped and finished using standard site practices.
The concrete achieved the required strength and durability characteristics while behaving much like a traditional mix during construction. This ease of adoption is significant, as perceived risk and complexity often remain barriers to the specification of innovative materials.
The project also highlighted the importance of early collaboration. Successful adoption required engagement between designers, contractors, suppliers, insurers and the client team. Through transparent sharing of performance data and open technical discussions, stakeholders were able to review evidence, address concerns and build confidence in the solution.
There is no single answer to the construction sector’s decarbonisation challenge, but calcined clay represents an increasingly valuable addition to the specification toolkit. Its ability to reduce embodied carbon, use locally sourced manufacturing by-products and integrate into existing construction practices makes it a compelling option for UK projects.
www.capitalconcrete.co.uk