Why no single solution will solve cement’s carbon problem

Work has begun on a new £100m train maintenance depot at Shipley, West Yorkshire. It’s the kind of construction story that might be easily overlooked, but the low-carbon concrete being poured there is the result of decades of effort to reduce the industry’s carbon footprint.

Developing a low-carbon mix that meets structural requirements, and can be produced in conventional plants and delivered by standard mixer trucks has proven to be an intractable challenge. Concrete is the world’s second most widely used material after water, and its binding agent – cement – accounts for 7-8% of global carbon dioxide (CO₂) emissions: more than aviation, shipping and long-distance trucking combined. 

Much of these emissions come from clinker, the primary ingredient in cement, produced by heating limestone and clay to around 1,450°C in a rotating kiln. As well as being highly energy-intensive, the chemical reaction itself releases CO₂, making cement fundamentally harder to decarbonise than many other industrial materials.

One option is to use less clinker. At Shipley, pile caps are being formed using Ecocem Act, a mix that contains up to 70% less clinker by replacing it with lower-carbon materials derived from industrial byproducts, natural minerals and recycled content – known as supplementary cementitious materials (SCM). It reportedly saves nearly 150kg of CO₂ emissions per cubic metre compared with conventional concrete.

Other construction companies are applying the same principle. Brickwork manufacturer Forterra and LKAB Minerals are exploring the use of recycled brick waste to produce calcined clay, another form of SCM. By repurposing material already fired at high temperatures, the emissions typically associated with clinker are avoided, while contributing to a more circular construction model. Calcined clay also increases the strength of concrete by reducing the material’s porosity, according to LKAB.

Brick waste from Forterra’s Kings Dyke factory near Peterborough is crushed and sent to LKAB Minerals’ plant in Flixborough, Lincolnshire, where it is milled and processed into a reactive calcined clay material. About 35,000 tonnes a year are expected to be produced – modest in the context of global cement demand, but indicative of how SCMs are beginning to offset clinker use.

Substitution alone will not solve concrete’s carbon problem, however; 70% less clinker still leaves a significant portion remaining, along with its processing emissions. That is why a second option – capturing emissions at source – is receiving increased attention.

Heidelberg Materials UK is building a carbon capture facility at its Padeswood cement works in North Wales, which it says will capture about 95% of CO₂ emissions from the production process. The project, part of the HyNet North West decarbonisation cluster, will transport captured emissions from the kiln via pipeline for permanent storage beneath Liverpool Bay.

Construction is already under way, with completion expected in 2029. Once operational, the facility will reportedly capture about 800,000 tonnes of CO₂ a year from Heidelberg’s existing works.

Cement production is a strong candidate for carbon capture and storage because a large share of emissions come from the chemical process itself, rather than the fuel used. Switching to renewable energy cannot eliminate those emissions – but carbon capture could offer a way to address them, potentially enabling the production of near-zero carbon cement when combined with biomass fuels.

Significant environmental, political and economic barriers still need to be overcome before we see widespread deployment, however. A more radical approach is to replace cement altogether.

Ureaka is developing a carbon-negative (removing more CO₂ than it produces) alternative that uses captured CO₂ to bind materials, effectively locking emissions into the concrete itself. The process relies on low-energy chemical reactions rather than high-temperature kilns, and is designed to be easier to deploy in real-world settings.

“We believe this is something that no one else is doing, replacing cement completely while storing CO₂ in a binder system,” says Phil Salter, inventor of Ureaka’s closed-loop carbon capture process. “It is one of the biggest environmental challenges there is, and concrete is one of the most difficult things to decarbonise.”

The company, a spin-out from the University of Strathclyde’s Department of Civil and Environmental Engineering, uses low-cost, plant-based enzymes to create a ‘bioconcrete’ that is up to 30% lighter than traditional concrete and suitable for use in most types of building.

Alongside new materials, Ureaka is also developing liquid systems to repair existing concrete. “The liquid you’re pumping in is like water. It has very low viscosity and can get to places that regular cement and chemically based grouts can’t. This makes it well-suited to applications like repair, remediation and treating cracked or damaged concrete,” Salter says.

Taken together, these approaches – clinker reduction, carbon capture and alternative binders – reflect the scale and complexity of the challenge. Each addresses a different part of the problem, and each comes with its own technical, commercial and regulatory constraints. What they do not offer, at least for now, is a single, agreed solution.

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.