Highs and lows

Rather than stipulate a certain proportion of ggbs, say, ask for the lowest carbon mix for your particular application

The UK was the scene of a world-first last month, when a cement kiln at Hanson’s Ribblesdale plant in Lancashire was operated using a wholly net-zero fuel mix. During the demonstration, the proportion of fuels in the kiln’s main burner was gradually switched over until it was entirely powered by biofuels and hydrogen.

This is a significant milestone on the route to netzero carbon, and a microcosm of what the UK’s cement manufacturers have been doing for some time: replacing fossil fuels with waste-derived alternatives has contributed to a 53% fall in the carbon impact of UK concrete against a 1990 baseline. Concrete doesn’t tend to travel so this local context matters: globally, cement production accounts for 8% of carbon emissions, but the equivalent figure for the UK is 1.5%.

There is still a lot to do before cement and concrete achieve decarbonisation on an industrial scale, but we don’t have to wait for other people to innovate: there is an enormous amount that architects, engineers and constructors can already do to reduce the embodied carbon of concrete buildings, within current standards and with tried-and-tested ingredients.

At The Concrete Centre, we’re receiving a great number of enquiries on this, from specifiers who have decided that concrete is the most appropriate choice – for reasons of fire safety, climate change resilience, or reducing and shifting peak loads in energy consumption – and who want to use it in the most sustainable way.

It’s heartening to see people challenging even recent guidance on low-carbon mixes, seeking to push it as far as they can. Designing structures to use materials more efficiently is one part of it. For example, simply by challenging the norm that a building has to have a 9m span, and going for 6m instead would save about one-third of the carbon footprint of the structure, before even considering the concrete itself.

When it comes to the mix, the best-known method is to replace some of the cement with secondary cementitious byproducts from industrial processes, such as GGBS or fly ash, but the British Standard is evolving to allow greater use of powdered limestone or other natural pozzolans. Concrete specification can be a complex art, especially with so many innovative products reaching themainstream, so unfortunately there isn’t always the same right answer.

The industry is working on helping to make the process simpler, but right now the best guidance is still to engage early with suppliers. Rather than stipulating a certain proportion of GGBS, say, ask for the lowest carbon concrete for your particular application, because there may be other ways to achieve it. There’s no such thing as a single “low-carbon concrete” – there are many different lower-carbon concretes, with different properties, and the key is establishing the mix with the lowest possible carbon for the job that you want it to do.

Elaine Toogood, head of architecture, The Concrete Centre