Sustainability Series: Week 3, Low carbon concrete

Webinar: Lower carbon concrete: revision of BS 8500

Recorded: 28 September 2023

The revision to BS 8500 will be published in November 2023 and will include the introduction of lower carbon ternary (or multi-component) cements, CEM II/C-M and CEM VI.

This webinar discussed the main revisions to the standard and how the method of specification has changed to facilitate the wider range of lower carbon concretes that will be available.

The presentation was followed by a Q&A (with questions from the audience) answered by industry experts who responded to queries on concrete and structural design.

A recording of this event is now available in the on-demand library.

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Blog: Evolution of low carbon concretes

In this blog, we delve into the current progress and future prospects for low carbon concretes, a vital step towards mitigating the carbon dioxide emissions associated with concrete construction. And we will also signpost readers to a wealth of information about cement decarbonisation, evolving specification standards, and product innovations. 

Now  

The cement industry is working to reduce the embodied carbon of Portland Cement (CEM I) through a range of levers with the remaining emissions addressed by carbon capture use and storage. By 2050 the concrete industry is aiming to have net zero carbon emissions (see the UK Concrete Roadmap).  

'Low carbon cements and concretes' is a lever in the Roadmap. This equates to a focus on innovations in concrete mix design, to utilise lower emission constituents, and the evolution of standards to enable these to be used at scale, which we are seeing in the forthcoming update to BS 8500 and the introduction of multi-component cement and concretes. There is also work underway to look at clinker content, alternative binders and cement formulations that reduce carbon emissions.

Understanding the use of supplementary cementitious materials (SCMs) to partially replace Portland cement is a current solution for lowering the carbon of concrete. Current SCMs, as featured in Concrete Futures, Spring 2023 include ground granulated blast-furnace slag (GGBS). GGBS is a by-product of the steelmaking process and is a popular SCM in the UK that is used both for its performance benefits, and because it reduces the carbon emissions in concrete. Although GGBS supply is expected to increase globally until at least 2025, it cannot entirely replace clinker due to the production capacity that would be required.  

Research conducted by BRE for MPA Cement has shown that incorporating limestone fines alongside GGBS improves material efficiency while maintaining performance, akin to binary cement concrete. This dual benefit enables designers to both lower carbon and optimise the use of GGBS. 

The new revision to the BS 8500 standard has taken advantage of this research and has expanded the use of multi-component cements, allowing for higher substitution rates of up to 65%. This change offers the potential to significantly reduce embodied carbon. Concrete plants in the UK are likely to adopt a combination of Portland limestone cement and GGBS or fly ash to create multi-component cements to lower embodied carbon without compromising strength and durability.  

GGBS can also be a significant component of Alkali Activated Cementitious Materials (AACMs). AACMs are not included in BS 8500 and can be specified using PAS 8820. Work is underway on a BSI Flex Standard for performance-based specification, with the aim of the project being guidance to specify concretes that use alternative cement technologies.  

New

The decreasing use of coal-fired power production in the UK and other European countries will impact the local supply of fly ash, another essential SCM. However, over 100 million tonnes of fly ash are currently stockpiled in the UK. This recovered fly ash has the potential to replace cement in concrete. Preliminary tests indicate that this material can meet relevant standards, and further research is underway to support its inclusion in future revisions of BS 8500.  

Calcined clay, abundant in the UK, is emerging as a promising SCM with performance similar to, and sometimes surpassing, fly ash. Research is being carried out by a team including MPA Cement and funded by Department for Energy Security and Net Zero (DESNZ) exploring the use of secondary sources of clay, diverting significant amounts of material from waste streams and further reducing embodied carbon.  

Next

The path to achieving net-zero carbon concrete will also involve exploring product innovation. A recent article in Concrete Futures, Autumn 2023 features some exciting progress, and pages in our own Innovation section may also be of interest. Some technologies of note:  

Seratech's Olivine-based technology: Utilises olivine, an abundant mineral, and incorporates CO2 in its manufacture process.  

Recycled cement: Utilises the unused cementitious properties of crushed concrete, reducing the need for virgin cement production.  

Graphene-enhanced admixtures: Enhance concrete strength, durability, and fire resistance, potentially reducing embodied carbon through material optimisation.

Biozeroc's microbial approach: Explores the use of microbes to "grow" concrete, presenting a novel way to produce low carbon concrete.  

All these innovations will need to prove their durability and their mechanical properties so that their appropriate application can be understood, as well as their potential to be produced at scale. What is known is that progress is being made to enable the ongoing reduction of the embodied carbon of concrete. 

As well as the ways for specifiers to reduce the carbon in their concrete mix, there are, of course, many other ways to lower the carbon in concrete construction.

We’ve shown that, using the same concrete mix, designing more efficiently can save 50% of the embodied carbon by looking at the loading, spans and structural system. Further savings can be made using innovative structural systems such as vaulted structures. These are all possible now with collaboration between designers, contractors and producers.  

In conclusion, the future of low carbon concretes is promising, with a range of strategies and innovative technologies at our disposal. As a specifier of concrete in the UK, you can be at the forefront of adopting these solutions to not only reduce the carbon footprint of concrete but also contribute to a more sustainable built environment.  

Written by Jenny Burridge, Director, Structural Design, The Concrete Centre