Concrete Compass: Low carbon concrete

Navigating to useful resources and guidance

In June 2020, The Concrete Centre began the Sustainability Series of live, on-demand and workshop events to share knowledge and engage in discussion to enable the sustainable use of concrete. The series started with a focus on Low Carbon Concrete.

In the seminar, Understanding Low Carbon Concrete, which can now be viewed on-demand, we explored what is meant by “low” carbon, how it is defined and how do designers benchmark the version of “low” that they want. We also shared work under way on defining low carbon concrete and addressing the barriers to the use of low carbon concrete. 

In this Concrete Compass on low carbon concrete, we navigate through the life cycle and provide guidance to support designing in low carbon concrete.

Key Guidance

• Specifying Sustainable Concrete - This key publication is intended to assist designers in optimising the sustainable credentials of concrete through specification. The guide focuses on concrete, its constituent materials and how the variation of specification can influence embodied carbon; the performance of fresh and hardened concrete (e.g. strength gain, durability); the use of recycled/secondary materials as well as information on responsible sourcing and assessment methods.
• Whole-life Carbon and Buildings - Concrete frame construction provides a durable structure, which is a fundamental aspect of whole-life performance. But less understood is its compelling whole-life CO2 performance, resulting from several attributes largely unique to concrete buildings. These are the focus of this guide, which sets out the ways in which these attributes can be used to minimise CO2 emissions.

Low embodied carbon constituents

Concrete is a low carbon material. Its versatility, performance and local availability has resulted in it being the second most consumed material globally (after water). The potential to reduce global carbon emissions, by reducing the embodied carbon of such a widely used material are not in doubt.

As shown in the figure above, the majority of the volume of concrete is aggregates that are low in embodied carbon. The majority of the embodied carbon of concrete comes from the binder, the cementitious material - this can be Portland cement (CEM1) or secondary cementitious materials, such as GGBS, FA or limestone. Secondary cementitious materials have a lower embodied carbon and can be used in combination with CEM1, as permitted in BS 8500. The embodied carbon of the constituent materials of concrete is published in Specifying Sustainable Concrete. More detail on cementitious materials can be found in MPA Cement's Factsheet 18. 

Table 10: Embodied CO2 for main constituents of reinforced concrete, Specifying Sustainable Concrete, 2020

The UK concrete and cement industry has reduced the embodied carbon of concrete by 30% (since 1990) and reports annually on its progress to decarbonise. There is a dedicated website for the Concrete Industry Sustainable Construction Strategy at www.sustainableconcrete.org.uk. Links to the industry performance report, as well as sector reports are below, in the final section of this page.
The industry is also committed to the aim of going beyond net zero by 2050 and the framework for the development of this roadmap has recently been published, with the roadmap expected later in 2020. Read more    

A recent article that may be of interest:

• No Offsets Required from Concrete Futures magazine (2020) by Claire Ackerman, director of The Concrete Centre discusses how the concrete and cement industry is working towards a carbon-negative built environment, without offsetting. 

Lower embodied carbon concrete

Concrete is a unique material in that the specifier has the ability to directly influence the constituent parts of the mix to ensure an optimum carbon footprint that meets performance criteria and addresses the design imperatives of resource and energy efficiency within a whole life context, that also address the precepts of a circular economy.

The Concrete Centre guide "Specifying Sustainable Concrete"  focuses on concrete, its constituent materials and how the variation of specification can influence the sustainability performance of concrete. Sustainable characteristics with the greatest scope for influence through specification include: the performance of fresh and hardened concrete (e.g. strength gain, durability); embodied CO2; CO2 associated with transportation; responsible sourcing and use of recycled or secondary materials.

Table 11: Embodied CO2 of designated concretes showing the influence of different cements, Specifying Sustainable Concrete, 2020

Related resources that may be of interest include:

• Visit the Sustainability Series hub to view a set of bitesize videos on specifying concrete to BS 8500, including Specifying Concrete for Lower Embodied Carbon.
• With concrete you can cut carbon now and also cut future carbon with the decisions you make now - this is explored by Elaine Toogood, Head of Architecture in Concrete Quarterly, issue 269, autumn 2019 - Target Zero

Lower embodied carbon structures using lean design 

The versatility of concrete results in a wide range of concrete frame solutions that play their part in reducing the amount of materials needed to construct our built environment. This is the next theme to be explored in The Concrete Centre Sustainability Series. The series will explore, during August, how to reduce embodied carbon using material efficient and lean structural solutions. In the interim online information that may be of interest: Post-tensioned concrete; Ribbed and waffle slabs; Void formers and hollowcore

Concrete can also avoid the need for finishing materials thorough the use of visual concrete.

Lowest whole life carbon

In addition to embodied carbon and operational carbon, designers need to consider the total, whole-life carbon. Whole-life carbon emissions are the most holistic measure of the total impact of our built environment and can help to avoid unintended consequences of focussing on embodied or operational carbon alone. The reason it is not referred to more, is that it is more complicated to measure than embodied and operational carbon. A methodology for determining whole-life carbon is set out in EN 15978:2011 Sustainability of Construction Works and at a product level the consistent measure for EPDs is EN 15804. 

To assist with whole-life assessment and design of concrete buildings, The Concrete Centre has published a guide entitled ‘Whole-Life Carbon and Buildings’, which sets out the specific qualities of concrete construction that can be used to help minimise carbon impacts including:

• Operational energy - Using the thermal mass provided by concrete to lower operational emissions.
• Designing for long life - The longevity of concrete allows a building’s useful life to be extended; a key tenet of whole-life thinking and a circular economy.
• Reuse and adaptability - Reducing whole-life CO2 through the ability to reuse concrete structures.
• End-of-life - The absorption of CO2 into concrete through the natural process of carbonation.

Focus on concrete industry sustainability performance reports

The Concrete Industry Sustainable Construction Strategy was first launched in 2008 and featured targets to be met in 2012. In 2012 the strategy was updated with targets set for 2020, and later this year the concrete industry will announce a revised strategy for the future. A commitment of the strategy is to publish data on the performance of the concrete industry, across a wide range of indicators including biodiversity, responsible sourcing, waste minimisation, wellbeing and carbon emissions. 

• Download the 12th Concrete Industry Sustainability Performance report, based on 2018 data.
• See all Concrete Industry Sustainability Performance reports.

The data collection for the concrete industry report includes data from BAR, on behalf of the reinforcement sector; UKQAA, on behalf of the fly-ash sector; CSMA, on behalf of the GGBS sector and the CAA, on behalf of the admixtures sector. The sectors below are part of the Concrete Industry Sustainable Construction Strategy and also publish their own sector reports. 

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