Lowering carbon

Carbonation is the process by which concrete absorbs carbon dioxide from the atmosphere

The natural process of concrete absorbing carbon is essentially a reversal of the process that occurs when making cement.

Carbonation is a slow and continuous process that progresses from the outer surface moving inwards.

The crushing of concrete at end of life increases the rate of carbonation and results in a low carbon concrete aggregate.

Carbonation during the building life cycle and its secondary life as a recycled aggregate can reduce the carbon footprint of concrete by around a third, as outlined in BS EN 16757:2017, Sustainability of construction works.

The environmental benefit of carbonation should be accounted for when carrying out a life cycle assessment when following the principles of a circular economy.

• Hear from researchers about how concrete absorbs carbon
• Did you know concrete can support mangroves to absorb carbon?
• Find out how the M3 smart motorway recycled and crushed concrete

_{Photo Global Research and Development Facility, Bern, Switzerland, courtesy of Cemex}

_{Videos via YouTube from This is UK Concrete courtesy of Cemex and Balfour Beatty}

The UK concrete industry has reduced the carbon dioxide emissions per tonne of concrete by 30%

Decarbonising cement and concrete has been a focus for over 30 years, with the UK cement sector reporting on its efforts since the Kyoto protocol in 1990.

A 30% reduction in embodied carbon per tonne of concrete has been achieved due to a range of measures including investment in fuel switching, with both biomass and waste materials, and producing low-carbon cement formulations.

Work is now underway to switch to zero-carbon fuels. In 2019, a BEIS-funded feasibility study found that a combination of biomass, hydrogen and plasma energy could eliminate fossil fuel CO2 emissions from cement manufacturing.

In 2020, a ground-breaking BEIS-funded project will involve trials at sites operated by Tarmac and Hanson Cement, one focusing on electrical plasma energy with biomass, the other on hydrogen and biomass.

• Hear from researchers about how mineralisers and admixtures can lower the embodied carbon of cement
• Find out about fuel switching to use materials diverted from landfill

_{Photo Global research and development facility, Bern, Switzerland, courtesy of Cemex}

_{Videos via YouTube from This is UK Concrete, courtesy of Cemex and BBC News}

Work is underway to establish carbon capture, utilisation and storage (CCUS) systems

Transforming technologies are needed to decarbonise UK manufacturing industries and reach the Government target of net zero. CCUS is an essential emissions reduction innovation that can prevent carbon dioxide from entering the atmosphere.

The cement and lime sectors are researching and testing the effectiveness of several carbon capture technologies through a number of initiatives.

For example, an EU-funded five-year programme that began in 2016, the LEILAC (Low Emissions Intensity Lime And Cement) project, has been testing "direct separation'.

This new system enables pure CO2 to be captured as it is released from the calcination process that occurs when limestone is heated.

• Part of the Leilac Expert Insight Series, hear from Jan Theulen, Heidelberg Cement Group, about the CCUS project at plant in Lixhe, Belgium

_{Photo LE/LAC project, courtesy of Carbon Trust
Video via YouTube from Calix Ltd courtesy of Heidelberg Cement Group}