GGBS’s use to reduce greenhouse gas (GHG) emissions in concrete needs to be carefully considered
A group of 13 experts from across structural engineering, concrete and cement industries, construction, academia, and civil society have collaborated on a paper that reviews the use of ground granulated blast furnace slag (GGBS) in concrete, and examining ways that this may change in the future.
The efficient use of GGBS in reducing global emissions aims to better understand this co-product of iron and steel manufacturing, especially at a time when the concrete industry is considering its role in the climate crisis, looking for ways to decarbonise its operations and products.
For many years GGBS has been specified as a partial replacement for Portland cement clinker (‘clinker’) in concrete due to its technical properties - such as improving concrete's durability. More recently reducing clinker with GGBS has become the ‘go-to’ method for decreasing the carbon intensity of concrete in the UK, as the production of GGBS results in far fewer greenhouse gas (GHG) emissions than the production of the clinker that it replace
The paper demonstrates that GGBS is a limited and constrained resource that is almost fully utilised globally. Any increase in its use in one geographic location is highly likely to result in a reduction elsewhere, balancing each other out overall.
The authors conclude that any local increase in the amount of clinker substituted with imported GGBS is unlikely to decrease global GHG emissions – which means that GGBS should not be used in high proportions just in the hope of reducing GHG emissions.
Will Arnold, head of climate action at The Institution of Structural Engineers (IStructE) led the project and co-authored the paper, and comments: “Our purpose is to explain that GGBS is not a silver bullet for GHG emissions in concrete production as our paper demonstrates global constraints in GGBS availability. As a material, GGBS needs to be carefully considered to ensure it’s being used efficiently, and in the most appropriate manner.”
The authors stress that this does not mean that GGBS’s use should cease altogether: such a move would increase global emissions as more clinker would need to be produced globally to compensate. A key recommendation is that global supplies of GGBS should continue to be fully utilised, and that GGBS should still be used, particularly where required technically, and should come from well-established supply chains.
Iva Munro, ConcreteZero Lead at Climate Group, explains: “Alternative options beyond GGBS exist for reducing clinker usage and global GHG emissions – and engineers and designers should work with the supply chain to identify the best way to do this on each individual project.”
Noushin Khosravi, Sustainable Construction Manager for the Mineral Products Association (MPA) adds: “Through collaboration with the value chain and a shared commitment to a sustainable future, the UK Concrete industry can create a blueprint for sector decarbnisation in a manner that is globally scalable. By encouraging efficient utilisation of SCMs at a local level and accelerating adoption of new technologies, we can effectively reduce global GHG emissions."
As a way forward, the paper recommends that designers, contractors and those along the supply chain ask three questions early in the design process to optimise GGBS use. These questions aim to secure a better understanding of the project opportunities regarding the need for, and availability of, GGBS:
- Do we need GGBS for technical reasons?
- Is there a well-established GGBS supply chain for our project?
- How else can we reduce concrete emissions?
The efficient use of GGBS in reducing global emissions: An appraisal of the global availability of ground granulated blast furnace slag summarises an extensive literature review undertaken by the authors over the last year. These experts are:
- Will Arnold, Head of Climate Action, The Institution of Structural Engineers (IStructE)
- Paul Astle, Decarbonisation Lead, Ramboll
- Michal Drewniok, Assistant Professor in Civil Engineering, Leeds University
- Tim Forman, Senior Teaching Associate and Director of Studies, University of Cambridge
- Ian Gibb, Technical Principal, Mott MacDonald
- Fragkoulis Kanavaris, Leading Concrete Materials Specialist and Principal Engineer, Arup
- Noushin Khosravi, Sustainable Construction Manager, Mineral Products Association
- Bruce Martin, Associate Director, Expedition Engineering
- Andy Mulholland, Director, AMCRETE UK
- Iva Munro, Senior Manager Industry, ConcreteZero lead, Climate Group
- Karen Scrivener, Professor of Construction Materials, École Polytechnique Fédérale de Lausanne (EPFL)
- Mike de Silva, Head of Sustainability, Clancy Group
- Gareth Wake, Director, British Ready-Mixed Concrete Association / MPA Ready-Mixed Concrete.
The paper is endorsed by The Institution of Structural Engineers, Climate Group, MPA The Concrete Centre, and the UK Low Carbon Concrete Group.