The efficient use of ground granulated blast furnace slag (GGBS) in reducing global emissions

A draft copy of a cross industry paper, which included contributions from TranFIRe researcher Michal Drewniok, has reported the current and future levels of availability of ground granulated blast furnace slag (GGBS) in concrete and has concluded that GGBS is a highly utilised and constrained material.  As such, it was noted that any local increase in the amount of clinker substituted with imported GGBS is unlikely to decrease global emissions.

GGBS is a co-product of the iron and steel industry obtained by water-cooling and grinding blast furnace slag. It is used as a supplementary cementitious material (SCM) in concrete due to its cementitious properties, which enhance the long-term strength and durability.

The technical benefits of including GGBS in concrete are now well understood and documented, but in recent years GGBS has also been a subject of discussion among concrete producers for its ability to partially replace Portland cement clinker and thus reduce the emissions of an individual concrete.

To help to determine whether this idea has merit, a group of experts, drawn from across the concrete and cement industry, construction, academia and civil society undertook a literature review to better understand global production and utilisation of GGBS and clinker, and how this balance could change in the near-future.

The review indicates that global clinker production is currently 8x to 12x higher than global GGBS production and will remain at this order of magnitude to 2030 and beyond.

Additionally, no references were found to demonstrate significant usable GGBS stockpiles.

The review demonstrates that GGBS is a limited and constrained resource that is almost fully utilised globally. Any increase in its use in one location is highly likely to result in a reduction in use elsewhere, balancing each other out overall.

This paper concludes that any local increase in the amount of clinker substituted with imported GGBS is unlikely to decrease global emissions.

GGBS should continue to be used where required technically, or where established local supplies exist anyway, but it should not be specified above locally available levels just in an attempt to reduce greenhouse gas emissions.

Alternative options exist for reducing clinker usage and thus reducing global emissions, and designers should work with the supply chain to identify the best way to do this on each project.

Will Arnold, Paul Astle, Michal Drewniok, Tim Forman, Ian Gibb, Fragkoulis Kanavaris, Noushin Khosravi, Bruce Martin, Colum McCague, Andy Mulholland, Iva Munro, Karen Scrivener, Mike de Silva, Gareth Wake