One of the presentations I attended during FOOTPRINT+ was titled “Concrete: Developments in the supply chain”, which focused on the problem of constrained resource GGBS and potential solutions in limestone fines and calcined clays.

Will Arnold gave an excellent whistle-stop explanation of a recent report, which assessed global GGBS resources and usage.

The Problem

Ground Granulated Blast Furnace Slag (GGBS) is a by-product of the iron and steel industry, obtained from blast furnaces as they process iron ore into iron. It is rapidly cooled with water and then ground to produce a granular product. GGBS is used as a supplementary cementitious material (SCM) in concrete, enhancing the durability and strength of concrete structures.

GGBS is considered a constrained resource because its production is limited to the output of the iron and steel industry. About 90% of all iron slag produced is already processed into GGBS, leaving little room for increased production. There are no significant stockpiles that can be used to increase supply and the global production of clinker (highly energy-intensive and CO2-emitting product used to make ordinary Portland cement) significantly outstrips that of GGBS.

The report recommends that GGBS should continue to be used in concrete where it is technically required, for instance, in applications requiring enhanced durability or specific performance characteristics like temperature and crack control. However, it should not be relied upon as a primary method for reducing environmental impact due to its limited supply. Increasing local use of GGBS is unlikely to reduce global emissions because it would simply shift the usage from one region to another - its a zero-sum.

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By Steve Gilchrist

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