An ingredient used to create ‘greener’ concrete might not be as effective in reducing greenhouse gas emissions as first hoped.
Ground granulated blast furnace slag (GGBS) is a by-product of the iron and steel industry and has become an increasingly popular replacement for the carbon intensive Portland cement clinker, which is produced in kilns with other materials when heated up to around 1,480°C.
But a report published this week by The Institution of Structural Engineers and others has found that increasing the use of the supplementary cementitious material in place of clinker in any one area is unlikely to have an impact on global emissions as GGBS is a “limited and constrained resource” that is already nearly fully utilised. Upping its use in one area would therefore reduce its use elsewhere as stockpiles of blast furnace slag around the world are “either small or unknown” and 90% of all iron slag is already being processed into GGBS annually.
Authors of the report encourage the continued use of GGBS though, calling it an “excellent supplementary cementitious material that helps displace clinker demand globally” which is currently eight to 12 times higher than the production of GGBS and will remain as such to 2030 and beyond, the review indicates.
It should not be used in high proportions in the hope of reducing greenhouse gas emissions though and should come from well-established supply chains. Alternative options to GGBS are also available, advises the report. It suggests that a study should be carried out to determine whether the use of GGBS in concrete for the sole purpose of reducing carbon intensity should be limited. An “acceleration in the development and scaling of other technologies is necessary,” it adds.