The greenhouse gas implications of using ground granulated blast furnace slag as a cement substitute

Abstract

The use of supplementary cementitious materials (SCMs) in concrete blends is often promoted as a way to reduce the environmental impacts of concrete. SCMs can include fly ash, silica fume or steel slag. Another SCM, and the focus of this paper, is ground-granulated blast furnace slag (GGBFS), which can be co-produced with pig iron. Previous studies that cite environmental benefits of GGBFS in concrete do not account for supply conditions of GGBFS. In this paper, this supply assumption is challenged through a market analysis. The environmental consequences of GGBFS supply conditions are assessed using a system expansion approach to life cycle assessment. When the supply of GGBFS is not constrained, greenhouse reductions of a given GGBFS-concrete blend are in the order of 47.5%. However, market analysis indicates that the supply of GGBFS can be constrained. Under a supply constraint, the 47.5% additional greenhouse reductions from the use of GGBFS are no longer applicable. Environmental certification schemes could ensure ongoing benefits of GGBFS by promoting the use of steel sourced from a supply chain which co-produces granulated blast furnace slag at the blast furnace.