Characterisation of alkali-activated stainless steel slag and blast-furnace slag cements

Rapid global industrial growth is causing an increase in the generation of large-scale by-products and waste materials, which can be recycled in the construction industry to decrease both the environmental impact of the sector and the impact of these waste materials, to ultimately contribute to the circular economy. In the current study, electric arc furnace stainless steel slag (EAFSS) as a potential precursor in the production of alkali activated materials (AAMs) is investigated, along and alternatively to the use of ground granulated blast-furnace slag (GGBFS). Five blended mixtures with different levels (0, 25, 50, 75 and 100 wt %) of EAFSS to replace GGBFS are activated with an alkaline silicate solution. Partially replacing GGBFS with EAFSS prolongs the dormant period in reaction and reduces the overall heat release of the paste mixtures. This results in a positive effect on fresh-state properties, increasing and prolonging workability and mixture setting times. A general decrease in strength is seen with EAFSS inclusion, although satisfactory compressive and flexural strength values of more than 85 and 9 MPa, respectively, were obtained at 28 days with up to 50% replacement of GGBFS by EAFSS. Most of the crystalline phases present within EAFSS do not participate notably in alkali-activation, other than merwinite which slowly dissolves and reacts to form a weak binder phase. The chromium present in the EAFSS is contained in a stable spinel phase; this element does not appear to be mobile in leaching tests.