The aim of this work was to investigate the hydraulic behaviour of a stainless steel converter slag after changing its chemical composition and cooling path. The target slag was designed to resemble ground granulated blast-furnace slag (GGBFS). A synthetic slag with a chemical composition close to stainless steel converter slags was mixed with 22, 30 and 38 wt% fly ash (FA) from lignite combustion, heated up to 1550 and then granulated by quenching in water; the solidified new slags were named FA22, FA30 and FA38 respectively. Quantitative X-ray diffraction on FA22 revealed that the amorphous phase was approximately 40 wt%, the rest being bredigite and merwinite. For FA addition of 30 wt% or more, the amorphous phase reached almost 100 wt%. The resulting slags showed significant hydraulic activity when mixed with sodium-based activators, with C-S-H, hydrotalcite and hydrogarnet being the main hydration products formed. The calorimetric behaviour and the mechanical properties of blended cements with 30 wt% FA30 and FA38 were comparable to a blended cement with GGBFS. Assuming that FA addition will take place during the liquid state of the slag, the proposed process can result in a new hydraulic binder.
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