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AOD stainless steel slags from but three different processes;(i) boron stabilized, cooled in a slag pot;(ii) boron stabilized, cooled in a slag yard and (iii) non-stabilized, powdered slag, were investigated for their hydraulic potential by thermo-alkali activation. Boron stabilized slags were milled in a ball mill where as the non-stabilized slag, as received, was sieved and particles finer than 80 μm were used for the examination of the reaction potential. 5 M NaOH and sodium silicate were used in three proportions, ie 25: 75, 50: 50 and 75: 25, as activators. Oxide composition determined with X-ray fluorescence, showed similar compositions of all the three slags; whereas mineralogical analysis, as measured with quantitative X-ray diffraction, showed a trace presence of β-dicalcium silicate in boron stabilized slag and substantial presence of γ-dicalcium silicate in non-stabilized slag. Boron stabilized slags had a higher presence of merwinite and bredigite. Isothermal conduction calorimetry measurements showed exothermic peaks corresponding to hydration reactions for all the slags. Compressive strength results on slag mortar samples showed that non-stabilized AOD slag develops strength faster than stabilized slag although, in the long term (90 days) all the slags reach similar compressive strength. Thermal analysis showed peaks corresponding to a CSH type hydration product. SEM analysis showed the presence of reaction products around the minerals but a known CSH morphology could not be recognised.