The aim of this work is to clarify the effect of various activation methods on the hydraulic properties of γ-C 2 S, one of the main phases in stainless steel slags. Synthetic C 2 S, sintered at 1450°C for 20h, consisted of 88wt.% γ-C 2 S and 12wt.% β-C 2 S. Two activation paths were followed: mechanical activation, by means of high energy milling, and chemical activation, by means of NaOH and Na 2 CO 3 addition. Results indicated that both mechanically and chemically activated γ-C 2 S hydrated at ambient temperature. XRD analysis showed that the amount of amorphous phase increased during hydration, whereas TGA/DTG data revealed weight loss in the decomposition region of C–S–H. Analyses by FTIR and SEM also support that C–S–H is one of the main hydration products. Mortars prepared with mechanically and chemically activated γ-C 2 S developed mechanical strength, reaching the values of 9.1MPa and 10.3MPa at 90days, respectively.