Three types of binders were investigated by combining a water granulated fayalite slag and three different activating solutions (NaOH, SH; Na-silicate, SS; and a 1:1 mixture of the two, SH+SS). A reactivity test proved that the slag dissolves in the alkaline environment, releasing both Si and Al. Through rheological measurements it was found that the most alkaline solution (SH) led to a very fast structure build-up, followed by the activating solution SS+SH; when SS was used, the storage modulus did not increase even after 2h. A similar trend was observed by calorimetry, where the paste with SH resulted in heat release within minutes, followed by SH+SS. These transformations were also followed by in situ ATR-FTIR, indicating changes in the vibrational bands attributed to asymmetric stretching vibration of [SiO4] with 3 or 4 NBO/Si. In the case of the sample activated with SH, a new band appeared after 96h and continued to increase in intensity at later times. For SS+SH activating solution, a new band appeared after 96h, increasing over time, whereas the originally present band at 940cm(-1) became more distinct. For the sample with only SS, no vibrational changes were detected after 24h. In conclusion, the fayalite slag is a reactive material that can undergo microstructural changes toward new reaction products, with the choice of the activating solution being a crucial factor in the process.