Early Age Microstructural Transformations of an Inorganic Polymer Made of Fayalite Slag

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 2 h. 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 [SiO 4 ] with 3 or 4 NBO /Si. In the case of the sample activated with SH , a new band appeared after 96 h and continued to increase in intensity at later times. For SS  +  SH activating solution, a new band appeared after 96 h, increasing over time, whereas the originally present band at 940 cm −1 became more distinct. For the sample with only SS , no vibrational changes were detected after 24 h. 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.