Valorization of gypsum waste for the cleaner production of a novel ettringite-based binder

The utilization of gypsum waste (GyW) as an additive for alkali-activated materials has already been addressed. However, using GyW as a partial replacement for aluminosilicate during the alkali-activation process is not sufficient for the full disposal of such waste. Accordingly, this communication focused on full transforming GyW from fertilizers industry into a novel AFt-binder using an eco-friendly method. Various amounts of NaAlO2 were added to gypsum waste (GyW) to yield a hardened binder with a considerable mechanical property. The findings demonstrated that NaAlO2 readily reacted with GyW to produce an AFt-based binder. The highest values for compressive strength, bulk density, and volume expansion were observed at a NaAlO2/GyW ratio of 0.2. This corresponded to the complete conversion of GyW into needle-shaped AFt crystals with a larger diameter compared to those formed in other mixtures. Notably, all hardened mixtures attained their optimum performance after 24 h, and further extension of the curing time did not yield any additional benefits. Consequently, this innovative binder has the potential to be employed as a fast-setting, energy-efficient cement for repair applications.