Effect of Sodium Sulfate and C-S-H Seeds on the Reaction of Fly Ash with Different Amorphous Alumina Contents

Fly ash (FA) is one of the largest industrial wastes in the world, and its storage is still accumulating. To meet this challenge, one of the most effective and promising ways is to increase the dosage of fly ash in cement-based materials. However, the slow reaction of FA restricts the high content substitution of cement by FA. Therefore, a better knowledge for enhancing the reaction of FA is essential toward achieving a green and sustainable cementitious binder. Previous research demonstrated the synergistic effect on enhancing the reaction of FA with the combined application of sodium sulfate (SS) and calcium silicate hydrates (C-S-H) seeds, while the mechanism of the synergistic effect is unclear. In this study, the effect of SS and C-S-H seeds on the reaction of FA with different amorphous alumina contents is systematically investigated. The results show that the effect of SS and C-S-H seeds on the reaction of FA is closely related to the amorphous alumina content and the reaction time. Moreover, the underlying mechanism is revealed and may provide guidance for the massive utilization of FA and other Al-rich mineral admixtures.