Effect of heat-treated flue gas desulfurization gypsum on the setting time of stabilized mortars: An experimental study

Abstract

Ready-mixed mortars are stabilized products formulated for to prolong the induction time necessary to achieve an application time for to 72 h. The high stabilizer additive content required to increase the setting time negatively affects the rheological properties and mechanical performance of these mortars. In this study, flue gas desulfurization (FGD) gypsum was evaluated as a setting-time control agent to reduce the amount of additive required to achieve longer setting times when added to stabilized mortars. Three heat treatments were applied to obtain dihydrate, hemihydrate, and anhydrite (50 °C for 48 h, 150 °C for 4 h, and 650 °C for 4 h, respectively). The effects of adding 15 % FGD and 0.5 % hydration-stabilizing additive to Portland cement pastes were evaluated based on their rheological properties and hydration kinetics. The fresh and hardened properties of mortars stabilized with FGD contents of 0 %, 2.5 %, and 15 % were characterized, and their mechanical performances were evaluated with stabilizing additive contents of 0.3 % and 0.6 %. FGD gypsum increased the setting time, decreased the maximum heat release peaks, and reduced the hydration degree compared with Portland cement paste, suggesting a slower hydration reaction. This trend, observed in both pastes and mortars, reduced the demand for stabilizing additives, which is essential for their proper use in ready-mixed mortars. Furthermore, the mechanical performance of the mortar improved with the addition of FGD gypsum. Taken together, these results highlight the potential of FGD gypsum as a promising regulator of the hydration kinetics in cementitious systems.