Influence of citric acid and triisopropanolamine on reactivity, hydration, and performance of Fe-rich CSA-gypsum/anhydrite blends containing bauxite residue and salt-slag by-product

This study explores using bauxite residue and salt slag residue from alumina and aluminum industries to synthesize Fe-rich calcium sulfoaluminate clinker as alternatives to bauxite. The impact of sulfate sources, citric acid, and triisopropanolamine (TIPA) on reactivity, hydration, and mortar performance was assessed. An M-ratio (sulfate to ye’elimite molar ratio) of at least 1.7 stabilized ettringite, prevented monosulfate, and improved strength. At M-ratio 2.4, gypsum blends showed reduced ye’elimite and ferrite dissolution after 24 h due to rapid ettringite formation, unlike anhydrite blends, which showed slower dissolution kinetics at early-age hydration but higher late-age strength. Adding 0.05 % citric acid and 0.1 % TIPA enhanced ferrite dissolution and ettringite formation. However, TIPA resulted in larger pores (50–100 nm), reducing compressive strength compared to citric acid, which better balanced pore structure and strength. Therefore the best performance was achieved with citric acid addition of 0.05 % in the CSA-F sulfate blends.