Effect of Different Dosages of Red Mud Calcined at 600 ℃ on the Frost Resistance of Anhydrous Phosphogypsum-Based Cementitious Materials

This study investigates the effect of the dosage of red mud calcined at 600 ℃ on the frost resistance of anhydrous phosphogypsum-based cementitious materials. The experiments used anhydrous phosphogypsum, cement clinker, and red mud calcined at 600 ℃ as raw materials. The mass loss, dynamic elastic modulus, flexural strength, compressive strength, and softening coefficient of the materials after freeze-thaw cycles were tested, and the microstructural changes were analyzed using XRD, BET, and SEM. The results show that an appropriate amount of red mud calcined at 600 ℃ can significantly improve the frost resistance of the material. The best performance was achieved when the mass ratio of anhydrous phosphogypsum, red mud, and cement clinker was 70:10:20. After 20 freeze-thaw cycles, the mass loss rate of the specimens was only 1.19%, and the compressive strength remained as high as 37.44 MPa. Microscopic analysis indicates that fine particles from the calcined red mud fill pores, while reactive SiO 2 and Al 2 O 3 promote the formation of hydration products such as ettringite and C-S-H gel, resulting in a denser material structure and thus mitigating freeze-thaw damage. However, excessive red mud reduces the efficiency of hydration product formation and weakens the improvement effect. This study provides a reference for the resource utilization of anhydrous phosphogypsum and red mud in building materials in cold regions.