Belite-calcium sulfoaluminate cement prepared with phosphogypsum: Influence of P2O5 and F on the clinker formation and cement performances

The phosphogypsum (PG) was used for the preparation of belite-calcium sulfoaluminate (BCSA) clinker and as the added gypsum of BCSA cement. The influences of P2O5 and F impurities in PG on clinker formation and cement hydration were investigated. Results demonstrate that the P2O5 and F impurities in PG could promote the formation of clinker at 1100 degrees C. The clinker prepared with PG could be obtained at 1200 degrees C which is similar to 50 degrees C lower than the clinker prepared with natural gypsum (NG). Both P2O5 and F could be immobilized in C(4)A(3)(S) over bar and stabilized cubic C(4)A(3)(S) over bar at the expense of orthorhombic C(4)A(3)(S) over bar. The hydration reactivity of C(4)A(3)(S) over bar in the BCSA cement lowered down. However, the impurities merely slightly affected the 6 h, 12 h and 1 d compressive strength development, which could be negligible. When the original PG was used as the added gypsum of BCSA cement, the soluble phosphorus impurity pronged the setting time of the cement. Besides, the soluble phosphorus impurity could also inhibit the hydration of C(4)A(3)(S) over bar and lower down the compressive strength of BCSA cement. The results will lay foundation for the utilization of PG in BCSA cement production. (C) 2019 Elsevier Ltd. All rights reserved.