Hardening Performance of Phosphogypsum-Slag-Based Material

Hardening, hydration performance and mechanism of the phosphogypsum-slag-based binding material were studied in this paper. The phosphogypsum-slag-based binding material was prepared by mixing 45% phosphogypsum, 48% slag, 7% cement clinker and chemical activator at 1% relative to the binder. The compressive and flexural strength of the phosphogypsum-slag-based binding material reached the standard for compound silicate cement grade 32.5. Moreover, the softening coefficient of mortars with phosphogypsum-slag-based binding material was the same as mortars with P•C32.5. In particular, the pH value of pastes or mortars with this binding material was far lower than those with P•C32.5 and it had small impact on environment. Microscopic analysis with XRD and SEM revealed that: bar-like ettringite crystals, portlandite and the rest dihydrate gypsum crystals contacted each other as structural framework. These crystals were bonded firmly together by foil-like C-S-H gels and formed compacted body with a dense structure of high strength and water resistance.