Greener phosphogypsum-based all-solid-waste cementitious binder with steel slag activation: Hydration, mechanical properties and durability

Abundance in waste phosphogypsum landfilling encourages the development of an eco-efficient Excess-sulfate Phosphogypsum Slag Cement (EPSC). This work evaluates steel slag powder (SSP) as the alkaline activator for EPSC, to fabricate greener all-solid-waste binders. Hydration properties, mechanical strength, carbonation resistance, and volumetric stability are researched. Results find that SSP in place of cement discernably improves the early properties, owing to advanced impurities removal by rapid dissolution of f-CaO, since impurities will delay both hydration of EPSC and activator cement. Increasing SSP content further improves early properties, yet will obstruct later development by forming ettringite coatings, while less content induces the opposite outcomes. In the cases with 7.5–12.5 wt% SSP, the strength of EPSC reaches 28 MPa of 7 d, 42 MPa for 28 d, and 56 MPa at 90 d. Besides, it has desirable carbonation resistance due to high hydration degree, and generates controllable expansions as hydration proceeds, with extreme economic and environmental benefits. This study facilitates comprehensions of the hydration mechanism and properties regulation of the well-promised EPSC with steel slag activation.