Abstract: Composite cementitious materials were prepared by using phosphogypsum (PG), hot-braised steel slag (HBSS), Portland cement and aluminate cement (CA) as main raw materials, and sodium silicate as alkali activator. In the curing age from 0 d to 28 d, the compressive strength and expansion rate of materials were tested in the experiments. Meanwhile, the synergic mechanisms of hydration synergism among phosphogypsum, hot-braised steel slag and aluminate cement were analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and specific surface area and porosity (BET) measurement. The results show that the steel slag powder through 0.300 mm sieve-aperture has both good skeleton filling and gelling properties. In the hydration process, sodium silicate increases the dissolving rate of vitreous network structure on the surface of steel slag and promotes the formation of C-A-S-H from steel slag and aluminate cement. Furthermore, the phase-transforming shrinkage of C-A-H is inhibited by the ettringite formed with the reaction of aluminate cement and phosphogypsum. In addition, a wealth of ettringite and C-A-H is rapidly generated and covered on the surface of steel slag with excessive addition of aluminate cement, which hinders the dissolution promoting effect of Na₂SiO₃ on the glass network structure of steel slag. This paper provides theoretical basis for the collaborative utilization of phosphogypsum and steel slag.

Key words: hot-braised steel slag, phosphogypsum, aluminate cement, sodium silicate, gelling property, phase-transforming shrinkage