Hydration Activity and Expansibility Model for the RO Phase in Steel Slag

The low hydration activity and volumetric instability of steel slag (SS) limits its application as a binding material. SS contains approximately 30 pct of a divalent metal oxide solid solution (RO phase). According to the XRD results of the RO phase extracted from SS, RO phases (MgO·xFeO) with different compositions were synthesized to study their hydration activity and expansibility. The hydration activity of the RO phase was found to exponentially decrease with the increasing molar ratio (x) of FeO to MgO in the RO phase. When x ≥ 1 .5, the RO phase could not be hydrated after autoclaving at 215 °C and 2 MPa for 3 hours. The RO phase was blended into cement to study the relationships among the expansibility and composition and content of the RO phase via an autoclave test. When x ≤0.5, more than 5 pct of the RO phase cracked the specimen. When 0.5 < x < 1.5, the autoclave expansion rate of the specimen decreased with the increasing value of x in the RO phase. When x ≥ 1.5, the autoclave expansion rate of the specimen linearly increased with the content of the RO phase and was independent of the composition of the RO phase.