Effect of High Cooling Rates on the Mineralogy and Hydraulic Properties of Stainless Steel Slags.

This article investigates the effect of chemical composition and cooling rate during solidification on the mineralogy and hydraulic properties of synthetic stainless steel slags. Three synthetic slags, covering the range of typical chemical composition in industrial practice, were subjected to high cooling rates, by melt spinning granulation or quenching in water, and to low cooling rates, by cooling inside the furnace. Both methods of rapid cooling led to volumetrically stable slags unlike the slow cooling which resulted in a powder-like material. Stabilized slags consisted predominantly of lamellar β-dicalcium silicate ( β-CS) and Mg, Ca-silicates (merwinite and bredigite); the latter form the matrix at low basicity and are segregated along the CS grain boundaries at high basicities. Slowly cooled slags consist of the γ-CS polymorph instead of the β-CS and of less Mg, Ca-silicates. Isothermal conduction calorimetry and thermogravimetric analysis indicate the occurrence of hydration reactions in the stabilized slags after mixing with water, while calcium silicate hydrates (C-S-H) of typical acicular morphology are identified by SEM. The present results demonstrate that the application of high cooling rates can result in a stable, environmental-friendly, hydraulic binder from stainless steel slags, rich in β-CS, without the necessity of introducing any additions to arrest the β polymorph. [ABSTRACT FROM AUTHOR]