Comparison of the Reactivities of Air- and Water-Granulated Iron Silicate Slag as Supplementary Cementitious Material

A potential approach to reduce the environmental impact of copper extraction and concrete production is utilizing iron silicate slag as a supplementary cementitious material (SCM) since it enhances resource efficiency and decreases CO₂ emissions per ton of cementitious material. To be utilized as an SCM, the slag must have an amorphous structure, which can be achieved by water granulation. However, water granulation is a water-intensive process that requires access to water and water purification, which makes air granulation an interesting alternative cooling method. For iron silicate slags, there is limited knowledge of whether air granulation can generate a slag with amorphous content comparable with water-granulated iron silicate slags and if possible structural variances in the amorphous structure might affect its reactivity and potential use as an SCM. Therefore, this study investigates the amorphous content and reactivity of an industrial iron silicate slag sample subjected to air and water granulation. The slag sample was first water granulated on an industrial scale followed by remelting before water and air granulation at a laboratory scale. The amorphous content of the three samples was studied using X-ray diffraction (XRD), and their reactivities were measured using R³ isothermal calorimeter testing. The XRD results showed that water granulation on both an industrial and laboratory scale generated a fully amorphous slag while the air-granulated slag had a minor formation of crystalline phases. Results from the R³ measurements showed that the water-granulated slags generated more heat after seven days than the air-granulated slag.