Utilisation perspective on water quenched and air-cooled blast furnace slags

Efficient utilisation and recycling of industrial waste along with minimum exploitation of natural resources are major challenge towards the circular economy and sustainability of the planet. Blast furnace slag is a by-product of the iron-making process while producing pig iron. The present research provides an understanding of the two different types of slags of water quenched granulated slag and air-cooled slag that are generated from iron making process through the blast furnace route. The chemical, mineralogical, physical, thermal and morphological properties of four different slags generated under different cooling condition are evaluated for recycling to cement and aggregate application. Results indicated that the cooling pattern of the slag significantly affects the particle morphology and phase formation, which determines their usage and utilisation. Air-cooled slag contains substantial quantity of crystalline phases (>50%) which prevents the slag to exhibit cementitious properties whereas water-quenched slag mainly contains amorphous phases (>90%). In addition, the applicability in cement and aggregate application of both mentioned types of slags were studied. It is concluded that water quenched slag is closely matching with the properties required to be utilised in Portland slag cement manufacturing process. On the other hand, air-cooled slag is suitable as an aggregate for application in the construction industry.