Development of a calcium aluminate cement from steelmaking slag by altering its mineralogical composition

Abstract

Strict environmental norms and increasing awareness of the need to recycle solid wastes generated during ironmaking and steelmaking processes are the key driving force for the development of various new materials and manufacturing technologies. In this study, a calcium aluminate clinker was prepared from steel ladle slag by modifying its mineral composition. The slag paste, prepared by mixing slag with water, exhibited flash setting behaviour due to the presence of C12A7 and C3A phases. In contrast, the slag clinker, developed by sintering a mixture of a pre-determined quantity of slag and aluminium oxide at 1400°C for 2 h and 4 h, contained CA, CA2, gehlenite and ‘Q’ phases. Hydrated slag clinker contained stable C3AH6, AH3 and stratlingite with preferential growth of calcium aluminate hydrate prisms along the c-axis, which provided a well-defined raceme-like morphology with an interlinked structure. This improved the setting time and crushing strength of the clinkers after 6 h and 24 h of curing at room temperature. Additionally, the presence of the Q phase, with lamellar prismatic crystals, also helped to enhance strength. The developed clinker also exhibited superior crushing strength as compared with commercially available calcium aluminate cement of medium purity. The slag, used as a source of calcium oxide, could replace calcium carbonate completely and thus contribute to reductions in carbon dioxide emissions during the clinker-making process.