Producing belitic calcium sulfoaluminate cement without bauxite: using aluminium slag and waste clays

Locally available waste materials from the UK are used to synthesize belitic calcium sulfoaluminate (BCSA) clinker/cement. The raw materials (limestone, waste clay, and gypsum) were sourced locally, and additionally the non-metallic by-product (NMP) from the processed black dross (formed during the secondary aluminium production; aluminium scrap recycling) was used to boost alumina content. BCSA clinker with a target composition of approximately 60% belite and 30% ye’elimite was synthesised on a laboratory scale under varying clinkering conditions. The results show the possibility of using NMP and local materials available within the UK to produce BCSA cement without the need for bauxite. The clinker formation was found to be influenced by the raw materials used, in particular iron content and/or clay mineral type, and the clinkering conditions. The raw meal containing a higher amount of iron required a higher burning temperature or longer dwell time for the desired clinker chemistry to be obtained. The synthesized BCSA cement was hydrated with gypsum at a water-to-cement ratio of 0.5 to assess the reactivity of the binder. At 56 d, there was complete consumption of ye’elimite, and initial reaction of belite was observed with ettringite, aluminium hydroxide, and strätlingite forming as the main hydration products, demonstrating reactivity of both major clinker phases.