Preparation of carbon-negative artificial lightweight aggregates by carbonating sintered red mud (SRM): CO₂ sequestration, microstructure and performance

This study investigated the possibility of employing CO₂ curing for the production of cement-free artificial aggregates using low-value sintering red mud (SRM) and fly ash (FA). The effects of different curing methods (CO₂ and air curing) and varying FA dosages on the properties of SRM artificial aggregates were analyzed. For SRM artificial aggregates subjected to CO₂ curing, the calcium silicates depleted accompanied by precipitation of calcite and aragonite. The carbonated SRM artificial aggregates (CRAAs), exhibited a denser microstructure, with the pores of the SRM filled with carbonation products. For CRAAs with 100 wt% SRM, up to 9.67 wt% CO₂ was sequestered and in turn produced calcium carbonate, which resulted in a 149.0% enhancement in crushing strength and a 29.5% reduction in water absorption compared to the similar aggregates under air curing. The introduction of FA led to an accelerated strength development in the CRAAs during subsequent air curing, which was attributed to the formation of carboaluminates as a result of the hydration between the carbonation products and aluminates derived from FA. From the perspective of environment, CRAAs was carbon-negative, with a potential reduction of up to 40.2 kg of CO₂ per ton of CRAAs production, presenting a cleaner and sustainable alternative to natural aggregates. The results of the study provided a feasible solution for the effective treatment of SRM on a large scale and can be used as a reference for subsequent studies.