Enhancing reactivity of basic oxygen furnace steel slag via aqueous carbonation in acetic acid: Influence on carbon capture, microstructure, hydration behaviour and mechanical properties

Aqueous carbonation emerged as a valuable technique to easily induce carbon capture in Basic Oxygen Furnace (BOF) steel slag. Nevertheless, there is an increasing need for novel mineralisation processes that are aimed at enhancing the reactivity of carbonated powder to promote their employment as supplementary cementitious materials (SCM) in cement blends. This paper investigates an innovative process that integrates the leaching behaviour of an acetic acid suspension with the CO2 mineralisation. The aim is to develop a process that enhances the pozzolanic reactivity of the carbonated particles, improves their microstructure and promotes the formation of calcium acetate contributing to the strength development. The analysis is conducted through a holistic approach, investigating: the calcium extraction capacity, the CO2 mineralisation process, the hydration mechanisms and the mechanical performance of cement blends that include the treated powder. The results are compared with studies from the literature as well as with the performance of standardised cement. The study shows that leaching pre-treatment in acetic acid exerts a substantial influence on the hydraulic reactivity of carbonated BOF. It induces the formation of less compact calcium carbonate layers with consequent higher portlandite consumption and bound water. Moreover, it results in the formation of calcium acetate salt, which promotes the reactivity in cement blends. In fact, the compressive strength at 28 days of cementitious samples including 20% of treated powder achieves up to about 96% of plain cement. At the same time, the carbonation degree remains relevant with CO2 uptake of 16.2% in the most reactive samples.