Performance investigation and optimization of the granulation-CO2 concentration for the production of high-strength BOFS aggregates

Abstract

Studies have demonstrated that basic oxygen furnace slag (BOFS) powder can be granulated to produce a strong artificial aggregate through strengthening with accelerated carbonation. However, our previous results showed that a 100% CO2 concentration applied during granulation could significantly degrade the properties of the produced BOFS aggregate due to the loss of bridging water upon undergoing a rapid exothermic reaction. Therefore, this paper aims to optimize the CO2 concentration during granulation of BOFS and investigate the impact on the subsequent post air or CO2 curing of the produced aggregates. According to X-ray computed tomography results, the CO2 applied during granulation should be controlled at 40 vol% or less in order to provide proper connective pores in freshly granulated BOFS aggregates for subsequent carbonation, thereby allowing higher CO2 uptake and better mechanical development of hardened BOFS aggregates. It was also noted that with a high granulation-CO2 concentration typically of 100% can result in the formation of multiple granules in a single produced BOFS aggregate, hence lowering the intrinsic structure and aggregate strength. Compared to the CO2 reaction that occurs during granulation, post CO2 curing plays the main role in developing the mechanical strength of hardened BOFS aggregates.