A comparative study of ethylenediamine tetraacetic acid induced gas-solid and liquid-solid accelerated carbonation for enhancement of steel slag aggregates

Abstract

Accelerated carbonation is an effective technique to enhance the hydration reactivity and volume stability of steel slag aggregates (SSA). However, due to limitations in CO2 transport and carbonation kinetics, carbonation of SSA is frequently carried out using pure CO2 under high pressures. In this study, carbonation under 10% CO2 concentration and ambient temperature and pressure was employed to treat SSA. To accelerate the carbonation of SSA, ethylenediamine tetraacetic acid (EDTA)-induced gas–solid (dry) and liquid–solid (wet) carbonation processes were proposed. Effect of EDTA on the physical and mechanical properties and microstructure of carbonated SSA; and the performance of resulting concrete with a selected mix design were examined. Dry carbonation of SSA, prior to which EDTA was sprayed on the surface of SSA, resulted in a denser carbonated layer and consequently higher specific gravity compared to uncarbonated SSA. Concrete samples involving carbonated SSA, on which 0.1 mol/L EDTA was sprayed at 50% of water absorption mass of SSA, followed by carbonation curing for 24 hrs, revealed 24% increase in strength and 75% reduction in expansion when compared to those containing uncarbonated SSA. Wet carbonation of SSA, during which CO2 was injected into SSA-EDTA solution, promoted both carbonation and hydration of SSA, especially in 0.2 mol/L EDTA solution, resulting in the consumption of periclase and enabling the formation of brucite. While strength improvement was not obvious in the presence of brucite that weakened the interfacial transition zone (ITZ) of concrete, expansion was further reduced by the reduced periclase in SSA. Comparatively, EDTA-induced dry carbonation was more effective and required only 0.4 kg EDTA per tonne of SSA.