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An innovative capsule using steel slag as the primary core material complemented by chitosan as a secondary core material was developed. Steel slag exhibited virtually no hydraulic reactivity but readily underwent carbonation. The designed capsule was proven to help enhance the self-healing capabilities of cement-based composites at CO2 concentrations of 3 %. This approach not only offers a cost-effective solution for artificial capsules but also proposes the possibility of using high CO2 environments (e.g., sewage) as natural carbonation chambers. Mineralogy analysis of steel slag, sourced from the Australian local industry, identified a composition primarily consisting of larnite, srebrodolskite, and RO phases. Larnite exhibits considerable reactivity to carbonation. The carbonation mechanism of steel slag at 3 % CO2 concentration was investigated. The addition of a minor content of chitosan can significantly improve the carbonation level of steel slag by promoting the dissolution of calcium ions. After 28 days of healing, the CO2 uptake of the slag mixed with chitosan reaches 4.6 %, resulting in the formation of 6.0 % by weight of CaCO3 in the paste. Such a carbonation level was sufficient to efficiently heal cracks and improve the self-healing performance of cement-based composites. Most cracks below 200 μm were highly possible to be closed at 28 days of carbonation healing. The main healing products consisted of cubic-shaped CaCO3 and C-(A)-S-H gel, deriving from the carbonation of steel slag and the pozzolanic reaction of silica gel after calcium leaching, respectively.
Liu et al. (Thu,) studied this question.