Production of carbonate aggregates using steel slag and carbon dioxide for carbon-negative concrete

•Utilizing CO2 to prime waste steel slag for use as an aggregate in concrete.•Artificial carbonate-aggregates comparable in performance to commercial benchmarks.•Prescribed processing presents potential to achieve carbon-negative concrete.

This work demonstrated the possibility of producing artificial carbonate aggregates from steel slag optimally activated by carbon dioxide for the purposes of waste recycling and carbon utilization in concrete. The value-added application is unique and oriented towards green concrete development. Processing of the slag involved successive carbonation treatments prior and post communition, yielding a final CO2-impregnated material suitably hardened and graded to replace natural aggregates in concrete. Standardized tests deemed the synthetic aggregate comparable in performance to commercial granite and Litex® lightweight aggregates. Compressive strength of concretes prepared using these artificial aggregates, where some specimens were further cured by carbonation, performed favorably against reference benchmark concretes. A standard full-size 20-cm concrete masonry block prepared in the manner prescribed can permanently store 2.93 kg of CO2, outweighing its embodied carbon footprint. Extending this to annual block production in the United States and Canada, around 12 million tons of CO2 could potentially be sequestered every year through such utilization. The final concrete products can be made carbon negative.

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