Carbon sequestration potential and mechanisms of shotcrete for tunnel support in underground metal mines through cement hydration

Growing concerns about greenhouse gas emissions from underground mining have intensified the need for carbon reduction strategies at every stage. Shotcrete used in tunnel support presents a promising opportunity for carbon emission reduction. This study investigates the carbon absorption capacity, mechanical strength, and underlying mechanisms of shotcrete when exposed to varying CO₂ concentrations during the mine support process. Findings reveal that higher CO₂ concentrations during the initial stages of carbonation curing enhance early strength but may impede long-term strength development. Shotcrete samples exposed to 2vol% CO₂ for 14 days exhibited a carbonation degree approximately three times higher than those exposed to 0.03vol% CO₂. A carbonation layer formed in the shotcrete, sequestering CO₂ as solid carbonates. In practical terms, shotcrete in an underground return-air tunnel absorbed 1.1 kg·m² of CO₂ over 14 days, equivalent to treating 33 m³ of contaminated air. Thus, using shotcrete for CO₂ curing in return-air tunnels can significantly reduce carbon emissions, contributing to greener and more sustainable mining practices.