• Higher CO2 concentrations during initial carbonation curing enhance early strength but may impede long-term strength development.
• Shotcrete exposed to 2vol% CO2 for 14 days achieved a carbonation degree approximately three times higher than at ambient CO2 levels.
• In field application, 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.
• Using shotcrete for CO2 curing in return-air tunnels offers a viable strategy for reducing carbon emissions and promoting sustainable mining.