CO2 uptake by concrete hardened in a simulated flue gas

The possibility of using concrete building products to absorb flue gas carbon dioxide through their curing process is studied. Portland cement based products were exposed to a simulated flue gas with a CO₂ concentration of 25%, under 5 bar pressure and in two-hour duration. Their carbon uptake and immediate strength gain were measured. It was found that the flue gas CO₂ uptake was in a range of 7-9% based on dry cement as reference. Its corresponding two-hour strength exceeded 8 MPa in a multiple injection - release procedure. To investigate the maximum possible CO₂ uptake by cement, loose powder samples of same mass were carbonated under the same condition. The uptake could reach approximately 17%. Microstructure of the carbonated cement and concrete indicated that the material was mainly composed of poorly crystalline calcium carbonate incorporated in the calcium silicate hydration products.