CO₂ uptake through carbonation of concrete using simulated and as-captured flue gas

Carbon dioxide (CO2) is one of the major greenhouse gases and its significantly increasing emission may lead to higher temperatures and cause climate change. The sequestration of CO2 becomes crucial in stabilizing the greenhouse gas concentration in the atmosphere.The objective of this research is to examine the feasibility of using calcium silicate concrete to absorb CO2 in a flue gas collected from a cement plant and to investigate the effects of material compositions and process conditions on the CO2 uptake. The influencing factors include cement properties such as porosity, chemical component, pre-setting and post-curing as well as reaction parameters like CO2 concentration, moisture, exposed time, injection and releasing procedures and thickness of the compact. The interaction mechanisms are discussed.Results of mass gain are verified by infrared CO2 analysis. The typical mass gain for a cement paste compact is about 9% with a blend gas of 25% CO2 concentration, 5 bars pressure and 2 hours exposure using a multiple injection/release procedure. Under the same carbonation conditions, the as-captured flue gas with 13.6% CO2 concentration in 20 hours curing generates a mass gain of around 8%. The maximum possible CO2 uptake was investigated using the powder samples carbonated in a multiple step process at the best conditions. It is approximately 17% by the use of a blend gas of 25% CO2 concentration and 13.5% by the use of CO 2 + N2 gas of 25% CO2 concentration. The microstructures of the carbonated cement and concrete examined using SEM demonstrate that the material is composed of mostly amorphous or poorly crystalline forms of calcium carbonate incorporated into the hydration products. The pressure drop is employed to predict the mass gain and the remaining CO2 content in the gas. The prediction compares well with the experimental results