Preliminary study on reaction of fresh concrete with carbon dioxide

In order to let fresh concrete react with carbon dioxide sufficiently, the carbon dioxide was added to mixing concrete. The study used three water cement ratio (0.55, 0.65, 0.75), three CO₂ pressures (0.2, 0.4, 0.6 MPa), and two CO₂ concentration (50% and 100%) to make concrete samples, and observed the effect of carbon dioxide adsorption in the above parameters. Finally, the compressive strength and carbonation degree of concretes were tested after three curing time (7, 14 and 28 days). The research showed that concrete could be more efficient to absorb carbon dioxide by using this pressure method. The results found that the mixing concrete react with carbon dioxide in a short time, and shorten the initial setting time of concrete. But this method would greatly reduce the workability of concrete after mixing with carbon dioxide and it might be enhanced by water or superplasticizer. The bond of cement matrix might cut down after reacting with carbon dioxide. Based on the above, the compressive strength of concrete which was mixed with carbon dioxide would be impaired. The proposed CO₂-mixing method has the capacity to uptake 9.5% carbon dioxide based on water cement ratio and CO₂ pressure.