Strength, microstructure and durability of concretes cured by flue gas vacuum carbonation

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Early age carbonation curing of concrete is considered as one of the promising technologies for carbon capture and utilization in greenhouse gas mitigation exercise. Gaseous carbon dioxide is converted into solid calcium carbonates by calcium silicate carbonation and stored in concrete as nano crystals for performance enhancement. The process makes concrete greener, stronger and more durable. Currently the carbonation process works in a pressure chamber and with a carbon dioxide gas of 99% purity. Although it provides the best conditions for high degree of reaction, there are technical and economical challenges for large scale implementation. The first challenge is the use of pressure chamber. Most of the concrete producers do not use pressure chamber. To promote carbonation technology, it is imperative to develop a system that requires no pressure chamber. The second challenge is the price of the high purity gas. The commercial carbon dioxide gas costs about $500/ton. Unless it can be reduced to $50/ton, the gas price will remain an obstacle for applications. The question is if the as-captured flue gas can be used directly without chemical separation. This proposed research is directed to address the two challenges. A flue gas vacuum carbonation system will be developed to replace the pressure chamber and the pure gas in early carbonation process. The research will be carried out in four tasks: Task 1 is to establish a vacuum carbonation system with pure gas in a sealed-only chamber. It will serve the scenario when the recover CO2 is affordable. Task 2 is to develop a flue gas carbonation process in a pressure chamber to study the reaction efficiency with low concentration gas. Task 3 is to combine the techniques developed in Tasks 1 and 2 to examine the possibility of the flue gas carbonation in a vacuum system without pressure chamber. Task 4 will perform comprehensive microstructural and durability analysis of the concrete produced by early carbonation. Innovative carbonation devices will be designed and implemented to meet industry scale and the effectiveness of the technology will be assessed by strength gain and carbon uptake. Two typical concrete products will be used to test the developed process. They are concrete paving stones as precast product and concrete slabs such as pavements or bridge decks as cast-in-place product. Both products serve in severe outdoor exposure conditions and will benefit from carbonate precipitation for durability improvement. If successful, early carbonation curing can find more applications in both precast and cast-in-place concretes for carbon storage and performance enhancement at an affordable price. The developed technology will become the "game changer" in the construction industry.