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

混凝土早期碳化养护被认为是温室气体减排中碳捕获和利用的最有前途的技术之一。气态二氧化碳通过硅酸钙碳化作用转化为固体碳酸钙，并以纳米晶体的形式储存在混凝土中以提高性能。这一过程使混凝土更环保、更坚固、更耐用。目前，碳化过程在压力室中进行，二氧化碳气体纯度为99%。虽然它为高度反应提供了最好的条件，但大规模实施仍存在技术和经济挑战。第一个挑战是压力室的使用。大多数混凝土生产商不使用压力室。为了推广碳化技术，开发一种不需要压力室的系统势在必行。第二个挑战是高纯度天然气的价格。商用二氧化碳气体的价格约为500美元/吨。除非能降至50美元/吨，否则天然气价格仍将是应用的障碍。问题是，捕获的烟气是否可以在不进行化学分离的情况下直接使用。这项拟议的研究旨在解决这两个挑战。开发一套烟气真空碳化系统，取代早期碳化过程中的压力室和纯气。这项研究将分四个任务进行：任务一是建立一个纯气体在纯密封腔中的真空碳化系统。它将服务于回收二氧化碳负担得起的情景。第二项任务是在加压室内开发烟气碳化工艺，以研究低浓度气体的反应效率。任务3是结合任务1和任务2中开发的技术，研究在没有加压室的真空系统中发生烟道气碳化的可能性。任务4将对早期碳化产生的混凝土进行全面的微观结构和耐久性分析。将设计和实施创新的碳化设备，以满足行业规模，并将通过强度增加和碳吸收来评估该技术的有效性。将使用两个典型的混凝土产品来测试所开发的工艺。它们是作为预制产品的混凝土铺路石和作为现浇产品的混凝土板，如人行道或桥面。这两种产品都适用于恶劣的户外暴露条件，并将受益于碳酸盐沉淀，以提高耐用性。如果成功，早期碳化养护可以在预制混凝土和现浇混凝土中找到更多的应用，以负担得起的价格储存碳和提高性能。研发出来的技术将成为建筑业的“游戏规则改变者”。

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.