[Analysis of Carbon Storage Potential of CO₂ Foamed Concrete]

The technology of carbon capture, utilization, and storage (CCUS) is an important component of carbon neutral technology systems. To confirm the carbon storage potential of CO₂ foamed concrete (CFC), this study addressed the principle of carbon storage in CFC materials. It is apparent that carbon storage of CFC materials includes carbon fixation in concrete skeletons and carbon storage in CFC bubbles. The carbon fixation of CFC skeletons is realized by CO₂ mineralization. As the concrete skeleton in CFC is in the CO₂ atmosphere, the carbonation of CFC materials or CO₂ mineralization is more complete. Research shows that the carbonation rate of CFC materials can reach almost 30% after acidification, foaming with high CO₂ pressure and curing in the atmosphere. The carbonation rate is higher than the rate in concrete curing with CO₂. A mathematical model was established to calculate carbon fixation capacity in CFC materials, and the carbon fixation and storage capacity in CFC material were estimated. The results showed that more than 99% carbon storage of CFC was realized by the chemical carbonization of the concrete skeleton. Comparatively, the potential of carbon storage in the bubble of CFC was small. In this study, carbon storage capacity was divided into three categories, i.e., theoretical maximum capacity, relative reliable capacity, and expected capacity or potential. The carbonation rate for theoretical maximum capacity was 100%, when all the concrete was considered to be carbonated. As the carbonation rate of concrete during the whole life cycle is approximately 55% all over the world, 50% was set as the carbonation rate for relative reliable capacity calculation. If at high temperatures, CO₂ curing with high pressure or accessory ingredients applied to silicate concrete can improve carbonation rate to be over 80%, when the carbon storage capacity is considered to be expected capacity or potential. In 2017-2021, the theoretical maximum capacity of carbon storage was 3.623×10⁹ t CO₂ in China, with 7.25×10⁸ t·a^-1. The relative reliable capacity was 3.75×10⁸ t·a^-1, and the expected capacity was 5.80×10⁸ t·a^-1. If the carbonation rate was 30%, the carbon storage of concrete produced annually in China during the whole life cycle reached 2.18×10⁸ t, which was more than the carbon sink of Daxing'anling forest for one year. In coal electricity integrated mining areas and large thermal, metallurgical, cement chemical, and other high-energy consuming enterprises, CFC has a good prospect of development to promote the recycling of solid waste and waste gas. Meanwhile, it is pointed out that the stability of CFC before solidification is a technical problem to be solved in the next step.