Carbonation and CO2 uptake of concrete

• CO2 uptake assessment approach owing to the concrete carbonation is developed.
• An equation to directly determine the absorbable CO2 amount in concrete is proposed.
• The carbonatable surface area of concrete crusher-runs for CO2 uptake is ascertained.
• This study provides typical data for uptake and emission of CO2 in concrete building.

This study developed a reliable procedure to assess the carbon dioxide (CO2) uptake of concrete by carbonation during the service life of a structure and by the recycling of concrete after demolition. To generalize the amount of absorbable CO2 per unit volume of concrete, the molar concentration of carbonatable constituents in hardened cement paste was simplified as a function of the unit content of cement, and the degree of hydration of the cement paste was formulated as a function of the water-to-cement ratio. The contribution of the relative humidity, type of finishing material for the concrete surface, and the substitution level of supplementary cementitious materials to the CO2 diffusion coefficient in concrete was reflected using various correction factors. The following parameters varying with the recycling scenario were also considered: the carbonatable surface area of concrete crusher-runs and underground phenomena of the decreased CO2 diffusion coefficient and increased CO2 concentration. Based on the developed procedure, a case study was conducted for an apartment building with a principal wall system and an office building with a Rahmen system, with the aim of examining the CO2 uptake of each structural element under different exposure environments during the service life and recycling of the building. As input data necessary for the case study, data collected from actual surveys conducted in 2012 in South Korea were used, which included data on the surrounding environments, lifecycle inventory database, life expectancy of structures, and recycling activity scenario. Ultimately, the CO2 uptake of concrete during a 100-year lifecycle (life expectancy of 40 years and recycling span of 60 years) was estimated to be 15.5%–17% of the CO2 emissions from concrete production, which roughly corresponds to 18%–21% of the CO2 emissions from the production of ordinary Portland cement.