Evaluation of atmospheric CO₂ sequestration by 50-year-old concrete structures based on 14C and 13C measurements

Abstract

This study examines the long-term sequestration of atmospheric CO₂ as an inorganic carbonate through carbonation in concrete structures. Two buildings, each approximately 50 years old, were analyzed using two cores per structure. Measurements of radiocarbon (¹⁴C) concentration, δ¹³C, and total inorganic carbon (TIC) of the core samples were conducted. For one building containing limestone aggregate, additional analyses, visual inspection, polarized light microscopy, and X-ray diffraction with Rietveld refinement were performed to evaluate the material and mineral distributions. The results indicate that δ¹³C varies with pH changes during carbonation, while the concentration of ¹⁴C reflects the historical fluctuations in atmospheric ¹⁴C. By applying the √t relationship for carbonation depth, the amount of CO₂ fixed from the atmosphere can be determined, even in the presence of limestone aggregate. This study provides a methodology for assessing long-term CO₂ sequestration in existing concrete structures.