Global CO₂ uptake of cement in 1930–2019

Abstract. Because of the alkaline nature and high calcium content of cements in general, they serve as a CO₂ absorbing agent through carbonation processes, resembling silicate weathering in nature. This carbon uptake capacity of cements could abate some of the CO₂ emitted during their production. Given the scale of cement production worldwide (4.10 Gt in 2019), a life-cycle assessment is necessary in determining the actual net carbon impacts of this industry. We adopted a comprehensive analytical model to estimate the amount of CO₂ that had been absorbed from 1930 to 2019 in four types of cement materials including concrete, mortar, construction waste and cement kiln dust (CKD). Besides, the process CO₂ emission during the same period based on the same datasets was also estimated. The results show that 21.12 Gt CO₂ (18.12–24.54 Gt CO₂, 95 % CI) had been absorbed in the cements produced from 1930 to 2019, with the 2019 annual figure mounting up to 0.90 Gt CO₂ yr⁻¹ (0.76–1.07 Gt CO₂, 95 % CI). The cumulative uptake is equivalent to approx. 52 % of the process emission, based on our estimation. In particular, China's dominant position in cement production/consumption in recent decades also gives rise to its uptake being the greatest with a cumulative sink of 6.21 Gt CO₂ (4.59–8.32 Gt CO₂, 95 % CI) since 1930. Among the four types of cement materials, mortar is estimated to be the greatest contributor (approx. 58 %) to the total uptake. Potentially, our cement emission and uptake estimation system can be updated annually and modified when necessary for future low-carbon transitions in the cement industry. All the data described in this study, including the Monte Carlo uncertainty analysis results, are accessible at https://doi.org/10.5281/zenodo.4064803.