Global CO2 uptake by cement from 1930 to 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 to determine 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). In addition, the process CO2 emission

during the same period based on the same datasets was also estimated. The

results show that 21.02 Gt CO2 (95 % confidence interval, CI: 18.01–24.41 Gt CO2) had

been absorbed in the cements produced from 1930 to 2019, with the 2019

annual figure mounting up to 0.89 Gt CO2 yr−1 (95 % CI: 0.76–1.06 Gt CO2). The cumulative uptake is equivalent to approximately 55 %

of the process emission based on our estimation. In particular, China's

dominant position in cement production or consumption in recent decades also

gives rise to its uptake being the greatest, with a cumulative sink of 6.21 Gt CO2 (95 % CI: 4.59–8.32 Gt CO2) since 1930. Among the four

types of cement materials, mortar is estimated to be the greatest

contributor (approximately 59 %) 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

(Wang et al., 2021).