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Cement is a widely used construction material globally. Its manufacturing contributes to anthropogenic CO2 emissions significantly. However, its alkaline compounds can absorb CO2 from the surrounding environment and engage in a carbonation reaction, thereby functioning as a carbon sink. As a major cement producer and consumer, China has an important responsibility to rigorously investigate and accurately account for cement carbon uptake. This study presents a comprehensive analytical model of cement carbon uptake from China, revealing a substantial increase in carbon uptake from 1930 to 2021, peaking at 426.77 MtCO2 (95% Confidence Interval: 317.67–874.33 Mt CO2) in 2021. The uptake accounts for 8.10% to 45.40% of China's annual land sink and 2.51% to 4.54% of the global land sink. The cumulative carbon uptake by cement is approximately 7.06 Gt CO2 (95% CI: 5.22–9.44 Gt CO2) during this period, offsetting 50.7% of the total emissions (13.91 Gt CO2, 95% CI: 12.44–17.00 Gt CO2) from the cement industry. Notably, cement mortar contributed to most absorption (65.64%). From a life cycle perspective, the service stage of cement materials is the period where the largest CO2 sink is formed, accounting for 90.03% of the total. Therefore, the potential for carbon sequestration in cement materials and their waste is enormous. Additionally, the model improves the accuracy of cement carbon accounting, supporting both China and global carbon neutrality assessments. Thus, it is crucial for China to achieve its carbon neutrality goals sooner by prioritizing the environmental benefits of cement materials and wastes, and accelerating the development and commercialization of CO2 sequestration technologies for cement and its by-products. [ABSTRACT FROM AUTHOR]

About two-thirds of global CO 2 emissions from the energy and industry sectors are generated in China, accounting for approximately 30% of total global CO 2 emissions. These carbon-intensive processes usually produce a large amount of so-called alkaline solid wastes e.g. blast furnace slag (BFS), which have shown great potential to serve as CO 2 absorbers. In this regard, the climate impacts of these human activities should be re-evaluated by considering the carbon offsetting effects. While recent studies have been focusing on accelerated carbonation of such 'waste' from a technical perspective, the natural carbonation of these solid residues has not been comprehensively investigated. In this research, combining experimental data, we established an analytical carbon sink accounting model to estimate the CO 2 uptake of 7 types of alkaline solid wastes produced in China between 1930 and 2020 using material flow analysis (MFA), life-cycle assessment (LCA), and Monte Carlo methods. The results show that China's alkaline solid wastes from the identified industrial and agroforestry processes in 2020 absorbed 64.27 Mt CO 2 (35.91–111.01, 95% CI), offsetting 2.2% of the CO 2 emissions from Chinese industrial production. Cumulatively, 1099.51 Mt CO 2 had been sequestered by natural carbonation, since 1930. The majority of CO 2 uptake is attributed to coal combustion ash (CCA) and biomass ash (BA), which accounted for 35.9% and 26.3% of the total uptake combined respectively. All types of solid wastes exhibited rapidly increasing sequestration from 1930 to 2020 apart from yellow phosphorous slag (YPS) and oil shale ash (OSA), with substantial interannual variability. Our results indicate that the natural carbonation of such 'waste' can reduce the carbon footprint of the corresponding industrial and agroforestry processes, and make the case for further research of their full potential. [ABSTRACT FROM AUTHOR]