Global carbon uptake of cement carbonation accounts 1930–2021

Abstract

Abstract. The main contributor to the greenhouse gas (GHG) footprint of the cement industry is the decomposition of alkaline carbonates during clinker production. However, systematic accounts for the reverse of this process – namely carbonation of calcium oxide and other alkaline oxides and/or hydroxides within cement materials during cements' life cycles – have only recently been undertaken. Here, adopting a comprehensive analytical model, we provide the most updated estimates of CO2 uptake by cement carbonation. The accumulated amount of global CO2 uptake by cements produced from 1930 to 2021 is estimated to be 22.9 Gt CO2 (95 % confidence interval, CI: 19.6–26.6 Gt CO2). This amount includes the CO2 uptake by concrete, mortar, construction waste and kiln dust, accounting for 30.1 %, 58.5 %, 4.0 % and 7.1 % respectively. The cumulative carbon uptake by cement materials from 1930 to 2021 offsets 55.1 % of the emissions from cement production (41.6 Gt CO2, 95 % CI: 38.7–47.2 Gt CO2) over the same period, with the greater part coming from mortar (58.5 % of the total uptake). China has the highest cement carbon uptake, with cumulative carbonation of 7.06 Gt CO2 (95 % CI: 5.22–9.44 Gt CO2) since 1930. In addition, the carbon uptake amounts of the USA, EU, India and the rest of the world took 5.0 %, 23.2 %, 5.6 % and 34.8 % separately. As a result of rapidly increased production in recent years, over three-quarters of the cement carbon uptake has occurred since 1990. Additionally, our results show little impact by the COVID-19 pandemic on cement production and use, with carbon uptake reaching about 0.92 Gt CO2 (95 % CI: 0.78–1.10 Gt CO2) in 2020 and 0.96 Gt CO2 (95 % CI: 0.81–1.15 Gt CO2) in 2021. Our uniformly formatted and most updated cement uptake inventories provide coherent data-based support for including cement carbon uptake into future carbon budgets from the local to global scale. The latest version contains the uptake data till 2021, showing the global uptake's increasing pattern and offering more usable and relevant data for evaluating cement's carbon uptake capacity. All the data described in this study are accessible at https://doi.org/10.5281/zenodo.7516373 (Bing et al., 2023).

Society’s material stocks as carbon pool: an economy-wide quantification of global carbon stocks from 1900–2015

“…Our estimate for the same year and components is in good agreement at 11.9 PgC, while our work includes additional components and enables regional differentiation. Huang et al [18] reported a concrete carbonation uptake of 22.9 Gt CO 2 until 2021, equivalent to 4.2 PgC in use until 2015, while our estimate of 2.7 PgC is 36% lower but still within the uncertainty range (2.3-4.9 PgC). For plastics, Stegmann et al [19] found a global inuse stock of 3.03 Gt in 2015, 28% higher than our estimate.…”

“…We estimated a C stock of 2.7 PgC in 2015, equivalent to 10.0 PgCO 2 removed from the atmosphere since 1900. Other estimates obtained an offset of 55.1% of cumulative process emissions from cement production between 1930 and 2021 [18]. Projections suggest a 30% offset from 2015 to 2100 [17].…”

“…Carbonation of concrete added nearly equal amounts of C to the socioeconomic C stock as plastic in 2015. Hydrated cement in concrete absorbs CO 2 via carbonation of calcium oxide [17,18,54]. We estimated a C stock of 2.7 PgC in 2015, equivalent to 10.0 PgCO 2 removed from the atmosphere since 1900.…”

“…Especially timber for construction is increasingly discussed, partly because production of wood-based elements is associated with smaller greenhouse gas (GHG) emissions than steel or concrete, but also because construction timber can act as medium-to long-term C storage [16]. Concrete sequesters C during the lifetime of concrete stocks and in the end-of-life waste management phase ('carbonation') [14,17,18]. A circular bio-based plastics sector has been assessed as potential C sink [19], leading Suh and Bradow [20] to suggest that societal material stocks in what they call the 'technosphere' can be conceptualized as distinct Earth system compartment storing C and thereby contributing to mitigating climate heating.…”