The equivalent of almost half of the CO2 produced during cement production in the past 70 years has subsequently been sequestered in cement products, reports a paper published online in Nature Geoscience this week.
Cement production accounts for 5% of all CO2 emissions from fossil fuel combustion and industrial processes. Cement production releases CO2 through a process called calcination. In the reversal of this process - known as carbonation - CO2 is taken up by cement products. However, carbonation has generally not been considered in assessments of cement’s carbon footprint, and although the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories provides methods for quantifying CO2 emissions during the cement production process, they do not consider CO2 absorbed by carbonation of cement materials.
Zhu Liu and colleagues used new and existing data on cement characteristics to mathematically model the amount of CO2 sequestered globally by four different cement materials during their service life, demolition and secondary use. They estimate that 4.5 gigatons of carbon were sequestered between 1930 and 2013, which is equivalent to 43% of the CO2 emitted from calcination during that period.
They note that cement production has long been considered an important source of anthropogenic CO2,but that their estimates of CO2 uptake presented here suggest that, following its production, cement also becomes an important CO2 sink.