Cement productions are considered to be doubly carbon-intensive because emissions come from both energy combustion and calcination chemical reaction. The cement industrial process emission from calcination chemical reaction account for 5% of global carbon dioxide from energy and all industrial emissions processes. Attention has been paid to quantify the emission amount during cement production. However, the natural reversal of the process - carbonation - has received little attention in carbon cycle studies. 

An international team led by XI Fengming from Institute of Applied Ecology of Chinese Academy of Sciences has found that over time, the widely used building materials uptake 43% of the carbon dioxide emitted during cement industrial process. Scientists use the term sink to describe a feature like a forest or ocean that takes carbon dioxide out of the atmosphere and permanently tucks it away so it can no longer contribute to climate change. In addition to carbon sink from ecosystem, the alkaline cement material is one of most important carbon sink. 

Researchers used new and existing data on cement materials during cement service life, demolition and secondary use of concrete waste to estimate regional and global CO₂ uptake between 1930 and 2013, and an analytical model describing carbonation chemistry.

The findings showed that carbonation of cement materials over their life cycle represents a large and growing net sink of CO₂, increasing from 0.10 GtC yr^-1 in 1998 to 0.25 GtC yr^-1 in 2013. In total, more than 76 billion tons of cement were produced around the world from 1930 to 2013 with four billion tons produced in 2013 alone. A cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO₂ emissions from production of cement over the same period, not including emissions associated with fossil use during cement production.  

“The global carbon uptake by cement carbonation is large and substantial, which give a new perspective for missing sink mystery and the carbon sink from human activities have not revealed comprehensively, the new technologies of carbon capture and storage using the cement wastes should be developed for climate change mitigation.” said XI Fengming.

The study entitled “Substantial global carbon uptake by cement carbonation” has been published in Nature Geoscience.