An international team of researchers has found that over time, cement reabsorbs a significant portion of the CO2 emitted when the material was manufactured.
A new study involving the University of East Anglia (UEA) shows that cement structures are a substantial but overlooked absorber of carbon emissions – offsetting some of those emitted during cement production itself.
Conducted by the China Emission Accounts and Datasets (CEADs) group, an international team of researchers found that the natural carbonation process of cement materials represents a large and growing ‘sink’ of CO2.
However, while the Intergovernmental Panel on Climate Change (IPCC) guidelines for emissions inventories provide methods for quantifying CO2 emissions during the cement production process, they do not consider carbon absorbed through cement carbonation.
Carbonation is a slow process that takes place throughout the life cycle of cement-based materials. As they weather, CO2 spreads into the pores and triggers a chemical reaction, starting at the surface and gradually moving inwards.
Using new data from field surveys in China and existing data and studies on cement material during its service life, demolition and secondary use of concrete waste, the researchers modelled the regional and global atmospheric CO2 uptake between 1930 and 2013.
The findings, published today in the journal Nature Geoscience, indicate that existing cement stocks worldwide absorb approximately one billion tons of atmospheric CO2 each year. The researchers focused on four cement materials – concrete, mortar, construction cement waste and cement kiln dust – in China, the US, Europe and the rest of the world.
It is estimated that 4.5 gigatons of carbon (GtC) has been reabsorbed in carbonating cement material from 1930 to 2013, offsetting 43% of the CO2 emissions from production of cement over the same period, not including emissions associated with fossil fuel use during cement production. An estimated 44% of cement process emissions produced each year between 1980 and 2013 has been offset by the annual cement sink.
The process CO2 emissions from cement production make up approximately 90% of global CO2emissions from all industrial processes and five per cent of global CO2 emissions from industrial processes and burning fossil fuels combined.