The carbon cost of cement
October 18, 2021 - Carbon dioxide emissions from cement production are a significant contributor to climate change, accounting for some 2.4 gigatonnes, or around seven per cent of global CO2 emissions in 2019.
A key ingredient of concrete, the most widely used construction material globally, cement production begins with mining and then grinding raw materials, including limestone and clay, to a fine powder called raw meal. The raw materials are then heated to a sintering temperature as high as 1,450°C in a rotary cement kiln.
In this process, the chemical bonds of the raw materials are broken down, and they are recombined into new compounds. The result is called “clinker.”
The clinker is ground to a fine powder in a cement mill and mixed with gypsum to create cement. The powdered cement is then mixed with water and aggregates to form the concrete used in construction.
The process produces two streams of carbon dioxide emissions: first from the fuel used to heat the kiln (traditionally coal) and second from the chemical reaction itself. For each tonne of cement produced, a further tonne of CO2 is released into the atmosphere. The emissions are more than the entire aviation industry and deforestation combined.
China is by far the largest producer of cement followed far behind by India and the combined countries of the EU. China used more cement in just three years than the U.S. did in the entire 20th century. America’s consumption during the century totals around 4.4 gigatonnes. In comparison, China used around 6.4 gigatonnes of cement between 2011 and 2013.
Most future growth is expected to happen in India and other emerging markets. However, Chinese consumption may be close to levelling off. In contrast, India’s consumption is set to increase significantly as it rapidly urbanises and builds infrastructure.