What is the Truth behind CO2 and the Cement Industry?
Here are some details on US and world cement production from the Concrete Thinker and the Portland Cement Association.
Carbon dioxide emissions from a cement plant are divided into two source categories: combustion and calcination. Combustion accounts for approximately 40% and calcination 60% of the total CO2 emissions from a cement manufacturing facility. The combustion-generated CO2 emissions are related to fuel use. The CO2 emissions due to calcination are formed when the raw materials (mostly limestone and clay) are heated to over 2500°F and CO2 is liberated from the decomposed limestone. As concrete ages, it carbonates and reabsorbs the CO2 released during calcination. Calcination is a necessary key to cement production. Therefore, the focus of reductions in CO2 emissions during cement manufacturing is on energy use.
In the US, cement manufacturing accounts for approximately 1.5 to 2% of CO2 emissions attributable to human activities. Worldwide, cement manufacturing accounts for approximately 5% of CO2 emissions. When all greenhouse gas emissions generated by human activities are considered, the cement industry is responsible for approximately 3% of global emissions. Using the same ratio of CO2 emissions to greenhouses gases in the U.S., 1% of the greenhouse gases are attributed to cement manufacturing. In the US and elsewhere, the industry strives to further reduce that contribution.China produces 37% of the world’s cement, followed by India with 6% and the U.S. with 5%. Most facilities in China rely on inefficient and outdated technologies; these plants contribute to 6 to 8% of the CO2 emissions in China.
The cement industry has made progress towards reducing energy associated with cement manufacturing and associated emissions. Since 1972, the cement industry has improved energy efficiencies by 33%. According to the U.S. Department of Energy, U.S. cement production accounts for only 0.33% of U.S. energy consumption.
Putting CO2 emissions into perspective
The manufacture of cement produces about 0.9 pounds of CO2 for every pound of cement. Since cement is only a fraction of the constituents in concrete, manufacturing a cubic yard of concrete (about 3900 lbs) is responsible for emitting about 400 lbs of CO2. The release of 400 lbs of CO2 is about equivalent to:
- The CO2 associated with using 16 gallons of gas in a vehicle
- The CO2 associated with using a home computer for a year
- The CO2 associated with using a microwave oven in a home for a year
- The CO2 saved each year by replacing 9 light bulbs in an average house with compact fluorescent light bulbs
Other sources responsible for CO2 emissions include:
- 28,400 lbs for an average U.S. house in a year
- 26,500 lbs for two family vehicles in the U.S. in a year
- 880,000 lbs for a 747 passenger jet traveling from New York to London
The reason concrete is responsible for 1.5 to 2% of the U.S. anthropogentic CO2 (that is, due to humans) is due to the vast quantities of concrete used in the world around us.
Cement will need to continue to be produced as our world continues to demand adequate housing, water and infrastructure for its people.