Recycled Materials in Concrete
Reduce CO2 Emissions
and Landfill Use
Like any manufacturing process, the production of cement used in concrete results in the creation of greenhouse gases, including CO2. The U.S. cement industry has reduced CO2 emissions by 30% since 1972 and now accounts for approximately 1.5% of U.S. emissions, well below other sources such as heating and cooling homes and buildings (33%), truck and auto use (27%) and industrial operations (19%). The CO2 embodied in concrete as a finished building product is a very small quantity considering that cement accounts for a small proportion of the finished product.
The concrete industry also uses industrial waste byproducts such as fly ash (from coal combustion) and blast furnace slag (created in iron manufacture) to constitute a portion of the cement used in producing concrete. Use of such byproducts in concrete prevents 15 million metric tons a year of these waste materials from entering landfills. Utilizing these "supplemental cementitious materials" as a replacement for cement improves the strength and durability of concrete and also further reduces the CO2 embodied in concrete by as much as 70%, with typical values ranging from 15% to 40%.
Finally, when a concrete structure has served its purpose, it can be crushed for use as aggregate in new concrete or as fill or base materials for roads, sidewalks and concrete slabs. Even the reinforcing steel in concrete (which often is made from recycled materials) can be recycled and reused.
For more information, please review NRMCA's June 2008 Concrete CO2 Fact Sheet (PDF).