Building products that have a portion of their constituent materials from recycled products reduce the need for virgin materials in new construction. Using recycled materials reduces the need to landfill these materials. It also reduces the environmental impacts from extracting and processing virgin materials.

Post-consumer recycled material is defined as waste generated by households or by commercial, industrial and institutional facilities as the end-users of a product. These are products that are sold and used for a specific purpose and then need to be disposed, such as newspaper, containers, computers, and batteries. Post-consumer materials include crushed concrete and masonry from demolished buildings that are reused as aggregate for concrete in new buildings.

 

Concrete incorporates three major types of recycled materials:

 

Fly ash, slag cement, and silica fume are industrial by-products that are used as a partial replacement for portland cement in concrete. These supplementary cementitious materials (SCMs) are pre-consumer materials.

 

Recycled material or recycled concrete can be used as aggregates in concrete.

  

Spent solvents, used oils, tires, and medical waste are used as fuel in many cement plants. Industrial byproducts are used as ingredients for manufacturing portland cement.

 

Fly ash, slag cement, and silica fume are industrial by-products; their use as a partial replacement for portland cement does not contribute to the energy and CO2 impacts of cement in concrete. If not used in concrete, these materials would use valuable landfill space. Fly ash is a by-product of the combustion of pulverized coal in electric power generating plants. Slag cement, also called ground granulated blast furnace slag, is made from iron blast-furnace slag. Silica fume is a by-product from the electric arc furnace used in the production of silicon or ferrosilicon alloy. These types of industrial by-products are considered post-industrial or pre-consumer recycled materials.

 

The environmental attributes of concrete can be further improved by using aggregates derived from industrial waste or using recycled concrete as aggregates. Blast furnace slag is a lightweight aggregate with a long history of use in the concrete industry.