Green in Practice 109 - The 3R’s - Reduce, Reuse, Recycle
3R’s > Reduce, Reuse, Recycle
The 3R’s of protecting our environment, depicted by arrows in this symbol, can be applied to the building industry.
Reduce the amount of material used and the toxicity of waste materials.
New concrete generally does not contribute significantly to construction waste. Only the quantities needed are brought to the site. When using ready mixed concrete, extra concrete is returned in the ready mix truck. When using precast, only the required concrete is used in the plant, and pieces are delivered to the site ready to be assembled. It is generally assumed that 2% of the concrete at a precast plant is waste, but since it is generated at the plant, 95% of the waste is used beneficially.
• Structures are designed to optimize (lessen) the amount of concrete used.
• Industrial by-products such as fly ash, slag cement, and silica fume are used as partial replacements for cement, thereby reducing the amount of cement used in concrete.
• The small amount of concrete waste generated has negligible toxicity.
Precast concrete is designed to optimize (lessen) the amount of concrete used and has minimal site waste. (Photo courtesy of Barber Architecture)
Reuse products and containers; repair what can be reused.
A key factor in building reuse is the durability of the original structure. Building reuse generally means leaving the main portion of the building structure and shell in place when renovating. This helps the environment by conserving resources and reducing wastes and the environmental impacts of new construction. Construction and demolition waste contribute to solid waste going to landfills. The production of new building materials depletes natural resources and can produce air and water pollution.
Concrete and masonry buildings in urban areas as well as small rural towns are frequently renovated on the inside while maintaining the original building shell. Concrete construction provides the opportunity to refurbish the building should the building use or function change, rather than tear down and start anew. Windows, floor coverings, partition walls, mechanical systems, and plumbing can be replaced and insulation can be added while maintaining the original concrete frame and exterior walls. Older buildings often exhibit superior detail and craftsmanship. Some states, such as North Carolina, provide grants to renovate vacant buildings in rural counties or in economically distressed urban areas. Concrete provides a long service life due to its durable and low-maintenance surface. Yearly maintenance should include inspection and, if necessary, repair.
• Precast concrete panels can be reused when buildings are expanded.
• Forms and formwork for precast concrete, ready mixed concrete, and masonry (molds) are reused. Wood or fiberglass forms can generally be used 40 to 50 times without major maintenance while concrete and steel forms have practically unlimited service lives.
• Wash water from ready mixed trucks is frequently recycled using trucks equipped with devices that collect wash water and return it to the drum where it can be returned to the ready mixed concrete plant for reuse.
• Concrete pieces from demolished structures can be reused to protect shorelines
Frank Lloyd Wright’s Unity Temple in Oak Park, IL (CTLGroup photo)
Vacant building ripe for reuse in North Carolina. (www.ncruralcenter.org/reuse
Recycle as much as possible, which includes buying products with recycled content.
Concrete in most urban areas is recycled as fill or road base. Steel forms are recycled when they become worn or obsolete. Virtually all reinforcing steel used in concrete is made from recycled steel.
Recycled materials are used to manufacture cement, and as aggregate and cementitious materials 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.
• Recycled material or recycled concrete can be used as aggregates in concrete.
• 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 industrial by-products; their use as a partial replacement for portland cement significantly reduces the energy and CO2 impacts of cement in concrete. If not used in concrete, these materials would use valuable landfill space. Fly ash is commonly used at replacement levels up to 25%; slag cement up to 60%; and silica fume up to 5% to 7%. When slag cement replaces 50% of the portland cement in a 7500 psi concrete, greenhouse gas emissions per cu yd of concrete are reduced by 45%.
Machinery taking portions of concrete walls, columns, and floors and crushing them to be used as fill material. (CTLGroup photo)
Fly ash (PCA No. 12190)
Slag cement (PCA No. 12191)
Silica fume (PCA No. 12192)
American Coal Ash Association
Slag Cement Association
Silica Fume Association
Concrete Reinforcing Steel Institute
www.wbdg.org/tools/cwm.php Whole Building Design Guide Construction Waste Management DataBase – enter your geographic information to determine where you can take concrete to be recycled
Available for free:
Marceau, M., Gajda, J., and VanGeem, M., Use of Fly Ash in Concrete: Normal and High Volume Ranges, PCA No. SN2604, 2002. [Also on PCA CD033]
LEED-NC 2.1 Guide: Using Slag Cement in Sustainable Construction, Slag Cement Association, 2005. www.slagcement.org
Steel Reinforcing Bars: Recycled, Concrete Reinforcing Steel Institute, 2002. www.crsi.org
Power Plant ByProducts, PCA No. IS331, 2005. www.cement.org
Iron and Steel ByProducts, PCA No. IS326, 2005. www.cement.org
Tire-Derived Fuel, PCA No. IS325, 2005 www.cement.org
For a fee:
Latham, Derek, Creative Re-Use of Buildings, Donhead Publishing Ltd, Port City Fulfillment Services, Kimball, MI. www.donhead.com
Thomas, M. and Wilson, M., Supplementary Cementing Materials For Use in Concrete, PCA No. CD038, 2002. www.cement.org
Design and Control of Concrete Mixtures, PCA No. EB001. www.cement.org
Detwiler, R., Bhatty, J., and Bhattacharja, S., Supplementary Cementing Materials for Use in Blended Cements, PCA No. RD112. www.cement.org
Innovations in Portland Cement Manufacturing, PCA No. CD400, 2004. www.cement.org
ACI 555 - Removal and Reuse of Hardened Concrete, American Concrete Institute. www.concrete.org