Long-lasting Sustainable Construction
Today’s reinforced concrete is a much greener and more flexible product. Significant environmental impact improvements are being made on many fronts including cement production and the use of recycled cementitious materials diverted from the waste stream. An increasing number of builders routinely divert waste concrete from the waste stream by utilizing demolished (crushed) concrete as drainage landfill or road base material. The mild steel reinforcing is exclusively produced from post-consumer and post-industrial recycled steel products such as cars, appliances and recycled building materials. By-products of industry and waste disposal such as fly-ash and silica fume are being effectively substituted as cementitious constituents in concrete, significantly reducing Portland Cement content without compromising strength or durability.
The steel reinforcing bars used in reinforced concrete consist of nearly 100% recycled material. More than 7 million tons of scrap steel is recycled into reinforcing bars every year, virtually the entire feedstock. This recycling avoids a massive energy expenditure — one ton of steel reinforcing bars would otherwise require about 2,500 pounds of ore, 1,400 pounds of coal, and 120 pounds of limestone. Reinforcing bar is typically made in electric arc furnaces, which produce about 45% of the steel products made in America. Nearly 100% of the feedstock used for producing reinforcing bars is provided by recycled ferrous scrap.
Likewise, concrete mix designs typically incorporate industrial by-products that would otherwise be considered unusable waste, such as fly ash, ground granulated blast furnace slag, silica fume, and other supplemental cementitious materials. They reduce the amount of cement required in the concrete while significantly improving durability. It is made with locally available materials and often is cast close to the site, minimizing transportation.
Reinforced concrete typically is cast to precise specifications, with little excess, reducing waste. Any generated waste can be recycled for another use. Its high-strength capabilities can minimize the number of columns, saving material and reducing environmental impact. It can be crushed and reused as aggregates in new concrete structures, in roadbeds, and for breakwaters as larger pieces. The combination of recycling activities for reinforcing steel and concrete make it a totally cradle-to-cradle building material that is recognized by sustainable-design organizations worldwide.
Leadership in Energy and Environmental Design (LEED)
The United States Green Building Council (USGBC) has created a credit-based rating system called Leadership in Energy and Environmental Design (LEED), to evaluate the environmental performance of virtually any building while promoting sustainable design. Projects earn points for environmentally friendly actions taken during the construction phase and beyond.
LEED products currently available:
- LEED – v3.0 for New Construction and Major Renovations
- LEED – for Homes
- LEED – for Core and Shell
- LEED – for Existing Buildings: Operations and Maintenance
- LEED – for Commercial Interiors
- LEED – for Schools
- LEED – for Retail
- LEED – for Healthcare
- LEED – for Neighborhood Development (in pilot stage)
USGBC has more detailed information on the LEED program at http://www.usgbc.org/ and outlines the categories for meeting each credit. Forty points is the least amount required under the LEED-NC v3.0 category, with silver, gold, and platinum levels also available.
Life cycle assessment (LCA) is the factual analysis of a product’s entire life cycle in terms of sustainability. With LCA, you can evaluate the environmental impacts of your product or service from cradle to grave. LCA is a standardized methodology, which gives it its reliability and transparency and provides tangible benefits in decision-making processes for a more sustainable structure.
Concrete components typically are cast as specified, with little excess produced. What waste accrues through cutouts, etc., can be recycled. Many steel and concrete plants have instituted water-recycling programs and other environmental processes to further reduce the manufacturing impact.
At the end of the structure’s useful service life, the concrete can be recycled to substitute for aggregate materials. Many concrete plants also have instituted waste-product fuel, water-recycling programs, and other environmental processes to further reduce the manufacturing impact.
Improved Energy Efficiency
Concrete thermal mass may be used for energy conservation. In regions of the country with strong diurnal gradients, adding thermal mass to a building reduces the demand for heating and cooling. In areas where energy costs vary with time of day, thermal mass can be used to achieve reductions in energy use during peak consumption periods. Some air conditioning systems utilize the thermal mass and conductivity of concrete piers as a reservoir or sink for heat using off the-shelf geothermal systems.
Concrete’s inherently reflective surfaces enhance both comfort and energy efficiency. Light-reflective floors and walls improve illumination inside buildings by reflecting light from both natural and artificial sources. Using light-colored concrete pavement on roadways and sidewalks allows site designers to use less artificial light while lessening the “urban heat island effect” the sun has on blacktop surfaces.
Improved Air Quality
Concrete buildings help to improve indoor air quality. Polished concrete floors do not require carpeting, which can be a source of VOCs. In addition, carpet is linked to higher levels of allergens because it holds dust and can harbor mites and mildew, so a finished concrete floor eliminates this as well.
The primary raw materials used to make concrete are abundant in most areas of the world. The cement, aggregates, and reinforcing steel used to make concrete are usually obtained or extracted from sources within 300 miles of the ready-mix, precast concrete, or masonry plant. Most ready-mixed plants are well within 100 miles of the project site. Fly ash, slag cement, and other supplementary cementitious materials are frequently taken from nearby sources, removing these products from the local waste stream, and reducing the volume of waste sent to landfills. In addition, a reduced shipping distance for local building materials minimizes fuel requirements for transportation and handling, as well as the associated energy and emissions.