Concrete has been called pourable stone. Extremely durable, it was used 3,600 years ago by the Egyptians to build columns that are still standing. It is the most frequently used structural building material in the United States today, the main component in buildings, bridges, pavement, dams, breakwaters and docks. Even barges and ships are made of it. It would be hard to imagine modern life today without concrete.
Conventional concrete combines sand, gravel and water with Portland cement to make a building material that is strong, inexpensive, and long lasting. To create Portland cement, alumina, silica, lime, iron oxide and magnesium oxide are burned together in a kiln at high temperatures. The result is then pulverized into a fine powder.
Because of the extreme heat needed to produce cement, the manufacturing process is relatively energy-intensive. It also releases large amounts of carbon dioxide, both from the fuels burned and the chemical reactions that occur in the product as it is created.
Since concrete is used in such large quantities, the building industry has developed alternatives to regular concrete that are more sustainable and environmentally friendly.
Alternatives to Regular Concrete
Fly-ash concrete, available in many regions, offers an alternative to conventional concrete.
Fly-ash is a waste material – the inorganic residue – that remains after pulverized coal is burned in coal-burning power plants. Disposing of it can be a problem. Fortunately, the construction industry has discovered that fly-ash can produce a superior concrete with excellent finishing characteristics. It can replace up to 35 percent of the Portland cement found in conventional concrete mixes.
Each ton of fly-ash used to replace a ton of cement saves the equivalent of approximately one barrel of oil. By replacing cement, the ash produces less of the greenhouse gases that contribute to global warming. Coal fly-ash can also replace clay, sand, limestone and gravel, saving the energy costs of mining such materials.
While fly-ash concrete offers a “greener” alternative to regular concrete mixes, it may not be appropriate for every use. Check with a qualified building professional to see if it fits your application.
Recycled aggregates and lightweight aggregates can replace the usual sand and gravel in some concrete applications.
Recycled aggregate can consist of crushed concrete, brick, or crushed glass. Lightweight concrete is made by using expanded volcanic materials – pumice and perlite, for example – to replace some of the usual stone aggregate. Because these materials place less weight on structures, they are of particular value when used on either wood or lightweight steel floors. Volcanic materials also add some thermal insulation value to the concrete.
Health Problems with Concrete
Manufacturing Portland cement creates a great deal of carbon dioxide, a gas that contributes to global climate change. Once concrete is in place in a structure, however, it emits very little air pollution. Because it is often confined to the foundations and concealed structural elements of a building, concrete has minimal exposure to the building’s air.
Experts, however, are debating the possibility that concrete produces radon emissions; testing is underway. Other possible sources of indoor air pollution are concrete additives such as water reducers or super-plasticizers, which may produce odors and can cause skin and bronchial irritation in some people.
Coating concrete forms with lubricants makes it easier to remove them once the concrete has set. These form-release agents – sometimes made from diesel oil or other odorous petroleum oils – can produce emissions if they are used in interior applications. Alternatives made from wax or mineral oil instead of petroleum are available as substitutes.
New construction designs use foam blocks as the forms for poured concrete. The forms remain in place, adding energy efficiency and soundproofing to the wall.