Fly ash, a byproduct of coal burning, can be used as an alternative or supplement to traditional Portland cement in concrete. It is considered environmentally friendly and can reduce contamination, but there are concerns about potential health risks and lack of regulation. Limits have been set on acceptable levels of toxins in fly ash cement.
Fly ash cement is a primary ingredient in some concretes that is often used as an alternative to Portland cement, which is a more traditional concrete base. The ash itself is a byproduct of coal burning, but once it forms into a cement, the ash usually binds in a way that neutralizes many of the chemicals and toxins that have made coal burning so controversial in recent years. As such, concrete is often thought of as a way to not only clean up the coal industry, but also leave fewer footprints and reduce the energy needed to form all kinds of concrete projects and structures. It is often advanced as a “green” concrete solution, although it is not without its critics. Fly ash is normally considered suitable for all kinds of concrete projects, but many places have set limits on how much it can be used at once pending further environmental impact reports. While many of the harmful chemicals associated with coal burning remain bound to the cement, it is unclear if or under what conditions they can begin to leach once again.
Basics of coal burning
When coal and waste are burned in power plants, they create a non-combustible byproduct called coal ash. Two distinct types of ash particles make up coal ash: bottom ash, which accumulates in the bottom of coal ovens, and fly ash, which gets caught in smokestacks as it “flies” up and away. The vast majority of non-combustible material consists of fly ash, which rises up in the fumes and gets stuck in the chimneys and chimney. This residue must be cleaned and disposed of regularly. One way this material can be reused is by combining it with other materials to create a concrete.
Uses in concrete
One of the most common uses for fly ash cement is as an additive to form concrete. Concrete is traditionally made with Portland cement, a powdered substance composed of ground clinker, calcium sulfate, and other minor additives. Clinker is a material usually made from limestone and minerals, which are crushed and ground together, then heated. Calcium sulfate is added and the clinker is ground into cement powder. The process requires a large amount of energy; it has a huge carbon footprint and accounts for about 7% to 8% of the carbon dioxide emitted each year.
Fly ash, which is largely made up of silicon dioxide and calcium oxide, can be used as a substitute for Portland cement or as a supplement to it. The materials that make up fly ash are pozzolanic, which means they can be used to bind – or cement – materials together. Pozzolanic materials generally add durability and strength to concrete.
Potential to reduce contamination
Concrete made with fly ash is often thought to be environmentally friendly. It binds the toxic chemicals found in fly ash in a way that should prevent them from contaminating natural resources. Using green concrete instead of or in addition to Portland cement uses less energy, requires less invasive mining, and reduces both resource consumption and CO2 emissions.
Surveys on the overall environmental impact
While not considered a hazardous material by most of the world’s regulatory agencies, including the United States Environmental Protection Agency (EPA), fly ash can include significant amounts of toxic materials. There have been incidents where fly ash has been leached into groundwater causing cancer, birth defects and other health problems. In many regions, there are no regulations or monitoring requirements for companies that create and dispose of fly ash. Ash that is not used to make products such as fly ash cement is often disposed of in abandoned landfills and mines.
It is currently unknown whether cement made from coal-burning by-products releases chemicals into the air or into the ground, and there is very little data on what could happen in the future when concrete made from it deteriorates and erodes. Several environmental agencies, such as the EPA, the Leadership in Energy and Environmental Design (LEED), and California’s Collaborative for High-Performance Schools (CHPS), have set limits on the acceptable levels of mercury in the fly ash used in fly ash cement. It is hoped that by limiting some of the more dangerous chemicals found in fly ash, potential future problems can be minimized.
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