In many ways, fly ash concrete is the ultimate paradox. Fly ash comes from one of the biggest sources of air pollution and carbon dioxide emissions on Earth, and yet it's considered to be a green material. What's the deal? The main reason that fly ash is considered to be eco-friendly when used in construction is because it's a recycled material. If power companies are going to burn coal and produce fly ash anyway, it makes sense to put it to good use, especially if it can save money and energy in the construction sector.
Making cement from scratch is a very energy-intensive process. Conservative estimates say that concrete production contributes between 5 and 8 percent of greenhouse gas emissions worldwide, but it could be even higher. We currently produce more than 2.6 billion tons of Portland cement per year, and that number figures to increase as populations climb, unless some greener option emerges to supersede it.
That's where fly ash concrete comes in. Fly ash concrete has the ability to simultaneously curb global carbon emissions while developing better and more durable infrastructure that wouldn't need to be rebuilt as often. In fact, one study even noted that fly ash bricks also have the ability to store carbon dioxide from the environment, adding another green benefit [source: Liu].
The U.S. Green Building Council seems to agree about fly ash's green cred; the preeminent arbiter of all matters relating to green building issues, Leadership in Energy and Environmental Design (LEED), credits substituting fly ash concrete for at least 40 percent of ordinary Portland cement [source: Portland Cement Association]. A life-cycle assessment, which is an analysis of every stage of production from cradle to grave, shows that replacing ordinary Portland cement with fly ash concrete can decrease carbon emissions by as much as 90 percent. That's largely because fly ash is a recycled material, and replacing new Portland cement with fly ash prevents unnecessary carbon dioxide emissions, and because it's more durable it doesn't need to be torn up and replaced as often [source: Salton].