Every time you drive over a stretch of the Illinois highway system, there's a good chance you're driving over waste from a coal plant. Yes, that sounds odd, but it's true; that's documented. According to the Illinois Department of Transportation's 2011 Physical Research Report No. 158, Illinois used 38,881 tons of fly ash in road construction in 2009 alone, at a cost of about $1.75 million to the department. That's a state agency finding a way to use a waste byproduct of a power plant instead of sending it to a landfill or mining new material to make cement.
What fly ash actually is, and why it ends up in your commute
Fly ash is not glamorous. It's the by-product of burning coal in coal-fired power plants. This finely divided powder is captured in smokestacks to prevent it from entering the atmosphere. According to IDOT, fly ash is divided into two classes based on the coal source it comes from: Class F fly ash is produced by burning anthracite or bituminous coal, while Class C fly ash comes from lignite or subbituminous coal. Class C fly ash is self-cementing, while Class F fly ash needs to react with lime to create a pozzolanic reaction. This means that when we add fly ash to concrete, it reduces the amount of Portland cement we need to use in the process of making concrete. Portland cement production is energy intensive, which is why reducing the amount needed is an economically attractive option for concrete producers.
What that 1.75 million dollars actually bought
At first glance, spending 1.75 million dollars on a power plant byproduct seems an odd line item. However, the IDOT report gives context for why it did so. The agency explains that using fly ash as a supplementary cementitious material in 2009 helped reduce the amount of landfill space needed and cut back on greenhouse gas emissions associated with producing new cement. In short, that spending was not an act of charity towards a coal plant. IDOT was using a material that could, in part, do the job of cement and cut back on its use of a resource that is intensive to produce.
