An industry perspective
According to the latest survey by the American Coal Ash Association (ACAA), approximately 38 million tons of fly ash were produced in 2017 and about 24 million tons of this amount were beneficially reused in a variety of applications—14 million tons of which was used in concrete. The balance of the fly ash produced—14 million tons—was disposed in landfills.
Why are millions of tons of fly ash being disposed of every year when the market is clearly asking for more? There are two primary reasons. The first is that power plants run year-round while the demand for concrete-grade fly ash tends to be seasonal following construction cycles. During slow construction periods, power plants fill up their storage capacity and the remainder goes to landfills. The second reason is the injection of activated carbon into the combustion steam to comply with the Clean Air Act, which makes the fly ash unusable in concrete.
The ACAA estimates that the gap between demand and supply of concrete-grade fly ash is about 25% nationally. In reality, availability is a regional issue and the gap between demand and supply is much greater in some areas. In large part, shortages are being driven by the retirement and capacity reductions of coal-fired power plants and the move toward natural gas and renewable energy sources.
According to Tom Adams, executive director of the ACAA, varying degrees of supply exist across the country. If you are in the central U.S., you are probably not having many problems with sourcing fly ash. If you are on the east or west coasts where there are decreasing levels of coal-fueled generation, then you are in an ash-starved situation.
Initiatives to boost supply
Decreasing levels of coal-fueled generation mean that growing proportions of fly ash are likely to be harvested from landfills to meet regional supply demands.
“Our industry is making significant strides in developing beneficiation technologies for utilizing the fly ash disposed of annually,” said Adams. “These technologies can remove excess carbon from fly ash, passivate the effects of carbon that remains in ash, and mitigate the effects of emissions control technologies on the ash. Strategies to harvest previously disposed fly ash are also are being deployed in various markets to create consistent, reliable supplies at a local level.”
There is also a flurry of activity by specifiers that will help increase the supply of fly ash and other SCMs for achieving concrete durability specifications. This includes a change in ASTM C 618 to classify fly ash by calcium oxide content rather than the sum of the oxides. Going forward, fly ash with a calcium oxide content of 18% or less will be classified as Class F and above 18% as Class C. The American Association of State Highway and Transportation Officials (AASHTO) approved this change in their M 295 specification.
- a new Class B on the use of milled bottom ash in concrete
- blending of in-spec and out-of-spec fly ash
- blending of Class C and Class F fly ash
- blending of fly ash, natural pozzolans, and other materials to create a new SCM
In addition, natural pozzolan producers are looking to break away from ASTM C 618 and have their own specification, and ground-glass producers are close to gaining approval for a new a specification.
A reliable, trusted resource
While the availability of fly ash varies across the U.S., trends indicate less volume and a more unpredictable supply in the future. If you are seeing spot shortages in your area, now is an opportune time to examine reliable sources of fly ash, as well as alternative SCMs to serve as a replacement.
With an expansive terminal network and world-class logistics system, LafargeHolcim has the reach and resources to reliably supply all kinds of SCMs to the market, including fly ash, slag cement, silica fume, blended cements, and different types of natural pozzolans. We have a rigorous quality assurance program, strong product standards, and a dedicated fly ash compliance and analytical testing center in Chicago, which is part of our nationwide network of strategically located quality-control laboratories.
Our well-established fly ash program is highly regarded by our utility partners, and we are strongly committed to looking into new techniques for boosting future supply. Whether it’s a simple flatwork job where fly ash can provide economic benefits or it’s a complex project to meet demanding performance specifications, we can provide you with fly ash technical advice and applications know-how to help you tailor the optimum concrete mix solution.
Contact your local LafargeHolcim sales representative to learn more about how we can assist you with your fly ash inventory planning. In our next newsletter story, we will review the features and benefits of slag cement and how you can use this widely used SCM to improve performance of concrete mixes.