How Coal Fly Ash Is Reducing CO2 Emissions and Improving Concrete
Concrete is the most widely used construction material in the world. One of the key ingredients in concrete is Portland cement. The American Concrete Institute explains that Portland cement is a product obtained by pulverizing material consisting of hydraulic calcium silicates to which some calcium sulfate has usually been provided as an interground addition. When first made and used in the early 19th century in England, it was termed Portland cement because its hydration product resembled a building stone from the Isle of Portland off the British coast.
Without going into detail, it suffices to say that a great deal of energy is required to produce Portland cement. The chemical and thermal combustion processes involved in its production are a large source of carbon dioxide (CO2) emissions. According to Chatham House, a UK-based think tank, more than 4 billion tonnes of cement are produced each year, accounting for about 8% of global CO2 emissions.
However, fly ash from coal-fired power plants is a suitable substitute for a portion of the Portland cement used in most concrete mixtures. In fact, substituting fly ash for 20% to 25% of the Portland cement used in concrete mixtures has been proven to enhance the strength, impermeability, and durability of the final product. Therefore, using fly ash for this purpose rather than placing it in landfills or impoundments near coal power plants not only reduces waste management at sites, but also reduces CO2 emissions and improves concrete performance.
Rob McNally, Chief Growth Officer and executive vice president with Eco Material Technologies, explained as a guest on The POWER Podcast that the ready-mix concrete industry has been reaping the benefits of using fly ash for years. “In terms of economics, fly ash was typically cheaper than Portland cement. It also has beneficial properties that typically makes it stronger long term and reduces permeability, which keeps water out of the concrete mixture and helps concrete to last longer. And, then, it’s also environmentally friendly, because they’re using what is a waste product as opposed to more Portland cement—and Portland cement is highly CO2 intensive. For every tonne of Portland cement produced, it’s almost a tonne of CO2 that’s introduced into the atmosphere. So, they have seen those benefits for years with the use of fresh fly ash,” McNally said.
However, as climate change concerns have grown, many power companies have come under pressure to retire coal-fired power plants. As plants are retired, fresh fly ash has become less and less available. “The availability of fresh fly ash is declining,” said McNally. “In some places—many places actually—around the country, replacement rates that used to be 20% of Portland cement was replaced by fly ash are now down in single digits. But that’s a reflection of fly ash availability.”
Eco Material Technologies, which claims to be the leading producer of sustainable cementitious materials in the U.S., has a solution, however. It has developed a fly ash harvesting process and has nine fly ash harvesting plants in operation or under development to harvest millions of tons of landfilled ash from coal power plants. Locations include sites in Arizona, Georgia, North Dakota, Oregon, and Texas.
One recently announced project is at Georgia Power’s Plant Branch, a coal-fired station that retired in 2015. Under the agreement, Eco Material will harvest approximately 600,000 tons of landfilled ash per year from the plant in Putnam County, Georgia. The effort is expected to remove and beneficially use more than 8 million tons of fly ash over a 15-year term.
The Branch project is being facilitated with assistance from the Putnam Development Authority (PDA), which works to promote investment in Putnam County and Eatonton, the county seat. The PDA has provided incentives to Eco Material to encourage fast track development of the Branch project.
“The Putnam Development Authority is proud to be able to assist in adaptive reuse of the Plant Branch site and resources by Eco Material,” Walter C. Rocker III, chairman of PDA, said in a statement. “Eco Material’s plan to work with Georgia Power to bring new, high-quality jobs and significant investment to our community represents a turning point toward reinvigorating the former Plant Branch site as an economic driver for our community.”
Yet, incentives are not necessary for harvesting projects to be financially viable. “For the most part, there’s an economic benefit both to Eco Material, as well as the power company, to beneficially use the fly ash or bottom ash that they’ve impounded,” McNally said.
The Plant Branch project is the second Eco Material fly ash harvesting plant sited in Georgia. The company is doing similar work at Plant Bowen, another Georgia Power facility. Construction on that project is underway and harvesting is expected to begin next year.
“There are billions—with a b—of tons of impounded fly ash around the country, so we have many, many years of supply,” McNally said. Still, Eco Material is not resting its business solely on fly ash harvesting, or marketing fresh fly ash, which it has also done for years. “The other piece where we will fill the gap that fresh fly ash leaves behind is with the green cement products. Because with those, we’re able to use natural pozzolans, like volcanic ash, and process those and replace 50% plus of Portland cement in concrete mixes. So, we think there’s an answer for the decline in fly ash and that’s where the next leg of our business is taking.”
To hear the full interview with McNally, which contains more about plant workforce requirements, benefits power companies reap, and more, listen to The POWER Podcast. Click on the SoundCloud player below to listen in your browser now or use the following links to reach the show page on your favorite podcast platform:
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—Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).