John Ward is chairman of the American Coal Ash Association’s Government Relations Committee and executive director of the National Coal Transportation Association.

If you watch the video associated with this profile, you’ll see that John Ward knows a lot about coal fly ash, a waste product from burning coal for generating electricity. He’s been in the coal fly ash industry since 1998, and his son used to call him a “used coal salesman.”

Coal fly ash can be used to make concrete that’s stronger and less permeable than the industry-standard concrete made with portland cement alone while releasing 50-100 percent less greenhouse gasses. How can this be done? Ward describes the history of cement and the processes involved.

Ancient History

“Coal ash is actually characterized as a pozzolan, which comes from the Italian town Pozzoli on the banks of Mount Vesuvius,” explains Ward. “The Romans, over 2,000 years ago, were using material like this to make very durable concrete structures for a very long time. The reason the Pantheon’s dome is still standing today, 2000 years later, is it was made from volcanic ash, which is chemically very similar to the fly ash we use today.”

According to Ward, Roman technology and techniques were lost during the “Dark Ages,” and it was only about 200 years ago that portland cement was invented for making concrete. “The advantage to portland cement over natural pozzolans is not everybody has a volcano in their backyard, but there’s limestone [the key ingredient in portland cement] everywhere,” he adds.

Environmental Impact

A key drawback to creating portland cement, of course, is how much energy and greenhouse gasses are emitted during the process. Although fossil-fuel-based energy generation is the largest producer of such gasses, cement and concrete constitute about 8 percent of global greenhouse-gas emissions. And concrete is the second-most-used substance on Earth, trailing only water.

“To make a ton of portland cement, you emit a full ton of carbon dioxide,” says Ward. “About half of that emission comes from the energy used in the portland cement production process. The other half is just direct release of carbon dioxide from limestone as you calcine it.”

Ward notes that using existing fly ash or other “green cement” replacements instead of developing “clinker” created from limestone at approximately 3,000 degrees Fahrenheit is a significant step to decarbonizing the concrete industry. Although many coal plants are shutting down to be replaced by renewable energy sources that don’t produce greenhouse gasses, the United States still disposes of almost 40 million tons of fly ash every year. In addition, an estimated 2 to 4 billion tons of fly ash have been dumped into landfills through the years, and that’s a massive resource going forward. Ward also cites companies such as Eco Material Technologies, which are creating “green cement” that uses chemical reactions combined with supplementary cementitious materials—instead of heat—to create concrete that’s better and stronger than what’s currently available.

“The [greener cement] quiver has a whole bunch of arrows in it,” he adds. “They’re all going to be important.”

How It Works

When you use fly ash or green cement in concrete production, it has mechanical and chemical benefits that make the concrete more durable, according to Ward. On a mechanical level, fly ash particles are smaller and spherical—they’re like little ball bearings.

“When you add fly ash to that mix, it physically fills in the gaps,” he says.

In addition, using these materials in concrete creates a chemical reaction. When portland cement gets wet, it hydrates, creates a lot of heat and makes two things: calcium silica hydrate, which is the durable binder that holds the concrete together, and calcium hydroxide (i.e., lime), which does nothing for the concrete.

“For every hundred pounds of cement, I make 34 pounds of lime that’s not doing anything for me,” notes Ward. “When I add a supplementary cementitious material like fly ash to that mix, it reacts with the lime created by the portland cement hydration process and makes more of that durable binder—the glue that holds the concrete together. It makes for much lower permeability and a much more durable concrete moving forward.”

Advice for Engineers

Ward cites a study from the American Road and Transportation Builders Association that showed fly ash used in concrete saves more than $5.5 billion a year on federal road and bridge construction just because such concrete lasts longer.

“As the world starts moving toward great new ideas and the need to decarbonize concrete, you’ve got a proven strategy that’s already out there, and the stars are aligning to keep that material available,” he explains. “So keep fly ash in your specifications, keep looking for the new applications that are coming to the market that actually will enable you to use more of that material to create even greater decarbonization benefits.”