New Use for Coal Ash

Coal ash is a byproduct of burning coal to generate electricity and is often stored in ponds near power plants. But when coal ash spilled out of a Duke Energy storage pond into the Dan River, it focused attention on the problem of storing coal ash. While some is currently used in concrete, NC A&T Researchers are finding a new use for coal ash as a super strong building material.

GREENSBORO — What’s happening outside a lab at North Carolina A&T State University’s Center for Composite Materials Research may be part of the solution to the state and the nation’s coal ash problem.

“This material stands out as superior,” explains Dr. Robert Sadler, a professor in the Center for Composite Materials Research, as lab technicians aim a blow torch at a panel that is held upright in a metal framework. A metal wall encloses the entire system and everything is sitting atop a wheeled cart.

The technician turns the valve on a tank of propane. You can hear the gas flow. He flicks an igniter in front of the torch and the flame ignites, blasting the center of the panel with a 2,000 degree flame.

A white ring grows in the center of the panel. It is obviously hot and getting hotter. However sensors on the back of the panel report the temperature is just over 100 degrees.  

Before the test, Dr. Sadler explained the panel that was being tested is called Eco-Core, which features an unexpected primary ingredient.

“Eco-Core is 95% fly ash that is held together with a liquid polymer resin, or binding material. The paste is then poured into a mold where it is hot pressed into the desired shape."

“I think this is miracle material,” explains Dr Sadler. “When we first started working on this for the Navy, the main objective was to create a material that was fire resistant. But we found out this stuff is strong, it resists sea and fresh water, and it has a compressive strength of 4000 psi.”

That’s pounds per square inch, which means you could stand up a car on a square inch of Eco-Core and you would not crush it.

Coal ash is the same material that poured out of the storage pond at a Duke Energy power plant and into the Dan River in February. Coal-fired powered plants produce two forms of ash. There’s heavy bottom ash, which stays in the furnace, and lighter fly ash, which is a refined component of coal ash and is captured in the smokestack. The two types of ash are dumped into storage ponds at power plants across North Carolina and the nation.

Ironically, the engineers decided to experiment with using fly ash as a building material as they were driving past a power plant on the way back from meeting with the Navy.

“We were discussing possible materials to use in the process when I happened to see the power plant in the distance and I said what about fly ash,” says Dr. Kunigal Shivakumar, Director of the Center for Composite Materials Research. “It has silica, because it is primarily ceramic, and it has hollow bubbles, which would be nice.”

“So that’s it,” Dr. Shivakumar adds as he holds up two tiny bottles with the ingredients of Eco-Core. “Eco-Core is made of two materials, the fly ash, which is very lightweight and has the hollow ceramic bubbles, and a binder.”

It turns out the little micro amounts of trapped air in those hollow bubbles that make up the fly ash are very important for heat and fire resistance.

“The grade of fly ash we use is little hollow spheres, and these range from 100-300 microns,” says Dr. Sadler, as he pours a small amount of fly ash into his palm. You can just barely discern the spheres. “We’re interested in the hollow spheres because we want thermal insulation and lightweight, and the spheres are what provide that. If it was solid, it wouldn’t do the things we want it to do.”

At the microscopic level, the recipe for creating Eco-Core calls for coating the tiny bubbles of fly ash with as thin a layer of polymer as possible. In addition, the polymer is the only place where the bubbles touch. And that’s what gives Eco-Core all of its properties, because there is as much trapped air as possible in the material, and it fits tightly together.

“It’s kind of like pushing ball bearings together,” explains. Dr. Shivakumar.

Fly ash is almost immune to fire because of the intense heat of power production. Researchers boosted the fire resistance even more, up to Navy standards, by heating Eco-Core in an oven.

The engineers spent almost a decade working on the Navy project and perfecting the properties of Eco-Core. The resulting material is useful as the interior part of a wall or ship’s hull. But after testing Eco-Core every way imaginable, its creators believe the uses for Eco-Core are almost limitless.
“There’s a big market for this kind of material out there, somewhere," says Dr. Sadler. "There has got to be, because we have not found anything this material cannot do, and there is plenty of fly ash to make it with.”

But the trouble is, the engineering team can only produce a small amount of Eco-Core in their lab. They’re looking for a manufacturing expert who can figure out how to produce it commercially, on a large scale.

The team admits it won’t solve the coal ash problem, but it will help.

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