Building Sustainability: Green Concrete


Bend native and OSU engineering student Kelsea Schwing is developing a use for coal-plant fly ash that saves energy and reduces greenhouse gas emissions. (Photo: Karl Maasdam)

October 28, 2009

Student takes a hard look at recycling fly ash

By Lee Sherman

Photo by Karl Maasdam

In Brief

Coal plant fly ash can improve concrete durability and reduce greenhouse gas emissions in the concrete industry, but most fly ash is dumped in landfills. Jason Ideker, assistant professor, and Kelsea Schwing, master’s student, in the College of Engineering are testing mixtures of fly ash in concrete recipes. Ideker is among the more than 70 OSU faculty affiliated with Oregon BEST (Built Environment and Sustainable Technologies), representing expertise in
new materials, energy systems, transparent electronics, wood chemistry and other topics. 

The concrete testing lab where Kelsea Schwing runs her experiments seems an unlikely place for saving the planet. Tucked away on a narrow alley between two engineering buildings, the vault-like space feels more like a machine shop than an environmental research facility. The steel-toed work boots Schwing wears add to the industrial aura. She laughs at the lack of fashion in the functional footwear.

"My friends think it's pretty funny to see me in these giant boots and lab coat," says the graduate student in the Oregon State University School of Construction and Civil Engineering.

Not that her pals haven't seen her in serious shoes before. Her well-worn Nevado hiking boots have taken her many miles through the mountains near her hometown of Bend, where her deep love of the outdoors took hold early and hung on tight.

"I explored the heck out of the eastern side of the Cascades," Schwing reports. "I love being outside."

Pounding Pavement

That passion for the natural world - along with a knack for math and physics - is how she wound up last summer wielding a hammer to pulverize blocks of concrete for a study on ways to make the material greener. "It's a workout," she says, grinning.

Her study centers on fly ash, a byproduct of coal-burning power plants. Engineers have long known that fly ash - a glass-like powder containing silica, alumina, iron and calcium - makes an excellent addition to concrete, which typically is a blend of aggregate (sand and rocks), water and Portland cement.  When mixed with cement, fly ash adds strength, durability and workability.

"Fly ash has good binding characteristics," Schwing explains. "It helps mitigate a problem called alkali-silica reaction (ASR). ASR causes the concrete to expand and crack."

As an added benefit, supplementing cement with fly ash reduces greenhouse gasses in the atmosphere. That's because cement manufacturing emits 5 percent of the world's CO2 today. Fly ash as a cement substitute could cut 14 million tons of carbon emissions annually, the American Coal Ash Association estimates. Another environmental bonus: Using fly ash in construction keeps it out of landfills, where millions of tons currently are dumped each year.

Hard Facts

But unknowns about fly ash's effects on the chemistry and structure of concrete have prevented wider use. To help fill the knowledge gap, Schwing and OSU Professor Jason Ideker - a specialist in innovative, high-performance construction materials - are investigating the chemical composition of fly ash in concrete and its implications for durability over time. Their study is supported by a grant from the Naval Facilities Engineering Service Center, Department of Defense.

In her steel-toed boots, Schwing mixes Portland cement with water and then adds differing levels and types of ash. Once the mixtures solidify, she crushes the paste samples and places them into a custom-made steel die called a pore press. Next she loads the die into a brand-new Forney FX700 hydraulic compression machine. "This is our baby," she says proudly, pointing at a shiny blue-and-orange machine about the size of a suburban refrigerator, where 250,000 pounds of pressure will squeeze the liquid from the paste. Afterward, she will chemically analyze each sample for its content of silica, sodium, calcium, potassium and trace minerals. Other variables under investigation are temperature and duration in the curing process.

Curious for Sustainability

"It's Kelsea's drive to dig deeper and discover that really sets her apart," Ideker says. "She truly understands the bigger meaning behind sustainability - that engineering new materials to be sustainable goes far beyond just incorporating recycled materials or developing a new manufacturing technique. It's about the entire process; a life-cycle assessment."

From her lab hidden away on the fringe of campus, Schwing can see the bright edge of a greener future.

"Right now, the creation of concrete is detrimental to the environment," she notes. "I'm OK with development. We're obviously a growing population. But we need to find better strategies to support that growth."

Download article as PDF