A Concrete Response to Climate Change
Berkeley civil engineering student Cagla Meral wants to shrink the enormous carbon footprint created by cement.
Up to 5 percent of the globe’s climate-changing carbon dioxide emissions result from manufacturing the durable and immensely popular construction material known as Portland cement, says Meral, a 27-year-old doctoral student in the civil and environmental engineering department. Convinced that cement is far too useful and ubiquitous to ever be replaced, Meral is working to develop a greener form of it. Her research explores how CO2 can be “sequestered” or locked back into blended cement while maintaining strength and other important properties of cement-based materials like concrete.
“Even if we can reduce emissions by a small percentage, it will have a tremendous impact on the environment,” says Meral, who is conducting her research with CEE professor Claudia Ostertag. The key to her work is “supercritical CO2,” the term for carbon dioxide that is pressurized and exposed to moderate temperatures that transform it into an intriguing material with characteristics of both a liquid and a gas.
Preliminary tests have shown that supercritical CO2 infiltrates cement particles and chemically locks carbon dioxide back into the material. “It’s a completely new approach,” says Ostertag, who thinks the strategy holds great potential.
Each year, some 2.5 billion tons of cement are produced worldwide, creating an equivalent amount of CO2 emissions in the process. “Cement is such a good and low-impact material,” explains Meral. “That is why we use so much of it.” Explosive growth in developing countries has added to the urgency of this environmental issue, she adds.
In industry, supercritical CO2 processing has been used in drug and polymer manufacturing. Capable of dissolving, spreading and carrying materials, it can extract caffeine from coffee, remove stains from clothing and even embed flavor into potato chips.
“What we want to find out is how much CO2 can be put back without losing the strength of cement-based materials,” says Meral, who is also studying how such materials as nanosilica or polymeric microfibers might fortify cement.
“It’s just the beginning,” she says. “We have a lot of work to do.”
Already, however, the approach is attracting attention. In September, Meral was invited to present her research as the Western U.S. representative at the Young Persons’ World Lecture Competition. The annual event, held this year at the University of Florida, Gainesville, is sponsored by the Institute of Materials, Minerals and Mining.
Portland cement—a mixture of limestone and clay heated in kilns and later ground with gypsum—is the binding agent for gravel, sand and other components that make up concrete. During the cement manufacturing process, carbon dioxide is released during calcination, the key reaction to breakdown of calcium carbonate into calcium oxide and CO2, as well as from the energy production needed to reach temperatures of up to 1500°C.
In another facet of her work, Meral is investigating the idea of replacing some of the cement typically used in concrete with greater quantities of industrial byproducts like fly ash and slag that might otherwise wind up in landfills. Here again, supercritical CO2 processing might be helpful. In this case, Meral is investigating whether supercritical CO2 could eliminate heavy metals from fly ash and make it more chemically reactive.
“We have to make sure we’re not compromising any properties of cement,” Meral says. To test her research, Meral has been working with an Irish materials processing company equipped with a specialized steel pressure chamber that can treat the cement samples with supercritical CO2.
If all goes well, Meral envisions installing CO2 treatment units within cement factories to capture and recycle the emissions so they don’t escape into the air.
A native of Ankara, Turkey, Meral comes from a family of engineers. She began her Ph.D. studies at UC Berkeley in 2005 but traces her interest in cement back to her undergraduate studies with experts in the field at the Middle East Technical University in Ankara. Noting that the use of cement dates back to ancient Greek and Roman times, Meral thinks the material is here to stay. “There’s no replacement yet,” she says.