Debalina Ghosh, a civil engineering doctoral student in the University of Tennessee, Knoxville’s Tickle College of Engineering, teamed up with researchers at Oak Ridge National Laboratory in collaboration with the Precast-Prestressed Concrete Institute to create a greener, faster-drying concrete.
“Growing up in India, concrete is the first thing that comes into my mind when I think about construction,” she said. “But unlike other construction materials like timber and steel, researchers have not yet found an easy way to reuse or recycle concrete. So developing green concrete is the only way to make sure we can reap its advantage for another hundred years.”
Concrete is the most widely used manufactured material on the planet, and the second most-used material in the world after water.
However, concrete accounts for a large percentage of global carbon dioxide emissions due to the way it is made. The four billion tons of concrete made each year is responsible for about 8 percent of the world’s carbon dioxide emissions—more than the entire agricultural industry or the heavily polluting aviation industry.
Ghosh developed a new concrete formula with two main features important to the industry: a quicker drying time and a reduced carbon footprint.
She is still trying to determine the exact carbon footprint of her mix.
“I am working on a life cycle assessment of this concrete,” she said. “This assessment considers the raw material use and energy consumption throughout the manufacturing process and provides a comparative impact on environment.”
Precast concrete—manufactured into a structure like a wall or slab and transported to the construction site—is more cost-effective and offers better quality control and sustainability than cast-in-place concrete. Ghosh’s concrete has demonstrated qualities that could double production capacity for the precast industry because it gains adequate strength in six hours, compared to several days needed for comparable concrete.
Additionally, Ghosh’s formula uses calcium sulfo-aluminate (CSA) cement, which emits 62 percent less carbon than the industry standard, which is Portland cement. This requires lower temperatures and less grinding during manufacturing.
The drying and hardening of concrete occur through a chemical reaction that emits carbon dioxide, and CSA has a faster reaction in an early stage of drying. Reducing the drying time also reduces the amount of labor needed, allowing for quicker placement.
Ghosh’s concrete contains slag, a byproduct material, to replace 60 percent of traditional Portland cement, further reducing the overall impact on the environment.
Additionally, Ghosh evaluated commercially available components—including steel, glass, and carbon fibers—and came up with a self-compacting mix that maintains its workability for 30 minutes. She chose to add steel fibers to increase the flexibility of the concrete, giving it greater bending strength and therefore making it more durable in situations where most concrete can snap.
“Having ORNL and the Joint Institute for Advanced Materials means we have access to advanced instruments if needed. I got to get involved with a lot of multidisciplinary research and industry partnership because of the UT–ORNL collaboration,” Ghosh said. “Right now we are studying how we can replace cement with industrial byproducts like slag without affecting the concrete performance. In the future, we will try to use local byproduct and recycled products in place of cement.”
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