Concrete is the most widely used manufactured material on the planet and the second-most used material in the world, after water.
It’s a composite, with aggregate materials that can be found nearly everywhere. Buildings, roads, and bridge construction projects depend on concrete for its high compressive strength of about 3,000–7,000 psi.
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 either the entire agricultural industry or the heavily polluting aviation industry.
All of this is on the mind of civil engineering doctoral student Debalina Ghosh, studying under Professor John Ma, who teamed up with researchers at Oak Ridge National Laboratory and in collaboration with the Precast–Prestressed Concrete Institute.
Ghosh developed a new formula for precast concrete 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 instead of being poured in place—is more cost-effective and offers better quality control 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.
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 less tempering and 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.