Introduction
There is an urgent problem at the heart of the construction industry. Even in this age of cutting-edge compounds and technological advances, the most common building material worldwide has barely changed over the past century: cement. It is versatile and inexpensive, but that convenience comes at a steep environmental cost. Each year, we produce over 4 billion metric tons of cement, and along with it, 1.5 billion tons of carbon dioxide, about 8% of total global carbon emissions. To move toward a net-zero emissions world and avoid the worst effects of climate change, we need to change how we make cement.
Greg Rorrer, professor of chemical engineering, has an idea that could help. Rorrer and his lab are investigating the potential of a tiny marine creature that, given enough time and the right conditions, can build mountains.
"Photosynthetic cement"
Coccolithophores are single-celled plankton found in every ocean on Earth. Using sunlight, carbon dioxide, and the dissolved minerals in seawater, they build calcium carbonate shells. When they die, these shells settle to the ocean floor and form an important natural carbon sink. Over time, they can accumulate into massive chalk deposits like the famous White Cliffs of Dover, which rise over 300 feet above the English Channel.
Rorrer looks to those ancient cliffs for a possible solution to our modern problems. Could these microscopic creatures and their carbon-rich shells be used to build a new kind of cement – one with the strength and durability of traditional cement without the carbon cost?
He calls the concept “photosynthetic cement,” using nature’s own evolved biochemistry rather than synthetic processes to build a durable building material that also sequesters carbon from water and air. If we can learn to harness these shell-building coccolithophores, they could supply cement without emissions and instead actually remove carbon dioxide from the surrounding water. If it can work at scale, it is a promising win-win for construction and the climate. Rorrer sees the greatest potential in large-scale, long-term civil engineering projects, such as seawalls, rather than in bricks or other small consumer cement products.
“It's a biological self-assembly system,” Rorrer said. “You’ve got to be patient, though. These processes aren't super-fast, but over time, they could build up to a big scale if you template it properly.”
Scaling up biocementation
Biocementation, the use of living organisms to create binding agents like cement, is not new. But most of that work is done by bacteria, which have limits that Rorrer hopes his coccolithophores can exceed. Biocementing bacteria can be useful for filling in cracks in existing cement or binding soil particles together. Coccolithophores can operate at a much larger scale and do so without the artificial inputs, like urea, that bacteria require. In sunlit seawater, they already have everything they need to start building.
The concept is a natural extension of Rorrer’s ongoing work on the carbon sequestration potential of marine organisms. One of Rorrer’s doctoral students, Arthur Veremchuk, is working on solutions to scale up production of the marine red seaweed Agarophyton vermiculophyllum, and intensify its dissolved carbon uptake from seawater, as part of a marine-based carbon dioxide removal effort supported by U.S. government agencies.
Rorrer has also worked extensively with diatoms, microscopic marine algae that take up dissolved silicon in seawater to make intricate silica cell walls through a process called biomineralization. These nanostructured solid materials have many advanced material applications. The coccolithophore marine algae in his new work also use biomineralization to convert dissolved carbon dioxide and calcium in seawater to solid calcium carbonate.
In 2022, Rorrer was a to Austria to develop this concept and advance his work on sustainable processes.
Last December, Rorrer $50,000 from the productivity software company Boomerang, which issues annual grants to U.S.-based academic labs for early-stage, high-potential carbon capture R&D. He hopes the grant will serve as the foundation for supporting a graduate student and moving the photosynthetic cement project from concept to a more concrete reality.
