During a tour of the outskirts of Tanzania when she was a graduate student, Raissa Ferron was struck by how many homes were made primarily out of dried soil, sometimes referred to as mud huts. It made her think about the durability of these homes, and what it is like for the people living inside.
She learned that not only are many of these earthen homes unsafe in harsh weather conditions, but there are also deep social and economic costs to rebuild homes that wash away from heavy rains and flooding.
Homes made from dried soil provide basic shelter for many people in rural parts of Africa, where there is a long history of homes constructed using earthen materials and where locals have passed down their expertise in these building methods for generations. Around the world, roughly 30 percent of the human population lives in homes made from earthen materials, such as soil, clay and adobe. Some types of earthen housing are also gaining interest in industrialized countries because of the environmental and health benefits of using natural materials.
“I’m interested in seeing if I can help people and communities live better lives,” said Ferron, an assistant professor in the Department of Civil, Architectural and Environmental Engineering. “We need to improve the water resistance of earthen masonry and increase its strength to make these homes safer and more permanent.”
But what began in Tanzania as a desire to build stronger earthen materials eventually became something very different upon her return to school, especially after meeting a visiting scholar from India who was working on “self-healing” materials, specifically adding bacteria to concrete.
When added to concrete, the bacteria, which she calls “probiotics for concrete,” secrete calcium carbonate, creating a strong substance similar to limestone. As cracks occur over time in the concrete, the bacteria release the limestone substance and fill in the holes and cracks.
It can be thought of in terms of sandstone, Ferron said, “when you go to the beach and there are particles of sand that have started to bind together, part of that is the bacteria excreting various minerals and binding the sand particles together.”
Since she arrived at the Cockrell School of Engineering a few years ago, Ferron’s self-healing research has gained momentum. She’s enlisted fellow engineering professor Mary Jo Kiristis, who has a background in microbiology.
Together, Ferron and Kiristis are addressing one of the challenges of the research — making sure that the bacteria has the proper nutrients to survive so its healing qualities can be activated. The nutrients for bacteria can be cost prohibitive, so researchers like Ferron are working to identify cheaper methods of keeping the bacteria alive. She and Kiristis published an article on their bacteria growth method earlier this year in the Journal of Industrial Microbiology and Biotechnology.
Ferron hopes to eventually take the knowledge she gains from her work on self-healing concrete and apply it to her earthen homes project so that people can live in safer, stronger and earth-friendly homes.
The hope is that one day these tough, tiny organisms can self-heal homes as well as concrete. She believes bacteria could be used to improve the homes’ strength, reducing the amount of water that might come inside them and permanently damage their structures.
“The great thing about bacteria is that they’re very resilient; they’ve been around for thousands and thousands of years,” Ferron said.
