Cement technology is not set in stone.
Civil and environmental engineers at UT are researching how to make better living cement. This biocement is capable of healing its own cracks, according to a study published in the Journal of Industrial Microbiology and Biotechnology. The cement is made from the same materials as standard cement with the addition of the bacteria Sporosarcina pasteurii, which increases the biocement’s durability and gives it self-healing properties.
Scientists typically make biocement by replacing mixing water with bacteria and yeast, which feeds the bacteria. This biocement usually takes longer to harden, which delays the construction process. The UT researchers replaced the yeast with a combination of meat extract and sodium acetate, which doesn’t slow the hardening process, according to the study.
The addition of microbial organisms strengthen cement and other construction materials through a process called microbial-induced calcium carbonate precipitation. The bacteria fill cracks in concrete with a material similar to limestone.
“The idea is that once you put these bugs inside concrete and you supply the right nutrients, it should be able to be a living system throughout the lifespan of the concrete’s life,” said co-author Raissa Ferron, an assistant professor in the department of civil, architectural and environmental engineering. “These bugs are strong, they know what they’re doing and they are able to survive.”
Scientists insert actively growing bacterial cells directly into the cement mix. In the study, bacteria survived for nearly a year in the concrete and some of the cells went into a dormant state. The researchers did not investigate what the cells used as long-term carbon and energy sources, according to co-author Mary Jo Kirisits, an associate professor in the department of civil, architectural and environmental engineering.
Biocement preempts instability caused by cracks in standard cement, even after workers have repaired them, according to Ferron.
“By the time you see the crack, it’s probably at the point that it may start causing damage to your structure,” Ferron said. “But if you have a concrete system that has even a nanocrack form and is able to fill that crack with calcium carbonate, you’re increasing the durability of your concrete.”
Ferron was fascinated by biocement when she arrived at UT in 2009. She shared this interest with Kirisits, who then joined as the other author of the study.
“I contacted Dr. Kirisits and told her about this idea that I wanted to look into developing concrete that can heal itself,” Ferron said. “She agreed to sign off on this crazy project, and I think the rest is history.”
Sarah Williams, who also authored the study, studied ways to use biocement to repair cracks in older concrete for her graduate thesis. Williams used biocement with sand, which acted as a bonding material and filled cracks in historical structures in Europe, where cultural buildings and monuments are much older.
Biocement is still a novel technology with a lot of potential, according to Ferron. Engineers need to conduct more research before it can be used on a large scale.
“I can count probably on two hands the number of groups around the world that are doing this work,” Ferron said. “It’s exciting to be at the cutting edge of infrastructure material and technology.”