University of Delaware (UD) (Newark, Delaware, USA) researchers recently conducted a study of bacterial communities living in concrete and found that they were not only able to live in such harsh habitats, but also thrive and even change.
Despite its hard, dry, and salty environment, concrete has been shown to sustain surface bacteria. For this reason, researchers want to understand how these microbial masses operate in order to understand the degradation of concrete structures, as well as their potential repair. The UD research team consisting of Julie Maresca, associate professor of civil and environmental engineering at the university, and her students have gone below the surface to study bacteria that was either included in the concrete mix or seeped in through cracks. Their study was recently published in the print journal of the American Society for Microbiology.
Previous research conducted by Maresca’s lab had detected small numbers of bacteria within concrete whose DNA could be extracted. What Maresca and her team discovered during their recent research is that time and weather can also affect bacterial communities as well. For instance, they learned that the diversity of bacteria declined over time but had some seasonal bounces. They also discovered that bacterial communities could provide early warning of alkali-silica reactions that degrade concrete and that certain bacteria have the potential to “biorepair” concrete despite previous research that showed such bacteria can only survive in concrete between one to two months.
In studying these concrete-based bacteria, Maresca’s team poured concrete samples into 40 cylinders, each about the size of a 1-liter bottle. They used two types of concrete mixes: a standard concrete mix prone to degradation from alkali-silica reactions and a mix with fly ash to reduce such reactions. In addition, control samples consisting of sterilized glass beads were used so that researchers could see how much contaminating DNA was introduced to the lab. From there, the cylinders were placed on the roof of UD’s Spencer Lab and DNA samples were collected about every six weeks over a two-year period before they were sequenced and analyzed.
When she first joined the UD faculty in 2011, Maresca hadn’t considered studying concrete. However, after conversations with a then-faculty member who studied bridges and the biorepair potential of concrete, she became intrigued.
“There was really nothing at all known about microbes in concrete,” says Maresca, a microbiologist who studies bacteria in natural and engineered environments. “It’s the most commonly used building material in the world, but we just don’t know anything about what lives in there. It’s in wet environments, sewer systems, bridge pilings and we know that microbes on surfaces can degrade it. But what’s in there and does it do anything? Can it tell us anything?”
In seeking answers to these questions, she and her team of researchers detected and excluded contaminants from animals, people, and the environment so that they could analyze bacteria associated with the concrete. In so doing, the researchers hoped “to get samples as pure as possible,” says Anders Kiledal, a doctoral student in Maresca’s lab and the first author on the paper.
The researchers were focused in determining how bacteria could exist in an inhospitable habitat like concrete. To that end, according to Maresca, the goal was to identify which bacteria indicate a normal concrete environment and which show that the concrete is damaged in some way. This information would be especially useful in determining where concrete infrastructure repairs and repairs need to be made.
“The earlier you can detect a problem, the more time you have to solve a problem before it becomes a real problem,” Maresca says. “And since we have all these roads and bridges at risk, we need a way to prioritize them. Which are in dire need and which aren’t?”
Before those issues can be resolved, more research is needed in order to determine a correlation between specific bacteria species and concrete damage.
“As far as we know, the microbes are not damaging the concrete,” Maresca says. “Microbes are not eating the foundations. We’re hoping to use them for information and potentially to help with repair.”
Source: UDaily, www.udel.edu.