Concrete may not seem like a suitable environment for life. However, bacteria actually live in concrete.
A new study led by the University of Delaware (USA) has examined this microbial ecosystem. They also investigated how microorganisms change over time and how we might use them in the future to monitor or repair defects.
Bacteria may have moved from the environment, seeping through cracks in the concrete.
The research team created 40 concrete columns divided into two groups: a standard mix prone to alkali-silica reaction (ASR) that degrades concrete, and a type made with fly ash that resists degradation. They were then left on a rooftop for about two years, with DNA samples taken every six weeks.
The researchers found that after removing laboratory contaminants, 50-60% of the bacteria in the samples had moved onto materials such as gravel and sand. Bacteria may have migrated from the environment, seeping through cracks in the concrete.
Overall, the diversity of bacteria in concrete decreases over time. However, this diversity slightly recovers in the summer. Nevertheless, many questions have arisen from the study.
“What are the bacteria eating? They might be consuming the remains of other bacteria. If there is nothing to eat, some of them may form spores or dormant cells and do nothing until it rains. Then, they eat as much as possible and go dormant again,” said Julie Maresca, the lead author of the study.
Although there is still much to learn about this tiny world, the potential impacts could be significant. The research team identified several types of bacteria that seem to be associated with degradation reactions, including: Arcobacter, Modestobacter, Salinicoccus, Rheinheimera, Lawsonella, and Bryobacter.
Theoretically, one day, monitoring these bacteria in concrete structures such as buildings and bridges could serve as an early warning system for collapse risks.
In the long term, the proliferation of bacteria could even play a positive role in repairing damage. Some may produce calcium carbonate that can seal cracks. Unfortunately, these bacteria currently do not survive long in concrete.
Scientists say that ongoing research is necessary. The next step is to analyze DNA from samples taken from concrete structures in the real world.
