The Concrete Microbiome
Microbial communities may predict
the integrity of concrete
Actinobacteria, one of the types of bacteria found in and on concrete.
As many may know, the gut microbiome has been a hot topic in microbiology in recent years. The National Institute of Health (NIH) has launched a Human Microbiome Project to better characterize them using metagenomics technologies. While we may have heard of the human microbiome or gut microbiome, another type of microbiome that is now being studied has materials engineering implications. It is the concrete microbiome. Yes, you read that right! – Concrete microbiome as in the concrete commonly used as a building material.
It has been recently discovered that concrete is actually home to a fascinating microbial community. Dr. Julie Maresca, an associate professor in the College of Engineering at University of Delaware, is a pioneer in this area of research. Recently, Dr. Maresca discussed the role of concrete microbiome in the June 2018 American Society of Microbiology (ASM) microTalk podcast titled “Content in Cement.”
In this microTalk podcast, Dr. Maresca explains how the environment created by concrete is a unique place for microorganisms to thrive as it has a very hard, dry, salty, and high pH environment with an abundance of cations such as magnesium, calcium, aluminum, and silica. When concrete is freshly poured, the pH is around 12.5, which is about the same pH of bleach. As we know, bleach has bactericidal properties. Nonetheless, even with this incredibly harsh and non-nutritious environment, there are over 100 species of bacteria that thrive in and on concrete. Some of these bacteria are alive and culturable in a laboratory setting, while most others are dormant. Through DNA extraction directly from concrete, it has been discovered that the bacteria that dominate these concrete microbial communities are usually Actinobacteria and Alphaproteobacteria, which are well adapted to dry, salty, alkaline environments.
Dr. Maresca’s research involves making test cylinders of concrete that are left in the external environment to be exposed to normal weather conditions and investigating these cylinders for changes in microbial communities.
|Concrete cylinders placed on the roof of Dr. Maresca’s research laboratory to study the effects of weathering|
on the concrete microbiome.
It was found that the same microbial communities growing on concrete are able to grow within concrete as well and may be at least partly responsible for the degradation of concrete. Furthermore, Dr. Maresca’s research suggests that the microbiome fluctuates as concrete degrades, especially in concrete that is susceptible to the alkali-silica reaction, also known as ASR, which is colloquially termed “concrete cancer.” It is associated with symptoms that include swelling and often occurs when concrete has been exposed to frequent moisture. Concrete cancer or ASR appears as a cracked-like appearance.
|Physical appearance of “concrete cancer,” or ASR, demonstrated by the cracked pattern.|
This research will allow for further insight into the identification of bioindicators that suggest concrete weakness before the damage becomes apparent. If we can use the fluctuating microbial communities in concrete as early warning signals of potential concrete damage, weakness, or decreased integrity, engineers can better anticipate structural deterioration of buildings without having to wait for visible signs of structure damage.
Technical Services Department