What is Microbially Induced Corrosion (MIC) of Concrete?

In a previous blog, “What are the Main Causes of Manhole Deterioration”, we highlighted various problem areas existing in manhole structures, and we mentioned Microbially induced corrosion (MIC) in passing. So, what is MIC and where does it come from?

Microbially induced corrosion (MIC) can be defined as the process by which live microorganisms cause changes in the physical properties of a structural material. You may have also heard it referred to as microbially influenced corrosion, biocorrosion, or just microbial corrosion.

In the case of concrete, a common material of construction for wastewater manholes, lift stations, and treatment plant structures, MIC can reduce lifespan by as much as 50%.

Sulfate naturally occurs in drinking water and so it eventually ends up in the wastewater stream. Those sulfates are converted to hydrogen sulfide gas (H₂S) by sulfate-reducing bacteria. This process starts in the sewage flow channel. The surface pH of new (but naturally porous) concrete is approximately 12, which is reduced to approximately 9 by the H₂S gas environment.

The H₂S gas environment and reduced surface pH allow bacteria to grow on the surface of the concrete. These bacteria produce sulfur and polythionic acid, further reducing the surface pH. At this point, the concrete corrosion process begins.

Finally, continued biological activity produces sulfuric acid (H₂SO₄) further reducing the surface pH to approximately 2. The sulfuric acid reacts with the calcium hydroxide present in concrete, eventually leading to the formation of gypsum and ettringite causing surface material expansion leading to concrete exfoliating and cracking, and at times, total collapse.

Below are two images of gypsum and ettringite that may help you identify them at your site:

(Source: Geotechnical and Geological Engineering)

(Source: Wikipedia)

We have simplified the explanation, eliminating biological words that are hard to pronounce and chemical formulations that are impossible to understand. What’s important to recognize is that MIC is a small but mighty ‘bad actor’ that is working 24/7 to deteriorate your wastewater system.

So, how do you stop or prevent microbial corrosion in concrete? You’ll need to repair it by cleaning, priming and lining the existing material with OBIC polymer lining systems that are nonporous and impervious to MIC and protect concrete substrates from MIC attack, typically adding 50 years of additional life. We also help municipalities across the country prevent MIC from attacking new wastewater assets, which helps protect it from the start. OBIC products are all backed by a team of chemists who work hard to ensure that our lining systems protect your water and sanitary sewer system from corrosion.

The OBIC team can help you find a cost-effective, no-dig solution to all of your municipal and industrial water and wastewater needs.  Complete the Contact us  form, or give us to call at 866-636-4854 to request information or schedule an OBIC product demonstration.