Solutions for Microbially Induced Concrete Corrosion (MICC)

written by Dr. Burke Nelson, Research Fellow, Research and Development North America

Microbially induced concrete corrosion is a critical issue in concrete sewage infrastructure such as pipes and manholes. Acid-loving microbes such as the Thiobacillus bacteria grow on the exposed surfaces of concrete and metabolize the hydrogen sulfide gas present in the sewer into sulfuric acid; this acid corrodes the concrete. Traditional approaches to extend the life of concrete employ admixes to improve acid resistance, water resistance, and/or densification of concrete, fortifying concrete against acid corrosion. While these measures do reduce the speed of the acid corrosion attack, they do nothing to inhibit the cause of the issue – the acid-producing microbes.

What Are the Causes of Corrosion in Concrete?

To understand how to approach this issue, it is important to understand how the MICC develops over time in a sewer by examining the causes of corrosion in concrete. New concrete has a very high pH (pH of 11-12). It is so alkaline that no organisms will grow, providing natural corrosion protection against microbial growth. Over time, sewer gases combine with moisture to gradually neutralize the concrete until the pH is low enough to allow biofilms of microorganisms such as Thiobacillus to start growing (around pH 9). In this second stage, the microbes accelerate the decline of the pH as they begin to produce sulfuric acid. Once the pH has been lowered to about 3, the acid will begin to corrode the cement binder in the concrete. As the pH drops even further, the corrosion accelerates and the sulfuric acid produced by the microbes converts the cement binder of concrete into non-load bearing gypsum, eventually destroying the concrete.

Traditional approaches to combating microbial induced concrete corrosion can have an adverse effect, and in some cases can make concrete more susceptible to microbial attach in sanitary sewer systems. The major challenge facing concrete is the MICC issue – an efficient, cost-effective solution to this issue actually makes concrete a more attractive choice. Builders using concrete as a primary material have an opportunity to address this issue by incorporating a concrete corrosion inhibitor into their process.

Microban Excalibur® is the Solution for Concrete Corrosion

Microban Excalibur® works differently than standard concrete admixtures. In addition to increasing the hydrophobicity of the concrete, which works to slow acid penetration, Excalibur® has been demonstrated to inhibit the growth of the organisms that cause MICC. Excalibur® contains an EPA-registered wide spectrum antimicrobial that has over 50+ years of safe use in many applications. By inhibiting the growth of the Thiobacillus and other organisms, Excalibur® slows the pH decline of the concrete before corrosion begins to occur, extending the lifetime of concrete structures by delaying the onset of acid corrosion.

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Compatible with both wet and dry cast concrete, Excalibur® is a permanent, easy-to-use, cost-effective solution for concrete corrosion that is added to a concrete mix with water. As it is fully incorporated into the concrete, it is not a delicate coating and so will not wear off or wash away. More importantly, Excalibur® will chemically bond with the concrete as it cures so it will not leach out into the sewer system. This not only gives Excalibur® its excellent durability, but also alleviates concerns about antimicrobials going into downstream sewage treatment plants.

Excalibur® provides a durable one-two punch against MICC in an easily incorporated liquid solution. Available research by the Microban® team demonstrates the efficacy and extension of the concrete lifespan when concrete is treated with Excalibur®. Additionally, the Excalibur® chemistry can be supplied worldwide, and implementation can be supported on a global basis. Lead your industry by helping your customers avoid the high cost of concrete failure.

Microban provides customers a suite of services, including technical, legal and regulatory support to ensure the successful applications of our technologies.

Contact us today to learn more about Microban Excalibur® for Concrete.