Microbial corrosion of concrete by bacteria, fungi and algae destabilize structures of home and environs. While the impact of weather, heavy traffic, and chemicals on concrete are well known, the appearance of corrosive microbes indicates a one-way track to total collapse.
These unseen creatures work as efficiently as possible. In the ecosystem their jobs involve breaking things down, often transforming impurities to nutrients, or in some cases, gold. Unfortunately, in human terms, damage to concrete warrants retribution.
What Causes Microbial Corrosion?
Microbial corrosion, also called biocorrosion or microbiologically influenced corrosion (MIC), occurs when microorganisms meet concrete. Bacteria and other microbes react to these materials in their environment, setting off the process of microbial deterioration.
This phenomenon is particularly pronounced in environments providing moisture, nutrients, and suitable temperature conditions for microbial growth. Factors contributing to microbial corrosion in concrete and other materials include:
Moisture
Concrete is inherently porous, allowing water to penetrate and create favorable conditions for microbial growth. Bacteria, mold and algae all enjoy the water.
High moisture levels and nutrient-rich environments, like those in sewage treatment plants or marine settings, are ideal for microbial growth. Concrete structures in these settings can have corrosion rates up to 30% higher than those in environments less microbe-friendly.
Nutrient Availability
Nutrients such as organic matter, phosphates, and sulfates can be derived from wastewater, soil, or even atmospheric deposits, providing sustenance for microbes. The organic ingredients of concrete consist of materials like limestone, clay and stone aggregates.
Aggregate stones include granite, shale and limestone, the three stones considered to carry the most radon gas. While this gas isn't found in a granite countertop it can accumulate in bedrock in amounts of up to 3%. Radon gas settles in corners and lower levels like cellars.
Homes built on such sites may face the additional challenge of illness and fatigue in the family, perhaps leaving homeowners too tired to do needed repairs. This can compound the problem of microbial corrosion.
Oxygen
Because concrete is porous, corrosion-causing microbes requiring oxygen do well in building environments. Oxygen freely enters concrete through cracks or pores. Size and distribution of pores in concrete dictate how easily microbes can invade.
pH Levels
While concrete is generally alkaline, certain microbial processes actually alter the pH. This continues to create a aggressive corrosive environment. Microbial corrosion primarily results from interactions between certain microorganisms and the concrete itself.
What Organisms Are Involved?
The microorganisms implicated in concrete corrosion are diverse and can be generally grouped into bacteria, fungi, and algae. These include:
Bacteria:
Sulfate-reducing bacteria (SRB), such as Desulfovibrio and Desulfotomaculum, are lethal warriors of concrete corrosion. These bacteria thrive in anaerobic environments and produce sulfide ions, leading to increased environmental acidity and corrosion.
Fungi
Certain fungi colonize concrete surfaces, breaking down organic materials. Their release of organic acids contribute to the deterioration of concrete. Some fungi, such as Aspergillus and Penicillium, can inhabit concrete and release organic acids that dissolve calcium hydroxide.
Algae and Cyanobacteria
These photosynthetic organisms can produce organic acids to erode concrete and create biofilms, increasing moisture retention and promoting further microbial colonization. A slimy layer of algae traps moisture and fosters bacterial growth.
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