text: Fungi can cause microbial corrosion of concrete. With adequate environmental factors, such as humidity, temperature, and organic carbon sources, fungi will produce colonies on concrete. Some fungi can reproduce asexually. This common process among fungi allows many new fungal spores to quickly spread to new environments, developing entire colonies where nothing existed. These colonies and the new spores produced use hyphae to absorb environmental nutrients.
  Hyphae are incredibly tiny and thin, growing only 2 to 6 micrometers in diameter. Fungal hyphae are used to reach deep into minuscule holes, cracks, and ravines in concrete. These areas contain moisture and nutrients the fungus survives on. As more hyphae force their way into these tiny cracks and crevices, the pressure causes those gaps to expand, similar to how water freezes in tiny holes and cracks, causing them to widen. The mechanical pressure enables cracks to expand, leading to more moisture getting inside, and thus, the fungi have more nutrients, allowing them to travel deeper into the concrete structure. By altering their environment, fungi break down concrete and its alkaline layer, thus providing ideal conditions for corrosion-causing bacteria to further degrade concrete structures. 
  Another way fungi cause corrosion on concrete is through organic acids naturally produced by the fungi. These organic acids chemically react with Calcium 2+ in the concrete which produces water-soluble salts as a product. The Calcium 2+ is then released, causing extensive damage over time to the structure. Due to the fact that fungi expel digestive juices to gain nutrients, the structure they grow on will begin to dissolve. This is no different for concrete when fungi such as Fusarium take root. An experiment compared the corrosion of the bacteria Tiobacillus to the corrosion of a fungus called Fusarium. In the experiment, both groups of organisms were provided with adequate conditions to grow, along with an equal piece of concrete in each experiment. After 147 days, the Tiobacillus bacterium caused an 18% mass reduction. However, the Fusarium fungus caused a 24% mass reduction in the same time frame, thus showcasing its corrosive abilities.
  Bhattacharyya did a study on the three separate types of fungi that are known to cause concrete corrosion: Aspergillus tamarii, Aspergillus niger, and Fusarium. Aspergillus tamarii was the most destructive of the three fungi. It causes cracks to widen and deepen, quickly and efficiently takes root, and promotes calcium oxalate. By causing calcium oxalate, there is an increase in the speed of calcium ion leaching, which lowers the overall strength of concrete. In 90 days, exposure to the fungus resulted in a mass reduction of 7.2% in the concrete. Aspergillus niger was the second worst offender out of the three, followed by Fusarium, which can lower the mass of concrete by 6.2 grams in a single year, as well as cause the pH to down from 12 to 8 in the same time frame.