Manhole Corrosion 101: What Causes Deterioration

America’s sewer system is an aging infrastructure. In fact, manholes have been a part of our wastewater collection system for over three centuries. Many of these early manholes were constructed of brick and mortar or cobblestone, while newer manholes are mostly constructed of concrete. No matter the material, many have long outlived their life expectancy, and even the newer concrete manholes cannot long withstand the often-high hydrogen sulfide environment they are subjected to, resulting in a deteriorating infrastructure. One solution for failing manholes is to replace them; however, rehabilitation is often ideal due to its cost benefits and the ability to avoid disturbing the surrounding area as much as possible.

Manhole Corrosion

When considering rehabilitation, it important to note the two most common types of corrosion attacking this infrastructure:

  • Hydrogen sulfide:

    This is one of the biggest factors leading to deterioration. The byproduct of H2S leads to sulfuric acid, which breaks down concrete and leads to structural failure if not addressed.

  • Inflow and Infiltration (I&I):

    Groundwater or rain coming through walls and manhole chimney seals begins breaking down structural components, making it the main culprit behind much of the unnecessary water that ends up in water treatment plants.

Considering the type of corrosion is key to choosing the right manhole rehabilitation system. Since a plethora of options are available in the manhole rehabilitation industry, including but not limited to epoxies, cementitious liners, polyurethanes, and hybrid epoxies, diagnosing the type of corrosion at fault will often lead to the most cost-effective solution.

For example, using an epoxy to rehabilitate a manhole that does not have high H2S is costly, and it may be overkill. in contrast, using a cementitious liner in an area with has a great deal of I&I is not a responsible choice since I&I will eventually erode a cementitious material liner.

Carefully considering of presence and type of corrosive factors is the first step in identifying the type of rehabilitation material that should be used.

By: Silvia Caputi, CLADLINER Marketing Coordinator
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