According to Castagra (www.castagra.com), a U.S. Water Industry Network survey estimated that the annual cost of sewage infrastructure corrosion (with structures that are primarily made of concrete and steel) in the U.S. is about $13.75 billion per year. The primary cause of the corrosion is hydrogen sulfide (H2S) from sewer gas.
Biogenic sulfide corrosion is a bacterially mediated process of forming H2S gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The H2S gas is biochemically oxidized in the presence of moisture to form sulfuric acid, which converts the calcium hydroxide in concrete to calcium sulfate. This change leads to spalling of the concrete. Aggregate particles and the weakened crown of the pipe can then collapse under heavy loads.
One utility dealing with the problem of corrosion was the city of Grand Junction, Colo., with its sewage system experiencing varying levels of H2S exposure, particularly concrete pipes and manhole structures.
The utility selected a solution called Ecodur 201, provided by Castagra, which is designed to protect concrete structures from a variety of chemicals, including acids and salts. A fascinating fact about the coating: It is comprised of completely natural, non-toxic products. Referred to as “veggie plastic,” the product is made from vegetable oil and either newly mined gypsum or recycled drywall that would otherwise end up in landfills. It’s even edible - although, the company admits, it’s not very tasty.
Ecodur 201 can be sprayed onto surfaces, providing excellent adhesion to concrete and maintaining its elasticity. Grand Junction utilized it on its precast manholes, including the steel ladders. Full cure and final inspection were complete in under 24 hours.
Since the product contains no volatile organic compounds or solvents, no separate air system was required during application. The only protection required for workers during the application process were standard filters and eye masks.
“We have utilized the Castagra product on six manholes,” said Bret Guillory, P.E., CFM, utility engineer for the City of Grand Junction. “Two were demonstrations, and four were part of an H2S mitigation project that we are completing. The applicator and crew we worked with were very knowledgeable regarding prep and application of the product.” Guillory added that his team will continue to evaluate the coatings over the coming year.
Castagra is a leader in the green coatings industry with over 20 years of performance and protection in some of the toughest industrial environments. To learn more, visit www.castagra.com.
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