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Background

Unanticipated microbial-induced concrete corrosion (MICC) continues to challenge the underground conduit networks that make up an important part of urban infrastructure. One of the most aggressive and ubiquitous forms of MICC stems from the biologically mediated production of sulfuric acid in sewers. Population centers around the world share this serious and growing problem. In the United States, local governments spend approximately $50 billion in the construction, operation, and maintenance of over 800,000 miles of sewers annually. In order to rehabilitate and expand the wastewater infrastructure, the United States Environmental Protection Agency estimates that $271 billion is needed over the next generation, a substantial fraction of which is dedicated to directly respond to widespread biogenic corrosion that is significantly reducing the service life of buried sewers. Sewer service life reductions result from the fact that conventional ordinary portland cement (OPC) concrete is rapidly compromised by biogenic sulfuric acid attack, producing gypsum and amorphous silica from the cementitious binder. The non-load bearing quality of gypsum leads to severe structural deterioration and, ultimately, pipe failure. Mitigation strategies for microbial-induced concrete corrosion are often short-term, relatively expensive, and site-limited. In order to provide in-situ acid protection for OPC concrete sewers, operators have used surface coatings and linings, concrete binder additives, and, even, antimicrobial additives.

Technology

Researchers at the University of Colorado have developed a method to create an acid-resistant inorganic coating to be applied to concrete sewer pipe conduit. The inorganic cements are made from a low-calcium metakaolin-based alkali-activated cement (AAC). The cements are doped with inorganic polyvalent cations (e.g., magnesium, iron, copper, cobalt), resulting in even lower permeable porosities and smaller acid corrosion depths compared to OPC.

Advantages

This acid resistant additive has the potential to increase the lifespan of OPC used for sewage 3-5X, essentially avoiding as many lifecycle CO2 emissions related to OPC production. A popular mitigation practice includes the use of acid resistant, cured-in-place resins. While seemingly effective in resisting acid exposure, the associated cost of these materials is high ($390-900 per linear meter), they require special curing conditions, and may not prevent corrosive gas infiltration, seriously compromising the effectiveness of this mitigation practice. Further, with the exception of antimicrobial additives, these mitigation strategies do not address one of the underlying causes of MICC in these environments: acidophilic microbial growth. However, incorporation of biocidal metals that, in micromolar concentrations, can function as antimicrobial agents into an alkali-activated cement (AAC), an acid-resistant alternative to OPC.

What's Next?

This technology is available for exclusive or non-exclusive licensing.