Public utilities often face significant investment gaps in maintaining water and wastewater infrastructure. The American Society of Civil Engineers (ASCE) has reported that the United States needs to invest hundreds of billions of dollars in the coming decades to address aging infrastructure, comply with regulatory requirements, and adapt to changing climates.

In 2019, utilities invested more than $3 billion — translating to more than $18 per customer — to replace nearly 4,700 miles (7,563.9 km) of pipeline across the country. However, the tide is turning; according to ASCE surveys, 62% of utilities have adopted asset management plans, shifting from a reactive to a proactive stance on maintaining wastewater infrastructure.

Municipalities can employ advanced coating and lining systems to shield their underground wastewater structures from environmental stresses, thus mitigating corrosion and wear. Consider these tactics to ensure these underground assets’ effective preservation and enduring dependability.

Understanding Coatings and Linings

Although “coatings” and “linings” are often used synonymously, they represent two distinct concepts. The Association for Materials Protection and Performance (AMPP) characterizes a coating as a material up to 0.125 inches (0.3175 cm) thick that forms an adhesive bond with substrates. In this instance, we’re considering systems on concrete.

Conversely, linings exceed this thickness and may be bonded or unbonded. Acknowledging this difference for those involved in underground utility protection specification and design remains critical for unified and effective communication among all stakeholders.

For example, epoxy coatings are thin-film epoxy resins that bond chemically with concrete and are frequently utilized in water and wastewater treatment facilities, while a high-build epoxy lining provides a robust and often impermeable protective layer for concrete. In short: Some consider coatings for the exterior and linings for internal protection.

Effectiveness of Polymer-Based Liners and Coatings

In the wastewater industry, polymer linings and coatings serve as formidable barriers against chemical corrosion, abrasion, debris, and the high impact of fast-moving water, extending the service life of infrastructure.

Polymers, in the context of the wastewater industry, are a class of synthetic substances made up of long chains of molecules with repeated units, known for their versatility and resilience.

Unlike other chemistries for coatings, polymers can be tailored during their chemical synthesis to achieve specific characteristics desirable for wastewater infrastructure protection. Notably, they can prevent groundwater from seeping into structures such as manholes and keep materials contained from leaking out.

Ongoing inspections of coated manholes reveal their enduring structural integrity (or lack thereof), validating the efficacy of these protective systems. These coatings are also useful for improving visibility within structures due to their usual lighter color, which aids in visual inspections.

Moreover, polymer-based coatings and linings guard against microbially induced corrosion (MIC), a severe threat to concrete wastewater systems. MIC is caused by Thiobacillus bacteria, which produces sulfuric acid, hastening concrete decay. Effective protective products resist such acidic conditions, where pH levels may drop below three, signaling rapid deterioration.

Choosing the Appropriate Protection

Selecting suitable protection requires a comprehensive assessment of the structure’s environment, materials, condition, and function. Currently, the market presents various options, including high-build and thin-film epoxies, elastomeric and moisture-curing polyurethanes, and polyurea hybrids.

Moisture presence is a crucial consideration. While high-build epoxies are known for their excellent adhesion to wet surfaces, polyureas and polyurethanes are less suitable for damp concrete. The solution often involves drying the area and applying a primer, with tri-hybrid polymer coatings particularly effective in such conditions.

Coating professionals must also weigh the need for tensile strength against flexibility. High-build epoxies have high tensile strength, whereas materials like polyurea, polyurethane, and tri-hybrids offer more flexibility. The choice depends on whether the structure experiences movement, with flexibility being more important in dynamic environments.

Other factors include hydrostatic and soil stresses, traffic, and live load. For example, traffic induces the most significant stress on vertical structures, including manholes, primarily affecting the cover and frame. Although intense at the surface, this stress diminishes with depth, so be sure to select materials for the cover to withstand these loads. Always choose the right polymer liner or coating based on recommendations from the product manufacturer, backed by historical case study performance and third-party testing.

Surface Prep, Specs, and Quality Assurance A successful application begins with meticulous surface preparation. It is essential to follow industry standards for surface preparation and cleaning. In fact, it’s been shown that 90% of coating failures occur due to poor surface preparation. A few high-level best practices include completing inspections to check substrate pH and surface profiles before coating application and ensuring that only trained and qualified installers are applying the coatings.

The substrate pH should be neutral or slightly above to ensure a clean surface. The surface profile, as defined by the International Concrete Repair Institute (ICRI), should ideally range between three and six, depending on the manufacturer’s specifications. Successfully applying a coating requires cleanliness and thoroughly removing existing coatings, dirt, and debris. Be sure that your team is made of only certified, trained, and qualified installers.

After the coating is applied, quality assurance and control are paramount, too. These involve tests for adhesion, pinhole detection, and thickness verification. These checkpoints validate the integrity of the coating system, preventing potential failures. Specifying minimum coating thickness and post-application quality assurance (QA) and quality control (QC) testing — including adhesion, pinhole, and mil thickness checks — ensures excellent product performance.

For example, a 16-year-old manhole protected with a lining system in Cedar Park, Texas, was inspected and found to have no visual defects or active leaks. The inspection included pull tests on the coating, indicating its strong adherence to the structure thanks to its superior performance, application, and QA/QC practices. These measures help to ensure the coating system’s integrity for years to come.

Team Effort

The advancement of coating and lining technologies is crucial to future wastewater infrastructure maintenance. Collaborations between manufacturers, engineers, and applicators optimize the effectiveness of protective solutions.

Experienced coatings and linings professionals — from manufacturer to contractor — are vital for informed decision-making regarding surface preparation, specifications, and quality practices. Such partnerships ensure the integrity and preparedness of underground wastewater infrastructure for upcoming challenges.

Editor’s note: This article first appeared in the July 2024 print issue of CoatingsPro Magazine. Reprinted with permission.