Manhole Rehab for Surf City, North Carolina

In 1963, the singing duo Jan and Dean glamorized a fictional California town called Surf City, where life centered around surfing all day and romancing at night.

The real Surf City, a quaint East Coast town on North Carolina’s Topsail Island, is known for its picturesque sandy beaches, just like the imaginary West Coast version. It’s also dealing with a real-life, unglamorous problem that’s far from beachgoers’ minds.

Recently, Surf City leaders discovered that a manhole leading from the street to underground sanitary sewers was deteriorating to the point of facing potential inflow and infiltration (I&I) issues. Alarm bells sounded because it was likely that other sewer infrastructure assets could be in similar condition. Damaged manholes can make it difficult for maintenance workers to access sewers for inspection and repair. In addition, manholes that aren’t watertight allow stormwater and abrasive surface materials like soil and gravel into sewers. That can ultimately accelerate wear on sewer infrastructure – and raise the cost of treating sewer contents.

To fix the deteriorated manhole and assess other assets, Surf City turned to Carolina Management Team (CMT), a North Carolina firm that specializes in restoring infrastructure assets like manholes, for help. For CMT, the solution was never in doubt. The company would rebuild the manhole’s deteriorated concrete and then apply a specific coating: Dura-Plate 6000 from Sherwin-Williams Protective & Marine. The two-component, high-build, high-strength, reinforced epoxy lining with 100 percent solids had become part of CMT’s regular manhole repair treatment arsenal for severe service assets.

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CMT completed the Surf City manhole rehab in spring 2022. Crewmembers successfully brought the concrete back to its original plane and applied a thick layer of Dura-Plate 6000 that is performing as well as expected. As a result, CMT anticipates restoring additional sewer infrastructure assets for Surf City.

A Common Problem

Municipalities across the United States are facing the same reality as Surf City. Sewer infrastructure is eroding – partly because infrastructure is aging, but also because sewers are carrying more waste for longer distances as cities grow geographically and in population. Therefore, the waste dwells in sewers for longer periods, which allows more time for damaging chemical reactions to occur.

Hydrogen sulfide (H2S), a colorless, poisonous and corrosive gas, is a natural byproduct of sewage and is present in sanitary sewers. It’s the result of microbes breaking down organic matter. In turn, H2S causes microbial-induced corrosion (MIC). With MIC, microorganisms such as bacteria eat H2S and excrete sulfuric acid as waste. The acid damages the concrete that makes up infrastructure like manholes and lowers its pH level, making it increasingly susceptible to spalling.

A Solid Solution

Various concrete structures in Surf City’s sewer system are about 30 years old and facing critical stages in their lifespans since they were never lined with a protective coating. For the deteriorated manhole, noticeable degradation probably first appeared about five years after it was built in 2001, but at the nearly 20-year mark, that deterioration had become significant, in part, due to the upstream infrastructure.

“This particular manhole had a sanitary sewer lift station nearby that flowed into the manhole via a vertical drop,” said CMT project manager Terry Boger. “This drop allowed greater turbulence in the sewer and greater H2S gas attack.”

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CMT recommended its normal repair protocol – replacing and repairing damaged concrete, then applying Dura-Plate 6000 – for the following reasons:

• Ease of application. CMT was able to apply Dura-Plate 6000 with a single-leg sprayer, eliminating the need to use bulky plural-component equipment.
• High build characteristics. Applicators were able to build the lining to a 125-mil dry film thickness (DFT) or higher with a single pass for greater durability.
• Low permeability. Dura-Plate 6000 is relatively impervious to moisture penetration. It contains reinforcing glass flakes that stack on top of each other and prevent moisture from reaching the substrate.
• Fast return to service. Newly lined assets can return to service about 10 hours after application using Dura-Plate 6000. Further, the product can be applied to damp concrete.

A Skillful Application

CMT’s first step was preparing the concrete substrate for repairs by clearing away degraded concrete inside the manhole.

“We used a chipping hammer with a 3-in.-wide blade to remove as much loose material as possible,” said Boger. “This allowed us to prevent excess debris from entering the wastewater.”
Then came high-pressure water cleaning at 5,000 psi to remove surface contaminants and any remaining deteriorated or loose concrete. Throughout the manhole, workers had to find a solid substrate in the original concrete with all areas having a pH reading of at least nine. To reach that pH level, they had to wash away three to four inches of acidified concrete in a manhole that had originally been nine inches thick.

For the next step, CMT had to rebuild what the crew had cut away. Using hand trowels, workers applied a microsilica mortar material with a blend of Portland cement and additives in two stages due to the thickness of the restoration. The material, filled with fiberglass strands that provide tensile strength, is a dense matrix that holds together over the long term.

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Finally, CMT coated the restored concrete surface with Dura-Plate 6000, following high-pressure water cleaning at 5,000 psi to remove any laitance or contaminants from the substrate.
“We sprayed using a crosshatch of six passes to ensure complete coverage while building the material to 125 mils DFT,” Boger says. “After spraying, we brushed over the coating lightly with a mortar brush to fill any pinholes and smooth it out. We also spot-checked with a wet film gauge regularly during application, followed by a final visual inspection.”

A Long Life

Surf City has checked the manhole several times following the restoration and found that Dura-Plate 6000 has passed the test. In fact, the manhole is expected to last at least another 50 years, its life more than tripled, with no deterioration. Due to its success, Dura-Plate 6000 is expected to be part of CMT’s future repairs of manholes, lift stations and wet wells for Surf City.

Brian Huffman and John Sierzega are business development managers for water infrastructure for Sherwin-Williams Protective & Marine Coatings.