**The Critical Role of Manhole Maintenance**
Manholes are often overlooked by the general public, yet their importance in maintaining the smooth functioning of urban infrastructure is undeniable. According to the Environmental Protection Agency (EPA), there are around 20 million manholes across the U.S., averaging one for every 400 feet of pavement. These unassuming structures are vital access points for sewer lines, allowing for regular maintenance and repairs. They also provide entry to critical utilities like water, electricity, telecommunication, and natural gas systems. Neglecting their upkeep can lead to significant problems, as an estimated 20% of manholes are now over 30 years old, with more than 3 million in urgent need of rehabilitation or replacement.
In Pima County, Arizona, 21 manholes originally built in the 1940s had undergone prior rehabilitation using a cementitious liner, which eventually failed. Over time, the liner eroded, losing its bond with the underlying concrete and shedding fragments into the sewage flow. This posed a serious risk to the county’s wastewater treatment infrastructure. To address this issue, the county decided to remove the faulty liner, reinforce the manholes, and protect them from Hydrogen Sulfide (H₂S) gas corrosion. The rehabilitation process included grinding down the existing surface, applying Quick-Set grout to even out the concrete, and sealing all cracks with a low-viscosity polymer. HJ3's CarbonSeal™ carbon fiber was then installed and saturated, followed by the application of a durable vinyl ester topcoat to shield against future erosion caused by H₂S exposure.
This innovative solution proved highly cost-effective, saving the county a staggering 80% compared to the expense of replacing all 21 manholes. Additionally, the project avoided lengthy road closures and prevented approximately 62,000 gallons of water waste typically associated with manufacturing new manholes.
Below are images illustrating the transformation:
The original cementitious liner installed in 1996, now cracked and deteriorated.
HJ3's CarbonSealâ„¢ being applied inside the manholes.
The final vinyl ester topcoat applied to protect against Hâ‚‚S gas and future damage.
This project underscores the immense value of modern materials and techniques in extending the lifespan of essential infrastructure. By investing in proper maintenance, communities can avoid costly replacements while ensuring the reliability of their underground networks.
