Manholes may seem like unassuming fixtures beneath our feet, yet they play an indispensable role in maintaining the functionality of urban infrastructure. The Environmental Protection Agency (EPA) reports that there are around 20 million manholes in the U.S., equating to about one manhole for every 400 feet of pavement. These structures act as vital access points for utilities like water, electricity, telecommunication, and natural gas systems, as well as serving as entryways for sewer line inspections and repairs. Neglecting their upkeep can lead to significant issues, including blockages, leaks, and even complete failure. Shockingly, an estimated 20% of manholes in the U.S. are over 30 years old, and more than 3 million are in such poor condition that they require urgent attention—either through rehabilitation or replacement.
In Pima County, Arizona, 21 manholes originally built in the 1940s underwent rehabilitation using a cementitious liner back in the 1990s. Unfortunately, this liner eventually failed due to erosion and loss of adhesion to the substrate. Fragments of the deteriorating material began falling into the sewage flow, posing risks to the county’s wastewater treatment processes. To address this issue, the manholes needed extensive repairs, including the removal of the faulty liner, structural reinforcement, and protection against Hydrogen Sulfide Gas, a common corrosive agent in sewer environments.
The rehabilitation project was undertaken with HJ3's advanced carbon fiber system. The first step involved thoroughly cleaning and grinding the surfaces of the manholes to remove the remnants of the old liner. Next, the team resurfaced the concrete using Quick-Set grout and sealed all cracks with a low-viscosity polymer to ensure airtightness. HJ3's CarbonSealâ„¢ carbon fiber was then saturated and installed across the interior walls to strengthen the structure and prevent further damage. Finally, a vinyl ester topcoat was applied to protect the carbon fiber from potential erosion caused by Hydrogen Sulfide gas.
This innovative approach proved both cost-effective and efficient. Compared to replacing all 21 manholes, HJ3's carbon fiber solution saved Pima County a staggering 80%. Moreover, the entire repair process was completed without requiring any road closures, saving months of downtime and avoiding the unnecessary wastage of nearly 62,000 gallons of water typically consumed in the production of new manholes.
The cementitious liner previously used for these manholes failed due to corrosion and cracking.
HJ3's CarbonSealâ„¢ is meticulously applied to reinforce the manholes.
CarbonSealâ„¢ strengthens the manholes against future damage.
The vinyl ester topcoat provides long-term protection against Hydrogen Sulfide gas and erosion.
By investing in sustainable solutions like HJ3's carbon fiber technology, cities can preserve their critical infrastructure while reducing costs and environmental impact. This case study underscores the importance of proactive maintenance and highlights how modern innovations can transform traditional practices in the field of civil engineering.
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