Five Years of Severe Duty Prove Durability of Plastic Manhole Grade Rings

By Lee Haessig, Cretex Specialty Products

In the spring of 2010, Cretex Specialty Products (Waukesha, Wis.) was looking for field test sites for a new product that had been recently introduced to the underground construction market. The new product was the PRO-RING™ Manhole and Catch Basin Grade Adjustment System. PRO-RING is the world’s first and only grade adjustment system made from Expanded Polypropylene (EPP). EPP is a high-strength, lightweight plastic, making it the ideal material to replace traditional construction methods using concrete grade rings, mortar or other masonry materials.

The PRO-RING system dramatically speeds repair time, making it more cost-effective.

A manhole identified for reconstruction by Narragansett Bay Commission of Providence, Rhode Island, was located on Putnam Pike (State Route 44) and positioned directly in the wheel path of all traffic moving northwest on the highway. The PRO-RING system was of significant interest to Narragansett Bay Commission due to the many benefits claimed, such as quick installation: One man can install the entire system in just minutes. PRO-RING weighs 95 percent less than concrete rings, making it safer by minimizing the risk of worker injury. The system dramatically speeds repair time, making it more cost effective: Manhole repair sites can be opened, repaired and closed in one day, reducing overall costs by as much as 20 to 30 percent.

Based on the known RI DOT traffic data, it is estimated that more than 100,000,000 (one hundred million) vehicular traffic impacts have occurred on this manhole since being installed more than five years ago. This repeated auto and truck traffic has had no negative effect on the PRO-RING installation and the surrounding pavement remains in stable condition showing no signs of cracking or fatigue.

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