Grade Adjustment System Offers Long-Term Seal to Wisconsin Utility

An expanded polypropylene grade adjustment system withstands the test of time in Beloit, Wisconsin.

Grade Adjustment System Offers Long-Term Seal to Wisconsin Utility

Workers install the PRO-RING manhole and catch basin grade adjustment system on top of a repaired manhole cone.

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In undertaking any rehabilitation project, the hope is that you and your crew won’t be back at that job site again anytime soon. That’s why it’s important to choose a solution that can withstand the test of time.

In the early winter of 2009, Cretex Specialty Products of Waukesha, Wisconsin, was looking for field test sites for a new product that was ready to be introduced to the underground construction market. That new product was the PRO-RING manhole and catch basin grade adjustment system.

The PRO-RING is the world’s first and only grade adjustment system made from expanded polypropylene — the same engineered polymer used in the automotive industry since the 1980s. This high strength, lightweight plastic is a suitable material to replace traditional construction methods, which use concrete grade rings, mortar and other masonry materials to adjust manhole frames to their final elevations. 

Finding a test site

Since the PRO-RING is engineered and designed to be watertight, a location with frame-chimney leakage was desired for the field test. A Cretex Specialty Products regional sales manager inquired to cities around Southeast Wisconsin looking for a location for the test installation.

As luck would have it, a manhole that would put the PRO-RING’s watertightness to the test was located on Crist Road in Beloit, Wisconsin. This manhole was selected because it was in an area with an underground aquifer and had a significant leak. The leakage was estimated to be between 35 and 50 gpm and had been contributing a significant amount of clear water into the sanitary sewer collection system for years.

Benefits of the system

The PRO-RING system was of significant interest to the city of Beloit due to the many benefits offered. The system is faster than traditional methods, with one worker being able to install the entire PRO-RING system in just minutes. The rings nest together, are easily sealed, and fit to within a quarter of an inch of finished grade. The system is safe, as it doesn’t use heavy concrete rings, which minimizes injury risk and helps reduce comp claims and down time. The PRO-RING weighs 95% less than concrete rings and stands up well to physical abuse.

The PRO-RING system speeds up manhole installation and repair time, making it more cost effective. Manhole repair sites can be opened, repaired and closed in one day, reducing overall costs from 20% to 30%, based on conditions. No water, sand, mortar or bricks are needed — just a few simple tools. 

Project details

On Dec. 17, 2009, a local excavation contractor hired by the city to assist arrived on site along with representatives from Cretex Specialty Products and city staff. Once traffic control was in place, the area around the manhole was excavated to expose the manhole frame and leaking concrete grade rings. As the excavation progressed, the amount of groundwater present required that two submersible pumps be positioned to keep the water level below the top of the manhole cone.

Once the water level was controlled, the manhole frame and cover were removed along with the existing 20 inches of concrete grade rings to expose the top of the precast manhole cone.

Since the manhole was off road in turf, the amount of adjustment required was the same as what was removed — 20 inches. Three 6-inch grade rings and a 2-inch finish ring were required to achieve the total adjustment.

Because the top of the existing manhole cone had some damage and did not provide a uniform flat bearing surface, the top of the manhole cone was repaired using a non-shrink, high-strength repair mortar. Once the repair mortar had set up, the first grade ring was ready to be installed.

Following the installation procedures that had been developed for the PRO-RING, the recommended M-1 structural adhesive/sealant was applied to the first grade ring, and then it was placed onto the top of the manhole cone.

After the first grade ring was installed, the remaining rings were installed using the M-1 adhesive. The manhole frame and cover were then positioned on top of the finish ring using the M-1 adhesive. Once complete, the pumps were removed, and the excavation was immediately backfilled, taking care to not displace the ring stack or manhole frame and cover.

The results

Since the original installation of the PRO-RING at this test location in 2009, representatives of Cretex Specialty Products have been inspecting the site and documenting the results. From the first post installation inspection performed in 2010, to the most recent inspection completed in the fall of 2020, the PRO-RING product is showing no sign of any leakage or deterioration after 11 years.

About the author: Lee Haessig is the regional sales manager at Cretex Specialty Products. He can be reached at 


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