The Light Fantastic

The PRO-RING system from Cretex Specialty Products uses lightweight foam rings that enable one worker to restore a manhole to grade level

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When roadway reconstruction raises the pavement level, manholes need to be repositioned so that they are once again level with the street. Typically, heavy concrete rings are used to build up the chimney so that the cover and its frame can be repositioned.

 

A new alternative is the PRO-RING system, a series of lightweight expanded polypropylene (EPP) rings that can be used to raise a manhole to grade level. PRO-RING is manufactured by JSP from the company’s ARPRO brand EPP material. It is distributed by Cretex Specialty Products, of Waukesha, Wis., a supplier of chimney seals and other manhole repair products. Cretex is a unit of Cretex Companies in Elk River, Minn.

 

Pete Tortorici, regional sales manager for Cretex based in Bartlett, Ill., demonstrated the PRO-RING system for Darin Severson, repair and excavation field supervisor for the City of Naperville, Ill., a Chicago suburb, on June 15.

 

Walk-around

The PRO-RING system consists of black EPP rings with a standard inner diameter of 24 inches and outer diameter of 36 inches. EPP is an engineered plastic foam that is lightweight and has a very high strength-to-weight ratio. It withstands multiple impacts without significant damage, resists water, chemicals and most oils, and withstands temperature extremes from -31 to 265 degrees F.

 

Cretex notes that while it usually takes up to four men to lift a concrete grade ring, a 6-inch-think PRO-RING unit weighs 14 pounds. One man can install the system in a few minutes. A site to be closed in one day at 20 to 30 percent reduced cost versus conventional methods, according to the company. No water, sand, mortar or bricks are needed.

 

There are three categories of rings: grade rings, finish rings and angle rings. Grade rings are used to raise the manhole to within an inch or two of grade. A finish ring is applied in the final layer between the grade rings and the reinstalled manhole frame. Angle rings are used when the grade surface is sloped.

 

Grade rings have two concentric 1-inch-wide channels on the underside and two corresponding concentric 1-inch-wide tongues on the upper side. The tongues and channels fit together so that rings align precisely when they are stacked. Finish rings have only the channels on the underside. The upper side is smooth to enable maximum surface contact, and therefore a maximum seal, with the underside of the manhole frame.

 

Grade rings are available in 2-, 4- and 6-inch thicknesses. Finish rings come in quarter-inch increments from 0.75-inch to 2.5 inches thick. Angle ring thickness transitions from 0.75 to 1.75 inches, the equivalent of a 1-degree pitch.

 

The PRO-RING system has been tested using M-1 construction adhesive, so Cretex conducts its demonstrations using that material.

 

Operation

Tortorici met with a city work crew headed by Severson at an intersection in a residential area that had been reconfigured several years before when one crossing street was widened. The project left a manhole at the location buried more than a foot below the new grade level on the roadside beneath the landscaping.

 

A week or so before the demonstration, a city crew had conducted a TV inspection and used a locating sonde to identify the manhole’s location, then hydroexcavated the site to expose the top of the manhole.

 

Workers used a backhoe to remove the manhole frame, exposing the top of the concrete manhole chimney. Naperville city worker Rick Flaar measured the depth from soil surface to the chimney at 15 inches. Allowing for the 7-inch height of the manhole frame, that left 8 inches to fill with new rings.

 

Tortorici applied a layer of adhesive to the top of the concrete manhole chimney, using a zigzag pattern that provided coverage for the chimney’s entire thickness. He then grabbed a 6-inch PRO-RING grade ring with one hand and lowered it into place, carefully aligning it with the chimney and twisting it slightly to spread adhesive.

 

Once that ring was in place, he laid down circular lines of adhesive on the two protruding tongues. Then he took a 1.5-inch-thick finish ring and aligned the grooves on the underside with the tongues on the upper side of the first ring, again twisting to spread the adhesive and ensure a complete seal.

 

Tortorici then applied adhesive in a zigzag pattern covering the entire top surface of the finish ring. City workers Flaar and Martin Alvarado lowered the manhole frame onto the adhesive on the finish ring. The city crew then backfilled the excavation with gravel.

 

Severson explained that at a later date, about 6 inches of gravel would be removed and replaced with black dirt and topsoil and topped with sod. The entire operation, from the first application of adhesive to backfilling, took less than 15 minutes.

 

The work crew then proceeded about a half-block south, where there was another manhole two feet below grade in the grass next to the street. Flaar measured the manhole’s depth at 25.5 inches below the grade, thus requiring 18 inches of filler between the top of the manhole chimney and the frame. He decided to use two 6-inch grade rings, two 2-inch grade rings and a 2-inch finish ring.

 

Because there was some moisture on the top of the manhole chimney, Flaar used a propane torch to dry the surface. This time, Flaar applied the adhesive, following the example that Tortorici had set with the first project. The manhole frame was then lowered on to the adhesive-covered finish ring, and the cavity was backfilled with gravel.

 

When the adhesive had set for about 45 minutes, a Naperville employee drove a combination truck to the work site. With the jetter hose turned on, crew member Josh Orin applied its end tightly to the surface of the gravel, sending water into the gravel surrounding the chimney. Through the open manhole, water could be seen slowly seeping in two small areas between the bottom 6-inch ring and the top of the concrete chimney.

 

Severson said he was not at all concerned. He noted that the chimney had been pitted in a few spots, possibly interfering with the seal. Furthermore, he said, the adhesive specifications strictly call for a total curing time of three to seven days.

 

Allowing more time to cure, leveling the top of the manhole chimney, or both would probably ensure a complete seal, he said, and applying a chimney seal, caulk or mortar to the area would probably resolve the matter. The rings themselves remained tight. “It’s a good seal,” he said. “Nothing’s leaking on those.”

 

Observer comments

The PRO-RING materials were remarkably lightweight, yet easily bore the weight of the heavy iron manhole frames without crushing. Workers moving around with the rings carried two or three at a time with no difficulty.

 

The system was easy to learn, as a Naperville crew member did the second job after merely watching Tortorici quickly dispatch with the first one. Severson said he was impressed by the system. “Concrete rings might be a little bit cheaper,” he said. But ease of use, the light weight of the PRO-RING system, and the greatly reduced risk of injury to workers all made the PRO-RING much more attractive in his eyes.

 

With concrete rings, “you have to have a tractor to set it,” he noted. “So you have to have another piece of equipment out there.”

 

Manufacturer comments

While Cretex conducts its PRO-RING demonstrations using M-1 adhesive, Tortorici said the company does not limit its recommended adhesive to that product. A variety of commercial construction caulks or adhesives can be used.

 

Tortorici said tests have demonstrated that the rings, when in place, can support substantial weight. Proof load tests have been conducted with the equivalent of 50,000 pounds and have shown no damage to the rings.

 

While a casual bystander at one demonstration broke a ring while holding it vertically and bending it, Tortorici noted that the ring had been subjected to a stress completely unlike what it would experience in service. Users are advised to take care in hauling the rings so that they are not subject to unusual stresses while loose in a truck.



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