Lightweight grade rings a fit for off-road manholes

Problem: The District of North Vancouver, British Columbia, faced a problem in the spring of 2015 when they were tasked with rehabilitating existing manhole grade rings located off road in remote easements. They had a list of approximately 50 manholes that required attention, and using a traditional concrete grade ring system made the project look daunting.

Solution: The district had heard about the expanded polypropylene PRO-RING system from Cretex Specialty Products. It meets AASHTO M306 requirements for HS-20 and HS-25 traffic loading to withstand repeated impacts without damage, and is resistant to many chemicals. A traditional concrete grade ring would require several crew members or equipment to lift, while a 6-inch-thick PRO-RING weighs just 14 pounds. The entire ring system is assembled and bonded together in minutes using a construction adhesive/sealant to create a watertight, testable system. It is also available in round, square and rectangular shapes. 

Result: The PRO-RING proved to be an effective solution, allowing crew members to easily handle and install the rings without risk of injury. It enabled the district to spend less time on the job site, use less material, and use a smaller crew. 



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