New plastic manhole adjustment rings are being installed in residential street projects in Minnesota.

Contractors and specifying engineers have never been able to specify the materials of concrete manhole adjustment rings used in sanitary and storm sewers. Different: construction companies use different mortar mixes. This results in unpredictable quality, compromising the entire sanitary or storm sewer installation. A new plastic adjustment ring made by LADTECH, Inc., Lino Lakes, Minnesota may help with this problem.

Poor quality concrete rings have resulted in several problems. Many of the concrete rings arrive at the job site broken and unusable, adding to the overall adjustment ring cost. In addition, the rings often do not maintain a watertight seal. Groundwater seeps into the sewer, substantially increasing the wastewater treatment volumes. Rehabilitation projects are needed to replace cracked and leaking concrete rings.

Dave Hanson, the area supervisor for Bonestroo & Associates, a consulting and engineering firm located in Minnesota, is responsible for specifying construction materials for the city of Woodbury and Cottage Grove. He has been concerned about the lack of specifications when it came to concrete adjustment rings. “We were not able to obtain consistency in the installation of concrete rings-a problem I have been trying to solve for some time,” he said.

Because of his concerns Hanson was eager to try a new plastic adjustment ring made from high-density polyethylene (HDPE). These rings are manufactured to meet ASTM and ASSHTO specifications and are designed to exceed the wheel-loading requirements of ASSHTO HS25. They have been subjected to more than one million impact/load cycles and exhibit no physical deformation. In addition, the plastic rings will not corrode or deteriorate when exposed to the harsh hydrogen-sulfide environment found in most sewer systems. The rings are installed in accordance with specific instructions to ensure consistent quality, and performance.

Hanson has monitored the adjustment rings in two locations. He was concerned the rings might not hold up during the harsh Minnesota spring thaw. However, through visual inspection over a two-year time frame, he did not see any separation or movement. Because of the success of the evaluation, Hanson has specified the rings on 12 additional residential street projects.

Hanson originally was interested in the plastic rings to improve the quality of sanitary and storm sewer installations. However, he has noticed several additional advantages these rings offer over concrete rings. “Construction crews have told me the rings are much easier and quicker to install,” he said.

A LADTECH ring weighs about six pounds. A comparable concrete ring weighs 85 pounds. This makes the plastic rings safer to handle, reducing on-the-job injuries and eliminating the need for heavy equipment.

Though the initial ring price is slightly higher than its concrete counterpart, the following advantages lower the overall costs of the rings.

  • The cost to replace concrete rings that have broken during shipping and storage is eliminated.
  • The mortarless system allows for fast, non-temperature-critical assembly. Properly installed rings maintain a watertight seal. controlling the infiltration of groundwater and reducing wastewater treatment costs.
  • Rehabilitation projects to replace cracked and leaking concrete rings are eliminated.
  • Time and expenses associated with handing and storing heavy concrete rings are eliminated.

these patented manhole adjustment ring systems are made from 100 percent recycled HDPE plastic.