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The University of Minnesota Duluth (UMD) installed three test sections of permeable pavers on campus next to conventional concrete pavers to test the difference in durability and stormwater management ability in the fall of 2007. When inspections of the surfacing were positive following a harsh Minnesota winter, UMD decided to expand its permeable paver installations. The sustainable stones held up admirably upon subsequent examination more than six years after construction.

Product case studies often examine the potential for problem-solving, considering attributes like speed of installation, labor savings and the like. When it comes to performance, however, most hardscapers have projections for the future of an installation but rarely follow up unless there is a significant problem, thus, the strength and reliability of a product months or even years later remains a mystery. The University of Minnesota Duluth (UMD) set out to dispel some of these mysteries by revisiting a permeable paver project six years after the pavers were installed side-by-side with traditional concrete pavers. 

In the fall of 2007, when UMD tested new permeable paver technology against traditional concrete pavers, the former was a recent invention, available only regionally and through architect specifications. The difference in comparison to concrete pavers is clearly visible: no signs of cracks, minimal wear and tear, damage or color change. The concrete pavers in the test area, however, had buckled and rose up on one side, and showed cracks and wear.

UMD deemed the test to be favorable for the new recycled-content permeable pavers in Spring 2008, and six years later, the university is still encouraged by the new pavers’ performance in all three locations. The school’s facilities division went on to complete 990 square feet of pavers in the loading dock area of the Civil Engineering Building, and the school also retained the test installations.

UMD’s need for a permeable solution came about when the school began construction on a new civil engineering building and wrestled with methods to manage stormwater runoff on impervious surfaces around the building, since the campus is adjacent to a designated trout stream that drains into Lake Superior. The university’s Storm Water Pollution Prevention program required stormwater treatment in new construction, so the designer suggested AZEK permeable pavers for their water infiltration properties, due to the spacer lugs on the sides of the pavers, and as much as 95 percent recycled content in the paving units. 

The pavers are comprised mostly of scrap auto tires and some plastics, and make it easier to attain LEED points than traditional pavers.

The soil at the installation site has high clay content and is not conducive to absorbing water, UMD Sustainability Coordinator Mindy Granley said. Without the permeable installations, “rainwater from the campus can get from the top of the hill to Lake Superior in just 10 to 15 minutes,” Granley added, noting that by controlling the volume and speed of the water flow, hill erosion and waterway pollution caused by runoff is reduced.

The big question was how the pavers would perform in subfreezing Minnesota temperatures, repetitious freeze-thaw cycles, the scraping of snow plows, the snow itself and salt used for deicing. Combined with heavy truck traffic in a loading dock area, the installation presented an all-out challenge between a new paver technology and a traditional installation. Management of rainwater runoff was also central to the case study.

The test was set up in two high traffic areas. The first was a 600 square foot loading and storage area expansion of UMD’s plumbing shop, where truck deliveries are made. UMD engineer Erik Larson said this was an appropriate test area since it had poor drainage and was frequently muddy after heavy rains, and had vehicle, forklift and truck traffic. Set into their unique 16 x 16 inch interlocking grids, the permeable pavers were installed next to traditional concrete pavers on the same engineered base.

Unlike concrete pavers in the same areas, the permeable paver installations were unaffected by several tough Minnesota winters and freeze-thaw cycles, showing no cracks or color fading.

The second area covered a 75 square foot triangular space outside the Sports and Health Center, where the unloading of sports teams and student foot traffic took a toll on the area. Despite attempts by the building and grounds division of facilities management to landscape the space, students kept walking through the area. It provided a good proving ground to see how the new permeable pavers handled foot traffic in winter conditions.

According to Mindy Granley, UMD’s sustainability coordinator, the new pavers have been an effective solution to UMD’s soil conditions, and have stood up to the extreme winter conditions and foot traffic. “We intend to use the pavers on future projects,” said engineer Erik Larson. According to the manufacturer, the production of these permeable pavers uses 95 percent less energy and produces 96 percent less in CO2 emissions than conventional pavers, plus has diverted more than 10 million pounds of scrap rubber and plastics from U.S. landfills.