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March 2017 47 Above & Right The 100 percent rubber XLS for the tree surrounds features special- size three-quarter inch recycled rubber chips in the cypress color to mimic bark mulch. The availability of different sizes and colors of recycled rubber chips makes the material versatile for landscape design. Above For the XL formulation, the product's recycled rubber chips are mixed with kiln-dried ag- gregate granite chips and a liquid binder in a portable mortar mixer. It pours in place, forms a continuous paved surface, and conforms to the shape of curves and corners. It is finished with standard hand tools that contractors use for cement, such bull floats and trowels, and cures in just 24 hours. The XLS formula- tion was used for the permeable tree surrounds. Environmentally Friendly Approach to the Project >> Porous Pave is an eco-friendly, highly porous and durable poured-in-place paving material. According to Ryan Potvin, operations manager, Peterson Companies (Chisago City, Minn.), the landscape contractor for the Commons, Porous Pave was selected for its permeability, durability and ease of installation and maintenance. The shredding and processing of discarded tires produces the recycled rubber chips incorporated into the surfacing product. The Commons installation includes rubber recovered from approximately 5,000 scrap tires. In contrast to permeable pavers that infiltrate stormwater only in the spaces between them, the entire surface of Porous Pave is permeable. It infiltrates stormwater at a tested rate of up to 6,300 gallons per hour per square foot. The Commons brings much needed green space to the downtown and improves stormwater management, especially important with the Mississippi River just four blocks away. Reducing harmful stormwater runoff and pollution was an important goal of the project. "As is typical for highly urbanized areas, much of downtown Minneapolis is impervious. The Great Lawn is a prominent element of the Commons, designed as an open space and for deep infiltration of stormwater," said Mary Lydecker, RLA, LEED AP, senior associate, Hargreaves Associates (San Francisco, Calif.), the landscape architecture firm that led the project. "Extensive native and adapted tree and groundcover plantings, as well as various permeable surfacing materials, make the Commons very effective at decreasing stormwater runoff." "The Downtown Commons is one of our largest projects to date in the Upper Midwest," said Dave Ouwinga, president, Porous Pave, Inc. "It helped us reach an important environmental milestone. In 2016, we surpassed a total 7.5 million pounds of recycled rubber used in manufacturing our permeable paving material." The liquid binder is moisture-cured. A light spray of water on the completed permeable pave - ment helped to accelerate the curing process. For the tree surrounds, the Porous Pave XLS all-rubber formulation was mixed with its spe - cial binder, shoveled into the wells atop the soil, and the workers finished it with trowels. Black - stone tapered and thinned the material at the tree trunks to allow for the expanding diameter of the trunks as the trees grow. Since the XLS was also used for tree surrounds in nearby streetscapes next the Commons, the Blackstone crew took small batches of the material in wheelbarrows for those trees. All tools and equipment were rigorously cleaned with bio-diesel and stiff brushes. LC DBM