Using plastic to save trees

Large old trees give so much. They provide beauty and shade, raise property values, remove pollutants, and have even been shown to bolster mental health.

However, their sprawling roots tilt up concrete sidewalks, posing physical risks in the form of tripping hazards that can open cities to costly lawsuits.

What's an environmentally conscious and legally liable community with mature trees to do?

In Logan, Utah, they are looking beyond the age-old solution of getting out the chainsaws. Instead, they have replaced some buckling slabs of cement with paving tiles made from 100 percent recycled low density polyethylene. Called Terrewalks, the 24-inch-by-30-inch tiles are 35 pounds each and can be easily removed to trim tree roots and then set back in place.

Not only have Terrewalks saved trees in at least 200 U.S and Canadian cities, the raw materials for the synthetic squares come from some of the lowest grades of LDPE. We're talking dirty agricultural film that previously had little if any demand, as well as by-products from composite wood deck maker Trex Co. Inc. And, that solves another issue of what to do with some problematic post-consumer waste.

Terrewalks are sold by Terrecon Inc., which is based in Fountain Valley, Calif. CEO and founder Lindsay Smith got the idea for the business in 2001 after seeing red Xs painted on 26 ficus trees marked for removal in her California neighborhood. Her company started out using rubber for the flexible sidewalks but added recycled plastic in 2007.

The raw materials, such as plastic wrap used to bale hay for dairy cows, are converted into Terrewalk tiles through a process called thermo-kinetic technology, which, unlike injection and extrusion molding, does not require plastic to be clean, sorted or pelletized.

“It's a form of compression molding that allows the plastic to be coarse and diverse,” Smith said in an email. “This contributes to the concrete-like appearance of Terrewalks.”

Terrecon has partnered with three different manufacturers in the western United States to date. But starting in April, Lehman & Sons Enterprise LLC of Bristol, Ind., will exclusively handle production. Smith said a central location is needed as plastic sidewalks make inroads across North America.

“This is part of the evolution of the company and a desire to lower costs of the products,” she said. “Being in the central U.S. will reduce the cost of shipping, but most importantly, it's because there is so much ag plastic in the Midwest. Before, we were spending a lot on moving plastic.”

Root of the problem

Logan, a college town in northern Utah, has won Tree City USA awards for 28 years and counting, so when some giant willows, cottonwoods and London planetrees were facing the ax in 12 residential and high-traffic areas, some people cringed.

“Public safety is at the top of the list for the city of Logan, so the tree often loses out when these conflicts arise,” Megan Dettenmaier, the forestry extension educator at Utah State University, said in an email.

She and her colleague had heard about plastic sidewalks being used to leave problem trees in place and they checked into it. Dettenmaier talked to local officials in Alaska and Wisconsin and after getting positive reviews she applied for and received an $8,000 state grant to try Terrewalks in Logan. The city matched the grant with $10,000 and provided the labor to install the tiles.

“Trees in Logan will be spared, and if they become a problem again, the tiles can be uplifted, problem roots can be trimmed, and the same tiles can be re-laid,” Dettenmaier said in an email. “This is a unique product that reduces waste, helps cities retain mature trees, and creates safe walkable sidewalks. And, even better, the construction can usually be completed in a day.”

Plastic sidewalks are more expensive than concrete — initially, she added.

“But there are high costs associated with the business-as-usual model, where trees that have buckled sidewalks are removed, new sidewalks are poured and new trees are planted, only to have the cycle repeated in the future when that new tree becomes a problem again.”

Terrewalk pavers, which have a 20-year warranty, were installed in Logan last summer and are being monitored as to how they hold up to heat, harsh winters and different snow removal methods.

“Weather is the biggest unknown at this time,” Dettenmaier said.

Branching out

While some municipalities consider themselves in the test stage for Terrewalks, Smith said the product is “tried and true” and gaining popularity for commercial, corporate and university applications. The plastic tiles can replicate the look of granite, marble and stone and they are promoted as slip-resistant and compliant with the American with Disabilities Act

“They've been installed throughout the country since 2008,” Smith said. “They are unbreakable — even when they are frozen solid. They're long lasting and pretty much indestructible. … They are also safer and more comfortable to walk or run — or fall — on.”

Terrecon recently announced that its paving tiles also will be specified for tee pads by Houck Designs, which it says is the No. 1 disc golf designer in the world, because they are easy to install, durable and cleanable.

The paving tiles also qualify for green building credits because they are made of recycled material and resist sunlight, which reduces the heat-island effect brought on by cement. In addition, the polymer pathways can play a role in storm water management. The bottom sides of Terrewalks have channels that serve as reservoirs and can hold 2.3 gallons of rain per paver. That allows storm water to slowly percolate to the soil below.

“Certainly preserving and maintaining the urban forest is its main benefit, but capturing storm water is a very big consideration these days,” Smith said.

Terrewalks also are good for construction sites, where they can't be marred by heavy equipment like poured concrete, she added.

With the benefits plastic sidewalks offer, Terrecon is on the path to wider acceptance but will it change our landscape underfoot? Smith said displacing concrete as the main material for sidewalks will take a paradigm shift.

“The greatest challenge is overcoming the habitual use of concrete for sidewalks,” she said. “The infrastructure for concrete is highly evolved with contractors, installers, internal and external relationships, and red tape. Change meets resistance — even when everyone knows that concrete breaks, causing trip hazards and lawsuits, and it cannot coexist with the urban forest.”