The idea surfaced in the early 1970s. When building a road, an innovative engineer reasoned, what would happen if you put fabric between the earth and the gravel grade to keep mud from seeping up?
“The original separator was nothing more than carpet backing,” Todd Anderson said. “Somebody looked at carpet backing and said, ‘I think if I incorporate this into a roadway, it might help.' And it did.”
Anderson is vice president of sales and marketing for TenCate Geosynthetics, a multinational company based in Atlanta that combines textile technology with chemical process and material technology.
More than 40 years later, he said, those technologies have advanced to the point that geosynthetics made by dozens of companies are used extensively in Montana and around the nation.
Jeff Jackson of the Montana Department of Transportation (MDT) estimates 75 percent of the state roads you drive on have a layer of textile material below.
“I think it’ll increase in the future, too,” he said. “Gravel is getting scarcer and scarcer. Just from an environmental standpoint, nobody wants to dig more gravel pits.”
Transportation funding continues to be a political hot potato in Washington, D.C. In late July, the Highway Trust Fund, which taps federal fuel taxes for road construction projects, was authorized for just three months. The battle over how to craft and pay for a long-term fund will be waged when Congress returns after Labor Day.
Meanwhile, state transportation departments are compelled to seek ways to get more bang from those uncertain bucks. Geosynthetics are a logical answer, some say, especially if you can figure out which ones work best.
“There are lots of different products coming onto the market with different shapes and sizes and different ways of building these products,” said Eli Cuelho of the Western Transportation Institute at Montana State University in Bozeman. “So the states are interested in knowing what properties of these products most relate to their performance.”
MDT and transportation departments from eight other states commissioned a 2012 study that compared and evaluated performances of a variety of geosynthetics from seven manufacturers. The test grounds were soft, mud-prone soils, such as those that pervade much of eastern Montana.
From mid-September to early November, a fully loaded, three-axle dump truck was driven 740 times over a grid 860 feet long divided into 50-foot test sections. The study occurred at Western Transportation’s TRANSCEND test facility in Lewistown.
The ruts were measured from each section, and they revealed that TenCate’s woven geotextile, called Mirafi RS580i, was the best in those conditions. It’s made of what looks like trampoline fabric.
“When you get down to the nitty gritty detail, TenCate’s was the only product that was a woven textile,” Cuelho said.
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With one exception, all the others were grids of plastic material welded or vibrated together. They looked like construction fences, Cuelho said. The exception was a non-woven product that “kind of looked like felt,” he said.
There are theories about why the woven geotextile finished at the top, but road builders and governments need more than theories.
Cuelho said he’s made a proposal to MDT for another study that looks specifically at that kind of subsurface. If it’s approved for funding, perhaps again with the team of state transportation departments, it’ll be conducted at Western Transportation's new indoor facility in Belgrade.
Anderson said the 2012 research was the most extensive of its type, and while TenCate was pleased with the outcome, the more important finding was that all of the synthetic surfaces performed better than the test control sections with no geosynthetics.
“It showed a legitimization of using, to put it simply, a piece of plastic in a road,” Anderson said. “What we have here is a full-scale study that not only shows that geosynthetics work, but all of them work, even the weakest. It could have a dramatic effect, but someone has to push it forward.”
Availability of gravel is a big expense in building new roads. Geosynthetics reduce the amount needed, which speeds up the construction phase. It also saves money on the other end by extending the life of a road, Anderson maintained.
Montana was the lead department in the 2012 study, which also included input and funding from those in Idaho, Oregon, Wyoming and South Dakota in this region, as well as Texas, Oklahoma, Ohio and New York.
While Cuelho is a Montana State University employee, he'll be traveling around Montana and to other states to discuss results and benefits of the Western Transportation Institute study on TenCate's dime.
Industry has been quicker than governments to embrace geosynthetics in road building, Anderson said.
“Montana is very progressive. They’ve invested money in this type of research,” he said. “But I think right now (states) are still in a very technical mindset that tends to be a little slower and a little less dynamic than maybe a financial mindset.”
Jackson is quick to point out that while the MDT-funded study showed TenCate’s offering was better on mud surfaces under specific parameters, “it’s not the one cure-all research” on geosynthetics.
That said, he added, “I think it was real successful research. I know it's helped us fine-tune how we proceed in Montana Department of Transportation projects.”