Liberty official: Rubber-modified asphalt is proven commodity

HILTON HEAD ISLAND, S.C—Barriers still exist to the expanded use of rubber-modified asphalt, despite the proven benefits of the technology, according to a speaker at the 32nd Clemson University Global Tire Industry Conference.

“One of the best ways to deal with scrap tires is to put them back into the road,” said Richard Gust, president, national accounts for Liberty Tire Recycling.

The idea of modifying asphalt with scrap rubber was advanced in Europe as early as 1938, and in 1949 an asphalt-rubber mix was used on an experimental stretch of road in Akron, according to Gust.

The commercial application of rubber-modified asphalt began in Arizona in the mid-1960s, and since then the technology has more than proven itself, he said.

Rubber-modified asphalt is safer and more durable than conventional asphalt, reduces both noise and costs, and is environmentally responsible and sustainable, according to Gust.

Nevertheless, many state highway departments are still leery of rubberized asphalt, and the reasons are somewhat complicated, he said.

In the 1960s and for years afterward, Gust said, rubberized asphalt technology was covered by a patent, which effectively prevented its expansion from Arizona. But even after the patents lapsed, major problems arose.

The biggest, according to Gust, was the provision in the Intermodal Surface Transportation Efficiency Act passed by Congress in 1991. That provision required state transportation agencies to use crumb rubber in federally funded highway paving projects, at a gradually increasing rate up to a final total of 25 percent, as a prerequisite for keeping federal funding.

“It was a good concept, but a concept the industry was not prepared to undertake,” he said.

Many states were not prepared to use rubberized asphalt, which requires substantially different methods of mixing and application from traditional asphalt. Most contractors lacked the expertise to apply rubberized asphalt, and several road projects failed as a result, turning state agencies against the technology, he said.

Soon, Congress was forced to repeal the rubberized asphalt mandate, according to Gust.

“This mandate created a black eye on the industry, and we still face this historical prejudice in many places today,” he said.

To overcome this prejudice, organizations such as Liberty Tire, the Rubber Manufacturers Association and the Tire Industry Association have devoted considerable time to educational efforts, Gust said.

Bridgestone Americas joined Liberty Tire in public recycling events in Atlanta, Wisconsin, Nashville, Akron and Florida between 2011-14, he said.

But many state DOTs require their own testing of paving materials, which takes considerable time, Gust said. In one case, the Florida DOT rejected the positive results of rubberized asphalt testing in Georgia on the grounds of climate differences between Georgia and Florida, he said.

“Testing for technology improvement is sound science,” Gust said. “However, when sound results are achieved in several states, and verified through nationally recognized test centers, like the National Center for Asphalt Technology, does every DOT really need to independently confirm these positive results?”

A number of states are increasingly specifying rubberized asphalt in road projects, but many place needless restrictions on its use, according to Gust. For instance, Georgia allows rubberized asphalt only in projects with an average daily traffic threshold of under 100,000—a limitation unsupported by science, he said.

The Federal Highway Administration has published a technical brief recommending that recycled materials be given first consideration in material selection, and that restrictions on their use that are not supported by scientific evidence should be removed from specifications, according to Gust.

“That's what we're trying to accomplish with state DOTs,” he said. “We seek a specification that allows ground tire rubber to compete on a performance-based, level playing field.”

One helpful fact is that many local road projects do not require state approval—only city and county specifications, Gust said.

“We're working with city and county engineers where they do not need DOT approval,” he said.

Demand for rubber-modified asphalt has improved since the 1990s, when the cost of crumb rubber exceeded that of oil, Gust said.

Equipment costs for rubberized asphalt also have dropped with the introduction of “dry” or “plant mix” processes, which allow crumb rubber to be introduced directly into the mill where heated aggregate and binder are mixed, he said.

Projects in Sweden and Saskatchewan have proved the performance of rubberized asphalt in cold and wet conditions, as have recent work in Massachusetts and New Jersey, according to Gust.

“Rubberized asphalt is a technology backed by decades of research and development,” he said. But it takes forward-thinking government officials, DOT engineers, road paving contractors and the tire recycling industry to bring an initiative like this to fruition.

“We need to forget all the reasons it won't work and remember the reasons it will,” he said.