Scrap tires - From waste material to raw material
Do tires belong on the road? Sure they do. But for roughly two decades now, they can increasingly be found in the road as well. Recycled tires and VESTENAMER®, a processing aid that Evonik Industries makes for the rubber industry, are what make that possible.
European highways today are nearly 75,000 kilometers and are constantly being expanded. Besides to the road construction, maintenance existing highways is an essential task to keep the traffic rolling and thus also economic growth on the old continent.
In addition, since 1975, the number of vehicles per 1000 inhabitants has more than doubled within the European Union. Long-distance road freight transport has also increased significantly. More and more trucks are on the road with increasingly large axle loads, posing new challenges for road surfaces.
Innovation for polymer-modified asphalt
Road quality and stability remain essential issues for the public sector. The clearly emerging need for high-performance road construction materials to prevent ruts and cracks—and thus reduce maintenance costs—is looming larger in the public consciousness. At the same time, the cost of the raw materials for asphalt, especially for asphalt modifiers, has risen exponentially, standing in contrast to the goal of cost-effective road construction.
Evonik Industries has patented a process that could help solve these problems while improving road conditions: it involves blending VESTENAMER®, a polyoctenamer, with crumb rubber from recycled tires and adding this mixture to the bitumen and asphalts used in pavement.
Asphalt blends containing rubber have been used in the United States for many decades now, and long-term studies there have verified significant improvements in stability. “The European market for elastomer-modified road surface has been growing for a few years,” says Frank Lindner, the sales and new business development manager for VESTENAMER®. “Its positive properties are obvious, because it significantly reduces the formation of ruts and potholes, as well as the susceptibility of the road surface to cracking—and that extends product life.”
Another one of our senses supports the use of rubber-modified bitumen as well: crumb rubber is often used in open-pored silent asphalt, where it reduces traffic noise. Scientific studies have shown that increasing the proportion of rubber used in pavement can lower noise levels by one to two decibels—a huge success, as Lindner points out, because reducing noise by three decibels cuts the perceived traffic volume down by half.
The addition of VESTENAMER® also delivers additional advantages over other rubber modifiers: using the process enhancer, he says, reduces the mixing temperature required to produce a homogeneous blend. “One consequence of that is a significant reduction in energy consumption. Another is the release of fewer emissions,” Lindner explains.
Making worthwhile use of scrap tires
And VESTENAMER® is clean: in one study, no emissions of critical compounds could be detected of any kind—neither during mixing, nor when laying down the asphalt on the road. No N-nitrosamines were found at all, while emissions of volatile and low-volatile compounds—including hydrocarbons and sulfur compounds—were considerably lower than is the case with traditional, polymer-modified asphalts.
In addition, the binding properties of VESTENAMER® prevent chemicals within the asphalt mixtures, such as sulfur or amine-containing compounds, from being washed out into the groundwater by the rain.
Using recycled tires makes environmental sense every time: “Recycling used tires protects valuable resources,” points out Dr. Sandra Reemers, who is responsible for the specialty polymers business. “The tires aren’t classified as garbage—they’re instead considered to be valuable materials that shouldn’t just go, say, to a landfill. And that makes the disposal question moot: instead of burning tires, we give them a new life on the road, albeit one as an elastomer in the road surface instead of a horsepower-driven one on the road.”
One recognized certification body conducted a study providing information on the environmental performance of the system: the study found that, for each metric ton of crumb rubber used, recycling eliminated roughly 1.7 metric tons of carbon dioxide emissions that would otherwise result from incineration. Use of this material, in other words, takes us a long way toward optimizing our carbon footprint, Reemers observes, noting that, when the road surface then needs to be replaced at some point, the asphalt can be recycled. “So you end up with a closed loop,” Reemers explains. In addition, the system developed by Evonik generates enormous potential for reducing CO2, as a life cycle assessment conducted by the Genan company has demonstrated. Growing numbers of European towns and cities are deciding to use elastomer-modified asphalt more and more often. Plus, polymer-modified asphalt blends were incorporated into road construction regulations in the spring of 2013.
VESTENAMER® was developed in the late 1970s as a processing aid for the rubber industry. Even today, its strengths lie in the positive properties that arise when it interacts with other rubber products. Within just the first few years, the processing aid had already gained a foothold among numerous rubber processing companies. In addition to its use on the tire market, the material is also worked into rubber products such as hoses, clutch linings, molded parts, and rubber coatings for rollers. Because state road authorities have long been on the lookout for an improved, longer-lasting material, the High Performance Polymers Business Line began conducting in-depth research in this area ten years ago. Since that time, VESTENAMER® has increasingly become the binder of choice in rubber-modified asphalt.