AIR POLLUTION ISN'T THE ONLY EVIL CARS LEAVE BEHIND. Every year, the U.S. scraps 275 million tires. Dumps already contain about 3 billion rubber carcasses--enough to circle the earth 34 times, according to researchers at North Carolina State University. Tires don't biodegrade. Burning them releases noxious fumes and liquids. And their shape makes them practically useless for any secondary purpose.
Unless, that is, you grind them into powder and combine that powder with cement. It's not a new idea, but after carefully analyzing various combinations of the two materials, North Carolina State civil engineering professor Shuaib H. Ahmad believes that he has found the optimum mix.
Up to 10% rubber can be added to road cement with only minor changes in the pavement's durability and resistance to inclement weather. Of course, shredding the used tires takes a bit of energy, which means burning fuel. "There's always going to be a trade-off," Ahmed says. But the engineer hopes that the new composite, which he calls "rubcrete," will pass the remaining fatigue tests in the next few months. Then, maybe, the rubber will really hit the road.