Each year, about 27 million tires end up in landfills, dumps and stockpiles, where they pose health and environmental hazards. These tires could get a second life as components of the roads they once traveled, but blends of ground tires and asphalt can be unstable. Now, researchers have identified polymer additives that increase the storage stability of asphalt rubber.
Because rubber is so resilient, scrap tires persist in the environment for a long time, creating fire hazards and breeding grounds for rodents and mosquitoes. This durability could make tires advantageous for producing rubber asphalt -- a mixture of ground tire rubber and bitumen (asphalt) used to pave and repair roads. Currently, about half of U.S. states use ground tire rubber as a component of asphalt mixes, citing better performance than regular asphalt, cost-effectiveness and environmental benefits. However, the material has two major challenges that limit wider use: its high viscosity and tendency to separate into rubber and bitumen layers during storage. Christopher Williams, Eric Cochran and colleagues wanted to identify polymer additives that mitigate these problems.
According to the new study by the American Chemical Society, researchers have identified polymer additives that increase the storage stability of asphalt rubber. The team found that, when mixed with asphalt, blends of recycled tire rubber (RTR) with trans-isoprene or polybutadiene performed best. These mixtures reduced the density of RTR so that it was similar to asphalt and did not settle during storage. The polymers also helped reduce the viscosity of the asphalt rubber so that the material was easier to work with.