Every year, around 27 million tires land in dumps, stockpiles, and landfills, creating environmental and health risks. These tires could possibly have a second life as components of the roads on which they once treaded.
A polymer additive stabilizes asphalt made with used tire components. (Image credit: Don Pablo/Shutterstock.com)
However, mixtures of asphalt and ground tires can be unstable. At present, scientists have found polymer additives that improve the storage stability of asphalt rubber. They have published their results in the
ACS journal Energy and Fuels.
Since the rubber is very durable, scrap tires pose fire hazards and serve as breeding grounds for mosquitoes and rodents as they stay in the environment for a long period. This resilience could render tires beneficial for manufacturing rubber asphalt, which is a blend of ground tire rubber and bitumen or asphalt used to overlay and repair roads.
Presently, around half of U.S. states use ground tire rubber as a constituent of asphalt blends, presenting superior performance, cost-effectiveness, and environmental benefits when compared to regular asphalt. Yet, there are two main challenges that restrict broader use of the material: its high viscosity and tendency to break up into rubber and bitumen layers during storage. Christopher Williams, Eric Cochran, and colleagues sought to determine polymer additives that alleviate these issues.
The scientists studied the stability of rubber asphalt produced by combining and extruding various quantities of the polymers trans-isoprene, cis-isoprene, polyisobutylene, or polybutadiene with ground tire rubber. The researchers identified that mixtures of ground tire rubber with polybutadiene or trans-isoprene in a 3:1 ratio worked best when they are mixed with asphalt.
These mixtures decreased the density of ground tire rubber so that it was similar to asphalt and did not sink at the time of storage. Furthermore, the polymers helped decrease the viscosity of the rubber asphalt so that it was easier to work with the material. The scientists suggest that the polymer additives are economical, leading to savings of about 7%–10% in comparison with regular asphalt.