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Science/Technology

Background | Innovative Uses for Scrap Tires | Pyrolysis | Other Innovative Uses in the News

Background

In recent years, research on uses for scrap tires and advances in technology have created many new markets and innovative applications. New uses for ground rubber and advances in civil engineering keep millions of tires out of landfills and stockpiles every year.

Photo: Tires used to protect marshlands

The Army Corps of Engineers used tires to protect marshland on Gaillard Island, Alabama from wave action, enabling plant root systems to establish.

EPA performs research and development to identify, understand, and solve current and future environmental problems. EPA's Office of Research and Development has conducted research projects on scrap tires through EPA's National Center for Environmental Research. Research topics have included rubberized asphalt, bridge erosion protection, air emissions from scrap tire combustion, and pyrolysis.

One EPA funded project investigated the use of scrap tires to form a protective system for mitigating local scour around bridge pier s. Local scour is the erosion of the riverbed around bridge piers. Bridge failure caused by this phenomenon has long been an important issue with respect to both public safety and maintenance costs. Nearly half a million bridges nationwide are potentially affected by local scour. A honeycomb structure of scrap tires can mitigate local scour by modifying the water flow in the vicinity of a bridge pier and adjacent riverbed (more information on this project).

The U.S. Department of Energy (DOE) also conducts research on innovative scrap tire uses. One project, sponsored by DOE's Office of Energy Efficiency and Renewable Energy, investigated the development of a method for treating rubber from scrap tires so that it can be used in various applications such as carpet underlay, automotive seals and gaskets, caulks, sealants, and adhesives. The treated rubber requires much less energy to produce than the polymers it replaces. More information on scrap tire research at DOE.

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Innovative Uses for Scrap Tires

Highway Sound Barriers -- Many states are turning to absorptive sound barriers—structures that soak up sound—to reduce highway noise. The "Whisper Wall" used in Northern Virginia, starts as a mixture of concrete aggregate, cement, water, and small pieces of shredded rubber from scrap tires. The wall deflects sound waves among its nooks and crannies until they lose energy.

Athletic and Recreational Applications -- Several brands of resilient playground rubber surfacing material are being made from recycled tires and sold at major retailers across the US The material can absorb much of the impact from falls providing added safety to children. This material can also be used as a mulch replacement in medians or decorative areas. Athletic and recreational applications are a fast growing market for ground rubber. An estimated 80 million pounds of scrap tire rubber were used in 2001 for athletic/field turf applications (50 million pounds)—above or below the ground—and as loose cover (30 million pounds).

Railroad Ties -- Highly durable, rubber-encased railroad ties are being produced using scrap tires. These railroad ties have a steel-beam core filled with concrete that is then encased in 80 pounds of ground-up scrap tires and discarded plastic bottles, held together with a special binder or glue. These railroad ties are over 200% stronger than creosote-soaked wooden ties, enabling railroads to use fewer ties per mile. Moreover, rubber-encased railroad ties could last 60 to 90 years versus 5 to 30 years for wood.

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Pyrolysis

Pyrolysis is the thermal distillation or decomposition of organic materials into oils, gases, and char. Pyrolysis has been proposed as a method to break down tires into usable end products including steel, oil, and carbon black.

Despite many efforts to commercialize this technology, it is not economically viable in the US at present. The products of tire pyrolysis have limited marketability due to their low quality compared to virgin materials.

High cost also inhibits this technology. Refining the end products to market specifications requires expensive equipment. The capital investment and operating costs usually make the products of tire pyrolysis too expensive.

Although many pyrolysis projects have been proposed, patented, or built over the past decade, none have been commercially successful. No tire pyrolysis plants are currently operating in the US, however, this technology continues to be explored for expanded use. One example is a project funded by EPA's Office of Research and Development exploring the processing of tire pyrolysis oils to produce high value carbon black products: The Manufacture of Carbon Black from Oils Derived from Scrap Tires.

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Other Innovative Uses in the News

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