"Innovations" Case Studies: New Uses for Old Tires
Supporting Tire Recycling Through Local Public Works ProjectsLocal government public works departments can play a key role in supporting the development of new markets for tires.
A key market for tires is the addition of crumb rubber to produce rubberized asphalt concrete (RAC). Caltrans began its use of rubberized asphalt concrete in 1980. Between 1980 and 1998, Caltrans used a total of 2,458,930 tons of RAC in every one of its regional districts. Based upon the formula developed by the Rubber Pavements Association, this translates to the use of 4.5 million discarded tires.
Caltrans estimated that it is currently using RAC on 10 to 12 percent of its projects. The Rubber Pavements Association estimates that Caltrans could use RAC on up to 40 percent of all paving projects.
Los Angeles County has been the leader among local governments in the use of RAC. The county established, with the assistance of the CalRecycle, the Southern California Rubberized Asphalt Concrete Technology Center to promote the use of RAC. While the county’s efforts are focused in Southern California, the center answers questions from local governments throughout the state.
Use of tires in rubberized asphalt concrete can produce significant cost savings and diversion potential for local paving and road maintenance operations. While the cost savings will vary based on the project, the Southern California Center has produced design examples with cost savings of $22,852 per mile for a simple asphalt overlay and savings of $170,776 per mile for roadway reconstruction. Based on LA County’s use of rubberized pavement since 1993, RAC diverts approximately 2,000 tires per lane mile.
The use of rubberized asphalt provides a variety of benefits, including:
- Longer lasting surface (50-100 percent).
- Resistance to rutting and cracking.
- Reduced road noise (50-80 percent).
- Less buildup of road surface.
- Reduced cost of project and/or ongoing maintenance expenses.
In addition to RAC, local governments may also consider the use of rubberized emulsion aggregate slurry (REAS) in street resurfacing projects. Although REAS is more expensive per lane mile, LA County’s experience shows it can divert almost 80 tires per lane mile. REAS also provides a number of other benefits, including increased performance and extending the roadway’s lifespan.
While RAC/REAS provides a number of benefits, it may not be appropriate in every application. The use of RAC/REAS should be determined on a case-by-case basis taking into account the uses of the roadway and its initial condition for compatibility.
Staff should work with city administrators and contractors to modify current practices to ensure that the use of RAC is considered. In addition, local governments can request that Caltrans use rubberized asphalt on projects within their jurisdiction. Construction contractors should be linked up with the tire processors to ensure that the bids are accurate. Special attention should be paid to projections of volume vs. weight used and the timing of use during construction.
To help local governments in considering its use, RAC is now specified in section 200 (page 98 and 258) of the “Green Book” (or Standard Specifications for Public Works Construction) used by local government throughout California.
The County of Santa Clara has established a resolution on the use of rubberized paving materials as part of its open bidding process. Contractors are required to submit bids that contain options using tire-derived paving materials. The county then can assess the up-front costs and performance projections, as well as any special factors that may effect the determination to use recycled materials.
The City of Thousand Oaks has used RAC to pave more than 130 miles of roadway since 1992 using 1.3 million tires. Recent costs for RAC have averaged $49 per ton. This includes application during day and night periods, as required by the urban nature of Thousand Oaks. The city found that the improvements of increased skid resistance, reduced road noise, improved riding qualities, and imperviousness to water have made the use of RAC cost-effective and desirable over traditional asphalt concrete.
Communication with public works departments and jurisdictions that have experience with paving and civil engineering application can help address local concerns or specific needs. Jurisdictions with RAC/REAS experience include the following cities and counties:
- Costa Mesa
- Culver City
- Garden Grove
- Huntington Beach
- San Clemente
- Santa Monica
- Thousand Oaks
- Santa Clara
- San Francisco
- Los Angeles
In an effort to document the use of RAC, the CalRecycle and the California Department of Transportation (Caltrans) have established a rubberized asphalt concrete pavements review team. Members included private contractors working in supply, production, and application of tire-derived paving materials. The team observes and assesses the performance of rubberized paving materials. The goal is to develop a database as well as experience and technical expertise in the rubberized paving field.
The preliminary report of the team found that 101 out of 113 projects were successful. Of the 12 projects rated fair or poor, most members of the team believed that the failures would have been greater with traditional asphalt concrete. These failures may also have been caused by using poor aggregates.
The picture below shows the application of rubberized asphalt concrete in Sacramento.
Civil Engineering Applications
The use of shredded tires as fill in civil engineering applications is a major potential market for waste tires, but it is currently only in the demonstration phase in California. In 2001, the CalRecycle sponsored a project in the San Francisco Bay area at a new interchange on Interstate 880. Six hundred thousand shredded tires were used as lightweight fill for a highway on-ramp built on unstable bay mud.
Shredded tires have an enormous potential to be used as lightweight fill in civil engineering applications, and they can replace other conventional lightweight fill such as expanded foam. Besides providing a major end use of tires, tires used as fill provide improved permeability and greater insulating properties than traditional fill materials.
Civil engineering fill has been limited to a few pilot projects in California (Humboldt County and Chico, in Butte County); however, the CalRecycle is strongly supporting the development of this market. The State of Maine has been a major user of tires for civil engineering fill, making it the predominant use for its abatement piles.
This market can have a significant impact on discarded tire use. Individual projects can use several hundred thousand tires. Civil engineering applications require that tires are shredded, and minor adjustments to project designs may need to be made. The performance of the material can exceed current options available and can substantially reduce costs associated with lightweight fill.
Examples of civil engineering projects include the following:
- Overpass fill.
- Levee slurry wall (mix with concrete).
- Retaining wall fill.
- Roadway base fill.
- Bridge abutment fill.
In addition to fill applications developed by Maine, here are some other potential civil engineering applications:
- The CalRecycle has guidelines regarding use of tire shreds in landfill applications. These uses include leachate drainage material, final cover foundation layer, operations cover, and gas collection layer. In Virginia, tire shreds have been used for septic tanks. Specifications are available for septic tank leach fields in an average four-bedroom home using 1,350 tires per system.
- The usage of tires in Virginia presents a viable option for rural areas. Depending on the contamination limits and the ability to store a stockpile of shreds, a local government could make available the shreds as a fill for the residents or for private contractors.
The CalRecycle is conducting a demonstration of tire shreds in leach fields at a highway rest stop along Interstate 5. The project was constructed in 1999-2000 and is currently being monitored. The picture below demonstrates efforts to replace playground equipment to achieve compliance with State and federal laws and to provide an opportunity to showcase new uses for recycled tires. (Source CalRecycle)
Recent State and federal laws have required schools and public agencies to renovate playground equipment in order to meet new safety and accessibility standards.
In an effort to encourage the development of new uses for tires, the California Legislature passed the Playground Safety and Recycling Act (AB 1055, Villaraigosa and Keeley, Chapter 712, Statutes of 1999). This law established a $2 million matching grants program to replace and upgrade public playground equipment. The act requires 50 percent of the funds be used to purchase equipment made from recycled materials such as tires.
The City of Torrance took part in a public/private partnership program with Sears, Roebuck and Co. In 1997, the city received 10,000 pounds of recycled rubber resurfacing products for several local schools as part of the store’s R.O.T.A.T.E. (Recycling Old Tires Aids The Environment) program.
The program includes special tire collection events. A local processor turns the tires into crumb rubber, and the R.O.T.A.T.E. program supplies products at no cost to the locality where the tires were collected. Los Angles County helped to coordinate the program and supplied curriculum materials on tires for elementary students. This program reached more than 500 students.
The City of Garden Grove is an example of a community that has used tires in a variety of ways. The city used 22,500 tires in projects, receiving a total of $195,000 in grant assistance. Tire projects included the following:
- Purchase of two railroad grade crossings using 3,500 tires and a $50,000 grant. The railroad installed the crossings.
- Four playgrounds were resurfaced using grants of $25,000 and $20,000, and recycling 10,000 tires.
- The city received a $100,000 grant for the use of resealing slurry (REAS) on local road projects using almost 9,000 tires.
The picture below demonstrates efforts to replace playground equipment to achieve compliance with State and federal laws and to provide an opportunity to showcase new uses for recycled tires. (Source CalRecycle)