"Innovations" Case Studies: New Uses for Old Tires

Case Studies

• Los Angeles County Use of Rubberized Asphalt
• State of Maine's Alternative Fill Programs

Los Angeles County Use of Rubberized Asphalt

Overview

The County of Los Angeles began limited use of rubber in asphalt in the 1970s. In 1985 the county used a 1½-inch layer of RAC to resurface a roadway that is holding up exceptionally well to this day. Federal regulations that had required the use of recycled rubber in paving projects under the Intermodal Surface Transportation Efficiency Act of 1990 served as an incentive for LA County in the use of RAC.

Since 1992 the county has been using both RAC and rubberized emulsion aggregate slurry (REAS) in its highway and street resurfacing products respectively. RAC use by the county since 1993 has resulted in diversion of more than 1.2 million tires, paving close to 600 lane miles (a diversion of 2,000 tires per lane mile). The county now uses RAC on 75 percent of its highway resurfacing projects, using funds for road construction generated by gasoline taxes.

Blending crumb rubber with asphalt and aggregate under specific conditions produces RAC. A crumb rubber producer grinds the waste tires into crumb rubber. The crumb rubber is then blended with the asphalt and aggregate in a preset formula at the asphalt plant

under the “wet” process and shipped to the construction site for use. A blender unit is needed at the asphalt plant.

REAS is defined as crumb rubber blended into asphalt emulsion at ambient temperature and used as slurry on road surfaces. Los Angeles has used REAS since 1993, paving more than 1,330 lane miles. This has resulted in diversion of 104,000 tires (at 78 tires per lane mile). REAS projects have been similarly paid for using gasoline taxes.

To support the use of RAC, LA County and the CIWMB jointly created the Southern California Rubberized Asphalt Concrete Technology Center (SCRACTC). The center serves as a professional outreach operation and as a clearinghouse for information regarding crumb rubber pavement use.

Program Characteristics

The LA County Department of Public Works operates the RAC/REAS program as part of its ongoing road construction and maintenance operations.

Los Angeles requires the use of RAC/REAS in paving projects, as appropriate. Staff members assess the projects that are suited for use of RAC/REAS materials, and contractors are asked to submit bids accordingly. Public works staff monitors both the blending and the application process to ensure project success.

This coordinated effort by the public works staff is the primary reason for LA County’s success in using RAC/REAS to divert tires from landfills. The SCRACTC assists local governments in making RAC use determinations. The center, on behalf of CIWMB, provides grants for both

roadway deflection testing and quality assurance control monitoring. These grants are given first to jurisdictions that have not used RAC before, then to others.

Costs, Economics, and Benefits

LA County requires large amounts of paving material in ongoing public works projects. The county has saved initial construction funds by using RAC, and administrators project substantial long-term savings in maintenance costs.

Two examples of cost savings are shown below (Source: SCRACTC):

The county found that RAC has a number of advantages over traditional asphalt concrete:

• Cost-effectiveness.
• Longevity.
• Increased skid resistance.
• Decreases in road noise (50-80 percent).
• Lower maintenance requirements.
• Better color contrast for striping.

Although REAS is more expensive per lane mile, it also provides a number of benefits:

• High skid resistance.
• Long-lasting color contrast for striping.
• Extension of the roadway’s life span.

Los Angeles has funded the use of both RAC and REAS directly through the use of gasoline tax revenue.

Local Government Challenges and Opportunities

The historic challenge in using RAC was that the technology/process was patented, and patent fees drove up costs. In 1992 the patents expired, putting RAC in the public domain.

The next challenge for LA County is to convince public works officials of the benefits of using a “new” paving material. The greatest opportunity in using RAC/REAS is the potential for diversion of tires from landfills (up to 2000 tires per lane mile).

Tips for Replication

• Ensure adequate stakeholder awareness and education.
• Promote communication between project engineers, local public works officials, private contractors, and crumb rubber producers.
• Understand the material processing requirements and application procedures-this is essential to a successful project.
• Provide adequate monitoring to ensure successful application.
• Conduct follow-up monitoring and testing of RAC/REAS paving projects.
• Recognize that RAC/REAS may not be suitable in every application.

Northern California RAC Center

The County of Sacramento opened a rubberized asphalt technology center in 2000. The center functions on the same model as the SCRACTC and assists local governments in Northern California with RAC use.

State of Maine’s Alternative Fill Programs

Overview

The State of Maine first began to explore the use of tires for transportation projects as a paving material in the early 1990s. Federal regulations targeting recycled tire use drove the effort. Finding the costs at the time to be prohibitive and the potential for use limited, the state began to look for another option.

Professor Dana Humphrey, a professor of civil engineering with the University of Maine, came up with the option of using tire shreds as an alternative to lightweight clean fill. The use of tires-at that time untested-could potentially save money as well as out-perform the other materials then being used as fill.

Professor Humphrey began working with the Maine Department of Transportation (DOT) and the Maine Department of Environmental Protection (MDEP). Representatives from these agencies formed the stakeholders group.

As projects were proposed, they were evaluated for the use of tires as applicable and where study would be possible to assess the value of tire shreds as a clean fill option. From 1993 to 1998, Maine DOT used 920,000 passenger tire equivalents in five fill projects. The MTA used 1.2 million tires in a single project in 1997-98 and plans to use a similar amount in a project in the summer of 2000.

Lightweight fill is now the primary use for tires removed from Maine’s abatement piles; however, it is not the primary use for the state’s current tire flow. More than 5 million passenger tire equivalents (PTE) are burned as fuel in three paper mills, making this the primary use. In addition, a total of 1.8 million tires were used as the operations layer in two landfills from 1997 through 1999.

Picture below shows use of tire shreds in civil engineering fill on Route 9, Days Hill, Maine. (Source: Dana Humphry)

Program Characteristics

The management of Maine’s tire diversion program falls into two distinct parts. The collection and stockpile management is coordinated by the MDEP, which permits both haulers and the tire chippers (shredders). Maine’s tire management program assesses a fee of $1.00 per tire for all after-market tires; these funds go into the general waste management account for various programs. Tires are accepted at tire dealers and transfer stations typically for an additional fee of between $1.00 and $5.00.

The tire fee covers the cost associated with handling and transportation of the waste tires to two tire chippers, one in Maine and the other in Massachusetts. Maine does not permit the landfilling of whole or shredded tires and exports only a small fraction to a cement kiln in the Canadian city of Montreal.

Maine’s Civil Engineering Project Examples:

1. Town road in Richmond: 20,000 tires in 600-foot road.
2. 2-lane secondary state highway in North Yarmouth: 100,000 tires in 400 feet of road.
3. 4-lane primary highway in T31MD: 200,000 tires in 400 feet of road.
4. Highway embankment in Portland: 1.2 million tires.

The end use of the tire shreds in roadway applications falls under the direction of Maine’s transportation agencies (MTA, MDOT, and municipalities) that incorporate the use of shreds as part of the bidding for the construction project. Shreds are specified for fill in a project, and the tire chippers supply them to the site.

The chips are processed to meet specific requirements including chip size, minimization of crumb rubber, and the mitigation of steel belts and wires for the project. Due to the specific characteristics of tire shreds, they have been used as fill in projects where they were desired for their lightweight, permeable, or insulating properties. The projects using tire shreds include drainage layers under roadways, frost barriers, lightweight fill for embankments and retaining walls, and highway edge drains.

In most cases, a contractor supplied tire shreds (as a subcontractor) to the contractor building the road. Local governments can request that contractors bidding on projects with fill requirements prepare a bid option using tire shreds as applicable.

Having this as an option-but not a requirement-is desirable. The availability of tire shreds, as well as the ability of the shredder to prepare the shreds to specification, may be an issue. This should be carefully and completely understood to avoid unnecessary and costly delays.

In cases where a locality has a tire stockpile on hand, the acceptability of those tires for the project is the primary consideration. Both the shredding contractor and the construction contractor need to assess the condition of the tires for contamination. Transport and shredding will be the determining factors in the cost-effectiveness of tire shreds for the project.

Costs, Economics, and Benefits

Funding for the State of Maine’s tire program come from a variety of sources. Ongoing collection of tires is paid for by a combination of the tip fee charged by the retailer and the revenue for selling the final product. Non-state funds are involved.

Collection of tires in abatement piles comes from MDEP’s general waste management fund, special bonds issued specifically for tire pile cleanup, and the party responsible for accumulating the tire pile.

Funding for the assessment of tire shred use, as well as the follow-up testing to monitor the quality of work, has been provided by MDEP and the transportation departments on a case-by-case basis.

Funding for the actual use of the shreds comes from Maine’s road construction funds. The use of shreds has actually resulted in savings for the fund. The exact amount, however, could not be determined.

The running average for costs associated with the purchase and placement of the shreds were approximately $38 per ton or $27 per cubic yard. These costs have declined as both contractors and public works officials have become more familiar with tire shred use. The cost for the tire shreds transported to the sites ranged from $12 to $30 per ton and placement from $5 to $8 per ton.

The use of tire shreds in civil engineering projects is economical. In most cases the cost of the tire shreds was less than that of comparable materials available on the market. Tires exceed the performance of the other available materials for most uses.

The primary expense for Maine has been in both the education of its civil engineering community and in the technical studies done on the projects. The primary benefit of the use of tire shreds has been that Maine now has an end market for the remediated tires from abatement piles. In addition to saving landfill space, Maine has improved the engineering performance of the projects that required clean lightweight fill. The state has also cut costs associated with the use of fill.

Challenges and Opportunities

The primary challenge was in determining whether or not tires could be used in the role of fill. Issues included settlement of the fill material over time and ability to handle tire shreds with standard equipment. Other factors included the performance of the shreds regarding frost penetration, exothermic reactions, and interaction with other construction materials.

Despite all of Maine’s concerns, tire shreds met or exceeded the standards. Maine closely studied each project and conducted exhaustive testing, gaining valuable insight into the use of shreds. With regard to exothermic reaction, it was noted that caution should be taken.

Guidelines to limit heating of tire shred fills as given in ASTM D6270 “Standard Practice for Use of Scrap Tires in Civil Engineering Application” should be followed. The tire fill should be separated from the surrounding soil by a geomembrane. It should not be exposed to the surface (free oxygen flow), and both crumb rubber particles and excessive exposed steel should be kept to a minimum.

While traditional equipment can be used, the exposed steel in the tire shreds caused flat tires for the construction vehicles. Tracked or solid wheel vehicles are recommended for application.

Tips for Replication

• Purchase tires by weight. This ensures that both the contractor and the site crews have better figures to calculate costs and delivery schedules.
• Ensure that you have a supply of tire shreds at the site adequate to keep up with the pace of work. This usually requires establishing a site stockpile prior to intended use.
• The shred producer will typically have a fixed volume at which they produce shreds or can transport them to the site. Project crews will apply tire shreds at a rate that typically exceeds the subcontractor’s ability to supply them to the site. Note that piles consisting of more than 500 tires must be permitted by the CIWMB.
• Remember communication. Design engineers, shred suppliers, and site contractors all need to understand the behavior of the material as well as its proper application to ensure success and to stimulate future use of tire shreds.

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Last updated: November 01, 2007