What is RAC?
Rubberized asphalt concrete (commonly known as RAC) is a road paving material made by blending ground-up recycled tires with asphalt to produce a binder which is then mixed with conventional aggregate materials. This mix is then placed and compacted into a road surface. There are two primary types of binders for RAC, asphalt-rubber and terminal blend. Note: Definitions to many terms are displayed as green links to the RAC site glossary. From the glossary, use your web browser’s “Back” button to return to your original page.
- Asphalt-Rubber. Asphalt-rubber is defined by American Society for Testing and Materials (ASTM) Standard D6114 as “a blend of paving grade asphalt cement, ground recycled tire (that is, vulcanized) rubber and other additives, as needed, for use as binder in pavement construction. The rubber shall be blended and interacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles prior to use.” The asphalt-rubber binder is field blended (at the hot mix plant) and requires specialized mobile mixing equipment to produce. Typical crumb rubber modifier (CRM) content for asphalt-rubber ranges from 18-22 percent. The crumb rubber modifier used in asphalt-rubber is in the 10-16 mesh range. Asphalt-rubber been successfully used in California for over 30 years.
- Terminal Blend. Terminal blends are binder materials that use finely ground (less than 30 mesh) crumb rubber modifier and are typically blended at the asphalt refinery. Historically, terminal blend binders contained 10 percent or less crumb rubber modifier. However, in recent years the crumb rubber modifier content has been increased to 15-20 percent in some projects. Terminal blend has 20 years of successful use in California.
Why Use RAC?
RAC is a proven product–one that has many benefits, including being cost effective, durable, safe, quiet, and an environmentally friendly alternative to traditional road paving materials.
- Cost-effective. In most applications, RAC can be used at a reduced thickness compared to conventional asphalt overlays–in some cases at half the thickness of conventional material–which may results in significant material reduction and cost savings. In addition there may be life-cycle cost savings from the reduction in maintenance costs and longevity of RAC.
- Durable, Safe and Quiet. RAC is long lasting. It resists cracking, which can reduce maintenance costs. Case studies have demonstrated repeatedly that RAC, when designed and constructed properly, lasts much longer–often 50 percent longer–than conventional materials. Additionally, RAC provides better skid resistance, which can provide better traction. Moreover, RAC retains its darker color longer so that road markings are more clearly visible and can reduce road noise.
- Environmentally Friendly. California produces more than 40 million waste tires annually, of which approximately 75 percent are diverted from landfill disposal. The state still faces the challenge of dealing with roughly10 million surplus tires annually. The majority end up in our landfills but some end up in illegal stockpiles. A two-inch-thick RAC resurfacing project uses about 2,000 scrap tires per lane mile. Over the past few years, California has used more than 10 million waste tires in RAC paving projects, diverting them from landfills or illegal disposal.
CalRecycle Supports RAC
CalRecycle supports the use of RAC in California through several programs:
- Grant Programs. There are several CalRecycle RAC grant programs that provide financial assistance to local governments specifically to fund RAC projects.
- Technical Assistance and Training. CalRecycle provides engineering technical assistance and training to local jurisdictions in California.
- Product and Vendor Information. View paving materials and product vendors in the California Tire-Derived Product Catalog.
- Green Roads Fact Sheet. This fact sheet can be used to educate local decision makers about the benefits, uses, and cost comparisons for RAC as a paving alternative.
In addition, under a contract from the California Integrated Waste Management Board (now known as the Department of Resources Recycling and Recovery, or CalRecycle) a curriculum was created titled Continuing Education and University Curricula of Rubberized Asphalt Concrete and Civil Engineering Application of Waste Tires, and translated into in Spanish. It is a college-level curriculum to encourage civil engineering graduates to consider use of rubberized asphalt concrete and tire-derived aggregate in their future infrastructure projects.