Asphalt Pavement Recycling

Introduction

Benefits of Recycling Asphalt
Recycling of asphalt pavement can save money for local governments and other purchasers, create additional business opportunities, save energy when recycling is done on site, conserve diminishing resources of aggregates and petroleum products, and help local governments meet the goal of reducing disposal by 50 percent by the year 2000.

See Recycled Aggregate for information about recycling asphalt pavement into aggregate base.

Quantities

Source
The 1990 waste stream composition data were reported to the California Integrated Waste Management Board, (now CalRecycle) by local governments in response to the Integrated Waste Management Act of 1989. These reports supplied the following information:

  • Construction and Demolition (C&D). C&D materials made up about 28 percent of California’s waste stream, or 11 million tons.
  • Asphalt Pavement. While recycled asphalt pavement was not reported separately in these data, generation of “inert solid waste,” which consists of concrete, asphalt, dirt, brick and other rubble, was conservatively estimated at 8.2 million tons. The estimated recycling rate for inert solid wastes was 57 percent; the remainder was disposed of.

Definitions

In the western United States, asphalt refers to the bituminous substance used to bind aggregate together to make asphalt concrete (AC). The aggregate makes up the bulk of the AC, while the asphalt binder comprises about
5 to 7 percent.

Reclaimed asphalt pavement (RAP) is used AC pavement that has been processed.

Recycled asphalt concrete (RAC) is the product of mixing RAP with new aggregates, asphalt and/or recycling agent.

A recycling agent is used to soften and rejuvenate the existing asphalt pavement.

Pavement is the top layer of roadway, and is made of portland cement concrete (PCC) or AC. The pavement is supported by the base and sub-base, which consist of aggregate and other materials. The pavement can be crushed and used as recycled aggregate base or, if it is AC, it can be reprocessed into RAC.

Cold planing, also called cold milling, is the removing or milling of a layer of pavement by a cold planing machine. The exposed surface can be used temporarily as a driving surface and is usually overlaid with new material.

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Road Recycling Methods

Purpose
Roads are rehabilitated to correct deficiencies such as rutting, cracking, oxidation, brittleness, irregular shrinkage, and aggregate stripped of asphalt.

Methods
The following methods of roadway rehabilitation recycle old pavement into new:

Cold, In-Place Recycling. The pavement is removed by cold planing to a depth of 3 to 4 inches. The material is pulverized, sized, and mixed with an additive. Virgin aggregate may be added to modify RAP characteristics. An asphalt emulsion or a recycling agent is added, then the material is placed and compacted. An additional layer is optional, such as a chip seal, or 1 to 3 inches of hot-mix asphalt.

A 3-piece “train” may be used, consisting of a cold planing machine, a screening/crushing/ mixing unit, and conventional laydown and rolling equipment. This “train” occupies only one lane, thus maximizing traffic flow. Caltrans has used cold in-place recycling in over 25 projects in California.

According to the Asphalt Recycling and Reclaiming Association, cost savings can range from 20 to 40 percent over conventional techniques. Because no heat is used, energy savings can be from 40 to 50 percent.

Hot Recycling. At a central plant, RAP is combined with hot new aggregate, and asphalt or a recycling agent to produce AC, using a batch or drum plant. The RAP is usually obtained from a cold planing machine, but could also be from a ripping/crushing operation.

Hot, In-Place Recycling. The pavement is softened by heating, and is scarified or hot milled to a depth of 3/4 to 1-1/2 inches and mixed. New hot mix material and/or a recycling agent is added in a single pass of the machine. A new wearing course may also be added with an additional pass after compaction.

Hot Mix–Remixing. The road is heated to 1-1/2 to 2 inches, and the existing AC is removed to that depth. It is then mixed with virgin mix and/or rejuvenating agents and laid as a single course.

Hot Mix–Repave. This method is the same as remixing, but it is overlaid with new hot mix.

Hot Mix–Heater Scarification. This method is appropriate for roadways that have a stable and structurally adequate base. The road is heated, scarifiers scrape and loosen the pavement, rejuvenating agent is applied, and the surface is leveled in preparation for the addition of a final, thin, wearing course.

Full-Depth Reclamation. All of the asphalt pavement section and a portion of the underlying materials are processed to produce a stabilized base course. The materials are crushed and additives are introduced; the materials are then shaped and compacted, and a surface or wearing course is applied.

RAC Producers

According to the CalRecycle’s current information, there are at least 25 plants producing RAC in California. Some receive RAP at the plant; others have mobile equipment for in-place recycling.

Purchasing

Caltrans and local public works departments put their road jobs out to bid. The contractors who win the bid are the actual purchasers of the AC. However, if a project is to use recycled AC, Caltrans or the local agency must specify recycled AC in the bid.

Markets

Uses
AC is found in roadways (State highways, local public roads, and private roads), airport runways, parking lots, driveways, and tennis courts. The primary market for RAC is roadways.

Southern California
There are many markets in southern California because most local governments use the Greenbook, which supplies RAP specifications. (See “Specifications,” next page.)

Northern California
Most local governments in Northern California, however, are waiting for Caltrans to finalize their specifications. RAC is not in ready supply in the area, because the AC recycling industry requires a certain volume of business before investing in equipment. One exception to this rule is Gallager & Burke, which supplies RAC to several cities in the East Bay.

Local Governments

Local governments can help promote markets for RAC because they are large purchasers of asphalt and other road construction products. Some communities are taking steps to promote RAC, including the following:

Los Angeles. In March 1995, the City of Los Angeles passed a motion requiring that all asphalt surfacing purchased by city departments include a minimum of 15 percent RAP.

Modesto. The City of Modesto has a purchasing practice for on-site street recycling that includes RAC.

San Diego. The City and County of San Diego routinely allows 15 percent RAP in new asphalt for public projects.

San Jose. The City of San Jose allows 15 percent RAP in asphalt base, the AC layer under the 2-inch surface layer.

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Specifications

Most local jurisdictions use Caltrans specifications. In southern California, the Greenbook is commonly used. (See Greenbook discussion below.) Where RAC is allowed, it must also, of course, meet the same grading and quality requirements as virgin AC.

Caltrans Specifications–Procedures

Caltrans takes a new “spec” through three stages:

1.  Special Provision (SP). First it is an SP where it is used initially on a number of projects.

2.  Standard Special Provision (SSP). After the SP has been used successfully for a period of time, then it usually becomes an SSP which means it is a method approved by Caltrans.

3. Standard Specification. After the SSP has been used successfully for a period of time, then it usually becomes a Standard Specification, and is included in the Caltrans Standard Specifications which is published every four years. The latest edition using English measurements is dated July 1992. A metric edition was published July 1995; all subsequent editions will be metric. The next edition is anticipated in 1998 or 1999.

Caltrans Specifications–Pending

Caltrans specifications for two AC processes are being modified: “Hot Recycling at a Central Plant” (25-50 percent recycled) and “Cold, In-Place” (100 percent recycled). The specifications are expected to be completed in 1997. Temporary versions are currently being used in Caltrans projects, and are available to local governments and the public through Caltrans.

Caltrans Specifications–Future

Caltrans is investigating various technologies for future specification:

Stockpile Study.  Caltrans is doing a “pilot study” to determine the feasibility of using up to 15 percent RAP from contractor-generated multisource stockpiles. Progress has been slow in this area because few projects have been constructed using this type of recycling. The evaluation period will continue at least through the 1997 construction season.

Microwave. One company produces 100 percent RAC by using a patented cool flow and microwave process to reheat it. Caltrans completed the second test project with this technology in the summer of 1995 using up to 70 percent RAP. Results have been evaluated. Although the process looks favorable, the recycle mix did not meet Caltrans specifications on this project.

Hot, In-Place. Caltrans also tested hot, in-place AC recycling on two projects. A recycling agent was used to rejuvenate the old asphalt. Up to 15 percent new AC was added in some sections; the new AC is 100 percent recycled. The process is available as a “Special Provision.” However, the results are inconclusive, so they classify the method as experimental, which means that Caltrans does not use the procedure routinely. Caltrans plans to use this type of recycling on future test projects.

Greenbook Specifications

What is the Greenbook? The Greenbook is another name for the Standard Specifications for Public Works Construction, and is used by the City and County of Los Angeles and 200 other local governments and agencies in the Los Angeles area. It is published by the Joint Cooperative Committee of the Southern California Chapter of the American Public Works Association, and the Southern California Districts of the Associated General Contractors of California.

The Greenbook is updated and republished every three years. Supplements are published yearly. It includes English and metric units, and is available through:

BNI Building News
990 Park Center Drive, Suite E
Vista, CA 92081-8352
(888) 264-2665

RAC Specifications. The Greenbook has specifications for “Recycled Asphalt Concrete–Hot Mixed” in Section 203-7. Methods are outlined for batch plants and drier-drums. Up to 15 percent of RAP is allowed in the virgin mix. Larger percentages of RAP are allowed if test data is submitted to the Chief Engineer of the Agency.

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Siting

Setting up a new asphalt recycling plant requires certain State and local permits, such as air, water, and zoning.

Where Can I Get Help?
Businesses starting or expanding into recycling activities may get financial, technical, marketing, business, and permitting assistance. For more information see our Financial and Market Development Assistance page.

Air Permits
The local air districts may be concerned about nuisance odors and various emissions, and may require processors to spray with water to control dust. Locate your local air district by contacting the Air Resources Board.

Water Permits
The Regional Water Quality Control District may need to permit the facility depending on feedstock and location. Look up your district on the State Water Resources Control Board’s Regional Water Quality Control Board page.

Solid Waste Permits
The CalRecycle is developing a tiered permitting system for solid waste facilities. However, processors that accept segregated C&D debris should not require a permit. Contact your Local Enforcement Agency (LEA) for updates. To find out who the LEA is for the project area, check our LEA Directory database.

Publications

To download or order CalRecycle publications, and to see a complete publications list, go to the CalRecycle Online Publications Catalog.

Free Magazine Subscription

C&D Debris Recycling,
Intertech Publishing
9800 Metcalf
Overland Park, Kansas 66212
(800) 441-0294

Reports

  • Asphalt Hot-Mix Recycling, The Asphalt Institute, Lexington, KY, $8, (606) 288-4960.
  • A Study of the Use of Recycled Paving Material, Report to Congress as specified in the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), Report No. FHWA-RD-93-147, EPA/600/R-93/095.

Additional Resources

For more information contact: C&D Program Staff, cdrecycling@calrecycle.ca.gov