Recycled aggregate is produced by crushing concrete, and sometimes asphalt, to reclaim the aggregate. Recycled aggregate can be used for many purposes. The primary market is road base. For information on recycling asphalt pavement into new asphalt pavement. See Asphalt Pavement Recycling.
Benefits of Recycled Aggregate: The use of recycled aggregate 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 urban aggregates, and help local governments meet the diversion goals of AB 939.
Source: According to the Board's 2008 Statewide Waste Characterization Study:
Construction and Demolition (C&D): C&D materials made up about 29 percent of California's disposed waste stream, or approximately 11.6 million tons.
Asphalt and Concrete: Asphalt and concrete represent over 977,000 tons of disposal or around 2.4 percent.
Aggregate consists of hard, graduated fragments of inert mineral materials, including sand, gravel, crushed stone, slag, rock dust, or powder.
Inert solid waste is concrete, asphalt, dirt, brick, and other rubble.
Portland cement concrete (PCC) and asphalt concrete (AC) consist primarily of aggregate. The cement and asphalt serve as binders. Some PCC contains steel reinforcement bars, or "rebar," such as a bridge deck or tilt-up slabs. When a road or structure is demolished, the rebar can often be seen protruding from the broken chunks of PCC.
Recycled aggregate comes primarily from PCC and AC from road rehabilitation and maintenance, demolition, and leftover batches of AC and PCC. After processing, the rocks retain bits of cement or asphalt.
A roadway is built in several layers: pavement, base, and sometimes subbase. The pavement is the surface layer, and is made of PCC or AC. The base layer supports the pavement, and is made of aggregate base (AB). The subbase layer supports the base and is made of aggregate subbase (ASB).The subbase layer allows more sand, silt and clay than the AB layer; the subbase layer has less strength, but is used because it is more economical when bringing the road up to grade.
The AC and PCC generally arrives at the processor in chunks. Heavy crushing equipment is required to break up the chunks into aggregate. Some equipment is portable and can be set up on site for immediate use of product. A crushing plant may include a hopper to receive the material, a jaw to break it into more manageable pieces, a cone or impact crusher to further reduce its size, a vibrating screen to sort to the required specification, and a conveyor belt with a rotating magnet to remove metal contamination such as rebar.
According to the CalRecycle's current information, there are approximately 100 producers of recycled aggregate in California. Some receive PCC and/or AC at the plant; others have mobile equipment for in-place recycling.
Uses: Recycled aggregate can be used:
- In paved roads as aggregate base, aggregate subbase, and shoulders.
- In gravel roads as surfacing.
- As base for building foundations.
- As fill for utility trenches.
At this time, the primary market is aggregate base and subbase in road projects.
Local Governments: Local governments can help promote markets for recycled aggregate because they are large purchasers of aggregate and other road construction products. Some communities are taking steps to promote recycled aggregate, including the following:
- Los Angeles. In March 1995, the City of Los Angeles passed a motion requiring that road base in all city projects include "crushed miscellaneous base" (CMB) with 100 percent recycled asphalt, concrete, and other inerts, except when site conditions or standards require another specification." (See discussion of CMB under Greenbook Specifications below.)
- Modesto. The City of Modesto has a purchasing practice for on-site street recycling that includes recycled aggregate.
- Palo Alto. The City of Palo Alto requires that concrete and asphalt in city projects be recycled.
- Butte County. Butte County does not require recycling of inerts; however, the local landfill does use clean loads of inerts on site as roadbase or wet weather pads.
Many local jurisdictions use Caltrans specifications. In Southern California, the Greenbook is commonly used. (See Greenbook discussion below.) Where recycled aggregate is allowed, it must also, of course, meet the same grading and quality specifications as virgin aggregate.
Caltrans Specifications-Procedures: Caltrans takes a new specification through three stages:
- Special Provision (SP). First it is an SP where it is used initially on a number of projects.
- Standard Special Provision (SSP). After the SP has been used successfully for a period of time, it usually becomes an SSP which means that it is a method approved by Caltrans.
- 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 Caltrans Standard Specifications which is published every four years.
Caltrans Specifications-Existing: Caltrans' Standard Specifications, May 2006 covers aggregate base and aggregate subbase in Sections 25 and 26. These sections were updated in February 2007 to allow up to 100% recycled aggregate. Caltrans' SSPs allow up to 100% processed glass in Class 2 and 3 aggregate base, and also in Class 1, 2, and 3 aggregate subbases.
What is the Greenbook? The Greenbook, or Standard Specifications for Public Works Construction, is used by the city and county of Los Angeles and 200 other local governments and agencies in the Los Angeles area.
Who Publishes It? 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.
How Often? It is updated and republished every three years. Supplements are published yearly.
Where Can I Get It? The Greenbook includes both English and metric units, and is available through:
BNI Building News
990 Park Center Drive, Suite E
Vista, CA 92081-8352
Aggregate Base Specifications. In Section 200-2, "Untreated Base Materials," the Greenbook includes four categories of aggregate base that are of interest here:
- Crushed Aggregate Base (CAB) does NOT include recycled aggregate. CAB may sometimes be specified where recycled base (CMB or PMB) would also meet requirements.
- Crushed Miscellaneous Base (CMB) allows recycled aggregate. The Greenbook states that CMB "shall consist of broken and crushed AC or PCC and may contain crushed aggregate base or other rock."
- Processed Miscellaneous Base (PMB) also allows recycled aggregate. The Greenbook states that PMB "shall consist of broken or crushed AC, PCC, railroad ballast, glass, crushed rock, rock dust, or natural material."
- Select Subbase is the Greenbook's only aggregate subbase category. It allows recycled aggregate.
Section 200-2.4 spells out the performance standards for CMB.
Setting up a new concrete and asphalt recycling plant requires certain State and local permits, such as air and water, and zoning.
Where Can I Get Help? Businesses starting or expanding into recycling activities may get financial, technical, marketing, business and permitting assistance from the "Zone Contacts" at CalRecycle, at (916)341-6526.
Air Permits: The local air districts may be concerned about nuisance odors and various emissions, and may require processors to spray materials with water to control dust. Locate your local air district by calling the Air Resources Board at (916) 322-2990 or by checking their website.
Water Permits: The Regional Water Quality Control Board may require a permit for the facility depending on feedstock and location. Look up your regional board in a local phone book under State Government, Water Quality Control Board.
Solid Waste Permits: Regulations affecting C&D and inert debris transfer/processing facilities became effective on August 9, 2003. Processors that accept segregated C&D debris may be required to have a solid waste facilities permit. Contact your Local Enforcement Agency (LEA) for information. To find out who the LEA is for the project area, check the LEA Directory on the Calrecycle's Web site or call the our LEA/EA Branch at (916) 341-6314. More information is available at the Calrecycle's Construction/Demolition and Inert Debris website.
California Construction and Industrial Materials Association (CalCIMA)
1029 J Street, #420
Sacramento, CA 95814
American Public Works Association
2345 Grand, Suite 500
Kansas City, MO 64105
See the CalRecycle's online Publications Catalog for a complete list of C&D publications, including downloadable Word versions and the option to order hard copies. The links below are to the HTML versions, if available.
Recycled-Content Construction Products. A searchable database of manufacturers of recycled construction products sold in California, including aggregate.
Asphalt Roofing Shingles in Aggregate Base. An overview of recycling ground asphalt roofing shingles into aggregate base. (Pub. #431-97-032)
Resource Guide for Recycling-Based Businesses. A 57-page directory of information from the public and private sectors, including business development, technical, financial, and feedstock assistance. (Pub. #412-97-028)
Market Status Report: Recycled Inerts (October 1996). An 11-page report discussing recycled aggregate, asphalt pavement, asphalt roofing shingles, and drywall. (Pub #431-96-063)
Free Directory of Construction Industry
The Blue Book--Building & Construction
PO Box 500
Jefferson Valley, NY 10535-0500
(916) 485-3832 (Sacramento rep)
Free Magazine Subscription
C&D Debris Recycling
Overland Park, KS 66212
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.