Summary of California Recycled Concrete Aggregate Review
October 21-24, 2003
The California Department of transportation's (Caltrans) current specifications allows the use of recycled concrete aggregate (RCA) for specific applications. Specifically, RCA can be used in pavement supporting layers as per sections 25-1.02A and 25-1.02B as well as sections 26-1.02A and 26-1.02B of the subject specifications. Caltrans initially limited the amount of RCA to 50 percent by weight of the total aggregate. Today, 100% of recycled concrete aggregate is allowed by a special provision.
Caltrans is working with the concrete and aggregate industries to develop further applications/uses of RCA.
Recently, the City of San Francisco approved the use of RCA as aggregate concrete in curbs, gutter, sidewalk, and street base. (flat work). Caltrans was going to review these city specifications for use in Caltrans provisions.
Caltrans and representatives from the Concrete and Aggregate Industry that participated in this review helped identify the following benefits of using RCA primarily as base and subbase material in state works and concrete at the local and private level:
- RCA used in the base and sub-base material has a beneficial performance
- Crack & seat has been used as reconstruction strategy.
- Ready Mix Industry suggested that plastic portland cement concrete (PPCC) can be reclaimed and separated in coarse aggregate, fines, and slurry. The reclaimed aggregate is used as aggregate for concrete or base material. Furthermore, the reclaimed slurry may also potentially be reused.
- Substitution of new aggregate by RCA can provide savings in the final cost of the project.
- Even though the initial production cost of RCA may be higher than that of new aggregate, the location of RCA plants near project areas lowers the final cost of using RCA primarily due to reduced hauling and overhead costs.
- Reduction of landfill disposal material.
- Preservation of natural aggregate resource.
- Ready Mix Industry's experience suggested an additional saving of energy (fuel, water consumption, crushing equipment, etc) and reduction of environment impact (dust emission, CO2, reused water) is achieved when reclaimed aggregate is obtained from PPCC.
- Ready Mix Industry suggested that the concrete plant could become a zero-waste facility through the reclaim of PPCC and hardened concrete.
Caltrans and the Concrete and Aggregate Industry have overcome some barriers. A summary of Caltrans and Industry's experiences are provided below.
- Experiences shared by the industry are:
- The use of two magnets, one after the primary crusher and the other after the cone crusher. The last magnet removes all the wire reinforcement.
- The use of an "air knife" (directed blast of air) removes effectively wood, plastic, and dust.
- Plastic fiber added to PPCC can be troublesome but has not been found to be problematic. A large size pump is recommended to alleviate clogging.
- Maintenance of good relations and partnership with local government:
- As a result of a joint committee among City of Los Angeles, Concrete and recycled aggregate producers ("Greenbook"), reclaimed PPCC is allowed to be used in concrete mixtures in a maximum of 15% by volume of concrete; RCA is allowed to be used in concrete in a maximum of 30% by weight of total aggregate.
- The City of San Francisco recently approved the use of RCA non-structural concrete.
- Orange County and Industry are working together to develop specifications for successful use of RCA.
- Establishment of Environmental Policy:
- California Integrated Waste Management Board (CIWMB) has encouraged recycling at local level through the Senate Bill (SB) 1374, which requires to develop voluntary Model Ordinances for local governments and three reports for diverting Construction and Demolition (C&D) materials, including road and building debris. These reports will provide recommendations to local governments and contractors on how to create markets and adopt methods for recovering C&D materials.
- CIWMB has encouraged recycling at state level through the Assembly Bill 75, which establishes an integrated waste management program to which cities, counties, and regional agencies are subject. The act requires implementing state programs designed to encourage the reduction of solid waste. The bill would require each state agency and each large state facility to divert at least 25% of the solid waste generated from landfill disposal or transformation facilities by January 1, 2002, and at least 50% by January 1, 2004. The bill would require each state agency to submit an annual report to the board regarding solid waste reduction.
Caltrans and industry suppliers are still looking to gain additional experience or information in the following areas:
- Initiatives on RCA uses promoted by Federal Agencies (project demonstration).
- Development of appropriate test procedures for specifying final products made with RCA.
- Development of performance based specification for RCA.
- Research related to:
- Effect on product made with recycled aggregate affected by alkali silica reaction.
- Shrinkage effect on product made with recycled aggregate.
People in Attendance at Discussion Groups
Environmental and Planning. October 22, 2003.
||Field Operation Engineer. FHWA, CA division|
||Office Chief. Department of Transportation, Division of Environmental Analysis. Sacramento, CA.|
Performance, Design, Materials, & Research. October 23, 2003.
||California Integrated Waste Management Board. Waste Prevention & Market Development.|
||Senior Transportation Engineer. Resource Conservation. Caltrans.|
|Vijay K. Jain
||Assoc. Chemical Testing Engineer. METS/ Rigid Pavement Materials and Structural Concrete. Caltrans.|
||Senior Transportation Engineer. Construction. Caltrans.|
||Maintenance, Rigid Pavement. Caltrans.|
||Senior Transportation Engineer. Design Pavements. Caltrans.|
Leadership. October 23, 2003
||Chief, Office of Rigid Pavement Materials and Structural Concrete. Caltrans. CA.|
||Director, Engineer Service. Division Office. FHWA. CA|
||Chief, Office of Construction Engineering. Caltrans. CA.|
The following is a list of the materials that have been provided to the review team:
"Admixtures For Recycling of Waste Concrete". Marco Paolini and Rabinder Khurana. Cement and Concrete Composite 20, pages 221-229. Elsevier Science, 1998.
"A Novel Method of Recycling Returned Concrete Using Extended Life Admixture- A Japanese Experience". Seiji Nakamure and Lawrence R. Roberts.
"A Study on The Reuse of Plastic Concrete Using Extended Set-Retarding Admixtures". Journal of Research of the National Institute of Standards and Technology. Volume 100, Number 5, pages 575-589. September-October 1995.
Concrete Paving Technology. Recycling Concrete Pavement. American Concrete Pavement Association, 1993.
Construction Productivity Advancement Research (CPAR) Program. Evaluation of Application of DELVO Technology. Steven A.Ragan, frank T. Gay. Final Report CPAR-SL-95-2. December 1995.
"Effect of Wash Water and Underground Water on Properties of Concrete". Nan Su, Buquan Miao, and Fu-Shun Liu. Cement and Concrete Research 32, pages 777-782. Pergamon, 2002.
"Evaluation of Applications of DELVO Technology". Final Report, CPAR-SL-92-2. Steven Ragan, Frank Gay. Construction Productivity Advancement Research (CPAR) Program. US Army Corps of Engineers. December 1995.
"Greenbook" Standard Specifications for Public Works Construction, 2003 Edition. Pages 58-60. Public Works Standards, Inc. 2003.
Recycled Concrete Aggregate Sheet. Example of RCA Properties and Concrete Mix Contents. City of San Francisco. October 20, 2003.
Recycled Concrete Memorandum. Response to request for information regarding the Department's reaction to legislation that would specifically authorize the use of "Recycled Concrete". State of California Department of Transportation. May 28, 2003.
"Recycling Returned Concrete". Concrete Engineering International, pages 56-61". April 1999.
"Reuse of Returned Concrete and Washout Material". Scoping Document. OPS Pavement Topic Scoping Document. May 2002.
"Use of Recycled Wash Water and Retuned Plastic Concrete in the Production of Fresh Concrete". Jeff Borger, Ramon Carrasquillo, and David Fowler. Advanced Cement Based Material 1994; 1:267-274.
The following is a list plant sites visited:
- The Red-I-Mix Concrete Inc. Plant was visited. It is located at 590 Live Oak Irwindole, CA. Plastic Portland cement concrete reclaim process was observed.
This summary will be posted at FHWA web site: www.fhwa.dot.gov/pavement/recycling