RECLAIMED CONCRETE MATERIALUser Guideline

Embankment or Fill

INTRODUCTION

Although the use of recycled concrete aggregate (RCA) in embankments or fill may not make the best use of the high quality aggregates associated with RCA, where no other applications are readily available, RCA can be satisfactorily used in this application. RCA aggregates are considered by many specifying agencies to be conventional aggregate. It requires minimal processing to satisfy the conventional soil and aggregate physical requirements for embankment or fill material.

The lower compacted unit weight of RCA aggregates compared with conventional mineral aggregates results in higher yield (greater volume for the same weight), and is therefore economically attractive to contractors. In addition, for large reconstruction projects, on-site processing and recycling of RCA is likely to result in economic benefits through reduced aggregate hauling costs.

PERFORMANCE RECORD

RCA has demonstrated satisfactory performance as an embankment or fill material. Its use is covered by special provisions to specifications in a number of jurisdictions. Desirable attributes of RCA for use in embankments or fill include high friction angle, good bearing strength, negligible plasticity, and good drainage characteristics.

Due to its high alkalinity, RCA in contact with aluminum or galvanized steel pipes can cause corrosion in the presence of moisture.

A potential for tufa-like precipitates to leach from RCA in granular base applications has been described in the literature, ⁽¹¹⁾ and may also be a consideration in embankment or fill applications.

MATERIAL PROCESSING REQUIREMENTS

Crushing and Screening

Prior to its use, any reinforcing steel must be removed and RCA must be broken or crushed and screened to satisfy the maximum size and gradation requirements for use in embankment construction.

Where the processed RCA contains some reclaimed asphalt pavement (RAP), which can occur when the RCA is derived from composite pavements, it is recommended that the RAP content in the RCA be limited to 20 percent to prevent a reduction in bearing strength due to the presence of RAP. ⁽¹²⁾

Washing

Washing of RCA aggregates is required by some agencies to remove the dust as a measure to reduce tufa formation potential. To control tufa precipitate formation, only suitable RCA that does not contain significant quantities of unhydrated cement or free lime should be used for embankment or fill applications.

Testing

Additional quality control testing (leachate testing) may be necessary to assess the tufa precipitate potential of RCA aggregates for embankment applications. A special procedure to identify the potential for tufa formation in steel slags was developed, which should be appropriate for RCA testing. ⁽¹⁰⁾

ENGINEERING PROPERTIES

Some of the engineering properties of RCA that are of particular interest when RCA is used as an embankment or fill material include gradation, specific gravity, stability, strength, durability, drainage, and corrosivity.

Gradation : RCA must be crushed and screened to satisfy AASHTO M145 ⁽²⁾ , and ASTM D2940 ⁽⁸⁾ gradation requirements for embankment or fill aggregates.

Specific Gravity : The specific gravity of RCA aggregates (ranging from 2.0 for fines to 2.5 for coarse particles) is slightly lower than that of virgin aggregates. ⁽¹⁾

Stability : RCA has high friction angle, typically in excess of 40° and consequently demonstrates good stability and little postcompaction settlement.

Strength Characteristics : Processed RCA, being 100 percent crushed material, is highly angular in shape. It exhibits California Bearing Ratio (CBR) values ranging from 90 to more than 140 percent (depending on the angularity of the virgin concrete aggregate and strength of the Portland cement matrix), which is comparable to crushed limestone aggregates. ^(15,14)

Durability : RCA aggregates generally exhibit good durability with resistance to weathering and erosion.

Drainage Characteristics : RCA (mainly coarse fraction) is free draining (more permeable than conventional granular material due to lower fines content). RCA is nonplastic and is not susceptible to frost.

Corrosivity : The high alkalinity of RCA (pH greater than 11) can result in corrosion to aluminum or galvanized steel pipes in direct contact with RCA and in the presence of moisture. ⁽¹³⁾

DESIGN CONSIDERATIONS

The design requirements for RCA in embankment construction are the same as for conventional aggregates. There are no standard specifications covering RCA use as embankment or fill material.

As recommended when RCA is used as a granular base it may be necessary to ensure the following; 1. the intentional inclusion of RCA fines (#4 minus) be eliminated in unstablized foundation layers, 2. drainage systems be designed to accommodated a limited quanity of crusher fines and insoluble bases, and 3. Open graded RCA be blended with new aggregates to provide gradations needed to improve the stability and density to reduce precipitate formation. This will mitigate potential drainage problems. ⁽⁹⁾

Structural design procedures for embankments or fill containing RCA are the same as design procedures for embankments or fill containing conventional materials.

CONSTRUCTION PROCEDURES

Material Handling and Storage

The same methods and equipment used to store or stockpile conventional aggregates are applicable for reclaimed concrete material. Some jurisdictions ( Ontario , Canada , for example) may restrict stockpiling and placement of RCA near watercourses to minimize the impact of the alkaline leachate on ambient water quality. Appropriate procedures may also be required to avoid segregation of coarse and fine materials during handling and storage. These include stockpile construction using radial stackers, with remixing using a front-end loader or bulldozer prior to load-out, and care during load-out and placement.

Placing and Compacting

Due to their high angularity, additional effort (for instance using vibratory rollers) may be required to compact RCA to its maximum density. The processor may be required to satisfy moisture content criteria according to AASHTO T99, ⁽⁷⁾ in order to achieve good compactibility. This usually requires the addition of water during placement and compaction.

Quality Control

The same test procedures used for conventional aggregate are appropriate for embankment applications when using RCA. Standard laboratory and field tests for compacted density and field measurement of compaction are given by AASHTO test methods: T191 ⁽⁵⁾ , T205 ⁽⁴⁾ , T238 ⁽³⁾ and T239. ⁽⁶⁾

Special Considerations

To avoid corrosion problems, RCA should not be placed in contact with aluminum or galvanized steel pipes. Caution is also warranted in locations subject to wet conditions, as tufa-like precipitates (CaCO₃) associated with the leachate from RCA may develop upon exposure to the atmosphere. ⁽¹⁾

ENVIRONMENTAL CONSIDERATIONS

For RCA, environmental considerations have focused on leachability of contaminants and pH changes from RCA storage and use. Previous research conducted on the leachability Portland cement concrete used the Toxicity Characteristic Leaching Procedure ⁽¹⁶⁾. Although leachability results were low ⁽¹⁶⁾, the TCLP simulates a municipal landfill setting and not a beneficial use environment, so results would not be applicable to environmental considerations for beneficial use. More recent research employed a serial batch test (Dutch Pre-Standard NVV 5432) ⁽¹⁷⁾. This research concluded that well-cured Portland cement concrete released no detectable concentrations of antimony, arsenic, beryllium, cadmium, chromium, lead, mercury, nickel and selenium ⁽¹⁷⁾. The internal alkaline nature of concrete is well known, but can change over time with weathering and age for numerous reasons (e.g., carbonation). RCA could also be alkaline, with potential pH values and changes similar to in-place concrete. Research conducted at Washington State University found that disposing of diamond grinding concrete slurry increased soil pH from 6.3 – 7.5 to 7.6 – 9.4 in once location and from 7.1 – 7.2 to 7.1 – 8.2 in a second location ⁽¹⁸⁾. Research conducted by the Ohio Department of Transportation and Iowa Department of Transportation found that the pH of RCA decreased little over time (was initially greater than 11 then decreased over time but remained above 9). The Ohio research concluded that using RCA as an aggregate base in low lying or wet areas where alkaline run-off would be likely to occur could have an adverse effect on the environment ⁽¹⁹⁾. The Iowa report found that the high pH of the drainage water from RCA use can kill or impede grass growth at a drain outlet ⁽²⁰⁾. Texas has also completed research in using RCA in mechanically stabilized earth (MSE) berms that involved thorough material characterization, pH measurements and an evaluation of use ^(21,22). They concluded that pH and resistivity specifications for MSE wall backfill materials should be waived for crushed concrete, concrete structures that have suffered sulfate attack should not be crushed and used as backfill in MSE walls, and MSE walls with crushed concrete backfill should include adequate drains and high permittivity filter fabrics behind the wall to avoid drainage problems ⁽²²⁾. The potential for a pH and drainage issues leads some jurisdictions to require that RCA stockpiles be separated (a minimum distance) from water courses.

UNRESOLVED ISSUES

Although problems associated with tufa precipitate formation in embankments containing RCA have not been identified, a study of the subject would provide useful technical data to better define the nature and degree of the problem, and to affirm the use of RCA in embankment construction.

REFERENCES

ACPA. "Concrete Paving Technology: Recycling Concrete Pavement," American Concrete Pavement Association, Illinois , 1993.
American Association of State Highway and Transportation Officials. Standard Method of Test, "The Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes," AASHTO Designation: M145-82, Part I Specifications, 14th Edition, 1986.
American Association of State Highway and Transportation Officials, Standard Method of Test, "Density of Soil and Soil-Aggregate in Place by Nuclear Methods (Shallow Depth)," AASHTO Designation: T238-86, Part II Tests, 14th Edition, 1986.
American Association of State Highway and Transportation Officials. Standard Method of Test, "Density of Soil In-Place by the Rubber-Balloon Method," AASHTO Designation: T205-86, Part II Tests, 14th Edition, 1986.
American Association of State Highway and Transportation Officials. Standard Method of Test, "Density of Soil In-Place by the Sand Cone Method," AASHTO Designation: T191-86, Part II Tests, 14th Edition, 1986.
American Association of State Highway and Transportation Officials. Standard Method of Test, "Moisture Content of Soil and Soil Aggregate in Place by Nuclear Methods (Shallow Depth)," AASHTO Designation: T239-86, Part II Tests, 14th Edition, 1986.
American Association of State Highway and Transportation Officials. Standard Method of Test, "The Moisture-Density Relations of Soils Using a 5.5-lb [2.5 kg] Rammer and a 12-in. [305 mm] Drop," AASHTO Designation: T99-86, Part II Tests, 14th Edition, 1986.
American Society for Testing and Materials. Standard Specification D2940-92, "Graded Aggregate Material for Bases and Subbases for Highways or Airports," Annual Book of ASTM Standards, Volume 04.03, West Conshohocken , Pennsylvania , 1996.
Gonzalez, G.P. and Moo-Young, H.K. Transportation Applications of Recycled Concrete Aggregate, FHWA State of the Practice National Review, September 2004.
Gupta, J. D., W. A. Kneller, R. Tamirisa, and E. Skrzypczak-Jankun, "Characterization of Base and Subbase Iron and Steel Slag Aggregates Causing Deposition of Calcareous Tufa in Drains, " Transportation Research Record No. 1434, 1994.
Gupta, J. D. and W. A. Kneller. Precipitate Potential of Highway Subbase Aggregates, Report No. FHWA/OH-94/004 prepared for the Ohio Department of Transportation, November 1993.
Hanks, A. J. and E. R. Magni. The Use of Recovered Bituminous and Concrete Materials in Granular Base and Earth, Ontario Ministry of Transportation Report MI-137, Downsview, Ontario, 1989.
Mabin, S. M. "Recycled Concrete Aggregate - New York State 's Experience." Recovery and Effective Reuse of Discarded Materials and By-Products for Construction of Highway Facilities, FHWA/EPA Symposium Proceedings, Denver , Colorado , October 1993.
Petrarca, R.W. and V.A. Galdiero, "Summary of Testing of Recycled Crushed Concrete," Transportation Research Record No. 989, pp. 19-26, Washington , D.C. , 1984.
Senior, S. A., S. I. Szoke, and C. A. Rogers, " Ontario 's Experience with Reclaimed Materials for Use as Aggregates." Presented at the International Road Federation Conference, Calgary , Alberta , 1994.
Kreitch, A.J. Leachability of Asphalt and Concrete Pavements, Heritage Research Group Report, Indianapolis , Indiana , March 1992.
Kreitch, A.J. Leachability of Asphalt and Concrete Pavements, Heritage Research Group Report, Indianapolis, Indiana , March 1992.
Hilliera, S.R., Sangha, C. M., Plunkettb, B. A., Waldena, P. J., Long-term leaching of toxic trace metals from Portland cement concrete, Cement and Concrete Research, Vol. 29, p. 515-521, 1999.
Shanmugam, Harini, Assessment and mitigation of potential environmental impacts of Portland Cement Concrete highway grindings, Thesis, Washington State University, 2004.
Ohio Department of Transportation, Recycled Materials Report, Box Test.
Steffes, R., Laboratory Study of the Leachate from Crushed Portland Cement Concrete Base Material, Iowa Department of Transportation, September 1999.
Ellen M. Rathje, Alan F. Rauch, Kevin J. Folliard, David Trejo, Dallas Little, Chirayus Viyanant, Moses Ogalla, Michael Esfelle, Recycled Asphalt Pavement and Crushed Concrete Backfill: State-of-the-Art Review and Material Characterization, Center for Transportation Research at The University of Texas at Austin, Texas Department of Transportation, Octboer, 2001.
Rathje, E., Rauch, A., Trejo, D., Folliard, K., Viyanant, C., Esfellar, M. Jain, A., Ogalla, M., Evaluation of Crushed Concrete and Recycled Asphalt Pavement as Backfill for Mechanically Stabilized Earth Walls, Center for Transportation Research at The University of Texas at Austin, Texas Department of Transportation, March 2006.

[ Material Description ] - [ Portland Cement Concrete ] - [ Granular Base ] - [ Embankment or Fill ]

Last Update 7/28/08