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Technical Advisory

Use of Recycled Concrete Pavement as Aggregate in Hydraulic-Cement Concrete Pavement

T 5040.37

July 3, 2007

  1. What is the purpose and scope of this Technical Advisory? This Technical Advisory issues information on state-of-the-practice and guidance for the use of recycled concrete pavement as aggregate in concrete used for pavements.

  2. Does this Technical Advisory supersede another Technical Advisory? No. This is a new Technical Advisory.

  3. What are the key definitions?

    1. Recycled concrete aggregate (RCA). RCA is granular material manufactured by removing, crushing, and processing hydraulic-cement concrete (see paragraph 3b) pavement for reuse with a hydraulic cementing medium to produce fresh paving concrete. The aggregate retained on the 4.75 mm (No. 4) sieve is called coarse aggregate; material passing the 4.75 mm (No. 4) sieve is called fine aggregate.

    2. Hydraulic-cement concrete. Historically, the term "portland cement concrete" or "PCC" has been used to describe pavements that use portland cement, a specific type of hydraulic cement, as the binder. Because of the widespread use of blended cements and supplementary cementitious materials, the term "portland cement" no longer accurately describes the binder. In this Technical Advisory, the broader, generic term "hydraulic-cement concrete" is used.

  4. What is the background on recycling concrete as aggregate for concrete pavement?

    1. Disposal of existing concrete pavements is often a problem faced on many pavement reconstruction projects. Recycling concrete, as an aggregate product, is common practice by several State Departments of Transportation (DOTs), private industry, and many foreign agencies. The Federal Highway Administration (FHWA) Policy Memorandum "Formal Policy on the Use of Recycled Materials," dated February 7, 2002, states that reusing the material used to build the original highway system "... makes sound economic, environmental, and engineering sense." It also emphasizes that recycled materials must be used in an appropriate manner that "... shall not affect the performance, safety or the environment of the highway system." Environmental issues and costs associated with removal and disposal of old concrete must be addressed early in the project development.

    2. Options for dealing with the old pavement include the following:

      1. (1) Removal from the site and disposal in a landfill, or usage in other environmentally favorable ways such as riprap.

      2. (2) Construction of an overlay on top of the old pavement.

      3. (3) Cracking and seating or rubblizing the old pavement, and constructing new pavement on top of it.

      4. (4) Processing the removed pavement into an aggregate product for use in granular or stabilized base, subbase, or shoulder materials.

      5. (5) Processing the removed concrete pavement into a RCA suitable for use as bedding, backfill, granular embankment, or in asphalt or hydraulic-cement concrete with lower performance expectations.

      6. (6) Processing the removed concrete pavement into a high-quality RCA product suitable for use in high performance hydraulic-cement concrete or asphalt.

    3. Discussions of the first five alternatives in paragraph 4b appear in other technical literature. This Technical Advisory deals only with a portion of the final alternative, recycling removed pavement, from a known source, into a high-quality aggregate product for use as aggregate in high performance hydraulic-cement concrete pavement.

  5. How can removed concrete pavement be processed into aggregate suitable for new concrete pavement? The first step in processing removed concrete pavement into aggregate suitable for new concrete pavement is to demolish the concrete pavement and remove the demolished material to a processing site. Initial processing removes steel, soil, and other contaminant material from the concrete. The demolished concrete is then crushed and sized by screening operations that result in an aggregate product that meets the specified grading requirements. Fine impurities, such as soil and loose cement mortar, should be removed by special crushing operations, washing, dry or wet screening or hydraulic sizing. Lightweight contaminates, such as wood or porous chert, may require the use of other aggregate beneficiation methods, such as hydraulic separation. Except for removing steel, impurities, and contaminates, this process is identical to the process used to produce aggregate from virgin stone materials.

  6. Can concrete exhibiting materials related distress (MRD) be recycled for use in new concrete pavements? Yes. Concrete exhibiting MRD may be recycled for use in new concrete pavements only if the distress mechanism is recognized prior to design, and proper mitigation measures are implemented in the new pavement to insure that the MRD will not recur. As part of the decision making process for recycling the old concrete pavement, a materials engineer should visit the site and observe the type and extent of distress. Pavement samples should be taken for laboratory evaluation (see paragraph 14o). The most common MRDs are Alkali-Silica Reaction (ASR) and D-cracking.

    1. ASR occurs when certain siliceous aggregates react with alkalis in the concrete paste to form gel that expands after absorbing water. Gel expansion can cause the concrete to crack. Using supplementary cementitious materials (i.e., fly ash or ground granulated blast furnace slag), or lithium admixture in the new concrete mixtures will help to mitigate ASR (see paragraph 14k).

    2. D-cracking is the result of water freezing in certain porous aggregates. The common mitigation method used by highway agencies is to reduce the maximum size of the aggregates subject to D-cracking. When pavement containing a D-cracking aggregate is recycled, the demolished concrete may require additional crushing to reduce the maximum aggregate size (see paragraph 14k).

  7. What are the requirements for insuring the quality of RCA?

    1. In order to produce high quality concrete for the new application, RCA aggregate should:

      1. (1) Be free of harmful components such as soil, asphalt, and steel. More than 90% of the material should be cement paste and aggregate. Asphalt content should be less than 1 percent;

      2. (2) Be free of harmful components such as chlorides and reactive materials unless mitigation measures are taken to prevent recurrence of MRD in the new concrete; and

      3. (3) Have an absorption of less than 10 percent.

    2. In general, the recycled materials used for concrete paving projects must meet the same quality requirements normally used for virgin aggregate. (See American Society for Testing and Materials (ASTM) C 33, "Standard Specification for Concrete Aggregates",or American Society of State Highway and Transportation Officials (AASHTO) M 80, "Coarse Aggregate for Portland Cement Concrete" and AASHTO M 6, "Fine Aggregate for Portland Cement Concrete"). Coarse RCA should meet the appropriate grading requirements. Fine RCA will be somewhat more coarse and angular than needed to produce good concrete. Because of the degradation of new concrete properties discussed in the following sections of this Advisory, use of fine RCA is not recommended. If, however, fine RCA must be used, it should be blended with a finer natural sand to improve performance.

    3. Density of RCA will typically be slightly less than that of the original material used. This will have an effect on proportioning the new concrete. Expect RCA to have higher water absorption than that of the original aggregate.

    4. The Los Angeles Abrasion Test (ASTM C 131, "Standard Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine") is used to determine an aggregate's resistance to breakdown during handling and mixing. RCA produced from all but the poorest quality recycled concrete should have little trouble meeting the abrasion requirements of ASTM C 33 or AASHTO M 80. Abrasion loss should be less than 5 percent.

    5. Freeze-thaw durability is primarily a function of the amount of entrained air and the quality of the air void system. If the concrete to be recycled has poor resistance to freeze-thaw action, the new concrete can be expected to have reduced freeze-thaw durability. The freeze-thaw durability of hydraulic-cement concrete with RCA is also impacted by the effect the RCA has on the effectiveness of air-entraining admixtures in the new concrete. A North Carolina study indicates that as the percentage of recycled fine aggregate increased, the air content of the fresh concrete decreased (see paragraph 14d). To meet target air contents, higher dosages of air entraining agent are needed for concrete mixtures utilizing fine and coarse recycled aggregates; other States have found that it is not possible to produce a mixture that satisfied target air content requirements (see paragraph 14d). Freeze-thaw testing (ASTM C 666, "Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing") should be done as part of the evaluation and qualification of concrete mixtures containing RCA, in areas where resistance to freeze-thaw action is required.

    6. RCA derived from concrete containing more than 0.04 kg of chloride ion per cubic meter (0.06 lbs of chloride ion per cubic yard) should not be used in concrete for Continuously Reinforced or Jointed Reinforced concrete pavement because accelerated steel corrosion could lead to early pavement failure. In doweled jointed plain concrete (JPC) pavement, use of epoxy-coated, stainless steel, and stainless steel clad or fiber reinforced plastic (FRP) dowels should be considered to mitigate the potential corrosion.

    7. Alkalis from deicer salt within the RCA must be considered if the RCA is prone to ASR, and it is to be used as an aggregate in concrete (see paragraph 14n).

    8. Shrinkage and thermal expansion characteristics of concrete containing RCA should be determined prior to pavement design so that the actual parameters can be used in the design process. Typically, concrete containing RCA will have a higher drying shrinkage and a higher coefficient of thermal expansion (ACI 555, "Removal and Reuse of Hardened Concrete") but testing must be performed on the proposed mixture to quantify the actual values. The most commonly used shrinkage test for concrete is ASTM C 157, "Standard Test Method for Length of Change of Hardened Hydraulic-Cement Mortar and Concrete." The coefficient of thermal expansion of concrete can be determined using methods described in AASHTO TP 60, "Standard Method Test for Coefficient of Thermal Expansion of Hydraulic Cement Concrete."

    9. Laboratory and field trials of the concrete mixture must be conducted to insure that the properties of the mixture containing RCA meet job requirements.

  8. What are the properties of new concrete when RCAs are used? RCA can have a profound impact on the properties of both fresh and hardened hydraulic-cement concrete. Tables 1, 2, and 3 summarize available information on the effect of RCA on properties of new concrete. In general, as is the case with virgin aggregates, improving the quality of RCA will lessen or eliminate any negative impact on the required engineering properties of the new concrete.

  9. What pavement design issues need additional consideration when using RCA in concrete? The pavement designer must be aware of potential strength reduction, increased shrinkage potential, and possible changes in the thermal characteristics of hydraulic-cement concrete produced with RCA. These properties may require the designer to increase pavement thickness or change joint spacing to accommodate the use of RCA in the project. The differences in some concrete properties may be beneficial to the performance of the pavement, depending on the particular design and environment. Prior to design, the properties of the specific concrete proposed for use should be determined. These design inputs can then be used in a mechanistic-empirical design procedure that accounts for temperature and shrinkage in determining joint spacing.

  10. . What mixture design and proportioning issues should be considered when proportioning concrete using RCA?

    1. Mixture design and proportioning of concrete containing RCA is accomplished using the same procedures used for concrete containing virgin aggregates. The water/cementitious material ratio should be 0.45 or less and a water-reducing admixture should be used. Additional cementitious material may be required to produce the required strength. Concrete containing coarse RCA may require approximately 5 percent more water than a similar concrete containing virgin coarse aggregate. Concrete containing fine and coarse RCA may require up to 15 percent more water (see paragraph 14a).

    2. In the event that fine RCA is used, a blended fine aggregate with no more than 30 percent fine RCA is recommended. This may reduce the water demand by about 10 percent compared to a similar concrete with 100 percent fine RCA. Fine RCA should not be used in concrete where freeze-thaw durability is required.

  11. What production issues should be considered when making concrete with RCA? Concrete containing RCA can be batched, mixed, delivered, placed, and finished using methods commonly used for concrete containing virgin aggregate. The primary caution for production is dealing with the increased water demand of RCA, even though proper processing should have removed the fine material prior to concrete production. RCA should be presoaked to help maintain uniformity of absorbed water during production. It should be stored and moistened using procedures commonly used for light weight and slag aggregate, such as continuous sprinkling prior to batching.

  12. What construction issues should be addressed when paving with concrete containing recycled aggregates? If the procedures described above for production of the RCA and the concrete are followed, construction issues should not be different from issues encountered when paving with concrete manufactured with virgin aggregate. Failure to properly address aggregate processing, water demand, or air entrainment will significantly increase the likelihood of problems in placing and finishing the new pavement.

  13. What are the costs associated with using high-quality RCA? Recycling demonstrates good environmental stewardship, and it may reduce the cost of a paving project, but economic and environmental costs are different on each project. Recycling existing pavement for use as RCA for new concrete pavement may or may not present the best recycling solution. Factors to be considered include availability and cost of virgin aggregate, processing and quality control costs to manufacture high-quality recycled aggregate for use in new concrete, hauling and tipping fees for land-fill disposal of old pavement, comparison with costs of lower-value recycling alternatives, and job specific environmental issues. The quantity of RCA available on a project may not be sufficient to fill the requirements of the new paving project. Pavement sections containing RCA may be thicker or require shorter joint spacing, which may increase the cost of the new pavement.

  14. Are there any reference materials on the use of recycled concrete as aggregate? The following references apply to using recycled demolished concrete as aggregate for concrete:

    1. American Concrete Institute (ACI) Committee 555, "Removal and Reuse of Hardened Concrete,"ACI 555R-01, American Concrete Institute, Farmington Hills, MI, 2001.

    2. American Concrete Paving Association (ACPA), "Recycling Concrete Pavement,"TB014P, American Concrete Pavement Association, Skokie, IL, 1993, 19 Pages.

    3. ASTM Committee C9, "Standard Specification for Concrete Aggregate,"ASTM C 33, ASTM International, West Conshohocken, PA, 2003.

    4. Ahmad, S.H., "Properties of Concrete Made with North Carolina Recycled Coarse and Fine Aggregate,"Center for Transportation Engineering Studies, North Carolina State University, Raleigh, NC, 1996.

    5. AASHTO Subcommittee on Materials, "Fine Aggregate for Portland Cement Concrete," AASHTO M 6, American Association of State Highway and Transportation Officials, Washington, DC, 2001.

    6. AASHTO Subcommittee on Materials, "Coarse Aggregate for Portland Cement Concrete," AASHTO M 80, American Association of State Highway and Transportation Officials, Washington, DC, 2001.

    7. Environmental Council of Concrete Organizations (ECCO), "Recycling Concrete and Masonry,"EV22, Skokie, IL, 1999, 12 Pages.

    8. FHWA Policy Memorandum "Formal Policy on the Use of Recycled Materials," February 7, 2002.

    9. FHWA Survey, Recycled Concrete Aggregate National Review, May 24, 2005.

    10. Klieger, P. and Lamond, J.F., "Significance of Tests and Properties of Concrete-Making Materials," STP 169C, ASTM International, West Conshohocken, PA, 1994.

    11. Kosmatka, S., Kerkoff, B. and Panarese, W., "Design and Control of Concrete Mixtures, 14th Edition," Portland Cement Association, Skokie, IL 2002.

    12. Melton, J.S., "Guidance for Recycling Concrete Aggregate Used in the Highway Environment," ACI SP-219, American Concrete Institute, Farmington Hills, MI, 2001.

    13. National Cooperative Highway Research Program (NCHRP), "2002 Design Guide, Design of New and Rehabilitated Pavement Structures," NCHRP 1-37-A, Transportation Research Board, Washington, DC, 2003.

    14. Stark, David,"The Use of Recycled-Concrete from Concrete Exhibiting Alkali-Aggregate Reactivity," Research and Development Bulletin RD114, Portland Cement Association, 1996.

    15. Van Dam, T.J., Sutter, L.L., Smith, K.D., Wade, M.J., and Peterson, K.R., "Guidelines for Detection, Analysis and Treatment of Materials-Related Distress in Concrete Pavements Vol. 2: Guidelines Description and Use," FHWA-RD-01-164, Federal Highway Administration, McLean, VA, August 2002.

    16. Yrjanson, William A., NCHRP Synthesis 154; "Recycling of Portland Cement Concrete Pavement," Transportation Research Board, Washington, D.C., December 1989.

King W. Gee
Associate Administrator
for Infrastructure

Table 1. Effect of RCA on Mechanical Properties of Concrete
Property Range of expected changes from similar mixtures using virgin aggregates. (ACI 555R)
Coarse RCA only Coarse and Fine RCA
Compressive Strength
5% to 24% less
15% to 40% less
Strength Variation
Slightly greater
Slightly greater
Modulus of Elasticity
10% to 33% less
25% to 40% less
Creep
30% to 60% greater
30% to 60% greater
Tensile Strength
10% less
10% to 20% less
Permeability
200% to 500% greater
200% to 500% greater
Thermal Expansion
Somewhat less than expected for coarse aggregate used
Somewhat less than expected for coarse aggregate used
Specific Gravity
5% to 10% lower
5% to 10% lower
Table 2. Effect of RCA on Fresh Concrete Properties
Property Range of expected changes from similar mixtures using virgin aggregates. (ACI 555R)
Coarse RCA only Coarse and Fine RCA
Water Demand
Greater
Much greater
Drying Shrinkage
20% to 50% more
70% to 100% more
Finishability
More difficult
More difficult
Table 3. Effect of RCA on Concrete Durability
Property Range of expected changes from similar mixtures using virgin aggregates. (ACI 555R)
Coarse RCA only Coarse and Fine RCA
Corrosion Rate
May be faster
May be faster
Freeze-thaw Durability
Dependent on air void system
Dependent on air void system
Carbonization
65% greater
65% greater
Sulfate Resistance
Dependent on mixture
Dependent on mixture
 
Updated: 04/07/2011
 

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