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

RECLAIMED CONCRETE MATERIALUser Guideline


Portland Cement Concrete

INTRODUCTION

Reclaimed concrete material (RCM) can be used as coarse and/or fine aggregate in Portland cement concrete (PCC) pavements. However, concrete incorporating more than about 10 to 20 percent fine RCM aggregates can suffer a reduction in quality because of the high amount of water required to maintain adequate workability of the concrete mix.

PERFORMANCE RECORD

RCM has been accepted by many jurisdictions and is covered by conventional aggregate specifications and by several highway agency specifications, including those in Colorado, Connecticut, Illinois, Indiana (special provisions), Iowa, Louisiana, Michigan, Montana, North Dakota, Oklahoma, and Wyoming. (14) For large projects and/or projects where suitable quality aggregate is not readily available, site-processed RCM can be significantly cheaper than new aggregate hauled to the site.

MATERIAL PROCESSING REQUIREMENTS

Material Handling

When RCM is collected from different sources or types of concrete, it should either be blended with other aggregates or separately processed and placed in separate stockpiles to ensure uniformity of RCM aggregate properties.

Crushing and Screening

Crushing and screening is required to produce aggregate within the limits for concrete mix gradation.

Quality Control

Levels of impurities such as sulfate and chloride ions, alkali-reactive aggregate and freeze-thaw expansion of large aggregate that can result in a breakdown of the concrete causing D-cracking in concrete pavements must be controlled to ensure that the finished concrete has consistent strength and durability. (17,21) D-cracks are closely spaced cracks parallel to transverse and longitudinal joints that multiply outward to the center of the pavement panel. These cracks typically start in the saturated aggregate at the base of the pavement and progress upward. Michigan found that the incidence of D-cracks can be reduced by using a smaller size aggregate. Michigan recommends that an increased foundation thickness, slab tension reduction, additional steel reinforcement, used of a deforemed wire mesh and use of hinge joints can effectively reduce cracking. (16) It has been recommended that the degree of contamination and potential reactivity of RCM aggregates should not exceed the limits permitted for virgin aggregates. (7)

ENGINEERING PROPERTIES

Some of the engineering properties that are of particular interest when RCM is used in Portland cement concrete applications include gradation, particle shape, specific gravity, absorption, moisture content, durability, and permeability.

Gradation : Recycled concrete material should be crushed and screened to produce aggregate that satisfies the AASHTO M6 (3) and M80 (4) gradation requirements for PCC. With appropriate adjustments, a plant can produce any desired gradation. Crushed fine aggregates (minus 4.75 mm (No.4 sieve)) are generally not used or are blended with natural sand.

Shape : Processed RCM, being 100 percent crushed material, is highly angular in shape. While this shape assists in increasing the strength of the mix, it can reduce its workability.

Specific Gravity : The specific gravity of processed coarse RCM aggregate ranges from 2.0 to 2.5, which is slightly lower than that of virgin aggregates. This is primarily due to the adhesion of mortar to virgin aggregate particles. The differences become more pronounced with decreasing particle size. The specific gravity of processed RCM fines is in the range of 2.0 to 2.3. (1)

Absorption : RCM aggregates can be expected to have higher absorption values than virgin aggregates. High absorption is particularly noticeable in crushed fine material (minus 4.75 mm (No.4) sieve) from air-entrained concrete. Absorption values for fine-grained RCM generally range from 4 to 8 percent (compared with 2 percent or less for fine virgin concrete aggregates). (1)

Moisture Content : The in-situ stockpile moisture content for processed RCM is typically the same as that for conventional granular material.

Durability : Coarse-grained RCM typically exhibits good soundness characteristics and abrasion resistance. Durability and soundness properties of processed RCM are similar to those of the virgin aggregates incorporated in the concrete and generally satisfy specification requirements for concrete aggregates. (17)

Permeability : Coarse-grained RCM is free draining (more permeable than conventional granular material due to lower fines content).

Some of the properties of concrete mixes containing RCM that are of interest include strength characteristics, workability, resistance to freeze-thaw, deleterious substances, alkali-aggregate reactivity, and corrosivity.

Strength Characteristics : In RCM mixes, compressive strength can be reduced up to 25 percent compared to mixes with conventional aggregates, with up to 30 percent improvement in the damping capacity, and higher amounts of drying shrinkage and creep. (20) For a given compressive strength (at 28 days), both the static and dynamic moduli of elasticity for recycled-aggregate concrete are significantly lower (up to 40 percent) than those for concrete containing virgin aggregate. (15,22) Concrete mixes incorporating coarse RCM aggregates generally can be expected to develop about 10 percent lower flexural strength at equal water/cement ratio and slump than conventional aggregates.

Workability : If fine RCM aggregates are used, concrete workability decreases (due to the high absorption and angularity of crushed RCM fines) and concrete flexural strength is reduced about 10 to 20 percent. (19) It is recommended that stockpiles be watered periodically and aggregate moisture content testing be done prior to incorporating the aggragate into a mix for improved mix workability. (16)

Resistance to Freeze-Thaw : Concrete incorporating RCM aggregates has good resistance to freeze-thaw exposure provided a suitable air void system is present in the mortar phase of the concrete containing RCM aggregate.

Deleterious Substances : Chlorides may be present in RCM as a result of many years of deicing salt application on an old pavement. High levels of chloride in the recycled aggregate can induce corrosion of reinforcing steel embedded in a new concrete. However, the quantity of chloride typically found in old concrete pavement is below critical threshold values. (23) A threshold value of 2.4 kg/m 3 (4 lbs/yd 3 ) is recommended by the American Concrete Pavement Association as a threshold to trigger the removal and replacement of concrete bridge decks due to corrosion potential. (1,18)

Recycled concrete material may also contain coarse and/or fine aggregates that are susceptible to alkali-silica reaction. (18,22)

DESIGN CONSIDERATIONS

Mix Design

Crushed RCM is considered a conventional coarse aggregate for Portland cement concrete mixtures by AASHTO M80. Coarse aggregates should conform to the grading requirements outlined in AASHTO M43 (5) for the grading specified. AASHTO M6 provides the physical properties and grading requirements for concrete fine aggregate.(2)

Prior to use, trial batches should be prepared according to ACI 211 procedures (8) and necessary mix adjustments made to ensure that the specified requirements are attained.

Special care is required when incorporating RCM fines to avoid dramatic reductions in concrete workability, strength, and finishability. Blending RCM fines with natural sand at substitution rates of 10 to 20 percent has resulted in satisfactory performance. Several trial mixes are often required to generate sufficient data to identify the optimum substitution rate.

Due to their high absorption, prewetting of RCM aggregates is important. Aggregates that are not saturated will absorb water from the concrete mix.

In addition to satisfying the requirements of AASHTO M43 and M6, consideration must be given to sulfate and chloride contamination of RCM aggregates. Chloride contamination is often due to the application of deicing salts (on pavements and sidewalks). High concentrations of chloride ions can result in corrosion of reinforcing steel. ACI 201.2R, "Guide to Durable Concrete," (6) provides guidance on the limits of such contaminants for various service conditions.

Where sulfate attack is of concern, the potential for deterioration should be evaluated by the ASTM C452 sulfate expansion test. (11) Sulfate-resistant cement such as Type II or V can be used, if necessary.

Where alkali-silica reactivity is of concern, the potential for deterioration should be evaluated by the ASTM C289 test. (12) Low-alkali Type II cement can be used if necessary.

For reinforced concrete pavement construction or plain jointed pavements without load transfer dowels, it is important to ensure that the top size coarse aggregate is sufficiently large (typically 40 mm) to provide adequate interlock across joints and cracks.

Structural Design

Conventional AASHTO rigid pavement thickness design procedures are appropriate for rigid pavements incorporating RCM.

CONSTRUCTION PROCEDURES

The same equipment and procedures used for concrete containing conventional aggregate may be used to batch, mix, transport, place, and finish concrete containing processed RCM aggregates. However, additional care and some minor changes are necessary to avoid potential problems.

Material Handling and Storage

The same methods and equipment used to store or stockpile conventional aggregates are applicable for RCM.

It is important to monitor the moisture content of RCM aggregates in stockpiles to permit determinations of the mix water requirements. Sprinkling stockpiles to keep RCM aggregates saturated is an effective method of minimizing their potential to absorb moisture from the concrete mix.

Mixing, Placing, and Compacting

The same methods and equipment can be used to mix, place, and compact RCM concrete mixes and conventional concrete mixes.

Slipforming and finishing concrete made with RCM aggregates is improved by reducing or eliminating the RCM fines content in favor of natural sand.

Quality Control

The same quality-control procedures for conventional Portland cement concrete pavement are required for Portland cement concrete incorporating RCM aggregates. The slump, air content, and temperature of the plastic concrete should be monitored at the time of placement, and compressive strength cylinders cast for compressive strength determinations in accordance with the ASTM C39 (9) procedure. Flexural strength can be determined using flexural strength prisms (ASTM C78) (10) or by splitting tensile tests (ASTM C496) (13) on cylinders. Due to the sensitivity of concrete pavement performance and durability to water-cement ratio, and the potential variability in RCM gradation, specific gravity, and absorption, particular attention should be given to these aggregate properties when using RCM in concrete pavement mixtures, and appropriate adjustments to the quantity of mixing water completed during concrete production.

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 (24). Although leachability results were low (24), 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) (25). This research concluded that well-cured Portland cement concrete released no detectable concentrations of antimony, arsenic, beryllium, cadmium, chromium, lead, mercury, nickel and selenium (25). 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 (26). 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 (27). 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 (28). 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 (29,30). 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 (30). 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

There is a need to obtain long-term performance and life-cycle cost data for concrete made with processed RCM aggregates to assess its durability, performance, and expected service life.

Limits on chloride and sulfate contents of concrete materials are well established. However, further investigation concerning the effect of other impurities that RCM may contain (other than chloride and sulfate) such as wood, asphalt, and earth on concrete performance is greatly needed. Also, there is a need for guidance regarding the monitoring and restriction of impurities in RCM.

Further, for concretes affected by alkali-silica reactive or D-cracking, specific knowledge of the concrete is needed to assure its reclcled use is appropriate. For instance, the potential for continued ASR needs to be evalauted and if found to be probablamatic then the mix must be mitigated. Like wise crushing a D-cracked concrete may in fact eliminate D cracking in the new concrete however it may not. Criteria for evaluating both cases are lacking to assure the safe and risk free use of these special concretes. There is an essential need to develop appropriate specifications for the use of such materials.

REFERENCES

  1. ACPA. Concrete Paving Technology: Recycling Concrete Pavement, American Concrete Pavement Association, Illinois , 1993.
  2. American Association of State Highway and Transportation Officials. Standard Specification "Fine Aggregate for Portland Cement Concrete," AASHTO Designation M6-65, Part I Specifications, 14th Edition, 1986.
  3. American Association of State Highway and Transportation Officials. Standard Specification for Materials, "Fine Aggregate for Portland Cement Concrete," AASHTO Designation: M 6-81, Part I Specifications, 14th Edition, 1986.
  4. American Association of State Highway and Transportation Officials. Standard Specification for Materials, "Coarse Aggregate for Portland Cement Concrete," AASHTO Designation: M80-77, Part I Specifications, 14th Edition, 1986.
  5. American Association of State Highway and Transportation Officials. Standard Specification for Materials, "Standard Sizes of Coarse Aggregate for Highway Construction," AASHTO Designation: M43-82 (1986), Part I Specifications, 14th Edition, 1986.
  6. ACI. "Guide to Durable Concrete," ACI Manual of Concrete Practice, ACI 201.R-77, Part 1, 1990.
  7. ACI. Recycling of Demolished Concrete and Masonry, RDCM.CT 95, American Concrete Institute, Detroit , Michigan 1995.
  8. ACI. "Standard Practice For Selecting Proportions for Normal , Heavy Weight, and Mass Concrete," ACI Manual of Concrete Practice, ACI 211.1-89, Part 1, 1990.
  9. ASTM C39. "Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens," American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken , Pennsylvania .
  10. ASTM C78. "Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)," American Society for Testing and Materials, Annual Book of ASTM Standards , Volume 04.02, West Conshohocken , Pennsylvania .
  11. American Society for Testing and Materials. Standard Specification C452-85a, "Potential Expansion of Portland Cement Mortars Exposed to Sulfate," Annual Book of ASTM Standards, Volume 04.01, 1987.
  12. ASTM C289. "Standard Test Method for Potential Reactivity of Aggregates," American Society for Testing and Materials, Annual Book of ASTM Standards , Volume 04.02, West Conshohocken , Pennsylvania .
  13. ASTM C496-86. "Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens," American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken , Pennsylvania .
  14. Collins, R. J. and S. K. Ciesielski. Recycling and Use of Waste Materials and By-Products in Highway Construction, National Cooperative Highway Research Program Synthesis of Highway Practice 199, Transportation Research Board, Washington, 1994.
  15. Frondistou-Yannas, S., "Waste Concrete as Aggregate for New Concrete," American Concrete Institute Journal, Vol. 14, No. 8, August 1977, pp. 373-376.
  16. Gonzalez, G.P. and Moo-Young, H.K. Transportation Applications of Recycled Concrete Aggregate, FHWA State of the Practice National Review, September 2004.
  17. Haas, R.G., W.R. Hudson, and J. Zaniewski. Modern Pavement Management , Krieger Publishing Company Melbourne , Florida , 1994.
  18. Handbook for the Identification of Alkali-Silica Reactivity in Highway Structures, SHRP-C/FR-91-101, Strategic Highway Research Program, National Academy of Sciences Washington , D.C. , 1991.
  19. Hanks, A. J. and E. R. Magni. The Use of Recovered Bituminous and Concrete Materials in Granular Base and Earth, Report MI-137, Ontario Ministry of Transportation, Downsview, Ontario 1989.
  20. Recycling of Demolished Concrete and Masonry, RILEM, International Union of Testing and Research Laboratories for Materials and Structures, E and FN Spon, New York , 1992.
  21. Shahin, M.Y. and S. D. Kohn. Development of Pavement Condition Rating Procedures for Roads, Streets and Parking Lots - Volume 1 Condition Rating Procedure, Technical Report M-268, Construction Engineering Research Laboratory, United States Corps of Engineers, 1979.
  22. Sri Ravindrarajah, R., C.T. Tam Be, et al. Properties of Concrete Made with Crushed Concrete as Coarse Aggregate, National University of Singapore , 1985.
  23. Yrjanson, W. Recycling of Portland Cement Concrete Pavements, National Cooperative Highway Research Program Synthesis of Highway Practice 154, Transportation Research Board, Washington, D.C., December 1989.
  24. Kreitch, A.J. Leachability of Asphalt and Concrete Pavements, Heritage Research Group Report, Indianapolis , Indiana , March 1992.
  25. 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.
  26. Shanmugam, Harini, Assessment and mitigation of potential environmental impacts of Portland Cement Concrete highway grindings, Thesis, Washington State University, 2004.
  27. Ohio Department of Transportation, Recycled Materials Report, Box Test.
  28. Steffes, R., Laboratory Study of the Leachate from Crushed Portland Cement Concrete Base Material, Iowa Department of Transportation, September 1999.
  29. 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.
  30. 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