RECLAIMED ASPHALT PAVEMENTUser Guideline

Embankment or Fill

INTRODUCTION

In addition to recycling into asphalt paving or incorporation into bases or subbases, some reclaimed asphalt pavement (RAP) has been used for embankment construction. It can also be used as a fill material. When used as an embankment or fill material, the undersize portion of crushed and screened RAP, typically less than 2 in, may be blended with soil and/or finely graded aggregate. Uncrushed or more coarsely graded RAP may be used as the embankment base.

Although the use of RAP in embankment construction does not take any advantage of the asphalt cement component, it does, nevertheless, provide an alternate application where no other markets for reuse are readily available, or where the RAP may be unsuitable for use in asphalt concrete pavement. The properties of RAP are largely dependent on the properties of the constituent materials and asphalt concrete type used in the old pavement. ^(10,14)

PERFORMANCE RECORD

Although use of RAP as an embankment construction material does not appear to be extensive, it has been reported that at least nine states have made some use of RAP for this purpose. States that have made use of RAP as an additive in embankment construction include Connecticut , Indiana , Kansas , Montana , New York , and Tennessee . States that have used RAP directly as an embankment base material include California, Connecticut, Illinois, Louisiana, and Tennessee. ⁽⁴⁾ The performance of RAP in these applications was generally considered to be satisfactory to good.

MATERIAL PROCESSING REQUIREMENTS

Crushing

Processing requirements for embankment or fill applications are minimal. Primary crushing may be necessary to satisfy gradation requirements. However, some jurisdictions permit the use of broken pieces of old asphalt pavement, provided the specified maximum size (similar to boulders) is not exceeded.

Blending

Crushed RAP is sometimes mixed with conventional earth fill materials or crushed aggregates and used in embankment construction.

ENGINEERING PROPERTIES

Some of the engineering properties of RAP that are of particular interest when RAP is used in embankment applications include gradation, compacted density, moisture content, shear strength, consolidation characteristics, permeability, durability, drainage characteristics, bearing strength, and corrosivity.

Gradation : The gradation of RAP is controlled by crushing and screening. The gradation and physical requirements of AASHTO M145 ⁽¹⁾ are usually readily satisfied by RAP or blends of RAP and soil or crushed aggregate. If used as an embankment base material, the maximum particle size of RAP will probably be less than 24 in.

Compacted Density : Due to its asphalt cement content, the compacted unit weight of RAP100 to 125 lbs/ft 3 is likely to be somewhat lower than that of earth or rock. ⁽¹⁵⁾ The finer the RAP is crushed and sized, the higher its compacted density.

Moisture Content : The optimum moisture content for RAP-aggregate blends is reported to be higher than for conventional embankment material, particularly for RAP from pulverizing operations, due to higher fines generation. ⁽¹¹⁾

Shear Strength : The shear strength of RAP that has been crushed and sized will be based on internal friction, with little or no cohesion, and should be comparable to that of a similarly graded natural aggregate. RAP-aggregate blends should also have an internal friction angle in the same range as the natural aggregate. The shear strength of RAP-soil blends will likely be based mainly on internal friction, with little or no cohesion, and will be dependent on the relative proportions of the RAP and the soil.

Consolidation Characteristics : The compressibility or consolidation characteristics of RAP-soil blends will probably be within the range of a granular soil, depending on the gradation, moisture content, and proportion of soil added to the RAP. For coarsely graded RAP, or RAP-aggregate blends, the potential for compressibility should, for all practical purposes, be negligible.

Permeability : The permeability of blended RAP is similar to that of conventional granular material or soil-aggregate blends having similar gradation. ⁽¹¹⁾

Durability : Since the quality of virgin aggregates used in asphalt concrete usually exceeds the requirements for embankment/fill material, there are generally no durability concerns regarding the use of RAP in this application.

Drainage Characteristics : RAP is nonplastic, free draining, is not frost susceptible, and can be blended and compacted with other suitable fill materials.

Bearing Strength : The bearing strength of an embankment is mainly of importance only in the top 3 ft, which is the portion of the embankment that provides the subgrade support for the pavement structure. The bearing strength of subgrade materials is usually determined by the California Bearing Ratio (CBR) test. The CBR value for RAP should be comparable to that of crushed stone of a similar gradation. The CBR of RAP-soil blends should be comparable to that of a well-graded granular soil. The top portion of an embankment will normally consist of soil like materials, with the coarser materials (crushed stone or rock) in the lower portions of the embankment.

Corrosivity : On the basis of limited testing results, RAP is considered noncorrosive. ^(9,12)

DESIGN CONSIDERATIONS

The design requirements for RAP in embankment construction are the same as for similar sized soil-aggregate blends, conventional aggregates, or shot rock fill. Where pieces of broken asphalt pavement are used as embankment base, size and placement restrictions should apply in the same manner as for boulders and cobbles. It is recommended that such uncrushed materials not be placed where they may have an impact on future construction activities. Some jurisdictions require that a minimum separation be maintained between watercourses and fill materials containing RAP to avoid submersion of RAP in water, which may or may not be a potential environmental concern. ⁽¹³⁾

Design procedures for embankments or fill containing RAP are the same as design procedures for conventional embankment materials. The design should take into consideration slope stability, settlement or consolidation, and bearing capacity concerns. If the embankment is to be constructed using a blend of RAP with soil and/or crushed aggregate, a representative sample of the blended material should be tested, if possible, for triaxial compression ⁽⁵⁾ and California Bearing Ratio (CBR). ⁽⁶⁾ The maximum particle size for the triaxial test is 5 mm (No. 4 sieve). The maximum particle size for the CBR test is 19 mm (3/4 in sieve).

CONSTRUCTION PROCEDURES

Material Handling and Storage

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

Since each source of RAP will be different, random sampling and testing of the RAP stockpile must be performed to quantify and qualify the RAP. Representative samples of the stockpiled RAP should be used in the optimum blend design. ⁽²⁾ Additional care is required during stockpiling and handling to avoid segregation or re-agglomeration.

Placing and Compacting

The same methods and equipment for compacting conventional fill can be used for compacting crushed RAP or blends of soil and RAP. It is reported that granular materials containing RAP appear to compact better if little or no water is used. ⁽¹⁵⁾ Where large, broken pieces of old asphalt pavement are incorporated in embankment construction, additional attention is needed during compaction to ensure that no large voids are formed within the fill that could contribute to subsequent long-term differential settlement. Standard laboratory and field test methods for compacted density are given by AASHTO T191, ⁽²⁾ T205, ⁽³⁾ T238, ⁽⁷⁾ and T239. ⁽⁸⁾

Quality Control

The same field test procedures used for conventional soils or crushed aggregate materials are also appropriate for RAP, or blends of RAP and soils or crushed aggregates.

When RAP is used for construction of an embankment base or foundation material, compaction operations must be visually inspected on a continuous basis to ensure that the specified degree of compaction can be achieved, or that there is no movement under the action of compaction equipment. The construction of embankment bases or foundations containing rock or oversize materials usually requires a method specification, in which the procedures and type of equipment for placement and compaction are stipulated, but no testing methods or acceptance criteria are indicated.

In Florida , testing has been done to determine the leaching characteristics of RAP. In all batch tests measurements of VOCs, PAHs, and heavy metals (Ba, Ca, Cr, Cu, Pb, Ni and Zn) were below the detection level and below the applicable regulatory groundwater guidance concentrations. This indicates that all RAP samples tested pose minimal risk under current waste policy in Florida . Lysimeter tests were also preformed and columns were leached for 42 days. The VOC, PAH and heavy metal (Ba, Ca, Cr, Cu, Ni and Zn) measurements were all below detection limits, except for lead. ⁽¹⁹⁾

ENVIRONMENTAL CONSIDERATIONS

Asphalt pavement consists of aggregate and petroleum derived asphalt binder containing volatile and semi-volatile constituents (e.g., polycyclic aromatic hydrocarbons (PAHs)) Additionally the asphalt pavement roadway may contain surface treatments, rubberized materials or contaminants from vehicle or other emissions (e.g., historically lead). The environmental issues are different for RAP based upon various beneficial uses. For unbound applications, such as embankment fill, leachability from the RAP may be a concern. This same leachability would be a concern if RAP was stockpiled or stored and exposed to precipitation. Testing has been conducted to determine the leaching characteristics of RAP in Florida. In all batch tests measurements of VOCs, PAHs, and heavy metals (Ba, Ca, Cr, Cu, Pb, Ni and Zn) were below the detection level and below the applicable state regulatory groundwater guidance concentrations. This indicates that all RAP samples tested pose minimal risk under current waste policy in Florida. Lysimeter (column leaching) tests were also performed and columns were exposed to synthetic precipitation for 42 days. The VOC, PAH and heavy metal (Ba, Ca, Cr, Cu, Ni and Zn) measurements were all below detection limits, except for lead which exhibited a concentration of 24 µg/L and 23 µg/L on days 12 and 14 of the experiment, but then was otherwise below the applicable Florida Groundwater Guidance Concentration (15 µg/L) for the duration of the experiment. ⁽¹⁶⁾ Other batch and column leaching tests were completed on RAP which also found constituents leached were low and generally below European drinking water standards (The Drinking Water Directive (DWD), Council Directive 98/83/EC). ⁽¹⁷⁾ Additionally, the University of Minnesota completed a review of current literature on PAHs in asphalt pavement concluding that PAH concentrations depend on the type of pavement (coal-tar versus petroleum based). Petroleum based asphalt pavement contained PAHs at concentrations below Minnesota Pollution Control Agency human health risk clean-up levels ⁽¹⁸⁾. The only exceedance was when when PAHs were converted to benzo(a)pyrene equivalents, they could exceed the lowest limit (Tier I). The report further concluded that when RAP is used as subbase aggregate, it is mixed with soils or other aggregates that do not contain PAH, so this mixture would not likely exceed applicable limits. ⁽¹⁸⁾

UNRESOLVED ISSUES

Although RAP is not frequently incorporated into embankments, there is a need to establish standard specifications for the use of RAP in embankment construction, either by itself as an embankment base material, or blended with soil and/or crushed aggregate.

REFERENCES

AASHTO Designation: M145-82. "Standard Method of Test for the Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes," American Association of State Highway and Transportation Officials, Part I Specifications, 16th Edition, 1993.
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, "Density of Soil In-Place by the Rubber-Balloon Method," AASHTO Designation: T205-86, Part II Tests, 14th Edition, 1986.
Ahmed, Imtiaz. Use of Waste Materials in Highway Construction . Federal Highway Administration, Report No. FHWA/IN/JHRP-91/3, Washington , DC , January, 1991.
ASTM D2850-87. "Standard Test Method for Unconsolidated, Undrained Compressive Strength of Cohesive Soils in Triaxial Compression." American Society for Testing and Materials, Annual Book of ASTM Standards , Volume 04.08, West Conshohocken , Pennsylvania .
ASTM D1883-87. "Standard Test Method for CBR ( California Bearing Ratio) of Laboratory-Compacted Soils." American Society for Testing and Materials, Annual Book of ASTM Standards , Volume 04.08, West Conshohocken , Pennsylvania .
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, "Moisture Content of Soil and Soil Aggregate in Place by Nuclear Methods (Shallow Depth)," AASHTO Designation: T239-86, Part II Tests, 14th Edition, 1986.
Bansci, J. J., A. Benedek, J. J. Emery, and J. Lawrence, "The Leaching of Toxic Organic Compounds from Solid Wastes," Presented at U.S. EPA National Conference on Management of Uncontrolled Waste Sites, Washington , DC , 1980.
Engineering and Environmental Aspects of Recycling Materials for Highway Construction , Federal Highway Administration, Report No. FHWA-RD-93-008, Washington , DC , May 1993.
Hanks, A. J. and E. R. Magni. The Use of Bituminous and Concrete Material in Granular Base and Earth . Materials Information Report MI-137, Engineering Materials Office, Ontario Ministry of Transportation, Downsview , Ontario , 1989.
Krietch, A.J. "Evaluation of RAP as Clean Fill," Asphalt , Vol.5, No.1, p.8, The Asphalt Institute, Lexington , Kentucky , Summer 1991.
Krietch, A.J. Leachability of Asphalt and Concrete Pavements , Heritage Research Group Report, Indianapolis , Indiana , March, 1992.
Pavement Recycling Executive Summary and Report , Federal Highway Administration, Report No. FHWA-SA-95-060, Washington , DC , 1995.
Senior, S. A., S. I. Szoke, and C. A. Rogers. " Ontario 's Experience with Reclaimed Materials for Use in Aggregates." Presented at the International Road Federation Conference, Calgary , Alberta , 1994.
Brantley, A.S. and Townsend, T., Leaching of pollutants from reclaimed asphalt pavement, Environmental Engineering Science , Vol. 16, no. 2, pp. 105-116. Apr. 1999.
Legret, M., Odie, L., Demare, D., Jullien, A., Leaching of heavy metals and plycyclic aromatic hydrocarbons from reclaimed asphalt pavement, Water Research, Vol. 39, 3675-3685, 2005.
Grosenheider, K., Bloom, P., Halbach T., Johnson, M., A Review of the Current Literature Regarding Polycyclic Aromatic Hydrocarbons in Asphalt Pavement, Mn/DOT contract No. 81655, October, 2005.

[ Material Description ] - [ Asphalt Concrete (Hot Recycling) ] - [ Asphalt Concrete (Cold Recycling) ] - [ Granular Base ] - [ Embankment or Fill ]

Last Update 7/28/08