HomeMy WebLinkAboutFile Documents.700 Gillespie St.0129.2018 (2).ACBKResearch, Development, and Technology
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296
Reclaimed Asphalt Pavement in Asphalt
Mixtures: State of the Practice
PublicAtion no. FHWA-HRt-11-021 APRil 2011
FOREWORD
Recycling asphalt pavement creates a cycle of reusing materials that optimizes the use of natural
resources. Reclaimed asphalt pavement (RAP) is a useful alternative to virgin materials because
it reduces the need to use virgin aggregate, which is a scarce commodity in some areas of the
United States. It also reduces the amount of costly new asphalt binder required in the production
of asphalt paving mixtures. This report informs practitioners about the state of the practice for
RAP use in the United States as well as best practices for increasing the use of RAP in asphalt
pavement mixtures while maintaining high-quality pavement infrastructures. High percentage
RAP mixtures are achieved with processing and production practices, resulting in cost and
energy savings. Based on an evaluation of pavements containing 30 percent RAP through the
Long-Term Pavement Performance (LTPP) program, it has been determined that the
performance of pavements containing up to 30 percent RAP is similar to that of pavements
constructed from virgin materials with no RAP. This report is of interest to engineers,
contractors, and others involved in the specification and design of asphalt mixtures for flexible
pavements, as well as those involved in promoting the optimal use of RAP.
Peter Stephanos Jorge E. Pagán-Ortiz
Director, Office of Pavement Technology Director, Office of Infrastructure
Research and Development
Notice
This document is disseminated under the sponsorship of the U.S. Department of Transportation
in the interest of information exchange. The U.S. Government assumes no liability for the use of
the information contained in this document. This report does not constitute a standard,
specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or
manufacturers’ names appear in this report because they are considered essential to the objective
of the document.
Quality Assurance Statement
The Federal Highway Administration (FHWA) provides high-quality information to serve the
Government, industry, and the public in a manner that promotes public understanding. Standards
and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its
information. FHWA periodically reviews quality issues and adjusts its programs and processes to
ensure continuous quality improvement.
TECHNICAL REPORT DOCUMENTATION PAGE
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
1. Report No.
FHWA-HRT-11-021
2. Government Accession No.
3. Recipient’s Catalog No.
4. Title and Subtitle
Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice
5. Report Date
April 2011
6. Performing Organization Code
7. Author(s)
Audrey Copeland
8. Performing Organization Report No.
9. Performing Organization Name and Address
Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101
10. Work Unit No. (TRAIS)
11. Contract or Grant No.
12. Sponsoring Agency Name and Address
Turner-Fairbank Highway Research Center
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296
13. Type of Report and Period Covered
14. Sponsoring Agency Code
15. Supplementary Notes
The Contracting Officer’s Technical Representative (COTR) was Audrey Copeland, HRDI-10.
16. Abstract
With increased demand and limited aggregate and binder supply, hot mix asphalt (HMA) producers discovered that
reclaimed asphalt pavement (RAP) is a valuable component in HMA. As a result, there has been renewed interest in
increasing the amount of RAP used in HMA. While a number of factors drive the use of RAP in asphalt pavements,
the two primary factors are economic savings and environmental benefits. RAP is a useful alternative to virgin
materials because it reduces the use of virgin aggregate and the amount of virgin asphalt binder required in the
production of HMA. Using RAP greatly reduces the amount of construction debris going into landfills, and it
does not deplete nonrenewable natural resources such as virgin aggregate and asphalt binder. Ultimately,
recycling asphalt creates a cycle of reuse that optimizes the use of natural resources and sustains the asphalt
pavement industry.
More widespread use of higher amounts of RAP in asphalt mixtures requires support from State transportation
departments and the HMA industry. State transportation departments have expressed concern over the lack of
guidance on the use of high percentages of RAP (high RAP) mixtures, as well as the lack of information on their
performance. As a result, there is a need for national guidance on best practices when using RAP and documented
information about long-term performance of high RAP pavements.
The intent of this report is to provide state-of-the-practice information on including higher amounts of RAP in
asphalt mixtures. The state of the practice for RAP use across the United States, as well as common challenges for
increasing the use of RAP, are identified. Best practices applicable for the use of RAP are presented to identify
general parameters that must be considered when developing specifications and to provide information on available
resources and best practices for sourcing, processing, stockpiling, testing, designing, evaluating, producing, and
placing high RAP mixtures, as well as practices to attain the best performance for high RAP mixtures .
17. Key Words
Reclaimed asphalt pavement (RAP), Recycled asphalt, Hot mix asphalt
(HMA), Asphalt mixtures, Superpave®, Performance
18. Distribution Statement
No restrictions.
19. Security Classif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified
21. No. of Pages
55
22. Price
ii
SI* (MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
in inches 25.4 millimeters mm
ft feet 0.305 meters m
yd yards 0.914 meters m
mi miles 1.61 kilometers km
AREA
in2 square inches 645.2 square millimeters mm2
ft2 square feet 0.093 square meters m2
yd2 square yard 0.836 square meters m2
ac acres 0.405 hectares ha
mi2 square miles 2.59 square kilometers km2
VOLUME
fl oz fluid ounces 29.57 milliliters mL
gal gallons 3.785 liters L
ft3 cubic feet 0.028 cubic meters m3
yd3 cubic yards 0.765 cubic meters m3
NOTE: volumes greater than 1000 L shall be shown in m3
MASS
oz ounces 28.35 grams g
lb pounds 0.454 kilograms kg
T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")
TEMPERATURE (exact degrees)
oF Fahrenheit 5 (F-32)/9 Celsius oC
or (F-32)/1.8
ILLUMINATION
fc foot-candles 10.76 lux lx
fl foot-Lamberts 3.426 candela/m2 cd/m2
FORCE and PRESSURE or STRESS
lbf poundforce 4.45 newtons N
lbf/in2 poundforce per square inch 6.89 kilopascals kPa
APPROXIMATE CONV ERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
mm millimeters 0.039 inches in
m meters 3.28 feet ft
m meters 1.09 yards yd
km kilometers 0.621 miles mi
AREA
mm2 square millimeters 0.0016 square inches in2
m2 square meters 10.764 square feet ft2
m2 square meters 1.195 square yards yd2
ha hectares 2.47 acres ac
km2 square kilometers 0.386 square miles mi2
VOLUME
mL milliliters 0.034 fluid ounces fl oz
L liters 0.264 gallons gal
m3 cubic meters 35.314 cubic feet ft3
m3 cubic meters 1.307 cubic yards yd3
MASS
g grams 0.035 ounces oz
kg kilograms 2.202 pounds lb
Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T
TEMPERATURE (exact degrees)
oC Celsius 1.8C+32 Fahrenheit oF
ILLUMINATION
lx lux 0.0929 foot-candles fc
cd/m2 candela/m2 0.2919 foot-Lamberts fl
FORCE and PRESSURE or STRESS
N newtons 0.225 poundforce lbf
kPa kilopascals 0.145 poundforce per square inch lbf/in2
*SI is the symbol for th International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. e
(Revised March 2003)
iii
TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION ................................................................................................ 1
BACKGROUND ..................................................................................................................... 2
HISTORICAL PERSPECTIVE ............................................................................................ 3
PURPOSE AND METHODOLOGY .................................................................................... 4
CHAPTER 2. STATE OF THE PRACTICE FOR RAP USE.................................................. 7
SURVEY OF RAP SPECIFICATIONS AND USE IN THE UNITED STATES ............. 8
Updated Survey Results and Progress .............................................................................. 10
CHALLENGES FOR INCREASING THE USE OF RAP ............................................... 13
ADDITIONAL SURVEY RESULTS .................................................................................. 15
RAP Fractionation ............................................................................................................ 16
Determining AC of RAP ................................................................................................... 16
Mix Design Methods for RAP Mixes ............................................................................... 17
Plant Type Restrictions ..................................................................................................... 17
RAP and WMA ................................................................................................................. 18
Liquid Asphalt .................................................................................................................. 18
CHAPTER 3. BEST PRACTICES FOR INCREASING RAP USE ...................................... 19
SOURCES OF RAP .............................................................................................................. 19
RAP CATEGORIES ............................................................................................................. 20
RAP PROCESSING ............................................................................................................. 21
STOCKPILING RAP ........................................................................................................... 23
RAP PERCENTAGES AND BINDER GRADE SELECTION ....................................... 24
RAP Percentage Based on Binder..................................................................................... 26
RAP TESTING AND FREQUENCY.................................................................................. 26
Obtaining Representative Samples ................................................................................... 27
Testing and Test Frequency .............................................................................................. 27
Determining Bulk Specific Gravity of the RAP Aggregate .............................................. 28
MIX DESIGN CONSIDERATIONS .................................................................................. 29
High RAP Mix Design ...................................................................................................... 30
Performance Testing ......................................................................................................... 31
PLANT CONSIDERATIONS.............................................................................................. 32
PLACEMENT OF RAP MIXES ......................................................................................... 33
PERFORMANCE OF RAP ASPHALT MIXTURES ....................................................... 34
CHAPTER 4. CONCLUSIONS AND RECOMMENDATIONS ........................................... 39
RECOMMENDATIONS ...................................................................................................... 40
ACKNOWLEDGEMENTS ....................................................................................................... 43
REFERENCES ............................................................................................................................ 45
iv
LIST OF FIGURES
Figure 1. Photo. Milled RAP .......................................................................................................... 2
Figure 2. Graph. Estimated asphalt production cost categories ...................................................... 3
Figure 3. Graph. Approximate tons of RAP used in recycled asphalt in New Jersey per year ..... 8
Figure 4. Graph. Usage and potential of various RAP percentages in the intermediate layer ........ 9
Figure 5. Graph. Usage and potential of various RAP percentages in the surface layer ................ 9
Figure 6. Map. States with increased RAP use since 2007 ........................................................... 11
Figure 7. Map. States that permit more than 25 percent RAP in HMA layers ............................. 11
Figure 8. Map. States that use more than 20 percent RAP in HMA layers .................................. 12
Figure 9. Map. States that have experimented with or routinely use high RAP mixtures ............ 13
Figure 10. Map. Ownership of RAP by State highway agency .................................................... 13
Figure 11. Graph. Quantification of the use of different methods for determining the AC of
RAP mixtures ................................................................................................................................ 17
Figure 12. Photo. Stockpile of unprocessed RAP millings ........................................................... 20
Figure 13. Photo. Specialized fractionation equipment ................................................................ 22
Figure 14. Photo. Close-up view of specialized fractionation equipment .................................... 22
Figure 15. Photo. Fine fractionated RAP stockpile ...................................................................... 22
Figure 16. Photo. Coarse fractionated RAP stockpile .................................................................. 23
Figure 17. Photo. RAP stockpile being maintained ...................................................................... 24
Figure 18. Graph. Percent RAP content versus high temperature PG .......................................... 25
Figure 19. Photo. Sampling RAP from the stockpile.................................................................... 27
Figure 20. Photo. Scalping screen for RAP feed .......................................................................... 33
Figure 21. Photo. Smaller scalping screen for large RAP particles .............................................. 33
Figure 22. Photo. Placement of a high RAP mixture .................................................................... 34
Figure 23. Photo. Compaction of a high RAP mixture ................................................................. 34
Figure 24. Graph. Pavement age in years versus percent RAP for FDOT projects with greater
than 5,000 tons of asphalt mix ...................................................................................................... 37
LIST OF TABLES
Table 1. Surveys on RAP usage .................................................................................................... 15
Table 2. Binder selection guidelines for RAP mixtures according to AASHTO M 323 .............. 24
Table 3. Performance tests for asphalt mixtures ........................................................................... 32
Table 4. Summary of statistical analyses from NCAT LTPP study ............................................. 36
v
ABBREVIATIONS AND SYMBOLS LIST
Abbreviations
AASHTO American Association of State Highway and Transportation Officials
AC Asphalt content
AMPT Asphalt mixture performance tester
BSG Bulk specific gravity
Caltrans California Department of Transportation
CDOT Colorado Department of Transportation
DOT Department of Transportation
DSR Dynamic shear rheometer
ESAL Equivalent single axle load
ETG Expert task group
FHWA Federal Highway Administration
HMA Hot mix asphalt
IRI International roughness index
JMF Job mix formula
LTPP Long-Term Pavement Performance
MTO Ministry of Transportation of Ontario
NAPA National Asphalt Pavement Association
NCAT National Center for Asphalt Technology
NCDOT North Carolina Department of Transportation
NCHRP National Cooperative Highway Research Program
ODOT Ohio Department of Transportation
PG Performance grade
QC Quality control
RAP Reclaimed asphalt pavement
RTFO Rolling thin film oven
SCDOT South Carolina Department of Transportation
VMA Voids in the mineral aggregate
WMA Warm mix asphalt
vi
Symbols
A RAP percent binder content
B RAP percent in mixture
C Total percent binder content in mixture
|E*| Mix dynamic modulus
G* Shear modulus
Gb Asphalt specific gravity
RAP
sbG Bulk specific gravity of RAP aggregate
RAP
seG Effective specific gravity of RAP aggregate
RAP
mmG Maximum theoretical specific gravity of the RAP mixture
Pb Asphalt content of the RAP mixture
Pba Asphalt absorption
TBlend Critical temperature of blended asphalt binder
Tc(High) Critical high temperature
Tc(Int) Intermediate critical temperature
Tc(Low) Low critical temperature which is the higher of Tc(S) or Tc(m)
Tc(m) Critical low temperature based on m-value
Tc(S) Critical low temperature based on s-value
TRAP Critical temperature of recovered RAP binder
Tvirgin Critical temperature of virgin asphalt binder
1
CHAPTER 1. INTRODUCTION
Over 90 percent of U.S. highways and roads are constructed with hot mix asphalt (HMA).
As the U.S. infrastructure ages, these highways and roads must be maintained and rehabilitated.
According to the Federal Highway Administration’s (FHWA) recycled materials policy:
The same materials used to build the original highway system can be re-used
to repair, reconstruct, and maintain them. Where appropriate, recycling of
aggregates and other highway construction materials makes sound economic,
environmental, and engineering sense.(1)
With increased demand and limited aggregate and binder supply, HMA producers have began
using reclaimed asphalt pavement (RAP) as a valuable component in HMA. As a result, there
has been renewed interest in increasing the amount of RAP used in HMA.
While several factors influence the use of RAP in asphalt pavement, the two primary factors are
economic savings and environmental benefits. RAP is a useful alternative to virgin materials
because it reduces the use of virgin aggregate and the amount of virgin asphalt binder required in
the production of HMA. The use of RAP also conserves energy, lowers transportation costs
required to obtain quality virgin aggregate, and preserves resources. Additionally, using RAP
decreases the amount of construction debris placed into landfills and does not deplete
nonrenewable natural resources such as virgin aggregate and asphalt binder. Ultimately,
recycling asphalt creates a cycle that optimizes the use of natural resources and sustains the
asphalt pavement industry.
In order for it to be successful, recycled asphalt pavement must be cost-effective, perform well,
and be environmentally sound. To ensure that these requirements are met, FHWA promotes
the following:
• The use of recycled material in the construction of highways to the maximum economical
and practical extent possible with equal or improved performance.
• The use of RAP in HMA because RAP can have a large economical, environmental, and
engineering impact in pavement recycling.
The use of RAP may grow by increasing the number of highway construction and rehabilitation
projects that use RAP, as well as by increasing the amount of RAP used in specific projects. To
meet these goals, the following tasks were identified:
• Establish a public and industry working group.
• Create funded and coordinated research and demonstrations projects.
• Research deployment and technology transfer for information dissemination and
education.
2
Through the establishment of a public and industry working group known as the RAP Expert
Task Group (ETG), one of the top needs for increased RAP use was identified in updated
literature on the state of the practice and guidelines for mix design and construction of recycled
asphalt pavements.
BACKGROUND
Existing asphalt pavement materials are commonly removed during resurfacing, rehabilitation, or
reconstruction operations. Once removed and processed, the pavement material becomes RAP,
which contains valuable asphalt binder and aggregate (see figure 1). In the early 1990s, FHWA
and the U.S. Environmental Protection Agency estimated that more than 90 million tons of
asphalt pavement were reclaimed (i.e., converted into material suited for use) every year, and
over 80 percent of RAP was recycled, making asphalt the most frequently recycled material.(2)
RAP is most commonly used as an aggregate and virgin asphalt binder substitute in recycled
asphalt paving, but it is also used as a granular base or subbase, stabilized base aggregate, and
embankment or fill material. It can also be used in other construction applications. RAP is a
valuable, high-quality material that can replace more expensive virgin aggregates and binders.
Figure 1. Photo. Milled RAP.
There are four major asphalt production cost categories: (1) materials, (2) plant production,
(3) trucking, and (4) lay down (i.e., construction). Materials are the most expensive production
cost category, comprising about 70 percent of the cost to produce HMA (see figure 2). The most
expensive and economically variable material in an asphalt mixture is the asphalt binder. It is
most commonly used in the intermediate and surface layers of flexible pavement to provide
tensile strength to resist distortion, protect the asphalt pavement structure and subgrade from
moisture, and provide a smooth, skid-resistant riding surface that withstands wear from traffic.(3)
As a result, the most economical use of RAP is in the intermediate and surface layers of flexible
pavements where the less expensive binder from RAP can replace a portion of the more
expensive virgin binder.
3
Figure 2. Graph. Estimated asphalt production cost categories.
HISTORICAL PERSPECTIVE
Recycling asphalt pavements became popular in the 1970s due to the high cost of crude oil
during the Arab oil embargo. FHWA provided partial funding to State transportation
departments through Demonstration Project 39 to construct paving projects using recycled
asphalt and to document the effective use of resources in light of increased material costs.(4) As a
result, construction practices and technologies quickly evolved to handle RAP. The National
Cooperative Highway Research Program (NCHRP) published Recycling Materials for Highways
in 1978 and Guidelines for Recycling Pavement Materials in 1980.(5,6) In the 1990s, FHWA
issued further guidance and provided information on the state of the practice regarding pavement
recycling by publishing Pavement Recycling Executive Summary and Report and Pavement
Recycling Guidelines for State and Local Governments: Participant’s Reference Book.(7,8)
RAP was successfully used by State transportation departments for many years before the
implementation of the Superior Performing Asphalt Pavements (Superpave®) mixture design
method in the late 1990s. When Superpave® was implemented, the Strategic Highway Research
Program did not provide guidance for the use of RAP in HMA. Furthermore, the Superpave®
mix design system encouraged the use of coarse-graded mixtures, which, in some cases, limited
the amount of RAP that could be used in the mix. In particular, due to the high fines content
frequently found in many RAP stockpiles, some of the specified mix design criteria (i.e., voids in
the mineral aggregate (VMA), dust to effective binder content, etc.) reduced the use of RAP.
Many State transportation departments stopped allowing the use of high amounts of RAP in
favor of implementing the Superpave® system with virgin materials to reduce variability.
However, since then, there has been an increasing effort to modify the Superpave® design
method to more effectively evaluate HMA containing RAP. In the late 1990s, FHWA’s
Superpave® Mixtures ETG developed interim guidelines for the use of RAP in the Superpave®
0
10
20
30
40
50
60
70
80
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100
Material Plant Production Trucking Lay DownPercent (%) of Cost
4
mix design method. These guidelines were verified and further developed under NCHRP Project
9-12.(9) The suggested guidelines for specifying agencies are available in NCHRP Research
Results Digest 253: Guidelines for Incorporating RAP in the Superpave System.(10) Guidance on
testing and designing with RAP in the Superpave® method in the lab and field is available in
Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method:
Technician’s Manual.(11)
Traditionally, many State transportation departments have limited the maximum amount of RAP
used in surface layers, certain mixture types, and, in some instances, large or critical projects.
Although many HMA producers continued to use RAP, the amount was typically less than
15 percent because there were no binder grade changes or additional tests required for these
lower percentages. Additionally, there was no significant economic incentive for using larger
percentages of RAP. However, in 2006 and again in 2008, there were sharp increases in asphalt
binder costs as well as diminishing supplies of quality aggregate. As a result, utilizing greater
amounts of RAP became a priority in the HMA industry once again. With changes in
construction materials economics, stricter environmental regulations, and an emphasis on
“green” technologies (e.g., warm mix asphalt (WMA)) and sustainable pavements, the highway
community is reassessing the economic and environmental benefits of allowing higher
percentages of RAP in premium pavements and asphalt surfaces while also maintaining
high-quality pavement infrastructures.
More widespread use of higher amounts of RAP in asphalt mixtures requires support from State
transportation departments and the HMA industry. State transportation departments have
expressed concern over the lack of guidance on the use of high percentages of RAP (high RAP)
in mixtures as well as information on their performance. There is a need for national guidance on
best practices when using RAP and documented information about long-term performance of
high RAP pavements.
PURPOSE AND METHODOLOGY
In 2007, FHWA created an ETG, known as the RAP ETG, for the use of RAP in the construction
and rehabilitation of flexible pavements. It is comprised of RAP experts from FHWA, State
transportation departments, the American Association of State Highway and Transportation
Officials (AASHTO), the National Asphalt Pavement Association (NAPA), the National Center
for Asphalt Technology (NCAT), and people from the industry and academia. The purpose
of the ETG is to advance the use of RAP in asphalt paving applications by providing State
transportation departments and the industry with information emphasizing the production of
high-quality high RAP mixtures, the performance of asphalt mixtures containing RAP, technical
guidance on high RAP projects, and RAP research activities.
This report is the result of RAP ETG activity to provide state-of-the-practice information for
including higher percentages of RAP in asphalt mixtures. For the purpose of this report, high
RAP is defined as using 25 percent or more RAP in an asphalt mixture by weight of the total
mix. The state of the practice for RAP use throughout the United States was determined through
a survey conducted by the RAP ETG and sponsored by the AASHTO Subcommittee on
Materials (see chapter 2). Several surveys regarding the specification and use of RAP have also
been conducted, and the results are also summarized in chapter 2. Common challenges for
5
increasing the use of RAP were identified through these surveys and were used to develop
guidance on the best practices.
The best practices discussion presents measures applicable for the use of RAP in asphalt
mixtures (see chapter 3). It identifies general parameters to consider when developing
specifications. Chapter 3 also provides information on available resources and best practices for
sourcing, processing, stockpiling, testing, designing, evaluating, producing, and placing high
RAP mixtures, as well as practices to attain the best performance for high RAP mixtures. This
information was compiled from current industry reports, State specifications, field projects and
demonstrations, and expert knowledge from RAP ETG representatives.
7
CHAPTER 2. STATE OF THE PRACTICE FOR RAP USE
According to NAPA, the current annual U.S. production of new asphalt pavement material is
approximately 500 million tons per year, which includes about 60 million tons of reclaimed
material that is reused or recycled directly into pavements.(12) As of 2007, about 40 million tons
of RAP is reused or recycled into other pavement-related applications every year for a total use
of over 100 million tons of RAP each year. This is an increase from 72 million tons of RAP used
each year in the early 1990s. Since most reclaimed asphalt is reused or recycled, asphalt
pavement has the highest recycling rate by percentage among recycled materials.
A survey was sent to FHWA division offices to seek information regarding RAP usage by each
State transportation department. In total, 18 out of 52 division offices responded, and 17 of the
18 respondents indicated that the use of RAP is optional and depends on the contractor to
propose its use based on economic considerations and material availability.
Survey responses confirmed that the use of RAP is primarily driven by the costs of materials and
transportation. As stated previously, the most economical use of RAP is in asphalt mixtures
where the full benefit of the RAP binder and aggregate is utilized. Most States do not track the
amount of RAP used or the cost savings. Only 3 of the 18 respondents indicated that they track
the amount of RAP used. A primary challenge in tracking the amount of RAP used is that HMA
is not bid based on its components or whether or not it contains RAP; rather, it is bid as a
material itself. The New Jersey Department of Transportation tracked the approximate quantities
of RAP used. It found a significant increase in the amount of RAP used from 2003–2005, as
compared to 2002 (see figure 3). Similarly, other respondents noted increases in the use of RAP
(8 out of 18, or about 45 percent), and some noted that contractors requested approval of
mixtures with higher percentages of RAP (i.e., more than 25 percent RAP).
8
Figure 3. Graph. Approximate tons of RAP used in recycled asphalt in New Jersey
per year.
SURVEY OF RAP SPECIFICATIONS AND USE IN THE UNITED STATES
In 2007, a survey was conducted by the North Carolina Department of Transportation (NCDOT)
on behalf of RAP ETG and sponsored by the AASHTO Subcommittee on Materials. The survey
asked the following questions regarding RAP use:
• How much RAP is permitted in mixtures?
• How much RAP is actually used?
• What are the main roadblocks to greater usage of RAP?
Survey responses were collected from all 50 States as well as Ontario, Canada. The
survey showed that the majority of State transportation department specifications allowed the
use of RAP in HMA mixtures. The 2007 average national usage rate was estimated to be
12 percent. RAP was typically permitted in subsurface, base, and shoulder mixtures but may
have been restricted in surface/wearing courses. Very few States allowed little or no RAP due to
concerns regarding performance.
The survey data also indicated the potential for increasing the amount of RAP used across the
United States. Figure 4 and figure 5 show the number of State transportation departments that
used and permitted a given amount of RAP in the intermediate and surface layers in 2007. There
was the potential for more State transportation departments to use up to the amount of RAP that
their specifications permitted. For example, in figure 4, only 10 State transportation departments
135000140000
105000
6500060000
89000
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60000
80000
100000
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2000 2001 2002 2003 2004 2005
YearTons of RAP
9
used up to 29 percent RAP in the intermediate layer. However, according to their specifications,
there was the potential for over 35 State transportation departments to use up to 29 percent RAP.
Similarly, less than 5 State transportation departments used up to 29 percent RAP in the
surface layer, while there was the potential for 20 State transportation departments to do so
(see figure 5). The data indicated that the maximum amount of RAP that was permitted was not
being used on a nationwide basis.
Figure 4. Graph. Usage and potential of various RAP percentages in the intermediate layer.
Figure 5. Graph. Usage and potential of various RAP percentages in the surface layer.
0
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Up to 10%Up to 19%Up to 29%30% & higherNumber of State AgenciesPotential
Usage
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Up to 10%Up to 19%Up to 29%30% & higherNumber of State AgenciesPotential
Usage
10
A survey of U.S. States conducted by the Materials Engineering and Research Office of the
Ministry of Transportation of Ontario, Canada, (MTO) further confirmed the 2007 NCDOT
survey results. MTO found that for base and binder courses, 20–50 percent RAP was typically
permitted. Permitted levels of RAP were higher in base courses and for light traffic roadways, as
compared to medium or heavy traffic roadways. Some States commented that although high
amounts of RAP were permitted, contractors typically did not submit mix designs for amounts
greater than 25 percent.
Generally, State transportation departments allow between 10 and 20 percent RAP for medium
and heavy traffic levels for surface courses. Medium traffic level roads are designed for
3–30 million equivalent single axle loads (ESALs) for a 20-year design. Heavy traffic roads have
greater than 30 million ESALs for a 20-year design. For light traffic roads, slightly more RAP is
typically allowed in surface courses, and light traffic levels have fewer than 3 million design
ESALs for a 20-year design. About 20 percent of the State transportation departments do not
allow RAP in surface courses with heavy traffic. Additionally, according to the MTO survey,
two State transportation departments did not permit RAP in surface courses and indicated several
reasons, such as poor past experiences, lack of expertise/confidence in using RAP in the surface
course, and the use of surface mixes with specific aggregate requirements (i.e., frictional
characteristics), that may preclude the use of RAP.
Updated Survey Results and Progress
In 2009, another similar survey was conducted by NCDOT on behalf of AASHTO and
RAP ETG. The survey asked the following questions:
1. What is the maximum percentage of RAP in HMA allowed by the State?
2. What is the average percentage actually used by contractors?
3. Does the State have special requirements or limitations when higher percentages are used?
4. Has the State experimented with or does it routinely use high RAP mixes?
5. Does the contractor retain ownership of RAP after it is milled?
6. Is the State utilizing WMA technologies in conjunction with increased RAP content?
Figure 6 shows that about half of all States reported increased RAP usage from 2007–2009.
Approximately half (23) of the State transportation departments reported experimenting with or
routinely using high RAP. While many State transportation departments increased the amount of
RAP used in HMA, the use of high RAP mixtures is still not common. As shown in figure 7,
many State transportation departments permit more than 25 percent RAP in HMA layers;
however, fewer than half of the States actually use more than 20 percent RAP in HMA layers
(see figure 8).
11
Figure 6. Map. States with increased RAP use since 2007.
Figure 7. Map. States that permit more than 25 percent RAP in HMA layers.
12
Figure 8. Map. States that use more than 20 percent RAP in HMA layers.
The majority of State transportation departments requires mixtures that incorporate RAP to meet
all conventional mix design requirements. However, most State transportation departments place
restrictions on the amount of RAP used overall as well as in certain mix types and pavement
layers. Conditions may be placed on the asphalt binder grade, aggregate type, and nominal
maximum aggregate size for use with RAP. The majority of respondents to a survey conducted
by the Ohio Department of Transportation (ODOT) indicated there are no special requirements
for high RAP mixtures beyond normal mix design procedures. About half of the States have
experimented with high RAP or routinely use high RAP mixes (see figure 9).
Louisiana did not respond.
*
*
13
Figure 9. Map. States that have experimented with or routinely use high RAP mixtures.
Many States specify RAP ownership with the contractor retaining RAP the majority of the time
(see figure 10). In 20 States, both the State transportation department and the contractor retain
ownership of RAP. Only three State transportation departments retain complete ownership of
RAP for other applications. RAP ownership depends on the State transportation department’s
specifications, the individual contract requirements, and utilization by the State transportation
department’s maintenance departments.
Figure 10. Map. Ownership of RAP by State highway agency.
CHALLENGES FOR INCREASING THE USE OF RAP
Average RAP use is estimated at 12 percent in HMA in the United States. Less than half of
State transportation departments use more than 20 percent RAP; however, based on State
transportation department specifications, it is possible for States to use up to 30 percent RAP in
CA
AZ
CO
NM
TX
OK AR
LA
MO KY
AL GA
FL
VA
OH
MI
VTAK
MT
NV
ME
WA
OR
UT
KS
ID WY
ND
SD
MN
NE
WI
IA
IL IN
MS
TN
SC
NC
WV
PA
NY
CT
NJ
DE
MD
DC
MA
NH
PR
HI
RI
Experimented with or routinely use high RAP
Do not use high RAP
14
the intermediate and surface layers of pavements. Currently, it is unknown why over half of the
country uses less than 20 percent RAP in HMA.
Despite similarities between producing virgin asphalt mixtures and RAP asphalt mixtures, there
are still challenges for maximizing RAP use and routinely using high RAP. According to
AASHTO M 323, the current binder selection guidelines for RAP mixtures were formulated
based on the assumption that complete blending occurs between the virgin and RAP binders.(13)
It is understood that the amount of blending that occurs between the virgin and RAP binder is
somewhere between complete blending and no blending at all; however, there is no direct
method available to accurately determine the amount of blending that occurs. Currently,
researchers are performing ongoing studies to develop methods to determine if proper blending
has occurred by using mixture properties such as dynamic modulus to estimate blended binder
properties and to compare estimate blended binder properties to measured binder properties.(14,15)
For high RAP mixtures, blending charts can be used to properly determine the virgin binder
grade. They can also be used to optimize the amount of RAP used if the virgin binder grade is
known. However, blending charts require expensive, time-consuming binder extraction and
recovery procedures that use hazardous solvents, which is followed by testing of the recovered
binder. Consequently, many State transportation departments are reluctant to permit RAP content
that require this testing. Additionally, many contractors are not equipped to perform binder
extractions and recoveries or the subsequent binder tests. In general, State transportation
departments are concerned with the consistency of RAP materials and whether mixtures with
high RAP are inferior and fail earlier than virgin mixtures. In some instances, State
transportation departments place limitations on the amount of RAP that can be used based on
previous bad experiences with RAP. According to the 2007 NCDOT survey, the four most
common factors preventing the use of additional RAP are as follows:
• Specification limitations.
• Lack of processing (i.e., variability of RAP).
• Lack of RAP availability.
• Past experiences.
In the 2009 NCDOT survey, participants were asked to identify major concerns and obstacles
that limit or preclude the use of RAP in HMA. The two concerns cited most often regarded the
quality of the blended virgin and RAP binder qualities, especially for high RAP mixes and
polymer modified binders, and stiffening of the mix from high RAP quantities and resulting
cracking performance. Several States were concerned that the use of RAP with polymer-
modified binders may reduce the quality of the polymer-modified virgin binder. Furthermore,
high RAP may affect binder properties resulting in an “overly stiff” mix that may experience
low-temperature cracking. There was also concern that an overly stiff mix may not be as resilient
and may crack prematurely for pavements experiencing high deflections.
15
The most common barriers among State transportation departments are as follows:
• Quality concerns.
• Consistency of RAP.
• Binder grade and blending.
• Mix design procedures.
• Volumetric requirements.
• Durability and cracking performance.
• Use with polymers.
The most common barriers among contractors are as follows:
• State transportation department specifications.
• Control of RAP.
• Dust and moisture content.
• Increased quality control (QC).
ADDITIONAL SURVEY RESULTS
In the past 2 years, several surveys regarding the use of RAP in asphalt mixtures have been
compiled. Table 1 presents the survey description, organization, date, and number of responses
for each survey summarized in this report.
Table 1. Surveys on RAP usage.
Survey Description Organization Date Number of Responses
FHWA Division Office
Pavement Engineers FHWA 2007 18
FHWA/AASHTO RAP
ETG survey NCDOT
July 2007 and
August 2009
51
(including Ontario)
Summary of States
extending RAP usage ODOT September 2008 29
RAP usage survey
Materials Engineering and
Research Office MTO November 2008
33
(including Ontario)
Nuclear asphalt content
(AC) gauge use on HMA
mixtures containing RAP
Colorado Department of
Transportation (CDOT) January 2008
29
(including Ontario)
RAP survey
South Carolina Department
of Transportation (SCDOT) April 2009
25
(including Ontario)
16
RAP Fractionation
Fractionation is the act of processing and separating RAP into at least two sizes, typically a
coarse fraction (+1/2 or +3/8 inches (+12.5 or +9.5 mm)) and a fine fraction (-1/2 or -3/8 inches
(-12.5 or -9.5 mm)). According to a survey conducted by ODOT in September 2008 that
compiled responses from 29 States, 3 States (South Carolina, Texas, and Alabama) have
specifications for fractionating RAP, and 3 States (Ohio, Wisconsin, and Illinois) are currently
drafting specifications for fractionating RAP. These six States allow higher amounts of RAP if it
has been fractionated. For example, in the Texas specification, unfractionated RAP is limited to
10, 20, and 30 percent by surface, intermediate, and base layers, respectively. However, by
special provision, fractionated RAP is allowed at up to 20, 30, and 40 percent in those same
layers. In the 2009 survey conducted by NCDOT, 10 State transportation departments reported
requiring fractionation. These 10 states are Arizona, Georgia, Illinois, Kansas, North Carolina,
Ohio, Texas, Utah, Wisconsin, and Washington, DC. Wisconsin allows an increase of 5 percent
binder replacement for surface mixes if fractionation is used. Some States consider crushing and
screening RAP over a single screen as fractionation, which is incorrect.
One of the reasons fractionation is required is that it is believed to improve the consistency of
RAP. However, data gathered by NCAT in 2008 and 2009 from contractors across the United
States showed that fractionated RAP stockpiles were no more consistent than processed
unfractionated RAP stockpiles.(16) Therefore, State transportation departments are not advised to
invoke a method specification for RAP management. Instead, they should develop an end-result
specification for RAP stockpiles that requires routine QC testing of RAP and establishes limits
for variability.
Determining AC of RAP
The most common method for determining the AC in a sample of RAP is to use the ignition oven
method specified in AASHTO T 308.(17) A CDOT survey compiled in January 2008 includes
responses from 29 State transportation departments and shows that almost half of them used
the ignition oven to determine the AC of the RAP fraction for mix design purposes. About
30 percent of the respondents used solvent or chemical extraction, while 3 out of the 29 States
used both solvent extraction and the ignition oven. The results are provided in figure 11.
17
Figure 11. Graph. Quantification of the use of different methods for determining the AC of
RAP mixtures.
Mix Design Methods for RAP Mixes
The Superpave® performance grade (PG) binder and volumetric mix design system has become
the most widely accepted design system for asphalt mixtures in the United States. According to a
survey conducted in 2008 by the Materials Engineering and Research Office MTO, Superpave®
is the most common method of mixture design used in the United States for RAP mixes,
including those that contain over 20 percent RAP. In total, 25 out of 33 State transportation
department respondents use the Superpave® method exclusively or some variation of the
Superpave® mix design procedure (i.e., agency-modified Superpave® mix design). Six of the
twenty-five also utilize the Marshall or Hveem mix design procedure for certain mix types.
According to the MTO survey, four State transportation departments do not use the Superpave®
mix design procedure—California and Nevada use the Hveem method for mix design, and
Rhode Island and Tennessee use the Marshall method exclusively.
The current Superpave® specification for selecting the virgin asphalt binder grade based on a
given RAP percentage is provided in table 2 of AASHTO M 323.(13) Most State transportation
departments use this specification. However, 12 out of 33 respondents have raised the lower
percent RAP limit for selecting a softer virgin binder grade from 15 to 20 percent or to
25 percent in a few cases. States that have raised the lower limit from 15 percent are Alaska,
Colorado, Florida, Illinois, Indiana, Kentucky, Maryland, Michigan, Minnesota, North Carolina,
Nebraska, New Jersey, South Dakota, and Washington.
Plant Type Restrictions
The majority of State transportation departments do not place restrictions on the use of RAP in
certain plant types. However, in some cases, there are more restrictions when RAP is used in
batch plants. According to the ODOT survey of 29 States, 5 State transportation departments
place restrictions on the amount of RAP used by plant type. For example, South Carolina does
not allow more than 15 percent RAP to be used in a batch plant with a hot elevator. Georgia and
New Hampshire limit batch plants to 25 percent RAP but allow up to 30 and 40 percent RAP in
drum plants. Massachusetts allows up to 40 percent RAP in a drum plant but limits the amount of
RAP used in a batch plant to 20 percent.
0
5
10
15
20
25
30
Ignition Oven Solvent/Chemical
Extraction
Both Ignition and/or
Extraction
NoneNo. of State Highway Agencies
18
RAP and WMA
The majority of State transportation departments responding to a survey conducted by SCDOT
and compiled in April 2009 reported no use of WMA; however, as of 2009, WMA projects
(i.e., State, private, or local projects) have been constructed in over 40 States. In total, 8 out of
24 State transportation departments are not currently specifying WMA. Additionally, CDOT and
the Virginia Department of Transportation do not allow RAP in WMA mixes. According to the
NCDOT survey compiled in August 2009, 12 State transportation departments utilized WMA
technologies in conjunction with increased RAP contents. These 12 State transportation
departments are Alabama, Delaware, Florida, Illinois, Indiana, Mississippi, Nebraska,
New Jersey, Ohio, South Carolina, Tennessee, and Texas. As of 2009, at least 14 State
transportation departments have adopted specifications to accommodate WMA. Five States
(Alabama, Florida, Illinois, Kentucky, and Texas) do not have any differences in allowances for
using RAP in WMA mixes compared to using RAP in HMA mixes. Two States (Ohio and South
Carolina) have modified their specifications to allow more RAP in WMA. For example, Ohio’s
recently modified specification allows the use of more RAP before a softer grade of binder is
required when using the water injection WMA process. South Carolina allows producers to use
up to 10 percent more fractionated RAP in WMA before changing the binder grade. A WMA
best practices guide and Web site is available from NAPA, which includes information on using
WMA and RAP.(18,19)
Liquid Asphalt
According to the 2009 SCDOT survey, the majority of State transportation departments that
responded (18 out of 23) do not pay for asphalt binder separately from the asphalt mixture.
Arkansas pays for liquid binder as a separate pay item; however, residual binder in RAP is paid
for at the same price as the contract unit bid price for virgin binder. In Colorado, two out of six
regions pay for binder separate. However, these regions are rural where RAP capabilities are
limited. In Georgia, an index for asphalt binder is paid based on the job mix formula (JMF), and
the asphalt binder in the RAP is accounted for in the mix design process. In North Carolina, the
asphalt cement is indexed based on the total percent asphalt cement in JMF. The binder from
RAP is included in the total binder index; however, in May 2009, North Carolina planned to start
indexing based on virgin asphalt cement only. In Utah, there is a separate pay item for liquid
binder for open-graded surface courses only. All other HMA products are paid by the mix ton,
and RAP is accounted for in the bidding process.
19
CHAPTER 3. BEST PRACTICES FOR INCREASING RAP USE
This chapter presents some of the current best practices for increasing the amount and frequency
of RAP use regarding the management, mix design, production, and placement of RAP asphalt
mixtures. The best practices were compiled from existing literature, experience from high RAP
projects and trial sections, State specifications, and the advice of experts in the industry. The best
practices address some of the specific concerns related to the production of high RAP mixtures.
They can be utilized by State transportation departments in preparing specifications and by
contractors who will be designing and producing high RAP mixtures. Several different options
are available to address potential concerns, and the most appropriate option will depend on
various factors such as material properties, plant type, and production rate.
In general, there is little difference in designing asphalt mixtures with RAP compared to virgin
asphalt mixtures until high RAP is used. However, the following issues should be considered
when increasing RAP use:
• Additional processing and QC.
• Characterizing RAP.
• Changing the virgin binder grade.
• Preparing materials for mix design.
• Blending/comingling the virgin and RAP binders.
• Performance.
Performing QCs throughout the entire processing and production process is critical. Processing
and stockpiling best practices are crucial to maintaining the quality and consistency of the RAP
stockpile. The RAP material must be properly characterized for mix design purposes. Best
practices used in the production of HMA will also address concerns when using high RAP. In
fact, it may not be possible to achieve high-quality high RAP mixes without the use of
processing and production best practices.
In most cases, it is the contractor’s responsibility to select the amount of RAP included in the
mixture, the type of RAP used in the mixture, and the level processing necessary to meet the
specifications. State transportation departments may specify the virgin binder grade based on the
amount and type of RAP being used. The RAP QC testing requirements and frequency should
also be specified or agreed upon by both parties prior to production.
SOURCES OF RAP
RAP will be collected from several sources over time. RAP is usually generated from milling,
full-depth pavement removal, and waste HMA materials generated at the plant. An important
consideration in RAP management is when to keep RAP from a new source separate and when
to combine RAP from different sources.
20
Milling is an important part of pavement rehabilitation used to remove any distressed upper
layer(s) of existing pavement to a given depth. The process involves machines that grind, pick
up, and load RAP into a truck for transportation. The mill speed at the job site should be
controlled and kept uniform to promote consistency in the resulting RAP. There is an advantage
to keeping millings from large jobs in separate stockpiles. Generally, these millings are very
consistent and can be used in new mixes without further screening or crushing, saving processing
costs. Figure 12 shows a stockpile of unprocessed millings.
Figure 12. Photo. Stockpile of unprocessed RAP millings.
In some cases, it may be beneficial to mill the surface layer or the surface and intermediate layers
separately from the asphalt base layer, as the upper layers often contain aggregates with special
characteristics such as polishing resistance and/or freeze/thaw durability. The nominal aggregate
size in upper pavement layers is also smaller and more suitable for direct use in new surface
mixtures without crushing.
Full-depth pavement removal involves the use of heavy equipment to break the pavement
structure into slabs. The slabs are then transported to a processing location where they are
crushed and processed to a manageable size for recycling. Asphalt mix material that is produced
and not used (i.e., “plant waste”) is typically added to the unprocessed RAP stockpile or is kept
in a separate stockpile for future processing.
It is critical that materials collected from any source be kept free from contamination. Incoming
materials should be visually inspected to avoid dumping of soil, construction debris, or any
deleterious material in the stockpile.
RAP CATEGORIES
Some State transportation departments only allow RAP obtained from specific projects or
pavement types to be used in their mixes. Such RAP is referred to as classified or traceable
source RAP. The restriction to allow only traceable source RAP in new State transportation
department asphalt mixes hinders the use of RAP to its full advantage; therefore, State
21
transportation departments should have an engineering basis for this requirement. Rather than
prohibiting RAP from non-State transportation department sources, the quality of materials in
RAP can and should be verified with routine testing as part of the RAP QC and mix design.
Most State transportation departments allow RAP from multiple sources to be used in recycled
asphalt mixes, provided that it is processed into a uniform material, and the aggregates contained
in the RAP meet typical source properties. Recommended tests and test frequency information
are provided in the RAP Testing and Frequency section below. This type of RAP is referred to as
unclassified RAP or multiple sources RAP.
RAP PROCESSING
RAP processing involves one or more steps to create consistent materials that can be used in high
percentages and meet standards for high-quality asphalt mixtures. Screening is used to separate
sizes. As noted previously, milled material from traceable sources can have very consistent
properties and may not require further processing. In some cases, it may be desirable to screen or
fractionate traceable source RAP to remove oversize particles or to separate RAP into coarse and
fine stockpiles to maximize the amount of RAP that can be used in particular mixes. RAP
separation based on size increases control and reduces variability. It also allows for adjustments
for variability to be made within the RAP blend rather than just the virgin aggregate blend. An
example of specialized RAP fractionation equipment is shown in figure 13 and figure 14.
Typically, RAP is sized into two (coarse or fine) or three (oversize, coarse, or fine) piles, as
shown in figure 15 and figure 16. With specialized fractionation equipment, it is possible to
screen to the -No. 4 sieve size (-0.25 inches (-4.75 mm)) or even to the -No. 8 sieve size
(-0.125 inches (-2.36 mm)). In this scenario, it is possible to have three sizes that are all
-1 inch (-25 mm).
For stockpiles of RAP from multiple sources, particularly stockpiles containing large chunks of
RAP or pavement slabs, it may be necessary to crush the material to produce RAP with a suitable
top size for use in new asphalt mixes. Crushing can also improve the consistency of the resulting
RAP if the multiple sources RAP is fed into the crushing unit from different locations of the
unprocessed stockpile. There are several types of crusher systems available, such as horizontal
impact crushers, hammer mill impact crushers, and jaw/roll combination crushers. More
information on crushing options is provided in Recycling Hot Mix Asphalt Pavements.(20)
Choosing the top size (i.e., maximum RAP particle size) for the crushing operation is an
important decision. Many contractors select the top size so that the crushed RAP can be used
in any type of mix. However, crushing to smaller top sizes will increase the dust content
(percentage passing the No. 200 (0.0029-inch (0.075-mm)) sieve) in RAP, which can limit how
much RAP can be used in new mix designs while meeting criteria such as VMA and dust-to-
binder ratio.
22
Figure 13. Photo. Specialized fractionation equipment.
Figure 14. Photo. Close-up view of specialized fractionation equipment.
Figure 15. Photo. Fine fractionated RAP stockpile.
23
Figure 16. Photo. Coarse fractionated RAP stockpile.
Processing RAP may include both crushing and screening to produce a uniform gradation, binder
content, and other properties. Agencies should not require specific types of processing operations
for RAP. Rather, they should limit the maximum amount of variability in the RAP material that
is fed into the plant. This will allow the contractor to utilize the most efficient and cost-effective
process for producing a consistent material. The end result type of specification is easier to
enforce because it avoids subjective interpretations of the suitability of the various options for
RAP processing.
It is recommended that RAP processing occurs prior to feeding to the plant. Earlier RAP systems
that included crushing and screening large pieces (2–4 inches (50–100 mm)) of RAP as part of
the cold feed system are not recommended. RAP uniformity as well as the ability to characterize
RAP during the mix design phase may be inadequate with in-line crushing systems.
STOCKPILING RAP
Normal practice should be used to prevent or limit segregation. Arc-shaped, uniformly layered
stockpiles are preferred for storing milled or unprocessed RAP material (i.e., material of various
sizes). As with virgin aggregate, conical stockpiles or small, low-sloped piles are preferred for
storing processed RAP material. RAP stockpiles should be placed on a base with adequate
drainage and constructed in layers to minimize segregation and ensure a workable face. To
maximize the percentage of RAP in a mix, consideration may be given to constructing separate
stockpiles for each source of RAP based on the category of RAP, the size of processed material,
the quality of the aggregate, and the type and quantity of asphalt binder. However, space
limitations must be considered.
All RAP stockpiles should be kept clean and free of foreign materials. RAP holds water and does
not drain as well as an aggregate stockpile, so efforts should be made to handle and store RAP in
such a way as to minimize moisture content. The crust formed on the surface of the stockpile
helps to shed water, but other measures can be taken, such as storing RAP on paved sloped
surfaces and covering RAP stockpiles with a roof from an open-sided building. In particular,
fine RAP holds high moisture content, and it may be desirable to use a building to cover the
stockpile. High moisture content in the stockpile may not be detrimental to HMA quality, but it
24
is an issue for the contractor since the moisture must be removed during production and could
cause increased fuel usage and reduced production rate.
RAP does not tend to recompact in large piles, but it can form an 8–10-inch (203–254-mm)-thick
crust over the surface that is easily broken by a front-end loader. If possible, heavy machinery
should not be driven on the RAP stockpile to avoid compaction. The RAP stockpiles should be
routinely skimmed to break lumps. An example of a properly maintained RAP stockpile is
shown in figure 17.
Figure 17. Photo. RAP stockpile being maintained.
RAP PERCENTAGES AND BINDER GRADE SELECTION
Typically, contractors determine the percentage of RAP to be used and select the binder grade
to meet the appropriate specifications. The percentage of RAP used in the mix may be selected
by determining the contribution of RAP in the total mix by weight or by determining the
contribution of the RAP binder in the total binder in the mix by weight while maintaining
volumetric properties requirements. Due to the stiffening effect of the aged binder in RAP, the
specified binder grade may need to be adjusted. The current national guideline for determining
the binder grade adjustment in HMA mixes incorporating RAP has three tiers.(13) Each tier has a
range of percentages that represents the contribution of RAP toward the total mix by weight
(see table 2). Some State transportation departments have modified the range of percentages
(e.g., increased the RAP percentage that can be used before a softer binder grade must be
chosen) based on conditions in that area and/or additional testing.
Table 2. Binder selection guidelines for RAP mixtures according to AASHTO M 323.(13)
Recommended Virgin Asphalt Binder Grade RAP Percent
No change in binder selection < 15
Select virgin binder one grade softer than normal (e.g.,
select PG 58-28 if PG 64-22 would normally be used) 15–25
Follow recommendations from blending charts > 25
25
For percentages of RAP greater than 25 percent, procedures for developing a blending chart are
provided in the appendix of AASHTO M 323.(13) Based on the desired final blended binder
grade, the desired percentage of RAP, and the recovered RAP binder properties, the required
properties of the appropriate virgin binder grade can be determined according to blending chart
procedures. If a specific virgin asphalt binder grade must be used and the desired blended binder
grade and recovered RAP properties are known, the allowable percentage of RAP is determined
according to blending chart procedures.
The blending chart process is time-consuming, involves hazardous solvents, and creates disposal
issues. It assumes complete blending between the virgin and RAP aggregate. More practical
alternate procedures have been suggested for determining the virgin binder PG and ensuring
proper blending. Most aged asphalts in a certain region have reached a level of maximum
stiffness. With this information, an asphalt grade of RAP can be assumed for 100 percent RAP.
For example, in the Southeast and Mid-Atlantic regions, researchers have determined that asphalt
in RAP usually has a high temperature grade between 190.4 and 201.2 °F (88 and 94 °C).
Thus, using 100 percent RAP, it is assumed that the high temperature grade is 197.6 °F (92 °C).
Using the high temperature grade of the virgin asphalt binder as the high temperature grade at
zero percent RAP, the RAP content versus high temperature binder grade can be plotted to
estimate the effect of RAP on stiffness, specifically the high temperature binder grade (see
figure 18). In cold regions, the low temperature grade should also be checked to avoid low
temperature cracking.(21)
Figure 18. Graph. Percent RAP content versus high temperature PG.
Through years of experience balancing the material quality requirements for the specific
application with the market availability and cost, many State transportation departments have
standardized the PG binder grade for HMA on a regional, project type, and/or program basis in
lieu of determining the project binder grade quality for the specific project location and
y = 3.57x -228.48
0
10
20
30
40
50
60
70
80
90
100
58 64 70 76 82 88 94 100Percent (%) RAP Content by weight of mixHigh Temperature Performance Grade
26
application. It is recommended that State transportation departments reassess the binder
quality requirement for the specific application utilizing the long-term pavement performance
(LTPP)Bind protocols to assess specific property requirements based on local environmental
conditions and design reliability of the application to gain more insight into the required
binder quality.(22)
Bonaquist developed a methodology to evaluate blending in RAP mixtures. The methodology
involves measuring the mix dynamic modulus, |E*|, with the asphalt mixture performance tester
(AMPT) which is referred to as measured |E*|.(14,23) The binder is extracted and recovered from
the mix, during which, the virgin and RAP binders become totally blended. Shear modulus (G*)
of the recovered binder is measured using the dynamic shear rheometer (DSR). The recovered
binder’s G* value is used as input into the Hirsch model to estimate the mix |E*|, which is
referred to as estimated |E*|.(24) The estimated |E*| is compared to the measured |E*|, and if the
data match, it is assumed there is good blending of the virgin and RAP binders. In addition to
using the Hirsch model to estimate mix |E*|, the Witczak model could also be used to estimate
mix |E*|.(25,15)
The procedure that uses |E*| of the mix to estimate blending or the procedure for determining the
RAP PG binder grade is not necessarily recommended for individual mix designs. Instead, these
approaches are an option for studies on which State transportation department requirements for
selection of virgin binder grade may be established.
RAP Percentage Based on Binder
Historically, State transportation department specifications limiting RAP in HMA have been
based on RAP percentage by weight of aggregate or by weight of the total mix. However, the
primary issue with higher RAP content in asphalt mixes is the amount of binder replacement
available since the use of RAP can reduce the need for virgin binder and impact the binder
properties. Thus, RAP may also be specified according to percentage binder replacement. The
percentage of RAP used in the mix can be selected by determining the contribution of the RAP
binder toward the total binder in the mix by weight (i.e., a specified maximum percentage of the
binder may come from RAP). In fact, several State transportation departments have specified a
minimum percentage of virgin binder content (e.g., 70 percent of the binder content must be
virgin binder). The amount of total binder replaced by binder in RAP is computed as follows:
(1)
Where:
A = RAP percent binder content.
B = RAP percent in mixture.
C = Total percent binder content in mixture.
RAP TESTING AND FREQUENCY
Good practice for sampling aggregate applies to the sampling of RAP. Samples may be obtained
during production or from a stockpile. Contractors should prepare a plan for sampling and testing
Binder Replacement, %=%100)(××
C
BA
27
RAP. The sampling plan should meet the minimum testing frequency requirements specified by
the owner (i.e., State transportation department, highway agency, etc.) and should detail the
procedure used to obtain representative samples throughout the stockpile for testing.
Obtaining Representative Samples
Sampling involves taking a number of random samples from the RAP stockpile, testing a portion
of each individual sample, and then combining the remainder of random samples into one
representative sample for developing the mix design (see figure 19). A minimum of 5, but
preferably 10 or more, individual samples should be used to determine the consistency of a RAP
stockpile. Proper sampling procedures normally used for virgin aggregates may also be used to
sample RAP aggregate and are provided in AASHTO T 2.(26)
Testing individual samples is required to determine the variability of the AC and aggregate
gradation. The size of the sample should be such that the amount of aggregate material recovered
will meet the size requirements of the gradation procedure.(27) After testing individual samples
is complete, combining the remainder of the individual random samples of each stockpile is
necessary to provide a representative sample for conducting mixture design. Projects that use
more than one stockpile for RAP require testing of each stockpile.
Figure 19. Photo. Sampling RAP from the stockpile.
Testing and Test Frequency
The representative sample of RAP should be oven dried to a constant mass prior to batching the
mix specimens. Moisture content of RAP may be initially determined to facilitate batching for
mix design. The sample used to determine the moisture content should not be used for other mix
testing since it was overheated.
Testing requirements and testing frequency vary according to the category of RAP and the
amount of RAP used in the mixture. RAP from multiple sources may be subject to more rigorous
28
testing than RAP from a single source. The frequency at which to perform tests should be in
accordance with agency specifications and should also be adequate to assess variability in RAP.
For all RAP stockpiles, the asphalt binder content and aggregate gradation must be determined.
The asphalt binder content may be determined according to AASHTO T 308 or AASHTO
T 164.(17,28) For the ignition method, an aggregate correction factor will have to be assumed. In
many locations, the aggregate correction factor is fairly consistent from mix to mix for the
aggregate materials currently being used in mix designs. If the aggregate sources currently being
used are the same or reasonably similar to the sources used 10–20 years ago in that location, then
it is reasonable to use the current typical correction factor for RAP because it is likely from the
same location. For RAP stockpiles containing aggregates of uncertain origins or for RAP
containing dolomitic limestone, which often has erratic aggregate correction factors, a solvent
extraction procedure may be used to determine the AC of the RAP samples.
If there is a need to test the binder properties of RAP, it is recommended to extract and recover
the binder and perform PG testing on the extracted RAP binder. A combined procedure for
extraction and recovery is given in AASHTO T 319.(29) This method was recommended in
NCHRP 9-12 because it was found to change the recovered binder properties less than
other methods.(9)
Gradation of the recovered aggregate is determined using AASHTO T 30.(30) The ignition oven
may change the physical characteristics of some aggregates. In general, RAP aggregates must
meet the same quality requirements specified for virgin aggregates. This includes evaluating
coarse aggregate angularity (ASTM D 5821), fine aggregate angularity (AASHTO T 304), and
flat and elongated requirements (ASTM D 4791).(31–33) According to AASHTO M 323, the sand
equivalent requirements (AASHTO T 176) are waived for RAP aggregate.(13,34) The Superpave®
aggregate consensus property requirements are also provided in AASHTO M 323.(13) Source
properties, such as abrasion resistance and frictional properties, may be performed according to
agency specifications.
Determining Bulk Specific Gravity of the RAP Aggregate
An important property that needs to be determined is the bulk specific gravity (BSG) of the RAP
aggregate, RAP
sbG . The BSG of the combined RAP and virgin aggregate is used to calculate the
VMA for the mix design. The BSG of the RAP aggregate cannot be directly measured. Studies
have shown that the BSG of the RAP aggregate recovered from the ignition oven is typically
significantly lower than that of the original aggregate. Furthermore, if solvent extraction is used
to remove the RAP aggregate, the aggregate will contain a small amount of unextractable asphalt
binder. However, the main issue is wetability and whether water absorption is affected by the
solvent residue, which will influence BSG results.
29
If the source of RAP is known and original construction records are available, the BSG value of
the virgin aggregate from the construction records may be used as the BSG value of the RAP
aggregate. However, if original construction records are not available, the recommended
procedure for estimating BSG of the RAP aggregate is a simple three-step process as follows:
1. Determine the maximum theoretical specific gravity of the RAP mixture, RAP
mmG , according to
AASHTO T 209.(35)
2. Calculate the effective specific gravity of the RAP aggregate RAP
seG using RAP
mmG , the AC of
the RAP mixture (Pb) and an assumed asphalt specific gravity (Gb) as follows:
(2)
McDaniel and Anderson recommend a value of 1.020 for Gb.(11) The effective specific gravity of
RAP
seG could be used as the value for BSG of the RAP aggregate, but this will overestimate the
combined aggregate Gsb. Furthermore, using higher amounts of RAP may magnify the error in
using RAP
seG as RAP
sbG .
3. Assume a typical value for asphalt absorption, Pba, and use this value to estimate the BSG of
the RAP aggregate, RAP
sbG , from the calculated RAP
seG based on experience with mix designs
for the specific location (see equation 3).
(3)
If absorption data are available from past records on similar aggregates, then that value should be
used as an estimate for Pba. If historical data are not available, a value for Pba may be estimated
as a percentage of the typical water absorption value. For example, Pba may be estimated to be
60–65 percent of the typical water absorption value of the aggregate. This estimate will take into
account the fact that the water absorption of aggregate varies based on region or area.
MIX DESIGN CONSIDERATIONS
The standard practice and specifications for designing asphalt mixtures according to the
Superpave® mix design system are AASHTO M 323 and AASHTO R 35.(13,36) AASHTO M 323
specifies the quality requirements for binder, aggregate, and HMA for Superpave® volumetric
mix design. AASHTO R 35 is a standard for mix design evaluation based on volumetric
properties, air voids, VMA, and voids filled with asphalt of the HMA.
The mix design process for mixes incorporating RAP is similar to the mix design for all virgin
materials. Once RAP has been characterized, it can be combined with virgin aggregate for
calculation of the mix gradation for mix design purposes. RAP is treated like a stockpile of
aggregate during this analysis. The composite properties for gradation, specific gravity, and
𝐺𝐺𝑠𝑠𝑠𝑠𝑅𝑅𝑅𝑅𝑅𝑅=100 −𝑅𝑅𝑏𝑏100𝐺𝐺𝑚𝑚𝑚𝑚−𝑅𝑅𝑏𝑏𝐺𝐺𝑏𝑏
𝐺𝐺𝑠𝑠𝑏𝑏𝑅𝑅𝑅𝑅𝑅𝑅=𝐺𝐺𝑠𝑠𝑠𝑠𝑅𝑅𝑅𝑅𝑅𝑅�𝑅𝑅𝑏𝑏𝑏𝑏−𝐺𝐺𝑠𝑠𝑠𝑠𝑅𝑅𝑅𝑅𝑅𝑅100𝐺𝐺𝑏𝑏+1��
30
consensus characteristics are used in determining acceptability of the blended aggregates. It
should be noted that the gradation of the RAP particles is not the original gradation of the
aggregate used in RAP because the binder film on RAP adds to the dimension of the aggregate.
However, the original gradation of the recovered RAP aggregate is used for design purposes.
Typical design software (i.e., spreadsheet programs) accounts for the differences in the batching
material gradation and the “true” gradation of the RAP material as well as for the binder
contained in the RAP material. Sand equivalent is tested on the composite aggregate blend
according to JMF without the RAP proportion.(34)
RAP material generally contains relatively high percentages of material passing the #200
(0.0029-inch (0.075-mm)) sieve as a result of the milling and/or crushing operations. This can
limit the amount of RAP that can be used in a mix design and meet the dust to asphalt ratio, air
voids, and VMA. The gradation of the virgin aggregate must compensate for this. Using more of
the coarse portion of fractionated RAP may help, as would washing the aggregate or removing
dust at the plant during production.
The percentage of asphalt binder in RAP should also be considered when determining the
trial asphalt binder content. The asphalt binder content of the total mixture for mix batching
includes virgin and reclaimed asphalt binder. The mixture trial AC is calculated or estimated by
experience during the trial blend analysis. Thus, the amount of binder in RAP is considered when
determining how much virgin asphalt binder is required. It may be necessary to adjust the virgin
asphalt binder grade when RAP is used in the mix to achieve the appropriate grade.
High RAP Mix Design
For asphalt mixtures containing high RAP, a method is needed to select the appropriate grade for
the virgin binder. A softer virgin binder may be required to balance the stiffer-aged RAP binder.
The techniques listed below may be used as part of a State or local transportation department
study for the selection of PG asphalt binder. The process involves the use of a blending chart or
blending equation to determine the amount of RAP to use if the virgin binder grade is known or
to select the grade of virgin binder if the percentage of RAP binder is known. Procedures for
using a blending chart are provided in the appendix of AASHTO M 323.(13)
RAP is subjected to a solvent extraction and recovery process to recover the RAP binder for
testing.(29) After, the physical properties and critical temperatures of the recovered RAP binder
are determined. The critical high temperature (Tc(High)) based on the original DSR and rolling
thin film oven (RTFO) DSR is determined. The high temperature PG of the recovered RAP
binder is the lowest of the original DSR and RTFO DSR critical temperatures. The intermediate
critical temperature (Tc(Int)) of the recovered RAP binder is determined by performing
intermediate temperature DSR testing on the RTFO-aged recovered RAP binder as if the
RAP binder were pressure aging vessel-aged. The critical low temperature (Tc(S) or Tc(m)) is
determined based on bending beam rheometer testing on the RTFO-aged recovered RAP binder,
or m-value. The low critical temperature (Tc(Low)) is the higher of the two low critical
temperatures, Tc(S) or Tc(m). The low temperature PG of the recovered RAP binder is based
on this low critical temperature value.
31
Once the physical properties and critical temperatures of the recovered RAP binder are known,
there are two options for blending as follows:
• Blending at a known RAP percentage.
• Blending with a known virgin binder grade.
Blending at a Known RAP Percentage
In the case where the desired final blended binder grade, the desired percentage of RAP, and the
recovered RAP binder properties are known, the required properties of a virgin binder grade can
then be determined at each temperature (high, intermediate, and low) separately as follows:
)%1(
)(%
RAP
TRAPTTRAPblend
virgin −
×−=
(4)
Where:
Tvirgin = Critical temperature of virgin asphalt binder (high, intermediate, or low).
TBlend = Critical temperature of blended asphalt binder (final desired) (high, intermediate, or
low).
%RAP = Percentage of RAP expressed as a decimal.
TRAP = Critical temperature of recovered RAP binder (high, intermediate, or low).
Blending with a Known Virgin Binder Grade
In the case where the final blended binder grade, the virgin asphalt binder grade, and the
recovered RAP properties are known, the allowable RAP percentage can be determined
as follows:
virginRAP
virginblend
TT
TTRAP−
−=%
(5)
This should be determined at high, intermediate, and low temperatures. The RAP content or
range of contents meeting all three temperature requirements should be selected.
NAPA, in partnership with AASHTO and FHWA, has published a guide for designing HMA
mixtures with high RAP percentages.(37) The guide includes information on evaluating RAP
material, mix design, plant verification, and QC.
Performance Testing
In addition to checking the volumetric properties, it may be desirable to evaluate mixture
performance of the designed asphalt mixture containing RAP, especially a high RAP content, to
assure that the mixture is able to resist low-temperature and fatigue cracking or rutting if a softer
virgin binder was used in the mix design. A variety of performance tests are available.(38)
32
The possible distress mechanisms that should be evaluated include permanent deformation
(i.e., rutting), moisture sensitivity, fatigue, and thermal cracking. Table 3 provides recommended
tests for each distress mechanism. More information on performance tests for high RAP mixtures
may also be found in Designing HMA Mixtures with High RAP Content: A Practical Guide.(37)
An NCHRP project 9-46 is underway and will make specific performance test recommendations
for high RAP mixtures.(39)
To ensure the long-term performance of RAP mixtures, a paved test strip, similar to conventional
virgin mixtures, is recommended to evaluate the in-place properties of the RAP mixture. Also,
proper monitoring of the pavement, while in service, and pavement preservation techniques over
the service life of the recycled pavement are encouraged.
Table 3. Performance tests for asphalt mixtures.
Distress
Mechanism Test Description Standard
Permanent
deformation
Asphalt pavement analyzer
AASHTO TP63(40)
(discontinued)
Hamburg wheel tracking device AASHTO T 324(41)
Repeated load triaxial creep
(flow number using AMPT) AASHTO TP79(42)
Moisture
sensitivity
Tensile strength ratio AASHTO T 283(43)
Hamburg wheel tracking device (wet) AASHTO T 324(41)
Fatigue
Four-point bending beam fixture AASHTO T 321(44)
Dynamic modulus—continuum fatigue
damage (push/pull)
NCHRP 9-29 updated
continuum fatigue damage
software for AMPT(45)
Thermal
cracking
Thermal stress restrained specimen test No standard available
Indirect tensile test No standard available
PLANT CONSIDERATIONS
Similar to the requirements for virgin aggregates, the RAP cold aggregate feed equipment should
be capable of accurately proportioning RAP into the mix. Superheated virgin aggregate is used
as a heat transfer medium for the ambient temperature RAP. Thus, it is important that RAP and
the virgin aggregate have low moisture content. The moisture content of the virgin and RAP
aggregates should be determined daily during production or as necessary, and the moisture test
results should be recorded. For continuous mix plants, the moisture content is input in the plant’s
controls to adjust the weight (tons/hour) measured with the belt scales.
When using RAP, a scalping screen or other device should be installed before the weighing
system to ensure that large RAP particles are not fed into the drum (see figure 20). It is
recommended that screens be installed at the RAP feed to prevent the introduction of particles
that are too large. As an alternative, a small crusher may be installed to break the larger RAP
particles into smaller sizes (see figure 21).(20)
RAP should be introduced into the drum downstream from the burner and away from the flame
and hot gases. Since processing RAP at a HMA facility involves heat transfer techniques, a
33
burner adjustment may be required when using RAP. Recycling Hot Mix Asphalt Pavements
contains detailed information on processing RAP in an HMA facility and specialized facilities
for high percentage recycling.(20)
Figure 20. Photo. Scalping screen for RAP feed.
Figure 21. Photo. Smaller scalping screen for large RAP particles.
PLACEMENT OF RAP MIXES
Construction issues for RAP mixes are not different from issues encountered when paving with
conventional HMA produced with virgin materials. However, failure to properly address
processing as well as inadequate QC of RAP and an improper mixture design will significantly
increase the likelihood of problems in placement and compaction of the new pavement.
No special equipment or techniques are required when placing and compacting mixtures
containing RAP (see figure 22 and figure 23). High RAP mixtures may require more attention
than conventional mixtures due to increased stiffness as a result of RAP. Achieving density with
RAP mixes is typically not a concern, but contractors should be aware that recycled mixtures
with high RAP are sometimes stiffer and/or may be produced at slightly higher production
temperatures to facilitate blending of RAP with the virgin materials. Like conventional mixes,
compaction should be monitored using a nondestructive device calibrated to cores to ensure that
adequate density is achieved.
34
Figure 22. Photo. Placement of a high RAP mixture.
Figure 23. Photo. Compaction of a high RAP mixture.
PERFORMANCE OF RAP ASPHALT MIXTURES
The long-term performance of recycled asphalt pavements, particularly when compared to
conventional HMA performance, has not been well documented. State transportation
departments that routinely used RAP in HMA production were convinced of its benefits and that
recycled asphalt pavement performance was comparable to conventional HMA performance.(7)
As a result, LTPP information has not been routinely collected. RAP is primarily used in base
and intermediate pavement layers precluding the use of surface condition evaluations and visual
observation techniques to assess performance.
In the 1990s, two reports were published evaluating the field performance of recycled asphalt
pavements with varying percentages of RAP. Kandhal et al. evaluated virgin and recycled
asphalt pavements containing 10–25 percent RAP.(46) After 1–2.5 years of service, there were
no signs of rutting, raveling, or fatigue cracking in any of the study sections. This indicated that
the virgin and RAP sections performed equally well. In a subsequent analysis, Kandhal et al.
expanded the study to more pavement sections including virgin and recycled asphalt pavements
with 10–40 percent RAP.(47) Based on visual observations, there was no significant difference
in the performance of the virgin and recycled pavement sections. It should be noted, however,
that 1–3 years is not sufficient to evaluate the long-term service performance of the
pavement sections.(47)
35
In Louisiana, Paul evaluated the field performance of conventional and recycled asphalt
pavements that were 6–9 years old.(48) He analyzed the pavements for condition, serviceability,
and structural analysis. The RAP sections contained 20–50 percent RAP. Paul found no
significant difference in terms of the pavement conditions and serviceability ratings.(48)
Most recently, NCAT completed a study comparing virgin and recycled asphalt pavements using
data from the LTPP program.(49) Data from 18 projects across North America were analyzed to
compare paired sections of virgin asphalt mix and recycled asphalt mix containing 30 percent
RAP. The projects ranged from 6 to 17 years. The distress parameters that were considered
were rutting, fatigue cracking, longitudinal cracking, transverse cracking, block cracking,
and raveling.
An analysis of variance test indicated that performance of recycled and virgin sections were
not statistically different except for fatigue, longitudinal cracking, and transverse cracking,
where the virgin sections performed slightly better overall than the RAP sections. Additional
statistical analyses using paired t-tests showed that the RAP mixes performed better than or equal
to virgin mixes for the majority of the locations for each distress parameter. Table 4 summarizes
the statistical analyses results for each distress parameter and shows that RAP performed equal
(i.e., insignificant difference between RAP and virgin mix, column 4) or better than (column 3)
virgin mixes as a majority percentage (column 5). NCAT concluded that, in most cases, using
30 percent RAP in an asphalt pavement can provide the same overall performance as virgin
asphalt pavement.(49)
In a separate analysis by FHWA’s LTPP program to determine the impact of design features
on performance, the majority of the 18 sites did not show significant differences in performance
between sections overlaid with virgin and recycled mixes.(50) Hong et al. also investigated
the LTPP-specific pavement studies category 5 test sections in Texas with 35 percent RAP.(51)
The performance monitoring period in Texas covered 16 years from 1991 to 2007, and
the performance indicators included transverse cracking, rut depth, and ride quality (i.e.,
international roughness index (IRI)). The high RAP sections were compared to virgin sections.
Overall, both types of sections had satisfactory performance over the performance monitoring
period. Compared with the virgin (no RAP) pavement sections, the sections with high RAP had
higher cracking amounts, less rut depth, and similar ride quality (i.e., roughness) change over
time. Based on the analysis of field data in this study, Hong et al. concluded that pavement
constructed with 35 percent RAP, if designed properly, can perform well and as satisfactorily as
a virgin pavement during a normal pavement life span.(51)
In a similar study, the California Department of Transportation (Caltrans) performed a
comparative analysis of 47 RAP sections and 7 other different treatments (located within a
reasonable distance on the same route) in 3 different environmental zones.(52) Caltrans allowed
up to 15 percent RAP to be substituted for virgin aggregate, which is the assumed RAP content
for the sections analyzed in this study. Comparisons were made for the following indices: in situ
structural capacity, distress condition, roughness condition, and construction consistency. The
long-term performance of RAP was found and expected to be comparable to the other treatments
based on deterioration models.(52)
36
Table 4. Summary of statistical analyses from NCAT LTPP study.
Distress
Parameter
Virgin
Performed
Significantly
Better than
RAP (Percent)
RAP Performed
Significantly
Better than
Virgin (Percent)
Insignificant
Difference
Between RAP
and Virgin
(Percent)
RAP Performed
Equal or Better
than Virgin
(Percent)
IRI 42 39 19 58
Rutting 33 29 38 67
Fatigue cracking 29 10 61 71
Longitudinal
cracking 15 10 75 85
Transverse cracking 32 15 53 68
Block cracking 3 1 96 97
Raveling 7 15 78 93
A study conducted by the Florida Department of Transportation (FDOT) took a random
sampling of mix designs with more than 30 percent RAP content (RAP content ranged from
30 to 50 percent).(53) The pavements were constructed between 1991 and 1999, and the age when
the pavements became deficient was noted. Florida’s most common mode of distress is cracking,
which was the only distress parameter considered in the analyses. Figure 24 shows a comparison
of pavement life in age for projects containing at least 5,000 tons of HMA. The average life of
virgin mixtures is 11 years. For 30, 35, 40, 45, and 50 percent RAP content mixes, the average
age ranges from 10 to 13 years. The primary conclusion of the study is that there does not
appear to be a significant difference in pavement life and performance between zero and
30 percent RAP.(53)
RAP has successfully been used for more than 30 years. Based on documented past experience,
recycled asphalt mixtures designed under established mixture design procedures and produced
under appropriate QC/quality assurance measures perform comparably to conventional
asphalt mixtures.
37
Figure 24. Graph. Pavement age in years versus percent RAP for FDOT projects with
greater than 5,000 tons of asphalt mix (53)
39
CHAPTER 4. CONCLUSIONS AND RECOMMENDATIONS
Based on the information in this report, the following conclusions can be made regarding the
state of the practice for RAP:
• RAP is a valuable, high-quality material that can replace more expensive virgin
aggregates and binders. The most economical use of RAP is in asphalt mixtures.
• The use of RAP is primarily driven by the costs of virgin materials and transportation.
Usage is optional and depends on the contractor to propose its use based on economic
considerations, availability of materials, plant site, and production capabilities.
• State transportation departments and contractors are reassessing the economic and
environmental benefits of allowing higher percentages of RAP in premium pavements
and asphalt surfaces while also maintaining a high-quality, well-performing pavement
infrastructure. However, many States are not currently tracking the amount of RAP used
or the cost savings associated with the use of RAP.
• More widespread use of higher amounts of RAP in asphalt mixtures requires support
from State transportation departments and contractors. State transportation departments
have expressed concern over the lack of guidance and information on the performance of
high RAP mixtures. Furthermore, some State transportation departments have previously
had poor experience with RAP in asphalt mixtures, necessitating contractors to
consistently demonstrate the ability to produce high-quality RAP mixes. There is a
need for national guidance on best practices when using RAP and documented
information about long-term performance of high RAP pavements.
• It is estimated that the average use of RAP across the United States is 12 percent.
However, according to State transportation department specifications, there is the
potential to use up to 30 percent RAP in the intermediate and surface layers of
pavements. As a result, the overall amount of RAP used in asphalt mixtures can
be increased.
• RAP mixtures must meet the same mix design specifications required for virgin mixtures.
The most common method of mix design for RAP mixtures, including high RAP, is the
Superpave® mix design process. For QC purposes, most State transportation departments
do not have additional means of determining acceptability of high RAP mixtures.
• The most common challenges to increasing the use of RAP are State transportation
department specification limits, lack of processing (i.e., variability of RAP), lack of RAP
availability, and past experiences. Furthermore, in regards to performance, the two most
common concerns are the quality of the blended virgin and RAP binders, especially for
high RAP mixes, as well as stiffening of the mix from high RAP quantities and resulting
cracking performance.
40
• The performance and life of pavement containing up to 30 percent RAP is similar to
virgin pavements with no RAP. A survey of LTPP sections containing at least 30 percent
RAP showed similar performance to virgin sections. The LTPP pavement sections were
located throughout the United States and Canada. An analysis of Florida pavements
show similar pavement life for pavements containing no RAP and pavements containing
30 percent RAP.
RECOMMENDATIONS
The following summary of current recommendations is provided to increase the use of RAP and
ensure asphalt mixture quality. However, it should be noted that ongoing and future research
may lead to refinements of these best practices.
• Proper techniques should be used for obtaining, stockpiling, and processing RAP to
maintain its quality. For high RAP mixtures, fractionation of the RAP material should
be considered.
• Sampling and testing of the RAP material should be performed. Random samples should
be taken to identify the variability of the RAP material properties. Test results, including
composition and variability, should be provided to the State transportation department
or owner.(7)
• The RAP material should be properly characterized for mix design purposes. The
laboratory mixture design should be established using RAP as a component. This is
especially important for State transportation departments considering permitting up to
20 percent RAP in mixtures without changing to a softer grade asphalt binder.
• With RAP contents greater than 25 percent, careful consideration should be given to the
selection of the grade of asphalt binder added to the recycled asphalt mixture according to
State transportation department specifications.
• Production sampling and testing programs should be implemented to verify mixture
design assumptions including the asphalt binder blend properties, especially for high
RAP mixtures.(7)
• Evaluating mixture performance of the designed asphalt mixture containing RAP,
especially high RAP, is recommended. There are a variety of performance tests available
for evaluating the probable permanent deformation, fatigue, and thermal cracking
performance of compacted asphalt mixtures.
• Plant production best practices used in the production and placement strategies during the
construction of HMA will address concerns when using high RAP. The plant production
best practices should regularly monitor and adjust for moisture content and scalping
screens. High-quality high RAP mixtures are achieved with processing and production
best practices, which result in cost and energy savings and reduced emissions.
41
• Further documentation of the production, construction, and long-term performance of
high RAP mixtures is needed.
• Consideration should be given to including documenting RAP use in a pavement
management system with details concerning RAP quantities used, sources, and
placement details.
43
ACKNOWLEDGEMENTS
The author would like to acknowledge the invaluable input and review provided by RAP ETG.
This report is the result of a RAP ETG activity to provide a state of the practice for including
higher amounts of RAP in asphalt mixtures.
The following individuals were members of the task group that provided expert input for
the information in this report: John D’Angelo (retired from FHWA), Jim Musselman, and
David Newcomb.
Special thanks go to the following members and friends of RAP ETG that provided technical
review of the final draft of this report: John D’Angelo, Randy West, Jim Musselman,
Rebecca McDaniel, Cindy Lafleur, Alan Carter, David Newcomb, Kent Hansen, Jack Weigel,
Jo Daniel, Andy Mergenmeier, Gerry Huber, and John Bukowski.
In addition, an internal FHWA review was conducted by Eric Weaver of the Office of
Infrastructure Research and Development and Brad Neitzke of Western Federal Lands.
45
REFERENCES
1. Wright, Jr., F. (2001). FHWA Recycled Materials Policy, Federal Highway Administration,
Washington, DC. Obtained from: http://www.fhwa.dot.gov/legsregs/directives/policy/
recmatpolicy.htm. Site last accessed December 14, 2009.
2. Federal Highway Administration. (1993). A Study of the Use of Recycled Paving Materials:
A Report to Congress, Report No. FHWA-RD-93-147, Federal Highway Administration,
Washington, DC.
3. The Asphalt Institute. (2007). The Asphalt Handbook: MS-4, 7th Ed., The Asphalt Institute,
Lexington, KY.
4. Federal Highway Administration. (1978–1983). Demonstration Project 39—Asphalt
Recycling, Federal Highway Administration, Washington, DC. Obtained from:
http://www.fhwa.dot.gov/publications/research/infrastructure/recycling/index.cfm. Site last
accessed January 6, 2011.
5. National Cooperative Highway Research Program. (1978). NCHRP Program Synthesis of
Highway Practice No. 54: Recycling Materials for Highways, Transportation Research
Board, Washington, DC.
6. Epps, J.A., Little, D.N., Holmgreen, R.J., and Terrel, R.L. (1980). Guidelines for Recycling
Pavement Materials, NCHRP Report No. 224, Transportation Research Board,
Washington, DC.
7. Sullivan, J. (1996). Pavement Recycling Executive Summary and Report, Report No.
FHWA-SA-95-060, Federal Highway Administration, Washington, DC.
8. Kandhal, P. and Mallick, R.B. (1997). Pavement Recycling Guidelines for State and Local
Governments—Participant’s Reference Book, Report No. FHWA-SA-98-042, Federal
Highway Administration, Washington, DC.
9. McDaniel, R. (1997). Incorporation of Reclaimed Asphalt Pavement in the Superpave
System, NCHRP Report No. 09-12, Transportation Research Board, Washington, DC.
Obtained from: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=948.
Site last accessed January 6, 2011.
10. Soleymani, H., et al. (2001). “Recommended Use of Reclaimed Asphalt Pavement in the
Superpave Mix Design Method: Guidelines,” Research Results Digest No. 253, National
Cooperative Highway Research Program, Washington, DC. Obtained from:
http://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rrd_253.pdf. Site last accessed
December 13, 2009.
11. McDaniel, R. and Anderson, R.M. (2001). Recommended Use of Reclaimed Asphalt
Pavement in the Superpave Mix Design Method: Technician’s Manual, NCHRP Report
No. 452, Transportation Research Board, Washington, DC.
46
12. Hansen, K. and Newcomb, D. (2007). RAP Usage Survey, National Asphalt Pavement
Association, Lanham, MD.
13. American Association of State Highway and Transportation Officials. (2010). “AASHTO
M 323: Standard Specification for Superpave Volumetric Mix Design,” Standard
Specifications for Transportation Materials and Methods of Sampling and Testing, 30th Ed.,
AASHTO, Washington, DC.
14. Bonaquist, R. (2007). “Can I Run More RAP?,” Hot Mix Asphalt Technology, 11–13,
National Asphalt Pavement Association, Landham, MD.
15. Copeland, A., et al. (2010). “Field Evaluation of a High Reclaimed Asphalt Pavement/Warm
Mix Asphalt Project in Florida: A Case Study,” Transportation Research Record 2179,
Transportation Research Board, Washington, DC.
16. West, R. (2008). Summary of NCAT Survey on RAP Management Practices and RAP
Variability, Federal Highway Administration, Washington, DC. Obtained from:
http://www.morerap.us/RAP%20Resources/reports.html. Site last accessed January 6, 2011.
17. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 308: Determining the Asphalt Binder Content of Hot Mix Asphalt by the Ignition Method,”
Standard Specifications for Transportation Materials and Methods of Sampling and Testing,
30th Ed., AASHTO, Washington, DC.
18. Prowell, B. and Hurley, B. (2007). Quality Improvement Series 125: Warm-Mix Asphalt:
Best Practices, National Asphalt Pavement Association, Lanham, MD.
19. National Asphalt Pavement Association. (2007–2011). Warm Mix Asphalt the Wave of the
Future, NAPA, Landham, MD. Obtained from: http://www.warmmixasphalt.org. Site last
accessed January 6, 2011.
20. National Asphalt Pavement Association. (2007). Information Series 123: Recycling Hot Mix
Asphalt Pavements, NAPA, Lanham, MD.
21. National Asphalt Pavement Association. (2009). How to Increase RAP Usage and Ensure
Pavement Performance, NAPA, Lanham, MD.
22. Federal Highway Administration. (1999). LTPPBind: A New Tool for Selecting Cost-
Effective Superpave Asphalt Binder Performance Grades, Report No. FHWA-RD-99-082,
Federal Highway Administration, Washington, DC.
23. Bonaquist, R.F., Christensen, D.W., and Stump, W. (2003). Simple Performance Tester for
Superpave Mix Design: First Article Development and Evaluation, NCHRP Report 513,
Transportation Research Board, Washington, DC.
24. Christensen, D., Pellinen, T., and Bonaquist, R. (2003). “Hirsch Model for Estimating the
Modulus of Asphalt Concrete,” Journal of the Association of Asphalt Paving Technologists,
72, 97–121.
47
25. Andrei, D., Witczak, M.W., and Mirza, M.W. (1999). Development of a Revised Predictive
Model for the Dynamic (Complex) Modulus of Asphalt Mixtures, NCHRP 1-37A Interteam
Report s.l., University of Maryland, College Park, MD.
26. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 2: Sampling of Aggregates,” Standard Specifications for Transportation Materials and
Methods of Sampling and Testing, 30th Ed., AASHTO, Washington, DC.
27. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 27: Sieve Analysis of Fine and Coarse Aggregate,” Standard Specifications for
Transportation Materials and Methods of Sampling and Testing, 30th Ed., AASHTO,
Washington, DC.
28. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 164: Quantitative Extraction of Asphalt Binder from Hot Mix Asphalt,” Standards
Specifications for Transportation Materials and Methods of Sampling and Testing,
30th Ed., AASHTO, Washington, DC.
29. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 319: Quantitative Extraction and Recovery of Asphalt Binder from Asphalt Mixtures,”
Standard Specifications for Transportation Materials and Methods of Sampling and Testing,
30th Ed., AASHTO, Washington, DC.
30. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 30: Mechanical Analysis of Extracted Aggregate,” Standard Specifications for
Transportation Materials and Methods of Sampling and Testing, 30th Ed., AASHTO,
Washington, DC.
31. American Society for Testing and Materials. (2006). “Standard D5821: Standard Test
Method for Determining the Percentage of Fractured Particles in Coarse Aggregate,” ASTM
International Book of Standards, ASTM International, West Conshohocken, PA.
32. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 304: Uncompacted Void Content of Fine Aggregate,” Standard Specifications for
Transportation Materials and Methods of Sampling and Testing, 30th Ed., AASHTO,
Washington, DC.
33. American Society for Testing and Materials. (2011). “Standard D4791: Standard Test
Method for Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse
Aggregate,” ASTM International Book of Standards, 04.03, ASTM International,
West Conshocken, PA.
34. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 176: Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test,”
Standard Specifications for Transportation Materials and Methods of Sampling and Testing,
30th Ed., AASHTO, Washington, DC.
48
35. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 209: Theoretical Maximum Specific Gravity and Density of Hot Mix Asphalt (HMA),”
Standard Specifications for Transportation Materials and Methods of Sampling and Testing,
30th Ed., AASHTO, Washington, DC.
36. American Association of State Highway and Transportation Officials. (2010). “AASHTO
R 35: Standard Practice for Superpave Volumetric Design for Hot Mix Asphalt (HMA),”
Standard Specifications for Transportation Materials and Methods of Sampling and Testing,
30th Ed., AASHTO, Washington, DC.
37. Newcomb, D., Brown, E.R., and Epps, J.A. (2007). Quality Improvement Series 124:
Designing HMA Mixtures with High RAP Content: A Practical Guide, National Asphalt
Pavement Association, Lanham, MD.
38. Mohammad, L. (2006). Performance Tests for HMA Including Fundamental and Empirical
Procedures, STP 1469, ASTM International, West Conshocken, PA.
39. National Cooperative Highway Research Program. (2008). NCHRP 9-46: Improved Mix
Design, Evaluation, and Materials Management Practices for HMA with High RAP Content,
Transportation Research Board, Washington, DC. Obtained from: http://apps.trb.org/
cmsfeed/TRBNetProjectDisplay.asp?ProjectID=1624. Site last accessed January 4, 2011.
40. American Association of State Highway and Transportation Officials. (2010). “AASHTO
TP 63: Determining Rutting Susceptibility of HMA Using the Asphalt Pavement Analyzer
(APA),” Standard Specifications for Transportation Materials and Methods of Sampling and
Testing, 30th Ed., AASHTO, Washington, DC.
41. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 324: Hamburg Wheel-Track Testing of Compacted Hot Mix Asphalt (HMA),” Standard
Specifications for Transportation Materials and Methods of Sampling and Testing, 30th Ed.,
AASHTO, Washington, DC.
42. American Association of State Highway and Transportation Officials. (2010). “AASHTO
TP 79: Determining the Dynamic Modulus and Flow Number for HMA Using the Asphalt
Mixture Performance Tester (AMPT),” Standard Specifications for Transportation Materials
and Methods of Sampling and Testing, 30th Ed., AASHTO, Washington, DC.
43. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 283: Resistance of Compacted HMA to Moisture-Induced Damage,” Standard
Specifications for Transportation Materials and Methods of Sampling and Testing, 30th Ed.,
AASHTO, Washington, DC.
44. American Association of State Highway and Transportation Officials. (2010). “AASHTO
T 321: Determining the Fatigue Life of Compacted HMA Subjected to Repeated Flexural
Bending,” Standard Specifications for Transportation Materials and Methods of Sampling
and Testing, 30th Ed., AASHTO, Washington, DC.
49
45. National Cooperative Highway Research Program. (2011). NCHRP 9-29: Simple
Performance Tester for Superpave Mix Design, Transportation Research Board,
Washington, DC. Obtained from: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp
?ProjectID=963. Site last accessed January 4, 2011.
46. Kandhal, et al. (1995). Performance of Recycled Hot-Mix Asphalt Mixtures in the State of
Georgia, NCAT Report No. 95-01, National Center for Asphalt Technology, Auburn, AL.
47. Al-Qadi, I., Elseifi, M., and Carpenter, S. (2007). Reclaimed Asphalt Pavement—A Literature
Review, Report No. FHWA-ICT-07-001, Illinois Center for Transportation, Rantoul, IL.
48. Paul, H.R. (1996). Evaluation of Recycled Projects for Performance, 65, Association of
Asphalt Paving Technologists, Lino Lakes, MN.
49. National Center for Asphalt Technology. (2009). “LTPP Data Shows RAP Mixes Perform as
Well as Virgin Mixes,” Asphalt Technology News, 21, 2, National Center for Asphalt
Technology, Auburn, AL.
50. Ayers, M., et al. (2009). Impact of Design Features on Pavement Response and Performance
in Rehabilitated Flexible and Rigid Pavements, Report No. FHWA-HRT-10-066, Federal
Highway Administration, Washington, DC.
51. Hong, F., et al. (2010). “Long-Term Performance Evaluation of Recycled Asphalt Pavement
Results from Texas: Pavement Studies Category 5 Sections from the Long-Term Pavement
Performance Program,” Transportation Research Record 2180, Transportation Research
Board, Washington, DC.
52. Zaghloul, S. and Holland, T.J. (2008). “Comparative Analysis of Long-Term Field
Performance of Recycled Asphalt in California Environmental Zones,” Transportation
Research Record 2084, Transportation Research Board, Washington, DC.
53. Musselman, J. (2009). High RAP Performance in Florida, HMA Recycling Expert Task
Group, Department of Transportation, Washington, DC. Obtained from: http://www.
morerap.us/12-09/Musselman.High_RAP_Performance_Florida.pdf. Site last accessed
January 4, 2011.
HRDI-10/04-11(WEB)E