Determination of Recycled Asphalt Pavement (RAP) Content in Asphalt Mixes Based on Expected Mixture Durability Prepared in Cooperation with The Ohio Department of Transportation and The U.S. Department of Transportation, Federal Highway Administration Final Report by Osama Abdulshafi, Ph.D., P.E. Bozena Kedzierski, M.S. Michael G. Fitch, M.S., P.E. The Ohio State University Department of Civil and Environmental Engineering and Geodetic Science 470 Hitchcock Hall, 2070 Neil Avenue Columbus, Ohio 43210-1275
71
Embed
Determination of Recycled Asphalt Pavement (RAP) …...Determination of asphalt binder content in RAP is left to the discretion of the agency. RAP addition over 16% requires determination
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Determination of Recycled Asphalt Pavement (RAP) Content
in Asphalt Mixes Based on Expected Mixture Durability
Prepared in Cooperation withThe Ohio Department of Transportation
and
The U.S. Department of Transportation,Federal Highway Administration
Final Report
by
Osama Abdulshafi, Ph.D., P.E.Bozena Kedzierski, M.S.
Michael G. Fitch, M.S., P.E.
The Ohio State UniversityDepartment of Civil and Environmental Engineering
and Geodetic Science470 Hitchcock Hall, 2070 Neil Avenue
Columbus, Ohio 43210-1275
2
December 2002
CHAPTER 1
INTRODUCTION
1.1. DESCRIPTION OF THE PROBLEM
Decreasing supplies of locally available quality aggregate in some areas, growing
concern over waste disposal, and the rising cost of asphalt binder have resulted in greater
use of recycled asphalt pavement (RAP) for new road construction. Unfortunately, the
incorporation of RAP introduces one more variable to consider when predicting the
durability of the newly-constructed asphalt concrete pavement. Traditional determination
of the RAP quantity allowed for addition to the virgin asphalt concrete mix has an
empirical nature and is based on viscosity measurement of a blended binder. Recently,
studies have been undertaken to address the problem of determining the optimum or
maximum allowable RAP addition in hot mix asphalt (HMA) designed in accordance
with the Superpave mix design method. These studies are based on binder testing
performed in conformance with new Superpave-recommended test methods, but do not
address properties of the resultant bituminous mixture. Equipment needed to conduct
Superpave binder testing is not readily available in a typical asphalt plant laboratory.
Consequently, a procedure that will allow for determination of RAP addition using
widely available tests, and takes into an account properties of the produced asphalt
concrete mixture, is needed.
During the period 1994 to1996, the Ohio Department of Transportation (ODOT)
and Federal Highway Administration (FHWA) sponsored a research project entitled
“Durability of Recycled Asphalt Concrete Surface Mixes” (7) which incorporated the
then-new concept of absorbed energy. As a result of this project, a procedure for
selection of optimum RAP content that considered the durability of recycled asphalt
3
mixes was developed. This simple procedure, which required equipment available in
typical asphalt concrete production facilities appeared promising but needed additional
refinement due to the fact that the study was limited to RAP from only two sources.
1.2. STUDY OBJECTIVES
The objectives of this study were to:
1. Develop an implementable testing procedure that efficiently
determines RAP content limits based on mix durability loss.
2. Make the volumetric mix design of bituminous mixes containing RAP a
definitive engineering process.
3. Provide the industry with RAP processing techniques to maximize
durability.
1.3. SCOPE OF WORK
This research project was directed toward determination of recycled asphalt pavement
(RAP) content in hot-mixed asphalt (HMA). Intermediate course mixes used in Ohio
were examined. The determination was based on testing of both binder and bituminous
concrete specimens.
4
CHAPTER 2
LITERATURE REVIEW
2.1. OVERVIEW
The use of recycled asphalt pavement (RAP) in asphalt concrete mixes has become a
common practice in the construction of new, and reconstruction of old, hot mix asphalt
(HMA) pavements. A research project conducted by the Texas Transportation Institute
(1) acknowledged wide use of RAP in most of the states but cites important differences in
RAP use policies. Some states prohibit the use of RAP on Interstate highways, while
others exclude its use in surface course mixes. The maximum amount of RAP allowed in
the HMA differs from state to state. Generally, a small amount of RAP (10 to 15%) is
used without altering the mix design. Incorporating higher percentages of RAP in HMA
requires mix designs that include adjustments for aggregates and asphalt binder that is
introduced into a virgin mix by RAP addition. Traditionally, the percent of RAP to be
used in bituminous concrete mixes designed by the Marshall Mix Design Method has
been estimated on the basis of the viscosity chart for a blend of virgin and recycled
asphalt binder content. This chart shows a linear relationship between the logarithm of
viscosity at 60°C and the percent of virgin or recycling agent in the blend. The Superpave
method of bituminous concrete mix design originally did not address the issues associated
with the use of RAP in HMA mixes. The lack of guidelines for selection of optimum
RAP content in Superpave-designed mixes resulted in further use of the blended binder
viscosity chart for determination of the amount of RAP that was allowed to be introduced
in new HMA. Since Superpave is gradually becoming the dominant HMA mix design
method, research has been undertaken to develop guidelines and procedures that
accommodate the incorporation of RAP in the Superpave system.
5
2. TECHNICAL BACKGROUND
The FHWA RAP Superpave Mixtures Expert Task Group, in a research paper
called “Guidelines for the Design of Superpave Mixtures Containing Reclaimed Asphalt
Pavement (RAP)” (2), provided the following requirements for inclusion of RAP in
Superpave volumetric mix design procedures based on the percent RAP used in the total
mix:
· Aggregate in the RAP should be considered as part of the aggregate content
of the total mixture.
· Asphalt binder in the RAP should be considered as part of the asphalt binder
content of the total mixture.
· All aggregate requirements for the aggregate blend must be satisfied.
· Asphalt binder grade should be adjusted depending upon the amount of RAP
included in the mixture.
Three levels of RAP addition are distinguished by different approaches
concerning its introduction into asphalt concrete mixes. RAP addition up to 15% (by
weight of total mix) does not require any modification of the mix design process, and the
selection of the grade of virgin asphalt binder is based on typical requirements for
climatic conditions and predicted traffic. Determination of asphalt binder content in RAP
is left to the discretion of the agency. RAP addition over 16% requires determination of
its asphalt binder content. At RAP contents between 16 and 25%, selection of a grade of
virgin asphalt binder is made by two methods:
· Grade of virgin asphalt is one grade lower than that usually selected for given
climatic conditions.
· RAP binder stiffness is measured and a blending chart is used to select the
proper grade of virgin asphalt binder.
6
RAP addition over 25% requires measurement of the RAP asphalt binder stiffness
and use of a blending chart as the basis for virgin asphalt binder grade selection.
In the paper “Designing Recycled Hot-Mix Asphalt Mixtures Using Superpave
Technology” (3), Kandhal developed a binder selection procedure for selecting the
performance grade (PG) of virgin asphalt binder in a recycled HMA mixture. The
selection was based exclusively on Dynamic Shear Rheometer (DSR) binder tests and,
therefore, used only testing criteria for high and intermediate test temperatures. As a
result of this study, a chart of the relationship between binder shear stiffness (expressed as
G*/sind) and the percent of virgin asphalt was developed for determination of virgin
asphalt content. This chart indicated a linear relationship between the logarithm of binder
shear stiffness and percent of virgin asphalt in a virgin and RAP binder blend. Based on
previous field experience and data obtained from this study, the following
recommendations were made for selection of PG asphalt binder used in mixes containing
recycled asphalt pavement (RAP):
· The selected PG grade of the virgin asphalt binder should be the same as the
Superpave-specified PG grade for mixes containing 15% or less RAP.
· The selected PG grade of the virgin asphalt binder should be one grade lower
(both high and low temperature grades) than the Superpave-specified grade for
mixes containing 15 to 25% RAP.
· A specific (prepared for a particular virgin and recovered asphalt) blending
chart should be used to select the high temperature grade for mixes containing
more than 25% RAP. The low temperature grade should be at least one grade
lower than the binder grade specified by Superpave.
· A high temperature sweep blending chart G*/sind = 1 is recommended over
the high temperature sweep blending chart G*/sind = 2.2 because it does not
require the Rolling Thin Film Oven Test (RTFOT) to be run before DSR
testing.
7
In 1997, the National Cooperative Highway Research Program (NCHRP) funded
Project 9-12 entitled “Incorporation of Reclaimed Asphalt Pavement in the Superpave
System”. Partial results of this project are presented in a 1999 Transportation Research
Board (TRB) paper entitled “Recovery and Testing of RAP Binders from Recycled
Asphalt Pavements”(4). These results refer to the variables in extraction and recovery
methods, and conclude that there are:
· Significant variations in properties of extracted asphalt binder with use of
different solvents and extraction and recovery methods.
· Insignificant changes in the blending of RAP binders due to the aging of the
recovered binders.
· Insignificant changes in RAP aggregate gradation with use of different
solvents and extraction and recovery methods.
In 1998, The University of Texas at Austin presented a report entitled “Effect
of Reclaimed Asphalt Pavement on Binder Properties Using the Superpave System”(5).
Based on results of extensive testing of binders and use of the Superpave binder
specification, this report proposed a new procedure for determination of the percentage of
RAP that can be used in construction of asphalt concrete pavements. Asphalt grade
PG58-28 is used instead of PG64-22, and the range of allowable RAP addition is as
determined for grade PG64-22. Calculation of minimum RAP addition is based on
unaged and aged virgin and RAP asphalt blends meeting the G*/sind specification at
64°C. Determination of maximum RAP addition is based on meeting the specification
for binder creep stiffness and creep rate at –12°C. Finally, at 25°C, the G*sind value is
checked for compliance with the 5000 kPa requirement. This last requirement determines
maximum RAP addition that is allowable and will not cause premature fatigue cracking
in a constructed pavement.
2.3. ADDITIONAL CONSIDERATIONS
The determination of allowable RAP content in all of the above-mentioned studies
8
is based on asphalt binder testing, and does not consider the durability of recycled asphalt
mixes. PG binder testing is not only time consuming but also requires expensive
equipment. Since both time and specialized equipment present a constraint at the typical
asphalt laboratory, there is still a need for development of a simple method to determine
optimum RAP addition to an HMA mix. Asphalt binder exposed to heat, light, and air
hardens. This hardening process results from irreversible oxidation reactions that occur in
the asphalt molecules, and to a lesser extent from a loss of volatile oils (which can be
reversed). Susceptibility to oxidation is asphalt-specific, and some asphalt binders oxidize
faster and become harder than others. Hardened asphalt binder becomes brittle, more
viscous, less ductile, and consequently results in cracking of the asphalt concrete
pavement. This fact has to be taken into consideration when introducing the recycled
asphalt pavement into new HMA. For years, the amount of RAP that should be allowed
in new HMA was an unresolved controversy. From the environmental and initial cost
point of view, it is desirable to use as much RAP as is available (no waste to haul to land
fill). From the pavement long-term performance point of view, use of RAP has to be
limited to the amount that will not have a detrimental effect on pavement longevity.
Developed by SHRP the Performance Grade asphalt specification introduced new tests
and requirements for asphalt binder. These tests allow the user to predict performance of
binder not only during construction but also after years of service, and could be used to
determine an optimum RAP content in newly-produced asphalt concrete mixes.
Unfortunately, SHRP testing methods do not address the durability of the HMA or
RAP/HMA mixes; therefore, there is a need to find an easy test method that will correlate
with data obtained from SHRP binder testing.
Moisture damage to HMA pavement typically causes significant increases in
distress levels and diminishes durability and service life. Although SHRP initiated several
research projects to develop new methods for predicting moisture damage susceptibility
in the mix design process, none of them provided a more accurate prediction than the
existing AASHTO T283. According to this test procedure the loose HMA is aged for 16
hours at 60°C. Six test specimens of 100mm diameter and 64mm height are impact
9
compacted to 7±1 percent air void content, conditioned at room temperature for 72 to 96
hours, and divided into two groups of three. This division is governed by a requirement of
mean value of air void content to be equal between the two subsets. One subset is placed
under water, saturated to a level between 55 and 80%, subjected to a minimum 16 hours
freezing (at –18°C), and thaw-soaked for 24 hours in a water-bath at 60°C. Finally, a
specimen is and cooled in water bath at 25°C for 2 hours. The removal of the test
specimens from the water bath is followed by performance of indirect tensile strength
testing. The resultant strength values are compared to those obtained from unconditioned
specimens. The Superpave volumetric design method uses test specimens that have
150mm diameter and 115mm height and are prepared by a gyratory compactor. For
AASHTO T283, SHRP recommended that the specimens be prepared from a mix aged
for 4 hours at 135°C prior to compaction, be 95mm high, and be compacted to7±1% air
void content. The change in test specimen size, method of conditioning, and compaction
method introduced significant variation of the testing conditions prescribed in the original
AASHTO T283 test method, and had to be addressed. Published in 2000, the National
Cooperative Highway Research Program Report No. 444, “Compatibility of a Test for
Moisture-Induced Damage with Superpave Volumetric Mix Design” (6), addresses the
problem of compatibility of AASHTO T283 with Superpave volumetric design. The
findings from this research indicate that:
· The method of loose- and compacted-mix aging influences tensile strength of
conditioned and unconditioned specimens.
· The tensile strength of unconditioned specimens is not consistently different
for Marshall (100mm diameter) and Gyratory (150mm diameter) specimens.
· The tensile strength of conditioned specimens is statistically different for
Marshall (100mm diameter) and Gyratory (150mm diameter) specimens.
· Level of saturation of the conditioned specimens has little effect on their
tensile strength.
The report recommends that a tensile strength ratio criteria developed for Marshall test
10
specimens be used for Gyratory test specimens having 150mm diameter. The report also
proposes changes to the AASHTO T283 and SHRP recommendations. The new
AASHTO T283 test procedure proposes a new aging procedure for test specimens
prepared by Gyratory compactor.
A research project “Durability of Recycled Asphalt Concrete Surface Mixes” (7)
conducted in 1994-1996 came with the new concept of absorbed energy. According to
this concept, every material has to absorb some level of energy prior to reaching its
failure point. In the indirect tensile strength test (used in AAHTO T283), this energy was
estimated by the following formula:
E = 0.5xPxd
where: E – energy (J);
P – ultimate load (N);
d – vertical deformation of the test specimen at the ultimate load (mm).
Using this principle and comparing results from the AASHTO T283 test with
results obtained from asphalt binder performance testing should bring a correlation
between these tests. Consequently, it should be possible to predict longevity of asphalt
pavement containing RAP by performing only AASHTO T283, and on the basis of the
results of this test determine the optimum RAP content for an asphalt concrete mixture.
The use of the absorbed energy principle appears to be very promising, but needs
some additional refinement due to the fact that the “Durability of Recycled Asphalt
Concrete Surface Mixes” study was limited to RAP from only two sources, and used
100mm diameter/64mm height specimens compacted by Marshall compactor.
11
CHAPTER 3
RESEARCH METHODS
3.1. RESEARCH ASSUMPTIONS
Laboratory experiments were conducted with the assumptions that:
· Virgin binder and binder from the recycled asphalt pavement (RAP)
completely blend with each other, producing a new rejuvenated binder.
· The new rejuvenated binder has uniform physical and chemical properties
that can be predicted by binder testing.
· Binder content of the bituminous concrete mixture is expressed as the sum of
virgin binder and RAP binder.
· Virgin aggregate and aggregate from RAP completely blend with each
other, producing a uniform mix. In order to meet the overall gradation
requirements for the mix, gradation of virgin aggregate is adjusted as
needed for the RAP aggregate gradation and RAP content.
3.2 EXPERIMENTAL DESIGN
A total of twenty intermediate bituminous concrete mixes were evaluated in
this project. The mixes consisted of six recycled asphalt pavements (RAP), four levels
of RAP addition (0, 10, 20, and 30%), and two types of aggregate (crushed gravel and
limestone). Virgin binder graded PG 64-28 was used in all mixes.
Table 3.1 presents the test matrix for mix variables.
12
Table 3.1. Test matrix for mix variables
Aggregate Type RAPSource
RAP Content, %
LimestoneA
010 20 30
B 10 20 30C 10 20 30
GravelD
010 20 30
E 10 20 30F 10 20 30
3.3. WORK PLAN
3.3.1. Examination of Asphalt Binders
Virgin binder was mixed with recovered, by use of trichloroethylene, binder
from RAP. The binder recovery process consisted of extraction and Abson recovery.
Four levels (0, 10, 20, and 30%) of recovered binder addition were examined for six
RAP sources. All blended binders were aged by the Rolling Thin Film Oven Test
(RTFOT) and Pressure Aging Vessel (PAV) procedures, and subjected to Dynamic
Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) testing. The results of
these tests established the reference properties of the examined binders.
3.3.2. Development of Bituminous Concrete Aging Procedure
The optimum binder content was determined for each of the twenty bituminous
concrete test mixtures. Eight selected mixes in a loose (uncompacted) form were
subjected to the following aging procedures:
· Short-term aging (2 hours conditioning at 135°C)
13
· Long-term aging (2 hours conditioning at 135°C, followed by 100°C
conditioning)
· Long-term aging (2 hours conditioning at 135°C, followed by 120°C
conditioning)
To prepare the specimens for aging virgin asphalt binder was mixed with
aggregate and RAP, and placed in a pan having dimensions 16 by 17 inches. The total
weight of a bituminous concrete specimen placed in one pan was about 4000g, giving a
resultant thickness of the loose mix layer of 22mm.
Binder was recovered from the short-term aged mixes (2 hours at 135°C) and
subjected to DSR and BBR testing. During long-term aging, the mixes were sampled
at two different times for extraction and Abson recovery. The first long-term aging
sampling took place after 4 hours for specimens conditioned at 100°C, and after 3
hours for specimens conditioned at 120°C. The recovered binder was tested by the
DSR and BBR procedures. The second long-term aging sampling took place after 6
hours for specimens conditioned at 100°C, and after 5 hours for specimens conditioned
at 120°C. Curves were created to find the relationship between properties determined
by DSR/BBR and the aging time. Using these curves the duration of an aging process
was determined. One long-term aging procedure was selected and all mixes were aged
according to it. Aging was to be terminated at the time when expected values resulting
from DSR and BBR tests were similar to reference properties determined during the
initial binder testing. Upon completion of the aging process, samples were taken for
extraction and Abson recovery. The recovered binder was subjected to DSR and BBR
testing.
3.3.3. Examination of Bituminous Concrete Mixes
Specimens made from bituminous concrete test mixes, aged according to the
selected aging procedure were subjected to volumetric analysis, and tested for moisture
damage durability and unconfined compressive strength.
14
15
3.4. PROGRAM OF TESTING
Samples of asphalt binder, aggregate, recycled asphalt pavement (RAP), loose
bituminous concrete, and compacted bituminous concrete were tested in this project.
3.4.1. Asphalt Binder
Samples of virgin binder and blended virgin/recovered binder were subjected
to the following tests:
· AASHTO T 240, “Effect of Heat and Air on a Moving Film of Asphalt
(Rolling Thin Film Oven Test)”.
· AASHTO Provisional Standard PP1-93, “Practice for Accelerating Aging
of Asphalt Binder Using a Pressurized Aging Vessel”.
· AASHTO Provisional Standard TP5-93, “Test Method for Determining the
Rheological Properties of Asphalt Binder Using a Dynamic Shear
Rheometer”.
· AASHTO Provisional Standard TP1-93, “Test Method for Determining the
Flexural Creep Stiffness Using the Bending Beam Rheometer”.
3.4.2. Aggregate
Samples of virgin aggregate and aggregate recovered from RAP were
subjected to the following tests:
· ASTM C 127, “Specific Gravity and Absorption of Coarse Aggregate”.
· ASTM C 128, “Specific Gravity and Absorption of Fine Aggregate”.
· ASTM C 136, “Sieve Analysis of Fine and Coarse Aggregate”.
· ASTM C 131, “Resistance to Degradation of Small-Size Coarse Aggregate
by Abrasion and Impact in the Los Angeles Machine”
16
3.4.3. Recycled Asphalt Pavement (RAP) and Loose Bituminous Concrete
Specimens
Samples of asphalt binder were obtained from RAP and loose bituminous concrete
mixes using the following procedures:
· ASTM D 2172, “Test Method for Quantitative Extraction of Bitumen from
Bituminous Paving Mixtures”.
· ASTM D 1856, “Test Method for Recovery of Asphalt from Solution by
Abson Method”.
3.4.4. Compacted Bituminous Concrete Specimens
The following methods were used to test compacted bituminous concretespecimens:
· ASTM D 2726, “Bulk Specific Gravity and Density of Compacted
Bituminous Mixtures Using Saturated Surface-Dry Specimens”.
· ASTM D 2041, “Theoretical Maximum Specific Gravity of Bituminous
Paving Mixtures”.
· AASHTO Designation TP4-94, “Preparing and Determining the Density of
Hot Mix Asphalt (HMA) Specimens by Means of SHRP Gyratory
Compactor”.
· AASHTO T 283, “Resistance of Compacted Bituminous Mixture to
Moisture Induced Damage”
· ASTM D 1074, “Compressive Strength of Bituminous Mixtures”
.
17
CHAPTER 4
TEST RESULTS AND ANALYSIS
The data collected in this study is summarized in Tables 4.1 through 4.28 and
Figures 4.1 through 4.30.
4.1 LABORATORY TESTING OF AGGREGATE AS DELIVERED
Table 4.1 presents results of gradation tests that were performed on aggregate
as delivered.
Table 4.1. Gradation of aggregate as delivered (% passing).
SieveSize(mm)
Gravel Mix Limestone Mix
#57 #8 Sand
#57 #8 Manufactured Sand
37.5 100 100 100 100 100 100
25.0 92.5 100 100 99.0 100 100
19.0 57.3 100 100 61.0 100 100
12.5 15.2 100 100 7.0 100 100
9.5 2.9 91.
2
100 1.0 91 100
4.75 1.3 5.5 99.8 1.0 27 100
2.36 1.0 1.8 89.3 1.0 3 96.0
1.18 1.0 0.9 62.2 1.0 1 62.0
0.60 1.0 0.7 33.9 1.0 1 36.0
0.30 1.0 0.6 15.9 1.0 1 18.0
0.15 1.0 0.6 6.8 1.0 1 6.0
0.075 1.0 0.6 3.5 1.0 1 2.4
18
Delivered aggregates were sieved into individual sizes and later blended to meet
441-T2 (intermediate mix) ODOT specifications.
4.2. LABORATORY TESTING OF RECYCLED ASPHALT PAVEMENT
(RAP)
Table 4.2 presents gradation (percent passing) and binder content of recycled
asphalt pavements (RAPs) that were used in the study. Table 4.3 presents specific
gravity data of aggregates recovered from RAPs.
Table 4.2. Gradation and binder content of RAP (% passing).
Sieve Size(mm)
RAPA
RAPB
RAPC
RAPD
RAPE
RAPF
25.0 100 100 100 100 100 100
19.0 99 100 99 98 100 99
12.5 96 99 98 90 99 98
9.5 92 97 94 82 95 95
4.75 67 69 70 61 70 73
2.36 49 50 51 49 49 54
1.18 36 37 40 38 36 43
0.60 26 26 30 27 26 32
0.30 17 17 17 13 16 22
0.15 11 11 9 7 9 13
0.075 8.4 7.1 6.1 5.1 6 8.6
BinderContent, %
5.7 5.8 6.3 5.3 5.5 5.8
Table 4.3. Specific gravity data of aggregates recovered from RAP.
Sieve Size (mm) RAPA
RAPB
RAPC
RAPD
RAPE
RAPF
19
Bulk SpecificGravity
2.518 2.571 2.533 2.509 2.494 2.530
ApparentSpecific Gravity
2.656 2.732 2.653 2.596 2.598 2.638
Absorption 2.1 2.4 1.8 1.4 1.6 1.6
4.3 LABORATORY TESTING OF AGGREGATE BLENDS
Tables 4.4 and 4.5 present, respectively, gradation requirements and specific
gravity test results of aggregate blends.
Table 4.4. Aggregate gradation and specification requirements (% passing).
Sieve Size(mm)
LimestoneMix
GravelMix
Specification Requirementsas for ODOT 441 type 2
25.0 100 100 95 – 100
19.0 99 95 85 – 100
12.5 92 81 65 – 85
9.5 83 72
4.75 38 51 35 – 60
2.36 23 40 25 – 48
1.18 15 31 16 – 36
0.60 10 20 12 – 30
0.30 7 10 5 – 18
0.15 4 6 2 – 10
0.075 3.5 4.5
The limestone and gravel aggregate gradations (columns 2 and 3 of Table 4.4)
were kept constant regardless of the level of RAP addition for each asphalt concrete
20
test mix. Consequently, gradation of the virgin aggregate was adjusted to accommodate
changes caused by varying additions of RAP.
21
Table 4.5. Specific gravity of virgin aggregate and RAP aggregate blends.
Mix Type BulkSpecificGravity
Apparent SpecificGravity
Absorption(%)
Limestone; No RAP 2.626 2.740 1.7
Limestone; 10% RAP A 2.621 2.728 1.5
Limestone; 20% RAP A 2.620 2.714 1.3
Limestone; 30% RAP A 2.615 2.715 1.4
Limestone; 10% RAP B 2.640 2.737 1.2
Limestone; 20% RAP B 2.634 2.732 1.4
Limestone; 30% RAP B 2.634 2.730 1.4
Limestone; 10% RAP C 2.634 2.720 1.2
Limestone; 20% RAP C 2.631 2.717 1.2
Limestone; 30% RAP C 2.613 2.710 1.2
Gravel; No RAP 2.546 2.715 2.5
Gravel; 10% RAP D 2.551 2.702 2.1
Gravel; 20% RAP D 2.534 2.691 2.2
Gravel; 30% RAP D 2.529 2.684 2.2
Gravel; 10% RAP E 2.533 2.702 2.5
Gravel; 20% RAP E 2.534 2.698 2.4
Gravel; 30% RAP E 2.539 2.687 2.2
Gravel; 10% RAP F 2.553 2.703 2.1
Gravel; 20% RAP F 2.554 2.703 2.2
Gravel; 30% RAP F 2.555 2.695 2.0
22
4.4 DESIGN OF JOB MIX FORMULAS AND VOLUMETRIC
PROPERTIES OF TRIAL MIXES
All Job Mix Formulas were determined by the volumetric Gyratory mix design
method. Aggregate blends were prepared to satisfy the gradation requirements
presented in Table 4.4. At least four levels of binder content were examined for each
aggregate blend, and a minimum of two test specimens were made at each binder
content.
Aggregate was heated to 180°C and mixed with RAP that was at room
temperature. After mixing, the aggregate/RAP blend was placed into the oven set at
180°C. After 20 minutes of reheating, the aggregate/RAP blend was mixed with
asphalt binder heated to 135°C. The aggregate/RAP/binder mix was aged for two
hours at 135°C before compaction. The number of gyrations used for initial, design,
and maximum compaction were selected at 8, 100, and 160 gyrations, respectively.
Test specimens used for the determination of the maximum theoretical specific gravity
(for the purpose of mix design) were aged for two hours at 135°C.
Table 4.6 presents the optimum total binder content and the value of the
maximum theoretical specific gravity (at the optimum binder content).
Initial determination of optimum binder content in the Superpave mix design
process is based on volumetric analysis of bituminous concrete test specimens
compacted by SHRP Gyratory compactor. Air voids analysis during compaction
process is one of the elements of optimum binder content determination. At the
selected optimum asphalt binder content, the bituminous concrete mix has to meet the
4 % air voids requirement at N design and satisfy two more air voids criteria. Air voids
at N initial have to be more than 11 %, and air voids at N max have to be more than 2
%.
23
Table 4.6. Optimum total binder content and dry maximum theoretical specific gravity of bituminous concrete mixes.
Mix Type Optimum Total Binder
Content % (1)
Maximum Theoretical
Specific Gravity
Limestone; No RAP 5.5 2.522
Limestone; 10% RAP A 5.3 2.508
Limestone; 20% RAP A 5.4 2.515
Limestone; 30% RAP A 5.4 2.498
Limestone; 10% RAP B 5.5 2.523
Limestone; 20% RAP B 5.6 2.511
Limestone; 30% RAP B 5.6 2.518
Limestone; 10% RAP C 5.7 2.500
Limestone; 20% RAP C 6.0 2.489
Limestone; 30% RAP C 6.0 2.505
Gravel; No RAP 3.7 2.533
Gravel; 10% RAP D 3.7 2.521
Gravel; 20% RAP D 3.7 2.523
Gravel; 30% RAP D 3.8 2.523
Gravel; 10% RAP E 3.5 2.528
Gravel; 20% RAP E 3.4 2.519
Gravel; 30% RAP E 3.7 2.516
Gravel; 10% RAP F 3.8 2.526
Gravel; 20% RAP F 3.8 2.523
Gravel; 30% RAP F 4.0 2.529
(1) percent by total weight of aggregate.
24
Table 4.7 presents air voids analysis results for the asphalt concrete test mixes at
the optimum binder contents.
Table 4.7. Air voids data determined for mixes at the optimum binder contents.
Mix TypeOptimu
mBinderContent
Air Voids at N initial Air Voids at N max
Actual Minimum
Required
Actual Minimum
RequiredLimestone; No RAP 5.5 17.2 11.0 2.4 2.0
Limestone; 10% RAPA
5.3 16.3 11.0 2.0 2.0
Limestone; 20% RAPA
5.4 16.5 11.0 2.0 2.0
Limestone; 30% RAPA
5.4 16.5 11.0 2.4 2.0
Limestone; 10% RAPB
5.5 16.6 11.0 2.3 2.0
Limestone; 20% RAPB
5.6 16.7 11.0 2.2 2.0
Limestone; 30% RAPB
5.6 16.3 11.0 2.1 2.0
Limestone; 10% RAPC
5.8 16.6 11.0 2.0 2.0
Limestone; 20% RAPC
6.0 17.3 11.0 2.5 2.0
Limestone; 30% RAPC
6.0 16.4 11.0 2.1 2.0
Gravel; No RAP 3.7 11.4 11.0 3.1 2.0
Gravel; 10% RAP D 3.7 11.0 11.0 2.8 2.0
Gravel; 20% RAP D 3.7 11.1 11.0 3.1 2.0
Gravel; 30% RAP D 3.8 11.0 11.0 3.1 2.0
Gravel; 10% RAP E 3.5 11.5 11.0 3.1 2.0
Gravel; 20% RAP E 3.4 11.3 11.0 3.3 2.0
25
Gravel; 30% RAP E 3.7 11.3 11.0 3.1 2.0Gravel; 10 % RAP F 3.8 11.6 11.0 3.2 2.0
Gravel; 20% RAP F 3.8 11.3 11.0 3.0 2.0
Gravel; 30% RAP F 4.0 11.1 11.0 3.0 2.0
The data presented in Table 4.7 shows that actual air voids at N initial range
from 16.3 to 17.3 % for mixes with limestone coarse aggregate, and from 11 to 11.6 %
for mixes with gravel coarse aggregate. This means that all mixes satisfied the 11 %
air voids requirement at initial number of gyrations. Air voids content at N max of all
examined mixes ranged from 2.0 to 3.3 % and satisfied the final air voids requirement.
Table 4.8 presents average values of voids in mineral aggregate (VMA) and
voids filled with asphalt (VFA) at N initial, N design, and N max for mixes at optimum
asphalt cement content. Voids in mineral aggregate (VMA) values were calculated
using dry bulk specific gravity of aggregates.
Table 4.8. Volumetric analysis of mixes at optimum binder content – VMA and VFA data at N initial, N design, and N max.
Aggregate Composition VMA VFA
N
initial
N
design
N
max
N
initial
N
design
N
max
Limestone; No RAP 24.4 12.8 11.1 30.3 66.6 78.5
Limestone; 10% RAP A 25.7 14.7 13.1 36.4 73.7 84.7
Limestone; 20% RAP A 24.6 13.2 11.5 31.9 67.9 81.7
Limestone; 30% RAP A 24.5 12.9 11.2 31.5 67.9 79.1
Limestone; 10 % RAP
B
24.5 13.2 11.5 32.0 68.5 80.3
Limestone; 20 % RAP
B
24.7 13.6 11.8 31.4 65.7 77.1
26
Limestone; 30 % RAP
B
24.2 13.1 11.3 32.1 69.0 81.0
Limestone; 10% RAP C 25.1 13.8 12.1 34.0 71.7 83.6
Limestone; 20% RAP C 26.2 14.8 13.0 34.0 69.5 80.5
Limestone; 30% RAP C 25.3 14.1 12.3 34.5 71.1 83.0
Gravel; No RAP 14.9 8.0 7.1 25.0 50.1 57.2
Gravel; 10% RAP D 15.1 8.2 7.4 28.7 57.0 64.0
Gravel; 20% RAP D 14.6 7.8 7.0 25.1 50.9 57.9
Gravel; 30% RAP D 14.4 7.5 6.7 21.9 45.1 51.4
Gravel; 10% RAP E 15.3 8.2 7.2 24.9 50.5 57.7
Gravel; 20% RAP E 14.8 8.0 7.2 24.8 49.0 55.9
Gravel; 30% RAP E 15.1 8.1 7.2 27.0 54.7 61.6
Gravel; 10% RAP F 15.8 8.9 7.9 25.7 50.2 57.0
Gravel; 20% RAP F 15.7 8.7 7.8 27.0 53.0 59.6
Gravel; 30% RAP F 15.1 8.3 7.3 26.0 51.3 58.3
All of the mixes investigated in this study were intermediate courses and as
such should have had a minimum of 13% VMA at Ndesign. All mixes with limestone
coarse aggregate fulfilled this requirement. However, Superpave specifies minimum
values for VMA at the designed 4 % air void content as a function of the nominal
maximum size of aggregate, which is defined as “one size larger than the first sieve to
retain more than 10 percent of aggregate”. Though both mix gradations were
considered intermediate, the gradation of the limestone mix was finer than the
gradation of the gravel mix. Consequently, the nominal maximum aggregate size in
this study was 12.5mm for limestone mixes and 19.0mm for gravel mixes. According
to Superpave requirements, a minimum VMA content at Ndesign should be 14 % for
mixes with 12.5mm, and 13% for 19.0mm nominal maximum size aggregate. As a
result, only three of the limestone mixes (10% RAP A, and 20 and 30% of RAP C)
27
satisfied the VMA requirement at Ndesign.
The acceptable range of VFA at Ndesign depends on the design traffic level.
Mixes studied in this project were designed for traffic levels of 10-30 million ESALs
and therefore should have 65-75 % VFA. All of the limestone mixes had VFA contents
in the required range.
None of the mixes with gravel coarse aggregate met the specifications for VMA
or VFA content. The explanation may be found in the fact that the initial JMF for the
gravel mix was prepared using the Marshall mix design method. Test specimens made
from this JMF and compacted by Marshall compactor fulfilled all volumetric
requirements. However, Gyratory compaction was used to prepare all test specimens in
this study. The fact that VMA and VFA requirements of the mix were not met when
Gyratory compaction was employed would suggest that VMA and VFA characteristics
are dependent not only on aggregate shape and gradation, but also at least partially on
method of compaction.
4.5. PROPERTIES OF VIRGIN BINDER AND BLENDS OF VIRGIN AND
RECOVERED (FROM RAP) BINDERS.
Seven asphalt binders were used in this study: one virgin binder and six binders
that came from RAP. Levels of each RAP addition were 10, 20, and 30%.
The Dynamic Shear Rheometerm(DSR) test is used to obtain values of
complex shear modulus (G*) and phase angle (d) for asphalt binders. These test values
are commonly used to calculate two measures: the rutting factor (G* divided by sind),
28
and the fatigue cracking factor (product of G* and sind). These measures provide a
more complete picture of the behavior of binder at pavement service temperature so
the temperature at which the DSR test is conducted is critical.
Tables 4.9 and 4.10 present average test results for DSR tests for mixes with
gravel and limestone aggregate, respectively. The superscript number in parenthesis
next to each reported value indicates the temperature at which the test was conducted.
(1) test temperature was 64°C
(2) test temperature was 70°C
(3) test temperature was 76°C
(4) test temperature was 22°C
The G*/sind value (called also a rutting factor) that is shown in the second
column of these tables relates to binder that has not been aged by Rolling Thin Film
Oven (RTFO) or Pressure Aging Vessel (PAV). This value of G*/sind represents the
high- temperature viscous component of the overall binder stiffness. The Superpave
performance graded (PG) asphalt specification placed a minimum requirement for
G*/sind value to be greater than 1.0 kPa for non-aged asphalt binders.
The G*/sind test value in the third column represents data for binder that was
aged according to RTFO procedure. The Superpave PG asphalt specification placed a
minimum requirement for this value to be greater than 2.2 kPa.
Intermediate temperature stiffness - G*sind (called also a fatigue cracking
factor) value shown in the fourth column represents test data for binder that was aged
according to RTFO and PAV procedures and tested at 22°C. For the binder to
effectively resist fatigue cracking the Superpave PG binder specification placed a
requirement for G*sind values to be less than 5,000 kPa.
29
Table 4.9. Dynamic Shear Rheometer test results for binders used with gravel aggregates.
20% RAP C; 80% Virgin Binder 6,724 43.4 4,62430% RAP C; 70% Virgin Binder 7,481 44.9 5,284* Value adjusted for 22°C** No original data available*** Value has to be erroneous.
The values of the complex shear modulus (G*) presented in Tables 4.11 and
4.12 vary from 2,884 to 9,300 kPa. Values of cracking factor (G*sind) vary from 2,522
to 7,050 kPa. The G* and G*sind parameters are greater for the binders containing
RAP than for those containing no RAP, and increase consistently with an increased
RAP content. Values of phase angle (d) vary from 49.0 to 43.0 degrees and decrease as
RAP content increases indicating that with greater RAP content binders are becoming
more viscous. The source of RAP seems to have much more limited influence on these
values.
Tables 4.13 and 4.14 present test data obtained by performing Bending Beam
Rheometer (BBR) test for mixes with gravel and limestone aggregate, respectively.
The BBR test was conducted at – 18°C and – 24°C.
The Bending Beam Rheometer (BBR) test measures creep stiffness, an
indicator of tensile strength of the asphalt binder. Binder that has high creep stiffness is
likely to be brittle at low temperatures and to experience low temperature cracking. To
prevent low temperature cracking, the maximum creep stiffness is limited to 300MPa.
32
Table 4.13. Average Bending Beam Rheometer test results for binders used withgravel aggregate.
5. Kennedy T.W., Tam, W.O., Solaimanian M., “Effect of Reclaimed AsphaltPavement on Binder Properties Using the Superpave System”, Center forTransportation Research, Bureau of Engineering Research, The University ofTexas at Austin. Research Report 1250-1, September 1998.
6. Epps Jon A., Sebaaly, Peter E., Penarande, Jorge, Maher, Michelle R., McCann,Martin, B., and Hand, Adam, J., “Compatibility of a Test for Moisture-InducedDamage with Superpave Volumetric Mix Design”, National Cooperative HighwayResearch Program NCHRP Report No. 444.
7. Abdulshafi Osama, Kedzierski Bozena, Fitch Michael G., “Durability of RecycledAsphalt Concrete Surface Mixes”, FHWA Report FHWA/OH-97/003.
8. Barksdale Richard D., “The Aggregate Handbook”, National Stone Association,1996.
9. Cominsky R., Leahy R.B., Harrigan E.T., “Level One Mix Design: MaterialSelection, Compaction and Conditioning”, SHRP-A-408, 1994.
66
APPENDIX
Proposed Procedure for
Determination of Recycled Asphalt Pavement (RAP) Content for aBituminous Concrete Mix Based on Expected Mixture Durability
67
Proposed Procedure for
Determination of Recycled Asphalt Pavement (RAP) Content for aBituminous Concrete Mix Based on Expected Mixture Durability
1. SCOPE1 This method covers laboratory preparation and testing of bituminous concrete specimens and
measurement of the value of absorbed energy needed to bring the specimen to failure. The resultsof this test may be used to select optimum content of recycled asphalt pavement in the newlydesigned bituminous mixture by way of predicting its long-term durability.
2 The values stated in customary units are to be regarded as standard.
2. REFERENCED DOCUMENTS1 AASHTO Standards:
TP 4 Preparing and Determining the Density of Hot Mix Asphalt (HMA) Specimensby Means of SHRP Gyratory Compactor.
T 283 Resistance of Compacted Bituminous Mixture to Moisture InducedDamage.
T 269 Percent Air Voids in Compacted Dense and Open Bituminous Paving Mixtures.2 ASTM Standards
D 2726 Bulk Specific Gravity and Density of Compacted Bituminous Mixtures UsingSaturated Surface-Dry Specimens.
D 2041 Theoretical Maximum Specific Gravity of Bituminous Paving Mixtures.D 3549 Test Method for Thickness and Height of Compacted Bituminous Paving
Mixture Specimens.
3. SIGNIFICANCE AND USE1 As noted in the scope, the proposed method is intended to evaluate the effects
of a recycled asphalt pavement (RAP) content on long-term durability of a bituminousconcrete mixture and may be used to select an optimum RAP content.
4. SUMMARY OF METHOD4.1 A set of six test specimens is prepared for each level of RAP addition. Suggested RAP
additions are at 0, 10, 20, and 30%. Each set of specimens is divided into two subsets to betested for indirect tensile strength. During the testing, load and deformation data arecontinuously collected, and the resultant energy needed to fail a specimen is calculated. Onesubset of test specimens is tested in dry condition. The other subset prior to testing issubjected to vacuum saturation, followed by a freeze cycle and warm water soaking.Numerical indices of absorbed energy are computed from the test data obtained for the dryand conditioned subsets of specimens. The mix that has the greatest index of absorbed energyis selected as having the optimum RAP content (assuming the mix does not exhibit anydisqualifying characteristics).
5. APPARATUS5.1 Equipment for preparing and compacting test specimens in accordance with
AASHTO TP4.5.2. Vacuum container, preferably type E, from ASTM D 2041 and vacuum pump with manometer
or vacuum gauge.5.3 Balance and water bath as in ASTM D 2726.5.4 Water bath capable of maintaining a temperature of 140±1.8°F (60±1°C).5.5 Freezer capable of maintaining a temperature of 0±5°F (-18±3°C).
68
5.6 Vacuum container (possibly a desiccator with a lid with valve) large enough to
accommodate a test specimen having 6-inch diameter and 4-inch height, and providing an
additional 1” to assure proper water level.
5.7 10-mL graduated cylinder5.8 Aluminum pans having a surface area of 240-290 square inches in the bottom, and a depth of
approximately 1 inch.5.9 Forced air draft ovens with a 212 to 360°F (100 to 180°C) range, and capability to maintain a
temperature with accuracy of ± 3.6°F (2°C).5.10 Loading jack or mechanical or hydraulic testing machine able to provide a
range of accurately controllable rates of vertical deformation of 2 inches per minute, andequipped with recorders capable to continuously measure and collect load and deformationdata.
5.11 Steel loading strips with a concave surface having a radius of curvature equal to the nominalradius of the test specimen, i.e. 6 inches (152.4mm). These strips should be 0.75 inches(19.05mm) wide and 4.2 inches (106.7mm) long. The length of the loading strips shall berounded by grinding.
6. PRINCIPLES OF THE MIX DESIGN PROCESS6.1 Virgin binder and a binder from the recycled asphalt pavement (RAP) completely blend with
each other producing a new rejuvenated binder.6.2 The new rejuvenated binder has uniform physical and chemical properties that can be
predicted by binder testing.6.3 Binder content of the bituminous concrete mixture is expressed as a sum of virgin and RAP
binder.6.4 Virgin aggregate and aggregate from RAP completely blend with each other, producing a
uniform mix. In order to meet the overall gradation requirements for the mix, gradation ofvirgin aggregate is adjusted as needed for the RAP aggregate gradation and RAP content.
7. PREPARATION OF LABORATORY MIXED, LABORATORY COMPACTED TEST SPECIMENS.
7.1 For every RAP content make at least six specimens for each test, half to be
tested dry and the other half to be tested after partial saturation, a freeze-thaw cycle, and
moisture conditioning.
Note 1It is recommended that two additional specimens for the set be prepared. These specimens canthen be used to establish the vacuum saturation techniques given in Section 9.3.
7.2 Specimens of 6 inches (150mm) diameter and 3.75 inches (95mm) thickness should beprepared.
3 Each specimen should be mixed separately.4 After mixing, the bituminous mixture shall be placed in an aluminum pan (having a surface
area 200-250 square inches in the bottom and a depth of approximately 1 inch) forconditioning. Conditioning of mix shall consist of pre-heated oven curing at 275±3.8°F(135±2°C) for two hours, followed by pre-heated oven curing at 212±3.8°F (100±2°C) for 4.5hours. Half an hour prior to compaction, the mix shall be placed in an oven pre-heated to thecompaction temperature. The pans should be placed on spacers in the ovens that have shelvesthat are not perforated.
69
5 Compact the specimen in accordance to AASHTO TP 4. The mixture shall be compacted to7±1% air voids. This level of air voids can be obtained by adjusting the number of gyrations.The exact procedure must be determined experimentally for each mixture before compactingthe test specimens.
6 After extraction from the mold, the test specimens shall be stored at room temperature for 24hours.
8. EVALUATION OF TEST SPECIMENS AND GROUPING8.1 Determine theoretical maximum specific gravity of mixture in accordance
with ASTM D 2041.
8.2 Determine specimen thickness and diameter in accordance with ASTM D
3549.
8.3 Determine the bulk specific gravity of the specimen in accordance with ASTM
D 2726.
8.4 Calculate air voids in accordance with AASHTO T 269.8.5. On the basis of specimen volume and air voids content, calculate the
volume of air voids in cubic centimeters (I) by use of the following equation:
I = H*E/100
Where:
I – volume of air voids, cm³
H – air voids, %
E – volume of specimen, cm³.
8.6 Sort the test specimens into two subsets so that the average air voids contents
of the two subsets are approximately equal.
9. PRECONDITIONING OF TEST SPECIMENS9.1 One subset will be tested dry and the other will be partially saturated, subjected to freezing,
and water soaked before testing.9.2 The dry subset will be stored at room temperature until testing. The specimens shall be
wrapped with plastic or placed in a heavy-duty leak proof plastic bag. These specimens shallbe placed in a 77°C (25°C) water bath for a minimum of two hours before testing as describedin Section 10.
70
3 The other subset shall be conditioned as follows:1 Place the specimen in a vacuum container (preferably desiccator equipped with lid with
valve) supported above the container bottom by a spacer. Fill the container with distilledwater of room temperature so that the specimen has at least 1 inch of water above its topsurface. Apply vacuum of 10-26 inches Hg partial pressure) for a short time (5 minutes).Remove the vacuum and leave the specimen submerged for a short time (5-10 minutes).
2 Determine bulk specific gravity in accordance with ASTM D 2726.3 Calculate volume (J) of absorbed water in cubic centimeters by use of the following
equation:J = B’ – B
Where: J – volume of absorbed water, cm³
B’ – mass of saturated surface-dry specimen after partial vacuum saturation, gramsB – mass of surface-dry specimen prior to partial vacuum saturation, grams.
4 Determine the degree of saturation by comparing volume of absorbed water (J) withvolume of air voids (I) from section 8.5 with the following equation:
S = 100J/I Where: S – degree of saturation, % J – volume of absorbed water, cm³ I – volume of air voids, cm³.
If degree of saturation is between 55 and 80 %, proceed to section 9.3.6.5 If degree of saturation is less than 55%, repeat the procedure beginning with Section 9.3.1
using more vacuum and/or time. If volume of water is more than 80%, specimen has beendamaged and shall be discarded. Repeat the procedure with Section 9.3.1 using lessvacuum and/or time.
6 Cover each of the vacuum-saturated specimens tightly with plastic film. Place eachspecimen in a plastic bag containing 10mL of water and seal the bag. Place plastic bagscontaining the specimens in a freezer at 0±5°F (-18±3°C) for a minimum of 16 hours.Remove specimens from the freezer. Remove plastic bag and film. Place specimens into anet bag made of fabric with openings of a minimum 0.25 inches.
7 Place the specimens in a bath containing distilled water at 140±2°F (60±1°) for 24±1hours.
8 After 24±1 hours, remove specimens from water bath having temperature of 140±2°F(60±1°), and place them in a water bath of 77±1°F (25±0.5°C) for 2 hours. It may benecessary to add ice to the water bath to prevent the water temperature from rising above77°F (25°C). Not more than 15 minutes should be required for the water bath to reach77°F (25°C).
9 Remove the specimens from the water bath, and net bag, and test as described in Section10.
10. TESTING10.1 Remove the specimen from the 77°F (25°C) water bath and place betweentwo loading strips in the testing machine. Care has to be taken so that the load willbe applied along the diameter of the specimen. Apply the load to the specimen bymeans of a constant rate of movement of the testing machine head at 2 inches(50mm) per minute.10.2 During loading, measure and record continuously load and deformationdata. If continuous recording is not possible collect maximum load anddeformation data.
11. CALCULATIONS11.1 If data of load and deformation is collected continuously, make a graph
71
with load values marked on the y-axis, and resultant deformation marked onx-axis. Calculate the value of absorbed energy at failure, with the most possibleaccuracy, by determining value (surface) of the field between x and y axes andload-deformation curve. Divide the calculated value of absorbed energy at failureby a specimen thickness.11.2 If only maximum load and resultant deformation data is available,calculate the value of absorbed energy at failure using the following equation:
E = (0.5 x P x d)/t Where: E – absorbed energy at failure P – maximum load, lb d – specimen vertical deformation at the maximum load, inch t – thickness of specimen, inch11.3 Calculate the average absorbed energy at failure for each subset ofconditioned (Econditioned) and control (Econtrol) specimens.11.4 Calculate for each tested asphalt concrete mix the percentage of absorbedenergy using the following equation:
PER = Econditioned /Econtrol
Where: PER – percent of absorbed energy Econditioned – average level of absorbed energy for conditionedspecimens Econtrol – average level of absorbed energy for control specimens.11.5 Select the percentage of RAP addition at the maximum percentage ofabsorbed energy level as being an optimum RAP content for the bituminous mix,provided that the resultant mix does not exhibit any disqualifying characteristics.