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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

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Page 1: 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

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

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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

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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.

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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.

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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.

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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.

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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

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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

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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

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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.

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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.

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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)

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· 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.

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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”

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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”

.

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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

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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

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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

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test mix. Consequently, gradation of the virgin aggregate was adjusted to accommodate

changes caused by varying additions of RAP.

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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

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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

%.

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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.

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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

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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

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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)

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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),

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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.

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Table 4.9. Dynamic Shear Rheometer test results for binders used with gravel aggregates.

Binder Composition G*/sind (kPa) G*sind (kPa)

Non-aged RTFO aged RTFO andPAV aged

0% RAP; 100% Virgin Binder 1.420(1) 2.395(1) 2,522(4)

10% RAP D; 90% Virgin Binder 0.952(2) 4.451(1) 3,953(4)

20% RAP D; 80% Virgin Binder 1.355 (2) 3.040 (2) 4,562(4)

30% RAP D; 70% Virgin Binder 1.975 (2) 4.252 (2) 6,436(4)

10% RAP E; 90% Virgin Binder 1.505(1) 3.628(1) 3,518(4)

20% RAP E; 80% Virgin Binder 1.732(1) 5.183(1) 3,682(4)

30% RAP E; 70% Virgin Binder 1.264(2) 3.214(2) 5,200(4)

10% RAP F; 90% Virgin Binder 1.013(2) 2.024(2) 3,234(4)

20% RAP F; 80% Virgin Binder 1.220(2) 2.831(2) 3,971(4) 30% RAP F; 70% Virgin Binder 1.508(2) 3.378(2) 4,921(4)

The fatigue cracking factor (G*sind) was of special interest in this research

study, since a primary objective was to determine durability of the asphalt concrete

mixes. Being the result of multiplication of two distinct values the same number

expressing fatigue cracking factor for several binders does not necessarily mean that

they have the same elastic qualities. The binder with smaller value of d would be more

elastic and have better fatigue properties.

Table 4.10. Dynamic Shear Rheometer test results for binders used with limestoneaggregate.

Binder Composition G*/sind (kPa) G*sind (kPa)

Non-aged RTFO aged RTFO andPAV aged

0% RAP; 100% Virgin Binder 1.420(1) 2.636(1) 2,522(4)

10% RAP A; 90% Virgin Binder 1.785(1) 4.519(1) 4,395(4)

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20% RAP A; 80% Virgin Binder 1.222(2) 2.950(2) 5,135(4)30% RAP A; 70% Virgin Binder 1.107 (3) 2.957(3) 7,050(4)*

10% RAP B; 90% Virgin Binder 1.018(2) 2.141(2) 4,006(4)

20% RAP B; 80% Virgin Binder 1.367(2) 3.227(2) 4,805(4)

30% RAP B; 70% Virgin Binder 1.863(2) 3.976(2) 5,601(4)

10% RAP C; 90% Virgin Binder 1.436(1) 3.210(1) 7,418(4)**

20% RAP C; 80% Virgin Binder 1.619(1) 3.579(1) 4,624(4)

30% RAP C; 70% Virgin Binder 1.708(1) 2.979(1) 5,284(4)* Value adjusted for 22°C** Value has to be erroneous.

Tables 4.11 and 4.12 show average values of complex shear modulus (G*) and

phase angle (d) as separate components of the fatigue cracking factor, (G*sind). All

data shown is based on a test temperature of 22°C.

Table 4.11. Average Dynamic Shear Rheometer test results – values of G*, d, andG*sind for binders used with gravel aggregate.

Binder Composition G*(kPa)

d (degree)

G*sind(kPa)

0% RAP; 100% Virgin Binder 2,884 49.0 2,52210% RAP D; 90% Virgin Binder 5,368 47.4 3,95320% RAP D; 80% Virgin Binder 6,480 44.7 4,56230% RAP D; 70% Virgin Binder 9,300 43.0 6,43610% RAP E; 90% Virgin Binder 4,645 49.2 3,51820% RAP E; 80% Virgin Binder 5,086 46.4 3,68230% RAP E; 70% Virgin Binder 7,385 44.8 5,20010%RAP F; 90% Virgin Binder 4,261 49.4 3,23420% RAP F; 80% Virgin Binder 5,498 46.2 3,97130% RAP F; 70% Virgin Binder 7,007 44.6 4,921

Table 4.12. Average Dynamic Shear Rheometer test results – values of G*, d, andG*sind for binders used with limestone aggregate.

Binder Composition G*(kPa)

d (degree)

G*sind(kPa)

0% RAP; 100% Virgin Binder 2,884 49.0 2,522

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10% RAPA; 90% Virgin Binder 5,935 47.8 4,39520% RAP A; 80% Virgin Binder 7,276 44.9 5,13530% RAP A; 70% Virgin Binder ** ** 7,050*

10% RAP B; 90% Virgin Binder 5,343 48.6 4,00620% RAP B; 80% Virgin Binder 6,775 45.2 4,80530% RAP B; 70% Virgin Binder 6,723 43.8 5,60110% RAP C; 90% Virgin Binder 10,620*** 44.3 7,418 ***

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.

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Table 4.13. Average Bending Beam Rheometer test results for binders used withgravel aggregate.

Binder Composition Stiffness (MPa) m-value0% RAP; 100% Virgin Binder @ -18°C 262 0.3160% RAP, 100% Virgin Binder @ -24°C 585 0.25410% RAP D; 90% Virgin Binder @ -18°C 287 0.31520% RAP D; 80% Virgin Binder @ -18°C 340 0.28730% RAP D; 70% Virgin Binder @ -18°C 330 0.28610% RAP E; 90% Virgin Binder @ -18°C 261 0.32520% RAP E; 80% Virgin Binder @ -18°C 284 0.30230% RAP E; 70% Virgin Binder @ -18°C 313 0.28610% RAP F; 90% Virgin Binder @ -24°C 566 0.24020% RAP F; 80% Virgin Binder @ -24°C 541 0.25030% RAP F; 70% Virgin Binder @ -24°C 586 0.238

The rate at which the binder stiffness changes with time at low temperature is indicated

by the m-value. A high m-value indicates relatively fast change of stiffness and ability

to shed stress, consequently limiting stress build-up and cracking. A minimum m-value

of 0.300 is required by the Superpave binder specification.

Table 4.14. Average Bending Beam Rheometer test results for binders used withlimestone aggregate.

Binder Composition Stiffness (MPa) m-value0% RAP; 100% Virgin Binder @-18°C

262 0.316

0% RAP; 100% Virgin Binder @-24°C

585 0.254

10% RAP A; 90% Virgin Binder @-18°C

287 0.313

20% RAP A; 80% Virgin Binder @-18°C

342 0.286

30% RAP A; 70% Virgin Binder @-18°C

406 0.263

10% RAP B; 90% Virgin Binder @ -24°C 607 0.23520% RAP B; 80% Virgin Binder @ -24°C 621 0.23430% RAP B; 70% Virgin Binder @ -24°C 643 0.22810% RAP C; 90% Virgin Binder @ -18°C 411 0.261

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20% RAP C; 80% Virgin Binder @ -18°C 413 0.25230% RAP C; 70% Virgin Binder @ -18°C 395 0.267

The values of creep stiffness presented in Tables 4.13 and 4.14 vary from 262

to 413 MPa for tests conducted @ -18°C, and from 585 to 643 MPa for tests conducted

@ -24°C. The rate of change of stiffness versus time (m-value) vary from 0.316 to

0.252 for tests conducted @ - 18°C, and from 0.254 to 0.228 for tests conducted

@ - 24°C. The value of creep stiffness is growing with an increased RAP content

exceeding the maximum allowable value of 300 MPa for all tested mixes having more

than 10% RAP. The m-value decreases with an increased RAP content.

Figures 4.1 to 4.10 present graphically the test data from Tables 4.11 through 4.14.

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4.6. PROPERTIES OF BINDERS RECOVERED FROM HOT MIX

BITUMINOUS CONCRETE SUBJECTED TO DIFFERENT AGING

PROCEDURES.

1. Description of Mixing and Aging Procedures

The experimental aging procedure was conducted on two types of bituminous

concrete mixtures. One type had gravel and another limestone coarse aggregate. Mixtures

with gravel coarse aggregate had 0, 10, 20, and 30% addition of RAP F. Mixtures with

limestone coarse aggregate had 0, 10, 20, and 30% addition of RAP A.

Before mixing, the aggregates were heated to 185°C (365°F), RAP was placed on

top of an oven which brought its temperature to around 40°C (104°F), and asphalt

binder was heated to 135°C (275°F). To achieve proper temperature of the aggregate

and RAP mixture before binder was added, these two components were blended and

placed in an oven set at 185°C (365°F) for 20 minutes. After removal from the oven,

binder was added and the three components were mechanically mixed and placed in

metal trays.

Initially, the experimental protocol of loose mixtures’ oven aging was set at:

· 2 hours at 135°C (275°F)

· 2 hours at 135°C (275°C) plus 4 hours at 100°C (212°F)

· 2 hours at 135°C (275°C) plus 6 hours at 100°C (212°F)

· 2 hours at 135°C (275°C) plus 3 hours at 120°C (248°F)

· 2 hours at 135°C (275°C) plus 5 hours at 120°C (248°F).

In addition, all four mixtures with limestone coarse aggregate were aged for 2

hours at 135°C (275°C) plus 20 hours at 100°C (212°F), and 2 hours at 135°C (275°C)

plus 45 hours at 100°C (212°F).

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4.6.2. Properties of Binders Recovered from Bituminous Concrete Subjected to

Different Aging Procedures.

After removal from the oven the mixes were cooled and subjected to the Abson

recovery process. Recovered binder was tested using the Dynamic Shear Rheometer

(DSR) and Bending Beam Rheometer (BBR). Results of this testing are presented in

Tables 4.15 to 4.22.

Table 4.15. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder and gravel aggregate.

Type of AgingType of Test

DSR @ 22°C BBR @ -18/-24°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 2,578 54.56 2,100 159*/371** 0.378*/0.308**2hr @135°C and 3hr @120°C 3,650 50.80 2,829 209*/466** 0.343*/0.285**2hr @135°C and 5hr @120°C 2,784 51.66 2,472 175*/372** 0.365*/0.306**2hr @135°C and 4hr @100°C 3,880 50.62 2,999 224*/449** 0.349*/0.282**2hr @135°C and 6hr @100°C 2,380 54.85 1,946 153*/360** 0.381*/0.310**Target Value 2,884 49.00 2,522 262*/585** 0.316*/0.254***Value for a test done @ -18°C**Value for a test done @ - 24°C

Table 4.16. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder, 10% RAP F, and gravel aggregate.

Type of AgingType of Test

DSR @ 22°C BBR @ -24°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 3,055 53.55 2,455 407 0.2822hr @135°C and 3hr @120°C 3,473 50.95 2,698 382 0.2862hr @135°C and 5hr @120°C 4,568 48.13 3,403 431 0.2702hr @135°C and 4hr @100°C 4,108 50.41 3,166 408 0.2852hr @135°C and 6hr @100°C 5,820 43.80 4,027 400 0.289

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Target Value 4,261 49.37 3,234 566 0.240

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Table 4.17. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder, 20% RAP F, and gravel aggregate.

Type of AgingType of Test

DSR @ 22°C BBR@ - 24°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 738 60.01 639 146 0.3762hr @135°C and 3hr @120°C 4,339 48.84 3,266 420 0.2692hr @135°C and 5hr @120°C 3,323 51.40 2,598 448 0.2492hr @135°C and 4hr @100°C 3,284 50.54 2,536 367 0.3022hr @135°C and 6hr @100°C 6,475 45.68 4,632 496 0.248Target Value 5,498 46.24 3,971 541 0.250

Table 4.18. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder, 30% RAP F, and gravel aggregate.

Type of AgingType of Test

DSR @ 22°C BBR@ - 24°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 6,708 42.56 4,540 590 0.2292hr @135°C and 3hr @120°C 6,820 43.66 4,708 492 0.2472hr @135°C and 5hr @120°C 8,808 43.22 6,029 546 0.2342hr @135°C and 4hr @100°C 7,446 41.35 4,921 460 0.2492hr @135°C and 6hr @100°C 6,753 44.47 4,731 471 0.250Target Value 7,007 44.62 4,921 586 0.238

Table 4.19. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder and limestone aggregate.

Type of AgingType of Test

DSR @ 22°C BBR @ -18/-24°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 2,248 56.18 1,868 180*/451** 0.372*/0.307**2hr @135°C and 3hr @120°C 2,540 55.32 2,089 172*/360** 0.377*/0.300**2hr @135°C and 5hr @120°C 2,740 54.37 2,227 187*/400** 0.363*/0.302**2hr @135°C and 4hr @100°C 2,857 54.38 2,323 176*/393** 0.373*/0.302**

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2hr @135°C and 6hr @100°C 2,204 56.34 1,835 172*/408** 0.362*/0.301**2hr @135°C and 20hr@100°C

2,524 53.76 2,029 157*/347** 0.387*/0.311**

2hr @135°C and 45hr@100°C

5,441 46.67 3,956 No data No data

Target Value 2,884 49.00 2,522 262*/585** 0.316*/0.254***Value for test done @ -18°C**Value for test done @ - 24°C

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Table 4.20. DSR and BBR data for binder recovered from bituminous concrete madeof

virgin binder, 10% RAP A, and limestone aggregate.

Type of AgingType of Test

DSR @ 22°C BBR@ - 18°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 2,112 56.30 1,757 132 0.4002hr @135°C and 3hr @120°C 2,384 55.10 1,955 150 0.3802hr @135°C and 5hr @120°C 3,280 51.81 2,578 155 0.3702hr @135°C and 4hr @100°C 2,608 54.88 2,133 204 03552hr @135°C and 6hr @100°C 2,460 56.20 2,045 150 0.3852hr @135°C and 20hr@100°C

4,032 50.87 3,128 223 0.350

2hr @135°C and 45hr@100°C

3,840 50.00 2,942 198 0.352

Target Value 5,935 47.76 4,395 287 0.313

Table 4.21. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder, 20% RAP A, and limestone aggregate.

Type of AgingType of Test

DSR @ 22°C BBR@ - 18°CG*

(kPa)d

(degree)G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 4,119 52.75 3,279 255 0.3342hr @135°C and 3hr @120°C 3,106 52.52 2,394 147 0.3762hr @135°C and 6hr @120°C 3,630 52.17 2,868 195 0.3542hr @135°C and 4hr @100°C 3,796 52.70 3,017 223 0.3452hr @135°C and 6hr @100°C 3,781 52.80 3,012 209 0.3502hr @135°C and 20 hr @ 100°C 4,493 49.97 3,443 256 0.3262hr @135°C and 45hr @100°C 4,858 48.45 3,6.35 230 0.333Target Value 7,276 44.88 5,135 342 0.286

Table 4.22. DSR and BBR data for binder recovered from bituminous concretemade of virgin binder, 30% RAP A, and limestone aggregate.

Type of AgingType of Test

DSR @ 22°C BBR@ - 18 °C

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G*(kPa)

d (degree)

G*sind(kPa)

Stiffness(MPa)

m-value

2hr @135°C 4,801 51.75 3,761 262 0.3262hr @135°C and 3hr @120°C 5,394 49.84 4,122 247 0.3302hr @135°C and 5hr @120°C 4,430 50.46 3,408 167 0.3562hr @135°C and 4hr @100°C 5,488 49.02 4,143 311 0.3082hr @135°C and 6hr @100°C 4,546 50.29 3,497 203 0.3502hr @135°C and 20 hr @ 100°C 4,895 49.53 3,721 225 0.3302hr @135°C and 45hr @100°C 8,495 43.79 5,879 350 0.290Target Value NA NA 7,050 406 0.263

Comparison of results of DSR and BBR testing for binder recovered from

concrete mixes aged in an oven with target values (obtained for binder subjected to

RTFOT and PAV procedures) indicates that there was no case in which a full match

was achieved. Consequently, since the objective of this research study was to

determine the durability of the asphalt concrete mixes containing RAP, the fatigue

cracking factor (G*sind) was selected as one to be matched during long-term aging

process of loose mixes.

Analyzing changes in the value of binders fatigue cracking factors (G*sind)

that resulted from oven aging of bituminous concrete with gravel aggregate, and

comparing them with values measured for RTFOT and PAV aged binders, it was

concluded that the closest match was achieved with an aging protocol that consisted of

2 hours at 135°C followed by 5 hours at 100°C. This match was not achieved in the

case of limestone mixes. Due to this fact, two additional aging protocols were tried. In

the first, aging at 100°C was extended to 20 hours; in the second, aging at 100°C was

extended to 45 hours. Both of these experiments proved to be unsuccessful. The reason

could be that a significant amount of the asphalt binder was absorbed into the

limestone pores, and thus was not affected by oxidation processes the same way as was

binder that remained on aggregate particle surfaces. Consequently, only part of the

binder was effectively aging. Therefore, a mixture of aged and non-aged binder was

recovered by the Abson method and tested. These tests results did not present any

trends. Facing these difficulties, it was decided to adopt the same aging protocol for all

mixes regardless of type of aggregate.

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Accordingly, an oven aging protocol of 2 hours at 135°C, followed by 5 hours at

100°C, was selected for both the gravel and limestone mixes.

6.

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PROPERTIES OF BINDERS RECOVERED FROM AGED

BITUMINOUS CONCRETE TEST SPECIMENS.

1. Description of Test Specimen Preparation

Before mixing, aggregates were heated to 185°C (365°F). RAP was placed on top

of an oven which brought its temperature to around 40°C (104°F. Virgin asphalt was

heated to 135°C (275°F). To achieve proper temperature of the aggregate and RAP

mixture these to components were blended and placed in an oven set at 185°C for 20

minutes, before virgin asphalt was added. Finally, the three components (aggregate, RAP,

and virgin asphalt) were mechanically mixed and placed in metal trays the dimensions of

16 by 17 inches.

Total weight of the test specimen was about 4000g. The bituminous concrete

mix was oven aged at 135°C for two hours, and at 100°C for four and half hours.

Before compaction, the mix was reheated to 135°C for 30 to 45 minutes, after which

specimens were compacted by a gyratory compactor to 7% air voids.

The desired 7% air void content was quite easy to achieve when compacting

specimens with gravel coarse aggregate, but severe difficulties were encountered when

compacting specimens with limestone coarse aggregate. For some mixes, 20

specimens had to be prepared before six usable specimens were available for testing.

The same compaction temperature and compaction effort produced specimens that

varied in air voids content from 4 to 10%. The coarse aggregate in the limestone

specimens was broken during compaction as was observed when preparing test

specimens for the Abson recovery test. There may be several possible of reasons by

which this breaking phenomenon could be explained. One hypotheses was that the

aggregate was not durable; however this proved not to be true. The Los Angeles (LA)

degradation test showed a degradation value of 27%. Limestone aggregate having an

LA degradation value less than 40% is considered to represent good, tough, and

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abrasion-resistant aggregate (8). The second reason is that reduced to 95mm height of

test specimens, as required by National Cooperative Highway Research Program

Report 444 is too low. With the reduced specimen volume, larger aggregate particles

had no freedom to be arranged with optimum orientation in the compacted specimens.

Consequently, a normal loading by the Gyratory compactor caused breakage of

aggregate particles. This breakage could have been different in each compacted

specimen, consequently causing different gradations of aggregate.

2. Testing of Binder Recovered from Specimens Subjected to

Moisture-Damage Test

After testing for indirect tensile strength, the specimens that were not

conditioned were reheated, disassembled, and subjected to the Abson recovery

procedure. Recovered asphalt was tested by DSR and BBR test methods. The DSR

and BBR test results are presented in Tables 4.23 and 4.24, respectively. Selected test

results are also presented in Figures 4.11 through 4.13.

The actual G*sind test values for mixes with limestone coarse aggregate (i.e.,

mixes with RAP A, B, and C) differ considerably from the values that were sought.

The same is true for values of stiffness and m-value. These differences were expected

because, as previously explained, part of the binder that is absorbed into the aggregate

particle seams not to age at the same rate as the part that remains on the particle

surface. When during the Abson recovery process these two binder parts are mixed, the

resulting binder has parameters that do not match parameters of the same binders aged

by RFTOT and PAV.

The actual G*sind values for mixes with gravel coarse aggregate and RAP D

differ about 20% from desired at 10% RAP addition, 50% from desired at 20% RAP

addition (this result is most likely erroneous), and match perfectly at 30% RAP

addition. The actual G*sind values for mixes with gravel coarse aggregate and RAP E

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are as desired matching perfectly at 10 and 30% RAP addition. At 20% RAP E

addition, the actual values of G*sind are about 30% lower than desired. Finally, the

actual G*sind values for mixes with gravel coarse aggregate and RAP F are as desired

matching perfectly at 10%, and differing about 15% at both 20 and 30% RAP F

addition.

The m-value was the best match between properties of RTFOT and PAV aged

binder and binder recovered from oven-aged bituminous concrete with gravel

aggregate, as graphically presented in Figures 4.14 through 4.16.

Table 4.23. Dynamic Shear Rheometer test results for aged binder.

Binder Composition G* (kPa) d (°) G*sind (kPa)

Actual Desired Actual Desired Actual Desired

Virgin Binder (1) 2,482 2,884 56.15 49.00 2,061 2,522

10% RAP A; 90% Virgin Binder 3,666 5,935 63.80 47.76 2,939 4,395

20% RAP A; 80% Virgin Binder 4,451 7,276 39.62 44.88 3,829 5,135

30% RAP A; 70% Virgin Binder 5,424 * 39.62 ** 3,459 7,050

10% RAP B; 90% Virgin Binder 2,116 5,353 52.00 48.58 1,667 4,006

20% RAP B; 80% Virgin Binder 4,966 6,775 48.5 45.17 3,718 4,805

30% RAP B; 70% Virgin Binder 4,548 6,723 49.5 43.78 3,458 5,601

10% RAP C; 90% Virgin Binder 2,962 10 ,62

0

53.6 44.33 2,389 7,418

20% RAP C; 80% Virgin Binder 2,639 6,724 53.25 43.45 2,113 4,624

30% RAP C; 70% Virgin Binder 3,658 7,481 50.85 44.94 2,833 5,284

Virgin Binder (2) 2,808 2,884 46.00 49.00 2,023 2,522

10% RAP D; 90% Virgin Binder 7,194 5,368 41.93 47.42 5,107 3,953

20% RAP D; 80% Virgin Binder 4,760 6,480 32.25 44.75 2,254 4,562

30% RAP D; 70% Virgin Binder 9,028 9,300 44.23 43.04 6,298 6,436

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10% RAP E; 90% Virgin Binder 4,730 4,645 49.22 49.22 3,580 3,518

20% RAP E; 80% Virgin Binder 7,155 5,086 46.29 46.37 5,172 3,682

30% RAP E; 70% Virgin Binder 8,827 7,385 37.68 44.80 5,397 5,200

10% RAP F; 90% Virgin Binder 4,068 4,261 51.65 49.37 3,190 3,234

20% RAP F; 80% Virgin Binder 6,723 5,498 45.05 46.24 4,759 3,971

30% RAP F; 70% Virgin Binder 8,827 7,007 41.58 44.62 5,857 4,921

Table 4.24. Bending Beam Rheometer test results for aged binder.

Binder Composition Creep Stiffness, (MPa) m-value

Actual Desired Actual Desired

Virgin Binder (1) 156(3)

371(4)

262(3)

585(4)

0.392(3)

0.313(4)

0.316(3)

0.254(4)

10% RAP A; 90% Virgin Binder 235(3) 292(3) 0.337(3) 0.313(3)

20% RAP A; 80% Virgin Binder 240(3) 342(3) 0.343(3) 0.286(3)

30% RAP A; 70% Virgin Binder 152(3) 406(3) 0.325(3) 0.263(3)

10% RAP B; 90% Virgin Binder 312(4) 635(4) 0.315(4) 0.235(4)

20% RAP B; 80% Virgin Binder 508(4 621(4) 0.260(4) 0.234(4)

30% RAP B; 70% Virgin Binder 440(4) 643(4) 0.270(4) 0.228(4)

10% RAP C; 90% Virgin Binder 200(3) 411(3) 0.365(3) 0.261(3)

20% RAP C; 80% Virgin Binder 167(3) 413(3) 0.397(3) 0.252(3)

30% RAP C; 70% Virgin Binder 229(3) 395(3) 0.336(3) 0.267(3)

Virgin Binder (2) 116(3)

261(4)

262(3)

585(4)

0.362(3)

0.328(4)

0.316(3)

0.254(4)

10% RAP D; 90% Virgin Binder 214(3) 287(3) 0.309(3) 0.315(3)

20% RAP D; 80% Virgin Binder 83(3) 340(3) 0.308(3) 0.287(3)

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30% RAP D; 70% Virgin Binder 310(3) 330(3) 0.274(3) 0.286(3)

10% RAP E; 90% Virgin Binder 214(3) 261(3) 0.335(3) 0.325(3)

20% RAP E; 80% Virgin Binder 340(3) 284(3) 0.301(3) 0.302(3)

30% RAP E; 70% Virgin Binder 282(3) 313(3) 0.273(3) 0.286(3)

10% RAP F; 90% Virgin Binder 415(4) 566(4) 0.298(4) 0.240(4)

20% RAP F; 80% Virgin Binder 471(4) 541(4) 0.247(4) 0.250(4)

30% RAP F; 70% Virgin Binder 490(4) 586(4) 0.242(4) 0.238(4)

Legend to Tables 4.23 and 4.24.

(1) Binder recovered from specimen with limestone aggregate

(2) Binder recovered from specimen with gravel aggregate

(3) Tested at –18°C, (4) Tested at –24°C

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7. PERFORMANCE EVALUATION OF AGED BITUMINOUS

CONCRETE MIXES.

Nine specimens were compacted for each examined bituminous concrete mix.

Six of these specimens were compacted to 7 ± 1% air voids and tested for resistance to

moisture-induced damage in accordance with AASHTO T 283. Additional data of

specimen deformation during loading was collected and used to present and discuss the

absorbed energy concept. Three specimens were tested for unconfined compressive

strength.

1. Resistance to Moisture Induced Damage

Six specimens for each mix were prepared and then sorted into two subsets of

three specimens each so that the average air voids content of the two subsets were

approximately equal. Three specimens were tested in a dry condition. The other three

specimens were first saturated with water, then frozen at –18 ± 3°C for 16 hours, and

then placed in a water bath at 60 ± 1°C for 24 hours. After removal from the

high-temperature water bath, specimens were cooled for two hours in a 25 ± 0.5°C

water bath and tested for indirect tensile strength. The results of this test are used to

predict the susceptibility of bituminous concrete to long-term moisture damage. This

susceptibility is expressed as a ratio of the indirect tensile strength of the conditioned

to unconditioned specimens. According to SHRP (9) the minimum acceptable ratio is

0.80 (i.e., 80% of strength retained).

Table 4.25 and Figures 4.17 through 4.22 show the resistance to

moisture-induced damage test results. The second column on Table 4.25 shows the

indirect tensile strength of control test specimens. The third column in this table shows

the indirect tensile strength of the conditioned test specimens. The ratio of retained

indirect tensile strength for each mix are shown in the last column of Table 4.25.

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Table 4.25. Resistance to Moisture Induced Damage Test Results

Binder Composition Control Sample,

Indirect Tensile

Strength (psi)

Conditioned Sample Ratio of

Retained

Strength

IndirectTensileStrength (psi)

% of AirVoids Filledwith Water

Virgin Binder (limestoneaggregate)

125.7 80.8 79 0.64

10% RAP A; 90% Virgin Binder 106.5 86.2 66 0.81

20% RAP A; 80% Virgin Binder 145.1 99.9 76 0.69

30% RAP A; 70% Virgin Binder 149.2 109.2 79 0.74

10% RAP B; 90% Virgin Binder 127.7 96.7 64 0.76

20% RAP B; 80% Virgin Binder 142.9 95.8 74 0.67

30% RAP B; 70% Virgin Binder 154.6 120.1 69 0.78

10% RAP C; 90% Virgin Binder 120.1 84.6 76 0.70

20% RAP C; 80% Virgin Binder 117.1 92.1 76 0.79

30% RAP C; 70% Virgin Binder 122.3 105.5 71 0.86

Virgin Binder (gravel aggregate) 189 103 75 0.55

10% RAP D; 90% Virgin Binder 207 130 75 0.63

20% RAP D; 80% Virgin Binder 202 106 80 0.52

30% RAP D; 70% Virgin Binder 258 127 80 0.49

10% RAP E; 90% Virgin Binder 188 119 75 0.63

20% RAP E; 80% Virgin Binder 187 107 79 0.57

30% RAP E; 70% Virgin Binder 209 126 73 0.60

10% RAP F; 90% Virgin Binder 174 107 76 0.61

20% RAP F; 80% Virgin Binder 191 105 76 0.55

30% RAP F; 70% Virgin Binder 226 123 76 0.54

Listings of RAP A, B, and C indicate bituminous concrete mixes with

limestone aggregate. Listings of RAP D, E, and F indicate bituminous concrete mixes

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with gravel aggregate.

Data presented in Figure 4.17 shows that for a particular RAP, no specific

trends can be observed between the value of indirect tensile strength and RAP content

in the control mixes made with limestone aggregate. However, average values

calculated for these mixes indicate the indirect tensile strength increases with an

increased RAP content.

Data presented in Figure 4.18 shows that in all cases of conditioned test

specimens made with limestone aggregate, the indirect tensile strength increases with

an increased RAP content.

Data presented in Figures 4.19 and 4.20 show no definitive trends between

indirect tensile strength and RAP content in control and conditioned mixes with gravel

aggregate.

The values of ratio of retained strength (last column in Table 25) indicate that

all gravel and all but two limestone mixes (10% RAP A and 30% RAP C) failed to

retain desirable strength, and could be susceptible to moisture induced damage. The

mixes with gravel aggregate retained less strength than the mixes with limestone

aggregate.

Bituminous mixes with limestone aggregate did not present consistent

behavior. The only trend that could be observed (Figure 4.21) was that regardless of

RAP content, mixes with RAP addition retained more strength than the mix without

RAP. Mixes at the 20% RAP A or B addition retained less strength that mixes with

10% or 30% RAP addition. Mixes containing RAP C show a definite trend of retained

strength; it increases with an increased RAP content.

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Figure 4.22 shows that mixes with gravel aggregate and no RAP addition

retained less strength than mixes containing 10% RAP, and mixes with 20% RAP

addition retained less strength than mixes with 10% RAP addition. This decreasing

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trend continued, in the cases of 30% RAP D and F addition. The mix with 30% RAP E

addition retained more strength than the same mix with 20% RAP E addition but less

than the mix with 10% RAP E addition. In all cases, the bituminous mixes with gravel

aggregates retained the most strength at the 10% RAP addition.

2. Absorbed Energy

Data to calculate the absorbed energy (applied load and resultant deformation)

was collected during the moisture damage test.

Table 4.26 and Figures 4.23 through 4.28 show the test results for absorbed

energy at failure. This absorbed energy was calculated on the assumption that for any

material to fail, it must absorb some level of energy. In the case of this research, the

absorbed energy at failure was calculated as a field below the curve that was

determined on the basis of continuous measurement of applied force and resulting

deformation during the moisture induced damage test. Approximation of this value

may be also calculated by the following formula:

E = (0.5 x P x D)/t

Where:

E –energy, lbs*inch/inch

P – ultimate load, lbs

d – specimen vertical deformation at the ultimate load, inch

t – specimen thickness, inch.

The second column on Table 4.26 shows the amount of absorbed energy

needed to break control test specimens in the indirect tensile loading. The third column

in this table shows the amount of absorbed energy needed to break, in the same type of

loading, the conditioned test specimens. The last column shows the amount of energy

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retained after moisture-damage conditioning.

Table 4.26. Absorbed Energy at Failure Test Results

Binder Composition Control Sample,

Absorbed

Energy

(lbs*inch/inch)

Conditioned Sample Ratio of

Energy

Retained

AbsorbedEnergy(lbs*inch/inch)

% of AirVoidsFilled withWater

Virgin Binder (limestoneaggregate)

89.7 78.1 79 0.87

10% RAP A; 90% Virgin Binder 95.3 81.0 66 0.85

20% RAP A; 80% Virgin Binder 129.2 99.9 76 0.77

30% RAP A; 70% Virgin Binder 112.3 102.5 79 0.91

10% RAP B; 90% Virgin Binder 96.7 85.0 64 0.88

20% RAP B; 80% Virgin Binder 120.3 92.1 74 0.77

30% RAP B; 70% Virgin Binder 129.3 102.8 69 0.79

10% RAP C; 90% Virgin Binder 100.4 76.3 76 0.76

20% RAP C; 80% Virgin Binder 100.0 92.7 76 0.93

30% RAP C; 70% Virgin Binder 106 103.1 71 0.97

Virgin Binder (gravel aggregate) 93.5 75.6 75 0.81

10% RAP D; 90% Virgin Binder 98.8 90.4 75 0.91

20% RAP D; 80% Virgin Binder 90.3 65.8 80 0.73

30% RAP D; 70% Virgin Binder 89 54.4 80 0.61

10% RAP E; 90% Virgin Binder 95.6 81.9 75 0.86

20% RAP E; 80% Virgin Binder 94.7 73.6 79 0.78

30% RAP E; 70% Virgin Binder 119.6 85.2 73 0.71

10% RAP F; 90% Virgin Binder 87.5 69.6 76 0.80

20% RAP F; 80% Virgin Binder 106.9 67.8 76 0.63

30% RAP F; 70% Virgin Binder 107.9 74.8 76 0.69

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RAP A, B, and C were used in asphalt concrete mixes with limestone

aggregate. RAP D, E, and F were used in asphalt concrete mixes with gravel aggregate.

The values of absorbed energy for each mix with RAP and conditioned mix

without RAP show that on average, specimens made from mixes with gravel aggregate

required less energy to break in control and moisture-damage condition than mixes with

limestone aggregate. However, this was not true for the control mixes without RAP as the

mix with gravel aggregate absorbed 93.5lbs*inch/inch versus 89.7lbs*inch/inch for the

mix with limestone aggregate.

On average, the difference in the values of absorbed energy is not significant for

control and conditioned specimens containing 0 or 10% RAP. However, energy required

to break conditioned test specimens that contain 20 or 30% RAP is greatly affected by

aggregate type. At the 20% RAP addition, mixes with gravel aggregate absorbed on

average 69lbs*inch per 1 inch thickness while the mixes with limestone aggregate

absorbed 94lbs*inch per inch. At the 30% RAP addition the same values are 71 versus

103.

Figure 4.23 shows data collected for control test specimens made with limestone

aggregate. This data shows that addition of RAP increases the absorbed energy values of

asphalt concrete mixes with limestone aggregate, as all mixes with RAP addition

absorbed more energy before failure than the mix without RAP. Mixes made with RAP B

and RAP C have continuously increasing trend of absorbed energy with an increased

RAP content. Mix made with RAP A has an increased trend up to 20% RAP addition,

then at 30% RAP addition a decrease in the absorbed energy value can be observed. The

average energy values for these mixes indicate that the absorbed energy values initially

increase with an increased RAP content (0, 10, and 20% RAP addition), and then level

off at 30% RAP content.

Data presented in Figure 4.24 shows that increased RAP content resulted in an

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increased level of absorbed energy in all conditioned test specimens made with limestone

aggregate.

Data presented in Figures 4.25 and 4.26 shows no definitive trends between

absorbed energy level and RAP content in control and conditioned mixes with gravel

aggregate.

Figure 4.27 shows that the average value of the percent of absorbed energy for

mixes with limestone aggregate is 87% for mix with no RAP, 83% for mixes with 10%

RAP, 81% for mixes with 20% RAP, and 89% for mixes with 30% RAP. The close range

of these values could indicate that mixes made with this particular limestone aggregate

may contain up to 30% RAP and still have acceptable durability, based on the absorbed

energy consideration.

Figure 4.28 shows that the average value of the percent of absorbed energy for

mixes with gravel aggregate is 81% for mix with no RAP, 86% for mixes with 10% RAP,

71% for mixes with 20% RAP, and 67% for mixes with 30% RAP. The average value of

the ratio of absorbed energy needed to fail specimens with gravel coarse aggregate peaks

around 10% RAP addition, indicating that RAP additions at this level have positive

influence on asphalt concrete durability based on the absorbed energy consideration.

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4.8.3. Unconfined Compressive Strength

Compressive strength testing was performed by applying a vertical compressive

load to each specimen along its cylindrical axis, at a specified loading rate of 0.05 in/min

per 1 inch of height. The molded specimens had height to diameter ratios in the range of

0.67 to 1 rather than 1:1 as specified in ASTM D 1074. This difference is not considered

to be problematic for this application as testing was performed to determine the relative

strengths of the trial mixes under this type of loading rather than absolute values.

Tables 4.27 and 4.28, and Figures 4.29 and 4.30 present the average values of

unconfined compressive strength of the examined bituminous concrete mixes with

limestone and gravel coarse aggregates, respctively.

Table 4.27. Unconfined Compressive Strength for mixes with limestone aggregate

Specimen ID Air Voids, % Ultimate Load, lbs Unconfined CompressiveStrength, psi

L – 0 5.4 28,640 1,048

A – 10 4.1 24,350 891

A – 20 5.3 23,450 945

A – 30 4.6 32,080 1,174

B – 10 4.1 29,630 1,084

B – 20 5.1 21,860 848

B – 30 5.5 25,440 931

C – 10 5.0 23,370 855

C – 20 5.7 21,020 769

C – 30 5.8 21,810 798

The average compressive strength of mixes with limestone aggregate was 943psi

at 10% RAP content, 854psi at 20% RAP content, and 967psi at 30% RAP content. All

these values are lower than the 1,048psi compressive strength of the limestone mix with

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Table 4.28. Unconfined Compressive Strength for mixes with gravel aggregate

Specimen ID Air Voids, % Ultimate Load, lbs Unconfined CompressiveStrength, psi

G – 0 4.8 41,730 1527

D – 10 4.4 48,510 1775

D – 20 4.3 49,580 1814

D – 30 5.1 53,730 1966

G – 0 5.7 37,110 1358

E – 10 5.8 37,630 1377

E – 20 5.2 43,320 1585

E – 30 5.9 43,040 1575

G – 0 4.8 41,730 1527

F – 10 5.0 43,890 1606

F – 20 3.8 51,110 1870

F – 30 4.6 38,540 1410

no RAP, though it is not true for individual cases as mixes with 30% RAP A and 20%

RAP B have greater compressive strength than the mix with no RAP. The compressive

strength of limestone mixes and 20% RAP addition was on average 23% lower than the

average compressive strength of limestone mix with no RAP.

The average compressive strength of mixes with gravel aggregate was 1,586psi at

10% RAP content, 1,756psi at 20% RAP content, and 1,650psi at 30% RAP content. All

these values are greater than the 1,527psi compressive strength of gravel mix with no

RAP, though it is not true for individual cases as mixes with 20% RAP E and 30% RAP

F have lesser compressive strength than the mix with no RAP. The compressive strength

of gravel and 20% RAP addition was on average 15% higher than the average

compressive strength of the gravel mix and no RAP.

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The average air voids content of specimens tested for compressive strength ranged

from 4.1 and 5.8% for mixes with limestone coarse aggregate, and 3.8 to 5.8% for mixes

with gravel coarse aggregate. Air voids content of specimens subjected to compressive

testing is not specified in ASTM D 1074. However, since numerous test specimens with

gravel aggregate and no RAP were made and could be selected for analysis by groups of

different air voids content, data at 4.8% was selected for mixes with RAP D and F and

5.7% was selected for mixes with RAP E to match better volumetric properties of

compared values.

The gathered compressive strength data does not permit clear conclusions regarding

trends in relation to RAP content, but seems to lead to a conclusion that the compressive

strength of aged asphalt concrete specimens is sensitive to RAP source and content.

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CHAPTER 5

FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS

Based on laboratory testing of twenty trial mixes, consisting of one aggregate

gradation, two aggregate types (crushed gravel and limestone), one virgin asphalt,

recycled asphalt pavement (RAP) from six sources, and three RAP contents, the

following findings, conclusions, and recommendations are presented relative to durability

of bituminous asphalt concrete containing different levels of RAP.

5.1. FINDINGS

1. At the optimum binder content, the trial mixes showed air void contents ranging

from 11.0 to 17.2% at Ninitial, and 2.0 to 3.2% at Nmax.

2. At the optimum binder content, the trial mixes with limestone aggregate showed,

at the designed number of gyrations, VMA ranging from 12.8 to 14.8%, and VFA

from 66.6 to 73.7%.

3. At the optimum binder content, the trial mixes with gravel aggregate showed, at

the designed number of gyrations, VMA ranging from 7.5 to 8.9%, and VFA from

45.1 to 57%.

4. Values of complex shear modulus (G*) for binders obtained by mixing virgin

asphalt with binder recovered from RAP vary from 2,994 to 9,300 kPa. Values of

fatigue cracking factor (G*sind) vary from 2,522 to 7,050 kPa.

5. Values of phase angle (d) for binders obtained by mixing virgin asphalt with

binder recovered from RAP range from 43.0 to 49.0 degrees.

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6. Creep stiffness values of binders obtained by mixing virgin asphalt with binder

recovered from RAP vary from 262 to 413MPa for tests conducted @ -18°C, and

from 585 to 643MPa for test conducted @ -24°C.

7. The rate of the change of stiffness versus time (m-value) of binders obtained by

mixing virgin asphalt with binder recovered from RAP vary from 0.316 to 0.252

for tests conducted @ -18°C, and from 0.254 to 0.228 for test conducted

@ -24°C.

8. Binders obtained, by the Abson recovery method, from oven-aged loose

bituminous concrete containing gravel aggregate and RAP F, subjected to five

different aging procedures, have the following parameters:

· A complex shear modulus (G*) in the 2,580 to 8,810 kPa range

· A fatigue cracking factor (G*sind) in the 2,100 to 6,030 kPa range

· A phase angle (d) in the 41.3 to 54.6 degree range

· Creep stiffness @ -24°C in the 360 to 590 MPa range

· The rate of the change of stiffness versus time (m-value) @-24°C in the

0.229 to 0.310 range.

9. Binders obtained, by the Abson recovery method, from oven-aged loose

bituminous concrete containing limestone aggregate and RAP A, subjected to

seven different aging procedures, have the following parameters:

· A complex shear modulus (G*) in the 2,200 to 8,430 kPa range

· A fatigue cracking factor (G*sind) in the 1,760 to 5,880 kPa range

· A phase angle (d) in the 43.8 to 56.3 degree range

· Creep stiffness @ -18°C in the 132 to 350 MPa range

· The rate of the change of stiffness versus time (m-value) @-18°C in the

0.290 to 0.400 range.

10. The actual fatigue cracking factor values (G*sind) for 10 binders obtained, by the

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Abson recovery method, from test specimens of bituminous concrete made from

gravel aggregate and RAP D, E, and F in the 2,020 to 6,300 range. The desired

values of these factors were in the 2,520 to 6,440kPa range.

11. The actual fatigue cracking factor values (G*sind) for 10 binders obtained, by the

Abson recovery method, from test specimens of bituminous concrete made from

limestone aggregate and RAP A, B, and C are in the 1,670 to 3,830kPa range. The

desired values of these factors were in the 2,520 to 7,050 kPa range.

12. The value of the indirect tensile strength of bituminous concrete with limestone

aggregate ranges from 106 to 155psi for control test specimens, and from 81 to

120psi for conditioned test specimens. Resulting percent of the retained strength is

in the 64 to 86 % range.

13. The value of the indirect tensile strength of bituminous concrete with gravel

aggregate ranges from 174 to 258psi for control test specimens, and from 103 to

130psi for conditioned test specimens. Resulting percent of the retained strength is

in the 49 to 63 % range.

14. The absorbed energy value of bituminous concrete with limestone aggregate

ranges from 90 to 129lbsinch/inch for control test specimens, and from 76 to

103.1lbsinch/inch for conditioned test specimens. Resulting percent of the

absorbed energy retained is in the 77 to 97 % range.

15. The average value of the percent of absorbed energy for mixes with limestone

aggregate is 87 % for mix with no RAP, 83 % for mixes with 10% RAP, 81 % for

mixes with 20% RAP, and 89 % for mixes with 30% RAP.

16. The absorbed energy value of bituminous concrete with gravel aggregate ranges

from 87 to 108lbs*inch/inch for unconditioned test specimens, and from 54 to

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90lbs*inch/inch for conditioned test specimens. Resulting percent of the absorbed

energy retained is in the 61 to 91 % range.

17. The average value of the percent of absorbed energy for mixes with gravel

aggregate is 81 % for mix with no RAP, 86% for mixes with 10% RAP, 71 % for

mixes with 20% RAP, and 67 % for mixes with 30% RAP.

18. The average compressive strength of mixes with limestone aggregate was

1,048psi for mix with no RAP, 943psi for mixes with 10% RAP, 854psi for mixes

with 20% RAP, and 967psi for mixes with 30% RAP.

19. The average compressive strength of mixes with gravel aggregate was 1,527psi

for mix with no RAP, 1,586psi for mixes with 10% RAP, 1,756psi for mixes with

20% RAP, and 1,650psi for mixes with 30% RAP.

5.2. CONCLUSIONS

1. Test results obtained for VMA and VFA content of a bituminous concrete

designed for mixes with gravel aggregate are affected by the selected method of

laboratory compaction.

2. Values of complex shear modulus (G*) and fatigue cracking factor (G*sind) are

greater for binders containing RAP than for binders that contain no RAP, and are

growing consistently with an increased RAP content when tests are conducted on

binders prepared by mixing virgin asphalt with binder recovered from RAP.

3. Parameters of blended binders, obtained by mixing virgin asphalt with binder

recovered from RAP, show that:

· Values of phase angle (d) are decreasing with an increased RAP content,

indicating binders are becoming more viscous with greater RAP addition.

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· Source of RAP has a limited influence on complex shear modulus (G*),

fatigue cracking factor (G*sind), and phase angle (d) values.

· Creep stiffness of binder increases with an increased RAP content.

· The rate of change of this stiffness (m-value) versus RAP content decreases

with an increased RAP content.

4. DSR and BBR tests results for binders, recovered by the Abson method from loose

bituminous concretes aged by different aging protocols, indicate that no one

protocol produces asphalt that would have all parameters matching the parameters

of binders subjected to RTFOT and PAV procedures. Consequently, since this

study was to determine durability of bituminous concrete containing RAP, the

fatigue cracking factor (G*sind) was selected as one to be matched during

long-term aging process of bituminous concrete.

5. Fatigue cracking factors (G*sind) of binders recovered from uncompacted mixes

with gravel aggregate have the values closest to these measured for the same

binders aged by RTFOT and PAV methods, when an aging protocol consisting of

2 hours @135°C followed by 5 hours @100°C was selected.

6. Fatigue cracking factors (G*sind) of binders recovered from uncompacted mixes

with limestone aggregate had random values, and no aging procedure produced

binders that would have parameters corresponding with binders aged by RTFOT

and PAV methods. The reason for this fact may be found in a significant amount

of binder being absorbed into limestone pores, and thus not affected by oxidation

processes the same way as binder that remained on the aggregate particle surface.

Consequently, only part of the binder was effectively aging, and DSR and BBR

tests were performed on binder consisting of aged and not aged part.

In recognition of this, the protocol selected for mixes with gravel aggregate was

adopted.

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7. The actual fatigue cracking factor values (G*sind) for 10 binders obtained, by the

Abson recovery method, from test specimens of bituminous concrete made from

gravel aggregate and RAP D, E, and F match perfectly the desired values in 4

cases, are 15 % off in 2 cases, and 20 to 30 % off in 3 cases. In one case (20% of

RAP D addition), the actual G*sind value is 50% off from the desired value and is

most likely representing the erroneous test result.

8. The actual fatigue cracking factor values (G*sind) for 10 binders obtained, by the

Abson recovery method, from test specimens of bituminous concrete made from

limestone aggregate and RAP A, B, and C differ considerably from the values that

were sought.

9. The moisture damage test results indicate that RAP addition has an effect on the

performance of bituminous concrete.

10. The absorbed energy data collected during the moisture damage test for

bituminous concrete with limestone aggregate shows an increasing trend with an

increased RAP content for unconditioned and control test specimens at least up to

the amount tested i.e.30%.

11. Values of the ratio of absorbed energy for specimens with limestone aggregate do

not show a specific trend; however, their close range could indicate that mixes

made with this particular limestone aggregate may contain up to 30% RAP and

still have acceptable durability, based on the absorbed energy consideration.

12. The absorbed energy data collected during the moisture damage test for

bituminous concrete with gravel aggregate does not show consistent trends.

However, the ratios of absorbed energy of conditioned to control specimens is

greatest at 10% RAP addition and decreases with an increase of RAP content

indicating that, based on absorbed energy consideration, a 10% RAP addition may

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have positive influence on bituminous concrete.

13. The compressive strength data shows that aged bituminous concrete is sensitive to

RAP source and content. However, presently collected data does not permit clear

conclusions regarding its trends in relation to RAP content, consequently proving

that, based on present experience, compressive strength may not be recommended

as a tool to determine optimum RAP content.

5.3. RECOMMENDATIONS

1. The absorbed energy procedure as presented in the Appendix could be adopted by

ODOT for use in determining optimum RAP content when designing a

bituminous concrete mix.

2. The following table could be used by ODOT to classify, based on indirect tensile

strength data, the different bituminous mixes as having high, acceptable, and low

strength.

General Indirect Tensile Strength (Shear) Values for HMA, psi

Material ITS Before Aging ITS After Aging

Low Strength HMA >80 >70

Acceptable HMA 90 - 130 80 - 120

High Strength HMA 130 - 300 100 - 240

3. The following table could be used by ODOT to further classify, based on the

absorbed energy principle, Ohio bituminous mixes as having potential for high,

acceptable, and poor performance.

General Absorbed Energy Values (AEV) for HMA, lbs*inch/inch

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Material AEV Before Aging AEV After Aging

Poor Performance HMA >50 >45

Acceptable HMA 70 – 120 55 - 90

High Performance HMA 120 – 200 110 - 180

REFERENCES

1. Estakhri C.K., Bullon J.W., “Routine Maintenance Uses for Milled ReclaimedAsphalt Pavements (RAP). Research Report 1272, Texas Transportation Institute,1992.

2. FHWA Superpave Mixtures Expert Task Group, “Guidelines for the Design ofSuperpave Mixtures Containing Reclaimed Asphalt Pavement (RAP)”, adiscussion paper, 1996.

3. Kandhal, P.S., Foo, K.Y., “Designing Recycled Hot-Mix Asphalt Mixtures UsingSuperpave Technology”, paper prepared for publication in ASTM STP 1322,1997.

4. Peterson, R.L., Anderson, R.M., Soleymani, H.R., McDaniel R.S., “Recovery andTesting of RAP Binders from Recycled Asphalt Pavements”, TransportationResearch Board, 1999.

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.

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APPENDIX

Proposed Procedure for

Determination of Recycled Asphalt Pavement (RAP) Content for aBituminous Concrete Mix Based on Expected Mixture Durability

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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).

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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.

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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.

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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

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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.