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IVESR SITY LI IBRARIES

IIIIIIIIIIIIIII I

 

 

 

 

 

 

 

IIIIIIIIIIIIIIIIIIIIIIIIIIIII III

THESIS

This is to certify that the

thesis entitled

An Investigation Of
The Fundamental Chemical, Physical and

Thermodynamic Properties of Polymer Modified Asphalt
Cement

presented by

Jeffrey C. Shull

has been accepted towards fulfillment
of the requirements for

M. S . degree in Chemical Engineering

 

 

MKM

Major professor

Dr. Martin C. Hawley
Date 6/30/95

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

—.—_._ _____.—_ A ____ -4

 

LIBRARY
Mlchlgan $tate
I University

 

 

 

I PLACE N RETURN BOX to remove We checked from your record.
TO AVOID FINES return on or before dete due.

DATE DUE DATE DUE DATE DUE

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU IeAnNflnnetive ActiorVEquel Opportmlty mutation
Wm:

——..___.—_..

An Investigation Of
The Fundamental Chemical, Physical and Thermodynamic Properties

Of Polymer Modified Asphalt Cement

by

Jefl‘rey C. Shull

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

Department of Chemical Engineering

1995

 

 

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ABSTRACT

An Investigation Of
- The Fundamental Chemical, Physical and Thermodynamic Properties
Of Polymer Modified Asphalt Cement

by
Jeffrey C. Shull

The chemical compositions and physical properties of straight and polymer
modified asphalts were studied using gel permeation chromatography, infrared
spectroscopy, dynamic mechanical analysis, thermal mechanical analysis, bending beam
rheometry, rotational viscometry, and differential scanning calorimetry.

It was concluded that the combination of chromatography and infrared
spectroscopy is an excellent tool for fingerprinting and quality control of polymers and
asphalt binders. The rheological properties of an asphalt binder were good indices for
determining the optimum polymer concentrations for efl‘ective modifications. The
calorimetry results indicated that different asphalt grades have different leveIs of polar
associations as detected from changes in enthalpy. Thermal mechanical analysis was a fast
method for determining the highest possible service temperature of the pavement. All of
the experimental work, also suggested that polymer modification reduces the aging

process that occurs during the processing and service-life of an asphalt pavement.

To my parents,
Jim and Pat

and

My wife,
Renee

Thank-you for your support, patience, and understanding.

 

 

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ACKNOWLEDGMENTS

The author wishes to thank Dr. Martin C. Hawley for his encouragement and
guidance during the course of this investigation. Thanks are also extended to Dr.
Lawrence T. Drzal and Dr. Gilbert Baladi who served as co-principle investigators on this
project. Thank-you to the staff at Michigan State University's Composite Materials and
Structures Center; especially Mike Rich for his guidance with respect to experimental
technique. Thank-you also to John Barak and the staff at the Michigan Department of
Transportation, Bituminous Lab for their experimental support concerning the new SHRP
equipment.

The author wishes to express his gratitude to his family for their emotional
support. Finally, the author wishes to thank his wife, Renee, for her understanding,
patience, and encouragement throughout the duration of this work.

This research was supported by the Michigan Department of Transportation.

TABLE OF CONTENTS

List of Tables ................................................................................................................ ix
List of Figures ............................................................................................................... xi
Chapter One: Scope ...................................................................................................... 1
Chapter Two: Introduction ............................................................................................ 5
2.1 Reasons for the modification of asphalt binders ................................................... 5

2.2 A systematic study of polymer-fiber-rubber modified asphalt

pavement ............................................................................................................ 7
Chapter Three: Background ........................................................................................ 14
3.1 Asphalt characterization .................................................................................... 14
3.2 The basic characteristics of potential polymer modifiers .................................... 21
3.3 Characteristics of polymer modified asphalt binders .......................................... 32
Chapter Four: Problem Definition And Research Goals ............................................... 35
4.1 ‘ Research goals .................................................................................................. 35
4.2 Materials .......................................................................................................... 36
4.3 Experimental Protocol ...................................................................................... 37

4.3.1 Preparation of aged asphalts .................................................................. 37

4.3.2 Thermal transitions and temperature dependent structure ...................... 37

4.3.3 Molecular weight distribution ................................ . ................................ 38

 

 

 

4

Chapter I

 

5.1 R;

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5.3 E—

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4.3.4 Determination of useful chemical firnctional groups ............................... 38

4.3.5 Bending beam analysis ........................................................................... 39
4.3.6 Viscosity measurement .......................................................................... 39
Chapter Five: Experimental Details .............................................................................. 41
5. 1 Raw material preparation .................................................................................. 41
5.2 Mixing procedure for asphalt and SB S/SEBS .................................................... 42
5 . 3 Experimental methods ...................................................................................... 43
5.3.1 Aging .................................................................................................... 45
5.3.1.1 Thin Film Oven Test (AASHTO T179 or ASTM
D 1754-87) ................................................................................ 46
5.3.1.2 Pressure Aging Vessel Test (AASHTO PPl) ............................. 48
5.3.2 Chemical properties ............................................................................... 50
5.3.2.1 High performance gel permeation chromatography
system ...................................................................................... 50
5.3.2.2 Liquid chromatography transform unit ....................................... 53
5.3.2.3 Fourier transform infrared spectrometer ..................................... 53
5.3.3 Physical properties ..................................................................... ‘ ........... 54
5.3.3.1 Dynamic mechanical analysis ..................................................... 54
5.3.3.2 Thermal mechanical analysis ...................................................... 59
5.3.3.3 Differential scanning calorimetry ................................................ 61
5.3.3.4 Bending beam rheometer ............................................. . .............. 62
5.3.3.5 Rotational viscometry ................................................................ 65
Chapter Six: Experimental Results and Discussion ....................................................... 68
6' 1 Chemical properties .......................................................................................... 68

vi

 

 

7.2

7.3

 

 

6.1.1 High performance gel permeation chromatography ................................ 68

6.1.2 Fourier transform infrared spectroscopy ................................................ 79

6.1.3 Liquid chromatography transform unit ................................................... 90

6.2 Physical properties ............................................................................................ 90
6.2.1 Dynamic mechanical analysis ................................................................. 93

6.2.2 Thermal mechanical analysis ................................................................ 114

6.2.3 Differential scanning calorimetry ......................................................... 124

6.2.4 Bending beam rheometer ..................................................................... 125

6.2.5 Rotational viscometry .......................................................................... 134
Chapter Seven: Conclusions and Theories ................................................................. 137
7. 1 Theoretical models .......................................................................................... 137
7.1.1 Asphalt ............................................................................................... 137

7.1.2 Network thennoplastics (SBS and SEBS) ........................................... 140

7.1.3 Dispersed Therrnoplastics (PE) 148

7.1.4 Reactive polymers (Elvaloy®AM) ....................................................... 148

7.1.5 Crumb rubber particles ........................................................................ 148

7-2 Mixing procedure theory ................................................................................. 152
7- 3 Aging phenomena ........................................................................................... 154
7.3.1 Effect of polymer modification ............................................................ 154

7.3.2 Effect of elevated temperatures during processing ............................... 157

7'4 Optimum and critical polymer contents ........................................................... 158
7: 5 Fingerprinting protocol ................................................................................... 164

vii

 

 

76 SF‘

7.6

Chapter Eié

 

 

8.1 Ma:

8.2 MO’I

7.5.1 Asphalt grades .................................................................................... 164

7.5.2 Polymer modifiers ............................................................................... 164
7.5.3 Polymer modified asphalt .................................................................... 165
7.5.4 Methodology ................................................................. 165
7.6 Specifications ................................................................................................. 167
7.6.1 SHRP binder specification ................................................................... 167
7.6.2 MDOT binder specification ................................................................. 172
Chapter Eight: Suggested Future Work ..................................................................... 176
8.1 Materials ........................................................................................................ 176
8.2 Modeling ........................................................................................................ 176
8.2.1 Level one modeling ............................................................................. 178
8.2.2 Level two modeling ............................................................................. 178
8.2.3 Level three modeling ........................................................................... 180
8-3 Topics and experiments .................................................................................. 181
List of References .................................................................. ‘ .................................... 1 83
General References .......... 187

viii

 

 

 

 

Table 3.1 J.

Table 3.2 .

 

Table 3.3

Table 3.4

lele 4.1

 

Table 5.1
Table 6.2
Table 6.3
Table 6. .1
Table 6.5

Table 6.6

 

 

LIST OF TABLES

Chapter Three
Table 3.1 - Elemental analysis ...................................................................................... 15
Table 3.2 - Asphaltene/resin/oil ratios .......................................................................... 18
Table 3.3 - Potential reacting functional groups in asphalt ............................................ 22
Table 3.4- Studied polymers ...................................................................... 24
Chapter Four
Table 4.1 - Materials used in the study ......................................................................... 37
Chapter Six

Table 6.1 - Percentages of constituents in an unaged, unmodified AC-S
grade asphalt ............................................................................................. 70

Table 6.2 - Percentages of constituents in an unaged, unmodified
AC-lO grade asphalt .................................................................................. 71

TIlble 6.3 - Molecular weight averages for unmodified, unaged AC-S
grade and AC—lO grade asphalts ................................................................. 72

Table 6.4 - Molecular weight averages for unmodified, aged and unaged
AC-S grade asphalt .................................................................................... 73

Til ble 6.5 - Molecular weight averages for pure SBS and SEBS polymer
modifiers ................................................................................................... 74

Table 6.6 - Percentage of SEBS polymer in unaged, polymer modified
AC-S grade asphalt .................................................................................... 76

 

 

 

Table 6.

Table 6..

Table 6.9

Table 7.1

Table 7.2 .

Table 7.3 .

Table 8.] .

Table 8.2 . _

 

 

Table 6.7 - Molecular weight averages for unaged, normally aged, and
severely aged unmodified AC-S grade asphalt ............................................ 78

Table 6.8 - Molecular weight averages for normally aged and severely
aged AC-S grade asphalt modified with three weight

percent SBS polymer ................................................................................. 80
Table 6.9 - Optimum and critical polymer contents of studied
asphalt/polymer blends based on rheological properties .............................. 94
Chapter Seven
Table 7.1 - Optimum and critical polymer contents of studied
asphalt/polymer blends based on rheological properties ............................ 163
Table 7.2 - SHRP performance graded asphalt binder specification ............................ 168
Table 7.3 - MDOT polymer modified asphalt specification ......................................... 175
Chapter Eight
Table 8.1 - Suggested materials for future research .................................................... 177
Table 8.2 - Suggested topics and experiments for fiature research ............................... 182

 

 

 

 

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LIST OF FIGURES

Chapter Two
Figure 2.1 - Modifier effect on rutting ........................................................................... 8
Figure 2.2 - Modifier effect on fatigue cracking ............................................................. 9
Figure 2.3 - Modifier effect on low temperature cracking ............................................ 10
Figure 2.4 - Modifier effect on ravelling/stripping ........................................................ 11

Figure 2.5 - Material and property hierarchy for modified asphalt

pavement ................................................................................................. 13

Chapter Three
Figure 3.1 - A typical organic structure of an asphalt molecule .................................... 16
Figure 3.2 - Two phase asphalt model ......................................... I ................................ 19
I“igure 3.3 - Three types of polymer modified binders .................................................. 23
Figure 3.4 - Chemical structure of Elvaloy®AM .......................................................... 30
Figure 3.5 - Viscoelastic asphalt model ........................................................................ 34

Chapter Five
Figure 5.1 - Schematic of mixing apparatus ................................................................. 44
Figure 5.2 - Thin Film Oven ........................................................................................ 47
Figlare 5.3 - Pressure aging vessel and components ....................................................... 49
Figure 5.4 - Reproducibility of refi'active index detector (AC-10) ................................ 52

xi

 

 

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Figure 5.5 - Stress-strain output for a constant strain rheometer .................................. 56
Figure 5.6 - Stress-strain response of a Viscoelastic material ........................................ 57
Figure 5.7 - Dynamic mechanical analysis asphalt specimen

calculations .............................................................................................. 58
Figure 5.8 - Storage modulus as a function of temperature for a

triplicate .................................................................................................. 60
Figure 5.9 - Schematic of the bending beam rheometer ................................................ 63
Figure 5.10 - Bending beam rheometer sample mold .................................................... 64
Figure 5.11 - Schematic of a rotational viscometer ...................................................... 67

Chapter Six

Figure 6.1 - Gel permeation chromatography raw data for unaged,

unmodified AC-S grade asphalt ................................................................ 70
Figure 6.2 - Gel permeation chromatography raw data for unaged,

unmodified AC-lO grade asphalt .............................................................. 71
Figure 6.3 - Comparison of molecular weight distributions between

unmodified, unaged AC-S grade and AC-lO grade asphalts ...................... 72
Figure 6.4 - Comparison of molecular weight distributions between

unmodified, aged and unaged AC-S grade asphalt .................................... 73
Figure 6.5 - Comparison of molecular weight distributions between pure

SBS and SBBS polymer modifiers ........................................................... 74
Figure 6.6 - HP-GPC raw data for unaged AC-S grade asphalt modified

with four weight percent SEBS polymer .................................................. 76
Figure 6.7 - HP-GPC raw data comparing aged, four percent SBS

polymer modified and unmodified AC-S grade asphalt ............................. 77
Figure 6.8 - Comparison of molecular weight distributions between

unaged, normally aged, and severely aged unmodified

AC-5 grade asphalt .................................................................................. 78

xii

 

 

 

 

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Figure 6.9 - Comparison of molecular weight distributions between
normally aged and severely aged AC-S grade asphalt

modified with three weight percent SBS polymer ..................................... 80

Figure 6.10 - Fourier transform infrared spectrum of an aged,
unmodified, AC-S grade asphalt sample ................................................. 81
Figure 6.11 - FTIR wavelength absorbance intensity ratios analysis ............................. 82
Figure 6.12 - FTIR spectrum of SBS polymer modifier ................................................ 83
Figure 6.13 - FTIR spectrum of SEBS polymer modifier ............... g .............................. 84

Figure 6.14 - Determination of absorbance band ratio for asphalt/SBS
polymer finger printing calibration curve ................................................ 86

Figure 6.15 - FTIR absorbance band ratio calibration curve for unaged
AC-S grade asphalt/SBS polymer blends ................................................. 87

Figure 6.16 - FTIR absorbance band ratio calibration curve for aged
AC-S grade asphalt/SBS polymer blends ................................................. 88

Figure 6.17 - FTIR wavelength absorbance intensity ratios analysis for
unmodified AC-S grade asphalt .............................................................. 89

Figure 6.18 - FTIR spectrum of SBS afier separation from an AC-5/SBS
blend using an LC-transform unit ........................................................... 91

Figure 6.19 - FTIR spectrum of A05 afier separation from an
AC-S/SBS blend using an LC-transfonn unit ........... 92

Figure 6.20 - Storage and loss moduli as a fianction of temperature for
AC-S grade asphalt modified with one weight percent SBS
polymer .................................................................................................. 95

Figure 6.21 - Storage and loss moduli as a function of temperature for
AC-5 grade asphalt modified with seven weight percent SBS
polymer .................................................................................................. 96

Figure 6.22 - Storage and loss moduli as a firnction of temperature for

AC-S grade asphalt modified with ten weight percent SBS
polymer .................................................................................................. 97

xiii

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Figure 6.23 - Storage and loss moduli as a fianction of temperature for
125/ 150 penetration grade asphalt modified with five

weight percent SBS polymer ................................................................... 98
Figure 6.24 - "Log" slope of storage and complex moduli as a function

of increasing SBS polymer content in AC-S from 25 to 60°C .............. 100
Figure 6.25 - Loss and storage moduli as a function of percent SBS polymer

content in AC-S at 60°C ...................................................................... 101
Figure 6.26 - Tan delta as a function of SBS polymer content in AC-S

at 60°C ............................................................................................... 102
Figure 6.27 - Inverse loss compliance as a function of SBS polymer

content in AC-5 at 60°C ...................................................................... 103
Figure 6.28 - Storage modulus ratio of SBS polymer modified AC-S to

unmodified AC-S grade asphalt binder at 60°C as a

firnction of polymer content ................................................................ 105
Figure 6.29 - Storage modulus ratio of SBS polymer modified AC-S

grade asphalt at 25°C to 60°C as a fimction of polymer

content ............. 106
Figure 6.30 - Sensitivity of tan delta with respect to SBS polymer content

and temperature for modified AC-S grade asphalt ............... , ................. 108
Figure 6.31 - Sensitivity criteria of tan delta as a function of SBS

polymer content for modified AC-5 grade asphalt ................................ 109
Figure 6.32 - Storage modulus as a function of temperature for

unmodified AC-S grade asphalt ............................................................ 110
Figure 6.33 - Loss modulus as a fianction of temperature for unmodified

AC-5 grade asphalt ............................................................................... 111
Figure 6.34 - Tan delta as a function of temperature for unmodified

AC-S grade asphalt ............................................................................... 112
Figure 6.35 - Percent increase in the storage modulus at 60°C as a

firnction of aging for unmodified AC-S grade asphalt ........................... 113
Figure 6.36 - Storage modulus as a fianction of temperature for AC-S

grade asphalt modified with three weight percent SBS

polymer ............................................................................................... 1 15

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Figure 6.37 - Loss modulus as a function of temperature for AC-S grade
asphalt modified with three weight percent SBS polymer ..................... 116

Figure 6.38 - Tan delta as a fimction of temperature for AC-S grade
asphalt modified with three weight percent SBS polymer ..................... 117

Figure 6.39 - Percent increase in the storage modulus at 60°C as a
fimction of aging for AC-S grade asphalt modified with
three weight percent SBS polymer ...................................................... 118

Figure 6.40 - TMA data for the determination of the glass transition
temperature of SBS polymer ................................................................ 119

Figure 6.41 - Final softening temperatures of asphalt grade/polymer
blends as a function of polymer content determined by
TMA ................................................................................................... 121

Figure 6.42 - Final softening temperatures of aged and unaged AC-5
grade asphalt/ SBS polymer blends as a fianction of
polymer content determined by TMA ................................................... 122

Figure 6.43 - Differences in the final softening temperatures of aged
versus unaged AC-S grade asphalt/SBS polymer blends as
a function of polymer content determined by TMA .............................. 123

Figure 6.44 - DSC data for the determination of the glass transition
temperature of AC-S grade asphalt ...................................................... 126

Figure 6.45 - DSC data depicting the intensity of transitions as a .
function of asphalt grade ...................................................................... 127

Figure 6.46 - DSC data depicting transitions as a function of temperature
history ................................................................................................. 128

Figure 6.47 - DSC data depicting transitions as a function of repetitive
temperature cycling .............................................................................. 129

Figure 6.48 - Bending beam rheometer measured stiffness for SBS
polymer modified AC-S grade asphalt at -24°C .................................... 130

Figure 6.49 - Bending beam rheometer measured stiffness for SBS
polymer modified AC-lO grade asphalt at -24°C .................................. 132

 

 

 

 

 

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Figure 6.50 - Bending beam rheometer m-value data as a fianction of
polymer content for SBS polymer modified AC-S grade
asphalt at -24°C .................................................................................. 133

Figure 6.51 - Viscosity of SBS polymer modified AC-S grade asphalt as a
function of temperature ........................................................................ 135

Figure 6.52 - Viscosity of SBS polymer modified AC-S grade asphalt at

270°F as a function of polymer content ................................................ 136
Chapter Seven
Figure 7.1 - Two phase asphalt model ....................................................................... 139
Figure 7.2 - Schematic of SBS polymer ..................................................................... 141
Figure 7.3 - Storage and loss moduli at 60°C as a function of polymer
content (AC-5/SBS) .............................................................................. 143
Figure 7.4 - Schematic of SBS modified asphalt at service temperatures .................... 144

Figure 7.5 - Depiction of SBS modified asphalt theory at service
temperatures .......................................................................................... 145

Figure 7.6 - Schematic of SBS modified asphalt at high (processing)
temperatures .......................................................................................... 146

Figure 7.7 - Depiction of SBS modified asphalt theory at high
(processing) temperatures ...................................................................... 147

Figure 7.8 - Schematic of PE modified asphalt at service temperatures ....................... 149

Figure 7.9 - Schematic of Elvaloy®AM modified asphalt at service
temperatures .......................................................................................... 150

Figure 7.10 - Schematic of crumb rubber modified asphalt at service
temperatures ........................................................................................ 151

Figure 7.11 - Tan delta as a fimction of temperature and mixing time for
AC-S grade asphalt modified with five weight percent SBS
polymer ............................................................................................... 153

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Figure 7.12 - Tan delta as a fimction of temperature and mixing time for
AC-S grade asphalt modified with seven weight percent

SBS polymer ........................................................................................ 155
Figure 7.13 - Comparison of mixing times for AC-20 grade asphalt

modified with seven weight percent SBS polymer ................................ 156
Figure 7.14 - Elevated temperature aging data ........................................................... 159
Figure 7.15 - Schematic of unaged asphalt constituents .............................................. 160

Figure 7.16 - Schematic of asphalt constituents after aging at normal
temperatures ........................................................................................ 161

Figure 7.17 - Schematic of asphalt constituents after aging at elevated
temperatures ........................................................................................ 162

Figure 7.18 - SHRP performance grading of AC-S grade asphalt/SBS

polymer blends .................................................................................... 173
Figure 7.19 - SHRP performance graded temperature range of A06 grade
asphalt/SBS polymer blends ................................................................ 174
Chapter Eight
Figure 8.1 - Schematic of proposed modeling hierarchy ............................................ 179

xvii

 

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Chapter One

Scope

The long term pavement performance of asphalt concrete surfaced roads is a
firnction of traffic load and volume, material properties, construction practices, and
environmental factors. A typical asphalt concrete surfaced pavement deteriorates over
time and with increasing number of load repetitions. Pavement deterioration manifests
itself in several common types of distress including rutting, fatigue cracking, low
temperature cracking, reflective cracking, aging, ravelling, and stripping”. The
conventional materials used in an asphalt concrete mixture may perform satisfactorily
relative to one distress type but fail prematurely relative to the others. For example,
asphalt concrete mixtures made by using hard binders will have low rutting but, high
fatigue and temperature cracking potentials. On the other hand, mixtures made with sofi
asphalt binders will have low fatigue and temperature cracking but, high rutting potentials.
Hence, modification of the asphalt to enhance its performance at extreme temperatures
and under traffic loading is essential to the success of constructing superior pavements.
Such modifications include the addition of polymers to enhance the binder properties at
both low and high temperatures. And indeed, it has been shown that polymer modified
asphalts can improve pavement performance“. However, most studies have been
concentrated on specific materials and properties. The need for a systematic study of

polymer-fiber-rubber modified asphalt pavement is required.

 

 

 

 

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Michigan State University is currently conducting a study of polymer modified

asphalt pavements that will address the above considerations. The study is divided into
three sections including: the fundamental physical, chemical, and thermodynamic
properties of asphalt binders; the basic morphology and microstructure of polymer-fiber-
asphalt-aggregate mixtures; and the structural and engineering properties of polymer-fiber-
asphalt-aggregate mixtures under the extreme low and high temperatures found in the
State of Michigan.

This major objective of this study was to provide a wealth of fundamental physical,
chemical, and thermodynamic data for the binder materials under study through both
experimental and theoretical investigations. These studies led to the major deliverable of
this research; initial, pictorial, physical and chemical models of polymer modified asphalt
blends that account for difi‘erent asphalt grades, sources, and polymer types. Secondary
deliverables of the study include: determination of the optimum polymer modification
contents required for optimum physical properties; a fingerprinting protocol for
determining the type and amount of polymer present in an unknown sample to be used by
the Michigan Department of Transportation (MDOT); and a review of the SHRP and
MDOT binder specifications with suggested revisions for use with polymer modified
aspalt binders.

Based on the suitability of materials for Michigan weather, the asphalt grades and
polymer modifiers used in this study were AC-2.5, A05, A010, AC-20, styrene-
butadiene-styrene, and styrene-ethylene-butylene-styrene. The asphalts were all supplied

by Amoco and were graded from low viscosity, AC-2.5, to high viscosity, AC-ZO. Both

 

 

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polymers are Shell Kraton polymers and were used in powder form. All possible

combinations of AC-S and AC- 1 O with styrene-butadiene-styrene and styrene-ethylene-
butylene-styrene were tested fi'om 1 through 10 weight percent polymer modification.

The deliverables of the research were accomplished through the completion of the
following set of experiments:

0 High Performance Gel Permeation Chromatography;

o Fourier Transform Infrared Spectroscopy;

0 Dynamic Mechanical Analysis;

0 Thermal Mechanical Analysis;

0 Differential Scanning Calorimetry;

- Bending Beam Rheometry;

o and, Rotational Viscometry.

Beyond the original deliverables, two additional findings concerning asphalt aging
processes were discovered. First, polymer modification was found to decrease the amount
of aging that occurs during the processing and service-life of an asphalt pavement.
Second, a degradation aging process was identified for asphalt when it is heated to
extremely high temperatures during processing.

Chapters Two and Three of this thesis will introduce the reader to the problem at a
more in depth level and provide any relevant background information found in recent
literature. Chapter Four is an expansion of the study's objectives and materials. Chapter
Five discusses the experimental procedures and theories used during this study and

3 Chapter Six presents the actual data collected for the studied materials. The thesis is

 

.l

 

conclude.

future res

 

 

 

4
concluded in Chapters Seven and Eight which provide the final findings as well as possible

future research.

 

 

 

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Chapter Two

Introduction

Asphalt concrete surfaced pavements are showing signs of premature distress in
the State of Michigan. It has been suggested in recent studies that polymer modification
of the asphalt binder will enhance the properties and thus the service life of the final
asphalt pavement. Research is currently being conducted at Michigan State University to
investigate the benefits of adding polymer modifiers to the asphalt mixture. The ultimate
goal of this study is to provide a systematic and comprehensive protocol for selecting
asphalt modifiers and for establishing asphalt mixture processing conditions to provide
pavements with long service lives. The focus of the research in this thesis is a greater
understanding of the firndamental physical, chemical, and thermodynamic properties of

straight asphalt binders, polymer modifiers, and polymer modified asphalt binders.

2. 1 Reasons for the modification of asphalt binders

The long term pavement performance of asphalt concrete surfaced roads is a
firnction of traffic load and volume, material properties, construction practices, and
environmental factors. A typical asphalt concrete surfaced pavement deteriorates over
time and with increasing number of load repetitions. Pavement deterioration manifests

itself in several common types of distress including:

 

 

 

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Slrc:

 

6

0 Rutting, which is caused by consolidation or lateral movement under traffic in one
or more of the underlying courses, or by displacement in the asphalt surface layer
itself. The rutting resistance can be improved by increasing the elasticity of the
asphalt binder at high temperatures.

0 Fatigue cracking, which is caused by excessive deflection of the surface over
unstable subgrade or lower courses of the pavement. An increase in the tensile
strength of the asphalt binder will reduce the fatigue cracking potential.

0 Low temperature cracking, which is caused by a volume change of aggregate and
binder in the mixture, especially in pavements with a high content of low
penetration asphalt. This distress can be reduced by increasing the tensile strength
and flexibility of the asphalt binder at low temperatures.

0 Joint reflective cracking, which is caused by vertical or horizontal movements in
the pavement beneath the overlay. This distress can be redUced by increasing the
flexibility and tensile strength of the asphalt mixture.

0 Ravellinystripping, which is caused by a lack of compaction during construction,
construction during wet or cold weather, dirty or disintegrating aggregate, too
little asphalt binder in the mixture, or over heating of the asphalt mixture.
Ravelling/stripping can be reduced if the adhesion between asphalt and aggregate
can be improved"3 .

In general. these distresses can be reduced by improving the temperature susceptibility,
moisture resistance, and rheological properties of asphalt binders and the adhesion

between binder and aggregate within the asphalt concrete mixture.

 

 

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Pavements

7
The conventional materials used in an asphalt concrete mixture may perform

satisfactorily relative to one distress type but fail prematurely relative to others. For
example, asphalt concrete mixtures made by using hard binders will have low rutting but,
high fatigue and temperature cracking potentials. On the other hand, mixtures made with
soft asphalt binders will have low fatigue and temperature cracking but, high rutting
potentials. Hence, modification of the asphalt to enhance its performance at extreme
temperatures and under traffic loading is essential to the success of constnrcting superior
pavements. Such modifications include the addition of polymers, fibers, and/or rubber
particles to enhance the binder properties at both low and high temperatures.

And indeed, it has been shown that polymer modified asphalts can improve pavement

performance“.

2.2 A systematic study of polymer-flber-ru bber modified asphalt pavement

Numerous studies have been conducted in the area of polymer modified asphalt
binders. However, due to the large scope of the final question of enhanced pavement
performance, most previous research has been limited in its objectives and has only
covered a few aspects of the modification and a small number of materials. Figures 2.1-
2.4 summarize the change of performance properties due to polymer modifications. The
inconclusiveness of the results suggest that a systematic study of polymer-fiber-rubber

modified asphalt pavement is required.

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12
Michigan State University is currently conducting a study of polymer modified

asphalt pavements that will address the above considerations. The study was constructed
according to the three parts of pavement processing including: 1) processing of the binder,
2) production of a binder/aggregate mixture, and 3) pavement construction (see Figure
2.5). These sections are in turn controlled by, the fundamental physical, chemical, and
thermodynamic properties of asphalt binders, the basic morphology and microstructure of
polymer-fiber-asphalt-aggregate mixtures, and the structural and engineering properties of
polymer-fiber-asphalt-aggregate mixtures under the extreme low and high temperatures
found in Michigan. When studied in conjunction with each other for a matrix of materials,
the above divisions form a systematic study that will enable relationships to be formed
between final pavement performance and the fundamental properties of the mixture
constituents. It will also allow for the identification of any control parameters that may be
ilnportant when selecting materials, specifications, and construction practices for designing
superior asphalt pavements.
This thesis will focus on the fundamental physical, chemical, and thermodynamic
properties of straight asphalt binders, polymer modifiers, and polymer modified asphalt
binders. -' Chapter three is a summary of the background information relevant to the

information presented in this thesis.

13

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Chapter Three

Background

In order to better understand the effect of polymer modifiers on the properties of
asphalt cement and the performance of asphalt concrete, it is necessary to first understand
the properties of the raw materials. Chapter three will present recent information found in
the literature regarding: 1) asphalt characterization, 2) the basic characteristics of potential

polymer modifiers, and 3) characteristics of polymer modified asphalt binders.

3. I Asphalt characterization

Asphalt is a complex mixture of many different hydrocarbons consisting primarily

of molecules that contain mainly carbon and hydrogen atoms. A generic asphalt elemental
analysis shows that approximately 84 percent of the sample is carbon, 10 percent
hydrogen, 1 percent oxygen, and the remainder consists of several trace elements
including nitrogen, sulfur, vanadium, nickel, and iron7. The average molecular weight of a
generic asphalt molecule ranges from 500 to 5000 as shown in Table 3.17. The
arrangement of the various elements in an asphalt binder is of much greater importance
than the total amounts of the elements themselves. Asphalt consists mainly of linear and
complex organic ring structures as shown in Figure 3.18. The ring structures can be

separated into two groups: naphthenic and aromatic. Naphthenic compounds are simple

14

 

 

 

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or complex saturated rings that have a large number of side chains. Aromatic compounds

are heavier molecules that consist of stable six atom rings with few side chains“.

For convenience, asphalt constituents are classified into three categories: oils,
resins, and asphaltenes. Oils are the light compounds in asphalt which have the lowest
molecular weights (24 - 800) and have a large number of side chains and few rings.
Accepted criteria for the oil classification are molecules with carbon/hydrogen atom ratios
less than 0.6 and are soluble in hexane'. Resins are intermediate molecular weight
compounds (800 - 2000). It is important to note that resins can contain sulfur and
nitrogen. Resins are polar, have carbon to hydrogen atom ratios between 0.6 and 0.8 and
are soluble in light petroleum naphtha'. Asphaltenes contain the trace elements

mentioned earlier which may react with potential polymers and are soluble in
carbont-errachloride. An average asphalt sample has an asphaltene/resin/oil ratio of
approximately 23/27/509 and the asphaltene content is higher for harder asphalts. High
performance gel permeation chromatography (HP-GPC) is usually used to determine the
molecular weight distribution, molecular weight, and the fraction of each constituent in an
asphalt sample. Table 3.2 shows the ratios for three different samples”. Note. that the
asphaltene content is larger for the harder sample.

Using the asphaltene/resin/oil classifications, a two phase asphalt model is
c1¢=‘~’eloped'. Phase 1 is an assembly phase consisting of asphaltenes and resins that is
dispersed in phase 2, the solvent phase consisting of the oily constituents. Figure 3.2 is a
syntbolic depiction of this model. The resins behave as peptizingagents that stabilize the

a$13 haltenes in the oily constituents.

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Phase 1 = Asphaltenes + Resins (Assemblies)

Phase 2 = Oils (Solvent)

Figure 3.2 - Two phase asphalt model

 

 

 

 

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20
The asphaltene core of the assembly phase can vary between 40 and 60 angstroms

in diameter. As the asphaltene content of an asphalt sample increases, the assembly phase
also increases. This adds structure to the asphalt and gives it better high temperature
properties and rutting resistance. The percentage of the assembly phase present is the
defining factor between different grades of asphalts. The resins contain aromatic
compounds substituted with longer alkyls and a larger number of side chains attached to
the rings than asphaltenes. The combination of the saturated and the aromatic
characteristics of the resins stabilizes the colloidal nature of the asphaltenes in the oil
medium. Asphaltenes are present as discrete or colloidally dispersed particles in the oily
phase. Colloidally dispersed asphaltenes are not stable in the oil medium by themselves,
but can be stabilized through polar resins. Asphaltenes can exist both in a randomly
oriented particle aggregate form or in an ordered micelle form. In micelle form, the polar
groups (water, silica, or metals such as V, Ni, an Fe) are either oriented toward the center
to form an oil-external micelle or oriented outward to form an oil-internal micelle (Hartley
trucelle). The growth and ultimate size of the micelles are dependent on temperature, resin
content, and the presence of other chemicals such as polymer modifiers. The engineering
PrOperties of asphalts are directly related to the quantity of asphaltenes, the size of the
micelle structure, and the nature of the dispersion medium, oils and resins.
Another important aspect of asphalts for polymer modification is that the
fi-ll'lctional groups present in asphalts may react with polymers during processing. Table
3 - 3 lists the functional groups that have been identified in asphalts including: carboxylic

acids, ketones, phenols, sulfoxides, acid anhydrides, pyrroles, and quincnes’.

 

12 The basic c'»

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2 1
3, 2 The basic characteristics of potential polymer modifiers

The basic criteria for selecting a polymer modifier are performance, ease of

processing, and economics. According to the firnctions and behaviors of various modifiers
in asphalts, modifiers can be categorized into five types: dispersed thennoplastics, network
thennoplastics, reacting polymers, fibers, and crumb rubber (CRM) particles. Dispersed
thennoplastics behave like asphaltenes and normally require peptizing agents like resins to
stabilize the modified systems. Usually, it requires a considerable amount of material
before forming a macrostructural network. Network thennoplastics behave like resins and
will form a network of themselves inside asphalts. Reacting polymers bond chemically to
the asphalt (normally to the asphaltenes) and form asphalt/polymer networks. CRM
particles behave as aggregates if there sizes are large and behave as dispersed
theflnOplastics if there sizes are small (below lOOum). Fibers increase the available
wetting surface area and behave as binder thickeners which reduce asphali bleeding.
Figure 3.3 is a pictorial representation of the polymer modified asphalt types". In all
cases, the goal is to create more structure inside an asphalt without losing its low
temperature properties.

Table 3.4 lists polymers that have been studied as additives to asphalt and their
resPfictive cost. Reactive polymers cost more than network polymers and dispersed
Polymers are the least expensive. However, a larger amount of dispersed polymer is
“med to create a network structure in an asphalt than that of a network polymer.

Reactive polymers require the least amount of material among the three polymer groups.

Func

 

 

 

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22
Table 3.3 - Potential reacting functional groups in asphalt

 

Functional Group Structure
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25
Modifiers that have been encountered in the literature are summarized according to

their type. One or two of the most promising modifiers in each category are selected
based on the results of prior studies.

For dispersed thennoplastics, modifiers that improved the low temperature
susceptibility of asphalts included ethylene acrylic copolymer‘, hydroxylterminated
polybutadiene (HTPBYZ, and polypropylene wax (PPW)‘2. Modifiers that improved the
fatigue cracking resistance included HTPB”, and PPW”. When polyethylene (PE) was
used to modify AC-20 asphalt, the modified binder had a higher resistance to permanent
deformation and thermal cracking'z'”.

Reviews of previous studies show that PE is the most promising candidate in the
dispersed thennoplastics family. The glass transition temperature of PE ranges from ~130
to -15°C. Polyethylene, however, is insoluble in asphalts (tends to phase separate in the
asphalt/polymer blend). For example, PE will coagulate and separate from the asphalt
phase in half an hour at 160°C after mixing if no stabilization technique is introduced. The
properties of a phase separated asphalt/polyethylene blend are less than those of straight
asphalt. Therefore, phase separation needs to be prevented.

There are two ways to prevent phase separation. One is to reduce the storage
time, such as done by Novophalt. This technique requires a huge mixing truck on the
construction site so that asphalt, aggregate and PE can be mixed just prior to being laid
down. Usually, the smaller the PE particle size, the better the performance of the PE
modified pavement. Another way to prevent PE phase separation is through stabilization

of the asphalt/PE blend.

 

 

 

  
    
 

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26
Many methods can be used for stabilizing an asphalt/PE blend. They are,

structural stabilization by gelling agents, specific polymer/asphalt functional reactivity,
specific asphalt selection/modification, partial dissolution by polymer oxidation, and steric
stabilization by an amphifatic block or graft copolymer.

For structural stabilization by gelling agents, both inorganic and organic agents
have been studied. When inorganic fillers are added to a liquid, a three dimensional
network is formed”. This has a thickening effect which tends to increase the brittle nature
of the composite. Therefore, when inorganic agents are added to asphalt, the agents may
introduce cracks at low temperatures. Organic gelling agents may give the blend macro
scale stability but micro scale phase separation can still occur.

Through the introduction of certain functional groups to the polymer backbone,
such as ester forming groups, polyethylene can be made partially soluble and stabilized in
liquid bitumen. These methods include phosphonization, chlorosulfonation, maleic
anhydride grafting, and acrylic acid grafting. If an asphalt only contains a small amount of
polar aromatics (<5%), PE is a good modifier and the asphalt/PE blend will be stable.
Polyethylene chlorinated to less than 15 weight percent and polyethylene maleat'ed to less
than four weight percent were used to modify asphalts and resulted in improved
properties” .

Partial dissolution by polymer oxidation is another method that can be used for
asphalt/PE stabilization. The oxidation of polymer makes PE more compatible with
asphalt. Oxidation techniques include hot air, high shear, and catalytic oxidation.

However, the method causes deterioration of the low temperature properties of asphalt.

In steric 5:3:

 

 

keep the particles a:
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thermal forces T
polyethylene Stab.
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27

In steric stabilization, PE coalescence is prevented using a form of sten’c barrier to
keep the particles apart far enough so that Van der Waals interactions can be overcome by
thermal forces. The steric barrier should be soluble in asphalt and reactive with
polyethylene. Stabilizers studied include styrene-butadiene rubber, Kraton (31652, and
styrene hydrogenated butadiene-styrene tri-block copolymer.

For network thennoplastics, modifiers that increased binder resistance to rutting
included styrene-butadiene-styrene (SBS)”‘mg, styrene-ethylene-butylene-styrene

5.6-16.19

(SEBS)"‘", and styrene-butadiene random c0polymer (SBR) . However, they only

improved binder low temperature properties slightly. SBR modified asphalts also had less

5.16.19

fatigue cracks However, ethylene-vinyl acetate (EVA) modified AC-20 showed

more rutting and fatigue cracking as well as a tendency of stripping"'2“7"9‘2°.

SBS/SEES and SBR are the most promising candidates in the network
thermoplastics family. SBR modifier is usually used in the latex form, a polymer/water
mixture. SBR latex is manufactured at temperatures of 100-110°P with a resulting
polymer size of 0.1 micron and an overall solid weight percentage of 31%. Mechanical
agglomeration is used to concentrate the latex and the final commercial product is 70
wt.% solids with a polymer size of half a micron. Typically, 3 to 5 wt.% of dry SBR is
added to asphalt. Generally, a homogeneous blend is desired with asphalt as the
continuous phase. In SBR modified asphalt, asphalt remains the continuous phase if the
SBR concentration is below approximately 7 wt.%. Molecular weight distribution and

average polymer size in the latex are two variables that can be adjusted to increase

compatibility between asphalts and polymers in the network thermoplastic family.

 

 

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28
For reacting polymers, epoxy“ and Elvaloy®AM modified asphalts showed less

rutting, thermal cracking, and temperature susceptibility. Furfiiralm22 modified asphalts
had lower temperature susceptibility, higher resistance to rutting and low temperature
cracking, higher fi'eeze-thaw resistance, and better adhesion, but lower cohesion. Maleic
anhydride (MAI-I)23 modified asphalts had lower temperature susceptibility, higher
resistance to rutting and low temperature cracking, and better adhesion, but lower
cohesion. For the reacting polymers, previous studies are very limited.

Polymers with epoxide and hydroxyl groups are recommended for the reacting
polymer family. Elvaloy®AM is a modified ethylene c0polymer with a reacting epoxide
group developed by DuPont/Chevron for the modification of asphalt cement.
Elvaloy®AM is the only polymer currently being manufactured in the reacting polymer
family.

Most polymers, when added to asphalt cement, become dispersed and upon
addition of more polymer, form a network which gives the desired properties.
Elvaloy®AM, on the other hand, chemically reacts with asphalt cement creating a new
material. Because of this reaction, DuPont claims that only 1-2 percent by weight of their
material needs to be added to asphalt cement versus 3-5 weight percent of most other
polymers to obtain the same desired properties. Elvaloy®AM contains an epoxy functional
group that DuPont believes reacts with aromatic carboxylic acid fiinctional groups found
in the asphaltene portion of asphalt cement. Figure 3.4 is a chemical schematic of

Elvaloy®AM.

 

 

The reac‘
measurements tr
uith asphalt cerr.
to the otter-sire
The amount of pt

DuPont t:
ml'Sis and four.
help Prevent nrtt;
those 0f Straight a
am“ 35th Shc

DuPont ant
beam “Sb sPlit te
Showed lhe DUPOm

 

 

29
The reaction of Elvaloy®AM with asphalt cement was tested by looking at infrared

measurements that showed the epoxy fiinctional groups disappeared after being reacted
with asphalt cement. Too much Elvaloy®AM will result in gelling the asphalt mixture due
to the extensive crosslinking structures caused by the reacted epoxy functional groups.
The amount of polymer needed for asphalts from different sources also varies.

DuPont tested Elvaloy®AM modified asphalt cements using dynamic mechanical
analysis and found that the material remained elastic at high temperatures which would
help prevent rutting. The binder properties remained the same at low temperatures as
those of straight asphalts. In order to improve both high and low temperature properties,
a softer asphalt should be used with Elvaloy®AM.

DuPont and Chevron tested their product using the Chevron creep test, bending
beam test, split tensile measurements, and resilient modulus measurements. All tests
showed the DuPont product to be superior to SBS and SBR. It should be noted that all of
these tests were conducted by the manufacturer of the superior polymer.

Mixing Elvaloy®AM with asphalt cement requires a low horse power stirrer, a
heated tank, and an elevator assembly that will transfer the polymer to the tank. The
polymer must be allowed to react with the asphalt cement for 2-48 hours at 350°F. The
polymer is mixed in a solid form and DuPont claims to have never gelled a tank.

Aging/oxidation was found not to be a problem when processing at these high

30

:VQASostw 252......- .3.=.§.U . V .M exam-E

._.
Dun—u oil-II

./\//\/ oil 2... Sisal o ../\,,,,/\/

/\V/\

 

 

temperatures beca
lhe manufacturer
for 100 days at iii
mixing period.
El\'alo)'g‘.\\
L‘i‘i’flih but has b-

uphahs. No rem

 

lstheirs. At the pre

MOS! fibers,

mm and elastic:

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MiCrolil 8 -

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malfiers (CRAISX

filmy-“26.27 Was

Mombasa» .
Inc
ltlleq

Though the 1
heat
0
“CM is

31
temperatures because the tanks are sealed and no air is allowed to circulate in the system.

The manufacturer stated a case where Elvaloy®AM modified asphalt cement was stored
for 100 days at 350°F, and no viscosity change was recorded with only a one hour per day
mixing period.

Elvaloy"AM is handled at temperatures similar to those of other polymer modified
asphalts, but has been found not to be stringy and sticky like SBS and SBR modified
asphalts. No recyclability experiments have been conducted on Elvaloy®AM modified
asphalts. At the present time, Elvaloy‘"AM costs between $1.20 and $2.00 per pound.

Most fibers, including cellulose, mineral, glass, and polyester, offered better
strength and elasticity to modified asphalts“. Cellulose fiber modified asphalts24 also
demonstrated less bleeding and better stabilization. Reviews on previous studies show
that cellulose and polyester fibers are the most promising materials in the fiber family.

Microfil 8 modified asphalts“ showed less rutting and low temperature
susceptibility as well as less fatigue cracking than straight asphalts. For cmmb rubber

modifiers (CRMs), both good and bad field results were reported. Good field

26.27

performance was reported for low temperature susceptibility. The reported bad field

performancesu'” included severe aging, lower tensile and shear strength, ravelling,
reflective cracking, and stripping.

Though the benefits of crumb rubber modification to asphalts are still being
debated. CRM has to be studied due to environmental regulations. The principle source
of CRM is scrap tire rubber in forms of whole tire, cut tire, shredded tire, or retread

buffing waste. Tire rubber is primarily a composite of a number of blends of natural and

I
nnthetic rubbers
emulator, crack;
rubber and cuts t
product of this pr
Silt range of 9 5
common process.
passing the mater.

is called ground C

 

‘25 um (No4 . .t

 

‘3? line ground p
has a large Surface
The “”386 com o
and medium Crumb
Aniong the
mmnolflastics. Tea
The CW particle

nprcmented “Quin‘

ASPhah is a ‘

t .
Mug Upon the t

 

32
synthetic rubbers and carbon black. There are three processing methods to produce CRM:

granulator, crackmill, and micromill. The granulator process shears apart the scrap tire
rubber and cuts the rubber with revolving steel plates that pass at a close tolerance. The
product of this process is called granulated CRM which has a low surface area and particle
size range of 9.5 mm to 2.0 m (3/8” - No.10 sieve). The crackmill process, the most
common process, tears apart scrap tire rubber and reduces the size of the rubber by
passing the material between rotating corrugated steel drums. The product of this process
is called ground CRM which has a large surface area and particle size range of 4.75 mm to
425 um (No.4 - 40 sieve). The micro-mill process fithher reduces the crumb rubber to
very fine ground particles. The product of this process is called fine ground CRM which
has a large surface area and a particle size range of 425 um to 75 um (No.40 - 200 sieve).
The average cost of commercial CRM ranges form 20 to 35 cents per kilogram for coarse
and medium crumb and up to 55 cents per kilogram for fine ground crumb.

Among the five types of modifiers, the order of importance in Michigan is network
thennoplastics, reacting polymers, dispersed thennoplastics, fibers, and CRM particles.
The CRM particles could become more important if congressional legislation is

implemented requiring their use.

3.3 Characteristics of polymer modified asphalt binders

Asphalt is a Viscoelastic material that displays a variety of different properties

depending upon the temperature of the sample. Goodrich proposed a model of asphalt

 

depicted 35 a Sh‘
represenlS the ‘05
It

At high it

a shock absorber
abnttle elastic s
analogy, the SP“
ocean. At high I
temperatures, the:
potential of ruttint.
polymers-fibers ru:
range of both the
Convenient measur
moo‘ulus (\15COUS)

uPOn addition of po

 

 

 

33
depicted as a shock absorber and a spring31 as shown in Figure 3.5. The shock absorber

represents the viscous properties of asphalt and the spring represents the elastic properties.

At high temperatures, asphalt shows good viscous flow properties and behaves as
a shock absorber with little or no elastic behavior. At low temperatures, asphalt becomes
a “brittle elastic solid” with little or no viscous properties. In the spring/shock absorber
analogy, the spring becomes over loaded and snaps when low temperature cracking
occurs. At high temperatures rutting occurs due to a lack of elastic properties. At low
temperatures, thermal cracking is induced due to a lack of viscous flow. To reduce the
potential of rutting at high temperatures and thermal cracking at low temperatures, various
polymers/fibers/rubbers can be added to asphalt. The goal is to increase the temperature
range of both the elastic and viscous properties of the asphalt binders and mixtures.
Convenient measures of these pmperties are 6’, storage modulus (elastic), and G”, loss
modulus (viscous). The ideal case will be that at high temperatures G’ and G” increase
upon addition of polymer (due to a network structure formation within the asphalt), and at
low temperatures the material becomes less brittle upon addition of polymer (due to a
decrease in the material’s effective glass transition temperature). The ideal case leads to
the improvement of both viscous and elastic properties over a wide range of temperatures.
The Strategic Highway Research Program has developed a specification sheet for asphalt
binders that addresses these characteristics”.

Chapter four will further define the research problem and goals.

 

ELASTIC

 

 

VISCO

 

 

 

 

 

 

 

 

34

 

 

 

 

 

 

 

 

 

 

m
35". u:
l:'a'=°
— 3
:50
mum
m
w

COLD

 

 

Figure 3. 5 - Viscoelastic asphalt model

 

Based u;
modified asphal:
pavements. lio
imam-cred ques
Fundamental cha

imperative if the

 

CGillidence in the
(I ResearCh g 0

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. temper

a...

Chapter Four

Problem Definition And Research Goals

Based upon the discussion in Chapters Two and Three, it is clear that polymer
modified asphalt binders exhibit considerable potential for creating superior asphalt
pavements. However, because of the lack of a systematic study, there are still numerous
unanswered questions revolving around the use of polymer modified asphalt pavements.
Fundamental characterization of polymer modified asphalt pavement constituents is
imperative if the potential of polymer modification is to be realized, and used with

confidence in the future.

4. I Research goals

The broad objective of this research effort was to provide a wealth of fundamental
physical, chemical, and thermodynamic data for the binder materials under study through
both experimental and theoretical investigations. These studies led to the major
deliverable of this research; initial, pictorial, physical and chemical models of polymer
modified asphalt blends that account for different asphalt grades, sources, and polymer
types. The models are able to explain the following:

o differences in the properties of different asphalt grades;

0 differences in the properties of different polymer modified binders;

0 temperature dependency of straight and polymer modified asphalts;

35

 

0 diff:-
asp‘r-

o and.

 

 

 

asph.’
Secondary de.
' the c
prope

' a fir?t
preset

Trans;

 

 

 

 

 

' an(La

TC\'1SlC

36
o differences in handling and mixing procedures for different polymer modified

asphalts including polymer content concerns;

0 and, differences in the aging phenomena of straight versus polymer modified
asphalts.

Secondary deliverables included:

0 the optimum polymer modification contents required for optimum physical
properties;

0 a fingerprinting protocol for determining the type and amount of polymer
present in an unknown sample to be used by the Michigan Department of
Transportation (MDOT);

o and, a review of the SHRP and MDOT binder specifications and suggested

revisions for use with polymer modified binders.

4.2 Materials

Based on the suitability of materials for Michigan weather, the asphalt grades and
polymer modifiers listed in Table 4.1 were used in this study. The asphalts were all
supplied by Amoco and were graded from low viscosity, AC-2.5, to high viscosity, AC-
20. Both polymers are Shell Kraton polymers and were used in powder form. All
possible combinations of AC-S and AC-10 with styrene-butadiene-styrene and styrene-
ethylene-butylene-styrene were tested from 1 through 10 weight percent polymer

modification.

37
Table 4. 1 - Materials used in the stuay

 

 

_A_sgha_lts Polymer Modifiers

AC-2.5

AC-S - A styrene-butadiene-styrene
AC-lO >< styrene-ethylene-butylene-styrene
AC-20

4.3 Experimental Protocol

4. 3. 1 Preparation of aged asphalts

To determine the effect on binder properties, straight and modified asphalt samples

were aged and tested. Aging during processing was simulated by using the:

0 Thin Film Oven Test (AASFTO T 240; ASTM D 2872);

o and, the Thin Film Oven Test (AASFTO T 240; ASTM D 2872) at a
temperature 10 to 15°C higher than the suggested value, depending on the
processing conditions required for the modification.

Aging during the service life was simulated by using the:

0 Pressure Aging Vessel Test (SHRP B-005).

4. 3. 2 Thermal transitions and temperature dependent structure
Asphalt is a very temperature dependent material. The ultimate goal of adding

polymer to an asphalt mixture is to reduce the blends temperature dependency. Improved

 

 

properties of ;

 

decreases irt th

analysis and di
h

 

transition tempe
used to locate a
B Wtil as any (

mmMatures are

 

analysis was us:
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38
properties of polymer modified asphalt binders at low temperatures are do partly to

decreases in the materials’ effective glass transition temperatures. Thermal mechanical
analysis and differential scanning calorimetry tests were used to measure the glass
transition temperature of selected materials. Differential scanning calorimetry was also
used to locate and examine any temperature dependent stnrcture in the studied materials
as well as any other phase transitions. Improved properties of asphalt binders at high
temperatures are due partly to an increase in a material’s viscosity. Thermal mechanical
analysis was used to measure the final softening temperature of selected materials.
Dynamic mechanical analysis was used to measure the Viscoelastic properties of binders

over a mid-temperature regime.

4. 3.3 Molecular weight distribution

High performance gel permeation chromatography (HP-GPC) was used to
determine the molecular weight distribution, molecular weight, and thus, fi'action of each
constituent in the studied binders. The study used a state of the art, Waters’ system
equipped with a Millennium software package. The results obtained from the HP-GPC
testing was applicable in every objective of the study with an emphasis placed on creating

a fingerprinting protocol.

4. 3. 4 Determination of useful chemical functional groups
Fourier transform infrared (FT IR) spectroscopy was used to determine usefiil

chemical functional groups and their relative amounts in asphalt binders. A liquid

 

droning-'43. '

 

rust‘orm Will it
spec-ta of spec-ft
tests were also a;

creation of a huge.

4.3.5 Bending bed

The SHRP
properties of asp:
determine any in
Unified binders
millimples a

‘5 in index for re

‘36 IlSCOSIlt' p

39
chromatography (LC)—transfonn unit was also used to accomplish this goal. The LC-

transfonn unit was part of the HP-GPC system and allowed for the inspection of infrared
spectra of specific molecular weight ranges of asphalt binders. The results from these

tests were also applicable to every objective of the study with an emphasis placed on the

creation of a fingerprinting protocol.

4. 3.5 Bending beam analysis

The SHRP bending beam test was conducted to examine the low temperature
properties of asphalt binders related to thermal cracking. The data was also used to
determine any modifications needed for the SHRP specifications to handle polymer
modified binders. In future studies, the change in fiexural properties between unaged
asphalt samples and unaged asphalt in combination with aged asphalt samples may be used

as an index for recyclability.

O 4. 3. 6 Viscosity measurement

Viscosities at various temperatures were measured using a Brookfield viscometer
to examine. how polymer modification will affect processing temperatures and equipment.
The data was also used to examine any high temperature structure present in polymer
modified asphalt as well as any modifications needed for MDOT and/or SHRP binder

specifications to handle polymer modified binders.

Chapter

smdy.

 

 

40
Chapter Five expands on the experimental details and procedures used in this

study.

 

such a

all exr

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5.1 R

Ifans:
Study
comm"
Place:
PrCVel

Salon

Chapter Five

Experimental Details

Extreme care was taken to ensure that all of the tested materials were handled in
such a way that the results could be trusted and compared. In order to accomplish this

task, protocols were established for raw material preparation, asphalt/polymer mixing, and

all experimental methods. Chapter Five will detail these procedures.

5. 1 Raw material preparation

Five gallon containers of asphalt were obtained from the Michigan Department of
Transportation at the initiation of the project in a large enough quantity to sustain the
StUdy through its conclusion. The material was stored in its original, sealed five gallon
containers. As the asphalt was needed for testing, it was handled using the following
Procedure to insure a uniform sampling base from which all testing could begin. This

Prevented non-uniform aging of samples due to a repetitive heating of the original five

8311011 container.

’ An oven was heated to an equilibrium temperature of 270 °F.

A covered five gallon sample of the asphalt was placed in the oven and heated

for 3.5 hours.

41

 

Chet:

“761:

5.2 .l

42
o The five gallon sample of asphalt was removed from the oven and stirred by

hand using a wood dowel for 1 minute to ensure a good melt and
homogeneity.

0 While still hot, the asphalt was poured directly into 17.25 x 11.5 x 1 inch
sampling trays lined with non-stick plastic. The trays were filled to a depth of
approximately 0.5 inches. This required approximately 12 trays per five gallon
container of asphalt.

o The asphalt was then covered with an additional piece of non-stick plastic,
cooled at room temperature for one hour, and stacked in a freezer at -10°C.
This temperature is close to the glass transition temperature of the material and
very little aging should occur.

0 For each test, the proper asphalt weight was determined and obtained by either
cutting the appropriate amount of binder from the fi'ozen asphalt sheet using a
hot wire or by cracking the frozen sheet using a hammer.

Kraton rubbers Gl650 (SEBS) and D1101 (SBS) were obtained fi'om Shell

Chemical Company. These materials were stored in their original containers, sealed

mastic bags, at room temperature in a dry location.
5-2 Mixing procedure for asphalt and SBS/SEES

In general, industry has recommended a mixing time that corresponds to a

homogeneous asphalt/polymer blend based on visual inspection. This was found to be a

 

 

poo: pnctzc
based upon
lining ten
to ten per:
properties
aspialt all
and aspha
”“237 m
Should be
“M 52
15 ll'lt m
limbo 1
fillings
Blend '

l"35 Chc

5.3 b

43
poor practice for laboratory procedures. A mixing procedure was therefore developed

based upon the improvement of rheological properties of an asphalt/polymer blend for
varying temperatures and mixing times. The polymer concentration was varied from zero
to ten percent by the total weight of the asphalt/polymer blend. It was found that the
properties of the blend were maximized for a procedure that included heating of the
asphalt at 270°F for one hour (to obtain a good melt) followed by mixing of the polymer
and asphalt at 350°F (industry standard for polymer modified asphalts) for two hours.
Longer mixing periods caused more aging and slightly lower rheological properties. It
should be noted that, to eliminate difi‘erences due to the effects of aging, the unmodified
asphalt samples used in this study were stirred at the same temperature and mixing period
as the polymer modified samples. The mixing was performed using a Fischer-Scientific
Jumbo 115V low shear mixer equipped with a four blade, 5 cm diameter impeller. The
stirring speed (~1600 rpm) varied as a function of the consistency and concentration of the
blend. Figure 5.1 is a schematic of the mixing apparatus. The above mixing procedure

was chosen based on a study detailed in Chapter Seven

5.3 Experimental methods

The experiments performed in this study can be divided into three sections. The
second and third groups of experiments examine the chemical and physical properties of
asphalt binders, respectively. The first set of experiments are aging procedures that

simulate the environments seen by an asphalt binder during its life span.

44

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5. 3. 1 Aging

According to the literature, asphalt binders age due to two individual
mechanisms”. The first process is an oxidation process, and the second is a volatilization
of the low molecular weight oils present in the material. The oxidation process occurs at
moderate and high temperatures in the presence of oxygen. The volatilization process,
however, occurs mostly only at very high temperatures. During processing, an asphalt
binder will encounter both high temperatures and a steady air flow, creating optimum
conditions for both aging mechanisms. After processing, during the service life of the
pavement, the extreme conditions are relaxed and the rate of aging is decreased. It was
therefore necessary to have two aging procedures, if the entire aging process was to be
simulated. It was determined that aging during processing would be simulated by using
the Thin Film Oven Test (TFOT) at normal (163°C) and elevated (177°C) temperatures.
The higher temperatures were investigated to determine if any significant property changes
occurred due to the increased temperatures required for processing of polymer modified
a$Phalts. Aging during the service life of an asphalt binder was simulated by using SHRP's
Pressure Aging Vessel Test (PAV). Only one set of temperature conditions was necessary
fm’ this Experiment because the service life temperatures of polymer modified and

“MOdified asphalts are the same. It is important to note that the PAV test was performed

0“ samples that had already been aged by the TFOT.

 

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46
5.3.1.1 Thin Film Oven Test (AASHTO T179 or ASTMD 1754-87)

The Thin Film Oven Test requires an electrically-heated convection oven that can
be maintained at a temperature of 163°C for a time period of five hours. The oven must
contain a circular, horizontal, rotating shelf suspended from the center that can hold the
sample containers. The shelf is required to rotate at a rate of 5.5 :t 1.0 revolutions per
minute. A thermometer should be located in the center of the oven just above the rotating
shelf. Figure 5.2 is a schematic of the Thin Film Oven

Samples are prepared by heating the material until it becomes the consistency of
motor oil. It is important to be careful of not over-heating the sample. A temperature of
150°C should not be exceeded during sample preparation. After heating, 50.0 t 0.5 grams
of material are poured into two or more previously weighed cylindrical pans. Each pan
should be 140 mm in diameter, 9.5 mm deep and have a flat bottom. The pans are allowed
to cool to room temperature after which the samples are weighed to the nearest 0.001
grams.

The pans are then quickly put into a preheated Thin Film Oven and allowed to heat
for five hours after the system has regained the equilibrium temperature. The total heating
time should be no longer than 5.25 hours. After heating, the pans are removed and again
allowed to cool to room temperature. The pans are weighed to the nearest 0.001 grams.

If the material is to be aged further using the Pressure Aging Vessel Test, the
samples may be stored in the pans. If not, the pans should be heated until the sample

flows and can be transferred into storage tins to be tested at a later date.

Motor

 

 

   
 
   

Thermometer

Sample Tins

47

if;

Controls

 

Figure 5.2 - Thin Film Oven

anc’canb

 

l‘QSSel c

 

Salim

 

48
A convenient and simple measure of aging during processing is percent mass loss

and can be calculated using the following equation:

Mass Loss, % = Original mass - Aged Mass x 100

Original mass

5.3.1.2 Pressure Aging Vessel Test (AASH T 0 PP!)

The Pressure Aging Vessel Test requires a pressure vessel and a forced-draft oven.
The vessel is connected to a regulated cylinder of clean, compressed air and a temperature
probe. The vessel must be able to withstand a pressure of 2070 kPa and a temperature of
100°C for a time period of twenty hours. The oven should be able to control the
temperature of the vessel to .4: 0.5°C during the twenty hours of heating. The pressure
vessel contains a sample rack that will hold at least ten TFOT sample pans. Figure 5.3 is a
schematic of the pressure aging vessel and its components.

The pressure vessel is preheated to a temperature of 100 i 2°C while still
unpressurized. When the equilibrium temperature is reached, the vessel is quickly opened,
the sample rack is loaded, and quickly closed again to prevent heat loss. When the vessel
has once again equilibrated at 100 :l: 2°C, the pressure is slowly increased to 2070 kPa.
After twenty hours of heating, the pressure is slowly released over a time span of ten to
twelve minutes. The samples can now be removed from the vessel. The samples are
heated at 163°C for 0.5 hours to remove air bubbles and transferred into storage tins for

testing at a later date.

I‘l' "II‘LEE E.‘

 

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5. 3. 2 Chemical properties

Basic chemical characteristics of asphalt binders were studied using a high
performance gel permeation chromatography (HP-GPC) system, a liquid chromatography
(LC) transform unit, and a Fourier transform infi'ared (FT IR) spectrometer. The

experimental details of each piece of equipment are summarized as follows.

5. 3. 2.1 High performance gel permeation chromatography system

High performance gel permeation chromatography is a separation technique based
on the sorting of particles by molecular size. A sample is put into solution and pumped
through a column packed with a porous material. As the solution flows through the
column, the smaller particles are faced with a longer and more tortuous path due to the
many pores that they encounter. The larger particles do not enter as many pores and
therefore exit the column first. By measuring the number of particles that exit the column
over a given time period, a size distribution of the sample can be created. The molecular
weight of a particle can be related to its molecular size through calibration of the column,
thus creating a molecular weight distribution. Gel permeation chromatography is
sometimes called size exclusion chromatography and has the ability to separate molecules
in the 100 to 1 million molecular weight range.

During this study, a MilliporeANaters' high performance gel permeation
chromatography system was used to analyze the molecular weight distributions of straight
asphalts, polymer modifiers, and polymer modified asphalt binders. The system was

equipped with a differential refractometer, a photodiode array detector, a chromatography

 

additiomi l
angel ll
mobile p'h

llllttofs

measure

“LII Will

L,

51
manager (Millennium software), a dual reciprocating pump, and a manual injection port.

A Lab Connections' liquid chromatography transform unit was also installed as an
additional detector for the system. The HP-GPC system was equipped with four Waters'
styragel HR columns that encompassed an effective molecular weight range fi'om 0 to
600,000. I-IP-GPC grade tetrahydrofiiran at a flow rate of 1.0 ml/min. was used as the
mobile’lphase for this study. The sample concentration was kept constant at 10 grams per
1 liter of solvent as was the injection volume of 250 ml.

A difi‘erential refractometer is a detection device that uses optical refraction to
measure the concentration of a given material dissolved in a solvent phase. A beam of
light will travel at different velocities when passing through different materials. Therefore,
if a beam of light enters a material at an angle that is not perpendicular to the material, it
will bend or refi'act. The refractive index of a material is a measure of this phenomena and
is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the '
given material. The refractive index of a medium is a constant for a given temperature,
pressure, and wavelength of light.

For this study, a Waters' 410 refractometer was used to measure the molecular
weight distributions of asphalts, polymers, and polymer modified asphalts. The
refiactometer was operated at 35°C, 20psi, and used a 930 nm monochromatic beam of
light. The differential refractometer was very reproducible. Figure 5.4 is an overlay of
two AC-10 chromatograms prepared independently fi'om each other.

The photodiode array detector allows for the characterization of usefirl chemical I

functional groups present in asphalt. PDA was not used extensively in this study, but will

S TD 3 332%» as}: 95.32%» \o beSBfiSanK t m. a. pint

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52

 

 

 

 

'II thrill lll‘lltllrn i ll

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53
be useful in the future to discriminate between certain asphalts and polymers based on

their ability to absorb UV light. The axes of PDA data are time (molecular weight), UV
absorbance, and wavelength. Using the Millennium software package, dissection of this
data is possible that allows individual spectra and chromatograms at a fixed molecular

weight or wavelength to be examined.

5. 3. 2. 2 Liquid chromatography transform unit

The LC-transform unit is an off-line system that collects the effluent from the
differential refractometer (separated by molecular weight) on a germanium disc that can be
analyzed using Fourier transform infrared spectrometry at a later date. The LC-
transform/FT IR arrangement allowed for the detection of useful chemical functional
groups that absorb infrared light. During this study, a Lab Connections' LC-transform unit

was used.

5. 3. 2. 3 Fourier transform infrared spectrometer

Fourier transform infrared spectroscopy is a technique that measures the infrared
absorbtion capabilities of functional groups present in a material. All molecules posses
natural resonating frequencies due to either elemental bond stretching, bending, or
twisting that fingerprint them. Infrared spectroscopy is able to detect this fingerprint by
shining an infrared beam through the sample and measuring the light transmitted through
the material. Wavelengths that are the same as those of the molecule are absorbed and not

detected, creating an infrared spectra.

 

 

 

 

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54
Fourier transform infrared spectroscopy was used to examine unaged, aged, and

polymer modified asphalts. The samples were prepared by evaporating a THE/binder
solution on a potassium bromide pellet leaving a thin film of the material to be examined.
The solution was mixed at a concentration of 0.5 g of sample per 10 ml of tetrahyrofuran.
0.35 milliliters of the solution was pipetted onto 0.35 g potassium bromide salt pellets and
allowed to dry for one hour at room temperature, followed by drying in an oven at 135°C
for fifteen minutes. The pellets were made using a dye under a pressure of six metric tons
for two intervals of five minutes each.

This study used a Perkin Elmer 1800 series spectrometer. The instrument was run
using a single beam arrangement with a scan time of 3 seconds. The detector used was a

Deuterated Triglycine Sulphate Detector with a diameter of 2mm.

5. 3. 3 Physical properties

Basic physical characteristics of asphalt binders were studied using dynamic
mechanical analysis (DMA), thermal mechanical analysis (TMA), differential scanning
calorimetry (DSC), a bending beam rheometer (BER), and rotational viscometry. The

experimental details of each technique are summarized as follows. f

5. 3. 3. 1 Dynamic mechanical analysis
Dynamic mechanical analysis is 3 experimental technique that measures the
Viscoelastic behavior of a material. The technique is conducted by sandwiching an asphalt

Wple between two plates. One plate oscillates at a predetermined sinusoidal frequency

 

 

 

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55
and the other plate remains motionless. As the one plate oscillates, the response of the

material is measured using a transducer connected to the opposite plate. If the material
responds with no lag time, the material is completely elastic. If the material shows a lag
time, the material has a viscous component.

The lag time is measured as the phase angle (delta) between the applied shear
strain and the resulting shear stress as seen in Figure 5.5”. A phase angle of zero degrees
is a perfectly elastic material and one of ninety degrees is a purely viscous material.
Polymer modified asphalt shows both viscous and elastic properties. At high
temperatures, asphalt is mostly viscous and thus ruts. At lower temperatures, asphalt
becomes mostly elastic and cracks.

Viscoelastic properties are reported as the loss (6", viscous) and storage (6',
elastic) moduli of a material. These moduli are both components of the complex moduli

(6") according to the following equation.

The instrument that was used in this study measures the complex modulus. The complex
modulus is the ratio of the total shear stress to the total shear strain as shown in Figures
5.6 and 5.7”.

In this study, dynamic mechanical experiments were performed using a
Rheometrics RMS-800 apparatus. All experiments utilized smooth, 25 mm diameter
plates in a parallel arrangement with a gap width between 1.4 and 2.0 mm. Sample
handling procedures were consistent with those used for the SHRP Bohlin instrument in

which the sample is poured hot directly onto the plates and allowed to cool to room

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temperature. Temperature sweeps were then conducted from 25 to 75°C with

measurements taken at five degree intervals with an equilibration period of two minutes.
A frequency of 10 radians per second was used in compliance with SHRP specifications
and strain levels were controlled to insure that the testing was conducted in the linear
Viscoelastic range. All tests were replicated between three and seven times to insure
accurate and reproducible results. For example, Figure 5.8 shows the reproducibility of

the storage modulus versus temperature data for a triplicate.

5. 3. 3. 2 Memo] mechanical analysis

Thermal mechanical analysis is an experimental technique that measures the change
in shape of a material as a function of temperature. A sample is heated at a given rate and
changes in its height are measured using a probe loaded with a predetermined force.
Distinct changes in the rate or direction of a height change represent a thermal transition in
the material.

For this study, thermal mechanical tests were performed on representative asphalt
binder samples using a Dupont Instruments, 943 Thermal Mechanical Analyzer. The
samples were placed in a 5 mm diameter by 5 mm deep glass boat at rooni temperature
and packed firmly forming a flat top surface. The sample was then covered with a 3.5 mm
diameter by 1.5 mm thick glass plate upon which a one gram load was placed. The sample
was then cooled at approximately 15°C per minute to a temperature of -70°C and allowed
to equilibrate. The temperature was then raised at a rate of 5°C per minute and the

sample's height change was measured until a total softening (corresponding to a 1 mm

depression of the sample) was achieved. After testing, the boats were retrieved to ensure

 

60

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61
that the sample did not flow over the glass cover/plate. All tests were duplicated to check

the reproducibility of the results.

5. 3. 3. 3 Differential scanning calorimetry

Differential scanning calorimetry is an experimental technique that measures the
heat absorbed by, and/or given off by a material under given environmental conditions.
This is accomplished by comparing the temperature of a loaded sample to that of a blank
sample and measuring the difference between the two. Distinct changes in the rate or
direction of the heat flow represent a thermal transition in the material.

For this study, differential scanning calorimetry tests were performed on
representative asphalt binder samples using a TA Instruments, 910 Differential Scanning
Calorimeter. A fifteen milligram asphalt sample was placed in a DSC sample pan and
allowed to equilibrate at a predetermined temperature for one hour. The sample was then
quenched in liquid nitrogen and placed in the DSC cell that had been previously cooled to
-70°C. The system was allowed to equilibrate for fifteen minutes, afier which the
temperature was ramped at 5°C per minute to a final temperature of 200°C. During this
time, changes in the heat flow were continuously measured. After testing, the sample was
retrieved to ensure that none of the sample had leaked out of the DSC pan. All tests were

repeated multiple times to ensure reproducible results.

 

5.3.3.4 Bent

 

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62
5. 3.3.4 Bending beam rheometer

The bending beam rheometer is an experimental technique that measures the
deflection of an asphalt beam under constant load at low temperatures. Specifically, the
instrument is set up as a three point bending beam test as can be seen in Figure 5.9”. The
data of the test is reported as the creep stiffness and the creep rate of the material at a
given temperature and loading time. Creep stiffness is defined as:

PL
4bh36(t)

S (t) =
where; S(t) is the creep stiffness (MPa) at time,t; P is the applied constant load; L is the
distance between beam supports; b is the beam width; h is the beam thickness; and S(t) is
the deflection in millimeters at time, t. Creep rate is defined as the slope of the curve,
log(stiffness) versus log(time). The creep stiffness is often called the m-value and thought
of as the rate at which the material can dissipate the applied energy. The bending beam
rheometer is used as a prediction method for low temperature thermal cracking when
specifying asphalt.

During this study, a bending beam rheometer was used to test representative
asphalt samples. The samples were prepared by heating a binder until it was the
consistency of motor oil and then pouring it into a mold similar to the one pictured in
Figure 5.10”. The mold was poured in such a way (single pass), as to eliminate the
possibility of creating any air bubbles or forced structure. The mold was allowed to cool

at room temperature for one hour and then put in a freezer for ten minutes to harden the

sample so that the mold could be removed. Afier removing the sample, it was placed in a

63

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65
low temperature bath (-6, -12, ~18, or -24°C) and allowed to equilibrate for another one

hour time period. The sample was then loaded into the bending beam apparatus. The test
used a 102 mm distance between beam supports and a 100 gram constant load. Data was
taken at thirty second time intervals over a four minute period, but only the sixty second
information was used for specification purposes. Upon completion of the test, the asphalt
beam was removed and broken to check that no air bubbles were captured inside the

sample. Selected samples were run multiple times to insure reproducibility of the results.

5. 3. 3.5 Rotational viscometry

Rotational viscometry is an experimental technique used to measure the viscosity
of a material at temperatures at which the material flows easily. Specifically, rotational
viscometry was used to test the viscosity of asphalt at processing temperatures to ensure
that the material could be pumped without using excessive energy. The viscosity of a
sample is determined by measuring the torque required to keep a spindle, immersed in the
sample, spinning at a given rotational velocity and temperature. The necessary torque is
directly related to the materials viscosity at the testing temperature. Figure 5.11 is a
schematic of the operation.

During this study, samples were tested using a Brookfield Viscometer. Samples
were prepared by heating them at 135°C until they were the consistency of motor oil.
Approximately ten grams of the material was then poured into a preheated sample
chamber. A preheated No.27 spindle was immersed in the sample, allowed to equilibrate

for thirty minutes at the initial temperature, and the test was started. The spindle was

programmed
n'scosin' of n.
was reported
sample was te:
of 30°F. At
fifteen minutes

lht reported re

Chapter

described in cr.

 

 

 

66 .
programmed to rotate at a rotational speed between 5 and 100 rpm depending on the

viscosity of the material. The final viscosity of the material at any one given temperature
was reported as the average of three data points taken at one minute intervals. Each
sample was tested over a temperature range between 220°F and 370°F with interval steps
of 30°F. At each proceeding temperature, the sample was allowed to equilibrate for

fifteen minutes. Selected samples were tested multiple times to insure reproducibility of

the reported results.

Chapter Six will discuss the experimental results found from using the tests

described in Chapter Five.

TORQUE

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67

 

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Chapter Six

Experimental Results and Discussion

The experimental results from this study can be divided into two sections: 1) the
chemical properties of asphalt binders, and 2) the physical properties of asphalt binders.
Both sections will explore unmodified asphalts and modifiers, polymer modified binders,

and materials that were aged according to different processes.

6. 1 Chemical properties

The basic characteristics of asphalt binders were studied using a high performance
gel permeation chromatography (HP-GPC) system, a liquid chromatography (LC)
transform unit, and a Fourier transform infrared (FT IR) spectrometer. The results and

discussion fi'om the use of each piece of equipment are summarized as follows.

6.1. 1 High performance gel permeation chromatography

Gel permeation chromatography was used to examine the differences between '
unaged AC-S grade asphalt and unaged AC-IO grade asphalt. Three distinct molecular
weight ranges (divided by lines A and B) were found to be present in straight asphalt as
shown in Figures 6.1 and 6.2. These separations do not correspond to the molecular
weight ranges that classify the oil, resin, and asphaltene constituents found in the

literature. However, the reported percentages of the constituents do exist if the molecular

68

 

 

weight ran:
61 and 61
separation r.
asphalt and

A o
asphalt and

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A05 grade,-

AC.5 Sta de a

69
weight ranges (divided by lines C and D) reported in the literature are followed. Tables

6.1 and 6.2 list the percentages of the constituents according to the chromatography
separation and separation according to reported literature values for unaged AC-S grade
asphalt and unaged AC-lO grade asphalt, respectively.

A comparison of HP-GPC chromatograms of unmodified, unaged AC-S grade
asphalt and unmodified, unaged AC-10 grade asphalt is depicted in Figure 6.3 and Table
6.3. As it can be seen, it is difficult to distinguish between asphalt grades at this time.

A comparison of HP-GPC chromatograms of aged and unaged AC-S grade asphalt
is shown in Figure 6.4. It can be seen that when AC-S grade asphalt is aged, there is an
increase in the high molecular weight material. During aging there is only approximately a
0.2% weight loss suggesting that the low molecular weight material is being reacted.

Gel permeation chromatography was also used to examine the differences between
pure SBS and SEBS polymers. Figure 6.5 and Table 6.5 indicateithat the SBS polymer
that was studied had a weight average molecular weight of approximately 62,000 g/mol
and a polydispersity of two. The SEBS polymer that was studied, on the other hand, had
a weight average molecular weight of about 45,000 g/mol and a polydispersity of 1.35.
These polymers may therefore, behave difl‘erently in an asphalt/polymer blend.

Because polymer molecules are larger than asphalt molecules, gel permeation
chromatography was used as an effective tool for determining the polymer content of the
aS‘Phtllt/polymer blends that were studied. Figure 6.6 is an example of this technique for
AC-S grade asphalt modified with four weight percent SEBS polymer. When the original

AC-S grade asphalt chromatogram is subtracted fi'om the asphalt/polymer blend

«coal
i

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Table 11 .

 

 

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80.00- D
60.00-
‘0000'

20.00.

0.00‘ V‘ V

22.00 24.00 26.00 20.00 30.00 32.00 34.00 36.00 38.00 40.00

 

 

 

 

 

 

 

 

mutate:

Figure 6. 1 - Gel permeation chromatography raw data for unaged, unmodified AC -5
grade asphalt

Table 6. 1 - Percentages of constituents in an unaged, unmodified AC -5 grade asphalt

Classification WM __:§% Ar
High MW (GPC) 7100 + 7
Mid MW (GPC) 2900 - 7100 12
Low MW (GPC) 2900 - 81

High MW (Literature) 2000 + 27
Mid MW (Literature) 800 - 2000 29

Low MW (Literature) 800 - 44

50.357
40.00
E 30.30.
20.00..
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Figure 6. 2 '

Tableaz.

 

 

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50.00-
40.00-

. ,/
30.00-
20.00-

10 0 00°

3., i if

22.00 24.00 26.00 20.00 30.00 32.00 34.00 36.00 30.00 40:00

 

 

 

 

 

 

 

 

minutes

Figure 6.2 - Gel permeation chromatography raw data for unaged, unmodified AG] 0
grade asphalt

Table 6.2 - Percentages of constituents in an unaged, unmodified AC -1 0 grade asphalt

Classification Mglgulag Weight Range % Arg
. High MW (GPC) 7200 + 6
Mid MW (GPC) 3000 - 7200 11
Low MW (GPC) 3000 - 83
High MW (Literature) 2000 + 24
Mid MW (Literature) 800 - 2000 31

Low MW (Literature) 800 - 45

 

 

 

 

 

 

 

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Table 6.3 .

“\me

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.4010

72

 

0.60- AC-lO

dwt/dtluqfll

0.40-

 

AC-S AC-S
AC-lO

0.20-

0.00-

 

 

4.40 4.20 4.00 3.00 3.60 3.00 3.20 3.00 2.00 2.00 2.00 2.20
Log lb). «2'

Figure 6.3 - Comparison of molecular weight distributions between unmodified, unaged
AC—5 grade and AG] 0 grade asphalts

Table 6.3 - Molecular weight averages for unmodified unaged AC -5 grade and AC -1 0

grade asphalts
Name Mn Mp Mw m Polydispersity
AC-S 669 862 2099 6725 3. 14

AC-lO 630 922 1865 5660 2.96

73

O ‘0-

02°-

 

 

0101: Id (109“!
“E
\
/‘

'. 004

0.00 0.00 0.20 0.00 3.00 3.00 3.00 ’ 3.20 3.00 ' 2.00 ' 2.00 ‘ 2.00' 2320
Log 0001 I:

Figure 6. 4 - Comparison of molecular weight distributions between unmodified, aged
and unaged AC -5 grade asphalt

Table 6.4 - Molecular weight averages for unmodified aged and unaged AC -5 grade
asphalt

Earns

m. M0 Mg ‘ _M_z 11011033313133
aged 792 876 3348 11121 4.23

unaged 669 862 2099 6725 3. l4

 

 

 

(flat I.‘ ( I any“)

 

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figure 6. 5

 

 

74

SEBS

 

dwt/dUogH)

 

 

 

 

 

0.00 0.00 5.00 5.00 5.205.00 0.00 0.00 0.00 0,200.00 3.00 3.00 3.003.20
Log 0001 we

Figure 6.5 - Comparison of molecular weight distributions between pure SBS and SEBS
polymer modifiers

Table 6. 5 - Molecular weight averages for pure SBS and SEBS polymer modifiers

SB S 30002 67865 61900 106729 2.06

SEBS 32730 44092 44445 58327 1 .36

 

 

75

chromatogram, the original chromatogram can be divided into three regions: A, B, and C
with corresponding areas of 2.52%, 1.49%, and 95.99%, respectively. The areas
represent the weight percent of each constituent because the refi'active index detector is a
mass sensitive instrument. Region A is the large polymer molecules that are totally
separated from the asphalt. Region B is the small polymer molecules that are eluted with
the asphalt. This can be easily seen by a comparison of Figure 6.4 with Figure 6.6. A
total of four weight percent SEBS polymer modifier can be identified from the HP-GPC
data as shown in Table 6.6. It is important to note that it appears that the polymer is being
degraded, sheared, or reacted during the mixing process. Similar results were obtained for
AC-S/SBS, AC-lO/SEBS, and AC-lO/SBS asphalt grade/polymer modifier blends.

A comparison of HP-GPC chromatograms of aged, unmodified AC-S grade
asphalt and aged, four weight percent SBS polymer modified AC-S grade asphalt is shown
in Figure 6.7. Upon addition of polymer to asphalt, we would expect to see an increase in
the amount of the high molecular weight asphalt constituent for the aged sample due to
both aging and possible polymer degradation. Instead, we see a decrease in this value
suggesting that the polymer has reduced the amount of aging that has occurred.

Gel permeation chromatography was also used to examine the difi‘erences between
unaged, aged at normal conditions, and severely aged unmodified AC-S grade asphalt and
three weight percent SBS polymer modified AC-S grade asphalt. Figure 6.8 and Table 6.7
show that severely aging unmodified AC-S grade asphalt changes the molecular weight

distribution very little as compared to the molecular weight distribution of the unmodified

" 40.4 m

3
’1
0
r.
!

 

76

 

500.002
400.009
300.009
200.009 AK

100.00‘

0.004 \A
22.00 20.00

26.00 28.00 30.00 32.00 34.00 36.00 30.00 40.00

 

 

 

 

Minutes

Figure 6. 6 - HP-GPC raw data for unaged AC-5 grade asphalt modified with four weight
[mercmnmtEBEHBEipnoiynmer

Table 6. 6 - Percentage of SEBS polymer in unaged, polymer modified AC -5 grade
asphalt

91235315906213 Start—Mm E___end Tim 23mm
SEES 22.38 24.58 2.52
degraded SEBS 25.33 27.28 1.49
AC-S 24.58 39.62 95.99

 

 

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4.40 4.20 4.00 3.80 3.60 3.40 3.20 3.00 2.80 2.60 2.40 2.201
200000101: '

Figure 6. 8 - Comparison of molecular weight distributions between unaged normally
aged, and severely aged unmodified AC -5 grade asphalt

Table 6. 7 - Molecular weight averages for unaged, normally aged and severely aged

unmodified AC-5 grade asphalt
N_L_§m be ME m M2. P 1 i
unaged 669 862 2099 6725 3. 14
normally aged 792 876 3348 l 1121 4.23

severely aged 786 876 3356 11213 4.26

 

“W‘

79
material aged under normal conditions. Figure 6.9 and Table 6.8 show a similar result for

three weight percent SBS polymer modified AC-S grade asphalt.

6. 1.2 Fourier transform infrared spectroscopy

Fourier-transform infrared spectroscopy (FTIR) was used to examine both aged
and unaged AC-S grade, and AC-lO grade asphalts. It was determined that there are
several defining wavelengths of interest including: 1375, 1450, 1600, and 1700 cm".
These wavelengths correspond to CH3, CH2, C=C, and C=O groups respectively. Figure
6.10 is a representation of these groups for an unmodified, aged AC-S grade asphalt
sample. Ratios of the absorbance intensities of these functional groups yielded useful
information when fingerprinting different asphalt grades. Figure 6.11 indicates that an
AC-lO grade asphalt sample has a greater percentage of double bonded carbon than an
AC-S grade asphalt sample as would be expected, suggesting a larger resin and/or
asphaltene content. However, the AC-lO grade asphalt sample appears to have less CH2
fianctional groups than the AC-S grade asphalt sample, suggesting a lesser resin content.
Analysis such as this in combination with gel permeation chromatography could be useful
when selecting materials for construction and dealing with recyclability concerns.

Fourier-transform infiared spectroscopy was also used to determine any possible
defining functional groups of styrene-butadiene-styrene (SB S) and styrene-ethylene-
butylene-styrene (SEBS) polymer modifiers that could be used for finger printing. Figures
6.12 and 6.13 are the infrared spectra of SBS and $1538 respectively. The SBS polymer

can be identified by a characteristic adsorption/transmitence peak at a wavelength of 965

 

80

 

 

 

 

0.00- ’
0.00-
6
0
:1
2
s 0000- l
3
severely aged 5
002°- /
normally aged
0.00- i
5.00 0.50 0.00 3.50 3.00 2.50
Log 0101 00:

Figure 6. 9 - Comparison of molecular weight distributions between normally aged and
severely aged AC—5 grade asphalt modified with three weight percent SBS
polymer

Table 6. 8 - Molecular weight averages for normally aged and severely aged AC -5 grade
asphalt modified with three weight percent SBS polymer

Hams m Mn m m 13936359553!
normally aged 803 876 5508 48220 6.86

severely aged 804 867 5692 49201 7.08

 

 

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polymer. A similar defining peak was not detected for SEBS polymer modifier.

The absolute ratio of the 965 cm'1 adsorption band to the 1375 cm”1 band allowed
for the construction of a calibration curve. Figure 6.14 is an example of how to determine
this ratio. A calibration curve was constructed by preparing samples that contained
known concentrations of SBS polymer modifier in an AC-S grade asphalt and plotting this
information against the respective absolute absorbance band ratios. It is important to note
that calibration curves are only valid for a specific asphalt/polymer blend. If difi‘erent
materials are used, a new calibration curve must be constructed. The curve must also be
corrected for aging discrepancies. Figures 6.15 and 6.16 are examples of calibration
curves for unaged and aged AC-S grade asphalt/SBS polymer blends, respectively. The
defining equation for the unaged calibration curve is:

Ratio = (0.064 "‘ polymer content) + 0.037 '
while that of the aged curve is:
Ratio = (0.051 "' polymer content) + 0.079.

Fourier-transform infrared spectroscopy was also used to examine the difi‘erences
between unaged; aged at normal conditions; and severely aged, unmodified AC-S grade
asphalt and four weight percent SBS polymer modified AC-S grade asphalt. Figure 6.17
is an analysis of absorbance intensity ratios for different wavelength pairs of the above
samples. An explanation for the results can be found in Chapter Seven. The calibration

curve created for SBS polymer modified AC-S grade asphalts that have been aged under

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normal conditions was used to predict the polymer content of severely aged four weight

percent SBS polymer modified AC-S grade asphalt. The calibration curve under predicted
the percent polymer content by approximately one-half percent. Based on this result,
binders aged at severe temperatures will need a separate wavelength ratio calibration

curve.

6.1.3 Liquid chromatography transform unit

Liquid chromatography was used to look at the infrared spectra of the individual
constituents of asphalt as well as a separation of the entire asphalts and. polymer modifiers.
Separation of the asphalt constituents showed very little without the purchase of software
that will allow for the creation of a three dimensional spectra with axes of molecular
weight, absorbance, and wavelength. Separation of polymer modifiers fiorn
asphalt/polymer blends was more successful. Figure 6.18 is the spectra of SBS polymer
that has been separated from a blend. Figure 6.19 is the spectra of the recovered asphalt.
This technique will prove to be extremely valuable when fingerprinting unknown samples

in the fixture.

6.2 Physical properties

The basic physical characteristics of asphalt binders were studied using dynamic

mechanical analysis (DMA), thermal mechanical analysis (TMA), differential scanning

 

 

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calorimetry (DSC), a bending beam rheometry (BER), and rotational viscometry. The

results and discussion from the use of each piece of equipment are summarized as follows.

6. 2. 1 Dynamic mechanical analysis

The creation of a polymer network structure inside an asphalt is the main cause of
improved binder properties seen in polymer modified asphalt. Regardless of polymer type,
binder properties will not be substantially improved until the formation of a network is
completed at an optimum concentration of modifier.

Several criteria were examined for selecting the optimum and critical polymer
contents, based on rheological properties, of the four asphalt/polymer blends (AC-S/SBS,
AC-SISEBS, AC-lO/SBS, and AC-lO/SEBS) studied during this project. The optimum
was defined as the point at which there was no longer a significant increase in the
rheological properties of the blend with increasing polymer content. The critical content,
on the other hand, was defined as the polymer concentration where a deviation fi'om the
normal trend in the rheological properties was detected. The optimum and critical
polymer contents for the asphalt/polymer blends being studied are reported in Table 6.9.
It should be noted that all of the asphalt/polymer blends (polymer contents from zero to
ten percent) used in this section of the study met the SHRP binder specification for
original asphalt binders.

AC-S modified with SBS polymer will be used to demonstrate the criteria used

when determining the optimum and critical polymer contents of a given asphalt/polymer

 

‘w cacti-Lain“ #
1 ' ,

94

Table 6. 9 - Optimum and critical polymer contents of studied asphalt/polymer blends
based on rheological properties

Optimum Content Critical Content

ercn ttlweihtofth ashal l erln

AC-S/SBS 3 or 5 4
AC-S/SEBS 2 or 5 3 - 4
AC-lO/SBS 2 3
AC-lO/SEBS 2 or 4 3

blend. The other asphalt/polymer blend combinations showed similar results as those seen
with the AC-S/SBS blends.

The initial criteria for selecting the optimum polymer content to be added to an
asphalt based on rheological properties was an intersection of the loss and storage moduli
when plotted versus temperature indicating the formation of a pseudo-crosslinked polymer
network within the asphalt. Figures 6.20, 6.21 and 6.22 show that this phenomena did not
occur until ten weight percent SBS was added to the AC-S grade asphalt.

At this time, it was suggested that the research was possibly being conducted with
an asphalt that was incompatible with SBS polymer. A second asphalt was tested and the
results were comparable to those seen previously as depicted in Figure 6.23.

It has also been reported that the minimum amount of polymer modification
required to significantly enhance the properties of an asphalt/polymer blend will be
recognized as a distinct change in the slope of the storage and/or complex moduli for most

asphalts that are modified with a styrenic block copolymer”. However, plots of the

 

 

 

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average ”log" slope of G' and G‘ from 25 to 60°C versus increasing polymer content

show a straight line with no distinct breaks as shown in Figure 6.24. This behavior does
not support the formation of an entangled and continuous polymer network. Instead, the
data suggests that this asphalt/SBS polymer blend forms localized and dispersed networks.
At approximately 8.5 percent SBS polymer content, the blend exhibits a ”matrix
inversion”. This phenomena is depicted in Figure 6.25 by an intersection of the storage
and loss moduli at 60°C and in Figure 6.26 by a tan5 value less than one at a polymer
content of about 8.5 percent. Similar observations were also reported by Brule who
witnessed matrix inversions at polymer contents between 7.5 and 12.5 percent polymer
content”.

King has reported that the loss modulus at 60°C can be used as a predictive tool
for determining the optimum polymer content necessary to maximize the rheological
properties of a polymer modified binder". In this study, no significant increase in the
values of G' and G” were measured by increasing the polymer content above five percent
as shown in Figure 6.25. It is important to note that the data shows a deviation from the
normal trend at four percent polymer content. This deviation was observed in every test.

The SHRP original binder specifications set a minimum l/J" value of 1 kPa at
60°C. Based on the SHRP specification and the test data shown in Figure 6.27, all of the
samples including the unmodified binder used in this study satisfy the specification. Once
again, a deviation from the normal trend in the rheological properties at four percent

polymer content can be seen.

 

 

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Bouldin has also suggested two ratios which may help in determining the effectiveness of a

polymer modification". These ratios are l) a comparison of the storage modulus for the

modified binder (G’m) versus that of the unmodified material (G’u) at 60°C, and 2) a

comparison of the storage moduli for the modified binder at 25°C versus 60°C

(G’zs/G’60)m. In an ideal asphalt/polymer blend, the ratio (G’m/G’u) should be a
maximum, while the ratio (G’zs/G’60)m should be one (rel). Figure 6.28 depicts the ratio

(G’m/G’u) versus polymer content. Examination of the figure indicates that:

0 Increasing SBS polymer content from zero to three percent causes about a 100

fold increase in the ratio.

0 At four percent SBS polymer content, there is a deviation (depression) from

the normal trend.
0 Increasing polymer content above five percent causes no significant change in
the ratio.
Based on these observations, it is concluded that the optimum polymer content is five
percent and the critical polymer content is four percent. On the other hand, Figure 6.29

shows that changes in the values of (G’zs/G’50)m are insignificant after an optimum SBS
polymer content of three percent. The data presented in Figures 6.28 and 6.29 imply that

the optimum polymer content is sensitive to the temperature at which properties are
measured and depends on the type of data analysis. .

The sensitivity of tanfi to temperature (a two-temperature curve) can also be a
powerful 'predictive tool for determining the optimum polymer content”. However, no

specifications of the average slope of the curve or tano values that denote the optimum

 

 

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polymer content have been suggested and/or reported. Figure 6.30 indicates a continual
flattening (decrease in the sensitivity) of the tan8 curve with increasing polymer content
which suggests improved rheological properties. Therefore, an exact optimum polymer
content cannot be determined without first specifying a flatness criteria or a degree of
sensitivity. In this study it is suggested that the following criteria for the temperature
sensitivity of tanfi, F(r.t.) be used.

F(r.t.) = {log [(tan5 @ 25°C) / (tan6 @ 60°C)]}

At a value of zero, tan5 is considered flat or insensitive to temperature (tan5250C = tano
60°C)' Figure 6.31 shows that "F(r.t.)" has a value of zero at five percent polymer

content agreeing with several of the previous data analyses. Moreover, the value of tan5
at 60°C versus polymer content depicted in Figure 6.26 shows a deviation fi'om the normal
trend at four percent polymer content. This further suggests the need for a specified value
of tanfi at a given temperature.

Dynamic mechanical analysis was also used to measure the storage modulus, G',
and loss modulus, G" at high pavement temperatures of AC-S/SBS polymer blends that
were aged under severe conditions (15°C higher than normal). Figures 6.32 through 6.34
are a comparison of G', G", and tan8, respectively of unaged, aged at normal conditions,
and aged at severe conditions of unmodified AC-S. It is clear that the elevated aging
temperature increased both the loss and storage moduli over the given temperature
regime. In addition, tan delta decreased with accelerated aging, suggesting that the
storage modulus was increasing at a faster rate than the loss modulus. Figure 6.35 depicts

the percent increase in G' at 60°C of the severely aged versus normally aged, and severely

 

 

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aged versus unaged, unmodified, AC-S grade asphalt. Increasing the processing

temperature, caused over 300 percent more aging based on this criteria for unmodified
AC-S.

Figures 6.36 through 6.38 are a comparison of G', G", and tanfi, respectively of
unaged, aged at normal conditions, and aged at severe conditions of A05 grade asphalt
modified with three weight percent SBS. It is clear that the severe aging process again
increased both the loss and storage moduli over the given temperature regime. In

addition, tan delta again decreased with accelerated aging, suggesting that the storage

 

modulus increased at a faster rate than, the loss modulus. Figure 6.39 depicts the percent
increase in G‘ at 60°C of the severely aged versus normally aged, and severely aged versus
unaged three weight percent SBS polymer modified AC-S grade asphalt. Increasing the
processing temperature, caused only 65 percent more aging based on this criteria for three
weight percent SBS polymer modified AC-S grade asphalt. It appears that even under
severe processing conditions, the addition of SBS polymer to AC-S grade asphalt may be

retarding the aging process.

6. 2. 2 Thermal mechanical analysis

Thermal mechanical analysis tests showed that the glass transition temperatures of
both SBS and SEBS polymers are in the range from -60 to -90°C as depicted in Figure
6.40 for the SBS polymer. These results agree with information supplied by the polymer

manufacturer.

 

 

 

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Thermal mechanical analysis tests were also used to look at the final sofiening

temperatures of the four asphalt grade/polymer blend combinations that were studied
during this project. Examination of Figure 6.41 indicates that:

1. All of the TMA data support the conclusions drawn in the critical and optimum
polymer content study.

2. The final softening temperature of AC-lO grade asphalt is greater than that of
AC-S grade asphalt as was expected.

3. At their respective optimum polymer contents, there is little difference in the
final softening temperatures of the difl'erent asphalt grade/polymer blends.

4. At their respective optimum polymer contents, there is an increase of
approximately 25°C in the final softening temperature of the asphalt
grade/polymer blends with respect to the unmodified asphalt.

It is very important to note however, that thermal mechanical analysis tests do not account
for any elastic recovery of the sample when the load is removed.

Aged AC-S grade asphalt/SBS polymer blends were also tested using thermal
mechanical analysis to determine the final softening temperatures of the samples.
Examination of Figure 6.42 indicates that increasing the polymer content beyond the
optimum percentage had an insignificant efi'ect on the final softening temperature of the
aged AC-S grade asphalt/SBS polymer blends. Figure 6.43 shows the difl‘erences in the
final softening temperatures of the aged versus unaged samples for increasing polymer

content. At approximately nine weight percent polymer modification, there is no

difference in the final softening temperatures between the aged and unaged samples. This

 

 

 

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polymer content corresponds to the level of modification thought to cause a matrix

inversion of the A05 grade asphalt/SBS polymer blend. It appears that addition of

polymer retards age hardening and at the matrix inversion, no further hardening occurs.

6. 2. 3 Differential scanning calorimetry

Differential scanning calorimetry was used to examine any temperature dependent
structure that may exist in asphalt. It was found that there are three distinct transitions
that exist in straight asphalt at approximately -12, 10, and 33°C as depicted in Figure 6.44.
Figure 6.45 shows that these transitions were more pronounced in the softer grades of
asphalt suggesting that they are dependent on the samples' oil contents. It was also shown
that upon heating for a period of one hour at various temperatures followed by quenching,
the transitions at 10 and 33° could be eliminated as seen in Figure 6.46. This was found to
be a reversible process however. If a heated sample was allowed to equilibrate at room
temperature, the transitions reappeared as shown in Figure 6.47 suggesting that these
were structural and not chemical transitions. It is believed that at the higher temperatures,
the aSphalt samples' polar structure is destroyed. Dr. Lawrence Drzal’s group has used an
environmental scanning electron microscope to visually examine asphalt structure. A
network-like structure was discovered at room temperature that is believed to correspond
to the transitions observed using differential scanning calorimetry. After heating the
samme, Dr. Drzal's group visually observed the structure disappear. The sample was

allow to equilibrate at room temperature and the stmcture reappeared.

125
This phenomena may be important for practical pavement construction practices.

Many asphalt pavement roads that are laid in the cold, Fall months crack before the
following Spring. Currently, the cracking has been contributed to poor compaction
practices. However, this study suggests that the cracking may be a material problem. If a
hot asphalt is compacted during construction with a cold, snowy roller, it may have the
efl‘ect of quenching in the structureless, high temperature properties. The final pavement
would be very brittle and crack easily.

Upon addition of polymer to asphalt, the transitions were altered in a different

manner and were difficult to analyze without further investigation.

6. 2. 4 Bending beam rheometer

The bending beam rheometer was used to measure the stiffness, and m-values of
SBS polymer modified AC-S grade asphalts that were aged at normal conditions. Figure
6.48 shows how the stiffness of SBS polymer modified AC-S grade asphalts that have
been aged at normal conditions vary as a function of polymer content at a temperature of -
24°C. As the polymer content is increased, the stiffness of the binder decreases thus
enhancing the low temperature properties. However, unmodified AC-S grade asphalt
behaves similarly to four weight percent SBS polymer modified AC-S grade asphalt. It
appears that initial addition of SBS polymer to AC-S grade asphalt may actually worsen
the low temperature properties of the binder. It is interesting to note that four weight
percent SBS polymer content was identified as the critical amount of polymer modification

based on high temperature rheological and thermal mechanical analysis results.

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Figure 6.49 is a similar presentation of the stiffness of SBS polymer modified AC-

10 grade asphalt samples that were aged under normal conditions. A similar trend of
enhanced low temperature properties was not seen for this asphalt/polymer blend. It is
important to note however, that the average difference in stiffness between AC-lO grade
and AC-S grade polymer modified asphalt samples was much greater than the
enhancement seen due to polymer modification. Therefore, it is suggested that the low
temperature properties of an asphalt/polymer blend be controlled by softening the asphalt
grade, and not by increasing the polymer content. Only the AC-S grade asphalt samples
modified with five or more weight percent SBS polymer met the applicable SHRP binder
specification.

Figure 6.50 shows the m-values, or creep rates, of SBS polymer modified AC-S
grade asphalts that have been aged at normal conditions vary as a function of polymer
content at a temperature of ~24°C. It appears that the m-value is not a function of
polymer content as suggested by the SHRP binder specifications for polymer modified
systems. A similar analysis of SBS polymer modified AC-lO grade asphalt samples draws
a similar conclusion. However, there is an average increase of the m-value by 10% when
comparing AC-S grade to AC-lO grade asphalt. This further suggests controlling the low
temperature properties of a polymer modified binder by softening the asphalt grade, and
not by increasing the polymer content. It should be noted that none of the samples tested

met the minimum SHRP m-value specification of 0.3 at -24°C.

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The bending beam rheometer was also used to measure the stiffness and m-values

of severely aged SBS polymer modified AC-S grade asphalt samples. It was determined
that severe aging caused the stiffness of the samples to decrease by an average of
approximately 30 MPa. The m-values of the severely aged samples were similar to those

of the samples aged under normal conditions.

6. 2.5 Rotational viscometry

Rotational viscometry was used to measure the viscosity of polymer modified
asphalts at processing temperatures, 220 - 370°F, to determine whether conventional
equipment could be used during road construction. Figure 6.51 is the data collected for
AC-S grade asphalt cement, modified with SBS polymer. It should be noted that all of the
materials tested met the appropriate SHRP specification for the viscosity of an original
binder. Figure 6.52 shows how viscosity is afi‘ected by increasing polymer content at the
specification temperature of 270°F. At processing temperatures, a critical polymer
content is no longer witnessed. All of the asphalt/polymer blend combinations studied,

showed similar results.

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Chapter Seven

Conclusions and Theories

7. 1 Theoretical models

7.1.1 Asphalt
Asphalt is a complex mixture of many different hydrocarbons consisting primarily
of molecules that contain mainly carbon and hydrogen atoms. A generic asphalt elemental
analysis shows that approximately 84 percent of the sample is carbon, 10 percent
hydrogen, 1 percent oxygen, and the remainder consists of several trace elements
including nitrogen, sulfur, vanadium, nickel, and iron’. The average molecular weight of a
generic asphalt molecule ranges from 500 to 5000. The arrangement of the various
elements in an asphalt binder is of much greater importance than the total amounts of the
elements themselves. Asphalt consists mainly of linear and complex organic ring
structures. The ring structures can be separated into two groups: naphthenic and
aromatic. Naphthenic compounds are simple or complex saturated rings that have a large
number of side chains. Aromatic compounds are heavier molecules that consist of stable
six atom rings with few side chains.
For convenience, asphalt constituents are classified into three categories: oils,
resins, and asphaltenes. Oils are the light compounds in asphalt which have the lowest
molecular weights (24 - 800) and have a large number of side chains and few rings.

Accepted criteria for the oil classification are molecules with carbon/hydrogen atom ratios

137

138
less than 0.6 and are soluble in hexane”. Resins are intermediate molecular weight

compounds (800 - 2000). It is important to note that resins can contain sulfiir and
nitrogen. Resins are polar, have carbon to hydrogen atom ratios between 0.6 and 0.8 and
are soluble in light petroleum naphtha“. Asphaltenes contain the trace elements
mentioned earlier which may react with potential polymers and are soluble in carbon
tetrachloride. An average asphalt sample has an asphaltene/resin/oil ratio of
approximately 23/27/509 and the asphaltene content is higher for harder asphalts. High
performance gel permeation chromatography (HP-GPC) is usually used to determine the
molecular weight distribution, molecular weight, and the fraction of each constituent in an
asphalt sample.

Using the asphaltene/resin/oil classifications, a two phase asphalt model is
developed“. Phase 1 is an assembly phase consisting of asphaltenes and resins that is
dispersed in phase 2, the solvent phase consisting of the oily constituents. Figure 7 .1 is a
symbolic depiction of this model. The resins behave as peptizing agents that stabilize the
asphaltenes in the oily constituents.

The asphaltene core of the assembly phase can vary between 40 and 60 angstroms
in diameter. As the asphaltene content of an asphalt sample increases, the assembly phase
also increases. This adds structure to the asphalt and gives it better high temperature
properties and rutting resistance. The percentage of the assembly phase present is the
defining factor between different grades of asphalts. The resins contain aromatic
compounds substituted with longer alkyls and a larger number of side chains attached to
the rings than asphaltenes. The combination of the saturated and the aromatic

characteristics of the resins stabilizes the colloidal nature of the asphaltenes in the oil

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medium. Asphaltenes are present as discrete or colloidally dispersed particles in the oily

phase. Colloidally dispersed asphaltenes are not stable in the oil medium by themselves,
but can be stabilized through polar resins. Asphaltenes can exist both in a randomly
oriented particle aggregate form or in an ordered micelle form. In micelle form, the polar
groups (water, silica, or metals such as V, Ni, an Fe) are either oriented toward the center
to form an oil-external micelle or oriented outward to form an oil-internal micelle (Hartley
micelle). The growth and ultimate size of the micelles are dependent on temperature, resin
content, and the presence of other chemicals such as polymer modifiers. The engineering
properties of asphalts are directly related to the quantity of asphaltenes, the size of the
micelle structure, and the nature of the dispersion medium, oils and resins.

Another important aspect of asphalts for polymer modification is that the
fiinctional groups present in asphalts may react with polymers during processing.
Functional groups that have been identified in asphalts include: carboxylic acids, ketones,

phenols, sulfoxides, acid anhydrides, pyrroles, and quinones".

7.1.2 Network thennoplastics (SBS and SEBS)

The theorized behavior of SBS in asphalt can best be examined by looking at the
effect of increasing polymer content at three temperature regimes. It should first be noted
that SBS is composed of two hard sphere-like styrene ends joined by an elastic butadiene
component. As depicted in Figure 7.2, the styrene ends are attracted to each other
forming a network-like polymeric structure.

At service temperatures, a plot of the storage modulus versus polymer. content

depicts a non-continuous curve with a distinct optimum and critical polymer content as

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seen in Figure 7.3. It is theorized that as the polymer is being added to the system, it is

slowly destroying the natural structure of the base asphalt by absorbing the oily
constituent. At some critical polymer content, this interaction affects the stability of the
asphalt system by interacting with the resin constituent. At the same time, the polymer is
adding structure to the blend and at a difi‘erent polymer content, a network structure is
achieved thus dramatically enhancing the properties of the system. Figures 7.4 and 7 .5 are
depictions of this theory. Experimental data on asphalts with varying amounts of oil
support the theory.

At high temperatures, the physical structures of both the asphalt and polymer
styrene interactions are overcome by the energy of the environment. The polymer acts as
simply a molecule of higher molecular weight in the system. This theory is supported by
linear viscosity data as a function of polymer content. Figures 7 .6 and 7 .7 are a depiction
of the high temperature theory.

At low temperatures, the system shows a critical polymer content with respect to
bending beam rheometry data. However, this data is hard to duplicate. At low
temperatures, it is believed that the polymer can not absorb as much of the oily constituent
and therefore does not affect the resin constituents. The difficulty in the reproduction of
experimental data may be due to sample handling. Samples for the bending beam
rheometer are prepared at high temperatures. The amount of oil absorption will depend
on the rate at which the samples are allowed to cool and the final equilibration

temperature.

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7.1.3 Dispersed Thermoplastic: (PE)

It is theorized that PE adds to asphalt in a dispersed fashion. There are no styrene
interactions like those found in SBS. Therefore, in order to form a network of dispersed
polymer, it must be added until a matrix inversion occurs and the system becomes asphalt
dispersed in PE. Much more PE will be needed to modify an asphalt than SBS. Figure

7.8 is a schematic of this model.

7.1.4 Reactive polymers (Elvaloy @AM)

It is theorized that Elvaloy®AM chemically reacts with asphalt cement creating a
new material. Elvaloy®AM contains an epoxy firnctional group that is believed to react
with aromatic carboxylic acid functional groups found in the asphaltene constituent of
asphalt cement. Because the system uses the asphalt itself to create a network-like
structure, less Elvaloy®AM would be needed for asphalt modification than SBS. Figure

7.9 is a schematic of this model.

7. 1.5 Crumb rubber particles

Crumb rubber, like asphalt, consists of three constituents: rubber, carbon black,
and oils. It is theorized that when crumb rubber is added to asphalt, there is a migration
and sharing of oily constituents thus forming an interpenetrating network or an adhesive-
like structure. From the literature it appears as if this process is extremely sensitive to

both time and temperature. Figure 7.10 is a schematic of this model.

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7.2 Mixing procedure theory

It has been the industry standard to mix asphalt and polymer unlit it appears
homogeneous to the naked eye. This has been found to be a poor practice for laboratory
procedures. A mixing procedure was therefore developed based upon the improvement of
rheological properties for varying temperatures and mixing times. The optimized
procedure calls for heating the asphalt at 270°F for one hour to obtain a good melt,
followed by mixing of the polymer and asphalt at 350°F for two hours. The above
procedure was chosen based on the following study.

Figure 7.11 depicts a typical curve of tan6 (G"IG') versus temperature at various
mixing times for an AC-S grade asphalt modified with five weight percent SBS polymer.
After a mixing period of forty-five minutes, the asphalt polymer blend appeared to be
homogeneous. However, the blend phase separated in two days. Seventy minutes of
mixing prevented the blend from separating for approximately one week and for mixing
times equal to or greater than two hours, no phase separation was ever observed within a
two month period. It can be seen that the curve corresponding to a two hour mixing
period shows insignificant changes of tan6 with increasing temperatures.

In addition, for all polymer contents used in this study, as the mixing time
increased from 0 to 120 minutes, the rheological properties (storage modulus, G'; loss
modulus, G"; and complex modulus, G“) of the material continued to increase. At a

mixing time of 180 minutes, however, the properties of the blend began to degrade as

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would be expected from the discussion given by Brule who stated that there is an optimum

mixing time for maximizing the mechanical properties of an asphalt/polymer blend”.

It was assumed that the highest concentration of polymer that would be added and
still be economically feasible was seven weight percent SBS. Figure 7.12 shows the effect
of mixing time on the rheological properties of an AC-S grade asphalt modified with seven

weight percent SBS polymer. After mixing for 120 minutes, no substantial change in tan6
can be detected. .

A worse case mixing scenario of A020 grade asphalt modified with seven weight
percent SBS polymer was also studied to ensure that the procedure was acceptable for all
asphalt/network thermoplastic blends. This combination of materials was chosen because
of the large polymer content and the lack of low molecular weight oils found in A020

grade asphalt that are beneficial to the mixing procedure. Figure 7 . 13 shows the effect of
mixing time on the rheological properties of the worse case scenario. It can be seen from
Figure 7.13 that increasing the mixing time beyond 120 minutes does not increase the

rheological properties of the blend.
7.3 Aging phenomena

7. 3. 1 Eflect of polymer modification
After carefiJl analysis of the data collected in this study, it has been concluded that
the addition of SBS and SEBS polymers to AC-S and AC-lO grade asphalt retards the

aging process. Data supporting this conclusion are as follows.

 

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0 Upon addition of polymer to asphalt, an increase in the amount of the high

molecular weight asphalt constituent for the aged sample would be expected
due to both aging and possible polymer degradation. Instead, a decrease in this
value is observed. This phenomena is seen for both normally aged and severely
aged material.

0 FTIR spectra of aged, polymer modified asphalt binders show the formation of
less C=O functional groups than those of unmodified materials. The formation
of C=O functional groups is an indication of oxidative aging. This phenomena
was also seen for both normally aged and severely aged asphalt binders.

0 Dynamic mechanical analysis shows that the storage modulus increases less for
asphalt that has been modified with SBS and SEBS polymers than for
unmodified asphalt, after aging. This phenomena was observed for both
normally aged and severely aged binders.

It is theorized that the decrease in aging is a result of low molecular weight

material entrapment through oil absorbtion and or physical hindrance. Future testing must

be conducted to determine the cause of this phenomenon.

7. 3. 2 Eflect of elevated temperatures during processing

Aging asphalt binders at elevated temperatures caused unexpected results when
testing the final materials using infrared spectroscopy, dynamic mechanical analysis, gel
permeation chromatography, and thermal mechanical analysis. It was theorized that

materials aged at elevated temperatures would show similar trends with respect to the

158
above experiments as materials aged under normal conditions. This was not the case

however. Figure 7.14 is a summary of the unanticipated results.

The results can be explained by the introduction of a second aging process. This
process is a degradation process that affects the resin type material found in asphalt.
Figures 7.15 through 7.17 are a theoretical depiction of the aging phenomena being

discussed. Future studies should be conducted to investigate this theory.

7.4 - Optimum and critical polymer contents

The optimum and critical polymer contents for asphalt modification were defined
based on rheological properties of asphalt/polymer blends. The optimum was defined as
the point at which there was no longer a significant increase in the rheological properties
with increasing polymer content. The critical content was defined as the polymer
concentration where a deviation from the normal trend in the rheological properties is
detected.

The optimum and critical polymer contents were determined for the
asphalt/polymer blends being studied in this project and are summarized in Table 7.1.
These polymer contents are specific to the sources of both the polymers and asphalts. It is
therefore suggested that the reported optimum contents be used only as a guide. It is
strongly suggested that the dynamic shear rheometer be used to examine the relative
increase in properties between the unmodified and modified material. Addition of the

optimum polymer contents resulted in average increases of approximately 1500°/o for the

 

 

159

FTIR:

CH2 (unaged) - CH: (normal aging temperature) < 932 (high aging temperature)
CH3 CHJ CHJ

Ci (unaged) = Cfl (high aging temperature) < E010“ aging temperature)
CH3 - CH3 CH3

Cimnaged) = C:C(high aging temperature) < Cgcmormal aging temperature)
CH2 CH2 CH2

EQ (unaged) < EEO (high aging temperature) < 932 (normal aging temperature)
CH3 CH3 CH3

DMA:

G' (unaged) < 0' (normal aging temperature) < 0' (high aging temperature)

GPC :

unaged MW < normal aging temerature MW = high aging temperature MW

TMA: (softening point)

unaged SP 5 high temperature aging SP < normal temperature aging SP -

Figure 7. 14 - Elevated temperature aging data

 

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5.x. :5... 202.82... £8. E 22.2.838 9...... .29 .2... .. 5.... 88.2..
on... :5... 2...... 2222.22 .252. 8.. 2.25:8... 32 2:8

 

82.24.

a
.s
:21

163

Table 7. I - Optimum and critical polymer contents of studied asphalt/polymer
blends based on rheological properties

Optimum Content Critical Content
erc nt ot wei ht f h MW 01 r l n

AC-S/SBS 3 or 5 4
AC-S/SEBS 2 or 5 3 - 4
AC-lO/SBS g 3
AC-lO/SEBS 2 or 4 3

SHRP original binder specification of (G‘lsin delta) at 60°C. The critical polymer
contents resulted in increases as low as 300% for the same specification. It is therefore
recommended that if the measured increase is less than 500%, more polymer should be
added and the property remeasured to determine if there is any substantial benefit. The
addition of the optimum polymer contents resulted in specification values of approximately
20 kPa. It should be noted that all of the tested samples (0-10 wt% polymer) met the
SHRP original binder specification of (G’lsin delta). At this time, there is no information
regarding the relation to pavement performance of the actual specification level and thus it

can not be said whether the specification value needs to be increased.

 

1 64
7. 5 Fingerprinting protocol

7.5.1 Asphalt grades

Asphalt grades are difficult to fingerprint. However, it is possible to characterize
an asphalt based on viscosity, DMA, GPC, FTIR TMA, DSC, and BBR. It is the industry
standard to grade an asphalt by using viscosity or penetration. This leads to
inconsistencies. Two AC-S grade asphalts may have the same viscosity but be very
difi‘erent chemically and thus show different performance properties. Viscosity, dynamic
mechanical analysis, thermal mechanical analysis, and the bending beam rheometer are
good methods of characterizing the physical properties of asphalts. Fourier transform
infrared spectroscopy and gel permeation chromatography can be used to characterize the
chemical structure of asphalts. GPC allows for the examination of the molecular weight
distribution of an asphalt and FTIR allows for the examination of the chemical functional
groups present in an asphalt. There are three distinct molecular weight ranges found in
asphalt that can be monitored using GPC. Similarly, there are four distinct absorption

wavelengths found in asphalt, that can also be monitored.

7. 5.2 Polymer modifiers

SBS and SEBS polymer modifiers can be fingerprinted using GPC and FTIR
technology. Every polymer will have a defining FTIR spectrum and a characteristic
molecular weight range associated with it. Upon construction of a central library of

spectra, polymer modifiers fiom specific companies will be easily identifiable.

 

1 65
7. 5. 3 Polymer modified asphalt

SBS and SEBS polymer modified asphalts can be fingerprinted through the use of
GPC, FTIR, and DMA in correlation with working libraries. GPC allows for the
determination of the exact amount of polymer modifier added. It also gives molecular
weight information about the base asphalt, polymer modifier, and the aging processes
experienced by the blend. FTIR gives a chemical fingerprint to all constituents of a
polymer/asphalt blend. Thus, it tags the polymer, asphalt grade, and any unusual aging
that has occurred. FTIR can also be used to check the polymer content with the use of a
calibration curve. DMA should be used as a final indicator of the blends performance over
a wide temperature range. Materials will behave in characteristic ways with respect to

rheological testing at difl‘erent temperatures.

7. 5. 4 Methodology
The following series of steps can be used as a method of fingerprinting asphalt
grades, polymer modifiers, and polymer modified asphalts.
1. Scan the sample using FTIR.
o- Ratios of characteristic asphalt peaks determine the asphalt grade.
:> Hard grade asphalts should show larger amounts of C=C (1600 cm“)
bonding than soft grade asphalts.
:> A large amount of the C=O (1700 cm") functional group indicates that
the material has been aged.

0 A peak at 965 cm" indicates the possible presence of an SBS or SBR polymer.

 

 

166
:> A ratio of the 965" (polymer) peak to the 1375" (asphalt) peak can be

used for the determination of the amount of polymer present in a
sample using calibration curves.
2. Examine the sample using HP-GPC.
o The areas of the three distinct regions under the chromatogram can be used for
determining asphalt grade.
:> Hard grade asphalts should show lager amounts of the high molecular

weight material than sofi grade asphalts.

 

:> The presence of excessive amounts of the high molecular weight
constituent suggests that the sample has been aged.

:> The presence of irregularities or sharp peaks in the low molecular
weight region may suggest that the sample has been spiked with oil to
meet a softer viscosity grade.

0 The presence of a high molecular weight peak greater than that of the asphalt
suggests the presence of a polymer modifier.

=> The percent area under the polymer peak with respect to the entire
chromatogram is the weight percent polymer in the binder.

* SBR is a broad peak that can be detected using FTIR.
* SBS is a sharp peak that can be detected using FTIR

* SEBS is a sharp peak that can not be detected using FTIR.

1 67
0 Further fingerprinting can be accomplished through the use of an LC-transform

unit. This system allows for the examination of the sample using FTIR after it
has been separated by molecular weight using HP-GPC.
3. Test the sample using dynamic mechanical analysis.
0 Check the results against a calibration-like curve to insure that the conclusions

drawn fi'om FTIR and HP-GPC analysis are correct.
7. 6 Specifications

7. 6.1 SHRP binder specification
At this time it is felt that the SHRP binder specification is a step in the right
direction. The reason for this support is because it is performance related, temperature
dependent, and material independent. However, there are some suggestions to be
considered about the specification. The specification can be found in Table 7 .232. The
following discussion is a critique of the specification based on its subheadings.
Performance Grade - This classification of asphalt performance is superior to
the standard viscosity and penetration graded systems because it is a function
of temperature. The performance grading system is based on the environments
that an asphalt will encounter during its life. It should be noted that the high
temperature classification is the maximum seven. day pavement temperature
and the low temperature classification is the maximum seven day pavement

temperature. It is felt that the binder classification should also be a filnction of

 

 

168

Table 7. 2 - SHRP performance graded asphalt binder specification

 

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1 69
the loading environment. Therefore, an asphalt grade may have to be increased

for a harsh loading environment, such as standing traffic.

0 Flash Point Temperature - The flash point temperature is a safety specification
placed on the original binder. The addition of polymer will not change this
specification. The material must still not flash. All of the samples tested met
the flash point temperature specification.

0 Viscosity - The viscosity of the original binder is a specification used to ensure
that the material is easily processable in conventional equipment. A polymer
modified material must be able to be handled at similar temperatures to those
of unmodified asphalt. Again, all of the samples tested met the viscosity
specification. Therefore, the SHRP viscosity specification of 3 Pa‘s at 135°C
appears to be appropriate for polymer modified asphalt.

- Dynamic Shear - The dynamic shear test of the original binder, thin film oven
residue, and the pressure aging vessel residue are extremely important tests.
They examine directly the visco-elastic nature of the binder material at three
different times in an asphalts life. The tests are used as high ternperature,

‘ rutting and fatigue life predictors. Although the test itself is a good one, the
actual specification value cannot be judged at this time without more
experimental data. To date, all of the samples tested met these specifications.

0 Mass Loss - The mass loss after TFO aging is a safety and quality control

specification. The addition of polymer will not change this specification. The

 

1 70
material must still not lose mass upon aging. All of the samples tested met the

mass loss specification easily.

Thin Film Oven Test - The thin film oven test simulates the aging that occurs
during processing and the early life of and asphalt. Polymer modified asphalt is
processed at a higher temperature (330 - 350°F) than that of unmodified
asphalt (270 - 290°F). It would therefore suggest that the thin film oven test
temperature should be raised to account for this difference. However, the thin
film oven test is already run at 325°F. Also, above 350°F, it appears that a
secondary high temperature aging reaction which degrades asphalt properties
becomes dominant that will not be seen in the field. Experimental results have
shown that the current test temperature best resembles the chemical
characteristics of recovered samples from the field. A test temperature of
355°F has shown signs of the degradation aging process. The degradation
aging process has not yet been seen in recovered samples. At this time, it is
suggested that the current TFOT temperature is applicable to the polymer
modified asphalts studied. However, this may not be the case for other
polymers and mixing procedures. 3 It should be noted that asphalt in the field
should not be elevated to high temperatures (>400°F) for long periods of time.
Pressure Aging Vessel - The pressure aging vessel test simulates long term
asphalt pavement aging. The addition of polymer to asphalt should not alter
this test. However, no long term aged, recovered samples have been tested to

verify the test itself.

 

171
o Creep Stiffness - The bending beam rheometer is used to measure the low

temperature properties, and thus thermal cracking resistance, of asphalt
binders. This specification is meant to be a function of temperature only and
should be the same for any material used including polymer modified asphalt.
The creep stimiess was effected more by asphalt grade than polymer content,
and thus it is suggested that low temperature properties be controlled by
changing to a softer asphalt grade. Also, the m-value (defined as the slope of
the log stiffness versus log time curve at 60 seconds) specification did not
appear to be affected by polymer content, but instead appeared to be affected
by asphalt grade. At this time, there is not enough data to suggest absolute
specification values with respect to pavement performance. It should be noted
though, that the m-value has been found to be the defining low temperature
specification.

0 Direct Tension - The tension test can not be used at this time because the
facilities do not exist. The direct tension test simulates the cohesive strength of
the asphalt binder at low temperatures. Some of the literature suggests that the

. test is dependent on the type of polymer modification. At this time, a judgment
can not be made concerning the direct tension test.

It is also suggested that a separation test and an adhesion test be added to the

specification. Chemical characterization tests such as FTIR and GPC would also be useful

but require specialized research equipment and add analysis. FTIR and GPC tests could

 

172
be used once per job or in random testing. FTIR and GPC tests can also be used when

problems arise concerning polymer content or type and asphalt quality.

The addition of the optimum amount of SBS and SEBS polymers to AC-S and
AC-10 grade asphalts will increase the high temperature SHRP specification by up to four
grades. The low temperature specification is not affected by the addition of polymer. It is
negatively affected, however, by one grade due to the mixing process required for polymer
modification. This is further support for selecting an asphalt that is one or two grades
softer than usual when using polymer modifiers. This procedure will result in the
enhancement of both low and high temperature properties with respect to the original,
unmodified binder. Figure 7.18 shows how SBS polymer modification affects the SHRP
performance grade of an AC-S grade asphalt. Figure 7 . 19 shows the increase in the
temperature range that the material can operate in as a function of increasing polymer

content.

7. 6.2 WOT binder specification

The MDOT polymer modified binder specification can be found in Table 7 .3. It is
intended to show improvements in an asphalt’s physical properties due to modification
with a polymer. It is suggested that the SHRP specification may be used in this same
fashion by grading both the straight and modified asphalt binder. FTIR and GPC can be
used in correlation with the MDOT binder specification to test for polymer content and,

type and quality of an asphalt.

 

173

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1 75
Table 7.3 - MDO T polymer modified asphalt specification

Testing and Acceptance .

Separation of Polymer - a sample of the polymer modified aspnalt cement will
be :ested for separation of the polymer (HTH 310-92). The seplrtthfl "St in"
insure that the modifier and the asphalt cement blend do not pose a storage
stability problem and that handling be the same as for conventional asphalt
cement. Acceptable differences for top and bottom halves of test specimens shall
not exceed:

Z.5°C in softening point per ASTM 0 36-86 (reapproved). Testing will be
done after 2 days of heating and 7 days of heating.

The polymer modified shall be compatible with the reference asphalt such that
the following properties are exhibited:

Softening Point. °C Raise from Reference
Asphalt. ASTM C 35. minimum

........... 8
Penetration at 25°C. 1009, 3 sec.. dml

drop from Reference Asphalt. ASTM D 5. minimum . . . . 6

l

Viscosity. Poises raise from Reference Asphalt.

60°C, minimum ................... 150 percent
Penetration at 4°C. 2909, 60 sec.. dllll increase

from Reference Asphalt ASTM D 5. minimum ....... 1
Elastic Recovery from 10 cm. 5 cm/min..

ZS'C. minimum .................... 40 percent

Original penetration and viscosity test results on the daily sample of polymer
modified asphalt cement shall meet the above specifications to show uniformity
in the product being supplied througnout the urine“-

The recovered penetration test results on the mixture sample must meet-the
reouirements of Taole 4.00-3 of the 1990 Standard Specifications. for
Construction.

 

Chapter Eight

Suggested Future Work

The research that has been started in this study is only the beginning of polymer
modified asphalt research. There is a limitless number of questions that have been left
unanswered. Chapter Eight will suggest some possibilities of fiiture work based on the

author's understanding of the subject.

8.1 Materials

This study used only a small number of materials. It is believed that every asphalt
grade and polymer type will behave differently when used in an asphalt pavement. It is
therefore necessary to study a wide array of materials. Table 8.1 is a list of some

suggested materials for future research.

8.2 Modeling

The ultimate goal of modeling polymer modified asphalt pavements should be to
be able to predict pavement performance based on the chemical composition of the
pavement constituents. This goal should include all of the processing steps needed to

produce a polymer modified asphalt pavement from its raw materials. It should be the

176

 

177

Table 8. 1 - Suggested materials for future research

 

 

Polymers

Fibers

Asphalts

 

SBR latex
Elvaloy®AM
Polyethylene

Crumb rubber in the form of
recycled tires

Polyester fibers
Cellulose fibers
AC-2.5 grade asphalt
AC-20 grade asphalt
Penetration graded asphalt
Different sources of asphalt
Engineered asphalt

Recycled asphalt

 

 

178
objective of this model to create a base on which sound engineering design of polymer

modified asphalt pavements may begin.

The suggested modeling approach can be divided into a hierarchy consisting of
three levels. Each proceeding level should be able to use the previous models as input for
the current model. The models should also be able to be used individually or in series
depending on the level of information available to the user. As would be expected, the
accuracy of the models, unfortunately, will most likely be reduced when used in series due
to added assumptions implemented at each level. Figure 8.1 is a schematic representation

of the suggested modeling hierarchy.

8. 2. 1 Level one modeling

Level one modeling should consist of developing a physical picture of the studied
asphalt/polymer blend. This model should be based on data gathered in the chemical
analysis of straight and blended materials but will ultimately be based on theory and

intuition. The models presented in this thesis can be used as level one modeling.

8. 2. 2 Level two modeling

Level two modeling should consist of creating empirical models that will correlate
chemical analysis data with physical property data of straight asphalts, polymer modifiers,
and asphalt/polymer blends. The chemical analysis data may come in several forms
including: high performance gel permeation chromatography, photo-diode array, liquid
chromatography-transform, Fourier transform infrared spectrosc0py, and differential

scanning calorimetry data. The physical property data should include: rheological, direct

 

179

 

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180
tensile, viscosity, and phase transition data. The data presented in this thesis will be of

great help when creating level two models.

This approach of empirical modeling could also be used to correlate chemical
analysis data with physical property data for aged, straight and polymer modified asphalts.
For example, it has been suggested that the aging kinetics of asphalt may be expressed in
the following form:

St = so + Kl/Z 1: t1/2
where S is a characteristic, or property depending linearly on the concentration of a
particular asphalt constituent. K is a complex rate constant and t is the time correlated to
the appropriate aging period. A similar model may be developed in future research at
Michigan State University if it is found necessary.
Models developed in level two should be able to be used directly to predict

physical properties of polymer/asphalt blends, or used as inputs for level three modeling.

8. 2. 3 Level three modeling

The goal of level three modeling should be to develop a blending model that will
approximate an asphalt/polymer blend's physical properties based on those of the systems
constituents. Level three modeling should utilize the physical property results obtained
from level two models or should use physical property data directly, based on the
availability of experimental data for the given material. It has been suggested that the
upper and lower bounds, respectively, of polymer blend data can be modeled using simple

parallel and series equations in the following forms:

 

181
E = v*E1 + (1- )*52 (parallel)

l/E = v/El + (l-v)/Ez (series)
where E is the physical property of the final blend; E1 and E2 are the physical properties

of the polymer and asphalt, respectively; and v is the volume or weight fraction of the
polymer’g’”. Several other equations have also been developed that modify these basic
equations by taking into account additional variables of the system being studied. These
equations include the Kemer’g'”, Tsai-Halpinag’”, Nielden-Lewis39'w, Halpin-Kardos”"3,
and parallel voids models”’“.

It should be the objective of level three modeling to modify the simple parallel

and/or simple series equations using the information obtained in levels one and two to

develop a predictive asphalt/polymer blend model.

8.3 Topics and aperiments

The author believes that in order to complete level two and level three modeling,
some topics must be explored in more depth and detail. It is also believed that
experiments must be conducted that further investigate the chemical structure of asphalt

binders. Table 8.2 is a list of suggested topics and experiments for fixture research.

Polymer modified asphalt will be used in the filture in large amounts and should

continue to be studied.

 

182

Table 8.2 - Suggested tapics and experiments for filture research

 

 

Topics

Experiments

 

Kinetics of temperature related structure of asphalt cement
Kinetics of aging processes of asphalt cement

Efl‘ect of polymer modification on the kinetics of temperature related
structure

Effect of polymer modification on the kinetics of aging processes
Engineered asphalts vs. polymer modified asphalts
Polymer swelling studies
Transmission Electron Microscopy
Nuclear Magnetic Resonance
X-Ray Diffraction

Photo Diode Array

 

 

LIST OF REFERENCES

9.

183

LIST OF REFERENCES

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