CA 02330431 2001-O1-08
The Ottawa-Carleton dnstitute for Civil Engineering
Design, Development and Validation of the
Ia-Situ Shear stif, fness Test
(InSiSST'~"')
Facility for Asphalt Concrete Pavements
Researched and Written by:
Stephen Norman Goodman, B.A.Sc., E.LT.
A thesis submitted to the
Faculty of Graduate Studies and Research
in partial fulfillment of the requirements for the degree of
Master of Engineering
Department of Civil and Environmental Engineering
Carleton University
Ottawa, Canada
September 2000
~ 2000, Stephen Norman Goodman
CA 02330431 2001-O1-08
TABLE OF CONTENTS - BRIEF
Abstract.......................................................................
........................................................
iii
Acknowledgements...............................................................
..............................................
iv
Table of Contents - Brief
...............................................................................
......................
v
Table of Contents -
Detailed.......................................................................
........................
vi
List of
Figures........................................................................
.............................................
xi
List of Tables
...............................................................................
.....................................xiii
Notations and Abbreviations
...............................................................................
.............xiv
List of
Appendices.....................................................................
.......................................xvi
CHAPTER 1:
INTRODUCTION...................................................................
.....................
1
CHAPTER 2: LITERATURE REVIEW
...........................................................................
28
CHAPTER 3: REVIEW OF PREVIOUS WORK AND ANALYTICAL MODELLING
80
CHAPTER 4: DEVELOPMENT OF THE IN-SITU SHEAR STIFFNESS
TEST
(InSISSTT'~s)
...............................................................................
......................................1O8
CHAPTER 5: PRELIMINARY TESTING AND
VALIDATION..................................142
CHAPTER 6: CONCLUSIONS AND
RECOMMENDATIONS...................................155
References.....................................................................
...................................................165
Appendices.....................................................................
..................................................175
v
CA 02330431 2001-O1-08
TABLE OF CONTENTS - DETAILED
Abstract.......................................................................
........................................................
iii
Acknowled~ements...............................................................
..............................................
a iv
Table of Contents - Brief
...............................................................................
......................
v
Table of Contents -
Detailed.......................................................................
........................
vi
Ltst of
Fyures.........................................................................
............................................
~a xt
List of Tables
...............................................................................
.....................................
xiii
Notations and Abbreviations
...............................................................................
.............
xiv
List of
Appendices.....................................................................
.......................................
xvi
CHAPTER l:
INTRODUCTION...................................................................
.....................
1
1.1 Asphalt Concrete Pavements in Canada
..........................................................."."..."wwww
1
1.1.1 Asphalt Concrete Pavements Defined
...............................................................................
............
1
1.1.2 Climatic Conditions
...............................................................................
........................................
3
1.1.3 Transportation and the Canadian
Economy..........................................................".,.www-wwww6
1.2 Pavement Structural Design and Loading
Conditions..............................8
..............................
1.2.1 Pavement Structural
Desi~n.........................................................................
..................................8
1.2.2 Pavement Loading
Conditions.....................................................................
..................................9
1.3 United States Strategic Highway Research ............................12
Program (US-SHRP)............
1.3.1 Background and Reason for Implementation
........................_......12
...............................................
1.3.2 The SUPERPAVET"' Mix Design
System.........................................................................
..........
12
1.3.3 Long Term Pavement Performance (US-LTPP)
...............................13
Project...............................
1.3.4 Introduction to the AASHTO 2002 Pavement
................................
Design Guide...................... 1~
1.4 Canadian Strategic Highway Research Program
.............................19
(C-SHRP)....................
1.4.1 Background and Reason for Implementation
...........................,~,..
.............................................. 19
1.4.2 Canadian Long Term Pavement Performance
................................20
(C-LTPP) Project................
1.5 Specific Problem Definitions and Need for
.............................21
New Test Facitity................
1.5.1 Improved Characterization of Pavement
Structure................................
and Design Inputs ........ 22
1.x.2 Simple Performance Test for Superpave
Verification................................23
and QC/QA Testing
1.5.3 The Need to Measure Field Properties
...............................................................................
.........23
1.6 The Innovations Deserving Exploratory
Analysis.............................24
(IDEA) Program .......
1.7 Organization and Scope of Thesis
...............................................................................
.........25
1.7.1 Chapter 1:
Introduction...................................................................
.............................................25
1.7.2 Chapter 2: Literature
Review.........................................................................
..............................26
1.7.3 Chapter 3: Review of Previous Work and Analytical Modellinc
................................................26
1.7.4 Chapter 4: Development of the In-Situ Shear Stiffness Test (InSiSSTTM)
........................"".,....27
1.7.5 Chapter 5: Preliminary Testing and Validation
...........................................................................27
1.7.6 Chapter 6: Conclusions and
Recommendations................................................................
...........27
CHAPTER 2: LITERATURE REVIEW
........................................................................... 28
vt
CA 02330431 2001-O1-08
2.1 Permanent Deformation of Asphalt Concrete
Pavements.....................................................28
2.2 Manifestations of Rutting
...............................................................................
......................28
2.3 Asphalt Surface and Overlay Rutting
...............................................................................
....30
2.3.1 Location of Pavement Rutting
...............................................................................
...................... 30
2.3.2 Surface/Overlay Rutting Mechanism # 1 - Traffic Induced Densification
..................................31
2.3.3 Surface/Overlay Rutting Mechanism # 2 - Shear (Plastic) Flow
..............................................w 32
2.3.4 The Rutting
Cycle..........................................................................
.............................................. 33
2.4 Quantification (Measurement) of
Rutting....................................................._....wwww.~~~~~~34
2.5 Categories for Rutting Variable
Classification......................................................_....ww...~
35
2.6 Category A-Bituminous Materials and
Additives......................................................_..ww36
2. .1 Effect of
Chemistry......................................................................
................................................36
6
37
2.6.2 Effect of
Penetration/Viscosity..........................................................
..........................................
38
2. .3 Effect of Modifiers
...............................................................................
.......................................
6 39
2.6.4 Effect of Other
Additives......................................................................
.......................................
2.7 Category B - Mineral Aggregates
...............................................................................
..........39
2.7.1 Effect of Source
Properties.....................................................................
.....................................39
40
2.7.2 Effect of Consensus Properties
......................................................................,
..............................
2.8 Category C - Mix Design (Volumetric)
Parameters........................................................~....41
2.8.1 Introduction to Volumetric
Parameters.....................................................................
...................41
2.8.2 Effect of Air Voids
...............................................................................
.......................................45
45
2.8.3 Effect of Asphalt Cement
Content........................................................................
.......................
46
2.8.4 Effect of Gradation
...............................................................................
.......................................
47
2. .~ Effect of VMA and
VFA............................................................................
.................................
8 48
2.8.6 Effect of Dust
Content........................................................................
.........................................
48
2.8.7 Effect of Laboratory Density and
Compaction..............................
..............................................
2.9 Category D - Strength/Resistance Properties............................51
of Mix ...............................
2.9.1 Effect of Marshall
Testing........................................................................
...................................51
2.9.2 Effect of Shear Strength and Stiffness ...............................
..........................................................~ 1
x.9.3 Effect of Resilient Modulus and Indirect
...............................53
Tensile Strength...........................
2.9.4 Effect of
Creep..........................................................................
...................................................
~4
x.10 Category E - Pavement Structural and
Geometric............................54
Design......................
x.10.1 Effect of Order of Rigidity of Pavement
......................,........54
Layers.........................................
2.10.2 Effect of Pavement Layer Thickness
...............................................................................
..........56
2.10.3 Effect of Surface (Wearing) Course vs.
...............................56
Base Coarse .................................
2.10.4 Effect of Pavement Alignment
...............................................................................
...................57
2.11 Category F - Construction-Related Factors .............................57
...........................................
2.11.1 Effect of Compaction and other
Construction................................57
Practices............................
?.11.2 Effect of Quality Control/Quality
Assurance................................59
(QC/QA).............................
2.12 Category G - Environmental Factors
...............................................................................
...60
''.12.1 Effect of
Temperature....................................................................
............................................60
o '
...............................................................................
..............................61
_.1_._ Effect of Atemg ...........
2.12.3 Effect of Moisture Damage (Stripping)
................................62
.....................................................
vii
CA 02330431 2001-O1-08
2.13 Category H - Traffic (Load) Related
Factors......................................................................63
2.13.1 Effect of Tire Contact Pressure (Load
Magnitude)....................................................................6
3
2.13.2 Effect of Tire Material
...............................................................................
................................64
2.13.3 Effect of Number of Load Applications
(ESAL's)....................................................................64
2.13.4 Effect of Rate of Loading
...............................................................................
........................... 65
2.14 Category X - Combinations of the Other Categories
.........................................................65
2.15 Summary of Rutting Variable Relationships
......................................................................66
2.16 State-of-the-Practice: Asphalt Rutting Testers
...................................................................68
2.16.1 LCPC (French) Rut
Tester.........................................................................
................................68
2.16.2 Hamburg Wheel Track Tester and Couch
..........................................70
Wheel Track Tester.......
2.16.3 Georgia Loaded Wheel Tester and
Asphalt..........................................
Pavement Analyzer..... 72
2.16.4 Accelerated Load
Facility.......................................................................
...................................74
2.16.5 Superpave Shear Tester
...............................................................................
..............................75
2.17 Deficiencies with Current
Testing/Modelling......................................76
Practices ...............
2.17.1 Discussion of Empirical Rut Testers
..........................................76
...............................................
2.17.2 Discussion of Existing Shear
Tests..........................................................................
..................78
CHAPTER 3: REVIEW OF PREVIOUS WORK AND ANALYTICAL MODELLING 80
3.1 Introduction and Chapter
Overview.......................................................................
...............80
3.2 Review of Previous Work - Laboratory Torsion Testing
of Asphalt Concrete ....................81
3.2.1 Introduction
...............................................................................
..................................................81
3.2.2 Deriving Shear Properties from Laboratory Torsion ..82
Tests........................................................
3.2.3 Major Findings of Laboratory Torsion Testing
...........................................................................
85
3.3 Analysis of Laboratory Mix, Shear and Rutting Database..85
........................:........................
3.3.1 Relation of Mix Characteristics to Shear
Properties....................................................................
85
3.3.2 Relation of Shear Properties to Ruttin~
...............................................................................
........94
3.4 Review of Previous Work - The Carleton In-Situ Shear ..99
Strenth Test (CiSSST)..............
3.4.1 Introduction
...............................................................................
..................................................99
3.4.2 Deriving Shear Properties from Field Torsion Tests 100
.................................................................
3.4.3 Main Results of Previous Experiment
...............................................................................
........102
3.4.4 Advantages of CiSSST
Prototype......................................................................
........................102
3.5 Improved Analytical Framework to Determine Asphalt
Shear Properties from the Surface
Plate Loading
Method.........................................................................
......................................103
3.5.1 Introduction
...............................................................................
................................................103
3.5.2 Reissner-Sagoci
Problem........................................................................
...................................103
3.5.3 Finite Element Modellin; and Verification
...............................................................................
106
CHAPTER 4: DEVELOPMENT OF THE IN-SITU SHEAR STIFFNESS TEST
(InSiSSTT"')
...............................................................................
......................................108
4.1 Introduction and Chapter
Overview.......................................................................
.............108
4.2 Critical Analysis of CiSSST Prototype
Deficiencies..........................................................108
4.2.1 Chassis Design and Weight
...............................................................................
........................109
viii
CA 02330431 2001-O1-08
4.2.2 Stabilization of Test
Device.........................................................................
..............................109
4.2.3 Epoxy System Used for Loading Plate
Attachment...................................................................11
0
4.2.4 Data Collection, Control System and Available .......110
Test Program...........................................
4.2.5 Overall Test Device
Performance....................................................................
..........................111
4.3 Design Objectives for InSiSSTTM Test
Facility..................................................................112
4.3.1 Mitigation of CiSSST Deficiencies
...............................................................................
............112
4.3.2 Reasonable Cost
...............................................................................
.........................................1
i2
4.3.3 Portability and Safety
...............................................................................
.................................112
4.3.4 Number of Operators and Ease of Use
...............................................................................
.......
113
4.3.5 Minimal Test Time and Damage to Pavement Surface........113
.....................................................
4.3.6 Correlate Results to Pavement Performance
Indicators.............................................................
113
4.4 Design of InSiSSTTM Facility
...............................................................................
..............114
4.4.1 Introduction and Overall
Design.........................................................................
.......................
114
4.4.2 The Primary Force Generation System
(Powertrain).................................................................
119
4.4.3 The Transportation
System.........................................................................
...............................
120
4.4.4 The Test Frame and Positioning System
...............................................................................
....120
4.4.5 The Stabilization System
...............................................................................
............................
123
4.4.6 Epoxy
System.........................................................................
...................................................126
4.4.7 The Test Control/Data Collection System
...............................................................................
..127
4.4.8 Overall System
Integration....................................................................
....................................129
4.4.9
Cost...........................................................................
.................................................................129
4.5 Fabrication, Debugging and "Shakedown"
Testing............................................................129
4.5.1 Positioning System
Debugging......................................................................
............................
130
4.5.2 Jacking System
Debugging......................................................................
..................................
130
4.5.3 Test System
Debugging......................................................................
.......................................
130
4.5.4 Shakedown
Testino........................................................................
............................................
131
4.6 Field Test Procedure
...............................................................................
............................132
4.6.1 Equipment
Checklist......................................................................
............................................132
4.6.2 Transportation
Safety.........................................................................
........................................ 132
4.6.3 Securing the Test Site
...............................................................................
.................................133
4.6.4 Preparation of Pavement Surface and Bonding the Loading
Plates........................................... 133
4.6.5 Rutting/Density Surveys (Optional)
...............................................................................
........... 134
4.6.6 InSiSSTTM Test
Procedure......................................................................
................................... 136
4.6.7 Leaving the Test Site
...............................................................................
.................................. 141
CHAPTER 5: Preliminary Testing and Validation
......................................................... 142
5.1 Introduction and Overview
...............................................................................
..................142
5.2 Analytical Models vs. Field Test
Results........................................................................
....142
5.2.1 Verification of Linear Elastic
Assumption................................
................................................142
5.2.2 InSiSSTTM vs. CiSSST
...............................................................................
...............................143
5.2.3 Practical Calculation of Shear Modulus
................................146
Using Equation 8........................
5.2.4 Asphalt Modulus vs. Torque Per Unit
Twist................................
............................................. 147
5.2.5 Effect of Loading Plate Diameter
...............................................................................
...............
149
5.2.6 Discussion of Field Test Results and
Analytical................................
Modelling...................... 153
5.2.7 Comparison of Field and Laboratory
Results................................
............................................ 154
CHAPTER 6: Conclusions and
Recommendations......................................................... 155
6.1 Review of Project
Objectives.....................................................................
.........................155
tx
CA 02330431 2001-O1-08
6.2 Review of Permanent Deformation and Previous Investigations
.......................................156
6.3 Asphalt Mix Properties and Shear
Characteristics..............................................................15
7
6.4 Asphalt Shear Characteristics and
Rutting........................................................................
..159
6.5 Modelling In-Situ Shear
Properties.....................................................................
................159
6.6 Design, Development and Verification of the
InSiSSTTM..................................................160
6.7 Recommendations for Future
Modifications......................................161
to INSISSTTM.........
6.7.1 Environmental
Chamber........................................................................
....................................
161
6.7.2
Hydraulics.....................................................................
.............................................................162
6.7.3 Shear
Vane...........................................................................
......................................................
162
6.8 Recommendations for Further Testing
......................................163
..........,..............................
6.8.1 Additional Verification
Testing........................................................................
.........................
163
6.8.2 Long Term
Performance....................................................................
........................................163
6.8.3 Additional Testing for QC/QA
Specification..........................................
Development............ 164
References.....................................................................
...................................................
165
Appendices.....................................................................
.................................................. 175
x
CA 02330431 2001-O1-08
LIST OF FIGURES
Figure 1: Typical Cross Section for Asphalt Concrete Pavement2
.................................-.-...
Figure 2: Canadian Soil Temperature Zones ..........................--...--.---
.--.--wwwwwwwww-4
Figure 3: Canadian Soil Moisture Zones
.............................................................................
5
Figure 4: Canada's National Highway System and Major US .
Border Crossings .............. 7
Figure 5: Common Loading Conditions of Asphalt Pavements 10
...............................---.---..
Figure 6: Transverse Profiles of Various Rutting Manifestations30
..............................--.--..
Figure 7: Illustration of Surface Rutting........................----.-.--.----
-wwwwwwwwwwww-~31
Figure 8: The Progression of Rutting with Traffic Loading 33
(Rutting Cycle)....................
Figure 9: Phase Diagram of Mix Constituents in Compacted 42
Specimen ..........................
Figure 10: Bitumen Stiffness vs. Mix Temperature for Three 60
Compaction Devices ........
Figure 11: LCPC Rutting
Tester.........................................................................
...............69
Figure 12: Hamburg Wheel Tracking
Tester.....................................................................71
Figure 13: Asphalt Pavement
Analyzer.......................................................................
......73
Figure 14: Accelerated Load Facility (ALF) ...........................----.----
-.--.-.wwwwwwwww~4
Figure 15: Superpave Shear
Tester.........................................................................
...........
7~
Figure 16: Torsion Test Equipment at Carleton University .
.................................-----.---.~- 81
Figure 17: Typical Failure of Asphalt Specimen in Torsion .
Test Device........................ 82
Figure 18: Determination of Shear Properties from Different.
Test Methods................... 84
Figure 19: Laboratory Rutting vs. Asphalt Mix Shear
Modulu......................................--.
97
Figure 20: Laboratory Rutting vs. Asphalt Mix Shear
Strength.....................................---
98
Figure 21: The Carleton In-Situ Shear Strength Test (CiSSST)..
Facility ........................ 99
Figure 22: Loading and Boundary Conditions of CiSSST
.....................................--.----..101
Figure 23: Load Plate Attached to Asphalt Concrete Pavement104
(ACP) Surface.............
xi
CA 02330431 2001-O1-08
Figure 24: Induced Failure in Asphalt Concrete Pavement
(ACP) Surface .................... 104
Figure 25: Differential Element Shear Stresses from ............
Reissner-Sagoci Problem. 105
Figure 26: Initial Finite Element Model
Verification..........................................--.-....-..-
107
Figure 27: Side View of InSiSSTTM
...............................................................................
.
116
Figure 28: Top View of
InSiSSTTM......................................................................
...........
117
Figure 29: InSiSSTT~f positioning System
......................................................................
118
Figure 30: Plan View of the Lower Positioning System.....-.-.....
.................................... 121
Figure 31: Plan View of InSiSSTTM Test Frame
......................................---.~.wwwwww
124
Figure 32: Outline of Rutting and Density
Survey...................................----~~..wwww~~-.
135
Figure 33: InSiSSTTM Trailer over Test Plates..............................-
.......---.--wwwww-~~~.
138
Figure 34: Chocking the Trailer
Tire...........................................................................
....
138
Figure 35: Attach Torque Cell Cable to Torque Cell ......--......
........................................ 139
Figure 36: InSiSSTTM Controls (Computer not shown) .......--~...~
.................................... 139
Figure 37: Connecting Collar from Torque Cell to ..............
Test Plate ......................... 140
Figure 38: Taking Pavement Temperature with IR Thermometer..............
.................... 140
Figure 39: Comparison of Field Results with Reissner-Sagoci
Model ........................... 143
Figure 40: Typical Torque vs. Twist Angle Graph from...............
InSiSSTTM ............... 147
Figure 41: Determining the Tangent of the Torque-Twist...............
"S" Curve.............. 147
Figure 42: Torque vs. Angular Displacement for InSiSSTTM...............
Tests ................. 151
xn
CA 02330431 2001-O1-08
LIST OF TABLES
Table l: Classification Criteria for Transverse Profiles
........................-.....-..........--..-.---.- 29
Table 2: Categories for Rutting Variable
Classification...........................................-----.-.. 35
Table 3: Various Asphalt Cement Modifiers.......................-
.................----......---.-...--........ 39
Table 4: Summary Table of Rutting Variables and Qualitative
Relationships.................. 67
Table 5: Characteristics of Rut Testers.......................................-
.------........--.--.wwwwww 77
Table 6: Mix Properties Available from Zahw (1995)
Database....................................... 86
Table 7: Engineering Properties Available from Zahw (1995)
Database.......................... 86
Table 8: Mix Properties Yielding Greatest Correlation to Shear Properties
..................... 87
Table 9: Regression Statistics for Shear Modulus (Equation
4)........................................ 93
Table 10: Regression Statistics for Shear Strength (Equation 5)
...................................... 93
Table 11: Contribution of Individual Variables Toward Shear
Properties........................ 94
Table 12: Rutting Models for Shear Strength and
Modulus..........................................-... 95
Table 13: Target Test Strain Rates and Associated Motor
Speeds.................................. 128
Table 14: Equipment
Checklist......................................................................
.................. 132
Table 15: Comparison of CiSSST and InSiSSTTM Results
............................................. 144
Table 16: Shear Modulus vs. Torque Per Unit Twist
............................................-....-..-. 148
Table 17: Comparison of Torque Per Unit Twist for 92mm and 125mm
Plates............. 152
Table 18: Results of InSiSST Testing with 125 mm
Plates............................................. 153
xiii
CA 02330431 2001-O1-08
NOTATIONS AND ABBREVIATIONS
Absorbed Binder Volume,
Vba............................................................................
...............
43
Accelerated Load Facility
(ALF)..........................................................................
.............
74
Aggregate Volume,
VS.............................................................................
..........................
42
41
Air Voids, V~
...............................................................................
......................................
American Association of State Highway and Transportation(AASHTO)...........
Officials 9
Apparent Aggregate Volume,
VS~............................................................................
..........
43
Asphalt concrete pavement (ACP)
...............................................................................
.......
1
Asphalt Pavement Analyzer
(APA)..........................................................................
.........
73
Average Rate of Densification
(ARD)..........................................................................
.....
90
Binder Volume, Vb
...............................................................................
.............................
42
Bulk Aggregate Volume,
Vsb............................................................................
.................
43
Canadian Long Term Pavement Performance (C-
LTPP)..................................................
20
Canadian Strategic Highway Research Program .............................
(C-SHRP) ................ 19
Carleton In-Situ Shear Strength Test (CISSST) .............................
................................... 99
Coefficient of variation
(COV)..........................................................................
..............
144
Effective Aggregate Volume, Vse
...............................................................................
.......
43
Effective Binder Volume,
Vbe............................................................................
................
43
Federal Highway Administration (FHWA)
.......................................................................
15
Field Shear Test
(FST)..........................................................................
.............................
76
Fine aggregate angularity
(FAA)..........................................................................
.............
40
Georgia Loaded Wheel Test (GLWT)
...............................................................................
72
Gross Domestic Product
(GDP)..........................................................................
.................
6
Gyratory shear index
(GSI)..........................................................................
......................
52
Gyratory testing machine (GTM)
...............................................................................
.......
52
Hot-mix asphalt concrete (HMAC)
...............................................................................
......
1
Innovations Deserving Exploratory Analysis ...............................
(IDEA) Program......... ?4
In-Situ Shear Strength/Stiffness Test (InSiSSTT"'')~",~"""~"""_~",.......
................-....~.~~~." ?7
Just-In-Time Delivery
(JIT)..........................................................................
.......................
8
Laboratoire Central des Ponts et Chaussees ...............................
(LCPC).......................... 68
xiv
CA 02330431 2001-O1-08
Linear variable differential transducer (LVDT) .-.-...wwww.
............................................ 72
National Aggregate Association
(NAA)..........................................................................
..
40
National Center for Asphalt Technology (NCAT)
......................................-..---...~ww.-~.~.
30
National Cooperative Highway Research Program
(NCHRP).........................................-
18
National Highway System
(NHS)..........................................................................
..............
6
Penetration-Viscosity Ratio
(PVR)..........................................................................
..........
90
Percent Air Voids, Va
...............................................................................
.........................
43
Present serviceability index or rating (PSI or .-.--~....~www.
PSR)...................................... 17
Quality control and quality assurance
(QC/QA)......................................--.~._~..ww.-~
~3, 114
Resilient modulus
Mj.............................................................................
............................
~3
Superior Performing Asphalt Pavements (SuperpaveTM~""~~~"".........
) ---_~..,~..~...,~,~~.""~~, 12
Superpave Shear Tester
(SST)..........................................................................
.................
75
Transportation Association of Canada (TAC)
.....................................................................
1
Transportation Research Board
(TRB)..........................................................................
....
?4
United States Long Term Pavement Performance (US-LTPP)......................
................... 13
United States Strategic Highway Research Program ......................
(US-SHRP) .............. 12
Voids Filled with Asphalt (VFA)
...............................................................................
.......
44
Voids in the Mineral Aggregate
(VMA)..........................................................................
..
43
xv
CA 02330431 2001-O1-08
LIST OF APPENDICES
Appendix A: Correlation Matrix for Zahw Database
..............................................~....... 164
Appendix B l: Selected Variables for Mixes 1 through
5................................................ 175
Appendix B?: Selected Variables for Mixes 6 through
12.............................................. 176
Appendix C 1: Shear and Rutting Properties for Mixes 1 through
5................................ 177
Appendix C?: Shear and Rutting Properties for Mixes 6 through
12.............................. 178
Appendix D: CiSSST Test Results
...............................................................................
... 179
Appendix E: InSiSSTTM Test
Results........................................................................
...... 180
xm
CA 02330431 2001-O1-08
CHAPTER 1: INTRODUCTION
1.1 Asphalt Concrete Pavements in Canada
1.1.1 Asphalt Concrete Pavements Defined
The term "pavement," although seemingly obvious in its usage, may have
different meaning to different people or agencies. For example, pavement may
simply refer to the surface layer of a road system, or may encompass
additional
underlying layers. The Transportation Association of Canada (TAC) has defined
the term "pavement" as consisting of all structural elements or layers,
including the
shoulders, above the subgrade. While the subgrade is not part of the pavement
structure by this definition, its characteristics such as strength or load can-
ying
capacity, drainage, etc. are implied (TAC 1997). This thesis has adopted the
TAC
pavement definition wherever pertinent.
The term "asphalt concrete" refers to a conglomeration of asphalt cement
(binder), aggregate and air (void space). Unless otherwise stated, the term
asphalt
concrete refers to hot-mix asphalt concrete (HMAC), the most common type of
asphalt concrete used in transportation systems, which is mixed and placed at
elevated temperatures.
Therefore, for the purposes of this thesis, an "asphalt concrete pavement
(ACP)" is a pavement structure whose upper layers are constructed with hot-mix
asphalt concrete unless otherwise stated. Figure 1 displays a typical cross
section of
an ACP, also commonly referred to as a flexible pavement.
1
CA 02330431 2001-O1-08
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1.1.2 Climatic Conditions
Pavements in Canada are subjected to particularly harsh climatic conditions.
Furthermore, these harsh conditions are not consistent throughout Canada due
to its
enormous size. For example, the Canadian Meteorological Centre (?000) reports
that northern cities such as Yellowknife in the Northwest Terntories
consistently
experience temperatures of -30 degrees Celsius (°C) for 3 months of the
year with
extreme temperatures of -51°C not uncommon. Central cities such as
Regina,
Saskatchewan may experience annual pavement temperature ranges of up to
80°C.
Finally, coastal cities such as St. John's, Newfoundland and Vancouver,
British
Columbia are subjected to 1.6 and 1.2 metres of rain respectively per year.
Figure 2 displays soil temperature zones across Canada. As shown, no less
than 7 individual temperature zones are present, ranging from Arctic (extreme
cold)
in the north to Mild along the Canadian-US border. With the exception of some
of
the Atlantic Provinces, each province or terntory contains at least 2 of these
zones
with many of the provinces containing 5 zones.
Figure 3 displays the distribution of soil moisture across Canada. As with
temperature, the distribution of soil moisture is extreme ranging from aquic-
perhumid areas where the soil is fully saturated for long periods of the year
to
subaquic-arid regions with severe groundwater deficits.
The large variation in climatic conditions across Canada presents pavement
designers and contractors with unique regional challenges.
CA 02330431 2001-O1-08
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CA 02330431 2001-O1-08
6
1.1.3 Transportation and the Canadian Economy
In 1999, transportation industries accounted for 30.6 billion Canadian dollars
(4.1 %) of Canada's Gross Domestic Product (Transport Canada 1999). The
trucking sector accounted for the largest proportion of the transportation
industries
at 1.7% of the GDP ($12.5 billion). The average annual growth of the trucking
sector between 1994 and 1999 was 7.7%, more than double of any other
transportation sector including rail, marine and air. In 1998/1999 alone, the
trucking sector annual growth was 8.2%. These statistics clearly indicate the
immense importance of trucking to the Canadian economy and that this
importance
is Growing at a high rate.
The National Highway System (NHS) is a network of roads identified by the
Council of Ministers Responsible for Transportation and Highway Safety during
a
multi-stage policy study initiated in September 1987. The network consists of
existing primary routes that provide interprovincial and international trade
and
travel by connecting a capital city or major provincial population or
commercial
centre in Canada with another capital city or major population centre, a major
point
of entry or exit to the United States highway network or another
transportation
mode served directly by the highway mode (Transport Canada 1999). The NHS is
illustrated in Figure 4
Although the NHS accounts for only 24500 kilometres of the entire Canadian
road
network of over 900000 kilometres (less than 3%), the NHS experiences nearly
one
quarter of the total vehicle-kilometres driven (Transport Canada 1999).
Ontario and
Quebec alone account for 60% of NHS traffic and these traffic levels are
increasing
every year.
<IMG>
CA 02330431 2001-O1-08
8
The large and continuing increase in truck traffic on Canadian roads may be
largely attributed to a new revolution in the way business is done in North
America
that started in the early 1990's. The main thrust of this new revolution was
the
implementation of a new manufacturing process referred to as "lean production"
- a
process that has been shown to improve productivity, efficiency and profits
(Earns
199?). While lean production involves numerous new procedures, an essential
component is a process called "Just-In-Time Delivery," or JIT. In essence, JIT
delivery systems require delivery of inventory only when needed, permitting
smaller
storage space and faster model change in response to consumer demands.
Therefore, the nations highways become linear warehouses for manufacturing
companies. This trend is not expected to reverse in the near future.
Unfortunately, although local government spending on transportation has
increased over the past five years, spending at the federal and
provincial/territorial
levels has declined (Transport Canada 1999), leaving an overall decrease in
funds
available for highway maintenance. Therefore, as truck traffic increases and
overall
government spending decreases, the pavement industry will face increasingly
difficult challenges to provide an adequate highway network for the public.
1.2 Pavement Structural Design and Loading Conditions
1.2.1 Pavement Structural Design
Methods of pavement structural design may be classified into three categories
as follows (TAC 1997).
i) Experience-based methods using standard sections;
CA 02330431 2001-O1-08
9
ii) Empirical methods in which relationships between some measured
pavement response, usually deflection, or field observations of
performance, and structural thickness are utilized;
iii) Theory-based methods, using calculated stresses, strains, or deflections.
These are also known as mechanistic-empirical methods.
Currently, most flexible pavement structural design methods are mostly
empirical methods that have been improved over the past 40 years to include
deflection measurements, subgrade compressive strains and asphalt layer
tensile
strains. Material properties are typically characterized using elastic or
resilient
modulus. The most common methods are the Asphalt Institute Thickness Design
Method (Asphalt Institute 1991) and the American Association of State Highway
and Transportation Officials (AASHTO) Flexible Pavement Design Method
(AASHTO 1993). Traffic loading in both methods consists of uniform vertical
pressures applied to a multi-layered elastic system.
t.2.2 Pavement Loading Conditions
Although traditional asphalt pavement analysis and design methods focus on
uniform vertical stresses applied by traffic loading, there are actually 10
loading
conditions commonly applied to pavements in service. These conditions are
illustrated in Figure ~ (Gerrard and Harnson 1970).
CA 02330431 2001-O1-08
1~
4
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s
w
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DISPLACEMENT
Figure 5: Common Loading Conditions of Asphalt Pavements
(from Gerrard and Harrison 1970)
CA 02330431 2001-O1-08
11
According to Gerrard and Harnson (1970), loading by uniform vertical
pressure (sub figure la) is typical of pneumatic tires and flexible
foundations, while
loading by uniform vertical displacement (sub figure 1b) corresponds to
relatively
rigid foundations. In addition to uniform vertical pressures/displacements,
linear
vertical pressures and displacements are also applied to pavement structures
(sub
figures 2a and ?b, respectively). Loading by linear vertical pressure
represents
moments about the horizontal axis applied to flexible pavements, while linear
vertical displacements represent moments about the horizontal axis applied to
rigid
pavements.
In addition to vertical loading, pavements are also subjected to numerous
loading conditions in shear. Linear radial shear stresses (sub figure 3a) are
developed at the surface of pavements due to the grip of pneumatic tires.
Measurements by Bonse and Kuhn (1959), as well as Marwick and Starks (1941),
indicate that the magnitude of the maximum stress is of the order of the tire
inflation
pressure. Linear radial shear stresses are present both at rest and during
constant
linear velocity. Linear radial shear displacement (sub figure 3b), when
coupled with
the uniform vertical pressure loading, gives the exact solution to the problem
of a
flexible foundation with a rough base (Gerrard and Harrison 1970).
The state of stress defined by linear torsional shear stress (sub figure 4a)
is
imposed as an automobile turns or enters a curved section of road. Linear
torsional
shear displacement on the other hand, may be applied to the analysis of vane
shear
tests at subgrade failure loads (subfigure 4b).
The final set of loading conditions consist of uniform unidirectional shear
stress and displacement (subfigures Sa and Sb). Unidirectional shear stress is
CA 02330431 2001-O1-08
12
applied during braking, acceleration and traction of pneumatic tires, while
unidirectional shear displacement represents lateral loads applied to
foundations.
According to Figure 5, six of the ten possible pavement loading conditions
involve shear, however, current practices only consider uniform vertical
pressure.
1.3 United States Strategic Highway Research Program (US-SHRP)
1.3.1 Background and Reason for Implementation
The United States Strategic Highway Research Program (US-SHRP) was a ~
year, $150 million dollar research program designed to improve the performance
and durability of highways and make them safer for motorists and highway
workers.
US-SHRP was initiated in response to the continuing deterioration of highway
infrastructure in the United States and was intended to make significant
advances in
traditional highway engineering and technology through the concentration of
new
research funds in four key technical areas - Asphalt, Pavement Performance,
Concrete and Structures, and Highway Operations (C-SHRP 1998). A total of 130
new products emerged from the US-SHRP research in the form of new equipment,
processes, test methods, manuals and specifications for the design,
maintenance and
operations of highways (US-SHRP 1992).
1.3.2 The SUPERPAVET~' Mix Design System
SuperpaveTM (Superior Performing Asphalt Pavements) was one of the major
products of the SHRP asphalt research program. Unveiled in 1992, the Superpave
system represented a fundamentally new system for designing asphalt concrete
mixes. The performance-based nature of the system not only promoted improved
CA 02330431 2001-O1-08
13
pavement life, but also the potential ability to predict pavement performance
based
on accelerated testing (C-SHRP 1999).
Briefly, the Superpave system incorporates performance-based asphalt
materials characterization with the design environmental conditions to improve
performance by controlling rutting, low temperature cracking and fatigue
cracking
(Asphalt Institute 1997a). The Superpave system consists of three main
components - the performance graded (PG) asphalt binder specification, the
mixture
design and analysis system, and a computer software system (Asphalt Institute
1997b).
Detailed discussion of the Superpave system is beyond the scope of this thesis
and has been documented in countless other reports. It should be mentioned
however, that by 2001, the AASHTO Task Force on SHRP Implementation predicts
that over 80% of the hot mix asphalt produced and constructed in the United
States
will be designed with the Superpave system (AASHTO 1999). It is therefore
clear
that Superpave will be the asphalt mix design system in the United States for
the
foreseeable future. In Canada, Superpave implementation has progressed at a
slower rate; however, it appears that Canadian agencies will also adopt
Superpave
as the new mix design system in the coming years.
1.3.3 Long Term Pavement Performance (US-LTPP) Project
As pan of the US-SHRP, a comprehensive 20-year study of in-service
pavements was initiated in 1987 to understand why some pavements perform
better
than others, with the ultimate Goal of building and maintaining a cost-
effective
highway system. This field experiment, known as the Long Term Pavement
Performance (US-LTPPj project, is unprecedented in scope, consisting of over
2400
CA 02330431 2001-O1-08
14
asphalt and Portland cement concrete pavement test sections across the United
States and Canada (FHWA 1998a).
The original US-LTPP research plan set forth six objectives for the program
(FHWA 1999a):
i) Evaluate existing pavement design methods.
ii) Develop improved design methodologies and strategies for the
rehabilitation of existing pavements.
iii) Develop improved design equations for new and reconstructed
pavements.
iv) Determine the effects of loading, environment, material properties and
variability, construction quality, and maintenance levels on pavement
distress and performance.
v) Determine the effects of specific design features on pavement
performance.
vi) Establish a national long-term database to support LTS-SHRP's
objectives and to meet the future needs of the highway industry.
To support these objectives, three types of studies were established: General
Pavement Studies (GPS), Specific Pavement Studies (SPS) and the Seasonal
Monitoring Program (SMP). The GPS experiments focus of the most commonly
used structural designs for pavement. Eight types of existing in-service
pavements
are currently being monitored throughout North America. The performance of
these
structural designs is tested against an array of climatic, geologic;
maintenance,
rehabilitation, traffic and other service conditions (FHWA 1999a).
CA 02330431 2001-O1-08
15
In contrast, the SPS test sections were specially constructed to investigate
certain pavement engineering factors. These sections allow critical design
factors to
be controlled and performance to be monitored for the initial date of
construction. It
is anticipated that the results from the SPS experiment will provide a better
understanding of how selected maintenance, rehabilitation, and design factors
affect
pavement performance.
The SMP experiment sections were also specially constructed to provide data
needed to determine the impacts of temperature and moisture variations on
pavement response.
The primary product of the LTPP experiment is the Information Management
System (IMS) database that contains the data collected from each of the three
LTPP
studies. Administered by the Federal Highway Administration (FHWA), the IMS
database is available to anyone at no cost. To make the data more accessible
and
user friendly, portions of the IMS database meeting all quality control levels
are
released on CD-ROM under the name "DataPave." The latest version of DataPave
- version 2.0 released in September of 1999, contains twice as much IMS data
as its
predecessor (FHWA 1999b).
1.3.4 Introduction to the AASHTO 2002 Pavement Design Guide
As mentioned, most pavement design procedures are based on the AASHTO
Guide for the Design of Pavement Structures (TAC 1997). All previous and
current
versions of this guide have been based on performance equations developed at
the
AASHO Road Test in the 1950's. While previous versions of the guide have
served
well for almost four decades, there are a number of serious limitations to
their
CA 02330431 2001-O1-08
16
continued use as the nation's primary pavement design procedures as outlined
by
McGee (1999):
~ Pavement rehabilitation design procedures were not considered at the AASHO
Road Test. Full consideration of rehabilitation design is required to meet
today's needs.
~ Since the road test was conducted at one specific geographic location, it is
difficult to address the effects of differences in climatic conditions on
pavement performance. For example, at the road test a significant amount of
distress occurred in the pavements during the spring thaw, a condition that
does not exist in a significant portion of the country.
~ One type of subgrade was used for all of the test sections at the road test.
Many types exist nationally.
~ Only unstabilized, dense granular bases were included in the main pavement
sections (limited use of treated bases was included for flexible pavements).
Various stabilized types now are used routinely.
~ Vehicle, suspension, axle configurations, and tire types were representative
of
the types used in the late 1950's. Many of these are outmoded in the 1990s.
~ Pavement designs, materials, and construction were representative of those
used at the time of the road test. No subdrainage was included in the road
test
sections.
CA 02330431 2001-O1-08
17
An additional problem with earlier AASHTO procedures is the order-of-
magnitude difference between AASHO Road Test traffic loads and the loads
carned
by modern new and rehabilitated pavements. Road test pavements sustained at
most
some 10 million-axle load applications; less than cart-ied by some modern
pavements in their first year of use due to the explosive growth of truck
traffic over
the last 40 years. Equations forming the basis of the earlier procedures were
based
on regression analyses of the road test data. Thus, application of the
procedure to
modern traffic streams meant the designer often was projecting the design
methodology far beyond the data and experience providing the basis for the
procedure. Clearly, the result was that the designer may have been working "in
the
dark" for highly trafficked projects. Such projects may well have been either
"under
designed" or "over designed" with the result of significant economic loss
(McGee
1999).
Another major extrapolation is design life. Because of the short duration of
the road test, the long-term effects of climate and aging of materials were
not
addressed. The AASHO Road Test was conducted over ? years, while the design
lives for many of today's pavements are 20 to 50 years.
Finally, earlier AASHTO procedures relate the thickness of the pavement
surface layers (asphalt layers or concrete slab) to performance. However, the
observed performance of pavements reveals that many pavements need
rehabilitation for reasons that are not directly related to pavement thickness
(i.e.
rutting, thermal cracking, faulting etc.). Further, the primary measure of
pavement
performance in the earlier procedures is present serviceability (PSI or PSR)
and the
dominant factor effecting serviceability is pavement ride. Yet, in many cases
CA 02330431 2001-O1-08
18
pavement managers find that distress factors other than ride, such as cracking
and
rutting, control when pavement rehabilitation is required. To improve the
reliability
of design and to meet the needs of asset management, the management criteria
and
the pavement design procedure must relate to the same performance factors. To
help alleviate these problems, the 2002 Guide will use the international
roughness
index (IRI) as a major pavement performance measure (McGee 1999).
The AASHTO Joint Task Force on Pavements (JTFP) has responsibility for
the development and implementation of pavement design technologies. In
recognition of the limitations of earlier Guides, the JTFP initiated an effort
to
develop an improved Guide by the year 2002. At the time of this writing, the
National Cooperative Highway Research Program (NCHRP) is developing a major
revision and update to the current AASHTO pavement design guide, under NCHRP
project 1-37A, due for release in 2002. A draft version of the new guide was
completed in April 1999 although it has not been formally published (McGee
1999).
Unlike previous design guides, the 2002 guide will incorporate mechanistic-
empirical concepts to better characterize the pavement structure and its
constituent
materi als.
Although this move represents a major step forward toward a more accurate
pavement design and analysis system, the 2002 guide will only focus on
vertical
loading conditions on a multi-layered elastic system. Researchers concede that
shear loading is important to pavement performance, however, Witczak (2000)
explained that the 2002 guide will not include shear properties or loading
conditions
as the guide is being developed from already existing databases and test
procedures.
CA 02330431 2001-O1-08
19
1.4 Canadian Strategic Highway Research Program (C-SHRP)
1.4.1 Background and Reason for Implementation
In 1987, The Canadian Strategic Highway Research Program (C-SHRP) was
created in response to the commencement of SHRP in the United States. The
objective of C-SHRP is to improve the performance and durability of highways
and
to make them safer to motorists and highway workers by extracting the benefits
of
the United States Strategic Highway Research Program (US-SHRP) and by solving
highway problems having a high priority in Canada that were related to, but
not
duplicates of, US-SHRP projects (RTAC 1986).
C-SHRP is a dedicated program of the Council of Deputy Ministers
Responsible for Transportation and Highway Safety and is managed by the C-SHRP
Executive Committee. Unlike US-SHRP, C-SHRP was always envisioned as a 15
year program with three 5-year program phases (C-SHRP 1998). Due to delays
with the US-SHRP, the C-SHRP Executive Committee extended the first program
phase by two years. C-SHRP Phase 1 ran from April 1987 until March 1994 and
involved coordinating Canadian involvement with the US-SHRP research as well
as
conducting independent Canadian research related to US-SHRP. The
complimentary C-SHRP research produced an additional 8 research products.
Phase 1 also saw the initiation of the Canadian Long Term Pavement Performance
(C-LTPP) project, an independent experiment designed with Canadian pavement
design and climatic conditions in mind.
The second phase of C-SHRP was completed between April 1994 and March
of 1999. The focus of Phase 2 was technology transfer in the form of
evaluating
CA 02330431 2001-O1-08
20
SHRP/C-SHRP research results and applying the findings to mainstream practice.
The C-LTPP project continued with a focus on data collection and management,
with initial analysis of performance through Bayesian modelling procedures
(Kaweski and Nickeson 1997).
The third and final phase of C-SHRP is currently underway and will conclude
in April of 2004. As with Phase 2, technology transfer of SHRP products will
continue as a primary focus, however, the range of products evaluated and
promoted
will be expanded to include products of the FHWA and AASHTO. The C-LTPP
experiment will conclude in 2004 and the resulting database will be completed
for
use by pavement designers and researchers to provide more cost effective
pavement
designs.
1.4.2 Canadian Long Term Pavement Performance (C-LTPP) Project
The Canadian Long Term Pavement Performance (C-LTPP) project was
initiated in 1987 as an independent Canadian experiment to investigate
pavement
performance. However, whereas the US-LTPP project covered all pavement types,
the overall goal of the C-LTPP project is to increase pavement life through
the
development of cost-effective pavement rehabilitation procedures, based upon
systematic observation of in-service pavement performance. As the majority of
Canadian roads are asphalt concrete pavements, only new asphalt concrete
overlays
were selected for investigation under C-LTPP. Therefore, if comparing to the
US-
LTPP project, the C-LTPP test sites could be considered SPS-5 sections,
although
the C-LTPP sites are independent of US-LTPP.
In formulating the overall goal of C-LTPP, four distinct objectives were
identified (C-SHRP 1997):
CA 02330431 2001-O1-08
21
i) to evaluate Canadian practice in the rehabilitation of flexible pavements,
and
to subsequently develop improved methodologies and strategies;
ii) to develop pavement performance prediction models and validate other
models or calibrate then to suit Canadian conditions;
iii) to establish common methodologies for long-term pavement evaluation, and
to provide a national framework for continued pavement research initiatives;
iv) to establish a national pavement database to support the preceding C-LTPP
objectives as well as future needs.
A total of 24 test sites were selected for C-LTPP each with 2 to 4 adjacent
test
sections for a total of 65 test sections within the experiment. Each test
section
received an asphalt concrete overlay for the experiment. The use of adjacent
sites
allows for the comparison of different rehabilitation methods under identical
traffic
loading, climate and soil conditions. The alternative rehabilitation
strategies
employed on the C-LTPP test sections included variable overlay thickness, hot
and
cold-mix recycling, milling, inclusion of performance enhancing additives, or
a
combination thereof.
As with the US-LTPP, the primary product of C-LTPP is the C-LTPP
pavement performance database.
1.5 Specific Problem Definitions and Need for New Test Facility
The preceding sections were included to provide some context of current
research
activities in the area of pavement performance, materials and design. While
the past
decade has seen many significant improvements in asphalt pavement technology,
there
CA 02330431 2001-O1-08
77
remains much room for improvement, particularly in the use of shear properties
to
design, construct, monitor and predict the performance of ACP's. The following
sections provide rationale for the current investigation; that being to
design, develop
and verify an advanced in-situ shear strength/stiffness test for asphalt
concrete
pavements.
1.5.1 Improved Characterization of Pavement Structure and Design Inputs
As outlined in Section 1.2, pavement design procedures in use today only
consider loading in the vertical direction, despite the fact that six of the
ten common
pavement loading conditions described involve shear stresses or displacements.
As
indicated, the NCHRP is developing a major revision and update to the current
AASHTO Guide for the Design of Pavement Structures (AASHTO 1993) under
NCHRP project 1-37A due for release in 2002. Unlike previous design guides,
the
2002 guide will incorporate mechanistic-empirical concepts to better
characterize
the pavement structure and its constituent materials. Although this move
represents
a major step forward toward a more accurate pavement design and analysis
system,
the 2002 guide will only focus on vertical loading conditions on a multi-
layered
elastic system. Although the vertical loading condition represents a large
portion of
the applied stress, the measurement of shear parameters of asphalt pavements
and
incorporation into analysis and design should significantly improve the
reliability of
pavement design, providing more cost effective pavements. Clearly, the
inclusion
of shear loading into the design process will be a complex undertaking that
will
require extensive research prior to implementation. Development of an in-situ
test
device will provide an important step toward this goal.
CA 02330431 2001-O1-08
23
1.5.2 Simple Performance Test for Superpave Verification and QC/QA Testing
One major issue not addressed in the original Superpave system was the
adoption of a strength or durability test. Unlike the Marshall or Hveem
methods
that utilize stability or flow tests, Superpave was originally based solely on
volumetric properties with no strength test for performance verification. To
address
this deficiency, the NCHRP initiated project 9-19 "Superpave Support and
Performance Models Management" to recommend a laboratory "simple
performance test" suitable for evaluating the rutting and fatigue performance
of
asphalt mixes and to ultimately provide input to performance models. In
addition to
performance testing, the simple performance test should also be capable for
use in
quality control and quality assurance (QC/QA) testing.
However, there is currently no in-situ performance test for Superpave or any
other asphalt mix design system. The development of an in-situ shear
strength/stiffness test would provide an excellent complimentary field test
device
allowing both faster and more cost effective performance testing and QC/QA
testing
due to its portable nature.
1.5.3 The Need to Measure Field Properties
Peck and Lowe ( 1960) perhaps gave the best reasoning for the introduction of
field shear testing (of soils) as opposed to laboratory testing during the
1960 ASCE
Research Conference on Shear Strength of Cohesive Soils in Colorado:
"It seems apparent that there are numerous unanswered questions with
regard to the shear strength of undisturbed soils. Many of these arise because
of
doubts regarding the applicability of laboratory f ridings to field
conditions. It is
recognized that the mere act of obtaining a sample front a natural deposit
CA 02330431 2001-O1-08
24
radically alters the state of stress and induces strains, and that natural
deposits
are rarely homogeneous. Yet there seems to be an inclination to feel that the
really fundamental research on shear strength of undisturbed soils must be
done
irz the laboratory, and tlzat the results of the laboratory studies nzay be
applied to
field conditions with a minimum of evidence to support the extrapolation. The
panel discussions have indicated that there may be dangerous pitfalls in tlais
path. "
1.6 The Innovations Deserving Exploratory Analysis (IDEA) Program
The Innovations Deserving Exploratory Analysis (IDEA) programs, managed by
the Transportation Research Board (TRB), provide start-up funding for
promising but
unproven concepts in surface transportation systems (TRB ?000).
The goal of the >DEA programs is to seek out and support new transportation
solutions unlikely to be funded through traditional programs. IDEA programs
differ
from the more traditional research programs in the following ways:
1. They offer an arena for innovation. Topics are not restricted; good ideas
that
support the general goals of safe and efficient surface transportation are
eligible.
?. Their impact is timely. Fledgling ideas take flight only when their
development is
nurtured. The IDEA programs foster good ideas at a critical early stage in the
hope
that they soon will take off on their own.
3. The proposal process is simple and accessible. Proposals are accepted at
any time
and awards are made twice each year. There are no prerequisites for submitting
proposals; good ideas are welcome from anyone.
CA 02330431 2001-O1-08
25
There are IDEA programs covering four major transportation areas - Highways,
High Speed Rail, Intelligent Transportation Systems and Transit. As part of
the
NCHRP, the Highway-IDEA program is managed by the TRB and jointly supported by
the FHWA and the member states of AASHTO. The program seeks advances in the
construction, safety, maintenance, and management of highway systems (TRB
?000).
In September of 1997, a proposal entitled "Design, Development and
Verification of an Advanced In-Situ Shear Strength Test for Asphalt Concrete
Pavements" was submitted to the TRB for a NCHRP Highway IDEA Concept
Exploration project (Goodman and Abd El Halim 1997). In February of 1999,
Carleton University was awarded NCHRP IDEA Project #55 to develop the in-situ
shear strength/stiffness test facility. The work completed for that project
constituted a
substantial portion of this thesis.
1.7 Organization and Scope of Thesis
1.7.1 Chapter 1: Introduction
Chapter 1 commences with a definition of asphalt concrete pavements and
their importance to the Canadian economy, followed by a description of the
various
pavement loading conditions. A brief introduction of the United States and
Canadian Strategic Highway Research Programs (US-SHRP and C-SHRP) is then
provided to introduce recent and ongoing research efforts, as well as give
context to
the specific problems associated with current practice and the need for a new
field
test device for asphalt concrete pavements. Chapter 1 finishes with an
introduction
to the Innovations Deserving Exploratory Analysis (IDEA) Program, which
CA 02330431 2001-O1-08
26
provided substantial funding toward the development of the test facility, as
well as
the organization and scope of this thesis.
1.7.2 Chapter 2: Literature Review
Chapter 2 consists of an extensive literature review completed to examine all
aspects of the asphalt pavement rutting phenomenon including its
manifestations,
mechanisms, procedures for quantification, and a detailed review of the
contribution
of numerous variables toward rutting resistance. Furthermore, a state-of-the-
practice review of current laboratory and field rutting test methods is
provided with
a discussion of the various limitations associated with these devices.
1.7.3 Chapter 3: Review of Previous Work and Analytical Modelling
The foundation for the current investigation was laid by two previous
investigations completed at Carleton University. The first was a comprehensive
laboratory investigation of asphalt shear properties and pavement rutting
completed
by Zahw (1995). Chapter 3 begins with a review of that investigation, followed
by
the results of a new study to investigate the relationships between asphalt
mix
characteristics, shear properties and pavement rutting, using data collected
during
his research. The second underlying research effort involved the construction
of a
first generation in-situ shear strength test device by Abdel Naby (1995). A
review
of the device, known as the Carleton In-Situ Shear Strength Test (CiSSST), is
provided including its main benefits and the results of his research
concerning in-
situ shear strength and its relation to pavement performance. The chapter
concludes
by introducing an improved analytical approach to derive asphalt pavement
shear
properties from the surface plate loading condition using closed form
equations and
the finite element method.
CA 02330431 2001-O1-08
1.7.4 Chapter 4: Development of the In-Situ Shear Stiffness Test (InSiSSTTM)
The primary basis for this thesis was the design and development of an
advanced in-situ shear stiffness test for asphalt pavements. The design of the
new
device, entitled the In-Situ Shear Stiffness Test (InSiSSTTM) was conceived
through
an analysis of the deficiencies observed with the CiSSST prototype built in
1995.
The advantages and benefits of the InSiSSTTM are described, as well as some of
the
challenges experienced during its fabrication. Chapter 4 concludes with an
initial
set of instructions and procedures to carry out field testing with the
InSiSSTT'''
1.7.5 Chapter 5: Preliminary Testing and Validation
Once fabrication of the InSiSSTTM was complete, preliminary field tests were
completed for validation purposes. Chapter ~ first presents the results of an
exercise
to validate the linear elastic assumption made by the analytical models
presented in
Chapter 3. Next, the results of comparison testing with the CiSSST and
InSiSSTT"'
devices are presented, as well as an interesting observation concerning the
test plate
diameter. Chapter 5 concludes with a comparison of field shear properties to
those
observed in the laboratory by Zahw (1995).
1.7.6 Chapter 6: Conclusions and Recommendations
The final chapter summarizes the project objectives and the rutting
phenomenon, as well as the conclusions observed during the investigation.
Recommendations for additional modifications to the InSiSSTTM and future
testing
are also presented.
CA 02330431 2001-O1-08
CHAPTER 2: LITERATURE REVIEW
2.1 Permanent Deformation of Asphalt Concrete Pavements
Although the term "rutting" is often used interchangeably with permanent
deformation, it is only one of four observed manifestations as described
below:
~ Rutting is characterized by channelized depressions (troughs) that run
longitudinally in the wheelpaths. Rutting may or may not be accompanied by
shoving of the pavement adjacent to the wheelpaths.
~ Correcgations and Slcovircg is characterized by ripples along the pavement
surface
formed by alternating areas of settlement and/or heave.
~ Grade Depressions and Settlement are manifested as irregular or localized
areas
of settlement (not specifically in the wheelpaths).
~ Upheaval or Swell consists of localized upward expansion of pavement due to
swelling of underlying soils (base or subgrade) through moisture infiltration
or
frost heave.
However, rutting is the most common form of permanent deformation analysed.
Therefore, the terms rutting and permanent deformation will be considered the
same
for the purposes of this thesis.
2.2 Manifestations of Rutting
Rutting itself is manifested in a number of forms depending on which of the
pavement layers was responsible for the deformation. A novel and accurate
method of
determining the layer at which rutting occurred was investigated by Simpson
et. al.
(1995). During their investigation, it was observed that the shape of the
pavement
28
CA 02330431 2001-O1-08
29
transverse profile was theoretically indicative of where the rutting
originated within the
pavement structure. Using data from the US-LTPP Program, it was shown that the
transverse profiles generally fit into one of four categories representing (a)
subgrade
rutting, (b) base rutting, (c) surface rutting, or (d) heave. Illustrations of
these
categories are shown in Figure 6.
Classification of transverse profiles into the four above categories was
completed
using the algebraic area between the transverse profile and the straight line
connecting
its end points as illustrated in Figure 6. Profile areas that were entirely
negative proved
to be the result of subgrade settlement while areas that were entirely
positive were the
result of heave. Furthermore, marginally positive profile areas were the
result of
surface rutting, whereas marginally negative areas were the result of base
layer rutting.
The criteria used to classify transverse profiles from the US-LTPP database
are shown
in Table 1. Of the 134 US-LTPP sections analyzed, only six transverse profiles
did not
agree with the classification system. Therefore, over 95% of transverse
profiles were
correctly classified using Table 1.
Table 1: Classification Criteria for Transverse Profiles
(from Simpson et. al. 1995)
Transverse
Profile
Layer Responsible
for Rutting Area of DistortionRatio of Positive to
(mm2) Negative
Area of Distortion
Subgrade < -4500 < 0.4
Granular Base -4500 to 700 0.4 to 1.25
Surface (Asphalt)700 to 5000 1.25 to 3.0
Heave > 5000 > 3.0
CA 02330431 2001-O1-08
30
a. SUBGRADE
b. BASE
c.SURFACE
d, HEAVE
Figure 6: Transverse Profiles of Various Rutting Manifestations
(from Simpson et. al. 1995)
2.3 Asphalt Surface and Overlay Rutting
2.3.1 Location of Pavement Rutting
Although rutting due to heave, subgrade or granular base failure can and does
occur, rutting in properly constructed pavements is usually observed due to
deformation of the asphalt layers. This statement was confirmed through a
comprehensive National Rutting Study that was completed in United States by
the
National Center for Asphalt Technology (NCAT) in 1987. As part of the
CA 02330431 2001-O1-08
31
investigation, trench cuts were made in selected roads to observe where in the
pavement structure that rutting was occurring. Reports by Cross and Brown
(199?,
1991) revealed that most of the rutting occurred in the top 75 to 100 mm (3 to
4 in.)
of the pavement, therefore, almost exclusively in the asphalt concrete liver.
The
amount of rutting in the base coarse was insufficient to measure. The results
of the
MCAT study have been confirmed in other studies including Gervais and Abd El
1-lalim (1990). Figure 7 illustrates a cross section of an asphalt pavement
section
displaying surface rutting. Note that the bottom edge of the asphalt layer is
almost
completely flat while the surface is severely rutted.
Figure 7: Illustration of Surface Rutting
(from Gervais and Abd EI Halim 1990)
2.3.2 Surface/Overlay Rutting Mechanism # 1 - Traffic Induced Densitication
With the exception of wear rutting caused by studded tires, surface or overlay
rutting is caused by two main mechanisms. The first is called "traffic-
induced," or
".......... ,_...."~"~;,.,~~,~,~r.~4:::.:-,_~:.~w,.:..
CA 02330431 2001-O1-08
J7
"post" densification. Initial densification of the various pavement layers,
including
the asphalt concrete, occurs during the construction phase in the form of
compaction. During compaction, the layers are compacted to form a dense,
consistent structure to resist traffic loading. However, layers that are not
compacted
to a high degree retain significant void space. Under subsequent traffic
loading, the
layers continue to consolidate as the excess voids are removed. This process
is
known as traffic induced densification.
For properly constructed pavements, L1S-SHRP (1994) reports that traffic
induced densification is generally not considered to be the cause of
substantial
rutti n a.
2.3.3 Surface/Overlay Rutting Mechanism # 2 - Shear (Plastic) Flow
The second and more critical rutting mechanism is shear or "plastic°'
flow of
the asphalt concrete mix under traffic loading. Shear flow involves lateral
movement of the asphalt cement and reorientation of aggregate particles under
traffic loading to a new or more stable equilibrium. The movement (strain)
incuwed
by the asphalt concrete is not recovered once unloaded, resulting in permanent
deformation. For properly constructed pavements, shear deformations caused
primarily by large shear stresses in the upper portions of the
asphalt/aggregate
layers are dominant (US-SHRP 1994j.
The shear flow phenomenon was the underlying reason for the development
of the InSiSSTT'''. It is hypothesized that increasing the resistance of the
asphalt
mix to shear deformation will reduce rutting and improve long-term pavement
performance significantly.
CA 02330431 2001-O1-08
33
2.3.4 The Rutting Cycle
The two rutting mechanisms mentioned above are not mutually exclusive.
Indeed, a rutting cycle is observed in most instances during the design life
of a
properly constructed asphalt pavement. The three stages of permanent
deformation
with traffic loading are listed below (Carpenter 1993):
1. Primary - initial compaction and traffic induced densification
?. Secondary - stable shear period
3. Tertiary - rapid unstable shear failure
Rutting is initiated with continued densification of the asphalt layer under
traffic loading. Kandhal et. al. (1993) explain that during this stage,
rutting is
directly proportional to traffic.
02
0 18
0 ~6
0
0
_ 0 ~2
0
d
0'
iv
c
0.08
a 0 06
O.Oc .
0 02 ~
Initial l)cn.iCir.aion
0
0 05 1 i5 2 25 3 35 4 45 5
Load Repetitions (Millions
Figure 8: The Progression of Rutting with Traffic Loading (Rutting Cycle)
(from Carpenter 1993)
CA 02330431 2001-O1-08
s4
The second phase involves a stable shear period during which the rate of
rutting decreases with increasing traffic until a condition of plastic flow
occurs and
the rate of rutting main increases (rapid unstable shear failure). Therefore,
prevention of the onset of the tertiary flow stage should increase pavement
life
considerably with respect to permanent deformation.
2.4 Quantification (Measurement) of Rutting
Rutting is quantified using various methods and measures for evaluation and
modelling purposes. Perhaps the most common measures are average rcet depth or
naccxintccm race depth in millimetres or inches as measured transversely
across the
pavement width using straightedges, profilometers, or other depth measuring
devices.
A second commonly used measure is average raetting rcate; the rut depth
divided
by the amount of traffic to which a particular pavement has been subjected.
This
measure allows different pavements to be compared directly. Previous work by
>=3rown
and Cross (1998), and Parker and Brown (1990) has shown that expressing the
rate of
rutting as a function of the square root of total traffic yields higher
correlation with
observed pavement behaviour when compared to other expressions (such as the
log of
traffic).
As previously presented, Simpson et. al. (1995) quantified rutting by
deteumining
the total area of deformation from transverse profiles obtained for the US-
LTPP
Project.
CA 02330431 2001-O1-08
2.5 Categories for Rutting Variable Classification
The rutting phenomenon is very complex. At present, there is no single
independent variable that completely captures or predicts rutting. In
addition, Kandhal
et. al. (1993) emphasized that a single "bad" property, such as excessive
asphalt
content, can nullify other good properties, such as coarse aggregate with 100
r'c
fractured faced count. Furthermore, there are also numerous interactions
between the
independent variables, making analysis or modelling more difficult.
For this investigation, the factors affecting permanent deformation were
classified into eight unique cate;ories and a ninth category encompassing
combinations
of the first eight. The categories are listed in 'fable 2 in no particular
order of
importance.
Table 2: Categories for Rutting Variable Classification
Category ~ Variable Grouping
i
A Bituminous Materials and Additives
I
B Mineral Aggregates
~ Mix Design Parameters o
C
D Strength/Resistance Properties
of Mix
E Pavement Structural Design I
F J Construction-Related
G Environmental-
H Traffic-Related
X Combinations of Above Categories
A breakdown of the individual categories and their variables is presented in
the
following sections.
CA 02330431 2001-O1-08
36
2.6 Category A - Bituminous Materials and Additives
As defined by the TAC (I997j, bituminous materials are petroleum-based
products of oil refining or naturally occurring asphalts. Asphalt is a dark
brown to
black solid or semisolid cementitious material that softens and liquefies when
heated.
Asphalt cement (ACj receives further refinement to meet specifications for
paving and
related purposes.
Although liquid asphalts (made from asphalt cement] are available, asphalt
cement is the only material used for the production of hot-mix asphalt
concrete
(HMAC). Liquid asphalts are used primarily for cold-mix asphalt concrete, a
less
durable material not regularly used for road construction in Canada.
Therefore, only
asphalt cement and HMAC-related variables were considered during this
investigation.
2.6.1 Effect of Chemistry
Asphalt cement consists of asphaltenes, oily constituents and asphaltic resins
(TAC 1997). At present, data that conclusively relates the chemical properties
of
asphalt cement to permanent deformation is relatively limited.
A 1983 study performed on Interstate 90 in Montana compared the
performance of asphalt cements from each of that state's oil refineries.
Reports by
Bruce (1987) and Jennings et. al. (1988] showed that asphalt cements
containinj
lower levels of asphaltenes and saturates were more susceptible to rutting. No
conclusive relationships were observed for other constituents such as polar
aromatics or naphthene aromatics. However, the authors cautioned that mix
design
asphalt content could have been an overriding factor for that investigation.
CA 02330431 2001-O1-08
., -,
W
2.6.2 Effect of Penetration/Viscosity
Penetration is an empirical measure of asphalt cement hardness. In theory, the
greater the penetration, the more susceptible the asphalt concrete pavement is
to
permanent deformation. However, the penetration test is performed at a
standard
temperature of 2~°C whereas rutting typically occurs at more elevated
temperatures
between 40°C and 60°C. Therefore, while various asphalt cements
may yield
similar penetration values, their high temperature performance may be markedly
different. This has been the case to date since little data conclusively
relates
penetration to permanent deformation.
Viscosity is a measure of the resistance of the asphalt binder to floe (shear)
at
a specified temperature. Unlike penetration, viscosity measurements are often
made
at high temperatures to better capture the asphalt cement properties at
temperatures
more indicative of rutting (see Category G for the effect of temperature on
pavement rutting).
Results of Bruce (1987) and Jennings et. al. (1988] did indicate that higher
penetration and viscosity numbers seemed to result in 'renter rutting.
However. this
trend may have been influenced by the aspl;alt content in the mixes.
The NCAT National Rutting Study completed by Cross and Brown (1992,
1991) indicated that hi'Ther penetration values were cowelated with increased
rutting
for mixes with more than '?.~~i'o air voids in-place. However, the degree to
which
penetration correlated with rutting was much lower than that observed for
ag're~~ate
properties. Conversely, a rutting study connpleted in Saskatchewan by Huber
and
CA 02330431 2001-O1-08
38
Heiman (1987) concluded that penetration and viscosity did not demonstrate a
significant effect on rutting performance.
Nievelt and Thamfld (1988) concluded that asphalt cements with higher
viscosity values produced asphalt mixes with greater rutting resistance as
tested
using wheel-tracking tests on samples at multiple test temperatures.
It should be mentioned that the new Superpave performance-graded (PG)
binder specification has been implemented in Ontario (MTO 1998). This new
specification does not rate asphalt cements based on penetration at a standard
test
temperature. Indeed, a rigorous testing regime using a combination of the
Dynamic
Shear Rheometer and Dynamic Viscometer measure viscosity at medium and high
temperatures to better characterize high terr~perature binder performance
(Asphalt
Institute 1997a). However, penetration has been included in this investigation
as the
vast majority of existing roads were designed using the Marshall method, not
the
Supeyave mix design system. Clearly, the effect of PG Binder properties would
be
applicable to new roads designed using Superpave.
2.6.3 Effect of Modifiers
As will be discussed further in Category G, asphalt cement properties are
highly temperature sensitive. As temperature of the asphalt cement increases,
its
stiffness decreases, thereby increasing the potential for permanent
deformation, as a
larger deflection of the asphalt layer is incurred under the same load. The
high
temperature susceptibility of asphalt cement may be reduced through the
addition of
polymer modifiers. Terrel and Epps (1988) list a number of modifiers in Table
3.
CA 02330431 2001-O1-08
39
Table 3: Various Asphalt Cement Modifiers
(from Terrel and Epps 1988)
Polymer Type
~j Example
Natural latex Natural rubber
~
Synthetic latexStyrene-butadiene (SBR)
Rubber Block copolymerStyrene-butadiene-styrene
(SBS)
Reclaimed rubberRecycled Tires
Polyethylene
Plastic Polypropylene
Ethyl-vinyl-acetate
(EVA)
~- Combinationcombination
I of above
2.6.4 Effect of Other Additives
In addition to polymer modifiers, other additives such as liquid anti-stnppina
agents or hydrated lime are used to improve the bond between the asphalt
cement
and the aggregate particles. Krutz and Stroup-Gardiner ( 1990) investigated
the
influence of moisture damage on rutting for the Nevada Department of
Transportation (DOT). The. loss of asphalt cement from stripping allowed the
ag'reaates to shift, causing severe rutting of the pavements analysed.
Therefore, the
use of anti-stripping additives should reduce rutting by reducing the loss of
asphalt
concrete through moisture damage.
2.7 Category B - Mineral Aggregates
2.7.1 Effect of Source Properties
Aggregate source properties include soundness, toughness and deleterious
materials. These propea-ties are empirical in nature and are usually used only
to
evaluate local aggre~uate sources on a comparison basis.
CA 02330431 2001-O1-08
40
While studying the effect of gradation on permanent deformation for the
Nevada DOT, ILrutz and Sebaaly (1993) compared source properties of various
aggregates. A test regime utilising standard triaxial and repeated triaxial
tests
revealed that rutting performance of mix gradations containing substantial
amount
of fine material (i.e. finer overall gradations) was directly linked to source
properties.
While not targeting any individual pavement distress, Wu et. al. (1998)
subjectively compared source properties to pavement performance. The Micro-
Deval (toughness) and Magnesium Sulphate Soundness (soundness) tests were more
strongly correlated with the subjective pavement penormance ratings compared
to
other source property tests such as the Los Angeles Abrasion and Freeze-Thaw
Soundness tests.
2.7.2 Effect of Consensus Properties
Aggregate consensus properties include coarse aggregate an~ularitv, fine
aggregate angularity, flat and elongated panicles and clay content.
The NCAT National Rutting Study concluded that the effect of aggregate
angularity on rutting was dependent on in-situ air voids (Cross and Brown
199?,
1991). For in-situ air voids above 2.S~lo, the angularity of the coarse
aggregate (two
or more crushed faces) and the National Aggregate Association uncompacted
voids
for the fine aggregate (now referred to as ''fine aggregate angularity"j were
highly
correlated with rate of rutting. If the in-situ voids were less than
2.5°~~, rutting was
likely to occur regardless of aggregate properties.
Marks et. al. (1990) concluded that the percentage of crushed aggregate
strongly influenced creep resistance factors. As the percentage of crushed
material
CA 02330431 2001-O1-08
41
increased, creep resistance factor also increased. The relationship of creep
to rutting
is presented in Category D.
Button et. al. (1990) observed the relationship between aggregate properties
and permanent deformation as the amount of manufactured (crushed) sand was
replaced with rounded natural sand in the mix. The first observation was that
the
texture, shape and porosity of the fine aggregate were major factors related
to
plastic deformation. Second, permanent deformation increased significantly as
the
percent of rounded natural sand increased (i.e. as manufactured sand was
replaced).
No information was found for flat/elongated particles or clay content at this
time. However, it is well known that flat and elongated particles tend to
break
under compactive effort, alterinU the gradation of the mix. Clay is a
compressive
soil that can potentially change volume with time and moisture causing
localized
swell or settlement in the pavement structure.
2.8 Category C - Mix Design (Volumetric) Parameters
2.8.1 Introduction to Volumetric Parameters
A comprehensive historical review (and reinterpretation) of mix design
volumetrics was presented by Coree (1999). Coree divided volumetric parameters
into two main categories - Primary and Secondary as detailed below.
Primary Volumetric Parameters
The primary volumetric parameters are those relating directly to the relative
volumes of the individual components:
~ Air Voids, V~ - the volume of air voids
CA 02330431 2001-O1-08
42
~ Binder Volume, Vb - the volume of the bituminous binder
~ Aggregate Volume, V; - the volume of the mineral aggregate
Figure 9, commonly referred to as a "phase diagram," displays the various
volumetric components.
Air Voids, Vv
Effective Binder
Total Binder Volume, Vbe
Volume, Vb
Total bsorbed Binder Volume, Vba
Volume,
Vtotal
Effective
Aggregate Bulk Aggregate Volume, Vsb
Volume, Vse
rigure 9: Phase Diagram of Mix Constituents in Compacted Specimen
(from Coree 1999)
As shown, the bituminous binder is absorbed into the external pore structure
of the aggregate such that a portion of the aggregate and bituminous binder
share
space. Therefore, the sum of the individual volumes (V~ + V5) is greater than
their
combined volume (Vh+s). This situation allows further sub-division of the
primary
parameters given above:
CA 02330431 2001-O1-08
43
~ Effective Binder Volume, Vhe - the volume of bituminous binder external to
the aggregate particles, i.e., that volume not absorbed into the aggregate
~ Absorbed Binder Volume, Vba - the volume of bituminous binder absorbed
into the internal pore structure of the aggregate
~ Bulk Aggregate Volume, Vsb - the total volume of the aggregate, comprising
the "solid" aggregate volume, the volume of the pore structure permeable to
water but not to bituminous binder and the volume of the pore structure
permeable to the bituminous binder
~ Effective Ag'Tregate Volume, VS~, - the volume of the aggregate comprising
the "solid" aggregate volume and the volume of the pore structure permeable
to water but not to bituminous binder.
~ Apparent Aa~Tregate Volume, V5~ - the volume of the "solid" aggregate, i.e.,
that volume permeable to neither water nor bituminous binder.
Secondary volumetric parameters
Three additional parameters have been widely used, and at various times, have
formed critical deli<m thresholds. These are the Percent Air Voids, V~, the
Voids in
the Mineral Aggregate, VMA, and the Voids Filled with Asphalt, VFA.
~ Percent Air Voids, V~ - simply V'- expressed as a percentage of the total
volume of the mixture.
~ Voids in the Mineral Aggregate, VMA - the sure of V~~ and ~',,~ expressed as
a percentage of the total volume of the mixture. This parameter is directly
analogous to "porosity" in soil mechanics.
CA 02330431 2001-O1-08
44
~ Voids Filled with Asphalt, VFA - the degree to which the VMA are filled
with the bituminous binder, expressed as a percentage. This property is
directly analogous to the "degree of saturation" in soil mechanics.
It is important to recognize that Va, VMA and VFA are highly dependent on
the decree of compaction and, according to Coree (1999), secondary parameters
should never be quoted without referencing the degree of compactive effort
used.
The following relationships may be derived from the above definitions and
Fi pure 9:
i
VFA = 1 ''e * 100 ~;, _ ~'= * 100 VMA = y + I'" * 100
T[~ r
t ' LE~ ~Irunl ~~lrrrrli
Simple algebraic manipulation reveals that the above equations are not
mutually exclusive, since:
VMA-V
~'FA = ° * 1 C)0
VMA
Coree (1999) explained that in the process of mixture design, it is frequently
necessary to seek to chance the magnitude of one or more of these parameters.
For
example, upon analyzing a mixture, it may appear desirable to increase the VMA
(a
relatively common problem), or to manipulate the air voids. Vauious
recommendations and techniques exist to achieve this. However, it is neither
clear
what effect such a change might have on the other parameters, nor whether that
change might, in itself, compromise compliance in another direction. Indeed,
no
such change in any one parameter should ever be contemplated without checking
the effects on the other two.
CA 02330431 2001-O1-08
4J
Although the interaction of volumetric properties is complex and greatly
affects pavement performance, the effects of individual properties have been
noted
by numerous studies and are presented below.
2.8.2 Effect of Air Voids
In-situ air void content has been identified as perhaps the most critical
parameter affecting rutting. Furthermore, the range of air voids identified
for good
rutting resistance is well known. Indeed, it was observed that for the roads
selected
during the NCAT study, none of the 50 or 75-blow mixes displayed unacceptable
rutting rates if in-situ air voids remained greater than 4%r.
Brown and Cross (1990) provide the following explanation:
An asphalt mixture with low voids acts very much like a saturated soil.
It has no shear strength. When the vc>ids are reduced to a very low level (2
to
3 percent), pore pressures terLd to build up Lender traffic, the effective
stress on
tire aggregate is reduced, and shear or plaszi.c floe takes place.
Therefore, pavements which retain 4~7o air voids or greater after years of
traffic loading show excellent performance with respect to rutting.
Both Huber and Heiman (1987) and Kandhal et. al. (1993) concluded that
pavements begin to exhibit plastic deformation when the air voids reached
threshold
values (usually 3~Ic or less).
2.8.3 Effect of Asphalt Cement Content
Asphalt cement content refers to the amount (percentage) of asphalt binder in
the asphalt mixture by weight. Effective asphalt content does not include the
asphalt binder absorbed in the mineral aggregate. For rutting resistance,
asphalt
cement content should be relatively low to prevent shear flow under loading
and
CA 02330431 2001-O1-08
46
elevated temperature. However, enough asphalt cement must be present to bind
the
aggregate particles in place.
Huber and Heiman (1987) concluded that asphalt content and voids filled with
asphalt were the most basic parameters affecting rutting, while Abd El Halim
et. al.
(199_5) indicated that rutting decreases with increasing asphalt content to a
maximum value, after which rutting increases with increasing asphalt content.
The Montana study, while not exploring the effect of asphalt content
specifically, indicated indirectly the importance of asphalt content by
cautioning
that mix design asphalt content could have been the oven-iding factor for that
investigation (Bruce 1987 and Jennings et. al. 1988).
Cross and Brown (199?, 1991) indicated that asphalt cement content was
extremely important to rutting resistance. Kandhal et. al. (1993) echoed the
importance of asphalt cement content by indicating that excessive asphalt
content
could effectively nullify other good properties of a mix such as crushed
aggregates.
2.8.4 Effect of Uradation
A study of 3? asphalt concrete overlays placed over rigid pavements
completed by Carpenter and Enockson (1987) indicated that the majority of
rutting
problems could be attributed to gradation. The tender mix phenomenon
associated
with a "hump" in the 0.45 power gradation chart was associated with rutting.
Furthermore, the percent passinj the No. 40 sieve and retained on the No. 80
sieve
was found to influence rutting.
As previously mentioned, the effect of gradation on permanent deformation
was studied by Krutz and Sebaaly (19931 for the Nevada Department of
Transportation (NDOT). ,A second conclusion from this study v.~as that rutting
CA 02330431 2001-O1-08
47
resistance of finer gradations was influenced by binder characteristics more
so than
for more coarse gradations. Conversely, the performance of coarse gradations
is
more dependent on aggregate properties and less sensitive to binder type.
Work completed by Anani et. al. (1990) in Saudi Arabia indicated that a finer
gradation of coarse portion of the aggregate (No. 4 and above) improved
rutting
resistance. This conclusion is in general disagreement with conventional
(North
American) mix design, however, as indicated by Krutz and Sebaaly (199p), finer
Gradations are more sensitive to binder type than more coarsely graded mixes.
The
binder used for the coarse mixes may have been different from that used for
the
finer graded mixes (or a different asphalt content). Furthermore, the loading
condition of the selected roads was not reported. The effects of loading
conditions
on rutting resistance are explored in Category E.
Brown and Bassett (1990) indicated that increasing the maximum aggregate
size of the mix increased the mix quality with regard to creep performance,
resilient
modulus and tensile strength. Each of these properties has an important
relationship
to rutting performance as will be presented in Category D.
2.8.5 Effect of VMA and ~'FA
The use of VMA and/or VFA to predict pavement performance has been
debated for almost 100 years. Specifications for VMA and VFA were originally
developed to provide a minimum asphalt content in the mix for durability and a
minimum voids content for rutting.
While various researchers argue which parameter better predicts performance,
most agree that increasing VMA and VFA (to maximum values) are good methods
CA 02330431 2001-O1-08
48
to reduce rutting. Sorne investigations concerning VMA and VFA with respect to
rutting are as follows.
Anani et. al. (1990) indicated that VMA was a primary variable with regard to
rutting for the surface coarse. VMA of the unrutted sections was higher than
that of
the rutted sections.
Huber and Heiman (1987) indicated that VFA was one of the most basic
parameters affecting rutting. Increasing VFA to a maximum value decreased
rutting, while Carpenter and Enockson (1987) expressed that VMA was a
significant variable for rutting.
The NCAT study indicated that VMA was more significant for the base coarse
than the surface coarse (Cross and Brown 1992, 1991).
2.8.6 Effect of Dust Content
Coarsely Graded asphalt mixes often include a relatively high proportion of
dust to increase the stiffness of the asphalt binder. This is particularly
true of Stone
:Mastic Asphalt (SM.A) mixes that require stiff mastics to prevent the lane
aggregate panicles from moving under load. As with polymer modification,
increasing the stiffness of the asphalt cement by increasing dust content
reduces
susceptibility to rutting (at the expense of fatigue resistance). However,
mixes with
too much dust may display poor adhesion between the asphalt cement and the
aggregate particles (stripping).
2.8.7 Effect of Laboratory Density and Compaction
One basic assumption underlying the mix design process is that prepared
laboratory specimens will have the same density (and air voids) as the mix in
the
field after years of traffic (typically 4 percent). Insufficient laboratory
compactive
CA 02330431 2001-O1-08
49
effort results in low in-situ air voids since primary (construction) and
secondary
(traffic) compactive effort will be greater. .As previously discussed, low air
voids
(below 3%) are a major cause of rutting in asphalt pavements. Conversely,
excessive laboratory compaction leads to in-service pavements with high air
void
contents (10% or even higher). This situation results in excessive traffic
induced
compaction. Furthermore, continuous air voids are formed at high voids
content,
increasing permeability, which can reduce durability through accelerated
ageing
and/or stripping.
For the Marshall method, the MCAT study observed that stronger
relationships between mix properties and rate of rutting were. found for 7>-
blow
mixes than with 50-blow mixes (Cross and Brown 1992. 1991). This result is
expected since 7>-blow Marshall mixes are designed specifically with rutting
resistance as the primary design criteria. Fifty-blow mixes are designed for
lower
volume roads, whose primary design criteria are likely fatigue and thermal
cracking
resistance as opposed to rutting.
Kandhal et. al. ( 1990 found that mixtures ~u-e generally compacted to a
higi~er
dejree by traffic than that provided by laboratory (Marshall) compaction. 1t
was
therefore recommended that laboratory compactive effort be increased for
pavements designed specifically for heavy traffic.
Particle orientation under compactive effort also contributes to rutting as
indicated by varyin~l performance observed with Marshall compaction, gyratory
compaction and roller compaction. ILandhal et. al. ( 199;x) concluded that a
Marshall
compactor with rotating base and slanted foot gave the highest density overall
when
compared to standard Marshall and gyratory compaction. However, the gyratory
CA 02330431 2001-O1-08
50
compactor achieved densities greater than the standard Marshall compactor for
large
aggregate gradations. Additional research concerning laboratory compactor type
was completed by SHRP. Studies by Harvey and Monismith (1993), and Sousa et.
al. (1991) have concluded that gyratory, rolling wheel, and kneading
compaction
produced specimens with significantly different permanent deformation
responses
to repeated shear loadin'T. This indicated that each compaction method caused
a
particular type of aggregate structure and binder-aggregate film. It has also
been
shown that fatigue behaviour of a compacted mix is influenced by the mixing
and
compaction viscosities of the binder (Harvey et. al. 1994).
It should be mentioned that the Superpave system has adopted gyratory
compaction, as the specimens are much smaller and easy to handle.
Unfortunately,
gyratory compaction does not produce the same aggregate and void structure as
field compaetion, therefore, permanent deformation response of gyratory
compacted
specimens will not be representative of an in-service. pavement.
Finally, consistency of laboratory specimen preparation is another important
consideration. A round-robin test program completed by Lai (1993) investigated
the variation in laboratory compacted specimens tested using the Georgia
Loaded
Wheel Tester by six different laboratories. Each laboratory prepared test
specimens
using materials provided by Georgia DOT. Lai observed that although the
variation
in density among specimens prepared within each laboratory was very low, the
variation among individual laboratories was very large. 'This indicated that
different
laboratories used different preparation techniques, which in turn affected the
performance of the laboratory specimens. Indeed, rutting observed from the LWT
was significantly different among the different laboratories for the exact
same mix.
CA 02330431 2001-O1-08
~l
The results clearly indicate that improvement and standardisation of
laboratory
preparation specifications is required.
2.9 Category D - Strength/Resistance Properties of Mix
2.9.1 Effect of Marshall Testing
Like penetration, the Marshall stability and flow tests are empirical in
nature.
Not surprisingly, results from Marshall tests have not yielded consistent
information
regarding rutting resistance. Huber and Heiman (1987) concluded that Marshall
stability and flow values did not show an independent effect on rutting
performance.
Similarly, the NCAT National Rutting Study concluded that Marshall
recompacted mix properties (stability and flow) did not correlate well with
rate of
rutting (Cross and Brown 1992, 1991).
Conversely, Anani et. al. (1990) concluded that Marshall stability was
generally higher for unrutted sections and was a significant variable for
rutting in
the base asphalt coarse.
It should be noted that Hveem stability has been directly correlated with
rutting since the test assesses the shear capability of the mix. However,
since the
Hveem method is not used in Canada, it will not be pursued further for this
project.
2.9.2 Effect of Shear Strength and Stiffness
Shear properties of an asphalt pavement are achieved through both aggregate
particle contact to foam a ti4~ht, load-bearing skeleton and the asphalt
binder that
holds the particles in place. At elevated temperatures, Alavi and Monismith
(1994)
concluded that the influence of the agare~ate skeleton is more pronounced than
CA 02330431 2001-O1-08
j~
binder properties. However, the influence of the binder on shear
stren~th/stiffness
increases dramatically at the onset of plastic failure as the in-situ air
voids decrease
below ?.5%.
During the NCAT study, gyratory testing machine (GTM) specimens were
tested for shear properties and showed that the gyratorv shear index (GSI) had
higher correlation with rutting than the Marshall stability and flow (Cross
and
Brown 199?, 1991). The best relationship found was between rutting and GTM
shear strength. As the shear strength decreased (GSI increased), the rate of
rutting
increased as well.
Kandhal et. al. X1993) also confirmed that GSI values were directly
proportional to ruttin~~ performance. Pavements displayin;~ high GSl values
indicated high potential for rutting.
The importance of shear strength and stiffness has been emphasised by the
United States Strategic Highway Research Program (US-SHRP 1994). US-SHRP
research has identified that rutting appears to be more closely related to
shear stress
than normal or horizcmtal stresses. The SHRP research also referenced work by
Celard (1977), who emphasised that based on the results of dynamic creep
tests, the
rate of permanent deformation was strongly related to shear stress. For
example,
Celard increased the shear stress from 0.1 MPa to 0.2~ MPa (at constant normal
stress of 0.1 MPa) and observed a 100-fold increase. in the rate of permanent
deformation. However, varying the normal stress did not appear to change the
rate
of permanent deformation.
CA 02330431 2001-O1-08
5~
Laboratory analysis of asphalt concrete cores by Abd EI Halim et. al. (1990
indicated that increasing the shear strength of any asphalt mix can reduce
surface
rutting significantly.
2.9.3 Effect of Resilient Modules and Indirect Tensile Strength
The resilient modules Mr, is defined by Huang (1993) as the elastic modules
based on recoverable strain under repeated loads. Although asphalt pavements
incur some permanent deformation after each load, if it is assumed that the
load is
small compared to the strength of the asphalt and is repeated a large number
of
times. the deformation under each load is almost completely recovered and can
be
considered as elastic (Huang 1993). The resilient modules is determined
through
the indirect tension apparatus, and is considered a non-destructive test,
allowing the
same sample to be used a number of times under different loading and
environmental conditions. The indirect tensile strength test, however, fails
the
sample.
The strength tests completed by Carpenter and Enockson (1987) showed that
resilient modules and indirect tensile strength bore a strong relationship to
rutting
for asphalt overlays placed over concrete bases.
Anani et. al. (1990) indicated that resilient modules was inversely related to
rutting for both the surface and base asphalt layers. Unrutted sections
generally
displayed higher M~ values than rutted pavements, however, threshold values
were
not given in the investigation.
Abdel Nabi ( 1995] observed a linear relationship between the laboratory shear
strength and indirect tensile strength of asphalt cores. This finding
indirectly
CA 02330431 2001-O1-08
~4
suggested a relationship between indirect tensile strength and rutting through
the
relationship to shear strength.
2.9.4 Effect of Creep
Because asphalt concrete is a viscoelastic material, its properties are
temperature and time dependent. One method to characterize this behaviour is
through creep compliance at various times. Huang (1993) noted that at constant
stress, the creep compliance is the reciprocal of Young's Modulus. Creep
compliance is determined through a creep test, involving either static or
dynamic
creep loading.
Van de Loo ( 1974) analysed the relationship between rutting and creep
testing. Data from static and dynamic creep tests indicated that mix stiffness
decreased as the number of load applications increased (likely due to strain
softenin~T). During the same. study, Van de Loo also developed a method of
estimating rut depth based on his results, often referred to as the "Shell
Method."
2.10 Category E - Pavement Structural and Geometric Design
2.10.1 Effect of Order of Rigidity of Pavement Layers
Structural design of asphalt pavements is a critical component to rutting
performance as the state of stress and strain under traffic loading is
directly related
to the structural system. Typical newly constructed pavements (asphalt
concrete or
PCC) are constructed such that the quality and strength of the pavement layers
decreases with depth. I=or example, the asphalt concrete (or PCC) is of higher
quality and strength (rigidity or stiffness) than the granular base layer(s).
which in
CA 02330431 2001-O1-08
J
turn is of higher quality and strength than the natural subgrade. Under this
condition, the compressive load applied by the tires causes beam action in the
asphalt layer subjecting the top of the granular base and subgrade to vertical
compressive stress while the bottom of the asphalt layer is subjected to
tensile
stress. The actual stresses expepenced in the pavement structure are dependent
on
the modular ratios of the constituent layers. Huang (1993] shows that, as the
modular ratio increases, the vertical compressive. stresses applied to the top
of the
subgrade are lowered significantly. A high modular ratio is therefore
desirable to
minimise rutting of the subgrade layer. Rutting of these pavements typically
occurs
over longer time as the ~~ranular layers and/or subgrade consolidate under the
asphalt layer.
However, in the early 1980's, observations made in Ontario and Nova Scotia
showed that rutting of asphalt overlays was occuu-ing after only a few years
in
service. It was apparent that this new type of rutting was not described using
the
conventional theory. Gervais and Abd El Halim (1990) used the concept of
relative
rigidity and field observations to explain this phenomenon. The premature
rutting
for these cases was a result of the low modular ratio between the overlay and
the
underlying mature asphalt for PCC) layer. Even after compaction, the new
overlay
remains relatively soft, producing a low relative rigidity between the asphalt
layers.
Under this condition, they showed that the asphalt overlay was in a state of
compressive stress. The compressive stresses measured were small and not
considered to be the rutting failure criterion. However, the resulting strain
condition
revealed that high tensile strains were produced within the asphalt overlay
causing
lateral flow of the soft overlay material. The compressive stress condition
acted to
CA 02330431 2001-O1-08
J6
confine the deformations such that only the overlay deformed, much like a
sandwich.
2.10.2 Effect of Pavement Layer Thickness
Pavement layer thickness also plays a major role in determining the stress and
strain distributions throughout the pavement structure. In General, increasing
asphalt layer thickness causes the same effect as increasing the modular ratio
of the
pavement layers, that being a reduction in the vertical compressive stress
applied to
the underlying base, sub base and subgrade layers. This in turn reduces
rutting.
Kandhal et. al. ( 1993) concluded that the underlying layer conditions
(modulus and thickness) contributed to the surface rut depth in the majority
of
cases. This is not surprising since that investigation examined asphalt
overlays on
top of PCC pavements. Although not referencing the relative rigidity concept
in
that report, the findings of Kandhal et. al. ( 1993) appear to confirm the
explanation
of premature rutting presented by Gervais and Abd El Halim (1990).
2.10.3 Effect of Surface (Wearing) Course vs. Base Coarse
Anani et. al. (1990) completed separate analyses for the surface (wearing)
course and the base asphalt course. Regression analysis indicated that
different
variables were significant for the individual asphalt layers. This observation
is not
surprising since applied stresses and strains are. significantly different
depending on
location in the pavement structure.
The NCAT study also completed separate analyses for surface and base
asphalt layers (Cross and Brown 199?, 1991). As with .Anani et. al. (1990),
different variables were significant for the respective asphalt layers,
however, the
CA 02330431 2001-O1-08
>7
strongest rutting relationships were observed in the surface layer. This is
not
surprising since almost all of the rutting was observed in the surface layer.
2.10.4 Effect of Pavement Alignment
Abdel Nabi (1995) demonstrated that route alignment significantly influences
rutting performance. Pavement sections on hills and curves often display
increased
rutting due to two (additive) mechanisms. First, traffic speed is reduced for
these
sections, thereby reducing the asphalt layer modulus and increasing rutting.
Second, the asphalt layers for these sections are subjected to sustained
loading
through the force of gravity. This gravity-induced creep was shown to
dramatically
reduce the shear strength of the asphalt, again increasing rutting under
traffic
loading.
2.11 Category F - Construction-Related Factors
2.11.1 Effect of Compaction and other Construction Practices
Field compaction must achieve specified in-situ density and air voids to
ensure adequate pavement performance. In addition to density/void
specifications,
field compaction must strive for consistency throughout the pavement
construction.
Inconsistent compaction causes localized areas containing too little or too
many air
voids, allowing shear flow or traffic induced densification, respectively.
Pavement surface permeability is an area of construction that is commonly
overlooked. A waterti,ht surface prevents the infiltration of moisture that
can cause
surface stripping of asphalt. Furthermore, infiltration of moisture into the
base and
subgrade layers can cause hydraulic scour under traffic loading. However. in
CA 02330431 2001-O1-08
~s
addition to a watertight surface, adequate drainage must be provided for the
granular
layers to prevent stripping from below. Good construction and compaction can
provide both adequate drainage and a watertight surface if completed properly.
Interestingly, the affect of aggregate particle contact has not been
investigated
until very recently. Particle contact is essential to transmit traffic loading
through
the asphalt layer and into the base and subgrade layers. A study underway at
the
Turner-Fairbank Highway Research Center (FHWA 1998b) involves analysing
particle contact in asphalt cores using computerized tomography, as known as
''CT"
scanning. Initial results indicate that cun-ent compaction practices produce
aggregate skeletons for which only 15% of aggregates carry over 50%n of the
applied
load and 50% of the particles carry over S0% of the load. These striking
results
clearly indicate room for improvement concerning the in-service contact of
a~are~ate particles under compactive effort.
J ~m
The round-robin investigation concerning laboratory compac>ion variability
completed by Lai ( 199x) also has application to field compaction. Clearly
different
paving contractors use different techniques to compact asphalt concrete,
leading to
significant variability between various sites and even along individual sites.
Field
compaction has long been touted as the most significant variable toward
pavement
performance (including rutting), however, little resources have been allocated
toward improvement in the cun-ent compaction techniques or equipment.
Carpenter (1993) reported that the nix parameters produced during the initial
construction of the pavement will influence how much permanent strain occurs
when the limiting voids develop. In more simple terms, initial mix properties
CA 02330431 2001-O1-08
59
produced during field compaction determine how much rutting occurs prior to
the
onset of plastic flow.
Of course, significant work has been completed by Abd El Halim in the field
of asphalt compaction. Numerous field tests with the AMIR compactor have
conclusively shown that improved compaction techniques reduce variability of
density throughout the pavement structure, reduce permeability and improve
pavement fatigue life by up to 50 percent (Abd El Halim et. al. 1990.
2.11.2 Effect of Quality ControUQuality Assurance (QC/QA)
Consistency during construction is critical to pavement performance. Poor
QC allows areas with varying parameters and promotes localized deformation.
Poor
QA allows global permanent deformation if critical rutting variables are poor.
The NCAT study recommended that the most important QC/QA test that can
be conducted during construction is to compact plant produced material in the
laboratory and evaluate the air voids of the specimens (Cross and Brown 199?,
1991). This recommendation makes a strong case to provide on-site evaluation
for
QC/QA purposes.
Kandhal et. al. ( 199x) indicated that asphalt content measured from field
cores
was ~enerallv deficient from the value specified for the job-mix formula
(laboratory
mix design). Clearly, improved control over asphalt content is required for
plant
production since asphalt content is one of the primary factors governing
rutting
performance of pavements.
CA 02330431 2001-O1-08
60
2.12 Category G - Environmental Factors
2.12.1 Effect of Temperature
Asphalt cement (and therefore asphalt concrete) is highly temperature
sensitive. Anani et. al. (1990) noted that, because asphalt concrete is black,
solar
energy is readily absorbed and then retained due to its low thermal
conductivity. As
the temperature of the pavement increases, the stiffness of the asphalt
layers)
decreases. Reduced asphalt cement stiffness allows aggregate particle movement
and reorientation under traffic loading causing permanent deformation.
Therefore. a
strong aggregate skeleton is required to resist rutting at elevated
temperatures.
An excellent illustration of the effects that temperature can impose on
asphalt
binder stiffness was published by Rickards (1998). Using the Shell Bands
program,
asphalt binder stiffness was plotted versus temperature in response to the
compactive effort of three different compaction devices as shown in Figure 10.
10000 _ _ . _.... _ _ _ -_ _ -_
fAMiR
1000 - _ , _ _ _ --Roller
~'"~""'--- ..... -~ Vibration _._
100 ~....~.."~~- _ _ _ _ - .._.
c 4 '-'----- _ ~ _ _ __.
1 ,I _ ._ ._
>
0.1 - _ ___ _
~ j
0.01
100 110 120 130 140 150 160
Mix Temperature (deg. C)
Figure 10: Bitumen Stiffness vs. Mix Temperature for Three Compaction Devices
(from Rickards 1998)
CA 02330431 2001-O1-08
61
Figure 10 clearly displays the reduction in binder stiffness with increasing
temperature for each of the compaction devices. As an example, an increase in
temperature of 40°C ( 110°C to 150°C) caused a 10-fold
reduction in stiffness.
While such elevated temperatures are not usually encountered during normal
operating conditions, extrapolation of Figure 10 suggests similar relative
changes in
stiffness could be experienced for more typical operating temperatures. This
statement is supported by Hofstra and Kolomp (1972) who observed the
significant
effect that normal operatinD temperatures can have on asphalt mixes. During
their
investigation, a change in temperature from 20°C to 60°C reduced
the modulus
(stiffness) of the asphalt concrete by a factor of 60, while rutting increased
by a
factor ranging from ?~0 to 350 times. Clearly, temperature has a significant
effect
on asphalt pavement rutting.
A final example of the significant effect that temperature (and direct
sunlight)
have over rutting performance was noted by Anani et. al. (1990) in Saudi
Arabia
where rutting was significantlwreduced, or even non-existent, under brides
where
the pavement is shaded by the bridge deck.
2.12.2 Effect of Ageing
Over time and environmental conditioning, asphalt cement loses some of its
flexibility (i.e. its stiffness increases). Therefore, the oxidation of
asphalt cement
actually increases the pavements resistance to permanent deformation so lon';
as the
bond between the asphalt cement and aggregate particles is maintained.
Kandhal et. al. (1993) explained that during early stages of a (newly
constructed] pavement life cycle, rutting is directly proportional to traffic.
CA 02330431 2001-O1-08
62
However, after this initial densification, the rate of rutting decreases with
increasing
traffic until finally a condition of plastic flow occurs and the rate of
rutting again
increases.
The importance of separating the rutting cycle into distinct periods was
further
held by Carpenter (1993). According to Carpenter, two vital criteria to judge
the
long term performance of a mixture are how quickly a critical rut depth is
reached in
the mixture, and the "rapidity" with which the mixture reaches the failure
point at
the onset of plastic flow. These criteria are not mutually inclusive as a
mixture may
reach critical rutting before the mixture becomes unstable, or it may become
unstable before it reaches the critical rut depth.
2.12.3 Effect of Moisture Damage (Stripping)
Stripping involves the removal of asphalt cement from the mineral aggregates
through moisture infiltration. Stripping can occur on the surface of the
pavement
causing loss of surface aggregate (ravelling) or can occur from below the
asphalt
layers due to poor drainage conditions or sealing of the asphalt surface. The
loss of
bond between asphalt and aggregate allows the aggregate particles to move or
shrift
under traffic loading, promoting permanent deformation.
As previously mentioned, Krutz and Stroup-Gardiner (1990) investigated the
influence of moisture damage on rutting of chip-sealed pavements for the
Nevada
DOT. They found that sealing of the surface with the chip-seal accelerated
stripping by trapping moisture under the asphalt layers. The loss of asphalt
cement
allowed the aggregates to shift, causing severe rutting of the pavements
analysed.
Drainage conditions of the pavements were likely insufficient in those cases.
CA 02330431 2001-O1-08
63
2.13 Category H - Traffic (Load) Related Factors
2.13.1 Effect of Tire Contact Pressure (Load Magnitude)
The size of the tire contact area depends on the contact pressure between the
tire and the pavement surface. Huang (1993) indicates that pavement contact
pressure is greater than the tire pressure for low-pressure tires, because the
walls of
the tire are in compression and the sum of the vertical forces due to wall and
tire
pressure must be equal to the force due to contact pressure. Contact pressure
is
smaller than the tire pressure for high-pressure tires, because the tire walls
are in
tension. For simplicity, most pavement designs assume that the contact
pressure is
equal to the tire pressure, which is consistent with the findings of Gerrard
and
Harnson (1970).
Kandhal et. al. (1993) have reported that tire pressures have increased
substantially in recent years. Tire pressures average 661 kPa (96 psi) and 689
kPa
(100 psi) in Illinois and Texas surveys, respectively. Therefore, increased
pressures
are applied to the pavement, which will cause increased pavement damage.
Substantial finite element modelling of the effect of tire pressure was also
completed during the SHRP research. Model runs were completed with tire
pressures of 690 kPa (100 psi), 1380 kPa (200 psi) and 3450 kPa (500 psi),
respectively. Results indicated that rut depth increased almost linearly with
increased maximum permanent strain, which was directly related to increased
tire
pressure (US-SHRP 1994).
CA 02330431 2001-O1-08
64
2.13.2 Effect of Tire Material
The concept of relative rigidity is also applicable to the modular ratio
between
the tire and the asphalt surface. Tires composed of different rubber/steel
combinations produce different modular ratios between the tire and the asphalt
surface, which affects the contact stresses. Gervais and Abd El Halim (1990)
proposed that the switch from bias-ply to radial tires by the automotive
industry
represented a fundamental increase in rutting damage to asphalt pavements.
2.13.3 Effect of Number of Load Applications (ESAL's)
Rutting usually occurs over an extended period of time with numerous load
applications according to the rutting cycle outlined by Kandhal et. al. (1993)
and
Carpenter (1993). With each applied load, a small amount of permanent
deformation is introduced within the asphalt layer. The magnitude of this
deformation is dependent on the stage of rutting.
Therefore, the number of applied ESAL's is directly proportional to rutting in
asphalt pavements, at least during the traffic densification stage. Many
rutting
models incorporate ESAL counts, whereas some investigations such as Anani et.
al.
(1990) do not incorporate traffic effects directly, considering traffic to be
an
uncontrollable variable.
Other researchers have convened the total amount of rutting into a rutting
rate
by normalizing with traffic such as Cross and Brown (199?, 1991) during the
NCAT National Rutting Study as well as Kandhal et. al. (1993). Other studies
by
Brown and Cross (1988) and Parker and Brown (1990) indicated that expressing
the
rate of rutting as a function of the square root of total traffic better
models pavement
behaviour than other expressions such as the arithmetic sum or log of total
traffic.
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65
2.13.4 Effect of Rate of Loading
Being a viscoelastic substance, the stiffness of an asphalt concrete pavement
is
dependent on load duration as well as temperature. Loads applied slowly cause
a
reduction in layer stiffness thereby increasing rutting by allowing asphalt to
flow
(similar effect to increasing temperature). Again, a strong aggregate skeleton
is
required to minimise rutting under these conditions.
Generally, the greater the speed, the larger the (asphalt concrete) layer
modulus, and the smaller the strains in the pavement (Carpenter and Enockson
1987). Therefore, higher travelling speeds actually cause less rutting than
lower
travelling speeds (all else equal). The effect of load rate is apparent at
areas of
reduced speed such as intersections, hills and curves that exhibit increased
rutting.
The effect of load application rate is also apparent in Figure 10 (Rickards
1998). The three separate lines in Figure 10 simulate three asphalt compactors
applying different load rates to the asphalt concrete. As shown, the higher
loading
rate of the vibratory compactor invokes a greater stiffness response of the
asphalt
binder than the static steel roller or AMIR roller, respectively.
2.14 Category X - Combinations of the Other Categories
Variables listed in the above eight categories have been reviewed
independently.
However, many of these variables are strongly colinear and therefore work
together (or
against each other) to provide resistance to rutting. The interaction of
aggregate
angularity and in-situ air voids towards rutting was observed during the NCAT
National Rutting Study. For in-situ air voids above 2.5%, the angularity of
the coarse
CA 02330431 2001-O1-08
66
aggregate (two or more crushed faces) and NAA uncompacted voids for the fine
aggregate (aka fine aggregate angularity) are highly correlated with the rate
of rutting.
If the in-situ voids were less than 2.5%, rutting is likely to occur
regardless of
aggregate properties (Cross and Brown 1992, 1991).
The interaction between asphalt cement and gradation towards rutting was
studied by Krutz and Sebaaly (1993). They concluded that rutting performance
of finer
gradations is influenced by binder characteristics more so than more coarse
gradations.
Conversely, the performance of coarse gradations is more dependent on
aggregate
properties and less sensitive to binder type.
The effect of asphalt-aggregate irneraction was also completed during the SHRP
research (US-SHRP 1994). Regression analysis of rutting induced by wheel-
tracking
devices displayed that asphalt-aggregate interaction accounted for upwards of
15% of
the observed rutting. Finally, the interaction of volumetric properties such
as air voids,
VMA and VFA was well examined by Coree (1999) as presented in Section 3.3.
2.1~ Summary of Rutting Variable Relationships
Table 4 summarizes the qualitative relationships between the categorized
variables and permanent deformation. An entry of "Increase" indicates that
rutting
resistance increases with an increase in that particular variable, while an
entry of
"Decrease" indicates that rutting resistance is reduced with an increase in
that variable
(i.e. rutting increases all else equal). The inclusion of a question mark "?"
indicates
that the general trend is not well defined or questionable. The use of the
word "max"
indicates an upper limit, above which rutting resistance is reduced.
CA 02330431 2001-O1-08
67
Table 4: Summary Table of Rutting Variables and Qualitative Relationships
Category
A - Bituminous
Materials
and Additives
Chemistry Penetration Viscosity Use
of
Modifiers
AsphaltenesSaturates Polymer Antistrip
I
Decrease? ncrease
Decrease Decrease Increase Increase'?
Category
B - Mineral
Aggregates
Source Consensus
Properties Properties
ToughnessSoundnessDeleteriousCoarse Fine Flat/ Clay
MaterialsAngularity Angularity Elongated Content
Increase?Increase?Decrease?Increase Increase Decrease? Decrease'?
Category
C - Mix
Design
Parameters
GradationAir VoidsCont nt VMA VFA Co Dust Content
pabtion
see sectionIncrease Increase Increase Increase Increase Increase
2.8.4 (max) (max) (max) (max) (max) (max)
Category
D - Engineering
Properties
of Mix
Marshall Shear Resilient
Testing Modulus/ Creep
StabilityFlow
Stren~th/Stiffness Indirect
Tensile
Increase?Increase?Dramatic Increase Decrease
Increase
Category
E - Pavement
Structural
Design
Asphalt Asphalt
Layer Layer
Stiffness Thickness
and Deflection
Increase Increase
Category
F - Construction-Related
Field Quality
Compaction Control
and
Assurance
(QC/QA)
Increase Increase
(max)
Category
G - Environmental
Temperature Aging Moisture
Dama;e
Decrease Increase Decrease
Category
H - Traffic-Related
Contact Number Rate
Pressure of ESAL's of
(Load) Loading
(Speed)
Decrease Decrease Increase
Category
X - Combinations
of Above
Categories
CA 02330431 2001-O1-08
68
2.16 State-of-the-Practice: Asphalt Rutting Testers
Pavement rutting testers are currently attracting much attention from the
asphalt
industry. While some of these devices have been used for years, the widespread
adoption of Superpave in the United States (more slowly in Canada), has re-
ignited the
search for a device that can both separate poor and good performing mixes, and
also
predict the long term field performance of pavements prior to construction. As
mentioned, Superpave currently is based solely on volumetrics, binder and
aggregate
selection criteria.
At this time, there are numerous asphalt rutting tests in use by various
agencies.
Some are empirical tests, not based on engineering properties or analysis.
Examples
include the French Rut Tester, the Hamburg Wheel-Tracking Device, the Asphalt
Pavement Analyzer (formerly Georgia Loaded Wheel Tester) and the Accelerated
Load Facility (ALF). Other rutting tests, such as the Superpave Shear Tester
(SST)
measure engineering properties such as the shear strength or modulus
(stiffness) of an
asphalt mix. It is believed that these performance-based tests hold the most
promise
for modelling and predicting long term performance of pavements since
engineering
properties can be directly related to performance.
The objective of this section is to review some of the existing devices, which
will
lead into the following section that discusses their benefits and weaknesses
with
respect to performance prediction.
2.16.1 LCPC (French) Rut Tester
The LCPC Rut Tester was developed at the Laboratoire Central des Ponts et
Chaussees (LCPC) in France. As shown in Figure 1 l, the device uses two
CA 02330431 2001-O1-08
69
reciprocating pneumatic tires with diameter of 415 mm and width of 110 mm to
assess the rutting resistance of mixes. Test slabs are 500 mm long, 180 mm
wide
and either 50 mm or 100 mm in thickness. A standard tire pressure of 0.60
~0.03
MPa is applied approximately 67 cycles per minute (about 1.1 Hz). One cycle
consists of a forward and backward pass of the loaded wheel; therefore, 134
individual passes are completed per minute (Romero and Stuart 1998). Test air
temperature of 60°C is maintained without regard to the environment
where the
pavement is located or the depth at which the mixture is located within the
pavement structure (Huber 1999). A LCPC Rut Tester costs about $125,000 CAD.
Interestingly, the developers of the French Rutting Test do not believe that
statistical correlation between rutting observed in the test and that observed
in the
field can be developed since the rut tester simulates extremely severe rutting
conditions (Huber 1999). However, LCPC reports that roads meeting the LCPC rut
tester specification do not exhibit rutting in service.
Figure 11: LCPC Rutting Tester
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70
Extensive work has been completed in Colorado using the LCPC device to
correlate laboratory and field rutting performance by Aschenbrener (1994). The
study investigated 33 pavement sections with satisfactory or poor performance
in
rutting resistance. Test slabs taken from the sites were tested with the LCPC
Rut
Tester and indicated that the French specifications were too severe for
Colorado
conditions. To reduce the severity, the test temperature was modified based on
the
actual field temperatures associated with Colorado conditions. Test data was
also
separated into high, medium and low categories. Regression analyses yielded
high
correlation (R'' of 0.87 for high traffic and 0.68 for medium traffic) between
field
rutting and the slope of the rutting curve observed with the French device.
LCPC Tests were also completed on specimens recovered from the Westrack
experiment. Good correlation (R'=69.4%) between laboratory values and rutting
observed at the test track was achieved through regression analysis (FHWA
1998c).
2.16.2 Hamburg Wheel Track Tester and Couch Wheel Track Tester
Esso AG developed the Hamburg Wheel Tracking Device in Hamburg,
Germany in the 1970's (Romero and Stuart 1998). A solid steel wheel with a
diameter of 204 mm and width of 47 mm rolls across an asphalt concrete slab
immersed in water kept at 40°C or 50°C as shown in Figure 12.
Immersion of the
test specimens in water allows for the simultaneous testing of rutting and
moisture
damage (stripping) resistance of various mixes. Test slabs are 320 mm long,
260
mm wide and may be 40, 80 or 120 mm thick. A fixed load of 0.69 kN is applied
to
the wheels producing an average contact stress of 0.73 MPa (although actual
contact
pressure varies due to variable contact area during the test). This contact
stress
approximates the stress produced by one rear tire of a double axle truck.
CA 02330431 2001-O1-08
71
Approximately 53 passes per minute (26 cycles per minute) are applied and the
original test was performed to 9500 wheel passes. However, it was later
discovered
that some mixes could deteriorate due to moisture damage shortly after 10,000
passes. The number of test passes was subsequently raised to 19,200 to observe
moisture damage. A Hamburg Wheel Tracking Device costs about $90,000 CAD.
',m.2~rS?~rePG n
.~;cpe. ~T2BG!rcm
~,
s
xnGaio~ I Z, .
HhHV".iGn I
I i .~
1 //99~~
I ~~//'~~__71
Sr~P:GrtY~ Point 1 I// S
!Is'iJO~'9CS I rr.3~.l.~ppny ~1
I ~ SI~E<.=::2ø'~.tm ~~~ .
t I
_20 l t
t 1 f
f ,I,
.-.t.--
0 5000 10DOD 15000 ?DD00
Number of Wheal Pasxes
Figure 12: Hamburg Wheel Tracking Tester
Performance correlation between field performance and results from the
Hamburg Wheel Tracking Device was also completed at the Colorado DOT by
Aschenbrener (1995). Although the Hamburg stripping slope and stripping
inflection point were able to distinguish between good and poor field
stripping
performances, the moisture conditioning system used by the device appeared too
severe for rutting determination. However, regression analysis between the
CA 02330431 2001-O1-08
Hamburg device and rutting at Westrack yielded good correlation
(RZ=75.6°l0)
(FHWA 1998c).
The Couch Wheel Track Tester is a variation of the Hamburg test. A single
solid rubber wheel with an approximate contact pressure of 950 kPa (140 psi)
is
used to rut an asphalt slab. As with the Hamburg test, specimen temperature is
controlled through submerging the specimen in a heated water bath. The number
of
wheel passes is counted with a digital counter while the rutting profile is
measured
with a linear variable differential transducer (LVDT). The LVDT measures the
rut
depth at the centre of the specimen and sends the signal to a linear graphing
printer
which provides continuous output during the test. An automatic cut-off switch
terminates the test if a specimen prematurely fails or reaches the complete
test cycle
of 20000 passes of the rutting wheel. From the graph of rut depth versus
number of
cycles, the average rutting rate may be determined from the slope of the
tangent
from the consolidation point (typically measured 10 minutes after the start of
the
test) to the stripping inflection point. The stripping inflection point (if
present)
indicates a change in the rate of rutting with time due to loss of bond
between the
asphalt binder and the mineral aggregates. If no stripping inflection point
occurs,
the average rutting rate is simply the slope of the tangent from the
consolidation
point to the 20000 cycle mark. The graph provides much additional information
including the stripping inflection point, as well as the rut rate prior to,
and after the
inflection point (Aschenbrener 1994).
2.16.3 Georgia Loaded Wheel Tester and Asphalt Pavement Analyzer
As the name implies, the Georgia Loaded Wheel Test (GLWT) was originally
developed at the Georgia Institute of Technology in the mid 1980's for the
Georgia
CA 02330431 2001-O1-08
73
Department of Transportation to test rutting resistance of asphalt mixes (Lai
1986).
Unlike the French or Hamburg devices, the GLWT assesses rutting resistance by
rolling a concave steel wheel across a pressurized rubber hose placed along a
test
beam. The 29 mm diameter hose is pressurized to 0.69 MPa. The device operates
at 67 passes per minute for 8000 cycles (16000 passes).
In 1995, the rights to commercially manufacture and market the GLWT were
purchased by Pavement Technology Inc. (Prowell and Schreck 2000). Numerous
improvements were introduced to the original design and the resulting device
was
renamed the Asphalt Pavement Analyzer (APA). Unlike the GLWT, the APA
includes a water storage tank for testing specimens under water, and is
capable of
testing both beam and gyratory specimens as shown in Figure 13.
t :~:'.
Figure 13: Asphalt Pavement Analyzer
CA 02330431 2001-O1-08
74
As with the French and Hamburg devices, good correlation between field
rutting performance and the GLWT/APA has been observed. For example,
regression analysis between the APA rut depth and field rutting observed at
Westrack has yielded R2=79.7% (FHWA 1998c).
2.16.4 Accelerated Load Facility
The Accelerated Load Facility (ALF) is a full scale wheel tracking device
incorporating one half of a single truck axle travelling along a 29 metre
frame over a
full scale pavement test section approximately 10 metres in length. Loads
between
44.5 to IOO.IkN may be applied. Unlike laboratory wheel tracking tests, the
ALF
applies loads in one direction only and can impose lateral distribution of the
load to
better simulate truck traffic loading (wander). ALF can simulate 20 years of
cumulative traffic in six months or less. The ALF is shown in Figure 14.
Figure 14: Accelerated Load Facility (ALF)
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75
2.16.5 Superpave Shear Tester
One of the major products developed during SHRP research in the US was the
Superpave Shear Tester (SST). SHRP researchers identified that rutting appears
to
be more closely related to shear stress than normal or horizontal stresses
(SHRP
1994). As previously mentioned, the SHRP research also referenced work by
Celard (1977), who emphasised that, based on the results of dynamic creep
tests, the
rate of permanent deformation was strongly related to shear stress. During
SHRP, it
was anticipated that the SST would provide input to the Superpave performance-
based models, although development of the performance models is not expected
until 2005. The SST is illustrated in Figure 15.
Figure 15: Superpave Shear Tester
CA 02330431 2001-O1-08
76
Performance testing with the SST to date has produced acceptable correlation
between shear properties and field rutting. At Westrack, correlation
coefficients
(Rz) of 0.55, 0.4 and 0.26 were observed for repeated shear at constant
height,
frequency sweep at constant height and simple shear at constant height,
respectively
(FHWA 1998c). While these values are significantly lower than those achieved
with wheel tracking tests, it is important to note that the shear properties
measured
by the SST are not specifically meant for regression analysis, but are to be
input into
performance-based prediction models that have yet to be developed.
A second device known as the Field Shear Test (FST) was subsequently
developed by Endura-Tec Systems as a field quality control device for
Superpave
(NCHRP 1998). The primary difference between the SST and FST are specimen
orientation and the fact that the FST is a portable test and that the specimen
is tested
diametrally with the FST (similar to the indirect tensile test). Both the SST
and FST
are under investigation as simple performance tests under NCHRP 9-19.
2.17 Deficiencies with Current Testing/Modelling Practices
2.17.1 Discussion of Empirical Rut Testers
Table 5 compares the characteristics of the LCPC, Hamburg, GLWT/APA and
ALF devices. With the exception of the ALF, all wheel tracking devices
incorporate a small rolling wheel across a prepared specimen or core of known
dimension. It is known that these tests can effectively rank asphalt mixes in
terms
of relative rutting resistance and, as previously mentioned, they have even
displayed
good con-elation to observed field rutting. However, there are numerous
CA 02330431 2001-O1-08
77
characteristics of these tests that preclude them from accurately predicting
rutting
performance of field pavements. First, laboratory wheel tracking tests do not
have
proper boundary conditions. The test specimens are surrounded by steel molds
and
are resting on a steel base, which is never the case with the testing of real
pavements
(Romero and Stuart 1998). Furthermore, stress development in laboratory rut
testers is never representative of real life conditions because the size and
pressure at
the test wheel are unlikely to be representative of real wheels.
Table 5: Characteristics of Rut Testers
(compiled from Huber 1999; Romero and Stuart 1998; Prowell and Schreck 2000)
Laboratory Full Scale
Wheel
Tracking
Tests
French Georgia-Type
ALF
Hamburg
LCPC GLWT APA
44500 to
Wheel Load 5000 705 700 533 to 100100
(N) 700
Contact Pressure600 730 to 1500690 690 to Variable
833
(kPa)
Loading Rate
(cycles per 60 to 26 to 60 33 to 45 6.3
67
minute)
Load MechanismPneumaticSteel WheelSteel Wheel
on Full Size
Tire Pressurized
Hose
Pneumatic
Load Wheel 400 (diameter)200 (diameter)
29 (hose Truck Tire
diameter)
Dimensions 110 (width)47 (width)
(mm)
Test Environment.Air Water Air Air or Air
Water
500 (length)320 (length) Beam or Full Scale
300 (length) 150
Specimen 180 (width)260 (width) (diameter)
125 (width) Section
Dimensions, 50 or 40, 80, Core/Gyro 9800 (length)
(mm) 100 120 ~
75 (thick)
(thick) (thick) specimen
l
Test Temperature60 40 or 50 40 49 to 60 Ambient
(C)
or 60
No. of Cycles30000 9500 to 8000 N/A
in 19200
S ecification
Max. Allowable10 4 ( 10000 7 N/A N/A
cycles)
Rut De th
(mm)
000 $15,000 $130,000 Variable
$125 CAD
Cost , $90,000 (minimum) CAD ($ millions)
CAD CAD
CA 02330431 2001-O1-08
78
Specimen size may also contribute to lack of correlation since the relative
size
of the wheel compared to material constituents (such as aggregates), is not
consistent with in service pavements. Finally, for any test to be valid, the
load
applied to a specimen should always be in proportion to the specimen size
(Romero
and Stuart 1998). This is not the case with most of the devices with the
exception of
the ALF.
However, although the ALF addresses the problems of dimensional
incompatibility due to its full-scale nature, the resulting properties (rut
depth or rate)
do not represent fundamental engineering properties that can be input into a
mechanics of materials model for performance prediction. Furthermore, the ALF
is
extremely expensive ($ millions) and not feasible for field QC/QA.
2.17.2 Discussion of Existing St~ear Tests
Although the development of the SST and the FST represented an important
step toward measuring asphalt shear properties, neither test is ideally suited
for
widespread implementation. The SST does provide a great deal of information
with
regard to mix shear properties, however, it is very expensive (approximately
$250,000 USD), confined to the laboratory, and requires a great deal of
training to
use correctly.
While the FST is a portable device, the diametral loading condition is not
representative of field loading conditions. Furthermore, Sousa et. al. (1991)
have
reported that diametral loading (from the indirect tension test) is
inappropriate for
permanent deformation characterization because the state of stress is non-
uniform
and strongly dependent on the specimen.
CA 02330431 2001-O1-08
79
Finally, both tests require the preparation of cylindrical specimens either
through gyratory compaction or coring of in-service pavements. As has been
discussed at length throughout this thesis, these preparation methods are
either non-
representative of the mix in the field, or damage the specimen to a large
degree.
The development of an in-situ test will both provide an excellent
complimentary test
device to existing laboratory tests, as well as better represent the
performance in the
field.
CA 02330431 2001-O1-08
CHAPTER 3: REVIEW OF PREVIOUS WORK AND
ANALYTICAL MODELLING
3.1 Introduction and Chapter Overview
Two previous research efforts formed the foundation for the current
investigation. The first was a comprehensive laboratory investigation of
asphalt shear
properties and pavement rutting completed at Carleton University by Zahw
(1995).
This chapter begins with a review of that investigation, followed by the
results of a
new study to investigate the relationships between asphalt mix
characteristics, shear
properties and pavement rutting, using data collected during his research.
The second underlying research effort involved the construction of a first
generation in-situ shear strength test device, also at Carleton University by
Abdel Naby
(1995). A review of the device, known as the Carleton In-Situ Shear Strength
Test
(CiSSST), is provided including its main benefits and the results of his
research
concerning in-situ shear strength and its relation to pavement performance.
The chapter concludes by introducing an improved analytical approach to derive
asphalt pavement shear properties from the surface plate loading condition
developed
using closed form equations and the finite element method.
CA 02330431 2001-O1-08
81
3.2 Review of Previous Work - Laboratory Torsion Testing of Asphalt
Concrete
3.2.1 Introduction
A comprehensive laboratory study of asphalt pavement rutting and shear
strength and stiffness was completed at Carleton University in 1995 (Zahw
1995).
The testing program involved the mixing, compaction and testing of over 1200
standard Marshall specimens representing a total of 58 different asphalt
mixes. Mix
shear strength and modulus were determined through laboratory torsion testing
of
cylindrical specimens to failure. The Tinius-Olsen torsion test machine is
shown
below in Figure 16.
Figure 16: Torsion Test Equipment at Carleton University
CA 02330431 2001-O1-08
82
Cylindrical Marshall specimens or cores were glued to steel plates using an
epoxy and loaded horizontally into the device. All testing was completed at
25°C.
Torque and twist angle at failure were recorded by the device and the
specimens
failed in shear with a characteristic 45° failure suuface as
highlighted in Figure 17.
Figure 17: Typical Failure of Asphalt Specimen in Torsion Test Device
Permanent deformation characteristics were determined through the Shell
Pavement
Design method utilizing uniaxial unconfined static creep tests at three stress
levels
(0.1 MPa, 0.3 MPa and 0.6 MPa).
3.2.2 Deriving Shear Properties from Laboratory Torsion Tests
By definition, fundamental engineering properties of materials such as tensile
or compressive strength, shear strength and stiffness, elastic modulus, etc.
are
unique to individual materials and not dependent on boundary conditions.
However, there are few testing procedures (if any) that directly measure
CA 02330431 2001-O1-08
83
fundamental properties. In most cases, a given load is applied to a test
specimen
and the desired fundamental property is then determined knowing the specimen
dimensions. For example, compressive strength (f'~), which is a fundamental
property of Portland Cement Concrete, is determined by applying an axial load
to
failure, and then using that failure load and the cross sectional area of the
specimen
to calculate f'~.. However, the measured values of the fundamental properties
can be
strongly dependent on the test conditions such as load rate, confining
pressure,
temperature etc. With PCC (and many other materials including asphalt
concrete),
the faster the applied load, the greater the resulting strength response.
Therefore,
various standards (CSA, ASTM, etc.) have been developed so that a single set
of
test parameters is used to produce comparable results.
Under similar test conditions, alternative methods may be used to determine
fundamental properties. For example, the Superpave Shear Test (SST) measures
shear properties of asphalt concrete by applying a force across an asphalt
core or
gyratory specimen. Given the specimen dimensions (cross sectional area), the
shear
properties of the mix are easily calculated. The same shear properties of the
core or
gyratory specimen may be determined using a torsion test as well. Again, given
the
specimen dimensions, the shear properties may be determined from the applied
torque. A comparison of the mechanics behind the SST and torsion test is shown
in
Figure 18.
While the method of force application is different, the differential elements
(dA) within the specimens are subjected to shear in both cases, thereby
allowing the
calculation of the shear properties independent of the test method or boundary
conditions.
CA 02330431 2001-O1-08
sa
F
z --
~- z
~~ ..
F
~dA~
~ C&~ ~.5
~=Gy
z __
Figure 18: Determination of Shear Prof~erties from Different Test Methods
As chown in Figure 1 s, the shear strength of the asphalt rni.x may be
determined
using Equation 1:
where:
(1)
J
T = the shear stren~tlu (MPaj
T = the maximum applied torque (!~'~m)
c = the radita of the test specimen (mm)
J = the polar moment of inertia (mm' J
CA 02330431 2001-O1-08
bi
3.2.3 Major Findings of Laboratory Torsion Testing
The work of Zahw (19>~) representec new and extensive research toward a
better understandin;v of the rutting phenomenon and its underlying causes. One
of
the main findings was that conventional asphalt design criteria such as
density alone
do not provide a reliable indicator of high rutting resistance, whereas the
use of
shear properties better characterized the mix performance. This finding was
supported by research completed during the Strategic Hiwhway Research Program
(LAS-SHRP 1994). which vvas being completed concurrently by Zahw ~19~)~).
In addition to the development and verification of a shear testing f~ramem.~rk
usin~T laboratory torsion testing. Zahw also ,venerated a large volume o1 dma
including mix properties, measured shear properties and mix performance as
determined through unconi'ined static creep tests. This database was utilized
during,
the current investigation to produce nevi and valuable m~~dels relating mi.x
properties to shear properties, as well as shear properties to calculated
rutting. The
results of this anal:;sis are presented in the followin'v section.
3.3 Analysis of Laboratory Min, Shear and Rutting Database
3.3.1 Relation of >ftia Characteristics to Shear Properties
Sixteen asphalt mix properties were available in the Zahw database for the
analysis as listed r~clow in Table O. These properties were subseduently
~~rouped
into three main ca~e«orie:; -- Asphalt Binder Properties, Mineral A'are';ate
Properties and'~'Iiv Deli<Tn Properties.
CA 02330431 2001-O1-08
86
Table 6: Mix Properties Available from Zahw ( 1995) Database
i
Asphalt Binder Mineral Aggregate ~ Mix Design j
Properties Properties i Properties
~ C.'oefficient of Cniformity
~ Penetration L 25C j ~ No. of Blows with
~ ~ Coefficient of C.'urvature
~ Rind= and Ball Softening ' Marshall Hamrr,er
~ F'ercentaUe of Coarse I
point '~ ~ ~ Final Specimen Density ;
I M uteri al '
~ hinematic Viscosity I ~ Asphalt Cement Content
~ Presence of Crushed ;
~ Penetration Index ~ I ~ Voids in the Mineral
Stone Present in Mix ~~
~ Viscosity @ ?~C A~~re~aate
~ Percentage of Mineral I
~ Binder Stiffness, Sbit ~ Dust to Binder Ratio
' Filler .
Table 7 displays the measured engineering properties includinU shear stress,
strain
and modulus, as well as the estimated rutting from unconfined uniaxial static
creep
testing at 0.1, 0.3 and 0.6 MPG stress levels.
Table 7: Engineering Yroperties Available from Zahw (1995) Database
Measured Shear Properties ', Estimated Rutting Yroperties*
~ Average Shear Stren~,th II ~ Rut Depth at 0. I MPG Stress i
I
~ Avera'e Shear Strain ~ Rut Depth at 0.:; MPG Stress '.
I
~ Average Shear Modulus ~ Rut Depth at 0.~~ N7Pa Stress
*Estimated rumn'_ prc~perues based on unec>nfined static ere~p tesunc (Shell
Wcthc>d~
The first step in the analysis involved relating the asphalt mix properties to
the
measured laboratory shear properties. A correlation matrix was developed for
all 16
variables usin~f the statistical features of Microsoft Excel. The seven mix
variables
yielding the Greatest cot~relation coefficients are displayed in Table b.
CA 02330431 2001-O1-08
S7
Table 8: Mix Properties Yielding Greatest Correlation to Shear Properties
Correlation Coefficients
Mix Property i Shear Strength , Shear Strain Shear Modules
I (MPa) ~ ( ~o ) (MI'a>
~I Penetration @ ''~(_' -0.67 -0.80* -0.49
_ _
~I V'iscosity C- ?SC ~ 0.44 ~~'~ 0.66** 0.1~
Coefficient of
0.~9 I negligible 0.70 I
Uniformity_ ~ _
I Presence of Crushed
I, 0.41 0.?2** 0.4b I
h CCoarse Aggregate _; __
Mo. of Blows with II ~, _
j Marshall Hammer 0'07 -0.'~ 0._''_'
i _
Density i _-0.~7 ~li<_'ibie 0.71
I _
Voids in Mineral (?.?1 -0.07
.=~~Qre~ate '
I " ' i _ ~
ceeYficient should have pc>sitive relationship
'* ~«cffi~i~nt should have ne~auve rel,uionship
examination of the correlation coefficients indicated that the effect of each
mix charge-ieristic on the shear properties made raticmal sense, with the
exceptio a of
some of the relationships between the mix properties and shear strain.
Intuitivc:lv, a
parameter that causes an increase in shear stren;~th or modules should have a
ne~Tative effect cm shear strain. However, in the cases of penetration,
viscosity un~i
the presence of crushed coarse u;»~reUate, tl~e correlation coefficients for
shear strain
did not display the ci>n-ect sense (positive or neeativej. relative to the
shear
strength and modules, however, much lower con-elation was displayed between
shear strain and many ol~ the mix properties. Therefore, as the shear strain
is
inherently contained within the shear modules, further <rnalysis of shear
strain w.rs
not completed in this investigation. A brief discussion of the resulting
relationships
is now presented.
CA 02330431 2001-O1-08
~8
Until the Superpave performance-graded binder specification was developed,
penetration was the pr-imarv criterion for thc~ selection of asphalt hinders
for road
construction in North America. Therefore, although it is an empirical measure
of
binder stiffness, it was not surprising to see that penetration was well
correlated
with rnix shear properties. Less correlation was observed with viscosity than
penetratron.
hhe coefficient of unifor-mitv is a measure taken from soil mechanics to
describe the shape of the gradation curve of the mineral a;;'re~aates used in
eaclu
mix. As indicated in previous sections, the aggregate skeleton is critical for
rutting
resistance, therefore. the shape of the gradation curve and its associated
packins,
configuration would likewise be highly cowelated with shear properties. The
high
cowelation with shear strength and modulus clearly indic<rted the importance
of
aggregate skeleton to transfer the load to the underlying layers of the
pavement.
The variable refer7~ed to as "Presence of Crushed Coarse Ag~lre'~ate~~ was
simply a binary choice of whether or not the coarse aggregates in the mix v,
ere
crushed (i.e quarried stone? or not (i.e. river '_=ravel). If floe a~~re'_ate
was crushed, a
value of "1'~ was assi'~nc:d. whereas a value of "0" was assigned if the
aggregates
were not crushed. ~~Ithou'~h it may have been desirable W have: a more
descriptive
measure of a~Tare~~te an~Tularim such as fractured face count, this
information was
not recorded durins; tire initial investigation by Z.ahw. Interestingly, the
binary
choice variable proved to he well correlated with shear strength and stiffness
and
was therefore kept in the analysis.
The number of blows with the Marshall hammer is a measure of compactive
effort. Marshall mixes designed for high truck traffic applications are
usually
CA 02330431 2001-O1-08
f; 9
designed as 7~-blow mixes, indicating that 75 blows with the Marshall hammer
are
applied per side of the specimen during mix design. Mixes designed for regular
traffic levels usually- are designed with ~0 Mows per side. Therefore, the
greater
number of blows required to achieve the design mix properties. the stron'er
the mix.
Final specimen density has long been the primary measure of mix adequacy,
therefore, it was not surprising to see a hi'~In correlation between density
and shear
properties. Finally. voids in the mineral aQ~regate (VM.A) is a measure of the
void
space within the compacted mix. Volumetric properties are the foundation of
mix
design, therefore good correlation was expected. It should be mentioned that
asphalt cement content was not selected as en independent variable, despite
its well-
known effect on rutting resistance. rfhis decision was largely made based on
the
greater con-elation observed between VMA and the shear and rutting properties
when compared to trsphalt content, as well as the fact that asphalt content
information is contained vyithin the VMA I~~urameter.
Based on the correlation matr7x, the dependent vanahles listed above in Table
~ should have provided the best input for regression models to explain the
measured
shear properties. However. some of the properties were ioi~hly conr-elated to
one
another, refen-ed to as collinear dependent war7ables. Such variables could
not be
used for regression in their cur-r-ent form. Vv'hile one option would be to
simply
remove the colline;~rr variables, the information associated with those
variables
would then be lost in the model. ;W other technique involves the use of
combination
variables. For example, Penetration and Viscosity @ ?>(_' were highly
ccsrrelated t-
0.66j and therefore could not both be incorporated into r::'~ression analysis.
However, instead of discarding the variable displaying tire lower ccmelation
to the
CA 02330431 2001-O1-08
shear properties (in this case Viscosity), the two var7ables were combined
into a
sin;le variable referred to as Penetration-Viscosity Ratio (PVR) as shogun
below, in
Equation 2:
~~',R _ Peltration C '>C ~~)
UL1' COS Itl' C ~~C~
A second conobination variable was also created from the original seven -
Average Rate of Densification CARD), whi~:h was defined as the ratio of final
specimen density to the compactive effort as expressed by the square root of
the
number of blows applied by the Marshall hammer as shown in Equation s:
LJ('lI S'Itv
AIUL) _ - I ;1
J# ~~Ort C
It should be stressed that combining cowelated dependent variables should nc>t
be completed haphazardly; the combined variable must make rational sense. In
the
case of PVR, the resulting correlation coefficient for shear strength was -
ti.67,
indic~7tin~ that ors PV'R increases, shear strength decreases. Examinin~~ the
ratio
itself, f'VR will increase with either an inc:rcase in penetration or a
decrease in
viscosity, or both. ('hereforf:, uccordin~ to the ratio, shear strength will
decrease
with an increase in penetration or a decrease: in viscosity ~i.c. a softer
asphalt is
used). This relationship makes sense since softer asphalts have a higher
tendency to
rut - all else equal.
Bv dividing the final density by the square root of the number of Marshall
hammer blows, the ARD variable represented an average slope of the
densific<ttion
curve. In other words. .~RD provides an indication of th;~ amount of
compactive
effort needed to ~tc~ieve the final density. .-lsphalt mixes that have stron'=
a'~gre'~ate
CA 02330431 2001-O1-08
91
skeletons typically require more compactive effort to obtain specified density
since
it is noore difficult to rearrange the aggregates during compaction.
Therefore, it was
expected that lower values of ARD would result in more rut resistant mixes.
T'he
square root of the number of Marshall hammer blows was selected as it has been
shown that field rutting is better described by the square root of traffic
when
compared to arithmetic or logarithmic functions (,Brown and Cross 1988. and
Parker
and Brown 1990).
A second con-elation matrix was developed for the resulting > selected mix
variables as shown in .Appendix A. Note that this matrix, displayed both
acceptably
loos cowelation between the individual dependent variables. and very hi~Th
cowelation between the dependent and independent variables.
Equations =I~ and ~ bclcwv were developed from multiple re'Tression analysis
of
the five selected mix variables to model measured shear stren«th and n~odulus.
The
actual data used in the regression analyses is reported in Appendices B (mix
variables] and C' (shear properties). .As shown by the coefficients of
determination
( R-). the dependent variables within Equations ~ and ~ explain a higi~ degree
of the
variability observed in the shear modulus and stren~~th. respectively.
(i =>6U-~.7*PF'R+ '~~=rCC-' -- ~-14"C;,:,: -l~l ~s"Ah'D+1OC80*1-'MA
(R' = 0.83)
i;5)
=-66-U.9*YVR-s0~' CC% +(i~~'C,."" _ ''=IIC)~'~ARD-~-'~~W'-VM.=~
(R' .- 0.88)
CA 02330431 2001-O1-08
9'
where:
G (kPa) = Shear Modulus (Stiffness) at '_'~''C;
i (kPa) = Shear Strength at 25°C;
PVR (mm/Pa*s) = Ratio of Penetration (mm) to Viscosity at ?~''C (Pa*sj;
CU= Coefficient of Uniformity (D60/D10);
Ch;" = Presence of Crushed Coarse Aggregate in Mix (Binary choice of 1
for 'r es or 0 for :xloj;
ARD = A~,era~~e Rate of Densification (ratio of final mix density to the
square root of the- number of blows with Marshal I hammer); and
VMA = Voids in the Mineral Aggregate (~r~ )
The use of the combination variables in Equations 4 and ~ maximized the
amount of inforn~ation contained per variable without introducing_, collinear
dependent variables. Furthern~ore, the dependent variables utilized cover all
of the
major areas govennin<~ mi.x performance; bitumen properties (PVR), gradation
(CU),
an'~ularitv/rou;~hness of the aggregates (Chin), density and compactive effort
(ARDI
and volumetric properties (~'MA).
Tables 9 and 10 display the regression statistics for the shear modulus and
shear strength equations respectively. In both equations. the intercept term
was
statistically insignificant as indicated by the low t statistic. All other
variables
yielded high t statistics, indicatin~~ hi'Th siy:nificance.
CA 02330431 2001-O1-08
y;
Table 9: Regression Statistics for Shear Modulus (Equation 4)
~ Coefficients Standard Errort Stat
1 ! I
--~ -
Intercept ~'I X60 I 7~> 0.~
~I Penetration-Viscosity
Ratio ? 0.?8 -9.7
7
(mm'/M C ?~C> .
_
i I
Coefficient of Uniformity~ ~ ~~ ='.
~., 0 ' 10
_ . .
'r 1D60/D 101 I ~ ' I
i - . _ _ _ --1
~
Ii -~~~ 119
I Presence of Crushed
Coarse
Aa~reaate _ ;i I
'~. n ',, D.,ro of Tl~"c;fi~t,nn .
~
s
I! [Fmal~Density/Sqrt(#hlcwv )] I -1~1 ~-
,,
_-_.__-_ ~ - ',, - - --
Voids in I~'Iineral .A~'.~re~ute Ii 1065(1 ~' '_9sS !~ ;.O
Table 10: Regression Statistics for Shear Strength (Equation ~)
Coeff icients t Stat
!1 Standard
Error
I
I
~ -Gt; I(W.i -0.4
~llntcrcept
-_ - ' II
~ Penetration-Viscosity -C).9=I ~ -I;s.l
;~;atio 0.()6?
' (mn1'/~ ~n~ 7wC)
-- ---
-__ - _ _
Coefficient of Uniformity~().-; ~ 10.(1
~.0
',1DC0/D10)
~ Presence of Crushed
C:~arse 6=I6 ?b.? j ?.~
!, j
,
~'~~~tc''ute
Avera'le Rate of Densrinc<ition
-?410 ~ (i(~~ _ .(~
', [Final Density/Sdrt(#b'
ows)] j _
-___
---- -
_____ - __ ~
_ - r--- _ __ '
oids in Mineral Ayyre'~ttte~ -'
The individual coefficient of detemination (R?) for each individual variahle
w-as also investi'~atcd and the results are displayed in Tahle 11. As shown.
the
Penetration-Viscosity Ratio (P~'R~ alone <:ould explain approximately '_'_".%~
of the
CA 02330431 2001-O1-08
~4
variation in shear modulus and ~4~Io of the ~, ariation in shear strength.
Coefficient
of Uniformity accounted for 49'~n of the shear modulus and =~~'7 of the shear
strength. Interestingly, the binary choice variable - "Presence of Crushed
Coarse
r'~~Qreaate in Mix" -- represented a lame portion of the shear properties;
'_'3°i~ of the
shear modulus and I7~i~ of the shear strength. The remaining variables, ARD
and
\'MA explained less of the variation in the shear properties; however. then
were
hi'hlv si'nificant in hoth equations.
The results of the individual regression analyses tended to confirm the
results
found in the SHRP research; that binder properties conmibute ~~pproximatelv ,
~~~a
toward rutting resistance, while the remaining contribution cones from the
a'7<yreyrates and the asphalt-aa~~reaate intera~=lion [US-SHRP 19~)~1].
Table 11: Contribution of Individual Variables Toward Shear Properties
Individual Individual
Coefficient of Coefficient c~f
Variable I Determination for Determination
for
Shear l~'lodulus ~ Shear Strength
(R~ ~%r ) ~ (IZ-~~c
P\'R '~ ~ 1.9 ' 4~.?
~
~ -IS.t~ _- _~4.7
Coefficient of L-nifu>rmitv
Crushed Coarse '_'?.S 1(.8
I' A RD ~; ~' . 7 9 . S
-~ ____ I___ ~.(~ .,
-_
~ VLVI~~
b.,~ ~ -
3.3.2 Relation of Shear Properties to 1W tong
Additional analyses were completed to investigate the relationship between
the she~ir properties of the mix and its rutting resistance as determined
throu<eh the
CA 02330431 2001-O1-08
9s
Shell procedure. Figure 19 displays the graphs of rut depth versus shear
modulus of
the mix for each unconfined creep test stress level. As shown, a high degree
of
con-elation was observed between shear modulus and rut depth with R~ values
ranging from 0.60 to 0.80 using a power relationship. Similar relationships
were
seen for shear strength as illustrated in Figure ?0, although less cowelation
was
observed than with shear modules. The results of the analysis ;:learly
indicated that
shear strength and rnodulus are able to explain a large an;ount of the
variability
observed in the rutting as measured through laboratory creep tests, although
shear
modules appeared to be a better indicator. The rutting me>dels displayed in
Fi~~ure
19 and ?0 are also listed in Table 1? below For reference, the actual shear
and
rutting_= data frorr~ the Zahw- ( 1990 database are attached as ,appendix C.
Table 12: Rutting Models for Shear Strength and Modules
(_'reep 'host laboratory Rutting 1\-lodels ~
S tress ~--- -_ _- -.,,
bevel Shear Modules @ 2~C Shear Strength C~? 2~C:
(MPa) (kl'a) ' (kPa) _
().l Rut = 2~~*C,-o w~ iR~=0.80) Rut = I 8.?J'v-° ~>> fR=-:().(>~,
Ij Rut _ -~;>Ol e'Gu o;, 1R=y0.6(i) ~I Rut = (~?.~)? '- T -~ c>,c~ 1R==t).-l70
0.
' i ___ _ __---
,- ~___ ___
-l.S?0 , ~ ~_ -1.3~_ ,
0.6 Rut = 3E6'~G (R'=0.7_a> Rut = 1 17W ' T (R =0.671 ',
Figures 19 and ~0 contain much important infonm~tion that necessitates
further discussion. First, the graphs cleurl~r~ show that as shear strength
and modules
increase, the amount of ruttinU experienced dining the test decreases
si~nif~icantl~,
particularly at him/her test stress levels. Fo.~ example, an increase in shear
mod~alus
CA 02330431 2001-O1-08
96
from '?>00 MPa to 3000 MPa (?0'ro increasel reduced the amount of ruttin,T
from '?
mm to 1.4 mm (a s0°i'o reduction) for the 0.6 MPa test stress level.
For the lower
stress levels, the graphs become flatter, indicating a reduced benefit for
increased
shear modules and strength for lower stress scenarios. .Although beyond the
scope
of this investigation, the information can potentially be used to optimize mix
design
selection (based on modules or stren'lthj for a desired level of p~rfounan~e
(rutt.in'~
limit) and a 'liven traffic loadin' scenario (stress level). 1=urthermore, the
results of
quality control and assurance testing (QC/Q.A) could be checked against the
;raphs
to ensure that the finished pavement will perform as specified, with possible
penalty
or hones implications to the contractor.
CA 02330431 2001-O1-08
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CA 02330431 2001-O1-08
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CA 02330431 2001-O1-08
9
3.:I Review of Previous Work - The Car leton In-Situ Shear Strength
Test (CiSSST)
3.4.1 I ntroduction
The concept oi~ testing the shear stren;Tth of asphalt pavement surfaces using
a
rotational load in the field was first conceived by Abd Cl Halim and Ahd Fl
Nahi in
the early l9)0's. To investi~~ate the feasii~i ity of this concept, the
Carletc>n In->>itu
Shear Streny~th Tesi (CiSSST) facility. shown in figure '? 1, was constructed
at
Carleton University
,. _ .
.. a e.~t"
. , . 4
.... _ ,.
. iy~,y', ,~.. _
~. f ~'~~,
hi~ure 21: The Carleton In-Situ Shear Strenbth 'Pest (CiSSST) h'acility
The facility consisted of a cart-like chassis on small castor wheels f'or
positionin~T. Force was applied via an electric motor coupled m a ~Te~u-
reducer and a
right-an'led aearhox. The ~~earhox transmitted the torque throu~~h a vertical
drive
shaft to a torque cell, which in twin was attached to a steel loading plate
honded to
the asphalt surface with a stoon~ epoxy resin. During the testinU procedure,
torque
CA 02330431 2001-O1-08
1 (O0
was applied until failure of the asphalt surface occurred. The failure torque
v as
measured with a torque cell and the failure strain was determined by
measurin4; the
angle of twist at failure with a protractor.
3.4.2 Deriving Shear Properties from Field Torsion Tests
The laboratory torsicm specimens tested by Zahw ( 199 j had clearly defined
houndarv conditions that allowed the calculation of shear properties usin'T
simple
closed form equations. However, deriving shear properties from torsion tests
with
the CiSSST was nnuch more difficult due to the field boundary conditions. The
method of testin« with the (~iSSST, known as the surface-plate method,
utilircd a
steel plate attached to the pavement sur-fac;. usin~~ epoxy resin. Therefore,
torsion
was heina applied tram a steel disc of finite dimension ( 100 mm diameter)
onto a
flat surface with (practically) infinite dimension, often r~:ferTed to as a
half-space.
This loading conditiim is similar to the linear torsional shear
stress/displacemcnt
conditions shown in Fi'ure ~, and represented a completely different set of
boundary conditions than the laboratory torsion test. Therefore, a different
set of
constitutive equations was required to determine the shear properties. The
surface
plate loading condition o1'the CiSSST device is illustrated in Fi~Ture 2~.
CA 02330431 2001-O1-08
1 p~~li~cf T;>rdue ( r 1
1_u<lulll'_' ~)I~~~ ~'l;'11
- 07,11 L lll~ Il~ ~ilf~l:lvv
~7
~ll~tll'4 ~~II~O~~>yl
i
,_ i
i J.
Figure 22: Loading and Boundary Conditions of CiSSST
In previous studies with the CiSSST device. Equation 6 was developed by
:abdel Nabv ( I99~ i for calculatin~T the mix shear stren~~th based on the
ussumytion
that the failed surface formed the frustum ;>f a cone as shown in Fiy~ure ~?.
r ,.- ._ ,-
_ " Jl , ~ r-;' (~)
J
where:
T = the maximum applied torque (~~~m>
T = the in-situ shear str~ n~lth (MPa I
h,-= the failure depth (mm)
J.
CA 02330431 2001-O1-08
10~
r; = the upper radius of the frustum c~f the failed cone (mm)
r" = the lower radius of the frustum of the failed cone (mmi
3.4.3 Main Results of Previous E~:periment
The results of Abdel'~aby (199>) provided two important conclusions. First,
the CiSSST was able to differentiate between the shear properties of different
mixes, as well as the differences within the same mix placed in different
weomc~tcies
(curved sections vs. straight sections). Thi;~ indicated that the device was
sensitive
to changes in mix shear properties and could potentially differentiate between
mixes
with good or poor rutting resistance.
Second, ~~reater variation between replicate specin-~en results was observed
Burin<.: laboratory testinV~ than in-situ testing. .As supported by Peck and
I_ow~e
(l9OOj, it was hypothesized that the coring process used for laboratory
specimen
preparation damaged the specimens to such an extent that a greater variation
was
observed during laboratory testing than that experienced during field testing.
3.4.4 Advantages of CiSSS'T Prototype
The concept behind the C;iSSST facility was quite simple, yet very effective.
~o special preparation of the asphalt surface was required and the test could
be
completed very quickly once the epoxy resin had cured. The applied rotational
force produced a state of pure shear stress without complicated bending.
tensile or
compressive forces. The test was very repeatable as indicated by the low
variation
between tests (Abd El .~Iabi 199>) and measured actual field shear properties
instead
of attempting to simulate field conditions usin~~ iahc»-amrv analysis.
CA 02330431 2001-O1-08
I~
3.~ Improved Analytical Framework to Determine Asphalt Shear
Properties from the Surface Plate Loading Wethod
3.x.1 Introduction
As previously presented, an equation for asphalt shear strength was developed
by Abdel Naby ( 19~)~) dunin;~ initial investigations with tnE CiSSST device.
However. shear strengths calculated using Equation 6 were consistently
';renter than
those determined by Zahw ( 1990 in the lalvoratory, often by as much as ~OO~i~
.
Notwithstandin47 the fact that laboratory anti field compaction methods
produce
different aggregate particle orientation as outlined in previous sections, it
was likely
that equation 6 did not fully- represent the r~oundarv conditions of the
paycmcno..
therefore, the calculated shear strength of the mix was not entirely coc~'ect.
It should
be stated that for comparative puyoses, this did not present a problem to the
analysis of Abdel Nahy ( 1990. However, for accurate modellin;~ of ruttim_~
resistance haled un shear properties, new constitutive relationships between
the
suria~e plate method and field shear properties ore can -ently' under
devele~pment at
Curleton University by Bekheet et. al. (x()00). Although non part of' this
thesis, these
relationships are b.-ieflv presented in the following section for
completeness.
3.,.2 Reissner-Sa~oci E'rohlern
~s outlined m Section ~.-I.?, the surf-ace plate tors;on test involves
applying a
torsional force throu',h a steel test plate epoxied to the asphalt surface as
shown in
Figure ?3. Torque is applied at a constant rate until failure of the asphalt
surface in
shear. The typical failure plain is shown i:n Figure ?4.
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104
Figure 23: Load Plate Attached to Asphalt Concrete Pavement (ACI') Surface
Figure 24: Induced Failure in Asphalt (_'oncrete Pavement (ACP) Surface
The prob3err~ of applying a torsional moment on the surface of a half-space
was developed by Reissner and Sa~oci ( 1944) and Sneddon (1946). For an
elastic,
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l~ OJ
homogeneous and isotropic material in cylindrical coordinates yr. ~j, all
stresses
vanish with the exception of shear stresses ~:;4.j and Tz« as shown in Fi~~ure
?~. A
simplified form of the shear stress iLo is available when z=(l (at the surface
of the
halt-space) as shown in Equation 7:
4~G (7 i
~ _-
W here:
G = .Shear modulus of the material
a = Radius of the loading plate
~ = nnUular displacement or the loading plate (radians)
r = L>istance from the centre of the loading plate (r<aj
Figure 2~: Differential Elennent Shear Stresses from Reissner-Saboci Problem
(from liekheet et. at. ?0()(k)
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I0~
It should be mentioned that lJquation 7 is only valir.i within the radius of
the
loading 'plate (r<a). 'rhe relationship betty-een the applied torque, T and
the resulting
angular displacement can be derived by integrating TL,j over the area of the
loading
plate as shown in Equation ~ (Bekheet et. al. ?000):
r _ 16 G~a' (S)
As shown, the shear modulus may be calculated fram the applied torque and
~tn~ular displacement (twist an~~le~. No closed form solution has been
developed by
Bekheet for shear stren~Tth to date. While such a relationship may be
developed in
the future, the me>dulus (stiffness) appears to better characterir,c ruttin~~;
therefore
effo?-ts were focussed on evaluatin~~ stiffness for this invstigation.
3.x.3 Finite Element '~~lodelling and Verification
Although Lquation 8 provided the means to directly calculate the shear
modulus of the pavement surface. the underlying assumptions of elastic.
homogeneous and isotropic conditions do not always reflect the properties of
asphalt concrete. Indeed. asphalt is a visccaelastic material dependin~~ on
its
temperature and rate of loadin<7. Therefcn~~, to further develop the Reissner-
Sago ci
equations for asphalt concrete. Bel<heet et al. (200()) im.esti~ated the use
of the
finite element method.
Briefly, a finilc element mesh was constructed using '_'0-node, 3 dimensional
bitch elements tc> simulate the Reissner-S;.yoci problems. Elastic,
homogeneous and
isotropic waterial propcrtic°s were lust entered into the model to
compare the results
of the model run uaith the dosed form solutions provided by the Reissncr-
Sa'loci
equations. Results of this model verification are illustrated in Fi~~ure ?(.
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107
As shown, the results of the initial model verification were almost identical
to
the closed form solutions, indicating that the finite element mesh modelled
the
Reissner-Sagoci problem very well.
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Radial distance (m)
Fibure 26: Initial Finite Element Model Verification
(from I3ekheet et. al. 2000)
The next step. which is currently underway, will l~e to take the verified
finite
element mesh and apply non-linear, viscoelastic material properties that
better
characterize asphalt concrete. The finite clement model may then be used hot.h
for
ar~alyzin~ the effect of nc>n-linear, viscoelastic properties on p;duation ~.
as well as
performance modellin~~ through repeated Loading.
CA 02330431 2001-O1-08
CHAPTER 4: DEVELOPMENT OF THE IN-SITU
SHEAR STIFFNESS TEST (InSiSSTThs)
~.l Introduction and Chapter Overviev~~
Based on the material presented in the Introduction ((-'hapter 1 ) and
Literature
Review (Chapter '_'), it is hoped that the need for an advanced test device
fco mea,;urin«
the in-situ shear properties of asphalt pavements is not only apparent, but
also
wau-anted and desirable. Chapter , "paved" the way for the development process
by
providing a sound analytical foundation for deriving shear properties from an
in-situ
test using the surface plate torsion method.
This chapter pr; sents the process completed durin~T the development of such a
device, known as the In-Situ Shear Stiffness '1.'est (InSiSST ~"' ).
Development of the
InSiSST~"f took a log=_ical, stele-wise approach. This approach commenced by
first
reviewin~T previous work of other reseurcher~, follow-ed by tm analysis of
ctament
deficiencies, which ultimately lead to the design and fabrication stales. Once
fabrication was completed, a series of validation, debug~~in;g and shakedown
exercises
were completed to ensure ruU~7edness of the device. An initial set of field
test
procedures is also presented to enahle others to use the InSiSST~".
:I.2 Critical Analysis of CiSSST Prototype Deficiencies
Design of the lnSiSST''" commenced with an anals-:~is of the deficiencies
observed with the CiSSST prototype. Althou;h the C'iSSST represented an
important
first step toward in-situ measurement of shear properties and yielded much
important
1 ()8
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10y
information, a numbe: of desi~en-related and operational deficiencies were
noticed.
during its use as outlined in the following sections.
4.2.1 Chassis Design and Weight
The chassis of the CiSSST device consisted of a metal cart mounted to small
castor wheels. Transportation of the test device was very inefficient and
dungeruus
due to its large we;ght, however. once on the pavement surface, the CiSSST was
relatively easy to t.~anoeuvre into position over the test plate. In total.
the CiSSST
device weighed aplaroximately ~0 kg (110 lbs.). Durin'; set-up and breakdown.
the
device had to be rrtanunllv lifted into and out of the transport vehicle by at
least tour
operators. Since only one or two operators were required during the actual
test
procedure, this was clearly an inefficient use of operator- time and
resources.
commodities that are in increasinUlv short .supply. Furthermore, lifting heavy
equipment inherently compromises operator safety, another important
consideration.
4.2.2 Stabilization of Test Device
A stable test device during the application of torque was critical to the
accurate measurement u1 pavement shear ~trengthlstiffness. Stabilization of
the
CiSSST was achieved thruu«h two methods. 'hhe first consisted of locking the
castor wheels to pt~event rullin'T. The wei;7ht of the device then acted to
prevent
movement during testing. ~hhis method proved unsatisfactory and a secundary
stabilization system w,.ts incorporated. This system consisted of six large
steel
stakes that were fed throu~Yh hollow tunnels welded verticaliv to each cut-
~~er and
midway along the sides of the test device. The stakes v'ere then driven mtu
the
pavement surface using a sledgehammer. Although relatively effective, problems
were identified witlo this method as well. In addition to the significant
operator
CA 02330431 2001-O1-08
110
effort required to drive the stakes into the pavement surface, the pavement
surface
was damaged throu~~h the use of the stakes. The most serious problem
associated
with this technique stemmed from the fact ~:nat the test device had to he
~rttached to
the test plate prior to stabilization. Therefore, the torque cell was already
attached
to the test plate as the stakes were driven into the pavement and the
sensitive
electronics within the torque cell were subjected to intense force as the
hamme;-ing
was applied. This rnay have eventually damaged the torque cell - the most
costly
component of the device. The hammering force maid have also affected the epoxy
bond between the steel loading plate and flue asphalt surface in some cases
where
bond failure was onserved.
4.2.3 Epoxy System Used for Loading Plate Attachment
The epoxy used for CiSSST testing required a relatively long cure period. of
?~L hours at temperatures above 10"C. This required the closure of the teal
site to
traffic mice within a 2~1-hour period - once to epoxy the loadin~l plates and
once for
actual testin'u. Closing? roads to traffic at any time period increases
con'estion and
driver stress, as well as presenting significant safety risk to highway
personnel.
Therefore, test preparation and execution must be completed in the shortest
duration
possible.
4.2.4 Data Collection, Control System and Available Test Program
Accurate data collection during testing was limited to applied tordue only.
Furthermore, althcuugh the datalogger rcc<rrded instantaneous torque readings,
the
data was not accessible for un-site viewin~~ unless downloaded into a portable
computer.
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Angle of twist at failure was measured crudely with a protractor-
instantaneous an~~le of twist was simply not possible with the CiSSST device.
Oue
to this limitation, a 4Traph of applied torque versus angle of twist (stress
vs. strain)
w as not possible.
Control of the CiSSS~r was also limited. Only two test (rotation) speeds were
availaL~le and there was no ~ a~ of monitoring for constant stress or strain
conditions.
l.?.s Overall Test Device Performance
To its credit, t-he CiSSST device performed extremely well Given its basic
construction and control system. However, there were a number of general
performance deficiencies that were ohserved durin'a testing that required
attention.
The first concerned the overall ''strength" or "capacity" of the test device.
The
motor and gearbox combination selected for the CiSSST was not able to provide
torque sufficient to fail some pavements at all test temperatures. A limiting
test
temperature of 10°C was assigned to the CSSST device to achieve
failure.
Secondly; the coupling used to transmit ti~r~.lue from the motor to the
~~e.u~box wus
under-designed an~1 failed durin~~ one test program.
It must be ay~un emplasiscd that the CiSSST performed extr°melv
wcll for
the purposes for which it was designed - a preliminary, research-oriented
device.
The results obtained with the CiSSST represented an all-important first step
toward
the development of a mainstream test facility.
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11?
4.3 Design Objectives f'or InSiSSTT~'t 'Test Facility
4.3.1 Mitigation of CiSSST Deficiencies
Defining the desi~~n objectives represented the nex-t step in the development
process of the InSiSSTT"' facility. The. objectives presented in this section
were
established largely through analysis of the CiSSST prototype deficiencies in
addition to other common sense objectives essential for designing a widely
used test
device.
4.3.2 Reasonable Cost
If a test device is to log successful in any market driven economic, its cost
must
be reasonable as compared to its value to users. Also, it does not matter how
much
benefit the test will provide if the user is unable to affor~_i its cost in
the First place.
Therefore, costs incur-r-ed 'by the end-user (-purchasing cost, operatin~~ and
maintenance, etc.) must be justified with regard to the benefits provided by
the test.
Furthermore, as the goal was to produce a platfon~~ for ti widely used test
device.
these costs must he within ~r reasonable range for the average user.
4.3.3 t'ortability and Safety
As road systems spurn thousands of 6;ilometres, the portability of an in-situ
pavement test device to various test sites is of great importance.
Furthermore. the
device must be easily mobile within indimdual test sites since numerous tests
are
performed to ensure statistical significance. Operator safety is another
important
consideration as injuries cause employers to incur loss mf productivity ~rnd
increased
compensation volts. Obviously injuries are also detrimental to the employees
as
well.
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1 13
4.3.4 Number of Operators and Ease of 1_!se
Employee salaries are usually the single lar=est expense that an employer will
incur. Therefore, minimizing the number of operators required to perform the
field
test will greatly increase the attractiveness of the device to both end-users
and their
clients. Additional savings may be realized by developing a test that is
simple to
perform such that specialized trainin~~ is not required for operators.
4.3.~ :Minimal Test 'Time and Damage to Pavement Surface
Minimizing the time required to perform a field test produces two substantial
advantages. First, more tests may he performed for a given time period,
increasing,
the amount of data acquired by the researcher and the amount of money
«enerated
by the contractor. The second advantage concerns the disruption to traffic
flov.-. As
this is an in-situ test, sections of road must be closed to her-form the test.
which
increases traffic con'Testion and the potential for worker injury.
Destructive pavement tests are becornin~ increasingly undesirable since the
result is usually an acceleration of pavement deterioration. Tests that are
non-
destructive or that produce lade disturbance (semi-destructive) to the
pavemern
structure are favoured.
4.3.6 Correlate Results to Pavement Performance Indicators
Perhaps the most important consideration when developing the InSiSST'"
facility was the need tc~ correlate the field test results to both standard
laboratory
values and pavement pertormance indicators such as rutting and cracking.
Achieving such ccorrelation would yield si~,nificant and immediate benefits to
the
three primary areas of pavement enaineerino. The first area is mix design. An
in-
situ shear stiffness test in conjunction will-; laboratory testing would be a
powerful
CA 02330431 2001-O1-08
114
combination for analyzing the potential of proposed mix designs. Also, the
results
of such a test apparatus could be used to produce "shift" or "master" curves
relating
in-situ shear stren~th/stiffness to various factors such as loading rate,
temperature
and asphalt content to name' a few. The se:ond area is the quality control and
quality assurance (QC/QA). 'Newly constructed asphalt pavements could be
tested
to verify acceptable construction practices through the nneasurement and
comparison of in-situ strength parameters with code requirements. The final
area is
the long term pavement performance (LTF'P?. :vlonitoring of actual field shear
stren'~th/stiffneas of pavements with time would assist in predictin~~ future
pavement
performance. fhhis, in turn. would allow f~~r more efficient allocation of
limited
rehabilitation funds and also help determine the effect oi'real world
conditions, such
as environmental factors, on pavement performance.
-L4 Design of InSiSST~rx' Facility
:~.:L1 Introduction and Overall Design
The desi~Tn or the InSiSST~~' facility was conceived based on the states
desi~Tn objectives and noted CiSSST deficiencies. Whil° complete
adherence to the
desi~~n objectives wus the ultimate goal. trade-offs between objectives were
necessary. Thererore, the lnSiSST'''' design represented an optimization of
the
individual design objectives into an integrated system.
~rhe completed InSiSST''''' device is shown in Fi«rres '~? through ~~). a's
shown. the components are mounted to a small A-f'ram~~ trailer to provide
exceptional portability. As with the CiSSST facility. the InSiSST' ~' utilises
an
CA 02330431 2001-O1-08
11>
electric motor and gearbox to produce the required torque. The motorlgearbox
combination is mounted vertically on a stee°.1 platform that is
attached to a
positioning system that incorporates two sets of worm-screw slides working in
tandem, also referred to as an "X-Y table." The top set ef slides allows
positioning
of the platform in tie transverse direction (with respect to the trailer
orientation).
The transverse slides are in turn mounted to a second set of slides
allow°in~T
positioning in the longitudinal direction. The entire positioning system is
mounted
to a box-tube frame occupyin~~ the space beuveen the tow bar and the axle of
the
trailer. The test frame is attached to the trailer frame via lour screw jacks,
one at
e~rch corner of the test frame. During translaortation of the InSiSST'"', the
jack:: are
retracted to hold the frame in the air to prevent damage. Once driven into
position.
the jacks are extended to lower the test frame to the ground and then continue
extending until the wei~Tht of the trailer is supported solely by the test
frame. As
with the positioninyT system, an electric motor is used to raise and lower the
jacla.
A sin'71e motor is used to deploy all four jacks using mitreboxes and
dr7veshahts.
Contri~l of the i~rck~, and positioning; slides is provided by commercially
available
electric motor controls. Control of the actual test procedure is provided by a
laptop
computer. Instantanec-pus torque and angle of twist measurements are collected
on
the computer during the test procedure. A large plastic storage hox is mounted
to
the front of the trailer to house the electronic cor~~ponent~ Finally. a
~~enerator is
mounted to the rear of the trailer to provide electricity for the InSiSST'~'.
A more
detailed explanation of the individual systems is provided in the following
sections.
<IMG>
<IMG>
<IMG>
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119
4.4.2 The Primary Force Generation System (Powertrain)
After investigating alternative methods to produce the required rotational
force (torque) for the test, it was concluded that, like the CiSSST, the use
of a
simple electric motor and gearing still represented the best choice for this
application. Systems incorporating hydraulics or pneumatics would certainly
produce acceptable, if not superior results. >=however, these systems were
simply too
expensive, at least at the concept exploration stage.
The first in-iport~mt improvement involved the vertical ali;~nment of the main
drive motor and gearbox. Ttae vertical ali~Tnment saved a si'.~nificant amount
of
space when compared to the CiSSST facility-, which utilized a right-angled
gear'nox
attached to a horizontally mounted motor. ~fhe straight gearbox an-angement
provided increased capacity and reduced backlash compared to right-angled
~7earboxes.
hhe overall capacity of the motor and gearbox system was increased
significantly to ensure failure of all asphalt surfaces encountered (over a
reasonable
temperature range). The gearbox is a triple reduction unit with a final ratio
of
8101:1. Therefore. 51()1 revolutions of the main drive motor arc required to
turn
the output shaft of t!~c gearl~c~x a single revolution. This lnu'Te reduction
was needed
not only to reduce the test speed to reasonaf~le levels, but also to increase
the
available torque to fail the ~isphalt surface. Whereas the f:_'iSSST device
produced a
maximum torque of approximately >08 N*rn (4>00 lbf'~in). the InSiSST'"' can
apply up to 1 »0 N" m ( I ,700 lbfrin) of torque, an increilse of ewer ''00<<
.
another siy7nificant improvement over the previous desiy'n was to mount the
motor directly to the <Tearbox. As mentioned earlier. the CiSSST had a
doveshait
CA 02330431 2001-O1-08
1'_'()
and coupling between the motor and gearbox which failed during one suite of
field
testing. The direct attachment also reduced power loss between the gearbox and
the
motor. A final benefit was that the direct motorlgearbox coupling provided a
ti~~ht
seal, thereby significantly reducing_= the likelihood of infiltration of water
and/or dirt
into the gearing.
One disadvantage of the vertically mounted gearbox and motor was a higher
centre of gravity. However. a restraint system was developed using tie sir aps
to
prevent movement of the gearbox and motor during transportation.
4.4.3 The Transportation System
One of the greatest pr~;~blems with the CiSSST facility was its lack of
portability. The integration of the facility ~a~~ith a trailer allows
exceptional
portability from site to site. Furthermore, the facility no loner requires
lifting i>r
lowering by human effort. This drastically reduces not only the potential for
injury,
but also the number of operators required f~~r testin~~. which will provide
si'~niticant
cost savings to the end-user. Another benefit of the trailer-mounted option is
that
any vehicle with a trailer hitch may tow th:; facility.
One disadvanta~~e of the trailer-mounted option is that the facility is
subjected
to a much harsher environment. such as the infiltration of water. dust and
dirt.
ljowever, judicious selection of rugged and/or sealed components reduced this
concern.
4.4.4 The Test Frame and Positioning System
The test frame fills the space betty-een the trailer axle and the front cross
bar,
providing the foundation for many of the ~=ssential InSi~ST"'' systems as
shown in
Fi~,ures ~7 and '_'8.
CA 02330431 2001-O1-08
l~l
There are two "levels'° to the test frame and p<asitionin~ system.
The lower
level houses the- lovler slidin' system, consistin' of the ~ sets of tandem
worm-
screw slides (i.e. ~ individual slides] mounted orthoyanally to allow movement
in
the longitudinal and transverse direction as shown in Figure 30. The bottom
woum
screw slides are mounted within I50 mm wide steel channels that run the
len~~th of
the test frame to prevent damage duuna transportation.
Legend:
I A - Transverse Slides
B - Longltud~nal Slides
C - Drive Belt
D - Motor
E - Test Frame
U
Fibure 30: Plan View of the Lower Positioning System
(Protective Steel Channels not shown)
CA 02330431 2001-O1-08
1 ~~'
The upper test frame and sliding svstern were developed to isolate the gearbox
from the worm screw slides for two main reasons. First, due to the lame weight
of
the gearbox (136 kg or 300 lb), it could not be directly mounted to the worm
screwy
slides according to the manufacturers specifications for static (dead) load.
Second,
if the ~Tearbox was mounted directly to the Slides, the reactionary force
produced by
the gearbox during an actual field test would be transmitted thr<~ugh the
slides
themselves. Even at low levels of applied torque, this reactionary force would
'ready exceed the manufacturers specifications for dynannic load and would
likely
damage the slides.
The upper level of the test frame consorts of >0 mm hollow structural sections
that provide support. t~or the upper sliding system. As shown in Pi'_ure ?~),
the
gearbox is mounted to a steel plate 300 mm (1? in) square. This plate is
mounted
on rollers and slides transversely across a set of connected ~0 mm HSS beams,
which arc also mounted on rollers and slide longitudinall v along tire upper
test
frame. The upper sliding system is attached to the worn screw slides below.
thus
allowing the slides to control the movemeno_ of the ~Tearhox within the test
frame.
Before a test is initiated, the connection between the upprr and lower sliding
systems is removed by clampin'1 the upper :Aiding system to the upper test
frame.
B~ isolating the upper and lower sliding systems, the large wei;_=ht of the
'rearhox
and reactionary forces are not applied to the worm screw slides.
A dedicated controller and control pad housed in the front stora',e box
control
the movement of the entire positionin' system. In its current configuration, a
net
travel distance of 1~0 mm (f~.~) in) in either direction fro»~ the centre
position is
capable with the transverse slides and a total longitudinal travel distance of
6~0 mm
CA 02330431 2001-O1-08
1_
(?>.? inj is capable with the longitudinal slides. Therefore, a total testin«
area of 0.1
my (148 in-) is available each time the test frame is lowered. If a 100 mm (~
in)
diameter test plate is used, four plates can be placed inline V.'ith a minimum
distance
between tests of 80 mm (3.1 in). If larger load plates such as 1?~ mm (> in)
and 1 >0
mm (6 in) plates are desired for lamer aggregate mixes, :~ plates should be
used to
provide a minimum between plate distance of 88 mrn (3.~ in) and 63 mm (~.~
;n1.
respectively. Initial analytical modelling by Belcheet et. al. (?C)00) has
indicated that
strains experienced outside of the test plate drop to less than one percent at
a
distance of 50-mm (~' in) from the outer ed~ae of the plate. Therefore. a
statistically
si~Tnificant number of tests can easily be performed for a sin~Tle test-frame
deployment. Furtloermcwe. 'the slides incorporate sealed motors and bearing;
to be
protected from the elements.
4.-t_~ The Stabilization System
A stahle test platform was a critical design factor f or the InSiSST'" faci
lity.
By lowering the test frame and liftin'T the trailer off its wheels
usin~l,jacks, the full
wei'I~t of the trailer is applied to the test frame. Stability against the
rotational force
applied to the teat plate is therefore achieved through frictional force
between the
bottom of the test frame and the pavement surface.
The test frame used in the lnSiSST' ~' facility presents a frictional
condition
very similar to that observed with thrust b:varinas or disk clutches called
''disk
friction'. An applicable f~rn~ula for disk ti~iction may t>e derived by
considering a
rotating hollow shaft. For a hollow shaft whose end is bearings against a
solid flat
surface, the minimum torque required to beep the shaft rotating may be
computed
using Equation J belay (Beer and Johnson 1988).
CA 02330431 2001-O1-08
1?4
R~ R' ( 'y
M =''~~PR~-R
~~~here R, and R_ are the inner and outer radii of the shaft respectively, A9
~s
the required torque, ,uA is the coefficient of dynamic friction and P is the
axial force
applied to the shaft. By replacing the dynarrtic friction coefficient ,uE,
with the static
friction coefficient fit" Equation 9 may be used to find the lar~~est torque
that may be
applied to the disk prior to slippage. For this application. the test frame
itself is
analo~Tous to the hollow shall. The force P is applied by the Gravitational
force of
the trailer and test frame on the pavement surface while the couple M is
applied by
the motor/Gearboa durinG the test procedure:. To find the magnitude of force P
sufficient to resist the rotational reaction, "equivalent radii" were
determined for the
test frame. Tha test f-rame is rectanGular m overall shape as shown in Fi~lure
>l.
1200mm
__ ______ _.--
i
_ f
.~i
i
-- ~ J~ Equiv.
j i, ~~i, ' Outar
' ~' Min. inner ', ''~ Radius
750mm ~ ~ Radius i ~! ~'~ ~ ~ / ' (600rnm)
i I, ' (450mm) J
i ~ , . ;
~---~ , I
_~
_____ _ - _
'_-i_ -__- _ -
- ~~_ ___ __. _._-_
1050mm _ ~,...'
Figure 31: t'lan ~- ieH of InSiSST~r"' Test Frame
CA 02330431 2001-O1-08
1_
Based on previous testing regimes with the CiSSST device, the maximum
failure torque applied to an asphalt pavement surface using a 100 mm (-t inch)
diameter test plate was approximately 508 N' m (4500 lbf*in). It was
reasonable to
assume that the weight of the trailer will b,; evenly distributed at each
corner c~f the
test frame via the ;acf:in~ system. Therefore, regardless of the position of
the :motor
and ~~earbox within the test frame, the full frictional resistance of the
interface
between the test frame and the pavement surface should be mobilized assuming
that
the pavement surface is relatively flat.
The total contact area between the test frame and the pavement surface is 0.~?
m- (5.6 ft-) includin'; the channels that protect the positioning glides. From
the
centre of the test fame. the minimum inner radius is 0.-Ii m (17.7 in). The
"equivalent" outer radius was then calculaed using the c=quation for the ~Irea
of a ?-
dimensional 17n~~ as shm~ n in Equation 10.
(~om;r~_ jumm ~,1 ~) )
W'hele:
,A = total contact area (0.5? mu);
r"",~_ = mintrnum inner radius (0.~5 rO
The resultins, equivalent outer radius eras found to be O.C~O In (''s.9 in).
L'tilizinU these radii with :'l~I = 50~ :~'~'m (=f~00 lbfwin). alr:d assuming
a cc~efl~icient oi~
static friction of (>.5, the minimum wei~T1 (normal W -ce. F') applied to the
test frame
must be approxim~Itelv 190 N. Therefore the load applied to the test frame
must be
lq5 1<g (-~?8 lbs.l according to Equation ~l.
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1?6
Much of the required weight is provided by the trailer and test frame, as well
as the equipment necessary for operating the test facility. This includes the
jacking
system and the data acquisition/control system.
A static coefficient value of 0.~ was selected for the analysis to ensure a
reasonable factor of safety. The actual coefficient of static friction between
the test
Irame and the pavement surface is likely to be 0.7 or greater as a neoprene
irubb;.r)
pad has been epoxied to the bottom of the test frame to increase the friction.
This s~~stem prc;ventcd movement dur-in~ testing and eliminated the need to
drive stakes into floe pavement surface. ~I~h~erefore, no damage is imposed on
the
pavement throu;=h stabilization and no operator efl~c»'t is required.
Furthermore, by
raving the stabilization completed prior to positioning and testing, the
sensitive
electronics of the tordue c~'~l are not subjected to unnecessary stress. To
prevent the
use of multiple motors. a set of custom driveshafts and mitreboxes was
fabricated to
connect all four ja~~ks to a single motor, ti~~=rebv reducincost ~rnd
ensurin~~ th~rt the
jacks do not operate independently of one another.
The jacks themselves are coated with a plastic layer to resist corrosion. and
accordion-like hclle>ws cover the serews to prevent the infiltration of wetter
and dirt
into the ~Tearin«.
4.4.6 Epoxy System
,~s mentioned. the epoxy system used preyiouslv required 2~ hours to cure
prior to testing. This limitation required two visits to the test site, an
inefficient and
costly method of testin~T.
During, the ir~vesti~~ttion. numerous adhesive systems were tested for
suitabilia°. Most :~vstems either required cure times that were similar
to the existing
CA 02330431 2001-O1-08
I?i
system or did not provide suitable strength at all. For e~;ample, instant
contact-type
adhesives were not effective as they rely on direct conta;a between the
asphalt
surface and the steel plate. Due to the rouhness of the asphalt surface, this
contact
was not provided.
iat this time, the best performing product is a two-part epoxy system that
provides adequate strength after ~ hours at room temperature. Therefore,
curin~~
time at elevated temperatures, such as those experienced in the field durin'1
testin'?
will reduce this tiroc. Two hours was deemed as an acc~.ptablv short time
interval
as the tests themselves can be completed ivy minutes once the epoxv~ has
cured.
-L4.7 The Test C:ontroUData Collection ~vstem
The main drive motor is controlled by using a variable speed motto controller
with a speed sensor connected directly to the motor shat-t. The speed sensor
provides a closed loop system and ensures ti~at the motor does not deviate
from the
desired test speed. Theref~me, the InSiSS~I''~' is a strain--controlled test
as the rote of
displacement ttwist an,Tlei is controlled, w-Nile the resultinC7 torque
lstres5) is
measured by the. torque cell. The accuracy of the mover controller is ~I
revolution
per minute :rpm).
The variable speed motor controller also allows thL selection of a variable
test
speed between zero revolutions per minute lrpml and 1 ~sQO rpm. T;rble I ~
displays
pre-programmed "train rates and there associated drive motor speed. The strarn
rote
of 0.000> revolutions per second corresponds with the strain rate used in the
Super-pave Shear rl_ester du~in~J lrequencv sw~ecp testin'T.
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1~8
Table 13: Target Test Strain Rates and Associated Motor Speeds
Target Strain Rate Required '\'Iotor
i Speed
( revs) (rpm)
1
0.000; A"
().0011) ~ -18C
_
I).~)~)1~ 7~y
-
O).~)~)~U~ ~~= _-
().00~'O - 1 '_' 1 1
1~~'i
i 0.0() i~ 1 i01
_ 1).007 ' 1500;:x_ i
_ _ _ __
* Strain rate i~f SS'T for frequence sv.~eep testing_
*' 1 SO(1 rpm is ttnc ma.vin~um available motor screed
Torque i5 recorded with a torque ce:l similar to th;~t used with the CiSSS~I-
facility, althou~,h of hi'her capacity. Both the InSiSST'h' torque cell and
the motor
controller have standard RS-?s~ (serial) connections for connection to a
computer.
However the laptop has only a sin'~le serial connection. To overcome tl;is
problem,
a Universal Serial Bus fUSB) adapter box was used. 1"this device allows the
connection of up to ~ individual serial connections into the adapter with a
sin«l:
LISB output to the laptop. Therefore, the laptop computer is able to contrc>I
and
acquire data from up to -1 individual serial devices simultaneously. .At
present, only
the torque cell and motor controller are attached to the laptop. The
positionin~T
system also has a serial connection and nvav he controli,~d with the laptop in
the
future.
This centralized control and data acquisition svstvm allows the collection of
instantaneous readin's at user-defined sa.nplin~ intervals. Results are saved
directly to the laptop and other relevant information su:;h as test site
location.
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1 , c~
weather conditions, temperatures, etc. ma.y also be directly entered into a
database
forfuture analysis.
4.4.8 Overall System Integration
All of the separate components were selected and designed to work well
to'7ether as a single unit. The result is a test facility that is portable,
stable, and
ru~a~ed. The test requires only a single operator, no heavy lifting or complex
set-up.
and can be completed rapidly. The test results are accurate and are available
instantly. All of the individual components operate under the same power
rcquaremcnts as provided hw the central generator.
4.4.9 Cost
As the InSiSST'"' is still in its prototype form. the actual cost of the
device is
not representative of a final production m~ndel. 'The component costs oi~ the
lnSiSST'''' totalled approximately $37.00 C.AD ($~>.000 USD). However, there
are many other coats such as labour, overhead, marketing, etc. that must he
factored
in when determining a final purchase price. Furthermore. the component costs
would likely decrease if produced in lar'Te;-quantities. E-Iowever, based on
the
component cost, it is estimated that <i final production model would be priced
below
50.000 LISD. w-hich was identified by th:v Ncitional Asphalt Pavement
:association
(I<.AP.A) as being a reasonable cost fur su~_h a performance test (IvHW.A
199~d1.
~.~ Fabrication, Debugging and ''Shakedown" 'Testing
All fabrication activities wore completed at Carfeton Lniyersity in the CiviE
and
Environmental En~~ineeriny Laboratories. As with any Nev. or complex
te~hnolo~v, a
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1s0
number of interestin? challenUes were encountered during the development of
the
lnSiSSTTh.f device. Perhaps the most frustrating were the long delays
experienced
when ordering and acquiring the component parts for the InSiSSTT'''. .Although
most
of the components were comrnerciallv available, they were not actually
fabricated or
assembled until ordered. thus requiring up to '_' months to receive and in
turn delaying
the fabrication of the InSiSSTT'f on multiple occasions.
4.5.1 Positioning System Debugging
When the p~>sitionin~z system was first installed and attached to the
<_earbox,
the system w-ould often "stall" while mcmm« the ~Tearbc>x bath and forth
within the
test frame. It first appeared that the steppin'; motors of~the positioning
slides v-ere
not powerful enough to move the ~enrbox. However, Moon further examination, it
was discovered that the slides were not completely parallel and that the
_>earbox was
hitting the slides at certain spots along the slide length. Once adjusted. the
positioning' svstern performed pr<aperlv.
1.~.? .lacking System I)t:inugging
The jacking system itself presented no major problems durin'; development.
although the rate .~f extension and retraction of the jacks is faster than
anticipated.
The addition of a year reducer to the jachin'~ motor is evpected to redact the
~,pe~d
nt which the jacks rcnated, although has n~~t been completed to date.
=1.x.3 Test System Debugging
Once constructed, the motor control ler and torque cell were connected to the
laptop cc»nputer via the L'SI3-to-Serial ronncction box (o herein the software
development. Lnfoutunately, tire test softG~~~rre conflicted with the LSB
adapter and
caused the computer to 'crash" evervtime the test softy are ~-as initialed.
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Isl
software patch was obtained from the manufacturer of the USB adapter and the
problem was solved.
4.x.4 Shakedown Testing
A series of shakedown exercises were completed v-vith the InSiSST'" to
ensure an acceptable amount of rubgedness prior to field testing. Most of the
shakedovm testing was connpleted in and around the Carleton University campus.
Tire most challenging test of ruggedness for the InSiSST'"' was completed
between July 16'h and 18'r' of 2000 when the trailer was driven from Ottawa to
College Park, Maryland and then to Washington, DC for a demonstration at the
Transportation Re~eurch Board. The total trip distance ~.vtis approximately
2000 hm
~ 1?~U miles). most o1 which was along mayor Canadian hi~hwuvs 1416. -101 )
and
US Interstates (S0. 9j) at speeds ranging from 80 to 120 km/h (~0 to 7~ mph).
«'hile in College Park and y'v'ashin~ton, tf,~e InSiSS~T'" was towed along
city streets,
many of which were in poor condition d~st7laving potholes, extensive cracking.
patchin4a and rutting. The InSiSST'"' trav::rscd countless shays bumps and
dips
durin« the journey and there was some concern for the foealth of the
electronic
equipment housed in the stora«e box. ~vo~cever. no danuaUe whatsoever was
observed upon return to Carlcton University, with the exception of some very
thin
surface rust on the metal test frame. The test frame will he soon cleaned and
painted to prevent future rusting_. To ensure that the electronic eduipment
does not
fail in future tops, hubble pud~iina will i,e installed to protect the
eduipment from
shock.
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I >_
4.6 Field Test Procedure
The following is an initial draft of the field test procedures for effectively
and
safely using the InSiSSTI"~. It is expected that more comprehensive versions
of l:hese
procedures will be developed with the increased use of the device.
4.6.1 Equipment Checklist
Before leaving to the test site. the operator or technician should ensure that
all
necessary equipment is packed and in proper v~orkina order. Table 14 lists the
eduipment needed for field testing.
Table I4: I~quipment Checklist
~ Sufficient epoxy for field testing and associated mixing equipment
~; ~ Sufficient loading plates (cleaned and roughened)
~~ ~ Fuel for the generator j
~ Infrared ti~erTmmeter
~ Stiff brush t.:~ elcan dust from asphalt surface
~ Callipers tot rneasurin~ the depth of failure
~ Dipstick profiler (if rutting survey desired)
_ _______-_._.___- ___ ___ __-_
~ ~ Nuclear Dcnsiv Ga~_y1e (it density survey desired)-__ .
~ laptop computer _
:L6.? Transportation Safety
The InSiSS~h'"' is a trailer-mounted device that is towed behind a vehicle to
w<crious test sites. Therefore, safmy must he an important consideration
during the
transpooation of the InSiSST'"'. Tu help ensure a safe journey, users of the
InSiSST'~" should follow towinV~ safety 'Juidelines recommended by trailer
manufacturers and/or aove~z~ment a«enci~°s. A comprehensive wide to
towiryT
safety is produced by Sherline Products Incorporated ('iherline 1999) and the
CA 02330431 2001-O1-08
., ,
1a>
Ontario Ministry of Transportation (MTO ?000) has developed a quick checklist
for
trailer safety.
Prior to transportation with the InSiSSTTM, the jacking sv~stem should be
completely retracted such that the test frame is in its uppermost position.
Fur-ther-more, the ,,earbox and drive motor must be secured to the test frame
and.~or
trailer using the ratchetin~ nylon straps error to transportation.
4.6.3 Securing the 'Pest Site
Closing of a road section or lane alv:ays involves some risk. Therefore.
traffic
control should oniv be car~r-ied out by trained professionals with the proper
equipment. If possible, traffic control measures should be initiated <rnd
completed
by local or provincial transportation aQencv personnel t<> ensure the safest
wcwkin~
conditions. I-~owever, if private traffic control is required (and permittedl,
the
contractor should ; ontact their local or provincial a'encv for appropriate
tratfic
control procedures and eduipment.
t.6.4 Preparation of Ya~~ement Surface and Bonding the Loading Plates
Pavements arc subjected to numerous types of dir!, c»1 and other chemicals
that are introducec.l and tracked by automobiles, trucks and other vehicles.
These
chemicals will often adversely affect the quality of the bond between the
asphalt
surface and the steel loadin~~ plate, therehs~. affecting_ the test results.
Tu ensure the
highest quality hand, the pavement surface should be free of deleterious
substances.
.At a minimum, a stiff brush car hroorn should he utilized to remove fine
particulate
materials. In some cases. rt may be also necessary to '~antlv v a.sh the
rrsphnlt
surface with soap and water to remove rn:»-e stubborn substances. Care should
he
CA 02330431 2001-O1-08
1 i ~l
taken in these cases not to dama~le or strip excess asphalt from the pavement
surface.
The surface should be completely dry prior to the placement of the loadin~a
plates. The epoxy must be prepared according to the manufacturers
specificatir~ns
to ensure maximum strength and bond. The epoxy sho~_~ld be spread evenly
across
the bottom of the loading plate with care such that air buhbles are not
entrapped.
Enough epoxy should be used such that when the plate is placed on the asphalt
surface and compressed. a small amount of epoxy is displaced along the
perimeter
of the loading plate. The loading plates should be placed in either a straight
fine or
staggered such that they will ~rll tit within the test frame when lowered.
Excess
epoxy may be removed with a clean towel. If possible, a small weight such as a
brick should be placed on the plate durzn« the curia' process. Pavement
temperature is measured with the thermometer and the required curing time
haled
on manufacturers information is assessed.
:~.6.s Ruttin<t;/Densitv Surveys (Optional)
While the epoxy is curing, a ruttin~_~ and/or density survey of the test
secaion
may be completed to provide additional i;aformation for analysis. :~ ~~rid
system
such as that illustrated in Fi~7ure s? can hG_ marked usin~~ a chalkline.
'hransverse
and longitudinal profiles may be measured using the Dipstick or similar
profiler to
provide rutting and roughness data. A nuclear density ~Tauge may also be used
to
measure the density of the asphalt both it the whe~lpatlrs and the midlane.
,an
example pattew for in-situ shear testing for research purposes (white circles)
and
c~rir~g ('rev circles) is also shown in Figure ;'', althou;;h the pattern
shown v,-c>uld
require the movement of the InSiSST'"' within the test site.
CA 02330431 2001-O1-08
1 i1
\li~ll;m~
lmm:- ( 7u;~~r
\\ Imll';nit ~ \1 I~~:~II'atl~
i
O O
CO
C_~
o c~~
nl,
o c_
O
O CO
Figure 32: Outline of Rutting and L)ensity Survey
CA 02330431 2001-O1-08
1 ,6
x.6.6 lnSiSSTT~' Test Procedure
Once the epoxy htis cured, the field tcstin~ with InSiSST'-" may commence.
~hhe followin~ steps should he completed in order:
Detach the InSiSST''~' from the tow vehicle and manoeuvre it over the test
plates such that all test plates will be within the test frame when lowered
(Figure s,).
?. Chock the tires of the trailer once in position to prevent movement of the
trailer. A brick or wooden wedge work well (Fissure 34).
.attach the torque cell cable to the torque cell (Figure ,5j.
-I. Install the torque cell ;end connecting collar onto the gearbox
driveshaft.
Lower the test frame to the 'round and ensure that the we°.i«ht of the
trailer has
been transfeurcd to the test Iramc (the trailer suspension will relax when
this
Occ L1 I's ).
(~. :attach the L'SB connemion to the laptop and tuc~n tf~e laptop on.
7. Turn on the slide controller.
S. Use the slide.~ontrol pad to align the torque cell ~and <~earhox) over the
tia~st
test plate (Ti'lure ;6).
~). :~ctivtlte the motor controller softwaro on the Iaptol~ and turn the
torque cell
until it is aliened with the load plate in the radial direction.
10. Lower the connectin'T collar on the torque cell into the load plate
(connectin~~
collarshovn in Fi~urc _s7).
I 1. Weasure the pavement temperature directly adjacent to the load plate and
record it for future ann°'vsls (Fissure s8 i.
1 ~. W'ith the torque cell tirn~ly connected to the land plt~te, activate the
torque cell
software. The soft~w~rt~ v ill he«in to t,Ike readm~s tit the predefined
samplin«
rate and recor~:1 them in a text file. Th::re should be very little load shown
for
these initial rcadin<7s as the drive motor has not bee°I restarted vet.
1 ~. Press the red calibr~Ition button to calibrate the torque cell (Fieure
>G). Ensure
that at least one calibration reading has keen recorded in the text file.
CA 02330431 2001-O1-08
-,
lm
14. Once calibrated, the test may be initiated. To do this, select the desired
strain
rate from the motor controller software. As the stain is applied. the torque
readings should increase until failure of the asphalt surface.
l~. When failure occurs, press the Escape key to stop the drive motor.
16. Inspect the failed asphalt surface and loading plate. Weasure the depth of
failure with the callipers and record it for later an,ilvsis.
1 i. Save the test file to the hard drive.
18. Repeat steps b throu«h 16 for the re;mainin' load plates.
CA 02330431 2001-O1-08
138
rigure 34: Chocking the Trailer 'fire
Ia figure 33: InSiSS'C~'M Trailer over 'Test Plates
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IsO
Figure 3~: Attach 'Torque Cell Cable to Torque Cell
Figure 36: InSiSS'I'T"' Controls (Computer not shown)
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1=lU
~.~"~
Torque Cell -~_
_..~r...-~ . _ . 'best .
,.N: ~ Plate
p~..a x
Co nnecting
.. ~- Collar ~ ..
a~ ~. ~ ~ .R
. ~ . ~, z .
.~
.. ._ :~ . ~ ,
Figure 37: Connecting Collar from 'Torque Cell to Test Plate
Figure 38: 'Taking Pavement Temperature with IR Thermometer
CA 02330431 2001-O1-08
1-f 1
4.6.7 Leaving the Test Site
After all of the desired tests have been completed, all equipment should be
collected and stored for transportation. The InSiSSTTh' test frame must be
fully
raised and the gearbox must be secured to ~.:he test frame and trailer usin~T
the
ratcheting straps. Reattach the InSiSSTT~' to the tow vehicle as per the
safety
recommendations discussed previously. Ensure that the site is left clean and
that the
small divots removed by the InSiSSTT"' durin~T testing are sealed with a
slunrv mix
to prevent moisture infiltration.
CA 02330431 2001-O1-08
CHAPTER ~: Preliminary Testing and Validation
~.1 Introduction and Overview
With the lnSiSSTTM facility constructed and the base analytical models
available.
the final stayTe of the investigation involved preliminary field testing for
validation
pw-poses. Chapter ~ first presents the results of an exercis=e to validate the
linear elastic
assumption made by the Reissner-Saaoci equations. lvext. the results of
comparison
testin' with the CiSSST and InSiSST~~'' devices are presented, includin<~ an
interesun;~
observation concernin<~ the test pl<rte diameter. Chapter s concludes with a
comparison
of field shear properties to those observed in the laborator;..
~.2 Analytical Models vs. h'ield Test Results
x.2.1 Verif ication of Linear Elastic .Assumption
As reported 1~v F3ekheet et. al. (''00O). preliminary field tests were
conducted
usin<T the CiSSST with the objective of verifying the applicability of the
linear
elastic assumption used ha the Reissner-Sa~oci equations for asphalt
concrete:. 1~0
this end, pilot testy mere completed at Carleton Llniversitv with a modified
test
procedure to accurately measure the suri~uce displacements (I3el<heet et_ al.
200U>.
The an~lulur displacement vulr.res lrr.m the tests were also compared to the
expected values using Equ~rtion 8, as shou.-n in Figure ~9. While the number
of data
points from the field tests was low, they displayed hi'Th cowelation with
Equation S
(R~=O.S6). This vesult implied that the linear-elastic ussumpuon for asphalt
pavement behaviour was reas«nable in this case. How<wcr, tf~e pavement
L
CA 02330431 2001-O1-08
1-L i
temperature durin; the test was close to room temperature (approximately ??"C
or
72°Fj, v hich would have contributed to the linear elast» response.
1.200 - _ __ - _._. __
1.000 ~ ~ Mathematical Model
--,
E
~ 0. 800 _.
~ 0.600 -
a~
U
Q 0.400
~ 0.200 -
0.000 ~ - -
0.00 0.10 0.20 0.30 0.~~0 0.50 0.60
Radial distance (m)
h,i~ure 39: Comparison of Field Results with Reiasner-Sal;oci Model
(from Bekheet 2000)
x.2.2 InSiSST'"' vs. (.'iSSST
The surface plate rruahod of testing is used for bath the CiSSST and
the°,
InSaSSTI"', however, a sct of comparison tests were completed to ensure that
similar results were achieved. The tests were completed in a purkiny lot at
Carleton
L:~niversitv consisting of an IdL~ asphalt concrete mix. HLS is a standard
sura~ace
mix used throughout Ontario for lov- to medium traffic volumes.
Unfuntun~ttely,
due to the aye of the mix c8 years), the actual mix desi_;n data was not
~~vailable for
analysis.
CA 02330431 2001-O1-08
144
Test plates of 9? mm i 3.6 in) diametc;r were epoxied to the pavement sunace
for each test device. The plates were placed in a straight line with a minimum
clear
spacing of 65 mm ('_'.5 inl between each plate. Testing vvas completed the
following day to ensure full cure of the epc.~xy. Results u~f the CiSSST
testin~~ are
given in detail in Appendix D, and summarized in Table 1 >. One of the CiSSST
tests failed between the epoxy and the steel test plate, while the remaining 5
tests
produced failure of the asphalt surface. 'The pavement surface temperature for
tests
C 1 through C4 was '__'9°C, while test C5 was tested at a surface
temperature of ?7'C.
The averay~e shear strength calculated through Equation 6 was ?058 kPtt with a
relatively high coefficient c~f variation (C'OV') of 19.?~~~.
Table 1~: COnI~aI'1S011 Of CISS~T and InSiSSTT"' Results
CiSSS~T Testing -i---_. IrI~iSST Testing
Ultimate Pavement Ultimate ' Pavement
~,
Surface Shear Surface
Shear ~
Test ~O. , Test ~O.
~I Strength rCemh. Strength' Temp.
(kPaj ~ (C) ~ (kPa) ("C'l
__ y ',:1~
CI __~77> II. '
,
__
__ C~ 1~ ~ ,1~~
I -~~~~
.~~)
-_ ~- I', -__ IT ~~~? -._ 5 -1
_ ~ I _
,~ _,I
_ ~r~
__
C;
_
-
~~ _
,:~>~ ~__
,~
_
_ _
_
_ Avera~t
, _?3(14
Average j
' ~'.(l5li
' ~
S'1'Dev ~'rD_ev
'~ ~~~~-._ __ I
- 166
I 9 C_O_V_
.2 I 7.2 i
CO V I -
~
_ uation
_ 6 ~ Abdel
"'Liltimate Nahy
Shear 1991
Stren,_tlv ~
calculated
with
E~.i
Once CiSSST the ~
testing InSiSS~r
was complete, pl4ttes
were
tested
-
however. ween the
each steel
test test
yielded plates
bond and the
failure epcy-.
het
As these it was
test hypothesized
plates that
were a thin
newly layer
machined. of
grease
or oil
was present
c}n the
steel
surface,
which
hail
compromised
the hand.
CA 02330431 2001-O1-08
1-l~
The plates were placed in an oven for 2 hours, roughened with a circular
Grinder and
then re-epoxied to the asphalt surface. ~~Jhen tested main, all 3 plates
produce°d the
desired failure in the asphalt surface.
Results of the lnSiSST testing are shoe-n in detail in Appendix E and also
summarized in fhable l~. (_'nfor-tunately, the pavement temperature at the
time of
InSiSST'~''' testing was hither than during the CiSSST testing. The surface
temperature for tests Il and I? was 3s°C, while I3 was tested at
~?°C. To compam
the results of the InSiSST'"' to the CiSSST, the shear strength of the
InSiSST'"
tests were calculated using Equation 6. .A.s shown in Table 1 ~. the avera~~e
shear
strength was ?~~0=I kPa, with a COV of 7.?'io.
A two-sample t-test was used to determine whether or not the mean valraes
were statistically the same. The null hypothesis assumed that the difference
between the means was zero, and the resG.ltin~r t statistic was calculated
using,
Equation 7 1 (Miller et. al. 1~~90):
~r~,(rn +rr. -?1
-_-_- _-- i -__ ( 1 1 )
y~ijt, -1).~i--t,y -t).~y ~' rl, T n-
v here:
x,, x_ = the sample means
c~ = the desired difference hetween the means (zero in this case)
n,, n ~ = the number of observations
s,. s~ = the sample standard deviations
The resultin~~ t statistic was x.36, w hich was less than the critical t of
~.7U 7 for
(n,+n,-?) _ (~ degrees of freedom at the I r~ confidence level. Therefore, the
null
CA 02330431 2001-O1-08
1~6
hypothesis was accepted and the difference between the mean values (d) was
statistically zero. These results indicated that both devices were tneasurzn'
the same
material property. althou,h the InSiSSTT"' results were much more consistent
(lower COV). however, it was expected that the InSiSSTT"' results would be
lower
than the CiSSST results as the asphalt temperature was <greater- and the
CiSSST test
had a faster loading, rate. While more testis' is clearly required. the high
COV of
the CiSSST tests t If~.7~~~.) could explain why the CiSSS f strengths were
lower: in
this ease.
x.2.3 Practical Calculation of Shear Modulus Using (:quation 8
As previously mentioned, the current an alvtical models were devcioped
asaumin~ linear elastic material properties,. I-Iowever, v. he-n actually
measuring
material properties in the field or laboratory usin' test equipment, the
resultin' data
i5 often not strictly linear. Fi'Ture =IO displays a typical :_rruph produced
during
testing with the InSiSST~~'. Although the 'uraph is fairly linear, an ''S"
type curve is
observed due to tolerances with the devrce at the beainnin~ of the test, as
well as
non-linear yieldin~~ of the asphalt close to the failure po;nt. Therefore, to
determine
the linear-elastic modulus usinU Equation ~u. the strain (resist anjle) was
corrected by
taking the tangent of the "S'~ curve. The eduation of thv tangent line was
determined as shown in Fi~trre -II . From the resultin' .:quation, the
intercept of the
tangent line with the x-axis (twist an~lel was then determined and used to
shift the
points of the torque-twist an'le 'rraph to zero. It shoulc be noted that the
tordue
values were not adjusted - ie. the maximi_rm torque value observed durin', the
test
was used in Equation ~.
CA 02330431 2001-O1-08
1-I7
900.0 __ - _
800.0 - -__-___- _ __.___. _ __ __.____ __._. ____- _ - __. --
_ 700.0 - _____ ____ __ _.. _ _ ._ __.._.._ ____ _- __.._ _ ___
600.0
Z 500.0 -__- _... _. ______ _ _ _ _ ___. ___-__ ___- __ .__.__ _.__ _ _ __- -.
.__ __ _
._________.__ _ -_ - -.- ___- _ _. - - _
400.0
>S
'0 300.0 _-. . __ _- _. ___________ _-__ .. ___ _ _-
H
200.0 ___-_._ __.. .__ ___.__ -_ _-. _
100.0 -___-- - _-. _. .. _____..
0.0 1- ~ ~--''~ _ _
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.'18
Angular Displacement (rad)
Figure 40: Typical Torque vs. Twist Angle Graph from InSiSST~'''
aoo - -.-_---_--._. ~-_.__ - ----_ . --_--------- --w--__ __,
700 _~Seriesl
600 Linear (Series' ) _ _
E 600 i
z
400 j -
y = t 1329x - 647.96
~ 300
0
200 _
t OC _
0 0.02 O G4 G.06 0.08 0 1 0.12 0.14
Angular Displa~~ement (rad)
Figure 41: Determining the Tangent of the 'Torque-Twist "S" Curve
x.2.4 Asphalt Mlodulus vs. Torque Yer Unit 'Twist
Using the technique pesented in the previous section, the modulus of the
asphalt pavement at failure was calculated for the 3 InSiSSTr~~ tests as shown
in
Tahle I6. From the ;~ InSiSST''' tests producing failure of the ~isphalt
ec>ncrete. the
average modulu:, ~,~~~s calculated at ?08~'S kPa usin<? Ey.mtion S, with a
('O\' of
17.6~~~. Examination of the test results indicated that to is I1 and I? had
nearly
CA 02330431 2001-O1-08
1.~ 8
identical values for rr~odulus ( 18909 and 18~? 1 lcPa, respectively), while
rest 1=s
yielded a higher modulus of ~~O~G kPa. Unfortunately, due tc~ time and
~aeathnr
constraints, additional testing with InSiSS I''~~' could not be completed
prior to the
completion of this thesis. However, an additional 8 tests had been completed
previously with InSiSSTT~' on the same asphalt concrete. although each of
those
tests produced bond failure between the steel loading plate and the epoxy.
Whilc
the modulus of the asphalt concrete at failure could not he calculated for
these tests,
there were enough data points poor to the bond failure tip calculate the
linear slope
of the torque-twist graph ( Fiytlre -f 1 ) for each test.
Table 16: Shear Modulus vs. Torque Per L-nit 'Twist
' i ~ Ultimate Torque
:asphalt j ~tlear I'er
Test Failure Unit
r
~ ~lodulus ~
~~~~lL, 'Twist
I 'surface I
I
No
( (kPa) I (N~'m/rad>
~
.
h ~
~ I1 18909 11100
I, ~
~_
~
_ -- ,_.--- ,
' --~
I? ' 18~'' I 13?9 I
As I
halt
'
~
i
1~ ' ~>o>f~ I I;laB
~~
-_~---___ ?U~~~ 11859
average
_
~.l,Dev 3666 1122
f
C'OV 17.6 ~ 9.;
t ''~
)
BFl I _ 10?'I
' _
BF? I 11961
~
BF, _
I 1 1 ~
7'
_
BFI I\;u>t i I ; ~
', I I
Epoxy-
~
Load
Plutc Applicable 6
BF> I l-118
I I I
lnterfare
-j
l I I ,1 I
B F6 _ ~_
~,
13~3-~7~~ I I ~ 1
' i'_'
I ;8?,
BF8
~ . _.
_ _
_____.-____. :lverager 12180
', II
S'TI)ev* 1104
CO~' ( ~'c 9.1
i' '
*includes te,t results fr~r I 1. I'_' and I
CA 02330431 2001-O1-08
I:l~9
The resultin; mix property, referred to as "Torque Per Unit Twist (N~m/rad)'~
was calculated for bc_>th those tests vieldin~ failure in the asph~rlt
concrete, as well as
those producing bond failure. The results are also presented in Table 16. A
number
of interesting observations were made based on this measure. First, the
'Torque per
Unit Twist (TLTTj values for the tests yielding failure in the asphalt
concrete v~~ere
much more consistent than the ultimate shear modules :rom ~Jquation b as
indicated
by the low COV (9.~'if~ vs. 17.6'0). Furthermore, the Tll~h values were
virtually
identical for all 1 I tests, regardless of whether asphalt failure or bond
failure v.vas
observed.
5.2.~ Effect of Loading Plate Diameter
InSiSST~r" testing was also completed wish 1''> ram (> in) plates to observe
the effect of test plate diameter on calculated material properties. Detailed
test
results are attached in Appendix E for reference. Two r nterestin'~ results
were
observed with the I~> mm plates. The first concerned the shape of the torque
vs.
twist an'11e ~iraph. .=~s shown in Pi'~ure -I_, the 1''~ mm plates displayed a
rapid
increase in torque to what appeared to he a yieldin'a point, and then a march
slower
increase in torque over a large increase in strain to an ultimate failure
point. Upim
further inspection of the data and Figure ~12, it was observed that tile
linear slope of
the torque-twist an<~le graph (Torque Per Unit Twist) was almost identical for
both
the 9? and I?5 mm plates as shown in ~I~able 17. The results of Table 17
implied
that the. onset of failure was independent of plate diameter.
For the 9'' mm platen, complete f~ulure occurred at this point, whereas
ultimate failure was not observed with the I?~ mm plates until a much larger
strain
was imposed. Tuo potential hypotheses were developed to explain this
behaviour.
CA 02330431 2001-O1-08
1 ~0
First, it was hypothesized that the initial yield point represented the
failure of the
asphalt-aQ~reQate interface ulon~ the failure plane, while the additional
increase in
torque required to mail the asphalt complete°.ly with the 1='~ mm
plates was needed to
overcome the ag~reaate interlock. It is not. known at this time why the same
behaviour was not observed with the 92 mm test plates since the failure
suuface
imposed by both plates was the same shop=.~ (Figure ?~). However, the lamer
failure
surface of the 1?~ mm plate may have simply required additional torque to
overcome the a~J~~rc<~ate interlock.
CA 02330431 2001-O1-08
1~1
~s
~s
c~
~
5
9
;c 0
~s o
9
~ ,
t"~ c:~
p
t
,...
,..,
c~
c~
a. ~~, a ... :.
a.. ~
'' ~ f
\ ~ ~' v f
0
~
,: ~ N :W1 ~ ~' '~'
~Cn
r C~ r~
~ f/
~ ' s~
r N C CO
u} 7 i n
a a
a, a~ a~ _
H- a~ ~ c~'~ ca
~-- f-
E-
~
K e~ ; x
c
i ~ ~ .
J 9 ._
p o 0
k
~6'p ~ i
~
cPt .
O v
9t
96, O
cr',
~
o <:i
c9 -~'
t
t o _
'~
5'U
9U
s~ ~
~o
~
0 0
O O o O O O O
o fl o '~ o '~ o
O O O O o c~
N O CO Cfl V'
(wN) anblol
CA 02330431 2001-O1-08
1>?
Table 17: Comparison of Turque Per Unit Twist for 92n1m and l2~mm Plates
_ - __ --_
Torque Per Cnit 'W vist
', ~i (N~'n~lrad >
__ _ -
92 mm Test Plates ~ 12> mm Test Plates
j --_ -_ __
11100 1~1s
- ,~ ,
113? I1_»
I, ! 1318
Average ~ 11~~9 ' 11706
STDev I 1122 ___- _ n/a -
COV ' 9.5 nla
A second possible explanation of this behaviour could be the existence caf an
"a'lin~' gradient" tllrou~Thout the depth of the asphalt pavement. As
previously
mentioned, asphalt concrete undergoes sti'fenin~ with time due to oxidation,
rain
and sunlight. However, it is unlikely that the stiffcnin' is consistent
thrcvu<ahout the
lover. It is more likely that the pavement surface is the mast stiff, and that
decreasin« stiffne.5s is observed with imreasin'a deluh. Therefore, it is
possible that
the initial yield point observed with the I '~ mm plates represented the
failure of the
upper "crust", while the lar~_e amount of secondary strain was associated with
the
softer asphalt concrete underneath. 'This sorter i:rver wus likely not
penetrated w-ith
the ~~'_' mm plates.
.Althou~Th the TC?T values were independent of lead plate diameter. the
resulting shear m~.>dulus values were not. Since v°irtualiy the same
tordue was
required to initially yield for Tail) the asphalt surface woth boll test plate
dianneters,
the shear rnodulus rcsultin<- from the 1 ~~ rt~m plates wns much lower than
the ~W
mm test plates accr~rdin~T m Eduation 8 as shown in ~raUle 18. The aspl;alt
moclulus
CA 02330431 2001-O1-08
l~
was calculated both at the initial yield point and at the ultimate. failure.
As shcwvn.
the average modulus at yield was 8610 kPa according to 'Equation S with a CO~V
of
14.8°lc. while the modulus at failure was ?'~88 kPa due tc> the large
strain incurred.
The shear modulus at yield represented a 6~'~~ reduction compared to the O? mm
test plate at the same temperature, reflectintT tf~e fact that the radius of
the test plate
is raised to the third power in Equation 8.
Table 18: Results of lnSiSST Testing with 12~ mm Plates
Shear ~~~i Shear'I Shear
Shear ~ Pavement
I
Modulus ' Strain l~lodulus Strain ,l.en~P,
Test i
'~io
. at Yield at 7'ieldI
at Failure at Failure
I~ i
'
I (kPa) (''~ ) (kPa) 1l %r)
(
'
i __ _ .--().074 __ -_ 0.~'8
I7 I c~>>'?.-10-~ :'_>~)3.0~- 0 ~~
I - I=f ~p?
~
IS 77~8.~8 ().09~ . .
~
'SS
____
__.~',era~e BC~II -- O.Ot~ ~~88 0.'
~ --__
S~'Dev 127( 0.01 7.7 O.fll
~ ~ i
~__
CO~' 1.1.b 1 s.6 0.30
, _._-_-_~ __- _.____ _
_ _._ __
- __ -
x.2.6 Discussion of Field Test Results and Analytical Modelling
In theory. th~~ ~l~ordue Per Unit Twist (TUT) measure is a load her unit
displacement, nut a stress h~cr unit strain. 'Therefore, wf~ile ii is not
strictly a
"stiffness" or rrtodulus. it i.<<; directly proportional to the muduius.
Indeed. for the ~l'
mm test plates, the ultimate shear mudulus (in kPa1 was 1.7~ times the 1 UT
(in
N'~m/rad). For the 1'~~mm Mates, the ultimate shear mc~dulua (in kPa) was 0.7~
times the TL 'T (in :sl*m/rad).
CA 02330431 2001-O1-08
I ~-I
As previously mentioned. fundamental engineering properties should be
unique to the individual material, not dependent upcm boundary conditions. or
loading plate diameter in the cuwent case. The discrepancy between modulus
values calculated for the 9'? and 12s mm test plates usiny~ Equation 8
appeared to
indicate that further investi~lation and potential modification to Equation 8
is
required prior tc»ts use to provide asphalt tnodulus. This is beyond the scope
of the
current investigation, however is under analysis at Carleton University at
this time.
However, the TUT values appear independent of load plate diameter. Therefore,
the
TLT measure may be considered a fundamental en~~ineerin~ property of the
asph~ilt
miwand will be investigated further during future testing, with the
InSiSST'"'.
~.?.7 Comparison of Field and Laboratory Results
A final exercise of the verification stage was to cc>mpare the field stiffness
calculated from the InSiSSTT"' results to the laboratory salues observed by
Iahvr
( 199>). As shown in Table 16, the aver~y~~ shear modulus was ?08?8 hPa for
the
HL~s mix. Modulus values Irom the Zahw database arc attached in Appendix C.
The laboratory shear modulus values ranged from 930 kPa for a sand-asphalt mix
to
X700 kPa for an HL=f mix. The various Hl.s mixes yielded shear rnoduli
ran~in<.~
bcmveen ?>00 and ~~00 kF'a. Therefore. tic field shear moduli were
approximately
C~ times ~areater then those ohserved in the lahoratory dunng the 199>
investi~ratim.
This result was rr~ost likel.~ due to a<,~in_~ of the asphalt mix. .As
previously
mentioned, the HL~ tested was construmed in I99?, th_;refore was 8 years old.
The
labc»watorv testin;~ in 199 was completed on newly cc»npacted asphalt,
therefore, it
hud not been suhjected to environmental aonditionin~T and sut~sequent
stiflenin« of
the asphalt binder.
CA 02330431 2001-O1-08
CHAPTER 6: C~onclnsions and Recommendations
6.1 Review of Project Objectives
The phenomenon of permanent deformation orruttin~: in asphalt concrete
pavements is extremely complex and has beer: the focus of ~_:oncentrated
research
efforts in the past decade. Although the term ~ rutting" is ofte-n used
interchan;eabls
with permanent defoonation, it is only one of four manifestations observed in
North
America. In general, rertti~a,~ is characterized by channelized depressions
(troughs) that
run longitudinally in the wheelpuths. However, rutting is usaally the most
common
formof permanent deionnation analyzed. The Strate~~ic Hi~~hwa~ Research
Pro'Tram
~SIiRP) has identified that ruttin'; appears to he more closely related to
sherir stresses
and strains than normal or horizontal ones. Subsequently, it is important to
mvesty~ate
the shear properties of asphalt layers. As explained earlier, shear strength
of an asphalt
concrete mix is achieved through both a~~gre~aate particle contact to form a
tight, load-
hearing skeleton and the asploalt hinder that holds the particles in place. As
:z result, the
main ohjectives of this thesis ~,~ere as tollows:
1. To review the phenomenon of permanent deformation and identify its
main causes,
?. To study the main factors contiibuting to the rutting phenomenon and
determine the relatvonship bem-een these factors and the shear properties
of the asphalt mix, and
3. To desi~~n and Build an advanced test facility to provide reliable data
concernine the shear properties of the mix in the field.
CA 02330431 2001-O1-08
1 i6
These objectives were achieved and discussed throughout the thesis. This
Chapter presents the main conclusions and major findin's oV the research as
related to
the above mentioned objectives.
6.? Review of Permanent Deformation and Previous Investigations
Permanent deformation or rutting of asphalt roads has been found to progress
in
three sta~7es. The first st~ye beg°.ins with continued densification of
the asphalt lave:r
under traffic loading. During this stage, ruttin~~ is directly proportional to
traffic. The
second stage involves a stable shear period drain'.: which the: rate of
ruttin'a decreases
with increasin; traffic until a third and final stage when a c~ mdition of
plastic flay.
occurs and the rate of rutting main increases (vapid unstable shear failure).
It is the
onset of rapid shear failure that is of particular interest to tl;e objectives
of this
investigation. In depth review of available information on the subject showed
that the
ruttin~l phenomenon is very complex. One of the main conclusions of this atudy
v.cts
that at present. there is no single independent variable that ;:aptures or
predicts ru2tin~~
with a significant dct~ree of confidence. In addition, a single "deficiency'
in a «iven
property, such as excessive asphalt content, can nullify the over all duality
obtained
when other good properties. such as coarse a~_gre~~ate with lUOch tractured
faced count.
are available. Another import,mt observation was the fact rutting is caused by
various
combinations of pavement layer instability and heavy tract,-tires. Until
recently,
laboratory and field ~nvesti'~ations of the rutting phenumelton did noU
address the
fundamental property <rf a pa a-ement to resist ruttin'a: ,sJneup srrerc,yth.
SHRI' research
has acknowledged the impui~tance of shear properties. and the now Supenpave
design
CA 02330431 2001-O1-08
I~i
method may soon incorporate shear propenies as important inputs toward the
long-
term performance of mixes in the field. However, it should be noted that
Superpave
shear tests are completed in the laboratory on laboratory prepared specimens
or cores
retrieved from constructed pavements.
These findinGs led to the consideration of data and test results reported by
two
previous studies on the subject completed at Carleton University. The first
study was
the comprehensive and intensive laboratory-testing proerar.~ carried out by
Zahw to
identity the influence of the rriain factors of an asphalt mix on rutting
resistance. In this
thesis, the author imported the data and test results reported by Zahw ~md a
more
rigorous analysis was perforir~ed. This step produced a set of new
statistically based
equations relating the most irnporiant factors affecting the rutting,
phenomenon to the
shear properties of the mix as shown in the following section.
The second study completed by .Abclel Naby resulted in the construction of a
first Generation test device, known as the (~'arleton In-Situ Shear Stren~_th
Tcst
(CiSSSTj. The re°_sults of ,~bdel Maby provided uvo important
conclusions. First,
the CiSSST w~is able to differentiate between the shear properties of
different
mixes, as well as the cliffrrences within the same mix Enlaced in different
'~eotnetries
(curved sections vs. straiylht sections). Sc°cond, «reater variation
between replicate
specimen results was observed during laboratory testing than in-situ testin'.
6.3 Asphalt Min; Properties and Shear Characteristics
Consideration of the extensive data collected by' Zahw ( 199>) showed that a
number of mix characteristics contribute to the shear properties of the mix.
Two
CA 02330431 2001-O1-08
1,s
equations were developed to d~°scribe the shear modulus and shear
strength. These
equations incorporate traditional mix properties that should be recorded by
any a~:encs.
However, many of these variables have been combined in such a way that all
aspects of
mix design (binder properties, gradation, aggregate angularity. density,
compactive
effort and volumetric properties] are included without the introduction of
collinear
variables. Equations 4 and ~ are shown below:
f4)
-~6()-~.7'~f'~'I~+~~~vC(r-;-f-1='°(' -1-113>~':1IZD+1U67()"'t~'~11A
(R~ -- 0.83)
;5)
--(~()-0.9~ P1'R-~U~ C't'+(o':C,,;, -~~I()*ARD+?~j,:>y,'hl.<1
(R~ = 0.88)
where: G LkPa) = Shear Modulus (Stiffness) at ?~"C;
z tkPa) = Shear Stren<7th at ?~"C;
PVR (mm/Pa s) = Ratio of Penetration (mmJ to y'iscosity at ~~'C (Pa~ s);
CL = Coefficient of llniformitv (D(i0/D10);
C,,;" = Crushed Coarse A'T~~regate Present in Mix'' (Binary choice of 1 for
1''es
l)r ~ f()r i\lo);
ARD = Average Rote o1 Densif~icati~:)n (ratio of- tinal mix density to the
square
root of the number of blov~°s with Marshal: hammer); and
VMA = Voids in the Mineral Ag~Tregate ('%~)
aecording to the models developed, tloe asphalt binder properties (PVR)
represented ~'?~i~ of the shear modulus and =f-~~~ of the shear strength.
Ag«regat~
CA 02330431 2001-O1-08
1~9
gradation (CL) accounted for ~9% of the shear modulus and s>°ic of the
shear strength,
while coarse aggregate angulantv (Cb;~) accounted for ~s~7c of the shear
modulus ~~.nd
17~i'c of the shear strength. Volumetric propenies (:~RD and ~'MA) represented
8'i~
and 7 r'r of the shear modulus and 10'%'~ and ~°la of the shear
strength, respectively.
These findings are in Ueneral a~'reement as research completed under the LTS-
SHRP
( 1994).
6.4 Asphalt Shear Characteristics and Rutting
Mix shear stren~Tt1 and modulus were hi~~hly correlated to rutuny at vanous
stress levels as predicted by laboratory creep testing (Shell Metho d),
althou«h mix
stiffness (modulusl appeared to he a sliUhtl~ better indicator of mix
performance.
Rutting models based on shear modulus and ~,tren~lth v~ere also developed ~m
shown
below.
Creep ~ Laboratory
T Rutting Models
-
Stress ---- _- T _
Shear l~IcrdulusO' ~sC ' Shear Strength ta~
?sC
Level j
r
VlPa ~ (kl'al ~ (kPa)
l
_- ~.1 Rut = ?-~j=i=G-u.~a~( R~=(l.t;()) = I ~.'? ~'e-o ; n
I Rut ( R-=0.O ; )
Rut = ~~~II''~i-1.U37(IZ~=~I.()~)) = ~~1,L~~. ~-0.66 (R~-().~~')
RLIt
~, ~ Rut = 3Ii~6 Rut = 11791 ~' z-''s~ (R':=().67)
0 ~G~'.r'Ju (R'=0.73) I
. i
6.~ Modelling In-Situ Shear Properties
A review of previous modellin~~ eflort:> as well the de°velopo~cnt
of nm
constitutive equations provided the follown<_ conclusions:
CA 02330431 2001-O1-08
160
i The boundary conditions observed during field testing with the CiSSST
device and tine InSiSST'~'vere significantly different than those experienced
in the laboratory torsion testing. During the development of the CiSSST
device by Abdel Naby, Equation 6 was developed to calculate shear strength
of the mix from field torsion testing. While acceptable for that
investigaticm,
it has been subsequently determined that Equation 6 does not likely best
characterize mix shear stren~~th. Therefore, a new analysis procedure based
on the Reissner-Sagoci problem was developed by Bekheet et. al. 0'000) and
adopted for this investigation. This model (Equati~an 8j directly provides
shear modules haled on applied torque, and was subsequently verified for the
linear elastic condition both with finit.~ element modellin<~ and field
testing at
room temperature.
iil Additional verification and/or modification to Equation S rrrav be
completed
in future investigations for cases of nom-linear behaviour such as those
encountered at lover test speeds and 1-~i'her pavement temperatures.
7~he conclusions and findtn~rs obtained after achieving the first two
objectives
paved the way to the development of the new lnSiSS~h''~' as discussed below
6.6 Design, Development and Verification of the InSiSST~'~"r
The primary objective of this investiaaticvn was the de;~elopme-nt of an
advanced
in-situ shear stiffness teat (InSiSST'"j for asphalt concrete pavements. The
:,uccesstul
completion of this objective provided the following c~mclusoms:
CA 02330431 2001-O1-08
16I
i j The InSiSSTT~' device was designed and developed based on a sound theory
and thorou;h analysis of deficiencies observed with the CiSSST device and
additional desi._~n considerations. The result is a test facility that is
portable,
stable, and rua;~ed. The test reduires oily a sin~7le operator, no heavy
Iiftin'= or
complex set-up, and can be completed rapidly. The test results are accurate
and
are available instantly. .~11 of the individual systems operate under the same
power reduirements as provided by the central Generator. To date. the newly
built InSiSS'1' fvas been towed a total of 4500 Km at speeds as high as
l~'Okm/h.
Clearly, this is a testimony to the reliability and tou'ulness of the new
facility.
ii ) Field verification of the InSiSSTT'' has indicated that the device
accurately and
repeatedly measures shear properties of the asphalt mix. Additional
verification
testing is reduircd, however, to further explore the efrect of test plate
diameter
on measured shear properties.
G.7 Recomoendations for Future Modifications to INSISST1~~'
G.7.1 h:nvironmental Chamber
Asphalt concrete shear strcn~Tth and stiflne5s are hi'nly dependent un
temperature due to its viscoelastic nature. In its cun-ent term, tl~c
InSiSST'~r can
test only at the pavement temperature present in the field. Therefore, the
r.sults
obtained in the field must be normalized to a standard or reference
temperature
before comparison with other sections may be completed. A temperature mastc:;
curve may be used t -~ do this, however, the master curve nnust first be
developed.
The addition of an environmental chamber t;~ the InSiSS~h'-"' test frame will
alloy
CA 02330431 2001-O1-08
16?
the development of temperature master curves, as well us reduce the cure time
for
the epoxy by allowing the introduction of heat prior to tl~e test.
6.7.2 Hydraulics
For this concept exploration project, the use of hydraulics or pneumatics
instead of the electromechanical system fo:r applying to torque was
prohibitive:v
expensive. However, if the lnSiSSTTM is to be developed further by a
manufactur~in~ company for mainstream use, it is recommended that hydraulics
or
pneumatics be used fur three primary reasons. First, all mechanical systems
including the jacking svstenn. positioning system and load application system
may
be driven from a single pump, thus reducing- the. number of components (the
InSiSST'-"' uses 4 individual electric motors). Second, hydraulic systems may
~c
very quickly and ac:curatelv reversed. thus allowing dynamic fc~ading of the
pamment in addition to the cuwent static testing. Finally, hvdr,.mlic systems
are
generally more rugged and resistant to the elements than electromechanical
systems.
V hen assembled in larger quantities, hydraulic systems would likely hecc~me
much
more cost effective than for a sin'lle prototype.
1.7.3 Shear Vane
Altllou~Th the InSiSS~I-'" desi'Tn ~greatlv r~:duced the time required for
testin<u
over the CiSSST, the epoxy cure time remained as the overall governing factor.
7,he use of epoxies with more rabid cure times improved the test time
si~;nificantlv,
hovyever, an improved affixation method is recommended to remove the
dependency on epoxy altogether. One such method would be the use of a shear
vane, similar to those used in soil mechanics to test the shear properties o1~
clays in-
situ. For newly constructed pavements, the vane could he placed on the asphalt
CA 02330431 2001-O1-08
16~
surface behind the spreader and compacted into the pavement, thus allowing for
both current and future testing. For existing pavements, a saw could be used
to cut
the pavement surface and tlue vane could be inserted for testin~~. Standard
formulas
exist for vane testing, homver, additional analysis would need to be completed
t<,
ensure the accuracy of the tf°_st. Comparison with laboratory values
could assist that
eff ort.
6.8 Recommendations f'or Further 'I'tysting
6.8.1 Additional ~ eritication 1'estin~
The initial verification testing completed during this investigation was
sufficient to provide ~~eneral trends and relationships to Ensure that the
InSiSS~,' ~'
device was measuring the desired shear properties accurately and repeatedly.
I-fowever, significant additional testis; will be required to further observe
the
effects of temperature, directly compare to laboratory torsion tests and
explore the
phenomenon observed with the I'_'s mm test plates.
6.8.2 Long 'Term Performance
One of the primary goals of in-situ ;hear testin~~ will be to ultimately model
and predict rutting in the field. Extensive field testis' at numerous test
cites will Lie
required to provide the necessary data to der:elop such models clue to the
iar~~e
number of variables that corntribute to rutting (as presented in Chapter ?).
.At the time of this waiting. Carleton I'niversitv has partnered with the
Ontario
Ministry of Transportation (MTOj to complete field and laboratory shear
testing on
approximately ~ of the 16 test sections.
CA 02330431 2001-O1-08
164
6.8.3 Additional Testing for QC/QA Specification Development
As mentioned previously, there is a sTreat need for a simple penormance test
for the Superpave asphalt naix design system, largely for use as a qu~tlitv
control and
duality assurance (QC/QA) test. In-situ shear testing with the InSiSST'" could
potentially provide such testing as the device is well suited for rapid and
accurate
testing in the field us opposed to in the laboratory.
Clearly, the continuous tasting and improvements of this new testing lacilitv
should ultimately provide the I>avement industry with a reliable tool that is
desi~~necl:
i 1 ) To enhance new construction methods thrnu~h adeduate duality control,
and (?) To
improve the ability to predict long term performance of' asphalt surfaces and
pavements.
CA 02330431 2001-O1-08
16S
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<IMG>
CA 02330431 2001-O1-08
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CA 02330431 2001-O1-08
17~
Appendix Bl: Selected Variables for Mixes 1 throubh
Selected 'v'ariables
~'lix _ =~w~
Penetration- Rate of
Uesi'~n Viscosity CeIfICIent Crushed .
I~ensification
of Luifonn7itvC_'oarse ~'W.A
DcsiynationRatio at J (1)cnsity/sdrt(#
?~C
tDE'()/~101 I~laterial
(mm/P a hlLVS))
*s) --
m1-1 56.~>0 1~.8; 'i 1 . 0.''~1 I O.Ia-(a
m1-? ~O.?>0 ~ 1i.83 ~ 1 I 0.'_'>? ~ U.I(~0
m l-; >6.?~0 j 1 ~.8s 1 ~ 0.~_'~s 0.1
70
ml-=1 ~ >6.''>0 ~~' 1~.8~; 0.?~~ o.l~',0
' I
IT71-1 I lG.~>o ~I 11,5 i ).W 1 i
- -_ I 1 (
--_.
_-
~ ~ . -__
! n7?-1 >6.'_'s0 19 1 ~ 0.?6~ ! o. l
I, ~ I
m'?-_' ' >G.?7O I9 I ! o.?6s ().
I (~
I '
11T~'-~ >6.'_'~O 1() I ! 7
i o. 65 ~ 0.1!1
I
m?-4 ~ >6.'?>0 19 1 ! 0.?(6 ~ o, l
~ ~ 1
In'_'-~ 5(.?i0 19 0.?f~4 l, 0.1~~
1 I I
!
ms-I _ - _ _
~6.~~( -- 0.?> 1 0.145
~
) I .S ~ 0
m;-~ i6.?i0 I?.SS I 0 0.''~~ 0.1~~
~ I
,
ms-~ ~6.'_'>0 1_~.SS I 0 0._'~i 0.1~~8
I
m~--l ~6.?>0 1_s.S; (? 0.?i:~ 0.175
1776-~ ~6.'_'~0 1: 0.''s > 0.1 b
.SS 8
()
n7=1-1 _ _ o.''i1 _
, 10.714 ', _ 0.I~19
1:>.S; ', 1
m-1-~ ' 10.7I~1 I 1:>.fis I o.~'~~ 0.160
m-1- ~ I 10.714 I _~.SS 1 ' 0.~~4 I 0.17()
m-1-~l , 10.714 ~, 1:~.~s 1 ' 0.~>6 ' ().1
SO
m-~-; 10.714 I 1:~.~~ I l ' 0.~'~4 o.lS
9
n7~-1 j 1 U.7I4 19 -- 1 _ ~ ~>7 _
I 0. I
~ I
m~-~' I 10.714 ~~, l9 ~I I 0.~'>~) ~' ().101
m ~-s 10.714 ' I ~~ I 1 o..'ti ~ ( ). l
7 1
17TH-4 10.714 1~~ 1 o.~os ' o.lsl
m~-~ 10.714 i I 9 i 1 0.?(77 0.1 ~)
1
CA 02330431 2001-O1-08
176
Appendix B2: Selected Variables for Mires 6 through 1?
Selected
Variables
Min Penetration-. .A~,~~,.
Rrite of
, Crushed
~.oeff
Desi~_rn Viscosity . Dcnsification
DesignationRatio at of L.Iniful-mrty Coarse (Dc.nsitvlsdrt(~
'?>(~
~D60/D10) Material
(mm/Pa*s) blow))
-- -
m6-1 10.71=1 1>.83 ~ 0 j 0.'_'S~' 0.148
m6-~ 10.71-1 1.83 I~ 0 ', 0.'_'i 3 0.18
~
m(-,- 3 10.71 1 J.S 3 0 ~, 0.''J 3 I 0.168
~ ';
rnC-~ 10.714 1 x.83 0 0.?49 j 0.178
~,
m6-~ 10.714 1 x.53 () ' 0.?47 ~ 0.158
_ _ _ -
_
m ~-1 356.36=1 15.53 ii 1 0.X50 0.1-I~~a
i
m7-'? ' 386.36-~ 13.53 ' I ().?~1 0.1c,(?
nl7-3 356.364 1;.53 1 u.~>~ 0.170
m7-4 386. 364 I >.83 1 ().~'~4 'i 0.1 SO
'
m7-~ ' 386.364__ 1 ~.8 3 1 ! (>.~> 3 ~ U.15~)
m5 386.364 1 c~ ~ - _ --().?6~' _0.1 ~
I = 1 --~. ~ I .
m5-~ 386.364 19 ~ 1 ' 0.?6-~ ', 0.161
Ills- 3 356.364 I ~) ~ 1 0.?6~ '~, 0. I /
i I
m5--1 386.364 ~, 19 ~~ I U.?U6 ' 0.181
m8-~ 386.364___ 19 1 ().?6~ 0.191
' __ '
m9-1 ! 386.364 j ~.8 ~ () -- --. ()..,49 0.148
~
nl9-'? 386.364 ' 1.53 0 (1.261 0.t>8
~~
m9-3 386.364 1 >.83 0 0.?~3 0.168
m9-4 ~, 356.364 I 1 >.5 3 0 I ().?l? ~ ().178
I i
:11~)-~ 356. 364 1 ~.5 3 0 i ().~'W ().155
--
-
_ _
IllIO-1 10.71=1 ,,, ___~ ().?7~ ().I43
~ II
!
Ill l ()-'_'10.714 I 77 ~ 1 i 0,?76 I 0. I ~
' 3 i
m10-3 10.714 ~ ''~ ~ 1 0.?7~ ' 0.164
11110-4 10.714 '_'~ ~ I I 0 0
' ?73 ' 17=1
.
- . .
~ -- _
n111-1 10.714 11.83 1 0.30? U.1=1o
' ; I
~:~~L-_ ~~.~~-+ ~.~.o, , u.,no o.ICm
nlll-3 10.714 ~ U.b3 ~~ 1 I 0.307 U.170
m 1 1-4 10.714 ' L ~.8 3 1 I 0.307 0.180
m l l -s 10.714 1 x.53 I I ~~ 0.307 0.189
~ _-
ml?-1 0 -().~lo I ~).1'4~
10.714 h
' m 1?-' 10.714 I l () i 0.~'?0 ' ~:).
I 3=1
nl 1 ~- 10.714 1 1 0 I U.? I 9 ~:). I
3 44
Ill 1 '--110.714 1 1 i 0 (1. ~' 16 ' i ).
I ~-~
CA 02330431 2001-O1-08
177
Appendix C1: Shear and Rutting Properties for Mixes 1 through 5
Shear Propertiesf Mix Rutti ng Propertiesf Mix
o o
~
_
Mean Rut Mean Rut Mean Rut
D Av. ShearAv'~. Ay. Shear
siU Shear
e Depth Depth Depth
n strength Stalin Modulus
Designation (().1 (0. (0
MPa) ~ MPa) 6 MP;z)
(kPa) at Peak (kPa) _ .
__ __ _tmm> (mm? (n1m)
_ _
ml-1 X81 0.?04 ?846 0.6~? 1.>7 1.479
~~ ~
ml-~ 61? . O.? 1 ?876 0.(>46 I.?38 ~ 1. 356
I ~ ; i
ml-3 641 ~ O.:s=11 ''763 0.6?~l ().974 1.907 I
~ ~ ~ i
ml--1 X41 0.~ ~'70i 0.699 1.5?7 ~ ?.19 I
'
m 1-> 5? 1 ~ ci.l9 _ ''69~ _0.709 1.7~'_' x.107
4 (
_ _
117-1 691 1.).~1 ;356 ~.6~ _ 1.493
I ' 0.917 T
m~'-~' 706 ci.~0-1 ;50i 0.609 0.908 I 1.s7~
I I
m~'-; 719 ~ (!.?03 ;59~ (?.~74 0.8~~ 1.18 i
rrl~'--171'_' C~.''01 3>56 0.74 ~ ().93-~ 1.?81
i i ~~,
n~~-; 711 i o.~06 ;.~6; 0.75 I 1.o1 1.5
~ __
~
_
' 1113-14-1-1 C'.197 ?31 ~ 1.113 ~ ?.696 ~.~'87
I ' I i -I
lTl3-? 463 b~.186 ~-193 0.887 ''.518 ?.:~61
~ ' I ~
r1~ l-1 -fib? (l. I '~97 U.8-11 1.817 i 1.8b
~ I 87 ' I
nn--1 ~ 10 , ?6~ 1 U.764 1.82 ; '.6? I
I (.1 ~)' I
np 3-> 471 () 184 ~~s4 __U.84-1 '_'.03~ ~.5~; -J
I ~ ~
m-~-1 ;99 U.~I ?85? ~J.s83 0.99~ 1.;9>
! I
m4-'_' 6~s () ~1 '991 ~1.~77 0.9>? ' 1.x;1
', 1
n14-; 6~(i ~i.~ ;116 O.i7 (1.9~.~ 1.()9-~
I 1 i '~
I no4-4 7()9 ' 0.~' 3J? 3 !7.61 O.8 L9 I .034
' 17 ~
I _-I?n4-- 6-14 O.~s?_' ?7(i~ --!1.;8> ().886 l.~'98
~~
_ _ -
i m~- 801 I 0.? 36 ;471 t). >66 0.77'7 1.1
I i ~ I
m~-~ 8?4 0.x'3 ;691 0.~6 ~ 0.7=19 1.088
i
I, m~-3 8 j 0.??6 379? 0.~~7 0.7?8 ().98?
', il
nr-4 84i ~ 0.~?6 375> t).~~~1 0.743 . I.()1
t ~! I
mi-3 8?I O.~n7 361? 1).>64 0.76? 1.102
~ ' I
CA 02330431 2001-O1-08
178
Appendix C2: Shear and Rutting Properties for Mixes 6 through 12
Shear Pro ~erties of Mir Ruttin~T f'ro enies of Mix
Mix Mean Rut ~ tMean Rut Wean Rut
Design ''''~ ~-;~ Shear Av~_. Shear Av~. Shear Depth Depth Depth
Strength Strain Modulus
Designation (0.1 MPa) (0.3 MPa) (0.6 MPa)
( hPa) at Peak (kPa)
_ (mm) _ (mmi Imm)
m6-1 503 0.~1? ?438 0.864 ~, 1.175 ' '.151
a
m6-~ ~ 575 IJ.? 1 ?47? 0.763 ~~ 1.171 ~'. 34?
m6-~ ' S4? 0.~' 16 ?56; 0.7?7 1i I .134 i x.573
m6-4 ~I 539 0.~ I 5 ' ?494 ~ 0.717 ; 1.108 ''.?6 3 I
m6-5 ~ 818 _0.'_' 1 I ?484 ~ _U.815 I _ 1.131 F 1.91
~~7_ I I ?41 r 0. I 56 ~ 1548 j 0.781 ~ l .70?
-m7-? ?s4 I I;).15 1690 ! 0.761 1.387 j
not
m7-3 I ?69 11.15 18'_'3 0.7?4 1.648
j m7--1 !~ X38 C!. I-14 1643 0.75(i 1.67 ~ !I a~ ailahle
! _ m7-5 ??7 ~ (:x.15 3 _ 1475 I 0.794 ' 1.831 I !
m8-1 I 3~2 (,x.148 ? 169 ().759 ' 1.07? j
m8-? j 340 0.15 3 ', ''~~8 0.741 i 1.087
not
m8-3 351 . 0.15> ~'?64 0.7? 1.06
,~ uvailahle j
m8-4 ,7? ' 0.156 X389 (1.69? I 1.'_'S8
I m8-5 367 0.157 X340 _().708 j _ 1.711 '
l,
m9-1 T _'15 I 0.1 s8 ~I I 380 1.~75~ ''.07s
m9-'_' ~'i 231 I i).16 1500 C .??6 j 1.909 ~, ',
I m9- 3 X40 ' O.14 3 , 1681 I .0 34 ?.1 14 ; not
n,9-~ ''i< I (I 1-1; ~ 17~;; I 199 1.97 I malilable
m9-> ' ' 17 0.159 I l .389 I l .988
398
', n~(o-i7~~ ~ 0:33 31~~ e).~7~ _ 0.88 l.;~s__
i
m10-? 737 'i (1.'_'3''3191 ().56? 0.864 1.14
~
j n~1()-3719 (1.~'?9 3136 0.57'' (1.93 1 ;55
~
j m1()-4 709 ().~'36 , ~ 0.661 0.9511.431
t 3054 ~
m11-1 418 ().~'~9 1837 1.'1 ~.4''I I ~.448
i ~-_ ; ,
, 4j~ t).~4 ' 188? 0.985 ~.?14 J x.4=11
I null-~ '
',
rr:l l-3 468 0 X46 ', I9ls ().9~6 x.074 x.681
!,
m I 1-4 486 0.? ~ 1947 ().9 1.995 ' ,.684
I I 5
~
m I I 469 _'44 1934 0.95? ~.?4~' ?.661
-5 0 ' _
I m 1 197 _ 946 _ _
'- I 0.'?09 1. 5?6
i
m I ~'_? ?38 !, U.~? 1 IC)1 1. 396 not not
I
I m1'_'-3~''~ I (1.'1l 1058 1.;99 available availah'~e
I '
m1~' 4 181 I 0.L97 931 1.575 I i
~, ~
CA 02330431 2001-O1-08
179
Appendix D: CiSSST Test Results
I Maximum ~ I Lpper Lower
Tcst Plate ! Failure
Torque Failure Failure
Test No. Temperature ~ _~-~ Diameter Depth i
-- ~ Diameter Diameter
(de~~. C) i
(lbf~in) N~'m ~, (rr_~) (n1) t,n) L (mj
- - -
C' ?9 331 > ;74.4 0.09? I 0.01 ~ 0.1 ~ 0.06
i
-_. _~ -
C ~9 360(t 406.7-~ 0.0''? ~ 0.01 ~ 0. ( 03 0.0~~,
I ~
C4 ' ?9 ~I 4>0() ~,I ~0~.4s 0.0~~., ,- (.).O 1._' ~I 0.10> ~ O.U,_
_ _
i--
C~ ?9 ~60i ) ~- s 19.73 ~ 0.092 0.01 I 0.11 0.0 7
('6 ?9 ', 460(i ~ ~ 19.73 ~II 0.()~)? (>.0I 0.10; ().07
<IMG>
CA 02330431 2001-O1-08
Isl
InSiSST Software
TEST 11
Test Speed (rpm)180C> Pavement 35
Temp (deq.
C)
Recording (s) 1 Test Plate 92
Diameter
(mm)
Calibration 23929 Date: Aug-04
First Reading -85 Time 18:' 0
RAW TEST DATA
Torque Cell Angle TorqueTorque TorqueShear
Output (radians) (Ib.ft)(Ib.in) (N.m.)Modulus
(kPa)
-42 0.0000 ? .1 12.7 1.4
27 0.0233 2.8 33.2 3.8 310.61
981 0.0465 5 1.0 6? 2.5 69.2 2864.80
7258 0.0698 81.4 2177.1 246.0 6788.08
14968 0.0931 3'1.9 446.'3.1 501.3 10436.56
20045 0.1163 497.4 5968.3 674.3 11165.24
7832 0.1396 ' 95.62347.3 265.2 3659.35
6617 0.1629 ? 65.61987.1 224.5 2655.22
6447 0.1861 ? 61 193E3.7 21 2264.39
.4 E3.8
__- _ _ _
Raw
Graph Ii
-
Torque
y.[ICI ~... ._. .. .___ _ .. .._...... .._ __.__.. ...........
_.._._.. _ _.
_-I_I O ~ -
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_
AngularDisplacement
(rad)
Processed Graph -Torque
CICO C - I I
-~- Torque _ _~~-
--. ,o~ ~ i
i, Z au'i I~ Linear (Torque) --_.__ - _-
=p0 C -___..____ - _ ~_
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CA 02330431 2001-O1-08
1 S ~'
InSiSST Software
TEST 12
Test Speed1800 Pavement 35
(rpm) Temp (deg.
C;
Recording 0.75 Test PlateDiameter 92
(s) (mm
Calibration23971 Date: Aug-04
First Reading-33 T ime 18:10
RAW TEST
DATA
Shear
Torque Angle Torque Torque Torque Modulus
Cell
Output (radians)(Ib.ft) (Ib.in) (N.m.) (kPa)
-27 0 0.1 1.8 0.2
0 0.0175 0.8 9.8 1.1 122.07
167 0.0349 4.9 59.3 6.7 369.91
1471 0.0524 37.2 446.1 50.4 1854.48
4230 0.0698 105.4 1264.4 142.9 3942.32
9646 0.0873 239.2 2870.8 324.4 7160.
7 2
16755 0.1047 414.9 4979.3 562.6 10350.08
21929 0.1222 542.8 6513.9 736.0 11605.66
23612 0.1396 584.4 7013.1 792.4 10933.15
8123 0.1571 201.6 2419.1 273.3 3352.21
7471 0.1745 185.5 2225.7 251.5 2775.80
I 9C10.0
U -__ -__._. ._----___ -_.
i
J
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.
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CI
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o~
Angular
Displacement
(rac
d
ull ~ _____-_ -r- ' ~ t Ir 1 ~-_ _._._____-__
';
l1
I
--~_Iflr~ if ~.~.uE_f~n~1 J -
f- ---_.. ~ -_ -_- __._. _
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r~ U 02 CC4 0 ~6 0 CI8 0 1 O J G~ C a s
Angular Displacement (rad)
CA 02330431 2001-O1-08
InSiSST Software
TEST 13
Test Speed 1800 Pavement C:) 32
Temp
(deg.
Recording 1 Test Diameterm) 92
Plate (m
Calibration 23977 Date: Aug-04
First Reading-32 Time 18:20
RAW TEST DATA
Torque Cell Angle Torque Torque Torque Shear
Output (radians)(Ib.ft) (Ib.in) (N.m.) Modulus
(kPa)
-28 0 0.1 1.2 0.1
0 0.0233 0.8 9.5 1.1 88. 7
6
99 0.0465 3.2 38.8 4.4 181.68
1095 0.0698 27. B 334.2 37.8 1042.00
5374 0.0931 133.6 1603.1 181.1 3748.72
15256 0.1163 377.8 4533.5 512.2 8481.01
23636 0.1396 584.9 7018.5 793.0 10941.51
8835 0.1629 219.1 2629.4 297.1 3513.54
7924 0.1861 196.6 2359.3 266.6 2758.49
7364 0.2094 182.8 2193.2 247.8 2279.40
FFd1 fl ~'1~7 1 F,d 1 q7R ~~'~ 1 R~r1
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--
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0 CI 0~' CI CI:1 I ) U'~ LI Ua 0 1 i I " ~' J 1 :1 O '1 r, IJ 1 _~ I
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CA 02330431 2001-O1-08
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CA 02330431 2001-O1-08
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CA 02330431 2001-O1-08
Is~
InSiSST Software
TEST: BF1 - BOND FAILURE
Test Speed 1800 Pavement 28
(rpm) Temp (deg.
C)
Recording 1 Test Plate ter (mm) 92
~s) Diame
Calibration 23954 Cate: Jul-31
First Reading -71 Time
RAW TEST DATA
Torque Cell Torque (Ib.ft)Torque (Ib.in)Torque Modulusa(kPa)
Output (N.m.)
(radians)
-45 0.0000 0.6 7.7 0.9
919 C.0233 24.4 293.4 33.1 2744.18
5490 0.0465 137.3 1648.0 186.2 7707.27
12676 0.0698 314.8 3777.5 426.8 1 1 7 77.80
19696 0.0931 488.1 5857.8 661.8 13E~98.04
24990 0.1163 618.9 7426.6 839.1 13893.32
26303 0.13 651.3 7815.7 883.1 12184.35
96
26753 0.1 662.4 7949.1 898.1 1 OE~21.92
E~29
27075 0.1861 670.4 8044.5 908.9 9405.75
27356 0.2094 677.3 8127.8 918.3 8447.21
27566 0.2 682.5 8190.0 925.3 7660.70
327
27756 0.2F>60687.2 8246.3 931.7 7012.15
-77 0.2792 _ -0.1 _ -1.8 -0.2 -'1.39
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._ _
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700 11
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Angular Displacement [rad) j
CA 02330431 2001-O1-08
1S?
InSiSST Software
TEST: BF2 - BOND FAILURE
Test 1800 Pavement 28
Speed Temp
(rpm) (deg.
C)
Recording 1 Test Plate 92
(s) Diameter
(rnm)
Calibration 23930 Date: ,!u1-31
First -75 Time
Reading
RAW
TEST
DATA
Angle Torque Shear Modulus
Torque (radians) Torque (Ib.in) Torque (N.m.)(kPa)
Cell (Ib.ft)
Output
-58 0.0000 0.4 5.0 0.6
24 0.0233 2.4 29.4 3.3 274.65
5471 0.0465 137.1 1644.9 185.8 7692.88
14626 0.0698 363.3 4360.1 492.6 13594.55
22086 0.0931 547.7 6572.7 742.6 15369.81
25029 0. "~ 163 620.5 7445.6 841.2 13928.75
24918 0.1396 617.7 7412.6 837.5 1 1555.9
7
448 0.1629 12.9 155.1 17.5 207.27
Haw Grap h -Torque
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Ins _____- ____
CA 02330431 2001-O1-08
I~8
TEST: BF3 - BOND FAILURE
Test 1800 Pavement 28
Speed Temp
(rpm) (deg.
C)
Recording 1 Test Plateameter 92
(s) Di (mm)
Calibration 2~~953 Date: Jul-31
First -67 Time
Reading
RAW
TEST
DATA
Torque Angle Torque (Ib.ft)Torque Torque Shear
Cell di in) (N.m.) Modulus
Output (1b (kPa)
( ans) .
ra
-57 0.0000 0.2 3.0 0.3
383 0.0233 1 1.1 133.4 15.1 1 247.61
2822 0.0465 71.4 856.3 96.7 4004.84
10862 0.0698 269.9 3239.4 366.0 1 C) 100.13
34 0.()9312.5 29.9 3.4 70.01
flaw Graph -
Torque
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CA 02330431 2001-O1-08
1s9
InSiSST Software
TEST: BF4 - BOND FAILURE
Test Speed (rpm) 1800 Pavement 28
Ter~p
(deg.
C)
Recording (s) 1 Test Plateameter 92
Di (mm)
Caiibration 23953 Date: Jul-31
First Reading -50 Time
RAW TEST DATA
Torque Cell Outputl Torque (Ib.ft)~~bqn~ Torque Modu us
(N.m.) (kPa)
(radia
ns)
-54 0.0000 -0.1 -1.2 -0.1
59 0.0233 2.7 32.3 3.7 302.41
642 0.0465 17.1 205.3 23.2 95'x.96
4373 0.0698 109.3 1311.9 148.2 4090.45
13615 0.0931 337.8 4053.2 458.0 94 7 8.18
-53 0.1 " -0.1 -0.9 -0.1 -1 .66
63
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CA 02330431 2001-O1-08
1y0
InSiSST Software
TEST: BF5 - BOND FAILURE
Test Speed (rpm) 1800 Pavement Te~np (deg. C) 28
Recording (s) 1 Test Plate Diameter (mm) 92
Calibration 23956 Date: Jul-31
First Reading -60 Time
RAW TEST DATA
a
Torque Cell (rad'ans)Torque (Ib.ft)~ bqn~ Torque (N.m.)Moduh s
Output (kPa)
-52 0.0000 0.2 2.4 0.3
0 0.0233 1.5 17.8 2.0 16E~.38
848 0.0465 22.4 269.2 30.4 1258.9?
5646 0.0698 141.0 1691.6 191.1 5274.13
13889 0.0931 344.6 4135.2 467.2 9669.93
-52 0.1163 0.2 2.4 0.3 4.44
Raw Graph - Torque
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f'rncesseil Graph - To«tue
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Angular Displacement (rad)
CA 02330431 2001-O1-08
191
InSiSST Software
TEST: BF6 - BOND FAILURE
Test 1800 Pavement 28
Speed Ten-p
(rpm) (deg.
C)
Recording 1 Test Platedieter (mm)92
(s) Dia
Calibration 23931 Date: Jul-31
First -69 Time
Reading
RAW
TEST
DATA
Shear
Torque i Torque (Ib.ft)~ bq~~ Torque (N.m.)Modulus
Cell
Output
(rad g (kPa)
ns)
-58 0.0000 0.3 3.3 U.4
574 0.0233 15.9 190.7 21.6 1784.19
5210 0.0465 130.5 1566.0 176.9 7324.05
13164 0.0698 327.1 3925.6 443.5 12239.59
21850 0.0931 541.9 6502.3 734.7 15205.14
26928 0.1 163 667.4 8008.7 904.9 1498a?,?
9
27003 0.1396 669.2 8030.9 907.4 12519.84
27491 0.1629 681.3 8175.7 923.7 10924.73
-72 0.1861 -0.1 -0.9 -0.1 -1.04
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(rad)
Processed Graph - l o«iue
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Angular Displacement (rad)
In
CA 02330431 2001-O1-08
19~
TEST: BF7 - BOND FAILURE
Test Speed (rpm) 1800 Pavement 28
Temp
(deg.
C)
Recording (sj 1 Test 92
Plate
Diameter
(mm)
Calibration 23924 C: ate: Jul-31
First Reading -82 Time
RAW TEST DATA
Shear
Torque Cell Output Torque (Ib.ft)~~bqn? Torque (N.m.)Modules
(radians) (kPa)
-67 0.0000 0.4 4.4 0.5
58 0.0;?33 3.5 41.5 4,7 388.37
1608 0.0465 41.8 501.2 56.6 2344.11
9654 0.0698 240.6 2887.5 326.2 9002.8'.6
18773 0.0~?31 466.0 5591.9 631.8 13076.:38
25221 0.1163 625.4 7504.3 847.9 14038.:8
27641 0.1396 685.2 8222.0 929.0 12817.70
28236 0.1629 699.9 8398.4 948.9 11222.40
28465 0.1861 705.5 8466.4 956.6 9899.01
0 0.2094 2.0 24.3 2.7 25.28
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Displacement
{rad}
Processed Graph - roaque
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Angular Displacement (rad)
Raw Graph-Torque
CA 02330431 2001-O1-08
1~>>
InSiSST Software
TEST: BF8 - BOND FAILURE
Test Speed (rpm)1800 Pavement ~~deg. 28
Temp C)
Recording (s) 1 Test Plate >ver 92
DiamE (mm)
Calibration 23952 Drite: Jul-31
First Reading -52 Time
RAW TEST DATA
Shear
l
Torque Cell Output Torque ~~bqn~ Torque Modulus
(Ib.ft) (N.m.)
(radia
ns)
(kPa)
-35 0.0000 0.4 5.0 0.6
0 0.0233 1.3 15.4 1.7 144.26
3486 0.04135 87.4 1049.4 118.6 4907.78
11893 0.0698 295.2 3542.9 400.3 11046.44
22687 0.0931 562.0 6744.4 762.0 15771.34
27383 0.1 163 678.1 8137.2 919.4 15222.
7 2
28260 0.1396 699.8 8397.4 948.8 13091.11
-69 0.1629 -0.4 -5.0 -0.6 -6.74
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Angular Displacement (rad)
CA 02330431 2001-O1-08
Design, Development and Verification of an Advanced In-Situ Shear Strength
Test Facility for Asphalt l.oncrete Pavements
~iCHItP-IDEA Project Ss
Abd El Halim Omar Abd EI Halim, Carlc.ton University, Ottawa, Canada
Stephen 1~. Goodman, Canadian Strategic Highway Res~,arch Pro~~rant, Ottawa,
Canada v
Wael Bekheet, Carleton University, Ottawa, Canada'
l~asaer Hassan. Carleton University, Ottawa. Canada
IDEA CONCEPT AND PRODUCT
The StrateyTic Highway Research I'ro'~r~am (SHRP) recotmised that shear
properties are an
important indicator to predict ruttin~~ potential of hot-mia~ asphalt concrete
{I-1MAC) pavements.
however, current methods of measuring such properties have been linuited to
time consumit~;"
expensive or unrepresentative laboratory analysis. The concept of measurin<~r
the in-situ shear
properties of an asphalt concrete pavement layer by applying a torque directly
to the surface has
been initiated at Carleton University in Ottawa. Canada. 'This concept allows
relatively quick
measurement of in-situ shear properties with a rninimun-. amount of damage
incurred by the
pavement surface.
Under the current NCHRP 1DI:A project, an advanced ire-situ device has been
developed and
fabricated at Carleton University. Know ~n as the In-Situ Shear
StrengtliiStiffness Test
{lnSiSST'~'~), the device provides the rapid and accurate rncasurement of in-
situ shear properties
of an asphalt concrete layer. Data collected with the InSiSSTT''~ will provide
input for more
accurate measurement and performance modelling of in-service pavemmnt
performance - the
fundamental basis of the SHRI' Supetpave system.
PROJECT UPD.~'CE
InSiSST' "' Design
The completed InSiSSTT"r device is presented in Figure 1. .As shown, the
components are
mounted to a small trailer to provide exceptional portability. The InSiSSTT~'
utilises an electric
motor and Gearbox to produce the torque required during the test. The
motor.%gearbox
combination is mounted vertically on a steel platform that is attached to a
positioning system
incorporating two sets of worm-screw slides working in tandem, also referred
to as an ''X-Y
table." The top set of slides allows positioning of the platform in the
transverse direction (with
respect to the trailer orientation). The transverse slides are in turn mounted
to a second set of
slides allowing positioning in the longitudinal direction. The entire
positioning system is
~ Professor, Department of Civil and Environmental Enoineerina. T:le: (613)
X20-~ ; 89, Fax: ('613) X20-39~ 1,
Email: ahalimoccs.carleton.ca
C-SHRP Pro=ram Manager. Tele: (613) 736-130, Fax: (613) 736-1396, Email
~godman~a?cshrp.or~z
' 1'h.D. Candidate. Tele: (613) >20-74?l-1961, Email
w~bekheet~iccs.carleton.ca
visiting Professor. Department of Civil and Environmental En~ine~rin~. Tele:
(61 ~) X20-2600 Ext. 862, Fax:
(til3j ~?0-3y~1. Email: vhassan~n~ccs carl~ton.ca
CA 02330431 2001-O1-08
mounted to a box-tube frame occulayin'r the space between the tow bar and the
axle of the trailer.
The test ti-ame is attached to the trailer ti~ame via four screw jacks, on~~
at each corner c~f the test
ii-ame. During tr~insportation of the InSiSS'hr", the jacla are retracted to
hold the frame in the
air to prevent damage. Once driven into position, the jacla are extenc7:d to
lower the test frantc
to the 'round and then continue cxtendin', until the wei~~l~t ofthe trail.;r
is supported solely Iv
the Pest frame. Control of the jacla and positionin<~ slides is provided by
commercially <m aii.ablc
electric motor controls. Control of the actual test procedure is provided by a
laptop computer.
Instantaneous torque and angle of twist uneasurcrnents arc collected oo the
computer during the
test procedure. A large plastic storage box is mounted n: the front of uhc
trailer to house the
electronic components. Finally. a gener~atur is mounted to the rear of the
trailer to provide
elcctricitl. for the InSiSSM'T"'.
Figure 1: The In-Situ Shear Strength Test (InSiSSTTnI) at C:arleton University
Calculation of ln-Situ Shears Properties
As mentioned, the hlSiSSTT"' applies a rotational load (torque) directly to
the surface of an
asphalt pavement. The tordue is transferred to the asphalt through a circular
steel loading plate.
epoxieci to the pavement surface as shown in Figure 2. 'he asphalt is loaded
to failure and the
induced failure surface is semi-spherical in shape.
CA 02330431 2001-O1-08
Figure 2: Method of Load Application for InSiSSTT"' (Side View)
The loading case used by the lnSiSSTTM device is very similar to that
investigated by Reissncr
and Sa'~oci in the early 1940's. With a circular loading plate affixed to a
linear elastic, isotropic
half space, the shear modulus of the half space (asphalt concrete) may be
deterwnined using the
following relationship:
T-l6Grh~l;
J
V~here: T = Applied tordue
G = Shear modules of the material
a = Radius of the loadin~~ plate
th = Angular displacement of the loading plate (radians )
The Reissner-Sagoci relationship above was also used to develop and verify a
finite element
model of the problem assuming linear elastic conditiuns. In future modellin;a
efforts, the
material properties will be altered to linear and non-linear visccrelastic
properties, more
representative of asphalt concrete, to obwem~c the affect ~.~n the resultiry~
stresses and strains.
Concept t'erificatio~t and Rug~~eduess Vesting
Initial verification testin~T was first completed at Carleton University in
July ?000 to observe the
results of the InSiSSTT'~. Subseduentlv, field tests have been completed in
the City of Ottawa
and in the Towns of Bancroft and Petawawa. Test results are very repeatable,
with coefficients
of variation as low as 1.S°ro. Complete test results will he presented
in the final report, which
will be prepared by the end of the year.
CA 02330431 2001-O1-08
PRODUCT PAYOFF POTENTIAL
The successful measurement of in-situ asphalt shear properties and the:
development of a
mainstream test facility will yield significant and immediate benefits t~~ the
three prirnar-~- areas
of pavement engineering. The first area is d~.sign. Utilization of the
IoSiSS~°r"r in conjunction
w°ith laboratory testing would be a powerful combinaticm for analmin~.~
the potential of proposed
mix desi'uns. The second area is yuulitv cc>ntrul. 'newly constructed asphalt
pavements could be
tested to verify acceptable construction practices throu~_h the measurement
and comparison of in-
situ strew<~th parameters with code requirements. The tiaal area is lonr~~-ter-
nr paverru~rrt
p~rfomruutcE~ (L7'PP~. Monitoring of field shear strength of pavements with
time would allow
periodic updating of performance models to more accurazely predict future
pavement
performance. This, in turn, would allo«~ for more efficient allocation <>f
limited rehabilitation
funds and also help determine the effect of~real world conditions, such as
environmental factors.
on pavement performance.
PRODUCT TRANSFER
The potential for a simple yet extremely effective in-situ test device has
already drawn
significant interest from both government and private inciustrv. In addition
to IDEA Program
funding. the Ontario Ministry of Transportation (MTO1 ~~nd Regional
Municipality of Ottawa-
C'arleton have conmnitted financial and in-hind support for this
investigation. Furthermore, a
number of independent consultants have also expressed interest in the
potential of the InSiSST.
Tu date, demonstrations of the h~SiSSTT"' have been completed for the Ontario
Ministry of
Transportation, the ~1CHRP IDEA Program and at the ~'~' International IZIl_EM
Conference on
Reflective C.'rackin;~ in Pavements. Once the current investigation is
completed, consultants and
contractors will be ~uiven instruction on h~w~ to use the InSiSSTr"'.
CA 02330431 2001-O1-08
Design, Development and Verification of an Advanced In-Situ Shear
Strength Test Facility for Asphalt Concrete Pavements
~C'HRP-IDE:~ Project ~~'
Abd EL Halim Omar Abd E1 Halim, Carleton University, Ottawa. Ontario, Canada?
IDE:~ CONCEPT :1ND PRODUCT
The Strategic I-Ii'~hway Research Program (SHRP) has reco~~nised shear
strength as an
important indicator to predict ruttin~~ potential of asphalt concret~°
pavements (ACP's1.
However, current methods of measuring the shear stren~Tth of an usphait mix
have been
limited to time consumin<~, expensive or unrepresemative laborat,~rv analysis.
Tl~
concept of measuring the in-.sitcr she~rr strejr~th oi~ «u asphalt con:vrete
pavement layer by
applying a tordue directly to the surtnce has been inAtiated at Carleton
University in
Ottawa. Canada. This concept allows relatively qujck measurement of in-situ
shear
su~en~'th with a minimum of damage incurred by the pavement surface. ,~ basic.
first
'generation prototype In-Situ Shear 'Test Facility (ISSTF) has yielc.!ed
promisiny~ results
relating the maximum applied torque to the shear strenygth of ~m .'MCP layer.
Wore
importantly, the ISSTF has determined that shear stren'=ths achie~.ed in the
field are very
different than those realized in the laboratory. These findings present strop
yg evidence .
that the development of such a test device is required for more accurate
measurement and
parfortnance modelling of in-service pavement performance - thr~ fundamental
basis of
the; SHRP Superpave progr~rm.
PLANNED INVESTIGATIO'_~1
The first-yreneration ISSTF consisted of an electric motor mounted to a cart-
like chassis.
A series of gears and driveshafts were used to transmit rotational force to a
circular
loading plate epoxied to the pavement surface. A torque cell and datalo~T~ler
were used to
measure torque while angle of twist at failure was measured with ;~
protractor. Two test
speeds were available. To prevent rotation of the test device duriry~ testing.
six steel
spikes were attached to the device and driven into the pavement. The tmt-ready
ISSTF
apparatus is shown in Figure 1. Test results achievcv with the device yielded
in-situ
shear strengths of up to 300°% greater than those achieved in paral lel
laboratory testing.
Although the basic prototype revealed significant differences between in-situ
and
Laboratory shear strength of asphalt pavements, a number of deficiencies were
noted
during initial investigations. In g=eneral, the cart-based test device was
cumbersome to
set-up and operate, limited in capability and required much effort and time to
perform
tests. Still, the potential for an in-situ facility to test and model pavement
performance
indicators wan-anted further consideration. Therefore, a comprehc,nsive three-
stage
~ This IDEA Project has not yet commenced An 18-month investigation has been
planned.
' Professor, Department of Civil and Environmental Engineering. Tele: (6l3)
5?0-?600 Ext. 5789, Fax:
(61s) S~p_~9~1
CA 02330431 2001-O1-08
investigation has been designed to continue the development of this innovative
test
device.
1'i'~ur~ l: First (uencratic.m ISSS'hI~ Prototype pest t~c~nfi'7uration
Sta~ac 1 will focus on three main activities. The first concerns imlorovcment
of evistin'~
theoretical models relating the torque applied by the test device to the shear
strength of
the ACP to reflect the effect of in-service confinin« pressure. The current
theory is most
applicable to unbound cylindrical specimens tested in the labor-at~,w.
Simulation of field
boundary conditions and loading will be accomplished usiy~ the finite element
technique.
An extremely desirable objective of this investigation is to correlate in-situ
shear strength
of asphalt pavements with~perfonnance indicators such as rutting and
crackin~a.
Therefore, results of the finite element analyses will be coupled with
traditional
revTression analysis to construct preliminary performance models relating
shear strength
and pavement performance. The resulting models will be subsequently verified
and
calibrated using field and laboratory test results obtained in Stay_c ~ of the
project.
The third activity completed in Staye 1 will concern the desiL~n of a second-
generation
test facility based on a critical analysis of the deficiencies obsen~ed with
the original
prototype. Conceptual models include a trailer-mou~ntcd or a vehicle mounted
system.
Both systems would allow the device to be more easily transported to test
sites and
reduce the number of required operators. The trailer could be sufficiently
loaded so that it
does not move duriniT the test procedure. The ''vehicle-mounted" system would
be similar
to a corin~~ rid,, and would swin~a or slide into position from the ba~:l: of
a pick-up n-ucl; or
van. The weight of the transport vehicle would be utilized to stabilize the
device. Both
CA 02330431 2001-O1-08
systems would eliminate the necessity for affixing the device to the pavement,
which in
turn would eliminate the extra operator effort and pavement damage.
To improve control and flexibility of the test procedure, the secon;l-
generation prototype
will utilize a computerized tordue cell and rotational extensometer
combination to apply a
number of different strains (i.e an~~l~ of twist) and or stress (i.e. torduc)
rates to the
asphalt. The computer will also record the instantaneous applied t~.n. lue and
angle of twist
during the test and produce a corresponding seraph. The dimensions of the
failed
specimen will be input and the maximum shear strength calculatco and displayed
instantly. Other notable conditions such as asphalt t::mperature test
locartion, sample
number, etc. could be input for future reference and modelling purposes.
Additional
improvement to the basic prototype will be accomplished through the use of
stron;~er
materials and a more powerful motor to allow testin;-~ at lower ternpcratur~s
(i.e. stiffer
pavements ).
Stage' will focus on the fabrication of the second-~Teneration prototype test
device.
Once constructed, a regime of "shakedown" tcstiu~; will be compl~tcd to
calibrate the test
instruments as well as note any deficiencies in construction. Final
adjustments will then
be completed to prepare the device fc~r the final stag: of the rovesr igation.
The third and final stage of this investigation concerns the verification of
the test device
and calibration of the analytical models constructed in Stage I . These
objectives will be
met through a series of field test regimes designed to analyse a number of
different
pavements displaying varying de~rrces of resistance to rutting ~rnd cracking.
The second-
<aeneration test facility will be utilised to measure in-situ shear strcr~'~th
values, while core
samples will also be extractccf for laboratory testin~~
.Analysis of the results will take on three priu~ary forms. 1'he first
analysis phase will
conGnn that the field test is repeatable and consistent. Based on results with
the first
ISSTF, no problems are anticipated in this regard_ !'next, the field and
laboratory results
will be correlated to determine if a common factor, or "multiplier", exists
between thenu.
The sensitivity of in-situ shear strength to critical factors such as unix
desi<~n (especially
gradation andJaggre'~ate type), traffic level and temt>eratnre will also be
analysed.
Finally, analysis will correlate the measured shear s'crcngth to in-~~rvice
periormancc
characteristics throuvTh calibration of the analytical models developed in
Sta;Te 1.
Commencement of the project is expected shortly and field trials should begin
by
summer 1999. By concentratin~~ on actual in-situ performance. it is
anticipated that more
accurate and meaningful pavement performance models will result from this
investigation.
PRODUCT PAYOFF POrfE:'.~TI.~~L.
The successful measurement of in-situ ACP shear p~~:-openties and the
development of a
main stream test facility would yield si~~niticant amt immediate benefits to
transportatie~n
practice. These benefits would be realized in three primary areas of pay ement
CA 02330431 2001-O1-08
eny.~ineerin~~. The first area is clesi~n .An in-situ she=ar strength test in
conjunction with
laboratory testin~~ would be a powertul combination fior analvzint: the
potential of
proposedJmix designs. Also, the results of such a test apparatus could horsed
to produce
"shut" or "master" curves relating in-situ shear stren~~th to various factors
such as loadin~~
rate, temperature and asphalt content to name a few-.
The second area is gualito ccmtrol. Newly constructed asphalt pavements could
be tested
to verify acceptable construction practices through the measurement and
comparison of
in-situ strength parameters with code requirements. The final area is long
teryn pcrmmem
perforrnunce (LTPP). Monitoring of field shear strength of pavements with time
would
allow periodic updating of initial perlbnnance models which tin-ther assist in
the
prediction of future pavement performance. This. is tum, would allow for snore
efficient
allocation of limited rehabilitation timds and also h:;lp determine the effect
of real world
conditions, such as environmental factors, on pavement performance.
PRODUCT TIR.ANSFER
The potential for a simple yet extremely effective in-situ test device has
already drawn
significant interest from both goven~ment and priv~:,te industry. In addition
to IDt?A
Program fundin~~, the Ontario Ministry of Transportation (M~hOI and Regional
;~-lunicipality° of~ Ottawa-C=arleton have committed financial and in-
l<inci support for this
investi~~ation. Furthermore. a number of independent consultants have also
expressed
interest in the potential of the test facility. To facilitate a more smooth
transition into
main stream use, these consultants will also be included durin;~ t1e
development of the.
test facility. Their role will initially focus on technical advice; he ~wever,
the consultants
are expected to acquire the technolo«y upon comhl~:aion of the investigation.
Continued
evaluation and assessment of market potential will he the primary i~ocus of
consultants at
that stare.
CA 02330431 2001-O1-08 - ". _.,_~_~...~~_~r, ,
DESIGN, DEVELOPMENT, AND VERIFICATION OF AN
ADVANCED IN-SITU SHEAR STRENGTH TEST FACILITY FOR
ASPHALT CONCRETE PAVEMENTS
NCHRP-IDEA Project 55
:\bd I:l I-lalim Omar:\bd EI Ilalixn, Carleton L'niversitv,
Ottawa. Ontario, Canada, I'rofcssor, '
Ilepartment of Civil and hnvironmental I~n~sineerin,~.
~
'Left: (613) 3?(,~-> ~ ~q, 1'aw (613) ~?0-39>1,
Ernail: cxhulim ecs.ccarletort.ea
Stephen N. Goodman, n;arleton L'niversiy, Ottawa, Ontario,
Canada, NI.Eng. Candidate.
Tele: (613) ~33-1961, Email s~;uoclrnunCeccs.cur/econ.cn
t
V'acl Bekhcct, Carlcton IJniyersity, Ottawa, Ontario, Canada,
Ph.U. Candidate. r
Tele: (613) >2t)-771-1961, Email 2e~bchheet@ccs.curletorr.cu
1-asser II lssan, <:arleton hn(versity, Ottawa, Ont.lrio,
( Inada, \visiting Professor,
I>epartnlent c>f (-;ivll anti Ellyironnlental Engineenn:;. ;
Tele: (613) S?()-260(1 Ext. h(i?~, F<t~: (trl3) i?()-39;1,
Email: ylwssun~a~ccs.curletom.ca
c
IDEA Concept and Product
The Str3tcgic Highway' Research Program (SHRP) has recognized~a.~"r
shear strength as an impor-
rant indicator to predict rutting potential of ho.:-min ~
:ISphalt c.eoncrete (Ih\-L1C ) pavements.
however, current methods of measuring the shear strength ,
of an asphalt mix have been lim-
ited to tune consuming, expensive, or unrepresentative laboraiorv"~'e~
analysis. The concept of
measuring the in-situ shear strenytlr of an asphalt concrete
pavement layer by applying a
torque directly to the aurface has keen initiated at C;arleton~~~
L'niversiy in Ottawa, Canada.
IhIS CoIlcCpt allolt'S rel:IClvel\' (Inick meaSllI'clnellt
Of Itl-SIClt 517c:1r Strcllgtl7 wlCh a IIlInImrIIn Of
d.rlna'e Incurred by th-'
. ~ pavement surface. A f~~isic, first generation prototype
called the
C:arleton In-Situ Shear Strength 'Ccst ((:ISSST) has yielded
prornising results relating the maei-
mum applied torque to the shear strength of an l Ib(.~\(-: T
layer. Alorc importantly. the CISSS
h:ls determined that shear strengths achieved in tllc field
arc very different from those realized
In the laboratory. These findings present strong evidence '
that tile devclopnlcnt of such a test .
~
device is required for more accurate measurement and performancef~'~'y
modeling of in-service
pavement pcrfarmanc=e--the fundamental basis of the 51-1RI'
Supcrpave system.
Project Results
The CISSST consisted of an electric motor mounted to a cart-like chassis as
shown in Figure 1.
a series of gears and driveshafts were used to transmit rotational force to a
circular loading
plate eposied to the pavement surface. A torque cell and datafot;ger were used
to measure
torque while angle of twist at failure was measured with a protractor. Two
test speeds were
available. To prevent rotati<m <7f the test device during testing, r~it steel
spikes were attached
to the device and driven into the pavement. Test results achieved with the
device yielded in-
situ shear strengths of up to 300°~ greater than those achieved in
parallel laboratory testing.
However, a number of deticic:ncics were noted during initial investigations
with the CI;3SST.
Therefore, a comprehensive three-stage investigation was presented to the
II>Er\ Program to
continue the development of this innovative test device.
CA 02330431 2001-O1-08
rrigure '1
lira (~enm-cuion GIS.SS~I~ f'rotoW pc Test Cnniv~urc ion
The pr«ject w<rs initiated in February of 19')9. \\'ithin ~ta~e l, completed
hetwcm February
and .Iune, three main objectives were addressed. These «bjectives were defined
as (i) n: carry
c>ut a critical analysis or the existiniC;ISSST t<t~~ilitv and demrmine its
main deticicncim, (ii) to
prepare a preliminary dcsi~;n o'i a second-,t~eneratic~n shear test t,tcility;
and liii) to develop a
framcvcorl< for <t set of analwical models to pre:lict paventcnt pcrf'nrmancc
based on field shear
cl,tt;t.
t\torc spccificall, tile first objective involved a critical evaluation of the
existing Carlet~.~n pro-
totvpc. It was evident that problems associated with the wui~;ht of the
facility. ~ortaL,ility,
smltilization, wpc of epoxy used, and lael: of accurate control and data
acquisition were among
the most important deficiencies of the (:ISSS'1_. The evaluation excrc~ise
prop idol c list of
tlcsi~Sn objectives f«r the second-t~eneratien tr.cilitv to si:nitieantlv
enhance its pcrforrrtanec.
'I'ha second objective concerned the design of the new facility. 'The research
leant at Carleton
Gniversitv held a number of internal mectin~;s to discuss a design approach to
provide an
ol~timurn~coml»nation of the design objectives. 'rhc rcsultin,~ new and
improved facility has
been dubbed the "In,Si,SST," an acronym for In-,~iru ,~W orr Str-c~yth host.
I3riet'lv, the InSiSST ine<>rporates a trailer-mounted sytcm for simplified
transportation.
stable test platform is provided through a solid testing zramc that is lowered
to the grc:und via
a jaelcin~ system. I'ositic>nin~; slides allow movement of the test motor and
gcarbo:c in the
CA 02330431 2001-O1-08
98
longitudinal and transverse dire~~tions. Test measurements are recorded using
a torque
mounted to the rusting plate, itself epoxied ro the asphalt pavement surface_
Control and c
acquisition will he handled using a laptop comp, ~ter and test software. In
its current form,
InSiSS'T is able to perform five replicate in-situ shear tests each time the
test frame is lowe
allowing more rapid testing and assuring statist ;:al significance of the
results.
The third and final olective of Stage 1 was to create a framework for a set of
analytical moc
to ultimately predict long-term pavement performance of asphalt pavement
surfaces basec
results obtained with the InSiSST device. This framework consists of numerous
tasks to r
matey achieve the kual of performance prediction. These tasks include the use
of fin
element modetin~ to simulate the asphalt layer and loading conditions imposed
by
InSiSST, obsen~ing and determining the resulting stress and strain behavior,
calibrating
finite-element models with simplified closed form solutions and field data,
and finally, pred
ing long-term pavement performance. The process of analytical me>dclin t; for
this problem
be an on going process, requiring long-term performance data for model
calibration not wit
the scope of this investigation. Stage 1 formed the foundation of the
framework by present
preliminary finite-element models of the pavement surface and various loading
conditio
Based on the gcocl correlation butu~een the prelirninarv finite element models
and closed fo
solution, for a simplified case, future modeling efforts will incorporate more
complex ~
coelastic material properties found in asphalt c,yncrete. :1s field lust
results are gathered
Stage 3 of the project, the finite element models may be letter calibrated.
Stage ? of the project commenced in July 1999 and fabrication of the second-
generation p
totype gust device is currently underway. Once constructed, a regime of
"shakedown" testi
will be cermpleted to calibrate the test instruments and mote any deficiencies
in constructic
Final adjustments will then be completed to prepare the device for the final
stage of the inm
tigationr. Completion of Stage 2 of the project is scheduled for h-larch
20(10.
The third and final stage of the investigation will consist of two sets of
field testing; one
<)ttawa and the other TRB selecte~J site. ~~nalvsi.s of the results will take
on numerous form
The first analysis phase will confirm that the field test is repeatable and
consistent. Next, t:
field results will be compared to replicate laf>oratc~rv test results to
ohsen~e if a common fact
or "multiplier", exists between them. 'I'hc sensitivity of in-situ shear
strength to critical fa
torn such as mix parameters, traffic Icvel and temperature will also tie
analysed. Finally, tl
results will be used to calibrate the analytical models developed. The project
completion da
is scheduled for August ?000.
Product Payoff Potential
The successful measurement of in-situ IIML:~C, shear properties and the
development of a mai
stream t<~st facility would yield significant and immediate benet""its to
transportation practic
These benefits would be realized in three primar~.~ areas of pavement
engineering. The fir
area is d~aihn. Utilization of the InSiSST in conjunction with laboratory
testing would be
powerful combination for analyzing; the potential ~ ~f proposed mix designs.
The second area
quality ccrrrtrol. Newly constructed asphalt pavements could be tested to
verify aceeptab
construction practices through the measurement and comparison <>f in-situ
strength paran
eters with code requirements. The final area is ~o~t~-term pavement
~>ertormance (LTPP
1\fonitoring field shear strength of pavements with time would allow periodic
updating of initi
performance models to more accurately predict future pavement performance.
This. in turn
CA 02330431 2001-O1-08
99
_ _ _ _ _~ ~_
would allow for more efficient allocation of limited rehabilit<rtion funds and
also help deter-
mine the effect of real world conditions, such as environmental factors, on
pavement perfor-
manse
Product Transfer
The potential for a simple vet e~tremelv effective in-situ test device has
already drawn signifi-
cant interest from both government and private industry. In addition to IDE.~
Program fund-
ing, the Ontario Vlinistrv of Transportation and Regional L-lunieipality of
Ottawa-Carleton have
committed financial and in-kind support for this investigation. Furthermore, a
number of
independent consultants have also etpressed interest in the potential of the
InSiSS'I'. To facili-
tate a more smooth transition into mainstream use, these consultants have
continued to be
included during the development of the test facility. Their role has initially
focused on techni-
cal advice: however, the consultants are e.tpected to acquire the technology
upon completion
of the investigation. Continued evaluation and assessment of market potential
will be the
primary focus of consultants at that stage
CA 02330431 2001-O1-08
Shear Vane for Asphalt Pavement Surface Testin
Overview
Currently, the In-Situ Shear Stiffness Test (InSiSST) facility developed at
Carleton University
uses a surface-plate method of testin<~ the .shear properties of an asphalt
pavement layer. This
surface-plate method entails epoxving a steel test plate to the pavement
surface, allowing the
epoxy to cure and then applying a ytorsional force to observe various shear
properties c>f the asphalt
mix (Figure 1 j. For ultimate strength/stiffness testing, th~, asphalt is
loaded to failure and the
induced failure surface is semi-spherical in shape.
Vertical shaft
T
EPOXY I I I Circular disc
L~CP
Figure 1: Surface-Plate Method of Load Application for InSiSSTTM (Elevation
View)
New Technique
To improve upon the current practice, a new method of applying the torsional
force has been
developed. Borrowing from soil mechanics. a shear vane for asphalt concrete
has been designed
as shown in Figure ?. The use of a shear vane provides two primary benetits
over the surface-
plate method. First, because the I>lades are embedded within the asphalt
layer, no epoav is
required. This reduces the time required for testing from hours to minutes.
Second, the shear vane
provides a defined, consistent failure plane, unlike the inconsistent
faili.ire plane shown in FicYure
1. The defined failure plane allows more accurate calculation of stresses
within the asphalt layer,
which are critical for determining the desired shear properties.
Like traditional vanes, the vane is formed by two perpendicular blades.
However, unlike a
traditional rectangular shear vane used for testing clays, the new shear vane
blades are semi-
spherical in shape. There were two primay reasons for selecting the semi-
spherical shape. First,
unlike clays, which are soft and allow a rectangular shear vane to be easily
inserted, compacted
asphalt concrete is relatively stiff and a shear vane of any configuration
could not be simply
punched or stamped into the compacted asphalt layer without damaging the
asphalt or destroying
the vane. Therefore, a saw must be used to cut into the asphalt to form the
channels for the vane.
Since cutting blades are circular in shape, the resulting cut is semi-
spherical. By matching the
vane diameter and shape to the selected saw blade, a perfect match may be
achieved in the asphalt
pavement.
CA 02330431 2001-O1-08
tfertical shaft
T
Vane ~ ~ ~ Circul,ar disc
ACP
Figure 2: New Shear Vane developed for lnSiSSTT'~ (Elevation View)
The second reason concerns the stress distribution around the steel plate.
During the test. the
stresses applied by the torsional force are greatest at the edge of the steel
plate and reduce to zero
at the centre of the plate. Due to the relatively high stiffness of asphalt
concrete. rectangular
blades would be subjected to extremely high stresses and would require a very
large blade
thickness to resist bending or breakage at the tips. For the semi-spherical
blades, the blade has
minimal cross sectional area at the edges of the steel plate and there is no
"tip". Therefore, the
blades are not subjected to the same level of stresses and can be made with
less thickness.
The actual width and depth of the shear vane can be customized for the
particular asphalt mix
design in question to accommodate the aggregate distribution in the mix. This
is important
because the failure depth must be equal to,Vor larger than, the largest
aggregate size to ensure that
the resulting shear properties are representative of the asphalt mix and not
simply the aggregates
themselves. Based on the relative cutting widths and depths that can be
achieved with a standard
l84 mm (7.25 inch) diameter saw blade, the Following standard vane sizes are
recommended, as
well as the recommended standard asphalt maximum aggre~~ate sizes for asphalt
mixes. Different
vanes may be produced for different saw blade diameters a s well.
Vane Width (mm) Resulting Vane Suggested Asphalt Mix
Depth (mm) ! Maximum Aggregate Size
150 40.6 > 24.5 nun
125 24.5 19.5 mm and ?4.5 mm
100 I 14.8 < 12.5 mrrr
As mentioned above, the new vane has been designed for testing existing (or
newly compacted)
asphalt pavements. However. before the pavement is compacted, the asphalt is
soft and the vane
can be easily inserted into the mix without damaging the surrounding asphalt.
I Iowever, the vane
must be made with sufficient strength to resist the large compactive force of
the compaction
equipment. In this case the semi-spherical shape is not required to prevent
damage to the asphalt,
however, it is required to prevent the large stress concentration at the vane
tip that would occur
with rectangular blades.
CA 02330431 2001-O1-08
Dynamic Testing with InSiSST
Currently, the In-Situ Shear Stiffness Test (InSiSST) facility developed at
Carleton University
completes a static strength/stiffizess test using a surface-plate method of
testing the shear
properties of an asphalt pavement layer. This static test involves the
application of a constant
strain (rate of twist) starting from a state of no applied load, until the
asphalt concrete fails. This
test provides the ultimate shear strength and stiffness of the asphalt rnix
for the conditions
experienced durin~~, the test (temperature, etc.).
To increase the amount of information gathered with the InSiSST, dynamic
testing capability will
likely be added. Dynamic testing involves the application of repeated, cyclic
or non-constant rate
Ic>ad or strain. The Superpave Shear Tester (SST?, which is a laboraturv shear
test facility, uses
dwamic testing in the following manner to test asphalt concrete specimens:
Repeated Shear Testing - involving the application a specific number of
repeated
loads/strains, each consisting of a load/strain pulse of specific duration
followed by a
relaxation period (no load/strain) to test the resistance of the asphalt mix
to permanent
strain.
Frequency Sweep Testing - involving the application of a specific number of
complete
load/strain cycles, each cycle consisting of a load/strain in one direction
followed by a
load/strain in the opposite direction, again to test the resistance to
permanent strain.
The above tests can be completed with the InSiSST device with modification.
Furthermore.. a
non-constant rate of strain can be applied to the asphalt surface with the
InSiSST in its current
configuration.
