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A prototype simple shear and compactionapparatus with application to asphaltic concrete.

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Authors Al-Tayer, Tariq Humaid

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A PROTOTYPE SIMPLE SHEAR AND COMPACTION APPARATUS

WITH APPLICATION TO ASPHALTIC CONCRETE

by

Tariq Humaid AI-Tayer

A Dissertation Submitted to the Faculty of the

DEPARTMENT OF CIVIL ENGINEERING AND ENGINEERING MECHANICS

In Partial FUlfillment of the Requirements For the degree of

DOCTOR OF PHILOSOPHY WITH A MAJOR IN CIVIL ENGINEERING

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 995

UMI Number: 9620420

UMI Microfonn 9620420 Copyright 1996, by UMI Company. All rights reserved.

This microfonn edition is protected against unauthorized copying under Title 17, United States Code.

UMI 300 North Zeeb Road Ann Arbor, MI 48103

THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE

2

As members of the Final Examination Committee, we certify that we have

read the dissertation prepared by Tariq Humaid Al-Tayer

entitled A Ptototype Simple Shear and Compaction Apparatus with

Appl ication to Asphaltic Concrete

and recommend that it be accepted as fulfilling the dissertation

requirement for the Degree of Doctor of Philosophy ----------------~~~--------------------

Dr. l'~niram Budhu ~ "0c4~ 1M, ~U-?z

Date

1),-1-9, Dr. Hilliam Isenhower Date

1tJtrt· f). /h' ==-=:; Dr. Panos Kiousis Date

9 /!9/9~ Date Dr. So~~~rmaleh_

.4II,(Cbn=:: ---Date j !ICf!1r

Dr. Mohammad Ehsani

Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.

b' ,,~~""L .. !-L~~~ Dhe

3

STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the library.

Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED: -;-?_tVY--,--i_/_7I--t--+~_e._?_~ ----'~~' __ ..-/_~_

4

ACKNOWLEDGEMENTS

In the name of Allah, the most Gracious, most Merciful

After all thanks and praises to Allah the Omnipotent, the Merciful, the Compassionate, the author acknowledges his indebtedness to his parents, brothers and sisters for their moral and financial support. The author would like to attribute a great appreciation to his wife for her infinite encouragement, inspiration, patience and support throughout the course of this graduate study.

The author would like to express his sincere appreciation and gratitude to his major advisor Professor M. Budhu for his continued guidance, enormous assistance and encouragement in carrying out this investigation and careful review of the manuscript and helpful comments. I am deeply indebted for his endless inspiration and invaluable assistance, especially his guidance and constructive criticism.

Sincere thanks and appreciations are also extended to Professor Panos Kiousis for his valuable discussion and help. Grateful appreciation is extended to other committee members, Professors William M. Isenhower, M. Ehsani and S. Armaleh for their careful review of the dissertation, cooperation, kindness, suggestions, valuable comments and time spent in serving in the author's committee.

The author would like to thank Professor Rudolf A. Jimenez for allowing the use of some of the equipment from the asphalt laboratory and for his cooperation and help.

A great appreciation is extended to Mr. Peter Boyle who assisted the author during the design period of the apparatus and who built the apparatus with his great experience and put beautiful final touches. Without Mr. Boyle this device would not have existed. Many thanks are extended to Mr. Tom Demma for his help on the electronic part of the apparatus. Thanks are also extended to Mr. Daniel Cisneros for helping the author. Thanks to the head of Civil Engineering and Engineering Mechanics department Professor D. N. Contractor for all the help he provided and the space for my new simple shear and compaction apparatus. Help and kindness of Ms. Barbara Graham, Mrs. Wanda Shirey, Ms. Mary Jankovsky and Miss. Bryan Scott, who edited my thesis, is greatly appreciated.

Finally, many thanks are given to the Government of the United Arab Emirates for their partial financial support.

DEDICATION

TO MY PARENTS, BROTHERS, SISTERS WIFE AND CHILDREN

5

TABLE OF CONTENTS

Content

LIST OF ILLUSTRATIONS

LIST OF TABLES

ABSTRACT

CHAPTERS

1. INTRODUCTION

1.1 Introduction ..... . 1.2 Statement of The Problem 1.3 Objectives . . . . . . .

2. LITERATURE REVIEW ON FLEXIBLE PAVEMENT AND THE NOTION OF SHAKEDOWN ........ .

2.1 General 2.2 Stress Distribution on Asphaltic Concrete Pavement

2.2.1 Tire/Road Contact Stresses . . . . . . . . 2.3 Design Methods . . . . . . . . . . . . . . . . 2.4 Permanent Deformation (Rutting) in Asphalt Concrete

2.4.1 General 2.5 Rutting Prediction ....... . 2.6 Shakedown . . . . . . . . . . . . 2.7 Inelastic Deformation and Shakedown 2.8 Development of Residual Stress 2.9 Material Characterization .... . 2.10 Summary ........... .

3. STRESS AND STRESS STATE IN ASPHALTIC CONCRETE DUE TO ROLLING CONTACT

6

page

. 9

15

16

17

17 23 24

25

25 26 28 31 33 33 41 41 43 44 49 50

62

3.1 General .............. .... 62 3.2 Shear From Tire/Pavement Friction and vertical Load 63

3.2.1 Friction "Factor" ........... 63 3.3 Shear Stress Due to Friction and Vertical Load 64 3.4 Stress State Due to Rolling Contact . . . . . 66

7

TABLE OF CONTENTS-continued

Content page

4. THE NEW SIMPLE SHEAR AND COMPACTION APPARATUS 77

4.1 General 77 4.2 The New Simple Shear and Compaction Apparatus 79

4.2.1 The Simple Shear Apparatus ..... 79 4.2.2 Description of the Compaction Apparatus 83

4.3 Data Collection and ACSSP ........ 84

5. MATERIALS, SAMPLE PREPARATION, TEST PROCEDURE, AND TESTS 101

5.1 General .... . 5.2 Materials ... . 5.3 Sample Preparation 5.4 Simple Shear Test Setup Procedure 5.5 Experimental Work . . .

6. RESULTS AND DISCUSSION

6.1 General 6.2 Compaction ..... . 6.3 Stress-Shear Strain Response

..

6.3.1 Simple Shear Behavior of Asphalt Concrete Using a Complete Cycle ....

6.3.2 Simple Shear Using One-half Cycle 6.3.3 Volumetric Deformation ....

7. CONCLUSIONS AND RECOMMENDATIONS

7.1 Conclusions .......... . 7.2 Recommendations for Future Research

101 101 113 117 118

126

126 126 135

135 140 141

168

168 171

Content

APPENDIX A

APPENDIX B

APPENDIX C

TABLE OF CONTENTS-continued

LIST OF REFERENCES

8

page

173

189

198

. 210

9

LIST OF ILLUSTRATIONS

Content page

FIGURE 2.1 Flexible and lligid Pavement 52

FIGURE 2.2 Distribution of Stresses U%, U2:, U max 53

FIGURE 2.3 Variation of Vertical Stress with Depth, Boussinesq Problem ....... 54

FIGURE 2.4 Total Deformation of Asphalt Mixture ...... 55

FIGURE 2.5 Types of Rutting . . . . 56

FIGURE 2.6 Factors Affecting Stability 56

FIGURE 2.7 Effect of Number of Passes on Transverse Surface Profile . . . . . . . . . . . . .... 57

FIGURE 2.8 Deformation of Plasticine Block Produced by Rolling. These figures show the heavy deformation and shearing at the center of the track . 58

FIGURE 2.9 Rolling Contact of Elastic-plastic Cylinders. Solid Lines-elastic Stresses at Depth z = 0.5aj Broken Lines-with Additional of (u~) and (u;) for Shakedown . . . . . . . . . . .. .. 59

FIGURE 2.10 Transient and Residual Maximum Shear Stress Patterns Calculated During the 6th Pass of lligid Roller and the Pneumatic Tire ...... 60

FIGURE 2.11 Maximum Horizontal Residual Stresses Versus Number of Passes . . . . . . . . . . 60

FIGURE 2.12 Residual Stress Distribution with Depth 61

10

LIST OF ILLUSTRATIONS-continued

Content page

FIGURE 3.1 Uniformly Distributed Horizontal Load on an Infinitely Long Strip . . . . . . 68

FIGURE 3.2 A Shear Stress Distribution Below the Pavement Surface Due to A Shear Stress Applied at the Pavement Surface. ..... 69

FIGURE 3.3 Shear Stress Distribution Below the Pavement Surface Due to a Static Vertical Load Applied at the Surface. . . . . . . . 70

FIGURE 3.4 Shear Stress Distribution Below a Pavement Surface Due to Vertical Stress and Shear Stress Applied at the Surface. . . . . . . . . .

FIGURE 3.5 Deformation in Rolling Contact. An Element of Material Experiences the Cycle of Reversed

. . . . 71

Shear and Compression A-B-C-D-E . .. ... 72

FIGURE 3.6 A Comparison of the Elastic, Shakedown and the Loading Limits for the Case of a Two-dimensional Hertzian Contact with Traction. The diagram also indicates whether the point of severest stress is at or below the surface and the value of the optimum residual stress need to achieve the load limit

FIGURE 3.7 Plastic Deformation in Rolling Contact:

73

Moderate Loads Cumulative Forward Displacement . 74

FIGURE 3.8 Cumulative Plastic Shear in Rolling Contact: Simplified Orthogonal Shear-Strain Cycle Experienced by an Element at Depth z = 0.5a . . . 75


Content

FIGURE 3.9 A Complete Cyclic Deformation of an Element Below a Surface . . .

FIGURE 4.1 lliustration of Calderon "Simple Shear"

11

page

. 76

Device .............. ..... 86

FIGURE 4.2 Schematic Representation of Simple Shear Test Equipment .... 87

FIGURE 4.3a Simple Shear Apparatus 88

FIGURE 4.3b Simple Shear Apparatus Front-View 89

FIGURE 4.4 Longitudinal Fixed Side Wall 90

FIGURE 4.5 Load Cell Used in the Fixed Side Wall and End Flap ......... ...... 91

FIGURE 4.6 The Fixed Side Wall with Load Cell Installed in Position

FIGURE 4.7 Back View of the End Flap "Vith Load Cell Installed . .

FIGURE 4.8 Vertical Roller Bearings .

FIGURE 4.9 Horizontal Roller Bearings

FIGURE 4.10 Control Valves

FIGURE 4.11 Position of Vertical Load Cell

. . . . . . . . 92

92

93

93

94

In Simple Shear Apparatus 95

FIGURE 4.12 Cartridge Heaters . . . . 96

FIGURE 4.13 Grooves in the Lower Platen and Lower Connectors . . . . . . . . . . 97

12


Content page

FIGURE 4.14 The New Semi-Roller Compaction Setup 98

FIGURE 4.15 Molding the Mixture . . . . . . . . . 99.

FIGURE 4.16 Flow Chart of Sensors and Control System 100

FIGURE 5.1 Aggregate Gradation Limits for Bowie Project 119

FIGURE 5.2 Lot No.5 Aggregate Gradation 120




FIGURE 5.6 FHWA 0.45 Power Chart 124

FIGURE 5.7 Compaction the Mixture Using a Full Cyclic Motion 125

FIGURE 6.1 Vertical Deformation of Asphalt Mixture During Different Stages of Compaction ..... 146

FIGURE 6.2 Shear Stress Versus Shear Strain (Temperature at 25°C (77°F)) for Complete Cycles in Simple Shear Test . . . . . 147



FIGURE 6.5 Vertical Pressure Fluctuation During Simple Shear Testing for Complete Cycles in Simple Shear Test .............. 150

13


Content page

FIGURE 6.6 Shear Stress Ration Versus Shear Strain (Temperature at 25°0 (77°F)) for Complete Cycles in Simple Shear Test .. . . . 151

FIGURE 6.7 Shear Stress Ratio Versus Shear Strain (Temperature at 60°0 (140°F)) for Complete Cycles in Simple Shear Test . . . . . 152

FIGURE 6.8 Shear Stress Ratio Versus Shear Strain (Temperature at 80°0 (176°F» for Complete Cycles in Simple Shear rrest . . . . . 153

FIGURE 6.9 Lateral Stresses (Flap Load Cell Readings) at Peak Versus Number of Cycles at Peak of the Amplitude for Complete Cycles in Simple Shear Test . . . . . . . . . . . . . . .. .. 154

FIGURE 6.10 Lateral Stresses (Side Wall Load Cell Readings) at Peak Versus Number of Cycles at Peak of the Amplitude for Complete Cycles in Simple Shear Test .................. 155

FIGURE 6.11 Aggregate Interlocking Around the Lateral Load cells . . . . . . . . . . . . . .. " 156

FIGURE 6.12 An Element Located Below a Pavement Surface Adjacent to a Wheel Path ........... 157

FIGURE 6.13 An Element Located Below a Pavement Surface in Front of a Braking Wheel or Behind an accelerating Wheel ............. 158

FIGURE 6.14 Shear Stress Ratio Versus Shear Strain (Temperature at 25°0 (77°F)) for One-half Cycles in Simple Shear Test ..... 159

FIGURE 6.15 Shear Stress Ratio Versus Shear Strain (Temperature at 60°0 (140° F)) for One-half Cycles in Simple Shear Test ..... 160

14


Content page

FIGURE 6.16 Shear Stress Ratio Versus Shear Strain (Temperature at 800 G (176°F» for One-half Cycles in Simple Shear Test ..... 161

FIGURE 6.17 Shear Stress Ratio Versus Shear Strain (Temperature at 25°G (77°F», 600 G (140°F», and 800 G (176°F»

for One-half Cycles in Simple Shear Test .. ... 162

FIGURE 6.18 Shear Stress Ration Versus Shear Strain at 2% (Temperature at 25°G (77°F» for One-half Cycles in Simple Shear Test .. ... 163

FIGURE 6.19 Shear Stress Ratio Versus Shear Strain at 2% (Temperature at 600 G (140°F» for One-half Cycles in Simple Shear Test ..... 164

FIGURE 6.20 Shear Stress Ratio Versus Shear Strain at 2% (Temperature at 800 G (176°F» for One-half Cycles in Simple Shear Test .. .. 165

FIGURE 6.21 Volumetric Strain Versus Number of Cycles (Temperature at 25°G (77°F», 600 G (140°F», and 800 G (176°F» for Complete Cycles in Simple Shear Tests .... 166

FIGURE 6.22 Volumetric Strain Versus Number of Cycles (Temperature at 25°G (77°F», 600 G (140° F», and 800 G (176°F» for One-half Cycles in Simple Shear Tests . . . . . 167

15

LIST OF TABLES

Content page

TABLE 2.1 Percentage of Permanent Deformation . 35

TABLE 2.2 Structural Layer Coefficient Proposed by AASHO Committees on Design . . . . . . . . . . 38

TABLE 5.1 Asphalt Cement Requirement (ADOT, 1990) 106

TABLE 5.2 Mix Design for Bowie Arizona Project 107

TABLE 5.3 Mixture Properties Before Field Compaction, LOT. No.5 . . . . . . . . . . . . . . . . . . . 108

TABLE 5.4 Mixture Properties Before Field Compaction, LOT. No.6 . . . . . . . . . . . . . . . . . . . 109

TABLE 5.5 Mixture Properties Before Field Compaction, LOT. No.7. . . . . . . . . . . . . . . . . . . 110

TABLE 5.6 Mixture Properties Before Field Compaction, LOT. No.8 .... . . . 111

TABLE 5.7 ASPHALT Program Output 112

TABLE 6.1 Properties of Samples After Compaction 129

TABLE 6.2 Air Voids of Samples After Compaction 131

TABLE 6.3 Comparison of Densities Obtained By Marshall Method and the New Compaction Device 133

TABLE 6.4 Properties of Samples After Testing 144

TABLE 6.5 Air Voids of Samples After Simple Shear Testing 145

16

ABSTRACT

The focus of this research is on simple shear deformation of asphaltic

concrete and its connection to the problem of permanent deformation (rutting)

in asphaltic concrete pavements caused by heavy traffic conditions and high

temperature. Emphasis is placed on the mechanics of damage (rutting) to the

upper asphaltic concrete layers.

Rutting is a major problem in countries with a hot climate, heavy

traffic, and unregulated axle weight. This research summarizes some infor

mation gathered from the literature on the importance given to the general

problem of permanent deformation of asphalt mixtures and the procedures

and constitutive models used to design asphaltic concrete mixture, pavemen

t structures, and to evaluate asphaltic concrete stability. Results from this

effort showed contact stresses are under-estimated in pavement structure, sur

face shear stress due wheel contact are not considered in asphalt concrete

design, and equipment used in asphalt concrete laboratories are not suitable

to simulate the state of stress at which an element under a wheel is subjected

to.

In this research, the behavior of an asphaltic concrete mixture, used

on a project in Arizona, is evaluated through fundamental mechanics and

appropriate laboratory experimental verification. Much of the research effort

is devoted to the design and development of a new compaction and simple

shear apparatus. The general behavior of asphalt concrete material under a

complete cyclic loading and under one-half cyclic loading is presented. The

general trend of the vertical deformation indicated that asphalt concrete tends

to shakedown after a sufficient number of cyclic loadings.

17

CHAPTER 1

INTRODUCTION

1.1 Introduction

Asphalt mixtures may be regarded as forming a macro-colloidal sys

tem composed of three phases: 1) the solid phase (aggregate) which ensures

elasticity and shear resistance; 2) the liquid phase (asphalt) which contributes

to the cohesion and viscoelasticity of the material; and 3) the gas phase (air)

which affects, though only indirectly, some of the physical and mechanical

properties of the mixture.

The resistance of asphalt mixtures to permanent deformation under

static or dynamic loading is described by the general term stability. Stabil

ity depends on friction, cohesion, and inertia forces. Each of these factors

influences the stability of Asphalt mixtures.

In asphalt aggregate mix design, the aggregate normally comprises be

tween 90 to 95 percent by weight, and between 80 to 85 percent by volume of

the mixture. Aggregates are considered to be the primary source of load sup

porting capacity of the asphaltic concrete mixture. Size and type selection of

aggregates are important factors in the asphaltic pavement structure, and the

asphaltic mixture design. Size distribution is usually controlled by specifica

tions which dictate the distribution of particle sizes to be used for a particular

project mix design. In general, gradation is the terminology used to describe

the size distribution of aggregates, determined by dry sieve analysis. Mate

rials retained on sieve number 4 are referred to as coarse. Coarse aggregate

18

consists of crushed stone, crushed air-cooled blast furnace slag, gravel or oth

er approved materials of similar characteristics, or any combination thereof,

which conform to AASHTO designation M 283-83 specifications (AASHTO,

1986). Fine aggregates are the material that passes sieve number 4. They

consist of natural sand, or of sand ,prepared from stone, crushed slag, gravel,

or any combination thereof. They also consist of hard, tough grains, free of

injurious amounts of clay, loam, or other deleterious substances (AASHTO

Designation: M 29-83, AASHTO, 1986). Mineral filler is a material that pass

es sieve number 200. Mineral filler consists of finely divided mineral matter

such as rock dust, slag dust, hydrated lime, hydraulic cement, fly ash, loess, or

other suitable mineral matter, and are dry to flow freely and are essentially free

from agglomerations which conform to AASHTO Designation M 17-83 spec

ifications (AASHTO, 1986). Both open-graded and dense graded aggregates

may be used for road, highway and runway flexible pavements. Gradations

become more dense-graded as the amount or proportion of fine material is in

creased, that is, gradation proceeds smoothly from coarse to fine. Therefore,

the denser the gradation of aggregate, the more contact areas in the compact

ed aggregate, the higher the asphalt content, the greater the internal friction

resistance, and the lower the void ratio.

Particle surface texture is considered to be one of the most important

characteristics of an aggregate. It is the primary responsible agent to the load

carrying capacity in asphalt mixture. Textures of aggregate are character

ized as polished, smooth, rough, and very rough. Irregular surfaced aggregate

should develop a greater internal friction for a given contact pressure, and

when mixed with optimum asphalt content it becomes less susceptible to den

sification under heavy traffic. However, angularly surfaced aggregate requires

19

higher compaction effort and higher workability during mixing. The reverse

is true for rounded and smooth or polished aggregates.

Interparticle friction is greatly influenced by the amount and type of

asphaltic cement used in a mixture. Increasing the amount of asphalt in a

mixture will increase the thickness of asphalt film at contact points between

aggregate particles. This will cause lesser stability in a mixture; as a result,

bleeding will occur under traffic loading.s especially during hot seasons. Sta

bility is defined as the resistance of the mix to deformation from imposed

loads and it is a function of friction cohesion or tensile strength and inertia.

Unstable pavements are marked by rutting, shoving or wavy conditions, and

deformation under the tires of a stationary vehicle (Wallace, 1967).

The asphalt cement quality depends on the project location environ

ment, where as the quantity depends on the gradation of the aggregate. Gen

erally, asphalt cement is available in five standard grades, from the hardest

40-50, 60-70, 85-100, 120-150, to the softest 200-300, in units of 0.1 mm, when

the empirical penetration (100 g, 5.0 sec. 25°C (77°F)) test is used. For

asphalt cement graded by viscosity, the grades are AC-2.5 (hardest), AC-5,

AC-10, AC-20, AC-30, and AC-40 (softest), with the numerical values indi

cating the viscosity in hundreds of poises at 60°C (140°F). The other series

consists of grades AR-1000, AR-2000, AR-4000, AR-8000, and AR-16000 with

the numerical values indicating the viscosity in poises. The viscosity is mea

sured after the asphalt cement has been subjected to the rolling thin film oven

test. The AR series is interpreted as an Aged Residue series.

When aggregates are mixed with the proper asphalt cement grade,

desirable mix properties such as stability, durability, flexibility, fatigue resis

tance, skid resistance, impermeability, and workability must be taken into

20

consideration. For example, mixing soft asphalt cement with a polished ag

gregate surface in hot climate countries will produce a very unstable mixture

and minimal subgrade protection against heavy traffic loadings. On the other

hand, mixing optimum content of hard asphalt cement with angular, durable,

rough surfaced, and well graded aggregates, will produce a strong mix design

that will sustain heavy traffic loadings and will provide adequate subgrade

protection.

The shear strength of asphaltic concrete mixture develops by interlock

and adhesion. The interlock is represented by the internal friction angle ¢>

and the cohesion is represented by c in Coulomb's equation, T = C + untan¢>.

The surface of a flexible pavement exposed to vehicular traffic must be tough

enough to resist distortion caused by shear and tensile stresses, and provide

skid resistance.

The current standard tests to determine the strength of the asphalt

mixture are the Marshall method (AASHTO Designation: T 245-82 or AST

M Designation: D 1559-76) and the Hveem method (AASHTO Designation:

T 246-82 or ASTM Designation: 1561-76). Both procedures are empirical

and do not relate to any rational analysis of the stresses and deformation in a

pavement due to traffic load and climatic conditions. In fact, when analyzing

Marshall stability and flow value (flow value is the axial deformation of a com

pacted specimen when tested under compression, expressed in units of 1/100

inch; for example, if the specimen deforms 3.0 mm (0.12 inch) the flow value

is 12), little or no correlation with plastic deformation can be found (Finn,

1990). The properties of asphalt paving mixture that are thought to influence

pavement structure design are: 1) stability; 2) durability; 3) flexibility; 4)

21

fatigue resistance; 5) skid resistance; 6) impermeability; and 7) workability

(The Asphalt Institute, 1989).

A major impact on pavement performance is permanent deformation,

or "rutting," which reduces the useful service life of the pavement structure

and creates serious hazards for highway users. Rutting is defined as a longitu

dinal depression in the wheel paths that mayor may not be accompanied by

an upheaval at the side of the wheel. Principally, rutting is caused by repet

itive shear deformation under traffic loading and mixture ·densification due

to compaction by traffic (volume change). Studies performed at the AASHO

Road-Test (Highway Research Board, 1962) and test-track studies reported

by Hofstra and Klomp (1972) indicated that the deformation due to shear,

rather than densification, was the primary cause of rutting. The factors that

influence the amount of rutting are tire loads (contact pressures), amount of

traffic, mixture properties, and thermal environment.

The current asphalt concrete structure design methods consider the

stresses on the pavement surface to be vertical stress only and are assumed

to be equal to the tire inflation pressure. This assumption is inaccurate and

misleading. Moreover, no consideration is taken in the design and testing

methods for shear stresses that are produced at tire/pavement contact due

to braking and acceleration of a wheel. As a consequence, the current design

methods underestimate the actual stresses produced by a wheel at the pave

ment surface, and as a result of that the initiation of permanent deformation

and/or cracking of asphalt concrete structure are unavoidable.

Currently, layer-strain (Barksdale, 1972 and Romain, 1972) and vis

coelastic (Maxwell and/or Kelvin) methodologies are used to predict the initi

ation of permanent deformation in asphalt layer and sublayers using laboratory

22

data from uniaxial and triaxial creep tests, uniaxial and triaxial repeated load

tests, triaxial dynamic tests, diametral tests, creep and repeated load tests,

hollow cylinder tests with a combination of axial and torsional loadings, and

wheel tract tests.

It is recognized that repetitively applied shear stresses from wheel load

ing are largely responsible for the development of permanent deformation (Hof

stra, and Klomp, 1972). Neither the layer strain procedure nor the conven

tional viscoelastic analysis considers shear and its not surprising that these

analyses are unable to accurately and reliably model the permanent deforma

tion of a pavement.

The resistance to rutting in asphaltic concrete pavement due to the ap

plication of wheel loads depends on the shear strength of the mixture (Hewitt,

1965). Therefore, design of asphaltic concrete mixture should consider the

shear strength properties under the stress state developed in the pavement.

Accumulation of plastic deformation in the asphaltic concrete surface

layer increases with the number of load applications, leading to incremental

plastic deformation. There is increasing evidence (Ponter, 1985) that plastic

deformation introduces residual stresses which play an important role in re

ducing or eliminating further plastic deformation. That is, plastic deformation

may cease after a certain number of load applications resulting in a stable re

sponse, or a shakedown condition. According to Melan's theory (Melan, 1938),

a system will shakedown under repeated cyclic loads if a self-equilibrated resid

ual stress field could be found such that equilibrium, boundary conditions, and

yield conditions are satisfied.

23

1.2 Statement of The Problem

Rutting of asphaltic concrete pavements is a major concern among

highways and airfield engineers. Rutting is caused by a combination of den

sification (volume change) and shear deformation. Shear deformation, rather

than densification, is considered to be the primary cause of rutting in properly

constructed pavements (Hofstra and Klomp, 1972).

Presently, two approaches are used for predicting pavement deforma

tion. First, there is the layer-strain procedure (Barksdale, 1972 and Romain

1972), which is a subgrade strain or stress criteria for limiting rutting in pave

ment systems. Limiting either subgrade stress or strain does not control

rutting in the material above the subgrade. Second, there is the viscoelas

tic approach (Barksdale and Leonards, 1967; Elliot and Moavenzadeh, 1971;

Thrower, 1977; Thrower, 1977; Thrower et al., 1986 and Nunn, 1986). In this

latter approach, wheel loads are considered in conjunction with time depen

dent material properties to define the state of stress and strain at particular

locations in the pavement structure, and the practice is to try to limit these.

However, this approach, with linearity assumption, seems to be questionable,

and the nonlinear viscoelastic model seems even more prohibitive in terms

of both computational effort and the scale of laboratory work necessary to

establish appropriate nonlinear, time dependent constitutive equations.

Both of the above approaches do not simulate the actual frequent occur

rence of the state of stresses that develop under a rolling wheel. For example,

measurements in a test track (Hofstra and Klomp, 1972) indicate that, in

many instances, layer-strain theory overestimates permanent strains in tensile

zones (bottom of the Asphalt layers). Moreover, both procedures (layer strain

and viscoelastic methods) predict only the rut under the centerline of loading,

24

where vertical loading is predominant, and do not consider the contribution of

rutting caused by the development of shear stresses at a distance from the tire

centerline. Therefore, a model that considers shear strain as the main mecha

nism that causes rutting, with suitable laboratory testing, will give important

clues to shear-induced permanent deformation.

1.3 Objectives

This research was directed toward understanding the effects of shear

stress and shear strain on the upper asphaltic concrete layer only. The objec

tives of the research are:

1) To design and construct an apparatus for specimen preparation

in the laboratory which simulates, as closely as possible, field

compaction.

2) To design and construct a simple shear apparatus to be capable

of testing asphalt concrete under different shear and vertical

loads, and temperatures.

3) To determine the shear stress and shear strain response of as

phaltic concrete mixtures simulating as closely as possible the

stress state in asphaltic concrete under a wheel load.

4) To interpret the results of the tests using the general concept of

shakedown.

CHAPTER 2

LITERATURE REVIEW ON FLEXIBLE PAVEMENT

AND THE NOTION OF SHAKEDOWN

2.1 General

25

The term pavement is defined as a whole structure (roadway, parking

area, airfield and other) built above the subgrade, including all existing layers

of a subbase, a base and a binder coarse or a surface coarse. The purpose of the

pavement structure is: i) to minimize the vertical stresses applied by various

vehicles on the subgrade layer; ii) to provide a smooth riding quality support

to prevent a driver's physiological fatigue due to excessive vibration that may

be caused by poorly constructed surface layer, i.e. segregation or unevenness

of the pavement, or by the development of cracks in the structure; and iii) to

provide an acceptable level of safety by limiting permanent deformation in the

asphaltic concrete structure which may cause hydroplaning when wet or loss

of vehicle control, and to provide skid resistance. This purpose is achieved by

designing and constructing a layered, densified composite consisting of vari

ous sizes of rock particles, often bonded with some type of cementing agent

such as Portland cement (rigid pavement) or bituminous material (asphalt

pavement). Typical cross sections of asphaltic concrete and portland cement

pavement structures are shown in Figure 2.1. In terms of classifications, there

are two major types of pavement structures: flexible, or asphaltic, concrete

pavement and rigid, or Portland cement, concrete (PCC) pavement. A com

bination of asphaltic concrete pavement and PCC pavement can be designed

26

and constructed. When PCC is used as a bottom layer and asphaltic concrete

is used as a surface layer, a pavement with desirable characteristics can be

developed. However, this type of pavement is very expensive and may not

be used as a design method for a new construction project. It may be cost

effective if the asphaltic concrete pavement is severely distressed and can be

used as a foundation for the PCC overlay. This type of pavement combination

is called a composite pavement.

2.2 Stress Distribution in Asphalt Concrete Pavement

Determining the distribution of stresses and strains in a semi-infinite,

elastic, isotropic solid bounded by a plane and loaded at a point on that plane

by a single concentrated force, was first solved by Lame and Capeyron (1833)

not long after the development by Navier (Cummings, 1935) of the differen

tial equations of elastic equilibrium. Their solutions in the form of quadruple

integrals are of little use for practical calculations. The same was developed

further in considerable detail by Boussinesq (1881). His solutions are much

more usable than the previous solutions and have become so well known that

the entire problem is often referred to as the "problem of Boussinesq" (Cum

mings, 1935).

Boussinesq discussed a number of cases of distributed loads. The sim

plest case is that of a load uniformly distributed over a circular area. The fact

that the area of loading beneath a tire is more nearly elliptical than circular,

and that the loading is not strictly uniform, is often neglected.

For the case of a uniform circular loading, the values of the vertical,

horizontal, and shear stresses are shown Figure 2.2. The distribution of these

stresses on the z-axis are such that the absolute maximum value of shear stress

does not occur within a region close to the surface. From Figure 2.2c, in which

27

1I = 0.5, the maximum shear stress occurs at a depth of 0.7 a (a is the radius

of the wheel contact area), as indicated by point B.

Foster and Ahlvin (1954), following the work of Boussinesq, developed

charts for computing vertical and horizontal stresses and vertical elastic s

trains, assuming 11 = 0.5, due to circular loaded plates. Mehta and Veletsos

(1959) published solutions for three- and four-layer systems on a subgrade.

The solutions are readily available for the vertical and radial stresses at the

interfaces and on the load axis. The work by Foster and Ulery (1962) provided

an extensive solution to the complete pattern of stress, strain and deflection

at any point in the homogeneous mass for different values of Poisson's ratio.

Jones (1962) and Peattie (1962) subsequently expanded the three layer solu

tions to a much wider range of parameters. A graphical solution to stresses

and deflection in Boussinesq's solid, assuming that the pressure distribution

at the surface was semiellipsoidal rather than uniformly distributed over a

circular contact area, is presented by Sanborn and Yoder (1967). By the end

of the 1960s, the analytical techniques were well developed and a wide range

of solutions were available for determining stresses and displacements within

layered elastic pavements. The finite element and the finite layer techniques

provided methods for more complex profiles to be studied (Zienkiewicz, 1977;

Cheung, 1976; Cheung 1979).

Vertical load {wheel load) is commonly assumed to be applied in the

form of a uniform stress distributed over a circular contact area. This stress

causes a tensile stress to develop at the base of the loaded layer, a vertical

stress at the top of the supporting layer, and a compressive stress at the

top and outside the loaded area. The development of stresses in pavement

structure are well established analytically.

28

It may be concluded that the stress regime to which pavement materials

are subjected is very complex. Moreover, it is the material behavior as it exists

in a pavement that is of great importance. Testing the pavement material

in situ to obtain some information for pavement evaluation is expensive and

difficult. Hence practitioners and engineers normally rely on laboratory testing

of samples of the pavement materials.

2.2.1 Tire/Road Contact Stresses

Stresses between tires and road surfaces are responsible for tire wear

and pavement damage. At the contact plane, stresses are comprised of nor

mal pressure to the road surface and shear stresses. Shear stresses may be

decomposed into two components, parallel and transverse to the direction of

the tire motion. Analyzing these stresses is a complicated issue.

Tires have direct contact with pavement, and are the supports on which

the whole vehicle load rests. This establishes a relatively small contact area

(footprint) between tread and pavement. The contact pressure distribution

over the contact area (tire footprint) is significantly affected by: wheelloadj

tire size; inflation pressure; vehicle speed; measuring stud height above road

surface; acceleration and deceleration; front or rear wheel; transverse position

of contact (distance between the center of the stud and the center line of the

contact area of the tire tread); type of tread (normal road or cross-country

type); shape of the contact area of the measuring stud; size of the contact area

of the stud; and the variation of the coefficient of friction between tire and

stud. This involves the roughness of the stud surface, material of the stud,

wetness of the tire and/or the stud surface, etc (Bonse, 1959).

By considering the contact stresses of a cylinder on an elastic semi

infinite solid, it was shown (Johnson, 1989), using the Tresca criterion, that

29

the elastic limit is first reached when Tmcu: = k at a point beneath a surface

(z = 0.78a) and along the centerline when the maximum contact pressure is

reached; a is the radius of the wheel contact area. The yield stress is given by

where:

4 p~ = -Pm = 3.3k = 1.67Y

7r

p~ = maximum pressure at yield.

pm = mean pressure.

k = yield stress of a material at yield.

Y = simple tension or compression value.

(2.1)

According to von Mises criterion (Johnson, 1989), yielding begins at a

point when z = 0.70a below the surface along the centerline of the loading

area, assuming 11 = 0.30 and the yield stress is

pE = 3.1k = 1.79Y (2.2)

It is important to design an asphalt concrete mix that can carry a

load without yielding. However, the stresses within the upper layers of a

pavement are complex and not well understood. It is a common practice

among pavement and material engineers to assume the contact pressure to

be equal to the tire inflation pressure. Figure 2.3 is an example of such an

assumption; tire inflation pressure is assumed to be constant. Different loads

are applied to the tire through an axle. The applied contact pressure is shown

to be the same. Huang (1993) stated

In the mechanic method of design, it is necessary to know

the contact area between tire and pavement, so the axle load can

be assumed to be uniformly distributed over the contact area.

The size of the contact area depends on the contact pressure.

The contact pressure is greater than the tire pressure for low

pressure tires, because the wall of tires is in compression and the

sum of vertical forces due to wall and tire pressure must equal to

the force due to contact pressure; the contact pressure is smaller

than the tire pressure for high- pressure tires, because the wall

of tires is in tension. However, in pavement design the contact

pressure is generally assumed to be equal to the tire pressure.

Because heavier axle loads have higher tire pressures and more

destructive effects on pavements, the use of tire pressure as the

contact pressure is therefore on the safe side.

30

This quotation is another misleading statement which most highway and pave

ment engineers take for granted.

Yap (1988) conducted an experimental study to determine the contact

pressure for different truck tire types and the response to different load and

inflation parameters. A combination of some of the factors mentioned earlier

by Bonse (1959), such as: tire type (radial-ply or bias-ply); tire size; loading;

and inflation pressure determines the shape of the vertical contact pressure

profile and the maximum contact pressure. Yap (1988) indicated that radial

ply truck tire contact pressures were generally higher than those of the bias-ply

truck tire. The tire loading influences the shoulder region contact pressures

whereas inflation pressure influences the center region contact pressures. At

a constant load, the maximum contact pressure may be near the periphery of

the area of contact. When inflation pressure is increased, while load is kept

constant, the point of maximum contact pressure shifted to the center region

of the contact width. Increasing tire load at a constant tire inflation pressure

shifted the point of maximum contact pressure to the shoulder region of the

31

contact width. The maximum level of vertical contact pressure was found to

be as high as twice the tire inflation pressure (Markwick, 1941; and Roberts,

1987). However, the normal contact stresses appear the same for moving and

for stationary tires, that is, the normal contact stresses are independent of

speed (Markwick, 1941).

It is possible to conclude, from the above theoretical and experimental

analysis, that the assumption of the tire/pavement contact pressure to be

equal to the tire inflation pressure is not necessarily correct. It should be at

least equal to 1.5pm, assuming Pm is the tire inflation pressure. Therefore, the

tire/pavement contact pressure would be 50% higher than the tire inflation

pressure. When tire treads and pavement surface studs are considered, the

tire/pavement contact pressure may be boosted to 100% higher than the tire

inflation pressure. That is, Po = 2pm.

2.3 Design Methods

The main objective of any pavement design procedure is to provide a

pavement structure that will be able to sustain different environmental condi

tions and anticipated traffic loadings. The design procedure does not involve

only the selection of thickness for the surface, base, subbase material type,

but it embraces construction procedures and techniques, cost analysis, main

tenance planning and surface-life design. Three types of flexible pavement

structures are recognized for design (Barker, 1977):

1) Conventional flexible pavement.

2) Asphalt concrete pavement.

3) Chemically stabilized pavement.

32

Historically, pavements have been constructed according to different

design methods. These design methods have been derived from observations

of existing pavements. In general, these methods fall into one of two basic

categories: (1) the empirical or phenomenological approach: and (2) the the

oretical or mechanistic approach. Various standard test methods are used for

determining subgrade and paving properties, some of these methods are listed

as the following:

1) The California Bearing Ratio (CBR) method.

2) The Plate Bearing Test method.

3) The Resistance-Value Method.

4) Road Test Method.

The following empirical design methods for flexible pavements which,

are based on some factors obtained from the above standards tests, are as

follows:

1) The AASHTO Design Chart.

2) The California Method.

3) National Crushed Stone Association (NCSA) Design Method.

Using the theory of elasticity for flexible pavement design, the following

simplifying assumptions are made to compute the response parameters:

a) The pavement is a multilayered structure, and each layer is lin

early elastic, homogenous, and isotropic.

b) The interface between layers is continuous, that is, the frictional

resistance between layers is greater than the developed shear

force.

33

c) The bottom layer is of infinite thickness.

d) All loads are circular and uniform over the contact area.

Following these assumptions, listed below are some of the design meth-

ods constructed based on the theory of elasticity:

1) The Shell International Petroleum Company Method.

2) The Asphalt Institute Method.

3) Chevron Research Co. Procedure, Highway Pavement.

4) The USSR Design Method.

5) Other Methods.

There are other methods developed and used by different agencies

around the world using the theory of elasticity. Most are similar to the Shell

method. Some of such methods are The Kentucky Method (Southgate, 1977),

Belgian Method (Verstraeten, 1977), The Italian Method (Giannini 1977) and

others (Santucci, 1977; Kenis, 1977; Eisenmann, 1977; Mitchell, 1977).

2.4 Permanent Deformation (Rutting) in Asphalt Pavement

2.4.1 General

As indicated earlier, rutting is defined as a permanent depression or de

formation along the wheel path. This type of failure occur in asphaltic concrete

pavements constructed with insufficient thickness of good quality materials or

inadequate shear strength. Failure may also occur in a well designed mixture

(sufficient amount of asphalt content, air voids, good aggregate gradation and

some other additives) from poor workmanship. McLeod (1954) stated that

it has been frequently observed that when an earth road

consisting of a relatively soft homogeneous clay or loam is over

loaded by traffic, a rut forms in each wheel path and upheaval of

the displaced material occurs on both sides of the lane. It is also

a matter of a common observation that when a flexible pave

ment consisting of subgrade, base coarse, and asphalt surface

is overloaded by traffic, similar rutting and upheaval develops.

Therefore, in a qualitative way at least, failure of the layered

system of a flexible pavement when overloaded by wheel traffic

seems to follow the general pattern of failure of a homogenous

soil that has been over stressed by traffic. In both of these cas

es, failure occurs because the applied wheel load exceeds the

ultimate strength of the roadway structure. Expressed in an

other way, failure takes place because the applied shearing stress

exceeds the shearing resistance of the loaded material.

34

The AASHO Road Test study conducted in 1959, however, revealed

that permanent deformation in the surface profile of a flexible pavement is a

result of total permanent deformation distributed among all the layers. Table

2.1 demonstrates the average proportion of permanent deformations in all

flexible pavement layers. Other researchers (Majidzadeh, 1973; and Hofstra,

and Klomp, 1972) indicated that rutting is due entirely to deformation within

the asphalt concrete.

35

Table 2.1

Percentage of Permanent Deformation

Component Layer Percentage of permanent deformation

AC Surface 32 Base 14 Subbase 45 Subgrade 9

In 1963, Shell International Petroleum Co. Ltd., London (Shell, 1963),

developed a pavement design approach which considered both fatigue and

rutting as mechanisms of distress. In this approach, deformation of the surface

under the action of repeated loadings by traffic is controlled by the vertical

stress or strain in the subgrade layer. The determination of stresses and strains

are based on the equations described by Peattie (1962), and the properties

of the subgrade and construction materials are obtained from measurements

described by Heulkelom and Klomp (1962). The thickness of the bitumen

bound layer required to withstand brittle "tensile stress," or fatigue "tensile

strain" fracture is dependent primarily on the properties of the subgrade. A

large increase in the thickness of the granular base showed little influence

on tensile stress or strain developed in the bitumen-bound layer, whereas a

small increase in thickness of the asphaltic concrete layer is needed to reduce

the tensile stress or strain developed in the asphaltic concrete layer (Dormon,

1962). Since the critical condition arising from the use of thick asphaltic

concrete layers is the compressive strain in the subgrade, it is undesirable

to use bitumen of low Penetration Index (PI), which are binders of a higher

36

temperature susceptibility. Dormon (1965) modified the Shell procedure to

account for fatigue behavior of the asphalt layer and the effect of repeated

loadings on the subgrade. It was found from this study that this modification

did not affect thickness requirements for flexible pavements.

Early efforts in predicting permanent deformation in flexible pavements

using the layer strain methodology are described by Romain (1972) and Braks

dale (1972). Other analytical procedures were also developed by McLean, et

al (1974) and Monismith (1976). These procedures utilize the elastic layer

theory in conjunction with a permanent deformation law found from labo

ratory repeated load tests on each layer of the material. Various laboratory

tests coupled to empirical methods for predicting permanent deformation have

been proposed (Monismith, 1976; Sara!, et al., 1976; van de Loo, 1976; Brown,

1976; Kenis, et al., 1976; Snaith, 1976; Majidzadeh, et al., 1976; Meyer, et al"

1976; James, et al., 1976 and Chou, 1976).

Permanent deformation is due to a combination of densification (vol

ume decrease) and shear deformation (plastic flow) of the asphalt mixture by

traffic loading. Figure 2.4 shows a conceptual illustration of total deforma

tion in a flexible pavement. The three basic types of undesirable permanent

deformation that can develop in asphaltic concrete or flexible pavements are

depicted in Figure 2.5. These undesirable permanent deformations many have

a variety of causes, which include (Dawley, et al., 1990):

1) Wear rutting, which is due to progressive loss of coated aggregate par

ticles from the pavement surface caused by a combination of environ

mental and traffic conditions.

37

2) Structural rutting, which is due to permanent vertical deformation of

the pavement structure under repeated traffic loads, and essentially a

reflection of permanent deformation within the subgrade.

3) Instability rutting, which is the resistance of the asphalt mixture to

permanent deformation under static or repetitive loading, is described

by the general form term stability. Stability is currently considered

to be one of the most important properties of asphalt concrete mix

tures. The stability should be adequate for the type and intensity of

traffic to be carried in order for the pavement to remain satisfactory

during its design life. Instability rutting may be attributed to densifica

tion or lateral displacement of the material within the pavement upper

layer and occurs within the wheel-paths. In relation to the inelastic

behavior of the materials, stability is governed by the gradation of the

aggregate, the shape and surface texture of the aggregate particles, the

relative coarseness or maximum size of the aggregate, the proportions

of aggregate to asphalt binder, the consistency of the asphalt binder,

asphalt type and asphalt temperature susceptibility, and the degree of

compaction, friction, cohesion and inertial forces. The factors affecting

stability are described in Figure 2.6 and Table 2.2.

Table 2.2

Structural Layer Coefficient Proposed by AASHO Committees

on Design (Sousa, 1991)

Factor Change in Factor Effect of Change in Factor on rutting

Resistance

Surface texture Smooth to rough Increase Gradation. Gap to continuous Increase

Aggregate Shape Rounded to angular Increase Size Increase in max. Increase

size

Binder Stiffness Increase Increase

Binder content Increase Decrease Air void content Increase Decrease

Mixture VMA Increase Decrease Compaction method

Temperature Increase Decrease

Test field State of stress Increase in tire Decrease conditions and strain contact pressure

Load repetitions Increase Decrease Water Dry to wet Decreases if mix is

water sensitive

38

39

When a wheel with high tire pressure rolls on an asphaltic concrete

pavement surface, high shearing stresses develops in the portion of the surface

and base coarse close to the loaded area. Eisenmann and Hilmer (1987) con

cluded from a study of plastic deformation in asphaltic concrete pavements

that rutting is mainly caused by deformation flow without volume change.

Figure 2.7 illustrates the effect of the number of wheel passes on the surface

profile of a wheel-track test slab form Eisenmann and Hilmer (1987). Sousa,

et al., (1991) interpreted Eisenmann and Hilmer's results as follows:

1) In the initial stage of trafficking, the increase of irreversible de

formation below the tires is distinctly greater than the increase

in the upheaval zones. In this initial phase, traffic compaction

influences rutting.

2) After the initial stage, the volume decrement beneath the tires

is approximately equal to the volume increment in the adjacent

upheaval zones. This is an indication that compaction under

traffic is almost complete and that further rutting is caused by

displacement with constancy of volume. This phase is represen

tative of the deformation behavior for the greater part of the

lifetime of a pavement.

Hofstra and Klomp (1972) used a circular laboratory test track to s

tudy rutting of flexible pavements. The results from the study indicate that

temperature has a great influence on the depth of rutting. When tempera

tures increase, rutting increases progressively. Increasing the number of wheel

passages resulted in a reduction of permanent deformation per wheel load

which indicates that asphalt mixtures build up more resistance to flow during

the process of deformation under repetitive loading. Permanent deformation

40

through the asphalt mix layer is found to be greatest near the loaded sur

face, and gradually decrease at lower levels. A report by U ge and van de

Loo (1974) indicated that the deformation within an asphalt layer no longer

increases with increasing layer thickness beyond a certain threshold thickness.

According to AASHO Road Test measurements (HRB 1962), the surface rut

depth reached a limiting value of 25.4 cm (10 inches) for asphalt mix thick

nesses. Thicker asphalt concrete (thicker than 25.4 cm) will not reduce the rut

depth in the asphalt concrete layer. This indicates that with reasonable stiff

supporting sublayers, most pavement rutting can be confined to the surface

asphalt mix layer. At a layer thickness of 10 cm and more the permanent

deformation was found to occur in the surface layer only with none in the sub

grade. This was observed in an experimental study conducted by Hofstra and

Klomp (1972). Therefore, a proper mix design, especially in the upper layers,

is a very important factor in designing a flexible pavement that will resist

permanent deformation under heavy wheel loads at elevated temperatures.

The severity of rutting is classified by the Federal Highway Adminis

tration (1979) into four levels. These levels are based on the absolute depth.

Absolute depth of the rut is normally measured from the edges to the bottom

of the deformed section under the wheel path. The depths of the deformed

section are listed as the following:

a) Hydroplaning, 0.5 cm to 0.64 cm (0.2 to 0.25 inch) in absolute

depth.

b) Low, 0.64 cm to 1.27 cm (0.25 to 0.5 inch) in absolute depth.

c) Medium, 1.27 cm to 2.54 cm (0.5 to 1.0 inch) in absolute depth.

d) High, > 2.54 em ( > 1.0 inch) in absolute depth.

41

Some researchers (Dawley, 1990), however, define the depth of a rut as

the vertical distance between the through and crest. The relative severity of

rut depth was defined as:

• Some- for a depth less than 1.27 cm (0.5 inch).

• Modest- for a depth greater than 1.27 em (0.5 inch).

• Severe- for a depth greater than 2.54 cm (1.0 inch).

Some highway and road authorities (OEeD, 1975) describe a rut in

terms of its relative depth, that is ll.u/ D.z;, where ll.zz; is the absolute depth

of the rut and ll.z; is the half width. In regard to the various disadvantages

of ruts, the relative depth method may be considered to be better than the

absolute depth method because it is the slope and curvature of the rut, not

depth, which most directly influences the risks involved. For example, when a

specified amount of water accumulates in a narrow rutted area, the depth of

the water is greater than that of less steep rutting slope. Therefore, relative

depth definition is a much better indicator of rutting severity.

2.5 Rutting Prediction

Two methods are currently used for predicting permanent deformation

in pavement structure layers, including the subgrade. These methods are

called creep under uniaxial stress and the viscoelastic methods using layer

strain method. A summary of models for rut prediction is shown in Appendix

A.

2.6 Shakedown

Shakedown analysis is an extension of plastic limit analysis for struc

tures subjected to variable repeated loads, such as on highways, air fields and

42

flexible roads. Shakedown analysis provides an estimate of the accumulation

of plastic strain increments over a certain number of load cycles.

Before 1940, a greater emphasis was placed on problems involving per

fect plasticity and the development of incremental constitutive relationships

for the hardening post-yield behavior of materials. In 1928, Prandtl attempt

ed to formulate general relations for hardening behavior followed by Melan,

who in 1938 generalized the perfect plasticity concept and gave incremental

relations for hardening solids with smooth or regular yield surfaces (Chen,

1988). In 1957, Prager and Rozenblum further extended the Melan's work to

account for thermal stresses.

When a structure is made of an elastic-plastic material and exposed to

cyclic loads, the following situations in general are possible (Konig 1987):

1) The response will be perfectly elastic when the load intensities

remain sufficiently low, below the elastic limit.

2) Plastic deformation will develop, as the instantaneous load car

rying capacity of the structure becomes exhausted when the load

intensities becomes sufficiently high, which may be followed by

unconstrained flow mechanism and structure collapse.

3) After a sufficient number of cycles, an incremental plastic strain

of the same sign may develop in which the total plastic strain

becomes so large that the structure departs from its original

form and becomes unserviceable. This phenomenon is called

incremental collapse.

4) When the strain increments change sign in every cycle and tend

to cancel each other out, this will cause the total strain to remain

small. This behavior is called alternating plasticity.

43

5) If after some plastic deformation in the initial load cycles the

structural behavior becomes eventually elastic, then the struc

ture is said to be stabilized and such stabilization of plastic

deformations is called shakedown or adaptation.

The displacements that occur during the shakedown process are treated

as infinitesimal. Accordingly, the stresses in a perfectly plastic material are

restricted by the yield limit. In order for plastic flow to occur, the state of

stress must exceed the yield stress.

The critical stress level at which plastic yielding starts is defined by a

yield condition as:

!(Uij) - k = 0 (2.12a)

(2.12b)

where, k is a material constant, determined from experiments, which usually

decreases with temperature.

2.7 Inelastic Deformation and Shakedown

Asphaltic concrete systems are subjected to repeated traffic loads of

varying magnitudes during their design life. There is ample evidence that

the elastic limit in asphaltic concrete layers is frequently exceeded, leading to

plastic flow (rutting) and initiation of residual stresses. Plastic deformation in

asphalt concrete pavement construction occurs in the early passes of the load

(compaction stage). Therefore, it is possible for the stresses in the steady-state

to lie entirely within the elastic limit, thereby leading to a stable response.

This process is known as "shakedown."

44

Johnson (1987) st.ated two separate effects that contribute to the shake

down process:

1) Residual stresses introduced during the early passes are protective and

make plastic deformation less likely during subsequent passes.

2) Plastic deformation in the early passes may cause the material to strain

harden, thereby raising the elastic limit.

The "statical" theorem due to Melan (1938) states that, "if at any time

an invariant residual stress field, satisfying the conditions of equilibrium, can

be found such that at no time the yield condition is violated, then shakedown

will occur" (Ponter, 1985). Melan's theorem may also be stated as: "if any

time-independent distribution of residual stresses can be found which, when

taken together with the "elastic" stresses (i.e. assuming perfectly elastic be

havior) due to the load, constitute system of stresses within the yield limit,

then the structure will shakedown" (Symond, 1951 and Johnson, 1962). How

ever, if no such system of residual stresses is developed, then the structure

will not shakedown and plastic flow will continue with every subsequent appli

cation of load. Neither incremental collapse nor cyclic plasticity are possible;

therefore, this theorem gives a lower bound to the true shakedown limit.

2.8 Development of Residual Stress

The origins of residual stresses may be defined by some examples: form

ing operations, welding, differential cooling rates, cold-working, permanent or

plastic deformation, restraint of deformations and phase deformations of some

alloyed metals. A common property of residual stresses is that they are pure

ly elastic, even if they result from plastic deformation. The residual stresses

45

may be released by all operations which release the elastic deformations cor

responding to the residual stresses, with consequent dissipation of the elastic

potential energy stored in the material. But this may be accomplished by

plastic deformation and new residual stresses (Osgood, 1954).

In the case of asphaltic concrete, and when the load applied by the

roller exceeds the elastic limit of the solid body, a local plastic deformation

will take place in the supporting layer at a depth approximately equal to 0.7 a

and after a passage of the load, the asphaltic concrete will be left in a state

of residual stress. This residual stress remains in the body after the load

has passed. That is, the only direct stresses acting parallel to the surface

can remain. However they may vary independently of each other, with depth

below the surface of the layer.

The only possible residual strain is the direct strain (f~) which accounts

for compression of the asphalt concrete normal to its surface, and the shear

strain ('Y~z) which, if it occurs, will produce a cumulative tangential displace

ment of the surface, as shown in Figure 2.8.

There are two types of stress states that can be distinguished: a) the

shakedown residual stress field (o'[j), which remains in the body after the

removal of all external loads; and b) the sum of residual stress field, (O'[j), and

the active stress, O'ij, that corresponds to the application of an external load.

The active stress can result from either simultaneous or sequential applications

of several external loads. In the sequential load application case, a separate

active stress field, 0'&, is associated with the nth external load, and each sum

of (O'rj) + 0'& must be considered separately. Therefore, the residual stresses

(O'rj) are considered unknown quantities in the formulation, while 0'& are the

46

known quantities determined from the external loads. Assuming shakedown

state, then:

F(urj) < 0

F (urj) + uij) < 0

(2.13a)

(2.13b)

where F describes the yield condition. The constraints given in the above

equations indicate that the residual stress is elastic, and the combined active

and residual stress field is elastic everywhere in the body. While the first

equation must hold for any residual stress state, the second equation is a

unique property of a shakedown state. The inequalities in the above equations

imply that both (urj) and (urj + uij) are entirely within an elastic stress field.

From the second equation, one can infer two main points:

1) the body will not shakedown if no candidate stress state can be found

to satisfy this equation. To say no candidate is found means that the

residual stress state will continue to change indefinitely as the number

of load cycles increases;

2) it is not necessary to analyze each and every possible active stress field,

uij, but only those of higher values that fall within the condition.

Residual stresses can be chosen to have any value at any depth in order

to avoid yielding. H, for example, the minor horizontal residual stress, (uD,

is chosen to be equal to U3, the minor principal stress, then to avoid yield and

by using '!'resca's criterion (x-axis along the nominal line of contact, y-axis

along a direction perpendicular to the x direction or the transverse direction

of rolling, and z-axis is perpendicular to the x-y plane of loading):

47

1 ( )2 2 '4 0'1 - 0'3 ::; k (2.16)

where 0'1 and 0'3 are defined as the major and minor principal stresses, respec

tively, k is the yield stress in simple shear and/or:

(2.17)

The above expression cannot be satisfied if Tu exceeds kj however, it

can be satisfied if Tu = k and (O'~) is chosen to be equal to the difference

between 0'% and 0',;, that is O'~ = 0'% - 0'';' Therefore, the limiting condition

for "statical" shakedown occurs when the maximum value of T%,; in the solid

at any location just reaches the yield stress value, k, in simple shear.

Stresses due to rolling contact at depth z = O.5a below the surface

are illustrated in Figure 2.9. The value of the maximum shear stress, T u ,

is equal to O.25po (where Po is the maximum contact pressure of an elliptical

contact pressure imposed by a wheel or a cylinder on a surface which is defined

as Hertzian pressure, see chapter 3) at a vertical distance equal to O.5a and

within ±O.87 a, where a is one-half the width of the roller strip. Therefore,

using Tresca's criterion, shakedown occurs at:

T%,; = O.25po ::; k

Therefore,

Po::; 4.00k

Using Figure 2.9 and O'~ = 0'% - 0',;, and at depth O.5a, the residual

stresses necessary to ensure shakedown are as follows:

48

O'~ = -0.134po

and

O'~ = -0.213po

which indicate that the residual stresses in the longitudinal rolling direction

are less than that of the transverse rolling direction. The maximum shear

stress distributions and the build-up of residual stress, (O'~) and (O'~), with

repeated rigid and pneumatic loading are illustrated in Figure 2.10. The full

lines represent the sum of the transient and the residual stresses. The broken

lines represent the residual stresses that remained in the compacted material

after the load was removed. Similar loads were used for the rigid roller and

the pneumatic tire compactors. However, the rigid roller induced more intense

stresses than the pneumatic tire compactor. The horizontal residual stresses,

(O'~), build up during the repeated rolling, are illustrated in Figure 2.11.

The build up of the horizontal residual stresses are considered to be

the most important properties of elastoplastic road materials (Yandell, 1971).

The pneumatic tire compactor caused the maximum horizontal residual stress

to build up below the surface, whereas the rigid roller compactor caused the

maximum residual stress to build up close to the surface (Figure 2.12). Resid

ual stresses induced by the rigid roller compactor is greater than that of the

pneumatic tire roller. Therefore, the preceding discussion may justify the use

of steel roller element in the new compaction device (chapter 4) developed to

simulate, in the laboratory, the compaction method used in the field.

49

2.9 Material Characterization

Resilient Modulus, MR, is the elastic modulus used with the theory

of elasticity. Asphaltic concrete is not totally elastic but experiences some

plastic deformation with every load application. In general, when a material

is subjected a number of repetitions, some amount of permanent deformation

occurs at the initial stage of the load applications. As the number of repe

titions increases, the permanent strain due to each load repetition decreases.

The strain becomes entirely recoverable after about 200 load repetitions. The

elastic modulus based on the fully recoverable strain under load repetitions is

called resilient modulus and is defined as M R = !!J.., in which U d is the devia-fr

toric stress (axial stress in an unconfined compression test or the axial stress

in excess of the confining pressure in a triaxial compression test) and €r is the

recoverable strain. The applied stress is normally small. The resilient modu

lus test is a nondestructive test, thus the same sample can be used for many

tests under different loading and environmental conditions. It is necessary to

apply a vertical load that varies with time to simulate the condition in the

field. There are various pulse shapes can be used for loading conditions such

as sinusoidal, square, triangular, and trapezoidal. Barksdale (1971) has indi

cated that sinusoidal or triangular shapes are the most appropriate for direct

simulation. Brown (1973) derived the loading time for bituminous pavement

as a function of vehicle speed and layer thickness.

In pavement design, dynamic complex modulus and dynamic stiffness

modulus have been used for pavement analysis and design. When a bitumi

nous mixture is tested under any loading of any waveform with a given rest

period, the test represents a resilient modulus. When a sinusoidal or haversine

loading with no rest period is used to test a bituminous mixture, then the test

50

represents a complex modulus (the modulus is a complex quantity, of which

the real part represents the elastic stiffness and the imaginary part character

izes the internal damping of the materials). This complex modulus is one of

many methods used to describe the stress-strain relation of viscoelastic ma

terials. The elastic modulus based on the resilient deformation of bituminous

beam at the 200th repetition is called the dynamic stiffness modulus.

2.10 Summary

The stress distribution in flexible pavement is well established. Two

approaches are used to design flexible pavement: 1) the empirical approach;

and 2) the theoretical approach. Both approaches were intended to minimize

cracking and deformation in the flexible pavement. Cracking is controlled by

tensile stress caused by wheel loading at the bottom of the asphalt concrete

layer. Deformation of the surface under the action of repeated loadings by

traffic is controlled by the vertical stress or strain in the subgrade layer.

The above two approaches are used as a guide to design a pavement

but not as a tool to determine the strength of asphalt mixture. The current

tests used to determine the strength of the asphalt mixture are the Marshall

and the Hveem standard methods. When analyzing the Marshall stability and

flow value, no correlation with permanent deformation can be found.

The thickness of each layer depends on wheel/pavement contact pres

sure, wheel load repetitions, and pavement surface life. The contact pressure

between the tire and the pavement surface is assumed by researchers and pave

ment engineers to be equal to tire inflation pressure, Po. It was demonstrated

in this chapter to be not always true. Contact stress, Pm, between a tire and

a pavement surface may be as high as double the tire inflation pressure or

po = 2pm. The maximum shear stress occurs below a loaded surface at depth

51

equal to O.78a (Johnson, 1989) assuming no friction between the tire and the

pavement surface.

Permanent deformation occurs only in the flexible pavement structure,

and in some cases, within the asphaltic concrete layers only due to inadequate

shear strength of asphaltic mixture. Researchers have used triaxial equip

ment and some flexure tests (beam test, rotating bending test, trapezoidal

cantilever, and etc.) to predict the permanent deformation and the shear

strength of an asphaltic concrete mixture. However, the reversal shear stress

es, due to contact rolling, that occur below a pavement surface cannot be

reproduced by triaxial or flexural tests. Therefore, it was necessary to design

a device that can be used to prepare specimens in the laboratory to simulate

as closely as possible the rolling action performed in the field and to test these

specimen in a new simple shear device.

The study of asphalt concrete structure and its post-yield behavior

using step by step procedure is, at the very least, tedious if not impossible

to do. This is because the asphalt concrete structure is subjected to many

repeated passes of traffic load during its life of service. Therefore, a convenient

approach to study a structure that may shakedown is to appeal to Melan's

theorem. This theorem is concerned with the search for a suitable residual

stress state matched to the expected loading conditions. A brief background

on the concept of shakedown theory was presented. The shakedown theory

attributed to Melan, simply states that if, at any time, an invariant residual

stress field satisfying the conditions of equilibrium can be found such that at

no time the yield condition is violated, then shakedown will occur.

(a) Iypical Cross Section of Flexible Pavemenl (b) Load Transmission in Flexible Pavement

Tack Coal Wearing Course Prime Caal- Binder Course

Bose Course

Highway Pavemenl

1-2in Hin

4-12in

Airparl Pavemenl

3-6 in

6-12in

I " I ,

/lll'l Wheel WJJ load

I , I ,

/ -1-1-1- , -kcJ'l f ! rth~ Subbase Course 12-IBin / " 12-36in / • ,

/ , 12-60in / _ _ _ _ _ _ _ _ _ _ \

.le-c1 1 I n fl ) J 1 ] 1 T- r-C'-,'-6-24in Prepared Subgrade

-----------Natural Subgrade t lin: 2.S4mml ' \

(c) Typical Cross Section of Rigid Pavement Highway Airporl Pavemenl Pavemenl

Concrete Slab 6-12in IO-24in

Base or Subbase 4-6 in 4-12in

_ ~!'p~r~~ :u~g~a~e ___ 6-12in 9 -IBin

Natural Sub grade Ilin: 2.S4mml

(d) Load Transmission in Rigid Pavement

laad :Wbm

Figure 2.1 Flexible and Rigid Pavement (Faw, 1995).

52

9 :::; ... ... -<

... o .,. :> Q -< ..

.,. -<

:: 0-Ao

Q

VERnCAL STRESS. a. AS '1. OF APPLIED LOADlNG,p o 30 so be 70 eo qo 100

o

I I I I

I I I I

a •• p [I---i...... ] (0'. ,?~

<a, Vetlleal ,trw on lile e&i.

HORIZONTAL STRESS, cJT AS "to OF APPLIED LOADING, p

10 10 30 '0 SO be 70 80 00 00

I I I I I I 17 I I I I I I I I 211 J

~

5

A

I

2

J I ~1 57

" 7

II I,.

aT. ,.- I.Z~ ----+--a P [c ~ HI.u)' .' ] 2 (0'. l'Y. (a'''')''

auumlnq (1. 'h

~) Hol1:z>nrool 'II'IU an rhe ali.

SHEAR STRESS, T AS '1. OF APPUED LOADING, p

10 20 30 ~ 50 be 70 eo qo 100

---I~D I I I I I I ~ I I I I I I I

8 10 C MaUn'" shea' IIItU ocar' on aai. o 10 B Malllll.llll shear s~u OCCII/1 .Isnrhcrc

T_!on ali. ap[O-ZII)+ ~·lIh _ 2::.... ] • 4 2(a' "')" ~ Co' H')'s

a.-a. aS1Ull\inq II. Vz --2-.. Ce) M ........ shear .lren

Figure 2.2 Distribution of Stresses U z , U z , Tmaz (HMSO, 1962).

53

15

,... 20 '" CIl

"fi 25 c: c :5 30 Co CIl

c 35

40

45

50

Vertical stress (psi) 40 80 120 160 200

55~~~--~~~--~~~--~~~

54

Figu~e 2.3 Variation of Vertical Stress with Depth, Boussinesq Problem

(Yoder, 1975).

CRACKING

Vertical displacement without lateral displacement (Volume reduction)

Vertical displacement with lateral displacement (Constant volume)

RUTTING

Figure 2.4 Total Deformation of Asphalt Mixture.

55

STABILITY (Resistance

to pennanent defonnation)

.. .., A. WEMI

RIJTTING

"""'''''' OtforM.lllOt'l ,n C)nf Of "'01' UW"I'U of N ,,""IN"" Sflv:tUl't btlo- ~l)'\Ilt Corw:t',u

•• STF.UCTURAL AUTTING

.... Dft."c~, O""l.ICtG to Dc"- ....

01 """", '11ft

C. INSTABILITY RLITTINC.

e 69HALT CONCllrTE

iSJJ BASE COUIU( 1C1IUS>4(DI

~SLeaAU II'IT IIUNI

ESUlGI\ADE

Figure 2.5 Types of Rutting (Dawley, 1990).

CO~Ul1NGFACTORS VARIABLE

1. Surface roughness of aggregate particles

Friction --,- Intetparticle -----\ 2. Intergranular contact pressures (Solid) (due to compaction and loading)

3. Asphalt amount (film thickness at points of contact)

4. Angularity (aggregate interlock)

I. Rheologic properties of Mass viscosity ____ -I asphalt: (liquid) (a) Initial consistency

(b) Tempemture

Cohesion --------------1 (Tensile strength)

(c) Rate ofloading (d) Effects oftime and

aging on consistency (Chemical composition)

2. Aggregate gradation and surface area

3. Aggregate density 4. Adhesion between asphalt

and aggregate

I. Magnitude of load Inertia ____________ -I (vehicle weight)

(Resistance to movement) 2. Rate and duration of loading (velocity of vehicle)

3. Mass of paving mixture affected

Figure 2.6 Factors Affecting Stability (Road Research, 1975).

56

&

.! " o

a

~ .., . 1

II

0

• I

, I

0 It 10 .. " I

, , •

\0

I

"

57

nume., .1 1 •• 4"'9 (,u ••

100 1000 Ino

1100 0\0

1000 12S0

1100 USO

1& 150 1'750

~.'" ~ .. ,

t:;" • "' ," 'w '" IUlc -II'

~ \~~dJ It.: .J

~ .~...,. ''\'

ml

Figure 2.7 Effect of Number of Passes on Transverse Surface Profile

(Eisenmann and Hilmer, 1987).

side view front view

·_·_·_·_·_·-1- _._._.-.

b

top view

58

Figure 2.8 Deformation of Plasticine Block Produced by Rolling. These

figures show the heavy deformation and shearing at the center

of the track (Eldredge and Tabor, 1955).

59

-1.0

Figure 2.9 Rolling Contact of Elastic-plastic Cylinders. Solid Lines

elastic Stresses at depth z = O.5a; Broken Lines-with Additional

of (O'~) and (O'~) for Shakedown (Johnson, 1989).

60

-t- travel of rigid roller

~ travel of pneumatic lyre

strf"SS in p.s;

Figure 2.10 Transient and Residual Maximum Shear Stress Patterns

Calculated During the 6th Pass of lligid Roller and the Pneu

matic Tire (Yandell, 1971).

MAXIMUM 6

HORIZONTAL 7

RESIDUAL 6

STRESS S

4

P. S.1. 2

0

3 4 S 6

NUMBER OF PASSES

Figure 2.11 Maximum Horizontal Residual Stresses Versus Number of

Passes (Yandell, 1971).

VERTICAL RES~ STRESS

YERTlCAL RESIDUAL STRESS

05

DEPTH

inches

2

HORIZONTAL RESIDUAL STRESS - P.SJ.

" , PASS II

- - Poissons R.atio = O' ~ • =0'33

(a) Rigid Roller

HORIZONTAL RESIDUAL STRESS - p.5.1.

o 0t-~_-'--~_~ __ ~_'-"'"

DEPTH

inches

2

( b) Pneumatic Tyre

61

Figure 2.12 Residual Stress Distribution with Depth (Yandell, 1971).

CHAPTER 3

STRESS AND STRESS STATE IN ASPHALTIC CONCRETE

DUE TO ROLLING CONTACT

3.1 General

62

It has been long recognized that asphalt concrete pavements are loaded

above their plastic limit and undergo cumulative plastic deformations. Shear

stress caused by traction from wheel rolling is believed to be the main source

of asphalt pavement depression. Yoder (1959) indicated that shear failures

are common in asphaltic concrete pavements. Lateral shoving and rutting are

examples of shear failures in flexible pavement. This type of failure occurs

when the surface and/or base courses become insufficient to resist shear stress

applied by vehicle or airplane wheels, especially during braking, driving and

steering situations. Yoder explained that the resistance of movement under

load is made up of shearing resistance along the logarithmic spiral plus weight

out side the loaded area, and shearing resistance depends upon the cohesion.

In the later edition of the text book (Yoder and Witczak, 1975), the section

of shear stress was omitted and no reason was given for excluding such an

important contribution.

Vertical plastic deformation in asphaltic concrete pavement occurs un

der two conditions. One is the plastic deformation from shear failure below

the pavement surface when the shear strength of the asphalt concrete mixture

is exceeded, and the other, is the horizontal (forward) plastic deformation that

63

occurs at the pavement surface, especially at traffic lights, bus stops, sharp

turns, etc.

When a certain friction factor, f, is exceeded, surface layers are progres

sively sheared in the direction of shearing relative to the 3ubsurface material.

Depending on the area of contact and surface layer thickness, the maximum

shear stress may occur in the surface layer or in the base layer (Chapter 2).

3.2 Shear From Tire/Pavement Friction and Vertical Load

3.2.1 Friction "Factor"

In order for a vehicle to move, at a specific load condition, from a static

to a dynamic state and maintain a steady speed, existing external forces must

be overcome. The external forces are rolling resistance, air or wind resistance,

inertia resistance when in an acceleration mode, and grade resistance. These

external forces are overcome by torque delivered to the drive wheels by the

engine through the transmission and differentials. Further, forces are trans

mitted between tire and pavement surface. The maximum force that can be

transmitted depends on tire/pavement friction. The smaller the coefficient of

friction between tire and pavement surface, the greater the likelihood that the

forces associated with "normal" maneuvering will exceed the capacity of the

interface to overcome the external forces, and hence the greater the likelihood

of a skid. The likelihood of a skid depends not only on pavement surface prop

erties but also on the characteristics of the tires and vehicle, as well as the

nature of the maneuvering (acceleration, braking and steering) as determined

and constrained by road geometry, control features and traffic conditions.

The coefficient of friction is a property of two surfaces, the pavement

and the tire, influenced by a variety of other conditions such as water, ice, oil

64

spills, debris and others (NCHRP, 1972). Thus, when the expression pavement

friction or skid resistance are used, they are meaningful only when the tire and

other conditions of measurement are specified. In other words, skid resistance

can be considered a property of pavement only when all other conditions are

held constant. Therefore, skid resistance is defined as the force developed

when a tire that is prevented from rotating slides along the pavement surface.

In the literature, the terms skid resistance, tire/pavement friction and

pavement friction have been used somewhat interchangeably. The term pave

ment friction is a misnomer because the coefficient of friction is a property

of two surfaces, as stated earlier. Therefore, the preferred term, in place of

coefficient of friction, is friction factor, I.

It is imprecise to say that a particular tire on a given pavement produces

a certain friction factor unless forward or sliding speed, temperature, load, tire

inflation pressure, water film thickness, and other details are specified. In order

to overcome these difficulties, standards have been developed that prescribe

all variables that influence the friction factor I.

3.3 Shear Stress Due to Friction and Vertical Load

Giles (1948) and Moyer (1951) reported values for friction factor, I, up

to 1.0 for slowly moving vehicles, and decreasing values of I with increasing

vehicle speed. McLeod (1953) suggested a value of 0.8 to be a more normal

top I value, with 0.4 to 0.6 as average values. The distribution of the vertical

«(j z), lateral «(j %) and shear ( T %Z) stresses below the pavement surface caused by

shear stresses applied at the contact area between the wheel and the pavement

surface are described theoretically by Florin (1959):

65

(3.1)

+11 2q J (x - E )Z2 d

u% = -; [(x _ E)2 + Z2]2 E -II (3.2)

_ 4aqxz2

- 11'[( a2 + X2 + Z2)2 - 4a2 X2]

(3.3)

q (t -1 a - x t -1 a + x) 4aqz a2 - X

2 + Z2 =- an --+an ---11' Z Z 11' (a2 + x 2 + Z2) - 4a2 x 2

where a is the radius of the contact area between the wheel and the pavement

surface, q is the average shear stress applied at the pavement surface within

the contact area of radius a, z is the vertical distance below the pavement

surface, x is the horizontal distance from the centerline of the contact area

to an element centerline located at or below the pavement surface, E is the

horizontal distance from the centerline of the contact area to an element of

width dE as illustrated in Figure 3.1 for all the above factors.

An element below a pavement surface is subjected to stresses acting on

it due to the approaching wheel load. These stresses are complex, depending

on the rolling condition (smooth rolling, braking or acceleration). The stresses

change with time as the wheel passes over the element. Figure 3.2 illustrates

the shear stress, Tzz , distribution below the pavement surface due to shear

66

stress applied by a wheel when a braking or acceleration mechanism is ap

plied. Friction factor equal to 1 was considered in Figure 3.2. The maximum

shear stress occurs at the surface. Figure 3.3 illustrates the shear stress, Tn,

distribution below the pavement surface due to stationary wheel or at a very

slow wheel speed. No traction forces were assumed in this figure and x/a=O.8.

A combination of the above two curves indicates that the maximum shear

stress, due to acceleration or braking and vertical wheel load, occurs closer to

the pavement surface; see Figure 3.4.

3.4 Stress State Due to Rolling Contact

The deformation expected in rolling contact is illustrated in Figure 3.5.

It is believed that first yield occurs in the element 0 by shear on planes at

45° to the surface during the initial rolling. The same element is compressed

normal to the surface and attempts to expand laterally. Since all elements

at a certain depth are plastically deformed in the same manner, the lateral

expansion must be annulled by the development of the residual compressive

stresses acting parallel to the surface to counteract this deformation. When

these residual compressive stresses reach a full development stage, elements,

such as 0, will no longer yield and normal plastic deformation of the surface

ceases. On the other, the alternating orthogonal shear, T %:I:, of the elements at

B and D cannot be reduced by the introduction of residual shear stress (TJ:z:).

Therefore, it is the orthogonal shear at the elements B and D that governs the

shakedown limit and the repeated plastic deformation which occurs when the

shakedown limit is exceeded.

The shakedown limit, when exceeded, will result in an increase in yield

stress value such, k, as that in the initial compaction procedure in hot-mix

asphalt (HMA). The k value may also increase due to other factors such as

67

a temperature drop in HMA and a hardening of asphalt due to oxidation.

An increase in surface layer temperature and/or cracking due to fatigue may

result in reducing the k value.

When the shakedown limit is exceeded, then it is expected that plastic

shear will occur in subsurface elements, such as the ones at B and D, as

shown in Figure 3.5, provided that the friction factor between the wheel and

the surface is small. For a large friction factor, f ~ 0.35, the plastic shear will

occur near or on the surface. This is illustrated in Figure 3.6 (Hills, 1982).

In repeated rolling cycles, and at loads in excess of the shakedown

limit, the yield criterion will always be exceeded on either side of the axis of

symmetry in the regions where the elastic shear stress (Tzz) value exceeds k.

According to Figure 3.7, plastic deformation accumulates in the direction of

flow so that the surface layers are displaced forward, relative to the deeper

layers. This type of deformation occurs in the upper asphalt concrete layer at

the round-abouts, bus stops, sharp turns areas, and traffic lights.

Figure 3.8 illustrates the cumulative plastic deformation in rolling con

tact. At the entry stage (A to Bt), the loaded region will deform elastically.

At B1, the yield stress is attained at Tzz = +k, and plastic deformation takes

place at a constant stress while the shear strain continues to increase to the

maximum, 'Yzz = 'Y;z, at B 2 • Unloading elastically from B2 to Dl through

C, the element deforms in the opposite direction until the yield point is at

tained at Tzz = -k. A reversed plastic deformation now takes place until the

maximum negative shear strain, 'Yzz = -'Y;z at D2, then the element unloads

until the active stress diminishes. This procedure is repeated until there is

no further change in (0';) and (O'~)i that is, the increment of (€~) per pass

approaches zero.

68

The new simple shear apparatus was designed with the intention of

reproducing as closely as possible the deformation patterns shown in Figure

3.5 and illustrated in Figure 3.9.

Figure 3.1 Uniformly Distributed Horizontal Load on an Infinitely Long

Strip (Florin, 1959).

o -r----------------------~--~

-1

-2

~ -3 1\1 z/a

-4

-5

-6

Friction factor,/=l.O, is used at wheel/pavement conctact area.

-7 ~ __ ~ ____ ~ __ ~ ____ ~ __ -L __ ~

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Shear stress in %

69

Figure 3.2 A Shear Stress Distribution Below the Pavement Surface

Due to A Shear Stress Applied at the Pavement Surface.

70

0 ~-- ......... 1.0./

\~O.~ ... '· 0., "

-1 0.2°7;Y'· ~X

/11/ -2 ~// l

~ It lr z/a N 1#: -3

f -4

Nwnbers on CUlVes indicate the

-5 distance ex/a) from the center line of the loading area

-6 0.0 0.2 0.4 0,6 0.8 1.0

Shear in % of surface contact pressure

Figure 3.3 Shear Stress Distribution Below the Pavement Surface Due

to a Static Vertical Load Applied at the Surface.

o ~--------------------~~~ Maximum 't'zx at depth z/a = 0.3

-1

-2

~ -3 I\j z/a

-4

-5

-6

Friction factor, /=l.0, is used at wheel/pavement conctact area.

-7 --'--__ ----1... __ -----L ____ L--__ ...I...--__ --L-__ ----l

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Shear stress in % due to vertical pressure and friction at wheel/pavement interface.

71

Figure 3.4 Shear Stress Distribution Below a Surface Due to Vertical

Stress and Shear Stress Applied at the Surface.

72

~ I R

JC

v o o A E

Figure 3.5 Deformation in Rolling Contact. An Element of Material

Experiences the Cycle of Reversed Shear and Compression A-

B-C-D-E (Johnson, 1989).

73

•

Figure 3.6 A Comparison of the Elastic, Shakedown and Loading Limits

for the Case of a Two-dimensional Hertzian Contact with Trac

tion. The diagram also indicates whether the point of severest

stress is at or below the surface and the value of the optimum

residual stress need to achieve the load limit (Hill, 1982).

74

(b)

Figure 3.7 Plastic Deformation in Rolling Contact: Moderate Loads

Cumulative Forward Displacement (Johnson, 1989).

.... "" ~/

".

/

A B. B2

-Ently-

75

---G.,:z+---'....::: ..... !"'I

(0)

(b)

Figure 3.8 Cumulative Plastic Shear in Rolling Contact: Simplified

Orthogonal Shear-Strain Cycle Experienced by an Element at

Depth z = O.5a (Johnson, 1989).

76

~p

B c D

~p ~p ~p

• '.:.~,. .... : r,,;,·

B C D

Figure 3.9 A Complete Cyclic Deformation of an Element Below a

Surface

4.1 General

CHAPTER 4

THE NEW SIMPLE SHEAR AND

COMPACTION APPARATUS

77

In this chapter, a new simple shear and compaction apparatus for as

phalt mixtures and other rock materials is discussed. In addition, sample

preparation, and test procedures are presented.

Simple shear apparatuses were developed for testing soils (Kjellman

(1951) and Roscoe (1953)). Two types of apparatuses were used. One called

the Cambridge simple shear apparatus was designed initially by Roscoe and

utilized cuboidal samples. The other is called the Norwegian Geotechnical

Institute (NGI) apparatus. The NGI apparatus utilized cylindrical samples

of soils enclosed in a rubber membrane and confined by using a spiral wire

to bind the cylindrical soil specimen (Bjerrum and Landva, 1966). Different

investigators (Silver and Seed, 1971; Youd, 1972; and Cassagrande, 1976)

have modified the NGI apparatus to study the behavior of soils under repeated

simple shear loading (e.g., seismic loadings). Differences between these devices

are described by Budhu (1984).

Another type of device for inducing shear was developed by Calderon

(1953). The device consisted of a metallic box whose side were hinged on the

corners. The box houses a cubical specimen. The inside faces of the box were

grooved to transmit the shear stresses imposed on the specimen when tension

or compression force was applied along one of the diagonals. The failure of

78

the specimen was manifested by the appearance of tension cracks or of planes

of shear failure. The device was initially designed for soils and then modified

for asphalt mixtures (Figure 4.1).

Recently, a simple shear apparatus for asphalt mixtures was developed

by the University of California at Berkeley (UCB) under the Strategic High

way Research Program (SHRP). A commercial version of the UCB device is

illustrated in Figure 4.2. It uses cylindrical samples, 15.24 cm (6.0 in.) in

diameter, and of different heights. The specimens are prepared by means

of a UCB rolling wheel compaction method, or by the gyratory compaction

method. The UCB rolling compactor is a single wheel roller weighing approx

imately 3.56 kN (800 lbs) and is available commercially. The roller can be

operated in the vibratory or in the static mode .. For the simple shear testing,

specimens are prepared using the static mode. The device is claimed (Sousa,

1993b) to be capable of determining stiffness moduli and permanent deforma

tion in shear over a range of temperatures of 0 to 60° C. It consists of two

hydraulic actuators which are controlled using servo-valves under feedback

close-loop algorithms. During testing, a specimen is glued to the aluminum

caps to ensure the transmission of axial and shear forces to the specimen.

Repetitive shear tests are executed at a constant height. The horizontal actu

ator, under control by the shear load cell, applies haversine loads. Shear stress

of 47 kPa (7 psi) is applied on a specimen with loading time of 0.1 sec and a

rest period of 0.5 sec. The number of load repetitions is computed when 3%

of permanent shear strain is reached. Therefore, the permanent deformation

is calculated based on the number of repetitions to reach 3% permanent shear

strain.

79

McLeod (1953) suggested friction factors with a top value of 0.8, and

between 0.4 to 0.6 as average values. In general, the tire pressure for a pas

senger car is equal to 188 kPa (28 psi) and is 536 kPa (80 psi) for a truck.

Assuming the friction factor is equal to 0.5, the shear stress applied to the

pavement surface by a passenger car and a truck, due to deceleration or sharp

turning, would equal 94 kPa (14 psi) and 268 kPa (40 psi), respectively. There

fore, the value of the shear stress used in the UCB device is 47 kPa (7 psi)

appears to be too low.

Depending on the season, surface temperature of an asphalt concrete

layer differs from top to bottom. For example, during the winter, the tem

perature at the top of asphaltic concrete layer is much cooler than that at

the bottom of the layer. To simulate field temperature in the laboratory, the

testing equipment must be provided with a differential temperature capability

to test asphalt concrete specimens. The UCB device lacks this capability.

4.2 The New Simple Shear and Compaction Apparatus

4.2.1 The Simple Shear Apparatus

A new simple shear and compaction apparatus was designed with the

intention of compacting and testing a cuboidal sample with a plan area of

15.24 cm (6 in.) x 15.24 cm (6 in.), and of variable heights from 3.18 cm (1.25

in.) to 7.62 cm (3.0 in).

The simple shear apparatus (Figure 4.3) transforms a cuboidal sample,

prepared by the above mentioned compaction apparatus, into a parallelepiped

to simulate the deformation and stress state similar to the elements B, C and

D, as shown in Figure 3.5.

80

The simple shear apparatus was constructed from 6061 aluminum and

alloy steel. It contained two removable steel side walls to support the longi

tudinal sides of the cuboidal sample (Figure 4.4). In order to measure lateral

stresses normal to the direction of shear, a commercially available load cell

with an output of 2.473 mv/v/full scale was used, as shown in Figure 4.5.

The load cell was placed in a predrilled hole with its loading face flush with

the fixed side walls (Figure 4.6).

Two aluminum end flaps, each connected with one hinge at one end

and a slider at the other, were connected between the top and the bottom

platens. The inner faces of the top and bottom platen were covered from the

inside with solid steel plates.

A load cell (output 2.419 mv/v/full scale) similar to the one used on

one of the fixed side walls was placed in a pre drilled hole on one of the end

flaps to deduce the lateral stress parallel to the direction of shearing (Figure

4.7).

During the initial testing and calibration stages, actual asphaltic con

crete specimens prepared in the laboratory, using the same device, were used.

This caused some small rock materials mixed with the asphalt cement to ad

here to the inner surfaces of the solid steel plates. As a result, rough surfaces

developed. The rough steel surface generates shear stresses during sample

testing. Unlike the UCB simple shear device, the new compaction and simple

shear device requires no glue when a simple shear test is performed, simply

because the specimen is confined in a simple shear box with rigid walls (two

side walls and two end flaps).

The top platen is fixed in the horizontal plane, but is allowed to move

freely in the vertical direction through "frictionless" roller bearings, one of

81

which is shown in Figure 4.8. The lower platen, which rests on the lower mobile

aluminum base plate, is allowed to move horizontally along "frictionless" roller

bearings in the direction of shearing via a step motor, as shown Figure 4.9.

Vertical force was applied to the top platen of the simple shear device

through a heavy duty double acting pneumatic air cylinder ram [15.24 cm (6

in) bore and 3.5 cm (1 3/8 in) rod diameter produced by the Speedair Com

pany] attached to the upper loading frame. An oil reservoir was placed at

the top of the air cylinder to minimize the amount of air needed to compress

the material during the compaction and testing stages. Also, a small pres

sure relief baffie, or expansion chamber, was provided to collect the oil mixed

with air during pressure release. A solenoid valve was used to control, via a

computer, the various load functions; for example, monotonic, sinusoidal, and

square wave variations can be easily applied to the sample.

There were four valves to control the pressure (Figure 4.10). Valves 0

(lower outlet valve) and 1 (lower inlet valve) were controlled manually. Valves

2 (upper inlet valve) and 3 (upper outlet valve) were controlled electronically

via a relay board through a computer software called Asphalt Concrete Simple

Shear Program (ACSSP), see section 4.3.

Two load cells (Appendix B), capable of measuring tension and com

pression loads, were designed for the new simple shear and compaction appa

ratus. One of the load cells, with a capacity 22.25 kN (5,000 lbs), was placed

above the upper platen between the connecting steel shaft and the tie rod

of the air cylinder. The main function of this load cell was to measure and

control the vertical load (Appendix B). The other load cell, with a capacity

8.9 kN (2,000 lbs), was placed horizontally, under the lower mobile base, to

measure the horizontal shear load applied through the stepper motor. The

82

horizontal (8.9 kN) and the vertical (22.25 kN) load cells calibration curves

are shown in Appendix B. Each of the above load cells was connected to a

high performance amplifier (amplification of 500 to 1000 times).

During simple shear deformation, the two hinged end flaps rotate and

the initial cuboidal sample was transformed into a parallelepiped. The vertical

deformation was recorded through a linear variable differential transformer

(LVDT), see Figure 4.11. Specifications and calibration of the LVDT are

shown in Appendix B. The horizontal displacement was obtained by recording

the number of steps of the stepper motor or by the horizontal LVDT placed on

one of the supporting rails to measure the horizontal motion of the aluminum

base plate.

The apparatus is equipped with a heating device and sensors to control

the required temperature for testing. The source of heat is from cartridge

heating elements inserted into drilled holes in the upper and lower platens.

Four cartridge heaters were used, two in each platen, separated from each

other by about 5 cm (2 in). The cartridge heaters are 1 cm (3/8 of an inch)

in diameter and 10.16 cm (4 in) long (Figure 4.12).

The temperatures of the upper and lower platens were controlled by

heat sensors obtained from Motorola Incorporated (Appendix B). A fully en

closed surface thermometer was used to calibrate the heat sensors in the upper

and lower platens. The calibrations of the platens were achieved by placing

the fully enclosed surface thermometer on the flat platen inner surface. Using

the computer, the output voltage of the sensors was recorded at room temper

ature. The cartridge heaters were turned on by the computer through a relay

board. Platen surface temperatures, along with sensors voltage output, were

83

measured and recorded. The calibration curves of the two platens are shown

in Appendix B.

Safety limit switches were provided for the lower movable base plate to

limit horizontal displacement for safety during compaction and testing oper

ations. Heat insulation for the instrumentation was provided by grooving the

lower connectors and the lower platen (Figure 4.13).

4.2.2 Description of the Compaction Apparatus

All compaction specifications for roads require rolling by pneumatic

or steel wheels to achieve a watertight, dense and durable asphaltic concrete

mixture. In general, compaction of thin-lift (courses of asphalt concrete placed

in compacted thicknesses of less than 10 cm (4 in) are considered thin lifts) of

asphaltic concrete mixture starts with applying a breakdown coverage with a

steel-wheel roller loaded to 89 kN (20,000 lbs). This is immediately followed

by rolling consisting of 4 overages of a pneumatic-tired roller inflated to a

pressure of 402 kPa (60 psi) minimum when cold and 603 kPa (90 psi) when

hot, followed by finish rolling which may consist of one coverage of a 71.2 kN

(16,000 lbs) tandem steel-wheel roller (The Asphalt Institute, 1987).

To simulate closely the field compaction operation required for asphaltic

concrete pavement, a compaction device (Figure 4.14) made of steel was de

signed to compact loose HMA in a square mold, as shown in Figure 4.15. The

mold was made of four steel walls [15.24 cm (6 in.) x 15.24 cm (6 in.)] con

nected by screws and was designed to prepare cuboidal specimens. The simple

shear loading frame system was utilized to apply vertical loads and horizontal

motion for compaction. This was accomplished by removing the simple shear

box and the upper platen, which is attached to a square shaft, from the simple

84

shear loading frame system. The compaction system which includes a Pheno

lic plate, the mold and the compaction device connected by a square shaft to

the rod of the air cylinder, can be placed easily in the simple shear loading

frame system. The high heat resistant Phenolic industrial laminate plate was

used as a base for the mold during sample preparation. The Phenolic plate,

grade name given as G-ll, was made of epoxy resin and medium glass cloth

base (Piper Plastic, Inc.).

The method of compaction was achieved by rolling and not by impact

(e.g., the Marshall method). Rolling compaction using the new compaction

apparatus is refered to, in this study, as the New Rolling Compaction Method

(NRCM). The method by which compaction is achieved has a significant effect

on aggregate orientation and the shape of the air voids developed in the com

pacted mixtures. When a roller is used to compact asphalt concrete mixture,

asphalt tends to deform without crushing the aggregate. No detailed study

was made on the effects of the toughness on the solid base surfaces on the

performance of asphaltic concrete sample in simple shear. Unlike the UCB

method for sample preparation, which involves coring samples from a larger

mold, the samples were tested as they were compacted without disturbance

(no cutting or coring was involved).

4.3 Data Collection and ACSSP

The responses from the vertical load cell, the LVDT, the longitudinal

load cell, the load cell within the flap, the fixed lateral wall load cell and the

temperature sensors (temperatures were measured at the top and bottom of

the specimen) were recorded through a data acquisition system. The data

acquisition system consists of 8 channels of Analog to Digital (A/D) and 2

channels of Digital to Analog (D/A). The two A/D channels were used to

85

power the cartridge heating source. Solenoid valves, which control the vertical

load, were continuously monitored through a relay board. The solenoid valves

were hooked to the vertical load cell in a closed loop system. The horizontal

displacement was determined by recording the number of motor steps (25,000

steps = 1 rev = 0.508 mm (0.2 in» or by the horizontal LVDT. A diagram

summarizing the above device elements and their connections is presented in

a flow chart in Figure 4.16.

The Aspahlt Concrete Simple Shear Program (ACSSP) was written

with a user friendly menu. A flow chart summarizes all the options, described

in a flow chart format, is presented in Appendix C.

86

Figure 4.1 Illustrations of Calder6n "Simple Shear" Device (Calder6n,

1953).

Hydraulic Actuator

LUCITE Chamber ~

Bearings

Servo Valve p

Hvdraulic Actuator

Axial Load Cell

Load

87

Figure 4.2 Schematic Representation of Simple Shear Test Equipment

(Monismith, 1992).

88

Figure 4.3a Simple Shear Apparatus.

Steel Columns

Ft=li-----1-l-- Penumatic Air Cylinder

;........j..----I--I-- Vertical Shaft

r-'--'----.l"r,i;;;::~=========+_ Vertical Loadcell

~lIlI~~[;~~~~~~~~-r- Upper Loading fraxne 1--+--+-- Upper Connector Bar

-+~~--1---1--- Upper Platen

1------ Side Wall 11----1'='&--- Lower Connector

.....:!::I==t-t-t-- Lower Platen I-!I--I-- Base Plate

~~~rrJL- Horizontal Slider m'Y.I&OAI'11

~~~~~::l-t-t-tt-- Horizontal Loadcell

Seating Plate

Figure 4.3b Simple Shear Apparatus-Front View.

89

90

•• 71lOO

5..1!500

T~~-I°_·5_000-llI--1-.1132-1--0-.1IIU8_0_.1_j-t-tH-I---tll.e321

Figure 4.4 Longitudinal Fixed Side Wall.

0.042 (l.06mm)

I~,J r·emm1

Figure 4.5 Load Cell Used in the Fixed Side Wall and End Flap.

91

92

Figure 4.6 The Fixed Side Wall with Load Cell Installed in Position.

Figure 4.7 Back View of the End Flap with Load Cell Installed.

93

Figure 4.8 Vertical Roller Bearings.

Figure 4.9 Horizontal Roller Bearings.

94

.~u~l1alic air cylinder

Figure 4.10 Control Valves.

95

Figure 4.11 Position of Vertical Load Cell in Simple Shear Apparatus.

96

Figure 4.12 Cartridge Heaters.

97

Figure 4.13 Grooves in the Lower Platen and Lower Connecters.

98

Figure 4.14 The New Semi-Roller Compaction Setup.

99

Figure 4.15 Molding the Mixture.

100

COMPUTERj

I I

~ AlDl RELAY l D/A j BOARD

AMPLIFIERS I LVDTSI SOLENOIL HEATING VALVES ELEMENTS

LOAD CELLS &

TEMPERATURE SENSORS

I THE NEW SIMPLE SHEAR APPARATUS I

Figure 4.16 Flow Chart of Sensors and Control System.

5.1 General

CHAPTER 5

MATERIALS, SAMPLE PREPARATION,

TEST PROCEDURE, AND TESTS

101

This chapter describes the properties of the material used in this re

search. These properties include aggregate gradation, asphalt cement per

centage and grade, stability due to Marshall test, bulk density, maximum

theoretical density, and percentage of air voids. The method of sample prepa

ration using the new compaction device is also presented. Tests and simple

shear test setup procedures using the new simple shear device are described.

5.2 Materials

The specification of the asphalt materials for surfacing for the state of

Arizona is presented in section-to05 of (ADOT, 1990). Table 5.1 summarizes

the Arizona specifications for asphalt cement. In hot environments, it is a

normal practice to use asphalt cement AC-40 (high viscosity) for pavement

surface layer, and AC-30 for a base layer.

Aggregates commonly used in asphalt concrete pavements are crushed

limestone, gravel, slag, blast, and sand. H required, the aggregates selected

are washed to remove clay and dirt. In order for the aggregates to be suitable

for use in asphalt pavements, the following must be determined:

1) Surface properties (hydrophobic or hydrophilic),

102

2) Soundness (resistance to disintegration due to the action of

weather),

3) Resistance to abrasion (resistance to degradation),

4) Grading (distribution of sizes),

5) Internal friction (interlocking and surface friction between adja

cent stone particles), and

6) Purity and cleanliness (objectionable materials such as vegeta

tion, soft particles, clay coatings on the aggregates, shale, and

clay lumps).

Improper aggregate gradation is identified as an important contributing

factor to the unsatisfactory behavior of bitumen-aggregate mixture. According

to ADOT Standard Specifications, mineral aggregates are separated into at

least three stockpiles. The gradation of each stockpiles is as follows:

Sieve Size Percent Passing

Coarse 25.40 mm (1.0 inch) 100

19.05 mm (3/4 inch) 75-100

9.53 mm (3/8 inch) 0-20

0.075 mm (No. 200) 0-2.0

Intermediate 12.70 mm (1/2 inch) 100

9.53 mm (3/8 inch) 80-100

6.35 mm (1/4 inch) 40-80

2.36 mm (No.8) 0-20

0.075 mm (No. 200) 0-3.0

103

Fine 6.35 mm (1/4 inch) 100

2.36 mm (No.8) 80-100

0.245 mm (No. 40) 15-35

0.075 mm (No. 200) 0-4.0

Section 408-3.05 (ADOT, 1990) stated that mineral aggregate compos

ite from the stockpile in the mix design percentages shall be such that the

sand equivalent (SE) is at least 45 when tested in accordance with the re

quirements of AASHTO T 176. The SE for the Bowie project was reported to

be 54 by ADOT (Table 5.2). According to ADOT section-406 (ADOT, 1990)

the percentage of the crushed surfaces is at least 30% (Table 5.2) when tested

in accordance with the requirements of Arizona Test Method 212 (ADOT,

1990). This is considered to be a low percentage of crushed surfaces. In gen

eral, this percentage varies from 40 to 100 percent (Kandhal, 1992). Wedding

and Gaynor (1961) reported a significant increase in stability when crushed

gravel was used in place of ~crushed natural gravel in an HMA mixture. The

Marshall stability of HMA mixture changed little when the percentage crushed

aggregates increased from 0 to 35%, and the stability increased consistently

as the percentage of crushed aggregates was increased to 100%.

Gradation specifications, percent of asphalt content, percent of air void

s, Marshall stability, bulk specific gravity, and the theoretical maximum specif

ic gravity (TMSG) and density of uncompacted paving mixture (Rice method

ASTM D 2041-91) for different lots of the Bowie project are presented in Ta

bles 5.3 to 5.6. A lot is considered to be one shift's production. If changes are

made in the mix design, a new lot is normally established. In Tables 5.3 to

5.6, the Upper Limit (UL) is the Target Value (TV) plus 0.0578 kg/rn3 (4.5

Ibs/ it3 ) and the Lower Limit (LL) is the target value minus 0.0578 kg/rn3

104

(4.5 Ibs/lt3 ). The target values (TV) for gradation, asphalt cement content,

effective air voids and stability are given in the contractor's mix design. The

upper limit (UL) and the lower limit (LL) are the values above and below

the TV of each measured characteristic which defines the upper and the low

er limits of acceptable production. No.1 through No.~ are sample numbers

and (Avg.) is the average values of the samples. Graphical illustration of

the gradation limits and distribution of aggregates for the Bowie project are

presented in Figures 5.1 to 5.5. Aggregate distributions fill within the limits

required for the project. Lot-5 and lot-6 aggregate distributions show that

aggregates greater than sieve size No.4 shifted toward the upper limit curve.

This indicates that there are more materials passing sieve size 9.525 mm (3/8

in) and more surface area needed to be covered by asphalt material. The

opposite is true for lots No.7 and No.8.

Using the FHWA 0.45 power gradation chart (the abscissa is an arith

metic scale of sieve size in millimeters raised to the 0.45 power), the aggregate

gradation curve was plotted (Figure 5.6). A straight line plotted from the ori

gin to the maximum effective size is the maximum density gradation line. The

maximum density gradation represents a gradation wherein the aggregate par

ticles fit together in their densest possible arrangement. The curve indicates

that the gradation is tight and no hump is shown above the maximum density

line between sieves No. 30 and No. 50. A hump above the maximum density

gradation line and around sieves No. 30 and No. 50 means an excess of fine

sand in relation to total sand. Excess of fine sand produces lower compacted

densities (higher VMA) and causes segregation of aggregates and destroys the

stability of the mixture. As a result, low air voids may develop in the field

after compaction.

105

The ASPHALT program (Jimenez, 1986) was used to analyze the aggre

gate mixture (Table 5.7). The analysis indicated that the aggregate gradation

is not very tight because the VMA is about 16.6%, which is greater than cri

terion minimum value (Table 5.2). When 5.91% asphalt content (by weight)

was selected, air voids were predicted to be as low as 3% after few years of

service. This air voids percentage is considered to be an acceptable one. An

air void below 2% will cause bleeding in asphaltic concrete pavement. Bleed

ing is defined as the exuding of binder from a asphalt surfacing in hot weather

(HMSO, 1962). In general, the asphalt layer must not show any bleeding or

rutting signs after it has been in service for about five years (Jimenez, 1993).

Normally when bleeding occurs, rutting becomes inevitable.

106

Table 5.1

Asphalt Cements Requirement (ADOT, 1990)

AASHTO

Test Method AC-5 AC-I0 AC-20 AC-30 AC-40

viscosity, 1400 F 400 800 1600 2400 3200

Posies, range T-202 600 1200 2400 3600 4800

viscosity, 2750 F, centistokes, minimum T-201 110 150 210 250 300

Penetration, 770 F 100 grams,

5 seconds minimum T-49 120 70 40 30 20

Flash point, Pensky-Martens of,

minimum T-73 350 425 450 450 450

TESTON AGED

ASPHALT CEMENT

viscosity, 1400 F poises, maximum T-202 2000 4000 8000 12000 16000

Ductility, 770 F centimeters minimum T-51 100 100 75 60 45

107

Table 5.2

Mix Design for Bowie Arizona Project

Material Classifications Results ADOT Requir.

Aggregate O.D. Sp. Gr. Coarse 2.381

O.D. Sp. Gr. Fine 2.551

% Crushed Faces 87 30 % Min.

Mix Design S.E. 54

ADOT S.E. 70

Abrasion 100 Rev. 5 9 Max.

500 Rev. 25 40 Max.

Mix Asphalt Source Chevron/Fina

Asphalt % 5.0

Asphalt Grade AC-30

Asphalt Sp. Gr. 1.041

Asphalt Absorption 0.78

Bulk Density 2.21 kg/rn3

Maximum Theoretical Density 2.36 kg/rn3 Rice Method

Marshall stability 1922 kg 796 kg Min.

Flow, 0.01 in. 11 7-17

% Retained strength 74.0

%VMA 15.3 %14.5 Min.

% Air Voids 6.2

% Voids Filled 59.6

% Wet Strength 3256 kPa 938 kPa Min.

108

Table 5.3

Mixtures Properties Before Field Compaction, LOT. No.5

UL Target LL No.1 No.2 No.3 No.4 Avg.

Values

(%) (%) (%) (%) (%) (%) (%) (%)

Pus. Pus. Pus. Pus. PUll. Pus. Pus. Pus.

3/8 In 82 14 66 19 11 10 80 16.5

No.8 liD 44 38 43 44 41 48 44.0

No.40 20 111 10 16 15 14 13 14.5

No.200 6.11 4.5 2.5 4.1 4.3 3.8 4.5 4.2

% uph. 11.50 5.0 4.5 5.02 4.91 4.61 5.22 4.96

% voids 1.2 6.2 3.8 1.0 1.2 1.1 1.4 1.2

Stabllhy

kg 1660 1115 1811 1636 1105

(Ibs) (3653) (3173) (3984) (3599) (3752)

Compaction

kg/cu.m 2.218 2.1114 2.090 2.178

(lbs/cu.!t) 138.4 134.4 130.4 135.9

Bulk Dens.

kg/cu.m 2.199 2.197 2.197 2.197 2.197

(Ibs/cu.f&) (137.2) (137.1) (137.1) (137.1) (137.1)

Rice Dens.

kg/cu.m 2.364 2.367 2.364 2.373

(lbs/cu.f&) (147.5) (147.7) (147.5) (148.1) (147.7)

109

Table 5,4



Valuell

(%) (%) (%) (%) (%) (%) (%) (%)

PUll. PUll. Pus. Pus. Pus. Pus. PUll. PUB.

3/8 In 82 74 66 80 71i 76 73 76.0

No.8 1i0 44 38 44 43 43 42 43.0

No.40 20 11i 10 14 11i 14 13 14.0

No.200 6.1i 4.1i 2.1i 4.9 1i.0 4.6 4.1 4.7

% uph. 1i.1i0 1i.0 4.1i 1i.50 5.21 5.17 5.03 5.23

% voids 7.2 6.2 3.8 6.9 6.5 7.3 7.7 7.1

Stablllty

kg 1627 1768 1730 1717 1711

(Ibs) (3580) (3890) (3807) (3779) (3764)

Compaction

kg/cu.m 2.208 2.144 2.080 2.168

(lbll/cu.ft) (137.8) (133.8) (129.8) (135.3)

Bulk Dens.

kg/cu.m 2.192 2.207 2.118 2.170 2.188

(Ibs/cu.ft) (136.8) (137.7) (135.9) (135.4) (136.5)

Rice Dens.

kg/cu.m 2.356 2.359 2.349 2.351 2.354

(lbB/CU.ft) (147.0) (147.2) (146.6) (146.7) (146.9)

110

Table 5.5

Mixtures Properties Before Compaction, LOT No.7


Valuell

(%) (%) (%) (%) (%) (%) (%) (%)

Pan. PUll. Pus. Pasll. Pass. Pus. Pasll. Pass.

3/8 In 82 74 66 68 76 68 73 71.3

No.8 50 44 38 39 43 39 43 41.0

No.40 20 15 10 13 15 15 14 14.3

No.200 6.5 4.5 2.5 4.6 5.0 4.7 4.5 4.7

% asph. 5.50 5.0 4.5 4.93 5.19 4.84 5.08 5.01

% voIds 7.2 6.2 3.8 6.9 7.1 6.50 7.1 6.9

Stability

kg 1948 1792 1926 1856 1881

(Ib) (4286) (3943) (4238) (4084) ( 4138)

Compaction

kg/cu.m 2.220 2.155 2.091 2.184

(Ibs/cu.ft) (138.5) (134.5) (130.5) (136.3)

Bulk Dens.

kg/cu.m 2.200 2.194 2.205 2.194 2.199

(Ibll/cu.ft) (137.3) (136.9) (137.6) (136.9) (137.2)

RIce Dens.

kg/cu.m 2.362 2.361 2.359 2.362 2.361

(Ibs/cu.ft) (147.4) (147.3) (147.2) (147.4) (147.3)

111

Table 5.6


UL TArget LL No.1 No.2 No.3 No.4 Avg.

V .. lues

% % % % % % % %

Pus. Pus. Pus. Pus. Pus. Pus. Pus. PILBS.

3/8 In 82 74 66 75 77 75 73 75

No.8 SO 44 38 43 43 43 40 42.3

No.40 20 15 10 16 15 14 12 14.3

No.200 6.5 4.5 2.5 5.3 5.4 4.8 4.4 5.0

% uph. 5.50 5.0 4.5 5.22 5.20 5.29 5.03 5.19

% voids 7.2 6.2 3.8 6.3 6.6 6.6 6.8 6.6

Stability

kg 1996 2000 2014 1820 1957

(Iba) (4391) ( 4399) (4430) (4003) (4306)

Compaction

kg/cu.m 2.218 2.154 2.090 2.189

(Ibs/cu.ft) (138.4) (134.4) (130.4) (136.6)

Bulk Dens.

kg/cu.m 2.205 2.202 2.196 2.183 2.197

(Ibs/cu.ft) (137.6) (137.4) (137.0) (136.2) (137.1)

Rice Dens.

kg/cu.m 2.353 2.357 2.351 2.357 2.351

(Ibs/cu.ft) (146.8) (147.1) (146.7) (146.1) (146.7)

Table 5.7

ASPHALT Program Output

Sieve (%) R Voidage Aggregate

Size Passing Reduction Voidage

(P) Factor (F) (%)

200 5.0 0.00 0.000 32.00

100 10.0 2.00 0.965 30.87

50 20.0 2.00 0.965 29.78

30 30.0 1.50 0.897 26.72

16 40.0 1.33 0.892 23.83

8 50.0 1.25 0.901 21.48

4 75.0 1.50 0.897 19.27

0.375 90.0 1.20 0.905 17.44

0.750 100.0 1.11 0.953 16.61

1.500 100.0 1.00 1.000 16.61

Air Voids Asphalt Film

Content Thickness

(%) (%) (Microns)

2.00 6.32 8.79

3.00 5.91 8.12

4.00 5.50 7.45

5.00 5.09 6.78

6.00 4.67 6.11

Effective Specific Gravity = 2.650

Asphalt Specific Gravity = 1.020

Asphalt Absorption Value = 0.700

112

Surface Surface

Area Area

Factor (ft2 /Lb)

160 8.00

60 6.00

30 6.00

14 4.20

8 3.20

4 2.00

2 1.50

0 2.00

0 0.00

0 0.00

:E32.90

113

5.3 Sample Preparation.

Test specimens were prepared to exact dimensions of the simple shear

box using a replica (mold). The heated asphalt mixture was placed in the

mold which was then positioned on the horizontal mobile base plate. The

compaction device was then placed on the top of the asphalt mixture. Cyclic

motion (back and forth) of amplitude equal to 77 mm was applied to the

mobile base by the stepper motor through the ACSSP.

The vertical pressure was measured by a pressure gauge installed on

the top of the oil reservoir. To insure accurate pressure readings, two gauges

were provided, one for low pressure readings [0 to 414 kPa (60 psi)] and the

other for high pressure readings [0 to 1380 kPa (200 psi)]. The pressure gauge

reading is not the true pressure applied to the asphaltic concrete mixture

during the compaction stage or during the simple shear testing. The pressure

gauge reading is an indication of the pressure applied to the pneumatic piston

[area= 7rr2 = 7r32 = 28.274 in2 ]. The actual platen area for simple shear

test is 36 in2 , which means the actual pressure when applied to the specimen,

is less than the gauge pressure by 21.5%. The exact pressure applied to the

specimen during compaction is not known. However, the pressure applied to

the compacted specimen is 283~7:n\n2 x gauge pressure. This correction was

considered in the ACSSP for the simple shear test.

To prevent the hot asphaltic mixtures from being shoved between the

compaction device and the mold, and to produce a specimen with a flat surface,

a low initial compaction pressure was applied. Therefore, compaction starts

initially at a low pressure, 35 kPa (5 psi) gauge pressure, and increases by the

end of the compaction period to a higher gauge pressure (up to 759 kPa or

110 psi).

114

The procedures for sample preparation are as follows:

1) Aggregate and asphalt cement mixtures were obtained from

Bowie, Arizona.

2) The apparent specific gravities of each sample (coarse, interme

diate and fine aggregates) were determined according to AASH

TO designation T 84-81. The gradation test was performed in

accordance with AASHTO designation T 27-82 standard. The

different sizes of aggregate were blended according to the State of

Arizona Standard Specifications for Road and Bridge Construc

tion (ADOT, 1990), and the overall apparent specific gravity of

the blended aggregates was calculated. Oil soak tests for coarse

aggregates, and CKE (Centrifuge Kerosene Equivalent, AASH

TO T 275-83) for fine aggregates, were performed to obtain the

optimum asphalt content using the Marshall method.

3) The prepared blended aggregates and the asphalt cement were

each heated to the desired temperature [between 107°C (225° F)

to 163°C (325°F)].

4) The aggregates and the asphalt cement were mixed, in plant, at

a selected optimum asphalt content, using the Marshall method.

5) Batches of asphaltic concrete mixtures, stored in paper bags or

in aluminum containers at the construction site, were transferred

to the University of Arizona Civil Engineering Laboratory.

6) Before compaction, the asphalt-aggregate mixture (obtained

from the Bowie project site) was kept in an oven for about t

wo hours prior to molding at a temperature of 140°C (284°F).

Fifteen minutes before the heating of the asphalt mixture was

115

completed, the cuboidal steel mold and the compaction device

were heated in an oven to a temperature of 140°0 (284° F). The

cuboidal steel mold was removed from the oven and placed on

the Phenolic plate. The inside of the mold, the Phenolic plate,

and the base of the compaction device were wiped with a rag or

a brush lightly moistened with kerosene or light lube oil. The

compaction device that connects the vertical load cell with the

tie rod of the air cylinder was attached and secured tightly. The

Phenolic plate and the mold were placed on the lower mobile

aluminum base plate. The asphalt mixture was spooned into

the cuboidal steel mold. About half of the amount of the as

phalt mixture (approximately 1.75 kg (3.85 lbs)), was placed

into the cuboidal steel mold. The mixture was rodded in the

mold about twenty times around the edges and at the center.

The remainder of the sample was added into the mold (approxi

mately 1.75 kg (3.85Ibs». The rodding procedure was repeated

for the added mixture. Finally, the surface of the mixture was

leveled by pressing down with a large spoon.

7) Using the ACSSP, the lower base was moved to the center of the

apparatus (home position). The mold was adjusted so that the

compaction device would drop inside the mold. Four aluminum

clamps were used to hold the mold down tightly and secure its

position.

8) The sample preparation option was selected from the ACSSP to

start compacting the mixture.

116

9) At the initial compaction stage, a small vertical load was se

lected, 35 kPa (5 psi), for about 10 cycles of compaction. Each

"cycle" was a linear horizontal motion (back and forth in the

shearing direction), as shown in Figure 5.7. The pressure was

then increased by 35 kPa (5 psi) for the next set of 10 cycles

of compaction. In the third set of 10 cycles of compaction, the

pressure was raised to 138 kPa (20 psi). Pressure levels of 207

kPa (30 psi), 276 kPa (40 psi), 345 kPa (50 psi) and 414 kPa (60

psi) for the fourth, fifth, sixth and the seventh sets of 10 cycles

of compaction, were used, respectively. An amplitude of about

76 mm was selected for the full cycle.

10) Some of the specimens were prepared using a manual pressure

increase. In this procedure, the same steps were followed (step 1

through step 8), except that in the sample preparation program,

the number of cycles were inserted as the total number of cycles

to be used to compact one specimen. As soon as the instruction

was given to the computer to start compacting, the pressure

was increased manually up to 759 kPa (110 psi). In this pro

cedure, 50 cycles were performed. This incremental application

was necessary to achieve a specimen with a flat surface.

11) When compaction was completed, the pressure was released au

tomatically by the electronic valve (outlet valve No.3). The

compacting device was lifted off by opening the manual inlet

valve (inlet valve No.O) while keeping the outlet valve No. 1

closed. After releasing the four clamps, the mold and the Phe

nolic plate were removed from the device. The side walls of

117

the mold were released by unscrewing the bolts attached to the

mold. The smaller bolts were used to dismantle the specimen

from the mold.

12) The prepared samples were marked and allowed to cool for at

least 48 hours before simple shear testing was started.

13) Bulk specific gravity for each specimen was obtained using the

saturated surface-dry (SSD) method of AASHTO Designation:

T 166-83 (AASHTO, 1986).

14) Percent water absorbed by the specimen (on volume basis) was

obtained, AASHTO Designation: T 166-83 (AASHTO, 1986).

15) Air void for each specimen was calculated before and after test

ing, AASHTO Designation: T 166-83 (AASHTO, 1986).

5.4 Simple Shear Test Setup Procedure:

1) The average height of each specimen was measured using a mi

crometer and recorded. At least twelve readings were taken

around the perimeter of the specimens.

2) The compacted specimen was placed in the shear box.

3) The shear box was positioned to its home position using the

home key in the ACSSP.

4) The sample in the simple shear box was maintained at the

desired temperature [25°0 (77°F), or 60°0 (140°F), or 85°0

(176° F)] for about one hour or more.

5) Vertical static load equivalent to a contact pressure of 600 kPa

was applied.

6) Horizontal shear displacement was applied at selected displace

ment rates.

118

5.5 Experimental Work

The experimental work was designed to examine the general behavior

of asphalt concrete mixture and to see whether or not a steady state "shake

down" can be reached during specimens preparation and testing. Three differ

ent temperatures [25°e (77°F), 600 e (140°F), 800 e (176°F)] were selected to

study the general behavior of an asphalt concrete mix. The 25°e (77°F) tem

perature is ambient temperature at which specimens were stored during the

recovery period and tested in simple shear without reheating. Engineers and

researchers in the field of asphalt concrete mix design tend to test specimens at

high temperatures, such as 600 e (140°F). The author could not find a reason

for selecting such a temperature other than that it is used as standard temper

ature in the Marshall test procedure. Moreover, no experimental procedure

or testing device known to the author is used to test asphalt concrete samples

at temperatures higher than 600 e (140°F), such as 800 e (176°F), as used

in this research. This temperature represents the temperature of the asphalt

pavement surface in Dubai, United Arab Emirates. Therefore, to simulate a

severe field condition, this temperature was included in this study.

The vertical pressure was selected to be equal to 600 kPa to simulate

the "assumed" truck tire pressure. The amplitudes used in the simple shear

cycles were selected based on the initial height of a compacted specimen x

1.6%. This factor is used for almost all the experimental work. Some of

the compacted and tested specimens are listed in tables presented in chapter

six. About 70% of the compacted specimens were used in the initial testing

program. These specimens were used for the calibration and modification of

the new simple shear device and for experimental program modifications.

119

100

90

80 1

/4 70

60 / It. L-

/ I::;. (J) c:

u::: 50 I~ / .1'

~ Iv

~ ~ ~ 40 .Il'~.! .;l ~

30 ~~~/ /~ /:. ",\2

20 / ~~~ /.~ -<,l(j

~/ 10 ..,/'A ..,/'----0

0.1 1 10

Grain size (mm)

Figure 5.1 Aggregate Gradation Limits for Bowie Project.

120 ..

100 -0- mmvUL

90 -0- mmvLL -6. - mm v L5S1 ~ mmvL5S2

80 .. ¢. mm v L5S3 -0- mmvL5S4

70

~ 60 Q)

~ 50

~ 40

30

20

10

0 0.1 1 10

Grain size (mm)

Figure 5.2 Lot No.5 Aggregate Gradation.

121

100 -0- mmvUL

90 -0- mmvLL

~- mmvL6S1

80 --'\l'- mm v L6S2

"0- mmvL6S3

-0- mmvL6S4 70

~ 60

.s:::: L1: 50 ~

40

30

20

10

0

0.1 1 10

Grain size (mm)


122

100 -0- mmvUL

90 -0- mmvLL -6. - mm v L7S1 -'ij- mm v L7S2

80 --0- mmvL7S3 -0- mmvL7S4

70

~ 60 Q)

.r::: Lt: 50 ~

40

30

20

10

0

0.1 1 10

Grain size (mm)


123

100 -0- mmvUL

90 -0- mmvLL -I:::. - mm v LBS1

80 -xv- mm v LBS2 --0- mmvLBS3 --0 - mm v LBS4

70

~ 60

cu .c: Li: 50 ~

40

30

20

10

0

0.1 1 10

Grain size (mm)


I'%j

~. CJ1 (,) I'%j ::t:

~ o ~ CJ1

'i:I

~ .., o ::r el ;t"

100 .. _ ... __ ... -- .. -

i-i-

) l-I-

90

f- -l-I- E r=i= 1-1

, I-l=t i

eo

l- i I-

7 , -1- -. f:: = ~ 6

i:i ~ 5

W U

cr: " W Q.

;;

2

,

J i- r--

1=1= [:: J

J

0 .r- :--

0

0

\-

.. i-+-

I

I:i= 1=

I-.1- -l-

'~ ~

.. I-i I .. -t

\= ~

~

-I-i= ,-

1= == I

I

-t

FI 0 " •• 200 100 '0 30

He. 10 40 fO

-I -I-\

\

I \ --t l---

I ==t--J \ I I I

~:-\ =I I I

1= I

J-~ I

-r-ir---,-.-1

===I l-l-

I~I= 1-

11==== I 1-

I I I

~~ -f to •

10 •

GRADATION CHART , SIMPLIFIED PRACTICE" SIZES 111

./- -. I I I

I 1

_L

~ 3/t I I SIEVES NO. I

"(T&I"[O R[T a PA'3INO OK WT. "I. 1

I I I

I I

4 3/." %" 'I."

SIEVE SIZES

ICATED BY •

1" 1X" TOTAL NO.

%

PASSING WT. "I.

100

90

80

70

60

1Yz" TOTAL

% PASSING

..... t-:) ,j::>.

125

Figure 5.7 Compacting the Mixture Using a Full Cyclic Motion.

126

CHAPTER 6

RESULTS AND DISCUSSION

6.1 General

The results of some of the experiments performed on the asphalt con

crete mixture obtained from Bowie, Arizona project are presented and dis

cussed in this chapter. Asphalt concrete mixture behavior during compaction

is also discussed. Properties of the prepared samples are summarized and p

resented. The general behavior of the asphalt concrete mix, tested in the new

simple shear apparatus under different temperatures using complete cycles

and one-half cycles, is described.

6.2 Compaction

Compaction was performed using the compaction apparatus discussed

in Chapter 5. The vertical deformation of the loose mixture was monitored by

an LVDT during the various compaction stages. A stage represents a certain

amount of load applied to the loose mixture during the compaction process.

A small load was applied to the loose asphalt-aggregate mixture at the initial

stage of compaction, then the load was increased in the subsequent stages.

This procedure was necessary to obtain a flat and smooth surface for the

compacted specimens. Specimens were subjected to ten cycles of horizontal

displacement at each stage. An amplitude of 76 mm and a velocity of 10

mm/sec were used for each of ten cycles of each stage. At some later stages

of compaction, the velocity was increased to 15 mm/sec. Most of the samples

127

were identically cDmpacted using five stages Df IDadings. It tDDk apprDximately

half an hDur to. cDmpact each specimen.

The vertical cDmpressiDn Df IDDse HMA during different stages Df the

cDmpactiDn prDcess using the new rDlling cDmpactiDn device is shDwn in Figure

6.1. AbDut 50% Df the tDtal vertical defDrmatiDn Df the IDose hDt asphaltic

mixture Dccurred during the first stage Df cDmpactiDn (Figure 6.1). Asphalt,

when hDt, acts like a lubricant between aggregate particles and facilitates

particle reorientatiDn. At the initial stages Df cDmpactiDn, the asphalt was at

its maximum temperature and a significant vertical defDrmatiDn was expected

to' Dccur at this stage. As time elapsed during cDmpactiDn, the mixture and

the mDld temperature decreased with a cDncDmitant decrease in the vertical

defDrmatiDn. UnfDrtunately, the temperatures Df the specimens at the end Df

the cDmpactiDn stages were nDt measured. Vertical defDrmatiDn did cease at

the final stage Df the cDmpactiDn prDcess (Figure 6.1) which indicates that the

shakedDwn limit was reached.

SDme Df the HMA were cDmpacted after almDSt Dne and a half years

frDm the date Df plant prDductiDn. These specimens were cDded as SL5S1x,

SL 7S3x and SL8S1x (S=simple shear, L=IDt, Sl=sample ND., and x=specimen

No.. x frDm sample ND.). IT a mixture is nDt cDmpacted immediately after plant

prDductiDn, the asphalt cement becDmes Dxidized and the aggregates absDrb a

certain amDunt Df asphalt cement. This prDcess causes the mixture to. becDme

difficult to. cDmpact to. the desired air vDids and density. HDwever, the new

cDmpactiDn device prDduced samples with air vDids and densities similar to.

the freshly cDmpacted sample using the Marshall methDd (Table 6.1).

Using the new cDmpactiDn device, it was pDssible to. achieve 92-94% Df

the maximum theoretical density. The range Df the air vDids Df the cDmpacted

128

samples is between 6.7 to 7.9% (Table 6.2). The density of the specimens pre

pared by the new rolling device was, on average, about 100% of the specimens

prepared by Marshall apparatus (Table 6.3).

The maximum pressure applied during the rolling compaction was

about 600 kPa (vertical load cell reading). More pressure, if applied, may

cause the specimen to reach higher density. However, because of the load

limitation of the apparatus, the author did not choose to study the higher

compaction stress.

129

Table 6.1

Properties of Samples After Compaction

(A) (C) (B) (B-A/B-C) A/(B-C) A/(B-C)

Sample Dry wt. Wt. in Surface % water Bulk Bulk

No. in air water dry sample absorbed Sp. Gr. Sp. Gr.

in air by volume

(kg) (kg) (kg) (%) kg/m3 (lbs/ft3)

CL7S11 3.6465 2.0113 3.6725 1.5651 2.1951 136.97

CL7S12 3.6025 2.0043 3.6253 1.4065 2.2224 138.68

CL7S13 3.7057 2.0590 3.7305 1.5256 2.2166 138.31

CL7S14 N/A N/A N/A N/A N/A N/A

CL7S15 3.6890 2.0399 3.7197 1.8276 2.1961 137.04

CL7S16 3.5693 1.9819 3.6097 2.4819 2.1927 136.83

CL7S31 3.7101 2.0400 3.7361 1.5329 2.1874 136.50

CL7S32 3.6498 2.0175 3.6744 1.4847 2.2028 137.45

CL7S33 3.7101 2.0627 3.7360 1.5473 2.2164 138.31

CL7S34 3.7490 2.0871 3.7707 1.2889 2.2268 138.95

CL7S35 3.8673 2.1495 3.8917 1.4005 2.2198 138.51

CL8S21 3.5921 1.9785 3.6250 1.9982 2.1817 136.14

CL8S22 3.6989 2.0460 3.7192 1.2132 2.2107 137.95

CL8S23 3.6840 2.0324 3.7145 1.8132 2.1901 136.66

CL8S24 3.7576 2.0709 3.7895 1.90564 2.1859 136.40

CL8S25 3.6522 1.9852 3.6872 2.0564 2.1458 133.90

130

Cont. Table 6.1

Properties of Samples After Compaction

(A) (C) (B) (B-A/B-C) A/(B-C) A/(B-C)



in air by volume

(kg) (kg) (kg) (%) kg/rn3 (lbs/It3)

CL5S31 3.0781 1.6878 3.1009 1.6135 2.1783 135.93

CL5S32 3.5374 1.9586 3.5625 1.5649 2.2055 137.62

CL5S33 3.5120 1.9437 3.5317 1.5880 2.2116 138.00


CL5S35 3.2900 1.7900 3.3170 1.7682 2.1546 134.45

CL5S36 3.2320 1.7590 3.2590 1.8000 2.1547 134.45

CL5S37 3.2610 1.7735 3.2870 1.8518 2.1567 134.58

CL6S31 3.4470 1.9116 3.4745 1.7596 2.2055 137.62

CL6S32 3.6587 2.0050 3.7245 3.8267 2.2178 138.39

CL6S33 3.0923 1.7000 3.1331 2.8470 2.1578 134.65

CL8s31 3.1078 1.7190 3.1274 1.392 2.2066 137.69

CL8s32 3.2475 1.7953 3.2940 3.1027 2.1669 135.21

131

Table 6.2

Air Voids of Samples After Compaction

Sample Samples Lots

No. Air Voids Air Voids

(NRCM) (Marshall Method)

(%) (%)

CL7S11 7.1 6.9

CL7S12 5.9

CL7S13 6.2 CL7S14 N/A CL7S15 7.0 CL7S16 7.2

avg.= 6.7 avg.= 6.9

CL7S31 7.3 6.5

CL7S32 6.6

CL7S33 6.0

CL7S34 5.9

CL7S35 7.5

avg.= 6.7 avg.= 6.5

CL8S21 7.5 6.6

CL8S22 6.2

CL8S23 7.1

CL8S24 7.3

CL8S25 9.0

avg.= 7.4 avg.= 6.6

132

Cont. Table 6.2

Air Voids of Samples After Compaction

Sample Samples Lots

No. Air Voids Air Voids

(NROM) (Marshall Method)

(%) (%)

OL5S31 7.8 7.1

OL5S32 6.7

OL5S33 6.4

OL5S34 N/A OL5S35 8.9

OL5S36 8.9

OL5S37 8.8

avg.= 7.9 avg.= 7.1

OL6S31 6.8 7.3

OL6S32 6.2

OL6S33 8.8

avg.= 7.3 avg.= 7.3

OL8S31 6.8 6.5

OL8532 8.5

avg.= 7.7 avg.= 6.5

Table 6.3

Comparison of Densities Obtained by Marshall Method

and the Compaction Device

(1) (2) (3) (1)/(2) (1)/(3)

Sample Samples Lots Lots (NRCM) (NRCM)

No. Densities Densities Density to to

(NRCM) (Marshall) (Rice) Marshall Rice

(kg/m3) (kg/m3

) (kg/m3) (%) (%)

CL7S11 2.1951 2.2003 2.3622 99.76 92.93

CL7S12 2.2224 101.00 94.08

CL7S13 2.2166 100.74 93.83

CL7S14 N/A N/A N/A N/A N/A

CL7S15 2.1961 99.81 92.97

CL7S16 2.1927 99.65 92.82

avg.= 2.2046 2.2003 2.3622 100.2 93.32

CL7S31 2.1874 2.2051 2.3590 99.19 92.73

CL7S32 2.2028 99.90 93.38

CL7S33 2.2164 100.51 93.96

CL7S34 2.2268 100.98 94.40

CL7S35 2.2198 100.67 94.10

avg.= 2.2106 2.2051 2.3590 100.25 93.71

CL8S21 2.1817 2.2019 2.3574 99.08 92.55

CL8S22 2.2107 100.40 93.78

CL8S23 2.1901 99.46 92.94

CL8S24 2.1859 99.27 92.73

CL8S25 2.1458 97.45 91.02

avg.= 2.1828 2.2019 2.3574 99.13 92.61

133

Cont. Table 6.3

Comparison of Densities Obtained by Marshall Method

and the Compaction Device

(1) (2) (3) (1)/(2) (1)/(3)

Sample Samples Lots Lots (NRCM) (NRCM)

No. Densities Densities Density to to

(NRCM) (Marshall) (Rice) Marshall Rice

(kg/rn3) (kg/rn3

) (kg/rn3) (%) (%)

CL5S31 2.1783 2.1971 2.3638 99.16 92.15

CL5S32 2.2055 100.38 93.30

CL5S33 2.2116 100.66 93.56

CL5S34 N/A N/A N/A N/A N/A

CL5S35 2.1546 98.07 91.15

CL5S36 2.1547 98.07 91.15

CL5S37 2.1567 98.16 91.24

avg.= 2.2088 2.1971 2.3638 99.08 92.09

CL6S31 2.2055 2.1779 2.3494 101.27 93.88

CL6S32 2.2178 101.83 94.40

CL6S33 2.1578 99.08 91.8

avg.= 2.1937 2.1779 2.3494 100.73 93.36

CL8s31 2.2066 2.1955 2.3510 100.51 93.86

CL8s32 2.1669 98.70 92.17

avg.= 2.1868 2.1955 2.3510 99.61 93.02

134

135

6.3 Shear Stress-Shear Strain Response

6.3.1 Simple Shear Behavior of Asphalt Concrete Using a Complete Cycle

A complete cycle is defined as a cycle of shear stress (±T zx) caused by

a cyclic shear strain (±"Yzx) at which an element, under the center line of a

wheel path, is subjected to during rolling contact (Figures 3.5 and 3.9). This

mechanism was simulated in the laboratory using the new simple shear device.

Typically a constant pressure (600 kPa) was imposed on a compacted asphaltic

concrete specimen, and then the specimen was subjected to a complete cyclic

simple shear. The temperature of the specimen, the shear strain magnitude,

and the rate of loading were selected based on some initial tests and kept

constant throughout the testing period. The initial tests were carried out to

give a general overview of HMA behavior at different pressures, temperatures,

shear strains, and to calibrate the new simple shear device. The intention

of the experimental work was to simulate the state of stresses in which an

element at positions B, 0, and D (Figure 6.2) is subjected to in the field.

The shear stress-shear strain behavior of a compacted HMA sample

tested at a temperature of 25°0 (77°F), and at a constant vertical pressure

of 600 kPa, using a complete cyclic loading, is presented in Figure 6.2. The

behavior can be summarized as the following:

• Path OA is the positive shearing path and represents part of the mono

tonic loading up to shear strain, "Yzx, at about 2.0%.

• At point A, the maximum positive shear stress, +Tzx , was about 335

kPa and the shear strain was reversed.

• The reversed shear stress passed through the zero stress point B before

reaching the transition point C. At point B, the shear stress was zero

136

at about 'Yzx = 0.8%. This indicates that approximately one-half of the

applied shear strain reversal remained as residual shear strain.

• At the transition point, 0, the shear strain was zero. A shear stress,

Tzx , of about -100 kPa accumulated due to the shear strain reversal.

Reverse monotonic loading continued from the transition point 0 to

the maximum negative shear strain at point D .

• At point D, the maximum negative shear strain was about -2.5%

("'(;x = -2.5%) and the maximum negative shear stress was about

-290 kPa (Tzx = -290 kPa). The shear stress at point D was lower

than the shear stress at developed at point A. There are many possible

reasons for the above observation:

1) The above represents the response of the HMA to reverse shear

straining. When the shear strain was reversed at A, the HMA

specimen was prestressed in the positive direction compared to

the zero shear stress at O. The applied positive shear stress,

from point A to point B, was resisted by aggregate interlock

and cohesive force of the asphalt between the aggregates in the

HMA. The reverse shear strain from point A to point D did

not encounter the same shear stress resistance. This can be

attributed to the fact that asphalt is a viscous material. Since

there was no rest period between positive (forward) and negative

(backward) shearing at point A, the asphalt did not contribute

to the reverse shearing resistance as it did during the positive

shearing.

137

2) It can be seen from Figure 6.2 that the maximum positive and

negative shear strains, ±""zz (%), are not equal. This is attribut

ed to either the slack that exists in the shear loading system

(ball nut, ball screw shaft, and end supports of the screw shaft)

and/or a delay of stepper motor operation at some points dur

ing cycling, which makes it difficult to control the peak shear

strain at the positive and negative limits. However, this is not

always the case for all the experiments. In some experiments,

when the loading system was tightened by the technicians be

fore testing, no inequality occurred for the positive and negative

maximum shear strains and the loading system remained very

stiff throughout the test (Figures 6.3 and 6.4).

• The specimen was then loaded monotonically (positive shear stress)

from point D until it was stress free at point E. The residual shear

strain at point E was 1.1%, which is higher than that of point B. This

is attributed to the difference of about 0.5% that occurred between the

maximum positive and negative shear strain, (±"";z).

• At point F, the shear stress was about 130 kPa, which was higher than

that of point C by about 30%.

• The monotonic loading continued from point F to point A. The shear

stress at A was higher than that at A, which indicates that the HMA

specimen was going through a stiffening process at the peak positive

shear strain, "";z. No evidence of any change in the negative maximum

shear stress, Tzz , at point D can be noticed. This may be due to the

fact that material stiffening in the initial positive shearing direction

was caused by the initial aggregate interlocking mechanism.

138

In general, the cyclic shear-strain curve is not smooth. Possible reasons

for this response are as follows:

• Inhomogeneity- the HMA consists of a mixture of stones, air,

and a viscous material (asphalt) which, due to reorientation and

internal movements of the mixture, can lead to a discontinuous

response.

• Inadequate stiffness of the loading system due to the slack in the

loading system as described before.

The vertical pressure applied to a specimen during testing was moni

tored by a gauge pressure and a load cell. From visual inspections of the gauge

during testing, no pressure fluctuation was observed. However, some minor

fluctuations in the vertical pressure during testing were detected electronically

by the vertical load cell (Figure 6.5). This fluctuation was caused by:

1) Noise effect or grounding problem in the device electronic sys

tem. The electronics fluctuations were measured to range be

tween ±5 mv/v, which accounts for fluctuation of vertical stress

of ±2 kPa.

2) Bending of load cell during cyclic loading. Because of the non

uniform distribution of shear stresses in simple shear devices

(Budhu, 1988), the top platen tended to tilt causing the vertical

shaft to rotate. Bending occurs in the load cell because the load

cell works as a connecting element between the upper hydraulic

shaft and the lower shaft attached to the upper platen; when

a specimen is sheared, both shaft tend to rotate in opposite

139

directions. This produces a bending moment on the load cell

causing some minor fluctuation in vertical pressure readings.

3) Another source of vertical pressure fluctuation may be due to oil

loss from the oil reservoir and material deformation and dilation.

Therefore, to account for such fluctuations, the shear stress, Tzx , was

divided by the vertical stress, (1z, (normalized shear stress T zx /(1z) and plotted

against shear strain, {zx (%), as illustrated in Figures 6.6 to 6.8. These

figures represent the general behavior of HMA material during a complete

cyclic loading in simple shear.

When the asphaltic concrete specimen was placed in the simple shear

box and loaded vertically, the vertical deformation was accompanied by lat

eral stresses (normal to the direction of the applied shear load). The lateral

stresses, (1x and (1y (inset diagram, Figure 6.2), tend to increase as the number

of cycles increase. An increase in lateral stresses at peak points (±{zx) during

testing may be attributed to the build up of axial deformation and aggre

gate reorientation. When the lateral stresses do not increase and the average

vertical strain changes are zero, the HMA may be said to have reached the

shakedown limit (Figures 6.9 and 6.10). Only the specimen tested at 80°C

showed an indication of stability. This stability indication is caused by a closer

contact between aggregate particles and the less role the asphalt plays as a

lubricating substance between aggregate particles.

Lateral stresses, (1x and (1y, were recorded using load cells described

in Chapter 4. The lateral load cells were inconsistent in recording the lateral

stresses for some duplicate experiments. This is attributed to the aggregates

interlocking around or at the load cells, see Figure 6.11. The diameter of

the load cells is 15.24 mm (0.6 in). To measure the lateral stresses of HMA,

140

when loaded vertically, the load cells size was found to be insufficient. This

problem precluded the author relay on load cells readings to estimate the

residual stresses of the tested specimens.

6.3.2 Simple Shear Using One-half Cycle

Normal and tangential loads occur under wheels rolling on pavement

surface at traffic lights (acceleration and deceleration), sharp turns, bus stops,

and others. When a tangential stress is considered, the maximum value of

shear stress, Tz:z;, occurs at a point closer to the surface of contact, as discussed

Chapter 3. An element of asphaltic concrete below the surface of contact is

illustrated graphically in Figure 6.12. In this Figure, the element is located at

a point adjacent to wheel path and below the surface. Normal pressure, p = Po-/1- (x - a)2, and tangential pressure, q = fPo-/1- (x - a)2, cause the

element to be sheared in one direction only. Figure 6.13 illustrates an element

located below a pavement surface and in front of a braking wheel or behind

an accelerating wheel. The above cases can be simulated in the laboratory by

using the new simple shear device and testing procedure explained in Chapter

5 with one-half cyclic loading rather than a complete cyclic loading.

A typical cyclic shear stress versus shear strain response for one-half

cycle using three different temperatures are presented in Figures 6.14 to 6.16.

The general behavior shows that the material under investigation was soft

ening rather than hardening in the positive shearing direction. Figure 6.17

illustrates the softening trend. It is noticed in the figure that the HMA spec

imen tested at room temperature, 25°C (77°F), started to harden at the

initial 10 cycles of testing. A material softening trend for the remaining cy

cles is evident. The softening trend may be attributed to the drop that may

have occurred in residual stresses at the plane of maximum shear stress. A

141

HMA specimen tested at 600 e (140°F) showed a drop of shearing resistance

up to cycle number 1000; then there was no indication of any changes in the

HMA shearing resistance for the remaining number of cycles. The stable s

hear strength is attributed to the stability in the particles arrangements and

orientations. However, this condition is not, by any means, an indication of

material stability nor is it to say that the material has shaken-down. A drop

of shear stress resistance in a HMA specimen tested at a temperature equal

to BOoe (176°F) can be noticed in the first twenty cycles, then a stable shear

stress resistance was maintained up to, approximately, cycle number 600. A

second round of shear stress drop was initiated around cycle number BOO. This

kind of trend may be attributed to the loss of cohesion between asphalt and

aggregate due to the high temperature.

Shear stresses of complete and one-half at shear strain equal to 2 per

cent and at different temperatures are compared, see Figures 6-1B to 6-20.

Figure 6-19 indicates that an HMA specimen tested in complete cycles at a

temperature equal to 25°e (77°F) maintained a higher shear resistance than

the HMA specimen tested under one-half cycles. The opposite is true for

the HMA specimen tested at higher temperatures. No justification for such

behavior can be presented at this stage.

6.3.3 Volumetric Deformation

When specimens were sheared in complete or one-half cycles, volumet

ric deformation occurred. The volumetric deformation is normally influenced

by testing temperature.

Asphalt material is known to be very susceptible to temperature. When

cooled to low temperatures (e.g. < 0° G), bitumen material behaves elastically.

On the other hand, when heated to a high enough temperature (e.g. < 100° e),

142

it behaves like a viscous material and displays a consistency of a lubricating

fluid. Therefore, temperature is considered to be a significant variable that af

fects the volumetric deformation. Another variable, which may be considered

to be significant in controlling the volumetric deformation, is the hardening

of asphalt cement. Since asphalt cement is an organic molecule, it reacts with

oxygen. This causes asphalt cement to become more brittle. The hardening

process is called "oxidative hardening" or "age hardening." The term "embrit

tlement" is sometimes used in the literature. Volatization hardening is due to

asphalt heating. This type of hardening occurs in short period of time. Ox

idative hardening causes the modulus of elasticity to become larger and elastic

strain becomes smaller. This process causes high tensile stress to develop at

the bottom of the asphalt layer when load. is applied by traffic. Cracks may

develop at the bottom of the asphalt layer and propagate upward toward the

surface.

Warmer specimens deformed more than the cooler specimens when test

ed in simple shear and under a full cyclic loading. Temperature influence on

the volumetric strain, €v, is shown in Figures 6.21 for complete cycles and

Figure 6.22 for one-half cycles. The volumetric strain occurrence was expect

ed higher for specimens tested at higher temperature and lower volumetric

strain for specimens tested at lower temperature. The volumetric strain for

a complete cyclic test for a HMA specimen tested at 80°C (176°F) indicat

ed otherwise (Figure 6.22) when compared to the specimen tested at 60°C

(140° F). This is attributed to the initial creep condition to which the speci

men was subjected during the heating stage prior to testing. The amount of

the initial vertical deformation during the heating stage is not known and was

not taken into account when calculating the vertical strain during and after

143

testing. HMA specimen tested at 60°0 (140°F) showed a tendency towards

shakedown limit after cycle number 1000.

All three different temperature HMA specimens tested under one-half

cycles show a continuation of further volumetric deformation at the late stages

of the experiments, which indicates that the shakedown limit is not reached

(Figure 6-22).

From the above figures, it can be noticed that maximum vertical de

formation occurred at the initial stages of the experiments. This deformation

may be attributed to the surface irregularities, such that contact occurs not

over a continuous area but over several high points, and aggregates reorienta

tions. Volumetric deformation causes air voids to drop, on an average, about

one percent after testing (Tables 6.4 and 6.5).

144

Table 6.4

Properties of Samples After Testing

(A) (C) (B) (B-A/f3..C) A/(B-C) A/(B-C)



in air by volume

(kg) (kg) (kg) (%) kg/rn3 (lbs/ it3)

CL7S11 3.6457 2.0134 3.6617 0.9707 2.2118 138.02

CL7S12 3.5989 2.0029 3.6165 1.0907 2.2304 139.17

CL7S13 3.6939 2.0611 3.6982 0.2627 2.2564 140.80


CL7S15 3.6960 2.0500 3.7219 1.5491 2.2107 137.95


CL7S31 3.7111 2.0359 3.7394 1.6613 2.1785 135.94

CL7S32 3.6509 2.0172 3.6778 1.6199 2.1985 137.19

CL7S33 3.7126 2.0730 3.7300 1.0501 2.2406 139.81

CL7S34 3.7474 2.0914 3.7652 1.0635 2.2389 139.71

CL7S35 3.8717 2.1509 3.8947 1.3190 2.2203 138.55

CL8S21 N/T N/T N/T N/T N/T N/T

CL8S22 3.7001 2.0480 3.7176 1.0482 2.2162 138.29

CL8S23 3.6819 2.0327 3.7076 1.5344 2.1983 137.17

CL8S24 3.7559 2.0678 3.7850 1.6946 2.1872 136.48

CL8S25 3.6520 1.9879 3.6851 1.9503 2.1518 134.27

145

Table 6.5

Air Voids of Samples After Simple Shear Testing

Sample Air Voids Air Voids

No. for Samples for Samples

Before Testing After Testing

(%) (%)

CL7S11 7.1 6.4

CL7S12 5.9 5.6

CL7S13 6.2 4.5

CL7S14 NIA NIA CL7S15 7.0 6.4

CL7S16 7.2 NIT

avg.= 6.7 avg.= 5.7

CL7S31 7.3 7.7

CL7S32 6.6 6.S

CL7S33 6.0 5.1

CL7S34 5.9 5.2

CL7S35 7.5 5.9

avg.= 6.7 avg.= 6.1

CLSS21 7.5 NIT CLSS22 6.2 6.0

CLSS23 7.1 6.S

CLSS24 7.3 7.2

CLSS25 9.0 7.3

avg.= 7.4 avg.= 6.S

146

0

E ~ -5

t:: .9 ~ C\l

E -10 ~

QJ

0 -.~ t

-15

~ 0

-20 Velocity of the compaction device

10 mm1sec 15 mm1sec

-25

0 1 2 3 4 5 6

Compaction Stages

Figure 6.1 Vertical Deformation of Asphalt Mixture During Different

Stages of Compaction.

-n1 a. ~ -

147

400 Cycle No.1, 2 & 3 i 't

zx Temp.= 25° C (77" F) 'tzx

300 Gz = 600 (kPal

200 E=57306 kPa (8305 psi)

100

o -t

2X

-100

-200

-300 ~-------l -'tzx

( )

-400 Negative shearing direction Positive shearing direction

-3 -2 -1 o 1 2 3

Shear Strain, 'Y (%)

Figure 6.2 Shear Stress Versus Shear Strain (Temperature at 25°

(77° F)) for Complete Cycles in Simple Shear Test.

~ ~ ........,

~~

148

400 Cycles 1,2, & 3 Temp. = 60°C (140° F)

300 lIz = 600 (kPa)

200

E=38786 kPa (5621 psi)

100

0

-100

-200

-300

-400 -1-----.---..------+---.---..----1

-3 -2 -1 o 1 2 3

y(%)

Figure 6.3 Shear Stress Versus Shear Strain (Temperature at 600

(140 0 F)) for Complete Cycles in Simple Shear Test.

149

300 Cycles No. 1,2 &3

Temp.= Br? C (17ft' F)

C1z=600kPa

200

---- E= 11612kPa (1683 psi) tt -~l:S 100 '-"'

.9 ..... & 0 ~ ~ .....

V) -100 10....

m ~

-200

-300 +------r----,---!-------,---.----l

-3 -2 -1 o 1 2 3

y (%)

Figure 6.4 Shear Stress Versus Shear Strain (Temperature at 80°

(176° F» for Complete Cycles in Simple Shear Test.

606

604

602

600 -m a.. ~ 598 .......

bN

596

594

592

590

1 10 100

Temp. = 25° C (77° F) crz = 600 (kPa)

1000 10000

Number of Cycle

150

Figure 6.5 Vertical Pressure Fluctuation During Simple Shear Testing

for Complete Cycles in Simple Shear Test.

'N b

~ p "-" .S! ..... & ~ ~ ~ " :B ~

151

0.8 Cycle No.1. 2 & 3

0 0

Temp. = 25 C (77 F)

0.6 a z = 600 (kPa)

0.4

0.2

0.0

-0.2

-0.4

-0.6

-0.8

-3 -2 -1 0 1 2 3

"((%)

Figure 6.6 Shear Stress Ratio Versus Shear Strain (Temperature at 25°


0.8 -.--------,-------, Cycles 1 , 2, & 3

Temp. =600

C (1400

F)

0.6 °z=600(kPa)

0.4

0.2

0.0 -/----"'7F------f--,,....L------l

-0.2

-0.4

-0.6

-0.8 -t----,---,----I----,---.--l

-3 -2 -1 o 1 2 3

y(%)

152



153

0.4 Cycles No. 1,2 &3

Temp.= 8if C (17£? F)

Oz=600kPa

,-... 0.2 tr ->(

N ... '-"

.9 ~

& 0.0 ~ ~ ~ V) ~

m 65 -0.2

-0.4 -3 -2 -1 o 1 2 3

"(%)



154

350

300

250

200

~ 150 ~ '--'

b~ 100

50

0

-50

-100

1 10 100 1000 10000

Number of cycles

Figure 6.9 Lateral Stresses (Flap Load Cell Readings) Versus Number

of Cycles at Peak of the Amplitude for Complete Cycles in

Simple Shear Test.

155

350

300

250

200 ~ ~ 150 '-"

b>'

100

50

0 2SOC(Tt' F)

-50

1 10 100 1000 10000

Number of cycles

Figure 6.10 Lateral Stresses (Side Wall Load Cell Readings) Versus

Number of Cycles at Peak of the Amplitude for Complete Cycles

in Simple Shear Test.

156

(oj (b)

(c) (cD

Figure 6.11 Aggregate Interlocking Around the Lateral Load cells.

157

B c

~p

B c

Figure 6.12 An Element Located Below a Pavement Surface Adjacent

to a Wheel Path.

158

~p

B

Figure 6.13 An Element Located Below a Pavement Surface In Front

of a Braking Wheel or Behind an Accelerating Wheel.

0.8 ...,---.,------------,

0.6

0.4

0.2

Cycles 1. 2 & 3

Temp.= 25° C (Tf' F)

Gz = 600 (kPa)

0.0 -j----f-----H7'-H-----i

-0.2

-0.4 --'----/---.-------.-----1

o 1 . 2 3

'Y (%)

159

Figure 6.14 Shear Stress Ratio Versus Shear Strain (Temperature at

2500 (770 F)) for One-half Cycles in Simple Shear Test.

t)N -~}

0.8 --,-----,------------,

0.6

0.4 -

0.2

0.0

-0.2

Cycles 1 ,2 & 3 Temp. = 60° C (140° F)

crz = 600 (kPa)

-0.4 --!-.--+---,---,----l

o 1 2 3

y(%)

160


60°C (140°F)) for One-half Cycles in Simple Shear Test.

161

0.7 Cyclos 1,2 & 3

Temp. = 800

C (1760

F)

0.6 <1z = 600 (kPa)

0.5

0.4

bN 0.3 -~ 0.2 ~

0.1

0.0

-0.1

-0.2 0 1 2 3 4

y(%)


80°C (176°F)) for One-half Cycles in Simple Shear Test.

0.75 ~------------

0.70

0.65

"N ...... 0.60 ~~

0.55

0.50

Oz = 600 (kPa)

1 10 100 1000 10000

Number of cycles

162

Figure 6.17 Shear Stress Ratio Versus Shear Strain (Temperatures at

250 (770 F), 600 (1400 F), and 800 (1760 F)) for One-half Cycles

in Simple Shear Test.

163

0.7 Complete cycles. '(=2% (Test. 5L7521)

0.6

0 0

0.5 Temp. = 25 C (77 F)

CJz= 600 (kPa)

-?-. 'ON 0.4 ~" ~<'~

......... '~ %

~}~ r,)o.

0.3 ~

'..1': :(6'~ ~

0.2

0.1

0.0

1 10 100 1000 10000

Number of Cycles

Figure 6.18 Shear Stress Ratio Versus Shear Strain at 2% (Tempera

ture at 250 (770 F)) for complete and One-half Cycles in Simple

Shear Tests.

-... I:;)N ->e ~N '-'

.~ 0\..1

~ ~ ~ ~ '-lB

65

0.60

0.58

0.56

0.54

0.52

0.50

0.48

0.46

0.44

0.42

1 10 100

Temp.= 60· C (140· F)

crz = 600 (kPa)

1000 10000

Number of cycles

164

Figure 6.19 Shear Stress Ratio Versus Shear Strain at 2% (Temperature

at 60° (140°F)) for complete and One-half Cycles in Simple

Shear Tests.

0.60 -.-----0--0-----------, Temp. = 80 C (176 F)

Gz = 600 (kPa)

0.55

0.50

.J2N 0.45

0.40

0.35

0.30

0.25 --l....-.-------.----.-------.-------.---J

1 10 100 1000 10000

Number of Cycles

165

Figure 6.20 Shear Stress Ratio Versus Shear Strain at 2% (Temperature

at 800 (1760 F)) for complete and One-half Cycles in Simple

Shear Tests.

0.0

-0.2

--. -0.4 :::R c -> w

-0.6

-0.8

-1.0

1

stmcomb tests SL7S33 SL7slS, SL7S21

10 100 1000 10000

Number of cycles

166

Figure 6.21 Volumetric Strain Versus Number of Cycles (Temperatures

at 250 (770 F), 600 (1400 F), and 800 (176 0 F)) for Complete

Cycles in Simple Shear Tests.

-::R 0 '-"'

> w

. 0.2 -,----------------,

0.0

-0.2

-0.4

-0.6

-0.8

az = 600 (kPa) SL8S22, 23 & 25 @ Home Position

-1.0 --'-,----,----,----,...----....--J

1 10 100 1000 10000

No. of Cycles

167

Figure 6.22 Volumetric Strain Versus Number of Cycles (Temperatures

at 25° (77°F), 60° (140°F), and 80° (176°F)) for One-half

Cycles in Simple Shear Tests.

168

CHAPTER 7

CONCLUSIONS AND RECOMMENDATIONS

7.1 Conclusions

Permanent deformation in asphaltic concrete pavement has a major

impact on pavement performance. It reduces the pavement service life and

causes safety hazards to the motorist. The main cause of permanent defor

mation in asphaltic concrete layers is shear. Mixture densification due to

compaction by traffic is considered to be a secondary factor in permanent de

formation provided that the asphalt concrete mixture is well compacted in the

first place. The primary cause of permanent deformation in asphaltic concrete

pavement is due to the excessive shear stress caused by repetitive vertical and

shear loadings imposed by traffic. Conclusions drawn from this research are

summarized as follows;

• The contact pressure at tire/pavement interface is under estimated in

the current flexible pavement design methods. The contact pressure

between the tire and the pavement surface is assumed by the researchers

and pavement engineers to be equal to tire inflation pressure, po. This is

demonstrated to be not always true. Mean contact stress, Pm, between

a tire and a pavement surface may be as high as double the tire inflation

pressure or po = 2pm;

• Current design methods do not consider shear stress imposed by wheels

on pavement surfaces;

169

• The maximum shear stress, Tmax, due to static or slowly moving wheel

s, occurs beneath the loaded plane or the pavement surface at a depth

equal to O.5a and at a distant equal to O.78a from wheel loading cen

terline (a is the radius of contact area). This depth tend to decrease

when shear stress, due to deceleration or acceleration of a wheel, is

included in the analysis of the maximum shear stress occurrence under

the pavement surface;

• The repeated reversal shear stresses that occurs in the field and under

a moving wheel can not be reproduced in the triaxial test or any other

tests that are currently used in asphalt concrete laboratories. There

fore, a new simple shear apparatus was designed to test HMA specimen

in a simple shear test. The simple shear test can provide the best ar

rangement for stresses to simulate, as closely as possible, the stress

state occurrence in the field;

• Compaction methods used in asphalt laboratories to prepare HMA

samples do not resemble the compaction method used in the field. A

new compaction apparatus capable of preparing asphaltic concrete or

any other rock or soil samples to fit exactly in the new simple shear

box was designed and constructed;

• The compaction procedure was developed to prepare a dense sample

with a smooth surface parallel to its base. Although the asphalt con

crete mixture was obtained from the field and was compacted after

some period of time (3 months to one and a half years), the density

and air voids of the compacted samples obtained in the new simple s

hear and compaction apparatus were very close to that of the Marshall

test. Between 92% to 94% of the maximum theoretical density and

170

6.5% to 7.3% air voids were achieved using the new rolling compaction

method (NRCM). About 50% of the total axial deformation of the loose

HMA occurred during the first stage of compaction. The shakedown

limit was reached after the final stage of compaction was completed;

• The shear stress-shear strain response of HMA using the new simple

shear apparatus can be summarized as follows:

o The stiffness of HMA tested at room temperature is higher for

specimens tested in a complete cycles than specimens tested in

one-half cycle test. The opposite was true for specimens tested

at higher temperature.

o Vertical deformation was expected to be higher for specimen

s tested at higher temperatures. This was true for specimens

tested at 25°C and 60°C in complete cycles. Volumetric defor

mation for specimen tested at 80°C was not as high as it was

suppose to be due to creep that was suspected to occur, and

not counted for in the ACSSP, during specimen heating process

(about one and one-half of an hour).

o Based on the limited number of tests conducted, using one-half

cycles, to evaluate the influence of temperature, the data indi

cated that a drop of residual stress is inevitable and axial de

formation cannot be ceased at high temperatures. Shear stress

softening occurred with every cycle. Shakedown limit was not

reached for all specimens tested in the one-half cycles.

171

7.2 Recommendations for Future Research

It took a very long time to design, engineer, modify, build, and calibrate

the new compaction and simple shear apparatus. Due to time and practical

limitations, the author could not perform some of the important research ideas.

Therefore, further research may include:

1. Different asphalt grades;

2. Different aggregate gradations;

3. Asphalt modifiers such as rubbers, plastics, fillers and fibers,

and other materials that may reduce asphalt viscosity variation

with temperature fluctuation;

4. Sample preparation using vibratory compaction while rolling;

5. Simple shear testing at asphalt softening point temperature;

6. A study of different amplitudes and velocities under simple shear

testing;

7. Influence of dynamic loadings during simple shear testing when

compared to the static loading;

8. Comparison between the results of testing asphaltic concrete

samples in rough and smooth internal surfaces of the simple

shear box; and

9. A study of axial deformation during compaction stages with the

possibility of driving a model or a program to predict density

and air voids during and after completion of compaction.

The new compaction and simple shear device is a prototype model

designed and constructed solely for this research. The following are notes

and recommendations to modify and improve the new compaction and simple

shear apparatus:

172

1. Modify the end supporters of the ball screw and ball nut at

tached to the stepper motor. The improvement should include

the stiffening of the end supporters;

2. Lateral movement of the vertical harden steel shaft was noticed

during testing and calibration stage of the device, specially at

high velocity and amplitude. In order to prevent shaft lateral

movement, different type of supporters may be suggested;

3. Temperature system should be controlled and adjusted manual

ly, or by an independent system other than a computer software,

or modify the computer program to allow for a better monitoring

and control procedure for the temperature;

4. Provide a heating system for the compaction device to maintain

a constant compaction temperature throughout the compaction

stages;

5. Install a gear system between the stepper motor and the screw

shaft to increase torque;

6. Different types of load cells for lateral stresses.

7. Install a more sensitive LVDT to measure the horizontal move

ment of the lower base.

173

Appendix A

Constitutive Models and Permanent Deformation Equations Overview

174

Table A.l


Author& Modez.,

Kirwan fn = Aab

Snaith Glynn (1977) where:

fn = induced axial permanent strain after elapsed time N,

A = function of elapsed time and material,

b = constant for the material,

a = applied axial compressive stress.

remark" The test used in this model is a uniaxial compression dynamic loading creep test. The calculated valued of the rut depth is higher than the obtained values in the Nottingham Test Track.

Tesing, fa = foexp[-( N ).8] Lytton

(1986)

where:

fa = permanent strain,

N = load cycles,

b = constant for the material,

fo, p, {3 = regression parameters.

remar~

Repeated load tesing.

175

Table A.1 (continued)


Au.thor" Model"

van de Loo Ep = cuN" (1976)

where:

Ep = axial permanent deformation,

c = constant,

U = axial stress level 15 psi,

N = number of load applications,

a = constant.

remarks This model, in general, overestimates the plastic deformation, and it is considered the basis of the Shell method.

Table A.l (continued)


Author"

Kenis (1977)

Mode'"

where: fp(N) = permanent deformation per pulse,

e = peak haversine load strain for load pulse of

duration d=O.1 second,

I' = Is/e, a = I-s,

s = slope of the line on log-log plot of permanent

strain versus number of load applications, N,

I = intercept.

remark" The model accounts for elastic and viscoelastic moduli, load amplitude, load duration, and load repetitions N as random

variables described by their mean and variance.

176

177



Author& Model&

Huschek eirr = cutA

(1977) eirr(T, 6.t l, t) = [,;(~:h] t 1- A

TJ(T, t) = (cA)

where:

eirr = permanent deformation,

c = constant,

U = stress level,

A = consolidation characteristic,

TJ = viscosity,

T = temperature,

6.tl = time of loading.

remar1c& The asphalt mixture was represented by a Maxwell element,

dashpot and spring in series {viscoelastic}. The viscoelastic theory was not used to calculate the stresses and strains in pavement under traffic load. Rather, the linear, elastic multi-layer theory was used to calculate the stresses and strains. The materials were characterized by unconfined compression creep-test. Conditions such as: temperature distribution, number and amount of loadings, transverse distribution of wheel passages, and speed of vehicles were taken into account.

178



Author" Modez.,

J(t) = JltOt Battiato perm 1 ( ) uik = -gik y, Z

fl. where:

(1977)

J(t) = creep compliance function,

t = "time,

Jl = shear creep parameters,

a = slope of line on a log-log between J(t) and time,

uf:rm = permanent deformation,

fl. = shear viscosity of Maxwell element in series,

9ik(Y, z) = tensor function,

remarlc& Two layered viscoelastic incompressible system was considered. Creep experiments were carried out. The study concluded that a considerable accumulation of the deformation was observed for the vertical and transverse deformation, and not for the longitudinal deformation.



Author&

Lai,

(1973)

Celard

(1977)

Model&

Evp = a( 0' )tb

where:

Evp = viscoplastic strain,

t = time,

a(O') = blO' + ~0'2, 0' = creep stress,

b, bl , ~ = regression constants,

remarks Uniaxial creep tests were used to obtain the constants.

Ine = A + BlnO'Vm + CO'H + DT

where:

e = rate of permanent deformation,

O'v m = compressive vertical stress,

0' H = Compressive horizontal stress,

0' = temperature,

A, B, C, D = coefficient constants,

remarks Isocreep curves were developed using dynamic creep tests

179

180



Author& Models

Monismith, E~ = [c5(T)nQqn-lt][O'z - ~(O'z + 0',)] et al. (1977) where:

E~ = vertical permanent deformation,

c5(T) = function of temperature,

Q = coefficient determined experimentally,

N = number of stress repetition,

if = equivalent stress, a function of 0'1 ,0'2 and 0'3, t = loading time,

remark& The experimental tests involved a triaxial compression repeated loading procedure. ELSYM elastic layered theory and layered strain method were used.

Brown and Ep = <C~ )b(N) Bell

(1979) where: Ep = permanent shear strain,

q = deviator stress,


a, b = constants,

remark& Axial repeated load tests were used. Good agreement with the test track was obtained.

181

Table A.I (continued)


Author" Model"

Meyer and Ep = F(0'1,0'2,T,N,AV) ± E Bass (1977) where:

Ep = axial permanent deformation,

0'1 = vertical stress,

0'2 = lateral stress,


T = temperature,

A V = air voids,

E = error of estimate,

remarh The pavement was analyzed by a computer program called FEPAVE II using a finite element layer strain method. Triaxial repeated load tests were used. Good agreement

between measured and predicted rut depth was obtained.



Author"

Francken (1977)

Modez"

For high stresses

E(t) = AtB + O(exp Dt -1) For low stresses E(t) = AtB

where:

Ep(t) = permanent strain,

A, B, 0, D = parameters,

A = 115(0"1 - 0"3)/IE*!, B = 0.182 + 0.294(O"Vm - O"Vt),

O"V m = maximum stress,

O"V L = plastic failure threshold.

remarL Dynamic triaxial tests at different temperatures, frequencies

and stress conditions were carried out. Samples were cylindrical in shape (32 cm high x 8 cm). Lateral pressure was kept constant and vertical pressure was varied sinusoidally at an angular frequency w.

182

183



Author~ Modez.,

Verstraeten,

Romain, and

Veverka (1977)

t fp(t) = A( 103 )B

0(0'1 - 0'3) - IE.I X (~)B where:

fp(t) = permanent strain at time t in sec.,

0'1 = amplitude of vertical stress,

0'3 = lateral stress,

0= f[Vb/(Vb + VII)], B = a coefficient varying between 0.14 and 0.37,

A = a coefficient depending on the mix composition

and on the experimental conditions such

as stresses, frequency and temperature.

remark" Repeated compression tests were performed on cylindrical

samples of different asphalt mixtures, subjected to a vertical stress. The vertical stress is sinusoidal function of the time,

0'11 = 0'1(1 + sin wt). Lateral stress was maintained at a constant level 0'1 = 0'3.

184

Table A.I (continued)


Authors Modeb

Uzan (1982) fp(N) = fruN-OI

where: fp(N) = permanent strain for Nth repetition,

fr = resilient strain,

N = number of repetition,

a = characteristics of materials based on intercept,

u = slope coefficients.

remarks This model is a modification of the AASHO Road Test serviceability model. The predicted rut depth was very sensitive to the plastic material properties of all layers, especially the upper asphaltic one.

The rut depth variance was affected by a of the upper asphaltic layer and its variation.

185



Author& Model&

Khedr (1986) ~ = AaNm

where:

fp = permanent strain,

N = number of load cycles,

Aa = materials properties function of modulus

and applied stress,

m = material parameter.

remarlc& The permanent deformation prediction is based on a theoretical approach which is based on the mechanical concepts. The experimental work is based on the dynamic loading cycles (dynamic creep) on

asphaltic concrete specimens.

186



Author~ Mode~

Thrower (1977)

u·· • 'J eaj =-

2'1 Um (9uij - um)

=-+ 3X 18'1

where: eij = rate of deformation,

U aj = state of stress,

(1 m = isotropic mean stress,

X = coefficient of volume viscosity,

'1 = coefficient of shear viscosity.

remarb A linear viscoelstic model and a separative method were used.

Permanent deformation due to a pulse load depends on the deformation properties of the layers.

187



Atl.thor~ Model~

Mahboub, 7f = aCTb

Little (1988) where:

E ;; = accumulated, viscoplstic deCormation per cycle,

CT = peak cyclic stress,

a, b = regression parameters,

remark~

Triaxial device was used Cor the experimental work. The regression parameters were obtained Crom the results when plotted.

188

Table A.1 (continued)


Author" Model"

Leahy

(1989) Ep = f(T, (1d, Voir, N, f106ph, PWcJIIPh)

where:

€p = plastic strain,

€r = resilient strain,

T = temperature,

(1 d = deviatoric stress,

Voir = volume of air,

f106ph = asphalt viscosity,

PWGIIPh = effective asphalt content.

remarks A laboratory study utilizing dynamic (repeated load triaxial) and static (creep) tests were performed. Prediction of the parameters a and I' as a function of test conditions and mix parameters was very poor. The elastic and plastic strain values were observed to be heavily dependent upon temperature, and to a much lesser degree, dependent upon deviator stress, asphalt type, compactive effort and asphalt content.

Appendix B

Figure B.1 (a) Vertical and (b) Horizontal Load Cells.

Figure B.2 Heat Sensors.

Figure B.3 Horizontal (8.9 kN) Load Cell Calibration.

Figure B.4 Vertical (22.25 kN) Load Cell Calibration.

Figure B.5 Vertical LVDT Calibrations.

189

Figure B.6 Calibration Curves for the Upper and Lower Heat Sensors.

Figure B. 7 Calibration Constant for the Load Cell Installed in the Side

Wall.

Figure B.B Calibration Constant for the Load Cell Installed in the End

Flap.

(a) Vertical Load Cell (22.25 kN)

Electronic connector at 45

with any two 6-32 hale -j t-O.400 to lock the ~ r-0.600

boll nut that (6-~2) 0 will b. fitted to the

loadeoll.

1.173-16 UNS-2

.50 ... 1 1-1.50 or 7-l

(+) 1/1 28 hoi .. equaly opo<:ed en 2.09 0;.,.

(b) Horizontal Load Cell (8.9 kN)

Figure B.1 (a) Vertical and (b) Horizontal Load Cells.

190

SILICON TEMPERATURE SENSORS

... designed for temperature sensing applications in automotive. consumer. and industrial products requiring low cost and high accuracy.

• Precise Temperature AccurllCY Over Extreme Temperature MTS102: ±2°C from -40°C to +150oC

• Precise Temperature Coefficient

• Fast Thermal Time Constant 3 Seconds - Uquid S Seconds - Air

• Llnoar VSE versus Temperature Curve Relationship

• Other Packagas Available

MAXIMUM RATINGS

Rltlng

Eminer·Base Voltage

Collector Current - Continuous·

Operaling and Slorage Junction Temperalure Range

·5 .. Noce 5. ~Q. 2.

Svmbol Vllue

VEB 4.0

IC 100

TJ. Tltg -5510 .150

FIGURE 1 - BASE·EMlTTl:n VOLTAGE venul AMBIENT TEMPERATURE

.'

Unit

Vd.

mAde

·C

1000

:;-

~ BOO

~ Q > a: 600 ~

~

- I =0.1 ~

~ ~ ~

~~t Base

Eminer

~ f--

i:--. VBe Inoml = 620 m~ ~ V """ §::::: I:::::--... VBe Inoml = 600 mV -VBe (noml = 5BO mV

-......;;;: ~ t::---~ ~ 400

.....

20~0 40 80 120 160 TA. AMBIENT TEMPERATURE ,oCI

SILICON TEMPERATURE

SENSORS

A ria

.un .. J;f-I-;T PLANE

F- ~ K

I D-~

~ -~ -J

r-t"R SE~. A·A

, ,. N PIN I. EMITTER

191

~STVLEI: N i ~~~ECTOR

MILLIMETERS INCHES DIM MIN MAX MIN MAX A 02 5.33 0.170 0.210 8 U~ .1 I 5 C 3.18 ~.19 0.125 0.165 0 0.41 O. 0.016 0.022 F 0.41 0.48 0.016 0.019 G 1.14 1.40 o.IMS- a.n55 H - 2. - 0.100 J 2.41 2. 7 0.095 0.105 K 12.70 - I 0.500 -L 6.35 - I 0~250 -N 2.03 .9 '-"11M 0.115 p 2.92 - 0.115 -R 4 - -S 41 4

All JEDEC dirncnsions and nolu.pply. CASE2!I'()2

iO·92

Figure B.2 Heat Sensors.

192

10

8

6

4

c 2 -0 > '-" 0 ..... ::s .& ::s -2 0

-4

-6

-8

-10

-3000 -2000 -1000 a 1000 2000 3000

Applied Load (Lhs)

Figure B.3 Horizontal (8.9 kN) Load Cell Calibration.

Z' -0 :> "-' ..... ::s ,e. ::s 0

-6.0

-6.5

-7.0

-7.5

-8.0

-8.5

-9.0

-9.5

-10.0

0 1000 2000 3000 4000 5000

Applied Load (Lbs)

Figure BA Vertical (22.25 kN) Load Cell Calibration.

193

~t J BBAT J ON r-lEC'QRQ

P.D. eo. 1lI Rovt, IJ Elh"Qton. CT U02'9 T,I 12'I1Jlln·a351 F.a. 1'<'Jlln·'Hi

MODEL • 02~~-OOOO

MOHimum Nonlino .... lty, O.ll~:c. F.S. CoJ.lc:uloJ.tion Mothod, [Hn.t Fit Straight Line ThJ"u Zot"C> C.lc:ul.t.d Lino. V. GO.374tt X + 0.0000 Wo ... klng Rano.s +/- 1 lI'Ic:h C •• ) 5.n~ltlv1tyJ 0.8485 voe I Inch I Volt Input Tested .t, 24.013 VOC lnput and) 1 MegOhm Output l.o.d

[f the Co .... IS not pOr"m.nently ",tt.ehod to tho u~tenl!lOr'l rod, then the tr.an~ducel"" WA. ci\llbr.tad with the eore's mat"kad end tow .... d the t .... nsduc .... ' '.S lead end.

CRl.lBRATION DRTA

POSIT JON OU1PUr voe I::UHUH ----------------------Inch (O~) DATA ZERO RUJUSTEO " F.S.

••••• n ... a ... ::n

-1.(100(1 -2C'.3360 -:::,1.3333 _(I. lOOY -0.8001.') -1&.2792 -16.J!76:5 -0).""'56::1 -0.6(1I)t.) -1«.1!l17 -12.17'30 -0.1121 -0.4000 -8.11al -~. 1094 -1).O:J91 -1.1. a,,{IO -4. o~a~ -If. ~I4'3~ -(I.C.I~ltI

0.0000 -0.0027 0.0·)01) I.I.'.IU(.II.I 0.'::1,.)1,.)0 4. (1578 4.(lQO~ -0.u.3tj3 0.4000 8.1323 8. 13~1) -0.03b": 0.6000 12.22(16 t2 • .2a33 -0.01;'33 0.8000 16.3'_24 lEt. 34:;1 0.1119 I. QOO() aC"I.349(1 2(1.3517 -0.0::i'!.7

Notol Please "'0'.'" to") Attached b'Jll .. tln fo ... olddltlc.rlal lnfo"'f,'atlon

BATCH CODE tt9a031 7C07!1~J'::

Figure B.5 Vertical LVDT Calibrations.

194

195

2600

2400

2200 -.. > E 2000 0<----~ ~" ,,~ - ~~ g 1800 '!'v~ '- £i{b r}7> :::::: '-E

1600 ~~ ~~

.S: 1Iye;

r} ...... -0~~ :::J .& 1400 :::J

0 1200

1000

800

20 30 40 50 60 70 80 90 100

Temperature (CO)

Figure B.6 Calibration Curves for the Upper and Lower Heat Sensors.

PRECISION MEASUREMENT CO. P.O. BOX 7676 ANN ARBOR, MI 4BI07

Miniature Pressure Transducer I. Model Special S/N--...::3~69::.::4t--__ _

Capacity 100 Ibs./sq. in. Calibration: 49.46 j.L£ I psi. ® G. F. =2.00

2.473 .mv/v F.S.

Red - ~P2

R= 350 OHMS White S2 Yellow,

Block P1 Recommended Excitation: , to to v

JL Operating Characteristics at 220 C ~72° F) ,. Zero Balance mV IV

. 2. Zero Shift Due to TemPilrature __ _ % Rated Output /tOo C

3. Compensated Temperature (2% Rated Output) °C

4 J.I.( ., G.F. = 2.0 mV/V >- 0 0 ,- 0 :0 50 2321 1.16

'3 too llqq-:s ? llq7

50 2359 1 1R ~ 0 0 4 o ,om' I rnV/V • 2000/l'

5. Non - Linearity ___ 1:....:..,:;:,,0 _% Rated Output 6. Hysteresis o. 8 % Rated Output

S1

196

Figure B.7 Calibration Constant for the Load Cell Installed in the Side Wall.

PRECISION MEASUREMENT CO. P.O. BOX 7676 A~N ARBOR, MI 48107

Miniature Pressure Transducer I. Model Special S/N_~36!o1.:9::..c:5:...-. __ _

Capacity 100 lbs./sq. in. Calibration: 48.37 J.lE I psi.

2.419 mv/v F.S.

Red ;, ~ P2

R= 350 OHMS White S2 Yellow, S1

Block P1 Recommended Excitation: , t010 Y

lI. Operating Characteristics at 220 C (720 F) t. Zero Balance mV IV 2. Zero Shift Due to Temperature __ _

% Rated Output /10 0 C 3. Compensated Temperature . I.

(2% Rated Output) °C

4 #Lf fl G.F. =2.0 mV/V >- 0 0 /' 0

'i 50 2393 1.197 100 4869 2.435 8 50 ?";A1 1 191 ~ 0 0 c; n.nn~

'rnV/V· 2000p,( 5. Non-Linearity 0.8 % Rated Output 6. Hysteresis ___ O_._2_% Rated Output

197

Figure B.B Calibration Constant for the Load Cell Installed in the End Flap.

Appendix C

The Aspahlt Concrete Simple Shear Program "ACSSP"

Program Flow Chart

198

I

Main Menu

:----t- samPle preparation cAlibration constants Simple shear test control Motor contRol relay read Channels conTrol temperature Quit

DO YOU WISH TO DO COMPACTION STUDY (YfN)? ~ I

Y

I VERTICAL TOTAL LOAD DESIRED (kg) ?

I PRESS ANY KEY WHEN YOU WISH TO OPEN AIR REGULATOR TO APPLY AXIAL PRESSURE

I STOP TURNING AIR REGULATOR WHEN DESIRED LOAD IS ACHIEVED

I CURRENT VERTICAL LOAD (kg) =

I PRESS ANY KEY TO STOP

I

199

N

200

TWO WAY TRIANGLE CYCLIC DISPLACEMENT ENTER AMPLITUDE (rom), NUMBER OF CYCLES?

~ N

YOU DESIRE AN AMPL. AND No. OF CYCLES: xx mm; xx CYCLESJ ARE THESE CORRECT

Y

ENTER VELOCITY (mm1sec; 1 REV. = 4.765 rom) ? N

YOU DESIRE A VELOCITY OF : X mm1sec N IS TIllS CORRECT? ENTER Y OR N ?

Y

NUMBER OF POINTS ON THE CURVE (lQUADRANT ONLY)?

PRESS ANY KEY TO CONTINUE WHEN MOTOR STOPS

'- Main Menu

samPle preparation cAlibration constants Simple shear test control Motor contRol relay read Channels conTrol temperature Quit

201

ENTERCHANNELNUMBERI~ ________________________ ~

THIS PROGRAM ONLY ALLOWS YOU TO CHANGE THE CALIBRATION CONSTANT FOR THIS TEST ONLY.

ENTER CHANNEL NUMBER

ENTER NEW CONSTANT I

DO YOU WISH TO CHANGE ANOTHER CHANNEL YIN?L Y 1--''--------'

N TO THE MAIN MENU

N '--- Main Menu


MENU 1 -~-------~

Main menu 1. Test information 2. Vertical load 3. Shear displacement 4. Temperature 5. date & time 6. Proceed

202

Test Number: Test Description: Constant Volume: Height (mm) :

MENU 1


I Is this a constant load ? N Enter vertical stress desired (kPa)? I I Enter vertical stress desired (kPa) ? I I Enter duration & Rest time (sec.) I

MENU 1


203

r-~ 1. Monotonic 2. One way cyclic 3. two way cyclic

MONOTONIC SHEAR DISPLACEMENT I Amplitude (mm) :

Enter Velocity (mm/sec) :

Enter number of points to define stress-strain cUive

TO MENU 1 for cyclic loading, specify the number of points for one quarter of a cycle

ONE WAY CYCLIC SHEAR Amplitude (mm) :


Enter Number of cycles:

Enter Number of Points TO MENU 1

TWO WAY CYCLIC SHEAR

I Amplitude (mm) :


I

MENU 1

MENU 1

Main menu 1. Test infonnation 2. Vertical load 3. Shear displacement

,---;-- 4. Temperature

Temperature (F.) Room Temp ?: Top ?: Bottom ?:

5. date & time 6. Proceed

MENU 1


204

205

I 1. Month 2. Day 3. Year 4. Hours 5. Minutes 6. Seconds

MENU 1


I IS YOUR INPUT DATA CORRECT (YIN)? N_

I Y I

Temperature Top. : Bot. :

I Temperature achieved I Press any key to continue

I Please wait 2 sec. I

I PRESS ANY KEY WHEN YOU WISH TO OPEN AIR REGULATOR TO APPLY AXIAL PRESSURE

I

206

STOP TURNING AIR REGULATOR VERTICAL STRESS IS ACHIEVED

CURRENT VERTICAL STRESS, BIT= xxx kPa PRESS ANY KEY TO STOP AND CONTINUE

TAKING READINGS READING NO.

CURRENT mST ANCE = xxx (rrun)

GRAPH PLOT

1. SHEAR STRAIN Vs SHEAR STRESS 2. SHEAR STRAIN Vs VERTICAL STRAIN 3. SHEAR STRAIN Vs SHEAR STRESS RATIO 4. MEAN STRESS Vs DEVIATORIC STRESS 5. SHEAR STRAIN Vs DEVIATORIC STRESS 6. SHEAR STRAIN Vs q/p 7. SHEAR STRAIN Vs THETA 8. MEAN STRESS Vs VERTICAL STRAIN 9. VERTICAL STRESS Vs VERTICAL STRAIN

10. PRINT RESULTS ON PRINTER? 11. RETURN TO PROGRAM

Main Menu


THIS ROUTINE WILL MOVE THE BOITOM PLATEN AS PER YOUR SELECTION. A NEGATIVE VALUE WILL MOVE THE MOTOR COUNTERCLOCKWISE

1. MOVE THE PLATEN FORWARD OR BACKWARDS 2. GO HOME - CENTER PLATENS (HOME SWITCH MUST BE INSTALLED 3. TWO TRIANGLE CYCLIC DISPLACEMENT 4. ONE WAY TRIANGLE CYCLIC DISPLACEMENT 5. END THE PROGRAM ENTER I, 2, 3, 4, OR 5 ?

Main Menu


DO YOU WISH TO o - Open A RELAY (ENERGIZE) C - Close A RELAY (DEENERGIZE) X - eXit THE PROGRAM

ENTER NUMBER OF RELAY TO RUN ON (0-7): I Y N

I I DO YOU WISH TO REPEAT THIS RELAY CONTROL PROGRAM (YIN)? I

207

Main Menu

samPle preparation cAlibration constants Simple shear test control Motor contRol relay

.....-'--'1- read Channels conTrol temperature Quit

ENTER LOWER CHANNEL NUMBER: ? 0 ENTER UPPER CHANNEL NUMBER :? 7

READING CHANNEL DATA

CH o 1 3 4 5 6 7

CHREADING

PRESS ANY KEY TO EXIT!

MILLIVOLTS

208

209

Main Menu

samPle preparation cAlibration constants Simple shear test control Motor contRol relay read Channels

.--- :- conTrol temperature Quit

ENTER ROOM TEMPERATURE (F)? I

ENTER THE DESIRED TOP BOTTOM TEMPERATURE? I

THE DESIRED TOP AND BOTTOM TEMPERATURES ARE XX, XX IS TIllS CORRECT (YIN)?

I y

I CURRENT TEMPERATURE

TOP.=XX BOT.=XX

TEMPERATURE ACHIEVED PRESS ANY KEY TO CONTINUE

210

LIST OF REFERENCES

AASHO (1962). "Interim Guide for the Design of Flexible Pavement Structure." The American Association of State Highway Officials, Washington D. C.

AASHTO (1986). "Standard Specifications for Transportation Materials and Methods of Sampling and Testing." Part I Specifications, Part II Tests, The American Association of State Highway and Transportation Officials, Washington D.C.

Acum, W. E. A. and L. Fox (1951). "Computation of Load Stresses in a Three-Layer Elastic System." Geotechnique, Vol. 2, 293-300.

ADOT (1990) "Standard Specifications for Road and Bridge Construction." Arizona Department of transportation, Highway division.

Akili, W., C. L. Monismith (1978). "Permanent Deformation Characteristics of Cemented-Emulsion Stahilized Sand." Proceedings, The Association of Asphalt Paving Technologists, Vol. 47, 281-301.

Barber, E. S. (1946). "Application of Triaxial Compression Test Results to the Calculation of Flexible Pavement Thickness", Proceedings, Highway Research Board.

Barber, E. S. (1957). "Calculation of Maximum Pavement Temperature From Weather Reports, Highway Research Bulletin, 168, Highway Research Board, 1-8.

Barker, E. R., W. N. Brabston, and Y. T. Chou (1977). "A General System for the Structural Design of Flexible Pavements.' Proceedings, Fourth International Conference on the Structural Design of Asphalt pavements, Volume I, Ann Arbor, Michigan, U.S.A. 209-248.

Barksdale, R. D. (1971). "Compressive Stress Pulse Time in Flexible Pavements for Use in Dynamic Testing." Highway Research Record, 345, Highway Research Record, 32-44.

Barksdale, R. D. (1972). "Laboratory Evaluation of Rutting in Base Course Materials." Proceedings, Third International Conference on the Structural Design of Asphalt Pavements, Volume I, London, 161-174.

Barksdale, R. D. and R.G. Hicks, (1973). "Material Characterization and Layered Theory for Use in Fatigue Analysis." Highway Research Board Special Report, 140, Highway Research Board, 20-48.

211

Barksdale, R. G.,and Leonards (1967). "Predicting Performance of Bituminous Surfaced Pavements." Proceedings, Second International Conference on the Structu.ral Design of Asphalt Pavements, Volume I, Ann Arbor, Michigan, U.S.A. 321-340.

Barksdale, R. G., and R. G. Hicks (1977). "Permanent Deformation." Proceedings, Fourth International Conference on the Structural Pavements, Volume II, Ann Arbor, Michigan, U.S.A. 153-189.

Barksdale, R. G. and J .H. Miller II, (1977). "Development of Equipment and Techniques for evaluating Fatigue and Rutting Characteristics of Asphalt Concrete Mixes." School of Civil Engineering, Georgia Institute of Technology, SCEGIT-77-149.

Battiato, G. F. Ronco, and C. Verga (1977). "Moving Loads on a Viscoelastic Double Layer: Prediction of Recoverable and Permanent Deformations." Proceedings, Fourth International Conference on the Structural Design of Asphalt Pavements, Volume I, Ann Arbor, Michigan, U.S.A. 459-466.

Biot, M. A. (1935). "Effect of Certain Discontinuities on the Pressure Distribution in loaded Soil." Physics, No.6, 619-625.

Bissada, A. F. (1983). "Compatibility of Asphalt Paving Mixtures and Relation to Permanent Deformation." Transportation Research Record, 911, Transportation Research Board, 1-10.

Bjerrm, L. and Landva, A. (1966). "Direct Simple Shear Tests on a Norwegian Quick Clay." Geotechnique, No.16, 1:1-20.

Bonnot, J. (1986). "Asphalt Aggregate Mixtures." Transportation Research Record, 1096, Transportation Research Board, 42-51.

Bonse, R. P. H. (1955). "Dynamic Forces Exerted by Moving Vehicles On a Road Surface." Flexible Pavement Design Research, National Research Council, Highway Research Board, Bulletin 233, 9-32.

Boussinesq, J. (1885). "Application des Potentials al'Etude de L'Equilibre et due Mouvementdes Soli des Elastiques." Gauthier-Villars, Paris.

Budhu, M. (1984). "Nonuniformaties imposed by simple shear apparatus." Canadian Geotechnical Journal, 21: 125-137.

212

Burmister, D. M. {1943}. "The Theory of Stresses and Displacements in Layered systems and Applications to the Design of Airport Runways." Proceedings, Highway Research Board. No. 23, 126-148.

Burmister, D. M. {1945}., "The general Theory of Stresses and Displacements in Layered Soil System." Journal of Applied Physics, Vol. 16.

Burmister, D. M. (1953). "The Theory of Stresses and Displacements in Layered Systems and Application to the Design of Airport Runways." Proceedings, Highway Research Board.

Burmister, D. M. (1958). "Evaluation of Pavement Systems of the WASHO Road Test by Layered System Methods." Highway Research Board Bulletin, No. 177.

Burmister, D. M. (1962). "Application of Layered System Concepts and Principles to Interpretations and Evaluations of Asphalt Pavement Performances and to Design and Construction." Proceedings, First International Conference on the Structural Design of Asphalt Pavements, Volume I, Ann Arbor, Michigan, U.S.A. 441-453.

Brown, Elton R. (1982). "Experiences of Corps of engineers in Compaction of Hot Asphalt mixtures." Placement and Compaction of Asphalt mixtures, Asymposium Sponsored by ASTM Committee D-4 on Road and Paving Materials, ASTM STP 829, F. T Wagner, editor.

Brown, S. F. (1973). "Determination of Young's Modulus for Bituminous Materials in Pavement Design." Transportation Research Record, 491, Transportation Research Board, 38-49.

Brown, S. F. {1975}. "Improved Framework for Predicting Permanent Deformation in Asphalt Layers." Transportation Research Record, 597, Transportation Research Board, 18-30.

Brown, S. F. (1976). "Laboratory Testing for Use in the Prediction of Rutting in Asphalt Pavements." Transportation Research Record, 616, Transportation Research Board, 22-27.

Brown, S. F. and C. A. Bell (1977). "The Validity of Design Procedure for The Permanent Deformation of Asphalt Pavements." Proceedings, Fourth International Conference on the Structural Design of Asphalt Pavements, Volume I, Ann Arbor, Michigan, U.S.A. 467-482.

213

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