• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Background and literature...
 Testing equipment and procedur...
 Temperature characteristics and...
 Load response of concrete...
 Modeling of pavement response
 Critical condition criteria for...
 Premature distress of pavements...
 Conclusions and recommendation...
 Appendix
 Reference
 Biographical sketch
 Copyright






Title: Comprehensive analysis of concrete pavement response to temperature and load effects
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Permanent Link: http://ufdc.ufl.edu/UF00089971/00001
 Material Information
Title: Comprehensive analysis of concrete pavement response to temperature and load effects
Physical Description: Book
Language: English
Creator: Armaghani, Jamshid Mohammad
Publisher: Jamshid Mohammad Armaghani
Publication Date: 1987
 Record Information
Bibliographic ID: UF00089971
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000979082
oclc - 17497210

Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
        Page v
        Page vi
    List of Tables
        Page vii
        Page viii
    List of Figures
        Page ix
        Page x
        Page xi
        Page xii
        Page xiii
        Page xiv
        Page xv
        Page xvi
        Page xvii
    Abstract
        Page xviii
        Page xix
        Page xx
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Background and literature review
        Page 6
        Page 7
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    Testing equipment and procedures
        Page 32
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    Temperature characteristics and response of concrete pavements
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    Load response of concrete pavement
        Page 116
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    Modeling of pavement response
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    Critical condition criteria for design of rigid pavements
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    Premature distress of pavements a case study: florida's interstate 75
        Page 272
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    Conclusions and recommendations
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    Appendix
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    Reference
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    Biographical sketch
        Page 499
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    Copyright
        Copyright
Full Text











COMPREHENSIVE ANALYSIS OF CONCRETE PAVEMENT
RESPONSE TO TEMPERATURE AND LOAD EFFECTS











By

JAMSHID MOHAMMAD ARMAGHANI


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY





UNIVERSITY OF FLORIDA


1987















ACKNOWLEDGMENTS

The author gratefully acknowledges the advice, help, and encourage-

ment of Dr. Byron Ruth. He is especially thanked for suggesting to the

author the concept of critical condition for pavement analysis and

design. Special appreciation is expressed to Dr. Mang Tia and Dr. John

Lybas for their valuable comments and suggestions. Sincere appreciation

is extended to Professors Morris Self, Walter Zimpfer, and Andrawus

Khuri for providing tools of knowledge in the respective areas of struc-

tural design, pavement materials and design, and statistics.

The author is also grateful to Mr. Lawrence Smith and Mr. Torbjorn

Larsen of the Bureau of Materials and Research-Florida DOT, for their

support, encouragement, and technical assistance. Thanks must also be

extended to the technical staff of the Bureau of Materials and Research,

especially to Randy Brown, Charles Davis, Guy Padgett, and Alan Hughes

for their help in pavement instrumentation and in the testing opera-

tions. Special thanks are also expressed to Gabriel Alungbe and Jeff

Couch for their assistance. The author also expresses his gratitude to

the University of Technology Baghdad, Iraq, for their support.

Finally, the author wishes to thank his family, and especially his

wife Bahar for her support, inspiration, and most of all her patience

during the course of this research.















TABLE OF CONTENTS

Page
ACKNOWLEDGMENTS ....................... .............. ........ ii

LIST OF TABLES...................................................... vii

LIST OF FIGURES ... ................................ ................ ix

ABSTRACT.................... ............................ .... xviii

CHAPTER

1 INTRODUCTION...... .............. ........................... 1

2 BACKGROUND AND LITERATURE REVIEW........................... 6

2.1 Historical Background of Jointed Concrete
Pavements ...................................... .... 6
2.2 Function of Joints in Concrete Pavements.............. 8
2.3 Pavement Slab Displacements........................... 9
2.3.1 Horizontal Slab Displacements.................. 9
2.3.2 Vertical Slab Displacements.................... 10
2.4 Distress Mechanisms in Concrete Pavements............. 14
2.5 Review of Concrete Pavement Research.................. 18
2.6 Computer Modeling and Applications................... 23
2.7 Design Procedures........................ ... ........ 29
2.7.1 The AASHTO Design Guide....................... 29
2.7.2 The PCA Thickness Design....................... 30

3 TESTING EQUIPMENT AND PROCEDURES......................... 32

3.1 Description of the Test Road.......................... 32
3.2 Testing Procedure for Pavement Temperature
and Response.......................... ............. 36
3.2.1 Temperature Data Collection................... 36
3.2.2 LVDT Installation............................ 36
3.2.3 Slab Displacement Measurements................. 37
3.3 Falling Weight Deflectometer Testing.................. 39
3.3.1 The Falling Weight Deflectometer (FWD)......... 39
3.3.2 FWD Testing Positions.......................... 44
3.3.3 FWD Deflection-Sensor Configurations........... 45
3.3.4 Magnitudes of FWD Loads....................... 51
3.3.5 Timing of Tests................................ 52
3.3.6 Testing Program................................ 52









4 TEMPERATURE CHARACTERISTICS AND RESPONSE OF
CONCRETE PAVEMENTS....................................... 55

4.1 Introduction................... ..................... 55
4.2 Analysis of Temperature Data.......................... 55
4.2.1 Relationship Between Air and Pavement
Temperatures......................... ......... 57
4.2.2 Temperature Distribution at Different Slab
Depths........................................ 66
4.2.3 Temperature Differential....................... 75
4.2.4 Temperature Gradient........................... 88
4.2.5 Effect of Weather Condition on Pavement
Temperature. ........................ ......... 91
4.3 Concrete Pavement Response to Temperature............. 99
4.3.1 Slab Deflection Profiles....................... 99
4.3.2 Analysis of Vertical Slab Displacements........ 102
4.3.3 Analysis of Horizontal Slab Displacements...... 109

5 LOAD RESPONSE OF CONCRETE PAVEMENT......................... 116

5.1 Introduction.......................................... 116
5.2 Undoweled Joint Response.............................. 116
5.2.1 Response at Undoweled Corner................... 117
5.2.2 Deflection Basins for Corner Loading........... 135
5.2.3 Effect of Void on Corner Response.............. 144
5.2.4 Response at Wheel Path......................... 148
5.2.5 Response at Joint Center....................... 157
5.3 Doweled Joint Response............................... 167
5.3.1 Response at Doweled Corner..................... 169
5.4 Slab Center Response................................. 183
5.5 Pavement Edge Response ............................... 190

6 MODELING OF PAVEMENT RESPONSE.............................. 195

6.1 Introduction.......................................... 195
6.2 FEACONS III Computer Program.......................... 195
6.2.1 Pavement Modeling.............................. 196
6.3 Procedure for Modeling Linear Pavement Response....... 199
6.3.1 FWD Load-Deflection Analysis................... 200
6.3.2 Evaluation of Subgrade Stiffness............... 200
6.3.3 Evaluation of Edge Stiffness................... 205
6.3.4 Evaluation of Undoweled Joint Stiffness........ 207
6.3.5 Evaluation of Doweled Joint Stiffness.......... 209
6.3.6 Effect of Slab Curling on Joint Stiffness...... 213
6.3.7 Effect of Seasonal Changes of Temperature
Joint Stiffness.............................. 222
6.3.8 Effect of Subgrade Void on Joint Stiffness..... 226
6.4 Modeling of Non-Linear Pavement Response.............. 229
6.4.1 Characteristics of Non-Linear Response......... 229
6.4.2 Procedure for Modeling Non-Linear Pavement
Response...................................... 234








7 CRITICAL CONDITION CRITERIA FOR DESIGN OF RIGID
PAVEMENTS...................................... ....... 244

7.1 Introduction.......................................... 244
7.2 Pavement Design and Performance....................... 245
7.3 Critical Condition of Concrete Pavement............... 247
7.3.1 Temperature and Load Response During
Critical Condition............................ 247
7.3.2 Stress Analysis of Critical Pavement
Condition..................................... 249
7.4 Critical Condition in Concrete Pavement Design........ 251
7.4.1 Design Example................................. 262

8 PREMATURE DISTRESS OF PAVEMENTS A CASE STUDY: FLORIDA'S
INTERSTATE 75............................................ 272

8.1 Introduction.......................................... 272
8.2 Scope of Problem on Interstate 75..................... 272
8.3 Investigation Program................................ 278
8.4 Assessment of Various Possible Causes................. 278
8.5 Establishing Causes of Distress....................... 281
8.6 Analysis of Factors Contributing to Distress.......... 284
8.6.1 Effects of Movement Restraints by Dowels &
Tie Bars...................................... 284
8.6.2 Effect of Econocrete Base...................... 295
8.7 Concluding Remarks ................................... 302

9 CONCLUSIONS AND RECOMMENDATIONS............................ 303

9.1 Conclusions........................................... 303
9.1.1 Temperature Characteristics and Response
of Concrete Pavement.......................... 303
9.1.2 Load Response and Modeling of Concrete
Pavement...................................... 308
9.1.3 Critical Condition Criteria for Design......... 311
9.1.4 Interstate 75 (1-75) Cracking Problem.......... 311
9.2 Recommendations................................. ..... 312
9.3 Future Research Needs.................................. 313

APPENDIX

A. TEMPERATURE AND DISPLACEMENT MEASUREMENTS.................. 317

B. FWD TEST DATA ............................... ............. 364

C. STATISTICAL ANALYSIS OF FWD DATA........................... 452

C.1 Regression Analysis of the Relationship Between
Deflections at Load Position 4.1 and Temperature
Differentials -- (Figure 5.11)........................ 453
C.2 Regression Analysis of the Relationship Between
Deflections at Load Position 4.1 and Average
Pavement Temperatures -- (Figure 5.12)................ 457









C.3 Regression Analysis of the Relationship Between
Deflections at Load Position 4.3 and Temperature
Differentials -- (Figure 5.25)........................ 460
C.4 Regression Analysis of the Relationship Between
Deflections at Load Position 4.3 and Average
Pavement Temperatures -- (Figure 5.26)................ 465
C.5 Regression Analysis of the Relationship Between
Deflections at Load Position 4.6 and Temperature
Differentials -- (Figure 5.33)........................ 468
C.6 Regression Analysis of the Relationship Between
Deflections at Load Positions 4.1 and 5.1, and
Temperature Differentials -- (Figure 5.45)............ 472
C.7 Regression Analysis of the Relationship Between
Slopes of Load-Deflection Curves and Temperature
Differentials -- (Figures 6.19 and 6.20).............. 476

D. INTERSTATE 75 TEST DATA.................................... 486

REFERENCES ........................ ...... ............. .......... 494

BIOGRAPHICAL SKETCH................................................. 499















LIST OF TABLES


Table Page

2.1 Concrete Pavement Distress................................... 15

3.1 FWD Testing Program.......................................... 53

3.2 Sensor Configuration for FWD Testing......................... 54

4.1 Most Frequent Times of Occurrence for Minimum and
Maximum Temperatures ...................................... 67

4.2 Comparison Between Slab Temperatures at Edge and
Shaded Center.............................................. 94

4.3 Comparison Between Slab Temperatures at Edge and
Unshaded Center........ ...... ............................. 96

4.4 Maximum Vertical Displacements of Test Road Slabs............ 108

4.5 Maximum Horizontal Displacements at Test Road Joints......... 114

5.1 Deflection Ratios at Various Distances From Corner Load:
Test Series 6.............................................. 140

5.2 Percent Ratio of Deflections Along Joint to Those at Load
Center: Load Position (4.6)............................... 165

6.1 Sensitivity of Computed Deflections to Variation of KL
and KR .............................. ..* ... ........... 208

6.2 Comparison of Stiffnesses Between Doweled and Undoweled
Joints..................................................... 213

6.3 Comparison of Stiffnesses for Corners With and Without
Void....................................................... 228

6.4 Measured Versus Predicted Deflections: Curve 1,
Figure 6.22................................................ 240

6.5 Measured Versus Predicted Deflections: Curve 2,
Figure 6.22....................................... ......... 241

6.6 Measured Versus Predicted Deflections: Curve 3,
Figure 6.22............................................... 242

6.7 Comparison Between Linear and Non-Linear Procedures.......... 243









Table Page

7.1 Stress Increase Due to Critical Condition.................... 252

7.2 Recommended Load Transfer Coefficient for Various Pavement
Types and Design Conditions................................ 255

7.3 Sample Distribution of Traffic by Hour of the Day and
Weight.................................... ................ 260

7.4 Axle Load Equivalency Factors for Rigid Pavements, Single
Axles and Pt of 2.5........................................ 264

7.5 Stress Reduction in Pavement Slab Designed by Considering
the Daily Critical Condition............................... 271

8.1 Information Related to 1-75 Concrete-Econocrete Pavement..... 274

8.2 Effect of Increased Stiffness on Curling Stresses for
23-foot Slab............................................... 296

8.3 Analyzed Cases for 1-75 Conditions........................... 298

8.4 Stress Analysis of 1-75 for Combined Curling and Load
Effects.................................................... 301


viii















LIST OF FIGURES


Figure Page

2.1 Curling and Warping of Pavement Slabs........................ 11

a) Flat c) Downward Curling
b) Upward Curling d) Moisture Warping
e) Shrinkage Warping

2.2 Types of Joint Distress.......................................... 17

2.3 Frieberg's Analysis of Dowel Bars in Concrete................ 20

3.1 Plan of Test Road and Void Locations......................... 33

3.2 Details of Instrumentation................................. .. 35

3.3 Monitoring Deflection Profile at the Joint................... 38

3.4 LVDT Arrangement at Joint 4................................. 40

3.5 The Falling Weight Deflectometer (FWD)....................... 42

3.6 View of the (FWD) Loading System............................. 42

3.7 Typical Configuration of Deflection Sensors Used in
FWD Tests.................................................. 43

a) Loaded Side
b) Unloaded Side

3.8 Layout of FWD Testing Positions on Test Road Slabs........... 46

3.9 Sensor Configurations for Testing Positions 3.1, 4.1,
and 5.1 .......................... .... ............. ....... 47

3.10 Sensor Configurations for Testing Positions 4.3 and 5.3...... 48

3.11 Sensor Configurations for Testing Positions 4.6 and 5.6...... 48

3.12 Sensor Configurations for Testing Position 3.6.............. 49

3.13 Sensor Configurations for Testing Position 3.12.............. 49

3.14 Sensor Configurations for Testing Positions 3E, 3C, 4E
and 4C..................................................... 50









Figure Page

4.1 Monthly Air Temperatures for Gainesville, Florida (Data
Recorded Between 1984 and 1986)............................ 58

4.2 Temperature Versus Time: January 26-28, 1986............... 59

4.3 Temperature Versus Time: April 16-18, 1986.................. 60

4.4 Temperature Versus Time: June 7-8, 1986..................... 61

4.5 Temperature Versus Time: July 12-14, 1985................... 62

4.6 Temperature Versus Time: October 7-9, 1985.................. 63

4.7 Effect of Weather on Temperature Variation:
December 27-29, 1985....................................... 65

4.8 Frequency of Occurrence: Minimum Air Temperature............ 68

4.9 Frequency of Occurrence: Minimum Pavement Temperature....... 68

4.10 Frequency of Occurrence: Maximum Air Temperature............ 69

4.11 Frequency of Occurrence: Maximum Pavement Temperature....... 69

4.12 Temperature Variation at Different Slab Depths:
January 26-28, 1986..... .............. .................... 70

4.13 Temperature Variation at Different Slab Depths:
April 16-17, 1986............. ....... ...... ................... 71

4.14 Temperature Variation at Different Slab Depths:
June 7-8, 1986............................................. 72

4.15 Temperature Variation at Different Slab Depths:
July 12-14, 1986....................... .............. ... .. 73

4.16 Temperature Variation at Different Slab Depths:
December 27-29, 1985............. ......................... 74

4.17 Frequency of Occurrence: Minimum Temperature
at Slab Surface................... ........... ............ 76

4.18 Frequency of Occurrence: Minimum Temperature
at Slab Center................. .............. ......... 76

4.19 Frequency of Occurrence: Minimum Temperature
at Slab Bottom............................................ 77

4.20 Frequency of Occurrence: Maximum Temperature
at Slab Surface.................... ...... .................. 77









Figure Page

4.21 Frequency of Occurrence: Maximum Temperature
at Slab Center............................................. 78

4.22 Frequency of Occurrence: Maximum Temperature
at Slab Bottom............................................. 78

4.23 Temperature Differential Versus Time:
January 26-28, 1986...................................... 79

4.24 Temperature Differential Versus Time: April 16-18, 1986...... 80

4.25 Temperature Differential Versus Time: June 7-8, 1986......... 81

4.26 Temperature Differential Versus Time: July 12-14, 1985....... 82

4.27 Temperature Differential Versus Time: October 7-9, 1985...... 83

4.28 Temperature Differential Versus Time: December 27-29, 1985... 84

4.29 Frequency of Occurrence: Maximum Negative Temperature
Differential ............................................... 86

4.30 Frequency of Occurrence: Maximum Positive Temperature
Differential............................................... 86

4.31 Frequency Analysis of Negative Temperature Differentials..... 87

4.32 Frequency Analysis of Positive Temperature Differentials..... 87

4.33 Temperature Gradients: January 27, 1986..................... 89

4.34 Temperature Gradients: April 17, 1986....................... 89

4.35 Temperature Gradients: June 27, 1986........................ 90

4.36 Temperature Gradients: July 13, 1985....................... 90

4.37 Temperature Variation With Shade at Slab Center.............. 93

4.38 Temperature Variation With Shade Removed From Slab Center.... 95

4.39 Effect of Sudden Exposure to Moisture on Concrete
Temperature................................................ 98

4.40 Deflection Profiles Along the Joint at Various Temperature
Differentials (AT) ....................................... 101

4.41 Vertical Displacements Versus Time: January 26-28, 1986..... 103

4.42 Vertical Displacements Versus Time: April 16-18, 1986....... 104

4.43 Vertical Displacements Versus Time: June 7-8, 1986 .......... 105









Figure Page

4.44 Horizontal Joint Displacements: January 26-28, 1986......... 110

4.45 Horizontal Joint Displacements: April 16-18, 1986........... 111

4.46 Horizontal Slab Displacements: June 7-8, 1986.............. 112

5.1 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Loaded Slab: Test Series 3........... 118

5.2 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Unloaded Slab: Test Series 3......... 119

5.3 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Loaded Slab: Test Series ,4........... 120

5.4 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Unloaded Slab: Test Series 4......... 121

5.5 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Loaded Slab: Test Series 5........... 122

5.6 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Unloaded Slab: Test Series 5......... 123

5.7 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Loaded Slab: Test Series 6........... 124

5.8 Load-Deflection Relations for Test Position 4.1 Undoweled
Joint, Deflection of Unloaded Slab: Test Series 6......... 125

5.9 The Concept of Load Response at Slab Corner................... 129

5.10 Variation of Load-Deflection Slopes With Increase in Load
Magnitude.................................................. 130

5.11 Actual and Predicted Deflections Versus Temperature
Differential: Corner Loading, Undoweled Joint............. 132

5.12 Actual and Predicted Deflections Versus Concrete
Temperature: Corner Loading, Undoweled Joint.............. 133

5.13 Deflection for Load Position 4.1 at High Negative Temper-
ature Differential: Test Series 3......................... 136

a) Loaded Slab
b) Unloaded Slab

5.14 Deflection Basins for Load Position 4.1 at High Positive
Temperature Differential: Test Series 3.................. 137

a) Loaded Slab
b) Unloaded Slab








Figure Page

5.15 Deflection Basins for Corner Loading, Position 4.1 at
Positive Temperature Differential: Test Series 6.......... 138

5.16 Deflection Basins for Corner Loading, Position 4.1 at
Negative Temperature Differential: Test Series 6.......... 139

5.17 Percent Ratios of Deflection at Different Positions to
Deflections at Load Position 4.1: Test Series 4........... 141

5.18 Effect of Temperature Differential on Joint Response:
Test Series 4........................................ 143

5.19 Load-Deflection Relations for Test Position 3.12 Undoweled
Joint With Void: Test Series 6............................ 145

5.20 Load-Deflection Relations for Test Position 3.1 Undoweled
Joint Without Void: Test Series 6......................... 146

5.21 Deflection Basins for Load Applied at Slab Corners With and
Without Void Positions 3.1 and 3.12: Test Series 6...... 147

5.22 Load-Deflection Relations for Test Position 4.3 Undoweled
Joint: Test Series 3...................................... 149

5.23 Load-Deflection Relations for Test Position 4.3 Undoweled
Joint: Test Series 5...................................... 150

5.24 Load-Deflection Relations for Test Position 4.3 Undoweled
Joint: Test Series 6...................................... 151

5.25 Actual and Predicted Deflections Versus Temperature
Differential: Load Position 4.3, Undoweled Joint.......... 153

5.26 Actual and Predicted Deflections Versus Concrete Temperature:
Load Position 4.3, Undoweled Joint......................... 154

5.27 Percent Ratio of Deflections at Load Position 4.3 to Those
at Position 4.1 for Various Temperature Differentials...... 155

5.28 Deflection Basins for Load Position 4.3 Undoweled Joint:
Test Series 6.............................................. 156

5.29 Load-Deflection Relations for Test Position 4.6 Undoweled
Joint: Test Series 3...................................... 158

5.30 Load-Deflection Relations for Test Position 4.6 Undoweled
Joint: Test Series 4...................................... 159

5.31 Load-Deflection Relations for Test Position 4.6 Undoweled
Joint: Test Series 5...................................... 160


xiii








Figure Page

5.32 Load-Deflection Relations for Test Position 4.6 Undoweled
Joint: Test Series 6...................................... 161

5.33 Actual and Predicted Deflections Versus Temperature
Differential: Load Position 4.6, Undoweled Joint.......... 162

5.34 Deflection Basins for Load Position 4.6 Undoweled Joint:
Test Series 6.............................................. 164

5.35 Deflection Basins for Load Position 4.6: Test Series 4...... 166

5.36 Percent Ratio of Deflections at Different Positions From
Center of Load Position 4.6: Test Series 4................ 168

5.37 Deflections at Each Dowel (Load Positions 5.1 to 5.12):
Test Series 1.............................................. 170

a) Loaded Slab
b) Unloaded Slab

5.38 Deflections at Each Dowel (Load Positions 5.1 to 5.12):
Test Series 6.............................................. 171

a) Loaded Slab
b) Unloaded Slab

5.39 Load-Deflection Relations for Test Position 5.12 Doweled
Joint, Loaded Slab Deflection: Test Series 2.............. 172

5.40 Load-Deflection Relations for Test Position 5.12 Doweled
Joint, Unloaded Slab Deflection: Test Series 2............ 173

5.41 Load-Deflection Relations for Test Position 5.1 Doweled
Joint, Loaded Slab Deflection: Test Series 4.............. 174

5.42 Load-Deflection Relations for Test Position 5.1 Doweled
Joint, Unloaded Slab Deflection: Test Series 4............ 175

5.43 Load-Deflection Relations for Test Position 5.1 Doweled
Joint, Loaded Slab Deflection: Test Series 6.............. 176

5.44 Load-Deflection Relations for Test Position 5.1 Doweled
Joint, Unloaded Slab Deflection: Test Series 6............ 177

5.45 Actual and Predicted Deflections Versus Temperature
Differential: Corner Loading, Doweled and Undoweled
Joints..................................................... 178

5.46 Deflection Basins for Load Position 5.1 at Negative
Temperature Differential: Test Series 6................... 181








Figure Page

5.47 Deflection Basins for Load Position 5.1 at Positive
Temperature Differential: Test Series 6................... 182

5.48 Load-Deflection Relations for Test Position 4C, Slab
Center: Test Series 6..................................... 184

5.49 Load-Deflection Relations for Test Position 3C, Slab
Center: Test Series 6..................................... 186

5.50 Deflection Basins for Load Position 4C....................... 187

5.51 Deflection Basins for Load Positions 3C and 4C: Test
Series 6................................................... 189

5.52 Load-Deflection Relations for Test Position 4E, Slab Edge:
Test Series 4.............................................. 191

5.53 Load-Deflection Relations for Test Position 3E, Slab Edge:
Test Series 6.............................................. 192

5.54 Load-Deflection Relations for Test Position 4E, Slab Edge:
Test Series 6.............................................. 193

6.1 FEACONS III Modeling of a Three-Slab Pavement System......... 197

6.2 Typical Load-Deflection Relations at Slab Center............. 201

6.3 Typical Load-Deflection Relations at Slab Corner............. 202

6.4 Deflection Basins in Transverse Direction: Load
Position 4C................................................ 204

6.5 Deflection Basins in Longitudinal Direction: Load
Position 4E................................................. 206

6.6 Deflection Basins Along Undoweled Joint, Loaded Slab:
Load Position 4.1, Thermal Condition A..................... 210

6.7 Deflection Basins Along Undoweled Joint, Unloaded Slab:
Load Position 4.1, Thermal Condition A..................... 211

6.8 Deflection Basins Along Both Sides of Doweled Joint:
Load Position 5.1.......................................... 212

6.9 Linear Load Deflection Relations for Load Positions
4.1, 4.3, and 4.6.................... ...................... 215

6.10 Deflection Basins Along Both Sides of Undoweled Joint:
Load Position 4.3, Thermal Condition A..................... 217

6.11 Deflection Basins Along Both Sides of Undoweled Joint:
Load Position 4.6, Thermal Condition A..................... 218









Figure Page

6.12 Deflection Basins for Load Position 4.1 at Thermal
Condition B................................................ 219

6.13 Deflection Basins for Load Position 4.6 at Thermal
Condition B................................................ 220

6.14 Effect of Temperature Condition on Variability of Joint
Stiffness.................................................. 221

6.15 Deflection Basins for Load Position 4.1 Tested
During Fall ................................................ 223

6.16 Deflection Basins for Load Position 4.1 Tested
During Winter.............................................. 224

6.17 Effect of Seasonal Changes in Pavement Temperature on
Joint Stiffness............................................ 225

6.18 Deflection Basins Along Undoweled Joint With Void: Load
Position 3.12.............................................. 227

6.19 Relationship Between Slope of Load-Deflection Curves and
Temperature Differential................................... 231

6.20 Predicted Slopes of Load-Deflection Curves Versus
Temperature Differential ................... ... .......... 233

6.21 Graphical Representation of Variable Stiffness Associated
With Non-Linear Response................................... 235

6.22 FEACONS III Modeling of Non-Linear and Linear Pavement
Responses.................................................. 237

7.1 Maximum Stresses Caused by Upward Slab Curling Only.......... 250

7.2 Maximum Stresses in Pavement Slab at -150F Temperature
Differential ............................................... 253

7.3 Design Chart for Rigid Pavement Based on Using Mean Values
for Each Input Variable (Segment 1)........................ 256

7.4 Design Chart for Rigid Pavements Based on Using Mean Values
for Each Input Variable (Segment 2)........................ 257

7.5 Representation of Roadbed Modulus Variations Throughout the
Year ............................................. ......... 258

7.6 Design Example (Segment 1)................................... 265

7.7 Design Example (Segment 2)................................... 266








Figure Page

7.8 Pavement Stresses During Daytime and Critical Condition
Period..................................................... 268

8.1 Typical Section of Interstate 75 Concrete Pavement in
Sarasota and Manatee Counties.............................. 273

8.2 Crack Survey on a Typical Test Section April, 1983......... 276

8.3 Crack Survey on a Typical Test Section January, 1984....... 277

8.4 Frequency analysis of FWD Deflection Data on 1-75 Pavement... 279

8.5 Flow Chart Showing Sequence of Events Leading to 1-75
Pavement Cracking.......................................... 282

8.6 Layout of Typical Test Site and Instrumentation Details
for 1-75 Pavement.......................................... 285

8.7 Daily Variation of Average Temperature on Interstate 75...... 287

8.8 Daily Variation of Temperature Differentials on
Interstate 75............................................. 288

8.9 Horizontal Displacements at Joint: Tie Bars Intact.......... 290

8.10 Horizontal Displacements at Joint: With Tie Bars Cut........ 291

8.11 Vertical Displacements of Interstate 75 Joints............... 292

8.12 Horizontal Joint Displacements for Undoweled, Doweled, and
Doweled-With-Ties Conditions.............................. 293

8.13 Vertical Slab Displacements for Undoweled, Doweled, and
Doweled-With-Ties Conditions............................... 294

8.14 FEACONS III Modeling of Cases A and B ....................... 299

8.15 FEACONS III Modeling of Cases C and D........................ 300


xvii














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


COMPREHENSIVE ANALYSIS OF CONCRETE PAVEMENT
RESPONSE TO TEMPERATURE AND LOAD EFFECTS

By

JAMSHID MOHAMMAD ARMAGHANI

August 1987


Chairman: Byron E. Ruth
Major Department: Civil Engineering


This research was developed to establish an improved conceptual

understanding of concrete pavement behavior. The major emphasis of the

research was to determine the effect of load and temperature on the

response of concrete pavements. The response characteristics were

evaluated primarily through testing and computer analysis of a model

Test Road. Information obtained from evaluation of pavement response

formed the basis for a new concrete pavement design approach. Further-

more, concepts developed from testing and analysis of the model Test

Road were utilized in an investigation of the premature cracking problem

on sections of Interstate 75 (1-75) south of Tampa, Florida.

The Test Road was constructed with doweled and undoweled joints,

and incorporated voids in the subgrade. Temperature sensors were

embedded in the slabs and displacement measuring gauges were attached at

key slab positions. Temperature and displacement measurements recorded

from the Test Road slabs over an extended time period were used to


xviii








establish temperature characteristics and response of pavement slabs.

The load response of the concrete test-pavement was evaluated and

analyzed based on data obtained from Falling Weight Deflectometer tests

which were performed at variable daily and seasonal temperature condi-

tions.

A finite-element computer program, FEACONS III, was used to model

and analyze the pavement response. Pavement deflections and stresses

were computed for different load and temperature conditions. The

stiffnesses of the subgrade (k), joint, and edge of the pavement were

accurately evaluated by correlation of computed and measured FWD deflec-

tion basins.

Evaluation and analysis of test data showed a strong relationship

between pavement load-response and daily variation of temperature. It

was determined that concrete pavements exhibit the lowest daily stiff-

ness between midnight and early morning hours, a period designated as

the critical condition period. The substantial reduction of stiffness

during the critical condition period was attributed to upward slab

curling and extensive opening of joints caused by temperature.

The concept of daily critical condition was applied to the design

of a concrete pavement. Considering critical-condition criteria, the

pavement design resulted in a 16-percent increase in slab thickness over

conventional design by the new AASHTO (American Association of State

Highway and Transportation Officials) Guide. It was emphasized that

failure to incorporate this significant parameter in design can lead to

premature pavement distress and a pavement life that is less than

originally predicted, especially when there is an unexpected increase in

traffic loads and volumes. The premature cracking problem on concrete









sections of 1-75 was investigated to compliment this research. The test

results and information obtained originally from the Test Road proved to

be applicable in this study. The investigation identified both the

source of the problem and the mechanisms which lead to cracking of this

segment of 1-75.














CHAPTER 1
INTRODUCTION


The design of pavements that meet the increasing traffic volumes

and vehicular weights is considered a major challenge for today's pave-

ment engineers. The problem of distress and failures on some of Flor-

ida's new concrete pavements, for example, Interstates 75 and 10, has

emphasized the urgent need for re-evaluation of current design proce-

dures. The task of improving design procedures is more complex since

many concrete pavements in Florida, such as Interstates 95, 4, and 275

(1-95, 1-4, and 1-275), State Road US 41 (near Fort Myers), and others,

are in good condition and performing satisfactorily considering their

age of service.

Current design guidelines and procedures developed by the American

Association of State Highway and Transportation Officials (AASHTO), and

the Portland Cement Association (PCA) in early 1960s, have accounted for

many parameters related to traffic, environment, and pavement perfor-

mance. Both design procedures are based on the fatigue criteria, but

with variable degrees of emphasis. The new versions of AASHTO (1986),

and PCA (1984) have included new design concepts based on experience and

findings from numerous research. For example, the new AASHTO design has

included among many new parameters a reliability factor, which is used

to reduce the risk of premature deterioration while PCA has considered

erosion of the subbase as an alternative criteria to the conventional

fatigue criteria.









However, an important parameter has been neglected by the design

procedures. Despite its significant role in stress development, the

effect of daily variation of pavement temperature has not been con-

sidered in these design methods. The temperature variation between mid-

night and early morning causes upward curling of pavement slabs and wide

opening of pavement joints. This in general, constitutes a critical

daily condition where the pavement is at its minimum stiffness. The

effect of traffic load and temperature can produce the highest daily

stresses and deflections in the pavement. Therefore a given axle load

will induce greater damaging effect to the pavement during this period

than any other time of the day--a fact that has not been recognized when

pavements are designed by the fatigue criteria. This can partially

explain early distress of some concrete pavements in Florida. Therefore

it is necessary to thoroughly examine and analyze temperature response

of pavement slabs especially during the daily critical condition. This

study approach can eventually lead to an improved design procedure for

Portland Cement Concrete (PCC) pavements.

Elements and features incorporated in the design of concrete pave-

ments can, under certain environmental conditions, cause premature dis-

tress. In current design practice, features and elements such as

dowels, tied shoulders, rigid subbases, skewed joints, and variable

length slabs have often been included in the design package. Those

design features were developed to achieve higher structural capability

and better riding comfort of pavements. However, there are strong indi-

cations that these features have collectively contributed to premature

distress of pavements on sections of 1-75 south of Tampa, Florida. This

problem highlights an important issue even though these design features








can, in certain situations, contribute to better performing pavements.

Dowels, tie bars, a rigid subbase, and variable lengths of adjacent

slabs can act together to restrain movement of the pavement slabs.

Stresses generated as a result of such restraints, when combined with

those caused by traffic, can lead to premature cracking of the pave-

ment. Analysis of the behavior of such elements can assist in iden-

tifying mechanisms that contribute to prematue distress, similar to

those observed on 1-75. (This can have serious implications on the

adequacy of future designs of this type.)

This background provided the basis for formulation of a compre-

hensive research plan. The primary objective of the research was to

develop a basic understanding of the response of concrete pavements,

then to proceed with analysis of load and temperature response to deter-

mine the causes of pavement cracking. Once the response has been

defined, new aspects of design based on critical condition of the pave-

ment could be evaluated. Furthermore, concepts obtained from this

research would be incorporated in the investigation of premature dis-

tress on 1-75. The specific objectives pursued in this research were

the following:

1. Measure and analyze the temperature variation in concrete pave-

ments, and characterize response of pavement slabs to the varia-

tion of temperature.

2. Measure and evaluate load response of concrete pavement slabs at

different temperatures and load magnitudes.

3. Evaluate the effect of types of joints and subgrade voids on re-

sponse characteristics of the pavement.








4. Develop a methodology for correlation between measured response

and predicted response to determine the stiffnesses of concrete

pavement systems.

5. Evaluate the concept of critical condition as a viable design

criteria for jointed concrete pavements.

6. Analyze the cracking problem of 1-75 by incorporating findings

from this research and other related field tests.

A model pavement (Test Road) was constructed August, 1982, at the

Bureau of Materials and Research, Florida Department of Transportation.

This Test Road incorporated doweled and undoweled joints and was de-

signed to simulate typical PCC pavements in Florida. Voids were intro-

duced at specific locations under the pavement slabs to model those

actually existing beneath in-service pavements. The Test Road was also

instrumented with gauges to monitor temperatures and displacements at

different slab positions within each slab. A computer data acquisition

system was used to collect and store the data for analysis.

Non-destructive load tests were conducted on the Test Road slabs

using the Falling Weight Deflectometer (FWD). A series of tests were

performed at different hours of the day. The tests were reported at

various seasons of the year. A unique pattern for testing developed to

enable more precise characterization of the load response.

The analytical aspect of this research included a finite-element

computer program called FEACONS III. This computer program was used to

analyze different pavement and load conditions. A procedure was

developed to estimate the pavement and subgrade stiffnesses at the

interior, edge, and joints. This procedure was based on correlation of









measured with computed deflection basins to determine the stiffness

parameters.

Testing and analysis were not limited to the Test Road. Field

testing and monitoring also became a part of this research. Test sec-

tions were established on Interstate 75 (1-75). The Falling Weight

Deflectometer was used to perform load tests in the field. Furthermore,

temperature and displacement data were obtained from designated slabs on

the test sections. Information acquired from the field, combined with

that obtained from the Test Road, provided an understanding of the

causes and mechanisms that led to distress on sections of 1-75.

Findings from this research emphasize the need to consider, as a

design criterion, the concept of daily critical condition of concrete

pavements. Such design consideration can become an integral part of the

conventional fatigue criteria. This research also indicated that there

is a need for re-evaluation of design practices that call for unbonded

rigid subbase, doweled and tied joints, and randomly spaced slabs to be

incorporated in the same design package. The interaction of these pave-

ment elements can contribute to premature distress and failure of PCC

pavements when subjected to certain traffic and environmental conditions.














CHAPTER 2
BACKGROUND AND LITERATURE
REVIEW

2.1 Historical Background of Jointed Concrete Pavements

Early concrete pavements which where built during the 1920s did not

include longitudinal or transverse joints (1). As a consequence, the

majority of pavements developed longitudinal cracks which led to serious

spelling, faulting, and separation. In an effort to alleviate such

problems, longitudinal joints were constructed along the pavement cen-

ter. Longitudinal joints thus divided the highway into two lanes.

In addition to longitudinal cracks, unjointed concrete pavements

also developed transverse cracks at variable spacings shortly after con-

struction. Such cracks were assoicated mainly with shrinkage of con-

crete. The difficulty of sealing the cracks led to spelling and the in-

filtration of incompressible materials, such as sand, into those cracks.

This in turn caused further distress in the form of buckling and blow-

ups of pavements. Therefore, transverse expansion and contraction

joints were introduced in an attempt to control the pavement cracks and

minimize pavement distress.

During the 1930s, concrete pavements were designed with mesh rein-

forcement to control temperature cracking. Pavement designs included

expansion and contraction joints at 90 ft. (28m), and 30 ft. (9.2m),

respectively. However, this design did not perform satisfactorily. The

joints failed to function after a short service life, as contraction

joints opened wider with time.








Later, in the 1940s, a new design procedure was developed using

plain concrete. Pavements were constructed with expansion joints locat-

ed at 120 ft. intervals, but without dowel bars. As a consequence, many

pavements exhibited faulting expansion joints and poor load transfer at

contraction joints.

In recent years two design alternatives for plain concrete have

been extensively used by pavement engineers. The first design calls for

concrete pavements with undoweled contraction joints, while the second

design specifies short slabs, normally 15 to 20 ft. long, which include

dowels at joints to minimize faulting. The performance of such pave-

ments has been reported to be satisfactory.

In some of the recently constructed pavements, skewed joints have

been used instead of the customary normal joints. Normally the joint

skewness has been one foot per lane. The skewed joints are supposed to

reduce riding roughness in case faulting develops at the joints.

Another trend in pavement design has been the use of randomized

spacing of joints. The reason for randomizing joint spacing is to mini-

mize the harmonic wheel thumps in vehicles. In the State of Florida for

example, consecutive sets of four slabs at 16 ft., 22 ft., 23 ft., and

17 ft. have been constructed on concrete pavement sections of Inter-

state 75. In an effort to minimize pavement cracking, many state high-

way agencies are designing shorter and thicker pavement slabs (2).

Despite numerous improvements in the design and construction

methods, concrete pavements are still exhibiting premature cracking and

other forms of distress. This highlights the need for better under-

standing of not only concrete pavement behavior, but also the parameters

that influence pavement behavior.








2.2 Function of Joints in Concrete Pavements

There is a tendency for cracks to develop shortly after placement

of concrete pavements. Such cracks normally result from pavement move-

ments associated with shrinkage of concrete and/or temperature changes.

The two main designs for concrete pavements, the continuously reinforced

concrete pavements (CRCP) and the jointed plain concrete pavements

(JPCP), are intended to mitigate and control pavement cracks. Steel

mesh provided in the CRCP does not prevent crack formation, but rather

keeps the cracks tightly closed. This maintains the continuity of load

transfer across the cracks, and consequently minimizes the potential for

premature distress or failure.

In the case of the jointed concrete pavements, the cracks are per-

mitted to develop only at predesignated locations. At such locations

joints are constructed, thus dividing the pavement into slabs. Joints

therefore permit slab movements associated with temperature and moisture

changes, without any further crack formation (3).

As soon as concrete attains sufficient strength, joints are intro-

duced to the pavement. Joint grooves are usually sawed to an approxi-

mate depth of one fourth the slab thickness. Shortly after this opera-

tion, the remaining three fourths of the thickness will become fully

cracked, as movements continue within the pavement. By restricting

crack development at joints (4) the potential for premature distress or

loss of ride quality can be minimized.

Despite full cracking of the pavement at joints, loads can still be

transferred between the adjoining slabs. Load transfer is made possible

through shear and moment resistance developing at the joint. The degree

of load transfer is dependent on the joint stiffness governed by shear








and moment resistance. In turn, the joint stiffness establishes load

response of the pavement. Greater load transfer, associated with high

joint stiffness, generates low deflections and stresses in pavement

slabs.

Load is transferred across joints by two means, 1) interlocking of

joint aggregates, and 2) dowel bars. At undoweled joints, load is

transferred mainly by the shear force developed through interlocking of

joint aggregates (5). The load transfer at doweled joints is provided,

by the shear and moment resistance, developed in dowel bars upon appli-

cation of load adjacent to the joint.

It has been a normal practice in construction of concrete pavements

to incorporate dowel bars at joints. The main function of the dowel

bars is to maintain surface alignment of the two adjacent slabs. When

incorporated with the aggregate interlocking mechanism, dowel action can

improve the joint stiffness and increase load transfer between pavement

slabs.



2.3 Pavement Slab Displacements

2.3.1 Horizontal Slab Displacements

Horizontal slab movements in the form of expansion or contraction

are generated by temperature and/or moisture changes in concrete. Such

movements start at mid-slab and reach maximum at the joints. Friberg

(6) reported that horizontal slab movements are often resisted by the

frictional force at slab-subgrade interface. The frictional resistance

develop stresses which increase in magnitude from the slab ends, reach-

ing maximum at mid-slab. However, the frictional resistance in short

slabs in not as significant as in long slabs (100 feet long). Friberg









developed mathematical equations to calculate friction at slab-subgrade

interface and the stresses developed due to movement restraints. How-

ever, such mathematical solutions are best suited for long-reinforced

slabs and do not apply to short 20-foot slabs.

A recent study (7) showed that excessive slab movements may result

in the lockup of joints. Furthermore, the restraint applied by locked

doweled joints may result in cracking and spelling of the concrete sur-

rounding the dowels. The study suggested that completely locked dowel

joints may develop tensile stresses at mid-slab. Also, it was mentioned

that a combination of restraint stresses and stresses associated with

temperature curling and traffic loads can result in transverse cracking

at mid-slab. However, no details were provided to support this claim.

Slab movements associated with temperature changes have not been

investigated adequately. The few studies that dealt with this subject

were conducted during the 1950s and early 1960s. Despite the signif-

icance of this subject, research with primary focus in this area seems

scarce.

2.3.2 Vertical Slab Displacements

The temperature through a pavement slab is not uniform. Changes in

ambient temperature during a 24-hour thermal cycle induce a wide variety

of temperature gradients in the slab (8). A temperature differential

(algebraic difference between temperatures at the surface and at the

bottom of slab) causes curling of the pavement slab in the direction of

the cooler surface. When the surface temperature (Tt) is equal to the

bottom temperature (Tb), the slab is in a no-curl or flat position, as

shown by Figure 2.1(a). During night and early morning hours, the cool-

est temperature is at slab surface. Figure 2.1(b) shows that when the







11





Tt Surface Temperature
Tb Bottom Temperature

Tt Tb

(a)
.*" . .* ...... . .. .. .*.* .*. .- .-. . . ..".' ..

a) Flat;

Tt
(b)
.'" .*.*.*.*.*.*.' .--.*.*.*.*.*.* .-.*.*.*.*.*."."' "*.*.'" .**.*.*.**" '.*.*.-'.*.*.*.

b) Upward Curling;

Tt > Tb


(c)


TMgPERATURE CTRLING

c) Downward Curling;

Dry





Trapped MOISTURE CARPING High Moisture
Water
d) Moisture Warping;




High Shrinkage

Low Shrinkage


(e)
...........................

SHRINKAGE WARPING
e) Shrinkage Warping.
Figure 2.1: Curling and Warping of Pavement Slabs.








temperature differential is negative, the slab tends to curl upward.

However, during the day, particularly in the afternoon, the slab curls

downward as shown in Figure 2.1(c). The temperature differential is

positive because the highest temperature is at the slab surface.

Since the 1920s curling was recognized as an important parameter

affecting stresses in pavement slabs. Westergaard (9) in 1926 published

the earliest analytical work on pavement stresses due to temperature

variation. Grinter (10) in 1931 presented a design method for rein-

forced concrete pavement slab which incorporated calculation of deflec-

tions and stresses associated with slab curling. Unlike Westergaard,

Grinter's analysis of curling deflections was made for a slab that had

actually been tested with curling measurements already recorded.

Harr and Leonards (11) in 1959 presented another analytical proce-

dure, to determine deflections and stresses in curled slabs. In this

analysis, finite-size slabs were assumed, and loss of subgrade support

was considered. Such conditions were not considered in the analysis

previously developed by Westergaard. Comparison with available measure-

ments conducted by Wiseman et al. (12), showed good agreement between

observed and computed deflections.

At the AASHO Road Test (13) temperatures were measured at different

depths of pavement slabs. Such measurements were taken at different

times during 24-hour temperature cycles. The slab temperatures were

also measured at different seasons. A relationship was established be-

tween slab curling and temperature differential. Data obtained from the

AASHO Road Test provided an excellent source of information regarding

the temperature distribution in pavement slabs and the subsequent pave-

ment response.








In the early 1970s Huang and Wang (14) developed a finite-element

computer program for analysis of concrete pavement slabs. The program

considered upward slab curling due to a negative temperature differen-

tial, assuming linear temperature gradient. Two recently developed pro-

grams, WESLIQID (15) and JSLAB (7), also include the capability for

computing curling stresses associated with temperature differential.

However, curling predicted from finite element computer programs

has not been correlated with actual measurements of slab curls. Lack of

such correlation may be due to the fact that poor agreement exists with

field measurements, because the slab displacements are only partially

related to temperature differential. It has been well recognized since

the early 1920s (16) that warping due to moisture may also contribute to

the slab deflection. Furthermore, evidence presented by Childs (17)

suggests that early concrete shrinkage can contribute to permanent slab

warping. Harr and Leonards (11) also acknowledged the possibility of

permanent slab warping due to slab shrinkage. Figure 2.1(d) and 2.1(e)

show the upward moisture and shrinkage warping. The upward slab warping

due to moisture and shrinkage differential may prevent the slab from

assuming a no-curl or flat position at zero temperature differential.

Furthermore, a positive temperature differential is required to offset

the upward warping effects of shrinkage and moisture. By assuming no-

curling condition at zero temperature differential, the finite-element

computer programs can actually underestimate the magnitude of slab

curling. It follows that calculated curling stresses will be lower than

stresses actually induced in the slab.

In an attempt to account for the effect of moisture warping, an

equivalent temperature differential is usually assumed. However,








according to the information acquired by the author, no field measure-

ment of slab deflections have been conducted to determine the tempera-

ture differential which would be equivalent to the effects of moisture

and/or shrinkage warping.



2.4 Distress Mechanisms In Concrete Pavements

Traffic loads and environment generate pavement response in the

form of deformation, stress, strain, or surface wear (18). Distress

occurs when pavement response exceeds the limiting values of strength,

stiffness, or durability. Initially, many forms of distress only cause

riding roughness and discomfort. However, lack of proper and effective

maintenance of early pavement distress can ultimately lead to failure.

Major types of pavement distress are listed in Table 2.1 (19, 20) which

also includes severity, description and mechanism of each distress.

Figure 2.2 presents schematic diagrams of the major types of pavement

distress. It is evident that most types of pavement distress are either

developed at the joints or associated with joint behavior.

A report on joint-related distress (4) considered heavy traffic

loads and extreme temperatures as responsible for initiating pavement

distress. However, stresses generated by load and/or temperature do not

result in pavement distress unless coupled with stresses caused by other

deficiencies. The report cited many pavement design and construction

deficiencies, as the possible contributors. Some of the deficiencies

listed were excessive slab length, narrow pavement, inadequate load

transfer, misalignment of dowels, improper joint construction, infiltra-

tion of incompressibles and pumping.










Table 2.1 Concrete Pavement Distress -- Ref. (19, 20)


Type of Distress Severity Description Mechanism

1- Pumping High to Ejection of mixtures of Free water in supporting layer
very high water and fine subgrade squeezed out under traffic load
materials through joints carries out fines from beneath
or cracks the slab

2- Faulting High to Differential vertical Differential settlement or swelling
very high displacement of adjoining between two adjacent slabs, or
slabs, creating a "step" uneven support under the slabs
deformation in the associated with pumping
pavement surface

3- Transverse High to A crack or break in the Insufficient contraction joints;
Cracking very high middle third of the slab overloading an upward curled slab
at right angles to the having inadequate subgrade support
pavement centerline
4- Corner High Diagonal crack extending Poor subgrade support at slab
Cracking from the joint to edge of corner associated with pumping
the pavement slab and/or excessive upward curling;
or overall weakness in subgrade
support










Table 2.1--Continued


Type of Distress Severity Description Mechanism

5- Longitudinal High A crack or break Lateral shrinkage; lateral
Cracking approximately parallel movement and loss of subgrade
to the pavement support; possible bending or
centerline curling
6- Spalling High Breakdown of slabs at Improper joint construction;
joints or cracks, resulting incompressibles in joint; dowel
in the removal of sound misalignment
concrete
7- Buckling- Very high Lateral break up of Joint lockup due to infiltration
Blowup concrete near the joint of incompressible, resulting in
with two sides of joint excessive bending stresses
lifted off the subgrade
8- Surface De- Moderate Progressive disintegration Concrete surface erosion by
terioration and loss of the concrete de-icing chemicals; improper con-
(scaling, wearing surface struction techniques; repetitive
traveling) freeze-thaw cycles
























Raveling


'I,


Faulting


Pumping


I


Blowup (buckling)


Keyway Failure


/


N ~

/


--


Compression Cracks


Corner Breaks


Types of Joint Distress Ref. (3)


/


Spalling


f


( .fl


- -----,


m I llml


/
oi


III


% I l


f


J


A


Figure 2.2:








It is important to note that pumping is not a stress initiator but

can cause other serious distress that ultimately lead to pavement fail-

ure. In fact, pumping is generally recognized as the major problem in

jointed concrete pavement. Hveem (21) viewed pumping as a phenomenon

which indicates imminent distress or failure of a pavement. He pre-

sented an accurate description of the events leading to the pumping

phenomena. The upward slab curling and/or warping in the vicinity of a

joint create a void beneath the slab. Water infiltrating the pavement

through the joint accumulates in the void. The entrapped water is sub-

jected to considerable pressure with each passage of heavy axle loads.

Water flows laterally at a high velocity forcing the removal of fine

materials from the subgrade, through the joint, and along the edge of

slab. As pumping action continues, a void will be created beneath the

joint. Loss of subgrade support at the joint combined with excessive

upward curling and heavy axle loads can induce stresses high enough to

cause corner cracking.



2.5 Review of Concrete Pavement Research

Analysis of concrete pavements started in the early 1920s. Inde-

pendent research by Goldbeck and Older in 1920 resulted in the develop-

ment of formulas for approximating stresses in concrete pavements. Such

formulas were used for many years as a basis for concrete pavement

design. Following a long period of study, Westergaard (22) in 1926,

presented the well-recognized stress analysis of concrete pavements. He

developed mathematical equations for computing critical stresses in

pavement slabs. Westergaard derived equations for critical stresses for

corner, edge, and interior loading cases. Despite some modifications,








Westergaard's equation for corner stresses, is still considered to be

the primary design formula for concrete pavements.

Recognizing the influence of temperature variation on stresses in

concrete, Westergaard (9.23) supplemented his original work on pavement

stresses, by developing equations to compute stresses caused by tempera-

ture. With the incorporation of dowels in pavement joints, Westergaard

published (24) the first analytical procedure for the evaluation of

doweled joints.

During the 1930s the Bureau of Public Roads (25) conducted a major

study of concrete pavements. Extensive tests were performed at a test

road in Arlington, Virginia. This study presented a wealth of informa-

tion not only on the load response of concrete pavement, but also on

parameters affecting pavement response, such as temperature, joint

efficiency, and subgrade properties.

Dowel joints have been a common design feature in concrete pave-

ments. Initially, dowels used in expansion joints were the only load

transfer device between adjoining slabs. Friberg (26) in 1938 developed

a general mathematical solution for analysis of behavior and load trans-

fer capacity of dowel bars. The model was based on a theory developed

by Timoshenko and Lessele. This theory assumes the dowel as an elastic

beam extending an infinite distance into an elastic mass (concrete).

Figure 2.3 presents the free-body diagram of a dowel bar and equations

for computation of shear and moment along with dowel. Friberg equations

are still being used for design of dowel joints. Recently developed

finite-element computer programs utilize Friberg equations for modeling

the dowel action between the adjoining slabs.












The relative stiffness of the dowel and the concrete mass is expressed by
4 J ............................. ...... (3)
G = modulus of support of concrete mass (1,500,C00 lb per cu in.)
d = diameter of dowel
E. = modulus of elasticity of dowel (29.000,000 psi)
I = moment of inertia of dowel
L = length of primary bearing pressure wave on dowel, in.
P A















FREE-BODY DIACGAM OF DOWEL



-7
The general equaton for the deflection of the dowel in the concrete mass :s:
.y P cn dz 9M. (con s4 sin xz)J ..................(4)
YI j E
e = base of Napierian logarithms
x = distance alcng the dowel from the slab face at the ioint
Po= concentrated load, Ib, acting downward on the dowel at the center of the ;oint
M.= bending moment in the dowel at the slab face, in.-lb. = Po W/2
T;:. mr.ent and shear at any point in the dowel may be found from the following equaticns which
a" ccvelcpment of the foregoing equation.
.11 E.I IPao sin ax M~. (sin z + Cie l. I............(5)

1' -- e-" (235.. I'D) sin .x + Pa coe Oz ................. (6)

T-.e ma.imum moment in the dowel occurs where y 0
idz
Then
P.+- P .......+(. +#W).. .... ............ 7)
2d
W = Icint wvdh opening
x. = distance 'rom the slab face to the point of maximum moment in the dowel, where
.rn ,x. = 1/(l + AW)
Cef:e:cn of the dowel with respect to the concrete at the face of the joint is y., and equals y
(Ec: :4] when x = C.
y. a(2 + 011)
SI = bearing pressure on the concrete under the dowel at the slab face = Gy. .. (8)


Figure 2.3: Frieberg's Analysis of Dowel Bars in Concrete -- Ref. (26)








Friberg also addressed a major problem associated with dowel bars.

The problem is dowel misalignment, which is normally caused by improper

construction techniques. He cited misaligned dowels as offering move-

ment restraint at joints. Such resistance increases in proportion to

the magnitude of joint movement. Friberg developed the relation between

the degree of misalignment and the stresses induced at the doweled

joint.

Evaluation of the load transfer efficiency of dowels was another

area of the research emphasis. Finney and Fermot (27) developed a test

procedure for evaluating the load transfer effecicency of dowels having

variable lengths and diameter. Marcus (28) presented the results of a

study conducted to determine the load carrying capacity of dowels. By

determining the bearing stress at the dowel-concrete interface, Marcus

attributed cracking of concrete surrounding the dowel bar to high stress

concentration around the dowel. He related increasing joint deflection

to the continual cracking of concrete surrounding the dowel bars.

In 1956 Keeton (29) presented test results for dowels in expansion

joints of an airfield pavement. Shear and moment in dowel bars were

obtained from strain measurements of dowels.

Teller and Cashell (30) conducted extensive laboratory tests to

study dowel joint response under repetitive loading. They devised an

elaborate loading system capable of subjecting jointed concrete slabs

with repeated loading on both sides of the joint. Parameters affecting

load transfer efficiency of the dowels were evaluated. The evaluated

parameters included dowel diameter, length of embedment, joint width,

and slab thickness. Based on the test results, the authors recommended

1) using dowels with diameters equal to one-eighth the slab thickness,









and 2) a six-inch embedment length of dowels. Another interesting con-

clusion of this study suggested that contraction joints perform better

than expansion joint. Furthermore, the authors attributed the reduction

in joint efficiency to increased dowel looseness brought about by

repeated loading, or bond preventive coatings.

The subbase is another important element influencing the load re-

sponse of a concrete pavement. The Portland Cement Association conduc-

ted a series of studies (31, 32, 33) to evaluate the effect of different

subbases on the structural behavior of pavement slabs. Under laboratory

conditions, pavement slabs were constructed on gravel, crushed stone,

and cement-treated subbases. Bonded and unbonded cement-treated sub-

bases were included in the evaluation. Other parameters considered in

the subbase study were, slab thickness, doweled and undoweled joints,

and temperature curling of slab. Slab deflections, strains, and pres-

sure response to static loads were measured during the tests. Some

interesting conclusions were drawn from these studies. Slab on the

cement-treated subbase offered the highest resistance to applied loads.

Moreover the load capacity of the pavement system was further improved,

when the cement-treated subbase was bonded to the slab. Joints of slabs

on cement-treated subbase effectively transferred loads. However,

doweled joints offered very little advantage over undoweled joints, when

cement-treated subbase was in full contact with slab. In regards to the

effects of slab curling, the study concluded that slabs with bonded

interface curled slightly less than those without bond. Meanwhile de-

flections and strains due to loads were generally higher when the slabs

were curled. Citing significant reductions in corner deflections, these









studies recommended that pavements should be designed such that traffic

load positions are away from the edges.

Aggregate interlocking mechanism of undoweled joints was investi-

gated by Colley and Humphrey (34). Repetitive motion of tandem truck

wheels across a joint, were simulated in the laboratory. Load transfer

across the tested joints was evaluated by measuring shear developed by

aggregate interlocking. Five variables were selected for the study

namely, width of joint opening, thickness of concrete slab, load magni-

tude, foundation support, and shape of aggregate particles. Correla-

tions were established between data obtained from the laboratory and

field tests. The study arrived at a number of important conclusions re-

garding the effectiveness of undoweled joints in load transfer. The

main conclusion was that load transfer effectiveness decreases with the

widening of the joint opening.

The AASHO (American Association of State Highway Officials) Road

Test during 1958 to 1961 is considered the most important test pavement

ever built (13). Results of the extensive tests performed on the con-

crete sections of the Road Test, not only provided valuable information

on concrete pavement performance, but were also used to develop the

well-recognized AASHTO Design Guide. Since the AASHO Road Test, major

research emphasis has been in the field of pavement rehabilitation.

Development of finite-element computer models has been another major

area of research.



2.6 Computer Modeling and Applications

Since the early 1970s, a number of finite-element computer pro-

grams have been developed for analysis of concrete pavements. The









finite-element method for modeling jointed concrete pavements generally

utilizes the plate theory (14). Using the plate theory provides a wide

range of modeling capabilities, which include different load-transfer

condition at joints, and partial subgrade support (35). However,

utilizing the plate theory will allow the computation of stresses only

in the concrete slab.

The use of layered theory for the analysis of the pavement system,

unlike the plate theory, will allow stress computation at any point

within the pavement system (36). The layered theory has been widely

used for analysis of asphalt pavements (35, 37). In concrete pavements

the use of layered theory has been limited to analyzing the continuously

reinforced concrete pavements and pavement overlays (36). It is not

used for analysis of jointed concrete pavements (38). The layered sys-

tem models are only capable of accurately modeling the slab interior.

Furthermore, the theory does not permit the analysis of pavements having

joints or those only partially supported by the foundation.

The foundations in the most recognized computer models are ideal-

ized either as a Winkler (dense liquid) foundation or as an elastic

solid foundation. The Winkler foundation implies that an applied force

over an area will produce a reaction that is equal to the deflection

multiplied by the modulus of subgrade reaction (k). The deflection at

any point on the foundation surface is a function of the force at that

point but independent of the forces at all the other points. A Winkler

foundation can be visualized as a bed of springs. The stiffness of such

springs represent the foundation stiffness.

The elastic solid foundation, idealizes the foundation as a homoge-

neous, elastic, and isotropic solid having a semi-infinite depth. The









foundation is characterized by modulus of elasticity (E) and Poisson's

ratio.

The issue of whether the Winkler or the elastic-solid models repre-

sent the true soil response, has been the subject of an ongoing debate.

Some researchers (36, 39, 40, 41) have expressed the opinion that, not

only is the Winkler foundation not a realistic representation of the

subgrade response, but that the modulus of subgrade reaction (k) is a

fictitious quantity not characteristic of soil behavior. Meanwhile they

consider the elastic solid foundation the true representative of the

soil, where the modulus of elasticity and Poisson's ratio could easily

be determined from lab tests.

Majidzadeh and llves (38), Chou and Huang (42) suggested that the

elastic solid subgrade is stiffer at the edge and corner than the

Winkler subgrade. Hence the deflection basin at slab corner, obtained

from Winkler foundation is steeper than that obtained from the elastic

foundation.

Others have reported (43, 44, 45) that the predicted pavement re-

sponse, using the Winkler assumption, correlates well with observed or

measured response. Huang (37) presented a strong argument in favor of

Winkler type foundation. He claimed that Winkler foundation can incor-

porate parameters such as voids or temperature curling much easier than

the elastic solid foundation.

However, both representations of the foundation have been used in

computer modeling of concrete pavements. Huang and Wang (14) developed

the first finite-element computer program capable of analyzing the

structural response of jointed concrete pavements. This model assumes a

Winkler type foundation. Huang (40) also developed a similar model








assuming a solid elastic foundation. Both models have similar capabil-

ities. The pavement is modeled by a series of up to three slabs con-

nected at the joints by dowels. Load transfer between the adjacent

slabs was only considered for doweled joints. Dowels were modeled to

transfer loads by shear only. The concept of joint efficiency was used

to represent the degree of load transfer between slabs. The joint effi-

ciency is a physical property of a joint defined as the percent rates of

the deflection on the unloaded side of the joint to that on the loaded

side. The programs also accounted for partial or full support condition

by the subgrade. Thus subgrade voids and/or temperature curling of slab

can be modeled in the program.

Huang and Deng (41) recently presented a computer package capable

of analyzing multiple jointed slabs on Winkler, elastic solid or elastic

layered foundation. Unlike the original programs the new package con-

siders both shear and moment transfer across joints. Dowel looseness

can also be accounted for. The joint stiffness is represented by linear

and rotational springs for shear and moment. The shear transfer is

expressed as the deflection differential across the joint multiplied by

the shear spring constant. Likewise the moment transfer is expressed as

the rotation differential multiplied by the rotational spring stiff-

ness. Shear transfer can also be analyzed in a different method, by

specifying the size, spacing, modulus of elasticity, and Poisson's ratio

of dowel bars together with joint width and modulus of dowel support, as

originally developed by Friberg (26). Dowel looseness can be considered

by designating the gap size at the dowel-concrete interaction.

The U.S. Army Engineer Waterways Experiment Station adopted Huang's

original concepts of pavement modeling, with few modifications, to








develop two finite-element computer programs called WESLIQID and

WESLAYER (15). WESLIQID is based on the plate theory, and assuming a

Winkler type foundation. However, in the WESLAYER program the founda-

tion is assumed as either a linear elastic solid or a linear elastic

layered system.

The two aforementioned programs are capable of analyzing the stress

condition in concrete pavements by considering a number of parameters.

These parameters include 1) load transfer at the joint, 2) single or

multiple-wheel loads, 3) temperature curling, and 4) full or partial
subgrade support conditions. However, the programs consider only the

shear transfer across joints. The moment transfer is generally assumed

to be either zero or 100 percent. The assumption of zero moment trans-

fer was justified (42) by the claim that a joint or a crack with large

opening fails to offer any moment resistance. The modeling of shear

transfer is similar to that provided earlier by Huang.

ILLI-SLAB is another finite-element computer program developed at

the University of Illinois (45). Assuming a Winkler type foundation,

the slab is modeled to incorporate one or two layers with the option of

being bonded or unbonded. Such capability provides the analysis for

concrete pavements with cement-treated base or an overlay. The program

is capable of modeling a series of up to six slabs, incorporating joints

and/or cracks. Shoulders with the option of incorporating ties or

no-ties are also modeled by the program.

Joint modeling by ILLI-SLAB depends on the load-transfer system

assumed. The aggregate interlocking mechanism is represented by shear

force developed by a series of vertical springs connecting the nodes of

adjacent slabs. For dowel joints, the program models a dowel as line









element with two degrees of freedom per node. The two displacement com-

ponents at each node are, vertical and rotational displacements corre-

sponding to a shear force and moment, respectively. However, the pro-

gram does not account for the loss of subgrade support associated with

temperature curling, and subgrade voids.

Correlation of ILLI-SLAB predicted-response with field test data

has been used to evaluate joint behavior, and to detect subgrade voids

beneath the joints. Corvetti and Darter (46) presented a procedure for

joint evaluation and void detection. The procedure involved comparing

load-deflection data from the Falling Weight Deflectometer, a non-

destructive loading device, with predicted deflections from the ILLI-

SLAB program.

Tayabji and Colley (7, 47, 48) utilized another computer program

called JSLAB, to evaluate the effect of joints with non-uniformly spaced

dowels. JSLAB developed by the Portland Cement Association has similar

modeling capabilities as the WESLIQID or Huang's models on Winkler foun-

dations. An interesting conclusion based on computer analysis suggests

that using six dowels per joint in each lane provides a joint response

similar to that provided by the traditional 12 uniformly-spaced dowels.

The study also claimed that using fewer dowels per joint can result in

less movement restraint normally associated with misaligned dowels

and/or locked joints.

Computer software has also been developed for speedy analysis of

test data from the Falling Weight Deflectometer (FWD). Ullidtz and

Stubstad (49) presented a procedure for evaluation of jointed concrete

pavements. A computer program called ELCON was utilized to analyze

field data from the FWD. It is suggested that ELCON program computes








the pavement parameters from the FWD data including the subgrade stiff-

ness, degree of load transfer at joints, and detection of voids.



2.7 Design Procedures

Many design procedures have been developed for concrete pavement

during the past 60 years. However, for the past 20 years the AASHTO

(American Association of State Highway and Transportation Officials)

design guideline (50) and the PCA (Portland Cement Association) design

procedure (51) have been the most widely used procedures for concrete

pavement design.

2.7.1 The AASHTO Design Guide

The AASHTO design was first developed and circulated in 1961 (52).

The guide was based on the results from the AASHO Road Test (13) supple-

mented by existing design procedures and available theory. Spangler's

(53) corner equation was used as the design equation because it showed

good correlation with Road Test measurements. It should be noted that

Spangler's corner equation is basically Westergaard's equation, modified

by the introduction of a load transfer coefficient.

In 1972, AASHTO published the "AASHTO Interim Guide for Design of

Pavement Structures" (50). Revisions were made to the chapter relative

to design criteria for concrete pavements. Conservatism was incorpo-

rated into concrete pavement design, by introducing a safety factor of

1.33 to the computed equivalent axle loads. As a consequence design

thickness became greater than that predicted by empirical formulas,

which were based on performance of pavement sections at the Road Test

(52). Accounting for high volume traffic the safety factor was further

increased to 2.0, in 1981. This added more conservatism and








subsequently greater pavement thickness over that of the basic perfor-

mance equation.

A new proposed AASHTO guide was published in 1986 (54). Some of

the new concepts and parameters introduced into the basic AASHTO design

are:

1- Reliability factor To account for shift in the design traffic.

2- Environment Adjustment of design for parameters such as freeze

and thaw, and swelling soils.

3- Drainage To provide guidance in the design of sub-surface

drainage systems, and modify design equations to take advantage

of improvements in pavement performance associated with good

drainage.

4- Loss of foundation support To account for possible soil ero-

sion under rigid pavements.

5- Effect of type of load transfer at joints Incorporating load

transfer coefficients based on type of joint, and support condi-

tion from the boundaries.

6- Effect of concrete shoulders A procedure is provided for the

design of rigid pavements with tied shoulders or widened outside

lane.

2.7.2 The PCA Thickness Design

The earlier version of the PCA design procedure had been published

in 1966. The designs were based on influence charts for stresses at

transverse joints and the design factors used were based on performance

at the AASHO Road Test and existing pavements around the country (52).

The design criteria is fatigue cracking in concrete slabs due to








repetitive traffic loading. The influence charts were developed in 1951

by Pickett and Ray (55) from the mathematical equations of Westergaard

(23).

The design thickness of concrete is modified to ensure resistance

to fatigue cracking during the design life of the pavement. Tables

including traffic data are provided to estimate fatigue that is used in

the thickness design of concrete pavements.

In 1984 PCA published and distributed Thickness Design for Concrete

Highway and Street Pavements (56). The new procedure includes recogni-

tion of:

1- Type of load transfer at transverse joints.

2- Effect of concrete shoulder.

3- Effect of using econocrete subbase.

4- Two design criteria a) fatigue to keep pavement stresses due to

loads within safe limits, and subsequent prevention of fatigue

cracking and, b) erosion, to limit the effects of pavement de-

flection at slab edges, joints, and corners, thus controlling

the erosion of subbase and shoulder materials.

The new criteria for erosion was needed since some modes of pavement

distress such as pumping, faulting and shoulder distress are unrelated

to fatigue (52).














CHAPTER 3
TESTING EQUIPMENT AND PROCEDURES

3.1 Description of the Test Road

A concrete pavement, constructed in August 1982, at the Bureau of

Materials and Research of the Florida Department of Transportation

(FDOT), was used as the testing facility for this research. The test

pavement, illustrated in Figure 3.1, consists of six slabs. Each slab

is 20 ft (6.1 m) long, 12 ft (3.66 m) wide, and 9 in (23 cm) thick.

Three of the five pavement joints were undoweled and the remaining two

(joints 2 and 5) were doweled joints.

The test road was constructed on native roadbed soil consisting

mainly of granular materials classified as A-3 (AASHTO Soil Classifica-

tion). The site was prepared by removing the top soil, and compacting

the subgrade surface. The average Limerock Bearing Ratio (LBR) for the

compacted subgrade was 50.

Voids were incorporated at different positions in the subgrade

beneath the slabs, except for the control slab (slab 4), as shown in

Figure 3.1. The voids were introduced in the subgrade by installing

0.75-inch (19-mm) and 1.5-inch (38-mm) styrofoam boards in the subgrade,

with their surfaces flush with the subgrade surface. Perforated hoses

were attached to each styrofoam board. Following the construction of

the concrete pavement, voids were created by passing ether through the

hoses to dissolve the styrofoam boards.












Joint Number
I r


S19 mm Void depth
(3/4 in)
* 38mm Void depth
(1 1/2 in)







Control Slab


Slab Number


I


Dowelled
Joint


2





3





4


Dowelled
Joint


Slab Thickness = 9in
(I in = 2.54cm)
Figure 3.1: Plan of Test Road and Void Locations


3.66 m
(12')








The test road was constructed in two consecutive days. In the

first day, concrete was placed for slabs 2, 3 and 4. In the second day,

forms were removed from the doweled ends on slabs 2 and 5, and concrete

was cast for the remaining slabs. Shortly after setting of the con-

crete, pavement joints were saw cut to a depth of 2.25 inches. After

curing, a loaded truck was used to insure complete cracking at the

undoweled joints 3, 4, and 6. At construction joints 2 and 5 the faces

of adjoining slabs were smooth, and were connected only by dowels.

Pavement temperatures were monitored by thermocouples embedded

during construction at four locations in slabs 3 and 4, as indicated by

Figure 3.2. Slab 3 included two arrays of thermocouples near the edge

and center of the slab. The thermocouples were attached to a wooden

dowel at 1 in. and 8 in. below the slab surface. In slab 4 each of the

remaining two arrays included five thermocouples attached to a wooden

dowel at 1, 2.5, 4.5, 6.5 and 8 inches from the slab surface, as shown

by the close-up in Figure 3.2. Another thermocouple was used to measure

the ambient temperature. This thermocouple was housed inside a perfo-

rated white wooden box, which was mounted on a 5 ft wooden pole and was

8 ft away from the nearest building.

This test road, which was constructed to be representative of in-

service Florida concrete pavements, was used to investigate the pavement

response to temperature and load. The instrumentation and testing

procedures for this research are discussed in the next segment of this

report.













3 |e ) 4 5


+ +
+


Joint 1 2 3 4 5 6


Joint Spacing = 20 ft.
Slab Thickness = 9 in.


Test Road


12 ft.


( Vertical LVDT

Z]--- Horizontal LVDT
Thermocouples


Bracket


1.5"


LVDT


Steel Rod


Thermocouples
(Slab 3)


Thermocouples
(Slab 4)


Vertical LVDT


Figure 3.2: Details of Instrumentation


Slab
No.


7


L









3.2 Testing Procedure For Pavement
Temperature and Response

Two major tests were planned for the study of temperature response

of concrete pavements. The first test involved measuring temperatures

of the test road slabs. The second test included, measurement of slab

displacements in the vertical and horizontal directions resulting from

changes in concrete temperatures.

3.2.1 Temperature Data Collection

The thermocouples were connected to a Fluke programmable data

logger. The Fluke was programmed to record temperature measurements

from the pavement and air thermocouples. In general, concrete and air

temperatures were recorded at one-hour intervals. However, during the

Falling Weight Deflectometer (FWD)*tests, temperatures were recorded at

30-minute or at 15-minute intervals. Consecutive 24-hour cycles of tem-

perature measurements were recorded. Temperature data were recorded

through the twelve months of the year, and over a period of two and one-

half years, starting from 1983. However, there were some discontinui-

ties in the data collection process. These discontinuities were mainly

due to servicing and equipment calibration, or the utilization of the

Fluke data logger in other studies.

3.2.2 LVDT Installation

Thermally induced displacements in the test road slabs were mea-

sured using Linear Variable Differential Transducers (LVDTs). The LVDTs

were installed to the pavement slabs in vertical and horizontal

directions. Positions and a schematic diagram of the LVDTs are shown in

Figure 3.2. The horizontal LVDTs were installed across the doweled

joint 5 and the undoweled joint 4. The brackets used to hold the LVDTs

were made out of a brown phenolic board that is highly weatherproof.









The vertical LVDTs were installed at slab 4, in the center and at

the midslab edge locations. Two more vertical LVDTs were installed at

the adjoining corners of slabs 3 and 4, two inches from joint 4. Figure

3.2 shows a schematic diagram of a typical vertical LVDT installation.

The LVDT was held from one end by a bracket glued and fastened to the

slab, while the transformer core was resting against a reference plate

fastened to a 10 ft long invar steel rod. The rod was housed inside an

8-ft-long plastic pipe driven into the ground. This testing assembly

was designed to prevent any possible displacement of the reference plate

and the LVDT, caused by movements of slab and subgrade.

Deflection profiles of slab 3 along the undoweled joint 4 were also

monitored at different temperatures. A wood frame, shown in Figure 3.3,

was placed over the slab and fastened to steel cups which were welded to

2-inch diameter steel pipes driven 5 ft into the ground. Seven LVDTs

attached to the frame were used to monitor surface elevations along

joint 4.

3.2.3 Slab Displacement Measurements

Response of the test road slabs to temperature changes was moni-

tored. Displacement and temperature measurements were recorded by a

Data Acquisition Unit (DAU). Two Hewlett Packard computers, HP85B and

HP9825A were used interchangeably with an HP3497A Data Acquisition Unit

to record the slab displacements and temperatures. The DAU was pro-

grammed to record the LVDT and thermocouple readings at specified time

intervals. The data was loaded into the computer to be stored and

printed out simultaneously.

The vertical pavement displacements were measured at the center,

edge and corner locations, while the horizontal slab displacements were













































Figure 3.3: Monitoring Deflection Profile at the Joint









monitored at the undoweled joint 4 and the doweled joint 5, as shown in

Figure 3.2. Figure 3.4 shows a picture of LVDTs at joint 4. All LVDTs

and thermocouples were recorded simultaneously by the DAU at one-hour

intervals. In some cases however, the measurements were recorded every

30 minutes. Consecutive 24-hour cycles of measurements were recorded to

evaluate slab movements with temperature changes under different weather

conditions. The tests were conducted between January and June, 1986,

with the exception of the month of March. The LVDTs, which were of the

weatherproof type, were calibrated regularly during the testing period.

In addition to the test program just mentioned, the surface of slab

3 along joint 4 was monitored separately, as shown in Figure 3.3. The

surface elevations of slab 3 were monitored during a 24-hour thermal

cycle to obtain the slab deflection profile at different temperature

conditions.



3.3 Falling Weight Deflectometer Testing

The prime objective of the Falling Weight Deflectometer (FWD) tests

was to characterize the load response of different segments of the test

road at different temperatures. The sections that follow describe the

FWD test device, the details of the testing plans and the testing pro-

gram.

3.3.1 The Falling Weight Deflectometer (FWD)

The load response of the test road slabs was evaluated using the

Dynatest 8000 Falling Weight Deflectometer testing device. The FWD

applies an impulse load on the slab surface and measures the correspon-

ding deflections at specified locations. This testing device consists







40



































Figure 3.4: LVT Arrangement at Joint 4










Figure 3.4: LVDT Arrangement at Joint 4









of a loading system and a set of six deflection sensors (velocity trans-

ducers) mounted on a trailer that is towed by a van, as shown in Figure

3.5. The data processing and computer system that control the testing

operation is housed inside the van.

The FWD loading device produces an impulse force closely simulating

the force generated by a moving wheel load of up to approximately 24

kips (105 kN). The impulse force is generated by adjustable weights

dropped from different heights onto a set of rubber buffers connected to

an 11.8-inch (30-cm) diameter loading plate. Figure 3.6 shows details

of the loading system. Conventional operation of the unit involves

using a pre-set weight (110, 220, 440 or 660-lb. weight levels) and

three or four drop heights (varied between 1 to 15 inches) which are

automatically obtained after initial adjustment. The resulting impulse

force can range between 1,300 Ibf to 24,000 Ibf. The load pulse is

approximately a half-sine wave form with a loading time between 25 to 30

milliseconds.

The force is applied to the pavement surface through the loading

plate and measured by a strain-gage type load cell. Deflections are

measured using six velocity tranducers. These transducers are normally

housed in brackets connected to a frame that can be lowered with the

loading plate. One of the transducers is located at the center of the

loading plate, the other five can be spread out at various distances

from the load center along the same direction of the trailer. However,

as illustrated in Figure 3.7, it was necessary to remove the transducers

from their brackets and position them at locations considered essential

for defining load response and characterizing slab behavior.











- V.," *


Figure 3.5:


The Falling Weight Deflectometer (FWD)


~~%i ~ 4. ." H .


Figure 3.6: View of the (FWD) Loading System


-"~' `~L I~C
























a) Loaded Side


b) Unloaded Side
Figure 3.7: Typical Configuration of Deflection Sensors
Used in FWD Tests


...~








The signals from the velocity transducers and the load all are

transmitted to a microprocessor-based control and recording system. The

system is powered from a 12VDC-110VAC invertor using the van's battery

system. The velocity transducer signals are automatically integrated

into deflection measurements through a set of amplifiers and rectifiers.

The load cell signals are also processed but without integration. The

deflection data and the load pressures are then fed into a Hewlett

Packard computer (HP85) which stores the information and prints it out

on a paper tape at the same time. The results are processed in metric

units, deflection in micrometers (m x 10-6) and load pressures in

killopascals (kPa).

3.3.2 FWD Testing Positions

It is generally acknowledged that joints are the critical segments

of concrete pavements. Thus the major testing effort was planned for

the undoweled and doweled joints. Testing was particularly emphasized

at slab corners which are considered the weakest regions of the slabs,

and even more critical when located on subgrade voids. Slab centers

were also considered in the FWD testing plan, as they represent the most

suitable testing position for subgrade stiffness characterization. Also

included in the testing plan were the edge locations at midslab. FWD

testing at the midslab edge was necessary to correlate its response, and

in particular the load transfer, with the response and load transfer at

the corner-joint position. The testing plan also included two other

joint positions representing the location of the wheel path (2.5 ft from

the edge), and the joint center (5.5 ft or 6 ft from the edge). These

two positions were selected along with the corner position (0.5 ft from

the edge) to evaluate the variability of joint stiffness along a joint.









The layout of the FWD testing positions is shown by Figure 3.8.

The numbering of the testing positions at joints represents the joint

number (first digit), and the dowel number (second digit). Doweled

joints 2 and 5 consisted of twelve dowels spaced at one-foot intervals,

with the first dowel being placed at 6 inches from the edge. The FWD

load was generally applied at locations corresponding to dowel positions

even when testing joints without dowels. An exception to this test

arrangement was position 3.6 which was located at 6 ft from the edge.

This testing position was at the center of the joint and would have been

between dowels number 5 and 6, had joint 3 included dowels.

On two occasions joint 5 was tested at each of the twelve dowel

locations (5.1 to 5.12). The dowel locations were tested consecutively.

The testing sequence including testing the first dowel location, then

moving the FWD and testing the second dowel location, and so on until

location 5.12 was tested.

3.3.3 FWD Deflection-Sensor Configurations

The second factor considered in the planning of FWD tests was the

deflection sensor configuration. It was realized that an accurate char-

acterization of pavement load response required not only measurement of

maximum deflection but also the determination of FWD deflection basin.

Therefore the configuration of the deflection sensors was designed to

obtain deflection data that would best define the load response for each

individual testing position.

Layouts of various classes of sensor configurations for different

testing positions are presented in Figures 3.9 thru 3.14. The number of

positions designated for deflection measurements generally exceeded the

available number of FWD sensors, hence, the FWD tests had to be repeated















JOINT
NO-


Layout of FWD Testing Positions on Test Road Slabs


SLAB
NO-


Distance From:
Loading Nearest Nearest
Position Edge (ft.) Joint (ft.)
3.1 0.5 0.5
3.6 6 0.5
3.12 0.5 0.5
3E 0.5 10
3C 6 10
4.1 0.5 0.5
4.3 2.5 0.5
4.6 5.5 0.5
4E 0.5 10
4C 6 10
5.1 0.5 0.5
5.3 2.5 0.5
5.6 5.5 0.5
5.12 0.5 0.5


Figure 3.8':













i<--- 12' ,-

A2 V A4

*00 *6"


Al A3




6 A


12"
*000@-


* *


* 45
R,


T 6"


S6e"


S......LOAD

O-- -*DEFLECTION
SENSOR








Note: Alpha numerical designations indicate sequence of deflection measurements.
Figure 3.9: Sensor Configurations for Testing
Positions 3.1, 4.1, and 5.1


B5



















I Ia' '1---12


SFigure 3.10: Sensor Configurations for Testing
Positions 4.3 and 5.3


E2 E4




El E3


* F


12"

0 0 0*0*0


6" iQ+ 0 0

.0


U-- A


6"






--LOAD

0----.SENSOR


Figure 3.11: Sensor Configurations for Testing
Positions 4.6 and 5.6


-V


__









I 12' -

12"

GI
6' I
------ 6---.-,.


Figure 3.12: Sensor Configurations for Testing
Position 3.6









O----LOAD


12' -1
2 0-----SENSOR
H2


6"T *


HI



Figure 3.13: Sensor Configurations for Testing
Position 3.12



















6o

* II


12
0

T


* Ji


Ja


---LOAD

O----SENSOR


----^------
Figure 3.14: Sensor Configurations for Testing
Positions 3E, 3C, 4E, and 4C









at the same loading position to allow deflection measurements of all

designated sensor positions. The sequence of deflection measurements is

indicated by the alpha-numeric designation for each configuration in

Figures 3.9 to 3.14.

It should be mentioned however, that deflections at slab positions

more than 5 ft from the load center were not necessarily measured in

every test cycle during any given testing day. Furthermore, some tests

required deflection measurements in radial directions such as Class B,

Figure 3.9 and Class F, Figure 3.10. This was designed to obtain re-

sponse at different directions along the slab to identify the weakest

structural response for the respective positions.

3.3.4 Magnitudes of FWD Load

The FWD was adjusted to apply at least four different load inten-

sities on each designated test position of the test road. The weight of

the falling mass was selected such that when dropped from four different

heights would generate, through the loading plate, pressure levels

ranging normally between 240 kPa (35 psi) and 940 kPa (136 psi), that

correspond respectively to 3,800-lb. and 15,000-lb. impulse force. This

range of pressures and total applied load represent the normal wheel

pressures expected presently on highway pavements.

Normally, a set of four consecutive drops could be triggered by the

FWD load system without requiring adjustment to weights or drop heights.

However, certain tests required more than four drops including drops

that were designed to produce pressures outside the normal range. Under

such conditions, four consecutive drops were applied first. Then the

remaining drops were executed after necessary adjustments were made to

drop heights and/or the weights of the falling mass.









3.3.5 Timing of Tests

The FWD tests were generally conducted between 5:00 a.m. and 3:30

p.m. This time interval was selected after careful examination of tem-

perature data obtained from the test road prior to this research. Ex-

amination of temperature data revealed that daily maximum temperature

differentials between surface and bottom of the concrete slabs occurred

most frequently at 5:00 a.m. and 3:30 p.m. Furthermore, minimum and

maximum average concrete temperatures also seemed to occur around these

times. Subsequently, it was established that testing between 5:00 a.m.

and 3:30 p.m. would provide information on pavement response through a

wide spectrum of temperature conditions.

The tests were performed during three different seasons. The sea-

sonal response measurements were necessary for the evaluation of joint

stiffnesses at different average concrete temperatures.

3.3.6 Testing Program

The FWD testing program is outlined in Table 3.1. The program

included six test series, four in the summer, one in the fall, and one

in winter. Testing was emphasized mainly at the undoweled (joint 4) and

doweled (joint 5). Each of the designated positions listed in Table 3.1

was tested between three to four times during the testing date. For

every test repetition, the FWD load magnitudes shown in column five of

Table 3.1 were applied to each designated testing position. The sensor

configuration for the individual testing positions are listed in Table

3.2.

The FWD tests during each individual testing day were performed

within a wide range of temperatures. Table 3.1 lists the ranges for the

temperature differentials (AT), the average concrete temperatures (Tc)









Table 3.1 FWD Testing Program


Test e n Testing Positions FWD Load AT (oF) T (oF) T (oF)
Series son Date (see Figure 3.8) Magnitudes (kPa) From To From To FroA To

1 Summer 7/17/84 5.1, 5.3, 240, 440, 540 -6 +19 82 102 85 95
7/18/84 (5.1 to 5.12) 690, 940


2 Summer 7/24/84 5.1, 5.3, 5.6 240, 440, 540 -5 +19 80 94 70 90
690, 940


3 Summer 7/25/84 4.1, 4.3, 4.6 240, 440, 540 -6.5 +24.5 82 101 72 92
7/26/84 690, 940
7/27/84
7/30/84


4 Summer 8/2/84 4.1, 4.6, 5.1, 440, 540, 690 -6 +20.5 80 102 73 94
5.6, 4E, 4C 940

5 Fall 10/5/84 4.1, 4.3, 4.6 250, 540, 940 -7.5 +14.5 74.5 87 64 80


6 Winter 1/8/85 3.1, 3.6, 3.12 160, 250, 310 -7.5 +8.5 50 58 41 70
1/9/85 4.1, 4.3, 4.6, 5.1 400, 450, 540
1/10/85 5.3, 5.6 (5.1 to 5.12) 760, 1,000
3E, 4E, 3C, 4C


NOTE: AT Temperature Differential,


TC Average Concrete Temperature,


TA Air Temperature









Table 3.2 Sensor Configuration for FWD Testing


Test Series


Sensor Configuration Class


1 C D


2 C D E


3 A D E


4 B F I J


5 A D E


6 C D E G H I J


Note: Figures 3.9 to 3.14 show
listed in this table.


all sensor configurations


and the air temperatures (TA). The temperature differential (AT) (which

is the result of the temperature at the top region of the slab minus

that at the bottom region of the slab), and the average concrete temper-

ature (TC) affect the structural response of the pavement slabs,

particularly at joints. Hence, FWD test repetitions during the testing

day resulted in a wide spectrum of responses at the various testing

positions. Furthermore, repeating the tests at different seasons pro-

vided an excellent opportunity to observe the effect of the seasonal

changes in temperature on pavement response.

In general, tests were performed during dry days so that moisture

would not influence the analysis. Furthermore, no attempt was made to

evaluate the influence, if any, of subgrade moisture on the test road

slabs.














CHAPTER 4
TEMPERATURE CHARACTERISTICS AND RESPONSE
OF CONCRETE PAVEMENTS

4.1 Introduction

Displacements of pavement slabs are mainly associated with changes

in concrete temperature. Curling of slabs and movement of pavement

joints produced by variation of pavement temperature, are important fac-

tors influencing pavement stiffness and response to loads. The extent

and direction of slab curling and joint movement change according to

daily variation of temperature. This implies that stiffness and re-

sponse of the pavement system varies at different times of the day de-

pending on degree of subgrade support and width of joint opening.

Therefore, accurate and realistic evaluation of structural response

of concrete pavements requires a thorough understanding of pavement tem-

perature. Such understanding should encompass daily and seasonal vari-

ations of concrete temperature and slab displacements corresponding to

those variations. This chapter focuses first on results of analysis of

temperature records obtained from the Test Road between 1983 and 1986.

This is followed by presentation of results from the study of slab dis-

placements conducted also on the Test Road during the period between

January and June of 1986.



4.2 Analysis of Temperature Data

Description of the Test Road and details of the thermocouple arrays

were presented in Chapter 3. Thermocouple arrays installed in slab 4









provided temperature measurements at five slab depths (1 in., 2.5 in.,

4.5 in., 6.5 in., and 8 in.). Included in the analysis, were tempera-

ture measurements recorded between January, 1983 and June, 1986. Infor-

mation derived from the temperature records included, 1) average pave-

ment temperatures, 2) variation of temperature with time at different

slab depths, 3) temperature differential across the slab thickness,

4) characterization of temperature gradients within the slab, and 5)

effects of sudden exposure to moisture, and shading on pavement tempera-

tures.

Average pavement temperature was the mean of temperatures recorded

at different slab depths. Variation of temperature with time was exam-

ined for each of the five slab depths. Temperature differentials were

computed by subtracting temperature readings at 8 inches below the slab

surface from those at 1 inch from the surface. A negative temperature

differential implied that surface temperature was lower than bottom tem-

perature, while a positive temperature differential was an indication of

warmer temperature at the surface. After thorough examination of hourly

temperatures at different slab depths, it was possible to identify cer-

tain trends in temperature distribution across slab thickness.

Two experiments were also performed to simulate the influence of

cloudy and rainy weather conditions on pavement temperatures. The first

experiment was performed to study the effect of shade on readings from

the thermocouple array at slab center with respect to the unshaded ther-

mocouple array near the edge. The second experiment modeled the effect

of sudden exposure to moisture on the temperature gradient throughout

the slab depth.









Sample data representing January, April, and June of 1986, and

July, October, and December of 1985, are used to illustrate variation of

temperatures and their characteristics at different seasons. Results of

the statistical analysis are also used to reflect general trends in tem-

perature data.

4.2.1 Relationship Between Air and Pavement Temperatures

It is a known fact that variation of pavement temperatures depends

mainly on changes of air temperature. Other climatic factors such as

solar radiation, wind, and moisture can also influence rate of heat flow

and temperature distribution within the concrete slab. The Test Road,

as mentioned earlier, was constructed in Gainesville, Florida. Figure

4.1 shows monthly air temperatures in Gainesville. Data shown in this

figure represent average high, low, and mean monthly temperatures re-

corded at Gainesville Airport between January of 1984 and October of

1986. The differences between average-high and average-low temperatures

ranged from 190F to 290F. The air temperatures were lowest during Janu-

ary, with a mean monthly temperature of approximately 50F, and were

highest during August, with mean monthly temperature of approximately

800F. Daily air temperature records during 1984 and 1986 indicate air

temperatures as low as 170F in January, and as high as 1000F in August.

The strong dependency of pavement temperature on air temperature is

clearly evident in Figures 4.2 to 4.6, which show typical daily varia-

tion of air and pavement temperatures in January, April, June, July, and

October, respectively. From these figures it can be observed that the

variation of pavement temperature follows a pattern that is similar to

that of air temperature. The rate of variation in pavement temperature

is higher during the day than during the night. During clear sunny






















---- LOW
-+- MEAN
---- HIGH


JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
MONTHS

Figure 4.1: Monthly Air Temperatures for Gainesville, Florida
(Data Recorded Between 1984 and 1986)


100


o 80

w
3 60-


I-
- 40-

l20-
-














55


50



0 45


0 40
401

E
* 35


+ Pavement
30 Air


25-



20 .. .
1200 1800 2400 0600 1200 1800 2400 0600 1200

Time (Miltaory)
Figure 4.2: Temperature Versus Time: January 26-28, 1986









90


85


80


75


70


65


60


55


50


45 --
1700


2300 500 1100 1700 2300 500 1100

Time (Military)
Figure 4.3: Temperature Versus Time: April 16-18, 1986


1700











110


105 r4 VaVuIItL +
0 Air.


100 -



L 95-











80







70 --r-,
2400 0600 1200 1800 2400 0600 1200 1800

Time (Mllltary)
Figure 4.4: Temperature Versus Time: June 7-8, 1986
I--















Figure 4.4: Temperature Versus Time: June 7-8, 1986











100

98
+ Pavement
96 0 Air

94

92

90

,_ g88
o
* 86

84
2 84-
82




76

74

72

70

68 ..
1045 1645 2245 445 1045 1645 2245 445 1045

Time (Millltary)
Figure 4.5: Temperature Versus Time: July 12-14, 1985











92-

90-

88

86

84

82

80
L
78 +

76 -
4e-
0
L 74 -
0 w
E 72 -
70-

68
8 + Pavement
66 I Air

64-

62-

60 -

58 -.
1400 2000 200 800 1400 2000 200 800 1400

Time (Military)
Figure 4.6: Temperature Versus Time: October 7-9, 1985









weather, pavement temperatures were found to be 150F to 250F higher than

air temperatures. Furthermore, the variation of air and pavement tem-

peratures can be approximated by a sine wave. However, the trend is

completely different during cloudy and rainy days. The differences be-

tween air and pavement temperatures drastically decrease, and the shape

of temperature variation does not seem to follow any distinguishable

pattern, as evident in Figure 4.7.

Temperature records obtained from the Test Road indicated that dif-

ferences in pavement temperature extremes between Winter and Summer sea-

sons ranged between 700F and 800F. However, seasonal variation occurred

gradually as illustrated in Figures 4.2 to 4.5. Pavement temperature

increased from 320F in January to 670F in April, then to 890F in June,

finally reaching as high as 1070F in July. Obviously, the increase in

pavement temperature was associated with seasonal changes of air temper-

ature.

The daily variation of temperature is important to the load re-

sponse of concrete pavements. Figures 4.2 to 4.6 show close relation-

ship between daily air and pavement temperatures. Minimum temperatures

occur early in the morning, and maximum temperatures occur during mid-

afternoons, regardless of the season. Minimum and maximum pavement

temperatures occur approximately one hour after air temperature has

reached its minimum and maximum. The range between daily maximum and

minimum temperature of the pavement, was between 100F to 200F.

Temperature records were statistically analyzed to identify times

of occurrence of maximum and minimum temperatures. A population of 230

sample days were randomly selected from data obtained between 1983 and











66 -

64 -

62 -
Clear Dry Rain Wet
60 -

58 -

56 -
6-'


L






46 + Pavement

44 O Air

42 -

40 -

38 -
3 6 I '

1818 0018 618 1218 1818 0018 618 1218

Time (Military)

Figure 4.7: Effect of Weather on Temperature Variation: December 27-29, 1985
Figure 4.7: Effect of Weather on Temperature Variation: December 27-29, 1985









1986. All months were represented by equal number of samples. Results

of frequency analysis of the temperature data are listed in Table 4.1.

The frequency of occurrences for minimum and maximum temperatures of air

and pavement are shown in Figures 4.9 to 4.11. Table 4.1 shows that

daily minimum air-temperature occurs most frequently between 5:00 a.m.

and 7:00 a.m. at 64 percent frequency, while the daily minimum pavement-

temperature occurs at a frequency of 81 percent between 6:00 a.m. and

8:00 a.m. The highest frequencies for maximum air and pavement tempera-

tures as listed in Table 4.1 indicate that maximum air temperature oc-

curs between 1 p.m. and 3:00 p.m. at 36 percent frequency, while the

maximum pavement temperature occurs between 2:00 p.m. and 4:00 p.m. at

68 percent frequency.

4.2.2 Temperature Distribution At Different Slab Depths

Figures 4.12 to 4.15 show typical variation of temperature at dif-

ferent slab depths for the months of January, April, June, and July.

These figures reflect the temperature variations during dry and sunny

days. It can be observed that rate of temperature change is highest at

slab surface and decreases with depth reaching a minimum at the slab

bottom. Slab temperatures during the night are coolest at the surface

and warmest at the bottom. After daybreak the trend is gradually re-

versed as temperature at slab surface starts to increase rapidly. Fol-

lowing a short transition period, slab temperatures become warmest at

the surface and coolest at the bottom.

Looking at wet-rainy conditions in Figure 4.16, an obvious differ-

ence can be observed in characteristics of slab temperatures. Tempera-

tures seem to remain almost uniform regardless of time of day. Further-

more, all slab temperatures seem to fall within a narrow band, and











Table 4.1: Most Frequent Times of Occurrence for
Minimum and Maximum Temperatures.


Description Minimum Maximum
Time Percent Time Percent
(Military) Frequency (Military) Frequency
Air Temperature 500 700 64 1300 1500 36

Average Pavement Temp. 600 800 81 1400 1600 68

Pavement Surface Temp. 600 800 72 1300 1500 71

Pavement Center Temp. 700 900 74 1500 1700 68

Pavement Bottom Temp. 800,- 1000 71 1700 1900 61

Negative Temp. Differential --- --- 500 700 54

Positive Temp. Differential --- 1200 1500 67


No. of Samples = 230


--- Not Applicable



































k--z---,.." 7"[. 'X'" .-., 0//. / 0.4

00 0300 0500 0700 0900 1100
TIME (MILITARY)
Figure 4.8: Frequency of Occurrence: Minimum Air Temperature


0400 0500 0600 0700 0800 0900 1000 1100
TIME (MILITARY)

Figure 4.9: Frequency of Occurrence: Minimum Average
Pavement Temperature


45

40j

351

i=30
(J 3



z 20
La
0 :


50-



40-


" i
z -
w
L.A
U 30
4
W J

U -







69



18.0
18-3 17.5 7 17.5
SF7-- // 716.7
16-





S0..o 1
CW 100


yw \ // > / / / / // 16.1




2 1.3 ^1.3
7 l~0.4

0900 1100 1300 1500 1700 1900
TIME (MILITARY)

Figure 4.10: Frequency of Occurrence: Maximum Air Temperature






40-n
\ 37.0
35-- '
30.9 .
30- F,,


-' **' / '1
25

204



10 9.1


5|/ 3.9, 3.9
0. 0/ '7/7'/7I // '*72
1000 1100 1200 1300 1400 1500 1600 1700 1800
TIME (MILITARY)
Figure 4.11: Frequency of Occurrence: Maximum Average
Pavement Temperature






































1200 1800 2400 0600 1200 1800 2400 0600 1200

Time (Military)
Figure 4.12: Temperature Variation at Different Slab Depths: January 26-28, 1986








100


95 -- --"
o 1.0
+- 2.5
S- 4.5
90 ^ 6.5
90 -V > s .O


L 85
0


2 80
-



E
0 75
I--


70


65


60
1700 2000 2300 200 500 800 1100 1400 1700

Time (Military)
Figure 4.13: Temperature Variation at Different Slab Depths: April 16-17, 1986










120


115- in.
+ 2.5
0 4.5
110 6.5
X 8

L" 105 -






* 95


90


85-


80
2400 0600 1200 1800 2400 0600 1?00 1800

Time (Military)
Figure 4.14: Temperature Variation at Different Slab Depths: June 7-8, 1986










108

106 -
Slab Depth
104 in.
01
102 + 2.5
0 4.5
100 A 6.5
X 8.o
98

96

94 -

a 92 -
E


88

86

84-



80
1045 1645 2245 445 1045 1645 2245 445 1045

Time (Military)
Figure 4.15: Temperature Variation at Different Slab Depths: July 12-14, 1986









70-

68 -

66-

64 Slab Depthi
in.
62 1 RAIN WET
+ 2.5
60 0 .4.5
o 8 6.5
58 X 8.0

- 56

S 54-

52

50

48

46

44

42 .. .
1818 0018 618 1218 1818 0018 618 1218

Time (Military)
Figure 4.16: Temperature Variation at Different Slab Depths: December 27-29, 1985









temperature magnitudes do not seem to follow distinctive patterns, un-

like those observed in the dry-sunny condition.

It can also be observed from Figures 4.12 to 4.15 that temperatures

at different slab depths reach minimum and maximum at variable times.

Obviously, temperature at slab surface reaches maximum or minimum first,

while temperature at the bottom reaches respective events last. Results

of frequency analysis of 230 sample days also illustrate this fact.

Figures 4.17, 4.18, and 4.19 show the frequencies of occurrence for

minimum temperatures at surface, center, and bottom of the slab, respec-

tively. The percent frequencies for maximum temperatures at surface,

center, and bottom of slab are shown in Figures 4.20, 4.21, and 4.22,

respectively. These figures and Table 4.1 indicate that surface temper-

ature reaches minimum and maximum one hour before the center tempera-

ture, and two hours before the bottom temperature. The minimum surface

temperature occurs most frequently between 6:00 a.m. and 8:00 a.m.,

while the maximum temperature occurs between 1:00 p.m. and 3:00 p.m. It

is interesting to note from Table 4.1 that minimum and maximum tempera-

tures at slab surface are concurrent with minimum and maximum average

pavement temperatures.

4.2.3 Temperature Differential

The temperature differential between surface and bottom of slab is

responsible for the magnitude and direction of slab curling. Figures

4.23 to 4.28 show typical variation of temperature differentials during

the months of January, April, June, July, October, and December. Except

in wet-rainy conditions (Figure 4.28), change of temperature differen-

tials approximates a sine wave. This pattern was also observed earlier

in variation of air and pavement temperatures.

























z20-
w
o
a 15-
-L


Figure 4.17:


0400 0500 0600 0700
TIME (MILITARY)

Frequency of Occurrence:
at Slab Surface


0800 0900 1000



Minimum Temperature


0.0 0.4


0400 0500
0400 0500


.,7 *./ /, / /// /A "0.4

0600 0700 0800 0900 1000 1100
TIME (MILITARY)


Figure 4.18:


Frequency of Occurrence:
at Slab Center


Minimum Temperature


50-1

45]

40-1

35
z i


25

20
u :



15



51

n-


0.4


0300












45

40

35

30

5" 25

z 20

S15

10

5


0500 0600 0700 0800 0900
TIME (MILITARY)


1000 1100 1200


Figure 4.19:


Frequency of Occurrence:
at Slab Bottom


Minimum Temperature


40.8




30.2
,/ /" / / / /1




I // //// '

/- // /


1400
TIME (MILITARY)


Figure 4.20:


Frequency of Occurrence:
at Slab Surface


Maximum Temperature


1100


1300


1500


1600


1700










45-
3 42.0
40o-

35-



25A 7
U/ //
20

15: 13.4

/ /// ,- / /
5.2 I
3.0
0 3
Z0.9 r / /z t o 0 r .=-._Z_^.OZ -y92 7 ;/'-- 9z 7 ;- -- : .
1100 1200 1300 1400 1500 1600 1700 1800 1900
TIME (MILITARY)
Figure 4.21: Frequency of Occurrence: Maximum Temperature
at Slab Center




40-
36.1







> 20- 18.3



10 8.3
Figure 4.22: Frequency of Occurrence: Maximum Temperature
-25- /

S2.20- 18.-/


/ '-"1,.
100 k / {74J'Y Z 8.3

"7 4.8 -'7'1


1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100
TIME (MILITARY)

Figure 4.22: Frequency of Occurrence: Maximum Temperature
at Slab Bottom










































1800 2400 0600 1200 1800 2400 0600


Figure 4.23:


Time(Military)
Temperature Differential Versus Time:
January 26-28, 1986


-8

-10

-12

-14


1200


1200















20



0

o 10







-10








-20
1700 2300 500 1100 1700 2300 500 1100 1700

Time (Mllltary)
Figure 4.24: Temperature Differential Versus Time:
April 16-18, 1986




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