• TABLE OF CONTENTS
HIDE
 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Review of the literature
 Airfield description and field...
 Laboratory testing and evaluation...
 Results and analyses of diametral...
 Analyses of field measured FWD...
 Stress analyses for pavement...
 Conclusions and recommendation...
 Appendices
 References
 Biographical sketch






Title: Evaluation and response of aged flexible airfield pavements at ambient temperatures using the falling weight deflectometer /
CITATION PDF VIEWER THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00097398/00001
 Material Information
Title: Evaluation and response of aged flexible airfield pavements at ambient temperatures using the falling weight deflectometer /
Physical Description: xvii, 315 leaves : ill. ; 28 cm.
Language: English
Creator: Manzione, Charles William, 1958-
Publication Date: 1988
Copyright Date: 1988
 Subjects
Subject: Runways (Aeronautics)   ( lcsh )
Pavements, Flexible -- Testing   ( lcsh )
Pavements, Asphalt concrete -- Testing   ( lcsh )
Asphalt concrete -- Effects of temperature on   ( lcsh )
Strains and stresses   ( lcsh )
Asphalt concrete -- Testing   ( lcsh )
Civil Engineering thesis Ph.D
Dissertations, Academic -- Civil Engineering -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Abstract: A research study was conducted to evaluate the response of aged flexible airfield pavements at varying ambient temperatures using the Falling Weight Deflectometer (FWD). Eight field tests were performed on three sites at Duke Field, Florida, at pavement surface temperatures ranging from 30 to 130.F. Monthly subgrade moisture readings were taken along with the measuring of pavement temperature profiles during each test. Laboratory tests were conducted on collected asphalt concrete and sand asphalt cores. Tests included low-temperature rheology tests, indirect resilient modulus, and indirect static creep tests (fracture energy). The analysis of the test data provided a reliable and effective method for predicting the asphalt modulus and fracture energy using asphalt viscosity and air void content. Back calculation of layer moduli using measured FWD data was performed by the layered elastic computer program BISDEF. The asphalt concrete modulus (E1)was computed using the developed asphalt modulus prediction equations which BISDEF iterated for the base and subgrade layer moduli. This technique greatly reduced the errors in determining E1 from the iteration process. Uncracked segments of pavement gave good results using the prediction equations for all asphalt layers. However, adjustments to E1 were necessary to accommodate the degradation of modulus due to pavement cracking.
Thesis: Thesis (Ph. D.)--University of Florida, 1988.
Bibliography: Includes bibliographical references.
Additional Physical Form: Also available on World Wide Web
General Note: Typescript.
General Note: Vita.
Statement of Responsibility: Charles William Manzione.
 Record Information
Bibliographic ID: UF00097398
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 - 001115078
oclc - 19879188
notis - AFL1793

Downloads

This item has the following downloads:

PDF ( 11 MBs ) ( PDF )


Table of Contents
    Title Page
        Page i
        Page i-a
    Dedication
        Page ii
    Acknowledgement
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
        Page viii
    List of Tables
        Page ix
        Page x
        Page xi
    List of Figures
        Page xii
        Page xiii
        Page xiv
        Page xv
    Abstract
        Page xvi
        Page xvii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Review of the literature
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
    Airfield description and field testing
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
    Laboratory testing and evaluation of pavement materials
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
    Results and analyses of diametral testing
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
    Analyses of field measured FWD data
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
        Page 148
        Page 149
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
        Page 155
        Page 156
        Page 157
        Page 158
        Page 159
        Page 160
        Page 161
        Page 162
        Page 163
        Page 164
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
        Page 170
        Page 171
    Stress analyses for pavement rehabilitation
        Page 172
        Page 173
        Page 174
        Page 175
        Page 176
        Page 177
        Page 178
        Page 179
        Page 180
        Page 181
        Page 182
        Page 183
        Page 184
        Page 185
        Page 186
        Page 187
        Page 188
        Page 189
        Page 190
        Page 191
        Page 192
        Page 193
        Page 194
        Page 195
        Page 196
    Conclusions and recommendations
        Page 197
        Page 198
        Page 199
        Page 200
        Page 201
        Page 202
        Page 203
    Appendices
        Page 204
        Page 205
        Page 206
        Page 207
        Page 208
        Page 209
        Page 210
        Page 211
        Page 212
        Page 213
        Page 214
        Page 215
        Page 216
        Page 217
        Page 218
        Page 219
        Page 220
        Page 221
        Page 222
        Page 223
        Page 224
        Page 225
        Page 226
        Page 227
        Page 228
        Page 229
        Page 230
        Page 231
        Page 232
        Page 233
        Page 234
        Page 235
        Page 236
        Page 237
        Page 238
        Page 239
        Page 240
        Page 241
        Page 242
        Page 243
        Page 244
        Page 245
        Page 246
        Page 247
        Page 248
        Page 249
        Page 250
        Page 251
        Page 252
        Page 253
        Page 254
        Page 255
        Page 256
        Page 257
        Page 258
        Page 259
        Page 260
        Page 261
        Page 262
        Page 263
        Page 264
        Page 265
        Page 266
        Page 267
        Page 268
        Page 269
        Page 270
        Page 271
        Page 272
        Page 273
        Page 274
        Page 275
        Page 276
        Page 277
        Page 278
        Page 279
        Page 280
        Page 281
        Page 282
        Page 283
        Page 284
        Page 285
        Page 286
        Page 287
        Page 288
        Page 289
        Page 290
        Page 291
        Page 292
        Page 293
        Page 294
        Page 295
        Page 296
        Page 297
        Page 298
        Page 299
        Page 300
        Page 301
        Page 302
        Page 303
    References
        Page 304
        Page 305
        Page 306
        Page 307
        Page 308
        Page 309
        Page 310
        Page 311
        Page 312
        Page 313
    Biographical sketch
        Page 314
        Page 315
        Page 316
        Page 317
        Page 318
Full Text







EVALUATION AND RESPONSE OF AGED FLEXIBLE AIRFIELD PAVEMENTS AT
AMBIENT TEMPERATURES USING THE FALLING WEIGHT DEFLECTOMETER





By

CHARLES WILLIAM MANZIONE


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


1988











DEDICATION


This dissertation is dedicated to my greatest blessings and joy,

Karen and Michael, in loving appreciation for their understanding,

comfort and endless love.












ACKNOWLEDGMENTS


There are many people the author would like to recognize and thank

for their part in making this research a success. Knowing that it is

impossible to cite all the individuals involved, the author wishes to

express his sincere appreciation to every person who has contributed

toward the completion of this study.

The author owes sincere gratitude to Captain (Dr.) Randall W. Brown

for his key role in getting this research started and for his sound

advice and friendship. The author also thanks the Air Force Engineering

and Services Center (AFESC) for their fiscal and logistical support.

The author is especially grateful to Mr. Albert J. Bush and

Mr. Dennis Mathews both from Waterways Experiment Station for providing

monthly logistical support and technical expertise. The assistance of

Mr. William D. Brunson, airfield manager at Duke Field, is also appre-

ciated.

The author owes sincere thanks to Dr. Byron E. Ruth for his inter-

est and guidance in the research as committee chairman and for the

giving of his time to educate the author. A very special thanks goes to

Dr. Michael C. McVay for serving as committee cochairman, offering words

of encouragement, and for sacrificing his time to help the author in

every way possible.

Gratitude is expressed to Dr. Mang Tia, Professor Walter H. Zimp-

fer, and Dr. Robert S. Mansell for their willingness to serve as commit-

tee members and for offering friendly advice. Special words of thanks






are extended to Drs. Frank C. Townsend, John L. Davidson, and David G.

Bloomquist for helping shape my formative years as a geotech and for

always being available for assistance.

The author wishes to acknowledge the invaluable contribution of the

Florida Department of Transportation, especially that of Mr. Ed Leitner,

Ms. Teresa Bailey, and other personnel of the Bituminous Materials

Research section.

Special recognition goes to Captain John J. Gill, the author's good

friend and study partner, for his quick wit and for helping to keep it

all in perspective.

The contributions of Messrs. Danny Richardson, Bill Studstill, Kirk

Waite, and Ed Dobson are also appreciated.

The author wishes to commend Ms. Candace Leggett for her profes-

sional skill and assistance in preparing this manuscript.












TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS................................ .... ................ iii

LIST OF TABLES...................................................... ix

LIST OF FIGURES.......................... ........................... xii

ABSTRACT.......................................................... xvi

CHAPTERS

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

1.1 Problem Statement................................... .. 1
1.2 Study Objectives...................................... 3
1.3 Scope of Work................................... ....... 4

2 REVIEW OF THE LITERATURE.................................... 5

2.1 Introduction........................................... 5
2.2 Design and Performance of Asphalt Concrete
Airfield Pavements.................................. .. 6
2.2.1 Background..................... ................. 6
2.2.2 Horizontal Strain Criteria in the
Asphalt Layer.................. .................. 7
2.2.3 Vertical Strain at the Top of the Subgrade....... 8
2.3 Nondestructive Testing (NDT) and Conventional
Analysis Procedures.................................... 10
2.3.1 Description of NDT Equipment..................... 10
2.3.2 Use of the Falling Weight Deflectometer (FWD)
and Conventional Analysis Procedures............. 12
2.3.3 Performance Predictions Using AIRPAVE............ 15
2.4 Causes and Effects for Failure in Flexible
Pavement Systems.................................... .. 16
2.4.1 General.......................................... 16
2.4.2 Cracking in Asphalt Concrete Pavement............ 18
2.4.3 Rutting in Asphalt Concrete Pavement............. 23
2.5 Rheological Properties of Asphalt Cement and Asphalt
Mixtures as Related to Pavement Performance............. 25
2.5.1 Asphalt Cement Properties........................ 26
2.5.2 Asphalt Mixture Properties....................... 27








3 AIRFIELD DESCRIPTION AND FIELD TESTING ...................... 32

3.1 Introduction............................. 32
3.2 Airfield Description................................... 33
3.2.1 Topography and Climatology ...................... 33
3.2.2 Test Locations and Layout........................ 35
3.2.3 Site Layer Profiles ............................ 42
3.2.4 Construction History............................. 46
3.2.5 Aircraft Traffic Data............................ 48
3.3 Field Testing and Environmental Monitoring.............. 50
3.3.1 Selection and Description of the Falling
Weight Deflectometer (FWD)....................... 50
3.3.2 FWD Field Testing Procedures..................... 58
3.3.3 Measurement of Subgrade Moisture................. 59
3.3.4 Measurement and Prediction of Pavement
Thermal Profiles ................................ 65

4 LABORATORY TESTING AND EVALUATION OF PAVEMENT MATERIALS...... 75

4.1 Introduction.......................................... 75
4.2 Classification of Subgrade Materials.................... 75
4.3 Determination of Air Void Content in Field
Extracted Bituminous Mixtures........................... 76
4.4 Determination of Maximum Density of Bituminous
Layers.................................................. 80
4.5 Determination of Asphalt Content and Gradation by
Quantitative Extraction................................ 81
4.6 Testing and Evaluation of Recovered Asphalts Using
Penetration and Viscosity Measurements.................. 87
4.7 Asphalt Viscosity Testing Using the Schweyer
Constant Stress Rheometer for the Determination
of Temperature and Shear Susceptibility................. 97
4.7.1 Background....................................... 97
4.7.2 Equipment and Test Procedures.................... 97
4.7.3 Data Acquisition and Analysis.................... 98
4.7.4 Relationship Between Viscosity and
Temperature................................. ... 102
4.8 Diametral Testing of Bituminous Field Samples.......... 105
4.8.1 General ........................................ 105
4.8.2 Laboratory Equipment............................ 106
4.8.2.1 Loading System ......................... 106
4.8.2.2 Electronic Control Console.............. 106
4.8.2.3 Recording System........................ 110
4.8.2.4 Temperature Control System.............. 110
4.8.3 Preparation of Test Specimens.................... 110
4.8.4 Preconditioning of Test Specimens................ 113
4.8.5 Dynamic Resilient Modulus Test................... 115
4.8.6 Indirect Tensile Test (Quick).................... 117
4.8.7 Static Creep Test (Fracture Energy).............. 118






5 RESULTS AND ANALYSES OF DIAMETRAL TESTING ................... 120

5.1 Introduction..... .................. ............. ....... 120
5.2 Dynamic Resilient Modulus .............................. 120
5.3 Tensile Strength...................................... 126
5.4 Indirect Static Creep .................................. 130
5.5 Summary .............................................. ..... 134

6 ANALYSES OF FIELD MEASURED FWD DATA ......................... 136

6.1 Introduction.. .......................................... 136
6.2 Computer Programs and Data Input........................ 137
6.3 Analysis of Site 3..................................... 138
6.4 Analysis of Site 2..................................... 150
6.5 Analysis of Site 1...................................... 164
6.6 Summary........................... ... .. ...... ........... 171

7 STRESS ANALYSES FOR PAVEMENT REHABILITATION ................. 172

7.1 Introduction..... ........... ........................... 172
7.2 Stress Analysis on the As-Constructed Pavements......... 173
7.2.1 Input Parameters................................ 173
7.2.2 Comparison of Pavement Response Using
As-Constructed and Improved Material
Design Methods................................... 175
7.3 Rehabilitation of Existing Pavements.................... 187
7.3.1 Rehabilitation of Site 3......................... 187
7.3.2 Rehabilitation of Site 2......................... 191
7.3.3 Rehabilitation of Site 1......................... 192
7.4 Summary ................................................ 194

8 CONCLUSIONS AND RECOMMENDATIONS............................ 197

8.1 Conclusions .......................................... 197
8.2 Recommendations........................................ 201


APPENDICES

A SUBGRADE MOISTURE PROFILES.................................. 205

B FIELD THERMAL PROFILES...................................... 207

C GRADATION TEST RESULTS...................................... 216

D PENETRATION-VISCOSITY CORRELATIONS .......................... 218

E SCHWEYER RHEOMETER TEST RESULTS ON RECOVERED FIELD CORES..... 223

F DIAMETRAL TEST RESULTS ON FIELD CORES ....................... 230

G FIELD FWD TEST RESULTS...................................... 256






REFERENCES......................................................... 304

BIOGRAPHICAL SKETCH................................................ 314


viii












LIST OF TABLES


Table Page

2.1 Typical Layered Elastic Methods of Matching Deflection
Basins .. .................................................... 14

2.2 Primary Types and Causes of Surface Distress in Asphalt
Concrete Pavements..................... ........... .......... 17

3.1 Site Layer Profiles In and Out of Wheel Path................. 45

3.2 Construction History......................................... 47

3.3 Annual Traffic Volume at Duke Field......................... 49

3.4 Aircraft Characteristics for C-130........................... 52

3.5 Typical Drop Sequence and Load............................... 58

3.6 Field Moisture Contents (w %) by Month....................... 63

3.7 Parametric Study of Mean Pavement Temperature (MPT).......... 74

4.1 Summary of Subgrade Classification.......................... 77

4.2 Maximum Density, Unit Weight, and Air Void Content for
Bituminous Layers In and Out of Wheel Path................... 79

4.3 Penetration, Absolute Viscosity, and Air Void Content for
Recovered Asphalts Inside the Wheel Path..................... 89

5.1 Results From Indirect Tensile Test With Viscosity and
Air Void Content at 25 C (77 F).............................. 127

7.1 Input Parameters and Results of Stress Analysis at 86 F
on Original Pavements. ..................................... 176

7.2 Input Parameters and Results of Stress Analysis at 23 F
on Original Pavements.................... .............. .. 177

7.3 Input Parameters and Results of Stress Analysis at 86 F
on Original Pavements Using the Texaco Air-Blown Asphalt..... 180

7.4 Input Parameters and Results of Stress Analysis at 23 F
on Original Pavements Using the Texaco Air-Blown Asphalt..... 181






7.5 Input Parameters and Results of Stress Analysis at 86 F
on Full-Depth Asphalt Concrete Pavements Using the Texaco
Air-Blown Asphalt......................................... 184

7.6 Input Parameters and Results of Stress Analysis at 23 F
on Full-Depth Asphalt Concrete Pavements Using the Texaco
Air-Blown Asphalt............................... .. .. ....... 185

7.7 Summary of Critical Response Parameters for the
As-Constructed Design Using Original and Texaco
Air-Blown Asphalts..................................... .. 186

7.8 Input Parameters and Results of Stress Analysis for
Overlay Rehabilitation at Site 3............................. 190

7.9 Input Parameters and Results of Stress Analysis for
Overlay Rehabilitation at Site 2............................ 193

7.10 Input Parameters and Results of Stress Analysis for
Recycling Rehabilitation at Site 1........................... 195

A.1 Results of Gravimetric and Volumetric Moisture Contents
Measured in the Field.................................... . 205

C.1 Gradation and Asphalt Content of Bituminous Layers........... 216

D.1 Correlation Between Penetration and Viscosity................ 218

E.1 Schweyer Rheometer Test Results on Asphalts Recovered
From Site 1.............................................. .. 223

E.2 Schweyer Rheometer Test Results on Asphalts Recovered
From Site 2............................................... 225

E.3 Schweyer Rheometer Test Results on Asphalts Recovered
From Site 3............................................... 227

F.1 Dynamic Resilient Modulus Test Results on 1AC-1.............. 230

F.2 Dynamic Resilient Modulus Test Results on 1AC-2.............. 231

F.3 Dynamic Resilient Modulus Test Results on ISA................ 234

F.4 Dynamic Resilient Modulus Test Results on 2AC-1.............. 237

F.5 Dynamic Resilient Modulus Test Results on 2AC-2.............. 239

F.6 Dynamic Resilient Modulus Test Results on 2AC-3.............. 240

F.7 Dynamic Resilient Modulus Test Results on 2SA................ 241

F.8 Dynamic Resilient Modulus Test Results on 3AC-1.............. 243

F.9 Dynamic Resilient Modulus Test Results on 3AC-2.............. 245






Dynamic Resilient Modulus Test Results on 3SA..............

Indirect Tensile Test Results...............................


F.12 Fracture Energy Parameters and Creep Test Data.............. 253


G.1 Results of FWD Tests on Site 1


G.2

G.3

G.4

G.5

G.6

G.7

G.8

G.9

G.10

G.11

G.12

G.13

G.14

G.15

G.16

G.17

G.18

G.19

G.20

G.21

G.22

G.23

G.24


Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results

Results


FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD

FWD


Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests

Tests


Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site

Site


(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test

(Test


1)....................

2).....................

3).....................

4).....................

5).....................

6).....................

7).....................

8).....................

1) .....................

2).....................

3).....................

4).....................

5).....................

6) .....................

7).....................

8).....................

1).....................

2) .....................

3) .....................

4).....................

5).....................

6).....................

7).....................

8).....................


F.10

F.11


247

252


256

258

260

262

264

266

268

270

272

274

276

278

280

282

284

286

288

290

292

294

296

298

300

302












LIST OF FIGURES


Figure Page

3.1 State Map of Florida Showing Location of Duke Field.......... 34

3.2 Plan View of Duke Field Showing Locations of the
Three Test Sites............................. ........ .... 36

3.3 Detail of Test Sites...................................... 37

3.4 Site 1: Severe Block Cracking With Spalling................. 39

3.5 Site 2: Longitudinal Crack at Edge of Wheel Path............ 40

3.6 Site 2: Rutting in Wheel Path............................... 41

3.7 Site 3: Longitudinal and Transverse Cracking................ 43

3.8 Site 3: Cracking Through Entire Pavement Thickness.......... 44

3.9 Wheel Gear Configuration for C-130 Aircraft .................. 51

3.10 C-130 Aircraft: Front and Rear View......................... 53

3.11 Main Landing Gear. a) Side View; b) Front View.............. 54

3.12 Falling Weight Deflectometer (FWD)........................... 56

3.13 Location of Loading Plate and Spacing of Geophones........... 57

3.14 Schematic of Installed Moisture Tube......................... 60

3.15 Nuclear Moisture Gage.. .................................... 61

3.16 Monthly Subgrade Moisture Contents: High, Low, and Average
Values. a) Center of Pavement; b) Edge of Pavement.......... 64

3.17 Schematic of Installed Temperature Profile Device (TPD)...... 68

3.18 Installing the Temperature Profile Device (TPD).............. 69

3.19 Temperature Measurement System.............................. 70

3.20 Nomograph for Determining Pavement Profile Temperatures....... 72

4.1 Grain Size Distribution for the Subgrade Soils............... 78






4.2 Gradation Range for Group A.................................. 83

4.3 Gradation Range for Group B.................................. 84

4.4 Gradation Range for Group C.................................. 85

4.5 Gradation Comparison of All Groups........................... 86

4.6 Relationship Between Penetration at 77 F and
Absolute Viscosity at 140 F.................................. 90

4.7 Relationship Between Penetration at 77 F and
Constant Power Viscosity at 77 F............................. 91

4.8 Relationship Between Penetration at 77 F and
Constant Power Viscosity at 59 F............................. 92

4.9 Range of Hardening for the Asphalt Cements................... 96

4.10 The Schweyer Rheometer Test System. a) Schweyer
Rheometer; b) IBM 9000 Computer ............................. 99

4.11 F-Tube (left) and G-Tube.................................... 100

4.12 Temperature Susceptibility Curves for the
Asphalt Cements. ......... ..... ................ ... .......... 104

4.13 Machine Test System (MTS)................................... 107

4.14 Loading System.. .... ... ............................. ....... 108

4.15 Electronic Control Console.................................. 109

4.16 Recording System............................................ 111

4.17 Temperature Control Chamber with Dummy Sample
and Thermal Probe....................................... ... 112

4.18 Strain Gaged Sample Ready for Indirect Tensile Testing....... 114

4.19 Typical Creep Response Curve for Asphalt Concrete............ 115

5.1 Dynamic Resilient Modulus Test Results....................... 122

5.2 Dynamic Resilient Modulus Test Results Using
Modified Equations................................ .. ......... 123

5.3 Modulus Ratios as a Function of Air Voids.................... 125

5.4 Tensile Strength Test Results ............................... 129

5.5 Results of Fracture Energy Tests............................. 131


xiii






5.6 Results of Fracture Energy Tests Using Modified Equation..... 133

5.7 Correlation Between Mix Viscosity, n and Constant
Power Viscosity, n .............. .0. .................... 135
100
6.1 Surface Deflection as a Function of Load at Site 3
(Most Linear Response)...................................... 140

6.2 Surface Deflection as a Function of Load at Site 3
(Least Linear Response)..................................... 141

6.3 Change in E and E With Temperature for Cracked
and Uncracked Pavement at Site 3............................. 143

6.4 E2 as a Function of Temperature at Site 3.................... 144

6.5 E. as a Function of n for Cracked and Uncracked
Pavements (All Sites)199 .................................... 145

6.6 E2 as a Function of n for Cracked and Uncracked
Pavements (All Sites) 0.1 .................. ..... .... ..... 147

6.7 Comparison of E4 Values as a Function of Temperature
at Site 3 ................................................... 148

6.8 Extreme Temperature Deflection Response at Site 3
(Normalized to 18-kip Load)................................... 149

6.9 Measured and Predicted Deflection Basins in Wheel Path
at Site 3 (Normalized to 18-kip Load)........................ 151

6.10 Measured and Predicted Deflection Basins Outside Wheel
Path at Site 3 (Normalized to 18-kip Load)................... 152

6.11 Surface Deflection as a Function of Load at Site 2
(Most Linear Response)...................................... 153

6.12 Surface Deflection as a Function of Load at Site 2
(Least Linear Response).................................. 154

6.13 E2 as a Function of Temperature at Site 2.................... 156

6.14 Comparison of E Values as a Function of Temperature
at Site 2.................................................. 157

6.15 Extreme Temperature Deflection Response at Site 2
(Normalized to 18-kip Load)................................. 158

6.16 Comparison of Low Temperature Deflection Response
Between Sites 2 and 3 (Normalized to 18-kip Load)............ 160

6.17 Comparison of High Temperature Deflection Response
Between Sites 2 and 3 (Normalized to 18-kip Load)............ 161






6.18 Measured and Predicted Deflection Basins in Wheel
Path at Site 2 (Normalized to 18-kip Load)................... 162

6.19 Measured and Predicted Deflection Basins Outside
Wheel Path at Site 2 (Normalized to 18-kip Load)............. 163

6.20 Surface Deflection as a Function of Load at Site 1
(Most Linear Response)...................................... 165

6.21 Surface Deflection as a Function of Load at Site 1
(Least Linear Response)......................... ............ 166

6.22 E1 as a Function of Temperature at Site 1.................... 167

6.23 Extreme Temperature Deflection Response at Site 1
(Normalized to 18-kip Load).................................. 168

6.24 Comparison of E Values as a Function of Temperature
at Site 1 ................................................... 170

7.1 Comparison of Modulus-Temperature Relationships Between
the Duke Field and Texaco Air-Blown Asphalts ................ 182

7.2 Radial Distances Used in Pavement Stress Analyses............ 189

B.1 Temperature Profile (Test 1)................................. 207

B.2 Temperature Profile (Test 2)................................. 208

B.3 Temperature Profile (Test 3)................................ 209

B.4 Temperature Profile (Test 4)................................. 210

B.5 Temperature Profile (Test 5)................................. 211

B.6 Temperature Profile (Test 6)................................. 212

B.7 Temperature Profile (Test 7)................................. 213

B.8 Temperature Profile (Test 8)................................. 214












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


EVALUATION AND RESPONSE OF AGED FLEXIBLE AIRFIELD PAVEMENTS
AT AMBIENT TEMPERATURES USING THE FALLING WEIGHT DEFLECTOMETER

By

Charles William Manzione


April 1983


Chairman: Byron E. Ruth
Cochairman: Michael C. McVay
Major Department: Civil Engineering


A research study was conducted to evaluate the response of aged

flexible airfield pavements at varying ambient temperatures using the

Falling Weight Deflectometer (FWD). Eight field tests were performed on

three sites at Duke Field, Florida, at pavement surface temperatures

ranging from 30 to 130 F. Monthly subgrade moisture readings were taken

along with the measuring of pavement temperature profiles during each

test. Laboratory tests were conducted on collected asphalt concrete and

sand asphalt cores. Tests included low-temperature rheology tests,

indirect resilient modulus and indirect static creep tests (fracture

energy). The analysis of the test data provided a reliable and effec-

tive method for predicting the asphalt modulus and fracture energy using

asphalt viscosity and air void content.

Backcalculation of layer moduli using measured FWD data was per-

formed by the layered elastic computer program BISDEF. The asphalt






concrete modulus (E ) was computed using the developed asphalt modulus

prediction equations, while BISDEF iterated for the base and subgrade

layer moduli. This technique greatly reduced the errors in determining

E from the iteration process. Uncracked segments of pavement gave good

results using the prediction equations for all asphalt layers. However,

adjustments to E1 were necessary to accommodate the degradation of

modulus due to pavement cracking. It was found that the reduction in E

values was largely dependent on the degree of cracking. In a severely

cracked test section, the modulus values for all layers remained almost

constant throughout the entire range of test temperatures. Modulus

values of the cracked sections could only be analyzed using FWD data

obtained over a large temperature range.

Stress analyses were performed using the elastic layer program,

BISAR. Results indicated that the tensile stresses in the sand asphalt

layer far exceeded maximum strengths. The original pavement was under-

designed and poorly maintained to meet current mission demands.

Specific scenarios were presented for the pavement rehabilitation.

Efforts were focused on the prevention of reflective cracking in the new

pavement layers while reducing stresses in the base and subgrade layers.


xvii












CHAPTER 1
INTRODUCTION


1.1 Problem Statement

The United States Air Force has approximately 4,000 miles of run-

ways throughout the world of which approximately 40 percent are flexi-

ble. Ninety percent of the airfield pavements are more than twenty

years old (design life) and 25 percent are significantly deteriorated

with anticipated replacement costs in the billions of dollars (1). Some

runways have been temporarily closed to air traffic prompting immediate

repair before being reopened. Other airfields have been neglected to

the point where serious distressed conditions threaten their closing

unless restorative action is taken. Many airfield pavements have stead-

ily deteriorated and soon could be rendered unsafe to accomplish Air

Force mission objectives.

Flexible pavement design has been relatively unaltered over the

past twenty years. Acceptable design is achieved when rutting (perma-

nent deformation), resilient (recoverable) deformation, and cracking in

the surface courses have been restricted to tolerable limits. The engi-

neer normally bases his analysis on one of the following: 1) layered

elastic theory, 2) transfer functions, 3) nondestructive insitu tests,

and 4) simple laboratory tests (2,3).

When evaluating flexible pavements, these methods do not account

for the changing theological properties of the asphalt binder caused by

age-hardening and seasonal temperature changes. Also, variations in








soil moisture, especially in silts and clays, can have dramatic effects

on subgrade and subbase properties. The theological properties of the

asphalt cement and existing soil conditions can substantially affect

both the short and long term performance of a flexible pavement.

The Air Force is concerned primarily with maintaining existing air-

field pavements since there is very little new construction being done.

Presently, rehabilitation of isolated problem areas and overlay work is

accomplished based on evaluations and recommendations by the Air Force

Engineering and Services Center (AFESC) and base engineers. Air Force

installations normally receive comprehensive pavement evaluations by

AFESC every five to seven years. Evaluations are either destructive

(e.g., conducting subgrade plate load tests) or nondestructive using the

Falling Weight Deflectometer (FWD). During an evaluation, there is

neither enough time or manpower to conduct both destructive and nonde-

structive tests (NDT). Cores recovered during NDT are used in obtaining

layer thicknesses for input into layered elastic computer programs.

Currently, no laboratory strength or modulus tests are conducted on the

asphalt concrete.

The AFESC acquired the FWD to speedily but accurately perform NDT

evaluations. Deflection basin data obtained by the FWD are used in an

iterative analysis to match the deflection basin and backcalculate layer

moduli. Layer moduli are then used in another program which uses

Miner's theory to compute life expectancy (passes to failure).

Problems arise using iterative approaches in that unique solutions

cannot be guaranteed and different sets of elastic moduli can produce

similar deflection basins. In 4-layer systems, for example, moduli

computed for the intermediate layers (base and subbase) are often times








reversed with the base yielding substantially lower values. In addi-

tion, iterative methods using FWD data have shown to be more reliable in

predicting the elastic modulus of the subgrade and least reliable in

predicting the modulus of the layers at the surface. Other concerns

come about when applying Miner's theory (cumulative damage or fatigue)

to predict the long term performance of flexible pavements. This is

especially true in aged airfield systems that already show the signs of

advanced distress (e.g., rut depths over one inch and/or severe block

cracking). Life expectancy can differ greatly depending on the time of

the year the evaluation is done. The fatigue approach has merit, but

other factors can also effect the long term performance of asphalt

concrete such as air void content and age-hardening of the binder.

A need, therefore, exists to understand what factors impact the

response and performance of flexible pavements and how to incorporate

them into a rational analysis. Only then can an accurate assessment of

flexible pavement response and performance be made.



1.2 Study Objectives

The primary objective of this research was to study the effects

that load and seasonal variations (temperature and moisture) have on the

response and performance of an aged asphalt concrete pavement using

field and laboratory measurements.

The secondary objective was to determine from laboratory tests

which factors and to what degree affect the resilient and creep

properties of bituminous mixtures and how to incorporate these factors

into the rational evaluation of flexible airfield pavements.







1.3 Scope of Work

Nondestructive field tests were conducted on an aged airfield pave-

ment, Duke Field, located in Crestview, Florida, using the FWD. Eight

tests were performed at three selected sites under extreme climatic

conditions during the 6-month testing phase. Subgrade moisture and

pavement temperature profiles were measured using semi-permanently

installed devices. Also, asphalt concrete and sand asphalt cores were

collected for a number of laboratory tests, including rheology and

indirect tensile tests. These were used to establish relationships

between viscosity and temperature and used to predict the moduli of the

bituminous mixtures. Other tests allowed the correlation between pene-

tration and viscosity that can be used in moduli prediction equations

when more exact methods are not performed.

The FWD data were analyzed to correctly assess the pavement layer

moduli for both cracked and uncracked sections. Analyses were then

performed to determine if the pavement stresses and strains produced by

past loading conditions were high enough to initiate the failure that

existed. Finally, scenarios for pavement rehabilitation were offered to

help minimize the potential for further degradation of the airfield.












CHAPTER 2
REVIEW OF THE LITERATURE


2.1 Introduction

The ability to structurally characterize pavement systems using

nondestructive testing (NDT) and predict their performance has intrigued

the pavement engineer for many years. Often, the engineer is left with

the task of selecting the correct pavement parameters such as modulus,

Poisson's ratio, and thickness for input into a mechanistic (analytical)

computer program, then go on to predict the expected life of the

pavement system. The approach is further complicated by the task of

defining failure, investigating the various modes and mechanisms for it,

and correlating it with assumedly correct NDT measurements. The air-

field offers even more elusive data for the engineer to obtain, espe-

cially traffic volume information accounting for aircraft wander, wheel

gear configuration, and taxiway usage. Considering this, the literature

review will help to serve two purposes,

1) to discuss current airfield design methodology along with the

uses of NDT and conventional analytical procedures as it

relates to the performance of asphalt concrete pavements, and

2) to define concepts, modes, and mechanisms for failure in

asphalt concrete pavements which are used to predict flexible

pavement response and performance.







2.2 Design and Performance of Asphalt Concrete
Airfield Pavements

2.2.1 Background

Design procedures for conventional flexible and rigid airfield

pavements, developed from data gathered over forty years of accelerated

traffic testing, have served the airfield requirements well in the past.

However, in the 1960s the engineering profession began to consider

design concepts that departed from conventional design approaches that

were widely used (4). As experience was gained with new approaches, the

potential for cost savings in the life-cycle design of pavements became

obvious, particularly in a predictive-type design system which con-

sidered new usages and maintenance strategies. What became apparent was

that empirical design methodology would not relate to stress analyses,

deflection analyses, or performance predictions.

Design procedures available today handle two modes of structural

deterioration either by limiting values of certain parameters or by

accounting for cumulative damage according to Miner's hypothesis. This

treatment implies the prediction of pavement performance on having a

value of "nonfailed" or "failed." In other words, failure occurs once a

limiting strain value is exceeded. For the design and evaluation of

pavement systems, these criteria are used extensively by pavement

engineers, including those in the USAF. Unfortunately, this methodology

does not realistically predict deterioration of pavements in the field.

For the design system, two types of strain are considered: 1) hor-

izontal tensile strain at the bottom of the asphalt layer and/or stabi-

lized layer and 2) vertical strain at the top of the subgrade. To fully

understand the design rational for asphalt pavement systems, one







must first look closely at the development of the strain criteria for

the asphalt and subgrade layers.

2.2.2 Horizontal Strain Criteria in the Asphalt Layer

Under traditional design approaches, failure in the asphalt layer

occurs when a specific number of load repetitions results in enough

cumulative strain (allowable strain) to equal the computed strain for

one load repetition. This allowable strain will vary depending on the

number of anticipated load repetitions and the elastic modulus of the

asphalt layer (5). According to Himeno et al. (6), this cumulative

damage (fatigue) is a function of the wheel load, vehicle speed, trans-

verse wheel position, and the temperature gradient in the asphalt

pavement layer.

The performance criteria for horizontal tensile strain are based on

the total number of strain repetitions which are determined from a

repetitive load, flexural beam test. The procedures for such tests are

described by Deacon and Monismith (7). These tests are conducted for

each temperature condition, therefore a value of limiting horizontal

tensile strain can be determined for the pavement design life. Barker

and Brabston (4) stated that researchers generally recognize that the

fatigue strength of bituminous materials is highly dependent not only on

the type of mix, but on temperature, stress history, and mode of

testing. A few researchers, including Ruth and Davis (8), contend that

increasing temperature is the greatest factor in relieving accumulated

stresses in the asphalt layer through increased flow. This flow can

partially or completely negate the cumulative fatigue damage.








2.2.3 Vertical Strain at the Top of the Subgrade

Gerritsen et al. (9) reported that most subgrade soils are not

linear elastic materials. They added, however, that their behavior can

reasonably be predicted by a linear elastic representation, provided the

elastic modulus is determined under conditions similar to those pre-

vailing in the pavement structure. Ruth (personal communication 1987)

thought that under dynamic loading conditions, a linear elastic assump-

tion for the subgrade is appropriate provided the pavement structure is

relatively stiff. However, since dynamic measurements of the subgrade

are not often available, the Shell Pavement Design Manual suggests the

use of the California Bearing Ratio (CBR). It cautions that deviations

using this method can be as high as a factor of two. However, since the

design and analysis of flexible pavements depend on properly predicting

strain at the subgrade surface, careful assessment of the subgrade

modulus must be made.

Environmental effects can play a significant role in altering

strain predictions in the subgrade. In asphalt concrete pavements,

where the bituminous layer is of moderate thickness, a temperature

change can alter the vertical stress transferred to the subgrade. Lambe

and Whitman (10) offered the opinion that the elastic modulus in soil is

stress dependent and decreases with increasing vertical stress. The

resilient modulus is also very sensitive to changes in moisture condi-

tions. Monismith and Finn (11) reported that the presence of water in

the pavement system is one of the most important environmental factors

to consider, because it affects the response of the pavement to load.

Hicks (12) showed that increased saturation lead to reduced resilient

moduli values for granular materials. This could result in higher







pavement deflections and associated distress. Darter et al. (13) listed

the more common types of distress from increased pavement deflections as

distortion, corrugation, rutting, depression, and potholes.

A suitable method for characterizing subgrade materials in the lab-

oratory, according to Seed and Fead (14), is the resilient modulus test

using the standard triaxial device. Recently, however, McVay and

Taesiri (15) reported that conventional triaxial testing was incapable

of reproducing the moving wheel stress path demonstrated in the lab-

oratory by Ishihara (16) using a hollow cylinder. Unlike the standard

triaxial device, the hollow cylinder is able to continuously rotate the

principal stress planes, and in effect, simulate the stress path pro-

duced by the moving wheel in the field. Ishihara showed that under

drained conditions (typical for low-volume airfield pavements), axial

strains produced in the hollow cylinder were 25 percent greater than

measured in the standard triaxial device after only three cycles under

similar stresses. Although both studies suggested further investigation

into this phenomenon, its relative importance in pavement design today

is still undecided.

The subgrade strain criteria were developed based on data from

conventionally designed pavement sections for which a performance life

could be assumed. Peattie (17) presented strain criteria based on

stress. His criteria are for 1,000,000 strain repetitions and are a

function of CBR. Edwards and Valkering (18) using the Shell CBR design

curves for 1,000,000 strain repetitions, arrived at a subgrade strain

criteria between 0.8xE-03 and 0.9xE-03 in./in. but gave no reason for

this. Witczak (19) developed subgrade strain criteria based on assumed

values of asphalt concrete moduli. All the comparisons made by Barker








and Brabston (4) indicated that for a given resilient strain, the speci-

mens of a weaker soil exhibited larger permanent strain than those of a

stronger soil. They concluded that the allowable resilient strain for a

weaker soil would have to be less than that for a stronger soil if the

amount of permanent strain is to be equal.



2.3 Nondestructive Testing (NDT) and Conventional
Analysis Procedures

2.3.1 Description of NDT Equipment

Smith and Lytton (20) gave four general classes of NDT equipment

that are routinely used to collect deflection data: static deflection

equipment, automated beam equipment, steady-state dynamic deflection

equipment, and impulse deflection equipment.

Static load devices measure the response of a pavement to slowly

applied loads. The most routinely used of this type of device is the

Benkelman beam. This device requires a loaded truck to create the

deflection basin to be measured. Normally, only the maximum deflection

is measured with beams. Technical difficulties in using this device

include 1) ensuring the front supports are kept out of the deflection

basin and 2) the inability to accurately define the basin itself.

The automated beam deflection equipment simply automates the

Benkelman beam. This device called the La Croix Deflectograph has been

widely used in Europe and other parts of the world but has not been used

much in the U.S. Although it allows for continuous recordings of data,

it still has the same inherent limitations of the Benkelman beam.

Devices that produce a sinusoidal vibration are classified as

steady-state dynamic deflection equipment. These devices, including the

Dynaflect and the Road Rater, place a static load on the pavement along








with a sinusoidal vibratory force produced by a dynamic force gener-

ator. Velocity transducers are positioned on the pavement surface and

measure the deflections. A static preload is applied to prevent

bouncing on the pavement. However, this preload must increase as the

dynamic force increases. Some researchers feel that this preload

changes the existing stress state in the pavement and may cause altered

response to the load (21). Given this, an inertial reference is used to

compare the deflection change with the change in the magnitude of the

dynamic force.

The last category of NOT equipment are the impulse deflection

devices. These devices deliver a transient force impulse to the pave-

ment surface which produces a dynamic deflection basin. The equipment

uses a weight that is raised and dropped from a predetermined height,

striking the impact plate which transmits the force directly to the

pavement surface. The advantage of using this type of NOT device is

that the drop height and weight can be easily changed to vary the

generated force impulse. In this way, loadings can be obtained for a

wide range of actual field loading conditions. Also, the static preload

is relatively small, so the deflection basin produced most closely

approximates the deflections produced by a moving wheel. The most

widely used impulse device is the Falling Weight Deflectometer (FWD).

The Air Force has adopted the FWD as its primary source for nondestruc-

tive testing.

Nazarian and Stokoe (22) cited the fundamental advantage of steady-

state devices over impulse devices is the ability of the former to vary

the loading frequency to minimize the effect of rebounding shock waves

caused by a rigid layer at shallow depth below the subgrade. This








critical depth is a function of the natural frequency of the pavement

layers, especially that of the subgrade. Although Nazarian confessed

that encountering such conditions in practice is rare, he admitted that

users of steady-state equipment do not adjust the frequency to account

for this phenomenon. Furthermore, impulse devices can not be adjusted

for the effects of reflecting waves, and if not considered in the final

analysis, large errors in deflection measurements may result.

2.3.2 Use of the Falling Weight Deflectometer (FWD)
and Conventional Analysis Procedures

The FWD was developed and employed based on early work conducted in

the 1960's by the Technical University of Denmark and the National

Danish Road Laboratory (23). The FWD was designed to simulate a heavy

moving wheel load at normal traffic speed while obtaining very accurate

deflection measurements at large distances from the load. According to

Sorensen and Hayven (24), proper assessment of the subgrade modulus is

vital since it contributes some 60 to 80 percent of the center deflec-

tion. A study by Uddin et al. (25) determined that the theoretical

deflection basin was most influenced by even a small change in subgrade

modulus and changes in the surface asphalt layer thickness. Moreover,

deflection basins were less influenced by changes in assumed moduli of

thin asphalt layers and changes in thickness of the intermediate layers.

Marchionna et al. (26) stated that the FWD can be used to estimate

bearing capacity of pavement systems and evaluate remaining pavement

life in terms of fatigue distress using computed moduli. In a study to

determine the structural properties of flexible pavements through the

use of NDT, Lytton et al. (27) ranked the FWD above other NDT devices

when comparing such factors as reliability, accuracy, and accessibility

to test sites, speed of operation, and cost.







The quick, accurate calculation of the insitu moduli is the goal of

the FWD and accompanying layered elastic programs. Uddin et al. (28)

reported that the inverse application of layered theory by fitting a

measured deflection basin using a iterative procedure is the most pro-

mising for predicting insitu moduli. During the past few years a number

of self-iterative approaches have been made available to handle flexible

pavement systems. Typical layered elastic programs are shown in Table

2.1.

The two self-iterative programs used primarily by the U.S. Air

Force for flexible pavements are BISDEF (also for rigid) and FPEDD1.

BISDEF is a layered linear elastic program developed by the COE. The

subroutine BISAR (Bitumen Structures Analysis in Roads) was developed by

Shell in 1972. FPEDD1 (Flexible Pavement Evaluation from Dynamic

Deflections) was developed by layered program ELSYM5. BISDEF was

developed for use on a microcomputer for quick calculations in the

field. FPEDD1 requires a main frame computer for down loading to a

personal computer.

The use of elastic layer analysis for the prediction of stresses,

strains, and deformations in the asphalt concrete layer is generally

accepted. However, there is concern about how well it predicts response

in unbound layers, although its suitability for bound layers is well

documented. Ros et al. (29) measured insitu the stresses and strains at

various locations in trial sections using standard wheel loads at dif-

ferent speeds and temperatures. They found good correlation between the

values measured in the field and those calculated using BISAR. Correla-

tion was especially good at high asphalt stiffness. Halim et al. (30)

and Waterhouse (31) also achieved good agreement using elastic layer
















L
a
4- a
E

E L
O L c

O










*r-M




















r-
4- l-


















t O 1
L
a)


JLL


00
























L 0
-4--)



1


n3
cE





'4-




Ero









0 "
Q-r


14









C CC





*(J *-- I
.4--
U 0











o o O O O O O




















>-a->
0 L L L .


M :U:- u LU
C LU n L cm CZ) Li CD L )
O _> 0 0













0

0 L- L- 0 L- C- L-
. a) a) 4-) a) a) a) a)






























- 0 + O a)
SQ o o u


LU () S U O LL-







theory. However, Brown and Pappin (32) questioned the ability of elas-

tic layer theory to predict response in the soil layers, although they

found it appropriate for the asphalt layer.

There are other methods for determining insitu moduli from NDT

data. Lytton et al. (27) listed them categorically as 1) equivalent

thickness methods, 2) finite element methods, 3) dynamic analysis

methods, and 4) wave propagation methods. Ruth et al. (33) developed a

series of algorithms using measured FWD deflections to determine the

insitu moduli in the pavement system. Their study revealed that for

narrow ranges of asphalt thickness, good prediction of the asphalt

concrete modulus was achieved. Moduli predictions for the base and

subbase were slightly better with the greatest consistency coming from

predicting the subgrade modulus. They recommended verifying these

moduli predictions with an other form of analysis, or through laboratory

resilient modulus testing, or the use of asphalt viscosity-modulus

relationships.

2.3.3 Performance Predictions Using AIRPAVE

The AIRPAVE program was developed by the Army Corps of Engineers

(COE) for evaluating military airfield pavements. The program uses the

resilient moduli, layer thicknesses, and Poisson's ratios to calculate

the stresses and strains produced in the pavement system due to a

selected aircraft wheel load (5). AIRPAVE makes use of the linear,

elastic layer program BISAR to calculate stresses and strains at criti-

cal locations in the pavement structure (34). Calculated stresses and

strains are compared with fatigue algorithms developed from laboratory

and field test data and empirically correlated to predict the number of







cycles to failure. Information on aircraft load, wheel gear configura-

tion, and passes-to-coverage ratios for seventeen aircraft types are

stored in an AIRPAVE data file called ACDATA.

The program calculates the horizontal tensile strain at the bottom

of the first layer. Therefore, multiple asphalt concrete layers must be

combined into a single thickness. Vertical stresses and strains are

normally calculated at the top of the subgrade, although AIRPAVE does

give some flexibility in computing the vertical stresses and strains at

other locations.



2.4 Causes and Effects for Failure in
Flexible Pavement Systems

2.4.1 General

The types of distress seen in asphalt pavement is highly recognized

and the causes behind them are at least generally understood. Table 2.2

lists the types and causes of distress common to bituminous pavements.

Failure in these systems can be primarily attributed to either cracking,

excessive rutting, or a combination of both.

Through the use of numerous pavement surveys taken in this country

and around the world, Finn (35) stated that load related cracking is the

number one priority item for improving and extending the performance of

asphalt pavement systems. Furthermore, he reported that load-induced

cracking is one of the first observable signs of distress and that ex-

cessive cracking could occur with little or no distortion. When

reviewing the results of the AASHTO Road Test, he found cracking often

led to other forms of distress such as rutting, and that it appeared to

be more pronounced during cold weather than warm. Information as to

when and where these cracks developed was lacking and only recently have












Table 2.2 Primary Types and Causes of Surface Distress in
Asphalt Concrete Pavements


Causes or Factors


1. Rutting


Consolidation
Lateral movement (shear)
Traffic
High temperatures
Low viscosity
Low stability
Poor compaction
Foundation quality
Drainage


2. Fatigue Cracking
(Load-Induced)





3. Thermal Cracking





4. Combined Load and Thermal
Cracking

5. Raveling and Weathering



6. Disintergration


Traffic--volume and
Asphalt viscosity
Layer moduli
Layer thickness
Drainage
Material quality


loads


Binder shrinkage
Thermal contraction
Low temperatures
Asphalt hardening
Fast cooling rates

Combination of factors
named in 2 and 3 above

Deterioration
Asphalt hardening
Time

Stripping--loss of bond
Chemical reactivity
Traffic abrasion


Source: Ruth et al. (36)


Type of Distress








full scale modeling been done to better understand the response of

asphalt pavement at low temperature and its relationship with cracking

(36).

2.4.2 Cracking in Asphalt Concrete Pavement

Traditionally, cracking in flexible pavements is thought to stem

from load or thermal effects with little regard for the combined effects

of the two. Anderson et al. (37) reported that low-temperature trans-

verse cracking has been recognized as the most common nontraffic asso-

ciated failure mode and is a serious problem in Canada and parts of the

United States. Hugo and Kennedy (38) emphasized that the design of

asphalt pavements must consider the distress due to cracking from both

load and nonload associated factors or a combination of the two.

The most recognized concept for use in the evaluation of load-

induced failure, is cracking in asphalt concrete due to fatigue distress

(39,40). Fatigue failure in asphalt pavements is the result of repeated

stresses below the tensile strength of the material. There are many

references, such as Witczak (41) and Barksdale (42), on the subject of

fatigue in asphalt concrete. The Air Force criterion for cracking is

based on limiting stress/strain conditions that are calculated by

AIRPAVE. The allowable tensile strain at the bottom of the asphalt

concrete layer is given by equation 2.1 and is dependent upon the

asphalt modulus and the number of aircraft coverages (5).

Allowable StrainAC = 10-A (2.1)

where EAC
N + 2.665 log (-422) + 0.392

5
N = log (aircraft coverages)

EAC = asphalt modulus







Since the fatigue life of asphalt concrete has been shown experi-

mentally to be dependent on temperature, researchers have proposed

modifications to fatigue life predictions taking into account seasonal

temperature variations. Rauhut and Kennedy (43) proposed such adjust-

ments and offered those given by others. They did, however, recognize

the difficulty in evaluating fatigue life of actual pavements in the

field, since reliable test data existed for only a limited number of

asphalt concrete mixtures. Furthermore, they pointed out that no

fatigue test can accurately simulate the complex mechanisms at work in

the field. Recently, Himeno et al. (6) offered a new fatigue failure

criteria based on energy dissipation. They found that bending fatigue

damage at the bottom of the mix slab is greatest in the spring and can

be ignored in the summer and winter.

Ruth and Maxfield (44) found the fatigue concept did not apply to

specimens from test roads in Florida. Their conclusion was that the

fracture of asphalt concrete was related to the accumulation of creep

strain and that fracture strain is dependent on asphalt viscosity and

loading conditions. Ruth et al. (45) emphasized that during warm

weather, temperatures are high enough to relieve stresses and strains,

and thus offset the cumulative damage of fatigue. Nevertheless, they

did not discount the concept of fatigue when asphalt pavements are

subjected to repetitive short-term loads where their theological pro-

perties remain fairly consistent. Asphalt binder viscosity and shrink-

age were clearly demonstrated as major factors leading to cracking.

Ruth et al. (46) reported that cracking will occur when a critical

condition is imposed on the asphalt pavement. They described a critical

condition as "any combination of materials, environmental, and loading







characteristics which produce stresses or strains equivalent to those

required for fracture" (46:53). Specific factors responsible for frac-

ture include excessive binder hardening and rapid cooling to suffi-

ciently low temperatures relative to the asphalt viscosity.

Resistance to thermal contraction during rapid cooling is the

mechanism causing high tensile stresses to develop in the asphalt

layer. Simply, as the temperature decreases, the asphalt wants to

contract but is resisted by the friction developed between the asphalt

layer and the base, and by the length of the pavement in the longitu-

dinal direction. This results in tensile stresses which are greater in

the longitudinal direction. During rapid cooling, these stresses build

rapidly with little chance for thermal creep to relieve them. Several

researchers (47,48,49) have postulated that cracking occurs when the

thermally induced tensile stresses exceed the tensile strength of the

asphalt concrete. This mechanism was confirmed by laboratory and field

investigations by the above researchers.

Ruth (50) concluded that cracking could be reduced by using asphalt

binders of lower viscosity and improved theological behavior at low

temperatures. Fabb (51) remarked that low viscosity and low temperature

susceptibility are vital to reducing the temperature required for frac-

ture. Ruth et al. (46) stated that temperature susceptibility per se is

not a critical factor since apparent viscosities will change according

to the creep strain rate that is induced by cooling the pavement at

different rates. They added that low-temperature viscosity is critical

since viscosity controls the creep rate and fracture characteristics of

asphalt concrete. Schmidt (52) reported that the glass transition

temperature of the asphalt is a more definitive measure of nonload








associated cracking behavior than measured viscosities since at that

temperature the asphalt behaves elastically while higher temperatures

result in viscoelastic response. Therefore, almost no potential for

stress relaxation exits below the glass transition temperature.

To deal with the effects of thermally induced stresses and strains

in the asphalt concrete, a computer program CRACK was developed by Ruth

et al. (46). This program computes the thermal stress, incremental

creep strains, and stress-strain energy developed at each time-

temperature increment during cooling of the pavement. The thermal

analysis was combined with the ELSYM5 stress analysis program to combine

the effects of load and nonload induced stresses. A second program

CRACK-2, developed by Hugo (53), permits the subdivision of the asphalt

surface into two layers, each with their own low-temperature thermal

characteristics.

Reflection cracking is another form of cracking that severely

effects much of North America and is considered the number one pavement

performance problem (54). Ponniah et al. (55) reported in a recent

paper that reflection cracking is caused by thermal cycles and/or load

induced stresses. Ignored, it can markedly decrease the structural

performance of the pavement through deterioration caused by the ingress

of water. They further added the importance of fracture mechanics in

determining the design method which offers the best alternative for

reducing stress concentrations around the crack front. Analyses can be

used to evaluate the relative effectiveness of such treatments as

geogrid reinforcement, stress absorbing membrane interlayers (SAMI), and

composite interlayers.








Aside from the conventional forms of thermally induced cracking,

lies the potential for thermal rippling or curling. In a recent study

by Ruth et al. (36) on low-temperature pavement response using a test-

pit facility, load-deflection data clearly indicated that the asphalt

pavement layer was uplifted from the base during cooling cycles then

settled as the temperature increased. They stated

it seems clear from these observations that the
unusual response observed was caused by the con-
traction and bending characteristics of the
asphalt concrete layer under a thermal gradient
and continued cooling .. however, the actual
mechanism that led to this behavior was unclear.

(36:328)

Curling is a phenomenon normally associated with portland cement

concrete slabs and not asphalt concrete pavements. However, at low

temperatures, the stiffness of asphalt concrete is high enough that its

behavior can approach that of concrete. The mechanism of curling in

asphalt concrete may be different then that for portland cement concrete

in that the former exhibits viscoelastic response (creep). This creep

could develop from the stresses induced by the uplifted slab causing it

to settle.

Ruth et al. (36) concluded that if this curling effect demonstrated

in the test pit occurs in actual pavements, it could explain some fail-

ures and causes of longitudnal.wheel path cracking. They emphasized the

importance of combining the properties of the asphalt with the combined

effects of thermal and load in the failure analysis of asphalt concrete

pavements.








2.4.3 Rutting in Asphalt Concrete Pavement

Gerlack et al. (56) described rut formation as a result of perma-

nent deformations of the individual pavement layers caused by progres-

sive stiffening of the pavement elements due to traffic loading. Ruth

(personal communication 1987) stated, however, that as the pavement

stiffens through consolidation and age-hardening, the potential for

further rutting is reduced. Furthermore, he cautioned that one must

distinguish rutting caused by consolidation from that caused by plastic

flow (low stability).

Work conducted by Freeme et al. (57) showed that permanent defor-

mation tends to occur within the asphalt layer under traffic loads at a

rate which depends predominately on the grading and properties of the

binder. They added that high stability asphalt mixes will deform less

than those with a low stability under the same loading and temperature

conditions. Barker and Brabston (4) reported that rutting can also

occur in the subgrade whereby little or none is assumed to occur in the

asphalt layers. Monismith et al. (58) stated the propensity for rutting

in thick pavement sections is dependent upon the stiffness and thickness

of the asphalt concrete and the stiffness of the subgrade. Given two

pavement systems with identical layer moduli and loading conditions,

more rutting can be expected in a system with a thinner bituminous

layer. This is due to the higher compressive stresses transferred into

the foundation layers resulting in greater deformations.

The intricacies of rut prediction is complex; however, models do

exist. Monismith et al. (58) offered a rut depth prediction model using

creep moduli for each sublayer in the pavement system. With computed







vertical normal stresses and corresponding creep moduli, rut depths can

be estimated using the following relationship:


n
rut depth = hi (2.2)
i=l


where

hi = thickness of sublayer

ai = average vertical stress in layer

Eci = creep modulus for average temperature in sublayer

Barber (59) gave the following expression for a two layer flexible

pavement system with an asphalt wearing course over a granular base:


rut depth = 1.94311 Pk'.3127 x tpo.0499 x RO.3249
rut depth = 1.9431{ ---- --J-- x^------
[log (1.25 Tac + Tbase)]3.4202 x C11.6877 x C20.1156

(2.3)

std error = 0.411

r = 0.8779

where

Pk = equivalent single wheel load (ESWL), kips

tp = tire pressure, psi

Tac = thickness of ac, in.

Tbase = thickness of base, in.

C1 = CBR on top of base

C2 = CBR on top of subgrade

R = repetition of load or passes

Barker (60) presented the following prediction based on the ratio

of permanent strain to resilient strain in the subgrade:










sp/er = 0.14 x 70800 (2.4)
Mr


where

R = 0.4 (stress repetitions) 0.12

ad
Mr = -, ksi
er'

ad = repeated deviator stress in laboratory triaxial test, ksi

er = measured resilient strain in laboratory triaxial test,

in./in.

sp = measured permanent strain in laboratory trixial device,

in./in.

This model assumes all rutting occurs in the subgrade.

Monismith et al. (58) stated that to estimate rutting in taxiway

sections on airfields, aircraft wander (passes-per-coverage) must be

considered. Accordingly, these procedures were developed by the COE.



2.5 Rheological Properties of Asphalt Cement and Asphalt
Mixtures as Related to Pavement Performance

Rheology involves the study and evaluation of the time-temperature

dependent response (flow) of materials which are subjected to an applied

force. The theological properties of bituminous mixtures can be altered

by either time, applied stress, or temperature. Moreover, this altera-

tion can be quite complex and even today is not fully understood. The

performance of asphalt concrete is greatly dependent on the properties

of asphalt binder itself. Unfortunately, conventional asphalt mix

design is based on empirical approaches as the Marshall and Hveem mix

design methods (39). Such methods do not account for asphalt properties







as failure stress, failure strain, temperature and shear susceptibility,

and stiffness. Conventional asphalt viscosity tests (e.g., absolute and

kinematic) are run at high temperatures and are not able to predict the

low-temperature behavior of asphalt cements.

2.5.1 Asphalt Cement Properties

Schweyer (61) stated that in general as the temperature is de-

creased, asphalt becomes more viscous and will eventually exhibited

glassiness where elastoviscous behavior is seen. Brittle fracture may

result from its inability to flow and relieve built-up stresses.

Jongepier and Kuilman (62) characterized asphalt as a viscoelastic

liquid. At low temperatures elastic behavior is observed, while at high

temperatures it flows like a viscous fluid. In the intermediate temper-

ature ranges, asphalt exhibits both elastic and viscous properties. By

using combinations of Hookean springs (elastic component) and Newtonian

dashpots (viscous component) it is possible to mathematically represent

the behavior of asphalt. The models, Maxwell, Kelvin, Van der Poel,

Burgers, and Kuhn and Rigden are among those kinds used to represent the

stress-strain-time relationship of asphalt. Burns and Schweyer take the

Kuhn and Rigden model one step further by accounting for the shear sus-

ceptibilty of the material. Full description and capabilities of each

model, along with their inherent limitations, are given by Teng (63).

Duthie (64) described the theological parameters of asphalt as its

viscosity, temperature susceptibility, and shear susceptibility. Vis-

cosity or consistency is simply defined as the applied shear stress over

the shear rate. Temperature susceptibility is the degree of the change

in viscosity with change in temperature. At low temperatures, asphalts

may become more shear susceptible, i.e., the change in creep strain is







not proportional to the change in applied stress. This inability to

creep can result in the accumulation of stresses which can ultimately

lead to failure through cracking.

Measurement of the above mentioned parameters at low temperature

can be difficult since asphalt behaves elastically with relatively low

creep rates. Therefore standard creep or viscosity tests would take an

extremely long time to obtain appreciable deformation at low stress

levels. High stress levels are required to achieve the desired defor-

mation, but shear susceptible asphalts may give results outside the

range of interest.

Schweyer et al. (65) reported that different asphalts having nearly

the same high temperature properties behaved quite differently at low

temperatures. They emphasized that absolute viscosity tests rather than

empirical tests should be used near the glass transition zone. This

understanding among researchers led to the development of the Schweyer

Constant Stress Rheometer (66). Keyser and Ruth (67) concluded that the

Schweyer rheometer is an excellent device for the low-temperature (e.g.,

-10 C (14 F) and lower) measurement of asphalt properties, especially

those that are highly shear susceptible. Furthermore, they added that

the concepts developed by Schweyer provided values of shear and strain

rates encountered in the laboratory, applicable to those measured in the

field.

2.5.2 Asphalt Mixture Properties

A number of laboratory tests exist to characterize asphalt mixtures

including compression, bending (flexure), tensile, and shear. Tests are

normally conducted to obtain the failure characteristics. However, the

increasing trend toward mechanistic approaches and the use of elastic







theory, has led researchers to define the stress-strain behavior of

bituminous mixtures (68). A study by the Highway Research Board (69)

showed that it is very difficult to uniquely characterize the stress-

strain properties of asphalt mixtures. This is due to the variability

of materials and the nature of pavement structures. A distinct disad-

vantage in conducting the aforementioned tests is the effect of time or

rate of loading which are disregarded by elastic equations used in

analyzing the data. Creep effects are normally ignored due to the

complexities involved by introducing them into the analysis. Many

researchers including Gonzalez et al. (70), Kennedy (71), and Puyana

(72) have recommended the indirect tensile test as the most suitable for

routine pavement characteristics in terms of practicality, simulation of

actual loading conditions, economy, and ease of testing. Mamlouk (73)

emphasized the importance of dynamic testing to most realistically

simulate the actual stress conditions of pavements. He cited that the

magnitude, shape, and duration of moving wheel stress pulses can only be

accounted for in dynamic testing.

Deacon (74) stated that four variables have a considerable effect

on the stiffness of asphalt paving mixtures: air void content, asphalt

content, viscosity, and filler content. Temperature, and its effect on

asphalt viscosity, was considered the major external factor on stiffness

and mixture behavior. Deacon also reported that linear response in-

creased with increasing load frequency, decreasing temperature and air

void content, and increasing asphalt content, asphalt viscosity, or

filler content.

Bazin and Saunier (75) studied the variation in modulus for differ-

ent asphalt mixtures. They reported that for correct binder amounts and







normal air void contents, (e.g., 4 to 8 percent), the other parameters

had little effect on stiffness when compared to the effects of variation

in binder type, temperature, and time of loading. They suggested a

linear relationship between the log of modulus and air void content.

Ruth et al. (76) gave a modulus ratio for air void contents to 9 per-

cent. They suggested a 11.5 percent decrease in dynamic modulus for

every 1 percent increase in air void content up to 9 percent.

Ruth et al. (46) were the first to present modulus relationships

based on direct evaluation of measured asphalt viscosity at different

temperatures. The dynamic modulus equations were developed for dense-

graded mixtures given a loading duration of 0.1 seconds. Required for

computation is the asphalt viscosity obtained for a particular tempera-

ture as measured in the Schweyer rheometer.

Limited work has been done to define the failure limits of asphalt

concrete mixtures in terms of stresses and strains. Ruth et al. (77)

stated that as temperature decreases, the failure stress increases but

remains constant below some transition temperature dependent on asphalt

properties. Finn (78) reported asphalt tensile strengths ranging from

290 to 580 psi for fast loading rates. Ruth and Olson (79) reported

failure stresses consistently between 380 and 440 psi and chose a value

of 400 psi as typical. They also demonstrated that as temperature

decreases, the strain at failure also decreases. Pavlovich and Goetz

(80) determined from direct tension tests that temperature is the most

significant factor affecting limiting strains. Strain rate has some

effect but not as much as temperature. Ruth and Maxfield (44) reported

that failure strain is primarily a function of viscosity. It was shown

by Ruth et al. (46) that energy required for fracture decreased as the







viscosity increased and that fracture energy may be the best measure for

predicting failure response in asphalt mixtures.

From the above studies, it is well documented that as the asphalt

binder hardens, the tolerance for strain decreases. As a result,

brittle failure of the asphalt concrete becomes more likely. Binder

hardening can be both instantaneous, due to changes in temperature, and

time dependent. Page et al. (81) blamed the premature hardening of

asphalt binders on plant hot-mix operations and in-service aging. Kumar

and Goetz (82) stated that the most important factor associated with

binder hardening is the oxidation of the asphalt throughout the entire

pavement thickness. Hardening at the surface is generally greater due

to ultraviolet radiation and higher temperatures experienced.

It is important to point out that the type of asphalt binder plays

a big part in the hardening of bituminous mixes. Some asphalts sub-

jected to the same exposure conditions are less susceptible to hardening

than others. The reasons for this are not well known. Currently,

research is being conducted at the University of Florida to specifically

address the issues associated with the hardening of asphalt with respect

to its chemical identity. The study proposes the use of infrared spec-

troscopy to determine the susceptibility of the asphalt to further oxi-

dation under plant mixing and in-service environments (83).

Since hardening of the asphalt increases its viscosity, the energy

required for fracture is reduced. Page et al. (81) further reported

that when the asphalt binder attains a critical degree of hardness for a

specified structural support system, the stress and strains imposed by

traffic loadings can exceed the tolerance of the asphalt concrete. This

will result in fracture of the material and the development of pavement







cracking. During rapid thermal cooling, the critical temperature

required for cracking increases as the viscosity increases (46). This

critical temperature can become even higher as the asphalt continues to

harden, causing cracking earlier than expected in the life of the pave-

ment. Huffman (84) stated that softer asphalts delayed cracking, and

cracking became evident when the viscosity at 25 C (77 F) exceeded 5

megapoises (Mp). Potts et al. (85) found viscosities in excess of 10 Mp

resulted in pavement cracking and poor performance. They also showed

that in-service air void contents in excess of 4 percent generally were

associated with poor pavements. Page et al. (81) concluded that

although the effects of age and air void content on binder hardening are

not clearly distinguishable, the recovered asphalt viscosity usually

indicated harder asphalt for higher air void content samples.












CHAPTER 3
AIRFIELD DESCRIPTION AND FIELD TESTING


3.1 Introduction

A flexible airfield pavement subjected to a wide range of environ-

mental and loading conditions was desired for this study. After dis-

cussing this matter with officials at the Air Force Engineering and Ser-

vices Center (AFESC), Duke Field (Eglin AFB Auxiliary Field 3) became

the prominent choice. Specifically, Duke Field was selected for the

following reasons:

1) its proximity to the University of Florida (five hours by car)

would make necessary monthly trips both geographically and

economically feasible,

2) its close proximity to AFESC (ninety minutes) would allow for

the lending of needed equipment (e.g., FWD) and technical

personnel,

3) accessibility to the airfield, especially during the day, was

virtually unlimited,

4) the entire airfield, excluding parking aprons, was comprised of

asphalt wearing courses and offered a vast selection of sites

for study, and

5) a wide range of pavement temperatures are experienced.

Another key consideration was that the research was to begin at the same

time the AFESC was scheduled to perform its periodic airfield inspection








of Duke Field. This enabled the team to evaluate the FWD data first

hand before choosing testing locations for study.



3.2 Airfield Description

3.2.1 Topography and Climatology

Duke Field, located in Crestview, Florida, is some 14 miles north

of Eglin AFB, 23 miles north of the Gulf of Mexico, and 6 miles south of

Interstate 10 just off U.S. 85 (Figure 3.1). Land areas surrounding the

airfield consist primarily of well-draining sands and sandy loams. The

terrain is undulating in most directions with the elevation on the air-

field being approximately 85 ft.

Climatic data have been recorded since 1939 (86). Annual tempera-

tures range from a mean daily maximum of 90 F in August to a mean daily

minimum of 42 F in January. The summer months average forty-one days

above 90 F with a recorded high of 106 F, while the winter months

average seventeen days below 32 F with a recorded low of 6 F. During

this study ambient air temperatures ranged from a low of 26 F in January

to a high of 91 F in July. Pavement surface temperatures during this

period ranged between 30 and 130 F.

Annual rainfall amounts average 62 in. per year with September

being the wettest (7.3 in.) and October the driest (3.3 in.). Thunder-

storms are a common occurrence in the area averaging twelve per month

from May to September. The airfield itself retains little surface mois-

ture after heavy rains due to adequate surface runoff, well-draining

soils, and infiltration through cracks in the pavement.



















DUKE
FIELD


Figure 3.1 State Map of Florida Showing Location of Duke Field








3.2.2 Test Locations and Layout

Three sites were chosen to test, analyze, and correlate data to

properly characterize the pavement conditions at Duke Field. As men-

tioned previously, the initial research effort ran concurrently with the

periodic evaluation of the airfield by the Pavement Evaluation Team

(PET) from the AFESC. The three sites were selected for monthly evalu-

ations after analyzing the FWD data obtained by the PET for the entire

airfield. Sites were chosen on taxiways instead of runways because of

easier access and known loading conditions. Figure 3.2 shows the

location of each site with respect to the entire airfield. Site 1 is

located at the north end of the parallel taxiway, site 2 at the south

end, and site 3 is located on the third ladder taxiway. The basis for

selection were 1) a uniform FWD test response over a sufficient segment

of taxiway and 2) varying degrees of surface distress present between

sites. These locations were chosen during ideal testing conditions,

i.e., overcast skies, and air temperatures around 55 F.

The horizontal layout of the test grid was basically similar for

each site. Eleven longitudinal stations (10 ft. spacing) and six trans-

verse stations (6 to 8 ft. spacing) were marked off at each site. The

longitudinal stations were offset between 6 and 7 ft. from the taxiway

centerline. This approximated the wheel path for the main landing gear

of the C-130 aircraft. Data obtained from the wheel path could then be

compared with those taken from the transverse stations outside the

loading area. Figure 3.3 depicts the location and spacing of the FWD

test stations, cores, and environmental instrumentation at each test

site.









0
C3


o
a

0
-N-


1 -


J7



c0

0TiS


en

Cc

ca

0 u LL
z .,
-i










Site 1 N
+ 1" = 20'


0 *
+

.4-

+ + + + + + + + + + +
10 LENGEND: + -Test Station
S0- -4"Core
O-6" Core
T- Thermal Sensor
+M Moisture Sensor


Site 2 N
T + 1" = 20'

10i +
+*+ + + + + +*+ +0 + +


+
+
+




Site 3
+ 1" = 20'


S* ,+ *




+ +
+ + + + + + +



1 + o


Figure 3.3 Detail of Test Sites







Special test stations were designated within each site to evaluate

the uncracked characteristics of the pavement. A primary concern was to

choose a station or stations that yielded results free of cracking

influence. However, site 1 had such a high crack density that it was

impossible to isolate an uncracked section within the site.

One reason for selecting the sites was based on visible surface

conditions. Site 1 showed extensive 4 to 5 ft. block cracking (Figure

3.4) which extended over the entire width of the pavement. Crack widths

up to 1 in. were measured with some spelling evident. Block cracking of

the asphalt concrete is caused mainly by shrinkage, and thermal contrac-

tion resulting from daily temperature cycling. It is not load-

associated, although aircraft wheel loadings can increase its severity

(87). Rutting up to 0.75 in. was measured at the center of the wheel

path at site 1 classifying it as medium severity (> 0.5 1 in.) by

Federal Highway Administration standards. Ravelling has begun to occur

and could present operational hazards in the near future if left

unchecked. As of this report, no operational restrictions apply to this

site.

Site 2 displayed moderate 10 to 15 ft. block cracking which tra-

versed the entire width. Load-induced longitudinal cracking was obvious

at this site and is shown in Figure 3.5. Rutting here was more pro-

nounced measuring 1.5 in. at the wheel path center (Figure 3.6).

Rutting exceeding 1 in. is classified high severity and is used to

quantify failure in Air Force flexible pavements. The rut basin was

more than 10 ft. wide which gave indication to excessive strains in

deeper layers, perhaps the subgrade. The longitudinal crack at the edge

of the wheel path was a direct result from this rutting. Crack widths
























































Figure 3.4 Site 1: Severe Block Cracking With Spalling















































Figure 3.5 Site 2: Longitudinal Crack at Edge of Wheel Path




























-< A -
S. (
r *- '-'" '' .

-- El~-
S. -. JC ;A' *
^.. -'- *< .'




.- .
a~~r+ __
le~ -rr L
rra ir-.r.


Site 2: Rutting in Wheel Path


Figure 3.6







at site 2 were up to 0.75 in. and were as wide at the edge of the pave-

ment as they were near the wheel path.

From a visual standpoint, site 3 showed the least distress. This

feature displayed 20 to 30 ft. transverse and longitudinal cracking with

no evidence of rutting (Figure 3.7). Most of the stations were out of

the immediate vicinity of cracking. However, cracking did extend the

entire width of this 150 ft. wide ladder taxiway. A core taken in a

cracked portion of the pavement revealed that cracking propagated the

entire thickness (Figure 3.8). Crack widths at this site also measured

up to 1 in. The lack of cracking and rutting at site 3 were initially

explained by the increase in aircraft wander (higher pass-to-coverage

ratios) and the decrease in aircraft weight after landing. Other expla-

nations dealing with asphalt rheology and mix parameters are discussed

in the next chapter.

One surface distress condition common to all three sites was the

moderate degree of weathering present. This form of distress, exhibited

by the wearing away of the binder material, leaves the surface rough and

pitted. Normally, it is an indication of significant binder hardening

(87).

3.2.3 Site Layer Profiles

All three sites had similar layer profiles with respect to material

type but varied somewhat in layer thickness. Each site consisted of two

or more asphalt concrete layers, a sand asphalt base, all overlying a

uniform, well-draining sand subgrade. The profiles for typical sections

both in and out of the wheel path are given in Table 3.1 for each site.

Construction history is discussed in the next section.









































Figure 3.7 Site 3: Longitudinal and Transverse Cracking




44



































3 ,3 t











Figure 3.8 Site 3: Cracking Through Entire Pavement Thickness

















Table 3.1 Site Layer Profiles In and Out of Wheel Path


Site
SNo.
Type Cores 1 2 3
Taken (in.) (in.) (in.)
Layer In/Out
In Out In Out In Out

AC surface
4/1 2.0 1.6 1.6 1.5 1.7 1.5
course

AC 4/1 1.8 2.3 1.5 1.3 1.8 2.5

AC 3/1 NA 1.8 1.9 NA

Total AC Thickness: 3.8 3.9 4.9 4.7 3.5 4.0

Sand Asphalt 4/1 7.5 7.8 6.4 6.5 8.0 9.5







Stratigraphy data were obtained from four 4-in. and two 6-in. core

samples extracted from each site. Core locations within each feature

are shown in Figure 3.3. At sites 1 and 2 there appears to be no

significant decrease in layer thickness inside the wheel path as opposed

to outside. This tends to indicate that rutting occurred primarily in

the subgrade and was not due to additional consolidation or plastic flow

in the bituminous layers. However, it is entirely feasible that the

areas inside the wheel paths were built up with subsequent overlays

where initial thicknesses were greater and where upon trafficking,

densification occurred. This was verified through specific gravity

tests where the densities in the asphalt concrete layers were generally

higher in the wheel path. At least some rutting, therefore, can be

attributed to additional consolidation of the flexible layers.

Extracted materials were taken back to the laboratory and subjected

to a variety of tests to determine their physical properties. These

tests will be discussed in detail in the next two chapters.

3.2.4 Construction History

The existing airfield is the product of several construction and

repair projects (88). Initial construction was performed in 1941-42 by

the U.S. Engineering Division (USED). The runways and taxiways were

originally designed for capacity gross loads of 34 kips. Site 3 was the

only evaluated feature built during initial construction and was once

used as a NE/SW runway. Sites 1 and 2 were added in 1949 by the Army

Corps of Engineers (COE). Since 1962, several overlay/rejuvenation

projects have been accomplished by the USAF at all three sites. Table

3.2 gives the summary of the construction history pertaining to the

three locations studied in this report.
























LL -

V)





0L


C-)


u co

<4- L C-

3 > >
V no) C: C:


LL
U-l





LL<

0
L

0 3



r) ro


1 > L
L 0)
v~


0)


eC
CU









O
0)









O-
4-

>









C

c



4-J




n C :


E

0)



















CL
0)
S=
-U 0)





u .0
*r- -0
CV CL



0
in











4-- 0


r- 0

OLL
LC 0)


eC 0
C-,












0-




0)







0)


01) C\j Cn)
-4 (. (-
= Y o
cr 0 y


0) COj C- C-
o~ocoY o
-4 4 h


>4







C -


C 1-
UJ 0)
Or i


L0 0l


































-TJ
*
ID OJ f-





C\ M ^









-r-


C- < C- u


0 0 C 0 0 C L L4

In Ls n cj -


>4,

3










LL
Cr
I-



-0




Z Q.


-4
0)
4-'








Detailed construction information is lacking for Duke Field.

Therefore, reasonable assumptions must be made on the types and grades

of asphalts used in construction in order to estimate the binder

hardening characteristics.

3.2.5 Aircraft Traffic Data

During World War II, the traffic consisted mainly of 4,000- to

8,000-lb. aircraft averaging between 145 and 275 cycles per day (88).

Since 1971, traffic primarily consisted of specially configured C-130

aircraft operated by the 919th Special Operations Group (SOG). Suppor-

ting the SOG was the main reason for the complete resurfacing of

existing runways and taxiways between 1972 and 1974. According to

officials at Duke Field, the increased weight of the C-130 caused exten-

sive cracking to the pavement surface (only one asphalt concrete layer

existed at that time) and prompted the overlay construction (89).

From available traffic information, the C-130 has averaged between

1,000 and 3,000 operations per year since 1971 accounting for 99 percent

of the total generated traffic at Duke Field. Since 1979 there have

been approximately 1,650 operations per year. Flying is normally done

at night between 9 p.m. and 12 mid-night with missions generally lasting

two to four hours. However, there is no data describing specific taxi-

way usage during this time period. From climatic data including wind

roses, and from observations made over many years, approximately 80

percent of the traffic traverses down site 1 (north end) and takes off

in a southerly direction on the active N/S runway. The same percentage

of aircraft are also recovered on site 3. Rarely do the aircraft need

the entire length of the runway to be recovered at the south end (site

2). Site 2 receives about 20 percent of the total launched and







recovered aircraft. Paradoxically, at least from initial observations,

this feature exhibited the greatest amount of rutting. This will be

examined more closely in subsequent chapters.

The number of passes of an aircraft over a pavement feature does

not necessarily represent an equivalent number of coverages at a parti-

cular point on the pavement surface. To account for this wander, engi-

neers have determined the number of passes required for one coverage in

terms of pass-to-coverage ratios (P/C) for all aircraft types (5). The

higher the P/C, the more wander taken by the design aircraft. Factors

that effect the P/C are 1) aircraft type, 2) wheel gear configuration,

3) type of pavement system (rigid or flexible), and 4) pavement designa-

tion (primary or secondary usage).

Traffic volume information is given below in Table 3.3.


Table 3.3 Annual Traffic Volume at Duke Field

Annual Traffic P/C Annual
Site Cycles (passes) Usage (C-130) Coverages

1 1,320 Primary 2.09 632

2 330 Primary 2.09 158

3 1,320 Secondary 4.05 326



It is important to point out that the P/C applies only to the asphalt

layer, and more specifically, the pavement surface since one is dealing

with aircraft coverages at a point. Failure in the subgrade is based on

repetitions (passes) because of the effect of lateral distribution of

loads in deeper layers. Simply, the wandering of aircraft will have

less an influence on the stress distribution in the subgrade than it

will at the asphalt surface.







Other factors affect the distribution of stress in flexible pave-

ments. These include load, gear type and configuration, tire pressure,

and tire contact area. Figure 3.9 depicts the wheel gear configuration

for the C-130 aircraft, and Table 3.4 gives its physical characteristics

(90). The design category and group index are used to classify like

aircraft into specific design groups which are used for design and eval-

uation purposes. The C-130 sits alone in design group 4 as no other

aircraft has its unique physical features. Figures 3.10 and 3.11 offer

an indication as to the size and wheel gear arrangement for the C-130

type aircraft stationed at Duke Field.



3.3 Field Testing and Environmental Monitoring

3.3.1 Selection and Description of the Falling
Weight Deflectometer (FWD)

The FWD is the nondestructive testing choice of the USAF. It was

chosen for this study because of the AFESC's ability to support the

research. The AFESC, along with the COE, provided the necessary equip-

ment and technical services for the project. Initially, the Center was

interested in performing a year-long evaluation to determine the effects

of seasonal variations (e.g., temperature and moisture) on NDT results

and associated pavement performance. Since this initial focus, the

research has evolved into many distinct facets including laboratory as

well as field testing. The intent was to determine the ability of the

FWD deflection data to accurately predict layer moduli values in re-

sponse to varying environmental and pavement distressed conditions.

This being the case, the FWD was a good selection to carry out the

investigation.


















-A --
-@@*1,





Si 1J


Figure 3.9 Wheel Gear Configuration for C-130 Aircraft













Table 3.4 Aircraft Characteristics for C-130

Characteristic Description

Common Name Hercules

Maximum Gross Weight (kips) 175

Design Category, AFM 86-2 4

Group Index, AFR 93-5 8

Maximum Single Wheel Load, Main Gear (kips) 41.9

Contact Pressure, Main Gear (psi) 105

Contact Area, Main Gear (in.2) 400

Tire Width (in.) 17.6

Tread Width (in.) 172

Wheel Base (in.) 388

A (see Figure 3.9) 24 in.

B (see Figure 3.9) 60 in.


Source: USAF (90)


































WLr l~C;"Z~ -t~j E .
-C.--.' L


-~~~ C.-
Lim-








-.--m r awe -
-. -- LA. -.e


Figure 3.10 C-130 Aircraft: Front and Rear View



























" .-_'.:--' -" . .- -
-- r f* r


S,," .o "






-l -.t. ,
a) Side View






























b) Front View


Figure 3.11 Main Landing Gear







The Dynatest 8000 FWD Test System chosen for this research simu-

lates the effects of a moving aircraft single wheel load. The system is

normally capable of applying loads up to 26,000 Ibs. for a pulse dura-

tion between 25 and 30 msec (86). The test load allows for nonlinear

and visco-elastic stress-strain response and very accurate deflection

measurements ( 0.5 percent).

The Dynatest FWD used in this study is shown in Figure 3.12 and

consisted of three main components,

1) a FWD,

2) a system processor (8600), and

3) a Hewlett-Packard Integral Personal Computer (IPC).

The FWD was a light-weight, trailer-mounted device which was towed

by a Suburban van. It came equipped with seven velocity transducers

(geophones) to measure deflections and a 12-in. impact plate with load

cell. The six outer sensors can have spacings preset to any desired

configuration. The arrangement used in this research is illustrated in

Figure 3.13.

The 8600 System Processor controlled the FWD operation. It also

supplied the power to the IPC and performed scanning and conditioning of

the eight transducers (one load plus seven deflection). The system

processor monitored the status of the FWD unit to ensure correct mea-

surements were obtained and safety precautions followed.

The IPC allowed for the input of control and site/test identifica-

tion, as well as displaying, printing, and storing of the FWD test data.

Other features allowed it to edit (e.g., change load and/or drop se-

quence), sort, and further process test information. The light weight

of the IPC made it easy to transport from the field to the office in





















--- ~--U ~ L-P~ur~rriv~ L~~-~IC- ~t- .- ~l--
L ..



- -- - _____ I;


Figure 3.12


Falling Weight Deflectometer (FWD)






























V)
Cd,
0
C
0



4-
0

c2)

0



a C C-




'-4-)







0~
0 ~a









0)0
0i

CCY
0) 0

~o o)
0I








c,-

cL

LJ







order to run various programs designed to match deflection basins, com-

pute layer moduli, and predict pavement life expectancy.

3.3.2 FWD Field Testing Procedures

Once the IPC was programmed to include information as test and site

description and loading, the FWD was ready to test. The testing se-

quence was the same for all three sites, i.e., longitudinal followed by

transverse stations. Once completed, the special stations were tested.

These locations were specific areas within the site that appeared free

from cracking effects.

Each FWD test station received four drops, starting from the

highest drop height working down to the lowest. The first drop was

considered a seating load. The normal drop configuration and load is

given in Table 3.5. A load of 12,000 Ibs. most closely approximates the

contact stress of a C-130 aircraft, although the total wheel load was

41,900 Ibs.


Table 3.5 Typical Drop Sequence and Load

Drop Sequence (IPC) Load

4 26,000
4 or 3 26,000 or 17,000
2 12,000
1 9,000


The research team was able to complete the testing of all three

sites in just over two hours. Eight tests were performed during the six

month field testing phase of the study. Tests were conducted at dif-

ferent times during the day under all weather conditions. Results are

discussed in Chapter 6.







3.3.3 Measurement of Subgrade Moisture

To accurately interpret and analyze FWD data, subgrade moisture

contents and pavement thermal profiles were measured using installed

equipment. For moisture determination, two aluminum access tubes were

installed at site 2. Water contents were obtained using a nuclear

moisture device at subgrade depths of 2, 3, 4, 5 and 6 ft. below the

pavement surface. A schematic showing the installed access tube is

given in Figure 3.14. Tubes were placed at the center and at the edge

of the taxiway to monitor horizontal as well as vertical moisture

gradients.

The Troxler 3220 Depth Moisture Gauge pictured in Figure 3.15 was

calibrated for Florida sands and gave water contents in volumetric units

using the following equation (91):



e = 0.361 CR 0.769 (3.1)



where,

CR = ratio of neutron count rate in the soil to the
standard count rate in the shield

Volumetric values are mostly used in agricultural sciences where soils

do not ordinarily undergo appreciable settlements. In civil engineering

applications, however, volumetric measurements are impractical,

therefore gravimetric (mass) values are used. Equation 3.2 was used to

convert volumetric water contents to mass values (92).


e (w
w = (3.2)
(Pb)










5" Brass Access Cover


6" Cast Iron
Housing


2" O.D. x 7'
Aluminum Tubing


I2" Rubber Stopper
S(Moisture Seal)


Figure 3.14 Schematic of Installed Moisture Tube


Silicone Seal.





61






























.- -. ." -. i .
r s g-3




-. :, 4








-44
Figure 3- 15 Nuclear Moisture Gage







where,

w = gravimetric water content

0 = volumetric water content

Pw = density of water, normally 1 gm/cc

Pb = dry bulk density, gm/cc

An average Pb value of 2.15 gm/cc was calculated from gravimetric and

volumetric readings listed in Appendix A. Hillel (92) reported a pb

value of 1.6 gm/cc as typical for uncompacted sandy soils. Lambe and

Whitman (10) gave a maximum value of 2.21 gm/cc for fine to coarse

compacted sands.

Monthly mass water contents determined from equation 3.2, are

presented in Table 3.6. Graphical illustrations representing the high,

low, and average values for moisture content are shown in Figure 3.16.

Little fluctuation of water content was observed throughout the entire

six-month study. There existed, however, a small moisture gradient

across the pavement section. The taxiway edge displayed a 10 to 20 per-

cent decrease in values of w from the centerline. A plausible reason

for this stems from the evapotranspiration of adjacent field moisture

resulting in higher soil suctions at the edge of the pavement. This, in

turn, pulls water from the center causing small horizontal gradients to

develop. In the vertical direction, there was a general reduction in

water content with depth. Surface cracks allowing the infiltration of

water into the subgrade can result in higher soil moisture near the

surface, especially after heavy rains. In contrast, the decreased water

contents at depth seemed to indicate the absence of a water table.

Maximum capillary rise for the type soil at Duke Field is approximately

3 ft. (10). Since no increase in water content was observed at 6 ft.,











Table 3.6 Field Moisture Contents (w %) by Month


Depth January February March

(ft.) Center Edge Center Edge Center Edge

2 6.8 6.0 6.1 5.5 6.0 5.5

3 5.3 4.8 6.0 5.8 6.0 5.7

4 5.0 4.8 5.8 5.4 5.9 5.5

5 5.2 4.2 5.5 4.8 5.7 4.9

6 5.3 4.5 5.2 4.8 5.2 4.8

AVE 5.5 4.9 5.7 5.3 5.8 5.3

Depth April May June

(ft.) Center Edge Center Edge Center Edge

2 6.1 5.7 6.2 5.8

3 6.0 5.5 5.9 5.5

4 5.9 5.2 6.0 5.2

5 5.8 4.8 5.8 4.8

6 5.3 4.7 5.4 4.8

AVE 5.8 5.2 5.9 5.2


* Did not test


























FEB MAR APR MAY
MONTH

a) Center of Pavement


FEB


MAR


APR


MAY


Figure 3.16


MONTH
b) Edge of Pavement
Monthly Subgrade Moisture Contents:
High, Low, and Average Values


6.5

6


5.5


5


4.5


4
JAN


6.5


5.5


A


JAN


JUN


b)





High
Average


Low



I I I I


JUN


4.5







the water table appeared to be of no influence to at least 9 ft. below

the pavement surface.

Due to the relatively low water content of the subgrade soil excess

pore water pressures are not generated under repeated aircraft load-

ings. Given similar loading conditions, the small variation of subgrade

moisture present would not be enough to significantly alter its modulus.

3.3.4 Measurement and Prediction of Pavement Thermal Profiles

The accurate measurement of temperatures within a flexible pavement

is extremely important to correctly assess its structural response to

changing load and environmental conditions. Measuring thermal gradients

at predetermined points in the pavement profile presented an interesting

challenge. A device was designed using nonconductive tubing and thermo-

couple wire that could be sealed from moisture intrusion and made flush

with the pavement surface. Information on the theory and use of

thermocouples presented by Schimmelpfennig (93) and Holman (94) was used

to design, calibrate, and construct the devices.

Trial tests were performed in the laboratory at temperatures

ranging from 32 to 144 F using type T (copper-constantan) thermocouple

wire. Water bath temperatures were verified with a Fluk 80T-150

temperature probe accurate to 0.01 F. Relative voltages were recorded

between the measuring junction (tip of thermal couple) and reference

junction using a standard Fluk True RMS multimeter accurate to 0.01

mv. Type T thermocouples show high sensitivity ( 1 F) when working in

thermal ranges below 600 F.

The reference junction must be known in order to compute tempera-

ture from measured voltages. Normally, the reference temperature (RT)

in the laboratory is set at 32 F (ice bath). However, maintaining this







temperature in the field is impractical and therefore sophisticated

devices are available to simulate this ice bath electronically. Since

the RT in the field approximates the ambient temperature, laboratory

calibration included recording relative voltages for five different RTs

(e.g., 32, 54, 74, 93, and 113 F). A correct reading of the RT is

essential to precisely measure pavement temperatures. This is because

the voltage generated is proportional to the relative temperature

between the two junctions. For example, if the ambient air temperature

(RT) is 50 F and a point within the pavement is 50 F, then the potential

difference is zero (0.00 on the multimeter). However, if the RT rises

to 60 F but the actual pavement temperature remains at 50 F, then a

negative potential will develop. Errors in the measured temperature are

directly related to the errors induced by incorrectly assessing the RT.

From the laboratory data, a plot of millivolt output versus temper-

ature was made and a linear regression analysis performed for each of

the five RTs. Very good correlations were obtained with R2 values

averaging 0.999. A multiple regression analysis was then performed for

the entire range of temperatures and equation 3.3 developed. Using this

equation, several trials were conducted to predict actual temperatures

at different RTs. Deviations from the actual temperatures varied

between 0.1 and 1.2 F. Considering the sensitivity of the thermocouple,

the predicted values were within acceptable limits. This equation was

subsequently used to measure temperature profiles in the field.



MT = 0.7933 + 43.6560 (MV) + 0.9891 (RT) (3.3)


R2 = 0.9996)


(N = 25







where

MT = measured temperature (F)

MV = output from volt meter (mv)

RT = reference temperature (F)

Two temperature profile devices (TPD) were constructed using 2-in.

PVC tubing, styrofoam (for added insulation), and thermocouple wire.

Illustrated in Figure 3.17 is a schematic of the installed TPD. Six

thermocouple sensors were prepositioned on each of the two devices at

points determined from a previous airfield evaluation (88). Note from

Figure 3.17 that four thermocouple sensors were placed in the asphalt

concrete layer. These, along with the surface temperature reading,

allowed for five thermal recordings within the top 3.5 in. of pavement,

where the largest temperature gradients were expected. The other two

sensors were placed in the sand asphalt and subgrade layers, respective-

ly.

The two TPDs were placed in previously drilled 6-in. core holes at

site 1, one at the centerline and one at the edge of the pavement. The

exposed thermocouples were covered with a slurry sand-asphalt mixture

and butted up firmly against the side of the core to secure intimate

contact with the existing pavement (Figure 3.18). The core was back-

filled with a cold-mix asphalt and lighlty tamped.

To obtain six simultaneous readings, a temperature measurement sys-

tem was built which consisted of a six-position switch box and two mul-

timeters (Figure 3.19). The meter on the left record the RT using the

Fluk 80T-150 temperature probe, while the one on the right measured the

voltage output from the TPD. The styrofoam mat was used to reduce heat










Pavement


Insulated
Brass Cover


PVC Cap


Asphalt
Concrete


Sand
Asphalt


Sand
Subgrade


G- 2"


0- 3 1/2"




0- 5 1/2"


0- 12'



Rubber Stopper
F (Moisture Seal)


Figure 3.17 Schematic of Installed Temperature Profile Device (TPD)











































Figure 3.18


Installing the Temperature Profile Device (TPD)












































Figure 3.19 Temperature Measurement System







loss from the TPD and limit the effects of heat gain on the reference

junction.

A nomograph was developed for temperatures typically experienced in

Florida throughout the year. It can be used for quick, approximate

temperature measurements. An example for using the nomograph is shown

in Figure 3.20, and is outlined below.



Given: Reference Temperature (RT) = 74 F

Output on voltmeter = 0.5 my @ 3.5 in.



Find: Pavement Temperature @ 3.5 in.



Procedure: 1) Locate 0.5 my on abscissa and read up until
intersection with RT (diagonal line).

2) Read across to pavement temperature.



Answer: 96.0 F



A parametric study was undertaken to compare measured field tem-

peratures with predicted temperatures using the 5-day mean pavement

temperature model developed by Southgate and Deen (95). This model

utilizes the prior 5-day mean air temperature added to the current pave-

ment surface temperature to arrive at the mean pavement temperature

(MPT). A Fortran computer program is available to quickly compute the

MPT and is presented by Bush (96).

In order to calculate the MPT from actual field measurements, ther-

mal profiles were first plotted as shown in Appendix B. An average was

then obtained for the entire depth of asphalt concrete, arriving at the






72

















C14)
a,
L
=r
4-,
ror
in L
a,


CDr aj
1~ 0.
E
a,



4-)
a,







00

LU
Uc,2






F-
CDc

0
>
o E E









C1 cu
L" ~ L
a,
.r1 a,






0 0

II ,

CI~










0 N 0 0 0 0

(=I) -
(d flVLVI3L3~







mean pavement temperature (MPT). Since horizontal thermal gradients did

not appear to be significant, the MPT was taken as an average between

the center and edge TPD. Finally, the measured MPT was compared with

the computed 5-day MPT for 3.5 and 5.5 in. layer thicknesses.

From the results given in Table 3.7, satisfactory agreement exists

between the measured MPT and the predicted MPT using the 5-day model.

The best correlations came during uniform gradient conditions. However,

it did not fair as well under positive or negative gradient situations.

This was somewhat expected due to the highly empirical nature of the

model. One inherent flaw shown by the data is the apparent trend of the

model to predict higher MPTs with decreasing layer thickness, regardless

of gradient conditions present. During thermal cooling, lower tempera-

tures are expected near the surface which results in a lower MPT at 3.5

in. than at 5.5 in. Using the 5-day model, the opposite occurred.

In summary, thermocouples provided very reliable pavement tem-

peratures which appeared to respond correctly to changing thermal

conditions. The predicted 5-day model is best used for initial esti-

mates but should not be relied upon to accurately define pavement

temperatures. This is especially true when predicting resilient charac-

teristics of bituminous layers where differences of just a few degrees

could result in significant errors.












Table 3.7 Parametric Study of Mean Pavement Temperature (MPT)

Pavement Measured 5-Day
Thickness MPT MPT Thermal(a)
Test (in.) (F) (F) Diff. Gradient


3.5
5.5

3.5
5.5

3.5
5.5

3.5
5.5

3.5
5.5

3.5
5.5

3.5
5.5

3.5
5.5


Note:

(a)


55.2
54.8

34.1
35.3

57.3
56.9

70.7
70.6

89.7
88.0

120.0
114.8

77.6
78.9

91.1
92.6


52.8
51.6

39.0
38.9

59.5
58.2

75.1
72.9

95.5
92.1

114.1
109.6

85.0
82.3

91.0
87.9


2.4
3.2

-4.9
-3.6

-2.2
-1.3

-4.4
-2.3

-5.8
-4.1

5.9
5.2

-7.4
-3.4

0.1
4.7


Uniform


Positive


Uniform


Uniform


Negative


Negative


Positive


Negative


Uniform No appreciable gradient exists
Positive Pavement temperature increasing with depth
Negative Pavement temperature decreasing with depth













CHAPTER 4
LABORATORY TESTING AND EVALUATION OF PAVEMENT MATERIALS


4.1 Introduction

Laboratory tests were performed on core material extracted from the

Duke Field test sites to determine the physical classifications and pro-

perties of the pavement layers. Discussed in this chapter are the basic

procedures and the results obtained from the following tests:

1) subgrade sieve analysis and specific gravity

2) bulk specific gravity

3) maximum density

4) asphalt content and gradation

5) penetration

6) absolute viscosity

7) Schweyer rheometer

8) indirect resilient modulus

9) indirect tensile (quick)

10) indirect static creep (fracture energy)

Results from the last three tests (indirect) are discussed in greater

detail in Chapter 5.



4.2 Classification of Subgrade Materials

Subgrade soils from each site were classified according to the

AASHTO and Unified systems using grain-size analysis (10,97). The

results of the sieve analyses along with a sensory assessment of the








materials are presented in Table 4.1. A corresponding grain-size

distribution is shown in Figure 4.1 for all three sites. From the

distribution curve, a Uniformity Coefficient (Cu) close to 2.0 was

computed for each feature indicating that the subgrade sands were

uniform in size. The low percentage of fines further identified the

soils as clean, poorly-graded sands.

Specific gravities were 2.63 and 2.64 for sites 1 and 2, respect-

ively, and slightly lower at 2.58 for site 3. The specific gravities at

sites 1 and 2 were close to the value of 2.65 given for quartz (98).

The lower value computed for site 3 was attributed to the small amount

of organic content found in the soil.



4.3 Determination of Air Void Content in Field
Extracted Bituminous Mixtures

Two specific tests were conducted to obtain air void contents for

both the asphalt concrete and the sand asphalt layers. Tests included

the determination of bulk specific gravity (AASHTO T 166-78) on each

core specimen and maximum theoretical specific gravity (AASHTO T 209-82)

on selected cores for each layer. Table 4.2 lists representative values

of unit weight and air voids for both in and out of the wheel path. The

data clearly show a marked increase in density inside the wheel path

with a corresponding decrease in air void content for each layer. There

appears even greater densification in the surface courses as compared to

underlying layers. This densification may appear significant from the

standpoint of reduced air voids, but it accounts for less than 0.1 in.

of additional consolidation in the surface courses. Site 3, which

displayed no measurable rutting, exhibited extremely high densities in

the surface and binder courses both in and out of the wheel path. The











Table 4.1 Summary of Subgrade Classification


Site
Sieve Diameter 1 2 3
No. (mm) ___
Percent Passing

20 0.840 99.84 99.16 99.34
40 0.420 72.35 70.23 67.03
60 0.250 15.89 20.04 19.36
Sieve 100 0.149 3.74 6.08 7.27
Analysis 140 0.105 1.68 2.24 4.29
200 0.074 0.78 1.10 2.49
wet(a) <0.074 1.60 4.30 5.70

Uniformity Coefficient, Cu 1.7 2.1 2.2

Specific Gravity, Gs 2.63 2.64 2.58

Plasticity none none none

Description fine fine fine
sand sand sand
Color orange medium light
tan brown
Odor none none burnt(b)

AASHTO A-3 A-3 A-3
Classifications
Unified SP SP SP


NOTE


(a) Wet sieve analysis performed to verify low percentage of fines
(b) Organic content of 1.09 % determined from AASHTO T 267-80





















i S i i i i I

coo




I ....... .. ....... ......... .. .... .... ......... ... .... ..... .. ........ .........
.................. .......... .....


I J





.......... ......... ......... .......... ......... .......... ....

.......... ......... ......... ......... ............




..................






t
........ ........... ............ ......... ........... ......... ....... .. ...... ..
............"...........





--- -------
81
. 1.
--------- m--- ---- ----

...... o ..... 0... ..... ..... ...... ...


bH3NId %


r







E
E,

LJ
r N
ch

z

cr
a


It


r
'i"














*r- *^j
*h -4
~CO .
-4D -4


00

-14~ -4
- ^ C\
^ ^-
d ] J ^ ^ J


-C









C



4-,

0


















C











E4
34
_I




























-4-J
0
4r-















E
C-



0



4r-



*-
4--
C,
o







































E

o
I-
c

+-










-r~










-r










(U

-Q

\-


,-4


-4) -4 -4 4' C:J C


0^ ^ 0
0O ^ CO -^ -0
-I


*e .0 U



c- CN~ i CD~
CD C\J O-

4 C\J C\J


CO
-* -*-LC

M- ^_ C-i^^


C\J
00
C: O


j- CZ r
CO .


-4 j-4 C\J


O















SCO
.00
-1

C\








C\

-I


C\J C\J C\J C\J C\J

dj d1 C-i C-i C-i


O
V)

0
C-,


I U I



U Q
C,,


+-

C13
(4-
M-i. C\J
I I I3 1 E
0 < -s= C 0
c:. V) V 4-J
0 ( 0

Co
I-O


04

0
S


U-
r U
Q.


a) 4-'
4-J CMjU
L-
C'- Q
tO (V


CO d c- 7CG
-4 ~ 4 4 \ C\J


=3
0
&^


4-J

0














^a


4-

C-


L


EL -







L i


I
0i C
1) I
>l CU


*r-




Ci



0
0





0
0
I-

II
o=
a







low air void contents tend to suggest good compaction during construc-

tion. Sites 1 and 2 exhibited appreciable rutting (0.75 and 1.5 in.,

respectively) when compared to site 3, but this could be attributed to

the subgrade and not necessarily to consolidation in the bituminous

layers.

Unlike the higher density courses at site 3, sites 1 and 2 had

binder courses of substantially lower densities (127.4 to 130.4 pcf). A

careful examination of the core material revealed a low-weight, porous

aggregate comprising the mix. These reduced densities could have possi-

bly resulted in lower overall strengths of the binder layers, thus

influencing the transfer of higher stresses to the underlying materi-

al. This premise will be discussed in Chapter 5.

The low densities and associated high air void contents of the sand

asphalt are typical for the type construction used back in the forties.

In conferring with officials at the Florida Department of Transporation

(FDOT), the popular construction method used then was an asphalt emul-

sion combined with the natural soil and compacted in approximately 4-in.

lifts. This technique, called a sand bituminous road mix or SBRM,

suited the era quite well. Today, however, it is unacceptable for use

in quality road construction because of the difficulty of controlling

aggregate gradation, asphalt content, and compaction in the field.



4.4 Determination of Maximum Density of Bituminous Layers

Tests for maximum specific gravity were done in accordance with

AASHTO T 209-82. Six-inch cores selected from each site were tested to

determine maximum densities for each asphalt pavement layer. Table 4.2

presents the maximum theoretical density.







Air void contents were calculated using the MTD. Given similar

mixtures, for every 1 percent increase in air void content, there is a

proportional decrease in bulk unit weight. Air void contents of an

asphalt concrete pavement which exceed the Marshall Mix Design criteria

of 3 to 5 percent can result in significant reductions in strength,

demonstrate high deformability, and exhibit lower fracture strain toler-

ance. The data in Table 4.2 shows air void contents above 5 percent for

every asphalt concrete layer except inside the wheel path of site 3.

Air void content is an indicator of the durability and performance life

of flexible pavements. Therefore, this could, in part, explain the

higher degree of cracking seen at sites 1 and 2. Lower MTDs in the

underlying asphalt concrete layers confirmed the use of low-weight

aggregates.

The relatively high MTDs and air voids (21.0 to 29.2 percent) for

the sand asphalt indicated poor field compaction during airfield con-

struction. Today, sand asphalt hot mix (SAHM), and not SBRM, is used to

meet design specifications which require air voids below 16 percent and

minimum asphalt contents of 6 percent (99).



4.5 Determination of Asphalt Content and Gradation
by Quantitative Extraction

Quantitative extraction was done on representative cores from each

site and layer in accordance with AASHTO T 164-80. The paving mixtures

were extracted using a solvent, trichloroethylene, to separate the bitu-

men from the aggregate. The asphalt content was calculated by the

difference between the mass of the original sample and the mass of the







extracted aggregate, moisture content, and ash from an aliquot of the

extract. Sieve analyses were performed on the separated aggregate to

determine the gradation of each bituminous layer. Results from these

tests are presented in Appendix C.

Plots of the sieve analyses are given in Figures 4.2 through 4.4.

Layers of similar gradation were grouped together and designated either

Group A, B, or C. A final comparison is made of all three groups in

Figure 4.5 using the average values from the first three plots. Plots

for Group A and B give the maximum density based on maximum aggregate

size and is shown by a dashed line through the origin. A deviation from

this line represents a more uniformly graded mixture. Design specifi-

cations, however, stipulate the range of deviation allowed that will

still meet strength and compaction requirements.

Six of the seven asphalt concrete layers were placed in Group A and

are shown in Figure 4.2. The gradation band shows well-graded mixtures

with an average filler content (< No. 200) of 5.1 percent. Mineral

filler contents under 6 percent are desired for reasons of stability.

Site 2, layer 2, was the only asphalt concrete layer in Group B

(Figure 4.3). This mixture was more uniformly graded then the other

asphalt concrete mixtures which accounted for its high air void content

(13.6 percent). The amount of mineral filler present was 5.0 percent.

Group C (Figure 4.4) contained the sand asphalt mixtures for all

three sites. These layers were uniformly graded and displayed high air

void contents (21 to 29 percent). Mineral filler ranged between 2.6 and

6.2 percent.

The binder contents for the asphalt concrete fell between 4.8 and

6.4 percent, while for the sand asphalt values ranged between 3.6 and




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs