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ASPHALT MIXTURE AND LOADING EFFECTS ON SURFACE-CRACKING OF PAVEMENTS

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ASPHALT MIXTURE AND LOADING EFFECTS ON SURFACE-CRACKING OF PAVEMENTS
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2008

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Asphalt ( jstor )
Crack propagation ( jstor )
Fatigue ( jstor )
Film thickness ( jstor )
Pavements ( jstor )
Perceptual localization ( jstor )
Stiffness ( jstor )
Structural deflection ( jstor )
Thermal stress ( jstor )
Viscosity ( jstor )
City of Gainesville ( local )

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University of Florida
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University of Florida
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Copyright the author. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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8/8/2002
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52244124 ( OCLC )

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ASPHALT MIXTURE AND LOADING EFFECTS ON SURFACE-CRACKING OF PAVEMENTS By OSCAR FERNANDO GARCIA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2002

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ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Reynaldo Roque, for his assistance, supervision and guidance throughout my graduate studies. Without his expertise and willingness to share his knowledge this thesis would not have been possible. Additional thanks go to Dr. Bjorn Birgisson and Dr. Mang Tia for participating as members of my committee. I would also like to thank the Florida Department of Transportation for its financial and technical support. I would like to thank George Lopp for his valuable help in the laboratory. Thanks are also extended to many others for their collaboration and friendship: Tom Grant, Mike Wagoner, Jeff Frank, D.J. Swan, Bensa Nukunya, Christos Drakos and the rest of the students from the Infrastructure Materials and Pavements Group. A very special acknowledgment is sent to Paola Ariza for her love, confidence and patience. Finally, I would like to thank my parents and brothers for their permanent encouragement and love and also my friends back home for their support and motivation while I attended the University of Florida. ii

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TABLE OF CONTENTS page ACKNOWLEDGMENTS..................................................................................................ii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES.........................................................................................................viii ABSTRACT......................................................................................................................xii CHAPTER 1 INTRODUCTION...........................................................................................................1 1.1 Background...............................................................................................................1 1.2 Objectives.................................................................................................................2 1.3 Scope.........................................................................................................................2 1.4 Research Approach...................................................................................................2 2 LITERATURE REVIEW................................................................................................4 2.1 Fracture in Asphalt Pavements.................................................................................4 2.2 Evaluation of Fatigue Fracture in Asphalt Pavements..............................................5 2.2.1 Traditional Fatigue Approach.....................................................................5 2.2.2 Fracture Mechanics Method.......................................................................7 2.2.3 Dissipated Creep Strain Energy..................................................................8 2.3 Mixture Properties Related To Fatigue Resistance.................................................10 2.3.1 Mixture Stiffness.......................................................................................10 2.3.2 Air Void Content.......................................................................................10 2.3.3 Voids in Mineral Aggregate (VMA).........................................................11 2.3.4 Asphalt Content and Film Thickness........................................................11 2.3.5 Binder Viscosity........................................................................................12 2.3.6 Aggregate Gradation.................................................................................13 2.4 Previous Studies......................................................................................................14 2.5 Summary.................................................................................................................14 3 DESCRIPTION OF TEST SECTIONS.........................................................................16 3.1 Locations and Age..................................................................................................16 3.2 Pavement Structure.................................................................................................18 iii

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3.3 Traffic Volumes......................................................................................................19 3.4 Environmental Conditions......................................................................................19 3.5 Performance of the Sections...................................................................................20 3.5.1 Overview...................................................................................................20 3.5.2 Field Observations....................................................................................20 4 MATERIALS AND METHODS...................................................................................24 4.1 Extraction of Field Cores........................................................................................24 4.2 Measuring and Slicing the Field Cores...................................................................24 4.3 Selecting Samples for Testing................................................................................26 4.4 Crack Depth............................................................................................................28 4.5 Mixture Testing.......................................................................................................29 4.6 Asphalt Extractions and Binder Testing.................................................................29 4.7 Aggregate Grading..................................................................................................30 4.8 Volumetric Properties.............................................................................................30 5 FINDINGS AND ANALYSIS......................................................................................31 5.1 Extraction-Recovery Results..................................................................................31 5.1.1 Air Void Content.......................................................................................32 5.1.2 Effective Asphalt Content.........................................................................33 5.1.3 Aggregate Gradation.................................................................................34 5.1.4 Film Thickness..........................................................................................41 5.1.5 Binder Viscosity........................................................................................42 5.2 Mixture Results.......................................................................................................43 5.2.1 Resilient Modulus.....................................................................................43 5.2.2 Creep Compliance.....................................................................................44 5.2.3 Indirect Tensile Strength...........................................................................45 5.2.4 m value......................................................................................................46 5.2.5 Failure Strain.............................................................................................47 5.2.6 Fracture Energy and Dissipated Creep Strain Energy..............................48 5.3 Non-Destructive Testing (FWD)............................................................................50 5.3.1 Pavement Structures..................................................................................51 5.3.2 Loading Stresses.......................................................................................52 5.3.3 Thermal Stresses.......................................................................................53 5.4 Crack Growth Model..............................................................................................54 5.5 Individual Analysis of the sections.........................................................................58 5.5.1 State Road 16 (SR 16)...............................................................................58 5.5.2 US 19........................................................................................................59 5.5.3 State Road 375 (SR 375)...........................................................................60 5.5.4 Florida Turnpike (TPK)............................................................................61 5.5.5 NW 39 th Avenue (NW 39)........................................................................61 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS..................................63 6.1 Summary of Findings..............................................................................................63 iv

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6.2 Conclusions.............................................................................................................63 6.3 Recommendations...................................................................................................64 APPENDIX A SUMMARY OF NON-DESTRUCTIVE TESTING (FWD) .......................................66 B SUMMARY OF FDOT FLEXIBLE PAVEMENT CONDITION SURVEY DATABASE ......................................................................................................................97 C SUMMARY OF VOLUMETRIC PROPERTIES ......................................................100 D SUMMARY OF MIXTURE TEST RESULTS..........................................................103 E CRACK GROWTH MODEL RESULTS ...................................................................107 LIST OF REFERENCES.................................................................................................112 BIOGRAPHICAL SKETCH...........................................................................................114 v

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LIST OF TABLES Table Page 3.1. Location of the Sections..............................................................................................17 3.2. Age of the Sections.....................................................................................................17 3.3. Thickness of the layers................................................................................................18 3.4. Layer Moduli of the Sections .....................................................................................19 3.5. Traffic Volume of the Sections...................................................................................19 4.1. Number and Location of the Cores.............................................................................25 4.2. Average Dimensions...................................................................................................27 4.3. Samples Average Bulk Specific Gravity ....................................................................27 4.4. Cracking Criteria.........................................................................................................28 4.5. Crack Ratings..............................................................................................................28 5.1. Air void contents.........................................................................................................32 5.2. Base, Sub-base and Sub-grade Moduli Values ..........................................................51 5.3. E 1 /E 2 ratios...................................................................................................................52 5.4. Estimated Loading Stresses ........................................................................................53 5.5. Thermal Stresses.........................................................................................................54 A.1. Deflections From US 19-1U......................................................................................66 A.2. Deflections From US 19-2C ......................................................................................70 A.3. Deflections From TPK-1U.........................................................................................74 A.4. Deflections From TPK-2C.............. ..........................................................................78 vi

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A.5. Deflections From NW 39-1C.....................................................................................82 A.6. Deflections From NW 39-2U.....................................................................................86 C.1. Bulk Specific Gravity for each sample ....................................................................100 C.2. Effective Asphalt Content, Film Thickness and VMA............................................101 D.1. Total Resilient Modulus...........................................................................................103 D.2. Creep Compliance....................................................................................................103 D.3. Indirect Tensile Strength Results.............................................................................103 D.4. m Value................................................................................................................... .104 D.5. Initial Tangent Modulus...........................................................................................104 D.6. Failure Strain............................................................................................................104 D.7. Fracture Energy........................................................................................................105 D.8. Dissipated Creep Strain Energy Calculation............................................................105 vii

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LIST OF FIGURES Figure Page 2.1 Fatigue Crack Growth Behavior (After Jacobs, 1995)..................................................8 2.2 Dissipated Creep Strain Energy (After Zhang et al., 2001)...........................................9 3.1 Longitudinal Crack from NW 39-1C...........................................................................21 3.2 Detail of Longitudinal Crack from NW 39-1C............................................................21 3.3 Coring Section on US 19-1U.......................................................................................22 3.4 Overview of US 19-2C................................................................................................22 3.6 Longitudinal Cracks on TPK-2C.................................................................................23 4.1 Coring at the Florida Turnpike....................................................................................25 4.2 Core from the Florida Turnpike...................................................................................26 5.1 Air Void Content and Comparison Between WP and BWP Sections . .......................33 5.2. Effective Asphalt Content...........................................................................................34 5.3 Gradation Curves from SR 16......................................................................................36 5.4 Gradation Curves from US 19.....................................................................................37 5.5 Gradation Curves from SR 375....................................................................................38 5.6 Gradation Curves from TPK........................................................................................39 5.7 Gradation Curves from NW 39....................................................................................40 5.8 Theoretical Film Thickness (micro-meters).................................................................41 5.9 Binder Viscosities........................................................................................................42 5.10 Resilient Modulus at 10C (GPa)...............................................................................44 viii

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5.11 Creep Compliance at 1000 Seconds (1/GPa).............................................................45 5.12 Indirect Tensile Strength (MPa).................................................................................46 5.13 m-Value......................................................................................................................47 5.14 Failure Strain from the Strength Test (microstrain)...................................................48 5.15 Fracture Energy from the Strength Test (KJ/m 3 ).......................................................49 5.16 Dissipated Creep Strain Energy (KJ/m 3 )...................................................................50 5.17. Number of Cycles to Failure for DCSE....................................................................55 5.18. Number of Cycles to Failure for FE.........................................................................56 5.19. Comparison Between DCSE and FE Predictions.....................................................57 5.20. Predictions for Propagation to 50mm.......................................................................58 A.1. US 19-1U Deflections for 7000 kips..........................................................................67 A.2. US 19-1U Deflections for 9000 kips..........................................................................68 A.3. US 19-1U Deflections for 11000 kips........................................................................69 A.4. US 19-2C Deflections for 7000 kips..........................................................................71 A.5. US 19-2C Deflections for 9000 kips..........................................................................72 A.6. US 19-2C Deflections for 11000 kips........................................................................73 A.7. TPK1U Deflections for 7000 kips.............................................................................75 A.8. TPK1U Deflections for 9000 kips.............................................................................76 A.9. TPK1U Deflections for 11000 kips...........................................................................77 A.10. TPK 2C Deflections for 7000 kips...........................................................................79 A.11. TPK 2C Deflections for 9000 kips...........................................................................80 A.12 TPK 2C Deflections for 11000 kips..........................................................................81 A.13 NW 39-1C Deflections for 7000 kips.......................................................................83 A.14 NW 39-1C Deflections for 9000 kips.......................................................................84 A.15 NW 39-1C Deflections for 11000 kips.....................................................................85 ix

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A.16 NW 39-2U Deflections for 7000 kips.......................................................................87 A.17 NW 39-2U Deflections for 9000 kips.......................................................................88 A.18 NW 39-2U Deflections for 11000 kips.....................................................................89 A.19 Measured and Computed Deflections for US 19-1U Location 2..............................90 A.20 Measured and Computed Deflections for US 19-1U Location 5 .............................90 A.21 Measured and Computed Deflections for US 19-1U Location 9 .............................90 A.22 Measured and Computed Deflections for US 19-2C Location 4..............................91 A.23 Measured and Computed Deflections for US 19-2C Location 8 .............................91 A.24 Measured and Computed Deflections for US 19-2C Location 9 .............................91 A.25 Measured and Computed Deflections for TPK 1U Location 1.................................92 A.26 Measured and Computed Deflections for TPK 1U Location 6.................................92 A.27 Measured and Computed Deflections for TPK 1U Location 10...............................92 A.28 Measured and Computed Deflections for TPK 2C Location 6.................................93 A.29 Measured and Computed Deflections for TPK 2C Location 7.................................93 A.30 Measured and Computed Deflections for TPK 2C Location 9.................................93 A.31 Measured and Computed Deflections for NW39-1C Location 2.............................94 A.32 Measured and Computed Deflections for NW39-1C Location 8.............................94 A.33 Measured and Computed Deflections for NW39-1C Location 10...........................94 A.34 Measured and Computed Deflections for NW39-2U Location 1.............................95 A.35 Measured and Computed Deflections for NW39-2U Location 5.............................95 A.36 Measured and Computed Deflections for NW39-2U Location 10...........................95 B.1 Cracking Ratings from SR 16 .....................................................................................97 B.2 Cracking Ratings from US 19.....................................................................................97 B.3 Cracking Ratings from TPK........................................................................................98 B.4 Cracking Ratings from NW 39 ...................................................................................98 x

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E.1 Crack Propagation Rate for SR 16-4C ......................................................................107 E.2 Crack Propagation Rate for SR 16-6U......................................................................107 E.3 Crack Propagation Rate for US 19-1U......................................................................108 E.4 Crack Propagation Rate for US 19-2C......................................................................108 E.5 Crack Propagation Rate for SR 375-1U....................................................................109 E.6 Crack Propagation Rate for SR 375-2C ....................................................................109 E.7 Crack Propagation Rate for TPK-1U ........................................................................110 E.8 Crack Propagation Rate for TPK-2C.........................................................................110 E.9 Crack Propagation Rate for NW 39-1C ....................................................................111 E.10 Crack Propagation Rate for NW 39-2U ..................................................................111 xi

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering ASPHALT MIXTURE AND LOADING EFFECTS ON SURFACE-CRACKING OF PAVEMENTS By Oscar Fernando Garcia August 2002 Chairman: Dr. Reynaldo Roque Cochairman: Dr. Bjorn Birgisson Major Department: Civil and Coastal Engineering The main mode of flexible pavement distress encountered in Florida is longitudinal cracking. It has been found that this mode of failure is caused primarily by the tensile stresses under radial truck tires and that it initiates in the top of the pavement and propagates downwards. Therefore, the asphalt layer immediately beneath the friction course is one factor that strongly affects crack propagation. Several sections of pavement throughout Florida, which exhibited variable levels of longitudinal wheel path cracking, were studied. Asphalt cores were obtained from all sections for laboratory evaluation. Falling weight deflectometer (FWD) tests were performed to evaluate pavement structure. Resilient modulus, creep compliance and indirect tensile strength tests were performed on the cores to obtain mixture properties known to relate to fracture resistance. xii

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Binder extraction and recovery were also performed on cores to determine aggregate gradation, binder viscosity and mixture volumetric properties. The data obtained were analyzed to identify the factors that appeared to most strongly affect the surface-cracking performance of the sections. The goal was to identify key mixture properties and characteristics, as well as loading, structural, and/or environmental conditions that most likely led to cracking in each cracked section or that mitigated cracking in uncracked sections. The findings indicated that surface cracking performance was adequately explained by the cracking mechanisms and associated crack growth model developed in prior research conducted at the University of Florida. In fact, it was necessary to analyze the properties within the context of this model to satisfactorily explain observed performance. The primary mixture factors found to result in poor cracking performance in these sections were high stiffness, low compliance, excessively fine mixtures, gap gradations and low film thickness. It was also determined that the quality of friction course and base course may also have a strong influence on surface cracking. xiii

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CHAPTER 1 INTRODUCTION 1.1 Background Today, in the state of Florida, one of the most common modes of fatigue distresses in flexible pavement is surface-initiated longitudinal wheel path cracking. This mode of failure was identified relatively recently, so the mechanisms that influence it are not clearly understood. Myers (1997) found that this mode of distress maybe initiated by tensile stresses under the ribs of radial truck tires, perhaps combined with thermally induced stresses. Trench section and cores from pavement sections with substandard crack ratings have proven that cracks initiate at the surface and propagate downwards reducing the serviceability of the pavements. Myers (1997) also found that longitudinal wheel path cracking primarily occurs under critical conditions. Therefore, existing design and evaluation methods that are based upon average conditions (e.g., traditional fatigue) may be inadequate to study this type of failure. Most of the traditional approaches do not consider critical conditions near the surface of the pavements. Additionally, the loading conditions and pavement structural characteristics considered in these approaches may not adequately represent important features of actual contact stresses and discontinuities that exist in real pavements. Moreover, temperature gradients, which Myers found to have a strong effect on stress development, are also not considered in traditional approaches. Surface initiated longitudinal cracking has resulted in significant rehabilitation costs, hence efforts must be made to understand more clearly the initiation and 1

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2 propagation mechanisms and to identify the key mixture properties that influence this form of distress. Acquiring further knowledge would lead to improved testing procedures, specifications and design criteria that result in mixtures and pavements that are more resistant to surface initiated cracking. 1.2 Objectives The main objectives of this research are Evaluate field sections to identify the key factors, particularly mixture characteristics and properties that most strongly influenced their surface cracking performance. Provide recommendations for improved guidelines for mixture design and evaluation, as well as for pavement design that would mitigate surface cracking in pavements. 1.3 Scope This study is mostly focused on performing an analysis of mixture properties and characteristics that are related to longitudinal cracking and to achieve a better understanding of how these properties affect the performance of pavements. For this purpose, more than 200 specimens were obtained from ten field sections throughout the state of Florida. 1.4 Research Approach The first step in this research was to perform a literature review in order to recognize and evaluate the different hypotheses related to the development of longitudinal wheel path cracks in flexible pavements. An evaluation of the different characteristics and properties that influence the cracking performance of mixtures was also part of the literature review. Subsequently, the field sections were selected by visual inspection from among a number of potential field sections. Age, traffic and performance were obtained for all the

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3 sections selected. The FDOT Flexible Pavement Condition Survey Database was consulted in addition to the visual ratings and performance evaluation performed as part of this research. Asphalt concrete cores from each section were obtained, measured and sliced. The mixture was then tested using the Superpave Indirect Tension Test.(IDT). The binder was extracted and recovered, and binder properties and aggregate gradations were obtained. Falling Weight Deflectometer (FWD) testing was performed in some of the sections in order to determine layer moduli required to calculate stresses relative to a design load and certain thermal conditions. Also, numbers of cycles to failure were predicted according to the crack growth model developed at the University of Florida.

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CHAPTER 2 LITERATURE REVIEW A literature review was conducted in order to understand more clearly the mechanisms of crack development and propagation and the properties and characteristics that influence such mechanisms. It was also necessary to examine the different fatigue approaches and evaluate their relevance in addressing the phenomenon of longitudinal wheel path cracking. 2.1 Fracture in Asphalt Pavements Among the different types of distresses in asphalt pavements, fracture or cracking is one of the most commonly encountered. This type of failure is influenced by many factors such as the thickness of the pavement layers and characteristics of the asphalt mixture. Two types of asphalt pavement cracking have been identified: thermal cracking, which occurs when contraction produced by temperature drops exceed the maximum fracture strain of the HMA layer. The other type of asphalt pavement cracking is associated with fatigue by traffic loads in which the pavement experiences fracture under the repetition of stresses. In recent work, Myers (1997) found that a probable cause of surface initiated longitudinal wheel path cracking is the high tensile stresses underneath the ribs of radial truck tires. In addition, this failure mechanism may be aggravated by thermal stresses. As a result, longitudinal cracks appear in the surface of the pavement and propagate downwards. 4

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5 2.2 Evaluation of Fatigue Fracture in Asphalt Pavements 2.2.1 Traditional Fatigue Approach This method considers that the maximum tensile strain occurs at the bottom of the AC layer developing cracks that propagate towards the surface. In order to predict failure and understand its behavior, several fatigue models have been developed providing different equations that predict fatigue life. Monismith (1981) proposed one of the first fatigue models, which considered the tensile strain applied and a couple of coefficients from strain-controlled laboratory fatigue tests. Later, this equation was improved by incorporating the mixture stiffness and a factor that relates asphalt content with the degree of compaction. This equation is: bmixatfSKN)1()1( where, N f is the number of load repetitions to cause failure, t is the tensile strain applied, S mix is the mixture stiffness, K is a field correlation coefficient and a and b are coefficients determined from beam fatigue. Another equation to determine fatigue life resulted from work under the SHRP program (Sousa et al, 1996). As in the previous model, stiffness and asphalt content were considered as factors that affect fatigue. The equation proposed is: 72.2624.3077.0510738.2ooVFBffSexSN where, N f is the number of load repetitions for failure, S f is the factor that correlates laboratory measurements to field results, e is the base of natural logarithm, VFB is the voids filled with bitumen and e o and S o are the strain and loss stiffness, respectively.

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6 The Asphalt Institute in 1982 developed the following empirical equation for a standard mix with fixed asphalt and air void volumes of 11% and 5% respectively 854.0*291.30796.0ENtf where, N f is again the number of load repetitions to failure, |E*| is the dynamic modulus of the asphalt mixture and t is the tensile strain at the bottom of the asphalt layer. All the different models show the complexity of fracture behavior and the need to include all the variables that influence fatigue failure on asphalt mixtures. These predictions for failure were obtained from laboratory tests developed to simulate field conditions, although the behavior of existing models based on the traditional fatigue approach have not been generally found to match observations in the field. Myers (2000) found that inducing a temperature gradient generates higher tensile stress intensities in asphalt concrete with differences in stiffness throughout the layer than a cracked pavement with uniform stiffness. The failure mechanism is intensified by the effects of the stiffness gradients, which are induced by temperature or aging. The traditional fatigue approach does not consider discontinuity in the AC mixtures nor the fact that the load positioning changes in the field. Likewise, this approach ignores the differential pavement temperature gradients as well as the healing potential of AC mixtures after repeated loading. She concluded that the existing design and evaluation methods are inadequate for predicting longitudinal wheel path cracking because they are based on average conditions and this mechanism occurs only under critical conditions.

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7 2.2.2 Fracture Mechanics Method This method of addressing fracture in AC mixtures introduces the concept of crack propagation and considers the existence of critical conditions near the surface of the pavement. The fracture mechanics approach defines crack growth by considering the stress concentrations caused by discontinuities in the mixture. Cracks initiate and grow as the fracture limits are exceeded at any point in the mixture. Traffic loads or temperature changes may induce stresses. As shown in Figure 2.1, fracture mechanics identifies three different stages; an initiation phase where micro cracks are developed, a propagation phase where micro cracks become macro cracks with stable crack growth; and a disintegration phase where the failure of the material is reached and crack growth become unstable. During the propagation phase it is possible to predict rate of crack propagation in AC mixtures using an empirical relationship known as Paris Law: nKAdNda)( where, a is the crack length, K is the difference between maximum and minimum stress intensity factors during cyclic loading, N is the number of load repetitions and A and n are mixture parameters.

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8 Figure 2.1. Fatigue Crack Growth Behavior (After Jacobs, 1995) A clear advantage of fracture mechanics approach is that crack length is a measurable interpretation of damage, which provides a sound base from which to proceed. 2.2.3 Dissipated Creep Strain Energy Roque et al. (1997) found that the Dissipated Creep Strain Energy (DCSE) limit is one of the most important factors that control crack performance in asphalt mixtures. The DCSE limit (DCSE f ) is the difference between the fracture energy (FE) and elastic energy (EE) at the instant of failure. The fracture energy can be obtained as the area under the stress-strain curve up to the point where the specimen begins to fracture and the elastic energy can be obtained, as shown in Figure 2.2, once the resilient modulus (M R ) of the mixture is known.

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9 Figure 2.2. Dissipated Creep Strain Energy (After Zhang et al., 2001) Zhang (2000) introduced the threshold concept, a state separating the micro-crack and the macro-crack states of a material. She determined that when the threshold was not reached, cracks will not propagate and the mixture will be able to heal. On the other hand, when the threshold is exceeded the crack will grow and the mixture will not heal. Zhang (2000) studied the DCSE f and the yield strength in order to determine which one can be used as a threshold and found that the yield strength is not a factor that affects cracking resistance significantly; therefore it should not be used as a threshold. In contrast, DCSE f was not related to the mode of loading and was found to be constant at a given temperature. For these reasons and because it is closely related to cracking resistance it was determined that DCSE f can be used as a threshold. Therefore, if DCSE f is exceeded, macro damage will occur. Zhang introduced a fundamental crack growth law based on this work and using the principles of viscoelastic fracture mechanics.

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10 2.3 Mixture Properties Related To Fatigue Resistance Fatigue resistance in asphalt mixtures incorporates different material properties that provide an indication of how the materials behave and perform when they are subjected to specific conditions. Therefore, it is necessary to briefly review such properties in order to achieve a better understanding of fatigue failure in asphalt pavements. 2.3.1 Mixture Stiffness Stiffness describes the relationship between stress and strain. For asphalt mixtures, stiffness is a function of loading, time, and temperature. Mixture stiffness is probably most strongly affected by binder stiffness; however, it is also associated with the gradation of the aggregates, the air voids and asphalt content in the mixture An asphalt mixture also stiffens as it ages. Aging in the field is caused by oxidation of asphalt binder, which makes the mixture harder and stiffer. As a consequence of this process, the mixture becomes more brittle and less crack resistant. 2.3.2 Air Void Content The presence of air voids in a compacted mixture allows air or water to flow through it. Air and water flow causes volatization and oxidation, and both processes increase the rate of aging of the mixture, making it stiffer and more brittle. High variation in the air void content along the same field mixture may due to aggregate segregation and/or inadequate compaction. Either is indication of a poor construction process. The air void content in an asphalt mixture is a function of the aggregate gradation, the asphalt content and the degree of compaction. Monismith et al (1985) found that by increasing the air void content substantially, the fatigue life of a mixture is reduced.

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11 2.3.3 Voids in Mineral Aggregate (VMA) VMA is the volume of intergranular void space between the particles of a compacted pavement mixture that includes the air voids and the asphalt not absorbed into the aggregates. VMA is believed to be dependent of the particle arrangement or degree of compaction, range of sizes between fine and coarse aggregate, aggregate shape and air voids. VMA is an important design factor related to the durability of the asphalt mixtures. Better durability can generally be achieved with higher VMA values. However, excessive VMA values with high asphalt content can affect the stability of the mixture because high binder content tends to allow aggregate to be pushed apart. Actually, in the Superpave Mix Design Procedure (SHRP, 1993), minimum VMA is a function of the nominal maximum aggregate size. Nukunya (2001) questioned the use of the same VMA criteria for all mixtures given that many other variables such as gradation, fines content, binder type and volumetric properties vary from mixture to mixture. He proposed that an effective film thickness, instead of VMA be used to control mixture durability. 2.3.4 Asphalt Content and Theoretical Film Thickness Asphalt Content is a very important factor related to the ability of a mixture to resist fatigue. This factor affects other mixture properties such as voids and film thickness. Lower asphalt content generally makes a mixture more stable, but less durable. Inadequate fatigue resistance has generally been associated with an inappropriate amount of asphalt in the mixture. However, Monismith (1981) found that there is a limit to the amount of asphalt that can be included in a mixture. Likewise, Pell and Taylor (1969)

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12 found that once the optimum level of asphalt content is exceeded, the fatigue resistance would decrease. Previous studies performed by Harm and Hughes (1989) demonstrated that small decreases in asphalt below the optimum content could drastically reduce the fatigue resistance of a mixture. The thickness of the asphalt cement film around a particular aggregate is a function of the diameter of the aggregate and the percent of asphalt cement in the mixture. For a given asphalt content, film thickness decreases as the size of the particles decrease or as the surface area of the aggregates increase. Very thin asphalt films contribute to excessive aging of the binder making mixtures less durable, more brittle and more susceptible to cracking. Conversely, thicker asphalt films make mixtures more flexible and durable. Kandhal and Chakraborty (1996) suggested a minimum asphalt film thickness required to produce durable mixtures. They concluded that the optimum film thickness for HMA, compacted to 4 to 5% air void content, should be higher than 9 to 10 microns. For dense mixtures, Campen et al. (1959) recommended that film thickness should be between 6 to 8 microns. 2.3.5 Binder Viscosity Pell and Taylor (1969) and Jimenez (1985) concluded that stiffness of the mixture is not only related to the binder viscosity but it also affects the fatigue resistance of the mixture. Higher binder viscosity was found to increase the number of load applications to cause failure in strain controlled tests. However, note that binder viscosity increases as the mixture ages. Other studies, Malan et al. (1989) and Grant et al. (1979) determined that because low viscosity binder is more favorable to the kneading action of wheels, it was more resistant to surface cracking in pavement sections with heavy volumes of traffic.

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13 Conversely, in pavements with light volumes of traffic, it was found that high viscosity binder reduces surface cracking. Binder viscosity influences performance of pavements, especially in mixtures with high asphalt content. Appropriate viscosity binder should be selected according to the climatic conditions where the mixture is going to be used. For example, unusually high viscosity binders (high stiffness) are not recommended for low temperature regions where climate may cause shrinkage. Likewise, low viscosity binders (low stiffness) may cause flushing or rutting when exposed to a high temperature environment. 2.3.6 Aggregate Gradation Aggregate gradation is one of the most important components of the mixture structure; it is primarily responsible for the mixture response to load. Aggregate gradations affects VMA, surface area and therefore asphalt film thickness. For this reason the selection of good quality aggregates and a suitable gradation are key elements in obtaining a resistant and durable mixture. There are divided opinions related to the effect of aggregate gradation in fatigue resistance. Monismith et al (1985) found that there is an insignificant effect on fatigue resistance that is not explained by air void content and asphalt content. In contrast, Dukatz (1989) stated that increasing the amount of fine aggregates could increase the fracture resistance of a mixture; by doing so, the mixture stiffness increases as well. A coarser structure would allow more fines to be added to the mixture; hence, the increase in the amount of fines depends on the amount of coarse aggregates. Since coarser structures have larger voids, such voids must be filled with finer aggregate in order to avoid permeability problems that can lead to oxidation and thus, reduction in fatigue resistance.

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14 2.4 Previous Studies Sedwick (1998) conducted a study on surface initiated longitudinal wheel path cracking. He used field sections in order to identify mixture characteristics and properties that may be associated with the development of this type of cracking. He concluded that fracture energy density correlated well with the performance of the sections evaluated, which had similar structure and traffic. He found that, since fracture energy density appeared to be the best indicator of crack resistant mixtures, using mixtures with higher fracture energy densities could generally reduce surface initiated longitudinal wheel path cracking. Higher fracture energy densities appeared to be achieved with better aggregate interlock, which depends on the quality and gradation of the aggregates. He also found, from aged field cores, that fracture energy densities lower than 1.0KJ/m3 seemed to indicate a poor crack resistant mixture. 2.5 Summary Traditional methods and approaches that evaluate failure in pavements are not appropriate to analyze longitudinal cracking. The conditions found in the field were found to be different from those considered by these methods and approaches. Fracture mechanics recognizes the existence of critical conditions in the surface of the pavement and introduces the concept of crack propagation. It also identifies the three different stages of cracking: initiation, propagation and disintegration. Cracks developed during the initiation phase are denominated micro-cracks while those developed during the propagation phase are known as macro-cracks. Micro-cracks appear to heal with the appropriate rest periods, while, macro-cracks may never heal. Dissipated Creep Strain Energy is one of the most important factors that control crack performance in asphalt mixtures. The Dissipated Creep Strain Energy limit (DCSE f ) can also be used as the threshold between micro-cracking and macro-cracking. Mixture stiffness is a function of loading, time and temperature; it is associated to the viscosity of the binder and the gradation of the aggregates

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15 Air void content is a key factor that affects age hardening and hence fatigue life. Film thickness is dependent on the size of the aggregate particles and it affects the aging of the binder and the durability and brittleness of mixtures. Aggregates are responsible for the loading response of the mixture. They also affect several mixture characteristics including its durability and resistance to rutting and cracking. For this reason special attention should be devoted to the quality and gradation of the aggregates In previous studies it was found that higher fracture energy densities seemed to reduce the development of surface-initiated longitudinal cracking.

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CHAPTER 3 DESCRIPTION OF TEST SECTIONS Ten field sections from 5 locations throughout the state of Florida were evaluated in this longitudinal cracking study. These sections were chosen in pairs of good and poor performance, with different mixtures, but having the same traffic and same age. This chapter provides a general description of the sections as well as detailed information related to their characteristics. 3.1 Locations and Age Ten sections in 5 counties throughout Florida were selected for the study. These sections are located as follows: State Road 16 (north central Florida), US 19 (north west Florida), State Road 375-377 (north west Florida), Florida Turnpike (south east Florida), and NW 39 th avenue or State Road 222 in Gainesville (north central Florida). Table 3.1 shows the location and characteristics of each section. 16

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17 Table 3.1: Location of the Sections. Section NumberSection NameConditionCodeCountyTravel DirectionSection Limits1State Road 16 Section 4CSR 16-4CBradfordNBMP 1.22 MP 1.772State Road 16 Section 6USR 16-6CBradfordNBMP 2.10 MP 2.153US 19 Section 1UCUS 19-1UTaylorNBMP 0 MP 7.794US 19 Section 2CUS 19-2CTaylorNBMP 7.79 MP 21.275State Road 375 Section 1UCSR 375-1UWakullaNBMP 3.75 MP 5.90 6State Road 375 Section 2CSR 375-2CWakullaNBMP 6.60 -MP 11.57Turnpike Section 1UCTPK 1USt. LucieNBMP 137.6 MP 142.88Turnpike Section 2CTPK 2CSt. LucieNBMP 143.0 MP 152.69NW 39th Ave. Section 1CNW39-1CAlachuaEB34th St. 24th St.10NW 39th Ave. Section 2UCNW39-2UAlachuaEB24th St. 13th St.Note:NB: NorthboundEB: EastboundC: CrackedUC: Uncracked The age of the sections ranged from 9 years to 14 years. Table 3.2 summarizes the age of each section. Table 3.2: Age of the Sections Section Year let Age as of 2002 SR 16-4C 1989 13 SR 16-6U 1989 13 US 19-1U 1993 9 US 19-2C 1993 9 SR 375-1U 1998 4 SR 375-2C 1998 4 TPK-1U 1992 10 TPK-2C 1992 10 NW 39-1C 1988 14 NW 39-2U 1988 14

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18 3.2 Pavement Structure By using a non-destructive testing device such as the Falling Weight Deflectometer (FWD), it was possible to determine the moduli of the pavement layers. It required a back-calculation using elastic layers analysis. The FWD test procedure used a SHRP sensor configuration (i.e. 8”, 12”, 18”, 24”, 36”, and 60”). Each section was tested at 10 locations in the wheel-path, over relatively uncracked pavement, on both sides of the coring area. A half-inch hole was drilled near the FWD test area for temperature measurements; it was filled with mineral oil or glycol for heat transfer. A 9-Kip seating load was applied followed by 7, 9, and 11 Kip loads during which deflection measurements were obtained. The ambient, surface, and sub-surface (2 inches depth) temperature and weather conditions were recorded. FWD tests were performed only for US 19, TPK and NW 39 th avenue. The layer thickness and moduli of the tested sections are shown in Tables 3.3 and 3.4 respectively. Table 3.3. Thickness of the layers (in) Section Friction Course AC Base Sub-base SR 16-4C 0.6 3.0 6.7 12.0 SR 16-6U 0.6 3.0 6.7 12.0 US 19-1U 0.5 9.0 8.0 12.0 US 19-2C 0.5 7.0 8.5 12.0 SR 375-1U 0.6 6.3 7.5 12.0 SR 375-2C 0.6 6.3 7.5 12.0 TPK-1U 0.5 7.0 12.0 12.0 TPK-2C 0.5 6.1 12.0 12.0 NW 39-1C 0.8 4.0 12.5 12.0 NW 39-2U 1.0 3.3 12.5 12.0

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19 Table 3.4: Layer Moduli of the Sections (ksi) Section AC Base Sub-base Sub-grade US 19-1U 550 51 37 24 US 19-2C 1,000 37 22 28 TPK-1U 800 97 39 17 TPK-2C 900 34 19 24 NW 39-1C 1,500 28 71 28 NW 39-2U 1,500 63 58 30 3.3 Traffic Volumes As shown in Table 3.5 the traffic volume, for the sections tested, expressed as Average Annual Daily Traffic, ranged between 3,600 on State Road 375 and 27,219 on Turnpike section 1. These counts correspond to the year in which cores were taken for testing and were provided by the FDOT. 3.4 Environmental Conditions The general environmental conditions of the sections were similar. Florida has a humid climate with average yearly temperatures between 20 and 25 C. Pavement temperatures during the summer increase considerably. Table 3.5: Traffic Volume of the Sections Section AADT (two-way) SR 16-4C 6,700 SR 16-6U 7,300 US 19-1U 5,200 US 19-2C 5,800 SR 375-1U 3,600 SR 375-2C 3,600 TPK-1U 27,219 TPK-2C 25,300 NW 39-1C 25,000 NW 39-2U 26,000

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20 3.5 Performance of the Sections 3.5.1 Overview The Flexible Pavement Condition Survey Database is a record maintained by the Florida Department of Transportation in which ratings of ride, rut and crack are kept in order to prioritize the sections that require rehabilitation. The ratings from the database are based on crack area and crack width. Sections with large cracked areas and sections with wide cracks will both receive a low rating. Appendix B contains the crack ratings of the sections according to the database. This method does not consider crack depth, thus, a section with extensive cracking in the friction course would receive a low crack rating even if the cracks did not propagate into the surface mixture below the friction course. Conversely, a section with limited extend of cracking would receive a higher crack rating, even though the cracks extended well into the pavement. Therefore, since more emphasis was placed on crack depth than on extend of cracking in this study; it was necessary to extract pavement cores directly through the crack in order to observe and measure crack depths 3.5.2 Field Observations Three field visits were conducted to document observations and take pictures of potential test sections. Once the sections were selected, another field trip was made to mark the location from where the cores would be extracted. Two sections were observed in northwest 39 th avenue in Gainesville. The first one (NW39-1C) was severely and continuously cracked. Additionally, it was possible to observe scattered rim marks throughout the section. It was determined that the inner lane was in a more favorable condition as in comparison with the outer lane. Figure 3.2 shows

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21 a crack from this section and Figure 3.3 shows a closer view of these cracks. The second section (NW39-2U) was, generally, in acceptable shape. Figure 3.1 Longitudinal Crack from NW 39-1C Figure 3.2 Detail of Longitudinal Crack from NW 39-1C US 19 sections were also inspected. Section one (US 19-1U) was in an acceptable condition (uncracked) as shown in Figure 3.4. Section 2 (US 19-2C) exhibited cracking right after the construction joint, between the two sections. There was a significant amount of surface cracking within the wheel paths as shown in Figure 3.5.

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22 Figure 3.3 Coring Section on US 19-1U Figure 3.4. Overview of US 19-2C In the Florida Turnpike it was found that in section one (TPK-1U) there were only a few small-scattered cracks on the surface. Conversely, as shown in Figure 3.6, section two (TPK-2C) showed more extensive and continuous cracks. This condition seemed to be worst in the outer lane.

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23 Figure 3.6 Longitudinal Cracks on TPK-2C Otoo (2000), studied field sections from SR 16 with different rubber content in the friction course. As part of his study, a field visit was conducted in October 1999. FDOT engineers that were part of the construction crew for that section assisted this visit and observed that the amount of cracking was relatively insignificant in the field section with 10% rubber content (SR 16-6U) in comparison with the amount of cracking encountered in the 17% rubber content section (SR16-4C).

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CHAPTER 4 MATERIALS AND METHODS After each section was identified and marked, cores were obtained. The cores were measured and sliced into individual specimens for testing. Their bulk specific gravity was determined and soon after they were tested using the Superpave indirect tension test (IDT) developed by Roque et al. (1997). Afterwards, the Rice specific gravity (maximum theoretical density) of the tested samples was determined. The binder and the aggregate were then separated for further individual testing. 4.1 Extraction of Field Cores Numerous cores were extracted from each of the ten sections. Cores were taken from the outside wheel path and from between wheel paths. In order to test the mixture in an undamaged state, care was taken to avoid extracting cores with cracks in them. Additional cores were extracted right in the path of the crack in order to measure its depth. Each core was marked and transported to the laboratory. Table 4.1 shows the number and location of the cores extracted for each section. Figure 4.1 shows coring performed at the Florida Turnpike and Figure 4.2 shows a core from the Turnpike right after extraction. Otoo (2000) analyzed field cores obtained from SR 16 in his study. Some of his cores were used in this study. 4.2 Measuring and Slicing the Field Cores Once the cores were taken to the laboratory, they were inspected and the lifts in each core were measured and recorded. Since cracks originate at the surface, the layer immediately beneath the friction course is primarily responsible for crack propagation. 24

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25 Therefore the properties of this asphalt layer were obtained and analyzed for purposes of the investigation. The limits of this specific layer were identified and marked for slicing. Table 4.1: Number and Location of the Cores Section WP BWP Total SR 16-4C 3 4 7 SR 16-6U 4 4 8 US 19-1U 18 18 36 US 19-2C 18 18 36 SR 375-1U 12 0 12 SR 375-2C 12 0 12 TPK-1U 12 12 24 TPK-2C 8 12 20 NW 39-1C 18 18 36 NW 39-2U 18 18 36 Total 227 Figure 4.1 Coring at the Florida Turnpike

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26 Figure 4.2 Core from the Florida Turnpike The thickness of the sample required for mixture testing should be between 1 to 2 inches, but in some cases the thickness of the samples was slightly less than one inch due to different reasons such as the condition and length of the cores. The average thickness and diameter of the samples for each section can be seen in Table 4.2. After slicing the cores, each sample was marked for future identification with the same code as was used for the core. Because the slicing procedure uses water, the samples remained in an air-conditioned room for a couple of days until they reached their natural moisture content, after which their bulk specific gravity was obtained. 4.3 Selecting Samples for Testing In order to test the mixture, three samples from each section were selected. The selection process consisted of choosing, from each section, the three samples having a bulk specific gravity (G mb ) closest to the average bulk specific gravity of the section. Table 4.3 shows the average bulk specific gravities for each section.

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27 Table 4.2: Average Dimensions Section Average Thickness (in) Average Diameter (in) SR 16-4C 1.054 5.990 SR 16-6U 0.871 5.979 US 19-1U 1.006 5.928 US 19-2C 1.056 5.769 SR 375-1U 0.931 5.937 SR 375-2C 0.969 5.941 TPK-1U 1.185 5.636 TPK-2C 1.223 5.641 NW 39-1C 1.203 5.930 NW 39-2U 1.166 5.921 Table 4.3: Samples Average Bulk Specific Gravity Section Average Gmb SR 16-4C 2.126 SR 16-6U 2.102 US 19-1U 2.299 US 19-2C 2.250 SR 375-1U 2.299 SR 375-2C 2.238 TPK-1U 2.257 TPK-2C 2.225 NW 39-1C 2.186 NW 39-2U 2.275

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28 4.4 Crack Depth As mentioned in section 4.2, additional cores were obtained right through the longitudinal crack in order to measure the depth of the cracks. Sedwick (1998) defined a rating criteria based on the crack depths measured. Tables 4.4 and 4.5 show the cracking criteria and the depth of cracks with the corresponding rating for each section respectively Table 4.4: Cracking Criteria (After Sedwick, 1998) Crack Depth (in) Rating < 0.25 10 0.26 – 0.75 8 0.76 – 1.25 6 1.26 2 4 2.01 3 2 > 3 0 Table 4.5: Crack Ratings Section Average Cracking Depth (in) Performance Rating SR 16-4C 3.163 0 SR 16-6U 1.213 6 US 19-1U Uncracked 10 US 19-2C 4.642 0 SR 375-1U Uncracked 10 SR 375-2C 1.86 4 TPK 1U Uncracked 10 TPK 2C 2.127 2 NW 39-1C 3.252 0 NW 39-2U Uncracked 10

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29 4.5 Mixture Testing The testing procedures used were developed for the FDOT by Roque et al, (1997). The tests performed were: Resilient Modulus, Creep Compliance and Tensile Strength. The results obtained from these three tests are reduced using software developed at the University of Florida. This procedure provided: Resilient Modulus (GPa), Creep Compliance as a function of time (1/GPa), Tensile Strength (MPa), m-value (slope of the linear portion of the compliance-time curve), Failure strain (microstrain), Fracture Energy (KJ/m3) and Dissipated Creep Strain Energy to failure. Additionally Poisson’s ratio is calculated for each set of tests. In preparation for mixture testing, a gage placement device was used to set brass gage points over the two surfaces of the specimens in both vertical and horizontal axes. After the gage points were set, the samples were placed in a low relative humidity chamber for one day to reduce any moisture that may affect the testing Prior to the testing, the specimens were cooled overnight in order to stabilize their temperature. A set of LVDTs were carefully placed on the brass gage points to measure deformations during loading. 4.6 Asphalt Extractions and Binder Testing Each sample was broken down in order to obtain the Theoretical Maximum Specific Gravity or Rice Gravity (G mm ) according to the ASSHTO specification designated as T 209-94. Once the Specific gravity was obtained it was possible to determine the percentage of air voids in each specimen. Later, the samples were placed in the extraction-recovery device where, by using trichloroethylene, the asphalt was separated from the aggregate. Later the trichloroethylene was evaporated from the binder, which was then prepared for testing. The tests performed on the binder consisted of

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30 viscosity determination (at 60C) by the Brookfield Thermosel Apparatus. This test was performed according to ASTM specification designated as D 4402-87. 4.7 Aggregate Grading Sieve analysis was performed on the aggregate once it was separated from the binder. Once the extraction procedure was finished the aggregate was left in the oven overnight in order to evaporate any remains of trichloroethylene in the particles. Then the procedure was completed according to the specifications designated by ASTM as C 136-95a (AASHTO T 27-97), Sieve Analysis of Fine and Coarse Aggregate. 4.8 Volumetric Properties In order to obtain more information related to the characteristics of the mixtures additional volumetric properties of the mixture such as effective asphalt content, and theoretical film thickness were determined. The Effective Asphalt Content was calculated based on the results from the extraction recovery procedure and the proportion of asphalt and aggregate in the mixture. The VMA was obtained from the bulk specific gravity of the mixture, the specific gravity of the aggregate and the aggregate content. Conversely, the film thickness was calculated using the Hveem method, which is based on the surface area factors. The percentage passing each sieve is multiplied by these factors and the surface area is obtained. The film thickness is then calculated by dividing the volume of effective asphalt by the surface area. Results of the volumetric properties calculations are presented in Appendix C.

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CHAPTER 5 FINDINGS AND ANALYSIS This chapter presents analysis of mixture and binder test results for all the sections studied as well as Falling Weight Deflectometer (FWD) test results and stress calculations for some of the sections. Similarly, this chapter includes an analysis to identify the mixture and/or binder properties that appeared to be most closely related to cracking performance. This was accomplished by comparing the properties between each pair of test sections having common traffic and environment. Analyses also involved the use of measured properties to predict cracking performance accounting for the effects of mixture stiffness and pavement structure, as well as the effects of different loading conditions. Further evaluations were conducted to identify mixture characteristics that were common to poor cracking performance. 5.1 Volumetric Properties and Extraction-Recovery Results Cores obtained from pavement sections were sliced and used to determine bulk specific gravities. Some of the specimens were heated and broken down to determine maximum specific gravity (Rice gravity) for calculation of air void content. The binder was then extracted and recovered for viscosity testing and determination of asphalt content. Aggregate gradations were also obtained and used to calculate theoretical film thickness. Results are presented in the sections that follow. 31

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32 5.1.1 Air Void Content Table 5.1 shows the average air void content and standard deviation for cores obtained from each test section. Figure 5.5 shows a comparison of air void content between the test sections. Table 5.1: Air void contents SectionAir void contentStandard DeviationAir void contentStandard DeviationSR 16-4C--10.840.80SR 16-6U--11.030.39US 19-1U2.930.433.180.52US 19-2C3.840.874.481.00SR 375-1U9.330.37--SR 375-2C8.821.08--TPK 1U4.150.303.810.30TPK 2C4.020.144.550.69NW 39-1C7.240.718.860.55NW 39-2U5.730.365.380.23Note: WP: Outside wheel-pathBWP: Between wheel-pathWPBWP

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33 0123456789101112SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSection% Air Void Content WP BWP Figure 5.1. Air Void Content and Comparison Between WP and BWP Sections. For all the sections, the air void content difference between the specimens from the wheel path and the between wheel path was very small. Air void contents from US 19 and TPK sections oscillated from 3% to 5% and had a slight difference with their respective pairs. Sections from NW 39 exhibited air void content between 5% and 9% and NW 39-1C had significantly higher air voids than NW 39-2U. Specimens from SR 16 and SR 375 showed considerably higher air void contents than other sections. Table 5.1 indicates that the air void content of specimens from the good performing sections typically exhibited lower variability (standard deviation from 0.23 to 0.52) than the poor performing sections (standard deviation from 0.14 to 1.08). 5.1.2 Effective Asphalt Content The effective asphalt content was determined from the percent binder absorbed using the aggregates from the extraction recovery. Low asphalt content indicates inadequate coating of the aggregate particles. The FDOT has specified a minimum effective asphalt content of 5.0%. Figure 5.2 show that most of the sections satisfied this

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34 requirement. Effective asphalt content from SR 16 and SR 375 appeared to be in the range of acceptance but all of them performed rather poorly. SR16-6U and SR 375-1U have higher content than their respective pairs. Conversely, US 19-1U, TPK 1U and NW 39-2U, the good performing sections, exhibited higher effective asphalt content than their respective poor performing pairs. For all of these poor performing sections (US 19-2C, TPK 2C and NW 39-1C) the effective asphalt content was lower than 5%. Although the content differences between good and poor performing sections were similar for all the sections, a remarkable difference in effective asphalt content was found in the sections from US 19. 4.24.44.64.85.05.25.45.65.8SR 16-6USR16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionEffective Asphalt Content Figure 5.2. Effective Asphalt Content 5.1.3 Aggregate Gradation Figures 5.3 to 5.7 show and compare the gradation for each pair of test sections. The aggregate from SR 16 was found to be fine-graded. Figure 5.3 shows that both sections appeared to have similar aggregate distribution, low dust content, significant

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35 amount of material between the #100 and #30 sieves and a gap between #30 and #8 sieves. SR 16-6U was found to be slightly finer than SR 16-4C. Similarly, Figure 5.4 shows the gradation curves from the US 19 sections. Both sections were found to be fine graded and had low dust content and large amount of material between #100 and #30 sieves. Additionally, US 19-1U had a gap between the #100 and #30 sieves. According to the curves, US 19-2C appear to have a finer gradation. Figure 5.5 shows the aggregate gradation for SR 375. Both sections had similar characteristics; both were fine graded with low dust content. SR 375-2C appeared to be slightly finer than SR 375-1U. For the TPK, Figure 5.6 shows that both sections had very similar gradation curves, both were found to be fine and slightly gap graded between #8 and #30 sieves. TPK 2C was finer than TPK 1U. Figure 5.7 shows significant differences between the gradations from the NW 39 th avenue sections. NW 39-1C was gap-graded between #50 and #8 sieves and is also coarser than NW 39-2U. On the other hand, NW 39-2U was found to be finer, had less material between the #200 and #30 sieves and was humped between the #100and #30 sieves. These gradations were expected to be slightly finer than the in-place gradations because of the use of aggregates from sliced samples extracted from cores.

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0102030405060708090100Sieve Sizes% Passing Upper Limit Lower Limit SR 16-4C SR 16-6U 0 200 100 50 30 16 8 4 3/8 1/2 3/4 1 36 Figure 5.3 Gradation Curves from SR 16

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0102030405060708090100Sieve sizes% Passing Upper Limit Lower Limit US 19-1U US 19-2C 0 200 100 50 30 16 8 4 3/8 1/2 3/4 1 37 Figure 5.4 Gradation Curves from US 19

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0102030405060708090100Sieve sizes% Passing Upper Limit Lower Limit SR 375-1U SR 375-2C 0 200 100 50 30 16 8 4 3/8 1/2 3/4 1 38 Figure 5.5 Gradation Curves from SR 375

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0102030405060708090100Sieve sizes% Passing Upper Limit Lower Limit TPK 1U TPK 2C 0 200 100 50 30 16 8 4 3/8 1/2 3/4 1 39 Figure 5.6 Gradation Curves from TPK

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0102030405060708090100Sieve sizes% Passing Upper Limit Lower Limit NW 39-1C NW 39-2U 0 200 100 50 30 16 8 4 3/8 1/2 3/4 1 40 Figure 5.7 Gradation Curves from NW 39

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41 5.1.4 Theoretical Film Thickness The theoretical asphalt film thickness of each section was determined from the aggregate gradation and effective asphalt content. The technique used was the Hveem method (NCAT, 1991), which is based on surface area factors. Previous studies, Kandhal proposed a minimum film thickness of 8 m, however, as shown in Figure 5.8, most of the sections studied exhibited lower thickness than the proposed. 012345678910SR 16-6USR16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionTheoretical Film Thickness (micro-meters) Figure 5.8 Theoretical Film Thickness (micro-meters) All the sections, except for SR 375-1U, exhibited lower film thickness than 8 m. Similarly, all the sections, except SR 16, showed significant differences between the good and poor performing sections. In every case, the good performing section had higher film thickness than the respective poor performing pair. This trend is probably due to the effective asphalt content, which was also found to be considerably low for the poor performing sections and in every case was lower than the respective good performing pair. The poor performing sections TPK 2C and NW 39-1C had film thickness below 6m which are considered to be excessively low.

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42 5.1.5 Binder Viscosity The viscosity of the binder increases as the mixture ages. Therefore, it is related to its age, cracking condition, air void content, and consequently to the degree of compaction. High air void content and variability could be a cause for high viscosities. Figure 5.9 shows the binder viscosities for the different test sections 05,00010,00015,00020,00025,00030,00035,00040,000SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionBinder Viscosity (poises) Figure 5.9 Binder Viscosities Figure 5.9 shows that in the SR 16 sections, despite their similar air void content; there was a significant difference in the viscosity of the binder. SR 16-4C had approximately twice the viscosity of SR16-6C probably due to the cracking condition which was more severe for SR 16-4C, which resulted in faster age-hardening than for SR 16-6C. For the US 19 sections, the difference found in the air void content seems to reflect in the binder viscosity, where, as occurred with the air void content, US 19-2C had higher values than US 19-1U. Similarly, the binder viscosities for the SR 375 sections were found to be, as the air void content, very similar between the two sections. The TPK

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43 and NW 39 th avenue sections show remarkable differences in binder viscosity in comparison with their respective pair. In both cases, the good performing sections (TPK 1U and NW 39-2U) had approximately twice the viscosity of the corresponding poor performing pair (TPK 2C and NW 39-1C) and there was no relationship between the air void content and the binder viscosity for these two sections. On average, higher binder viscosities were found in SR 16 and NW 39 th avenue, which are the oldest sections (13 and 14 years old as of 2002, respectively). Lower viscosities corresponded to the younger sections, TPK, US 19 and SR 375 (10, 9 and 4 years old as of 2002, respectively). 5.2 Mixture Results As previously stated, the mixture tests performed were resilient modulus, creep compliance at 1000 seconds and tensile strength. All tests were performed at 10C. As a result of these tests several mixture properties were obtained, including resilient modulus, creep compliance, mvalue, tensile strength, fracture energy density, failure strain, initial tangent modulus and dissipated creep strain energy limit (DCSE f ). 5.2.1 Resilient Modulus The resilient modulus (M R ) is a measure of the elastic stiffness of the mixture; increasing binder stiffness and/or improving aggregate interlock increases M R . Figure 5.10 shows the results obtained from this test. A remarkable difference in M R was found on US 19, where US 19-2C had approximately 70% higher M R than US 19-1U. Similarly, TPK 1U had almost 40% higher M R than TPK 2C. The differences found in these sections may be related to the binder viscosity, which were significantly higher for the stiffer mixtures (higher M R ). Another difference in M R results was found on the SR 375 sections, where SR 375-1U had the highest MR value of all the sections, almost 40%

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44 higher than SR 375-2C. M R . Results from SR 16 and NW 39 th avenue were very similar for each pair. It was not possible to establish a straight relationship between the stiffness of the mixtures (M R ) and the performance of the sections, however, the stresses in the bottom of the AC layer are expected to be higher for those sections with higher M R . 02468101214161820SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionResilient Modulus (GPa) Figure 5.10 Resilient Modulus at 10C (GPa) 5.2.2 Creep Compliance Creep compliance relates to a mixture’s ability to relax stresses, particularly thermal stresses. Mixtures with higher compliance can relax stresses more quickly and will develop less thermal stresses than mixtures with lower compliance. Figure 5.11 shows the creep compliances at 1000 seconds loading time for each test section. Significant differences were found among the pairs of every section except for SR 16 where compliances at 1000 seconds were similar. US 19-2C and SR 375-1U exhibited lower creep compliance and higher M R than their respective pairs. In contrast, TPK 1U, which had higher M R also had higher creep compliance. The sections from NW 39 th

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45 avenue, despite their similar M R , showed a considerable difference in creep compliance, where NW 39-2U has a higher compliance than NW 39-1C which has a very low value, the lowest of all the sections. Again, the results imply that there is not a direct relationship between the creep compliance at 1000 seconds of the sections and their performance. A major effect of thermal stresses was expected in the sections with lower compliance, such as US 19-2C, TPK 1U, and NW 39-1C 0123456789SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionCreep Compliance at 1000 seconds (1/GPa) Figure 5.11 Creep Compliance at 1000 Seconds (1/GPa) 5.2.3 Indirect Tensile Strength Tensile strength is the maximum tensile stress that a specimen can tolerate before fracture. Figure 5.12 shows the tensile strength for each section. Tensile strength results were consistent with the previous results. US 19-2C exhibited higher tensile strength than its respective pair. According to its performance and high stiffness and since high tensile strength is generally encountered on brittle mixtures, it is possible that US 19-2C was, in fact, a brittle mixture. Similar conclusion could be made for the SR 375 pair of sections;

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46 both had high tensile strength (SR 375-1U higher than SR 375-2C) and excessively high stiffness. For SR 16 low tensile strength was found, which agrees with their poor performance and low stiffness. The TPK and NW 39 th avenue results exhibited similar tensile strength between the two pairs of sections. 0.00.51.01.52.02.53.0SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionIndirect Tensile Strength (MPa) Figure 5.12 Indirect Tensile Strength (MPa) 5.2.4 m value The m-value is an indirect measurement of creep rate of the mixture. Higher m-values indicate higher creep rates, which imply a higher rate of damage for a given stress condition, but also imply higher rates of stress relaxation. In addition, higher m-values are typically associated with softer binders and mixtures with higher Fracture Energy thresholds. Therefore, as with other mixture parameters, a clear relationship between m-value and performance should not be expected, but they correlated reasonably to other binder and mixture properties and characteristics. The different m-values for each test section are presented in Figure 5.13. These m-values were determined by fitting the

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47 measured creep compliance data with the following relationship: D(t)= D 0 +D 1 t m , where D(t) is compliance at time t, D 0 and D 1 are model parameters and m is the m-value. 0.000.100.200.300.400.500.600.70SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionm Value Figure 5.13 m-Value The most significant difference in m-values between paired sections was found on SR 375. For SR 375-2C, the cracked section, the much higher m-value appears to indicate that this section creeped excessively under load, which may have contributed to its poor performance. For SR 16, both sections had relatively high m-values, however SR 16-4C had a higher value than its pair, which agrees with the higher binder viscosity determined on the SR 16-4C section. For US 19, TPK and NW 39, there was no significant difference among the average m values found. 5.2.5 Failure Strain Failure strain is defined as the horizontal strain when cracking initiates during the tensile strength test where the sample is loaded to failure. Generally, mixtures with higher failure strain tend to be more resistant to cracking. Failure strain is a direct measure of a mixture’s brittleness. The failure strain for each section can be seen in Figure 5.14.

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48 020040060080010001200140016001800SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionFailure Strain (microstrain) Figure 5.14 Failure Strain from the Strength Test (microstrain) As shown in Figure 5.14, the sections appeared to have similar Failure Strain between their respective pairs, except for TPK and NW 39 th avenue where TPK 2C and NW 39-2U had significantly higher failure strain than their respective pairs. Low failure strain was found in the SR 16 sections and in NW 39-1C, which indicate that these mixtures maybe brittle and therefore performed poorly. However, from the results there was not a clear relationship between the failure strain obtained and the performance of the sections studied. 5.2.6 Fracture Energy and Dissipated Creep Strain Energy Fracture energy density is the energy per unit volume required to cause fracture of an asphalt mixture. It is determined by calculating the area under the stress-strain curve at the point where the sample begins to fracture. Previous studies (Sedwick, 1997) have concluded that fracture energy can be a good indicator of cracking performance in the field when other conditions such as pavement structure, traffic, and environment are the

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49 same. Figure 5.15 shows the fracture energy values obtained for the different test sections. 0.00.51.01.52.02.53.0SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionFracture Energy (KJ/m3) Figure 5.15 Fracture Energy from the Strength Test (KJ/m 3 ) Fracture energy depends partly on the mixture tensile strength, therefore similar trend was found between the tensile strength results and the fracture energy. Low fracture energies, below 1.0, were found for the SR 16 sections and for NW 39-1C. TPK and US 19 had considerable differences among the pairs. TPK 2C and US 19-2C had higher fracture energies than their respective pairs. Similarly, SR 375-1U had higher fracture energy than SR 375-2C. There was not a clear relationship between the fracture energies found and the performance of the sections; this indicates that factors other than the mixture were probably important for these sections. As mentioned in Chapter 2, the DCSE is the difference between the fracture energy and the elastic energy. Zhang (2000) studied eight field sections and found slightly disagreement determined the DCSE and the fracture energy. However, for the ten test sections corresponding to this study, agreement was found between the fracture energy

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50 and the DCSE. Figure 5.16 shows the DCSE obtained for every test section, and it shows a very similar trend as the fracture energy (Figure 5.15). Sections with higher fracture energy than their respective pair also had higher DCSE. Nevertheless, the findings do not allow establishing a clear relationship between DCSE and the performance of the sections. Calculations of the DCSE for each test section are presented in Appendix D. 0.00.51.01.52.02.5SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionDCSE (KJ/m3) Figure 5.16 Dissipated Creep Strain Energy (KJ/m 3 ) 5.3 Non-Destructive Testing (FWD) As mentioned in Chapter 3, FWD testing was performed on some of the sections in order to determine the layer moduli of the layers through back calculation, which were used to calculate stresses relative to a design load and thermal conditions. According to the deflection basins it was found that for the same loading conditions US 19-2C, TPK 2C and NW 39-1C had higher maximum and average deflections. The measured deflections for each sensor and location are shown in Appendix A.

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51 5.3.1 Pavement Structures The deflection basins were used to obtain layer moduli through back calculation using elastic layer analysis. Table 5.2 shows the layer moduli determined for base, sub-base, and sub-grade using BISDEF and the data from three locations within the tested section with high, intermediate and low deflections. Appendix A also includes the measured and calculated deformations obtained from the back calculation. Measures where cracks were present were not considered. Table 5.2 Base, Sub-base and Sub-grade Moduli Values (ksi) Section AC Base Sub-base Sub-grade US 19-1U 550 51 37 24 US 19-2C 1,000 37 22 28 TPK-1U 800 97 39 17 TPK-2C 900 34 19 24 NW 39-1C 1,500 28 71 28 NW 39-2U 1,500 63 58 30 The modulus values obtained indicated that there were some structural differences between the sections. For US 19 it was found that US 19-2C had almost twice the AC stiffness of US 19-1U. Both sections had also slight differences in base stiffness and subgrade modulus. The difference in sub-base stiffness is very likely associated with fitting error and in every case, would have a relatively small influence on surface stresses. On the other hand, TPK sections had similar AC stiffness, but TPK 2C had significantly lower base stiffness than TPK1U. Similarly, identical AC stiffness were found for the NW 39 sections but, NW 39-1C had lower base stiffness and stiffer sub base than its corresponding pair.

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52 The ratio of AC and base moduli (E 1 /E 2 ) is a good indicator of the magnitude of bending stresses in the surface layer. For similar loading conditions it is known that the higher the E 1 /E 2 ratio is, the higher the bending is. Table 5.3 shows the E 1 /E 2 ratios for the sections analyzed. Table 5.3 E 1 /E 2 ratios Section E 1 /E 2 US 19-1U 11 US 19-2C 27 TPK-1U 8 TPK-2C 26 NW 39-1C 52 NW 39-2U 24 Table 5.3 shows that the E1/E2 ratios were in every case higher for the cracked sections, it was more than double for US 19 and NW 39 th avenue and it was three times higher for the TPK. 5.3.2 Loading Stresses From the layer moduli obtained and using BISAR, it was possible to estimate the relative horizontal stresses at the bottom of the AC layer produced by applying a design load of 9,000 pounds. Since the FWD is rather poor at capturing AC stiffness, the M R values obtained from the laboratory were used to determine the stresses. However, the AC stiffness determined from the FWD tests kept, similar proportion with the M R values. Table 5.4 summarizes the maximum tensile stresses calculated at the bottom of the AC layer.

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53 Table 5.4 Estimated Loading Stresses Section (psi) US 19-1U 87 US 19-2C 151 TPK-1U 116 TPK-2C 162 NW 39-1C 282 NW 39-2U 208 According to the findings from Table 5.4, it was found that the higher stresses of each pair correspond to the cracked section. US 19-2C attracted about 75% higher stresses than US 19-1U, which was almost exclusively due to the higher AC stiffness in the cracked section. Conversely, for the TPK sections, TPK 2C had 40% higher stresses than TPK 1U. Finally, for NW 39 sections, 36% higher stresses were found in NW 39-1C than for NW 39-2U. The stresses found correspond to the E 1 /E 2 ratio from Table 5.3, where the sections with higher modulus ratios also had higher stresses than their respective pairs. 5.3.3 Thermal Stresses In order to determine the effect of thermal stresses on the sections, a simple thermal stress analysis was performed. The thermal strain and the creep compliance at different times were calculated. The thermal stresses were obtained by dividing the strain by the compliance. Table 5.5 summarizes the thermal stresses found for thermal strains associated with 1000 seconds. A high cooling rate of 10C/hour was assumed in these calculations, which are primarily intended to provide a relative comparison between the sections.

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54 Table 5.5 Thermal Stresses Section psi) US 19-1U 1.10 US 19-2C 2.18 TPK-1U 4.04 TPK-2C 2.21 NW 39-1C 13.46 NW 39-2U 9.05 Higher thermal stresses of each pair from US 19 and NW 39 th avenue corresponded to the cracked section. For the US 19 sections it was found that, for the different times, US 19-2C had around twice the stresses of US 19-1U, this result follows the same trend of previous findings of AC stiffness and loading stresses where the same proportion between these two sections was found. The sections from TPK also exhibited significant differences in the thermal stresses encountered, for the different times; TPK 1U had around 85% higher stresses than TPK 2C. Conversely, NW 39-1C had about 48% higher stresses than NW 39-2U. Despite the differences in thermal stresses encountered, due to the low magnitude of these stresses, it was assumed that thermal stresses are inconsequential for TPK and US19 sections. 5.4 Crack Growth Model As mentioned in Chapter 2, Zhang (2000) developed a crack growth model that is actually being improved at the University of Florida. This model is useful in predicting pavement cracking. It is based on the fracture energy of the mixtures. Two phases are studied by the model, an initiation phase where the model predicts the cycles of loading required to begin macro-cracks (threshold point) and a propagation

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55 phase where the model predicts the cycles of loading that an assumed initial crack requires to propagate to different lengths. For the initiation phase, the cycles to initiate macro-cracks were calculated for low, intermediate and high load levels (7000, 9000, and 11000 lbs, respectively). The model predicts the number of cycles according to fracture energy and according to DCSE. Each pair of sections was analyzed at the same time in order to compare the results from the model with the difference in field performance. Figures 5.17 and 5.18 show the predictions for DCSE and FE, respectively. 02,0004,0006,0008,00010,00012,00014,000SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionDCSE Nf 7000 9000 11000 Figure 5.17. Number of Cycles to Failure for DCSE.

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56 02,0004,0006,0008,00010,00012,00014,000SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionFE Nf 7000 9000 11000 Figure 5.18. Number of Cycles to Failure for FE From Figures 5.17 and 5.18, it was found that the good performing sections required, for every loading condition, more cycles in order to achieve the threshold than their corresponding poor performing section. Significant differences in Nf were found, especially for the TPK section where, in average, TPK 1U required 130% more cycles to achieve failure than TPK 2C. Also, NW 39-2U required about 70% more cycles to achieve failure than NW 39-1C. A comparison between the predictions from DCSE and FE from the intermediate loading level condition is shown in Figure 5.19.

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57 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,000SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionNf DCSE FE Figure 5.19. Comparison Between DCSE and FE Predictions From Figure 5.19, it was possible to observe that in most of the cases, except for SR 16-4C and NW 39-1C, Nf was lower for the DCSE than for the FE; this indicates that DCSE appeared to be more critical for these sections. For SR 16-4C and NW 39-1C, the excessively low fracture energy found on the mixture testing made this property more critical than the DCSE. For the propagation phase, every section was analyzed individually. The number of cycles required to reach cracks lengths of 10, 20, 30, 40 and 50 mm for stresses from the same loading conditions as in the initiation phase (7000, 9000, and 11000 lbs) were obtained An initial crack length of 4 mm was assumed. Figure 5.20 shows the number of cycles predicted for the different stress levels for the worst scenario: crack length of 50 mm.

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58 02,0004,0006,0008,00010,00012,000SR 16-6USR 16-4CUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-2UNW 39-1CSectionNf to propagation 7000 9000 11000 Figure 5.20. Predictions for Propagation to 50mm From this figure it is possible to observe that, as occurred in the initiation analysis, in each pair, the good performing section required higher number of cycles in order to propagate the initial crack than the poor performing section. Similarly, the TPK sections showed the most significant difference between sections, TPK 1U required more than 100% repetitions than TPK 2C for every loading condition. Complete results from the model are shown in Appendix E. 5.5 Individual Analysis of the sections 5.5.1 State Road 16 (SR 16) Both of the sections studied in this location, SR 16-4C and SR 16-6U exhibited some cracking. However, Otoo (2000) observed that SR 16-4C exhibited more cracking than SR 16-6U. These sections may have failed due to the high air void content and m-value with very low fracture energy. Additionally, the difference in friction course could have

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59 affected the performance. The 10% rubber content in the friction course of SR 16-6U may have mitigated cracking better than the 17% friction course rubber content on SR 16-4C. The mixture tested, which was immediately beneath the friction course was initially supposed to be the same for both sections, but laboratory results have proven that there were differences in the mixtures properties. From the volumetric properties it could be seen that SR 16-4C had slightly lower air voids, which were high in both sections, and had lower asphalt content than SR 16-6U. Conversely, a noteworthy difference in binder viscosity was found, SR 16-4C had double the viscosity of SR 16-6U. Since SR 16-4C had cracked more severely it is possible to assume that it had age-hardened at a faster rate than SR 16-6U. From the aggregate gradation (Figure 5.3) it was possible to observe that, despite the fact that SR 16-6C is slightly finer than SR 16-4C, both gradations follow the same gap graded trend and the difference among them did not contribute to the performance dissimilarities. From the mixture testing results it could be seen that both sections had similar mixture properties. The most relevant properties found were high m-value and extremely low fracture energy and low DCSE probably caused by the gap-graded distribution. 5.5.2 US 19 According to the mixture testing results, specially fracture energy, it would be expected that US 19-2C would exhibit better performance than US 19-1U but the high stresses due to high stiffness encountered in US 19-2C seemed to overwhelm its higher fracture energy. Failure of US 19-2C was possible due to low asphalt content and film thickness but mainly because of its high stiffness that attracted higher stresses, which could not be released due to its low creep compliance.

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60 Several differences were found between the two sections from this location. From the volumetric properties it was found that US 19-1U had a lower air void content than US 19-2C, however it also had a higher air void variability in the measurements. Additionally, US 19-1U had a higher asphalt content and film thickness than US 19-2C. The binder viscosities were very different for both sections; US 19-2C had more than double the viscosity of US 19-1U. The aggregate gradation was also different; US 19-2C is has finer gradation than US 19-1U (Figure 5.4). This high binder viscosity in addition to the low asphalt content and film thickness and fine gradation for US 19-2C contribute to the poor field performance. From the mixture testing results it was found that the remarkable difference in binder viscosity reflected on the mixture stiffness (MR), likewise, US 19-2C had almost twice the mixture stiffness than US 19-1U. The same trend was observed in the creep compliance, where the section with higher stiffness had the lower compliance and vice versa. US 19-2C also had higher tensile strength and fracture energy than US 19-1U.. 5.5.3 State Road 375 (SR 375) Low fracture energy in addition with high m-value and high air void content maybe the possible causes of failure for SR 375-2C. From the extraction-recovery results it was found that both sections from this location had very similar air void content (high in both sections) and asphalt content, yet SR 375-1U had around 24% more film thickness than SR 375-2C. The binder viscosity test showed that SR 375-1U had a slightly (3%) higher binder viscosity than SR 375-2C. Both aggregate gradations had the same trend; therefore there was no apparent gradation effect on the different performance of these sections. The mixture property results showed that the SR 375-1U mixture is 36% stiffer than SR 375-2C. Correspondingly, SR 375-1U had lower creep compliance than SR 375

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61 2C. Another difference was found in the m-value and fracture energy where SR 375-2C had higher and lower values respectively. 5.5.4 Florida Turnpike (TPK) Probable failure causes for TPK 2C might be related to low stiffness encountered in the base in combination with high m-value with low film thickness in a fine graded mixture. From the volumetric properties it was found that air void content was very alike between both sections; it ranged from 3.81 to 4.55 with variability between 0.3 and 0.69 (Table 5.1). The asphalt contents were also similar for both sections; TPK 1U had only 6% more asphalt than TPK 2C. In contrast, a remarkable difference was found in the film thickness, TPK 1U was 22% higher than TPK 2C. The binder viscosities were also different; TPK 1U had twice the viscosity of TPK 2C. The aggregate gradation showed no particular difference between the two sections. The mixture testing results show that, the difference in binder viscosity reflected on the mixture stiffness, TPK 1U had a higher MR than TPK 2C; similarly, creep compliance was lower for TPK 1U. Tensile strength values were in average higher for TPK 2C as well as m-value. Fracture energy was very similar, although TPK 2C has slightly higher fracture energy than TPK 1U. 5.5.5 NW 39 th Avenue (NW 39) It was possible to believe that failure in this section was caused by low compliance with high concentration of thermal and loading stresses. Furthermore, low compaction (high air void content), accompanied by low asphalt content and low film thickness. All the characteristics mentioned above, seemed to have caused to low tensile strength and facture energy that led to poor performance. Additionally, it was observed

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62 during the field visits that the friction course in NW 39-1C was in a very poor condition exposing the AC layer directly to traffic and environmental effects. Volumetric properties results showed that NW 39-1C had a higher air void content (64%) than NW 39-2U. It also had slightly lower asphalt content and a film thickness 30% lower than NW 39-2U. The binder viscosity for NW 39-1C was around half of the obtained for NW 39-2U. From the mixture testing results it was found that resilient modulus values were very close for both sections. Creep compliance was found to be considerably lower for NW 39-1C as well as the tensile strength. Similarly, failure strain, fracture energy and DCSE were significantly lower for NW 39-1C.

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CHAPTER 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 6.1 Summary of Findings Analyses were conducted to evaluate binder, mixture, structural and environmental effects on observed cracking performance of pavement sections in Florida. The results of these analyses and tests led to the following findings: Pavement structure was found to have an effect on surface-initiated cracking. Prior studies on interstate pavements had indicated that the effects of structure were negligible. Mixtures with excessively high M R and/or low creep compliance appeared to perform poorly because of the higher load and thermal stresses resulting from these properties. It was necessary to consider the effects of thermal stresses to explain the relative cracking performance of some of the sections. This indicates that cracking may result from combined thermal and load stresses. The HMA fracture mechanics based cracking model developed at the University of Florida and associated fundamental mixture properties appeared to properly explain the differences in mixture performance in the field. There was not a clear relationship between any single property and observed field performance. Therefore, it appears that no single property will assure adequate mixture performance. 6.2 Conclusions Based on the findings, the following conclusions may be drawn: It may be necessary to establish specification limits for maximum allowable stiffness (M R ) and minimum allowable creep compliance to assure adequate mixture performance. Thermal stresses were found to be an important part of the cracking mechanism. Therefore, it may be necessary to consider these stresses in the pavement structural design process. 63

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64 It is critical to identify an appropriate design condition that is suitable to evaluate the cracking performance of asphalt mixtures using the fracture resistance parameters from the laboratory. The design condition may be different for mixtures used in different facilities, environments or locations. Since in some of the sections analyzed the friction course appeared to influence differences in performance, more attention should be paid to the evaluation and appropriate design of friction courses. The cracking model developed at the University of Florida appears to adequately represent the cracking mechanisms of asphalt mixtures in the field. 6.3 Recommendations Continue detailed evaluation of field performance of additional test sections to improve the understanding of cracking mechanisms. Create a database of mixture, traffic, environment, and pavement structural characteristics that can be used for the development of future specification criteria. Conduct research to specifically focus on the effects of friction course and pavement structure on surface-cracking performance. Perform mixture tests at two or more temperatures in future investigations, so that the effects of thermal stresses can be analyzed more accurately. Identify appropriate design conditions for mixtures and pavements. Conduct research to specifically focus on the determination of appropriate design conditions for mixtures and pavements..

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APPENDIX A SUMMARY OF NON-DESTRUCTIVE TESTING (FWD)

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Table A1: Deflections (mils) From US 19-1U Sensor Spacing (in) Load Milepost 0 8 12 18 24 36 60 (kips) 1.01 5.18 4.42 3.88 3.24 2.74 1.94 1.08 7,000 1.02 4.62 3.85 3.38 2.80 2.33 1.62 0.85 7,020 1.03 5.17 4.27 3.68 3.03 2.48 1.73 0.90 7,116 1.04 5.62 4.69 4.05 3.28 2.71 1.83 0.96 7,203 1.05 5.22 4.23 3.70 3.04 2.52 1.84 0.98 7,044 1.06 4.83 4.41 3.64 3.00 2.56 1.80 1.03 6,965 1.07 5.43 4.40 3.79 3.15 2.63 1.82 0.96 6,853 1.08 5.41 4.31 3.74 3.09 2.59 1.80 0.99 6,888 1.09 5.82 4.57 3.95 3.22 2.68 1.83 1.08 6,861 1.10 5.03 4.24 3.75 3.14 2.61 1.82 1.08 6,960 1.01 7.03 6.07 5.46 4.57 3.82 2.72 1.46 9,073 1.02 6.43 5.38 4.72 3.93 3.24 2.20 1.19 9,200 1.03 6.78 5.65 4.94 4.02 3.34 2.28 1.20 8,975 1.04 7.37 6.19 5.37 4.37 3.62 2.40 1.27 9,057 1.05 6.98 5.72 5.02 4.13 3.43 2.45 1.30 8,951 1.06 6.59 5.66 5.01 4.17 3.53 2.50 1.41 9,073 1.07 7.34 6.00 5.24 4.33 3.62 2.51 1.33 8,922 1.08 7.34 5.91 5.17 4.30 3.60 2.53 1.37 8,994 1.09 7.76 6.21 5.39 4.42 3.67 2.56 1.38 8,879 1.10 6.85 5.91 5.23 4.39 3.67 2.55 1.48 9,208 1.01 8.93 7.67 6.81 5.72 4.82 3.41 1.78 11,075 1.02 8.15 6.83 6.02 5.04 4.19 2.87 1.49 11,175 1.03 8.63 7.24 6.30 5.23 4.30 2.97 1.50 10,972 1.04 9.26 7.81 6.83 5.57 4.62 3.09 1.58 10,932 1.05 8.87 7.33 6.41 5.33 4.43 3.14 1.65 11,001 1.06 8.30 7.15 6.33 5.29 4.47 3.18 1.74 10,901 1.07 9.20 7.61 6.63 5.54 4.63 3.20 1.67 10,925 1.08 9.15 7.45 6.48 5.43 4.54 3.17 1.71 10,996 1.09 9.83 7.91 6.88 5.67 4.70 3.26 1.72 10,940 1.10 8.46 7.31 6.53 5.49 4.65 3.30 1.78 10,977 66

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01234567891011121314150102030405060Sensor Spacing (inches)US 19-1U Deflections (mils) for 7000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 67 Figure A.1. US 19-1U Deflections for 7000 kips

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01234567891011121314150102030405060Sensor Spacing (inches)US 19-1U Deflections (mils) for 9000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 68 Figure A.2. US 19-1U Deflections for 9000 kips

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01234567891011121314150102030405060Sensor Spacing (inches)US 19-1C Deflections (mils) for 11000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 69 Figure A.3. US 19-1U Deflections for 11000 kips

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70 Table A2: Deflections (mils) From US 19-2C Sensor Spacing (in) Load Milepost 0 8 12 18 24 36 60 (kips) 2.01 5.52 4.85 4.34 3.66 3.00 1.98 1.09 7,151 2.02 5.55 4.66 4.07 3.31 2.72 1.78 0.89 7,095 2.03 5.82 5.06 4.46 3.63 2.96 1.80 0.89 7,028 2.04 5.19 4.22 3.78 3.04 2.48 1.37 0.77 7,095 2.05 5.89 4.70 4.10 3.33 2.67 1.59 0.78 7,060 2.06 6.19 5.18 4.44 3.59 2.88 1.93 1.04 7,063 2.07 5.96 5.07 4.39 3.63 2.91 1.97 1.04 7,004 2.08 5.65 4.77 4.14 3.48 2.71 1.85 1.10 7,036 2.09 6.67 5.13 4.41 3.53 2.84 1.67 0.80 6,960 2.10 6.38 5.24 4.56 3.68 3.03 2.00 0.94 7,012 2.01 7.26 6.36 5.69 4.82 4.00 2.72 1.41 9,054 2.02 7.21 6.09 5.34 4.38 3.60 2.33 1.17 9,041 2.03 7.87 6.79 5.99 4.90 3.97 2.55 1.19 9,089 2.04 7.00 5.81 5.11 4.18 3.39 2.20 1.09 8,895 2.05 7.67 6.28 5.49 4.42 3.57 2.35 1.12 8,922 2.06 8.04 6.79 5.91 4.83 3.97 2.68 1.38 8,951 2.07 7.98 6.67 5.86 4.83 3.95 2.67 1.35 8,875 2.08 7.68 6.42 5.59 4.64 3.72 2.47 1.14 8,903 2.09 8.69 6.91 5.95 4.82 3.90 2.54 1.17 8,803 2.10 8.31 6.96 6.06 4.93 4.05 2.66 1.24 8,835 2.01 9.14 7.93 7.14 6.02 5.04 3.42 1.77 11,075 2.02 9.03 7.63 6.77 5.56 4.57 3.01 1.46 11,175 2.03 9.94 8.39 7.45 6.15 5.00 3.34 1.48 10,972 2.04 9.01 7.44 6.64 5.42 4.34 2.79 1.43 10,932 2.05 9.52 7.96 7.01 5.68 4.59 3.04 1.43 11,001 2.06 10.22 8.49 7.51 6.21 5.12 3.46 1.73 10,901 2.07 10.19 8.48 7.46 6.17 5.07 3.43 1.70 10,925 2.08 9.89 8.22 7.16 6.04 4.81 3.28 1.71 10,996 2.09 10.93 8.76 7.58 6.12 4.96 3.30 1.46 10,940 2.10 10.70 8.89 7.74 6.35 5.22 3.45 1.57 10,977

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01234567891011121314150102030405060Sensor spacing (inches)US 19-2C Deflections (mils) for 7000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 71 Figure A.4. US 19-2C Deflections for 7000 kips

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01234567891011121314150102030405060Sensor spacing (inches)US 19-2C Deflections (mils) for 9000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 72 Figure A.5. US 19-2C Deflections for 9000 kips

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01234567891011121314150102030405060Sensor spacing (inches)US 19-2C Deflections (mils) for 11000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 73 Figure A.6. US 19-2C Deflections for 11000 kips

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74 Table A3: Deflections (mils) From TPK-1U Sensor Spacing (in) Load Milepost 0 8 12 18 24 36 60 (kips) 1.01 5.37 4.49 3.96 3.33 2.83 2.16 1.40 7,116 1.02 4.81 4.10 3.72 3.19 2.82 2.15 1.38 7,195 1.03 4.87 4.18 3.79 3.31 2.94 2.28 1.42 7,047 1.04 4.65 3.89 3.52 3.05 2.63 2.21 1.40 7,063 1.05 5.19 4.26 3.83 3.33 2.93 2.27 1.46 6,920 1.06 4.91 4.08 3.62 3.06 2.66 2.00 1.23 6,917 1.07 4.61 3.87 3.49 3.04 2.68 2.08 1.30 6,917 1.08 4.44 3.70 3.34 2.89 2.55 2.00 1.31 6,980 1.09 4.80 4.04 3.63 3.11 2.75 2.13 1.36 7,028 1.10 5.69 4.70 4.14 3.56 3.10 2.32 1.43 6,941 1.01 7.20 6.04 5.36 4.57 3.92 2.97 1.80 9,166 1.02 6.41 5.52 4.98 4.37 3.84 2.97 1.88 9,153 1.03 6.29 5.47 4.99 4.41 3.90 3.00 1.79 8,986 1.04 6.05 5.15 4.64 4.03 3.52 2.77 1.74 9,157 1.05 7.07 5.93 5.34 4.66 4.11 3.15 1.93 9,110 1.06 6.63 5.61 5.02 4.24 3.65 2.77 1.71 8,927 1.07 6.30 5.35 4.85 4.22 3.70 2.87 1.79 9,070 1.08 5.86 4.93 4.45 3.87 3.41 2.67 1.74 8,927 1.09 6.39 5.47 4.93 4.24 3.72 2.88 1.83 9,216 1.10 7.39 6.14 5.45 4.69 4.10 3.07 1.87 8,824 1.01 9.22 7.76 6.89 5.88 5.06 3.82 2.29 11,211 1.02 8.21 7.04 6.37 5.58 4.90 3.77 2.33 11,295 1.03 8.09 6.98 6.38 5.62 4.97 3.83 2.30 11,059 1.04 7.63 6.52 5.90 5.14 4.49 3.53 2.20 11,144 1.05 8.83 7.43 6.69 5.82 5.09 3.95 2.39 11,112 1.06 8.57 7.21 6.44 5.44 4.70 3.52 2.14 11,033 1.07 7.96 6.75 6.11 5.28 4.66 3.63 2.24 11,048 1.08 7.63 6.45 5.82 5.06 4.45 3.46 2.21 11,059 1.09 8.17 6.98 6.33 5.39 4.76 3.72 2.30 11,144 1.10 9.41 7.87 7.00 6.04 5.25 3.94 2.37 10,921

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01234567891011121314150102030405060Sensor spacing (inches)TPK 1U Deflections (mils) for 7000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 75 Figure A.7. TPK1U Deflections for 7000 kips

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01234567891011121314150102030405060Sensor spacing (inches)TPK 1U Deflections (mils) for 9000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 76 Figure A.8. TPK1U Deflections for 9000 kips

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01234567891011121314150102030405060Sensor spacing (inches)TPK 1U Deflections (mils) for 11000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 77 Figure A.9. TPK1U Deflections for 11000 kips

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78 Table A4: Deflections (mils) From TPK-2C Sensor Spacing (in) Load Milepost 0 8 12 18 24 36 60 (kips) 1.01 6.45 5.48 4.78 4.00 3.33 2.31 1.16 7,068 1.02 5.86 4.99 4.41 3.72 3.14 2.23 1.15 6,877 1.03 6.07 5.08 4.53 3.79 3.22 2.31 1.22 7,036 1.04 6.01 4.96 4.37 3.64 3.04 2.13 1.09 6,830 1.05 6.02 5.04 4.43 3.75 3.18 2.18 1.13 6,944 1.06 6.42 5.31 4.58 3.69 2.98 1.98 1.04 6,989 1.07 6.91 5.72 4.91 3.89 3.11 2.03 1.04 6,893 1.08 5.89 4.78 4.12 3.39 2.77 1.87 0.99 6,928 1.09 5.03 4.15 3.63 2.98 2.50 1.78 0.98 6,980 1.10 5.51 4.49 3.87 3.15 2.61 1.80 0.92 7,012 1.01 8.46 7.19 6.34 5.30 4.44 3.09 1.50 9,161 1.02 7.93 6.75 6.01 5.04 4.31 3.11 1.66 9,030 1.03 7.89 6.69 5.98 5.05 4.29 3.02 1.54 9,057 1.04 8.07 6.72 5.94 5.00 4.20 2.92 1.48 9,010 1.05 8.05 6.80 6.04 5.08 4.26 3.00 1.55 9,041 1.06 8.13 6.77 5.88 4.75 3.84 2.62 1.33 8,827 1.07 8.75 7.31 6.31 5.02 4.04 2.63 1.28 8,919 1.08 7.71 6.31 5.48 4.52 3.73 2.53 1.32 9,038 1.09 6.66 5.52 4.82 4.04 3.38 2.40 1.32 9,038 1.10 7.28 5.96 5.19 4.26 3.57 2.48 1.30 8,914 1.01 10.42 8.89 7.85 6.59 5.55 3.87 1.90 11,207 1.02 9.87 8.43 7.51 6.35 3.84 1.94 11,234 1.03 9.81 8.33 7.46 6.29 5.35 3.80 1.95 11,218 1.04 9.94 8.35 7.41 6.23 5.24 3.72 1.91 11,179 1.05 9.85 8.35 7.42 6.26 5.25 3.71 1.90 11,080 1.06 10.14 8.50 7.39 6.02 4.90 3.29 1.69 11,009 1.07 10.85 9.14 7.93 6.37 5.16 3.42 1.73 11,136 1.08 9.54 7.85 6.79 5.61 4.61 3.20 1.67 11,155 1.09 8.28 6.92 6.08 5.07 4.26 3.04 1.65 11,203 1.10 9.00 7.44 6.48 5.33 4.47 3.11 1.63 11,199 5.39

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01234567891011121314150102030405060Sensor spacing (inches)TPK 2C Deflections (mils) for 7000 kips 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 79 Figure A.10. TPK 2C Deflections for 7000 kips

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01234567891011121314150102030405060Sensor spacing (inches)TPK 2C Deflections(mils) for 9000 kips 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 80 Figure A.11. TPK 2C Deflections for 9000 kips

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01234567891011121314150102030405060Sensor spacing (inches)TPK 2C Deflections (mils) for 11000 kips 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 81 Figure A.12 TPK 2C Deflections for 11000 kips

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82 Table A5: Deflections (mils) From NW 39-1C Sensor Spacing (in) Load Milepost 0 8 12 18 24 36 60 (kips) 1.01 7.31 5.43 4.17 3.08 2.24 1.59 0.76 7,095 1.02 7.89 5.94 4.48 3.09 2.11 1.50 0.77 7,068 1.03 7.68 5.47 4.19 3.04 2.06 1.24 0.73 7,143 1.04 6.57 4.93 3.73 2.72 1.91 1.44 0.78 7,132 1.05 7.22 5.49 4.06 2.77 2.06 1.35 0.82 7,179 1.06 8.59 6.66 5.22 3.15 2.51 1.96 0.93 6,984 1.07 8.80 7.50 5.30 3.91 2.92 1.64 1.24 6,992 1.08 9.30 7.32 5.07 3.77 2.78 1.81 1.07 6,984 1.09 6.14 4.89 3.56 2.25 1.48 0.54 0.39 6,687 1.10 7.69 5.12 3.62 2.31 1.51 0.78 0.36 6,933 1.01 9.48 7.03 5.49 4.09 2.98 2.22 1.04 9,184 1.02 10.10 7.63 5.84 4.09 2.79 1.89 1.02 9,224 1.03 9.72 7.08 5.46 3.99 2.84 1.61 0.97 9,240 1.04 8.51 6.44 4.96 3.64 2.61 1.73 1.03 9,221 1.05 9.74 7.09 5.41 3.85 2.79 1.85 1.15 9,277 1.06 11.04 8.56 6.76 4.32 3.43 2.46 1.28 9,065 1.07 11.14 9.40 6.87 5.14 3.78 2.41 1.30 9,110 1.08 11.89 9.57 6.80 5.06 3.85 2.46 1.37 9,089 1.09 9.37 6.45 4.76 3.06 2.00 1.21 0.50 8,763 1.10 9.67 6.54 4.76 3.15 1.89 0.98 0.48 9,038 1.01 10.91 8.35 6.64 4.95 3.80 2.42 1.36 10,961 1.02 12.02 9.04 6.96 4.96 3.45 2.39 1.24 11,017 1.03 11.41 8.40 6.56 4.85 3.53 2.19 1.22 11,028 1.04 10.21 7.76 6.01 4.46 3.24 2.22 1.26 11,048 1.05 11.29 8.40 6.41 4.62 3.39 2.48 1.35 10,977 1.06 13.22 10.19 8.13 5.38 4.26 3.05 1.63 10,897 1.07 13.11 10.96 8.21 6.18 4.61 2.95 1.73 10,885 1.08 14.05 11.32 8.20 6.22 4.64 3.26 1.62 10,845 1.09 10.80 7.73 5.85 3.84 2.48 1.69 0.65 10,635 1.10 11.22 7.70 5.63 3.67 2.31 1.16 0.53 10,829

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01234567891011121314150102030405060Sensor spacing (inches)NW 39-1C Deflections (mils) for 7000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 83 Figure A.13 NW 39-1C Deflections for 7000 kips

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01234567891011121314150102030405060Sensor spacing (inches)NW 39-1C Deflections (mils) for 9000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 84 Figure A.14 NW 39-1C Deflections for 9000 kips

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01234567891011121314150102030405060Sensor spacing (inches)NW 39-1C Deflections (mils) for 11000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 85 Figure A.15 NW 39-1C Deflections for 11000 kips

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86 Table A6: Deflections (mils) From NW 39-2U Sensor Spacing (in) Load Milepost 0 8 12 18 24 36 60 (kips) 2.01 6.23 4.69 3.66 2.64 1.96 1.32 0.69 7,100 2.02 6.10 4.59 3.56 2.59 1.94 1.02 0.61 7,063 2.03 5.83 4.35 3.49 2.56 1.94 1.56 0.76 7,119 2.04 7.08 5.40 4.28 3.21 2.29 1.78 0.70 7,111 2.05 7.18 5.33 4.11 3.06 2.22 1.59 0.78 7,063 2.06 6.00 4.41 3.44 2.51 1.91 1.41 0.72 7,087 2.07 6.95 5.16 4.02 2.96 2.24 1.14 0.76 7,044 2.08 7.01 5.15 3.95 2.86 2.06 1.52 0.79 7,063 2.09 3.85 2.58 2.26 2.17 2.00 1.17 0.83 7,584 2.10 5.48 3.66 2.69 1.91 1.44 0.95 0.59 7,095 2.01 8.06 6.15 4.82 3.49 2.64 1.75 1.02 9,166 2.02 7.91 6.07 4.89 3.65 2.57 1.84 0.93 9,205 2.03 7.65 5.82 4.68 3.49 2.66 1.93 1.04 9,169 2.04 9.13 7.17 5.73 4.33 3.22 2.07 1.06 9,197 2.05 9.42 7.11 5.59 4.18 3.12 2.21 1.09 9,169 2.06 7.94 5.91 4.67 3.48 2.67 1.78 1.05 9,089 2.07 9.10 6.96 5.49 4.14 3.01 2.39 1.09 9,105 2.08 9.18 6.87 5.35 3.94 2.89 1.96 1.08 9,126 2.09 4.87 3.38 3.00 2.81 2.59 1.89 1.05 9,666 2.10 7.02 4.93 3.73 2.70 1.96 1.46 0.95 9,173 2.01 9.66 7.46 5.90 4.37 3.24 2.27 1.25 11,072 2.02 9.50 7.40 5.97 4.48 3.22 2.22 1.14 11,112 2.03 9.23 7.09 5.79 4.40 3.28 2.54 1.28 11,064 2.04 11.22 8.77 7.06 5.39 3.95 2.68 1.22 11,120 2.05 11.35 8.69 6.87 5.20 3.89 2.73 1.35 11,033 2.06 9.66 7.30 5.85 4.40 3.33 2.51 1.28 11,083 2.07 11.06 8.56 6.85 5.18 3.83 2.75 1.40 11,025 2.08 11.06 8.40 6.63 4.91 3.63 2.59 1.32 11,017 2.09 5.86 3.95 3.60 3.33 3.04 2.31 1.28 11,211 2.10 8.55 6.09 4.61 3.37 2.51 2.02 1.10 10,985

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01234567891011121314150102030405060Sensor spacing (inches)NW 39-2U Deflections (mils) for 7000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 87 Figure A.16 NW 39-2U Deflections for 7000 kips

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01234567891011121314150102030405060Sensor spacing (inches)NW 39-2U Deflections (mils) for 9000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 88 Figure A.17 NW 39-2U Deflections for 9000 kips

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Deflections for 11000 kips (NW39-2)01234567891011121314150102030405060Sensor spacing (inches)NW 39-2U Deflections (mils) for 11000 kips 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 89 Figure A.18 NW 39-2U Deflections for 11000 kips

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90 0123456701020304050607Sensor Spacing (inches)Deflection (mils) for US 19-1U Location 2 0 Measured Computed Figure A.19 Measured and Computed Deflections for US 19-1U Location 2 01234567801020304050607Sensor Spacing (inches)Deflection (mils) for US 19-1U Location 5 0 Measured Computed Figure A. 20 Measured and Computed Deflections for US 19-1U Location 5 012345678901020304050607Sensor Spacing (inches)Deflection (mils) for US 19-1U Location 9 0 Measured Computed Figure A. 21 Measured and Computed Deflections for US 19-1U Location 9

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91 01234567801020304050607Sensor Spacing (inches)Deflection (mils) for US 19-2C Location 4 0 Measured Computed Figure A.22 Measured and Computed Deflections for US 19-2C Location 4 01234567890102030405060Sensor Spacing (inches)Deflection (mils) for US 19-2C Location 8 70 Measured Computed Figure A. 23 Measured and Computed Deflections for US 19-2C Location 8 024681001020304050607Sensor Spacing (inches)Deflection (mils) for US 19-2C Location 9 0 Measured Computed Figure A. 24 Measured and Computed Deflections for US 19-2C Location 9

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92 0123456780102030405060Sensor Spacing (inches)Deflection (mils) for TPK 1U Location 1 70 Measured Computed Figure A.25 Measured and Computed Deflections for TPK 1U Location 1 0123456780102030405060Sensor Spacing (inches)Deflection (mils) for TPK 1U Location 6 70 Measured Computed Figure A.26 Measured and Computed Deflections for TPK 1U Location 6 0123456780102030405060Sensor Spacing (inches)Deflection (mils) for TPK 1U Location 10 70 Measured Computed Figure A.27 Measured and Computed Deflections for TPK 1U Location 10

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93 01234567890102030405060Sensor Spacing (inches)Deflection (mils) for TPK 2C Location 6 70 Measured Computed Figure A.28 Measured and Computed Deflections for TPK 2C Location 6 024681001020304050607Sensor Spacing (inches)Deflection (mils) for TPK 2C Location 7 0 Measured Computed Figure A.29 Measured and Computed Deflections for TPK 2C Location 7 0123456780102030405060Sensor Spacing (inches)Deflection (mils) for TPK 2C Location 9 70 Measured Computed Figure A.30 Measured and Computed Deflections for TPK 2C Location 9

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94 02468101201020304050607Sensor Spacing (inches)Deflection (mils) for NW 39 0 1C Location 2 Measured Computed Figure A.31 Measured and Computed Deflections for NW39-1C Location 2 0246810121401020304050607Sensor Spacing (inches)Deflection (mils) for NW 39 0 1C Location 8 Measured Computed Figure A.32 Measured and Computed Deflections for NW39-1C Location 8 02468101201020304050607Sensor Spacing (inches)Deflection (mils) for NW 39 0 1C Location 10 Measured Computed Figure A.33 Measured and Computed Deflections for NW39-1C Location 10

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95 01234567890102030405060Sensor Spacing (inches)Deflection (mils) for NW 39 70 2U Location 1 Measured Computed Figure A.34 Measured and Computed Deflections for NW39-2U Location 1 024681001020304050607Sensor Spacing (inches)Deflection (mils) for NW 39 0 2U Location 5 Measured Computed Figure A.35 Measured and Computed Deflections for NW39-2U Location 5 01234567801020304050607Sensor Spacing (inches)Deflection (mils) for NW 39-2U Location 10 0 Measured Computed Figure A.36 Measured and Computed Deflections for NW39-2U Location 10

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APPENDIX B SUMMARY OF FDOT FLEXIBLE PAVEMENT CONDITION SURVEY DATABASE

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024681019881990199219941996199820002002YearCrack Rating SR 16-4C SR 16-6U Figure B1: Cracking Ratings from SR 16 024681019881990199219941996199820002002YearCrack Rating US 19-1U US 19-2C Figure B2: Cracking Ratings from US 19 97

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98 024681019881990199219941996199820002002YearCrack Rating TPK 1U TPK 2C Figure B3: Cracking Ratings from TPK 024681019881990199219941996199820002002YearCrack Rating NW 39-1C NW 39-2U Figure B4: Cracking Ratings from NW 39

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APPENDIX C SUMMARY OF VOLUMETRIC PROPERTIES

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Table C1: Bulk Specific Gravity for each sample SR16-4CSR 16-6UUS 19-1U SR 375-1USR 375-2CSampleWPWPWPBWPWPBWPBWPBWPWPBWPWPBWPWPBWPWPWP12.0582.1082.2872.2912.3092.2492.2452.2572.2442.2562.2572.2282.0982.1202.2632.27722.1092.2822.2912.3242.2342.3252.2602.2482.2592.2512.2262.1202.1722.2712.26632.1152.1002.2962.1882.3172.3172.2892.2472.2642.2552.2562.2222.1342.2232.2832.27242.1532.0982.2922.1882.3142.2792.3112.2332.2512.2382.2542.2322.0422.2022.2642.27252.2892.2582.2862.2422.3082.2552.2592.2042.2502.2432.0772.1472.2742.27962.2802.2752.2382.2922.3042.1982.2492.4162.2492.2182.1202.0962.2452.27372.2782.2942.2822.3052.2452.1952.2482.2662.2582.2212.2272.0672.2762.26982.2922.2742.3062.2672.2522.1932.2582.2572.2562.1902.7582.1982.2762.26692.2992.2832.3442.2692.3102.2292.2382.2492.2532.2062.1462.1872.2662.274102.3052.2782.3312.2692.2612.2352.2482.2262.2542.2312.2482.1832.2622.275112.2962.3052.1962.2592.2552.2622.2512.2112.2512.2452.1642.1082.2632.276122.2762.3002.2682.2512.3172.2232.2462.2522.2492.2452.1862.1012.2672.283132.2762.3022.2462.2602.3132.1222.2642.280142.2712.2922.2992.2312.2512.1432.2682.271152.2782.2982.2472.2872.2542.6482.2622.281162.2732.2962.3212.2502.2312.2032.2562.288172.2832.2992.2182.2632.4622.2112.2732.282182.2752.3122.2182.2692.2142.2152.2742.271Average2.1092.1022.2852.2792.2812.2662.2852.2322.2502.2572.2532.2262.2252.1862.2672.275Stand.Dev.0.0390.0050.0100.0360.0450.0230.0310.0260.0070.0540.0030.0160.1650.1250.0090.006NW 39-1CNW 39-2UUS 19-2CTPK 1UTPK 2C 100

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101 Table C2: Effective Asphalt Content, Film Thickness and VMA FactorsSizeft2/lbSR16-4CSR 16-6UUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-1CNW 39-2U192100.00100.00100.00100.00100.00100.00100.00100.00100.00100.0012.5299.0698.8396.6799.5190.5190.00100.0099.3191.0199.219.5289.7289.3494.6792.5582.5681.4794.8794.8176.2393.024.75259.1564.1368.6173.3556.5660.2169.9467.9152.6669.022.36446.9051.6745.4555.5347.0050.1651.6154.2440.2650.261.18841.1344.8637.8743.2134.7437.2444.3246.7336.2941.960.061436.5139.6733.1534.6622.1822.4636.6137.5133.9936.210.033018.8625.0725.3027.3311.2712.6024.5822.8628.1817.560.015607.789.078.5911.706.258.759.1010.7118.918.460.00751605.255.615.194.733.235.664.317.315.475.39SizeSR16-4CSR 16-6UUS 19-1UUS 19-2CSR 375-1USR 375-2CTPK 1UTPK 2CNW 39-1CNW 39-2U192.02.02.02.02.02.02.02.02.02.012.52.02.01.92.01.81.82.02.01.82.09.51.81.81.91.91.71.61.91.91.51.94.751.21.31.41.51.11.21.41.41.11.42.361.92.11.82.21.92.02.12.21.62.01.183.33.63.03.52.83.03.53.72.93.40.065.15.64.64.93.13.15.15.34.85.10.035.77.57.68.23.43.87.46.98.55.30.0154.75.45.27.03.85.35.56.411.35.10.00758.49.08.37.65.29.16.911.78.88.636.040.237.740.626.732.837.843.444.236.6Surface area, m 2 /kg7.198.047.558.135.336.577.558.688.847.335.285.686.297.425.586.615.495.235.376.025.055.305.594.775.094.985.234.954.675.002.3652.3632.3542.3722.3802.3702.3482.3322.3992.391147.6147.4146.9148.0148.5147.9146.5145.5149.7149.2139.8139.1137.7137.0140.2138.1138.5137.9141.6140.250275589519455673738453752285983626351367.57.88.27.17.67.47.77.27.07.50.10.10.10.10.10.10.10.10.10.12.4E-052.2E-052.5E-052.0E-053.2E-052.6E-052.3E-051.9E-051.8E-052.3E-057.206.797.676.169.827.887.125.845.427.0512.0512.8215.5517.8415.3016.6115.3115.2618.7915.88Surface areaGradationSurface area, ft2/lbTotal ACEffective AC, %GmmDensity of mix, lb/ft3Weight of agg, lbsFilm thickness, mVMAAgg. surface area, ft 2 Wt.effective AC, lbsVolume AC, ft3Film thickness, ft

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APPENDIX D SUMMARY OF MIXTURE TEST RESULTS

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Table D1: Total Resilient Modulus 1231234C----8.318.168.248.246U----8.278.238.158.221U7.657.567.467.567.937.947.847.902C13.2113.0413.0313.0913.2312.9212.9513.031U18.1118.2718.1218.17----2C13.3513.3113.1813.28----1U10.9010.6810.7210.7714.0913.8113.9913.962C9.399.229.219.279.179.039.049.081C13.8313.8113.8413.8313.8913.6513.4913.682U13.2112.9913.1213.1114.5414.0914.1414.26SectionAverage MR WP CyclesBWP CyclesAverage MR SR 16ProjectSR 375NW 39TPKUS 19 Table D2: Creep Compliance WPBWP4C-3.6426U-2.8731U9.2367.3812C3.3173.3471U2.474-2C6.092-1U1.8531.7592C4.2733.4321C0.7770.5972U2.1201.078Creep Compliance @1000 Sec. (1/Gpa)TPKNW 39Project SR 16US 19SR 375Section Table D3: Indirect Tensile Strength Results 1231234C----0.830.751.100.896U----1.311.101.321.241U1.741.511.851.701.921.311.351.532C1.712.622.142.162.563.092.552.731U2.742.052.982.59----2C2.282.431.742.15----1U1.412.390.671.491.802.281.811.962C2.371.951.882.071.801.961.331.701C2.332.802.962.701.271.651.301.412U1.822.761.952.182.642.722.592.65US 19TPKNW 39BWP CYCLESSR 375SectionAverage (MPa) SR 16Average (MPa)WP CYCLESProject 103

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104 Table D4: M Value ProjectSectionWPBWP4C-0.636U-0.531U0.530.582C0.410.581U0.46-2C0.65-1U0.550.362C0.440.531C0.540.422U0.550.48NW 39 SR 16US 19SR 375TPK Table D5: Initial Tangent Modulus WPBWP4C-3.26U-3.51U2.73.02C3.84.61U4.9-2C5.2-1U4.34.52C3.73.61C7.96.32U5.55.7Modulus (microstrain)SR 375TPKSectionNW 39Project SR 16US 19 Table D6: Failure Strain WPBWP4C-481.386U-657.171U1612.631480.672C1406.401739.091U1218.41-2C1073.05-1U800.26902.482C1346.701134.541C786.35397.872U929.621148.76SR 375TPKSectionNW 39Failure Strain (microstrain)Project SR 16US 19

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105 Table D7: Fracture Energy WPBWP4C-0.36U-0.51U1.81.72C2.13.31U2.3-2C1.7-1U0.91.12C1.91.31C1.40.32U1.32.0Fracture Energy (KJ/m3)SR 375TPKSectionNW 39Project SR 16US 19 Table D8: Dissipated Creep Strain Energy Calculation MRefSteOEEFEDCSESR 16-4CBWP8.24481.380.89481.270.04810.30.2519SR 16-6UBWP8.22657.171.24657.020.09350.50.4065WP7.561612.631.71612.410.19111.81.6089BWP7.901480.671.531480.480.14821.71.5518WP13.091406.402.161406.230.17822.11.9218BWP13.031739.092.731738.880.28602.21.9140SR 375-1UWP18.171218.412.591218.270.18462.32.1154SR 375-2CWP13.281074.032.151073.870.17401.71.5260WP10.77800.261.49800.120.10310.90.7969BWP13.96902.481.96902.340.13761.10.9624WP9.271346.702.071346.480.23111.91.6689BWP9.081134.541.71134.350.15911.31.1409WP13.83786.352.7786.150.26361.41.1364BWP13.68397.871.41397.770.07270.30.2273WP13.11926.622.18926.450.18131.31.1187BWP14.261148.762.651148.570.24622.01.7538SectionNW 39-1CNW 39-2UUS 19-1UUS 19-2CTPK 1UTPK 2C

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APPENDIX E CRACK GROWTH MODEL RESULTS

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0100020003000400050006000700080009000100001100041020304050Crack Length (mm) 7000 9000 11000 Figure E1: Crack Propagation Rate for SR 16-4C 0100020003000400050006000700080009000100001100041020304050Crack Length (mm) 7000 9000 11000 Figure E2: Crack Propagation Rate for SR 16-6U 107

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108 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00041020304050Crack Length (mm) 7000 9000 11000 Figure E3: Crack Propagation Rate for US 19-1U 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00041020304050Crack Length (mm) 7000 9000 11000 Figure E4: Crack Propagation Rate for US 19-2C

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109 0100020003000400050006000700080009000100001100041020304050Crack Length (mm) 7000 9000 11000 Figure E5: Crack Propagation Rate for SR 375-1U 0100020003000400050006000700080009000100001100041020304050Crack Length (mm) 7000 9000 11000 Figure E6: Crack Propagation Rate for SR 375-2C

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110 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00041020304050Crack Length (mm) 7000 9000 11000 Figure E7: Crack Propagation Rate for TPK-1U 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00041020304050Crack Length (mm) 7000 9000 11000 Figure E8: Crack Propagation Rate for TPK-2C

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111 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00041020304050Crack Length (mm) 7000 9000 11000 Figure E9: Crack Propagation Rate for NW 39-1C 01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00011,00041020304050Crack Length (mm) 7000 9000 11000 Figure E10: Crack Propagation Rate for NW 39-2U

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LIST OF REFERENCES Dukatz, E.L., “Aggregate Properties Related to Pavement Performance,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 58, pp. 492-501, 1989 Grant, M.C., C.P. Marais and D.G. Uys, “An Investigation of an Asphalt Overlay on a Lightly Trafficked Road Showing Premature Cracking,” Proceedings of the Third Conference of Asphalt Pavements in South Africa, Vol. 32, pp. 97-116, 1979. Harm, E.E. and C.S. Hughes, “Paving Specifications and Inspection Related to Pavement Performance,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 58, pp. 595-607, 1989. Honeycutt, K. E., “Effect of Gradation and Other Mixture Properties on the Cracking Resistance of Asphalt Mixtures,” Master’s Thesis, University of Florida, 2000. Huang, Y.H., Pavement Analysis and Design , Prentice Hall, Englewood Cliffs NJ,1993. Jacobs, M.M.J., “Crack Growth in Asphaltic Mixes,” Ph.D. Dissertation, Delft, The Netherlands, Delft University of Technology, 1995. Jimenez, R.A., “A Look at the Art of Asphaltic Mixture Design,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 54, pp. 454-496, 1985. Kandhal P.S. and S. Chakraborty, “Evaluation of Voids in the Mineral Aggregates,” NCAT Report No. 96-4, National Center for Asphalt Technology, March 1996 Malan, G.W., P.J. Strauss and F. Hugo, “A Field Study of Premature Surface Cracking in Asphalt,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 58, pp. 142-162, 1989. Monismith, C.L., “Fatigue Characteristics of Asphalt Paving Mixtures and Their Use in Pavement Design,” Proceedings of the Eighteen Paving Conference, Vol. 54, pp. 124-132, 1981. Monismith, C.L., J.A. Epps, and F.N. Finn, “Improved Asphalt Mix Design,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 55, pp. 347-406, 1985. Myers, L.A., “Mechanism of Wheel Path Cracking That Initiates at the Surface of Asphalt Pavements,” Master’s Thesis, University of Florida, Gainesville, 1997 112

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113 Myers, L.A., “Development and Propagation of Surface-initiated Longitudinal Wheel Path Cracks in Flexible Highway Pavements,” Ph.D. Dissertation, University of Florida, Gainesville, 2000. Nukunya, B. “Evaluation of Aggregate type, Gradation and Volumetric Properties for Design and Acceptance of Durable Superpave Mixtures,” Ph.D. Dissertation, University of Florida, Gainesville, 2001. Otoo, E.A., ”Evaluation of Field Performance of Open Graded Asphalt Rubber Friction Course,” Master’s Thesis, University of Florida, Gainesville, 2000. Paris, P.C. and F. Erdogan, “A Critical Analysis of Crack Propagation Laws,” Transactions of the ASME, Journal of Basic Engineering, Vol. 85, pp. 528-534, 1963. Pell, P. and F. Taylor, “Asphaltic Road Materials in Fatigue,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 38, pp. 371-421, 1969. Roque, R. and B.E. Ruth, “Mechanisms and Modeling of Surface Cracking in Asphalt Pavements,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 50, pp. 396-431, 1990. Roque, R., W.G. Buttlar, B.E. Ruth, M. Tia, S.W. Dickison, and B. Reid, “Evaluation of SHRP Indirect Tension Tester to Mitigate Cracking in Asphalt Pavements and Overlays,” Final Report to the Florida Department of Transportation, University of Florida, Gainesville, 1997. Roque, R., B. Sankar, and Z. Zhang, “Determination of Crack Growth Rate Parameters of Asphalt mixtures Using the Superpave IDT,” Proceedings of the Association of Asphalt Paving Technologists, Vol. 68, pp. 404-433, 1999. Sedwick, S.C., “Effect of Asphalt Mixture Properties and Characteristics on Surface-Initiated Longitudinal Wheel Path Cracking,” Master’s Thesis, University of Florida, Gainesville, 1998 Sousa, J.B., G. Way and J. Harvey, “Performance Based Mix Design and Field Quality Control for Asphalt-Aggregate Overlays,” Transportation Research Board, Record No. 1543, pp. 46-62, 1996. Zhang, Z., “Identification of Suitable Crack Growth Law for Asphalt Mixtures Using the Superpave Indirect Tensile Test (IDT),” Ph.D. Dissertation, University of Florida, Gainesville, 2000.

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BIOGRAPHICAL SKETCH Oscar Fernando Garcia was born in Bogot, Colombia, on January 19, 1976. He graduated from the Colegio Agustiniano Norte in 1993. Later he gained admission to the Pontificia Universidad Javeriana where he received a Bachelor of Science degree in civil engineering in October 1999. Oscar began studying for his master’s degree in civil engineering at the University of Florida in January 2000. 114