Iiil’lwilliilmuul This is to certify that the thesis entitled EFFECT OF POLYMER MODIFICATION ON THE PROPERTIES OF ASPHALT CONCRETE presented by ALEKH S. BHURKE has been accepted towards fulfillment of the requirements for M.S. degree in MATERIALS SCIENCE Major professor Date ///!9~/?9 1/ / , 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution —— LIBRARY Michlgan State University PLACE IN RETURN BOX to remove this checkout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE wgm -...__._._._. 11100 chlRC/DataDmpGS-p.“ EFFECT OF POLYMER MODIFICATION ON THE PROPERTIES OF ASPHALT CONCRETE By Alekh S. Bhurke A THESIS Submitted to Michigan State University In partial fulfillment of the requirements For the degree of MASTER OF SCIENCE Department of Materials Science & Mechanics 1999 A: degradatit a method binder am ot‘this rest Fir Styrene 15 used to m mOT'pholhE fiphalt bi fiphalt C0; mlCmgth “halts b ABSTRACT EFFECT OF POLYMER MODIFICATION ON THE PROPERTIES OF ASPHALT CONCRETE By Alekh S. Bhurke Asphalt pavements fail due to variety of reasons ranging from climatic changes to degradation of material properties. Polymer modification of asphalt has been evaluated as a method to enhance pavement performance. The interfacial adhesion between asphalt binder and aggregate and its effect on the final properties of asphalt concrete is the focus of this research. Five polymers, Styrene Butadiene Styrene (SBS), Styrene Ethylene Butylene Styrene (SEBS), Styrene Butadiene Rubber (SBR), Elvaloy AM and Crumb Rubber were used to modify two viscosity graded asphalt binders, AC5 and ACIO. The microstructure, morphology, failure mechanisms and locus of failure were identified in polymer modified asphalt binder and concrete. Fracture toughness and lap-shear adhesive strength of asphalt concrete were measured. Asphalt binder was found to have an intrinsic network microstructure which plays a role in fracture process. Polymer modification was found to enhance binder-aggregate adhesion, engineering properties and resistance to aging in asphalt concrete. Copyright by ALEKH S. BHURKE 1999 To My loving parents And Sir Pelham Grenville Wodehouse Whose writings never fail to Gruntle me. iv I M directed thi guidance: Il results pres: Dr. Joan Le: I aim research and not hax e bee ACKNOWLEDGEMENTS I wish to thank Dr. Lawrence T. Drzal for his guidance and patience which directed this work. I also thank Dr. Martin Hawley and Dr. Gilbert Baladi for their guidance; their research into other aspects of this tOpic has lent more meaning to the results presented herein. Dr. Eugene Shin, Dr. Steven Rozeveld, Dr. Sia Ravanbaksh and Dr. Joon Lee for their invaluable collaboration and help. I also wish to thank the Michigan Department of Transportation who funded this research and provided access to their laboratory facilities without which this work would not have been possible. List of T31 list of Fig ChapterO 1.1 T) 1.3 X: 1.3 At 1.4 A.‘ 1.5 Pr. Chapter I\ TABLE OF CONTENTS List of Tables ........................................................................................................ viii List of Figures ....................................................................................................... x Chapter One - Introduction ................................................................................... 1 1.1 Types of Pavement Distresses ................................................................. 3 1.2 Need for Polymer Modification of Asphalt ............................................. 5 1.3 Automobile Shredder Residue (ASR) ...................................................... 7 1.4 ASR Modified Cement Concrete ............................................................. 11 1.5 Problem Statement ................................................................................... 14 Chapter Two - Materials ....................................................................................... 16 2.1 Cement and Asphalt Concrete ................................................................. 16 2.2 Asphalt Binder ......................................................................................... 17 2.3 Aggregates Used in Asphalt Concrete ..................................................... 20 2.4 Role of Polymer Modifiers in Improving Asphalt Concrete Properties .. 23 2.5 Description of Polymer Modifiers ........................................................... 25 2.5.1 Styrene Butadiene Styrene (SBS) ................................................... 26 2.5.2 Styrene Ethylene Butylene Styrene (SEBS) ................................... 27 2.5.3 Styrene Butadiene Rubber Latex (SBR) ......................................... 28 2.5.4 Elvaloy® AM ................................................................................. 28 2.5.5 Crumb Rubber ................................................................................. 29 2.5.6 Optimum Asphalt-Polymer Mixing Conditions .............................. 30 2.6 Composition of ASR (Automobile Shredder Residue) ............................ 31 Chapter Three - Automobile Shredder Residue Modified Cement Concrete ....... 32 3.1 Surface Treatments for ASR .................................................................... 32 3.2 Experimental ............................................................................................ 34 3.2.1 Contact Angle Measurement ........................................................... 34 vi 3.2.2 Direct Tensile Tests ........................................................................ 3.2.3 Fracture Surface Morphology ......................................................... 3.3 Results ...................................................................................................... 3.3.1 Contact Angle ................................................................................. 3.3.2 Direct Tensile Test .......................................................................... 3.3.3 Fracture Surface Morphology ......................................................... 3.4 Discussions .............................................................................................. 3 .5 Conclusions .............................................................................................. Chapter Four - Asphalt Concrete .......................................................................... 4.1 Asphalt Binder Morphology .................................................................... 4.2 Polymer Phase Morphology ..................................................................... 4.3 Void Morphology ..................................................................................... 4.3.1 Sample Preparation ......................................................................... 4.3.2 Thin Section Image Analysis .......................................................... 4.3.3 Void Casting Method ...................................................................... 4.4 In-situ ESEM Tensile Tests ..................................................................... 4.4.1 Sample Preparation and Testing ..................................................... 4.5 Fracture Toughness .................................................................................. 4.5.1 Sample Preparation and Testing ..................................................... 4.5.2 Effect of Aggregate Gradation ........................................................ 4.5.3 Selection of Fine Aggregate Gradation ........................................... 4.5.4 Binder Film Thickness in Asphalt Concrete ................................... 4.6 Lap-Shear Adhesion ................................................................................. 4.7 Summary .................................................................................................. Chapter Five - Results ........................................................................................... 5.1 Asphalt Binder Morphology .................................................................... 5.1.1 Morphology of Aged Asphalt Binders ............................................ 5.1.2 Effect of Polymer Addition on the Morphology of Aged Asphalt Binders ............................................................................................ Vii 36 38 4O 40 41 45 48 50 52 53 56 57 57 59 63 65 65 67 69 71 72 74 78 79 80 80 83 84 5.1.3 5 1 P01\ 5.3 VOII '.1 '1 1,) J) 5.- .I 5.4 ln-s 5.4.1 5.5 Fran 5.6 La; ChapterSix 6.1 Dis 6.] .\'e‘ 6.3 Re. 6.4 Par 65 La 6.6 SU ChapterSe 7.1 .\1 7.2 \‘r 7.3 Fr 7.4 (I 7.5 R 5.1.3 Effect of Asphaltene Content on the Morphology of Asphalt Binders ............................................................................................ 5.2 Polymer Phase Morphology ..................................................................... 5.3 Void Morphology ..................................................................................... 5.3.1 Thin Section Image Analysis .......................................................... 5.3.2 Void Casting Method ...................................................................... 5.4 In-situ ESEM Tensile Tests ..................................................................... 5.4.1 Role of Binder Morphology in Fracture Process ............................ 5.5 Fracture Toughness Test Results ............................................................. 5.6 Lap-Shear Adhesion ................................................................................. Chapter Six - Discussions ..................................................................................... 6.1 Dispersed Polymers (SBS/SEBS) ............................................................ 6.2 Network Polymers (SBR Latex) .............................................................. 6.3 Reactive Polymers (Elvaloy AM) ............................................................ 6.4 Particulate Polymers (Crumb Rubber) ..................................................... 6.5 Lap Shear Tests as Indicators of Interfacial Adhesion ............................ 6.6 Summary .................................................................................................. Chapter Seven - Conclusions and Recommendations .......................................... 7.1 Microstructure and Morphology .............................................................. 7.2 Void Morphology and Fracture in Asphalt Concrete .............................. 7.3 Fracture Toughness and Lap Shear Tests ................................................ 7.4 Optimum Polymer Concentration ............................................................ 7.5 Recommendations for Future Work ......................................................... Appendix A - Fracture Toughness Load-Displacement Plots .............................. Appendix B - Lap-Shear Test Results for Fresh Asphalt ..................................... Appendix C - Lap-Shear Test Results for Aged Asphalt ...................................... List of References ................................................................................................. General References .............................................................................................. viii 86 90 94 94 96 101 109 111 118 131 131 133 137 138 139 140 142 142 144 145 147 150 153 169 174 179 186 Table 1.1 Table 1.3 Table 2.1 Table 2.2 Table 3.3 Table 2.4 Table 2.5 Table 4.1 Table 4.3 Table 4.3 Table 4,4 Table 4.5 Table 5,] Table 5.2 Table 5 _ 3 Table 5.4 Table 55 Table 5.6 Table 1.1 Table 1.2 Table 2.1 Table 2.2 Table 2.3 Table 2.4 Table 2.5 Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 5.1 Table 5.2 Table 5.3 Table 5.4 Table 5.5 Table 5.6 LIST OF TABLES Typical pavement distresses and their causes .................................... Typical composition and production of ASR .................................... Elemental analysis of asphalt binders ................................................ Types of aggregates used in asphalt concrete .................................... Aggregate gradation (G7) used for Marshall samples ....................... Fine Mix Gradation (F MG) used for fracture toughness tests ........... Optimum mixing conditions for different polymer modifiers ........... Equations Used in Image Analysis .................................................... Effect of aggregate size on peak load of notched three-point bending beam test samples ................................................................ Fine Mix Gradation (FMG) used for Fracture Toughness Tests ....... Surface area factors for aggregate ..................................................... Asphalt Binder Film Thickness for G7 and Fine Mix Gradations ..... Air void content of SBS and SEBS modified asphalt concrete by image analysis .................................................................................... Air void content of SBR and Elvaloy AM modified asphalt concrete calculated by void casting ................................................... Distribution of void volume in SBR and Elvaloy AM modified AC5 .................................................................................................... Summary of changes in fracture morphology of asphalt due to polymer modification ......................................................................... Summary of fracture toughness test results ....................................... Failure modes in SBS modified AC5 lap shear tests ......................... ix 10 18 21 22 22 31 62 72 73 76 78 95 97 98 110 117 120 Table 7.1 Table 7.2 Table 7.3 Table 5.7 Table 5.8 Table 5.9 Table 5.10 Table 7.1 Table 7.2 Table 7.3 Failure modes in SEBS modified AC5 lap shear tests ....................... 122 Failure modes in SBR modified AC5 lap shear tests ......................... 124 Failure modes in Elvaloy AM modified AC5 lap shear tests ............ 126 Failure modes in Crumb Rubber modified AC5 lap shear tests ........ 128 Lap shear cohesive-adhesive failure transition temperatures for polymer modified AC5 asphalt concrete ........................................... 146 Optimum polymer concentrations suggested for AC5 (PG 58-28) asphalt binder ..................................................................................... 149 SHRP performance grades for polymer modified AC5 (PG 58-28) asphalt binder ..................................................................................... 149 Figure 1.1 Figure 1.2 Figure 1.3 .J) Figure 2.- Figure 3.4 Figure 3.1 PiSure 3. I.) FiElite 3.3 Figure 3. '1: Figure 3. 3‘ .— . ("‘4 L: *1 (D J I Figure 1.1 Figure 1.2 Figure 1.3 Figure 1.4 Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 3.1 Figure 3.2 Figure 3.3 Figure 3.4 Figure 3.5 Figure 3.6 Figure 3.7 Figure 3.8 Figure 3.9 LIST OF FIGURES Schematic of the adhesive bond interphase ....................................... Schematic of the polymer modified asphalt binder-aggregate interphase ........................................................................................... Different types of Polymer Modified Asphalt Concrete (PMAC) ..... Crack propagation in a particle modified/reinforced matrix .............. Schematic representation of concrete ................................................ Schematic representation of 3-phase model of asphalt binder showing the asphaltene, resin and low molecular weight oil phases . Schematic representation of the Styrene and Butadiene phase segregation in SBS ............................................................................. Suggested chemical Reaction of Elvaloy AM with asphaltenes ........ Schematic representation of the contact angle (9) ............................. Tensile test sample configuration ...................................................... Tensile test specimen showing locus of failure and strain guage fixture ................................................................................................. Contact angles of surface treated ASR .............................................. Tensile strength of untreated ASR modified Cement Concrete ........ Tensile strength of Detergent Washed ASR modified Cement Concrete ............................................................................................. Tensile strength of Sulphonated ASR modified Cement Concrete Summary of tensile test results for other ASR surface treatments Surface morphology of cement matrix in control cement concrete samples at IOOX. (White bar = 400nm) ............................................. xi 13 16 19 27 29 36 39 39 41 43 43 44 44 45 Figure 3.“) a .a a Figure ~11 Figure 3.12 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 5,] I:lE‘Ure Ll! I J Figure 3.10 Figure 3.11 Figure 3.12 Figure 3.13 Figure 3.14 Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 5.1 Figure 5.2 Surface morphology of ASR particle (left) and cement matrix (right) in untreated ASR-concrete samples at IOOX. (White bar = 400 um) .............................................................................................. Surface morphology of ASR particle (left) and cement matrix (right) in detergent washed ASR-concrete samples at 100X. (White bar = 400nm) ..................................................................................... Surface morphology of ASR particle (left) and cement matrix (right) in sulphonated ASR-concrete samples at IOOX. (White bar = 400 um) .............................................................................................. Surface morphology of ASR particle (left) and cement matrix (right) in detergent washed+sulphonated ASR-concrete at IOOX. (White bar =400 um) ......................................................................... Air void content of surface treated ASR modified cement concrete . Philips Electroscan 2020, Environmental Scanning Electron Microscope ......................................................................................... Typical network structure seen in asphalt binder thin films after exposure to the electron beam in the ESEM (White bar = 250 um)... Three-dimensional voids in asphalt concrete ..................................... Sample configuration for in-situ ESEM tensile test .......................... Three-point bending beam sample configuration for low temperature fracture toughness tests .................................................. Comparison between Fine Mix Gradation used for fracture toughness samples and G7 Gradation used for Marshall samples ..... Network morphology of asphalt binder. Left : Featureless surface of asphalt film immediately after exposure to the electron beam (150X, white bar = 300nm). Right : The randomly oriented network structure seen after exposure to the electron beam for 2-3 minutes (300x, white bar = 150 um) ................................................. Network structure in asphalt binder film under progressive tensile loading (150X). The network aligns itself in the direction of loading (indicated by arrow.) Left: White bar = 300nm. Right: White bar = 200nm. ........................................................................... xii 46 46 47 47 49 54 55 65 67 7O 75 81 81 ‘l! a .3 lie" e Figure 5.4 ”T1 ”75' E (b '1‘ '1- Figure 5.6 figure 58 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Figure 5.10 Figure 5.11 Figure 5.12 Pre-strained AC10 asphalt binder thin film, exposed to the electron beam shows network structure aligned in the direction of applied strain (indicated by arrow) at 155X. White bar = 300 um .................. Typical morphology of aged asphalt binders. The network fibrils appear coarse and the network can only be seen after substantially long (5-10 minutes) exposure to the electron beam (SOOX). White bar = 100 um ...................................................................................... Morphology of aged AC10-0% Elvaloy AM (left) and AC10-3% Elvaloy AM (right) after 7 minutes of exposure to the electron beam (SOOX, white bar = 100 um.) .................................................... Morphology of aged AC10-0% Crumb Rubber (left) at 300x (white bar = 150nm) and AC 10-10% Crumb Rubber (right) at SOOX (white bar = lOOum) after 2 minutes of exposure to the electron beam. .................................................................................... Morphology of 8.8% asphaltene content binder. Left: the network is visible in 15 seconds (white bar = 100 um). Right: surface returns to original state 30 seconds after beam removal (white bar = 150 um) .............................................................................................. Morphology of 15.5% asphaltene content binder. Left: the network is visible in 30 seconds (white bar = 150 um). Right: surface returns to original state 1 minute after beam removal (white bar = 150 um) .............................................................................................. Morphology of 20.4% asphaltene content binder. Left: the network is visible in 1 minute (white bar = 150 um). Right: surface returns to original state 4 minutes after beam removal (white bar = 150 um) ..................................................................................................... LSM micrograph of unmodified AC10 binder in fluorescent mode . LSM micrograph of AC10 with 5% SBS and SEBS modifier in fluorescent mode (dark areas indicate the polymer phase) showing discrete polymer phase in the asphalt binder (200X) ........................ LSM micrograph of AC10 with 5% SBR latex modifier in fluorescent mode (dark areas indicate the polymer phase) showing the fine network of SBR strands in the asphalt binder (333 X) ......... xiii 82 83 84 85 87 88 89 9O 92 Tieure 5.13 Figure 5.14 FigureSlS Figure 5.16 llgLL'E 5.17 Figure 5.18 Figure 5.19 ( Figure 5.21;; Figure 5.21 figure S.‘ . F1E’Ute 5.: Figure 5.13 Figure 5.14 Figure 5.15 Figure 5.16 Figure 5.17 Figure 5.18 Figure 5.19 Figure 5.20 Figure 5.21 Figure 5.22 Figure 5.23 Figure 5.24 Figure 5.25 ESEM micrographs of AC10 asphalt binder with 0% SBR (left, white bar = 250 um) and 5% SBR (right, white bar = 200 pm). The network fibrils in the control sample are random while the SBR modified sample shows an alignment of the network fibrils ............. Void volume distribution in AC5 with 0% and 5% SBR .................. Void volume distribution in AC5 with 0% and 2% Elvaloy AM ...... ESEM micrographs showing adhesive failure in asphalt concrete at 0°C at 65X (left, white bar = 500 um) and cohesive failure at 25°C at 100X (right, white bar = 450 um) .................................................. Typical fracture in unmodified AC5 asphalt concrete. Left: 370x (white bar = 100 um), Right: 100X (white bar =450 um) ................ Micrographs showing cohesive failure and increased fibril formation in AC5-5%SBS asphalt concrete. Left: 400X (white bar = 100 um), Right: lOOX (white bar = 450 um) ................................ Micrographs showing failure process in AC5-2%SEBS asphalt concrete. Left: 100X (white bar = 450 um), Right: 415X (white bar = 100 um.) ......................................................................................... Typical fracture surface in AC5-2%Elvaloy showing low fibril density. Lefi: 150X, Right: 150X. White bar = 300 um. ................... Micrographs showing cohesive failure and increased fibril formation in AC5-5%SBR asphalt concrete. Left: 3OOX (white bar = 150 um), Right: 1000X (white bar = 45 um.) ............................... Micrographs showing aligned network fibrils across the fracture surface in AC5-10% Crumb Rubber. Left: 65X (white bar = 500 um), Right: 100X (white bar = 450 um.) ......................................... Micrographs showing details of the network structure seen in asphalt concrete and its deformation as the sample is subjected to a tensile load. Left: 305x, Right: 350X. White bar = 150 um ............ Fracture toughness of SEBS modified AC5 asphalt concrete at -10°C .................................................................................................. Fracture toughness of Elvaloy modified AC5 asphalt concrete at -10°C .................................................................................................. xiv 93 99 100 102 103 104 105 106 107 108 110 113 113 . < Fizurf -- Figure 5.. Figure 5.. '1‘ Figure Figure 5.. Figure 5.3 Figure 5.: J “$114661 Figure 6.: Figure 5.26 Figure 5.27 Figure 5.28 Figure 5.29 Figure 5.30 Figure 5.31 Figure 5.32 Figure 5.33 Figure 5.34 Figure 5.35 Figure 6.1 Figure 6.2 Fracture toughness of SBR modified AC5 asphalt concrete at -10°C .................................................................................................. Fracture toughness of SBS modified AC5 asphalt concrete at -10°C .................................................................................................. Fracture toughness of Crumb Rubber (CRM) modified AC5 asphalt concrete at -10°C ............................................................................... Failure modes in lap shear test specimen. Type l-V show cohesive failure in the binder at high temperatures. Type VI shows binder- aggregate interfacial (adhesive) failure at low temperatures (11X) Lap shear strength of SBS modified AC5 as a function of polymer concentration and temperature ........................................................... Lap shear strength of SEBS modified AC5 as a function of polymer concentration and temperature ........................................................... Lap shear strength of SBR modified AC5 as a function of polymer concentration and temperature ........................................................... Lap shear strength of Elvaloy modified AC5 as a function of polymer concentration and temperature ............................................ Lap shear strength of Crumb Rubber modified AC5 as a function of polymer concentration and temperature ............................................ Lap shear strength of aged SBR modified AC5 binders at various temperatures ....................................................................................... Lap shear load-displacement curves for AC5-SBR and Granitic aggregate at -10°C. SBR coated aggregate systems have a higher displacement at failure due to toughening of the asphalt-binder interface ............................................................................................. ESEM micrographs of (a) Interaction of asphalt binder network with crumb rubber particles (left, white bar = 45 um) and (b) Fracture surface of crumb rubber modified AC10 showing significant amount of asphalt binder residue on the rubber particle surface (right, white bar = 450 um) ................................................... XV 115 116 117 119 121 123 125 127 129 130 136 139 Tb the rest of required dei'eloprni across the paxements of pai'eme extremess 40°C durir problem 01 Th; States Cm Performam 30mg 01511 p0ll'mers a CHAPTER ONE INTRODUCTION The vast network of asphalt concrete pavements in the State of Michigan, as in the rest of the United States, is showing signs of premature distress. The frequent repairs required by failed pavements is a concern for the authorities charged with the development and maintenance of road transport. Various Departments of Transportation across the country are looking at methods for improving the lifetime and performance of pavements in an effort to reduce the overall costs. In the State of Michigan, this problem of pavement failure is particularly serious due to the geographical location and climatic extremes seen in the state. Temperatures vary widely during the course of a year, nearing 40°C during the summer and drop well below -20°C during the winters, which makes the problem of pavement distress even more acute. The Strategic Highway Research Program (SHRP) was established by the United States Congress in 1987 as a 5-year, $150 million research program to improve the performance and durability of the nation's roads and to make them safer for motorists. Some of the studies undertaken by SHRP indicate that the modification of asphalt with polymers and other additives can improve the lifetime of asphalt concrete pavements. Asphalt concrete is a mixture of asphalt binder (asphalt cement) and aggregate (crushed stone). Asphalt binder is a black, viscous liquid at high temperatures (~ 40- 60°C) and becomes a hard and very brittle solid at low temperatures (~0°C). The aggregates are the load-bearing phase held together by the asphalt binder, making asphalt concrete a composite material. Asphalt binder is a mixture of hydrocarbons left over from variations in the sat? enhance 11 [1]. For IT 31111011ng C their STFUT ditTerent. modilieati. Speeitieati. 01 asphalt account an set of speei \l'h 1116 C356 0 added 10 a mall be 1'; appllCdil(ij 1813112111 c NDOTT blFlthrS‘ t‘ the refining of crude oil. It consists of the last remaining fractions of processed crude and depending on the quality of the crude, the composition and properties of the asphalt binder can change. Asphalt binder thus produced rarely has uniform properties; subtle variations in properties are detectable in different batches produced from the same crude in the same process facility. Modifiers are typically added to the asphalt binder phase to enhance the properties of asphalt binder which in turn enhance pavement performance [1]. For this reason, asphalt binders are characterized on the basis of their viscosity and although different binders with the same viscosity grade can be said to behave similarly, their structure, chemical, physical and thermodynamic properties may be entirely different. It is this variability that adds to the difficulty of evaluating different methods of modification of asphalt. As a result, SHRP recommended a set of performance based specifications based on chemical and thermodynamic properties for the characterization of asphalt binders used in pavements [2]. The SHRP specifications do not take into account any modifications that may be made to the asphalt binder, recommending that the set of specifications be applied to the final asphalt binders. While this approach may be pragmatic, it may prove to be inadequate by itself in the case of modified asphalts. Various types of modifiers, especially polymers, when added to asphalt can cause different properties to change in different ways [3-5]. There may be various ways in which different modifiers can work to improve properties and the application of one set of standards may not be able to predict all the properties of the asphalt concrete. Keeping this in mind, the Michigan Department of Transportation (MDoT) has initiated research into the use of SHRP specifications for modified asphalt binders, especially polymer modified asphalt binders. As part of this study at Michigan State 1111‘ p11} sisal :1 properties concrete. 1 1110911010; 1.1 T} Th cracking. these failL dirierent rt EXp-ansion can enter expansion in 1116 Tom temperatur fIIiCllll’e up. binder Emu 113303in ( loads. A. aCCeleraR. State University, a three pronged program was founded to characterize: i) chemical, physical and thermodynamic properties of asphalt; ii) microstructural and morphological properties of asphalt binder and asphalt concrete and iii) engineering properties of asphalt concrete. This thesis presents some of the investigations into the microstructural and morphological properties of polymer modified asphalt binder and asphalt concrete. 1.1 Types of Pavement Distresses The main types of pavement distresses found in asphalt concrete are thermal cracking, fatigue cracking, rutting, ravelling, stripping and aging [6-8]. The causes for these failures are summarized in Table 1.1. Thermal cracking can result from three different mechanisms which are not mutually exclusive. Different coefficients of thermal expansion can cause thermal strains leading to cracking of the asphalt concrete. Water can enter the existing cracks and during winters, the freeze-thaw cycling can lead to expansion and widening of these cracks. Catastrophic failures of this nature can be seen in the form of eruption of pavements. The third cause for thermal cracking is the low temperature brittleness during winter which makes the pavement more susceptible to fracture under applied traffic loads. Aging of the asphalt occurs due to oxidation of the binder and the loss of oils due to volatilization during service. This can increase the viscosity of the asphalt, making it very brittle, hard and susceptible to fracture under loads. Aging of asphalt occurs over years during normal service and the process is accelerated by high temperatures and other environmental factors. Aein Fatig Rutti: Rat el F: is essenti STOW me: the aSphal microstnn under but due to n aggregate tempem. defohnatl Increases as the “c; Table 1.1 Typical pavement distresses and their causes Pavement Distress Cause Thermal Cracking - Freeze-thaw cycling - Low temperature embrittlement during winter - Different coefficients of thermal expansion Aging - Embrittlement caused by oxidation Fatigue Cracking - Tensile failure due to cyclic loading Rutting - Microstructural rearrangement of asphalt due to plastic flow under load at high temperatures Ravelling/Stripping - Adhesive fracture due to poor asphalt-aggregate adhesion Fatigue cracking is caused by cyclic stresses. The nature of loading on pavements is essentially cyclic and with the passage of every vehicle, a small initiating flaw can grow over time into a large crack. Fatigue failure is generally initiated at the bottom of the asphalt layers where tensile strain is greatest. Rutting is a type of failure caused by the microstructural rearrangement of the asphalt binder due to plastic deformation (flow) under load. This is typically a high temperature failure; a common indication of failure due to rutting being tire tracks left in the pavement surface during summer. Ravelling/stripping is a failure of the concrete caused by poor adhesion between the aggregate and the asphalt binder. This type of failure is particularly disastrous at low temperatures. At high temperatures, the asphalt binder is sufficiently soft to allow deformation of the binder phase, but at low temperatures when the binder modulus increases and it becomes brittle, the applied strain is transferred more efficiently to the binder-aggregate interface. With poor adhesion between the two phases, the interface acts as the weak link and cracks in the pavement can easily propagate. 13 Neel The asphalt bin: low creep resistance t polymers c: adhesion :11 particles en The characterla into No C0 m0dlllll dc Polymers t pml‘mlane At high 1e: ”101111115 31 low glass : blend-111d} 31031 01‘ ’. P Ollmfls ATICCI [h "e' Crack3125 1.2 Need for Polymer Modification of Asphalt The various types of failures in asphalt can be overcome by modification of the asphalt binder with polymers [9-21]. Polymer modifiers offer several advantages such as low creep at high temperatures, high ductility at low temperatures, high toughness, resistance to moisture and temperature, high cohesive and adhesive strength. Blended polymers can modify the binder properties such as complex modulus, ductility, interfacial adhesion and cohesive strength while binders modified with heterogeneous fibers and particles enhance the final properties by changing the locus and mechanism of failure. The complex modulus (G*) of the binder is a convenient parameter to characterize the asphalt binder rheologically [22]. The complex modulus can be resolved into two components, the elastic modulus, G’, and the viscous modulus, G” [20]. These modulii determine the behaviour of the asphalt during deformation and fracture. Polymers can increase both the elastic and viscous modulii and thus extend the performance envelope of the asphalt binders at high as well as low temperatures [23-24]. At high temperatures, the polymer modifier can toughen the binders due to their high modulus and viscosity, preventing failures such as rutting while at low temperatures, the low glass transition (Tg) of the polymer phase can depress the Tg of the polymer-asphalt blend, making the asphalt binder softer and thus prevent brittle low temperature cracking. Most of the pavement distresses ultimately lead to fracture by various mechanisms. Polymers, whether blended with binder or particulate reinforcement, have the ability to affect these fracture processes by altering the initiation, locus and propagation of cracks[25]. Anol distribution propagation expanSion at suriicienI air crack initiate void size and also alleviate One 0 the asphalt bit The strength I role in the loo modulus incre. tough interface inter/Eire is a It not a simple Iv- than the bulk 01 re{lion forming Should be used Occurg A schen the 11116th del‘endent 0n chemical Comp Another factor affecting the performance of asphalt concrete is the size and distribution of air voids. Void microstructure and morphology is related to initiation and propagation of cracks [18, 25]. Voids are necessary in asphalt concrete to provide for expansion and flow of the binder at high temperatures as well as water drainage. Without sufficient air voids, asphalt binder can bleed to the surface, while large voids can act as crack initiators. The addition of polymer modifiers to asphalt can cause changes in the void size and distribution and these changes must be studied. Polymer modification can also alleviate the effects of aging in asphalt [26]. One of the objectives of this research is to study the effect of adhesion between the asphalt binder and aggregate on the properties of polymer modified asphalt concrete. The strength of the asphalt binder-aggregate interface is believed to play an important role in the low temperature behavior of asphalt concrete. At low temperatures, the binder modulus increases and failure proceeds along the relatively weaker interface. A strong, tough interface can thus enhance the low temperature properties. The asphalt-aggregate interface is a misnomer since the boundary between the asphalt and aggregate phases is not a simple two dimensional boundary but a region with different physical properties than the bulk of the two phases. The asphalt-aggregate interphase, the three-dimensional region forming the boundary between the two bulk phases, is a more accurate term that should be used to describe the region where asphalt binder and aggregate interaction occurs. A schematic model of an adhesive interphase was proposed by Drzal [27] where the interphase between a viscoelastic adhesive and solid substrate is shown to be dependent on the surface chemistry, morphology, topography, microstructure, local chemical composition as well as the bulk properties of the two adhering phases. Figure 1.1 shoves i must take it this schemf: 8; binder pt in the aggt interphase 2 asphalt conc Pol} thermoplasti particulate p basis of the reactive pOl\ (PK-MC) that t L3 Autom AUIOmC 1.1 shows a schematic of such an interphase. The study of any interfacial phenomenon must take into account all these factors. In the case of polymer modified asphalt concrete, this schematic model can be extended to include aggregate surface properties, interfacial & binder phase voids, asphalt binder & polymer phase morphology and binder absorption in the aggregate. Figure 1.2 is a schematic model of the asphalt binder-aggregate interphase and shows the various factors that can affect the interfacial properties in asphalt concrete. Polymer modifiers for asphalt can be classified into five categories: dispersed thermoplastic polymers, network thermoplastic polymers, reactive polymers, fibers and particulate polymers. Asphalts modified with these polymers can be classified on the basis of the final morphology as homogeneous asphalts (thermoplastic, network and reactive polymers) and non-homogeneous asphalts (fiber and particulate polymers). Figure 1.3 shows a schematic of the various types of polymer modified asphalt concretes (PMAC) that can be obtained. 1.3 Automobile Shredder Residue (ASR) Automobiles are the most recycled high-volume consumer product in the US. Every year more than 10 million American cars are shredded, producing nearly 10 million tons of metallic scrap, 50 million tires, and 2.5 million tons of non-metallic scrap. The process consists of dismantling and stripping of vehicles followed by reduction of the size by shredding and separation of metals Recovery of metals is the primary motive for shredding automobiles, but due to the increasing use of plastics and composites, the amount of non-metallic residue is significant. M —1 Pol mo- Poly; Surfa “glue [2 I BULK ADHESIVE POLYMER of DIFFERENT PROPERTIES ADSORBED MATERIAL OXIDE CHEMISTRY OXIDE TOPOGRAPHY THERMAL. OXIDE agimfhfiéfi MORPHOLOGY ~ BULK ADHEREND ENVIRONMENTS t ADHESIVE BOND INTERPHASE O LTD,MSU.1992 Figure 1.1 Schematic of the adhesive bond interphase Binder Bulk binder microstructure & morphology Polymer Binder phase morphology voids Interfacial Polymer rich voids surface layer . Interfacial adhesion Aggregate Absorbed porosrty binder Bulk aggregate Figure 1.2 Schematic of the polymer modified asphalt binder-aggregate interphase Homogeneous Asphalt Modifiers : Dispersed Thermoplastics Network Thermoplastics Reacting Polymers Non-homogeneous Asphalt Modifier : Fibers (organic and inorganic) Non-homogeneous Asphalt Modifier : Particulate polymer (Rubber particles) Figure 1.3 Different types of Polymer Modified Asphalt Concrete (PMAC) The paper. IEI‘I'TC is collectix'el and is treatec recycling of separating the landfills and alternative. \‘2 are not attrac produced. \ Material PVC PP ABS PA PE PL’R Elastomer Other PlasnlI , Fibers 00¢ Meta] .. The non-metallic residue comprising of various kinds of plastics, rubber, wood, paper, fabrics, glass, sand, dirt, metal pieces and traces of automotive fluids such as oils, is collectively termed as Automobile Shredder Residue (ASR). ASR has no direct value and is treated as a hazardous waste product which is usually disposed in landfills. Direct recycling of the various polymers found in ASR is hampered by the difficulty faced in separating the various components. The loss of potentially usable material, rising cost of landfills and environmental concerns have led to research focussing on finding alternative, value added uses for ASR. Traditional means of disposal, like incineration, are not attractive for ASR due to the toxic by-products of combustion that may be produced. Table 1.2 Typical composition and production of ASR Amount Annual Production of ASR (1995) Material Composition Per Car (x 103 Metric Tonnes) (Kg) Europe USA Other Total PU Foam 9 % 20 154 121 165 440 PVC 9% 19 150 118 161 430 PP 8% 17 132 103 141 378 ABS 5 % 12 92 72 99 264 PA 4 % 8 61 48 65 174 PB 2 % 5 38 3O 41 110 PUR 11 % 24 189 148 202 540 Elastomers 6 % 14 108 85 116 310 Other Plastics 11 % 23 182 143 195 522 Fibers 18 % 39 308 242 330 880 Wood, Metals, etc. 18 % 39 308 242 330 880 Total 100 % 220 1,725 1,355 1,848 4,929 10 The C Poburethane Acnlonitrile- Poburethane gives a typic: [SA and the 1 1.4 ASR .‘ C emer applications :1: been shovm t. [33:39]. \"arit improved by Particulate ad. material. The C051 mOCllchrg concrete. has a The the cement COncrc tailUre in Gem, unique PTOpen abSorbjng The DIIICIEHI DOTV The composition of ASR varies constantly and some of the constituents are Polyurethane foam (PU foam), Polyvinylchloride (PVC), Polypropylene (PP), Acrylonitrile-Butadiene-Styrene (ABS), Polyamides (PA), Polyethylene (PE), Polyurethane rubber (PUR) and various other materials including dirt and oil. Table 1.2 gives a typical composition of ASR and the approximate amounts produced in Europe, USA and the rest of the world. 1.4 ASR Modified Cement Concrete Cement concrete is commonly used for slab-on-grade applications. These applications are generally pavement and building construction. Polymer modification has been shown to be an effective method for improving the properties of cement concrete [28-29]. Various properties such as tensile, flexural, compressive, fatigue, etc. can be improved by the addition of specific polymers. The use of a polymer rich ASR as particulate additive to cement concrete is an attractive and value-added use for a waste material. The large volume of cement concrete used every year demands the use of low cost modifiers and ASR, if shown to maintain or improve the properties of cement concrete, has a high potential for widespread use. The mechanisms by which particulate polymer additives enhance the properties of cement concrete are similar to those seen in asphalt concrete [43]. The manifestation of failure in cement concrete is fracture, or cracking of the material. Polymers, due to their unique properties such as high toughness and ductility, can act as crack inhibitors by absorbing the fracture energy or by changing the locus and mechanism of failure. Different polymer modifiers may have different mechanisms by which they work, but 11 one Of Ih‘ polymer \1 asphalt) C0 material is Reta-ability . interfacial :- adequately. act as a flaw potential fail polymer and interface betv l:lgure 1.3 sh matrix interfa. water based rr. ASR‘Cement l! The int meme b." sur abrasion and C11 be USed 10 Imp in ~ the lmpml‘t‘.’ one of the essential properties of a good polymer modifier is the interaction of the polymer with the bulk material. In the case of particulate modification of cement (or asphalt) concrete, the interaction of the surface of the polymer particle with the matrix material is critical. This interaction can be quantified in terms of interfacial adhesion or wettability of the particle surface by the matrix [30]. A high wettability indicates high interfacial adhesion which is necessary for any particulate reinforcement to perform adequately. If the interface of a particulate inclusion in a matrix is weak, the particle can act as a flaw and the stress transfer that can occur via the interface is limited making it a potential failure site. A strong interface allows stress transfer from the matrix to the polymer and is necessary for dissipation of fracture energy. Thus the need for a strong interface between the additive and the matrix material is an important consideration. Figure 1.3 shows a schematic representation of crack propagation along the polymer- matrix interface. The addition of ASR may present problems in this regard. Cement is a water based material and the oils and dirt on the ASR surface may lead to a very weak ASR-cement interface and cause the properties of the concrete to deteriorate. The interfacial properties of ASR can be improved prior to addition to cement concrete by surface treatments. Various methods such as detergent washing, mechanical abrasion and chemical modification of the surface by processes such as sulphonation can be used to improve the wettability and surface energy of the ASR. The effect of these improvements in the interaction between the polymer particles and the matrix can result in the improvement of the final properties of cement concrete. 12 Polymer particle in the path of propagating crack Bulk Matrix Crack propagation along particle interface due to weak interfacial adhesion Crack propagation through bulk particle due to strong interfacial adhesion Figure 1.4 Crack propagation in a particle modified/reinforced matrix. of asphalt him access the eff; adhesion and f should be cha poltrner modi: tthich ultimate modification or has not been th- Ialte into accot Properties of t Bphalt P3V€me 11 is pro Changes OCCUR lechrljClues to mechanisms 1h developed to . ”1003110109; P “18511311151113. characterjzflm 1.5 Problem Statement Asphalt concrete pavements fail due to a variety of distresses such as thermal cracking, aging, fatigue cracking, rutting and ravelling/stripping. Polymer modification of asphalt binder has the potential to improve the performance of these pavements. To access the effects of polymer modification on asphalt, the microstructure, morphology, adhesion and fracture toughness of the asphalt binder and concrete are key properties that should be characterised. The microstructure and morphology of the polymer and the polymer modified binder are controlled by the mix ingredients and mixing procedures which ultimately have an effect on pavement performance. The effect of polymer modification on the interfacial properties, or the role of interfacial adhesion is an area that has not been thoroughly explored and current building practices and specifications do not take into account the microstructure and morphology of the asphalt binder used. Bulk properties of the binder, aggregate and concrete are commonly used to characterise asphalt pavements. It is proposed that the systematic study of the microstructural and morphological changes occurring due to polymer modification can lead to development of evaluation techniques to measure the effectiveness of asphalt additives and an understanding of the mechanisms that enhance pavement performance. Several laboratory tests have been developed to measure specific properties such as: asphalt binder microstructure and morphology, polymer phase morphology, void analysis, fracture morphology, fracture mechanisms, fracture toughness and lap-shear adhesion. These tests allow the characterization of polymer modified asphalt binder and concrete which, when studied along with the chemical [31,32] and engineering [33] properties, provide a set of tools for 14 the charac polymer IT evaluated 2 discussed. The changes in t concrete spe by the applit on the surfac The 1 properties 01 Properties of Study, Chapte 0n ASR modi theories used 1 Presents the re Properties 0]“- reSPFC‘llvelg- in Obtained, The Plesemed alon the “fillerstam cement COHCT; the characterization and specification for polymer modified asphalt concrete. Five polymer modifiers: SBS, SEBS, SBR latex, Elvaloy AM and Crumb Rubber were evaluated and the optimum compositions and their effect on key properties will be discussed. The effect of addition of ASR to cement concrete were characterized by the changes in the tensile strength and fracture morphology of cured ASR modified cement concrete specimen. The role of interfacial adhesion in ASR modified cement was studied by the application of various mechanical and chemical surface treatments and their effect on the surface energy and wettability of the ASR. The focus of this research is to study the effect of polymer modification on the properties of asphalt and cement concrete. Chapter Two describes the nature and properties of various polymer modifiers, asphalt binders and cement concrete used in the study. Chapter Three describes in detail the experiments and results obtained from studies on ASR modified cement concrete. Chapter Four describes the different experiments and theories used to characterize polymer modified asphalt binder and concrete. Chapter Five presents the results of investigations into the microstructural, morphological and adhesive properties of polymer modified asphalt binder and concrete. Chapter Six and Seven respectively include the discussions and conclusions that can be drawn from the results obtained. The advantages and disadvantages of different polymer systems will be presented along with recommendations for future work that can be undertaken to promote the understanding of the role of the interface in composite systems such as asphalt and cement concrete. 15 This c tvide variety 1‘ concrete hay morphology a 2.1 Cemt Asphal stone) as the COmposite can Crosslinked. el [his Study the an(112151311411 Ct M {asphall bmc‘ CHAPTER TWO MATERIALS This chapter provides an overview of the various materials used in this study. A wide variety of materials such as asphalt cement, aggregate, various polymers and cement concrete have been studied and brief descriptions of their microstructures and morphology are provided in the following sections. 2.1 Cement and Asphalt Concrete Asphalt and cement concretes are composite materials with aggregate (crushed stone) as the discontinuous load bearing component. The continuous matrix of the composite can be of different types ranging from thermoplastic, viscoelastic bitumens to crosslinked, elastic cements. Figure 2.1 shows a schematic representation of concrete. In this study the term used to refer to bituminous binders and concrete is "asphalt binder" and "asphalt concrete" respectively. Reinforcing Aggregate (crushed stone) Matrix (asphalt binder or cement) Figure 2.1 Schematic representation of concrete 2.2 ASP!“ Aspha distillation of asphalt. An approximatelj amounts of n analysis of th have been \vi asphalts are aromatics. an. of the four g Asphaltenes C GT 1.1:]. A5 “aPhIhenic fir Silt TS 011 lht diSPCISlng age the lightest m weight napht} and albi'l-na; [lilac] COnSIE . 2.2 Asphalt Binder Asphalt binders are complex mixtures of hydrocarbons derived from the fractional distillation of crude oil where the heaviest residue is processed into different grades of asphalt. An elemental analysis of asphalt shows that the composition by weight is approximately 82-86% carbon, 8-1 1% hydrogen, 0-1.5% oxygen, 0-6% sulfur, with trace amounts of nitrogen, vanadium, nickel, and iron [34]. Table 2.1 shows the elemental analysis of three different viscosity graded asphalt binders. Chromatographic techniques have been widely used in the evaluation of asphalt constitution; based on these studies asphalts are typically divided into four major groups, namely: asphaltenes, resins, aromatics, and saturates [3 5]. Asphaltenes are the highest molecular weight constituent of the four groups and are considered highly polar and complex aromatic materials. Asphaltenes constitute 5% to 25% of the total asphalt and have a hydrogen / carbon ratio of 1.1:1. Asphaltenes are believed to be stacks of plate-like sheets of aromatic and naphthenic ring structures held together by hydrogen bonds [36]. The asphaltene particle size is on the order of 5-30nm. Resins are also very polar in nature and act as a dispersing agent or peptisers for the asphaltenes. Finally, the aromatics and saturates are the lightest molecular weight group in asphalt. The aromatics are the lowest molecular weight naphthenic compounds and the saturates consist of both aliphatic hydrocarbons and alkyl-napthenes and alkyl aromatics. Together, the aromatics and saturates (oily phase) constitute the major portion of the total asphalt (40-50%). 17 \ Bphaltene re shows a 5C1]: considered to mixture. The dispersed as dj OllS. Expenm demOTlSIfalsd I ”16 Constituem dePTEe of &S\ lflil‘LIenCe The be gOI‘emS the T:' Table 2.1 Elemental analysis of asphalt binders [34]. AC-5 AC-lO AC-20 Carbon (%) 85.7 82.3 84.5 Hydrogen (%) 10.6 10.6 10.4 Oxygen (%) —- 0.8 1.1 Nitrogen (%) 0.54 0.54 0.55 Sulphur (%) 5.4 4.7 3.4 Vanadium (ppm) 163 220 87 Nickel (ppm) 36 56 35 Iron (ppm) -- 16 100 Aromatic Carbon (%) 32.5 31.9 32.8 Aromatic Hydrogen (%) 7.24 7.12 8.66 Molecular Weight 570-890 810-930 840-1300 Asphalt is often regarded as a colloidal system consisting of high molecular asphaltene/resin micelles dispersed in a lower molecular weight oily medium. Figure 2.2 shows a schematic of this three phase structure of asphalt binders. The micelles are considered to be an ensemble of asphaltenes with a sheath of resins which stabilizes the mixture. The asphalt and resins may be linked in an open network but may also be dispersed as discrete particles depending on the relative amounts of resin, asphaltene, and oils. Experiments involving systematic blending of resins, oils, and asphaltenes have demonstrated that the rheological properties of the asphalt cements depend strongly on the constituents, especially the asphaltene content in the mixture. Thus, the interaction or degree of association between the asphaltene, as well as their size and shape, will influence the viscosity of the binder [37]. The arrangement and degree of association between asphaltene particles within the oily phase is important since this ultimately governs the rheological properties of the asphalt cement binder [35,3 8,3 9]. 18 - 1 :z.r_—-- ~ ‘ .. Figure hho Figure 2.2 Schematic representation of 3-phase model of asphalt binder \showing the asphaltene, resin and low molecular weight oil phases. The as were classifier according to S to minimize tl‘ 23 Aggre The as quarries and I sandstone. Th used in the asp Tvvo dl gradation [40] fracture tough tests is discus Show] in Tab aggregate gym- 5-71’9111' "\v) asp The asphalt samples used in this study were supplied by Amoco Corporation and were classified as the low viscosity (AC-5) grade or a moderate viscosity (AC-10) grade according to standard pen tests. The asphalts were stored at -10°C, which is near the Tg, to minimize the effects of aging. No emulsifiers were added to the binders. 2.3 Aggregates Used in Asphalt Concrete The aggregate used for making asphalt concrete was obtained from Michigan quarries and consisted mainly of granite, quartzite, greenstone, limestone, basalt and sandstone. The properties of the different types of aggregate and the relative proportions used in the asphalt concrete mix are summarized in Table 2.2. Two different aggregate gradations were used to make asphalt concrete mixes: G7 gradation [40] for preparing Marshall samples and a fine mix gradation for preparing fracture toughness samples. The rationale for using a fine mix for fracture toughness tests is discussed in Chapter 5. Marshall samples were made with the G7 gradation shown in Table 2.3 while fracture toughness test beams were prepared using a finer aggregate gradation as shown in Table 2.4. Mixes made with both gradations had 5.7%(w/w) asphalt binder content. 20 Type Granite Basalt Quartzitc Greenstor Sandstont Limestone Table 2.2 Types of aggregates used in asphalt concrete [40] Type Volume Compressive Schmidt Composition/Description in mix Strength Hardness (%) (108 N/mz) Granite 28 2.5 — 5.5 52 - 90 Coarse crystalline igneous rocks. Basalt 19 2.0 — 3.5 50 - 90 Fine grained igneous rocks. Quartzite 23 2.9 — 5.0 30 - 70 Tough but brittle rock, fully or partially metamorphosed quartz sandstone. Greenstone 10 2.0 — 3.0 60 - 80 Dense fine crystalline basaltic rock. Sandstone 11 0.3 — 2.0 20 - 60 Highly variable distribution ranging from lithic fragments to quartz sands. Limestone 9 0.2 — 2.0 30 - 60 Varies from limy mudstones to crystalline carbonate rocks. CaCO3 and CaMg(CO3)2, 21 Table 2.3 Aggregate gradation (G7) used for Marshall samples Size (mm) Passing % Retained % Weight (gm) Cumulative weight (gm) 19 100 0 0 0 12.5 99 l 54 54 9.5 81 18 972 1026 7.7 63 18 972 1998 4.75 35 28 1512 3510 2.37 22 13 702 4212 1.18 16 6 324 4536 0.6 1 1 5 270 4806 0.3 9 2 108 4914 0.15 7 2 108 5022 0.075 5 2 108 5130 Fly ash 0 5 270 5400 Table 2.4 Fine Mix Gradation (F MG) used for fracture toughness tests Size (mm) Passing % Retained % Weight (gm) Cumulative weight (gm) 19 100 0 0 0 12.5 100 0 0 0 9.5 100 0 0 0 7.7 99 1 32.5 32.5 4.75 68 31 1007.5 1040 2.37 38 30 975 2015 1.18 26 12 390 2405 0.6 14 12 390 2795 0.3 10 4 130 2925 0.15 7 3 97.5 3022.5 0.075 4 3 97.5 3120 Fly ash 0 4 130 3250 22 2.4 prope conter their b tern per normal time. c and per improvi viscositj flexible applicati relative - Propertie teI'llperzttt P0Timer mOdilied Iemi‘erittu AI. is b). mot— 2.4 Role of Polymer Modifiers in Improving Asphalt Concrete Properties The performance of asphalt concrete is greatly influenced by the rheological properties of the asphalt binder as well as the mix composition, aggregate properties, void content, and other parameters [31-33, 35]. Asphalt binders are visco-elastic materials and their behavior ranges from purely elastic to completely viscous depending on the service temperature and time of loading. Pavement grade asphalts undergo cyclic loads under normal service conditions and a large accumulation of permanent strain develops over time, eventually leading to failure [3 3]. Other failures may be caused by loss of adhesion and permanent plastic deformation. In recent years polymer modifiers have been added to asphalts with the goal of improving the resistance to failure at extreme service temperatures. Conventionally low viscosity (sofi) asphalts are used for low temperature service due to their ability to remain flexible at lower temperatures and high viscosity (hard) asphalts used in high temperature applications to prevent plastic flow (rutting). This leads to pavements performing well relative to one type of failure, but poorly relative to others. Polymers have unique properties such as low glass transition temperatures and high viscosities at elevated temperatures. Asphalts benefit from the unique properties imparted by polymers. Polymer modification can increase the storage and loss moduli of asphalt, making modified asphalts more flexible at low temperatures and more viscous at high temperatures. Another mechanism by which polymers can enhance the properties of pavements is by modifying the binder-aggregate interface [15-19, 25]. The interface in asphalt concrete is an area that has not been studied widely and yet it is critical to the failure of 23 pavements interphase I and the 89:1 phases and generally re temperature: brittle and t1 resistance. t1 binder modu the interface know as adl The presence C)‘Clirtg u'hicl these problem binder and fig befler \vettin: pavements at low temperatures. The binder-aggregate interface (2 dimensional) or interphase (3 dimensional) is the region surrounding the boundary of the asphalt binder and the aggregate. This region can have very different properties than the bulk of either phases and can play a critical role in the fracture process. The strength of the interface generally relates to the level of adhesion between the two bulk phases. At low temperatures (below or near the Tg of the asphalt binder), the binder becomes more brittle and the modulus increases. Since any failure process follows the path of least resistance, the weakest region of the concrete acts as the locus of failure. With a high binder modulus and the high strength of aggregate, the weaker region is generally along the interface and cracks proceed along the aggregate boundaries. This type of failure is known as adhesive failure and accounts for cracking occurring at very low temperatures. The presence of cracks along the interface can be further complicated by freeze-thaw cycling which tend to widen and grow cracks. Polymers added to the binder can alleviate these problems to a great degree by creating independent networks that associate with the binder and aggregate or by changing the surface energy of the binder and allowing for better wetting of the aggregate. This can lead to a tougher interface that resists the propagation of cracks and alleviates low temperature cracking in asphalt concrete. This behaviour is seen in homogeneous polymer modified asphalts. Particulate modifiers like crumb rubber act in a different way. Although the rubber does not interact chemically with the asphalt, at low temperatures it can serve as the toughening elastomeric phase in a brittle matrix. At high temperatures, it can increase the viscosity of the asphalt making it resistant to rutting [42]. 24 Po [#1]. This oxidation : also absorb the case of imagined a replenish th Due is possible ‘ those relatin application c 25 Descr Five deSCTlpllOns Q Dispersed m, Network filer Rewins Pot. Polymers can also retard the natural oxidative aging of asphalt binders in service [41]. This may be due to a variety of mechanisms such as provision of sacrificial oxidation sites and reaction with unsaturated sites in the asphalt. Many polymers can also absorb the low molecular weight oils in asphalt. This can be observed very easily in the case of crumb rubber particles which swell due to absorption of oils. These can be imagined as in-situ reservoirs of oils which initially protect them from oxidation and can replenish the asphalt binder with oils as natural aging processes occur. Due to the various types of polymers available, tailoring the properties of asphalt is possible with judicious selection of modifiers. The different mechanisms, especially those relating to the binder-aggregate interface need to be studied carefully to aid proper application of polymer modifiers in asphalt concrete. 2.5 Description of Polymer Modifiers Five polymers representing four different polymer types were used. Brief descriptions of the polymers are presented in this section. Dispersed Thermoplastic : SBS (Kraton D1101; Shell Chemical Co.) SEBS (Kraton G1650; Shell Chemical Co.) Network Thermoplastic : SBR latex (Ultrapave; UP70) Reacting Polymer : Epoxy based reacting polymer (Du Pont; Elvaloy AM®) Particulate Polymer : Crumb Rubber (Rouse Rubber, GF-SOA); 25 monomer can consi a mo pl] polxstyre. common SBS pol; Compatib polymer ( oxidize d1 help the a the t'iscoc l0 degrad‘ Used by 1 “eight of 2.5.1 Styrene-Butadiene-Styrene (SBS) SBS block copolymers consist of segments of styrene and butadiene rubber monomer units with a styrenezbutadiene monomer ratio of 30:70. Each block segment can consist of many monomer units and the common morphology at room temperature is a two phase structure as shown in Figure 2.3. The styrene blocks segregate into hard polystyrene domains which are connected by soft polybutadiene segments The most common form used in asphalt modification is a linear styrene-butadiene-styrene structure. SBS polymers are physically dispersed in asphalt, but do not react chemically. Compatibility of the SBS with the binder is important to prevent segregation of the polymer during processing. The butadiene midblock in SBS is unsaturated and it can oxidize during processing or service in the pavement. This sacrificial aging of SBS can help the asphalt resist aging initially, but once oxidation of the rubber midblock occurs, the viscoelastic properties of the polymer can be adversely affected. The polymer begins to degrade at temperatures above 380°F due to oxidation. Typical SBS concentrations used for modification of asphalt range from 1-5 % by weight (w/w). The molecular weight of the SBS used was approximately 30,000 [31]. 26 2.5.2 SQTC Styrer ethylene but} domains con polytethylene- temperature It: form of pelle Weight of the Used for mod j ——> Polystyrene domain /I: Polybutadiene . rubbery matrix Figure 2.3 Schematic representation of the Styrene and Butadiene phase segregation in SBS 2.5.2 Styrene-Ethylene-Butylene-Styrene (SEBS) Styrene-Ethylene-Butylene-Styrene (SEBS) is a block copolymer of styrene and ethylene/butylene. The physical structure is similar to that of SBS with hard styrene domains connected by rubbery ethylene-butylene midblocks. The fully saturated poly(ethylene-butylene) rubbery blocks are less susceptible to oxidation and thus the high temperature tolerance of the polymer is better than that of SBS. SEBS is obtained in the form of pellets and the polymer is dispersed physically in the asphalt. The molecular weight of the SEBS used was approximately 30,000 [31]. Typical SEBS concentrations used for modification of asphalt range from 1-5 % (w/w). 27 butadien (~0.5_um achieved in the as; solx‘ating network vi [PM (U 34:76. Typ l-D % (W is 2.5.4 my, E l\ al EGA (ethyle and glycidtl mo‘llfié‘d wit; 2.5.3 SBR Latex SBR latex is an emulsion polymerized random copolymer of styrene and butadiene in a water-based system. In latex form, the SBR particles are very small (~0.5um) and as a result, physical dispersion of the polymer particles in asphalt can be achieved easily. Heat and mechanical agitation produces a homogenous blend of polymer in the asphalt. As the latex is added, the polymer particles swell from the heat and solvating effects of the resins and oils in the asphalt. After mixing, the SBR forms a network within the asphalt binder. The latex used in this study was an anionic emulsion, UP-70 (Ultrapave/Goodyear) with 70% solids and a styrene:butadiene monomer ratio of 24:76. Typical concentration of SBR latex used for modification of asphalt ranges from 1-5 % (w/w). 2.5.4 Elvaloy® AM Elvaloy® AM (DuPont) is a reactive terpolymer with the chemical designation EGA (ethylene/glycidyl/acrylate). It is a random terpolymer of ethylene, n-butylacrylate and glycidyl methacrylate (GMA). The polymer consists of an ethylene backbone modified with two types of functional groups. The glycidyl group acts as the main reaction site while the acrylate functionalities add flexibility and elastomeric properties to the chain. Since the ethylene backbone is saturated, the polymer itself is relatively resistant to oxidation or aging. The GMA portion of the molecule is believed to be responsible for the reaction observed when Elvaloy is mixed and heated with asphalt. The epoxide ring in the glycidal structure is believed to react with various functional groups in the asphaltene molecule. Asphaltenes which have carboxylic acid 28 function Shaun tr ASPHALT Figu E l \‘t temperature reaction wit. Tl’pical COIN b)'\1‘eigm of ftmctionalities can open the epoxy ring in an addition reaction to form aromatic esters as shown in the suggested reaction mechanism in Figure 2.4 [31]. HO CH2 CH2 \l l l H CH2 /CH2 ' ASPHALTENE—CO—H + o l —> ASPHALTENE —C-—O—CH2 \CH2 Figure 2.4 Suggested chemical Reaction of Elvaloy AM with asphaltenes Elvaloy AM is obtained in the form of solid pellets. The pellets melt at high temperature and react with asphalt at 380°F to form a stable, homogenous binder. The reaction with asphalt assures a permanent and uniform dispersion within the binder. Typical concentration of Elvaloy AM used for modification of asphalt ranges from 1-3 % by weight of asphalt. 2.5.5 Crumb Rubber The use of recycled crumb rubber as an additive to asphalt concrete pavements is mandated by congressional legislation to address the problem of recycling used automobile tires. The tires are ground to a very fine powder called crumb rubber. Due to the recycled nature of the material, the composition of the rubber particles varies and cannot be accurately determined. The crumb rubber used in the study had an average particle size of 80 um. Since most rubber used in tires is vulcanized, crumb rubber particles are vulcanized and may have various additives such as anti-oxidants and UV 29 stabilizers ‘ a large suri oils from tl rubber parti up to 200‘ concentratiti surrounding 2.5.6 Opti The l manufacture the POlymer lead to exce: Oxidation du: “ll-ting Condi the resulting ‘, at Which then Table 2.5 Sho‘ 8V0 polymers ext 38055 Afte I Odealll‘e 32} tngmemne. .v stabilizers which make the rubber resistant to oxidative attack. The rubber particles have a large surface area due to the small particle size and can absorb low molecular weight oils from the surroundings. This is an important characteristic to bear in mind since the rubber particles are physically dispersed in the asphalt binder and crumb rubber loadings up to 20% by weight of asphalt binder can be used. The combination of high concentration and high surface area can lead to significant absorption of oils from the surrounding asphalt binder. 2.5.6 Optimum Asphalt-Polymer Mixing Conditions' The blending of polymer modifiers with asphalt binder is an important step in the manufacture of modified asphalts. Inadequate mixing can lead to phase segregation of the polymer modifier while very aggressive mixing conditions at high temperatures can lead to excessive oxidation/aging and degradation of the asphalt. To avoid excessive oxidation during processing while achieving good dispersion of the polymer, various mixing conditions were evaluated for each polymer [31]. The rheological properties of the resulting blends were characterized and the optimum conditions defined as the point at which there is no longer a significant increase in properties with additional mixing. Table 2.5 shows the optimum mixing conditions determined for different polymers. To avoid degradation of the polymers, mixing temperatures were limited to 350°F for all polymers except Elvaloy AM which has a supplier recommended mixing temperature of 380°F. After mixing, all binders not used immediately were stored at -10°C to avoid oxidative aging. ' Experimental work conducted by Hawley M., Shull J ., Lee Y. and France L., Dept. of Chemical Engineering, Michigan State University. 30 Table I W SEBS SBR Lati Elvaloy .‘ C RM 2-6 Compt Polymc nature of the materials Were Various Glastor Pl’lor 10 illch addition On me Table 2.5 Optimum mixing conditions for different polymer modifiers Polymer Modifier Mixing Time Temperature Conditions SBS 2 hours 350°F High shear (1600 rpm) SEBS 2 hours 350°F High shear (1600 rpm) SBR Latex 30 minutes 350°F High shear (1600 rpm) Elvaloy AM 2 hours 380°F High shear (1600 rpm) CRM 30 minutes 350°F Low shear (1200 rpm) 2.6 Composition of ASR (Automobile Shredder Residue) Polymer rich ASR with a maximum particle size of 12 mm was used. Due to the nature of the material, exact compositional analysis was not possible. The following materials were identified in the ASR obtained: HDPE, PVC, PP, ABS, PS, nylon, rubber, various elastomers, wood and fibers. Various surface treatments were applied to the ASR prior to incorporation in cement concrete. Chapter Three describes the effect of ASR addition on the properties of cement concrete in greater detail. 31 A [To Th aummobllt [ensik stre expected 1C strength an cement mat and Cement ASR inclusi some cases. propagation l 3.1 Surfa In orc various surfai Used for AS R Control : ll“ Acid [Ir/2m; dichrornate s CHAPTER THREE AUTOMOBILE SHREDDER RESIDUE MODIFIED CEMENT CONCRETE The addition of ASR to cement concrete is a value added application for automobile shredder residue. The ASR used had a high polymer content and the high tensile strength and toughness of the polymers compared to that of cement concrete are expected to enhance the final prOperties of the cement concrete. An enhancement in the strength and toughness is possible if the ASR particles have good interaction with the cement matrix, which can be related to the interfacial adhesion between the ASR particle and cement matrix [44]. Strong adhesion between the ASR and the matrix can cause the ASR inclusions to behave as a toughening phase by dissipating fracture energy and in some cases, bridging the cracks in the brittle cement matrix and inhibiting crack propagation [45]. 3.1 Surface Treatments for ASR In order to achieve a good interfacial bond between the cement and the ASR, various surface treatments were evaluated. The 7 different types of surface treatments used for ASR are described below. Control : The ASR was used as received. Acid Etching : The ASR is dipped in a Chromerage (sulphuric acid and sodium dichromate solution) for 1 hour at 55°C. After the material is removed from the acid bath, 32 it is rinsed if material is d” Detergent ”id air dried at 1T Triton PH 00 degradable liq .llechunicul R the dry combi: Latex Coating Repellent. Ko] Sulphonution seconds which on the surfac exPosing it to it is rinsed in water for 30 minutes to remove any acid residue from the surface. The material is dried in air at room temperature for 24 hours prior to use. Detergent Wash : The ASR particles were dipped in a detergent solution for 10 sec. and air dried at room temperature for 24 hours. The detergent used was a 0.1% solution of Triton X-100 (iso-octyl phenoxy polyethoxy ethanol and ethylene oxide) which is a bio- degradable liquid with 100% active non-ionic surface-active agent. Mechanical Rubbing : The ASR was combined with 0.75 inch crushed stone gravel and the dry combination mixed in a concrete mixer for 30 minutes. Latex Coating : The ASR was dipped in a latex solution (Wolman® Raincoat Water Repellent, Kop—Coat, Inc.) and dried in air at room temperature for 24 hours. Sulphonation : The ASR was exposed to a stream of sulphur trioxide gas for a few seconds which modifies the surface chemically by adding high energy sulphonate groups on the surface. The surface thus obtained is acidic in nature and it is neutralised by exposing it to calcium carbonate. 33 3.2 system. \ spreads o The angle the contact ofthe solid Where. 751' = sur The (f and [be solid “er the Solic area 0f the S 3.2 Experimental Three types of experiments were performed to investigate the surface energy, mechanical properties and fracture morphology of the ASR modified cement concrete. 3.2.1 Contact Angle Measurement Contact angles are a thermodynamic measure of the wettability of a solid-liquid system. When a sessile drop of liquid is placed on a solid surface, the drop of liquid spreads or contracts and eventually the solid-liquid-vapour system reaches equilibrium. The angle the drop makes with the solid at the point of contact at equilibrium is termed the contact angle (0). The contact angle is related to the surface and interfacial energies of the solid and liquid by Young’s Equation (Eq. 3.1) [30] 0056 = —————y“"' _ 7“" (3'1) 7 H. where, ySV = surface tension of the solid in equilibrium with vapour 751. = interfacial tension of the solid in equilibrium with liquid YLv = surface tension of the liquid in equilibrium with vapour 0 = contact angle in degrees The quantity (ygv-ygL) is the difference in energy between the free solid surface and the solid surface wetted by the liquid. This provides the driving force for the liquid to wet the solid surface. The total energy gained by the system when the liquid covers a unit area of the solid surface is then given by the term {yLv + (ysv-ySL)} which is called the 34 thermod.man the thermod-V Thus thermOdln‘m from-10° to lg This represen and covers th the liquid is s incomplete co Surfac surface energ} contact angles A com deionised “at. pure deioniset The goniome (ASR) partici and the dro; pmdUCES a calibrated at The Point of thermodynamic work of adhesion (WSW). Young’s equation can be expressed in terms of the thermodynamic work of adhesion to yield the Young-Dupré equation (Eq. 3.2) [30] WW 2 7,,(1 + c056) (3'2) Thus it can be seen that contact angles can be used as a measure of the thermodynamic work of adhesion for a given solid-liquid pair. Contact angles can vary from 0° to 180°. For a contact angle equal to 0°, the liquid is said to spread on the solid. This represents the ideal state where a liquid has complete affinity for the solid surface and covers the solid surface spontaneously. For values of contact angles higher than 90°, the liquid is said to be non-wetting and presents practical problems for adhesion due to incomplete contact between the two phases. Surface treatments for enhancement of adhesion are designed to increase the surface energy of the solid and thus lower the contact angle. By measuring the changes in contact angles, the efficiency of different surface treatments can be compared. A contact angle goniometer was used to measure the wettability of ASR with pure deionised water. Since the cement matrix is hydrophilic, the contact angles of ASR with pure deionised water can give a measure of the wettability of the ASR with the cement. The goniometer (Rame-Hart Goniometer) has a leveling platform on which the solid (ASR) particles are placed. A small drop (approx. 2ul volume) is placed on the surface and the drop is examined directly through a low power traveling microscope which produces a sharply defined silhouette of the drop. The microscope has a protractor calibrated at 1 degree intervals. The tangential angle the drop makes with the surface at the point of contact is measured as shown in Fig. 3.1. Contact angles were measured for 35 the 6 ditl’er treatments. 3.2.2 Direct Direct Cured Cement 01 increase in adheSlOH hem the pmlCleS i C0 ”Centratim. the 6 different surface treatments and also for combinations of different surface treatments . Drop of Solid Surface Figure 3.1 Schematic representation of the contact angle (0) 3.2.2 Direct Tensile Tests Direct tensile tests were performed to measure the change in tensile strength of cured cement concrete after addition of ASR. Particulate inclusions can lead to a decrease or increase in the tensile strength of a material depending on the amount of interfacial adhesion between the inclusions and the cement matrix. In case of poor adhesion between the particles and the matrix, the particles can act as flaws and give rise to sharp stress concentrations and ultimately nucleate cracks. However, with good interfacial adhesion, particulate inclusions can act as toughening phases. When a propagating crack reaches such an inclusion, the fracture energy can be absorbed by the elastomeric polymer particles and dissipated in different directions. This reduces the stress concentration at the crack tip and terminates the propagation of the crack. Thus, tensile tests can provide 36 Sflme limb.- Cement cc UBEUITCIIIS. Tensile Sa FOL ll) Bowotic plates. {2) tapered end avoid direct Ll-Shaped er C0!) 0f the be Unsatislat Stress concc F' * lgure 5.2 sh The t lCSting mach j some information about the interfacial strength of the ASR-cement concrete system. Cement concrete samples were prepared with different ASR content and ASR surface treatments. Tensile Sample Preparation and Testing Four different ASR-cement concrete sample configurations were evaluated. (1) Bow-tie tensile specimen clamped by means of wedge action between tapered end- plates, (2) Bow-tie specimen notched at the sides and clamped by wedging between tapered end-plates, (3) Bow-tie specimen with ends epoxied to U-shaped end plates to avoid direct clamping of the concrete samples and (4) Tensile dog-bone specimen with U-shaped end plates glued at the ends with epoxy (MS-907, Miller-Stephenson Chemical Co.) Of the four types of specimen described above, types 1, 2 and 3 were determined to be unsatisfactory due to premature failure near the clamped ends caused by unfavourable stress concentrations. The square dog-bone configuration was thus used for all tests. Figure 3.2 shows the dog-bone sample configuration. The tensile tests were performed on a UTS mechanical screw driven mechanical testing machine (SF M-20, United Test Systems) at ambient temperature and humidity conditions. The samples were aligned accurately along the tensile axis. A mechanical linear extensometer with 1 inch guage length was attached to the center portion of the dogbone with metal extension strips (Figure 3.3) to measure the strain accurately. After the test, the validity of the data was ensured by noting that the locus of failure was in the center of the sample and not near the clamped ends. The tests were performed with a crosshead speed of 0.04 inch/min. and a preload of 5 lb. to ensure proper alignment. 37 3 3,3 Frac The informaIiOD material. In testspecimet examined in (ESEM). Th samples by t diamond bla aluminum fo coolant used Optically for ' marked and f 3.2.3 Fracture Surface Morphology The examination and analysis of the fracture surface morphology can yield information about the nature, locus and mechanism of the failure processes in the material. In the case of ASR modified cement concrete, the fracture surfaces of tensile test specimen were examined to determine the locus of failure. The fracture surfaces were examined in a Philips Electroscan 2020 Environmental Scanning Electron Microscope (ESEM). The fracture surfaces were first isolated from the tested dogbone tensile test samples by cutting approximately 1/4 inch thick sections near the fractured end with a diamond blade saw. Prior to cutting it is important to cover the fracture surface with aluminum foil or plastic film to prevent contamination of the fracture surface with the coolant used by the saw. After isolating the fracture surfaces, they were examined optically for regions of interest. Regions with ASR particles on the fracture surface were marked and further examined in the ESEM at high magnifications. 38 Fig“ re 33 I] U-shaped end-clamp 2 inch x 2 inch 1/ square 1 0” L l to Figure 3.3 Tensile test specimen showing locus of failure and strain guage fixture 39 33 Result Result: presented belo 33.1 Contai The co It is ditlicult mixture of va- process. To 1 particles (rubl nature of the i he the same C0Imposition 3 0f mhber \Ver (mom l}'pes can be Seen ir 3.3 Results Results for the three types of tests described above for cement concrete are presented below. 3.3.1 Contact Angle The contact angle data was obtained by selecting representative particles of ASR. It is difficult to isolate and analyse the substrate material accurately since ASR is a mixture of various types of plastics and rubbers in different stages of the natural aging process. To maintain some standard for purposes of comparison, elastomeric ASR particles (rubber particles) were selected for contact angle measurements. Due to the nature of the ASR, the various substrates used for contact angle measurements could not be the same and the results should be interpreted with the knowledge that the exact composition and state of the different substrates used could not be ascertained. Flat pieces of rubber were chosen for the tests and care was taken to choose similar particles for the various types of surface treated ASR. The contact angles obtained afier surface treatment can be seen in Fig. 3-4. 40 Control (untte Detergent W a Detergent + Ru Mediantcal Ru Detergent + Latex C Sulpho AodE Detergent - “mm were obtaincc Some surface etching incre dEtergem “(1 indicate any : matrix for tht 332' Di ['0 Base 0f SurfaCe if Control (untreated) r . ‘ a - H—I 63.74 Detergent Washed CZE—l 16.96 Detergent+Rubbing l . H—l 28.66 Mechanical Rubbing L . .1.» :5 -- 9,;qu 57.38 Detergent+Latex l ;., -_, ~ _ , WBBJB Latex Coated] . . , ~~ . 5W 76.21 Sulphonated T‘ 7 ' . _ U f" HH 82.00 Acid Etched L_ e -. . Fig-4 84.15 Detergent+Acid L - __ ' ‘ ., . 7 . W ; :3. 121.86 a £0 4b 6‘0 ’ 8‘0 “130 135140 Contact Angle (degrees) Figure 3.4 Contact angles of surface treated ASR The contact angles show a wide variation with surface treatment. The best results were obtained with detergent washing. The contact angle decreases to from 64° to 17°. Some surface treatments were seen to increase the contact angle. Sulphonation and Acid etching increased the contact angles to 82° and 85° respectively. Combination of detergent washing with acid etching, latex coating and mechanical rubbing did not indicate any additional benefits. The contact angle results were used to determine the test matrix for the direct tensile tests. 3.3.2. Direct Tensile Test Based on the contact angle results, tensile tests were performed on various types of surface treated ASR-cement concrete compositions as well as combinations of surface 41 33111161115: T by fitting [l The I 35 sho\VS 1T tensile stren‘: and 4% ASR I)eun sudacetreaU' water. Deter; ASR has a \' tensile stren; contact angle anecuyeh' show any st; ASR concer sdphonadon Cmnhnanoni DDES of surf The Onti treatments. The effect of ASR content on the cement concrete properties was determined by varying the ASR content from 2% to 4% by volume. The peak load at failure was determined from the load-displacement curves. Fig. 3.5 shows the effect of ASR addition on the tensile strength of cement concrete. The tensile strength wasn’t affected adversely by the inclusion of ASR and addition of 3% and 4% ASR showed a slight improvement in strength. Detergent wash and sulphonation were selected for comparison from the various surface treatments for ASR due to the wide difference observed in the contact angles with water. Detergent washed ASR has a very low contact angle with water while sulphonated ASR has a very high contact angle. This can result in a large difference in the ultimate tensile strength of the material due to the dependence of interfacial adhesion on the contact angles. Fig. 3.6 and 3.7 show the effects of detergent washing and sulphonation respectively on the tensile strength of the cement concrete. Detergent washing did not show any statistically significant effect on the tensile strength and with higher (3-4%) ASR concentration, the average tensile strength showed a slight increase. With sulphonation, the tensile strength was seen to decrease. Other surface treatments and combinations of these treatments were also tested. The summary of results for all other types of surface treatments can be seen in fig. 3.8. The various surface treatments for ASR did not affect the tensile strength of the ASR modified cement concrete significantly. However, the concentration of ASR was seen to control the ultimate tensile strength. 3% ASR loading was determined to be the Optimum concentration. 42 2500 C C C 0 0 8 Wm alto. r.. l l: O O O O r. 5 0 W m 5. 2 1. 1 g F 3: 6.3.. 2.2:: 8:2:qu 3: .23.. 2.2.: £35.85. Fig"? 3r. 2500 2301 2387 .3. E 2000 A 1752 o .4 g 1500 a S '— 5 1000 .§ :5 E 500 - 0 ~ l l * Control 3% 4% (0% ASR) untreated untreated untreated ASR ASR ASR Figure 3.5 Tensile strength of untreated ASR modified cement concrete 2500 § 2000 . 1: fl 3 2 1500 . '5 E '— E 1000 . . 3 .E a 5 500 o .2 . g 7 Z, : Control 2% ASR + 3% ASR + 4% ASR + (0% ASR) Detergent Detergent Detergent Figure 3.6 Tensile strength of detergent washed ASR modified cement concrete 43 2500 P.— 2000 1 500 O O 0 0 0 0 5 3: one; 2.2:; 83:.an Figure 3.7 \ 2 m m w 1 m 1 m 3: .26.. 2.2.0... 83::qu 0 “gm: 331 2500 2000 v 1901 § 13 1500 at .l 2 2 1000 ,, ,2 g 500 E a 5 o a Control (0% ASR) 2% 2% 3% ASR+Sulfonation ASR+Detergent+ ASR+Detergent+ Sulfonation Sulfonation Figure 3.7 Tensile strength of sulphonated ASR modified cement concrete 2500 3 2‘ Maximum Tensile Load (lb) g 9 0 + + + + c: m? +*-' +“m mp (D' n:=x (EC: 5 .0 (003 (005 << 031 ND ND Figure 3.8 Summary of tensile test results for other ASR surface treatments 44 l \ l 3.3.3 Fracture Surface Morphology In characterizing the surface morphology, the surface of the ASR, cement matrix and the interface between them was the main criterion. The samples tested were : (1) control samples, (2) untreated ASR, (3) detergent washed ASR, (4) sulphonated ASR and (5) detergent washed + sulphonated ASR. The surface morphologies of these different types of concrete, and the surfaces of treated ASR particles can be seen in Figures 3-9 to 3-13. Figure 3.9 Surface morphology of cement matrix in control cement concrete samples at 100X. (White bar = 400um) 45 ..+3¢w.wwulsauadflirwlnw4ififl75...!» 4.. ..--$..w.w_ VI; in :1? findiithwxfiflafiwwkawwlaimumfl .yfl P... Figure 3.10 Surface morphology of ASR particle (left) and cement matrix (right) in untreated ASR-concrete samples at 100X. (White bar = 400 um) Figure 3.11 Surface morphology of ASR particle (left) and cement matrix (right) in detergent washed ASR-concrete samples at 100X. (White bar = 400nm) 46 3a.! . l A a. “as; ‘.Ill.& l ‘ Aha- . air; H.1329 .rv. Figure 3.12 Surface morphology of ASR particle (left) and cement matrix (right) in sulphonated ASR-concrete samples at max. (White bar = 400 um) Figure 3.13 Surface morphology of ASR particle (left) and cement matrix (right) in detergent washed+sulphonated ASR-concrete at 100x. (White bar =400 um) 47 3,4 Discus The su concentration effective in re mixing proce: energetics 3 ie The to addition of Af “ith the help Specimen. The m mainly pull ( cleavage of ti dlm‘rence in 1 howeyer Shov Sulphonated I fmCture surfd number 0f \ dEtergem \\ 3.4 Discussions The surface treatments for ASR prior to use were found to be less critical than the concentration of ASR used in cement concrete. Surface treatments were seen to be effective in reducing the contact angles of the ASR with water, but in the cement concrete mixing process, the forced contact between the ASR and the cement makes surface energetics a less critical factor. The tensile strength of the cement concrete was found to be unaffected by the addition of ASR particles except in the case of sulphonated ASR. This can be explained with the help of morphological data obtained from the fracture surfaces of tensile test specimen. The macroscopic observation of the fracture surfaces show that the ASR particles mainly pull out from the matrix. In the few cases of mechanical interlocking, there is cleavage of the ASR particles. From the morphological analysis, there is no apparent difference in the surface of the ASR inclusions in the different samples. The matrix phase however shows different features. In the 2% Sulphonated and 2% Detergent washed + Sulphonated ASR samples, a large number of voids were observed throughout the fracture surface. This correlates with the low tensile strength of these samples. The number of voids in the matrix were qualitatively smaller and less frequent in the detergent washed, untreated and control samples. Thus from the fracture surface morphology it can be seen that the void content and distribution in the cement phase can be a controlling factor in the ultimate tensile properties of ASR modified cement concrete. The total void content of cement concrete specimen was measured in a related 48 Study [46l an surface treatc 1C AIR convent (56) L) FlgUre 3_1. ln Ill-c This surface acidic surfat ‘he ASR Willem fOI' \ findings fro: study [46] and results for the net air void content in cement concrete samples for different surface treated ASR is shown in Figure 3.14. Air Content Figure 3.14 Air void content of surface treated ASR modified cement concrete In the case of sulphonation, the surface of the treated particles is acidic in nature. This surface is neutralised by CaC03, but in the case of incomplete neutralisation this acidic surface can react with the basic cement matrix and cause formation of voids along the ASR-cement interface as seen in the last two columns in Figure 3.14. The air void content for other surface treated ASR were lower than sulphonated ASR and confirms the findings from microstructural observations. The high amount of resultant voids can give 49 rise to high tensile stren concrete “:1 of the cemi sufficient to premature f; dcpendent or evaluated in improvement not improve received Ag; An e) the effect of Compressll‘e Shrinkage. im Scaling resis: It “a. rise to high stress concentrations and promote the crack growth process leading to low tensile strength. 3.5 Conclusions The objective of the investigation into the suitability of ASR as a filler in cement concrete was to find a value added application for ASR without affecting the properties of the cement concrete adversely. It was shown that 3-4% ASR concentration was sufficient to retain and in some cases improve the tensile properties of concrete. The premature failure of cement concrete modified with sulphonated ASR was found to be dependent on the void morphology in the cement phase. Various surface treatments were evaluated in order to enhance the wettability of the polymer particles, but despite the improvement in wettability seen from contact angle experiments, the tensile strength does not improve significantly and the best performance was obtained from untreated, as received ASR. An extended study2 was undertaken at Michigan State University, to investigate the effect of ASR addition on the engineering properties of cement concrete such as compressive strength, flexural strength, water absorption, free and restrained drying shrinkage, impact strength, rapid chloride permeability, freeze-thaw durability, deice salt scaling resistance and abrasion resistance [46]. It was determined from these studies that the addition of ASR to cement concrete has some benefits such as improvement in resistance to shrinkage and water absorption, higher abrasion resistance, tensile and impact strength. However there are adverse effects like reduction in chloride permeability, compressive and flexural strength. Afier 50 balancing volume fr; improved c 50mm.“ p balancing the improvements and the adverse effects it was determined that the use of 3% volume fraction of ASR as an additive to cement concrete yielded a product with improved overall performance for slab-on-grade pavement applications [46]. 2 Sorushian P., Department of Civil and Environmental Engineering, Michigan State University, USA. 51 In the important to st components a and morpholo properties fro understanding modification 2 "v’m’ironmental structural and IOUglmess mea With ch‘mcmzatio . ASPhahlfii . \rOId Mon ' FrEICture 1(- . Poll'mer p . Lap Shear CHAPTER FOUR ASPHALT CONCRETE In the study of a complex material like polymer modified asphalt concrete, it is important to study the key morphological and microstructural properties of the individual components as well as their interactions and failure mechanisms [47]. Microstructural and morphological information is extremely important in the prediction of pavement properties from the physical and chemical data for binders and aggregates. An understanding of the morphological changes occurring in asphalt as a result of polymer modification and their effect on the locus and mechanism of failure as a function of environmental conditions is a critical factor in pavement design and optimization. The structural and engineering properties of asphalt concrete can be predicted from fracture toughness measurements and fracture morphology. With these objectives, experimental methods have been developed for the characterization of the following properties - o Asphalt binder morphology o Void Morphology - Fracture toughness o Polymer phase morphology o Fracture surface morphology 0 Lap shear adhesion 52 The l fundamental a predictive t 4.1 Asph An e1 3030. was us: modified and Electron Mic: 0f the ESEN conductive co the microstru‘ «1nd CL‘Phall Cc The pressure typically used either C02 0r destrum‘e en the ESEM in. Melamine M All Ex binder thin fi mold in 3 hot tempera“ire n The cumulative information obtained from these experiments will provide a fundamental understanding of the materials and processes in asphalt concrete and provide a predictive tool for pavement performance. 4.1 Asphalt Binder Morphology An environmental scanning electron microscope (ESEM), Phillips ElectroScan 2020, was used to investigate the microstructure and morphology of unmodified, polymer modified and aged asphalt binders. The ESEM (Figure 4.1) is similar to the Scanning Electron MicrOSCOpe (SEM) in operation, but has a few advantages. The main advantage of the ESEM is the ability to observe non-conductive materials without the use of conductive coatings on the surface. This makes the instrument an ideal choice to observe the microstructure, crack growth mechanisms and fracture morphology of asphalt binders and asphalt concrete; materials which would be susceptible to charging effects in a SEM. The pressure level in the ESEM specimen chamber is significantly higher than that typically used in an SEM and pressure is maintained between 2 to 5 torr by introducing either C02 or water vapor in the chamber. This provides a relatively benign and non- destructive environment in which sample damage is minimized. The conditions used in the ESEM for all experiments were: 2 to 2.5 torr pressure using water vapor, 20keV accelerating voltage, 55% condenser lens setting and 2.1 second scan time. All ESEM morphological studies on asphalt binders were performed on asphalt binder thin films of thickness 0.005 inch prepared using a picture frame compression mold in a hot press. The thickness of the picture frame used was 0.005 inch. The molding temperature used was 15°C below the softening temperature of the asphalt system which 53 was measured of 509C lunmi asphalt binder postcured sil- binder for S". asphalt hindc preparation. tl aluminum foi was measured by thermal-mechanical analysis (TMA). Typical values were in the range of 50°C (unmodified AC-lO) and 60°C (AC-10-5%SBS). Afier preheating the plates, the asphalt binder was placed in the open mold between paper release liners treated with a post-cured silicone based release coating. Contact pressure was applied to preheat the binder for 5-10 minutes and the press closed at a rate of 2kips/min. All the prepared asphalt binder films were stored in a refrigerator till used. For final ESEM sample preparation, the release paper was removed and the asphalt binder thin film placed on an aluminum foil substrate. Figure 4.1 Philips Electroscan 2020, Environmental Scanning Electron Microscope The prepared samples were mounted in the ESEM and the surface observed extensively for any features. Because of the absence of a conductive layer on the sample surface, evaporation of oils from the surface region is believed to occur and it was found that asphalt binder thin films exposed to the electron beam, for times ranging from 0.5 to 5 minutes depending on the type of binder, showed a network structure [47, 48] in the 54 binc the ' cont tensi perfc asph; churn detail F [fill alti- binder as seen in Figure 4.2. This network structure was found to be a characteristic of the binder and showed changes in structure with polymer addition, aging and asphaltene content of the binder. Tests were performed on binder films strained in the ESEM using a tensile loading stage to observe the deformation of the network structure. Tests were also performed on pre-strained asphalt binder films and asphalt binders having different asphaltene contents to verify the deformation behavior of the asphalt network and it's characterize it's dependence on the asphaltene content. These results are discussed in detail in Chapter 5. sfifi s. Figure 4.2 Typical network structure seen in asphalt binder thin films after exposure to the electron beam in the ESEM (White bar = 250 um) 55 4.2 fihei inth by ut can 1 can t condi “hen the p( featur fluore aPpro Capnn lnt'en in\‘ers neg 4.2 Polymer Phase Morphology The polymer phase morphology in PMA was studied [47, 48] using the Confocal Laser Scanning Microscope (LSM, Zeiss 10) which works on the principle of fluorescence. Unsaturated bonds in materials can fluoresce when exciting light at specific frequencies is incident upon that material. When a polymer containing unsaturated bonds is excited with a laser , the emitted fluorescence can be observed with the help of suitable filters. This is useful in determining the shape, size and distribution of the polymer phase in the asphalt binder matrix. The confocal LSM differs from other microscopic methods by utilizing an intense laser source which collects light only from the focal plane, which can be below the material surface. This allows the observation of the polymer phase distribution in the bulk of the asphalt binder instead of the surface where the morphology can be affected by any number of factors including the processing methods, storage conditions, etc. Polymers like SBS, SEBS and SBR were observed to fluoresce strongly when illuminated with blue light (488 nm) thereby revealing the size and distribution of the polymer constituent phase. Under reflected light, the modified asphalt binder appears featureless. However, when examined under blue laser excitation (488 nm wavelength), fluorescence was obtained in the red region (590-620 nm wavelength). Using the appropriate band pass filter (590-620 nm) the polymer phase is seen clearly. The image is captured by a computer and is saved in gray scale in PIC format. The gray scale is then inverted using an image processing software (Corel Photopaint) for better clarity. Afier inversion, the polymer phase can be seen as a dark area over a light background. The ESEM technique used for determining asphalt binder morphology was also used to determine the polymer phase morphology of the particulate Crumb Rubber 56 (C101) and excitation l unsaturatior low temper morphology 4.3 Volt TM analysis. vi experiment their distrib 43-1 San The al‘ht'lll COI prepaTEIIOr aid Culling in the San. abSEnce or hinder Res er633 an TE Cleaner f0: (CRM) and Elvaloy AM (Elvaloy) since these polymers did not show fluorescence under excitation by blue, green or red laser. This could be due to the very low amount of unsaturation in these polymers. ESEM imaging of SBR modified asphalt binder films at low temperatures (5°C) using the same technique employed for observing asphalt binder morphology showed the morphology of the SBR phase. 4.3 Void Morphology Two experimental methods were evaluated for void morphology and void analysis, viz. Thin Section Image Analysis [25] and Void Casting. The aim of the experiments was to identify the different types of air-voids present in asphalt concrete, their distribution and microstructure. 4.3.1 Sample Preparation The void analysis samples were prepared from 15mm thick sections cut from asphalt concrete Marshall samples using a Felker 41-AR diamond blade saw. Section preparation followed the method of Kirsten Ericksen [49-51] and Edward Scott [25]. To aid cutting, the samples were refrigerated for 24 hours prior to cutting and the water bath in the saw was filled with ice to keep the sample and blade temperature low. In the absence of such precautions there can be a large amount of local softening of the asphalt binder near the cutting edge. This is caused by frictional heat generated during the cutting process and can damage the blade and the sample. Sections of dimensions 70 x 50 x 15 mm were cut in this manner. These sections were cleaned in a Bransonic ultrasonic cleaner for 2 minutes using de-ionized water and then dried at room temperature for 24 57 hours. Aftc asphalt cor fluorescent m'th flUOl't' light and b at 53.0 nm filter. The sections in The sectioi immediate] reduced to held at this as the air t from the S Pf0cess he subsides. 1 imPregnate tempeTaIUf Lem Wale polishinQ \ carbide arbl each grit :1 dried Secij hours. After air-drying, the samples were placed in a desiccator for 24 hours. The cleaned asphalt concrete sections were vacuum impregnated with a two part epoxy resin and a fluorescent dye (Struers Epofix/Epodye resin impregnation system) to fill the air-voids with fluorescent epoxy. The Epodye (Hudson Yellow) fluoresces at 440nm in visible light and between 256 nm and 285 nm in ultraviolet light. Fluorescence emission occurs at 530 nm making the impregnated voids detectable through an appropriate band pass filter. The impregnated samples were prepared by immersing the dry asphalt concrete sections in the mixed Epofix resin with 5 grams Epodye added to 1 liter of Epofix resin. The sections were immersed in an aluminum tray containing the fluorescent resin and immediately placed in a vacuum chamber (VWR 1410, General Electric) and the pressure reduced to -0.97 bar. It takes 2 to 2.5 minutes to reach this pressure and the samples are held at this pressure for 3 minutes. Outgassing occurs within the asphalt concrete samples as the air entrapped in the voids is removed. The epoxy foams till all the air is removed from the samples. Partially releasing the vacuum 2 to 3 times during the outgassing process helps to get thorough impregnation of the samples. When the outgassing subsides, the chamber is vented to the atmosphere slowly over 2 to 3 minutes. The impregnated samples are removed and placed on a flat surface for curing at room temperature for 7 days. After cure, the impregnated sections were rough polished on a Leco water cooled belt grinder (BG-20) to remove excess epoxy from the surface. Final polishing was done on a Struers Abramin Automated polisher progressively using silicon carbide abrasive paper of grits 120, 240, 320, 600, 1000, 2400 and 4000, polishing at each grit for 2 minutes. The samples were then rinsed and dried at room temperature. The dried sections were glued to flat glass petrographic slides (dimensions 51x75 m) using 58 EPON 5 Petro—Il mm thic impregn; are hence 43.2 T Tl observed An excite second ha source Use Were Capil CUE-2 im imlmgnate m3 fluoreg “helm l.67X Pllo Thi ”Dag“ \k kl Si‘aleg ETC EPON 828 epoxy and V-40 curing agent (Shell Oil Co.) A thin sectioning saw (Buehler Petro-Thin) was used to cut and polish the asphalt section on each slide to about 1-1.5 mm thickness. Final polishing was done in small increments till the thickness of the impregnated asphalt concrete section was 30 microns. Sections prepared in this manner are henceforth referred to as thin sections and used for image analysis of voids. 4.3.2 Thin Section Image Analysis The void microstructure and morphology of thin asphalt concrete sections was observed under a BH-2 Olympus microscope using reflected light and a set of two filters. An exciter filter was used to cut off the source light above 515 nm wavelength and a second band pass filter at 530 run was used in the path of the reflected light. The light source used was a 100W TH3 Olympus power source with a halogen bulb. The images were captured by a CCD video camera and the output directed to a computer running CUE-2 image analysis software (Olympus). The thin sections, as explained earlier, are impregnated with fluorescent epoxy that fills the air-voids in the asphalt concrete, thus the fluorescent areas observed are directly related to the shape and size of the voids seen in the 2-dimensional section. A 2.5X objective lens was used in the microscope and a 1.67X photo relay lens was used in the CCD camera giving a net magnification of 38X. The CUE—2 system analyses images in 256 color gray scale. The images captured by the camera were digitized and converted to gray scale. To achieve better contrast, the images were converted to black and white by selecting a dividing value on the gray scale histogram. All the gray scales below the dividing value were converted to black and the scales greater than the dividing value were converted to white. A dividing value of 40 59 was 566“ dependent cont'ersior areas on a the image Th: identifiabli specific le the object 1 the object. 171110 15 the factor is; circle and length of ti aImyzed. ] is the d151, Starling fro Tht Sample are a minim“ SecziOn. r. and 34 th was seen to give the best results. The selection of the dividing value is operator dependent and care should be taken to remain consistent over multiple samples. Afier conversion of the 256 gray scale image to bi-level, the fluorescing areas are seen as white areas on a black background. Since the software is designed to analyze the black areas, the image is inverted so that voids appear as black areas on a white background. The analysis was performed by the software and the parameters recorded for each identifiable void were: area, perimeter, Ferret’s diameter, aspect ratio, shape factor, specific length, areafract and average radius. The Ferret’s diameter is the projection of the object measured at predetermined angles through the center of gravity to the edges of the object. This was measured at four different angles; 0°, 45°, 90° and 135°. The aspect ratio is the ratio of the minimum Ferret diameter to the maximum Ferret diameter. Shape factor is a measurement of the sharpness of an object. A shape factor of 1 refers to a circle and a shape factor of 0 refers to a straight line. The specific length is the total length of the object. Areafract is the ratio of the area of the object to the total frame area analyzed. The average radius is the mean of the eight Martin radii, where a Martin radius is the distance from the center of gravity to the object edge measured at 45° intervals starting from 0°. The area analyzed for each sample should be at least 500 mm2 spread over a total sample area of 7,000 mm2 [25,50]. The thin sections have an area of 3,500 mm2 and thus a minimum of two sections were analyzed for each sample. The field image area at 38X was found to be 17.5 mmz. Thus a minimum of 29 samplings have to be taken from every section. To enhance accuracy, an average of 70 samplings were done on each thin section and 2-4 thin sections were analyzed for each composition. 60 The was further area (N); E Form factor Dun sample was software as told sizes eliminatinc The raw data was saved by the CUE—2 software in spreadsheet format. This data was further processed to obtain the following parameters: Air void content (Pa); Average area (A*); Equivalent circle diameter (Da); Average equivalent circle diameter (Da*) and Form factor (F). The equations used for these calculations are shown in Table 4.1 [25]. During image analysis, irregularities in the lighting and refraction from the sample was seen to give rise to electrical noise which is interpreted by the image analysis software as voids. Previous studies have shown that noise is prevalent in the analyzed void sizes smaller than 50 microns [25, 50]. Most of this noise was rejected by eliminating void sizes smaller than 50 microns during the pre-processing step. 61 (nmnnu 1 Average arc Tl - Equu'alent h-~2 l | 1 Average ldlameter. lj l\ lhmFWt l \ mm A: Table 4.1 Equations Used in Image Analysis [25] . . 2A Total Arr Vord Content, Pa Pa = (4-1) Number - 0f - fields x field - area A Average area of air-voids, A* A* = Z . . (4-2) Number-0f -alr-v01ds Equivalent circle diameter, Da Da _—_ 2 [A (4-3) ‘ H D Average equivalent circle D; = Z a . . (44) diameter, Da“ Number-0f -a1r-v01ds L 2 (Da) Form Factor, F* F = 2 *100 (4-5) Fe Note: A = Area of void 62 quantitatch main probl- analysis of The values 35% of tilt“ 4-59'6. Thfil representat accuracy 0 Concrete 35 asPhalt can for analysil Tilt 4.3.3 Void Casting Method An alternate method for void analysis was developed to achieve better quantitative results than those obtained from the thin section image analysis method. The main problem encountered in the thin section image analysis was the two-dimensional analysis of the irregularly shaped three-dimensional air-voids found in asphalt concrete. The values for total air-void content obtained by the image analysis were generally about 25% of the expected air void content based on the Marshall sample design expectation of 4-5%. The void casting method provides a way to obtain three-dimensional representations of the air-voids from the bulk of the asphalt concrete; thus increasing the accuracy of the data obtained. The concept involves visualizing the air-voids in asphalt concrete as ‘molds’. These ‘molds’ can be impregnated with epoxy and after cure the asphalt can be extracted with solvents to provide 3-dimensional castings of the air-voids for analysis. The initial sample preparation for this method was similar to that used for thin sections used in image analysis. Asphalt concrete sections 15 mm in thickness were cut from asphalt concrete Marshall samples using a diamond blade saw (Felker 41-AR). The cut sections were dried in air at room temperature for 24 hours and vacuum impregnated with fluorescent epoxy. The impregnated sections were allowed to cure for 7 days at room temperature. After full cure was achieved, the excess epoxy from the surface of the impregnated sections was removed using a water cooled belt grinder (Leco, BG-20) till only the asphalt concrete surface was visible. The sections were polished on all sides till it assumed a rectangular shape with even thickness. This was done to ease the measurement of the total volume of the section. The impregnated samples were heated in 63 an oxen at apart into . mmmm structure it excess of' binder and chloroethy remox'ed. ' retained pl fluorescen‘ Figure 43 epoxy pan gm. and 1h 0792.86 [ each epox CUl'fllllalin V’Oid Cont: dismbutio an oven at 100°C for 10 minutes to soften the asphalt. The softened samples were broken apart into 4 to 5 smaller parts by gently applying pressure with a glass rod. Care was taken to avoid using excessive force during this step in order to keep the epoxy filled void structure intact. The samples (approx. 35 x 50 x 15 mm) were immersed for 10 minutes in excess of tri-chloroethylene (100 to 200 ml) which is a very good solvent for asphalt binder and does not affect the epoxy when exposed for short times. The mixture of tri- chloroethylene and asphalt concrete was put in a centrifuge and all the solvent was removed. This process was repeated till all the binder in the sample was extracted. The retained portion in the centrifuge consists of clean aggregates and the voids cast in fluorescent epoxy. The epoxy particles were separated from the aggregates manually. Figure 4.3 shows the voids typically obtained from a section of asphalt concrete. The epoxy particles were weighed individually using a Sartorus balance accurate to 0.0001 gm. and the weights recorded. The density of the epoxy used was calculated using ASTM D792-86 [52] and found to be 1.1144 gm/cc at 23°C. Using the density and the weight of each epoxy particle, the volume of each air-void in the sample was calculated. The cumulative void volume and the net volume of the sample was used to calculate the air- void content of the sample. Since the volume of each void is known, the void size distribution can be plotted accurately. 64 magnifica of aSplint SamPlcs \lefir 10 r gross SUr: . Figure 4.3 Three-dimensional voids in asphalt concrete 4.4 In-situ ESEM Tensile Tests The ESEM tensile test was used to study the fracture morphology, locus of failure and the failure mechanisms in asphalt concrete [19, 48]. Thin asphalt concrete sections were loaded in a tensile stage in the ESEM and the failure process was observed at high magnifications. 4.4.] Sample Preparation and Testing The samples used for the ESEM tensile test were 30 x 15 x 1 mm sections of asphalt concrete cut from 63.5 x 101.6 mm diameter asphalt concrete Marshall samples using a Felker 41-AR diamond blade saw. The cut sections were washed in water to remove debris and polished lightly using 120 grit abrasive paper to remove any gross surface imperfections. The polished sections were dried at room temperature for 24 65 hours in Stephens 8010) wi stage. Th The poly section to hacking \ stage. Th: by a suit entire sur. crack init process. b that the s ObSEn'e a load-diSpl Observed. mechanisz q - Selling ZiI' temperate Ti “'35 a l SQ Used fOr c hours in a desiccator. The dried sections were adhesively bonded with epoxy (Miller Stephenson Chemical Co., M8907) to strips of 0.01 inch thick polycarbonate film (Lexan 8010) with dimensions 40 x 20 mm. to facilitate loading and clamping in the tensile stage. The sample configuration for in-situ ESEM tensile tests can be seen in figure 4.4. The polycarbonate backing film was notched under the center of the asphalt concrete section to keep the locus of failure in that physical region. The edges of the polycarbonate backing were drilled to accommodate the mounting screws on the ESEM tensile loading stage. The tensile stage is mounted in the ESEM and the strain rate is manually controlled by a switch. This is necessary since the samples are strained in small increments, the entire surface of the sample scanned for initiation of cracks, and then strained again till crack initiation is observed. This method allows for careful observation of the failure process, but does not allow the monitoring of sustained load on the sample. It was found that the samples relaxed and the applied load decreased during the time it takes to observe and record the features on the sample surface, thus preventing any quantitative load-displacement correlations to be made with the fracture surface morphology observed. When a crack is located, the sample is strained further and the crack growth mechanism is observed and recorded. The operating conditions in the ESEM were : 2 to 2.5 torr pressure using water vapor, 20keV accelerating voltage, 55% condenser lens setting and 2.1 second scan time. In addition, some tests were performed at -20°C temperature, to observe the low temperature adhesive failure processes. The fracture surface images were saved as graphic files and the fracture process was also saved on video for fixture analysis and reference. Samples of fresh PMAC were used for characterizing fracture morphology 66 Asphalt Concrete / Sample ‘/|7/A A lfi :—> Tensile Load \ Notched Polycarbonate Sheet Sample Dimensions : 30 mm x 15 mm x 1mm Figure 4.4 Sample configuration for in-situ ESEM tensile test 4.5 Fracture Toughness Fracture toughness is the energy required per unit area to create a new crack surface [53 ]. The value of the fracture toughness relates to the resistance of the material to crack propagation. This property is thus important to characterize the performance of asphalt concrete. At temperatures below 0°C, the fracture in asphalt concrete was observed to be adhesive. Adhesive failure is defined as fracture surface propagation via the asphalt binder-aggregate interface. Thus at low temperatures, the fracture toughness can be used to characterize the interfacial strength or adhesive strength of the asphalt concrete. There are several different methods and definitions of the fracture toughness [54]. For elastic materials fracture toughness can be measured in terms of the critical stress intensity factor (Krc) or the critical strain energy release rate (Glc). These parameters are defined by the principles of Linear Elastic Fracture Mechanics (LEFM) and describe linearly elastic materials very well. However, non—homogenous, viscoelastic materials like asphalt concrete are not linearly elastic and have a large amounts of plastic 67 deformat Thus it 5 fracture lllUS glVI paramete crack pri fracturet 55]. Exp testing a B thickness and failur maximum encrg} [0 “llcre. deformation, especially at the crack tip, which is not accounted for in the LEF M theories. Thus it is necessary to devise experiments based on the principles of Elastic Plastic Fracture Mechanics (EPF M) which account for plastic deformation at the crack tip and thus give a better representation of the fracture toughness of the material. One such parameter used to determine the fracture toughness is the J-contour integral [54-55]. The J -contour integral is a path independent measure of the energy required for crack propagation at a notch tip. The critical value of the J-contour integral gives the fracture toughness of an elastic-plastic material with a large plastic deformation zone [54- 55]. Experimentally, the critical J-integral fracture toughness (Jrc) is determined by testing a series of notched beams in a 3-point bending beam configuration. Beams notched to different lengths ranging from 40% to 60% of the beam thickness were tested. A load vs. midpoint deflection curve was recorded for each sample and failure (crack propagation) was defined as the point at which the load on the beam is maximum. The energy under the curve till the ‘failure point’ is termed as the ‘total strain energy to failure’. The critical value of the J -integral, JIC, is given by Equation 4-6 [56]: 1 d U J ,C = — — — (4-6) b da where, J 1c = critical value of J-integral in plane strain, Pa-m (lb—in/inz) b = beam width, mm (in.) U = total strain energy to failure in the notched beam, J (lb-in) a = notch length, mm (in.) 68 4.5.1 Sample Preparation and Testing At the present time, ASTM standard tests do not exist specifically for the testing of notched asphalt concrete beams. Hence the following sample preparation and test procedures were used. Asphalt concrete beams of dimensions 50.8 x 50.8 x 203.2 mm (2 x 2 x 8 in.) were used for testing. These beams were cut from a larger beam of dimensions 101.6 x 101.6 x 406.4 mm (4 x 4 x 16 in.) compacted using the California Kneading Compactor in the Soils Testing Laboratory of the Michigan Department of Transportation, Materials Research Lab, Lansing, Michigan. The beam mixes were prepared in the Dept. of Civil & Environmental Engineering at Michigan State University as described in previous chapters. Each beam was made from 10 kg. asphalt concrete mix divided into three equal parts of 3334 gm. each. The beam mixes were heated at 175°C (350°F) for 2 hours and allowed to equilibrate prior to compaction. The number of blows used for each specimen was modified to achieve an expected air void content between 3 and 5 percent. Each compacted beam was cut into four identical beams of dimensions 50.8 x 50.8 x 203.2 mm (2 x 2 x 8 in.) using a diamond blade saw. All surface irregularities were polished and a notch was cut in the center along the beam width to the required depth ( 40% to 60% of the beam width) with a diamond blade saw. 69 A minimum of 4 different notch lengths were used for each composition. The notched beams were allowed to dry for 24 hours at room temperature and then equilibrated at -10°C (14°F) for 2 hours in a temperature controlled chamber using liquid nitrogen as cooling agent. The 3-point bending beam test was performed in the UTS using a LVDT to measure the mid-point deflection. The tests were performed at a constant loading rate of 1.27 mm/min. (0.05 in./min.) and 117.8 mm (7 in.) span. A schematic of the sample configuration is shown in Figure 4.5. Load 0 I V I l ’ M 0.8- 1.2 in. notch E 7in. ] E 8in. E )2 K Figure 4.5 Three-point bending beam sample configuration for low temperature fracture toughness tests 70 Load - deflection curves were plotted and the point of failure determined. The total strain energy per unit width (U/b) was plotted against the notch length and a linear fit to these points was obtained through regression. The slope of this line gives the rate of change of strain energy per unit width with respect to the notch length at failure, or the critical value of the J -contour integral fracture toughness (11c). 4.5.2 Effect of Aggregate Gradation Aggregate gradation is an important factor to be considered in fracture toughness measurement. The repeatability of the data obtained improves significantly with a reduction in the aggregate size compared to the G7 gradation used for Marshall samples. When the aggregate size is large compared to the beam width, the aggregate size distribution at the notch tip can be very non—uniform. Since the fracture toughness measures the energy required for crack initiation at the notch tip, the presence of a large aggregates at the notch-tip can lead to scattered results due to the difference in modulus between the aggregate and asphalt binder. The repeatability increases as the ratio of aggregate size and beam width decreases. It was found that by using an aggregate gradation where 99% of the maximum aggregate size was 25% or smaller than the minimum beam dimension, the repeatability increased significantly. In repeatability tests performed on notched beam samples, the percent standard deviation was found to be greater than 10% for beams made with the G7 gradation. Beams made with the Fine Mix have higher repeatability and standard deviations were found to be below 10%. Representative repeatability test data is given in Table 4.2. 71 4.5.3 Selection of Fine Aggregate Gradation The asphalt concrete beam width used for fracture toughness measurement was limited to 2 inches due to limitations of available material and equipment. Thus the G7 gradation could not be used for the fracture toughness samples. Due to the necessity of maintaining the maximum aggregate size in the asphalt concrete to 25% of the beam width, it was considered necessary to use a finer aggregate gradation. The fine mix gradation (FMG) used for fracture toughness tests is shown in Table 4.3. The rationale for selecting this gradation is given in the following section. Table 4.2 Effect of aggregate size on peak load of notched three-point bending beam test samples Asphalt Binder AC10 AC 10 AC5 Notch Length 50% of width 60% of width 50% of width Gradation G7 G7 Fine Mix Sample 1, peak load (lb) 136 108 113 Sample 2, peak load (lb) 198 136 113 Sample 3, peak load (lb) 196 133 123 Sample 4, peak load (lb) 244 110 126 Average 193.5 121.8 118.8 Std. Deviation 22.9 % 12.2% 5.7% 72 Table 4.3 Fine Mix Gradation (FMG) used for Fracture Toughness Tests FINE MIX GRADATION Size (mm) Passing % Retained % Weight (gm) Cumulative weight (gm) 19 100 0 0 0 12.5 100 0 0 0 9.5 100 0 0 0 7.7 99 1 32.5 32.5 4.75 68 31 1007.5 1040 2.37 38 30 975 2015 1.18 26 12 390 2405 0.6 14 12 390 2795 0.3 10 4 130 2925 0.15 7 3 97.5 3022.5 0.075 4 3 97.5 3120 Fly ash O 4 130 3250 73 4.5.4 Binder Film Thickness in Asphalt Concrete The bulk modulus of asphalt concrete is dependant on the aggregate gradation used. Due to the change in gradation between the Marshall samples and the fracture toughness samples, a difference in the bulk modulus between the two types of mixes is expected. The fracture toughness, however, is a material property and thus does not depend on the sample geometry or the bulk modulus. It is a microscopic property and not a macroscopic property. Asphalt concrete is a composite material and it may be visualized as comprising of three major regions: aggregate, asphalt binder and the asphalt binder-aggregate interface. The fracture toughness is strongly dependant on the average thickness of the asphalt film between aggregates. The film thickness is also related to the durability of the asphalt concrete as thin films are more susceptible to aging by oxidation. In order to maintain a good basis of comparison between two mix gradations, it is deemed more important by the author to have similar asphalt binder film thickness than to have similar values of bulk modulus. For a given composition of asphalt concrete (94.3% aggregate, 5.7% asphalt binder) the asphalt film thickness is inversely dependant on the surface area of the aggregates. As the aggregate size reduces, the surface area increases leading to a decrease in the average binder film thickness. The selection of the fine mix gradation was guided by a need to minimize the change in surface area while reducing the maximtun aggregate size. This was accomplished by increasing the percent composition of the aggregates for the larger sizes and keeping the composition unchanged for the finer sizes. This can be seen more clearly in Figure 4.6. 74 The film thickness of the asphalt binder was calculated for the G7 and Fine Mix Gradation. The methods used for these calculations are empirical in nature due to the non-uniformity of aggregates. The equations used for calculation of the aggregate surface area [57] and asphalt film thickness [58] are shown below. 100 90 ' " .1 mot—“p 80 +Fine Mix ( 70 .E’ 60 m 13 50 - O. o\° 40 - 30 20 10 0 . , - O) In to N to N co (0 ('0 l0 '- oi or N N ‘9. ". o' o ". ‘- v N ‘- o 0 075 Fly ash Sieve Size (mm) Figure 4.6 Comparison between Fine Mix Gradation used for fracture toughness samples and G7 Gradation used for Marshall samples. 75 Aggregate Surface Area Calculations The surface area of aggregates was calculated according to the following equation [57]. SA=Z(SAF;*P;) where SA = Surface area of aggregate (sq.ft. / lb.) SAFi = Surface area factor for it'1 sieve Pi = Fraction of total aggregate passing the ith sieve The surface area factors for sieve sizes are empirical values calculated to approximate the surface area of the irregular aggregates. Table 4.4 shows the surface area factors used in calculations. Table 4.4 Surface area factors for aggregate [57]. Sieve Size Surface Area Factors Percent Passing Maximum Sieve Size 2 Percent Passing No. 4 2 Percent Passing No. 8 4 Percent Passing No. 16 8 Percent Passing No. 30 14 Percent Passing No. 50 30 Percent Passing No. 100 60 Percent Passing No. 200 160 76 Asphalt Film Thickness Calculation The film thickness of the asphalt binder in the mix is not only a function of binder content and surface area. It is found that the asphalt binder penetrates the porous aggregate surfaces and thus the total amount of binder available for forming a film between two aggregate particles is reduced. The average asphalt binder film thickness in the mix taking into account the absorbed binder volume is given by [5 8] : V0,, * (304,800) f = (4.8) SA * W where Tr = Average film thickness (microns) V,up = Effective Volume of asphalt cement (cu. ft.) SA = Surface area of aggregate (sq. ft./lb aggregate) W = Weight of aggregate (lb) The Effective Volume of asphalt binder (Vasp) is the amount of material available for coating the aggregates and is the difference between the total asphalt binder added to the mix and the amount of asphalt binder absorbed by the aggregates. The average asphalt absorption capacity of the aggregates used was found to be 1.1% [40]. The asphalt binder film thickness calculated for the G7 and FMG mix (5.7% asphalt binder content) is shown in Table 4.5. The binder film thickness was found to be 1 1.1 pm for the G7 mix and 10.5 pm for the FMG. 77 Table 4.5 Asphalt Binder Film Thickness for G7 and Fine Mix Gradations Aggregate Gradation G7 Fine Mix Aggregate Surface Area 21.3 22.5 sq.ft./Ib. Weight of Aggregates 1 1.9 1 1.9 lb Weight of Asphalt Binder 0.7 0.7 lb Density of Asphalt Binder 63.6 63.6 lb/cu.ft Aggregate Absorption Capacity 1.1% 1.1% Effective Volume of Asphalt Binder 0.01 0.01 cu.ft. Asphalt Binder Film Thickness 11.1 10.5 microns 4.6 Lap-Shear Adhesion The Lap-shear test gives a measurement of the adhesive bond strength between two flat parallel plates having an overlap adhesive joint, when pulled apart under tensile loads. The test samples were prepared with aggregate sections and asphalt binder thin films similar to those used for characterization of asphalt binder morphology . The substrate sections were made from 5mm thick slabs cut out from large aggregates. These were cut into sections 1”x1” in area, using a diamond saw. The cut sections were polished with a 200 grit abrasive paper for 20 minutes until no saw marks were visible on the surface. They were cleaned with alcohol and preheated in an air oven to the same temperature used for compression molding of the asphalt film. The asphalt film was cut into 7/8”x7/8” squares and sandwiched between two preheated rock sections. A 1 kg load was applied to the specimen assembly and the compression load 78 increased to 10 kg after the specimen cooled down to room temperature in an hour. The prepared specimen were tested in lap-shear mode3. Lap-shear tests were performed at five test temperatures (20°C, 10°C, 0°C, -10°C, -20°C) for polymer modified AC5 and AC10 binders with polymer content ranging from 0% to 6%. Fracture surfaces of the tested lap-shear samples were examined to characterize the failure modes using optical microscopy. The failure modes were broadly classified into three categories : adhesive, cohesive and mixed mode failure. 4.7 Summary The experimental plan used for characterization of polymer modified asphalt concrete was structured to provide systematic information about the binder-aggregate interface, the microstructure and morphology of the binder and the mechanics of the failure processes in asphalt concrete. The information obtained from these experiments provides insight into the complex processes occurring within the asphalt concrete which lead to pavement distress under service conditions. The changes in properties of asphalt concrete due to polymer modification of the binder can be characterized using this information. With a database of these fundamental properties available, these tests can serve as tools for the prediction of asphalt concrete behaviour from the properties of the component materials. The results obtained from these tests are presented in Chapter 5. 3 Lap-shear tests were performed by Dr. E. Eugene Shin, Research Specialist, Advanced Materials Engineering Experiment Station (AMEES), Michigan State University, USA. 79 CHAPTER FIVE RESULTS 5.1 Asphalt Binder Morphology The morphology of asphalt binder can be revealed in the Environmental Scanning Electron Microscope (ESEM) after exposure to the electron beam (e-beam). When the asphalt binder film is initially viewed, the surface appears to be featureless. However, after the e-beam has been allowed to raster across the surface of the film for 2-3 minutes, a network structure appears. The proposed mechanism for this is based upon the three phase structure of asphalt binder. Asphalt consists of three phases: high molecular weight asphaltenes, medium molecular weight resins and low molecular weight oils. The asphaltenes create a continuous networked phase and are surrounded by a sheath of resin [25,36,48]. The oils make up the rest of the volume and plasticize the asphaltene network. When the asphalt binder is exposed to the electron beam, the oils are believed to evaporate from the surface due to local heating and the underlying network is revealed in the area exposed to the electron beam as seen in Figure 5.1. On removal of the electron beam, the network structure disappears and the surface becomes featureless in 2-3 minutes as the oils from the surrounding asphalt diffuse back into the region. This process can be repeated several times on the same area to reproduce the network structure. The network is capable of deformation under applied loads. Figure 5.2 shows a series of micrographs of the asphalt network subjected to tensile load. The network gradually deforms and aligns itself in the direction of the load. 80 Figure 5.1 Network morphology of asphalt binder. Left : Featureless surface of asphalt film immediately after exposure to the electron beam (150X, white bar = 300nm). Right : The randomly oriented network structure seen after exposure to the electron beam for 2-3 minutes (300x, white bar = 150 um). Figure 5.2 Network structure in asphalt binder film under progressive tensile loading (150X). The network aligns itself in the direction of loading (indicated by arrow.) Left: White bar = 300nm. Right: White bar = 200nm. 81 In order to determine if the network structure is real or an artifact induced by the electron beam as it rasters the surface of the binder, thin films were pre-strained before exposing them to the electron beam in the ESEM. The network structure in these films was seen to be aligned in the direction of the strain as shown in Figure 5.3. Figure 5.3 Pre-strained AC10 asphalt binder thin film, exposed to the electron beam shows network structure aligned in the direction of applied strain (indicated by arrow) at 155x. White bar = 300 um. Since the films were strained prior to e-beam exposure and the network in unstretched films does not show any alignment, it is evident that the network structure is real and exists within the asphalt and that the deformation causes alignment of the network in the direction of the applied strain. 82 5.1.1 Morphology of Aged Asphalt Binders Aged asphalt binders have a significantly different morphology than fresh binders. During the aging process, asphalt undergoes extensive oxidation and there is an increase in the molecular weight of the constituents [31-32]. Low molecular weight fractions, i.e. oils, decrease and the fraction of high molecular weight constituents (resins and asphaltenes) increase. This leads to an increase in the viscosity and modulus of the binder, but adversely affects the toughness and the fracture properties of asphalt concrete. Aging of asphalt binder was simulated using the Thin Film Oven Test (TF OT, AASHTO T179 or ASTM D1754-87) followed by the Pressure Aging Vessel (PAV, AASHTO PPl) Test. Details of the aged sample preparation are discussed in more detail by Shull [31]. One of the prominent features of aged asphalt is the appearance of the network structure. The smooth network fibrils seen in fresh binders appear very coarse and thickened after aging as seen in Figure 5.4. Figure 5.4 Typical morphology of aged asphalt binders. The network fibrils appear coarse and the network can only be seen after substantially long (5-10 minutes) exposure to the electron beam (500K). White bar = 100 um. 83 5.1.2 Effect of Polymer Addition on the Morphology of Aged Asphalt Binders Polymer modified asphalt binders have an enhanced resistance to aging which can be measured in terms of retention of properties in aged polymer modified asphalt binder and concrete. These differences are also seen in the morphology of the binder. The network morphology of polymer modified asphalt is similar to that of fresh asphalt and the network fibrils do not appear coarse. Figure 5.5 shows the morphology of aged AC10—0% Elvaloy AM and AC10-3% Elvaloy AM. In the unmodified binder which is severely aged due to the combined effect of the high temperature used for blending Elvaloy AM into the asphalt and accelerated aging in the Thin Film Oven Test-Pressure Aging Vessel (TFOT-PAV) tests, the network structure is barely visible afier an exposure of 7 minutes while the polymer modified binder with an identical history has a network structure similar to a fresh binder. Figure 5.5 Morphology of aged AC10-0% Elvaloy AM (left) and AC10-3% Elvaloy AM (right) after 7 minutes of exposure to the electron beam (500x, white bar = 100 um.) 84 Similar behaviour is observed in the case of SBS, SEBS and SBR latex modified AC5 and AC10 asphalt binders. However, the behaviour of crumb rubber is contrary to this. The morphology of crumb rubber modified asphalt binders appears very coarse, while that of binder with 0% crumb rubber is similar to fresh binders as seen in Figure 5-6. This may be explained by the fact that the mixing conditions for crumb rubber modified binders are mild (350F, 30 minutes) and consequently the binders do not undergo significant oxidation during mixing. Binders with 0% crumb rubber, when aged further by TFO-PAV, retain most of their original properties. However, in the case of binders with added crumb rubber, the rubber particles are believed to absorb the oils and thus give the binders the characteristic coarse appearance of aged binders. 1("3‘0 HKO‘ ‘ ‘7‘V\ ‘(ul‘flv Figure 5.6 Morphology of aged AC10-0% Crumb Rubber (left) at 300x (white bar = 150um) and AC10-10% Crumb Rubber (right) at 500x (white bar = 100nm) after 2 minutes of exposure to the electron beam. 85 This characteristic of the crumb rubber modified binders may be worthy of further study, especially in the context of durability of asphalt concrete. The rubber particles may act as reservoirs for the low molecular weight fractions of asphalt during the life-span of the road; effectively preventing the oxidation of oils early in the life span of the pavement and maintaining a steady supply of these absorbed oils to the asphalt binder as the pavement ages naturally and the concentration of oils outside the rubber particles decreases. 5.1.3 Effect of Asphaltene Content on the Morphology of Asphalt Binders Asphalt binders from different sources having different asphaltene content were obtained from MDoT to study the effect of asphaltene content on binder morphology. Three asphalt binders were obtained - Source Asphaltene Content Koch Matls. Co., IL 8.8% Amoco Oil Co., IN 15.5% T-M Oil Co., MI 20.4% The network structure was observed in all three binders, but the rate at which the asphalt network becomes visible was found to be dependent on the asphaltene content of the binder. The differences observed in the three binders are discussed below. 86 8.8 % Asphaltene Content The 8.8% asphaltene content binders form the network structure rapidly (approx. 15 sec.) at 300X magnification. On removal of the e-beam, the oils diffuse back into the area rapidly and the surface returns to its original featureless state in approximately 30 seconds. The fibril density is low and fibrils have a larger diameter. Figure 5-7 shows the network formation of an asphalt binder with 8.8% asphaltene content at different times and stages of formation. Figure 5.7 Morphology of 8.8% asphaltene content binder. Left: the network is visible in 15 seconds (white bar = 100 um). Right: surface returns to original state 30 seconds after beam removal (white bar = 150 um). 87 15.5% Asphaltene Content The 15.5% asphaltene content binder network resembles the AC5 and AC10 binders used in the study. The network density is higher than the 8.8% asphaltene binders and the network fibril diameters are smaller. Network formation is slower ( approximately 30 seconds) and on removal of the e-beam the oil diffusion process takes longer ( approximately 1 min). Figure 5-8 shows the network formation seen in binder with 15.5% asphaltene content at different times and stages of formation. Figure 5.8 Morphology of 15.5% asphaltene content binder. Left: the network is visible in 30 seconds (white bar = 150 um). Right: surface returns to original state 1 minute after beam removal (white bar = 150 um). 88 20.4 % Asphaltene Content The 20.4% asphaltene content binders have the highest network density. F ibril diameters are smallest among the three binders. The kinetics are slow and it takes 1-2 minutes to form the network and afier the e-beam is removed, the oils take 3-4 minutes to diffuse back into the region. Figure 5-9 shows the network formation seen in binder with 20.4% asphaltene content at different times and stages of formation. Figure 5.9 Morphology of 20.4% asphaltene content binder. Left: the network is visible in 1 minute (white bar = 150 um). Right: surface returns to original state 4 minutes after beam removal (white bar = 150 pm). From these results it can be suggested that the process involved in the revelation of the network structure by e-beam exposure and the disappearance of the structure on e-beam removal is diffusion controlled and directly related to the asphaltene content and rheological characteristics of the binder. 89 5.2 Polymer Phase Morphology Laser scanning confocal microscopy was used to determine morphology of the SBS, SEBS and SBR polymer phase in AC10 asphalts. As described previously, blue laser (488 nm) was used for excitation and the fluorescence was measured using a red band pass filter (590-620 nm). The images obtained were inverted for clarity and thus the polymer phase appears as a dark region over a light background which represents asphalt. Figure 5-10 shows a LSM micrograph of unmodified asphalt at a magnification of ZOOX. The surface is featureless and a small amount of background fluorescence fi'om the unsaturation in the asphalt binder is observed. i"‘ '5 57. a :, ' t" I: ," lliniothlictl.\('l 0 . _,- '“. tOOtnn Figure 5.10 LSM micrograph of unmodified AC10 binder in fluorescent mode. In polymer modified asphalt, the LSM was able to detect the distribution of the polymer in the binder. AC10 binder modified with 5% polymer was used to compare the morphology of SBS, SEBS and SBR. Figure 5.11 shows LSM micrographs of SBS and SEBS modified AC-lO asphalt binder. It is seen that SBS and SEBS form discrete phases at a concentration of 5% by weight. The size of the SBS and SEBS phases ranges from 1 to 20 um and appears to consist of spherical or slightly elongated microscopic domains. 90 Such morphology for SBS has been reported by Adedeji et. a1. [59] where the SBS network is not formed below 10 wt.% SBS and discrete SBS rich microdomains are observed which undergo transformation from short cylinders to lamellae and finally to spheres. Similarly, Ho et a1. [60] report an elongated hexagonal cylinder-like microstructure in SEBS modified asphalt. This is consistent with the morphology of SBS and SEBS observed in the LSM. The LSM was also used to investigate AC10 modified with 5wt% SBR. SBR latex fluoresces strongly and forms a networked phase in the asphalt as shown in Figure 5.12. The SBR network is made up of fine, well aligned strands approximately 0.5 pm in diameter. It is interesting to compare the LSM images of the SBR modified asphalt to ESEM images of these same samples. As in previous ESEM experiments with asphalt binder thin films, the electron beam was allowed to raster over an unmodified AC10 asphalt film and an AC10-5%SBR film. Initially, the control AC10 asphalt is featureless but a network structure is visible afier 3 minutes of exposure and the fibrils in the network are randomly oriented and have a diameter of ~10 pm, which is similar to that observed in SBS and SEBS modified asphalts. However, the network structure of the SBR modified asphalt is significantly different. After exposure to the electron beam, the fibrils in the SBR modified asphalt were seen to be strongly aligned compared to the control sample as seen in Figure 5.13. 91 5% SBS v 5: ,.. as; Figure 5.11 LSM micrograph of AC10 with 5% SBS and SEBS modifier in fluorescent mode (dark areas indicate the polymer phase) showing discrete polymer phase in the asphalt binder (200X). 92 5% SBR Figure 5.12 LSM micrograph of AC10 with 5% SBR latex modifier in fluorescent mode (dark areas indicate the polymer phase) showing the fine network of SBR strands in the asphalt binder (333 X). Figure 5.13 ESEM micrographs of AC10 asphalt binder with 0% SBR (left, white bar = 250 um) and 5% SBR (right, white bar = 200 pm). The network fibrils in the control sample are random while the SBR modified sample shows an alignment of the network fibrils. 93 The binder morphology seen in the ESEM qualitatively agrees with results using fluorescence microscopy. The ESEM investigations show that the network structure in the SBR modified asphalt is well aligned - this is anticipated since the SBR is strongly textured according to the LSM results. However, there is a discrepancy in that the diameter of the fibrils observed with the ESEM and LSM are quite different. The SBR strands shown in Figure 5.11 are ~0.S-1.0 um in diameter, which is smaller than the fibrils shown in Figure 5.12 (~5.0 um diameter). This is attributed to the fact that the fluorescent images show only the SBR phase, while the ESEM images rely on the removal of the low molecular weight oils to reveal the network structure and therefore the fibrils seen in the ESEM micrographs contain asphaltene, resin and polymer constituents. 5.3 Void Morphology 5.3.1 Thin Section Image Analysis Void analysis provides an understanding of the different types of voids found in asphalt concrete, viz. interfacial voids, binder phase voids and isolated voids [25]. Binder phase voids are small in size and are completely surrounded by the asphalt binder. Interfacial voids are large irregular shaped air-voids found near the surface of the aggregates. Isolated voids are air-voids trapped between aggregates where the binder does not penetrate. The image analysis system used statistical mean circle diameters and aspect ratios of voids in a thin plane section to calculate the net air-void content. This method, however, did not give an accurate measure of the actual net air-void content in the asphalt concrete since the void distribution and void shapes in asphalt concrete samples are non-uniform. A quantitative two—dimensional analysis of such voids thus 94 does not yield good results for the sampling size used. Table 5-1 shows the results of the thin section void analysis performed on SBS and SEBS modified asphalt concrete (AC5 and AC10). Table 5.1 Air void content of SBS and SEBS modified asphalt concrete by image analysis. ACS- AC 10- AC10 . o o - Image Analysrs AC5 5 ASSB AC10 5 ASSB 5%SEBS Air Void Content (vol. %) 1.28 0.97 1.58 1.56 0.70 Number of Air Voids 547 107 118 124 396 Avg. Equivalent Circle Dia. (mm) 0.09 0.16 0.39 0.32 0.10 Avg. Form Factor 37 39 40 41 38 Total Area of Section (cmz) 30 30 32 32 32 Total Scan Area (cmz) 21 21 24 24 24 The approximate void content of the asphalt concrete used in the above tests was 4—5% according to the mix design and bulk measurement of the sample density. Thus the thin section void analysis was found to be unrepresentative of the true air void content of asphalt under the test conditions used. The main reason for this is the difficulty in representing irregular three-dimensional voids by a two-dimensional technique. This is acknowledged by Scott [25] and Rouge et a1. [61-63] have shown that it is possible to obtain relationships between the observed surface porosity from 2-dimensional image analysis and the 3-dimensional void volume obtained by a bulk technique such as mercury porosimetry in materials with regular, open pores such as brake pads. At the current time, it is the opinion of the author that the 2-dimensional image analysis technique for analysis of air-voids in asphalt concrete needs further refinement and study before it can be applied quantitatively with confidence. 95 5.3.2 Void Casting Method The void casting method gives a more accurate measure of the net air-void content in asphalt concrete. It also allows the visualization of air voids (interfacial and binder phase voids) in three dimensions. This is a better method to characterize void shapes and sizes than the image analysis which only characterizes the uneven voids in two dimensions and extrapolates the results. The void content and distribution in asphalt concrete was characterized for SBR and Elvaloy AM modified binders using this method. Table 5-2 shows the net air void content of the modified asphalt concrete samples. The distribution of voids in the asphalt concrete can be characterized by considering the distribution of void volume. Two major types of voids, binder phase voids and interfacial voids were characterized. Binder phase voids are generally small in size and experimental observations suggest they have void volumes smaller than approximately 10 cumm. Binder phase voids are beneficial to the properties of asphalt concrete as they allow for expansion of the binder at high temperatures preventing bleeding of the binder from the concrete. For the purposes of semi-quantitative analysis of the change in void distribution due to polymer modification, all voids smaller than 10 cu.mm. were considered as binder phase voids and all voids greater than 10 cu.mm. were considered as interfacial voids. Interfacial voids are large, irregular and not beneficial since they provide starting points for adhesive fracture in asphalt concrete. Environmental freeze-thaw cycling during winter can lead to adhesive failure if a large number of interfacial voids are present by providing initiation points for cracks. 96 Table 5.2 Air void content of SBR and Elvaloy AM modified asphalt concrete calculated by void casting Material Volume Sampled Air Void Content (cu. mm) (volume °/o) AC5-0%SBR 27104 4.04 AC5-5%SBR 38280 4.66 AC5-0%Elvaloy AM 27825 6.95 AC5-2%Elvaloy AM 28224 4.97 The normalized distribution of void volume in SBR and Elvaloy modified AC5 is shown in Figures 5.14 and 5.15 respectively. In unmodified AC5 asphalt concrete, the void distribution shows approximately 80% interfacial voids while the content increases to approximately 86% with SBR modification. Elvaloy AM modified asphalt, which has a higher binder processing temperature than SBR modified binder, was found to have approx. 89% interfacial voids without any polymer added and approx. 95% interfacial voids for 2% Elvaloy AM content. The change in void volume distribution between unmodified and modified asphalt for both types of polymer shows that a significant amount of the void volume is contributed by interfacial voids (voids larger than 10 cum.) and polymer modification increases the proportion of interfacial voids by a small fraction. The consistent increase in the interfacial void volume may be a result of the processing conditions of the asphalt concrete samples. All Marshall samples used in the study were mixed at the same temperature. Polymer modified asphalt binders generally have a higher viscosity than unmodified asphalt binders and when processed at the same temperature, binders with different viscosities are likely to have different flow and Wetting behaviour. Interfacial voids are formed due to incomplete wetting of the aggregate by the binder during mixing and a binder with higher viscosity may be e"Pectted to have more interfacial voids as seen in these results. The total change in void 97 volume distribution for the four types of samples, the melt temperature of the binder and the viscosity of the binders at 275°F is shown in Table 5.3. Table 5.3 Distribution of void volume in SBR and Elvaloy AM modified AC5 Material Binder Phase Interfacial Melting Viscosity Voids Voids Temperature at 275°F (<10mm3) (>10mm3) (°C) (op) AC5-0%SBR 20 % 80 % 38 260 AC5-5%SBR l4 % 86 % 46 2337 AC5-0%Elvaloy AM 11 % 89 % 52 988 AC5-2%Elvaloy AM 5 % 95 % 57 3715 The increase in net interfacial void volume correlates with the increase in binder viscosity as a result of polymer addition and this may be a key factor that should be taken into account. The proper selection of processing temperatures is important in the case of polymer modified asphalts and care should be taken to maintain the binder viscosity at a level at which good wetting of the aggregate is achieved. 98 25 ACS-0%SBR Net Air Void Content = 4.21% 20 E 215 29 o > g... "6 .\° 5 N V (D (D ‘- 6) In N O) O C) O O sodqaa+eegggg§§ ". ‘J’ “5 " d :— 00 ID is g 8 O O O O N Void Volume (cu.mm) 25 —#v ACS-5%SBR Net Air Void Content = 4.89% 20 E 215. I! o > .310. ‘5' .\° 5 0 . . N V (D (D 1- (0 ID I\ O) O O O O O q‘dqqsda&écbobgggge§ "'. “5 “7 '5 0 ~— 03 in N 8 8 O O O O N Void Volume (cu.mm) Figure 5.14 Void volume distribution in AC5 with 0% and 5% SBR 99 .h O 00 0'! OJ 0 25 20 15 % of total void volume .5 O 40 35 30 25 15 °/o of total void volume 10 ACS-0% Elvaloy Net Air Void Content = 7.47% 20. ‘1’ N IDN‘O) si'cbab 10—20 Void Volume (cu.mm) "P N units a) sl'cbob 1 0—20 N ‘1' (D (I) v- o‘ o' o’ 0 d5 .L_ «5. «5. K o’ o o o o F AC5-2% Elvaloy Net Air Void Content = 5.23% N1 it (D co ‘- o‘ o’ o' o‘ d: .5 «*2 vi a. o O O O O void volume (cu.mm) 0—40 50-60 30-40 50-60 70-80 90-100 ‘ 200.300 70-80 90-1 00 ZOO-300 Figure 5.15 Void volume distribution in AC5 with 0% and 2% Elvaloy AM 100 5.4 In-situ ESEM Tensile Tests The in-situ tensile test performed on asphalt concrete sections is an excellent method to identify the fracture mechanisms and fracture morphology in asphalt concrete. The network structure seen in asphalt binder thin films is also seen in asphalt concrete specimen during the tensile fracture tests. The network strands in the binder play an important role during the fracture process of asphalt concrete. Polymer modified asphalt concrete shows a vastly different fracture morphology than unmodified asphalt concrete due to the changes in binder morphology. These changes include a reduction in adhesive (interfacial) failure, a corresponding increase in cohesive (binder phase) failure and the appearance of crack bridging mechanisms. The fracture process is seen to progress in three stages: void formation, void growth and crack propagation [19,25]. When the asphalt concrete specimen is strained, isolated voids develop in the binder phase. After sustained deformation the voids increase in size and finally interconnect giving rise to a continuous crack. As the voids grow in size, the binder between voids necks and forms long asphalt bridges (fibrils) across the growing crack. In order for the crack to grow, these fibrils have to be fractured and this process absorbs a part of the fracture energy, thus providing a mechanism for energy dissipation which improves the resistance offered by the material to fracture processes. The ESEM tensile test results show differences in the fracture morphology of‘ the different types of polymer modified asphalt concretes. Adhesive and cohesive failure modes were observed. Adhesive failure is defined as failure where crack prOpagation occurs at the asphalt binder-aggregate interface and is generally seen at low temperatures due to the increase in the binder modulus. Cohesive failure is defined as 101 failure where the crack propagates through the asphalt binder phase only. This type of failure is seen at higher temperatures (above 0°C) where the asphalt binder modulus is very low. Figure 5-16 shows micrographs of typical adhesive and cohesive failure in asphalt concrete. Figure 5.16 ESEM micrographs showing adhesive failure in asphalt concrete at 0°C at 65X (left, white bar = 500 um) and cohesive failure at 25°C at 100x (right, white bar = 450 um) Cohesive failure is the preferred type of fracture mechanism since it is associated with fibril formation, an energy dissipating process. Adhesive failure is a more serious problem at low temperatures, leading to extensive cracking and stripping. The locations at which fibrils are formed can be considered to be areas with very good asphalt- aggregate adhesion. 102 Unmodified AC5 Unmodified AC5 shows a tendency for the fracture to proceed along the aggregate boundaries. The failure was observed to be both adhesive and cohesive. The mechanism of cohesive failure starts with void formation in the binder phase. These voids grow and interconnect, leaving a few fibrils which act as crack bridges. The fibrils are about 6-7 microns in diameter and begin to neck after being sufficiently strained. Fibril rupture occurs at about 2 micron neck diameter and 50-100 micron length. Only a few fibrils were observed across the fracture surface in unmodified concrete samples. Figure 5.17 shows a typical fracture in unmodified AC5 asphalt concrete at 370X and 100X. Figure 5.17 Typical fracture in unmodified AC5 asphalt concrete. Left: 370x (white bar = 100 um), Right: 100X (white bar =450 pm). 103 AC5-SBS The fracture morphology is strongly affected by the addition of SBS. Figure 5.18 shows a large number of fibrils across a crack in AC5-5%SBS at 400X and IOOX. The most noticeable feature is an increase in the number of fibrils formed and their deformation behavior. The fibrils are thinner, longer and appear to be interconnected. They are more elastic and have higher elongation at break. Most fibrils are stable up to elongations of 130 microns. The number of fibrils forming across the crack increase in direct proportion to the concentration of the polymer added. There do not seem to be any apparent morphological changes in the fibrils due to increasing polymer concentration. Figure 5.18 Micrographs showing cohesive failure and increased fibril formation in AC5-5%SBS asphalt concrete. Left: 400x (white bar = 100 um), Right: 100X (white bar = 450 pm). 104 AC5-SEBS The morphology seen in SEBS modified AC5 samples is similar to that of SBS modified AC5. Figure 5.19 shows the failure process in AC5-2%SEBS asphalt concrete at 100X and 415x. The fibril formation is not as dense as that seen in SBS. The elongation at break is approximately 70-130 microns. Failures were mostly cohesive and gross adhesive failure was only seen in a few instances. Compared to unmodified AC5, SEBS modified AC5 shows higher fibril formation and elongation. Figure 5.19 Micrographs showing failure process in AC5-2%SEBS asphalt concrete. Left: 100x (white bar = 450 um), Right: 415x (white bar = 100 um.) AC5-ELVALOYAM® Elvaloy modified AC5 binders appear to have a much higher stiffness compared to other previously studied polymer modified systems. Figure 5-20 shows a typical fracture in AC5-2%Elvaloy, exhibiting an extremely low fibril density (150X). Fracture was observed to predominantly occur near the binder-aggregate interface rather than in the binder phase. The modified binder forms coarse bridges across the crack face, but very low fibril densities 105 were observed. The number of fibrils formed were fewer than seen in the unmodified material and decreased rapidly with increasing polymer concentration. The individual binder fibrils are about 7-8 microns in diameter at the base and about 2 microns at the neck at the point of failure. Elvaloy concentration does not visibly affect the morphology at this level. From the change in fibril density and fracture morphology, Elvaloy modified binders appear to have reduced viscoelastic behavior. Figure 5.20 Typical fracture surface in AC5—2%Elvaloy showing low fibril density. Left: 150x, Right: 150x. White bar = 300 um. AC5-SBR With the addition of SBR latex, binder morphology undergoes a vast change. Figure 5.21 shows a typical fracture in AC5-5%SBR at 300x and 1000X. The micrographs show a high density of tough fibrils at large crack widths. The binder remains soft and can sustain high plastic deformation. The aspect ratio and appearance of the binder fibrils changes with longer, thinner strands connecting the two fracture surfaces. The fibril density obtained with SBR is the highest amongst all the polymer modified binders studied. The deformation 106 behavior is also different in that the entire fibril elongates instead of necking. SBS, SEBS, Elvaloy and unmodified binders normally show fibril rupture at a crack width of 50 pm to 300 um. SBR fibrils remain stable even when the crack width is on the order of millimeters, and macroscopic observations indicate that some fibrils extend to approximately 25-50 mm before rupture. The fibril density is seen to be directly proportional to the concentration of SBR latex in the binder. Most fibrils have an extremely high aspect ratio, remaining stable even up to diameters of 700 nm. Fibrils are also seen to be clearly attached to the aggregates at their ends. This type of morphology is likely to prove beneficial in terms of crack inhibition and crack healing in asphalt concrete. Figure 5.21 Micrographs showing cohesive failure and increased fibril formation in AC5-5%SBR asphalt concrete. Left: 300x (white bar = 150 um), Right: 1000X (white bar = 45 um.) AC5 - Crumb Rubber With the addition of crumb rubber, the asphalt binder fibrils were observed to have much higher elongation at break (~600 microns) and the fibril density shows a slight 107 increase as compared to unmodified AC5. The fracture surfaces appear to be covered with asphalt and no bare aggregate surfaces were observed. Figure 5.22 shows the failure surface of AC5-10% Crumb Rubber with long fibrils bridging the fracture. The network structure seen in asphalt binder thin films can also be seen in the tensile tests. The asphalt binder network fibril seen in the figure has a diameter of ~8um which correlates with the network dimensions observed in the ESEM studies of asphalt binder. Figure 5.22 Micrographs showing aligned network fibrils across the fracture surface in AC5-10% Crumb Rubber. Left: 65X (white bar = 500 um), Right: 100x (white bar = 450 pm.) 108 5.4.1 Role of Binder Morphology in Fracture Process The observation of the asphalt binder network in tensile fracture tests further validates the physical nature of the network. The network fibrils are believed to be responsible for the strength of the asphalt binder. As has been noted before, asphalt bridges form across the fracture surfaces as the crack progresses. Closer observation of these fibrils shows that the binder morphology in asphalt concrete remains similar to that seen in pure binder films. As the fracture process in asphalt concrete progresses, the binder fibrils deform in a manner similar to that seen in pure binder films. Figure 5.23 shows the systematic deformation of binder network fibrils. The asphalt bridges initially consist of a group of binder network fibrils which align themselves in the direction of strain and slowly deform and rupture as the strain increases over a critical value. This process of deformation dissipates fracture energy and increases the overall fracture resistance of asphalt concrete. The overall changes seen in the fracture morphology of asphalt are semi-quantitatively summarized for all types of polymer modifiers in Table 5.4. 109 Figure 5.23 Micrographs showing details of the network structure seen in asphalt concrete and its deformation as the sample is subjected to a tensile load. Left: 305x, Right: 350x. White bar = 150 um. Table 5.4 Summary of changes in fracture morphology of asphalt due to polymer modification. Average Average Fibril Fibril Density Material Fibril Diameter at Relative to Length Break Unmodified Asphalt AC5 50-100 pm 2 pm AC5 - SBS 70-130 pm 2 um + AC5 - SEBS 70-130 pm 2 mm + AC5 - SBR l - 2 mm 700 nm +++ AC5 - Elvaloy AM® 70-100 pm 2 pm - AC5 - Crumb Rubber 600 pm 2 um + (+) indicates increase in fibril density (-) indicates decrease in fibril density 110 5.5 Fracture Toughness Test Results The J-contour integral fracture toughness is an estimate of the fracture toughness of a material near the initiation of slow stable crack growth. The low temperature fracture toughness of asphalt concrete was determined by 3-point bending beam tests using beams notched to different depths. Notch lengths corresponding to 40%, 45%, 50%, 55% and 60% of the sample width were used for each composition at a temperature of -10°C. The test temperature was chosen based on the failure modes observed in lap-shear tests. At temperatures above -10°C, cohesive failure in the asphalt-binder system was observed in lap shear test specimens while at temperatures below -10°C the failure was observed to be interfacial adhesive failure. The primary failure process in asphalt concrete is low temperature fracture caused by freeze-thaw cycling and thus the effect of adhesion on the fracture toughness can be determined by low temperature fracture tests. Asphalt concrete is a composite material consisting of three components: aggregate reinforcement, asphalt binder matrix and the aggregate-binder interface. The properties of the concrete are affected by the properties of the individual constituents. A change in the quality of aggregate, gradation, angularity, porosity or any other property can change the ultimate properties of the concrete. Similarly, the quality of the asphalt binder, film thickness and viscosity change the properties of the concrete. For this reason it is important to realise that the absolute values obtained in fracture tests are not of much consequence by themselves, but must be used for purposes of comparison and identification of trends. Since the various binders used have different processing conditions and final properties, comparisons will be made only within each type of modified binder system. It should be noted that SBS and Crumb Rubber samples used in 111 fracture toughness tests were made using AC5 binder obtained from a different batch from that used in all the other tests described previously. Since the properties of asphalt binder may differ from batch to batch, direct comparisons between two systems can be lead to erroneous conclusions. Fracture toughness test results are shown in the following sections. In all fracture toughness results, error bars represent the standard error in calculation of he. The load-displacement curves for all compositions tested are provided in Appendix A. AC 5 - SEBS Polymer modified AC5 concrete beams were tested at concentrations of 0%, 3% and 5% SEBS. These concentrations were chosen based on the optimum concentrations of SEBS modifier determined from rheological studies. The fracture toughness improves with the addition of 3%SEBS but with an increase in the concentration to 5%SEBS, the toughness decreases below that of 3% SEBS, but still shows an improvement over unmodified AC5. Figure 5.24 shows the change in fracture toughness due to SEBS modification. AC5 - Elvaloy AM Elvaloy AM modified AC5 samples were made at 0%, 1% and 2% concentration. The addition of Elvaloy AM does not seem to have any effect on the low temperature fracture toughness of ACS asphalt concrete. The fracture toughness is almost constant for 0% and 1% concentration and decreases slightly at 2% Elvaloy concentration as seen in Figure 5.25. 112 3.00 - 2.00 ch (lb-inlin 2) 1.00 l 0.00 A05-0% SEBS A05-3% SEBS ACS-5% SEBS Figure 5.24 Fracture toughness of SEBS modified AC5 asphalt concrete at -10°C 4.00 3.00 2.00 7 ch (Ib-inlin 2) 1.00 _, 0.00 » A05 0% Elvaloy A05 1% Elvaloy A05 2% Elvaloy Figure 5.25 Fracture toughness of Elvaloy modified AC5 asphalt concrete at -10°C 113 AC5 — SBR The addition of SBR latex to AC5 at 3% and 5% concentration causes a decrease in the fracture toughness of asphalt concrete at -10°C as seen in Figure 5.26. The decrease in toughness is incremental and contrary to the conclusion suggested by the ESEM fracture tests where an extremely high amount of fibril formation is observed. The presence of asphalt fibrils is expected to absorb fracture energy and increase the toughness at low temperatures. SBR modified binders have low stiffness and thus a decrease in the low temperature fracture toughness is unexpected. However, the term "low-temperature" is relative to the cohesive-adhesive failure transition temperature as seen in the Lap-Shear tests. For the other polymer modified systems studied, this temperature is found to be in the 0°C to -10°C region. SBR, having a lower Tg than the other polymers studied (SBS and SEBS), could cause a depression in this failure mode transition temperature. This is supported by the lap-shear test data which shows that the binder properties decrease linearly in the high temperature region. The fracture toughness is dependent on a variety of material properties, including the yield strength of the binder. The low Tg of SBR latex makes the SBR modified asphalt binder more viscous at the test temperature than other binders and failure occurs at correspondingly lower energy levels than expected. In effect, the SBR modified asphalt may have a tendency to fail cohesively in the binder phase at -10°C instead of interfacial adhesive failure seen in other binders. This is supported by the failure modes seen in lap shear tests where mixed adhesive and cohesive failure was observed in SBR modified AC5 at -10°C. This suggests that the direct comparison of the effect of polymer modification on the fracture toughness must take into account the failure mode and the difference 114 between the test temperature and Tg of the polymer modifier. Various polymer modified asphalts tested at a common test temperature may not provide meaningful direct comparisons regarding the intrinsic properties of the asphalt concrete. Different standards based on the rheological properties of the polymer modifiers would be more suitable for evaluation of properties of polymer modified asphalt concrete. 3.00 JIc (lb-inlinz) N 8 A 'o o 0.00 A05 0% SBR A05 3% SBR A05 5% SBR Figure 5.26 Fracture toughness of SBR modified AC5 asphalt concrete at -10°C AC5 - SBS Polymer modified AC5 concrete beams were tested at concentrations of 0%, 3% and 5% SBS. Due to unforeseen high usage of the asphalt binder obtained at the start of the program, a shortage of AC5 binder was experienced. Thus it was necessary to use AC5 binder from a different batch for making SBS modified fracture toughness samples. These results thus should not be assumed to correlate with other data presented. The SBS concentrations were chosen based on the optimum concentrations of SBS in AC5 115 determined from rheological studies. The fracture toughness of SBS modified AC5 was seen to decrease compared to that of unmodified asphalt concrete. Figure 5.27 shows the change in fracture toughness with SBS modification. 6.00 ch (Ib-in/in’) A05 0% SBS A05 3% SBS A05 5% SBS Figure 5.27 Fracture toughness of SBS modified AC5 asphalt concrete at -10°C AC5 — CRM Crumb Rubber modified ACS concrete was tested at concentrations of 0%, 5% and 10% CRM concentration. The AC5 asphalt binder used for these samples was not from the same batch used for all other testing described in this thesis. The fracture toughness shows an initial decrease in toughness but increases at higher concentrations. The changes, however are not statistically significant as seen in Figure 5.28. Table 5.5 gives a summary of all fracture toughness test results. 116 JIc (lb-inlinz) 5.00 A05 0% CRM A05 5% CRM A0510% CRM Figure 5.28 Fracture toughness of Crumb Rubber (CRM) modified AC5 asphalt concrete at -10°C Table 5.5 Summary of fracture toughness test results Composition ch Fracture Toughness Remarks (lb-in/inz) AC5-0% SEBS 1.6:0.16 . . AC5 - 3% SEBS 3.3 i 0.19 onifiefcs AC5 - 5% SEBS 2.4 :r 0.13 AC5 - 0% SBR 2.5 i 0.16 . . AC5 - 3% SBR 2.0 i 0.14 Duffie?“ AC5-5%SBR 1.71-0.11 AC5 - 0% Elvaloy 2.9 i 0.40 . . AC5 — 1% Elvaloy 2.9 i- 0.10 oni‘i‘l‘lfile’r‘cs AC5 - 2% Elvaloy 2.7 i 0.19 AC5 - 0% Crumb Rubber 3.0 i 0.18 N w AC5 AC5 - 5% Crumb Rubber 2.7 i 0.38 :inder AC5 - 10% Crumb Rubber 3.5 i- 0.45 AC5 - 0% SBS 4.3 i 0.52 AC5 - 3% SBS 3.4 i 0.50 Nag? AC5 - 5% SBS 2.6 i 0.44 117 5.6 Lap-Shear Adhesion Lap shear tests give a measurement of the bond strength between two flat parallel plates having an overlap adhesive joint in shear (Mode 11) when pulled apart under tensile loads. The test results show that the lap shear tests can identify the effects of polymer modification, temperature and failure modes on the asphalt binder-aggregate bond strength. Tests were performed on Granite, the prominent type of aggregate found in the aggregate mix [40]. Fracture surface analysis was used to identify the failure modes as a firnction of polymer content and temperature using optical microscopy. The failure surfaces were classified into six types - Type I to Type VI. The gradual change in appearance of the failure surfaces can be seen in Figure 5.29. Type I, II, 11, IV and V are cohesive failures in the asphalt binder and the appearance of asphalt ligaments gets progressively finer from Type I to Type V. The Type VI failure is an interfacial adhesive failure where the fracture progresses along the asphalt binder-aggregate interface. This failure is seen exclusively at low temperatures where the asphalt binder modulus increases above that of the interface. This is the most important region for the study of low temperature adhesive fracture processes since at high temperatures the cohesive failure measures the properties of the asphalt binder and not the interface. The change in failure modes was characterized for each polymer modifier as a function of temperature. It can be seen that as the temperature decreases, the shear strength of the bond increases. The cohesive-adhesive transition temperature for most materials was found to be -10°C. 118 -V show cohesive inder-aggregate Type I rmen. lap shear test spec' m h temperatures. 1 (adhes ilure modes ' 5.29 Fa Figure Type VI shows b failure at low temperatures (11X) der at h' in terfac the b ilure in fa ) ive 1a In 119 A summary of illustrative lap-shear test results for fresh polymer modified asphalt binders is given in the following sections. Complete tables of lap shear results can be found in Appendix B. AC5 - SBS In SBS modified binders, there is a minor change in the lap shear bond strength at temperatures above 0°C. It is also seen that at high temperatures the lap shear strength decreases slightly at polymer loadings above 3%. At temperatures below 0°C, the positive effect of polymer modification can be clearly seen. The transition in failure mode from cohesive to adhesive occurs between 0°C and -10°C for SBS modified binders. Table 5.6 shows the change in failure mode as a fimction of polymer concentration and temperature. It should be noted that the onset of adhesive failure is depressed by 10°C by the addition of SBS modifier. The variation of lap shear strength of SBS modified AC5 with polymer content and temperature is seen in Figure 5.30. In the adhesive failure region (-10°C to -20°C) SBS modified AC5 shows improvement over unmodified AC5. Since the failure is interfacial, this increase can be directly correlated to the improvement in adhesion due to polymer modification. Table 5.6 Failure modes in SBS modified AC5 lap shear tests 20°C 10°C 0°C -10°C -20°C 120 La p Shear Strength (N) 1% SBS Figure 5.30 Lap shear strength of SBS modified AC5 as a function of polymer concentration and temperature. 121 AC5 - SEBS In SEBS modified binders, there is no significant change in the lap shear bond strength at temperatures above 0°C. At temperatures below 0°C, addition of SEBS leads to an improvement in the lap shear strength. The transition in failure mode from cohesive to adhesive occurs between 0°C and -10°C. Table 5-7 shows the change in failure mode as a function of polymer concentration and temperature. It should be noted that the onset of adhesive failure is depressed from 0°C to -10°C by the addition of SEBS modifier. The variation of lap shear strength of SEBS modified AC5 with polymer content and temperature is seen in Figure 5.31. In the adhesive failure region (-10°C to -20°C) SEBS modified AC5 shows improvement over unmodified AC5, especially at 1% and 2% SEBS concentrations. Since the failure is interfacial, this increase can be directly correlated to the improvement in adhesion due to polymer modification. Table 5.7 Failure modes in SEBS modified AC5 lap shear tests 20°C 10°C 0°C -10°C -20°C 122 fi g g E 1 Lap Shear Strength (N) 6% SEBS Figure 5.31 Lap shear strength of SEBS modified AC5 as a function of polymer concentration and temperature. 123 AC5 - SBR The addition of SBR causes no significant change in the lap shear bond strength at low polymer concentrations above 0°C. As the amount of SBR latex in the binder is increased, the cohesive strength of the binder decreases due to the increasing viscous modulus of the binder. At temperatures below 0°C, addition of SBR leads to an improvement in the lap shear strength. The transition in failure mode from cohesive to adhesive occurs between 0°C and -10°C for SBR concentrations below 3% and is depressed to —20°C when SBR content increases to 5%. Table 5.8 shows the change in failure mode as a function of polymer concentration and temperature. The variation of lap shear strength of SBR modified AC5 with polymer content and temperature is seen in Figure 5.32. In the adhesive failure region (-10°C to -20°C) SBR modified AC5 shows improvement over unmodified AC5, especially at 5% concentration. Table 5.8 Failure modes in SBR modified AC5 lap shear tests 10°C 0°C -10°C -20°C 124 Lap Sheer Strength (N) 0% SBR 1% SBR 3% SBR 5% SBR Figure 5.32 Lap shear strength of SBR modified AC5 as a function of polymer concentration and temperature. 125 AC5 - Elvaloy AM Similar to other polymer modifiers studied, the addition of Elvaloy does not affect the lap shear strength significantly at temperatures above 0°C. At temperatures below 0°C, addition of Elvaloy leads to an improvement in the lap shear strength. The transition in failure mode from cohesive to adhesive occurs near -10°C. Table 5.9 shows the change in failure mode as a function of polymer concentration and temperature. The variation of lap shear strength of Elvaloy modified AC5 with polymer content and temperature is seen in Figure 5.33. In the adhesive failure region (~10°C to -20°C) Elvaloy modified AC5 shows improvement over unmodified AC5. The concentration of Elvaloy does not appear to affect the properties. Table 5.9 Failure modes in Elvaloy AM modified AC5 lap shear tests 10°C 0°C -10°C -20°C 126 be. 2500 ’ . “$23333, 2000 1000 Lap Sheer Strength (N) 0% Elvaloy 1% Elvaloy 2% Elvaloy 3% Elvaloy Figure 5.33 Lap shear strength of Elvaloy modified AC5 as a function of polymer concentration and temperature. 127 AC5 - Crumb Rubber The addition of Crumb Rubber at a low concentration of 5% causes a decrease in the lap shear strength. At higher concentrations, the lap shear properties recover and increase above those of unmodified asphalt. Of the various concentrations used, 15% Crumb Rubber was found to perform the best at low temperatures. The transition in failure mode from cohesive to adhesive generally occurs between -10°C and -20°C. However, AC5 with 5% crumb rubber was found to fail cohesively at -10°C. Table 5.10 shows the change in failure mode as a function of polymer concentration and temperature. The variation of lap shear strength of Crumb Rubber modified AC5 with polymer content and temperature is seen in Figure 5.34. Table 5.10 Failure modes in Crumb Rubber modified AC5 lap shear tests 20°C 0°C -10°C -20°C 128 Lap Shear Strength (N) .20 c ’aoc Figure 5.34 Lap shear strength of Crumb Rubber modified AC5 as a function of polymer concentration and temperature. 129 Lap shear testing of aged asphalt Lap shear tests on aged asphalt binders indicate that polymer modification retards the aging processes and improve the residual properties of the asphalt binder. Figure 5.35 shows the lap shear strength of aged SBR binders. At high temperatures, the lap shear strength of aged SBR modified binder follows the same trends as fi'esh asphalt SBR modified binders. Complete lap shear test results for aged polymer modified asphalt binders can be found in Appendix C. Lap Shear Strength (N) 0% SBR 5% SBR Figure 5.35 Lap shear strength of aged SBR modified AC5 binders at various temperatures 130 CHAPTER SIX DISCUSSIONS The results obtained from the morphological and microstructural characterization of asphalt concrete present new understanding of the mechanisms of failure in pavements. Proper analysis and implementation of these results can be beneficial in developing new performance based specifications for polymer modified asphalt concretes. Specifically, the benefits of polymer modification need to be viewed in terms of improvements in key properties, e.g. resistance to aging, low temperature fracture toughness, asphalt-aggregate adhesion, etc. In the effort to improve the performance of pavements at low and high temperatures, it is imperative for the effects of additives on the fundamental properties of the component materials to be understood. This chapter discusses the effects of various polymer modifiers on the properties of asphalt concrete and asphalt binder. 6.1 Dispersed Polymers (SBS/SEBS) The addition of SBS and SEBS to asphalt binder causes a change in the morphology of the binder. The network microstructure of the binder does not appear to change visibly, yet room temperature fracture morphology shows a significant increase in fracture energy dissipating mechanisms like crack bridging by asphalt fibrils. This is an effect of the decrease in the glass transition of the asphalt binder due to the addition of SBS/SEBS. There is also an increase in the number of fibrils formed during fracture and this may be due to an overall increase in asphalt-aggregate adhesion with the locations of 131 fibril formation representing areas with increased adhesion and acting as anchor points for the fibrils during the process of crack widening and deformation. Using the mixing procedures outlined earlier, SBS and SEBS form discrete, well-dispersed spherical phases about 1-20 pm in diameter. Even at polymer concentrations of 5 wt.%, no continuous polymer networks are observed in the binder. Continuous networks of SBS and SEBS (phase inversion) in asphalt are expected only at concentrations approaching 10 wt% [59,60]. Asphalt-aggregate adhesion increases with the addition of SBS/SEBS as seen in lap shear test results. In the adhesive failure region (-10°C and below) the modified asphalt binder has higher ultimate lap shear strength. The quantitative lap shear test data must be taken in conjunction with the qualitative analysis of various failure modes observed. The failure mode is seen to change from cohesive to adhesive around 0°C for unmodified AC5 and -10°C for SBS/SEBS modified AC5. Direct comparison of lap shear strength of unmodified and modified AC5 at 0°C is misleading since the measured quantity indicates the adhesive strength of unmodified AC5 and cohesive strength of SBS/SEBS modified AC5. The depression of this failure transition by 10°C is a significant step towards improving low temperature pavement performance where the predominant failure is adhesive. At low temperatures (-10°C) the fracture toughness of the SEBS modified asphalt concrete increases, whereas the fracture toughness of SBS modified asphalt concrete decreases. The binders used to make the SBS fracture toughness samples was from a different batch and thus the precise reason for the decrease in fracture toughness cannot be determined at this time. 132 6.2 Network Polymers (SBR Latex) SBR latex is a network forming polymer and after addition to asphalt, it forms an independent network of SBR strands of ~10um diameter. The asphalt fibrils formed during fracture of asphalt concrete are longer than those seen in SBS and SEBS. The SBR modified binder is softer than the SBS and SEBS modified binders, which is evident by the lower softening and melting points. There are two reasons for this : (1) The binder is mixed at 350°F for 30 minutes which reduces the amount of oxidative aging during the blending process and (2) The Tg of the SBR latex is lower than that of SBS and SEBS. The lap shear strength data for SBR modified asphalt shows an improvement in strength as well as depressing the cohesive-adhesive failure transition from 0°C to -10°C. Moreover, the amount of fibril formation during fracture is very high compared to the other polymers studied and fibrils across the growing crack were observed to remain intact even at crack widths on the order of inches. The factors responsible for this behaviour are the formation of the SBR network inside the asphalt as well as the improvement in interfacial adhesion. To further validate the theory of improvement in interfacial adhesion, experiments were performed where the SBR was localised at the interface by independently coating the aggregates with SBR latex. Latex coatings of Sum and 10pm thickness were applied on the aggregates and the lap-shear strength and toughness were measured. Figure 6.1 shows the typical load-displacement response of SBR coated aggregate-binder systems at ~10°C and -20°C. It can be seen that the strain to failure increases by 400 to 500% when SBR is concentrated at the asphalt-aggregate interface with no significant change in the ultimate lap-shear strength. The effect of the interfacial coating decreases as the coating thickness increases. The binder also has an 133 effect on the lap shear properties. Unmodified AC5 and AC5-5 wt.% SBR were used along with SBR coated aggregate to make lap-shear specimen. It was observed that at high temperatures there is no significant change in properties due to addition of SBR but at lower temperatures (-10°C and -20°C) the addition of SBR to the binder further enhances the ultimate lap shear strength as well as the strain to failure. The enhancement in properties due to the presence of SBR at the interface indicates the importance of the interface in the final properties of asphalt concrete. It is believed that polymer modification of the binder also leads to the modification of the binder-aggregate interface in asphalt concrete. The cumulative effect of interfacial and matrix modification ultimately leads to enhanced low temperature properties and the interfacial/adhesive failure transition in asphalt concrete occurs at a lower temperature, effectively extending the low temperature performance envelope. Williams et a1. [64] have recently shown that SBR coating on aggregates improved the resistance to moisture damage (improved interfacial adhesion). Although excellent low temperature properties are observed after applying SBR coatings directly to the aggregates, it is estimated that the amount of polymer utilized in this study is too high to be of commercial importance. The average asphalt binder film thickness in Marshall samples is approximately llum based on design calculations shown earlier. By applying 5 and 10pm SBR coatings on the aggregate surface, the net polymer to asphalt binder ratio ranges from approximately 50 to 100% making such modification schemes unrealistic in terms of commercial application. However, the effect of the interface and interfacial adhesion on the low temperature performance of asphalt concrete can be understood by such experiments. SBR latex coatings for aggregate as 134 anti-stripping additives have recently been made available commercially (Ultracote UP- 5000, Goodyear/Ultrapave) [65] with SBR particle sizes on the order of 0.5um. Provided sufficiently thin coatings can be applied to the aggregates, this approach may prove to be beneficial especially for low temperature applications. Direct coating of aggregates with polymer was only possible with SBR latex as the other polymers studied, SBS, SEBS, Elvaloy and Crumb Rubber were not available in a physically convenient form for coating purposes. 135 3000 1 n 1 .-1-—.. 1 1 1 l 1 1 ’u" N... ”rd. M 7 AC-S/SBR w/ GRANITIC @ -10°C --—-- 1MB -1 “1."... \\ I...‘ my... M .II. R] __,.. 5m 1. z l‘.‘ d i". < l a O a ‘. .1 l \_ i 1 l '\ 1 l \ l ". i ‘. l ‘x if“ ..................... - f I T r I T 2 3000 1 1 1 l 1 4 1 l 1 - AC-5/SBR w/ SBR COATED — 0M6: Sun GRANITIC @ ~10°C --- M:10um ---- M: 10am 2 d < O .J 0 fi 1 T l I t T I V I 0 l 2 DISPLACEMENT. mm Figure 6.1 Lap shear load-displacement curves for AC5-SBR and Granitic aggregate at -10°C. SBR coated aggregate systems have a higher displacement at failure due to toughening of the asphalt-binder interface. 136 6.3 Reactive Polymers (Elvaloy AM) Reactive polymers react chemically with the asphalt binder and effectively cross- link the asphalt. This leads to a binder with very high modulus. Although there is no significant change in the binder morphology after addition of Elvaloy AM, the binder microstructure appears similar to aged asphalt with coarse network features and the binder has very high stiffness. This was found to be due to the high mixing temperatures (380°F) used to blend Elvaloy and asphalt in ambient environment. The mixing of Elvaloy in the presence of air causes oxidation to occur in the binder. The lap-shear properties are comparable to other polymer modifiers studied but there is no change in the failure transition from cohesive to adhesive, which occurs at 0°C for unmodified asphalt. After Elvaloy addition the failure mode at -10°C is mixed adhesive and cohesive with an increase in the ultimate lap-shear strength indicating an increase in the binder properties while the pure adhesive failure at this temperature occurs at a lower load indicating that the interfacial adhesion remains unaffected by addition of Elvaloy. This is also seen in the fracture toughness tests where no change is observed after addition of Elvaloy. To avoid the problem of binder oxidation during initial processing (mixing) the mixing should be done in a closed container with a nitrogen purge. This procedure was found to be effective and the resulting Elvaloy modified binder did not appear to have the coarse network structure typical of aged asphalt. Future tests with Elvaloy modified asphalts should be performed with binders mixed under Nitrogen atmosphere. 137 6.4 Particulate Polymers (Crumb Rubber) Crumb rubber particles added to asphalt also cause a slight coarsening of the binder network microstructure. This is expected to be due to the rubber particles absorbing the low molecular weight oils in the asphalt. This is similar to the loss of low molecular weight fractions due to oxidation, but since this loss of oils is not permanent, the long term properties of the addition of crumb rubber remain to be evaluated. One theory is that the oils absorbed by the rubber particles are stored and can diffuse back into the asphalt binder as the binder ages naturally and maintain a steady concentration of oils in the asphalt. The interaction of the rubber particles and asphalt binder is shown in Figure 6.2. The asphalt network fibrils are seen in the ESEM micrograph to have a very good interaction with the rubber particles. The fracture surface of crumb rubber modified asphalt concrete shows no signs of adhesive failure along the asphalt-rubber interface. The lap shear properties of crumb rubber modified asphalt show an increase in the ultimate strength with the addition of rubber and the change in transition from cohesive to adhesive failure is seen to occur between -10°C and -20°C. The AC5 asphalt binder used for Crumb Rubber fracture toughness tests was from a different batch than the binder used for other tests and this should be taken into account when comparing results. There is no significant change in the fracture toughness at -10°C due to addition of crumb rubber. 138 Figure 6.2 ESEM micrographs of (a) Interaction of asphalt binder network with crumb rubber particles (left, white bar = 45 um) and (b) Fracture surface of crumb rubber modified AC10 showing significant amount of asphalt binder residue on the rubber particle surface (right, white bar = 450 um). 6.5 Lap Shear Tests as Indicators of Interfacial Adhesion The use of lap shear tests to indicate changes in the interfacial adhesion between asphalt binder and aggregates, although useful in evaluating the interaction between the binder and aggregate as materials, cannot be used as a direct indicator of the true interfacial adhesion in real asphalt concrete. The reason for this is that the aggregate samples used in lap shear tests are necessarily cut and polished aggregate surfaces while aggregates used in actual pavement construction are angular and have a high degree of roughness. Although the roughness of the aggregates does not affect the energetic interactions between the materials, interfacial adhesion generally improves with increasing roughness due to the contribution from mechanical interlocking. This is termed as mechanical adhesion. The absence of significant mechanical adhesion in the lap shear tests thus makes quantitative application of the lap shear test results to 139 pavement design impractical. Instead, the lap shear tests provide a useful method to evaluate the changes in the interface caused by the addition of polymers. Assuming that final mix processing is carried out at equivalent binder viscosity such that the physical interaction between the asphalt binder and aggregates is similar, the lap shear properties of various polymer modified asphalts determined in the laboratory can be scaled to the real properties expected to be seen in the field. With all other factors being equal, the lap shear test provides a reliable method to compare different modifiers and asphalt binders. 6.6 Summary The use of polymer modification of asphalt to improve pavement properties has been shown to be effective by enhancing the bulk and the interfacial properties of asphalt concrete. Of the four types of polymer modifiers, dispersed thermoplastics and network forming polymers like SBS, SEBS and SBR show the highest potential for improving prOperties at low temperatures by strengthening the binder-aggregate interface while reacting polymers and particulate reinforcements like Elvaloy and Crumb Rubber respectively work by enhancing the properties of the bulk binder. Since the binder properties become less important at low temperatures where distress is primarily located at the interface, reacting polymers and rubber particle reinforcement has a lower potential of enhancing the low temperature properties. At high temperatures (above 0°C) polymer modification does not significantly affect the properties of asphalt concrete as detected by lap shear tests. With the exception of SBR, lap shear properties at high temperatures remain constant as polymer is added to the binder. However, lap shear tests are not useful in detecting the potential for high 140 temperature distresses such as rutting and further experimentation and field tests are necessary to evaluate the high temperature performance of polymer modified asphalt concrete. The characterization of asphalt binders by ESEM microscopy has provided a new understanding of the nature and structure of asphalts. The changes seen in the network structure of asphalt can be used as a qualitative tool to determine aging in asphalt binders as well as serve as a tool to develop other polymer modifiers which will exploit the microstructure and morphology of the binders. For example, combinations of polymer modifiers like SBR and Elvaloy might lead to interesting changes in the binder microstructure with the reacting polymers enhancing binder properties by crosslinking and reducing the number of sites available for oxidative attack in the binder and the network forming polymers providing high interfacial interaction between the asphalt binder network and the aggregates. The fracture morphology of asphalt concrete can also be used to design pavement repair schemes. The formation of asphalt fibrils across growing cracks can be a useful property to exploit in pavement healing. The heating of cracks in the pavement caused at low temperatures can close the cracks due to the re-distribution of the binder and a higher amount of fibril formation in the binder can assist this process, even after the cracking has occurred. In summary, polymer modification has been shown to positively affect the low temperature properties of asphalt concrete. Additional research has been performed to test the bulk properties of asphalt concrete which shows that polymer modification also enhances the high temperature tensile and fatigue strength of asphalt concrete [33, 66]. 141 CHAPTER SEVEN CONCLUSIONS AND RECOMMENDATIONS The main objective of this study was to characterize the microstructure and morphology of straight and polymer modified asphalt (PMA) binder-aggregate mixtures and their failure mechanisms. Microstructural and morphological information is important in predicting pavement performance based on the physical and chemical properties of binders and aggregates. The identification of morphological changes in asphalt and their effect on the locus of failure and failure mode under a combination of stress and environmental factors is a critical element necessary to evaluate pavement performance 7.1 Microstructure and Morphology Asphalt binder morphology was characterized successfully using an ESEM and a well defined 3-dimensional entangled network was observed in asphalt binder films and asphalt concrete sections. The network structure is seen in unmodified as well as polymer modified asphalt binders and changes with the asphaltene content. Comparison of the morphology of three different asphalts shows that the density of the network is proportional to the asphaltene content. It is suggested that the segments in the network are mainly composed of associations of asphaltene particles and resins, the interstices filled with plasticizing oils. The oxidative aging of asphalt leads to changes in the network morphology. The smooth network segments in fresh asphalt have a mottled and coarse texture after aging. This can be used as a qualitative test to determine the extent of 142 aging in asphalt. Whereas classification of asphalt binders strictly by rheological analysis may show no difference between a high viscosity asphalt and blown (oxidised) asphalt, the changes in morphology are easily detectable and should be taken into account to predict long term performance. The morphology the polymer phase in modified asphalt is important to develop new specifications and understanding of the precise mechanisms by which improvements in pavement performance are realised. Polymer morphology can be characterized easily with a Confocal Laser Scanning Microscope (LSM) for polymers like SBS, SEBS and SBR which exhibit strong fluorescence. The current industrial standard to confirm homogeneous mixing of polymers and asphalt is visual observation. The ability of the LSM to map depth profiles of the polymer distribution in asphalt is an analytical tool that can be used to determine the homogeneity of PMA. A limitation of this technique is the inability to determine the morphology of polymers that do not exhibit fluorescence. Crumb rubber and Elvaloy AM could not be detected by the LSM and the distribution of these two modifiers could not be characterized. In the case of non-homogeneous polymer modified asphalts such as crumb rubber, it is possible to look at individual particles and their interaction with asphalt binder using microscopic techniques. SBS and SEBS were found to form a dispersed phase in asphalt at concentrations up to 5%(w/w) while SBR forms a strand-like continuous network at concentrations of 3%(w/w) and higher. Crumb rubber particles were well dispersed in the asphalt and have good interaction with the asphalt network. 143 7.2 Void Morphology and Fracture in Asphalt Concrete The presence of voids in asphalt concrete is essential to allow expansion of the asphalt binder at high temperatures without bleeding and for water drainage. The size, location and abundance of air voids play a critical role in fracture processes. The voids in asphalt can be characterized into two main categories from the morphological perspective: binder phase voids and interfacial voids. Binder phase voids are typically small spherical voids while interfacial voids tend to be large and irregular voids encircling the aggregate. The analysis of air-voids in polymer modified asphalt concrete suggests adaptation of asphalt concrete mixing procedures based on the rheological properties of the binder. Due to the increase in viscosity of asphalt binders after polymer modification, the wetting and penetration of the aggregate with binder may be different than that in unmodified asphalt. A direct comparison between polymer modified and unmodified asphalt concrete mixed using identical conditions (temperature and time) may not provide an accurate representation of the effect of polymer modification on the void morphology in different systems. The fracture process in asphalt concrete was studied using an ESEM and the fracture mechanism was determined to progress in three main stages: void formation, void growth and void interconnection. As the asphalt concrete sections were strained, at temperatures above 0°C, voids begin to form in the binder phase. These voids grow in size with increasing strain and finally interconnect as the crack propagates. The propagation of the crack is slow and inhibited by the formation of asphalt ligaments or fibrils across the crack face. The fibrils elongate and rupture, thus dissipating some of the fracture energy. The addition of polymer to asphalt, with the exception of Elvaloy 144 AM, leads to an increase in the density of fibrils formed during fracture. This is expected to enhance the resistance to crack growth exhibited by asphalt concrete. The fracture process at low temperatures (below 0°C) is different than that at high temperatures and fracture occurs mainly along the binder-aggregate interface due to adhesive failure. The presence of interfacial air-voids can accelerate the fracture process and crack growth can be qualitatively characterized as rapid. Low temperature fracture is one of the prevalent pavement failures in cold climes like Michigan and thus the presence of interfacial voids is considered to be detrimental to low temperature pavement performance. 7.3 Fracture Toughness and Lap Shear Tests Fracture toughness and lap shear tests were used to determine the changes in asphalt binder-aggregate adhesion due to polymer modification. Lap shear tests indicate that the failure mode in asphalt concrete is determined by a transition temperature above which failure is mainly cohesive in the binder phase. At temperatures below the transition adhesive, interfacial failure is observed. Lap shear tests were performed at various temperatures in 10°C increments from 20°C to -20°C. The addition of polymers has shown that the cohesive to adhesive failure transition temperature decreases from approximately 0°C for unmodified asphalt to atleast -10°C for polymer modified asphalt along with an improvement in the ultimate lap-shear strength. This is an important indication of the improvement in binder—aggregate adhesion due to polymer modification. Table 7.1 shows the adhesive and cohesive failure transition temperatures for different polymer modified AC5 asphalt binders. Lap shear tests also show a higher retention of 145 properties in aged polymer modified asphalt. Along with supporting evidence from the binder morphology, it can be claimed that polymer modification retards the aging of asphalt binders. Table 7.1 Lap shear cohesive-adhesive failure transition temperatures for polymer modified AC5 asphalt concrete Composition Cohesive Failure Adhesive Failure Unmodified AC5 10°C 0°C AC5-3% SBS 0°C ~10°C A05-2% SEBS 0°C -10°C AC5-5% SBR -10°C -20°C AC5-1% Elvaloy® AM 0°C -10°C AC5-5% Crumb Rubber 0°C -10°C Fracture toughness tests were performed for various polymer modified asphalt compositions at -10°C, as a measure of the resistance of the material to adhesive fracture. Polymer modification improves the J~integral fracture toughness for SEBS, but a decrease in fracture toughness was observed in the case of SBS and SBR latex modified systems. This may be due to the choice of testing temperatures as the SBR modified binder-aggregate fails adhesively at a lower temperature (-20°C) in lap shear tests. This can be attributed to the fact that SBR is a random copolymer with a Tg of -50°C, which is much is lower than that of SBS and SEBS which have discrete polystyrene domains with a Tg of 100°C. In order to compare the effect of polymer modification on the adhesion in different systems, it may be more appropriate to conduct fracture toughness tests at 146 temperatures relative to the Tg of the modified asphalt binders instead of a single temperature for all systems. Another factor that must be taken into account is that the cohesive and adhesive failures reported in Table 7.1 were observed in lap shear test samples which are made from smooth aggregate sections cut with a diamond blade. This renders an aggregate surface that is smooth while aggregate used in pavement construction has a high degree of surface roughness and porosity. Thus the effects of mechanical adhesion due to the absorption of asphalt into the aggregate are minimised in lap shear tests leading to a slight underestimation of the temperature at which adhesive failure occurs in the binder- aggregate interface. 7.4 Optimum Polymer Concentration The recommendation of an optimum concentration of a polymer for modification of asphalt binders is a process that must take into account the chemical, rheological, interfacial and the engineering properties of the asphalt concrete [67]. Research under the direction of Prof. Hawley and Baladi has evaluated the rheological properties [31,32] and the engineering properties of the systems [33] studied here.4 The recommended optimum concentrations of different polymers for modification of AC5 asphalt from the perspective of : (i) chemical, physical and thermodynamic properties, (ii) microstructural and morphological properties and (iii) structural and engineering properties are shown in Table 7.2 and should only be used as guidelines since a change in the source and 4 Hawley M., Department of Chemical Engineeering, Michigan State University, USA and Baladi G., Department of Civil and Environmental Engineering, Michigan State University, USA 147 composition of asphalt binder, quality and composition of the aggregate and mixing conditions can yield different results. The SHRP performance grades for the different types of polymer modified asphalt binders are shown in Table 7.3 for reference. It can be seen that as polymer is added to the asphalt binder, the high temperature SHRP performance grade (PG) increases while the low temperature SHRP PG remains ahnost constant at low concentrations. This suggests enhanced binder rheological properties at high temperatures. Since the SHRP PG only represents binder properties and not those of asphalt concrete, it can be concluded that polymer modified asphalt binders show an improvement in the high temperature performance without deteriorating the low temperature performance of the binder. The results from lap-shear and fracture toughness tests on the other hand represent the low temperature properties of the asphalt concrete and show clearly that the low temperature performance of asphalt concrete is enhanced in most cases. Since most high temperature failures are dependent on binder properties and low temperature failures on the interfacial properties, polymer modification presents itself as a very attractive modification process. 148 Table 7.2 Optimum polymer concentrations suggested for AC5 G’G 58-28) asphalt binder [31-33, 67] Suggested optimum concentration (wt.%) Chemical, Physical Microstructural and Structural and and Thermodynamic Morphological Engineering Properties Properties Properties SBS 3 or 5 % 1-3 % 5 % SEBS 20r5% 1-3% 5% SBR 3 % 5 % 2 % Elvaloy® AM 1.5 % 1 % 1 % Crumb Rubber 10% 10-15% 10% Table 7.3 SHRP performance grades for polymer modified AC5 (PG 58-28) asphalt binder [31-32,67] SBS SBR Elvaloy®AM Crumb Rubber 0 % PG 58-22 0 % PG 58-28 0 % PG 76-16 0 % PG 58-18 1 % PG 64-22 1 % PG 58-28 1 % PG 76-16 5 % PG 64-N/A 2 % PG 70-22 2 % PG 64-28 2 % PG 82-16 10 % PG 70-N/A 3 % PG 70-22 3 % PG 64-28 3 % PG 82-16 15 % PG 82-18 4 % PG 70-22 4 % PG 64-28 4 % PG 82-16 20 % PG 82-N/A 5 % PG 76-16 5 % PG 70-28 Note: SHRP PG grades (PG XX-XAO represent the high and low temperature ratings. The first number is the high temperature and the second number is the low temperature. PG 58-22 represents 'Performance grade 58 0C high temperature SHRP grade and -22 ‘C low temperature SHRP grade. ' 149 7.5 Recommendations for Future Work Based on the results from this study and the information available, there is a need for further research into polymer modification of asphalt. Various areas worthy of further exploration are described below. Eflect of asphalt source. Asphalt is obtained from the last remaining fractions of crude oil and with changes in the raw material, the quality of asphalt also changes. In order to generalize the results obtained here, polymer modifiers need to be tested with asphalts from different sources. The use of multiple asphalt sources can facilitate the generalization and application of the results already obtained. Asphalts with different known asphaltene contents should be studied in order to find the relationship between the binder microstructure and the rheological and engineering properties of asphalt binder and concrete. Eflect of aggregate. Aggregate used in pavement construction is usually obtained from local quarries and the quality of the aggregate varies widely. While it is assumed that different types of aggregate will exhibit similar behaviour with polymer modified asphalt binders, the evaluation of aggregate from different parts of the country may yield different results. In this study the aggregate used comprised mainly of granite, greenstone, basalt, quartzite, sandstone and limestone. Out of these, granite was chosen as a representative model surface. However, interfacial properties are highly dependent on the nature of the aggregate surface and the varying degrees of crystallinity and grain structure found in different types of aggregates may have an impact on these properties. 150 Polymer-asphalt interaction. Although asphalt binder and polymer phase morphology has been characterized individually, there is a need to develop new experimental techniques that can determine the interaction between the two materials on the microstructural scale. The presence of a network structure in asphalt opens up new avenues for investigation: Do thermoplastic polymer modifiers like SBS, SEBS and SBR associate with the asphaltene network? Do polymer modifiers blend into the asphalt network segments or segregate to the surface, effectively forming a polymer rich sheath around the asphaltenes? These are issues that are of deep importance in understanding the process of polymer modification of asphalt. It has been shown that binder-aggregate failure is characterized by the formation of fibrillar structures that bridge the growing cracks and polymer modification is capable of making changes in these structures. The ability to control the size and strength of these fibrils through polymer modification opens new doors for establishing direct relationships between asphalt binder morphology and pavement performance. Efforts must also be made to pinpoint the failure mode transition temperatures in terms of different polymer modifier types and concentrations. Combination of Polymer Modifiers. The results obtained in this study consistently show that none of the polymers studied perform very effectively at both high and low temperatures. Whereas from the point of view of interfacial failures, low temperature performance is more relevant than high temperature performance, in reality, high temperature distresses are as common as low temperature distresses. The solution to this may lie in using a combination of polymer modifiers which individually enhance performance at extremes of temperatures. One such suggested example is the use of SBR 151 latex as a coating for aggregate to enhance low temperature properties with an Elvaloy modified asphalt binder. Road tests. It is vital for the results obtained in the laboratory to be validated in the field. This can be accomplished by undertaking road tests using the same materials used in this work to evaluate the performance of various systems. Properties such as rutting, fatigue and thermal cracking behaviour of the pavement subjected to traffic and environmental forces can make these results more valuable as there is no equivalent laboratory technique to a real pavement test section. This work has sought to identify the various materials and factors that play a key role in pavement performance. With better understanding of the materials and mechanisms involved on a fundamental level, pavement design can be refined and tailored to overcome the various challenges encountered during service. 152 APPENDIX A F RACTURE TOUGHNESS LOAD-DISPLACEMENT PLOTS 153 250 200 0.0 inch add: 0.0 ' ~ notch 11 *—\ 1.1 hen notch 0.04 0.05 0.00 0.07 deflation (huh) Figure A.1 Load-deflection curves for AC5 0% SBS beam samples for various notch lengths at -l0°C 154 0.08 250 200 Load (the) a - ' inch notch z 1 0 inch notch d 1.21ncnnotcn/ ' 1.1 inch notch 0 01 0.02 0.03 o 04 0.05 0.06 MM Figure A.2 Load-deflection curves for AC5 3% SBS beam samples for various notch lengths at -l0°C 155 0.07 L006 (lb!) 250 200 150 100. fir 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 Deflection (Inch) Figure A.3 Load-deflection curves for AC5 5% SBS beam samples for various notch lengths at -10°C 156 200 150..- ... -,_..._ l 1.0mm R l \\ k \ \\ MID) W/ / \N N . K-\ x M 0 0 0.” 0.01 0.015 0.02 QM 0.03 am 0.00 M0000 (he'll Figure A.4 Load-deflection curves for AC5 0% SEBS beam samples for various notch lengths at -10°C 157 .Ohnotch \ £ > ”\x 0 0.01 0% 0.03 0.04 0.“ 0.“ 0.07 0.00 Dhaka (lick) Figure A.5 Load-deflection curves for AC5 3% SEBS beam samples for various notch lengths at -l0°C 158 0.“ ‘/ \ % 0 0.005 0.01 0.015 0.010.025 0.03 thbn (hell) Figure A.6 Load-deflection curves for AC5 5% SEBS beam samples for various notch lengths at -10°C 159 0.035 0.04 0.045 load (I!) 130 .. 160~ 140 ~- 120 -- 100~ 301. 0.40 notch 1 0 50ndch 0.45 notch / 1 A T Y 0.00 Melt y , J L l L T 0.005 0.01 0.015 0.02 0.025 0.00 0.005 0.04 deflection (In) Figure A.7 Load-deflection curves for AC5 0% SBR beam samples for various notch lengths at -10°C 160 0.0.5 Load (lb) 0.03 0.04 0.05 0.“ 0.07 Deflection (In) 0 0.01 0.02 Figure A.8 Load-deflection curves for AC5 3% SBR beam samples for various notch lengths at -10°C 161 Load (lb) 250 200. \Oflhnotch 0.0010083! / \ m / x \ \\ \ \ \\ \.- Rx \\\ \ 0.01 0.010 Deflection (in) 0.02 0.025 Figure A.9 Load-deflection curves for AC5 5% SBR beam samples for various notch lengths at -10°C o A 1 1 a n A L j T 7 V I o 0.02 0.04 0.08 0.00 0.1 0.12 0.14 Deflection (In) Figure A.10 Load-deflection curves for AC5 0% Elvaloy AM beam samples for various notch lengths at -10°C 163 0.16 1.00600) 0.40 “011 0.005 0.01 0.015 QM 0&5 0% 0.03 Deflection (In) Figure A.ll Load-deflection curves for AC5 1% Elvaloy AM beam samples for various notch lengths at -10°C 164 0.04 0.4 notch 250 «- 200 1r 5 t .. notch 3 150 v . 5 notch 1m 41- 50 d)- 0. 1‘ '~° CD 0.6 notch 0 ' . . - t . 0 0.005 0.01 0.015 0.02 0.025 Deflection (In) Figure A.12 Load-deflection curves for AC5 2% Elvaloy AM beam samples for various notch lengths at -10°C 165 O.” 180 140 120-7 0.01 0.02 0.03 0.04 0.05 0." 0.07 0.“ 0.09 Figure A.13 Load-deflection curves for AC5 0% Crumb Rubber beam samples for various notch lengths at -10°C 166 0.1 250 load (the) i 100 0.01nchnotch “l OMS 0.01 0.015 0.02 0.025 deflection (belt) 000 0.035 0.045 Figure A.14 Load-deflection curves for AC5 5% Crumb Rubber beam samples for various notch lengths at -10°C 167 250 1.0 hch notch i .. 100 <- l 1 1 inch notch 50 0 . , A, 37 iv 0 0.01 0.02 0.03 0.04 0.05 Figure A.15 Load-deflection curves for AC5 10% Crumb Rubber beam samples for various notch lengths at -10°C 168 APPENDIX B LAP-SHEAR TEST RESULTS FOR FRESH ASPHALT 169 Table B.1 Lap shear strength and displacement of SBS and SEBS modified asphalt with granitic rock substrate. TEST ULTIMATE LAP SHEAR 3111331071100 31 DiSPLACEMEN’flmm) common ~ 1.55., 3121303113311 20°C 10°C 0°C -10°c -20°c 0 171 0.26 576 0.55 1339 0.37 1139 0.33 1351 0.31 154 0.37 627 0.41 - - - - 1453 0.23 ' 351 0.35 2300 0.75 2195 0.53 369 0.30 2336 1.12 - - 2 35 0.45 330 0.30 1326 0.60 1970 0.49 1904 0.49 3133 77 0.41 496 0.44 1290 0.71 1139 0.33 1760 0.25 “‘7‘ 3 54 0.53 493 1.33 1079 0.37 636 0.39 1626 0.21 109 1.16 493 120 1101 1.12 1323 0.27 2290 0.23 ‘ 53 0.90 359 0.41 394 0.45 1432 0.42 2053 0.27 AC 5 67 0.75 - - 393 0.49 - - 2004 025 5 90 1.62 431 023 930 0.60 1777 050 1134 0.16 vs. 37 1.10 440 0.37 1016 0.36 920 0.25 1636 0.19 m. 2617 0.33 1365 024 11c ' “' 03‘ 1453 0.42 1237 0.23 ROCK 2 143 0.59 603 0.39 1443 0.59 974 0.52 2730 0.34 - - 623 0.42 1439 0.71 1209 0.49 1355 0.21 3 35 0.23 550 0.42 1074 0.75 1423 :35 2127 0.42 97 0.20 434 0.43 930 0.55 1539 - 1294 0.16 seas “‘5 4 115 0.62 633 0.63 1239 0.99 1033 0.33 1530 027 115 0.46 521 0.60 1443 0.36 1360 0.23 1392 0.17 5 111 1.04 612 0.74 1243 0.35 1439 0.29 1139 0.14 100 0.75 513 0.32 1139 0.53 - - 2351 0.33 6 123 1.06 640 0.35 1397 0.76 1694 0.53 1272 0.15 134 1.00 643 1.23 1406 0.92 - - 1497 0.26 0 219 0.40 353 0.60 1621 0.66 1106 0.24 1630 0.15 250 0.32 763 0.35 1931 0.60 . - 1111 0.13 2 93 0.21 671 0.79 1492 0.95 1343 0.26 634 0.03 99 0.29 515 0.27 1434 1.37 2073 0.32 1536 0.19 3 135 1.43 539 1.22 1414 1.45 2202 0.30 2507 0.36 ses 144 1.43 694 1.57 1136 1.56 . - 2273 0.22 W" 4 173 1.24 697 1.49 1470 1.04 1624 0.36 1421 0.34 162 1.20 637 1.13 1550 0.91 1265 0.43 1091 0.21 4040 5 144 1.01 636 0.39 1252 0.53 1465 0.25 1179 0.16 vs 157 1.14 663 0.36 1342 0.44 1032 0.13 1067 0.15 6 174 1.55 636 1.03 1477 0.37 1333 0.29 1641 0.27 GRAN- 164 1.67 617 1.10 1467 0.90 536 0.26 1074 0.14 me 2 140 0.23 609 0.34 1470 0.35 367 0.24 1233 0.19 aocx 101 0.21 669 0.45 1743 0.92 1439 0.33 1632 0.19 3 39 0.25 705 0.57 1602 0.37 1252 0.40 1332 0.20 157 0.23 741 0.77 1692 0.94 1339 0.32 1755 0.20 seas ‘ 146 0.75 303 0.61 1655 1.00 1313 0.23 2036 0.23 mi. 135 0.72 764 1.01 1653 0.93 1335 0.26 1174 0.13 5 213 0.73 324 1.25 1592 1.32 1350 0.36 999 0.17 199 0.96 739 0.76 1504 0.95 1939 0.33 1655 0.19 6 135 1.30 333 0.79 1760 0.9 1277 0.27 1260 0.13 204 1.07 913 1.06 - - 1697 0.42 1152 0.36 170 Table B.2 Lap shear strength, and toughness of SBR modified asphalt with granitic rock substrate. PROPERTIES U11. Strength (N) Toughness (N -m) Failure Mode COMPOSITION 0°C -10°C 0°C -10°C 0°C -10°C Granitic Rock AC-S/ 1440 2356 2597 394 0011: ADI-I: uncoated 0wt% SBR 1523 1873 2550 342 LT4&5 LT6 AC-S/ 967 2795 3741 3204 0011: C011: 5339/. SBR 1057 2983 3465 3091 LT4 LT4 Granitic Rock AC-SI 924 1 191 4100 145 001-1: ADI-I: coated with 0wt°/. SBR 844 2338 3200 663 L15 LT6 58195363110120) Solution AC-5/ 678 l 166 2100 145 com ADH: (1... 3 micron thick) 5wt% SBR 629 1244 390 197 LT4 LT6 Granitic Rock AC-S/ 1421 2852 2718 3731 0011: ADI-1: coated with 0wt% SBR 1338 3044 2345 2941 LT4 LT6 108/903 (SBR/1120) Solution AC-S/ 1030 1505 2900 940 0011: ADH: (3 ~ 7 m thick) .5wa SBR 911 1671 3000 450 LT2&4 LT6 Granitic Rock AC-S/ - 1465 - 740 - ADI-1: coated with 0wt% SBR - 2327 - 1800 LT6 30377036311!!! 0) Solution 2 AC-S/ . 2459 - 2300 - “on: (5 ... 10 micron thick) 5wt% SBR - 2341 - 2360 LT6 Greemtone AC-5/ 859 2338 3850 857 COI-t ADI-I: coated with 0wt°/o SBR 1000 927 1700 153 LT4&5 LT6 53/953 (SBR/H20) Solution AC-S/ 575 1698 3600 4500 0011: 0011: (1 2. 3 micron thick) 5wt% SBR 644 1894 3000 4400 LT4&5 LT4&5 171 Table B.3 Lap shear strength, strain energy and toughness of Elvaloy modified asphalt with granitic rock substrate. PROPERTIES ~ Ultimate Strength (N) Elastic Strain Energy (N-mm) Toughnees (N-mm) composmON 1 10°C 0°C 40°C -20'c 10°C 0°C 40°C .20'c 10°C o'c -10°c -20'c 473 1425 1640 1269 140 900 435 225 2040 3530 435 225 463 1435 1904 1069 130 390 440 160 1335 2000 440 160 A“ 165 1303 3363 305 25 365 1300 110 210 1375 2100 110 ,, Elvaloy 253 1440 2402 2435 35 315 950 670 200 945 950 670 0mm “’1 ‘5 419 1371 1713 1069 35 370 345 325 1330 3000 345 325 13°“ 439 1391 2132 1977 35 375 535 750 1650 3120 535 750 351 1 142 2699 1264 350 355 1190 270 2600 1430 2230 270 370 1033 2635 1635 230 760 390 415 1350 2665 390 415 300 1345 1562 320 195 600 320 95 1900 375 320 95 315 1731 1136 531 190 515 215 50 1630 515 215 50 .4010 741 1571 1249 517 130 540 215 70 1620 1440 215 70 ,3. mm” 702 1537 1659 344 195 935 275 105 1760 2120 275 105 0m“ M 95 437 1532 1322 1239 120 700 270 190 1660 1350 270 I90 R°°k 531 1369 2294 1015 120 1230 370 170 1430 2260 370 170 339 2221 2343 751 340 1630 775 100 390 2420 775 100 439 1777 1311 1313 100 320 415 215 1425 3030 415 215 172 Table B.4 Lap shear strength, strain energy and toughness of Crumb rubber modified asphalt with granitic rock substrate. PROPERTIES * Ultimate Strength (N) Elastic Strain Energy (N-mm) Toughness (N-mrn) COMPOSITION 1 20°C 0°C 40°C -20°C 20°C 0°C 40°C -20°C 20°C 0°C.. -10°C .2021: ‘ 0 32 1244 2039 1010 15 320 1600 190 575 1940 2150 190 72 131 1 2239 1923 30 1600 1900 320 520 1375 1900 320 5 53 1034 1322 1679 50 750 510 390 35 1200 510 390 AC5 53 1274 931 1503 20 600 260 430 250 950 260 430 vs. Em 10 53 1117 2011 1693 5 590 1030 495 135 950 1290 495 w? x 63 1000 2221 1635 35 360 1330 515 110 630 1670 515 S3?” 15 53 1 131 2626 1339 15 670 2040 500 250 1350 2430 500 53 1103 2494 2319 35 530 1710 745 600 1210 3130 745 20 92 1303 1763 1557 25 320 1150 490 275 1340 1700 490 32 1161 2153 2177 25 550 2020 645 135 1170 2550 645 0 97 1674 1220 1639 20 350 325 415 500 3000 325 415 37 1360 1196 961 20 1200 365 130 700 1430 366 130 5 32 1536 2361 1015 25 735 2900 330 200 1375 2900 330 4010 53 1474 1044 1191 15 430 310 450 140 1100 310 450 vs. $13 10 72 1674 2455 1279 25 1050 1140 315 250 1550 1140 315 w? ,5 77 1430 2597 1313 60 360 1170 230 700 1370 1170 230 30"?“ 15 126 1576 2675 1703 40 350 1700 400 450 1400 2075 400 131 2362 1752 1 131 40 1530 660 255 230 2000 660 255 20 131 1493 1650 1376 50 735 685 330 410 1390 300 330 116 1542 1054 1191 45 360 420 250 345 1435 420 250 173 APPENDIX C LAP-SHEAR TEST RESULTS FOR AGED ASPHALT 174 Table C.1 Lap shear strength and displacement of aged SBS modified asphalt with granitic rock substrate. Binder System LAP-SHEAR STRENGTH, N ELASTIC STRAIN ENERGY, N-mm 20°C 10°C 0°C -10°C -20°C 20°C 10°C 0°C -10°C -20°C AC-5/ 1 wt% 160 450 1350 1400 1000 30 100 350 150 110 SBS 3 wt% 200 400 1000 1400 1200 150 90 320 200 200 6 wt% 190 l 100 2300 175 730 740 0 wt% 320 920 1300 900 850 145 260 210 70 130 AC-lO/ 2 wt% 230 1200 1000 120 330 60 SBS 3wt% 300 570 1530 1200 1300 l 10 200 500 125 100 5 wt% 330 1300 1450 210 375 120 6 wt% 210 1500 1450 345 340 210 175 Table C.2 Lap shear strength, and toughness of aged SBR modified asphalt with granitic rock substrate. PROPERTIES Ultimate Strength (N) Toughness (N—mm) COMPOSITION 0°C -10°C -20°C 0°C -10°C - 0°C 1330 1552 1576 549 349 173 0"“ .- 1330 1415 -- 339 135 A AC-S/SBR 8“] my 1703 1264 1039 1300 163 192 vs. ‘ 1713 2113 1264 1400 453 153 .. 3wt‘/ 1322 2317 946 1200 2557 163 5mm“ M ' 1269 2060 1342 2100 491 255 my 1054 2337 3276 1500 1330 1909 ° 1073 2475 4233 1300 2074 2960 cf“! AC‘WSBR 0479/. 1737 1391 344 690 167 75 0 .66“ 1 2001 1957 912 395 420 161 176 Table C.3 Lap shear strength, strain energy and toughness of aged Elvaloy AM modified asphalt with granitic rock substrate. PROPERTIES - Ultirnate Strength (N) Strain Energy (N ~mm) Toughness (N-rum) COMPOSITION 1 IO’C 0°C ~10°C 10°C O’C -10°C 10°C O’C ~10'C Aged 0 was 927 1469 934 365 260 100 1645 260 100 A05] 942 1399 901 470 475 90 2475 475 90 El 31 V °’ 1 wt% 354 1630 1912 735 540 500 2335 540 500 vs. 305 1339 1433 740 1500 195 1320 1500 195 . _ 2 was 751 1673 1603 245 700 270 700 900 270 grain” 771 1350 1336 390 745 290 625 745 290 OC . 3wt% 1015 1461 996 735 290 190 1335 290 190 610 2001 963 95 1075 240 295 1320 240 Aged 097193 1000 1249 751 150 175 50 150 175 50 AC-lO/ 1064 1269 765 210 160 55 210 160 55 1:1 31 V °’ 1 wt% 1233 1747 762 330 320 65 1055 320 65 Vt 1112 1562 1216 420 235 130 1040 235 130 , , 2 wt% 1152 1364 357 540 395 35 315 395 35 3"?“ 1913 1371 1036 610 330 145 770 330 145 OC 3 wt% 1049 1331 1260 755 215 160 1745 215 160 1 156 1923 333 325 490 175 1690 490 175 177 Table C.4 Lap shear strength, strain energy and toughness of aged Crumb rubber modified asphalt with granitic rock substrate. u PROPERTIES -° Ultimate Elastic Strain Toughness Strength (N) Energy (N-mm) (N-mm) composmom Binder Condition wt % 0°C -10°C 0°C -10°C 0°C -10°C AC-S/ Stored 0 1243 2039 320 1600 1940 2150 CRM @350? 1311 2239 1600 1900 1375 1900 vs. forO . . 10 1117 1322 590 1030 950 1290 G u m“ c hm“ 1000 931 360 1330 630 1670 Rock Stored 0 1440 1103 1020 345 1470 345 @ 350°F 1332 1313 1360 445 1990 445 r h “5 m 10 1220 2143 645 605 1140 605 1327 1864 715 490 1150 490 Stored 0 1205 512 475 30 475 30 @ 350°F 1191 1131 405 305 405 305 f 24 Sum 10 1401 310 360 130 795 435 1923 373 450 300 450 395 AC-lO/ Stored 0 1674 1220 350 325 3000 325 CRM @ 350°F 1360 1196 1200 365 1430 365 . r 011 vs itic °r ”"8 10 1674 2455 1050 1140 1550 1140 Gm" 1430 2597 360 1170 1370 1170 Rock Stored 0 1313 1503 1630 515 2140 515 0 350°F 1536 1503 1190‘ 430 1190 430 f 5 11 °r “"8 10 1415 1536 1210 620 1550 620 1293 346 975 40 1250 40 Stored 0 712 936 170 290 170 290 @ 350°F 315 1112 450 325 450 325 for 24 hours 10 233 190 40 20 ‘ 135 20 1440 ... 720 «- 1100 .— 178 LIST OF REFERENCES 179 10. 11. 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