PERFORMANCE AND SUSTAINABILITY – BASED ANALYSIS OF DIFFERENT CRUMB RUBBER MODIFIED ASPHALT MIXTURES By Berkay Tascioglu A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Civil Engineering – Master of Science 2013 ABSTRACT PERFORMANCE AND SUSTAINABILITY – BASED ANALYSIS OF DIFFERENT CRUMB RUBBER MODIFIED ASPHALT MIXTURES By Berkay Tascioglu Disposal of scrap tires in stockpiles is one of the most significant environmental problems in the U.S. In order to reduce the negative effects of the scrap tires, tire management programs have been developed by different states. One method of beneficially re-using the scrap tires is the construction of crumb rubber (CR) modified asphalt pavements. Today, many states, local agencies and municipalities are using crumb rubber modified asphalt mixtures in pavement construction. There are currently three major methods of introducing CR in asphalt mixtures, namely; wet process (CRWet), dry process (CRDry), and the terminal blend process (CRTB). Most past research focused on each of these technologies individually and compared with traditional or polymer modified asphalt mixtures. There is a need to comparatively evaluate the performances of these technologies and unmodified (traditional) asphalt mixtures. In order to address this issue, a comprehensive study of three different CR types (CRWet, CRDry and CRTB) was conducted in this research. The scope of this study included both asphalt binder tests (Brookfield viscosity, resilience, needle penetration and softening point tests) and asphalt mixture tests (Dynamic modulus (|E*|) test, flow number (FN) test, four point bending beam (FPBB) test and tensile strength ratio (TSR)). Samples were compared in terms of their rutting, fatigue cracking and moisture susceptibility performances. The scope of this research also included sustainability-based analysis of CR modified HMA pavements. Four sustainability rating tools (LEED, Greenroads, GreenLITES and INVEST) were studied and compared to each other in terms of their applicability to CR modified HMA’s. To My Family iii ACKNOWLEDGMENTS I would like to express the deepest gratitude to my advisor, Dr. Muhammed Emin Kutay, who was an inspiration when it came to clarifying my goals. Throughout my academic studies, he continuously and convincingly encouraged me and made me feel as if I could overcome any obstacles. Without his guidance, endless support and friendship, this thesis would not have been possible. I am indebted to my committee members, Dr. Syed Waqar Haider and Dr. Karim Chatti for their help and guidance in my engineering studies. I would like to thank to the Department of Civil and Environmental Engineering for giving me this great opportunity to continue my academic studies at the Michigan State University. The atmosphere was conducive to academic excellence in conducting research and teaching. I would like to acknowledge the support from Michigan Department of Transportation (MDOT) and Michigan Department of Environmental Quality (MDEQ) for sponsoring and funding this study. I would also like to appreciate my research group members – Hande Ozturk, Salih Kocak and Gerrit Littrup for their endless help and motivation in and out of the laboratory. Finally, it gives me a great pleasure in acknowledging the endless support of my family, especially my beloved sister, who is recently fighting against cancer, and friends, who were always with me during my graduate studies. iv TABLE OF CONTENTS LIST OF TABLES…………………………………………………………………………….……….………...vii LIST OF FIGURES…………………………………………………………………………………..….………..ix CHAPTER 1 ................................................................................................................................... 1 INTRODUCTION .......................................................................................................................... 1 CHAPTER 2 ................................................................................................................................... 4 LITERATURE REVIEW ............................................................................................................... 4 2.1 INTRODUCTION ................................................................................................................ 4 2.2 CRUMB RUBBER ............................................................................................................... 8 2.2.1 Crumb Rubber Production Methods .............................................................................. 9 2.2.2 Early Research on Crumb Rubber Modified Asphalt .................................................. 11 2.2.3 Advantages of Crumb Rubber ..................................................................................... 12 2.2.4 History of Crumb Rubber ............................................................................................ 13 2.3 CRUMB RUBBER MODIFIED ASPHALT METHOD ................................................... 14 2.3.1 Wet Process .................................................................................................................. 15 2.3.2 Dry Process: ................................................................................................................. 16 2.3.3 Terminal Blend Process ............................................................................................... 16 2.3.4 State Experiences with Crumb Rubber Modified Asphalt Pavements ........................ 17 2.4 SENTHESIS OF THE PREVIOUS WORK AND MOTIVATION FOR THE CURRENT STUDY ..................................................................................................................................... 21 CHAPTER 3 ................................................................................................................................. 22 LABORATORY INVESTIGATIONS AND TEST PROCEDURES .......................................... 22 3.1 LABORATORY EQUIPMENT ......................................................................................... 22 3.2 HOT-MIX ASPHALT TESTS ........................................................................................... 27 3.2.1 Dynamic Modulus (|E*|) Test ..................................................................................... 27 3.2.2 Flow Number (FN) Test............................................................................................... 30 3.2.3 Four Point Bending Beam (FPBB) Fatigue Test ......................................................... 32 v 3.2.4 Tensile Strength Ratio (TSR) Test ............................................................................... 33 3.3 ASPHALT BINDER TESTS .............................................................................................. 34 3.3.1 Brookfield Viscosity Test ............................................................................................ 34 3.3.2. Softening Point Test........................................................................................................ 35 3.3.3. Needle Penetration Test .................................................................................................. 37 3.3.4. Resilience Test ................................................................................................................ 38 CHAPTER 4 ................................................................................................................................. 39 MIXTURE PROPERTIES AND DATA ANALYSIS ................................................................. 39 4.1 CRUMB RUBBER BINDER ANALYSIS ........................................................................ 39 4.1.1 Tests Run on Crumb Rubber Modified Binders .......................................................... 40 4.2 ASPHALT MIXTURE DESIGN ........................................................................................ 43 4.3 MECHANICAL TESTING OF ASPHALT MIXTURES .................................................. 50 4.3.1 Dynamic Modulus (|E*|) Test ..................................................................................... 51 4.3.2 Flow Number (FN) Test............................................................................................... 53 4.3.3 Four Point Bending Beam (FPBB) Test ...................................................................... 56 4.3.4 Tensile Strength Ratio (TSR) Test ............................................................................... 58 CHAPTER 5 ................................................................................................................................. 60 SUSTAINABILITY ANALYSIS ................................................................................................. 60 5.1 SUSTAINABILITY ............................................................................................................ 60 5.2 RATING TOOLS................................................................................................................ 64 5.2.1 Leadership in Energy and Environmental Design (LEED) ......................................... 64 5.2.2 Greenroads ................................................................................................................... 70 5.2.3 GreenLITES ................................................................................................................. 76 5.2.4 INVEST ....................................................................................................................... 78 5.2.5 Comparison of Rating Systems and Proposed Improvements on Sustainability Measurement for CRM HMA Pavements............................................................................. 80 CHAPTER 6 ................................................................................................................................. 85 SUMMARY AND CONCLUSIONS ........................................................................................... 85 REFERENCES ............................................................................................................................. 89 vi LIST OF TABLES Table 1 Crumb rubber mesh sizes by different markets (Recycling Research Institute, 2013).... 11 Table 2 Different crumb rubber modified HMA design types ..................................................... 17 Table 3 Wet process mix aggregate gradation comparison (FHWA, 1994) ................................. 19 Table 4 Laboratory tests for hot-mix asphalt and asphalt binder specimens ................................ 22 Table 5 Crumb rubber gradations ................................................................................................. 39 Table 6 Viscosity measurement for CRWet binder samples (2 Replicates) ................................. 41 Table 7 Viscosity measurement for CRTB binder (1 Replicate) .................................................. 41 Table 8 Compaction and mixing temperatures for 4 different binders ......................................... 42 Table 9 Properties of crumb rubber modified binders .................................................................. 43 Table 10 Control and CRTB mix design gradations ..................................................................... 47 Table 11 CRWet mix design gradation ......................................................................................... 48 Table 12 CRDry mix design gradation ......................................................................................... 49 Table 13 Material distribution in each design mix ....................................................................... 49 Table 14 Tensile strength ratio (TSR) for Control samples .......................................................... 59 Table 15 Tensile strength ratio (TSR) for CRTB samples ........................................................... 59 Table 16 Tensile strength ratio (TSR) for CRWet samples .......................................................... 59 Table 17 LEED Neighborhood Development evaluation points .................................................. 65 Table 18 Potential points earned for LEED ND rating system ..................................................... 70 Table 19 Greenroads evaluation points......................................................................................... 70 Table 20 Points earned based on recycled material usage ............................................................ 74 vii Table 21 Points earned based on fronthaul distance ..................................................................... 74 Table 22 Potential points earned for Greenroads rating system ................................................... 75 Table 23 GreenLITES evaluation points ...................................................................................... 76 Table 24 Potential points earned for GreenLITES rating system ................................................. 78 Table 25 INVEST Project Development Paving evaluation points .............................................. 79 Table 26 Points earned based on recycled material usage ............................................................ 80 Table 27 Comparison of rating systems based on CRM HMA usage .......................................... 81 Table 28 Proposed points for CRM HMA samples ...................................................................... 84 viii LIST OF FIGURES Figure 1 Distribution of number of scrap tires by generated in different states ............................. 4 Figure 2 Distribution of scrap tires usage by industries (RMA, 2009). For Interpretation of the references to color in this and all other figures, the reader is referred to the electronic version of this thesis......................................................................................................................................... 6 Figure 3 Ground rubber production rate with years (RMA, 2009). Note: GR= ground rubber production, TM= total market ......................................................................................................... 7 Figure 4 Flow chart of ambient grinding process ......................................................................... 10 Figure 5 Flow chart of cryogenic grinding process ...................................................................... 10 Figure 6 Crumb rubber modified asphalt types (FHWA, 1994) ................................................... 14 Figure 7 Wet process on site flow chart (Way, Kaloush & Biligiri, 2011) .................................. 15 Figure 8 Environmental chamber.................................................................................................. 23 Figure 9 Shearbox slab compactor ................................................................................................ 24 Figure 10 Superpave gyratory compactor and shearbox slab compactor ..................................... 25 Figure 11 AMPT device................................................................................................................ 26 Figure 12 Material testing system (MTS) ..................................................................................... 26 Figure 13 Illustration of phase angle and dynamic modulus ........................................................ 28 Figure 14 Illustration of development of |E*| master curve ......................................................... 29 Figure 15 Permanent deformation due to a repeated load. (In the figure, Creep = permanent viscoplastic strain, ∆L = recovered viscoelastic strain) ................................................................ 31 Figure 16 Permanent strain versus number of loads ..................................................................... 31 Figure 17 Ring-and-Ball apparatus ............................................................................................... 36 Figure 18 Penetration apparatus.................................................................................................... 37 ix Figure 19 Compaction and mixing temperature determination for CRWet and CRTB binders .. 42 Figure 20 Graphical representation of mix design gradations ...................................................... 50 Figure 21 |E*| master curves of all asphalt mixtures .................................................................... 53 Figure 22 Permanent (plastic) strains vs. cycles obtained from FN tests (T=64˚C, σd=30 psi, σc=0 psi) ....................................................................................................................................... 55 Figure 23 Permanent (plastic) strains vs. cycles obtained from FN tests (T=45˚C, σd=70 psi, σc=0 psi)................................................................................................................................................. 56 Figure 24 FPBB testing device ..................................................................................................... 57 Figure 25 Four point bending beam (FPBB) test .......................................................................... 57 Figure 26 Triple bottom line of sustainability .............................................................................. 62 Figure 27 Cradle-to-cradle cycle for sustainable pavements ........................................................ 62 x CHAPTER 1 INTRODUCTION In developed societies, scrap tires are produced at an annual human population growth rate (Sousa, Way & Carlson, 2006). Every year, almost 300 million new scrap tires (more than 1 tire/person/yr) were discarded in the United States and more than 275 million tires were compiled in stockpiles (EPA, 2010). Unfortunately, disposal of scrap tires in these stockpiles is one of the biggest environmental problems in the world (Fontes, Pereira, Pais & Triches, 2006). Increased amount of tire stockpiles and landfills threatens environment and public health (Chiu & Pan, 2006). First, they occupy valuable lands that otherwise can be used for farming or infrastructure (Sousa et al., 2006). Second, they cause large fires, which reveal toxic chemicals and air pollutants (Rubber Pavement Association, 2013). Third, these piles create optimum environment for mosquitoes and pests leading to various health problems including malaria, yellow fever, West Nile virus, encephalitis and dengue fever (EPA, 2010). In addition to stockpiling and landfilling, scrap tire management recommends the usage of scrap tires in different categories (Fontes et al., 2006). These include waste prevention (education), recycling (breakwaters, playground fills, erosion control, highway barriers etc.), and energy recovery (Department of Conservation and Natural Resources, 1994). One of the most effective recycling options for scrap tires is their use (in the form of ground-crumb rubber) in hot mix asphalt pavements (EPA, 2010). The use of crumb rubber from waste tires in hot asphalt created a relatively new terminology called “asphalt rubber” (Zareh & Way, 2006). According to American Society of Testing and Materials (ASTM, 2005), asphalt rubber is “… a blend of asphalt cement, reclaimed tire rubber and certain additives, in which the 1 rubber component is at least 15% by weight of the total blend and has reached in the hot asphalt cement sufficiently to cause swelling of the rubber particles…”. Literature has shown that crumb rubber modified (CRM) hot mix asphalt (HMA) increases resistance against aging, reflective cracking, stripping and rutting. Moreover, CRM HMA typically creates more flexible and durable pavement (Fontes et al., 2006). CRM HMA also generally leads to safer pavement surface by improving the friction, reducing the splach-spray (Wen-Yuan, Yung-Chieh & LiTing, 2006). It has been shown that CRM HMA reduces the temperature susceptibility (Chiu & Pan, 2006) and traffic noise level (Zareh, Way & Kaloush, 2006). CRM HMA has also higher elastic absorption capacity against vibrations (Madella, Ferrariis & Simone, 2006). Lastly, less thermal storage capacity is created by pavement structure when the pavement thickness is reduced by using crumb rubber modified HMA (Belshe, Kaloush & Golden, 2006). Scrap tires in asphalt pavement have been used extensively in pavement construction since 1940’s (Fontes et al., 2006), especially in Florida, Texas, California and Arizona (Cao, Guo & Bai, 2006). Different techniques for introducing rubber into asphalt pavement were studied by several states and local agencies (Santucci, 2009). Today, there are three major methods of mixing ground rubber with asphalt pavement: (i) wet process (CRWET), (ii) dry process (CRDRY) and (iii) terminally blend (CRTB). There are several methods of utilization of crumb rubber particles in pavements. These methods have varying degrees of influence on material properties and cost. However, literature is lacking on relative engineering performance of different crumb rubber mixing technologies as well as their performance in terms of sustainability. The main objectives of this research are: 1) to investigate crumb rubber modified asphalt binder characteristics, 2) to compare mechanical properties of three different CRM techniques 2 with conventional HMA, and 3) to analyze three CRM HMA methods in terms of their sustainability. In order to achieve this goal, a research plan was developed. This plan includes following major tasks:  Literature review  Development of test matrix: o Binder testing o Mixture testing  Laboratory performance data analysis  Sustainability analysis This thesis consists of 6 chapters: 1) introduction, 2) literature review, 3) laboratory investigations and test procedures, 4) mixture properties and data analysis, 5) sustainability analysis, and 6) conclusions. The remainder of this thesis is structured as follows: Chapter 2, “Literature Review”, discusses recent crumb rubber HMA practices, which were studied by different DOT’s and academia. Chapter 3, “Laboratory Investigations and Test Procedures”, includes explanation of tests conducted on Hot-Mix Asphalt (HMA) and asphalt binder samples. Chapter 4, “Mixture Properties and Data Analysis”, includes mix design and binder properties. This chapter also presents HMA mechanical testing results. Chapter 5, “Sustainability Analysis”, evaluates CRM HMA pavement in terms of recycled material usage, and CO2 emissions by comparing 4 green rating systems for highway and pavements. Contribution of CR modified pavement into rating systems are studied in this chapter. Chapter 6, “Conclusions”, summarizes the research, discusses the results and gives recommendations for future work. 3 CHAPTER 2 LITERATURE REVIEW 2.1 INTRODUCTION In the United States, approximately 275 million scrap tires were stored in stockpiles in 2003 (EPA, 2013). This number has increased by almost 6% within 6 years. According to Rubber Manufacturers Association (RMA)’s U.S. Scrap Tire Management Summary Report in 2011, total number of scrap tires generated in 2009 became 291.8 millions. About 90% of these tires were generated in 11 states: Texas, New York, Colorado, Michigan, Connecticut, Alabama, Ohio, Pennsylvania, Massachusetts, New Jersey and Washington (Michigan Department of Environmental Quality, 2006). Figure 1 shows the distribution of scrap tires by States according to data presented in Michigan Department of Environmental Quality in 2006. Number of Scrap Tires (in million) Scrap Tire Distribution by States 60 50 40 30 20 10 0 53 40 35 25 20 20 20 12 10 8 State Figure 1 Distribution of number of scrap tires by generated in different states 4 6 According to the graph in figure 1, Texas is the leading state with 55 million of scrap tires generated each year. New York and Colorado follow Texas with 40 and 35 million of scrap tires, respectively. Michigan is the 4th largest contributor to scrap tire waste stream with 25 million. Michigan also has 10 million used tires generation capacity, anually (Michigan Deparment of Enviromental Quality, 2010). Used tires are one of the major waste management issues in United States (Sousa et. al, 2006). Although there has been always an effort to reduce the number of scrap tires in landfills during the past 20 years (EPA, 2006), the amount of tire waste keeps increasing (RMA, 2011). This significantly increases the landfill waste stream (Sousa et. al, 2006), but it also puts environment and public health in danger (EPA, 2010). One of the major environmental problems is the fire hazard (C2S2 Group, 1990). Since most tires constitute compounds and metals like acetone, aniline, benzene, cloroethane, methyl ethyl ketone, nylon, polyester, latex etc. (EPA, 2009), they are extremely flammable (EPA, 2004). These fires continue to air, water and soil pollutions due to hazardaous waste leachates and gas emisions ( C2S2 Group, 1990). Water and soil pollution can lead to damages to groundwater and fresh water resources; whereas, air pollution might cause depression, mutation or even cancer (EPA, 2010). Fighting against these type of fires would also give damage to country’s economy every year (EPA, 2004). Another major environemental problem is that lanfills and stockpiles provide optimum condition for bacterias and mosquitos. the mosquitos can carry serious diseases such as malaria, yellow fever, West Nile virus, encephalitis and dengue fever (EPA, 2010). Because of these negative impacts of landfill-collected scrap tires, government and local agencies brought tire management legislation to nationwide laws and regulations level (EPA, 1991). 5 Generated tire waste in lanfills and stockpiles shows important resource (California Integrated Waste Management Board, 1993). Scrap tire management recommends the usage of this resource in different categories (Fontes et al., 2006) including alternative energy source (40.3%), ground rubber production (26.2%), landfill storage (12.6%), other purposes such as export material (8.2%), new tire production (7.2%), and civil engineering purposes (5.5%). Distribution of scrap tire usage by industries is shown in Figure 2. Scrap Tire Distribution 8.20% 5.50% 40.30% 7.20% Energy Production Ground Rubber Disposal 12.60% Tire Reproduction Civil Engineering Others 26.20% Figure 2 Distribution of scrap tires usage by industries (RMA, 2009). For Interpretation of the references to color in this and all other figures, the reader is referred to the electronic version of this thesis. As shown in Figure 2, 47% of generated scrap tires were used for recycling purposes (Ground rubber, tire reproduction, civil engineering and others) (RMA, 2009). Ground rubber production constitutes more than half of all the recycling alternatives with 55.5% (26.6% out of 47%). The same study also indicated that ground rubber production has increased from 552,100 6 tons to 1,354,170 tons between 2005 and 2009. Graphical representation of this trend is presented in Figure 3 (RMA, 2009). Ground Rubber Production Rate by Years Thousans of Tons 5000 4000 GR/TM=19.2% GR/TM=30.8% GR/TM=5.3% Ground Rubber Production Total Market 3000 2000 1000 0 2005 2007 Years 2009 Figure 3 Ground rubber production rate with years (RMA, 2009). Note: GR= ground rubber production, TM= total market In Figure 3, bar chart displays that rubber production was 15.3% of total scrap tire market in 2005. However, this value has increased to 30.8% in 4 years and became one of the important recycling industries in 2009. Today, asphalt rubber is the leading ground rubber production market with almost 99,000 tons of scrap tire usage (EPA, 2013). Crumb rubber modified asphalt, railroad crossings, soil filligs, rubber and plastic products such as playground floors, carpet padding, floor mats, are the most common products/applications of crumb rubber material (Department of Conservation and Natural Resources, 1994). 7 2.2 CRUMB RUBBER Crumb rubber modified asphalt technologies have been developing during the last 70 years (Fontes et al., 2006). However, after 1980’s, emphasis of scrap tire usage started to focus on the solution of environmental issues and energy crisis. With the new law of “Discarded Tires: Energy Conservation Through Alternative Uses” by United States Department of Energy in 1979, new studies on crumb rubber were started (Sousa, Way & Carlson, 2006). As mentioned in the previous chapter, rubber has a major role as energy resource. Combustion industry already consumes 26 million tires every year and many other industries take their benefits from scrap tire energy (FHWA, 1992). On the other hand, asphalt rubber has 12 million tires consumption potential annually and it is the leading market of ground rubber (EPA, 2013). This type of rubber is produced by (i) shredding the scrap tires into granular sizes and (ii) removing fiber and metal particles from the body. The process is called “crumb rubber” (Zhu & Carlson, 1999). Introducing crumb rubber into pavement materials is also known as “Crumb Rubber Modifier” technology since rubber particles modify the conventional asphalt properties (FHWA, 1992). According to American Society of Testing and Materials (ASTM), crumb rubber is defined as “… a blend of asphalt cement, reclaimed tire rubber and certain additives, in which the rubber component is at least 15 percent by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles…” (ASTM D 6114, 2012). It is noted that there are also other different terminologies used for crumb rubber, such as “scrap rubber” and “reclaimed rubber”. Studies for introducing natural rubber into asphalt started in 1840’s. However, there has been a great effort of finding the optimum blend of natural rubber (latex) and polymers to improve the elastic properties of hot mixed asphalt (Heitzman, 1992). Crumb rubber is not pure 8 polymer (Fontes, Pereira, Pais & Triches, 2006). Instead, it is already-available product of natural and synthetic rubber, carbon black, antioxidants, filler and oil (Caltrans, 2003). 2.2.1 Crumb Rubber Production Methods There are several types of crumb rubber production methods depending on surface morphology and desired mesh size (Takallou, 1995). The most common methods are listed as follows:  Crackermill process  Granular process  Micro-mill process  Cryogenic process Crackermill, granular and micro-mill processes are also called ambient grinding techniques since temperature is the leading parameter in production of crumb rubber (Fontes et al, 2006, Hinchey, 1991). Figure 4 illustrates the ambient grinding process. In crackermill process, rubber is shredded into small pieces before placing in a corrugated steel drum. Then, it starts rotating in drums that have different sizes and the CR particles get torn in room temperature (FHWA, 1993). In contrast, granular process uses steel plates to shred the waste tires into small pieces. This process is also performed in ambient temperature. Similarly, micromill process includes rotating discs instead of steel plates (Amirkahnian and Arnold, 1993). Cryogenic progress, on the other hand, takes the advantage of low freezing point of liquid nitrogen. Rubber pieces become more brittle after mixing with liquid nitrogen. Then, these particles are cut into desired sizes (Fontes et. al., 2006). Baker et al. in 2003 (as cited in Fontes et al., 2006) state that ambient techniques are cheaper and easier to operate when compared to 9 cryogenic process. However, cryogenic process is faster and has smaller rubber size production capacity. This type of process is shown in Figure 5. Shredder Granulator Removal of Steel and Fiber Rubber Production and Storage Final Grinding/Magn etic Seperation/Fibe r and Dust Removal Grinding Steps (Dryer and Classifier) Figure 4 Flow chart of ambient grinding process Shredder Granulator Removal of Steel and Fiber Rubber Production and Storage Final Grinding Grinding Steps (Dryer and Classifier) Figure 5 Flow chart of cryogenic grinding process 10 Based on different production methods, common mesh sizes and popular industries, that uses crumb rubber, given in Table 1 below. Table 1 Crumb rubber mesh sizes by different markets (Recycling Research Institute, 2013) Market Type Mesh (or CR particle) Size Rubber, Construction & Automation Industry Tire Production Applications for HMA Pavement 10-40 mesh 80-100 mesh 16-40 mesh 2.2.2 Early Research on Crumb Rubber Modified Asphalt Performance of crumb rubber modified asphalt is the most important factor when determining the use of scrap tires into pavement technology (Heitzman, 1992). Early research studies raised the concerns about crumb rubber in terms of cost and environment. Equipment requirements, personnel health, stability of material, lack of proper mix design procedures, variations in scrap tire components, hazardous by-products were some of these problems (Decker, 1993). According to a final report prepared by New York State Department of Transportation in 1989, addition of crumb rubber material into pavement increased the construction cost up to 50%. Trials on obtaining a proper gradation, additional mixing effort, lack of on-site labor training and cost of additional labor were stated in this study. Alaska Department of Transportation also mentioned the problems caused by sensitivity in gradation changes due to crumb rubber addition (Esch, 1984). Higher energy requirements for mixing rubber with asphalt, extra care needed during transportation, potential air pollution, health issues 11 at mixing plant, weather and equipment limitations were other issues raised in crumb rubber modified pavement construction. 2.2.3 Advantages of Crumb Rubber Early research studies discuss the additional cost of construction due to crumb rubber material (FHWA, 1993). However, more recent studies have shown that crumb rubber modified hot mix asphalt pavement (CRM HMA) is cost effective, sustainable and perform better in the long term (Carlson and Zhu, 1999). There might be high initial cost (20% - 50% depending on the availability of the mixing equipment); however, crumb rubber modified pavements typically provide longer service life than conventional pavements (Becsey, 2012). Way (2012) observed that, CRM HMA is more suitable for both hot and cold climates, has better rut and skid resistance, and high resistance against reflective cracking and raveling, than conventional pavement. Literature has also shown that crumb rubber modified (CRM) hot mix asphalt (HMA) increases resistance against aging, stripping, rutting, provides long term durability, and creates more flexible and durable pavement (Fontes et al., 2006). CRM HMA gives softer and safer pavement surface to passengers (Wen-Yuan, Yung-Chieh & Li-Ting, 2006). It reduces temperature susceptibility (Chiu & Pan, 2006), traffic noise level (Zareh, Way & Kaloush, 2006), and increases fatigue life (Carlson, n.d.). CRM HMA has also higher elastic absorption capacity of vibrations (Madella et. al, 2006). Furthermore, CR reduces wintertime stopping distance due to ice significantly (Esch, 1984). Lastly, less thermal storage capacity is created by pavement structure since the pavement thickness is reduced by using crumb rubber (Belshe, Kaloush & Golden, 2006). 12 2.2.4 History of Crumb Rubber Original development of crumb rubber modified asphalt mixtures was performed in 1940’s by Vicksburg, which is a U.S. Rubber Reclaiming Company located in Mississippi. Company’s effort was on marketing crumb rubber material as an aggregate in asphalt mixture (dry process) (Baker et al., 2003, as also cited in Fontes et al., 2006). Between 1950 and 1960, first, Lewis and Welborn of the Bureau of Public Roads tested rubber properties on asphalt performance. Then, Symposium on Rubber in Asphalt was held in Chicago by Asphalt Institute (Caltrans, 2003). In 1960’s, crumb rubber was firstly used for maintenance purposes by Charles McDonald, who was a materials engineer for the city of Phoenix. The technique was so successful that Arizona Department of Transportation used crumb rubber as Stress Absorbing Membrane Interlayer (SAMI). Introducing crumb rubber into asphalt cement was named “wet process”. Wet process is also known as McDonald technology (Heitzman, 1992). While wet process development was in progress in the U.S., dry process was improved in Sweden by Skega AB and AB Vaegfoerbaettringar (Esch, 1984). Then, this technology got its patent “Plusride” in the United States in 1978 and it was widely used by Alaska Department of Transportation almost ten years. Crumb rubber studies were broadened with the involvement of Federal Highway Administration (FHWA) in 1970’s. Many field trial projects were constructed with crumb rubber modified asphalt during 1970’s and 1980’s (FHWA, 1992). By the 1990’s, more than 600 miles of highway were constructed by using crumb rubber technology. During these years, asphalt rubber was mainly used as stress absorbing membrane (SAM) or stress absorbing interlayer (SAMI) instead of slurry material and chip seal. After 1990, FHWA and 13 many state highway departments funded research projects to have better understanding of asphalt rubber applications on highway construction (Rubber Pavement Association, 2013). Today, around 80% of total crumb rubber is processed by State of California and Arizona. Florida, Texas, Nebraska, South Carolina and New York are the following states, which also incorporate asphalt rubber into their road constructions (EPA, 2013). 2.3 CRUMB RUBBER MODIFIED ASPHALT METHOD Crumb rubber is typically introduced into hot mix asphalt via two major processes: (i) wet process and (ii) dry process. Basic difference between wet process and dry process is that crumb rubber is added to binder prior to HMA mixing in wet process (as crumb rubber modifier), whereas in dry process, rubber particles are added to HMA mixture directly (as rubber aggregate) (Heitzman, 1992). Terminal blend is a type of wet process and rubber particles are mixed into asphalt at refinery (Santucci, 2009). Figure 6 illustrates the different crumb rubber modification process. Batch Wet Process Continuous Terminal Crumb Rubber Modified Asphalt Techniques Dry Process Figure 6 Crumb rubber modified asphalt types (FHWA, 1994) 14 Rubber Modified HMA 2.3.1 Wet Process Asphalt rubber, “wet process”, was developed by Charles McDonald in 1960’s and has been successfully used in Arizona and California over 35 years (Shatnawi, 2011). From the definition by ASTM (ASTM 2005), this process is based on the mixture of rubber particles with asphalt binder. Since rubber reacts with asphalt cement, it is also considered as crumb rubber modifier. This reaction depends on temperature, size and type of crumb rubber, aromatic type of asphalt binder (Heitzman, 1992). Typical mixing temperature is 325 to 400 F and duration is 45 minutes to 1 hour (FHWA, 1992). During wet process, rubber particles absorb the aromatic oils from binder and swell. Therefore, viscosity and stiffness of binder increase (Fontes et. al, 2006). Mixture process and on site equipment are illustrated in Figure 7. Asphalt Tank Heat Tank Asphalt Rubber Blend Tank (Ground Rubber+Heated Virgin Binder) Reaction Vessel Figure 7 Wet process on site flow chart (Way, Kaloush & Biligiri, 2011) Literature indicates 2 types of wet process: (i) type I and (ii) type II. Type I requires the mixture of 18-20% rubber with binder and it is widely used in Arizona and Texas. Type II, 15 however, includes 20% rubber (75% of ground rubber and 25% of natural rubber) in asphalt cement. Type II binder is used in California (Shatnawi, 2011). 2.3.2 Dry Process: Dry process was firstly developed in Sweden in 1960’s and entered the US market under the name of “PlusRide”. It is also called as “non-reacted system”, “asphalt concrete rubber filled” and “rubber modified hot mix asphalt” (FHWA, 1994). Dry process is a process where rubber particles are added to pre-heated aggregates prior to binder mixing (FHWA, 1992). In this process, CR is added as a replacement of fine aggregate up to 5% by total weight of the mixture. Wet process can accommodate dense, gap and open graded mix design. However, dry process gives the best performance with gap-graded mixes. Gap graded mixes do not only provide space for binder but also increase the resistance against fatigue cracking since more binder is introduced into aggregate skeleton (Fontes et. al, 2006). Even though anti-oxidants are not completely mixed with binder, dry process provides good skid resistance and deicing properties. More crumb rubber particles are utilized in this process as compared to the wet process. 2.3.3 Terminal Blend Process FHWA divides the crumb rubber modified HMA design types into two: (i) wet process and (ii) dry process. Terminal blend is placed under wet process. This has been a controversial issue over the years. According to some researchers, terminal blend is not a wet process. Indeed, it is the third type of HMA design (Fontes et. al, 2006). Terminal blend can be accepted as a special type of wet process. In terminal blend, rubber particles are mixed with asphalt cement at the asphalt refinery. The amount of rubber might differ from 5 to 20% in the mix (Santucci, 2009). This type of binders has been widely used in Florida and Texas since 1960’s. Terminal 16 blend binders are composed of fine rubber gradations and their viscosity is less than wet process. This type of binders is more suitable for dense graded mixes (Shatnawi, 2011). A comparison of these 3 different crumb rubber modified HMA design types is given in Table 2, which includes description of each design type, their advantages and disadvantages. Table 2 Different crumb rubber modified HMA design types Technique Description Dry Crumb rubber (CR) is added as Process a replacement of fine aggregate up to 5% by total weight of the mixture. Advantages (i) Good skid resistance and de-icing properties. (ii) Less expensive (iii) More crumb rubber is utilized Wet CR is added to liquid asphalt at (i) Well known to provide Process temperatures around 325-400oF. superior performance About 15% by weight of the compared to many binder is utilized (1-1.5% by polymer modified asphalt total weight of the mix) pavements Terminally Similar to wet process, CR is (i) Well known to provide Blend added to liquid asphalt at superior performance temperatures around 375-400oF. compared to many About 10 % by weight of the polymer modified asphalt binder is utilized (0.6% by total pavements weight of the mix). The main (ii) No segregation of CR difference is in the additive used particles to keep the CR particles (iii) Can be hauled for suspended in the mixture. long distances. Disadvantages (i) Anti-oxidants are not completely mixed with binder (i) Possible segregation of CR grains if not mixed properly. (i) More costly than the other processes (ii) Less crumb rubber is utilized 2.3.4 State Experiences with Crumb Rubber Modified Asphalt Pavements Crumb rubber has been studied many years by local agencies, department of highways and academic institutions (Santucci, 2009). Arizona, California and Florida are the leading states in utilizing crumb rubber modified asphalt pavements in the U.S. (FHWA, 1995). Texas, Nebraska, South Carolina, New York and New Mexico are also using asphalt rubber in their state and county roads (EPA, 2013). A summary of different state practices in using crumb rubber modified asphalt pavement is given below: 17 Arizona has been using crumb rubber since 1960’s. All three types of mixing procedures were used in Arizona. Wet process is the most commonly used process in Arizona. Both open and gap graded mixes were tried in wet process. Binder content varies from 6% to 10%. Typical CRM content is 20%. California started using asphalt rubber in 1975 as chip seal. Dry process was applied in 1992 last time in the state. Wet process has been used extensively. Open, gap and dense aggregate mixes were used in wet process. Binder content changes from 6% to 8%. Common CRM content is 14-20% (FHWA, 1995). The usage of crumb rubber was started in late 1970’s in Florida. Wet, dry and terminal blend processes were used in asphalt mixes. A research report by Choubane et al. (1998) showed that crumb rubber modified mixtures made with wet process performed better performance than those made with dry process (Choubane, Sholar, Musselman & Page, 1998). Wet process is used widely in Florida. Compared to Arizona and California, open and dense aggregate mixes were used in wet process. Binder content changes from 6.5% to 7.1%. CRM content is mininum 5% for dense graded mixes and 12% for open graded mixes. In overall, Arizona showed the best performances in wet processed HMA pavements. California had moisture damage problems (potholes) with dry process. Early wet process applications also led to rutting and bleeding. However, most of the projects had pavements in very good condition. Florida also showed good performance in AR applications (FHWA, 1995). Table 10 gives the gradation examples by California, Arizona and Florida. In Texas, wet process has been used widely since 1976 (Tahmoressi, 2001). There is variety of projects on crumb rubber applications on pavement. Chip seal coating, undersealing, hot mix asphalt and porous friction course are the most common wet process applications. Tahmoressi (2001) mentioned that all porous friction course projects showed excellent 18 performance. On the other hand, seal coating applications had bleeding problems due to small size of rubber particles. Moreover, hot mix asphalt projects showed satisfactory performance. Table 3 Wet process mix aggregate gradation comparison (FHWA, 1994) Arizona Florida 1/2" Max Gap Graded 100 100 95-100 85-100 79-87 10-40 32-40 18-24 4-12 9-12 California 1/2" Max Open Graded 100 95-100 78-89 32-40 18-24 - Max Open Graded Sieve Size Gap Graded Open Graded Dense FC-3 25 mm (1") 19mm (3/4") 12.5 mm (1/2") 9.5 mm (3/8") 4.75 mm (No. 4) 2.36 mm (No. 8) 2 mm (No. 10) 0.6 mm (No. 30) 0.425 mm (No. 40) 0.075 mm (No. 200) 100 80-100 65-80 28-42 14-22 - 100 30-45 6-10 - 100 88-98 60-90 40-70 - - - 20-45 - - - - 0-2.5 0-2.5 2-6 2-5 2-7 - - 10 Mesh 10 Mesh 40 or 80 Mesh 40 or 80 Mesh 10 Mesh 10 Mesh 10 Mesh Min 20% Min 20% 5% 12% 17-22 17-22 17-22 Typical CRM Gradation Typical CRM Percentage by Weight of AC Open FC-2 100 100 100 90-100 29-36 7-18 - South Carolina has been studying waste tires usage in pavement construction since 1991. Literature shows that both dry (Pelham Road Project in 1992) and wet processes (US-76, Marion County in 1994) were tried. Pelham road (dry process mix) showed some deterioration after 8 years. However, US-76 (wet process mix) is still in good condition (Amirkhanian, 2001). 19 New York tried dry process in 1989 with 3 different rubber gradations (1%, 2% and 3%). However, research showed that these mixes did not perform better than conventional ones after 5 years (VanBramer, 1997). New Mexico started using crumb rubber in 1984 with dry process (Chama Project). Then, wet process (NM 206 Project) was applied in 1985. However, both practices failed. After 1990’s, state started using rubberized open graded friction course overlays by using wet process (US 54, US 62, I 10 and I 25 Highways). Research indicated that these pavement sections showed very good performance after 4 years later with no rutting or cracking (Bandini, 2011). Nebraska constructed its first CRM projects in 2001, however there is no recently published data on the current condition of these pavements (Washington State Department of Transportation, 2003). Idaho tried wet process in 1993 but it failed because of stripping problem. Colorado, Minnesota, New Jersey and Maine also included crumb rubber in their research studies. However, the initial construction cost of the crumb rubber modified mixtures was very high although the performance was the same with conventional mixes. Illinois and Kansas used both wet and dry process mixes starting from 1990 (Washington State Department of Transportation, 2003). 20 2.4 SENTHESIS OF THE PREVIOUS WORK AND MOTIVATION FOR THE CURRENT STUDY Literature has shown that there has been an effort on introducing crumb rubber material in pavement industry since 1940’s (Fontes et al., 2006). Due to environmental concerns, different mixing types and production techniques of crumb rubber have also been developed during these years. Today, most of the states, local agencies and municipalities are using crumb rubber material in pavement construction (Santucci, 2009). Even though there are enormous studies and research on development of crumb rubber modified asphalt, literature is lack of a detailed study comparing different crumb rubber modification process. Either field or laboratory testing has been done in most of the research, and typically one type of process was studied. Performance of CR HMA was measured based on one or two parameters like fatigue cracking, rutting or moisture susceptibility. In addition to mechanical testing, literature does not have an extensive study on sustainability of crumb rubber. This study presents a comprehensive study of three different types. The scope of this study includes:  Evaluation of three crumb rubber asphalt types in terms of their mechanical properties,  Sustainability evaluation of Wet Process, Dry Process and Terminal Blend crumb rubber modified asphalt mixtures 21 CHAPTER 3 LABORATORY INVESTIGATIONS AND TEST PROCEDURES This chapter includes the explanation of tests conducted on Hot-Mix Asphalt (HMA) and asphalt binder samples. Hot-mix asphalt tests conducted in this study include dynamic modulus (|E*|) test, flow number (FN) test, four-point bending beam (FPBB) fatigue test and tensile strength ratio (TSR) test. The asphalt binder tests conducted in this study were Brookfield viscosity test, softening point test (Ring-and-Ball apparatus), needle penetration test and resilience test. Procedure for each HMA and binder test has been explained in this chapter. Furthermore, special equipments that were used during HMA and/or binder tests were also mentioned. Table 4 provides the list of the tests conducted as part of this research. Table 4 Laboratory tests for hot-mix asphalt and asphalt binder specimens No. Hot-Mix Asphalt Test Asphalt Binder Tests 1 Dynamic Modulus (|E*|) Test Brookfield Viscosity 2 Flow Number (FN) Test Softening Point Test 3 Four Point Bending Beam (FPBB) Fatigue Test Needle Penetration Test 4 Tensile Strength Ratio (TSR) Test Resilience Test 3.1 LABORATORY EQUIPMENT The list of equipment used as part of the asphalt mixture and binder testing program is given below: 22 Environmental Chamber – An environmental chamber (produced by Russels) was used to condition HMA samples. Since Dynamic Modulus Test, Flow Number Test and Four Point Bending Beam Fatigue Test were conducted at different temperatures, the samples were conditioned with environmental chamber according to AASHTO specifications. This chamber is able to condition samples from -70 oC to 155 oC. Figure 8 Environmental chamber Slab Compactor and Gyratory Compactor – In this research, two different compactors were used; a gyratory compactor and a special slab compactor called “Shearbox” compactor. According to AASHTO T 312-08 “Preparing and Determining the Density of Hot Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor”, Superpave gyratory compactor applies 600  18 kPa with 1.16  0.02 degrees internal angle to compact cylindrical specimen. On the other hand, slab compactor can create prismatic samples with dimensions of  150 mm wide 450 mm by 150-190 mm tall. This specially made compactor (called Shearbox by 23 compactor) can apply shear during compaction by moving the sides with longest dimension (450 mm) from left to right. The motion is similar to that of the gyratory compactor. The angle of shearing is approximately 4o, which is the manufacturer’s recommendation. Once slabs were compacted, they were cored into cylindrical samples (150 mm tall with 100 mm diameter) for different testing purposes. Figure 9 and 10 show these compactors used for this research. 600 kPa Figure 9 Shearbox slab compactor 24 Superpave Gyratory Compactor Shearbox Compactor Figure 10 Superpave gyratory compactor and shearbox slab compactor Asphalt Mixture Performance Tester (AMPT) – Dynamic Modulus (|E*|) and Flow Number (FN) Tests were conducted using the AMPT device shown in Figure 11. The AASHTO TP 79-11 “Developing Dynamic Modulus Master Curves for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT)” specifies this device for measuring and developing |E*| master curve of asphalt mixtures. The details of dynamic modulus |E*| data analysis is covered in Chapter 4. Material Testing System (MTS) - This is another laboratory equipment used in this research. This general purpose testing system can perform either displacement or load controlled material testing. Four Point Bending Beam Fatigue Test and Tensile Strength Ratio Test were conducted by using the MTS device, which is shown in Figure 12 below. 25 Figure 11 AMPT device Figure 12 Material testing system (MTS) 26 3.2 HOT-MIX ASPHALT TESTS 3.2.1 Dynamic Modulus (|E*|) Test This test produces the dynamic modulus (|E*|) and phase angle of asphalt mixtures at different temperatures and loading frequencies. The |E*| is one of the key inputs in the mechanical-empirical pavement design as stated in AASHTO 2002 Guide for the Design of Pavement Structures. The AASHTO T 342-11 was followed to measure the modulus and shear angle. Then, AASHTO PP 62-10 “Developing Dynamic Modulus Master Curves for Hot Mix Asphalt (HMA)” was used to construct the master curves. AASHTO T 342-11 standard requires sample tests based on five different temperatures (10 C, 4 C, 21 C, 37 C, and 54 C) and six frequencies (25 Hz, 10 Hz, 5 Hz, 1 Hz, 0.5 Hz, and 0.1 Hz). For each frequency, specified load cycles (200 cycles for 25 Hz, 200 cycles for 10Hz, 100 cycles for 5 Hz, 20 cycles for 1 Hz, 15 cycles for 0.5 Hz, and 15 cycles for 0.1 Hz) are applied by AMPT Machine, which is shown in Figure 13. By using the formulas given in the standard, phase angle and dynamic modulus values are calculated below (see Figure 13):   2 *  * t * f 3.1   2 * * f 3.2 qo | E *( f ,T ) |= o e 3.3 27 where; | E * ( f ,T ) | = Dynamic modulus for f Hz; at T,  o = Peak Stress, o = Peak Strain. Δt =1/f σ σ° 0 0 1 2 3 4 5 6 δt ε ε° -2 Time Figure 13 Illustration of phase angle and dynamic modulus 28 After obtaining the dynamic modulus values at specified temperatures (T) and frequencies (f), dynamic modulus master curves are plotted by using “time-temperature superposition” principle. Then these dynamic modulus curves are combined into a single |E*| master curve by shifting the data obtained at different temperatures. Figure 14 shows the graphical explanation of obtaining the single |E*| curve. |E*| versus Reduced Frequency 100000 |E*| (MPa) 10000 T= 4 oC T=19 oC T=31 oC 1000 T=46 oC T=58 oC 100 10 1.0E-05 1.0E-03 1.0E-01 1.0E+01 Reduced Frequency (Hz) 1.0E+03 Figure 14 Illustration of development of |E*| master curve As shown in Figure 14, the y-axis represents the dynamic modulus in MPa and x-axis represents the reduced frequency in Hz. Reduced frequency fR is defined below: f R  f * a(T) 3.4 log( f R )  log( f )  log(a(T))   3.5 29 where; fR= Reduced frequency, a(T) = Shift factor coefficient. In order to create this single master curve, a reference temperature is chosen. In figure 14, reference temperature is chosen as 19 oC. Then, this value is multiplied by a shift factor coefficient so that the |E*| at temperatures below that reference temperature shift to left and the |E*| at temperatures above the reference temperature shift to right. Time temperature superposition principle would be only valid when all these temperatures lie on a smooth curve. Once the curve is obtained, |E*| for any temperature and frequency can be determined. 3.2.2 Flow Number (FN) Test Rutting is one of the major flexible pavement distress types. It is the “w” shaped permanent deformation on pavement surface along the wheel paths. This damage or depression might be occurred due to poor mixture design, soft binder, and/or subgrade/base failure. (http://www.pavementinteractive.org, 2008). One of the commonly used permanent deformation tests for rutting is the repeated load test. One of the commonly used repeated load tests is the Flow Number (FN) test. FN test applies a haversine load to HMA specimen at a constant temperature. The haversine load is applied for every 0.1s followed by 0.9s rest period as shown in Figure 15. During this 0.9s time period, it is observed that the specimen recovers. However, recovery cannot be fully completed because of viscoplastic deformation. This viscoplastic deformation is typically as a function of number of applied load cycles, which is related to 30 rutting in the field. Figure 16 shows the cumulative permanent deformation versus number of cycles. HMA samples can be compared for the same number of applied load cycle. Based on the same number of cycles, the sample with low strain is considered as more resistant to rutting when compared to the one that has higher cumulative permanent strain (Kutay, 2010). L o a d Time D ef or m at io n ∆L Creep Time Figure 15 Permanent deformation due to a repeated load. (In the figure, Creep = permanent viscoplastic strain, ∆L = recovered viscoelastic strain) 80 Cumulative Permanent Strain 70 60 Primary 50 Tertiary Secondary 40 30 ∆V = 0 ∆V > 0 20 10 Flow Number, FN 0 0 10 20 30 40 Number of Loads Figure 16 Permanent strain versus number of loads 31 50 60 70  3.2.3 Four Point Bending Beam (FPBB) Fatigue Test Four-point bending beam fatigue test is a traditional test to determine fatigue life and energy of hot mix asphalt specimens. In order to conduct this test, AASHTO T 321-07 “Determining the Fatigue Life of Compacted Hot Mix Asphalt (HMA) Subjected to Repeated Flexural Bending” standard method was used in this research. According to this standard, a material test system and environmental chamber are required. It is a strain controlled test and 380 mm long, 50 mm thick and 63 mm wide beam shaped HMA specimens are used. The test system should have a load range between 0 kN to 5 kN; displacement measurement capacity between 0 to 5 mm; frequency applicability range between 5 and 10 Hz. Environmental chamber helps specimen to maintain its temperature at 20.0  0.5 C during test. Control and data system records applied load, load cycles, deflection measurement so that  maximum tensile stress, maximum tensile strain, flexural stiffness, phase angle, dissipated energy can be calculated. By using these parameters, dissipated energy versus load cycles or stiffness versus number of repetitions can plotted. Stiffness vs. number of repetitions graph helps to determine cycles to failure. Typically, the 50% reduction in initial stiffness of HMA specimen is considered the point of failure. Typically, an exponential best fit line is used as follows; S  A*eb*n 3.6 where; S is stiffness (in Pa), A is initial stiffness, b is constant, n is load cycle number and e is natural logarithm. Rearranging equation 3.6 reveals the following for the number of cycles to failure (nf,50) based on 50% reduction in stiffness criterion. 32 n f ,50  [ln(S f ,50 / A]/b  3.7 where; Sf,50 is the 50% stiffness value of initial stiffness and nf,50 is the number of load cycles to failure. 3.2.4 Tensile Strength Ratio (TSR) Test Tensile strength test is the most commonly used method to assess the moisture susceptibility of asphalt mixtures. In order to evaluate the resistance of HMA pavement to moisture damage, AASHTO T 283-07 “Resistance of Compacted Hot Mix Asphalt (HMA) to Moisture-Induced Damage” was used in this research. By conducting this test, the saturation and freeze-thaw effects are evaluated with respect to dry and conditioned HMAs. AASHTO specification requires minimum six samples, half of which are evaluated and tested dry. Other half of HMA samples go through vacuum saturation and freeze thaw cycles before applying indirect tensile test. Preparation of test samples and test procedure were explained in AASHTO T 283-07 in detail. Important part of the test comes in calculation the tensile strength ratio. Tensile strength can be measured with the formula given below. St   (2000* P) *t*D 3.8 where; 33  P = Max load in N, t = Thickness of specimen in mm, D = Diameter of specimen in mm. Tensile strength ratio (TSR) is the ratio of indirect tensile strength of the conditioned sample to that of dry (unconditioned) sample. TSR  S2 /S1 3.9 where; S1 = average tensile strength of dry specimens in kPa, S2 = average tensile strength of condition specimens in kPa. AASHTO specification requires minimum 0.80 TSR value since the samples are prepared and tested in laboratory. 0.70 minimum TSR ratio value is also used if the specimen were obtained from existing pavement structure. 3.3 ASPHALT BINDER TESTS 3.3.1 Brookfield Viscosity Test Brookfield viscosity test was done based on AASHTO T 316-06 “Viscosity Determination of Asphalt Binder Using Rotational Viscometer” standard. The aim of this test was to determine viscosity of modified asphalt binder by increasing the temperature from 60 to 34 200C by using rotational viscometer. This test is needed as part of the AASHTO M 320 “Performance-Graded Asphalt Binder” and R 29 “Grading or Verifying the Performance Grade (PG) of an Asphalt Binder” standards. Rotational viscometer test gave the information about temperature at which hot-mix asphalt pavement should be mixed and compacted (Kutay, 2010). According to AASHTO T 316-06, an oven, thermometer, balance, cylindrical spindles, rotational viscometer and temperature controller are required to conduct this test. As a rotational viscometer device, Brookfield viscometer apparatus, was used in this test. Samples are prepared according to AASHTO T 40 “Sampling Bituminous Materials” standard. Before running the test, calibration of the equipment is typically checked. In order to obtain acceptable test results recommended by AASHTO T 316-06, a Newtonian reference fluid is used for calibration verification purposes. The basic principle of this test is to measure the torque with the constant speed of 20 rpm of a cylindrical spindle in asphalt binder at a desired temperature (http://www.pavementinteractive.org/article/rotational-viscometer/, 2008). AASHTO T 316-06 standard requires taking three consecutive measurements with one-minute intervals. Then, these measurements are converted into viscosity. Knowing viscosity values of asphalt binder at different temperatures also helps in assessing the workability of the pavement mixtures. 3.3.2. Softening Point Test Test is commonly used as a tool for assessment of rutting susceptibility of asphalt binders (http://cait.rutgers.edu/prp/softening-point-test, 2011). Softening point test is conducted according to ASTM D 36-95 “Standard Test Method for Softening Point of Bitumen (Ring-andBall Apparatus)” standard. Test apparatus, as shown in Figure 17, includes 2 brass rings, a 50 by 75 mm pouring plate, two 3.5 g steel balls, ring holder, bath and a thermometer. 35 Figure 17 Ring-and-Ball apparatus Test method is based on softening point of two bitumen samples poured into two disk shaped rings. Then, 3.5 g steel balls are replaced on top of bitumen samples before putting test equipment into water bath. Then the temperature is increased gradually at a certain rate so that softening point can be determined when bitumen gets softer and leaves from ring about 25 mm (1 in). The ability of bitumen samples to flow in water bath also allows steel balls to move downward since bitumen leaves from disk shaped rings. The average temperature when samples are 25 mm (1 in.) away from their first position gives the softening point for tested bitumen samples. At some conditions glycerin bath is used instead of water bath. Details of the procedure are available in ASTM D 36-95 “Standard Test Method for Softening Point of Bitumen (Ringand-Ball Apparatus)”. 36 3.3.3. Needle Penetration Test Penetration Test is believed to be one of the oldest asphalt tests (http://www.pavementinteractive.org, 2007). Basic goal of this test is to determine how far the No. 2 needle is going to penetrate into binder sample when it is released from a certain height and at a certain temperature, which are specified in ASTM D5 – 06 “Standard Test Method for Penetration of Bituminous Materials and ASTM D53 – 29 “Standard Test Methods for Sealants and Fillers, Hot-Applied, for Joints and Cracks in Asphaltic and Portland Cement Concrete Pavements”. To conduct the test, penetration apparatus, which is shown in Figure 18, needle, sample container, timing device and thermometer are required (ASTM D5-06). The needle used for this test should be stainless steel and have 50  0.05 g or 100  0.05 weight. There are different needle sizes specified in the standard and any of these needles can be used as long as   the needle release height is determined proportionally. After choosing the most appropriate needle and preparing the binder sample, the test can be conducted at the room temperature (25 C (77 F)). Figure 18 Penetration apparatus 37 3.3.4. Resilience Test This test is used to determine the asphalt binder’s ability to recover after loading. In this research, ASTM D 5329-09 “Standard Test Methods for Sealants and Fillers, Hot-Applied, for  Joints and Cracks in Asphaltic and Portland Cement Concrete Pavements” standard was used. According to this standard, same penetration apparatus, which is shown in Figure 20, can be  used. However, a steel ball, which weighs 75 0.01 g, is used instead of the needle. According to this standard, binder sample is conditioned under water at room temperature (25  0.1 C). Then, the surface of sample is covered by talc and ball is released for penetration. When ball is taken to its original position, binder specimen starts to recover. Difference of the  gauge reading gives the recovery of this asphalt binder specimen. The formula for this calculation is given below. One can refer to ASTM D 5329-09 standard for detailed information and test procedure. Recovery (%) = P +100 – F 3.10 where; P = Penetration reading after ball released, F= Gauge reading when binder recovers. 38 CHAPTER 4 MIXTURE PROPERTIES AND DATA ANALYSIS 4.1 CRUMB RUBBER BINDER ANALYSIS Crumb rubber modified binder and mixture design is very important for long-term field performance. As mentioned early in the Chapter 3, three methods were studied in this research. These are (i) Terminal Blend (CRTB), (ii) Wet Process (CRWet) and (iii) Dry Process (CRDry). They were all made with a PG 64-22 control binder. CRTB was supplied from a local petroleum company and had a PG 76-22 grade and produced with fine crumb rubber particles (Table 5). CRWet and CRDry were prepared in the laboratory. In the CRWet, CR acts as a binder modifier, while in the CRDry, CR is used as if it is fine aggregate. Table 5 shows the crumb rubber gradations, which were used in terminal blend binder preparation, wet and dry process mixture design. As shown in Table 5, most of the crumb rubber particles used in wet and dry process were smaller than #40 mesh and retained #100 mesh; whereas, CRTB had slightly coarser gradation than the CR used in CRWet/CRDry mixtures. Table 5 Crumb rubber gradations % Passing Sieve Terminal Blend Binder (CRTB) Wet and Dry Process (CRWet/CRDry) No. 16 100 100 No. 30 98 100 No. 40 72 94 No. 100 45 16 No. 200 9 2 39 In wet process (CRWet), the base (Control) binder (PG 64-22) was heated up to 190 ˚C and 12% (by weight of binder) crumb rubber was added to base binder. Then, the binder was mixed with crumb rubber particles with the aid of a mixer at a rate of 2000±100 rpm (rotation per minute) for 60 ± 5 minutes. CR was homogeneously distributed within the binder, with all CR clumps eliminated in the CR/binder mixture. A digital dual-range mixer was used with a blade diameter of 1/3 of the bucket size, which was 3.6 liters. Mixing temperature was kept constant by a bucket heater. In dry process (CRDry), rubber particles were mixed with heated aggregates before mixing with base binder. Then, the binder, aggregates and rubber particles were mixed at the same time. In dry process, the percentage of crumb rubber was 2% by weight of HMA mix. 4.1.1 Tests Run on Crumb Rubber Modified Binders ASTM D 6114/D 6114/M “Standard Specification for Asphalt Rubber Binder” standard specifies several binder tests for the CRWet method. These include Resilience (ASTM D5329-09), Ring and Ball Softening Point (ASTM D36-09), Penetration (ASTM D5-06) and Brookfield Viscosity (AASHTO T316-06). As explained in Chapter 3, these tests were conducted for CRWet binder. Brookfield Viscosity Test: Compaction and mixing temperatures were determined by using Brookfield viscosity test. For CRWet process, 2 samples were tested. Viscosity measurements were taken at the temperature of 145 C, 155 C and 175 C. Viscosity values for CRTB binder was provided by Seneca Petroleum Company, which is the CRTB supplier. However, one CRTB sample was also tested 40 to verify the results. Instead of taking viscosity measurements at 3 different temperatures, which is specified in AASHTO T 316-06, 5 different viscosity measurements (at the temperatures of 135 C, 145 C, 155 C, 165 C and 175 C) were taken. The results are provided in Tables 6 and 7. These values were also plotted on viscosity versus temperature graph (Figure 19). The mixing and compaction temperatures of the CR modified HMA mixtures were determined based on the viscosities of 2.2 Pa.s and 3.0 Pa.s, respectively. These target viscosities were based on the CRTB manufacturer’s recommendation for workability. These values are also listed in Table 8 below. Table 6 Viscosity measurement for CRWet binder samples (2 Replicates) 2860 2860 2860 2860 2620 2620 2600 2613 Average Viscosity Reading for Both Replicates (Pa.s) 2737 1820 1820 1820 1820 1640 1620 1620 1627 1723 840 840 740 733 787 Sample 1 (Viscosity Reading Pa.s) Reading (Temp. C) 145 155 175 1st 2nd 840 3rd Average 840 Sample 2 (Viscosity Reading Pa.s) 1st 2nd 740 3rd 720 Table 7 Viscosity measurement for CRTB binder (1 Replicate) Reading (Temp. C) Sample 1 (Viscosity Reading Pa.s) 5900 3900 2760 2060 1740 135 145 155 165 175 41 Average Viscosity versus Temperature Relationships 7000 Viscosity (Pa.s) 6000 5000 Wet Process 12% y = 350787e-0.031x R² = 0.9778 Terminal Blend 4000 3000 2000 1000 y = 1E+06e-0.041x R² = 0.9982 0 130 140 150 160 170 180 Temperature (oC) Figure 19 Compaction and mixing temperature determination for CRWet and CRTB binders Table 8 Compaction and mixing temperatures for 4 different binders Binder Type Base Binder Terminal Blend (CRTB) Wet Process (CRWet) Dry Process (CRDry) Mixing Temperature (oC) Compaction Temperature (oC) 153 163 151 153 143 153 141 143 Penetration test, softening point test, and resilience test were also conducted for CRWet and CRTB binders. The results of tests and ASTM 6114 limits are given in Table 9. Some of the test results (e.g., viscosity) are outside the limits of ASTM 6114. This was because of the compaction problems that were experienced in gyratory compactor. Therefore, CRWet binder was designed such that it had low viscosity at the 177oC. This ensured proper compaction in the gyratory compactor. Softening point test was conducted for only CR modified binder (CRWet 42 and CRTB) because DSR and BBR tests could not be used for CRWet and CRTB. Softening point and penetration test results for the CRTB binder were supplied by the Seneca Petroleum Company. For each binder test (except Brookfield Viscosity test for CRTB), 2 replicates were tested. Table 9 Properties of crumb rubber modified binders Asphalt Binder Type Property CRTB CRWet 1452 681 Softening Point (oC) 61 65 Penetration (mm) 59 40 Resilience (%) Base Binder PG 15 PG 64-22 33 PG 64-22 Brookfield Viscosity (Pa.s) 177 oC ASTM D6114 limits (TYPE II) 1.5 – 5 min. 54 oC min. 25 & max. 75 (at 25°C, 100g, 5 s) min. 20% (at 25 oC) N/A 4.2 ASPHALT MIXTURE DESIGN In order to develop mix designs for each CR modified and control HMA, several state practices, as well as, Standard Practice for Superpave Volumetric Design Manual (AASHTO R35) were studied. Literature shows a common practice of gap-graded gradation for wet process (CRWet) due to better expected aggregate-to-aggregate contact (Caltrans, 2003). Gap graded mixes also reduce the thickness of pavement and allows more asphalt content which increases the resistance against fatigue and cracking (Fontes et. al, 2006). Because of these reasons, CRWet and CRDry mixtures were produced with slightly different gap-graded aggregate structure. On the other hand, coarse-graded aggregate gradation was used for Control and CRTB samples. Same gradation was used for Control and CRTB mixes. This gradation was provided by 43 Ingham County. These gradations as well as material percentages for each blend are showed in Table 10, Table 11, Table 12 44 and Table 13 below. Table 10 Control and CRTB mix design gradations Sieve Size Metric Aggregate Gradations Blend Retained Retained Standard Sand 1/2 3/8 #4 Hydrated Baghouse RAP Lime Control/CRTB Gradation 50 2" 100 100 100 100 100 100 100 100.0 37.5 25.0 3/2" 100 100 100 100 100 100 100 100.0 1" 100 100 100 100 100 100 100 100.0 19.0 3/4" 100 100 100 100 100 100 100 100.0 12.5 1/2" 100 0 100 100 100 100 97.5 91.5 9.5 3/8" 98.5 0 0 98.9 100 100 93.1 84.4 4.75 #4 81.9 0 0 5.5 100 100 70.5 38.5 2.36 #8 63 0 0 1.7 100 100 51.7 29.0 1.18 #16 42 0 0 1.3 100 100 41.2 21.1 0.600 #30 22.8 0 0 1.2 100 100 31.6 13.9 0.300 #50 6.6 0 0 1.1 100 100 19.9 7.6 0.150 #100 2.5 0 0 1 95 100 11.2 5.3 0.075 #200 1.1 0 0 0.7 90 100 7.3 4.3 47 Table 11 CRWet mix design gradation Sieve Size Aggregate Gradations Metric Standard Blend Sand Retained 1/2 Retained 3/8 #4 Retained #8 Hydrated Lime RAP CRWet HMA Gradation 50 2" 100 100 100 100 100 100 100 100.0 37.5 25.0 3/2" 100 100 100 100 100 100 100 100.0 1" 100 100 100 100 100 100 100 100.0 19.0 3/4" 100 100 100 100 100 100 100 100.0 12.5 1/2" 100 0 100 100 100 100 97.5 89.8 9.5 3/8" 98.5 0 0 98.9 100 100 93.1 70.7 4.75 #4 81.9 0 0 5.5 100 100 70.5 29.4 2.36 #8 63 0 0 1.7 0 100 51.7 14.2 1.18 #16 42 0 0 1.3 0 100 41.2 10.8 0.600 #30 22.8 0 0 1.2 0 100 31.6 7.9 0.300 #50 6.6 0 0 1.1 0 100 19.9 5.1 0.150 #100 2.5 0 0 1 0 100 11.2 3.8 0.075 #200 1.1 0 0 0.7 0 100 7.3 3.1 48 Table 12 CRDry mix design gradation Sieve Size Metric Standard Aggregate Gradations Blend Sand Retained 1/2 Retained 3/8 #4 Hydrated Lime RAP CRDry HMA Gradation 50 2" 100 100 100 100 100 100 100.0 37.5 3/2" 100 100 100 100 100 100 100.0 25.0 1" 100 100 100 100 100 100 100.0 19.0 3/4" 100 100 100 100 100 100 100.0 12.5 1/2" 100 0 100 100 100 97.5 89.8 9.5 3/8" 98.5 0 0 98.9 100 93.1 65.1 4.75 #4 81.9 0 0 5.5 100 70.5 26.6 2.36 #8 63 0 0 1.7 100 51.7 19.7 1.18 #16 42 0 0 1.3 100 41.2 14.6 0.600 #30 22.8 0 0 1.2 100 31.6 9.9 0.300 #50 6.6 0 0 1.1 100 19.9 5.6 0.150 #100 2.5 0 0 1 100 11.2 4.0 0.075 #200 1.1 0 0 0.7 100 7.3 3.2 49 Table 13 Material distribution in each design mix % in Blend Material Control CRTB CRWet CRDry Blend Sand 32.00 32.00 10.00 19.00 Retained 1/2 8.30 8.30 10.00 10.00 Retained 3/8 5.70 5.70 18.00 23.50 #4 41.00 41.00 40.00 35.50 Retained #8 0.00 0.00 10.00 0.00 Baghouse 1.00 1.00 0.00 0.00 Hydrated Lime 2.00 2.00 2.00 2.00 RAP 10.00 10.00 10.00 10.00 100.00 100.00 100.00 100.00 Total As it is seen in Table 13, Control, CRTB and CRDry mixes have blend sand, retained 1/2, retained 3/8 and baghouse aggregates. CRWet mix also includes blend sand, retained 1/2, retained 3/8, and #4 aggregates. However, retained #8 was added to the mix instead of baghouse. All mixes contain 2% hydrated lime and 10% RAP aggregates in their gradations. Figure 20 presents the graphical distribution of these 4 mixes. 49 Mix Design Gradations #16 #8 #4 3/8" 1/2" 3/4" 1" 3/2" 2" #8 #4 3/8" 1/2" 3/4" 1" 3/2" 2" #50 #30 #16 CRDry #200 #100 CRWet #200 #100 Control and CRTB 100.0 90.0 80.0 % Passing 70.0 60.0 50.0 40.0 30.0 20.0 10.0 #50 #30 0.0 Sieve Size Figure 20 Graphical representation of mix design gradations 4.3 MECHANICAL TESTING OF ASPHALT MIXTURES The performances of mixes were evaluated based on their resistance to fatigue, rutting, low temperature cracking and moisture susceptibility. Four separate tests were conducted on multiple specimens in this research. In order to determine dynamic modulus values of asphalt specimens in different temperatures and frequencies, firstly, Dynamic Modulus Test was 50 conducted and |E*| master curves were generated. This test also gave general information about low temperature cracking and rutting susceptibility of mixtures. After that, rutting susceptibility of the mixtures was tested with Flow Number (FN) tests. Followed by FN Test, fatigue-cracking susceptibility was analyzed by using Four Point Bending Beam (FPBB) fatigue test. Lastly, tensile strength ratio (TSR) test was conducted to determine moisture susceptibility of specimens. 4.3.1 Dynamic Modulus (|E*|) Test |E*| test is a non-destructive test to determine primary responses (i.e., undamaged, lowstrain response) of asphalt mixtures in different temperatures and loading frequencies. After determining |E*| values, they can be transformed into a master curve using the TimeTemperature Superposition (TTS) Principle. The |E*| master curve is used in the Mechanistic – Empirical Design Guide (currently called Pavement-M software to predict distresses such as fatigue cracking and rutting). As shown below in Figure 21, there are 4 different HMA specimens (with 2 replicates) used for this test. All these specimens were tested in -10 oC, 4 oC, 21 oC, 37 oC and 54 oC in a range of frequencies between 0.1 and 25 Hz. After that, dynamic modulus values for each specimen, obtained from each temperature and frequency, were shifted to a master curve graph, which is given in Figure 21. In this graph, horizontal axis represents reduced frequencies in hertz (Hz.) and vertical axis represents dynamic modulus in MPa. It should be also noted that both axes are in logarithmic scale. 51 Typically, mixtures with relatively low |E*| values at high reduced frequencies (i.e., low temperatures/high frequencies) are more flexible (and less brittle), therefore more resistant to fatigue cracking. On the other hand, mixtures with high |E*| at low reduced frequencies (i.e., high temperatures/low frequencies) are stiffer and are more resistant to rutting. At high frequencies/low temperatures, Control mixture is the stiffest (highest |E*| values). This might be an indicator of its potential brittleness and thus its susceptibility to fatigue cracking as compared to the other mixtures. When low frequencies/high temperatures are considered, stiffest mixtures were CRTB and CRDry, which indicates that they might have better potential to resist rutting. CRWet has much lower |E*| values at low frequency/high temperature region, therefore, this mixture may be more prone to rutting as compared to Control and the other mixtures. Further “damaging” tests are needed to verify these preliminary findings. These damaging tests are the Flow Number test for rutting and Four Point Bending Beam test for fatigue cracking. 52 log-log scale Less cracking 1.0E+05 |E*| MPa 1.0E+04 1.0E+03 Control 1.0E+02 Less rutting CRTB CRWet CRDry 1.0E+01 1.0E-08 1.0E-06 1.0E-04 1.0E-02 1.0E+00 1.0E+02 1.0E+04 1.0E+06 Reduced Frequency (Hz) Figure 21 |E*| master curves of all asphalt mixtures 4.3.2 Flow Number (FN) Test Rutting, depression of pavement surface along the wheelpath, is one of the major pavement distress types. One of the ways to determine rutting susceptibility of asphalt mixtures is the Flow Number Test. Flow Number Test is a repeated load test. Although load is applied repeatedly, its magnitude is fixed and temperature of testing chamber is kept constant during the test. This test can be done either under confined or unconfined condition. Basic operation principle of Flow Number Test is based on 0.1 sec. of loading followed 0.9 sec. of rest period. This loading/ unloading makes up one cycle. At the end of each cycle, cumulative strain values 53 are measured and recorded. After tests are done, these strain values are plotted with respect to each cycle and results are analyzed according to obtained graph. In this study, 2 different Flow Number Tests were conducted. First, a FN Test was performed at 64 0C with 30 psi deviatoric stress and 0 psi confining stress on 2 CRWet, 2 CRDry, 2 CRTB and 2 Control specimens. After this test, plastic strain values for each cycle (N) were plotted as shown in Figure 22. In this figure, x-axis represents cycles and y-axis shows permanent microstrains at the end of each cycle. A good comparison can be done by looking at these permanent strains for a given N value. As shown in Figure 22, CRWet samples performed the worst, because of largest permanent deformation at any cycle. Control mixtures performed better than CRWet and worse than CRDry and CRTB. CRDry and CRTB mixtures performed very well in rutting test when compared to CRWet and Control. These results agreed with the results of |E*| tests. 54 FN Tests at 64 oC (30 psi deviatoric stress, 0 psi confinement) 80000 CRWet Permanent Microstrain 70000 Control 60000 50000 40000 30000 20000 CRDry CRTB_1 CRTB_2 Control_1 Control_2 CRDry_1 CRDry_2 CRWet_1 CRWet_2 10000 CRTB 0 0 1000 2000 3000 4000 5000 Cycle N Figure 22 Permanent (plastic) strains vs. cycles obtained from FN tests (T=64˚C, σd=30 psi, σc=0 psi) In order to further evaluate the relative performance of the mixtures under different temperatures, tests were repeated at 45 oC with 70 psi deviatoric stress and 10 psi confinement. Local weather conditions were taken into consideration for testing temperature selection. The tests were conducted on CRTB, Control and CRWet mixtures as shown in Figure 23. This was primarily to investigate if the gap-graded CRWet mixture would perform better in confined conditions. However, the ranking of the mixtures did not change and CRWet mixtures performed the worst. 55 FN Tests at 45 oC (70 psi deviatoric stress, 10 psi confinement) Permanent Microstrain 25000 Control_1 Control_2 CRTB_1 CRTB_2 CRWet_1 CRWet_2 20000 15000 10000 5000 0 0 2000 4000 6000 Cycle N 8000 10000 12000 Figure 23 Permanent (plastic) strains vs. cycles obtained from FN tests (T=45˚C, σd=70 psi, σc=0 psi) 4.3.3 Four Point Bending Beam (FPBB) Test FPBB test is used for determining the fatigue life and fatigue energy of Hot Mix Asphalt beam specimen. In FPBB test, specimen is subjected to a pure bending moment in the midspan of the simply supported beam with two point loads applied at one-third distance from the two ends of the sample. Moreover, this system, which is shown in Figure 24, allows specimen to have horizontal translation and free rotation at the locations of point loads. Grips at the locations of point loads help the specimen to come back its original position (which means zero permanent deflection) after each loading cycle. After the test, stiffness vs. loading cycles graph is plotted. In this study, the FPBB tests were conducted at a temperature of 18 oC and a frequency of 10Hz. Applied actuator strain level was 500 microstrain () and on-specimen LVDT strain level ranged from 300 to 500 (increased during testing). 56 Figure 24 FPBB testing device FPBB Test (Stiffness (MPa) vs. Cycles) 16000 CRTB_1 CRTB_2 CRDry_1 CRDry_2 CRWet_1 CRWet_2 Control Stiffness (S) (MPa) 14000 12000 10000 8000 6000 4000 2000 0 0 2000 4000 6000 Cycles Figure 25 Four point bending beam (FPBB) test 57 8000 10000 12000 In this test, 2 CRWet, 2 CRDry, 2 CRTB and one Control specimen were used. Figure 25 shows the stiffness versus loading cycles of these mixtures. As shown, Control specimen failed with abrupt decrease in stiffness at around 4000 cycles. On the other hand, CRWet samples did not show abrupt decease in stiffness. Although Control samples failed at around 4000 cycle of loading, CRWet samples continued to resist against this repetitive loading even after 12000th cycle. In addition to CRWET samples, CRTB samples also performed better than Control and CRDRY samples. These samples failed around 7000 and 10000 cycles, respectively. Among the three crumb rubber modified mixtures, CRDry specimen exhibited the worst performance and both replicate mixtures failed just after the test started (in less than 1000 cycles) and this can be clearly seen in the figure. This indicates that CRDry mixtures have poor fatigue cracking behavior. 4.3.4 Tensile Strength Ratio (TSR) Test TSR tests were conducted according to AASHTO T 283. The procedure was explained earlier in Chapter 3. For this test, Control, CRWet and CRTB samples were used. As shown in Tables 14, 15 and 16, TSR values were 95%, 90% and 82% for Control, CRTB and CRWet, respectively. All of the mixtures passed the minimum requirement of 80%. However, CR modified mixtures exhibited slightly lower TSR values as compared to the Control mixture. 58 Table 14 Tensile strength ratio (TSR) for Control samples Sample # Control 1 Control 2 Control 3 Conditioned Set Tensile Tensile Strength Strength (psi) (psi) 129.89 112.57 118.7 113.64 Unconditioned Set Tensile Tensile Strength Strength (psi) (psi) 121.23 119.07 125.32 135.67 Tensile Strength Ratio (TSR) 95 Table 15 Tensile strength ratio (TSR) for CRTB samples Sample # CRTB 1 CRTB 2 CRTB 3 Conditioned Set Tensile Tensile Strength Strength (psi) (psi) 102.76 96.7 98.53 96.12 Unconditioned Set Tensile Tensile Strength Strength (psi) (psi) 112.92 105.94 109.43 83.71 Tensile Strength Ratio (TSR) 90 Table 16 Tensile strength ratio (TSR) for CRWet samples Sample # CRWet 1 CRWet 2 CRWet 3 Conditioned Set Tensile Tensile Strength Strength (psi) (psi) 66.68 80.82 75.98 80.45 Unconditioned Set Tensile Tensile Strength Strength (psi) (psi) 75.4 123.54 92.52 78.66 59 Tensile Strength Ratio (TSR) 82 CHAPTER 5 SUSTAINABILITY ANALYSIS 5.1 SUSTAINABILITY The current construction applications, human behaviors and the negative effects of postindustrial economy have brought some limitations on usage of raw materials and nonrenewable energy sources. Today it is known fact that these resources are not even enough for current generations. This problem leads to other obstacles today and will be larger in the future. In order to prevent this problem and leave a better future for next generations, green movement has been started (Yudelson, 2009). The green building revolution started early in 1980s. First, the chlorinated fluorocarbons were limited in Montreal Protocol and then first definition of sustainability was made in Brundtland Commission. According to this definition, sustainability was being able to supply the current generations’ needs without taking anything from the future ones or without damaging the future generations. It was one of the important moments for human history because everything, which comes after that, was shaped with this definition. When it comes to 1990s, the movement towards green design got bigger and US Green Building Council (USGBC) was formed in 1993. It was a consensus-based group including everyone from different sectors like health care, education, government and private. Starting from this year, the number of its members has increased dramatically. In 2000, USGBC released LEED rating system. This system was the first rating system in the United States because it included everything from energy consumption to waste management. Although energy star was used before LEED rating system, it was only based on energy use (Yudelson, 2008). 60 After LEED release, other rating systems such as Green Globes, CASBEE, BREEAM, were also developed for building usage. Transportation was only a sub-section in these rating systems and building envelope was the main focus. According to U.S. Energy Information Administration in 2007, transportation was responsible for 32% of greenhouse gas emission in the U.S. (USGBC, 2011). It was known that buildings were the leading contributor to annual carbon dioxide emission with 37% in the U.S (Peterson, 2007). However, recent studies have shown that transportation also has the impact on environment. In 2002, FHWA initiated a program in order to reduce the cultural and natural environment impact of highway systems. This program is called “Green Highways Partnerships” which aims to combine triple bottom lines, “social, environmental and economic”, while addressing the current infrastructure problems (Osterhues, 2006). The term “triple bottom line” was first defined by John Elkington in 1994 and today it is considered as the basis of sustainability (USGBC, 2011). Good pavement engineering deals with limited resources to create best design and product. On the other hand, sustainable green pavements mix the good engineering with triple bottom line for the life cycle performance (Dam & Taylor, 2009). Figure 27 shows the “cradleto-cradle” cycle for sustainable pavements (McDonough &Braungart, 2002). 61 Economic Environmental Social Figure 26 Triple bottom line of sustainability Design Material Extraction and Process Recycling Operation &Maintena nce Constructi on Figure 27 Cradle-to-cradle cycle for sustainable pavements 62 According to FHWA, sustainable transportation means “providing exceptional mobility and access in a manner that meets development needs without compromising the quality of life of future generations. A sustainable transportation system is safe, healthy, affordable, renewable, operates fairly, and limits emissions. The development and use of a sustainability framework and rating system allows for the establishment of a shared vision of sustainability in planning, design, construction, operations, and maintenance” (FHWA, 2011). Since the highways are the part of transportation and transportation is the human necessity, the focus of sustainability should be given to pavement development. One of the ways of measuring the level of sustainability is to use rating tools. Measuring sustainability via rating tools helps people to understand sustainability efforts, level of achievements, and current engineering applications. Quantification of sustainability also encourages people to identify tradeoffs and difficulties faced by design and construction (FHWA, 2013). Each rating tool might have different rating system, awarding points, application procedure and different rating industry such as only buildings or only transportation. Rating systems are mostly self-assessed, third-party verified and performance based systems. Since the rating systems are point based, it gives chance to compare different sustainability applications at the same time. This approach creates a competition in green industry, but also helps society to go beyond and above the minimum requirements. Systems have a dynamic structure and they can be updated any time according to society needs and technology changes (Yudelson, 2008). In this chapter, 4 different sustainability rating tools are presented. These are (i) Leadership in Energy and Environmental Design (LEED), (ii) Greenroads, (iii) GreenLITES and (iv) INVEST. These rating tools are studied and available points for CR modified pavement are identified. Then, these points are compared to each rating system to find out how many credits 63 CR modified pavement can get the most among 4 popular rating systems in the U.S. Identifying points for CRM HMA pavement represents the contribution of CR modified asphalt pavement on sustainable infrastructure projects. 5.2 RATING TOOLS It is important to note that all the rating tools are project specific, i.e., the scores are given to a certain construction project. The rating tools presented below illustrate the categories where the points can be earned. The purpose of this section is (1) to investigate the amount of extra points that can be claimed because of use of CRM HMA pavements instead of unmodified asphalt mixture and (2) to investigate whether these existing rating tools are adequate to evaluate the ‘sustainability’ of CRM HMA fairly. 5.2.1 Leadership in Energy and Environmental Design (LEED) LEED rating system, which is originally developed for buildings, has 4 certification levels, which are Certified, Silver, Gold and Platinum (Yudelson, 2008). The initial LEED rating system covered only new constructions and major renovations. This type of system then became as LEED NC (New Construction). After LEED NC, several other types of rating systems were also released. Commercial interiors (CI), operations and maintenance of existing buildings (O&M), core and shell buildings (CS), neighborhood development (ND) and homes, schools, and healthcare were the other rating systems. Each rating system has main category. Sustainable sites, water efficiency, energy & atmosphere, materials & resources, and indoor environmental quality credits are listed under main category. There are also additional credits for neighborhood development and homes categories. These are smart location and linkage credits, neighborhood pattern and design credits and green infrastructure and building credits for neighborhood development category. For homes category, location and linkage and education credits are 64 available. LEED rating system has also bonus innovation in design and regional priority credits (USGBC, 2009). LEED ND (Neighborhood Development) category rates not only buildings but also infrastructure within the buildings. Because of this reason, pavement can be studied and -rated under LEED ND category. However, it should be noted that this rating system was not developed for pavements. LEED ND rating system has 106 points in total. There are 4 credit category; smart location & linkage (27 points), neighborhood pattern & design (44 points), green infrastructure & buildings (29 points) and innovation & design (6 points). The points for each category are listed in Table 17 below. It can be seen from Table 17 that most categories are geared towards buildings. Neighborhood can be LEED certified for 40-49 points, Silver for 5059 points, Gold 60-79 points and Platinum for above 80 points (USGBC, 2009). Table 17 LEED Neighborhood Development evaluation points LEED Neighborhood Development 2009 Smart Location and Linkage Smart location Max Points Max 27 Points in Total Required Imperiled species and ecological communities conservation Required Wetland and water land conservation Agricultural land conservation Floodplain avoidance Preferred locations Brownfields redevelopment Locations with reduced automobile dependence Bicycle network and storage Housing and job proximity Steep slope protection Required Required Required 10 2 7 1 3 1 65 Table 17 (cont’d) Site design for habitat or wetland and water body conservation Restoration of habitat or wetlands and water bodies Long-term conservation management of habitat or wetlands and water bodies Neighborhood Pattern and Design Walkable streets Compact development Connected and open community Walkable streets Compact development Mixed-use neighborhood development Mixed-income diverse communities Reduced parking footprint Street network Transit facilities Transportation demand management Access to civil and public space Access to recreation facilities Visitability and universal design Community outreach and involvement Local food production streets Tree-lined and shaded streets Neighborhood Schools Green Infrastructure and Buildings Certified green building Minimum building energy efficiency Minimum building water efficiency Construction activity pollution prevention Certified green buildings 66 1 1 1 Max 44 Points in Total Required Required Required 12 6 4 7 1 2 1 2 1 1 1 2 1 2 1 Max 29 Points in Total Required Required Required Required 5 Table 17 (cont’d) Building energy efficiency Building water efficiency Water efficient landscaping Existing building reuse Historic resource preservation and adaptive use Minimized site disturbance in design and construction Rainwater management Heat island reduction Solar orientation On-site renewable energy sources District heating and cooling Infrastructure energy efficiency Wastewater management Recycled content in infrastructure Solid waste management infrastructure Light pollution reduction Introduction/Other Innovation and exemplary performance LEED Accredited Professional 2 1 1 1 1 1 4 1 1 3 2 1 2 1 1 1 Max 6 Points in Total 5 1 In green infrastructure section, CR modified pavement can be directly evaluated in two different credits. These are:  GIBc 15 Recycled content in infrastructure (1 point)  GIBc 16 Solid waste management infrastructure (1 point). The goal of recycled content in infrastructure credit is to reduce the environmental impact of construction by reducing the use of virgin materials in nature. Based on the guidelines, credit can only be achieved if minimum 50% of total materials used in new construction are postconsumer recycled materials. In this research, both RAP and crumb rubber particles were 67 used in pavement design. RAP content was 10% for each blend (Control, CRWet, CRDry and CRTB). Moreover, 2% crumb rubber (by weight of mix) was used for CRDry mixture and 12% crumb rubber (by weight of binder) was mixed with virgin binder. Recycle material content for 4 asphalt mixtures do not meet the minimum credit requirement. However, they are counted with the other recycled materials used in the construction. So, this credit can be achieved by using crumb rubber in pavements. It should be noted here that the improved pavement life does not have any effect on the points earned. However, if the pavement life is doubled as compared to traditional asphalt, points should be given to CR. For example, of regular asphalt lasts 10 years, whereas CR asphalt lasts 20 years, regular asphalt needs to be replaced in 10 years and new/virgin materials needs to be used in 10 years. But, since the CR modified asphalt will last 10 more years, effectively, 100% recycling is done at 10 years, which should result in points. However, this fact is ignored in the LEED analysis. Soil waste management aims to reduce the volume of waste deposited in landfills. Waste materials should include paper, cardboard, glass, plastics and metal. Literature has already shown that there are almost 300 millions of scrap tires stored in the landfills and stockpiles and they are already threatening environment and human health. Using CR modified pavement in any neighborhood development project will not only reduce the amount of scrap tires in landfills but also help project to get 1 point under green infrastructure section in LEED rating system. In innovation and design category, projects can earn 1 point due to fact that crumb rubber usage might be considered as an innovative engineering application. Table 17 shows that any project can get 1 point by conserving the nature and animal habitat; 1 point by restoring the environment, animal wildlife and water resources; 1 point by implementing a long term environment conservation management. However, while CR modified 68 asphalt pavements save valuable landfill space and affect these categories, based on guidelines, points cannot be granted to crumb rubber modified asphalt mixture. The indirect effect of CR usage in asphalt on the nature and habitat, restoring environment, animal wildlife and water resources are ignored by this system. Literature already showed that old tire stockpiles threaten the environment and human health. Using crumb rubber particles in hot-mixed asphalt pavement will reduce the area, which is reserved for stockpiling the scrap tires, so that it will preserve the nature, animal habitat and also water bodies. Rating system includes heat island reduction and building energy efficiency under green infrastructure and buildings category. These activities do not consider the effects of usage of crumb rubber particles either. First, solar reflectance index (SRI) value of asphalt might be low. However, it should be noted that the use of crumb rubber in pavement reduces the volume of scrap tires in landfills. If these landfills are reduced and/or removed completely, these areas will be planted again, which drastically reduces the solar heat effect of landfills. Second, the use of crumb rubber in asphalt pavement reduces the energy spent and saves money due to less maintenance. In overall, these categories do not include the life cycle effect of crumb rubber particles. Moreover, it is hard to compare the recycle content used in CRTB, CRWet and CRDry samples. Even though the CRDry mixture has more crumb rubber content in the gradation, the calculation method of recycled material content in this rating system is not effective on comparing these 3 CRM HMA samples. LEED is one of the common rating systems used for measuring the level of sustainability of buildings. Rating system does not focus on only pavement evaluation, but it also rates different categories. Using CR modified HMA can help projects to earn up to 3 credits under LEED ND rating systems. However, rating system does not consider the environmental and economic benefits of crumb rubber usage. Based on the discussion made above, it is concluded 69 that this rating system is not suitable for pavement sustainability evaluation. Table 18 summarizes these points. Table 18 Potential points earned for LEED ND rating system Earned Points CRWet CRTB 0 0 Total Points 27 Control 0 Neighborhood Pattern & Design 44 0 0 0 0 Green Infrastructure & Buildings Introduction/Other (Innovation & Design) Total 29 2 2 2 2 6 0 1 1 1 106 2 3 3 3 LEED ND Credit Category Smart Location & Linkage CRDry 0 5.2.2 Greenroads The Greenroads rating system is used for highway design and construction. It can be applied for both new road construction and existing roads for rehabilitation purposes. Similar to LEED rating system, Greenroads also uses points. Based on earned points, roads can be certified for 4 different levels; Certified (32-42 points), Silver (43-53 points), Gold (54-63 points) and Evergreen (64 points and above). Rating system has 11 Project Requirement activities and 37 Voluntary credits. In total, system can rate any road with 118 points in total (Greenroads, 2011). These activities and points are listed in Table 19 below. Table 19 Greenroads evaluation points Greenroads Rating System Project Requirements (PR) Environmental Review Process Lifecycle Cost Analysis (LCCA) Lifecycle Inventory (LCI) 70 Max Points Mandatory for all projects Required Required Required Table 19 (cont’d) Quality Control Plan Noise Mitigation Plan Waste Management Plan Pollution Prevention Plan Low Impact Development (LID) Pavement Management System Site Maintenance Plan Educational Outreach Environment & Water (EW) Environmental Management System Runoff Flow Control Runoff Quality Stormwater Cost Analysis Required Required Required Required Required Required Required Required Max 21 Points in Total 2 3 3 1 Site Vegetation Habitat Restoration Ecological Connectivity Light Pollution Access & Equity (AE) Safety Audit 3 3 3 3 Max 30 Points in Total 2 Intelligent Transportation Systems (ITS) 5 Context Sensitive Solutions Traffic Emissions Reduction Pedestrian Access Bicycle Access Transit Access Scenic Views Cultural Outreach Construction Activities (CA) Quality Management System Environmental Training Site Recycling Plan Fossil Fuel Reduction 71 5 5 2 2 5 2 2 Max 14 Points in Total 2 1 1 2 Table 19 (cont’d) Equipment Emissions Reduction Paving Emissions Reduction 2 1 Water Tracking 2 Contractor Warranty Materials & Resources (MR) Life Cycle Assessment (LCA) Pavement Reuse Earthwork Balance Recycled Materials Regional Materials Energy Efficiency Pavement Technologies (PT) Long Life Pavement Permeable Pavement Warm Mix Asphalt (WMA) Cool Pavement Quiet Pavement Pavement Performance Tracking Custom Credits (CC) Custom Credit 1 Custom Credit 2 3 Max 23 Points in Total 2 5 1 5 5 5 Max 20 Points in Total 5 3 3 5 3 1 Max 10 Points in Total 5 5 This rating system has 7 categories. These are: project requirements (no points earned), environment & water (21 points), access & equity (30 points), construction activities (14 points), materials & resources (23 points), pavement technologies (20 points) and custom credits (10 points) (Greenroads, 2011). When the activities listed in Table 19 studied, it is observed that CRM HMA should earn points from environmental management system, runoff flow control, habitat restoration, ecological connectivity, fossil fuel reduction, paving emissions reduction, life cycle assessment, recycled materials, regional materials, energy efficiency, long life pavement and pavement 72 performance tracking activities. However, with this current rating system, there is no specific calculation method and/or any category prepared for CRM HMA pavement. This limits the points earned for the use of CRM HMA. If the current system is used, CRM HMA pavement can only achieve up to 11-12 points. These activities, as well as points, are explained below. In construction activities section, 2 credits can be achieved if CR modified pavement is used. These are:  Site recycling plan and (1 point) and  Paving emissions reduction (1 point) Site recycling plan includes proper recycling plan of excess paving materials after construction. These materials might be hot-mix asphalt, concrete, glass, metal, plastic tubes, steel bars, paper, paper products, household waste, aluminum, land clearing debris, topsoil, milling waste and packaging products. With proper recycling of excess crumb rubber particles or CR modified asphalt pavement, project can earn 1 point. If construction is done with a paver, which is accepted by National Institute for Occupational Safety and Health (NIOSH), road can also get another point under paving emissions reduction activity. In materials and resources section, 6 credits can be achieved with CR modified asphalt pavement. Available activities for this category are:  Recycled materials (1 points) and  Regional materials (5 points). In recycled materials activity, roads can get up to 5 points if pavement binder material and/or HMA use recycled material (by total weight). Table 18 shows the point distribution for % recycled material used in construction. 73 Table 20 Points earned based on recycled material usage # of Points 1 2 3 4 5 Percent recycled material 10% 20% 30% 40% 50% For the use of CR modified pavement (10% RAP content), pavement can get 1 point. Since amount of crumb rubber, which is used in dry and wet process, is not significantly high, its contribution is relatively small. Other 5 points can be earned from regional materials activity. The aim of this activity is to reduce the emissions caused by transportation and help local economy. Table 19 gives the points distribution based on travel distance for construction. In this research, aggregates were supplied by Spartan Asphalt Paving Company, which was closer than 100 miles. Since the distance between aggregate supplier and mixing place is closer, carbon dioxide emission due transportation will be decreased. Working with local supplier will be also beneficial for local economy. Because of these reasons, 5 points can be earned. Table 21 Points earned based on fronthaul distance # of Points Max. fronthaul distance (miles) 1 2 3 4 5 500 337.5 225 150 100 In pavement technologies section, CR modified HMA pavement can be used for 2 activities. These are:  Quiet pavement (2-3 Points) and  Pavement performance tracking (1 point). 74 Literature review has already shown that noise level can be reduced by 3 to 6 dB (Zareh, Way & Kaloush, 2006). Road can get 3 points if maximum noise level is 95 dB and 2 points if noise level is 99 dB for 60 mph test speed. For 35 mph test speed, same road can get 3 points if maximum noise level is 88 dB and 2 points if noise level is 91 dB. Using CR modified HMA can help any road to earn 3 points under quiet pavement activity. However, detailed study should be done to measure noise level first. Pavement can also earn 1 point if there is a pavement performance tracking system. This system collects data for density, water content, air content, asphalt content, gradation test and slump test, on regular basis and records the pavement condition. If system is already developed, it can be also applied for CRM HMA. Greenroads is a great tool for rating any highway projects when compared to other 3 rating systems. However, this system should be updated for crumb rubber material and point distribution should be calibrated based on this change. Table 22 Potential points earned for Greenroads rating system Greenroads Credit Category Earned Points Total Points Control CRTB CRWet CRDry Environment & Water 21 0 0 0 0 Access & Equity 30 0 0 0 0 Construction Activities 14 2 2 2 2 Materials & Resources 23 6 6 6 6 Pavement Technologies 20 3-4 3-4 3-4 3-4 Custom Credits 10 0 0 0 0 118 11-12 11-12 11-12 11-12 Total 75 5.2.3 GreenLITES GreenLITES (Leadership in Transportation and Environmental Sustainability) rating system is developed to divert the focus on buildings, which are rated via LEED system, into sustainability projects in transportation. This rating system is created by New York State Department of Transportation in 2008. Additional spreadsheets were developed for Maintenance and Operations in 2009. Then, Regional Pilot Program was released in 2010 (NYSDOT, 2010). GreenLITES rating system is “self-certification program” and it is mainly developed for the State of New York’s sustainability practices. Projects can earn up to 288 points based on scorecard. There are 4 different levels of certification: Certified (15-29 points), Silver (30-44), Gold (45-59 points) and Evergreen (60 points & up) (NYSDOT, 2010). The categories and points given for each category are listed in Table 23 below. Table 23 GreenLITES evaluation points GreenLITES Rating System Sustainable Sites (S) Alignment Selection Context Sensitive Solutions Land Use/ Community Planning Protect, Enhance or Restore Wildlife Habitat Protect, Plant or Mitigate for Removal of Trees & Plant Communities Water Quality (W) Stormwater Management (Volume & Quality) Best Management Practices 76 Points Max 81 in Total 13 15 20 19 14 Max 20 in Total 10 10 Table 23 (cont’d) Materials & Resources (M) Reuse of Materials Recycled Content Local Materials Bio-engineering Techniques Hazardous Material Minimization Energy & Atmosphere ( E) Max 66 in Total 32 16 4 8 6 Max 104 in Total Improved Traffic Flow 29 Reduce Electrical Consumption Reduce Petroleum Consumption Improve Bicycle & Pedestrian Facilities Noise Abatement Stray Light Reduction Innovation/Unlisted (I) 10 15 35 12 3 Max 17 in Total Innovation 4 Unlisted NYCDOT Street Design Manual 10 3 Rating system has 5 categories. These are: sustainable sites (81 points), water quality (20 points), materials & resources (66 points), energy & atmosphere (104 points) and innovation (17 points and up). According to GreenLITES, a project, where CRM HMA is used, should earn points from content sensitive solutions, protect, enhance and restore wildlife habitat, protect, plan or mitigate from removal of trees and plant communities, stormwater management, reuse of materials, recycled materials, local materials, and reduce petroleum consumption activities. However, this system does not also take the environmental effects of CRM HMA pavements into account when rating for these possible activities. With the current system, CR modified pavement can only earn points from following activities: 77  Use recycled tire rubber (2 points),  Use crumb rubber or recycled plastic for noise reduction (2 points),  Specify asphalt pavement mixes containing RAP (2 points) and  Specify local material and plant (4 points), By using CR modified HMA pavement, newly constructed road can get 10 more points. Other categories do not include specific activities for the use of crumb rubber modified pavement. However, like the other rating system, GreenLITES should be also updated and its points should be calibrated based on the crumb rubber usage. Summary of possible earned points for GreenLITES rating system is given in Table 24. Table 24 Potential points earned for GreenLITES rating system GreenLITES Credit Category Total Points Possible Earned Points Control CRTB CRWet CRDry 0 0 0 0 Sustainable Sites 81 Water Quality 20 0 0 0 0 Materials & Resources 66 10 10 10 10 Energy & Atmosphere 104 0 0 0 0 Innovation/Unlisted 17 0 0 0 0 288 10 10 10 10 Total 5.2.4 INVEST Infrastructure Voluntary Evaluation Sustainability Tool (INVEST) is developed by the Federal Highway Administration (FHWA) to evaluate and rate the infrastructure studies and highway projects in terms of sustainability. Recent version of INVEST (Version 1.0) was released in 2012. Rating system is “self evaluation web based tool”. INVEST has 3 modules 78 (System Planning, Operations & Maintenance and Project Development) and 6 different scoring systems. These are paving, rural basic, rural extended, urban basic, urban extended and custom. For this study, paving rating system is selected. In this rating system, any pavement or highway can be certified for 4 different levels of achievement. These are Bronze (17 points), Silver (23 points), Gold (29 points) and Platinum (34 points). Rating system does not have sub categories like the other ratings systems listed above. There are 12 activities in total (Table 25). These are lifecycle cost analyses, highway and traffic safety, educational outreach, tracking environmental commitments, reduce and reuse materials, recycle materials, long-life pavement design, reduced energy and emissions in pavement materials, contractor warranty, construction equipment emission reduction, construction quality control plan and construction waste management (INVEST, 2010). Among these activities, using CRM HMA pavement might address to lifecycle cost analyses, recycle materials, long-life pavement design and reduced energy and emissions in pavement materials sections. However, based on the credit descriptions, CRM HMA can only earn points from recycle materials activity. In 3 different CRM techniques, 10% RAP is used. Contribution of crumb rubber particles in CRWet, CRDry and CRTB mixes is negligibly low in earning points for recycled materials section. However, CRM HMA can still get 1 point due to fact that 10% RAP is used in design mix. Table 26 shows the point distribution for recycled materials section. Table 25 INVEST Project Development Paving evaluation points INVEST Project Development-Paving Lifecycle cost analyses Highway and traffic safety Educational outreach Tracking environmental commitments Reduce and reuse materials 79 Points 3 10 2 5 8 Table 25 (cont’d) Recycle materials Long-life pavement design 8 5 Reduced energy and emissions in pavement materials 3 Contractor warranty Construction equipment emission reduction 3 Construction quality control plan 5 Construction waste management 3 2 Based on the activities compared to LEED rating system, INVEST is a better sustainability evaluation tool. This system includes life cycle analyses, recycle material usage, long life pavement design and reduced energy and emissions in materials. However, the way these activities calculate the points does not include different crumb rubber modified pavement types. Moreover, the rating system cannot emphasize the advantages of crumb rubber usage Because of these reasons, this rating system should be also revised for CRM HMA. Table 26 Points earned based on recycled material usage Point 1 2 Percent recycled material 10% 20% 3 4 30% 40% 5 50% and more 5.2.5 Comparison of Rating Systems and Proposed Improvements on Sustainability Measurement for CRM HMA Pavements When 4 rating systems are compared, it is found out that there is no specific activity for CRM HMA pavement evaluation. As it is seen from the Tables 18, 22 and 24, CRDry, CRWet and CRTB mixes are earning the same points based on these rating systems. Moreover, these 80 points are mainly coming from materials category. Table 27 shows the summary of the points, which CRM HMA can contribute to. Table 27 Comparison of rating systems based on CRM HMA usage Total Points # of Points that CR Modified HMA can contribute LEED ND 106 3 Greenroads 118 11-12 GreenLITES 288 10 57 1 Rating Tools INVEST Among these 4 rating tools, LEED ND and INVEST focus on the least on pavement recycling. Greenroads rating system is the most suitable for CRM HMA pavement evaluation. This system does not only deal with recycled materials but it also evaluates different asphalt technologies. System also considers regional materials, which reduce the carbon dioxide emissions due to transportation. Because of these reasons, contribution of CRM HMA into sustainable highways is higher if Greenroads rating system is used. Greenroads might be the best sustainability evaluation tool among these 4 rating systems. However, when the life cycle effect of crumb rubber is considered, it is seen that the use of crumb rubber in pavement construction has larger positive impact on environment. This positive impact, however, is not considered in these rating systems. A proper point distribution system should be developed based on energy & fuel consumption, environmental protection, cost saving, and long life pavement performance for different CRM HMA pavements. These major categories are studied below: 81 Recycled material usage - Each of three CRM HMA mixes has RAP and crumb rubber content. When the rating systems are studied, it is seen that the calculation method for recycled material content is based on the weight ratio of used recycled material to the total amount of material used in the construction. In CRWet, CRDry, CRTB and Control mixes, RAP content was the same and it was dominant when compared to used crumb rubber material amount. Because of this reason, these mixes could not be compared to each other according to the current rating tools. However, it is already known that CRDry mixes use more crumb rubber content in its gradation. When the points are assigned for recycled material content, more points to CRDry mixes should be given. For instance, if CRWet and CRTB mixes are earning 1 point because of the fact that crumb rubber is used in binder preparation, CRDry mixes should earn more than 1 point. This can be calculated by comparing the amount of crumb rubber used in CRTB and CRWet to the ones used in CRDry mixes. In addition, instead of weight-based percentage, perhaps volumetric percentage should be used. Since the rubber has one-third of the specific gravity of the aggregates, even though a large volume of the crumb rubber is used in the mixture, its weight based percentage is small. Considering that the volume is more important than weight in occupying landfill space, volume should be the basis of the percentages used. Life cycle cost analyses and long life pavement life - Greenroads and INVEST rating systems have life cycle cost analyses and long life pavement life categories. However, these tools do not consider the effect of improved life on the other subcategories such as emissions, fuel usage etc. This category should be also modified based on the CRM HMA pavement use. In chapter 4, FPBB fatigue tests were performed on CRWet, CRDry, CRTB and Control samples. Results showed that Control sample failed around 4000th cycle. On the other hand, 82 CRTB samples failed around 9,000th cycle; whereas, CRWet samples did not fail until 12,000th cycle at all. Figure 25 shows the performance improvement of CRWet and CRTB samples over the Control sample in fatigue cracking. This improvement indicates that pavement life is almost doubled if CRTB HMA is used. Moreover, pavement life increased around 4-5 times if CRWet HMA is used. Increased pavement life leads to less maintenance efforts, which saves money and energy spent during maintenance and construction operations. Increased pavement life will also reduce the carbon footprint of construction since there will be no need of extracting and using virgin materials, and processing oil for binder production. Trucks will not operate for transportation during construction and this will also decrease the carbon dioxide emissions. In overall, improved pavement design life has a large impact of crumb rubber life cycle on sustainability and environment. Because of this reason, more points should be given to CRWet and CRTB mixes when using rating systems. If Control mix is earned 1 point for life cycle cost and/or long life pavement life, CRTB mixes should get 2-3 points; CRWet mixes should earn 4-5 points. These points will not only include the economic savings but also show the energy and carbon footprint reduction due to less maintenance requirements. Nature and wild habitat protection - Literature showed that scrap tires stored in landfills threaten the environment and human health. Fire caused by scrap tire landfills, does not only poison the soil layer and water bodies, but also causes huge amount of carbon dioxide emission to the atmosphere. CRM HMA might not have porous structure, which helps rainwater runoff and its SRI value might not be very high for reducing the heat island effect. However, using crumb rubber particles into HMA pavement will reduce the landfill use. When the landfills are reduced, these places can be planted or they can be wetland. This helps nature and wild habitat 83 protection. Moreover, carbon dioxide emissions due to potential fires will be eliminated. Wetlands will be also protected against any chemical toxicity due to fire. Furthermore, runoff problem will be balanced by creating more planted spaces in nature. The amount of used crumb rubber particles in HMA applications might seem low. However, its environmental impact is considerably large. All these positive effects of CR usage should be transferred to rating systems. Again here, CRDry samples should get more points because of their CR content. Then, CRTB and CRWet samples follow. Based on the discussions made above, proposed points for each CRM HMA mixes are given in Table 28. According to this table, CRWet mixes can earn the highest points among 4 different HMA mixes. It should be noted that these are only suggested points. The aim of giving these points is to show that CRM HMA mixes should earn more points than the ones listed in current rating systems. Crumb rubber has a large impact on environment, economy and society. Because of this reason, effects of CRM HMA pavements on triple bottom line of sustainability should be studied and the rating system should be calibrated carefully. Table 28 Proposed points for CRM HMA samples Proposed Points for CRM HMA Samples Control CRDry CRTB CRWet Activities Recycled material usage 1 2-4 1-2 1-2 Life cycle cost analysis Long life pavement life 1 n/a 2-3 4-5 1 n/a 2-3 4-5 Nature protection n/a 2-4 1-2 1-2 3 4-8 6-10 10-14 Total 84 CHAPTER 6 SUMMARY AND CONCLUSIONS This thesis consisted of 2 major parts. In the first part, the impact of crumb rubber modified binder properties on hot mix asphalt pavement performance was studied. In order to evaluate the effect of crumb rubber particles on the performance of HMA pavement, binder and asphalt tests were conducted. Binder tests included Brookfield test, resilience test, penetration test and softening point test. These tests were conducted on CRWet and CRTB binder samples. In terms of asphalt mixture tests, dynamic modulus (|E*|) tests, flow number (FN) tests, four point bending beam (FPBB) fatigue tests and tensile strength ratio (TSR) tests were conducted on CRTB, CRWet, CRDry (except TSR test) and Control asphalt mixture samples. In the second part of the thesis, four different sustainability rating tools were utilized to assess crumb rubber modified asphalt mixtures and results were compared. Based on the results of the analyses conducted in this study, the following major conclusions were drawn:  Based on binder tests conducted on CRWet and CRTB samples, CRWet binders gave higher values in resilience and softening point tests, which indicates that CRWet binder is expected to perform better in rutting and recovers better when loaded. On the other hand, CRTB samples showed higher values in Brookfield viscosity and penetration tests. This means that CRTB binder is more viscous than CRWet binder at high temperatures, as a result, CRWet is expected to be more workable during construction. Penetration test indicates that, at intermediate temperatures (20-30oC), it is easier to penetrate through 85 CRTB as compared to CRWet, indicating CRWet is possibly less susceptible to microdamage (such as micro-cracking) as compared to CRTB.  In |E*| tests run on asphalt mixtures, it was observed that Control mixture was the stiffest at high frequencies/low temperatures. It can be concluded that this is an indicator of its potential brittleness and thus its susceptibility to fatigue cracking as compared to the other mixtures. On the other hand, CRTB and CRDry were stiffest at low frequencies/high temperatures, which shows that they have better potential to resist rutting. Test results also revealed that CRWet had much lower |E*| values at low frequency/high temperature region, therefore, this mixture may be more prone to rutting as compared to Control and the other mixtures.  The Tensile Strength Ratio (TSR) test was conducted on CRTB, CRWet and Control samples. Test results showed that Control samples performed the best (95%), followed by CRTB (90%) and CRWet (82%).  In fatigue cracking and rutting tests, CRTB samples performed better than Control samples. CRWet performed well (better than the Control) in fatigue testing but poorly (worse than the Control) in rutting. CRDry performed poorly (worse than the Control) in fatigue testing but well in rutting (better than the Control).  It should be noted that Michigan has a cold climate and fatigue cracking is the major concern. Test results indicated that CRWet samples have shown excellent performance in fatigue cracking even though they have poor rutting test results. Based on climatic evaluation, CRWet can be a good alternative to traditional HMA pavements. In contrast, CRDry HMA mixture performed very well in rutting but very poorly in fatigue cracking. 86 According to limited laboratory tests conducted in this study, CRDry mixture can be recommended in hot and tropical climates where rutting is a major concern.  Four common sustainability rating systems were analyzed. Based on their current rating systems, it was concluded that Greenroads is the most suitable sustainability measurement tool for CRM HMA. However, none of the sustainability rating systems (including the Greenroads) includes the crumb rubber’s environmental and economical impacts because of improved performance and service life. Therefore, new points were proposed based on recycled material usage, life cycle cost analysis, long-life pavement performance, nature and wild life habitat protection and restoration. 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