AAPT 2004 Conference

Association of Asphalt Paving Technologists Schedule for 2004 Annual Meeting and Technical Sessions March 8 – 10, 2004 Radisson Hotel, Baton Rouge, Louisiana GOVERNMENT ENGINEERS' FORUM Sunday, March 7, 2004, 1:00 pm, Rita B. Leahy Presiding ♦ "Evaluation of Mechanical Mixture Simulation in the Measurement of the Dynamic Internal Angle of Gyration" T. Harman, G. Al-Khateeb, K. Stuart ♦ "Implementation Status, Assessment and Benefits of Superpave" V. Tandon, I. Avelar, E. Rodzik, J. D'Angelo WORKSHOP SESSIONS Monday, March 8, 2004, 10:15 am, Rita B. Leahy Presiding ♦ "Laboratory Evaluation of Secondary Aggregates in Bituminous Mixtures" G. Airey, A. Collop, N. Thom, S. Zoorob, A. Shiratori ♦ "Preliminary Investigation of a Test Method to Evaluate Bond Strength of Bituminous Tack Coats" G. Sholar, G. Page, J. Musselman, R. Upshaw, H. Moseley ♦ "Superpave Design Compactive Effort: Validity of Using Density at the End of Service Life as a Parameter to Define N-Design" G. Huber, R.M. Anderson SESSION I Monday, March 8, 2004, 1:30 pm, John D'Angelo Presiding ♦ "Mechanical Characterization of Combi-layer" M. van de Ven, A. Molenaar ♦ "The Need for Inducing Shear Instability to Obtain Relevant Parameters for HMA Rut-Resistance" B. Birgisson, D. Darku, R. Roque, G. Page ♦ "Damage Evolution in Triaxial Compression Tests of HMA at High Temperatures" L. Tashman, E. Masad, D. Little, R. Lytton ♦ "Effect of Binder and Mixture Variables on Glass Transition Behavior of Asphalt Mixtures" K. Nam, H. Bahia ♦ "The Effect of Vertical Inhomogeneity on Compressive Properties of Asphalt Mixtures" H. Azari, R. McCuen, K. Stuart -i- SESSION II Tuesday, March 9, 2004, 9:00 am, Gerald Huber Presiding ♦ "Performance-Based Pay Factors for Asphalt Concrete Construction; Comparison with a Currently Used Experience-Based Approach" C. Monismith, L. Popescu ♦ "In-Place Density Evaluation of Stone Matrix Asphalt (SMA) Mixes in Alabama" M. Buchanan, J. Turner, J. Barton ♦ "Development and Field Evaluation of Energy-Based Criteria for Top-down Cracking Performance of Hot Mix Asphalt" R. Roque, B. Birgisson, C. Drakos, B. Dietrich ♦ "Performance of Coarse-Graded Superpave HMA Mixtures" L. Mohammad, Z. Wu, A. Raghavendra, C. Abadie ♦ "Evaluation of Rutting Performance on the 2000 NCAT Test Track" E.R. Brown, B. Prowell, A. Cooley, J. Zhang, R. Powell ♦ By Title Only "Conceptual Performance Criteria for Asphalt Mixtures" T. Pellinen SESSION III Wednesday, March 10, 2004 - 9:00 am, Larry Michael Presiding ♦ "Simplifying the Hollow Cylinder Tensile Test Procedure through Volume-based Strain" W. Buttlar, M. Wagoner, Z. You, S. Brovold ♦ "Evaluation of the Low Temperature Fracture Resistance of Asphalt Mixtures Using the Semi- Circular Bend Test" X. Li, M. Marasteanu ♦ "The Virginia Smart Road: The Impact of Pavement Instrumentation on Understanding Pavement Performance" I. Al-Qadi, A. Loulizi, M. Elseifi, S. Lahouar ♦ "Characterization of Aggregates and Asphalt Concrete Using X-ray Computerized Tomography" L. Wang, H. Paul, T. Harman, J. D'Angelo ♦ "Use of GPR for Thickness Measurement and Quality Control of Flexible Pavements" I. Al-Qadi, S. Lahouar ♦ By Title Only "A Really Simple Performance Test" I. Oh, B. Coree - ii - SESSION IV Wednesday, March 10, 2004, 1:00 pm, Frank Fee Presiding ♦ "Fatigue Evaluation of Asphalt Mixtures Using Dissipated Energy and Viscoelastic Continuum Damage Approaches" J. Daniel, W. Bisirri, Y. Kim ♦ "A Distinctive Fatigue Failure Criterion" G. Al-Khateeb, A. Shenoy ♦ "Two-Stage Weibull Approach for Asphalt Concrete Fatigue Performance Prediction" B. Tsai, J. Harvey, C. Monismith ♦ "An Investigation of the Applicability of Schapary's Work Potential Model for Characterization of Asphalt Fatigue Behavior" R. Lundstrom, U. Isacsson ♦ By Title Only "A Study of Crack-Tip Deformation and Crack Growth in Asphalt Concrete Using Fracture Mechanics" Y. Seo, Y. Kim, R. Schapery, M. Witzak, R. Bonaquist - iii - Harman, Al-Khateeb, Stuart 1 Evaluation of Mechanical Mixture Simulation In the Measurement of the Dynamic Internal Angle of Gyration Thomas Harman1, Ghazi Al-Khateeb2, and Kevin Stuart3 Abstract The Superpave® gyratory compactor (SGC) fabricates laboratory specimens for volumetric and mechanical assessment under the Superpave asphalt mixture design system. The current standard practice specifying the operation of the SGC allows two different, non-equivalent methods of angle calibration: external and internal. The internal method employs the Dynamic Angle ValidatorTM (DAV), developed by the Federal Highway Administration (FHWA) in partnership with the Test Quip Inc. Pervious studies have demonstrated the need to calibrate Superpave gyratory compactors using internal angle measurement (1). However, the DAV procedure, although effective, is labor intensive and time-consuming requiring up to a day for the required angle measurements and compactor calibration. A mechanical system has been developed to work with the DAV to simulate mixture resistance during angle measure. The Hot-Mix Simulator (HMS) greatly reduces the time required for measurement and calibration. This study employs a commercial version of the gyratory loadplate developed by the University of Wisconsin, Madison to characterize forces and eccentricities present during mixture gyratory compaction to evaluate the effectiveness of the HMS. 1 Asphalt Pavement Team Leader, R&D, Federal Highway Administration (FHWA), Turner-Fairbank Highway Research Center (TFHRC), McLean, VA 22101, [email protected] 2 Senior Research Engineer, SaLUT Inc., TFHRC, McLean, VA 22101, [email protected] 3 Highway Research Engineer, FHWA, TFHRC, McLean, VA 22101, [email protected] Implementation Status, Assessment, and Benefits of Superpave Vivek Tandon1, Ivan Avelar2, Ewa Rodzik3, and John D’Angelo4 Abstract To overcome premature failure problems and improve the nation’s highways, a five year 150 million dollar Strategic Highway Research Program was initiated in 1987. A major component of this research was a 50 million dollar asphalt program that led to the development of Superpave. At the end of Strategic Highway Research Program, the Federal Highway Administration assumed responsibility for further development and validation of Superpave system. It also initiated a national program to encourage the adoption of the system by all state highway agencies. The American Association of State Highway and Transportation Officials Task Force on Strategic Highway Research Program implementation developed the concept of Lead States for uniform implementation of Superpave. Although initial implementation progress and state highway agency needs were documented by the Lead States, the implementation status and needs beyond 2000 are not known. This information is essential for future implementation planning, allocation of resources, and current costs of Superpave mixes in comparison of conventional mixes. To identify Superpave implementation status, benefits and concerns, a review of existing literature was performed and state highway agencies were contacted. Based on the gathered information, a questionnaire was developed and state highway agencies, Superpave centers, User Producer groups, and hot mix asphalt contractors were surveyed. The literature review information and results of the survey are presented in this paper. 1 Assistant Professor, The University of Texas at El Paso, El Paso, Texas Undergraduate Research Assistant, The University of Texas at El Paso, El Paso, Texas 3 Training Program Manager, National Highway Institute, FHWA 4 Team Leader, Asphalt Team, Office of Pavement Technology, FHWA 2 LABORATORY EVALUATION OF SECONDARY AGGREGATES IN BITUMINOUS MIXTURES Gordon D. Airey1, Andrew C. Collop2, Nicholas H. Thom3, Salah E. Zoorob4 and Akira Shiratori5 Abstract With a greater understanding of the need for sustainable development, the use of primary aggregates in asphalt mixtures for road or airfield pavements is seen as a wasteful use of a finite natural resource. Therefore the reuse of primary aggregates and/or the use of waste (secondary) materials are seen as being of benefit to society. Of the various waste streams, the by-products of the iron and steel making industries (blast furnace and steel slags) and recycled crushed glass (cullet) can be considered sensible alternative sources of aggregate for asphalt mixture production. These secondary aggregates have similar physical properties to conventional, primary aggregate and can be processed, crushed and screened into practical sizes for easy batching into both surfacing and base asphalt materials. This paper assesses the mechanical performance and durability of a range of both base and surfacing materials incorporating different combinations, size fractions and percentages of two primary aggregates (limestone and gritstone) and three secondary aggregates (basic oxygen steel slag, blast furnace slag and glass cullet). The mechanical properties of the asphalt mixtures have been measured using the suite of tests (stiffness modulus, 1 Senior Lecturer, Nottingham Centre for Pavement Engineering, University of Nottingham, UK 2 Reader in Civil Engineering, Nottingham Centre for Pavement Engineering, University of Nottingham, UK 3 Lecturer, Nottingham Centre for Pavement Engineering, University of Nottingham, UK 4 Research Fellow, Nottingham Centre for Pavement Engineering, University of Nottingham, UK 5 Researcher, Nottingham Centre for Pavement Engineering, University of Nottingham, UK 1 Preliminary Investigation of a Test Method to Evaluate Bond Strength of Bituminous Tack Coats Gregory A. Sholar Gale C. Page James A. Musselman Patrick B. Upshaw Howard L. Moseley Florida Department of Transportation 5007 NE 39th Avenue Gainesville, FL 32609 Phone: 352.955.6600 August 1, 2003 Prepared for the 2004 Annual Meeting of the Association of Asphalt Paving Technologists Abstract It is generally recognized that a bituminous tack coat is beneficial for improving the bonding strength between two hot-mix asphalt layers. It is also qualitatively recognized that moisture on the surface of the tack coat can impede the bonding performance of the tack coat. Furthermore, varying tack coat application rates and aggregate interaction between hot-mix asphalt layers are also considered to have an effect on the bonding performance of the tack coat. In an effort to quantify the effects of moisture, tack coat application rate and aggregate interaction on bonding performance, a test apparatus and procedure were developed. Three field projects were also constructed and evaluated at various time intervals. Results indicate that water applied to the surface of the tack coat, representing rainwater, significantly reduced the shear strength of the specimens when compared to equivalent sections without water applied. Varying tack coat application rates within the range of 0.091 to 0.362 L/m2 had less of an effect on shear strengths. The use of a tack coat to increase bonding strength was more effective for fine graded mixtures compared to coarse graded mixtures. Aggregate gradations of the mixtures being bonded together played a critical role in the magnitude of the shear strengths achieved. Fine graded mixtures achieved significantly lower shear strengths than the coarse graded mixtures. A field project containing a milled interface achieved the greatest strengths of the projects tested. The single-operator standard deviation of the test procedure was determined to be 66.2 kPa. Superpave Design Compaction Effort: Validity of Using Density at the End of Service Life as Parameter to Define N-Design Gerald A. Huber1 R. Michael Anderson2 ABSTRACT When the Superpave method of mix design was introduced in 1993, the method included a new Superpave gyratory compactor and a table of design compaction effort based on the premise that density in the laboratory compactor should match density at the end of service life. The experiment underpinning the N design was done on pavements at least 12 years old. Post SHRP attempts to expand that database to include pavements of all ages and refine the table of design compaction have been unsuccessful and lead to the conclusion that density at the end of service life is not a reasonable parameter to define design compaction. The Superpave Mixtures and Aggregates Expert Task Group have recommended changes to the original design compaction. These are based on compactability of the aggregate skeleton to changes in N design and on changes in mixture stiffness with changes in N design. Change to the design compaction level (N-design) does not change asphalt content, it changes mixture mechanical properties (stiffness). Current levels of N-design in the Superpave system are rational and reasonable. Key words: N-design Hot Mix Asphalt, Superpave, Design compaction, INTRODUCTION When Superpave was introduced in 1993, the asphalt industry was introduced to a new laboratory compactor, the Superpave gyratory compactor. Although not entirely new, the 1 Associate Director of Research Heritage Research Group, Indianapolis, IN Director of Research, Asphalt Institute, Lexington, KY The oral presentation was made by Gerald Huber 2 Mechanical Characterization of Combi-layer Martin F.C. van de Ven1, Andre A.A. Molenaar2 Abstract Combi-layer consists of a porous asphalt concrete layer with very high voids content (25 percent), of which the voids are filled with cement slurry. In this paper research is reported into the mechanical characterization of combi-layer. This was necessary because many asphalt technologists see combi-layer as an intermediate between asphalt concrete and cement concrete with some concrete-like properties at high temperatures. No relevant material characterization was available from literature. The normal testing procedures for the mechanical characterization of asphalt concrete mixtures have been executed. From the test results master curves for the stiffness over a large temperature area, indirect tensile strength and fatigue lines at design temperatures are reported. Because of the suggested difference with the standard asphalt concrete mixes a fundamental characterization of the material was deemed necessary. Uni-axial tension and compression tests were performed at several temperatures and strain rates. In this paper monotonic tension and compression tests with a constant strain rate are reported. In the paper the uni-axial properties of the combi-layer material are compared with asphalt concrete and cement concrete. From the comparison it becomes clear that the combilayer behaves similar to an asphalt mix. At high temperatures it cannot perform without confinement under loading like cement concrete. This is best shown with the temperature dependence of the material properties. 1 Associate Professor, Road and Railway Engineering, Faculty of Civil Engineering and Geo Sciences, Delft University of Technology, the Netherlands. 2 Professor, Road and Railway Engineering, Faculty of Civil Engineering and Geo Sciences, Delft University of Technology, the Netherlands. THE NEED FOR INDUCING SHEAR INSTABILITY TO OBTAIN RELEVANT PARAMETERS FOR HMA RUT-RESISTANCE Bjorn Birgisson1 Assistant Professor (Corresponding Author) Daniel Darku1 Post-Doctoral Graduate Reynaldo Roque1 Professor Gale C. Page2 State Bituminous Materials Engineer Abstract Instability rutting is a major distress mode in hot mix asphalt pavements, which occurs when the structural properties of the compacted mix cannot resist near surface critical stress conditions caused by traffic loads. The critical stress conditions for rutting instability include high near surface shear stresses and low confinement. On the mixture level, instability rutting is manifested in a rearrangement of the aggregate structure. This paper illustrates that it may be necessary to induce instability in mixtures to determine parameters that are relevant to mixture rut resistance. The SuperpaveTM gyratory compactor with shear measurements and the option of changing the compaction angle during compaction was used in this study. Mixtures were compacted to a density that is consistent with the air voids of field pavements immediately after construction, namely 7 percent (± 0.5) percent air voids. The subsequent application of high shear stresses by increasing the gyratory angle from 1.25 degrees to 2.5 degrees results in the rearrangement of the aggregate structure during which parameters can be measured that define clear differences in mixtures. Based on the testing of 31 mixtures with different void structure and aggregate characteristics, three distinctive responses were observed: a) brittle response, b) plastic response, under which once the mixtures loose strength due to rearrangement they never regain another stable rearrangement, and c) optimal response, which is bracketed by the plastic and brittle types of responses. Key parameters were identified that are relevant to the rut-resistance of mixtures. Using these new parameters, a framework 1 Dept. of Civil & Coastal Engrg., University of Florida, 365 Weil Hall, PO Box 116580, Gainesville, FL 32611-6580, Tel: (352) 392-9537, Fax: (352) 392-3394, E-mail: [email protected] 2 Florida Dept. of Transportation, State Materials Office, 2006 NE Waldo Rd, Gainesville, FL 32609 1 Damage Evolution in Triaxial Compression Tests of HMA at High Temperatures Laith Tashman1, Eyad Masad2, Dallas Little3, and Robert Lytton4 Abstract This paper presents the results of an experiment aimed at capturing and characterizing damage evolution in hot mix asphalt (HMA) at relatively high temperatures. HMA specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. X-ray computed tomography (CT) was used to capture the microstructure of the HMA specimens before and after loading, and image analysis techniques (IAT) were used to characterize the evolution of air voids and cracks throughout the deformation process. Image analysis techniques were developed to distinguish between air void growth and crack evolution. This is extremely important as the underlying mechanisms for these two phenomena are different. The term “voids” is used throughout this paper to refer to air voids and cracks combined. Damage in HMA was found to initiate following a period of microstructure hardening. In addition, damage was found to be localized in a critical section in a specimen that was mainly responsible for failure. The growth and propagation of cracks in this critical section was significantly larger than that in the rest of the specimen. The study showed that the top part of the specimens exhibited significant cracking, the middle part exhibited significant amount of dilation, and minor microstructural changes occurred in the bottom part. These variations within a specimen are attributed mainly to the heterogeneity of the HMA microstructure. -----------------------------------------------------------------------------------1 Graduate Research Assistant, 2Assistant Professor, 3Professor, 4 Professor: Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3135. EFFECT OF BINDER AND MIXTURE VARIABLES ON GLASS TRANSITION BEHAVIOR OF ASPHALT MIXTURES A paper submitted for presentation at the 2004 Annual Meeting of the Association of Asphalt Paving Technologists By Kitae Nam Hussain U. Bahia The Asphalt Research Group Department of Civil and Environmental Engineering The University of Wisconsin-Madison Madison, Wisconsin 53706 [email protected] July 2003 Nam and Bahia 1 Abstract The thermal coefficient of contraction of asphalt mixtures is one of the required properties in the prediction of thermal cracking of asphalt pavements. Due to the significant influence of asphalt binders on asphalt mixtures’ thermal properties, asphalt mixtures are expected to show a significant glass transition behavior. In the current practice, however, the thermal coefficient of contraction of mixtures is assumed to be linear, and determined from a simplistic relationship with binders that takes into account volumetric and physical mixture properties. Although measuring thermal properties of asphalt mixtures has been a longstanding research topic for the last decade, a limited number of studies have explored the methods for the direct measurements of these properties. Using the findings of previous studies, a system was developed in this project for the direct measurement of change in linear length of mixtures as a function of change in temperature. The system was used to show the significant glass transition experienced by mixtures and to evaluate the effect of mix variables on the thermal properties. The investigation included the thermal properties of 23 mixture specimens produced from six types of asphalt binders, two sources of aggregates, and two levels of gradation. In the test, a wide temperature range from +40°C to –90°C induced a thermal change in the specimens. In order to study the effect of cooling rates on the properties of interest, two different cooling rates were applied while the specimens’ thermal contraction was continuously measured. The measured data allowed an estimation of the Glass Transition (Tg) and thermal coefficients of contractions above and below Tg for each mixture. Statistical analysis was conducted to relate the mix variables with the thermal properties. The results indicated the developed system is practical and repeatable, offering a means for reliable evaluations of glass transition of the asphalt mixtures. The results showed the need for considering dual thermal coefficients of contraction and that such an approach would provide more accurate results in the prediction of thermal stress. The results also indicated that the asphalt binder THE EFFECT 1OF VERTICAL INHOMOGENEITY ON COMPRESSIVE PROPERTIES OF ASPHALT MIXTURES Haleh Azari1, Richard McCuen2, and Kevin Stuart3 Abstract Vertical inhomogeneity, which is defined as the separation of the original mix design gradation into finer and coarser gradations along the depth of the specimen, is often observed in laboratory compacted asphalt mixture specimens. This phenomenon is believed to be the result of the heavier, coarse aggregates gravitating to the bottom of the mold thus preventing the fine aggregates from sinking. Also, the kneading effort of compaction forces the larger particles to the bottom of the mold. While inhomogeneities exist, the effect of the vertical inhomogeneity on mechanical properties of asphalt mixtures is not known. To study this effect, homogeneous and vertically inhomogeneous asphalt mixtures specimens were fabricated. In order to characterize the degree of inhomogeneity, non-destructive x-ray computed tomography (CT) was used to scan cross-sectional images of the specimens. An index of inhomogeneity was developed to evaluate the level of inhomogeneity of the scanned images. The results clearly showed that the index could distinguish between homogeneity and inhomogeneity. The compressive modulus of the mixture was evaluated at test temperatures of 21°C and 45°C by means of frequency sweep simple performance dynamic modulus test. The resistance of the material to axial permanent deformation was measured using the simple performance flow number test at 45°C. The effects of vertical inhomogeneity on the compressive properties of the specimens were investigated at the two test temperatures. Neither dynamic modulus at both test temperatures nor the permanent axial deformation changed significantly with vertical inhomogeneity. Although, the correlation between the compressive properties and the inhomogeneity index is generally very poor, the correlation is higher at the test temperature of 21°C than at the test temperature of 45°C. The results of this study indicate that simple performance tests are not sensitive to even an extreme level of vertical inhomogeneity. Regardless of the separation of the original mixture to the coarser and the finer gradations, an average property value that is comparable to the properties of homogeneous specimens is measured. This shows that predicting the performance of the material in the field based on the compressive properties of laboratory-made specimens as they are measured using Simple Performance Tests could be reliable. 1 Research Engineer, Turner-Fairbank highway Research center, McLean VA 2 Professor, University of Maryland, College Park MD 3 Research Engineer, Turner-Fairbank highway Research center, McLean VA 1 Performance-Based Pay Factors for Asphalt Concrete Construction; Comparison with a Currently Used ExperienceBased Approach Carl L. Monismith,1 Lorina Popescu,1 and John Harvey1 Abstract The paper briefly summarizes a procedure to quantitatively establish pay factors for asphalt concrete pavement construction using performance models for fatigue and rutting based on the analysis of accelerated pavement tests from the Caltrans Heavy Vehicle Simulator (HVS) and the WesTrack accelerated pavement performance test program. For rutting, the influence of asphalt content, air-void content, and aggregate gradation are considered. For fatigue, air-void content, asphalt content, and asphalt concrete thickness are included. Costs are established using a cost model considering only agency cost consequences of delaying or accelerating the time to the next rehabilitation. For the asconstructed mix, the relative performance (RP)—the ratio of offtarget ESALs to target ESALs—is determined for both fatigue and rutting. The shortest RP for the combined RP’s for mix and pavement characteristics considered for a specific distress mode permits determination of the pay factor from the cost model. Pay factors determined by this methodology are compared with those that have been used by the California Department of Transportation (Caltrans), termed an experience-based approach. This set of pay factors has been in use since 1997 for Quality Control/Quality Assurance projects. Comparisons are included for approximately 80 projects constructed in the period January 1997 to June 2000. Only a limited number of these contained measured rutting and fatigue cracking data that had been incorporated in the Caltrans Pavement Management System. Comparisons of pay factors for these projects determined by the two methodologies are also included. An analysis is presented which compares pay factors calculated at the end of the project based on the total 1 Pavement Research Center, University of California, Berkeley IN-PLACE DENSITY EVALUATION OF STONE MATRIX ASPHALT (SMA) MIXES IN ALABAMA M. Shane Buchanan1, Johnny R. Turner2, and James C. Barton3 Abstract The accurate measurement of the in-place density of hot mix asphalt (HMA) mixtures is essential for quality control and assurance, performance prediction, and pay factor determination. Currently the most common methods for in-place density determination through cores and nuclear density gauge testing. An evaluation of the in-place density determination using cores and nuclear gauge testing was conducted for four stone matrix asphalt (SMA) and one Superpave HMA mix in Alabama. The use of surface filler with nuclear gauges was evaluated along with different method of nuclear gauge calibration as methods to improve the accuracy and precision of the nuclear gauges relative to the core density. Additionally, the effect of lift thickness to nominal maximum aggregate size (LT/NMAS) on the achieved in-place density was investigated for each of the mixes. Using the nuclear gauge with surface filler resulted in improved accuracy and precision relative to the nuclear gauge without surface filler being used. Also, the use of a 10-point forecasting method of gauge calibration was found to yield the most accurate and precise “predicted core density” results of the methods evaluated. No relationship for any of the mixes evaluated was determined between the in-place density and the lift thickness to nominal maximum aggregate size. Key Words: In-Place Density, Nuclear Gauge, Stone Matrix Asphalt, Cores, Surface Filler 1 Assistant Professor of Civil Engineering, Mississippi State University, Mississippi State, MS Quality Control Manager, ST Bunn Construction Company, Inc., Tuscaloosa, AL 3 Quality Control Technician, ST Bunn Construction Company, Inc., Tuscaloosa, AL 2 Development and Field Evaluation of Energy-Based Criteria for Topdown Cracking Performance of Hot Mix Asphalt Reynaldo Roque1, Bjorn Birgisson2, Christos Drakos3, and Bruce Dietrich4 Abstract It is now well-recognized that top-down cracking is a major form of distress in hot mix asphalt pavements A detailed analysis and evaluation of 22 field test sections throughout the state of Florida resulted in the development and verification of energy-based criteria for top-down cracking of hot mix asphalt. The work clearly indicated that there is no single mixture property or characteristic that can reliably predict top-down cracking performance of hot mix asphalt. A parameter termed the Energy Ratio, which was derived using the HMA Fracture Mechanics Model developed at the University of Florida, was determined to accurately distinguish between pavements that exhibited top-down cracking and those that did not, except for mixtures with excessively low or unusually high dissipated creep strain energy thresholds. The Energy Ratio, which is defined as the dissipated creep strain energy threshold of the mixture divided by the minimum dissipated creep strain energy required, is determined on the basis of tensile properties that can be obtained from a modulus, creep, and strength test performed with the Superpave IDT at a temperature of 10°C. The Energy Ratio accounts for the effects of pavement structural characteristics on top-down cracking performance. Therefore, it can be used to suitably integrate asphalt mixture properties in the pavement design process. In addition, a rational approach was developed to adjust the minimum Energy Ratio criterion for different traffic level pavements. In conclusion, two energy-based criteria were recommended to control top-down cracking of hot mix asphalt: 1) a minimum dissipated creep strain energy threshold; and 2) a minimum Energy Ratio for mixtures with a dissipated creep strain energy threshold greater than the minimum. Key Words: Top-Down Cracking, Pavement Performance, Fracture Mechanics 1 Professor, 2 Assistant Professor, 3 Assistant-in-Engineering, University of Florida, Gainesville FL, and 4 State Pavement Design Engineer, Florida Department of Transportation, Tallahassee, FL Comparison of Aggregate Gradation and Mixture Physical Properties to Performance Tests of Coarse-Graded Superpave Mixtures in Louisiana Louay N. Mohammad1, Zhong Wu2, Amar Raghavendra3, and Christopher Abadie4 Abstract This paper presents the comparison of laboratory performance tests of coarse-graded Superpave HMA mixtures in Louisiana with physical properties of mixtures including volumetrics, aggregate gradation analysis, and field performance. Eight Superpave HMA mixtures were evaluated. Six of the eight mixtures were designed for high-volume traffic (greater than 30 million ESALs), while the other two mixtures were designed for low-volume traffic (less than 3 million ESALs). Theses mixtures includes two aggregate types: limestone and sandstone, and two binder types: PG 70-22M and PG 76-22M. Laboratory mechanistic tests conducted include indirect tensile (IT) strength, IT and axial creep, frequency sweep at constant height (FSCH) and repeated shear at constant height (RSCH). The aggregate gradation analysis was characterized using a Power-law to evaluate the effects of gradation on mixture mechanistic properties. Laboratory test results showed that highvolume mixtures appeared to have higher IT strengths, lower IT and axial creep slope and higher shear stiffness when compared to those of low-volume mixtures. This indicates that high volume mixtures generally possessed better rut-resistance than low volume mixtures considered. All four Power-law gradation parameters (aCA, nCA, aFA and nFA) were sensitive to the mixture mechanistic properties evaluated. Key Words: Coarse graded Superpave mixtures, Aggregate gradation analysis, Mechanistic tests, Voids in the mineral aggregate, 1 Associate Professor, Louisiana State University and Louisiana Transportation Research Center, Baton Rouge LA 2 Research Associate, Louisiana Transportation Research Center, Baton Rouge, LA 3 Research Associate, Louisiana Transportation Research Center, Baton Rouge, LA 4 Materials Research Administrator, Louisiana Transportation Research Center, Baton Rouge, LA EVALUATION OF RUTTING PERFORMANCE ON THE 2000 NCAT TEST TRACK E. R. Brown, Brian Prowell, Allen Cooley, Jingna Zhang, R. Buzz Powell Introduction Background Empirical laboratory tests have been used for years to test HMA for determining the potential of various mixtures to perform well in the field. As the amount of traffic has increased (higher volumes, higher loads, and increased tire pressures) the ability of these laboratory tests to evaluate potential performance has become even more important. To keep up with these increased loads, the overall quality of the HMA has had to increase significantly to continue to provide satisfactory performance. Some of the deficiencies in material quality and construction procedures that were used in the past when traffic levels were lower have been corrected so that satisfactory performance has continued in most instances under these higher loads. As the amount of traffic has increased, better laboratory tests and material specifications have been developed to help ensure that high quality mixtures are produced. Superpave technology and Stone Matrix Asphalt (SMA) are two examples of improvements that have been made. Satisfactory performance under future loadings will require that our technology base continue to improve. One of the problems in developing new tests is that it takes many years to determine whether or not these tests do a good job of predicting performance or at least providing information that will allow subjective ranking of different materials. Some tests that are not used to predict performance are still helpful in ensuring high quality mixes due to their ability to relatively rank the quality of the mixes. Better methods to evaluate the ability of laboratory tests to predict performance are needed. One way that has been used to evaluate new tests and materials is through the use of accelerated loading facilities. There are many types of facilities available including the ALF (Accelerated Conceptual Performance Criteria for Asphalt Mixtures T. K. Pellinen1 Abstract The empirical nature of performing mix designs has led to significant differences in the volumetric composition for an acceptable asphalt mix. A key to successful mix design is the balance between the volumetric composition and the raw materials used (binder, aggregate, filler, and additives) at specific climatic and traffic conditions. Thus, a balanced design can be achieved only when the climatic considerations are taken into account while selecting the volumetric criteria. A delicate balance between mixture stiffness and shear strength appears to provide the key to a successful design. Based on these findings, fundamentally-based conceptual performance criteria are presented; the criteria rely on stiffness and shear strength to explain the mechanical behavior of asphalt mixtures. _________________________________________________________ Assistant Professor, School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907-2051 1 Buttlar et al. Hollow Cylinder Volume Strain Simplifying the Hollow Cylinder Tensile Test Procedure through Volume-Based Strain William G. Buttlar1, Michael P. Wagoner2, Zhanping You3, and Shawn T. Brovold4 Abstract A hollow cylinder tensile tester (HCT) has been developed, which can be used to obtain fundamental properties of asphaltic paving mixtures, such as creep compliance, tensile strength, and dynamic modulus, at low and intermediate temperatures. By applying pressure to the inner cylinder wall of the specimen, a tensile or ‘hoop’ response is induced. In previous studies, strain gages were used to obtain tensile strain along in the inner circumference. While satisfactory results can be obtained, the application of strain gages is difficult, time-consuming and costly. Fortunately, one of the inherent benefits of the HCT is that, in theory, the cavity volume change can be estimated from the movement of the piston used to pressurize the fluid in the cavity. The volume-based strain measurement system simplifies specimen preparation by eliminating the need for mounted sensors, resulting in a more practical test method. This paper describes the development of such a system, including the sealing system used to retain the cavity pressurizing membrane and the analysis procedure to remove bulk fluid compression and other sources contributing to system compressibility from the computation. The volume-based strain measurement system was evaluated by comparing volume-based strain measurements to strain gage results for reference specimens of Delrin plastic, followed by tests on asphalt binders and mixtures. Although not a primary objective of this study, excellent agreement was obtained between creep compliances measured with the hollow cylinder tensile tester and bending beam rheometer. Once sources of trapped fluid between the pressurizing membrane and asphalt concrete specimens were eliminated, good agreement was found when comparing strain gage results to volume-based strains obtained from the same hollow cylinder specimen. Also discussed in this paper is a recent analysis performed to better understand effects of material heterogeneity on the accuracy and repeatability of bench-scale tests, such as the HCT. A series of two-dimensional discrete element models were developed based upon actual asphalt concrete microstructures, which were used to simulate the complex modulus test. The analysis gave considerable insight towards the effects of nonuniform aggregate and air void dispersion on modulus prediction for specimens of varying wall thickness. The results of this analysis, combined with ongoing work in fracture simulations and validation through laboratory testing, will be used to optimize HCT specimen dimensions in the future, particularly wall thickness. 1 Associate Professor, University of Illinois at Urbana-Champaign; 2,3Graduate Research Assistants, University of Illinois at Urbana-Champaign, Department of Civil and Environmental Engineering; 4Graduate Research Assistant, University of Minnesota, Department of Mechanical Engineering 1 1 Evaluation of the Low Temperature Fracture Resistance of Asphalt Mixtures Using the Semi Circular Bend Test Xue Li1 and Mihai Marasteanu2 Abstract Low temperature cracking is the main distress in asphalt pavements built in the northern US and Canada. Currently, there is no standard method to characterize the resistance to cracking of asphalt mixtures. This paper investigates the use of a Semi Circular Bend test as a candidate for a low-temperature cracking specification. A specimen preparation procedure, a test protocol, and methods to calculate the fracture toughness and the fracture energy are proposed. Three similar Superpave mixtures with different asphalt binders (PG 58-40, PG58-34, and PG58-28) used in the MnRoad pavement facility were tested at -30C and –40C and fracture properties were obtained. A split-plot analysis was performed on the experimental data to determine if these mixtures were statistically different; based on the fracture energy, the binder type effect was significant. Preliminary results showed that advanced acoustic emission (AE) techniques could be used to study the low temperature cracking mechanism in asphalt mixtures. Key Words: asphalt mixtures, fracture toughness, fracture energy, acoustic emission, low temperature cracking, fictitious crack model Introduction Low temperature cracking represents the most significant distress in asphalt pavements built in the northern US and Canada. 1 2 Graduate Research Assistant, University of Minnesota Assistant Professor, University of Minnesota 1 THE VIRGINIA SMART ROAD: THE IMPACT OF PAVEMENT INSTRUMENTATION ON UNDERSTANDING PAVEMENT PERFORMANCE Imad L. Al-Qadia, Amara Loulizib, Mostafa Elseific, and Samer Lahouard Abstract This paper presents the description, calibration procedures, installation, and performance of the instrumentation used at the Virginia Smart Road to measure flexible pavement response to loading. Also presented are the measured horizontal transverse and longitudinal strains induced in the hot-mix asphalt (HMA) during compaction with a steel drum compactor both with and without vibrations. In addition, this paper presents the data collected and used to determine the vertical compressive stress pulse induced by a moving truck at different locations beneath the pavement surface. These data were also used to determine the effects of temperature, speed, and tire inflation pressure on the measured vertical compressive stress and measured horizontal transverse strain, induced by a steering-axle tire of 25.8kN, under the HMA layer. The data were used make a comparison between measured pavement responses to truck loading with those calculated using linear elastic theory. It was found that HMA is subjected to very high horizontal strains during compaction— especially when vibration is used. It was also found that a haversine equation well represents the measured normalized vertical compressive stress pulse for a moving vehicle. Haversine duration times varied from 0.02s for a vehicle speed of 70km/h at a depth of 40mm to 1.0s for a vehicle speed of 10km/h at a depth of 597mm. As expected, temperature was found to significantly affect the measured vertical compressive stress and measured horizontal transverse strain under the HMA layer. Although speed a The Charles E. Via, Jr. Professor of Civil and Environmental Engineering, Virginia Tech b Research Scientist, Virginia Tech Transportation Institute c Senior Research Associate, Virginia Tech Transportation Institute d Senior Research Associate, Virginia Tech Transportation Institute 0 CHARACTERIZATION OF AGGREGATES AND ASPHALT CONCRETE USING X-RAY COMPUTERIZED TOMOGRAPHY A STATE-OF-THE-ART REPORT Linbing Wang Ph.D., P.E., JFAP Assistant Professor Louisiana State University/Southern University Baton Rouge, LA 70803 (Contact Author) Harold Skip Paul, P.E., Associate Director Louisiana Transportation Research Center Baton Rouge, LA 70808 Thomas Harman, P.E. FHWA Asphalt Team Leader, FHWA Office of Infrastructure Research and Development, McLean, VA 22101 John D’Angelo, P.E., Asphalt Materials Engineer FHWA Office of Pavement Technology, Washington, DC 20590 2004 AAPT Baton Rouge, Louisiana 1 Characterization of Aggregates and Asphalt Concrete using X-ray Computerized Tomography-A State-of-the-Art Report Linbing Wang1, Harold Skip Paul2, Thomas Harman3 and John D’Angelo4 ABSTRACT X-ray computerized tomography is a viable non-destructive method to material characterization. Its capability of obtaining three-dimensional (3D) material structure enables the characterization of aggregates and asphalt mixture on a new horizon promising applications in characterization, modeling and computational simulation to optimize mix design, predict performance and conduct forensic studies. This paper reviews the fundamentals of X-ray Computerized Tomography (XCT), its capability, and recent development in applying this tool to characterize aggregates and asphalt mixtures. Key Words: X-ray Computerized Tomography, Aggregates, Asphalt Concrete, Internal Structure INTRODUCTION Fundamentals of X-ray Computerized Tomography X-ray was discovered by a Germany physicist Wilhelm Conrad Roentgen in 1895 during his study of electrical discharge. In performing the discharge tests, Roentgen noticed some invisible and unknown rays that could penetrate into metals, cause 1 Ph.D., P.E., JFAP Assistant Professor Louisiana State University/Southern University, Baton Rouge, LA 70803 2 P.E., Associate Director, Louisiana Transportation Research Center, Baton Rouge, LA 70808 3 P.E., FHWA Asphalt Team Leader, FHWA Office of Infrastructure Research and Development, VA 22101. 4 P.E., Asphalt Materials Engineer, FHWA Office of Pavement Technology, DC 20590. Use of GPR for thickness measurement and quality control of flexible pavements Imad L. Al-Qadia and Samer Lahouarb Abstract This paper evaluates the performance of ground penetrating radar (GPR) in estimating the layer thicknesses of flexible pavements. The findings presented are based on field data collected from the Virginia Smart Road’s pavement test facility, from a newly built section of a state highway (Route 288, Virginia), and from a section of an in-service interstate highway (I81). The GPR data collected from the Virginia Smart Road were successfully used to evaluate the physical GPR detection limitations and to evaluate GPR’s accuracy for flexible pavement layer thickness determination. The data analysis was facilitated by a complete knowledge of the different structures and compositions of the various sections of the road, and by copper plates (perfect electromagnetic reflectors) that were embedded at the different layer interfaces during the construction of the pavement. Based on the collected data, it was found that current GPR analysis approach fails to detect layer interfaces in some circumstances because of physical limitations (such as low dielectric constant contrast between the layers combined with relatively high material loss or the presence of thin layers, compared to the GPR resolution, within the surveyed pavement system). However, GPR is a feasible nondestructive tool for estimating the layer thicknesses of HMA layers, provided that the appropriate data analysis technique for the type of surveyed pavement is used. For newly constructed pavements, GPR can be successfully used as a quality control/quality assurance tool using simple data acquisition techniques. However, for in-service a The Charles E. Via, Jr. Professor of Civil and Environmental Engineering, Virginia Tech b Senior Research Associate, Virginia Tech Transportation Institute 1 A REALLY SIMPLE PERFORMANCE TEST Il-Seok Oh, Ph.D.1 Brian J. Coree, Ph.D., P.E.2 Introduction The objective of this study was to develop a rapid performance test for Superpave mixtures. A new test should be practical enough so that it can be routinely used during mix design and during construction to differentiate potentially stable mixtures from potentially unstable HMA mixtures. Accordingly, the major considerations emphasized in the development of performance testing were as follows: a) the cost of test equipment, b) time required to complete a test, c) the feasibility of testing, and d) the quality of test results. In order to meet these, it was felt that the test equipment needed to be already available and familiar to practitioners. This brought the Superpave Gyratory Compactor (SGC) into consideration. The SGC to some extent shears the mixture during compaction and many attempts have been made to utilize the SGC to characterize HMA mixtures. Further, this equipment has now been in use in the paving industry for almost a decade, and contractors are therefore familiar with it. Specific objectives that this study sought to accomplish are as follows: 1. to re-examine the conditions under which the SGC can be used to better represent performance conditions 2. to establish a test protocol for a rapid performance test (RPT) for Superpave mixtures using the SGC 3. to examine the potential of the RPT and analyze the responses of HMA mixtures to the RPT through a pilot test 4. to establish criteria and a practical guide for the RPT by conducting extensive laboratory testing. Literature Review An excellent literature review of the development and use of the Superpave Gyratory Compactor (SGC) can be found in the dissertation of Oh (1). Only selected highlights are addressed herein. During the early 1990s, significant efforts, including the SHRP research, were made to find the most suitable laboratory compaction methods for HMA mixtures. Most of the work performed at that time, was devoted to evaluating several laboratory compaction methods and 1 2 Assistant Professor, SUNY at Alfred State College, Alfred, NY Assistant Professor, Iowa State University, Ames, Iowa Fatigue Evaluation of Asphalt Mixtures Using Dissipated Energy and Viscoelastic Continuum Damage Approaches Jo Sias Daniel1, William Bisirri2, and Y. Richard Kim3 Abstract The fatigue performance of asphalt mixtures has historically been evaluated using phenomenological approaches. As the asphalt industry moves towards more mechanistic and performance-based design methods, researchers have developed more fundamental approaches to evaluate fatigue. This paper presents a comparison of the viscoelastic, continuum damage (VECD) and dissipated energy (DE) approaches using uniaxial direct tension fatigue tests performed on eight WesTrack mixtures. The two approaches are also compared to the traditional phenomenological approach relating the initial strain to the number of cycles to 50 percent reduction in initial stiffness. The number of cycles to failure calculated using the VECD and DE failure criterion are highly correlated and are very similar if a modified DE failure criterion is applied. The VECD approach successfully ranks the fatigue performance of mixtures with various air void and asphalt contents for a particular gradation, but the ranking between two gradations did not agree with the observed field performance. The DE approach shows promise for ranking the field performance of the mixtures; however limited data at different strain amplitudes made it difficult to state any conclusions with confidence. Key Words: Asphalt, Mixtures, Viscoelasticity, Continuum Damage Mechanics, Fatigue Cracking, Dissipated Energy 1 Assistant Professor, University of New Hampshire, Durham, NH Graduate Research Assistant, University of New Hampshire, Durham, NH 3 Professor, North Carolina State University, Raleigh, NC 2 Al-Khateeb and Shenoy 1 A Distinctive Fatigue Failure Criterion Ghazi Al-Khateeb1 and Aroon Shenoy2 Abstract This paper presents a new fatigue failure criterion for asphalt paving mixtures that is simple, unique, and distinctive. Bending beam fatigue testing in the controlled strain mode at a 1000microstrain level and 19C temperature was performed on eleven asphalt mixtures that included unmodified and modified binders. Analysis of fatigue load-deformation raw data for each fatigue load cycle was conducted to determine the true point of fatigue failure. With application of a sinusoidal strain on a sample, a sinusoidal response stress is expected even for a heterogeneous material like asphalt concrete. In such a case, a smooth traditional load-deformation (or stress-strain) hysteresis loop is anticipated. This holds true as long as there is no fatigue damage induced in the material. With repeated load applications, the sample starts to fatigue and microcracks are induced. These microcracks introduce discontinuities in the stress paths and the stress response starts to distort. This gets reflected in the load-deformation hysteresis loop, which in turn shows this distortion. Similar distortion can also be seen by observing the sinusoidal load-deformation waveform, where the stress response is no longer dependent on the strain input due to the formation of interconnected fatigue cracks. By tracking the distortion in the hysteresis loop or in the waveform, one is able to get a clear indication of when the first microcracks appeared, and how they progressed up to the point of complete fatigue failure. Key Words: Fatigue Failure, Failure Criterion, Fatigue Damage, Repeated Loading, Hysteresis Loop, Waveform. 1 Senior Research Engineer, SaLUT Inc., Turner-Fairbank Highway Research Center (TFHRC), McLean, VA 22101, [email protected]. 2 Senior Research Rheologist, SaLUT Inc., TFHRC, McLean, VA 22101, [email protected]. 1 Two-Stage Weibull Approach for Asphalt Concrete Fatigue Performance Prediction Bor-Wen Tsai1, John T. Harvey2, Carl L. Monismith3 Abstract This paper presents the two-stage Weibull approach, a phenomenological approach to characterize the fatigue damage process of asphalt concrete mixes for both the crack initiation and crack propagation phases. For each test, parameter estimation can be performed using the Lagrange-Newton algorithm. This algorithm can clearly identify the number of repetitions at which crack initiation and crack propagation are separated. A set of WesTrack tests was utilized as the demonstration example. The WesTack mixes consisted of three gradations: fine, fine plus, and coarse. For each gradation, 12 beam tests were conducted at three temperatures (10, 20, and 30C) with various strain levels. After collecting all the information for the repetitions at which separation occurs for a series of tests, integrated Weibull-type regression equations can be obtained for crack initiation and crack propagation. To correct the difference between in-situ and laboratory boundary conditions, correction factors for the twostage Weibull approach are also discussed. Finally, with the integrated regression equations and correction factors for crack initiation and crack propagation, the fatigue performance prediction of a WesTrack section was simulated with a “damage 1 Assistant Research Engineer University of California, Berkeley Institute of Transportation Studies, Pavement Research Center 1353 S. 46th St., Bldg. 480 Richmond, CA 94804 2 Associate Professor University of California, Davis 3 Professor Emeritus of Civil Engineering University of California, Berkeley An Investigation of the Applicability of Schapery´s Work Potential Model for Characterization of Asphalt Fatigue Behavior Robert Lundstrom1 and Ulf Isacsson2 Abstract This paper presents an investigation of Schapery´s work potential model applied to asphalt concrete characterization. Six asphalt concrete mixtures, all consisting of one and the same aggregate and particle size distribution, manufactured using unmodified and SBS modified binders were used. An elastic-viscoelastic correspondence principle and the time-temperature superposition principle are utilized to obtain material characteristic functions, C1(S1), using uniaxial monotonic (constant-strain rate) and cyclic (fatigue) tests at 0, 10 and 20C. The results indicate that consistent and reliable results are obtained for the mixtures investigated using monotonic testing, provided that the applied strain rate is not too low at a given temperature. It was also indicated that the time-temperature superposition principle is applicable as a single material function can be obtained at the reference temperature chosen. Results similar to those obtained at monotonic tests were also obtained at cyclic testing. However, based on statistical analysis, it was noticed that cyclically established C1(S1) curves often differ slightly between different temperatures even when shifted to the reference temperature. This result is probably due to the more complicated excitation history applied during fatigue tests. However, even though it is possible to obtain characteristic material functions from both types of tests, it was not possible to show that monotonic and cyclic testing lead to similar results, i.e. more or less identical C1(S1) curves. It was also investigated, using thermocouples, whether, and if so, to what extent hysteretic self-heating influences fatigue test results. In general, a significant influence was indicated at 10 and 20C, and especially for high amplitude tests (low cycle fatigue tests). Even though several questions still are to be answered, the model based on the work potential theory remains interesting, and is possibly, the most versatile damage model for asphalt characterization available today. 1 PhD Student, Division of Highway Engineering, Royal Institute of Technology, S-100 44, Stockholm, Sweden 2 Professor, Division of Highway Engineering, Royal Institute of Technology, S100 44, Stockholm, Sweden 1 A Study of Crack-Tip Deformation and Crack Growth in Asphalt Concrete Using Fracture Mechanics Youngguk Seo1, Y. Richard Kim2, Richard. A. Schapery3, Matthew W. Witczak4, Ramon Bonaquist5 Abstract This paper presents findings from a comprehensive experimental/analytical study of crack growth in asphalt concrete using fracture mechanics. The primary objective of this study is to provide critical information that is complementary to the viscoelastoplastic continuum damage model (1) in modeling crack growth using finite element analysis. To simulate mode I fracture, uniaxial monotonic and cyclic tension tests were conducted on prismatic specimens with symmetric double notches. Digital Image Correlation (DIC), a noncontact, full-field displacement/strain measurement technique, was utilized to investigate the size and shape of the fracture process zone (FPZ). Irrespective of the notch size and testing conditions, the FPZ was observed to be similar in size and shape for the mixture. Also, it was found that the strain at the crack tip immediately before crack initiation is a decreasing function of strain rate. The experimental data were analyzed using several fracture mechanics theories, including the cohesive crack model and crack growth rate laws based on the stress intensity factor, KI. The cohesive crack model analysis provides the fracture energy and softening function that describe the post-peak behavior with strain localization. The analysis based on KI shows that the specimen size has no significant effect on the crack growth rate laws. The effect of temperature is pronounced in the crack growth rate law using temperature-reduced crack speed based on KI. The timetemperature superposition principle, with the shift factor from the linear viscoelastic range, was applied to these crack growth rate laws and successfully collapsed the curves at different temperatures into a single relationship. 1 Graduate Research Associate, North Carolina State University Professor, North Carolina State University 3 Professor, University of Texas at Austin 4 Professor, Arizona State University 5 Advanced Asphalt Technologies 2