49th Petersen Asphalt Research Conference 

Rendezvous in Laramie July 9-11, 2012

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49th PETERSEN

ASPHALT RESEARCH CONFERENCE

Organized by

WESTERN RESEARCH INSTITUTE

in cooperation with the

FEDERAL HIGHWAY ADMINISTRATION

Hilton Garden Inn and University of Wyoming Conference Center

Laramie, Wyoming, July 9-11

7:30 AM Registration—Pick up conference materials Hilton Garden Inn and UW Conference Center

8:00-8:20 Welcome, Jean-Pascal Planche and Don Collins Opening Remarks, Stephen Salmans SESSION 1—Session Chair, Eric Kalberer NuVention Solutions, Inc. 8:20-8:55 Development of Biopolymers from Soybean Oil Eric Cochran, Nacu Hernandez Cantu, Andrew Cascione, and R. Christopher Williams Iowa State University 8:55-9:30 Asphalt Binder Modification with Re-Refined John D’Angelo Engine Oil Residue (REOR) D’Angelo Consulting, LLC, Ken Grzbowski PRI Asphalt, and Steve Lewis Safety-Kleen Systems

Monday, July 9

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9:30-10:05 How to Design a Different Pavement Robert Kluttz Kraton Polymers, Y. Richard Kim NCSU, Raj Dongre DLSI, Harold von Quintus Applied Research Associates, Inc., Nam Tran NCAT and Nelson Gibson FHWA 10:05-10:25 Break 10:25-11:00 Geometry Effects and Binder Grade Influence on Adrian Andriescu SES Group & CTOD Parameter from DENT Test for Fatigue Grading Associates, LLC; and Nelson of Asphalt Binders Gibson and Jack Youtcheff Turner Fairbank Highway Research Center, FHWA 11:00-11:35 Modeling Asphalt Concrete in Compression Yuqing Zhang Texas A&M University, Rong Luo Texas Transportation Institute, and Robert L. Lytton Texas A&M University 11:35-12:10 Improved Asphalt Absorption Measurements Guanlan Liu, Xin Jin Using Density Gradient Columns and Charles J. Glover Texas A&M University 12:10-1:10 pm Lunch—Speakers: Chavawn Kelley, WRI, and Scott Walker, Fort Laramie National Historic Site, “Alfred Jacob Miller, Artist of the 1837 Rendezvous” SESSION 2—Session Chair, Geoff Rowe Abatech 1:10-1:45 Understanding the Physico-Chemical Interaction in Cristian S. Clopotel, Asphalt-Filler Mastics Raul A. Velasquez and Hussain U. Bahia University of Wisconsin-Madison 1:45-2:20 Interpretation of Complex Infrared Spectra Ron Glaser, Fred Turner and Jean-Pascal Planche Western Research Institute 2:20-2:55 Nanoscale Thermo-mechanical Analysis and IR Kevin Kjoller, Michael Lo, Spectroscopy: Applications in Polymer and Asphalt Craig Prater and Roshan Shetty Characterization Anasys; Alexandre Dazzi University of Paris; and Curtis Marcott Light Light Solutions 2:55-3:15 Break

Monday, July 9, continued

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PARALLEL SESSION 2A —Session Chair, Geoff Rowe Abatech 3:15-3:50 ‘Stickiness’ Measurement of Asphalt Binder Using Xiaokong Yu, Nancy A. Atomic Force Microscopy Burnham, Rajib B. Mallick and Mingjiang Tao Worcester Polytechnic Institute 3:50-4:10 Development of an AFM-Based Fracture Energy Test R. Will Grimes and A.T. Pauli Western Research Institute; and Mengxi Wang and Peng Lu University of Wyoming/Western Research Institute 4:10-4:35 Asphalt Fracture Energy as Measured Using a New Mengxi Wang University of AFM Technique Wyoming/Western Research Institute; R. Will Grimes and A.T. Pauli Western Research Institute; and Peng Lu University of Wyoming/Western Research Institute 4:35-5:00 Utilization of Viscoelastic Contact Mechanics Peng Lu and Mengxi Wang Models to Describe Fatigue and Self-Healing in University of Wyoming/Western Asphalt Pavements Research Institute and R. Will Grimes and A.T. Pauli Western Research Institute PARALLEL SESSION 2B—Session Chair, Fred Turner Western Research Institute

Location: Ballroom C 3:15-3:50 Towards Performance-related Specification for Frank Farshidi R-HMA Binders University of California, Davis 3:50-4:25 Application of Chemical Testing Techniques to the Benjamin F. Bowers, Study of Recycled Asphalt Pavement Blending Baoshan Huang and Xiang Shu Efficiency University of Tennessee- Knoxville 4:25-5:00 Estimating Diffusion Rates and Ultimate Blending Daniel Swiertz, Farhad Yousefi between Reclaimed and Fresh Asphalt Binders and Hussain Bahia University of Wisconsin-Madison MONDAY EVENING—Dinner on your own.

Monday, July 9, continued

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SESSION 3—Session Chair, Ron Glaser Western Research Institute 8:00-8:35 am Refinement and Evaluation of the Cup and Bob John D’Angelo D’Angelo Geometry for Testing of Crumb Rubber Modified Consulting, LLC, Gaylon (CRM) Binder over the Full Range of PG Test Baumgardner Paragon Technical Temperatures Services, and Mike Farrar WRI 8:35-9:10 Field QC/QA Test for Asphalt Binder Raj Dongre DLSI; Jack Youtcheff and Nelson Gibson FHWA; and John W. Newman LTI 9:10-9:45 Effect of Foaming on Poly-phosphoric Acid (PPA) Olga V Shulga, Rene Maldonado Modified Binders and Henry Romagosa ICL Performance Products; and Cristian Clopotel, Raquel Moraes and Hussain Bahia Modified Asphalt Research Center- University of Wisconsin 9:45-10:05 Break 10:05-10:40 A Simple Test to Determine Workability of Warm Raj Dongre and Eugeniu Morari Mix Asphalt (WMA) DLSI 10:40-11:15 Neutron Scattering for Moisture Detection in Foamed Yang Zhang Oak Ridge National Warm Mix Asphalt Laboratory; and Baoshan Huang, Philip Ye, and Xiang Shu University of Tennessee 11:15-11:50 Lubricity Properties of Asphalt Binders Used in Hot-Mix Gaylon L. Baumgardner and Warm-Mix Asphalt Pavements Paragon Technical Services, Inc., and Gerald R. Reinke Mathy Technology and Engineering, Inc.

11:50-1:00 Lunch—Speaker: David French, ENS Resources

“Federal Outlook − The Good, the Bad and the Ugly”

Tuesday, July 10

David R. French is Senior Vice President for ENS Resources Inc. based in Washington, D.C. He joined the firm in 2000 and works closely with clients to develop and implement strategies for legislative and regulatory programs and policy initiatives related to transportation, economic development, infrastructure, homeland security, criminal justice, rural governance, land use, and water resources. Clients include cities and counties, research entities, and regional and national organizations.

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SESSION 4—Session Chair, Henry Romagosa ICL Performance Products LP 1:00-1:35 Effect of Cooling Medium on Asphalt Binder Augusto Cannone Falchetto, Strength at Low Temperature Mugurel I. Turos and Mihai O. Marasteanu University of Minnesota 1:35-2:10 Construction of Master Curves for Asphalt Binders David A. Anderson Consultant and Prof. Emeritus, The Penn State University; and Geoff Rowe Abatech, Inc. 2:10-2:45 Evaluation of the LAS Test Raj Dongre DLSI; Adrian Andriescu SES Group & Assoc., LLC; and Nelson Gibson and Jack Youtcheff FHWA 2:45-3:05 Break 3:05-3:40 The Effect of Thermal Equilibrium on the Accuracy of David A. Anderson DSR Measurements Consultant and Prof. Emeritus, The Penn State University 3:40-4:15 Defining Good Measuring Practice in Asphalt Joerg Laeuger Rheology Testing Anton Paar Germany and Darin Hunter Anton Paar USA

Tuesday, July 10, continued

Tuesday Evening

WESTERN THEME DINNER

at the Wildcatter Stadium Club

5:30 Social Hour (Cash Bar)

6:30 Dinner

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SESSION 5—Session Chair, Jeramie Adams Western Research Institute 8:00-8:35 Evaluation of the Effect of Polymer Modification on Iliya Yut and Adam Zofka Aging Properties of SHRP Core Asphalts University of Connecticut 8:35-9:10 Effect of Oxidative Aging on the Relaxation Spectrum Mohammad Zia Alavi, of Asphalt Mixtures Obtained from Dynamic Modulus Nathaniel E. Morian, and Test Data Elie Y. Hajj University of Nevada, Reno 9:10-9:45 Binder Oxidative Aging Chemical Changes John F. Schabron Western Research Institute 9:45-10:05 Break 10:05-10:40 An Oxidative Aging Study on Seal Coat Treated Yuanchen Cui and Pavement Charles J. Glover Texas A&M University 10:40-11:15 The Influence of Sunlight on the Aging of Hilde Soenen, Serge Heyrman, Bituminous Binders Xiaohu Lu and Per Redelius Nynas 11:15-11:50 Significance of Mixture Parameters on Binder Nathan Morian University of Aging in HMA Mixtures Nevada-Reno/Nevada DOT; and Elie Y. Hajj and Peter E. Sebaaly University of Nevada-Reno 11:50 Closing Remarks

Wednesday, July 11

Acknowledgement

Western Research Institute expresses appreciation to the

Federal Highway Administration for its long-term support of much of the research

reported at the Petersen Asphalt Research Conference.

ABSTRACTS

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Monday, July 9

Session 1

Development of Biopolymers from Soybean Oil

Eric Cochran, Nacu Hernandez Cantu, Andrew Cascione, and R. Christopher Williams Iowa State University Asphalt cement is commonly modified with an SBS tri-block copolymer to improve its performance grade and enhance the performance of asphalt paving mixtures. Currently, the butadiene monomeric species in SBS poly-mers is derived from petrochemical feedstocks which are rapidly increasing in price to due global market shifts in supply and demand. At the same time, there is growing interest in sustainable biopolymers synthesized from plant based feedstocks to replace the need for their petrochemical counterparts. Recent advances in polymerization tech-nology have led to the development of thermoplastic styrenic block copolymers produced with polystyrene and polymerized soy-derived triglycerides. These new breeds of coblock biopolymers have elastomeric properties at room temperature and can be processed as a liquid at high temperatures. Preliminarily data indicates they can be formulated as an asphalt modifier with property enhancements comparable to established SBS polymers. The ini-tial research was conducted on 52-34 virgin bitumen modified with the biopolymer at several percentages and compared to the bitumen modified with two commonly available SBS polymers. The modified bitumen was tested in accordance with AASHTO M320. The results show that the developed biopolymers have comparable rheologi-cal effects on the asphalt as the commercially available SBS polymers. Asphalt Binder Modification with Re-Refined Engine Oil Residue (REOR)

John D’Angelo (1), Ken Grzbowski (2), and Steve Lewis (3) (1) D’Angelo Consulting, LLC; (2) PRI Asphalt; (3) Safety-Kleen Systems Asphalt binders used in the paving industry are required to perform under extreme conditions. At high tempera-tures when the binder is softer it must withstand heavy traffic loading to prevent rutting. At low temperatures it must remain flexible to resist cracking from traffic and thermal stresses. Additives have been used to improve the performance of asphalt binders and extend the temperature range where they can be used. These additives include many different organic polymers and chemicals to change the morphology or chemistry of the binders. One of these additives is the residue from the re-refining of used engine oil.

In this study an in-depth evaluation was performed to determine the performance characteristics of asphalt binders modified with re-refined engine oil residue, at several different levels. Chemical analysis of the REOR and the asphalt binders was performed to determine what changes are taking placed in the modified asphalt binder. Extensive rheological testing was also run on the binders to evaluate the physical properties of the binders under several different aging conditions. The study provides a full evaluation of the real nature of the effects of REOR modification of asphalt binders and its performance implications.

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How to Design a Different Pavement

Robert Kluttz (1), Y. Richard Kim (2), Raj Dongre (3), Harold von Quintus (4), Nam Tran (5), and Nelson Gibson (6) (1) Kraton Polymers; (2) North Carolina State University; (3) Dongre Laboratory Services, Inc.; (4) Applied Re-search Associates, Inc.; (5) National Center for Asphalt Technology; (6) Federal Highway Administration Developing new and improved materials for asphalt paving technology is an exciting and fruitful pursuit. However, a new material may well behave quite differently than conventional hot mix asphalt, especially with respect to stan-dard pavement design methodologies. Some states have developed design protocols that take advantage of concepts such as endurance limit but for the design of flexible pavements many use the AASHTO Design Guide which uses structural coefficients or the Mechanistic-Empirical Pavement Design Guide which relies on the national calibration factors.

With new materials, existing standard layer coefficients or, for the MEPDG, national calibration factors, may not give accurate representations of material properties for predicting performance. With this in mind, we have investi-gated alternate, practical material property models as tools for determining appropriate revised calibration factors for use with MEPDG modeling. In this report we will discuss and give examples of the application of these models in practical pavement design using highly modified binders, both as a tool for design of new structures and to model the performance of existing pavements for validation. Geometry Effects and Binder Grade Influence on CTOD Parameter from DENT Test for Fatigue Grading of Asphalt Binders

Adrian Andriescu (1); and Nelson Gibson and Jack Youtcheff (2) (1) SES Group & Associates, LLC; (2) Turner Fairbank Highway Research Center, FHWA Most recent developments in asphalt producing technologies along with the increased variability of crude sources require a better understanding of the relation between the field performance and material properties. The Essential Work of Fracture (EWF) Method uses Double Edge Notched Tension (DENT) specimens with various ligament lengths that are tested at a continuous monotonic speed and ambient temperature until failure.

An approximated Critical Tip Opening Displacement (CTOD) calculated from intermediate temperature Double Edge Notched Tension (DENT) test has been shown to adequately discriminate fatigue cracking performance of mixtures. The approach measured on Pressure Aging Vessel (PAV) aged material quantifies the ductile strain toler-ance response in the presence of stress concentrations. The CTOD parameter has been investigated for a wide range of asphalts from different sources, modifications and Performance Grades with a select group evaluated with differ-ent sample geometries. Temperature and rate dependency of the parameter will be reviewed. This research is part of DENT method development to optimal testing conditions and establishes CTOD criteria which may be more prop-erly grade dependent.

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Modeling Asphalt Concrete in Compression

Yuqing Zhang (1), Rong Luo (2) and Robert L. Lytton (1) (1) Texas A&M University; (2) Texas Transportation Institute The mechanisms of rutting has not been well addressed due to the complexities of asphalt concrete (AC) includ-ing: 1) distinctions between compression, extension and tension; 2) rate and temperature dependence; 3) dilative volumetric change; 4) frictional material with cohesion; 5) inherent anisotropy due to preferential aggregates’ ori-entation; 6) stress-induced anisotropy due to crack growth; 7) strain hardening during viscoplastic accumulation; and 8) strain softening during viscofractural evolution.

All of the aforementioned fundamentals of AC were simultaneously characterized by a comprehensive vis-coplastic-fractural mechanistic model, which incorporated with a modified effective stress to consider the inherent and stress-induced anisotropy, a smooth, convex, hydrostatic pressure and intermediate principal stress dependent yield surface, a non-associated flow rule, and a rate and temperature dependent strain hardening rule. The vis-cofractural evolution was modeled by an anisotropic damage density based pseudo J-integral Paris’ law which demonstrated that AC in compression exhibited brittle-like fracture at low air voids (4%) and ductile-like fracture at high air voids (7%). The model parameters were related to fundamental material properties which could be de-termined accurately with simple tests in one day. Testing indicates that the mechanistic model can accurately pre-dict AC behaviors in compression at varieties of loading and environmental conditions. Improved Asphalt Absorption Measurements Using Density Gradient Columns

Guanlan Liu, Xin Jin and Charles J. Glover Artie McFerrin Department of Chemical Engineering, Texas A&M University Asphalt absorption represents an economic loss of effective binder, and may change binder properties. In pave-ment design, determination of asphalt absorption by standard methods is used to estimate air voids. However, a more precise method is necessary to provide an improved fundamental understanding of asphalt binder absorption.

Density gradient columns (DGC), fluid columns of linear density gradient, allow measurements of bulk den-sity, apparent density, void volume, water absorption and asphalt absorption for single aggregate pieces. The DGC method allows accurate measurements, superior to those of standard methods, of absorption as a function of aggre-gate characteristics such as mass of aggregate or void volume or aggregate type, thereby providing an improved fundamental understanding of asphalt absorption.

In this research, asphalt absorption at various conditions was measured. Experimental data show that even though aggregates may possess totally different bulk and apparent densities and void volume fractions from piece to piece, the asphalt binder absorption correlates very well with the void volume and not well at all with aggregate mass. This result indicates that void volume is an essential factor determining binder absorption.

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Session 2

Understanding the Physico-Chemical Interaction in Asphalt-Filler Mastics

Cristian S. Clopotel, Raul A. Velasquez, and Hussain U. Bahia University of Wisconsin-Madison The current design standards for asphalt mixtures provide detailed guidance on selection of aggregates and binder. However, it includes only a simple requirement for the mineral filler in the mix. This requirement limits the filler/binder ratio by mass to the range of 0.6 -1.2. This range is based on experience rather than on scientific evaluation of the interaction between filler and binder. In this study the effect of interactions between selected fillers and binders were estimated based on changes in the glass transition temperature. Experimental results indicate that there is sig-nificant interaction at the surface of fillers and that asphaltenes (i.e., polar groups) can be adsorbed on the mineral surface. This measurable adsorption is assumed responsible for changes in the properties of the mastic.

Experimental measurements indicate that asphaltenes are adsorbed on the filler surface as a monolayer, and that the amount is independent on the concentration but rather dependent on the Braunauer-Emmett-Teller (BET) surface area of the filler. The higher the BET surface area, the greater the amount of asphaltenes adsorbed and the lower the glass transition temperature. Preliminary results raise important questions about whether surface chemistry or surface area is the driving factor for interaction and adsorption. Interpretation of Complex Infrared Spectra

Ron Glaser, Fred Turner and Jean-Pascal Planche Western Research Institute Infrared spectra analysis is a popular tool for examining the complex chemistry of asphalt binder materials because of its ability to identify changes in functional group content. This ability provides a great simplification in a material with thousands of molecular species present. Unfortunately, an examination of literature reveals that there are many ways that the original spectral data are manipulated to obtain some sort of “absorbance” or even “molar concentra-tion” value. Some of these methods are examined in detail and a case is made for using total peak height as a correla-tion metric based upon the authors’ experience with correlations and in-depth peak separation studies. The unfortu-nate truth is that even mathematical separation of the peaks does not yield perfect results, but this study does suggest that some approximation methods are better than others. In addition to the interpretation of classical transmission infrared spectra, attenuated total reflectance (ATR) spectrometry is also employed in asphalt studies because of its ease of use. However, ATR generally has much lower signal-to-noise ratios, and does not conform to Beer’s law. Adjustments must be made to account for penetration depth variations, and rigorous corrections are rarely made since a detailed understanding of the material index of refraction at each wave number is required. The presentation is not a final answer to these problems, rather an effort to begin a discussion in the asphalt research community to-ward a rational, standard technique for measurement and analysis.

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Nanoscale Thermo-mechanical Analysis and IR Spectroscopy: Applications in Polymer and Asphalt Characterization

Kevin Kjoller, Michael Lo, Craig Prater and Roshan Shetty (1); Alexandre Dazzi (2); and Curtis Marcott (3) (1) Anasys; (2) University of Paris; (3) Light Light Solutions Recently two analytical techniques have been developed which combine Atomic Force Microscopy (AFM) with thermal analysis and IR spectroscopy. The AFM creates a topography image of the sample such that locations can be selected for analysis. In nanoscale thermal analysis a microfabricated AFM probe which can locally heat a sam-ple is used to determine the transition temperature of a sample by sensing when the material softens. In nanoscale IR spectroscopy (AFM-IR), the AFM probe monitors the local rapid expansion of material due to absorption of IR illumination from a pulsed tunable IR source. AFM-IR can be used both to obtain absorption spectra at arbitrary points and to spatially map IR absorption at selected wavelengths. Simultaneous measurement of the AFM cantile-ver’s contact resonance frequency as excited by the IR absorption provides a complementary measurement of sam-ple stiffness. The AFM-IR technique has been used to chemically identify individual chemical components in poly-mer blends and nanocomposites with spatial resolution as high as 100 nm. The thermal analysis technique measures surface properties and as such has been useful in monitoring aging and chemical degradation. This presentation will describe the techniques and present data showing the utility of the techniques in analyzing polymer and asphalt samples. Parallel Session 2A

‘Stickiness’ Measurement of Asphalt Binder Using Atomic Force Microscopy

Xiaokong Yu, Nancy A. Burnham, Rajib B. Mallick and Mingjiang Tao Worcester Polytechnic Institute There have been observations that the “stickiness” of asphalt binder has diminished, which might have led to the loss of the aggregate in asphalt pavement. In this project, the stickiness of one old binder and three new binders used in Maine is characterized by adhesion measurement using Atomic Force Microscopy (AFM). The thin film samples of the different binders were prepared by solution cast approach and the surface roughnesses are found to be less than 2nm. Preliminary experiments show that adhesion force between the AFM tip and binder film is af-fected by many AFM operation parameters, such as the maximum applied load, approach and retraction velocities, and the size and shape of the AFM tips. The adhesion force increases as the maximum load increases; it increases as the retraction velocity increases whereas decreases as the approach velocity increases. Parameter-independent adhe-sion force can be acquired by carefully controlling the operation factors to prevent the occurrence of plastic defor-mation of the binder film at the force-curve acquisition points. Statistical adhesion measurements are being per-formed in order to compare the stickiness of the four different binders, which would help identify the cause of the aggregate loss distress and build more sustainable asphalt pavement.

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Development of an AFM-Based Fracture Energy Test

R. Will Grimes and A.T. Pauli (1); and Mengxi Wang and Peng Lu (2) (1) Western Research Institute; (2) University of Wyoming Graduate Research Assistant/Western Research Institute The lack of a convenient method to quantify fracture energy severely restricts efforts to model and predict pave-ment performance in terms of fracture propensity. It is well known that the rheological properties of asphalt change as the material ages, and available tools allow us to quantify these changes in meaningful terms (i.e. storage and loss moduli). It is also known anecdotally that asphalt cements also tend to become brittle and more susceptible to cracking as they age. However, the relationship between oxidative aging and cracking susceptibility is poorly de-fined, at least partially due to the lack of a convenient method to quantitatively measure and assess changes in frac-ture susceptibility. We report the development of an AFM-based direct tension fracture test that allows for the con-venient determination of fracture energy (i.e. strain energy release rate) in terms of reversible and dissipative com-ponents. Like rheological properties, fracture energy is a function of both temperature and fracture rate, and, as such, cannot be adequately characterized as a single value. We show how fracture energy can be plotted against the stress rate to generate figures resembling rheological master curves, and how we can separate the reversible and dissipative components of the total energy. Asphalt Fracture Energy as Measured Using a New AFM Technique

Mengxi Wang (1); R. Will Grimes and A.T. Pauli (2); and Peng Lu (1) (1) University of Wyoming Graduate Research Assistant/Western Research Institute; (2) Western Research Institute We report the results when a new AFM direct tension fracture test is used to measure the energy (in terms of strain energy release rate) associated with the fracture of an asphalt adhesive joint. Tests were conducted using three SHRP core asphalts. Asphalt adhesive joints were prepared in a standardized manner and then fractured using in-creasing separation rates. From force versus time plots recorded during fracture the total fracture energy as well as the thermodynamic and reversible components can be derived. We show fracture energy as a function of separation rate and temperature for three SHRP core asphalts representative of different crude sources. Utilization of Viscoelastic Contact Mechanics Models to Describe Fatigue and Self-Healing in Asphalt Pavements

Peng Lu and Mengxi Wang (1); and R. Will Grimes and A.T. Pauli (2) (1) University of Wyoming Graduate Research Assistant/Western Research Institute; (2) Western Research Institute

Contact mechanics is the field of study which describes the deformation of solids that touch each other at one or more points (Johnson, K. L, 1985, Contact mechanics, Cambridge University Press). Both static and dynamic con-tact mechanics theories have been extensively investigated. Historical theories were primarily concerned with elas-tic solid bodies in contact, but recent models advance these theories to include viscoelastic and viscoplastic behav-ior in semi-solids and adhesive films. Some of these newer theories will be discussed in regard to how they may be utilized at different length scales to study asphalt fatigue and self-healing in asphalt mastics and extended to asphalt pavements. Preliminary data discussing nano-contact mechanics measurements employing atomic force microscopy will be presented, which will be related back to fatigue and self-healing behavior in asphaltic material adhesive properties.

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Parallel Session 2B

Towards Performance-related Specification for R-HMA Binders

Frank Farshidi University of California, Davis

An experiment involving three different asphalt binder sources and their mixtures with crumb rubber modifier using the wet process was conducted to investigate the feasibility of understanding and characterizing rubberized binders with the Dynamic Shear Rheometer (DSR) in lieu of empirical tests currently specified by California Department of Transportation. This preliminary study was conducted as the first step towards developing a performance-related specification for rubberized binders using DSR with the new cup and bob geometry.

DSR using a cup and bob geometry was used to handle the large particle sizes in this study (-14 mesh). Rheological properties of the samples were measured at both high and intermediate temperatures. The multiple stress creep recovery (MSCR) test was conducted to study the creep and recovery behavior of the rubberized bind-ers at high temperatures in terms of rutting resistance. Frequency sweep test was also used in this research to inves-tigate time-dependent deformation behavior at both high and intermediate temperatures on all samples using the DSR with cup and bob geometry.

The preliminary results indicated that characterizing rheological properties of the rubberized binder with the new geometry is feasible. The results showed that the MSCR test results can describe and characterize the rheologi-cal behavior and the effect of crumb rubber modifier in terms of rutting resistance of the rubberized binders. Application of Chemical Testing Techniques to the Study of Recycled Asphalt Pavement Blending Efficiency

Benjamin F. Bowers (1), Baoshan Huang (2), and Xiang Shu (3) Department of Civil and Environmental Engineering, University of Tennessee-Knoxville (1) Graduate Student; (2) Associate Professor; (3) Research Assistant Professor Gel Permeation Chromatography (GPC) is a chemical testing technique that is used to identify the molecular weight distribution within a medium. Another chemical testing technique, Fourier Transform Infrared Spectroscopy (FTIR), identifies the chemical functional groups within a medium. These two testing methods have been used ex-tensively to study different phenomena within the chemistry of asphalt. Many GPC and FTIR researches have fo-cused on aging characteristics of asphalt binders and are useful tools in studying oxidation, a major mechanism of asphalt binder aging. In this study, staged extraction is performed on a RAP/virgin pavement blend on the premise that individual layers of asphalt binder can be removed from the mixture until all that remains is the aggregate. Each binder layer is then tested and compared quantitatively using GPC and FTIR to identify the extent to which RAP and virgin binder blend. Many studies have been conducted with regard to the effect of RAP inclusion in the pave-ment structure and its mechanical performance, yet the blending efficiency of the RAP and virgin binder is still un-known. It is often assumed that a complete blend between the RAP binder and virgin binder does occur, however, if there is not a complete blend concerns arise that the long-term pavement life could be compromised. Results of this study have shown that a certain degree of blending does occur throughout all layers of the mixture.

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Estimating Diffusion Rates and Ultimate Blending between Reclaimed and Fresh Asphalt Binders

Daniel Swiertz (1), Farhad Yousefi (2), and Hussain Bahia (3) University of Wisconsin – Madison, Modified Asphalt Research Center (1) Research Engineer; (2) Graduate Research Assistant; (3) Professor A fundamental concern in designing asphalt mixtures with a high percentage of reclaimed asphalt pavement (RAP) is estimating the extent to which the virgin and recycled binders blend within the mixture. Complete or near com-plete blending is often assumed in order to exploit the full cost savings potential of using RAP. Inadequate perform-ance of some high-RAP mixes has prompted several recent studies to call into question the degree of blending that truly occurs in RAP mixes. It is expected that the degree of bending between the RAP and virgin binder is dependent on temperature, time, and binder chemistry.

This work investigates a simple means to estimate the time–temperature dependency of virgin and RAP binder blending through diffusion. Virgin and ‘artificial RAP binder’ samples conditioned at predetermined temperatures and time intervals are tested to predict the rate of diffusion between the binder samples. The binder blending esti-mates can be subsequently verified with finite element diffusion simulations. Binders with considerable differences in chemistry were tested to demonstrate the effect of binder compatibility on blending. Several field RAP materials from Wisconsin were tested to demonstrate the effect of in-service binder aging on blending capacity. Results indi-cate that diffusion can be detected and thus near full blending is plausible if and when temperature and time condi-tions are favorable.

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Tuesday, July 10

Session 3

Refinement and Evaluation of the Cup and Bob Geometry for Testing of Crumb Rubber Modified (CRM) Binder over the Full Range of PG Test Temperatures

John D’Angelo (1), Gaylon Baumgardner (2), and Mike Farrar (3) (1) D’Angelo Consulting, LLC; (2) Paragon Technical Services; (3) Western Research Institute A cup and bob Searle system is currently being evaluated to allow Superpave PG testing of Crumb Rubber Modified asphalt binder with rubber sizes greater than 600µm.. Previous evaluations have verified that the new geometry can be used for high temperature testing of neat binders, polymer modified binders and specifically CRM binders with rubber particles up to 1mm in size. The new geometry has significantly more surface area than the current parallel plate geometry and therefore requires significantly more torque for the dynamic shear rheometer (DSR) to make reading on binder. At typical binder high temperature testing the torque requirements are still within a typical DSR’s compliance calibration of the equipment and provide accurate results. However, at the typical intermediate tempera-tures for PG testing the increased torque required to operate the cup and bob system is outside the compliance cali-bration range and provides inaccurate result.

This study is to evaluate new approaches to applying a compliance correction to the DSR to achieve accurate results when testing binders at intermediate temperatures using the cup and bob system. Several approaches using materials with known stiffness were evaluated to determine the proper compliance correction. Once the correct com-pliance correction is determined a complete set of materials will be tested to verify the accuracy of testing at inter-mediate temperatures using the cup and bob system, which will lead to the final development of the PG specification for CRM binders with larger size rubber particles.

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Field QC/QA Test for Asphalt Binder

Raj Dongre (1); Jack Youtcheff and Nelson Gibson (2); and John W. Newman (3) (1) DLSI; (2) FHWA; (3) LTI A proof of concept field QC/QA test was reported on at last year’s Petersen Conference. Data generated using a working prototype was used to demonstrate the feasibility of such a test method. A first article version of the QC/QA device has now been developed by Laser Technology Inc. (LTI).

The test method provides a quick turnaround time for results and the equipment is easy to operate. This device uses a computer controlled air jet to induce creep and recovery loading. The resulting displacement and recovery is measured using laser interferometry. This presentation will discuss the status of the ongoing QC/QA test method development undertaken by FHWA and LTI. The fundamentals of ‘Shearography’ and its potential applications will also be discussed.

One such application being conducted at FHWA and LTI uses the working prototype to study the long term steric hardening behavior of unaged and RTFO aged asphalt binders.

Dongre Laboratory Services, Inc.  

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Your Leading AMRL Accredited Independent  Asphalt Laboratory for the Paving Industry 

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19

Effect of Foaming on Poly-phosphoric Acid (PPA) Modified Binders

Olga V Shulga, Rene Maldonado and Henry Romagosa (1); and Cristian Clopotel, Raquel Moraes and Hussain Bahia (2) (1) ICL Performance Products; (2) Modified Asphalt Research Center–University of Wisconsin Addition of the PPA is known to improve high temperature stiffness, without affecting negatively low temperature properties. It is however not known if foaming of PPA modified binders can interfere with the improvements gained.

Properties of foamed PPA binders were investigated in this study. Two binders of different composition (PG 64-22 and PG 64-16) were modified with 0.8% PPA and 1.5% PPA to achieve a one- and a two-grade improvement (PG70, PG76). Binders were foamed using a Wirtgen WLB-10 machine with 2-3% water injection. DSR and RV tests were used to measure properties immediately after foaming and after two different curing conditions: at 135°C in the oven, and at room temperature. Samples were tested after 2 hours and 24 hours of curing in the above men-tioned conditions.

The results show viscosity and stiffness of the neat and the PPA binders reduce initially. The reduction is pro-portional to grade of binders. After conditioning, binders rapidly recover stiffness and viscosity. Conditioning at 135 C caused faster recovery of the rheological properties. Minor differences are observed between the neat and PPA modified binders’ recovery. This presentation will cover the details of data and give an overview of the results of foaming modified binders. A Simple Test to Determine Workability of Warm Mix Asphalt (WMA)

Raj Dongre and Eugeniu Morari DLSI At present there is no simple and easy to use workability test for WMA. There are methods that are currently being evaluated such as the binder tribology test, the Casola method for compaction temperatures, the Reinke shear flow method. But these methods only test the binder and not the mix (HMA or WMA) which can lead to significant error in determining the correct field workability and hence compaction temperatures. Few years ago a bucket mixer type test method was presented at the Petersen conference by Dongre et al., which was designed to test the mix but the results were found to be inconsistent at best. Another problem was that the bucket mixer was unwieldy to use and requires large quantities of mix that is not always available in a laboratory.

A simple method was developed to determine the workability of mixes using existing equipment so new testing device needs to be purchased. Several WMA technologies and polymer modified hot mixes (both lab and field pro-duced) were tested using this method. It was found that the new method provides reasonable estimates of compac-tion temperatures (and/or Workability) for PMAs and WMAs. This presentation discusses the development, use and findings from this new simple workability test method.

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Neutron Scattering for Moisture Detection in Foamed Warm Mix Asphalt

Yang Zhang, Ph.D. (1); and Baoshan Huang, Ph.D, P.E, Philip Ye, and Xiang Shu, Ph.D. (2) (1) Oak Ridge National Laboratory; (2) University of Tennessee Foamed warm-mix asphalt (WMA) has been widely accepted and used in the US and many other countries in the world. However, concerns about WMA technology still need to be answered, among which moisture-induced dam-age is a major one. Due to the reduced production temperatures and the foaming process with water, moisture may be entrapped in pavements after compaction. The trapped moisture decreases the adhesion between asphalt binder and aggregates as well as the cohesion among asphalt binder, resulting in stripping and other forms of pavement dis-tress.

Neutron scattering technique provides a unique tool for the determination of the microscopic structure of asphalt and for the detection of the presence of moisture and its spatial distributions in asphalt. In particular, small angle neutron scattering (SANS) in the wave vector transfer range from 0.003 Å-1 to 0.5 Å-1 is suitable to probe the spatial density fluctuations in the real space from 0.2 micron to 1 nm, which is of orders of magnitude higher resolution than direct imaging techniques. Furthermore, the scattered signal from different parts of the asphalt and water can be separated by contrast variations using isotopic substitution.

In this study, SANS technique was utilized to detect water spatial distributions in foamed WMA. Two types of asphalt binder and ordinary and heavy water were used to make samples at 150°C via a laboratory foaming device. The samples were then measured using the SANS instrument at NIST Center for Neutron Research (NCNR). The results show that there is no water entity less than 0.2 micron present in the foamed WMA. Even if moisture does exist in WMA, it did not cause any structural changes to the asphalt mixtures within 0.2 micron. Lubricity Properties of Asphalt Binders Used in Hot-Mix and Warm-Mix Asphalt Pavements

Gaylon L. Baumgardner (1) and Gerald R. Reinke (2) (1) Paragon Technical Services, Inc.; (2) Mathy Technology and Engineering, Inc.

The more common science used in determination of a materials coefficient of friction is known as Tribology. Tribiology is de-

fined as the science and technology of interacting surfaces in relative motion, including the study of friction, wear, and lubrica-

tion and is derived from the Greek tribo (to rub) and the Latin – logia (study or learning). The coefficient of friction of a material

is empirical – it has to be measured experimentally, and cannot be calculated. Rough surfaces like hot-mix aggregates tend to

have higher coefficients than smooth surfaces. Boundary fluids (like asphalt binders) can serve to reduce the coefficient of fric-

tion of aggregates during production asphalt mixtures.

The concept of testing asphalt binders in thin films and suggested “lubricity” and internal friction reduction as a potential

explanation of the mechanism allowing production of asphalt mixtures at reduced temperature, warm-mix asphalt (WMA), was

first suggested by Reinke and Baumgardner at the warm-mix technical working group (WMA TWG) in Baltimore, MD, Decem-

ber 2007. Further work was later reported by Hanz, Faheem, Hahmoud and Bahia at the 89th Annual Meeting of the Transporta-

tion Research Board, January, 2010.

Presented is a continuation of the work of Reinke and Baumgardner moving from gap-dependent rheology to tribology util-

izing a newly designed fixture and methods for testing asphalt binders with a dynamic shear rheometer. The work consists of

evaluations of various asphalts used to produce hot-mix asphalt mixtures and the affect that their composition might have on

friction characteristics, allowing production of warm-mix asphalt through non-chemical techniques such as foaming; and evalua-

tion of Lubricity Optimized Asphalts™ (LOA) and the effect additives have on friction characteristics in asphalt mixtures pro-

duced with LOA asphalt binders.

Published text is available from the proceedings of the 2012 Eurobitume/Euroasphalt (EE) Congress, Istanbul, Turkey, 13-

15 June 2012.

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22

Session 4

Effect of Cooling Medium on Asphalt Binder Strength at Low Temperature

Augusto Cannone Falchetto, Mugurel I. Turos and Mihai O. Marasteanu University of Minnesota Currently, asphalt binder low temperature behavior is characterized using the Bending Beam Rheometer (BBR) and the Direct Tension Tester (DTT). In this study, the possibility of obtaining asphalt binder bending strength is investi-gated. A modified Bending Beam Rheometer (BBR), capable of applying loads at different rates, is used to obtain asphalt binder flexural strength. Strength values obtained from BBR testing are compared with strength values ob-tained from Direct Tension Tester (DTT) and significant differences were found between the two tests. Additional BBR strength tests were run on asphalt binder beams after replacing the ethanol used in the cooling bath with potas-sium acetate, similar to DTT testing conditions, and significantly larger flexural strengths were obtained compared to ethanol. Weakest link theory is used to convert three-point bending strength to direct tension strength and to perform volume correction of DTT values. Based on the corrected values, BBR and DTT strength measurements are similar, when the same cooling medium is used. The effect of cooling medium on BBR creep stiffness is also evaluated. From the limited experimental tests it appears there are no significant differences in stiffness and m-value after one hour of isothermal storage. Construction of Master Curves for Asphalt Binders

David A. Anderson, P.E. (1) and Geoff Rowe (2) (1) Consultant and Prof. Emeritus, The Penn State University; (2) Abatech, Inc. Once considered tools of the advanced researcher, master curves are being increasingly used as a tool for the devel-opment of new binders, in forensic analyses, and other routine binder applications. A master curve constructed from measured data is not unique but depends upon the technique used in its construction. Also of importance is the man-ner in which the data are obtained - data must be obtained in the linear viscoelastic region without an undue influ-ence of thermal history, or at least obtained with a consistent thermal history. Currently used techniques include the use of a predetermined model to generate the master curve as well as statistical procedures without a predetermined model. The generated master curve is also dependent upon assumptions with respect to the form of the time-temperature shift function. In this presentation the effects of data quality are discussed and the resulting master curves generated for a variety of materials using different statistical techniques including EXCEL Solver and the Gordon-Shaw protocol are discussed.

23

Evaluation of the LAS Test

Raj Dongre (1); Adrian Andriescu (2); and Nelson Gibson and Jack Youtcheff (3) (1) DLSI; (2) SES Group & Associates, LLC; (3) FHWA The Linear Amplitude Sweep Test (LAS) was developed as a surrogate test to characterize the fatigue behavior of asphalt binders. This presentation summarizes the findings of an evaluation of the LAS test with reference binders.

Slippage phenomena and apparent compliance at the DSR plate where asphalt binder adheres to the steel plate was found. DSR machines from different manufacturers commonly used in the asphalt industry exhibited similar results. Various laboratories where the LAS test was repeated confirmed that the error due to compliance was a sig-nificant part of the data as previously observed. This is a major hurdle in obtaining any meaningful binder fatigue data from the LAS test if this is to be used as a surrogate test.

The causes of the apparent compliance and its implications to the LAS test data and binder fatigue surrogate characterization will be discussed in detail. The Effect of Thermal Equilibrium on the Accuracy of DSR Measurements

David A. Anderson, P.E. Consultant and Prof. Emeritus, The Penn State University The measured properties of asphalt binders are strongly affected by their thermal history. Thermal equilibrium dur-ing test measurements is not obtained instantaneously but within a finite period of time during which thermal gradi-ents within the DSR and the test specimen become stabilized. Thermal equilibrium issues as well as DSR design is-sues must be carefully considered if accurate measurements are to be obtained with the DSR. The current DSR test method specifies that test measurements shall be initiated 10 minutes after the DSR temperature is constant within ±0.1°C of the target test temperature. It appears as though a 10 minute wait time is excessive for most rheometers given that specimen thermal equilibrium is typically obtained after only a few minutes after the DSR indicates a con-stant temperature. However, long-term drift in the DSR measurements are also observed with both the reference fluid and asphalt binders. This long-term drift can be significant when isothermal measurements are taken over an extended time. Defining Good Measuring Practice in Asphalt Rheology Testing

Joerg Laeuger (1) and Darin Hunter (2) (1) Anton Paar Germany; (2) Anton Paar USA With the evolving of binder testing beyond the limitations of specification tests it is becoming apparent that defining good measuring practice in these exotic tests is paramount. Depending on the specific tests different parameters or a combination of parameters can be of relevance. Much effort has been made to optimize the temperature control for standard binder testing. Going to different geometries require the same type of quality in the temperature control. Torsional compliance effects might come into play when stiff samples are measured in new testing configurations. Even if all instrument parameters are within the operational tolerances of the rheometer the obtained results can show atypical responses if the sample itself is not behaving as expected or the sample is not exposed to the com-manded strain as in the case of slippage of the measuring plates. Therefore, having a command of rheometers tech-nology and the knowledge to understand the domain in which one tests is a critical skillset.

Examples covering the topics of temperature, compliance, slippage and test parameters with an eye towards ac-knowledging test artifacts’ superimposed on data will be discussed.

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Wednesday, July 11

Session 5 Evaluation of the Effect of Polymer Modification on Aging Properties of SHRP Core Asphalts Iliya Yut and Adam Zofka University of Connecticut The undergoing research study offers a new perspective on aging properties of asphalts from multiple crude sources. Nine SHRP core asphalts are modified by 3 wt% of radial Styrene-Butadiene-Styrene polymer and oxidized in re-cently proposed compact aging apparatus consisting of Attenuated Total Reflection spectrometer and Aging Cell (ATRAC). Oxidation rates of original/aged and modified/non-modified asphalt samples in ATRAC are used to rank asphalt performance at high and intermediate temperatures. In addition, an innovative 2-D Correlation Spectroscopy method is applied to spectral data to compare aging kinetics of SHRP asphalts and evaluate significance of the effect of crude source on aging properties of asphalts in presence of polymer additive.

Effect of Oxidative Aging on the Relaxation Spectrum of Asphalt Mixtures Obtained from Dynamic Modulus Test Data Mohammad Zia Alavi and Nathaniel E. Morian (1); and Elie Y. Hajj (2) Civil and Environmental Engineering Department, University of Nevada, Reno (1) PhD Candidate, Pavements/Materials Program; (2) Asst. Professor The generalized Maxwell model has been successfully used to represent the viscoelastic behavior of asphalt mix-tures. As the asphalt binder oxidizes in a mix, Carbonyl (C=O) is formed which can lead to changes in fundamental properties of the asphalt binder and thus the corresponding mixture. There are relatively few studies conducted to understand and quantify the influence of binder aging on the viscoelastic behavior of asphalt mixtures. This study proposes a method to relate the amount of oxidative aging in asphalt binder to the viscoelastic behavior of asphalt mixtures. For this purpose, Superpave gyratory compacted specimens of asphalt mixtures were subjected to four lev-els of long-term aging (0, 3, 6, 9 months at 60°C). The dynamic moduli of the mixtures at the four aging levels were measured, and the carbonyl of the recovered binders from the various aged mixtures was also determined by FT-IR methods. The relaxation spectra of the aged mixtures were determined based on the generalized Maxwell model from dynamic modulus test data. Finally, the relationship between amount of carbonyl as an aging index and the re-laxation spectrum of asphalt mixtures were developed.

Alfred Jacob Miller, Artist of the 1837 Rendezvous Images throughout this program are from paintings by Alfred Jacob

Miller, a Baltimore-born artist who was employed by William Drummond Stewart, a wealthy Scot, to serve as expedition artist for an 1837 journey into the Wind River country of the vast American West. Miller recorded scenes and landscapes along the trail, dramatic moments at camp, and the pageantry of Rendezvous—a gathering of Indian peoples, trappers, and representatives of the American Fur Company near today’s Pinedale, Wyoming. His pictures, many of which are housed at the University of Wyoming’s American Heritage Center, give us the only contemporaneous visual record of the Rendezvous period of the Rocky Mountain fur trade.

25

Binder Oxidative Aging Chemical Changes

John F. Schabron Western Research Institute Reference binders and extracts from slices of naturally aged cores from the Turner-Fairbank Accelerated Load Facil-ity (ALF) and Arizona Comparative Site sections, sampled at several depths were analyzed. These represent materi-als subjected to a wide range of oxidative aging severities. Analyses included using infrared spectroscopy, the WRI Asphaltene Determinator, differential scanning calorimetry, and elemental analysis (CHNOS). Selected materials were also analyzed by high resolution Fourier transform ion cyclotron resonance mass spectrometry at the Florida State University High Magnetic field laboratory. Results show the typical increases of carbonyl and sulfoxide infra-red absorbance with aging, and a significant oxygen uptake, especially in the asphaltenes. The amount of naphthenic pericondensed aromatic molecules decreases with aging, with a concurrent increase in the amount of more pericon-densed and oxygenated aromatic molecules, resulting in increasing asphaltene content, and increasing total pericon-densed aromatic content. The differential scanning calorimetry (DSC) glass transition temperature width increases with aging. Physical tests conducted on the samples include dynamic shear rheometry (DSR) and the linear ampli-tude sweep test (LAST). An Oxidative Aging Study on Seal Coat Treated Pavement

Yuanchen Cui and Charles J. Glover Artie McFerrin Department of Chemical Engineering, Texas A&M University Projecting pavement oxidation over time requires oxidation kinetics and hardening properties of the specific binder used in the pavement, but is complicated by factors such as variation in binder properties throughout pavement con-struction, and the presence of a seal coat, not to mention the fact that the pavement of interest may have no prior his-tory, including any samples of original binder.

By using a fast PAV method for measuring a binder’s constant-rate activation energy and pre-exponential factor, together with knowledge of universal interrelations between the various kinetics parameters, along with a pavement oxidation model, measurements on binder recovered from a pavement can be used to project oxidation and harden-ing in the pavement over time.

Using this approach on a seal coat treated pavement, binder properties for the seal coat binder and the pavement binder were found to be distinctly different. Furthermore, the first layer underneath the seal coat was found to have properties intermediate between the two, reflecting the presence of both binders in that layer, but not in deeper lay-ers. From these data, both seal coat and pavement binder hardening were estimated over time and as a function of depth below the surface, and compared to measurements.

26

The Influence of Sunlight on the Aging of Bituminous Binders

Hilde Soenen, Serge Heyrman, Xiaohu Lu and Per Redelius Nynas Aging of asphalt, especially of the bituminous component can induce a number of pavement failures, including different forms of cracking, and surface defects like stone loss. In this study, bituminous binders were aged using various procedures: outdoor aging with and without exposure to sun radiation, indoor aging, and accelerated aging using the pressure aging vessel (PAV). The samples were investigated by Fourier transform infra red spectroscopy (FT-IR), in attenuated reflection mode (ATR). This technique is excellent to investigate surface characteristics, since the infra red radiation is only penetrating the first 2 to 3 micrometer of the surface. For some of the binders, the depth of aging was evaluated using a macrotome to slice the aged films. As expected, under ambient conditions bitumen ages more severely at the top surface compared to the bottom surface. A study as a function of aging time, showed that after less than 8 days, the ambient aged samples have at the surface obtained an infra- red spectrum similar as is found after aging in the PAV (20 h, 100ºC). The tests also show clear differences in the FT-IR spectra, depending on whether the binders were exposed to sunlight. As the extent of aging found at the surface of these samples is high, these infrared spectra are extremely useful to investigate chemical changes occurring upon aging. Significance of Mixture Parameters on Binder Aging in HMA Mixtures

Nathan Morian (1); and Elie Y. Hajj and Peter E. Sebaaly (2) (1) PhD Candidate, University of Nevada-Reno/Nevada DOT; (2) University of Nevada-Reno A study was initiated by the FHWA to evaluate the effects of different aggregate sources and different binders on the aging characteristics of asphalt binders aged in mixtures over a range of air void levels. Those same binders were also aged in pressure aging vessel (PAV) pans in laboratory ovens to determine the aging characteristics of the binders, as is the current state of practice without the influence of the mixtures. These characteristics were determined by the binder kinetics, in terms of the carbonyl area measured from the Fourier Transform Infrared Spectroscopy spectra as a function of aging time and temperature. The low shear viscosity was also determined as a function of aging, yielding the hardening susceptibility (HS) relationships which were the oxidation parameters used to compare the mixture and binder aging as well as the effect of the mixture parameters on the binder aging.

This study found statistically different HS relationships between some of the mixtures and was validated by considering the time to an arbitrary oxidation level and dynamic modulus results on the mixtures. The mixture HS relationships of the binders aged in the mixtures were compared to the binders aged in PAV pans and were likewise found to be statistically dissimilar.

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Western Research I N S T I T U T E

Alfred Jacob Miller, Artist of the 1837 Rendezvous Images throughout this program are from paintings by Alfred Jacob Miller, a Baltimore-born artist who was employed by William Drummond Stewart, a wealthy Scot, to serve as expedition artist for an 1837 journey into the Wind River country of the vast American West. Miller recorded scenes and landscapes along the trail, dramatic moments at camp, and the pageantry of Rendezvous—a gathering of Indian peoples, trappers, and representatives of the American Fur Company near today’s Pinedale, Wyoming. His pictures, many of which are housed at the University of Wyoming’s American Heritage Center, give us the only contemporaneous visual record of the Rendezvous period of the Rocky Mountain fur trade.

Western Research I N S T I T U T E