2013 Session: 604

• Simplification of Linear Amplitude Sweep Test and Specification Parameters
  Abstract: The Linear Amplitude Sweep (LAS) test has recently been approved by AASHTO as a provisional standard, and is currently being considered for specification of asphalt binder fatigue resistance. The LAS test is a cyclic torsion test, conducted in the Dynamic Shear Rheometer (DSR) that uses increasing loading amplitudes to accelerate damage. The LAS test has being proposed as a surrogate to the time sweep (TS) test, which is a conventional fatigue test consisting of repeated cyclic loading at constant amplitude. The TS test is considered unsuitable for specification due to the uncertainty in the test duration required to induce and quantify fatigue. Recent ruggedness testing efforts have shown that the LAS test cannot be conducted by all DSRs. This study evaluates a simpler amplitude ramping procedure that resolved the difficulties with some rheometers. Additionally, a simple specification parameter is introduced to offer a practical approach to define damage tolerance. The definition of failure is based on a more recent study to explain the mechanisms of fatigue damage under TS testing in the DSR. Based on a comparison between TS and LAS test results, it is demonstrated that the damage evolution in the two tests differs, indicating the LAS test is very complex and is better referred to as a “damage tolerance” test rather than true fatigue test. Using the simplified analysis approach for the modified LAS procedure, a critical cracking length signifying the start of rapid crack growth is proposed for specification of binder damage tolerance at intermediate temperature.
  Authors: Hintz, Cassie A; Bahia, Hussain U.
  Authors: Hintz, Cassie A; Bahia, Hussain U.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-0963
• Phase Field Modeling of Mode I Cracking Failure in Asphalt Binder
  Abstract: Cracking failure in asphalt binder in winter has always been one of the most serious problems in pavement structures. Classical fracture mechanics is the most widely used method to analyze the initiation and propagation of cracks. In this paper, a new modeling and computational tool, namely, the phase-field method is proposed for modeling the Mode I cracking failure in asphalt binder. This method describes the microstructure using a phase-field variable which assumes one in the intact solid and negative one in the crack region. The fracture toughness is modeled as the surface energy stored in the diffuse interface between the intact solid and crack void. To account for the growth of cracks, a non-conserved Allen-Cahn equation is adopted to evolve the phase-field variable. The energy based formulation of the phase-field method handles the competition between the growth of surface energy and release of elastic energy in a natural way: the crack propagation is a result of the energy minimization in the direction of the steepest descent. Both the linear elasticity and phase-field equation are solved in a unified finite element frame work, which is implemented in the commercial software COMSOL. The mode I crack simulation is performed for validation. It was discovered that the onset of crack propagation agrees very well with the Griffith criterion and experimental results.
  Authors: Hou, Yue; Yue, Pengtao; Wang, Linbing; Sun, Wenjuan; Pauli, Adam Troy; Wang, Dong; Zhou, Wenhuan; Hu, Mingfang
  Authors: Hou, Yue; Yue, Pengtao; Wang, Linbing; Sun, Wenjuan; Pauli, Adam Troy; Wang, Dong; Zhou, Wenhuan; Hu, Mingfang
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-1554
• Structural Characterization of Micromechanical Properties in Asphalt Using Atomic Force Microscopy
  Abstract: This paper presents the findings from a study that semi-quantitatively evaluates the micro-rheological properties of the asphalt binder using Atomic Force Microscopy (AFM). The paper also presents the differences between these properties amongst the various microstructures within an asphalt binder as well as the influence of oxidative aging on these properties. The following sections describe background information and the research approach used to achieve the aforementioned objectives. The approach described uses nano-indentation experiments performed within a micro-grid of asphalt phases to determine micromechanical properties such as stiffness, adhesion and elastic/plastic behavior. The materials evaluated include asphalts AAB and AAD from the Materials Reference Library (MRL) of the Strategic Highway Research Program (SHRP), chosen due to variations in crude source, chemical composition and elemental analysis for each asphalt type. The analysis of nano-indentation creep measurements corresponding to phase-separated regions revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging was found to induce substantial microstructural change within these domains, including variations in phase structure, phase properties and phase distribution. The form and extent of these changes, however, were different for each asphalt studied. The interpretation of data collected from the AFM experiments in this study advances the understanding of the microstructural makeup of asphalt binders and the response of the microstructural phases of the asphalt binder under load as well as how the mechanical responses in the phases change with aging.
  Authors: Allen, R. Grover; Little, Dallas N.; Bhasin, Amit
  Authors: Allen, R. Grover; Little, Dallas N.; Bhasin, Amit
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-2734
• Is Atomic Force Microscopy Suited as Tool for Fast Screening of Bituminous Materials? Interlaboratory Comparison Study
  Abstract: Bituminous binders are known to have microstructures at typical length scales of micrometers. This microstructure can be probed with Atomic Force Microscopy (AFM). Now that worldwide several research groups are reporting AFM results on bitumen, it is becoming important to improve the understanding of the reproducibility and objectivity of the technique for studying bituminous samples. When reproducibility and stability are proven, AFM can be a tool for asphalt professionals to rapidly screen bituminous binders. In this context two independent laboratories have developed a standard method for preparing and conditioning bitumen for AFM imaging. By means of an inter-laboratory comparison of independently imaged specimen, the reproducibility of microstructure measurements was investigated. A quantitative comparison on different microstructures was developed, and the consistency of independently obtained results was confirmed. The results from both labs were comparable: the microstructural properties were found to be randomly distributed within a 5% interval. Also the influence of temperature on the microstructure was demonstrated to be reproducible and consistent. With the increase of temperature, the microstructure gradually disappeared, however traces of the microstructure remained visible up to the highest measurement temperature of 60°C. It is concluded that given well defined sample preparation and measurement procedures, the microstructure of bitumen can be reproducibly imaged by AFM from room temperature up to temperatures where bitumen becomes liquid.
  Authors: Nahar, Sayeda Nowrozon; Dillingh, Bert; Erkens, Sandra; Fischer, Hartmut; Schitter, Georg
  Authors: Nahar, Sayeda Nowrozon; Dillingh, Bert; Erkens, Sandra; Fischer, Hartmut; Schitter, Georg
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-4131
• Obtaining Nanorheology of Asphalt Binders Using Atomic Force Microscope and Modified Fischer-Cripps Solution
  Abstract: During the last few years several researchers have used the Atomic Force Microscope (AFM) to visualize the microstructure of asphalt binder and also to evaluate the influence of aging, nanomodification, and thermal history on this microstructure. More recently, owing to the low stiffness of asphalt binders, researchers have used the AFM to perform nano-indentation on asphalt binders. This paper presents and exemplifies the use of modified analytical solutions to determine the nano-rheology of asphalt binders using the AFM as a nano indenter. More specifically the solution presented is based on a corrected Fischer-Cripps viscoelastic spherical indentation solution. AFM indentations were performed on asphalt thin film using a conospherical tip, and the analytical solutions were used to determine the creep compliance parameters with minimal error. The results and methodology presented in this paper can be used to determine the time dependent behavior of microphases within the asphalt binder, to study the effect of modifiers such as polymers or other organic additives on the nanorheology of asphalt binder, and to obtain mechanical properties required for computational micro-mechanics of asphalt binders at a micrometer length scale.
  Authors: Jahangir, Rezwan; Allen, R. Grover; Little, Dallas N.; Bhasin, Amit
  Authors: Jahangir, Rezwan; Allen, R. Grover; Little, Dallas N.; Bhasin, Amit
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-4144
• Using Poker Chip Test for Determining Bulk Modulus of Asphalt Binders
  Abstract: The properties of asphalt binders strongly influence the overall mechanical response of asphalt mixture composites. A thorough understanding of the mechanistic behavior of asphalt binders is important in order to fully and accurately characterize the behavior of the asphalt mixture. The mechanical properties of the asphalt binder, the matrix in the asphalt mixture composite, are time and temperature dependent and have a lower stiffness compared to the inclusions (aggregate particles). However, computational methods used to model the micromechanics of asphalt mixtures typically assume a constant bulk modulus or Poisson’s ratio for asphalt binders. This study investigates the time-dependence of the bulk modulus of an asphalt binder. Several approaches for measuring the bulk modulus were explored and the poker-chip geometry was found to be the most suitable one. The boundary value problem for the poker-chip geometry was solved to determine the bulk modulus and Poisson’s ratio of an asphalt binder as a function of time. The findings from this research improve the understanding of asphaltic materials behavior, and also guide important assumptions typically made during computational modeling of asphaltic materials.
  Authors: Motamed, Arash; Bhasin, Amit; Liechti, Kenneth M.
  Authors: Motamed, Arash; Bhasin, Amit; Liechti, Kenneth M.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-3480
• Modification of Particulate Additive Test for Determination of Styrene Butadiene Rubber Polymer Content of Asphalt Binders
  Abstract: As it is in many countries, Costa Rica is implementing the use of polymer modified asphalts for road construction. A growing market offers various types of polymers that significantly improve the rheological properties of the asphalts, like SBR, SBS, rubber, EMA, EVA among others, which are commonly added at percentages between 1 and 5% mass / mass of binder. However, little research has been conducted on quantifying the amount of polymer incorporated to the asphalt binders.This study presents a modification to the Particulate Additive Test (PAT) proposed by Bahia et al. (2001) to determine in a qualitative and quantitative way the presence of SBR type polymers on local asphalts (PG64-22). Two types of SBR polymers were used. However, the scope of this methodology does not include the identification of SBS polymers.The results obtained show an acceptable rate of polymer recovery. The results can be later verified by means of the Fourier Transform Infrared Spectroscopy (FTIR). Also the solvents can be changed to apply this method for SBS type polymers or other polymers, turning this method into a quick, easy and low cost quality control tool to verify the amount of polymer added to the plant asphalt mixtures.
  Authors: Corrales-Azofeifa, Jose; Salazar, Jorge; Aguiar-Moya, José Pablo; Loria-Salazar, Luis
  Authors: Corrales-Azofeifa, Jose; Salazar, Jorge; Aguiar-Moya, José Pablo; Loria-Salazar, Luis
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-4275
• Critical Problems with Using Asphalt Ductility Test as Performance Index for Modified Binders
  Abstract: Despite the adaptation of advanced binder rheology characterization methods by many agencies, the asphalt ductility test is still under use in some specifications in the USA and a few countries as a performance indicator for asphalt modification. In the present study a set of binders modified with two types of commonly used elastomeric polymer modifiers were characterized in terms of fundamental, well-defined, binder properties known to reflect rutting and fatigue resistance, results of which showed no correlations with binder ductility.Additionally, a test procedure was developed using a Dynamic Shear Rheometer (DSR) as a surrogate to the conventional ductility test, results of which showed that both elastomeric modified binders are much more ductile than conventional binders, even when conventional ductility showed a loss of ductility. Finite Element Modeling (FEM) was used to show the significant effects of decreasing true strain rates with elongation on the sample’s stress and strain state due to the constant cross head speed in the conventional ductility test. Due to the well-known dependency of failure stress and strain of viscoelastic material on strain-rate and temperature, comparing binders with varying ductility values measured in the conventional test is essentially flawed as it is equivalent to comparing them at different temperatures, thus fundamentally unreliable as an indicator of the asphalt’s performance in the pavement. It is therefore strongly recommended that the practice of using low temperature conventional ductility be removed from modified binder specifications, or the DSR procedure proposed in this paper be used to evaluate modified asphalts.
  Authors: Tabatabaee, Hassan A.; Clopotel, Cristian; Arshadi, Amir; Bahia, Hussain U.
  Authors: Tabatabaee, Hassan A.; Clopotel, Cristian; Arshadi, Amir; Bahia, Hussain U.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-4125
• Using Gel Permeation Chromatography to Predict Viscoelastic Properties of Recycled Asphalt Shingle Binder and Its Use in RAS Blending Efficiency
  Abstract: Reuse of the asphalt binder from Recycled Asphalt Shingles (RAS) is at the forefront of the industry due to dwindling natural resources and the potential economic benefits. However, the blending efficiency of RAS binder with virgin binder remains unknown to the asphalt industry. This paper conducted research on the correlation between percentages of large molecules (LMS) defined by Gel Permeation Chromatography (GPC) with viscoelastic properties of RAS binders and investigated the blending efficiency of RAS binders based on this relationship. Aggregate size, RAS content and mixing time were evaluated as factors that affect the blending efficiency. The test results showed that percentages of LMS were highly correlated with the complex modulus. Based on GPC test results, increasing mixing time led to better blending of RAS mixture and the size of virgin aggregate didn't affect the blending efficiency. Partial blending was investigated in this study and the best blending efficiency may occur with the addition of around 5% RAS by weight.
  Authors: Zhao, Sheng; Bowers, Benjamin F.; Huang, Baoshan; Shu, Xiang; Woods, Mark
  Authors: Zhao, Sheng; Bowers, Benjamin F.; Huang, Baoshan; Shu, Xiang; Woods, Mark
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 604
  Paper Number: 13-5013
• Structural Characterization of Micromechanical Properties in Asphalt Using Atomic Force Microscopy
  Authors: Allen, R.
  Authors: Allen, R.
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-2734
• Obtaining Nanorheology of Asphalt Binders Using Atomic Force Microscope and Modified Fischer-Cripps Solution
  Authors: Jahangir, Rezwan
  Authors: Jahangir, Rezwan
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-4144
• Critical Problems with Using Asphalt Ductility Test as Performance Index for Modified Binders
  Authors: Tabatabaee, Hassan
  Authors: Tabatabaee, Hassan
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-4125
• Is Atomic Force Microscopy Suited as Tool for Fast Screening of Bituminous Materials? Interlaboratory Comparison Study
  Authors: Nahar, Sayeda
  Authors: Nahar, Sayeda
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-4131
• Modification of Particulate Additive Test for Determination of Styrene Butadiene Rubber Polymer Content of Asphalt Binders
  Authors: Aguiar-Moya, Jose
  Authors: Aguiar-Moya, Jose
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-4275
• Using Gel Permeation Chromatography to Predict Viscoelastic Properties of Recycled Asphalt Shingle Binder and Its Use in RAS Blending Efficiency
  Authors: Zhao, Sheng
  Authors: Zhao, Sheng
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-5013
• Using Poker Chip Test for Determining Bulk Modulus of Asphalt Binders
  Authors: Motamed, Arash
  Authors: Motamed, Arash
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 604
  Paper Number: 13-3480