2020

Mrinali Rochlani, Technische Universität Dresden
Sabine Leischner, Technische Universitat Dresden
David Wareham, University of Canterbury
Silvia Caro, Universidad de Los Andes
Gustavo Canon Falla, Technische Universitat Dresden
Frohmut Wellner, Technische Universitat Dresden

In recent years, crumb rubber (CR) has become an attractive option to modify bitumen. In this research, a set of Dynamic Shear Rheometer (DSR) tests were used to gauge the effect of CR on different rheological and mechanical properties of CR bitumen (CRB). To achieve this goal,  temperature and frequency sweep tests were conducted on three CRB bitumen and one penetration 50/70 reference bitumen, and Single Stress Creep Recovery (SSCR) tests were used to quantify the susceptibility of the bitumen to permanent deformation. Moreover, a new specialized cryogenic test and a recently developed fatigue test conducted on cylindrical column bitumen samples were implemented in the rheometer and used to assess the low-temperature cracking and fatigue properties of the materials. The results indicate that CR substantially improves the performance of bitumen when compared to the reference bitumen. All modified bitumen admixtures had better cryogenic, fatigue and rutting performance than the reference bitumen. A pictorial representation mapped all performance parameters obtained in this research and identified the best overall performing CRB admixture.

Panos Apostolidis, TU Delft: Technische Universiteit Delft
Xueyan Liu, Delft University of Technology
Paul Marocho, Delft University of Technology
Martin van de Ven, Delft University of Technology
Sandra Erkens, Delft University of Technology
Athanasios Skarpas, Khalifa University

In-depth understanding of the synergetic effect between the various incorporating constituents in asphalt binders (e.g., polymer-based modifiers, fillers) is needed to design durable paving materials with desired properties. In this research, the focus was first on the effect of the reactivity of fillers on the evolution of adhesive strength between stone aggregates and epoxy-asphalt (EA) mastics during the epoxy polymerization. Uniaxial tensile tests were performed on different combinations of fillers and EA binders with and without the epoxy-based polymer, and at different modification levels. Based on the results of the tensile tests, the increase of the adhesive strength of mastic with aggregates was lower when reactive filler particles (i.e., hydrated lime) were added than of EA binders with non-reactive filler. In other words, the non-reactive fillers did not influence the adhesion process and were thus selected for the next step studies on aging. The chemo-mechanical changes of EA mastics were analysed after PAV and oven-aging after various aging times by means of Fourier transform infrared spectroscopy and dynamic shear rheometry. Considering the sulfoxide compounds as representative aging index for the EA binders, a linear relationship between viscoelastic properties (i.e., complex modulus and phase angle) and increase in sulfoxides was observed. Finally, the extend of sulfoxide index was dependent on the level of epoxy modification in asphalt binder. Overall, the enhanced resistance against oxidative aging has the potential to become an effective technology for developing durable and long-lasting asphaltic materials.

Panos Apostolidis, TU Delft: Technische Universiteit Delft
Xueyan Liu, Delft University of Technology
Sandra Erkens, Delft University of Technology
Athanasios Skarpas, Khalifa University

Asphalt binders incorporating different modifiers is a common practice but empirically driven in most of the cases. Therefore, the fundamental understanding of modification mechanisms in asphalt binders is needed to design compatible polymer modified binders in a controllable manner, especially today in which new modification technologies are proposed. Among others, epoxy-based polymers have been accepted as a promising solution for asphalt binders to develop durable and long-lasting pavement materials. Nevertheless, a relationship between processing of epoxy-asphalt binders and their properties built-up is of high importance to prevent phenomena such as over-curing during the material production. In this research, the use of standard and modulated differential calorimetric measurements is discussed by performing analyses to asphalt binders modified with two epoxy formulations having a commercially available epoxy-asphalt binder as reference. The kinetic parameters and the Tg change of various crosslinking epoxy-based binders was assessed for the different formulations. According to the results, the Tg is shifting to higher temperatures as cure progresses and crosslinks are formed, with the neat epoxy modifiers to crosslink faster than epoxy-asphalt binders. The asphalt binder prohibits the interaction between the two reactive epoxy components and therefore reduction of the Tg evolution. Difference on the crosslinking performance between the two epoxy modifiers was noticed as well. This research provided valuable insight into the chemical thermodynamics of crosslinking epoxy-asphalt that can help the future material designers to control reaction-induced phenomena, such as the phase separation.

Panos Apostolidis, TU Delft: Technische Universiteit Delft
Xueyan Liu, Delft University of Technology
Sandra Erkens, Delft University of Technology
Athanasios Skarpas, Khalifa University

In this research, the binary (two-component) material design approach is introduced representing the co-polymerization mechanism that bears compatible and high-performance epoxy-asphalt (EA) systems. The implementation of the proposed approach in an interface diffuse-reaction model is presented within an effort to demonstrate the importance of designing EA systems based on crosslinking two originally dissimilar components. A theoretical framework is proposed to describe the relationship of cure kinetics during the mutual diffusion, or inter-diffusion, of crosslinking EA systems. In this study, a master expression of cure rate is used to predict the crosslinking of EAs at both cure stages in an interface diffuse-reaction model able to simulate the mass transport based on the reaction kinetics and the free-volume theory. From the numerical analyses, the influence of reactivity (activation energy and reaction rate) and physical (diffusion coefficient) parameters on cure-induced diffuse-reaction phenomena was obvious showing the importance of selecting the proper constituents to generate compatible asphaltic systems. The predictive capacity of the current model can be extended to similar inter-diffusion phenomena of asphalt binder with various reactive constituents.

Long Cheng, Southeast University School of Transportation
Jiang Yu, Xinjiang University
Lei Zhang, Southeast University

Recently, rock asphalt has been widely used to modify bitumen due to its remarkable high-temperature performance and lower costs than polymer modified asphalt. The objective of this study was to investigate the aging behavior of bitumen with 0%, 8%, 12%, 16% and 20% content of XRA. The rolling thin-film oven (RTFO) and pressure aging vessel (PAV) tests were performed to simulate short-term and long-term aging. The evolution of the chemical and rheological characteristics of the binders before and after aging were monitored with Fourier transform infrared (FTIR), frequency sweep, multiple stress creep recovery (MSCR) and bending beam rheometer (BBR) tests. The FTIR results indicated that the carbonyl functional group of the binders was reduced with the introduction of XRA modifier, and the carbonyl index was more stable than the sulfoxide index to characterize the aging extent of the XRA-modified bitumen binders. The rheological indexes showed that the XRA could reduce excessive plastic deformations and broaden the final performance grade (PG) of the binders, while a high XRA addition ratio could compromise the low-temperature stress relaxation properties of the bitumen. Furthermore, principal component analysis (PCA) suggested that ten parameters employed in this paper (such as rutting factor, Jnr3.2 and phase angle and etc.) have similarity and can be explained by two variable: PG and carbonyl index. Based on the changing rate of the comprehensive evaluation index before and after aging, 12% XRA was the optimum dose for base bitumen to exhibit the best anti-aging characteristics.

Sharareh Shirzad, Appalachian State University
Marwa Hassan, Louisiana State University
Louay Mohammad, Louisiana Department of Transportation and Development
Sreelatha Balamurugan, Louisiana State University

The objective of this study was to develop an optimized process for the production of a polyurethane modified asphalt binder with self-healing abilities. A reactive approach was adopted to eliminate issues related to the phase separation of polymer and asphalt binder. In addition, since the pre-polymer is in a liquid state, it was mixed with asphalt binder at a lower temperature compared to traditional polymer modification processes.  Different production parameters such as materials dispersion approach, polyurethane mixing temperature and agitation rate, -NCO:-OH ratio, curing days, and UV exposure were evaluated using the rutting factor as the performance parameter. Results showed that the materials dispersion method does not have a significant effect while the increase in the polyurethane mixing temperature and agitation rate can lead to an enhanced rutting performance. Furthermore, the number of curing days and exposure to UV light can also increase the rate of polymer formation in the asphalt binder. Finally, the rheological properties of the binder blend prepared using the optimum process were compared to the unmodified binder using the Superpave performance grading system, multiple stress creep-recovery test, linear sweep amplitude test, and pure linear amplitude sweep test. Results showed a significant increase in high-temperature performance and percent recovery of the binder blends modified with self-healing polyurethane compared to the unmodified binder. However, fatigue performance of the modified binder blends was negatively affected due to the application of self-healing polyurethane.

Sharareh Shirzad, Appalachian State University
Marwa Hassan, Louisiana State University
Louay Mohammad, Louisiana Department of Transportation and Development

The objective of this study was to evaluate the effect of an innovative UV light-activated self-healing polyurethane prepolymer (SPP) on the rheological, mechanical, and self-healing properties of asphalt mixture. For this purpose, asphalt mixtures were prepared with asphalt binder modified with three percentages (5, 10, and 15%) of self-healing polyurethane prepolymer. A self-healing test was performed to evaluate the rate of crack healing in asphalt mixtures prepared with or without self-healing polyurethane. Furthermore, semi-circular bending test and loaded wheel tracking test were conducted to study the fatigue and rutting resistance of the prepared samples. Finally, asphalt binder was extracted from the aged samples and was tested using the dynamic shear rheometer, bending beam rheometer, multiple stress creep recovery (MSCR), and linear amplitude sweep test. An increase in the crack healing rate was observed with 5 and 10% self-healing polymer; however, when the SPP percentage was increased to 15%, the healing efficiency was affected adversely. The addition of SPP also led to an improvement in the cracking and rutting resistances. Results from the rheological test showed that SPP application caused an increase in high-temperature grading, while the low-temperature grading was not affected. Furthermore, MSCR results showed an improvement in the elastic recovery and rutting resistance of the binder extracted from aged and unaged asphalt mixtures.

Haopeng Wang, University of Nottingham
Xueyan Liu, Delft University of Technology
Panos Apostolidis, TU Delft: Technische Universiteit Delft
Martin van de Ven, Delft University of Technology
Sandra Erkens, Delft University of Technology
Tom Scarpas, Khalifa University of Science and Technology

Aging during construction and in-service substantially changes the chemical composition and physical properties of bitumen thereof influences the performance of asphalt pavements. The modification of bitumen by crumb rubber modifier (CRM) significantly increases the complexity of the aging mechanism and is expected to improve the aging resistance of bitumen. This study aims to investigate the effects of laboratory short-term and long-term aging on the chemistry and rheology of crumb rubber modified bitumen (CRMB). Neat bitumen and CRMB with four different CRM contents were studied. Fourier transform infrared spectroscopy (FTIR) and dynamic shear rheometer (DSR) were employed to measure the change in the chemical composition and rheological properties of binders at different aging states. Bitumen hardening, which was rheologically revealed by the frequency sweep and multiple creep recovery (MSCR) test results, was also reflected in the growth of carbonyl and sulfoxide functional groups. In addition, the aliphaticity and aromaticity indices of binders before and after aging were also investigated. CRMB binders showed improved aging resistance compared to neat bitumen as reflected by the decreased carbonyl and sulfoxide indices as well as the lower change in rheological parameters. Higher resistance against aging was achieved when increasing the CRM content. The results also highlight the correlation between chemistry and rheology of bitumen. Among six selected mechanical parameters of binder, the non-recoverable creep compliance and percent recovery show better correlations with the combined chemical aging index (sum of carbonyl and sulfoxide indices) than the parameters derived from the linear viscoelastic region.

Nazmus Sakib, University of Texas, Austin
Ramez Hajj, University of Illinois, Urbana-Champaign
Rachel Hure, University of Texas, Austin
Ayah Alomari, University of Texas, Austin
Amit Bhasin, UT Austin: The University of Texas at Austin

The chemical composition of a bitumen dictates its rheological properties as well its performance in an asphalt mixture.  Any bitumen comprises a wide variety of complex hydrocarbons and its chemical composition can characterized by many different parameters.  Similarly, the mechanical properties of any given bitumen are typically characterized based on its time-temperature dependent rheological properties at different stress levels.  This study characterizes the chemical makeup of a set of bitumens from several different producers based on their polarity and compares these characteristics to mechanical properties associated with the Performance Grading (PG) of bitumen and its tensile strength.  Results show that high temperature stiffness is strongly dictated by the asphaltene content and the low temperature stiffness is strongly dictated by the aromatic and resin content.  The useful temperature interval showed a good correlation with asphaltenes and resins.  Finally, the tensile strength of the bitumens also showed a strong correlation with SARA parameters.  Bitumens that deviated from some of these correlations also showed an uncharacteristic response in some other mechanical or elemental property  measurements.  The relationship between time-dependent characteristics and polar fractions was not strong and requires further understanding.

Michele Lanotte, Khalifa University of Science and Technology
Sepehr Soleimani, Michigan State University

The nature of the interaction between bitumen and crumb rubber during the production of rubberized asphalt binders has been only partially demonstrated. These phenomena are extremely variable and substantially dependent on the characteristics of the base materials and blending conditions. The ability to anticipate the product of the interaction for a given set of materials and mixing settings can help materials engineer to forecast the optimal blending conditions. Among different physical parameters, viscosity has been recognized as the most suitable for monitoring the results of the interaction phenomena. This study presents a mathematical model developed by the Multi-Gene Genetic Programming (MGGP) algorithm for the prediction of the viscosity of crumb-rubber modified asphalt binders as a function of crumb rubber physical properties and mixing conditions. Four crumb rubber types were combined with a standard base bitumen to produce a wide array of CR-bitumen blends. The main physical characteristics of the crumb rubber, as well as the variation of the dynamic viscosity as a function of mixing time and temperature, were recorded in the laboratory. This database was used as an input for the MGGP algorithm to develop the predictive model.

Yi Zhang, Chang'an University
Xueyan Liu, Delft University of Technology
Panos Apostolidis, TU Delft: Technische Universiteit Delft
Wolfgang Gard, Technische Universiteit Delft
Natascha Poeran, Boskails
Martin van de Ven, Delft University of Technology
Sandra Erkens, Delft University of Technology
Athanasios Skarpas, Khalifa University

ABSTRACT This study evaluated the effect of lignin on the rheology of bitumen during ageing. Thin film oven tests and pressure ageing vessel were used to simulate short-term and long-term ageing processes, and the lignin-modified binders were characterized by an environmental scanning electron microscope (ESEM), Fourier transform infrared spectroscopy (FTIR) and dynamic shear rheometer (DSR). From ESEM analyses, a uniform microstructure was observed indicating that the addition of lignin did not affect the worm structure of bitumen. Based on FTIR tests, the lignin modified binders showed lower carbonyls and sulfoxides compounds generated after ageing than the neat bitumen. With the DSR, three different test methods were performed; frequency sweep, linear amplitude sweep and relaxation tests, for the different combinations of lignin in bitumen. The addition of lignin in bitumen reduced slightly the predicted fatigue life based on the LAS results. From the frequency sweep tests, it became clear that addition of lignin in bitumen acts more as filler than as a polymer modifier. The findings from this study revealed that the physical interaction between lignin and bitumen affects predominantly the material rheology. Lignin is still a promising addition in order to improve the performance of bitumen binders due to its economic and environmental benefits. Keywords: Lignin, Bitumen, Ageing, Microstructure, Chemistry, Rheology

Anas Jamrah, Marathon Petroleum Company LP
Muhammed Kutay, Michigan State University

Crumb Rubber Modified (CRM) binder testing and characterization methods continue to rely on empirical tests that provide an indication of existence of modification, but do not always address fundamental engineering behavior linked to pavement performance. A better understanding of Crumb Rubber (CR) modification techniques within the context of performance-related specifications on asphalt binders will better assess the adequacy of CRM asphalt mixture technologies in paving applications. This study produced a new analysis methodology for evaluating performance characteristics in CRM binders based on the temperature when the rubber and binder stiffnesses coincide. A new rheological parameter “Crossover Temperature” has been introduced, based on the stiffnesses of CRM binder and residual (rubber filtered out after interaction) binder. This new parameter provided strong correlations to CRM binder fatigue and rutting characteristics, without the need for micromechanical modeling, laboratory short term aging, or advanced testing/characterization techniques. This new parameter is recommended for Quality Control screening of CRM binders. A wide range of base asphalt binder Performance Grades and CR sizes were utilized in developing this parameter.

Haopeng Wang, University of Nottingham
Xueyan Liu, Delft University of Technology
Panos Apostolidis, TU Delft: Technische Universiteit Delft
Sandra Erkens, Delft University of Technology
Tom Scarpas, Khalifa University of Science and Technology

Rubber swelling in bitumen, which is a diffusion-induced volume expansion process, plays a dominant role in the design of crumb rubber modified bitumen (CRMB) binders and their properties development. This study aims to investigate the kinetics of bitumen diffusion into truck tire rubber, the equilibrium swelling characteristics of rubber and the mechanical properties of rubber before and after swelling at different high temperatures. Fourier transform infrared spectroscopy (FTIR) results indicate that no rubber dissolution happens during the interaction in the temperature range from 160 to 200 °C. Aliphatic compounds from bitumen preferentially diffused into rubber during the swelling process. The diffusion coefficients of bitumen into rubber were determined by the sorption test using the gravimetric method. The diffusion coefficient increases with the increase of temperature in an Arrhenius form. The volume expansion of rubber during swelling was captured by the X-ray computed tomography (CT) scan images. Rubber swells faster at the earlier stages then the expansion rate slows down. The swelling ratio of rubber increased from 1.97 at 160 °C to 3.03 at 200 °C after 36 h interaction. Mechanical tests by dynamic shear rheometer (DSR) reveal that swollen rubber becomes softer comparing to the dry rubber and exhibits obvious viscoelastic behaviors. With the increase of temperature, the softening and viscous effect are more significant. The obtained parameters can be implemented to swelling and micromechanical models to better predict the binder properties.

Haopeng Wang, University of Nottingham
Xueyan Liu, Delft University of Technology
Hong Zhang, Delft University of Technology
Sandra Erkens, Delft University of Technology
Tom Scarpas, Khalifa University of Science and Technology

Crumb rubber modified bitumen can be considered as a binary composite system where rubber particles are embedded in the bitumen matrix. The bitumen-rubber interaction process (mainly swelling) significantly changes the mechanical properties of both bitumen and rubber phases. This study aims to predict the complex moduli of CRMB binders with more representative constituent parameters using micromechanical models. To achieve this goal, frequency sweep tests using DSR were performed on the liquid phase of CRMB and swollen rubber samples to represent the essential properties of bitumen matrix and rubber inclusion. Rheological tests on neat bitumen and all CRMB binders were also conducted for comparison purpose. In addition, the numerical swelling model was used to estimate the effective volume concentration of rubber after the swelling process. Results show that the liquid phases of CRMB binders are stiffer and more elastic than the neat bitumen while the swollen rubber is softer and more viscous than the elastic dry rubber. The effective volume concentration of rubber can increase to 2.126 times as the blend percentage based on the analysis from the numerical swelling model. Using the liquid phase of CRMB binder and swollen rubber properties as the micromechanical model inputs yield more accurate predictions. The used four micromechanical models predict well at higher frequencies while underestimating the complex modulus at lower frequencies. Interparticle interactions in CRMB at high temperatures should be considered to further improve the prediction accuracy of micromechanical models.

Aimin Sha, Chang'an University
WANG TONG, Chang'an University
Wei Jiang, Chang'an University
Baowen Lou, Chang'an University

This research explores the influence of the waste engine oil bottom (WEOB) on the rheological properties of asphalt binders. Two asphalt types were modified with WEOB of different concentrations (2, 4, and 8 wt%). The main chemical components of the WEOB were determined by gas chromatography-mass spectrometry, and the chemical functional groups of the WEOB-modified asphalt were characterized by Fourier transform infrared spectroscopy (FTIR). The high-temperature rheological properties were evaluated by frequency sweep, temperature sweep, and multiple stress creep and recovery tests. The main constituents of WEOB were aromatic solvents, paraffin oil, and polyolefin oil with similar functional groups to asphalt, along with maleic anhydride (MAH) and downstream anhydride products. In the rheological tests, adding WEOB enhanced the phase angle and unrecoverable flexibility of the matrix asphalt (MA), and reduced the dynamic shear modulus and the average recovery rate. These trends completely opposed those of modified styrene–butadiene–styrene (SBS) asphalt, suggesting that WEOB improves the high-temperature stability of SBS asphalt, but weakens the high-temperature stability of MA. The FTIR results confirmed that MAH chemically reacts with SBS to form a strong polar SBS–g-MAH ternary graft product. The morphological features obtained by fluorescence microscopy indicate that WEOB promotes swelling and homogeneous distribution of the polymers in SBS, thus strengthening the polymer's cross-linked network. However, the increased dispersed phase in the MA degrades the elastic properties.

Jin Li, Tongji University
Feipeng Xiao, Tongji University
Serji Amirkhanian, University of Alabama

Rubberized asphalt binders have many benefits; however, storage instability has been reported to be one of the challenging issues that significantly affected the engineering performances of these binders. For this research project, cold plasma was utilized in activating the inert surface of Crumb Rubber (CR) particles for improvement in compatibility with the binder. The mechanism of Cold Plasma Effect (CPE) were investigated by studying the rheological and chemical properties of the matrix. In terms of the rheological characterization by Dynamic Shear Rheometer (DSR) test, the CR Effect (CRE) on binder has been identified as the primary Particle Effect (PE) and the secondary Interaction Effect (IE). Similarly, CPE was also found to be composed by the PE and IE portions, and the PE portion still played a dominant role. Furthermore, CPE together with its PE and IE portion constantly increased with an increase in CR content, while no significant tendency was found between the varying size and CPE on rheology. With respect to the chemical characterization by Gel Permeation Chromatography (GPC) test, the results indicated that the cold plasma treatment significantly resulted in an increase in the Large Molecular Size (LMS) fraction of binder and this effect was more evident as the CR content was increased and the size was reduced. Furthermore, the regression analysis reported a strong correlation between the above corresponding changes in rheology and chemistry of binders caused by cold plasma treatment, with the removal of CR particles.

Angelo Filonzi, University of Texas, Austin
Sang Ki Lee, University of Texas, Austin
Wellington Ferreira, Universidade Federal Rural do Semi-Arido
Ramez Hajj, University of Illinois, Urbana-Champaign
Amit Bhasin, UT Austin: The University of Texas at Austin

Current extraction procedures for asphalt materials require a large amount of material and also the use of a large volume of toxic solvents. To overcome these challenges, a micro-extraction method for extracting and recovering asphalt binder from small amounts of asphalt mix or reclaimed asphalt pavement (RAP) is presented. Sixteen laboratory long term aged mixes were used to extract the binder and evaluate its properties, using both the micro-extraction and conventional extraction methods. The Bending Beam Rheometer (BBR) and Dynamic Shear Rheometer (DSR) with the 4 mm parallel plate geometry were used to determine the low temperature properties of the extracted materials. The DSR was used with samples obtained using the conventional extraction method and proposed micro-extraction method. Low temperature properties from the three different procedures (conventional extraction with BBR, conventional extraction with DSR, and micro-extraction with DSR) were compared. Results indicate that the 4 mm plate method is a viable surrogate to measure low temperature properties in lieu of the BBR for recovered and recycled materials. The combined use of micro-extraction and 4 mm parallel plate geometry is a viable technique for extracting binder from small amounts of asphalt materials, and validate previous work done with the 4 mm plate. The combined micro-extraction and 4 mm method was used to demonstrate the high variability (up to 12 ºC low continuous grade) among different RAP stockpiles collected from across the state of Texas.

Saqib Gulzar, North Carolina State University
B. Underwood, NCSU: North Carolina State University

Agencies have been increasing their use of polymer modified asphalt binders in recent years to address performance issues and lengthen the useful life of their pavements. When deployed, these materials likely experience strain levels exceeding their linear viscoelastic (LVE) limits. The same situation exists in non-polymer modified asphalt binders as well, but the effects may be more pronounced in polymer modified systems due to their bi-phasic nature. In this study, terminally blended crumb rubber (CR-TB) modified asphalt is studied to understand and quantify the nonlinear viscoelastic response under large strains. These binders are extensively used in pavements subjected to high vehicular loads and extreme climatic conditions. The current standard characterization techniques are based on LVE response using small amplitude oscillatory shear rheology only and do not consider the behavior of binders under large strains. In this study, large amplitude oscillatory shear (LAOS) rheology is used as a framework to more thoroughly investigate the complete response of the CR-TB modified asphalt binder under large strains at 30°C, 40°C, 50°C and 60°C at the frequencies of 0.1, 1, and 5 Hz. The LAOS response is analyzed using Fourier-transform rheology and stress decomposition method involving Chebyshev polynomial representation. It is found that nonlinearity manifests greatly in this study material as strain increases and frequencies decrease. The relative nonlinearity increases with increasing strain amplitude and is more significant towards lower end of the tested temperature range. The CR-TB binder shows strain stiffening/softening and shear thinning/thickening behavior depending upon a specific temperature, strain and frequency.

Lu Zhou, Tongji University
Weidong Huang, Tongji University
Chuanqi Yan, Tongji University
Quan Lv, Tongji University

Adhesion and self-healing are two inherent properties of asphalt binder and it would be more consistent with the practical pavement situ if the self-healing behavior is considered when evaluating asphalt binder adhesion performance. In this paper, binder bond strength (BBS) test was applied to evaluate the adhesion and self-healing property of 5 representative modified binders at varying dosages. Fourier transform infrared spectroscopy (FTIR) test was conducted to study the influence of asphalt binder long-chain structure on self-healing behavior. Furthermore, the mixture four-point beam (4PB) fatigue healing test was conducted and correlated with BBS testing results. It was found that linear styrene-butadiene-styrene, high-density polyethylene (HDPE), crumb rubber and terminal blend rubber powder all had a negative effect on the initial asphalt adhesion strength while only gilsonite could enhance the initial adhesion. HDPE, crumb rubber and gilsonite at proper dosages could improve the asphalt self-healing property. 8% HDPE-modified binder even showed a healing rate of 102%, which was believed to be attributed to its long-chain molecular structure. FTIR test indicated that self-healing and the aggregate selective adsorption of long-chain molecules were highly correlated. Furthermore, the strong correlation between binder healing property and mixture healing property was validated.

Zhe Zeng, North Carolina State University
B. Underwood, NCSU: North Carolina State University
Cassie Castorena, NCSU: North Carolina State University

Currently, the bending beam rheometer (BBR) test is the standard method for evaluating the low temperature Superpave performance grade (PG) of asphalt binders. Despite its use, there are some limitations with the BBR test in relation to other Superpave binder tests with respect to the amount of asphalt binder that is needed for test specimens, the relative difficulty in preparing specimens, and the overall testing efficiency. On the contrary, the dynamic shear rheometer (DSR) is an efficient test method that is used by agencies and contractors to determine the performance grade at intermediate and high temperatures. In this study, DSR temperature and frequency sweep tests using the 8 mm parallel plate geometry is proposed as an alternative to the BBR for the determination of the low temperature PG. The method takes advantage of the time temperature superposition principle and linear viscoelastic interconversion to predict the BBR creep stiffness and m-values at 60 s from the modulus and phase angle measured by the DSR at intermediate temperatures. Two conversion methods were used to verify the ability to predict BBR properties using DSR testing at intermediate temperatures using 45 binders of diverse PG. The DSR-based method yields good agreement with measured BBR data. On average, the continuous low temperature PG predicted using the DSR method is within 2.7°C of that measured using the BBR.

Naipeng Tang, Chongqing Jiaotong University
Ruikun Dong, Chongqing University

In the production of terminal blend (TB) rubberized asphalt binder, crumb rubber is digested into asphalt matrix. Meanwhile, to meet the performance grade criteria, TB hybrid binder is produced through further addition of polymers and crosslinking agent. The effect of crosslinking agent sulfur on aging characteristics of TB hybrid binder is not clear yet. The present study aims to investigate the crosslinking agent sulfur on aging characteristics of TB hybrid binder. Fourier transform infrared (FTIR) spectroscopy, Gel permeation chromatography (GPC) and rheological master curve were used to capture the evolution of asphalt binders with aging. The results indicate that crosslinking agent sulfur does not affect the carbonyl growth of TB hybrid binders in this laboratory aging study. However, for rheological compatible TB hybrid binders, 0.3% or 0.4% sulfur can improve the resistance to polymer degradation. In addition, sulfur can improve elastic response of TB hybrid binder at low frequency domain (high temperature) even for PAV aged binder.

Faisal Kabir, Arizona State University
Elham Fini, Arizona State University

The application of crumb rubber in asphalt has a positive environmental and economic impact. To realize the advantages of introducing rubber to asphalt, the interaction between rubber and asphalt needs to be ensured. There have been many studies to ensure rubber is properly treated, cured, and swelled via various physical and mechanical treatments. However, such methods increase the associated cost of rubberized asphalt and are only partially effective at preventing segregation of rubber from the asphalt. This study examines the merits of surface activation of rubber using various bio-oils. Selected plant-based bio-molecules are adsorbed onto the surface of rubber particles to facilitate rubber's interaction with asphalt binder. Five surface‑activated rubbers were prepared using waste vegetable oil, wood pellet, miscanthus, corn stover, and castor oil. A hybrid method combining microwave irradiation and bio-chemical treatment was used in an attempt to graft bio-molecules onto the surface of the rubber. The effectiveness of each oil was examined by measuring the chemisorption of the bio-oil, followed by examining the surface-activated rubber's tendency to separate from bitumen. In addition, the percent recovery and moisture susceptibility of each samples was studied to evaluate the effect that each surface-activated rubber imparts to asphalt. While all bio-oils were able to improve the percent recovery to some extent, some did not adsorb well. Overall, wood-based bio-oil was shown to adsorb quite well to the rubber and reduce its tendency to separation by 82%. The percent recovery was nearly doubled (from 13% to 24%) when wood-based bio-oil molecules were grafted onto the surface of rubber. The wet/dry peak tensile force ratio was found to be 89%, indicating acceptable resistance to moisture damage. FTIR studies showed the peak between 1540-1580 cm‑1 was eliminated as a result of microwave irradiation, indicating breakage of C=C bonds. In the case of treating rubber with wood-based oil, a new peak appeared at 1206 cm-1 associated with C-N stretching, indicating successful grafting of bio-oil to rubber. Among all the scenarios, asphalt containing rubber particles activated with miscanthus bio-oil showed the highest reduction (32%) in tensile peak strength, indicating the most vulnerability to moisture damage.

Mayzan Isied, North Carolina State University
Mena Souliman, University of Texas, Tyler

Crumb rubber surface activation and pretreatment are promising newly introduced methods for asphalt rubber production. Reacted and Activated Rubber (RAR) is an elastomeric asphalt extender produced by the hot blending and activation of crumb rubber with asphalt and Activated Mineral Binder Stabilizer (AMBS). Besides its ability in enhancing the performance of asphaltic mixtures, RARs dry granulate industrial form enabled its addition directly into the mixture utilizing pug mill or the dryer drum with very minimal to no modification required on the plant level. This study aims to evaluate the rotational viscosity of RAR modified binders. Three different Performance Graded (PG) asphalt binders modified by ten dosages of RAR were tested and evaluated under this study. Sixty-six samples that generated more than three thousand viscosity data points were utilized in binder viscosity evaluation. The study concluded that RAR addition decreased binder temperature susceptibility in considerable amounts when compared to the virgin binders. Furthermore, it was demonstrated that the testing shearing rate had a significant effect on the measured viscosity values for binders modified with high RAR content.

Mayzan Isied, North Carolina State University
Mena Souliman, University of Texas, Tyler

Crumb rubber surface activation and pretreatment are some of the promising newly introduced methods for asphalt rubber production. Reacted and Activated Rubber (RAR) is an elastomeric asphalt extender produced by the hot blending and activation of crumb rubber with asphalt and Activated Mineral Binder Stabilizer (AMBS). Besides RARs ability in enhancing the performance of asphaltic mixtures, its dry granulate industrial form enables its addition directly into the mixture utilizing pugmill or the dryer drum with minimal to no modification required on the plant level. This study aims to develop an Artificial Neural Network (ANN) viscosity prediction model for extracting a stand-alone viscosity prediction equation. Three different Performance Graded (PG) asphalt binders modified by ten dosages of RAR were tested and evaluated under this study. Sixty-six samples that generated more than three thousand viscosity data point were utilized in ANN modeling. The developed ANN model as well as the extracted stand-alone viscosity prediction equation had a high value of the coefficient of determination and were statistically valid. Both have the ability to predict the RAR modified binder viscosity as a function of binder grade, temperature, testing shearing rates, and RAR content.

Md Tanvir Ahmed Sarkar, Auburn University
Md Nafiur Rahman, Arizona State University
Mostafa Elseifi, Louisiana State University
Corey Mayeux, Louisiana Department of Transportation and Development
Samuel Cooper, Louisiana Transportation Research Center (LTRC)

An experimental study was conducted to characterize the chemical, molecular, and rheological properties of different asphalt emulsions including a newly introduced tire rubber modified asphalt emulsion.  One tire rubber modified asphalt emulsion (CRS-2TR), two conventional emulsions (CRS-2 and CRS-2P), and one asphalt rubber binder (AC20-5TR) were evaluated. The differences in functional groups, chemical composition, and molecular weight distribution of the asphalt binders were evaluated by the Saturates, Aromatics, Resins and Asphaltenes (SARA) fractionation test, High-Pressure Gel Permeation Chromatography (HP-GPC), and Fourier Transform Infrared Spectroscopy (FTIR) test, respectively. Superpave Performance Grade (PG), Surface Performance Grade (SPG), and the Multiple Stress Creep Recovery (MSCR) test were also conducted to evaluate the rheological and rutting susceptibility of the binder residues. Chemical and molecular characterization test results indicated that the tire rubber modified emulsion had lower carbonyl indices (Ic=o) and colloidal instability indices (Ic) as compared to the other conventional emulsions, indicating higher resistance to aging. HP-GPC test results showed that CRS-2TR and AC20-5TR had similar High-Molecular Weight (HMW) content compared to that of conventional asphalt emulsions indicating similar susceptibility to brittleness with age. On the other hand, rheological investigation results showed that the performance of CRS-2TR can be comparable with CRS-2P and is expected to perform better than CRS-2. In addition, moisture susceptibility of the binder residues from the Bitumen Bond Strength (BBS) test showed that CRS-2TR had higher pull-off tensile strength in both dry and wet conditions as compared to CRS-2 and had statistically equivalent performance results as compared to CRS-2P.

Guilian Zou, South China University of Technology
Xiaoyan Xu, South China University of Technology
Jianxin Li, Petrochina Fuel Oil Company Limited Research Institute
Huayang Yu, South China University of Technology
Changjun Wang, Petrochina Fuel Oil Company Limited Research Institute
Xinhai Liu, Guangdong Hualu Traffic Technology Co., Ltd.

As asphalt binders greatly influence the engineering performance of the gussasphalt concrete for bridge deck pavement, selecting the right asphalt is a critical procedure for mixture design. In this study, five different combinations of asphalt binder potentially used in the project “Hong Kong-Zhuhai-Macao Bridge” were prepared and tested, namely 75% Pen20/40 ordinary asphalt + 25% TLA, 40% Pen20/40 asphalt + 60% TLA, 30% Pen60/70 asphalt + 70% TLA, SBS modified asphalt, and Pen15/25 hard asphalt. To meet the strict requirements of quality control, a new Guss-Mastic Asphalt (GMA) system was developed. Three key indexes, Lueer fluidity, impact toughness and dynamic stability, were used for GMA design and construction quality control. Test results shown that the fluidity of the GMA mixtures was significantly affected by the shear thinning phenomenon. After mixing for 3 hours, the Lueer value of all GMA mixtures met the requirements of pouring construction. The deformation resistance of GMA with 40% Pen20/40 + 60% TLA was the strongest, followed by those with 30% Pen60/70 + 70% TLA, Pen15/25 hard asphalt and 75% Pen20/40 + 25% TLA. Moreover, it is found that the influence of mixing duration on GMA with SBS modified asphalt were different to other prepared mixtures. This is ascribed to the degradation of SBS during the blending process at elevated temperature. Finally, the blended asphalt (30% Pen60/70 + 70% TLA) has been selected to be applied in the project of Hong Kong-Zhuhai-Macao Bridge.

Mostafa AboHashema, Fayoum University
Ragab Mousa, Cairo University
Hilal Al Abdel Salam, Ministry of Transport and Communications, Oman

The evolution of Superpave system throughout the world makes the identification of bitumen Performance Grade (PG) a key requirement for Superpave mix design and an important step for the implementation of Superpave system. This paper presents the analysis of meteorological data in Oman, collected at 16 weather stations covering 24 years, to identify the proper Superpave PG grades. Pavement temperatures were predicted as a function of air temperature and other parameters using LTTP models, and asphalt binder PG grades were determined at 95% and 98% reliability levels. A PG contour map was also developed to facilitate the selection of the PG grade at any location in Oman. PG grades of the 98% reliability map are PG 64-10, 70-10, 76-10, and 82-10. These grades checked against traffic speed and load conditions. Design axle loads were estimated and presented on another map to show which roads would need an adjustment in the PG grade. The penetration grade 60/70, currently used in one project in Oman, was tested for meeting the required Superpave grade performance (PG 76-10), which is identified for this project location. Test results indicated that mixing 1.5% of Styrene Butadiene Styrene (SBS) polymer with 60/70 bitumen using high shear mixer for one hour has resulted in a polymer modified bitumen (PMB) satisfying the requirements of PG 76-10. The general findings of this paper are considered an important step towards the implementation of the Superpave system in Oman.

Zhibin Ren, Harbin Institute of Technology
Jiangmiao Yu, South China University of Technology
Zeyu Zhang, Rheinisch-Westfalische Technische Hochschule Aachen
Feng Guo, University of South Carolina
Huayang Yu, South China University of Technology

Different polymers have been used to modify virgin asphalt towards enhanced engineering performance. Although certain chemical similarities exist between polymers and asphalt fractions, phase separation always happen within the polymer modified asphalt (PMA) binders due to the density difference, especially during long-term storage at elevated temperaute. The storage stability concern has limited the widespread application of PMA. So far, very few practical approaches have been proposed for the improvement of storage stability. This study aims to evaluate the feasibly of using nano-montmorillonite (nanoclay) to address the workability concern of PMA. To achieve this goal, three types of nanoclay and three kinds of modifiers, i.e. crumb rubber (CRM), styrene-butadiene-rubber (SBR) and styrene–butadiene-styrene (SBS), were selected to prepare nanoclay-polymer modified asphalts (NPMA). A comprehensive performance evaluation on storage stability and rheological properties was conducted. Among three polymer modifiers, CRM resulted in superior fatigue and low-temperature cracking resistance in comparison with the other two modifiers. Nevertheless, SBR and SBS modified binders exhibited much better workability than CRM modified binder. The incorporation of nanoclay exhibited remarkable effect on enhancing the storage stability of CRM modified binder, but limited positive effect for the SBR and SBS modified binders. Among the different types of nanoclay, the purring montmorillonite with Hydroxyl organic ammonium, which has strongest hydrophilic property and smallest layer gap, performed the best on enhancing storage stability of polymer modified asphalt. This paper suggests that nano-montmorillonite is a promising modifier to alleviate the storage stability concern for asphalt with polymer modifers.

Xuejuan Cao, Chongqing Jiaotong University
Mei Deng, Chongqing Jiaotong University
Yongjie Ding, Chongqing Jiaotong University
Boming Tang, Chongqing Jiaotong University
Xiaoyu Yang, Chongqing Jiaotong University
Bailin Shan, Chongqing Jiaotong University

The application of photocatalysts on pavement engineering to degrade automobile exhaust have been a hot topic for researchers. However, the effect of photocatalysts on pavement materials have not been fully investigated. The primary purpose of this study is to investigate the effect of titanium dioxide (TiO2) photocatalysts on the chemical structure and properties of asphalt by laboratory experiments and molecular dynamics (MD) simulation. The performance test indicated that the physical properties of asphalt modified by TiO2 changed more significantly compared with calcium carbonate (CaCO3) and silica (SiO2) which might due to the smaller partial size of TiO2. The atomic force microscopy (AFM) test suggested that the addition of TiO2 resulted in a smoother asphalt surface and the vanish of bee structure. The Fourier infrared spectrum (FI-IR) analysis demonstrated that the addition of TiO2 accelerate the aging process of asphalt and might affect the performance of asphalt pavement. The results of MD simulation suggested a more significant interaction exited TiO2 and asphalt compared with CaCO3 and SiO2, which resulted in a tighter asphalt molecule and smaller free volume fraction (FFV) for asphaltic model.

Rituraj Patel, Indian Institute of Technology, Tirupati
Vinay Nanjegowda, Indian Institute of Technology, Tirupati
Jagadeesh Mahimaluru, Indian Institute of Technology, Tirupati
Krishna Prapoorna Biligiri, Indian Institute of Technology, Tirupati

The major objective of this study was to develop a foaming additive, and characterize its effect on virgin binder that would ascertain the modifier as a potential warm-mix asphalt (WMA) additive. The foaming agent was prepared using the following reagents via hydrothermal reaction: sodium aluminate, tetraethyl ammonium hydroxide, montmorillonite, and water (STEAM). Two STEAM additive variants from the selected compounds with different molar ratios were synthesized, and later blended with a viscosity grade VG-30 virgin binder. Infrared spectroscopy on STEAM modifier revealed the presence of specific vibrational bands that are typical of zeolite materials. The STEAM-modified asphalt binders exhibited a reduction of mixing and compaction temperatures by around 4-6 °C compared to the virgin binder. Further, the upper performance grade (PG) temperature of STEAM-modified binders had an increment of 6 °C compared to VG-30 (PG76-XX) while the rutting parameter (|G*|/sinδ) at 64 °C ranged between 6 and 8 kPa, which was about 60-70% higher than virgin binder (|G*|/sinδ = 4.75 kPa). Furthermore, the introduction of STEAM additives reduced the non-recoverable creep compliance Jnr and increased recovery R of the virgin binder by 31.89-62.80% and 0.13-2.68%, respectively. Overall, the STEAM additives were found to be promising asphalt foaming candidates due to their effectiveness in reducing mixing and compaction temperatures, while also augmenting stiffness and elastic parameters of the base binder. Overall, the characteristic viability of the STEAM synthesis technique will definitely promote avenues to create novel and possibly cost-effective foaming additives as alternatives to existing WMA agents.

Eslam Deef-Allah, Missouri University of Science and Technology
Magdy Abdelrahman, Missouri University of Science and Technology
Yanxiao Li, Missouri University of Science and Technology
Chenglin Wu, Missouri University of Science and Technology

Crumb rubber modifier (CRM) is considered one of the most commonly used modifiers that enhances the rheological properties of asphalt binders. Optimizing the interaction process between CRM and asphalt binder to enhance the asphalt binder’s elasticity without additional additives is the main purpose of the article. Rheological and Nano properties were measured in this article for neat asphalt and crumb rubber modified asphalt (CRMA) binders. One interaction temperature (190 °C), one interaction speed (50 Hz), and different interaction times (0.5-, 1-, 2-, 4-, and 8-hr) were used. Thermogravimetric analysis (TGA) was performed on CRM particles before and after their interaction with asphalt binder after different interaction times. The CRMA binders that interacted for the entire 4-hr and/or 8-hr interaction times had significantly enhanced properties especially the elasticity, as compared to the neat asphalt binder. The highest Young’s modulus and adhesion force values for CRMA binders were obtained for samples that interacted at 190°C and 50 Hz for 4-hr and/or 8-hr showing the highest CRM dissolution percentage by the dissolution and TGA testing. At these interaction conditions, more CRM components were released into the asphalt binder liquid phase, which were detected by observing Fourier-transform infrared (FTIR) peaks at 966 cm -1 for polypropylene (PB) and 699 cm -1 for polystyrene (PS).

David Jones, University of California, Davis
Hashim Rizvi, University of California, Davis
Yanlong Liang, Granite Construction
Mohamed Alavi, University of Tehran

Testing asphalt rubber (AR) binders, especially those containing relatively large rubber particles, can be challenging. The standard Rolling Thin-film Oven (RTFO) test was originally developed to simulate aging during mix production, silo storage, transport, placement, and compaction. The procedure is based on typical parameters associated with conventional mixes produced with unmodified binders, and are not necessarily representative of the parameters associated with mixes produced with AR binders. AR mixes are produced at between 190°C and 220°C, considerably higher than conventional mixes. Consequently, RTFO testing temperatures need to be increased to reflect this. The sample size also needs to be increased to 45g to account for the presence of the rubber particles (18 to 22% by weight of the binder in California) and to ensure that the same quantity of actual bitumen is tested (i.e., 35g in the standard test). Given the higher viscosity of the binder, preheating of the RTFO bottles is also proposed to facilitate pouring and to improve initial coating. Testing to assess the implications of these changes was carried out by comparing the results of tests following the standard and proposed procedures. Experiments were run on laboratory- and field-produced binders with different rubber particle sizes, with and without extender oil. High temperature testing was conducted using a dynamic shear rheometer with concentric cylinder geometry. Chemical analyses were conducted using a Fourier Transform Infra-Red spectroscope. Results showed that the proposed testing modifications are likely to be more representative of actual field conditions than the standard procedures.

M Morshed, Arkansas State University
Zahid Hossain, Arkansas State University
Dao-Hao Chen, Texas A&M University, College Station
Gaylon Baumgardner, Ergon Energy

For characterizing the polymer modified binders, different state Departments of Transportation (DOTs) use different laborious and empirical Performance Grade (PG) Plus test methods such as Elastic Recovery (ER) and tenacity. However, the effects of the elastomeric and/or plastomeric polymers are not accurately identified through these conventional tests. Thus, the main research goal of this study is to recommend alternative test method(s), which can possibly be pursued by using a commonly available device, a Dynamic Shear Rheometer (DSR). In addition to Multiple Stress Creep Recovery (MSCR) and Elastic Recovery using a DSR (ER-DSR) as possible alternative of the ER test, the DSR-based Linear Amplitude Sweep (LAS) and Binder Yield Energy Test (BYET) were explored to evaluate the fatigue resistance of asphalt binders. Two types of polymer modified binders from ten sources, which are approved by the ARDOT and TxDOT were evaluated in this study. Test results and analyses suggest that without risking the suppliers or users, the ER-DSR test can be a good replacement of the ER test method. A new ER-DSR binder grading system has been proposed. The MSCR test can also be an alternative of the ER test method. The LAS test results were used to determine number of cycles to failure at 2.5% strain. A viscoelastic continuum damage (VECD) model was developed for characterizing fatigue cracking. The BYET results were found to be related to fatigue damage.

Zhaoxing Xie, Louisiana Department of Transportation and Development
Ayman Ali, Rowan University
Yusuf Mehta, Rowan University
Ahmed Saidi, Rowan University
Sai Venkata Gnaneswari Chitikela, Indian Institute of Technology-Tirupati
Neirouz Bouhrira, Rowan University
Wade Lein, U.S. Army Engineer Research and Development Center
Christopher DeCarlo, U.S. Army Engineer Research and Development Center

Cracking is the main distress in asphalt pavement in cold region (such as the arctic and subarctic regions) as the climate in these areas is severe in winter. While soft asphalt binders (such as PG 58-28 and PG 52-34) are used in the cold regions, asphalt pavements can still exhibited premature cracking failures. One of the approaches to solve this issue is to modify binders using additives. It is not clear, however, which additives can significantly improve the cracking resistance of binder, especially at low temperatures. Therefore, there is a need to find potential additives resulting in improved resistance to cracking because of extreme low temperatures experienced in cold regions. In this study, five additives (Nano TiO 2 and SiO 2 , Styrene-butadiene-styrene (SBS), Ground tire rubber (GTR), and bio-based softening agent (SA)) were applied at various dosages with two soft base binders (PG 52-34 and PG 64E-40). Performance properties of modified binders were evaluated using the Dynamic Shear Rheometer (DSR), standard Bending Beam Rheometer (BBR), BBR strength, Linear Amplitude Sweep (LAS), and time sweep tests. The testing results indicated that the combination of 7% softening agent and 7.5% SBS exhibited the highest improvement in the resistance to thermal cracking and fatigue cracking. Meanwhile, this combination also resulted in two performance grade bump at high temperature. Based on the laboratory testing results, the combination of softening agent and SBS could be potential additives to create high performance binders for cold region.

Akshay Gundla, Arizona State University
Ramadan Salim, Arizona State University
B. Underwood, NCSU: North Carolina State University
Kamil Kaloush, Arizona State University, Tempe

Over the past 20 years, changes in asphalt binders, the widespread adoption of polymer modified asphalts, and the need to bump asphalt binder grades to consider traffic conditions exposed the gaps in the AASHTO M 320 specification, and subsequently led to AASHTO M332 specification. The state of Arizona initiated an experimental study to explore the possibility of adopting AASHTO M 332 into its binder specifications. In this paper, the specific challenges, technical implications of some key differences in the current Arizona standard are compared with the AASHTO M 332 standard and the approach taken to overcome the differences are explored and documented. Some of the key issues include the shortcomings of the Jnr difference parameter, uncertainty of the PAV temperature to be used, effect on |G*|sinδ parameter, and the prospective distribution of asphalt binder grades if the new specification is adopted. Overall, AASHTO M 332 specification is promising for state of Arizona with minor changes recommended to prevent changes in binder formulations and influx of asphalt binder’s inferior to what currently available.    Keywords: AASHTO M 332, Asphalt Binder Specifications, Polymer Modified Asphalt Binders, Jnr Difference.

Md Mehedi Hasan, University of New Mexico
Rafiqul A. Tarefder, University of New Mexico

Past studies have shown that the SBS polymer modified binders perform reasonably well against rutting and fatigue cracking. However, the effects of SBS modification on their low-temperature cracking performances are not well understood. In this study, thermo-viscoelastic analyses are performed on laboratory tested data to determine the effects of SBS modification on low-temperature cracking performance of a binder. One base binder was mixed with SBS polymer at three different percentages in laboratory. Next base binder and three modified binders were tested using bending beam rheometer (BBR) and direct tension (DT) devices. Using the test results, thermo-viscoelastic analyses were performed to understand four sub-processes of a low-temperature cracking, namely, stress generation during thermal contraction, stress relaxation under viscoelasticity, stress accumulation during continuous temperature drop, and failure due to excessive stress accumulation. The thermo-viscoelastic analysis illustrates that the SBS modification reduces the magnitude of stress generation, increases the stress relaxation rate, decelerates the stress accumulation rate, and delays the failure. As a result, the SBS modification lowers down the binder critical temperature and improves overall low-temperature performances of SBS modified binders through reduction in creep stiffness and increase in tensile strength. To validate the binder results at mixture level, thermal stress restrained specimen test (TSRST) was performed on corresponding asphalt concrete samples. The mixture performance from the TSRST agrees with the binder performance from the thermo-viscoelastic analyses.

Ahmed Hemida, Missouri University of Science and Technology
Magdy Abdelrahman, Missouri University of Science and Technology

This research looks at a partial replacement of asphalt-rubber (AR) binder by Guayule Resin (BGR), at least to compensate the original asphalt (AC) high-temperature performance. In particular, storage stability and phase separation (essential parameters affected by modified-binder storage) were addressed in this regard. AR-BGRs were compared to their corresponding ARs, to judge the BGR contribution. The binder whole matrix (WM) storage stability relied on the viscosity, density, and CRM dissolution. Measurements related to these parameters and storage stability were taken. Thermogravimetric analysis (TGA) was used to analyze CRM dissolution. Comparisons between WMs vs. liquid phases (LPs) were established as could show the variation between their storage stability and LP separation. Rheological analysis by master curves was provided for top and bottom fractions of WMs and LPs to judge the effect of remaining CRM (residue) and LP separation on the behavior. TGA and Fourier-transform infrared spectroscopy (FTIR) were utilized to verify the LP separation analysis. Outcomes showed that AR-BGR WMs yielded lower storage stability compared to ARs. The authors see that the viscosity difference between AC and BGR was the crucial reason. Nevertheless, perfect storage stability and no LP separation were observed with either AR-BGRs or ARs as proven by rheological analysis and verified by TGA and FTIR analyses for selected binder fractions. Accordingly, the study claimed BGR (PG52) could replace a portion of AR on the LP scale to at least compensate the original asphalt (PG64) performance (e.g., LP of 75%AR (including 20%CRM by wt. of AC) plus 25%BGR).

Pouria Hajikarimi, Qazvin Islamic Azad University
Mohammad Ali Notani, Purdue University
Reyhaneh Rahbar Rastegar, Purdue University
John Haddock, Purdue University

This study proposes an experimental-numerical approach to determine the Poisson’s ratio of asphalt binders at low temperatures. According to this method, the time-dependent Poisson’s ratio of asphalt binder can be obtained using a recursive numerical approach based on rheological and mechanical data acquired from bending beam and dynamic shear rheometer tests. Since asphalt binder is a viscoelastic material, this approach considers the loading frequency and temperature effects on asphalt binder response. For an elastic medium, Poisson’s ratio is a direct relation between tension/compression/bending and shear modulus. This concept can be applied to asphalt binder in which the tension/compression/bending and shear modulus are a function of time and frequency. Therefore, an analytical approach was developed to determine relaxation shear and relaxation bending moduli from standard rheometer test data at various low test temperatures. The findings reveal the proposed method can successfully determine time-dependent asphalt binder Poisson’s ratios at low temperatures.

Mehdi Zadshir, Columbia University
Xiaokong Yu, Columbia University
Irene Nigro, Universita degli Studi di Perugia
Huiming Yin, Columbia University

This paper explores the opportunities of incorporating carbon nanotubes (CNT) as a modifier in asphalt binder to improve binder’s thermal properties using a foaming method. The foaming process has many advantages such as better coating of aggregates, reduction in the viscosity, mixing temperature, and accordingly lowering energy consumption. However, no previous study has been done on using the foaming method to disperse CNT modifiers in asphalt binder. In this work, two solvents of ethanol and a surfactant are used to disperse the multi-walled carbon nanotubes. Different percentages of 0, 3, and 6% wt. of the carbon nanotube solution is prepared. Then, the CNT solution is used to foam a PG 64-22 asphalt binder via an in-house foaming machine. Initial assessment of the two CNT solutions via images from scanning electron microscopy showed that while ethanol caused the nanotubes to agglomerate, a more homogenous dispersion of the CNTs was achieved using the surfactant solution. Complex moduli of the asphalt binder did not significantly change after addition of the CNTs. Results showed that the specific heat capacity of the foamed samples was smaller than the neat binder, whereas the glass transition temperature of the foamed samples slightly shifted to lower temperature as compared to that of the neat binder. It is observed that the thermal conductivity of the 6% CNT sample (0.24% wt. in asphalt) was improved by two fold compared with the foamed unmodified asphalt. These findings approve the potential of using carbon nanotubes in binder for future applications.