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Asphalt emulsions and cutbacks are mainly used for surface preservation treatments and as bonding layer during pavement construction. Cutback and emulsion residues are routinely evaluated to ensure specification compliance for quality control and assurance purposes. The current test methods for residue recovery of asphalt emulsions and cutbacks are resource intensive, have a low throughput, and require distillation apparatus with a large lab footprint. This study developed two separate test methods that are simple and repeatable for emulsion and cutback residue recovery using a vacuum oven with the ultimate goal that these tests can be used for routine testing. These methods recover small quantity of the residue that is adequate to perform one test with 25 mm plate using dynamic shear rheometer (DSR). This study examines the repeatability of the new method by (1) using a variety of different grades obtained from different suppliers for both cutbacks and emulsions; and (2) participation of two laboratories with different brands of equipment. The mass loss during the residue recovery and the DSR parameter G*/sinδ were used to examine repeatability. The results show that the test methods developed are repeatable between the replicates and between the two participating research laboratories. [ABSTRACT FROM AUTHOR]

Developing new and efficient methods to simulate the aging of asphalt binders and mixtures continues to be an important area of research for the asphalt community around the world. Temperatures exceeding pavement service temperatures are typically used to accelerate and simulate long-term aging in laboratory settings. However, it is unclear whether the use of such higher temperatures would have an adverse influence when simulating the aging of typical polymer modified binders. Specifically, the influence of thermal degradation of polymers at elevated temperatures and the resulting deterioration of the aging-related properties of the asphalt binder could be unrealistic when considering polymer degradation in the field. This study explores the use of an oxidative and nonoxidative environment to deconvolute the different aging characteristics of unmodified and styrene butadiene styrene (SBS) modified asphalt binders. Six binders, including two unmodified binders and four SBS-modified binders with two polymer contents (3% and 4.5% binder weight), were aged in two different aging conditions, i.e., under an air blanket and nitrogen blanket, at a temperature of 100°C. The resulting changes in material behavior were investigated using thin film poker-chip testing, dynamic shear rheometer testing, and Fourier transform infrared spectroscopy. Overall, the results from this investigation suggest that long-term aging of asphalt binders or mixtures conducted using temperatures not exceeding 100°C does not result in any significant degradation of polymers in modified asphalt binders. [ABSTRACT FROM AUTHOR]

There is limited information on the characteristics and performance of paving mixtures made with 100% bio-binders. Moisture damage resistance of this type of mixture is a concern since the components of the bio-binder may have a higher affinity with water than asphalt binders. In this context, this paper presents a moisture damage susceptibility evaluation of wood-based bio-binder-aggregate interfaces in terms of energy parameters calculated from surface free energy components. The bio-binder was used as a total replacement for asphalt binders, and the responses were compared to a neat- and a highly modified-asphalt binder, considering different aggregate sources. Results suggest the bio-binder has similar moisture damage resistance to the neat asphalt binder and higher resistance than the highly modified asphalt binder, providing a first indication for the potential use of this bio-binder as 100% asphalt binder replacement. However, additional research is still required to validate these findings at the mixture level. [ABSTRACT FROM AUTHOR]

There has been growing interest in the use of polyethylene (PE) in the asphalt industry as one way to mitigate the adverse environmental impact of waste plastics. The main goal of this study was to evaluate the potential use of low-density polyethylene (LDPE) as a modifier for use in asphalt mixtures. In addition, this study also explored the potential synergistic impact of using elastomeric polymers typically used with asphalt binders as a co-modifier along with LDPE. This study was based on a comprehensive evaluation of the rheological and performance-related properties of asphalt binder from two very different sources as well as asphalt mixtures produced using a subset of these binders. Typical methods that are standard practice in the industry and methods that are being developed to evaluate the performance metrics of asphalt binders and mixtures were used. The two chemically diverse base binders and redundancy in the evaluation process were introduced to ensure a more robust evaluation of the expected properties. Overall, results demonstrate that although the impact of LDPE on the expected performance of the binder may vary with the source of binder, LDPE can be successfully used to enhance the properties of the asphalt binder in most respects, particularly with the synergistic use of a conventional elastomeric modifier. [ABSTRACT FROM AUTHOR]

It has become clear over the last few years with an increasing use of asphalt binder modifiers, additives and recycled materials that there is a need to develop methods and concomitant parameters that can evaluate the full tensile behaviour including nonlinearity and damage resistance of asphalt binders. This study presents a simple, repeatable test method to examine the tensile strength and ductility of asphalt binders using a poker-chip geometry. The poker-chip geometry has previously been used to induce a realistic stress state in asphalt binder similar to that exerted on asphalt binder confined between two aggregates. This study develops and presents a new simplified procedure for specimen fabrication and preparation using the poker-chip geometry. A set of nearly 100 asphalt binders including different aging conditions, different levels and types of modification, and recycled asphalt binders and contents were examined using the proposed approach. The results indicate that a ductility parameter obtained using the test is highly repeatable with an average coefficient of variation of 9%. In addition, the test was able to distinguish between different levels of modification and was sensitive to aging, recycled binder ratio and modifier type.v [ABSTRACT FROM AUTHOR]

The use of reclaimed asphalt pavement (RAP) is believed to contribute significantly towards overall energy conservation and environmental protection efforts. However, the recycling of aged binder from RAP requires a fundamental understanding of the interaction mechanism between such rejuvenators with recycled and unmodified binders. This study quantitatively investigated the impact of such agents in combination with the aging-rejuvenation process and other binder modifiers (SBS, crumb rubber, and a high viscosity modifier) on the fractional composition, rheology, and colloidal structural stability of asphalt binders. Based on these results, a rejuvenation index (RI) was proposed to quantitatively evaluate the rejuvenation of aged asphalt binder. Aging increased the proportion of resins and asphaltenes of asphalt binders which resulted in the decrease of its rheological properties. After the addition of the rejuvenators, the complex modulus of all aged binders were reduced. Certain rejuvenators transformed up to 5 percentage points of asphaltenes into other fractions. The aromatic oil-based rejuvenator showed the best rejuvenation of unmodified asphalt binder, but theRI was only 0.33. Overall, the results implied that rejuvenation of asphalt binders is a complex topic and further studies should be conducted to correlate the rheological behaviour with rejuvenation mechanisms beyond chemical fractions. [ABSTRACT FROM AUTHOR]

We observed and analysed the early stages of formation and growth of instabilities in binders that lead to crack formation. A monotonic mechanical strain was applied to a thin, confined film of binder between two transparent plates; meanwhile, the bulk of the binder was observed using dark field microscopy to capture its behaviour as the strain increased. During the application, the formation of small cavities that rapidly grew was observed, which corresponded with notable points on a similar test that measured the load in the specimen. A three-stage model is used to describe the nucleation of the first cavity, of subsequent cavities and the growth of existing cavities that closely track the engineering stress–strain behaviour. In addition, it was observed that a cavity forms from a single microstructural feature, but not every feature forms a cavity. A theoretical model for this formation is presented. The growth of these cavities and their choice of nucleation sites suggests that although the density and distribution of the microstructure may not be critical to the formation of cavities that lead to failure, the presence and material properties of these microstructural entities compared to the matrix may be the factor that dictates damage nucleation. [ABSTRACT FROM AUTHOR]

In recent years, the use of reclaimed asphalt pavement (RAP) in pavement construction has become a common practice in the U.S. Addition of RAP with virgin asphalts alters the properties of base binders, resulting in a different in-service performance. Superpave tests are routinely used to characterise modified asphalt binders even though they are applicable for unmodified binders and cannot capture properties of modified asphalts. Recently, several researchers used Atomic Force Microscopy (AFM) techniques to characterise asphalt binders at an atomic level. In this study, binders from two field RAP samples collected from I-40 and I-30 in Arkansas were recovered using a Rotavapor (AASHTO T 319-08). Different amounts (25, 40, and 60%) of RAP binders were blended with a Performance Grade (PG 64-22) binder. Selected microscale (stiffness) and nanoscale (e.g. morphology and elastic modulus) properties of the blended binders were evaluated in the laboratory through test results obtained from selected Superpave tests and the PeakForce Quantitative Nanomechanical Mapping™ (PFQNM) mode of an AFM, respectively. As expected, the addition of RAP binder with the base binder increased the stiffness, thereby increasing the high PG temperature up to 85 °C for 60% RAP. The micro-structures as well as the nanomechanistic properties of the blended binders were found significantly different from those of the base binder; the elastic modulus of 60% RAP was over 70% higher than that of the base binder. The modulus was found to be correlated with the morphology. The nanoscale properties were in agreement with microscale properties of the tested binders. [ABSTRACT FROM AUTHOR]

Fatigue cracking is a common form of pavement failure and is strongly tied to the properties of the asphalt binder used in the mix. The Superpave grading procedure is currently used in the United States and in other parts of the world to classify and select asphalt binders for the design of asphalt mixtures. The parameter, , in the Superpave grading system is used to control the quality of the binder at intermediate temperatures. It is also used by many as a metric to measure the inherent fatigue cracking resistance of an asphalt binder. It is widely recognised that while this parameter was a significant improvement over previous binder grading and selection methods, it does not accurately measure the inherent fatigue damage resistance of asphalt binders. This paper provides a review of several studies that have attempted to develop methods to measure the fatigue damage resistance of asphalt binders during the last two decades. The studies reviewed in this paper have been classified into four main categories based on the type of test method employed. The four categories include: time sweep performed using the Dynamic Shear Rheometer (DSR), amplitude sweep using the DSR or its variations, ductility-based test methods and strength-based tests. This paper focuses primarily on tests developed in the United States with an emphasis to improve the existing Superpave criteria along with relevant research from other parts of the world. [ABSTRACT FROM AUTHOR]

Asphalt mixtures are engineered and designed by treating the mixture as a two-component composite of the binder and mineral aggregate. Typically, asphalt binder is regarded as a homogeneous ‘glue’ that binds the mineral aggregates. However, there is a strong body of evidence in the literature spanning over five decades that indicates that the asphalt binder can be modelled as a colloid with a distinct microstructure. The introduction of advanced microscopic techniques such as Atomic Force Microscopy has generated a renewed interest in being able to better understand the relationship between the chemical makeup of the asphalt binder, its microstructure and engineering properties. The objective of this paper is to present a preliminary phase field model that was used to model the evolution of microstructure of a mixture comprising four fractions with different polarities, analogous to that of the asphalt binder. This work extends the concepts developed in previous research studies to explain the evolution of damage and self-healing at a micrometre length scale in asphalt binders. Although the model and parameters presented in this paper are not a definitive description of the microstructure evolution in asphalt binders, results show that with additional work on rigorous parameter estimation this methodology can be used as a reasonable approach to better understand the relationship between binder composition and microstructure evolution. [ABSTRACT FROM AUTHOR]

Some researchers have used the fine aggregates matrix (FAM) as a means to evaluate the influence of material properties on the expected changes in the performance of hot mix asphalt (HMA). Based on the most commonly used definition, the FAM is composed of part of the fine aggregates (smaller than 1.18 mm), mineral filler, and asphalt binder. Different studies have used different methods to design such FAM mixes. In this study, the fatigue characteristics of different FAM designs (by varying their maximum aggregate size and binder content) were evaluated and compared to the fatigue characteristics of a corresponding full asphalt mixture. The goal of this exercise was to identify a FAM design that was most similar to the full asphalt mixtures in terms of its damage characteristics. The viscoelastic continuum damage approach was used to make such comparisons. Results show that FAM mixes with a maximum nominal aggregate size (MNS) of 2.00 mm have similar damage evolution trends as that of the full hot mix asphalt with a maximum aggregate size of 12.50 mm. Also, through the results and using a failure criterion based on energy, cyclic tests can be simulated at different loading conditions in order to construct Wöhler curves. The results showed that smaller MNS mixtures present better damage performance for strain levels lower than 500 microstrain. [ABSTRACT FROM AUTHOR]

The use of foamed asphalt binder to produce warm-mix asphalt has increased significantly during the past few years. It is recognized that (1) foaming characteristics of the binder influence the workability of the asphalt mix, and (2) different asphalt binders tend to foam differently with all other factors being the same. The causes for the latter are relatively less explored and is the focus of this paper. The research reproted in this paper investigated the influence of the properties of asphalt binder on its foaming characteristics. A physical model for expansion of asphalt binder foam based on foam physics was used to quantify the effect of water content, temperature, surface tension, and liquid additive (through its effect on surface tension) on the expansion ratio of asphalt binder foam. Analysis of results demonstrates that the bubble size distribution (up to a certain limit) does not directly dictate the maximum expansion ratio of the asphalt binder foam. The analysis also shows that only a fraction of the water added to the binder is effective in creating the foam. The effective water content was strongly correlated with the surface tension of the binder, which was also substantiated by the solubility theory. Surface tension of the asphalt binder was also found to be strongly correlated to the stability of the foam. Foam characteristics of binders modified with additives also demonstrated that stability and expansion of foams can be significantly improved using carefully selected liquid additives. [ABSTRACT FROM AUTHOR]

In this study atomic force microscopy (AFM) creep indentations were performed to extract viscoelastic properties of the different domains (defined as microrheology) observed in bitumen samples from two different sources. The microrheology and geometry obtained using the AFM were used to perform finite element (FE) simulations to study the effect of bitumen microstructure on internal stress distribution. FE analyses suggest that microstructures with varying mechanical properties cause localised stress amplification that can lead to cracking/phase separation. A custom-made loading frame in conjunction with an AFM was used to examine the effects of tensile strain on bitumen microstructure. FE simulation and experimental results show that applying strain resulted in damage/phase separation concentrated in the interstitial zone between neighbouring bee structures, defined as load-induced phase separation. This study suggests that evaluating the bitumen microstructure and microrheology is critical to understanding the mechanisms of damage evolution in bitumen and engineering binders with higher inherent durability. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rate dependent tensile failure/fracture of asphalt binder was investigated. [•] Correspondence principles and VECD model were used to unify rate dependent failure in binders. [•] Fracture by cavitation is observed at high aspect ratios & flow at low aspect ratios. [Copyright &y& Elsevier]

The primary objective of this paper was to investigate the impact of asphalt chemical composition on the microstructure and performance characteristics of asphalt binder. The methods implemented in this study include adsorption–desorption chromatography analysis and a range of atomic force microscopy (AFM) and chemical force microscopy techniques. It was revealed through the study that certain asphalt chemical parameters have a consistent and measureable effect on the asphalt microstructure that is observed with AFM. Particular microstructures that emerged via chemical doping were then discovered to have unique chemical polarity, which explicitly impact durability and performance of asphalt. In fact, a surprising correlation was found between thesaturateschemical parameter and the effects of oxidative aging on asphalt behaviour. The findings from this research directly contribute to the improvement of modelling capability while also creating new prospects for enhancing the performance characteristics and durability of asphalt binder. [ABSTRACT FROM PUBLISHER]

Several different modifiers are increasingly being used to improve the performance of asphalt binders (e.g., polymers) or to promote environmentally friendly technologies (e.g., warm-mix asphalt, ground tire rubber, and organic waste). In such cases, it is important to evaluate the inherent improvement in engineering properties and damage resistance of the asphalt binders while being subjected to a state of stress that is similar to full asphalt mixtures. The first part of the paper presents a review of the literature that investigates the state of stress of the asphalt binder in an asphalt mixture as well as the test methods that have been used to achieve this state of stress experimentally. The second part of the paper presents a test method by which the fatigue-cracking characteristics of four different asphalt binders with similar true temperature grades were evaluated. Composite test specimens were fabricated using asphalt binders and glass beads with a specified gradation. The viscoelastic and fatigue-cracking characteristics of the binders were measured using the glass bead-binder composite specimens in a dynamic shear rheometer at an intermediate temperature. Results were analyzed using viscoelastic continuum damage theory. Damage evolution in the glass bead-binder test specimens used in this study was qualitatively very similar to the damage evolution in full asphalt mixtures using the same binders. [ABSTRACT FROM AUTHOR]

Highlights: [•] We used an environmental room to simulate extended aging of asphalt composites. [•] Fine aggregate mixtures (mortars) compacted after short-term and long-term aging had similar internal microstructures. [•] We examined stiffness and fatigue lifer of WMA and HMA mixtures. [•] We compared fatigue life rankings of short-term and long term aged mixtures. [Copyright &y& Elsevier]

The use of nanoindentation to study asphalt is aimed at understanding the relationship between properties of asphalt binder at various length scales. A combination of atomic force microscopy (AFM) imaging and nanoindentation is used to determine the relaxation moduli of bimodal and trimodal distributions of asphalt microphases to assess differences between macroscale and composite nanoscale viscoelastic behavior. The relaxation modulus values extracted from age-altered phases of the same asphalts provide important relationships between microstructural changes depicted in AFM images and changes in composite viscoelastic properties obtained from the measurements. This paper provides key information regarding asphalt microrheology, which will yield improved input values for asphalt prediction models and enhanced pavement performance. Based on comparison of the composite viscoelastic properties obtained from this study to values obtained at larger length scales, it is apparent that relaxation modulus values decrease as the length scale increases. This finding serves as the basis for ongoing studies by the authors and other researchers in the areas of asphalt nanomodification, chemical mapping, and modeling of nanodamage using AFM. [ABSTRACT FROM AUTHOR]

This paper semiquantitatively evaluates the microrheological properties of asphalt binder using atomic force microscopy. It also presents differences between these properties amongst the various microstructures within an asphalt binder, in addition to the influence of oxidative aging on these properties. Nano-indentation experiments performed within a microgrid of asphalt phases determined micromechanical properties such as stiffness, adhesion, and elastic/plastic behavior. The evaluated materials include asphalts AAB, AAD, and ABD from the Materials Reference Library of the Strategic Highway Research Program, chosen because of variations in crude source, chemical composition, and elemental analysis. Analysis of nano-indentation creep measurements corresponding to phase-separated regions revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging induced substantial microstructural change within these domains, including variations in phase structure, properties, and distribution. The form and extent of these changes, however, were different for each asphalt. Interpretation of data collected from the atomic force microcopy experiments in this study advances understanding of the microstructural composition of asphalt binders and the response of the microstructural phases of the asphalt binder under load, in addition to how the mechanical responses in the phases change with aging. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure of the fine aggregate matrix has a significant influence on the mechanical properties and evolution of damage in an asphalt mixture. This paper presents the findings from a study conducted to identify a quantitative method to characterize the three-dimensional microstructure of the matrix in an asphalt mixture. The influence of binder content, coarse aggregate gradation, and fine aggregate gradation on the microstructure of the matrix was also investigated. Results indicate that for a given aggregate type, binder content and aggregate gradation influence the degree of anisotropy whereas gradation of the coarse aggregate has the most influence on the direction of anisotropy of the asphalt mastic. Addition of asphalt binder or adjustments to the fine aggregate gradation also resulted in a more uniform spatial distribution of the asphalt mastic. [Copyright &y& Elsevier]

Despite the importance of hysteresis of water diffusion in polymeric materials, only limited literature is available on this subject. The FT-IR-ATR spectroscopy technique was used to investigate the effect of cycling moisture boundary conditions on the diffusivity of moisture of three asphalt binders. Each sample passed through three hydration cycles and two dehydration cycles. The existence of hysteresis of moisture diffusivity in asphalt binders is validated. The increase in moisture diffusivity is primarily attributed to the change in microstructure of the asphalt binder after being exposed to moisture. This is supported by atomic force microscope images of asphalt binder before and after exposure to water. Evidence to an increase of water trapped in the form of vapour even after dehydration was observed, and this may also contribute to the increase in diffusivity. This topic is still under investigation by this research group. [ABSTRACT FROM AUTHOR]

Cracking is a prevalent form of distress in flexible pavements. A thorough understanding of the mechanisms that lead to fatigue cracking and self-healing in bituminous materials is the essential and first step towards improving the performance of pavements and the bituminous materials used to construct these pavements. During the last two decades, several researchers have addressed the problem of understanding and modelling fracture and self-healing in bituminous materials at several different length scales. The first part of this paper presents a comprehensive review of the development of an energy-based fracture mechanics model to characterise the crack growth in bituminous materials. A few other approaches to model crack growth in viscoelastic materials that have not been widely used with bituminous materials are also briefly discussed. The second part of this paper presents a comprehensive review of an analytical model that can be used to represent self-healing in asphalt binders. The advantages, limitations and approximations associated with the implementation of the fracture and self-healing models are also discussed. [ABSTRACT FROM AUTHOR]

The water diffusion attributable to concentration gradients is among the main mechanisms of water transport into the asphalt mixture. The transport of small molecules through polymeric materials is a very complex process, and no single model provides a complete explanation because of the small molecule's complex internal structure. The objective of this study was to experimentally determine the diffusion of water in different fine aggregate mixtures (FAM) using simple gravimetric sorption measurements. For the purposes of measuring the diffusivity of water, FAMs were regarded as a representative homogenous volume of the hot-mix asphalt (HMA). Fick's second law is generally used to model diffusion driven by concentration gradients in different materials. The concept of the dual mode diffusion was investigated for FAM cylindrical samples. Although FAM samples have three components (asphalt binder, aggregates, and air voids), the dual mode was an attempt to represent the diffusion process by only two stages that occur simultaneously: (1) the water molecules are completely mobile, and (2) the water molecules are partially mobile. The combination of three asphalt binders and two aggregates selected from the Strategic Highway Research Program's (SHRP) Materials Reference Library (MRL) were evaluated at room temperature [23.9°C (75°F)] and at 37.8°C (100°F). The results show that moisture uptake and diffusivity of water through FAM is dependent on the type of aggregate and asphalt binder. At room temperature, the rank order of diffusivity and moisture uptake for the three binders was the same regardless of the type of aggregate. However, this rank order changed at higher temperatures, suggesting that at elevated temperatures different binders may be undergoing a different level of change in the free volume. [ABSTRACT FROM AUTHOR]

The fatigue-cracking life of an asphalt mixture measured in the laboratory is generally a small fraction of the fatigue-cracking life observed in the field. One of the reasons for this large difference is the self-healing property of asphalt binders. Self-healing is a process that reverses the growth of fatigue cracks during rest periods between load applications. A thorough understanding of the healing mechanism is required to accurately model and predict the influence of healing on the fatigue-cracking life of asphalt mixtures. Previous studies have used experimental evidence to demonstrate a correlation between chemistry of asphalt functional groups, such as chain length and branching, and healing measured in asphalt binders. One of the mechanisms of healing is the self-diffusion of molecules across the crack interface. This paper demonstrates the use of molecular simulation techniques to investigate the correlation of chain length and chain branching to self-diffusivity of binder molecules. The findings reported in this paper are consistent with observations reported in previous studies and expand on the understanding of the relationship between molecular architecture, self-diffusivity, and self-healing properties of asphalt binders. [ABSTRACT FROM AUTHOR]

Adhesion between asphalt binder and aggregate in a dry state as well as in the presence of water is critical to the performance and durability of asphalt mixtures. According to the literature, distress mechanisms in asphalt mixtures such as rutting, fatigue cracking, and moisture-induced damage are correlated to the nature and quality of adhesion between asphalt binder and aggregate. Surface free energy components of aggregates and asphalt binders can be used to compute the work of adhesion between the two materials in a dry condition as well as the thermodynamic potential of water to displace the asphalt binder from the surface of the aggregate. This paper presents a methodology to estimate the surface free energy components of aggregates using the microcalorimeter. The microcalorimeter is a relatively fast and simple alternative tool to estimate surface free energy components of aggregates compared to other techniques such as the gas adsorption method. In addition to surface energy measurement, the application of the microcalorimeter to directly measure the total energy of adhesion between the asphalt binder and the aggregate at mixing temperatures and the hydrophilicity of different aggregates at ambient temperatures is also demonstrated. Both of these properties influence the performance of asphalt mixtures in dry conditions and in the presence of water. [ABSTRACT FROM AUTHOR]

Different methods have been developed to assess fatigue cracking of asphalt mixtures based on dissipated energy. Most of these methods have been motivated by the need to develop a unified fatigue criterion that is independent of the mode of loading. This paper offers critical analyses of the energy methods based on their theoretical ability to: (1) unify the results from controlled-strain and controlled-stress modes of testing for the same material; and (2) accurately assess the fatigue cracking life of different materials. The efficacy of these methods is quantitatively compared using a common set of fatigue test data. The fatigue test data were obtained using the dynamic mechanical testing of three different mixtures that have been shown to exhibit different fatigue cracking resistance in the field. [ABSTRACT FROM AUTHOR]

This study presents an approach to help understand moisture damage mechanisms and to evaluate the effects of hydrated lime as moisture damage resisting agents. To this end, various performance testing of hot mix asphalt (HMA) samples induced by moisture damage and several fundamental property measurements (stiffness, strength, toughness, and bonding energy) of mixture components were conducted. Testing data and analyses demonstrated that hydrated lime contributed to moisture damage resistance due to synergistic effects of mastic stiffening, toughening, and advanced bonding characteristics at mastic-aggregate interfaces. However, a well-controlled lime treatment is required to maximize distribution and dispersion of lime particles on aggregate surfaces. In addition to the clear effects of hydrated lime, mineral filler in the HMA samples showed its effects on damage resistance in an early stage of moisture damage due to substantial stiffening-toughening effects from filler addition. Properties and damage characteristics of mixture components measured in this study were related to macroscopic performance behavior of asphalt concrete samples, which infers that the approach herein based on the mixture components can be effectively used to evaluate (or predict) moisture damage of asphalt mixtures and pavements with much less effort. [ABSTRACT FROM AUTHOR]

The ability to quantify adhesion based on surface energies of the bitumen and aggregate components enables selection of compatible materials and quantitative assessment of moisture susceptibility. Reliable surface energy characterization is required in order to implement this technology successfully. One proven method to estimate bitumen surface energy is to calculate it using contact angles measured with various liquids. However, improper selection of probe liquids or interpretation of resulting data can easily mislead users into drawing inaccurate conclusions. This paper presents a refined test method and analysis procedure customized to estimate bitumen surface energy using contact angles measured by the Wilhelmy plate. Results for five neat and three modified bitumen are presented and results are interpreted to study the relationships between contact-angle based surface energies and damage in hot mix asphalt. In a separate study by Bhasin et al. in 2004, surface energy characteristics of bitumen determined using methods described in this paper were combined with surface energies of aggregates to successfully predict moisture susceptibility of mixes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Machine learning can be leveraged to design performance based hot mix asphalt. • Hamburg wheel test rut depth and indirect tensile strength are predicted. • Recycled asphalt materials and aggregate gradation influence mixture performance. • Decision tree based ensemble methods and support vector regression analysis are used. • Gradient boosting and support vector regression can learn from imbalanced data. Agencies responsible for construction and maintenance of roadways often use some measure of performance to qualify asphalt mixtures before being used in construction. As of this writing, the state of Texas uses the Hamburg wheel tracking test and indirect tensile strength test to qualify a hot mix asphalt produced for roadway construction and maintenance. Optimizing the mixture design to produce mixtures with the desired performance criteria has been a topic of interest for asphalt researchers and industry personnel. This study explores the use of machine learning methods to estimate the rut depth from the Hamburg wheel tracking test and the indirect tensile strength from the mixture design and volumetric information. Support vector regression analysis and decision tree based ensemble methods, including bagging, random forests, extra-trees, and gradient boosting algorithms were trained with data collected by the Texas Department of Transportation for quality control and quality assurance purposes. Metrics related to mixture design including aggregate gradation and absorption, asphalt binder content and performance grade, use of warm mix asphalt, recycled materials, and laboratory-molded density as well as test information, such as number of wheel-passes applied in the Hamburg wheel tracking test, were used as input variables. The analysis showed that all of the machine learning algorithms adopted in this study were able to estimate the mixture performance criteria from the mixture design and volumetric properties when the models were trained with curated and sufficient data. While extra-trees provided the best performance in terms of the coefficient of determination, gradient boosting and support vector regression models were found to learn from the imbalanced data better than the other methods. This study offers opportunities for the development of data-driven performance-oriented mixture design optimization technique that can potentially replace the trial and error, mostly experience based, and time consuming processes preceding the laboratory verification during the mix design process. [ABSTRACT FROM AUTHOR]

Asphalt binders are vital components in the construction of roadways, and their quality significantly impacts the performance and durability of asphalt mixtures. However, it is possible for binders to exhibit different performance with identical Performance Grade (PG) due to variations in source, refining processes, and modifiers (if any). This paper presents a comprehensive study aimed at identifying candidate tests to detect variances in the quality of the binders in terms of cracking resistance. Eight PG 64–22 asphalt binders were selected and subjected to multiple laboratory tests, including X-ray fluorescence (XRF), Dynamic Shear Rheometer (DSR), Poker chip, and Bending Beam Rheometer (BBR) tests. The binders were then incorporated into asphalt mixtures, and their cracking resistance was evaluated using the IDEAL cracking test (IDEAL-CT) and Overlay test (OT). The study findings revealed that phase angle test, poker chip test, and Glover–Rowe (G–R) parameter test emerged as promising candidates to detect variations in the quality of binders of the same grade based on their cracking resistance. Notably, phase angle and G-R tests, both utilizing DSR, offered valuable supplementary assessments to the traditional PG grading system, proving crucial in evaluating cracking resistance. Furthermore, the poker chip test, an affordable alternative to DSR, demonstrated its effectiveness in evaluating binder quality for cracking performance. In conclusion, the identified candidate tests provide valuable insights into evaluating the quality of asphalt binders. By incorporating these tests into mix design and evaluation processes, engineers can make informed decisions to optimize the performance and durability of asphalt pavements. • A higher sulfur content in the binder is associated with lower cracking resistance in the asphalt mixture. • Both δ 8967 kPa and MG-R value demonstrate reasonable correlations with the CTindex and CPR. • A strong relationship exists between the cracking indexes and the poker chip test parameters. • The most predictive parameters for the CTindex are the δ 8967 kPa , poker chip ductility, and sulfur content. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents analysis of the effects of mechanical and physical material properties and loading conditions on the response of asphalt mixtures subjected to moisture diffusion processes. The analysis was conducted by using a finite element micromechanical model which couples the effects of moisture transport and mechanical loading. The maximum total force of resistance offered by the asphalt mixture microstructure model for a simulated displacement controlled load in the presence and absence of moisture was used as an indicator of its susceptibility to moisture damage. The results suggest that the diffusion coefficient of the asphalt matrix and aggregates, as well as the bond strength of the aggregate–matrix interface have the most influence on the moisture susceptibility of the materials. [Copyright &y& Elsevier]

Studies involving the investigation of the influence of aggregate structure on the performance of an asphalt mixture are time and resource intensive in the laboratory. To efficiently conduct experimental research of this nature, computational models are highly beneficial due to their ability to execute broad parametric and probabilistic analyses. In this regard, previous study has examined the feasibility of using a Bullet physics engine based computational model to virtually compact asphalt mixtures using a simulated gyratory compactor and digitized aggregate particles. This study examines the effect of three parameters from this computational model that control the bonding or adhesive behavior, viscous damping, and mortar film thickness between discrete coarse aggregate particles. The model was calibrated based on the laboratory compaction of 15 different asphalt mixtures by developing prediction models to estimate parameters that drive the three aforementioned properties. The calibrated model was validated using three additional asphalt mixtures that were virtually compacted using the computational model. Results demonstrate that the compaction behavior from the calibrated computational model was very similar to the compaction behavior recorded from laboratory measurements. • Feasibility of a computational model for asphalt mix compaction was demonstrated. • Effect of three parameters from the model on compaction characteristics was studied. • The three parameters were calibrated using laboratory compaction of 15 asphalt mixes. • The study quantitatively validates the calibrated model using three asphalt mixtures. [ABSTRACT FROM AUTHOR]

Optimization of asphalt mixtures in the laboratory is essential to maximize its performance in a pavement structure and reduce the likelihood of expensive premature failures. Several material and mixture variables affect the performance of an asphalt mixture. Evaluating the innumerable combinations of these variables in the laboratory to optimize an asphalt mixture is onerous. Computational models can supplement such laboratory-based optimization studies due to their capability of executing a broad range of parametric and probabilistic analyses. This study demonstrates the potential of using a physics engine to simulate the asphalt mixture compaction process. Physics engines were originally developed for animation and video games, however, with improvement in their accuracy, they are currently being used in many research areas. This study presents a computational model developed using an open source physics engine to virtually compact asphalt mixtures in a gyratory compactor. This model uses 3D laser-scanned representations of real aggregate particles and incorporates the viscous and cohesive nature of the asphalt mortar through customized subroutines. To demonstrate the feasibility of this model, the effect of the three key compaction parameters (i) angle of gyration, (ii) compaction pressure, and (iii) specimen height on the compaction characteristics were analyzed and compared with laboratory findings from various studies. Results suggest that the developed model can be used as a reasonably accurate means to simulate asphalt mixture compaction. This study also demonstrates that such simulations can be carried out using realistic and representative particle shapes in 3D, in a reasonable time using desktop computers. • The study presents a new computational model to compact asphalt mixtures. • The model uses 3D laser-scanned real aggregate particles. • The model incorporates the cohesive and viscous nature of asphalt mortar. • Feasibility of the model was demonstrated by varying different compaction parameters. [ABSTRACT FROM AUTHOR]

Proper bonding between different layers of a composite pavement is a major factor in ensuring that the entire structure acts as a monolithic layer under load. This paper studies the bonding between hot mix asphalt (HMA) overlay and Portland cement concrete (PCC) pavement using tack coats. An in-situ pull-off test method was developed for use on project sites on a routine basis to screen and test the quality of bond between asphalt layer and concrete layer. This test replaces the arduous process of coring through often times very thick concrete layer with steel rebars, transporting the core to a lab, trimming the concrete side of the core to fit the shear jig, and finally conducting a shear test. Results show that the in-situ pull-off test method developed in this study is strongly correlated to the laboratory based direct shear test. Limits were also suggested to indicate an adequate bond strength in the PCC–HMA interlayer on the basis of laboratory and field testing. This study also evaluates the influence of various factors on the performance of the interlayer bond in laboratory. These factors include the type of tack coat, application rate, the texture of the concrete pavement surface, the surface cleanliness and the surface moisture. Results indicate that sandblasting and hydro-demolition textures offer the best interlayer bond strength, the influence of application rate is not significant on the interlayer bond strength and the influence of surface moisture and cleanliness are dependent on the type PCC surface texture. • The study develops a pull-off test method to test the HMA–PCC interlayer bond. • This test has a potential to replace the direct shear test performed in laboratory. • This test is performed on-site which requires only 1.5 h to test four replicates. • Pull-off strength strongly correlates with the direct shear strength. [ABSTRACT FROM AUTHOR]

• Global interlaboratory study to investigate the effectiveness of antioxidants for asphalt binders. • Analysis of large dataset with diverse materials using rheological and chemical tools. • Effect on rheology is complicated and related to unique physicochemical interactions. • Understanding fundamental mechanisms of interaction is critical for routine application. The design and use of antioxidant additives to reduce or slow down the aging of asphalt binders can bring about tremendous benefits to the asphalt industry. Despite many isolated and scattered research efforts showing mixed results, the application of this science to engineering-based solutions has been limited due to variability in results and conflicting data available. This work presents the results from a global interlaboratory study to test the effectiveness of promising antioxidant additives, namely kraft lignin, calcium hydroxide, zinc diethyldithiocarbamate and phenothiazine to increase the resilience of asphalt binders and provide insights towards understanding the complex intricacies between chemistry and rheology. Specifically, seven different binders from various geographical regions in the world i.e., Texas (USA), Vienna (Austria), Illinois (USA), Antwerp (Belgium), and Delft (Netherlands) were blended with the antioxidants at two proportions. Subsequently, the chemical and rheological properties of the blends were evaluated using Fourier transform infrared (FTIR) spectroscopy and dynamic shear rheometer (DSR). The results indicate that although some antioxidants may reduce oxidation based chemical indices, their effect on rheology is more complicated and possibly related to unique physicochemical interactions in each binder. From a macro-perspective, zinc diethyldithiocarbamate showed promising results with a good correlation between rheology and chemistry for the majority of the binders. These additives or other additives with the same working principles should be investigated further. Additionally, significant research efforts must also be directed towards approaches aimed at understanding mechanisms of interaction and relating results with specific binder compositions. [ABSTRACT FROM AUTHOR]

Economic and environmental factors mandate the use of engineered materials as well other waste or industrial by-products as an additive or extender in asphalt binders and mixtures. In most cases, the impact of these materials on the long-term performance of asphalt binders and concomitant mixtures is evaluated on an ad hoc basis. This study explores the use of chemical compatibility based on the Hansen Solubility Parameters (HSP) to better understand and predict the performance of modified asphalt binder blends. Specifically, this approach is applied to the case of plastic materials that are increasingly being evaluated as a value-added extender for binders. In order to investigate the role of chemical compatibility on the macroscopic performance of such modified blends, two different types of polyethylene (PE) plastics with varied compositional characteristics were studied, referred to as PE-1 and PE-2. Additionally, the impact of using elastomeric polymers as co-modifiers with plastics were also examined. From a solubility perspective, the results indicated that PE-1 and asphalt binders show reasonable compatibility, whereas PE-2 was incompatible. Further analyses were conducted to correlate these results using microscopic and rheological tools. PE-1 modified binders were seen to be well dispersed in the binder matrix and had acceptable performance, particularly with the combined use of co-modifiers. On the other hand, all PE-2 modified binders showed poor dispersion and consequently inferior rheological performance. The results also indicated that the addition of co-modifiers will only improve the compatibility of plastics in blends on a selective basis. Overall, the work conducted in this study demonstrates the impact of chemical compatibility on the macroscopic performance of different plastic modified blends. The approach used in this study can also be extended for use with other additives used in asphalt binders to better understand the chemo-mechanics of the different additive-binder blends and impact on performance. • The use of Hansen solubility parameters (HSP) to examine the material compatibility between plastics and asphalt binder. • Fundamental chemical compatibility of plastics with binder changes based on composition. • Decreased levels of compatibility associated with poor rheological performance. • Closer examination of plastics required to design high quality mixes. [ABSTRACT FROM AUTHOR]

• Use of Vocus PTR-TOF spectrometer to investigate accelerated aging mechanisms of binders. • Formation of oxygenated species significantly higher under oxidative gas-based environment as compared to air. • Upscaling of an oxidative gas based aging method for the large-scale evaluation of loose mixtures. • Mixture and binder results indicate the clear effectiveness of the developed approach. The simulation of field aging using laboratory techniques is an essential prerequisite in the design of high-quality asphalt mixtures. Previous studies in this area have indicated the potential to use an accelerated method for aging loose mixtures using highly oxidative gases, namely ozone and other reactive oxygen species (ROS). Based on that, the present work was concerned with the investigation of the accelerated aging mechanisms in effect and upscaling of the experimental setup to accommodate larger quantity of mixes. Firstly, the chemical transformations and real time oxidation products formed under an ozone rich environment were compared to an air-based environment for three binders using a Vocus proton transfer reaction (PTR-TOF) time-of-flight mass spectrometer. It was observed that the formation of oxygenated species was significantly higher under an ozone rich environment, indicating higher levels of oxidation. The high-resolution level characterization of the oxidation series of several different molecules provided definitive evidence to support the previous hypothesis of using ozone and ROS to fast-track the oxidation of asphalt mixtures. Following this, an experimental method was developed to age up to nine kilograms (kg) of loose mixtures obtained from a mixing plant using ozone and ROS, in a duration of 22 h. After aging, different properties of the mixtures were compared to analogous mixtures aged as per a benchmark method of loose mixture aging at 95 °C for 5 days in a laboratory oven. The various results obtained from the IDEAL-CT tests, rheological and chemical property analyses of extracted binders clearly illustrated the effectiveness of the oxidative gas based aging method for the accelerated aging of loose mixtures, providing comparable levels of aging as traditional methods. Overall, the work conducted in this study provides comprehensive results regarding critical aspects of the developed method and alludes to the opportunity for wide scale applicability. [ABSTRACT FROM AUTHOR]

Asphalt binders are complex mixtures with a molecular configuration that varies with source and its chemical composition is not fully understood. Understanding the building blocks of binders is critical to fully interpret important characteristics including oxidative transformations. This study explored the use of the Vocus proton transfer reaction time-of-flight (PTR-TOF) mass spectrometer for the high resolution chemical fingerprinting of asphalt binders along with the observation of their real time oxidation dynamics. Three different binders were selected to examine the sensitivity of this technique under different gas blankets namely nitrogen, volatile organic compounds (VOC) free air and ozone-enriched VOC free air. Hierarchical clustering revealed differences in the degree of chemical expression of various molecules in different binders, which could be attributed to their unique primary differences and chemical transformations. The results also indicated that even higher intensities of molecules could be observed under the ozone-enriched blanket and increased temperatures indicating that this environment contains reactive precursors which could promote oxidation. Finally, real-time oxidation characteristics of binders were explored through factor analysis (FA) which elucidated possible pathways for binder oxidation, for example, through benzylic routes. Overall, the work conducted in this study points to the remarkable potential of this novel analytical technique to fingerprint asphalt binders with a high time and chemical resolution. This work also sets the stage for further work in understanding asphalt binder composition and multi-scale transformations, inspiring a database of chemical fingerprints related to macro-level properties. • Novel chemical fingerprinting of asphalt binders using Vocus PTR-TOF spectrometer. • Quantitative differences were observed in the degree of chemical expression of various molecules. • Real-time oxidation characteristics of binders explored through factor analysis. • Pathways for binder oxidation were elucidated, for example, through benzylic routes. [ABSTRACT FROM AUTHOR]

• A method for the accelerated aging of loose asphalt mixtures using ozone and other reactive oxygen species (ROS) was proposed in this study. • Oxidation metrics studied include rheological parameters, FTIR analysis and SARA fractionation. • ROS aging method showed similar or higher levels of aging just after 24 h compared to the conventional 5-day oven aging method. • Results indicated that the ROS aging method could be promising approach towards the development of an accelerated aging protocol. Efficient and practical techniques to simulate aging of asphalt mixtures is a focus area for practitioners around the world. In this study, a laboratory procedure was developed for accelerated aging of loose asphalt specimens using highly oxidative gas consisting of two types of reactive oxygen species (ROS) i.e., ozone (O 3) and nitrogen oxides (NO x). The procedure involved the aging of loose mixtures in an enclosed ROS rich environment for a period of 1 day at 95 °C. The chemical and rheological properties of the extracted binders from 5 different mixtures aged using this method were then compared to analogous binders aged using a benchmark of loose mixture aging at 95 °C for 5 days in a laboratory oven. Different metrics for oxidation and aging were comprehensively evaluated including extent of oxidative groups by Fourier transform infrared spectroscopy (FTIR), high and low temperature rheological properties using dynamic shear rheometer (DSR), and polarity based chemical fractionation into saturates, aromatics, resin and asphaltene (SARA) fractions. Favorable chemo-mechanical correlations were obtained from the results which confirmed that the mixtures aged using the ROS aging method showed similar or higher levels of aging just after 24 hrs when compared to the conventional 5-day aging method. Overall, the procedure developed serves as a proof of concept and provides encouraging results for further work towards the development and standardization of such an approach. [ABSTRACT FROM AUTHOR]

• Aging heterogeneities within RAP binder based on rheological and chemical properties; • Asphalt mix design considering a scenario in which the RAP binder is partially activated; • High aging heterogeneity within RAP binder limits the percentage of RAP in asphalt mixtures. The degree of binder activation in reclaimed asphalt pavement (RAP) is a critical aspect that should be considered in the design of recycled asphalt mixtures. It is widely believed that binder from RAP is less than 100% activated, which implies that part of the RAP binder will be inactive in the mixing process. It is important to quantitatively assess whether there is any significant difference between the active and the inactive binder as typical recycled mixture design insinuates 100% binder activation and complete homogenization of the virgin and RAP binder. The objective of this study is to evaluate aging heterogeneities within RAP binder as an imperative step to improve the design of recycled asphalt mixtures. Stages of binder extraction were performed on six RAP materials to artificially activate different RAP binder layers. After each extraction, the binder recovered was evaluated in terms of its rheological properties, polarity-based fractions, and Fourier transform infrared spectroscopy. Based on the results, an asphalt mix design was simulated using different RAP percentages considering the impact of RAP binder aging heterogeneities. Overall, the analysis implied that it may not be a realistic assumption to consider full RAP binder homogeneity. Based on the simulation performed, blending charts used to design recycled asphalt mixtures should be ideally based on the active RAP binder properties instead of the properties of the RAP binder after complete binder extraction. This would facilitate in choosing the correct virgin binder when the partial RAP binder activation scenario is considered. [ABSTRACT FROM AUTHOR]

• Sulfur extended asphalt mixtures can provide similar rutting and cracking performance compared to conventional mixes. • Sulfur may have the potential to compensate for polymer modification in asphalt mixtures. • Pre-blending sulfur with asphalt binder may enhance properties of sulfur extended asphalt. • Replacing asphalt binder with sulfur by volume is a good starting point for mix design using sulfur. Several laboratory and field studies from the last five decades, predominantly from the 1970s and 80s, have demonstrated that elemental sulfur is a viable binding material that can be used to partially or fully replace conventional asphalt binder in pavement construction applications. The main goal of this study was to determine and demonstrate the impact of different mix design factors on the performance of sulfur extended asphalt (SEA). These factors include sulfur content, the use of polymer modified versus unmodified base binder, and the method of sulfur addition to the mix. The Hamburg Wheel Tracking test was used to characterize rutting resistance and the Illinois Flexibility Index Test (I-FIT) was used to characterize the cracking performance at both short and long-term aging conditions. Overall, sulfur was found not to compromise the very good rutting resistance of the mix, and optimum binder and sulfur contents were determined based on long term cracking resistance of the mix. It is notable that the optimum binder content did not change when sulfur was used based on the long-term cracking resistance. Results, although with a limited set of materials, demonstrate the feasibility of replacing 30% of asphalt binder with elemental sulfur to produce SEA mixes. [ABSTRACT FROM AUTHOR]

• A method to extract and recover asphalt binder from a small sample of mix or RAP. • Low temperature properties of samples from this method can be evaluated using DSR. • Proposed method correlates very well with traditional extraction and recovery methods. • Low temperature properties of RAP vary substantially with the source of the RAP. Current procedures to extract and recover asphalt binders require a large amount of material and consequently a large volume of toxic solvents. To reduce exposure and consumption of such solvents, 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 to extract binder from small amounts of asphalt materials. The combined micro-extraction and 4 mm method was also used to demonstrate the high variability (up to 12 °C low continuous grade) among different RAP stockpiles collected from across the state of Texas. [ABSTRACT FROM AUTHOR]