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• The microscale dynamic X-ray tomography was used to observe the flow of asphalt. • The activation energy of the asphalt binder was calculated. • The contact angles between the asphalt binder and aggregates were analyzed. • Molecular Dynamics (MD) was used to simulate the flow process of asphalt. The objectives of this study are to explore the mechanism of the self-healing or flow of asphalt binder on the surface of the aggregates and evaluate the contact angle between the asphalt binder and aggregates. The mastic samples (small size) were prepared with asphalt binder and fine aggregates of a small size (below 0.3 mm). The microscale dynamic X-ray tomography was used to observe the flow of asphalt binder in the mastic sample at 353.15 K (80 °C) using the Advanced Photon Source (APS) beamline 2-BM at Argonne National Laboratory. The activation energy for flow of the asphalt binder and the contact angle between the asphalt binder and aggregates were analyzed to explain the self-healing characteristics of the asphalt binder materials. The Molecular Dynamics (MD) method was employed to simulate the flow process of the molecules of asphalt binder at different temperatures and mimic the contact angle difference between the asphalt binder and aggregate models. Simultaneously, in the laboratory, the contact angle goniometer was selected to measure the contact angle between the asphalt binder droplet and aggregates at different temperatures. The results of tests and MD simulations show that (1) asphalt binder diffused after heating from the X-ray images, and the stages and mechanism of the flow process of asphalt binder on aggregates were investigated; (2) low contact angle was observed in the interface model of asphalt binder and aggregates at high temperatures using the MD method. The wetting condition changed from partial non-wetting to wetting after heating in the interface model; (3) contact angle results between the asphalt binder and aggregates demonstrated flow steps of the asphalt binder material. The test data was also compared with the MD simulation results at different temperatures. [ABSTRACT FROM AUTHOR]

The objectives of this study are, 1) to simulate asphalt binder modified with exfoliated multi-layered graphite nanoplatelets (xGNP) using the Molecular Dynamics (MD) method, and 2) to analyze different modulus properties of these asphalt binder models compared with those of the control asphalt binder model. The multi-layered graphene model was used to represent the xGNP particles, which were used to modify the control asphalt in the laboratory. The three-component control asphalt binder model was used as in the authors’ previous study. The xGNP modified asphalt binder model was built by incorporating the xGNP model and control asphalt binder model and controlling mass ratios to represent the laboratory prepared samples. After the xGNP modified asphalt binder model was generated, the densities of the control and xGNP modified asphalt binder models were computed and verified. Mechanical properties of these models were simulated and calculated in MD simulations using procedures similar to those in the experiments, which include the bulk modulus, Young’s modulus, shear modulus and Poisson’s ratio. The simulation results indicate that the temperature-modulus trends of these asphalt binder models were comparable to those of the laboratory data. The MD simulation data were larger than the laboratory results due to limitations of the current MD simulation, which are discussed in this study. In addition, Poisson’s ratios calculated from the MD simulations coincided with the laboratory results. [ABSTRACT FROM AUTHOR]

The objective of this study is to explore the self-healing process or diffusion of the asphalt materials on aggregates through the experiments and molecular dynamics (MD) simulations. The asphalt mastic samples were prepared with binders and fine aggregates. The microscale dynamic X-ray computed tomography was conducted to capture the self-diffusion process of the binder in the asphalt mastic controlled at 353.15 K using Advanced Photon Source beamline 2-BM. The Mean Square Displacements were analyzed to describe the self-healing behaviors of binders by an MD method. The results of tests and MD simulations show that the molecules of the asphalt model on the nanoscale at high temperatures move faster those at low temperatures. The asphalt molecules move forward to aggregate layer and expand contact area to reduce the system energy. [ABSTRACT FROM AUTHOR]

The properties of asphalt blended with the direct coal liquefaction residue (DCLR) and Trinidad Lake asphalt (TLA) materials were analyzed and compared in order to study the feasibility of using DCLR to replace TLA for asphalt modification. In this study, four DCLR and TLA contents (5, 10, 15, and 20 %) were mixed with the SK-90 base asphalt. The high- and low-temperature performances of the DCLR and TLA modified asphalt were evaluated by the Superpave $${^{\rm TM}}$$ and penetration grade systems. The chemical compositions of these materials were analyzed using the Fourier transform infrared spectroscopy and gel permeation chromatography. The test results indicate that (1) the DCLR and TLA materials in the asphalt can improve the high-temperature performance of the modified asphalt; (2) the effect of DCLR on improving the performance of asphalt is better than TLA under high temperatures; and (3) it is possible that most of the DCLR and TLA particles are physically dispersed in the asphalt. Therefore, it is better to use the DCLR material for the replacement of TLA considering the cost and performance of DCLR and TLA modified asphalt. [ABSTRACT FROM AUTHOR]

Due to the consideration of energy conservation and emission reduction, Warm Mix Asphalt (WMA) is used in construction and foamed asphalt is a common agent in WMA. The objective of this paper is to explore the foaming mechanism and distribution law of asphalt and its components, as well as its basic properties. The expansion rate and half-life were used to describe the foaming properties of the foamed asphalt and to determine the optimum water content. The microscopic images were aided to study morphological changes in the foamed asphalt. Moreover, Molecular Dynamics (MD) simulations were widely used in the study of asphalt materials such as self-healing, interfacial behaviors, and mechanical properties. Based on intermolecular interactions, energies, and trajectories, the mechanism and performance of foamed asphalt can also be investigated. The molecular model of the foamed asphalt was established, and the foaming process of the foamed asphalt was discussed based on the perspectives of the energy, density, and intermolecular agglomerations. The simulation results can be a valuable reference for industry and fundamental research. [ABSTRACT FROM AUTHOR]

The purpose of this study is to use multiple-layer graphite nanoplatelets to modify the asphalt due to the special features of the graphite nanoplatelets. These include the high optical absorption, self-lubrication, and high thermal stability and conductivity. The graphite nanoplatelets with different weight contents (1% and 2%) were slowly added into the asphalt. The modified asphalt binder was mixed in the high shear mixer. Different tests were used to evaluate the properties of the modified asphalt binder, including the Rotational Viscometer (RV), Modular Compact Rheometer (MCR), Asphalt Binder Thermal Cracking (ABCD) Test, Fourier Transform Infrared Spectroscopy (FTIR) and electromagnetic radiation absorption tests. The test results demonstrate that 1) the viscosity of the modified asphalt binder increases at various temperatures and the activation energy of the modified asphalt binder decreases compared to the control one; 2) the complex shear modulus of the modified asphalt binder also rises at different temperatures and frequencies and the high-temperature of the modified asphalt binder improves; 3) the cracking temperatures, fracture stresses, and strains of the modified asphalt binder improve and the low-temperature performance of the modified asphalt binder is enhanced; 4) the aging groups increase in the modified asphalt binder and more aging groups in asphalt may help to increase the resistance to the rutting and moisture damage in asphalt mixtures; and 5) the absorption of lights with different wavelengths increases in the modified asphalt binder compared to the control one. Therefore, the resistance to rutting and cracking of graphite nanoplatelets modified asphalt binder is improved and they can be applied to the field for different purposes considering the advanced properties. [ABSTRACT FROM AUTHOR]

The objectives of this molecular dynamics study are to simulate the asphalt model using the common components from the references, and to predict the physical properties of asphalt material. The asphalt model consists of three components: the asphaltene, aromatic, and saturate, at the ratio of 5:27:41. The docosane and 1,7-dimethylnaphthalene represents the saturate and naphthene aromatic, respectively. The Amber Cornell Extension Force Field was adopted and utilized in the asphalt model system, and the experimental parameters associated with this force field were obtained from the General Amber Force Field (GAFF). The geometry and energy optimizations of the molecular components were used to establish the stable asphalt model system. The density of the asphalt model system was calculated with the Amber Cornell Extension Force Field. The predicted densities were compared with the laboratory data to verify the model. Moreover, the glass transition temperature range of the molecular asphalt model was computed from the relationship between the specific volumes and temperatures after the molecular dynamics experimental simulation. The glass transition temperature range had a good correlation with the experimental data. The viscosity data of the molecular asphalt model was calculated using the Muller-Plathe algorithm. The predicted viscosities at specific temperatures were also compared and discussed with the laboratory data and other published results. In addition, the bulk modulus of the molecular asphalt model was determined and obtained by applying the infinitesimal strain in the model boundaries. The results of the analysis of the bulk modulus in the asphalt model were compared to the reference data, and these predicted results were better than the reference values. [ABSTRACT FROM AUTHOR]

The objectives of this research are to use micro- and nanomaterials to modify the asphalt mixture and to evaluate the mechanical performance of asphalt mixtures. These micro- and nanomaterials, including carbon microfiber, Nanomer material, nanosilica, nonmodified nanoclay, and polymer modified nanoclay, were selected to blend with the control asphalt to improve the overall performance of the modified asphalt binders and mixtures. The microstructures of original materials and asphalt binders were observed by the field emission scanning electron microscope (FE-SEM). The mixture performance tests were employed to evaluate the resistance to rutting and permanent deformation of the modified asphalt mixtures. Test results indicate that (1) the dynamic modulus of micro- and nanomodified asphalt mixtures improved significantly; (2) the rutting susceptibility of the modified asphalt mixtures was reduced significantly compared to that of the control asphalt mixture; (3) the microstructures of modified asphalt binders were different from the control asphalt, and the structures determine the improvement in the performance of modified asphalt mixtures. These results indicate that the addition of micro- and nanomaterials enhanced the rutting performance and strength of asphalt mixtures. In addition, the analysis of variance (ANOVA) was used to analyze the modifying effects of micro- and nanomaterials on the performance. [ABSTRACT FROM AUTHOR]

The objective of this study is to analyze the effect of aging on asphalt binders under the conditions of dry and sufficient oxygen, and to identify the functional groups related to the fatigue and rutting of asphalt mixtures. During the asphalt aging process, the six functional groups (carboxylic acids, aldehydes, amides, anhydrides, esters and ketones) containing the carbonyl group can be found in the asphalt binders based on the Fourier Transform Infrared Spectroscopy (FTIR) test results and references. The functional groups containing the carbonyl group in the asphalt binders can be also used to correlate to the oxidation extent of asphalt binders. Three nanomaterials were added into the control asphalt binder to study the effect of aging. The three materials included polymer modified nanoclay (PMN), non-modified nanoclay (NMN) and nanosilica (NS). The rolling thin film oven (RTFO) and pressure aging vessel (PAV) aging effects of the asphalt binders were analyzed to understand the functional polar groups in the asphalt system under short- and long-term aging conditions, respectively. The different asphalt binders were tested by FTIR to obtain the spectra of chemical groups. The FTIR characterization results indicate that the carboxylic acids and ketones are the main aging components in the asphalt when exposed to air and oxygen. The esters and aldehydes in the asphalt are kept to a limited amount. Furthermore, these functional groups, along with the carbonyl group are closely related to the susceptibility of rutting and the fatiguing of asphalt mixtures. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the moisture susceptibility of nano hydrated lime (NHL) modified asphalt mixtures and determine the fundamental factors of moisture damage in asphalt mixtures using the molecular dynamics (MD), as well as analyze the effect that the aging of asphalt binders has on the moisture damage in asphalt mixtures. The NHL was added to the control asphalt to make NHL modified asphalt. The modified asphalt was mixed with aggregates to form NHL modified asphalt mixtures. The tensile strength ratio (TSR) test was used to evaluate the moisture susceptibility of asphalt mixtures. When the TSR test was done, different solutions were used to extract the polar groups from the tested asphalt mixtures, and the polar groups were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) attenuated total reflection (ATR). When asphalt oxidizes, the six functional groups (ketones, carboxylic acids, anhydrides, aldehydes, amides and esters) with the carbonyl group can be found in the polar part of asphalt based on FTIR ATR spectral data and references. The polar groups with the carbonyl group also indicate the oxidation extent of asphalt binders. The FTIR test results indicate that carboxylic acids and ketones were the primary aging products in asphalt, and these two carbonyl groups relate to the rutting resistance and moisture susceptibility of asphalt mixtures. Furthermore, the MD interface systems of asphalt–aggregate and aggregate–water were created, as well as the separated systems (asphalt, water, and aggregates). The essential mechanisms for the moisture susceptibility of asphalt mixtures were explored with MD simulations. The potential energies of the interface systems and each separated system were computed to obtain the adhesion energies of the interface MD models. The differences in adhesion energy between the asphalt–aggregate and aggregate–water systems show that water tends to bond to the aggregate rather than the asphalt. This also explains the displacement of water that occurs in asphalt mixtures when there is moisture damage. In addition, the effect of asphalt aging on the moisture susceptibility of the asphalt mixture was also analyzed using MD interface models. The MD results demonstrate that the aging group in asphalt is helpful in reducing the moisture damage in asphalt mixtures. [ABSTRACT FROM AUTHOR]

The textural roughness of asphalt pavement surface is an important indicator to characterize pavement skid resistance. In this paper, multi-visual technology was applied to capture the surface image of asphalt pavement which was transformed into a visualized 3D point cloud model. Then, based on the principle of the digital elevation model (DEM), the disordered 3D point cloud is rasterized and projected into a 2D matrix which contains generalized point cloud elevation information. Meanwhile, the 2D matrix is transformed into grayscale to build the equivalent grayscale image. Furthermore, the fractal dimensions were calculated in terms of one-dimensional pavement section profile, two-dimensional grayscale, and equivalent grayscale to characterize the pavement roughness. The results showed that the fractal dimensions are positively correlated with the mean texture depth (MTD), and the fractal dimension of equivalent grayscale has the best correlation with MTD. It should be highlighted that the equivalent grayscale image is directly transformed by the reconstruction of the three-dimensional point cloud, and the grayscale value of each point can represent the elevation of different pavement surfaces. Therefore, the equivalent grayscale image can better reflect the real roughness of the pavement surface. Meanwhile, the proposed method in this paper can effectively reduce the influence of some factors (e.g., light and color, etc..) on the texture detection of the pavement surface. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate the rheological properties and chemical bonding of nano-modified asphalt binders blended with nanosilica. In this study, the nanosilica was added to the control asphalt at contents of 4% and 6% based on the weight of asphalt binders. Superpave binder and mixture tests were utilized in this study to estimate the characteristics of the nano-modifed asphalt binder and mixture. The rotational viscosity (RV), dynamic shear rheometer (DSR), bending beam rhometer (BBR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), asphalt pavement analyzer (APA), dynamic modulus (DM) and flow number (FN) tests were used to analyze rheological properties and chemical bonding changes of the nano-modified asphalt binder and the performance of the nano-modified asphalt mixture. In addition, the performance of nano-modified asphalt after rolling thin-film oven (RTFO) short-term and pressure-aging vessel (PAV) long-term aging was assessed as well. The dissipated work per load cycle for the asphalt binder was used to evaluate the rheological properties of the nano-modified asphalt binder. Based on the binder test results, it was found that the additional nanosilica in the control asphalt binder slightly decreased the viscosity of the control asphalt binder, maintained low dissipated work per load cycle, held a similar low-temperature performance to the control asphalt, and had a positive effect on antioxidation. From the mixture test results, the dynamic modulus and flow number of nano-modified asphalt mixtures improved, and the rutting susceptibility of nano-modified asphalt mixtures was reduced compared to the control asphalt mixture. In general, the findings from this study show that the antiaging property and rutting and fatigue cracking performance of nanosilica modified asphalt binders are enhanced, and the addition of nanosilica in the control asphalt mixture significantly improves the dynamic modulus, flow number, and rutting resistance of asphalt mixtures. [ABSTRACT FROM AUTHOR]

The application of asphalt materials in pavement engineering has been increasingly widespread and sophisticated over the past several decades. Variations in the properties of asphalt binder during mixing, transportation, and paving can affect the performance of asphalt pavement. However, the asphalt material is a non-homogeneous and complex organic substance, consisting of various molecules with widely various molecular weights, elemental compositions, and structures. This complexity leads to difficulties for researchers to clearly and immediately understand the properties of asphalt materials and their variations. The multi-scale research approach combines macroscopic experimental data and microscopic simulation results from a practical engineering perspective. It helps to improve the understanding of asphalt materials. The molecular dynamics (MD) simulation proposes a corresponding molecular model of asphalt material based on experimental data, and the simulation algorithm is able to derive properties similar to those of real asphalt. This paper provides a comprehensive review of the current studies on MD simulation of asphalt materials, including modeling, properties, and multi-scale analysis. As a key part of the computational simulation, this paper discusses the typical asphalt binder and asphalt-aggregate interface models constructed by different groups, and also presents their differences from real samples and their feasibility based on fundamental properties. After the introduction of molecular models, the extensive work made by researchers based on molecular models is categorically reviewed and discussed. The strengths and weaknesses of MD simulation methods in the study of asphalt materials are also summarized in order to provide the reader with a more comprehensive understanding of the relevant contents and to guide subsequent research. [Display omitted] • The advantages and disadvantages of the Molecular Dynamics method were demonstrated. • A comprehensive discussion of the Molecular Dynamics Method in asphalt material was explored. • Many research directions of the Molecular Dynamics Method in asphalt material were discussed and guided. [ABSTRACT FROM AUTHOR]

Abstract: This work aims to improve the rutting and fatigue cracking resistance of asphalt binders using selected nano- or micro-sized materials and to shed light on the microstructure changes induced by such modification to asphalt binders. The four modifiers (Nanomer I.44P, carbon microfiber, non-modified nanoclay and polymer modified nanoclay) were added into the control asphalt binder (PG 58-34). The Superpave™ tests and Fourier transform infrared spectroscopy (FTIR) measurements were conducted for obtaining the complex shear modulus G * and microstructure distribution of modified asphalt binders. Meanwhile, the short-term and long-term aging processes of asphalt binders are simulated by rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests. From the dynamic shear rheometer (DSR) and FTIR tests results, the complex shear modulus G * values of nano- or micro-materials (Nanomer I.44P, non-modified nanoclay and carbon microfiber) modified asphalt binders increase, and the performance of resistance to rutting is improved compared to the control asphalt binder. The addition of polymer modified nanoclay (PMN) into the control asphalt binder decreases the complex shear modulus, and enhances the resistance to fatigue cracking. Moreover, the addition of four modifiers into the control asphalt binder can delay and weaken the aging and oxidation effect. [Copyright &y& Elsevier]

Abstract: This study investigated the rheological properties of asphalt binders modified with nanomaterial additives. The additives used are non-modified nanoclay (NMN) and polymer modified nanoclay (PMN). They were added to the control PG 58-34 asphalt binder at concentrations of 2% and 4% by the weight of the asphalt binder, respectively. Superpave™ binder tests were employed to evaluate the characteristics of the nano-modified binders. Rheological properties of nano-modified asphalt were analyzed by use of asphalt binder tests such as Rotational Viscosity (RV), Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR). In addition, the short- and long-term aging properties of nano-modified asphalt were analyzed, with the aging process simulated by Rolling Thin Film Oven (RTFO) and the Pressure Aging Vessel (PAV). The dissipated work per load cycle of all asphalt binders was examined, in order to better understand the properties of nano-modified asphalt. The results reveal that both viscosity and complex shear modulus of asphalt binder remarkably increase when the NMN is added into the control asphalt, and decrease slightly when the PMN is added. In addition, from the dissipated work perspective, the overall performance of PMN modified asphalt binder is improved in terms of rutting and fatigue cracking resistance relative to the NMN modified asphalt binder. [Copyright &y& Elsevier]

This study aims to investigate the effect of compatibilization methods on the compatibility between asphalt and direct coal liquefaction residue (DCLR) components to identify the key components in DCLR and asphalt that affect their compatibility. In this article, three types of compatibilizers, including benzyl alcohol (BA), dioctyl phthalate (DOP), and BA/DOP, were selected and acted on asphalt's components and DCLR's components, respectively. The molecular models of asphalt components, asphalt components with compatibilizers, DCLR components, and DCLR components with compatibilizers were established. The compatibility between DCLR and asphalt's four components, as well as between asphalt and DCLR's three components, were evaluated by solubility parameter difference (SPD) and interaction energy (IE). The compatibility between DCLR and asphalt was analyzed by Segregation test and Scanning Electron Microscope. Results indicate that the SPD and IE values between DCLR and asphalt components declined after adding compatibilizers, which implies that the repulsion decreased and the attraction increased between asphalt components and DCLR and the compatibility between asphalt components and DCLR improved. The IE values between DCLR components and asphalt increased after adding compatibilizers, which indicates that the compatibility was reduced between DCLR components and asphalt. The SPD values between DCLR components and asphalt increased after adding the BA/DOP. The SPD values between pre-asphaltene and asphalt decreased after adding the BA and DOP. The SPD value between asphaltene in DCLR and asphalt increased after adding the BA and decreased after adding the DOP. Moreover, the storage stability and homogeneity of DCLR-modified asphalt improved after adding compatibilizers, indicating that the compatibilizers enhanced compatibility between DCLR and asphalt. Finally, comparing the results of the tests, it could be found that compatibilizers preferentially acted on the asphalt components and mainly affected the aromatics in asphalt, thereby improving the compatibility between asphalt and DCLR. The effect of BA/DOP on improving the compatibility between asphalt and DCLR was better than that of BA and DOP. • The compatibility between DCLR and asphalt with four/three components was studied by SPD and IE. • Compatibilizers preferentially act on the aromatics in asphalt components. • BA/DOP is better than BA and DOP for improving the compatibility between DCLR and asphalt. [ABSTRACT FROM AUTHOR]

Due to viscoelastic characteristics, the strength values of the high-modulus asphalt mixtures (HMAM) obtained under different conditions (temperatures, loading rates, and stress states) are quite different, and the serving conditions of asphalt pavements are also varied. Thus, the strength under fixed conditions cannot reflect the mechanical performances of materials under real serving conditions, which leads to inaccuracies in the asphalt pavement structural design. To develop a precise strength evaluating method for high-modulus asphalt mixtures, the strength tests of high-modulus asphalt mixtures were implemented under different conditions (temperatures, loading rates, and stress states) in this study. The test results indicated that for each stress state, the variation of strength with loading rates under different temperatures can be characterized by power functions, and the variation of strength with temperatures under different loading rates can be characterized by exponential functions. The uniform characterizing model of strength under different conditions was established through the dimensionless method and the sigmoidal function. With the effects of temperature, loading rates, and stress states included, the strength obtained can better reflect the mechanical performances in actual pavement serving conditions. The research results contribute to the improvement of the structural resistance design of the asphalt pavement with high-modulus asphalt mixtures. [ABSTRACT FROM AUTHOR]

In order to study the influence of different factors on the early strength of the cold recycled emulsified asphalt mixtures, 16 different types of cold recycled mixtures were designed and produced, which were combined with different cement content, water content, and cement-water ratio. The indirect tensile strength (IDT), compressive strength (UCS), tensile strength at 15°C (TS), and indirect tensile strength ratio (ITSR) tests were used to test the early strength of the cold recycled mixture. The variance analysis method was utilized to analyze the influence of the single factor on the early strength of the cold recycled mixture. The results show that appropriate cement-water ratio content can effectively improve the early strength of cold recycled mixtures. According to the Spearman correlation coefficient and comparison of each evaluation indicator, IDT and ITSR are significantly affected by various factors, and the results are relatively stable and well-differentiated, which is recommended as indicators of early strength evaluation. Cement-water ratio is recommended as the main control factor to control the early strength of the cold recycled emulsified asphalt mixtures. The optimal cement-water ratio ranges from 0.6 to 1.0, while the cement content is controlled from 1.2% to 1.5% and the water content from 3.8% to 4.3%. This study is of great significance for promoting the design of emulsified asphalt cold regenerative mixture with cement-water ratio and improving and accelerating its early strength development. [ABSTRACT FROM AUTHOR]

Two new test methods were proposed to measure the different moduli of asphalt mixtures simultaneously based on four-point bending and indirect tensile tests. The new calculating formulas were derived for tensile and compressive moduli of asphalt mixtures under four-point bending loading model, which combining the equilibrium condition and the plane hypothesis in elastic mechanics theory. Meanwhile, on the basis of the test principle of indirect tensile moduli and Hooke’s law in two-dimensional stress states, the new calculating formulas were derived in indirect tensile loading model. The moduli tests of four-point bending, indirect tensile, direct tension and unconfined compression were carried out separately to verify effectiveness of the new methods. The results of tensile and compressive moduli from the two new methods were compared with the direct tension moduli tests and unconfined compression moduli tests. The correlations among them were analyzed. The result indicates that the tensile and compression moduli of asphalt mixtures show a significant difference, and can be obtained by two methods simultaneously. The two new methods realize the synchronous measuring of various moduli of asphalt mixtures. [ABSTRACT FROM AUTHOR]

This study aims to characterize the rate of change that takes place in the rheological properties of asphalt binders modified with numerous types and contents of nano-materials. The effects of nano-materials on the activation energy of modified asphalt binders under the viscous and visco-elastic behavior were also investigated. Through the research findings, the application of non-dimensional analyses using relative viscosity and relative G ∗ /sin δ (NSRP) are very meaningful to evaluate the rate of change in the rheological properties of asphalt binder per one unit percent of nano-material. It is also found that the non-dimensional viscosity index (∇ η ) and non-dimensional Superpave™ rutting factor gradient (∇NSRP) are influenced by the type and content of nano-material, and test temperature. The activation energy analysis has confirmed that the changes in amount of energy consumed are not only influenced by the type and content of nano-material, but also the physical phase of the modified asphalt binders. [ABSTRACT FROM AUTHOR]

The goal of this paper is to reveal the influence of temperatures on the triaxial strength of asphalt mixtures. The triaxial compression and triaxial tensile tests, as well as plane tensile and compression/axial tensile tests, which were developed by the self-developed triaxial test equipment to carry out the complex stress state under different temperatures (5°C, 10°C, 15°C, 20°C, and 25°C), were performed on the asphalt mixture. The ultimate failure strength of the material shows that the temperature and stress state significantly affect the triaxial strength characteristics of the asphalt mixture, and the three-dimensional strength decreases by the increase in temperature. Under the triaxial compression and triaxial tensile stress state, the resistance of the octahedral shear stress increases with the hydrostatic stress. A three-dimensional strength calculation model is established based on the influence of temperature and characterization by the tensile meridian, compression meridian, and failure strength envelope. It reveals the change of failure strength envelope with increasing temperatures and decreasing hydrostatic stress under complex stress state. It provides experimental and theoretical references to the design of asphalt pavement structure of different temperature conditions according to the three-dimensional stress state. [ABSTRACT FROM AUTHOR]

Highlights • Identification of wet-freeze climate zones in the United States and parts of Canada. • Summary of material selections of asphalt pavements in wet-freeze climate zones. • Introduction of current practices, and the emerging technologies/materials. • Discussion of asphalt binders and up to mixtures related test/design methods. Abstract The objectives of this review paper are to document current practices in wet-freeze climate zones and introduce emerging technologies that would be largely implemented in wet-freeze climate zones in the near future. A current practice is defined as a procedure that has been shown by research or experience to produce acceptable results and that is established or proposed as a standard suitable for widespread adaptation. An emerging technology is defined as a technique or a material that can improve the asphalt pavement performance, partly replace general materials, and contribute to more sustainable asphalt pavements. This review identified the criteria used to determine locations in the United States and two Canadian provinces with a similar wet-freeze climate. In addition, asphalt binders, asphalt additives/modifiers, asphalt mixture types, reclaimed asphalt mixtures, asphalt mixture test methods, asphalt mixture design methods, and deicers were reviewed. This review concluded with some recommendations in terms of using environmentally friendly materials and selecting cracking and rutting failure criteria to design asphalt mixtures with enhanced performance in wet-freeze climates. [ABSTRACT FROM AUTHOR]

Due to its superior mechanical properties, carbon nanotubes (CNTs) can be applied for material reinforcement and modification. However, the relatively high cost for CNTs synthesis limits their large application in construction materials. This study employed the microwave irradiation method to produce CNTs with low cost and high efficiency. The ferrocene powder was mixed with graphite surfaces and irradiated with the microwave. Particularly, the flake graphite and exfoliated graphite nanoplatelets (xGNP) were applied in this study as substrate. The high temperature generated by the microwave irradiation can decompose ferrocene into iron and hydrocarbons, which serve as the catalyst and carbon source for the CNTs growth, respectively. The morphology, internal structure and chemical composition of the synthesized CNTs were then examined with SEM, TEM and EDS. The Raman test was also conducted to investigate the defect level of synthesized CNTs. Then the adhesion energy between the CNTs and substrate was evaluated with the MD simulation. The obtained adhesion energy between CNTs and non-oxidized graphene layers was slightly higher than the calculated results between CNTs and oxidized graphene layers. Finally, the hybrid CNTs-graphite powders were used for the modification of asphalt binder. The test results of viscosity and dynamic shear modulus tests demonstrate that the hybrid CNTs-graphite powders can further improve the mechanical properties of asphalt, especially at high service temperatures. [ABSTRACT FROM AUTHOR]

• The Desai three-dimensional strength criterion was improved by including the effects of loading velocities. • A new approach for fatigue characterization under three-dimensional stress state was proposed. • The fatigue life values obtained under distinct stress states were uniformly characterized. To improve the durability of asphalt pavement, high modulus asphalt mixtures were developed and widely utilized to construct heavy trafficked pavements to resist rutting. Except for rutting, serving under repeated heavy loads, pavements with high modulus asphalt mixtures are also vulnerable to fatigue cracking. To prevent fatigue cracking, the fatigue resistance of high modulus asphalt mixtures is a crucial indicator for pavement structural design and checking computations, which is generally obtained by laboratory tests. However, the current test methods are generally based on maximum tensile stress or strain theory and neglecting the effects of loading velocities, so the fatigue resistance obtained cannot match that under actual pavement serving conditions. Moreover, the fatigue performance of high modulus asphalt mixtures obtained by different test methods are quite different, which caused random and disunity when selecting fatigue parameters for pavement structural design. Therefore, the objective of this paper is to accurately and uniformly characterize the fatigue resistance of high modulus asphalt mixtures. To this end, the indirect tensile, direct tensile, unconfined compressive strength and fatigue tests of high modulus asphalt mixtures were implemented under distinct loading velocities. Based on the Desai yield criterion, the strength yield surfaces under diverse loading velocities and the fatigue path of high modulus asphalt mixtures in three-dimensional stress state were established. Finally, the fatigue life values of high modulus asphalt mixtures obtained under distinct test methods and loading velocities were uniformly characterized by the relationship between fatigue life and equivalent stress ratio Δ , which was N f = Δ - 5.42 . With the uniform characterizing model, the disunity of fatigue parameters can be eliminated, and the fatigue resistances of high modulus asphalt mixtures under three-dimensional stress states and different loading velocities can be evaluated. [ABSTRACT FROM AUTHOR]