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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 greatest difficulty of grouting fractures under flowing condition was that the slurry was easily washed out by the flowing. To raise the sealing efficiency (SE) and dynamic flowing resistance of slurry, carbon fiber was added into the grout and a new grout for flowing water environmental was provided. Contrast tests and SEM tests were conducted to investigate the effect of carbon fiber. The result showed that the solidification velocity and dynamic flowing resistance increased with an increase of carbon fiber content due to the stochastic distribution and great surface friction of carbon fiber. In addition, a series of orthogonal tests were conducted to investigate the effect of some factors on the SE. The result showed that the SE decreased with the increase of initial flow speed and aperture width, and it increased with the increase of cement water ratio and additive content. Finally a fitting equation was acquired to provide reference to the practical engineering. [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 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 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]

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]

• Effect of various nanoparticles on the grouting performance was investigated. • The grouting performance increased with an increase of GO content. • The sealing efficiency of nano-SiO 2 composite gouts were greatest. • Nanoparticles effectively improved the grouting performance of grouts. A series of physical simulation experiments were conducted to investigate effects of nanoparticles (carbon nanotube (CNT), graphene oxide (GO), nano-SiO 2 , and nano-Al 2 O 3) on the grouting performance in dynamic water condition. Experimental results show that the use of nanoparticle could effectively improve the grouting performance. CNT composite grout was excellent for the maximal fluid pressure and residual grouts percentage. The sealing efficiency of nano-SiO 2 composite grout was the greatest while that of nano-Al 2 O 3 composite grout was the lowest among all nanoparticle composite grouts. The grouting performance increased with an increase of GO content. [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]

• Pre-cracking degree of static compaction specimen changed significantly. • Indirect tensile strength performance of static compaction specimen was the worst. • Pre-cracking both reduced shrinkage of two kinds of specimen effectively. • Crack resistance of vibration compaction specimen was better. The cement-stabilized macadam formed by static (SC) and vibration compaction (VC) were pre-cracked and their properties comparison were conducted. It indicated that the lowest self-healing rate of VC and SC at 7 days were 57.1% and 54.2%, respectively, with the pre-cracking time of 3 days and degree of 40%. It proved that the shrinkage strains of VC and SC were reduced at most by 35.8% and 35.3%, respectively, with the pre-cracking time of 2 days and degree of 40%, respectively, and the corresponding crack resistance were improved by nearly 300%, with the time of 2 days and degree of 30%. The results showed that VC had a better performance. [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]

• 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]

• The correlation relationship between pavement detection indicators is examined. • The key detection indicators are identified and extracted by the Gini importance of RF algorithm. • The cost-effective index PEI for pavement condition assessment is proposed based on regression analysis. • The feasibility of the proposed method is verified by a comparison of the traditional method. The condition assessment of in-service asphalt pavement plays a key role in pavement maintenance and rehabilitation. Driven by historical data, the Random Forests algorithm with the Gini importance measurement was employed to identify and extract key detection indicators from the pavement assessment standards. On top of that, a cost-effective method for pavement condition assessment based on the key detection indicators was proposed by decreasing unnecessary data dimensions. A comparison between the proposed method and the traditional method has been made to verify the feasibility of pavement condition assessment. The results show that the pavement assessment results based on the proposed method matched well with those based on the traditional method, which achieved a more than 90% consistency of overall assessment results in validation samples. Hence, they demonstrated that the proposed method utilized fewer pavement detection indicators to reduce the burden of data collection and improve the cost-effectiveness of pavement condition assessment tasks. In the future, it will be a promising alternative to assist pavement maintenance and rehabilitation. [ABSTRACT FROM AUTHOR]