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Mesoscale contact networks for asphalt mixtures play a crucial role in load resistance. However, there is a lack of quantitative characterization methods for contact networks. Topology can describe the contact relationships between multiple objects through points and lines. In this study, aggregate information was extracted by industrial computed tomography (CT) and digital image processing technology (DIP). The classification of disruption aggregates was determined by a two-dimensional (2D) topological contact model. Then, the correlation mechanism between topological indices and topologies was established based on the topological matrix. The algebraic connectivity (La) of nine different asphalt mixture disruption aggregates was analyzed. The results revealed that each type of asphalt mixture disruption aggregate was dominated by a certain La with higher frequency. As the nominal maximum size (NMAS) increased, there was a shift in the dominant topologies of different asphalt mixture disruption aggregates from those associated with lower La to those linked to higher La. Based on the higher frequency of La, there were 8 topologies with frequencies exceeding 20%; 5 with frequencies surpassing 10%; and 14 and 17 with frequencies greater than 5% and 2%, respectively. Furthermore, it was observed that the topologies of disruption aggregates predominantly consisted of simple topologies. Additionally, the frequency of complex topologies decreased as the number of nodes and connectivity increased. [ABSTRACT FROM AUTHOR]

Although previous studies have broadly explored the aging process of styrene-butadiene-styrene (SBS)-modified asphalt, there still is a lack of understanding of the precise evolution patterns of its phase structure during aging, and whether aged SBS-modified asphalt retains its modified properties or reverts to conventional asphalt. To fill these gaps, this paper focused on key performance characteristics that differentiate SBS-modified asphalt from conventional asphalt, including viscosity, elasticity, and toughness properties; evaluated how aging influences mechanical properties; and examined morphological changes at different aging stages. The effective method for phase structure characterization was established. Based on the results, it was found that mechanical property variations, especially in the toughness curve, effectively indicate the phase structure. The fracture strength σB and fracture elongation εB of SBS-modified asphalt after rolling thin-film oven (RTFO) aging for 8 h closely matched those of 70# base asphalt after RTFO aging for 8 h, with values of 1,364.32 and 0.005, compared with 1,421.07 and 0.007, respectively. This curve helps determine whether aged SBS-modified asphalt remains modified or reverts to conventional asphalt. Aging primarily affected instantaneous elastic deformation, and had a minimal impact on delayed elastic deformation. Morphological analysis supported these findings, and showed that SBS polymer degradation precedes significant network disruption, and increased toughness results mainly from SBS polymer presence. [ABSTRACT FROM AUTHOR]

The asphalt binder is exposed to unfavorable coupling aging of UV radiation, high temperature, and moisture, which accelerates the deterioration of the binder's rheological properties. To investigate the effect of this coupled aging on the rheological properties of asphalt binder, an accelerated environmental aging oven considering ultraviolet (UV) radiation, temperature, and moisture was used in this paper to carry out multifactor coupling aging tests for the binder. The coupling aging test parameters are determined by the central composite design-response surface methodology (CCD-RSM). The rheological properties of asphalt binder before and after aging were examined by dynamic shear rheometer, and the effects of the coupling aging on the viscoelastic, high-temperature, fatigue, and low-temperature properties of the binders were evaluated by employing the complex shear modulus (G*); the aging index (GI), which was established with G* ; the rutting factor (G*/sinδ); the Glover–Rowe (G-R) parameter; and the ratio of asphalt binder creep rate to stiffness modulus (m/S), respectively. Further, the effect of the coupling aging on the chemical properties of the asphalt binder was evaluated with carbonyl index obtained from the Fourier transform infrared spectrometer. The results showed that the optimal values (temperature: 68.3°C; irradiation intensity: 2,221 W/m2 ; spraying interval: 250 min) of the coupled aging parameters were determined by the CCD-RSM, and the relationship between the coupled aging time and the carbonyl index was established by the Verhulst model with an R2 value larger than 0.98. As the coupling aging degree increases, the G* , GI , and G*/sinδ show an increasing trend, whereas the G-R parameter, m/S , shows a decreasing trend, indicating that the aging increases the stiffness and high-temperature resistance of the binder and decreases its fatigue properties and low-temperature properties. Based on the correlation analysis, the G-R parameter showed good correlation with the GI , G*/sinδ (45°C, 55°C, and 65°C), m/S (−6°C , −12°C , and −18°C), respectively, and the average R2 value is larger than 0.98. Therefore, the G-R parameter can be used as a comprehensive index for evaluating the rheological properties of binders. [ABSTRACT FROM AUTHOR]

The low-temperature performance of asphalt mixtures was a critical factor that investigated the thermal cracking of asphalt pavement in cold regions of the world. Many scholars have affirmed that the failure temperature of the thermal stress restrained specimen test (TSRST) could be an index to evaluate the low-temperature performance of asphalt mixtures. However, the influence of transient heat transfer on asphalt mixtures was ignored in the TSRST, potentially leading to inaccurate evaluation indexes for low-temperature performance. In this paper, the thermal contraction strain and the effective temperature of asphalt mixtures were analyzed considering transient heat transfer in the TSRST. First, the effective temperature and the thermal contraction strain were captured during the cooling process. Then, the calculation model of thermal stress was improved. The pseudo strain energy density was calculated based on the energy theory. Finally, the calculation model of thermal stress was evaluated with the failure temperature as the standard. The difference between the failure temperature calculated by the calculation model of thermal stress without considering the transient heat transfer and the failure temperature calculated considering the transient heat transfer was at least 2°C. [ABSTRACT FROM AUTHOR]

This study investigated the effects of a diatomite/tetradecane composite shaped phase change material (CSPCM) on the mechanical properties and thermoregulation performance of styrene-butadiene-styrene (SBS)- and styrene-butadiene-styrene/crumb rubber (SBS/CR)-modified asphalt binders. The heat transfer and latent heat characteristics of phase change asphalt mortars (PCAMs) were analyzed using a thermal constant analyzer and differential scanning calorimeter. Furthermore, a thermoregulation test was devised to confirm the temperature-regulating characteristics of PCAMs. The rheological properties of PCAMs were analyzed using the dynamic mechanical analysis (DMA) method, and low-temperature fracture characteristics were evaluated using the single edge notched beam (SENB) test. The results indicated that the incorporation of CSPCM decreased the thermal conductivity and thermal diffusivity of SBS- and SBS/CR-modified asphalt binders but increased their specific heat capacity. CSPCM can be stably present in modified asphalt and still have good phase change properties in the phase change temperature range, as well as the temperature regulation effect of PCAMs is excellent. The melting enthalpy for the PCAMs was as high as 73.29 J/g. Compared to the modified asphalts, the heating time of the PCAMs increased by up to 34.1% as the dosage of CSPCM gradually increased. The incorporation of CSPCM enhanced the viscous components of modified asphalt binders, improved intermediate-temperature fatigue resistance and low-temperature fracture resistance, and reduced high-temperature permanent deformation resistance. [ABSTRACT FROM AUTHOR]

This study fully intends to elucidate the mechanism of waste wood oil (WWO) modifier content on the microscopic action of bio-asphalt by utilising molecular dynamics simulations. Molecular models of virgin asphalt and its components, WWO modifier, and bio-asphalt with different WWO contents were created and verified by the fluctuation parameters, radial distribution function (RDF), and thermodynamics parameters. In addition, the influence of WWO content on thermodynamic and structural properties of bio-asphalt and interactions between components was quantitatively evaluated through Hansen solubility parameter, intermolecular interaction energy, mean square displacement, RDF, and fraction of free volume. The simulation findings show that the compatibility of bio-asphalt is associated with the composition of the asphalt molecule and the compatibility ranking is not affected by the WWO content. In addition, the WWO modifier is most compatible with the resin and least with the saturate. The interaction energy between virgin asphalt and WWO and the particle migration in the asphalt models increases with increasing WWO content. Furthermore, the introduction of WWO increases the first RDF peak intensity of each asphalt component. An increase in WWO content does not change its own chemical composition. Moreover, the free volume of the system decreased as the WWO was added. [ABSTRACT FROM AUTHOR]

Past studies broadly discussed the effect of sulfur on the rheological properties of styrene–butadiene–styrene (SBS) modified asphalt, while the relationships between the rheological properties and phase behaviour of SBS-modified asphalt after sulfur vulcanisation have received less attention, which limits the further understanding of the relations between the structure and performance. To this end, this paper is aimed to discuss viscoelastic response at the molecular level and reveal the enhancement mechanism of SBS-modified asphalt after adding sulfur. Thus, the morphology, phase structure, and rheological behaviour of SBS/Sulfur modified asphalt were investigated by experimental assessment and molecular dynamics. Based on the results, it was found that the polybutadiene segments in SBS copolymer are the leading reactive site of vulcanisation, the interactions between SBS copolymer and light components were enhanced by sulfur treatment, the orderliness of asphalt molecules in SBS/sulfur modified asphalt was strengthened, and SBS copolymer presents a stronger attraction to aromatic after vulcanisation, which means the increase of boundary layer is also the significant cause to the improvement of compatibility. The findings are expected to deepen understanding of the vulcanisation mechanism and the rheological behaviour of SBS/Sulfur modified asphalt. [ABSTRACT FROM AUTHOR]

The chemical–physical hybrid cross-linked double network gel poly (acrylamide-co-acrylic acid)/Sodium alginate/Fe3+ (P(AM-co-AA)/SA/Fe3+, simplified as P-gel) was synthesised by free radical polymerisation combined with hydrogen bonding and ion coordination, which was in turn compounded with styrene–butadiene-styrene (SBS) to prepare P-gel gel/SBS modified asphalt. FT-IR, UV, XRD and SEM analyses confirmed the successful synthesis of P-gel. FM analysis revealed that the volume of P-gel increased after the long-term aging of asphalt. The physical, Dynamic Shear Rheometer (DSR), multi-stress creep recovery (MSCR), and time sweep tests showed that the addition of P-gel improved the road performance of the SBS modified asphalt. At a P-gel amount of 5%, the high-temperature performance grade (PG high temperature) of SBS modified asphalt improved from PG70 to PG76 and the recovery rate (64 oC) was increased by 17.08% and 41.13% at the stress of 0.1 and 3.2 kPa, respectively. The underlying mechanism behind these improvements in the mechanical properties of the composite modified asphalt was the different competitive relationship between the 'softening' effect of P-gel in asphalt and the 'strengthening' effect of the asphalt itself at different temperatures. This project provides an alternative strategy for preparing P-gel gel/SBS modified asphalt with enhanced mechanical properties for applications in the highway and construction industries. [ABSTRACT FROM AUTHOR]

The thermal cracking behaviour of asphalt pavement is complex and includes thermal contraction, low-temperature relaxation, and low-temperature damage. However, using relaxation characteristics alone instead of low-temperature properties leads to an incomplete evaluation. In this paper, the relationship between viscoelastic properties and relaxation characteristics was analyzed. Based on the time domain characteristics of relaxation, the relaxation rate and cumulative stress at per unit strain rate (CSSR) were proposed as evaluation indexes corresponding to the long-term/short-term characteristics of the relaxation. By combining the relationship among the low-temperature performance obtained by Thermal Stress Restrained Specimens Test (TSRST) and relaxation characteristics, evaluation indexes for the low-temperature performance of asphalt mixture were preferably selected. The results show that asphalt binders dominate the relaxation characteristics of asphalt mixtures, but do not directly replace the low- temperature performance of asphalt mixtures. The relaxation characteristics expressed by the traditional viscoelastic indexes were insufficient to fully evaluate the low- temperature performance of asphalt mixtures. Furthermore, the results of the relaxation characteristic index for evaluating the low-temperature performance were different under different temperature conditions, indicating that performance at a single temperature cannot replace the low-temperature performance at all temperatures. [ABSTRACT FROM AUTHOR]

Asphalt pavements are continuously subjected to cyclic temperature variations induced by varying day–night and seasonal temperatures. However, the effect of thermal cycling on asphalt materials has not been thoroughly documented. This study conducted accelerated thermal cycling tests on asphalt mastics to simulate the environmental temperature variation. The evolution of the rheological properties and phase behaviors under cyclic temperature variations was clarified. The temperature factors sensitive to damage were identified by establishing the quantitative relationship between the cyclic temperature parameters and these properties. Results demonstrated that, as the expansion of cyclic temperature ranges, the three asphalt mastics gradually lost their viscosity properties and became increasingly elastic. Thermal cycling increased the stiffness and high temperature deformation resistance of the three asphalt mastics, but significantly reduced their stress relaxation capability. The phase structures were degraded upon thermal cycling, weakening the asphalt-aggregate interaction. The temperature difference and cyclic high temperature were the primary factors affecting the rheological performance of the asphalt mastics. SBS modified asphalt mastic displayed remarkable resistance to thermal cycling, demonstrating its potential for application in regions with frequent temperature fluctuations. This research can help us understand the evolution of asphalt pavement performance in areas with frequent temperature changes at a macro-level. [ABSTRACT FROM AUTHOR]

In order to effectively evaluate the regeneration effects of different rejuvenators on aged asphalt binder, this study carried out a series of tests and evaluations on the macroperformance of virgin asphalt binder at various aging-regeneration stages. A commercial rejuvenator, aromatic oil, and warm mix agent were selected as rejuvenators. Fifteen asphalt binder samples involved various aging methods, including water-ultraviolet aging, water-free ultraviolet aging, rolling thin film oven test (RTFOT), and accelerated aging by pressurized aging vessel (PAV). High-temperature properties of asphalt binders were evaluated by softening point, and low-temperature properties of asphalt binders were evaluated by stiffness modulus and m-value. The viscoelastic properties were evaluated by complex modulus G*. Test results show that the regeneration effects of different rejuvenators were reflected in the reduction of softening point, stiffness modulus, and complex modulus. Based on performance changes of asphalt binder before and after aging, the reversibility indexes Rsp , RG* , RS , and Rm for quantitative evaluation of macroperformance of rejuvenated asphalt binders were proposed. Through linear fitting, it was found that R2 between the reversibility index Rsp and the reversibility index RG* reached 0.7574, and R2 between RS and Rm reached 0.8683. This provided the possibility of mutual transformation between those reversibility indexes. Last, the macroreversibility index of virgin asphalt binder (ARIV) was proposed. The softening point and stiffness modulus were taken as representative indexes to comprehensively evaluate the recovery of high-temperature, low-temperature, and viscoelastic properties of aged asphalt binder by different rejuvenators. This study provided a unified indicator to quantitatively evaluate the regeneration effect of rejuvenator on virgin asphalt binder. It is helpful for better understanding the aging-regeneration process of virgin asphalt binder and determining the optimum regeneration time and rejuvenator. [ABSTRACT FROM AUTHOR]

Asphalt mixture has complex gradation and mesostructure. Accurate prediction of the relationship between gradation and mesostructure is of great significance for the establishment of mesostructure numerical simulation model and image-based gradation detection. In this paper, featurization, stepwise regression, econometric hypothesis test are utilized for establishing the predicting models. Firstly, asphalt mixtures with 64 kinds of gradation are scanned by Computed Tomography (CT) to obtain the mesostructure images; Then a series of mesostructure parameters of voids and aggregates are put forward. On this basis, the relationship model between gradation and mesostructure is established and verified by featurization and statistical modeling method. The results show that for predicting the passing percentage of the 4.75 mm sieve and the mean value of average distance between aggregate centroids for 9.5–4.75 mm aggregates, the prediction error of passing percentage is acceptable. It illustrates that the relationship model between gradation and mesostructure established by statistical method is effective, and it is significance for material design and testing under the condition of big data in the future. [ABSTRACT FROM AUTHOR]

During the long-term service of asphalt pavement, under the combined action of repeated loads and environmental factors, asphalt pavement will gradually appear small damage. When the damage accumulates to a certain extent, the asphalt pavement will have serious rutting deformation, resulting in poor highway flatness and greatly reducing the service life of the asphalt pavement. The traditional monitoring methods of pavement rutting deformation need high environmental detection conditions. At the same time, there are some problems, such as subjective judgment standard and unable to monitor in real time. The commonly used road surface coring detection methods will destroy the original continuous structure of the pavement and easily cause internal damage of the pavement under the action of rain and snow environment. In this study, based on the intelligent aggregate (IA) equipped with high-precision attitude sensor, a new pavement rutting deformation monitoring method was proposed. Combined with the indoor rutting experiment, the relationship model between intelligent aggregate attitude change and rutting deformation was established, and the relationship model between real pavement rutting deformation and intelligent aggregate attitude change was established by finite element method, so as to realize the rutting deformation monitoring method based on Intelligent aggregate. [ABSTRACT FROM AUTHOR]

The adhesion between asphalt binder and aggregate is very important to the performance and durability of asphalt pavement. In order to explore the characterisation of modified asphalt binder in microstructure during aging and rejuvenation, the virgin asphalt binder and three kinds of modified asphalt binder (styrene‐butadiene‐styrene block copolymer (SBS), rubber powder and high viscosity and high elasticity [HVHE] modifier) in different aging and rejuvenation condition were prepared. The micromorphology and surface adhesion were measured by atomic force microscopy. The average roughness value was used as the index to evaluate the micromorphology of asphalt binder. The surface adhesion was used as the index to evaluate the adhesion properties of asphalt binder. Results show that the "bee" structure of SBS‐modified asphalt binder increased slightly after long‐term aging, and the recovery effect of aromatics oil was the closest to that of the unaged one. The rubber powder‐modified asphalt binder and HVHE‐modified asphalt binder showed the spot structure. And no matter for short‐term aging or long‐term aging, aromatics oil had the best recovery effect on micro morphology. The adhesion of the three modified asphalts would decrease gradually after aging. The effects of three kinds of rejuvenator on the adhesion of SBS‐modified asphalt binder and rubber powder‐modified asphalt binder were different. Rejuvenator, aromatic oil and warm mix asphalt mixture (WMA) additive could rejuvenate the loss of adhesion of HVHE‐modified asphalt binder to a certain extent. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel asphalt fume suppressant oil-absorbing organogel polystyrene-stearyl methacrylate (P(S-SMA)) was synthesized. • P(S-SMA) can absorb the lighter components of asphalt binder. • Adding P(S-SMA) can improve the rheological properties and reduce the fume particles and VOCs release of asphalt binder. • The interaction between the P(S-SMA) and asphalt components caused the above advantages. Hazardous fumes can be generated during the high-temperature construction of asphalt pavement. Various fume suppressants have been developed, but many may compromise the performance of asphalt binder, which shortens the service life of asphalt pavement. This study aims to investigate the performance of a novel fume suppressant, namely oil-absorbing organogel polystyrene-stearyl methacrylate (P(S-SMA)), which can reduce the construction fumes of asphalt binder while maintaining good rheological performance. The results of the Fourier Transform Infrared Spectroscopy (FT-IR), Fluorescence Microscopy (FM) and asphalt fume mass tests showed that adding P(S-SMA) can improve the aging resistance of asphalt binder and reduce the particles (≥1 μm) and volatile organic compounds (VOCs) released up to 19.6 % and 30.4 % within 1 h, respectively. The rheological test results indicated that P(S-SMA) could effectively improve the viscoelastic properties, high-temperature performance and fatigue resistance of asphalt binder due to the combination of "supporting" and "hardening" effects after adding P(S-SMA). With 5% P(S-SMA) added, elastic and viscosity properties were increased by 90.6 % and 25.3 % and fatigue life was increased by 38.9 % and 26.4 % at the strain levels of 2.5% and 5%, respectively. This study proved the feasibility of using P(S-SMA) as a novel performance-enhancing fume suppressant of asphalt binder. [ABSTRACT FROM AUTHOR]

The property of asphalt mastics consisting of asphalt binder and mineral fillers significantly affects the performance of asphalt mixture and also results in several forms of distresses in pavements. In addition to the materials properties, the interfacial interaction between asphalt binder and mineral fillers has a significant impact on the performance of asphalt mastics. This research aims to study the influence factors of interaction between asphalt binder and mineral fillers, and explore its relationship to viscoelasticity of asphalt mastics. Two kinds of asphalt binders, four kinds of mineral fillers and five filler/asphalt ratios were selected to prepare forty asphalt mastic samples. The interaction degree between asphalt binder and mineral fillers was characterised by a new introduced parameter C. The influence factors including the properties of asphalt and fillers were analysed. The correlations between interaction and mastics' rheological properties at different temperatures were statistically investigated. Results show that increasing the polar components ratio of asphalt binder, raising the specific surface area of fillers, making the size composition of fillers finer or increasing temperature all can increase the interaction degree between asphalt binder and mineral fillers. Linear relationship was considered to be an optimum type to represent the correlation between interaction degree and viscoelastic properties of asphalt mastic at temperatures between 15°C and 65°C. There was a very significant correlation between dynamic shear modulus/rutting factor/fatigue factor and C value when the temperature was between 25°C and 45°C. This kind of correlation weakened at 15°C and 55°C, but still significant. The phase angle of asphalt mastic has a significant correlation with interaction parameter C value only at 25°C and 35°C. [ABSTRACT FROM AUTHOR]

This study focused on the application of Rayleigh wave technology on a non-destructive determination of dynamic modulus of asphalt mixtures. A 3-D finite element numerical algorithm was developed to simulate Rayleigh wave propagation in a multi-layer half-space system. Numerical analysis verified the feasibility of Rayleigh wave technology to capture the mechanical property differences in shallow structures within asphalt pavements. Then, five asphalt mixtures were used in the experimental application of Rayleigh wave technology. A multichannel simulation with one receiver (MSOR) was adopted to generate Rayleigh waves in asphalt mixture samples. Changes in phase velocity-frequency energy spectra and wave velocity were used to evaluate effects of ambient air temperature and asphalt mixture type on wave propagation evolution in asphalt mixtures. Rayleigh wave technology was introduced to dynamic modulus analysis using various experimental temperatures and asphalt mixtures. Obtained modulus was compared with that using impact resonance method to evaluate the prediction precision for analysis dynamic modulus of asphalt mixtures. [ABSTRACT FROM AUTHOR]

It has long been recognized that fine aggregate (FA) plays a crucial role in the performance of asphalt mixture, especially for the viscoelastic behavior. In this research, 13 types of FA (1 natural sand, 5 stone chips, and 7 machine-made sands) were selected for investigation. Three indirect indicators (uncompact void content test, flow time test, and standard test method for index of aggregate particle shape and texture ASTM D3398) and three types of direct indicators (form, angularity, and texture) were employed to evaluate the geometric characteristics of FA and conduct comprehensive studies on the indicator system. Meanwhile, the effects of FA geometrical properties on the viscoelastic behavior of asphalt mortar were investigated. The results show that only the form indicator ratio of equivalent ellipse axis (E) and angularity indicator surface parameter (SP) can effectively distinguish different types of fine aggregates. The correlation analysis reveals that the parameters of the four elements in the Burgers model are negatively related to the form index (E) but positively related to the angularity index (SP), while the parameter retardation time ( τ r ) exhibits the opposite. This indicates that the use of less flat-elongated and more angular FA can increase both the overall stiffness and elastic component of asphalt mortar. [ABSTRACT FROM AUTHOR]

• The optimum preparation technology of CF-GT conductive asphalt mixture with low resistivity are clarified. • The resistance and stress of the mixture have an excellent linear correlation in NPC stage. • The feasibility of applying graphite tailings to prepare the conductive asphalt mixture is demonstrated. The massive accumulation of graphite tailings (GT) brings huge pressure to environmental engineers. Meanwhile, the conductive asphalt pavement industry is suffering from the high construction cost and the complex acquisition of conductive materials. The application of GT in asphalt mixture as a conductive material may be a win–win solution for the above concerns. This study aims to evaluate the feasibility of preparing carbon fiber graphite tailings (CF-GT) conductive asphalt mixture. The optimum preparation technology and material ratio were explored. The service performance tests of the conductive asphalt mixture were conducted, including conductive characteristics, electrothermal performance and pavement performance. Based on the experimental results, 0.3% (mass fraction) 6 mm-polyacrylonitrile (PAN)-based carbon fiber (CF) and 12% (mass fraction) GT were selected as conductive materials to prepare conductive asphalt mixture with resistivity of 5.75 Ω∙m. The addition of GT reduced the resistance by a maximum of 59.8%. The temperature-sensitive and pressure-sensitive characteristics of the mixture have staged characteristics. Moreover, the resistance and stress of the mixture have an excellent linear correlation in the positive pressure coefficient (PPC) effect stage and negative pressure coefficient (NPC) effect stage respectively, especially NPC. Conductive asphalt mixture has a good heating effect after being powered on. GT combined with CF enhanced the high-&low-temperature performance but deteriorated the moisture damage resistance performance of the asphalt mixture. The feasibility of CF-GT conductive asphalt mixture was demonstrated. [ABSTRACT FROM AUTHOR]

Individual effect of aging and rejuvenator recycling on basic properties of asphalt is readily recognized, but there is only limited understanding about whether the recycling of SBS- (styrene-butadiene-styrene-) modified asphalt is an inverse process of aging or not. To compare the effects of aging and rejuvenator on microproperties and molecular composition of SBS-modified asphalt, comprehensive performance tests and physical-chemistry experiments were conducted. The results of infrared spectroscopy tests demonstrate that the reticular crosslinking structure of asphalt was destroyed and SBS's modification effect was gradually lost after aging. This can cause the strengthening of high-temperature performance and reduction of the low-temperature anticrack property of SBS-modified asphalt. Scanning electron microscope shows that the island structure of SBS-modified asphalt disappeared after aging. Energy spectrum analysis shows that the C (carbon) content of aged SBS-modified asphalt has decreased, while the O (oxygen) content and S (sulfur) content have increased obviously. Results of the fluorescence microscope, SEM, and rheological tests show that the epoxy functional group compounds of aliphatic glycidyl ether resin had high reactivity; the triblock molecular structure of SBS and the mechanical performance of SBS-modified asphalt were recovered. [ABSTRACT FROM AUTHOR]

• Perform fractal and multifractal analysis on the asphalt mixture's aggregate skeleton and void structure. • The influence of design and construction indicators on the microstructural features of pavement materials. • The fractal/multifractal parameters' physical sense and role in characterizing the 3D microstructure are clear. The aggregate skeleton and void structure in the asphalt mixture are critical and highly correlated to the mechanical performance of the pavement. However, the extreme heterogeneity and complexity bring devastating difficulties to characterizing and analyzing the mixtures' mesostructure. Therefore, this study aimed to propose a novel depicting scheme accounting for the size distribution and spatial arrangement of the mixtures' components utilizing the fractal and multifractal analysis. Two compaction methods (Marshell and Superpave) and three design indexes (gradation, NMAS, and compaction work) were adjusted to prepare the samples, which were then scanned and digitally reconstructed. The fractal dimension (D) and related multifractal indicators (i.e., Δ α and Δ f (α)) were determined and applied to quantitative assess the structural changes. Finally, the relationships of design indexes to fractal and multifractal behaviors were comprehensively discussed. Results indicate that fractal and multifractal theories are feasible in describing the heterogeneous particle skeleton and void structure in the asphalt mixture. Firstly, the multifractal approach was proven to allow a more informative characterization of 3D systems than simple fractal theory. Moreover, the excellent correlation between the design/construction and fractal/multifractal indicators has been confirmed for asphalt pavement. Overall, the fractal and multifractal indicators enriched the options for microstructural evaluation, which will be conducive to revealing the relationship between the microstructural characteristics and mechanical performance of the asphalt mixture. [ABSTRACT FROM AUTHOR]

The thermodynamic behavior of asphalt mixtures is critical to the engineers since it directly relates to the damage in asphalt mixtures. However, most of the current research of the freeze-thaw damage of asphalt mixtures is focused on the bulk body from the macroscale and lacks a fundamental understanding of the thermodynamic behaviors of asphalt mixtures from the microscale perspective. In this paper, to identify the important thermodynamic behaviors of asphalt mixtures under freeze-thaw loading cycle, the information entropy theory, an X-ray computerized tomography (CT) scanner and digital image processing technology are employed. The voids, the average size of the voids, the connected porosity, and the void number are extracted according to the scanned images. Based on the experiments and the CT scanned images, the information entropy evolution of the asphalt mixtures under different freeze-thaw cycles is calculated and the relationship between the change of information entropy and the pore structure characteristics is established. Then, the influences of different freezing and thawing conditions on the thermodynamic behaviors of asphalt mixtures are compared. The combination of information entropy theory and CT scanning technique proposed in this paper provides an innovative approach to investigate the thermodynamics behaviors of asphalt mixtures and a new way to analyze the freeze-thaw damage in asphalt mixtures. [ABSTRACT FROM AUTHOR]

The low-temperature performance of an asphalt mixture plays important roles in the thermal cracking mechanism of asphalt pavements in cold regions. However, the existing asphalt mixture design process does not involve a design parameter for low temperature performance as the asphalt content is determined. In this study, two types of asphalt mixtures are involved, Asphalt Concrete (AC) and Stone Mastic Asphalt (SMA), which are the most widely used materials for surface layer. The zone for low-temperature performance was defined on the basis of a survey of pavement distresses and numerical analysis. The design parameter was captured from an indirect tensile test by using Digital Image Correlation (DIC) analysis, considering the universalizability and simplification of the indirect tensile test. The selected indicators, such as tensile failure strain, validated that significant linear correlations existed between bending beam test and thermal stress restrained specimens test. Thus, the design parameter, which was defined as the tensile failure strain ( ε DIC ), could characterize low-temperature property with asphalt content. Moreover, the critical strain of ε DIC was proposed. The low-temperature design parameter ( ε DIC ) was applied to the Marshall design method. The optimum asphalt content based on the new design method was slightly greater than that of the conventional Marshall design method. The evaluation methods used in this paper indicate that the low-temperature property of the asphalt mixture created by the new design method was better. [ABSTRACT FROM AUTHOR]

The interfacial behavior between asphalt binder and mineral fillers directly effects the performance of asphalt mastics or asphalt mixture. However, the understanding about the interfacial interaction between these components is very limited, although the role of individual ingredients on its performance is readily recognized. In order to study the interactions between asphalt binder and mineral fillers, it is necessary to propose an effective evaluation indicator. In this research, dynamic mechanical analysis (DMA) was used to obtain the viscoelastic parameters of different asphalt binder and asphalt mastics. The interfacial interaction parameters between asphalt binder and fillers were calculated based on the viscoelastic parameters and relevant theoretical models. The interaction parameters were compared and the calculated methods were improved. The results show that compared to interfacial interaction parameters Luis Ibrarra- A and K. Ziegel- B , C value based on Palierne theoretical model had the least sensitivity to the volume fraction of fillers. The checking of fitting goodness of improved interaction parameter C value shows a high determination coefficient. It demonstrates that the C value can effectively evaluate the interfacial interaction. The interfacial interaction becomes stronger with the temperature increasing. The higher the specific surface area of filler, he stronger the interfacial interaction between it and asphalt binder. [ABSTRACT FROM AUTHOR]

• Emphasize the impact of meso-structural variability and uncertainty of HMA. • Provide a system for evaluating and analyzing the meso-structural skeleton. • Clarify the relationship between the IC particles and the DASR-based skeleton. The variability and uncertainty bring great trouble to the application and in-depth research of asphalt mixture. This study aimed to detect the microstructural differences between the asphalt specimens after fixing the experimental and environmental inputs. To this end, the digital image correlation (DIC) method was utilized to propose reliable skeletal and disruptive meso-parameters. Besides, the close packing theory and digital sieving technique were combined to classify the internal particles of the mixture structure. Afterward, the stochastic behaviors of the particle systems containing the dominant aggregate size range (DASR) and interstitial component (IC) aggregates were thoroughly discussed. Finally, the disruption effect of IC on the skeletal structure was also investigated. The analysis results show that the microstructure of the asphalt mixture was a typical random system with a great deal of contingency. The aggregate contact index (ACI) was the most variable among the overall skeletal parameters, with a variation coefficient (COV) of 13.24 %. Besides, almost all the microstructural indexes indicated that about 4% of the specimens in parallel tests showed significant variability behavior, e.g., N a ,13.2 > N a ,16.0. Besides, the microstructural uncertainty of the minority class, e.g., the 16-mm aggregates with a 4% ∼7% COV higher than the other classes, was particularly significant. Finally, the interference effect was proven to focus on the contact behavior of DASR particles, thus damaging the DASR-based system. This study not only emphasizes the impact of variability but provides implications for controlling the performance of asphalt pavement. [ABSTRACT FROM AUTHOR]

• The periodic perturbation method is adopted to calculate the ZSV of asphalt binder MD models. • Asphaltene and saturates more easily reorient their conformation in shear flow. • Short, unordered planar accumulations structures dominate asphalt binder microstructure. This study aims to develop molecular model of asphalt binder and investigate the reasonable simulation scale of molecular dynamics (MD) in researching the viscosity property and microstructure of asphalt binder. Eighteen MD models with atom numbers in the range of 10,000–750,000 for the three typical asphalt binder AAA-1, AAK-1, and AAM-1 in the Strategic Highway Research Program (SHRP) were constructed. Density, Zero Shear Viscosity (ZSV), and microstructure characters of the asphalt binders were analyzed by MD to compare with experiment data. The result shows that densities and the ZSV values of the MD models are all close to the experimental values. These models with atom numbers of 130,000–375,000 are well stabilized and have lower errors, which is recommended to research the density and viscosity properties. In the shearing process, the shear flow induces the conformational transitions of the asphalt binder, and most molecules tend to parallel the shear direction. Asphaltenes and saturates components are easier to reorient their conformation in shear flow. Through the density map obtained by MD simulation and the asphaltenes image from the High-resolution transmission electron microscopy in literature, we speculate that short and unordered planar accumulations structures dominate the asphalt binder microstructure, which is a further explanation of the colloidal theory. [ABSTRACT FROM AUTHOR]

• Investigated the effects of damage and thixotropy on viscoelastic parameters; • Obtained a linear relationship between G ∗ E and θ under the influence of thixotropy; • Developed a thixotropy model to characterize the change of G ∗ E under the influence of thixotropy; • Calculated damaged density separating the influence of thixotropy. Accurate characterization of the fatigue resistance of asphalt binder is of great significance to the prediction of asphalt pavement performance. Traditionally, apparent changes in viscoelastic parameters, including dynamic shear modulus and phase angle, with the number of loading cycles are used to define the fatigue performance of the asphalt binder. However, thixotropy also leads to changes in these viscoelastic parameters, and its contribution is not yet well understood. This study develops a method to quantify the effects of damage and thixotropy on the changes of viscoelastic parameters under the cyclic stress-controlled loading mode. The new method includes the four key steps: (1) determining the thixotropy influence-dominated phase; (2) establishing a thixotropy model to characterize the influence of thixotropy on the effective dynamic shear modulus; (3) calculating damage density from the apparent and effective dynamic shear moduli; and (4) characterizing thixotropy behavior based on Black space diagram. The effectiveness of the newly developed method is verified by the time sweep test, which is conducted on two types of asphalt binder under varying stress levels.with a loading frequency of 10 Hz and a test temperature of 25 °C. The results show that: (1) the change of dynamic shear modulus is resulted from the damage and thixotropy, while that of phase angle is only caused by the thixotropy; (2) thixotropy leads to the decrease of dynamic shear modulus and increase of phase angle; and its influence on viscoelastic parameters increases with the loading time and stress level increased; (3) under the influence of thixotropy, the dynamic shear modulus is linearly related to the phase angle, which is independent of the stress level applied and the damage accumulated in the asphalt binder. [ABSTRACT FROM AUTHOR]

[Display omitted] • The relationships among phase behavior, aging mechanism and modification effect were established. • Different aging rate exist with the raising aging time. • The aging process can be divided into three regions according to modification effect and phase behavior. • It is suggested that the parameter of toughness curve can be used as one of the critical indicators of modification effect. Aging behavior has always been a key issue in the asphalt industry, and the undetermined extent of the residual modification effect in aged SBS-modified asphalt can lead to uncertain performance. The relationship between the modification effect and aging mechanism has not been well examined, which leads to whether aged asphalt can be regarded as modified asphalt or conventional asphalt. To overcome this issue, this paper conducted fluorescence microscopy tests, dynamic shear rheometer tests, multiple stress creep recovery tests and toughness and tenacity tests on aged SBS-modified asphalt. Five quantization parameters were proposed to determine the phase structure and modified effect. Multinomial logistic regression analysis was performed to categorize the phase structure with increasing aging time. Based on the results, it was found that the aging process can be divided into three regions according to the modification effect. The first region presented a slower aging rate, and copolymer relaxation appeared, but chemical crosslinking still existed during this period. Aging dominated the second region, in which copolymers dissolved out and the polymer network was destroyed, and the quantization parameters sharply changed, eventually, the network structure was completely destroyed in the third region. The failure of the modification effect is also determined by evaluating the toughness curve. It is reasonable to assume that there is no difference between SBS-modified asphalt and conventional asphalt after RTFOT 6 h in terms of toughness curve. It is suggested that the toughness curve parameter can be used as one of the critical indicators to determine whether aging asphalt can be regarded as modified asphalt or conventional asphalt. [ABSTRACT FROM AUTHOR]

Highlights: [•] Long rest periods and few loading cycles result in improved healing. [•] The effect of terminal cases on healing is greater than the effect of rest periods. [•] We established a universal healing evaluation index for asphalt binder. [•] The healing ranking of binders suggested by HIm-c, HIem-c and HIvm-c are the same. [•] The healing ranking of the binders is the same as the ranking of the corresponding. [ABSTRACT FROM AUTHOR]

Highlights: [•] We determined best contents of raw materials of composite modified asphalt sealant. [•] Central composite design is effective in optimizing performance of composite modified asphalt sealant. [•] It is effective to use energy method to evaluate viscoelastic properties of asphalt. [•] We analyzed the effects of rubber powder, additive, SBS and SBR on rheological behavior of modified asphalt. [Copyright &y& Elsevier]

Highlights: [•] We studied phase behavior of asphalt mastic upon DMA, DSC and Brookfield viscometer. [•] The addition of fillers can increase Tg and glass transition activation energy. [•] The addition of fillers can improve the temperature sensitivity of asphalt mastic. [•] The addition of fillers can promote phase separation occur in modified asphalt. [•] Fillers have little impact on the discrete distribution of wax in asphalt. [Copyright &y& Elsevier]

Highlights: [•] Sessile drop method can characterize surface free energy of viscoelastic materials. [•] Column wicking technique can characterize surface free energy of solid powders. [•] Specific surface area effects interaction between asphalt and fillers remarkably. [•] The adhesion work can response the moisture sensitivity of asphalt mixtures. [•] A good correlation exists between complex modulus G ∗ and work of adhesion. [Copyright &y& Elsevier]

Highlights: [•] We study hardening mechanism of cement asphalt paste when fixing asphalt emulsion to cement ratio. [•] Type of emulsifier and its dosage both affect the hardening process of cement. [•] Significant differences in hydration parameters are detected utilizing different emulsifier. [•] Emulsifier with less retarding effect can develop a high early strength CA mortar. [Copyright &y& Elsevier]

[Display omitted] • The dipole moment was used to represent the molecular polarity and further divided the aromatics and resins molecules. • The HOMO-LUMO gap shows that resins and aromatics molecular are more stable than asphaltenes. • 1H-NMR, elements analysis, SARA components tests were used to solve asphalt the molecular ratio. To further develop the microscopic structure of asphalt, the new asphalt molecular model including 50 types of molecules was proposed. The dipole moment, molecular electrostatic potential, and HOMO-LUMO gap were calculated by quantum chemistry methods. Based on the polarity represented by dipole moment and molar mass, the molecules were further divided into the aromatics and resins molecules in theory. The result shows that the donor atoms are located in the benzene concentrated region are easily attacked by electrophiles. The accept atoms are located in saturated branched chains and cycloalkanes are easily attacked by nucleophiles. The HOMO-LUMO gap shows that the asphaltene molecular meets with the experiment results of the asphaltene optical gap. The resins and aromatics molecular own similar chemical stability, both of them are more stable than asphaltene. Finally, 1H-NMR, elements analysis, and SARA components experiments were connected with the molecular model we presented to solve the molecular ratio of fourteen kinds of asphalt. [ABSTRACT FROM AUTHOR]

• The uncertainty of permanent deformation process of asphalt mixture was analyzed. • The method to determine damage states for permanent deformation was proposed. • The characteristic points at strain rate curves complied with normal distribution. • The fragility curves for permanent deformation of asphalt mixture were established. This study aims to develop a fragility analysis methodology for asphalt mixture to assess the uncertainty of the permanent deformation development of asphalt mixture subjected to repeated load based on parallel tests. The methods to determine limit states and damage states for the permanent deformation process based on characteristic points at the strain rate curve were proposed. The distribution types of characteristic points were tested, and the corresponding probability distribution function was employed to plot fragility curves for limit states. According to the relationship between limit states and damage states, fragility curves for damage states were established subsequently. [ABSTRACT FROM AUTHOR]

Abstract: Asphalt binder has a critical effect on the performance of asphalt mixtures. Thus, asphalt binder is of great concern to pavement engineers and researchers. Usually, asphalt binder is studied in dynamic space and steady-state space separately, and the property indices are researched separately. As researchers delved deeper, they found that it is important to combine the dynamic properties and steady-state properties, especially for establishing rheological curves and constitutive equations. The Cox–Merz relationship can connect the properties in dynamic space to those in steady-state space. This relationship is widely used in polymer system and shows good results. This study focused on the applicability of the Cox–Merz relationship as it pertains to asphalt binder. The Cox–Merz relationship was applied to six neat asphalt binders. Then, the applicability of the Cox–Merz relationship for asphalt binder was studied and the criterion to verify whether the Cox–Merz relationship is followed or not was established. Finally the viscosity functions when the Cox–Merz relationship used were studied, and the Cross model and the Carreau model were compared. The results show that the Cox–Merz relationship is followed in the shear-thinning region and not always followed in the zero-shear-rate-limiting viscosity region, and it is useful when obtaining the viscosity function. [Copyright &y& Elsevier]

Abstract: The healing performance of asphalt binder has a critical impact on the fatigue performance of asphalt binders, mixture and pavement. Although studies of the healing characteristics of asphalt binder can be found in some references, the subject has not been researched thoroughly. No universal healing evaluation index currently exists, and the fatigue and healing processes are not fully understood. For this study, experiments were performed to characterize the healing characteristics of four typical asphalt binders. Healing indices are put forward, and factors that affect healing performance are examined in this paper. Finally, the fatigue and healing processes of asphalt binder are investigated by analyzing test specimen cross-sections. The findings from this study, although based on a limited number of binders, suggests that HI1 (the modulus ratio) and HI2 (the cycle number ratio) are suitable healing indices. Rest periods and microstructural configurations significantly affect the healing performance of asphalt binder. Healing affects the fatigue performance only when the modulus value is greater than the modulus value when rest periods are applied. During fatigue testing, damage starts at the outer edge of the specimen, and then develops towards the middle of the specimen. [Copyright &y& Elsevier]

Abstract: Low temperature cracking is the major damage in asphalt pavement, and many test methods have been used to evaluate the anti-cracking property of asphalt mixture. This paper evaluates the low temperature performance of asphalt mixture using four tests namely: beam bending test, indirect tensile test, contraction coefficient test and thermal stress restrained specimen test. Five types of asphalt mixtures namely: A, B, C, D and E were evaluated. Results show that compared with the thermal stress restrained specimen test, beam bending test, indirect tensile test and contraction coefficient test are not appropriate for the evaluation of asphalt mixtures low temperature performance. Moreover, results of gray relational analysis demonstrate that the bending strain energy density is significantly correlated to fracture temperature. It is reasonable to adopt the critical values of bending strain energy density to evaluate the low temperature performance of asphalt mixture in the absence of fracture temperature. [Copyright &y& Elsevier]

Volumetric properties are essential for a better understanding of how to design the mixtures. Due to the irregularity of aggregate shape, these properties vary randomly with the same gradation. In this paper, the volumetric properties [bulk specific gravity (γf), air voids (VV), voids in mineral aggregate (VMA), and voids filled with asphalt (VFA)] were determined on two mixtures types, namely, A and B. These mixtures were statistically analyzed using different distribution methods. Seventy-two samples of Mixture A and 52 of Mixture B were fabricated using the Marshall design method. Results of the study showed that the Weibull distribution could reflect the probability distribution law of the volumetric properties of the mixtures. The two-parameter Weibull distribution function appears to be more appropriate or use with γf and VFA, whereas the three-parameter Weibull distribution function was most appropriate for VV and VMA. The analysis of test results also revealed that there are significant differences in the volumetric properties of the two mixtures tested at the same confidence level. The confidence interval decreases with a decrease in reliability. [ABSTRACT FROM AUTHOR]

• The equivalence of strain method and strain rate method was assessed. • A novel method termed local fitting method based on strain rate was developed. • A comparison of difference models based on strain method and strain rate methods was performed. To accurately determine the flow point of asphalt mixture, the flow number test was performed, and an analysis was conducted on the methods of calculating flow point. Three defects of the existing methods were highlighted, and a novel method termed local fitting method was proposed. The flow number and flow rate were both considered in this research. Strain method and strain rate method were proved to be not equivalent and the extensively employed strain method might present a misleading flow point. In addition, the four-step algorithm of the local fitting method based on strain rate was developed, and the optimal range coefficient K of the present study was calculated as 1.5 based on the alteration trend of flow point. A comparison of the local fitting method and the global fitting method was performed, and significant differences were identified in the fitting curves and calculated results. Moreover, equivalence of Francken and Hoerl strain rate models from the two methods was also assessed, and it was found that significant differences might exist between the two models when using global fitting method, whereas no significant difference was identified based on local fitting method. The novel local fitting method was considered a better analytical procedure to determine the flow point of asphalt mixtures. [ABSTRACT FROM AUTHOR]

Measuring the skid resistance of asphalt pavement by pavement texture using non-contact measurement technology has attracted attention in recent years. However, there was no consensus about evaluation method for capturing and characterizing texture of asphalt pavement. This gives rise to the different prediction result of skid resistance for asphalt mixture from the perspective of pavement texture. On this basis, this paper provides an up-to-date review of pavement skid resistance prediction by non-contact approach. In the first section, the Bibliometric analysis was used to analyze the research trend. Subsequently, the friction mechanism and the role of texture under different condition were reviewed. In this direction, the characterization of texture relating to skid resistance was summarized. Finally, the texture-based skid resistance evaluation model was reviewed. The result indicates that the effective contact texture is occurred within 1 to 3 mm or 20%− 90% of top topography surface. Non-contact approach enables to capture the texture/skid resistance of pavement in a labor-slight, time-saving manner. It is consistent with the demand of intelligentization of transportation infrastructure. The high-resolution point cloud data provided by non-contact approach is the basis for evaluation of skid resistance accurately. Note that, the geometric parameter provides the indicator basis for multi-scale characterization derived from spectral and fractal approach. In addition, deep learning model is a promising method and in line with the development of artificial intelligence era. The finite element model considers the coupling effect of tire-water-road-temperature especially water film. As another important method, energy-based model allows to reflect the viscoelastic behavior of rubber and the multi-scale fractal features of pavement. To sum up, this paper offered some positive guidance for predicting the skid resistance by using non-contact methods. [Display omitted] [ABSTRACT FROM AUTHOR]

• Determined reasonable image processing methods through the comparison of method. • Established the topological network model of the void by morphological processing. • Determine the preferential path of flow by using Dijkstra algorithm. • Verified the flow preferential path by the computational fluid dynamics model. The void structures in permeable asphalt pavements are capable of creating space for fluid flow, and the preferential paths of fluid most significantly impact its flow features. In the present study, the aim was to investigate the preferential path of fluid flow using topological network model of permeable asphalt mixtures. Permeable asphalt mixtures were produced in the laboratory, and their internal structure images were captured with the computed tomography. To eliminate the interference of noise and defects in the image, reasonable image processing methods of image de-noising and defect processing were identified. The Otsu method and three-dimensional reconstruction technology were employed to build the three-dimensional structure of the voids. The void contents calculated in the experiment were adopted to verify the feasibility of the void reconstruction. On that basis, the topological network model of the void was further built by morphological processing. Subsequently, Dijkstra algorithm was adopted for comparing the flow resistance of different paths in the topological network, as well as for the determination of the preferential path of flow. The computational fluid dynamics model was employed to verify the feasibility of the preferential flow path by analyzing the distribution rules of flow velocity and streamline of fluid. [ABSTRACT FROM AUTHOR]

Rutting has always been considered the main disease in asphalt pavement. Dealing with rutting disease would be benefitted by understanding the formation of rutting and testing the rutting performance of mixtures more reasonably. The objective of this paper is to systematically investigate the rutting mechanism by employing a self-designed rutting tester along with the corresponding numerical simulations. The deformation of different positions of the existing tracking tester was found to be inconsistent, and the loading was not in line with reality. Accordingly, a more practical tester was proposed: the reduced scale circular tracking (RSCT) tester integrates the functions of asphalt mixture fabrication and rutting monitoring. The results demonstrated that the loading of the new tester is closer to the actual situation. In addition, determining the stress and displacement characteristics of particles in the asphalt mixture was found to be difficult due to the limitations of the testing methods. Therefore, a two-dimensional virtual rutting test based on the RSCT was built using PFC2D (Particle Flow Code 2 Dimension) to investigate the mechanism of formation in rutting and to obtain the corresponding guidance. The numerical simulation showed that all particles of the specimen tended to move away from the load location. The main cause of rutting formation was the eddy current flow of asphalt mastic driven by coarse aggregates. The aggregates with diameters ranging from 9.5 to 4.75 mm were observed to have the greatest contribution to rutting deformation. Therefore, the aggregate amount of these spans should be focused on in the design of mixture grading. [ABSTRACT FROM AUTHOR]

Warm mix asphalt mixtures have the advantages of energy saving, emission reduction and good road performance. Zeolite asphalt mixtures, as a warm mixing technology, have been applied in the world. To understand the warm mix mechanism of zeolite warm mix asphalt mixture, the mesoscale structure of zeolite asphalt is studied. Micro computed tomography (CT) is utilized to obtain the internal structure image of zeolite-modified asphalt and asphalt mixture. The quantity and volume of voids are used as internal void distribution evaluation indexes. The results indicate that with respect to the void distribution in zeolite-modified asphalt, with the increase of temperature, there is an obvious evolution trend of smaller voids to larger voids. With respect to the voids in the zeolite-modified asphalt mixture, the zeolite asphalt mixture is equivalent to hot mix asphalt mixture when it is above 120 °C, while below 120 °C, the maximum and average void volumes increase significantly, making it difficult for the mixture to achieve ideal compaction effect. [ABSTRACT FROM AUTHOR]

• Vulcanized Eucommia ulmoides gum modified asphalt made from natural plant materials was created. • The optimal preparation parameters of vulcanized Eucommia ulmoides gum modified asphalt were determined. • Clarified the relationship between the dosage of Eucommia ulmoides gum and the optimal dosage of sulfur. • The modification mechanism of vulcanized Eucommia ulmoides gum modified asphalt is clarified from the microstructure. • The combustion products of vulcanized Eucommia ulmoides gum modified asphalt were clarified. In this study, a vulcanized Eucommia ulmoides gum modified asphalt (VEUGMA) was prepared using a natural plant-based renewable rubber Eucommia ulmoides gum (EUG) as the matrix. The preparation process and microstructural and thermal properties of VEUGMA were investigated. The results showed that the optimum shearing time for preparing VEUGMA was 45 min, and the optimum development time was 120 min. Moreover, the EUG dosage follows a monotonically decreasing linear relationship with the optimum sulfur dosage. The VEUGMA exhibited a preferable corrugated network structure, and the vulcanization process of EUG in asphalt can be divided into three stages: slight crosslinking, deep crosslinking, and supreme crosslinking. The X-ray diffraction pattern displayed that only new diffraction peaks of ZnO appeared in the VEUGMA, and the EUG and asphalt exhibited better compatibility under the action of vulcanization aids. After EUG was vulcanized in asphalt, the aromatic ring hydrogen in the asphalt was replaced by aliphatic chains. The VEUGMA exhibited a lower glass transition temperature that suggests a better low-temperature crack resistance. Two maximum decomposition temperatures were noted in the thermal decomposition process of VEUGMA. Moreover, the main gases released were CO 2 , CO, CH 4 , SO 2 , NO 2 , and NO; of which, CO 2 and CO exhibited the highest content, whereas the inferior emissions of SO 2 , NO 2 , and NO, can be ignored. The VEUGMA can effectively reduce the release of CO 2 and CO but has no significant effect on the release of CH 4. Further, VEUGMA demonstrated a smaller storage modulus (E'), loss modulus (E"), and loss factor (tanδ), which suggested better flexibility at low temperatures. Therefore, this work demonstrated the preferable modification effect achieved by adding 3.5 wt% EUG and 6 phr (parts per hundred parts of resin) sulfur to the matrix asphalt. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cracking performance of asphalt binder was studied using various rheological indicators. • G-R parameters and ΔT c are most sensitive to aging effects. • G-R parameter is the potential indicator for evaluating the low-temperature cracking of asphalt binders. • The aging model using G-R parameter could describe the aging rule of asphalt binder. The cracking resistance of asphalt pavement is significantly affected by the aging of asphalt binder. A better understanding of the effect of aging on the cracking resistance of virgin asphalt binders can help to determine the optimum maintenance time. In this study, the rolling thin film oven test (RTFOT) and pressure aging vessel (PAV) test were conducted to simulate short-term aging and long-term aging of asphalt binders, respectively. Frequency sweep tests were conducted on two asphalt binders at different aging conditions. The Glover-Rowe (G-R) parameter, stiffness modulus (S), creep rate (m), continuous grading temperature (T c), critical temperature difference (ΔT c), relaxation time (λ), dissipation energy ratio (W d /W s), low-temperature indicator ratio (m/S), low-temperature comprehensive compliance parameter (J c) were obtained. Meanwhile, the sensitivities of different indicators to aging were analyzed and the correlations between G-R parameter and various low-temperature indicators were discussed. Subsequently, a nonlinear model of asphalt binder aging was established by a rheological indicator. The results showed that aging had a significant impact on the low-temperature properties of asphalt binder. G-R parameter, T c , λ increased with the growth of aging severity, whereas m , ΔT c , W d /W s were contrary to this trend. S , m/S , J c had no significant relationship with the degree of aging. Moreover, G-R parameter and ΔT c were very sensitive to aging. The G-R parameter had a good correlation with m , T c , λ, ΔT c and W d /W s , respectively. It indicated that G-R parameter was closely related to the low-temperature properties of asphalt binders. The aging nonlinear model containing G-R parameter could exactly describe the aging evolution of virgin asphalt binder. It is helpful for the prediction of cracking resistance of asphalt binder and determination of maintenance plan. [ABSTRACT FROM AUTHOR]

The interfacial interaction between asphalt binder and mineral aggregate makes different components have different diffusion behavior. It influences the performance of interface and consequently that of the mix. In this research, the models of four asphalt components (asphaltene, resin, aromatics and saturate) and five minerals were constructed individually, and then the Al2O3-asphalt interface model was constructed by adding the asphalt layer and mineral layer together. The interfacial behavior at molecular scale was simulated by setting boundary conditions, optimizing the structure and canonical ensemble. The mean square displacement (MSD) and diffusion coefficient of particles were selected as indicators to study the diffusion of asphalt components on the surface of Al2O3. The results show that when the temperature was 65 °C, asphalt binder showed more viscosity, the diffusion speed of asphalt components ranked according to their molecular mass, which was saturate > aromatics > resin > asphaltene. At 25 °C and 165 °C, the resin had the fastest diffusion speed, which was nearly twice of asphaltene. The interaction between asphalt components and Al2O3 mineral surface can make the diffusion of asphalt components independent on temperature. [ABSTRACT FROM AUTHOR]

• Capture appropriate models in the discussion of TNn, TN5d and CR. • TNn and TN5d extreme events influence on pavement temperature with depth. • Identify the low-temperature performance based on winter temperature extremes. Winter temperature extremes are of major interest due to their potential damaging impacts related to pavement temperature and thermal cracking. In the present paper, three climate indices are adopted to describe the feature of winter temperature extremes. Statistical models for indices are analyzed based on the observed data in Harbin. The threshold values with their 99.9% cumulative frequency are proposed. Experiments were carried out in order to investigate the impacts of winter temperature extremes on pavement temperature and low-temperature performance of asphalt mixture. The results show that Weibull distribution is an appropriate model in the discussion of air temperature and its duration, and Frechet is the best-fitted model for the rate of air temperature change. Comparisons of experimental results indicate the importance of winter temperature extremes to asphalt pavement temperature. The influence of low-temperature properties by different temperature conditions is also analyzed. The low-temperature performance in Harbin can be accurately quantified by linear interpolation. [ABSTRACT FROM AUTHOR]

Highlights • Aggregates are divided into main skeleton, disruption and mortar aggregate. • Contact number and distance between different aggregates are obtained. • Disruption factor can well represent the expanding effect of aggregates. Abstract Aggregate skeleton is the main load carrying part, which is important for the performance of asphalt mixture. Fine aggregate break the skeleton of coarse aggregate is defined as disruption. Based on the X-ray computed tomography and digital image process method, this paper aim to evaluate and verify the disruption in asphalt mixture, and then discuss the effect of disruption on the mesostructure and aggregate contact. Firstly, the aggregate classification and contact property calculation method are proposed. Based on the methods, the relation between disruption factor and contact property is analyzed. The results indicate that there is a strong linear trend between the distance of the main skeleton aggregate and disruption factor, and the disruption factor can well represent the expanding effect of disruption aggregate on the main skeleton aggregate. Additionally, higher disruption factor will leads to the decrease of the number of contact between the main skeleton aggregate and the increase of the contact number of the disruption aggregate. Further, if asphalt mixture has lower disruption factor, the internal contact between the main skeleton aggregates is closer. [ABSTRACT FROM AUTHOR]