Elastomer/plastic compound-modified bitumen was created by adding reactive elastomeric terpolymer (RET) to plastic-modified bitumen, made of either high-density polyethylene (HDPE) or recycled polyethylene (RPE). The rheological properties of the modified bitumen were analyzed. The results indicated that RET elastomer improved high-temperature modulus, temperature insensitivity, anti-rutting properties, elastic recovery, and shear-resistance of both HDPE and RPE-modified bitumen. A high dosage of RET had a negative impact on the cracking resistance of plastic-modified bitumen, thus it is recommended to use 1wt% for optimal results. The increased elasticity in the bitumen was attributed to the creation of a polymer network by RET.

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The rapid development of economy has led to an increase of acid rain that can react with the bitumen physically and chemically, causing further damage to the bitumen properties. Therefore, the effects of acid rain on the chemical composition and rheological properties of bitumen at different depths were investigated in this study. Fourier transform infrared spectroscopy and dynamic shear rheometer tests were performed on the bitumen samples after immersion in acid rain. The results show that in the early stage of immersion, acid rain leads to carbonyl dissolution, reduction of complex modulus, increase of phase angle, and softening of bitumen, thus improving the fatigue cracking resistance. In the late stage of immersion, bitumen is gradually oxidized to form carbonyl group. The change degree of complex modulus and phase angle decreases, and the fatigue cracking resistance is weakened with time. The effect of acid rain on the fatigue cracking resistance fluctuates more for bitumen at 0~50 μm and is more stable for bitumen at 50~100 μm.

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Based on the efficient resource utilization of scrap tires, pyrolysis carbon black (PCB), and pyrolysis oil of waste tire (TPO), scrap tires' products were treated using dry styrene-butadiene-styrene (SBS) polymer modification of asphalt. The products of scrap tires, PCB and TPO, were handled using dry SBS polymer modification of asphalt based on the effective resource use of scrap tires. The consequences of scrap tires, PCB and TPO, were taken using dry SBS polymer modification of asphalt based on the effective resource use of scrap tires. PCB and TPO composite effect seriously degraded. Based on this, the impact of dry SBS polymer modification on the functionality of PCB-TPO-modified asphalt and the mechanism of modification was examined. According to the investigation, the SBS polymer was evenly distributed and fully developed in the asphalt mixture, which significantly enhanced the qualities of asphalt and the asphalt mixture and performed a positive role in the internal structure of the asphalt mixture.

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Bitumen fatigue resistance is critical to determine the overall fatigue performance and service life of asphalt pavements. However, the mechanisms responsible for fatigue damage of bitumen have previously not been well understood. Molecular dynamics (MD) simulation has recently emerged as a powerful computer-aided numerical technique to model the microscopic failure behaviours in materials. This study aims to use the MD method to investigate the molecular origin of bitumen fatigue damage. The molecular models of the virgin and aged PEN70/100 bitumen were firstly constructed based on their saturate, aromatic, resin and asphaltene (SARA) four fractions. An MD equilibrium was run on the developed bitumen models with the assigned interatomic potentials. Following an MD-based tensile simulation, a strain-controlled fatigue simulation was performed to study the nanostructure and damage behaviours of the virgin and aged bitumen under fatigue loading by calculating the stress-strain response, potential energy, molecular structure and nanovoid volumes. Furthermore, a rheometer measurement was also conducted to characterise the fatigue damage of the bitumen directly by a crack length at the macroscale. Results indicate that the bitumen molecules become unfolded and tend to align along the loading direction when fatigue loading was applied. The change in the molecular configuration helped the molecular chains move closer together and thus contributed to the reduction of the intermolecular interactions including the van der Waals and Coulombic energies. With the increasing load cycles, nanovoids were formed and grew in the bitumen through molecular rearrangement and movement, leading to microscopic fatigue damage of the bitumen. It was found that the aged bitumen produced more severe fatigue damage than the virgin bitumen, which was indicated by the MD-based nanovoid volume at the molecular scale and the DSR-based crack length at the macroscale. The findings from MD simulation provide a fundamental understanding of the molecular origin of fatigue damage, that cannot be experimentally detected for bitumen materials.@en

Two types of elastomer/plastic compound-modified bitumen were developed by means of incorporating the reactive elastomeric terpolymer (RET) into the plastic (high-density polyethylene HDPE or recycled polyethylene RPE) modified bitumen and adding the wax residue (WR) into the bitumen/elastomer (crumb rubber CR or styrene–butadiene–styrene SBS) blends. The rheological properties, morphology microstructure and storage stability of these novel elastomer/plastic compound-modified binders were characterised. The results revealed that RET elastomer positively improved the high-temperature modulus, temperature insensitivity, rut resistant, elastic recovery and shear-resistance of HDPE- and RPE-modified bitumen. However, excessive RET dosage adversely influenced the cracking resistance of plastic-modified bitumen, and its optimum dosage was recommended as 1 wt%. Moreover, RET elastomer significantly strengthened the storage stability of HDPE and RPE-modified binders. The elasticity improvement effect of RET was attributed to the generated polymer network. On the other hand, adding WR limitedly deteriorated the rutting resistance and weakened the elastic recovery performance of elastomer (CR and SBS) modified bitumen. To ensure the low-temperature performance, the optimum level of WR was 2 wt%. Furthermore, the addition of WR promoted the compatibility and dispersion of CR and SBS modifiers in bitumen.@en

Cow dung waste has caused severe environmental pollution and public health issues in China. In this study, the cow dung residues were used as a cheap renewable fiber to modify asphalt binder, providing a new solution for the proper disposal of cow dung waste. Three cow dung fibers with two lengths were prepared using different treatments, including original cow dung fiber (CDF), surface treatments of cow dung fiber (STCDF) and alkali treatments of cow dung fiber (ATCDF). The physicochemical properties of CDF, STCDF and ATCDF were analyzed by scanning electron microscope (SEM) and thermogravimetry (TG). The viscidity, rheological properties and fatigue characteristics of CDF modified asphalt binders (CDFMA) were evaluated using Brookfield viscometer and dynamic shear rheometer. The results showed that the rough surfaces of STCDF and ATCDF improved their thermal stability. STCDF and ATCDF enhanced the resistance to permanent deformation under high temperature conditions of modified asphalt binder. STCDF modified asphalt binders exhibited the best viscosity and rheological performance. The increase of fiber length was positively correlated with the high temperature deformation resistance of CDFMA. CDF, STCDF and ATCDF inhibited fatigue cracking of modified asphalt binders compared to base asphalt binders. ATCDF modified asphalt binders exhibited higher fatigue life and smaller crack under the same cyclic loading. The increase in fiber length had a slight improvement on the fatigue resistance of modified asphalt binders.

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Surface energy is a key material property and can work as a crucial parameter in various mechanical models to predict the moisture sensitivity and fatigue damage of asphalt mixtures. The calculated surface energy values of the aggregate minerals strongly depend on their surface roughness. Therefore, it is very relevant for accurate calculation of surface energy to study the relationship between roughness and surface energy. This study aims to investigate the relationship between surface roughness and surface energy of aggregate minerals. Two minerals—quartz and calcite—were used for this study. The surfaces of the mineral specimens were treated to achieve four levels of roughness. Their surface roughness was described by three roughness parameters. Based on the sessile drop method, an optical tensiometer with a 3D topography module was employed to measure the contact angle and the surface energy of the minerals with different roughness. The influences of surface roughness on the contact angle and the surface energy were then analyzed. The results showed that the contact angle for both quartz and calcite decreases with the increasing surface roughness when it is less than 90° and increases when it is greater than 90°. The Wenzel equation can remove the effect of surface roughness on the contact angles of the minerals. The surface energy of quartz and calcite in the presence of roughness at the microscale would be underestimated when using the measured (apparent) contact angle. The corrected surface energy based on the Wenzel equation must be applied to represent the real surface energy of the minerals.

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The occurrence of cohesive/adhesive hybrid failure at the bitumen-aggregate interface is widely acknowledged, however, the quantitative evaluation of the cohesion/adhesion proportion is relatively weak. This study explored cohesive/adhesive hybrid failure and provided a quantitative analysis of the proportion between cohesion and adhesion. For this reason, this study considered a variety of experimental factors that included temperature (5 °C, 15 °C, and 25 °C), mineral morphology (three mineral types and three surface textures), and measured film thickness (varying from 10 μm to 900 μm). By performing the bonding strength test, the strength was recorded and interface failure was accordingly captured. The results indicated that the cohesion/adhesion proportion varied significantly with the temperature, mineral morphology, and measured film thickness. In addition, it was found that bonding strength decreased with the increase in the film thickness and temperature, which can be well explained by variation in adhesion/cohesion proportion. Complete cohesive failure was observed when the film thickness increased beyond a critical value at a relatively high temperature. An additional noteworthy finding was the resemblance of a lunar crater for the failure interface at high temperatures, signifying the heterogeneous composition of the bituminous binder around the interface.

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Usage of asphalt mixture with poor gradation will most likely lead to pavement deficiency. There is a growing need for rapid and non-destructive methods to extract pavement aggregate gradation. In this study, a deep learning-based method that utilizes point clouds data for gradation extraction was proposed. Firstly, a data enhancement algorithm along with three data format conversion methods (aligned point cloud, voxel, and depth image) were proposed to preprocess the original collected point clouds. Subsequently, different neural network models were designed for each data format to extract gradation. Finally, a multi-feature fusion network was developed, which using extraction network as the backbone and additional auxiliary information. In the case study, the MAE loss of multi-feature fusion networks with PointNet, Vox-ResNet34 and GoogLeNet-v4 as the backbone respectively achieved 0.202, 0.142 and 0.046 on the test set, which means an estimation accuracy of more than 95% for the pavement aggregate gradation.

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The special environment conditions in high altitude areas leads to serious cracking and peeling of road hot-melt marking coatings. In order to improve the durability of marking paint, a durable hot-melt marking paint was designed by modifying the paint with toughening-agent, rheological agent, and anti-aging agent. The modification mechanism of the modified coating was revealed through TG and FTIR analysis. The low-temperature anti cracking, adhesion, and anti-aging properties of the modified coating were studied by low-temperature bending test, interlaminar shear test and UV aging test. Besides this, the workability of modified coatings was tested onsite. The results showed that the mass loss rate of the rheological agent is 0.15% at 240 °C, the modified coating had good thermal stability within the mixing temperature range of the coating. There was no chemical change between the modifier and the coating, which was a physical blend. The modified marking paint had good fluidity, softening point and drying time, but its compressive strength was slightly reduced. With the increase of the content of the toughener, the low temperature crack resistance and adhesion of the marking coating gradually increase. When the toughener is 5%, the flexural tensile strain of the marking coating beam increased by 79.1%, and the adhesion strength of asphalt concrete increased by 53.4%. The anti-aging agent can shield most of the UV radiation and improve the anti-aging property of the coating by about 30%. The field process validation achieved the expected results. The modifier coating has excellent low temperature crack resistance, adhesion, UV aging resistance, and other properties, and has good application prospects in harsh environment areas.

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This study aims to multiscale investigate the effects of rejuvenator type, temperature, and aging degree of bitumen on the diffusion behaviors of rejuvenators (bio-oil BO, engine-oil EO, naphthenic-oil NO, and aromatic-oil AO) in aged binders. The molecular dynamics (MD) simulation method is performed to detect the molecular-level diffusion characteristics of rejuvenators and predict their diffusion coefficient (D) parameters. At an atomic scale, the mutual but partial interfacial diffusion feature between rejuvenators and aged bitumen molecules is observed. Moreover, Fick’s Second Law well fits the concentration distribution of rejuvenator molecules in aged bitumen. The magnitude for D values of four rejuvenators varies from 10-11 to 10-10 m2/s, and the diffusive capacity order is BO > EO > NO > AO. Meanwhile, diffusion tests and dynamic shear rheometer (DSR) characterizations are employed to validate the MD simulation outputs. The experimental results in magnitude and order of D values agree well with MD simulation outputs. Lastly, the increased aging degree of bitumen exhibits a negative impact on the molecular diffusivity of BO, EO, and NO rejuvenators, while the D value of AO molecules enlarges as the aging level deepens. The underlying mechanism may be composed of the free volume fraction in aged bitumen and the intermolecular force between rejuvenator and aged bitumen molecules, which differs remarkably for various rejuvenators.@en

Molecular dynamics (MD) simulation is an advanced tool to explore the interaction mechanism between aged bitumen and rejuvenators at the nanoscale. However, the general MD molecular structures of rejuvenators led to the lower quantify and inaccuracy of the simulation outputs. This study aims at developing more realistic molecular models to represent the generic rejuvenators for MD simulation of aged bitumen recycling. Four types of rejuvenators (bio-oil, engine-oil, naphthenic-oil, and aromatic-oil) are characterized in terms of element analysis, functional groups distribution observed from Attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy, and average molecular weight. Afterward, the average molecular structures of rejuvenators are determined and validated. Further, the MD simulations are performed to predict the energetic, dynamic, volumetric,
and structural properties of various rejuvenators. Based on the chemical characteristics, the average chemical formula of bio-oil, engine-oil, naphthenic-oil, and aromatic-oil is derived as C19H36O2, C22H44, C26H48, C30H40. From MD simulations, the ranking of density and glass transition temperature for four different rejuvenators is AO > NO > BO > EO, which is same as the experimental results. It proves that the established average molecular structures of four rejuvenators are reasonable. Various rejuvenators display different thermodynamics and structural properties. The aromatic-oil exhibits the highest potential energy, cohesive energy density, and solubility parameter. Besides, the order of expansion coefficient and diffusion coefficient of the four rejuvenators is the same as BO > EO > NO > AO, while the viscosity presents the opposite sequence. Moreover, the fractional free volume values follow EO > BO > NO > AO. The occurrence probability between bio-oil and aromatic-oil molecules is higher than engine-oil and naphthenic-oil. This study develops the representative average molecular models for generic rejuvenators and helps understand the difference in chemo-physical and thermodynamics properties among various rejuvenators.@en

Conventional asphalt mixture has poor microwave absorbing performance and microwave heating efficiency. Based on the characteristics of dielectric loss of scrap tire pyrolysis carbon black (PCB), it is proposed to improve the microwave absorbing performance and self-healing rate of bitumen. The phase composition and electromagnetic parameters of PCB were tested to reveal its microwave heating mechanism. The preparation parameters, heating characteristics and self-healing properties of PCB modified bitumen were studied through the dispersion uniformity test, microwave heating test and SCB test. The main phases of PCB are microwave absorbing carbon and silicon, indicating that PCB is a good electric loss microwave absorbing material. 40 min is the recommended mixing time of 15% PCB modified bitumen. PCB's dosage, microwave frequency and microwave heating time have significant effects on the microwave heating characteristics of PCB modified bitumen. PCB can improve high-temperature stability, thermal conductance, heat storage capacity and self-healing rate of bitumen.

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Molecular dynamics (MD) simulation plays an effective role in predicting the critical properties and explaining the macroscale phenomenon at the nanoscale. This review summarized the application cases of MD simulations in various bitumen systems, considering aging, modification, and rejuvenation factors. Meanwhile, the potential relationships between the nanoscale parameters predicted from MD simulations and macroscale properties measured from experimental tests were discussed for the first time. Different molecular models of virgin bitumen, commonly-used Forcefields, and validation parameters for MD simulations on bituminous materials were summarized. Based on the reactive MD simulation outputs, the oxidative aging reaction path at the atomic scale of bitumen molecules was reviewed. Furthermore, the influence of aging (short-term and long-term), modification (polymers, fillers, and bio-bitumen), and rejuvenation (various rejuvenators) on the molecular-scale properties of virgin bitumen models would be evaluated through MD simulations. This review could help us further explore the main functions of MD simulations in different bulk bitumen systems and build an integral multi-scale research method from the molecular design and performance prediction to material optimization and synthesis of bituminous materials without lots of experimental attempts.@en

Bitumen in asphalt pavements reacts slowly with atmospheric oxygen, resulting in oxidative ageing. This oxidative reaction is strongly dependent on the physical diffusion of the oxygen into the bitumen. This study aims to use molecular dynamics (MD) simulation to investigate the oxygen diffusion into the bitumen film and analyse the effects of anti-ageing compounds (AACs) on the oxygen diffusion. The MD diffusion simulations using a Polymer Consistent Force Field (PCFF) were conducted on a bitumen-air bi-layer model at different temperatures. Fick's second law was used to calculate the diffusion coefficient of the oxygen in the bitumen film. It is found that the oxygen diffusion coefficients ranged from 6.67 × 10⁻¹⁰ to 7.45 × 10⁻¹¹ m²/s for the unmodified and AAC-modified bitumens at the simulating temperatures of 25, 50 and 100 °C. Irganox acid and DLTDP (Dilauryl thiodipropionate):furfural showed two different anti-aging mechanisms, i.e., reducing the oxygen physical diffusion and controlling the chemical oxidative reaction. Reducing the oxygen diffusivity by constructing a network in the bitumen to retard oxygen diffusion and increase the transport path is an efficient way to slow down the bitumen aging without the antioxidant consumption. This work proposed a MD-based computational approach, contributing to 1) determination of the oxygen diffusion coefficient of the existing bitumen that is extremely challenging for the experimental measurement and 2) instruction of developing new antioxidant.

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Owing to the continuous increase of traffic loads, bitumen modification has been manifested as an efficient methodology to enhance asphaltic pavement performance. Currently, the modification index, defined as the ratio of mechanical properties (e.g., complex modulus) before and after bitumen modification, is extensively adopted to evaluate the modification degree. However, bituminous materials behave as temperature-dependent, which indicates that the mechanical property varies with measured temperatures. As a result, the calculated modification index also shows temperature-dependent property, which inhibits the use of modification index. For this reason, this study introduced a method to eliminate the temperature-dependency of the modification index. In specific, a mathematical model considering the properties of modifiers was firstly established to predict the modification index-temperature curve (MI-T curve). In what follows, the temperature-dependency of modification index was analyzed to verify the proposed model on three types of modifiers, which were graphene, Styrene-Butadiene-Styrene (SBS), and Ethyl-Vinyl-Acetate (EVA), respectively. The results indicated that the developed model could efficiently predict the MI-T curves. Besides, the effective modification area (EMA) and optimal modification index (OMI) were two reasonable indicators that evaluate the bitumen modification without considering the temperature-dependency.@en

To meet the needs of the road industry for maintenance operations, a new cement emulsified bitumen mixture (CEBM) with early-strength, self-compacting, and room-temperature construction characteristics was designed. The strength formation mechanism of CEBM was revealed with a scanning electron microscope (SEM) and the surface free energy (SFE) theory. The mechanical properties and road performance of the CEBM were investigated extensively. The results show that before the demulsification of emulsified bitumen, the SFE of the bitumen–aggregate–water three-phase system was reduced due to the replacement of the bitumen–aggregate interface with water. The adhesion work between the emulsified bitumen and the aggregate is negative, which means the adhesion between the emulsified bitumen and the aggregate will not occur spontaneously due to the existence of water. The liquid emulsified bitumen improves the workability of the mixture and ensures that the mixture can be evenly mixed and self-compacted. After demulsification, the work of adhesion between the residual bitumen and the aggregate is positive, which means residual bitumen and aggregate can bond spontaneously. In addition, the hydration products of cement and aggregate form a skeleton, and the emulsified bitumen film wraps and bonds the cement and aggregate together, creating strength. The emulsified bitumen, cement content, and curing conditions have significant effects on the stability of CEBM. The recommended dosage of emulsified bitumen and cement is 8% and 8–10%, respectively. This material integrates the hardening effect of cement and the viscoelastic performance of bitumen and has good workability, mechanical properties, and road performance. Therefore, the CEBM is technically feasible for application to bitumen pavement.

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The compatibility potential of rejuvenators plays an important role in improving the blending degree of rejuvenated bitumen. This study aims at estimating the efficiency of molecular dynamics (MD) simulation in predicting the compatibility between rejuvenators and aged bitumen, and exploring the influence of rejuvenator type, aging degree of bitumen, and temperature on the compatibility potential. The thermal storage stability of rejuvenated binders is evaluated to validate the compatibility prediction. Afterward, the underlying mechanism for the storage stability difference between rejuvenators and aged bitumen is explained with the atomic-scale parameters. The results revealed that the ranking on predicted compatibility and experimentally measured thermal storage stability for four rejuvenators is the same as AO > BO > NO > EO. Furthermore, the thermodynamic parameters of solubility parameter difference Δδ, Flory-Huggins parameter χ, and mixing free energy ΔGm are efficient for estimating the compatibility potential of various rejuvenators with aged bitumen. Moreover, the separation index (SI) parameters based on rheological and chemical indices are available to assess the phase stability of rejuvenated bitumen. At the molecular scale, the compatibility and phase stability issues between rejuvenators and aged bitumen are complicated and related to different aspects of intermolecular interaction, dispersion degree, and molecular mobility.@en

A self-compacting steel slag epoxy resin concrete (SERC) was designed with steel slag as aggregate and epoxy resin as binder for rapid repair of road expansion joints and pavement. At the same time, a group of self-compacting basalt epoxy resin concrete (BERC) with basalt as coarse aggregate and limestone as fine aggregate was set up as the control group. The element analysis and micro morphology of SERC and BERC were studied by X-ray fluorescence spectrometry (XRF) and scanning electron microscope (SEM) to reveal the strength-forming mechanism of the two epoxy resin concretes. The cube compression test and Marshall stability test were used to study the effect of the strength formation rate and temperature of SERC and BERC on the strength. In addition, the high-temperature stability, low-temperature crack resistance, water damage resistance, fatigue resistance and interlayer bonding properties of SERC and BERC were also studied. The results showed that both SERC and BERC have good mechanical properties, high temperature properties and good bonding properties, and the low-temperature crack resistance and fatigue properties of SERC are better than that of BERC. According to the verification of the actual project that has been in service for one year, SERC can be perfectly used for road expansion joints.

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Traditional asphalt mixtures can't absorb microwave energy efficiently, which limits the development of microwave heating technology in the field of road maintenance. Based on the microwave heating characteristics of basalt aggregates, the overall microwave self-healing rate of the asphalt mixture can be enhanced. The basalt was tested by XRF, XPS, XRD and electromagnetic parameters to reveal its microwave heating mechanism. Through the heating rate test, SCB test and fatigue test of asphalt mixture, its heating characteristics, flexural strength, fatigue resistance and self-healing performance were studied. The results showed that the excellent wave-absorbing properties of basalt are highly correlated with the elements of Si, Fe and Al. Its TanδM was slightly larger than TanδE, which indicated that basalt can absorb microwave energy through dielectric loss and magnetic loss. The aggregate type and particle size both affected the microwave heating rate of the aggregates. After microwave heating, the flexural strength and fatigue resistance of asphalt mixture with basalt and limestone aggregates can recover at least 65% and 23% respectively.@en