Asphalt-aggregate Interface Research Articles

Adhesion failure mechanism of asphalt-aggregate interface under an extreme saline environment: A molecular dynamics study

The extreme saline environment seriously threatens the service life of asphalt pavement. The interface adhesion failure between asphalt and aggregate is fundamental to pavement diseases. Therefore, the interface of asphalt-NaCl solution-mineral was simulated by molecular dynamics to investigate the adhesion failure mechanism between asphalt and aggregate in an extremely saline environment. The results show that the polarization-inducing effects of sodium and chloride ions promote the cross-sectional diffusion of the NaCl solution at the interfaces and contribute to the redistribution and rediffusion of asphalt components, and the formation of hydrogen bonds between water and asphalt components. The NaCl solution prevents the accumulation of saturates, resins, and asphaltenes on the SiO2 surface, and strips aromatics from the SiO2 surface due to the interaction. Sodium ions can be attracted to the oxygen atoms on CO32– to occupy active sites on the CaCO3 than asphalt, which makes it easier for chloride ions to penetrate the asphalt molecule and asphalt components to detach from CaCO3. These behaviors effectively impair the adhesion at the asphalt-mineral interface. The 3 wt% and 20 wt% NaCl solutions have the greatest effect on the adhesion work of the asphalt-SiO2 and asphalt-CaCO3, reducing them by 55.93 % and 66.03 %, respectively.

The investigation of surface free energy components and moisture sensitivity damage of asphalt mixes modified with carbon black using the sessile drop method

Asphalt pavement is vulnerable to moisture damage when water infiltrates the asphalt-aggregate interface and weakens their bond. To prevent this problem, researchers have explored the use of additives to increase resistance against moisture damage. The moisture sensitivity of asphalt mixtures can be assessed by measuring their basic properties related to the mechanism of moisture damage. One effective approach to this is using the surface free energy method, which calculates bond energies between different materials’ surfaces and identifies the most appropriate combination of asphalt and aggregate. High cohesion or adhesion bonding is crucial for the proper performance of asphalt mixtures, such as moisture damage resistance. This study aimed to investigate the effect of carbon black additive on moisture damage resistance using surface free energy methods, comparing results with the Tensile Strength Ratio (TSR) test. Modified asphalts containing 4, 8, 12, and 16% carbon black were tested, with natural base asphalt as a control sample. The study used surface free energy theory to determine moisture sensitivity parameters of asphalt mixtures by obtaining surface free energy components of the raw materials and testing the ratio of tensile strength. Results showed that adding 8% carbon black to the asphalt mixture improved moisture sensitivity, and increasing additive content up to 16% reduced it but still provided better results than samples made with pure asphalt. The study concluded that the surface free energy method can determine the suitable combination of asphalt and aggregate materials for resistance against moisture damage.

Effects of freeze–thaw cycles on micro and meso-structural characteristics and mechanical properties of porous asphalt mixtures

Abstract Porous asphalt concrete (PAC) have a typical big void-skeleton structure, and porous asphalt mixtures with large voids are more prone to freeze–thaw damage. As a result, research on the influence of freeze–thaw cycles on the micro-structure and mechanical characteristics of porous asphalt mixes offers a theoretical framework for overcoming water stability concerns in porous asphalt mixtures in practice, as well as for further popularization and application. In this study, styrene–butadiene–styrene (SBS)-modified asphalt and high viscosity modified asphalt were constructed on the basis of the original asphalt, and the mix proportions of asphalt mixes PAC-13, AC-13, and SMA-13 were designed. To begin, molecular dynamics simulations were used to look into the effects of freeze–thaw cycles on asphalt–aggregate interface adhesion and mixture micro-mechanical properties. Second, the effects of freeze–thaw cycles on the void characteristics of porous asphalt mixtures were explored utilizing digital image processing technologies. Finally, the freeze–thaw split test was utilized to evaluate the macroscopic mechanical properties of a porous asphalt mixture after freezing and thawing cycles. According to the study findings, high viscosity modified asphalt made with 4% SBS/8% TPS has the greatest performance. The application of SBS/TPS-modified asphalt can considerably improve the damage resistance of porous asphalt mixes. The micro-structure and mechanical qualities of porous asphalt mixtures are damaged by freeze–thaw cycles, and the damage gets worse as the number of cycles rises. The study’s conclusions provide a theoretical justification for the application of porous asphalt pavement.

Adhesion Properties of Recycled High-Viscosity Asphalt-Aggregate Interface under Dynamic Water Erosion.

The drainage of asphalt pavement requires the use of a large amount of high-viscosity-modified asphalt, which faces the service environment under dynamic water erosion. The feasibility of recycling high-viscosity-modified asphalt should be investigated to facilitate sustainable infrastructure construction. This study used ultrasonic equipment to simulate dynamic water erosion test conditions and tested the adhesion performance of different types of recycled high-viscosity asphalt at various environmental temperatures. The adhesion energy index and microstructure of recycled high-viscosity asphalt were analyzed using the contact angle test and AFM test. The results demonstrate that the higher the environmental temperature, the worse the anti-stripping performance of recycled high-viscosity asphalt. From the perspective of adhesion performance indicators, a 6% recycling agent dosage is more conducive to restoring the performance of aged high-viscosity -modified asphalt. The AFM test showed that the microstructure of high-viscosity -modified asphalt represented significant changes with an increase in the recycling agent content, and the change in the adhesion force of recycled high-viscosity -modified asphalt was consistent with the results of macroscopic adhesion performance tests. This study illustrates the applicability of implementing regeneration technology for the recycling of aged drainage asphalt pavement.

Study on the Adhesion Characteristics of Asphalt-Aggregate Interface in Cold Recycled Asphalt Mixtures

The reclaimed asphalt pavement materials have been used for sustainable cold-recycling, significantly benefiting air quality and resource conservation, while its microscale interface properties greatly affected road performance during the cold-recycling processes. In this investigation, the cold recycled asphalt mixtures were prepared with different mixing proportions, considering the effects of cement content and mixing water amount. The adhesion characteristics of the asphalt-aggregate interface in different cold recycled asphalt mixtures have been comprehensively investigated based on the atomic force microscopic (AFM). The microscale morphology and the adhesion properties, including roughness, inclination angle, adhesion force, Derjaguin–Muller–Toporov (DMT) modulus, and dissipated energy were evaluated at the interface and noninterface regions. The micromorphology results showed that the addition of cement could enhance the roughness and inclination in interface regions. In addition, the content of mixed water showed the most significant effect when the water amount was 80%. The results showed that the adhesion force, DMT modulus, and dissipated energy increased with the addition of cement, indicating that the cement could improve the microscale mechanical properties of cold recycled asphalt mixtures. With the increase of mixing water content, the adhesion characteristics showed varied results, and the optimum water content of 80% contributed to the adhesive properties. In addition, the adhesion force, DMT modulus, and dissipated energy were all higher in the interface region by comparing with the noninterface region. The correlations between the macroscale splitting tensile strength and microscale adhesion characteristics of cold recycled asphalt mixtures were established.

Effect of water molecular behavior on adhesion properties of asphalt-aggregate interface

Asphalt-aggregate interfaces are prone to damage by moisture, leading to a decrease in interfacial adhesion. However, the precise mechanism governing water molecule behavior at these interfaces remains poorly understood. To address this, we employed molecular dynamics simulation to investigate the interaction of water molecules with aggregates and asphalts, as well as the adhesion properties of the interfaces. Simulations revealed that thin water films formed on SiO2, CaO, and MgO surfaces, while water molecules aggregated on Al2O3, Fe2O3, and CaCO3 surfaces due to hydrogen bonding and physical adsorption. Aged asphalt would adsorb more water due to more hydrogen bonds of water molecules with sulfoxide and carbonyl. Furthermore, the adhesion between asphalt and aggregates followed the order: alkaline aggregates > neutral aggregates > acid aggregates under dry conditions. However, in moist environments, the adhesion between asphalt and alkaline aggregates decreased sharply due to stable occupancy of water molecules in the interfacial gap, limiting the interaction between asphalt and aggregates. Additionally, the adhesion of interfaces decreased with increasing temperature due to higher mobility of water molecules, which pushed asphalt molecules further away from the aggregate layer. Conclusively, the molecular behavior of water is the key cause of adhesive damage at asphalt-aggregate interface under moisture condition. Type of aggregate, aging state of asphalt, water content, and temperature all affected the water molecular behavior, ultimately affecting interfacial adhesion.

Effect of thickness on the behavior of aggregate-asphalt-aggregate film subjected to dynamic shearing and uniaxial tension

Although the asphalt-aggregate interface and its film thickness present important effect on performance of asphalt mixtures, there are no effective methods to accurately evaluate those factors. This study focuses on the effect of aggregate-asphalt-aggregate thickness on the shearing and tension mechanical properties of the asphalt-aggregate by using aggregate developed Dynamic Shearing Rheometer (DSR). Utilizing microscopic techniques to observe the surface morphology of different aggregates and the adhesion state of asphalt-aggregate micro-interface zone, and then carried out the dynamic shear rheological test and uniaxial tension test analysis of aggregate-asphalt-aggregate system under different interlayer thickness and different aggregate adhesion conditions. Results indicate that the developed DSR using aggregate plates is a helpful device to simulate the interface in asphalt mixtures. Differences in microscopic morphology and chemical adhesion have a significant impact on the shearing and tension behavior of aggregate-asphalt-aggregate system. The influence of microscopic interaction between aggregate and asphalt on the mechanical behavior of asphalt is dependent on temperature, frequency, interlayer thickness, and loading pattern. The thickness of the interlayer shows different modes subjected to loading, which is reflected as that film thinning means modulus softening during shearing loading and film thinning means modulus strengthening during tension loading.

Variation and mechanism of asphalt-aggregate interface features under ultraviolet aging based on meso- and micro-observations

Time-dependent variation and mechanism of asphalt-aggregate interface features under ultraviolet (UV) aging have not yet been illustrated. This study explored the time-dependent variation and mechanism of asphalt-aggregate interface features under UV aging. To this end, six asphalt binders were chosen and subjected to different durations of UV aging, and then the variation behaviors of their cohesion-adhesion ability with the changing UV radiation time were analyzed through surface energy theory. Further, the microscopic attributes of asphalt binders experiencing the various UV aging durations were measured and their varying rules were investigated with a series of micro observations. Finally, the relationship between cohesion-adhesion characteristics and microscopic properties were illustrated and thus the variation mechanism of interfacial cohesion and adhesion were revealed by mathematical statistics and image presentation. The results showed that UV aging weakened the cohesion and multi-working adhesion of asphalt binders and the moisture stability of asphalt-aggregate systems, and overall presented a gradually strengthened influence on them with the prolonged UV radiation time, especially the UV radiation exceeded 6 days. The variation of phase morphology of asphalt binders under UV aging depended on the asphalt types and neat asphalt oil sources, and there existed a favorable linear relationship between Catana phase of asphalt binders and surface roughness. Adhesion force, function group and four components (saturate (S), aromatics (Ar), resin (R) and asphaltene (As)) also exhibited a gradually increasing variation as the UV radiation duration went on, and among which, the UV aging reduced the adhesion force of asphalt binders. Adhesion force Fad demonstrated the highest Pearson relevance with the cohesion and aqueous-condition adhesion and the moisture stability of asphalt-aggregate system, and the cohesion-adhesion properties of asphalt binders under UV aging met the multivariate linear mathematical relationship with the microscopic attributes screened, with the goodness-of-fit greater than 0.7000.

Interfacial interaction behavior of recycled asphalt pavement: Molecular dynamics simulation

Recycling waste asphalt mixture (WAM) to prepare recycled asphalt pavement (RAP) is an important measure to handle road construction waste. Asphalt-aggregate interface (AAI) and matrix-aged asphalt interface (MAI), as weak interfaces in RAP, interface interaction behavior directly affects the road performance of RAP. In this paper, molecular models of asphalt and aggregate were constructed. Molecular dynamics simulation was used to analyze and evaluate the interaction behavior of the AAI and the MAI in RAP. The mean square displacement (MSD), relative concentration function (RCP), and radial distribution function (RDF) were used to quantitatively analyse the interface interaction behavior. The research results are as follows: For the AAI, the temperature, the aging level of asphalt, and chemical composition of aggregates will affect the interaction behavior of the AAI. Increasing temperature accelerates the diffusion of asphalt on the surface of aggregate. However, the increase of the aging level of asphalt and the alkalinity of aggregate will decrease the interaction rate of asphalt on the surface of aggregate. For the MAI, the temperature and the ratio of filler-asphalt (RFA) significantly affect the interaction behavior of the MAI. The molecular diffusion rate of matrix asphalt and aged asphalt increases significantly with the increasing temperature. The addition of filler will decrease the diffusion rate of asphalt, and the diffusion rate decreases with the increase of RFA. This article comprehensively and systematically studies and evaluates the effect of various factors on the interface interaction behavior. The results provide guidance for improving the adhesion ability of AAI and enhancing the degree of incorporation of MAI.

Investigating the deterioration mechanism of adhesion between asphalt and aggregate interface under acid rain erosion

To further reveal the effect of acid rain on the interfacial adhesion of asphalt mixtures, molecular dynamics (MD) simulation was used to investigate the interfacial damage mechanism. A water layer containing hydrogen ions, sulfate ions, and nitrate ions was inserted between the asphalt and aggregate to simulate the effect of acid rain attack on the interface. The interfacial bonding strength under three conditions of dry, pure and acidic water was analyzed. The effect of acidic ions on the spatial arrangement and movement of asphalt molecules was discussed. The damage of the asphalt-aggregate interface under both pure water and acidic water attack was investigated. The results showed that the acidic ions promote the rearrangement distribution of asphalt molecules at the interface, reduce the concentration of asphalt molecules at the interface, and weaken the adhesion ability at the interface. The degree of aggregation of polar components increases, resulting in a reduction in the movement migration capacity of asphalt and poor mobility, increasing the possibility of asphalt stripping from the aggregate surface. Under the influence of acidic ions, less separation energy is required for interfacial adhesion damage to occur between asphalt and aggregate, and the amount of deformation at interfacial failure is smaller.

Revealing the Thermodynamic Characteristics, Bonding Behavior, and Failure Patterns of the Asphalt-Aggregate Interface Containing SBS/CNT Micronanoparticles at the Molecular Scale

Revealing the Thermodynamic Characteristics, Bonding Behavior, and Failure Patterns of the Asphalt-Aggregate Interface Containing SBS/CNT Micronanoparticles at the Molecular Scale

Study on Adhesion Performance and Aging Strength Degradation Mechanism of SBS Modified Asphalt with Different Anti-Aging Additive.

After aging, the adhesiveness of asphalt deteriorates, leading to a reduction in the durability of asphalt mixtures and affecting the service life of asphalt pavements. To enhance the anti-aging performance of asphalt, this study employed the method of melt blending to prepare three types of modified asphalt: graphene/SBS modified asphalt (G/SBSMA), crumb rubber/SBS modified asphalt (CR/SBSMA), and petroleum resin/SBS modified asphalt (PR/SBSMA). Different dosages of the three types of modified asphalt were tested for changes in conventional performance indicators. The optimal dosages of graphene, crumb rubber, and C9 petroleum resin were determined to be 2%, 15%, and 5%, respectively. Based on the theory of surface free energy, the effects of anti-aging agents on the microscopic properties of SBS modified asphalt before and after aging were analyzed using the three-liquid method. The mechanisms of strength attenuation at the asphalt-aggregate interface under water exposure and aging were revealed. The results showed that with the increase of aging gradient, the asphalt-aggregate biphasic system became more active. The cohesive energy and peel energy of SBS modified asphalt increased continuously, while the adhesive energy decreased continuously, leading to a decrease in the energy ratio parameter. Resin-based anti-aging agents exhibited the most significant improvement in asphalt adhesion performance, while graphene demonstrated a more stable enhancement in asphalt's water stability during the aging stage.

Adhesion Characteristics of Graphene-Modified Asphalt Using Surface-Free Energy Method

Graphene is an auspicious nanomodified material for asphalt pavements. This study aims to evaluate the effect of graphene composites (GCs) on the adhesion characteristics of asphalt based on surface-free energy (SFE) theory. The surface-free energy of graphene-modified asphalt was measured by the sessile drop method. The work of adhesion and stripping between asphalts and two kinds of aggregates were calculated through using their surface-free energy components. The macroadhesion property between asphalts and aggregates was obtained by the improved boiling method. Immersion Marshall test and freeze–thaw splitting test were conducted to verify the effectiveness of surface-free energy indexes. The results demonstrated that GC significantly increased total surface-free energy and dispersion components of asphalt but reduced the polarity components. The adhesion work between asphalt and both aggregates increased after modification, whereas the stripping work decreased after modification. GC can substantially improve the adhesion and resistance to moisture damage at the asphalt–aggregate interface, and the effect on asphalt-limestone is more obvious. There are strong correlations between macro evaluation indicators and surface-free energy calculated indexes, where the macro indicators are more strongly correlated with stripping work. Limestone is generally better at resisting moisture damage than granite. GC remarkably improved the water stability of the mixture, which further indicates that energy indexes are a good method to quantize the moisture damage resistance of hot mix asphalt (HMA). The high dosage of graphene-modified asphalt is potentially applicable to porous asphalt concrete (PAC) pavement with extra-large voids.

Physical and chemical evaluation of adhesion recovery property of aged high-viscosity asphalt based on specialized composite rejuvenators

With the wide application of porous asphalt pavement, the techniques for recycling aged porous asphalt mixture have attracted more attention for facilitating its sustainable development. One of the most critical issues is how to recover the adhesion properties of aged high-viscosity asphalt (HVA). In this study, different specialized composite rejuvenators types on the adhesive properties of aged asphalt binder were designed and evaluated for the goal of adhesion recovery. A bond strength test was used to evaluate the macroscale adhesion properties between the regenerated asphalt and aggregate. Micro-scale chemical and physical tests were utilized to discover the regeneration mechanism of specialized composite rejuvenators on asphalt adhesion. The results showed that the proposed three kinds of composite rejuvenators can effectively restore and improve the adhesive properties of aged HVA. The results of differential scanning calorimetry (DSC) represented that recycled HVA with smaller Tg and total heat absorption showed better adhesion properties. The FT-IR and AFM test results showed that the adhesion of recycled HVA is highly correlated with the C–O functional group index and micro adhesion. In addition, the concave structure in the asphalt surface is more beneficial to improve the asphalt-aggregate interface bonding, and the scheme of adding 8% optimized rejuvenator based on graft co-polymerization had the best effect, which could be promoted for the future application in the recycling of HVA in porous asphalt pavement.

Interfacial Adhesion Property of Asphalt Binder with Calcium Alginate Carrier of Asphalt Rejuvenator.

Recently calcium alginate has been successfully applied to encapsulate asphalt rejuvenator, which can protect asphalt rejuvenator from early leakage and release asphalt rejuvenator when triggered by specific factors such as cracks. The interfacial adhesion property of asphalt binder with calcium alginate carrier is of great importance to its actual performance. In this paper, the molecular model of the interface region between asphalt binder and calcium alginate was established, and molecular dynamics simulations were performed on it to investigate the molecular interaction at the interface region. By extracting and processing the data during the simulation process, the interfacial adhesion behavior was expounded using the spreading coefficient (S), permeation depth and permeation degree. Furthermore, the interfacial adhesion strength was evaluated by adopting the interfacial adhesion work. Results showed that the value of S was greater than 0, implying that asphalt binder could wet the surface of calcium alginate. Saturate had the highest value of permeation degree, followed by resin, aromatic and asphaltene. However, asphalt binder could not infiltrate into the interior of TiO2, only accumulating and spreading on the surface of TiO2. The interfacial adhesion work of unaged and aged asphalt binder to calcium alginate was -114.18 mJ/m2 and -186.37 mJ/m2, respectively, similar to that of asphalt-aggregate interface. The van der Waals interactions contributed the most to the formation of the interfacial adhesion strength. In addition, a certain degree aging of asphalt binder and addition of titanium dioxide in the calcium alginate carrier were helpful to enhance the interfacial adhesion strength.

Effects of Aging and Immersion on the Healing Property of Asphalt-Aggregate Interface and Relationship to the Healing Potential of Asphalt Mixture.

The self-healing ability of asphalt-aggregate bonding interfaces can maintain the mechanical properties of asphalt mixtures. However, the interface's healing ability will also be affected by moisture and aging. In order to clarify the influence of moisture and aging on the healing ability of a bonding interface, the effects of healing period and temperature on the self-healing level of interfacial strength were measured. The healing master curve of the strength was established. Thereafter, the effects of soaking time, salt solution concentration, and thermal aging on the healing degree of interfacial strength were measured. Based on digital image processing technology and the meso-finite element method, the influence of the interface on the healing performance of the mixture was simulated and analyzed, which was then verified by the beam bend healing test. The results show that the healing index of bonding strength increases with the ascent of healing temperature and period. Healing index gradually decreases with the extension of soaking period, and the higher the concentration of salt in the solution, the worse the healing performance of interfacial strength. After asphalt aging, the healing potential of the interface is weakened. There is a good linear relationship between the healing level of an asphalt-aggregate interface and the level of strength and fracture energy of the mixture. However, the actual healing level of an asphalt mixture is obviously lower than that of the interface, due to the addition of mineral filler. This paper provides a method for predicting the recovery performance of asphalt pavement.

Effect of dynamic water pressure on the adhesion behavior of recycled asphalt-aggregate interface by molecular dynamics method

The integrity of the asphalt-aggregate interface is challenged by the dynamic water pressure under traffic loads, especially for recycled asphalt mixtures that represent lower moisture damage resistance by comparing with virgin asphalt mixtures. The effect of dynamic water pressure on the microscale interfacial adhesion properties between the waste-oil recycled asphalt and aggregate was comprehensively investigated based on the molecular dynamic simulation. The molecular models of recycled asphalt and aggregate were calibrated based on the chemical and physical analysis in experiments. The interfacial contact models between recycled asphalt with different regenerants (waste cooking oil-WCO, waste vegetable oil-WVO, and waste engine oil-WEO) and basalt aggregate were established, which also incorporated the thermodynamic process of water intrusion into the interface. The interface behaviors were studied by analyzing the cohesion energy of asphalt, the adhesion energy of interface, and the distribution of asphalt and water concentration on the aggregate surface. The results demonstrated that the dynamic water pressure can accelerate the water to penetrate the asphalt film. The recycled asphalt was pushed away from the basalt aggregate surface after the water film was formed at the interface, where the four components of asphalt leave the interface at different rates. Compared with the other two kinds of waste-oil recycled asphalt and conventional recycled asphalt, the WEO recycled asphalt-aggregate interface represented the optimum moisture damage resistance. The decrease of interface adhesion energy is about 55.7 % subjected to the coupling effects of the high-temperature and dynamic water pressure at 0.5 MPa.

Prediction and evaluation the moisture damage resistance of rejuvenated asphalt mixtures based on neural network

The aim of this paper is to establish a model for predicting the moisture damage resistance of the rejuvenated asphalt mixture. Based on the surface free energy theory, the contact angels between asphalt and aggregate were measured with known reagents using the sessile drop method. The adhesion work, spalling work and moisture damage resistance index of the asphalt-aggregate interface system were then calculated. Secondly, the tensile strength ratio of the rejuvenated asphalt mixture was determined, and the influence of six indices, including RAP content, rejuvenator content, adhesion work, spalling work, per cent air voids in bituminous mixtures (VV) and freeze–thaw cycle on the performance of the moisture damage resistance of rejuvenated asphalt mixture was analyzed using the gray correlation entropy method. Finally, a three-layer neural network was used to predict the moisture damage resistance of the rejuvenated asphalt mixture. The results show that as the content of aged asphalt increases, the adhesion work of the asphalt- aggregate interface system decreases. Furthermore, for the system of the same rejuvenated asphalt and different aggregates, the rank of adhesion and water resistance from strong to weak is asphalt-limestone＞asphalt- granite, and the rank of the gray entropy correlation between six indices and moisture damage resistance from strong to weak is adhesion work＞spalling work＞VV＞rejuvenator content＞RAP content＞freeze-thaw cycles. Finally, the accuracy of the neural network predicting the moisture damage resistance of rejuvenated asphalt mix reaches 96.188%, which provides a new method to predict the moisture damage resistance of rejuvenated asphalt mixture.

Revealing Mechanisms of Aging and Moisture on Thermodynamic Properties and Failure Patterns of Asphalt-Aggregate Interface from the Molecular Scale

The primary purpose of this study was to reveal the effect of aging and moisture on the failure behavior of asphalt binder–aggregate interfaces from thermodynamic properties and the molecular scale and to provide ideas for improving the service life and weather resistance of materials. A 12-component asphalt binder model, an oxidation-aged asphalt binder model, three types of aggregates (i.e., SiO2-, CaO-, and Al2O3-based) models, and corresponding confined asphalt-aggregate models in dry or wet conditions were developed using Materials Studio version 2019 software. Thermodynamic parameters that characterize interfacial failure behavior, including surface free energy, cohesive work, and adhesion work between asphalt binder (unaged and aged samples) and aggregates were obtained by molecular dynamics simulations. A pull-off test was simulated using molecular dynamics to analyze asphalt-aggregate failure patterns and mechanisms. Five tensile rates were applied in tensile simulations of asphalt-SiO2 aggregate, and bond strength at various temperatures was investigated. The findings suggested that oxidative aging reduces thermodynamic properties such as the surface free energy and cohesive energy of asphalt binders but enhances the potential and nonbond energy of asphalt binders. The ranking of the adhesion between unaged asphalt binder and various aggregates is as follows: SiO2>CaO>Al2O3. Oxidative aging has a distinct influence on the adhesion properties of the aforementioned asphalt binder–aggregate interfaces. Furthermore, outcomes for debonding energy and energy ratio (ER) value in the asphalt-CaO aggregate system exhibited the best water stability. Increasing tensile rate caused the failure patterns of the asphalt-aggregate mixes to change from adhesive failure damage between asphalt and aggregate to cohesive failure within the asphalt binder. Temperature had a nonnegligible impact on bond strength at the asphalt-aggregate interface.

Molecular simulation and experimental analysis on co-aging behaviors of SBS modifier and asphalt in SBS-modified asphalt

ABSTRACT Styrene-butadiene-styrene block copolymer (SBS) is the most commonly used asphalt modifier. Studying the aging process of SBS-modified asphalt and clarifying the role of SBS and asphalt in the aging process can provide a basis for the targeted regeneration of SBS-modified asphalt. In this research, the physical and chemical changes of SBS and asphalt in the aging process were studied by FTIR (Fourier Transform Infrared Spectroscopy) analysis and SARA (Saturate, Aromatic, Resin, and Asphaltene) analysis. The effects of the thermal oxidation of asphalt and SBS on the viscosity and tensile properties of the SBS-modified asphalt were investigated by Brookfield Rotational Viscosity Test, force ductility test, and molecular dynamics simulation. Furthermore, the influence of asphalt and SBS aging on the adhesion property of the asphalt-aggregate interface was analyzed. The results show that the impact of SBS aging on the increase of viscosity and tensile yield stress was far less than that of asphalt aging. The adhesion energy of the modified asphalt-silica interface increases with both aging of SBS and asphalt. SBS and asphalt jointly influence the performance of modified asphalt in the aging process, but asphalt aging is the dominant factor.