Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation

Effects of a Complex Environment on Fatigue and Self-Healing Characterization of Asphalt Composites Containing Rock Asphalt

In recent years, asphalt pavement has been subjected to varied environmental conditions during its service life, conditions that predispose it to deformation and cracking. To enhance the performance of asphalt pavement, rock asphalt has been selected as a modifier due to its good compatibility with virgin asphalt binder and its ability to improve the fatigue cracking resistance of asphalt mixtures. Although scholars have conducted some studies on rock asphalt mixtures, research on the fatigue and self-healing performance of these mixtures under conditions such as ultraviolet (UV) aging and freeze-thaw remains limited. This paper presents findings from a study that employs a combined fatigue-healing test to assess the impact of such complex environmental factors on the fatigue and self-healing properties of fine aggregate matrix (FAM) mixtures containing three types of rock asphalts, i.e., Buton, Qingchuan (QC), and Uintaite Modifier (UM). The analysis of fatigue-healing test results, grounded in viscoelastic continuum damage (VECD) theory, indicates that rock asphalt can extend the fatigue life of FAM mixtures, albeit with a concomitant decrease in their self-healing capabilities. The study further reveals that UV aging, freeze-thaw, and UV aging-freeze-thaw conditions all led to a diminution in the fatigue and self-healing properties of FAM mixtures. However, FAM mixtures containing rock asphalt demonstrated greater resilience against these reductions. Atomic force microscope (AFM) results indicate that UV aging reduced the number of bee-structures and enlarged their area, whereas the incorporation of rock asphalt enhanced the uniformity of these structures' distribution, thereby improving the fatigue cracking resistance of FAM mixtures. Fourier transform infrared spectroscopy (FTIR) analysis reveals that while UV aging increased the carbonyl and sulfoxide indices within the asphalt binder, rock asphalt is effective in mitigating this effect to a certain degree, thereby enhancing the aging resistance of FAM mixtures.

Atomistic Modeling of the Effect of Temperature on Interfacial Properties of 3D-Printed Continuous Carbon Fiber-Reinforced Polyamide 6 Composite: From Processing to Loading

The combination of continuous fiber-reinforced thermoplastic composites (CFRTPCs) and the continuous fiber 3D printing (CF3DP) technique enables the rapid production of complex structural composites. In these 3D-printed composites, stress transfer primarily relies on the fiber-resin interface, making it a critical performance factor. The interfacial properties are significantly influenced by the temperatures applied during the loading and forming processes. While the effect of the loading temperature has been extensively researched, that of the forming temperature remains largely unexplored, especially from an atomistic perspective. Our research aims to employ molecular dynamics simulations to elucidate the effect of temperature on the interfacial properties of continuous carbon fiber-reinforced polyamide 6 (C/PA6) composites fabricated using the CF3DP technique, considering both loading and forming aspects. Through molecular dynamics simulations, we uncovered a positive correlation between the interfacial strength and forming temperature. Moreover, an increased forming temperature induced a notable shift in the failure mode of C/PA6 under uniaxial tensile loading. Furthermore, it was observed that increasing loading temperatures led to the deterioration of the mechanical properties of PA6, resulting in a gradual transition of the primary failure mode from adhesive failure to cohesive failure. This shift in the failure mode is closely associated with the glass transition of PA6.

Double Effects of Oxidative Aging on Carbon Nanotube-Asphalt Nanocomposite Interfaces: Enhancement and Deterioration

Understanding the mechanisms of oxidative aging effects on the carbon nanotube (CNT)-asphalt nanocomposite interface has long been a challenge, as there are two opposing effects: enhancement and deterioration. In this study, a multiscale coupling method is proposed to analyze the dual effect of oxidative aging on the CNT-asphalt nanocomposite. The method is based on density functional theory (DFT) and molecular dynamics (MD) simulations, supported by microscopic interface observation and macroscopic property testing with a focus on the composite interface. The results show that oxidative aging has a resetting effect on benzene ring stacking at the interface and enhances the binding energy of CNT-asphalt. Meanwhile, oxidative aging enhanced the interfacial charge transfer, but no chemical reaction occurred between CNT-aged asphalt. This is also verified by Fourier Transform Infrared Spectroscopy (FTIR). Enhancement and degeneration effects of oxidative aging occur via distinct mechanisms. Oxidative aging enhanced the interfacial shear barrier by approximately 5% and the energy barrier by 44.87%, which increased the high-temperature deformation resistance of the CNT-asphalt nanocomposites. However, molecular oxidation was not responsible for the decline in the fatigue resistance. According to scanning electron microscopy (SEM) and atomic force microscopy (AFM) results, oxidative aging elevates the content of polar molecules, leading to an increase in the solid properties of asphalt and a 39.6% decrease in surface adhesion. This disrupts the three-dimensional network of the CNT and ultimately leads to a reduction in crack resistance. This study clarifies the mechanism underlying the dual effect of oxidative aging and provides fundamental support for understanding asphalt aging behavior and the interfacial behavior of composites.

Research Progress on Factors Affecting Oil-Absorption Performance of Cement-Based Materials

With the wide application of petroleum resources, oil substances have polluted the environment in every link from crude oil extraction to utilization. Cement-based materials are the main materials in civil engineering, and the study of their adsorption capacity for oil pollutants can expand the scope of functional engineering applications of cement-based materials. Based on the research status of the oil-wet mechanism of different kinds of oil-absorbing materials, this paper lists the types of conventional oil-absorbing materials and introduces their application in cement-based materials while outlining the influence of different oil-absorbing materials on the oil-absorbing properties of cement-based composites. The analysis found that 10% Acronal S400F emulsion can reduce the water absorption rate of cement stone by 75% and enhance the oil-absorption rate by 62%. Adding 5% polyethylene glycol can increase the oil-water relative permeability of cement stone to 1.2. The oil-adsorption process is described by kinetic and thermodynamic equations. Two isotherm adsorption models and three adsorption kinetic models are explained, and oil-absorbing materials and adsorption models are matched. The effects of specific surface area, porosity, pore interface, material outer surface, oil-absorption strain, and pore network on the oil-absorption performance of materials are reviewed. It was found that the porosity has the greatest influence on the oil-absorbing performance. When the porosity of the oil-absorbing material increases from 72% to 91%, the oil absorption can increase to 236%. In this paper, by analyzing the research progress of factors affecting oil-absorption performance, ideas for multi-angle design of functional cement-based oil-absorbing materials can be obtained.

Study on Properties and Micro-Mechanism of RHB-SBS Composite-Modified Asphalt

Rice husk biochar (RHB) is a renewable agricultural waste, and its fixation on pavements helps develop environmentally friendly, economical, and sustainable asphalt pavements. This paper used RHB to replace part of styrene-butadiene-styrene (SBS) for the composite modification study of matrix asphalt. The high- and low-temperature properties and microscopic mechanisms of the composite-modified asphalt were studied through a series of tests. The results showed that, compared with SBS-modified asphalt, the softening point, viscosity, complex shear modulus, stiffness modulus, and rutting factors of RHB-SBS composite-modified asphalt were improved. In contrast, the ductility and creep rate were slightly decreased, indicating an improvement in the high-temperature performance of composite-modified asphalt, but a slight decrease in its low-temperature performance. The process of RHB and SBS composite modification was mainly physical blending, with only a small number of chemical reactions, and no new functional groups were generated. The porous structure of RHB enables it to adhere better to the network crosslinked continuous phase system formed by SBS and matrix asphalt. This results in composite-modified asphalt with good high-temperature storage stability and rheological properties. Therefore, RHB-SBS composite-modified asphalt can be applied to high-temperature areas and rice-producing areas, and the optimal content of RHB is suggested to be 15%.

Research on the synergistic modification effect and the interface mechanism of GO/SBS compound-modified asphalt based on experiments and molecular simulations

Although there have been reports showing the modification effect of carbon nanomaterials on asphalt, there are few studies on whether carbon nanomaterials and polymers can have synergistic modification effects on asphalt. At the same time, the complex composition of asphalt makes it difficult to determine the interface mechanism between the modifier and the asphalt. In this study, graphene oxide (GO) and styrene-butadiene-styrene block copolymer (SBS) were selected as modifiers. A combined experimental and molecular simulation research method was used to study the synergistic modification effect and the interface mechanism between the modifier and the asphalt. The results show that the modification effect of GO/SBS incorporated into asphalt is significantly superior to that of GO or SBS incorporated individually and GO/SBS has a synergistic modification effect. Although the binding strength between SBS and asphalt is weak, the GO surface (GO (0 0 1)) can simultaneously bind with SBS and asphalt, increasing the binding strength of SBS and asphalt as well as promoting the dispersion of SBS in asphalt, so that GO/SBS shows a synergistic modification effect and improves properties such as low-temperature ductility, rheology and storage stability at macroscopic level. Intercalated and exfoliated structure can be formed between GO side (GO (0 1 0)) and asphalt, which improves the anti-aging properties of the asphalt. Physical bonding is the main interface binding for GO/SBS compound-modified asphalt. GO bonds to asphalt or SBS by hydrogen bonds and there are only dispersion forces between SBS and asphalt, resulting in a higher binding strength between GO and asphalt or SBS than between SBS and asphalt.

A Review of Oil-Solid Separation and Oil-Water Separation in Unconventional Heavy Oil Production Process

Unconventional heavy oil ores (UHO) have been considered an important part of petroleum resources and an alternative source of chemicals and energy supply. Due to the participation of water and extractants, oil-solid separation (OSS) and oil-water separation (OWS) processes are inevitable in the industrial separation processes of UHO. Therefore, this critical review systematically reviews the basic theories of OSS and OWS, including solid wettability, contact angle, oil-solid interactions, structural characteristics of natural surfactants and interface characteristics of interfacially active asphaltene film. With the basic theories in mind, the corresponding OSS and OWS mechanisms are discussed. Finally, the present challenges and future research considerations are touched on to provide insights and theoretical fundamentals for OSS and OWS. Additionally, this critical review might even be useful for the provision of a framework of research prospects to guide future research directions in laboratories and industries that focus on the OSS and OWS processes in this important heavy oil production field.

Biobased Spore Microcapsules for Asphalt Self-Healing

Asphalt pavements and bituminous composites are majorly damaged by bitumen aging and fatigue cracking by traffic load. To add, maintenance and reparation of asphalt pavements is expensive and also releases significant amounts of greenhouse gases. These issues can be mitigated by promoting asphalt self-healing mechanisms with encapsulated rejuvenators. The ability of the required microcapsules to be resilient against high temperatures, oxidation, and mechanical stress is essential to promote such self-healing behavior without compromising the field performance of the asphalt pavement. This work proposes, for the first time, the use of extremely resistant biobased spores for the encapsulation of recycled oil-based rejuvenators to produce more resilient self-healing pavements. Spore encapsulants were obtained from natural spores (Lycopodium clavatum) by applying different chemical treatments, which enabled the selection of the best morphologically intact and clean spore encapsulant. The physical, morphological, and physicochemical changes were examined using fluorescence images, ATR-FTIR, SEM, size distribution, XRD, TGA and DSC analyses. Sunflower oil was used as the encapsulated rejuvenator with an optimal sol colloidal mixture for sporopollenin-oil of 1:5 (gram-to-gram). Vacuum, passive, and centrifugal encapsulation techniques were tested for loading the rejuvenator inside the clean spores and for selecting the best encapsulation technology. The encapsulation efficiency and the profiles of the accelerated release of the rejuvenator from the loaded spores over time were studied, and these processes were visualized with optical and inverted fluorescence microscopy. Vacuum encapsulation was identified as the best loading technique with an encapsulation efficiency of 93.02 ± 3.71%. The rejuvenator was successfully encapsulated into the clean spores, as observed by optical and SEM morphologies. In agreement with the TGA and DSC, the microcapsules were stable up to 204 °C. Finally, a self-healing test was conducted through fluorescence tests to demonstrate how these biobased spore microcapsules completely heal a crack into an aged bitumen sample in 50 min.

Investigating the aging mechanism of asphaltene and its dependence on environmental factors through AIMD simulations and DFT calculations

To understand the complex aging mechanism of asphalt and its dependence on environmental factors, the chemical reactivity of asphaltene during aging under different environmental conditions was studied through first-principles molecular simulations and density functional theory calculations. The aging of asphaltene was demonstrated to involve a series of subreactions along different pathways on the asphaltene molecules, including hydrogen abstraction from carbon, formation of polar groups, aromatization of cycloalkanes, and homolysis of side chains. These subreactions occurred with different free-energy barriers and, therefore, had different kinetic rates. Asphaltene aging was found to be slightly accelerated in the presence of water owing to the improved electron transfer ability of the asphaltene molecule in an aqueous solvent. Under ultraviolet radiation, the asphaltene molecule transitioned to an excited state with an excitation energy of 348.7 kJ/mol, significantly increasing its aging rate. This work bridges the gap between electronic-scale modeling and diversified experimental observations related to asphalt aging and is expected to provide theoretical guidance for strategies to prevent or delay the aging-induced failure of asphalt pavements.

Study on the Adhesion Performance of Asphalt-Calcium Silicate Hydrate Gel Interface in Semi-Flexible Pavement Materials Based on Molecular Dynamics

The interface between an asphalt binder and a calcium silicate hydrate (C-S-H) gel is a weak point of semi-flexible pavement material. In this study, the adhesion performance of asphalt-C-S-H gel interface in semi-flexible pavements at a molecular scale has been investigated. Molecular dynamics (MD) simulations were applied to establish three asphalt binders: 70# asphalt binder (the penetration is 70 mm), PG76-22 modified asphalt binder (a kind of asphalt binder that can adapt to the highest temperature of 76 °C and the lowest temperature of -22 °C), and S-HV asphalt binder (super high viscosity). The effects of different temperatures and SBS modifier contents on interfacial adhesion were explored. The obtained results showed that temperature variations had little effect on the adhesion work of the asphalt-C-S-H gel interface. It was also found that by increasing the content of SBS modifier, the adhesion work of the asphalt-C-S-H gel interface was increased. The molecular weight of each component was found to be an important factor affecting its molecular diffusion rate. The addition of SBS modifier could regulate the adsorption of aromatics by C-S-H gel in the four components of asphalt binder and improve the adsorption of resins by C-S-H gel.

Effect of Graphene on Modified Asphalt Microstructures Based on Atomic Force Microscopy

Atomic force microscopy (AFM) was used to explore the effects of graphene modifier on the microstructure of asphalt. The morphologies of the before- and after-aged base asphalt and modified asphalt were performed and compared with analysis. The formation mechanism of asphaltic “bee structures” and the influence mechanism of graphene on asphalt were discussed from the classical theory of material science (phase transformation theory and diffusion theory). The results show that graphene facilitates the nucleation of “bee structures”, resulting in an increasing number and decreasing volume of “bee structures” in modified asphalt. Additionally, the anti-aging performance of the modified asphalt improved significantly because of graphene incorporation.

Multiscale mechanisms of asphalt performance enhancement by crumbed waste tire rubber: insight from molecular dynamics simulation

The recycling of waste tires is a major environmental problem facing mankind, and the addition of crumbed waste tire rubber (CWTB) to the base asphalt is an extremely promising recycling method. However, the modification mechanism of CWTB to asphalt is not well understood, which restricts the development of CWTB modified asphalt. In this study, the mechanism of CWTB modification of asphalt was explored by dynamic mechanical analysis (DMA), fluorescence microscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and molecular dynamic (MD) simulations. After verifying the asphalt reasonableness using glass transition temperature, CWTB modified asphalt was simulated and experimented. The results showed that CWTB enhanced the high temperature performance of the base asphalt. The microscopic mechanism by which this phenomenon occurs is that CWTB has the largest binding energy with the aromatics (1150-1350 kcal/mol), followed by the saturates (740-830 kcal/mol), followed by the resins (90-330 kcal/mol), and the smallest binding energy with the asphaltenes (100-140 kcal/mol), which causes CWTB to absorb the light components of the asphalt (aromatics and saturates). In addition, the introduction of CWTB reduces the diffusion coefficient of asphalt. In this process, CWTB will gradually swell, which causes CWTB to bind more and more tightly with the base asphalt, and eventually the good high temperature performance of CWTB is transferred to the base asphalt. The macroscopic manifestation of this process is that the rutting factor of CWTB-modified asphalt is significantly higher than that of virgin asphalt. This study can provide basic theoretical support for the application of CWTB-modified asphalt.

Using Silane Coupling Agent Coating on Acidic Aggregate Surfaces to Enhance the Adhesion between Asphalt and Aggregate: A Molecular Dynamics Simulation

Acidic aggregates have the merits of high strength and good abrasion resistance capacity. However, its poor adhesion with asphalt binder constrains its application in pavement construction. Among these, the granite aggregate is the typical one. Therefore, this study modified granite aggregates’ surface to improve their adhesion property with the asphalt binder. Specifically, the silane coupling agent (SCA) KH-560 was adopted to achieve the modification purpose. Subsequently, asphalt mixtures with modified and unmodified granite, basalt, and limestone were subjected to the boiling test, immersion test, and freeze-thaw splitting test to estimate the asphalt adhesion property. Moreover, a molecular dynamic simulation was employed to characterize the asphalt-aggregate interface from the molecular scale. The radius distribution function (RDF) and interaction energy were used as the primary indicators. The results showed that the SCA could efficiently improve the adhesion between asphalt and granite aggregates, comparable with the alkaline aggregates. In terms of the molecular scale, the incorporation of SCA could significantly increase the concentration distribution of asphalt molecules on the aggregate surface. Meanwhile, the interaction energy was correspondingly increased due to the considerable growth of non-bond interaction.

Molecular Dynamic Investigations on the Adhesion Behaviors of Asphalt Mastic-Aggregate Interface

The asphalt mastic–aggregate interface plays an essential role in determining the service performance of asphalt mixtures. The objective of this paper was to investigate the adhesion behaviors and mechanism between asphalt mastic and aggregate based on molecular dynamic (MD) simulations. First, the asphalt mastic model considering the actual mass ratio of filler to asphalt (F/A) condition was established and validated in terms of thermodynamic properties. Second, the molecular arrangement characteristics of polar components on the aggregate substrate were analyzed by radial distribution function (RDF), relative concentration (RC), and mean square displacement (MSD). Third, the interfacial adhesion ability between asphalt and aggregate was quantitively evaluated based on the work of adhesion. Finally, the coupling effect of moisture and temperature on interfacial adhesion behaviors was investigated to explore the adhesion failure characteristics of the asphalt–aggregate interface. The results demonstrate that the thermodynamic properties could be employed to validate the reliability of the asphalt mastic model. The self-aggregation degree of polar components in base asphalt could be significantly increased with the addition of silica particles, exhibiting a change of configuration from “parallel arrangement” into “stack distribution” due to the high polarity of silica particles. The polar components in asphalt mastic exhibit a more uniform distribution state and lower mobility capability than base asphalt owing to the adsorption effect of silica particles. Silica particles with amounts of residual charges could significantly increase the electrostatic energy of the asphalt mastic–aggregate interface, contributing to an improvement of the adhesion between asphalt mastic and aggregate. The increase of temperature enhances the work of adhesion of the asphalt mastic–aggregate interface, which is opposite to that of the base asphalt–aggregate interface. The asphalt mastic exhibits a greater sensitivity to interfacial moisture damage than base asphalt. The findings would provide insights into a better understanding on the micro adhesion mechanism of the asphalt mastic–aggregate interface.

Investigation of γ-(2,3-Epoxypropoxy)propyltrimethoxy Silane Surface Modified Layered Double Hydroxides Improving UV Ageing Resistance of Asphalt

γ-(2,3-Epoxypropoxy)propyltrimethoxy silane surface modified layered double hydroxides (KH560-LDHs) were prepared and used to improve the ultraviolet ageing resistance of asphalt. The results of X-ray photoelectron spectrometry (XPS) indicated that KH560 has been successfully grafted onto the surface of LDHs. The agglomeration of LDHs particles notably reduced after KH560 surface modification according to scanning electron microscopy (SEM), which implied that the KH560 surface modification was helpful to promote the dispersibility of LDHs in asphalt. Then, the influence of KH560-LDHs and LDHs on the physical and rheological properties of asphalt before and after UV ageing was thoroughly investigated. The storage stability test showed that the difference in softening point (ΔS) of LDHs modified asphalt decreased from 0.6 °C to 0.2 °C at an LDHs content of 1% after KH560 surface modification, and the tendency became more pronounced with the increase of LDH content, indicating that KH560 surface modification could improve the stability of LDHs in asphalt. After UV ageing, the viscous modulus (G’’) of asphalt significantly reduced, and correspondingly, the elastic modulus (G’) and rutting factor (G*/sin δ) rapidly increased. Moreover, the asphaltene increased and the amount of “bee-like” structures of the asphalt decreased. Compared with LDHs, KH560-LDHs obviously restrained performance deterioration of the asphalt, and helped to relieve the variation of the chemical compositions and morphology of asphalt, which suggested that the improvement of KH560-LDHs on UV ageing resistance of asphalt was superior to LDHs.