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Article

Effect of Simultaneous Changes in Asphalt Binder Bee Structure Components on Mechanical Properties during the Aging and Rejuvenation Process

by
Donghui Huo
1,
Xiupeng Yao
2,
Meng Guo
2,* and
Daisong Luo
2
1
Hebei Transportation Investment Luqiao District Construction Development Co., Ltd., Qinhuangdao 066000, China
2
State Key Laboratory of Bridge Engineering Safety and Resilience, The Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(18), 10308; https://doi.org/10.3390/app131810308
Submission received: 24 July 2023 / Revised: 6 September 2023 / Accepted: 11 September 2023 / Published: 14 September 2023
(This article belongs to the Special Issue Pavement Construction: Material Characterization and Durability Analysis)
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Abstract

:
The bee structure of an asphalt binder surface changes during the aging and rejuvenation process, and the effect of this microstructural change on the mechanical properties of the asphalt binder is not clear. Therefore, in this paper, a two-dimensional finite element model of an asphalt binder microstructure was constructed based on processed AFM images, and the contents of bee phases and bee casings were varied at the same time to analyze the stress and strain distribution law of the asphalt binder microstructure. The results of the study show that in the bee structure, the stress in the bee phase is obviously greater than that in the bee casing, and the stress in the interstitial phase is the lowest. With the simultaneous enhancement in the proportion of the bee phase and the bee casing, the stresses in the asphalt samples increased in all phase structures. Under the combined effect of the decrease in the content of the bee phase and the increase in the content of the bee casing, there is a certain degree of increase in the internal stresses and strains in the asphalt binder, the effect of the bee casing on the internal stresses in the asphalt binder is more pronounced, and the bee phase and the bee casing play better roles in resisting the external deformation due to the increase in the volume fraction. For a recycled asphalt binder, whether there is an increase in the dosage of the old asphalt binder or an enhancement in the interfacial diffusion and a fusion of new and old asphalt binders, the level of tensile strain within the recycled asphalt binder will increase to a certain extent, which, in turn, will put forward a higher requirement for its anti-cracking ability.

1. Introduction

Asphalt mixtures are composite materials consisting of mineral aggregates and asphalt binders [1]. Asphalt pavement, in the long-term use of the process, is vulnerable to environmental factors and vehicle loading continuous action, during which the asphalt binder aging is deepened, resulting in a reduction in the comprehensive application of asphalt mixture performance [2,3,4]. To conserve natural resources, reduce economic costs, and protect the environment, aged asphalt mixtures are rejuvenated to replace some of the virgin material [5,6]. Owing to the aging process, asphalt binders will occur a series of physical and chemical reactions, which will lead to asphalt binder road performance degradation. Asphalt pavement rejuvenation technology, through the addition of an asphalt binder rejuvenator to regulate the aging asphalt binder component, changes to restore its road performance [7,8,9].
At present, more precise experimental instruments are needed to study the microstructure and performance changes during the aging and rejuvenation process of asphalt binders. Atomic force microscopy (AFM) provides a promising method for researchers to study asphalt binders on a micro scale from different perspectives [10]. The first application of AFM in asphalt binders was made by Loeber, who discovered the bee structure in asphalt binders [11]. Waxes in asphalt binders can occur as bee structures [12]. The bee structure of asphalt binders is of interest because of its unique morphology, and the microstructure has three distinct phases: the catana phase, the peri phase, and the para phase (the terms ‘bee phase’, ‘bee casing’, and ‘interstitial phase’ are used in this article, which refer to the ‘catana phase’ or the ‘peri phase’ and ‘para phase’, respectively) [13]. Blom et al. [14] linked the appearance of the bee structure to the presence of wax, while Hofko et al. [15] discovered a connection among asphaltene and the bee structure. Nahar et al. [16] found that the formation of the bee structure was observed in asphalt binders during cooling, and the disappearance of the bee structure was observed during heating. Several studies have analyzed the surface properties of recycled asphalt binders after the addition of rejuvenators. For example, the addition of rejuvenators resulted in dramatic changes in the asphalt binder morphology [17,18]. In a study by Cavalli et al. [1], in order to better understand the variations in the microstructures of aged asphalt binders after the addition of rejuvenators, or the variations in the microstructures of asphalt binders before and after aging, the modulus of elasticity of the surfaces of all asphalt binders before and after aging was measured using an AFM, and a comparative analysis of the modulus of elasticity of the surface of the bee structure with the bulk modulus of elasticity of the unaged asphalt binder was also performed.
Lyne et al. [11] used AFM quantitative nanomechanical property maps to demonstrate the morphology of an asphalt binder and its relationship with the local mechanical properties. Some special structures on the surfaces of asphalt binders, including the bee structure, can adversely affect the micromechanical properties of asphalt binders [19]. Xie et al. [19] studied the microstructures and micromechanical properties of four types of asphalt and SARA (saturated hydrocarbons, aromatics, resins, and asphaltenes) components in the temperature range of 25 °C to 65 °C using quantitative nanomechanical performance maps equipped in AFM. The morphology of the bee structure changed significantly at temperatures between 50 °C and 56 °C, and the bee structure disappeared completely at temperatures above 57 °C [20].
A comparison of unaged and aged asphalt binders via AFM testing confirms that the lightweight component content is greatly reduced during the aging process. The aging of an asphalt binder is a slow process, and the content and microstructure of its internal components will change with aging. Rejuvenators do not restructure the composition of aged asphalt binders. The rejuvenation process of a rejuvenator is a physical interaction, and the type and content of rejuvenator will not change the microstructure of the recycled asphalt binder [21].
The microrheology and geometry obtained using AFM were used to perform a finite element simulation to investigate the influence of the asphalt binder microstructure on the internal stress distribution [22]. The detection of the microstructure of the asphalt binder was based on the AFM technique. The microstructural finite element model (FEM) developed independently was used to comprehensively simulate the micromechanical response of asphalt binders with different bee structures [23]. However, there is still a lack of systematic research on how the rejuvenator can change the chemical composition, microstructure, and mechanical properties of the aging asphalt binder. The aging of the asphalt binder’s molecular motility is reduced, and the polar component aggregation is hindered, so that the size of the bee structure depends on the size of the decrease, the number of increasements in the proportion of the area, and the height of the decrease. The rejuvenator can enhance the ability of the molecular motility of the asphalt binder to promote the aggregation of polar components so that the microstructure of the asphalt binder can be restored [24].
At present, the microstructure of an asphalt binder changes after aging and rejuvenation, and the distribution pattern of stress and tensile strain within it is not clear. Aging causes an increase in the number of bee structures within the asphalt binder [25]. Rejuvenation can restore the surface morphology of an asphalt binder up to a point, but the degree of restoration varies depending on the rejuvenators. Furthermore, according to Allen [26], the bee structure itself may serve as a nucleation site for cracks. Based on this assumption, Allen used fracture mechanics to describe the crack propagation caused by a high tensile strain in materials. Chen et al. [21] and Ganter et al. [27] found that the bee phase of an asphalt binder increased after the aging process, and the regenerator significantly reduced the bee phase of the aged asphalt. A bee casing, which surrounds the bee structures, is stiff, while the hard interstitial phase is softer and more viscous among the other phases [20,28]. Therefore, it is possible to expect an increment in the interstitial phase due to aging, since the materials become stiffer. In the same matter, rejuvenating the aged samples increases the volume of the interstitial phase via the addition of an oily fraction into the asphalt binder [27]. There are many studies related to AFM and the aging of asphalt binders, which proves that the microstructure of an asphalt binder changes through the aging process [27,29,30]. Bee structures, which are the result of the wrinkling of very thin surface films that are 10 nm thick, characterize areas of higher and lower stiffness compared with the surrounding area [31]. It is possible to observe the bee structures in the topographic images of the asphalt binder depending on the amount of waxy components in the material [32]. Therefore, an evaluation of the appearance of the bee structure might be proof of a good rejuvenation of an RAP asphalt binder. Fang et al. [33] showed that the aging of an asphalt binder reduces the number and area ratio of ‘bee structures’. The addition of a rejuvenator can significantly improve the micromechanical properties of an aged asphalt binder and show a good rejuvenation effect. Aghazadeh et al. [34] showed that an unaged asphalt binder had the highest content of interstitial phase, an aged asphalt binder had the highest content of bee casing, and the content of interstitial phase in the bee structure was increased by the addition of rejuvenators to the aged asphalt binder.
Based on the AFM microscopic images and the mechanical parameters measured via AFM, a two-dimensional FEM was built to analyze the stress and strain distribution law of the asphalt binder microstructure. In Figure 1, the AFM image consists of three parts, the darkest colored bee phase (Phase I), the bee casing (Phase II) that wraps around the bee phase (the bee casing content in the later text includes the bee phase), and the interstitial phase (Phase III) that fills in between the bee casings [35,36]. It is interesting to note that the bee phase can also be seen as the old asphalt binder in the recycled asphalt binder, and the bee casing can be considered as the interfacial phase where the old and new asphalt binders mix. Additionally, the interstitial phase can be viewed as either the new asphalt binder or the rejuvenator. The effect of the old material dosing below the critical dosing level on the micromechanical properties of the recycled asphalt binder is analyzed by simultaneously varying the content of the bee phase and the content of the bee casing.

2. Objectives of the Study

This paper establishes a two-dimensional finite element model based on AFM images. The effect of the change in the bee structure components on the microscopic properties of an asphalt binder is explored. The stress and strain changes inside the asphalt binder are analyzed when the contents of the bee phase and bee casing change simultaneously. The bee phase in the bee structure is analogous to the aged asphalt binder. The bee casing is compared to the interface phase between the old and new asphalt binders. The interstitial phase is analogous to the unaged asphalt binder or rejuvenator. The process of aging and rejuvenation of the asphalt binder is explored via a finite element simulation of the bee structure. This can provide some basic theoretical data to support the application of recycled asphalt mixtures.

3. Materials and Methods

3.1. AFM Test Materials and Methods

In this study, the test material applied to explore the aging and rejuvenation process of asphalt binder is Pen.90 virgin asphalt binder, whose basic properties are shown in Table 1. All test methods are based on the China Code (JTJ052-2011) [37].
Short-term and long-term aging tests were successively carried out on virgin asphalt binder according to the China Code (JTJ052-2011) [37]. A total of 35 g asphalt binder was taken into a rolling thin film oven (RTFO) with a temperature of 163 °C for 75 min to obtain short-term aged samples. Then, 50 g short-term aged samples was taken into the pressure aging vessel (PAV) with a temperature of 100 °C and an air pressure of 2.1 MPa for 20 h. The long-term aged samples were obtained.
In this study, AFM was chosen to observe and characterize the micromorphology of asphalt binder as well as its surface properties. In the AFM sample preparation, the asphalt binder was first heated to 140 °C, and 20 ± 0.5 g of asphalt binder was weighed and dropped onto the center of the slide, as shown in Figure 2a. Then, the samples were placed in an oven at 100 °C for 30 min (this step was performed to reduce the effect of thermal history on the test results), and the heated samples are shown in Figure 2b. Finally, the samples were stored in a Petri dish with a lid to prevent dust from falling on the surfaces of the samples. We prepared for AFM characterization experiment, which was conducted in Peak Force QNM mode with a peak force set point of 10 nN and a scanning area of 30 × 30 µm2.

3.2. Finite Element Modeling of AFM Microforms

In order to study the effect of this change in the bee structure on the surface of asphalt binder on the micromechanical behavior of asphalt binder, the AFM images were processed, as shown in Figure 1. The process of finite element modeling of AFM microforms in two dimensions was divided into the following steps: (1) raw image data processing; (2) two-dimensional geometric model construction; (3) definition of cell geometry; (4) definition of physical and mechanical parameters of the material; (5) discretization and ensemble of the cells; (6) definition of the model boundary constraints and application of tensile loads; and (7) analysis of the results of the finite element simulation calculations. In Figure 3, the boundary conditions of the 2D finite element model are fixed at the left-end boundary, and the tensile load is applied at the right part, which is loaded at a constant displacement rate of 1.5 µm/s.
This paper is a study of a two-dimensional finite element model, where the interfacial interactions between different units are defined through the nodal zone option. Details on the processing of the AFM images can be found in Appendix A of the manuscript. Based on the geometric information of the asphalt binder, six finite element models with different bee structure components were created in the finite element software ABAQUS. By using AFM to study binder asphalt samples, a variety of properties could be obtained, such as modulus, adhesion, dissipation, and deformation (relevant findings were published in [36]). In this study, the elastic modulus of each phase of the bee structure was obtained from the Derjaguin–Muller–Toporov (DMT) modulus measured via AFM. The DMT modulus characterizes a material with significant surface adhesion, which is calculated by adding the loading force and the adhesion force. The modulus of elasticity of the bee phase is 0.000260 N/µm2, the modulus of elasticity of the bee casing is 0.000196 N/µm2, and the modulus of elasticity of the interstitial phase is 0.000125 N/µm2. The other parameters of the components used for the simulation were obtained from the AFM tests, and a Poisson’s ratio of 0.4 was used.

4. Analysis of Results

A simultaneous variation in the contents of the bee phase and the bee casing was achieved via finite element simulation to explore the effect of internal microstructural changes on the micromechanical property of an asphalt binder during aging and rejuvenation. It also illustrates the effect of the old material dosage on the micromechanical behavior of a recycled asphalt binder when the old material dosage is below the critical dosage. The doping of the bee phase and bee casing selected for this paper included six groups, three of which were increased in both the bee phase (B) and bee casing (BC) contents, specifically (a) B 4%, BC 35%; (b) B 15%, BC 50%; and (c) B 24%, BC 75%. The other three groups were decreased in the bee content and increased in the bee casing content, specifically (d) B 24%, BC 35%; (e) B 15%, BC 50%; and (f) B 4%, BC 75%. It should be noted that the content of each phase in the honeycomb structure was determined by the area of the image. The constructed finite element model is shown in Figure 4.

4.1. Analysis of Internal Stress Distribution Pattern

The internal stress distribution law of an asphalt binder and the internal distribution law of tensile strain were further investigated by calculating and analyzing the established finite element model, in which the internal stress distribution state is shown in Figure 5 and Figure 6.
In analyzing Figure 5, it is evident that the stress of the bee phase is significantly higher than that of the bee casing. Furthermore, the interstitial phase experiences the lowest level of stress, which implies that in the event of an external load effect on the asphalt binder, the bee structure is more prone to stress concentration and early damage. As the bee phase and bee casing increase simultaneously, the corresponding force within the material becomes more pronounced, indicating that the aging of the asphalt binder leads to greater internal stresses, making it more susceptible to issues such as fatigue cracking. If the bee structure is considered as an aged asphalt binder, when the dosage of the old material is increased (less than the critical volume), the interfacial diffuse phase is also gradually increased, and the internal stress state of the asphalt binder is increased. The internal stress also increases gradually as the simulation time increases. The stress accumulation distribution curves of each component of the asphalt binder microstructure under a 1 s loading time when the bee phase increases at the same time as the bee casing are shown in Figure 7.
In Figure 7, with the simultaneous increase in the proportions of the bee phase and the bee casing, the stresses in each phase structure in the asphalt binder samples increase. This can indicate that the level of rejuvenation of the old asphalt binder has not yet reached the upper limit when the content of old materials doping in the rejuvenation process is below the critical doping level. With the increase in the old material doping (i.e., the increase in the bee phase), its interfacial interaction capacity with the new asphalt binder gradually increases, leading to the increase in the interfacial bee casing and the gradual increase in the internal stress of the recycled asphalt binder. In Figure 6, the interstitial phase has the fastest rate of stress increase, and the bee phase and bee casings have similar rates of stress increase.
In Figure 6, with the decrease in the bee phase proportion and the increase in the bee casing content, there is a slight increase in the stress inside the asphalt binder. This suggests that under the combined effect of the decrease in the bee phase content and the increase in the bee casing, the internal stress still exhibits a certain increase, although the change is not very obvious. Overall, the current change in the content of the three-phase structures suggests that the bee casing has a relative impact on the internal stress of the asphalt binder. If the bee phase is regarded as an aged asphalt binder, part of the old asphalt binder gradually penetrates into the new asphalt binder and transforms into the bee casing, the internal stresses in the asphalt binder still increase, and the overall modulus of strength rises. The stress integration curves of the various phases of the bee structure under a 1 s loading time are shown in Figure 8.
From Figure 8, it appears that as the proportion of the bee casing increases and the proportion of the bee phase decreases, there is an overall increase in the stress within the asphalt binder. However, there are also some smaller changes in the corresponding forces of the interstitial phase and the bee phase. It is important to note that these changes are relative and depend on the current magnitude of change in the three-phase content. This suggests that when the bee phase and bee casing change simultaneously in the microstructure, the influence on the internal stress is complex, and the bee casing plays a dominant role that is relative to the bee phase. This can also indicate that when the recycled asphalt mixture in the rejuvenation process gradually interacts with the unaged asphalt binder, part of the aged asphalt binder and the unaged asphalt binder are fused together to form an interfacial phase (bee casing), which causes a decrease in the aged asphalt binder (bee phase) and an increase in the interfacial phase (bee casing), and at this time, the internal stresses of the recycled asphalt binder become larger.

4.2. Analysis of the Internal Distribution Law of Tensile Strain

Figure 9 shows the internal strain distribution of the asphalt binder when both the bee phase and the bee casing contents are increased. The internal strain distribution of the asphalt binder with a decreased bee phase content and an increased bee casing content is shown in Figure 10.
In Figure 9, the strains of all the three-phase systems of the asphalt binder gradually increase as the bee phase and the bee casing become larger. The overall total deformation remains constant due to the transformation of some of the interstitial phases into the bee phases and the bee casings. This indicates that the bee phases and the bee casings are better able to perform their roles in resisting external deformation due to the enhancement in the volume fraction. At the same time, the strain inside the asphalt binder increases gradually with the enhancement in the loading time. The cumulative distribution curves of the internal strains of the various phases of the bee structure under a 1 s loading time when the bee phase and the bee casing are increased simultaneously are shown in Figure 11.
From Figure 11, with the simultaneous increase in the proportions of the bee phase and bee casing, the proportion of the interstitial phase decreases, but the tensile strains of the three-phase structure in the asphalt binder are increased, among which the increase in the interstitial phase strain is the most significant, which is consistent with the findings of Du et al. [22]. This indicates that when the recycled asphalt mixture dosing gradually increases but does not exceed the critical ratio, the aging asphalt binder phase and the interface phase will grow at the same time. At this time, the asphalt binder internal tensile strain under the action of the displacement load will increase; the greater the old material dosing, the more the strain increases; and the interstitial phase has the highest increase. This also indicates that the more the old material is mixed, the more attention should be paid to the low-temperature cracking resistance of recycled asphalt mixtures.
From Figure 9, when the contents of both the bee phase and the interstitial phase in the microstructure of the asphalt binder decrease, while the content of its bee casing increases, the strain within the three phases of the asphalt binder increases, the strain distribution within the three phases is more homogeneous, and the variability decreases. This suggests that the strain distribution within the asphalt binder will be more uniform when more of the bee phase is transformed into the bee casing, i.e., when interfacial diffusive fusion between the old and new asphalt binders better occurs during the rejuvenation process. The maximum strain value inside the asphalt binder increases any time the load action time increases. When the content of the bee phase decreases, the proportion of the bee casing increases, and the cumulative distribution curves of the internal strains of each phase of the asphalt binder microstructure under a 1 s loading time are shown in Figure 12.
From Figure 12, it appears that decreasing the bee phase content and increasing the bee casing content leads to an increase in the internal three-phase tensile strain of the asphalt binder. However, there seems to be a decrease in the honeycomb phase strain at the current magnitude of change in the three-phase content. The gap strain remains unchanged when the proportion of the bee phase is lowered by 9%, and the shell content is increased by 15%, which is similar to the change in the internal stresses. The overall situation is likely due to the recycled asphalt binder in the aged asphalt binder dosage being fixed, and with the gradual integration of the old asphalt binder and the new asphalt binder, the proportion of the old asphalt binder (bee phase) is adjusted to reduce the contents of the interfacial phase (bee casing) and the interface phase, and at some point in time, the overall tensile strain will be increased. Therefore, synthesizing Figure 10 and Figure 12, for recycled asphalt binder, whether there is an increase the dosage of old material or an enhancement in the interfacial diffusion and fusion degree of the original and aging asphalt binders, the level of tensile strain within the recycled asphalt binder will be increased to a certain extent, which will then put forward a higher requirement for its anti-cracking ability.

5. Conclusions

A simultaneous variation in the contents of the bee phase and bee casing was realized via finite element simulation to explore the influence of internal microstructural changes on the micromechanical behavior of an asphalt binder in the aging and rejuvenation process, which provided theoretical references for the application of a regenerated asphalt binder, and several conclusions were obtained as follows:
(1)
The stress in the bee phase is significantly greater than that in the bee casing, and the stress in the interstitial phase is minimal. When the asphalt binder is aged, the proportions of the bee phase and bee casing increase, which will produce greater internal stresses within the asphalt binder, which, in turn, is more prone to fatigue cracking and other problems.
(2)
With the simultaneous increase in the contents of the bee phase and the bee casing, the stress in each phase structure in the asphalt binder samples increase. The stress of the interstitial phase increases at the fastest rate, and the stresses of the bee phase and the bee casing increase at a similar rate. The rejuvenation level of the aged asphalt binder has not yet reached the upper limit, and with the increase in the dosage of the old material, its interfacial interaction capacity with the new asphalt binder also gradually increases, leading to an increase in the interfacial bee casing, and a gradual increase in the internal stress of the recycled asphalt binder.
(3)
Under the combined effect of the decrease in the proportion of bee phase and the increase in the proportion of the bee casing, there is a certain degree of increase in the internal stresses and strains in the asphalt binder, the effect of the bee casing on the internal stresses in the asphalt binder is more pronounced, and the bee phase and the bee casing play a better role in resisting external deformation due to the increase in the volume fraction. When the aged asphalt binder in the rejuvenation process gradually interacts with the unaged asphalt binder, part of the aged asphalt binder and the unaged asphalt binder are fused together to form an interfacial phase (bee casing), resulting in a decrease in the aged asphalt binder and an increase in the interfacial phase, and at this time, the internal stress of the regenerated asphalt binder becomes larger.
(4)
Under the action of a displacement load, the internal tensile strain of the asphalt binder increases, the magnitude of strain increases with the increase in old material mixing, and the interstitial phase is the most sensitive. For a recycled asphalt binder, whether it is used to improve the old material doping or to enhance the new and old asphalt binders’ interfacial diffusion fusion, it will, to a certain extent, increase the level of tensile strain within the recycled asphalt binder, which, in turn, puts forward higher requirements for its anti-cracking properties.

Author Contributions

Conceptualization, M.G.; methodology, D.L.; software, D.L.; validation, X.Y. and D.H.; formal analysis, X.Y.; investigation, X.Y.; resources, D.L.; data curation, D.L.; writing—original draft preparation, D.H. and D.L.; writing—review and editing, D.H. and X.Y.; visualization, M.G.; supervision, M.G.; funding acquisition, M.G. All authors have read and agreed to the published version of the manuscript.

Funding

The authors would like to acknowledge that this paper was financially supported by the National Key Research and Development Program of China (2022YFE0137300) and the National Natural Science Foundation of China (52078018).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are conditionally available upon request to the corresponding authors.

Acknowledgments

We are grateful to RWTH Aachen University, Germany, for discussing exchanges and for helping us with model building, parameter setting, and setting the contents of bee phase and shell in the simulation. Special thanks to Debao Hou, Wei Gao, Changchun Yu, Ling Jia, and Baolin Chang from Hebei Transportation Investment Luqiao District Construction Development Co., Ltd. for providing experimental materials, and for their assistance in the data analysis, finite element simulation, and other aspects of this paper.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Processing of AFM micromorphological images.
In order to perform finite element simulation and an analysis of the AFM micromorphology images, they need to be converted into a valid ‘.sat’ file format and imported into the Abaqus software. In this study, they were processed using GIMP, Inkscape, and Autodesk Fusion 360, respectively, where GIMP was used to separate the different phase structures in the asphalt binder morphology image acquired via AFM and exported to ‘.png’ format, and Inkscape was used to improve the quality of the image and further convert it to ‘.svg’ format. Autodesk was used to import the ‘.svg’ file into a 3D coordinate system and convert it into ‘.sat’ format.

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Figure 1. AFM image analysis; 30 × 30 µm. (a) The original image. (b) Extraction of bee phase. (c) Extraction of bee phase and bee casing.
Figure 1. AFM image analysis; 30 × 30 µm. (a) The original image. (b) Extraction of bee phase. (c) Extraction of bee phase and bee casing.
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Figure 2. Preparation of AFM samples. (a) Before heating; (b) After heating.
Figure 2. Preparation of AFM samples. (a) Before heating; (b) After heating.
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Figure 3. Boundary load condition. Notes: A is the direction of load application; B is the applied boundary condition.
Figure 3. Boundary load condition. Notes: A is the direction of load application; B is the applied boundary condition.
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Figure 4. Finite element model.
Figure 4. Finite element model.
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Figure 5. The internal stress distribution of the sample when the bee phase contents and bee casing contents were 4 + 35%, 15 + 50%, and 24 + 75%, respectively. The unit is N/µm2.
Figure 5. The internal stress distribution of the sample when the bee phase contents and bee casing contents were 4 + 35%, 15 + 50%, and 24 + 75%, respectively. The unit is N/µm2.
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Figure 6. The internal stress distribution of the sample when the bee phase contents and bee casing contents were 24 + 35%, 15 + 50%, and 4 + 75%, respectively. The unit is N/µm2.
Figure 6. The internal stress distribution of the sample when the bee phase contents and bee casing contents were 24 + 35%, 15 + 50%, and 4 + 75%, respectively. The unit is N/µm2.
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Figure 7. Stress cumulative distribution curves of asphalt samples with increases in bee phase contents and bee casing contents.
Figure 7. Stress cumulative distribution curves of asphalt samples with increases in bee phase contents and bee casing contents.
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Figure 8. Stress cumulative distribution curves of asphalt samples with a reduction in bee phase contents and an increase in bee casing contents.
Figure 8. Stress cumulative distribution curves of asphalt samples with a reduction in bee phase contents and an increase in bee casing contents.
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Figure 9. The internal distribution of tensile strain when bee phase content and bee casing content were 4 + 35%, 15 + 50%, and 24 + 75%, respectively.
Figure 9. The internal distribution of tensile strain when bee phase content and bee casing content were 4 + 35%, 15 + 50%, and 24 + 75%, respectively.
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Figure 10. The internal distribution of tensile strain when bee phase contents and bee casing contents were 11.4 + 51.3%, 8.9 + 61.3%, and 3.9 + 81.3%, respectively.
Figure 10. The internal distribution of tensile strain when bee phase contents and bee casing contents were 11.4 + 51.3%, 8.9 + 61.3%, and 3.9 + 81.3%, respectively.
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Figure 11. Internal strain cumulative distribution curves of asphalt samples with increases in the bee phase content and bee casing content.
Figure 11. Internal strain cumulative distribution curves of asphalt samples with increases in the bee phase content and bee casing content.
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Figure 12. Internal strain cumulative distribution curves of asphalt samples with increases in bee phase content and bee casing content.
Figure 12. Internal strain cumulative distribution curves of asphalt samples with increases in bee phase content and bee casing content.
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Table 1. Basic properties of asphalt binders.
Table 1. Basic properties of asphalt binders.
Test ItemUnitTest ResultStandard ValueTest Method
Penetration (25 °C, 5 s, 100 g)0.1 mm8180~100T0604
Penetration index (PI)—−1.48−1.5~+1.0T0604
Ductility (10 °C, 5 cm/min)cm>100≥30T0605
Ductility (15 °C, 5 cm/min)cm>100≥100T0605
Softening point (TR and B)°C45.0≥44T0606
Wax content (distillation method)%0.3≤2.2T0615
Flash point°C301≥245T0611
Solubility%99.84≥99.5T0607
Dynamic viscosity (60 °C)Pa·s181≥140T0620
Density (15 °C)g/cm31.010measured resultT0603
Thin film heating (163 °C, 5 h)Mass change%−0.122≥−0.8, ≤0.8T0609
Penetration ratio (25 °C)%76≥57T0604
Ductility (10 °C)cm32≥8T0605
Ductility (15 °C)cm>100≥20T0605
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MDPI and ACS Style

Huo, D.; Yao, X.; Guo, M.; Luo, D. Effect of Simultaneous Changes in Asphalt Binder Bee Structure Components on Mechanical Properties during the Aging and Rejuvenation Process. Appl. Sci. 2023, 13, 10308. https://doi.org/10.3390/app131810308

AMA Style

Huo D, Yao X, Guo M, Luo D. Effect of Simultaneous Changes in Asphalt Binder Bee Structure Components on Mechanical Properties during the Aging and Rejuvenation Process. Applied Sciences. 2023; 13(18):10308. https://doi.org/10.3390/app131810308

Chicago/Turabian Style

Huo, Donghui, Xiupeng Yao, Meng Guo, and Daisong Luo. 2023. "Effect of Simultaneous Changes in Asphalt Binder Bee Structure Components on Mechanical Properties during the Aging and Rejuvenation Process" Applied Sciences 13, no. 18: 10308. https://doi.org/10.3390/app131810308

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