Aging performance evaluation method of SBS modified asphalt based on molecular simulation

Abstract

The present invention discloses a method for evaluating the aging performance of SBS modified asphalt based on molecular simulation, the method comprising the following steps: determining the molecular structures of SBS molecules and asphalt before and after aging, determining the content changes of four components of asphalt (aromatic fraction, saturated fraction, colloid and asphaltene) before and after aging, establishing a molecular model of SBS modified asphalt and verifying the rationality of the model with test data (density, glass transition temperature, solubility parameter, cohesive energy density and viscosity), and molecular dynamics evaluation of the performance changes of SBS modified asphalt before and after aging (viscosity and tensile shear behavior) and verifying the evaluation with test data.

Description

Technical Field

[0001] The invention belongs to the field of modified asphalt, and in particular relates to an aging performance evaluation method of SBS modified asphalt based on molecular simulation. Background Art

[0002] At present, modified asphalt is widely used in road engineering due to its excellent performance. The most commonly used modifier is styrene-butadiene-styrene block copolymer (SBS). During the production and long-term use of SBS modified asphalt, it will be affected by various natural factors such as oxygen, temperature, water, ultraviolet rays, and vehicle loads, and will undergo a series of volatilization, oxidation, polymerization, and even internal structural changes. The properties of asphalt gradually change (aging), which will eventually lead to road surface diseases. With the widespread application of modified asphalt mixtures, the study of its aging process and its performance recovery has received widespread attention.

[0003] At present, the study of the changes in asphalt aging performance can be analyzed from the following aspects: (1) Component changes. The aging process of asphalt is a very complex physical and chemical process, which is difficult to describe with a structural formula. It is generally believed that during the aging process of asphalt, its saturated components are relatively stable and do not change much during the entire aging process. The aromatic components are more likely to undergo oxidative polymerization to form colloids. The components containing polar functional groups in the colloids undergo intermolecular polymerization and are converted into asphaltene through condensation. The asphalt components generally change towards the heavy direction along the route of aromatics-colloids-asphaltene. (2) The compatibility of modified asphalt decreases. Aging will change the chemical structure of each component in asphalt, increase the difference in the solubility parameters of asphalt, reduce the compatibility of the components, deteriorate the stability, and deteriorate the road performance. Therefore, the degree of asphalt aging can be expressed by the rate of decrease in the content of small molecular components and the rate of increase in the content of large molecular components: the more significant the decrease in the content of small molecular components, the greater the increase. Changes in the content of large molecular components indicate a higher degree of aging.

[0004] At present, the research on the aging of modified asphalt generally uses Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), dynamic viscoelasticity and other methods to analyze the structural and performance changes of SBS modified asphalt before and after film oven aging. The overall aging problem of SBS modified asphalt has been widely studied through macroscopic laboratory experiments. Previous studies tested SBS modified asphalt and original asphalt before and after aging by FTIR, pointing out that the evaluation of asphalt aging is based on the spectral peak area corresponding to the C=O bond. The larger the absorption peak area, the greater the aging degree. After 24 hours, almost all SBS was degraded and turned into low molecular weight substances. However, the change in the asphalt phase is the opposite, forming a large number of macromolecular substances. Fourier transform infrared spectroscopy experiments found that the addition of SBS modifiers affects the non-Newtonian properties of modified asphalt. The temperature sensitivity and viscosity changes of modified asphalt after aging depend on the aging of the original asphalt and the degradation of the modifier. All of the above indicate that the degradation of SBS polymers and the cross-linking coupling reaction of polymers and asphalt occurred during the aging of SBS modified asphalt. A large number of experimental studies involve the aging of SBS modified asphalt and its mechanism, but little is known about the aging of modifiers and the interaction between modifier aging and asphalt aging. There are few studies on the effects of separate base asphalt and SBS polymer on the aging of SBS modified asphalt. Therefore, the present invention adopts FTIR and component analysis methods from a microscopic perspective to analyze the interaction between SBS and asphalt during the aging of SBS modified asphalt; from a macroscopic perspective, DSR tests and force ductility tests are performed to evaluate the effects of aging on the thermodynamic properties of SBS modified asphalt; and from a molecular nanoscopic perspective, the aging reaction process of SBS and asphalt and the viscosity and tensile shear behavior of SBS modified asphalt at different aging stages are analyzed, which has guiding significance for the analysis of the coupling effect between SBS and asphalt during the aging process.

[0005] In recent years, the development of material characterization technology has helped to better explain the aging behavior of asphalt materials at the microscopic level. Among different simulation methods, molecular dynamics (MD) simulation has been proven to be a powerful means to study the physicochemical properties of asphalt materials from a nanoscopic perspective. Molecular dynamics can simulate density, solubility, radial distribution function (RDF), glass transition temperature, cohesive energy density, viscosity, thermal conductivity, shear stress-strain curve, tensile stress-strain curve, Poisson's ratio, etc. In the field of SBS modified asphalt, molecular simulation has been applied. For example, molecular dynamics simulation is used to study the interfacial heat transfer between asphalt and aggregate, considering the type of aggregate, the structure of SBS molecules (radial and linear), and the content of SBS modifier. The radial distribution function is calculated by molecular simulation, and the influence of different types of SBS on the agglomeration behavior of asphalt binder is analyzed. These studies have successfully applied molecular simulation and compared it with experimental tests, providing a basis for analyzing the performance of SBS modified asphalt. The present invention proposes to establish a molecular model of the aging process of SBS modified asphalt, calculate viscosity and tensile and shear stress-strain curves, and compare and analyze the effects of SBS and asphalt aging on the performance of modified asphalt.

[0006] The present invention combines laboratory experiments and molecular dynamics simulations to study the aging mechanism of SBS modified asphalt binder, clarifies the respective roles of SBS and asphalt in the aging process and their influence on asphalt performance, and provides a basis for accurate evaluation of SBS asphalt aging performance. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to study the aging of modifier and asphalt during the aging process of SBS modified asphalt and the interaction between modifier aging and asphalt aging, to explore the degradation mechanism of SBS aging performance, to provide an SBS modified asphalt aging performance evaluation method based on molecular simulation, and to provide a basis for the regeneration of aged SBS modified asphalt.

[0008] Technical solution: In order to achieve the above-mentioned purpose, the present invention adopts the following technical solution: an SBS modified asphalt aging performance evaluation based on molecular simulation, comprising the following steps:

[0009] (1) Aging tests were performed on SBS, base asphalt, and SBS modified asphalt to obtain samples of the three materials with different aging degrees;

[0010] (2) determining the component composition and content ratio of the three materials at different aging degrees obtained in step (1) through microscopic experiments;

[0011] (3) obtaining macroscopic performance indicators of the base asphalt and the SBS modified asphalt at different aging degrees obtained in step (1) through a macroscopic performance test;

[0012] (4) establishing a molecular model of SBS modified asphalt with different aging degrees based on the results obtained from the microscopic test in step (2);

[0013] (5) The performance indicators of SBS modified asphalt at different aging degrees are obtained through molecular simulation, and are linked with the macro performance indicators obtained in step (3), thereby finally completing the aging performance evaluation of SBS modified asphalt.

[0014] As a preferred embodiment of the present invention, in step (1), a thin film oven is used for SBS aging, and the aging time is 1 hour at a temperature of 163°C. A rotary thin film oven test is used for short-term aging of the base asphalt and SBS modified asphalt, and the aging time is 85 minutes at a temperature of 163°C; a pressure aging test is used for long-term aging of the base asphalt and SBS modified asphalt, and the time is 5 hours, 10 hours, 20 hours, and 30 hours, respectively, at a temperature of 100°C.

[0015] As a preferred embodiment of the present invention, in step (2), the types and content changes of chemical reaction functional groups of the three materials are determined by infrared spectroscopy test, the molecular weight and compatibility of the three materials are determined by gel chromatography test, and the changes in the contents of the four components of asphalt during the aging process of base asphalt and SBS modified asphalt are determined by asphalt four-component test.

[0016] As a preferred embodiment of the present invention, in step (3), the macro performance indicators include: 135°C viscosity and force ductility curves of the base asphalt and SBS modified asphalt at different aging stages obtained based on the Brookfield rotational viscosity test and force ductility test.

[0017] As a preferred embodiment of the present invention, in step (4), the establishment of the SBS modified asphalt molecular model at different aging stages is based on the results of the microscopic experiment in step (2). That is, the composition of each molecular component in the SBS modified asphalt is determined by a four-component test; the change of chemical functional groups during the aging process is determined by an infrared spectrum test; and the mass of each molecule in the SBS modified asphalt is determined by a gel chromatography test. The above microscopic experiments can accurately characterize the establishment of the SBS modified asphalt molecular model.

[0018] As a preferred embodiment of the present invention, in step (5), the SBS modified asphalt model is established in material studio, and is run for 10 ns in the NVE ensemble (N: number of atoms, V: volume, E: energy) in the lammps software by the equilibrium state method, and the 135°C viscosity value at different aging stages is obtained by integrating the pressure autocorrelation function; the yield stress, ductility, Young's modulus and shear modulus of the SBS modified asphalt at different aging degrees are obtained by stretching and shearing the model at a set strain rate.

[0019] As a preferred embodiment of the present invention, combining the molecular simulation results in step (5) with the macroscopic test results in step (3), the aging properties evaluation of SBS modified asphalt includes: 135°C viscosity characterizing high temperature performance, ductility results characterizing low temperature performance, and Young's modulus and shear modulus characterizing strength performance.

[0020] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0021] At present, modified asphalt is widely used in road engineering due to its excellent performance, and the most commonly used modifier is styrene-butadiene-styrene block copolymer (SBS). During the production and long-term use of SBS modified asphalt, it will be affected by various natural factors such as oxygen, temperature, water, ultraviolet rays, and vehicle-borne, and a series of volatilization, oxidation, polymerization, and even internal structural changes (aging) will occur. With the occurrence of aging, the service performance of modified asphalt will be seriously reduced. When it reaches a certain degree of decline, the road surface can no longer be used and needs to be reconstructed using hot regeneration or cold regeneration technology. Analyzing and evaluating the aging performance of SBS modified asphalt helps to grasp the degree of decline in the performance of modified asphalt, the decline mechanism, and make targeted regeneration strategies. The present invention proposes a method for evaluating the aging performance of SBS modified asphalt based on molecular simulation. Specifically, in the aging process of modified asphalt, the combination of macroscopic performance test, microscopic component analysis, and nanoscopic molecular simulation can accurately, quickly and effectively analyze the aging mechanism of SBS and asphalt in the aging process of modified asphalt and the mutual coupling effect. The present invention will be effectively applied in the practice of evaluating the aging performance of modified asphalt, providing an analytical means and evaluation basis for the regeneration of aged asphalt materials, and providing a guarantee for ensuring the long-term service performance of the pavement. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a flow chart of the implementation of molecular simulation and macroscopic experiments of the present invention;

[0023] Figure 2 The infrared spectra of SBS modified asphalt at different aging times;

[0024] Figure 3 This is the change diagram of the four-component content of SBS modified asphalt at different aging stages;

[0025] Figure 4 Molecular model diagram of asphalt and aged asphalt;

[0026] Figure 5 Diagram of the molecular model of SBS and aged SBS. DETAILED DESCRIPTION

[0027] The present design method is further illustrated below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present design method. It should be understood that this embodiment is only used to illustrate the present design method and is not used to limit the scope of the present design method.

[0028] Embodiment 1:

[0029] (1) Select 90# base asphalt and add SBS to obtain SBS#70 modified asphalt. The SBS used in the present invention is a linear structure, and the butadiene:styrene (PB:PS) ratio of the SBS polymer is 3:7. The short-term and long-term aging of SBS, asphalt and SBS modified asphalt are achieved by rotating thin film oven test (RTFOT) and accelerated aging test (PAV (5h, 10h, 20h, 30h)).

[0030] (2) The types and content changes of the chemical reaction functional groups of the material are determined by infrared spectroscopy test, the molecular weight and compatibility of the material are determined by gel chromatography test, and the changes of the content of the four components of asphalt during aging are determined by asphalt four-component test. Infrared spectra of SBS modified asphalt at different aging times are shown in Figure 2. Figure 2 As shown in Figure 2, the content of the four components of SBS modified asphalt at different aging stages varies as follows: Figure 3 shown.

[0031] (3) The 135℃ viscosity and force-ductility curves of base asphalt and SBS modified asphalt at different aging stages obtained based on the Brookfield rotational viscosity test and force-ductility test.

[0032] (4) According to the microscopic test results in step (2), SBS modified asphalt models are established in Material Studio at different aging stages. The established asphalt and aged asphalt molecular models are as follows: Figure 4 The molecular models of SBS and aged SBS are shown in Figure 5 shown.

[0033] (5) Export the molecular model to Lammps software and run it. Calculate the 135°C viscosity of SBS modified asphalt at different aging stages by the equilibrium method. Run it for 10 ns under the NVE ensemble (N: number of atoms, V: volume, E: energy). Obtain the viscosity coefficient by integrating the pressure autocorrelation function, draw the time-viscosity curve, and select the viscosity value after the curve stabilizes. Perform tensile and shear simulations on the model in the lammps software. Obtain the yield stress, ductility, Young's modulus and shear modulus of SBS modified asphalt at different aging degrees by stress-strain curve analysis. According to the test results obtained in step (3), comprehensively evaluate the aging performance of SBS modified asphalt, and evaluate the aging degree of the modified asphalt according to the change rate of the above performance parameters.

Claims

1. A method for evaluating the aging performance of SBS modified asphalt based on molecular simulation, characterized in that: The method comprises the following steps: (1) Aging tests were performed on SBS, base asphalt, and SBS modified asphalt to obtain samples of the three materials with different aging degrees; (2) determining the component composition and content ratio of the three materials at different aging degrees obtained in step (1) through microscopic experiments; (3) obtaining macroscopic performance indicators of the base asphalt and the SBS modified asphalt at different aging degrees obtained in step (1) through a macroscopic performance test; (4) establishing a molecular model of SBS modified asphalt with different aging degrees based on the results obtained from the microscopic test in step (2); (5) obtaining the performance index of SBS modified asphalt at different aging degrees through molecular simulation, and establishing a connection with the macro performance index obtained in step (3), and finally completing the aging performance evaluation of SBS modified asphalt; In step (2), the types and content changes of chemical reaction functional groups of the three materials are determined by infrared spectroscopy test, the molecular weight and compatibility of the three materials are determined by gel chromatography test, and the changes of the content of the four components of asphalt during the aging process of base asphalt and SBS modified asphalt are determined by asphalt four-component test; In step (3), the macro performance indicators include: 135°C viscosity and force ductility curves of the base asphalt and SBS modified asphalt at different aging stages obtained based on the Brookfield rotational viscosity test and force ductility test; In step (5), the SBS modified asphalt model is established in the material studio, and the equilibrium state method is used in the lammps software to run for 10 ns under the NVE ensemble, and the 135°C viscosity value at different aging stages is obtained by integrating the pressure autocorrelation function; the model is stretched and sheared at a set strain rate to obtain the yield stress, ductility, Young's modulus and shear modulus of the SBS modified asphalt at different aging degrees; Combining the molecular simulation results in step (5) with the macroscopic test results in step (3), the aging evaluation of SBS modified asphalt includes: 135°C viscosity characterizing high temperature performance, ductility results characterizing low temperature performance, and Young's modulus and shear modulus characterizing strength performance.

2. The method for evaluating the aging performance of SBS modified asphalt based on molecular simulation according to claim 1, characterized in that: In step (1), a thin film oven is used for SBS aging, the aging time is 1 hour, and the temperature is 163°C; a rotary thin film oven test is used for short-term aging of the base asphalt and SBS modified asphalt, the aging time is 85 minutes, and the temperature is 163°C; a pressure aging test is used for long-term aging of the base asphalt and SBS modified asphalt, the time is 5 hours, 10 hours, 20 hours, 30 hours, respectively, and the temperature is 100°C.

3. The method for evaluating the aging performance of SBS modified asphalt based on molecular simulation according to claim 1, characterized in that: In step (4), the establishment of the molecular model of SBS modified asphalt at different aging stages is based on the results of the microscopic experiment in step (2), that is, the composition of each molecular component in SBS modified asphalt is determined by the asphalt four-component test; the infrared spectroscopy test determines the changes in chemical functional groups during the aging process; and the gel chromatography test determines the molecular weight of each molecule in SBS modified asphalt.

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