A method for characterizing modulus degradation law of asphalt mixture under three-dimensional stress state

Abstract

The application discloses a kind of characterization methods of asphalt mixture modulus decay law under three-dimensional stress state, comprising the following steps: preparation asphalt mixture direct tensile, indirect tensile and uniaxial compression test specimen;Asphalt mixture direct tensile, indirect tensile and uniaxial compression strength and fatigue test are carried out;Power function relationship equation of asphalt mixture strength and loading rate is established;Respectively establish the modulus decay equation of asphalt mixture under direct tensile, indirect tensile and uniaxial compression mode;According to the initial equivalent stress of fatigue and the equivalent stress when fatigue failure, fatigue stress intensity ratio is calculated;Establish the characterization model of asphalt mixture modulus decay law under three-dimensional stress state;The application realizes the unified characterization of modulus decay law of asphalt mixture under different loading modes, provides theoretical, method and technical basis for realizing the scientific conversion from material fatigue damage to structure fatigue damage.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and in particular to a method for characterizing the modulus decay law of asphalt mixtures under three-dimensional stress. Background Technology

[0002] Asphalt pavement is the main pavement structure type used in my country's high-grade highways. Under the influence of factors such as vehicle load and natural environment, fatigue damage will gradually occur inside the structure. As the damage accumulates, the pavement material and structural performance will gradually degrade and eventually be destroyed.

[0003] To extend the service life of asphalt pavements, scientific and timely maintenance measures are necessary. Studying the development process of fatigue damage in asphalt mixtures is crucial for scientific maintenance decisions. The modulus of asphalt pavement materials is a key mechanical parameter determining pavement service life, and its decay pattern generally reflects the damage pattern of the asphalt pavement. However, on the one hand, asphalt pavement materials possess viscoelastic properties, and their modulus is not an inherent property of asphalt mixtures, exhibiting a certain stress dependence; its modulus changes with varying load conditions. On the other hand, the modulus of asphalt pavement materials is dependent on the pavement structure; different layers of the asphalt mixture within the pavement structure experience different stress states, resulting in varying modulus levels. Therefore, studying the modulus characteristics and decay patterns of asphalt mixtures solely through simple indoor loading modes, such as direct tension, indirect tension, and uniaxial compression, differs significantly from actual pavement service conditions. This is detrimental to evaluating the fatigue damage performance of asphalt pavement structures and hinders scientific maintenance decisions.

[0004] In summary, to achieve the scientific transformation from material fatigue damage to structural fatigue damage, it is urgent to invent a method that can establish a model characterizing the modulus decay law of asphalt mixtures under three-dimensional stress state through mechanical property tests of asphalt mixtures under simple stress states, so as to achieve a unified characterization of the modulus decay law of asphalt mixtures under different loading modes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for characterizing the modulus decay law of asphalt mixtures under three-dimensional stress, which solves the problem that the existing technology has a large difference from the actual service condition of the pavement, which is not conducive to evaluating the fatigue damage performance of asphalt pavement structure and to scientific maintenance decision-making.

[0006] This invention is implemented as follows: a method for characterizing the modulus decay law of asphalt mixtures under three-dimensional stress state, comprising the following steps:

[0007] S1. Prepare specimens for direct tensile, indirect tensile and uniaxial compression tests of asphalt mixtures;

[0008] S2. Conduct direct tensile, indirect tensile, and uniaxial compressive strength and fatigue tests on asphalt mixtures;

[0009] S3. Establish the power function equation relating the strength of asphalt mixture to the loading rate;

[0010] S4. Establish the modulus decay equations of asphalt mixtures under direct tension, indirect tension and uniaxial compression modes respectively.

[0011] S5. Calculate the fatigue stress-intensity ratio based on the initial equivalent fatigue stress and the equivalent stress at fatigue failure.

[0012] S6. Establish a characterization model for the modulus decay law of asphalt mixture under three-dimensional stress state.

[0013] Furthermore, the asphalt mixture strength test in step S2 adopts a displacement control mode and a stress control mode. Under the displacement control mode, the loading rates for the direct tensile, indirect tensile, and uniaxial compression strength tests of the asphalt mixture are 5 mm / min, 50 mm / min, and 2 mm / min, respectively. Under the stress control mode, the asphalt mixture strength test is carried out at different loading rates. The direct tensile, indirect tensile, and uniaxial compression modes all adopt 0.02 MPa / s, 0.05 MPa / s, 0.1 MPa / s, 0.5 MPa / s, 1 MPa / s, 2 MPa / s, 4 MPa / s, and 6 MPa / s.

[0014] Furthermore, the fatigue test of the asphalt mixture in step S2 adopts a stress control mode. The fatigue test stress level can be selected based on the strength test results under the displacement control mode. The selected fatigue test stress level shall not be greater than the strength of the asphalt mixture.

[0015] Furthermore, the power function equation for fitting the asphalt mixture strength value to the loading rate in step S3 is:

[0016] S=αv β

[0017] Where: S is the asphalt mixture strength; v is the loading rate; α and β are equation parameters;

[0018] The parameters α and β of this equation can be obtained by fitting the strength test results of asphalt mixtures under different loading rates in stress control mode.

[0019] Furthermore, the modulus in step S4 can be continuously measured using strain or displacement sensors during fatigue testing without affecting the material's properties. It decreases continuously as internal damage accumulates. The modulus can effectively describe the damage to asphalt mixtures. The damage variable is defined as:

[0020]

[0021] Where: D is the damage degree of the specimen, E is the modulus of the material after fatigue, and E0 is the initial modulus of the specimen;

[0022] Furthermore, the asphalt mixture modulus decay equations under the direct tension, indirect tension, and uniaxial compression modes in step S4 are fitted using Equation 2:

[0023]

[0024] Where: m is the parameter of the modulus decay equation, and 0 < m < 1, which can be obtained by fitting through fatigue test; E is the effective modulus of the material, E0 is the initial modulus of the material, and N is the number of load cycles in the fatigue test. f This refers to fatigue life.

[0025] Furthermore, the fatigue stress-intensity ratio in step S5 is calculated using the following formula:

[0026] Fatigue stress strength ratio

[0027] in: σ is the initial equivalent stress due to fatigue. es This is the equivalent stress during fatigue failure;

[0028] The equivalent stress in step S5 is calculated by the following formula:

[0029]

[0030] Where: σ e For equivalent stress, σ1, σ2, and σ2 are the first, second, and third principal stresses at a point, respectively.

[0031] Furthermore, the fatigue stress strength ratio in step S5 is a new fatigue analysis index based on the three-dimensional stress state strength yield surface theory of asphalt mixture, and taking into account the influence of stress state and loading rate.

[0032] Furthermore, the specific method for establishing the characterization model of the modulus decay law of asphalt mixture under three-dimensional stress state in step S6 is as follows:

[0033] S61. Fit the modulus decay equation parameters in step S4 with the fatigue stress intensity ratio in step S5 using Equation 3 (power function equation):

[0034] m = Δ n Formula 3

[0035] Where: m is the parameter of the modulus decay equation, Δ is the fatigue stress-intensity ratio, and n is the fitting parameter;

[0036] S62. Combine the power function equation of the modulus decay equation parameter m and the fatigue stress-intensity ratio Δ with the modulus decay equation in step S4 to obtain a characterization model of the modulus decay law of asphalt mixture under three-dimensional stress state:

[0037]

[0038] Where: E is the dynamic modulus during fatigue, E0 is the initial value of the dynamic modulus, N is the number of fatigue load cycles, and N f denoted as fatigue life; m is a parameter of the modulus attenuation equation, which can be obtained by fitting the fatigue test; Δ is the fatigue stress-intensity ratio, which takes into account the influence of stress state and loading rate, and represents the ratio of stress level to corresponding material resistance during asphalt mixture fatigue test; n is a regression coefficient, which is obtained by fitting the fatigue stress-intensity ratio Δ with the modulus attenuation equation parameter m.

[0039] The beneficial effects of this invention are as follows: Based on the three-dimensional stress state strength yield surface theory of asphalt mixtures, this invention employs a fatigue analysis method that considers the influence of stress state and loading rate to calculate the fatigue stress-intensity ratio through direct tensile, indirect tensile, uniaxial compression fatigue tests and strength tests. This leads to the establishment of a characterization model for the modulus decay of asphalt mixtures under three-dimensional stress states. Using the method of this invention, a model characterizing the modulus decay law of asphalt mixtures under three-dimensional stress states can be established through fatigue and strength tests under simple stress states. This invention achieves a unified characterization of the modulus decay law of asphalt mixtures under different loading modes, providing theoretical, methodological, and technical basis for the scientific transformation from material fatigue damage to structural fatigue damage. Attached Figure Description

[0040] Figure 1 This is a flowchart of the characterization method for the modulus decay law of asphalt mixture under three-dimensional stress state according to the present invention;

[0041] Figure 2 This is a graph showing the power function fitting relationship between strength and loading rate under different stress states according to an embodiment of the present invention;

[0042] Figure 3 This is a fitting curve of modulus decay at different stress levels under the direct tensile mode of an embodiment of the present invention; wherein... Figure 3 a is 0.2 MPa; Figure 3 b is 0.4 MPa; Figure 3 c is 0.6 MPa; Figure 3 d is 0.8 MPa; Figure 3 e is 1 MPa;

[0043] Figure 4 This is a fitting curve of modulus decay at different stress levels under the indirect tensile mode of this invention; wherein... Figure 4a is 0.2 MPa; Figure 4 b is 0.4 MPa; Figure 4 c is 0.6 MPa; Figure 4 d is 0.8 MPa; Figure 4 e is 1 MPa;

[0044] Figure 5 This is a fitting curve of modulus decay under different stress levels in the uniaxial compression mode of an embodiment of the present invention; wherein Figure 5 a is 1.5 MPa; Figure 5 b is 2.0 MPa; Figure 5 c is 0.6 MPa; Figure 5 d is 3.0 MPa; Figure 5 e is 3.5 MPa;

[0045] Figure 6 This is a load-carrying waveform diagram during fatigue testing in an embodiment of the present invention;

[0046] Figure 7 This is a graph showing the fitting relationship between the modulus decay equation parameters and the power function of the fatigue stress intensity ratio in an embodiment of the present invention.

[0047] Figure 8 This is a surface diagram representing the modulus decay of asphalt mixture under three-dimensional stress state according to the present invention. Detailed Implementation

[0048] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0049] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0050] This invention provides a method for characterizing the modulus decay law of asphalt mixtures under three-dimensional stress conditions, the characterization method comprising the following steps:

[0051] S1. Prepare asphalt mixture test specimens under different stress loading conditions;

[0052] S2. Conduct asphalt mixture tests under different stress loading strengths and fatigue tests;

[0053] S3. Establish the power function relationship equation between the strength and recording rate of asphalt mixture under different stress states;

[0054] S4. Establish the modulus decay equations of asphalt mixtures under different stress loading modes respectively;

[0055] S5. Calculate the fatigue stress-intensity ratio based on the initial equivalent fatigue stress and the equivalent fatigue failure stress;

[0056] S6. Establish a characterization model for the modulus decay law of asphalt mixture under three-dimensional stress state.

[0057] Example 1:

[0058] (1) Preparation of specimens for direct tensile, indirect tensile and uniaxial compression tests of asphalt mixtures

[0059] According to the Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011), direct tensile, indirect tensile, and uniaxial compression specimens were prepared. For direct tensile specimen preparation, the asphalt mixture was first compacted into 300mm × 300mm × 50mm rutting slabs using a rutting wheel roller, and then cut into 250mm × 50mm × 50mm beam specimens. The asphalt mixture beam specimens were fixed between two jointed iron discs using epoxy resin AB glue. The tensile strength of the air-dried epoxy glue was much greater than that of the asphalt mixture, and its deformation was small, so it would not affect the test results of the asphalt mixture. Two displacement sensors were symmetrically fixed on both sides of the asphalt mixture beam specimens for fatigue testing.

[0060] For the preparation of indirect tensile specimens, the specimens were first formed using an SGC rotary compactor, resulting in cylindrical specimens with a height of 100±2 mm and a diameter of 100±2 mm. The vertical loading pressure for rotary compaction was 600 kPa±18 kPa, the effective internal rotation angle was 1.16±0.02°, and the compaction speed was 30 r / min±0.5 r / min. The specimens were then cut into pieces with a height of 60±2 mm and a diameter of 100±2 mm for indirect tensile testing. Uniaxial compression specimens were prepared using the SGC rotary compactor, with dimensions of 100±2 mm in height and diameter. The rotary compaction method was the same as that used for the indirect tensile specimens.

[0061] (2) Conduct direct tensile, indirect tensile, and uniaxial compressive strength and fatigue tests on asphalt mixtures.

[0062] In this embodiment, the fatigue test adopts a stress-controlled mode, defining the fatigue life as the number of loading cycles at which the specimen fails (obvious fracture or deformation). During the fatigue test, an LVDT sensor is used to monitor the displacement of the specimen in real time to analyze the modulus changes during the fatigue test. The strength test employs both stress and displacement control methods. All tests are conducted at 15±1℃. Before the test, the specimen is kept at 15±1℃ for at least 4 hours. Direct tensile beam specimens are connected to the MTS testing machine via a circular iron disc and connecting rod for strength and fatigue tests. Indirect tensile and uniaxial compressive strength and fatigue tests are also conducted on the MTS.

[0063] Prior to the direct tensile, indirect tensile, and uniaxial compressive fatigue tests, strength tests under displacement control mode were conducted. The loading rates for direct tensile, indirect tensile, and uniaxial compressive tests were maintained at 5 mm / min, 50 mm / min, and 2 mm / min, respectively (JTG E20-2011). For the stress-controlled direct tensile, indirect tensile, and uniaxial compressive strength tests, eight loading rates were used: 0.02 MPa / s, 0.05 MPa / s, 0.1 MPa / s, 0.5 MPa / s, 1 MPa / s, 2 MPa / s, 4 MPa / s, and 6 MPa / s. Each test group consisted of three parallel specimens, and the maximum load P (N) was recorded when the specimen failed.

[0064] Direct tensile strength calculation formula:

[0065]

[0066] In the formula: S t , represents the direct tensile strength, MPa; a and b are the width and height of the direct tensile specimen, respectively, mm.

[0067] Formula for calculating indirect tensile strength:

[0068]

[0069] In the formula: S it is the indirect tensile strength, MPa; P is the maximum load on the specimen, N; h is the height of the specimen, mm.

[0070] Formula for calculating uniaxial compression test strength:

[0071]

[0072] In the formula: S c d is the compressive strength of the specimen, MPa; P is the maximum load on the specimen, N; d is the diameter of the specimen, mm.

[0073] The average strengths under direct tension, indirect tension, and uniaxial compression displacement control modes are listed in Table 1.

[0074] Table 1 Average strength under displacement control mode under different stress states

[0075] Stress state Average strength (MPa) Direct stretching 1.071 Indirect stretching 2.180 Uniaxial compression 7.448

[0076] Based on the asphalt mixture strength test results under displacement control mode, appropriate stress levels were selected for direct tensile, indirect tensile, and uniaxial compression fatigue tests. In this example, the stress levels selected for the direct and indirect tensile fatigue tests were 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, and 1 MPa. The stress levels for the uniaxial compression fatigue tests were set to 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, and 3.5 MPa. Four parallel specimens were tested at each stress level. The loading frequency was 10 Hz, and the loading waveform was a continuous half-sine wave.

[0077] (3) Establish the power function equation relating the strength of asphalt mixture to the loading rate.

[0078] This embodiment, based on the results of direct tensile, indirect tensile, and uniaxial compressive strength tests of asphalt mixtures under different loading rates, fits the asphalt mixture strength values ​​to the loading rate using a power function, such as... Figure 2 As shown, the power function equations are obtained as follows:

[0079] Direct stretching S t =2.275v 0.213 ,R 2 =0.965

[0080] Indirect stretching S it =1.994v 0.195 ,R 2 =0.978

[0081] Uniaxial compression S c =11.602v 0.154 ,R 2 =0.985

[0082] (4) Establish the modulus decay equations of asphalt mixtures under direct tension, indirect tension and uniaxial compression modes respectively.

[0083] In this embodiment, the modulus of asphalt mixture can be continuously measured by displacement sensors during fatigue testing without affecting the material's properties. It decreases continuously as internal damage accumulates. The modulus can effectively describe the damage to the asphalt mixture. The damage variable is defined as follows:

[0084]

[0085] Where: D is the damage degree of the specimen, E is the modulus of the material after fatigue, and E0 is the initial modulus of the specimen;

[0086] Furthermore, the modulus decay equations of asphalt mixtures under direct tension, indirect tension, and uniaxial compression modes are fitted using the following model:

[0087]

[0088] Where: m is the parameter of the modulus decay equation, and 0 < m < 1, which can be obtained by fitting through fatigue test; E is the effective modulus of the material, E0 is the initial modulus of the material, and N is the number of load cycles in the fatigue test. f This refers to fatigue life.

[0089] Based on the above model, the decay data points of modulus ratio with lifetime ratio are fitted, and the parameters m of the fitted modulus decay model are summarized in Tables 2, 3, and 4. An example of a modulus decay graph is provided. Figure 3 , Figure 4 and Figure 5 As shown.

[0090] Table 2. Parameter m in the direct tensile modulus decay equation

[0091]

[0092] Table 3. Parameter m of the indirect tensile modulus decay equation

[0093]

[0094] Table 4. Parameter m in the uniaxial compressive modulus decay equation

[0095]

[0096] (5) Calculate the fatigue stress-intensity ratio based on the initial equivalent fatigue stress and the equivalent stress at fatigue failure.

[0097] Under actual traffic loads, the stress state of asphalt pavement is highly complex. The strength and fatigue performance of asphalt mixtures are related to their stress state and loading rate. Traditional fatigue analysis methods do not consider these factors, which is clearly unscientific. Therefore, this embodiment, based on the concept of a three-dimensional stress state strength yield surface, applies a new method for analyzing the fatigue characteristics of asphalt mixtures that matches the actual service conditions of pavements, to compensate for the shortcomings of traditional fatigue performance analysis methods that do not consider the influence of stress state and loading rate. This embodiment calculates the fatigue stress-strength ratio Δ according to the following formula:

[0098]

[0099] in: σ is the initial equivalent stress due to fatigue. es This is the equivalent stress during fatigue failure.

[0100] The above formula represents the ratio of the stress level to the corresponding material resistance during the fatigue test of asphalt mixture.

[0101] In this example, the initial equivalent stress of the fatigue test The equivalent stress at fatigue failure can be calculated according to Table 5, and according to Table 6.

[0102] Table 5 Initial Equivalent Stress Calculation method

[0103]

[0104] Table 6 Equivalent stress σ at fatigue failure es Calculation method

[0105]

[0106] The fatigue loading rates corresponding to fatigue tests under different stress levels are different, and the strength of asphalt mixtures varies with different loading rates. Therefore, the yield strength of asphalt mixtures in fatigue tests under different stress levels is also different. The fatigue test uses a 10Hz continuous half-sine waveform, such as... Figure 6 As shown.

[0107] The corresponding loading rate can be calculated from the loading frequency f (period T) and stress level σ of the fatigue test, as shown in Equation 1:

[0108]

[0109] According to Equation 1, the loading rate corresponding to different stress levels in the fatigue test can be calculated. Based on the power function equation of asphalt mixture strength and loading rate under different stress states established in step (3) of this embodiment, the ultimate strength under different stress states and stress levels can be calculated. The initial equivalent stress is calculated based on Tables 5 and 6 respectively. Equivalent stress σ at fatigue failure es The fatigue stress-intensity ratio Δ was calculated, and the results are shown in Table 7.

[0110] Table 7 Calculation results of fatigue stress strength ratio Δ

[0111]

[0112] (6) Establish a characterization model for the modulus decay law of asphalt mixture under three-dimensional stress state.

[0113] In step (4) of this embodiment, the modulus attenuation equation for asphalt mixture under different loading modes was established. In step (5) of this embodiment, the fatigue stress-intensity ratio under different loading modes and stress levels was calculated. The modulus attenuation equation parameter m and the fatigue stress-intensity ratio Δ are summarized in Table 8.

[0114] Table 8 Fatigue stress-intensity ratio Δ and modulus decay equation parameter m

[0115]

[0116] The relationship between the modulus decay equation parameter *m* and the fatigue stress-intensity ratio *Δ* is plotted on the same coordinate system. Overall, the modulus decay equation parameter increases with the increase of the fatigue stress-intensity ratio. Fitting the two according to a power function growth law, as shown below... Figure 7 As shown, the following regression equation is obtained (where 0 < m < 1, 0 < Δ < 1):

[0117] m = Δ 0.328 R 2 =0.910

[0118] By combining the power function equations of the modulus decay equation parameter m and the fatigue stress intensity ratio Δ with the modulus decay equation in step (4) of this embodiment, a characterization model of the modulus decay law of asphalt mixture under three-dimensional stress state is obtained:

[0119]

[0120] The characterization model of the modulus decay law of asphalt mixture under three-dimensional stress state established based on this embodiment can be plotted using Origin software as follows: Figure 8 The figure shows the modulus decay surface of asphalt mixture under three-dimensional stress. For asphalt pavement structures, the fatigue stress-intensity ratio at a certain point within the structure's entire life cycle is constantly changing. The modulus decay of the asphalt pavement structure is represented by a curve in the modulus decay surface of asphalt mixture under three-dimensional stress. Therefore, by analyzing the variation law of the fatigue stress-intensity ratio under different damage conditions, the connection mechanism between material modulus and structural modulus can be established, thereby establishing a modulus decay model for asphalt pavement structures. This invention provides a method for characterizing the modulus decay law of asphalt mixture under three-dimensional stress, providing theoretical, methodological, and technical basis for realizing the scientific transformation from material fatigue damage to structural fatigue damage.

[0121] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for characterizing the modulus decay law of asphalt mixtures under three-dimensional stress state, characterized in that, The characterization method includes the following steps: S1. Prepare asphalt mixture test specimens under different stress loading conditions; S2. Conduct asphalt mixture tests under different stress loading strengths and fatigue tests; S3. Establish the power function relationship equation between the strength of asphalt mixture and the loading rate under different stress states: Based on the test results of the stress loading strength of asphalt mixture under different loading rates, the strength value of asphalt mixture is fitted with the loading rate using a power function; S4. Establish the modulus decay equations of asphalt mixtures under different stress loading modes; based on the asphalt mixture modulus decay equations, obtain the modulus decay equation parameters through fatigue testing. ; S5. Calculate the fatigue stress-intensity ratio based on the initial equivalent fatigue stress and the equivalent fatigue failure stress: The fatigue stress-intensity ratio is based on the three-dimensional stress state strength yield surface theory of asphalt mixture, and the fatigue analysis takes into account the influence of stress state and loading rate. S6. Establish a characterization model for the modulus decay law of asphalt mixture under three-dimensional stress state: based on the modulus decay equation parameters in step S4. The fatigue stress strength ratio of step S5 The power function equation is obtained by fitting the power function growth law. The power function equation is then combined with the asphalt mixture modulus decay equation in step S4 to obtain the characterization model of the asphalt mixture modulus decay law under three-dimensional stress state. In step S4, the modulus of the asphalt mixture can be continuously measured in the fatigue test using strain or displacement sensors. The modulus describes the damage to the asphalt mixture, and the damage variable is defined as follows: in: The degree of damage to the specimen. This refers to the modulus of the material after fatigue. The initial modulus of the specimen; The asphalt mixture modulus decay equation is fitted using model 2: Formula 2 in: For the modulus decay equation parameters, and It can be obtained through fatigue testing and fitting. The effective modulus of the material. The initial modulus of the material. The number of load cycles in the fatigue test. For fatigue life; The fatigue stress-intensity ratio in step S5 is calculated using the following formula: Fatigue stress strength ratio in: This is the initial equivalent stress of fatigue; This is the equivalent stress during fatigue failure; The equivalent stress is calculated by the following formula: in: For equivalent stress, , , These are the first, second, and third principal stresses at a point, respectively. The specific method for establishing the representation model in step S6 is as follows: S61. Fit the modulus decay equation parameters in step S4 with the fatigue stress intensity ratio in step S5 using Equation 3 (power function equation): Formula 3 in: For the parameters of the modulus decay equation, The fatigue stress-strength ratio These are the fitting parameters; S62, Parameters of the modulus decay equation and fatigue stress strength ratio The power function equation and the modulus decay equation in step S4 are combined to obtain a characterization model of the modulus decay law of asphalt mixture under three-dimensional stress state: in: This represents the dynamic modulus during fatigue. This is the initial value of the dynamic modulus. The number of fatigue load cycles. For fatigue life; The parameters of the modulus decay equation can be obtained through fatigue testing. The fatigue stress-strength ratio is a ratio that takes into account the effects of stress state and loading rate. It represents the ratio of stress level to material resistance during fatigue testing of asphalt mixture. The regression coefficient is obtained by comparing the fatigue stress intensity ratio. With modulus decay equation parameters The results were obtained through fitting.

2. The method for characterizing the modulus decay law of asphalt mixture under three-dimensional stress state according to claim 1, characterized in that, Stress loading includes direct tension, indirect tension, and uniaxial compression. In step S1, asphalt mixture test specimens for direct tension, indirect tension, and uniaxial compression are prepared respectively.

3. The method for characterizing the modulus decay law of asphalt mixture under three-dimensional stress state according to claim 1, characterized in that, In step S2, the strength test adopts displacement control mode and stress control mode; the fatigue test adopts stress control mode, and the fatigue test stress level can be selected based on the strength test results under displacement control mode. The selected fatigue test stress level shall not be greater than the strength of the asphalt mixture.

4. The method for characterizing the modulus decay law of asphalt mixture under three-dimensional stress state according to claim 1, characterized in that, The power function equation for fitting the asphalt mixture strength value and loading rate in step S3 is as follows: in: Strength of asphalt mixture; For loading rate; For equation parameters; parameters It can be obtained by fitting the strength test results of asphalt mixtures at different loading rates under stress control mode.

5. The method for characterizing the modulus decay law of asphalt mixture under three-dimensional stress state according to claim 4, characterized in that, Based on the loading frequency of the fatigue test The cycle is and stress level The corresponding loading rate can be calculated. See Equation 1: Formula 1 According to Equation 1, the loading rate corresponding to different stress levels in fatigue tests can be calculated. Based on the established power function equation of asphalt mixture strength and loading rate under different stress states, the ultimate strength under different stress states and stress levels can be calculated.

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