Method for measuring and calculating tensile and compressive mechanical parameters of asphalt mixture based on three-dimensional complex stress state

Abstract

The application discloses a kind of based on three-dimensional complex stress state asphalt mixture tension-compression mechanical parameter measurement method, comprising the following steps: preparation asphalt mixture cuboid test piece and after keeping temperature specified time length in constant temperature environment, put into the test fixture of true triaxial test system and carry out tensile test test and compression test test, strain combination corresponding to different stress combinations under each three-dimensional stress state is obtained by summarizing test results;According to the basic assumption of three-dimensional bimodulus constitutive model calculation formula under the principal stress discrimination rule and bimodulus theory, the mechanical parameter calculation relationship formula of asphalt mixture under each three-dimensional stress state is established, the data of stress combination and corresponding strain combination under each three-dimensional stress state are substituted into corresponding asphalt mixture mechanical parameter calculation relationship formula and then solved, corresponding mechanical parameter is obtained.The application can more accurately obtain the tension-compression mechanical parameter characteristics of asphalt mixture in actual service process.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, specifically to a method for calculating the tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states. Background Technology

[0002] In my country's existing high-grade highways, asphalt pavement is the primary pavement structure. However, judging from the usage of these operational asphalt pavements, most have experienced significant functional degradation and structural damage before reaching their service life. Besides construction quality and overloading, a significant deviation between the structural design and actual conditions, as well as insufficient reliability, are also important factors. Therefore, ensuring the accuracy and reliability of structural design is paramount, especially in obtaining accurate and reliable material design parameters, particularly mechanical parameters.

[0003] However, the testing methods and instruments commonly used in existing pavement research can only apply simple stress or triaxial stress with equal minor and major principal stresses. This is significantly different from the three-dimensional complex stress state of actual asphalt pavement. It cannot effectively characterize the three-dimensional stress characteristics of actual pavement materials, nor can it accurately obtain strain data under complex stress states. As a result, the research on the mechanical properties of pavement materials under three-dimensional complex stress states has progressed slowly, which seriously affects the accuracy of mechanical calculations and performance predictions of asphalt pavement structures, thus causing huge deviations between pavement structure design and reality.

[0004] Currently, some researchers have studied the constitutive mechanical parameters of asphalt mixtures for road surfaces based on a dual-modulus constitutive model under two-dimensional stress. However, the actual structure of the road surface is subjected to complex three-dimensional stress, and there is still no method that can accurately and effectively reflect the tensile and compressive mechanical parameters of asphalt mixtures under three-dimensional stress. Summary of the Invention

[0005] The technical problem this invention aims to solve is that there is currently no experimental method that can accurately and effectively reflect the tensile and compressive mechanical parameters of asphalt mixtures under three-dimensional stress.

[0006] To address the aforementioned problems in existing technologies, a simple and reliable method for calculating the tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states is provided. This method facilitates more accurate acquisition of the tensile and compressive mechanical parameter characteristics of asphalt mixtures during actual service, laying the foundation for asphalt pavement mechanics technology and structural design, and thereby improving the actual service life of asphalt pavements.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for calculating the tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states includes the following steps:

[0009] Prepare cuboid specimens of asphalt mixture, keep the cuboid specimens of asphalt mixture in a constant temperature environment for a specified time, and then place them in the test fixture of a true triaxial testing system to conduct tensile and compressive tests. Summarize the test results to obtain the strain combination corresponding to different stress combinations under each three-dimensional stress state.

[0010] Based on the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of the bimodulus theory, the calculation relationship of the mechanical parameters of asphalt mixture under each three-dimensional stress state is established. After substituting the data of the stress combination and the corresponding strain combination under each three-dimensional stress state into the corresponding calculation relationship of the mechanical parameters of asphalt mixture, the corresponding mechanical parameters are obtained.

[0011] Furthermore, in preparing the asphalt mixture cuboid specimen, the mineral aggregate that has been screened layer by layer is dried and then mixed with asphalt to obtain an asphalt mixture. The asphalt mixture is then sheared and compacted to form the first cuboid specimen. Finally, the first cuboid specimen is cut with high-precision machinery to obtain the second cuboid specimen as the final asphalt mixture cuboid specimen.

[0012] Furthermore, when performing tensile and compressive tests within the test fixture of a true triaxial testing system, the specific procedures include:

[0013] During the compression test, a three-way sliding interlocking loading plate was used to place the asphalt mixture cuboid specimen on the clamp and perform friction reduction treatment. After the asphalt mixture cuboid specimen was installed, the clamp was placed on the lower loading shaft, the lower loading shaft was raised to the predetermined position, and then the upper loading shaft was controlled to contact the clamp. The left and right loading shafts were controlled to move synchronously and contact the clamp. Finally, the front and rear loading shafts were controlled to contact the clamp synchronously.

[0014] During the tensile test, a loading plate fixed to the loading shaft is used. The loading plate for applying tensile stress is first bonded to the tension surface of the corresponding specimen using adhesive. Then, a pin is used to connect the tensile fixture to the loading shaft.

[0015] The test software synchronously controls the loading axis to apply force to the specimen for preloading, and then resets it to zero. After the preloading is completed, the target loads in three dimensions under different three-dimensional stress states in the compression test or tension test are input into the control software, and a proportional loading path is adopted. During the loading process, the changes in the three-dimensional principal stress and the three-dimensional principal strain are recorded in real time to obtain the strain combination corresponding to different stress combinations under three-dimensional stress states.

[0016] Furthermore, based on the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of the bimodulus theory, when establishing the calculation relationship of the mechanical parameters of asphalt mixture under each three-dimensional stress state, specifically, according to the direction cosine constraint condition between the rectangular coordinate system and the principal direction coordinate system, the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion is transformed from the principal stress coordinate system to the ordinary rectangular coordinate system. Then, the basic assumption formula of the bimodulus theory and the transformed three-dimensional bimodulus constitutive model calculation formula are combined to obtain the calculation relationship of the mechanical parameters of asphalt mixture under each three-dimensional stress state.

[0017] Furthermore, the expression for the direction cosine constraint condition between the rectangular coordinate system and the principal direction coordinate system is as follows:

[0018]

[0019] in, l p , m p , n p These are the direction cosines between the x-axis in the rectangular coordinate system and each direction in the principal direction coordinate system. l q , m q , n q These are the direction cosines between the y-axis in the rectangular coordinate system and each direction in the principal direction coordinate system. l r , m r , n r These are the direction cosines between the z-axis in the rectangular coordinate system and each direction in the principal direction coordinate system.

[0020] Furthermore, the calculation formula for the three-dimensional bimodal constitutive model under the principal stress criterion is as follows:

[0021]

[0022] In the formula:

[0023] ɛ x , ɛ y , ɛ z These are the principal strains; s 1. s 2. s 3 is the principal stress; E 1 , E2 , E 3 For modulus, m 1 , m 2 , m 3 Poisson's ratio; A 1. A 2. A 3 represents the compliance matrix. G 1. G 2. G 3 represents the shear modulus in the direction of the principal stress;

[0024] The calculation formula for the transformed three-dimensional dual-modulus constitutive model is as follows:

[0025]

[0026]

[0027] in a,b =x,y,z i,j =p,q,r d This represents the Kronecker-Delta function.

[0028] Furthermore, the three-dimensional stress state includes a triaxial compressive stress state. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model to obtain the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state, the following are included:

[0029] In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli in all three dimensions are replaced with the compressive modulus to be solved. E c Replace the Poisson's ratios in all three dimensions with the pressure Poisson's ratio to be solved. m c Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. m t / E t = m c / E c Jointly established, among which, E t For the amount of drawing, m t It is Laposon's ratio.

[0030] Furthermore, the three-dimensional stress state includes a triaxial tensile stress state. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model to obtain the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state, the following are included:

[0031] In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli in all three dimensions are replaced with the tensile modulus to be solved. E t Replace the Poisson ratios in all three dimensions with the Lapoisson ratios to be solved. m t Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. m t / E t = m c / E c Jointly established, among which, E c For compression molding amount, m c It is the Poisson's ratio.

[0032] Furthermore, the three-dimensional stress state includes a biaxial tensile and uniaxial compressive stress state. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model to obtain the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state, the following are included:

[0033] In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli of two of the three dimensions are replaced with the tensile modulus to be solved. E t The modulus in the other direction is replaced by the compression modulus to be solved. E c Replace two of the three Poisson ratios with the Lapoisson ratio to be solved. m t The Poisson's ratio in the other direction is replaced by the pressure Poisson's ratio to be solved. m c Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. m t / E t = m c / E c Jointly established.

[0034] Furthermore, the three-dimensional stress state includes a biaxial compressive and uniaxial tensile stress state. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model to obtain the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state, the following are included:

[0035] In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli of two of the three dimensions are replaced with the compressive modulus to be solved. E c The modulus in the other direction is replaced by the tensile modulus to be solved. E t Replace two of the three Poisson ratios with the pressure Poisson ratio to be solved. m c The other Poisson's ratio is replaced with the Lapoisson's ratio to be solved. m t Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. m t / E t = m c / E c Jointly established.

[0036] Compared with the prior art, the advantages of the present invention are as follows:

[0037] This invention utilizes a true triaxial testing system to test the stress-strain mechanical parameters of asphalt mixtures under compressive stress using a three-dimensional sliding interlocking loading plate; and to test the stress-strain mechanical parameters of asphalt mixtures under tensile stress using a tensile loading plate that is bonded to the loading shaft with a steel adhesive. By summarizing the test results, the possible strain combinations under different stress combinations for each three-dimensional stress state are obtained, which can truly reflect the complex working conditions of actual roads.

[0038] Based on the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of the bimodulus theory, this invention establishes the calculation relationship of mechanical parameters of asphalt mixture under three-dimensional complex stress state, which more comprehensively describes the mechanical behavior and can realize the accurate simulation of three-dimensional stress state. Furthermore, by substituting the corresponding stress combination and strain combination into the calculation relationship, the mechanical parameters under different stress combinations can be obtained, which can yield richer calculation information and improve the accuracy of parameter calculation. Attached Figure Description

[0039] Figure 1 This is a flowchart of a method according to an embodiment of the present invention. Detailed Implementation

[0040] The present invention will be further described below with reference to specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0041] Existing testing methods and instruments commonly used in pavement research can only apply simple stress or triaxial stress with equal minor and major principal stresses. This differs significantly from the actual three-dimensional complex stress state of asphalt pavement and cannot effectively characterize the three-dimensional stress characteristics of actual pavement materials. Similarly, it cannot accurately obtain strain data under complex stress states, resulting in slow progress in the study of the mechanical properties of pavement materials under three-dimensional complex stress states. This seriously affects the accuracy of mechanical calculations and performance predictions of asphalt pavement structures, leading to huge deviations between pavement structure design and reality.

[0042] To address the aforementioned issues, this embodiment discloses a method for calculating the tensile and compressive mechanical parameters of asphalt mixtures under three-dimensional complex stress conditions. This method fills the gap in testing the mechanical parameters of asphalt mixtures under three-dimensional stress conditions, thereby facilitating more accurate acquisition of the tensile and compressive mechanical parameter characteristics of asphalt mixtures during actual service. This lays the foundation for asphalt pavement mechanics technology and structural design, and ultimately improves the actual service life of asphalt pavements.

[0043] like Figure 1 As shown, the method in this embodiment includes the following steps:

[0044] S1) Stress and strain mechanical parameter measurement stage: Prepare asphalt mixture cuboid specimens, keep the asphalt mixture cuboid specimens at constant temperature for a specified time, and then put them into the test fixture of the true triaxial test system to conduct tensile test and compressive test. Summarize the test results to obtain the strain combination corresponding to different stress combinations under each three-dimensional stress state.

[0045] S2) Calculation stage of mechanical parameters of modulus and Poisson's ratio: Based on the calculation formula of the three-dimensional double modulus constitutive model under the principal stress criterion and the relationship between tensile and compressive modulus and tensile and compressive Poisson's ratio in the basic assumptions of the double modulus theory, the calculation relationship of mechanical parameters of asphalt mixture under each three-dimensional stress state is established. After substituting the data of stress combination and corresponding strain combination under each three-dimensional stress state into the corresponding calculation relationship of mechanical parameters of asphalt mixture, the corresponding tensile and compressive modulus and tensile and compressive Poisson's ratio are obtained.

[0046] The relevant steps are explained in detail below.

[0047] Step S1 in this embodiment specifically includes the following steps:

[0048] First, asphalt mixture cuboid specimens were prepared according to the test requirements of the "Test Procedures for Asphalt and Mixtures in Highway Engineering" (JTG E20-2011) for later use. Specifically, in the preparation process, the aggregates that had been screened layer by layer were dried and then mixed with asphalt to obtain asphalt mixtures. Then, cuboid specimens with a length of 450mm × width of 150mm × height of 150mm were formed using an asphalt mixture shear compactor. Finally, the specimens were cut into cuboid specimens with a length of 100mm × width of 50mm × height of 50mm using high-precision machinery.

[0049] Then, the prepared specimen was placed in a constant temperature chamber at 15℃ for 4-5 hours. Afterward, the prepared cuboid specimen was placed in the test fixture of a true triaxial material testing system. A true triaxial material testing system is an experimental device used to study the mechanical properties of materials such as rocks and soils. It can apply three mutually perpendicular principal stresses to the specimen. s 1. s 2. s 3) These three principal stresses can be controlled independently, thus simulating the mechanical response of materials under complex stress paths. Compared with traditional uniaxial or triaxial tests, true triaxial tests can more realistically reflect the deformation and failure characteristics of materials under multiaxial stress states.

[0050] Finally, tensile and compressive tests are conducted. Under three-dimensional stress, asphalt mixtures may exhibit four different stress states: triaxial tension, triaxial compression, biaxial compression with monoaxial tension, and biaxial tension with monoaxial compression. In this embodiment, tensile and compressive tests are performed for each stress state, including both compression and tensile tests.

[0051] During the asphalt mixture compression test, a three-way sliding interlocking loading plate is used. The specimen is placed on the clamp and friction reduction treatment is performed. After the specimen is loaded, the clamp is placed on the lower loading shaft. The lower loading shaft is raised to the predetermined position, and then the upper loading shaft is controlled to contact the clamp. The left and right loading shafts are controlled to move synchronously and contact the clamp. Finally, the front and rear loading shafts are controlled to contact the clamp synchronously.

[0052] During the tensile test of asphalt mixture, a loading plate fixed to the loading shaft is used. The loading plate for applying tensile stress is first bonded to the corresponding tensile surface of the specimen using adhesive. Then, a pin is used to connect the tensile clamp to the loading shaft.

[0053] During the tensile and compressive tests, the test temperature was maintained at 15℃. The loading axis was synchronously controlled by the testing software to apply preload to the specimen, followed by zeroing. After preloading, the target loads in three dimensions under different stress states in the compressive or tensile tests were applied in the control software, using a proportional loading path and stress control mode. During loading, the three principal stresses were recorded in real time by strain sensors and stress sensors in three directions. s 1. s 2. s 3. Triaxial principal strain ɛ 1. ɛ 2. ɛ By varying the values ​​of 3, the mechanical parameters of stress and strain of asphalt mixtures under different stress combinations under three-dimensional stress states are obtained, and finally, the strain combination corresponding to different stress combinations under each three-dimensional stress state is obtained.

[0054] Under different stress combinations, tensile strain may occur in the direction of compressive stress, and compressive strain may occur in the direction of tensile stress. That is, the strain exhibits different strain properties as the load changes. Therefore, the strain properties that may occur under different stress combinations are shown in Table 1.

[0055] Table 1. Possible strain combinations under various stress states

[0056]

[0057] In this embodiment, step S2 establishes the calculation formula for the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of bimodulus theory, thereby establishing the calculation relationship for the mechanical parameters of asphalt mixture under three-dimensional complex stress states. Then, using the stress and strain mechanical parameter values ​​obtained in step S1, the mechanical parameters under different stress combinations are calculated. Specifically, the steps include:

[0058] ① Based on the direction cosine constraint condition between the rectangular coordinate system and the principal direction coordinate system, the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion is transformed from the principal stress coordinate system to the ordinary rectangular coordinate system. Then, the basic assumption formula of the bimodulus theory is combined with the transformed three-dimensional bimodulus constitutive model calculation formula to calculate the mechanical parameter relationship of asphalt mixture under each three-dimensional stress state (triaxial compressive stress state, triaxial tensile stress state, biaxial tensile and uniaxial compressive stress state, biaxial compressive and uniaxial tensile stress state), thus realizing the construction of the mechanical parameter calculation relationship of asphalt mixture under three-dimensional complex stress state;

[0059] Specifically, the calculation formula for the three-dimensional bimodal constitutive model under the principal stress criterion is as follows:

[0060]

[0061] In the formula:

[0062] ɛ x , ɛ y , ɛ z These are the principal strains; s 1. s 2. s 3 is the principal stress; E 1 , E 2 , E 3 For modulus, m 1 , m 2 , m 3 Poisson's ratio; E 1 , E 2 , E 3 , m 1 , m 2 , m 3 Take the tensile modulus when under tension E t and Lapozonbi m t , E 1 , E 2 , E 3 , m 1 , m 2 , m 3 Compressive modulus under pressure E c and Poisson's ratio m c ; A 1. A 2. A 3 represents the compliance matrix. G 1. G 2. G 3 represents the shear modulus in the direction of the principal stress.

[0063] To facilitate practical application, this embodiment transforms the calculation formula for the three-dimensional bimodal constitutive model established in the principal stress direction into a calculation formula for the three-dimensional bimodal constitutive model in a general rectangular coordinate system. (The rectangular coordinate system...) x、y、z Triaxial and Principal Stress , , The direction cosines between the directions are shown in Table 2;

[0064] Table 2. Direction cosines between the general coordinate system and the principal direction coordinate system.

[0065]

[0066] The constraint conditions for the direction cosine satisfy the following relationship:

[0067]

[0068] in, l p , m p , n p These are the direction cosines between the x-axis in the rectangular coordinate system and each direction in the principal direction coordinate system. l q , m q , n q These are the direction cosines between the y-axis in the rectangular coordinate system and each direction in the principal direction coordinate system. l r , m r , n r These are the direction cosines between the z-axis in the rectangular coordinate system and each direction in the principal direction coordinate system.

[0069] Based on the aforementioned constraint condition of direction cosine, the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion is transformed, and combined with the basic assumptions of the bimodulus theory, the calculation relationship of the mechanical parameters of asphalt mixture under each three-dimensional stress state is converted.

[0070] The basic assumptions of the bimodulus theory are expressed as follows:

[0071] m t / E t = m c / E c

[0072] in, E t For the amount of drawing, m t For Lapozon's ratio, Ec For compression molding amount, m c The modulus is the compressed Poisson's ratio; in the calculation formula of the transformed three-dimensional bimodulus constitutive model, the modulus is... E 1 , E 2 , E 3 and the corresponding Poisson's ratio m 1 , m 2 , m 3 Take the tensile modulus when under tension E t and Lapozonbi m t The compressive modulus is measured under pressure. E c and Poisson's ratio m c

[0073] therefore:

[0074]

[0075]

[0076] in a,b =x,y,z i,j =p,q,r d Represents the Kronecker-Delta function, in shear strain ,

[0077] Under triaxial compressive stress, since all three dimensions are under compression, the moduli of the three dimensions in the transformed three-dimensional bimodulus constitutive model calculation formula are... E 1 , E 2 , E 3 And the three-dimensional Poisson ratio m 1 , m 2 , m 3 Compression modulus E c and Poisson's ratio m c Therefore, the calculation relationship of the tensile and compressive mechanical parameters of asphalt mixture after conversion is:

[0078]

[0079] Under triaxial tensile stress, since all three directions are under tension, the moduli of the three directions in the calculation formula of the transformed three-dimensional bimodulus constitutive model are... E 1 , E 2 , E 3 And the three-dimensional Poisson ratio m 1 , m 2 , m 3 Take tensile modulus E t and Lapozonbi m t Therefore, the calculation relationship of the tensile and compressive mechanical parameters of asphalt mixture after conversion is:

[0080]

[0081] Under a biaxial tension and uniaxial compression stress state, since two of the three directions are under tension and the other under compression, the moduli of the three directions in the transformed three-dimensional bimodulus constitutive model calculation formula are... E 1 , E 2 , E 3 And the three-dimensional Poisson ratio m 1 , m 2 , m 3 The modulus in both directions and the Poisson's ratio are taken as the tensile modulus. E t and Lapozonbi m t The modulus in the other direction and the Poisson's ratio are taken as the compression modulus. E c and Poisson's ratio m c The calculation formulas for the converted mechanical parameters of asphalt mixtures are as follows:

[0082]

[0083] Under a biaxial compressive and uniaxial tensile stress state, since two of the three directions are under compression and the other under tension, the moduli of the three directions in the transformed three-dimensional bimodal constitutive model calculation formula are... E 1 , E 2 , E 3 And the three-dimensional Poisson ratio m 1 , m2 , m 3 The modulus in both directions and the compressive modulus of Poisson's ratio E c and Poisson's ratio m c The modulus in the other direction and the Poisson's ratio are taken as the tensile modulus. E t and Lapozonbi m t The calculation formulas for the converted mechanical parameters of asphalt mixtures are as follows:

[0084]

[0085] In the above formula: ɛ 1. ɛ 2. ɛ 3 is the primary strain; s 1. s 2. s 3 is the principal stress. E t Let the tensile modulus be the value to be solved. m t Let Laposon's ratio be the solution. E c Let the compression molding amount be the solution. m c Let be the Poisson's ratio to be solved.

[0086] ② For each three-dimensional stress state, the target load in the three directions measured in step S1 ( s 1. s 2. s 3) and the measured strain value after reaching the target load ( ɛ 1. ɛ 2. ɛ 3) Substitute the corresponding mechanical parameters of the asphalt mixture into the calculation formula;

[0087] ③ The calculation formula for the mechanical parameters of asphalt mixtures and 6 known parameters are derived from the constructed formula. s 1. s 2. s 3. ɛ 1. ɛ 2. ɛ 3) The four unknown parameters can then be obtained. E c , m c , E t , m t That is, to obtain the tensile and compressive mechanical parameters of asphalt mixture under three-dimensional complex stress state.

[0088] Taking the calculation of mechanical parameters of asphalt mixture under biaxial tension and uniaxial compressive stress as an example, an implementation example analysis is carried out. The three-dimensional target load is input into the control software. After the load and strain values ​​stabilize, the real-time strain of the three dimensions is read, as shown in Table 3. The negative sign indicates that the specimen is under compression, and the positive sign indicates that the specimen is under tension.

[0089] Table 3. Stress-strain data under biaxial tension and uniaxial compression stress combination.

[0090]

[0091] Substituting the stress and strain data of each group into the calculation formula for the mechanical parameters of asphalt mixture under biaxial tension and uniaxial compressive stress state, the tensile and compressive mechanical parameters of asphalt mixture under three-dimensional complex stress state can be obtained, as shown in Table 4:

[0092] Table 4. Tensile and compressive mechanical parameters of asphalt mixtures under three-dimensional complex stress conditions.

[0093]

[0094] The corresponding mechanical parameters were calculated by measuring the stress and strain data and compared with the experimental results. The results are shown in Table 5, which show that the errors are all less than 10%, verifying that the method has high accuracy.

[0095] Table 5 Error Table of Tensile and Compressive Mechanical Parameters of Asphalt Mixtures under Three-Dimensional Complex Stress State

[0096]

[0097] In summary, this invention proposes a method for calculating the tensile and compressive mechanical parameters of asphalt mixtures under three-dimensional complex stress states. A true triaxial testing system is used with a triaxial sliding interlocking loading plate method to test the mechanical parameters of asphalt mixtures under compressive stress. A tensile loading plate, fixed to the loading shaft with a steel-bonded adhesive connection, is used to test the mechanical parameters of asphalt mixtures under tensile stress. A table of possible strain properties for different stress combinations under three-dimensional stress states is proposed. Based on the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of bimodulus theory, calculation formulas for the mechanical parameters of asphalt mixtures under each three-dimensional stress state are established. Then, measured stress-strain data under three-dimensional stress are input to calculate the mechanical parameters of asphalt mixtures under three-dimensional stress states and verify their accuracy. This invention fills the gap in the testing of mechanical parameters of asphalt mixtures under three-dimensional stress states, thereby facilitating more accurate acquisition of the tensile and compressive mechanical parameter characteristics of asphalt mixtures during actual service, laying the foundation for asphalt pavement mechanics technology and structural design, and ultimately improving the actual service life of asphalt pavements.

[0098] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for calculating the tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states, characterized in that, Includes the following steps: Asphalt mixture cuboid specimens were prepared. After being kept at a constant temperature for a specified period, the specimens were placed in the test fixture of a true triaxial testing system for tensile and compressive tests. The test results were summarized to obtain the strain combinations corresponding to different stress combinations under each three-dimensional stress state. The stress combination data included the triaxial principal stresses. σ 1. σ 2 and σ 3. The strain combination data includes triaxial principal strain. ɛ 1. ɛ 2 and ɛ 3; Based on the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of bimodulus theory, calculation formulas for the mechanical parameters of asphalt mixtures under each three-dimensional stress state are established. The stress combination and corresponding strain combination data under each three-dimensional stress state are substituted into the corresponding calculation formulas for the mechanical parameters of asphalt mixtures for solution. The calculation formulas for the mechanical parameters of asphalt mixtures and the known parameters are then used to obtain the final solution. σ 1. σ 2. σ 3. ɛ 1. ɛ 2. ɛ 3. The corresponding mechanical parameters are calculated, including tensile modulus. E t Lapozon's ratio μ t Compression molding amount E c Poisson's ratio μ c ; Based on the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion and the basic assumptions of the bimodulus theory, when establishing the calculation relationship of the mechanical parameters of asphalt mixture under each three-dimensional stress state, the calculation formula of the three-dimensional bimodulus constitutive model under the principal stress criterion is transformed from the principal stress coordinate system to the ordinary rectangular coordinate system according to the direction cosine constraint condition between the rectangular coordinate system and the principal direction coordinate system. Then, the basic assumptions of the bimodulus theory are simultaneously established. μ t / E t = μ c / E c By combining the transformed three-dimensional dual-modulus constitutive model calculation formula, the calculation relationship of asphalt mixture mechanical parameters under each three-dimensional stress state is obtained.

2. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, In preparing cuboid specimens of asphalt mixture, the mineral aggregate that has been screened layer by layer is dried and then mixed with asphalt to obtain asphalt mixture. The asphalt mixture is then sheared and compacted to form the first cuboid specimen. Finally, the first cuboid specimen is cut with high precision to obtain the second cuboid specimen, which is the final cuboid specimen of asphalt mixture.

3. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, When placing the sample into the test fixture of a true triaxial testing system for tensile and compressive testing, the specific procedures include: During the compression test, a three-way sliding interlocking loading plate was used to place the asphalt mixture cuboid specimen on the clamp and perform friction reduction treatment. After the asphalt mixture cuboid specimen was installed, the clamp was placed on the lower loading shaft, the lower loading shaft was raised to the predetermined position, and then the upper loading shaft was controlled to contact the clamp. The left and right loading shafts were controlled to move synchronously and contact the clamp. Finally, the front and rear loading shafts were controlled to contact the clamp synchronously. During the tensile test, a loading plate fixed to the loading shaft is used. The loading plate for applying tensile stress is first bonded to the tension surface of the corresponding specimen using adhesive. Then, a pin is used to connect the tensile fixture to the loading shaft. The test software synchronously controls the loading axis to apply force to the specimen for preloading, and then resets it to zero. After the preloading is completed, the target loads in three dimensions under different three-dimensional stress states in the compression test or tension test are input into the control software, and a proportional loading path is adopted. During the loading process, the changes in the three-dimensional principal stress and the three-dimensional principal strain are recorded in real time to obtain the strain combination corresponding to different stress combinations under three-dimensional stress states.

4. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, The expression for the direction cosine constraint condition between the rectangular coordinate system and the principal direction coordinate system is as follows: in, l p , m p , n p These are the direction cosines between the x-axis in the rectangular coordinate system and each direction in the principal direction coordinate system. l q , m q , n q These are the direction cosines between the y-axis in the rectangular coordinate system and each direction in the principal direction coordinate system. l r , m r , n r These are the direction cosines between the z-axis in the rectangular coordinate system and each direction in the principal direction coordinate system.

5. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 4, characterized in that, The calculation formula for the three-dimensional bimodal constitutive model under the principal stress criterion is as follows: In the formula: ɛ x , ɛ y , ɛ z These are the principal strains; σ 1. σ 2. σ 3 is the principal stress; E 1 , E 2 , E 3 For modulus, μ 1 , μ 2 , μ 3 Poisson's ratio; A 1. A 2. A 3 represents the compliance matrix. G 1. G 2. G 3 represents the shear modulus in the direction of the principal stress; The calculation formula for the transformed three-dimensional dual-modulus constitutive model is as follows: in a,b =x,y,z i,j =p,q,r δ This represents the Kronecker-Delta function.

6. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, The three-dimensional stress state includes triaxial compressive stress state. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model, the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state are obtained, including: In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli in all three dimensions are replaced with the compressive modulus to be solved. E c Replace the Poisson's ratios in all three dimensions with the pressure Poisson's ratio to be solved. μ c Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. μ t / E t = μ c / E c Jointly established, among which, E t For the amount of drawing, μ t It is Laposon's ratio.

7. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, The three-dimensional stress state includes a triaxial tensile stress state. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model, the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state are obtained, including: In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli in all three dimensions are replaced with the tensile modulus to be solved. E t Replace the Poisson ratios in all three dimensions with the Lapoisson ratios to be solved. μ t Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. μ t / E t = μ c / E c Jointly established, among which, E c For compression molding amount, μ c It is the Poisson's ratio.

8. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, The three-dimensional stress states include biaxial tensile and uniaxial compressive stress states. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model, the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state are obtained, including: In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli of two of the three dimensions are replaced with the tensile modulus to be solved. E t The modulus in the other direction is replaced by the compression modulus to be solved. E c Replace two of the three Poisson ratios with the Lapoisson ratio to be solved. μ t The Poisson's ratio in the other direction is replaced by the pressure Poisson's ratio to be solved. μ c Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. μ t / E t = μ c / E c Jointly established.

9. The method for calculating tensile and compressive mechanical parameters of asphalt mixtures based on three-dimensional complex stress states according to claim 1, characterized in that, The three-dimensional stress states include biaxial compressive and uniaxial tensile stress states. When combining the basic assumptions of the bimodulus theory with the calculation formulas of the transformed three-dimensional bimodulus constitutive model, the calculation relationships of the asphalt mixture mechanical parameters under each three-dimensional stress state are obtained, including: In the transformed three-dimensional bimodulus constitutive model calculation formula, the moduli of two of the three dimensions are replaced with the compressive modulus to be solved. E c The modulus in the other direction is replaced by the tensile modulus to be solved. E t Replace two of the three Poisson ratios with the pressure Poisson ratio to be solved. μ c The other Poisson's ratio is replaced with the Lapoisson's ratio to be solved. μ t Then, the calculation formula of the three-dimensional bimodal constitutive model after parameter replacement is compared with the basic assumption formula of bimodal theory. μ t / E t = μ c / E c Jointly established.

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