Method for analyzing indirect tensile internal synergistic stress of asphalt mixture

Abstract

The invention discloses a method for analyzing indirect tensile internal synergistic stress of an asphalt mixture. The invention aims to solve the problem of lack of internal stress data during indirect tensile stress of the asphalt mixture and a method for reasonably evaluating synergistic stress of the asphalt mixture. The analysis method comprises the following steps: 1, constructing a coarse aggregate template library; 2, establishing a Marshall test piece discrete element geometric model; 3, endowing each component and an interface with contact parameters; 4, performing indirect stretching simulation; 5, evaluating the simulation accuracy rate; 6, determining two feature time points, and obtaining internal force chain information of the feature time points; 7, quantifying the strength distribution of the interfacial force chain; 8, quantifying the direction distribution of the interfacial force chain; and 9, evaluating the internal collaborative stress capacity and evolution capacity. According to the method, the discrete element modeling method is adopted to obtain the force chain data of the internal components of the asphalt mixture, the force chain uniformity probability and the force chain angle distribution uniformity index are provided, and the cooperative stress capacity and the evolution rate of the asphalt mixture are effectively and quantitatively evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of digital design and evaluation of asphalt mixtures, and in particular relates to an analysis method for internal coordinated force of an indirect tensile asphalt mixture. Background Art

[0002] The indirect tensile test (IDT) of asphalt mixture, also known as the splitting test, is a common test method used to evaluate the crack resistance and durability of asphalt mixtures to ensure that their performance in actual road projects meets the design requirements. The indirect tensile test is almost a necessary test for asphalt mixture testing and is widely used in the performance testing of various asphalt mixtures. However, the test results can only reflect the overall performance, lacking the stress data of each component inside the asphalt mixture, and can only be used to evaluate whether the performance is qualified, and have limited reference value for design and improvement. At present, there is no effective method to obtain the internal stress of asphalt mixtures. Sensors can only obtain partial data and will change the internal structure to cause data distortion; the digital speckle method is limited to obtaining surface strain, and internal mechanical data is difficult to obtain. Internal synergistic stress is crucial for evaluating the uniformity of stress of asphalt mixtures and improving bearing capacity.

[0003] Discrete Element Method (DEM) is a numerical calculation method used to simulate and analyze the behavior of granular materials. It is suitable for studying systems composed of a large number of interacting discrete bodies. Asphalt mixtures are composed of coarse aggregates, asphalt mortar, and voids, which conforms to the basic idea of ​​the discrete element method. Asphalt mixtures are regarded as composed of many independent, discrete particles. These particles are regarded as units with mechanical properties in the calculation. The behavior of the entire system is simulated by calculating the interactions between these units. The mass, shape, size, motion state and other characteristics of each particle are considered in the model, thereby effectively obtaining the mechanical characteristics of each internal component. Therefore, using the discrete element method to achieve efficient and high-precision indirect tensile simulation, and proposing internal component force analysis methods and evaluation indicators are of great significance for solving the current dilemma of asphalt mixture performance evaluation and guiding its structural design and improvement. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the internal stress data of asphalt mixture when it is subjected to indirect tensile stress and the method for reasonably evaluating the coordinated stress of asphalt mixture are currently lacking, which makes it impossible to guide the structural design and optimization of asphalt mixture, and to provide an analysis method for the internal coordinated stress of asphalt mixture when it is subjected to indirect tensile stress.

[0005] The indirect tensile internal synergistic force analysis method of asphalt mixture of the present invention is implemented according to the following steps:

[0006] Step 1: Scan a single coarse aggregate through CT, establish templates of coarse aggregates with different shapes, and construct a coarse aggregate template library;

[0007] Step 2: Generate a Marshall specimen model of the corresponding gradation using a random generation algorithm according to the gradation, obtain the position of the constituent particles as the coarse aggregate position, randomly call the coarse aggregate template in the coarse aggregate template library to replace the randomly generated constituent particles, build a skeleton, randomly generate mortar at the voids according to the void ratio, and construct a discrete element geometric model of the Marshall specimen;

[0008] Step 3: assign corresponding contact models and mechanical contact parameters to the interior and interface of each component in the discrete element geometric model of the Marshall specimen;

[0009] Step 4: Rectangular walls are constructed at the top and bottom of the side of the Marshall specimen discrete element geometric model, with the top being the loading wall and the bottom being the bearing wall. The speed of the loading wall is controlled to simulate the indirect tensile test, and the discrete element simulation results (force-displacement curve) are obtained. Aggregates, asphalt and mineral powder are mixed according to the same gradation and asphalt-stone ratio, and asphalt mixture specimens are prepared after compaction. Indirect tensile tests are carried out to obtain the force-displacement curve of the indoor experiment.

[0010] Step 5: Evaluate the indirect tensile simulation effect using the discrete element simulation results and the force-displacement curve of the indoor experiment. Obtain the load peak difference and the maximum load difference from the force-displacement curve (the maximum load difference is the maximum value of the load difference of the force-displacement curve). Use the load peak difference and the maximum load difference as evaluation indicators. The load difference is calculated according to the following formula (1);

[0011]

[0012] Where Dif is the load difference, F dem is the load of discrete element simulation, F test is the corresponding indoor test load;

[0013] When the peak load difference is within 10% and the maximum load difference is within 15%, the discrete element simulation results are accepted. If they do not meet the requirements, the mechanical contact parameters in step 3 are readjusted;

[0014] Step 6. Determine two characteristic time points, which are 75% peak load in the rising stage of the force-displacement curve and 75% peak load in the falling stage of the force-displacement curve. The internal synergistic force capacity is characterized by the 75% peak load in the rising stage, and the evolution of the synergistic capacity is characterized by the 75% peak load in the falling stage. The force chains of each component in the discrete element geometric model of the Marshall specimen at the two characteristic time points during the indirect tensile test are traversed to extract the force chain information, which includes the force chain strength, the number of force chains and the force chain angle.

[0015] Step 7: The force chain uniformity probability P of the coarse aggregate-asphalt mortar interface 均匀 As an indicator for evaluating the uniformity of internal force, s is the relative strength of the force chain, which represents the ratio of the force chain strength to the average force chain strength, P 均匀 is the probability of force chain when s is between 0.5 and 1.5, and the uniform probability of force chain P 均匀 Calculate according to the following formula;

[0016]

[0017] Where n 均匀 is the number of force chains with a relative strength of 0.5 to 1.5, and n is the total number of force chains in the indirect stretching process;

[0018] Step 8: Quantify the directional geometric characteristics of the force chains of different components in the discrete element geometric model of the Marshall specimen. The angle between the normal force chain and the vertical direction is used as a quantitative indicator to characterize the directional distribution characteristics of the force chain. The relative strength of the interface force chain in the angle range of 120° to 150° is statistically expressed as s. 角 express;

[0019] Step 9: Calculate the uniform probability P of the force chain at two characteristic time points respectively 均匀 and 角 , to evaluate the synergistic force bearing capacity of asphalt mixture, thus completing the synergistic force analysis method of indirect tensile internal of asphalt mixture.

[0020] The present invention adopts the discrete element modeling method to obtain the force chain data of the internal components of the asphalt mixture, which overcomes the problem that the internal component forces cannot be obtained; two quantitative evaluation indicators, load peak difference and maximum load difference, are proposed to efficiently evaluate and thus ensure the high accuracy of the simulation effect; the loading characteristic time point is determined to effectively analyze the evolution of the asphalt mixture loading process; force chain uniformity probability and force chain angle distribution uniformity indicators are proposed to effectively quantitatively evaluate the coordinated force bearing capacity and evolution rate of the asphalt mixture. The present invention provides an important research method for accurately analyzing the internal coordinated force bearing capacity and evolution of asphalt mixtures; and provides an effective reference indicator for guiding the design and optimization of asphalt mixtures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the discrete element simulation diagram of the indirect tensile asphalt mixture in Example 1;

[0022] Figure 2 This is a test diagram of the force-displacement curve of the indirect tensile test of the asphalt mixture in Example 1;

[0023] Figure 3 Schematic diagram of the structure of the force chain contained in the discrete element geometric model of the AC13 Marshall specimen in Example 1;

[0024] Figure 4 Schematic diagram of the structure of the force chain contained in the discrete element geometric model of the SMA13 Marshall specimen in Example 1. DETAILED DESCRIPTION

[0025] Specific implementation method 1: The indirect tensile internal synergistic force analysis method of asphalt mixture in this implementation method is implemented according to the following steps:

[0026] Step 1: Scan a single coarse aggregate through CT, establish templates of coarse aggregates with different shapes, and construct a coarse aggregate template library;

[0027] Step 2: Generate a Marshall specimen model of the corresponding gradation using a random generation algorithm according to the gradation, obtain the position of the constituent particles as the coarse aggregate position, randomly call the coarse aggregate template in the coarse aggregate template library to replace the randomly generated constituent particles, build a skeleton, randomly generate mortar at the voids according to the void ratio, and construct a discrete element geometric model of the Marshall specimen;

[0028] Step 3: assign corresponding contact models and mechanical contact parameters to the interior and interface of each component in the discrete element geometric model of the Marshall specimen;

[0029] Step 4: Rectangular walls are constructed at the top and bottom of the side of the Marshall specimen discrete element geometric model, with the top being the loading wall and the bottom being the bearing wall. The speed of the loading wall is controlled to simulate the indirect tensile test, and the discrete element simulation results (force-displacement curve) are obtained. Aggregates, asphalt and mineral powder are mixed according to the same gradation and asphalt-stone ratio, and asphalt mixture specimens are prepared after compaction. Indirect tensile tests are carried out to obtain the force-displacement curve of the indoor experiment.

[0030] Step 5: Evaluate the indirect tensile simulation effect using the discrete element simulation results and the force-displacement curve of the indoor experiment. Obtain the load peak difference and the maximum load difference from the force-displacement curve (the maximum load difference is the maximum value of the load difference of the force-displacement curve). Use the load peak difference and the maximum load difference as evaluation indicators. The load difference is calculated according to the following formula (1);

[0031]

[0032] Where Dif is the load difference, F dem is the load of discrete element simulation, F test is the corresponding indoor test load;

[0033] When the peak load difference is within 10% and the maximum load difference is within 15%, the discrete element simulation results are accepted. If they do not meet the requirements, the mechanical contact parameters in step 3 are readjusted;

[0034] Step 6. Determine two characteristic time points, which are 75% peak load in the rising stage of the force-displacement curve and 75% peak load in the falling stage of the force-displacement curve. The internal synergistic force capacity is characterized by the 75% peak load in the rising stage, and the evolution of the synergistic capacity is characterized by the 75% peak load in the falling stage. The force chains of each component in the discrete element geometric model of the Marshall specimen at the two characteristic time points during the indirect tensile test are traversed to extract the force chain information, which includes the force chain strength, the number of force chains and the force chain angle.

[0035] Step 7: The force chain uniformity probability P of the coarse aggregate-asphalt mortar interface 均匀 As an indicator for evaluating the uniformity of internal force, s is the relative strength of the force chain, which represents the ratio of the force chain strength to the average force chain strength, P 均匀 is the probability of force chain when s is between 0.5 and 1.5, and the uniform probability of force chain P 均匀 Calculate according to the following formula;

[0036]

[0037] Where n 均匀 is the number of force chains with a relative strength of 0.5 to 1.5, and n is the total number of force chains in the indirect stretching process;

[0038] Step 8: Quantify the directional geometric characteristics of the force chains of different components in the discrete element geometric model of the Marshall specimen. The angle between the normal force chain and the vertical direction is used as a quantitative indicator to characterize the directional distribution characteristics of the force chain. The relative strength of the interface force chain in the angle range of 120° to 150° is statistically expressed as s. 角 express;

[0039] Step 9: Calculate the uniform probability P of the force chain at two characteristic time points respectively 均匀 and 角 , to evaluate the synergistic force bearing capacity of asphalt mixture, thus completing the synergistic force analysis method of indirect tensile internal of asphalt mixture.

[0040] The present implementation aims to establish an indirect tensile discrete element simulation model of asphalt mixture while taking into account both efficiency and accuracy, and proposes acceptance criteria for simulation result evaluation. The peak load difference is within 10%, and the maximum load difference is within 15%. If both requirements are met, the simulation results are accepted.

[0041] This implementation method is to propose a corresponding algorithm to traverse the force chains of each component inside the asphalt mixture during the indirect stretching process and extract information such as the strength, quantity, and angle of the force chains;

[0042] This implementation method is to determine two characteristic time points, 75% peak load in the rising phase of the mechanical curve and 75% peak load in the falling phase of the mechanical curve. The 75% peak load in the rising phase characterizes the internal coordinated force bearing capacity, and the 75% peak load in the falling phase characterizes the evolution of the coordinated capacity.

[0043] The present embodiment is to use the uniform probability P of the force chain at the interface of coarse aggregate and asphalt mortar 均匀 As an indicator for evaluating internal force uniformity.

[0044] This embodiment is to count the relative strength of the interface force chain within the angle range of 120° to 150°, using s 角 Indicates that 角 The closer it is to 1, the more uniform the direction distribution is, and s 角 The larger it is, the more likely it is to crack.

[0045] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that in step 1, an STL format file of a single coarse aggregate is generated by CT scanning.

[0046] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that in step two, the Marshall specimen discrete element geometric model is constructed using PFC3d software.

[0047] Specific implementation method 4: This implementation method is different from any one of specific implementation methods 1 to 3 in that the mechanical contact parameters described in step 3 include normal contact stiffness, tangential contact stiffness, shear parameter, tensile parameter, Poisson's ratio, friction coefficient and damping ratio.

[0048] Specific implementation method five: This implementation method is different from specific implementation methods one to four in that the loading rate of the loading wall is controlled to be 50 mm / min during the simulated indirect tensile test in step four.

[0049] Specific implementation method 6: This implementation method is different from the specific implementation methods 1 to 5 in that s 角 The closer it is to 1, the more uniform the direction distribution is, and s 角 The larger the value, the more likely it is to crack.

[0050] Specific implementation method 7: This implementation method is different from the specific implementation methods 1 to 6 in that in step 9, the uniform probability P of the force chain at two characteristic time points is calculated. 均匀 and 角 The more uniform the force chain uniform probability distribution is, the more uniform the force chain strength-angle distribution is, indicating that the coordinated force bearing capacity is stronger.

[0051] Specific implementation eight: This implementation differs from specific implementation seven in that in step nine, Δ 强度 and Δ 角度To characterize the synergistic force bearing capacity of asphalt mixture, where Δ 强度 The calculation formula is as follows:

[0052]

[0053] Where P U75 It represents the probability of uniform force chain at the moment of 75% peak load in the rising phase of the force-displacement curve, P D75 It represents the probability of uniform force chain at the moment of 75% peak load in the descending phase of the force-displacement curve.

[0054] Specific implementation method 9: This implementation method is different from the specific implementation method 7 in that Δ 角度 The calculation formula is as follows:

[0055] Δ 角度 =|S D75 -1|-|S U75 -1|

[0056] In the formula, S U75 s represents the moment when 75% of the peak load occurs in the rising phase of the force-displacement curve 角 , S D75 s represents the moment when 75% of the peak load occurs in the descending phase of the force-displacement curve 角 .

[0057] Specific implementation method 10: This implementation method is different from specific implementation methods 8 or 9 in that Δ 强度 Positive means the uniformity is getting better, negative means the uniformity is getting worse; Δ 角度 A negative value indicates that the angle uniformity is improved, and a positive value indicates that the angle uniformity is deteriorated.

[0058] Embodiment: The indirect tensile internal synergistic force analysis method of asphalt mixture in this embodiment is implemented according to the following steps:

[0059] Step 1: Generate an STL file of a single coarse aggregate through CT scanning, use PFC3d to establish templates of coarse aggregates of different shapes to build a coarse aggregate template library, and combine the generation efficiency and accuracy to determine the coarse aggregate generation parameters as distance (distance, representing the smoothness of the model surface) = 150, ratio (ratio, representing the ratio of the minimum particle size to the maximum particle size of the internal components of the coarse aggregate model) = 0.3;

[0060] Step 2: Use PFC3d software to generate two Marshall specimen models of SMA13 and AC13 using a random generation algorithm according to the gradation, obtain the position of the constituent particles as the coarse aggregate position, randomly call the coarse aggregate template in the coarse aggregate template library to replace the randomly generated constituent particles, build a skeleton, and randomly generate mortar in the voids according to the void ratio to construct a discrete element geometric model of the Marshall specimen;

[0061] Step 3: Assign corresponding contact models and mechanical contact parameters to the interior and interface of each component in the constructed Marshall specimen discrete element geometric model. The specific parameters are as follows:

[0062] Between coarse aggregates, the elastic modulus of coarse aggregate is 55 GPa, the normal-tangential stiffness ratio is [1 / 0.25], the friction coefficient is 0.35, and the damping ratio is set to 0.7;

[0063] The microscopic contact parameters between mortar units are shown in Table 1.

[0064] Table 1 Mesoscopic contact parameters between mortar units

[0065]

[0066] The contact parameters between asphalt mortar and aggregate units are assigned the contact stiffness between coarse aggregate and asphalt mortar units according to the principle of attribute inheritance; the tensile strength and shear strength between asphalt mortar and coarse aggregate units are 0.8 times that between asphalt mortar units; the friction coefficient is set to 0.5, and the damping ratio is set to 0.7;

[0067] Step 4: Build rectangular walls at the top and bottom of the side of the AC13 and SMA13 Marshall specimen models. The top is the loading wall and the bottom is the bearing wall. The speed of the loading wall is controlled to achieve the indirect tensile test simulation. The loading rate is set to 50 mm / min and the width of the "rectangular wall" is 12.7 mm. The simulation process is as follows: Figure 1 As shown;

[0068] Aggregate, asphalt and mineral powder were mixed according to the same gradation and asphalt-stone ratio, and asphalt mixture specimens were prepared after compaction. Indirect tensile tests were carried out to obtain the force-displacement curve of the indoor experiment.

[0069] Step 5: Use UTM-250 to conduct indirect tensile test at room temperature, adopt displacement control, set the loading rate to 50mm / min, and the temperature to 25℃. The indirect tensile simulation effect is evaluated by the discrete element simulation results and the force-displacement curve of the indoor experiment. The results are as follows: Figure 2 As shown;

[0070] The peak load difference and the maximum load difference are used as evaluation indicators, and the load difference is calculated as follows. The peak load difference of AC13 is 2.3%, and the maximum load difference is 9.7%; the peak load difference of SMA13 is 2.4%, and the maximum load difference is 8.9%; the peak load difference is within 10%, and the maximum load difference is within 15%, which meets the requirements and accepts the simulation results;

[0071]

[0072] Where Dif is the load difference, F dem is the load of discrete element simulation, F test is the corresponding indoor test load;

[0073] Step 6. Determine two characteristic time points: 75% peak load in the rising stage of the mechanical curve and 75% peak load in the falling stage of the mechanical curve. The 75% peak load in the rising stage characterizes the internal synergistic force bearing capacity, and the 75% peak load in the falling stage characterizes the evolution of synergistic capacity. Traverse the force chains of each component in the discrete element geometric model of the Marshall specimen at two characteristic time points during the indirect tensile process, and extract the force chain information, which includes the force chain strength, the number of force chains and the force chain angle. Figure 3 and Figure 4 The implicit force chain of the discrete element geometric model of the Marshall specimen at the first characteristic time point;

[0074] Step 7: The force chain uniformity probability P of the coarse aggregate-asphalt mortar interface 均匀 As an indicator for evaluating the uniformity of internal force, s is the relative strength of the force chain, which represents the ratio of the force chain strength to the average force chain strength, P 均匀 is the force chain probability when s is between 0.5 and 1.5, and is calculated as follows;

[0075]

[0076] Where n 均匀 is the number of force chains with relative strength ranging from 0.5 to 1.5, and n is the total number of force chains in the indirect stretching process;

[0077] The uniform probability of interface force chain is 34.3% when the peak load is 75% in the rising stage of the mechanical curve of AC13, and 35.6% when the peak load is 75% in the falling stage of the mechanical curve; the uniform probability of interface force chain is 33.9% when the peak load is 75% in the rising stage of the mechanical curve of SMA13, and 36.8% when the peak load is 75% in the falling stage of the mechanical curve;

[0078] Step 8: Quantify the directional geometric characteristics of the force chains of different components of asphalt mixtures. The angle between the normal force chain and the vertical direction is used as a quantitative indicator to characterize the directional distribution characteristics of the force chain. The relative strength of the interface force chain within the angle range of 120° to 150° is calculated using s. 角 Indicates that 角 The closer to 1, the more uniform the distribution. 角 The larger it is, the more likely it is to crack;

[0079] Interface s at 75% peak load in the rising stage of AC13 mechanical curve 角 The interface s is 1.002, and the interface s is 75% of the peak load in the descending stage of the mechanical curve. 角The interface s is 0.993; when the SMA13 mechanical curve is in the rising stage and the peak load is 75%, the interface s 角 The interface s is 1.084, and the interface s is 75% of the peak load in the descending stage of the mechanical curve. 角 is 1.076;

[0080] Step 9: Evaluate the synergistic force bearing capacity and evolution capacity of asphalt mixture. The more uniform the probability distribution of force chain strength and the more uniform the force chain strength-angle distribution, the stronger the synergistic force bearing capacity. The evolution capacity is calculated as follows:

[0081]

[0082] Where P U75 It represents the probability of uniform force chain at the moment of 75% peak load in the rising phase of the force-displacement curve, P D75 It represents the probability of uniform force chain at the moment of 75% peak load in the descending phase of the force-displacement curve.

[0083] Δ 角度 =|S D75 -1|-|S U75 -1|

[0084] In the formula, S U75 s represents the moment when 75% of the peak load occurs in the rising phase of the force-displacement curve 角 , S D75 s represents the moment when 75% of the peak load occurs in the descending phase of the force-displacement curve 角 .

[0085] Δ 强度 Positive means the uniformity is getting better, negative means the uniformity is getting worse; Δ 角度 A negative value indicates that the angle uniformity is improved, and a positive value indicates that the angle uniformity is deteriorated.

[0086] The probability of uniform force chain at AC13 interface is greater than that of SMA13, and its strength uniformity is better than that of SMA13. 角 It is closer to 1 than SMA13, and has better directional uniformity. AC13 is better than SMA13 in terms of synergistic force.

[0087] Δ of AC13 sample 强度 =3.79%, Δ 角度 =0.005; Δ of SMA13 sample 强度 =8.55%, Δ 角度 =-0.008;

[0088] As loading progresses, the force uniformity improves, the uniformity in the AC13 direction deteriorates, and the uniformity in the SMA13 direction improves; the evolution rate of SMA13 is stronger than that of AC13, but its uniformity is still weaker than that of AC13.

Claims

1. Indirect tensile internal synergistic force analysis method for asphalt mixture, characterized in that asphalt The indirect tensile internal synergistic force analysis method of the mixture is implemented according to the following steps: Step 1: Scan a single coarse aggregate through CT, establish templates of coarse aggregates with different shapes, and construct a coarse aggregate template library; Step 2: Generate a Marshall specimen model of the corresponding gradation using a random generation algorithm according to the gradation, obtain the position of the constituent particles as the coarse aggregate position, randomly call the coarse aggregate template in the coarse aggregate template library to replace the constituent particles, build a skeleton, randomly generate mortar at the voids according to the void ratio, and construct a Marshall specimen discrete element geometric model; Step 3: assign corresponding contact models and mechanical contact parameters to the interior and interface of each component in the discrete element geometric model of the Marshall specimen; Step 4: Rectangular walls are constructed at the top and bottom of the side of the Marshall specimen discrete element geometric model, with the top being the loading wall and the bottom being the bearing wall. The speed of the loading wall is controlled to simulate the indirect tensile test to obtain the discrete element simulation results. Aggregates, asphalt and mineral powder are mixed according to the same gradation and asphalt-stone ratio, and asphalt mixture specimens are prepared after compaction. Indirect tensile tests are carried out to obtain the force-displacement curve of the indoor experiment. Step 5: Evaluate the indirect tensile simulation effect using the discrete element simulation results and the force-displacement curve of the indoor experiment. Obtain the load peak difference and the maximum load difference from the force-displacement curve. Use the load peak difference and the maximum load difference as evaluation indicators. The load difference is calculated according to the following formula; Where Dif is the load difference, F dem is the load of discrete element simulation, F test is the corresponding indoor test load; When the peak load difference is within 10% and the maximum load difference is within 15%, the discrete element simulation results are accepted. If they do not meet the requirements, the mechanical contact parameters in step 3 are readjusted; Step 6: Determine two characteristic time points, which are 75% peak load at the rising stage of the force-displacement curve and 75% peak load at the falling stage of the force-displacement curve, traverse the force chains of each component inside the discrete element geometric model of the Marshall specimen at the two characteristic time points during the indirect tensile test, and extract the force chain information, which includes the force chain strength, the number of force chains and the force chain angle; Step 7: The force chain uniformity probability P of the coarse aggregate-asphalt mortar interface 均匀 As an indicator for evaluating the uniformity of internal force, s is the relative strength of the force chain, which represents the ratio of the force chain strength to the average force chain strength, P 均匀 is the probability of force chain when s is between 0.5 and 1.5, and the uniform probability of force chain P 均匀 Calculate according to the following formula; Where n 均匀 is the number of force chains with a relative strength of 0.5 to 1.5, and n is the total number of force chains in the indirect stretching process; Step 8: Quantify the directional geometric characteristics of the force chains of different components in the discrete element geometric model of the Marshall specimen. The angle between the normal force chain and the vertical direction is used as a quantitative indicator to characterize the directional distribution characteristics of the force chain. The relative strength of the interface force chain in the angle range of 120° to 150° is statistically expressed as s. 角 express; Step 9: Calculate the uniform probability P of the force chain at two characteristic time points respectively 均匀 and 角 , to evaluate the synergistic force bearing capacity of asphalt mixture, thus completing the synergistic force analysis method of indirect tensile internal of asphalt mixture.

2. The indirect tensile internal synergistic force analysis method for asphalt mixture according to claim 1 is characterized in that In step 1, an STL format file of a single coarse aggregate is generated through CT scanning.

3. The indirect tensile internal synergistic force analysis method of asphalt mixture according to claim 1 is characterized in that In step 2, the PFC3d software is used to construct the discrete element geometric model of the Marshall specimen.

4. The indirect tensile internal synergistic force analysis method of asphalt mixture according to claim 1 is characterized in that The mechanical contact parameters described in step three include normal contact stiffness, tangential contact stiffness, shear parameter, tensile parameter, Poisson's ratio, friction coefficient and damping ratio.

5. The asphalt mixture indirect tensile internal synergistic force analysis method according to claim 1 is characterized in that In step 4, the loading rate of the loading wall is controlled to be 50 mm / min during the simulated indirect tensile test.

6. The asphalt mixture indirect tensile internal synergistic force analysis method according to claim 1 is characterized in that Step 8 角 The closer it is to 1, the more uniform the direction distribution is, and s 角 The larger the value, the more likely it is to crack.

7. The asphalt mixture indirect tensile internal synergistic force analysis method according to claim 1 is characterized in that In step nine, the uniform probability P of the force chain at two characteristic time points is calculated. 均匀 and 角 The more uniform the force chain uniform probability distribution is, the more uniform the force chain strength-angle distribution is, indicating that the coordinated force bearing capacity is stronger.

8. The asphalt mixture indirect tensile internal synergistic force analysis method according to claim 7 is characterized in that In step nine, Δ 强度 and Δ 角度 To characterize the synergistic force bearing capacity of asphalt mixture, where Δ 强度 The calculation formula is as follows: Where P U75 It represents the probability of uniform force chain at the moment of 75% peak load in the rising phase of the force-displacement curve, P D75 It represents the probability of uniform force chain at the moment of 75% peak load in the descending phase of the force-displacement curve.

9. The asphalt mixture indirect tensile internal synergistic force analysis method according to claim 8 is characterized in that Δ 角度 The calculation formula is as follows: D 角度 =|S D75 -1|-|S U75 -1| In the formula, S U75 s represents the moment when 75% of the peak load occurs in the rising phase of the force-displacement curve 角 , S D75 s represents the moment when 75% of the peak load occurs in the descending phase of the force-displacement curve 角 .

10. The asphalt mixture indirect tensile internal synergistic force analysis method according to claim 8 or 9, characterized in that Step 9 Δ 强度 Positive means the uniformity is getting better, negative means the uniformity is getting worse; Δ 角度 A negative value indicates that the angle uniformity is improved, and a positive value indicates that the angle uniformity is deteriorated.

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