Indirect tensile internal force analysis method for asphalt mixture

Abstract

The application discloses an indirect tensile internal synergic stress analysis method of asphalt mixture. In order to solve the problems of lacking internal stress data of the asphalt mixture under the indirect tensile stress and the reasonable evaluation method of the synergic stress of the asphalt mixture, the application discloses the following analysis method: one, constructing a coarse aggregate template library; two, establishing a discrete element geometric model of a Marshall test piece; three, giving each component and interface contact parameters; four, performing indirect tensile simulation; five, evaluating the simulation accuracy; six, determining two characteristic time points and obtaining internal force chain information of the characteristic time points; seven, quantifying the strength distribution of the interface force chain; eight, quantifying the direction distribution of the interface force chain; nine, evaluating the internal synergic stress capacity and evolution capacity. The application adopts the discrete element modeling method to obtain the internal component force chain data of the asphalt mixture, proposes force chain uniformity probability and force chain angle distribution uniformity indexes, and effectively quantifies and evaluates the synergic stress capacity and evolution rate of the asphalt mixture.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of digital design and evaluation of asphalt mixture, and particularly relates to an internal synergistic stress analysis method for indirect tensile test of asphalt mixture. BACKGROUND

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

[0003] The discrete element method (DEM) is a numerical calculation method for simulating and analyzing the behavior of granular materials, which is suitable for studying systems composed of a large number of interacting discrete bodies. Asphalt mixture is composed of coarse aggregate, asphalt mortar and voids, which meets the basic idea of the discrete element method. Asphalt mixture is regarded as being composed of many independent and discrete particles. These particles are regarded as individual units with mechanical properties in the calculation, and the behavior of the entire system is simulated by calculating the interaction between these units. The mass, shape, size, motion state and other characteristics of each particle are considered in the model, and the mechanical characteristics of the internal components are effectively obtained. Therefore, it is of great significance to realize efficient and accurate indirect tensile simulation by means of the discrete element method, propose an internal component stress analysis method and evaluation index, and solve the current performance evaluation dilemma of asphalt mixture and guide its structure design and improvement. SUMMARY

[0004] The present application aims to solve the problem that the internal stress data of asphalt mixture during indirect tensile test and the reasonable method for evaluating the synergistic stress of asphalt mixture are lacking, which leads to the inability to guide the structure design and optimization of asphalt mixture, and provides an internal synergistic stress analysis method for indirect tensile test of asphalt mixture.

[0005] The internal synergistic stress analysis method for indirect tensile test of asphalt mixture according to the present application is realized according to the following steps:

[0006] Step one, by CT scanning single coarse aggregate, establishing different forms of coarse aggregate template, constructing coarse aggregate template library;

[0007] Step two, according to the gradation, the corresponding Marshall specimen model is generated by random generation algorithm, the position of the constituent particles is obtained as the position of the coarse aggregate, the coarse aggregate template in the coarse aggregate template library is randomly called to replace the randomly generated constituent particles, the skeleton is constructed, the mortar is randomly generated in the void according to the void ratio, and the Marshall specimen discrete element geometric model is constructed;

[0008] Step three, the corresponding contact model and mechanical contact parameters are given to the internal and interface of each component in the Marshall specimen discrete element geometric model;

[0009] Step four, a rectangular wall is constructed on the side and top of the Marshall specimen discrete element geometric model, the top is a loading wall, and the bottom is a bearing wall, the speed control is carried out on the loading wall to simulate the indirect tensile test, and the discrete element simulation result (force-displacement curve) is obtained; the aggregate, asphalt and mineral powder are mixed according to the same gradation and oil stone ratio, and the asphalt mixture specimen is prepared after compaction, and the indirect tensile test is carried out, and the force-displacement curve of the indoor experiment is obtained;

[0010] Step five, the indirect tensile simulation effect is evaluated by the discrete element simulation result and the force-displacement curve of the indoor experiment, the load peak difference and the load maximum difference (the maximum value of the load difference of the force-displacement curve) are obtained from the force-displacement curve, the load peak difference and the load maximum difference are taken as the evaluation indexes, and the load difference is calculated according to the following formula (1);

[0011]

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

[0013] When the load peak difference is within 10% and the maximum load difference is within 15%, the discrete element simulation result is accepted, and if it does not meet the requirements, the mechanical contact parameters in step three are adjusted again;

[0014] Step six, two characteristic time points are determined, the two characteristic time points are 75% peak load of the force-displacement curve in the rising stage and 75% peak load of the force-displacement curve in the descending stage, the internal cooperative stress capacity is represented by the 75% peak load in the rising stage, and the cooperative capacity evolution is represented by the 75% peak load in the descending stage, the force chains of each component in the Marshall specimen discrete element geometric model at the two characteristic time points in the indirect tensile test process are traversed, and the force chain information is extracted, the force chain information includes force chain strength, force chain number and force chain angle;

[0015] Step seven, the uniform probability P of the force chain of the coarse aggregate-bitumen mortar interface 均匀 As the evaluation index of internal stress uniformity, s is the relative strength of the force chain, indicating the ratio of the force chain strength to the average force chain strength, P 均匀 is the probability of the force chain with s between 0.5 and 1.5, the uniform probability P of the force chain 均匀 The calculation is carried out according to the following formula:

[0016]

[0017] In the formula, n 均匀 is the number of force chains with the relative strength of the force chain between 0.5 and 1.5, and n is the total number of force chains in the indirect tensile process;

[0018] Step eight, the directional geometric characteristics of the force chain of the discrete element geometric model of the Marshall specimen are quantified, the angle between the normal force chain and the vertical direction is used to represent the quantification index of the directional distribution characteristics of the force chain, and the relative strength of the force chain in the angle range of 120°-150° is counted, and s 角 is used to represent;

[0019] Step nine, the uniform probability P 均匀 and s 角 of the force chain at two characteristic time points are calculated respectively to evaluate the synergistic stress capacity of the asphalt mixture, so as to complete the synergistic stress analysis method of the indirect tensile internal force of the asphalt mixture.

[0020] The discrete element modeling method is used to obtain the force chain data of the internal components of the asphalt mixture, which overcomes the problem that the internal component stress cannot be obtained; two quantification evaluation indexes of load peak difference and maximum load difference are proposed, which can efficiently evaluate and ensure the high accuracy of the simulation effect; the effective analysis of the evolution of the asphalt mixture under load is determined; the force chain uniform probability and the force chain angle distribution uniformity index are proposed, which effectively quantize and evaluate the synergistic stress capacity and evolution rate of the asphalt mixture. The present application provides an important research means for accurately analyzing the internal synergistic stress capacity and evolution of the asphalt mixture; and provides an effective reference index for guiding the design and optimization of the asphalt mixture. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

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

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

[0026] Step one, a single coarse aggregate is scanned by CT to establish different morphological coarse aggregate templates, and a coarse aggregate template library is constructed;

[0027] Step two, a Marshall specimen model corresponding to the gradation is generated by using a random generation algorithm according to the gradation, the position of the constituent particles is obtained as the position of the coarse aggregate, the coarse aggregate template in the coarse aggregate template library is randomly called to replace the randomly generated constituent particles, a skeleton is constructed, and mortar is randomly generated at the voids according to the void ratio, and a Marshall specimen discrete element geometric model is constructed;

[0028] Step three, the corresponding contact model and mechanical contact parameters are given to the internal and interface of each component in the Marshall specimen discrete element geometric model;

[0029] Step four, a rectangular wall is constructed on the side top and bottom of the Marshall specimen discrete element geometric model, the top is a loading wall, and the bottom is a bearing wall, the speed of the loading wall is controlled to simulate the indirect tensile test, and the discrete element simulation result (force-displacement curve) is obtained; the aggregate, asphalt and mineral powder are mixed according to the same gradation and oil-stone ratio, and the asphalt mixture specimen is prepared after compaction, and the indirect tensile test is carried out, and the force-displacement curve of the indoor experiment is obtained;

[0030] Step five, the indirect tensile simulation effect is evaluated by the discrete element simulation result and the force-displacement curve of the indoor experiment, the load peak difference and the load maximum difference (the maximum value of the load difference of the force-displacement curve) are obtained from the force-displacement curve, the load peak difference and the load maximum difference are taken as evaluation indexes, and the load difference is calculated according to the following formula (1);

[0031]

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

[0033] When the load peak difference is within 10% and the maximum load difference is within 15%, the discrete element simulation result is accepted, and if the requirement is not met, the mechanical contact parameters in step three are adjusted again;

[0034] Step six, two characteristic time points are determined, the two characteristic time points are 75% peak load of the rising stage of the force-displacement curve and 75% peak load of the descending stage of the force-displacement curve, the 75% peak load of the rising stage is used to represent the internal synergistic stress capacity, the 75% peak load of the descending stage is used to represent the evolution of the synergistic capacity, the internal component force chains of the Marshall specimen discrete element geometric model at the two characteristic time points in the indirect tensile test process are traversed, and force chain information is extracted, the force chain information includes force chain strength, force chain quantity and force chain angle;

[0035] Step seven, the force chain uniform probability P of the coarse aggregate-bitumen mortar interface is calculated according to the following formula: 均匀 As an evaluation index of internal stress uniformity, s is the relative strength of the force chain, indicating the ratio of the force chain strength to the average force chain strength, P 均匀 is the force chain probability of s between 0.5 and 1.5, the force chain uniform probability P 均匀 is calculated according to the following formula:

[0036]

[0037] In the formula, n 均匀 is the number of force chains with a relative strength of 0.5-1.5, and n is the total number of force chains in the indirect tensile process;

[0038] Step eight, the directional geometric characteristics of different component force chains of the Marshall specimen discrete element geometric model are quantified, the angle between the normal force chain and the vertical direction is used to represent the quantification index of the directional distribution characteristics of the force chain, and the relative strength of the force chain in the angle range of 120°-150° is counted, and s 角 is used to represent;

[0039] Step nine, the force chain uniform probability P 均匀 and s 角 at the two characteristic time points are calculated respectively to evaluate the synergistic stress capacity of the asphalt mixture, so as to complete the synergistic stress analysis method of the indirect tensile internal force of the asphalt mixture.

[0040] The embodiment aims to establish an indirect tensile discrete element simulation model of the asphalt mixture by taking into account the efficiency and accuracy, and proposes an evaluation acceptance standard for the simulation results, the load peak difference is within 10%, the maximum load difference is within 15%, and the requirements are met at the same time, and the simulation results are accepted.

[0041] The embodiment aims to propose a corresponding algorithm, to traverse the internal component force chains of the asphalt mixture in the indirect tensile process, and to extract force chain strength, quantity, angle and other information;

[0042] The embodiment is to determine two characteristic time points, 75% peak load in the rising stage of the mechanical curve and 75% peak load in the descending stage of the mechanical curve, the 75% peak load in the rising stage representing the internal synergistic stress capacity, and the 75% peak load in the descending stage representing the evolution of the synergistic capacity.

[0043] The embodiment is to determine the uniform probability P of the force chain at the coarse aggregate-bituminous mortar interface 均匀 as an index for evaluating the uniformity of internal stress.

[0044] The embodiment is to statistically determine the relative strength of the force chain of the interface in the angle range of 120°-150°, denoted by s 角 , s 角 closer to 1, the more uniform the direction distribution, and s 角 greater, the more prone to cracking.

[0045] Specific embodiment two: The difference between this embodiment and specific embodiment one is that in step one, the STL format file of a single coarse aggregate is generated by CT scanning.

[0046] Specific embodiment three: The difference between this embodiment and specific embodiment one or two is that in step two, the discrete element geometric model of the Marshall specimen is constructed by using PFC3d software.

[0047] Specific embodiment four: The difference between this embodiment and one of specific embodiments one to three is that in step three, the mechanical contact parameters include normal contact stiffness, tangential contact stiffness, shear resistance parameter, tensile resistance parameter, Poisson's ratio, friction coefficient, and damping ratio.

[0048] Specific embodiment five: The difference between this embodiment and one of specific embodiments one to four is that in step four, the loading rate of the loading wall in the simulation of the indirect tensile test process is controlled to be 50 mm / min.

[0049] Specific embodiment six: The difference between this embodiment and one of specific embodiments one to five is that in step eight, s 角 closer to 1, the more uniform the direction distribution, and s 角 greater, the more prone to cracking.

[0050] Specific embodiment seven: The difference between this embodiment and one of specific embodiments one to six is that in step nine, the uniform probability P of the force chain at two characteristic time points 均匀 and s 角 is calculated, the more uniform the distribution of the uniform probability of the force chain, the more uniform the strength-angle distribution of the force chain, indicating a stronger synergistic stress capacity.

[0051] Specific embodiment eight: The difference between this embodiment and specific embodiment seven is that in step nine, Δ 强度 and Δ 角度to characterize the synergistic stress capacity of the asphalt mixture, wherein Δ 强度 The calculation formula of Δ is as follows:

[0052]

[0053] In the formula, P U75 represents the uniform probability of the force chain at the time of 75% of the peak load in the rising stage of the force-displacement curve, P D75 represents the uniform probability of the force chain at the time of 75% of the peak load in the falling stage of the force-displacement curve.

[0054] Specific embodiment nine: different from the specific embodiment seven, the calculation formula of Δ 角度 is as follows:

[0055] Δ 角度 = |S D75 -1|-|S U75 -1|

[0056] In the formula, S U75 represents s 角 at the time of 75% of the peak load in the rising stage of the force-displacement curve, and S D75 represents s 角 at the time of 75% of the peak load in the falling stage of the force-displacement curve.

[0057] Specific embodiment ten: different from the specific embodiment eight or nine, Δ 强度 positive indicates that the uniformity becomes better, and negative indicates that the uniformity becomes worse; Δ 角度 negative indicates that the angle uniformity becomes better, and positive indicates that the angle uniformity becomes worse.

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

[0059] Step one, generate an STL file of a single coarse aggregate through CT scanning, use PFC3d to establish a coarse aggregate template library of different morphologies, and determine the coarse aggregate generation parameters as distance (distance, representing the smoothness of the model surface) = 150 and ratio (ratio, representing the ratio of the minimum particle size to the maximum particle size of the internal constituent particles of the coarse aggregate model) = 0.3 in combination with the generation efficiency and accuracy.

[0060] Step two, use PFC3d software to generate SMA13 and AC13 Marshall test models according to the gradation using a random generation algorithm, obtain the positions of the constituent particles as the positions of the coarse aggregates, randomly call the coarse aggregate templates in the coarse aggregate template library to replace the randomly generated constituent particles, construct the skeleton, and randomly generate mortar at the voids according to the void ratio to construct the discrete element geometric model of the Marshall test piece.

[0061] Step three, the internal and interface of the components in the constructed Marshall specimen discrete element geometric model are given corresponding contact model and mechanical contact parameters, and the specific parameters are given as follows:

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

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

[0064] Table 1 Mesoscopic contact parameters between mortar units

[0065]

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

[0067] Step four, a rectangular wall is constructed on the side of the AC13 and SMA13 Marshall specimen model, the top and bottom, the top is the loading wall, and the bottom is the bearing wall. The loading wall is controlled by speed to achieve indirect tensile test simulation, the loading rate is set to 50 mm / min, the width of the "rectangular wall" is 12.7 mm, and the simulation process is as shown in Figure 1 ;

[0068] The aggregate, asphalt and mineral powder are mixed according to the same gradation and oil-stone ratio, and the asphalt mixture specimen is prepared after compaction, and the indirect tensile test is carried out to obtain the force-displacement curve of the indoor experiment;

[0069] Step five, UTM-250 is used for indirect tensile test at room temperature, displacement control is adopted, loading rate is set to 50 mm / min, and temperature is 25℃. The discrete element simulation results and the force-displacement curve of the indoor experiment are used to evaluate the indirect tensile simulation effect, and the results are as shown in Figure 2 ;

[0070] The load peak difference and the maximum load difference are used as evaluation indexes, and the load difference is calculated according to the following formula. The load peak difference of AC13 is 2.3%, and the maximum load difference is 9.7%; the load peak difference of SMA13 is 2.4%, and the maximum load difference is 8.9%; the load peak difference is within 10%, the maximum load difference is within 15%, which meets the requirements, and the simulation results are accepted;

[0071]

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

[0073] Step six, two characteristic time points are determined: 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 represents the internal synergistic stress capacity, and the 75% peak load in the falling stage represents the evolution of the synergistic capacity; the internal force chains of each component of the Marshall specimen discrete element geometric model at the two characteristic time points in the indirect tensile process are traversed, and force chain information is extracted, including force chain strength, force chain quantity and force chain angle; Figure 3 and Figure 4 is the force chain contained in the Marshall specimen discrete element geometric model at the first characteristic time point;

[0074] Step seven, the uniform probability P 均匀 of the coarse aggregate-bituminous mortar interface force chain is taken as an evaluation index of internal stress uniformity, s is the relative strength of the force chain, indicating the ratio of the force chain strength to the average force chain strength, P 均匀 is the force chain probability of s between 0.5 and 1.5, which is calculated according to the following formula;

[0075]

[0076] where n 均匀 is the number of force chains with a relative strength of 0.5-1.5, and n is the total number of force chains in the indirect tensile process;

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

[0078] Step eight, the directional geometric characteristics of different component force chains of asphalt mixture are quantified, the angle between the normal force chain and the vertical direction is taken as a quantitative index of the directional distribution characteristics of the force chain, the relative strength of the force chain in the angle range of 120°-150° is counted, and is represented by s 角 , s 角 closer to 1 indicates more uniform direction distribution, and s 角 larger is more prone to cracking;

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

[0080] Step nine, evaluate the synergistic stress ability and evolution ability of asphalt mixture, the more uniform the probability distribution of force chain strength, the more uniform the force chain strength-angle distribution, the stronger the synergistic stress ability, and the evolution ability is calculated as follows:

[0081]

[0082] In the formula, P U75 represents the uniform probability of force chain at the time of 75% peak load in the rising stage of force-displacement curve, P D75 represents the uniform probability of force chain at the time of 75% peak load in the descending stage of force-displacement curve.

[0083] Δ 角度 = |S D75 -1|-|S U75 -1|

[0084] In the formula, S U75 represents s 角 at the time of 75% peak load in the rising stage of force-displacement curve, S D75 represents s 角 at the time of 75% peak load in the descending stage of force-displacement curve.

[0085] Δ 强度 positive indicates that the uniformity is better, and negative indicates that the uniformity is worse; Δ 角度 negative indicates that the angle uniformity is better, and positive indicates that the angle uniformity is worse.

[0086] The uniform probability of AC13 interface force chain is greater than that of SMA13, and the strength uniformity is better than that of SMA13; the s 角 of AC13 interface is closer to 1 than that of SMA13, and the direction uniformity is better. The synergistic stress of AC13 is better than that of SMA13.

[0087] The Δ 强度 of AC13 sample is 3.79%, and the Δ 角度 is 0.005; the Δ 强度 of SMA13 sample is 8.55%, and the Δ 角度 is -0.008;

[0088] With loading, the stress uniformity becomes better, the direction uniformity of AC13 becomes worse, and the direction uniformity of SMA13 becomes better; the evolution rate of SMA13 is stronger than that of AC13, but the 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 for mixtures is implemented by 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 component particles as the coarse aggregate position, randomly call the coarse aggregate template in the coarse aggregate template library to replace the component 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; Step 3: Assign corresponding contact models and mechanical contact parameters to the interior and interfaces of each component in the discrete element geometric model of the Marshall specimen; Step 4: Construct rectangular walls 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 loading wall is velocity-controlled to simulate an indirect tensile test, obtaining discrete element simulation results. Aggregate, asphalt, and mineral powder are mixed according to the same gradation and asphalt-to-stone ratio, and compacted to prepare asphalt mixture specimens. Indirect tensile tests are performed to obtain force-displacement curves for indoor experiments. 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 peak load difference and the maximum load difference from the force-displacement curve. Use the peak load 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% of the peak load in the rising phase of the force-displacement curve and 75% of the peak load in the falling phase of the force-displacement curve. Traverse 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 and extract the force chain information, which includes the force chain strength, the number of force chains, and the force chain angle. Step 7: Take the uniform probability of force chain P at the interface of coarse aggregate and asphalt mortar as the 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 with s 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 during indirect stretching; 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 to represent the quantitative index of the force chain directional distribution characteristics. The relative strength of the interface force chain in the angle range of 120° to 150° is statistically calculated using s 角 express; Step 9: Calculate the uniform probability P of the force chain at two characteristic time points respectively 均匀 and s 角 , to evaluate the synergistic force bearing capacity of asphalt mixture, thereby completing the synergistic force analysis method of indirect tensile internal asphalt mixture.

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

3. The asphalt mixture indirect tensile internal synergistic force analysis method 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 asphalt mixture indirect tensile internal synergistic force analysis method 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 During the simulated indirect tensile test in step 4, the loading rate of the loading wall is controlled to be 50 mm / min.

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 s 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 load-bearing capacity of asphalt mixture, where Δ 强度 The calculation formula is as follows: Where, P U75 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| Where 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 angular uniformity is improved, and a positive value indicates that the angular uniformity is deteriorated.

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