A discrete element compaction modeling method for accurately tracking asphalt mixture particles

Abstract

The present invention specifically relates to a discrete element compaction modeling method for accurately tracking asphalt mixture particles, comprising the following steps: S1. Using PFC3D simulation software, calling a pre-established coarse aggregate model library according to the gradation of a real asphalt mixture, generating coarse aggregate in a virtual asphalt mixture; using a spherical unit with a radius of 0.7 mm to simulate asphalt mortar and voids in the asphalt mixture, and finally obtaining a virtual asphalt mixture; S2. Using PFC3D simulation software to import the virtual asphalt mixture, performing a virtual uniaxial penetration test on the coarse aggregate, and performing a uniaxial penetration test on the real asphalt mixture, comparing the two test results, and determining the friction coefficient of the mineral surface; S3. In the PFC3D simulation software, setting a Burgers model between asphalt mortars; S4. Using an SPT tester to carry out an asphalt mortar dynamic modulus test on the real asphalt mixture to determine the Burgers model parameters in the PFC3D simulation software; S5. Establishing a three-dimensional dynamic discrete element compaction model of asphalt mixture.

Description

Technical Field

[0001] The invention relates to the field of road engineering, and in particular to a discrete element compaction modeling method for accurately tracking asphalt mixture particles. Background Art

[0002] Asphalt mixture is a typical granular material. Under the action of compaction load, the particles coated with asphalt migrate and rearrange. In-depth analysis of the migration mechanism of mineral particles helps to reveal the compaction mechanism and then control the compaction of asphalt mixture.

[0003] Although existing technologies are capable of studying the compaction process of asphalt mixtures at a microscopic level, due to the lack of relevant experimental verification, the relevant conclusions need to be further verified. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a discrete element compaction modeling method for accurately tracking asphalt mixture particles, which can be used to carry out real mineral migration tracking experiments to verify the compaction model.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions to achieve it.

[0006] A discrete element compaction modeling method for accurately tracking asphalt mixture particles includes the following steps:

[0007] Step S1, using PFC3D simulation software, calling the pre-established coarse aggregate model library according to the gradation of the real asphalt mixture, generating the coarse aggregate in the virtual asphalt mixture; using a spherical unit with a radius of 0.7 mm to simulate the asphalt mortar and voids in the asphalt mixture, and finally obtaining the virtual asphalt mixture.

[0008] Step S2, using PFC3D simulation software to import virtual asphalt mixture, conduct a virtual uniaxial penetration test on coarse aggregate, and conduct a uniaxial penetration test on the real asphalt mixture, compare the two test results, and determine the friction coefficient of the mineral surface.

[0009] Step S3, in the PFC3D simulation software, setting a Burgers model between the asphalt mortars;

[0010] Step S4, using the SPT tester to carry out an asphalt mortar dynamic modulus test on a real asphalt mixture to determine the Burgers model parameters in the PFC3D simulation software.

[0011] Step S5, establishing a three-dimensional dynamic discrete element compaction model of asphalt mixture in PFC3D simulation software.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: a coarse aggregate model library is established through real aggregate information, and spherical units with a radius of 0.7 mm are used to simulate asphalt mortar and voids, so that the compaction model has very high accuracy; the microscopic parameters of the model are determined by uniaxial penetration test and dynamic modulus test, and the compaction model parameters are more accurate; real mineral migration tracking tests can be carried out to verify the discrete element compaction model, which solves the technical problem that the asphalt mixture compaction model is difficult to verify. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] FIG. 1( a ) is a schematic diagram of real aggregates used to establish a coarse aggregate model library in the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention;

[0015] FIG. 1( b ) is a schematic diagram of some virtual aggregates in the coarse aggregate model library of the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention;

[0016] FIG. 2( a ) is a schematic diagram of a clump model under different filling parameters in the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention;

[0017] FIG. 2( b ) is a graph showing the relationship between the values ​​of the parameter radio and the parameter distance under different numbers of pebble in the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention;

[0018] Figure 3 It is a schematic diagram of the process of a virtual uniaxial penetration test in the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention;

[0019] FIG4( a ) is a first schematic diagram of establishing a three-dimensional dynamic discrete element compaction model of asphalt mixture in an embodiment of the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention;

[0020] FIG. 4( b ) is a second schematic diagram of establishing a three-dimensional dynamic discrete element compaction model of asphalt mixture in an embodiment of the discrete element compaction modeling method for accurately tracking asphalt mixture particles of the present invention. DETAILED DESCRIPTION

[0021] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0022] A discrete element compaction modeling method for accurately tracking asphalt mixture particles includes the following steps:

[0023] Step S1, using PFC3D simulation software, calling the pre-established coarse aggregate model library according to the gradation of the real asphalt mixture, generating the coarse aggregate in the virtual asphalt mixture; using a spherical unit with a radius of 0.7 mm to simulate the asphalt mortar and voids in the asphalt mixture, and finally obtaining the virtual asphalt mixture.

[0024] Specifically, the coarse aggregate model library was established by using a blue light 3D scanner to collect the 3D contour information of aggregates with a particle size of 4.75 mm to 9.5 mm, as shown in Figure 1(a). The 3D contour information data was imported into Geomagic Studio reverse engineering software to generate the 3D shell structure of the real aggregate and saved as a stereolithography (STL) file, as shown in Figure 1(b). In order to improve the measurement accuracy, the number of aggregate samples was designed to be 48.

[0025] The bubble pack algorithm in the PFC3D simulation software is used to fill the three-dimensional shell structure of the aggregate with spheres (pebbles) to generate rigid clusters (clumps) to simulate aggregate particles larger than 2.36 mm. The number of filling spheres is determined by the values ​​of radio and distance. The coarse aggregate is simulated for different radio-distance combinations, as shown in Figure 2(a). From the perspective of model efficiency and computing time, as shown in Figure 2(b), radio and distance are determined to be 0.3 and 150 respectively.

[0026] Step S2, using PFC3D simulation software to import virtual asphalt mixture, conduct a virtual uniaxial penetration test on coarse aggregate, and conduct a uniaxial penetration test on the real asphalt mixture, compare the two test results, and determine the friction coefficient of the mineral surface.

[0027] Specifically, the PFC3D simulation software was used to set a contact stiffness sliding model between the aggregates of the virtual asphalt mixture, and the Poisson's ratio of the coarse aggregate was set to 0.25 and the elastic modulus was set to 55 GPa. Three friction coefficients were initially set to 0.15, 0.35, and 0.55, respectively. A cylindrical wall was generated as the loading head of the coarse aggregate virtual uniaxial penetration test, and the loading speed of the head was set to 50 mm / min. The test was terminated when the penetration depth reached 15 mm, and the displacement and force of the loading head were detected, such as Figure 3 shown.

[0028] The virtual uniaxial penetration test results of coarse aggregate were compared with the real uniaxial penetration test results to determine the friction coefficient.

[0029] Step S3, in the PFC3D simulation software, setting a Burgers model between the asphalt mortars;

[0030] Step S4, using the SPT tester to carry out an asphalt mortar dynamic modulus test on a real asphalt mixture to determine the Burgers model parameters in the PFC3D simulation software.

[0031] Specifically, the asphalt mortar specimens were made by static pressure method, and the SPT testing machine was used to apply sine waves to the asphalt mortar specimens to measure their dynamic modulus. The load frequencies were 0.1 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, and 25 Hz, and the test temperatures were 4.4 °C, 21.1 °C, and 37.8 °C;

[0032] Taking 21.1℃ as the reference temperature and based on the time-temperature equivalence principle, the dynamic modulus test results were translated along the logarithmic coordinates to obtain the master curve of the dynamic modulus of the real asphalt mortar. Then, nonlinear regression analysis was performed on the master curve of the dynamic modulus to obtain the Burgers model parameters of the asphalt mortar at a compaction temperature of 150℃.

[0033] Step S5, establishing a three-dimensional dynamic discrete element compaction model of asphalt mixture in PFC3D simulation software.

[0034] Specifically, the virtual asphalt mixture obtained in step S1 is imported using the PFC3D simulation software to generate a virtual specimen; then the friction coefficient determined in step S2 and the Burgers model parameters determined in step S4 are used to assign values ​​to the compaction parameters of the three-dimensional dynamic discrete element compaction model; then two walls are generated at the top and bottom of the virtual specimen, and the specimen is rotated at a uniform speed by adjusting the speed of the wall until the rotation angle reaches the required value; at the same time, during the compaction process, the top wall is controlled by the servo mechanism to apply a vertical load to the specimen and keep it stable so that the wall rotates at a uniform speed. At this point, the three-dimensional dynamic discrete element compaction model of asphalt mixture is established.

[0035] Example

[0036] A three-dimensional dynamic discrete element compaction model of asphalt mixture is established for asphalt mixture with gradation type AC-20Z.

[0037] The pass rates of various sieve holes of asphalt mixture with gradation type AC-20Z are shown in Table 1.

[0038] Table 1 Passage rate of AC-20Z asphalt mixture at various sieve holes

[0039]

[0040] Step 1, using PFC3D simulation software, call the pre-established coarse aggregate model library according to the pass rate of each sieve hole of the asphalt mixture with grading type AC-20Z to generate the coarse aggregate in the virtual asphalt mixture; use spherical units with a radius of 0.7mm to simulate the asphalt mortar and voids in the asphalt mixture, and finally obtain the virtual asphalt mixture.

[0041] Step 2: Use PFC3D simulation software to import virtual asphalt mixture, conduct virtual uniaxial penetration test on coarse aggregate, and conduct uniaxial penetration test on real asphalt mixture, compare the two test results, and determine the friction coefficient between aggregates.

[0042] The friction coefficient of aggregate was calibrated through a virtual uniaxial penetration test of coarse aggregate. When the friction coefficient was set to 0.35, it was closest to the actual test result, and the friction coefficient between aggregates was determined to be 0.35.

[0043] Step 3: In the PFC3D simulation software, set up the Burgers model in the asphalt mortar room.

[0044] Step 4: Use the SPT tester to carry out the asphalt mortar dynamic modulus test on the real asphalt mixture, and determine the Burgers model parameters in the PFC3D simulation software as shown in Table 2.

[0045] Table 2 Burgers model parameters of AC-20Z asphalt mixture

[0046]

[0047] Step 5: Establish a three-dimensional dynamic discrete element compaction model of asphalt mixture in the PFC3D simulation software.

[0048] The effective internal rotation angle of the gyratory compactor is set to 1.16°, the vertical pressure is 600 Kpa, the rotation rate is 30 r / min, and the designed compaction times are 100 times.

[0049] First, a virtual specimen with a size of φ100mm*h100mm was generated, and then two walls were generated at the top and bottom of the specimen. The specimen was rotated at a uniform speed by adjusting the speed of the wall until the rotation angle reached 1.16°, as shown in Figure 4(a). During the compaction process, the top wall was controlled by the servo mechanism to apply a vertical load of 600KPa to the specimen and keep it stable. At the same time, the wall rotated at a uniform speed of 30r / min, as shown in Figures 4(a) and 4(b).

[0050] Finally, in the PFC3D simulation software, the aggregate particles were tracked and the horizontal migration indicators under different compaction rates were counted.

[0051] The horizontal migration index L of aggregates with a diameter of 4.75 mm to 9.5 mm was calculated. xoy , as shown in Table 3.

[0052] Compaction rate (%) 40％ 50％ 60％ 70％ 80％ 100％ <![CDATA[L xoy ]]> 0.61 0.8 1.37 2.41 4.37 15.61

[0053] By using particle marking, step-by-step compaction and CT tracking scanning, we can design and carry out real mineral migration tracking tests, compare the real migration results with the migration results of the three-dimensional dynamic discrete element compaction model of asphalt mixture, and verify the accuracy and reliability of the established three-dimensional dynamic discrete element compaction model.

[0054] Although the present invention has been described in detail in general terms and in specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements may be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A discrete element compaction modeling method for accurately tracking asphalt mixture particles, characterized in that: The following steps are involved: Step S1, using PFC3D simulation software, calling a pre-established coarse aggregate model library according to the gradation of the real asphalt mixture, generating coarse aggregate in the virtual asphalt mixture; using a spherical unit with a radius of 0.7 mm to simulate the asphalt mortar and voids in the asphalt mixture, and finally obtaining the virtual asphalt mixture; Step S2, using PFC3D simulation software to import a virtual asphalt mixture, conduct a virtual uniaxial penetration test on the coarse aggregate, and conduct a uniaxial penetration test on the real asphalt mixture, compare the two test results, and determine the friction coefficient of the mineral aggregate surface; Step S3, in the PFC3D simulation software, setting a Burgers model between the asphalt mortars; Step S4, using an SPT tester to conduct an asphalt mortar dynamic modulus test on a real asphalt mixture to determine the Burgers model parameters in the PFC3D simulation software; Step S5, establishing a three-dimensional dynamic discrete element compaction model of asphalt mixture in PFC3D simulation software; The three-dimensional dynamic discrete element compaction model of asphalt mixture is established by using PFC3D simulation software, importing the virtual asphalt mixture obtained in step S1, and generating a virtual specimen; then using the friction coefficient determined in step S2 and the Burgers model parameters determined in step S4, the compaction parameters of the three-dimensional dynamic discrete element compaction model are assigned; then two walls are generated at the top and bottom of the virtual specimen, and the specimen is rotated at a uniform speed by adjusting the speed of the wall until the rotation angle reaches the requirement; at the same time, during the compaction process, the top wall is controlled by a servo mechanism to apply a vertical load to the specimen and keep it stable so that the wall rotates at a uniform speed.

2. The discrete element compaction modeling method for accurately tracking asphalt mixture particles according to claim 1 is characterized in that: In step S1, a coarse aggregate model library is pre-established. Specifically, a blue light 3D scanner is used to collect 3D contour information of aggregates with a particle size of 4.75 mm to 9.5 mm, and the 3D contour information data is imported into Geomagic Studio reverse engineering software to generate a 3D shell structure of the real aggregate and save it as a stereolithography file; the bubble pack algorithm in the PFC3D simulation software is used to fill the 3D shell structure of the aggregate with spheres, thereby generating a rigid cluster to simulate aggregate particles larger than 2.36 mm; the radio and distance values ​​that determine the number of filled spheres are 0.3 and 150, respectively.

3. The discrete element compaction modeling method for accurately tracking asphalt mixture particles according to claim 1 is characterized in that: In the virtual uniaxial penetration test of coarse aggregate in step S2, specifically, the PFC3D simulation software is used to set a contact stiffness sliding model between the aggregates of the virtual asphalt mixture, and the Poisson's ratio of the coarse aggregate is set to 0.25, and the elastic modulus is set to 55 GPa; three friction coefficients are initially set to 0.15, 0.35, and 0.55, respectively; a cylindrical wall is generated as a loading pressure head for the virtual uniaxial penetration test of coarse aggregate, and the loading speed of the pressure head is set to 50 mm / min. When the penetration depth reaches 15 mm, the test is terminated, and the displacement and stress of the loading pressure head are detected.

4. The discrete element compaction modeling method for accurately tracking asphalt mixture particles according to claim 1 is characterized in that: In the asphalt mortar dynamic modulus test in step S4, specifically, the asphalt mortar specimen is made by the static pressure method, and a sine wave is applied to the asphalt mortar specimen using an SPT testing machine to measure its dynamic modulus, the load frequency is 0.1 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, 25 Hz, and the test temperature is 4.4°C, 21.1°C, and 37.8°C; Taking 21.1℃ as the reference temperature and based on the time-temperature equivalence principle, the dynamic modulus test results were translated along the logarithmic coordinates to obtain the master curve of the dynamic modulus of the real asphalt mortar. Then, nonlinear regression analysis was performed on the master curve of the dynamic modulus to obtain the Burgers model parameters of the asphalt mortar at a compaction temperature of 150℃.

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