A method for evaluating the skeleton structure of asphalt mixture based on main chain

Abstract

The present invention discloses a method for evaluating the skeleton structure of asphalt mixture based on the main force chain, which is specifically as follows: Step 1: assemble the digital specimen of asphalt mixture according to the composition of asphalt mixture; Step 2: conduct virtual experiments on the digital specimen of asphalt mixture to obtain contact information and aggregate information; Step 3: classify the aggregates according to the contact information between aggregates to obtain the set TAM, the set BAM and the set MAAAM; Step 4: set the force chain chain criterion according to the contact information between aggregates; Step 5: select the main force chain in the generated force chain; Step 6: according to the skeleton degree of the i-th grade aggregate in the main force chain, and determine the role of the i-th grade aggregate in the skeleton structure of asphalt mixture. The present invention realizes accurate evaluation of the skeleton structure from a mechanical point of view.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering. Background Art

[0002] Rutting is one of the main diseases of asphalt pavement. According to the research results of the US SHRP program, 71% of the anti-rutting ability of asphalt pavement depends on the skeleton structure formed by the aggregate gradation. Therefore, correctly and reasonably evaluating the skeleton structure has always been one of the research hotspots in the field of asphalt mixtures.

[0003] Currently, the research on skeleton structure has focused on the microscopic scale, and researchers mostly use digital image processing technology to analyze the contact characteristics between coarse aggregates in asphalt mixtures. However, the above method analyzes the skeleton structure of asphalt mixtures from the perspective of geometric composition. The skeleton structure is the main carrier of asphalt mixtures to resist and transmit external load stress. Analyzing the skeleton structure only from the perspective of geometric composition cannot effectively determine the relationship between the contact characteristics of coarse aggregates and the load transferred by the skeleton structure.

[0004] In asphalt mixture, granular aggregate accounts for more than 90% by mass, so asphalt mixture can be regarded as a granular material. Therefore, the force chain theory, which is theoretically used to study the load transfer characteristics of granular materials, is also applicable to the relevant research on asphalt mixture. Although there have been relevant studies on analyzing the performance of asphalt mixtures through force chains, the existing research has not really established the relationship between the force chain characteristics and the effective external load transfer characteristics of the asphalt mixture skeleton structure, resulting in inaccurate skeleton evaluation results. Summary of the invention

[0005] Purpose of the invention: In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for evaluating the skeleton structure of asphalt mixture based on the main chain.

[0006] Technical solution: The present invention provides a method for evaluating the skeleton structure of asphalt mixture based on the main chain, which specifically includes the following steps:

[0007] Step 1: Assemble the asphalt mixture digital specimen according to the composition of the asphalt mixture;

[0008] Step 2: Setting a virtual bearing plate on the asphalt mixture digital specimen, conducting a virtual experiment on the asphalt mixture digital specimen, and obtaining contact information and aggregate information; the contact information is contact information between aggregates or contact information between aggregates and external objects, and the contact information includes: normal contact force values ​​between aggregates or between aggregates and external objects, and coordinates of each aggregate; the external object includes a virtual bearing plate and a lower bearing layer, and the lower bearing layer is a virtual platform for placing the asphalt mixture virtual specimen in the virtual experiment;

[0009] Step 3: Classify the aggregates according to the contact information between aggregates: the aggregates that directly bear the load of the virtual bearing plate and whose normal contact force with the virtual bearing plate is greater than or equal to the normal contact force threshold are stored in the set TAM; the aggregates that are in contact with the lower bearing layer and whose normal contact force with the lower bearing layer is greater than or equal to the normal contact force threshold are stored in the set BAM; the aggregates in the asphalt mixture digital specimen except the aggregates that directly bear the load of the virtual bearing plate and the aggregates that are in contact with the lower bearing layer are regarded as other aggregates, and the aggregates that satisfy the normal contact force between aggregates greater than or equal to the normal contact force threshold are selected from other aggregates and stored in the set MAAM;

[0010] Step 4: Set the force chain formation criteria according to the contact information;

[0011] Step 5: Perform force chain search according to the force chain chaining criterion and the set where the starting aggregate in the force chain is located, and obtain several force chains; the several force chains include main force chains, and the main force chains include type I force chains and type II force chains; type I force chains are force chains in which the starting aggregate is in the set TAM and can transfer the external load to the lower bearing layer; type II force chains are force chains in which the starting aggregate is in the set MAAM and can transfer the internal load of the asphalt mixture digital specimen to the lower bearing layer;

[0012] Step 6: According to the number of the i-th aggregate in the main chain and the number of the i-th aggregate in the asphalt mixture digital specimen, calculate the skeleton degree of the i-th aggregate, and determine the role of the i-th aggregate in the asphalt mixture skeleton structure based on the skeleton degree of the i-th aggregate.

[0013] Furthermore, the normal contact force threshold in step 3 is the average value of the normal contact force in the asphalt mixture digital specimen.

[0014] Furthermore, the force chain formation criteria in step 4 include the following conditions:

[0015] Principle 1, search one force chain at a time;

[0016] Criterion 2: The next level aggregate is the aggregate that is in contact with the current aggregate in this force chain and whose height is less than or equal to the height of the current aggregate;

[0017] Criterion 3: The number of normal contact forces in the force chain is greater than or equal to N, where N is a positive integer; the normal contact force is the normal contact force between aggregates, the normal contact force between aggregates and a virtual bearing plate, or the normal contact force between aggregates and a lower bearing layer;

[0018] Criterion 4: Select the next level of aggregate according to the normal contact force saturation, the expression of which is as follows:

[0019]

[0020] Among them, f AB It represents the normal contact force between the previous aggregate A and the current aggregate B in this force chain. Represents aggregate B and the jth next level aggregate C j Initial normal contact force between j f AB and The angle between AB ·cosθ j is the jth next level aggregate C j The normal contact force component of

[0021] Criterion 5: Normal contact force update principle: After the next level aggregate C is determined, if the normal contact force saturation η between the current aggregate B and aggregate C in this force chain is BC If it is less than 1, then according to the initial normal contact force between aggregate B and aggregate C and f AB , calculate the remaining normal contact force between aggregates B and C And Update the initial normal contact force between aggregates B and C and use it as the normal contact force f between aggregates B and C in this force chain. BC , used to search for the next level aggregate of aggregate C; if there are other force chains including aggregates B and C in the subsequent search, as the initial normal contact force between aggregates B and C on the other force chain; the other force chain is the first force chain including aggregates B and C that is searched again after this search; if aggregates B and aggregates C constitute part of the force chain for the first time in this force chain search, then the initial normal contact force between aggregates B and aggregates C is the normal contact force between aggregates B and C obtained when conducting a virtual experiment on the asphalt mixture digital specimen;

[0022] If η BC ≥1, it is considered that after this force chain search, aggregate B and aggregate C no longer form other force chains, and the initial normal contact force between aggregates B and C is As the normal contact force between aggregate B and aggregate C in this force chain.

[0023] Furthermore, the criterion 4 selects the next aggregate according to the normal contact force saturation, specifically:

[0024] If the normal contact force saturation between each next-level aggregate and the current aggregate B is less than 1, the aggregate with the largest normal contact force saturation is selected;

[0025] If the normal contact force saturation between each next-level aggregate and the current aggregate B is greater than or equal to 1, the aggregate with the largest normal contact force with the current aggregate B is selected;

[0026] If there is a next-level aggregate whose normal contact force saturation with the current aggregate B is less than 1, and there is also a next-level aggregate whose normal contact force saturation with aggregate B is greater than or equal to 1, then the aggregate with the largest normal contact force component is selected from the next-level aggregates whose normal contact force saturation is less than 1, recorded as aggregate C1, and the aggregate with the largest initial normal contact force with aggregate B is selected from the next-level aggregates whose normal contact force saturation is greater than or equal to 1, recorded as aggregate C2, and the normal contact force component f of aggregate C1 is compared. AB Initial normal contact force between cosθ1 and aggregate C2, B Select the aggregate with larger value as the next level aggregate.

[0027] Furthermore, the several force chains in step 5 also include non-main force chains, and the non-main force chains include type III force chains and type IV force chains; type III force chains are force chains in which the starting aggregates are in the set TAM and can transfer external loads to the inside of the asphalt mixture digital specimen; type IV force chains are force chains in which the starting aggregates are in the set MAAM and only transfer loads to the inside of the asphalt mixture digital specimen without having any stress relationship with the outside world.

[0028] Furthermore, in the criterion 5, the following formula is used to update

[0029] f BC =f AB ·cosθ C

[0030] where θ C is the angle between the normal contact force of aggregates A and B and the initial normal contact force of aggregates B and C. For type I and type III force chains, if aggregate B is the first aggregate in the force chain, the virtual bearing plate is used as aggregate A, f AB is the normal contact force between the virtual bearing plate and aggregate B. For type II and type IV force chains, if aggregate A is the first aggregate in the force chain, then f AB is the normal contact force between aggregate A and aggregate B in the force chain;

[0031] The remaining normal contact force between aggregates B and C is calculated according to the following formula:

[0032]

[0033] Furthermore, when searching for force chains according to the force chain formation criterion in step 5, the search process for type I force chains or type III force chains is as follows:

[0034] Step ①: Traverse the set TAM, select the aggregate with the largest normal contact force with the virtual bearing plate as the starting aggregate, increase the normal contact force by 1, and delete the starting aggregate from the set TAM;

[0035] Step ②: Determine whether the current aggregate is an aggregate in the BAM set. If not, go to step ③. If yes, go to step ⑤.

[0036] Step ③: Determine whether there is a next-level aggregate in the set MAAM or the set BAM that meets criterion 2 with the current aggregate. If so, go to step ④; otherwise, determine whether the number of normal contact forces in the current force chain meets criterion 3. If criterion 3 is met, the current force chain search is completed, a type III force chain is obtained, and go to step ① to search for the next force chain; if criterion 3 is not met, stop the search for this force chain, and go to step ① to search for the next force chain;

[0037] Step ④: Determine the next level aggregate of the current force chain according to criterion 4, add 1 to the number of normal contact forces, and update the normal contact forces between aggregates according to criterion 5, and take the next level aggregate determined as the current aggregate to proceed to step ②;

[0038] Step ⑤: Determine whether the normal contact force between the current aggregate and the lower bearing layer is 0. If not, go to step ⑥. If it is 0, determine whether the number of normal contact forces in the current force chain meets criterion 3. If so, the force chain search is completed, and a type III force chain is obtained, and go to step ① to search for the next force chain. If criterion 3 is not met, stop the search and go to step ① to search for the next force chain.

[0039] Step ⑥: Add 1 to the number of normal contact forces to determine whether the number of normal contact forces in the current force chain meets criterion 3. If so, the force chain search is completed, a type I force chain is obtained, and the next force chain search is performed at step ①. If criterion 3 is not met, the search is stopped and the next force chain search is performed at step ①.

[0040] Furthermore, when searching for force chains according to the force chain formation criterion in step 5, the search process for type II force chains or type IV force chains is as follows:

[0041] Step A: Select the aggregate with the highest height in the MAAM set as the starting aggregate, and delete the starting aggregate in the MAAM set;

[0042] Step B: Determine whether there is a next-level aggregate in the MAAM set that meets criterion 2 with the starting aggregate. If so, the next-level aggregate that meets the condition is formed into an aggregate group and the process goes to step C. Otherwise, the process goes to step A.

[0043] Step C: traverse the aggregate group, select the aggregate with the largest normal contact force with the starting aggregate in the aggregate group, use the selected aggregate as the current aggregate B, delete the selected aggregate in the aggregate group, increase the number of normal contact forces by 1, and go to step D;

[0044] Step D: Determine whether the current aggregate is an aggregate in the BAM set, if so, go to step H, otherwise go to step E;

[0045] Step E: Determine whether there is a next-level aggregate in the set MAAM or the set BAM that meets criterion 2 with the current aggregate. If so, form a data group with the next-level aggregate that meets criterion 2 and go to step F, otherwise go to step G;

[0046] Step F: Select the next level aggregate C in the data set according to criterion 4, and update the normal contact force between aggregate B and aggregate C according to criterion 5, increase the number of normal contact forces by 1, take the next level aggregate C as the current aggregate and go to step D;

[0047] Step G: Determine whether the number of normal contact forces in this force chain search satisfies criterion 3. If so, this force chain search is completed, a type IV force chain is obtained, and the process goes to step K. If not, the search is stopped and the process goes to step K.

[0048] Step H: Determine whether the normal contact force between the current aggregate and the lower bearing layer is 0. If not, go to step J. If yes, determine whether the number of normal contact forces in the force chain searched this time satisfies criterion 3. If yes, the force chain search is completed, a type IV force chain is obtained, and go to step K. If not, stop the search and go to step K.

[0049] Step J: The number of normal contact forces is increased by 1 to determine whether the number of normal contact forces in the force chain being searched satisfies criterion 3. If so, the force chain search is completed, a type II force chain is obtained, and the process goes to step K. If criterion 3 is not met, the force chain search is stopped and the process goes to step K.

[0050] Step K: Determine whether the aggregates in the aggregate group have been traversed and analyzed. If not, go to step C to search for the next force chain; otherwise, go to step A to search for the next force chain.

[0051] Furthermore, in step 6, the skeleton degree C of the i-th aggregate is calculated according to the following formula: i :

[0052]

[0053] Among them, m i is the total number of aggregates in the i-th gear on the main chain, M i It is the total number of the i-th aggregate on the main chain in the asphalt mixture digital specimen.

[0054] Furthermore, in step 6, the role of the i-th grade aggregate in the skeleton structure of the asphalt mixture is determined based on the skeleton degree of the i-th grade aggregate. Specifically, if the skeleton degree of the i-th grade aggregate is between A2 and A1, it is determined that the aggregate of this grade participates in the skeleton construction; if it is between A3 and A2, it is considered that the aggregate of this grade mainly participates in the skeleton construction, and plays a secondary role in filling the skeleton; if it is between A4 and A3, it is considered that the aggregate of this grade mainly plays a role in filling the skeleton, and plays a secondary role in participating in the skeleton construction; if it is between 0% and A4, it is considered that the aggregate of this grade plays a role in filling the skeleton structure. A1, A2, A3 and A4 are all preset thresholds, and A4<A3<A2<A1.

[0055] Beneficial effects: Based on the method proposed in the present invention, the main chain structure in the asphalt mixture that meets the characteristics of the skeleton structure to bear and transfer external loads can be identified. Based on the identified main chain structure, the aggregate particles inside the asphalt mixture that are closely related to the performance of the skeleton structure to effectively transfer external loads can be found, thereby achieving accurate evaluation of the skeleton structure from a mechanical perspective, overcoming the deficiency that the evaluation of the asphalt mixture skeleton structure from a geometric perspective cannot reflect the effective transfer of external loads by the skeleton. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is the AC16 gradation curve diagram;

[0057] Figure 2 This is the AC16 asphalt mixture digital specimen diagram;

[0058] Figure 3 This is a schematic diagram of aggregate grouping;

[0059] Figure 4 Schematic diagrams of four types of force chains;

[0060] Figure 5 It is a schematic diagram of force chain saturation;

[0061] Figure 6 Retrieve the flow chart for type I and type III force chain structure of asphalt mixture;

[0062] Figure 7 Flow chart for searching type II and type IV force chain structures of asphalt mixture;

[0063] Figure 8 This is a proportional diagram of the various grades of aggregate participating in the skeleton construction of AC16. DETAILED DESCRIPTION

[0064] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0065] This embodiment provides an asphalt mixture skeleton structure evaluation method based on the main chain, which mainly includes the following steps:

[0066] (1) According to the composition of asphalt mixture materials, assemble asphalt mixture digital specimens and conduct virtual experiments. The virtual laboratory is as follows: apply load to the asphalt mixture digital specimens through a virtual load-bearing plate; Figure 1 The gradation curve of AC16 in the test piece is assembled with a digital specimen of 30 cm in length and 8 cm in width using PFC2D software. Figure 2 shown.

[0067] (2) The fish language in the PFC2D software is used to write a program to output the contact information between the virtual bearing plate and the aggregate, the contact information between the aggregates, the contact information between the aggregate and the lower bearing layer, and the aggregate information at the end of the virtual bearing plate test; the contact information includes the contact number, coordinates, normal contact force, and the number, coordinates, and particle size of the aggregate that forms the contact; the aggregate information specifically includes: the aggregate number, coordinates, and particle size. At the same time, the contact information and the aggregate information are saved in separate Excel tables. The lower bearing layer is a virtual table for placing the virtual specimen of asphalt mixture in the virtual experiment.

[0068] (3) Figure 3 As shown, the aggregate set that is directly subjected to the load of the tire (the tire is a virtual bearing plate in the virtual laboratory) and the normal contact force between the aggregate and the tire is greater than or equal to the normal contact force threshold is recorded as TAM; the aggregate set that is in contact with the lower bearing layer and the normal contact force between the aggregate and the lower bearing layer is greater than or equal to the normal contact force threshold is recorded as BAM; the aggregates in the asphalt mixture digital specimen except the aggregates that directly bear the load of the virtual bearing plate and the aggregates in contact with the lower bearing layer are regarded as other aggregates, and the aggregates that meet the aggregate selection criteria are selected from other aggregates and stored in the set MAAM; in this embodiment, the normal contact force threshold is the average value of the normal contact force in the asphalt mixture digital specimen.

[0069] (4) Based on the Matlab software platform, according to the force chain formation criteria set in this embodiment, an algorithm is compiled to carry out force chain search in the asphalt mixture digital specimen to obtain a number of force chains, including main force chains and non-main force chains. The main force chains include type I force chains and type II force chains; type I force chains are force chains in which the starting aggregate is in the set TAM and can transfer external loads to the lower bearing layer; type II force chains are force chains in which the starting aggregate is in the set MAAM and can transfer internal loads of the asphalt mixture digital specimen to the lower bearing layer; non-main force chains include type III force chains and type IV force chains; type III force chains are force chains in which the starting aggregate is in the set TAM and can only transfer external loads to the inside of the asphalt mixture digital specimen; type IV force chains are force chains in which the starting aggregate is in the set MAAM and can only transfer loads to the inside of the asphalt mixture digital specimen and have no stress relationship with the outside world. Figure 4 As shown, only type I and type II force chains can effectively transfer the external load to the lower bearing layer. Therefore, in this embodiment, type I and type II force chains are defined as main force chain structures.

[0070] The force chain formation criteria include the following:

[0071] Principle 1: Search one force chain at a time; in this embodiment, the force chains are searched one by one in the order of first searching type I force chain, type III force chain, and then searching type II force chain and type IV force chain.

[0072] Criterion 2: Position requirement of lower-level aggregate particles: The lower-level aggregate in this force chain is in contact with the current aggregate, and the height of the lower-level aggregate is less than or equal to the height of the current aggregate.

[0073] Criterion 3: The number of contact forces on the main chain is greater than or equal to N. In this embodiment, N=2.

[0074] Criterion 4: Normal contact force saturation: Select the next level of aggregate according to the normal contact force saturation, such as Figure 5 As shown in the figure, aggregate A is the previous aggregate in this force chain; aggregate B is the current aggregate, and aggregates C1 and C2 are the next-level aggregates of potential force chain extension. The normal contact force saturation between all the next-level aggregates in this force chain and the current aggregate B is calculated:

[0075]

[0076] Among them, f AB It represents the normal contact force between the previous aggregate A and the current aggregate B in this force chain. Represents aggregate B and the jth next level aggregate C j Initial normal contact force between j f AB and The angle betweenAB ·cosθ j is the jth next level aggregate C j The normal contact force component.

[0077] If the normal contact force saturation between each next-level aggregate and the current aggregate B is less than 1, the position with a larger normal contact force saturation is selected as the force chain extension direction. For example, the normal contact force saturation η between the next-level aggregate C1 and the current aggregate B is BC1 Greater than or equal to η BC2 , then the C1 aggregate particle is determined to be the extension direction of this force chain. η BC2 is the normal contact force saturation between the next level aggregate C2 and the current aggregate B.

[0078] If the normal contact force saturation between each next-level aggregate and the current aggregate B is greater than or equal to 1, the position with the larger normal contact force is the extension direction of the force chain (the normal contact force at this time is relatively initial). For example, the initial normal contact force between the next-level aggregate C1 and the current aggregate B is Greater than the initial normal contact force between the next level aggregate C2 and the current aggregate B The C1 aggregate particles are determined to be the extension direction of this force chain, that is, C1 is determined to be the next level aggregate of the current aggregate B.

[0079] If the contact force saturation is greater than 1 and less than 1 at the same time (that is, there is a next-level aggregate with a normal contact force saturation less than 1 between the current aggregate B and the next-level aggregate with a normal contact force saturation greater than or equal to 1), then the aggregate with the largest normal contact force component is selected from the next-level aggregate with a normal contact force saturation less than 1, recorded as aggregate C1, and the aggregate with the initial normal contact force component with aggregate B is selected from the next-level aggregate with a contact force saturation greater than or equal to 1. The largest aggregate, denoted as aggregate C2, is compared with the normal contact force component f of aggregate C1. AB ·cosθ1 and initial normal contact force The size of is determined by selecting the position of the aggregate with a large value as the extension direction of this force chain, that is, selecting the aggregate with a large value as the next level aggregate.

[0080] Criterion 5: Normal contact force update principle: After the next level aggregate C is determined, if the normal contact force saturation η between the current aggregate B and aggregate C in this force chain is BC If it is less than 1, then according to the initial normal contact force between aggregate B and aggregate C and f AB , calculate the remaining normal contact force between aggregates B and C And The updated initial normal contact force between aggregates B and C is used as the normal contact force f between aggregates B and C in this force chain. BC , used to search for the next level aggregate of aggregate C.

[0081] f BC The expression is as follows:

[0082] f BC =f AB ·cosθ C

[0083] θ C is the angle between the normal contact force of aggregates A and B and the initial normal contact force of aggregates B and C. For type I and type III force chains, if aggregate B is the first aggregate in the force chain, the virtual bearing plate is used as aggregate A, f AB is the normal contact force between the virtual bearing plate and aggregate B. For type II and type IV force chains, if aggregate A is the first aggregate in the force chain, then f AB is the normal contact force between aggregate A and aggregate B in the force chain;

[0084] Remaining normal contact force between aggregates B and C The expression is as follows:

[0085]

[0086] If there are other force chains including aggregates B and C in the subsequent search, then As the initial normal contact force between aggregates B and C on the other force chain (BC at this time is in contact with each other and constitutes a part of the other force chain); the other force chain is the first force chain including aggregates B and C that is searched again after this search (if aggregates B and aggregate C constitute a part of the force chain for the first time in this force chain search, then the initial normal contact force between aggregates B and aggregate C is the normal contact force between aggregates B and C obtained during the virtual experiment of the asphalt mixture digital specimen.

[0087] If η BC ≥1, it is determined that after this force chain search, there are no other force chains including aggregate B and aggregate C, that is, The initial normal contact force between aggregates B and C is As the normal contact force between aggregate B and aggregate C in this force chain,

[0088] (5) Calculate the skeleton degree of each aggregate: Use the fish language in the PFC2D software to write a program to classify and count the number of aggregates of each grade on the main chain and the number of aggregates of each grade in the digital specimen. By calculating the skeleton degree of each grade, the role of each grade of aggregate in the skeleton composition is evaluated. The skeleton degree calculation is shown in the following formula:

[0089]

[0090] Among them, m i is the total number of aggregates in the main chain, M i It is the total number of the i-th aggregate on the main chain in the asphalt mixture digital specimen.

[0091] If the skeleton degree of the i-th grade aggregate is between A2 and A1, it is considered that the aggregate in this grade participates in the skeleton construction; if it is between A3 and A2, it is considered that the aggregate in this grade mainly participates in the skeleton construction, and fills the skeleton as a supplement; if it is between A4 and A3, it is considered that the aggregate in this grade mainly fills the skeleton, and participates in the skeleton construction as a supplement; if it is between 0% and A4, it is considered that the aggregate in this grade plays a role in filling the skeleton structure. A1, A2, A3 and A4 are all preset thresholds.

[0092] In this embodiment, A1=100%, A2=80%, A3=50%, and A4=20%.

[0093] The search process of the force chain in this embodiment is as follows: Figure 6 ,7 shown; Figure 6 It is a search process for searching type I force chain or type III force chain; the identified type I force chain and type III force chain are counted into the corresponding force chain arrays, which are recorded as FchainsTBM and FchainsTMM force chain arrays respectively;

[0094] Specifically:

[0095] Step ①: Traverse the set TAM, select the aggregate with the largest normal contact force with the virtual bearing plate as the starting aggregate, increase the normal contact force by 1, and delete the starting aggregate from the set TAM;

[0096] Step ②: Determine whether the current aggregate is an aggregate in the BAM set. If not, go to step ③. If yes, go to step ⑤.

[0097] Step ③: Determine whether there is a next-level aggregate in the set MAAM or the set BAM that meets criterion 2 with the current aggregate. If so, go to step ④; otherwise, determine whether the number of normal contact forces in the current force chain meets criterion 3. If criterion 3 is met, the current force chain search is completed, a type III force chain is obtained, and go to step ① to search for the next force chain; if criterion 3 is not met, stop the search for this force chain, and go to step ① to search for the next force chain;

[0098] Step ④: Determine the next level aggregate of the current force chain according to criterion 4, add 1 to the number of normal contact forces, and update the normal contact forces between aggregates according to criterion 5, and take the next level aggregate determined as the current aggregate to proceed to step ②;

[0099] Step ⑤: Determine whether the normal contact force between the current aggregate and the lower bearing layer is 0. If not, go to step ⑥; if it is 0, determine whether the number of normal contact forces in the current force chain meets criterion 3. If so, the force chain search is completed, and a type III force chain is obtained, and go to step ① to search for the next force chain; if criterion 3 is not met, stop the search and go to step ① to search for the next force chain;

[0100] Step ⑥: Add 1 to the number of normal contact forces to determine whether the number of normal contact forces in the current force chain meets criterion 3. If so, the force chain search is completed, a type I force chain is obtained, and the next force chain search is performed at step ①. If criterion 3 is not met, the search is stopped and the next force chain search is performed at step ①.

[0101] The above steps ① to ⑥ are repeated until the aggregate in the set TAM is taken as the current aggregate B and the virtual bearing plate is taken as the "aggregate" A. All analyses are completed, and the force chain search is terminated.

[0102] Figure 7 In order to search for the search process of type II force chain or type IV force chain, the identified type II force chain or type IV force chain is counted into the corresponding force chain array, which is recorded as FchainsMBM and FchainsMMM force chain array respectively. Specifically:

[0103] Step A: Select the aggregate with the highest height in the MAAM set as the starting aggregate A, and delete the starting aggregate in the MAAM set;

[0104] Step B: Determine whether there is a next-level aggregate in the MAAM set that meets criterion 2 with the starting aggregate A. If so, the next-level aggregates that meet the conditions are formed into an aggregate group and go to step C, otherwise go to step A;

[0105] Step C: traverse the aggregate group, select the aggregate with the largest normal contact force with the starting aggregate in the aggregate group, use the selected aggregate as the current aggregate B, delete the selected aggregate in the aggregate group, increase the number of normal contact forces by 1, and go to step D;

[0106] Step D: Determine whether the current aggregate is an aggregate in the BAM set, if so, go to step H, otherwise go to step E;

[0107] Step E: Determine whether there is a next-level aggregate in the set MAAM or the set BAM that meets criterion 2 with the current aggregate. If so, form a data group with the next-level aggregate that meets criterion 2 and go to step F, otherwise go to step G;

[0108] Step F: Select the next level aggregate C in the data set according to criterion 4, and update the normal contact force between aggregate B and aggregate C according to criterion 5, increase the number of normal contact forces by 1, take the next level aggregate C as the current aggregate and go to step D;

[0109] Step G: Determine whether the number of normal contact forces in this force chain search satisfies criterion 3. If so, this force chain search is completed, a type IV force chain is obtained, and the process goes to step K. If not, the search is stopped and the process goes to step K.

[0110] Step H: Determine whether the normal contact force between the current aggregate and the lower bearing layer is 0. If not, go to step J. If yes, determine whether the number of normal contact forces in the force chain searched this time satisfies criterion 3. If yes, the force chain search is completed, a type IV force chain is obtained, and go to step K. If not, stop the search and go to step K.

[0111] Step J: The number of normal contact forces is increased by 1 to determine whether the number of normal contact forces in the force chain being searched satisfies criterion 3. If so, the force chain search is completed, a type II force chain is obtained, and the process goes to step K. If criterion 3 is not met, the force chain search is stopped and the process goes to step K.

[0112] Step K: Determine whether the aggregates in the aggregate group have been traversed and analyzed. If not, go to step C to search for the next force chain; otherwise, go to step A to search for the next force chain.

[0113] The above steps A to K are repeated until all the aggregates in the set MAAM as the starting aggregates are analyzed, and the force chain search is terminated.

[0114] In this embodiment, the calculation results of the aggregate skeleton degree of each grade are as follows: Figure 8 As shown. Figure 8 From the results, we can see that the aggregates with particle sizes between 13.2-16mm and 16-19mm all participate in the skeleton construction; the aggregates with particle sizes between 2.36-4.75mm, 4.75mm-9.5mm and 9.5-13.2mm mainly participate in the skeleton construction and have a filling role as a supplement; the aggregates with particle sizes between 1.18-2.36mm mainly play a filling role and have a supplementary role in the skeleton construction; the aggregates with a particle size less than 1.18mm all participate in the filling role of the skeleton.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for evaluating the skeleton structure of asphalt mixture based on the main chain, characterized in that: The specific steps include: Step 1: Assemble the asphalt mixture digital specimen according to the composition of the asphalt mixture; Step 2: Setting the virtual bearing plate on the asphalt mixture digital specimen, conducting a virtual experiment on the asphalt mixture digital specimen, and obtaining contact information and aggregate information; The contact information is the contact information between aggregates or the contact information between aggregates and external objects, and the contact information includes: the normal contact force value between aggregates or between aggregates and external objects, and the coordinates of each aggregate; the external object includes a virtual bearing plate and a lower bearing layer, and the lower bearing layer is a virtual table for placing a virtual specimen of asphalt mixture in a virtual experiment; Step 3: Classify the aggregates according to the contact information between aggregates: the aggregates that directly bear the load of the virtual bearing plate and whose normal contact force with the virtual bearing plate is greater than or equal to the normal contact force threshold are stored in the set TAM; the aggregates that are in contact with the lower bearing layer and whose normal contact force with the lower bearing layer is greater than or equal to the normal contact force threshold are stored in the set BAM; the aggregates in the asphalt mixture digital specimen except the aggregates that directly bear the load of the virtual bearing plate and the aggregates that are in contact with the lower bearing layer are regarded as other aggregates, and the aggregates that satisfy the normal contact force between aggregates greater than or equal to the normal contact force threshold are selected from other aggregates and stored in the set MAAM; Step 4: Set the force chain formation criteria according to the contact information; Step 5: Perform force chain search according to the force chain chaining criterion and the set where the starting aggregate in the force chain is located, and obtain several force chains; the several force chains include main force chains, and the main force chains include type I force chains and type II force chains; type I force chains are force chains in which the starting aggregate is in the set TAM and can transfer the external load to the lower bearing layer; type II force chains are force chains in which the starting aggregate is in the set MAAM and can transfer the internal load of the asphalt mixture digital specimen to the lower bearing layer; Step 6: According to the number of the i-th aggregate in the main chain and the number of the i-th aggregate in the asphalt mixture digital specimen, calculate the skeleton degree of the i-th aggregate, and determine the role of the i-th aggregate in the asphalt mixture skeleton structure based on the skeleton degree of the i-th aggregate.

2. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 1 is characterized in that: The normal contact force threshold in step 3 is the average value of the normal contact force in the asphalt mixture digital specimen.

3. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 1 is characterized in that: The force chain formation criteria in step 4 include the following conditions: Principle 1, search one force chain at a time; Criterion 2: The next level aggregate is the aggregate that is in contact with the current aggregate in this force chain and whose height is less than or equal to the height of the current aggregate; Criterion 3: The number of normal contact forces in the force chain is greater than or equal to N, where N is a positive integer; the normal contact force is the normal contact force between aggregates, the normal contact force between aggregates and a virtual bearing plate, or the normal contact force between aggregates and a lower bearing layer; Criterion 4: Select the next level of aggregate according to the normal contact force saturation, the expression of which is as follows: Among them, f AB It represents the normal contact force between the previous aggregate A and the current aggregate B in this force chain. Represents aggregate B and the jth next level aggregate C j Initial normal contact force between j f AB and The angle between AB ·cosθ j is the jth next level aggregate C j The normal contact force component of Criterion 5: Normal contact force update principle: After the next level aggregate C is determined, if the normal contact force saturation η between the current aggregate B and aggregate C in this force chain is BC If it is less than 1, then according to the initial normal contact force between aggregate B and aggregate C and f AB , calculate the remaining normal contact force between aggregates B and C And Update the initial normal contact force between aggregates B and C and use it as the normal contact force f between aggregates B and C in this force chain. BC , used to search for the next level aggregate of aggregate C; if there are other force chains including aggregates B and C in the subsequent search, then as the initial normal contact force between aggregates B and C on the other force chain; the other force chain is the first force chain including aggregates B and C that is searched again after this search; if aggregates B and aggregates C constitute part of the force chain for the first time in this force chain search, then the initial normal contact force between aggregates B and aggregates C is the normal contact force between aggregates B and C obtained when conducting a virtual experiment on the asphalt mixture digital specimen; If η BC ≥1, it is considered that after this force chain search, aggregate B and aggregate C no longer form other force chains, and the initial normal contact force between aggregates B and C is As the normal contact force between aggregate B and aggregate C in this force chain.

4. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 3 is characterized in that: The criterion 4 selects the next aggregate according to the normal contact force saturation, specifically: If the normal contact force saturation between each next-level aggregate and the current aggregate B is less than 1, the aggregate with the largest normal contact force saturation is selected; If the normal contact force saturation between each next-level aggregate and the current aggregate B is greater than or equal to 1, the aggregate with the largest normal contact force with the current aggregate B is selected; If there is a next-level aggregate whose normal contact force saturation with the current aggregate B is less than 1, and there is also a next-level aggregate whose normal contact force saturation with aggregate B is greater than or equal to 1, then the aggregate with the largest normal contact force component is selected from the next-level aggregates whose normal contact force saturation is less than 1, recorded as aggregate C1, and the aggregate with the largest initial normal contact force with aggregate B is selected from the next-level aggregates whose normal contact force saturation is greater than or equal to 1, recorded as aggregate C2, and the normal contact force component f of aggregate C1 is compared. AB Initial normal contact force between cosθ1 and aggregate C2, B Select the aggregate with larger value as the next level aggregate.

5. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 3 is characterized in that: The several force chains in step 5 also include non-main force chains, which include type III force chains and type IV force chains; type III force chains are force chains in which the starting aggregates are in the set TAM and can transfer external loads to the asphalt mixture digital specimen; type IV force chains are force chains in which the starting aggregates are in the set MAAM and only transfer loads to the asphalt mixture digital specimen without generating any stress relationship with the outside world.

6. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 5 is characterized in that: In the criterion 5, update according to the following formula f BC =f AB ·cosθ C where θ C is the angle between the normal contact force of aggregates A and B and the initial normal contact force of aggregates B and C. For type I and type III force chains, if aggregate B is the first aggregate in the force chain, the virtual bearing plate is used as aggregate A, f AB is the normal contact force between the virtual bearing plate and aggregate B. For type II and type IV force chains, if aggregate A is the first aggregate in the force chain, then f AB is the normal contact force between aggregate A and aggregate B in the force chain; The remaining normal contact force between aggregates B and C is calculated according to the following formula:

7. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 5 is characterized in that: When searching for force chains according to the force chain formation criterion in step 5, the search process of type I force chains or type III force chains is as follows: Step ①: Traverse the set TAM, select the aggregate with the largest normal contact force with the virtual bearing plate as the starting aggregate, increase the normal contact force by 1, and delete the starting aggregate from the set TAM; Step ②: Determine whether the current aggregate is an aggregate in the BAM set. If not, go to step ③. If yes, go to step ⑤. Step ③: Determine whether there is a next-level aggregate in the set MAAM or the set BAM that meets criterion 2 with the current aggregate. If so, go to step ④; otherwise, determine whether the number of normal contact forces in the current force chain meets criterion 3. If criterion 3 is met, the current force chain search is completed, a type III force chain is obtained, and go to step ① to search for the next force chain; if criterion 3 is not met, stop the search for this force chain, and go to step ① to search for the next force chain; Step ④: Determine the next level aggregate of the current force chain according to criterion 4, add 1 to the number of normal contact forces, and update the normal contact forces between aggregates according to criterion 5, and take the next level aggregate determined as the current aggregate to proceed to step ②; Step ⑤: Determine whether the normal contact force between the current aggregate and the lower bearing layer is 0. If not, go to step ⑥. If it is 0, determine whether the number of normal contact forces in the current force chain meets criterion 3. If so, the force chain search is completed, and a type III force chain is obtained, and go to step ① to search for the next force chain. If criterion 3 is not met, stop the search and go to step ① to search for the next force chain. Step ⑥: Add 1 to the number of normal contact forces to determine whether the number of normal contact forces in the current force chain meets criterion 3. If so, the force chain search is completed, a type I force chain is obtained, and the next force chain search is performed at step ①. If criterion 3 is not met, the search is stopped and the next force chain search is performed at step ①.

8. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 5, characterized in that: When searching for force chains according to the force chain formation criterion in step 5, the search process of type II force chains or type IV force chains is as follows: Step A: Select the aggregate with the highest height in the MAAM set as the starting aggregate, and delete the starting aggregate in the MAAM set; Step B: Determine whether there is a next-level aggregate in the MAAM set that meets criterion 2 with the starting aggregate. If so, the next-level aggregate that meets the condition is formed into an aggregate group and the process goes to step C. Otherwise, the process goes to step A. Step C: traverse the aggregate group, select the aggregate with the largest normal contact force with the starting aggregate in the aggregate group, use the selected aggregate as the current aggregate B, delete the selected aggregate in the aggregate group, increase the number of normal contact forces by 1, and go to step D; Step D: Determine whether the current aggregate is an aggregate in the BAM set, if so, go to step H, otherwise go to step E; Step E: Determine whether there is a next-level aggregate in the set MAAM or the set BAM that meets criterion 2 with the current aggregate. If so, form a data group with the next-level aggregate that meets criterion 2 and go to step F, otherwise go to step G; Step F: Select the next level aggregate C in the data set according to criterion 4, and update the normal contact force between aggregate B and aggregate C according to criterion 5, increase the number of normal contact forces by 1, take the next level aggregate C as the current aggregate and go to step D; Step G: Determine whether the number of normal contact forces in this force chain search satisfies criterion 3. If so, this force chain search is completed, a type IV force chain is obtained, and the process goes to step K. If not, the search is stopped and the process goes to step K. Step H: Determine whether the normal contact force between the current aggregate and the lower bearing layer is 0. If not, go to step J. If yes, determine whether the number of normal contact forces in the force chain searched this time satisfies criterion 3. If yes, the force chain search is completed, a type IV force chain is obtained, and go to step K. If not, stop the search and go to step K. Step J: add 1 to the number of normal contact forces to determine whether the number of normal contact forces in the force chain searched this time satisfies criterion 3. If so, the force chain search is completed, a type II force chain is obtained, and the process goes to step K. If criterion 3 is not met, stop searching for this force chain and go to step K; Step K: Determine whether the aggregates in the aggregate group have been traversed and analyzed. If not, go to step C to search for the next force chain; otherwise, go to step A to search for the next force chain.

9. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 1, characterized in that: In step 6, the skeleton degree C of the i-th aggregate is calculated according to the following formula: i : Among them, m i is the total number of aggregates in the main chain at the i-th level, M i It is the total number of the i-th aggregate on the main chain in the asphalt mixture digital specimen.

10. The method for evaluating the skeleton structure of asphalt mixture based on the main chain according to claim 9, characterized in that: In step 6, the role of the i-th grade aggregate in the skeleton structure of the asphalt mixture is determined based on the skeleton degree of the i-th grade aggregate. Specifically, if the skeleton degree of the i-th grade aggregate is between A2 and A1, it is determined that the aggregate of this grade participates in the skeleton construction; if it is between A3 and A2, it is considered that the aggregate of this grade mainly participates in the skeleton construction, and plays a secondary role in filling the skeleton; if it is between A4 and A3, it is considered that the aggregate of this grade mainly plays a role in filling the skeleton, and plays a secondary role in participating in the skeleton construction; if it is between 0% and A4, it is considered that the aggregate of this grade plays a role in filling the skeleton structure. A1, A2, A3 and A4 are all preset thresholds, and A4<A3<A2<A1.

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