CN111680373A - Drainage asphalt mixture gradation design method based on virtual test - Google Patents

Drainage asphalt mixture gradation design method based on virtual test Download PDF

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CN111680373A
CN111680373A CN202010606996.6A CN202010606996A CN111680373A CN 111680373 A CN111680373 A CN 111680373A CN 202010606996 A CN202010606996 A CN 202010606996A CN 111680373 A CN111680373 A CN 111680373A
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aggregate
contact
displacement
virtual
asphalt mixture
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马涛
林子豪
顾临皓
黄晓明
张伟光
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Southeast University
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Southeast University
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    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00Computer-aided design [CAD]
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    • G06F30/23Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]

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Abstract

The invention discloses a drainage asphalt mixture gradation design method based on a virtual test. The method is characterized in that three groups of coarse aggregates are prepared in a trial mode according to aggregate raw materials to form different PAC (programmable automation controller) gradations; generating a coarse aggregate mixture discrete element model with the particle size of more than 2.36mm according to trial gradation; performing a virtual uniaxial penetration test, and acquiring critical load and pressure head displacement according to a uniaxial penetration deformation stress diagram; extracting coordination numbers, contact ratios, force chain distribution and displacement conditions of all grades of aggregate particles at a critical load point, and visualizing a skeleton structure; comprehensively comparing each skeleton mesoscopic index of the three groups of grading schemes, and selecting one group with the best overall mechanical property as the coarse aggregate part of the design grading. The method can visually observe the state of the framework structure under different gradation, and solves the problems of framework structure loss, low bearing capacity and the like caused by the current method only paying attention to the void ratio and neglecting the optimization of the composition of the coarse aggregate.

Description

Drainage asphalt mixture gradation design method based on virtual test
Technical Field
The invention relates to an asphalt mixture design method, in particular to a drainage asphalt mixture gradation design method based on a virtual test.
Background
The grading skeleton structure of the drainage asphalt mixture is an important guarantee of the bearing capacity of the drainage asphalt mixture, whether a skeleton is formed or not is generally judged by means of macroscopic parameters such as the coarse aggregate clearance ratio VCA, and the like, but the skeleton forming condition in the mixture cannot be observed in a conventional indoor test; meanwhile, the key point of the grading design of the drainage asphalt mixture at present is to achieve the designed target void ratio, however, even under the same void ratio, the skeleton structure of the mixture can be greatly different, and an optimization space exists in the composition of coarse aggregates. With the development of computer simulation technology, discrete element software has a large application space in simulation of asphalt mixture routine tests, aggregates in asphalt mixtures can be granulated and visualized through generating virtual test pieces, rich microscopic information can be obtained, and design guidance and reference basis for grading design from a skeleton structure can be provided. Therefore, the visual drainage asphalt mixture gradation design can be carried out through the virtual test, technicians are allowed to carry out analysis evaluation on the current gradation framework and make adjustment and selection in the design stage, and manpower, material resources and time consumed by the indoor test are saved.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a drainage asphalt mixture gradation design method based on a virtual test, which can realize the visual design of a skeleton structure, allow technicians to analyze, evaluate and adjust and select a current gradation skeleton in a design stage, and save manpower, material resources and time consumed by an indoor test.
The technical scheme is as follows: the invention provides a drainage asphalt mixture gradation design method based on a virtual test, which comprises the following steps:
(1) trial preparing three groups of coarse aggregates to form different PAC grades according to the aggregate raw materials;
(2) generating a coarse aggregate mixture discrete element model with the particle size of more than 2.36mm according to trial gradation;
(3) performing a virtual uniaxial penetration test, and acquiring critical load and pressure head displacement according to a uniaxial penetration deformation stress diagram;
(4) extracting coordination numbers, contact ratios, force chain distribution and displacement conditions of all grades of aggregate particles at a critical load point, and visualizing a skeleton structure;
(5) comprehensively comparing each skeleton mesoscopic index of the three groups of grading schemes, and selecting one group with the best overall mechanical property as the coarse aggregate part of the design grading.
Further, in the step (1), the PAC grading with different composition of the three groups of coarse aggregates in trial assembly means that the relative content of each grade of coarse aggregate is adjusted under the condition that the content of the coarse aggregate is not changed, that is, the passing rate of a sieve pore of 2.36mm is not changed.
Further, in the step (2), the generating of the coarse aggregate mixture discrete element model with the particle size of more than 2.36mm includes calculating the number of aggregate particles of each grade required to be generated; generating a virtual mold; in order to ensure the compaction quality, the aggregate particles are generated in three batches, and first batch of aggregate particles are generated; applying gravity and vibration to the first batch of aggregate particles; placing a loading plate on top of the aggregate mixture; giving speed to the loading plate wall body to apply load; slowly moving the load plate upward until there is no contact with the aggregate mixture, slowly eliminating the unbalanced forces between the particles; removing the loading plate; generating a second batch of aggregate particles based on the first batch of compacted aggregate; repeating the steps to complete the generation, falling, vibration, compaction and stabilization of the second batch of aggregate and the third batch of aggregate.
Further, in the step (3), the performing of the virtual uniaxial penetration test refers to arranging a cylindrical pressure head (with a diameter of preferably 28.5mm) on the top surface of the center of the generated aggregate mixture, moving the pressure head downwards at a constant speed, drawing a deformation stress diagram of the uniaxial penetration, and observing the critical load and the pressure head displacement at the breaking inflection point of the uniaxial penetration curve.
Further, in the step (4), the extracting coordination number and the contact ratio of the aggregate particles of each grade refers to judging object types at two ends of contact by traversing contact pointers in the whole model, counting the contact numbers of different contact objects before and after penetration, and calculating the average coordination number of the aggregate particles of each grade and the proportion of each important contact in all contacts based on the contact numbers.
Further, in the step (4), the extraction of the distribution and displacement conditions of the aggregate particle force chains of each grade means that, in a critical load point state of a single-axis penetration test of the aggregate mixture model, on one hand, all contact forces in the model are extracted by traversing contact pointers in the whole model and classified according to the integral level of absolute values of the contact forces, and the number of different force chains is counted and displayed in the model according to different colors; meanwhile, a program is written to extract the number of the medium-strength chains expanded at the tail end of the strong chain, and the probability of the medium-strength chain expanded at the tail end of the strong chain is calculated. On the other hand, the displacement of all aggregate particles in the model in the x direction, the y direction and the z direction is extracted, the displacement in the x direction and the y direction is synthesized into horizontal displacement, and the displacement conditions of the aggregate particles in the horizontal direction and the vertical direction are observed; and synthesizing the displacement in the horizontal direction and the vertical direction, and observing the total displacement condition of the aggregate particles.
Further, in the step (4), the skeleton structure visualization means that a contact force chain network is displayed in PFC3D software, and after a weak force chain is displayed in a shielding manner, the remaining force chain network can be regarded as a concrete representation of the skeleton structure.
Further, in the step (5), the selection of the group with the best overall mechanical property as the design grading refers to that the grading has a large uniaxial penetration critical load value and a large corresponding indenter displacement, the aggregate coordination number of the important part of the skeleton is in a reasonable range (for example, under a PAC-13 spherical particle model, the 9.5mm grade aggregate coordination number is between 7 and 8, the 4.75mm grade aggregate coordination number is between 3 and 4), the important contact proportion is large (for example, the contact between the 9.5mm grade and the 4.75mm grade aggregate), the proportion of the strong chain and the medium-strong chain is large, the probability of the medium-strong chain expanding at the end of the strong chain is large, the vertical displacement is small, and the total displacement is small.
Has the advantages that: according to the invention, a series of microscopic indexes related to the graded framework structure are obtained through a discrete element virtual test, important indexes such as the bearing capacity, coordination number, contact proportion, force chain network and displacement condition of the aggregate framework structure are comprehensively considered, the visualization of the framework structure is realized, the states of the framework structures under different grades can be visually observed, technical personnel are allowed to analyze and evaluate the current graded framework and make adjustment and selection in the design stage, the manpower, material resources and time consumed by an indoor test are saved, the problems of framework structure loss and low bearing capacity caused by the fact that the porosity is only concerned and the optimization of coarse aggregate composition is neglected in the graded design of the current drainage asphalt mixture are solved, and a guide and reference basis is provided for the graded design of the drainage asphalt mixture.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a diagram of a process for producing a coarse aggregate mixture;
FIG. 3 is a deformation stress diagram for a virtual uniaxial penetration test;
figure 4 is a graph of the force chain network of the aggregate mixture under load.
Detailed Description
Example 1
As shown in fig. 1, the method for optimally designing a drainage asphalt mixture based on a composition mechanism of the embodiment includes the following steps:
(1) three groups of coarse aggregates are prepared according to the aggregate raw materials to form different PAC grades: under the condition that the content of the coarse aggregates is not changed, namely the passing rate of a sieve pore of 2.36mm is not changed, the relative content of the aggregates of each grade of the coarse aggregates is adjusted.
(2) Generating a coarse aggregate mixture discrete element model with the particle size of more than 2.36mm according to trial gradation: calculating the number of aggregate particles of each grade required to be generated; generating a virtual mold; in order to ensure the compaction quality, the aggregate particles are generated in three batches, and first batch of aggregate particles are generated; applying gravity and vibration to the first batch of aggregate particles; placing a loading plate on top of the aggregate mixture; giving speed to the loading plate wall body to apply load; slowly moving the load plate upward until there is no contact with the aggregate mixture, slowly eliminating the unbalanced forces between the particles; removing the loading plate; generating a second batch of aggregate particles based on the first batch of compacted aggregate; repeating the steps to complete the generation, falling, vibration, compaction and stabilization of the second batch of aggregate and the third batch of aggregate. The process of creating a coarse aggregate mixture is shown in fig. 2, wherein (a) a virtual mold is created; (b) generating a first batch of aggregate; (c) applying gravity to the first batch of aggregate; (d) applying vibration to the first batch of aggregate (e) placing a loading plate on top of the aggregate (f) and compacting to a specified height; (g) slowly moving the loading plate upwards; (h) removing the loading plate and standing; (i) a second batch of aggregate is generated.
(3) Carrying out virtual single-axis penetration test, acquiring critical load and pressure head displacement according to a single-axis penetration deformation stress diagram: a cylindrical indenter having a diameter of 28.5mm was placed on the central top surface of the resulting aggregate mixture, the indenter was moved downward at a constant rate, a deformation stress map of uniaxial penetration was plotted, and the critical load and indenter displacement at the failure inflection point of the uniaxial penetration curve were observed as shown in fig. 3.
(4) Extracting coordination number, contact ratio, force chain distribution and displacement conditions of each grade of aggregate particles at a critical load point, and visualizing a skeleton structure: firstly, extracting coordination numbers and contact ratios of aggregate particles of all grades, namely, judging object types at two ends of contact by traversing contact pointers in the whole model, counting the contact numbers of different contact objects before and after penetration, and calculating the average coordination number of the aggregate particles of all grades and the proportion of all important contacts in all contacts based on the contact numbers; secondly, under the critical load point state of the single-axis penetration test of the aggregate mixture model, on one hand, all contact forces in the model are extracted by traversing contact pointers in the whole model, classification is carried out according to the integral level of the absolute value of the contact forces, the number of different force chains is counted and displayed in the model according to different colors; meanwhile, a program is written to extract the number of the medium-strength chains expanded at the tail end of the strong chain, and the probability of the medium-strength chain expanded at the tail end of the strong chain is calculated. On the other hand, the displacement of all aggregate particles in the model in the x direction, the y direction and the z direction is extracted, the displacement in the x direction and the y direction is synthesized into horizontal displacement, and the displacement conditions of the aggregate particles in the horizontal direction and the vertical direction are observed; synthesizing the displacement in the horizontal direction and the vertical direction, and observing the total displacement condition of the aggregate particles; thirdly, displaying a contact force chain network in PFC3D software, and after shielding and displaying a weak force chain, regarding the rest force chain network as the concrete representation of a skeleton structure, as shown in fig. 4, wherein (a) a strong force chain + a medium strong force chain network and (b) all force chain networks.
(5) Comprehensively comparing each skeleton mesoscopic index of three grading schemes, selecting a group with the best overall mechanical property as a coarse aggregate part of design grading: the single-shaft penetration critical load value of the grading is large, the displacement of a corresponding pressure head is large, the aggregate coordination number of an important part of a framework is in a reasonable range (for example, under a PAC-13 spherical particle model, the 9.5mm grade aggregate coordination number is between 7 and 8, and the 4.75mm grade aggregate coordination number is between 3 and 4), the important contact proportion is large (for example, the contact between 9.5mm grade and 4.75mm grade aggregates), the proportion of a strong chain and a medium-strength chain is large, the probability of the medium-strength chain expanding at the tail end of the strong chain is large, the vertical displacement is small, and the total displacement is small.

Claims (7)

1. A drainage asphalt mixture gradation design method based on a virtual test is characterized by comprising the following steps: the method comprises the following steps:
(1) trial preparing three groups of coarse aggregates to form different PAC grades according to the aggregate raw materials;
(2) generating a coarse aggregate mixture discrete element model with the particle size of more than 2.36mm according to trial gradation;
(3) performing a virtual uniaxial penetration test, and acquiring critical load and pressure head displacement according to a uniaxial penetration deformation stress diagram;
(4) extracting coordination numbers, contact ratios, force chain distribution and displacement conditions of all grades of aggregate particles at a critical load point, and visualizing a skeleton structure;
(5) comprehensively comparing each skeleton mesoscopic index of the three groups of grading schemes, and selecting one group with the best overall mechanical property as the coarse aggregate part of the design grading.
2. The drainage asphalt mixture gradation design method based on the virtual test according to claim 1, characterized in that: in the trial preparation method in the step (1), under the condition that the content of the coarse aggregates is not changed, namely the passing rate of the 2.36mm sieve holes is not changed, the relative content of each grade of aggregates of the coarse aggregates is adjusted.
3. The drainage asphalt mixture gradation design method based on the virtual test according to claim 1, characterized in that: the generation method of the discrete element model in the step (2) comprises the steps of calculating the number of aggregate particles of each grade required to be generated; generating a virtual mold; in order to ensure the compaction quality, the aggregate particles are generated in three batches, and first batch of aggregate particles are generated; applying gravity and vibration to the first batch of aggregate particles; placing a loading plate on top of the aggregate mixture; giving speed to the loading plate wall body to apply load; slowly moving the load plate upward until there is no contact with the aggregate mixture, slowly eliminating the unbalanced forces between the particles; removing the loading plate; generating a second batch of aggregate particles based on the first batch of compacted aggregate; repeating the steps to complete the generation, falling, vibration, compaction and stabilization of the second batch of aggregate and the third batch of aggregate.
4. The drainage asphalt mixture gradation design method based on the virtual test according to claim 1, characterized in that: and (4) performing a virtual uniaxial penetration test in the step (3) means that a cylindrical pressure head is arranged on the top surface of the center of the generated aggregate mixture, the pressure head moves downwards at a constant speed, a deformation stress diagram of uniaxial penetration is drawn, and the critical load and the pressure head displacement at the damage inflection point of the uniaxial penetration curve are observed.
5. The drainage asphalt mixture gradation design method based on the virtual test according to claim 1, characterized in that: the step (4) of extracting the coordination number and the contact proportion of the aggregate particles of each grade refers to the steps of judging the object types at two ends of contact by traversing the contact pointers in the whole model, counting the contact numbers of different contact objects before and after penetration, and calculating the average coordination number of the aggregate particles of each grade and the proportion of each important contact in all contacts based on the contact numbers.
6. The drainage asphalt mixture gradation design method based on the virtual test according to claim 1, characterized in that: the extraction of the distribution and displacement conditions of the aggregate particle force chains of each grade in the step (4) refers to that under the critical load point state of the aggregate mixture model single-axis penetration test, on one hand, all contact forces in the model are extracted by traversing the contact pointers in the whole model and classified according to the integral level of the absolute value of the contact forces, and the number of different force chains is counted and displayed in the model according to different colors; meanwhile, a program is written to extract the number of the medium-strength chains expanded at the tail end of the strong chain, and the probability of the medium-strength chain expanded at the tail end of the strong chain is calculated. On the other hand, the displacement of all aggregate particles in the model in the x direction, the y direction and the z direction is extracted, the displacement in the x direction and the y direction is synthesized into horizontal displacement, and the displacement conditions of the aggregate particles in the horizontal direction and the vertical direction are observed; and synthesizing the displacement in the horizontal direction and the vertical direction, and observing the total displacement condition of the aggregate particles.
7. The drainage asphalt mixture gradation design method based on the virtual test according to claim 1, characterized in that: the skeleton structure visualization in the step (4) is to display a contact force chain network in PFC3D software, and after the weak force chain is displayed in a shielding manner, the rest force chain network can be regarded as the concrete representation of the skeleton structure.
CN202010606996.6A 2020-06-29 2020-06-29 Drainage asphalt mixture gradation design method based on virtual test Pending CN111680373A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113434933A (en) * 2021-06-25 2021-09-24 长安大学 Simulation analysis method for breakage of microcapsules in asphalt mixture mixing process

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106950120A (en) * 2017-02-16 2017-07-14 浙江大学 A kind of asphalt mixture gradation optimization method under virtual state
CN107014679A (en) * 2017-03-13 2017-08-04 东南大学 A kind of evaluation method of asphalt frame strength
CN109030246A (en) * 2018-06-07 2018-12-18 南京工程学院 A kind of virtual reloading creep test method of asphalt
CN109279818A (en) * 2018-11-23 2019-01-29 佛山科学技术学院 A method of index Design framework compact type asphalt mixture is seen based on thin
CN110331632A (en) * 2019-06-27 2019-10-15 东南大学 A kind of method that limestone is used for double-layer drainage sub-surface structure

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106950120A (en) * 2017-02-16 2017-07-14 浙江大学 A kind of asphalt mixture gradation optimization method under virtual state
CN107014679A (en) * 2017-03-13 2017-08-04 东南大学 A kind of evaluation method of asphalt frame strength
CN109030246A (en) * 2018-06-07 2018-12-18 南京工程学院 A kind of virtual reloading creep test method of asphalt
CN109279818A (en) * 2018-11-23 2019-01-29 佛山科学技术学院 A method of index Design framework compact type asphalt mixture is seen based on thin
CN110331632A (en) * 2019-06-27 2019-10-15 东南大学 A kind of method that limestone is used for double-layer drainage sub-surface structure

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113434933A (en) * 2021-06-25 2021-09-24 长安大学 Simulation analysis method for breakage of microcapsules in asphalt mixture mixing process

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Application publication date: 20200918