CN112528470B - Coarse aggregate composite geometric feature calculation model of particle system and establishment method thereof - Google Patents
Coarse aggregate composite geometric feature calculation model of particle system and establishment method thereof Download PDFInfo
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Abstract
The invention discloses a particle system coarse aggregate composite geometric feature calculation model and a method for establishing the calculation model, which comprises the following steps: s1, screening aggregates into aggregates of different grades to obtain a grading particle system; s2, measuring sphericity, texture index and edge angle gradient of single-grade aggregate based on an AIMSII system; s3, spreading the shape, texture and edges of each grade of coarse aggregate respectively, and then recombining the coarse aggregate into a one-dimensional straight line, a two-dimensional plane and a three-dimensional structure; s4, calculating according to the mesh size to obtain the average particle size of each grade of aggregate; s5, calculating a one-dimensional weighted perimeter, a two-dimensional weighted surface area and a three-dimensional weighted volume, and combining the calculated average particle size and geometric indexes to construct a calculation model. The calculation model provided by the invention is based on an AIMSII system, and the composite geometric index under each grading can be accurately calculated only by inputting the mass fraction of each grade of aggregate.
Description
Technical Field
The invention belongs to the technical field of road engineering, and particularly relates to a particle system coarse aggregate composite geometric feature calculation model and an establishment method thereof.
Background
In asphalt mixtures, the volume of mineral aggregate is about 90% of the total volume. The rock quality, geometric characteristics and particle size of the mineral aggregate determine the contact state, friction characteristics and migration mechanism of mineral aggregate particles, so that the road performance of the asphalt mixture is affected. According to three types of macroscopic, microscopic and microscopic scales. The geometric characteristics of the particles can be divided into three layers, namely a shape dimension, an angular dimension and a texture dimension.
Krumbein proposes to evaluate the three-dimensional shape characteristics of particles in terms of sphericity and roundness. Wang et al used fourier morphology to quantify the shape, angularity and texture of the aggregate. Li recommends evaluating the shape characteristics of coarse aggregates using the flatness-elongation coefficient (FEC) and evaluating the angularity using the particle index. Sun Yangyong the surface micro-texture characteristics of coarse aggregates are studied by adopting a fractal theory. The Zhu calculates the angular index of the coarse aggregate by adopting a compression method and an ellipsometry, realizes the independent characterization of the angular property and improves the measurement precision. Massd researches the relation between the surface parameters and the edges and textures of fine aggregates through an image analysis technology, and proposes to measure the edges and the textures of the surface by adopting a low-resolution image and a high-resolution image. Xie measures the shape, angle and texture index of the fine aggregate by Digital Image Processing (DIP), and it is considered that selecting particles with a particle size of 0.6mm explores the morphological characteristics of the fine aggregate more representatively. Gao proposed a three-dimensional angular index (3 DA) based on X-ray tomography, and researches show that the angular character of coarse aggregates has a significant influence on the framework structure of asphalt mixtures. The Masad analyzes the differences of the shapes and the angularity among different aggregates through a clustering statistical method, and the AIMS is considered to be capable of accurately measuring the morphological parameters of the aggregates. Wang measured the angular index, sphericity, flatness and elongation of coarse aggregate using AMIS system, found that the particle size of coarse aggregate did not greatly affect the angular index, but the shape of the particles was increasingly approaching cubes against the increase in particle size. Ding adopts a Discrete Element Method (DEM) and combines a digital image processing technology to provide a coarse aggregate modeling method based on particle morphological characteristics.
In order to reduce pavement diseases and improve durability, students at home and abroad develop a large number of experiments to explore the influence of aggregate geometric features on the road performance of the mixture. The geometrical characteristics of aggregate particles are tested by using an AIMS system, and the study shows that the larger the edge angle of the aggregate is, the better the adhesiveness between the aggregate and asphalt is, and the optimal edge angle and sphericity value exist to maximize the Marshall stability of the asphalt mixture. Liu adopts an FTI image acquisition system to obtain grains, edges and corners and sphericity indexes of aggregate particles, and researches show that the fatigue resistance of the SMA asphalt mixture can be effectively improved by increasing the sphericity and reducing the content of needle-shaped aggregates. Arasan found that the morphology of the aggregate significantly affected the volume index of the asphalt mix. Flat, elongated aggregates can reduce marshall stability; the higher the content of particles with a shape close to a sphere and no roughness on the surface, the smaller the flow value of the asphalt mixture. Li adopts Flatness (FER), angular Index (AI) and Surface Roughness (SR) to represent the shape, angular property and surface texture of the coarse aggregate, and explores the relationship between the morphological index of the coarse aggregate and the mechanical property of cement concrete. It was found that the split tensile and compressive strength of concrete increased with increasing SR, but decreased significantly with increasing FER or AI. The elastic modulus and poisson's ratio both decrease slightly with increasing FER or AI, but increase with increasing SR. Yang investigated the effect of coarse aggregate shape and angularity on asphalt mix creep deformation dynamic modulus. Aggregates with a larger shape index and smaller corners increase creep deformation and reduce dynamic modulus. Cheng uses roundness, perimeter index and erosion expansion area ratio to evaluate the morphological characteristics of coarse and fine aggregates and the influence of the morphological characteristics on the high and low temperature viscoelastic properties of asphalt mixtures. The morphological index of the fine aggregate has better correlation with the viscoelasticity parameter. Kuang analysis found that the average angular coefficient was positively correlated with good linearity of the dynamic stability and tensile split ratio of the asphalt mix, and negatively correlated with the low temperature flexural tensile strength. Gao explored the effect of the angular character of coarse aggregates on asphalt mix compaction characteristics and skid resistance. The more angular the aggregate is, the harder the asphalt mixture is compacted, but the skid resistance is improved.
Asphalt mixtures are multiphase particulate mineral aggregate/asphalt systems composed of an asphalt binder, a particulate system, and voids, wherein the particulate system is composed of a series of aggregate particles of different particle sizes. The scholars at home and abroad mainly develop researches on the measurement method of aggregate geometric features and the influence of partial aggregate geometric features on the performance of asphalt mixtures, but lack deep discussion on the composite geometric features of graded mineral aggregates, the relation between the composite geometric features and the contact characteristics of a particle system and the action mechanism at a mineral aggregate/asphalt system interface.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a particle system coarse aggregate composite geometric feature calculation model and an establishment method thereof.
The first object of the invention is to provide a particle system coarse aggregate composite geometric feature calculation model, which is:
wherein: the geometric index refers to sphericity, surface texture index or angular gradient of the shape index, and the indexes can be obtained by directly testing the shape index by using a AIMSII system.
Preferably, the composite geometry index of the particulate system coarse aggregate refers to a composite shape index, a composite texture index or a composite angular index, a composite shape index (CI SP ) Composite texture index (CI) TX ) And composite angular index (CI) GA ) Calculated according to the following formulas (1) - (3), respectively:
wherein: CI (CI) SP The composite shape index of coarse aggregate of the particle system; CI (CI) TX Is a particle systemUnifying the composite texture index of coarse aggregate; CI (CI) GA The composite edge angle index is the coarse aggregate of the particle system; m is the total mass of mineral aggregates; g i The volume relative density of the i-th grade aggregate; SPi is a granule sphericity index; GA (GA) i The edge angle gradient of the i-th coarse aggregate; TX (transmission x) i Texture index of the i-th coarse aggregate; a, a i The screen residue percentage is calculated for the i-th grade aggregate in the grading design; c (C) wi The weighted perimeter of the aggregate particle shape is obtained by the formula (4); v (V) wi A weighted volume for the aggregate particle shape, obtained by equation (5); SA (SA) wi The weighted surface area for the aggregate particle shape is obtained by equation (6); d, d i The average particle diameter of the ith grade aggregate is obtained by a formula (7);
C Wi ＝C ci ×SP i +C si ×(1-SP i ) (4)
V Wi ＝V ci ×SP i +V si ×(1-SP i ) (5)
SA Wi ＝SA ci ×SP i +SA si ×(1-SP i ) (6)
wherein: c (C) ci Is a cubic perimeter; c (C) si Is the circumference of the sphere; v (V) si Calculated volume for sphere; v (V) ci A calculated volume that is a cube; SA (SA) si Calculating a surface area for the sphere; SA (SA) ci Calculating a surface area for the cube; p (P) i+1 Is the mesh size of the i+1 th gear.
The second object of the invention is to provide a method for establishing a particle system coarse aggregate composite geometric feature calculation model, which comprises the following steps:
s1, screening aggregates into aggregates of different grades to obtain a grading particle system;
s2, measuring sphericity, texture index and edge angle gradient of single-grade aggregate in the grading particle system obtained in the S1 based on the AIMSII system to obtain geometric indexes of the single-grain-size particle system in the grading particle system;
s3, spreading the shape, texture and edges of each grade of coarse aggregate in the grading particle system obtained in the S1 respectively, and then recombining the coarse aggregate into a one-dimensional straight line, a two-dimensional plane and a three-dimensional structure, wherein the measures corresponding to the shape, texture and edges of the coarse aggregate are determined to be perimeter, surface area and volume respectively;
s4, calculating according to the mesh size to obtain the average particle size of each grade of aggregate;
and S5, constructing and obtaining the particle system coarse aggregate composite geometric feature calculation model by calculating the one-dimensional weighted perimeter, the two-dimensional weighted surface area and the three-dimensional weighted volume obtained in the step S3 and combining the average particle size obtained by the calculation in the step S4 and the geometric index obtained in the step S2.
Preferably, in step S1, the aggregate is screened according to the size of the particle size.
Preferably, in step S2, the AIMSII system measures sphericity, texture index and angular gradient of the single-grade aggregate, and the measurement steps are as follows:
s21, placing single-grade test aggregate particles one by one through a circular tray, and transferring the single-grade test aggregate particles into an imaging range;
s22, projecting and displaying particle contours through a backlight illumination system, acquiring particle contour images through a high-resolution camera, and calculating the acquired particle contour images through a connected computer to obtain the sphericity and the angular gradient of the shape index of the single-grade aggregate;
s23, acquiring an aggregate surface texture image through a top illumination system and a multi-magnification microscope, and calculating the acquired surface texture image through a connected computer to obtain the texture index of the single-grade aggregate.
Compared with the prior art, the invention has the beneficial effects that:
the invention unifies the geometric form and the particle size distribution of coarse particles in a particle system by considering the influence of the particle size of the particles on the geometric form expression capability; the spreading-recombination principle is put forward to construct a composite shape index, a composite texture index and a composite texture index calculation model. The calculation model provided by the invention is based on the AIMSII system, and the composite geometric index under each grading can be accurately calculated only by inputting the mass fraction of each grade of aggregate, so that the influence of any grade of aggregate on the contact characteristic of the particle system can be obtained.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 is a one-dimensional spreading-reconstruction of the shape of particles provided by the present invention;
FIG. 2 is a two-dimensional spreading-reconstruction of the shape of particles provided by the present invention;
FIG. 3 is a three-dimensional spreading-reconstruction of the particle shape provided by the present invention;
fig. 4 is a grading graph provided by the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. The test methods in the following examples, in which specific conditions are not noted, are generally conducted under conventional conditions or under conditions recommended by the respective manufacturers.
Example 1
The particle system coarse aggregate composite geometric feature calculation model provided by the embodiment of the invention specifically comprises the following steps:
wherein: the geometric index refers to sphericity, surface texture index or angular gradient of the shape index, and the indexes can be obtained by directly testing the shape index by using a AIMSII system.
The composite geometry index of the coarse aggregate of the particle system refers to a composite shape index, a composite texture index or a composite angle index, and depends on the relative density, the particle volume and the particle surface area size of the coarse aggregate used in the design, and is influenced by the sphericity index of the aggregate particles, the composite shape index (CI SP ) Composite texture index (CI) TX ) And composite angular index (CI) GA ) Calculated according to the following formulas (1) - (3):
wherein: CI (CI) SP The composite shape index of coarse aggregate of the particle system; CI (CI) TX The composite texture index of coarse aggregate of the particle system; CI (CI) GA The composite edge angle index is the coarse aggregate of the particle system; m is the total mass of mineral aggregates; g i The volume relative density of the i-th grade aggregate; SPi is a granule sphericity index; GA (GA) i The edge angle gradient of the i-th coarse aggregate; TX (transmission x) i Texture index of the i-th coarse aggregate; a, a i The screen residue percentage is calculated for the i-th grade aggregate in the grading design; c (C) wi The weighted perimeter of the aggregate particle shape is obtained by the formula (4); v (V) wi A weighted volume for the aggregate particle shape, obtained by equation (5); SA (SA) wi The weighted surface area for the aggregate particle shape is obtained by equation (6); d, d i The average particle diameter of the ith grade aggregate is obtained by a formula (7);
C Wi ＝C ci ×SP i +C si ×(1-SP i ) (4)
V Wi ＝V ci ×SP i +V si ×(1-SP i ) (5)
SA Wi ＝SA ci ×SP i +SA si ×(1-SP i ) (6)
wherein: c (C) ci Is a cubic perimeter; c (C) si Is the circumference of the sphere; v (V) si Calculated volume for sphere; v (V) ci A calculated volume that is a cube; SA (SA) si Calculating a surface area for the sphere; SA (SA) ci Calculating a surface area for the cube; p (P) i+1 Is the mesh size of the i+1 th gear.
The method for establishing the particle system coarse aggregate composite geometric feature calculation model specifically comprises the following steps:
s1, screening aggregates into aggregates with different grades, wherein the aggregate screening is to screen the aggregates according to the particle size to obtain a grading particle system;
s2, acquiring sphericity, texture index and edge angle gradient of single-grade aggregates with the diameter of more than 4.75mm in the grading particle system obtained in S1 through a high-resolution camera and a multi-magnification microscope based on the AIMSII system to obtain geometric indexes of the single-grain-diameter particle system in the grading particle system, and measuring the sphericity, texture index and edge angle gradient of the single-grade aggregates by utilizing the AIMSII system, wherein the specific measurement steps are as follows:
s21, placing single-grade test aggregate particles one by one through a circular tray, and transferring the single-grade test aggregate particles into an imaging range;
s22, projecting and displaying particle contours through a backlight illumination system, acquiring particle contour images through a high-resolution camera, and calculating the acquired particle contour images through a connected computer to obtain the sphericity and the angular gradient of the shape index of the single-grade aggregate;
s23, acquiring an aggregate surface texture image through a top illumination system and a multi-magnification microscope, and calculating the acquired surface texture image through a connected computer to obtain the texture index of the single-grade aggregate.
S3, spreading the shape, texture and edges of each grade of coarse aggregate in the grading particle system obtained in the S1 respectively, and then recombining the coarse aggregate into a one-dimensional straight line, a two-dimensional plane and a three-dimensional structure, wherein the measures corresponding to the shape, texture and edges of the coarse aggregate are determined to be perimeter, surface area and volume respectively;
s4, calculating according to the mesh size to obtain the average particle size of each grade of aggregate;
and S5, constructing and obtaining the particle system coarse aggregate composite geometric feature calculation model by calculating the one-dimensional weighted perimeter, the two-dimensional weighted surface area and the three-dimensional weighted volume obtained in the step S3 and combining the average particle size obtained by the calculation in the step S4 and the geometric index obtained in the step S2.
In the step S3 of the embodiment 1 of the invention, a one-dimensional linear structure obtained by recombination is paved, as shown in figure 1, and each length in figure 1 is represented by a first-grade coarse aggregate; in step S3 of embodiment 1 of the present invention, two-dimensional planar and three-dimensional structures obtained by recombination are laid out, as shown in fig. 2 and 3.
The following further describes the calculation model and the establishment method provided in embodiment 1 of the present invention through experimental tests, and specific experimental steps are as follows:
step 1: selecting raw materials and mineral aggregate grading
The test adopts limestone in a certain place of Shaanxi, main technical indexes of coarse aggregates and fine aggregates are measured according to the specification of the highway engineering aggregate test procedure (JTGE 42-2005), and the corresponding technical indexes of materials are recorded through the test, as shown in tables 1-2.
TABLE 1 main technical index of coarse aggregate
TABLE 2 main technical index of fine aggregate
The AC upper limit grading recommended in the Highway asphalt pavement construction technical specification (JTGF 40-2004) is selected, a grading curve is shown in fig. 4, and the larger the maximum nominal particle size of coarse aggregate is, the lower the grading curve is, namely the larger the coarse aggregate ratio in the grading system is, and the larger the number of large-particle-size particles is, so that the stability of asphalt mixture provided by an aggregate embedding skeleton is facilitated.
Step 2: aggregate composite geometry index calculation
The composite geometric feature calculation model provided in the embodiment 1 of the present invention calculates the composite shape index, the composite texture index and the composite edge angle index of aggregates with different nominal maximum particle diameters respectively, and the calculation results are shown in the following tables 2 to 4.
TABLE 3 composite shape index of aggregates of different particle sizes
| 10 | 13 | 16 | 20 | |
| AC-S | 0.002369 | 0.003048 | 0.004018 | 0.004264 |
TABLE 4 composite texture index for aggregates of different particle sizes
| 10 | 13 | 16 | 20 | |
| AC-S | 72.12539 | 113.1391 | 154.5121 | 188.032 |
TABLE 5 composite angular index for aggregates of different particle sizes
| 10 | 13 | 16 | 20 | |
| AC-S | 6698.868 | 10452.55 | 13372.79 | 17297.72 |
Step 3: evaluation and effectiveness verification of composite geometric characteristics of particle system
As can be seen from tables 3 to 5, for the AC-class grading upper limit, the composite shape index, the composite texture index, and the composite angular index of the AC-S particle system all tended to increase with increasing nominal maximum particle size (NMAS). The larger the maximum nominal particle diameter is, the more the shape of the particle system is close to a cube, the coarser the texture surface is, the stronger the angularity is, which is obviously more favorable for forming embedded friction among particles, thereby being more favorable for the contact friction characteristic of asphalt mixture; the larger the maximum nominal particle size is, the lower the grading curve is, which means that the coarse aggregate ratio in the grading system is larger, thus being more beneficial to the aggregate embedding and extrusion to form a framework to provide the stability of asphalt mixture. As is well known in the art, the shape, texture and edges and corners are external expression forms of particles, the particle system is under the action of external force, the edges and corners of internal coarse particles are mutually contacted, the surface textures are mutually rubbed, a framework structure is formed, and the shape of the particles influences the stability of the framework structure by influencing the self moment of inertia.
In the invention, the shape of coarse aggregates in a particle system is spread and recombined to obtain a one-dimensional straight line, the total length of the straight line is the product of the number of particles and the corresponding circumference, the circumferences of aggregates in each stage are not greatly different and are mainly influenced by the number of particles; the texture is distributed on the surface of the aggregate particles, the composite texture index constructed after spreading and recombination is a two-dimensional plane index, and compared with the one-dimensional perimeter, the difference between the two-dimensional areas of the coarse aggregate particles is increased, and the difference between the two-dimensional areas of the fine aggregate particles is reduced, so that the influence of the particle size of the coarse aggregate on the composite texture index is increased to a certain extent, and the influence of the number of the fine aggregates is weakened. The composite angular index is a three-dimensional index, and reflects the comprehensive effect of coarse aggregate angles with different expressive power on the contact strength of a particle system, and the difference between aggregate volumes with different particle sizes is further amplified or reduced, so that the smaller the particle size of the aggregate, the smaller the influence of the quantity of the aggregate; conversely, the larger the particle size of the aggregate, the greater the effect of its quantity. The larger NMAS, the greater the amount of coarse aggregate and the smaller the amount of fine aggregate in the particle system, so the composite shape index, composite texture index, composite angular index gradually increase, which means that the more intense the contact friction effect between particles. Therefore, the conclusion obtained by calculation of the calculation model of the invention is basically consistent with the conclusion acknowledged in the prior study and practical application, namely, the greater the nominal maximum particle size is, the greater the inter-particle embedding friction strength is.
In summary, it is feasible to evaluate the comprehensive geometry of coarse aggregates and the contact friction effect between particles in the particle system by using the particle system coarse aggregate composite geometry calculation model provided by the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (3)
1. The method for establishing the particle system coarse aggregate composite geometric feature calculation model is characterized in that the calculation model is as follows:
wherein: the geometric index refers to the sphericity of the shape index, the surface texture index or the angular gradient;
the composite geometric index of the particulate system coarse aggregate refers to a composite shape index, a composite texture index, or a composite angular index, and the composite shape index (CI SP ) Composite texture index (CI) TX ) And composite angular index (CI) GA ) Calculated according to the following formulas (1) - (3), respectively:
wherein: CI (CI) SP The composite shape index of coarse aggregate of the particle system; CI (CI) TX The composite texture index of coarse aggregate of the particle system; CI (CI) GA The composite edge angle index is the coarse aggregate of the particle system; m is the total mass of mineral aggregates; g i The volume relative density of the i-th grade aggregate; the SPi is the sphericity index of the i-th coarse aggregate particles; GA (GA) i The edge angle gradient of the i-th coarse aggregate; TX (transmission x) i Texture index of the i-th coarse aggregate; a, a i The screen residue percentage is calculated for the i-th grade aggregate in the grading design; c (C) wi The weighted perimeter of the particle shape of the i-th-level aggregate is obtained by a formula (4); v (V) wi The weighted volume for the i-th grade aggregate particle shape is obtained by the formula (5); SA (SA) wi The weighted surface area for the i-th order aggregate particle shape is obtained by equation (6); d, d i The average particle diameter of the ith grade aggregate is obtained by a formula (7);
C Wi ＝C ci ×SP i +C si ×(1-SP i ) (4)
V Wi ＝V ci ×SP i +V si ×(1-SP i ) (5)
SA Wi ＝SA ci ×SP i +SA si ×(1-SP i ) (6)
wherein: c (C) ci Is a cubic perimeter; c (C) si Is the circumference of the sphere; v (V) si Calculated volume for sphere; v (V) ci A calculated volume that is a cube; SA (SA) si Calculating a surface area for the sphere; SA (SA) ci Calculating a surface area for the cube; p (P) i+1 Is the mesh size of the i+1st gear;
the method for establishing the calculation model comprises the following steps:
s1, screening aggregates into aggregates of different grades to obtain a grading particle system;
s2, measuring sphericity, texture index and edge angle gradient of single-grade aggregate in the grading particle system obtained in the S1 based on the AIMSII system to obtain geometric indexes of the single-grain-size particle system in the grading particle system;
s3, spreading the shape, texture and edges of each grade of coarse aggregate in the grading particle system obtained in the S1 respectively, and then recombining the coarse aggregate into a one-dimensional straight line, a two-dimensional plane and a three-dimensional structure, wherein the measures corresponding to the shape, texture and edges of the coarse aggregate are determined to be perimeter, surface area and volume respectively;
s4, calculating according to the mesh size to obtain the average particle size of each grade of aggregate;
and S5, constructing and obtaining the particle system coarse aggregate composite geometric feature calculation model by calculating the one-dimensional weighted perimeter, the two-dimensional weighted surface area and the three-dimensional weighted volume obtained in the step S3 and combining the average particle size obtained in the step S4 and the geometric index obtained in the step S2.
2. The method for building a composite geometric feature calculation model of coarse aggregate in a particle system according to claim 1, wherein in step S1, the aggregate is screened according to the size of the particle size.
3. The method for building a composite geometric feature calculation model of coarse aggregate in a particle system according to claim 1, wherein in step S2, the AIMSII system measures sphericity, texture index and angular gradient of single-grade aggregate, and the measurement steps are as follows:
s21, placing single-grade test aggregate particles one by one through a circular tray, and transferring the single-grade test aggregate particles into an imaging range;
s22, projecting and displaying particle contours through a backlight illumination system, acquiring particle contour images through a high-resolution camera, and calculating the acquired particle contour images through a connected computer to obtain the sphericity and the angular gradient of the shape index of the single-grade aggregate;
s23, acquiring an aggregate surface texture image through a top illumination system and a multi-magnification microscope, and calculating the acquired surface texture image through a connected computer to obtain the texture index of the single-grade aggregate.
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