A method for evaluating uniformity of recycled asphalt mixture based on CT and three-dimensional division

Abstract

This invention discloses a method for evaluating the uniformity of recycled asphalt mixtures based on CT and 3D partitioning, belonging to the field of recycled asphalt mixture uniformity testing. The evaluation method uses CT technology to construct a 3D model of the recycled asphalt mixture; identifies each component of the 3D model; extracts a cubic region from the 3D model and divides this cubic region into several areas; counts the volume of new and old asphalt binder in each area, and calculates the uniformity coefficient M of the new and old asphalt binder. i ; Calculate M in different regions i The standard deviation and coefficient of variation are used to evaluate the uniformity of the distribution of new and old asphalt binders throughout the specimen. This invention overcomes the shortcomings of current two-dimensional evaluation methods, which fragment the integrity of the mixture and have large calculation errors, and is used for refined characterization of the uniformity of recycled asphalt mixtures. This invention solves the problem that it is currently impossible to characterize the uniformity of new and old asphalt binders, and contributes to in-depth research on the clumping phenomenon of recycled asphalt mixtures.

Description

Technical Field

[0001] This invention belongs to the field of uniformity testing of recycled asphalt mixtures, and specifically relates to a method for evaluating the uniformity of recycled asphalt mixtures based on CT and three-dimensional segmentation. Background Technology

[0002] With the rapid development of my country's economy, the development of highways nationwide has long since shifted from "construction-oriented" to "construction and maintenance in tandem." Many highways built in the early stages can no longer meet the demands of current high traffic volume and heavy-duty traffic, facing issues such as reconstruction, expansion, and upgrading. Large-scale road renovation and reconstruction inevitably generate a large amount of road waste materials. Simply discarding these materials not only occupies a significant amount of space and land resources but also pollutes the surrounding environment. Furthermore, stone resources have gradually become strategic resources, and the imbalance between supply and demand has led to soaring stone prices. Therefore, asphalt pavement recycling technology is receiving increasing attention from scholars.

[0003] Recycled asphalt mixtures are mixtures obtained by pre-treating old asphalt pavement materials through crushing and screening, and then adding a certain proportion of new aggregates, mineral powder, new asphalt, and recycling agents. Studies have shown that inhomogeneity in recycled asphalt mixtures reduces the pavement's resistance to water damage, accelerates early pavement failure, and shortens its service life. Therefore, researching the homogeneity of recycled asphalt mixtures is of great significance.

[0004] At present, most studies on the internal structure uniformity of asphalt mixtures are based on CT scan slices, which has the following limitations: (1) There are many CT slices of the specimen, and it is necessary to calculate the cross-sectional evaluation index of many slices to evaluate the uniformity of the specimen, which is a complicated process; (2) There is a certain error in the calculation of the uniformity index of each cross section, which eventually produces a large cumulative error.

[0005] In recycled asphalt mixtures, clumping caused by the uneven distribution of new and old asphalt binders is the main factor contributing to the uneven distribution of new and old materials. However, current research on the homogeneity of asphalt mixtures mainly focuses on aggregate homogeneity, neglecting the homogeneity of asphalt binders, and therefore cannot adequately evaluate the homogeneity of new and old materials in recycled asphalt mixtures. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a method for evaluating the uniformity of recycled asphalt mixtures based on CT and three-dimensional segmentation.

[0007] The specific steps of this invention are as follows:

[0008] Step 1: Obtain cylindrical specimens of recycled asphalt mixture using an indoor molding method, scan them using a CT scanning device, and construct a three-dimensional visualization model of the scanned specimens;

[0009] Step 2: Perform digital image processing on the three-dimensional visualization model to identify the various components of the recycled asphalt mixture, including coarse aggregate, old asphalt mastic, new asphalt mastic, and voids.

[0010] Step 3: Using Mimics software, a cubic region is cut from the processed 3D specimen image, with the specimen's volume center as the cutting center, as the research object. This cube is further divided into m... 3 A grid of equal area;

[0011] Step 4: Calculate the volume of new and old asphalt mortar in each grid, and then calculate the ratio M of old asphalt mortar to all asphalt mortar in each grid based on the volume of new and old asphalt mortar. i M i The calculation formula is as shown in equation (1):

[0012]

[0013] In the formula: A Vi Let i be the volume of the new asphalt mortar within the i-th small cube.

[0014] 4 Ri Let i be the volume of the old asphalt mortar within the i-th small cube.

[0015] i is the grid number, i = 1, 2, 3, ... m 3

[0016] Step 5: Based on the proportion M of old asphalt mortar within each grid division... i Calculate m 3 M i The standard deviation (SD) and coefficient of variation (COV) are used as evaluation indicators of the uniformity of the distribution of new and old asphalt mortar within the entire three-dimensional specimen image. The calculation formulas are as shown in equations (2) to (4). The smaller the standard deviation and coefficient of variation, the better the uniformity of the mixture; conversely, the larger the standard deviation and coefficient of variation, the worse the uniformity of the mixture.

[0017]

[0018] In the formula: M within a single specimen i The overall mean.

[0019] Furthermore, the method for molding the cylindrical specimen of the recycled asphalt mixture includes the following steps:

[0020] Step A1. Add an appropriate amount of titanium dioxide powder to the old asphalt mortar to prepare waste asphalt mixture, wherein titanium dioxide is replaced by mineral powder by the same mass, and mineral powder is no longer used to prepare asphalt mixture;

[0021] Step A2. Waste asphalt mixture prepared from old asphalt mortar mixed with titanium dioxide powder is mixed with new aggregate and matrix asphalt in a fixed proportion to form recycled asphalt mixture specimens.

[0022] Furthermore, the cylindrical specimen in step 1 has dimensions of Φ101.6mm × 63.5mm.

[0023] Furthermore, the identification of each component of the recycled asphalt mixture involves determining a grayscale image threshold. The threshold determination method is the bimodal method, which includes the following steps:

[0024] Step B1. Qualitatively determine the composition of different materials based on the cross-sectional images;

[0025] Step B2. Read the CT value of the location of the component and preliminarily determine the CT value range of each component;

[0026] Step B3. Output the CT value histogram of the image using Mimics software;

[0027] Step B4. Repeatedly adjust the interval boundaries of the CT value of this component using the bimodal method;

[0028] Step B5. Determine the threshold for classifying coarse aggregate, new and old asphalt mortar, and voids in the CT image.

[0029] Furthermore, in step 3, the height of the cube should be less than the height of the specimen to eliminate errors caused by tilting the specimen during scanning and to ensure that the maximum inscribed cube size of different specimens is consistent.

[0030] Furthermore, the specific division of the cube image in step 3 is as follows: the side length m of the cube is divided into equal parts, with an average of m... 3 A small cube with equal length, width, and height.

[0031] Furthermore, in step 3, m ≥ 2.

[0032] Furthermore, the method for obtaining the cube study range and geometric center of each 3D visualization model in step 3, and for obtaining the horizontal and vertical coordinates of the m equal divisions in step 3, is as follows: the 3DProperties function in Mimics software is used to statistically analyze the dimensions of the 3D visualization model, and the crop mask function is used to cut the 3D visualization model and the cube.

[0033] Beneficial effects: This invention uses CT and three-dimensional image segmentation to evaluate the uniformity of the entire raw asphalt mixture specimen in three dimensions. Compared with the existing two-dimensional evaluation methods, it overcomes the shortcomings of the two-dimensional evaluation methods, such as the fragmentation of mixture integrity and large calculation errors.

[0034] This invention distinguishes between new and old asphalt mortars by replacing titanium dioxide with mineral powder of equal mass, and proposes an index for evaluating the uniformity of new and old asphalt mortars, thus solving the problem that existing evaluation methods cannot evaluate the uniformity of new and old asphalt mortars. Attached Figure Description

[0035] Figure 1 This is a flowchart of the method of the present invention;

[0036] Figure 2 This is the gradation curve diagram of this embodiment;

[0037] Figure 3 These are two-dimensional cross-sectional images of the recycled asphalt mixture in this embodiment, wherein (a) is an axial two-dimensional cross-sectional image and (b) is a radial two-dimensional cross-sectional image;

[0038] Figure 4 This is a three-dimensional visualization image of the specimen in this embodiment;

[0039] Figure 5 These are screenshots of the component division in this embodiment, where (a) is an image of coarse aggregate, (b) is an image of old asphalt mastic, (c) is an image of new asphalt mastic, (d) is an image of voids, and (e) is an overall three-dimensional image.

[0040] Figure 6 This is a schematic diagram of three-dimensional image cutting in this embodiment. Detailed Implementation

[0041] The implementation of the technical solution is described in further detail below. The following examples are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0042] This invention provides a method for evaluating the uniformity of recycled asphalt mixtures based on CT and three-dimensional segmentation. Figure 1 This is a flowchart of the method of the present invention, which includes the following steps:

[0043] Step 1: Ten types of recycled asphalt mixture cylindrical specimens were prepared using indoor molding methods, with aging times of 2 days and 4 days, and mixing times of 30s, 60s, 120s, 180s, and 240s. The cylindrical specimen dimensions were Φ101.6mm × 63.5mm. The composite gradation is shown in Table 1, and the gradation curve is shown in... Figure 2 As shown. The molding method for cylindrical specimens of recycled asphalt mixture includes the following steps:

[0044] Step A1. Add an appropriate amount of titanium dioxide powder to the old asphalt mortar to prepare waste asphalt mixture, wherein titanium dioxide is replaced by mineral powder by the same mass, and mineral powder is no longer used to prepare asphalt mixture;

[0045] Step A2. Waste asphalt mixture prepared from old asphalt mortar mixed with titanium dioxide powder is mixed with new aggregate and matrix asphalt in a fixed proportion to form recycled asphalt mixture specimens.

[0046] CT tomography was performed on the specimen to obtain two-dimensional cross-sectional images of the asphalt mixture in three mutually perpendicular directions in space, as shown below. Figure 3 As shown. The three-dimensional model of the specimen was reconstructed using Mimics software through volume rendering methods, as shown. Figure 4 .

[0047] Table 1. Synthetic Gradation of AC-13 Type Recycled Asphalt Mixture

[0048]

[0049] Step 2: Perform digital image processing on the 3D visualization model of the recycled asphalt mixture to identify its various components, including coarse aggregate, old asphalt binder, new asphalt binder, and voids. Figure 5 The image is divided into components: orange represents coarse aggregate components, green represents old asphalt mastic mixed with titanium dioxide, and blue represents new asphalt mastic. Voids are distinguished using pink. Identifying each component of the recycled asphalt mixture involves determining the grayscale image threshold, which is determined using the bimodal method. The specific operation of the bimodal method is as follows:

[0050] Step B1. Qualitatively determine the composition of different materials based on the cross-sectional images;

[0051] Step B2. Read the CT value of the location of the component and preliminarily determine the CT value range of each component;

[0052] Step B3. Output the CT value histogram of the image using Mimics software;

[0053] Step B4. Repeatedly adjust the interval boundaries of the CT value of this component using the bimodal method;

[0054] Step B5. Determine the threshold for classifying coarse aggregate, new and old asphalt mortar, and voids in the CT image.

[0055] The threshold values ​​of each component in the internal structure of recycled asphalt mixture are as follows: coarse aggregate CT value is 2546-3071HU, old asphalt mastic CT value is 2209-2296HU, new asphalt mastic CT value is 1638-2209HU, and void CT value is -1024-1200HU.

[0056] Step 3: Using Mimics software, the volume center of the specimen was used as the cutting center from the processed 3D specimen image. The 3D Properties function in Mimics was used to statistically analyze the dimensions of the 3D visualization model. A 60mm × 60mm × 60mm cube was cut from the specimen model as the research object. The crop mask function was then used to divide this cube into 8 equal-area grids. A cutting diagram is shown below. Figure 6 As shown.

[0057] Step 4: Calculate the volume of new and old asphalt mortar in each grid, and then calculate the ratio M of old asphalt mortar to all asphalt mortar in each grid based on the volume of new and old asphalt mortar. i M i The calculation formula is as shown in equation (1):

[0058]

[0059] In the formula: A Vi Let be the volume of the new asphalt mortar within the i-th small cube;

[0060] A Ri Let be the volume of the old asphalt mortar within the i-th small cube;

[0061] i is the grid number, i = 1, 2, 3, ... 8.

[0062] Step 5: Based on the proportion M of old asphalt mortar within each grid division... i Calculate 8 M i The standard deviation (SD) and coefficient of variation (COV) are used as evaluation indicators of the uniformity of the distribution of new and old asphalt mortar within the entire three-dimensional specimen image. The calculation formulas are as shown in equations (2) to (4). The smaller the standard deviation and coefficient of variation, the better the uniformity of the mixture; conversely, the larger the standard deviation and coefficient of variation, the worse the uniformity of the mixture.

[0063]

[0064] In the formula: M within a single specimen i The overall mean.

[0065] Table 2 shows the standard deviation (SD) and coefficient of variation (COV) of the ratio of old asphalt mastic to total asphalt mastic in 10 types of recycled asphalt mixtures. Smaller standard deviations and coefficients of variation indicate better uniformity of the mixture; conversely, larger standard deviations and coefficients of variation indicate poorer uniformity. The recycled asphalt mixture with an aging time of 4 days and a mixing time of 120 seconds has the smallest standard deviation and coefficient of variation, indicating the best uniformity.

[0066] Table 2. Standard deviation and coefficient of variation of the ratio of used asphalt mastic to total asphalt mastic in recycled asphalt mixtures.

[0067]

[0068]

Claims

1. A method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division, characterized in that, The method comprises the following steps: Step 1: Obtain a recycled asphalt mixture cylindrical test piece by using indoor molding method, and scan the test piece by using a CT scanning device to construct a three-dimensional visual model of the recycled asphalt mixture test piece; Step 2: Perform digital image processing on the three-dimensional visual model to identify each component of the recycled asphalt mixture, and the components include coarse aggregate, old asphalt mortar, new asphalt mortar and voids; Step 3, using Mimics software, a cube range is cut in the specimen model as the research object from the processed three-dimensional specimen image with the volume center of the specimen as the cutting center, and the cube is further divided into m 3 equal grids. Step 4, respectively, statistics in each grid of new and old asphalt mortar volume, according to the volume of new and old asphalt mortar to calculate the ratio of old asphalt mortar in each grid of all asphalt mortar M i , M i The formula is as formula (1): wherein: Vni is the volume of new asphalt mortar within the ith small cube; Vi is the volume of old bituminous mortar in the ith small cube; i is the number of the divided grid, i = 1, 2, 3, …m 3 ; Step 5: Based on the ratio M of old asphalt mortar to all asphalt mortar in each divided grid, i Calculate m 3 M i The standard deviation SD and coefficient of variation COV are used as evaluation indicators of the uniformity of the distribution of new and old asphalt mortar in the entire three-dimensional specimen image. The calculation formulas are as follows (2) to (4). The smaller the standard deviation and coefficient of variation, the better the uniformity of the mixture; conversely, the worse the uniformity of the mixture. wherein: M is the overall average of M within a single test piece. i the overall average of M within a single test piece.

2. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, In step 1, the molding method of the recycled asphalt mixture cylindrical test piece comprises the following steps: Step A1: After adding a proper amount of titanium dioxide powder to the old asphalt mortar, prepare the waste asphalt mixture, wherein the titanium dioxide is replaced with the mineral powder in equal mass, and the mineral powder is no longer used to prepare the asphalt mixture; Step A2: Form the recycled asphalt mixture test piece by using the waste asphalt mixture prepared by adding the titanium dioxide powder to the old asphalt mortar, and using new aggregate and base asphalt in a fixed proportion.

3. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, The size of the cylindrical test piece in step 1 is Φ101.6mm*63.5mm.

4. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, In step 2, the identification of each component of the recycled asphalt mixture involves determination of the gray-scale image threshold value, and the threshold value is determined by using a bimodal method, comprising the following steps: Step B1: Qualitatively judge different material components according to the cross-sectional image; Step B2: Read the CT value of the position of the component and preliminarily determine the CT value range of each component; Step B3: Output the CT value histogram of the image by using the Mimics software; Step B4: Adjust the interval boundary of the CT value of the component by using the bimodal method repeatedly; Step B5: Determine the division threshold value of the coarse aggregate, new and old asphalt mortar and voids in the CT image.

5. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, In step 3, the height of the cube should be less than the height of the test piece, so as to eliminate the error caused by the inclined scanning of the test piece and ensure that the maximum inscribed cube sizes of different test pieces are consistent.

6. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, In step 3, the cube image is further divided as follows: the edge length m of the cube is equally divided into m 3 small cubes with equal length, width and height.

7. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, In step 3, m≥2.

8. The method for evaluating the uniformity of recycled asphalt mixture based on CT and three-dimensional division according to claim 1, characterized in that, In step 3, the method for obtaining the cube and geometric center of each three-dimensional visual model is as follows: use the 3D Properties function in the Mimics software to statistically analyze the size of the three-dimensional visual model, and use the crop mask function to cut the three-dimensional visual model and the maximum inscribed cube.

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