Fiber spatial distribution detection method in asphalt mixture based on nano-ferroferric oxide

Abstract

The present invention discloses a method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide. The method comprises preparing a fiber-containing asphalt concrete test piece; attaching a nano-Fe3O4 metal film to the fiber surface; scanning the test piece layer by layer using CT, obtaining a three-dimensional reconstructed image of the asphalt concrete test piece through image accumulation, and performing ROI segmentation on the three-dimensional image. The grayscale values ​​of the three-dimensional image and the portion within a preset grayscale value range are determined as the fiber component imaging portion, and the spatial distribution of the fiber component imaging portion in the three-dimensional image is used as the spatial distribution of the fibers in the asphalt concrete test piece; the preset grayscale value range is 180 to 255. This detection method accurately detects the spatial distribution of fibers in asphalt concrete because the nano-Fe3O4 forms a film on the fiber surface that is not easily detached. Compared with existing heavy metal element tracer methods for detecting fiber spatial distribution, the detection results are more accurate and quantifiable.

Description

Technical Field

[0001] The present invention belongs to the field of highway construction materials, and more specifically, relates to a method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide. Background Art

[0002] To prevent premature pavement failure and extend its service life, current research continues to explore new pavement strengthening technologies to meet the performance requirements of asphalt pavements. Incorporating fibers during the pavement construction process to improve pavement performance is a common reinforcement method. Commonly used fibers include lignin fibers, polyester fibers, and basalt fibers. Basalt fibers, in particular, possess a fracture strength and elastic modulus that are difficult to achieve with plant and polymer fibers, along with excellent corrosion resistance, making them widely used. The addition of fibers effectively bridges the asphalt and aggregate, preventing the formation of internal defects in the asphalt mixture and thereby improving the overall pavement performance of the asphalt mixture. However, the distribution of fibers within the asphalt mixture directly affects the performance of the mixture.

[0003] Current fiber detection techniques in asphalt mixtures primarily include extraction and scanning electron microscopy. The extraction method involves cutting the asphalt mixture into blocks and soaking them in trichloroethylene for extraction, separating the fibers from the mixture. However, this only yields fiber mass data, not the spatial distribution of the fibers within the mixture. Scanning electron microscopy involves cutting the asphalt mixture into centimeter-scale samples to qualitatively observe fiber morphology at the microscopic scale, but this makes it difficult to observe the spatial distribution of the fibers as a whole and conduct quantitative analysis. Although the existing patent CN 113049624 A employs a heavy metal tracer detection method, in which heavy metal inorganic salts are added during the basalt fiber impregnation stage to obtain labeled basalt fibers, followed by preparation of the asphalt mixture for testing, the heavy metal inorganic salts can easily fall off during the asphalt mixture preparation process, resulting in detection bias and even misinterpreting the distribution of the detached heavy metal inorganic salts as the fiber distribution, leading to misjudgment.

[0004] To date, the three-dimensional spatial distribution of fibers in asphalt mixtures has been difficult to accurately and intuitively observe and continuously quantify. Therefore, it is extremely important to develop a method that can accurately observe and quantify the three-dimensional spatial distribution of fibers in asphalt mixtures. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the purpose of which is to attach a layer of nano-Fe3O4 film on the surface of the fiber so that it can be detected by CT and can be quantitatively detected, thereby solving the technical problem in the prior art that the spatial distribution of fibers in asphalt concrete cannot be accurately detected.

[0006] To achieve the above object, according to one aspect of the present invention, a method for detecting the spatial distribution of fibers in asphalt mixture based on nano-ferroferric oxide is provided, which comprises the following steps:

[0007] Prepare an asphalt concrete test piece containing fibers; and adhere a layer of nano-Fe3O4 metal film to the surface of the fibers;

[0008] The test piece is scanned layer by layer using CT, and a three-dimensional reconstructed image of the asphalt concrete test piece is obtained by image accumulation. The three-dimensional image is segmented into ROIs, and the grayscale value in the three-dimensional image and the part within the preset grayscale value range are determined as the fiber component imaging part. The spatial distribution of the fiber component imaging part in the three-dimensional image is used as the spatial distribution of the fibers in the asphalt concrete test piece; the preset grayscale value range is 180 to 255.

[0009] Preferably, the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide further includes quantitatively detecting the spatial distribution of fibers in the test piece, specifically according to the following principles:

[0010] According to the spatial distribution of fibers in the asphalt concrete test piece, the distance Ds between each fiber and point C in the test piece is calculated;

[0011] A fiber spatial distribution diagram is drawn based on the distance Ds, and the fiber spatial distribution diagram in the test piece quantitatively reflects the spatial distribution of the fibers in the test piece.

[0012] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the distance Ds is the distance between the fiber centroid and the center of the test piece, which is specifically calculated as follows:

[0013]

[0014] Where xi and xc are the abscissas of the fiber centroid and the test piece center, respectively; yi and yc are the ordinates of the fiber centroid and the test piece center, respectively.

[0015] Preferably, the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide further includes quantitatively detecting the spatial angular distribution of fibers in the test piece, specifically according to the following principles:

[0016] According to the spatial distribution of fibers in the asphalt concrete test piece, the angle α formed by the fibers and the midplane C of the test piece is calculated;

[0017] A fiber space angle distribution diagram is drawn according to the angle α, and the fiber space angle distribution diagram in the test piece is used to quantitatively reflect the fiber space angle distribution in the test piece.

[0018] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the angle α is the angle formed by the fiber and the center plane of the test piece, which is specifically calculated as follows:

[0019]

[0020] Where xi and xc are the abscissas of the fiber centroid and the test piece center, respectively; yi and yc are the ordinates of the fiber centroid and the test piece center, respectively.

[0021] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the fiber-containing asphalt concrete test piece is prepared according to the following method:

[0022] The silane coupling agent solution, fiber and nano-Fe3O4 are uniformly mixed according to a preset ratio, and dried to obtain a modified fiber with a layer of nano-Fe3O4 metal film attached; the preset ratio, in parts by mass, is silane coupling agent solution: fiber: nano-Fe3O4 = 800-1000 parts: 100-200 parts: 10-30 parts;

[0023] The fibers in the original asphalt mixture were replaced with the modified fibers, and asphalt concrete test pieces were prepared according to the proportions of the components in the original asphalt mixture.

[0024] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the silane coupling agent is one or more combinations of KH550, KH560, and KH570 silane coupling agents.

[0025] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferrosoferric oxide, the silane coupling agent is prepared as a solution with a mass fraction of 0.5% to 10%.

[0026] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the fibers are non-metallic fibers with a diameter of more than 15 microns.

[0027] Preferably, in the method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, the nano-Fe3O4 has a particle size of 100-200 nm.

[0028] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0029] The present invention provides a method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide. By attaching a layer of nano-Fe3O4 metal film to the fiber surface, the nano-Fe3O4 is interconnected to a micron level or above, and the nano-Fe3O4 is determined by determining that the grayscale value range in the three-dimensional reconstructed image obtained by CT detection is 180-255. Since the nano-Fe3O4 metal film is attached to the fiber surface, the nano-Fe3O4 can represent the spatial distribution of the fibers in the test piece, and the nano-Fe3O4 metal film is not easy to fall off the fiber. Compared with the heavy metal element tracing method, the detection is more accurate.

[0030] In addition, this detection method can quantitatively detect the spatial distribution of fibers in asphalt concrete by calculating the distance Ds between the fiber and a certain point in the test piece and / or the angle α between the fiber and a certain plane, and making a fiber spatial distribution map based on the calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the distribution map of fiber spatial distance;

[0032] Figure 2 It is the distribution diagram of fiber space angle. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0034] Adding fibers during the preparation of asphalt mixtures is beneficial to improving the road performance of asphalt concrete, but it is currently difficult to accurately and quantitatively detect the spatial distribution of fibers in asphalt mixtures.

[0035] Industrial CT, a type of imaging that uses X-rays as a radiation source, is currently widely used in industrial nondestructive testing. The basic principle of CT imaging is to scan a layer of a certain thickness within the inspection area using X-rays, such as X-rays. The radiation that passes through this layer is received by a detector and converted into visible light. After a series of processing steps, it is converted into small grayscale blocks ranging from black to white, known as pixels. A computer reconstructs the industrial CT slice image from the collected projection data, obtaining three-dimensional information about the object being inspected. Because components of different densities have different attenuation or absorption coefficients for radiation, they appear as different pixels in the CT image. Different grayscale values ​​within the CT image can be used to distinguish and identify these components.

[0036] However, the non-metallic fiber components in asphalt concrete cannot be distinguished by CT detection. This is because the density of non-metallic fibers is similar to that of other components in asphalt concrete, and they cannot be distinguished by CT detection. If a layer of material with high density or that can be distinguished by CT detection is attached to the surface of the fiber, it can be used to detect and distinguish the fibers. For example, the existing heavy metal element tracer method soaks the fiber in heavy metal inorganic salts such as ZrCl4 to obtain fibers labeled with heavy metals. The heavy metal elements are detected by CT to reflect the spatial distribution of the fibers. However, during the preparation of the test piece, the heavy metal element inorganic salts are easy to fall off, which can easily cause detection deviations. The distribution of the fallen heavy metal inorganic salts may even be regarded as the distribution of the fibers, resulting in inaccurate test results. Therefore, higher requirements are required for the substances attached to the fibers. First, the substance attached to the fibers is not easy to fall off. Second, even if it falls off from the fibers, the substance cannot be detected by CT to avoid misjudgment and affect the accuracy of the test results.

[0037] This study found that fibers with attached nano-Fe3O4, prepared under certain conditions by using fibers, nano-Fe3O4 and silane coupling agent, were added to asphalt concrete. CT can detect and distinguish the nano-Fe3O4 attached to the fibers of the test piece, and the distribution of nano-Fe3O4 in the CT image can be regarded as the distribution of fibers. Furthermore, this study examined test specimens containing the same amount of nano-Fe₃O₄. CT scans failed to detect the distribution of nano-Fe₃O₄. This may be because the asphalt concrete specimens tested are typically 2cm*2cm*2cm (to ensure sufficient aggregate within the specimens). At this size, CT scan accuracy can only reach the micron level, preventing direct detection of nano-Fe₃O₄ dispersed in the asphalt concrete. However, nano-Fe₃O₄ attached to the fibers can be detected. This is presumably because the nano-Fe₃O₄ forms a metallic film on the fiber surface, interconnecting the nano-Fe₃O₄ to the micron level, making it detectable by CT. The distribution of nano-Fe₃O₄ in the CT image represents the distribution of the fibers, enabling the detection of the spatial distribution of fibers in asphalt concrete. Furthermore, the nano-Fe₃O₄ forms a film on the fiber surface that is difficult to fall off. Even if a small amount of nano-Fe₃O₄ falls off the fibers, it will not cause a misinterpretation of the test results, thus preventing the influence of the falling nano-Fe₃O₄ on the fiber distribution test results.

[0038] Furthermore, based on the obtained fiber distribution position in the test piece, the distance between the fiber and a certain point in the test piece is calculated, and the spatial distribution of the fiber in the asphalt concrete can be quantitatively detected. The distance between the fiber center of mass and the center of the test piece is preferably quantitatively detected, which can be used to evaluate the uniformity of the fiber spatial distribution.

[0039] At the same time, the angle between the fiber and a certain plane in the test piece can be calculated based on the fiber distribution position in the test piece, and the spatial angular distribution of the fiber in the asphalt concrete can be quantitatively detected, which is conducive to further understanding the spatial distribution state of the fiber in the asphalt concrete.

[0040] Based on this discovery, the present invention proposes a method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, comprising the following steps:

[0041] Prepare an asphalt concrete test piece containing fibers; and adhere a layer of nano-Fe3O4 metal film to the surface of the fibers;

[0042] The test piece is scanned layer by layer using CT, and a three-dimensional reconstructed image of the asphalt concrete test piece is obtained by image accumulation. The three-dimensional image is segmented into ROIs, and the grayscale value in the three-dimensional image and the part within the preset grayscale value range are determined as the fiber component imaging part. The spatial distribution of the fiber component imaging part in the three-dimensional image is used as the spatial distribution of the fibers in the asphalt concrete test piece; the preset grayscale value range is 180 to 255.

[0043] In some embodiments, 1000 CT layer-by-layer images are selected to three-dimensionally reconstruct an asphalt concrete test specimen.

[0044] Furthermore, the spatial distribution of fibers in the test piece is quantitatively detected, specifically according to the following principles:

[0045] According to the spatial distribution of fibers in the asphalt concrete test piece, the distance Ds between each fiber and point C in the test piece is calculated;

[0046] A fiber spatial distribution diagram is drawn based on the distance Ds, and the fiber spatial distribution diagram in the test piece quantitatively reflects the spatial distribution of the fibers in the test piece.

[0047] Preferably, the center of mass (xi, yi) of each fiber and the center coordinates (xc, yc) of the test piece are obtained, and the distance Ds from the fiber to the center point is calculated as follows:

[0048]

[0049] Furthermore, the spatial angle distribution of the fibers in the test piece is quantitatively detected, specifically according to the following principles:

[0050] According to the spatial distribution of fibers in the asphalt concrete test piece, the angle α formed by the fibers and the midplane C of the test piece is calculated;

[0051] A fiber space angle distribution diagram is drawn according to the angle α, and the fiber space angle distribution diagram in the test piece is used to quantitatively reflect the fiber space angle distribution in the test piece.

[0052] Preferably, the centroid (xi, yi) of each fiber and the center coordinates (xc, yc) of the test piece are obtained, and the angle α formed by the fiber and the center plane is calculated.

[0053]

[0054] The spatial distribution of the fibers in the test specimen reflects the spatial distribution of the fibers in the asphalt mixture, that is, the spatial distribution of the fibers in the asphalt mixture can be detected according to the above detection method.

[0055] The fiber-containing asphalt concrete test piece was prepared as follows:

[0056] (1) Preparing modified fiber; the modified fiber is prepared according to the following method:

[0057] The silane coupling agent solution, fiber and nano-Fe3O4 are uniformly mixed according to a preset ratio, and dried to obtain modified fiber;

[0058] Preferably, the preset ratio, in parts by mass, is silane coupling agent solution: fiber: nano-Fe3O4 = 800-1000 parts: 100-200 parts: 10-30 parts; the silane coupling agent is one or more combinations of KH550, KH560, and KH570 silane coupling agents, and the mass fraction of the silane coupling agent solution is preferably 0.5% to 10%;

[0059] The fibers are non-metallic fibers with a diameter of more than 15 microns, including lignin fibers, polyester fibers and basalt fibers; the fiber length is usually 6-9 mm;

[0060] The nano-Fe3O4 preferably has a particle size of 100-200nm. Theoretically, the larger the particle size of the nano-Fe3O4, the easier it is to detect. However, if the particle size is too large, if the nano-Fe3O4 falls off and aggregates, it may cause misjudgment, thereby affecting the detection result. In addition, in the present invention, the nano-Fe3O4 with a particle size of less than 100nm can also be detected.

[0061] (2) Preparation of test specimens: The fibers in the original asphalt mixture were replaced with modified fibers, and asphalt concrete test specimens were prepared according to the proportions of the components in the original asphalt mixture.

[0062] The following are examples:

[0063] Example 1 Detection of fiber spatial distribution in asphalt mixture

[0064] In this embodiment, the fiber added to the original asphalt mixture to be tested is basalt fiber, and the method specifically includes the following steps:

[0065] Preparation of modified basalt fiber: 1000 parts of 1% KH-550 solution, 200 parts of basalt fiber and 10 parts of nano-Fe3O4 were uniformly mixed, ultrasonically shaken for 12 hours, and then dried at 110°C to obtain the modified basalt fiber intermediate;

[0066] 1000 parts of 1% KH-550 solution, 200 parts of modified basalt fiber intermediate and 10 parts of nano-Fe3O4 were uniformly mixed, ultrasonically shaken for 12 hours, and then dried at 110°C. The above operation was repeated twice to obtain modified basalt fiber;

[0067] Preparation of test specimens: SMA-13 ​​graded asphalt mixture was selected, and the modified basalt fiber was used to replace the basalt fiber in the original asphalt mixture. Aggregate, mineral powder, basalt fiber, and asphalt in the original asphalt mixture were weighed according to their mass. Aggregate, mineral powder, and asphalt were placed in an oven and heated to 165°C. The mixer temperature was 175°C. Aggregate, modified basalt fiber, asphalt, and mineral powder were added to the mixer in sequence and stirred for 90 seconds each. The mixture was then placed into a mold and struck 75 times forward and backward using a Marshall compactor to obtain a Marshall specimen with a diameter of 100 mm and a height of 63.5 mm.

[0068] Fiber detection: Perform CT scanning on the asphalt concrete test specimen to obtain more than 1,000 CT layer-by-layer images, and select 1,000 CT layer-by-layer images. Use the selected 1,000 CT images to 3D reconstruct the asphalt concrete test specimen, and select the basalt fiber component in the specimen based on the grayscale value corresponding to the density in the 3D reconstructed asphalt concrete specimen image, as follows:

[0069] By 3D reconstructing the asphalt concrete specimen image, ROI segmentation is performed. The grayscale range of 0-30 represents voids, 30-50 represents asphalt mortar, 50-180 represents aggregate, and 180-255 represents nano-Fe3O4 (i.e., basalt fiber). The distribution of fibers in the test piece is determined based on the distribution of grayscale values.

[0070] Example 1 Detection of fiber spatial distribution in asphalt mixture

[0071] In this embodiment, the fiber added to the original asphalt mixture to be tested is lignin fiber, and the method specifically includes the following steps:

[0072] Preparation of modified lignin fiber: 800 parts of 5% KH-550 solution, 100 parts of lignin fiber and 15 parts of nano-Fe3O4 were uniformly mixed, ultrasonically shaken for 12 hours, and then dried at 110°C to obtain the modified lignin fiber intermediate;

[0073] 800 parts of 5% KH-550 solution, 100 parts of modified lignin fiber intermediate and 15 parts of nano-Fe3O4 were uniformly mixed, ultrasonically shaken for 12 hours, and then dried at 110°C. The above operation was repeated twice to obtain modified lignin fiber;

[0074] Other operations and detections are the same as in Example 1.

[0075] Example 3 Detection of Fiber Spatial Distribution in Asphalt Mixture

[0076] The test specimens in Examples 1 and 2 can both detect and distinguish the fiber distribution in asphalt concrete using CT. Furthermore, based on the three-dimensional reconstructed asphalt concrete specimen image obtained in Example 1, the spatial distribution of the fibers in the asphalt concrete specimen is quantified. Specifically, the quantification is performed according to the following principles:

[0077] 1. Spatial distance

[0078] According to the processing software of the CT equipment, the centroid (xi, yi) of each fiber is obtained, and the center coordinates (xc, yc) of the specimen are determined at the same time, and then the distance Ds from the fiber to the center point is calculated.

[0079]

[0080] According to the above formula, the spatial distance of the fibers is calculated and a fiber spatial distribution diagram is drawn, such as Figure 1 shown.

[0081] Figure 1 is the spatial distance between 823 fibers in the test sample, Figure 1 It can be seen that the spatial distance between fibers is mainly concentrated between 0.2 and 1.2, and there is no local concentration of fiber distance, which also shows that the fibers are not agglomerated and are evenly distributed in the sample.

[0082] 2. Spatial perspective

[0083] According to the processing software of the CT equipment, the centroid (xi, yi) of each fiber is obtained, and the center coordinates (xc, yc) of the specimen are determined at the same time, and then the angle α formed by the fiber and the center plane is calculated.

[0084]

[0085] According to the above formula, the spatial angle of the fiber is calculated and the fiber spatial angle distribution diagram is drawn, as shown in the figure. Figure 2 shown.

[0086] Figure 2 is the spatial angle of 823 fibers in the test sample, Figure 2It can be seen that the spatial angle of the fibers is evenly distributed in the range of 0 to 90°, indicating that there is no agglomeration of the fibers in space, which is beneficial to the enhancement of the pavement performance of asphalt concrete.

[0087] In summary, the spatial distribution of the modified fibers in the test specimen reflects the spatial distribution of the fibers in the original asphalt mixture, that is, the spatial distribution of the fibers in the original asphalt mixture can be detected according to the above detection method.

[0088] Comparative Example 1 Detection of fiber spatial distribution in asphalt mixture

[0089] In this embodiment, no nano-Fe3O4 modified fiber is added to the asphalt mixture to be tested, and the specific steps include:

[0090] An asphalt concrete test specimen was prepared, wherein the fibers were basalt fibers. A CT scan of the test specimen revealed that the fibers in the asphalt mixture could not be distinguished.

[0091] Comparative Example 2 Detection of spatial distribution of nano-Fe3O4 in asphalt mixture

[0092] In this embodiment, nano-Fe3O4 is added to the asphalt mixture to be tested but no fiber is added, and the following steps are specifically included:

[0093] An asphalt concrete test specimen was prepared, in which nano-Fe3O4 was added. A CT scan was performed on the test specimen, but no nano-Fe3O4 image was obtained, and nano-Fe3O4 in the asphalt mixture could not be directly detected.

[0094] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide, characterized in that: The following steps are involved: Prepare a fiber-containing asphalt concrete test piece; and attach a layer of nano-Fe3O4 metal film to the surface of the fiber, as follows: The silane coupling agent solution, fiber and nano-Fe3O4 are uniformly mixed in a preset ratio, and dried to obtain a modified fiber with a layer of nano-Fe3O4 metal film attached thereto; the preset ratio, in parts by mass, is silane coupling agent solution: fiber: nano-Fe3O4 = 800-1000 parts: 100-200 parts: 10-30 parts; the particle size of the nano-Fe3O4 is ≤200nm; The test piece is scanned layer by layer using CT, and a three-dimensional reconstructed image of the asphalt concrete test piece is obtained by image accumulation. The three-dimensional reconstructed image of the asphalt concrete test piece is segmented into ROIs, and the portion of the three-dimensional reconstructed image of the asphalt concrete test piece whose grayscale value is within a preset grayscale value range is determined as the fiber component imaging portion, and the spatial distribution of the fiber component imaging portion in the three-dimensional image is used as the spatial distribution of fibers in the asphalt concrete test piece; the preset grayscale value range is 180 to 255.

2. The method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide according to claim 1, wherein: It also includes quantitative detection of the spatial distribution of fibers in the test piece, specifically according to the following principles: According to the spatial distribution of fibers in the asphalt concrete test piece, the distance Ds between each fiber and point C in the test piece is calculated; A fiber spatial distribution diagram is drawn based on the distance Ds, and the fiber spatial distribution diagram in the test piece quantitatively reflects the spatial distribution of the fibers in the test piece.

3. The method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide according to claim 2, wherein: The distance Ds is the distance between the fiber centroid and the center of the test piece, which is calculated as follows: Where xi and xc are the abscissas of the fiber centroid and the test piece center, respectively; yi and yc are the ordinates of the fiber centroid and the test piece center, respectively.

4. The method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide according to claim 1, wherein: It also includes quantitative detection of the spatial angle distribution of fibers in the test piece, specifically according to the following principles: According to the spatial distribution of fibers in the asphalt concrete test piece, the angle α formed by the fibers and the midplane C of the test piece is calculated; A fiber space angle distribution diagram is drawn according to the angle α, and the fiber space angle distribution diagram in the test piece is used to quantitatively reflect the fiber space angle distribution in the test piece.

5. The method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide according to claim 4, characterized in that: The angle α is the angle formed by the fiber and the center plane of the test piece, and is specifically calculated as follows: Where xi and xc are the abscissas of the fiber centroid and the test piece center, respectively; yi and yc are the ordinates of the fiber centroid and the test piece center, respectively.

6. The method for detecting fiber spatial distribution in asphalt mixture based on nano-ferroferric oxide according to claim 1, characterized in that: The fiber-containing asphalt concrete test pieces were prepared as follows: The silane coupling agent solution, fiber and nano-Fe3O4 are uniformly mixed according to a preset ratio, and dried to obtain a modified fiber with a layer of nano-Fe3O4 metal film attached; the preset ratio, in parts by mass, is silane coupling agent solution: fiber: nano-Fe3O4 = 800-1000 parts: 100-200 parts: 10-30 parts; The fibers in the original asphalt mixture were replaced with the modified fibers, and asphalt concrete test pieces were prepared according to the proportions of the components in the original asphalt mixture.

7. The method for detecting fiber spatial distribution in asphalt mixture based on nano-ferroferric oxide according to claim 6, characterized in that: The silane coupling agent is one or more combinations of KH550, KH560, and KH570 silane coupling agents.

8. The method for detecting the spatial distribution of fibers in asphalt mixtures based on nano-ferroferric oxide according to claim 7, wherein: The silane coupling agent is prepared as a solution with a mass fraction of 0.5% to 10%.

9. The method for detecting fiber spatial distribution in asphalt mixture based on nano-ferroferric oxide according to claim 6, characterized in that: The fibers are non-metallic fibers with a diameter of more than 15 microns.

10. The method for detecting fiber spatial distribution in asphalt mixture based on nano-ferroferric oxide according to claim 6, characterized in that: The nano Fe3O4 has a particle size of 100-200nm.

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