A method for designing the dosage and grading of skeleton fibers of a grouting composite asphalt mixture

Abstract

The application discloses a kind of skeleton fiber content gradation design methods of grouting composite asphalt mixture, with the porous asphalt mixture skeleton of grouting composite mixture as research object, respectively make cylindrical test piece and rectangular test piece without fiber to obtain binary image of horizontal plane and vertical plane, respectively make cylindrical test piece of different single length fiber and obtain dispersion effect extraction graph, the proportion of guiding coefficient of single length fiber and bottom horizontal plane angle between 0° and 45° and 45° and 90° is counted, combined with the relative proportion of different horizontal plane and vertical plane length fiber, the proportion of guiding coefficient of different single length fiber is determined, to determine the final design proportion based on three-dimensional feature combination length fiber.The fiber content gradation design method of the application can form the structure of "three-dimensional network" by mixing different length fibers in mixture, realize the maximum promotion of fiber for semi-flexible pavement performance enhancement;And for a kind of porous mixture skeleton with same void ratio and maximum stone particle size, the design method can be directly used for batch application, and has important engineering value for actual production.

Description

Technical Field

[0001] The invention belongs to the field of fiber content gradation design methods, and in particular relates to a skeleton fiber content gradation design method for a grouting composite asphalt mixture. Background Art

[0002] Semi-flexible pavement, a composite of porous asphalt (20%-30% porosity) and cement-based grouting within the interconnected pores, offers a "hard-flexible" combination of rigidity and flexibility. This pavement exhibits excellent high-temperature deformation resistance. However, the porous asphalt skeleton of the grouting composite mixture exhibits poor mechanical properties. Furthermore, its modulus differs significantly from that of the hardened cement-based grouting. When subjected to stress and deformation, the porous asphalt skeleton struggles to coordinate deformation with the grouting, leading to cracking in the semi-flexible pavement.

[0003] As a common material for reinforcing the skeleton of porous asphalt mixtures, fibers can effectively improve the mechanical properties of porous asphalt mixture skeletons. Fibers are distributed within the asphalt mixture in a three-dimensional network, forming a three-phase load-bearing system of aggregate skeleton, asphalt mortar, and fiber. Fibers primarily act as reinforcement, effectively dissipating and partially dissipating stress within the asphalt mixture, restraining and slowing the initiation and expansion of microcracks. This manifests itself macroscopically as an increase in the asphalt mixture skeleton's failure strength and failure strain.

[0004] The spatial distribution of fibers within an asphalt mixture is influenced by their length. If the fibers are too short, they will not overlap; if they are too long, they will clump together. In either case, the fibers will not form an effective reinforcement network within the porous asphalt mixture, severely impacting the mixture's mechanical properties. Fibers of varying lengths, however, overlap within the porous asphalt mixture, forming a stable "three-dimensional enveloping grid" that better synergizes with the asphalt mixture's skeleton in stress and deformation, resisting deformation and transferring and dissipating loads. At present, the design of composite fibers of different lengths is mostly carried out using orthogonal test methods or uniform test methods, and the final composite fiber ratio is finally determined by mechanical property verification through macroscopic tests, which lacks relevant support in terms of mechanism. There are also related methods that propose to guide the design of composite fiber lengths based on the microscopic characteristics of the skeleton, but only consider the microscopic characteristics of the skeleton on the transverse surface (the surface parallel to the bottom surface), and lack the extraction and research of the microscopic characteristics of the skeleton on the longitudinal surface (the surface perpendicular to the bottom surface). As a result, the composite fibers of different lengths designed based on the transverse skeleton characteristics cannot achieve true "three-dimensional" overlap inside the asphalt mixture, making it difficult to fully improve the mechanical properties of the mixture.

[0005] Therefore, truly achieving a "three-dimensional network" of overlapping fibers of varying lengths within the mixture is closely tied to the three-dimensional microscopic characteristics of the porous asphalt mixture's skeleton. Determining the blending ratio of fibers of varying lengths based on the microscopic characteristics of the porous asphalt mixture's transverse and longitudinal skeletons, maximizing their reinforcing effect on the porous asphalt mixture's skeleton and thereby improving the crack resistance of semi-flexible pavements, has become a significant challenge in current technology applications. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a fiber dosage and gradation design method based on the porous asphalt mixture skeleton of the grouting composite mixture. This method can realize the overlapping of fibers of different lengths inside the mixture to form a "three-dimensional network" structure, thereby maximizing the improvement of the performance enhancement of semi-flexible pavement by fibers.

[0007] Technical solution: The fiber content and gradation design method of the porous asphalt mixture skeleton of the present invention comprises the following steps:

[0008] (1) According to the gradation and asphalt-to-stone ratio of porous asphalt mixture, cylindrical and rectangular specimens without fibers were prepared respectively;

[0009] (2) According to the gradation, asphalt-stone ratio and fiber volume content of porous asphalt mixture, 3n mm single-parameter fiber cylindrical specimens were made, where n is a positive integer;

[0010] (3) Obtaining skeleton feature images of different horizontal layers of the cylindrical specimen and skeleton feature images of different vertical layers of the rectangular specimen in step (1), and performing binary image processing on both, respectively, to distinguish the skeleton and the gap between the skeletons of the porous asphalt mixture, and obtaining binary images of the horizontal and vertical surfaces;

[0011] (4) Based on the binary images of the horizontal and vertical surfaces, the skeleton gap features of the binary images of the porous asphalt mixture are extracted, and the length data of the skeleton gap are arranged in intervals to count the number of different intervals [3n-3,3n) mm and determine the different Xm 3nmm and Ym 3nmm The relative mass ratio of the length of the fiber; where X represents the transverse section, Y represents the longitudinal section, n is a positive integer, and m is the mass;

[0012] (5) Obtain cross-sectional images of cylindrical fiber specimens with different fiber lengths in step (2) respectively, obtain the dispersion effect extraction diagram of single-length fiber in asphalt mixture, calculate the fiber angle, and calculate the guide coefficient ratio of single-length fiber with the bottom cross-plane angle between 0°~45° and 45°~90°, which is defined as X 3nmm (0~45°), Y 3nmm(45°~90°), X represents the transverse section, and Y represents the longitudinal section;

[0013] (6) Combine the different Xm in step (4) 3nmm and Ym 3nmm The relative ratio of the length fibers and the guide coefficient ratio of the single length fibers in step (5) determine the final design ratio of the length fibers based on the three-dimensional feature combination:

[0014] M 3n mm :M 3(n-1)mm :┄┄:M3 mm =[Xm 3n mm *X 3n mm (0°~45°)+Ym 3n mm *Y 3n mm

[0015] (45°~90°)]:[Xm 3(n-1)mm *X 3(n-1)mm (0°~45°)+Ym 3(n-1) *Y 3(n-1)mm (45°~90°)]:┄┄:[Xm 3mm *X 3mm (0°~45°)+Ym 3mm *Y 3mm (45°~90°)];

[0016] Where: * represents the multiplication sign, M 3nmm is the mass ratio of 3n mm fibers, n is a positive integer; Xm 3nmm is the mass ratio of fibers of different lengths in the transverse section; X 3nmm (0-45°) is the guide coefficient ratio of fibers of different lengths with an angle of 0-45° to the transverse section; Ym 3nmm is the mass ratio of fibers of different lengths in the longitudinal section; Y 3nmm (45°~90°) is the ratio of the guidance coefficients of fibers of different lengths whose angles with the longitudinal section are between 45° and 90°.

[0017] Furthermore, in step (3) of the present invention, the binarization image processing is performed based on MATLAB software to achieve the distinction between the skeleton and the gap between the skeletons.

[0018] Furthermore, in step (4) of the present invention, the extracted characteristic parameter is the principal axis length of the skeleton gap in the binary image.

[0019] Furthermore, in step (4) of the present invention, the value of n is 1≦n≦4, and the corresponding distribution interval of the length data of the skeleton gap is (0,3), [3,6), [6,9), [9,12]. Based on this, the relative proportions of the combined length fibers determined in the transverse and longitudinal planes are Xm respectively. 3mm :Xm 6mm :Xm 9mm :Xm 12mm and Ym 3mm :Ym 6mm :Ym 9mm :Ym 12mm In step (6), the fiber length design ratio based on the three-dimensional feature combination is:

[0020] M 3mm :M 6mm :M 9mm :M 12mm =[Xm 3mm *X 3mm (0°~45°)+Ym 3m *Y 3mm (45°~90°)]:

[0021] [Xm 6mm *X 6mm (0°~45°)+Ym 6mm *Y 6mm (45°~90°)]:[Xm 9mm *X 9mm (0°~45°)+Ym 9mm *Y 9mm (45°~90°)]:[Xm 12mm *X 12mm (0°~45°)+Ym 12mm *Y 12mm (45°~90°)].

[0022] Beneficial effects: Compared with the existing technology, the significant advantages of the present invention are: the fiber content gradation design method is based on the porous mixture skeleton characteristics of the semi-flexible pavement grouting composite asphalt mixture. By combining the ratio of the combined length fibers of the cross- and longitudinal sections of the skeleton and the ratio of the guide coefficients of the single-length fibers, it can form a "three-dimensional network" structure for overlapping fibers of different lengths inside the mixture, thereby maximizing the improvement of the performance enhancement of the semi-flexible pavement by fibers; and for a type of porous mixture skeleton with the same porosity and maximum particle size of stone particles, the design method can be directly used for batch application, which has important engineering value for actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1It is a binary image of a certain cross section of the porous asphalt mixture specimen of the present invention; wherein a is the original image of a certain cross section; b is the image enhancement grayscale image; c is the denoised image; d is the binary image;

[0024] Figure 2 This is a schematic diagram of the dispersion of a single-length fiber within the mixture of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] The fiber content and gradation design method of the porous asphalt mixture skeleton of the present invention comprises the following steps:

[0027] (1) According to the Marshall mix design method, the gradation and asphalt-aggregate ratio of the porous asphalt mixture were determined, and its void ratio was calculated. Fiber-free cylindrical and rectangular specimens were prepared respectively;

[0028] (2) According to the gradation, asphalt-stone ratio and fiber volume content of porous asphalt mixture, 3n mm single-parameter fiber cylindrical specimens were made, where n is a positive integer;

[0029] (3) Obtaining skeleton feature images of different horizontal layers of the cylindrical specimen and skeleton feature images of different vertical layers of the rectangular specimen in step (1), and performing binary image processing on both, respectively, to distinguish the skeleton and the gap between the skeletons of the porous asphalt mixture, and obtaining binary images of the horizontal and vertical surfaces;

[0030] (4) Based on the binary images of the horizontal and vertical surfaces, the skeleton gap features of the binary images of the porous asphalt mixture are extracted, and the length data of the skeleton gap are arranged in intervals to count the number of different intervals [3n-3,3n) mm and determine the different Xm 3nmm and Ym 3nmm The relative mass ratio of the length of the fiber; where X represents the transverse section, Y represents the longitudinal section, n is a positive integer, and m is the mass;

[0031] (5) Obtain cross-sectional images of the cylindrical specimens with different single-parameter fibers in step (2) respectively, obtain the dispersion effect extraction diagram of the single-length fiber in the asphalt mixture, calculate the fiber-fiber angle, and calculate the guide coefficient ratio of the single-length fiber with the bottom cross-plane angle between 0°~45° and 45°~90°, which is defined as X 3nmm (0°~45°), Y 3nmm (45°~90°), X represents the transverse section, and Y represents the longitudinal section;

[0032] (6) Combine the different X in step (4) 3nmmand Ym 3nmm The relative ratio of the length fibers and the guide coefficient ratio of the single length fibers in step (5) determine the final design ratio of the length fibers based on the three-dimensional feature combination:

[0033] M 3n mm :M 3(n-1)mm :┄┄:M3 mm =[Xm 3n mm *X 3n mm (0°~45°)+Ym 3n mm *Y 3n mm

[0034] (45°~90°)]:[Xm 3(n-1)mm *X 3(n-1)mm (0°~45°)+Ym 3(n-1) *Y 3(n-1)mm (45°~90°)]:┄┄:[Xm 3mm *X 3mm (0°~45°)+Ym 3mm *Y 3mm (45°~90°)];

[0035] Where: * represents the multiplication sign, M 3nmm is the mass ratio of 3n mm fibers, n is a positive integer; Xm 3nmm is the mass ratio of fibers of different lengths in the transverse section; X 3nmm (0-45°) is the guide coefficient ratio of fibers of different lengths with an angle of 0-45° to the transverse section; Ym 3nmm is the mass ratio of fibers of different lengths in the longitudinal section; Y 3nmm (45°~90°) is the ratio of the guidance coefficients of fibers of different lengths whose angles with the longitudinal section are between 45° and 90°.

[0036] Specifically, taking the value of n as 1≦n≦4 as an example, the fiber content gradation design method for porous asphalt mixture grouting composite asphalt mixture skeleton of the present invention includes the following steps:

[0037] (1) According to the requirements of the "Technical Specifications for Highway Asphalt Pavement Construction" (JTG F40-2004) and the "Testing Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the gradation and asphalt-stone ratio of porous asphalt mixture (void ratio 20%-30%) were determined. A rotary compaction specimen with a diameter of 150 mm and a height of 170 mm (without fiber) was formed. The core was cut into a cylindrical specimen with a diameter of 100 mm and a height of 150 mm (with 10 mm cut on the top and bottom) (without fiber). A rutting plate specimen (300 mm × 300 mm × 50 mm) was formed (without fiber). 100 mm on both sides of the length and width were cut off, and the specimen was cut into a rectangular specimen (100 mm × 100 mm × 50 mm) along the height direction (without fiber). The gradation and asphalt-stone ratio of porous asphalt mixture are shown in Tables 1 and 2.

[0038] (2) According to the fiber volume fraction of 1%, single-fiber doping of 3mm, 6mm, 9mm, and 12mm was used to prepare fiber-containing rotary compaction specimens with a diameter of 150mm and a height of 170mm. A cylindrical core sample (containing fiber) with a diameter of 100mm and a height of 100mm was drilled using a coring machine.

[0039] (3) Obtaining the skeleton feature image of the porous asphalt mixture without fibers can be done in two ways: ① or ②:

[0040] ① Photo acquisition: After core cutting, the specimen (without fiber, 100 mm diameter, 150 mm height) was cut into sections every 10 mm to obtain 15 sections with a height of 10 mm and a diameter of 100 mm. The longitudinal surface (100 mm × 50 mm) of the rectangular specimen (100 mm × 100 mm × 50 mm, without fiber) was cut and photographed, with sections cut every 10 mm to obtain 10 images of each layer of the longitudinal surface of the specimen.

[0041] ② CT scanning: An industrial CT machine was used to perform cross-sectional scanning on the cored and cut specimen (100 mm in diameter, 150 mm in height, and fiber-free). The specimen was scanned every 10 mm for 15 times, and 15 CT images of each layer of the transverse surface of the specimen were obtained. The longitudinal surface (100 mm × 50 mm) of the rectangular specimen (100 mm × 100 mm × 50 mm, fiber-free) was scanned every 10 mm, and 10 CT images of each layer of the longitudinal surface of the specimen were obtained.

[0042] (4) The cross-sectional image is processed with histogram equalization using MATLAB software to make the grayscale distribution of the image more balanced; then the noise is reduced by median filtering to make the image boundary clearer; finally, the threshold iteration algorithm is used to perform binarization processing to distinguish the skeleton and the gap between the skeletons, and the horizontal and vertical binary images of each layer are obtained respectively; the image processing process of a certain horizontal cross section is as follows Figure 1 shown.

[0043] (5) The main axis length of the skeleton gap in the image is selected as the extracted characteristic parameter. The binary image of the porous asphalt mixture skeleton is calibrated using Image Pro Plus software. The skeleton gap to be measured is selected, and the main axis length of the skeleton gap to be measured is determined. Finally, the software built-in macro command is used for programming, the image is batch processed, and the data is exported.

[0044] (6) Using statistics, the length data of the skeleton gaps are arranged into intervals, and the number of fibers in different intervals is counted. The distribution intervals are (0,3), [3,6), [6,9), and [9,12]. According to the relative proportion of the number of distribution intervals, the relative proportion of fibers of different lengths is determined. The length of the fiber is slightly longer than the main axis length, so the mass ratio of fibers of different lengths is m 3mm :m 6mm :m 9mm :m 12mm =Num(0,3):Num[3,6):Num[6,9):Num[9,12]; where Num is the number of skeleton gap main axis lengths in the corresponding interval; using the above method, the skeleton gap main axis lengths of the transverse and longitudinal surfaces of the porous asphalt mixture are extracted and counted respectively, and the relative proportions of the combined length fibers determined according to the transverse surface X and the longitudinal surface Y are Xm and Y respectively. 3mm :Xm 6mm :Xm 9mm :Xm 12mm and Ym 3mm :Ym 6mm :Ym 9mm :Ym 12mm .

[0045] (7) CT scans were performed on cylindrical core samples (100 mm in diameter and 100 mm in height) of single-length fibers, 3 mm, 6 mm, 9 mm, and 12 mm, with horizontal scans performed every 0.1 mm. The scanned files were imported into Mimics software, and the files were reconstructed using the built-in algorithm of Mimics to extract the fibers. The final dispersion effect of single-length fibers in the asphalt mixture was extracted as shown in the figure below. Figure 2 shown.

[0046] According to the results extracted by Mimics software, the angle of single-length fiber (the angle between the fiber and the bottom surface, ranging from 0° to 90°) was calculated using the built-in function of MATLAB software. The proportion of single-length (3 mm, 6 mm, 9 mm and 12 mm) fibers with angles between 0° and 45° and 45° to 90° with the bottom transverse plane was counted. Fibers with angles between 0° and 45° with the bottom transverse plane were considered to be inclined to the transverse plane, while those with angles between 45° and 90° with the bottom transverse plane were considered to be inclined to the longitudinal plane. Therefore, the dispersion results (ratio of guidance coefficient) of single-length fibers (3 mm, 6 mm, 9 mm and 12 mm) were recorded as X 3mm (0°~45°), Y 3mm (45°~90°), X 6mm (0°~45°), Y 6mm (45°~90°), X 9mm (0°~45°), Y 9mm (45°~90°), X 12mm (0°~45°), Y 12mm (45°~90°).

[0047] (8) Calculate the final combined length fiber ratio: M 3mm :M 6mm :M 9mm :M 12mm =Xm 3mm *X 3mm (0°~45°)+Ym 3m *Y 3mm (45°~90°):Xm 6mm *X 6mm (0°~45°)+Ym 6mm *Y 6mm (45°~90°):Xm 9mm *X 9mm (0°~45°)+Ym 9mm *Y 9mm (45°~90°):Xm 12mm *X 12mm (0°~45°)+Ym 12mm *Y 12mm (45°~90°).

[0048] This embodiment uses steel fiber to enhance the performance of the grouting composite mixture. The fiber is added externally, and its volume fraction is 1.0% of the porous asphalt mixture. The length of the main axis of the transverse skeleton gap of the grouting composite asphalt mixture is Xm. 3mm :Xm 6mm :Xm 9mm :Xm 12mm=298:432:347:161, the length distribution of the longitudinal skeleton gap main axis is Ym 3mm :Ym 6mm :Ym 9mm :Ym 12mm =241:354:208:101, the fiber dispersion results (guide coefficient ratio) are X 3mm (0°~45°)=0.31,Y 3mm (45°~90°)=0.69,X 6mm (0°~45°)=0.24,Y 6mm (45°~90°)=0.76,X 9mm (0°~45°)=0.42,Y 9mm (45°~90°)=0.58,X 12mm (0°~45°)=0.64,Y 12mm (45°~90°)=0.36. Determine the mass ratio of the four steel fibers of different lengths as M 3mm :M 6mm :M 9mm :M 12mm =298*0.31+241*0.69:347*0.24+354*0.76:347*0.42+208*0.58:161*0.64+101*0.36≈19:25:19:10.

[0049] In order to compare the performance enhancement effect of combined length fibers on grouting composite mixtures, grouting composite mixtures without fiber addition, single addition of 6mm steel fiber, single addition of 9mm steel fiber and combined length steel fiber designed based on transverse skeleton characteristics were used as comparative examples (the volume fraction of external fiber addition was 1.0%).

[0050] Among them, the preparation steps of the grouting composite asphalt mixture are as follows: based on the fiber doping gradation determined in the above step (8), the porous asphalt mixture (void ratio 20%-30%) gradation and oil-stone ratio of step (1) are prepared, and when the mixture is cooled to about 50°C, the cement-based grouting material is mixed, and the cement grouting material slurry is evenly poured into the upper surface of the grouting composite asphalt mixture until the voids at the bottom of the mixture are filled with the grouting material, and finally the grouting composite asphalt mixture is placed under standard curing conditions (temperature 20±1°C, humidity 90%) and cured to the age.

[0051] In accordance with the "Test Procedures for Asphalt and Asphalt Mixtures for Highway Engineering" (JTG E20-2011) and the "Specifications for Design of Highway Asphalt Pavements" (JTG D50-2017), the -10°C splitting tensile strength and tensile strain at failure, 20°C elastic modulus, and 60°C shear strength of grouted composite asphalt mixtures with different fiber conditions were tested to characterize the tensile, deformation, and shear resistance of the grouted composite asphalt mixtures under different conditions. The results are shown in Tables 3 to 5.

[0052] Table 1 Gradation of porous asphalt mixture

[0053]

[0054] Table 2 Marshall index of porous asphalt mixture

[0055]

[0056] Table 3 Splitting test results of grouting composite mixture

[0057]

[0058]

[0059] Table 4 Dynamic modulus results of grouting composite mixture

[0060]

[0061] Table 5 Uniaxial penetration test of grouting composite mixture

[0062]

[0063] Combining Tables 3 to 5, it can be seen that compared with the grouting composite mixture without fiber, the mechanical indicators of the grouting composite mixture with fiber added are improved to varying degrees, and the mechanical indicators of the grouting composite mixture with combined length fibers based on the transverse and longitudinal skeleton characteristics have the highest increase. This proves that the combined length fibers designed based on three-dimensional characteristics can maximize the reinforcement effect of the fibers on the porous asphalt mixture skeleton, and thus maximize their performance improvement effect on semi-flexible pavement. It is very feasible to design fiber grading based on the three-dimensional characteristic skeleton gap characteristics of the grouting composite mixture.

Claims

1. A method for designing the gradation of skeleton fiber content in grouting composite asphalt mixture, characterized in that: The steps include: (1) According to the gradation and asphalt-to-stone ratio of porous asphalt mixture, cylindrical and rectangular specimens without fibers were prepared respectively; (2) According to the gradation, asphalt-stone ratio and fiber volume content of porous asphalt mixture, 3n mm single-parameter fiber cylindrical specimens were made, where n is a positive integer; (3) Obtaining skeleton feature images of different horizontal layers of the cylindrical specimen and skeleton feature images of different vertical layers of the rectangular specimen in step (1), and performing binary image processing on both, respectively, to distinguish the skeleton and the gap between the skeletons of the porous asphalt mixture, and obtaining binary images of the horizontal and vertical surfaces; (4) Based on the binary images of the horizontal and vertical surfaces, the skeleton gap features of the binary images of the porous asphalt mixture are extracted, and the length data of the skeleton gap are arranged in intervals to count the number of different intervals [3n-3,3n) mm and determine the different Xm 3nmm and Ym 3nmm The relative mass ratio of the length of the fiber; where X represents the transverse section, Y represents the longitudinal section, n is a positive integer, and m is the mass; (5) Obtain cross-sectional images of cylindrical fiber specimens with different fiber lengths in step (2) respectively, obtain the dispersion effect extraction diagram of single-length fiber in asphalt mixture, calculate the fiber angle, and calculate the guide coefficient ratio of single-length fiber to bottom cross-plane angle between 0°~45° and 45°~90°, which is defined as Xm 3nmm (0~45°), Ym 3nmm (45°~90°), X represents the transverse section, and Y represents the longitudinal section; (6) Combine the different X in step (4) 3nmm and Ym 3nmm The relative ratio of the length fibers and the guide coefficient ratio of the single length fibers in step (5) determine the final design ratio of the length fibers based on the three-dimensional feature combination: M 3nmm :M 3(n-1)mm :┄┄:M 3mm =[Xm 3nmm *X 3nmm (0°~45°)+Ym 3nmm *Y 3nmm (45°~90°)]:[Xm 3(n-1)mm *X 3(n-1)mm (0°~45°)+Ym 3(n-1) *Y 3(n-1)mm (45°~90°)]:┄┄:[Xm 3mm *X 3mm (0°~45°)+Ym 3mm *Y 3mm (45°~90°)]; Where: * represents the multiplication sign, M 3nmm is the mass ratio of 3n mm fibers, n is a positive integer; Xm 3nmm is the mass ratio of fibers of different lengths in the transverse section; X 3nmm (0-45°) is the guide coefficient ratio of fibers of different lengths with an angle of 0-45° to the transverse section; Ym 3nmm is the mass ratio of fibers of different lengths in the longitudinal section; Y 3nmm (45°~90°) is the ratio of the guidance coefficients of fibers of different lengths whose angles with the longitudinal section are between 45° and 90°.

2. The method for designing the skeleton fiber dosage and gradation of the grouting composite asphalt mixture according to claim 1 is characterized in that: In step (3), the binarization image processing is performed based on MATLAB software to achieve the distinction between the skeleton and the gap between the skeletons.

3. The method for designing the skeleton fiber dosage and gradation of the grouting composite asphalt mixture according to claim 1, characterized in that: In step (4), the extracted characteristic parameter is the principal axis length of the skeleton gap in the binary image.

4. The method for designing the skeleton fiber dosage and gradation of the grouting composite asphalt mixture according to claim 1, characterized in that: In step (4), the value of n is 1≦n≦4, and the corresponding distribution interval of the length data of the skeleton gap is (0,3), [3,6), [6,9), [9,12].

5. The method for designing the gradation of skeleton fiber content of grouting composite asphalt mixture according to claim 4, characterized in that: The relative proportions of the combined length fibers determined by the transverse and longitudinal planes are Xm 3mm :Xm 6mm :Xm 9mm :Xm 12mm and Ym 3mm :Ym 6mm :Ym 9mm :Ym 12mm .

6. The method for designing the gradation of skeleton fiber content of grouting composite asphalt mixture according to claim 5, characterized in that: In step (6), the design ratio of the fiber length based on the three-dimensional feature combination is: M 3mm :M 6mm :M 9mm :M 12mm =[Xm 3mm *X 3mm (0°~45°)+Ym 3m *Y 3mm (45°~90°)]: [Xm 6mm *X 6mm (0°~45°)+Ym 6mm *Y 6mm (45°~90°)]:[Xm 9mm *X 9mm (0°~45°)+Ym 9mm *Y 9mm (45°~90°)]:[Xm 12mm *X 12mm (0°~45°)+Ym 12mm *Y 12mm (45°~90°)]。

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