An evaluation method for the cracking performance of asphalt mixture

Abstract

An evaluation method for the cracking performance of asphalt mixtures, which belongs to the technical field of asphalt mixture evaluation, and specifically relates to an evaluation method for the cracking performance of asphalt mixtures. The purpose of the present invention is to solve the problems that pavement cracking has a great impact on the pavement and a wide range, and the current evaluation of the cracking performance of asphalt mixtures is limited to the overall cracking performance and does not involve the specific cracking performance. Method: First, cutting; Second, conduct an indirect tensile test on the Marshall specimens of asphalt mixtures, and obtain photos of the asphalt mixtures during the loading process of the indirect tensile test through a digital speckle image acquisition system; Third, import the collected photos into the VIC analysis software supporting the digital speckle image acquisition system for analysis; Fourth, extract the horizontal strain information at 75% of the peak load before the peak load; Fifth, only count the tensile strain; Sixth, determine whether the high-strain points belong to the same area; Seventh, evaluate the cracking performance of the asphalt mixtures based on the number of high-strain areas.

Description

Technical Field

[0001] The present invention belongs to the technical field of asphalt mixture evaluation, and particularly relates to a method for evaluating the cracking performance of asphalt mixtures. Background Art

[0002] Pavement cracking, also known as reticulated cracks, is specifically manifested as irregular cracks where cracks are connected to form a tortoise shell pattern. It has the characteristics of large area, strong destructiveness, and high repair difficulty, seriously affecting the pavement comfort and traffic efficiency. The degree and scope of the impact far exceed ordinary linear cracks and should be taken seriously. However, the current evaluation of the cracking performance of asphalt mixtures is limited to the overall evaluation of the cracking performance. The test methods are complex and diverse, but the cracking performance is not refined, and the evaluation of the cracking performance is not involved. Cracking is an important sign of asphalt pavement damage.

[0003] Digital Image Correlation (i.e., DIC technology) is a technical method for measuring the surface strain and deformation of an object. By tracking the deformation process of the speckle pattern on the object surface and calculating the change in the gray value of the speckle domain, the deformation and strain data of the surface of the object to be measured can be obtained. At present, the application of DIC technology in asphalt mixtures is relatively less. Most studies focus on its surface deformation, ignoring the relationship between strain and cracking, while the high-strain area is the source of cracking. The dispersion or concentration of the high-strain area determines the crack morphology. Therefore, by means of DIC technology, proposing a corresponding evaluation method to evaluate the cracking performance of asphalt mixtures is of great significance for accurately evaluating the road performance of asphalt mixtures and effectively guiding the design of asphalt mixtures. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that pavement cracking has a large impact on the pavement in terms of degree and scope, while the current evaluation of the cracking performance of asphalt mixtures is limited to the overall cracking performance and does not involve specific cracking performance, and to provide a method for evaluating the cracking performance of asphalt mixtures.

[0005] A method for evaluating the cracking performance of asphalt mixtures includes the following steps:

[0006] Step 1: Cut the upper and lower surfaces of the standard asphalt mixture Marshall specimen to expose the aggregates, and use the aggregates as speckles for observation to obtain the pre-treated asphalt mixture Marshall specimen;

[0007] Step 2: Synchronously control the UTM-250 loading device and the digital speckle image acquisition system. Use the UTM-250 loading device to conduct an indirect tensile test on the pre-treated asphalt mixture Marshall specimen, and obtain photos of the asphalt mixture during the loading process of the indirect tensile test through the digital speckle image acquisition system; the UTM-250 loading device records the curve of the loading force changing with time;

[0008] Step 3: Import the photos collected by the digital speckle image acquisition system into the VIC analysis software supporting the digital speckle image acquisition system, select an appropriate size of the analysis sub-region, and use the VIC analysis software to calculate the deformation information, so as to obtain the surface deformation field of the asphalt mixture Marshall specimen during the indirect tensile test; based on the deformation information, use the VIC analysis software to calculate the strain, and obtain the horizontal strain information, with positive values being tensile strain and negative values being compressive strain. Tensile strain is related to cracking.

[0009] Step 4: Based on the fact that the UTM-250 loading device takes pictures simultaneously with the digital speckle image acquisition system, determine the time corresponding to 75% of the peak load before the load peak, and then determine the image corresponding to 75% of the peak load before the load peak through the time, and extract the strain information of this image. The strain information is the position coordinates and the magnitude of the strain value.

[0010] Step 5: Statistically quantify and characterize the magnitude of the horizontal strain field under the indirect tensile test, only count the tensile strain, and define the strain points with tensile strain values greater than 50% of the average tensile strain as high-strain points.

[0011] Step 6: Judge the high-strain points to determine whether the high-strain points belong to the same region. The judgment criteria are as follows: If the distance between the two nearest adjacent high-strain points is greater than r, then the two points do not belong to the same region. The calculation of r is as follows:

[0012]

[0013] In the formula, x n and x n+1 are the abscissas of the position coordinates of adjacent nodes, and y n and y n+1 are the ordinates of the position coordinates of adjacent nodes.

[0014] Step 7: Statistically count the number n of high-strain regions, and evaluate the cracking performance of the asphalt mixture based on the number n of high-strain regions. The evaluation criteria are as follows:

[0015] If 0 < n ≤ 10, the anti-cracking performance grade of the asphalt mixture Marshall specimen is excellent, and there is no need to consider the uniformity distribution. It is recommended for use.

[0016] If 11 < n ≤ 20, the anti-cracking performance grade of the asphalt mixture Marshall specimen is good, and it can be used without special requirements.

[0017] If 20 < n ≤ 30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is qualified, and its use should be restricted.

[0018] If n > 30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is unqualified, and its use is prohibited.

[0019] Advantages of the present invention:

[0020] For the first time, the present invention proposes an evaluation method for the cracking performance of asphalt mixtures by means of DIC technology, providing an important reference index for accurately evaluating the road performance of asphalt mixtures; the impact of cracking on the road surface far exceeds that of ordinary cracks, and overall evaluation of the cracking performance of asphalt mixtures while ignoring the cracking performance will lead to inconsistent evaluation results with the actual application effects; the digital speckle method is easy to operate, and the high-speed shooting of the loading process also makes the obtained data more accurate, effectively avoiding human errors; the definition of high-strain points is proposed to determine the judgment criteria for high-strain regions, providing data support for the evaluation of cracking performance, and the consistency between the high-strain region and the actual cracking position indicates the rationality of the judgment criteria. Using the number of high-strain regions as a quantitative evaluation criterion conforms to the actual characteristics of multiple cracks in cracking, providing an effective reference index for subsequent evaluation of the overall road performance of asphalt mixtures and guiding the design of asphalt mixtures. Description of the drawings

[0021] Figure 1 Digital photo of the pre-treated Marshall specimen of asphalt mixture obtained in Example 1;

[0022] Figure 2 Installation diagram of the digital speckle image acquisition system in Example 1;

[0023] Figure 3 Calibration plate in Example 1;

[0024] Figure 4 Curve of the loading force varying with time recorded by the UTM-250 loading device in Example 1;

[0025] Figure 5 Digital speckle analysis sub-region in Example 1;

[0026] Figure 6 Calculation of the deformation field of the Marshall specimen of asphalt mixture;

[0027] Figure 7 Calculation of the strain field of the Marshall specimen of asphalt mixture. Detailed implementation manners

[0028] Detailed implementation manner 1: An evaluation method for the cracking performance of an asphalt mixture in this implementation manner includes the following steps:

[0029] Step 1: Cut the upper and lower surfaces of the standard Marshall specimen of asphalt mixture to expose the natural aggregate, and use the natural aggregate as a speckle for observation to obtain the pre-treated Marshall specimen of asphalt mixture;

[0030] Step 2: Synchronously control the UTM-250 loading device and the digital speckle image acquisition system. Use the UTM-250 loading device to conduct an indirect tensile test on the preprocessed asphalt mixture Marshall specimen, and obtain photos of the asphalt mixture during the loading process of the indirect tensile test through the digital speckle image acquisition system. The UTM-250 loading device records the curve of the loading force changing with time.

[0031] Step 3: Import the photos collected by the digital speckle image acquisition system into the VIC analysis software supporting the digital speckle image acquisition system. Select an appropriate size of the analysis sub-region, and use the VIC analysis software to calculate the deformation information to obtain the surface deformation field of the asphalt mixture Marshall specimen during the indirect tensile test. Based on the deformation information, use the VIC analysis software to calculate the strain, and obtain the horizontal strain information. A positive value is tensile strain, and a negative value is compressive strain. Tensile strain is related to cracking.

[0032] Step 4: Based on the fact that the UTM-250 loading device and the digital speckle image acquisition system take pictures simultaneously, determine the time corresponding to 75% of the peak load before the load peak, and then determine the image corresponding to 75% of the peak load before the load peak through the time, and extract the strain information of this image. The strain information is the position coordinates and the magnitude of the strain value.

[0033] Step 5: Statistically quantify and characterize the magnitude of the horizontal strain field under the indirect tensile test. Only statistically analyze the tensile strain, and define the strain points with a tensile strain value greater than 50% of the average tensile strain as high strain points.

[0034] Step 6: Judge the high strain points to determine whether the high strain points belong to the same region. The judgment criteria are as follows: If the distance between the two nearest adjacent high strain points is greater than r, then the two points do not belong to the same region. The calculation of r is as follows:

[0035]

[0036] where x n and x n+1 are the abscissas of the position coordinates of adjacent nodes, and y n and y n+1 are the ordinates of the position coordinates of adjacent nodes.

[0037] Step 7: Statistically count the number n of high strain regions, and evaluate the cracking performance of the asphalt mixture based on the number n of high strain regions. The evaluation criteria are as follows:

[0038] If 0 < n ≤ 10, the anti-cracking performance grade of the asphalt mixture Marshall specimen is excellent, and it is recommended to use.

[0039] If 11 < n ≤ 20, the anti-cracking performance grade of the asphalt mixture Marshall specimen is good, and it can be used without special requirements.

[0040] If 20<n≤30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is qualified and should be used with restrictions;

[0041] If n>30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is unqualified and is prohibited from use.

[0042] The present implementation method is that the indirect tensile test can characterize the anti-cracking performance of the asphalt mixture, the upper and lower surfaces are cut to facilitate photographing and observation, and the surface natural aggregate is used as speckle to reduce the speckle production procedure and reduce the difficulty of operation.

[0043] The present embodiment is to calculate the deformation field under load based on the rapidly acquired speckle photographs to obtain the horizontal tensile strain to characterize the cracking information in accordance with the actual cracking characteristics, and is accurate at the eve of cracking at 75% peak load. The high strain areas in various places are about to crack, and the crack image acquisition of the specimen at the peak is not accurate enough.

[0044] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that: in step 2, the UTM-250 loading device is used to perform an indirect tensile test on the pretreated asphalt mixture Marshall specimen, the loading rate is set to 50 mm / min, and the loading bar width is 12.7 mm. The other steps are the same as those in specific implementation method 1.

[0045] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that: the method of obtaining the loading process photos of the asphalt mixture through the digital speckle image acquisition system in step two is: level the camera bracket, fix the camera on the bracket, turn on the incandescent light source for fill light, adjust the camera angle as well as the eyepiece and aperture to make the target specimen surface clearly imaged; select a calibration plate to calibrate the distance between the camera and the specimen surface, the calibration plate and the photographed specimen surface should be placed in the same position, and the calibration plate used is 7mm apart. The other steps are the same as specific implementation methods one or two.

[0046] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that the image acquisition frequency of the digital speckle image acquisition system described in step 2 is set to 5 images per second. The other steps are the same as those of specific implementation methods 1 to 3.

[0047] The present embodiment aims to obtain a reasonable number of high-precision photos for analysis, while ensuring that loading and image acquisition are performed simultaneously to facilitate determination of images when the required load is loaded.

[0048] Specific implementation mode 5: This implementation mode is different from specific implementation modes 1 to 4 in that the size of the analysis sub-areas in step 3 is 10 to 30, and the step length is 5 to 10. The other steps are the same as those in specific implementation modes 1 to 4.

[0049] The beneficial effects of the present invention are verified by the following embodiments:

[0050] Embodiment 1: A method for evaluating the cracking performance of asphalt mixture, comprising the following steps:

[0051] I. Preparing standard Marshall specimens of asphalt mixture

[0052] In this study, the aggregate used is basalt aggregate, and the mineral powder is ground from limestone. Aggregate tests are carried out in accordance with the "Test Regulations for Highway Engineering Aggregates" JTG E42-2005 and the "Technical Specifications for Construction of Highway Asphalt Pavements" JTGF40-2004. The basic properties of the aggregate are shown in Table 1, and the basic properties of the mineral powder are shown in Table 2;

[0053] Table 1 Basic properties of aggregate

[0054]

[0055] Table 2 Basic properties of mineral powder

[0056]

[0057] Liaohe No. 90 base asphalt is used, and its basic properties are shown in Table 3;

[0058] Table 3 Basic properties of base asphalt

[0059]

[0060] The formed SMA-graded asphalt mixture uses lignin fiber, and the ex-factory technical indicators are shown in Table 4, meeting the technical requirements for lignin fiber in the "Test Regulations for Highway Engineering Aggregates" (JTG E42-2005).

[0061] Table 4 Technical indicators of fiber

[0062]

[0063] SMA13 asphalt mixture is selected as the research object. According to the grading range of different types of asphalt mixtures specified in the "Technical Specifications for Construction of Highway Asphalt Pavements" (JTGF40-2019), the median grading is selected as the target grading, and the optimum asphalt content is determined according to the test methods specified in the specification. The grading and asphalt content of the asphalt mixture are shown in Table 5. The lignin content of the SMA13-graded asphalt mixture is 3‰ of the aggregate mass.

[0064] Table 5 Grading of SMA13 asphalt mixture

[0065]

[0066] According to the Marshall specimen forming and preparation method specified in the "Test Regulations for Bitumen and Bituminous Mixtures of Highway Engineering" (JTG E20-2011), standard Marshall specimens of asphalt mixtures (standard Marshall specimens of SMA13 asphalt mixtures) were prepared;

[0067] Step 2: Cut the upper and lower surfaces of the standard Marshall specimen of asphalt mixture to expose the natural aggregates, and use the natural aggregates as speckles for observation to obtain the pre-treated Marshall specimen of asphalt mixture, as Figure 1 shown;

[0068] Figure 1 is the digital photo of the pre-treated Marshall specimen of asphalt mixture obtained in Example 1;

[0069] Step 3: According to the "Test Regulations for Bitumen and Bituminous Mixtures of Highway Engineering" (JTG E20-2011), use the universal dynamic servo hydraulic material testing system (UTM-250) loading equipment to conduct an indirect tensile test on the standard Marshall specimen, set the loading rate to 50 mm / min, and the loading bar width to 12.7 mm; synchronously control the UTM-250 loading equipment and the digital speckle image acquisition system, set the image acquisition frequency to 5 frames per second, and obtain the photos of the asphalt mixture during the indirect tensile test by the digital speckle image acquisition system; the UTM-250 loading equipment records the curve of the loading force changing with time, as shown in Figure 4 shown;

[0070] The method for obtaining the photos of the asphalt mixture during the loading process by the digital speckle image acquisition system in Step 3 is: level the camera bracket, fix the camera on the bracket, turn on the incandescent light source for supplementary lighting, adjust the angle of the camera and the eyepiece and aperture to make the surface of the target specimen clearly imaged; select a calibration plate to calibrate the distance between the camera and the specimen surface, the calibration plate and the surface of the specimen to be photographed should be placed in the same position, and the calibration plate used is 7 mm spacing; the installation diagram of the digital speckle image acquisition system is shown in Figure 2 shown, and the calibration plate is shown in Figure 3 shown;

[0071] Step 4: Import the photos collected by the digital speckle image acquisition system into the VIC-3D (non-contact strain measurement and analysis system) supporting the digital speckle image acquisition system, the analysis sub-region size is 11, and the step size is 7, as shown in Figure 5 shown; use the VIC analysis software to calculate the deformation information, and obtain the surface deformation field of the Marshall specimen of asphalt mixture during the indirect tensile test, as shown in Figure 6 shown; based on the deformation information, use the VIC analysis software to calculate the strain, obtain the horizontal strain information, the positive value is the tensile strain, the negative value is the compressive strain, and the tensile strain is related to cracking, as shown in Figure 7 shown;

[0072] Step 5: Simultaneously with the photographing of the UTM-250 loading device and the digital speckle image acquisition system, thereby determining the time corresponding to 75% of the peak load before the load peak, and then determining the image corresponding to 75% of the peak load before the load peak through the time, and extracting the strain information of this image. The strain information is the position coordinates and the magnitude of the strain value.

[0073] Step 6: Statistically quantify and characterize the magnitude of the horizontal strain field under the indirect tensile test, only counting the tensile strain. Define the strain point with a tensile strain value greater than 50% of the average tensile strain as a high-strain point. In this embodiment, based on this definition, high-strain points are discriminated, and it is determined that the strain greater than 0.0004 is a high-strain point.

[0074] Step 7: Judge the high-strain points to determine whether the high-strain points belong to the same region. The judgment criteria are as follows: If the distance between the two closest adjacent high-strain points is greater than r, then the two points do not belong to the same region. The calculation of r is as follows:

[0075]

[0076] where x n and x n+1 are the abscissas of the position coordinates of adjacent nodes, and y n and y n+1 are the ordinates of the position coordinates of adjacent nodes.

[0077] In this embodiment, it is determined that the distance between adjacent high-strain points greater than 0.75 mm does not belong to the same region.

[0078] Step 8: Count the number n of high-strain regions, and evaluate the cracking performance of the asphalt mixture based on the number n of high-strain regions. The evaluation criteria are as follows:

[0079] If 0 < n ≤ 10, the anti-cracking performance grade of the asphalt mixture Marshall specimen is excellent, and it is recommended for use.

[0080] If 11 < n ≤ 20, the anti-cracking performance grade of the asphalt mixture Marshall specimen is good, and it can be used without special requirements.

[0081] If 20 < n ≤ 30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is qualified, and its use should be restricted.

[0082] If n > 30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is unqualified, and its use is prohibited.

[0083] Judgment by the method of this embodiment shows that: the number of high-strain regions of the standard Marshall specimen of SMA13 asphalt mixture is 13, and the cracking performance is good.

Claims

1. An evaluation method for the cracking performance of asphalt mixture, characterized in that It includes the following steps: Step 1: Cut the upper and lower surfaces of the standard asphalt mixture Marshall specimen to expose the aggregates, and use the aggregates as speckles for observation to obtain the pre-treated asphalt mixture Marshall specimen; Step 2: Synchronously control the UTM-250 loading device and the digital speckle image acquisition system. Use the UTM-250 loading device to conduct an indirect tensile test on the pre-treated asphalt mixture Marshall specimen, and obtain photos of the asphalt mixture during the loading process of the indirect tensile test through the digital speckle image acquisition system; the UTM-250 loading device records the curve of the loading force changing with time; Step 3: Import the photos collected by the digital speckle image acquisition system into the VIC analysis software supporting the digital speckle image acquisition system, select an appropriate analysis sub-region size, and use the VIC analysis software to calculate the deformation information to obtain the surface deformation field of the asphalt mixture Marshall specimen during the indirect tensile test; Based on the deformation information, use the VIC analysis software to calculate the strain, obtain the horizontal strain information, with positive values being tensile strains and negative values being compressive strains, and tensile strains are related to cracking; Step 4: Based on the fact that the UTM-250 loading device and the digital speckle image acquisition system take pictures simultaneously, determine the time corresponding to 75% of the peak load before the load peak, and then determine the image corresponding to 75% of the peak load before the load peak through the time, and extract the strain information of this image. The strain information is the position coordinates and the magnitude of the strain value; Step 5: Statistically quantify and characterize the magnitude of the horizontal strain field under the indirect tensile test, only count the tensile strains, and define the strain points with tensile strain values greater than 50% of the average tensile strain as high strain points; Step 6: Judge the high strain points to determine whether the high strain points belong to the same region. The judgment criteria are as follows: If the distance between the two closest adjacent high strain points is greater than r, then the two points do not belong to the same region. The calculation of r is as follows: where x n , x n+1 are the abscissas of the position coordinates of adjacent nodes, and y n , y n+1 are the ordinates of the position coordinates of adjacent nodes; Step 7: Statistically count the number n of high strain regions, and evaluate the cracking performance of the asphalt mixture based on the number n of high strain regions. The evaluation criteria are as follows: If 0 < n ≤ 10, the anti-cracking performance grade of the asphalt mixture Marshall specimen is excellent and it is recommended for use; If 11 < n ≤ 20, the anti-cracking performance grade of the asphalt mixture Marshall specimen is good and it can be used without special requirements; If 20 < n ≤ 30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is qualified and its use should be restricted; If n > 30, the anti-cracking performance grade of the asphalt mixture Marshall specimen is unqualified and its use is prohibited.

2. The evaluation method for the cracking performance of asphalt mixture according to claim 1, characterized in that In Step 2, use the UTM-250 loading device to conduct an indirect tensile test on the pre-treated asphalt mixture Marshall specimen, with the loading rate set at 50 mm / min and the loading bar width at 12.7 mm.

3. The evaluation method for the cracking performance of an asphalt mixture according to claim 1, wherein, The method for obtaining photos of the asphalt mixture during the loading process through the digital speckle image acquisition system in Step 2 is as follows: level the camera stand, fix the camera on the stand, turn on the incandescent light source for supplementary lighting, adjust the angle of the camera, as well as the eyepiece and aperture to make the surface of the target specimen clearly imaged; select a calibration plate to calibrate the distance between the camera and the surface of the specimen. The calibration plate and the surface of the specimen to be photographed should be placed at the same position, and the calibration plate used has a pitch of 7 mm.

4. The evaluation method for the cracking performance of an asphalt mixture according to claim 1, wherein, The image acquisition frequency of the digital speckle image acquisition system described in Step 2 is set to 5 frames per second.

5. The evaluation method for the cracking performance of an asphalt mixture according to claim 1, characterized in that, The size of the analysis sub-region described in Step 3 is 10 - 30, and the step size is 5 - 10.

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