Asphalt concrete ultraviolet aging depth characterization method based on nanoindentation test

Abstract

The invention discloses an asphalt concrete ultraviolet aging depth characterization method based on a nanoindentation test. The method comprises the following steps: (1) forming an asphalt concrete test piece; (2) performing ultraviolet radiation treatment on the asphalt concrete test piece in an ultraviolet accelerated aging testing machine, and simulating ultraviolet aging of the asphalt concrete; (3) cutting the test piece to obtain small samples required by nanoindentation; (4) grinding and polishing the sample, and grinding off a certain thickness to obtain an asphalt concrete sample at a corresponding depth; and (5) carrying out nanoindentation test on the asphalt concrete samples at different depths to obtain elastic moduli at different depths, and characterizing the ultraviolet aging gradient effect of the asphalt concrete by using aging factors. The method has the advantages of being simple, convenient to operate, clear and visual in result and the like, and the gradient aging behavior of the asphalt concrete under the action of ultraviolet irradiation can be effectively represented.

Description

Technical Field

[0001] The invention belongs to the technical field of asphalt concrete aging tests, and in particular relates to a method for characterizing the ultraviolet aging depth of asphalt concrete based on nanoindentation testing. Background Art

[0002] Asphalt is susceptible to aging under the influence of high temperatures and ultraviolet rays, causing it to become brittle and hard, reducing the adhesion between asphalt and aggregate, and adversely affecting the crack resistance of asphalt concrete. It is generally believed that ultraviolet radiation has a limited impact on asphalt pavements because it only penetrates a few centimeters to the surface. Furthermore, ultraviolet radiation exhibits a distinct gradient effect on asphalt aging damage, with asphalt directly exposed to UV aging experiencing greater degradation than asphalt within the pavement. However, due to the limited depth of UV aging and the difficulty in extracting and separating different asphalt layers, the pattern of UV aging as a function of depth is not easily determined.

[0003] Most of the existing research on asphalt UV aging focuses on asphalt. However, in the actual service life of pavement, the target of ultraviolet radiation is asphalt concrete. The asphalt in asphalt concrete is in a multiphase structure including aggregates and initial voids, and its UV aging behavior may show characteristics different from those of pure asphalt.

[0004] Chinese Patent 201710437576.8 proposes a method for testing the longitudinal depth of UV aging of asphalt. This method uses a carbon disulfide solution to peel the surface layer of UV-aged asphalt layer by layer. Dynamic shear rheometers and Fourier transform infrared spectroscopy are then used to test the asphalt's conformal modulus and carbonyl gene. The depth of UV aging is determined based on the changes in the asphalt's properties during each peeling. This method requires the use of carbon disulfide to peel the asphalt film, which is cumbersome. Furthermore, the properties of the asphalt film obtained cannot truly represent the performance of asphalt concrete after UV aging in actual service.

[0005] Chinese patent application 202210109819.6 proposes an in-situ characterization method for the aging gradient of asphalt mixtures based on indentation testing. Nanoindentation testing is performed on mixture specimens obtained by drilling cores from the pavement. The elastic modulus of asphalt concrete at different layers is determined, and the in-situ aging gradient of the pavement is then evaluated. This method is suitable for evaluating the aging performance of in-situ asphalt concrete specimens obtained on site, but it cannot reflect the gradient aging effects of ultraviolet radiation on asphalt concrete.

[0006] Chinese patent 202111268955.1 proposes a method for testing the UV aging of epoxy asphalt based on nanoscratch technology, which can evaluate the depth of UV aging of epoxy asphalt. However, this method still studies asphalt rather than asphalt concrete. Furthermore, the scratch test only reveals the depth of UV aging effects on asphalt and cannot characterize the effects of UV aging on asphalt properties through physical quantities such as modulus. Summary of the Invention

[0007] In response to the above problems, the present invention provides a method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing, which is simple to operate, intuitive and clear, and can effectively evaluate the performance of asphalt concrete after being aged by ultraviolet radiation.

[0008] The present invention adopts the following technical solutions:

[0009] The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing of the present invention comprises the following steps:

[0010] (1) Preparation of test specimens: Asphalt concrete cylindrical specimens were obtained by rotary compaction molding method, and two asphalt cylindrical specimens were prepared respectively, one asphalt cylindrical specimen was used for UV aging test, and the other asphalt cylindrical specimen was not subjected to UV aging as a control group;

[0011] The number of asphalt cylinder specimens to be subjected to UV aging tests is several;

[0012] (2) The asphalt cylinder specimens were subjected to aging and irradiation treatment, and small pieces of samples were cut out and marked; similarly, samples were taken from the asphalt cylinder specimens of the control group;

[0013] (3) Cold-mounting and curing the two small test pieces cut in step (2);

[0014] (4) Preliminary grinding of several asphalt cylinder samples after aging treatment;

[0015] (5) finely grinding the aged asphalt cylinder samples obtained in step (4) at different grinding heights;

[0016] (6) Determine the measuring point: Place the sample to be tested under a microscope and select an area with a larger asphalt area to determine the measuring point;

[0017] (7) After fine polishing in step (5), nanoindentation tests are performed on the measuring points of the aged asphalt cylinder specimens at different heights and the unaged asphalt cylinder specimens; the indentation test obtains the nanoindentation modulus values ​​of the asphalt concrete at different depths and the nanoindentation modulus values ​​of the unaged asphalt concrete, and a gradient curve of the modulus and depth is drawn;

[0018] The aging factor I is used to evaluate the degree of UV aging at different depths of asphalt concrete, as follows:

[0019]

[0020] The aging gradient attenuation factor Q evaluates the attenuation degree of the ultraviolet aging phenomenon of asphalt concrete at depth, as follows:

[0021]

[0022] in:

[0023] I n is the depth at the nth gradient depth;

[0024] E n is the nanoindentation modulus value of asphalt concrete at the nth gradient depth;

[0025] E0 is the nanoindentation modulus value of unaged asphalt concrete;

[0026] Q mn is the aging gradient attenuation factor of asphalt concrete at the nth and mth depths;

[0027] h is the gradient thickness determined in the study.

[0028] The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing described in the present invention comprises the following steps: in the step (1), a rotary compaction molding method is used to obtain an asphalt concrete cylindrical specimen with a diameter of 150 mm or 100 mm and a height of 170 mm; the height of the asphalt concrete specimen obtained by cutting is 30 mm to 50 mm.

[0029] In the method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing described in the present invention, the gradient thickness determined in step (5) should be no less than 0.5 mm and no more than 2 mm, and the sample shape is cylindrical or cubic.

[0030] In the method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing described in the present invention, the number of samples of different heights obtained in step (5) is no less than 5.

[0031] In the method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing described in the present invention, the grinding time of each mesh of sandpaper in the step (5) should be no less than 1 minute, and the grinding time of 2000 mesh sandpaper should be no less than 2 minutes.

[0032] In the method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing of the present invention, the gradient thickness h used in the study is determined in the step (5), and one, two or even several gradient thicknesses are polished away using 400 mesh, 800 mesh, 1200 mesh and 2000 mesh metallographic sandpaper respectively.

[0033] If the asphalt cylinder specimen is polished to the specified gradient thickness h, no further polishing with subsequent sandpaper is required;

[0034] During the polishing process, measure the sample height every 30s to 60s until the sample reaches the expected height. Then use 0.25μm diamond polishing liquid and polish it on a polishing instrument for no less than 30min.

[0035] In the method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing described in the present invention, the number of measuring points in step (6) is no less than 10, and the distance between adjacent measuring points in the X and Y directions is 80 to 100 μm.

[0036] Beneficial effects

[0037] Compared with the existing technology, the present invention uses asphalt concrete as the research object of ultraviolet aging, which can be close to the ultraviolet aging conditions faced by asphalt pavements in actual operation, and more realistically simulate the aging effects of ultraviolet radiation on asphalt concrete. At the same time, in view of the limited depth of ultraviolet aging's influence on asphalt and the characteristics of the gradient effect, the asphalt concrete at a specific depth is obtained by grinding off a certain thickness of concrete layer, and the elastic modulus of asphalt concrete at different depths is obtained by nanoindentation testing. The method is simple and easy to operate. Finally, the aging factor I is used to evaluate the degree of ultraviolet aging of asphalt concrete at different depths, and the aging gradient attenuation factor Q is used to evaluate the attenuation degree of the ultraviolet aging phenomenon of asphalt concrete at depth. This can intuitively and clearly characterize the degree of aging of asphalt concrete at different depths by ultraviolet radiation, and obtain the law of how the degree of ultraviolet aging of asphalt concrete changes with depth. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a gradient curve of asphalt concrete modulus and depth at different depths of the present invention;

[0039] Figure 2 is a gradient curve of asphalt concrete aging factor and depth at different depths of the present invention;

[0040] Figure 3 It is the aging gradient attenuation factor between different depth positions of the asphalt concrete of the present invention. DETAILED DESCRIPTION

[0041] To make the purpose and technical solutions of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] A method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing comprises the following steps:

[0043] (1) Specimen molding: Asphalt concrete cylindrical specimens were obtained by rotary compaction molding, and asphalt cylindrical specimens suitable for placement in a UV accelerated aging tester were obtained by cutting. In addition, an asphalt concrete cylindrical specimen without UV aging treatment was prepared as a control group;

[0044] The asphalt concrete cylindrical specimens with a diameter of 150 mm or 100 mm and a height of 170 mm were obtained by the rotary compaction molding method. The height of the asphalt concrete specimens obtained by cutting was 30 mm to 50 mm.

[0045] (2) Ultraviolet aging: Wrap the sides of the asphalt concrete specimen tightly with tin foil to ensure that ultraviolet rays can only affect the top surface of the asphalt concrete specimen, and place the asphalt concrete specimen in an ultraviolet accelerated aging tester for ultraviolet irradiation treatment; the ultraviolet accelerated aging tester can simulate the ultraviolet radiation that asphalt concrete pavement is exposed to in actual work.

[0046] (3) Cutting and marking: After the UV irradiation treatment, the asphalt concrete specimens were taken out and the top surface of the asphalt concrete was cut to obtain several small asphalt concrete specimens with a side length of 15 mm. The top of the specimens were painted with color using a colored fluorescent pen to mark the top surface. At the same time, the unaged asphalt concrete was cut to obtain small specimens.

[0047] (4) Cold mounting and curing: Using epoxy resin, the cut small sample is cold mounted and cured in a rubber mold;

[0048] The specific steps are as follows: epoxy resin and curing agent are fully mixed in proportion, and poured together with a small asphalt concrete sample into a cylindrical or square rubber mold with a diameter of 2 to 3 cm. After the epoxy resin is cured, the nanoindentation sample to be polished is demoulded;

[0049] (5) Preliminary grinding: Use 150-grit metallographic sandpaper to grind a small sample at a metallographic grinding machine speed of 500 rpm until the color mark on the asphalt concrete surface is exposed. Measure and record the height of the resin sample at this time.

[0050] (6) Fine grinding: Determine the gradient thickness h used in the study, and use 400-mesh, 800-mesh, 1200-mesh, and 2000-mesh metallographic sandpaper to grind off one, two, or even several gradient thicknesses. During the grinding process, measure the sample height every 30s to 60s until the sample reaches the expected height. The determined gradient thickness should be no less than 0.5mm and no more than 2mm.

[0051] Then use 0.25μm diamond polishing liquid on the polishing instrument to polish for no less than 30min;

[0052] The number of samples of different heights obtained in step (6) should be no less than 5;

[0053] In step (6), the grinding time of each mesh sandpaper should be no less than 1 minute, and the grinding time of 2000 mesh sandpaper should be no less than 2 minutes;

[0054] In step (6), the height of the sample is measured after the polishing process is completed. If the difference between the height before polishing is within 0.1 times the gradient thickness, the sample can continue to be used; if the difference is greater than 0.1 times the gradient thickness, the sample is discarded;

[0055] (7) Determine the measuring points: Place the sample to be tested under a microscope and select an area with a larger asphalt area to determine the measuring points; the number of measuring points should be no less than 10, and the distance between adjacent measuring points in the X and Y directions should be 80 to 100 μm.

[0056] (8) Nanoindentation test: Asphalt concrete resin samples at different depths and unaged asphalt concrete resin samples were subjected to nanoindentation tests to obtain the nanoindentation modulus values ​​of asphalt concrete at different depths and the nanoindentation modulus values ​​of unaged asphalt concrete. Gradient curves of modulus and depth were drawn, and the aging factor I was used to evaluate the degree of ultraviolet aging of asphalt concrete at different depths. The aging gradient attenuation factor Q was used to evaluate the attenuation degree of ultraviolet aging of asphalt concrete at depth. The calculation formula is:

[0057]

[0058] in:

[0059] I n is the depth at the nth gradient depth;

[0060] E n is the nanoindentation modulus value of asphalt concrete at the nth gradient depth;

[0061] E0 is the nanoindentation modulus value of unaged asphalt concrete;

[0062] Q mnis the aging gradient attenuation factor of asphalt concrete at the nth and mth depths;

[0063] h is the gradient thickness determined in the study.

[0064] The Berkovich indenter was used for the nanoindentation test, with a full load time of 180 s, a loading rate of 0.01 mN / s, and a maximum load of 1 to 10 mN.

[0065] Example 1

[0066] The asphalt used in this example is AH-70# base asphalt, and the aggregate is basalt. The performance indicators of the asphalt, aggregate, and mineral powder all meet industry standards, as shown in Tables 1 to 4.

[0067] Table 1 Properties of base asphalt

[0068]

[0069] Table 2 Technical indicators of coarse aggregate

[0070]

[0071] Table 3 Technical indicators of fine aggregate

[0072]

[0073] Table 4 Technical indicators of mineral powder

[0074]

[0075] The asphalt concrete gradation used in this example is AC-13, with an optimal asphalt-aggregate ratio of 4.9%. The upper and lower limits of the mixture gradation were determined according to the current Chinese standard, "Technical Specifications for Highway Asphalt Pavement Construction" (JTG F40-2004), and the median value was used as the design gradation. The pass rates for each sieve aperture are shown in Table 5.

[0076] Table 5 Asphalt concrete AC-13 gradation

[0077]

[0078] (1) Asphalt concrete cylindrical specimen molding method:

[0079] The rotary compaction method was used for compaction molding to obtain a cylindrical specimen with a height of 170 mm and a diameter of 150 mm. After the specimen cooled, a cutting machine was used to cut the cylindrical specimen along the generatrix direction to obtain a cylindrical specimen with a diameter of 150 mm and a thickness of 50 mm.

[0080] (2) UV aging:

[0081] Use tin foil to tightly wrap the bottom and sides of the asphalt concrete cylindrical specimen, and then place the concrete specimen into the UV accelerated aging tester.

[0082] This example uses a UV accelerated aging tester produced by Guangdong Ouke Instruments. The environmental chamber has 8 built-in UVA-340 fluorescent UV lamps, which can well simulate the UV radiation with a wavelength of about 340nm, which is consistent with the UV wavelength that asphalt pavement is exposed to during actual operation. The irradiation intensity of each fluorescent UV lamp is set to 0.89W / m 2 According to the technical standards of UVA-340 fluorescent ultraviolet lamp, the irradiance is set to 0.68W / m 2 (at a wavelength of 340nm), the corresponding total radiation per hour is 1120Wh / m 2 , further converted to irradiance setting of 0.89W / m 2 The total radiation per hour is 1466Wh / m 2 , that is 5.28MJ / m 2 , the total radiation of 8 fluorescent UV lamps in the UV aging environment box is 42MJ / m per hour 2 Taking Lhasa, located in the Qinghai-Tibet Plateau, as an example, its annual average total radiation is about 6600MJ / m 2 The daily radiation dose is about 18MJ / (m 2 d), it can be assumed that 1 hour of UV exposure is equivalent to 2.3 days of natural light aging of the asphalt pavement. 160 hours of UV exposure on asphalt concrete specimens is equivalent to 1 year of natural light aging of the asphalt pavement. The temperature inside the UV accelerated aging test chamber was set at 60°C.

[0083] (3) Cutting mark:

[0084] After the UV treatment, the asphalt concrete specimens were removed and, using a small cutter, six small 15mm-long asphalt concrete blocks were cut from the center of the specimens. The top surfaces of the blocks were fully painted with a colored fluorescent marker to mark the top surface. A small block of the same size was also cut from the bottom of the concrete specimens to serve as an unaged control group.

[0085] (4) Cold mounting and curing:

[0086] Epoxy resin and curing agent are fully mixed in proportion and poured into a rubber mold together with a small piece of asphalt concrete sample. After the epoxy resin is cured, the mold is removed to obtain the nanoindentation sample to be polished;

[0087] (5) Preliminary polishing:

[0088] First, use 150-grit metallographic sandpaper to polish the surface of a small sample for 2 minutes until the colored surface of the asphalt concrete is exposed. Use a vernier caliper to measure the height at this time. Measure three times along different diameter directions and record the average value.

[0089] (6) Fine grinding:

[0090] Use 400-grit sandpaper to polish for 2 minutes, 800-grit and 1200-grit sandpaper to polish for 1 minute, and then use 2000-grit sandpaper to polish. The above-mentioned small samples are polished off in thickness of 1mm, 2mm, 3mm, 4mm, and 5mm in sequence. The sample height is measured and recorded every 30 seconds. The polished sample is then polished on a polishing instrument with 0.25μm diamond polishing liquid for 30 minutes. After the polishing process, the thickness of the sample is measured again with a vernier caliper. The difference between the two measurement results is 0.08mm, which is less than 0.1 gradient thickness (0.1mm). The sample can continue to be used. After these steps, the samples with a thickness of 1mm, 2mm, 3mm, 4mm, and 5mm polished off represent the samples at a depth of 1mm, 2mm, 3mm, 4mm, and 5mm on the asphalt concrete, respectively. The sample without the thickness polished off is the sample on the asphalt concrete surface directly exposed to ultraviolet radiation, resulting in a total of 6 experimental nanoindentation samples and 1 control sample.

[0091] (7) Determine the measuring point:

[0092] Under a microscope, a larger area of ​​asphalt was selected to make a dot matrix, resulting in a 4×4 dot matrix with a total of 16 dots. The distance between adjacent dots in the X and Y directions was 80 μm.

[0093] (8) Nanoindentation test:

[0094] The Berkovich indenter was used for the test, with a full load time of 180 s, a loading rate of 0.01 mN / s, and a maximum load of 1 mN.

[0095] (9) Experimental data processing:

[0096] Draw the gradient curve of asphalt concrete modulus and depth at different depths. Figure 1 As shown in the figure, the aging factor I is used to evaluate the degree of ultraviolet aging at different depths of asphalt concrete, and the aging gradient attenuation factor Q is used to evaluate the attenuation degree of ultraviolet aging phenomenon of asphalt concrete at depth. The calculation formula is:

[0097]

[0098] in:

[0099] I n is the depth at the nth gradient depth (n=1, 2, 3, 4, 5);

[0100] E n is the nanoindentation modulus value of asphalt concrete at the nth gradient depth;

[0101] E0 is the nanoindentation modulus value of unaged asphalt concrete, which is 0.20 GPa in this test;

[0102] Q mn is the aging gradient attenuation factor of asphalt concrete at the nth and mth depths;

[0103] h is the gradient thickness determined by the study, and in this experiment h = 1 mm.

[0104] Depend on Figure 1 As can be seen, the modulus of the surface asphalt is the largest and the degree of aging is the most severe, because it is directly exposed to ultraviolet radiation. As the depth increases, the modulus of the asphalt gradually decreases, and the degree of aging gradually decreases. The modulus of asphalt at 3mm and deeper has stabilized at 0.22GPa, which is almost the same as the modulus of asphalt that has not been UV-aged (0.20GPa), indicating that the asphalt at 3mm and deeper has basically not aged. The impact of ultraviolet radiation on asphalt aging is about 3mm deep. At the same time, it can be found that the modulus of asphalt at a depth of 0-1mm decreases less, while the modulus of asphalt at a depth of 1-2mm decreases significantly, and then the downward trend slows. This may be because the asphalt at a depth of 0-1mm is closer to the surface and is more affected by ultraviolet radiation, and has already fully aged. Therefore, the difference in modulus between asphalts at different depths is not large, that is, the degree of aging is similar. After 1mm, the impact of ultraviolet radiation weakens, and the degree of UV aging of asphalt varies significantly with increasing depth.

[0105] The gradient curves of asphalt concrete aging factor and depth at different depths are as follows: Figure 2 shown.

[0106] Depend on Figure 2 The modulus of asphalt at different depths can be more clearly and intuitively compared to the modulus of unaged asphalt. An aging factor of 0 indicates no aging, while a larger aging factor indicates deeper aging. The aging factors for asphalt at depths of 0 mm, 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm are 2.25, 2.00, 0.75, 0.2, 0.1, and 0.05, respectively. This clearly shows that asphalt aging decreases with increasing depth. The aging degree varies significantly between 1 and 2 mm, but stabilizes after 3 mm, indicating no aging.

[0107] The aging gradient attenuation factor between different depths of asphalt concrete is as follows: Figure 3 shown.

[0108] The aging gradient attenuation factor can evaluate the aging changes between different depths of asphalt concrete. The larger the factor, the more dramatic the change in the interlayer modulus and the greater the difference in aging degree; the smaller the factor, the closer the interlayer modulus and the closer the aging degree. As shown in Table 6, Q 12 The maximum is 1.25, which means that the aging degree of asphalt concrete at the depth of 1mm and 2mm is the largest, which is consistent with the Figure 1 and Figure 2 The conclusion of the analysis is consistent with that of 34 , Q 35 and Q 45 The modulus of asphalt concrete at depths of 3 mm, 4 mm, and 5 mm are relatively small, and their aging conditions are relatively close.

[0109] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for characterizing the depth of UV aging of asphalt concrete based on nanoindentation testing, characterized by: Here are the steps: (1) Preparation of test specimens: Asphalt concrete cylindrical specimens were obtained by rotary compaction molding method, and two asphalt cylindrical specimens were prepared respectively, one asphalt cylindrical specimen was used for UV aging test, and the other asphalt cylindrical specimen was not subjected to UV aging as a control group; The number of asphalt cylinder specimens to be subjected to UV aging tests is several; (2) The asphalt cylinder specimens were subjected to aging and irradiation treatment, and small pieces of samples were cut out and marked; similarly, samples were taken from the asphalt cylinder specimens of the control group; (3) Cold-mounting and curing the two small test pieces cut in step (2); (4) Preliminary grinding of several asphalt cylinder samples after aging treatment; (5) finely grinding the aged asphalt cylinder samples obtained in step (4) at different grinding heights; (6) Determine the measuring point: Place the sample to be tested under a microscope and select an area with a larger asphalt area to determine the measuring point; (7) After fine polishing in step (5), nanoindentation tests are performed on the measuring points of the aged asphalt cylinder specimens at different heights and the unaged asphalt cylinder specimens; the indentation test obtains the nanoindentation modulus values ​​of the asphalt concrete at different depths and the nanoindentation modulus values ​​of the unaged asphalt concrete, and a gradient curve of the modulus and depth is drawn; The aging factor I is used to evaluate the degree of UV aging at different depths of asphalt concrete, as follows: The aging gradient attenuation factor Q evaluates the attenuation degree of the ultraviolet aging phenomenon of asphalt concrete at depth, as follows: in: I n is the depth at the nth gradient depth; E n is the nanoindentation modulus value of asphalt concrete at the nth gradient depth; E0 is the nanoindentation modulus value of unaged asphalt concrete; Q mn is the aging gradient attenuation factor of asphalt concrete at the nth and mth depths; h is the gradient thickness determined in the study.

2. The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing according to claim 1 is characterized in that: In the step (1), a rotary compaction molding method is used to obtain an asphalt concrete cylindrical specimen with a diameter of 150 mm or 100 mm and a height of 170 mm. The height of the asphalt concrete specimen obtained by cutting is 30 mm to 50 mm.

3. The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing according to claim 1 is characterized in that: The gradient thickness determined in step (5) should be no less than 0.5 mm and no more than 2 mm, and the shape of the sample should be cylindrical or cubic.

4. The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing according to claim 1 is characterized in that: The number of samples of different heights obtained in step (5) is no less than 5.

5. The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing according to claim 1 is characterized in that: In the step (5), the grinding time of each mesh sandpaper should be no less than 1 minute, and the grinding time of 2000 mesh sandpaper should be no less than 2 minutes.

6. The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing according to claim 1 is characterized in that: The gradient thickness h used in the fine grinding in step (5); Several aged asphalt cylinder samples were polished with 400-mesh, 800-mesh, 1200-mesh and 2000-mesh metallographic sandpapers, respectively. The aged asphalt cylinder samples had gradient thicknesses of different heights.

7. The method for characterizing the depth of ultraviolet aging of asphalt concrete based on nanoindentation testing according to claim 1, characterized in that: The number of measuring points in step (6) is no less than 10, and the distance between adjacent measuring points in the X and Y directions is 80 to 100 μm.

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