Asphalt mixture freeze-thaw damage evaluation method and system based on ultrasonic technology

Abstract

The invention discloses an asphalt mixture freeze-thaw damage evaluation method and an asphalt mixture freeze-thaw damage evaluation system based on an ultrasonic technology, which are applied to the technical field of road material detection and comprehensively consider the influence of freeze-thaw cycle action on acoustic parameters and volume parameters of an asphalt mixture by means of an elastic fluctuation theory. A freeze-thaw damage variable unified calculation expression containing ultrasonic longitudinal wave velocity and void ratio is obtained through derivation, and the asphalt mixture freeze-thaw damage evaluation method and system based on the ultrasonic technology are established on the basis of the freeze-thaw damage variable unified calculation expression. Freeze-thaw damage evaluation of the graphene-basalt fiber asphalt mixture is taken as an embodiment to verify feasibility and reliability of the method and the system, the lossless evaluation method and the lossless evaluation system are provided for comprehensively and accurately performing freeze-thaw damage evaluation of the asphalt mixture, and the method and the system are good in stability, high in credibility and high in reliability. And the method has the advantages of no damage in the whole process, rapidness, simplicity, convenience, low cost and the like, and can greatly reduce test wastes to realize the purposes of low carbon and energy conservation.

Description

Technical Field

[0001] The present invention relates to the technical field of road material detection, and more specifically, to an evaluation method and system for freeze-thaw damage of asphalt mixture based on ultrasonic technology. Background Art

[0002] Due to advantages such as smooth surface, high driving comfort, wear resistance, renewable utilization, and suitability for various climate conditions and traffic loads, asphalt pavements have been widely used in road engineering construction. Affected by special natural climate factors, asphalt pavement projects in seasonal frozen regions are severely affected in terms of road use quality and service life during service due to repeated freeze-thaw cycles. The reason is that the damage effects caused by freeze-thaw cycles continuously accumulate, resulting in the gradual deterioration of the performance of asphalt mixtures. Therefore, for asphalt pavement projects in seasonal frozen regions, accurately and quickly evaluating their damage status under freeze-thaw cycles has become a key task in pavement material selection, road use performance evaluation, and ensuring use quality. Currently, the common practice is to define and calculate damage variables through mechanical property parameters obtained from indoor destructive tests to evaluate the freeze-thaw damage of asphalt mixtures. Although this method is easy to operate and can intuitively reflect the degree of freeze-thaw damage deterioration of asphalt mixtures, the evaluation results are greatly affected by test methods and conditions. At the same time, it requires a large number of test specimens and generates a lot of test waste, which is not conducive to promoting energy conservation and emission reduction work in the transportation field.

[0003] As a non-destructive testing technology, ultrasonic technology was first applied to rock damage detection. Due to advantages such as low cost, fast and simple operation, and non-destructive throughout the process, its application in the field of asphalt mixtures has become increasingly widespread in recent years. So far, the application of ultrasonic technology in the research of asphalt mixtures has mainly focused on exploring the relationship between its physical, mechanical, road use performance parameters and ultrasonic acoustic parameters. Some scholars have also used relevant acoustic parameters to evaluate the damage of asphalt mixtures, but there is a lack of clear physical meaning and theoretical basis. Moreover, asphalt mixture is a complex multiphase system. Under freeze-thaw cycles, in addition to the change of acoustic parameters, its volume parameters will also change accordingly. Simply using ultrasonic acoustic parameters to evaluate freeze-thaw damage will not be able to accurately and comprehensively evaluate its damage degree and reflect its freeze-thaw damage mechanism.

[0004] Aiming at the above research deficiencies, how to establish a convenient and non-destructive evaluation method and system for freeze-thaw damage of asphalt mixtures using ultrasonic technology to accurately, comprehensively, and non-destructively evaluate the freeze-thaw damage degree of asphalt mixtures and reflect its freeze-thaw damage mechanism has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for evaluating freeze-thaw damage of asphalt mixtures based on ultrasonic technology to solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention discloses a method for evaluating freeze-thaw damage of asphalt mixtures based on ultrasonic technology, and the specific steps are as follows:

[0008] Select the asphalt mixture to be evaluated for freeze-thaw damage. On the basis of testing the physical property indexes of the raw materials, complete the mix design of the asphalt mixture according to the test procedures and prepare the test specimens required for freeze-thaw damage evaluation.

[0009] Combined with the natural climate environment characteristics, asphalt mixture type and application occasion of the project location, formulate a freeze-thaw damage evaluation plan for the asphalt mixture and conduct a freeze-thaw cycle test on the asphalt mixture.

[0010] Measure the wave velocity of the asphalt mixture by ultrasonic wave velocity testing on the asphalt mixture specimens that have not undergone freeze-thaw cycle action and those that have reached a fixed number of freeze-thaw cycle actions.

[0011] After the wave velocity test, conduct quality parameter testing on the asphalt mixture specimens that have not undergone freeze-thaw cycle action and those that have reached a fixed number of freeze-thaw cycle actions, and calculate and determine the void ratio according to the test results; after the test is completed, repeat the above freeze-thaw cycle test until the number of freeze-thaw cycle actions determined by the evaluation plan is reached.

[0012] According to the measured wave velocity and void ratio of the asphalt mixture, use the freeze-thaw damage variable formula to calculate the freeze-thaw damage variable values at each number of freeze-thaw cycle actions, analyze its freeze-thaw damage evolution characteristics, and obtain the freeze-thaw damage evaluation result of the asphalt mixture.

[0013] Preferably, in the above method for evaluating freeze-thaw damage of asphalt mixtures based on ultrasonic technology, the specific steps for preparing the test specimens required for freeze-thaw damage evaluation are as follows:

[0014] Determine the gradation type and value of the mineral aggregate of the asphalt mixture to be evaluated, determine the optimal mix of the asphalt mixture to be evaluated according to the Marshall test mix design method, and based on the determined optimal mix, use the standard compaction method to form Marshall test cylindrical specimens as test specimens. Cut and process the top and bottom surfaces of each specimen to ensure close fitting of the transducer and the test specimen during ultrasonic wave velocity testing, and mark a number of measuring points on the corresponding top and bottom surfaces of each test specimen after cutting and processing.

[0015] Preferably, in the above method for evaluating freeze-thaw damage of asphalt mixtures based on ultrasonic technology, the specific steps of the freeze-thaw cycle test of the asphalt mixture are as follows:

[0016] The asphalt mixture specimens to be evaluated for freeze-thaw damage are saturated with water for 15 min under a vacuum of 97.3 - 98.7 kPa, soaked for 0.5 h at normal pressure after restoring the normal pressure, the specimens are taken out and put into plastic bags, 10 ml of water is added, the bags are tied tightly, and then placed in a freeze-thaw box at -18°C ± 2°C for freezing for 16 h ± 1 h. The specimens are taken out and immediately immersed in a water bath at 20°C ± 0.5°C and the plastic bags are removed, and kept at a constant temperature for 8 h. A total of 24 h is regarded as one process of freeze-thaw cycle action.

[0017] Preferably, in the above asphalt mixture freeze-thaw damage evaluation method based on ultrasonic technology, the specific steps for ultrasonic wave velocity testing are as follows:

[0018] Take the asphalt mixture specimens to be tested that are not subjected to freeze-thaw cycle action, have reached a fixed number of freeze-thaw cycle actions and are left to stand until completely dry. After evenly applying an appropriate amount of vaseline near the measuring points on the end face, place the transmitting transducer and the receiving transducer at the corresponding measuring points on the end face of the specimen respectively, rotate them moderately and align the transducers horizontally. After inputting the height of the specimen to be tested into the ultrasonic tester and performing time-of-flight zero adjustment, start the ultrasonic tester to measure the longitudinal wave velocity. After the waveform is stable, store the ultrasonic test results of each measuring point, and take the average value of each measuring point as the longitudinal wave velocity of each specimen. Take the average value of the wave velocities of multiple parallel test specimens as the longitudinal wave velocity at each number of freeze-thaw cycle actions.

[0019] Preferably, in the above asphalt mixture freeze-thaw damage evaluation method based on ultrasonic technology, the void ratio calculation formula is as follows:

[0020]

[0021] In the formula: VV is the void ratio of the asphalt mixture; γ f is the bulk relative density of the asphalt mixture, m a 、m f and m w are respectively the mass in air of the dry asphalt mixture, the saturated surface-dry mass of the specimen and the mass in water. According to the applicable conditions, methods such as the wax-coated method, the water immersion method, the wax-sealing method and the volumetric method in the "Test Procedures for Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E20 - 2011) are selected for testing; γ t is the theoretical maximum relative density of the asphalt mixture, which is obtained by calculating the measured mass parameters through the vacuum method, the solvent method or directly using the recommended formula in accordance with the provisions of the "Test Procedures for Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E20 - 2011).

[0022] Preferably, in the above asphalt mixture freeze-thaw damage evaluation method based on ultrasonic technology, the formula for the freeze-thaw damage variable of the asphalt mixture is as follows:

[0023]

[0024] VV is the void ratio of the asphalt mixture that has not undergone freeze-thaw cycles, is the void ratio of the asphalt mixture after experiencing a fixed number of freeze-thaw cycles; V P is the longitudinal wave velocity of the asphalt mixture that has not undergone freeze-thaw cycles; is the longitudinal wave velocity of the asphalt mixture after experiencing a fixed number of freeze-thaw cycles.

[0025] On the other hand, the present invention discloses an asphalt mixture freeze-thaw damage evaluation system based on ultrasonic technology, including:

[0026] A test specimen preparation module, which selects the asphalt mixture to be evaluated for freeze-thaw damage, and based on the test of the physical property indexes of the raw materials, completes the mix design of the asphalt mixture according to the test procedures and prepares the test specimens required for freeze-thaw damage evaluation;

[0027] A freeze-thaw cycle test module, which formulates an asphalt mixture freeze-thaw damage evaluation plan in combination with the natural climate environment characteristics, asphalt mixture type and application occasion of the project location, and conducts the freeze-thaw cycle test of the asphalt mixture;

[0028] A wave velocity and void ratio test module, which measures the ultrasonic wave velocity of the asphalt mixture specimens that have not undergone freeze-thaw cycles and have reached a fixed number of freeze-thaw cycles to obtain the wave velocity of the asphalt mixture;

[0029] After the wave velocity test is completed, the quality parameters of the asphalt mixture specimens that have not undergone freeze-thaw cycles and have reached a fixed number of freeze-thaw cycles are tested, and the void ratio is calculated and determined according to the test results; after the test is completed, the above freeze-thaw cycle test is repeated until the number of freeze-thaw cycles determined by the evaluation plan is reached;

[0030] A damage evaluation module, which calculates the freeze-thaw damage variable values at each number of freeze-thaw cycles by using the freeze-thaw damage variable formula according to the measured wave velocity and void ratio of the asphalt mixture, analyzes its freeze-thaw damage evolution characteristics, and obtains the freeze-thaw damage evaluation result of the asphalt mixture.

[0031] Preferably, in the above asphalt mixture freeze-thaw damage evaluation system based on ultrasonic technology, the calculation formula for the void ratio is as follows:

[0032]

[0033] Where: VV is the void ratio of the asphalt mixture; γf is the bulk relative density of the asphalt mixture, m a , m f and m w are respectively the mass of the dry asphalt mixture in the air, the saturated surface-dry mass of the specimen and the mass in water. According to the applicable conditions, methods such as the surface-dry method, the submerged weight method, the wax-sealing method and the volumetric method in the "Test Regulations for Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E20-2011) are selected for testing; γ t is the theoretical maximum relative density of the asphalt mixture. According to the provisions of the "Test Regulations for Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E20-2011), it is obtained by calculating the measured mass parameters through the vacuum method and the solvent method or directly using the recommended formula.

[0034] Preferably, in the above asphalt mixture freeze-thaw damage evaluation system based on ultrasonic technology, the formula for the freeze-thaw damage variable of the asphalt mixture in the damage evaluation module is as follows:

[0035]

[0036] VV is the void ratio of the asphalt mixture without undergoing freeze-thaw cycles, is the void ratio of the asphalt mixture after undergoing a fixed number of freeze-thaw cycles; V P is the longitudinal wave velocity of the asphalt mixture without undergoing freeze-thaw cycles; is the longitudinal wave velocity of the asphalt mixture after undergoing a fixed number of freeze-thaw cycles.

[0037] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses an asphalt mixture freeze-thaw damage evaluation method and system based on ultrasonic technology. With the help of the elastic wave theory, considering the influence of freeze-thaw cycles on the acoustic parameters and volume parameters of asphalt mixtures, through rigorous theoretical derivation, a calculation expression for the freeze-thaw damage variable containing two variables, namely the ultrasonic longitudinal wave velocity and the void ratio, is obtained, and an asphalt mixture freeze-thaw damage evaluation method based on ultrasonic non-destructive testing technology is given; the present invention has good stability and high credibility, and has the advantages of being non-destructive throughout the process, fast, simple and inexpensive, and can reduce test waste and thus achieve the purpose of low-carbon energy conservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0039] Figure 1 It is the flowchart of the method according to the embodiment of the present invention;

[0040] Figure 2 It is the aggregate gradation curve diagram according to the embodiment of the present invention;

[0041] Figure 3 It is the relationship diagram of time and temperature of the freeze-thaw cycle test scheme according to the embodiment of the present invention;

[0042] Figure 4 It is the comparison diagram of ultrasonic wave velocity test specimens according to the embodiment of the present invention;

[0043] Figure 5 It is the layout diagram of wave velocity measuring points according to the embodiment of the present invention;

[0044] Figure 6 It is the relationship diagram between the longitudinal wave velocity and the number of freeze-thaw cycles according to the embodiment of the present invention;

[0045] Figure 7 It is the relationship diagram between the porosity and the number of freeze-thaw cycles according to the embodiment of the present invention;

[0046] Figure 8 It is the dynamic modulus test results of graphene-basalt fiber asphalt mixture under different conditions according to the embodiment of the present invention;

[0047] Figure 9 It is the master curve of the dynamic modulus of graphene-basalt fiber asphalt mixture (reference temperature 20°C) according to the embodiment of the present invention;

[0048] Figures 10(a)-(e) are respectively the diagrams of the change of the dynamic modulus of graphene-basalt fiber asphalt mixture with the freeze-thaw cycle at -10°C, 5°C, 20°C, 35°C, and 50°C according to the embodiment of the present invention;

[0049] Figure 11 It is the relationship diagram between the number of freeze-thaw cycles and the damage variable of graphene-basalt fiber asphalt mixture based on ultrasonic technology according to the embodiment of the present invention;

[0050] Figure 12 It is the relationship diagram between the number of freeze-thaw cycles and the damage variable of graphene-basalt fiber asphalt mixture based on the definition of elastic modulus according to the embodiment of the present invention;

[0051] Figure 13 It is the comparison diagram of the deviation of the freeze-thaw damage variable according to the embodiment of the present invention. Detailed implementation manners

[0052] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0053] An embodiment of the present invention discloses an evaluation method and system for freeze-thaw damage of asphalt mixture based on ultrasonic technology. By means of elastic wave theory, comprehensively considering the influence of freeze-thaw cycle on the acoustic parameters and volume parameters of asphalt mixture, through strict theoretical derivation, a calculation expression of freeze-thaw damage variable containing two parameters of ultrasonic longitudinal wave velocity and void ratio is obtained, and an evaluation method for freeze-thaw damage of asphalt mixture based on ultrasonic non-destructive testing technology is established. The present invention has good stability and high credibility, and has the advantages of non-destructive throughout the process, fast, simple and low cost, etc., which can reduce test waste and thus achieve the purpose of low-carbon energy conservation.

[0054] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0055] An embodiment of the present invention discloses an evaluation method for freeze-thaw damage of asphalt mixture based on ultrasonic technology, as Figure 1 shown, the specific steps are as follows:

[0056] S100 Select the asphalt mixture to be evaluated for freeze-thaw damage. On the basis of testing the physical property indexes of the raw materials, complete the mix design of the asphalt mixture according to the test procedures and prepare the test specimens required for freeze-thaw damage evaluation;

[0057] S200 Combine the natural climate environment characteristics, asphalt mixture type and application occasion of the project location to formulate an evaluation plan for freeze-thaw damage of the asphalt mixture, and conduct a freeze-thaw cycle test on the asphalt mixture;

[0058] S300 Conduct ultrasonic wave velocity tests on the asphalt mixture specimens that have not undergone freeze-thaw cycle and have reached a fixed number of freeze-thaw cycles to measure the wave velocity of the asphalt mixture;

[0059] After the wave velocity test is completed, conduct quality parameter tests on the asphalt mixture specimens that have not undergone freeze-thaw cycle and have reached a fixed number of freeze-thaw cycles, and calculate and determine the void ratio according to the test results; after the test is completed, repeat the above freeze-thaw cycle test until the number of freeze-thaw cycles determined by the evaluation plan is reached;

[0060] The S400 calculates the freeze-thaw damage variable values at different numbers of freeze-thaw cycles according to the measured wave velocity and void ratio of the asphalt mixture, analyzes the evolution characteristics of its freeze-thaw damage, and obtains the freeze-thaw damage evaluation results of the asphalt mixture.

[0061] To further optimize the above technical solution, in S100, the specific steps for preparing the test specimens required for freeze-thaw damage evaluation are as follows:

[0062] Determine the aggregate gradation type and its value of the asphalt mixture to be tested, determine the optimal mix ratio of the asphalt mixture to be evaluated according to the Marshall test mix design method. Based on the determined optimal mix ratio, use the standard compaction method to form Marshall test cylindrical specimens as test specimens. Cut and process the top and bottom surfaces of each specimen to ensure close contact between the transducer and the test specimen during ultrasonic wave velocity testing, and mark several measuring points corresponding to the top and bottom surfaces of each test specimen after cutting and processing.

[0063] To further optimize the above technical solution, in S200, the specific steps for the freeze-thaw cycle test of the asphalt mixture are as follows:

[0064] Saturate the asphalt mixture specimens to be evaluated for freeze-thaw damage under a vacuum of 97.3 - 98.7 kPa for 15 minutes, soak them for 0.5 hours under normal pressure after restoring the pressure. Take out the specimens and put them into plastic bags, add 10 ml of water, tie the bags tightly, and then place them in a freeze-thaw box at -18°C ± 2°C for freezing for 16 h ± 1 h. Take out the specimens and immediately immerse them in a water bath at 20°C ± 0.5°C and remove the plastic bags, keep them at a constant temperature for 8 h. A total of 24 h is regarded as one cycle process; the number of freeze-thaw cycles is selected as 0, 3, 6, 9, 15, 21, and 27 times.

[0065] To further optimize the above solution, in S300, the specific steps for ultrasonic wave velocity testing are as follows:

[0066] Take the prepared asphalt mixture test specimens that have not undergone freeze-thaw cycles and those that have reached a fixed number of freeze-thaw cycles and have been left to dry completely. After evenly applying an appropriate amount of vaseline near the measuring points on the end faces, place the transmitting transducer and the receiving transducer at the corresponding measuring points on the end faces of the specimens respectively, rotate them moderately with force and align the transducers horizontally. Input the height of the test specimen to be measured into the ultrasonic tester and perform time-of-flight zero adjustment, then start the ultrasonic tester to measure the longitudinal wave velocity. After the waveform is stable, store the ultrasonic test results of each measuring point, and take the average value of each measuring point as the longitudinal wave velocity of each specimen. Take the average value of the wave velocities of multiple parallel test specimens as the longitudinal wave velocity at different numbers of freeze-thaw cycles.

[0067] Furthermore, it should be noted that:

[0068] Ultrasonic waves are sound waves with a frequency higher than 20,000 Hz that cannot be recognized by the human ear. The frequency range commonly used in engineering practice is usually 20 kHz to 100 kHz. The essence of the propagation of ultrasonic waves in a substance is a process of the propagation of mechanical vibrations in an elastic medium. Ultrasonic waves penetrate into the interior of the medium in the form of high-frequency mechanical waves and transfer energy, and they follow the wave transmission law. According to the direction of wave transmission and the vibration direction of the particles, ultrasonic waves can be divided into types such as longitudinal waves, transverse waves, and surface waves, and the acoustic parameters characterizing their own properties include wave velocity, amplitude, acoustic time, and main frequency, etc.

[0069] Since ultrasonic waves have both physical acoustics and geometric acoustics characteristics, they have good beam radiation and directivity when propagating in a medium, and the energy loss is small during the propagation process. This is also the basis for ultrasonic damage detection. Asphalt mixture is a multiphase system composed of asphalt, ore aggregates, and gas, etc. The propagation effect of ultrasonic waves in a medium is closely related to the acoustic impedance of the medium itself. Therefore, when the freeze-thaw cycle causes changes in the internal structure of the asphalt mixture, some of the sound beams propagating through the interior of the asphalt mixture will inevitably produce phenomena such as scattering, refraction, or reflection, making the acoustic parameters such as wave velocity, amplitude, and acoustic time of the asphalt mixture under different influence conditions show different change characteristics, and the changes in these parameters contain relevant information about the changes in the microscopic structure and mechanical properties of the asphalt mixture itself. Through analysis, the changes in the internal structure and freeze-thaw damage of the asphalt mixture can be reflected.

[0070] Specifically, the definition of damage variables based on ultrasonic technology;

[0071] According to the elastic wave theory, the longitudinal wave velocity V of a substance P and the transverse wave velocity V S have the following relationship with its own physical and mechanical parameters:

[0072]

[0073]

[0074] In the formula: ρ represents the density of the substance, and λ and μ are parameters describing the elastic properties of the substance, and the two are collectively called Lame coefficients.

[0075] After derivation, the Lame coefficients have the following relationship with the elastic modulus E and Poisson's ratio ν of the substance:

[0076]

[0077]

[0078] Substituting the above formulas (3) and (4) into formulas (1) and (2) and sorting them out, we can get:

[0079]

[0080]

[0081] It can be analyzed from the above formula that the change of ultrasonic wave velocity is closely related to the physical properties (density) and mechanical properties (elastic modulus) of the material itself. The acoustic wave velocity essentially characterizes the stress-strain state of the material, which is the theoretical basis for the evaluation of freeze-thaw damage of asphalt mixture by using ultrasonic technology in this invention.

[0082] Since the measurement of ultrasonic shear wave velocity is difficult, the test result has poor stability, and it requires testers to have relatively professional test experience. Therefore, in this embodiment, the ultrasonic longitudinal wave velocity is selected as the acoustic index for establishing the evaluation method of freeze-thaw damage of asphalt mixture. Then, it can be derived from the above formula (5):

[0083]

[0084] The definition of damage variable based on elastic modulus can be derived from the equivalent strain hypothesis proposed by French scholar Lemaitre:

[0085]

[0086] In the formula: E is the elastic modulus of the undamaged material, is the elastic modulus of the damaged material.

[0087] Without considering the change of Poisson's ratio of asphalt mixture under freeze-thaw cycles, it can be derived from formulas (7) and (8):

[0088]

[0089] In the formula: ρ, V P are the density and longitudinal wave velocity of asphalt mixture without experiencing freeze-thaw cycles respectively; are the density and longitudinal wave velocity of asphalt mixture after experiencing a certain number of freeze-thaw cycles respectively.

[0090] Under freeze-thaw cycles, the mass m of asphalt mixture will not change, and there is the following relationship between density ρ and volume v:

[0091]

[0092] Then, it can be obtained from formulas (9) and (10):

[0093]

[0094] In the formula: v, They represent the volumes of asphalt mixture before and after a certain number of freeze-thaw cycles respectively.

[0095] Under the saturated water state, the voids inside the asphalt mixture are occupied by water. The freeze-thaw cycles cause the water in the voids to freeze and melt repeatedly. This process promotes the continuous generation and evolution of the voids inside the asphalt mixture, and then causes irreversible deformation of the asphalt mixture. Therefore, the volumes of asphalt mixture before and after a certain number of freeze-thaw cycles can be expressed as:

[0096] v = v s + v o (12);

[0097]

[0098] In the formula: v s , v o , Δv o are the solid volume, void volume and void volume increment of the asphalt mixture respectively.

[0099] And there is the following relationship between the bulk relative density and the air voids of the asphalt mixture:

[0100]

[0101] In the formula: VV is the air voids of the asphalt mixture; γ f is the bulk relative density of the asphalt mixture, calculated according to formula (15); γ t is the theoretical maximum relative density of the asphalt mixture, calculated according to formula (16).

[0102]

[0103]

[0104] In the formula: ρ f is the bulk density of the asphalt mixture, calculated according to formula (17); ρ t is the theoretical maximum density, calculated according to formula (18); ρ w is the density of water at 25°C, taking 0.9971 g / cm 3 .

[0105]

[0106]

[0107] In the formula: m, v a , v b are the dry mass, apparent volume and bulk volume of the asphalt mixture respectively.

[0108] Substituting equations (15) to (18) into equation (14) and simplifying, we get:

[0109]

[0110] For asphalt mixtures that have not undergone freeze-thaw cycles, the apparent volume \(v\) a and the bulk volume \(v\) b can be calculated according to equations (20) and (21) respectively.

[0111] \(v\) a = \(v\) s (20);

[0112] \(v\) b = \(v\) s + \(v\) o (21);

[0113] For asphalt mixtures that have undergone a certain number of freeze-thaw cycles, the apparent volume and the bulk volume can be calculated according to equations (22) and (23) respectively.

[0114]

[0115]

[0116] Substituting equations (20), (21), (22), and (23) into equation (19) respectively, the calculation formulas for the void ratio of asphalt mixtures expressed by volume parameters before and after freeze-thaw cycles can be derived as shown in equations (24) and (25):

[0117]

[0118]

[0119] Where: \(VV\) is the void ratio of asphalt mixtures that have not undergone freeze-thaw cycles, is the void ratio of asphalt mixtures that have undergone a certain number of freeze-thaw cycles.

[0120] Combining equations (12) and (24), we can derive:

[0121]

[0122] Similarly, combining equations (13) and (25), we can derive:

[0123]

[0124] From equations (11), (26), and (27), we get:

[0125]

[0126] Formula (28) is the unified damage variable expression of asphalt mixture under freeze-thaw cycles based on elastic wave theory and ultrasonic technology. As can be seen from the above formula, the formula contains both the volume parameters of asphalt mixture and the acoustic parameters of asphalt mixture, which can accurately and comprehensively reflect the damage evolution characteristics of asphalt mixture under freeze-thaw cycles and is applicable to the freeze-thaw damage evaluation of asphalt mixture in seasonal freezing regions.

[0127] Another embodiment of the present invention discloses a freeze-thaw damage evaluation system for asphalt mixture based on ultrasonic technology, including:

[0128] A test specimen preparation module, which selects the asphalt mixture to be evaluated for freeze-thaw damage, and on the basis of testing the physical property indexes of raw materials, completes the mix design of asphalt mixture according to the test procedures and prepares the test specimens required for freeze-thaw damage evaluation;

[0129] A freeze-thaw cycle test module, which formulates a freeze-thaw damage evaluation plan for asphalt mixture in combination with the natural climate environment characteristics, asphalt mixture type and application occasion of the project location, and conducts the freeze-thaw cycle test of asphalt mixture;

[0130] A wave velocity and void ratio test module, which conducts ultrasonic wave velocity tests on asphalt mixture specimens that have not undergone freeze-thaw cycles and have reached a fixed number of freeze-thaw cycle times to measure the wave velocity of asphalt mixture;

[0131] After the wave velocity test is completed, mass parameter tests are conducted on asphalt mixture specimens that have not undergone freeze-thaw cycles and have reached a fixed number of freeze-thaw cycle times, and the void ratio is calculated and determined according to the test results; after the test is completed, the above freeze-thaw cycle test is repeated until the number of freeze-thaw cycle times determined by the evaluation plan is reached;

[0132] A damage evaluation module, which calculates the freeze-thaw damage variable values at each freeze-thaw cycle time by using the freeze-thaw damage variable formula according to the measured wave velocity and void ratio of asphalt mixture, analyzes its freeze-thaw damage evolution characteristics, and obtains the freeze-thaw damage evaluation result of asphalt mixture.

[0133] In order to further optimize the above technical solution, the calculation formula of the void ratio in the wave velocity and void ratio test module is as follows:

[0134]

[0135] In the formula: VV is the void ratio of asphalt mixture; γ f is the bulk relative density of asphalt mixture, m a 、m f and mw They are the aerial mass of the dry asphalt mixture, the saturated surface-dry mass of the specimen, and the submerged mass in water respectively. According to the applicable conditions, methods such as the surface-dry method, the submerged-weight method, the wax-sealing method, and the volumetric method in the "Test Procedures for Bitumen and Bituminous Mixtures of Highway Engineering" (JTG E20-2011) are selected for testing; γ t is the theoretical maximum relative density of the asphalt mixture, which is obtained by calculating the measured mass parameters through the vacuum method and the solvent method or directly using the recommended formula in accordance with the provisions of the "Test Procedures for Bitumen and Bituminous Mixtures of Highway Engineering" (JTG E20-2011).

[0136] To further optimize the above technical solution, the formula for the freeze-thaw damage variable of the asphalt mixture in the damage evaluation module is as follows:

[0137]

[0138] VV is the void ratio of the asphalt mixture that has not undergone freeze-thaw cycles, is the void ratio of the asphalt mixture after experiencing a fixed number of freeze-thaw cycles; V P is the longitudinal wave velocity of the asphalt mixture that has not undergone freeze-thaw cycles; is the longitudinal wave velocity of the asphalt mixture after experiencing a fixed number of freeze-thaw cycles.

[0139] To illustrate that the method provided by the present invention can be applied to the freeze-thaw damage evaluation of asphalt mixtures, the following examples are used for verification.

[0140] 1 Raw materials and mix design:

[0141] 1.1 Physical properties of raw materials;

[0142] (1) Bitumen: Kramay AH-70 # heavy traffic road petroleum bitumen is adopted, and the technical indicators are shown in Table 1.

[0143] Table 1 Basic performance indicators of matrix bitumen

[0144]

[0145] (2) The coarse aggregate used in the test is andesite, the fine aggregate and the manufactured sand are limestone, and the mineral powder is limestone powder. The technical performance indicators of the test aggregate and mineral powder all meet the requirements of the "Technical Specification for Construction of Highway Asphalt Pavements" (JTGF40-2004).

[0146] (3) Basalt fiber: Short-cut basalt fiber produced by Jilin Tongxin Basalt Fiber Co., Ltd. is adopted, with a diameter of 13μm and a length of 6mm. The technical indicators are shown in Table 2.

[0147] Table 2 Basic technical indicators of basalt fiber

[0148]

[0149]

[0150] (4) Graphene: The graphene powder produced by Qingdao Yanhai Carbon Materials Co., Ltd. is adopted, and the technical indicators are shown in Table 3.

[0151] Table 3 Basic Technical Indicators of Graphene

[0152]

[0153] 1.2 Mix Proportion Design;

[0154] The mineral aggregate gradation of the graphene-basalt fiber asphalt mixture is based on that of the fine-grained asphalt mixture AC-13 (see Figure 2 ). According to the Marshall test mix proportion design method, with the asphalt-aggregate ratio, graphene dosage and basalt fiber dosage as influencing factors, and the void ratio, void in mineral aggregate (VMA), asphalt saturation, stability and flow value as response values, the response surface method is used for optimization design. Finally, the optimal asphalt-aggregate ratio of the graphene-basalt fiber asphalt mixture is determined to be 5.3%, the graphene dosage is 0.2% (externally added), and the basalt fiber dosage is 0.3% (externally added).

[0155] 2. Test Equipment and Test Methods:

[0156] 2.1 Test Equipment;

[0157] The freeze-thaw cycle test is completed in a high and low temperature alternating test chamber. This equipment has a fast and accurate temperature control system, which can realize continuous switching and constant temperature of any temperature in the range of -70°C to 150°C, with a temperature deviation ≤ ±1.5°C. The number of high and low temperature alternating cycles can be set according to the test requirements, meeting the requirements of the freeze-thaw cycle test of the graphene-basalt fiber asphalt mixture.

[0158] The ultrasonic longitudinal wave velocity test is carried out using a ZBL-U5200 non-metallic ultrasonic detector. This equipment consists of a transmitting transducer, a receiving transducer, wires and a main unit, etc. It is mainly used for non-destructive testing of materials such as concrete, rock, ceramics and plastics, and can be used for the physical and mechanical property testing and evaluation of non-metallic materials. The specific technical indicators are shown in Table 4.

[0159] Table 4 Main Technical Parameters of the Ultrasonic Detector

[0160]

[0161] The uniaxial compression dynamic modulus test uses a DTS-30 multi-functional pavement material dynamic testing system. The loading range of this equipment can reach ±30 kN, the actuation frequency is 100 Hz, the stroke is 100 mm, and the temperature control unit ranges from -40°C to +80°C. It consists of a hydraulic servo actuator, a hydraulic power unit, a channel data collector and control system, a load sensor, an actuator displacement sensor LVDT, and a temperature control box, etc., and can perform various mechanical property tests such as tension, compression, and dynamic loading on materials such as asphalt mixtures, geotechnical materials, fibers, and plastics.

[0162] 2.2 Test methods;

[0163] (1) Freeze-thaw cycle test

[0164] Currently, there is no consensus on the freeze-thaw cycle test method for asphalt mixtures. Most relevant studies follow the freeze-thaw splitting test method in the "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). However, the melting process of keeping the temperature constant in a 60°C water bath for 24 hours in this method seriously does not match the actual freeze-thaw cycle process experienced by asphalt pavement engineering in seasonal frozen areas. Therefore, considering the specific natural climate characteristics and actual use conditions of asphalt pavement engineering in seasonal frozen areas, the freeze-thaw cycle test method in this embodiment is determined as follows: First, saturate the asphalt mixture specimen to be evaluated for freeze-thaw damage in a vacuum state of 97.3 - 98.7 kPa for 15 minutes, then restore normal pressure and soak for 0.5 h. Take out the specimen and put it into a plastic bag, add about 10 ml of water, tie the bag tightly, and then place it in a freeze-thaw box at -18°C ± 2°C for freezing for 16 h ± 1 h. Finally, take out the specimen and immediately immerse it in a water bath at 20°C ± 0.5°C and remove the plastic bag, and keep the temperature constant for 8 h. A total of 24 h is regarded as one cycle process, as Figure 3 shown. Current relevant research on the influence of freeze-thaw on the road performance of asphalt mixtures shows that the mechanical properties of asphalt mixtures basically tend to be stable after about 15 freeze-thaw cycles. In order to systematically and deeply verify the feasibility and reliability of the method and system disclosed in the present invention applied to the evaluation of freeze-thaw damage of asphalt mixtures, the number of freeze-thaw cycles in this embodiment is selected as 0, 3, 6, 9, 15, 21, and 27 times. At the same time, in order to reduce the error in the evaluation of freeze-thaw damage, the number of parallel specimens in the freeze-thaw cycle test is taken as 9.

[0165] (2) Ultrasonic wave velocity test

[0166] 1) Test specimen treatment

[0167] For the ultrasonic wave velocity test, Marshall test cylindrical specimens formed by the standard compaction method are used. Considering that factors such as rough surface, many voids, and poor flatness on the top (bottom) surface of the specimen may affect the fitting degree between the transducer and the test specimen, resulting in relatively large errors in the wave velocity test results. In this embodiment, the top (bottom) surface of the graphene-basalt fiber asphalt mixture specimen is cut and processed so that the top and bottom surfaces of the specimen in contact with the transducer are smooth and flat during the wave velocity test operation, ensuring close fitting between the transducer and the test specimen (see Figure 4 , where a is the graphene-basalt fiber asphalt mixture specimen after cutting and processing; b is the graphene-basalt fiber asphalt mixture specimen without cutting and processing). In order to verify the necessity of processing the test specimen and its influence on the ultrasonic wave velocity test results, the graphene-basalt fiber asphalt mixture specimen without freeze-thaw cycle action is used as the test object, and a comparative analysis of the test results of the processed specimen and the unprocessed specimen is carried out. The results are shown in Table 5. It can be seen from the table that the standard deviation and coefficient of variation of the unprocessed test specimen are significantly larger, while the average value and representative value are smaller, indicating that the surface condition of the specimen has a significant influence on the ultrasonic wave velocity test results, and it is necessary to cut and process its surface. Therefore, in this embodiment, 5 mm is cut from each of the top and bottom surfaces of the specimen, that is, the height of the standard specimen for ultrasonic wave velocity test after cutting and processing is 53.5 mm ± 1.3 mm.

[0168] Table 5 Comparison of Ultrasonic Wave Velocity Tests

[0169]

[0170] 2) Test Method

[0171] Take the standard specimen for ultrasonic wave velocity test after cutting and processing, and mark five measuring points on the corresponding top and bottom surfaces of each specimen (see Figure 5) During the test, the average value of five measurement points is taken as the test result of the longitudinal wave velocity of the specimen. The specific test process and method are as follows: First, install and debug the ultrasonic tester. After taking the specimen to be tested and evenly applying an appropriate amount of vaseline near the measurement points on the end face, place the transmitting transducer and the receiving transducer at the corresponding measurement points on the end face of the specimen respectively, rotate with moderate force and align the transducers horizontally; Then, input the height of the specimen to be tested into the ultrasonic tester and perform zero adjustment of the acoustic time; Finally, start the ultrasonic tester to test the longitudinal wave velocity. After the waveform is stable, store the ultrasonic test results of each measurement point, and take the average value of 5 measurement points as the longitudinal wave velocity of each specimen. Take the average value of the wave velocities of 9 parallel test specimens as the longitudinal wave velocity under each freeze-thaw cycle number. After the test of each test specimen is completed, the quality parameters for calculating and determining the void ratio of the asphalt mixture should be tested quickly, then vacuum saturated with water and enter the next round of freeze-thaw cycle test. After reaching the predetermined number of freeze-thaw cycles, let it stand until completely dry and repeat the above test process until all the freeze-thaw cycles required by the freeze-thaw damage evaluation scheme are tested.

[0172] (3) Determination of void ratio

[0173] The table dry method in the "Test Regulations for Asphalt and Asphalt Mixtures of Highway Engineering" (JTG E20 - 2011) is used to determine the void ratio of the graphene - basalt fiber asphalt mixture. The specific test and determination process is as follows: First, clean the floating particles on the surface of the specimen and weigh the in-air mass m of the dry specimen a ; Then, place the specimen in an overflow water tank with the water temperature maintained at 25°C ± 0.5°C and soak it for 3 - 5 minutes, weigh the in-water mass m w , and take out the specimen from the water, wipe off the surface water of the specimen with a clean and soft wrung-dry towel, and weigh the surface-dry mass m of the specimen f ; Finally, calculate the relative bulk density of the asphalt mixture specimen according to Equation (29), and calculate the void ratio of the specimen to be tested according to Equation (14).

[0174]

[0175] (4) Dynamic modulus test

[0176] For the dynamic modulus test, a DTS-30 multi-functional dynamic testing system for pavement materials was used. In accordance with the provisions in the "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the test specimens were core samples with a diameter of 100 mm and a height of 150 mm, which were formed by rotary compaction, cored, and cut. After reaching the predetermined number of freeze-thaw cycle actions, in the test sequence from low temperature to high temperature and from high frequency to low frequency, data such as the loading cyclic stress amplitude and strain amplitude were measured at five temperature conditions of -10°C, 5°C, 20°C, 35°C, and 50°C and six frequencies of 25 Hz, 10 Hz, 5 Hz, 1 Hz, 0.5 Hz, and 0.1 Hz. The dynamic modulus of the specimen under different test combination conditions was calculated through Equation (30).

[0177]

[0178] In the formula: σ0 and ε0 are the axial stress amplitude and axial strain amplitude respectively.

[0179] 2.3 Test and measurement results

[0180] According to the aforementioned ultrasonic wave velocity test method, the test results of the ultrasonic wave velocity of graphene-basalt fiber asphalt mixture under freeze-thaw cycle actions are as Figure 6 shown. It can be seen from the figure that the ultrasonic wave velocity gradually decreases with the increase in the number of freeze-thaw cycle actions, dropping from 3.512 km / s without experiencing freeze-thaw cycle actions to 3.218 km / s after 27 freeze-thaw cycle actions, with a decrease of up to 8.37%; among them, the attenuation amplitude in the first 3 freeze-thaw cycles is the largest, accounting for 39.5% of the attenuation amplitude in the entire 27 freeze-thaw cycles; subsequently, the attenuation amplitude gradually weakens and basically stabilizes after experiencing about 15 freeze-thaw cycle actions, and the decrease in wave velocity caused by the 15th to 27th freeze-thaw cycle actions is only 0.65%.

[0181] After the ultrasonic wave velocity test was completed, in accordance with the aforementioned relevant quality parameter test and void ratio determination method, the change results of the void ratio of graphene-basalt fiber asphalt mixture under freeze-thaw cycle actions are as Figure 7 shown. It can be seen from the figure that the void ratio of graphene-basalt fiber asphalt mixture gradually increases with the increase in the number of freeze-thaw cycle actions, increasing from 3.88% without experiencing freeze-thaw cycle actions to 4.76% after 27 freeze-thaw cycle actions, with an increase of up to 23%; among them, the increase amplitude of the void ratio caused by the first 6 freeze-thaw cycle actions is the largest, accounting for 55.3% of the increase amplitude in the entire 27 freeze-thaw cycles; subsequently, the increase amplitude gradually decreases and gradually eases after experiencing about 15 freeze-thaw cycle actions, and the increase amplitude of the void ratio caused by the 15th to 27th freeze-thaw cycle actions is only 2.07%.

[0182] The variation law of the dynamic modulus of graphene-basalt fiber asphalt mixture without freeze-thaw cycles with temperature and loading frequency is as follows Figure 8 shown. It can be seen from the figure that at the same test load frequency, the dynamic modulus of the graphene-basalt fiber asphalt mixture gradually decreases with the increase of the test temperature. Among them, when the test temperature rises from -10°C to 20°C, the downward trend of the dynamic modulus of the graphene-basalt fiber asphalt mixture begins to accelerate gradually, and its downward trend gradually increases with the decrease of the loading frequency; when the test temperature rises from 20°C to 50°C, with the gradual decrease of the loading frequency, the downward trend of the dynamic modulus also slows down. In addition, the dynamic modulus of the graphene-basalt fiber asphalt mixture gradually decreases with the decrease of the loading frequency. The reason is that the gradual increase of the test temperature causes the asphalt binder inside the asphalt mixture to soften, and its properties gradually change from a solid to a viscoelastic-plastic body, and the bonding property is greatly reduced. Moreover, the higher the test temperature, the more significant the softening effect of the asphalt and the worse the bonding property.

[0183] Usually, the dynamic modulus parameters of asphalt mixtures should conform to the common Sigmoidal model, and the Mechanistic-Empirical Pavement Design Guide (MEPDG) in the United States also uses this model to characterize the dynamic modulus of asphalt mixtures. Therefore, in this embodiment, based on the dynamic modulus of the asphalt mixture at 20°C, the Sigmoidal model is used to fit the master curve of the dynamic modulus of the graphene-basalt fiber asphalt mixture, and its mathematical expression is shown in Equation (31):

[0184]

[0185] In the formula: lg|E * | is the dynamic modulus in logarithmic coordinates; δ is the minimum dynamic modulus in this coordinate; α is the corresponding maximum dynamic modulus; λ, β, and γ are shape coefficients.

[0186] The master curve of the dynamic modulus of the graphene-basalt fiber asphalt mixture is as follows Figure 9 shown. It can be seen from the figure that the correlation coefficient R 2 = 0.99 of the master curve of the dynamic modulus, and the fitting effect is good, which can accurately reflect the change trend of the dynamic modulus of the asphalt mixture with frequency, that is, the change of the dynamic modulus with frequency is relatively gentle in the high-frequency and low-frequency intervals at both ends of the S-shaped growth curve model, but the change in the middle part of the curve is relatively drastic.

[0187] The variation of the dynamic modulus test results of graphene-basalt fiber asphalt mixture with the number of freeze-thaw cycles is shown in Figure 10. Through the analysis of the test data, it can be seen that under the same test conditions, the dynamic modulus of graphene-basalt fiber asphalt mixture shows an obvious downward trend with the increase of the number of freeze-thaw cycles. In the test environment of low temperature and high frequency, the dynamic modulus decays violently with the increase of the number of freeze-thaw cycles, but the downward trend is mitigated with the increase of the test temperature and the decrease of the loading frequency.

[0188] 3. Evaluation of freeze-thaw damage and verification of method for graphene-basalt fiber asphalt mixture:

[0189] Based on the test results of ultrasonic longitudinal wave velocity and porosity, using the freeze-thaw damage variable calculation formula in the method and system disclosed in the present invention, the damage variables of graphene-basalt fiber asphalt mixture under different numbers of freeze-thaw cycles can be calculated, and the variation law of the damage variables with the number of freeze-thaw cycles is as follows Figure 11As shown. It can be seen from the figure that the freeze-thaw damage variable of the graphene-basalt fiber asphalt mixture gradually increases with the increase in the number of freeze-thaw cycles. Among them, the damage change caused by the first 15 freeze-thaw cycles is the most significant, especially the freeze-thaw damage change in the first 3 cycles is the most intense, and its damage variable rapidly increases from 0 to 0.068; after 15 freeze-thaw cycles, the change trend of the freeze-thaw damage gradually flattens out, and the freeze-thaw damage variable is basically stable at about 0.17. The reason is that the freeze-thaw damage of the graphene-basalt fiber asphalt mixture is mainly caused by the different thermophysical properties of its constituent media during the freezing and melting processes. The graphene-basalt fiber asphalt mixture in the saturated water state is a complex multiphase system composed of mineral aggregate particles, asphalt binder, water, etc. The mineral aggregate particles form the skeleton of the asphalt mixture, and water and asphalt binder fill the pores of the skeleton. In the frozen state, due to the non-single composition of the graphene-basalt fiber asphalt mixture, the volume shrinkage of each constituent component is not uniform. At the same time, the water inside the mixture pores freezes and generates a volume expansion of about 9%. Due to the restraint of the surrounding mineral aggregates and asphalt binder, a frost heaving force is generated. When this frost heaving force exceeds a certain limit, it will change the space and shape of its internal pores. This process will cause the internal pores of the asphalt mixture to continuously increase and new cracks to germinate; in the melting state, during the melting process of the ice in the pores, the release of the frost heaving force and the migration of water are accompanied, but the pores and newly added cracks changed by freezing cannot return to their original state. With the increase in the number of freeze-thaw cycles, the pore space and shape change continuously, new cracks are continuously added and further expanded, and the internal structure of the asphalt mixture is damaged due to continuous disturbance, which is macroscopically manifested as the continuous increase in the porosity of the graphene-basalt fiber asphalt mixture, the continuous attenuation of the longitudinal wave velocity and elastic modulus, and the gradual increase in the freeze-thaw damage variable. After multiple freeze-thaw cycles, the internal structure of the asphalt mixture gradually tends to be stable, and the graphene-basalt fiber asphalt mixture reaches a new equilibrium state, then the change of its freeze-thaw damage variable gradually flattens out.

[0190] To verify the feasibility and reliability of the freeze-thaw damage evaluation method and system for asphalt mixtures based on ultrasonic technology proposed in this embodiment, based on the dynamic modulus test data, the freeze-thaw damage variables of the graphene-basalt fiber asphalt mixture at various loading frequencies at 20 °C were calculated using Equation (8) (see Figure 12 ).

[0191] By comparative analysis Figure 11 and Figure 12 it can be found that both the damage variable defined based on ultrasonic technology and the damage variable defined based on elastic modulus gradually increase with the increase in the number of freeze-thaw cycles, and the change trends of the two are basically the same, indicating that the freeze-thaw damage evaluation method and system for asphalt mixtures based on ultrasonic technology proposed in this embodiment are reasonable and feasible.

[0192] In order to more accurately evaluate the reliability of the asphalt mixture freeze-thaw damage evaluation method and system based on ultrasonic technology proposed in this embodiment, Figure 13 The deviation calculation results between the evaluation results based on the ultrasonic method and the damage variables defined by the elastic modulus method are given. It can be clearly seen from the figure that the deviations of the damage variables measured by the ultrasonic method and the elastic modulus method are relatively small, and they are all concentrated near the horizontal line with a deviation of 0. Except for some data with larger deviations, the remaining deviations are basically between ±0.05. Moreover, the data deviation measured by the elastic modulus method has a larger discreteness, while the damage variable data deviation obtained by the ultrasonic method is smaller and more stable, which fully demonstrates the reliability and superiority of the asphalt mixture freeze-thaw damage evaluation method and system based on ultrasonic technology proposed in this embodiment.

[0193] In summary, this embodiment adopts an asphalt mixture freeze-thaw damage evaluation method and system based on ultrasonic technology disclosed in the present invention. Through the evaluation and analysis of the freeze-thaw damage of graphene-basalt fiber asphalt mixture, it shows that the asphalt mixture freeze-thaw damage evaluation method and system based on ultrasonic technology has good stability, high credibility, and has the advantages of non-destructive throughout the process, fast, simple, and low cost. It can reduce test waste and thus achieve the purpose of low-carbon energy conservation, and is applicable to the freeze-thaw damage evaluation of various asphalt mixtures in cold regions.

[0194] The various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0195] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An evaluation method for freeze-thaw damage of asphalt mixture based on ultrasonic technology, characterized in that, The specific steps are as follows: Select the asphalt mixture to be evaluated for freeze-thaw damage. Based on the test of the physical property indexes of the raw materials, complete the mix design of the asphalt mixture in accordance with the test regulations and prepare the test specimens required for freeze-thaw damage evaluation; Combined with the natural climate environment characteristics, asphalt mixture type and application occasion of the project location, formulate a freeze-thaw damage evaluation plan for the asphalt mixture and conduct a freeze-thaw cycle test on the asphalt mixture; Conduct ultrasonic wave velocity testing on the asphalt mixture specimens that have not undergone freeze-thaw cycle action and have reached a fixed number of freeze-thaw cycle action times to obtain the wave velocity of the asphalt mixture; After the wave velocity testing is completed, conduct quality parameter testing on the asphalt mixture specimens that have not undergone freeze-thaw cycle action and have reached a fixed number of freeze-thaw cycle action times, and calculate and determine the void ratio according to the test results; after the testing is completed, repeat the above freeze-thaw cycle test until the number of freeze-thaw cycle actions determined by the evaluation plan is reached; According to the measured wave velocity and void ratio of the asphalt mixture, use the freeze-thaw damage variable formula to calculate the freeze-thaw damage variable values at each number of freeze-thaw cycle actions, analyze its freeze-thaw damage evolution characteristics, and obtain the freeze-thaw damage evaluation results of the asphalt mixture.

2. The asphalt mixture freeze-thaw damage evaluation method based on ultrasonic technology according to claim 1, wherein The specific steps for preparing the test specimens required for freeze-thaw damage evaluation are as follows: Determine the aggregate gradation type and value of the asphalt mixture to be tested, determine the best mix of the asphalt mixture to be tested according to the Marshall test mix design method, and use the standard compaction method to form Marshall test cylindrical specimens as test specimens according to the determined best mix. The top and bottom surfaces of each specimen are cut and processed to ensure the close fit of the transducer and the test specimen during ultrasonic wave velocity testing, and a number of measuring points are marked corresponding to the top and bottom surfaces of each test specimen after cutting and processing.

3. A method for evaluating freeze-thaw damage of asphalt mixture based on ultrasonic technology according to claim 1, wherein the asphalt The specific steps for the freeze-thaw cycle test of the mixture are as follows: Saturate the asphalt mixture specimens to be evaluated for freeze-thaw damage under a vacuum of 97.3 - 98.7 kPa for 15 min, soak them under normal pressure for 0.5 h, take out the specimens and put them into plastic bags, add 10 ml of water, tie the bags tightly and then place them in a freeze-thaw box at -18°C ± 2°C for freezing for 16 h ± 1 h. Take out the specimens and immediately immerse them in a water bath at 20°C ± 0.5°C and remove the plastic bags, keep them at a constant temperature for 8 h. A total of 24 h is regarded as one freeze-thaw cycle action process.

4. A method for evaluating freeze-thaw damage of asphalt mixture based on ultrasonic technology according to claim 1, characterized in that, The specific steps for ultrasonic wave velocity testing are as follows: Take the prepared asphalt mixture test specimens that have not undergone freeze-thaw cycle action and have reached a fixed number of freeze-thaw cycle action times and are left to stand until completely dry. Place the transmitting transducer and the receiving transducer at the corresponding measuring points on the specimen end face respectively, start the ultrasonic wave tester to conduct longitudinal wave velocity testing. After the waveform is stable, store the ultrasonic test results of each measuring point, and take the average value of each measuring point as the longitudinal wave velocity of each specimen. Take the average value of the wave velocities of multiple parallel test specimens as the longitudinal wave velocity at each number of freeze-thaw cycle actions.

5. The asphalt mixture freeze-thaw damage evaluation method based on ultrasonic technology according to claim 1, characterized in that, The formula for calculating the void ratio is as follows: Where: VV is the void ratio of the asphalt mixture; γ f is the bulk relative density of the asphalt mixture, m a 、m f and m w are the mass of the dry asphalt mixture in air, the saturated surface-dry mass of the specimen, and the mass of the specimen in water, respectively; γ t is the theoretical maximum relative density of the asphalt mixture.

6. A method for evaluating freeze-thaw damage of asphalt mixture based on ultrasonic technology according to claim 1, wherein the asphalt The formula for the freeze-thaw damage variable of the mixture is as follows: VV is the void ratio of the asphalt mixture that has not undergone freeze-thaw cycles, is the void ratio of the asphalt mixture after undergoing a fixed number of freeze-thaw cycles; V P is the longitudinal wave velocity of the asphalt mixture that has not undergone freeze-thaw cycles; is the longitudinal wave velocity of the asphalt mixture after undergoing a fixed number of freeze-thaw cycles.

7. An evaluation system for freeze-thaw damage of asphalt mixture based on ultrasonic technology, characterized in that, Including: Test specimen preparation module: Select the asphalt mixture to be evaluated for freeze-thaw damage. Based on the test of the physical property indexes of the raw materials, complete the mix design of the asphalt mixture according to the test procedures and prepare the test specimens required for freeze-thaw damage evaluation; Freeze-thaw cycle test module: Combine the natural climate environment characteristics, asphalt mixture type and application occasion of the project location to formulate a freeze-thaw damage evaluation plan for the asphalt mixture and conduct the freeze-thaw cycle test of the asphalt mixture; Wave velocity and void ratio test module: Conduct ultrasonic wave velocity test on the asphalt mixture specimens that have not undergone freeze-thaw cycle action and those that have reached a fixed number of freeze-thaw cycle action times to obtain the wave velocity of the asphalt mixture; After the wave velocity test, conduct quality parameter test on the asphalt mixture specimens that have not undergone freeze-thaw cycle action and those that have reached a fixed number of freeze-thaw cycle action times, and calculate and determine the void ratio according to the test results; After the test is completed, repeat the above freeze-thaw cycle test until the number of freeze-thaw cycle actions determined by the evaluation plan is reached; Damage evaluation module: According to the measured wave velocity and void ratio of the asphalt mixture, use the freeze-thaw damage variable formula to calculate the freeze-thaw damage variable values at each number of freeze-thaw cycle actions, analyze its freeze-thaw damage evolution characteristics, and obtain the freeze-thaw damage evaluation results of the asphalt mixture.

8. The asphalt mixture freeze-thaw damage evaluation system based on ultrasonic technology according to claim 7, characterized in that, The calculation formula for the void ratio in the wave velocity and void ratio test module is as follows: Where: VV is the void ratio of the asphalt mixture; γ f is the bulk relative density of the asphalt mixture, m a 、m f and m w are the mass in air of the dry asphalt mixture, the saturated surface-dry mass of the specimen, and the mass in water, respectively; γ t is the theoretical maximum relative density of the asphalt mixture.

9. The asphalt mixture freeze-thaw damage evaluation system based on ultrasonic technology according to claim 7, characterized in that, The freeze-thaw damage variable formula for the asphalt mixture in the damage evaluation module is as follows: VV is the void ratio of the asphalt mixture that has not undergone freeze-thaw cycles, is the void ratio of the asphalt mixture after undergoing a fixed number of freeze-thaw cycles; V P is the longitudinal wave velocity of the asphalt mixture that has not undergone freeze-thaw cycles; is the longitudinal wave velocity of the asphalt mixture after undergoing a fixed number of freeze-thaw cycles.

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