Method for evaluating low-temperature fatigue performance of asphalt mixture

Abstract

The invention discloses a method for evaluating the low-temperature fatigue performance of an asphalt mixture, belongs to the technical field of road engineering, and aims to solve the technical problem of how to more accurately and comprehensively evaluate the fatigue performance of the asphalt mixture in a low-temperature environment. According to the technical scheme, the method comprises the following steps: preparing a prismoid test piece and a beam test piece made of the same asphalt mixture as the prismoid test piece; acquiring a temperature change sequence of the pavement structure in the target test environment for a plurality of continuous hours through temperature acquisition equipment; taking the collected temperature change sequence as an environment control condition, carrying out a constraint test piece temperature stress test on the prismoid test piece, and synchronously recording the axial force per hour in the test process; calculating the average temperature stress value in the test period according to the axial force per hour and the size of the prism test piece; the average temperature stress value serves as the initial stress level of the four-point bending fatigue life test and is pre-loaded on the beam test piece, and a plurality of different load stress levels are selected for testing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road engineering, in particular to a method for evaluating low-temperature fatigue performance of asphalt mixture. BACKGROUND

[0002] Fatigue performance, as a key performance index of asphalt pavement under repeated traffic load, directly determines the service life and use quality of the pavement, and is an important basis for pavement material design and structure design.

[0003] A significant limitation exists in the current test evaluation method for the fatigue performance of asphalt mixture: the loading mode is usually set as a cycle process from zero stress (or zero strain) to a peak stress (or strain). This loading mode simulates the ideal state that the stress of the pavement is zero when there is no vehicle and the pavement bears the load stress when there is a vehicle under normal temperature conditions. However, in a large seasonal freezing area or an area with a significant day-night temperature difference, the asphalt layer as the uppermost structure of the pavement is directly exposed to the natural environment and bears a cyclically changing temperature field. Under low-temperature conditions, the stress relaxation capacity of the asphalt mixture will be significantly reduced, resulting in the constraint of the shrinkage deformation caused by temperature drop, thereby accumulating a non-negligible temperature stress in the internal structure of the pavement. This temperature stress still exists when there is no vehicle load. Therefore, the real stress state of the asphalt pavement serving in such an environment is not from zero, but is always in a "preloading" state composed of temperature stress. When the vehicle load acts, the pavement actually bears a cycle change between a "low stress level" (only temperature stress) and a "high stress level" (the sum of temperature stress and vehicle load stress). The existing fatigue loading mode starting from zero cannot truly reflect the actual working condition of the high-low stress level cycle under the above low-temperature environment, and ignores the driving effect of the continuously existing temperature stress on the accumulation of material fatigue damage.

[0004] Therefore, how to more accurately and comprehensively evaluate the fatigue performance of asphalt mixture under low-temperature environment is a technical problem to be solved at present. SUMMARY

[0005] The technical task of the present application is to provide a method for evaluating the low-temperature fatigue performance of asphalt mixture, to solve the problem of how to more accurately and comprehensively evaluate the fatigue performance of asphalt mixture under low-temperature environment.

[0006] The technical task of the present application is achieved in the following way: a method for evaluating the low-temperature fatigue performance of asphalt mixture, which is specifically as follows:

[0007] Prepare a prism test piece and a beam test piece made of the same asphalt mixture as the prism test piece;

[0008] obtaining a temperature variation sequence of the pavement structure in the target test environment for continuous hours through a temperature acquisition device;

[0009] performing a restrained specimen temperature stress test on the prism specimen with the temperature variation sequence as the environmental control condition, and recording the axial force every hour during the test;

[0010] calculating the average temperature stress value during the test according to the axial force every hour and the size of the prism specimen;

[0011] preloading the average temperature stress value as the initial stress level of the four-point bending fatigue life test on the beam specimen, selecting a plurality of different load stress levels for testing, and recording the vertical force of the loading indenter and the vertical displacement of the center of the beam specimen during the test;

[0012] calculating the bending stiffness modulus and the dynamic curve thereof varying with time according to the vertical force of the loading indenter and the vertical displacement of the center of the beam specimen;

[0013] obtaining the fatigue life of the beam specimen under different load levels according to the unified failure criterion, establishing the fatigue life equation of the asphalt mixture under the synchronous action of temperature stress and load stress, and evaluating the low-temperature fatigue performance of the beam specimen under the coupling action of temperature and load.

[0014] Preferably, the temperature variation sequence for continuous hours has typical representativeness of the environment to be tested, and the continuous acquisition time is at least 24 hours or an integral multiple of 24 hours.

[0015] More preferably, the temperature variation sequence as the environmental control condition means that the annual average temperature of the region where the pavement to be evaluated is located is searched for in the climate data as the reference temperature or a specific temperature is selected as the reference temperature according to the research needs, the temperature of the environmental chamber is set to the reference temperature, the prism specimen is placed in the environmental chamber for heat preservation, the heat preservation specimen is not less than 3 hours; and according to the temperature variation sequence, the temperature every hour is input into the temperature control system of the environmental chamber, so that the temperature in the environmental chamber changes linearly with time according to the set value of each time node.

[0016] Preferably, the prism specimen is a specimen with a square cross section cut from a rutting test specimen, and the size of the prism specimen is determined according to the nominal maximum particle size of the asphalt mixture, specifically as follows:

[0017] For the asphalt mixture with a nominal maximum particle size of less than or equal to 9.5 mm, the specimen size is 40 mm x 40 mm x 160 mm;

[0018] For the asphalt mixture with a nominal maximum particle size of 13.2 mm to 19 mm, the specimen size is 50 mm x 50 mm x 160 mm;

[0019] The asphalt mixture with a nominal maximum aggregate size greater than 26.5 mm, and the specimen size is 60 mm x 60 mm x 160 mm.

[0020] Preferably, during the constraint temperature stress test, the length of the prism specimen changes due to temperature change, and the length change of the prism specimen is measured in real time by the multi-functional material testing machine UTM. When the length change of the prism specimen is greater than a set threshold (such as 2 μm), the prism specimen is stretched or compressed according to the measured length change of the prism specimen, so that the length of the prism specimen remains unchanged, and the instantaneous load, displacement and temperature are collected and recorded in real time by the multi-functional material testing machine and the built-in data acquisition system.

[0021] Preferably, the formula of the average temperature stress value during the test period is as follows:

[0022]

[0023] wherein, σ thermal represents the average temperature stress; F i represents the axial force of the loading ram at the end of each hour; i represents the i-th hour, i is a positive integer; b represents the width of the specimen; h represents the height of the specimen; and n represents the total time length of the temperature change sequence.

[0024] Preferably, the four-point bending fatigue life test includes a stress control mode and a strain control mode.

[0025] More preferably, when the four-point bending fatigue test is performed in the stress control mode, before the four-point bending fatigue test starts, the vertical force of the loading ram corresponding to the average temperature stress is calculated according to the size of the beam specimen and the average temperature stress value, and the position of the loading ram and the size of the vertical force are adjusted so that the beam specimen reaches the set pre-stress state.

[0026] The beam specimen repeatedly experiences periodic load from a low stress level to a high stress level during the loading process, the low stress level is the average temperature stress, and the high stress level is the average temperature stress plus the load stress. The fatigue life equation is as follows:

[0027]

[0028] wherein, N f应力 represents the fatigue life in the stress control mode; σ max represents the maximum stress loaded on the beam specimen in the stress control mode; σ min represents the minimum stress loaded on the beam specimen in the stress control mode; a 应力 , b 应力 , c 应力 and d 应力 respectively represent fitting parameters.

[0029] More preferably, when the four-point bending fatigue test is carried out in the strain control mode, the temperature strain corresponding to the average temperature stress is calculated according to the uniaxial compression static modulus corresponding to the average temperature of the current asphalt mixture under the temperature change sequence, and the displacement of the loading indenter corresponding to the strain equal to the temperature strain in the middle of the beam specimen is calculated, and the position of the loading indenter is adjusted to make the beam specimen reach the set pre-deformation state.

[0030] More preferably, when the four-point bending fatigue life test is carried out in the strain control mode, the beam specimen repeatedly experiences periodic load from a low stress level to a high stress level in the loading process, the low stress level is embodied by the temperature strain converted from the average temperature stress, and the high stress level is embodied by the superposition of the temperature strain and the load strain, and the fatigue life equation is as follows:

[0031]

[0032] Wherein, N f应变 represents the fatigue life under stress control mode; ε max represents the maximum stress loaded on the beam specimen under stress control mode; ε min represents the minimum stress loaded on the beam specimen under stress control mode; a 应变 , b 应变 , c 应变 and d 应变 respectively represent fitting parameters.

[0033] The asphalt mixture low-temperature fatigue performance evaluation method has the following advantages:

[0034] (1) The present application simulates the actual temperature environment of the pavement, quantifies the stress level of the pavement, and simultaneously considers the actual fatigue stress characteristics of the pavement under the coupling action of high-frequency vehicle load and continuous temperature stress, fills the gap in the evaluation method of the fatigue performance of asphalt pavement under the action of temperature, can more accurately and widely evaluate the actual fatigue performance of asphalt pavement under the coupling action of temperature and load in various environments, and can further master the development law of low-temperature cracking of pavement;

[0035] (2) The present application can scientifically reveal the damage evolution law and life of asphalt mixture under low-temperature high-low stress cycle by establishing test conditions closer to the actual stress state, more accurately and comprehensively evaluate the fatigue performance of asphalt mixture under low-temperature environment, thereby providing reliable theoretical basis and technical support for material optimization design, performance degradation accurate prediction and timely formulation of preventive maintenance and repair strategies of asphalt pavement in low-temperature areas, and has important engineering practical value;

[0036] (III) The present application can quantify the temperature stress level of asphalt pavement by simulating the actual low-temperature environment and the change state of the road surface temperature; the temperature stress level is used as the initial stress state of the fatigue service of the asphalt mixture, the stress condition of the pavement is more truly simulated, so that the fatigue performance of the pavement under the coupling action of the temperature stress and the repeated vehicle load can be more accurately evaluated, the prediction precision of the fatigue life of the asphalt mixture is improved, and a reliable basis is provided for optimizing the material design of the asphalt pavement structure. BRIEF DESCRIPTION OF DRAWINGS

[0037] The present application will be further described below in combination with the drawings.

[0038] FIG. 1 is a flow chart of the asphalt mixture low-temperature fatigue performance evaluation method of the present application. Figure 1 FIG. 2 is a schematic diagram of the temperature change sequence of the environmental box.

[0039] Figure 2 FIG. 3 is a schematic diagram of the axial force of the loading pressure head changing with time in the temperature stress test of the constrained test piece.

[0040] FIG. 4 is a schematic diagram of the fatigue loading waveform superimposed by the temperature stress and the load stress. Figure 3 FIG. 5 is a schematic diagram of the bending stiffness modulus changing with the loading times in the four-point bending fatigue test.

[0041] Figure 4 FIG. 6 is a fatigue test loading waveform diagram of the four working conditions in Example 2.

[0042] FIG. 7 is a fatigue test loading waveform diagram of the three working conditions in Example 3. Figure 5 DETAILED DESCRIPTION

[0043] Figure 6 The present application is a kind of asphalt mixture low-temperature fatigue performance evaluation method, which is described in detail below in combination with the drawings and specific examples.

[0044] Example 1: Figure 7 As shown in FIG. 1, the present embodiment provides a kind of asphalt mixture low-temperature fatigue performance evaluation method, and the method is specifically as follows:

[0045] Example 1:

[0046] As shown in FIG. 1, the present embodiment provides a kind of asphalt mixture low-temperature fatigue performance evaluation method, and the method is specifically as follows:

[0047] As shown in FIG. 1, the present embodiment provides a kind of asphalt mixture low-temperature fatigue performance evaluation method, and the method is specifically as follows: Figure 1 DETAILED DESCRIPTION

[0048] ​​​​S1. Preparation of prism specimens and beam specimens using the same asphalt mixture as the prism specimens. Prism specimen preparation process: Plate specimens with a length of 300mm, a width of 300mm, and a thickness ≥50mm (≥75mm when the nominal maximum particle size is ≥26.5mm) are formed using the wheel-rolling method (T 0703) in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG 3410—2025). After demolding, the specimens are cut to obtain prism specimens that meet the dimensional requirements. During cutting, the longitudinal axis of the prism specimen must be aligned with the rolling direction during the forming of the rutted slab. Beam specimen preparation process: Plate specimens with a width of 300mm, a length of 400mm, and a thickness of 75mm are formed using the same wheel-rolling method and cut into standard specimens with a width (63mm±6mm), length (380mm±5mm), and height (50mm±6mm).

[0049] S2. Obtain the temperature change sequence of the road surface structure in the target test environment for several consecutive hours using a temperature acquisition device. The continuous acquisition time is 24 hours.

[0050] S3. Using the collected temperature change sequence as environmental control conditions, conduct a constrained temperature stress test on the prism specimen. Simultaneously record the hourly change in axial force during the test, as shown in the attached figure. Figure 3 As shown;

[0051] S4. Calculate the average temperature stress value during the test period based on the hourly axial force and the size of the prism specimen.

[0052] S5. The average temperature stress value is used as the initial stress level for the four-point bending fatigue life test and preloaded onto the beam specimen. According to different loading control modes, combined with the beam specimen size calculation, the stress (or strain) in the middle of the beam specimen is equal to the vertical displacement of the loading head corresponding to the temperature stress (or strain). The position of the loading head and the magnitude of the vertical force are adjusted so that the beam specimen reaches the set prestress (or strain) state.

[0053] S6. Apply load stress (or strain) to the prestressed (deformed) state; the fatigue loading waveform is shown in the attached figure. Figure 4 As shown in the attached figure; and based on the vertical force of the loading head and the vertical displacement of the beam specimen center, the bending stiffness modulus and its dynamic curve over time are calculated, as shown in the attached figure. Figure 5 As shown;

[0054] S7. Obtain the fatigue life of beam specimens under different loading levels using a unified failure criterion, establish the fatigue life equation of asphalt mixture under the simultaneous action of temperature stress and load stress, and evaluate the low-temperature fatigue performance of beam specimens under the coupled action of temperature and load.

[0055] In this embodiment, the temperature change sequence collected is taken as the environmental control condition, that is, the average annual temperature of the region where the road surface to be evaluated is located is taken as the reference temperature in the climate data, the temperature of the environmental chamber is set to the reference temperature, and a prismatic specimen with a size of 50mm*50mm*160mm is placed in the environmental chamber for heat preservation, and the heat preservation specimen is not less than 3 hours; and according to the temperature change sequence, the temperature of each hour is input into the temperature control system of the environmental chamber, so that the temperature in the environmental chamber changes linearly with time according to the set value of each time node, as shown in FIG. 2. Figure 2

[0056] In this embodiment, during the constraint temperature stress test, the length of the prismatic specimen changes due to temperature change, the length change of the prismatic specimen is measured in real time by the multifunctional material testing machine UTM, when the length change of the prismatic specimen is greater than a set threshold value (such as 2μm), the prismatic specimen is stretched or compressed according to the measured length change of the prismatic specimen, so that the length of the prismatic specimen remains unchanged, and the instantaneous load, displacement and temperature are collected and recorded in real time by the multifunctional material testing machine and the built-in data acquisition system matched therewith.

[0057] In this embodiment, the formula of the average temperature stress value during the test period is as follows:

[0058]

[0059] Wherein, σ thermal represents the average temperature stress; F i represents the axial force of the loading ram at the end of each hour; i represents the i-th hour, i is a positive integer; b represents the width of the specimen; h represents the height of the specimen; and n represents the total duration of the temperature change sequence.

[0060] The four-point bending fatigue life test in this embodiment includes stress control mode and strain control mode.

[0061] In this embodiment, when the four-point bending fatigue test is performed in the stress control mode, before the four-point bending fatigue test starts, the vertical force of the loading ram corresponding to the average temperature stress is calculated according to the size of the beam specimen and the average temperature stress value, the position of the loading ram and the size of the vertical force are adjusted, so that the beam specimen reaches the set pre-stressed state;

[0062] The beam specimen repeatedly experiences periodic load from a low stress level to a high stress level during the loading process, the low stress level is the average temperature stress, and the high stress level is the average temperature stress superimposed with load stress, and the fatigue life equation is as follows:

[0063]

[0064] Wherein, N f应力 ​σ represents fatigue life under stress control mode; max σ represents the maximum stress applied to the beam specimen under stress-controlled mode; min This represents the minimum stress applied to the beam specimen under stress-controlled mode; a 应力 b 应力 c 应力 and d 应力 These represent the fitting parameters. The fatigue equation is based on an improvement of the classic SN fatigue model. It is based on the nonlinearity of damage evolution and has undergone a large number of indoor fatigue tests, including various stress levels and material types. Combined with a large amount of nonlinear data fitting and experimental verification, four key fitting parameters were finally obtained.

[0065] In this embodiment, when conducting a four-point bending fatigue test in strain control mode, the temperature strain corresponding to the average temperature stress is calculated based on the uniaxial compression static modulus corresponding to the average temperature of the current asphalt mixture under the temperature change sequence. The displacement of the loading head corresponding to the strain in the middle of the beam specimen being equal to the temperature strain is further calculated, and the position of the loading head is adjusted so that the beam specimen reaches the set pre-deformation state.

[0066] The beam specimen repeatedly experienced cyclic loading from low stress levels to high stress levels during the loading process. The low stress level was represented by the temperature strain calculated from the average temperature stress, while the high stress level was represented by the superposition of temperature strain and load strain. The fatigue life equation is as follows:

[0067]

[0068] Where, N f应变 Indicates fatigue life under stress control mode; ε max ε represents the maximum stress applied to the beam specimen under stress-controlled mode; min This represents the minimum stress applied to the beam specimen under stress-controlled mode; a 应变 b 应变 c 应变 and d 应变 These represent the fitting parameters. This fatigue equation is based on an improvement of the classic SN fatigue model. It is based on the nonlinearity of damage evolution and has undergone a large number of indoor fatigue tests, including various strain levels and material types. By combining a large amount of nonlinear data fitting and experimental verification, four key fitting parameters were finally obtained, which can effectively reflect the influence of high and low stress on the service life of asphalt mixtures.

[0069] Example 2:

[0070] In this embodiment, the low-temperature fatigue performance of an asphalt mixture under four different load levels in a low-temperature region was compared and evaluated, considering the coupled effects of temperature stress and load stress. A fatigue equation for this asphalt mixture under temperature and load coupling was established to comprehensively evaluate its fatigue performance under various loading conditions in the region. The four load conditions are defined as follows: light traffic (with a representative strain of 200 με), medium traffic (with a load stress level of 500 με), heavy traffic (with a load stress level of 700 με), and extremely heavy traffic (with a load stress level of 900 με). Except for the different load stress levels in the four-point bending fatigue test, all other relevant conditions are consistent across the four load conditions.

[0071] During fatigue testing under conditions A, B, C, and D, the stress levels increase sequentially. Under the same material conditions, the higher the stress level, the greater the material damage caused by each fatigue loading, and the fewer loading cycles required to cause material failure. Therefore, the fatigue life should gradually decrease. Simultaneously, temperature stress increases the overall road surface stress level, accelerating the accumulation of fatigue damage in the specimens and thus reducing fatigue life. In this embodiment, the method proposed in this invention will be used to compare the differences in fatigue performance exhibited by the material under four types of load levels. Furthermore, a fatigue equation for this type of asphalt mixture under the temperature and load coupling effect in this region will be established to comprehensively evaluate the material's fatigue performance and further verify the reliability of the method proposed in this invention.

[0072] First, three prism specimens of asphalt mixture, each measuring 50mm × 50mm × 160mm, were prepared for a constrained temperature stress test. The reference temperature of the environmental chamber was set at 10℃. The prism specimens were placed in the environmental chamber and kept at that temperature for at least 3 hours. The 24-hour road surface temperature curve was collected and input into the environmental chamber temperature control system. The temperature stress change curves were tested separately, and the average temperature stress value was calculated. The average of the three parallel tests was taken as the temperature stress value that the pavement would bear under the environmental conditions of this region, which was 0.32MPa. The corresponding temperature strain ε could be calculated based on the uniaxial compression static modulus of the asphalt mixture (800MPa can be used by default if measured data is unavailable). thermal It is 400 με.

[0073] Four sets of asphalt mixture beam specimens, each measuring 380mm × 63mm × 50mm, were prepared using the same material type and subjected to four-point bending fatigue tests. This example employs a strain-controlled loading mode. Based on the position of the loading head, the specimen dimensions, and the positional relationship between the fixture and the specimen, the formula was substituted... The calculated vertical displacement of the loading head required for the specimen to reach the pre-deformation equal to the temperature strain is 0.217 mm.

[0074]

[0075] Where δ is the vertical force displacement (m) of the loading head required to make the specimen reach the pre-deformation, and ε thermal The average temperature strain is given by L, which is the beam span (i.e., the distance between the two clamps at the outer end, typically 0.357m) (m), a is the center-to-center distance between adjacent clamps (L / 3, typically 0.119m) (m), and h is the beam height (m).

[0076] After the beam specimen was installed and fixed, the vertical displacement of the loading head was adjusted to 0.217 mm along the loading direction to subject the specimen to temperature stress. Different load-strain levels were input into the fatigue test control system, and the test was started. Three parallel tests were conducted for each load condition. The vertical force of the loading head and the vertical displacement of the beam specimen center were recorded synchronously during the test, and the dynamic curve of the flexural stiffness modulus over time was calculated. In this example, the failure criterion was: the fatigue life was defined as the number of loading cycles corresponding to the flexural stiffness modulus decaying to 50% of the initial stiffness modulus. The initial stiffness modulus was the average value of the modulus during the 50th to 100th loading cycles. The loading waveform curves for the four load conditions are attached. Figure 6 As shown in Table 1, the fatigue life values ​​of the specimens under four load levels (A, B, C, and D) are determined based on the final test results.

[0077] Table 1. Fatigue life values ​​of specimens under four working conditions: A, B, C, and D.

[0078]

[0079]

[0080] As shown in Table 1, the fatigue life N of the specimen in working condition A f应变 The average value is 2,485,389, and the fatigue life N of the specimen in working condition B is... f应变 The average value is 213416, and the fatigue life N of the specimen in working condition C is... f应变 The average value is 65243, and the fatigue life N of the specimen in working condition D is... f应变 The average value is 10147. According to N... f应变 Following the principle that higher numerical values ​​indicate better fatigue performance, the fatigue performance of the specimens under the four working conditions can be ranked as A > B > C > D. Further based on... Furthermore, by combining test data from more loading conditions, the fatigue equation for this asphalt mixture can be obtained by substituting the test data into the fitting:

[0081] N f应变 =1.4794×10 12 ×(ε max -ε min ) -2.5081 -117.443×(εmax +ε min ) 0.8071

[0082] This fatigue equation allows us to understand the fatigue performance of this type of asphalt pavement under the coupled effects of different temperature stress levels and load stress levels, quantifying the impact of thermal shrinkage tensile stress generated in different climatic environments, especially low-temperature environments, on road fatigue performance. The evaluation results are consistent with the working principle, further demonstrating the rationality and reliability of the method proposed in this invention.

[0083] Example 3:

[0084] This embodiment compares the fatigue performance differences of the same asphalt mixture under the same load level in three different climatic environments. The first category is a generally mild climate, defined as working condition ①; the second category is a generally cold climate, defined as working condition ②; and the third category is a severely cold climate, defined as working condition ③. Except for the temperature stress level, all other relevant conditions are consistent across the three working conditions.

[0085] During the temperature stress test of the constrained specimen, the temperature levels of conditions ①, ②, and ③ decrease sequentially, and the measured average temperature stress should gradually increase. Under the same load stress level, the fatigue life decreases sequentially. In this embodiment, the method proposed in this invention will be used to compare the differences in fatigue performance of the same material under three environmental conditions, further verifying the reliability of the method proposed in this invention.

[0086] First, three sets of asphalt mixture prism specimens with dimensions of 50mm×50mm×160mm were prepared for constrained temperature stress tests. 24-hour continuous temperature variation curves representing three working conditions were input into the temperature control system. The ambient chamber reference temperature was selected as 10℃. The average temperature stress value σ for the three working conditions was calculated using Formula 1. thermal The values ​​are 0.24 MPa, 0.37 MPa, and 0.53 MPa, respectively.

[0087] Three sets of asphalt mixture beam specimens, each measuring 380mm × 63mm × 50mm, were prepared using the same material type and subjected to four-point bending fatigue tests. This example employs a controlled stress loading mode. Based on the position of the loading head, the specimen dimensions, and the positional relationship between the fixture and the specimen, the following parameters were applied:

[0088] The calculated vertical forces of the loading head required to bring the prestress of the specimen to equal the temperature stress are 107N, 164N, and 236N, respectively.

[0089] In the figure, P is the vertical force (N) of the loading head required to make the specimen reach the prestress equal to the temperature stress; σ thermal1 is temperature prestress (Pa); w is beam width (m); h is beam height (m); L is beam span, i.e., the distance between the two clamps at the outer end (generally 0.357m) (m).

[0090] After the beam specimen was installed and fixed, the vertical force of the loading head was adjusted along the loading direction to subject the specimen to temperature stress. The load stress level was input into the fatigue test control system and the test was started. In this example, the load stress level was 0.7 MPa. Three parallel tests were conducted for each load condition. The vertical force of the loading head and the vertical displacement of the beam specimen center were recorded synchronously during the test, and the dynamic curve of the flexural stiffness modulus over time was calculated. In this example, the failure criterion was: the fatigue life was defined as the number of loading cycles corresponding to the flexural stiffness modulus decaying to 50% of the initial stiffness modulus. The initial stiffness modulus was the average value of the modulus during the 50th to 100th loading cycles. The loading waveform curves for the three load conditions are attached. Figure 7 As shown in the figure. Based on the final test results, the fatigue life values ​​of the specimens under three temperature stress levels (①, ②, and ③) are shown in Table 2.

[0091] Table 2. Fatigue life values ​​of specimens under three working conditions: ①, ②, and ③.

[0092]

[0093] As shown in Table 2, the fatigue life N of the specimen under working condition ① is... f应力 The average value is 174400, and the fatigue life (N) of the specimen in working condition ② is... f应力 The average value is 45088, and the fatigue life N of the specimen in working condition ③ is... f应力 The average value is 8281. According to N... f应力 Following the principle that higher numerical values ​​indicate better fatigue performance, the fatigue performance of the material under the three working conditions is ①>②>③. When the ambient temperature is lower and the range of temperature variation is greater, the accumulated temperature stress level on the asphalt pavement is higher, raising the baseline stress level of the pavement. Under the same level of load, the overall stress level of the pavement is higher, resulting in greater damage to the material with each loading and a shorter fatigue life. These evaluation results are consistent with the working principles of the three working conditions, further demonstrating the rationality and reliability of the method proposed in this invention.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the low-temperature fatigue performance of asphalt mixtures, characterized in that, The method is as follows: Prepare prism specimens and beam specimens using the same asphalt mixture as the prism specimens; The temperature change sequence of the road surface structure in the target test environment over several consecutive hours was obtained using temperature acquisition equipment. The collected temperature change sequence was used as environmental control conditions to conduct a constrained temperature stress test on the prism specimen. The axial force was recorded simultaneously every hour during the test. The average temperature stress during the test period was calculated based on the hourly axial force and the dimensions of the prism specimen. The average temperature stress value was used as the initial stress level for the four-point bending fatigue life test and preloaded onto the beam specimen. Multiple different load stress levels were selected for the test. During the test, the vertical force of the loading head and the vertical displacement of the center of the beam specimen were recorded simultaneously. The bending stiffness modulus and its dynamic curve over time are calculated based on the vertical force of the loading head and the vertical displacement of the beam specimen center. The fatigue life of beam specimens under different loading levels was obtained using a unified failure criterion. The fatigue life equation of asphalt mixture under the simultaneous action of temperature stress and load stress was established to evaluate the low-temperature fatigue performance of beam specimens under the coupled action of temperature and load.

2. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 1, characterized in that, A continuous temperature change sequence over multiple hours is typical of the environment under test, and the continuous acquisition time is at least 24 hours, or in multiples of 24 hours.

3. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 1 or 2, characterized in that, Using the collected temperature change sequence as environmental control conditions means finding the annual average temperature of the area where the road surface to be evaluated is located in the climate data as the reference temperature, or selecting a specific temperature as the reference temperature according to the research needs, setting the environmental chamber temperature to the reference temperature, and placing the prism specimen in the environmental chamber for insulation for no less than 3 hours; and inputting the hourly temperature into the environmental chamber temperature control system according to the temperature change sequence, so that the temperature inside the environmental chamber changes linearly with time according to the set value at each time point.

4. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 1, characterized in that, Prismatic specimens are specimens with a square cross-section cut from rutted slab specimens. The dimensions of the prismatic specimens are determined based on the nominal maximum particle size of the asphalt mixture, as follows: For asphalt mixtures with a nominal maximum particle size of 9.5 mm or less, the specimen size is 40 mm × 40 mm × 160 mm. For asphalt mixtures with a nominal maximum particle size of 13.2 mm to 19 mm, the specimen size is 50 mm × 50 mm × 160 mm; For asphalt mixtures with a nominal maximum particle size greater than 26.5 mm, the specimen size is 60 mm × 60 mm × 160 mm.

5. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 1, characterized in that, During the constrained temperature stress test, the length of the prism specimen changes due to temperature variations. The length change of the prism specimen is measured in real time using a multi-functional material testing machine (UTM). When the length change of the prism specimen exceeds a set threshold, the prism specimen is stretched or compressed according to the measured length change to maintain its initial length. The instantaneous load, displacement, and temperature are collected and recorded in real time by the multi-functional material testing machine and its built-in data acquisition system.

6. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 1, characterized in that, The formula for the average temperature stress value during the test period is as follows: Where, σ thermal F represents the average temperature stress. i denoted by , where represents the axial force of the loading head at the end of each hour; i represents the i-th hour, where i is a positive integer; b represents the specimen width; h represents the specimen height; and n represents the total duration of the temperature change sequence.

7. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 1, characterized in that, The four-point bending fatigue life test includes stress control mode and strain control mode.

8. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 7, characterized in that, When conducting a four-point bending fatigue test in stress control mode, before the four-point bending fatigue test begins, the vertical force of the loading head corresponding to the stress in the middle of the beam specimen being equal to the average temperature stress is calculated based on the size of the beam specimen and the average temperature stress value. The position of the loading head and the magnitude of the vertical force are adjusted to make the beam specimen reach the set prestress state. The beam specimen repeatedly experienced cyclic loading from low stress levels to high stress levels during the loading process. The low stress level was due to the mean temperature stress, and the high stress level was due to the superposition of the mean temperature stress and the load stress. The fatigue life equation is as follows: Where, N f应力 σ represents fatigue life under stress control mode; max σ represents the maximum stress applied to the beam specimen under stress-controlled mode; min This represents the minimum stress applied to the beam specimen under stress-controlled mode; a 应力 b 应力 c 应力 and d 应力 These represent the fitting parameters.

9. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 7, characterized in that, When conducting a four-point bending fatigue test in strain control mode, the temperature strain corresponding to the average temperature stress is calculated based on the uniaxial compressive static modulus corresponding to the average temperature of the asphalt mixture under the temperature change sequence. Further calculations are performed to determine the displacement of the loading head that causes the strain in the middle of the beam specimen to be equal to the temperature strain. The position of the loading head is then adjusted to make the beam specimen reach the set pre-deformation state.

10. The method for evaluating the low-temperature fatigue performance of asphalt mixtures according to claim 9, characterized in that, When conducting a four-point bending fatigue life test using strain control mode, the beam specimen repeatedly experiences cyclic loading from low stress levels to high stress levels during the loading process. The low stress level is represented by the temperature strain obtained from the average temperature stress, while the high stress level is represented by the superposition of temperature strain and load strain. The fatigue life equation is as follows: Where, N f应变 Indicates fatigue life under stress control mode; ε max ε represents the maximum stress applied to the beam specimen under stress-controlled mode; min This represents the minimum stress applied to the beam specimen under stress-controlled mode; a 应变 b 应变 c 应变 and d 应变 These represent the fitting parameters.

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