A prediction method for asphalt fatigue life at different frequencies

Abstract

The present invention relates to the field of road engineering technology, specifically to a method for predicting asphalt fatigue life at different frequencies, including: preparing a standard asphalt sample for dynamic shear rheometer testing; loading the prepared standard asphalt sample onto the parallel plate of the dynamic shear rheometer, performing a linear amplitude scanning test at different frequencies, and obtaining test data; using a suitable fatigue damage theory to calculate the fatigue life of the asphalt sample; establishing the relationship between the performance parameters and the loading frequency in the fatigue damage theory, constructing a prediction model for asphalt fatigue life, and realizing the prediction of asphalt fatigue life at different frequencies. The asphalt fatigue life prediction model proposed by the present invention takes into account the influence of strain level and loading frequency, and realizes the prediction of asphalt fatigue life at different frequencies. The constructed prediction model is simple in form, the prediction is convenient and fast, and the results are accurate, and it has high practicality.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering, and in particular to a method for predicting asphalt fatigue life under different frequencies. Background Art

[0002] Asphalt pavement is the main form of high-grade highways in my country. Due to the influence of vehicle loads and environmental factors, fatigue damage will occur during its service life, which will shorten the service life of asphalt pavement. Asphalt is an important component of asphalt mixture. In asphalt mixture, asphalt is the only continuous phase material and plays a key role in cementation. The asphalt selected for asphalt mixture directly affects the performance and service life of asphalt pavement. Therefore, in-depth research on the fatigue life of asphalt has important theoretical significance and guiding value for improving the fatigue performance of asphalt pavement.

[0003] The time sweep test applies a constant load to the asphalt sample to obtain the law of change of asphalt performance over time, thereby evaluating the fatigue performance of asphalt. The test can be carried out using stress control or strain control. Although the time sweep test can well evaluate the fatigue resistance of asphalt, the time sweep test has many limitations. First, the time sweep test is long, usually several hours, which leads to a significant reduction in the repeatability of the test and greatly limits the efficiency of the fatigue test. Secondly, the fatigue failure criterion and fatigue life determination method of the time sweep test are still under study. The fatigue life obtained under different evaluation methods is different, and the fatigue failure judgment criteria have not yet been unified.

[0004] To address this problem, researchers developed an accelerated fatigue test method for asphalt based on DSR, namely the linear amplitude sweep test, and applied viscoelastic continuum damage mechanics to data analysis, which can predict fatigue life at any strain level. In addition to the strain level, the loading frequency also has a significant effect on the fatigue life of asphalt. However, the existing method only considers the effect of strain level on fatigue life and cannot effectively evaluate the effect of frequency on asphalt fatigue life. In order to obtain the fatigue life of asphalt at different frequencies, it is necessary to repeatedly perform linear amplitude sweep tests, which increases the experimental amount and complexity of the test. In order to solve the above technical problems, it is necessary to propose a calculation method that takes into account the effect of loading frequency on fatigue life, so as to quickly predict the fatigue life of asphalt at different frequencies. Summary of the invention

[0005] In order to address the shortcomings of the prior art, the present invention provides a method for predicting the fatigue life of asphalt at different frequencies, which can quickly obtain the fatigue life of asphalt at different frequencies without repeated testing, effectively reducing the test time and improving the test efficiency. At the same time, the results are accurate and highly practical.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for predicting the fatigue life of asphalt at different frequencies, comprising the following steps:

[0007] S1. Prepare standard asphalt samples for dynamic shear rheometer testing;

[0008] S2. Load the prepared standard asphalt sample on the parallel plates of the dynamic shear rheometer, perform linear amplitude scanning tests at different frequencies, and obtain test data;

[0009] S3. Use fatigue damage theory to analyze the linear amplitude sweep test data and calculate the fatigue life of the standard asphalt sample;

[0010] S4. Establish the relationship between performance parameters and loading frequency in fatigue damage theory and construct a prediction model for asphalt fatigue life;

[0011] S5. Based on the constructed asphalt fatigue life prediction model, the fatigue life of the target asphalt is predicted at different frequencies.

[0012] Preferably, in step S1, the standard asphalt sample is a cylindrical sample with a radius of 8 mm and a height of 2 mm.

[0013] Preferably, in step S2, during the linear amplitude sweep test, the frequency is controlled to be 5-20 Hz. As for the linear amplitude sweep test, the specific test process specification AASHTO TP 101 has been described in detail, and will not be described in detail here.

[0014] Preferably, in step S2, the standard asphalt sample cannot be tested repeatedly, and after completing the linear amplitude sweep test at a certain frequency, the standard asphalt sample needs to be replaced to perform the linear amplitude sweep test at another frequency.

[0015] Preferably, in step S2, the test data includes frequency scanning data and amplitude scanning data.

[0016] Preferably, in step S3, the fatigue damage theory adopts a simplified viscoelastic continuum damage theory based on virtual dissipated energy. The fatigue damage calculation method is as follows:

[0017] The virtual strain calculation formula is:

[0018] in, is the virtual strain calculated based on the reference modulus; G R is the reference modulus, with a value of 1; |G * | LVE is the linear viscoelastic modulus in the frequency sweep test; γ P is the peak strain at the selected cycle.

[0019] The dynamic modulus ratio calculation formula is:

[0020] Where DMR is the dynamic modulus ratio; |G * | fingerprint is the modulus of the first cycle in the amplitude sweep test.

[0021] The calculation formula of virtual stiffness is:

[0022] Where C is the virtual stiffness; |G * | initial is the initial dynamic modulus; |G * |(t) is the dynamic modulus at time t.

[0023] The calculation formula of asphalt internal damage degree is:

[0024]

[0025] in, m is the slope of the fitting curve of storage modulus and angular frequency in logarithmic coordinates; DMR is the dynamic modulus ratio; is the virtual strain of the selected cycle; C i is the virtual stiffness of the ith cycle; t is the time.

[0026] The relationship between virtual stiffness C and damage degree S is:

[0027] Among them, C is the virtual stiffness; S is the damage degree; C0 is the initial virtual stiffness, and its value is 1; A1 and A2 are curve fitting parameters.

[0028] Preferably, in step S3, when calculating the fatigue life of the standard asphalt sample, the 35% damage level of the standard asphalt sample is used as the fatigue failure criterion.

[0029] Fatigue failure criterion formula for asphalt 35% damage level:

[0030] The calculation formula of fatigue life parameters A and B is: B=2α

[0031] Wherein, k=1+(1-A2)·α; f is the loading frequency.

[0032] Fatigue life expression: N f =A(γ) B

[0033] Among them, N f is the fatigue life of asphalt; A and B are fatigue life parameters; γ is the given strain level.

[0034] Preferably, in step S4, the fatigue damage theory performance parameters that establish a relationship with the loading frequency are A1 and A2.

[0035] Preferably, in step S4, the asphalt fatigue life prediction model constructed is as follows:

[0036]

[0037] Among them, N f is the fatigue life of asphalt; K, M, N are the parameters of the asphalt fatigue life prediction model, which are obtained by substituting the test data obtained in step S2 and iteratively optimizing through MATLAB or Excel; |G * | LVE is the linear viscoelastic interval modulus in the amplitude sweep test; γ is the given strain level.

[0038] The present invention provides a method for predicting the fatigue life of asphalt at different frequencies, which has the following beneficial effects compared with the prior art:

[0039] The present invention uses a simplified viscoelastic continuum damage theory based on virtual dissipated energy to process the linear amplitude sweep test. The fatigue life prediction model obtained by this method takes into account the influence of strain level and loading frequency at the same time, solving the limitation that conventional asphalt fatigue test cannot obtain fatigue life at different frequencies. This method can quickly obtain the fatigue life of asphalt at different frequencies without repeated testing, which can effectively reduce the test time and improve the test efficiency. At the same time, the results are accurate and have high practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0041] Figure 1 This is a stress-strain relationship diagram in the amplitude sweep test at 5 Hz of the present invention;

[0042] Figure 2 This is a stress-strain relationship diagram in the amplitude sweep test at 20 Hz of the present invention;

[0043] Figure 3 This is a relationship diagram between storage modulus and angular frequency in logarithmic coordinates at 5 Hz of the present invention;

[0044] Figure 4 This is a relationship diagram between storage modulus and angular frequency in logarithmic coordinates at 20 Hz of the present invention;

[0045] Figure 5This is a graph showing the variation of fatigue parameter A1 with loading frequency according to the present invention;

[0046] Figure 6 This is a graph showing the variation of fatigue parameter A2 with loading frequency according to the present invention;

[0047] Figure 7 This is a relationship diagram between the predicted value and the measured value of the fatigue life of asphalt of the present invention;

[0048] Figure 8 The present invention is a flow chart of the method for predicting the fatigue life of asphalt. DETAILED DESCRIPTION

[0049] The following examples are used to explain the implementation methods of the present application in detail, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0050] Example

[0051] A prediction method for asphalt fatigue life at different frequencies.

[0052] S1. Prepare standard asphalt samples for dynamic shear rheometer testing;

[0053] The preparation of standard asphalt samples was carried out with reference to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). After heating the 70# asphalt, it was introduced into the dynamic shear rheometer mold to form a standard asphalt sample. After the standard asphalt sample was cooled, the sample was demoulded. The size of the standard asphalt sample was a cylindrical sample with a diameter of 8 mm and a height of 2 mm.

[0054] S2. Load the prepared standard asphalt sample on the parallel plates of the dynamic shear rheometer, conduct linear amplitude sweep tests at different frequencies, and obtain test data. The test temperature is 15°C.

[0055] The detailed steps of the linear amplitude test can be referred to the specification AASHTO TP 101, which will not be repeated here. It is worth noting that the test frequency in the specification AASHTO TP 101 is 10Hz, but the present invention is not limited to 10Hz, and tests at any frequency can be performed to obtain test data. The test frequencies used in this embodiment are 5Hz and 20Hz. The test content includes frequency scanning test and amplitude scanning test. The frequency scanning test is carried out at the frequency specified in the specification to obtain test data such as angular frequency, dynamic modulus and phase angle; in the amplitude scanning test, the strain level increases linearly from 0.1% to 30%, and stress, strain, dynamic modulus and phase angle test data are obtained. In this embodiment, the stress-strain relationship when the loading frequency is 5Hz and 20Hz is as shown in the attached figure. Figure 1 , Attachment Figure 2 shown.

[0056] The test frequencies of this embodiment are 5 Hz and 20 Hz. It should be noted that the asphalt sample cannot be tested repeatedly. After completing the linear amplitude sweep test at a certain frequency, the sample needs to be replaced to perform the linear amplitude sweep test at another frequency.

[0057] S3. Use fatigue damage theory to analyze the linear amplitude sweep test data and calculate the fatigue life of the standard asphalt sample;

[0058] In order to more accurately predict the fatigue life of linear amplitude sweep tests at different frequencies, the simplified viscoelastic continuum damage theory based on virtual dissipated energy is used to analyze and calculate the test data. The calculation process is shown below.

[0059] First, calculate the frequency scan data to obtain the parameter a. The steps are as follows:

[0060] Calculate the storage modulus: G'=|G * |·cosδ

[0061] Where G' is the storage modulus; |G * | is the dynamic modulus; δ is the phase angle.

[0062] Define m as the slope of the fitting curve of storage modulus and angular frequency in logarithmic coordinates, that is:

[0063] log G'=m(logω)+b

[0064] In this embodiment, the fitting curves of storage modulus and angular frequency in logarithmic coordinates when the loading frequency is 5 Hz and 20 Hz are shown in the attached figure. Figure 3 , Attachment Figure 4 shown.

[0065] Thus, α is calculated, and the calculation formula is:

[0066] The calculation formula of asphalt internal damage degree is:

[0067]

[0068] Among them, C is the virtual stiffness, and the calculation formula is: is the virtual strain of the selected period, and the calculation formula is: G R is the reference modulus, with a value of 1; |G * |L VE为 Linear viscoelastic modulus in frequency sweep tests; γ P is the peak strain of the selected cycle; DMR is the dynamic modulus ratio, calculated as: |G* | fingerprint is the modulus of the first cycle in the amplitude sweep test.

[0069] The above formula is used to calculate the asphalt damage degree at different times. Table 1 shows the calculation process when the frequency is 5 Hz and the time is 101-110 s. At the same time, the fitting parameters A1 and A2 are obtained by fitting the following formula: Among them, C is the virtual stiffness; S is the damage degree; C0 is the initial virtual stiffness, and its value is 1; A1 and A2 are curve fitting parameters.

[0070] In this example, the 35% damage level of asphalt is used as the fatigue failure criterion to calculate the fatigue life of asphalt. The fatigue life calculation method is as follows:

[0071] Fatigue failure criterion formula for asphalt 35% damage level:

[0072] The calculation formula of fatigue life parameters A and B is: B=2a

[0073] Wherein, k=1+(1-A2)·a; f is the loading frequency.

[0074] Fatigue life expression: N f =A(γ) B

[0075] Among them, N f is the fatigue life of asphalt; A and B are fatigue life parameters; γ is the given strain level.

[0076] The fatigue life calculation of 70# asphalt at 5Hz and 20Hz was completed by using the simplified viscoelastic continuum damage theory based on virtual dissipated energy. The theoretical calculation parameters and fatigue life at different frequencies and strains are summarized in Tables 2 and 3.

[0077] Table 1 Calculation of damage degree of 70# asphalt at 50Hz, 101-110s

[0078]

[0079]

[0080] Table 2: Linear amplitude sweep test data of # asphalt at 5 Hz

[0081]

[0082] Table 3 Linear amplitude sweep test data of # asphalt at 20Hz

[0083]

[0084] S4. Establish the relationship between performance parameters and loading frequency in fatigue damage theory and construct a prediction model for asphalt fatigue life;

[0085] Through data analysis, it can be seen that the fatigue damage theory performance parameters A1 and A2 have a significant relationship with the loading frequency. The results are shown in the attached Figure 5 , Attachment Figure 6 shown.

[0086] Substitute the data into the fatigue life prediction model considering the effect of loading frequency:

[0087]

[0088] Among them, N f is the fatigue life of asphalt; K, M, N are the parameters of the asphalt fatigue life prediction model, which are obtained by substituting the test data obtained in step S2 and iteratively optimizing through MATLAB or Excel; |G * | LVE is the linear viscoelastic interval modulus in the amplitude sweep test; γ is the given strain level.

[0089] Substituting the data and fitting the parameter values ​​of K, M, and N, K is 6.8477E+21, M is -3.5425, and N is -2.3371. The fatigue life prediction model of 70# asphalt in this embodiment is obtained as follows:

[0090]

[0091] S5. Based on the constructed asphalt fatigue life prediction model, the fatigue life of the target asphalt is predicted at different frequencies.

[0092] The fatigue life prediction model is used to predict the asphalt fatigue life at 5 Hz, 10 Hz, 15 Hz, and 20 Hz, and the measured values ​​are obtained through experiments. The asphalt fatigue life data at all different frequencies are summarized, as shown in Table 4.

[0093] Table 4 Summary of fatigue life of 70# asphalt at different frequencies

[0094]

[0095]

[0096] It can be seen from the results that the fatigue life at different frequencies predicted by this method has higher accuracy compared with the measured values. The relationship curve between the measured values ​​and the predicted values ​​is shown in the attached figure. Figure 7 shown.

[0097] The present invention takes into account the influence of frequency on the fatigue life of asphalt. By performing linear amplitude scanning tests at two frequencies and fitting the fatigue life prediction model parameters, a fatigue life prediction model can be obtained, thereby realizing the prediction of the fatigue life of asphalt at different frequencies, significantly improving the test efficiency while ensuring accuracy.

[0098] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for predicting asphalt fatigue life at different frequencies, characterized in that: The following steps are involved: S1. Prepare standard asphalt samples for dynamic shear rheometer testing; S2. Load the prepared standard asphalt sample on the parallel plates of the dynamic shear rheometer, perform linear amplitude scanning tests at different frequencies, and obtain test data; S3. Use fatigue damage theory to analyze the linear amplitude sweep test data and calculate the fatigue life of the standard asphalt sample; S4. Establish the relationship between performance parameters and loading frequency in fatigue damage theory and construct a prediction model for asphalt fatigue life; S5. Predict the fatigue life of the target asphalt at different frequencies based on the constructed asphalt fatigue life prediction model; In step S4, the asphalt fatigue life prediction model constructed is as follows: Among them, N f is the fatigue life of asphalt; K, M, N are the parameters of the asphalt fatigue life prediction model, which are obtained by substituting the test data obtained in step S2 and iteratively optimizing through MATLAB or Excel; |G * | LVE is the linear viscoelastic interval modulus in the amplitude sweep test; γ is the given strain level.

2. The method for predicting fatigue life of asphalt at different frequencies according to claim 1, characterized in that: In step S1, the standard asphalt sample is a cylindrical sample with a radius of 8 mm and a height of 2 mm.

3. The method for predicting fatigue life of asphalt at different frequencies according to claim 1, characterized in that: In step S2, during the linear amplitude sweep test, the frequency is controlled to be 5-20 Hz.

4. The method for predicting asphalt fatigue life at different frequencies according to claim 1, characterized in that: In step S2, the standard asphalt sample cannot be tested repeatedly. After completing the linear amplitude sweep test at a certain frequency, the standard asphalt sample needs to be replaced to perform the linear amplitude sweep test at another frequency.

5. The method for predicting fatigue life of asphalt at different frequencies according to claim 1, characterized in that: In step S2, the test data includes frequency scanning data and amplitude scanning data.

6. The method for predicting fatigue life of asphalt at different frequencies according to claim 1, characterized in that: In step S3, the fatigue damage theory adopts a simplified viscoelastic continuum damage theory based on virtual dissipated energy.

7. The method for predicting fatigue life of asphalt at different frequencies according to claim 1, characterized in that: In step S3, when calculating the fatigue life of the standard asphalt sample, the 35% damage level of the standard asphalt sample is used as the fatigue failure criterion.

8. The method for predicting fatigue life of asphalt at different frequencies according to claim 1, characterized in that: In step S4, the fatigue damage theory performance parameters that establish a relationship with the loading frequency are A1 and A2.

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