A method for testing the crack resistance of the upper layer components of asphalt pavement structures in areas with large temperature differences

Abstract

The present invention relates to an asphalt pavement structure in an area with a large temperature difference and a method for testing its crack resistance performance. The structure comprises an upper layer, a lower layer and a base layer, wherein the components of the upper layer are determined by a crack resistance test, and the crack resistance test comprises testing the crack resistance performance of an asphalt mixture at low temperature, high temperature and frequency on a test block, and determining the components of the upper layer after the above tests; the components of the asphalt pavement with a large temperature difference are designed using two intervals of high temperature and low temperature, and the crack resistance performance thereof is tested, and by testing the influence of temperature on the mechanical properties of the viscoelastic material, the sensitivity of the viscoelastic properties of the asphalt material to temperature is obtained, and the influence of temperature on the dynamic modulus and phase angle of the asphalt mixture is analyzed; the purpose of the present invention is to solve the technical problems in the prior art that the temperature difference causes pavement cracking and the existing crack resistance test cannot provide accurate crack resistance results.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt pavement structures, and in particular to a method for testing the crack resistance of upper layer components of asphalt pavement structures in areas with large temperature differences. Background Art

[0002] The Marshall method is the most widely used asphalt mixture design method. It uses volumetric parameters such as void ratio, aggregate interstitial ratio, and asphalt saturation, as well as empirical parameters such as stability and flow value, to design the mixture. However, studies have shown that the empirical parameter Marshall stability has a poor correlation with the high-temperature performance of asphalt mixtures, making it impossible to guarantee the high-temperature performance of asphalt mixtures. Dynamic stability indirectly reflects the high-temperature performance of asphalt pavements, but its test parameters are based on deformation 15 minutes after rolling for one hour. This is not rigorous and lacks a direct correlation with the mechanical properties of the material itself, making objective and scientific evaluation impossible.

[0003] Therefore, developing a technical method that can address the problem in existing technologies where large temperature differences cause cracking of pavement structures and existing anti-cracking tests cannot provide accurate anti-cracking results, that is, a testing method for asphalt pavement structures and their anti-cracking performance in areas with large temperature differences, is an issue that needs to be studied and resolved urgently. Summary of the Invention

[0004] In view of the climate characteristics of the large temperature difference between day and night in desert areas, the road surface in this area needs to be driven under high temperature during the day and low temperature at night. Therefore, the pavement structure is required to have high-temperature rutting resistance and low-temperature cracking resistance. Therefore, the present invention discloses a method for testing the cracking resistance of the upper layer components of asphalt pavement structures in areas with large temperature differences.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solutions: a method for testing the crack resistance performance of the upper layer components of an asphalt pavement structure in a large temperature difference area, characterized in that the asphalt pavement structure includes an upper layer, a lower layer, and a base layer, and the components of the upper layer are determined by a crack resistance test. The crack resistance test includes testing the crack resistance performance of the asphalt mixture at low temperature, high temperature, and frequency on a test block. After the above test, it is determined that the upper layer includes SBS modified asphalt, aggregate, and filler. The ratio of the SBS modified asphalt is 93.35% Karamay asphalt, 4.5% SBS modifier, 2% rubber oil, and 0.15% stabilizer; the aggregate includes coarse and fine aggregates produced by a gravel field, and its parent rock is biotite plagioclase gneiss; the filler is a mineral powder made by grinding fine-grained limestone. The method for testing the crack resistance performance of the upper layer of the asphalt pavement structure includes the following steps:

[0006] Step 1: Test the effects of temperature and frequency on asphalt mixture performance;

[0007] Step 2: Test the dynamic modulus of asphalt mixture:

[0008] (1) The reduced frequency values ​​corresponding to the two different frequencies at different temperatures are obtained through formula ①:

[0009] f r =fα T ①

[0010] Where: f r —Reduction frequency, i.e. frequency at reference temperature, Hz; α T —shift factor, a function of temperature T; f—frequency, Hz;

[0011] (2) Using formula ② and the dynamic modulus values ​​of different oil-stone ratios to fit the Sigmoidal function, the values ​​of the parameters in the formula can be obtained. The main curve after fitting is "S" shaped:

[0012]

[0013] Where: |E * |—dynamic modulus, MPa; δ—minimum value of dynamic modulus, MPa; δ+α—maximum value of dynamic modulus, MPa; β, γ—descriptive parameters of the S-shaped function, β, γ depend on the characteristics of the asphalt binder and the size of δ and α; α—variable, a function of grade, δ and α depend on aggregate gradation, asphalt content and void ratio;

[0014] (3) Use the quadratic polynomial function for analysis, see formula ③, and obtain the fitting result graph:

[0015] lgα T =aT 2 +bT+c ③

[0016] Where: T is temperature, °C; a, b, c are coefficients of the quadratic polynomial;

[0017] (4) By fitting the relationship diagram between the asphalt mixture reduction frequency and the dynamic modulus, the relationship diagram between the asphalt mixture temperature and the displacement factor, and the dynamic modulus comparison diagram of the asphalt mixture at different temperatures, the dynamic modulus value of the asphalt mixture is predicted in the full frequency domain, thereby obtaining the dynamic modulus of the asphalt mixture;

[0018] Step 3: Conduct tensile strength test on the test block.

[0019] Furthermore, the method for testing the influence of temperature and frequency on asphalt mixture performance in step 1 includes:

[0020] (1) Determine construction parameters: Use the SPT tester to conduct triaxial dynamic modulus tests to determine the effects of different temperatures and different action times on the dynamic modulus of asphalt mixtures;

[0021] (2) Select the test temperature: Use three test temperatures of 4°C, 20°C, and 40°C to study the law of the change of dynamic modulus with frequency at different temperatures;

[0022] (3) Select the test frequency: use four frequency levels: 0.1, 1, 10, and 25 Hz;

[0023] (4) Conducting tests and analysis: The asphalt mixture was tested using an SPT tester to obtain the dynamic modulus and phase angle of the asphalt mixture. The changes in the phase angle at 4°C, 20°C, and 40°C at the same frequency were analyzed to determine the dependence and sensitivity of the asphalt mixture response results on temperature.

[0024] Furthermore, the method of performing a tensile strength test on the test block in step 3 includes:

[0025] (1) The test adopts the wheel pressing method to obtain the load-displacement curve of the semicircular bending test of the asphalt mixture, and analyzes the change of the failure rate of the asphalt mixture specimens after the load peak at different temperatures;

[0026] (2) Obtain the stiffness diagram of asphalt mixture at different test temperatures and analyze the stiffness of asphalt mixture under three groups of temperature conditions;

[0027] (3) Calculation of crack resistance based on fracture energy:

[0028] Fracture toughness K IC At the critical load P C The stress intensity factor K I , the critical load is set as the maximum load during the test, and the fracture toughness K is calculated IC

[0029]

[0030] Where: Y I(0.8) is the standard stress intensity factor; σ0 is the stress corresponding to the critical load; P C is the critical load, i.e. the peak load, MN; r is the specimen radius, m; t is the specimen thickness, m; a is the crack length, m;

[0031] Calculate the fracture energy G f :

[0032]

[0033] Where: G f is the fracture energy, J / m2; W f is the work of fracture, J, W f =∫Pdu, P is the applied load (N), u is the average displacement of the load (m); Alig is the area of ​​the toughness zone m2, A lig =(ra)*t, r is the specimen radius, m; t is the specimen thickness, m; a is the crack length, m;

[0034] According to formula ⑦, the fracture energy of asphalt mixture under different test temperature conditions is obtained by integrating the load-displacement curve of asphalt mixture and the area enclosed by the X-axis.

[0035] After adopting the above technical solution, the beneficial effects of the present invention are:

[0036] The asphalt pavement top layer component obtained after the anti-cracking test of the present invention in the large temperature difference area can provide stable anti-cracking performance. While solving the technical problem of low adhesion between coarse aggregate and asphalt, it also solves the technical problem of the influence of high and low temperatures on the anti-cracking performance of asphalt pavement components.

[0037] The anti-crack test of the present invention clearly demonstrates the dependence and sensitivity of the response results of the viscoelastic material on temperature, the change of the dynamic modulus with frequency at different temperatures, and the clear prediction of the mechanical indicators of the viscoelastic material within a wider frequency domain. The difference between the predicted value and the measured value is within an acceptable range, making the anti-crack performance test more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 Schematic diagram of the load form and response strain of the dynamic modulus test provided in the embodiment of this application.

[0040] Figure 2 Schematic diagram of the dynamic modulus and phase angle of SBS asphalt mixture provided in the embodiment of this application.

[0041] Figure 3 Schematic diagram of the dynamic modulus and phase angle of SBR asphalt mixture provided in the embodiment of this application.

[0042] Figure 4 Schematic diagram of the dynamic modulus and phase angle of RK300 asphalt mixture provided in an embodiment of the present application.

[0043] Figure 5 Schematic diagram of the relationship between the reduction frequency and dynamic modulus of asphalt mixture provided in the embodiment of this application.

[0044] Figure 6 Schematic diagram of the relationship between the temperature and displacement factor of three asphalt mixtures provided in the implementation mode of this application.

[0045] Figure 7 A schematic diagram comparing the dynamic moduli of three asphalt mixtures at different temperatures provided in the embodiment of this application.

[0046] Figure 8 Schematic diagram of a semicircular bending test provided in an embodiment of the present application.

[0047] Figure 9 Schematic diagram of load-displacement curves of three asphalt mixture semicircular bending tests provided in the implementation manner of this application.

[0048] Figure 10 Schematic diagram of the stiffness of three asphalt mixtures at different test temperatures provided in the embodiment of this application.

[0049] Figure 11 Schematic diagram of the fracture toughness of three asphalt mixtures at different test temperatures provided in the embodiment of this application.

[0050] Figure 12 Schematic diagram of the fracture energy of three asphalt mixtures at different test temperatures provided in the embodiment of this application. DETAILED DESCRIPTION

[0051] The following description of the embodiments will help the public better understand the present invention, but the specific embodiments given by the applicant cannot and should not be regarded as limitations on the technical solutions of the present invention. Any changes to the definitions of the technical features should be regarded as the scope of protection defined by the technical solutions of the present invention.

[0052] Example: This example is an asphalt concrete highway project for an expressway in a region with a large temperature difference in the Xinjiang Uygur Autonomous Region. Asphalt concrete pavement is used throughout. The asphalt structure is divided into two layers: the upper layer is a 5 cm medium-grained modified asphalt concrete (AC-16), the lower layer is a 7 cm coarse-grained asphalt concrete (AC-25), and below the asphalt layer is a 36 cm 4.5% cement-stabilized gravel base.

[0053] 1. Selection of upper layer raw materials and specimen forming

[0054] (1) Karamay asphalt was selected as the base asphalt and used to prepare SBS modified asphalt. The SBS ratio was 93.35% base asphalt, 4.5% SBS modifier, 2% rubber oil, and 0.15% stabilizer. The indoor test results of SBS (IC) modified asphalt and SBR modified asphalt are shown in Tables 1 and 2.

[0055] Table 1 Performance indicators of SBS (IC) modified asphalt

[0056]

[0057] Table 2 Properties of SBR modified asphalt

[0058]

[0059]

[0060] (2) The coarse and fine aggregates are produced by a gravel yard. The parent rock is biotite gneiss. The adhesion between the coarse aggregate and asphalt is relatively low. The other performance indicators meet the requirements of the specifications.

[0061] (3) The artificial mineral powder of filler is made by grinding limestone (fine-grained limestone), and its various performance indicators meet the requirements of the specifications.

[0062] (4) The gradation of the aggregate for the specimens was consistent with the target mix ratio of AC-16, and the optimal asphalt-to-stone ratio was 4.8%. The mixture specimens were formed using the rotary compaction method.

[0063] 2. Selection of test parameters

[0064] like Figure 1 As shown in the figure, the SPT tester can be used to carry out triaxial dynamic modulus tests to measure the effects of different temperatures and different action times on the dynamic modulus of asphalt mixture.

[0065] (1) Test temperature

[0066] The SPT tester can provide a test temperature range of 4 to 60°C. In order to explore the impact of different temperatures on the performance of asphalt mixtures and study the changing pattern of dynamic modulus, this test adopted three test temperatures of 4°C, 20°C, and 40°C. The test studied the changing pattern of dynamic modulus with frequency at different temperatures.

[0067] (2) Test frequency

[0068] Due to the viscoelastic properties of asphalt mixtures, loading time is a key parameter in performance testing. Loading time is often characterized by loading frequency. Actual pavement loads are affected by factors such as vehicle speed, pavement smoothness, and pavement thickness. Driving loads are typically simulated at 10 Hz. This study used four frequency levels: 0.1, 1, 10, and 25 Hz.

[0069] 3. Influence of temperature and frequency on asphalt mixture performance

[0070] Temperature is one of the main factors affecting the mechanical properties of viscoelastic materials, making the viscoelastic properties of asphalt materials highly sensitive to temperature. This section will analyze the effect of temperature on the dynamic modulus and phase angle of asphalt mixtures. The results are shown in Figure 2 、3 、4.

[0071] Depend on Figure 2 、 3 As can be seen from Figure 4, with the increase of frequency, the dynamic modulus of the three asphalt mixtures gradually increases, and the phase angle gradually decreases at 4°C and 20°C, while the phase angle gradually increases at 40°C. With the increase of temperature, the dynamic modulus at the same frequency tends to decrease, while the phase angle tends to increase at 4°C and 20°C. The phase angle at 40°C is between 4°C and 20°C at 0.1Hz, and the phase angles at 1Hz, 10Hz, and 25Hz all increase with increasing temperature.

[0072] Taking 10 Hz as the research frequency, the dynamic moduli of SBS, SBR and RK300 asphalt mixtures at 4°C are 11932 MPa, 11476 MPa and 12829 MPa respectively. It can be seen that the performance of RK300 asphalt mixture is better than that of SBS and SBR, and the performance of SBS asphalt mixture is better than that of SBR. The dynamic moduli at 40℃ were 1320MPa, 1072.4MPa and 1673.5MPa respectively. After the temperature rose from 4℃ to 40℃, the dynamic moduli of SBS, SBR and RK300 asphalt mixtures decreased by 88.94%, 90.66% and 86.96% respectively, with a large decrease, indicating that the influence of temperature was large; the phase angles of SBS, SBR and RK300 asphalt mixtures at 4℃ were 15.765°, 15.81° and 13.4° respectively, and the phase angles at 40℃ were 39.005°, 37.315° and 33.495° respectively. After the temperature rose from 4℃ to 40℃, the phase angles increased by 2.47 times, 2.36 times and 2.50 times respectively, with a large change, which also shows that the response results of viscoelastic materials are highly dependent on and sensitive to temperature.

[0073] 4. Determination and analysis of the main curves of the dynamic modulus of three asphalt mixtures

[0074] From the above analysis, it can be seen that temperature and frequency have a great influence on the mechanical properties of asphalt mixture. For asphalt mixture, its viscoelastic properties show an equivalent relationship under high temperature and low frequency and low temperature and high frequency conditions, that is, high temperature corresponds to a load with a smaller frequency (longer time), and low temperature corresponds to a load with a larger frequency (shorter time). The temperature effect and time effect of asphalt mixture are equivalent. At the same time, vehicle loads act on pavements paved with asphalt mixtures. Due to the large differences in driving speeds, the frequency domain corresponding to the load action is wide. In addition, asphalt pavements are used in a wide range of regions, and the generally usable temperature range is -40°C to 60°C, corresponding to a wide temperature domain. However, during the test, considering the accuracy and operability of the test, it is impossible to guarantee that the test will be conducted at higher or lower frequencies and temperatures. Therefore, in order to obtain results in the full frequency domain and full temperature domain using the limited feasible test frequencies and temperatures, it is necessary to use the time-temperature equivalence principle to translate the test results obtained under different temperature and loading frequency conditions into a smooth curve. This curve is called the master curve. The mechanical indicators of the viscoelastic material within a wide frequency domain can be predicted based on the drawn master curve.

[0075] This study analyzes the dynamic modulus of asphalt mixtures and determines their dynamic modulus master curves. The test temperatures are 4°C, 20°C, and 40°C. Using 20°C as the reference temperature, the shift factors corresponding to 4°C and 40°C are calculated. Equation ① then yields the reduced frequency values ​​corresponding to the different frequencies at the two temperatures.

[0076] f r =fα T ①

[0077] Where: f r —Reduction frequency, i.e. frequency at reference temperature, Hz; α T —shift factor, a function of temperature T; f—frequency, Hz;

[0078] Using formula ② and the dynamic modulus values ​​of different oil-stone ratios to fit the Sigmoidal function, the values ​​of the parameters in the formula can be obtained. The main curve after fitting is "S" shaped:

[0079]

[0080] Where: |E * |—dynamic modulus, MPa; δ—minimum value of dynamic modulus, MPa; δ+α—maximum value of dynamic modulus, MPa; β, γ—descriptive parameters of the S-shaped function, β, γ depend on the characteristics of the asphalt binder and the size of δ and α; α—variable, a function of grade, δ and α depend on aggregate gradation, asphalt content and void ratio;

[0081] In order to further express the relationship between temperature and shift factor, a quadratic polynomial function can be used for analysis, see formula ③, and the fitting results are shown in Figures 10-12 .

[0082] lgα T =aT 2 +bT+c ③

[0083] Where: T is temperature, °C; a, b, c are coefficients of the quadratic polynomial;

[0084] The specific results of the displacement factors, coefficients in formula ②, and parameters in formula ③ corresponding to the three asphalt mixtures are shown in Table 3.

[0085] Table 3 Dynamic modulus master curve parameters of three asphalt mixtures

[0086]

[0087] From Table 3 and Figure 5 It can be seen that the relationship curve between the reduction frequency and the dynamic modulus fitted by the Sigmoidal function has a high correlation coefficient, both greater than 0.98. The dynamic modulus master curve reflects the relationship between the loading frequency and the properties of the viscoelastic material and can predict the dynamic modulus value from the full frequency domain. Due to the large correlation coefficient, the difference between the predicted value and the measured value is within an acceptable range.

[0088] Figure 6 The shift factor in reflects the influence of temperature on viscoelastic materials. It can be seen that there is a quadratic polynomial relationship between the temperature and the shift factor of asphalt mortar under the three oil-stone ratio conditions, and the correlation coefficient is 1. This is consistent with the result of Wang Duanyi's suggestion to use a quadratic curve to fit the temperature and shift factor curve of the time-temperature equivalent conversion of asphalt mixture.

[0089] like Figure 7 The dynamic modulus of the three asphalt mixtures at 4°C, 20°C, and 40°C (Figure 2) shows that the dynamic modulus increases with increasing loading frequency. For each temperature, the order of dynamic modulus is RK300 asphalt mixture > SBS modified asphalt mixture > SBR modified asphalt mixture. A higher dynamic modulus indicates greater rutting resistance and high-temperature stability.

[0090] 5. Research on semicircular bending test based on fracture mechanics

[0091] The test temperatures for this part of the SCB test are 0℃, -10℃ and -15℃, and two SCB specimens are prepared at a single temperature for each asphalt mixture. In the test, the SCB specimens are formed by the rotary compaction method. First, a cylindrical asphalt mixture specimen with a diameter of 150mm and a height of 150mm is obtained. A semicircular specimen with a diameter of 150mm and a thickness of 25mm is obtained from the middle of the rotary compaction specimen. A slit is cut perpendicular to the diameter direction from the center of each semicircular specimen, with a depth of 15mm and a width of 1.5mm. Semicircular bending test of different asphalt mixtures is shown above. Figure 8 .

[0092] (1) Effect of temperature on fracture process

[0093] Temperature has a significant impact on the performance of asphalt mixtures and is the main factor affecting the evolution of asphalt mixtures from low-temperature elasticity to medium- and high-temperature viscoelastic-plastic mechanical properties. Generally speaking, as the temperature decreases, the modulus of asphalt mixtures gradually increases. When the test temperature is high, the asphalt mixture exhibits viscoelasticity and more ductile failure occurs. When the test temperature is low, the asphalt mixture mainly exhibits elasticity and is prone to brittle fracture. The load-displacement curves of the three AC-16 asphalt mixtures at different temperatures are shown in Figure 2. Figure 9 .

[0094] from Figure 9 It can be seen that the load initially increases and then decreases with increasing displacement. As the load gradually increases to its peak value, tiny cracks begin to appear at the bottom cut of the specimen and gradually expand, causing the asphalt mixture's ability to resist the load to gradually decrease. After the peak load, the cracks continue to extend and expand, but the load gradually decreases until the specimen completely breaks. Under the three temperature conditions, the lower the temperature, the greater the peak load, indicating that the asphalt mixture has greater stiffness and can withstand greater loads at lower temperatures. However, after the peak load, the load-displacement curve at low temperatures is shorter, indicating that the specimen failure rate is faster at lower temperatures after the peak load. Among the three asphalt mixtures, the SBS modified asphalt mixture withstands the highest load at both 0°C and -10°C. At -15°C, the SBR asphalt mixture withstands slightly higher loads than the SBS asphalt mixture, with the SBR asphalt mixture's maximum load only increasing by 3.1% compared to the SBS asphalt mixture. Overall, the SBS asphalt mixture exhibits relatively good low-temperature performance. It can also be seen from the figure that at -10℃ and -15℃, the failure strain of SBS asphalt mixture is the largest, which is far better than SBR and RK300 asphalt mixture, that is, it has better ability to resist low-temperature cracking.

[0095] (2) Analysis of force-displacement characteristics during fracture

[0096] Stiffness S characterizes the deformation resistance of asphalt mixture, also known as stiffness. By calculating the slope of the linear rising elastic stage of the test load-displacement curve, the value of stiffness S can be obtained in kN / mm. The stiffness of different asphalt mixtures can be seen in Figure 10 .

[0097] from Figure 10 As can be seen from the data, temperature significantly affects the stiffness of various asphalt mixture specimens. As the temperature decreases, the stiffness of the mixtures gradually increases, reflecting the enhanced deformation resistance of the three asphalt mixtures at low temperatures. Compared with 0°C, the stiffness of the SBS, SBR, and RK300 asphalt mixtures at -10°C increases by 9.87%, 36.86%, and 26.22%, respectively. At -15°C, the stiffness of the SBS, SBR, and RK300 asphalt mixtures increases by 14.32%, 41.21%, and 31.84%, respectively. The low-temperature stiffness of SBR and RK300 exhibits significant variability, with increases exceeding 25% at -10°C and over 30% at 15°C, indicating that the performance of the SBS asphalt mixture is relatively stable. Furthermore, with the exception of RK300, where the stiffness is higher than that of SBR at 0°C, the stiffness of the different asphalt mixtures under all three temperature conditions follows the order of SBS > SBR > RK300.

[0098] (3) Crack resistance based on fracture energy

[0099] Fracture toughness K IC

[0100] Fracture toughness K IC At the critical load P C The stress intensity factor K I , the critical load is set as the maximum load during the test. K IC It can reflect the ability of asphalt mixture to consume and absorb energy during the fracture process. IC The larger it is, the better the material’s ability to hinder crack propagation is. IC The calculation of is shown in formula ④, and the fracture toughness of different asphalt mixtures under different temperature conditions is shown in Figure 12 .

[0101]

[0102] Where: Y I(0.8) is the standard stress intensity factor; σ0 is the stress corresponding to the critical load; P C is the critical load, i.e. the peak load, MN; r is the specimen radius, m; t is the specimen thickness, m; α is the crack length, m;

[0103] Depend on Figure 11Temperature significantly influences the fracture toughness of the three asphalt mixture specimens. As the temperature decreases, the fracture toughness of the asphalt mixture increases, reflecting the increased energy required to fracture the asphalt mixture at low temperatures. Except for -15°C, where the fracture toughness of the SBS-modified asphalt mixture is lower than that of the SBR-modified asphalt mixture, the SBS-modified asphalt mixture exhibits the highest fracture toughness at all temperatures, followed by SBR. This indicates that the SBS-modified asphalt mixture exhibits the best low-temperature fracture resistance of the three asphalt mixtures. At 0°C, the fracture toughness of the SBS-modified asphalt mixture is 11.65% higher than that of SBR and 6.77% higher than that of RK300. At -10°C, the fracture toughness of the SBS-modified asphalt mixture is 1.74% higher than that of SBR and 10.47% higher than that of RK300. At -15°C, the fracture toughness of the SBS-modified asphalt mixture is -3.2% higher than that of SBR and 19.47% higher than that of RK300.

[0104] Fracture energy G f

[0105] Fracture energy G f It is one of the main parameters calculated in the SCB test. It is defined as the work required for a crack to initiate, propagate, and eventually break in the specimen (when the load drops to 0.1 kN or less). It is expressed by the area under the load-displacement curve. f As the basis for evaluation, the internal stress of the specimen is closer to the actual stress state of the road surface, which can better simulate the crack expansion behavior of the specimen and comprehensively reflect the crack resistance of the asphalt pavement. The greater the fracture energy, the better the crack resistance of the asphalt mixture at a certain temperature. f It is calculated from the ratio of the fracture work of the rotary compacted specimen before the test to the area of ​​the tough zone, see formula ⑦.

[0106]

[0107] Where: G f is the fracture energy, J / m2; W f is the work of fracture, J, W f =∫Pdu, P is the applied load (N), u is the average displacement of the load (m); A lig is the area of ​​the toughness zone m2, A lig =(ra)*t, r is the specimen radius, m; t is the specimen thickness, m; a is the crack length, m;

[0108] According to formula ⑦, by integrating the load-displacement curves of various asphalt mixtures and the area enclosed by the X-axis, the fracture energy of asphalt mixtures under different test temperature conditions is obtained. Figure 12 .

[0109] Depend on Figure 12It can be seen that the fracture energy of SBS asphalt mixture increases with decreasing temperature, while the fracture energy of SBR and RK300 asphalt mixtures decreases with decreasing temperature. Except for 0℃, the fracture energy of SBS asphalt mixture is the largest under other temperature conditions. At -10℃, the fracture energy of SBS modified asphalt mixture is 1.297 and 1.723 times that of SBR and RK300 asphalt mixture. At -15℃, the fracture energy of SBS modified asphalt mixture is 1.547 and 1.955 times that of SBR and RK300 asphalt mixture. This shows that SBS asphalt mixture has the best crack resistance under low temperature conditions, followed by SBR asphalt mixture.

[0110] Those skilled in the art should understand that they can implement variations by combining the prior art with the above embodiments, which will not be described in detail here. Such variations do not affect the essence of the present invention and will not be described in detail here.

[0111] Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for testing the crack resistance of the upper layer components of asphalt pavement structures in areas with large temperature differences, characterized in that: The asphalt pavement structure includes an upper layer, a lower layer, and a base layer. The components of the upper layer are determined by a crack resistance test. The crack resistance test includes testing the crack resistance of the asphalt mixture at low temperature, high temperature, and frequency on a test block. After the above test, it is determined that the upper layer includes SBS modified asphalt, aggregate, and filler. The ratio of the SBS modified asphalt is 93.35% Karamay asphalt, 4.5% SBS modifier, 2% rubber oil, and 0.15% stabilizer. The aggregate includes coarse and fine aggregates produced by a gravel field, and its parent rock is biotite plagioclase gneiss. The filler is a mineral powder made by grinding fine-grained limestone. The method for testing the crack resistance of the upper layer of the asphalt pavement structure includes the following steps: Step 1: Test the effects of temperature and frequency on asphalt mixture performance; Step 2: Test the dynamic modulus of asphalt mixture: (1) The reduced frequency values ​​corresponding to the two different frequencies at different temperatures are obtained through formula ①: f r =fα T ① Where: f r —Reduction frequency, i.e. frequency at reference temperature, Hz; α T —shift factor, a function of temperature T; f—frequency, Hz; (2) Using formula ② and the dynamic modulus values ​​of different oil-stone ratios to fit the Sigmoidal function, the values ​​of the parameters in the formula can be obtained. The main curve after fitting is "S" shaped: Where: |E * |—dynamic modulus, MPa; δ—minimum value of dynamic modulus, MPa; δ+α—maximum value of dynamic modulus, MPa; β, γ—descriptive parameters of the S-shaped function, β, γ depend on the characteristics of the asphalt binder and the size of δ and α; α—variable, a function of grade, δ and α depend on aggregate gradation, asphalt content and void ratio; (3) Use the quadratic polynomial function for analysis, see formula ③, and obtain the fitting result graph: lgα T =αT 2 +bT+c ③ Where: T is temperature, °C; a, b, c are coefficients of the quadratic polynomial; (4) By fitting the relationship diagram between the asphalt mixture reduction frequency and the dynamic modulus, the relationship diagram between the asphalt mixture temperature and the displacement factor, and the dynamic modulus comparison diagram of the asphalt mixture at different temperatures, the dynamic modulus value of the asphalt mixture is predicted in the full frequency domain, thereby obtaining the dynamic modulus of the asphalt mixture; Step 3: Conduct tensile strength test on the test block.

2. The method for testing the crack resistance of the upper layer components of an asphalt pavement structure in a large temperature difference area according to claim 1 is characterized by: The method of testing the influence of temperature and frequency on the performance of asphalt mixture in step 1 includes: (1) Determine construction parameters: Use the SPT tester to conduct triaxial dynamic modulus tests to determine the effects of different temperatures and different action times on the dynamic modulus of asphalt mixtures; (2) Select the test temperature: Use three test temperatures of 4°C, 20°C, and 40°C to study the law of the change of dynamic modulus with frequency at different temperatures; (3) Select the test frequency: use four frequency levels: 0.1, 1, 10, and 25 Hz; (4) Conducting tests and analysis: The asphalt mixture was tested using an SPT tester to obtain the dynamic modulus and phase angle of the asphalt mixture. The changes in the phase angle at 4°C, 20°C, and 40°C at the same frequency were analyzed to determine the dependence and sensitivity of the asphalt mixture response results on temperature.

3. The method for testing the crack resistance of the upper layer components of an asphalt pavement structure in a large temperature difference area according to claim 1 is characterized in that: The method of performing a tensile strength test on the test block in step 3 includes: (1) The test adopts the wheel pressing method to obtain the load-displacement curve of the semicircular bending test of the asphalt mixture, and analyzes the change of the failure rate of the asphalt mixture specimens after the load peak at different temperatures; (2) Obtain the stiffness diagram of asphalt mixture at different test temperatures and analyze the stiffness of asphalt mixture under three groups of temperature conditions; (3) Calculation of crack resistance based on fracture energy: Fracture toughness K IC At the critical load P C The stress intensity factor K I , the critical load is set as the maximum load during the test, and the fracture toughness K is calculated IC Where: Y I(0.8) is the standard stress intensity factor; σ0 is the stress corresponding to the critical load; P C is the critical load, i.e. the peak load, MN; r is the specimen radius, m; t is the specimen thickness, m; a is the crack length, m; Calculate the fracture energy G f : Where: G f is the fracture energy, J / m2; W f is the work of fracture, J, W f =∫Pdu, P is the applied load (N), u is the average displacement of the load (m); A lig is the area of ​​the toughness zone m2, A lig =(ra)*t, r is the specimen radius, m; t is the specimen thickness, m; a is the crack length, m; According to formula ⑦, the fracture energy of asphalt mixture under different test temperature conditions is obtained by integrating the load-displacement curve of asphalt mixture and the area enclosed by the X-axis.

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