CN110501243A - A test method for fatigue performance of asphalt mixture based on rutting tester - Google Patents

Abstract

The invention relates to a method for testing fatigue performance of asphalt mixture based on a rutting tester, involving equipment improvement, test piece preparation, data collection, data analysis and the like. The present invention utilizes the rutting tester to simulate the characteristics of actual road surface moving wheel load and road surface structural conditions and improves them to provide indoor test conditions similar to the actual asphalt concrete pavement stress conditions and structural conditions, and at the same time combines the relevant theories and analysis methods of dissipated energy Evaluate the anti-fatigue cracking performance of asphalt mixture, and realize the new function of traditional rutting tester for evaluating the fatigue performance of asphalt mixture. The invention has the advantages of easy-to-obtain, economical, and strong applicability of test equipment, strong simulation of on-site road surface in loading form and structural environment, simple, fast, easy-to-control testing process, efficient and feasible analysis method, and the like. It can better test and evaluate the fatigue performance of asphalt mixture, and also provides a new test idea and method for the pavement structure-material integrated design.

Description

A test method for fatigue performance of asphalt mixture based on rutting tester

technical field

The invention relates to the technical field of road engineering, in particular to a method for testing the fatigue performance of asphalt mixture based on a rutting tester, which is used for testing the fatigue cracking resistance of the asphalt mixture.

Background technique

With the development of highway traffic construction, especially high-grade pavement with asphalt pavement as the main form has higher and higher requirements for the quality of road materials. The performance and composition design of road materials affect the quality of pavement, and the use of scientific and reasonable test methods to test the performance of asphalt mixture is very important for the correct use of materials, scientific design of pavement and evaluation of road performance. .

Fatigue cracking is one of the main damage forms of asphalt pavement, so the anti-fatigue cracking performance of asphalt mixture is also an important part in the process of asphalt pavement design and performance evaluation. For the research on the fatigue performance of asphalt mixture, the main test methods include test road, full-scale test, scale test (sample test method) and indoor test. The test road method is a study on the fatigue damage of the actual road surface under real vehicle loads, such as the AASHTO test road in the United States, but it is usually time-consuming and easily affected by the on-site climate and environment. Full-scale tests, such as accelerated pavement testing (APT) and loop tests, are based on the effect of moving loads and can be used to simulate the loading conditions of actual road surfaces, but they have the disadvantages of complex test devices, long test periods, and high costs. , so it is not suitable for the control of fatigue performance by most institutions in the process of conventional pavement design and construction. Scaled-scale tests, such as the proportional accelerated loading test MMLS3, can realize the indoor simulation of the fatigue process of the pavement structure under moving loads. Although it overcomes the shortcomings of full-scale equipment such as time-consuming, high cost, and difficult environmental control to a certain extent, it cannot be compared with the full-scale Get the real loading environment just like the experiment. In contrast, indoor tests are widely used in testing and evaluating the fatigue performance of asphalt mixtures because of their advantages such as simple test, economy, easy control, and easy access to equipment. There are different indoor fatigue test methods for asphalt mixture. There are many current test methods at home and abroad, mainly including simple bending test (including three-point bending, four-point bending, semicircular bending fatigue, elastic foundation beam bending method, cantilever beam bending, etc.), supported Bending test, uniaxial test, triaxial test, fracture mechanics test, direct tensile test, indirect tensile fatigue test, split fracture test, etc., usually use beam or cylindrical specimens formed indoors or sampled on site under medium temperature conditions. Apply the load below. Among these test methods, based on the simulation degree of the test method to the field situation, the simplicity of the test method and the applicability of the test results, SHRP considers that the repeated bending fatigue test (such as the four-point bending beam test) and the indirect tension The comprehensive evaluation of the tensile fatigue test is good, and it has been widely used. Repeated bending fatigue test mainly performs simple repeated loading on the beam specimen to generate bending stress (or strain) in the beam, which can simulate the whole process of asphalt mixture from crack occurrence to development, and use special evaluation indicators to define damage or fatigue. However, there are also problems such as complicated preparation of beam-type specimens, easy breakage of specimens, and large discreteness, which have a certain impact on the research of fatigue performance. The indirect tensile fatigue test is used to test the tensile strength of the asphalt mixture and evaluate the possibility of fatigue damage by applying repeated loads on the cylindrical specimen along the vertical diameter direction, but the internal stress distribution of the experimental specimen is complex , the accuracy of the experimental results is poor. Most of these indoor test methods are used to evaluate the fatigue cracking resistance of asphalt mixture, but they often rely on special test equipment. In addition, the fatigue cracking of asphalt mixture is closely related to the load form and pavement structure. The cracking of asphalt pavement is affected by the pavement structure layer. However, the above indoor tests cannot well simulate the moving load and structural conditions of the actual pavement, which affects the fatigue performance of the mixture. There are some differences between the evaluation and the actual road surface.

The loading mode and test environment of the fatigue performance test of asphalt mixture have a very important influence on the test results, and the test form different from the actual road surface moving load and multi-layer structure conditions may lead to large deviations in test conclusions and unreasonable results. design results. However, the existing indoor test methods have deficiencies. Therefore, a test method for the fatigue performance of asphalt mixtures is developed, so that the loading method can be close to the moving load form of the actual pavement, and the test environment can simulate the multi-layer structure of the actual pavement. It is of great significance to study the fatigue performance of asphalt mixture. In addition, if the existing test methods and instruments can be fully used to improve the equipment, the loading method and test conditions will be closer to the actual road conditions; at the same time, the existing fatigue evaluation methods can be used to quickly verify and evaluate the fatigue performance of asphalt mixture. It is of great significance to study the fatigue performance of asphalt mixture, evaluate its anti-fatigue cracking performance and carry out the integrated design of pavement structure materials.

Rutting tester or wheel load tester is a kind of instrument widely used in testing the performance of asphalt mixture. The Hamburg Wheel-tracking Device (HWTD) and Asphalt Pavement Analyzer (Asphalt Pavement Analyzer) are widely used at home and abroad. ,APA) etc. The rutting tester can be defined as a test that uses moving wheel loads to evaluate the performance of asphalt mixtures under certain test conditions. Currently, it is mainly used to test the high-temperature rutting and water damage resistance of asphalt mixtures. Its working principle is to apply repeated wheel loads to the specimen in a dry or wet environment, and test the rutting of the specimen under the wheel load and the failure point under the water immersion condition. Compared with other indoor tests, the rutting test can better simulate the state of the actual road surface subjected to repeated moving loads and the structural conditions of the road surface, making the stress state inside the test piece closer to the real situation of the road. At the same time, compared with the full-scale or reduced-scale test, the rutting tester has a wider range of equipment, corresponding specifications for test methods, lower test time and capital costs, and more convenient preparation of test pieces. It can be seen that on the basis of making full use of the characteristics and advantages of the rutting tester and making minor changes, a new and effective test method for evaluating the fatigue performance of asphalt mixtures can be developed, and existing resources can be fully and rationally utilized Implement new functions and save costs.

Contents of the invention

The purpose of the present invention is exactly to provide a kind of asphalt mixture fatigue performance testing method based on the rutting tester in order to overcome the defective that above-mentioned prior art exists, make full use of the characteristics of the rutting tester to simulate actual road surface moving wheel load and road surface structure condition and carry out Improvement, the present invention can make up for the deficiencies of the existing asphalt mixture fatigue performance test method, is simple, economical, convenient and feasible, can provide indoor test conditions similar to the actual asphalt concrete pavement stress status and structural conditions, and combine corresponding analysis methods, and then Evaluate the anti-fatigue cracking performance of asphalt mixture, and realize the new function of traditional rutting tester for evaluating the fatigue performance of asphalt mixture.

The purpose of the present invention can be achieved through the following technical solutions:

A test method for the fatigue performance of asphalt mixture based on a rutting tester. The test system matched with the test method includes a rutting tester or a wheel loader with wheel rolling as the loading method, a test piece, a resistance strain gauge, a flexible pressure sensor, a data Acquisition subsystem and data analysis method, the method includes the following steps:

Step 1: Prepare the specimens required for the fatigue performance test of asphalt mixture based on the rutting tester;

Step 2: Set up the test environment for rutting test;

Step 3: Carry out actual test and data collection;

Step 4: Analyze the fatigue performance of asphalt mixture based on the collected data based on the theoretical method of dissipation energy developed based on repeated bending fatigue tests, and obtain the final performance test results and corresponding conclusions.

Further, the step 1 specifically includes: determining the size of the test piece according to the specific size of the rutting tester mold and the test requirements, and forming the asphalt mixture test piece; Install resistance strain gauges and flexible pressure sensors, and perform insulation protection on all sensor surfaces.

Further, the step 2 specifically includes: placing a rubber plate in the mold of the rutting tester to simulate the actual pavement structure layer, placing the test piece prepared in step 1 on the rubber plate, and installing wood on both sides of the test piece. At the same time, place another test piece that is also pasted with strain gauges and sensors in the test tank of the rutting tester as a temperature compensation block to eliminate the influence of temperature changes; the sensor connection lines of each test piece lead out the rutting test The instrument is connected to the data acquisition subsystem; the wheel load size and loading frequency of the rutting test instrument are adjusted.

Further, the asphalt mixture test piece is formed by wheel rolling method, the asphalt mixture test piece is a plate-type test piece, its length and width are determined according to the specific model of the rutting tester, and its thickness is determined according to the The mixture gradation (thickness of the specimen shall not be less than 2 times the maximum mineral particle size) or the thickness of the test road; the pretreatment process of the original specimen includes the cutting of the specimen and the grinding of the pasted sensor area And glue coating, the surface of all the sensors is insulated and protected by silicone glue.

Further, the rubber sheet is made of neoprene with a modulus similar to that of the asphalt mixture, its length and width are determined according to the mold size of the rutting tester, and its thickness is determined according to the test requirements or the required simulated road surface structure The length, width and height of the wooden strips are determined according to the model of the rutting tester mold and the size of the test piece; Or adjust the loading contact pressure to adjust, the loading frequency of the rutting tester is adjusted by adjusting the speed control of the loading wheel of the rutting tester, usually select the maximum loading speed to shorten the test time.

Further, the step 3 specifically includes: applying a periodic moving load to the test piece after being insulated by the temperature compensation block in step 2; measuring the test piece by the resistance strain gauge and the flexible pressure sensor respectively The tensile deformation strain and the vertical pressure change produced by the piece, the data acquisition subsystem simultaneously and continuously records the data, that is, the rut depth, the number of wheel load actions, the number of wheel loads, and Strain and stress change data.

Further, in the step 3, the heat preservation is carried out at the test temperature for not less than 2 hours, and the temperature is controlled throughout the test; the wheel load is constant during the test, and the wheel load working mode is stress control mode.

Further, the step 4 specifically includes: firstly obtain the change curve of the rebound strain of the mixture with time according to the change curve of the specimen strain with the loading times or time, and obtain the change curve of the mixture at Fatigue life under different evaluation indicators; then calculate the phase angle of the test piece according to the relationship between the pressure-strain during the loading process of the test piece and the number of times of loading or time, and combine the loading stress, frequency and the measured rebound strain and phase angle data Calculate the dissipated energy (Dissipated Energy, DE) and the relative rate of change of dissipated energy (Ratio of Dissipated Energy Change, RDEC); finally calculate the plateau value (Plateau Value, PV) of the relative rate of change of dissipated energy, so that the Fatigue performance was evaluated.

Further, the rebound strain of the mixture is the amplitude of the tensile deformation strain curve of the specimen during a single loading cycle; the fatigue life of the mixture includes a turning point in the growth rate of the stiffness modulus, that is, the rebound strain curve The number of loadings corresponding to the turning point of the growth rate, and the stiffness modulus decays to 50% of the initial value, that is, the number of loadings corresponding to the rebound strain increasing to twice the initial value in the stress control mode.

According to the change curve of the rebound strain curve, the fatigue life _Nf50 of the mixture is determined by the traditional analysis method of dissipative energy theory, which means that the stiffness modulus decays to 50% of the initial value (in the stress control mode, the rebound strain value increases to the initial value 2 times the value), and according to the loading characteristics of this test, the fatigue life N _fp of the mixture is defined as the number of loadings corresponding to the turning point of the stiffness modulus growth rate (that is, the turning point of the growth rate of the rebound strain curve) , these two indicators will be used for follow-up analysis; the relative change rate of dissipated energy, the valley value PV, depends on the determined fatigue life N _f and the exponential fitting curve slope k of the dissipated energy change in the corresponding loading times, the present invention relates to PV under two evaluation indicators.

Further, the formula for calculating the dissipated energy is:

In the formula, DE _i represents the dissipated energy during the i-th loading, and the stress is constant as σ _i , is the phase angle, ε _i represents the springback strain;

The formula for calculating the relative rate of change of the dissipated energy is:

In the formula, RDEC _a represents the relative change rate of the average dissipated energy between the loading times a and the next loading times a, and DE _a and DE _b represent the corresponding dissipated energy at the loading times a and b, respectively;

The formula for calculating the flat valley value is:

In the formula, PV represents the flat valley value, _Nf represents the fatigue life determined by the mixture, and k represents the slope of the exponential fitting curve of the fatigue life determined by the mixture corresponding to the change of dissipated energy within the loading times.

Compared with the prior art, the present invention has the following advantages:

(1) In the present invention, the structure and shape of the test piece, the force characteristics, and the action environment can better simulate the situation of the real road surface. During the test, the strain and pressure changes of the test piece can be obtained through the strain and pressure sensors. The evolution of the anti-fatigue cracking performance of asphalt mixtures is studied by the theoretical method of energy dissipation, and the fatigue cracking behavior of the mixture is explored. That is to say, the present invention, on the basis of minor improvements to the currently widely used and mature rutting tester or wheel load tester, can well simulate real road conditions and can be used to quickly and reliably test the resistance of asphalt mixtures. Fatigue cracking performance, new capabilities developed for traditional rutting test instruments.

(2) The present invention has the characteristics of easy-to-obtain, economical, and strong applicability of test equipment, strong test loading form and structural environment for on-site road simulation, simple, fast, easy-to-control test process, and efficient and feasible test analysis method. The size of the test wheel load and the support conditions at the bottom of the specimen can be adjusted according to the actual road conditions or design requirements. The stress characteristics and environment of the specimen during the test are also similar to the real asphalt concrete pavement, making the test evaluation results more reasonable. This test can be used as a supplement between indoor test and accelerated loading test. It can better test and evaluate the fatigue performance of asphalt mixture, and provides a new test idea and method for pavement structure-material integrated design. .

Description of drawings

Fig. 1 is a side view of the rutting tester fatigue performance test system of the present invention;

Fig. 2 is the bottom view of the rutting tester fatigue performance test system of the present invention;

Fig. 3 is the change situation diagram of strain and pressure with loading time or number of times in the fatigue test of the method embodiment test piece of the present invention;

Fig. 4 is the change situation figure of test piece longitudinal strain with loading time of the method embodiment of the present invention;

Fig. 5 is the variation trend figure of longitudinal springback strain of different types of mixture test pieces of the method embodiment of the present invention;

Fig. 6 is the schematic diagram of defining two kinds of fatigue life _Nf50 and _NfP in the fatigue test of the rutting tester of the embodiment of the present invention;

Figure 7 is a typical (Carpenter et al., 2003) relationship diagram of relative change rate of dissipated energy RDEC and loading times;

Figure 8(a) is a fitting curve of the relationship between the specific stress of dissipated energy (DE/σ) and the number of loadings determined according to N _f50 ;

Fig. 8(b) is a fitting curve of the relationship between the specific stress of dissipated energy (DE/σ) and the number of loadings determined according to _NfP ;

Fig. 9 is the double-logarithmic relationship diagram of the flat valley value of the relative rate of change curve of the dissipated energy and different fatigue lives _Nf50 and _NfP of the method embodiment of the present invention;

Among them, 1 is the loading wheel of the rutting tester, 2 is the test piece, 3 is the rubber plate, 4 is the mold steel plate of the rutting tester, 5 is the first wooden strip, 6 is the second wooden strip, and 7 is the longitudinal-track direction resistance Type strain gauge, 8 is a horizontal-vertical wheel track direction resistance strain gauge, 9 is a first thin-film pressure sensor, and 10 is a second thin-film pressure sensor.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

As shown in Figures 1 and 2, before the test, the resistance strain gauges (longitudinal-wheel track direction resistance strain gauges 7, Horizontal-vertical wheel track direction resistive strain gauge 8) and flexible pressure sensor (the first thin film pressure sensor 9, the second thin film pressure sensor 10), to test the specimen under the wheel track in the test under the action of repeated moving load The longitudinal (wheel track direction) and transverse (perpendicular to the wheel track direction) tensile strain changes and the vertical pressure changes at this position (in this embodiment, only representative longitudinal strain data are analyzed). A neoprene sheet 3 with the same thickness as the test piece is placed on the bottom of the test piece 2 to simulate the actual pavement base structure. In addition, the two sides of the test piece are fixed with the first wooden bar 5 and the second wooden bar 6 of the same thickness and length as the test piece, so as to prevent the lateral movement of the test piece during the test loading process. A fixed moving load is used in this test, so this test can be regarded as a stress control mode, and the surface stress of the specimen is constant during the test. The phase angle can be calculated by the time difference between the strain lagging the stress (pressure) generated by the specimen during the test, and the rebound strain value of the specimen in each loading cycle can be calculated by using the strain change curve, so that it can be correlated according to the dissipated energy Theory and method for fatigue performance analysis of asphalt mixture.

This embodiment takes the PAVELAB DWT two-wheel rutting instrument (77-PV3UP10) as an example, and uses the test method of the present invention to carry out fatigue performance tests on several different asphalt mixtures.

Three different asphalt mixtures were involved in the test, the designed mixture gradation was AC-13C, the new aggregate was limestone, and the new asphalt was Jinshan A-70 matrix asphalt (PG 64-22). According to the Superpave volumetric design method (AASHTO M323), the optimal asphalt content of 4.58% was used in the design mixture A, the lower asphalt content of 3.85% was used in the mixture B, and 40% of recycled asphalt pavement materials (Reclaimed asphalt pavement, RAP) replaces the new aggregate, the final mixing asphalt ratio is 4.58%, and the best new asphalt dosage is 2.23%. The above three kinds of mixtures consider the influence of asphalt content and RAP material on the fatigue cracking resistance of asphalt mixtures, so as to evaluate the sensitivity of wheel load tester fatigue performance test to the fatigue cracking resistance of different asphalt mixtures. The asphalt mixture is compacted by a wheel mill to form a plate-type test piece, and the porosity is controlled to be 7±1%. The new aggregate gradation and RAP material gradation in this test are shown in Table 1.

Table 1. Grading of new aggregate and RAP material

The specific implementation process of this embodiment is as follows:

1. Determine the size of the loaded test piece. In order to simulate the situation that the fatigue cracks in the actual pavement are mostly transverse cracks, and at the same time ensure that the fatigue cracking phenomenon occurs in the specimen within a reasonable loading time, according to the finite element analysis results, it is determined that the test specimen should have a smaller width-to-length ratio. The width of the test piece 2 described in is 150mm, which is 1/2 of the original test piece width, and 3 times the width of the loading wheel. At the same time, according to the specification (AASHTO T325) that the thickness of the test piece should not be less than twice the maximum mineral particle size, the thickness of the test piece 2 is determined to be 40mm.

2. Determine the supporting conditions of the specimen. In order to simulate the base structure of the actual pavement, a neoprene rubber sheet 3 with a modulus similar to the flexible base layer of the actual pavement is used to pad the bottom of the specimen. The Shore hardness of the rubber sheet is D70 and the thickness is 40 mm. As shown in Figure 1, it is placed Rutting tester die plate 4 on.

3. Determine the sensor and data acquisition system. In this test, because the bottom surface of the specimen 2 is in direct contact with the rubber plate 3 in the mold, a flexible chip sensor with high strength and light enough thickness is selected to measure the strain and pressure. The resistance strain gauge used is the rosette (BX120-10CA), the resistance is 120±0.8Ω, and the sensitivity is 2.08; the flexible pressure sensor (DF9-40@10kg), the thickness is 0.35mm, and the response time and recovery time are respectively 1ms and Within 15ms. The DH3820TM strain acquisition system was used to record the stress-strain response during the test.

4. Formed test piece. In this example, 6 samples were prepared for 3 kinds of asphalt mixtures, and the rutting slab with the size of 400mm×300mm×(40±1)mm was formed by a wheel milling machine.

5. Specimen pretreatment. First cut the rutting plate, take the part with the middle size of 400mm×150mm×(40±1)mm as the loading test piece; then use the grinding wheel and sandpaper to polish the area where the sensor is pasted in the mid-span of the lower bottom of the test piece, and the grinding width is controlled to the length of the test piece Within 5mm of the direction, the grinding thickness is controlled within 1mm; finally, after cleaning and drying the grinding surface, apply epoxy resin AB glue evenly, and stick the sensor after the strength is formed.

6. Paste the sensor. Paste the sensor with 502 glue on the mid-span part of the lower bottom of the test piece. After the strength is formed, evenly paint 704 silicone glue with a thickness of no more than 1mm on the surface of the sensor to play the role of insulation and protection. The schematic diagram of the pasting position is shown in Figure 2, wherein the longitudinal-wheel-track direction resistance strain gauge 7 is used to measure the longitudinal (wheel-track direction) tensile strain of the specimen, and the transverse-vertical wheel-track direction resistance strain gauge 8 is used to measure the specimen Transverse (vertical wheel track direction) tensile strain, the first film pressure sensor 9 and the second film pressure sensor 10 are used to measure the vertical pressure change and its corresponding moment during the experiment.

7. Follow steps 5 and 6 to perform the same treatment on the remaining specimens after cutting, and paste the same strain gauges for temperature compensation during the experiment.

8. Place a set of prepared parallel specimens (two specimens of the same mixture) in the middle of the Hamburg rut mold with a rubber plate, and use the first and second specimens with a size of 400mm×75mm×40mm on both sides. The wooden strips 5 and 6 are fixed, and the sensor wires are drawn out through the holes on both sides of the mould, and connected with the data acquisition system. The mold is placed in the test tank together with the parallel test piece and the temperature compensation block.

9. Before the test, keep warm at the test temperature (in this embodiment, the control test temperature is 30°C) to make the test piece reach the test temperature, generally not less than 2h;

10. Determine the fatigue loading test conditions. The wheel load of this embodiment is 900N, and the counterweight of the loading arm needs to be increased on the basis of the traditional Hamburg rutting test; at the same time, the loading rate is set to 60 times/min, and the response loading frequency is 1Hz;

11. Input the parameters such as the resistance and sensitivity of the sensor into the data acquisition system, balance each sensor, and set the data acquisition to the continuous sampling state at the same time, and the sampling frequency is 100Hz.

12. During the test, the data acquisition instrument synchronously records the changes of the strain and pressure of the specimen with the loading of the specimen, as shown in Figure 3. Figure 4 shows the variation of the longitudinal strain of the specimen with loading time.

13. After the test, as shown in Figure 4, use MATLAB to perform preliminary processing on the original data, calculate the rebound strain value of each loading cycle, and obtain the change curve of the longitudinal rebound strain of each specimen with the number of loading times, as shown in Figure 5 shown.

After determining the change curve of the rebound strain with the number of loading times, the fatigue life N _f50 of the mixture is determined according to the traditional analysis method of dissipative energy theory, which is the number of loading times corresponding to the stiffness modulus decaying to 50% of the initial value. The loading characteristics of this test define the fatigue life N _fp of the mixture as the number of loadings corresponding to the turning point of the stiffness modulus growth rate. These two indicators will be used in subsequent analysis.

In addition, the relationship between strain and pressure (stress) as shown in Figure 3 can be used to calculate the phase angle during the loading process of the specimen, combined with Figure 5, the rebound strain can be used to calculate the dissipated energy DE, thereby calculating the relative change rate of dissipated energy RDEC And its flat valley value PV is used to evaluate the fatigue performance of different asphalt mixtures.

Specifically, it can be calculated according to the following formula and definition.

In this embodiment, because the magnitude of the applied moving load is fixed, its loading mode can be regarded as a control stress mode. Therefore, assuming that the stress at the bottom of the specimen is constant throughout the test, the dissipation energy of the specimen at each loading Can be expressed as:

The stress is constant, and the dissipation energy of the specimen at each loading can be expressed as:

Wherein, the loading mode of this embodiment is a stress control mode, and the stress at the bottom of the test piece is constant during the test, which is _σi ; _εi is the rebound strain; is the phase angle, and the phase angle can be calculated according to the time difference Δt that the strain generated by the specimen lags behind the stress in the test, f=1Hz is the test loading frequency.

The relative rate of change of dissipated energy, RDEC, can be calculated by the following formula:

Among them, RDEC _a is the relative change rate of the average dissipated energy at the loading time a compared with the next loading time a; DE _b is the dissipated energy at the loading time b; DE _a is the dissipation energy at the loading time a Can; In this embodiment, the interval between two loading times is 180, so ba=180.

The change of the typical relative change rate of dissipated energy RDEC with the number of loadings is shown in Figure 7, where LoadCycle represents the loading cycle and Plateau Stage represents the flat valley stage. Plateau value (PV) is selected as the evaluation index, and the smaller the PV value, the better the fatigue cracking resistance of the mixture. The calculation formula of PV value is as follows:

Among them, N _f is the two kinds of fatigue life N _f50 and N _fp of different mixtures in the fatigue performance test of the rutting tester determined in Fig. 6; k is an index determined according to the variation trend of DE/σ same loading times under different N _f The slope of the fitting curve, typical fitting curves are shown in Figures 8(a) and 8(b).

In this embodiment, the longitudinal stress-strain data is selected for analysis. Finally, according to the calculated PV values of the three kinds of asphalt mixtures, the double-logarithmic relationship between the PV value and the loading times under two kinds of fatigue life _Nf can be obtained as shown in Figure 9 shown. The results show that there is a good correlation between the PV value and the two types of fatigue life _Nf , which is independent of the type of mixture, indicating that it is feasible to use the theory of dissipation energy correlation as a data analysis method in this test; The life N _f50 is also the fatigue life N _fp proposed in this test method, and the two fitting lines are almost on the same trend line, which shows that the fatigue life index proposed in this test is consistent with the results obtained by the traditional method index.

The final results of the fatigue performance test of the rutting tester are shown in Table 2.

Table 2. Summary of fatigue performance test results of rutting tester

Note: t _f50 and t _fp represent the test loading time corresponding to the fatigue life N _f50 and N _fp times respectively.

The results of the fatigue performance test in this example show that under the two fatigue life evaluation indicators, no matter using the fatigue life _Nf or the relative change rate of the dissipated energy Pinggu PV, the fatigue cracking resistance of the three mixtures is A>B>R , which is consistent with the actual performance characteristics, indicating that the experimental method of the present invention can distinguish asphalt mixtures with different fatigue properties. At the same time, although the overall test was loaded 100,000 times (about 27.8h) to observe the development of cracks in the specimen, in this example, the cracks of each mixture appeared near the number of loading times or the time corresponding to the fatigue life N _fp , that is, t _fp , it can be seen from the table that fatigue cracking occurs in the average 2.4h of the mixture A with the best fatigue resistance, while it only needs 1h to be defined as fatigue failure when the traditional fatigue life N _f50 is adopted, which shows that the test and analysis method of the present invention can be effectively The test time is shortened, and the fatigue performance of different mixtures can be analyzed and evaluated by the theoretical method of dissipation energy. In addition, the rutting tester can also measure the change of the rut depth of the specimen during the loading process. It can be seen from the table that the asphalt mixture with better anti-fatigue cracking performance shows poor anti-rutting performance, indicating that the mixture with relatively high asphalt content Mixtures with lower asphalt content exhibit better flexibility and resistance to fatigue cracking, but may exhibit poorer rutting resistance than mixtures with lower asphalt content.

According to the above test and analysis results, the following conclusions can be drawn:

The fatigue performance test method of asphalt mixture proposed by the present invention on the basis of minor improvements to the currently widely used and mature rutting tester or wheel load tester can well simulate real road conditions and quickly and reliably test asphalt mixture The anti-fatigue cracking performance of materials has developed new functions of traditional rutting test instruments; the analysis method based on the theory of dissipative energy is suitable for accurately and effectively analyzing the test data of the present invention; the fatigue life evaluation index N _fp proposed in this test and the corresponding consumption The results of the correlation analysis of energy dissipation are in good agreement with the results obtained by the traditional fatigue life evaluation index N _f50 , which can distinguish asphalt mixtures with different fatigue properties, and the analysis method based on the two indexes can effectively shorten the test time and greatly improve the fatigue performance. Test efficiency; the test method of the invention takes into account the test of anti-rutting performance of asphalt mixture, and provides a new test idea and method for the integrated design of pavement structure-material.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can easily think of various equivalents within the technical scope disclosed in the present invention. Modifications or replacements shall all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (9)

1. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument, matched test system, test method institute System includes adopting by the Measuring Device of loading method or wheel load instrument, test specimen, resistance strain gage, pliable pressure sensor, data of rolling Subsystem and data analysing method, which is characterized in that method includes the following steps:

Step 1: test specimen needed for preparing the fatigue performance of asphalt mixture test based on vehicle tracking test instrument；

Step 2: setting wheel tracking test tests environment；

Step 3: carrying out actual tests test and data acquisition；

Step 4: as based on Dissipated energy correlation theory method obtained by repeated bending fatigue developing test for acquisition data into The data of row fatigue performance of asphalt mixture are analyzed, and final performance test result and corresponding conclusion are obtained.

2. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 1, special Sign is that the step 1 specifically includes: sample dimensions are determined according to vehicle tracking test instrument mold specific size and test requirements document, Shaping asphalt test specimen；Resistance strain gage is installed in the test specimen bottom surface span centre position after pre-processing to original test specimen With pliable pressure sensor, and all the sensors surface carry out insulating protection processing.

3. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 2, special Sign is that the step 2 specifically includes: in vehicle tracking test instrument mold place rubber slab to simulate practical road surface structare layer, Test specimen ready in step 1 is placed on rubber slab, in test specimen two sides installation batten with fixation；Simultaneously by another The test specimen of same stickup foil gauge and sensor is placed in the experimental tank of the vehicle tracking test instrument as temperature compensation block to eliminate temperature Degree variation influences；The sensor connecting line of each test specimen draws the vehicle tracking test instrument and is connected to data acquisition subsystem；Adjustment The wheel load size and loading frequency of the vehicle tracking test instrument.

4. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 2, special Sign is that the bitumen mixture specimen is molded with by the rolling method of forming, and the bitumen mixture specimen is board-like Test specimen, length and width depending on the vehicle tracking test instrument concrete model, thickness according to mixture gradation or test road thickness Depending on degree；The original test specimen carries out the cutting that pretreated process includes test specimen, the polishing and painting for pasting sensor region Glue, all the sensors surface carry out insulating protection processing by silica gel glue.

5. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 3, special Sign is that the rubber slab is made of neoprene, thick depending on length and width are according to the vehicle tracking test instrument die size Degree is depending on the pavement structure situation of test requirements document or required simulation；The length, width and height of the batten are according to the vehicle tracking test instrument Depending on the model of mold and the size of the test specimen；The wheel load size of the vehicle tracking test instrument is by increasing and decreasing the wheel tracking test Instrument loading arm weight adjusts load contact pressure to adjust, and the loading frequency of the vehicle tracking test instrument is by adjusting the track examination Instrument loading wheel speed control is tested to adjust.

6. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 3, special Sign is that the step 3 specifically includes: applying week to the test specimen after keeping the temperature in step 2 by the temperature compensation block The traveling load of phase property；Drawing caused by the test specimen is measured respectively by the resistance strain gage and pliable pressure sensor Stretch deformation strain amount and vertical pressure variation, data acquisition subsystem simultaneously continuously record data, i.e., the described vehicle tracking test instrument and Rut depth, wheel load effect number, strain and the stress variation data for the test specimen that sensor obtains respectively.

7. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 6, special Sign is, is kept the temperature no less than 2 hours in the step 3 at a temperature of experimental test, experimental test whole process temperature control；Test Wheel load constant magnitude in test process, and wheel load operating mode is Stress Control mode.

8. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 6, special Sign is that the step 4 specifically includes: being strained according to the test specimen obtain with load number or the change curve of time first The rebound of mixture strains versus time curve, and obtains the mixture under different evaluation index by change curve Fatigue life；Then examination is calculated with load number or the variation relation of time according to pressure-strain in the test specimen loading procedure The phase angle of part calculates Dissipated energy and the opposite change of Dissipated energy in conjunction with the strain of loading stress, frequency and institute's survey time bullet, phase angles data Rate；Dissipated energy relative change rate curve Pinggu value is calculated, finally to evaluate fatigue performance of asphalt mixture.

9. a kind of fatigue performance of asphalt mixture test method based on vehicle tracking test instrument according to claim 8, special Sign is that the rebound strain of the mixture is the amplitude of test specimen stretcher strain strain curve during single loaded cycle；Institute The fatigue life for stating mixture includes that stiffness modulus growth rate is transferred, i.e., rebound strain curve growth rate turning point institute is right The load number and stiffness modulus answered decay to rebound strain under 50% namely Stress Control mode of initial value and rise to just Load number corresponding to 2 times of initial value.