Asphalt mixture dynamic modulus testing method and system based on axial bending and tension loading

Abstract

The present invention discloses a method and system for testing the dynamic modulus of asphalt mixtures based on axial bending and tension loading, which relates to the field of road engineering technology and includes the following steps: obtaining a cylindrical asphalt mixture specimen; wherein the specimen is obtained on-site by core sampling and indoors by a rotary compactor or a Marshall compactor; fixing the sidewalls of the asphalt mixture specimen and applying an axial bending and tension cyclic load to the specimen, recording a curve showing the load and the deflection at the center of the bottom surface of the asphalt mixture specimen as a function of loading time, and obtaining the load and deflection values ​​of the asphalt mixture specimen based on the curve; substituting the load and deflection values ​​into a dynamic modulus calculation formula for the asphalt mixture to obtain the dynamic modulus value of the asphalt mixture specimen. The present invention solves the problems of existing asphalt mixture dynamic modulus test methods that cannot simulate on-site stress conditions and that specimen molding is difficult, and can more accurately and conveniently measure the dynamic modulus of asphalt mixtures.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering, and in particular to a method and system for testing the dynamic modulus of asphalt mixture based on axial bending and tensile loading. Background Art

[0002] Asphalt mixture is a typical viscoelastic material, and dynamic modulus is an important indicator of its viscoelastic and mechanical properties, serving as a key input for pavement design and evaluation. Current methods for measuring the dynamic modulus of asphalt mixtures include the uniaxial compression dynamic modulus test and the beam bending-tension dynamic modulus test. The uniaxial compression dynamic modulus test is the most commonly used test method for obtaining dynamic modulus, and current specifications all use this method as the standard test method for determining the dynamic modulus of asphalt mixtures.

[0003] The one-dimensional modulus obtained from the uniaxial compression dynamic modulus test cannot strictly describe the mechanical response of the asphalt mixture under the three-dimensional stress state of the pavement. Furthermore, the test specimen thickness is 150mm, while the thickness of the upper, middle, and lower layers of the pavement on site is typically 40mm-60mm, which does not meet the 150mm requirement for uniaxial compression. This makes on-site sampling difficult. The beam bending dynamic modulus test can only simulate the mechanical response of the asphalt mixture under a unidirectional bending stress state. However, actual asphalt pavements are subject to multi-directional bending and tensile stresses under load. The stress state of the specimen in the beam bending test is still different from the actual stress state of the asphalt pavement, resulting in inaccurate dynamic modulus of the final test. In addition, the beam bending test specimens usually require cutting of the asphalt mixture slab, which is very difficult to form the specimens. Summary of the Invention

[0004] Based on the defects of the above-mentioned existing technologies, the present invention provides a dynamic modulus testing method and system for asphalt mixture based on axial bending and tensile loading, which solves the problems that the existing dynamic modulus testing method for asphalt mixture cannot simulate the on-site stress state and the difficulty in sample molding, and can more accurately and conveniently measure the dynamic modulus of asphalt mixture.

[0005] The present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for testing the dynamic modulus of asphalt mixture based on axial bending-tension loading, comprising the following steps:

[0007] Obtain cylindrical asphalt mixture specimens; whereby they are obtained on site by core sampling or indoors by a rotary compactor or Marshall compactor;

[0008] Fix the side wall of the asphalt mixture specimen and apply axial bending-tension cyclic load to it, record the change curve of the load and the deflection at the center of the bottom surface of the asphalt mixture specimen with the loading time, and obtain the load value and deflection value of the asphalt mixture specimen according to the change curve;

[0009] Substitute the load value and deflection value into the dynamic modulus calculation formula of the asphalt mixture to obtain the dynamic modulus value of the asphalt mixture specimen; wherein, the dynamic modulus calculation formula of the asphalt mixture is specifically as follows:

[0010] ;

[0011] Where, E is the dynamic modulus of the specimen, is Poisson's ratio, P is the load value, is the specimen deflection value, h is the thickness of the specimen, a is the radius of the specimen, c is the radius of the load head.

[0012] Preferably, the diameter of the asphalt mixture specimen is in the range of 100 mm to 150 mm, and the thickness is in the range of 20 mm to 50 mm.

[0013] Preferably, the type of axial bending-tension cyclic load applied to the asphalt mixture specimen is a circular uniformly distributed load, the diameter of which ranges from 10 mm to 40 mm.

[0014] Preferably, the calculation formula for the dynamic modulus of asphalt mixture is obtained by:

[0015] The first calculation formula is derived based on the plate and shell theory. The plate and shell theoretical deflection in the first calculation formula is It is only applicable to asphalt mixture specimens with a thickness of less than 10 mm. The first calculation formula is as follows:

[0016] ;

[0017] Where, is the theoretical deflection of the plate and shell;

[0018] Calculation of the deflection of the bottom center of asphalt mixture specimens with a thickness range of 20mm-50mm based on the finite element model , and calculate the deflection and The ratio between n , as the theoretical deflection of the shell Correction factor n , the correction coefficient is specifically as follows:

[0019] ;

[0020] Through the correction factor n The theoretical deflection of plate and shell in the first calculation formula obtained from plate and shell theory After correction, the calculation formula of dynamic modulus of asphalt mixture is obtained:

[0021] .

[0022] In a second aspect, the present invention provides an asphalt mixture dynamic modulus testing system based on axial bending and tensile loading, comprising:

[0023] An acquisition module is used to acquire cylindrical asphalt mixture specimens; wherein, the specimens are acquired on site by core sampling and indoors by a rotary compactor or a Marshall compactor;

[0024] A load module is used to fix the side wall of the asphalt mixture specimen and apply axial bending and tension cyclic load to it, record the change curve of the load and the deflection at the center of the bottom surface of the asphalt mixture specimen with the loading time, and obtain the load value and deflection value of the asphalt mixture specimen according to the change curve;

[0025] The calculation module is used to substitute the load value and the deflection value into the asphalt mixture dynamic modulus calculation formula to obtain the dynamic modulus value of the asphalt mixture specimen; wherein the asphalt mixture dynamic modulus calculation formula is specifically as follows:

[0026] ;

[0027] Where, E is the dynamic modulus of the specimen, is Poisson's ratio, P is the load value, is the specimen deflection value, h is the thickness of the specimen, a is the radius of the specimen, c is the radius of the load head.

[0028] Compared with the prior art, the at least one technical solution adopted by the present invention can achieve the following beneficial effects:

[0029] The present invention first obtains a cylindrical asphalt mixture specimen. This specimen can be formed on-site through core drilling or directly formed to the required specifications indoors using a gyratory compactor or Marshall compactor, thus resolving the difficulty of obtaining specimens. The sidewalls of the asphalt mixture specimen are then secured and subjected to axial bending and tension cyclic loading. This more accurately simulates the lateral and longitudinal bending and tension stresses experienced by asphalt pavement under vehicle loads, more realistically reflecting the stress conditions of actual pavement surfaces.

[0030] The present invention solves the problems that the existing asphalt mixture dynamic modulus test method cannot simulate the on-site stress state and the sample molding is difficult, and can more accurately and conveniently measure the dynamic modulus of the asphalt mixture. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a flow chart of a method for testing the dynamic modulus of asphalt mixture based on axial bending-tension loading according to the present invention;

[0033] Figure 2 Calculating accurate deflection diagrams of asphalt mixture specimens for the finite element model of the present invention;

[0034] Figure 3 The precise deflection of the present invention Theoretical deflection of plates and shells ratio n ;

[0035] Figure 4 Schematic diagram of the loading of the axial bending-tension dynamic modulus test of the present invention;

[0036] Figure 5 is the load-time distribution curve of the specimen of the present invention;

[0037] Figure 6 is the displacement-time distribution curve of the specimen of the present invention;

[0038] Figure 7 The figure is a comparative bar graph of the axial bending dynamic modulus and the uniaxial compression dynamic modulus of the test piece of the present invention;

[0039] Figure 8 This is a relationship diagram between the axial bending dynamic modulus and the uniaxial compression dynamic modulus of the test piece of the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The present invention constructs a dynamic modulus test method that is easy to form a specimen and can simulate the actual bending and tensile stress of asphalt pavement on site. Specifically, it is a dynamic modulus test method for asphalt mixture based on axial bending and tensile loading. Figure 1 As shown, the specific steps include:

[0042] S1: Prepare asphalt mixture specimens.

[0043] The present invention's cylindrical specimens, typically 20mm to 50mm thick, facilitate on-site core sampling. Furthermore, they can be compacted to the required specifications indoors using a gyratory compactor or Marshall compactor. This solves the challenges of obtaining specimens on-site and the cumbersome laboratory preparation process.

[0044] S2: Apply axial bending-tension cyclic load to the specimen, and simultaneously record the change curves of load and displacement at the center of the specimen bottom surface with loading time. Calculate the load amplitude and deflection amplitude at the center of the bottom surface of the specimen based on the change curves.

[0045] The loading diagram of the axial bending dynamic modulus test is as follows: Figure 4 As shown, the gradation of the asphalt mixture specimen used is AC-13, AC is asphalt-concrete, and 13 represents the maximum particle size of the aggregate (13mm). a The steel sheet has a diameter of 75 mm and a thickness of 40 mm. A uniformly distributed load was applied using a cylindrical steel indenter with a radius c of 15 mm. Axial bending-tension cyclic loading was performed using a half-sine wave at a loading temperature of 21.1°C and loading frequencies of 0.1 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, and 25 Hz. Each specimen was subjected to at least three such axial bending-tension cyclic loading tests.

[0046] After the boundaries were fixed, an axial bending load was applied to the center of the specimen. This is consistent with the wheel loads experienced by asphalt pavements in real-world conditions: when a wheel passes over the pavement, it experiences lateral and longitudinal bending stresses (multi-directional bending stresses), and there is a confining pressure around the stress-exerting location (i.e., boundary constraints). Therefore, the load-exerting method used in this invention more accurately simulates the lateral and longitudinal bending stresses experienced by asphalt pavements under vehicle loads, more realistically reflecting the stress conditions experienced by actual pavement surfaces.

[0047] The LVDT displacement sensor is installed at the bottom of the specimen to record the vertical displacement at the center of the specimen bottom surface. The load and displacement of the asphalt mixture specimen change with time as shown in the following figure: Figure 5 and Figure 6 The load amplitude and displacement amplitude of the specimen calculated in the last five cycles are taken as the load value of the specimen and the deflection value at the bottom center.

[0048] S3: Based on the plate-shell theory and the Abaqus (Advanced Simulation for Engineering and Sciences) finite element model, a calculation formula for the dynamic modulus of asphalt mixture under axial bending-tension loading mode is established.

[0049] The steps for calculating the dynamic modulus of asphalt mixture under axial bending-tension loading mode are as follows:

[0050] First, based on the plate-shell theory, the calculation formula for the dynamic modulus of the asphalt mixture specimen under the axial bending-tension loading mode is derived as shown in formula (1), which is the first calculation formula. The plate-shell theoretical deflection in this calculation formula is It is only applicable to asphalt mixture specimens with a thickness of less than 10 mm and needs to be corrected.

[0051] (1);

[0052] Where, E represents the dynamic modulus of the specimen (Pa), is the center deflection of the bottom surface of the specimen in the plate and shell theory (m), P is the load value (N), represents Poisson's ratio, h represents the thickness of the specimen (m), a is the radius of the specimen (m), c is the radius of the load head (m).

[0053] Further based on Figure 2 The finite element model shown calculates the exact deflection of the bottom center of the asphalt mixture specimen with normal thickness (20mm-50mm) , and calculate the exact deflection Theoretical deflection of plates and shells The ratio between n , as the theoretical deflection of the shell Correction factor. n Is related to the specimen thickness h Related functions, such as Figure 3 shown.

[0054] (2);

[0055] Where, n Indicates exact deflection Theoretical deflection of plates and shells The ratio between h Indicates the thickness of the specimen (m).

[0056] Substituting formula (2) into formula (1), we can get the correction coefficient nThe dynamic modulus calculation formula obtained by the plate-shell theory is modified to obtain the final dynamic modulus calculation formula of the asphalt mixture specimen as shown in formula (3):

[0057] (3);

[0058] S4: Calculate the dynamic modulus of the specimen based on the load amplitude and the deflection amplitude at the center of the bottom surface.

[0059] Finally, the obtained load value and the deflection value at the center of the specimen bottom surface are substituted into the formula (3) P and

[0060] , the dynamic modulus value of the specimen can be obtained.

[0061] To further illustrate the advantages of the dynamic modulus test method based on the axial bending-tension loading mode proposed in the present invention, a traditional uniaxial compression dynamic modulus test was simultaneously performed in this embodiment, and the test results of the two test methods were compared. Figure 7 As shown in the figure, the axial flexural dynamic modulus increases with increasing loading frequency, reaching a maximum at 25 Hz, similar to the variation of the uniaxial compression dynamic modulus. Furthermore, the axial flexural dynamic modulus is consistently smaller than the uniaxial compression dynamic modulus at the same frequency, which is consistent with actual conditions. This is because the axial flexural dynamic modulus test simulates the mechanical response of an asphalt pavement under a three-dimensional stress state, while the uniaxial compression dynamic modulus test simulates the mechanical response of an asphalt pavement under a one-dimensional stress state. Aggregate interlocking primarily resists deformation when the mixture is under compression. Therefore, aggregate interlocking is stronger when the mixture is subjected to pure compression, while it is weaker when the mixture is subjected to tension. This results in the mixture exhibiting greater deformation resistance (modulus) under compressive loads. In uniaxial compression dynamic modulus tests, the mixture specimens are subjected to pure compression, while in axial flexural dynamic modulus tests, the specimens are subjected to both tension and compression. Therefore, the uniaxial compression dynamic modulus value of the mixture measured under the same conditions in the experiment is greater than the axial bending dynamic modulus value, which proves the rationality and reliability of the method proposed in the present invention.

[0062] Figure 8 The relationship between the axial bending dynamic modulus and the uniaxial compression dynamic modulus is plotted. It can be seen that the axial bending dynamic modulus and the uniaxial compression dynamic modulus have a high linear correlation (R 2 =0.9978), which further proves the rationality and reliability of the method proposed in the present invention.

[0063] In addition, the method proposed in this patent takes into account the actual stress state of the asphalt pavement on site, overcomes the problem of difficulty in on-site molding of specimens, simplifies the test process, and can evaluate the viscoelastic properties of asphalt mixtures more accurately and efficiently.

[0064] The dynamic modulus test method proposed in the present invention can simulate the actual load state of asphalt pavement on site, and the specimen preparation and on-site acquisition are more convenient; at the same time, it simplifies the dynamic modulus test process and can more accurately evaluate the dynamic modulus characteristics of asphalt pavement.

[0065] Based on the same concept, the present invention also provides an asphalt mixture dynamic modulus testing system based on axial bending and tensile loading, including an acquisition module, a load module and a calculation module.

[0066] The acquisition module is used to obtain cylindrical asphalt mixture specimens; among them, they are obtained on site through core sampling and indoors through a rotary compactor or a Marshall compactor.

[0067] The load module is used to fix the side wall of the asphalt mixture specimen and apply axial bending and tension cyclic load to it, record the change curve of the load and the deflection at the center of the bottom surface of the asphalt mixture specimen with loading time, and obtain the load value and deflection value of the asphalt mixture specimen based on the change curve.

[0068] The calculation module is used to substitute the load value and deflection value into the asphalt mixture dynamic modulus calculation formula to obtain the dynamic modulus value of the asphalt mixture specimen; the asphalt mixture dynamic modulus calculation formula is as follows:

[0069] ;

[0070] Where, E is the dynamic modulus of the specimen, is Poisson's ratio, P is the load value, is the specimen deflection value, h is the thickness of the specimen, a is the radius of the specimen, c is the radius of the load head.

[0071] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0072] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A method for testing the dynamic modulus of asphalt mixture based on axial bending and tension loading, characterized in that: The following steps are involved: Obtain cylindrical asphalt mixture specimens; whereby they are obtained on site by core sampling or indoors by a rotary compactor or Marshall compactor; Fix the side wall of the asphalt mixture specimen and apply axial bending-tension cyclic load to it, record the change curve of the load and the deflection at the center of the bottom surface of the asphalt mixture specimen with the loading time, and obtain the load value and deflection value of the asphalt mixture specimen according to the change curve; Substitute the load value and deflection value into the dynamic modulus calculation formula of the asphalt mixture to obtain the dynamic modulus value of the asphalt mixture specimen; wherein, the dynamic modulus calculation formula of the asphalt mixture is specifically as follows: ； Where, E is the dynamic modulus of the specimen, is Poisson's ratio, P is the load value, is the specimen deflection value, h is the thickness of the specimen, a is the radius of the specimen, c is the radius of the load head.

2. The asphalt mixture dynamic modulus test method based on axial bending and tension loading according to claim 1 is characterized in that: The diameter of the asphalt mixture specimen ranges from 100 mm to 150 mm, and the thickness ranges from 20 mm to 50 mm.

3. The asphalt mixture dynamic modulus test method based on axial bending and tension loading according to claim 1 is characterized in that: The type of axial bending-tension cyclic load applied to the asphalt mixture specimen is a circular uniformly distributed load, the diameter of which ranges from 10 mm to 40 mm.

4. The asphalt mixture dynamic modulus test method based on axial bending and tension loading according to claim 1, characterized in that: The calculation formula for the dynamic modulus of asphalt mixture specifically includes: The first calculation formula is derived based on the plate and shell theory. The plate and shell theoretical deflection in the first calculation formula is It is only applicable to asphalt mixture specimens with a thickness of less than 10 mm. The first calculation formula is as follows: ； Where, is the theoretical deflection of the plate and shell; Calculation of the deflection of the bottom center of asphalt mixture specimens with a thickness range of 20mm-50mm based on the finite element model , and calculate the deflection and The ratio between n , as the theoretical deflection of the shell Correction factor n , the correction coefficient is specifically as follows: ； Through the correction factor n The theoretical deflection of plate and shell in the first calculation formula obtained from plate and shell theory After correction, the calculation formula of dynamic modulus of asphalt mixture is obtained: 。 5. A dynamic modulus test system for asphalt mixture based on axial bending and tensile loading, characterized in that: include: An acquisition module is used to acquire cylindrical asphalt mixture specimens; wherein, the specimens are acquired on site by core sampling and indoors by a rotary compactor or a Marshall compactor; A load module is used to fix the side wall of the asphalt mixture specimen and apply axial bending and tension cyclic load to it, record the change curve of the load and the deflection at the center of the bottom surface of the asphalt mixture specimen with the loading time, and obtain the load value and deflection value of the asphalt mixture specimen according to the change curve; The calculation module is used to substitute the load value and the deflection value into the asphalt mixture dynamic modulus calculation formula to obtain the dynamic modulus value of the asphalt mixture specimen; wherein the asphalt mixture dynamic modulus calculation formula is specifically as follows: ； Where, E is the dynamic modulus of the specimen, is Poisson's ratio, P is the load value, is the specimen deflection value, h is the thickness of the specimen, a is the radius of the specimen, c is the radius of the load head.

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