Shear type road surface anti-reflection crack test method and test loading device

Abstract

The application discloses a shearing type pavement anti-reflection crack test method, which comprises the following steps: test piece preparation, test piece storage, test piece preparation, test piece placement, test parameter selection, preloading, test and test termination, etc. The method adopts a clamp loading mode simulating a vehicle load passing through a crack and a joint, forms similar shearing strain in a test piece as that formed in a cover layer by a vehicle passing through a crack and a joint, and accumulates the number of actions when the maximum loading force drops to half of the initial value as the shearing fatigue life by repeatedly loading a constant shearing strain. The method can comprehensively consider the shearing strain level and the shearing fatigue life of a material, and evaluate the service life of a cover. In addition, the method can evaluate the anti-reflection crack capacity of a material, and compare the shearing fatigue life of different materials under the same shearing strain level.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road detection, in particular to a shearing type pavement anti-reflection crack test method and a test loading device. BACKGROUND

[0002] The main index for evaluating the service life of asphalt material is the four-point bending fatigue test with the bottom layer tensile strain and tensile stress as the main control index. In China, semi-rigid pavement is mainly used, and the tensile stress and tensile strain are not the main mode of crack development, and the reflection of transverse and longitudinal cracks is the most common mode of pavement structure damage. Mechanical analysis shows that the main occurrence mode of reflection cracks is the abnormal increase of local shear stress and shear strain, and some researchers also believe that traffic load is the main cause of reflection cracking, and shear stress is the most unfavorable factor for the generation and expansion of reflection cracks, so the four-point bending fatigue test is not suitable for evaluating the service life of semi-rigid pavement.

[0003] The model of traffic type reflection crack test usually has a preset joint or cut, to induce the initiation and expansion of reflection cracks. According to the loading mode, it can be divided into rolling wheel load and static vertical load. The rolling wheel load is continuous loading, and according to the distance between the load and the joint crack, the bending and shear stress is applied to the upper pavement layer. According to the position relationship between the load and the joint crack, the vertical load directly opposite to the joint crack simulates the opening type reflection crack, and the shear type reflection crack deviates from the joint crack.

[0004] At present, more test methods are used to simulate the opening type reflection crack, and the simulation of shear type reflection crack is less. The simulation of reflection crack occurrence conditions is not comprehensive, and is only suitable for specific conditions. The crack development depends on observation, and lacks quantitative basis. The present application provides a shear type pavement reflection crack test method for quantifying the shear fatigue life of pavement structure and material, and providing basis for the material and structure optimization of the cover. SUMMARY

[0005] In view of the defects in the prior art, the first purpose of the present application is to provide a shear type pavement anti-reflection crack test method.

[0006] The specific technical solution is: a shear type pavement anti-reflection crack test method, comprising the following steps:

[0007] S1. Test piece preparation: prepare the asphalt mixture test piece according to the method in the T 07032011 section of the specification JTG E20-2011, and cut it into a small beam test piece with a length of 380mm±5mm, a thickness of 50-100mm±5mm, and a width of 63mm±5mm;

[0008] S2. Test piece storage: the test piece storage temperature is not more than 35℃, and the test piece is horizontally placed on a hard board with a flat surface and a certain rigidity to prevent deformation of the test piece, and the test piece should be tested within 30 days;

[0009] S3. Test piece preparation: the test piece is bonded with the test piece template by using epoxy resin and other curing materials, and is cured for 24 hours, and is placed in an environmental chamber for constant temperature incubation, and the test can be performed only after incubation for more than 4h at a test temperature of ±0.5℃;

[0010] S4. Test piece placement: the test piece after constant temperature incubation is installed in the placement slot of the loading device, and after being fixed, the displacement sensor contacts the bottom of the loading frame, and the sensor position is adjusted and the sensor reading is zeroed;

[0011] S5. Test parameter selection: select the loading mode, set the parameters of the target shear strain, the loading frequency and the test termination standard, and determine the loading position and the loading displacement according to the target shear strain; wherein the calculation of the shear stress in the target shear strain is calculated according to the following formula;

[0012] με = -29.87 + 138.30L + 86639.31D - 2.48L 2 + 176.44DL + 5837.85D 2 + 0.01L 3 + 4.34

[0013] Wherein L represents the distance between the pressure head support and the end of the movable support, and D represents the displacement size of the pressure head;

[0014] S6. Preloading: preloading for 50 cycles at the target test strain, calculating the loading force value of the test piece at the 50th loading cycle as the initial loading force value, and taking it as the reference loading force value for the test piece fatigue failure criterion;

[0015] S7. Test and test termination: after the initial loading force value is determined, the testing machine should automatically adjust and stabilize to the target tensile strain level required by the test within 50 cycles, and monitor and record the test parameters and test results at the selected loading cycle interval, and ensure correct system operation; the maximum loading force is continuously tested during the test, and the test is terminated when the loading force decreases to half of the initial value, and the loading number is recorded.

[0016] Preferably, in S3, the test temperature is 10-30℃.

[0017] Compared with the existing indoor reflective cracking simulation test, the test method has a wider application range and a simpler test method, can provide a basis for material research and structure optimization of the old road surface, specifically including evaluating the service life of the old road surface structure, the comprehensive shear strain level and the shear fatigue life of the material, evaluating the service life of the surface, recommending the non-excavation reinforcement method of the old road surface structure, and evaluating the effectiveness of different non-excavation reinforcement methods until the shear stress is reduced to a reasonable range, and evaluating the anti-reflection cracking ability of the material under the same shear strain level.

[0018] The second object of the application is to provide a test loading device for a shear type pavement anti-reflection cracking test method, comprising a clamp assembly and a loading assembly; the clamp assembly comprises a clamp bottom plate, one end of the clamp bottom plate is provided with a fixed end, one end is provided with a movable end, the upper end of the movable end is hinged with a movable plate, the upper end of the fixed end is provided with a fixed plate, and the movable plate is opposite to the fixed plate when the movable plate is rotated to a horizontal position; the loading assembly comprises a loading frame slidingly arranged on the movable plate, the loading frame is provided with an opening for the test piece to pass through horizontally, and a pressure head for connecting a dynamic loading head is rotatably arranged above the opening.

[0019] The technical solution cooperates with the corresponding test method to simulate the application of dynamic load on the road test piece, obtain the distribution of the internal shear stress and shear strain stress at the target structure during the passage of the target type vehicle, and obtain the position and value of the maximum shear stress and shear strain. During the test, the two ends of the road test piece are fixed on the movable plate and the fixed plate respectively, the loading frame slidingly arranged on the movable plate can be slid to the corresponding position, and after sliding to the position, the dynamic load is applied to the test piece through the pressure head. The loading position and loading displacement can be adjusted as needed to achieve the purpose of obtaining test data. The number of load actions after reaching the test threshold value is the shear fatigue life of the material.

[0020] Preferably, the upper end of the movable end is provided with a hinge part on both sides, and the movable plate is rotationally connected to the hinge part on both sides.

[0021] Preferably, the upper end of the movable plate and the fixed plate is provided with a test piece template, the test piece template on the movable plate is provided with a first slot on both sides in the length direction, and the first adjusting screw is arranged in the first slot.

[0022] Preferably, the opening of the loading frame is provided with a sliding groove on both sides of the bottom, which is slidingly connected to the movable plate on both sides.

[0023] Preferably, the inside of the opening is provided with a rotating shaft horizontally passing through both ends of the pressure head, so that the pressure head can rotate around the rotating shaft.

[0024] Preferably, the upper end of the press head is provided with a connecting hole.

[0025] Preferably, it also includes a base located below the fixture base plate, wherein the fixture base plate is provided with a plurality of second strip grooves arranged along the length of the fixture base plate, and a second adjusting screw is provided in the second strip groove.

[0026] Preferably, the upper end of the base is provided with a mounting groove arranged along the length of the clamp base plate. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0028] Figure 1 This is a flowchart of the shear-type pavement anti-reflection crack test method provided in the embodiments of the present invention.

[0029] Figure 2 This is a perspective view of the test loading device for the shear-type pavement anti-reflection crack test method provided in this embodiment of the invention.

[0030] Reference numerals: Fixture base plate 100, fixed end 110, movable end 120, hinge part 121, second strip groove 130, movable plate 200, fixed plate 300, loading frame 400, opening 410, slide 420, pressure head 500, connecting hole 510, specimen template 600, first strip groove 610, first adjusting screw 700, rotating shaft 800, base 900, second adjusting screw 1000, test specimen 1100. Detailed Implementation

[0031] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0032] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0033] Example 1

[0034] like Figure 1 As shown in the figure, this embodiment provides a test method for shear-type pavement anti-reflection cracking, including the following steps:

[0035] Step 1. Test piece preparation: The test piece is prepared according to the method in the section T 0703 2011 of the specification JTG E20-2011 or is prepared by asphalt mixture test piece, and is cut into a small beam test piece with a length of 380 mm ± 5 mm, a thickness of 50-100 mm ± 5 mm, and a width of 63 mm ± 5 mm; the test piece in this step needs to be strictly prepared according to the specification, and the size of the test piece is adjusted according to the need within the accommodation space of the loading device; the test piece can be made by rolling more than two materials in multiple layers.

[0036] Step 2. Test piece storage: The test piece storage temperature is not more than 35℃, and at the same time, the test piece is horizontally placed on a hard board with a flat surface and a certain rigidity to prevent the test piece from deforming, and the test piece should be tested within 30 days.

[0037] Step 3. Test piece preparation: The test piece is placed in an environmental chamber for curing, and is required to be cured for more than 4h at a test temperature ± 0.5℃; wherein, the test temperature is usually 10℃-30℃, and is generally preferably 25℃, and in actual application, the test temperature can also be adjusted, and the matching degree of the temperature in the environmental chamber and the test temperature is required to be ± 0.5℃.

[0038] Step 4. Test piece placement: The test piece after constant temperature curing is installed in the placement groove of the loading device, is fixed, contacts the bottom of the loading frame with a displacement sensor, adjusts the position of the sensor and makes the sensor reading zero.

[0039] Step 5. Test parameter selection: The loading mode is selected, the parameters such as target shear strain, loading frequency and test termination standard are set, and the loading position and loading displacement are determined according to the target shear strain.

[0040] In this step, the setting of the target shear strain should first calculate the shear stress of the actual pavement crack cover layer, obtain the maximum shear stress, and determine the test target shear strain according to the magnification; and then set the crack width of the test piece according to the representative crack width. In the case of a crack of 6mm, the relationship between the shear micro-strain of the test piece and the displacement load application position and the displacement load size is calculated; wherein L represents the distance between the pressure head support and the end of the movable support, and D represents the displacement size of the pressure head, and the units are mm.

[0041]

[0042]

[0043] In addition, in order to facilitate the determination of the size of the micro-strain under different loading conditions, or according to the target strain to determine the required loading condition, the present application also fits the model according to the finite element calculation results, and adopts a polynomial regression model to predict the micro-strain of the asphalt mixture in the shear type reflection crack test equipment; the polynomial regression model is mainly selected because it can adapt to the nonlinear characteristics of the data by introducing the high-order terms of the variables, thereby improving the accuracy of the prediction.

[0044] The model selects a cubic polynomial, including the cubic terms of the displacement position and the displacement load and their interaction terms. The decision is based on the cross-validation results, which are determined by comparing the prediction effects of models of different orders. The model parameters are estimated by the least squares method, which finds the optimal solution by minimizing the sum of squares of errors between the predicted values and the actual values. In order to verify the effectiveness of the model, the data set is divided into a training set and a test set; the model is trained on the training set and evaluated on the test set to test its performance on unknown data. The main evaluation indicators of the model performance include mean square error (MSE) and coefficient of determination (R 2 ), which can comprehensively reflect the prediction accuracy and interpretability of the model. All data are standardized before being input into the model to eliminate the influence of different dimensions and ensure the reliability of the prediction. The model expression is as follows:

[0045] με = -29.87 + 138.30L + 86639.31D - 2.48L 2 + 176.44DL + 5837.85D 2 + 0.01L 3 + 4.34

[0046] Step 6. Preloading: preloading for 50 cycles at the target test strain, calculating the test piece loading force value of the 50th loading cycle as the initial loading force value, which is used as the reference loading force value for the test piece fatigue failure criterion;

[0047] Step 7. Test and test termination: after the initial loading force value is determined, the testing machine should automatically adjust and stabilize to the target tensile strain level required for the test within 50 cycles, while monitoring and recording the test parameters and test results at the selected loading cycle interval to ensure correct system operation. The maximum loading force is continuously tested during the test, and when the loading force drops to half of the initial value, the test is terminated, and the number of loadings is recorded.

[0048] Compared with the existing indoor reflection crack simulation test, the above test method has a wider range of application and a simpler test method; it can provide a basis for material research and structure optimization of old road overlays:

[0049] Specifically, the service life of the old pavement overlay structure can be evaluated, the shear strain level and the shear fatigue life of the material are comprehensively evaluated, and the service life of the overlay is evaluated; the non-excavation reinforcement method and method of the old pavement structure can be recommended, for the case that the shear strain is too large due to insufficient bearing capacity of the old pavement structure and the material cannot withstand it, the effectiveness of different non-excavation reinforcement methods is recommended and evaluated until the shear stress is reduced to a reasonable range by the reinforcement measures; the anti-reflection crack resistance of the material can also be evaluated, and the shear fatigue life of different materials is compared under the same shear strain level.

[0050] Embodiment two

[0051] As shown in Figure 2 , the embodiment two of the present application provides a test loading device for a shear type pavement anti-reflection crack test method, which specifically comprises a clamp assembly and a loading assembly; the clamp assembly comprises a clamp bottom plate 100, one end of the clamp bottom plate 100 is provided with a fixed end 110, and the other end is provided with a movable end 120, the movable end 120 is hingedly connected with a movable plate 200 at the upper end, the fixed end 110 is provided with a fixed plate 300 at the upper end, and the movable plate 200 is opposite to the fixed plate 300 when the movable plate 200 is rotated to a horizontal position; the loading assembly comprises a loading frame 400 slidingly arranged on the movable plate 200, the loading frame 400 is provided with an opening 410 for the test piece 1100 to pass through horizontally, and the opening 410 is provided with a pressure head 500 for connecting a dynamic loading head and rotatingly arranged above the test piece 1100.

[0052] As shown in Figure 2 , through the above setting, the device is used for installing the road test piece 1100, and simulating the application of dynamic load on the road test piece 1100 by cooperating with the corresponding test method, so as to obtain the distribution of the internal shear stress and shear strain stress at the target structure in the process of passing through the target type vehicle, and obtain the position and value of the maximum shear stress and shear strain. The whole device adopts a semi-cantilever beam semi-simply supported design, one end of the test piece 1100 is installed on the fixed plate 300 before the test; the other end is placed on the movable plate 200, and the movable plate is adjusted to make the test piece 1100 horizontal. The road test piece 1100 used in the test adopts a long strip structure, and is fixed by using epoxy resin or other curing adhesive during installation. The loading frame 400 slidingly arranged on the movable plate 200 can be slid to the corresponding position, the loading frame adopts displacement control, and after sliding to the position, the pressure head 500 is connected with the dynamic load loading head, the dynamic load is applied to the test piece 1100 through the pressure head 500, which can reciprocate up and down according to a specific loading waveform, and can simulate the action when the wheel passes through the crack position of the old pavement with a newly paved overlay under the movement of the loading frame 400.

[0053] As shown in Figure 2As shown, the embodiment is provided with a test piece template 600 on the upper end of the movable plate 200 and the fixed plate 300, and the test piece template 600 on the movable plate 200 is provided with a first slot 610 on both sides in the length direction, and the first slot 610 is provided with a first adjusting screw 700. In this way, the test piece 1100 is firmly pasted on the test piece template 600 by a curing adhesive such as epoxy resin before being placed, and the test piece template 600 is firmly installed on the fixed plate 300 and the movable plate 200 through the first slot 610. Due to the existence of the first slot 610, the preset crack width W between the two test piece templates 600 can be adjusted within a certain range. Through such a setting, the device is used for installing the asphalt mixture test piece 1100, the distance between the loading frame 400 and the preset crack is adjusted through the sliding groove 420, and the relative position of the clamp bottom plate 100 and the base 900 is adjusted correspondingly through the slot 130, so that the loading is centered. The loading equipment applies a dynamic load (in displacement control mode) to the loading frame 400; the parameters that can be adjusted by the device during the test include the size of the test piece, the distance between the loading frame 400 and the preset crack, and the width W of the preset crack. The adjustment of the three parameters can simulate the influence of different old road crack widths, old road bottom void conditions and overlay thickness conditions on crack reflection.

[0054] As shown in the figure, Figure 2 In order to rotate and install the movable plate 200 on the upper end of the movable end 120, the embodiment is provided with a hinge part 121 on both sides of the upper end of the movable end 120, and the end parts of the movable plate 200 are rotationally matched with the hinge part 121. The movable plate 200 can be rotationally installed, thereby forming a semi-cantilever structure.

[0055] As shown in the figure, Figure 2 Since the loading frame 400 needs to slide along the movable plate 200, the embodiment is provided with a sliding groove 420 on both sides of the bottom of the opening 410 of the loading frame 400, which is slidingly matched with both sides of the movable plate 200. The sliding groove 420 is matched with the movable plate 200 to enable the loading frame 400 to move to the corresponding position to implement the dynamic load simulation operation.

[0056] As shown in the figure, Figure 2 When the device is used, the pressure head 500 is connected with the dynamic loading head equipment, so that the pressure head 500 applies a dynamic load to the test piece. The embodiment is provided with a rotating shaft 800 horizontally penetrating through both ends of the pressure head 500 inside the opening 410, so that the pressure head 500 can rotate around the rotating shaft 800. At the same time, the upper end of the pressure head 500 is provided with a connecting hole 510. The connecting hole 510 can be used to connect the dynamic loading head equipment, and after the pressure head rotates, it can be used to adjust the internal space of the loading frame 400, so as to place test pieces 1100 of different specifications.

[0057] As shown in the figure, Figure 2As shown, the embodiment also provides a base 900 for supporting the whole device, the base 900 is located below the clamp bottom plate 100, the clamp bottom plate 100 is provided with a plurality of second strip-shaped grooves 130 arranged along the length direction of the clamp bottom plate 100, and the second strip-shaped grooves 130 are provided with second adjusting screws 1000. In this way, the clamp bottom plate 100 can slide along the second strip-shaped grooves 130 for adjusting the relative position of the remaining base 900, in addition, the upper end of the base 900 is provided with mounting grooves arranged along the length direction of the clamp bottom plate 100. The mounting grooves are provided for improving the accuracy and stability of the sliding adjustment of the clamp bottom plate 100.

[0058] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application.

Claims

1. A test method for shear-type pavement anti-reflective cracking, characterized in that; Includes the following steps: S1. Specimen preparation: Asphalt mixture specimens were prepared according to the method in section T 0703 2011 of specification JTG E20-2011, and cut into small beam specimens with a length of 380mm±5mm, a thickness of 50-100mm±5mm, and a width of 63mm±5mm. S2. Test specimen storage: The test specimen storage temperature shall not exceed 35℃. At the same time, the test specimen shall be placed horizontally on a flat and rigid plate to prevent deformation. The test specimen shall be tested within 30 days. S3. Test specimen preparation: Use epoxy resin curing material to bond the test specimen to the test specimen template, cure for 24 hours, and place it in an environmental chamber for constant temperature curing. It is required to cure for more than 4 hours at the test temperature ±0.5℃ before testing can be carried out. S4. Test specimen placement: Install the test specimen that has been cured at constant temperature into the placement slot of the loading device. After fixing, use the displacement sensor to contact the bottom of the loading frame, adjust the sensor position and make the sensor reading zero. S5. Test Parameter Selection: Select the loading mode, set the parameters for target shear strain, loading frequency, and test termination criterion, and determine the loading position and loading displacement based on the target shear strain; the calculation of shear stress in the target shear strain is performed according to the following formula; Where L represents the distance between the pressure head support and the end of the movable support, and D represents the magnitude of the pressure head displacement; S6. Preloading: Preload the specimen for 50 cycles under the target test strain, calculate the loading force value of the specimen in the 50th loading cycle as the initial loading force value, and use it as the benchmark loading force value for fatigue failure criterion of the specimen. S7. Testing and Termination: Once the initial loading force value is determined, the testing machine should automatically adjust and stabilize to the target tensile strain level required for the test within 50 cycles. At the same time, the test parameters and test results should be monitored and recorded according to the selected loading cycle interval to ensure correct system operation. During the test, the maximum loading force should be tested continuously. When the loading force drops to only half of the initial value, the test should be terminated, and the number of loading cycles should be recorded.

2. The test method for shear-type pavement anti-reflection cracking according to claim 1, characterized in that... In S3, the test temperature is 10℃-30℃.

3. A test loading device for the shear-type pavement anti-reflective cracking test method as described in claim 1, characterized in that; Includes fixture components and loading components; The clamp assembly includes a clamp base plate (100), one end of which is provided with a fixed end (110) and the other end with a movable end (120). A movable plate (200) is hinged to the upper end of the movable end (120), and a fixed plate (300) is provided at the upper end of the fixed end (110). When the movable plate (200) is rotated to a horizontal position, it is directly opposite the fixed plate (300). The loading assembly includes a loading frame (400) slidably disposed on a movable plate (200). The loading frame (400) has an opening (410) through which the test piece (1100) passes horizontally. Above the opening (410) is a pressure head (500) rotatably disposed for connecting a dynamic loading head.

4. The test loading device according to claim 3, characterized in that; The upper ends of the movable plate (200) and the fixed plate (300) are provided with specimen templates (600). The specimen templates (600) located on the movable plate (200) are provided with first strip grooves (610) on both sides along their length. The first strip grooves (610) are provided with first adjusting screws (700).

5. The test loading device according to claim 3, characterized in that; The bottom sides of the opening (410) of the loading frame (400) are provided with grooves (420) that slide in cooperation with the sides of the movable plate (200).

6. The test loading device according to claim 3, characterized in that; The opening (410) has a rotating shaft (800) that passes horizontally through both ends of the pressure head (500), so that the pressure head (500) can rotate around the rotating shaft (800).

7. The test loading device according to claim 3, characterized in that; The pressure head (500) has a connection hole (510) at its upper end.

8. The test loading device according to claim 3, characterized in that; The movable end (120) has hinge parts (121) on both sides of its upper end, and the movable plate (200) is rotatably engaged with the hinge parts (121) on both sides of its end.

9. The test loading device according to claim 3, characterized in that; It also includes a base (900) located below the fixture base plate (100), the fixture base plate (100) is provided with a plurality of second strip grooves (130) arranged along the length of the fixture base plate (100), and a second adjusting screw (1000) is provided in the second strip groove (130).

10. The test loading device according to claim 9, characterized in that; The upper end of the base (900) is provided with an installation groove arranged along the length of the clamp base plate (100).

Images