Shearing type pavement anti-reflection crack test method and test loading device

Abstract

The invention discloses a shear type pavement anti-reflection crack test method. The method comprises the steps of test piece preparation, test piece storage, test piece preparation, test piece placement, test parameter selection, preloading, testing, test termination and the like. According to the method, a clamp loading mode for simulating a vehicle load to pass through a crack and a joint is adopted, similar shear strain formed in a finishing coat by a vehicle passing through the crack and the joint is formed in a test piece, and through repeated constant shear strain loading, the accumulated action times are used as the shear fatigue life when the maximum loading force is reduced to half of an initial value. According to the method, the service life of the overlay can be evaluated by integrating the shear strain level and the shear fatigue life of the material; and the reflection crack resistance of the material can be evaluated, and the shear fatigue life of different materials can be compared under the same shear strain level.

Description

Technical Field

[0001] The invention relates to the technical field of road detection, and in particular to a shear type road surface anti-reflection crack test method and a test loading device. Background Art

[0002] The main indicator for evaluating the service life of asphalt materials is the four-point bending fatigue test with the tensile strain and tensile stress at the bottom of the layer as the main control indicators. my country mainly uses semi-rigid pavement, and tensile stress and tensile strain are not the main mode of crack development. The reflection of transverse and longitudinal joints is the most common mode of pavement structure damage. Mechanical analysis shows that the main mode of occurrence of reflective cracks is the abnormal increase of local shear stress and shear strain. Some researchers also believe that traffic load is the main cause of reflective cracking, and shear stress is the most unfavorable factor for the generation and expansion of reflective cracks. Therefore, the four-point bending fatigue test is not suitable for evaluating the service life of semi-rigid pavement.

[0003] The model of traffic-type reflective crack test is usually equipped with preset joints or cuts to induce the initiation and expansion of reflective cracks. According to the loading method, it can be divided into rolling wheel load and static vertical loading. Rolling wheel load is a continuous load, which applies bending and shear stress to the overlay layer above according to its distance relationship with the joint crack; static vertical loading is based on the positional relationship between its loading and the joint crack: the vertical loading with the loading position directly opposite the crack simulates an open-type reflective crack; the vertical loading with the loading position deviating from the joint crack simulates a shear-type reflective crack.

[0004] At present, most test methods simulate opening type reflective cracks, but there are few simulations for shear type reflective cracks. The simulation of the working conditions of reflective cracks is not comprehensive and only applicable to specific conditions. The development of cracks depends on observation and lacks quantitative basis. The present invention provides a test method for shear type pavement reflective cracks, which is used to quantify the shear fatigue life of pavement structures and materials, and provide a basis for the optimization of materials and structures of the overlay. Summary of the invention

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

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

[0007] S1. Preparation of test specimens: prepare asphalt mixture test specimens according to the method of Section T 07032011 of JTG E20-2011, and cut them into small beam test specimens with a length of 380 mm ± 5 mm, a thickness of 50-100 mm ± 5 mm, and a width of 63 mm ± 5 mm;

[0008] S2. Storage of test pieces: The storage temperature of the test pieces shall not exceed 35°C. The test pieces shall be placed horizontally on a hard plate with a flat surface and a certain rigidity to prevent deformation of the test pieces. The test of the test pieces shall be completed within 30 days.

[0009] S3. Test piece preparation: Use epoxy resin or other curing materials to bond the test piece to the test piece template, solidify for 24 hours, and place it in an environmental chamber for constant temperature curing. The test can only be carried out after curing for more than 4 hours at the test temperature ±0.5℃;

[0010] S4. Placement of test piece: Install the test piece that has been cured at constant temperature in the placement slot of the loading device, fix it, contact the bottom of the loading frame with a displacement sensor, adjust the sensor position and return the sensor reading to zero;

[0011] S5. Test parameter selection: select the loading mode, set the parameters of the target shear strain, loading frequency and test termination criteria, and determine the loading position and loading displacement according to the target shear strain; 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] Where L represents the distance between the pressure head support and the end of the movable support, and D represents the displacement of the pressure head;

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

[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 for the test within 50 cycles. At the same time, the test parameters and test results should be monitored and recorded at the selected loading cycle interval to ensure correct system operation. The maximum loading force should be tested continuously during the test. When the loading force drops to only half of the initial value, the test is terminated and the number of loading times is recorded.

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

[0017] Compared with the existing indoor reflection crack simulation test, the above test method has a wider range of applications and a simpler test method; it can provide a basis for material research and structural optimization of old road surfaces: specifically, it can evaluate the service life of the old road surface structure, comprehensively evaluate the shear strain level and the shear fatigue life of the material, and evaluate the service life of the surface; it can recommend non-excavation reinforcement methods and methods for old road structures, and recommend and evaluate the effectiveness of different non-excavation reinforcement methods for situations where the shear strain is too large due to insufficient bearing capacity of the old road structure and the material cannot withstand it, until the reinforcement measures reduce the shear stress to a reasonable range; it can also evaluate the material's ability to resist reflection cracks, and compare the shear fatigue life of different materials at the same shear strain level.

[0018] The second purpose of the present invention is to provide a test loading device for a shear-type pavement anti-reflective crack test method, comprising a fixture assembly and a loading assembly; the fixture assembly comprises a fixture base plate, a fixed end is provided at one end of the fixture base plate, a movable end is provided at the other end, a movable plate is hinged on the upper end of the movable end, a fixed plate is provided on the upper end of the fixed end, and the movable plate is opposite to the fixed plate when rotated to a horizontal position; the loading assembly comprises a loading frame slidably arranged on the movable plate, an opening is provided on the loading frame for the test piece to pass horizontally, a pressure head for connecting a dynamic loading head is rotatably arranged above the opening corresponding to the test piece.

[0019] This technical solution, in conjunction with the corresponding test method, can simulate the application of dynamic loads to road test pieces, and obtain the distribution of internal shear stress and shear strain stress at the crack tip of the asphalt structure layer during the passage of the target type of vehicle, thereby obtaining the location 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, and the loading frame on the sliding movable plate can slide to the corresponding position. After sliding into place, 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 is the shear fatigue life of the material.

[0020] Preferably, hinged parts are provided on both sides of the upper end of the movable end, and both sides of the end of the movable plate are rotatably matched with the hinged parts.

[0021] Preferably, the upper ends of the movable plate and the fixed plate are provided with specimen templates, the specimen templates on the movable plate are provided with first strip grooves on both sides in the length direction, and the first adjusting screws are provided in the first strip grooves.

[0022] Preferably, two sides of the opening bottom of the loading frame are provided with sliding grooves that slidably cooperate with two sides of the movable plate.

[0023] Preferably, a rotating shaft is provided on the inner side of the opening and passes horizontally through the two ends of the pressing head, so that the pressing head can rotate around the rotating shaft.

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

[0025] Preferably, it further comprises a base located below the fixture bottom plate, the fixture bottom plate is provided with a plurality of second strip grooves arranged along the length direction of the fixture bottom plate, and second adjusting screws are provided in the second strip grooves.

[0026] Preferably, the upper end of the base is provided with a mounting groove arranged along the length direction of the fixture bottom plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. 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 according to the actual scale.

[0028] Figure 1 The present invention is a flowchart of a shear-type pavement anti-reflective crack test method provided in an embodiment of the present invention.

[0029] Figure 2 It is a stereoscopic diagram of a test loading device for the shear type pavement anti-reflective crack test method provided in an embodiment of the present invention.

[0030] Figure numerals: fixture base plate 100, fixed end 110, movable end 120, hinged portion 121, second strip groove 130, movable plate 200, fixed plate 300, loading frame 400, opening 410, slide groove 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 piece 1100. DETAILED DESCRIPTION

[0031] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0032] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the invention belongs.

[0033] Embodiment 1

[0034] like Figure 1 As shown, this embodiment provides a shear type pavement anti-reflective crack test method, comprising the following steps:

[0035] Step 1. Preparation of test pieces: Prepare asphalt mixture test pieces according to the method of Section T 07032011 of JTG E20-2011 or cut into small beam test pieces with a length of 380 mm ± 5 mm, a thickness of 50-100 mm ± 5 mm, and a width of 63 mm ± 5 mm; in this step, the test pieces need to be prepared strictly in accordance with the specifications, and the size of the test pieces can be adjusted as needed within the accommodating space of the loading device; the test pieces can be made by multi-layer rolling of more than two materials.

[0036] Step 2. Storage of test pieces: The storage temperature of the test pieces shall not exceed 35°C. The test pieces shall be placed horizontally on a hard plate with a flat surface and a certain rigidity to prevent deformation of the test pieces. The test of the test pieces shall be completed 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 at the test temperature ±0.5°C for more than 4 hours; the test temperature is usually 10°C-30°C, and 25°C is generally preferred. In actual applications, the test temperature can also be adjusted as required, and the temperature in the environmental chamber is required to match the test temperature by ±0.5°C.

[0038] Step 4. Placement of test piece: Install the test piece that has been cured at constant temperature in 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 return the sensor reading to zero.

[0039] Step 5. Test parameter selection: Select the loading mode, set the target shear strain, loading frequency, test termination criteria and other parameters, and determine the loading position and loading displacement according to the target shear strain.

[0040] In this step, to set the target shear strain, the shear stress of the actual pavement crack overlay layer should be calculated first, the maximum shear stress should be obtained, and the test target shear strain should be determined according to the magnification factor; then the crack width of the test piece should be set according to the representative crack width. This application calculates the relationship between the shear microstrain of the test piece and the displacement load application position and displacement load size when the crack is 6mm; where L represents the distance between the pressure head bracket and the end of the movable bracket, and D represents the pressure head displacement size, both in mm.

[0041]

[0042]

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

[0044] The model uses a cubic polynomial, which includes the cubic terms of displacement position and displacement load and their interaction terms. The decision was made based on the cross-validation results by comparing the prediction effects of models of different orders. The model parameters were estimated using the least squares method, which finds the optimal solution by minimizing the sum of squared errors between the predicted values ​​and the actual values. In order to verify the effectiveness of the model, this application divides the dataset into a training set and a test set; the model is trained on the training set and evaluated on the test set to verify its performance on unknown data. The main evaluation indicators of model performance include the mean square error (MSE) and the coefficient of determination (R 2 ), these two indicators can fully reflect the prediction accuracy and interpretability of the model. All data are standardized before entering 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: preload for 50 cycles under the target test strain, calculate the loading force value of the test piece at the 50th loading cycle as the initial loading force value, and use it as the reference loading force value for the fatigue failure criterion of the test piece;

[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, and monitor and record the test parameters and test results according to the selected loading cycle interval to ensure the correct operation of the system. The maximum loading force is tested continuously during the test. When the loading force drops to only half of the initial value, the test is terminated and the number of loading times is recorded.

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

[0049] Specifically, it can evaluate the service life of the old pavement overlay structure, comprehensively consider the shear strain level and the shear fatigue life of the material, and evaluate the service life of the overlay; it can recommend trenchless reinforcement methods and methods for the old pavement structure, and recommend and evaluate the effectiveness of different trenchless reinforcement methods when the shear strain is too large due to insufficient bearing capacity of the old pavement structure and the material cannot withstand it, until the reinforcement measures reduce the shear stress to a reasonable range; it can also evaluate the material's ability to resist reflective cracks, and compare the shear fatigue life of different materials at the same shear strain level.

[0050] Embodiment 2

[0051] like Figure 2 As shown, the second specific embodiment of the present invention provides a test loading device for a shear-type pavement anti-reflective crack test method, which specifically includes a fixture assembly and a loading assembly; the fixture assembly includes a fixture base plate 100, the fixture base plate 100 is provided with a fixed end 110 at one end and a movable end 120 at the other end, the movable end 120 is hinged with a movable plate 200 at the upper end, and 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 rotated to a horizontal position; the loading assembly includes a loading frame 400 slidably arranged on the movable plate 200, the loading frame 400 is provided with an opening 410 for the test piece 1100 to pass horizontally, and the opening 410 corresponds to the test piece 1100 and is provided with a rotatable pressure head 500 for connecting a dynamic loading head above the opening 410.

[0052] like Figure 2 As shown, through the above settings, the device is used to install the road test piece 1100, and cooperate with the corresponding test method to simulate the application of dynamic load to the road test piece 1100, and obtain the distribution of internal shear stress and shear strain stress at the crack tip of the asphalt structure layer during the passage of the target type of vehicle, so as to obtain the location and value of the maximum shear stress and shear strain. The device adopts a semi-cantilever beam and semi-simply supported design as a whole. Before the test, one end of the test piece 1100 is installed on the fixed plate 300; 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 with a curing adhesive such as epoxy resin during installation. The loading frame 400 on the sliding movable plate 200 can slide to the corresponding position. The loading frame adopts displacement control. After sliding into place, the pressure head 500 is connected to the dynamic load loading head. The dynamic load is applied to the test piece 1100 through the pressure head 500. It can reciprocate up and down according to a specific loading waveform, and the movement of the loading frame 400 can simulate the effect of the wheel passing through the crack position of the old road surface where the overlay layer has just been paved.

[0053] like Figure 2As shown, in this embodiment, a specimen template 600 is provided at the upper end of the movable plate 200 and the fixed plate 300, and the specimen template 600 located on the movable plate 200 is provided with first strip grooves 610 on both sides in the length direction, and a first adjustment screw 700 is provided in the first strip groove 610. In this way, before the test piece 1100 is placed, it is firmly attached to the specimen template 600 by curing adhesive such as epoxy resin, and the test piece template 600 is firmly installed on the fixed plate 300 and the movable plate 200 through the first strip groove 610. Also due to the existence of the first strip groove 610, the preset crack width W between the two specimen templates 600 can be adjusted within a certain range. Through such a setting, the device is used to install the asphalt mixture test piece 1100, and the distance between the loading frame 400 and the preset crack is adjusted through the sliding groove 420. At the same time, the relative position of the fixture bottom plate 100 and the base 900 is adjusted accordingly through the strip groove 130, so that the loading is centered. The loading device applies a dynamic load to the loading frame 400 (using a displacement control mode); the parameters that can be adjusted 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 working conditions on crack reflection due to different widths of old road cracks, the hollowing condition of the bottom of the old road, and the thickness of the cover.

[0054] like Figure 2 As shown, in order to rotatably mount the movable panel 200 on the upper end of the movable end 120, hinges 121 are provided on both sides of the upper end of the movable end 120, and both sides of the ends of the movable panel 200 rotatably cooperate with the hinges 121. The movable panel 200 can be rotatably mounted, thereby forming a semi-cantilever structure.

[0055] like Figure 2 As shown, since the loading frame 400 needs to slide along the movable plate 200, in this embodiment, the two sides of the bottom of the opening 410 of the loading frame 400 are provided with slide grooves 420 that slide with the two sides of the movable plate 200. The slide grooves 420 cooperate with the movable plate 200 so that the loading frame 400 can move to the corresponding position to implement the dynamic load simulation operation.

[0056] like Figure 2 As shown, when the device is in use, the pressure head 500 is connected to the dynamic loading head device, so that the pressure head 500 applies a dynamic load to the test piece. In this embodiment, a rotating shaft 800 is provided inside the opening 410, which passes horizontally through both ends of the pressure head 500, so that the pressure head 500 can rotate around the rotating shaft 800. At the same time, a connecting hole 510 is provided at the upper end of the pressure head 500. The connecting hole 510 can be used to connect the dynamic loading head device, and after the pressure head is rotated, 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] like Figure 2As shown, this embodiment further provides a base 900 for supporting the entire device, the base 900 is located below the fixture bottom plate 100, and the fixture bottom plate 100 is provided with a plurality of second strip grooves 130 arranged along the length of the fixture bottom plate 100, and a second adjustment screw 1000 is arranged in the second strip groove 130. In this way, the fixture bottom plate 100 can slide along the second strip groove 130 to adjust the relative position of the remaining bases 900. In addition, the upper end of the base 900 is provided with a mounting groove arranged along the length of the fixture bottom plate 100. The mounting groove is provided to improve the accuracy and stability of the sliding adjustment of the fixture bottom plate 100.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. 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 invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A shear type pavement anti-reflective crack test method, characterized in that; The steps include: S1. Preparation of test specimens: prepare asphalt mixture test specimens according to the method of Section T 0703 2011 of JTG E20-2011, and cut them into small beam test specimens with a length of 380 mm ± 5 mm, a thickness of 50-100 mm ± 5 mm, and a width of 63 mm ± 5 mm; S2. Storage of test pieces: The storage temperature of the test pieces shall not exceed 35°C. The test pieces shall be placed horizontally on a hard plate with a flat surface and a certain rigidity to prevent deformation of the test pieces. The test of the test pieces shall be completed within 30 days. S3. Test piece preparation: Use epoxy resin or other curing materials to bond the test piece to the test piece template, solidify for 24 hours, and place it in an environmental chamber for constant temperature curing. The test can only be carried out after curing for more than 4 hours at the test temperature ±0.5℃; S4. Placement of test piece: Install the test piece that has been cured at constant temperature in the placement slot of the loading device, fix it, contact the bottom of the loading frame with a displacement sensor, adjust the sensor position and return the sensor reading to zero; S5. Test parameter selection: select the loading mode, set the parameters of the target shear strain, loading frequency and test termination criteria, and determine the loading position and loading displacement according to the target shear strain; the calculation of the shear stress in the target shear strain is calculated according to the following formula; with=-29.87+138.30L+86639.31D-2.48L 2 +176.44DL+5837.85D 2 +0.01L 3 +4.34 Where L represents the distance between the pressure head support and the end of the movable support, and D represents the displacement of the pressure head; S6. Preloading: Preload for 50 cycles at the target test strain, calculate the loading force value of the test piece at the 50th loading cycle as the initial loading force value, and use it as the reference loading force value for the fatigue failure criterion of the test piece; 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 for the test within 50 cycles. At the same time, the test parameters and test results should be monitored and recorded at the selected loading cycle interval to ensure correct system operation. The maximum loading force should be tested continuously during the test. When the loading force drops to only half of the initial value, the test is terminated and the number of loading times is recorded.

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

3. A test loading device for a shear type pavement anti-reflective crack test method, characterized in that; including a fixture assembly and a loading assembly; The clamp assembly comprises a clamp base plate (100), one end of the clamp base plate (100) is provided with a fixed end (110), and the other end is provided with a movable end (120), the upper end of the movable end (120) is hinged with a movable plate (200), the upper end of the fixed end (110) is provided with a fixed plate (300), and the movable plate (200) is directly opposite to the fixed plate (300) when it is rotated to a horizontal position; The loading assembly comprises a loading frame (400) slidably arranged on a movable plate (200), the loading frame (400) being provided with an opening (410) for the test piece (1100) to pass horizontally, and a pressure head (500) rotatably arranged above the opening (410) corresponding to the test piece (1100) for connecting to 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 a specimen template (600), and the specimen template (600) on the movable plate (200) is provided with first strip grooves (610) on both sides in the length direction, and a first adjustment screw (700) is provided in the first strip groove (610).

5. The test loading device according to claim 3, characterized in that: Both sides of the bottom of the opening (410) of the loading frame (400) are provided with sliding grooves (420) that are slidably matched with both sides of the movable plate (200).

6. The test loading device according to claim 3, characterized in that: A rotating shaft (800) is provided inside the opening (410) and horizontally passes through both ends of the pressing head (500), so that the pressing head (500) can rotate around the rotating shaft (800).

7. The test loading device according to claim 3, characterized in that: The upper end of the pressure head (500) is provided with a connection hole (510).

8. The test loading device according to claim 3, characterized in that: Both sides of the upper end of the movable end (120) are provided with hinged parts (121), and both sides of the end of the movable plate (200) are rotatably matched with the hinged parts (121).

9. The test loading device according to claim 3, characterized in that: The device 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 second adjustment screws (1000) are provided in the second strip grooves (130).

10. The test loading device according to claim 9, characterized in that: The upper end of the base (900) is provided with a mounting groove arranged along the length direction of the fixture bottom plate (100).

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