Indoor test method for testing rollability of asphalt mixture

Abstract

The invention discloses an indoor test method for testing the rollability of an asphalt mixture, and relates to the field of road engineering. The method solves the problem that the cracking resistance and the damage resistance of the material in the curling process cannot be quantitatively and accurately evaluated in the prior art. According to the scheme, a standard test piece is prepared through a wheel rolling method; a rigid supporting surface with a preset curvature is formed through a flexible plate, a supporting hole array and an angle-adjustable rotating and sliding clamp by utilizing a special mold and a curvature adjusting and supporting system; fixing one end of the test piece on a rotary clamp and keeping tangent to the flexible plate, and pushing a walking roll shaft at a constant speed through a driving system to bend the test piece and finally fit the curved surface; synchronously acquiring a thrust-displacement curve, multi-point strain data and crack initiation time, and evaluating the bending toughness and the cracking resistance; the test piece is kept deformed after being completely attached, attenuation of maintenance force along with time is monitored, and the stress relaxation characteristic is evaluated. The device is used for testing the crimpability of the asphalt mixture.

Description

Technical Field

[0001] This invention belongs to the field of road engineering and relates to an indoor test method for testing the curlability of asphalt mixtures. Background Technology

[0002] Hot-mix asphalt pavement, represented by asphalt mixtures, has been widely used in highway engineering worldwide due to its advantages such as high smoothness, driving comfort, and convenient maintenance. However, in special scenarios such as tunnel lining, old road overlay, bridge paving, and temporary access roads, traditional heavy rigid or semi-rigid pavement structures often exhibit insufficient adaptability. Against this backdrop, "carpet-like" asphalt pavement, as a new structural form that combines flexibility and rollability, is attracting increasing attention due to its potential for rapid transportation, on-site paving, and recycling.

[0003] The core function of this "carpet-like" pavement relies on its excellent rollability. This property directly relates to the material's ability to resist cracking and structural damage during the roll-up process, and is crucial to its successful application. However, current evaluation systems for the mechanical properties of asphalt mixtures, both domestically and internationally, mainly focus on traditional road performance such as rutting resistance, crack resistance, and fatigue resistance, lacking standardized test methods specifically for characterizing its rollability. Existing technologies, such as bending tests used to evaluate the low-temperature crack resistance of asphalt mixtures or beam bending tests used to evaluate flexibility, cannot effectively simulate the complex stress states experienced by the material during actual roll-up. These methods typically only obtain the material's ultimate flexural strength or flexural strain, failing to quantitatively characterize whether cracking or structural failure will occur at specific bending radii and roll-up speeds, thus making it difficult to directly and effectively evaluate its rollability.

[0004] Furthermore, some researchers rely on empirical judgment or simple manual bending for qualitative assessment. This method is highly subjective, lacks repeatability, and fails to provide accurate and comparable data, severely hindering the material design, quality control, and engineering application of rollable asphalt mixtures. Therefore, there is an urgent need in this field for a standard, easily operable, and quantitatively sound test method for evaluating the rollability of asphalt mixtures, capable of being implemented indoors, to fill the technological gap and provide crucial testing methods and evaluation criteria for the development and engineering promotion of "carpet-bomb" pavement materials. Summary of the Invention

[0005] The purpose of this invention is to address the problem that existing methods for evaluating the rollability of asphalt mixtures lack standardized testing methods specifically designed to simulate the stress state during roll formation, resulting in an inability to quantitatively and accurately evaluate the material's resistance to cracking and damage during the roll formation process. Therefore, this invention provides an indoor testing method for assessing the rollability of asphalt mixtures.

[0006] The technical solution of this invention is:

[0007] This invention provides an indoor test method for testing the flexural properties of asphalt mixtures, comprising the following steps:

[0008] Step 1: Fabrication of Flexible Pavement Structure Specimens: The flexible pavement structure specimens are fabricated using the wheel rolling method;

[0009] Step 2: Assemble the test mold:

[0010] The test mold includes:

[0011] The base and limiting system are used to form the basic frame of the mold and to precisely fix the initial position of the specimen.

[0012] The curvature adjustment and support system is used to form a rigid curved surface with adjustable curvature to support the bendable pavement structure specimen to complete bending deformation;

[0013] The specimen driving system is used to smoothly and uniformly push the flat asphalt mixture specimen onto a flexible plate with a preset curvature, simulating the curling process.

[0014] Step 3: Conduct a loading test:

[0015] Step 31: The loading test is completed by the drive unit. One end of the formed rollable pavement structure specimen is fixed, while the other end is free. The fixed end is kept tangent to the bending plate in the curvature adjustment and support system.

[0016] Step 32: The rigid connecting rod of the traveling roller shaft in the drive system of the flexible road surface structure specimen is pushed by the universal testing machine, so that the traveling wheel on the traveling roller shaft rolls at a uniform speed along the track towards the free end;

[0017] During this process, the rollable pavement structure specimen, pushed by the connecting rod, gradually bends from its initial straight state and eventually fits completely onto the surface of the flexible plate with a preset curvature.

[0018] Step 4: Evaluation of Curability:

[0019] Step 41: Control the loading rate using a universal testing machine. During the loading process, the universal testing machine automatically collects and records the force-displacement curve.

[0020] Step 42: Attach strain gauges at the fixed end of the flexible pavement structure specimen and at longitudinal distances of 5cm, 10cm, and 15cm from the fixed end to monitor the stress and strain conditions and crack development at different locations of the flexible pavement structure specimen during the curling process.

[0021] Step 43: Plot the bending tensile stress-specimen curves at different locations and count the time when cracks appear, as the main indicator for evaluating the curlability of the mixture;

[0022] Step 5: Evaluation of stress relaxation performance:

[0023] Once the rollable pavement structure specimen is pushed by the specimen driving system to a flexible plate that fully conforms to the preset curvature, the driving is immediately stopped and the current position is locked. At this time, the rollable pavement structure specimen is in a fixed bending strain state.

[0024] By using a force sensor installed in the specimen driving system, the curve of the force required to maintain this bending deformation over time is continuously recorded and monitored, serving as an indicator for evaluating the stress relaxation performance of asphalt mixtures.

[0025] Furthermore, the length-to-width ratio of the rollable pavement structure specimen prepared in step one is 1:1, 3:1, or 5:1.

[0026] Furthermore, the base and limiting system in step two includes a bottom plate and a raised strip. The raised strip is arranged along the center of the length direction of the bottom plate. The cross-sectional shape of the raised strip is trapezoidal, rectangular or semi-circular. The side end face of the bottom plate is provided with scale lines for reading and controlling the position of the right baffle.

[0027] Furthermore, the base and limiting system in step two also includes a right baffle. The bottom of the right baffle has a groove that matches the shape and size of the central protrusion of the bottom plate. Through the cooperation of the groove and the protrusion, the right baffle is locked onto the bottom plate and can move freely horizontally along the protrusion to adjust the effective length of the mold.

[0028] Among them, a continuous vertical groove is provided on the surface of the right baffle along the height direction of the right baffle to facilitate the up and down movement of the flexible sheet material.

[0029] Furthermore, the base and limiting system in step two also includes a front baffle, a rear baffle, and multiple hinges. The front baffle and rear baffle are connected to the bottom plate via hinges to achieve free opening and closing.

[0030] Furthermore, the curvature adjustment and support system includes an overlapping anchoring mechanism, which is a sliding clamp. The sliding clamp includes a clamp and a fastening bolt. The clamp is installed on the right baffle through the fastening bolt. When the fastening bolt is loosened, the clamp and the flexible plate are adjusted steplessly along the vertical slide groove. After tightening the fastening bolt, it is fixed at the target height.

[0031] Furthermore, the curvature adjustment and support system also includes a flexible plate with a matrix of circular holes for filling with a flowing support medium.

[0032] Furthermore, the curvature adjustment and support system also includes a rotating clamp. An adjustable and lockable rotating clamp is provided on the left side of the bottom plate to fix the left end of the flexible sheet and simultaneously provide an anchoring reference for the rollable pavement structure specimen.

[0033] Furthermore, the specimen driving system in step two includes a traveling roller shaft, which includes a rigid connecting rod and two traveling wheels. The two traveling wheels are connected by a rigid connecting rod, and the center of the rigid connecting rod is a force application port, which is connected to an external driving device.

[0034] Furthermore, it also includes the following steps:

[0035] Step Six: If it is necessary to study the effect of temperature on the rollability of asphalt mixture, a heating layer is laid on top of the flexible sheet to heat the rutted slab specimen and maintain a constant temperature T, so as to study the effect of temperature change on the rollability of asphalt mixture.

[0036] Step 7: If it is necessary to study the effect of curling speed on the curlability of asphalt mixture, the movement speed v of the traveling roller is controlled by controlling the external drive equipment to simulate different curling rate conditions, thereby analyzing the effect of loading rate on the bending behavior and cracking sensitivity of the material.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. This invention effectively solves the problem that traditional bending test methods cannot simulate the actual stress state during the curling process by designing a specialized test mold with an adjustable curvature support system and uniform speed drive function. Existing tests such as beam bending can only determine the ultimate tensile strength of materials and cannot reflect the actual curling behavior of materials under specific curvature radii and loading rates. Specifically, this invention uses a combination of flexible plates and support hole arrays to form a rigid surface with continuously adjustable curvature, combined with a uniform speed propulsion system composed of traveling rollers, to accurately reproduce the gradual bending process of asphalt mixture from a flat state to a predetermined curvature. This design enables the test to realistically simulate actual curling conditions, and by measuring the crack initiation time, strain distribution, and propagation law, a scientific quantitative evaluation of the material's resistance to curling cracking is achieved.

[0039] 2. This invention significantly improves the standardization of experiments and the comparability of data by establishing a standardized specimen preparation process, a modular mold assembly process, and a multi-parameter synchronous acquisition system. Addressing the problems of poor repeatability and strong subjectivity in current evaluation methods, this invention uses a wheel-rolling method compatible with rut slab preparation to form standard specimens, and ensures the consistency of test conditions through an assembled mold system. During testing, strain gauges are placed at key locations on the specimen, force sensors are integrated into the drive system, and a universal testing machine is used to synchronously acquire mechanical response data throughout the entire process, achieving objective recording of the material's bending behavior. This systematic technical solution enables the material's rollability to be quantitatively characterized through multiple indicators such as critical curvature, strain development rate, and stress relaxation characteristics, providing a reliable basis for material performance comparison and quality control.

[0040] 3. This invention achieves low cost, multifunctionality, and engineering practicality by combining general-purpose testing equipment with a simple mold and incorporating a stress relaxation test into the testing process. The core mold of this invention consists only of basic mechanical structures such as a base, flexible sheet, anchors, and rollers. The drive unit can be directly adapted to conventional universal testing machines or stepper motors in the laboratory, requiring no special equipment. In particular, after completing the bending deformation test, a stress relaxation test step is added to monitor the attenuation of support force while maintaining a fixed curvature. This not only expands the functional scope of the test, making it possible to simultaneously evaluate the material's curl crack resistance and curl storage stability, but also provides crucial data for predicting the performance retention capability before paving. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the bottom plate structure in this invention;

[0042] Figure 2 This is a schematic diagram of the front and rear baffles in this invention;

[0043] Figure 3 This is a schematic diagram of the right baffle in this invention;

[0044] Figure 4 This is a schematic diagram of the flexible sheet material in this invention;

[0045] Figure 5 This is a schematic diagram of the structure of the traveling roller shaft in this invention;

[0046] Figure 6 This is a schematic diagram of the sliding clamp in this invention;

[0047] Figure 7 This is a schematic diagram of the rotating clamp in this invention;

[0048] Figure 8 This is a schematic diagram of the combined mold in this invention.

[0049] The components include: 1. bottom plate; 2. raised strip; 3. right baffle; 4. groove; 5. vertical slide; 6. clamp; 7. fastening bolt; 8. front baffle; 9. rear baffle; 10. hinge; 11. flexible sheet material; 12. circular hole; 13. rotating clamp; 14. rigid connecting rod; and 15. traveling wheel. Detailed Implementation

[0050] Specific implementation method one: Combining Figures 1 to 8 This embodiment describes the following steps:

[0051] Step 1: Fabrication of Flexible Pavement Structure Specimens: The flexible pavement structure specimens are fabricated using the wheel rolling method;

[0052] Step 2: Assemble the test mold:

[0053] The test mold includes:

[0054] The base and limiting system are used to form the basic frame of the mold and to precisely fix the initial position of the specimen.

[0055] The curvature adjustment and support system is used to form a rigid curved surface with adjustable curvature to support the bendable pavement structure specimen to complete bending deformation;

[0056] The specimen driving system is used to smoothly and uniformly push the flat asphalt mixture specimen onto a flexible plate with a preset curvature, simulating the curling process.

[0057] Step 3: Conduct a loading test:

[0058] Step 31: The loading test is completed by the drive unit. One end of the formed rollable pavement structure specimen is fixed, while the other end is free. The fixed end is kept tangent to the bending plate 11 in the curvature adjustment and support system.

[0059] Step 32: The rigid connecting rod 14 of the traveling roller shaft in the drive system of the flexible road surface structure specimen is pushed by the universal testing machine, so that the traveling wheel 15 on the traveling roller shaft rolls at a uniform speed along the track towards the free end.

[0060] During this process, the rollable pavement structure specimen, pushed by the connecting rod, gradually bends from its initial straight state and eventually fits completely onto the upper surface of the flexible plate 11 with a preset curvature.

[0061] Step 4: Evaluation of Curability:

[0062] Step 41: Control the loading rate using a universal testing machine. During the loading process, the universal testing machine automatically collects and records the force-displacement curve.

[0063] Step 42: Attach strain gauges at the fixed end of the flexible pavement structure specimen and at longitudinal distances of 5cm, 10cm, and 15cm from the fixed end to monitor the stress and strain conditions and crack development at different locations of the flexible pavement structure specimen during the curling process.

[0064] Step 43: Plot the bending tensile stress-specimen curves at different locations and count the time when cracks appear, as the main indicator for evaluating the curlability of the mixture;

[0065] Step 5: Evaluation of stress relaxation performance:

[0066] Once the rollable pavement structure specimen is pushed by the specimen driving system to the flexible plate 11 that fully conforms to the preset curvature, the driving is immediately stopped and the current position is locked. At this time, the rollable pavement structure specimen is in a fixed bending strain state.

[0067] By using a force sensor installed in the specimen driving system, the curve of the force required to maintain this bending deformation over time is continuously recorded and monitored, serving as an indicator for evaluating the stress relaxation performance of asphalt mixtures.

[0068] This implementation method constructs a complete evaluation system for the rollability of asphalt mixtures through a systematic and standardized step design. Step one uses a wheel-rolling method to prepare specimens, ensuring that the specimens are consistent with the actual pavement structure and process, thus guaranteeing the representativeness of the test subjects. Step two involves assembling a specialized mold that includes a base and limiting system, a curvature adjustment and support system, and a specimen driving system. This provides a physical platform for precise curvature control and stable loading, laying the foundation for subsequent quantitative testing.

[0069] Step three involves a loading test, where a drive system pushes the specimen to bend at a uniform speed and conform to a surface with a preset curvature, realistically simulating the continuous deformation path and stress state during the curling process. Step four, the curlability performance evaluation stage, simultaneously collects force-displacement curves, multi-point strain data, and crack initiation time to achieve an objective quantitative characterization of the material's bending toughness, crack resistance, and damage development process. Step five, the stress relaxation performance evaluation, further monitors the decay of internal stress over time in the specimen under a fixed bending state, providing crucial evidence for evaluating the structural stability and deformation recovery characteristics of the material after curling.

[0070] Overall, this method, through the aforementioned interconnected steps, systematically covers the entire process from specimen preparation, working condition simulation, process monitoring to performance evaluation. It not only solves the problems of existing methods being unable to realistically simulate the curling process and having a single evaluation index, but also provides a quantifiable and repeatable standardized testing approach, offering reliable support for the research and development of curlable asphalt mixtures.

[0071] Specific Implementation Method Two: Combining Figure 8To illustrate this embodiment, the length-to-width ratio of the rollable pavement structure specimen prepared in step one of this embodiment is 1:1, 3:1, or 5:1.

[0072] In this embodiment, a test specimen with the same structure and process as the actual road surface is produced by the wheel rolling method. By controlling the length-to-diameter ratio (e.g., 1:1, 3:1, 5:1) and thickness parameters (which can be selected in the range of 0.5~7cm, with preferred thicknesses such as 1.5cm, 3cm, 4.5cm), carpet-like road surfaces of different structural types and thicknesses can be flexibly simulated, ensuring that the test has broad engineering representativeness and applicability.

[0073] Specific implementation method three: Combining Figure 1 This embodiment describes the base and limiting system in step two, which includes a bottom plate 1 and a raised strip 2. The raised strip 2 is arranged along the center of the length direction of the bottom plate 1. The cross-sectional shape of the raised strip 2 is trapezoidal, rectangular or semi-circular, and scale lines are provided on the side end face of the bottom plate 1 for reading and controlling the position of the right baffle.

[0074] This embodiment provides a stable and reliable longitudinal positioning reference for the specimen through the raised strip, effectively preventing the specimen from sliding laterally during bending. On the other hand, it enables precise reading and adjustment of the right baffle position by using scale lines, ensuring that the initial position and boundary conditions of the specimen are highly consistent in each test, thereby guaranteeing the controllability of the test process and the repeatability of the test results.

[0075] Specific implementation method four: Combination Figure 1 and Figure 3 In this embodiment, the base and limiting system in step two further includes a right baffle 3. The bottom of the right baffle 3 has a groove 4 that matches the shape and size of the central protrusion 2 of the bottom plate 1. Through the cooperation of the groove 4 and the protrusion 2, the right baffle 3 is snapped onto the bottom plate 1 and can move freely horizontally along the protrusion 2 to adjust the effective length of the mold. On the surface of the right baffle 3, a continuous vertical groove 5 is provided along the height direction of the right baffle 3 to allow the flexible sheet 11 to move up and down.

[0076] In step two of this embodiment, the right baffle achieves locking and horizontal movement through the cooperation of the bottom groove and the central protrusion. This design allows for flexible adjustment of the effective length of the mold, thereby adapting to the testing requirements of specimens of different sizes. Simultaneously, the vertical groove on the right baffle surface allows for positional adjustment of the flexible sheet material in the height direction, ensuring stable alignment and smooth operation of the support system during bending curvature adjustment, further improving the mold's adaptability and ease of operation.

[0077] Specific Implementation Method Five: Combining Figure 1 and Figure 2In this embodiment, the base and limiting system in step two further includes a front baffle 8, a rear baffle 9, and multiple hinges 10. The front baffle 8 and the rear baffle 9 are connected to the bottom plate 1 by the hinges 10 to achieve free opening and closing.

[0078] In this embodiment, the front and rear baffles are connected to the bottom plate via hinges, enabling the baffles to open and close freely. This structure allows for quick opening after the test, enabling thorough cleaning of the mold interior and any remaining support medium or specimen debris that may have been present during the bending process. This effectively simplifies the mold maintenance process, improves testing efficiency, and ensures the cleanliness and consistency of the mold during continuous use.

[0079] Specific Implementation Method Six: Combination Figure 4 and Figure 6 This embodiment describes a curvature adjustment and support system that includes an overlapping anchoring mechanism, which is a sliding clamp. The sliding clamp includes a clamp 6 and a fastening bolt 7. The clamp 6 is mounted on the right baffle 3 via the fastening bolt 7. When the fastening bolt 7 is loosened, the clamp 6, together with the flexible plate 11, can be infinitely adjusted along the vertical slide groove 5. After tightening the fastening bolt 7, it is fixed at the target height.

[0080] The sliding clamp in the curvature adjustment and support system of this embodiment achieves stepless height adjustment of the flexible sheet within the vertical slide groove of the right baffle through the cooperation of the clamp and the fastening bolt. This mechanism allows for flexible adjustment of the sheet's position when the bolt is loosened to match different curvature settings; tightening it provides stable locking, ensuring the flexible sheet maintains the set support height during testing, thus achieving a good balance between ease of operation and system stability.

[0081] Specific implementation method seven: Combination Figure 4 To illustrate this embodiment, the curvature adjustment and support system of this embodiment also includes a flexible plate 11, on which a plurality of circular holes 12 are provided in a matrix distribution for filling a flowing support medium.

[0082] The flexible sheet has several circular holes arranged in a matrix to be filled with a flowing support medium such as dry fine sand.

[0083] The flexible sheet in this embodiment is made of materials with excellent bending stiffness and fatigue performance, such as spring steel or high-performance engineering plastics. A matrix of circular holes on the sheet allows for the filling of a flowing support medium, such as dry fine sand, during testing. This design enables the flowing medium to adaptively fill the gaps at the bottom of the sheet during bending, forming a continuous and uniform support surface. This effectively simulates the contact response between the road surface and the base layer under real-world bending conditions, while reducing stress concentration caused by uneven local support, thus improving the simulation realism and result stability of the test.

[0084] Specific implementation method eight: Combination Figure 4 and Figure 7 This embodiment describes a curvature adjustment and support system that also includes a rotating clamp 13. An adjustable and lockable rotating clamp 13 is provided on the left side of the bottom plate 1 to fix the left end of the flexible plate 11 and simultaneously provide an anchoring reference for the rollable road surface structure specimen.

[0085] The angle of the clamp can be adaptively adjusted according to the target radius of curvature, thus ensuring that the clamped specimen is strictly tangent to the bending start end of the flexible sheet at any curvature.

[0086] In this embodiment, an adjustable and lockable rotating clamp is provided on the left side of the bottom plate to fix the left end of the flexible sheet and provide an anchoring reference for the specimen. The clamp can be locked at the angle using mechanical methods such as threaded locking, pin fixing, or friction braking. Its function is to flexibly adjust the clamping angle according to a preset radius of curvature, ensuring that the specimen and the starting end of the flexible sheet bending remain strictly tangent, thereby providing accurate initial boundary conditions under any curvature conditions, ensuring the geometric consistency of the curling process and the reliability of the test results.

[0087] Specific Implementation Method Nine: Combining Figure 5 This embodiment describes the specimen driving system in step two, which includes a traveling roller shaft. The traveling roller shaft includes a rigid connecting rod 14 and two traveling wheels 15. The two traveling wheels 15 are connected by the rigid connecting rod 14. The center of the rigid connecting rod 14 is a force application port, which is connected to an external driving device.

[0088] The rigid connecting rod is a solid round rod made of high-strength alloy steel with a diameter of not less than 20 mm; the traveling wheel adopts a standard deep groove ball bearing, with the outer ring serving as the rolling contact surface; the force application port is located at the geometric center of the rigid connecting rod and has a section of external thread machined for connection with the drive equipment.

[0089] In this embodiment, the traveling roller shaft in the specimen driving system uses a high-strength alloy steel solid round rod as a rigid connecting rod. The force-applying port machined at its geometric center has external threads, allowing direct engagement with the threaded joint or adapter rod of the external driving equipment for reliable force transmission. This design provides the traveling roller shaft with sufficient structural strength and rigidity. Two deep groove ball bearings, acting as traveling wheels, ensure smooth rolling and low friction, thereby uniformly and smoothly transmitting the thrust provided by the external driving equipment to the specimen surface, achieving a uniform and controllable bending loading process.

[0090] Specific Implementation Method Ten: Combining Figures 1 to 8 This embodiment describes an implementation method that also includes the following steps:

[0091] Step 6: If it is necessary to study the effect of temperature on the rollability of asphalt mixture, a heating layer is laid on the top of the flexible sheet 11 to heat the rutted slab specimen and maintain a constant temperature T, so as to study the effect of temperature change on the rollability of asphalt mixture.

[0092] Step 7: If it is necessary to study the effect of curling speed on the curlability of asphalt mixture, the movement speed v of the traveling roller is controlled by controlling the external drive equipment to simulate different curling rate conditions, thereby analyzing the effect of loading rate on the bending behavior and cracking sensitivity of the material.

[0093] In step six, by adding a heating layer to the upper part of the flexible sheet, the specimen can be heated during the test and maintained at a set constant temperature T, thereby studying the effect of temperature changes on the curlability of asphalt mixtures. Step seven then uses external drive equipment to precisely control the movement speed v of the traveling roller, simulating different curling rate conditions, and analyzing the effect of loading rate on the bending behavior and crack sensitivity of the material. These two extended steps together enhance the scalability and research depth of this experimental method, enabling it to evaluate the curling performance of materials under the coupled conditions of multiple factors such as temperature and speed, and more comprehensively revealing its applicability in practical engineering environments.

[0094] Combination Figures 1 to 8 The implementation scheme of the present invention is described as follows:

[0095] The present invention will now be described in detail.

[0096] (1) Specimen preparation: A rollable pavement structure specimen with dimensions of 300 mm (length) × 100 mm (width) × 30 mm (thickness) was formed by roller rolling. After the specimen cooled, it was cut into beam-type specimens with dimensions of 250 mm (length) × 50 mm (width) × 15 mm (thickness) for subsequent tests. The length-to-diameter ratio of the specimens was 5:1.

[0097] (2) Assembly and parameter setting of the test system: Connect the front and rear baffles to the bottom plate via a hinge structure and erect them, locking them with pins to form a concave groove with an open top. Secure the bottom groove of the right baffle to the strip protrusion of the bottom plate. Place the left end of the 1 mm thick flexible sheet in the rotating clamp on the left end of the bottom plate. Calculate the initial angle based on the target radius of curvature of 500 mm, and adjust and lock the clamp angle. Attach the right end of the flexible sheet to the sliding clamp of the right baffle. By moving the right baffle horizontally and adjusting the height of the sliding clamp vertically, the flexible sheet forms a smooth, uniform arc surface, with a radius of curvature verified to be 500 mm using a special ruler or calculation. Finally, tighten the fastening bolts of the sliding clamp to fix the entire curved surface shape. Fill the closed space formed by the bottom plate, front and rear baffles, and flexible sheet with dry standard sand through the holes in the flexible sheet until it is full, providing uniform support for the flexible sheet.

[0098] (3) Place the specimen and drive system: Place the left end of the specimen (10-50 mm) into the pre-locked angle rotating fixture and clamp it to ensure that the specimen is strictly tangent to the curved surface of the flexible plate. Place the traveling roller on the flexible plate (where the specimen is tangent to the flexible plate), and place the rigid connecting rod above the rut plate specimen. Attach strain gauges to the surface of the rut plate specimen in the bending state (at the fixed end, 5 cm from the fixed end, and 10 cm from the fixed end).

[0099] (4) Curling and stress relaxation test: Start the universal testing machine connected to the traveling roller shaft and set the pushing speed to 50 mm / min. The testing machine begins to push the traveling roller shaft at a uniform speed, causing the specimen to bend. During this process, the testing machine automatically records the thrust-displacement curve. The resistance strain gauge attached to the surface of the specimen synchronously collects strain data to monitor the initiation of cracks. When the specimen is completely attached to the surface of the flexible plate with a radius of curvature of 500 mm, the testing machine is immediately stopped and its position is maintained to start the stress relaxation test. During the 60-minute holding time, the attenuation of the force required to maintain the bending deformation is continuously recorded by the force sensor built into the testing machine.

[0100] (5) Performance evaluation and data analysis: Extract the thrust (cracking load) and displacement (cracking displacement) when the first visible microcrack appears on the specimen surface from the recorded thrust-displacement curves and strain data. Plot the bending tensile stress-strain curves at different locations and calculate their fracture energy. Process the force-time data recorded within 60 minutes of load holding and calculate the stress relaxation rate ((initial force - force at 60 minutes) / initial force × 100%).

[0101] (6) Comprehensive evaluation: Compare the test results of the same formulation mixture at different radii of curvature such as 0.5 m and 0.75 m, or compare the test results of different formulation mixtures at the same curvature. High cracking load, large cracking displacement, high fracture energy, and low stress relaxation rate are used as the evaluation criteria for excellent asphalt mixture curlability.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laboratory test method for testing the curlability of asphalt mixtures, characterized in that: Includes the following steps: Step 1: Fabrication of Flexible Pavement Structure Specimens: The flexible pavement structure specimens are fabricated using the wheel rolling method; Step 2: Assemble the test mold: The test mold includes: The base and limiting system are used to form the basic frame of the mold and to precisely fix the initial position of the specimen. The curvature adjustment and support system is used to form a rigid curved surface with adjustable curvature to support the bendable pavement structure specimen to complete bending deformation; The specimen driving system is used to smoothly and uniformly push the flat asphalt mixture specimen onto a flexible plate with a preset curvature, simulating the curling process. Step 3: Conduct a loading test: Step 31: The loading test is completed by the drive unit. One end of the formed rollable pavement structure specimen is fixed, and the other end is free. The fixed end is kept tangent to the bending plate (11) in the curvature adjustment and support system. Step 32: The rigid connecting rod (14) of the traveling roller shaft in the drive system of the flexible road surface structure specimen is pushed by the universal testing machine, so that the traveling wheel (15) on the traveling roller shaft rolls at a constant speed along the track towards the free end; During this process, the rollable pavement structure specimen gradually bends from its initial straight state under the push of the connecting rod, and finally completely adheres to the upper surface of the flexible plate (11) with a preset curvature. Step 4: Evaluation of Curability: Step 41: Control the loading rate using a universal testing machine. During the loading process, the universal testing machine automatically collects and records the force-displacement curve. Step 42: Attach strain gauges at the fixed end of the flexible pavement structure specimen and at longitudinal distances of 5cm, 10cm, and 15cm from the fixed end to monitor the stress and strain conditions and crack development at different locations of the flexible pavement structure specimen during the curling process. Step 43: Plot the bending tensile stress-specimen curves at different locations and count the time when cracks appear, as the main indicator for evaluating the curlability of the mixture; Step 5: Evaluation of stress relaxation performance: When the rollable pavement structure specimen is pushed by the specimen driving system to a flexible plate (11) that fully conforms to the preset curvature, the driving is immediately stopped and the current position is locked. At this time, the rollable pavement structure specimen is in a fixed bending strain state. By using a force sensor installed in the specimen driving system, the curve of the force required to maintain this bending deformation over time is continuously recorded and monitored, serving as an indicator for evaluating the stress relaxation performance of asphalt mixtures.

2. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 1, characterized in that: The length-to-width ratio of the rollable pavement structure specimen prepared in step one is 1:1, 3:1, or 5:

1.

3. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 2, characterized in that: The base and limiting system in step two includes a bottom plate (1) and a raised strip (2). A raised strip (2) is arranged along the center of the length direction of the bottom plate (1). The cross-sectional shape of the raised strip (2) is trapezoidal, rectangular or semi-circular, and scale lines are provided on the side end face of the bottom plate (1) for reading and controlling the position of the right baffle.

4. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 3, characterized in that: The base and limiting system in step two also includes a right baffle (3). The bottom of the right baffle (3) has a groove (4) that matches the shape and size of the central protrusion (2) of the bottom plate (1). Through the cooperation of the groove (4) and the protrusion (2), the right baffle (3) is fitted onto the bottom plate (1) and can move freely horizontally along the protrusion (2) to adjust the effective length of the mold. Among them, on the surface of the right baffle (3), a continuous vertical groove (5) is provided along the height direction of the right baffle (3) so that the flexible plate (11) can move up and down.

5. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 4, characterized in that: The base and limiting system in step two also includes a front baffle (8), a rear baffle (9) and multiple hinges (10). The front baffle (8) and the rear baffle (9) are connected to the bottom plate (1) by the hinges (10) to achieve free opening and closing.

6. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 5, characterized in that: The curvature adjustment and support system includes an overlap anchoring mechanism. The overlapping anchoring mechanism is a sliding clamp, which includes a clamp (6) and a fastening bolt (7). The clamp (6) is installed on the right baffle (3) by the fastening bolt (7). When the fastening bolt (7) is loosened, the clamp (6) together with the flexible plate (11) can be infinitely adjusted along the vertical slide groove (5). After tightening the fastening bolt (7), it is fixed at the target height.

7. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 6, characterized in that: The curvature adjustment and support system also includes a flexible plate (11), which has a number of circular holes (12) arranged in a matrix to fill the flow support medium.

8. A laboratory test method for testing the flexural properties of asphalt mixtures according to claim 1 or 7, characterized in that: The curvature adjustment and support system also includes a rotary clamp (13). The bottom plate (1) has an adjustable and lockable rotating clamp (13) on the left side for fixing the left end of the flexible plate (11) and simultaneously providing an anchoring reference for the rollable pavement structure specimen.

9. The indoor test method for testing the flexural properties of asphalt mixtures according to claim 8, characterized in that: The specimen driving system in step two includes a walking roller shaft, which includes a rigid connecting rod (14) and two walking wheels (15). The two walking wheels (15) are connected by the rigid connecting rod (14). The center of the rigid connecting rod (14) is the force application port, which is connected to an external driving device.

10. A laboratory test method for testing the flexural properties of asphalt mixtures according to claim 1 or 9, characterized in that: It also includes the following steps: Step 6: If it is necessary to study the effect of temperature on the rollability of asphalt mixture, a heating layer is laid on the top of the flexible board (11) to heat the rutted board specimen and keep it at a constant temperature T, so as to study the effect of temperature change on the rollability of asphalt mixture. Step 7: If it is necessary to study the effect of curling speed on the curlability of asphalt mixture, the movement speed v of the traveling roller is controlled by controlling the external drive equipment to simulate different curling rate conditions, thereby analyzing the effect of loading rate on the bending behavior and cracking sensitivity of the material.

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