A fixture for testing asphalt concrete

Abstract

This utility model discloses a fixing device for testing asphalt concrete, including a tensile mold arranged opposite each other for fixing the two ends of an asphalt concrete specimen. The tensile mold has a cavity for accommodating the ends of the specimen, the cross-sectional shape of which matches the specimen. An epoxy resin adhesive layer is filled between the cavity and the specimen ends to achieve a firm bond. The inner wall of the cavity is roughened, and the mechanical interlocking force with the epoxy resin is enhanced by machining threads, grooves, or dotted pits. The inner wall is also coated with a thick coupling agent to further improve the chemical bonding strength. A positioning protrusion is provided at the bottom of the cavity, which mates with the positioning hole at the end of the specimen to ensure axial alignment. A mounting plate with a central bolt is installed on the outside of the tensile mold by screws for connecting an external tensile testing device, achieving modular adaptation. This device effectively avoids stress concentration and end damage caused by traditional clamping, is suitable for specimens with various cross-sectional shapes, and offers high testing accuracy, convenient operation, and strong versatility.

Description

Technical Field

[0001] This utility model relates to the field of asphalt concrete material performance testing technology, and in particular to a fixing device for asphalt concrete tensile testing, which is suitable for testing the tensile properties of asphalt concrete specimens with different cross-sectional shapes in laboratories and engineering sites. Background Technology

[0002] In the research and development, production quality control, and engineering acceptance stages of asphalt concrete pavement materials, direct tensile testing is a core method for evaluating their crack resistance and determining whether the material meets the requirements for heavy-duty traffic pavement use. In existing technologies, tensile testing of asphalt concrete specimens mostly employs direct clamping with mechanical fixtures. This method has the following key problems: Stress concentration leads to premature specimen failure: Asphalt concrete is brittle and hard. When mechanical clamps are tightened by bolts, the clamping force is concentrated at the edge of the specimen end, which can easily cause the specimen to crush or crack prematurely in the non-calibrated test section (near the clamp). About 30% of the tests cannot obtain true tensile strength data due to this problem. Unreliable clamping of irregular cross-section specimens: For non-rectangular cross-section specimens such as circular and polygonal specimens, traditional clamps are difficult to fit the specimen surface and are prone to slippage, resulting in uneven tensile force transmission and further affecting the accuracy of test results.

[0003] Therefore, there is an urgent need for a fixing device that can achieve "firm fit, uniform force transmission, and avoid end damage" to solve the problems of distorted test data and poor applicability in existing technologies. Utility Model Content

[0004] The technical problem to be solved by this utility model is to overcome the problem that existing mechanical clamping methods are prone to damage to the end of the specimen and inaccurate test data, and to provide a simple, reliable clamping and accurate testing device for asphalt concrete testing.

[0005] To achieve the above objectives, this utility model provides a fixing device for asphalt concrete testing, comprising a pair of opposing tensile molds for fixing the two ends of an asphalt concrete specimen, each tensile mold having a cavity for accommodating the end of the asphalt concrete specimen. An epoxy resin adhesive layer is filled between the cavity and the end of the asphalt concrete specimen to achieve a fixed bond between the tensile mold and the asphalt concrete specimen. The inner wall of the cavity of the tensile mold is provided with an uneven, rough surface to enhance the mechanical interlocking force with the epoxy resin adhesive layer. The tensile mold is provided with a mounting plate for connecting to an external tensile testing device.

[0006] Furthermore, the mounting plate is fixedly mounted on the outside of the tensile mold with screws, and a bolt is provided in the center of the mounting plate to connect to the external tensile testing device. The modular design, using a split configuration and screw connection, achieves modularity between the mounting plate and the tensile mold. This facilitates the replacement of different types of mounting plates according to different testing equipment interfaces or the rapid installation of other tensile molds, enhancing the versatility and adaptability of the device. Simultaneously, the split structure reduces the overall processing difficulty and cost, and individual components are easy to replace if damaged, facilitating maintenance.

[0007] Furthermore, the cross-sectional shape of the cavity matches the cross-sectional shape of the asphalt concrete specimen, being circular, rectangular, or square. This ensures that the epoxy resin adhesive layer has a uniform thickness in the circumferential direction of the specimen, allowing the tensile force to be uniformly transferred from the mold through the adhesive layer to the entire cross-section of the specimen. This avoids local stress concentration caused by uneven force distribution, making it particularly suitable for the reliable fixation of specimens with irregular cross-sections.

[0008] Furthermore, the roughened surface is formed by machining threads, grooves, grids, or dotted pits on the inner wall. Utilizing the principle of mechanical interlocking, when liquid epoxy resin flows into these uneven structures and cures, an anchoring effect is formed, greatly increasing the contact area and mechanical interlocking force between the epoxy resin and the inner wall of the mold. This effectively prevents the bonding interface from debonding or slipping under high tensile loads, ensuring the reliability of the bonding strength and making the bonding interface strength higher than the strength of the specimen material itself.

[0009] Furthermore, the inner wall of the stretching die cavity is coated with a coupling agent with a thickness of 5-10 μm to further improve the bonding strength between the epoxy resin and the metal mold. The coupling agent can form molecular bridges between the inorganic metal mold surface and the organic epoxy resin, generating chemical bonds. On the basis of the original mechanical interlocking force, it further significantly improves the chemical bonding force between the epoxy resin and the metal mold, doubly ensuring the interfacial bonding strength and making force transmission more reliable.

[0010] Furthermore, the bottom of the cavity of the stretching die is provided with a positioning protrusion, which matches the positioning hole at the end of the asphalt concrete specimen. This protrusion is used to axially position the asphalt concrete specimen before the epoxy resin adhesive layer cures, preventing it from deviating, ensuring the axial alignment of the test, and improving the accuracy of the test data.

[0011] This utility model also provides an asphalt concrete tensile testing system, comprising: a fixing device as described above; and a tensile testing device connected to the fixing device via the mounting plate, for applying tensile force to the asphalt concrete specimen.

[0012] Compared with the prior art, the beneficial effects of this utility model are as follows: Reliable clamping and prevention of end damage: Utilizing epoxy resin for surface contact bonding replaces point or line contact mechanical clamping, effectively dispersing stress, preventing stress concentration and premature failure at the specimen ends, and ensuring that the specimen breaks within the gauge length.

[0013] High testing accuracy: Since the specimen breaks in the effective segment, the measured tensile strength data can truly reflect the performance of the material itself, greatly improving the accuracy and reliability of the test results.

[0014] Wide applicability: By changing the tensile mold with different cross-sectional shapes and sized cavities, it can be applied to asphalt concrete specimens of various shapes such as round, square, and rectangular, and has strong versatility.

[0015] Simple structure and easy operation: The device has a simple structure and low manufacturing and maintenance costs. The positioning protrusions and cavity design make specimen installation and alignment simple, facilitating its widespread use in laboratories and engineering sites. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is an overall schematic diagram of an embodiment of the present utility model; Figure 2 An exploded view diagram provided for an embodiment of this utility model; Figure 3 Overall sectional view provided for an embodiment of this utility model; Figure 4 , 5 This is a partially enlarged schematic diagram of an embodiment of the present utility model; Figure 6 A schematic diagram of a cubic asphalt concrete specimen provided for an embodiment of this utility model.

[0018] The following are the labeling elements in the figure: 1. Asphalt concrete specimen; 2. Epoxy resin adhesive layer; 3. Tensile die; 4. Screw; 5. Mounting plate; 6. Bolt; 7. Positioning protrusion.

[0019] The accompanying drawings have illustrated specific embodiments of the present invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the present invention in any way, but rather to illustrate the concept of the present invention to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present utility model.

[0021] To make the technical solution and advantages of this utility model clearer, the embodiments of this utility model will be described in further detail below with reference to the accompanying drawings.

[0022] Please see Figures 1-6 As shown, the fixing device for testing asphalt concrete in this embodiment includes a pair of opposing tensile molds 3. The pair of tensile molds 3 fix the two ends of the asphalt concrete specimen 1 respectively. In order to achieve stable accommodation of the ends of the specimen, each tensile mold 3 has a cavity. The cross-sectional shape of the cavity matches the cross-sectional shape of the asphalt concrete specimen 1 to be tested. Specifically, it can be set to a circle, rectangle or square according to the requirements of the specimen, so as to ensure that the bonding material filled later can form a uniform thickness in the circumference of the specimen, laying the foundation for the uniform transmission of tensile force.

[0023] When fixing the tensile mold 3 to the asphalt concrete specimen 1, an epoxy resin adhesive layer 2 is used as the adhesive medium. The epoxy resin adhesive layer 2 is filled between the cavity and the end of the asphalt concrete specimen 1. Through the adhesive effect of the epoxy resin after curing, the tensile mold 3 and the asphalt concrete specimen 1 are firmly bonded. Compared with the point or line contact of traditional mechanical clamping, this surface contact bonding method can effectively disperse stress and avoid premature crushing or cracking of the specimen end due to stress concentration.

[0024] like Figure 4 , 5 As shown, to further enhance the connection reliability between the tensile die 3 and the epoxy resin adhesive layer 2, the inner wall of the cavity of the tensile die 3 is designed as an uneven rough surface. This rough surface is formed by machining threads, grooves, grids, or dotted pits on the inner wall of the cavity. When liquid epoxy resin fills the cavity, it flows into the interior of these uneven structures. After the epoxy resin cures, it forms the epoxy resin adhesive layer 2, which forms a mechanical interlocking structure with the rough surface. This greatly improves the mechanical interlocking force between the two, prevents the bonding interface from debonding or slipping under high tensile loads, and ensures that the strength of the bonding interface is higher than the strength of the asphalt concrete specimen 1 itself, thereby ensuring that the specimen can break within the gauge length during the test.

[0025] Meanwhile, to further improve the bonding performance between the epoxy resin and the stretching die 3, a coupling agent is pre-coated on the inner wall of the cavity of the stretching die 3, with the coating thickness strictly controlled within the range of 5~10μm. The coupling agent can form molecular bridges between the inorganic surface of the metal die and the organic component of the epoxy resin, achieving chemical bonding. This superimposes chemical bonding force on top of mechanical interlocking force, providing double protection for interfacial bonding strength and making the transmission of tensile force more stable and reliable.

[0026] Considering that the asphalt concrete specimen 1 is prone to skewing before the epoxy resin adhesive layer 2 cures, affecting the axial alignment of the test, such as Figure 5 As shown, a positioning protrusion 6 is also provided at the bottom of the cavity of the stretching mold 3. The shape and size of the positioning protrusion 6 match the positioning hole preset at the end of the asphalt concrete specimen 1. When installing the specimen, the positioning hole at the end of the specimen is aligned with the positioning protrusion 6 and inserted, so that the specimen can be axially positioned during the epoxy resin curing process, effectively preventing the specimen from tilting and further improving the accuracy of the test data.

[0027] For the connection structure between the tensile mold 3 and the external tensile testing device, this embodiment uses a mounting plate 5 as a transition component. The mounting plate 5 is fixedly installed on the outside of the tensile mold 3 by screws 4, forming a split modular structure. A bolt 51 is integrally formed or fixedly installed in the center of the mounting plate 5. This bolt 51 is used to connect with the interface of the external tensile testing device, realizing a stable assembly between the fixing device and the tensile testing device. When it is necessary to adapt to external tensile testing devices with different interface types, it is not necessary to replace the entire tensile mold 3; only the screws 4 need to be removed and the corresponding type of mounting plate 5 replaced. At the same time, if a single component of the mounting plate 5 or the tensile mold 3 is damaged, the damaged component can be replaced individually. This not only enhances the versatility and adaptability of the device but also reduces the overall processing difficulty and maintenance cost.

[0028] Based on the above-mentioned fixing device, this embodiment also provides an asphalt concrete tensile testing system. In addition to the fixing device mentioned above, the testing system also includes a tensile testing device. The tensile testing device is connected to the fixing device through a mounting plate 5. Specifically, the mounting plate 5 is fastened to the corresponding interface of the tensile testing device through a bolt 51 in the center of the mounting plate 5. When conducting tensile tests on asphalt concrete, the assembly of the fixing device and the asphalt concrete specimen 1 is completed first: a coupling agent with a thickness of 5-10 μm is coated on the inner wall of the cavity of the tensile mold 3. The two ends of the asphalt concrete specimen 1 are inserted into the cavities of a pair of tensile molds 3 respectively. The axial alignment of the specimen is achieved by the positioning protrusion 6 at the bottom of the cavity engaging with the positioning hole at the end of the specimen. Then, epoxy resin is filled into the gap between the cavity and the end of the specimen. After the epoxy resin cures to form the epoxy resin bonding layer 2, the assembly of the specimen and the fixing device is completed. Then, the fixing device of the assembled specimen is connected and fixed to the tensile testing device through the bolt 51 in the center of the mounting plate 5. The tensile testing device is started, and the tensile testing device applies tensile force to the tensile mold 3 through the mounting plate 5. This tensile force is evenly transmitted to the asphalt concrete specimen 1 through the tensile mold 3 and the epoxy resin bonding layer 2 until the specimen breaks within the gauge length. The force value data recorded by the tensile testing device can be used to accurately calculate the tensile strength of the asphalt concrete specimen 1. The tensile strength truly reflects the crack resistance of asphalt concrete materials.

[0029] The fixing device and testing system in this embodiment replace traditional mechanical clamping with a surface-contact epoxy resin adhesive layer 2, effectively avoiding stress concentration and premature failure at the ends of the asphalt concrete specimen 1; the cavity design with multiple cross-sectional shapes is suitable for specimens of different shapes such as round, rectangular, and square, and has strong versatility; the setting of positioning protrusions 6 and coupling agent further ensures the accuracy of testing and the reliability of bonding; the design of the split mounting plate 5 improves the adaptability and maintenance convenience of the device. The overall structure is simple, easy to operate, and has low manufacturing cost, making it easy to promote and apply in laboratories and engineering sites.

[0030] It is important to note that the epoxy resin used in this embodiment is a high-strength adhesive with excellent bonding performance and tensile strength, typically exceeding 10-30 MPa. In contrast, the tensile strength of asphalt concrete is usually lower, generally ranging from 0.5-5 MPa, depending on the materials and mix proportions. Therefore, under normal circumstances, the bonding strength of the epoxy resin should be significantly higher than the tensile strength of the asphalt concrete to ensure that the specimen fractures before the bond slips or detaches at the adhesive joint.

[0031] To ensure the reusability of the stretching die 3, the die 3 with the residual specimen can be placed in an oven at a temperature slightly higher than the glass transition temperature of the epoxy resin, controlled between 120-180℃, avoiding exceeding the heat resistance limit of the die 3 material. For metal molds, oxidation or deformation caused by high temperatures must be avoided. The oven should be kept at this temperature for 10-15 minutes to gradually soften the epoxy resin adhesive layer 2. At this point, wearing heat-resistant gloves, remove the die and use a special tool to pry along the gap between the residual specimen and the cavity. Utilizing the reduced strength of the softened adhesive layer, the residual specimen can be separated from the stretching die 3.

[0032] Other embodiments of the present invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the foregoing claims.

[0033] It should be understood that this invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this invention is limited only by the appended claims.

Claims

1. A fixture for asphalt concrete testing, characterized by, include: A pair of opposing tensile molds (3) are used to fix the two ends of the asphalt concrete specimen (1) respectively; The stretching die (3) has a cavity for receiving the end of the asphalt concrete specimen (1); An epoxy resin bonding layer (2) is filled between the cavity and the end of the asphalt concrete specimen (1) to achieve a fixed bond between the tensile mold (3) and the asphalt concrete specimen (1). The inner wall of the cavity of the stretching die (3) is set as an uneven rough surface to enhance the mechanical interlocking force with the epoxy resin adhesive layer (2). The tensile mold (3) is provided with a mounting plate (5) for connecting to an external tensile testing device.

2. The fixture for testing asphalt concrete according to claim 1, wherein: The mounting plate (5) is fixedly mounted on the outside of the tensile mold (3) by screws (4), and a bolt (51) is provided in the center of the mounting plate (5) to connect to the external tensile testing device.

3. The fixture of claim 1, wherein: The cross-sectional shape of the cavity matches the cross-sectional shape of the asphalt concrete specimen (1), and is circular, rectangular or square.

4. The fixture of claim 1, wherein: The rough surface has threads, grooves, grids, or dotted pits machined on its inner wall.

5. The fixture of claim 1, wherein: The inner wall of the cavity of the stretching die (3) is also coated with a coupling agent with a coating thickness of 5~10μm.

6. The fixture of claim 1, wherein: The bottom of the cavity of the stretching die (3) is provided with a positioning protrusion (6), which matches the positioning hole at the end of the asphalt concrete specimen (1) and is used to axially position the asphalt concrete specimen (1) before the epoxy resin adhesive layer (2) is cured.

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