An asphalt concrete flexural creep test device

Abstract

The present invention discloses an asphalt concrete flexural creep test device, which includes a flexural creep testing machine, a displacement sensor, a magnetic base, and a data acquisition system. The flexural creep testing machine includes a main body frame and a loading assembly. The present invention can measure the flexural stress, flexural deflection, flexural strain, creep compliance, creep stiffness, and strain rate of asphalt concrete, and analyze the adaptability of the asphalt concrete impervious panel in actual engineering to the settlement of the foundation or dam under the action of water load.

Description

Technical Field

[0001] The present invention relates to a concrete test device, in particular to a bending creep test device for asphalt concrete materials. Background Art

[0002] Asphalt concrete is a typical viscoelastic material at normal temperature. Currently, the impervious panels of the upper reservoir, lower reservoir or conventional reservoir of pumped-storage power stations and earth-rock dams often adopt asphalt concrete materials. The loads they bear are mainly water loads. Generally, the maximum water level rise and fall speed is also 6 - 7 / h, and the corresponding water pressure loading rate is about 0.06 MPa / h, which is very slow. Therefore, it is necessary to study the deformation ability of asphalt concrete to analyze the adaptability of the asphalt concrete impervious panel in engineering practice to the settlement of the foundation or dam under the action of water load.

[0003] The bending creep test of asphalt concrete is the most suitable test for studying the adaptability of the asphalt concrete impervious panel in engineering practice to the settlement of the foundation or dam. At present, the research on the bending creep test device for asphalt concrete in China is still in the relatively early stage. The "Test Code for Hydraulic Asphalt Concrete" DL / T5362 - 2018 of the electric power industry standard in China stipulates that the asphalt concrete creep testing machine adopts a servo-type press or a universal material testing machine, with some requirements for a measurement and data acquisition system, an environmental temperature control box, beam-type supports, etc., and draws a schematic diagram of the test equipment for the beam-type supports; the "Test Code for Bitumen and Bituminous Mixtures for Highway Engineering" JTGE20 - 2011 of the Ministry of Transport stipulates that the creep testing machine preferably adopts an electro-hydraulic servo universal testing machine that can apply a constant load, and a lever-type creep testing machine loaded with weights can also be used, as well as some requirements for load sensors, beam-type supports, and environmental insulation boxes. However, there is no mature product for the specific style of the domestic formed bending creep testing machine. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a bending creep test device for asphalt concrete materials. By measuring the displacement of the lower center of the mid-span cross-section of the beam specimen, the mid-span deflection of the specimen at different time intervals is calculated, and then the mid-span stress, mid-span deflection, mid-span strain, creep compliance, creep stiffness, and strain rate of the specimen are calculated to analyze the adaptability of the asphalt concrete impervious panel in engineering practice to the settlement of the foundation or dam under the action of water load.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: An asphalt concrete flexural creep test device, comprising a flexural creep testing machine, a displacement sensor, a magnetic base, and a data acquisition system. The flexural creep testing machine includes a main body frame and a loading assembly. The main body frame consists of a horizontally arranged square top plate, a horizontally arranged square bottom plate, and 4 vertically arranged cylinders connecting the upper and lower four corners of the top plate and the bottom plate. A pair of oppositely arranged plate-shaped bearing supports for supporting asphalt concrete specimens are vertically fixed on the bottom plate. The upper end of the cross-section of the bearing support is semi-circular. The distance between the two bearing supports matches the length of the asphalt concrete specimen to be tested. A magnetic base is placed on the bottom plate between the two bearing supports. The displacement sensor is installed on the magnetic base and contacts the bottom surface of the asphalt concrete specimen. The center of the top plate is provided with an installation through hole for hanging the loading assembly. The loading assembly includes a guide rod. The upper part of the guide rod passes through the installation through hole in the center of the top plate and is locked by a nut, suspending the guide rod below the top plate. The bottom end of the guide rod is fixedly connected to a horizontally arranged pressure tray. The center of the bottom surface of the pressure tray is provided with a pressure head in contact with the upper surface of the asphalt concrete specimen. The pressure head is a plate-shaped structure, and the lower end of the cross-section of the pressure head is semi-circular. Weights of different weights are inserted into the guide rod and placed on the pressure tray to transfer the load to the pressure head and apply force to the upper surface of the asphalt concrete specimen.

[0006] The upper and lower ends of the cylinder are respectively provided with threads, and the upper and lower four corners of the top plate and the bottom plate are respectively provided with through holes. The top plate and the bottom plate are fixed on the cylinder by nuts.

[0007] The weights are of 8 different weights.

[0008] The guide rod and the pressure tray, the pressure tray and the pressure head, and the bearing support and the bottom plate are respectively connected by threads.

[0009] The beneficial effects of the present invention are as follows: It has a reasonable design, strong operability, and direct test results. It has a very positive significance for measuring the flexural stress, flexural deflection, flexural strain, creep compliance, creep stiffness, and strain rate of asphalt concrete, and analyzing the adaptability of the asphalt concrete impervious panel to the settlement of the foundation or the dam body under the action of water load. Description of the Drawings

[0010] Figure 1 is a schematic structural diagram of the asphalt concrete flexural creep test device of the present invention.

[0011] Figure 2 is a schematic diagram of the specimen under stress. Detailed Embodiments

[0012] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "top / bottom end", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0014] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "provided with", "sheathed / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0015] Such as Figure 1As shown in the figure, the asphalt concrete bending creep test device of the present invention includes a bending creep testing machine, a displacement sensor 12, a magnetic base 14, and a data acquisition system 13. The bending creep testing machine includes a main body frame and a loading assembly. The main body frame is composed of a horizontally arranged square top plate 1, a horizontally arranged square bottom plate 2, and 4 vertically arranged cylinders 3 connecting the upper and lower four corners of the top plate 1 and the bottom plate 2. On the bottom plate 2, a pair of relatively arranged plate-shaped bearing supports 11 for supporting the asphalt concrete specimen 10 are vertically fixed. The upper end of the cross-section of the bearing support 11 is semi-circular. The distance between the two bearing supports 11 matches the length of the asphalt concrete specimen to be measured. On the bottom plate 2 between the two bearing supports 11, a magnetic base 14 is placed. The displacement sensor 12 is installed on the magnetic base 14 and contacts the bottom surface of the asphalt concrete specimen 10. The center of the top plate 1 is provided with an installation through hole for hanging the loading assembly. The loading assembly includes a guide rod 6. The upper part of the guide rod 6 passes through the installation through hole in the center of the top plate 1 and is locked by a nut 5, hanging the guide rod 6 below the top plate 1. The bottom end of the guide rod 6 is fixedly connected to a horizontally arranged pressure tray 8. The center of the bottom surface of the pressure tray 8 is provided with a pressure head 9 that contacts the upper surface of the asphalt concrete specimen 10. The pressure head 9 is a plate-shaped structure, and the lower end of the cross-section of the pressure head 9 is semi-circular. Weights 7 of different weights are inserted into the guide rod 6 and placed on the pressure tray 8, transmitting the load to the pressure head 9 and applying force to the upper surface of the asphalt concrete specimen 10.

[0016] Preferably, the upper and lower ends of the cylinder 3 are respectively provided with threads, and the upper and lower four corners of the top plate 1 and the bottom plate 2 are respectively provided with through holes, and the top plate 1 and the bottom plate 2 are fixed on the cylinder 3 by nuts.

[0017] The weights 7 are of 8 different weights.

[0018] Preferably, the guide rod 6 and the pressure tray 8, the pressure tray 8 and the pressure head 9, and the bearing support 11 and the bottom plate 2 are respectively connected by threads.

[0019] Specifically, the main body frame is composed of 1 top plate, 1 bottom plate, 4 cylinders, 16 large nuts, 2 bearing supports, and 6 screws with a major thread diameter of 6 mm, a thread pitch of 1 mm, and a length of 45 mm. The longitudinal center line distance between the left and right 2 bearing supports is 200 mm; the distance from the longitudinal center line position of the left bearing support to the upper edge of the left side of the bottom plate is 150 mm, and the distance from the longitudinal center line position of the right bearing support to the upper edge of the right side of the bottom plate is 150 mm; the bottom end of the bearing support and the bottom plate are connected by an embedded screw.

[0020] The top plate is made of stainless steel, with a length of 500 mm, a width of 500 mm, and a thickness of 30 mm. A round hole with a diameter of 10 mm is provided in the center, and round holes with a diameter of 30 mm are provided at the four corners, 12 mm away from the edge.

[0021] The bottom plate is made of stainless steel, with a length of 500 mm, a width of 500 mm, and a thickness of 30 mm. There are round holes with a diameter of 30 mm and smooth inner walls at the four corners, 12 mm away from the edges. On both the left and right sides of the bottom plate, 100 mm away from the bottom plate edge, there is a row of 3 round holes with a diameter of 6 mm each. The center distance between the round hole centers in this row is 40 mm. The center of the center round hole in this row is 250 mm away from the upper and lower edges of the bottom plate. The inner wall of the round hole is provided with threads with a thread pitch of 0.5 mm.

[0022] The cylinder is made of stainless steel, with a diameter of 30 mm and a length of 700 mm. The surface of the middle part with a length of 500 mm is smooth; on both ends with a length of 100 mm, there are threads with a pitch of 1 mm each, and it can be tightly connected to the top plate and the bottom plate through large nuts.

[0023] The 16 large nuts in the main body frame are standard M30 hexagonal nuts.

[0024] The pressure-bearing support is made of stainless steel, with a main body height of 188 mm, a length of 120 mm, and a thickness of 16 mm. The top surface is a semi-circular arc with a radius of 8 mm and a smooth surface. Along the length center line direction at the bottom end of the pressure-bearing support, there are three round holes with a diameter of 6 mm. The inner surface of the hole has a thread pitch of 1 mm and a depth of 15. The bottom end of the pressure-bearing support and the bottom plate can be internally connected by inlaying 6 screws with a major thread diameter of 6 mm, a thread pitch of 1 mm, and a length of 45 mm.

[0025] The loading system includes 1 anti-falling metal nut, 1 guide rod, 1 pressure plate, 1 pressure head, an appropriate number of weights of 8 different weights, and 2 screws with a major thread diameter of 6 mm.

[0026] The anti-falling metal nut is a standard M8 hexagonal nut. Its function is to prevent the guide rod, pressure plate, pressure head, and weights from falling when the specimen is compressed and fractured, damaging the pressure-bearing support, displacement sensor, magnetic base, etc., and also preventing itself from deforming due to falling and collision.

[0027] The guide rod is made of stainless steel, with a diameter of 8 mm and a length of 500 m; the surface of the middle part with a length of 480 mm is smooth; on both ends with a length of 10 mm, there are threads with a pitch of 1 mm each. The upper end of the guide rod can pass through the top plate of the main body frame and be connected to the anti-falling metal nut, and the lower end can pass through the center hole of the pressure plate and be embedded in the center screw hole of the pressure head for mutual connection.

[0028] The pressure plate is made of stainless steel, with a diameter of 160 mm and a thickness of 8 mm. There is 1 round hole in the center, with a diameter of 8 mm and a smooth inner wall. Taking the positions 40 mm away from the center of the center round hole on both sides of the pressure plate as the centers, there is 1 round hole with a diameter of 6 mm each. The inner wall of the round hole is provided with threads with a thread pitch of 0.5 mm, and is used for a screw with a major thread diameter of 6 mm and a thread pitch of 0.5 mm to pass through the bottom of the pressure plate and be embedded in the pressure head for mutual connection.

[0029] The material of the pressing head is stainless steel. The main body of the pressing head is 20 mm high, 120 mm long and 16 mm thick. The lower end surface is a semi-circular arc with a radius of 8 mm, and the surface is smooth. There is a central round hole with a diameter of 8 mm and a depth of 16 mm at the center of the top end of the pressing head. The inner wall surface is provided with threads with a thread pitch of 1 mm for embedding and connecting with the guide rod passing through the pressing tray; along the length center line direction, there are 1 round hole with a diameter of 6 mm on each side, with a depth of 16 mm, centered at a position 40 mm away from the center of the central round hole. The inner surface of the round hole has a thread pitch of 0.5 mm for the screw rod with an outer diameter of 6 mm and a thread pitch of 0.5 mm to pass through the bottom of the pressing tray and embed into the pressing head for mutual connection.

[0030] The material of the weights is cast iron. The weights have different weights, divided into 8 types: 0.0375, 0.075, 0.15, 0.3, 0.6, 1.2, 2.4, 4.8 kg, and the quantity is appropriate. The shape of the weights is circular, with a round hole with a radius of 8 mm at the center, the inner wall is smooth, and there is an opening with a width of 16 mm on one side of the weights.

[0031] The specific implementation manner of the present invention is as follows:

[0032] (1) Connect each component of the main frame of the flexural creep testing machine, and adjust the horizontality of the bottom plate and the top plate.

[0033] (2) Symmetrically place a prismatic asphalt concrete specimen with dimensions of 250 ± 2 mm in length, 30 ± 2 mm in width, and 35 ± 2 mm in height on the bearing supports of the flexural creep testing machine. The up and down directions of the specimen should be consistent with the direction during specimen preparation and molding. The lengths of the extended parts remaining outside the two bearing supports of the asphalt concrete specimen are equal.

[0034] (3) Place a displacement sensor between the two bearing supports of the flexural creep testing machine below the asphalt concrete specimen. The displacement sensor is fixed on the bottom plate of the testing machine with a magnetic base. The measuring head of the displacement sensor is located at the exact center position of the lower edge of the mid-span cross-section of the specimen. The effective range of the displacement sensor should be greater than 1.2 times the maximum deflection of the specimen expected in the test. Record the initial indication of the displacement sensor as the initial reading U0 of the test.

[0035] (4) Place the weights with the calculated weight on the pressure tray, and then apply the loading system (including the anti-fall metal nut, guide rod, pressure tray, weights, and pressure head) with a weight equal to the predetermined load P to the upper edge of the cross-section at the mid-span of the asphalt concrete specimen through the pressure head at one time. When applying the pressure, the pressure head is longitudinally perpendicular to the length direction of the asphalt concrete specimen. At the same time, start recording the readings Ut of the displacement sensor. The initial recording interval is 15 s. After 10 minutes, it can be gradually increased to 30 s and 1 minute according to the change rate of the readings. After 30 minutes, the recording interval can be increased to 3 minutes. The total test time is about 4 hours for the specimen. The number of specimens in a group is generally 3.

[0036] (5) Let the load borne by the mid-span of the asphalt concrete specimen be P (N), the self-weight be q (N / mm), the net span length be L (mm), the length of the extended part of the support be L1 (mm), the mid-span deflection changing with time be ft (mm), the width of the specimen cross-section be b (mm), and the height be h (mm). The schematic diagram of the specimen under stress is shown in Figure 2 .

[0037] Use the following data and formulas to calculate the mid-span stress, mid-span deflection, mid-span strain, creep compliance, creep stiffness, and strain rate of the specimen.

[0038] Mid-span stress

[0039] Mid-span deflection f t = Ut - U0

[0040] Calculation of mid-span strain

[0041] Creep compliance J t = ε t / σ0

[0042] Creep stiffness S t = σ0 / ε t

[0043] Strain rate ε speed = (ε2 - ε1) / (t2 - t1)

[0044] In the above formulas: ε1 and ε2 are the strains corresponding to time t1 and t2 during the stable period, respectively.

[0045] The present invention is used in combination with a displacement sensor, a magnetic base, and a data acquisition system to jointly form a bending creep test device for conducting a bending creep test on a specimen prepared from asphalt concrete materials, and obtaining the mid-span stress, mid-span deflection, mid-span strain, creep compliance, creep stiffness, and strain rate of the specimen. The specimen prepared from asphalt concrete materials is in a prismatic shape, with dimensions of 250 ± 2 mm in length, 30 ± 2 mm in width, and 35 ± 2 mm in height. During the test, the displacement sensor is placed and fixed on the bottom plate between two bearing supports by using a magnetic base, and the probe is vertically upward and in contact with the center of the lower edge of the cross-section in the middle of the vertical length direction of the specimen. By measuring and recording the readings of the displacement sensor, the mid-span deflection of the specimen at different time intervals is obtained, and then the mid-span stress, mid-span deflection, mid-span strain, creep compliance, creep stiffness, and strain rate of the specimen are calculated.

[0046] The working mechanism of the present invention is as follows: The bending creep testing machine is a testing machine that uses weights for loading and a guide rod to limit the loading direction to be vertically downward. The applied load is calculated from the total weight of the anti-fall metal nut, guide rod, pressure tray, pressure head, and test weights. The applied load is applied once to the center position of the mid-span cross-section of the asphalt concrete specimen placed on the bearing support through the pressure head. When applying the pressure, the pressure head is longitudinally perpendicular to the length direction of the asphalt concrete specimen. The deflection of the center position of the lower edge of the mid-span of the asphalt concrete specimen at different time intervals is measured by using a displacement sensor fixed on the bottom plate of the testing machine. The mid-span stress, mid-span deflection, mid-span strain, creep compliance, creep stiffness, and strain rate of the specimen are calculated by using the deflection, length, width, height, self-weight, and time of the specimen, and the bending creep test is completed.

[0047] The above-described embodiments are only used to illustrate the technical ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The patent scope of the present invention cannot be limited only by these embodiments. That is, any equivalent changes or modifications made based on the spirit disclosed by the present invention still fall within the patent scope of the present invention.

Claims

1. An asphalt concrete flexural creep test device, comprising a flexural creep testing machine, a displacement sensor (12), a magnetic base (14) and a data acquisition system (13), characterized in that, The flexural creep testing machine comprises a main body frame and a loading assembly. The main body frame consists of a horizontally arranged square top plate (1), a horizontally arranged square bottom plate (2), and 4 vertically arranged cylinders (3) connecting the upper and lower four corners of the top plate (1) and the bottom plate (2). A pair of oppositely arranged plate-shaped bearing supports (11) for supporting the asphalt concrete specimen (10) are vertically fixed on the bottom plate (2). The upper end of the cross-section of the bearing support (11) is semi-circular. The distance between the two bearing supports (11) matches the length of the asphalt concrete specimen to be tested. A magnetic base (14) is placed on the bottom plate (2) between the two bearing supports (11). The displacement sensor (12) is installed on the magnetic base (14) and contacts the bottom surface of the asphalt concrete specimen (10). The center of the top plate (1) is provided with an installation through hole for hanging the loading assembly; the loading assembly includes a guide rod (6). The upper part of the guide rod (6) passes through the installation through hole at the center of the top plate (1) and is locked by a nut (5), suspending the guide rod (6) below the top plate (1). The bottom end of the guide rod (6) is fixedly connected to a horizontally arranged pressure tray (8). The center of the bottom surface of the pressure tray (8) is provided with a pressure head (9) contacting the upper surface of the asphalt concrete specimen (10). The pressure head (9) is a plate-shaped structure, and the lower end of the cross-section of the pressure head (9) is semi-circular. Weights (7) of different weights are inserted into the guide rod (6) and placed on the pressure tray (8), transferring the load to the pressure head (9) and applying force to the upper surface of the asphalt concrete specimen (10).

2. The asphalt concrete flexural creep test device according to claim 1, wherein The upper and lower ends of the cylinder (3) are respectively provided with threads. The upper and lower four corners of the top plate (1) and the bottom plate (2) are respectively provided with through holes, and the top plate (1) and the bottom plate (2) are fixed on the cylinder (3) by nuts.

3. The asphalt concrete flexural creep test device according to claim 1, wherein The weights (7) are of 8 different weights.

4. The asphalt concrete flexural creep test device according to claim 1, wherein, The guide rod (6) and the pressure tray (8), the pressure tray (8) and the pressure head (9), and the bearing support (11) and the bottom plate (2) are respectively connected by threads.

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