Constant loading device for durability test of concrete test piece

Abstract

The invention relates to the technical field of concrete durability, and discloses a concrete test piece durability test constant loading device which comprises a bottom plate and a test piece, a sliding groove is formed in the top surface of the bottom plate, a second sliding block is slidably connected into the sliding groove, a placing platform is fixedly connected to the top surface of the second sliding block, and a loading cylinder is placed on the top surface of the placing platform; the loading cylinder is composed of a cylinder body and a cylinder cover, the cylinder cover is in threaded connection with the cylinder body, a containing cavity is formed in the side wall of the cylinder body, a plurality of electric heating rods are fixedly connected in the containing cavity, the containing cavity is filled with heat conduction oil, the inner bottom face of the cylinder body is fixedly connected with a limiting ring, a test piece is placed in the limiting ring, seawater is injected into the loading cylinder through the water injection mechanism, and corrosion of the seawater is simulated. Water is drained through the water draining assembly, the loading cylinder is heated and dried through the electric heating rod, the test piece achieves the multi-factor coupling effect of dry-wet circulation, seawater erosion and constant pressure, the service conditions of marine bridge concrete can be better restored, and the durability test of the concrete test piece is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete durability, and in particular to a constant loading device for durability tests of concrete specimens. Background Art

[0002] As one of the most commonly used materials in modern construction projects, the performance of concrete directly affects the safety and service life of buildings. To ensure the quality of concrete, various performance tests are usually required, and among them, durability tests are particularly important.

[0003] When a concrete structure is in use, it is not only affected by factors such as loads, but also faces complex environmental factors. The deterioration of concrete under the coupling action of multiple factors is more complex than that under single-factor or two-factor actions. It is very necessary to study the coupling action of multiple factors. Existing devices cannot achieve the coupling action of concrete under loads, seawater erosion, and wet-dry cycles, and can only achieve the coupling action of concrete under single-factor or two-factor actions, which is not conducive to restoring the use environment of concrete for coastal bridges, and thus is not conducive to the durability test of concrete specimens.

[0004] Therefore, the present invention provides a constant loading device for durability tests of concrete specimens. Summary of the Invention

[0005] In order to make up for the deficiencies of the prior art and solve at least one of the technical problems proposed in the background art.

[0006] The present invention provides a constant loading device for durability tests of concrete specimens, including a bottom plate and a specimen. A chute is provided on the top surface of the bottom plate, and a second slider is slidably connected in the chute. A placement platform is fixedly connected to the top surface of the second slider, and a loading cylinder is placed on the top surface of the placement platform. The loading cylinder is composed of a cylinder body and a cylinder cover, and the cylinder cover is threadedly connected to the cylinder body. A cavity is provided inside the side wall of the cylinder body, and a plurality of electric heating rods are fixedly connected in the cavity, and the cavity is filled with heat-conducting oil. A limiting ring is fixedly connected to the inner bottom surface of the cylinder body, the specimen is placed inside the limiting ring, and a pressure sensor is provided inside the limiting ring, and the pressure sensor abuts against the bottom surface of the specimen. A through groove is provided on the top surface of the cylinder cover, and the through groove is arranged in a manner that fits the specimen. A support frame is fixedly connected to the top surface of the bottom plate, a hydraulic cylinder is fixedly connected to the top surface of the support frame, and the output end of the hydraulic cylinder penetrates through the support frame and is fixedly connected to a pressing plate. The pressing plate is arranged above the specimen, and a drainage assembly is communicated with the side wall of the cylinder body; An injection mechanism is provided on the side wall of the support frame, and the injection mechanism is used to inject seawater into the cylinder body. A drying auxiliary mechanism is provided on the support frame, and the drying auxiliary mechanism is used to accelerate the drying of the loading cylinder. A water pump is provided between the injection mechanism and the drainage assembly; A control panel is provided on the top surface of the bottom plate, and the control panel is used to control the hydraulic cylinder, the drying auxiliary mechanism, the drainage component, the water injection mechanism and the water pump.

[0007] Preferably, the drying auxiliary mechanism includes a motor fixed on the top surface of the support frame. The output end of the motor penetrates through the support frame and is fixedly connected with a first lead screw. The first lead screw is a reciprocating lead screw and is rotationally connected to the top surface of the bottom plate. A movable block is threadedly connected to the first lead screw, and a lifting ring is fixedly connected to the side surface of the movable block. The lifting ring is an incomplete ring body and is concentric with the pressing plate. A plurality of first magnets are fixedly connected inside the lifting ring. A plurality of fixed blocks are fixedly connected to the inner wall of the cavity, and a first slider is slidably connected to the outer peripheral portion of the fixed block. A second magnet is fixedly connected to the side wall of the first slider, and a connecting rod is also fixedly connected to the side wall of the first slider. The second magnet and the first magnet attract each other.

[0008] Preferably, the water injection mechanism includes a driving wheel fixed on the first lead screw. A second lead screw is rotationally connected to the inner top surface of the support frame, and the second lead screw penetrates through the bottom plate and is rotationally connected to the bottom plate. A driven wheel is fixedly connected to the second lead screw, and a belt is provided between the driven wheel and the driving wheel. The driving wheel and the driven wheel are connected by belt drive. A lifting block is threadedly connected to the second lead screw, a right-angle block is fixedly connected to the side surface of the lifting block, and a pushing plate is fixedly connected to the top end of the right-angle block. A fixing plate is fixedly connected to the side wall of the support frame, and an elastic air bag is fixedly connected to the bottom surface of the fixing plate. The pushing plate is arranged at the bottom of the elastic air bag. A water storage tank is placed on the top surface of the bottom plate. An air delivery pipe is communicated between the elastic air bag and the water storage tank. A water delivery pipe is threadedly communicated between the water storage tank and the cylinder body. The water delivery pipe is a flexible pipe, and a one-way valve is arranged on the water delivery pipe. The flow direction of the one-way valve is from the inside of the water storage tank to the inside of the cylinder body.

[0009] Preferably, support legs are fixedly connected to the four corners of the bottom surface of the bottom plate, and an additional support leg is also fixedly connected to the center of the bottom surface of the bottom plate.

[0010] Preferably, a rubber plate is fixedly connected to the top surface of the pushing plate.

[0011] Preferably, the drainage component includes a drainage box fixed on the support leg. A drainage pipe is threadedly communicated between the drainage box and the cylinder body. The drainage pipe is a flexible pipe, and a valve is arranged on the drainage pipe.

[0012] Preferably, both the first magnets and the second magnets are circumferentially distributed around the center of the cylinder body, and the number of the first magnets and the second magnets is equal and they are equidistantly distributed.

[0013] Preferably, a limiting rod is fixedly connected between the support frame and the bottom plate, and the limiting rod penetrates through the movable block and is slidably connected to the movable block.

[0014] Preferably, another limiting rod is fixedly connected between the support frame and the bottom plate, and the limiting rod passes through the lifting block and is slidably connected with the lifting block.

[0015] The beneficial effects of the present invention are as follows: For a constant loading device for durability test of concrete specimens of the present invention, a constant pressure is applied to the specimens in the loading cylinder by a hydraulic cylinder driving a pressing plate, seawater is injected into the loading cylinder by a water injection mechanism to simulate the corrosion of seawater, drainage is carried out by a drainage component, and the loading cylinder is heated and dried by an electric heating rod. Thus, multi-factor coupling effects of wet-dry cycle, seawater erosion and constant pressure are realized for the specimens, and the use conditions of concrete for coastal bridges can be better restored, which is beneficial to the durability test of concrete specimens.

[0016] For a constant loading device for durability test of concrete specimens of the present invention, the drying auxiliary mechanism can accelerate the flow of the heat-conducting oil, thereby increasing the diffusion of heat in the cavity, which is beneficial to accelerating the drying of the loading cylinder. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of the present invention; Figure 2 is the present invention Figure 1 an enlarged view of part A in; Figure 3 is a schematic structural diagram of the support frame of the present invention Figure 1 ; Figure 4 is a schematic structural diagram of the support frame of the present invention Figure 2 ; Figure 5 is a schematic structural diagram of the support frame of the present invention Figure 3 ; Figure 6 is a cross-sectional view of the loading cylinder of the present invention Figure 1 ; Figure 7 is a cross-sectional view of the loading cylinder of the present invention Figure 2 ; Figure 8 is the present invention Figure 7 an enlarged view of part B in.

[0018] Description of the reference numerals: 1. Bottom plate; 2. Support frame; 3. Loading cylinder; 31. Cylinder body; 311. Cavity; 312. Electric heating rod; 32. Cylinder cover; 33. Limiting ring; 4. Specimen; 5. Hydraulic cylinder; 6. Pressing plate; 7. Drying auxiliary mechanism; 71. Motor; 72. First lead screw; 73. Movable block; 74. Lifting ring; 75. First magnet; 76. Fixed block; 77. First slider; 78. Second magnet; 79. Connecting rod; 8. Control panel; 9. Water injection mechanism; 901. Driving wheel; 902. Driven wheel; 903. Second lead screw; 904. Lifting block; 905. Pushing plate; 906. Fixed plate; 907. Elastic airbag; 908. Air supply pipe; 909. Water storage tank; 910. Water supply pipe; 911. Check valve; 10. Drainage tank; 11. Drain pipe; 12. Valve; 13. Chute; 14. Second slider; 15. Limiting rod; 16. Rubber plate; 17. Pressure sensor; 18. Water pump. Detailed implementation mode

[0019] Now, the subject matter described herein will be discussed with reference to exemplary embodiments. It should be understood that discussing these embodiments is only to enable those skilled in the art to better understand and thus implement the subject matter described herein. Without departing from the scope of protection of the content of this specification, changes can be made to the functions and arrangements of the elements discussed. Each example can omit, substitute, or add various processes or components as needed. Additionally, the features described relative to some examples can also be combined in other examples. Embodiment

[0020] As Figures 1 to 8 shown, a constant loading device for durability test of concrete specimens according to an embodiment of the present invention is described with emphasis on reference to Figure 1 , Figure 3 , Figure 6 , Figure 7, including a bottom plate 1 and a test piece 4. A chute 13 is formed on the top surface of the bottom plate 1, and a second slider 14 is slidably connected in the chute 13. A placement platform is fixedly connected to the top surface of the second slider 14. An electric push rod is fixedly connected to the side wall of the bottom plate 1, and the output end of the electric push rod is fixedly connected to the side surface of the placement platform. A loading cylinder 3 is placed on the top surface of the placement platform. The loading cylinder 3 is composed of a cylinder body 31 and a cylinder cover 32. The cylinder cover 32 is threadedly connected to the cylinder body 31. A cavity 311 is formed in the side wall of the cylinder body 31. A plurality of electric heating rods 312 are fixedly connected in the cavity 311, and the cavity 311 is filled with heat-conducting oil. A limiting ring 33 is fixedly connected to the inner bottom surface of the cylinder body 31. The test piece 4 is placed in the limiting ring 33, and a pressure sensor 17 is arranged in the limiting ring 33. The pressure sensor 17 abuts against the bottom surface of the test piece 4. A through groove is formed on the top surface of the cylinder cover 32, and the through groove is arranged in a manner that fits the test piece 4. A support frame 2 is fixedly connected to the top surface of the bottom plate 1. A hydraulic cylinder 5 is fixedly connected to the top surface of the support frame 2. The output end of the hydraulic cylinder 5 penetrates through the support frame 2 and is fixedly connected to a pressing plate 6. The pressing plate 6 is arranged above the test piece 4. A drainage assembly is communicated with the side wall of the cylinder body 31; Please refer to Figure 1 , Figure 3 , Figure 6 , Figure 7 , a water injection mechanism 9 is arranged on the side wall of the support frame 2. The water injection mechanism 9 is used to inject seawater into the cylinder body 31. A drying auxiliary mechanism 7 is arranged on the support frame 2. The drying auxiliary mechanism 7 is used to accelerate the drying of the loading cylinder 3. A water pump 18 is arranged between the water injection mechanism 9 and the drainage assembly; Please refer to Figure 1 , Figure 3 , Figure 6 , Figure 7 , a control panel 8 is arranged on the top surface of the bottom plate 1. The control panel 8 is used to control the hydraulic cylinder 5, the drying auxiliary mechanism 7, the drainage assembly, the water injection mechanism 9 and the water pump 18.

[0021] Specifically, the hydraulic cylinder 5 drives the pressing plate 6 to apply pressure to the test piece 4 in the loading cylinder 3. The hydraulic cylinder 5 is controlled by the control panel 8. An ARM architecture chip is arranged in the control panel 8. The pressure sensor 17 monitors the change of the loading force in real time and transmits the signal to the control panel 8. The control panel 8 dynamically adjusts the output of the hydraulic cylinder 5 according to the data fed back by the pressure sensor 17 to ensure that the loading force is always maintained at the set value. Seawater is injected into the loading cylinder 3 through the water injection mechanism 9 to simulate the corrosion of seawater. Drainage is carried out through the drainage assembly, and the loading cylinder 3 is heated and dried by the electric heating rods 312. The test piece 4 thus realizes the multi-factor coupling effect of constant pressure, seawater erosion and wet-dry cycle, can better restore the use conditions of the concrete of the coastal bridge, and is conducive to the durability test of the concrete test piece.

[0022] Please refer to Figure 1 , Figure 7 ,Figure 8 , the drying auxiliary mechanism 7 includes a motor 71 fixedly connected to the top surface of the support frame 2. The output end of the motor 71 penetrates through the support frame 2 and is fixedly connected with a first lead screw 72. The first lead screw 72 is a reciprocating lead screw, and the first lead screw 72 is rotatably connected to the top surface of the bottom plate 1. A movable block 73 is threadedly connected to the first lead screw 72, and a lifting ring 74 is fixedly connected to the side surface of the movable block 73. A limiting rod 15 is fixedly connected between the support frame 2 and the bottom plate 1, and the limiting rod 15 penetrates through the movable block 73 and is slidably connected to the movable block 73. The lifting ring 74 is an incomplete ring body, and the lifting ring 74 is concentric with the pressing plate 6. A plurality of first magnets 75 are fixedly connected inside the lifting ring 74. A plurality of fixing blocks 76 are fixedly connected to the inner wall of the cavity 311, and a first slider 77 is slidably connected to the outer peripheral part of the fixing block 76. A second magnet 78 is fixedly connected to the side wall of the first slider 77, and a connecting rod 79 is also fixedly connected to the side wall of the first slider 77. The second magnet 78 and the first magnet 75 attract each other. The first magnets 75 and the second magnets 78 are both distributed in a circumferential manner around the center of the cylinder 31, and the number of the first magnets 75 and the second magnets 78 is equal and they are equidistantly distributed.

[0023] Specifically, the driving motor 71 drives the first lead screw 72 to rotate. Since the first lead screw 72 is a reciprocating lead screw, the movable block 73 and the lifting ring 74 thereon perform reciprocating lifting motions, that is, the first magnets 75 perform reciprocating lifting motions. The first magnets 75 attract the second magnets 78, and thus the second magnets 78 and the connecting rod 79 can be driven to perform reciprocating lifting motions. The up and down movement of the connecting rod 79 will cause the heat-conducting oil to flow. The flowing heat-conducting oil can more effectively contact the cavity 311, the electric heating rod 312, etc., thereby improving the heat transfer efficiency, increasing the heating speed of the cylinder 31, and facilitating the drying of the cylinder 31.

[0024] Please refer to Figure 1 、 Figure 2 、 Figure 4 、 Figure 5, the water injection mechanism 9 includes a driving wheel 901 fixedly connected to the first lead screw 72. A second lead screw 903 is rotatably connected to the inner top surface of the support frame 2. The second lead screw 903 is a reciprocating lead screw, and the second lead screw 903 penetrates through the bottom plate 1 and is rotatably connected to the bottom plate 1. A driven wheel 902 is fixedly connected to the second lead screw 903, and a belt is provided between the driven wheel 902 and the driving wheel 901. The driving wheel 901 and the driven wheel 902 are connected by belt drive. A lifting block 904 is threadedly connected to the second lead screw 903. Another limiting rod 15 is fixedly connected between the support frame 2 and the bottom plate 1, and the limiting rod 15 penetrates through the lifting block 904 and is slidably connected to the lifting block 904. A right-angle block is fixedly connected to the side surface of the lifting block 904, and a push plate 905 is fixedly connected to the top end of the right-angle block. A fixing plate 906 is fixedly connected to the side wall of the support frame 2, and an elastic airbag 907 is fixedly connected to the bottom surface of the fixing plate 906. The push plate 905 is arranged at the bottom of the elastic airbag 907. A rubber plate 16 is fixedly connected to the top surface of the push plate 905. A water storage tank 909 is placed on the top surface of the bottom plate 1. An air delivery pipe 908 is connected between the elastic airbag 907 and the water storage tank 909. A water delivery pipe 910 is threadedly connected between the water storage tank 909 and the cylinder body 31. The water delivery pipe 910 is a flexible pipe, and a one-way valve 911 is provided on the water delivery pipe 910. The flow direction of the one-way valve 911 is from the inside of the water storage tank 909 to the inside of the cylinder body 31. The one-way valve 911 is an electromagnetic valve, which is convenient for the control panel 8 to control. The elastic airbag 907 is provided with an air inlet, and another one-way valve 911 is installed at the air inlet. The flow direction of the one-way valve 911 at the air inlet is from the outside of the elastic airbag 907 to the inside of the elastic airbag 907.

[0025] Specifically, the rotation of the first lead screw 72 drives the rotation of the driving wheel 901 and the driven wheel 902, and then can drive the rotation of the second lead screw 903. Since the second lead screw 903 is a reciprocating lead screw, the lifting block 904 thereon can perform reciprocating lifting motion, so that the push plate 905 performs reciprocating lifting motion to repeatedly squeeze the elastic airbag 907. After being squeezed, the elastic airbag 907 generates a rebound restoring force to restore its original shape. Due to the repeated squeezing and rebounding of the elastic airbag 907, the gas inside it is transported to the water storage tank 909 through the air delivery pipe 908, and the height of the pipe orifice of the air delivery pipe 908 is lower than the water level in the water storage tank 909. The pressure in the water storage tank 909 increases, and the seawater flows to the water delivery pipe 910 and is transported into the cylinder body 31 to complete the injection of seawater. The one-way valve 911 on the water delivery pipe 910 can prevent backflow.

[0026] Please refer to Figure 1 , support legs are fixedly connected to the four corners of the bottom surface of the bottom plate 1, and another support leg is also fixedly connected to the center of the bottom surface of the bottom plate 1. The drainage assembly includes a drainage tank 10 fixedly connected to the support legs. A drainage pipe 11 is threadedly connected between the drainage tank 10 and the cylinder body 31. The drainage pipe 11 is a flexible pipe, and a valve 12 is provided on the drainage pipe 11. The valve 12 is an electromagnetic valve, which is convenient for the control panel 8 to control.

[0027] Specifically, the valve 12 is opened to drain the cylinder 31 and discharge the water into the drainage tank 10, and the seawater in the drainage tank 10 is conveyed to the water storage tank 909 by the water pump 18.

[0028] Working principle Applying constant pressure: The specimen 4 is placed in the cylinder 31, the hydraulic cylinder 5 is driven, and the pressure plate 6 is driven by the hydraulic cylinder 5 to apply pressure to the specimen 4 in the loading cylinder 3. The hydraulic cylinder 5 is controlled by the control panel 8. The control panel 8 is provided with an ARM architecture chip. The pressure sensor 17 monitors the change of the loading force in real time and transmits the signal to the control panel 8. The control panel 8 dynamically adjusts the output of the servo hydraulic cylinder 5 according to the data fed back by the pressure sensor 17 to ensure that the loading force is always maintained at the set value. Simulating the seawater erosion environment: In the initial state, the specimen 4 is placed in the cylinder 31 and seawater is injected. Chemical components such as chloride ions and sulfates in the seawater will corrode the bridge concrete through different mechanisms to simulate the real seawater environment. Wet-dry cycle: After the seawater has stagnated in the cylinder 31 for a sufficient length of time, the valve 12 is opened through the control panel 8 to drain the cylinder 31. After the drainage is completed, the electric heating rod 312 is driven by the control panel 8 to heat and dry the loading cylinder 3. At the same time, the motor 71 is driven to drive the first lead screw 72 to rotate. Since the first lead screw 72 is a reciprocating lead screw, the moving block 73 and the lifting ring 74 on it make reciprocating lifting motions, that is, the first magnet 75 makes reciprocating lifting motions. The first magnet 75 attracts the second magnet 78, which can drive the second magnet 78 and the connecting rod 79 to make reciprocating lifting motions. The up and down movement of the connecting rod 79 will cause the heat-conducting oil to flow. The flowing heat-conducting oil can more effectively contact the cavity 311, the electric heating rod 312, etc., thereby improving the heat transfer efficiency, increasing the heating speed of the cylinder 31, and facilitating the drying of the cylinder 31. The rotation of the first lead screw 72 drives the driving wheel 901 and the driven wheel 902 to rotate, and then can drive the second lead screw 903 to rotate. Since the second lead screw 903 is a reciprocating lead screw, the lifting block 904 on it can make reciprocating lifting motions, so that the push plate 905 makes reciprocating lifting motions to repeatedly squeeze the elastic airbag 907. After the elastic airbag 907 is squeezed, it generates a resilience restoring force to restore its original shape. The repeated squeezing and resilience of the elastic airbag 907 cause the gas inside it to be conveyed to the water storage tank 909 through the air delivery pipe 908, and the pipe orifice height of the air delivery pipe 908 is less than the water level height of the seawater in the water storage tank 909. The pressure in the water storage tank 909 increases, and the seawater flows to the water delivery pipe 910 and is conveyed into the cylinder 31 to complete the injection of seawater. The one-way valve 911 on the water delivery pipe 910 can prevent backflow. The seawater in the drainage tank 10 is conveyed to the water storage tank 909 by the water pump 18, thereby realizing the wet-dry cycle in the cylinder 31. Specimen 4 is subjected to the multi-factor coupling action of constant pressure, seawater erosion and wet-dry cycles, which can better restore the service conditions of concrete for coastal bridges and is conducive to the durability test of concrete specimens.

[0029] The above embodiments of the specific implementation manners have been described, but this embodiment is not limited to the above specific implementation manners. The above specific implementation manners are merely illustrative rather than restrictive. Under the inspiration of this embodiment, those of ordinary skill in the art can also make many forms, all of which fall within the protection scope of this embodiment.

Claims

1. A constant loading device for durability test of concrete specimens, characterized in that: It includes a bottom plate (1) and a test piece (4). A chute (13) is provided on the top surface of the bottom plate (1), and a second slider (14) is slidably connected in the chute (13). A placement platform is fixedly connected to the top surface of the second slider (14), and a loading cylinder (3) is placed on the top surface of the placement platform. The loading cylinder (3) consists of a cylinder body (31) and a cylinder cover (32). The cylinder cover (32) is threadedly connected to the cylinder body (31). A cavity (311) is provided inside the side wall of the cylinder body (31). A number of electric heating rods (312) are fixedly connected in the cavity (311), and the cavity (311) is filled with heat-conducting oil. A limiting ring (33) is fixedly connected to the inner bottom surface of the cylinder body (31). The test piece (4) is placed inside the limiting ring (33), and a pressure sensor (17) is arranged inside the limiting ring (33). The pressure sensor (17) abuts against the bottom surface of the test piece (4). A through groove is provided on the top surface of the cylinder cover (32), and the through groove is arranged in a manner that fits the test piece (4). A support frame (2) is fixedly connected to the top surface of the bottom plate (1). A hydraulic cylinder (5) is fixedly connected to the top surface of the support frame (2). The output end of the hydraulic cylinder (5) penetrates through the support frame (2) and is fixedly connected to a pressing plate (6). The pressing plate (6) is arranged above the test piece (4). A drainage assembly is communicated with the side wall of the cylinder body (31); An injection mechanism (9) is provided on the side wall of the support frame (2). The injection mechanism (9) is used to inject seawater into the cylinder body (31). A drying assistance mechanism (7) is provided on the support frame (2). The drying assistance mechanism (7) is used to accelerate the drying of the loading cylinder (3). A water pump (18) is arranged between the injection mechanism (9) and the drainage assembly; A control panel (8) is provided on the top surface of the bottom plate (1). The control panel (8) is used to control the hydraulic cylinder (5), the drying assistance mechanism (7), the drainage assembly, the injection mechanism (9) and the water pump (18).

2. The constant loading device for durability test of concrete specimens according to claim 1, wherein: The drying assistance mechanism (7) includes a motor (71) fixedly connected to the top surface of the support frame (2). The output end of the motor (71) penetrates through the support frame (2) and is fixedly connected to a first lead screw (72). The first lead screw (72) is a reciprocating lead screw, and the first lead screw (72) is rotatably connected to the top surface of the bottom plate (1). A movable block (73) is threadedly connected to the first lead screw (72). A lifting ring (74) is fixedly connected to the side surface of the movable block (73). The lifting ring (74) is an incomplete ring body. The lifting ring (74) is concentric with the pressing plate (6). A number of first magnets (75) are fixedly connected inside the lifting ring (74). A number of fixed blocks (76) are fixedly connected to the inner wall of the cavity (311). A first slider (77) is slidably connected to the outer peripheral part of the fixed block (76). A second magnet (78) is fixedly connected to the side wall of the first slider (77). A connecting rod (79) is also fixedly connected to the side wall of the first slider (77). The second magnet (78) and the first magnet (75) attract each other.

3. The constant loading device for durability test of concrete specimens according to claim 2, characterized in that: The water injection mechanism (9) includes a driving wheel (901) fixedly connected to the first lead screw (72). A second lead screw (903) is rotatably connected to the inner top surface of the support frame (2). The second lead screw (903) is a reciprocating lead screw, and the second lead screw (903) penetrates through the bottom plate (1) and is rotatably connected to the bottom plate (1). A driven wheel (902) is fixedly connected to the second lead screw (903), and a belt is arranged between the driven wheel (902) and the driving wheel (901). The driving wheel (901) and the driven wheel (902) are connected by belt drive. A lifting block (904) is threadedly connected to the second lead screw (903). A right-angle block is fixedly connected to the side surface of the lifting block (904), and a push plate (905) is fixedly connected to the top end of the right-angle block. A fixing plate (906) is fixedly connected to the side wall of the support frame (2), and an elastic airbag (907) is fixedly connected to the bottom surface of the fixing plate (906). The push plate (905) is arranged at the bottom of the elastic airbag (907). A water storage tank (909) is placed on the top surface of the bottom plate (1). An air supply pipe (908) is communicated between the elastic airbag (907) and the water storage tank (909). A water supply pipe (910) is threadedly communicated between the water storage tank (909) and the cylinder body (31). The water supply pipe (910) is a flexible pipe, and a check valve (911) is arranged on the water supply pipe (910). The flow direction of the check valve (911) is from the inside of the water storage tank (909) to the inside of the cylinder body (31).

4. A constant loading device for durability test of concrete specimens according to claim 1, characterized in that: Support legs are fixedly connected to the four corners of the bottom surface of the bottom plate (1), and an additional support leg is also fixedly connected to the center of the bottom surface of the bottom plate (1).

5. The constant loading device for durability test of concrete specimens according to claim 3, characterized in that: A rubber plate (16) is fixedly connected to the top surface of the push plate (905).

6. The constant loading device for durability test of concrete specimens according to claim 4, characterized in that: The drainage assembly includes a drainage tank (10) fixedly connected to the support legs. A drainage pipe (11) is threadedly communicated between the drainage tank (10) and the cylinder body (31). The drainage pipe (11) is a flexible pipe, and a valve (12) is arranged on the drainage pipe (11).

7. A constant loading device for durability test of concrete specimens according to claim 2, characterized in that: Both the first magnet (75) and the second magnet (78) are circumferentially distributed around the center of the cylinder body (31), and the number of the first magnet (75) and the second magnet (78) is equal and they are equidistantly distributed.

8. A constant loading device for durability test of concrete specimens according to claim 2, characterized in that: A limiting rod (15) is fixedly connected between the support frame (2) and the bottom plate (1), and the limiting rod (15) penetrates through the movable block (73) and is slidably connected to the movable block (73).

9. A constant loading device for durability test of concrete specimens according to claim 3, characterized in that: An additional limiting rod (15) is fixedly connected between the support frame (2) and the bottom plate (1), and the limiting rod (15) penetrates through the lifting block (904) and is slidably connected to the lifting block (904).

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