Concrete test piece testing device for coupling axial load and freeze-thaw cycle

Abstract

A concrete test piece testing device for axial load and freeze-thaw cycle coupling comprises a constant-temperature and constant-humidity box machine internally provided with a concrete load holding device, the concrete load holding device comprises a third base plate, the top of the third base plate is fixedly connected with a spiral column, the spiral column penetrates through a first base plate and is fastened at the top of the first base plate through a nut, and the top of the first base plate is fixedly connected with a second base plate. A concrete test piece to be tested is placed between the third base plate and the first base plate, a second base plate parallel to the third base plate and the first base plate is arranged above the concrete test piece, and a pressure sensor is arranged between the second base plate and the first base plate; a temperature sensor is arranged in the concrete test piece; a telescopic rod is installed on the spiral column in the horizontal direction, and the other end of the telescopic rod is connected with an acoustic emission probe used for being attached to a concrete test piece. The problems that the size of an existing applied load is limited by a spring device, and the pressure change, the change of the internal temperature of a test piece and the real-time damage change cannot be monitored in the test process are solved.

Description

Technical Field

[0001] This utility model relates to the field of concrete specimen testing technology, specifically to a concrete specimen testing device for coupling axial load and freeze-thaw cycle. Background Technology

[0002] In northern China, concrete structures are subjected to the coupled effects of continuous loads and freeze-thaw cycles during their service life, leading to durability degradation. For example, fluctuations in dam water levels cause axial self-weight stress in concrete due to constraint; road concrete bears axial stress under vehicle and pedestrian loads; furthermore, temperature and humidity changes cause the internal moisture of concrete to undergo freeze-thaw cycles—pore water freezes and expands when the temperature is below freezing, and melts and contracts when the temperature rises. This repeated phase change generates microcracks within the concrete, which gradually expand over time to form through cracks, ultimately leading to decreased structural stability, strength reduction, and shortened service life.

[0003] Currently, existing concrete load-bearing devices tested in China mainly use bolts and springs to fix the distance between upper and lower pads, and then use jacks and hydraulic devices for loading. However, these methods still have some shortcomings:

[0004] First, the magnitude of the applied load is limited by the spring device, making it impossible to meet the requirements of high-load tests; temperature changes will affect the elastic properties of the spring, causing changes in the spring force. Under long-term load, stress relaxation problems will occur, which will affect the experimental data.

[0005] Second, during the freeze-thaw cycle, it is not possible to monitor changes in pressure and internal temperature of the specimen in real time.

[0006] Third, damage changes inside the concrete specimen cannot be observed in real time during load-freeze-thaw coupling tests. Utility Model Content

[0007] To address the shortcomings of the existing technology, the purpose of this invention is to provide a concrete specimen testing device for coupling axial load and freeze-thaw cycle, which solves the problems that the magnitude of the applied load is limited by the spring device and that pressure changes, internal temperature changes of the specimen, and real-time damage changes cannot be monitored during the test.

[0008] To achieve the above objectives, this utility model provides the following technical solution:

[0009] A testing device for concrete specimens coupled with axial load and freeze-thaw cycle is characterized by: a constant temperature and humidity chamber with an internal concrete holding device, the concrete holding device including a No. 3 pad, the bottom of which is connected to the constant temperature and humidity chamber; several spiral columns fixedly connected to the top of the No. 3 pad, the spiral columns passing through a No. 1 pad and fastened to the top of the No. 1 pad by nuts; a concrete specimen to be tested placed between the No. 3 pad and the No. 1 pad; a No. 2 pad, parallel to the No. 3 and No. 1 pads, is placed above the concrete specimen; a pressure sensor connected to a pressure digital display is placed between the No. 2 pad and the No. 1 pad; a temperature sensor connected to a temperature display is installed inside the concrete specimen; a telescopic rod is installed horizontally on the spiral columns, the other end of which is connected to an acoustic emission probe for contacting the concrete specimen, and the signal from the acoustic emission probe is transmitted to a computer.

[0010] Furthermore, the cross-sections of the No. 3 pad and the No. 1 pad are rectangular, while the cross-section of the No. 2 pad is trapezoidal.

[0011] Furthermore, the plurality of spiral columns specifically comprises 6 columns, of which 4 columns are evenly distributed at the four corners of the No. 3 pad; the remaining 2 columns are distributed at the midpoint of the long side of the No. 3 pad; acoustic emission probes are installed on the spiral columns distributed at the midpoint of the long side of the No. 3 pad.

[0012] Furthermore, the spiral column is a cylindrical structure with spiral patterns on its surface. The spiral column passes through the first pad and is fastened to the top of the first pad by a nut, which is a hexagonal structure.

[0013] Furthermore, the acoustic emission probe is positioned at the midpoint of the concrete specimen along its height.

[0014] Furthermore, the concrete specimen is a prismatic structure.

[0015] Furthermore, a lifting ring is fixedly installed on the top of the first pad.

[0016] Furthermore, several spiral columns are welded to the top of the No. 3 pad.

[0017] Compared with the prior art, the beneficial technical effects of this utility model are:

[0018] This invention secures concrete specimens to a concrete loading device, applies load to the specimens via a pad, and monitors load changes using a pressure sensor. A temperature sensor is placed inside the concrete specimen to monitor its internal temperature in real time. An acoustic emission device is installed to accurately and effectively monitor the ringing count and amplitude parameters of the concrete specimens under load-freeze-thaw coupling, thereby understanding the damage to the internal structure of the concrete. This invention provides a simple and effective way to test and evaluate the durability of concrete under load-freeze-thaw cycle coupling, offering technical support for the durability design and material selection of large-scale engineering structures under complex service conditions such as severe cold.

[0019] The No. 2 pad of this utility model adopts a trapezoidal structure. The pressure is transmitted to the interior through the upper surface of the No. 2 pad. Since the inclined side of the trapezoid has a certain angle of inclination, the force will generate a component force on the inclined surface. These component forces will cause the pressure to diffuse inside the pad, thereby forming a relatively uniform pressure distribution on the lower surface of the pad and transmitting it to the concrete specimen. Attached Figure Description

[0020] Figure 1 This is a front view of the present invention.

[0021] Figure 2 This is the left view of the present invention.

[0022] Figure 3 This is a schematic diagram of the acoustic emission device in the concrete load-bearing device of this utility model.

[0023] In the diagram: 1. Pad No. 1; 2. Pad No. 2; 3. Pad No. 3; 4. Spiral column; 5. Pressure sensor; 6. Concrete specimen; 7. Nut; 8. Lifting ring; 9. Pressure digital display; 10. Acoustic emission probe; 11. Telescopic rod; 12. Computer; 13. Constant temperature and humidity chamber; 14. Temperature sensor; 15. Temperature display. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this utility model clear and complete, the embodiments of this utility model will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some, not all, embodiments of this utility model, and are merely used to explain the embodiments of this utility model. They are not intended to limit the embodiments of this utility model. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0025] like Figure 1As shown, a concrete specimen testing device for coupling axial load and freeze-thaw cycle includes a constant temperature and humidity chamber 13 and a concrete holding device. The constant temperature and humidity chamber 13 is equipped with a concrete holding device, which includes a No. 3 pad 3, a No. 2 pad 2, and a No. 1 pad 1 arranged in parallel from bottom to top. The No. 3 pad 3 and the No. 1 pad 1 have rectangular cross-sections, while the No. 2 pad 2 has a trapezoidal cross-section.

[0026] The bottom of the No. 3 pad 3 is connected to the constant temperature and humidity chamber 13. Six spiral columns 4 are welded to the top of the No. 3 pad 3, with four evenly distributed at the four corners and the remaining two at the midpoints of the long sides. Each spiral column 4 is a cylindrical structure with spiral patterns on its surface. The spiral columns 4 pass through the No. 1 pad 1 and are secured to the top of the No. 1 pad 1 with nuts 7, which are hexahedral in shape. A lifting ring 8 is also fixed to the top of the No. 1 pad 1. The No. 2 pad 2 is movably positioned between the No. 3 pad 3 and the No. 1 pad 1. The cavity formed between the No. 3 pad 3 and the No. 2 pad 2 is used to place a concrete specimen 6, which is a prism structure. A pressure sensor 5 is installed between the No. 2 pad 2 and the No. 1 pad 1, and is connected to a pressure digital display 9. The function of the pressure sensor 5 is to precisely control the applied load and observe load changes caused by gas heave and thawing during the test. A temperature sensor 14 is installed inside the concrete specimen 6, and the temperature sensor 14 is connected to a temperature display instrument 15; the temperature sensor 14 can effectively monitor the temperature inside the concrete specimen 6 in real time during the air freezing test.

[0027] like Figure 2 and 3 As shown, grooves are provided on the spiral columns 4 located at the midpoint of the long side of the No. 3 pad 3. A telescopic rod 11 is installed in the groove in the horizontal direction. The other end of the telescopic rod 11 is connected to an acoustic emission probe 10 for fitting to the concrete specimen 6. The acoustic emission probe 10 is arranged at the middle measuring point in the height direction of the concrete specimen 6.

[0028] The signal from the acoustic emission probe 10 is transmitted to the computer 12. The purpose of the acoustic emission probe 10 is to monitor the ring count and amplitude parameters inside the concrete specimen 6 under long-term load-freeze-thaw coupling, and to observe the internal damage of the concrete specimen 6 through the ring count and amplitude parameters.

[0029] Working principle and usage process of this utility model:

[0030] Step 1: Prepare concrete according to the test requirements, make concrete specimen 6, and place temperature sensor 11 inside concrete specimen 6 when pouring half of concrete specimen 6. Then cure the specimen to the specified age.

[0031] Step 2: Place the No. 3 pad 3 and the spiral column 4 directly under the press, then place the concrete specimen 6 on the No. 3 pad 3 and in the middle of the pad, then place the No. 2 pad 2 on the concrete specimen 6, the pressure sensor 5 is located above the No. 2 pad 2 and in the middle, and connect the pressure digital display instrument 9, the No. 1 pad 1 is located on top of the pressure sensor 5, and the spiral column 4 passes through the through hole and is located on top of the No. 1 pad 1.

[0032] Step 3: After installing the three pads, the specimen, and the pressure sensor, start the press to apply the set load to pad 1. Once the set load is reached, stabilize the load and tighten it above pad 1 using nut 7. After the pressure stabilizes, remove the load from the press.

[0033] Step Four: According to Figure 2 After loading is completed in step three, the temperature sensor 14 is connected to the temperature display instrument 15, and the acoustic emission probe 10 is fixed to the surface of the concrete specimen 6 through the telescopic rod 11, and the probe 10 is connected to the computer 12.

[0034] Step 5: Place the installed concrete load-bearing device into the constant temperature and humidity chamber 13 via the lifting ring 8. Set the temperature to -20℃~10℃ and conduct a freeze-thaw cycle test according to the designed freeze-thaw parameters.

[0035] Step Six: After the number of freeze-thaw cycles is reached, remove the specimen, test its mass and dynamic modulus of elasticity, and calculate the mass loss rate and dynamic modulus of elasticity loss rate before and after freeze-thaw. Repeat the above steps until the concrete mass loss rate is ≥5%, the dynamic modulus of elasticity loss rate is ≥40%, or the maximum number of freeze-thaw cycles is reached.

[0036] Step 7: When the dynamic elastic modulus of concrete is ≥40% or the mass loss rate is ≥5%, the corresponding load and the number of freeze-thaw couplings are the critical values ​​for concrete failure under the coupling effect of the test load and freeze-thaw parameters.

[0037] Step 8: After the experiment, remove the concrete load-bearing device, turn off the instrument, and clean it.

[0038] In this embodiment, the duration of a single air-freezing test is 8 hours, of which the freezing time of the concrete prism specimen is 4 hours, and the lowest internal temperature of the concrete prism specimen is controlled at -15 to -20℃; the thawing time is 4 hours, and the highest internal temperature of the concrete prism specimen is controlled at 5 to 10℃.

Claims

1. A testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle, characterized in that: The test chamber includes a constant temperature and humidity chamber (13) with an internal concrete holding device. The concrete holding device includes a No. 3 pad (3). The bottom of the No. 3 pad (3) is connected to the constant temperature and humidity chamber (13). Several spiral columns (4) are fixedly connected to the top of the No. 3 pad (3). The spiral columns (4) pass through the No. 1 pad (1) and are fastened to the top of the No. 1 pad (1) by nuts (7). The concrete specimen (6) to be tested is placed between the No. 3 pad (3) and the No. 1 pad (1). Above the concrete specimen (6) is a device that connects to the No. 3 pad (13). 3) A second pad (2) parallel to the first pad (1), a pressure sensor (5) connected to a pressure digital display (9) is provided between the second pad (2) and the first pad (1); a temperature sensor (14) connected to a temperature display (15) is provided inside the concrete specimen (6); a telescopic rod (11) is installed on the spiral column (4) in the horizontal direction, and the other end of the telescopic rod (11) is connected to an acoustic emission probe (10) for fitting to the concrete specimen (6), and the signal of the acoustic emission probe (10) is transmitted to the computer (12).

2. The testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle as described in claim 1, characterized in that: The cross-sections of pad No. 3 (3) and pad No. 1 (1) are rectangular, while the cross-section of pad No. 2 (2) is trapezoidal.

3. The testing device for concrete specimens coupled with axial load and freeze-thaw cycle according to claim 2, characterized in that: The spiral columns (4) are specifically 6 columns, of which 4 columns are evenly arranged at the four corners of the No. 3 pad (3); the remaining 2 columns are arranged at the midpoint of the long side of the No. 3 pad (3); acoustic emission probes (10) are installed on the spiral columns (4) arranged at the midpoint of the long side of the No. 3 pad (3).

4. The testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle as described in claim 3, characterized in that: The spiral column (4) is a cylindrical structure with spiral patterns on its surface. The spiral column (4) passes through the first pad (1) and is fastened at the top of the first pad (1) by a nut (7). The nut (7) is a hexagonal structure.

5. The testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle as described in claim 1, characterized in that: The acoustic emission probe (10) is positioned at the middle measuring point in the height direction of the concrete specimen (6).

6. The testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle according to claim 1, characterized in that: The concrete specimen (6) is a prism structure.

7. The testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle according to claim 1, characterized in that: A lifting ring (8) is fixedly installed on the top of the first pad (1).

8. The testing apparatus for concrete specimens coupled with axial load and freeze-thaw cycle according to claim 1, characterized in that: The top of the No. 3 pad (3) is welded with several spiral columns (4).

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