A concrete self-shrinkage device applicable to low-pressure low-temperature environment

Abstract

The utility model discloses a kind of concrete self-shrinkage devices for low pressure low temperature environment, belong to concrete shrinkage and deformation test technical field, including anti-seismic base, simulation box, compressor refrigeration system, vacuum pump system and self-shrinkage tester;The compressor refrigeration system and vacuum pump system are all inside and outside machine separation type structure, the compressor refrigeration system includes the compressor being set in simulation box outside, condenser, throttling device and the evaporator being set in the simulation box inner wall, the vacuum pump system includes the rough pumping pump and high vacuum pump being set in simulation box outside, the simulation box inner wall is hung with the air intake and exhaust box corresponding vacuum pump system, the high vacuum pump is connected with air intake and exhaust box by pipeline. The concrete self-shrinkage device for low pressure low temperature environment, by separating main vibrating components such as compressor, condenser and simulation box body, ensure that self-shrinkage tester works in non-interference environment.

Description

Technical Field

[0001] This utility model belongs to the field of concrete shrinkage deformation testing technology, and in particular relates to a concrete self-shrinkage device that can be used in low-pressure and low-temperature environments. Background Technology

[0002] Concrete shrinkage deformation testing is a scientific method for assessing, predicting, and ultimately controlling the risk of cracking caused by volume shrinkage in concrete, thereby ensuring the long-term durability, safety, and service performance of concrete structures. Specifically, this test precisely quantifies the shrinkage of concrete from the plastic stage to long-term use, providing crucial data support for optimizing mix design, developing precise construction and curing plans, and verifying the crack-resistant effects of admixtures and additives. It is an indispensable technical means for preventing early cracking and improving the impermeability and erosion resistance of structures.

[0003] As major projects like the Sichuan-Tibet Railway extend into ultra-high altitude (above 4500 meters) regions, the cracking problem of concrete structures under low-pressure and low-temperature environments is becoming increasingly prominent. In such environments, atmospheric pressure can drop to approximately 56.3 kPa, and temperatures remain consistently low, causing significant changes in the autogenous shrinkage behavior of concrete, directly impacting the long-term durability and safety of the structure. Therefore, accurately measuring the autogenous shrinkage value of concrete under specific low-pressure and low-temperature conditions is crucial for revealing its cracking mechanism and optimizing mix design.

[0004] Currently, when simulating the above conditions in a laboratory environment, concrete specimens are usually placed in a simulation chamber (10) that creates a low-pressure, low-temperature environment, and measured using a high-precision autogenous shrinkage tester (such as a bellows method tester). However, the existing technical solutions have a significant drawback: most common low-pressure, low-temperature simulation chambers (10) are integral structures, and the vibrations generated by their compressor refrigeration system and vacuum pump system during operation are directly transmitted to the inside of the chamber. Since concrete autogenous shrinkage testers (especially precision instruments using LVDT sensors) need to capture micron-level (approximately 10⁻) measurements, the impact on the concrete specimens is significant. 6 The length changes (strain) of these vibrations can severely interfere with the signal stability of displacement sensors, leading to distorted test data that cannot accurately reflect the volume shrinkage of concrete caused solely by cement hydration.

[0005] To address this issue, we propose a self-shrinking device for concrete that can be used in low-pressure and low-temperature environments. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that in the existing technology, the vibration generated by the integral structure during operation is directly transmitted to the inside of the box, which seriously interferes with the signal stability of the displacement sensor, resulting in distorted test data and failing to truly reflect the problem of concrete self-shrinkage caused solely by cement hydration. Therefore, this invention proposes a concrete self-shrinkage device that can be used in low-pressure and low-temperature environments.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A self-shrinkage device for concrete that can be used in low-pressure and low-temperature environments includes an anti-seismic base, a simulation chamber, a compressor refrigeration system, a vacuum pump system, and a self-shrinkage measuring instrument. The earthquake-resistant base includes a fixed bracket, and the lower part of the fixed bracket is provided with casters and adjustable feet for fixing and moving the simulation box. The compressor refrigeration system and the vacuum pump system are both of the separate indoor and outdoor unit structures. The compressor refrigeration system includes a compressor, a condenser, a throttling device and an evaporator located on the inner wall of the simulation chamber. The compressor is connected to the evaporator through a pipe. The vacuum pump system includes a coarse pump and a high vacuum pump located on the outside of the simulation chamber. The inner wall of the simulation chamber is suspended with an inlet and outlet box corresponding to the vacuum pump system. The high vacuum pump is connected to the inlet and outlet box through a pipe. The self-shrinkage measuring instrument includes a sealing mold consisting of a bellows and an end sealing joint, a rigid support, and a displacement sensor with an integrated linear variable differential transformer; the sealing mold is fixed on the rigid support, and one end of the bellows is in contact with the iron core of the displacement sensor. The displacement sensor is electrically connected to a controller located outside the simulation chamber.

[0008] Preferably, the liftable support leg is a hydraulically damped support leg or a mechanically helical support leg.

[0009] Preferably, the vacuum pump system is equipped with a high vacuum valve and a venting valve on its piping.

[0010] Preferably, the controller integrates a display screen for displaying the autogenous shrinkage strain value of the concrete.

[0011] Preferably, both the compressor refrigeration system and the vacuum pump system outdoor unit are integrated with a display screen for real-time display of temperature and pressure data inside the simulation chamber.

[0012] In summary, the technical effects and advantages of this utility model are as follows: This utility model separates the main vibrating components such as the compressor and condenser from the simulation chamber body. At the same time, the anti-vibration base can further absorb and isolate residual vibrations, ensuring that the self-shrinkage measuring instrument can work in an interference-free environment and can capture minute length changes of concrete in real time and accurately.

[0013] This invention integrates an environmental simulation system with a measurement system, solving the problems of scattered equipment, external control terminals, and inconvenient operation in traditional experiments. Technicians can directly read the shrinkage data through the display screen of the data acquisition and display unit outside the simulation chamber, and can synchronously monitor environmental parameters through the external display screen, which facilitates real-time observation and recording and improves experimental efficiency.

[0014] This utility model, through the universal wheels and height-adjustable support legs set at the bottom of the anti-vibration base, forms a dual-purpose structure for both mobility and fixation. When moving, the universal wheels provide convenience; during testing, the height-adjustable support legs support and level the equipment, enhancing overall stability. This allows the device to ensure testing accuracy while also taking into account the ability to be flexibly deployed, making it more convenient to move and meeting the experimental needs in various scenarios. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of this utility model; Figure 2 This is a schematic diagram of the structure of the earthquake-resistant base in this utility model; Figure 3 This is a schematic diagram of the compression refrigeration system in this utility model; Figure 4 This is a schematic diagram of the vacuum pump system in this utility model; Figure 5 This is a schematic diagram of the self-shrinkage measuring instrument in this utility model.

[0016] In the diagram: 1. Rigid support; 2. Displacement sensor; 3. Controller; 4. End sealing joint; 5. Bellows; 6. Compressor; 7. Condenser; 8. Throttling device; 9. Evaporator; 10. Simulation chamber; 11. Coarse pump; 12. High vacuum pump; 13. Vent valve; 14. Pipeline; 15. Inlet and outlet boxes; 16. Casters; 17. Adjustable support legs; 18. Fixed support. Detailed Implementation

[0017] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0018] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0019] Reference Figure 1A device for measuring the self-shrinkage of concrete in low-pressure and low-temperature environments includes an anti-seismic base, a simulation chamber 10, a compressor refrigeration system, a vacuum pump system, and a self-shrinkage measuring instrument. This invention isolates the main vibration source from the precision measuring unit through a separate structure, thereby ensuring the accuracy of concrete self-shrinkage measurement while simulating high-altitude, low-pressure, and low-temperature environments.

[0020] The simulation chamber 10, placed on a shock-resistant base, is the core cavity for creating and maintaining a specific test environment, achieving a stable low-temperature and low-pressure environment.

[0021] The seismic base includes a fixed bracket 18, which is firmly connected to the upper simulation box 10 to ensure the stability of the overall structure. The fixed bracket 18 is equipped with casters 16 and adjustable feet 17 at the bottom for fixing and moving the simulation box 10. When the equipment needs to be moved, the adjustable feet 17 are raised and the casters 16 bear the weight, making it easy to move flexibly in the laboratory. When performing precise shrinkage tests, the adjustable feet 17 are lowered to support the ground stably. At this time, the casters 16 are off the ground, effectively isolating the small vibrations transmitted from the ground and the interference that may be caused by the movement of the operator. The adjustable feet 17 can be selected as hydraulic damping feet or mechanical spiral feet, providing reliable height adjustment and vibration damping functions.

[0022] The compressor refrigeration system has a separate indoor and outdoor unit structure. It includes a compressor 6, a condenser 7, and a throttling device 8 located outside the simulation chamber 10, and an evaporator 9 located on the inner wall of the simulation chamber 10. After the refrigerant completes compression, condensation, heat release, and throttling processes outside the chamber, it is transported to the interior of the simulation chamber 10 through pipe 14. Valves on the internal pipes of the compressor refrigeration system's outdoor unit control the flow of the refrigerant. The evaporator 9 is suspended on the inner wall of the simulation chamber 10, where the low-temperature, low-pressure refrigerant absorbs heat from the air inside the chamber, achieving refrigeration and providing the required low-temperature environment for the concrete specimen.

[0023] The vacuum pump system includes a rough pump 11 and a high vacuum pump 12 located outside the simulation chamber 10. The power components of the rough pump 11 and the high vacuum pump 12 are also located outside the simulation chamber 10. The high vacuum pump 12 is connected to the inlet and outlet chamber 15 on the inner wall of the simulation chamber 10 through another pipeline 14. The vacuum pump system pipeline is equipped with a high vacuum valve and an outlet valve 13. During operation, the rough pump 11 is started first to pump the air pressure in the simulation chamber 10 to the pre-stage pressure. Then, the high vacuum pump 12 is started and the high vacuum valve is opened to continuously reduce the pressure to the target vacuum level. After the experiment, the pressure in the simulation chamber 10 can be restored to normal pressure by closing the high vacuum valve and opening the outlet valve 13.

[0024] Referring to the figure, both the compressor refrigeration system and the vacuum pump system outdoor unit have integrated displays for real-time display of temperature and pressure data inside the simulation chamber 10.

[0025] The self-shrinkage tester is installed inside the simulation chamber 10. The self-shrinkage tester includes a sealed mold consisting of a bellows 5 and an end sealing joint 4, a rigid support 1, and a displacement sensor 2 with an integrated linear variable differential transformer (LVDT). Freshly mixed concrete is poured into the sealed mold, which is fixed on the rigid support 1 to ensure that the sealed mold does not undergo unexpected displacement during the measurement process. One end of the bellows 5 is in contact with the iron core of the displacement sensor 2. The iron core of the LVDT is in contact with the end sealing joint 4 of the bellows 5, so that any slight length change caused by self-shrinkage during the hardening process of the concrete can be directly and without hysteresis transmitted to the iron core of the LVDT.

[0026] The displacement sensor 2 is electrically connected to the controller 3 located outside the simulation chamber 10. The controller 3 integrates a display screen. The displacement sensor 2 can convert this micron-level mechanical displacement into a linear electrical signal in real time and accurately, and transmit it to the controller 3. The data acquisition system inside the controller 3 continuously records these signal changes and converts the signal into the length change value of the concrete specimen through its integrated display screen. Then, it calculates the self-shrinkage strain relative to the initial length and finally displays it intuitively. Placing the display screen outside the simulation chamber 10 avoids frequently opening the chamber door to read the data during the experiment, which would disrupt the stable internal testing environment.

[0027] Working principle: First, the separate compressor refrigeration system is started. The external compressor 6 starts working, driving the refrigerant to release heat through the condenser 7 and reduce pressure through the throttling device 8. Then, it is transported through the pipe 14 to the evaporator 9 inside the simulation chamber 10. The refrigerant absorbs heat and vaporizes in the evaporator 9, continuously absorbing heat from the air inside the simulation chamber 10, thereby creating and maintaining a stable low-temperature environment for the concrete specimens to be poured later.

[0028] While the refrigeration system is operating, the vacuum pump system is started to create a low-pressure environment. First, the vent valve 13 is closed, and the coarse pump 11 is started to reduce the air pressure in the simulation chamber 10 from atmospheric pressure to the pre-stage pressure. Then, the high vacuum pump 12 is started and the high vacuum valve is opened to continuously pump the pressure in the simulation chamber 10 to the target vacuum level. The displays on the compressor refrigeration system and the vacuum pump system outdoor unit will display the temperature and pressure data in the chamber in real time for easy monitoring.

[0029] Once the low-pressure and low-temperature environment stabilizes, freshly mixed concrete is poured into a sealed mold consisting of a corrugated pipe 5 and an end sealing joint 4. The sealed mold is then fixed to a rigid support 1. During the hardening process, the concrete undergoes self-shrinkage due to the hydration reaction, causing a slight change in the axial length of the corrugated pipe 5. This change is transmitted to the core of the displacement sensor 2 connected to it, converting the microscopic mechanical displacement of the concrete into a corresponding electrical signal. This signal is then transmitted to the controller 3 located outside the simulation chamber 10. The data acquisition system inside the controller 3 continuously records these signals and converts them into real-time length change values ​​of the concrete specimen through a built-in software algorithm. Finally, the self-shrinkage strain value relative to the initial length is calculated and displayed on the screen integrated into the controller 3.

[0030] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A device for detecting the self-shrinkage of concrete under low pressure and low temperature conditions, comprising an anti-seismic base, a simulation chamber (10), a compressor refrigeration system, a vacuum pump system, and a self-shrinkage measuring instrument, characterized in that: The seismic base includes a fixed bracket (18), and the fixed bracket (18) is provided with casters (16) and adjustable feet (17) at the bottom for fixing and moving the simulation box (10). The compressor refrigeration system and the vacuum pump system are both of the separate indoor and outdoor unit structures. The compressor refrigeration system includes a compressor (6), a condenser (7), a throttling device (8) located outside the simulation chamber (10), and an evaporator (9) located on the inner wall of the simulation chamber (10). The compressor (6) is connected to the evaporator (9) through a pipe (14). The vacuum pump system includes a rough pump (11) and a high vacuum pump (12) located outside the simulation chamber (10). The inner wall of the simulation chamber (10) is suspended with an intake and exhaust box (15) corresponding to the vacuum pump system. The high vacuum pump (12) is connected to the intake and exhaust box (15) through a pipe (14). The self-shrinkage measuring instrument includes a sealing mold consisting of a bellows (5) and an end sealing joint (4), a rigid support (1), and a displacement sensor (2) with an integrated linear variable differential transformer; the sealing mold is fixed on the rigid support (1), and one end of the bellows (5) is in contact with the iron core of the displacement sensor (2); The displacement sensor (2) is electrically connected to the controller (3) located outside the simulation box (10).

2. The self-shrinking device for concrete in low-pressure and low-temperature environments according to claim 1, characterized in that, The liftable support leg (17) is a hydraulic damping support leg or a mechanical spiral support leg.

3. The self-shrinking device for concrete in low-pressure and low-temperature environments according to claim 1, characterized in that, The vacuum pump system is equipped with a high vacuum valve and a venting valve (13) on its pipeline.

4. The self-shrinking device for concrete in low-pressure and low-temperature environments according to claim 1, characterized in that, The controller (3) is integrated with a display screen for displaying the self-shrinkage strain value of concrete.

5. A concrete self-shrinkage device applicable to low-pressure and low-temperature environments according to claim 1, characterized in that, The compressor refrigeration system and the vacuum pump system outdoor unit are both equipped with display screens to display the temperature and pressure data inside the simulation box (10) in real time.

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