Concrete oxygen diffusion coefficient testing device and testing method thereof

Abstract

The application discloses a kind of concrete oxygen diffusion coefficient testing device and testing method thereof, belong to building engineering material performance determination technical field, the concrete oxygen diffusion coefficient testing device of the present application includes upstream pipe, downstream pipe, clamping mechanism and data acquisition and processing unit, upstream pipe is internally provided with upstream sealing plug and upstream oxygen sensor;Downstream pipe is internally provided with downstream sealing plug and downstream oxygen sensor, the length of upstream pipe is greater than the length of downstream pipe;Clamping mechanism is used to seal and clamps the concrete test piece to be measured;Data acquisition and processing unit are connected with upstream oxygen sensor and downstream oxygen sensor respectively, and data acquisition and processing unit are configured to calculate the oxygen diffusion coefficient of concrete test piece.The test time is controlled within the time threshold of the significant change of humidity inside test piece, so as to eliminate the influence of humidity change on oxygen diffusion coefficient test result in the test process, realize the rapid and accurate determination of concrete oxygen diffusion coefficient.

Description

Technical Field

[0001] This invention relates to the field of building materials performance testing technology, and in particular to a concrete oxygen diffusion coefficient testing device and testing method. Background Technology

[0002] The oxygen diffusion coefficient of cement-based materials is a key parameter for assessing the corrosion rate of reinforcing steel in concrete structures. After the steel surface is depassivated, oxygen in the air diffuses through the concrete cover to the steel surface, and its diffusion rate directly determines the corrosion rate of the steel, thus affecting the service life of the concrete structure. Therefore, accurately determining the oxygen diffusion coefficient in cement-based materials has significant scientific and engineering application value for the durability design and assessment of concrete structures under harsh conditions such as chloride environments.

[0003] Currently, Chinese invention patent CN107290250B discloses a method and apparatus for determining the oxygen diffusion coefficient in cement-based materials. This method involves clamping the test specimen between two gas chambers, introducing oxygen and nitrogen into each chamber to establish a concentration gradient, and calculating the oxygen diffusion coefficient based on Fick's law and the ideal gas law by monitoring the change in oxygen concentration in the two chambers over time. However, this method requires continuous monitoring until the oxygen concentration in the two chambers reaches equilibrium, with testing times lasting several hours or even a day. Because cement-based materials are extremely sensitive to humidity, the oxygen diffusion coefficient can increase by nearly two orders of magnitude when the water saturation of the specimen drops from 100% to 85%. Therefore, during the several-hour testing process, even in a standard laboratory environment, the moisture inside the specimen will continue to evaporate, leading to a significant decrease in water saturation. This humidity change will severely interfere with the oxygen diffusion coefficient test results, making the measured data unable to accurately reflect the intrinsic diffusion performance of the material under the target humidity conditions. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a concrete oxygen diffusion coefficient testing device and method, which can control the testing time within a time threshold of significant changes in the humidity inside the specimen, thereby eliminating the influence of humidity changes during the testing process on the oxygen diffusion coefficient test results, and realizing rapid and accurate determination of the concrete oxygen diffusion coefficient.

[0005] This invention also proposes a method for testing the oxygen diffusion coefficient of concrete.

[0006] According to a first aspect of the present invention, a concrete oxygen diffusion coefficient testing device includes: an upstream pipe having an upstream sealing plug disposed inside, the upstream sealing plug being configured to jointly define an upstream chamber with the upstream pipe of a fixed volume, an upstream oxygen sensor being disposed in the upstream chamber for real-time detection of oxygen concentration in the upstream chamber; a downstream pipe having a downstream sealing plug disposed inside, the downstream sealing plug being configured to jointly define a downstream chamber with the downstream pipe of a fixed volume, a downstream oxygen sensor being disposed in the downstream chamber for real-time detection of oxygen concentration in the downstream chamber, the length of the upstream pipe being greater than the length of the downstream pipe; a clamping mechanism disposed between the upstream pipe and the downstream pipe, the clamping mechanism being used to seal and clamp the concrete specimen to be tested, so that oxygen can only diffuse from the upstream chamber to the downstream chamber through the concrete specimen; and a data acquisition and processing unit connected to the upstream oxygen sensor and the downstream oxygen sensor respectively, the data acquisition and processing unit being configured to calculate the slope of change of oxygen concentration over time detected by the downstream oxygen sensor within a preset short-time test window, and to calculate the oxygen diffusion coefficient of the concrete specimen based on the slope of change. The invention offers at least the following advantages: It employs an asymmetric dual-chamber structure, where the upstream pipe is longer than the downstream pipe. The larger volume of the upstream chamber ensures that the upstream oxygen concentration remains essentially constant within a short testing window, while the smaller volume of the downstream chamber makes the downstream oxygen concentration more sensitive to diffusion and exhibits good linearity. The use of a sealing plug that fixes the chamber volume ensures that changes in downstream oxygen concentration are caused solely by diffusion through the concrete specimen, avoiding interference from volume changes. Furthermore, by setting a large initial concentration difference between the upstream and downstream chambers, it ensures that diffusion is initially in a stable linear phase, creating the physical conditions for calculating the oxygen diffusion coefficient of the concrete specimen based on the slope of the oxygen concentration change over time in the downstream chamber. During testing, the upstream inlet valve introduces a high concentration of oxygen into the upstream chamber, while the downstream inlet valve introduces nitrogen into the downstream chamber, establishing a stable oxygen concentration gradient. Driven by this concentration gradient, oxygen diffuses from the upstream chamber through the concrete specimen to the downstream chamber. Within a short testing window, the influence of humidity changes inside the concrete specimen on the diffusion coefficient is negligible. The data acquisition and processing unit obtains the change in oxygen concentration over time detected by the downstream oxygen sensor within the preset short testing window, calculates the slope of the change, and calculates the oxygen diffusion coefficient of the concrete specimen accordingly. Therefore, the technical solution of this invention can control the testing time within a preset short testing window, fundamentally eliminating the interference of humidity changes on the test results, ensuring the accuracy of the test results, simplifying the data processing process, and realizing rapid and accurate determination of the oxygen diffusion coefficient of concrete, providing reliable technical support for the durability assessment of concrete structures.

[0007] According to some embodiments of the present invention, the system further includes an upstream inlet valve, an upstream outlet valve, a downstream inlet valve, and a downstream outlet valve. The upstream inlet valve and the upstream outlet valve are respectively connected to an upstream chamber. The upstream inlet valve is connected to an oxygen supply system. The upstream outlet valve is configured to discharge the original gas in the upstream chamber during the inflation phase. The downstream inlet valve and the downstream outlet valve are respectively connected to a downstream chamber. The downstream inlet valve is connected to a nitrogen supply system. The downstream outlet valve is configured to discharge the original gas in the downstream chamber during the inflation phase.

[0008] According to some embodiments of the present invention, the upstream sealing plug is detachably disposed in the upstream pipe, and the downstream sealing plug is detachably disposed in the downstream pipe.

[0009] According to some embodiments of the present invention, the upstream sealing plug includes a first piston and a first push rod, the first piston being adapted to the inner diameter of the upstream pipe, and the first push rod being detachably connected to the first piston; the downstream sealing plug includes a second piston and a second push rod, the second piston being adapted to the inner diameter of the downstream pipe, and the second push rod being detachably connected to the second piston.

[0010] According to a second aspect of the present invention, a method for testing the oxygen diffusion coefficient of concrete is applied to a concrete oxygen diffusion coefficient testing apparatus as described in the first aspect of the present invention. The method includes: S1: Cut the cement-based material specimen to be tested into a concrete specimen of a preset size, and place the concrete specimen in a constant temperature and humidity chamber until the mass of the concrete specimen is constant. S2: A clamping mechanism is used to clamp the concrete specimen between the upstream pipe and the downstream pipe; S3: Remove the upstream sealing plug from the upstream chamber and the downstream sealing plug from the downstream chamber. Maintain natural ventilation in the upstream and downstream chambers for a first preset time and calibrate the upstream and downstream oxygen sensors. S4: Move the upstream sealing plug to the first initial position of the upstream pipe, move the downstream sealing plug to the second initial position of the downstream pipe, open the upstream inlet valve, the upstream outlet valve, the downstream inlet valve and the downstream outlet valve, fill the upstream chamber with oxygen, fill the downstream chamber with nitrogen, close the upstream outlet valve when the oxygen concentration in the upstream chamber reaches the upstream preset value, and close the downstream outlet valve when the oxygen concentration in the downstream chamber reaches the downstream preset value. S5: Continuously fill the upstream chamber with oxygen and the downstream chamber with nitrogen. After the upstream sealing plug moves to the first working position, close the upstream air inlet valve. After the downstream sealing plug moves to the second working position, close the downstream air inlet valve. Fix the upstream sealing plug in the first working position and the downstream sealing plug in the second working position so that the volume of the upstream chamber and the downstream chamber remains fixed. S6: Within a preset short-time test window, the oxygen concentration detected by the downstream oxygen sensor is collected in real time by the data acquisition and processing unit. The oxygen diffusion coefficient of the concrete specimen is calculated based on the slope of the change of the oxygen concentration detected by the downstream oxygen sensor over time within the short-time test window.

[0011] It has at least the following beneficial effects: This method for testing the oxygen diffusion coefficient of concrete has all the beneficial effects brought about by the above-mentioned test device for testing the oxygen diffusion coefficient of concrete, which will not be repeated here.

[0012] According to some embodiments of the present invention, in S2, before clamping the concrete specimen between the upstream pipe and the downstream pipe using the clamping mechanism, the method further includes: uniformly applying glass glue to the side of the concrete specimen.

[0013] According to some embodiments of the present invention, in S3, removing the upstream sealing plug from the upstream chamber includes: mounting a first push rod on a first piston and using the first push rod to remove the first piston from the upstream chamber; removing the downstream sealing plug from the downstream chamber includes: mounting a second push rod on a second piston and using the second push rod to remove the second piston from the downstream chamber. According to some embodiments of the present invention, in S3, the oxygen concentration in both the upstream chamber and the downstream chamber after calibration is consistent with the oxygen concentration in the ambient air.

[0014] According to some embodiments of the present invention, in S5, before fixing the upstream sealing plug in the first working position, the method further includes: uniformly applying sealant to the side of the upstream sealing plug; before fixing the downstream sealing plug in the second working position, the method further includes: uniformly applying sealant to the side of the downstream sealing plug.

[0015] According to some embodiments of the present invention, in S6, calculating the oxygen diffusion coefficient of the concrete specimen based on the slope of the change of oxygen concentration detected by the downstream oxygen sensor over time within a short-time test window includes: obtaining the fixed volume of the downstream chamber, the thickness of the concrete specimen, and the cross-sectional area of ​​the concrete specimen; obtaining the first oxygen concentration value, the second oxygen concentration value, the third oxygen concentration value, and the fourth oxygen concentration value of the upstream chamber corresponding to the three equally divided time intervals within the short-time test window; obtaining the slope of the change of oxygen concentration in the downstream chamber over time within the short-time test window; and calculating the oxygen diffusion coefficient of the concrete specimen.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the concrete oxygen diffusion coefficient testing device in this specific embodiment; Figure 2 for Figure 1 A schematic diagram of the upstream and downstream pipes and the clamping mechanism; Figure 3 This is a flowchart illustrating the concrete oxygen diffusion coefficient testing method in this specific embodiment. Figure 4 The results show the monitoring of downstream oxygen content changes in concrete specimens in the humidity simulation chamber for supersaturated lithium chloride solution in Example 5. Figure 5 The results show the monitoring of changes in downstream oxygen content in the concrete specimen in the humidity simulation chamber of the supersaturated potassium chloride solution in Example 5. Figure 6 This is the monitoring result of the downstream oxygen content change of the concrete specimen in the humidity environment simulation chamber of distilled water in Example 5.

[0018] Figure label: Upstream pipe 1, upstream sealing plug 11, first piston 111, first push rod 112, upstream chamber 12, upstream oxygen sensor 13, upstream inlet valve 14, upstream outlet valve 15; Downstream pipe 2, downstream sealing plug 21, second piston 211, downstream chamber 22, downstream oxygen sensor 23, downstream inlet valve 24, downstream outlet valve 25. Clamping mechanism 3; Data acquisition and processing unit 4; Oxygen cylinder 51, oxygen cylinder valve 52, high-precision oxygen flow meter pressure reducer 53, oxygen tubing 54; Nitrogen cylinder 61, nitrogen cylinder valve 62, nitrogen high-precision flow meter pressure reducer 63, nitrogen conduit 64. Detailed Implementation

[0019] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, left, right, front, back, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0020] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, while "above," "below," "within," etc. are understood to include the stated number. If "upstream," "downstream," etc. are used, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0021] In the description of this invention, unless otherwise explicitly defined, terms such as "set", "install", and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0022] Please refer to Figures 1 to 2 This embodiment discloses a concrete oxygen diffusion coefficient testing device, including: an upstream pipe 1, a downstream pipe 2, a clamping mechanism 3, and a data acquisition and processing unit 4. The upstream pipe 1 has an upstream sealing plug 11 configured to jointly define an upstream chamber 12 with the upstream pipe 1, containing an upstream oxygen sensor 13 for real-time detection of the oxygen concentration within the upstream chamber 12. The downstream pipe 2 has a downstream sealing plug 21 configured to jointly define a downstream chamber 22 with the downstream pipe 2, containing a downstream oxygen sensor 23. The upstream oxygen sensor 23 is used to detect the oxygen concentration in the downstream chamber 22 in real time. The length of the upstream pipe 1 is greater than the length of the downstream pipe 2. The clamping mechanism 3 is set between the upstream pipe 1 and the downstream pipe 2. The clamping mechanism 3 is used to seal and clamp the concrete specimen to be tested, so that oxygen can only diffuse from the upstream chamber 12 to the downstream chamber 22 through the concrete specimen. The data acquisition and processing unit 4 is connected to the upstream oxygen sensor 13 and the downstream oxygen sensor 23 respectively. The data acquisition and processing unit 4 is configured to calculate the slope of change of oxygen concentration over time detected by the downstream oxygen sensor 23 within a preset short-time test window, and calculate the oxygen diffusion coefficient of the concrete specimen based on the slope of change. like Figures 1 to 2As shown, an upstream sealing plug 11 is installed inside the upstream pipe 1. The outer wall of the upstream sealing plug 11 seals with the inner wall of the upstream pipe 1, and the two together define an upstream chamber 12 with a fixed volume. The upstream chamber 12 is used to contain high-concentration oxygen, and an upstream oxygen sensor 13 is installed inside it to detect the oxygen concentration in the upstream chamber 12 in real time. Similarly, a downstream sealing plug 21 is installed inside the downstream pipe 2. The outer wall of the downstream sealing plug 21 seals with the inner wall of the downstream pipe 2, and the two together define a downstream chamber 22 with a fixed volume. The downstream chamber 22 is used to contain low-concentration oxygen, and a downstream oxygen sensor 23 is installed inside it to detect the oxygen concentration in the downstream chamber 22 in real time. A clamping mechanism 3 is installed between the upstream pipe 1 and the downstream pipe 2. It can clamp the concrete specimen to be tested between the upstream chamber 12 and the downstream chamber 22, and ensure that oxygen can only diffuse from the upstream chamber 12 to the downstream chamber 22 through the concrete specimen. The data acquisition and processing unit 4 is connected to the upstream oxygen sensor 13 and the downstream oxygen sensor 23 respectively. It acquires the change of oxygen concentration over time detected by the downstream oxygen sensor 23 within a preset short-time test window, calculates the slope of the change of oxygen concentration within the short-time test window, and calculates the oxygen diffusion coefficient of the concrete specimen based on the slope of the change.

[0023] It should be noted that cement-based materials are extremely sensitive to humidity. The water saturation of the specimen and the oxygen diffusion coefficient are exponentially negatively correlated; when the water saturation decreases by 15%, the oxygen diffusion coefficient can increase by nearly two orders of magnitude. In a standard laboratory environment, the moisture inside the specimen continues to evaporate. Specifically, the water saturation can decrease by approximately 2.1% within one hour and by nearly 20% within 24 hours. Therefore, excessively long testing times can lead to significant changes in the internal humidity of the specimen, severely interfering with the test results. Current techniques require several hours or even a day for the concentrations in the two chambers to reach equilibrium, inevitably making the test results highly susceptible to changes in humidity.

[0024] Based on this, the present invention proposes a time window within which the influence of changes in humidity inside the specimen on the test results is negligible. Experimental verification shows that the critical point of this time window is approximately 1 hour. To compress the test time to within this threshold, the present invention employs an asymmetric dual-chamber structure, where the length of the upstream pipe 1 is greater than the length of the downstream pipe 2. The larger volume of the upstream chamber 12 ensures that the upstream oxygen concentration remains essentially constant within the short-term test window, while the smaller volume of the downstream chamber 22 makes the downstream oxygen concentration more sensitive to diffusion and exhibits good linearity. A sealing plug capable of fixing the chamber volume is used, ensuring that changes in oxygen concentration in the downstream chamber 22 are caused only by diffusion from the concrete specimen, avoiding interference from volume changes on oxygen concentration changes. Furthermore, by setting a large initial concentration difference between the upstream and downstream chambers, a stable linear diffusion segment is ensured in the initial stage of diffusion, creating the physical conditions for calculating the oxygen diffusion coefficient of the concrete specimen based on the slope of the oxygen concentration change over time in the downstream chamber. During testing, the upstream inlet valve 14 introduces a high concentration of oxygen into the upstream chamber 12, and the downstream inlet valve 24 introduces nitrogen into the downstream chamber 22, establishing a stable oxygen concentration gradient. Driven by this concentration gradient, the oxygen diffuses from the upstream chamber 12 through the concrete specimen to the downstream chamber 22. Within a short testing window, the effect of humidity changes inside the concrete specimen on the diffusion coefficient is negligible. The data acquisition and processing unit 4 acquires the change in oxygen concentration over time detected by the downstream oxygen sensor 23 within the preset short testing window, calculates the slope of the change, and calculates the oxygen diffusion coefficient of the concrete specimen accordingly. Therefore, the technical solution of this invention can control the testing time within a preset short testing window, eliminating the interference of humidity changes on the test results from the source, ensuring the accuracy of the test results, simplifying the data processing process, and realizing rapid and accurate determination of the oxygen diffusion coefficient of concrete, providing reliable technical support for the durability assessment of concrete structures.

[0025] It should be noted that during the testing process, the volumes of the upstream chamber 12 and the downstream chamber 22 in this invention are fixed values. By fixing the chamber volume with a sealing plug, the increase in downstream oxygen concentration is entirely caused by the diffusion of oxygen through the concrete specimen, avoiding interference with the test results caused by passive concentration changes due to changes in chamber volume.

[0026] Furthermore, the duration of the preset short-time test window is configured to be less than the time threshold at which a significant change in the internal humidity of the concrete specimen occurs. Preferably, the duration of this short-time test window is 15 minutes.

[0027] It should be noted that the length of the upstream pipe 1 is greater than the length of the downstream pipe 2. In this specific embodiment, the length of the upstream pipe 1 is designed to be 1000 mm, and the length of the downstream pipe 2 is designed to be 250 mm, with a length ratio of 4:1. The longer upstream pipe 1, together with the upstream sealing plug 11, defines a larger volume in the upstream chamber 12, capable of storing more oxygen. Therefore, within the short 15-minute test window, even if some oxygen diffuses through the concrete specimen into the downstream chamber 22, the oxygen concentration in the upstream chamber 12 decreases extremely slowly, remaining essentially constant, thus providing a stable driving force for oxygen diffusion. The shorter downstream pipe 2, together with the downstream sealing plug 21, defines a smaller volume in the downstream chamber 22, making it more sensitive to changes in oxygen concentration. When a small amount of oxygen diffuses from the upstream to the downstream, the oxygen concentration in the downstream chamber 22 changes significantly, exhibiting a good linear upward trend, which is beneficial for the oxygen sensor to accurately detect changes in concentration over time. This avoids the problem that as oxygen continues to diffuse into the chamber, the oxygen concentration in the chamber gradually increases, causing the concentration difference on both sides of the specimen to continuously decrease, the diffusion rate to become slower and slower, and the downstream oxygen concentration to change non-linearly over time.

[0028] Furthermore, the clamping mechanism 3 includes a first flange located at the end of the upstream pipe 1 near the concrete specimen, a second flange located at the end of the downstream pipe 2 near the concrete specimen, and several sets of double-ended bolts and matching nuts connecting the first and second flanges. During installation, silicone sealant is first evenly applied to the side of the concrete specimen. Then, the concrete specimen is placed between the first and second flanges, so that both ends of the concrete specimen abut against the end faces of the upstream pipe 1 and the downstream pipe 2, respectively. The first and second flanges are locked together using the double-ended bolts and nuts. Under pressure, the silicone sealant fills the gap between the specimen side and the flanges, and after curing, forms an elastic sealing layer, thereby ensuring that oxygen can only diffuse from the upstream chamber 12 to the downstream chamber 22 through the internal pores of the concrete specimen, and cannot leak from the side of the specimen or the connection point.

[0029] In some specific embodiments of the present invention, an upstream inlet valve 14, an upstream outlet valve 15, a downstream inlet valve 24, and a downstream outlet valve 25 are also included. The upstream inlet valve 14 and the upstream outlet valve 15 are respectively connected to the upstream chamber 12. The upstream inlet valve 14 is connected to the oxygen supply system. The upstream outlet valve 15 is configured to discharge the original gas in the upstream chamber 12 during the inflation stage. The downstream inlet valve 24 and the downstream outlet valve 25 are respectively connected to the downstream chamber 22. The downstream inlet valve 24 is connected to the nitrogen supply system. The downstream outlet valve 25 is configured to discharge the original gas in the downstream chamber 22 during the inflation stage.

[0030] like Figure 1As shown, the upstream inlet valve 14 and the upstream outlet valve 15 are respectively connected to the upstream chamber 12. The upstream inlet valve 14 is connected to the oxygen supply system to fill the upstream chamber 12 with a high concentration of oxygen; the upstream outlet valve 15 is configured to open during the filling phase to cooperate with the upstream inlet valve 14 to discharge the original gas in the upstream chamber 12, thereby ensuring that the upstream chamber 12 ultimately obtains a high-concentration oxygen environment. Similarly, the downstream inlet valve 24 and the downstream outlet valve 25 are respectively connected to the downstream chamber 22. The downstream inlet valve 24 is connected to the nitrogen supply system to fill the downstream chamber 22 with nitrogen; the downstream outlet valve 25 is configured to open during the filling phase to cooperate with the downstream inlet valve 24 to discharge the original gas in the downstream chamber 22, thereby ensuring that the downstream chamber 22 ultimately obtains a lower oxygen concentration environment, forming a stable oxygen concentration gradient with the upstream chamber 12.

[0031] It should be noted that during the inflation phase, the upstream exhaust valve 15 and the downstream exhaust valve 25 are open, allowing the existing air in the upstream chamber 12 and the downstream chamber 22 to be expelled by the inflation gas. Once the oxygen concentration in both the upstream and downstream chambers reaches a preset value, the upstream exhaust valve 15 and the downstream exhaust valve 25 are closed. This ensures the uniqueness of the oxygen diffusion path during the test, avoids interference from residual air on the initial concentration gradient, and provides accurate prerequisites for subsequent calculations based on the slope of change.

[0032] In some specific embodiments of the present invention, the upstream sealing plug 11 is detachably disposed in the upstream tube 1, and the downstream sealing plug 21 is detachably disposed in the downstream tube 2. Specifically, when the oxygen sensor needs to be calibrated, the upstream sealing plug 11 is removed from the upstream tube 1, and the downstream sealing plug 21 is removed from the downstream tube 2. At this time, the upstream chamber 12 and the downstream chamber 22 are in communication with the atmosphere, and the upstream oxygen sensor 13 and the downstream oxygen sensor 23 are exposed to the ambient air, thereby allowing the upstream oxygen sensor 13 and the downstream oxygen sensor 23 to be calibrated, adjusting the sensor readings to match the oxygen volume fraction in the ambient air. After calibration, the upstream sealing plug 11 and the downstream sealing plug 21 are respectively reinstalled into the upstream tube 1 and the downstream tube 2 for subsequent testing. This detachable design allows the oxygen sensor to be calibrated on-site before each test, ensuring that the sensor is in an accurate calibrated state at the start of the test, thereby guaranteeing the accuracy and reliability of the test data.

[0033] In some specific embodiments of the present invention, the upstream sealing plug 11 includes a first piston 111 and a first push rod 112. The first piston 111 is adapted to the inner diameter of the upstream pipe 1, and the first push rod 112 is detachably connected to the first piston 111. The downstream sealing plug 21 includes a second piston 211 and a second push rod. The second piston 211 is adapted to the inner diameter of the downstream pipe 2, and the second push rod is detachably connected to the second piston 211.

[0034] like Figure 2 As shown, the outer diameter of the first piston 111 is matched with the inner diameter of the upstream pipe 1, allowing it to slide within the upstream pipe 1 and form a sealing fit with the inner wall of the upstream pipe 1. The first push rod 112 is threadedly connected to the first piston 111 for a detachable connection. Similarly, the outer diameter of the second piston 211 is matched with the inner diameter of the downstream pipe 2, and the second push rod is also threadedly connected to the second piston 211 for a detachable connection. Therefore, when calibration of the upstream oxygen sensor 13 and the downstream oxygen sensor 23 is required, the first push rod 112 is installed on the first piston 111, and the first piston 111 is removed from the upstream pipe 1 by operating the first push rod 112; simultaneously, the second push rod is installed on the second piston 211, and the second piston 211 is removed from the downstream pipe 2 by operating the second push rod, exposing the upstream oxygen sensor 13 and the downstream oxygen sensor 23 to ambient air for calibration. After calibration, the first piston 111 and the second piston 211 are reinstalled into the upstream tube 1 and the downstream tube 2, respectively, and the first push rod 112 and the second push rod are removed for subsequent testing.

[0035] Reference Figure 3 This embodiment discloses a method for testing the oxygen diffusion coefficient of concrete, which is applied to a concrete oxygen diffusion coefficient testing device. The method includes: S1: Cut the cement-based material specimen to be tested into a concrete specimen of a preset size, and place the concrete specimen in a constant temperature and humidity chamber until the mass of the concrete specimen is constant. S2: The concrete specimen is clamped between the upstream pipe 1 and the downstream pipe 2 using the clamping mechanism 3; S3: Remove the upstream sealing plug 11 from the upstream chamber 12 and the downstream sealing plug 21 from the downstream chamber 22. Maintain natural ventilation in the upstream chamber 12 and the downstream chamber 22 for a first preset time, and calibrate the upstream oxygen sensor 13 and the downstream oxygen sensor 23. S4: Move the upstream sealing plug 11 to the first initial position of the upstream pipe 1, move the downstream sealing plug 21 to the second initial position of the downstream pipe 2, open the upstream inlet valve 14, the upstream outlet valve 15, the downstream inlet valve 24 and the downstream outlet valve 25, fill the upstream chamber 12 with oxygen, fill the downstream chamber 22 with nitrogen, close the upstream outlet valve 15 when the oxygen concentration in the upstream chamber 12 reaches the upstream preset value, and close the downstream outlet valve 25 when the oxygen concentration in the downstream chamber 22 reaches the downstream preset value. S5: Continuously fill the upstream chamber 12 with oxygen and the downstream chamber 22 with nitrogen. After the upstream sealing plug 11 moves to the first working position, close the upstream air inlet valve 14. After the downstream sealing plug 21 moves to the second working position, close the downstream air inlet valve 24. Fix the upstream sealing plug 11 in the first working position and the downstream sealing plug 21 in the second working position so that the volumes of the upstream chamber 12 and the downstream chamber 22 remain fixed. S6: Within a preset short-term test window, the oxygen concentration detected by the downstream oxygen sensor 23 is collected in real time by the data acquisition and processing unit 4. The oxygen diffusion coefficient of the concrete specimen is calculated based on the slope of the change of the oxygen concentration detected by the downstream oxygen sensor 23 over time within the short-term test window.

[0036] In some specific embodiments of the present invention, in S2, before using the clamping mechanism 3 to clamp the concrete specimen between the upstream pipe 1 and the downstream pipe 2, the method further includes: uniformly applying glass glue to the side of the concrete specimen.

[0037] In some specific embodiments of the present invention, in S3, removing the upstream sealing plug 11 from the upstream chamber 12 includes: mounting the first push rod 112 onto the first piston 111, and using the first push rod 112 to remove the first piston 111 from the upstream chamber 12; removing the downstream sealing plug 21 from the downstream chamber 22 includes: mounting the second push rod onto the second piston 211, and using the second push rod to remove the second piston 211 from the downstream chamber 22.

[0038] In some specific embodiments of the present invention, in S3, the oxygen concentration of the upstream chamber 12 and the oxygen concentration of the downstream chamber 22 after calibration are consistent with the oxygen concentration in the ambient air.

[0039] In some specific embodiments of the present invention, before fixing the upstream sealing plug 11 in the first working position in S5, the method further includes: uniformly applying sealant to the side of the upstream sealing plug 11; before fixing the downstream sealing plug 21 in the second working position, the method further includes: uniformly applying sealant to the side of the downstream sealing plug 21.

[0040] In some specific embodiments of the present invention, in S6, calculating the oxygen diffusion coefficient of the concrete specimen based on the slope of the change of oxygen concentration with time within a short-time test window detected by the downstream oxygen sensor 23 includes: obtaining the fixed volume of the downstream chamber 22, the thickness of the concrete specimen, and the cross-sectional area of ​​the concrete specimen; obtaining the first oxygen concentration value, the second oxygen concentration value, the third oxygen concentration value, and the fourth oxygen concentration value of the upstream chamber 12 corresponding to the three equally divided time interval points within the short-time test window; obtaining the slope of the change of oxygen concentration in the downstream chamber with time within the short-time test window; and calculating the oxygen diffusion coefficient of the concrete specimen.

[0041] The following five embodiments, in conjunction with the accompanying drawings, further illustrate the specific implementation of the present invention. Embodiment 1 specifically describes the structure of the concrete oxygen diffusion coefficient testing device and the connection relationships between its components; Embodiment 2 specifically describes the complete method and steps for testing the oxygen diffusion coefficient of concrete using this device; Embodiment 3 verifies the airtightness of the device by using an airtight rubber specimen; Embodiment 4 studies the change law of water saturation of concrete specimens over time and the influence of water saturation on the oxygen diffusion coefficient through experiments, to clarify the principle basis of the short-time testing window used in the present invention; Embodiment 5 verifies the effectiveness and reliability of the present invention by testing the oxygen diffusion coefficient of concrete specimens under different humidity conditions.

[0042] Example 1: Reference Figures 1 to 2 This embodiment discloses a concrete oxygen diffusion coefficient testing device, including an upstream pipe 1, a downstream pipe 2, a clamping mechanism 3, and a data acquisition and processing unit 4.

[0043] The upstream pipe 1 contains an upstream sealing plug 11 and an upstream oxygen sensor 13, with the upstream sealing plug 11 detachably connected to the upstream pipe 1. The downstream pipe 2 contains a downstream sealing plug 21 and a downstream oxygen sensor 23, with the downstream sealing plug 21 detachably connected to the downstream pipe 2. The upstream pipe 1 is 1000 mm long and has an inner diameter of 100 mm, while the downstream pipe 2 is 250 mm long and has an inner diameter of 100 mm. When the corresponding sealing plugs of the upstream and downstream pipes 2 are fixed at the working positions away from the concrete specimen, the volumes of the upstream chamber 12 and the downstream chamber 22 are known constants. The upstream sealing plug 11 includes a first piston 111 and a first push rod 112 detachably connected to it, and the downstream sealing plug 21 includes a second piston 211 and a second push rod detachably connected to it, so that the sealing plugs can be removed for on-site calibration of the sensors. The upstream pipe 1 is equipped with an upstream inlet valve 14 and an upstream outlet valve 15, while the downstream pipe 2 is equipped with a downstream inlet valve 24 and a downstream outlet valve 25. The upstream inlet valve 14 and downstream inlet valve 24 are used for filling with gas, while the upstream outlet valve 15 and downstream outlet valve 25 are used for venting the existing gas in the chamber. A clamping mechanism 3 is located between the upstream pipe 1 and the downstream pipe 2 to seal and clamp the concrete specimen to be tested between them, ensuring that oxygen can only diffuse from the upstream chamber 12 to the downstream chamber 22 through the concrete specimen. The data acquisition and processing unit 4 is connected to the upstream oxygen sensor 13 and the downstream oxygen sensor 23, respectively. Based on the slope of the oxygen concentration change detected by the downstream oxygen sensor 23 within a preset short-term test window, it calculates the oxygen diffusion coefficient of the concrete specimen.

[0044] Furthermore, the oxygen supply system comprises an oxygen cylinder 51, an oxygen cylinder valve 52, an oxygen high-precision flow meter pressure reducer 53, and an oxygen conduit 54. The oxygen high-precision flow meter pressure reducer 53 is installed on one side of the oxygen cylinder valve 52, and the oxygen conduit 54 is installed on the oxygen high-precision flow meter pressure reducer 53. Similarly, the nitrogen supply system comprises a nitrogen cylinder 61, a nitrogen cylinder valve 62, a nitrogen high-precision flow meter pressure reducer 63, and a nitrogen conduit 64. The nitrogen high-precision flow meter pressure reducer 63 is installed on one side of the nitrogen cylinder valve 62, and the nitrogen conduit 64 is installed on the nitrogen high-precision flow meter pressure reducer 63.

[0045] Example 2: Reference Figure 3 This embodiment discloses a method for testing the oxygen diffusion coefficient of concrete, which is applied to the apparatus described in Embodiment 1. The method includes the following steps.

[0046] S1: Cut the cement-based material specimen to be tested into concrete specimens with a diameter of 100 mm and a thickness of 16 mm. Place the concrete specimens in a constant temperature and humidity chamber until their mass is constant to eliminate the influence of initial humidity differences on the test results.

[0047] S2: Apply glass glue evenly to the side of the concrete specimen, and then use the clamping mechanism 3 to seal and clamp the concrete specimen between the upstream pipe 1 and the downstream pipe 2, so that oxygen can only diffuse from the upstream chamber 12 to the downstream chamber 22 through the internal pores of the concrete specimen.

[0048] S3: Install the first push rod 112 onto the first piston 111, and use the first push rod 112 to remove the first piston 111 from the upstream chamber 12; simultaneously, install the second push rod onto the second piston 211, and use the second push rod to remove the second piston 211 from the downstream chamber 22. Maintain natural ventilation in the upstream chamber 12 and downstream chamber 22 for 5 minutes, while calibrating the upstream oxygen sensor 13 and downstream oxygen sensor 23. After calibration, the oxygen concentration in both the upstream chamber 12 and downstream chamber 22 should be consistent with the oxygen concentration in the ambient air, approximately 21%.

[0049] S4: Move the upstream sealing plug 11 to the first initial position near the end of the upstream pipe 1 closest to the concrete specimen, and move the downstream sealing plug 21 to the second initial position near the end of the downstream pipe 2 closest to the concrete specimen. Open the upstream inlet valve 14, the upstream outlet valve 15, the downstream inlet valve 24, and the downstream outlet valve 25 to fill the upstream chamber 12 with high-concentration oxygen and the downstream chamber 22 with nitrogen. When the oxygen concentration in the upstream chamber 12 reaches 99.5%, close the upstream outlet valve 15; when the oxygen concentration in the downstream chamber 22 reaches less than or equal to 0.05%, close the downstream outlet valve 25.

[0050] S5: Continuously fill the upstream chamber 12 with oxygen and the downstream chamber 22 with nitrogen. The upstream sealing plug 11 moves under air pressure. After it moves to the first working position away from the concrete specimen end of the upstream pipe 1, close the upstream air inlet valve 14. Similarly, after the downstream sealing plug 21 moves to the second working position away from the concrete specimen end of the downstream pipe 2, close the downstream air inlet valve 24. Apply sealant evenly to the sides of the upstream sealing plug 11 and the downstream sealing plug 21 to fix the upstream sealing plug 11 in the first working position and the downstream sealing plug 21 in the second working position, while simultaneously enhancing the sealing effect.

[0051] S6: Within a short 15-minute test window, the data acquisition and processing unit 4 collects real-time oxygen concentration data detected by the upstream oxygen sensor 13 and the downstream oxygen sensor 23. It performs linear fitting on the data showing the change in oxygen concentration in the downstream chamber 22 over time to obtain the slope of the oxygen concentration change over time in the downstream chamber 22. Based on this slope, it calculates the oxygen diffusion coefficient of the concrete specimen. The oxygen diffusion coefficient calculation model is as follows:

[0052] In the formula, The volume of downstream chamber 22 is given in units of... ; The thickness of the specimen is given in units of 1. K represents the slope of the oxygen concentration in the downstream chamber 22 over time. The cross-sectional area of ​​the specimen is expressed in units of 1000 m². ; , , and These represent the oxygen concentrations in upstream chamber 12 corresponding to the three equal time intervals in the oxygen diffusion experiment, in percentages (%). The oxygen diffusion coefficient of cement-based materials, in units of... .

[0053] It should be noted that the embodiments of the present invention use concrete specimens as an example for description, but those skilled in the art should understand that cement-based materials include, but are not limited to, concrete, mortar, cement paste, and their composites. All of the above materials use cement as a binder and have similar pore structures and gas diffusion characteristics. The apparatus and method described in this invention are also applicable to the oxygen diffusion coefficient testing of the above-mentioned cement-based materials. The testing principle and implementation method are the same as those for concrete specimens and will not be repeated here.

[0054] Example 3: In this embodiment, an airtight rubber specimen is used instead of a concrete specimen, and the test is conducted according to the method described in Embodiment 2 to verify the airtightness of the device.

[0055] A rubber specimen with a diameter of 100 mm and a thickness of 18 mm was selected. This rubber specimen has air-impermeable properties, preventing oxygen from diffusing through its internal pores. The test was conducted according to steps S1 to S6 of Example 2, and the changes in oxygen concentration in the upstream chamber 12 and the downstream chamber 22 were recorded.

[0056] Within 15 minutes of the start of the test, the oxygen concentration in downstream chamber 22 remained stable at 0.03%, while the oxygen concentration in upstream chamber 12 remained stable at 99.50%. Since the rubber specimen is impermeable, theoretically, oxygen cannot diffuse from upstream to downstream, and the downstream oxygen concentration should remain constant. The actual test results were consistent with the theoretical expectation, proving that the device has good airtightness and no gas leakage. This embodiment verifies that the device of the present invention has good sealing performance. When the specimen is made of a permeable material, the change in downstream oxygen concentration during the test is entirely caused by the diffusion of oxygen through the specimen, rather than by leakage from the device itself.

[0057] Example 4: This embodiment studies the change of water saturation of concrete specimens over time through experiments, as well as the influence of water saturation on the oxygen diffusion coefficient, thereby determining a reasonable test duration and clarifying the design principle of the short-time test window of this invention.

[0058] Concrete specimens with a water-cement ratio of 0.40 were molded and cured for 28 days under standard conditions. These specimens were then cut into standard specimens with a diameter of 100 mm and a thickness of 16.5 mm. The concrete specimens were placed in a vacuum saturation chamber for saturation until surface-dry. They were then placed in a standard laboratory under specific conditions, and the mass of the specimens was measured at multiple time points. The water saturation was calculated based on the mass of the dried specimens. The experimental data are shown in Table 1.

[0059] Table 1. Water saturation test data of concrete specimens

[0060] As shown in Table 1, under standard laboratory conditions, the water inside the concrete specimen continued to evaporate, and the water saturation decreased significantly over time, specifically by 2.1% in 1 hour, nearly 20% in 24 hours, and more than 36% in 72 hours.

[0061] Using the apparatus and testing method of this invention, a concrete specimen in a humidity simulation chamber containing a supersaturated potassium chloride solution was tested. The water saturation of the concrete specimen was 85%, and the oxygen diffusion coefficient was measured to be 9.25 × 10⁻⁶. -8 m² / s; A concrete specimen in a distilled water humidity simulation chamber was selected for testing. The water saturation of the concrete specimen was 100%, and the oxygen diffusion coefficient was measured to be 8.16 × 10⁻⁶ m² / s. - ¹ 0 m² / s. This indicates that a 15% decrease in water saturation leads to a nearly two-order-of-magnitude increase in the oxygen diffusion coefficient, demonstrating the extreme sensitivity of concrete materials to humidity changes. Combined with the aforementioned trend of water saturation changes in concrete specimens under standard laboratory conditions over time—a 2.1% decrease within 1 hour and a nearly 20% decrease within 24 hours—the oxygen diffusion coefficient test results are significantly affected by changes in water saturation. Therefore, the test duration should be strictly controlled within 1 hour to avoid significant interference from humidity changes in the test results. This invention controls the test duration to 15 minutes, far less than 1 hour, effectively controlling water saturation changes to within 0.5%, thereby effectively eliminating the influence of humidity changes on the test results.

[0062] Example 5: like Figures 4 to 6 As shown, this embodiment uses the device described in Embodiment 1 and the method described in Embodiment 2 to test the oxygen diffusion coefficient of concrete specimens under different humidity conditions, so as to verify that the present invention can effectively distinguish the oxygen diffusion performance under different humidity conditions.

[0063] Concrete specimens with a water-cement ratio of 0.28 were molded and cured for 28 days under standard conditions. These specimens were then cut into standard specimens with a diameter of 100 mm and a thickness of 16.5 mm. The concrete specimens were dried in a 60°C oven to constant weight, and then subjected to isothermal adsorption tests in three environmental simulation chambers with different humidity levels for a period of two years. It should be noted that this embodiment uses a relatively long test period as an example to ensure that the internal humidity of the specimens reaches a stable state of equilibrium with the environment. In practical applications, the equilibrium of the specimens can be adjusted appropriately according to the required accuracy. The three environmental simulation chambers with different humidity levels were a humidity simulation chamber using supersaturated lithium chloride solution, a humidity simulation chamber using supersaturated potassium chloride solution, and a humidity simulation chamber using distilled water. The relative humidity of the supersaturated lithium chloride solution environment simulation chamber was approximately 11%, the relative humidity of the supersaturated potassium chloride solution environment simulation chamber was approximately 85%, and the relative humidity of the distilled water environment simulation chamber was approximately 100%.

[0064] Following the test method described in Example 2, the oxygen diffusion coefficient of the specimens under three humidity conditions was tested, and the results are as follows: Oxygen diffusivity of concrete specimens in a humidity simulation chamber with supersaturated lithium chloride solution for:

[0065] Oxygen diffusivity of concrete specimens in a humidity simulation chamber with supersaturated potassium chloride solution for:

[0066] Oxygen diffusivity of concrete specimens in a distilled water humidity simulation chamber for:

[0067] The test results above show that the oxygen diffusion coefficient of the concrete specimens treated with supersaturated lithium chloride solution and supersaturated potassium chloride solution is around 10. -8 The oxygen diffusion coefficient of the distilled water treated specimens was on the order of magnitude, while that of the specimens treated with distilled water was around 10. - ¹ 0 The latter is nearly two orders of magnitude smaller than the former. This indicates that humidity has a significant impact on the oxygen diffusion performance of concrete materials; the higher the humidity of the specimen, the more difficult oxygen diffusion is; the lower the humidity of the specimen, the easier oxygen diffusion is.

[0068] Based on the variation of water saturation in the concrete specimen over time in Example 4, the oxygen diffusion coefficient test results are extremely sensitive to changes in water saturation. If the existing testing method, which takes several hours, is used, the internal humidity of the specimen will have changed significantly, and the measured diffusion coefficient will not accurately reflect the intrinsic diffusion performance of the material under the target humidity condition.

[0069] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0070] Of course, the present invention is not limited to the above-described embodiments. Those skilled in the art can make equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A device for testing the oxygen diffusion coefficient of concrete, characterized in that, include: An upstream pipe (1) is provided with an upstream sealing plug (11) inside. The upstream sealing plug (11) is configured to define an upstream chamber (12) with a fixed volume together with the upstream pipe (1). An upstream oxygen sensor (13) is provided in the upstream chamber (12). The upstream oxygen sensor (13) is used to detect the oxygen concentration in the upstream chamber (12) in real time. The downstream pipe (2) is provided with a downstream sealing plug (21) inside. The downstream sealing plug (21) is configured to define a downstream chamber (22) with a fixed volume together with the downstream pipe (2). A downstream oxygen sensor (23) is provided in the downstream chamber (22). The downstream oxygen sensor (23) is used to detect the oxygen concentration in the downstream chamber (22) in real time. The length of the upstream pipe (1) is greater than the length of the downstream pipe (2). The clamping mechanism (3) is disposed between the upstream pipe (1) and the downstream pipe (2). The clamping mechanism (3) is used to seal and clamp the concrete specimen to be tested, so that oxygen can only diffuse from the upstream chamber (12) to the downstream chamber (22) through the concrete specimen. The data acquisition and processing unit (4) is connected to the upstream oxygen sensor (13) and the downstream oxygen sensor (23) respectively. The data acquisition and processing unit (4) is configured to calculate the slope of change of oxygen concentration detected by the downstream oxygen sensor (23) within a preset short-time test window, and calculate the oxygen diffusion coefficient of the concrete specimen based on the slope of change. It also includes an upstream inlet valve (14), an upstream outlet valve (15), a downstream inlet valve (24), and a downstream outlet valve (25). The upstream inlet valve (14) and the upstream outlet valve (15) are respectively connected to the upstream chamber (12). The upstream inlet valve (14) is connected to the oxygen supply system. The upstream outlet valve (15) is configured to discharge the original gas in the upstream chamber (12) during the inflation stage. The downstream inlet valve (24) and the downstream outlet valve (25) are respectively connected to the downstream chamber (22). The downstream inlet valve (24) is connected to the nitrogen supply system. The downstream outlet valve (25) is configured to discharge the original gas in the downstream chamber (22) during the inflation stage. The upstream sealing plug (11) includes a first piston (111) and a first push rod (112). The first piston (111) is adapted to the inner diameter of the upstream pipe (1). The first push rod (112) is detachably connected to the first piston (111). The downstream sealing plug (21) includes a second piston (211) and a second push rod. The second piston (211) is adapted to the inner diameter of the downstream pipe (2). The second push rod is detachably connected to the second piston (211).

2. The concrete oxygen diffusion coefficient testing device according to claim 1, characterized in that, The upstream sealing plug (11) is detachably disposed in the upstream pipe (1), and the downstream sealing plug (21) is detachably disposed in the downstream pipe (2).

3. A method for testing the oxygen diffusion coefficient of concrete, characterized in that, The method, applied to the concrete oxygen diffusion coefficient testing device as described in claim 2, comprises: S1: Cut the cement-based material specimen to be tested into a concrete specimen of a preset size, and pre-treat the concrete specimen with humidity until the mass of the concrete specimen is constant. S2: The concrete specimen is clamped between the upstream pipe (1) and the downstream pipe (2) using the clamping mechanism (3); S3: Remove the upstream sealing plug (11) from the upstream chamber (12), remove the downstream sealing plug (21) from the downstream chamber (22), maintain natural ventilation of the upstream chamber (12) and the downstream chamber (22) for a first preset time, and calibrate the upstream oxygen sensor (13) and the downstream oxygen sensor (23); S4: Move the upstream sealing plug (11) to the first initial position of the upstream pipe (1), move the downstream sealing plug (21) to the second initial position of the downstream pipe (2), open the upstream inlet valve (14), the upstream outlet valve (15), the downstream inlet valve (24) and the downstream outlet valve (25), fill the upstream chamber (12) with oxygen, fill the downstream chamber (22) with nitrogen, close the upstream outlet valve (15) when the oxygen concentration in the upstream chamber (12) reaches the upstream preset value, and close the downstream outlet valve (25) when the oxygen concentration in the downstream chamber (22) reaches the downstream preset value. S5: Continuously fill the upstream chamber (12) with oxygen and the downstream chamber (22) with nitrogen. After the upstream sealing plug (11) moves to the first working position, close the upstream air inlet valve (14). After the downstream sealing plug (21) moves to the second working position, close the downstream air inlet valve (24). Fix the upstream sealing plug (11) in the first working position and the downstream sealing plug (21) in the second working position so that the volume of the upstream chamber (12) and the downstream chamber (22) remains fixed. S6: Within the short-time test window, the oxygen concentration detected by the downstream oxygen sensor (23) is collected in real time by the data acquisition and processing unit (4), and the oxygen diffusion coefficient of the concrete specimen is calculated based on the slope of the change of the oxygen concentration detected by the downstream oxygen sensor (23) over time within the short-time test window.

4. The method for testing the oxygen diffusion coefficient of concrete according to claim 3, characterized in that, In S2, before clamping the concrete specimen between the upstream pipe (1) and the downstream pipe (2) using the clamping mechanism (3), the method further includes: uniformly applying glass glue to the side of the concrete specimen.

5. The method for testing the oxygen diffusion coefficient of concrete according to claim 3, characterized in that, In S3, removing the upstream sealing plug (11) from the upstream chamber (12) includes: mounting the first push rod (112) onto the first piston (111) and using the first push rod (112) to remove the first piston (111) from the upstream chamber (12); Removing the downstream sealing plug (21) from the downstream chamber (22) includes: mounting the second push rod onto the second piston (211) and using the second push rod to remove the second piston (211) from the downstream chamber (22).

6. The method for testing the oxygen diffusion coefficient of concrete according to claim 3, characterized in that, In S3, the oxygen concentration in the upstream chamber (12) and the oxygen concentration in the downstream chamber (22) after calibration are consistent with the oxygen concentration in the ambient air.

7. The method for testing the oxygen diffusion coefficient of concrete according to claim 3, characterized in that, In S5, before fixing the upstream sealing plug (11) in the first working position, the method further includes: uniformly applying sealant to the side of the upstream sealing plug (11); before fixing the downstream sealing plug (21) in the second working position, the method further includes: uniformly applying sealant to the side of the downstream sealing plug (21).

8. The method for testing the oxygen diffusion coefficient of concrete according to claim 3, characterized in that, In S6, the oxygen diffusion coefficient of the concrete specimen is calculated based on the slope of the change in oxygen concentration over time within the short-time test window detected by the downstream oxygen sensor (23), including: Obtain the fixed volume of the downstream chamber (22), the thickness of the concrete specimen, and the cross-sectional area of ​​the concrete specimen; Obtain the first oxygen concentration value, the second oxygen concentration value, the third oxygen concentration value and the fourth oxygen concentration value of the upstream chamber (12) corresponding to the three equally divided time interval points within the short-time test window; Obtain the slope of the change in oxygen concentration in the downstream chamber (22) over time within the short-term test window; Calculate the oxygen diffusion coefficient of the concrete specimen.

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