A test apparatus and method for hydrostatic pressure-sulfate coupled corrosion of concrete

Abstract

This invention provides a hydrostatic pressure-sulfate coupled corrosion test device and method for concrete, belonging to the field of concrete durability testing technology. The device includes a water pressure control system and a reaction system. The water pressure control system includes a nitrogen cylinder, a pressure reducing valve, and connecting pipelines. The reaction system includes a high-pressure reactor, a pressure gauge, an inlet valve, and a sealing structure. The pressure reducing valve is installed at the outlet of the nitrogen cylinder and connected to the inlet valve via the connecting pipeline. The pressure gauge is connected to the internal cavity of the reactor, and the sealing structure is located at the reactor opening. The test method includes steps such as device sealing and debugging, specimen loading, coupled loading, periodic liquid replacement, sampling at different ages, and nanoindentation and mass loss testing. This invention can realistically simulate the hydrostatic pressure-sulfate dual degradation environment of concrete in underground and underwater engineering projects. The test boundary conditions are controllable, the pressure holding is stable, and the long-term reliability is high. It can comprehensively reveal the material degradation law by combining micromechanical characterization, and the test results are highly consistent with engineering practice.

Description

Technical Field

[0001] This invention relates to the field of concrete durability testing technology, and in particular to a concrete hydrostatic pressure-sulfate coupled erosion test apparatus and method. Background Technology

[0002] Concrete, as a primary building material, is widely used in important infrastructure projects such as underground engineering and marine engineering. It is subject to long-term corrosion by sulfate ions. Sulfate ions penetrate into the interior of concrete through penetration and diffusion, generating expansive products such as ettringite and gypsum. This leads to concrete expansion and cracking, strength reduction, and peeling of the protective layer, significantly reducing the safety and durability of the structure.

[0003] In the aforementioned engineering environments, concrete structures are typically subjected to the combined effects of high hydrostatic pressure and sulfate attack. High hydrostatic pressure not only acts as an external load but also serves as a key driving force for ion transport, altering the pore structure of concrete, accelerating the development of microcracks, and thus significantly increasing the penetration and diffusion rate and degree of sulfate ion attack, exacerbating material degradation. Compared to atmospheric pressure environments, the degradation mechanism, ion transport behavior, and performance decline patterns of concrete under high hydrostatic pressure exhibit significant differences. Therefore, studying the impact of high hydrostatic pressure on sulfate diffusion and transport and the material degradation process is of great significance for evaluating the durability of underwater and underground concrete structures and developing effective protective measures.

[0004] However, current research largely focuses on the degradation of concrete performance under sulfate attack or single loads, with insufficient understanding of the evolution mechanism of sulfate attack driven by high hydrostatic pressure. Furthermore, existing experimental setups struggle to achieve long-term stable operation under the coupled environment of high hydrostatic pressure and sulfate attack, failing to quantitatively reveal the intrinsic relationship between ion transport and material degradation in the coupled field. This makes it difficult to directly apply research findings to the durability assessment of concrete structures under high hydrostatic pressure. Therefore, developing experimental devices and corresponding methods capable of simulating the coupled environment of high hydrostatic pressure and sulfate attack has become a pressing technical problem in this field. Summary of the Invention

[0005] This invention provides a concrete hydrostatic pressure-sulfate coupled corrosion test device and method, which is used to achieve dual-factor coupled control of water pressure and sulfate concentration, and supports long-cycle, high-precision, and repeatable durability tests.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a concrete hydrostatic pressure-sulfate coupled erosion test device, characterized in that it includes a water pressure control system and a reaction system; The water pressure control system is used to provide and stably set the water pressure for the reaction system. The water pressure control system includes a nitrogen cylinder, a pressure reducing valve, and connecting pipelines. The reaction system is used to contain concrete specimens and corrosive solutions and withstand water pressure. The reaction system includes a high-pressure reactor, a pressure gauge, an air inlet valve, and a sealing structure. The pressure reducing valve is installed at the outlet of the nitrogen cylinder, and the outlet of the nitrogen cylinder is connected to one end of the connecting pipe through the pressure reducing valve; the other end of the connecting pipe is connected to the inlet valve on the high-pressure reactor; the pressure gauge is connected to the internal cavity of the high-pressure reactor for monitoring the internal pressure of the high-pressure reactor; the sealing structure is set at the opening of the high-pressure reactor for sealing the reactor lid and the reactor body.

[0007] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled corrosion test device, the high-pressure reactor is also equipped with a pressure relief valve to release the internal pressure of the high-pressure reactor.

[0008] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled erosion test device, the high-pressure reactor adopts a strong end-face sealing structure and is equipped with sealing screws.

[0009] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled erosion test device, the water pressure control system is used to stably output multiple levels of constant water pressure to compare the effects of different water pressures on sulfate erosion.

[0010] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled erosion test device, the high-pressure reactor is used to load sodium sulfate solution with multiple mass fractions and to achieve non-destructive liquid replacement every preset number of days to maintain a stable concentration.

[0011] Secondly, the present invention provides a method for testing the coupled hydrostatic pressure and sulfate attack on concrete, based on the apparatus described above, comprising the following steps: The water pressure control system pressurizes the reaction system to the detection pressure and maintains the pressure for a predetermined time. If there is no pressure drop, the seal is deemed qualified. The concrete specimen was placed into the high-pressure reactor after it was sealed and qualified, sodium sulfate solution was injected, and the reactor body was sealed by the sealing structure. The nitrogen cylinder is pressurized to the set water pressure, the air inlet valve is closed and the pressure is maintained to carry out the coupled erosion test, and the erosion solution is replaced every preset number of days. Concrete specimens with the same mix proportions were placed in an atmospheric pressure immersion environment and simultaneously etched in sodium sulfate solution of the same temperature and concentration as a control group. When the erosion age is within the first preset age range, sampling and testing shall be conducted according to the first sampling cycle; when the erosion age is within the second preset age range, sampling and testing shall be conducted according to the second sampling cycle. The rate of change of mass and elastic modulus of the test specimen are used to evaluate the degree of material degradation.

[0012] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled erosion test method, the test shall be stopped when one of the following conditions occurs: the mass loss rate of the specimen reaches a preset threshold; the elastic modulus of the specimen decreases to a preset percentage of the initial value; or the specified erosion test cycle is reached.

[0013] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled erosion test method, the test process of the mass change rate includes: after reaching the set sampling age, taking out the specimen, wiping off the surface scum and solution, weighing the mass, and calculating the mass change rate by dividing the difference between the mass after the test and the initial mass by the initial mass and then multiplying by 100%.

[0014] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled erosion test method, the elastic modulus is tested using a nanoindentation tester. Before the test, the sample is cut, hydration is terminated, inlaid, ground and polished in sequence. During the test, the test points are arranged in a lattice, and the average value of the effective data range is taken as the elastic modulus result.

[0015] Preferably, in the above-mentioned concrete hydrostatic pressure-sulfate coupled corrosion test method, the process for determining whether the seal is qualified includes: after pressurizing to the test pressure, closing the air inlet valve; if the pressure gauge reading does not drop within the predetermined pressure holding time, the seal is deemed qualified; otherwise, the sealing structure is retightened until the pressure holding requirement is met.

[0016] The concrete hydrostatic pressure-sulfate coupled corrosion test apparatus and method provided by this invention have at least the following beneficial effects: 1. The concrete hydrostatic sulfate coupled erosion test device provided by the present invention sets up a water pressure control system and a reaction system. The water pressure control system includes a nitrogen cylinder, a pressure reducing valve and connecting pipelines. The reaction system includes a high-pressure reactor, a pressure gauge, an inlet valve and a sealing structure. The pressure reducing valve is installed at the outlet of the nitrogen cylinder. The two ends of the connecting pipeline are connected to the pressure reducing valve and the inlet valve respectively. The pressure gauge is connected to the internal cavity of the high-pressure reactor. The sealing structure is set at the reactor mouth to seal the connection between the reactor lid and the reactor body. Thus, the device realistically reproduces the water pressure and sulfate coupled erosion environment faced by concrete structures in engineering, significantly improving the simulation degree of the test and the reliability of the test results.

[0017] 2. The device of this invention achieves stable and reliable pressure output of the water pressure control system by installing a pressure relief valve on the high-pressure reactor and adopting a strong end-face sealing structure with sealing screws. Specifically, the device can maintain pressure for tens of hours at several megapascals without pressure drop, thus making it suitable for long-term tests lasting hundreds of days or more.

[0018] 3. The high-pressure reactor of the present invention can be filled with sodium sulfate solution of multiple mass fractions and can perform non-destructive liquid replacement every preset number of days to maintain the stability of the corrosion solution concentration, avoiding the adverse effects of concentration drop on the test results and ensuring the concentration controllability of long-term coupled corrosion test.

[0019] 4. The test method provided by this invention sets up a normal pressure immersion control group for synchronous erosion after the coupled erosion loading step, and takes samples according to the first sampling cycle when the erosion age is within the first preset age range, and takes samples according to the second sampling cycle when the erosion age is within the second preset age range, thereby distinguishing the latent expansion period and the significant expansion period, and more accurately depicting the whole process of concrete deterioration.

[0020] 5. The modular and quick-release design of the device of the present invention, combined with the pressure relief function of the pressure relief valve and the repeated opening and closing characteristics of the end face sealing structure, makes the device easy to operate, and the efficiency of liquid replacement and sampling is higher, which is conducive to carrying out comparative tests under multiple batches and multiple water pressure conditions. Attached Figure Description

[0021] Figure 1 A structural diagram of a concrete hydrostatic pressure-sulfate coupled erosion test device provided in an embodiment of the present invention; Figure 2 A flowchart of a concrete hydrostatic pressure-sulfate coupled erosion test method provided in an embodiment of the present invention; Figure 3 This is a graph showing the change of nanoindentation elastic modulus with age under 0MPa water pressure, provided in an embodiment of the present invention. Figure 4 A graph showing the change of nanoindentation elastic modulus with age under 1.2 MPa water pressure, provided for an embodiment of the present invention; Figure 5 A graph showing the change of nanoindentation elastic modulus with age under 2.4 MPa water pressure provided in an embodiment of the present invention; Figure 6 The graph shows the rate of change of concrete mass under different water pressures during 420 days of erosion, as provided in this embodiment of the invention.

[0022] Explanation of reference numerals in the attached figures: 10. Water pressure control system; 101. Nitrogen cylinder; 102. Pressure reducing valve; 103. Connecting pipeline; 20. Reaction system; 201. High-pressure reactor; 202. Pressure gauge; 203. Air inlet valve; 204. Sealing structure; 205. Pressure relief valve.

[0023] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0024] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0025] It should be noted that in the embodiments of the present invention, certain software, components, models and other existing solutions in the industry may be mentioned. These should be regarded as exemplary and are only intended to illustrate the feasibility of implementing the technical solution of the present invention. However, they do not mean that the inventor has used or necessarily used the solution.

[0026] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0027] Example 1: This invention provides a concrete hydrostatic pressure-sulfate coupled corrosion test apparatus, comprising a water pressure control system 10 and a reaction system 20. The water pressure control system 10 provides and stably sets the water pressure for the reaction system 20, and includes a nitrogen cylinder 101, a pressure reducing valve 102, and a connecting pipeline 103. The reaction system 20 contains the concrete specimen and the corrosion solution and withstands the water pressure, and includes a high-pressure reactor 201, a pressure gauge 202, an air inlet valve 203, and a sealing structure 20. 4; The pressure reducing valve 102 is installed at the outlet of the nitrogen cylinder 101, and the outlet of the nitrogen cylinder 101 is connected to one end of the connecting pipe 103 through the pressure reducing valve 102; the other end of the connecting pipe 103 is connected to the inlet valve 203 on the high-pressure reactor 201; the pressure gauge 202 is connected to the internal cavity of the high-pressure reactor 201 and is used to monitor the pressure inside the high-pressure reactor 201; the sealing structure 204 is set at the mouth of the high-pressure reactor 201 and is used to seal the lid of the high-pressure reactor 201 to the reactor body.

[0028] In operation, the device first places the concrete specimen into the internal cavity of the high-pressure reactor 201, and injects an etching solution into the reactor. Then, the reactor lid and body are sealed together via a sealing structure 204. Next, the nitrogen cylinder 101 is opened, and high-pressure nitrogen flows out from its outlet, passing through a pressure reducing valve 102, which adjusts the nitrogen pressure to the required water pressure. The adjusted high-pressure gas is then transported through a connecting pipe 103 to an inlet valve 203, and enters the internal cavity of the high-pressure reactor 201, applying pressure to the etching solution. A pressure gauge 202 is connected to the internal cavity of the high-pressure reactor 201 to monitor the pressure in real time. Once the pressure reaches the set water pressure, the inlet valve 203 is closed to maintain a constant internal pressure. Through this process, the device provides a coupled etching environment for the concrete specimen, where a set water pressure and the etching solution work together.

[0029] The device achieves precise regulation and stable maintenance of water pressure through the cooperation of nitrogen cylinder 101, pressure reducing valve 102, connecting pipeline 103 and air inlet valve 203; real-time monitoring by pressure gauge 202 ensures the controllability of water pressure; and reliable sealing of high-pressure reactor 201 by sealing structure 204 prevents solution leakage under high pressure, thereby ensuring stable operation of long-term coupled erosion test.

[0030] For example, when conducting a hydrostatic pressure-sulfate coupled corrosion test on concrete using the above-described apparatus, the following steps are included: The surface of the standard-cured concrete specimen is wiped clean, and its initial mass is weighed and recorded. Then, the sealing structure 204 of the high-pressure reactor 201 is opened, and the concrete specimen is smoothly placed into the internal cavity of the high-pressure reactor 201. Sodium sulfate solution is injected into the high-pressure reactor 201, ensuring that most of the specimen is submerged in the solution. Next, the lid of the high-pressure reactor 201 is sealed to the reactor body using the sealing structure 204. The outlet valve, pressure reducing valve 102, connecting pipe 103, and inlet valve 203 of the nitrogen cylinder 101 are checked for proper connection. The outlet of the nitrogen cylinder 101 is slowly opened, and the pressure reducing valve 102 is adjusted to the target water pressure value. High-pressure gas enters the internal cavity of the high-pressure reactor 201 through the connecting pipe 103 and the inlet valve 203. Observe pressure gauge 202. Once the pressure gauge reading reaches the set water pressure, close the air inlet valve 203 to maintain a constant internal pressure in the high-pressure reactor 201. During the pressure holding process, the etching solution can be replaced every certain number of days according to the test requirements: first, release the internal pressure of the high-pressure reactor 201 through the pressure relief device, open the sealing structure 204, remove the old solution and inject fresh sodium sulfate solution, then reseal and pressurize to the set water pressure. During the test, periodically remove the specimens according to the preset age to test their performance indicators such as the rate of change of mass and elastic modulus.

[0031] The above exemplary embodiments are only for illustrating the specific use of the device. In actual operation, parameters such as specimen size, solution concentration, water pressure, liquid replacement cycle and test age can be adjusted according to the test requirements.

[0032] In some embodiments, the high-pressure reactor 201 is also equipped with a pressure relief valve 205 for releasing the internal pressure of the high-pressure reactor 201. When it is necessary to replace the corrosive solution or remove the concrete specimen, the pressure relief valve 205 can be opened first to safely release the internal pressure of the high-pressure reactor 201 to atmospheric pressure, avoiding the safety hazards caused by directly opening the sealing structure 204 under high pressure. After the test, the pressure relief valve 205 can quickly remove the residual pressure inside the reactor, facilitating subsequent operations. In addition, when the pressure gauge 202 detects that the internal pressure of the high-pressure reactor 201 has abnormally increased beyond the safe range, the pressure relief valve 205 can be used to actively release the pressure, preventing equipment damage or safety accidents caused by overpressure, thereby improving the overall safety and ease of operation of the device.

[0033] In some embodiments, the high-pressure reactor 201 employs a strong end-face sealing structure 204 and is equipped with sealing screws. Through the cooperation of the strong end-face sealing structure 204 and the sealing screws, the contact surfaces between the reactor lid and the reactor body remain tightly fitted when the reactor 201 is subjected to high water pressure, preventing gas or liquid leakage along the reactor opening and thus maintaining long-term stability of the internal pressure. The sealing screws provide uniform and adjustable clamping force, facilitating adjustment of the sealing degree according to actual pressure requirements and enhancing sealing reliability. Simultaneously, through the above design, the sealing structure 204 is easy to open and close repeatedly. When periodically changing the corrosive solution or taking samples, simply loosening the sealing screws allows the reactor body to be opened, and tightening them again after the operation restores the seal, balancing the reliability of long-term pressure maintenance with the convenience of daily maintenance.

[0034] In some embodiments, the water pressure control system 10 is used to stably output multiple levels of constant water pressure to compare the effects of different water pressures on sulfate corrosion. Specifically, through the cooperation of the nitrogen cylinder 101, pressure reducing valve 102, and connecting pipeline 103 in the water pressure control system 10, the water pressure in the high-pressure reactor 201 can be set to multiple different constant pressure values, such as low water pressure, medium water pressure, and high water pressure, thereby enabling multiple sets of comparative tests to be conducted within the same experimental framework. By comparing the differences in performance indicators such as the mass change rate and elastic modulus of concrete specimens under different water pressure conditions, the influence of water pressure on the sulfate ion corrosion rate and the degree of material degradation can be quantitatively revealed. In addition, the multi-level water pressure output capability allows the device to simulate the hydrostatic pressure of different water depth environments, providing more comprehensive experimental data support for the durability assessment of concrete in different application scenarios such as underground engineering and marine engineering.

[0035] In some embodiments, the high-pressure reactor 201 is used to load sodium sulfate solution with multiple mass fractions and to achieve non-destructive liquid replacement every preset number of days to maintain stable concentration.

[0036] This embodiment uses a high-pressure reactor 201 to fill sodium sulfate solutions of different mass fractions, such as low, medium and high concentrations, to simulate the diversity of sulfate concentrations in actual engineering environments. This allows for comparative analysis of the effects of different sulfate concentrations on the degree of concrete deterioration under the same experimental setup, revealing the coupling effect between concentration and hydrostatic pressure factors.

[0037] Achieving non-destructive solution replacement every preset number of days means replacing the etching solution without damaging the concrete specimen or disrupting the sealing structure 204 of the high-pressure reactor 201, while ensuring the complete drainage of the old solution before injecting fresh sodium sulfate solution. This design avoids concentration drops due to sulfate ion consumption or solution deterioration during long-term testing, thus maintaining the long-term stability of the etching solution concentration and ensuring the controllability of experimental conditions and the repeatability of experimental results.

[0038] In addition, regular non-destructive fluid replacement can promptly remove loose products generated on the surface of concrete specimens due to the erosion reaction, preventing these products from hindering the contact between fresh solution and the specimen surface, making the erosion process closer to the continuous penetration and diffusion state in engineering practice, thereby improving the simulation degree of the test.

[0039] Example 2: This invention provides a method for testing the coupled hydrostatic pressure and sulfate attack on concrete, based on the apparatus in any of the embodiments in Example 1, such as... Figure 2 As shown, the concrete hydrostatic pressure-sulfate coupled erosion test method includes the following steps S10-S60.

[0040] S10: Pressurize the reaction system 20 to the detection pressure through the water pressure control system 10 and maintain the pressure for a predetermined time. If there is no pressure drop, the seal is deemed qualified.

[0041] This embodiment effectively verifies the airtightness of the high-pressure reactor 201 and the sealing structure 204 by applying a test pressure to the reaction system 20 in advance and maintaining it for a predetermined time. This avoids pressure leakage during long-term coupled erosion tests and ensures that subsequent tests are conducted under stable and controllable pressure conditions.

[0042] For example, tighten the sealing structure 204 of the high-pressure reactor 201, close the inlet valve 203, open the nitrogen cylinder 101, adjust the pressure reducing valve 102 to the detection pressure of 5MPa, maintain the pressure for 72 hours, and observe that the reading of the pressure gauge 202 does not drop, then the seal is deemed qualified.

[0043] S20: Place the concrete specimen into the sealed high-pressure reactor 201, inject sodium sulfate solution, and seal the reactor body through the sealing structure 204.

[0044] In this embodiment, the concrete specimen can be completely immersed in the corrosive solution through the operation of step S20 above. At the same time, the sealing structure 204 is used to seal the vessel, providing a sealed environment for subsequent application of hydrostatic pressure and ensuring that the solution will not leak under high pressure.

[0045] For example, open the sealing structure 204, place the standard cured concrete specimen smoothly into the internal cavity of the high-pressure reactor 201, inject a 5% sodium sulfate solution until the liquid level is above the upper surface of the specimen, reposition the sealing structure 204 and tighten the sealing screws.

[0046] S30: Pressurize the nitrogen cylinder 101 to the set water pressure, close the air inlet valve 203 and maintain the pressure to carry out the coupled erosion test, and replace the erosion solution every preset number of days.

[0047] In this embodiment, high-pressure gas supplied by nitrogen cylinder 101 is regulated by pressure reducing valve 102 before entering the high-pressure reactor 201 to apply a constant hydrostatic pressure to the solution. Long-term pressure maintenance is achieved by closing the inlet valve 203. Regularly replacing the etching solution maintains a stable sulfate ion concentration, preventing a decrease in concentration due to ion consumption, thus ensuring the controllability and repeatability of the experimental conditions.

[0048] For example, the pressure reducing valve 102 is slowly adjusted to pressurize the high-pressure reactor 201 to a set water pressure of 2.4 MPa through the nitrogen cylinder 101. The air inlet valve 203 is then closed, and pressure-holding coupling erosion begins. The sodium sulfate solution is replaced every 15 days. When replacing the solution, the pressure relief valve 205 is opened to release the internal pressure, the sealing structure 204 is opened, the old solution is poured out, and fresh sodium sulfate solution of the same concentration and volume is injected. Then the reactor is resealed and pressurized to the set water pressure.

[0049] S40: Concrete specimens with the same mix proportions were placed in an atmospheric pressure immersion environment and simultaneously etched in sodium sulfate solution of the same temperature and concentration as a control group.

[0050] This embodiment, through the setting of the above step S40, allows for the absence of hydrostatic pressure under the same temperature and solution concentration conditions, forming a comparison with the pressurized group. This facilitates the elimination of interference from environmental factors and reveals the effect of hydrostatic pressure on the sulfate erosion process independently.

[0051] For example, concrete specimens with the same mix proportion and size are placed in a sealed plastic box, injected with a 5% sodium sulfate solution, and placed in a constant temperature curing room similar to the high-pressure reactor 201 for immersion at normal pressure. The solution is replaced synchronously every 15 days.

[0052] S50: When the erosion age is within the first preset age range, sampling and testing shall be conducted according to the first sampling cycle; when the erosion age is within the second preset age range, sampling and testing shall be conducted according to the second sampling cycle.

[0053] Based on the different degradation rates during the latent expansion phase and the significant expansion phase in the sulfate corrosion process, this embodiment uses a longer sampling interval during the slow degradation phase and a shorter sampling interval during the accelerated degradation phase, thereby accurately capturing the turning point changes in material properties and completely depicting the entire degradation process.

[0054] For example, during the latent expansion period (0 to 240 days of erosion age), samples were taken and tested every 60 days; during the significant expansion period (more than 240 days of erosion age), samples were taken and tested every 30 days. At each sampling, specimens were taken from both the pressurized group and the control group for testing.

[0055] S60: Test the mass change rate and elastic modulus of the specimen to evaluate the degree of material degradation.

[0056] This embodiment reflects the combined effect of material spalling and expansion products by measuring the mass change of the specimen before and after erosion, and reflects the decrease in material stiffness by testing the elastic modulus through nanoindentation method. Thus, it quantitatively evaluates the degree of deterioration of concrete under hydrostatic pressure-sulfate coupling from two dimensions: macroscopic mass and microscopic mechanical properties.

[0057] For example, after reaching the set sampling age, the specimen is removed, and the surface scum and solution are gently wiped away with a damp cloth. The mass is measured under constant temperature and humidity conditions, and the mass change rate is calculated by dividing the difference between the post-test mass and the initial mass by the initial mass and then multiplying by 100%. The specimen is cut into small pieces, immersed in isopropanol solution to terminate hydration, embedded in resin molding, and successively polished with sandpaper of different grits and diamond suspension. A nanoindentation tester is used to test the specimen in a load-hold-unload manner, with measuring points arranged in a lattice. The average value of the effective data interval is taken as the elastic modulus result.

[0058] In some embodiments, the test is stopped when one of the following occurs: the mass loss rate of the specimen reaches a preset threshold; the elastic modulus of the specimen decreases to a preset percentage of the initial value; or the specified erosion test cycle is reached.

[0059] This embodiment uses a preset threshold for mass loss rate as a stopping condition, enabling timely termination of the test when macroscopic spalling or expansion cracking of concrete specimens reaches a significant level. This avoids the inability to obtain effective degradation endpoint data after complete specimen failure and provides a unified termination criterion for tests under different water pressure or concentration conditions. By setting a preset percentage decrease in elastic modulus to its initial value as a stopping condition, the failure state of concrete can be defined from the perspective of material mechanical property degradation. The test stops when the elastic modulus decreases to an insufficient level to withstand the design load. This indicator is directly related to structural safety, making the test endpoint more meaningful in engineering practice. By setting a specified erosion test period as a stopping condition, all test groups have a unified test endpoint at the longest preset time point, facilitating horizontal comparison of test results under different water pressure, concentration, and other variable conditions. It also avoids indefinitely extending the test due to individual specimens failing to reach the first two thresholds. The test can be stopped if any one of the above three stopping conditions is met, considering both the objective physical indicators of material failure and the time constraints of the test period, making the test termination rules more flexible, scientific, and operable.

[0060] In some embodiments, the test process for the rate of change of mass includes: after reaching the set sampling age, taking out the specimen, wiping away the surface scum and solution, weighing the mass, and calculating the rate of change of mass by dividing the difference between the mass after the test and the initial mass by the initial mass and then multiplying by 100%.

[0061] This embodiment eliminates the interference of loose corrosion products and residual solution adhering to the specimen surface on the mass measurement by wiping away surface scum and solution before weighing, making the measured post-test mass more accurately reflect the net mass change of the specimen material during the corrosion process. The calculation method of dividing the difference between the post-test mass and the initial mass by the initial mass and then multiplying by 100% can eliminate individual differences in the initial size and mass of the specimens, making the mass loss rate between different specimens comparable. This facilitates the quantitative evaluation of the influence of factors such as hydrostatic pressure, sulfate concentration, and corrosion age on the degree of concrete deterioration. At the same time, this test process is simple to operate, highly repeatable, and suitable for long-term multi-age sampling tests, providing reliable data support for plotting the mass change rate evolution curve with age.

[0062] In some embodiments, the elastic modulus is tested using a nanoindentation tester. Before the test, the sample is cut, hydrated, inlaid, ground, and polished in sequence. During the test, the test points are arranged in a lattice, and the average value of the effective data range is taken as the elastic modulus result.

[0063] This embodiment achieves a smooth, clean test sample with a stopped hydration reaction by cutting, terminating hydration, embedding, grinding, and polishing the sample. This meets the requirements of the nanoindentation tester for surface roughness and internal hydration state, ensuring the accuracy and repeatability of the elastic modulus test. The hydration termination treatment prevents the sample from undergoing further hydration reactions during test preparation, thus avoiding changes in the microstructure and ensuring that the measured elastic modulus truly reflects the mechanical properties of the sample at the time of sampling. The test points are arranged in a lattice pattern to cover multiple representative areas of the sample surface, avoiding measurement deviations caused by local defects or inhomogeneities. Taking the average value of the effective data range as the elastic modulus result eliminates abnormal data points caused by microcracks, pores, or impurities, making the final result more objective and reliable. This provides an accurate quantitative basis for evaluating the degradation of the micromechanical properties of concrete under hydrostatic pressure-sulfate coupled erosion.

[0064] In some embodiments, the process for determining whether a seal is qualified includes: pressurizing to the detection pressure and then closing the intake valve 203; if the pressure gauge 202 reading does not drop within a predetermined pressure holding time, the seal is deemed qualified; otherwise, the sealing structure 204 is tightened again until the pressure holding requirement is met.

[0065] This embodiment, by pressurizing and then closing the inlet valve 203 and observing whether the pressure gauge 202 reading drops within a predetermined time, can directly and quantitatively verify the airtightness of the high-pressure reactor 201 and the sealing structure 204, avoiding the uncertainty caused by subjective judgment. Using no pressure drop within the predetermined pressure holding time as the pass standard provides a quantifiable technical indicator for sealing performance, ensuring that no pressure leakage occurs during subsequent long-term coupled erosion tests, thereby guaranteeing the stability of test conditions and the validity of test results. When a failure is determined, by retightening the sealing structure 204 and conducting another pressure test, the sealing fault can be quickly eliminated without replacing the entire equipment, improving the efficiency of the test device. Simultaneously, it ensures that the sealing condition meets the requirements before each test, enhancing the repeatability and reliability of the test.

[0066] Example 3: Based on specific experimental data, this invention provides a specific implementation method for a concrete hydrostatic pressure-sulfate coupled erosion test, which includes the following steps 1 to 6.

[0067] Step 1: Prepare standard concrete specimens, cure them according to standard conditions to the specified age, and then remove and air dry them for later use. The specimen dimensions should be made into suitable block-shaped specimens based on the space of the reactor. Curing conditions: temperature 20±2℃, relative humidity ≥95%. Before immersion in the test, wipe the specimens clean, weigh them initially, and record the results.

[0068] Step 2: Check that the reactor gasket, pipelines, and valves are intact; close the reactor inlet valve and tighten the reactor body sealing screws to ensure the reactor body is completely sealed; open the nitrogen cylinder main valve and adjust the pressure reducing valve to stabilize the output pressure at 5MPa; close the nitrogen cylinder outlet valve and maintain the pressure for 72 hours; observe the pressure gauge: if the pressure does not drop significantly, the seal is considered qualified; if the pressure drops, check the seals and retighten them until the pressure holding requirements are met.

[0069] Step 3: Place the concrete specimen steadily into the high-pressure reactor; inject sulfate solution into the reactor to ensure that most of the specimen is submerged; wipe the sealing surface of the reactor mouth, tighten the upper sealing screw, and ensure that the reactor body is completely sealed.

[0070] In this embodiment, the injected sulfate solution is 800 mL of a 5% sodium sulfate solution.

[0071] Step 4: Connect the nitrogen cylinder, pressure reducing valve, and gas inlet of the reactor; slowly open the pressure reducing valve and gradually increase the pressure to the set water pressure value; after the pressure stabilizes, close the gas inlet valve to enter the constant pressure erosion stage; the test is conducted in a constant temperature environment to ensure temperature stability; open the reactor every 15 days to replace the sodium sulfate solution to maintain a stable erosion concentration.

[0072] In this embodiment, the set water pressure values ​​are 0MPa, 1.2MPa and 2.4MPa.

[0073] Step 5: Set up the same mix ratio and the same number of test pieces, immerse them in a sealed plastic box containing sulfate solution, and place them in the same constant temperature curing room as the pressure group for synchronous etching.

[0074] Step 6: Based on the characteristics of the latent expansion period and the significant expansion period of sulfate erosion, perform the following tests: latent expansion period (0-240 days): sample and test once every 60 days; significant expansion period (after 240 days): sample and test once every 30 days; test items include but are not limited to mass change and nanoindentation elastic modulus.

[0075] Mass loss test. After the set time is reached, the specimen is removed and the surface scum and solution are gently wiped away with a damp cloth; the specimen mass is weighed under constant temperature and humidity conditions; the mass change rate is calculated according to the formula: mass change rate = (sample mass after test - initial sample mass) / initial sample mass × 100%; the average value of 3 specimens in the same water pressure group is taken as the test result for this age.

[0076] Nanoindentation testing. Before nanoindentation testing, the sample was cut into small blocks, immersed in isopropanol solution to terminate hydration, embedded in quick-setting resin, and then polished sequentially with sandpaper of different grits, followed by polishing with diamond suspensions of different particle sizes to ensure the sample surface met the testing requirements. A nanoindentation testing instrument was used, employing a conventional load-hold-unload method. Measurement points were arranged in a lattice on the sample surface to avoid mutual interference between measurement points. After testing, outlier data was discarded, and box plot statistical processing was used. The average value of the data within the valid interval was taken as the elastic modulus result.

[0077] The experimental results obtained through steps 1 to 6 above are as follows: Figures 3-6 As shown. By Figure 3 , Figure 4 and Figure 5 It can be seen that the elastic modulus increases slightly in the early stage and decreases significantly in the later stage. When the erosion time is 420 days, the elastic modulus of the 0 MPa, 1.2 MPa, and 2.4 MPa water pressure groups decreased by 56.18%, 61.68%, and 71.82%, respectively. Figure 6 It can be seen that the mass loss increases with the increase of erosion time. When the erosion time is 420 days, the mass decreases by 5.3% at a water pressure of 0 MPa; and by 6.2% at a water pressure of 1.2 MPa.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A concrete hydrostatic pressure-sulfate coupled erosion test device, characterized in that, Including a water pressure control system and a reaction system; The water pressure control system is used to provide and stably set the water pressure for the reaction system. The water pressure control system includes a nitrogen cylinder, a pressure reducing valve, and connecting pipelines. The reaction system is used to contain concrete specimens and corrosive solutions and withstand water pressure. The reaction system includes a high-pressure reactor, a pressure gauge, an air inlet valve, and a sealing structure. The pressure reducing valve is installed at the outlet of the nitrogen cylinder, and the outlet of the nitrogen cylinder is connected to one end of the connecting pipe through the pressure reducing valve; the other end of the connecting pipe is connected to the inlet valve on the high-pressure reactor; the pressure gauge is connected to the internal cavity of the high-pressure reactor for monitoring the internal pressure of the high-pressure reactor; the sealing structure is set at the opening of the high-pressure reactor for sealing the reactor lid and the reactor body.

2. The concrete hydrostatic pressure-sulfate coupled corrosion test device according to claim 1, characterized in that, The high-pressure reactor is also equipped with a pressure relief valve to release the internal pressure of the high-pressure reactor.

3. The concrete hydrostatic pressure-sulfate coupled erosion test device according to claim 1, characterized in that, The high-pressure reactor adopts a strong end-face sealing structure and is equipped with sealing screws.

4. The concrete hydrostatic pressure-sulfate coupled corrosion test apparatus according to claim 1, characterized in that, The water pressure control system is used to stably output multiple levels of constant water pressure to compare the effects of different water pressures on sulfate corrosion.

5. The concrete hydrostatic pressure-sulfate coupled corrosion test device according to claim 1, characterized in that, The high-pressure reactor is used to load sodium sulfate solutions of multiple mass fractions and to replace the solution without damage every preset number of days to maintain a stable concentration.

6. A method for testing the coupled hydrostatic pressure and sulfate attack on concrete, characterized in that, The apparatus based on any one of claims 1 to 5 includes the following steps: The water pressure control system pressurizes the reaction system to the detection pressure and maintains the pressure for a predetermined time. If there is no pressure drop, the seal is deemed qualified. The concrete specimen was placed into the high-pressure reactor after it was sealed and qualified, sodium sulfate solution was injected, and the reactor body was sealed by the sealing structure. The nitrogen cylinder is pressurized to the set water pressure, the air inlet valve is closed and the pressure is maintained to carry out the coupled erosion test, and the erosion solution is replaced every preset number of days. Concrete specimens with the same mix proportions were placed in an atmospheric pressure immersion environment and simultaneously etched in sodium sulfate solution of the same temperature and concentration as a control group. When the erosion age is within the first preset age range, sampling and testing shall be conducted according to the first sampling cycle; when the erosion age is within the second preset age range, sampling and testing shall be conducted according to the second sampling cycle. The rate of change of mass and elastic modulus of the test specimen are used to evaluate the degree of material degradation.

7. The concrete hydrostatic pressure-sulfate coupled corrosion test method according to claim 6, characterized in that, The test shall be stopped when any of the following conditions occur: the mass loss rate of the specimen reaches the preset threshold; the elastic modulus of the specimen decreases to a preset percentage of the initial value; or the specified corrosion test cycle is reached.

8. The concrete hydrostatic pressure-sulfate coupled corrosion test method according to claim 6, characterized in that, The test process for the mass change rate includes: after reaching the set sampling age, taking out the specimen, wiping away the surface scum and solution, weighing the specimen, and calculating the mass change rate by dividing the difference between the mass after the test and the initial mass by the initial mass and then multiplying by 100%.

9. The concrete hydrostatic pressure-sulfate coupled corrosion test method according to claim 6, characterized in that, The elastic modulus was tested using a nanoindentation tester. Before the test, the sample was cut, hydrated, inlaid, ground and polished in sequence. During the test, the test points were arranged in a lattice and the average value of the effective data range was taken as the elastic modulus result.

10. The concrete hydrostatic pressure-sulfate coupled corrosion test method according to claim 6, characterized in that, The process for determining whether a seal is qualified includes: pressurizing to the detection pressure and then closing the air inlet valve; if the pressure gauge reading does not drop within the predetermined pressure holding time, the seal is deemed qualified; otherwise, the sealing structure is tightened again until the pressure holding requirement is met.

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