A test system and method for corrosion metal-cement interface shear properties

Abstract

This invention discloses an experimental system for assessing the shear properties of a corroded metal-cement interface. The system includes a direct shear testing machine and an in-situ electro-accelerated corrosion device. The direct shear testing machine includes a shear fixing part for fixing the metal-cement sample, a vertical loading part, and a horizontal loading part. The in-situ electro-accelerated corrosion device includes an in-situ electrolytic cell containing an electrolyte, a first electrode located within the in-situ electrolytic cell and in contact with the electrolyte, and a power supply. The in-situ electrolytic cell is mounted on the shear fixing part. The metal-cement sample is placed in the in-situ electrolytic cell, with the cement layer immersed in the electrolyte. The positive terminal of the power supply is connected to the metal layer, and the negative terminal is connected to the first electrode. This invention achieves metal-cement / concrete interface corrosion under in-situ normal load constraints, enabling monitoring of the influence of interface corrosion on normal force or normal displacement. This is more consistent with actual working conditions and facilitates direct monitoring of the interface corrosion process and deformation and failure characteristics.

Description

Technical Field

[0001] This application relates to the technical field of structural engineering, and in particular to a test system and method for the shear properties of the corroded metal-cement interface. Background Technology

[0002] Metal-cement composite structures are a common structural form in underground engineering. While the metal or cement itself possesses good integrity and mechanical properties, the metal-cement interface is a weak point dominated by bonding. Compared to surface structures, underground structures operate in a more complex environment, with groundwater corrosive ions easily leading to metal corrosion. After corrosion, corrosion products accumulate at the metal-cement interface, causing complex changes in interfacial properties. These changes include increased expansion force, decreased chemical bonding, increased friction coefficient due to increased rust products, and weakened mechanical interlocking effects due to reduced metal ribs or roughness. Ultimately, this leads to interfacial shear slip, reduced load-bearing capacity, and structural failure.

[0003] Metal corrosion failure in actual underground engineering is often slow, taking decades. Indoor accelerated corrosion tests can simulate the corrosion and deterioration of metals in actual engineering projects. By combining electrochemical theory, time similarity theory, and mechanical theory, the entire process of structural corrosion and deterioration can be analyzed in a short period of time. This allows for the determination of the relationship between metal corrosion and structural deterioration failure, providing a basis for the design, maintenance, and repair of underground engineering metal-cement / concrete structures.

[0004] Currently, accelerated corrosion tests on underground structures are often conducted on individual components, typically using electrochemical methods to accelerate the corrosion of certain components (such as reinforced concrete segments or mortar anchors), followed by mechanical testing of the corroded samples. This testing method has three main problems: (1) it ignores the influence of normal constraints on metal corrosion and performance degradation; (2) it cannot directly obtain the shear constitutive relationship of the interface; and (3) it is difficult to directly observe interface changes. However, underground engineering structures are constrained by the surrounding rock and soil, and the normal constraint state has a significant impact on interface corrosion and mechanical behavior. Mechanical testing of corroded components reflects the overall mechanical properties of the structure, and the most fundamental shear constitutive relationship of the corroded metal-cement / concrete interface is difficult to clarify. The metal-cement interface of the component is located internally, making it difficult to observe or monitor directly. Therefore, there is currently a lack of effective, simple, and scientific methods and devices for directly testing the shear properties of the corroded metal-cement / concrete interface. Summary of the Invention

[0005] This application provides a test system and method for the shear properties of the corroded metal-cement interface to solve the above-mentioned problems.

[0006] A testing system for the shear properties of a corroded metal-cement interface, the testing system comprising:

[0007] A direct shear testing machine includes a shear fixing part for fixing a metal-cement specimen, a vertical loading part for applying a force perpendicular to the metal-cement interface, and a horizontal loading part for applying a force parallel to the metal-cement interface.

[0008] In-situ electro-accelerated corrosion device, comprising:

[0009] An in-situ electrolytic cell is used to hold an electrolyte; the in-situ electrolytic cell is installed on the shearing and fixing part; the metal-cement sample is placed in the in-situ electrolytic cell, and the cement layer of the metal-cement sample is immersed in the electrolyte;

[0010] The first electrode is located in the in-situ electrolytic cell and is in contact with the electrolyte in the in-situ electrolytic cell;

[0011] A power source, the positive terminal of which is connected to the metal layer of the metal-cement sample, and the negative terminal of which is connected to the first electrode;

[0012] In the shear property test of the corroded metal-cement interface, the first electrode is at least partially immersed in the electrolyte, and the cement layer of the metal-cement sample is immersed in the electrolyte; the vertical loading part applies a constant vertical load to the metal-cement sample through the shear fixing part; then the power supply is turned on, and the positive terminal of the power supply, the metal layer, the cement layer, the electrolyte, the first electrode, and the negative terminal of the power supply form a current loop, and corrosion occurs at the interface of the metal layer near the cement layer; after a set corrosion time, the horizontal loading part applies a horizontal load to the cement layer, and the metal-cement sample undergoes shearing at the interface between the metal layer and the cement layer.

[0013] In some embodiments, the shearing fixing part includes a first fixing member and a second fixing member; the first fixing member and the second fixing member are staggered in the vertical direction; the first fixing member and the second fixing member cooperate to define an accommodating space for fixing the metal-cement sample;

[0014] The metal layer of the metal-cement sample is fitted with the first fixing member, and the vertical loading part corresponds to the first fixing member and is used to apply a vertical load to the first fixing member.

[0015] The in-situ electrolytic cell is installed on the second fixing member, and the horizontal loading part cooperates with the second fixing member to apply a horizontal load to the second fixing member.

[0016] In some embodiments, the first fixing member includes a first fixing plate that mates with the wall surface of the metal layer away from the cement layer; the second fixing member includes a second fixing plate that mates with the wall surface of the cement layer away from the metal layer.

[0017] In some embodiments, a first recess is formed on the first fixing plate, and the first recess engages with the end of the metal layer away from the cement layer;

[0018] A second recess is formed on the second fixing plate, and the second recess cooperates with the in-situ electrolytic cell.

[0019] In some embodiments, the first fixing member includes a first limiting plate connected to the first fixing plate, the first limiting plate being located at one end of the first fixing plate away from the horizontal loading portion and extending downward from the end of the first fixing plate.

[0020] In some embodiments, the first limiting plate is provided with a first limiting groove extending through one end away from the first fixing plate. When the metal-cement sample is installed in the shearing fixing part, the end of the metal layer near the first limiting plate is installed in the first limiting groove.

[0021] In some embodiments, the second fixing member includes a second limiting plate connected to the second fixing plate. The second limiting plate is located at one end of the second fixing plate near the horizontal loading portion and extends upward from the end of the second fixing plate.

[0022] In some embodiments, the surfaces of the shearing and fixing parts are all covered with an anti-corrosion coating; the surfaces of the metal layer, except for the wall surface in contact with the cement layer, are all covered with an anti-corrosion coating.

[0023] In some embodiments, the test system for the shear properties of the corroded metal-cement interface includes a DIC non-contact strain field monitoring system, which is used to monitor the changes in the metal-cement interface and the shear formation failure process.

[0024] In some embodiments, a test method using the above-described test system for the shear properties of the corroded metal-cement interface includes the following steps:

[0025] (1) Sample preparation: Place the metal layer into a detachable mold, apply release oil to the mold, then pour cement slurry into the mold, use a vibration table to remove air bubbles, remove the mold after a predetermined time for standard curing, and spray scattered spots on the sample surface.

[0026] (2) Corrosion of metal-cement interface direct shear test: The metal-cement sample and the in-situ electrolytic cell are installed on the direct shear machine through the shear fixing part, and the cement layer is immersed in the electrolyte of the in-situ electrolytic cell; the vertical loading part applies vertical constraint to carry out electrochemical corrosion; then the horizontal loading part applies horizontal load to carry out shear test, and the amount of corrosion and the average corrosion depth are calculated.

[0027] (3) Combining the three-stage interface shear constitutive model, the average corrosion depth is introduced to establish a shear constitutive model of the corroded metal-cement interface.

[0028] (4) Based on the cohesive interface element, numerical development and shear simulation of the interface element are carried out.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention discloses a test system for the shear properties of a rusted metal-cement interface. The test system includes: a direct shear testing machine and an in-situ electro-accelerated corrosion device. The direct shear testing machine includes a shear fixing part for fixing the metal-cement sample, a vertical loading part for applying a force perpendicular to the metal-cement interface direction, and a horizontal loading part for applying a force parallel to the metal-cement interface direction. The in-situ electro-accelerated corrosion device includes: an in-situ electrolytic cell for holding an electrolyte, a first electrode located within the in-situ electrolytic cell and in contact with the electrolyte, and a power supply. The in-situ electrolytic cell is mounted on the shear fixing part. The metal-cement sample is placed in the in-situ electrolytic cell, with the cement layer of the metal-cement sample immersed in the electrolyte. The positive terminal of the power supply is connected to the metal layer of the metal-cement sample, and its negative terminal is connected to the first electrode. During the shear property test of the rusted metal-cement interface, the first electrode is at least partially immersed in the electrolyte, and the cement layer of the metal-cement sample is immersed in the electrolyte. The vertical loading part applies a constant force to the metal-cement sample through the shear fixing part. A fixed vertical load is applied; then the power is turned on, and a current loop is formed between the positive terminal of the power supply, the metal layer, the cement layer, the electrolyte, the first electrode, and the negative terminal of the power supply. Corrosion occurs at the interface between the metal layer and the cement layer. After a set corrosion time, a horizontal load is applied to the cement layer by the horizontal loading part, and the metal-cement sample undergoes shearing at the interface between the metal layer and the cement layer. The present invention is based on the principle of electrochemical accelerated corrosion and utilizes an existing direct shear testing machine to realize in-situ corrosion of the metal-cement / concrete interface under normal load constraints. This allows for monitoring the influence of interface corrosion on normal force or normal displacement, and further enables direct shear testing of the rusted metal-cement interface. The deformation and failure characteristics of the exposed side of the interface can be directly monitored through the DIC non-contact strain field monitoring system. The test system and method for the shear properties of the rusted metal-cement interface of the present invention conveniently consider the interaction between normal constraints and metal corrosion, and directly realizes the test of the shear properties of the rusted metal-cement interface, facilitating direct monitoring of the interface corrosion process and deformation and failure characteristics.

[0031] The experimental system and testing method for the shear properties of the corroded metal-cement interface of the present invention are conducted in an environment under the combined action of normal constraint and corrosion, which is closer to the actual corrosion environment of underground structures. It can accurately obtain the interaction relationship between normal constraint and metal corrosion, and flexibly and conveniently measure the evolution law of shear properties of metal-cement interfaces with different corrosion levels under different normal constraints, providing more reliable experimental data for the design and maintenance of tunnel engineering. Attached Figure Description

[0032] Figure 1 A schematic diagram of a direct shear testing machine is shown for a test system of shear properties of a corroded metal-cement interface according to some embodiments;

[0033] Figure 2 A schematic diagram of the test system for assessing the shear properties of the corroded metal-cement interface according to some embodiments is shown.

[0034] Figure 3 A structural schematic diagram of the test system for assessing the shear properties of the corroded metal-cement interface according to some embodiments is shown from another perspective.

[0035] Figure 4 An exploded structural diagram of a test system for the shear properties of a rusted metal-cement interface according to some embodiments is shown, including a shear fixation device, a metal-cement sample, and an in-situ electrolytic cell.

[0036] Figure 5 A schematic diagram of the assembly structure of a test system for the shear properties of a corroded metal-cement interface according to some embodiments is shown, comprising a shear fixation device, a metal-cement specimen, and an in-situ electrically accelerated corrosion device.

[0037] Figure 6 A schematic diagram from another perspective of the assembly structure of a test system for the shear properties of the corroded metal-cement interface according to some embodiments, including a shear fixation device, a metal-cement specimen, and an in-situ electrically accelerated corrosion device, is shown.

[0038] Figure 7 A schematic diagram showing the relative positions of the metal-cement specimen and the in-situ electro-accelerated corrosion device in a test system for assessing the shear properties of the corroded metal-cement interface according to some embodiments is provided.

[0039] Figure 8 A schematic diagram of the relative positions of a metal-cement specimen and an in-situ electro-accelerated corrosion device from another perspective is shown in the test system for the shear properties of the rusted metal-cement interface according to some embodiments.

[0040] Figure 9 A schematic diagram of the in-situ electrolytic cell and the first electrode of a system for assessing the shear properties of the corroded metal-cement interface according to some embodiments is shown.

[0041] Figure 10 A schematic diagram of a shear fixing part of a system for the shear properties of a rusted metal-cement interface according to some embodiments is shown.

[0042] Figure 11 Another schematic diagram of the shear fixing part of a system for the shear properties of a rusted metal-cement interface according to some embodiments is shown.

[0043] Figure 12 It shows Figure 11 A three-dimensional structural schematic diagram of the shearing and fixing part shown;

[0044] Figure 13 It shows Figure 11 A three-dimensional structural diagram of the shearing and fixing part from another perspective.

[0045] The numbers in the above attached figures are:

[0046] Direct shear testing machine 1; upper reaction seat 11; lower reaction seat 12; left reaction seat 13; right reaction seat 14; vertical loading part 15; horizontal loading part 16; shear fixing part 3; first fixing member 4; first fixing plate 41; first recess 42; first limiting plate 43; first limiting groove 44; second fixing member 5; second fixing plate 51; second recess 52; second limiting plate 53; second limiting groove 54; in-situ electrolytic cell 20; power supply 21; first electrode 22; second electrode 23; plug-in part 24; metal-cement sample 6; metal layer 61; cement layer 62. Detailed Implementation

[0047] To make the objectives and implementation methods of this application clearer, the exemplary implementation methods of this application will be clearly and completely described below with reference to the accompanying drawings of the exemplary embodiments of this application. Obviously, the exemplary embodiments described are only some embodiments of this application, and not all embodiments.

[0048] It should be noted that the brief descriptions of terms in this application are only for the convenience of understanding the embodiments described below, and are not intended to limit the embodiments of this application. Unless otherwise stated, these terms should be understood in their ordinary and common meaning.

[0049] The terms "first," "second," "third," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar or related objects or entities, and do not necessarily imply a specific order or sequence, unless otherwise specified. It should be understood that such terms are interchangeable where appropriate.

[0050] The terms “comprising” and “having”, and any variations thereof, are intended to cover but not exclude inclusion, for example, a product or device that includes a range of components is not necessarily limited to all of the components that are clearly listed, but may include other components that are not clearly listed or that are inherent to such product or device.

[0051] A test system for the shear properties of a corroded metal-cement interface, such as Figures 1-13 As shown, the testing system includes a direct shear testing machine 1 and an in-situ electro-accelerated corrosion device for accelerating the corrosion rate of the metal-cement interface. In this invention, the metal-cement sample 6 is fixed on the direct shear testing machine 1 and connected to the in-situ electro-accelerated corrosion device; rapid electro-corrosion is performed after the metal sample is fixed on the direct shear testing machine 1 (with vertical constraint applied), and shear tests are conducted in situ after the electro-corrosion is completed. The test conditions are closer to actual engineering conditions, and the influence of metal corrosion on the interface shear properties can be obtained more accurately. The evolution law of the shear performance of the corroded metal-cement interface can be obtained more accurately, providing a more reliable scientific basis for the design and maintenance of underground metal-cement / concrete structures.

[0052] like Figures 1-8 As shown, the direct shear testing machine 1 includes an upper reaction seat 11 and a lower reaction seat 12 arranged opposite each other in the vertical direction, and a left reaction seat 13 and a right reaction seat 14 arranged opposite each other in the horizontal direction; wherein, the upper reaction seat 11 is provided with a vertical loading part 15 on the side near the lower reaction seat 12, and the right reaction seat 14 is provided with a horizontal loading part 16 on the side near the left reaction seat 13.

[0053] The direct shear testing machine 1 includes a shear fixing part 3 for fixing the sheared specimen. Specifically, the shear fixing part 3 includes a first fixing member 4 and a second fixing member 5, which together define an accommodating space. The first fixing member 4 is located above the second fixing member 5; and the first fixing member 4 and the second fixing member 5 are staggered along the vertical direction. The upper end of the first fixing member 4 engages with the vertical loading part 15, the lower end of the second fixing member 5 engages with the lower reaction seat 12; the left end of the first fixing member 4 engages with the left reaction seat 13, and the right end of the second fixing member 5 engages with the horizontal loading part 16. During the shear test loading, the first fixing member 4 applies a load to the metal-cement specimen 6 under the vertical loading action of the vertical loading part 15; and applies vertical constraint to the metal-cement specimen 6 under the combined action of the vertical loading part 15, the first fixing member 4, the second fixing member 5, and the lower reaction seat 12; the second fixing member 5 moves horizontally under the horizontal loading action of the horizontal loading part 16.

[0054] The tested metal-cement specimen 6 comprises a metal layer 61 and a cement layer 62. The interface connecting the metal layer 61 and the cement layer 62 is designated as the first interface. During the shear test, the normal direction of the first interface is aligned with the vertical direction of the direct shear testing machine 1. The metal-cement specimen 6 is installed within a space defined by the first fixing member 4 and the second fixing member 5. The first fixing member 4 and the second fixing member 5 work together to constrain the normal direction of the metal-cement specimen 6, while not constraining the horizontal direction of the first interface. This maintains a constant vertical constraint during the shear test, and a horizontal load is applied by the horizontal loading part 16 to complete the shear test of the metal-cement specimen 6 at its first interface along the horizontal direction. Alternatively, the first fixing member 4 can be coupled to the metal layer 61, and the second fixing member 5 can be coupled to the cement layer 62. The first interface connecting the metal layer 61 and the cement layer 62 can be configured with various shapes, such as rough, straight, or serrated. The metal layer 61 of the metal-cement sample 6 can be made of low-carbon steel, alloy steel of different grades, or other metals. As one possible configuration, the metal layer 61 of the metal-cement sample 6 can be made of Q235 steel, and the cement-based material can be various materials such as cement, concrete, and mine backfill.

[0055] The in-situ electro-accelerated corrosion device includes an in-situ electrolytic cell 20 for holding an electrolyte, a power supply 21, and a first electrode 22 located inside the in-situ electrolytic cell 20. During testing, the in-situ electrolytic cell 20 is mounted on a second fixing member 5, and the cement layer 62 of the metal-cement sample 6 is placed inside the in-situ electrolytic cell 20 and immersed in the electrolyte.

[0056] Specifically, in this invention, a second electrode 23 is provided on the metal layer 61 of the metal-cement sample 6, which is connected to the positive terminal of the power supply 21; at least a portion of the first electrode 22 is immersed in the electrolyte, and the end of the first electrode 22 exposed outside the electrolyte is connected to the negative terminal of the power supply 21. This arrangement, with the first electrode 22 connected to the negative terminal of the power supply and the second electrode 23 connected to the positive terminal, effectively ensures the conductivity stability and service life of the first electrode 22, and causes the electrochemical corrosion of the metal layer 61 to mainly concentrate at the first interface.

[0057] When the metal-cement sample 6 is installed in the in-situ electrolytic cell 20 and immersed in the electrolyte, the power supply 21 is turned on. A current loop is formed from the positive terminal of the power supply to the second electrode 23, then to the metal layer 61, the cement layer 62, the electrolyte, the first electrode 22, and finally the negative terminal of the power supply. The metal layer 61 loses electrons at the first interface where it connects with the cement layer 62, thereby achieving electro-accelerated corrosion.

[0058] In some embodiments of this application, the surface of the metal layer 61, except for the first interface in contact with the cement layer 62, has an anti-corrosion coating to precisely limit the location of electrochemical corrosion at the first interface.

[0059] In addition, the first electrode 22 is made of a metal that is more inert than the metal of the metal-cement sample 6 being tested; as an alternative configuration, the metal layer 61 of the metal-cement sample 6 is made of Q235, and the first electrode 22 can be made of copper rod, titanium mesh, copper sheet, etc.

[0060] In some embodiments of this application, a small area of ​​anti-corrosion coating is scraped off on the side of the metal layer 61 away from the first electrode 22 as an exposure point, which serves as the second electrode 23 connected to the positive terminal of the power supply.

[0061] In some embodiments of this application, the first electrode 22 is located at the end of the in-situ electrolytic cell 20 away from the right reaction seat 14, and the second electrode 23 is located at the end of the metal layer 61 away from the left reaction seat 13. The horizontal positioning of the first electrode 22 and the second electrode 23 increases the horizontal distance between them, thereby increasing the path of current flow through the metal layer 61 and guiding the current to flow through the first interface of the metal layer 61 in a covering manner, thus improving the uniformity of metal corrosion at the first interface.

[0062] As an alternative configuration, the distance between the second electrode 23 and the first interface is less than 1 cm, so that corrosion is concentrated at the first interface of the metal layer 61.

[0063] In some embodiments of this application, the in-situ electrolytic cell 20 is made of an acrylic sheet. The sidewalls of the in-situ electrolytic cell 20 surround the cement layer 62, and the end wall of the cement layer 62 on the side away from the metal layer 61 is bonded to the bottom of the in-situ electrolytic cell 20 with epoxy resin and cement to define the relative position of the in-situ electrolytic cell 20 and the cement layer 62.

[0064] In some embodiments of this application, a limiting portion (not shown in the figure) is formed on the bottom of the in-situ electrolytic cell 20, and the end of the cement layer 62 away from the metal layer 61 is installed in the limiting portion to limit the relative position of the in-situ electrolytic cell 20 and the cement layer 62.

[0065] As a configurable method, such as Figure 9 As shown, the bottom of the in-situ electrolytic cell 20 is provided with a plug-in part 24, which is used to install the first electrode 22, making it convenient to install and remove the first electrode 22.

[0066] In some embodiments of this application, the power supply 21 can be a common DC regulated power supply 21, an electrochemical workstation, or other instrument that applies current.

[0067] In some embodiments of this application, the electrolyte in the in-situ electrolytic cell 20 may be set as a 3% NaCl solution.

[0068] like Figure 10As shown, in some embodiments of this application, the first fixing member 4 includes a first fixing plate 41, and the second fixing member 5 includes a second fixing plate 51. The first fixing plate 41 cooperates with the wall surface of the metal layer 61 away from the cement layer 62, and the second fixing plate 51 cooperates with the wall surface of the cement layer 62 away from the metal layer 61, so as to constrain the metal-cement sample 6 under the action of the vertical loading part 15. As one possible configuration, a first recess 42 is formed on the first fixing plate 41, and the first recess 42 cooperates with the end of the metal layer 61 away from the cement layer 62, so that the metal layer 61 is embedded in the first fixing plate 41 to fix the metal layer 61. A second recess 52 is formed on the second fixing plate 51, and the second recess 52 cooperates with the in-situ electrolytic cell 20, so that the in-situ electrolytic cell 20 is embedded in the second fixing plate 51 to fix the in-situ electrolytic cell 20.

[0069] Combination Figures 2-6 ,like Figures 11-13 As shown, in another possible configuration, the first fixing member 4 includes a first limiting plate 43 connected to the first fixing plate 41, and the second fixing member 5 includes a second limiting plate 53 connected to the second fixing plate 51. Specifically, the first limiting plate 43 is located at the end of the first fixing plate 41 away from the right reaction seat 14 and extends downward from the end of the first fixing plate 41; the second limiting plate 53 is located at the end of the second fixing plate 51 near the right reaction seat 14 and extends upward from the end of the second fixing plate 51. In the vertical direction, the first limiting plate 43 and the second limiting plate 53 are staggered. When the metal-cement sample 6 is installed in the shear fixing part 3, the end wall of the metal layer 61 near the left reaction seat 13 cooperates with the first limiting plate 43, and the end wall of the in-situ electrolytic cell 20 near the right reaction seat 14 cooperates with the second limiting plate 53. As an optional configuration, the first limiting plate 43 is provided with a first limiting groove 44 penetrating its end away from the first fixing plate 41, and the second limiting plate 53 is provided with a second limiting groove 54 penetrating its end away from the second fixing plate 51. When the metal-cement sample 6 is installed in the shear fixing part 3, the end of the metal layer 61 near the left reaction seat 13 is installed in the first limiting groove 44, and the end of the in-situ electrolytic cell 20 near the right reaction seat 14 is installed in the second limiting groove 54. The setting of the first limiting groove 44 effectively limits the relative displacement of the metal-cement sample 6 in the third dimension perpendicular to the horizontal direction in the horizontal plane, and the setting of the second limiting groove 54 limits the position of the in-situ electrolytic cell 20, further ensuring the relative displacement of the metal-cement sample 6 in the third dimension perpendicular to the horizontal direction in the horizontal plane, thereby effectively ensuring the accuracy of the shear test.

[0070] As an optional feature, the surfaces of the first fixing member 4 and the second fixing member 5 of the shear fixing part 3 are coated with an anti-corrosion coating to prevent corrosion of the first fixing member 4 and the second fixing member 5 during electrochemical testing. Specifically, the anti-corrosion coating on the first fixing member 4 and the second fixing member 5 is an epoxy resin anti-corrosion coating.

[0071] In some embodiments of this application, the test system for the shear properties of the corroded metal-cement interface also includes a DIC non-contact strain field monitoring system. The DIC non-contact strain field monitoring system employs Digital Image Correlation (DIC) combined with binocular stereo vision technology. Two high-speed cameras are used to acquire speckle images of the object at various deformation stages in real time, calculating the overall strain and deformation to intuitively monitor the change process of the first interface and the shear formation and failure process.

[0072] A test method for the shear properties of a corroded metal-cement interface, using the aforementioned test system for the shear properties of a corroded metal-cement interface, specifically includes the following steps:

[0073] (I) Sample preparation:

[0074] (1) Place the metal layer 61 into the detachable mold, apply release oil to the inside of the mold to facilitate demolding, then pour cement slurry into the mold, use a vibrating table to remove air bubbles, demold after 24 hours, and then cure for 28 days according to standard.

[0075] The metal used is Q235 thick steel plate; Q235 is the most commonly used steel in underground engineering.

[0076] The cement mix design is based on the design of carbon storage well cement, and follows GB / T19139-2012 "Test Methods for Cement in Oil Wells". The cement is grade G cement with a water-cement ratio of 0.45. 10% microsilica is added as an admixture, 0.6% water-reducing agent G33S and 0.1% USZ dispersant to improve cement stability.

[0077] To reduce the resistivity of the cement samples and facilitate subsequent electro-accelerated corrosion tests, 3% sodium chloride was added to all samples. This did not affect the mechanical properties of the cement samples themselves.

[0078] (2) Spraying speckles onto the sample surface for DIC strain field monitoring.

[0079] (3) Prepare multiple standard specimens and test parameters such as cement strength, elastic modulus, and Poisson's ratio to ensure that the prepared specimens meet the specifications. In this embodiment, 6 standard specimens are prepared for testing to ensure that the prepared specimens meet the specifications; 12 specimens are prepared for the corrosion specimen shear test.

[0080] Since the shear behavior of the metal-cement interface mainly depends on the bonding force and the coefficient of friction, metal corrosion directly affects the interfacial bonding force, coefficient of friction, and normal stress. To obtain basic metal-interface properties and consider broader application scenarios, the specimen was designed with a thick metal layer 61 bonded to a cement block interface. In this embodiment, both the metal layer 61 and the cement layer 62 of the metal-cement specimen 6 are cuboids with a length of 100 mm, a width of 100 mm, and a height of 50 mm. The assembled specimen measures 100 mm × 100 mm × 100 mm.

[0081] Correspondingly, the mold used for sample preparation has a size of 100mm×100mm×100mm.

[0082] (II) Direct shear test of corroded metal-cement interface:

[0083] (1) Apply epoxy resin thin-layer anti-corrosion treatment to the shearing and fixing part 3. Apply epoxy resin anti-corrosion treatment to the surface of the metal except the interface, and leave only the interface area to be corroded.

[0084] (2) The additional in-situ electrolytic cell 20 is fixed with strong resin glue, and the metal-cement sample 6 is placed between the in-situ electrolytic cell 20 and the first fixing member 4; wherein, the cement layer 62 is placed in the in-situ electrolytic cell 20 and immersed in the electrolyte in the in-situ electrolytic cell 20, so that the cement layer 62 is in full contact with the electrolyte and soaked for a period of time so that the electrolyte permeates the cement layer 62.

[0085] The positive terminal of the power supply 21 is connected to the second electrode 23 on the metal layer 61, and the negative terminal of the power supply 21 is connected to the cathode located in the in-situ electrolytic cell 20.

[0086] In this embodiment, a CS350M electrochemical workstation is used as the DC external power supply 21 to apply a constant current density of 10μA / m2 to accelerate interface corrosion.

[0087] The electrolyte in the salt tank is a 3% NaCl solution.

[0088] A copper rod is built into the left side of the salt tank and connected to the cathode of the electrochemical workstation. A small area of ​​the anti-corrosion coating is scraped off on the right side of the metal layer 61 as an exposure point, which is then connected to the anode of the workstation.

[0089] The electrochemical workstation (power source 21), salt solution, copper rod and metal layer 61 sequentially constitute the power source 21, electrolyte, cathode and anode in the electrochemical system.

[0090] The above settings ensure that corrosion is concentrated in the interface metal region, and the electrons lost by the metal reach the cathode copper rod through the cement sample and electrolyte.

[0091] (3) Apply a constant normal constraint (stress or stiffness) to the direct shear test machine 1; then turn on the power supply 21 and conduct a direct shear test at different times, and record the change of normal load reaction force during the corrosion process.

[0092] As a feasible approach, when conducting direct shear tests, a constant normal stiffness constraint of 10 GPa / m is designed, and the initial normal stress is designed to be 3 MPa. Then, the output of power supply 21 of the electrochemical workstation is turned on, and the corrosion is accelerated for 6 h, 12 h, 18 h and 24 h respectively before conducting direct shear tests.

[0093] To avoid randomness in the test, three samples were set for each corrosion time, and a total of 12 direct shear tests were conducted.

[0094] During the loading process, the direct shear testing machine 1 records the shear stress-displacement curve and uses the DIC non-contact strain field monitoring system to obtain the real-time strain field.

[0095] (4) After the metal-cement sample 6 was destroyed, the interface corrosion products were washed with acid solution. The surface corrosion characteristics were obtained by using a three-dimensional laser scanning surface morphology testing system, and the amount of corrosion and the average corrosion depth were calculated. The influence of corrosion on the normal load, interfacial shear strength, peak displacement, ultimate displacement and residual strength was quantitatively analyzed, and the evolution mechanism of the shear properties of the corroded metal-cement interface was explained.

[0096] (III) Introduce the average corrosion depth and establish a shear constitutive model of the corroded metal-cement interface;

[0097] Specifically, based on the experimental results, combined with the classic three-stage interface shear constitutive model, as shown in Equation (1); considering the influence of corrosion on the shape of the shear stress-displacement curve, a quantitative relationship between the average corrosion depth and the normal load reaction, interface shear strength, peak displacement, ultimate displacement and residual strength is established. The average corrosion depth is introduced into the interface shear constitutive model to establish a unified constitutive model describing the metal-cement interface shear behavior before and after corrosion, as shown in Equation (2).

[0098] τ=f(δ0,τ max δ f , τ res , σ n (1)

[0099] τ=f(δ0,τ max ,δ f ,τ res ,σ n ,η) (2)

[0100] In the formula, τ is the shear stress, which is the peak shear displacement δ0 and the shear strength τ. max Ultimate shear displacement δ f and residual shear strength τres The function of σ. Its parameters are generally related to the normal stress σ. n Relevant. In equation (2), η is the average corrosion depth.

[0101] (iv) Numerical development and shearing simulation of interface units;

[0102] Based on the ABAQUS zero-thickness cohesive interface element framework, a user-defined material subroutine VUMAT was written in Fortran to write the derived constitutive model into the ABAQUS three-dimensional zero-thickness cohesive element (COH3D8) to establish a numerical model of the same size as the test specimen, with the interface embedded in the zero-thickness cohesive element (COH3D8).

[0103] Using the measured parameters such as interfacial shear strength, peak displacement, ultimate displacement, residual strength, and corrosion depth, constant normal stress and normal stiffness were applied to simulate the shear deformation and failure process of the metal-cement interface before and after corrosion, and the results were compared and verified with the experimental results.

[0104] This invention, based on the principle of electrochemical accelerated corrosion, utilizes an existing direct shear testing machine to achieve in-situ corrosion of the metal-cement / concrete interface under normal load constraints. This allows for monitoring the impact of interface corrosion on normal force or normal displacement, and further enables direct shear tests on the corroded metal-cement interface. Furthermore, a DIC non-contact strain field monitoring system (high-speed camera, digital speckle technology) can directly monitor the deformation and failure characteristics of the exposed side of the interface. The aforementioned experimental system and method for assessing the shear properties of the corroded metal-cement interface in this invention conveniently considers the interaction between normal constraints and metal corrosion, directly realizing the testing of the shear properties of the corroded metal-cement interface, facilitating direct monitoring of the interface corrosion process and deformation and failure characteristics.

[0105] The experimental system and testing method for the shear properties of the corroded metal-cement interface of the present invention are conducted in an environment under the combined action of normal constraint and corrosion, which is closer to the actual corrosion environment of underground structures. It can accurately obtain the interaction relationship between normal constraint and metal corrosion, and flexibly and conveniently measure the evolution law of shear properties of metal-cement interfaces with different corrosion levels under different normal constraints, providing more reliable experimental data for the design and maintenance of tunnel engineering.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application.

[0107] For ease of explanation, the above description has been provided in conjunction with specific embodiments. However, the above exemplary discussion is not intended to be exhaustive or to limit the embodiments to the specific forms disclosed above. Various modifications and variations can be obtained based on the above teachings. The selection and description of the above embodiments are for the purpose of better explaining the principles and practical applications, thereby enabling those skilled in the art to better utilize the described embodiments and various different variations of embodiments suitable for specific use considerations.

Claims

1. A test system for the determination of the corrosion metal-cement interfacial shear properties, characterized in that, The test system includes: A direct shear testing machine includes a shear fixing part for fixing a metal-cement specimen, a vertical loading part for applying a force perpendicular to the metal-cement interface, and a horizontal loading part for applying a force parallel to the metal-cement interface. In-situ electro-accelerated corrosion device, comprising: An in-situ electrolytic cell is used to hold an electrolyte; the in-situ electrolytic cell is installed on the shearing and fixing part; the metal-cement sample is placed in the in-situ electrolytic cell, and the cement layer of the metal-cement sample is immersed in the electrolyte; The first electrode is located in the in-situ electrolytic cell and is in contact with the electrolyte in the in-situ electrolytic cell; A power source, the positive terminal of which is connected to the metal layer of the metal-cement sample, and the negative terminal of which is connected to the first electrode; The shearing and fixing part includes a first fixing member and a second fixing member; the first fixing member and the second fixing member are staggered in the vertical direction; the first fixing member and the second fixing member cooperate to define the accommodating space for fixing the metal-cement sample; The metal layer of the metal-cement sample is fitted with the first fixing member, and the vertical loading part corresponds to the first fixing member and is used to apply a vertical load to the first fixing member. The in-situ electrolytic cell is installed on the second fixing member, and the horizontal loading part cooperates with the second fixing member to apply a horizontal load to the second fixing member; A second electrode is provided on the metal layer, and the second electrode is connected to the positive terminal of the power supply; the first electrode is located at the end of the in-situ electrolytic cell away from the horizontal loading part, and the second electrode is located at the end of the metal layer away from the first electrode; In the shear property test of the corroded metal-cement interface, the first electrode is at least partially immersed in the electrolyte, and the cement layer of the metal-cement sample is immersed in the electrolyte; the vertical loading part applies a constant vertical load to the metal-cement sample through the shear fixing part; then the power supply is turned on, and the positive terminal of the power supply, the metal layer, the cement layer, the electrolyte, the first electrode, and the negative terminal of the power supply form a current loop, and corrosion occurs at the interface between the metal layer and the cement layer; after a set corrosion time, the horizontal loading part applies a horizontal load to the cement layer, and the metal-cement sample undergoes shearing at the interface between the metal layer and the cement layer; The first fastener includes a first fastening plate, which mates with the wall surface of the metal layer away from the cement layer; the second fastener includes a second fastening plate, which mates with the wall surface of the cement layer away from the metal layer. A first recess is formed on the first fixing plate, and the first recess engages with the end of the metal layer away from the cement layer; A second recess is formed on the second fixing plate, and the second recess cooperates with the in-situ electrolytic cell.

2. The test system for corrosion metal-cement interfacial shear properties of claim 1, wherein, The first fixing member includes a first limiting plate connected to the first fixing plate. The first limiting plate is located at the end of the first fixing plate away from the horizontal loading part and extends downward from the end of the first fixing plate.

3. The test system for corrosion metal-cement interfacial shear properties of claim 2, wherein, The first limiting plate is provided with a first limiting groove that passes through the end away from the first fixing plate. When the metal-cement sample is installed in the shearing fixing part, the end of the metal layer near the first limiting plate is installed in the first limiting groove.

4. The test system for corrosion metal-cement interfacial shear properties of claim 2, wherein, The second fixing member includes a second limiting plate connected to the second fixing plate. The second limiting plate is located at one end of the second fixing plate near the horizontal loading part and extends upward from the end of the second fixing plate.

5. A test system for the corrosion metal-cement interfacial shear properties according to claim 1 or 3 or 4, characterized in that, The surfaces of the shearing and fixing parts are all covered with anti-corrosion coatings; the surfaces of the metal layer, except for the wall surface in contact with the cement layer, are all covered with anti-corrosion coatings.

6. A test system for the corrosion metal-cement interfacial shear properties according to claim 1 or 3 or 4, characterized in that, The test system for the shear properties of the corroded metal-cement interface includes a DIC non-contact strain field monitoring system, which is used to monitor the changes in the metal-cement interface and the shear formation failure process.

7. A test method for the shear properties of a corroded metal-cement interface, performed using the test system for the shear properties of a corroded metal-cement interface as described in any one of claims 1-6, characterized in that, The experimental method includes the following steps: (1) Sample preparation: Place the metal layer into a detachable mold, apply release oil to the mold, then pour cement slurry into the mold, use a vibration table to remove air bubbles, remove the mold after a predetermined time for standard curing, and spray scattered spots on the sample surface. (2) Corrosion of metal-cement interface direct shear test: The metal-cement sample and the in-situ electrolytic cell are installed on the direct shear test machine through the shear fixing part, and the cement layer is immersed in the electrolyte of the in-situ electrolytic cell; the vertical loading part applies vertical constraint to carry out electrochemical corrosion; then the horizontal loading part applies horizontal load to carry out shear test, and the amount of corrosion and the average corrosion depth are calculated. (3) Combining the three-stage interface shear constitutive model, the average corrosion depth is introduced to establish a shear constitutive model of the corroded metal-cement interface. (4) Based on the cohesive interface element, numerical development and shear simulation of the interface element are carried out.

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