Method for evaluating the itz permeability coefficient of concrete

Abstract

The present application relates to a kind of aggregate type evaluation concrete ITZ permeability coefficient method, belong to the field of permeability coefficient determination, including selection mould and model aggregate, model aggregate is bonded with concrete columnar mould bottom, calculate the average thickness of concrete ITZ;Calculate ITZ area and cement mortar area, determine D SU With D CE ;The present application only considers the type of model aggregate, the complex three-dimensional permeation is simplified to two-dimensional by experimental means, the permeation area of ITZ and cement mortar on the cross section of test piece is calculated, the permeability coefficient of concrete ITZ is quantitatively calculated, only the number of model aggregate and the permeation area of erosive medium on the cross section are considered, the complexity of the calculation of the permeability coefficient of concrete ITZ is reduced, a quantitative research method for the permeability coefficient of concrete ITZ test research is provided, scientific basis is provided for the application of different types of aggregate in engineering structure, and it has important theoretical significance and practical value.

Description

Technical Field

[0001] This invention relates to a method for evaluating the ITZ permeability coefficient of concrete based on aggregate type, belonging to the technical field of permeability coefficient determination. Background Technology

[0002] The interfacial transition zone (ITZ) is the weakest link in concrete, characterized by low density, high porosity, and low hardness. The structure and properties of the ITZ largely determine the overall performance of cement concrete. Due to the high porosity of the ITZ, under the coupled effects of load and environmental factors, cracks initially originate and propagate in the ITZ during the service life of concrete structures. Corrosive media travel more rapidly within the ITZ, and the entry of environmental corrosive media causes changes within the concrete. Therefore, the permeability of the ITZ directly determines the durability of the concrete. Especially in reinforced concrete structures, the passivation film of the reinforcing steel is easily eroded by corrosive media, generating soluble products. The erosion of the passivation film leads to corrosion of the reinforcing steel, resulting in reduced concrete durability.

[0003] The intima-tone zone (ITZ) thickness of concrete is typically 20-50 μm, and research methods are relatively limited. The volume of the ITZ mainly depends on factors such as the surface area, quantity, gradation, aspect ratio, and curvature of the aggregate. Since aggregate type, shape, and size are irregular, and aggregate type has a crucial impact on the concrete ITZ, establishing experimental methods for evaluating the ITZ permeability of concrete with different types of aggregates is essential for assessing concrete durability. Summary of the Invention

[0004] To address the challenges of varying aggregate types and complex calculation processes in concrete ITZ permeability coefficient research, current research largely relies on numerical simulations and theoretical models, lacking experimental data verification. This invention proposes a method for evaluating concrete ITZ permeability coefficient based on aggregate type. This invention uses several columnar model aggregates of specified shapes and sizes to create concrete specimens simulating the ITZ in concrete, changing only the type of model aggregate. After standard curing, the ITZ thickness of the concrete on the cross-section is observed through microscopic tests such as SEM, simplifying the complex three-dimensional permeability calculation process to two dimensions. This invention only considers the type of model aggregate and the permeation area of ​​the corrosive medium on the cross-section, reducing the complexity of concrete ITZ permeability coefficient calculation. It provides a quantitative testing method for concrete ITZ permeability research, comprehensively evaluating the impact of different aggregates on concrete ITZ permeability, and providing a scientific basis for the application of different types of aggregates in engineering structures. It has significant theoretical and practical value.

[0005] The present invention adopts the following technical solution:

[0006] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type includes the following steps:

[0007] (1) Select a suitable mold:

[0008] Select a concrete column mold with a racetrack-shaped cross-section. The height of the concrete column mold is 50mm. The concrete column mold consists of two symmetrical and equal-sized semi-circular areas. A non-removable baffle with the same height as the concrete column mold is set between the two semi-circular areas. The two semi-circular areas are used to fill the ITZ area (including model aggregate) and the cement mortar area (excluding model aggregate), respectively. Let the sum of the cross-sectional areas of the two semi-circular areas be A. The bottom of the concrete column mold is a removable wooden board.

[0009] (2) Select a cuboid or cylinder of equal diameter with a side length of 100mm as the model aggregate (other shapes may be selected if there are special requirements). The material of the model aggregate should be consistent with that of the real aggregate. When the actual roundness σ of the aggregate is ≥0.75, select cylindrical model aggregate; when the actual roundness σ of the aggregate is <0.75, select cuboid model aggregate.

[0010]

[0011] In the formula: σ is the actual roundness of the aggregate; A0 is the projected area of ​​the coarse aggregate particles in the maximum contour image; L0 is the perimeter of the projected contour of the coarse aggregate particles in the maximum contour image;

[0012] The roundness measuring instrument includes a camera and an image processing device. It can take pictures through the camera and obtain the outline image of the aggregate through image processing, and select the largest outline image from it.

[0013] (3) After determining the type and shape of the model aggregate, place a number of model aggregates with a height of 50mm into one of the semi-circular areas of the concrete column mold prepared in step (1). The bottom of the model aggregate is bonded to the bottom of the concrete column mold. To avoid the overlap of the ITZ around the model aggregate, the model aggregates should be evenly distributed when they are placed. Then, pour cement mortar into the two semi-circular areas of the concrete column mold. When pouring cement mortar, you can follow the "Test Procedure for Cement and Cement Concrete in Highway Engineering" (JTGE30). When pouring, make the slurry evenly distributed on both sides of the mold. After pouring, place it in a standard curing room for curing. After curing for the specified age, remove the specimen and separate the concrete column mold from the bottom of the specimen to obtain specimens containing model aggregate and cement mortar specimens respectively.

[0014] (4) Prepare multiple parallel specimens containing model aggregate specimens (parallel specimens are specimens with the same mix proportion, mixing time, curing method and other parameters as the specimens used in the experiment, and can be regarded as one or more identical specimens under the same conditions). Dry, clean and polish the surface according to the requirements of the "General Rules for Analysis Methods of Scanning Electron Microscopy" (JY / T 0584-2020). After the sample is sent into the sample chamber, select the magnification, focus the scanning electron microscope, adjust the contrast, brightness and other parameters, take pictures and save the image after it is clear, and determine the single measurement thickness value of the interface transition zone according to the scale and the length in the screenshot. Observe the thickness value of the concrete ITZ through the scanning electron microscope and record it. Select 4 model aggregates at the corner and 1 at the center as representatives. Record the thickness 20 times along the perimeter of each model aggregate and take the average value. Record the average thickness of the concrete ITZ as d.

[0015] (5) After determining the thickness of the ITZ as d, calculate the area A of the ITZ region. ITZ And the cement mortar area A in the ITZ region CE ;

[0016] (6) The aggregate specimens and cement mortar specimens obtained in step (4) are subjected to a permeability test of the corrosive medium (chloride ions, O2 and CO2, etc.), and the permeability coefficient D of the aggregate specimens is determined simultaneously. SU Permeability coefficient D of cement mortar specimen CE ;

[0017] For the permeability test, in specimens containing model aggregate, the permeability coefficient of the specimen satisfies:

[0018]

[0019] The permeability coefficient D of the concrete interfacial transition zone (ITZ) can be derived from the above formula. ITZ :

[0020]

[0021] In the formula: D SU D is the permeability coefficient of the specimen containing the model aggregate, obtained from the permeability test of the specimen with the model aggregate; CE is the permeability coefficient of a pure cement mortar specimen, obtained from a pure cement mortar specimen permeability test; A is the total cross-sectional area of ​​the two semi-circular regions; A AGG D represents the cross-sectional area of ​​the aggregate in a single model. ITZ The permeability coefficient of the interface transition zone (ITZ).

[0022] The permeability coefficient measuring device of this invention can simultaneously measure the permeation area of ​​ITZ and cement mortar on the cross-section of the specimen, and quantitatively calculate the ITZ permeability coefficient of concrete.

[0023] Preferably, in step (1), the radius of the semicircular area is 50mm and the thickness of the baffle is 12mm.

[0024] Preferably, in step (3), the number of model aggregates is 10. This number is appropriate, which can make the model aggregates be placed evenly in the mold and have a large ITZ area, thus reducing measurement error.

[0025] It is preferable to use adhesives such as epoxy resin to bond the bottom of the model aggregate to the bottom of the concrete column mold.

[0026] Preferably, in step (5):

[0027] ① When the model aggregate is square aggregate, let its side length be l, A ITZ =n×(πd) 2 +4dl)(The area of ​​the ITZ on each side of the square aggregate is dl, while the shape of the ITZ on each corner of the square aggregate is a quarter circle with an area of ​​πd. 2 / 4),

[0028] ② When the model aggregate is circular, let its radius be r, A ITZ = n×π[(r+d)] 2 -r 2 ],

[0029] In the formula: A is the total cross-sectional area of ​​the two semicircular regions, in mm. 2 n represents the number of aggregates in the model, taken as 10; A ITZ The ITZ area is the cross-sectional area of ​​the specimen containing the model aggregate, in mm². 2 A CE The area of ​​the cement mortar zone in the cross-section of the specimen containing the model aggregate is expressed in mm. 2 ; d is the ITZ thickness in mm; l is the side length of the cuboid model aggregate, taken as 10 mm; r is the radius of the circular model aggregate, taken as 5 mm.

[0030] Preferably, in step (6), the device for the permeation test includes four sealing grooves, two of which are permeation medium sealing grooves and two are ordinary medium sealing grooves. The specimens containing model aggregate and cement mortar that have been cured in step (3) are placed between the four sealing grooves. The specimens containing model aggregate and cement mortar together form a cylinder with a radius of 50 mm and a height of 50 mm.

[0031] Preferably, the specimens containing model aggregate and cement mortar are coated with epoxy resin or similar material on the sides before being placed in the four sealing grooves to prevent the permeating medium from seeping in from the sides.

[0032] Preferably, in step (6), a semi-circular cross-sectional opening is provided between the permeating medium sealing tank and the ordinary medium sealing tank. The specimen is placed in the permeating medium sealing tank at one end through the opening and in the ordinary medium sealing tank at the other end.

[0033] A fixing mesh is set between the connecting port and the specimen. The fixing mesh is a semi-circular copper mesh with a radius of 50 mm and a thickness of 1 mm. Multiple evenly distributed through holes are set in the middle to ensure that chloride ions can freely permeate between the solution, the copper mesh and the specimen. The fixed mesh has a thin iron sheet with a height of 10 mm on the round edge.

[0034] A rubber ring is installed in the test area between the permeation medium sealing tank and the ordinary medium sealing tank. The rubber ring is 50mm high and has a racetrack-shaped cross-section, which can simultaneously hold two semi-cylindrical specimens, namely a specimen containing model aggregate and a cement mortar specimen. The radius of the rubber ring is slightly smaller than that of the specimen. The material is high-temperature resistant and anti-aging butyl rubber, which can freely expand and contract to tightly wrap the specimen, preventing the permeation medium from seeping from the side of the specimen, thus making the experimental results more accurate. A 5mm thick soft rubber baffle is set in the middle of the rubber ring to separate the two specimens. Both ends of the rubber ring are equipped with pipe clamps to fix the specimen, the rubber ring, and the thin iron sheet on the fixing net. The permeation test device of this invention can simultaneously measure the permeation coefficient of two semi-cylinders.

[0035] Where this invention is not detailed, existing technologies may be used.

[0036] The beneficial effects of this invention are as follows:

[0037] The method of this invention uses model aggregates of specified shape and size to create concrete specimens to simulate the infiltration zone (ITZ) in concrete. It only considers the type of model aggregate and simplifies the complex three-dimensional permeability calculation to two dimensions through experimentation. It calculates the permeation area of ​​ITZ and cement mortar on the cross-section of the specimen and quantitatively calculates the ITZ permeability coefficient of concrete. It only considers the quantity of model aggregate and the permeation area of ​​the corrosive medium on the cross-section, reducing the complexity of calculating the ITZ permeability coefficient of concrete. It provides a method for quantitative research on the permeability coefficient of concrete ITZ and provides a scientific basis for the application of different types of aggregates in engineering structures. It has important theoretical significance and practical value. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the concrete column mold of the present invention;

[0039] Figure 2 This is a schematic diagram of the distribution of aggregate in the model, where (a) the aggregate is a cuboid and (b) the aggregate is a cylinder.

[0040] Figure 3 This is a schematic diagram of the apparatus for a permeation test;

[0041] Figure 4 This is a schematic diagram of the rubber ring structure;

[0042] Figure 5 This is a schematic diagram of the pipe clamp fixing method;

[0043] Among them, 1-baffle, 2-permeable medium sealing groove, 3-ordinary medium sealing groove, 4-thin iron sheet, 5-pipe clamp, 6-rubber ring, 7-bracket. Detailed Implementation

[0044] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. However, this description is not limited thereto. All aspects not described in detail in the present invention are based on conventional techniques in the field.

[0045] Example 1:

[0046] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type includes the following steps:

[0047] (1) Select a suitable mold:

[0048] Choose a concrete column mold with a racetrack-shaped cross-section, such as... Figure 1 As shown, the height of the concrete column mold is 50mm. The concrete column mold consists of two symmetrical and equal-sized semi-circular areas. A non-removable baffle 1 with the same height as the concrete column mold is set between the two semi-circular areas. The two semi-circular areas are used to fill the ITZ area (including model aggregate) and the cement mortar area (excluding model aggregate), respectively. Let A be the sum of the cross-sectional areas of the two semi-circular areas. The bottom of the concrete column mold is a removable wooden board.

[0049] (2) Select a cuboid or cylinder of equal diameter with a side length of 100mm as the model aggregate (other shapes may be selected if there are special requirements). The material of the model aggregate should be consistent with that of the real aggregate. When the actual roundness σ of the aggregate is ≥0.75, select cylindrical model aggregate; when the actual roundness σ of the aggregate is <0.75, select cuboid model aggregate.

[0050]

[0051] In the formula: σ is the actual roundness of the aggregate; A0 is the projected area of ​​the coarse aggregate particles in the maximum contour image; L0 is the perimeter of the projected contour of the coarse aggregate particles in the maximum contour image;

[0052] The roundness measuring instrument includes a camera and an image processing device. It can take pictures through the camera and obtain the outline image of the aggregate through image processing, and select the largest outline image from it.

[0053] (3) After determining the type and shape of the model aggregate, place a number of model aggregates with a height of 50mm into one of the semi-circular areas of the concrete column mold prepared in step (1). The bottom of the model aggregate is bonded to the bottom of the concrete column mold. To avoid the overlap of the ITZ around the model aggregate, the model aggregates should be evenly distributed when they are placed. Then, pour cement mortar into the two semi-circular areas of the concrete column mold. When pouring cement mortar, you can follow the "Test Procedure for Cement and Cement Concrete in Highway Engineering" (JTGE30). When pouring, make the slurry evenly distributed on both sides of the mold. After pouring, place it in a standard curing room for curing. After curing for the specified age, remove the specimen and separate the concrete column mold from the bottom of the specimen to obtain specimens containing model aggregate and cement mortar specimens respectively.

[0054] (4) Prepare multiple parallel specimens containing model aggregate specimens (parallel specimens are specimens with the same mix proportion, mixing time, curing method and other parameters as the specimens used in the experiment, and can be regarded as one or more identical specimens under the same conditions). Dry, clean and polish the surface according to the requirements of the "General Rules for Analysis Methods of Scanning Electron Microscopy" (JY / T 0584-2020). After the sample is sent into the sample chamber, select the magnification, focus the scanning electron microscope, adjust the contrast, brightness and other parameters, take pictures and save the image after it is clear, and determine the single measurement thickness value of the interface transition zone according to the scale and the length in the screenshot. Observe the thickness value of the concrete ITZ through the scanning electron microscope and record it. Select 4 model aggregates at the corner and 1 at the center as representatives. Record the thickness 20 times along the perimeter of each model aggregate and take the average value. Record the average thickness of the concrete ITZ as d.

[0055] (5) After determining the thickness of the ITZ as d, calculate the area A of the ITZ region. ITZ And the cement mortar area A in the ITZ region CE ;

[0056] (6) The aggregate specimens and cement mortar specimens obtained in step (4) are subjected to a permeability test of the corrosive medium (chloride ions, O2 and CO2, etc.), and the permeability coefficient D of the aggregate specimens is determined simultaneously. SU Permeability coefficient D of cement mortar specimen CE ;

[0057] For the permeability test, in specimens containing model aggregate, the permeability coefficient of the specimen satisfies:

[0058]

[0059] The permeability coefficient D of the concrete interfacial transition zone (ITZ) can be derived from the above formula. ITZ :

[0060]

[0061] In the formula: D SU D is the permeability coefficient of the specimen containing the model aggregate, obtained from the permeability test of the specimen with the model aggregate; CE The permeability coefficient of a pure cement mortar specimen is obtained from a pure cement mortar specimen permeability test (D). SU D CE (Existing standards and techniques can also be used for measurement); A is the total cross-sectional area of ​​the two semi-circular regions; A AGG D represents the cross-sectional area of ​​the aggregate in a single model. ITZ The permeability coefficient of the interface transition zone (ITZ).

[0062] The permeability coefficient measuring device of this invention can simultaneously measure the permeation area of ​​ITZ and cement mortar on the cross-section of the specimen, and quantitatively calculate the ITZ permeability coefficient of concrete.

[0063] Example 2:

[0064] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type, as described in Example 1, except that the radius of the semicircular region is 50 mm and the thickness of the baffle is 12 mm.

[0065] Example 3:

[0066] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type, as described in Example 2, except that the number of model aggregates is 10. This number is appropriate, as it allows the model aggregates to be placed evenly in the mold and has a larger ITZ area, thus reducing measurement errors.

[0067] Example 4:

[0068] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type, as described in Example 3, except that an adhesive such as epoxy resin is used to bond the bottom of the model aggregate to the bottom of the concrete column mold.

[0069] Example 5:

[0070] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type, as described in Example 4, except that in step (5):

[0071] ① When the aggregate is square, such as Figure 2 As shown in (a), let its side length be l, A ITZ =n×(πd) 2 +4dl)(The area of ​​the ITZ on each side of the square aggregate is dl, while the shape of the ITZ on each corner of the square aggregate is a quarter circle with an area of ​​πd. 2 / 4),

[0072] When type ② aggregate is round aggregate, such as Figure 2 As shown in (b), let its radius be r, A ITZ = n×π[(r+d)] 2 -r 2 ],

[0073]

[0074] In the formula: A is the total cross-sectional area of ​​the two semicircular regions, in mm. 2 n represents the number of aggregates in the model, taken as 10; A ITZ The ITZ area is the cross-sectional area of ​​the specimen containing the model aggregate, in mm². 2 A CE The area of ​​the cement mortar zone in the cross-section of the specimen containing the model aggregate is expressed in mm. 2 ; d is the ITZ thickness in mm; l is the side length of the cuboid model aggregate, taken as 10 mm; r is the radius of the circular model aggregate, taken as 5 mm.

[0075] Example 6:

[0076] A method for evaluating the ITZ permeability coefficient of concrete by aggregate type, as described in Example 5, except that in step (6), as... Figure 3 As shown, the device for the permeation test includes four sealing grooves, two of which are permeation medium sealing grooves 2 and two are ordinary medium sealing grooves 3. The specimens containing model aggregate and cement mortar that have been cured in step (3) are placed between the four sealing grooves. The specimens containing model aggregate and cement mortar together form a cylinder with a radius of 50 mm and a height of 50 mm.

[0077] Before placing the model aggregate specimens and cement mortar specimens into the four sealing grooves, apply epoxy resin or similar coating to the sides to prevent the penetrating medium from seeping in from the sides.

[0078] In step (6), a semi-circular cross-sectional opening is provided between the permeating medium sealing tank 2 and the ordinary medium sealing tank 3. The specimen is placed in the permeating medium sealing tank 2 through one end of the opening and in the ordinary medium sealing tank 3 through the other end.

[0079] A fixing mesh is set between the connecting port and the specimen. The fixing mesh is a semi-circular copper mesh with a radius of 50 mm and a thickness of 1 mm, which is fixed on the connecting port. Multiple evenly distributed through holes are set in the middle to ensure that chloride ions can freely permeate between the solution, the copper mesh and the specimen. The fixed mesh has a thin iron sheet 4 with a height of 10 mm on the round edge.

[0080] A rubber ring, 50mm high, is placed in the test area between the permeation medium-sealed tank 2 and the ordinary medium-sealed tank 3. Its cross-section is racetrack-shaped, capable of simultaneously accommodating two semi-cylindrical specimens. Figure 4As shown, the test specimen includes a model aggregate specimen and a cement mortar specimen. The radius of the rubber ring is slightly smaller than that of the specimen. The material used is high-temperature resistant and anti-aging butyl rubber, which can freely expand and contract to tightly wrap the specimen, preventing the permeating medium from seeping from the side of the specimen, thus making the experimental results more accurate. A 5mm thick soft rubber baffle is set in the middle of the rubber ring to separate the two specimens. Both ends of the rubber ring are equipped with pipe clamps 5 to fix the specimen, rubber ring 6, and thin iron sheet 4 on the fixing net. The permeation test device in this embodiment can simultaneously measure the permeation coefficient of two semi-cylinders.

[0081] like Figure 5 As shown, the thin iron sheet 4 is an extension of the permeation test device. The specimen and the rubber ring 6 are inserted into the thin iron sheet and then clamped by the external pipe clamp 5 to connect the permeation device to the specimen and maintain its seal.

[0082] The device is also equipped with a bracket 7 for fixing the permeation medium sealing tank and the ordinary medium sealing tank.

[0083] In this embodiment, a 5mm thick soft rubber baffle is provided in the middle of the rubber ring 6 to separate the two specimens. The gap between the two permeation medium sealing tanks 2 or the two ordinary medium sealing tanks 3 is also 5mm, which is just enough to fix the racetrack-shaped rubber ring and the specimen.

[0084] In this embodiment, the permeability coefficient D of the specimen containing model aggregate is determined using a permeability test apparatus. SU Permeability coefficient D of cement mortar specimen CE At that time, it is possible Figure 3 The control program inputs several commonly used methods for determining permeability coefficients. Taking rapid chloride ion permeation as an example, the chloride ion diffusion coefficient is measured using the ASTM C1202 method. Two equal portions of the specimen, after treatment (vacuum water retention, etc.), are placed between four electrolytic cells (i.e., between two permeation medium sealed tanks and two ordinary medium sealed tanks). A 5% NaCl solution is placed at the cathode, and a 0.3 mol / L NaOH solution is placed at the anode. A 22V voltage is applied through the control program, and the chloride ion concentration in the anode solution is measured every six hours using a rapid chloride ion test (RCT). When the linear regression coefficient of the cumulative chloride ion concentration and time is greater than 0.9, a steady state is reached, and the system automatically stops and proceeds according to the formula input in the control program. The chloride ion permeability coefficient is calculated using a unified expression.

[0085] Where R is the gas constant (R = 8.31 J / mol / K), T is the experimental temperature (T = 293 K), L is the specimen thickness (L = 0.05 m), V is the volume of the anode cell (V = 2.1 L), Z is the absolute value of the chloride ion charge (Z = 1), and F is the Faraday constant (F = 96.49 × 10⁻⁶). 3C / mol), E is the applied voltage (E = 22V), γ is the activity coefficient (γ = 1), c0 is the chloride ion concentration in the cathode cell (c0 = 52.6 g / L); A is the effective cross-sectional area of ​​the specimen (A = 0.006362 m²). 2 ); The slope of the cumulative chloride ion concentration versus time curve is given.

[0086] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the ITZ permeability coefficient of concrete based on aggregate type, characterized in that, Includes the following steps: (1) Select a suitable mold: Select a concrete column mold with a cross-section shaped like a racetrack. The height of the concrete column mold is 50mm. The concrete column mold consists of two symmetrical and equal-sized semi-circular areas. A non-removable baffle with the same height as the concrete column mold is set between the two semi-circular areas. The two semi-circular areas are used to fill the ITZ area and the cement mortar area, respectively. Let the sum of the cross-sectional areas of the two semi-circular areas be A. The bottom of the concrete column mold is a removable wooden board. (2) Select a cuboid or cylinder of equal diameter with a side length of 100mm as the model aggregate. The material of the model aggregate should be the same as that of the real aggregate. When the actual roundness σ of the aggregate is ≥0.75, select the cylindrical model aggregate; when the actual roundness σ of the aggregate is <0.75, select the cuboid model aggregate. In the formula: σ is the actual roundness of the aggregate; A0 is the projected area of ​​the coarse aggregate particles in the maximum contour image; L0 is the perimeter of the projected contour of the coarse aggregate particles in the maximum contour image; (3) After determining the type and shape of the model aggregate, place a number of model aggregates with a height of 50mm into one of the semi-circular areas of the concrete column mold prepared in step (1). The bottom of the model aggregate is bonded to the bottom of the concrete column mold. To avoid the overlap of the ITZ around the model aggregate, the model aggregates should be evenly distributed when they are placed. Then, pour cement mortar into the two semi-circular areas of the concrete column mold. After pouring, place it in a standard curing room for curing. After curing for the specified age, remove the specimen and separate the concrete column mold from the bottom of the specimen to obtain specimens containing model aggregate and cement mortar specimens respectively. (4) Prepare multiple parallel specimens containing model aggregate specimens, observe and record the ITZ thickness value of concrete using a scanning electron microscope, select 4 at the corners and 1 at the center as representatives, record the thickness 20 times along the perimeter of each model aggregate and take the average value, and record the average ITZ thickness of concrete as d. (5) After determining the thickness of the ITZ as d, calculate the area A of the ITZ region. ITZ And the cement mortar area A in the ITZ region CE ; (6) The aggregate-containing specimens and cement mortar specimens obtained in step (4) are subjected to a permeability test of the corrosive medium, and the permeability coefficient D of the aggregate-containing specimens is determined simultaneously. SU Permeability coefficient D of cement mortar specimen CE ; For the permeability test, in specimens containing model aggregate, the permeability coefficient of the specimen satisfies: The permeability coefficient D of the concrete interface transition zone can be derived from the above formula. ITZ : In the formula: D SU D is the permeability coefficient of the specimen containing the model aggregate, obtained from the permeability test of the specimen with the model aggregate; CE is the permeability coefficient of a pure cement mortar specimen, obtained from a pure cement mortar specimen permeability test; A is the total cross-sectional area of ​​the two semi-circular regions; A AGG D represents the cross-sectional area of ​​the aggregate in a single model. ITZ This represents the permeability coefficient of the interface transition zone.

2. The method for evaluating the ITZ permeability coefficient of concrete by aggregate type according to claim 1, characterized in that, In step (1), the radius of the semi-circular area is 50mm and the thickness of the baffle is 12mm.

3. The method for evaluating the ITZ permeability coefficient of concrete by aggregate type according to claim 2, characterized in that, In step (3), the number of model aggregates is 10, and it is preferable to use epoxy resin adhesive to bond the bottom of the model aggregates to the bottom of the concrete column mold.

4. The method for evaluating the ITZ permeability coefficient of concrete by aggregate type according to claim 3, characterized in that, In step (5): ① When the model aggregate is square aggregate, let its side length be l, A ITZ =n×(πd) 2 +4dl), ② When the model aggregate is circular, let its radius be r, A ITZ = n×π[(r+d)] 2 -r 2 ], In the formula: A is the total cross-sectional area of ​​the two semicircular regions, in mm. 2 n represents the number of aggregates in the model, taken as 10; A ITZ The ITZ area is the cross-sectional area of ​​the specimen containing the model aggregate, in mm². 2 A CE The area of ​​the cement mortar zone in the cross-section of the specimen containing the model aggregate is expressed in mm. 2 ; d is the ITZ thickness in mm; l is the side length of the cuboid model aggregate, taken as 10 mm; r is the radius of the circular model aggregate, taken as 5 mm.

5. The method for evaluating the ITZ permeability coefficient of concrete by aggregate type according to claim 4, characterized in that, In step (6), the device for the permeation test includes four sealing grooves, two of which are permeation medium sealing grooves and two are ordinary medium sealing grooves. The specimens containing model aggregate and cement mortar that have been cured in step (3) are placed between the four sealing grooves. The specimens containing model aggregate and cement mortar together form a cylinder with a radius of 50 mm and a height of 50 mm.

6. The method for evaluating the ITZ permeability coefficient of concrete by aggregate type according to claim 5, characterized in that, Before placing the model aggregate specimens and cement mortar specimens into the four sealing grooves, apply epoxy resin or similar coating to the sides to prevent the penetrating medium from seeping in from the sides.

7. The method for evaluating the ITZ permeability coefficient of concrete by aggregate type according to claim 5, characterized in that, In step (6), a semi-circular cross-sectional opening is provided between the permeating medium sealing tank and the ordinary medium sealing tank. The specimen is placed in the permeating medium sealing tank at one end through the opening and in the ordinary medium sealing tank at the other end. A fixing mesh is set between the connecting port and the specimen. The fixing mesh is a semi-circular copper mesh with a radius of 50 mm and a thickness of 1 mm. Multiple evenly distributed through holes are set in the middle to ensure that chloride ions can freely permeate between the solution, the copper mesh and the specimen. The fixed mesh has a thin iron sheet with a height of 10 mm on the round edge. A rubber ring is installed in the test area between the permeation medium sealing tank and the ordinary medium sealing tank. The rubber ring is 50mm high and has a racetrack-shaped cross-section, which can simultaneously hold two semi-cylindrical specimens, namely a specimen containing model aggregate and a cement mortar specimen. The radius of the rubber ring is smaller than that of the specimen. The material is high-temperature resistant and anti-aging butyl rubber, which can freely expand and contract to tightly wrap the specimen. A 5mm thick soft rubber baffle is set in the middle of the rubber ring to separate the two specimens. Both ends of the rubber ring are equipped with pipe clamps to fix the specimen, the rubber ring, and the thin iron sheet on the fixing net.

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