Method and device for preparing internal cracks of cement mortar sample based on sublimability of camphor

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly relates to a method and a device for preparing internal cracks of a cement mortar sample based on camphor sublimability. According to the invention, an alkaline reaction is blocked by the paraffin isolation layer, and the problems of residue, thermal damage and chemical interference in the traditional technology are solved by combining a sectional volatilization control process (paraffin isolation, supercritical CO2 dissolution, sectional volatilization and vacuum improvement). The refitted vacuum device realizes low-temperature efficient sublimation through pressure control and condensation recovery, and supports accurate preparation of a complex fracture network. Experiments show that the compressive strength loss of the sample is reduced to be within 5%, and the mechanical test precision is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and particularly relates to a method and a device for preparing internal cracks in a cement mortar sample based on the sublimation of camphor. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] In geotechnical engineering research, prefabricating internal fractures with precise geometric features is an important technical means for studying the mechanical behavior of fractured media. Conventional fracture prefabrication methods currently use 3D printing technology to prepare a thin mold of a simulated fracture plate, which is then embedded within the specimen. However, this method has two key technical drawbacks: (1) The sample structure is easily damaged during the mold removal process, and it is difficult to completely remove it, resulting in the formation of foreign material residues inside the sample; (2) The difference in elastic modulus between the residual mold material and the matrix material (usually more than 2 orders of magnitude) will significantly change the stress field distribution of the specimen, seriously affecting the accuracy of mechanical test results such as uniaxial compression and three-point bending.

[0004] Although the existing patented technology proposes the use of naphthalene-based water-soluble materials (commonly known as mothballs) as a crack mold, serious technical defects have been found in actual application: (1) In order to make the mothballs sublime quickly, oven heating was used. Although effective, it may cause temperature gradients, thus affecting the uniformity of the sample. At the same time, the mechanical properties of the sample will also change at high temperatures, causing errors in subsequent research. (2) When cement-based materials (strong alkaline environment with pH ≥ 13) come into contact with naphthalene-based materials, a violent hydration reaction will occur, causing plastic deformation and volume expansion of the mold material, resulting in a significant deviation between the final crack geometry and the design parameters.

[0005] In view of the above technical problems, if the conventional wax coating method is directly used to avoid the influence of the alkaline environment mentioned above, and the vacuum decompression method is used to reduce the sublimation temperature of camphor to solve the problem (1), although it is feasible to a certain extent, this method is prone to the following problems when using gasoline to dissolve paraffin due to the mechanical properties of the cement mortar sample: 1) After gasoline dissolves paraffin, gasoline residue is likely to remain in the cavity inside the specimen. During vacuum decompression, the gasoline evaporates rapidly, generating local high pressure, which can cause microcracks in the specimen (the risk is higher when the porosity is greater than 15%). 2) At the same time, high pressure causes the gasoline to evaporate quickly, which also generates local high temperatures, causing thermal damage to the sample (due to high temperature, the sample will be locally cracked and deformed, and its mechanical properties will change), affecting the accuracy of subsequent research; 3) Gasoline vapor contaminates vacuum equipment, which greatly increases maintenance costs.

[0006] 4) Conventional paraffin layers may still undergo microscopic penetration in a long-term alkaline environment (pH ≥ 13), resulting in local hydration and deformation of camphor.

[0007] Therefore, those skilled in the art are in urgent need of an innovative method for preparing internal cracks in cement mortar specimens that can avoid residue, thermal damage and chemical reactions. Summary of the Invention

[0008] In response to the needs of the prior art, the purpose of the present invention is to provide a method and device for preparing internal cracks in cement mortar samples based on the sublimation of camphor. The present invention systematically solves the core problems of the prior art, such as residues, thermal damage, chemical reactions and equipment pollution, through an innovative combination of multiple steps (paraffin isolation, supercritical CO2 dissolution, segmented volatilization, and vacuum improvement). That is, while avoiding the internal residue of hard solid substances, the present invention reduces the problem of thermal damage to the sample caused by high temperature accelerated camphor volatilization, avoids the problem of change in the shape of prefabricated internal cracks caused by chemical reactions of solid camphor in an alkaline environment, and avoids the problem of gasoline treatment affecting the accuracy of the research.

[0009] Specifically, the present invention provides the following technical solutions: A first aspect of the present invention provides a method for preparing internal cracks in a cement mortar sample based on the sublimation of camphor, comprising the following steps: S1. Coating a paraffin layer on the surface of solid camphor to construct a chemical isolation barrier; S2. Fix the waxed camphor in a cement mortar mold, cast and cure the sample; S3. Camphor is removed through a staged volatilization control process of supercritical CO2 dissolution, pre-drying and vacuum sublimation to form internal cracks.

[0010] Preferably, in step S2, the solid waxed camphor prepared in step S1 is fixed in the middle of the sample in a mold of the cement mortar sample, specifically by means of a thin cotton thread, and cement mortar is poured so that the cement mortar completely wraps the solid camphor.

[0011] Preferably, in step S3, the supercritical CO2 dissolution is performed by placing the sample in a vacuum chamber and introducing supercritical CO2, wherein the parameters in the vacuum chamber are set to: temperature 35°C and pressure 10 MPa. The high diffusivity and strong dissolving power of supercritical CO2 dissolution penetrate the pores of the sample to achieve efficient dissolution and removal of paraffin.

[0012] Preferably, in step S3, after the supercritical CO2 is dissolved, the mixture of paraffin and CO2 is separated through a waste treatment system, including reducing the pressure to normal pressure through a pressure reducing valve, so that the paraffin is precipitated and trapped by a ceramic filter; the CO2 is liquefied through a condenser and stored in a liquid CO2 storage tank.

[0013] Preferably, in step S3, the pre-drying temperature is 48-55°C, preferably 50°C.

[0014] Preferably, in step S3, the vacuum sublimation is controlled by gradient pressure reduction, specifically: first reducing the pressure to 50 kPa and maintaining it for 2 to 2.5 hours; then reducing it to 10 kPa and maintaining it for 1 to 1.5 hours.

[0015] A second aspect of the present invention provides a device for preparing internal cracks in a cement mortar sample based on the sublimation property of camphor, comprising: A vacuum chamber for accommodating cement mortar samples; The micro-CT scanning module is isolated from the vacuum chamber by a beryllium window and is used to scan the interior of the sample; A pressure control module is connected to the vacuum chamber through a pipeline and includes a pressure sensor and a vacuum pump connected in sequence; The waste treatment module is connected to the outlet of the vacuum chamber through a pressure reducing valve, and includes a ceramic filter, a condenser and a liquid CO2 storage tank connected in sequence.

[0016] Preferably, the micro CT scanning module is embedded in the normal pressure isolation module on the side wall of the vacuum chamber, with the beryllium window facing the interior of the chamber.

[0017] Preferably, the micro CT scanning module is wirelessly connected to the CT scanning control system to control the scanning process and display the results.

[0018] Preferably, the vacuum pump and the pressure sensor of the pressure control system are connected in series on the pipeline of the vacuum chamber.

[0019] Preferably, the input end of the pressure reducing valve of the waste treatment system is connected to the outlet of the vacuum chamber, and the output end is connected to the ceramic filter; the outlet of the ceramic filter is connected to the condenser and the liquid CO2 storage tank in sequence through a pipeline.

[0020] Preferably, the device for preparing internal cracks in cement mortar samples based on the sublimation of camphor also includes a paraffin concentration monitoring device, which is arranged on the pipeline between the vacuum chamber and the pressure reducing valve to detect the residual paraffin concentration in the discharged CO2 in real time.

[0021] The third aspect of the present invention provides a cement mortar sample for preparing internal cracks in the cement mortar sample based on the sublimation of camphor, which is prepared by the method for preparing internal cracks in the cement mortar sample based on the sublimation of camphor described in the first aspect.

[0022] The beneficial effects achieved by one or more of the above technical solutions of the present invention are as follows: (1) Using CO2 under conditions close to its critical point (temperature 35°C, pressure 10 MPa), a special fluid (supercritical CO2) is formed that has both high gas diffusivity and strong liquid solubility. It can efficiently dissolve paraffin and penetrate into the tiny pores of cement, and leaves no residue after evaporation.

[0023] (2) The present invention reduces the sublimation time of camphor by modifying the vacuum chamber device: the sample is placed in the modified vacuum chamber device and the absolute pressure is set to 10-50 kPa. After the camphor is completely sublimated, a cavity is formed inside the sample. At the same time, the addition of the CT scanning module prevents solid camphor residue from remaining in the sample.

[0024] (3) The method and device for preparing internal cracks in cement mortar samples based on the sublimation of camphor prepared by the present invention achieve zero residue: 1) Supercritical CO2 dissolution to eliminate paraffin residue; 2) Low temperature safety: vacuum sublimation temperature is lower than 50°C to avoid thermal damage to the sample; 3) Morphological fidelity: Prevents microscopic penetration in long-term alkaline environments (pH ≥ 13), prevents hydration and deformation of solid camphor, and avoids minor damage caused by local high pressure generated by rapid evaporation of gasoline; 4) Equipment compatibility: avoids gasoline contamination of vacuum devices and extends the life of vacuum equipment; 5) Flexible fabrication: supports customized design of single fractures or complex networks (e.g., cross-sections, fractal fractures); 6) Engineering application significance: The improvement of specimen strength can effectively support the improvement of engineering safety, cost control, and reduction of disaster risks.

[0025] (4) The improved method and device of the present invention achieves a 6% increase in the compressive strength of cement mortar samples, which can bring benefits in many aspects to engineering construction, such as: enhancing rock stability and safety, optimizing support structure design, improving blasting and excavation efficiency, extending the service life of the project, and reducing the risk of site disasters. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 This is a schematic diagram of the structure of the cement mortar sample of the present invention, wherein: 1. Cement mortar sample; 2. Solid camphor; 3. Thin cotton thread; Figure 2 This is a flow chart of the segmented volatilization control of the present invention; Figure 3 This is a schematic diagram of the structure of the modified vacuum device of the present invention, wherein: 4, vacuum chamber; 5, micro CT scanning module; 6, pressure control module; 7, vacuum pump; 8, pressure sensor; 9, pressure reducing valve; 10, ceramic filter; 11, condenser; 12, liquid CO2 storage tank; 13, waste treatment module; 14, paraffin concentration monitoring equipment. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0029] Current methods for prefabricating internal cracks in cement specimens rely primarily on 3D-printed molds or naphthalene-based water-soluble materials (such as camphor). However, existing technologies carry risks of mold residue, heat damage, chemical reactions, and gasoline residue. Therefore, an innovative method that avoids these residues, heat damage, and chemical reactions is urgently needed.

[0030] A first exemplary embodiment of the present invention provides a method for preparing internal cracks in a cement mortar sample based on the sublimation of camphor, comprising the following steps: S1. Coating a paraffin layer on the surface of solid camphor to construct a chemical isolation barrier; S2. Fix the waxed camphor in a cement mortar mold, cast and cure the sample; S3. Camphor is removed through a staged volatilization control process of supercritical CO2 dissolution, pre-drying and vacuum sublimation to form internal cracks.

[0031] In one or more embodiments of this embodiment, in step S2, in the mold of the cement mortar sample, specifically by means of thin cotton thread, the solid waxed camphor prepared in step S1 is fixed in the middle position of the sample, and cement mortar is poured so that the cement mortar completely wraps the solid camphor.

[0032] In one or more embodiments of this embodiment, in step S3, the supercritical CO2 dissolution is to place the sample in a vacuum chamber, introduce supercritical CO2 (35°C, 10 MPa), and use its high diffusivity and strong dissolving power to penetrate the pores of the sample to achieve efficient dissolution and removal of paraffin.

[0033] In one or more embodiments of this embodiment, in step S3, after the supercritical CO2 is dissolved, the mixture of paraffin and CO2 is separated through a waste treatment system, including reducing the pressure to normal pressure through a pressure reducing valve, so that the paraffin is precipitated and retained by a ceramic filter; the CO2 is liquefied through a condenser and stored in a liquid CO2 storage tank.

[0034] In one or more examples of this embodiment, in step S3, the pre-drying temperature is 48-55°C, preferably 50°C.

[0035] In one or more examples of this embodiment, in step S3, the vacuum sublimation is controlled by gradient pressure reduction, specifically: first reducing the pressure to 50 kPa and maintaining it for 2-2.5 hours; then reducing it to 10 kPa and maintaining it for 1-1.5 hours.

[0036] It should be noted that the present invention produces solid camphor with a desired crack shape. For example, if the desired crack shape is 1 mm×1 mm×1 mm, the solid camphor is produced into a shape of 1 mm×1 mm×1 mm. This shape is not unique and can be dynamically adjusted according to experimental needs.

[0037] It should be noted that the 10 MPa pressure required to introduce supercritical CO₂ in the present invention does not cause structural damage to samples with a compressive strength of 30 MPa or above. The inventors verified through 15 MPa preload experiments that the structural integrity of the samples was intact (porosity change <0.5%). Supercritical CO₂ applies pressure through uniform penetration rather than mechanical impact, avoiding stress concentration and preventing sample damage caused by localized stress concentration.

[0038] A second typical embodiment of the present invention provides a device for preparing internal cracks in a cement mortar sample based on the sublimation property of camphor, comprising: A vacuum chamber for accommodating cement mortar samples; The micro-CT scanning module is isolated from the vacuum chamber by a beryllium window and is used to scan the interior of the sample; A pressure control module is connected to the vacuum chamber through a pipeline and includes a pressure sensor and a vacuum pump connected in sequence; The waste treatment module is connected to the outlet of the vacuum chamber through a pressure reducing valve, and includes a ceramic filter, a condenser and a liquid CO2 storage tank connected in sequence.

[0039] In one or more embodiments of this embodiment, the micro-CT scanning module is embedded in a normal-pressure isolation module on the sidewall of the vacuum chamber, with the beryllium window facing the interior of the chamber. Placing the micro-CT scanning module within the normal-pressure isolation module allows for non-destructive radiation penetration through the beryllium window of the normal-pressure isolation module. This ensures that CT scanning operates at standard atmospheric pressure while preventing damage to the CT scanning module equipment caused by pressures of 10 MPa.

[0040] In one or more examples of this embodiment, the micro-CT scanning module is wirelessly connected to a CT scanning control system to control the scanning process and display the results. The micro-CT scanning module and the CT scanning control system use a wireless connection to transmit data and images for real-time monitoring of solid camphor residue in the sample.

[0041] In one or more embodiments of this implementation, the vacuum pump and the pressure sensor of the pressure control system are connected in series on the pipeline of the vacuum chamber.

[0042] In one or more embodiments of this implementation, the input end of the pressure reducing valve of the waste treatment system is connected to the outlet of the vacuum chamber, and the output end is connected to the ceramic filter; the outlet of the ceramic filter is connected to the condenser and the liquid CO2 storage tank in sequence through a pipeline.

[0043] In one or more embodiments of this embodiment, the device for preparing internal cracks in cement mortar samples based on the sublimation of camphor also includes a paraffin concentration monitoring device, which is arranged on the pipeline between the vacuum chamber and the pressure reducing valve for real-time detection of the residual paraffin concentration in the exhausted CO2.

[0044] It should be noted that the present invention selects a vacuum chamber with controllable temperature and a pressure resistance of more than 10 MPa to introduce supercritical CO2. At the same time, a micro CT scanning module is added to the side wall inside the vacuum device to prevent the solid camphor from not completely volatilizing and remaining inside the sample, affecting the accuracy of subsequent mechanical experimental research.

[0045] It should be noted that after using supercritical CO2 to dissolve paraffin, the paraffin molecules are dispersed in the supercritical CO2 in a single-molecule state, forming a supercritical composite phase, and are carried out by the flowing supercritical CO2. The supercritical CO2 containing paraffin passes through a waste treatment system (pressure reducing valve, ceramic filter, condenser, liquid CO2 storage tank) to process the paraffin and CO2. At this time, the pressure reducing valve reduces the pressure to 0.1 MPa, the normal pressure, and the paraffin precipitates due to a sudden drop in solubility, and is thus trapped by the ceramic filter. Under the action of the condenser, the supercritical CO2 is gradually condensed into liquid CO2 and stored in the liquid CO2 storage tank, avoiding discharge into the atmosphere and polluting the environment, and can be reused.

[0046] It should be noted that the pressure control module in the present invention is composed of a vacuum pump and a pressure sensor. The module monitors the pressure in the vacuum chamber in real time through the pressure sensor and controls the pressure through the vacuum pump.

[0047] A third typical embodiment of the present invention provides a cement mortar sample for preparing internal cracks in the cement mortar sample based on the sublimation of camphor, which is prepared by the above-mentioned method for preparing internal cracks in the cement mortar sample based on the sublimation of camphor.

[0048] The paraffin wax coating on the surface of the solid camphor in this invention is due to the fact that cement slurry (or liquid concrete) is typically highly alkaline, and solid camphor undergoes a hydration reaction when it comes into contact with cement slurry, affecting the final internal crack shape. Therefore, the paraffin wax coating is intended to prevent the solid camphor from reacting with the cement slurry, creating a chemical isolation layer that blocks alkaline ions, thus stabilizing the solid camphor in an alkaline environment and preserving the final internal crack shape, thereby ensuring the accuracy of subsequent research.

[0049] The cement mortar sample, after dissolving paraffin, was placed in a vacuum chamber at a controlled pressure of 10–50 kPa (absolute). This method exploits the principle that, under vacuum conditions, reducing external pressure lowers the sublimation temperature, thereby promoting the volatilization of camphor. This method accelerates the volatilization of solid camphor without requiring high temperatures. The pressure within the vacuum chamber can be adjusted based on the experimental requirements for solid camphor volatilization. Compared to traditional methods that accelerate the sublimation of solid camphor in an oven at high temperatures, this method avoids the effects of high temperatures on the mechanical properties of the sample, thereby enabling more precise subsequent research. The vacuum pressure can be controlled using a gradient to protect the sample structure (avoid stress damage) and improve the fidelity of the crack morphology (uniform sublimation).

[0050] Among them, the volatilization time of camphor needs to be judged based on parameters such as its size and the porosity of the cement mortar sample, and manual intervention can be performed if necessary.

[0051] Among them, the pre-drying time of the hot air circulation box needs to be determined according to the amount of paraffin and CO2 used when making the sample.

[0052] Among them, this method can not only produce a single crack of arbitrary shape, but also produce a crack network of arbitrary shape.

[0053] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0054] Example : like Figure 1As shown, a cement mortar sample 1 with a size of 200 mm × 200 mm × 200 mm is made by a mold, and a solid camphor 2 with a size of 1 mm × 1 mm × 1 mm is made by a mold. The solid camphor 2 is fixed to the center position of both sides of the mold for making the cement mortar sample 1 by thin cotton thread 3, that is, the solid camphor 2 is fixed to the center position of the cement mortar sample 1 (the shape of the internal crack finally formed is the same as that of the solid camphor 2).

[0055] like Figure 2 As shown, the present invention sets a micro CT scanning module 5 to be placed on the inner side of the side wall of the vacuum chamber 4, and the CT scanning control system controls the CT scanning process and displays the CT scanning results. The entire system pipeline path starts from the vacuum chamber 4 and is connected in series to the pressure control module 6. The pressure control module 6 is composed of a vacuum pump 7 and a pressure sensor 8. The module monitors the real-time pressure of the entire pipeline in real time through the pressure sensor 8 and performs pressure control through the vacuum pump 7, that is, the system controls the real-time pressure of the entire pipeline. The micro CT scanning module 5 is controlled by the CT scanning control system and is used to monitor the solid camphor residue in the sample in real time. After the supercritical CO2 dissolves the paraffin, the paraffin molecules are dispersed in the supercritical CO2 in a single molecule state to form a supercritical composite phase, and are carried out by the flowing supercritical CO2. The supercritical CO2 containing paraffin passes through the waste treatment module 13 (pressure reducing valve 9, ceramic filter 10, condenser 11, and liquid CO2 storage tank 12). At this time, the pressure reducing valve 9 reduces the pressure to 0.1 MPa, the atmospheric pressure. The paraffin precipitates due to a sudden drop in solubility and is then retained by the ceramic filter 10. The supercritical CO2 is gradually condensed into liquid CO2 by the condenser 11 and stored in the liquid CO2 storage tank 12. The paraffin concentration monitoring device 14 is used to monitor the paraffin concentration in the supercritical CO2 containing paraffin discharged from the vacuum chamber 4, ensuring that the final paraffin concentration is less than 0.1 ppm, thus ensuring that no paraffin remains in the cement mortar sample 1.

[0056] The manufacturing process of preparing internal cracks in cement mortar specimens based on the sublimation of camphor is as follows: (1) Preparation of solid camphor: Camphor powder was pressed into a 1 mm 3 Cube, surface coated with 20 μm paraffin layer; (2) Sample casting: In a 200 mm × 200 mm × 200 mm sample mold, camphor was fixed at the center of the mold with a thin cotton thread, cement was poured and standard curing was carried out for 28 days.

[0057] (3) Segmented volatilization (e.g. Figure 3 shown): Phase 1: Place the cement mortar sample in a vacuum chamber 4, introduce CO2, control the chamber temperature at 35°C, control the chamber pressure at 10 MPa, and maintain it for 40 minutes. At this time, CO2 is in a supercritical state. The high diffusivity and strong dissolving power of supercritical CO2 are used to penetrate the sample pores, achieving efficient dissolution and removal of paraffin. The discharged CO2 and paraffin are collected by the waste treatment module 13.

[0058] Stage 2: The sample is removed from the vacuum chamber 4 and pre-dried at 50°C for 10 min (in a hot air circulation oven) to remove the remaining CO2. Stage 3: The sample is placed in the vacuum chamber 4 again, and the real-time pressure in the entire pipeline is monitored by the pressure sensor 8 in the pressure control module 6, and the real-time pressure in the entire pipeline is adjusted by the vacuum pump 7.

[0059] Pressure Control Method: The vacuum pressure was controlled using a gradient (first decreasing to 50 kPa and maintaining it for 2 hours, then decreasing to 10 kPa to accelerate sublimation and maintaining it for 1–1.5 hours). This gradual pressure reduction method protected the sample structure (avoiding stress damage caused by sudden pressure changes) and improved the fidelity of the crack morphology (ensuring uniform sublimation of the solid camphor and avoiding drastic changes in its morphology caused by sudden pressure drops). During the vacuum sublimation process, real-time CT scanning of the solid camphor inside the sample was performed. If any solid camphor remained after the set vacuum pressure time, the vacuum pressure was maintained until the solid camphor was completely sublimated.

[0060] Test Example 1 This test example investigates the performance of the traditional oven method and the method for preparing internal cracks in cement mortar samples based on camphor sublimation provided by the present invention. Due to the different residual error problems, all for the purpose of subsequent mechanical property testing of the samples, the compressive strength test was compared between the traditional oven method (e.g., 80°C for 1 h) and the method involved in the embodiment of the present invention. It can be seen that the method of the present invention effectively reduces the damage problem of the sample strength as a whole (as shown in Table 1).

[0061] Table 1 Comparison of compressive strength between the conventional oven method (80°C for 1 h) and the method of the present invention

[0062] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing internal cracks in cement mortar samples based on the sublimation of camphor, characterized in that: The following steps are involved: S1. Coating a paraffin layer on the surface of solid camphor to construct a chemical isolation barrier; S2. Fix the waxed camphor in a cement mortar mold, cast and cure the sample; S3. Camphor is removed through a staged volatilization control process of supercritical CO2 dissolution, pre-drying and vacuum sublimation to form internal cracks.

2. The method for preparing internal cracks in cement mortar samples based on camphor sublimation as claimed in claim 1, wherein In step S2, the solid waxed camphor prepared in step S1 is fixed in the middle of the sample in a mold of the cement mortar sample by means of a thin cotton thread, and cement mortar is poured so that the cement mortar completely wraps the solid camphor.

3. The method for preparing internal cracks in cement mortar samples based on camphor sublimation as claimed in claim 1, wherein In step S3, the supercritical CO2 dissolution is to place the sample in a vacuum chamber and introduce supercritical CO2, and the parameters in the vacuum chamber are set as follows: temperature 35°C, pressure 10 MPa; Preferably, after the supercritical CO2 is dissolved, the mixture of paraffin and CO2 is separated through a waste treatment system, including reducing the pressure to normal pressure through a pressure reducing valve, so that the paraffin is precipitated and trapped by a ceramic filter; the CO2 is liquefied through a condenser and stored in a liquid CO2 storage tank.

4. The method for preparing internal cracks in cement mortar samples based on camphor sublimation as claimed in claim 1, wherein: In step S3, the pre-drying temperature is 48-55°C, preferably 50°C.

5. The method for preparing internal cracks in cement mortar samples based on camphor sublimation as claimed in claim 1, wherein: In step S3, the vacuum sublimation is controlled by gradient pressure reduction, specifically: first reducing the pressure to 50 kPa and maintaining it for 2-2.5 hours; then reducing it to 10 kPa and maintaining it for 1-1.5 hours.

6. A device for preparing internal cracks in cement mortar samples based on the sublimation of camphor, characterized in that: include: A vacuum chamber for accommodating cement mortar samples; The micro-CT scanning module is isolated from the vacuum chamber by a beryllium window and is used to scan the interior of the sample; A pressure control module is connected to the vacuum chamber through a pipeline and includes a pressure sensor and a vacuum pump connected in sequence; The waste treatment module is connected to the outlet of the vacuum chamber through a pressure reducing valve, and includes a ceramic filter, a condenser and a liquid CO2 storage tank connected in sequence.

7. The device according to claim 6, characterized in that The micro CT scanning module is embedded in the atmospheric pressure isolation module on the side wall of the vacuum chamber, with the beryllium window facing the interior of the chamber; Preferably, the micro CT scanning module is wirelessly connected to the CT scanning control system to control the scanning process and display the results.

8. The device according to claim 6, wherein The vacuum pump and pressure sensor of the pressure control system are connected in series on the pipeline of the vacuum chamber; Preferably, the input end of the pressure reducing valve of the waste treatment system is connected to the outlet of the vacuum chamber, and the output end is connected to the ceramic filter; the outlet of the ceramic filter is connected to the condenser and the liquid CO2 storage tank in sequence through a pipeline.

9. The device according to claim 6, wherein The device for preparing internal cracks in cement mortar samples based on the sublimation of camphor also includes a paraffin concentration monitoring device, which is arranged on the pipeline between the vacuum chamber and the pressure reducing valve to detect the residual paraffin concentration in the discharged CO2 in real time.

10. A cement mortar sample for preparing internal cracks in a cement mortar sample based on the sublimation of camphor, characterized in that: The method for preparing internal cracks in cement mortar samples based on the sublimation of camphor as described in any one of claims 1 to 5 is obtained.

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