Porous material moisture transmission behavior characterization method based on strain distribution

Abstract

The invention relates to a porous material moisture transmission behavior characterization method based on strain distribution. Comprising the following steps: (1) sequentially adhering a to-be-tested porous material sample, a supporting piece and a water container to form an experimental device; (2) carrying out tomography imaging on the device to obtain the spatial distribution of the absorption coefficient of the non-water-absorbing sample line; (3) injecting water into the water container; (4) after water absorption, carrying out tomography imaging analysis to obtain line absorption coefficient spatial distribution of the water absorption sample; (5) performing image registration on the water absorption experiment devices in the non-water absorption state and the water absorption state by taking the supporting piece as a reference; (6) moving the position of the sample in the water absorption state; (7) carrying out DVC analysis on a sample which does not absorb water and the registered sample to obtain the strain of the sample in the water absorption height direction in the water absorption process; and (8) converting the local strain into local pore saturation so as to obtain the moisture content distribution of the sample along the height direction. The method is accurate, reliable and easy to operate.

Description

Technical Field

[0001] The invention belongs to the field of building material characterization, and in particular relates to a method for characterizing moisture transmission behavior of porous materials based on strain distribution. Background Art

[0002] Concrete and rock are porous materials that are widely found in nature. The moisture transfer process inside them has a crucial impact on the performance, stability and durability of the materials.

[0003] As a complex porous medium, concrete has internal pores filled with fluids (solutions and humid air). Due to the mechanical and thermodynamic imbalance of the fluids and their components in the pores, various mass transfer phenomena will occur in concrete, such as diffusion and infiltration. The transmission of water in concrete not only causes changes in the effective stress of concrete, but also plays a role in transporting corrosive substances. In addition, the water saturation in various parts of the concrete also directly affects the speed and degree of various damage processes, such as the corrosion rate, carbonization reaction rate, and the degree of freeze-thaw damage. Rocks also have porous and multi-phase coupling characteristics, and contain many joints and fissures inside, which are generally associated with hydraulic seepage (saturated and unsaturated) under the surrounding water environment conditions. Seepage in the rock mass is both a medium and a load, and it also has an impact on the physical and mechanical parameters of the joint interface, which plays an important role in the deformation stability of the rock mass.

[0004] At present, in order to study the moisture transport process inside porous materials such as concrete and rock, researchers and engineers have developed a variety of methods. A traditional and intuitive method is the weighing method. This method analyzes the water absorption depth of the specimen by weighing the weight of the specimen at different time points during the test. The advantage of this method is that it is simple to operate, easy to implement, and can directly reflect the change in the water absorption of the specimen. However, the weighing method also has obvious disadvantages. Due to the complex and diverse pore structures inside porous materials, not all pores can be completely saturated with water. Therefore, the exact water absorption depth of the specimen cannot be accurately obtained only by weighing. In addition, the weighing method cannot provide detailed information about the dynamic process and distribution of moisture transport inside the material. Another relatively advanced method is X-ray tomography. X-ray tomography can obtain three-dimensional structural information inside the material without damage, so it has potential application value in studying the moisture transport of porous materials. However, X-rays are less sensitive to water. When directly scanning water-containing porous materials, it is often difficult to clearly show the trace of water. To improve this situation, researchers have tried to use contrast agents to enhance the contrast of water. Although the use of contrast agents does improve the imaging effect of X-ray tomography on water to a certain extent, the surface tension of the contrast solution is different from that of water, which may lead to inconsistent transport laws of the contrast solution and pure water inside the material. Therefore, the method using contrast agents still has certain limitations in accuracy. There are also some other methods used to study the moisture transport of porous materials, such as nuclear magnetic resonance imaging (MRI), electrical impedance tomography (EIT), etc. But these methods all have some deficiencies. For example, although MRI can provide high-resolution moisture distribution images, the equipment is expensive, the operation is complex, and there are certain limitations on the size and shape of the specimen; EIT is sensitive to the change in the conductivity of the material, but it may face problems of non-uniqueness and instability of the solution when dealing with complex porous structures. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for characterizing the moisture transport behavior of porous materials based on strain distribution.

[0006] The technical solution for achieving the purpose of the present invention is as follows: A method for characterizing the moisture transport behavior of porous materials based on strain distribution includes the following steps:

[0007] Step (1): Use a fixing agent to sequentially paste the specimen of the porous material to be tested, the support, and the water container to form a water absorption experimental device, ensuring that there is no relative movement between the specimen of the porous material to be tested, the support, and the water container, and the support does not hinder the water absorption process of the specimen;

[0008] Step (2): Before the water absorption experiment starts, place the entire water absorption experimental device on the sample stage of the tomographic imaging device, conduct a tomographic imaging once, and obtain the spatial distribution of the linear absorption coefficient of the non-water-absorbed specimen.

[0009] Step (3): Inject water into the water-containing vessel to ensure that the bottom surface of the specimen is immersed in water, and replenish water periodically to maintain the liquid level in the vessel.

[0010] Step (4): At the water absorption time t, using exactly the same test parameters as in step (2), conduct a tomographic imaging analysis again to obtain the spatial distribution of the linear absorption coefficient of the water-absorbed specimen.

[0011] Step (5): Using the support as a reference, perform image registration on the water absorption experimental device in the non-water-absorbed and water-absorbed states to obtain the position movement of the entire water absorption experimental device between the two tests.

[0012] Step (6): Using the position movement result obtained in step (6), perform position movement on the specimen in the water-absorbed state to eliminate the displacement in the non-water-absorbed and water-absorbed states, thereby completing the registration.

[0013] Step (7): Using the non-water-absorbed specimen and the specimen after registration in step (6), conduct DVC analysis to obtain the strain ε generated by the specimen in the water absorption height direction during the water absorption process. z ;

[0014] Step (8): Combining the material porosity, using the water absorption rate and strain correlation formula, convert the local strain ε z into the local pore saturation, and then obtain the water content distribution of the specimen along the height direction at the water absorption time t:

[0015]

[0016] In the formula, f(ω) is the water absorption rate, ρ water is the density of water, ρ is the density of the material, f(φ) is the material porosity distribution, and f(ε z ) represents the material strain.

[0017] Furthermore, the porous material specimen in step (1) is a water-insoluble rock, concrete or sponge.

[0018] Furthermore, the water-containing vessel and the support in step (1) need to be prepared from low-density waterproof materials.

[0019] Furthermore, the low-density waterproof material is plastic, glass or ceramic.

[0020] Furthermore, the support is multiple PVC thin rods with a diameter of 2 - 3 mm and a length of 2 - 3 cm.

[0021] Furthermore, the radiation source of the tomographic imaging device is X-ray, neutron source or gamma ray.

[0022] Compared with the prior art, the remarkable advantages of the present invention are as follows:

[0023] 1. High accuracy: Compared with the conventional water absorption method based on contrast agent, this method does not need to add other contrast substances to water, so it will not change the surface tension of water, and the obtained water absorption behavior is more accurate and reliable.

[0024] 2. Strong applicability: Compared with the prior DVC method, this method uses a vessel / pad rod as a marker, and through image registration technology, the position movement information of the sample during multiple scans can be obtained. Therefore, the sample is allowed to move during the water absorption process, so it is applicable to the detection of long-term moisture content.

[0025] 3. Non-destructive: This method uses non-contact tomographic scanning technology and does not cause any damage to the sample itself. Therefore, the sample can be retained for subsequent other tests or analyses.

[0026] 4. Conversion from strain to water absorption rate: By using the correlation formula between water absorption rate and strain, the mechanical strain information is converted into the water absorption rate information of the sample, providing a new method and idea for the research of material water absorption rate. Description of the Drawings

[0027] Figure 1 It is an unabsorbed picture of the sample before registration in the initial state.

[0028] Figure 2 It is a water absorption picture of the sample after 24 hours of water absorption.

[0029] Figure 3 It is a picture of the water absorption experimental device in the initial state after registration.

[0030] Figure 4 It is a curve of the calculated water absorption rate varying with height.

[0031] Figure 5 It is a three-dimensional map of the water absorption distribution of the sample calculated by DVC.

[0032] Figure 6 It is an X-Z cross-sectional view of the water absorption distribution of the sample calculated by DVC.

[0033] Figure 7 It is a Y-Z cross-sectional view of the water absorption distribution of the sample calculated by DVC.

[0034] Figure 8 It is an X-Z cross-sectional view of the water absorption distribution of the sample obtained by the traditional CT scanning method.

[0035] Figure 9 It is a Y-Z cross-sectional view of the water absorption distribution of the sample obtained by the traditional CT scanning method. Specific implementation mode

[0036] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the scope of protection required by the present invention is not limited thereto.

[0037] Embodiment 1

[0038] The present invention discloses a method for characterizing the moisture distribution of porous materials based on registration-digital image correlation.

[0039] S1. Prepare two kinds of foam concrete materials with different mix ratios for alternating printing. The mix ratio of the foam concrete printing strip A is 500 g of cement, 100 g of fly ash, 1 g of water reducing agent, 200 g of water, 1 g of foaming powder, and 0.2 g of foam stabilizing powder; the mix ratio of the foam concrete printing strip B is 500 g of cement, 100 g of fly ash, 1 g of water reducing agent, 200 g of water, 0.8 g of foaming powder, and 0.16 g of foam stabilizing powder.

[0040] S2. Adopt a printing speed of 20 cm / min and the extrusion speed of a circular printing head to prepare 3D printed foam concrete, and change the printing formula for each layer to achieve the effect of layer-by-layer alternating foam concrete printing.

[0041] S3. After covering the specimen with a plastic film for 24 h, cure the specimen in a standard curing environment for 28 days, and then cut a specimen of 2 cm×3 cm×10 cm from the cured specimen. The specimen contains two printing strips and a printing gap, and the printing gap is consistent with the water absorption direction.

[0042] S3. Stick the water container, the spacer rod and the specimen to be water-absorbed tightly together as Figure 1 shown, ensuring that there is no relative movement among the three during the whole experiment to obtain the water absorption experimental device.

[0043] S4. Put the specimen into a vacuum drying oven at 45°C for more than 14 days, seal the side and top surfaces of the specimen with epoxy resin, and only leave the bottom surface for the water absorption experiment. At the same time, stick a water container made of PVC material (diameter 3 cm, height 1 cm) and a support (consisting of 3 PVC thin rods with a diameter of 2 mm and a length of 2 cm) to the specimen to be water-absorbed to form a water absorption experimental device. The overall water absorption device is as Figure 1 shown. Ensure that there is no relative movement among the water container, the support and the specimen after the resin hardens.

[0044] S5. Place the experimental device in the sample chamber of the Xradia 515Versa micro-computed tomography system (X-CT) of Carl Zeiss, and conduct the first CT scan. The voltage used for the scan is 100 KeV, the current is 0.3 A, and the effective resolution is 53 μm to obtain the three-dimensional spatial distribution of the linear absorption coefficient of the unabsorbed water specimen.

[0045] S6. Remove the water absorption device, fill the water container with water to keep the bottom of the specimen immersed in water. Complement water periodically to maintain the liquid level in the water container.

[0046] S7. After water absorption for 24 h (as Figure 2 shown), place the specimen in the CT sample chamber again, and conduct another CT scan using exactly the same test parameters as in S5 to obtain the three-dimensional spatial distribution of the linear absorption coefficient of the partially water-absorbed specimen.

[0047] S8. Using the support as the registration reference, calculate the position movement of the specimen during the two CT scans; then bring the position movement information into the results of the second CT scan to match the spatial positions of the specimen before and after water absorption; as Figure 3 shown.

[0048] S9. Based on the registered CT results, segment the water-absorbed specimen, and use the digital image correlation (DVC) algorithm to calculate the local strain field ε z along the water absorption height during the water absorption process of the specimen;

[0049] S10. Substitute the strain field ε z into the porosity of the specimen, and according to the following formula, calculate the water content distribution of the specimen along the height direction, Figure 4 where is the calculated water absorption rate curve varying with height:

[0050]

[0051] In the formula, f(ω) is the water absorption rate, ρ water is the density of water, ρ is the density of the material, f(φ) is the material porosity distribution, and f(ε z ) represents the material strain.

[0052] S11. The three-dimensional water absorption distribution of the sample calculated by DVC is as Figure 5 shown, Figure 6 is the X-Z cross-sectional view of the water absorption distribution of the sample calculated by DVC, Figure 7 is the Y-Z cross-sectional view of the water absorption distribution of the sample calculated by DVC.

[0053] The X-Z cross-section of the water absorption distribution of the sample obtained by the traditional CT scan method is Figure 8 , and the Y-Z cross-section isFigure 9 , by comparing the result diagrams obtained by the present invention, it can be seen that the water absorption distribution obtained by the present invention is more intuitive and clear.

Claims

1. A method for characterizing moisture transport behavior of porous materials based on strain distribution, characterized in that: The steps include: Step (1): using a fixing agent to sequentially adhere the porous material sample to be tested, a support member and a water container to form a water absorption experimental device, ensuring that there is no relative movement between the porous material sample to be tested, the support member and the water container, and that the support member does not hinder the water absorption process of the sample; Step (2): before the water absorption experiment begins, the entire water absorption experiment device is placed on the sample stage of the tomography imaging device, and a tomography imaging is performed to obtain the spatial distribution of the linear absorption coefficient of the non-water-absorbed sample; Step (3): Pour water into the water container to ensure that the bottom surface of the sample is submerged in water, and periodically add water to maintain the liquid level in the container; Step (4): At the water absorption time t, using the same test parameters as step (2), a tomographic imaging analysis is performed again to obtain the spatial distribution of the linear absorption coefficient of the water absorption sample; Step (5): using the support as a reference, performing image registration on the water absorption experimental device in the non-water absorption state and the water absorption state to obtain the position movement of the entire water absorption experimental device between two tests; Step (6): using the position movement result obtained in step (6), the sample in the water-absorbing state is moved to eliminate the displacement between the non-water-absorbing state and the water-absorbing state, thereby completing the alignment; Step (7): Use the unabsorbed sample and the sample aligned in step (6) to carry out DVC analysis to obtain the strain ε generated by the sample along the water absorption height direction during the water absorption process. z ; Step (8): Combine the porosity of the material and use the water absorption rate and strain correlation formula to convert the local strain ε z Converted into local pore saturation, and then the moisture content distribution of the sample along the height direction at the water absorption time t is obtained: Where f(ω) is the water absorption rate, ρ water is the density of water, ρ is the density of the material, f(φ) is the porosity distribution of the material, and f(ε z ) represents the material strain.

2. The method according to claim 1, characterized in that The porous material sample to be tested in step (1) is rock, concrete or sponge that is insoluble in water.

3. The method according to claim 2, characterized in that The water container and the supporting member in step (1) need to be made of low-density waterproof material.

4. The method according to claim 3, characterized in that Low-density waterproof materials are plastic, glass or ceramic.

5. The method according to claim 4, characterized in that The supporting members are multiple PVC thin sticks with a diameter of 2-3 mm and a length of 2-3 cm.

6. The method according to claim 5, characterized in that The radiation source of the tomography imaging device is X-ray, neutron source or gamma ray.

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