阅读说明：本技术 一种结合断层扫描成像与增强造影的局部孔隙率表征方法 (Local porosity characterization method combining tomography imaging and contrast enhancement ) 是由 崔冬 卫浩 于 2021-08-04 设计创作，主要内容包括：本发明属于建筑材料性能表征领域,具体涉及一种结合断层扫描成像与增强造影的局部孔隙率表征方法。首先选取样品,将其浸入酒精溶液；采用抽真空与磁力搅拌相结合的方法,加速样品内部饱和酒精的进程。在样品完全饱和后,采用断层扫描成像仪对其进行第一次扫描；随后,将样品浸入造影剂酒精溶液,再次结合抽真空与磁力搅拌方法,并在样品完全饱和后,进行第二次扫描。利用图像配准方法,匹配两次扫描结果,再结合酒精及造影剂酒精溶液的局部线吸收系数,即可得出岩石或混凝土的局部孔隙率空间分布。本发明结果精准可靠,为表征岩石或混凝土局部孔隙率提供有利证据。(The invention belongs to the field of building material performance characterization, and particularly relates to a local porosity characterization method combining tomography imaging and enhanced radiography. Firstly, selecting a sample, and immersing the sample into an alcohol solution; and a method combining vacuumizing and magnetic stirring is adopted to accelerate the process of saturating alcohol in the sample. After the sample is completely saturated, performing first scanning on the sample by using a tomography imaging instrument; subsequently, the sample was immersed in a contrast alcohol solution, again combining the vacuum and magnetic stirring methods, and after the sample was completely saturated, a second scan was performed. And matching the scanning results of the two times by using an image registration method, and combining the local linear absorption coefficients of alcohol and a contrast agent alcohol solution to obtain the local porosity spatial distribution of the rock or the concrete. The method has accurate and reliable results and provides favorable evidence for representing the local porosity of the rock or the concrete.)

1. A method of characterizing local porosity in conjunction with tomographic imaging and contrast enhancement, comprising the steps of:

step (1): processing a sample to be detected;

step (2): placing a sample and a magnetic stirring rod at the bottom of a container in an environment below 5 ℃, immersing the sample by using an alcohol solution, connecting a vacuum pump with the container, sealing the container, vacuumizing the container until the quality of the sample does not change under the assistance of a magnetic stirring device, and scanning the sample for the first time by using a tomography scanner to obtain a three-dimensional line absorption coefficient reconstruction result of the sample; the linear absorption coefficient of any position is the sum average of the linear absorption coefficient of the partial line of the basal body and the linear absorption coefficient of the alcohol part, and is shown in a formula (1.1);

μ_before＝μ_mat·w_max+μ_alcohol·w_pore (1.1)

wherein, mu_beforeThe linear absorption coefficient of the sample before radiography; mu.s_mat，μ_alcoholThe linear absorption coefficients of the sample matrix and the alcohol are respectively; w is a_mat，w_poreVolume fractions of the matrix and the pores, respectively;

and (3): placing the sample scanned in the step (2) into the container again, placing the sample and the magnetic stirring rod at the bottom of the container in an environment of lower than 5 ℃, and immersing the sample in a contrast agent alcohol solution; sealing the container, vacuumizing on the basis of assisting magnetic stirring until the quality of the sample does not change any more, taking the sample, and performing secondary scanning under the same test parameters to obtain a three-dimensional line absorption coefficient reconstruction result of the sample; at this time, the linear absorption coefficient at any position is the sum average of the local basal body partial line absorption coefficient and the contrast agent alcohol solution partial line absorption coefficient, as shown in the formula (1.2);

μ_after＝μ_mat·w_mat+μ_staining·w_pore (1.2)

wherein, mu_afterThe linear absorption coefficient of the sample after radiography; mu.s_stainingIs the linear absorption coefficient of the contrast agent alcohol solution;

and (4): adopting an image registration technology to spatially register scanning results before and after radiography;

and (5): respectively testing the linear absorption coefficients of the alcohol solution and the contrast agent alcohol solution by adopting the same test parameters; combining the spatial distribution results of the absorption coefficients of the front line and the rear line of the radiography after spatial registration, calculating the local porosity of the sample, as shown in a formula 1.3;

wherein Φ is the local porosity of the sample;

in a tomographic imaging apparatus, the local line absorption coefficient is presented in the form of gray values, while under fixed test parameters, the local gray values are regarded as a linear mapping of the local line absorption coefficient, so equation 1.3 can be transformed into equation 1.4,

wherein G is_before，G_afterGray values of the scanning areas before and after radiography respectively; g_stainingIs the gray value of the contrast agent alcohol solution; g_alcocholThe grey value of the alcohol solution.

2. The method of claim 1, wherein the sample to be tested is rock or concrete.

3. The method of claim 2, wherein the source of radiation of the tomographic imaging apparatus is X-rays, gamma rays, or neutron rays.

4. The method of claim 3, wherein the contrast agent is an agent containing a heavy metal element and capable of substantially increasing the local linear absorption coefficient of the rock or concrete sample.

5. The method of claim 4, wherein the contrast agent is potassium iodide.

Technical Field

The invention belongs to the field of building material performance characterization, and particularly relates to a local porosity characterization method combining tomography imaging and enhanced radiography.

Background

At present, concrete and stone are still widely applied to building and manufacturing in the world. The pores within concrete and rock, which are typical porous materials, can have a significant impact on the strength and durability of the material itself. Taking concrete as an example, the internal capillary pores can significantly affect the strength of the concrete; the gel pores inside the concrete are related to the creep performance of the concrete. In addition, the pores can also be used as a rapid channel for the transmission of moisture and harmful substances (chloride ions, sulfate ions, carbon dioxide, etc.), thereby accelerating the deterioration process of concrete or rock. Since the pores of concrete and rock directly affect the mechanical properties and durability, it is very important to characterize the internal pores of concrete and rock.

The pore information mainly includes porosity, pore size distribution, and pore morphology. The porosity, i.e. the proportion of the internal pore volume to the total volume of the sample, is an important component of the pore information. At present, methods for measuring the porosity of concrete or rock comprise a vacuum saturation method, a mercury intrusion method, an X-ray tomography method and a linear absorption coefficient attenuation method.

Wherein, the basic operation of the vacuum water saturation method for determining the porosity is as follows: weighing the mass of the dry sample, saturating the sample, weighing the mass of the water-saturated sample in air and water respectively, and calculating the internal porosity of the sample by using the masses of the sample in three states. The method is simple and feasible, but only the average porosity of the whole sample can be measured, so that the local porosity of the sample cannot be characterized.

The basic operation of the mercury pressing method is as follows: and taking a dry concrete sample, filling liquid mercury into sample pores through external pressure, and measuring the volume fraction occupied by pores with different sizes in the sample by combining the corresponding relation between the mercury inlet amount and the external pressure. Mercury porosimetry requires the application of pressure to the sample, which may destroy the internal pore structure of the sample. Meanwhile, as a non-wetting medium, mercury is difficult to enter gel pores in the concrete, so that the porosity obtained by the mercury intrusion method is lower than the actual porosity of the concrete.

The X-ray tomography imaging technology belongs to the field of nondestructive testing technology, and does not need to carry out pretreatment on a sample, so that the original microstructure of the sample can be retained to the maximum extent. However, the spatial resolution of this method is low (typical tomographic imager resolution is only tens of microns), and thus the porosity test method cannot cover most of the capillary pores and gel pores.

The linear absorption coefficient attenuation method calculates the local porosity of the sample by utilizing the gray value difference of the sample in a water-saturated state and a dry state. The method uses water as the immersion medium, and thus the porosity test results cover the gel pores. However, this method requires a drying process on the sample, which may cause damage to the microstructure of the sample; furthermore, during the saturation of the sample with water, the water may change the hydration level of the sample and cause erosion of the sample, which may cause changes in the microstructure of the sample.

Disclosure of Invention

The invention aims to provide a local porosity characterization method combining tomography imaging and contrast enhancement.

The technical solution for realizing the purpose of the invention is as follows: a method of local porosity characterization combining tomographic imaging with contrast enhancement, comprising the steps of:

step (1): processing a sample to be detected;

step (2): placing a sample and a magnetic stirring rod at the bottom of a container in an environment below 5 ℃, immersing the sample in an alcohol solution, connecting a vacuum pump with the container, sealing the container, vacuumizing the container with the aid of a magnetic stirring device until the quality of the sample does not change any more, and taking the sample for first scanning to obtain a three-dimensional line absorption coefficient reconstruction result of the sample; the linear absorption coefficient of any position is the sum average of the linear absorption coefficient of the partial line of the basal body and the linear absorption coefficient of the alcohol part, and is shown in a formula (1.1);

μ_before＝μ_mat·w_mat+μ_alcohol·w_pore (1.1)

wherein, mu_beforeThe linear absorption coefficient of the sample before radiography; mu.s_mat，μ_alcoholThe linear absorption coefficients of the sample matrix and the alcohol are respectively; w is a_mat，w_poreVolume fractions of the matrix and the pores, respectively;

and (3): placing the sample scanned in the step (2) into the container again, placing the sample and the magnetic stirring rod at the bottom of the container in an environment of lower than 5 ℃, and immersing the sample in a contrast agent alcohol solution; sealing the container, vacuumizing on the basis of assisting magnetic stirring until the quality of the sample does not change any more, taking the sample, and performing secondary scanning under the same test parameters to obtain a three-dimensional line absorption coefficient reconstruction result of the sample; at this time, the linear absorption coefficient at any position is the sum average of the local basal body partial line absorption coefficient and the contrast agent alcohol solution partial line absorption coefficient, as shown in the formula (1.2);

μ_after＝μ_mat·w_mat+μ_staining·w_pore (1.2)

wherein, mu_afterThe linear absorption coefficient of the sample after radiography; mu.s_stainingIs the linear absorption coefficient of the contrast agent alcohol solution;

and (4): adopting an image registration technology to spatially register scanning results before and after radiography;

and (5): respectively testing the linear absorption coefficients of the alcohol solution and the contrast agent alcohol solution by adopting the same test parameters; combining the spatial distribution results of the absorption coefficients of the front line and the rear line of the radiography after spatial registration, calculating the local porosity of the sample, as shown in a formula 1.3;

wherein Φ is the local porosity of the sample;

in a tomographic imaging apparatus, the local line absorption coefficient is presented in the form of gray values, while under fixed test parameters, the local gray values are regarded as a linear mapping of the local line absorption coefficient, so equation 1.3 can be transformed into equation 1.4,

wherein G is_before，G_afterGray values of the scanning areas before and after radiography respectively; g_stainingIs the gray value of the contrast agent alcohol solution; g_alcocholThe grey value of the alcohol solution.

Further, the sample to be tested is rock or concrete.

Further, the ray source of the tomography imaging instrument is X-ray, gamma ray or neutron ray.

Furthermore, the contrast agent contains heavy metal elements and can greatly improve the local linear absorption coefficient of the rock or concrete sample.

Further, the contrast agent is potassium iodide.

Compared with the prior art, the invention has the remarkable advantages that:

compared with the traditional tomography imaging method, the method has the advantages that the characteristic of high contrast of the sample is improved by means of the contrast agent, the three-dimensional porosity is represented by the difference of the gray values of the sample before and after the contrast, and the defect of poor resolution caused by single scanning in the traditional method can be overcome;

compared with the traditional linear absorption coefficient attenuation method, the method carries out saturated alcohol treatment on the sample before and after radiography, avoids the drying step of the traditional method, does not need to carry out additional drying on the sample, and can protect the microstructure of the sample to the maximum extent;

the method adopts alcohol as an immersion medium, thereby avoiding the influence of moisture on the hydration degree and the corrosion degree of the sample;

the method greatly improves the accuracy of the measurement result of the local porosity of the concrete or rock;

the invention provides a new idea for representing the spatial distribution of the local porosity, and perfects and improves the defects of the traditional tomography imaging method.

Drawings

FIG. 1 shows the results of a scan of a sample before imaging in accordance with the present invention.

FIG. 2 shows the scanning results of the sample after the inventive process.

Fig. 3 shows the scan results after sample registration according to the present invention.

FIG. 4 is a three-dimensional porosity spatial distribution of the present invention.

FIG. 5 is a two-dimensional porosity spatial distribution of the present invention.

FIG. 6 is a one-dimensional porosity distribution of the present invention.

Detailed Description

The invention discloses a local porosity characterization method combining tomography and contrast enhancement, which specifically comprises the following steps: firstly, selecting rock with a size suitable for being analyzed by a tomography scanner or preparing a concrete sample, and immersing the rock or the concrete sample into an alcohol solution. And a method combining vacuumizing and magnetic stirring is adopted to accelerate the process of saturating alcohol in the sample. After the sample is completely saturated, performing first scanning on the sample by using a tomography imaging instrument; subsequently, the sample is immersed in a contrast alcohol solution, the vacuum and magnetic stirring methods are combined again to accelerate the sample saturation process, and after the sample is completely saturated, a second scan is performed. And matching the two scanning results by using an image registration method, and combining the linear absorption coefficients of alcohol and a contrast agent alcohol solution to obtain the local porosity spatial distribution of the rock or the concrete. The method has accurate and reliable results and provides favorable evidence for representing the local porosity of the rock or the concrete.

The invention comprises the following steps:

in step 1, cement, sand, water and the like are firstly adopted to prepare mortar. Wherein, the cement is P.II 42.5 cement produced by small-field cement plants, the sand is machine-made fine sand, the maximum diameter is about 1.2mm, and the water-cement ratio is 0.45. The sample size was 40X 160mm³. After molding, the specimens were covered with a plastic film for 24h and then cured for 28 days under standard curing conditions. To accelerate the sample saturation process, the sample was divided into slices of about 5 mm thickness using water cutting.

Step 2 the sample of step 1 and a magnetic stirring rod are placed at the bottom of a drying dish in an environment below 5 ℃, and the sample is immersed in an alcohol solution. And (3) connecting a vacuum pump with a drying dish, and vacuumizing until the quality of the sample is not changed (more than 14 days) on the basis of assisting magnetic stirring. After saturation was complete, the sample was scanned for the first time, and the test used a tomographic imaging apparatus, YXLON Precision Scanner, Germany. The X-ray beam energy and current were 195KeV and 0.34mA, respectively, and an aluminum-copper doubler plate was used as the radiation filter. The effective resolution of the device is 20 μm. Each scan projection time is 2 s. A typical slice of the scan results is shown in figure 1. The gray value of each pixel point is the mapping of the line absorption coefficient of the corresponding position, and the line absorption coefficient can be regarded as the sum average of the matrix line absorption coefficient and the alcohol line absorption coefficient of the local part of the sample, as shown in the formula (1.1).

μ_before＝μ_mat·w_mat+μ_alcohol·w_pore (1.1)

Wherein, mu_beforeThe local linear absorption coefficient of the sample before radiography; mu.s_mat，μ_alcoholThe linear absorption coefficients of the mortar matrix and water are respectively; w is a_mat，w_poreThe volume fractions of the sample matrix and the pores, respectively.

And 3, placing the scanned sample into the drying dish again, placing the sample and the magnetic stirring rod at the bottom of the drying dish in an environment of lower than 5 ℃, and immersing the sample by using an alcohol solution. And (3) connecting a vacuum pump with a drying dish, and vacuumizing until the quality of the sample is not changed (more than 14 days) on the basis of assisting magnetic stirring. And taking the sample, and performing second scanning under the same test parameters to obtain a three-dimensional line absorption coefficient reconstruction result of the sample. Since potassium iodide is very susceptible to decomposition by light, it is necessary to ensure that step 3 is developed in a dark vessel.

And 4, taking out the sample when the quality of the sample does not change any more, and carrying out second X-ray tomography imaging on the sample, wherein a typical section result after scanning is shown in fig. 2, and the scanning result is the linear absorption coefficient of the sample after radiography, namely the sum average of the linear absorption coefficient of the matrix and the linear absorption coefficient of the contrast agent alcohol solution, as shown in a formula (1.2).

μ_after＝μ_mat·w_mat+μ_staining·w_pore (1.2)

Wherein, mu_afterThe local linear absorption coefficient of the sample after radiography; mu.s_stainingIs the linear absorption coefficient of the contrast agent alcohol solution.

And 5, in order to completely unify the two groups of results before and after radiography on the spatial position, the two groups of results are subjected to spatial matching by adopting an image registration technology. A typical slice result after registration is shown in fig. 3.

And 6, combining the local linear absorption coefficient (formula 1.1) of the sample before radiography and the local linear absorption coefficient (formula 1.2) of the sample after radiography to obtain the local porosity of the sample according to the formula 1.3.

To achieve visualization of the results, the distribution of the three-dimensional line absorption fractions is mapped to a distribution of three-dimensional gray values. If the test parameters are controlled to be fixed during two scans, the line absorption coefficient of the sample can be in direct proportion to the gray value of the corresponding reconstruction area. The formula 1.3 can be further converted into the formula 1.4, so that the three-dimensional porosity distribution, the two-dimensional porosity distribution and the one-dimensional porosity distribution of the sample can be obtained, as shown in fig. 4, 5 and 6, respectively.

Wherein G is_before，G_afterGray values of the scanning areas before and after radiography respectively; g_stainingIs the gray value of the contrast agent alcohol solution; g_alcocholThe grey value of the alcohol solution.