CN107024492A - A kind of method that use CT technical research high-temperature damages concrete defect develops - Google Patents
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- 238000007664 blowing Methods 0.000 claims description 2
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- 238000010894 electron beam technology Methods 0.000 claims description 2
- NUHSROFQTUXZQQ-UHFFFAOYSA-N isopentenyl diphosphate Chemical compound CC(=C)CCO[P@](O)(=O)OP(O)(O)=O NUHSROFQTUXZQQ-UHFFFAOYSA-N 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
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- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
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- 229910052790 beryllium Inorganic materials 0.000 description 1
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium atom Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention discloses a kind of method that use CT technical research high-temperature damages concrete defect develops.This method includes：Prepare test block, experimental method determination, the processing of the X ray CT image reconstruction of X-ray CT scan, concrete sample, X ray CT image binaryzation, defect in concrete rate EVOLUTION ANALYSIS.The present invention, which is proposed, is used for CT technologies in concrete elevated temperature property analysis；Employ heated in real-time device；Improve the accuracy of test；Numerically modeling is carried out by defect analysis；Bonding strength test, the constitutive relation of material microscopical structure feature and mechanical behavior can be reflected by establishing, and it is significant to damage concrete defect to researching high-temperature.
Description
Technical Field
The invention relates to a method for researching defect evolution of high-temperature damaged concrete, in particular to a method for researching defect evolution of high-temperature damaged concrete by adopting an X-ray CT technology.
Background
A high-performance concrete fire deterioration mechanism and damage evaluation thereof are key for solving the bottleneck and difficulty of improving fire resistance and identifying post-disaster damage of modern engineering structures, and revealing the high-temperature deterioration evolution law and mechanism of internal microstructures thereof, researchers use digital image association to analyze and research the cracking condition of the concrete surface, find that the method is more effective in observing small cracks on the concrete surface, analyze the internal characteristics of two-dimensional fault cracks, mainly use an X-ray CT method, find that the method is suitable for observing large cracks in the concrete, combine the two methods to effectively reflect the influence of crack initiation and evolution processes on the concrete mesoscopic structure change condition, use test pieces formed by different aggregates to perform compression scanning experiments under CT equipment, have a detailed understanding on the cracking process, so that their effect on the strength of the concrete can be clearly seen.
On the basis of a CT test of concrete mesoscopic damage, researchers base on density damage (CT number change) variables and establish a concrete segmental damage evolution equation, so that the numerical simulation of the uniaxial compressed mesoscopic damage of a concrete test piece is carried out. And from concrete failure patterns and loads. The numerical simulation result and the CT test result are compared in two aspects of the displacement curve chart, and the result shows that the crack propagation process is similar to that observed by CT when the test piece is damaged, thereby realizing the connection between the microscopic density damage and the degradation of the macroscopic mechanical property of the test piece, providing a mechanical basis for improving the test design and making the replacement of part of the test by a numerical method possible on the premise of reliability and effectiveness.
With the progress of science and technology and the development of experimental research in recent years, high and new technologies are widely applied to the high-temperature performance research of concrete, wherein the X-ray CT test has become a hot topic for researching the microscopic structure evolution process of concrete materials.
Disclosure of Invention
The invention aims to provide a method for researching defect evolution of high-temperature damaged concrete by adopting a CT technology.
The invention provides a method for researching defect evolution of high-temperature damaged concrete by adopting a CT technology, which comprises the following steps:
the method comprises the following steps: preparation of the experiment
(ii) test Material
Cement, mineral admixture, aggregate, admixture, tap water and the like;
the concrete mixing proportion is as follows:
according to the design of common concrete mix proportion design rules (JGJ55-2011) and JGJ/T281-2012 technical rules for high-strength concrete application, the strength grade of the test concrete is designed to be C40-C80.
Design of test piece
The strength grade of the test concrete is designed to be C40-C80.
Design of test piece
And manufacturing a cubic compressive strength test block, and placing a thermocouple in the concrete test block, wherein the thermocouple is placed in the center of the test block. The CT scan test piece was sampled by core drilling from the fabricated concrete test block.
Step two: experimental methods
Concrete stirring and forming
Heating mechanism
Firstly heating the hearth temperature of the muffle furnace from room temperature to a target temperature, then placing the test piece into the muffle furnace, closing the furnace door, slightly reducing the temperature in the hearth at the moment, and keeping the temperature constant after the temperature in the hearth is raised to the required target temperature again. The average heating rate of the muffle furnace is 5-10 ℃/min, the resistance furnace is provided with an automatic controller, the temperature in the hearth can be automatically controlled, the constant temperature is kept after the required temperature is reached, the temperature inside and outside the test piece is measured through the thermocouple, and the furnace is considered to be completely burnt when the temperature displayed in the furnace is consistent with the temperature displayed by the external sensor of the thermocouple. The test piece was removed and allowed to cool under natural conditions.
An X-ray CT scanning test piece is dried for 24 hours to constant weight by a 101-type electrothermal blowing drying oven and immediately placed into a sample bottle, and the drying temperature is 100 ℃. In order to truly reflect the occurrence and development rules of concrete pores and cracks at different temperatures, after a concrete sample is fixed on a CT machine, the concrete sample is not disassembled and assembled, a heating device is adopted to directly heat the concrete sample, and then CT scanning is carried out, so that comparative analysis of the cracks in the concrete at the same position at different temperatures is realized.
And continuously heating the same test block in a natural atmosphere by the atmosphere furnace, keeping the temperature for 20min after the temperature reaches a target temperature, and then carrying out X-ray CT scanning to obtain an X-ray CT scanning image of the concrete test block.
Step three: x-ray CT scan
The computer system of the industrial CT system can realize digital image processing and CT reconstruction of the micro CT image and mainly comprises two modules: image reconstruction and binary processing.
Step four: x-ray CT image reconstruction of concrete specimen
An image reconstruction module in an industrial CT computer system is utilized to reconstruct a perspective view of CT scanning of a test piece into 1500 cross-sectional images (x-y surfaces), and the 1500 cross-sectional images are combined and then orthogonally sliced to generate 2041 orthogonal slice images (x-z surfaces) of the test piece. The imaging error and the non-uniform randomness of the concrete are considered, the image with larger shadow is removed, and the pore distribution, the pore diameter change, the crack growth and the gray level change of each layer of the concrete at each temperature can be directly observed by utilizing the X-ray CT image in the CT generated image;
step five: x-ray CT image binaryzation processing
In order to establish the correlation between the internal defects of the concrete after high temperature and the temperature, the strength and the like, the concept of defect rate is provided.
The defect rate is the ratio of the total of the internal defect areas of the concrete to the surface area of the test piece (the total of the internal defect areas of the concrete can be obtained by using Image-ProPlus Image analysis software). The expression is as follows:
wherein C represents the number of layers, PcRepresents the defect rate, mcThe area sum of the internal defects of the test piece is shown, and m is the surface area of the test piece.
Selection of threshold value
The threshold value is a critical value, and in the binarization of the CT image, all pixel points larger than the threshold value are converted into white, and pixel points smaller than the threshold value are converted into black. The threshold is calculated by adopting an Otsu method, the method is based on the histogram of the original image, and a discrete probability density function is assumed:
where n is the total number of pixels in the image, nqIs a gray level of rqL is the number of all possible gray levels in the image. Suppose a threshold k, C is selected0Is a group of gray levels of [0, 1.,. k-1 ]]Pixel of (2), ClIs a group of pixels with a gray level [ k, k + 1., L-1 ]. Otsu method selection maximization of inter-class varianceThreshold k, inter-class variance definition:
wherein,
in matlab, a histogram of the CT image is drawn with respect to gray values using a function gradythresh to find a maximumIs measured.
The average value of the threshold values of the surface layers of all generations is the average value of the threshold values of the CT images of the same surface layer of the generations at different temperatures; the average value of the threshold values at different temperatures is the average value of the threshold values of different generation surface CT images at the same temperature.
Binary image
For a binarized image of a concrete X-ray CT image at normal temperature:
assuming a graph function f (x, y), an image g (x, y) after appropriate thresholding is defined as
The pixel labeled 1 corresponds to the object, while the pixel labeled 0 corresponds to the background, T is the threshold. Pixel points with the gray scale value of 0 in the binary image represent the internal defects of the test piece; when the gradation value is 1, the test piece is indicated by a portion excluding the defect.
Step six: evolution analysis of internal defect rate of concrete
Analyzing the binary image by using IPP image analysis software, and counting the number of pixel points with gray scale value of 0 in the CT image by ncExpressing, the number of all pixel points is expressed by n, wherein nc＝mcN is m, defect rateAnd calculating the defect rate of each generation of surface layer after high temperature.
Step seven: outlier determination
The test adopts the Grabbs test method to judge abnormal values of n defect rate values at the same temperature. Arranging n defect rate values at the same temperature in the order from small to large and respectively marking as X1、X2、...、XnIf the deviation from the normal value is found, the minimum value or the maximum value is suspected first, and the difference between the average value and the minimum value and the difference between the average value and the maximum value are takenAnd (4) taking the value with larger difference value as a suspicious value. Statistic GiCalculated as follows:
wherein: i is the sequence number of the suspicious value;
average value:
standard deviation:
test level α ═ 5%, GiAnd a threshold value G95(n) comparing if Gi>G95(n), the measured data can be judged to be abnormal values and needs to be removed, if Gii<G95(n), there is no abnormal value. The remaining 9 data are calculated according to the above steps, if G is calculatedi>G95(n), still being an outlier, culling; if G isi<G95(n), if not an abnormal value, not eliminating. Only one set of data needs to be complemented. And so on.
Step eight: influence factor of internal defect rate of concrete
Firstly, the influence of two factors, namely selection of different generation surface layers and different temperature effects on the internal defects of the concrete is researched by utilizing variance analysis of the two factors in mathematical statistics.
And performing defect fitting on the temperature and the defect rate by using excel software.
The invention discloses a method for researching defect evolution of high-temperature damaged concrete by applying a CT technology, which is to analyze and research the high-temperature damaged concrete by a digital image association technique. In the research process, a concrete compression-resistant test block with a certain specification is manufactured, the test block is heated by a heating device, after the heating is finished, the test block is scanned by adopting an X-ray CT test technology to obtain a series of CT images, and image reconstruction and image binarization processing are carried out. The selection of the threshold value directly influences the analysis of the CT number in the CT image. The threshold value is more accurately selected and the abnormal value is determined. And quantitatively analyzing the binary Image of the concrete test piece by using Image-Pro Plus Image analysis software to obtain the defect rates of different generation surface layers of the test piece after high temperature, and analyzing factors influencing the defect rates and the temperature threshold value section with the largest influence. The anti-burst performance of the concrete at different temperatures is intuitively analyzed, and the change of the internal microscopic structure after the high temperature is scientifically and strictly described by using a mathematical statistics method.
The invention has the beneficial effects that:
(1) the CT technology is used for analyzing the high-temperature performance of the concrete;
(2) a real-time heating device is adopted; the accuracy of the test is improved;
(3) numerical studies were performed by defect analysis; the bond strength test establishes an constitutive relation capable of reflecting the microscopic structural characteristics and the mechanical behavior of the material, and has important significance for researching the defects of the high-temperature damaged concrete.
Drawings
FIG. 1 is a schematic view showing the placement of a thermocouple in a test piece according to the present invention.
FIG. 2 is a CT image of high-strength concrete at normal temperature.
FIG. 3 is an X-ray CT image of a 1200 th layer of high-strength concrete after high temperature.
FIG. 4 is an X-ray CT image of the normal section of the high-strength concrete after high temperature.
FIG. 5 is a mean value of surface CT image threshold values of each generation.
FIG. 6 threshold mean values of CT images at different temperatures.
FIG. 7 is a binarized image of a high-strength concrete X-ray CT image at normal temperature.
FIG. 8 shows the mean value of the internal defect rate of the high-strength concrete under the action of different temperatures.
In the figure: 1 is a thermocouple and 2 is a temperature sensor.
Detailed Description
The present invention is further illustrated by, but is not limited to, the following examples.
Example (b):
the method comprises the following steps: preparation of the experiment
High strength concrete mixing proportion
The test piece was designed to have a strength rating of C80.
The cubic compressive strength test block is 150mm multiplied by 150mm, a thermocouple is arranged in one test block corresponding to each target temperature of the high-strength concrete test piece, and the thermocouple is arranged in the center of the test block, as shown in figure 1.
CT scanning test piece utilizes the core drilling to sample, and test piece size phi 6mm is multiplied by 20 mm.
Step two: experimental methods
Concrete stirring and forming
Heating mechanism
The cube compression strength high-temperature test adopts an SRJX type box type resistance furnace, the rated voltage of the SRJX type box type resistance furnace is 220V, the output power is 15kW, the highest working temperature is 1200 ℃, and the length, the width and the height of a hearth are as follows: 600 mm. times.400 mm. The target heating temperature is 100 ℃, 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃.
The following temperature rise regime was used for this experiment: firstly heating the hearth temperature of the muffle furnace from room temperature to a target temperature, then placing the test piece into the muffle furnace, closing the furnace door, slightly reducing the temperature in the hearth at the moment, and keeping the temperature constant after the temperature in the hearth is raised to the required target temperature again. The average heating rate of the muffle furnace is 5-10 ℃/min, the resistance furnace is provided with an automatic controller, the temperature in the hearth can be automatically controlled, the constant temperature is kept after the required temperature is reached, the temperature inside and outside the test piece is measured through the thermocouple, and the furnace is considered to be completely burnt when the temperature displayed in the furnace is consistent with the temperature displayed by the external sensor of the thermocouple. The test piece was removed and allowed to cool under natural conditions.
The resistance furnace has stable working performance, the temperature fluctuation of the hearth is kept within +/-10 ℃, and the requirement of test accuracy can be met.
The test adopts a high-temperature atmosphere furnace developed by the research institute of mining technology of Taiyuan university and a CT machine for matching use. The volume of the atmosphere furnace is very small, the external dimension is phi 100mm multiplied by 150mm, the furnace hearth dimension is phi 20mm multiplied by 80mm, an inner insulating layer and an outer insulating layer are adopted, 300W resistance wires are used for heating, and the bottom of the furnace is open, so that the sample can be conveniently put in and taken out. The atmosphere furnace is fixed on the rotary bracket, the bracket is connected with the telescopic support through a nut, the bracket can rotate in the horizontal direction to adjust the horizontal position of the atmosphere furnace, and the telescopic support adjusts the vertical position of the atmosphere furnace.
The gas-filled tube, the temperature sensor and the atmosphere furnace are bonded by high-temperature-resistant glue, the sample is bonded to the quartz tube by the high-temperature-resistant glue, the quartz tube is clamped to the rotary table, the bracket and the support are moved during heating to enable the atmosphere furnace to cover the sample, and the sample is preferably positioned in the middle of the hearth of the atmosphere furnace. The average heating rate of the atmosphere furnace is 10 ℃/min, and the temperature control precision is +/-1 ℃.
The test piece is placed in a high-temperature atmosphere furnace, the target heating temperature is 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃ under natural atmosphere, and the normal temperature of the X-ray CT test represents 100 ℃ drying temperature. And continuously heating the atmosphere furnace in natural atmosphere, keeping the temperature for 20min after the target temperature is reached, and carrying out CT scanning.
Step three: x-ray CT scan
The experiment adopts a mu CF225FCB high-resolution micro CT system which is jointly developed by the Taiyuan university and the institute of engineering and physics, China institute of applied electronics, and an X-ray imaging system of the system comprises: high-precision working rotary tables and clamps, an X-ray machine, a digital flat panel detector, a horizontal moving mechanism, a machine base, an acquisition and analysis system and the like.
The X-ray machine is an X-ray emitting device, and electrons are generated by a cathode electron gun, accelerated by a high-voltage field, and bombarded by a high-speed electron beam on an anode target (the target material is beryllium) to generate X-rays. The minimum focus size of the X-ray machine is 3 mu m, the ray cone angle is 25 degrees, the minimum focal length is 4.5mm, the high voltage range is 10-225 kV, and the current is 0.01-3 mA.
The system adopts a Paxscan4030 flat panel detector as an X-ray receiver, and can resolve the size of a tiny defect in a material. Detector panel size: 500mm × 367mm × 47mm, imaging window: 406mm × 293mm, effective window: 406mm by 282 mm.
Technical indexes of a mu CF225FCB high-resolution micro CT system are as follows: the system can carry out three-dimensional CT scanning analysis on different types of metal and non-metal materials, the size range of a test piece is phi 1 mm-50 mm, the magnification is 1-400 times, and the resolution of a scanning unit is 0.5-194 mu m.
The experiment adopts 80kV tube voltage, 90 muA tube current and 53.85 times amplification factor.
The computer system of the mu CF225FCB high-resolution micro CT system can realize the digital image processing and CT reconstruction of a micro CT image and mainly comprises two modules: image reconstruction and binary processing. Image reconstruction: performing median filtering on the CT image by adopting a large cone angle three-dimensional reconstruction module; and selecting proper focal length and offset value to carry out three-dimensional reconstruction on the CT image to generate a high-resolution cross-section image, wherein the image is an 8-bit image. In the binary module, orthogonal slicing and image format conversion are performed on the CT image.
The actual height of CT image scanning is 5.65mm, and the scanning size of a test piece is phi 6mm multiplied by 5.65 mm.
Step four: x-ray CT image reconstruction of concrete specimen
And (3) removing the image with large shadow by considering imaging error and non-uniform randomness of concrete, and selecting 300 layers, 400 layers, 500 layers, 600 layers, 700 layers, 800 layers, 900 layers, 1000 layers, 1100 layers and 1200 layers on an x _ y plane in the CT generated image as substitute layers, wherein the substitute layers are shown in the figure 2 and the figure 3. The 985 th layer image in the x _ z plane is selected as the orthogonal slice image at the corresponding maximum diameter, see fig. 4.
Step five: x-ray CT image binaryzation processing
Selection of threshold value
The table below shows the threshold values for the cross-section of each representative layer of PPHSC at different temperatures. Because the concrete is a non-uniform body and the mutual linear attenuation coefficients of the representative layers are different, the gray values represented by the volume elements are different, and the threshold value difference of the representative layers is obvious. The threshold value is distributed between 18 and 57.
Threshold value of cross section of each representative layer of high-strength concrete at different temperatures
Fig. 5 and 6 show the mean threshold values of CT images for each generation of surface layer and at different temperatures, respectively. The average value of the threshold values of the surface layers of all generations is the average value of the threshold values of the CT images of the same surface layer of the generations at different temperatures; the average value of the threshold values at different temperatures is the average value of the threshold values of different generation surface CT images at the same temperature. As can be seen from FIG. 5, the difference of the threshold values of the surface CT images of each generation is obvious, the threshold value range is 25.3-41.5, the difference value is 16.2, and the difference value is greater than 46% of the mean value of all the threshold values of the CT images; as can be seen from fig. 6, the threshold values of the CT images at different temperatures are slightly different.
The threshold range is 31.8-37.7, the difference is 5.9, the difference is 16.8% of the average value of all thresholds of the CT image, and the threshold difference of the CT image is smaller except for 400 ℃ and 500 ℃.
Binary image
As shown in fig. 7, the binary image has obvious defects, reflects reality, and can be used as a basis for calculating the defect rate.
Step six: evolution analysis of internal defect rate of concrete
Defect rate of each generation of surface layer after high temperature
Step seven: outlier determination
GiSystem meter
GiAnd a threshold value G95(10) Comparison, G95(10)＝2.176，GiAre all less than G95(10) There is no abnormal value among them.
Step eight: influence factor of internal defect rate of concrete
Firstly, the influence of two factors, namely selection of different generation surface layers and different temperature effects on the internal defects of the concrete is researched by utilizing variance analysis of the two factors in mathematical statistics.
Two-factor analysis of variance table
The influence of the selected different generation surface layers and different temperatures on the internal defect rate of the high-strength concrete is highly obvious through the analysis of the table.
And performing defect fitting on the temperature and the defect rate by using excel software. As shown in fig. 8.
Claims (7)
1. A method for researching defect evolution of high-temperature damaged concrete by adopting a CT technology is characterized by comprising the following steps:
the method comprises the following steps: manufacturing a cubic compressive strength test block;
step two: experimental methods
Firstly, stirring and forming concrete;
heating mechanism
Firstly, heating the hearth temperature of the muffle furnace from room temperature to a target temperature, then placing the test piece into the muffle furnace, closing a furnace door, slightly reducing the temperature in the hearth at the moment, and keeping the temperature constant after the temperature in the hearth is raised to the required target temperature again; the average heating rate of the muffle furnace is 5-10 ℃/min, the resistance furnace is provided with an automatic controller, the temperature is kept constant after the required temperature is reached, the temperature inside and outside the test piece is measured through a thermocouple, when the temperature displayed in the furnace is consistent with the temperature displayed by an external sensor of the thermocouple, the test piece is considered to be completely burnt, and the test piece is taken out and cooled under natural conditions;
drying an X-ray CT scanning test piece for 24 hours to constant weight through a 101-type electrothermal blowing drying oven, and immediately filling the test piece into a test piece bottle, wherein the drying temperature is 100 ℃;
continuously heating the same test block in a natural atmosphere by an atmosphere furnace, keeping the temperature for 20min after the temperature reaches a target temperature, and then carrying out X-ray CT scanning to obtain an X-ray CT scanning image of the concrete test block;
step three: x-ray CT scan
The computer system of the industrial CT system can realize digital image processing and CT reconstruction of the micro CT image and mainly comprises two modules: image reconstruction and binary processing;
step four: x-ray CT image reconstruction of concrete specimen
Reconstructing a perspective view of a CT scan of a test piece into 1500 cross-sectional images by using an image reconstruction module in an industrial CT computer system: and (3) combining 1500 cross-section images and then performing orthogonal slicing on the cross-section images on an x-y plane to generate 2041 test piece orthogonal slice images: an x-z plane; the imaging error and the non-uniform randomness of the concrete are considered, the image with larger shadow is removed, and the pore distribution, the pore diameter change, the crack growth and the gray level change of each layer of the concrete at each temperature can be directly observed by utilizing the X-ray CT image in the CT generated image;
step five: x-ray CT image binaryzation processing
The total of the internal defect areas of the concrete can be obtained by using Image-Pro Plus Image analysis software, the defect rate is the ratio of the total of the internal defect areas of the concrete to the surface area of the test piece, and the expression is as follows:
wherein C represents the number of layers, PcRepresents the defect rate, mcThe area sum of the internal defects of the test piece is shown, and m is the surface area of the test piece;
step six: evolution analysis of internal defect rate of concrete
Analyzing the binary image by using IPP image analysis software, and counting the number of pixel points with gray scale value of 0 in the CT image by ncExpressing, the number of all pixel points is expressed by n, wherein nc＝mcN is m, defect rateAnd calculating the defect rate of each generation of surface layer after high temperature.
2. The method for researching defect evolution of high-temperature damage concrete by adopting CT technology as claimed in claim 1, wherein: the cube compressive strength test block is used for testing concrete with the strength grade of C40-C80; and a thermocouple is arranged in the concrete test block and is arranged in the center of the test block.
3. The method for researching defect evolution of high-temperature damage concrete by adopting CT technology as claimed in claim 1, wherein: after the concrete sample is fixed on the CT machine, the concrete sample is not disassembled and assembled, a heating device is used for directly heating the concrete sample, and then CT scanning is carried out, so that comparative analysis of the concrete internal cracks at the same positions at different temperatures is obtained.
4. The method for researching defect evolution of high-temperature damage concrete by adopting CT technology as claimed in claim 1, wherein: in the fifth step, the binarization processing method comprises the following steps:
selecting a threshold value:
the threshold value refers to a critical value, all pixel points larger than the threshold value are converted into white in the binarization of the CT image, and pixel points smaller than the threshold value are converted into black; the threshold is calculated by adopting an Otsu method, the method is based on the histogram of the original image, and a discrete probability density function is assumed:
where n is the total number of pixels in the image, nqIs a gray level of rqL is the number of all possible gray levels in the image. Suppose a threshold k, C is selected0Is a group of gray levels of [0, 1.,. k-1 ]]Pixel of (2), ClIs a group of pixels with a gray level [ k, k + 1., L-1 ]; otsu method selection maximization of inter-class varianceThreshold k, inter-class variance definition:
wherein,
in matlab, a histogram of the CT image is drawn with respect to gray values using a function gradythresh to find a maximumA threshold value T of (1);
the average value of the threshold values of the surface layers of all generations is the average value of the threshold values of the CT images of the same surface layer of the generations at different temperatures; taking the average value of the thresholds of different generation surface CT images at the same temperature as the average value of the thresholds at different temperatures;
binary image
For the binary image of the X-ray CT image of the concrete sample:
assuming a graph function f (x, y), an image g (x, y) after appropriate thresholding is defined as
The pixel labeled 1 corresponds to the object, while the pixel labeled 0 corresponds to the background, T is the threshold; pixel points with the gray scale value of 0 in the binary image represent the internal defects of the test piece; when the gradation value is 1, the test piece is indicated by a portion excluding the defect.
5. The method for researching defect evolution of high-temperature damage concrete by adopting CT technology as claimed in claim 1, wherein: the external dimension of the high-temperature atmosphere furnace is phi 100mm multiplied by 150mm, the furnace hearth dimension is phi 20mm multiplied by 80mm, an inner insulating layer and an outer insulating layer are adopted, 300W resistance wires are used for heating, and the bottom of the furnace is open, so that a sample can conveniently come in and go out; the atmosphere furnace is fixed on the rotary bracket, the bracket is connected with the telescopic support through a nut, the bracket can rotate in the horizontal direction to adjust the horizontal position of the atmosphere furnace, and the telescopic support adjusts the vertical position of the atmosphere furnace; the gas-filled tube, the temperature sensor and the atmosphere furnace are bonded by high-temperature-resistant glue, the sample is bonded to the quartz tube by the high-temperature-resistant glue, the quartz tube is clamped to the rotary table, and when the sample is heated, the bracket and the support are moved to enable the atmosphere furnace to cover the sample, and the sample is positioned in the center of the hearth of the atmosphere furnace; the average heating rate of the atmosphere furnace is 10 ℃/min, and the temperature control precision is +/-1 ℃.
6. The method for researching defect evolution of high-temperature damage concrete by adopting CT technology as claimed in claim 1, wherein: the CT system is a mu CF225FCB high-resolution micro CT system, and an X-ray imaging system of the system comprises: the device comprises a high-precision working turntable, a clamp, an X-ray machine, a digital flat panel detector, a horizontal moving mechanism, a base and an acquisition and analysis system;
the X-ray machine is an X-ray emitting device, electrons are generated by a cathode electron gun, accelerated by a high-voltage field, and bombarded by a high-speed electron beam on an anode target to generate X-rays; the minimum focus size of the X-ray machine is 3 mu m, the ray cone angle is 25 degrees, the minimum focal length is 4.5mm, the high voltage range is 10-225 kV, and the current is 0.01-3 mA;
the system adopts a Paxscan4030 flat panel detector as an X-ray receiver, and can distinguish the size of a tiny defect in a material; panel size of the digital flat panel detector: 500mm × 367mm × 47mm, imaging window: 406mm × 293mm, effective window: 406mm by 282 mm.
7. The method for researching defect evolution of high-temperature damage concrete by adopting CT technology as claimed in claim 6, wherein: the technical indexes of the mu CF225FCB high-resolution micro CT system are as follows: the size range of the test piece is phi 1 mm-50 mm, the magnification is 1-400 times, and the resolution of the scanning unit is 0.5-194 mu m; the tube voltage is 80kV, the tube current is 90 muA, and the amplification factor is 53.85 times.
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108280290A (en) * | 2018-01-22 | 2018-07-13 | 青岛理工大学 | Concrete aggregate numerical model reconstruction method |
| CN108280290B (en) * | 2018-01-22 | 2020-12-01 | 青岛理工大学 | Concrete aggregate numerical model reconstruction method |
| CN108931542A (en) * | 2018-07-16 | 2018-12-04 | 东南大学 | A kind of non-destructive testing foam concrete method that internal pore structure develops under different larval instar |
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| CN111060440B (en) * | 2020-01-13 | 2022-11-08 | 湖南工程学院 | Detection method for compressive strength of foam concrete |
| CN111351810A (en) * | 2020-03-30 | 2020-06-30 | 山东省分析测试中心 | Analysis method for fracture failure behavior of metal with multi-scale defects |
| CN114235861A (en) * | 2021-12-20 | 2022-03-25 | 北京路生工程技术有限公司 | X-ray CT image fault matching test device and fault matching method |
| CN114235861B (en) * | 2021-12-20 | 2023-11-28 | 北京路生工程技术有限公司 | Testing device and fault matching method for X-ray CT image fault matching |
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