Method for testing content of free mica in machine-made sandstone powder

Abstract

The invention relates to a method for testing the content of free mica in machine-made sandstone powder, which comprises the following steps: pre-treating machine-made sand, and plating a carbon layer on the surface of a pre-treated sample; performing grating type point-by-point scanning on the surface of the prepared sample to generate and obtain a high-resolution back scattering image; calculating the area of stone powder particles according to the back scattering image, and calculating the area of a mica particle region to obtain the content of free mica in the stone powder; performing EDS scanning on the range of the free mica particles to obtain an X-ray spectrum, and analyzing the X-ray spectrum through software to generate a multicolor layered element diagram; and combining the element diagrams to generate a multicolor layered energy dispersion spectrum element diagram, calculating the area of a corresponding region according to the monochromatic energy dispersion spectrum diagram of the potassium element, calculating the area of a corresponding region according to the monochromatic energy dispersion spectrum diagram of the magnesium element, and further calculating the content of free muscovite and the content of other free mica.

Description

Technical Field

[0001] The present application relates to the technical field of building material testing, and in particular to a method for testing the free mica content in machine-made sand and gravel powder. Background Art

[0002] Mica is a common rock-forming mineral, a general term for layered aluminosilicates composed of potassium, aluminum, magnesium, iron, and lithium, and is widely found in natural rocks. When rolling manufactured sand from parent rock with a high mica content, the rolling process results in the formation of numerous free mica particles within the manufactured sand and gravel particles, as the strength of the mica is generally lower than that of the parent rock. This results in mica content meeting current standards, but when mixed with this manufactured sand, the fresh mix performance is poor. This is primarily manifested in high water consumption, difficulty in air entrainment, large air content and slump loss, and poor workability. The resulting concrete also suffers from poor durability and crack resistance, significantly impacting the safety of concrete structures. To ensure construction quality, large-scale concrete projects have been forced to abandon the use of manufactured sand with high mica content. For example, the original rock of the Three Gorges Project excavated pyrophyllite granite contains approximately 10% to 15% mica, and this excavated material is ultimately used as the coarse aggregate for rolled concrete.

[0003] There are two main technical solutions for detecting the free mica content in stone powder. One is to quantitatively detect the mica content in manufactured sand through X-ray diffraction technology. This method requires the stone powder particles to be ground to a certain fineness. The test operation is difficult and requires the operator to have rich experience in data collection and analysis to ensure the accuracy and reliability of the test results. When the mica content is low and the degree of crystallization is poor, it will affect the analysis results. The other is to quantitatively detect the mica content in manufactured sand through image recognition technology. This detection method extracts mica images from stone powder particles and cannot completely distinguish between mica particles and sand particles, resulting in significant fluctuations in the results. Summary of the Invention

[0004] The present application provides a method for testing the content of free mica in machine-made sand and gravel powder. The method for testing the content of free mica in machine-made sand and gravel powder can more conveniently and accurately test the content of free mica in machine-made sand and gravel powder, and can distinguish the content of muscovite in free mica, guide the concrete mix ratio and construction method during the construction process, and ensure the safety and durability of the project.

[0005] The method for testing the free mica content in machine-made sand and gravel powder provided in this application comprises the following steps:

[0006] 1) Sample preparation: pre-treating the machine-made sand and coating the surface of the pre-treated sample with a carbon layer of 10 to 20 nm;

[0007] 2) Sample backscattering test: perform raster scanning on the prepared sample surface point by point to generate a backscattering image, which is further adjusted to obtain a high-resolution backscattering image;

[0008] 3) Backscattered image analysis: Calculate the area A1 of the stone powder particles and the area A2 of the mica particles based on the backscattered image to obtain the content of free mica in the stone powder.

[0009] 4) Energy Dispersive Spectroscopy (EDS) of the sample: perform EDS scanning on the free mica particle range to obtain X-ray spectra, which are analyzed using Aztec software to generate a multi-color layered elemental map.

[0010] 5) Energy dispersion spectrum image analysis: Combine the various element maps to generate a multi-color layered energy dispersion spectrum element map, calculate the area A3 of the corresponding region based on the monochromatic energy dispersion spectrum of potassium, and calculate the area A4 of the corresponding region based on the monochromatic energy dispersion spectrum of magnesium, and then calculate the content of free muscovite The content of the remaining free mica is Q3 = Q1-Q2.

[0011] In an optional solution, in step 3), when performing backscattered image analysis, the following steps are specifically included:

[0012] According to the backscattered image, the black area is resin and the gray / white area is stone powder particles. The gray threshold software is used to identify and delete the black area, highlight the stone powder particle area, and calculate the area A1 of the stone powder particles.

[0013] According to the needle-like characteristics of free mica in the backscattered image, the measured aspect ratio is set to 2.8, where the aspect ratio is the ratio of the length to the width of a single particle; the circularity is set to 0.5, Where P is the particle perimeter and A is the particle area; the circularity of a circle is 1, and slender and irregular particles have a lower circularity;

[0014] According to the input measurement values, the particle regions with an aspect ratio less than 2.8 and a circularity greater than 0.5 are eliminated. The remaining particle regions are the mica particle regions, and the area A2 of the mica particle regions is calculated.

[0015] In an optional solution, in step 5), before generating the multi-color layered energy dispersion spectral elemental map, the following steps are included:

[0016] Using the mapping function of Aztec software, each element in the energy dispersion spectrum mapping is assigned a color, the free mica in the backscattered image is colored according to the elemental composition, and then the individual element maps are combined to generate a multi-color layered energy dispersion spectrum element map.

[0017] In an optional solution, the step 2) uses a variable voltage scanning electron microscope to perform backscattering testing on the sample, which specifically includes the following steps:

[0018] The prepared sample is placed in the sample chamber of a variable-voltage scanning electron microscope. At 20 kV, an electron beam is emitted from an electron gun. Under the action of the magnetic field of the scanning coil, the incident electron beam performs a raster scan point by point on the sample surface to generate a backscattered image. The working distance and focus are adjusted to obtain a high-resolution backscattered image.

[0019] In an optional solution, when using the variable-voltage scanning electron microscope, the setting parameters of the variable-voltage scanning electron microscope are: using an aperture of 30 μm or above, setting the EHT to 20 kV, selecting the BSD Gain level to high, and setting the working distance to 5 to 10 mm.

[0020] In an optional solution, the pretreatment in step 1) includes the following steps:

[0021] Place the machine-made sand in a drying oven and dry it to constant weight at a temperature of 105±5°C. After cooling to room temperature, sieve out the stone powder sample with a particle size less than 0.075mm for later use.

[0022] The stone powder sample was mixed thoroughly and placed in a low-fluorine cold-setting resin for curing;

[0023] After curing, the resin was polished to a thickness of 30 μm to form a thin sheet with exposed sand particles. The sheet was then gently wiped with ethanol, and the residual fibers on the surface of the sheet were removed with a nitrogen gun and then dried.

[0024] The beneficial effects of this application are:

[0025] The method for testing the content of free mica in manufactured sand and gravel powder in the present application distinguishes free mica by the appearance morphology and chemical composition characteristics of free mica particles, and can be automatically calculated by a computer to avoid the influence of subjective factors of the test personnel on the test results, thereby more accurately determining the total content of free mica, free muscovite and other free mica in the manufactured sand and gravel powder, which is beneficial to the quality control of concrete, and thus conducive to guiding the concrete mix ratio and construction methods during the construction process, ensuring the safety and durability of the project.

[0026] It should be understood that the foregoing general description and the following detailed description are merely illustrative and are not restrictive of the present application. DETAILED DESCRIPTION

[0027] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below.

[0028] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other technical solutions obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0029] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0030] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0031] The present invention provides a method for testing the free mica content in machine-made sand and gravel powder. The method mainly comprises the following steps:

[0032] 1) Sample preparation: Place the machine-made sand in a drying oven at (105±5)°C and dry it to constant weight. After cooling to room temperature, use a 0.075mm sand sieve to sieve out the stone powder sample with a particle size less than 0.075mm for later use.

[0033] The stone powder sample was thoroughly mixed and placed in a low-fluorine cold-setting resin (the size was selected according to the scanning electron microscope model), and then cured. After curing, the resin was polished to a thickness of 30 μm to produce a thin slice with the sand particles exposed;

[0034] The slice was gently wiped with ethanol, and residual fibers on the surface of the slice were removed with a nitrogen gun. After drying, a 10-20 nm carbon layer was plated on the sample surface using a high vacuum carbon plater specially designed for electron microscopy.

[0035] 2) Sample backscatter (BSE) testing: Place the prepared sample in the sample chamber of a variable-voltage scanning electron microscope (SEM), use an aperture of 30 μm or larger, set the EHT to 20 kV, select the BSD gain level to high, and set the working distance to 5-10 mm.

[0036] At 20 kV, an electron beam is emitted from an electron gun. Under the action of the magnetic field of the scanning coil, the incident electron beam performs a raster scan point by point on the sample surface to generate a backscattered light (BSE) image. The working distance (WD) and focus are adjusted to obtain a high-resolution BSE image.

[0037] 3) Backscatter (BSE) image analysis: The black area in the backscatter (BSE) image is resin, and the gray / white area is stone powder particles. Gray threshold software is used to identify and delete the black area, highlight the stone powder particle area, and calculate the area A1 of the stone powder particle;

[0038] According to the needle-like characteristics of free mica in the backscattered (BSE) image, the measured value aspect ratio was set to 2.8 (the aspect ratio is the ratio of the length to the width of a single particle) and the circularity was set to 0.5 ( Where P is the particle perimeter and A is the particle area; the circularity of a circle is 1, and the circularity of slender and irregular particles is smaller. Based on the input measurement values, the particle areas with aspect ratios less than 2.8 and circularity greater than 0.5 are eliminated. The remaining particle areas are the mica particle areas. The area A2 of the mica particle area is calculated. The content of free mica in the stone powder is

[0039] 4) Energy Dispersive Spectroscopy (EDS) testing of the sample: EDS scanning of the free mica particle range is performed to obtain an X-ray spectrum, which is analyzed using Aztec software to generate a multi-color layered elemental map.

[0040] 5) Energy Dispersive Spectroscopy (EDS) Image Analysis: Using the mapping function of Aztec software, the EDS-mapped elements, including C, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Mn, and Fe, were assigned a color to each element selected for analysis. Free mica in the backscattered (BSE) image was also colored according to its elemental composition. The individual element maps were then combined to generate a multi-color layered EDS element map.

[0041] The area A3 of the corresponding region can be calculated from the monochromatic EDS image of potassium (K), and the area A4 of the corresponding region can be calculated from the monochromatic EDS image of magnesium (Mg), and the content of free muscovite can be calculated. The content of the remaining free mica is Q3 = Q1-Q2.

[0042] This method for testing the free mica content in manufactured sand and gravel powder uses a scanning electron microscope (SEM) to perform backscattered light (BSE) analysis on the sample. BSE images require no complex preparation, are relatively simple to acquire, and offer high resolution and contrast. Compared to existing image recognition technologies, BSE images offer higher resolution, making it easier to distinguish particle features and providing highly stable test results. Combined with the irregular, needle-like morphology of free mica particles, threshold software is used to accurately calculate the total free mica content.

[0043] Energy dispersive spectroscopy (EDS) was performed on samples using a scanning electron microscope. This analysis of the chemical composition of mica particles was performed using EDS. Different micas were distinguished based on their distinct chemical compositions. Micas such as biotite and phlogopite are composed of elements such as silicon, aluminum, potassium, magnesium, iron, and titanium, while muscovite contains only a small amount of iron (Fe) and no magnesium (Mg). Using monochromatic images of potassium and magnesium, muscovite can be distinguished and the content of free muscovite and other free micas can be calculated. This method is simpler to operate and provides more accurate quantitative calculations than existing X-ray diffraction techniques.

[0044] The above are merely preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for testing the content of free mica in machine-made sand and gravel powder, characterized in that: The following steps are involved: 1) Sample preparation: pre-treating the machine-made sand and coating the surface of the pre-treated sample with a carbon layer of 10 to 20 nm; 2) Sample backscattering test: perform raster scanning on the prepared sample surface point by point to generate a backscattering image, which is further adjusted to obtain a high-resolution backscattering image; 3) Backscattered image analysis: Calculate the area A1 of the stone powder particles and the area A2 of the mica particles based on the backscattered image to obtain the content of free mica in the stone powder. 4) Energy Dispersive Spectroscopy (EDS) of the sample: perform EDS scanning on the free mica particle range to obtain X-ray spectra, which are analyzed using Aztec software to generate a multi-color layered elemental map. 5) Energy dispersion spectrum image analysis: Combine the various element maps to generate a multi-color layered energy dispersion spectrum element map, calculate the area A3 of the corresponding region based on the monochromatic energy dispersion spectrum of potassium, and calculate the area A4 of the corresponding region based on the monochromatic energy dispersion spectrum of magnesium, and then calculate the content of free muscovite The content of the remaining free mica is Q3 = Q1-Q2.

2. The method for testing the free mica content in machine-made sand and stone powder according to claim 1, wherein: In the step 3), the backscattered image analysis is specifically performed by: According to the backscattered image, the black area is resin and the gray / white area is stone powder particles. The gray threshold software is used to identify and delete the black area, highlight the stone powder particle area, and calculate the area A1 of the stone powder particles. According to the needle-like characteristics of free mica in the backscattered image, the measured aspect ratio is set to 2.8, where the aspect ratio is the ratio of the length to the width of a single particle; the circularity is set to 0.5, Where P is the particle perimeter and A is the particle area; the circularity of a circle is 1, and slender and irregular particles have a lower circularity; According to the input measurement values, the particle regions with an aspect ratio less than 2.8 and a circularity greater than 0.5 are eliminated. The remaining particle regions are the mica particle regions, and the area A2 of the mica particle regions is calculated.

3. The method for testing the free mica content in machine-made sand and stone powder according to claim 1 or 2, wherein: In the step 5), the following steps are included before generating the multi-color layered energy dispersion spectrum element map: Using the mapping function of Aztec software, each element in the energy dispersion spectrum mapping is assigned a color, the free mica in the backscattered image is colored according to the elemental composition, and then the individual element maps are combined to generate a multi-color layered energy dispersion spectrum element map.

4. The method for testing the free mica content in machine-made sand and stone powder according to claim 3, wherein: In step 2), a backscattering test is performed on the sample using a variable voltage scanning electron microscope, which specifically includes the following steps: The prepared sample is placed in the sample chamber of a variable-voltage scanning electron microscope. At 20 kV, an electron beam is emitted from an electron gun. Under the action of the magnetic field of the scanning coil, the incident electron beam performs a raster scan point by point on the sample surface to generate a backscattered image. The working distance and focus are adjusted to obtain a high-resolution backscattered image.

5. The method for testing the free mica content in machine-made sand and stone powder according to claim 4, wherein: When using the variable voltage scanning electron microscope, the setting parameters of the variable voltage scanning electron microscope are: using an aperture of 30 μm or above, setting the EHT to 20 kV, selecting the BSD Gain level to high, and setting the working distance to 5-10 mm.

6. The method for testing the free mica content in the machine-made sand and gravel powder according to any one of claims 1-2 or 4-5, characterized in that: The pre-treatment in step 1) comprises the following steps: Place the machine-made sand in a drying oven and dry it to constant weight at a temperature of 105±5°C. After cooling to room temperature, sieve out the stone powder sample with a particle size less than 0.075mm for later use. The stone powder sample was mixed thoroughly and placed in a low-fluorine cold-setting resin for curing; After curing, the resin was polished to a thickness of 30 μm to form a thin sheet with exposed sand particles. The sheet was then gently wiped with ethanol, and the residual fibers on the surface of the sheet were removed with a nitrogen gun and then dried.

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