A quantitative method for the distribution of residual mortar layer on the surface of recycled aggregate

Abstract

The present invention discloses a method for quantifying the distribution of residual mortar layers on the surface of recycled aggregate. The method comprises: 1. bonding the recycled aggregate with a cementitious material, and preparing a microscopic test sample comprising original recycled aggregate particles, residual mortar, and adhesive by cutting and polishing; then acquiring cross-sectional images of the sample using an optical microscope; 2. preprocessing the acquired images to extract the surface profiles of the original recycled aggregate particles and the recycled aggregate containing the mortar layer based on the color differences of the three materials; and 3. calculating analytical expressions for each profile based on Fourier transform, thereby quantifying the content and distribution of residual mortar in the recycled aggregate. The present invention can accurately and conveniently quantify the residual mortar distribution of recycled aggregate, achieve a precise description of the characteristics of the recycled aggregate, and facilitate the rational and efficient application of recycled aggregate.

Description

Technical Field

[0001] The invention belongs to the field of recycled aggregate concrete, and particularly relates to a method for quantifying the distribution of residual mortar layers on the surface of recycled aggregate. Background Art

[0002] Recycled aggregate produced through simple crushing and screening of waste concrete often retains hardened cement mortar on its surface, resulting in disadvantages such as high porosity, high water absorption, low bulk density, and a high crushing index. Recycled concrete produced using this type of recycled aggregate exhibits multiple transition zones. The old-mortar-new-mortar interface is the primary weak spot in the mechanical properties of recycled aggregate concrete and the primary factor affecting its hardened strength, elastic modulus, impermeability, frost resistance, carbonation resistance, and chloride ion penetration resistance. Determining the content, thickness, and degree of mortar coating on the surface of recycled aggregate and quantitatively describing its characteristics are crucial for its application. Existing methods usually use acid dissolution method, which can only measure the content of residual mortar, but cannot determine the thickness of the mortar layer, the wrapping position and other residual mortar distribution conditions on the surface of the recycled aggregate particles; in view of this, CN110823060A uses asphalt to wrap the recycled aggregate, and uses the difference in nanomechanical parameters between the residual mortar and the recycled aggregate and asphalt mortar to perform hardness testing using an in-situ nanomechanical measurement system to determine the residual mortar thickness at the characteristic position. However, this method requires high precision in polishing and sample preparation, and can only achieve local thickness testing, and still does not provide a method for determining the residual mortar wrapping degree. Summary of the Invention

[0003] In order to address the shortcomings of the above-mentioned prior art, the present invention proposes a quantification method for the distribution of the residual mortar layer on the surface of recycled aggregate, so as to accurately and conveniently quantify the residual mortar of the recycled aggregate and achieve an accurate description of the characteristics of the recycled aggregate, thereby facilitating the rational and efficient application of the recycled aggregate.

[0004] In order to achieve the above-mentioned object, the present invention adopts the following technical solutions:

[0005] The method for quantifying the distribution of residual mortar layer on the surface of recycled aggregate of the present invention is characterized in that it comprises the following steps:

[0006] Step (1): After the recycled aggregate concrete formed by mixing recycled aggregate and cementitious material is hardened, cutting along the height direction of the specimen to obtain a small cross-section containing three areas: original recycled aggregate particles, residual mortar layer, and cementitious material;

[0007] Step (2): polishing the cut small cross-section to remove grooves on the cross-section caused by bubbles, and obtaining a sample for optical microscope photography; and photographing the sample under the optical microscope to obtain a cross-sectional image of the sample;

[0008] Step (3): preprocessing the cross-sectional image to eliminate grayscale value singularities to obtain a preprocessed cross-sectional image; establishing a rectangular coordinate system of the image with any vertex of the preprocessed cross-sectional image as the origin and two sides adjacent to the origin as the x-axis and the y-axis respectively;

[0009] Step (4): extracting the edge contour pixel coordinates of the recycled aggregate original particle area and the recycled aggregate area in the pre-processed cross-sectional image in the rectangular coordinate system and converting them into the polar coordinate system;

[0010] Step (5): resampling the polar angles under polar coordinates at equal angle intervals to obtain the polar coordinate data points of the contour points corresponding to the original particle area of ​​the recycled aggregate and the recycled aggregate area after resampling;

[0011] Perform Fourier transform on the resampled polar coordinate data points to obtain the analytical expression of the original particle profile of the recycled aggregate and the analytical expression of the recycled aggregate profile including the residual mortar layer;

[0012] The analytical expression describing the outline of the original particles of the recycled aggregate and the analytical expression describing the outline of the recycled aggregate are subtracted and plotted in a rectangular coordinate system to obtain the distribution law of the residual mortar layer on the surface of the recycled aggregate.

[0013] Step (6): According to the distribution law of the residual mortar layer on the surface of the recycled aggregate, the numerical integration method in the polar coordinate system is used to calculate the wrapping perimeter ratio and residual mortar content of the residual mortar layer on the surface of the recycled aggregate and use them as quantitative results.

[0014] The quantification method of the present invention is also characterized in that in the step (1), during the molding process of the recycled aggregate concrete, the cementitious material used is white cement or epoxy resin or other cementitious materials that have a color different from the original particles of the recycled aggregate and the residual mortar layer.

[0015] The step (4) comprises:

[0016] Step (4-1): setting different grayscale thresholds, and using the grayscale thresholds to perform binarization processing on the preprocessed cross-sectional image, respectively, to obtain a binary image of the original particles of the recycled aggregate and a binary image of the recycled aggregate including the mortar layer;

[0017] Step (4-2): extracting the pixel coordinates of the edge contour points and the pixel coordinates of the region center point in the binary image, and converting the pixel coordinates of the edge contour points in the binary image into actual coordinates according to the scale;

[0018] Step (4-3): Select the center point of the region of the binary graph of the original particles of the recycled aggregate as the reference point, translate the origin of the rectangular coordinate system, and obtain the coordinates of the surface contour pixel points after the coordinate translation;

[0019] Step (4-4): transforming the coordinates of the surface contour pixel points after the coordinate translation into a polar coordinate system, thereby obtaining the coordinate data of the contour points corresponding to the recycled aggregate original particle area and the recycled aggregate area in polar coordinates.

[0020] The step (5) comprises:

[0021] Step (5-1): Let the total number of equal-angle resampling points N of the polar angle be 2 L , and N is not less than k; L is a positive integer, k represents the minimum number of sampling points;

[0022] Step (5-2): Use the interpolation method to obtain the corresponding contours of the recycled aggregate original particle area and the recycled aggregate area at equally spaced sampling angles θ j The extreme value r n (θ j ) and r r (θ j ), where θ j =2πj / N, j=0,1,2,3...,N-1;

[0023] Step (5-3): Use equations (1) and (2) to obtain the analytical expressions of the original particle profile r1(θ) of the recycled aggregate and the analytical expression of the recycled aggregate profile r2(θ) including the residual mortar layer:

[0024] (1)

[0025] (2)

[0026] In formula (1) and formula (2), θ is the polar angle of each contour point; M is the Fourier expansion order, and M≤N / 2, N is the total number of contour resampling points; A0 and C0 are the average polar diameter values ​​of the original particle contour and the recycled aggregate contour in the recycled aggregate, respectively; A m and B m is the mth-order Fourier coefficient describing the original particle profile of the recycled aggregate; C m and D m is the mth-order Fourier coefficient describing the profile of the recycled aggregate containing the residual mortar layer.

[0027] The step (6) comprises:

[0028] Step (6-1): Calculate the residual mortar wrap perimeter ratio P1 using formula (3):

[0029] (3)

[0030] In formula (3), S is the number of continuous wrapping areas of the recycled aggregate residual mortar layer; θs1 and θ s2 are the upper and lower limits of the angle of the sth mortar distribution area, respectively;

[0031] Step (6-2): Calculate the total residual mortar content S1 using formula (4):

[0032] (4).

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present invention utilizes the color differences of various phases in recycled aggregate concrete and employs optical microscopy and digital imaging technology to accurately extract the original particle contours and the outer contours of the recycled aggregate. Furthermore, Fourier transform is used to obtain analytical expressions for each contour. Then, numerical integration is used to calculate indicators such as the wrapping perimeter ratio and residual mortar of the residual mortar layer on the recycled aggregate surface. These quantitative indicators can more accurately and comprehensively characterize the distribution of residual mortar on the recycled aggregate surface, providing a basis for in-depth research on the impact of residual mortar distribution on the performance of recycled aggregate concrete.

[0035] 2. Compared with the existing acid dissolution method for measuring the residual mortar content, the present invention can further quantitatively characterize the distribution of residual mortar in recycled aggregates through numerical integration of the contour analytical formula, which is very important and necessary for the evaluation and application of recycled aggregates.

[0036] 3. Compared with the existing method of measuring the local wrapping thickness of the residual mortar layer using nanomechanics technology, the present invention uses an optical microscope combined with digital imaging technology. The operation process is more convenient and effective, and the distribution of the residual mortar of the recycled aggregate can be characterized from a global level. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Flow chart of the method for quantifying the distribution of residual mortar layer on the surface of recycled aggregate according to the present invention;

[0038] Figure 2 Schematic diagram of the optical microscope observation area of ​​the recycled aggregate concrete of the present invention;

[0039] Figure 3 This is a schematic diagram of the recycled aggregate after contour point extraction, coordinate system transformation, and equal-interval sampling in the present invention;

[0040] Figure 4 This is a schematic diagram of the recycled aggregate original particle profile and the recycled aggregate profile analytical expression drawn in a rectangular coordinate system after making a difference. DETAILED DESCRIPTION

[0041] In this embodiment, Figure 1As shown, a method for quantifying the distribution of residual mortar layer on the surface of recycled aggregate includes the following steps:

[0042] Step (1): Recycled aggregate and cementitious materials are mixed to form recycled aggregate concrete. In order to avoid the contact between recycled aggregate particles and affect the subsequent digital image processing, the recycled aggregate content should be adjusted to ensure the separation of recycled aggregates. The hardened recycled aggregate concrete is cut along the height direction of the specimen. The small cross section obtained contains three areas: recycled aggregate original particles-residual mortar layer-cementitious material, such as Figure 2 As shown; in the specific implementation, during the molding process of recycled aggregate concrete, the cementitious material used is white cement or epoxy resin or other cementitious materials with a color difference from the original particles of recycled aggregate and the residual mortar layer, so as to ensure that the grayscale threshold method can accurately distinguish the three-phase areas.

[0043] Step (2): Grind the small cross-section obtained by cutting, remove the grooves on the cross-section caused by bubbles, and obtain a sample for optical microscope photography; and photograph the sample under the optical microscope to obtain a cross-sectional image of the sample. Considering the thickness range of the residual mortar package, the pixel resolution is generally controlled at 10-20μm to ensure that there are enough pixels along the thickness direction of the mortar package;

[0044] Step (3): Preprocess the cross-sectional image to eliminate grayscale singular points and obtain a preprocessed cross-sectional image; establish a rectangular coordinate system of the image with any vertex of the preprocessed cross-sectional image as the origin and the two sides adjacent to the origin as the x-axis and y-axis respectively. In digital images, it is generally assumed that the upper left corner vertex of the image is the origin, the horizontal right direction is the positive direction of the x-axis, and the vertical downward direction is the positive direction of the y-axis;

[0045] Step (4): Extract the edge contour pixel coordinates of the recycled aggregate original particle area and the recycled aggregate area in the rectangular coordinate system in the pre-processed cross-sectional image; Since Fourier transform can only process single-valued functions, it is necessary to convert the coordinate data of the contour in the rectangular coordinate system to the polar coordinate system, such as Figure 3 Shown: r n (θ1) and r r (θ2) are the polar diameter values ​​of the natural particle outline and the recycled aggregate particle outline in the recycled aggregate at polar angles θ1 and θ2, respectively;

[0046] Step (4-1): setting different grayscale thresholds, and using the grayscale thresholds to perform binarization processing on the preprocessed cross-sectional images, respectively, to obtain a binary image of the original particles of the recycled aggregate and a binary image of the recycled aggregate including the mortar layer;

[0047] Step (4-2): extracting the pixel coordinates of the edge contour points and the pixel coordinates of the region center point in the binary image, and converting the pixel coordinates of the edge contour points in the binary image into actual coordinates according to the scale;

[0048] Step (4-3): Since the center of the recycled aggregate original particle area must be within the recycled aggregate original particle area and the recycled aggregate area, the center point of the binary image of the recycled aggregate original particle area is selected as the reference point, and the origin of the rectangular coordinate system of the image is translated to obtain the coordinates of each contour pixel point after the coordinate system is translated;

[0049] Step (4-4): Convert the coordinates of the translated surface contour pixel points into a polar coordinate system, thereby obtaining the coordinate data of the contour points corresponding to the recycled aggregate original particle area and the recycled aggregate area in polar coordinates.

[0050] Step (5): The polar coordinate data of each contour obtained in step (4) are a number of discrete data points, but the polar angles of these discrete data points are not uniformly distributed. In order to use discrete Fourier series expansion, first step (5-1): It is necessary to resample the polar angles under polar coordinates at equal angle intervals. In order to ensure that FFT transformation can be used, the number of resampling points must be guaranteed to be a power of 2, so that the total number of equal angle interval resampling points N of the polar angle is 2 L , and N is not less than k; L is a positive integer, and k represents the minimum number of sampling points; thereby ensuring that fast Fourier transform (FFT) can be used to improve efficiency.

[0051] Step (5-2): Use the interpolation method to obtain the corresponding contours of the recycled aggregate original particle area and the recycled aggregate area at equally spaced sampling angles θ j (θ j =2πj / N, j=0,1,2,3……,N-1) n (θ j ) and r r (θ j );

[0052] After resampling, the polar coordinate data points of the contour points corresponding to the original particle area of ​​the recycled aggregate and the recycled aggregate area after resampling are obtained;

[0053] Step (5-3): Perform FFT transformation on the resampled polar coordinate data points, and use equations (1) and (2) to obtain the analytical expressions of the original particle profile r1(θ) of the recycled aggregate and the profile r2(θ) of the recycled aggregate including the residual mortar layer, respectively:

[0054] (1)

[0055] (2)

[0056] In formula (1) and formula (2), θ is the polar angle of each contour point; M is the Fourier expansion order. According to the Nyquist sampling theorem, M≤N / 2, and N is the total number of contour resampling points; A0 and C0 are the average polar diameter values ​​of the original particle contour and the recycled aggregate contour in the recycled aggregate, respectively; A m and B m is the mth-order Fourier coefficient describing the original particle profile of the recycled aggregate; C m and D m is the mth-order Fourier coefficient describing the profile of the recycled aggregate containing the residual mortar layer.

[0057] Step (6): Difference the analytical expression describing the original particle profile of the recycled aggregate and the analytical expression describing the recycled aggregate profile and plot them in a rectangular coordinate system to obtain the distribution law of the residual mortar layer on the surface of the recycled aggregate, as shown in the following example: Figure 4 As shown;

[0058] According to the distribution law of the residual mortar layer on the surface of recycled aggregate, the wrapping perimeter ratio and residual mortar content of the residual mortar layer on the surface of recycled aggregate were calculated using the numerical integration method in the polar coordinate system and used as quantitative results.

[0059] Step (6-1): Calculate the residual mortar wrap perimeter ratio P1 using formula (3):

[0060] (3)

[0061] In formula (3), S is the number of continuous wrapping areas of the recycled aggregate residual mortar layer; θ s1 and θ s2 They are the upper and lower limits of the angle of the mortar distribution area of ​​the sth block respectively.

[0062] Step (6-2): Calculate the total residual mortar content S1 using formula (4):

[0063] (4).

[0064] Example: In one embodiment, the following steps are used to measure and calculate the characteristic parameters of the residual mortar of recycled aggregate:

[0065] Preparation of test specimens: Recycled aggregate concrete was prepared by mixing 10 recycled aggregate particles with a particle size of 5-10 mm with white cement at a water-cement ratio of 0.4. The fresh concrete was poured into a 40×40×160 mm test mold and placed in a humid curing room (20±2°C, relative humidity >95%) for 24 hours. After demolding, it was placed in a rapid curing box and cured for 1 day. The recycled aggregate concrete was then cut into small pieces along the height direction using a cutting machine. The cross-section of the recycled aggregate concrete small pieces after cutting included three regions: the original recycled aggregate particles, the residual mortar layer, and the white cement.

[0066] Polishing the sample: Polish the small cross-section obtained by cutting to remove the grooves caused by bubbles on the cross-section to obtain samples for optical microscope shooting;

[0067] Optical microscope photography: Select a clear and flat cross-section containing the three areas of recycled aggregate original particles, residual mortar layer, and white cement. Use an optical microscope to take pictures of the test sample cross-section. The image pixel value is 1600×1200. Using a ruler, we can calculate that the actual distance of 1mm is equal to the distance of 55 pixels, and the pixel resolution is 18μm.

[0068] Digital image preprocessing: The cross-sectional images were imported into Image J image processing software, the RGB images were converted into 8-bit grayscale images, and the grayscale image singularities were manually eliminated;

[0069] Contour extraction: setting different thresholds, and using grayscale thresholds to perform binarization on the pre-processed cross-sectional image, respectively, to obtain a binarized image of the original particles of the recycled aggregate and a binarized image of the recycled aggregate containing the mortar layer; extracting the pixel coordinates of the edge contour points in each binarized image and obtaining the actual coordinates of each contour point according to the pixel resolution (at this time, the origin of the coordinate system is at the pixel position in the upper left corner of the image, the horizontal right is the positive direction of the x-axis, and the vertical downward is the positive direction of the y-axis); selecting the center point of the region of the binarized image of the original particles of the recycled aggregate as the reference point, translating the origin of the rectangular coordinate system of the image, and obtaining the coordinates of each contour pixel point after the coordinate system is translated; converting the coordinates of each contour pixel point after the translation into a polar coordinate system, thereby obtaining the coordinate data of the contour points corresponding to the original particles of the recycled aggregate and the recycled aggregate area in polar coordinates;

[0070] Resampling coordinates: Let the total number of equally spaced resampling points of the polar angle be 1024, and use the interpolation method to obtain the corresponding contours of the original particle area of ​​the recycled aggregate and the recycled aggregate area at equally spaced sampling angles θ j (θ j =2πj / N, j=0,1,2,3……,1023) n (θ j ) and r r (θ j );

[0071] Fourier transform: The mathematical analytical expressions r1(θ) and r2(θ) of the original particle profile and the recycled aggregate profile are calculated according to equations (1) and (2) respectively; the difference between r1(θ) and r2(θ) is plotted in a rectangular coordinate system, and the distribution law of the residual mortar layer on the surface of the recycled aggregate can be intuitively seen (e.g. Figure 4 );

[0072] Calculate the characteristic parameters of residual mortar: According to Figure 4The distribution law of the residual mortar layer on the surface of the recycled aggregate was calculated by numerical integration method. The residual mortar wrapping perimeter ratio and residual mortar content were 29.69% and 14.71 mm, respectively. 2 .

[0073] In summary, the method of the present invention utilizes digital image technology and adopts FFT transformation to calculate the original particle profile and recycled aggregate profile of the recycled aggregate, and thus accurately calculate the residual mortar wrapping perimeter ratio and residual mortar content based on numerical integration. Such quantitative indicators for quantitatively evaluating the distribution of residual mortar can provide a basis for in-depth study of the influence of residual mortar distribution on the performance of recycled aggregate concrete.

Claims

1. A method for quantifying the distribution of residual mortar layer on the surface of recycled aggregate, characterized in that: The following steps are involved: Step (1): After the recycled aggregate concrete formed by mixing recycled aggregate and cementitious material is hardened, cutting along the height direction of the specimen to obtain a small cross-section containing three areas: original recycled aggregate particles, residual mortar layer, and cementitious material; Step (2): polishing the cut small cross-section to remove grooves on the cross-section caused by bubbles, and obtaining a sample for optical microscope photography; and photographing the sample under the optical microscope to obtain a cross-sectional image of the sample; Step (3): preprocessing the cross-sectional image to eliminate grayscale value singularities to obtain a preprocessed cross-sectional image; establishing a rectangular coordinate system of the image with any vertex of the preprocessed cross-sectional image as the origin and two sides adjacent to the origin as the x-axis and the y-axis respectively; Step (4): extracting the edge contour pixel coordinates of the recycled aggregate original particle area and the recycled aggregate area in the pre-processed cross-sectional image in the rectangular coordinate system and converting them into the polar coordinate system; Step (5): resampling the polar angles under polar coordinates at equal angle intervals to obtain the polar coordinate data points of the contour points corresponding to the original particle area of ​​the recycled aggregate and the recycled aggregate area after resampling; Perform Fourier transform on the resampled polar coordinate data points to obtain the analytical expression of the original particle profile of the recycled aggregate and the analytical expression of the recycled aggregate profile including the residual mortar layer; The analytical expression describing the outline of the original particles of the recycled aggregate and the analytical expression describing the outline of the recycled aggregate are subtracted and plotted in a rectangular coordinate system to obtain the distribution law of the residual mortar layer on the surface of the recycled aggregate. Step (6): According to the distribution law of the residual mortar layer on the surface of the recycled aggregate, the numerical integration method in the polar coordinate system is used to calculate the wrapping perimeter ratio and residual mortar content of the residual mortar layer on the surface of the recycled aggregate and use them as quantitative results.

2. The quantization method according to claim 1, characterized in that In the step (1), during the molding process of the recycled aggregate concrete, the cementitious material used is white cement or epoxy resin.

3. The quantization method according to claim 1, characterized in that The step (4) comprises: Step (4-1): setting different grayscale thresholds, and using the grayscale thresholds to perform binarization processing on the preprocessed cross-sectional image, respectively, to obtain a binary image of the original particles of the recycled aggregate and a binary image of the recycled aggregate including the mortar layer; Step (4-2): extracting the pixel coordinates of the edge contour points and the pixel coordinates of the region center point in the binary image, and converting the pixel coordinates of the edge contour points in the binary image into actual coordinates according to the scale; Step (4-3): Select the center point of the region of the binary graph of the original particles of the recycled aggregate as the reference point, translate the origin of the rectangular coordinate system, and obtain the coordinates of the surface contour pixel points after the coordinate translation; Step (4-4): transforming the coordinates of the surface contour pixel points after the coordinate translation into a polar coordinate system, thereby obtaining the coordinate data of the contour points corresponding to the recycled aggregate original particle area and the recycled aggregate area in polar coordinates.

4. The quantization method according to claim 1, characterized in that The step (5) comprises: Step (5-1): Let the total number of equal-angle resampling points N of the polar angle be 2 L , and N is not less than k; L is a positive integer, k represents the minimum number of sampling points; Step (5-2): Use the interpolation method to obtain the corresponding contours of the recycled aggregate original particle area and the recycled aggregate area at equally spaced sampling angles θ j The extreme value r n (θ j ) and r r (θ j ), where θ j =2πj / N, j=0,1,2,3...,N-1; Step (5-3): Use equations (1) and (2) to obtain the analytical expressions of the original particle profile r1(θ) of the recycled aggregate and the analytical expression of the recycled aggregate profile r2(θ) including the residual mortar layer: (1) (2) In formula (1) and formula (2), θ is the polar angle of each contour point; M is the Fourier expansion order, and M≤N / 2, N is the total number of contour resampling points; A0 and C0 are the average polar diameter values ​​of the original particle contour and the recycled aggregate contour in the recycled aggregate, respectively; A m and B m is the mth-order Fourier coefficient describing the original particle profile of the recycled aggregate; C m and D m is the mth-order Fourier coefficient describing the profile of the recycled aggregate containing the residual mortar layer.

5. The quantization method according to claim 4, characterized in that The step (6) comprises: Step (6-1): Calculate the residual mortar wrap perimeter ratio P1 using formula (3): (3) In formula (3), S is the number of continuous wrapping areas of the recycled aggregate residual mortar layer; θ s1 and θ s2 are the upper and lower limits of the angle of the sth mortar distribution area, respectively; Step (6-2): Calculate the total residual mortar content S1 using formula (4): (4)。

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