A method for ensuring the performance of recycled coarse aggregate without strengthening treatment

Abstract

A method for ensuring the performance of recycled coarse aggregate without strengthening treatment, including two steps of mortar adhesion rate test and morphological analysis. The mortar adhesion rate test uses image processing and segmentation techniques, including image acquisition, grayscale conversion, normalization processing and other techniques. The morphology includes image analysis of the front projection and side projection of recycled coarse aggregate, and uses image recognition and automatic screening techniques, including one or more methods such as global (local) threshold segmentation, OTSU threshold segmentation, iterative threshold segmentation, watershed segmentation, etc. The present invention can achieve the purpose of automatically sorting recycled coarse aggregate and batch replacing natural aggregate, and has the characteristics of simple operation, low price, environmental protection, etc. Compared with other methods with complex strengthening processes, the digital image method adopted by the present invention can realize automatic recognition and automatic sorting, and does not adopt any chemical treatment measures, has no negative impact on the mechanical properties of the prepared recycled coarse aggregate concrete, has no impact on the workability of the mixture, and significantly improves the utilization rate of recycled coarse aggregate.

Description

Technical Field

[0001] The present invention belongs to the technical fields of building materials and computer technology, and relates to a method for ensuring the performance of recycled coarse aggregate without strengthening treatment. Background Art

[0002] The mortar adhesion rate of recycled coarse aggregate is an important basis for its strengthening treatment. The aggregate morphology is a key factor affecting the workability of the recycled coarse aggregate concrete mixture and the mechanical properties after hardening, and is of great significance for the recycling of construction waste. The performance difference between recycled aggregate and natural aggregate is directly related to the old mortar adhered to its surface. Usually, strengthening treatment is required to improve its performance disadvantages and ensure the performance of recycled coarse aggregate concrete. However, the strengthening process is cumbersome and consumes a large amount of material and financial resources. Therefore, there is an urgent need to develop a method that can ensure the performance of recycled coarse aggregate without strengthening treatment.

[0003] Currently, pre-wetting, pickling, inorganic material filling and other methods are mainly used to strengthen recycled coarse aggregate, so as to narrow the performance gap between it and natural aggregate. The strength of the prepared recycled coarse aggregate concrete has also been improved in terms of permeability and durability, but there are different limitations in mortar viscosity, acid concentration and carbonization time, and the strengthening process is complicated, requiring special operation and consuming a large amount of material and financial resources. The performance difference between recycled coarse aggregate and natural aggregate stems from the adhered old mortar layer, which is also an important basis for determining the strengthening treatment method and action time. Therefore, the mortar adhesion rate on the surface of recycled coarse aggregate is an important parameter determining the performance of recycled coarse aggregate; in addition, the morphology of recycled coarse aggregate is affected by the crushing process and there are also significant differences from natural aggregate. After replacing natural aggregate with recycled coarse aggregate, the aggregate morphology also has a certain impact on the workability of the concrete mixture and the mechanical properties after hardening. Taking the mortar adhesion rate and morphology as the screening conditions for recycled coarse aggregate, using digital image methods to automatically count the two indicators, and then achieving the purpose of automatic sorting and batch replacement of natural aggregate with recycled coarse aggregate, and finally realizing the goal of ensuring the performance of recycled coarse aggregate without strengthening. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for ensuring the performance of recycled coarse aggregate without strengthening treatment, which can significantly improve the reasonable utilization rate of recycled coarse aggregate and achieve the purpose of automatic sorting and batch replacement of recycled coarse aggregate.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for ensuring the performance of recycled coarse aggregate without strengthening treatment, including two steps of mortar adhesion rate test and morphology analysis. The mortar adhesion rate test uses image processing and segmentation techniques; the morphology includes image analysis of the front projection and side projection of recycled coarse aggregate, and uses image recognition and automatic screening techniques;

[0007] The mortar adhesion rate test uses image processing technology, including but not limited to image acquisition, grayscale conversion, normalization and other processing technologies. It mainly uses digital image methods to convert a three-dimensional image into a one-dimensional grayscale image, and then through image normalization processing, reads the distribution law of grayscale values from the histogram, and then obtains the segmentation boundary between the "target area" and the "background area".

[0008] The mortar adhesion rate image segmentation method includes one or more of global (local) threshold segmentation, OTSU threshold segmentation, iterative threshold segmentation, watershed segmentation, etc.

[0009] The morphology uses image analysis technology, including but not limited to image erosion, boundary extraction, image matrix conversion and other analysis technologies. It mainly converts the one-dimensional grayscale image into a matrix, calculates the boundary matrix of the image, and then obtains parameters such as the minimum circumscribed rectangle, centroid, and maximum inscribed circle of the image through boundary matrix analysis, and calculates the shape coefficient.

[0010] The morphology uses image recognition and automatic screening technology, including the morphology recognition of natural aggregates and recycled coarse aggregates, the determination of the shape coefficient, and the determination of the replacement rate of recycled coarse aggregates relative to natural aggregates. It mainly uses image recognition technology to test the shape coefficient of natural aggregates, and based on its value, adjusts the coefficient of the waste concrete crushing process, and then obtains recycled coarse aggregates with the same shape coefficient to achieve the replacement of natural aggregates, so that the mechanical properties of the prepared recycled coarse aggregates and the workability of the concrete mixture are no different from those of the original concrete.

[0011] Preferably, the mortar adhesion rate of the recycled coarse aggregate should not be greater than 30%.

[0012] Preferably, the recycled coarse aggregate and the replaced natural aggregate should have the same shape coefficient.

[0013] Preferably, the replacement rate of the recycled coarse aggregate does not exceed 45%.

[0014] A method for ensuring the performance of recycled coarse aggregates without strengthening treatment according to the present invention can specifically adopt the following steps:

[0015] (1) Image acquisition: Place the recycled coarse aggregate on a single-color background without overlapping coverage, and select a bottom plate with a large difference in color from the aggregate; use a camera with a pixel count of not less than 50 million to take a picture at a position 500 mm above its vertical height, and store it as a picture.

[0016] (2) Image grayscale conversion: Convert the picture obtained in step (1) into a grayscale image, and then perform image normalization processing to avoid overflow during the calculation process.

[0017] (3) Image segmentation: The threshold algorithm is used for the primary segmentation of the background and the target to obtain the optimal threshold for the primary segmentation. Based on this threshold, the mortar and coarse aggregate within the target are subjected to secondary segmentation and marked separately;

[0018] (4) Calculate the mortar adhesion rate: Count the number of pixel points occupied by the mortar and coarse aggregate, and calculate the mortar adhesion rate through formula (1);

[0019]

[0020] Where: P: Mortar adhesion rate, %A 1 : Number of pixels of mortar, piece

[0021] A 2 : Number of pixels of recycled coarse aggregate, piece

[0022]

[0023] Where: ρ 1 : Density of mortar, g / cm 3 ρ 2 : Density of recycled coarse aggregate, g / cm 3

[0024] h 1 : Average thickness of mortar, mmh 2 : Average thickness of recycled coarse aggregate, mm

[0025] a: When taking 0.025, it is the same as the value measured by the traditional manual method;

[0026] (5) Calculate the morphology of coarse aggregate: Corrode and extract the boundary of the coarse aggregate image after the primary segmentation, convert the boundary image into a matrix, and calculate the morphology of the coarse aggregate according to formula (3) and formula (4);

[0027]

[0028]

[0029] Note: τ: Flakiness index; ψ: Irregularity coefficient;

[0030] L / W / T: Length / width / thickness of recycled coarse aggregate in three-dimensional projection (L>W>T);

[0031] S 1 / S 2 : Front / side projection area of coarse aggregate;

[0032] (6) Statistics and calculation: Batch test the mortar adhesion rate and morphology of recycled coarse aggregate, and record the analysis results in a spreadsheet.

[0033] Compared with other methods with complex strengthening processes, the present invention is simple and easy to operate, inexpensive, environmentally friendly. The digital image method adopted can achieve automatic identification and automatic sorting, and no chemical treatment measures are used, which has no negative impact on the mechanical properties of the prepared recycled coarse aggregate concrete, has no negative impact on the workability of the concrete mixture, and significantly improves the utilization rate of recycled coarse aggregate. Detailed implementation manners

[0034] The present invention will be further described in conjunction with the following embodiments.

[0035] Embodiment 1

[0036] A method that can ensure the performance of recycled coarse aggregate without strengthening treatment. The shape coefficients of natural aggregates (ψ = 0.2 - 0.4 and τ = 1.1 - 2.5) are tested using Matlab software, and recycled coarse aggregates with consistent shape coefficients are selected for replacement at a mass ratio of 15%. The natural coarse aggregate is limestone gravel with a particle size of 5 - 20 mm and continuous grading; the recycled coarse aggregate is obtained by crushing and screening waste concrete test blocks with a jaw crusher, with a particle size of 5 - 20 mm and continuous grading. The mix proportion of the recycled coarse aggregate is shown in Table 1; in Table 1, the concrete mix proportion of No. A0 uses only natural aggregates, and the concrete mix proportion of No. A1 uses recycled coarse aggregates, both of which are screened by an automatic sorting system, with a mortar adhesion rate of not more than 30% and the same shape coefficient as the natural aggregate. The concrete mix proportion of No. B1 uses recycled coarse aggregates without any treatment;

[0037] Table 1 Mix proportion of recycled coarse aggregate concrete

[0038]

[0039] For the method of automatic sorting and batch replacement of recycled coarse aggregate in this embodiment, in terms of the workability of the concrete mixture, the measured values of groups A0, A1, and B1 are 210 mm, 210 mm, and 170 mm respectively. It can be seen that under the method of this example, when the replacement rate of recycled coarse aggregate is 15%, the slump loss is 0 mm, while for the untreated recycled coarse aggregate, the slump loss of the prepared concrete mixture is 40 mm; in terms of mechanical properties, the measured 7-day compressive strengths of groups A0, A1, and B1 are 32.8 MPa, 33.4 MPa, and 29.8 MPa respectively, and the measured 28-day compressive strengths are 37.6 MPa, 38.7 MPa, and 34.3 MPa respectively. It can be seen that under the method of this example, the 7-day and 28-day compressive strengths increase by 0.6 MPa and 1.1 MPa respectively, while the untreated group B1 decreases by 3.0 MPa and 3.3 MPa, indicating that the recycled coarse aggregate screened by this method has no difference from natural aggregate in terms of the workability of the concrete mixture and the mechanical properties after hardening;

[0040] Example 2

[0041] A method that can ensure the performance of recycled coarse aggregate without strengthening treatment. Use Matlab software to test the shape coefficients of natural aggregates (ψ = 0.2 - 0.4 and τ = 1.1 - 2.5), and select recycled coarse aggregates with the same shape coefficient for replacement at 30% by mass ratio. The natural coarse aggregate is limestone gravel with a particle size of 5 - 20 mm and continuous grading; the recycled coarse aggregate is obtained by screening the waste concrete test blocks crushed by a jaw crusher, with a particle size of 5 - 20 mm and continuous grading. The mix proportion of the recycled coarse aggregate is shown in Table 1. In Table 1, the concrete mix proportion of No. A0 uses only natural aggregates, and the concrete mix proportion of No. A2 uses recycled coarse aggregates, both of which are screened by an automatic sorting system, with a mortar adhesion rate of not more than 30% and the same shape coefficient as the natural aggregate. The concrete mix proportion of No. B2 uses recycled coarse aggregates without any treatment;

[0042] Table 1 Mix proportion of recycled coarse aggregate concrete

[0043]

[0044] For the method of automatic sorting and batch replacement of recycled coarse aggregate in this example, in terms of the workability of the concrete mixture, the measured values of groups A0, A2, and B2 are 210 mm, 210 mm, and 150 mm respectively. It can be seen that under the method of this example, when the replacement rate of recycled coarse aggregate is 30%, the slump loss is 0 mm, while for the untreated recycled coarse aggregate, the slump loss of the prepared concrete mixture is 60 mm; in terms of mechanical properties, the measured 7-day compressive strengths of groups A0, A2, and B2 are 32.8 MPa, 34.9 MPa, and 26.3 MPa respectively, and the measured 28-day compressive strengths are 37.6 MPa, 38.5 MPa, and 29.2 MPa respectively. It can be seen that under the method of this example, the 7-day and 28-day compressive strengths are increased by 2.1 MPa and 0.9 MPa respectively, while those of the untreated group B1 are decreased by 6.5 MPa and 8.4 MPa. This shows that the recycled coarse aggregate screened by this method has no difference from natural aggregate in terms of the workability of the concrete mixture and the mechanical properties after hardening;

[0045] Example 3

[0046] A method that can ensure the performance of recycled coarse aggregate without strengthening treatment. Use Matlab software to test the shape coefficients of natural aggregates (ψ = 0.2 - 0.4 and τ = 1.1 - 2.5), and select recycled coarse aggregates with the same shape coefficient for replacement at 45% by mass ratio. The natural coarse aggregate is limestone gravel with a particle size of 5 - 20 mm and continuous grading; the recycled coarse aggregate is obtained by crushing and screening waste concrete test blocks with a jaw crusher, with a particle size of 5 - 20 mm and continuous grading. The mix proportion of the recycled coarse aggregate is shown in Table 1. In Table 1, the concrete mix proportion of No. A0 uses all natural aggregates, and the concrete mix proportion of No. A3 uses recycled coarse aggregates, both of which are screened by an automatic sorting system, with a mortar adhesion rate of not more than 30% and the same shape coefficient as the natural aggregate. The concrete mix proportion of No. B3 uses recycled coarse aggregates without any treatment.

[0047] Table 1 Mix Proportion of Recycled Coarse Aggregate Concrete

[0048]

[0049] For the method of automatic sorting and batch replacement of recycled coarse aggregate in this example, in terms of the workability of the concrete mixture, the measured values of groups A0, A3, and B3 are 210 mm, 200 mm, and 130 mm respectively. It can be seen that under the method of this example, when the replacement rate of recycled coarse aggregate is 45%, the slump loss is only 10 mm, while for the untreated recycled coarse aggregate, the slump loss of the prepared concrete mixture is 70 mm. In terms of mechanical properties, the measured 7-day compressive strengths of groups A0, A3, and B3 are 32.8 MPa, 33.1 MPa, and 23.7 MPa respectively, and the measured 28-day compressive strengths are 37.6 MPa, 38.4 MPa, and 27.5 MPa respectively. It can be seen that under the method of this example, the 7-day and 28-day compressive strengths are increased by 0.3 MPa and 0.8 MPa respectively, while for the untreated group B1, they are decreased by 9.1 MPa and 10.1 MPa respectively, indicating that the recycled coarse aggregate screened by this method has no difference from natural aggregate in terms of the workability of the concrete mixture and the mechanical properties after hardening.

[0050] The performance differences between recycled aggregates and natural aggregates are directly related to the old mortar adhering to their surfaces. Strengthening treatment is required to improve their performance disadvantages. However, the strengthening process is cumbersome and consumes a large amount of material and financial resources. Therefore, a method that can ensure the performance of recycled coarse aggregates without strengthening treatment needs to be developed. Therefore, this invention takes the two indicators of the mortar adhesion rate and morphology of recycled coarse aggregates as the screening conditions for automatic sorting, and uses digital image methods for processing. It is replaced according to the principle that the mortar adhesion rate determined in the experiment does not exceed 30% and the morphology of the coarse aggregates is consistent, so as to achieve the purpose of automatically sorting recycled coarse aggregates and batch replacing natural aggregates. When the replacement rate does not exceed 50%, the compressive strength and slump of recycled coarse aggregate concrete are the same as those of the reference concrete, and the 7-day and 28-day compressive strength values are also basically close to those of the concrete prepared with recycled coarse aggregates after strengthening treatment. This proves that recycled coarse aggregates with a mortar adhesion rate not exceeding 30% can meet the expected workability and mechanical performance requirements without strengthening treatment, and the replacement rate does not exceed 50%, so the technology proposed in this invention is feasible.

Claims

1. A method for ensuring the performance of recycled coarse aggregate without strengthening treatment, characterized in that, it includes two steps: mortar adhesion rate test and morphological analysis; For the mortar adhesion rate test, image processing and image segmentation are used; for the image processing, digital image methods are mainly used to convert a three-dimensional image into a one-dimensional grayscale image, and then through image normalization processing, the distribution law of grayscale values is read from the histogram, and then the segmentation boundary between the "target area" and the "background area" is obtained; for the image segmentation, it includes one or more of global threshold segmentation, OTSU threshold segmentation, iterative threshold segmentation, and watershed segmentation; The morphological analysis includes image analysis of the front projection and side projection of the recycled coarse aggregate, and image recognition and automatic screening technologies are used; The morphological analysis includes image erosion, boundary extraction, and image matrix conversion. The one-dimensional grayscale image is converted into a matrix, the boundary matrix of the image is calculated, and then the minimum circumscribed rectangle, centroid, and maximum inscribed circle of the image are obtained through the analysis of the boundary matrix, and the shape coefficient is calculated; The image recognition and automatic screening include the morphological recognition of natural aggregate and recycled coarse aggregate, the determination of the morphological coefficient, and the determination of the replacement rate of recycled coarse aggregate relative to natural aggregate. The morphological coefficient of natural aggregate is tested by using image recognition technology. Based on its value, the coefficient of the waste concrete crushing process is adjusted, and then recycled coarse aggregate with the same morphological coefficient is obtained to realize the replacement of natural aggregate, so that the mechanical properties of the prepared recycled coarse aggregate and the workability of the concrete mixture are no different from those of the original concrete; The specific steps are as follows: (1) Image acquisition: Place the recycled coarse aggregate on a background of a single color without overlapping coverage, and select a bottom plate with a large difference in color from the aggregate; use a camera with a pixel count of not less than 50 million to take pictures at a vertical height of 500 mm and store them as pictures; (2) Image grayscale conversion: Convert the picture obtained in step (1) into a grayscale image, and then perform image normalization processing to avoid overflow during the calculation process; (3) Image segmentation: Use a threshold algorithm to perform a primary segmentation of the background and the target to obtain the optimal threshold for the primary segmentation. Based on this threshold, the mortar and coarse aggregate within the target are subjected to secondary segmentation and marked respectively; (4) Calculate the mortar adhesion rate: Count the number of pixel points occupied by the mortar and coarse aggregate, and calculate the mortar adhesion rate through formula (1); Wherein: P: mortar adhesion rate %A 1 ; number of pixels of the mortar, piece; A 2 : The number of pixels of recycled coarse aggregate, piece; Where: ρ 1 : The density of mortar, g / cm 3 ρ 2 : The density of recycled coarse aggregate, g / cm 3 h 1 : Average thickness of mortar, mm h 2 : Average thickness of recycled coarse aggregate, mm a: When taking 0.025, it is the same as the value measured by the traditional manual method; (5) Calculate the morphology of the coarse aggregate: Corrode and extract the boundary of the coarse aggregate image after the primary segmentation, and convert the boundary image into a matrix, and calculate the morphology of the coarse aggregate according to formula (3) and formula (4); Where: τ: flaky and elongated particle coefficient; ψ: irregular coefficient; L / W / T: length / width / thickness of the recycled coarse aggregate in the three-dimensional projection; S 1 / S 2： Front / side projected area of coarse aggregate (6) Statistics and calculation: Batch test the mortar adhesion rate and morphology of the recycled coarse aggregate, and record the analysis results in a spreadsheet.

2. The method for ensuring the performance of recycled coarse aggregate without strengthening treatment according to claim 1, further characterized in that, the mortar adhesion rate of the recycled coarse aggregate should not be greater than 30%.

3. The method for ensuring the performance of recycled coarse aggregate without strengthening treatment according to claim 1, further characterized in that, The recycled coarse aggregate and the natural aggregate to be replaced should have the same form factor.

4. A method for ensuring the performance of recycled coarse aggregate without strengthening treatment according to claim 1, further characterized in that, the replacement rate of the recycled coarse aggregate does not exceed 45%.

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