A method for evaluating the slip resistance of a slip-form paving concrete based on digital image processing technology

Abstract

The application relates to a method for evaluating the slippability of slip-form paving concrete based on a digital image processing technology, belonging to the technical field of road engineering, and comprising the following steps: completing a molding experiment according to the mixing proportion of concrete, that is, molding a concrete test piece in a cubic mold; after demolding, the concrete is collapsed, and then photographing can be started; when photographing, the images of four sides of the molded concrete test piece are sequentially photographed by moving a camera; the obtained images of the four sides are respectively processed, including image preprocessing to obtain the concrete part in the image, and then the preprocessed image is grayed and binarized by using MATLAB; the size of the gap, the void ratio, the edge collapse value and the uniformity index of each side image are calculated, and the slippability of the concrete under the mixing proportion is quantitatively analyzed. The application changes the traditional qualitative analysis by naked eye observation into quantitative analysis, and proposes evaluation indexes, so that the condition of the slip-form paving concrete can be quickly and accurately quantified to guide the actual construction.

Description

Technical Field

[0001] This invention relates to a method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology, belonging to the field of road engineering technology. Background Technology

[0002] Slipform paving is a construction process that uses slipform pavers to pave concrete pavements. Because it does not require the erection of edge fixing templates, it can complete the functions of spreading, vibrating and compacting, extruding and shaping, and finishing in one go. It has the advantages of good construction continuity, fast progress and high efficiency, and is a commonly used construction process in modern road construction.

[0003] Concrete suitable for slipform paving should possess good slipability (uniformity, formwork stability, and other workability properties); therefore, mix design selection is crucial. In practical engineering, assessing the slipability of fresh concrete is essential. However, existing standards typically only use slump as an evaluation index for the workability of slipform-paved concrete, neglecting the influence of vibration on slipform-paved concrete, as well as important slipability indicators such as uniformity and formwork stability. Currently, there is a lack of rapid and effective methods for slipability testing and assessment. Digital image processing technology, with its advantages of high processing accuracy and strong comprehensiveness, is a commonly used analytical method in engineering analysis. Therefore, it is necessary to propose an assessment method for the slipability of slipform-paved concrete based on digital image processing technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology. This method transforms the traditional qualitative analysis based on visual observation into a quantitative analysis and proposes evaluation indicators. As a result, it can quickly and accurately quantify the condition of slipform paved concrete to guide actual construction.

[0005] The present invention adopts the following technical solution:

[0006] A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology includes the following steps:

[0007] (1) Complete the molding experiment according to the concrete mix proportion, that is, mold concrete specimens in a cubic mold;

[0008] (2) After demolding, wait for the concrete to collapse before taking pictures. When taking pictures, move the camera and take pictures of the four sides of the molded concrete specimen in sequence.

[0009] (3) Process the images of the four sides respectively, including image preprocessing to obtain the concrete part in the image, and then use MATLAB to convert the preprocessed image to grayscale and binarize.

[0010] (4) Calculate the void size, void ratio, collapse value and uniformity index of each side image, and quantitatively analyze the slipperiness of concrete under this mix proportion.

[0011] Preferably, in step (1), the concrete of the present invention is freshly mixed concrete. The cubic mold has dimensions of 300*300*300mm and consists of two equilateral L-shaped metal plates, a base plate, and a rubber sleeve. It has no top cover. The two L-shaped metal plates and the base plate are joined together and fixed on the outside with a rubber sleeve to form the concrete. To reduce voids during pouring and improve the density of the concrete, a vibrator is used when mixing the concrete, with a frequency of 12500r / min.

[0012] The process of pouring concrete into a cubic mold is called a "molding test". The specific process of the molding test is as follows: assemble the mold and put a rubber sleeve on the outside; mix the concrete according to the pre-designed mix ratio, and the mixing should be uniform; brush oil on the inside of the mold to facilitate demolding; pour the mixed concrete into the mold, quickly insert the vibrator into the lower middle part of the concrete, vibrate for 20-30 seconds, and after vibration, the height of the concrete should not be more than 5 cm from the top surface, and slowly remove it; remove the rubber sleeve, and remove the two L-shaped metal plates vertically upwards. The demolding process should avoid disturbing the sides as much as possible, and the required specimen can be obtained.

[0013] Preferably, in step (2), in order to quickly and conveniently acquire surface images of concrete, the image is captured by means of a positioning image acquisition device. The positioning image acquisition device includes a circular metal base plate located at the bottom, and a groove is provided at the center of the circular metal base plate. The size of the groove matches the cube mold and is used to place the cube mold.

[0014] A circular slide rail with a surrounding groove is welded onto the circular metal base plate. The circular slide rail, the groove and the center of the circular metal base plate coincide. A slider is provided on the circular slide rail. The camera is fixed on the slider and the slider can drive the camera to slide on the circular slide rail.

[0015] Preferably, a positioning device is provided on the annular slide rail at a position directly opposite the four sides of the molded concrete specimen to position the slider, thereby positioning the camera and ensuring that the camera is parallel to the side of the concrete when taking pictures.

[0016] Preferably, the annular slide rail is provided with a long strip-shaped slide groove in the middle, the slide groove has a convex cross-section, narrow at the top and wide at the bottom, and the bottom of the slider is provided with a convex strip that cooperates with the slide groove. The convex strip is embedded in the long strip-shaped slide groove to achieve sliding cooperation.

[0017] The number of positioning devices is four. Each positioning device includes two positioning plates, which are located on both sides of the slider to accurately position the slider. One end of the positioning plate is hinged to one side of the annular slide rail, and the other end can rotate freely. A limiting block is provided on the positioning plate. When the positioning plate rotates and engages with the annular slide rail, the limiting block is located in the slide groove, thereby positioning the slider. When the positioning plate is released, the slider can slide freely on the slide rail.

[0018] After shooting one side view, release the positioning plate, move the camera along the slider to the next shooting position, lock the positioning plate, and take the shot. Repeat the above process for shooting the other two sides.

[0019] Preferably, in step (2), when taking images of the four sides of the molded concrete specimen, the distance between the camera and the test side is equal, preferably 50cm;

[0020] Before taking the actual photo, set the camera parameters, such as focal length (40-80mm), exposure (set to 0 when the ambient light is moderate; increase exposure compensation when the environment is dark; decrease exposure compensation when the environment is bright), and pixels (2 million to 50 million pixels). The positioning image acquisition device is suitable for places with sufficient and uniform lighting.

[0021] Select continuous shooting mode for shooting; the collapse ends when the concrete height stops changing or the collapse time exceeds 30 seconds.

[0022] Preferably, in step (3), the image is preprocessed using Photoshop software to extract the concrete part, that is, there is no white space in the whole picture; then, the image is processed by grayscale and partitioned using MATLAB to facilitate subsequent analysis. The area with a grayscale value of 0 to 100 is the gap area, and the value is specified as 0. The area with a grayscale value of 101 to 255 is the flat area, and the value is specified as 1.

[0023] Preferably, in step (4):

[0024] ①The process of calculating the gap size is as follows:

[0025] In MATLAB, the gap diameter α is defined as α≥30mm, 10<α<30mm, and α≤10mm, which are respectively defined as large gap, medium gap, and small gap. The number of gaps in each level is counted.

[0026] When a large gap with a diameter of 30mm or more is found, the slipability is directly deemed unqualified.

[0027] When the number of voids with a diameter of 10-30 mm accounts for more than 15% of the total number of voids, the smoothness of the concrete is not up to standard.

[0028] All other cases are considered to have passed the slippage test under the gap size index;

[0029] The process of calculating the gap diameter α and the number of gaps is as follows: After binarizing the image using MATLAB, gap regions (values ​​of 0) and flat regions (values ​​of 1) are first distinguished based on grayscale values. Then, a distance measurement function, such as the dist function, is called to measure the distance between the two farthest 0 values ​​within the same gap region, which is the gap diameter α. Regions with the same diameter α are labeled with the same annotation, for example, as vectors. The number of items with the same label was then counted, which represents the number of gaps with the same diameter.

[0030] ②The process of calculating porosity is as follows:

[0031] The formula for calculating porosity β is as follows:

[0032]

[0033] Among them, the void area is the area of ​​the void region. When the void ratio β>30%, the slipperiness of the concrete is unqualified; when the void ratio β≤30%, the slipperiness of the concrete is qualified under the void ratio index.

[0034] ③ The process of calculating the collapse value is as follows:

[0035] The collapse value includes the top collapse value and the bottom collapse value. The top collapse value is defined as the vertical distance from the widest point after the top collapses to the initial top point, denoted as γ. 顶 The bottom collapse value is defined as the vertical distance from the widest point after the bottom collapses to the initial side edge, denoted as γ. 底 The initial height and width of the concrete specimen, as well as its height and width after collapse, were measured using MATLAB. The formula for calculating the collapse value γ is as follows:

[0036] Bottom collapse value: γ 底 = Width at widest point after bottom collapse - Initial width of side

[0037] Top collapse value: γ 顶 = Initial height of the top - Height of the widest point after the top collapses

[0038] Take γ 底 γ 顶 The maximum value in the value is taken as the collapse value γ. When the collapse value γ > 6mm, the slipability of the concrete is unqualified; when the porosity γ ≤ 6mm, the slipability of the concrete is qualified under the collapse value index.

[0039] ④ The process of calculating uniformity is as follows:

[0040] The entire image is divided into 9 regions along its length and width, and the porosity β of each region is calculated. ′The calculation method is consistent with that of porosity β; the dispersion of porosity β in the 9 regions is used to characterize the uniformity of concrete in the entire image, and a uniformity coefficient δ is defined. The calculation process is as follows:

[0041] Porosity β of 9 regions ′ Average value:

[0042]

[0043]

[0044] Where, β j ′ β represents the porosity of the j-th region, where j is an integer from 1 to 9. ′ max Indicates β j ′ The maximum value in, β ′ min Indicates β j ′ The minimum value in;

[0045] The uniformity coefficient δ is: δ = max{δ1, δ2}

[0046] When the uniformity coefficient δ>30%, the smoothness of the concrete is unqualified; when the uniformity coefficient δ≤30%, the smoothness of the concrete is qualified under the uniformity index.

[0047] The evaluation of each indicator is shown in Table 1:

[0048] Table 1: Evaluation Results for Each Evaluation Indicator

[0049]

[0050]

[0051] Preferably, when the slipperiness of the concrete meets all individual performance indicators, the overall slipperiness of the concrete is comprehensively evaluated, defined as follows:

[0052] α ′ This represents the maximum value of the gap diameter α on a single side surface, when α ′ <8mm, score A is 10; 8mm≤α ′ ≤20mm, score A is 6; 20mm<α ′ <30mm, score A is 4 points;

[0053] Porosity β < 10%, score B is 10; porosity 10% ≤ β ≤ 30%, score B is 6;

[0054] The edge collapse value γ < 3, and the score C is 10; when the edge collapse value 3mm ≤ γ ≤ 6mm, the score C is 6;

[0055] The uniformity coefficient δ ≤ 15%, and the score D is 10; when the uniformity coefficient 15% < δ ≤ 30%, the score D is 6;

[0056] As shown in Table 2 below:

[0057] Table 2: Evaluation Item Score Table

[0058]

[0059] Note: During comprehensive evaluation, α ′ represents the maximum value of the void diameter α on a single side, that is:

[0060] α ′ = max{α}

[0061] Calculate the concrete quality Q of a single side i , and the calculation formula is:

[0062] Q i = 0.2×A + 0.2×B + 0.4×C + 0.2×D

[0063] In the formula, 0.2 and 0.4 are importance coefficients, indicating the influence degree of this evaluation index on the slidability of slip-form paving concrete; i represents the i-th side, and the value range of i is 1 to 4, representing the 1st to 4th sides; A, B, C, and D respectively represent the scores corresponding to the void size, void ratio, edge collapse value, and uniformity;

[0064] Evaluate the slidability level of the entire concrete, that is, find the average quality score of the concrete on the four sides. The calculation formula is:

[0065]

[0066] When , the grade of this concrete specimen is excellent; when the grade of this concrete specimen is qualified; when the grade of this concrete specimen is unqualified.

[0067] The present invention first forms a concrete specimen in a mold. After demolding, images of the four sides of the concrete specimen are collected, and through digital image processing technology, the surface conditions of the slip-form paving concrete are analyzed, including the void ratio, void size, uniformity, and edge collapse value of the concrete surface, so as to quantitatively analyze the slidability of the concrete under this mix ratio, further judge whether this mix ratio is suitable for the slip-form paving construction process, and then guide engineering practice.

[0068] For the parts not elaborated in the present invention, existing technologies can be adopted.

[0069] The beneficial effects of this invention are as follows:

[0070] This invention utilizes camera photography combined with digital image processing technology and statistical analysis to evaluate the slipperiness of slipformed concrete. It transforms the assessment of slipperiness of slipformed concrete from traditional qualitative analysis based on visual observation into quantitative analysis, and proposes evaluation indicators. Therefore, it can quickly and accurately quantify the condition of slipformed concrete to guide actual construction. Attached Figure Description

[0071] Figure 1 Flowchart of a method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology;

[0072] Figure 2 Top view of the positioning image acquisition device;

[0073] Figure 3 A partial cross-sectional view of the positioning image acquisition device;

[0074] Figure 4 This is a schematic diagram of image partitioning;

[0075] Figure 5 The diagram illustrates the solution for the collapse edge value, where (a) represents the bottom collapse edge and (b) represents the top collapse edge.

[0076] In the diagram, 1-camera; 2-sample; 3-circular slide rail; 4-slider; 5-limiting block; 6-slide groove; 7-positioning plate. Detailed Implementation

[0077] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. However, this description is not limited thereto. All aspects not described in detail in the present invention are based on conventional techniques in the field.

[0078] Example 1

[0079] A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology, such as Figure 1 As shown, it includes the following steps:

[0080] (1) Complete the molding experiment according to the concrete mix proportion, that is, mold concrete specimens in a cubic mold;

[0081] (2) After demolding, wait for the concrete to collapse before taking pictures. When taking pictures, move the camera and take pictures of the four sides of the molded concrete specimen 2 in sequence.

[0082] (3) Process the images of the four sides respectively, including image preprocessing to obtain the concrete part in the image, and then use MATLAB to convert the preprocessed image to grayscale and binarize.

[0083] (4) Calculate the void size, void ratio, collapse value and uniformity index of each side image, and quantitatively analyze the slipperiness of concrete under this mix proportion.

[0084] Example 2

[0085] A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology, as described in Example 1, differs in that, in step (1), the concrete used in this invention is freshly mixed concrete, and the cubic mold has dimensions of 300*300*300mm, consisting of two equilateral L-shaped metal plates, a base plate, and a rubber sleeve, without a top cover. The two L-shaped metal plates and the base plate are joined together and fixed on the outside with a rubber sleeve to form the concrete. To reduce voids during pouring and improve the density of the concrete, a vibrator is used during concrete mixing at a frequency of 12500r / min.

[0086] The process of pouring concrete into a cubic mold is called a "molding test". The specific process of the molding test is as follows: assemble the mold and put a rubber sleeve on the outside; mix the concrete according to the pre-designed mix ratio, and the mixing should be uniform; brush oil on the inside of the mold to facilitate demolding; pour the mixed concrete into the mold, quickly insert the vibrator into the lower middle part of the concrete, vibrate for 20-30 seconds, and after vibration, the height of the concrete and the top surface should not be more than 5 cm, and slowly remove it; remove the rubber sleeve, and remove the two L-shaped metal plates vertically upwards. The demolding process should avoid disturbing the sides as much as possible, and the required specimen 2 can be obtained.

[0087] Example 3

[0088] A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology, as described in Example 1, differs in that, in step (2), to quickly and conveniently acquire surface images of the concrete, the image is captured using a positioning image acquisition device, such as... Figure 2 As shown, the positioning image acquisition device includes a circular metal base plate at the bottom, with a groove in the center of the circular metal base plate, the size of which matches the cube mold for placing the cube mold;

[0089] A circular slide rail 3 with a surrounding groove is welded onto a circular metal base plate. The circular slide rail 3, the groove and the center of the circular metal base plate coincide. A slider 4 is set on the circular slide rail 3. The camera 1 is fixed on the slider 4. The slider 4 can drive the camera 1 to slide on the circular slide rail 3.

[0090] Positioning devices are installed on the annular slide rail 3 at positions directly opposite the four sides of the molded concrete specimen to position the slider, thereby positioning the camera and ensuring that the camera is parallel to the side of the concrete when taking pictures.

[0091] like Figure 3 As shown, a long strip-shaped groove 6 is provided in the middle of the annular slide rail 3 along its length direction. The cross-section of the groove 6 is convex, narrow at the top and wide at the bottom. A convex strip that mates with the groove is provided at the bottom of the slider 4. The convex strip is embedded in the long strip-shaped groove to achieve sliding engagement.

[0092] There are four positioning devices, each including two positioning plates 7, which are located on both sides of the slider to accurately position the slider. One end of the positioning plate 7 is hinged to one side of the annular slide rail 3, and the other end can rotate freely. A limiting block 5 is provided on the positioning plate. When the positioning plate rotates and engages with the annular slide rail, the limiting block 5 is located in the slide groove 6, thus positioning the slider. When the positioning plate is released, the slider can slide freely on the slide rail.

[0093] After shooting one side view, release the positioning plate, move the camera along the slider to the next shooting position, lock the positioning plate, and take the shot. Repeat the above process for shooting the other two sides.

[0094] In step (2), when taking images of the four sides of the molded concrete specimen, the distance between the camera and the test side is equal, which is 50cm.

[0095] Before taking the actual photo, set the camera parameters, such as focal length (40-80mm), exposure (set to 0 when the ambient light is moderate; increase exposure compensation when the environment is dark; decrease exposure compensation when the environment is bright), and pixels (2 million to 50 million pixels). The positioning image acquisition device is suitable for places with sufficient and uniform lighting.

[0096] Select continuous shooting mode for shooting; the collapse ends when the concrete height stops changing or the collapse time exceeds 30 seconds.

[0097] Example 4

[0098] A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology is described in Example 3. The difference is that in step (3), the image is preprocessed using Photoshop software to extract the concrete part, i.e., there is no white space in the whole image. Then, the image is processed by grayscale and partitioned using MATLAB to facilitate subsequent analysis. The area with a grayscale value of 0 to 100 is the void area, and the value is specified as 0. The area with a grayscale value of 101 to 255 is the flat area, and the value is specified as 1.

[0099] Example 5

[0100] A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology, as described in Example 4, except that in step (4):

[0101] ①The process of calculating the gap size is as follows:

[0102] In MATLAB, the gap diameter α is defined as α≥30mm, 10<α<30mm, and α≤10mm, which are respectively defined as large gap, medium gap, and small gap. The number of gaps in each level is counted.

[0103] When a large gap with a diameter of 30mm or more is found, the slipability is directly deemed unqualified.

[0104] When the number of voids with a diameter of 10-30 mm accounts for more than 15% of the total number of voids, the smoothness of the concrete is not up to standard.

[0105] All other cases are considered to have passed the slippage test under the gap size index;

[0106] The process of calculating the gap diameter α and the number of gaps is as follows: After binarizing the image using MATLAB, gap regions (values ​​of 0) and flat regions (values ​​of 1) are first distinguished based on grayscale values. Then, a distance measurement function, such as the dist function, is called to measure the distance between the two farthest 0 values ​​within the same gap region, which is the gap diameter α. Regions with the same diameter α are labeled with the same annotation, for example, as vectors. The number of items with the same label was then counted, which represents the number of gaps with the same diameter.

[0107] ②The process of calculating porosity is as follows:

[0108] The formula for calculating porosity β is as follows:

[0109]

[0110] Among them, the void area is the area of ​​the void region. When the void ratio β>30%, the slipperiness of the concrete is unqualified; when the void ratio β≤30%, the slipperiness of the concrete is qualified under the void ratio index.

[0111] ③ The process of calculating the collapse value is as follows:

[0112] The collapse value includes the top collapse value and the bottom collapse value. The top collapse value is defined as the vertical distance from the widest point after the top collapses to the initial top point, denoted as γ. 顶 The bottom collapse value is defined as the vertical distance from the widest point after the bottom collapses to the initial side edge, denoted as γ. 底 ,like Figure 5 As shown; the initial height and width of the concrete specimen, as well as its height and width after collapse, were measured using MATLAB. The formula for calculating the collapse value γ is as follows:

[0113] Bottom collapse value: γ 底 = Width at widest point after bottom collapse - Initial width of side

[0114] Top collapse value: γ 顶 = Initial height of the top - Height of the widest point after the top collapses

[0115] Take γ 底 γ 顶 The maximum value in the value is taken as the collapse value γ. When the collapse value γ > 6mm, the slipability of the concrete is unqualified; when the porosity γ ≤ 6mm, the slipability of the concrete is qualified under the collapse value index.

[0116] ④ The process of calculating uniformity is as follows:

[0117] The entire image is divided into 9 equal regions along its length and width, such as... Figure 4 Calculate the porosity β of each region. ′ The calculation method is consistent with that of porosity β; the dispersion of porosity β in the 9 regions is used to characterize the uniformity of concrete in the entire image, and a uniformity coefficient δ is defined. The calculation process is as follows:

[0118] Porosity β of 9 regions ′ Average value:

[0119]

[0120]

[0121] Where, β j ′ β represents the porosity of the j-th region, where j is an integer from 1 to 9. ′ max Indicates β j ′ The maximum value in, β ′ min Indicates β j ′ The minimum value in;

[0122] The uniformity coefficient δ is: δ = max{δ1, δ2}

[0123] When the uniformity coefficient δ>30%, the smoothness of the concrete is unqualified; when the uniformity coefficient δ≤30%, the smoothness of the concrete is qualified under the uniformity index.

[0124] The evaluation of each indicator is shown in Table 1:

[0125] Table 1: Evaluation Results for Each Evaluation Indicator

[0126]

[0127] Preferably, when the slipperiness of the concrete meets all individual performance indicators, the overall slipperiness of the concrete is comprehensively evaluated, defined as follows:

[0128] α ′ This represents the maximum value of the gap diameter α on a single side surface, when α ′ <8mm, score A is 10; 8mm≤α ′ ≤20mm, score A is 6; 20mm<α ′ <30mm, score A is 4 points;

[0129] Porosity β < 10%, score B is 10; porosity 10% ≤ β ≤ 30%, score B is 6;

[0130] If the collapse value γ < 3, the score C is 10; if the collapse value 3mm ≤ γ ≤ 6mm, the score C is 6.

[0131] If the uniformity coefficient δ ≤ 15%, the score D is 10; if the uniformity coefficient 15% < δ ≤ 30%, the score D is 6.

[0132] As shown in Table 2 below:

[0133] Table 2: Evaluation Item Score Table

[0134]

[0135] Note: In the comprehensive evaluation, α ′ This represents the maximum value of the gap diameter α on a single side, i.e.:

[0136] α ′ =max{α}

[0137] Calculate the concrete mass Q of a single side i The calculation formula is:

[0138] Q i = 0.2×A + 0.2×B + 0.4×C + 0.2×D

[0139] In the formula, 0.2 and 0.4 are importance coefficients, representing the degree of influence of the evaluation index on the slipperiness of slipform paved concrete; i represents the i-th side, and the value of i ranges from 1 to 4, representing the 1st to 4th sides; A, B, C, and D represent the scores corresponding to void size, void ratio, collapse value, and uniformity, respectively.

[0140] To evaluate the overall slipperiness level of the concrete, i.e., to calculate the average mass score of the concrete on each of the four surfaces, the formula is as follows:

[0141]

[0142] When it is the case, the grade of the concrete specimen is excellent; when it is the case, the grade of the concrete specimen is qualified; when it is the case, the grade of the concrete specimen is unqualified.

[0143] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as within the protection scope of the present invention.

Claims

1. A method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology, characterized in that, Includes the following steps: (1) Complete the molding experiment according to the concrete mix proportion, that is, mold concrete specimens in a cubic mold. The size of the cubic mold is 300*300*300mm. (2) After demolding, wait for the concrete to collapse before taking pictures. When taking pictures, move the camera and take pictures of the four sides of the molded concrete specimen in sequence. (3) Process the images of the four sides respectively, including image preprocessing to obtain the concrete part in the image, and then use MATLAB to convert the preprocessed image to grayscale and binarize it. (4) Calculate the void size, void ratio, collapse value, and uniformity index of each side image, and quantitatively analyze the slipperiness of the concrete under this mix proportion. In step (4): The process of calculating the gap size is as follows: Specifying the gap diameter in MATLAB ,Right now They are defined as large gaps, medium gaps, and small gaps, and the number of gaps in each level is counted. When a large gap with a diameter of 30mm or more is found, the slipability is directly deemed unqualified. When the number of voids with a diameter of 10~30mm accounts for more than 15% of the total number of voids, the smoothness of the concrete is not up to standard. All other cases are considered to have passed the slippage test under the gap size index; The process of calculating porosity is as follows: porosity The calculation formula is Among them, the void area is the area of ​​the void region, and when the porosity is... When the concrete's slipability is unsatisfactory, and when the porosity is... At that time, the concrete's slipability was qualified under the void ratio index. The process of calculating the collapse value is as follows: The collapse value includes the top collapse value and the bottom collapse value. The top collapse value is defined as the vertical distance from the widest point after the top collapses to the initial top point, denoted as . The bottom collapse value is defined as the vertical distance from the widest point after the bottom collapses to the initial side edge, denoted as . ; MATLAB was used to measure the initial height and width of the concrete specimen, as well as the height and width after collapse, and the collapse edge value. The calculation formula is: Bottom collapse value: Top collapse value: Pick , The maximum value in the range is used as the collapse value. When the collapse value At that time, the concrete's slipability was unqualified; when the collapse value... At that time, the concrete's slipability was qualified under the collapse value index; The process of calculating uniformity is as follows: The entire image is divided into 9 regions along its length and width, and the porosity of each region is calculated. , with porosity The calculation methods are consistent; porosity in the 9 regions The discreteness of the image is used to characterize the uniformity of the concrete throughout the image, and a uniformity coefficient is defined. The calculation process is as follows: Porosity of 9 regions in, This represents the porosity of the j-th region, where j is an integer from 1 to 9. express The maximum value in, express The minimum value in; Uniformity coefficient for: When the uniformity coefficient When the smoothness of the concrete fails to meet the standard, and the uniformity coefficient is... When the content is ≤30%, the smoothness of the concrete meets the homogeneity index. When the slipperiness of concrete meets all individual performance indicators, the overall slipperiness of the concrete is comprehensively evaluated and defined as follows: Indicates the diameter of the gap on a single side. The maximum value when Score A is 10; The score for A is 6; Score A is 4 points; porosity Score B is 10; porosity The score for B is 6; Collapse value The score C is 10; the collapse value The score C is 6; Uniformity coefficient The score D is 10; the uniformity coefficient The score for D is 6; Calculate the concrete mass of a single side The calculation formula is: In the formula, 0.2 and 0.4 are importance coefficients, which indicate the degree of influence of the index on the slipperiness of concrete in slipform paving; Indicates the first There are three sides, where i ranges from 1 to 4, representing the 1st to 4th sides; A, B, C, and D represent the scores corresponding to the gap size, porosity, edge collapse value, and uniformity, respectively. To evaluate the overall slipperiness level of the concrete, i.e., to calculate the average mass score of the concrete on each of the four surfaces, the formula is as follows: when When the value is ≥9, the concrete specimen is rated as excellent; when the value is ≤6, the grade is excellent. <9, the concrete specimen grade is qualified; when If the value is less than 6, the concrete specimen is considered unqualified.

2. The method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology according to claim 1, characterized in that, In step (1), the cube mold consists of two equilateral L-shaped metal plates, a base plate and a rubber sleeve. When mixing concrete, it is equipped with a vibrator with a frequency of 12500r / min.

3. The method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology according to claim 1, characterized in that, In step (2), the shooting is achieved by means of a positioning image acquisition device. The positioning image acquisition device includes a circular metal base plate located at the bottom. A groove is provided in the center of the circular metal base plate, the size of which matches the cube mold, for placing the cube mold. The circular metal base plate is provided with an annular slide rail with a surrounding groove. The annular slide rail and the groove coincide with the center of the circular metal base plate. A slider is provided on the annular slide rail, and the camera is fixed on the slider. The slider can drive the camera to slide on the annular slide rail.

4. The method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology according to claim 3, characterized in that, Positioning devices are provided on the annular slide rail at positions directly opposite the four sides of the molded concrete specimen to position the slider. The annular slide rail has a long strip-shaped groove in the middle. The groove has a convex cross-section, which is narrow at the top and wide at the bottom. The bottom of the slider has a convex strip that mates with the groove. The convex strip is embedded in the long strip-shaped groove to achieve a sliding fit. The number of positioning devices is four. Each positioning device includes two positioning plates, which are located on both sides of the slider to accurately position the slider. One end of the positioning plate is hinged to one side of the annular slide rail, and the other end can rotate freely. A limiting block is provided on the positioning plate. When the positioning plate rotates and engages with the annular slide rail, the limiting block is located in the slide groove, thereby achieving the positioning of the slider.

5. The method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology according to claim 1, characterized in that, In step (2), when taking images of the four sides of the molded concrete specimen, the distance between the camera and the test side is equal, which is 50cm. Before taking the actual photo, set the camera parameters: focal length, exposure, and resolution.

6. The method for evaluating the slipperiness of slipform paved concrete based on digital image processing technology according to claim 1, characterized in that, In step (3), the image is preprocessed using Photoshop software to extract the concrete part. Then, the image is processed and partitioned using MATLAB. The area with a gray value of 0 to 100 is the void area, with a value of 0. The area with a gray value of 101 to 255 is the flat area, with a value of 1.

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