Method for evaluating asphalt-aggregate adhesion considering aggregate geometric characteristics

Abstract

The application discloses an asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics, and comprises the following steps: S1, preparing asphalt-coated aggregate; S2, obtaining three photos of the aggregate from different angles through a camera device; S3, obtaining the peeling area of the asphalt film on the surface of the aggregate by using image processing software; and S4, dividing the adhesion grade according to the asphalt peeling area ratio. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics has the advantages that the defects of the traditional water boiling method, i.e., the defects of relying on subjective experience and not considering the geometric characteristics of the aggregate, are overcome, objective and quantitative evaluation of the asphalt-aggregate adhesion is realized, the influence of the geometric characteristics of the aggregate on the adhesion can be reflected, the method is suitable for different types of asphalt and aggregate, and scientific basis is provided for engineering material selection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of asphalt aggregate determination, and in particular to a method for evaluating asphalt-aggregate adhesion considering the geometric characteristics of aggregates. BACKGROUND

[0002] Asphalt-aggregate adhesion is one of the important basic technical properties of asphalt and is a key indicator to ensure the water stability of asphalt mixture. In existing specifications, the evaluation method of asphalt-aggregate adhesion mainly adopts the water boiling method: ① Tie the aggregate in the middle with a fine line, and place it in a 105℃±5℃ oven for 1h; ② Lift the dried aggregate with a fine line and immerse it in preheated asphalt for 45s, so that the aggregate is completely covered with asphalt; ③ Hang the asphalt-covered aggregate on a test rack, allowing excess asphalt to flow off, and cool for 15min at room temperature; ④ Lift the cooled aggregate with a fine line and immerse it in a beaker containing hot water for 3min, keeping the water slightly boiling but not allowing any boiling foam; ⑤ Take the boiled aggregate out of the water, cool it, and observe the degree of asphalt peeling on the aggregate, and determine the asphalt-aggregate adhesion grade (1 to 5) according to the tester's subjective experience.

[0003] However, the existing asphalt-aggregate adhesion evaluation method has the following shortcomings:

[0004] (1) Strong subjective dependence: The current adhesion grade determination highly depends on the experience of the test personnel, and there are significant differences in the visual judgment of "asphalt peeling degree" among different operators.

[0005] (2) Lack of geometric characteristics: The traditional method does not take into account the influence of key geometric parameters such as aggregate shape and surface texture; the existing method only classifies "coarse aggregate" and "fine aggregate" simply, and cannot quantify the contribution of features such as angularity and surface porosity to adhesion, resulting in evaluation results that cannot reflect the differences in microstructure of aggregates.

[0006] (3) Unclear test conditions: The description of "slightly boiling water but not allowing any boiling foam" in the existing regulations lacks quantitative standards. In actual operation, water temperatures ranging from 85℃ to 98℃ may be judged as "slightly boiling", and for every 2℃ increase in water temperature, the risk of thermal damage to the asphalt film increases by about 7%, resulting in a 2-grade fluctuation in the evaluation results of the same aggregate at different temperatures, which seriously affects the repeatability of the test.

[0007] The above defects make it difficult for the traditional method to meet the demand for precise evaluation in the design of high-performance asphalt mixture, therefore, it is urgent to introduce a new evaluation system that is objective, quantitative and multi-factor coupled. SUMMARY

[0008] The present application aims to provide a method for evaluating asphalt-aggregate adhesion considering the geometric characteristics of aggregate, which is different from the prior art that relies on the subjective judgment of the tester on asphalt-aggregate adhesion, and quantitatively evaluates the asphalt stripping rate, and takes into account the geometric characteristics of the aggregate, such as the aspect ratio of the aggregate, to solve the defects of the traditional method that does not consider the influence of the geometric characteristics of the aggregate.

[0009] To achieve the above-mentioned purpose, the present application provides a method for evaluating asphalt-aggregate adhesion considering the geometric characteristics of aggregate, comprising the following steps:

[0010] S1, preparing aggregate coated with asphalt;

[0011] S2, obtaining three photos of the aggregate from different angles by a camera device;

[0012] S3, obtaining the stripping area of the asphalt film on the surface of the aggregate by using image processing software;

[0013] S4, dividing the adhesion grade according to the asphalt stripping area ratio.

[0014] Preferably, S1 specifically comprises the following steps:

[0015] S11, tying the aggregate with a fine line at the middle part, and placing it in a 105℃±5℃ oven for drying for 1h;

[0016] S12, lifting the dried aggregate with a fine line, and immersing it in asphalt heated to a molten state, so that the aggregate is completely coated with asphalt;

[0017] S13, hanging the aggregate coated with asphalt on a test rack, allowing the excess asphalt to flow off, and cooling it at room temperature for 15min;

[0018] S14, lifting the cooled aggregate with a fine line, and immersing it in a beaker containing pure water at a temperature of 90℃-94℃ for boiling for 3min;

[0019] S15, taking out the boiled aggregate from the water, hanging it on a test rack for cooling for 15min, to obtain the aggregate coated with asphalt.

[0020] Preferably, in S12, if the asphalt is base asphalt, the immersion time is 45s; if the asphalt is modified asphalt, the immersion time is 30s.

[0021] Preferably, in S2, the cooled aggregate is placed on a white hard board, sufficient light is ensured, and three photos of the aggregate with a pixel density of not less than 240dpi are taken in the range of -90°-0°, 0°, and 0°-90° around the vertical direction as the center line.

[0022] Preferably, S3 specifically comprises the following steps:

[0023] S31, input the photo into image processing software, and set the photo image bit depth to 8-bit;

[0024] S32, use the image processing software to count the length-diameter ratio and aggregate area of each photo, and sum the aggregate areas of the three photos to obtain the total aggregate area S;

[0025] S33, perform binaryzation processing on the photo with the pixel gray value t i as the threshold value, after the binaryzation processing, the white area of the photo is the asphalt peeling area, and the black area is the asphalt non-peeling area;

[0026] calculate the average value of the length-diameter ratio of the aggregate in the three photos determine the binaryzation threshold value t i :

[0027]

[0028] then the pixel gray value t i is calculated as follows:

[0029]

[0030] obtained:

[0031]

[0032] wherein i is a natural number greater than 0, LD1, LD2 and LD3 are the length-diameter ratios of the aggregate in the three photos;

[0033] the binaryzation processing formula is as follows:

[0034]

[0035] wherein x and y are the horizontal and vertical coordinates of the pixel points in the photo; B(x, y) is the gray value of the pixel point with coordinates (x, y) in the image after the binaryzation processing; f(x, y) is the gray value of the pixel point with coordinates (x, y) in the original image;

[0036] S34, perform binaryzation processing on the three aggregate photos with t i and t i+1 as the threshold values, use the image processing software to count the white area of each photo, and sum the white areas of the three photos to obtain the total white area;

[0037] S35, calculate the difference of the total white area under the threshold values t i and t i+1 , until the difference of the total white area is greater than 5% of the total aggregate area, and record the total white area under the threshold value t i .

[0038] Preferably, in S34, the area of the white region of a single photo is calculated according to the following formula:

[0039]

[0040] wherein A k,i represents the area of the white region of the kth photo under the threshold value t i , k = 1, 2, 3, corresponding to three different photos; i represents the number of the threshold value used; B k,i (x, y) is the value of the pixel point with coordinates (x, y) in the kth photo after binarization processing; W and H are the width and height of the photo, respectively;

[0041] The total area of the white region of the three photos under the threshold value t

[0042]

[0043] wherein S i is the total area of the white region of the three photos under the threshold value t i ;

[0044] The difference ΔS i in the total area of the white region under adjacent threshold values t i+1 and t i is:

[0045] ΔS i = |S i+1 - S i | (7) ;

[0046] wherein S i+1 is the total area of the white region of the three photos under the threshold value t i+1 , and S i is the total area of the white region under the threshold value t i ;

[0047] It is determined whether the difference in the total area of the white region under adjacent threshold values is greater than 5% of the total area of the aggregate, i.e., when ΔS i > 0.05 x S, the threshold value iteration is stopped, and the total area of the white region S i under the current threshold value t i is recorded, which is used for subsequent calculation of the asphalt stripping area ratio.

[0048] Preferably, in S4, the calculation formula of the asphalt stripping area ratio P is as follows:

[0049]

[0050] wherein m is the mass of the aggregate, ρ is the apparent density of the aggregate, d is the maximum nominal size of the aggregate, S i is the total area of the white region of the three photos under the threshold value t iS is the total area of the white region, and S is the total area of the aggregate.

[0051] Preferably, the adhesion level is divided according to the asphalt peeling area ratio P:

[0052] When the asphalt peeling area ratio P is less than 5%, the adhesion level is 5;

[0053] When the asphalt peeling area ratio P is between 5% and 10%, the adhesion level is 4;

[0054] When the asphalt peeling area ratio P is between 10% and 20%, the adhesion level is 3;

[0055] When the asphalt peeling area ratio P is between 20% and 30%, the adhesion level is 2;

[0056] When the asphalt peeling area ratio P is greater than 30%, the adhesion level is 1.

[0057] Therefore, the present application adopts the above-mentioned asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate, and has the following beneficial effects:

[0058] (1) The asphalt peeling area ratio is introduced, which can objectively and quantitatively evaluate the adhesion level of asphalt-aggregate: The present application accurately counts the peeling area of the asphalt film on the surface of the aggregate by image processing technology, and calculates the asphalt peeling area ratio, which is used as a quantitative index for evaluating the adhesion level. Compared with the traditional method which relies on the subjective judgment of the asphalt peeling degree by the test personnel, the present application divides the adhesion level into 5 levels based on the clear calculation formula and grading standard, which avoids the evaluation deviation caused by the cognitive difference of different personnel, and significantly improves the objectivity, accuracy and repeatability of the evaluation results. Whether in laboratory testing or engineering site evaluation, this method can provide reliable and consistent evaluation data, and provide a solid basis for quality control of asphalt mixture.

[0059] (2) The influence of the geometric characteristics of aggregate on the adhesion of asphalt-aggregate is considered: The present application fully considers the geometric characteristics of aggregate in the evaluation process, and integrates it into the threshold calculation and other key links of image processing. The interlocking and physical adsorption of aggregate with different shapes and surface characteristics and asphalt are different, which can more comprehensively and accurately reflect the adhesion performance between asphalt and aggregate, and provide more scientific guidance for reasonable selection of aggregate type and optimization of asphalt mixture mix proportion.

[0060] The technical solutions of the present application will be further described in detail below with the help of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is the overall flow chart of an embodiment of the asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate of the present application;

[0062] Figure 2 is the aggregate after the boiling water test on the white plate of an embodiment of the asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate of the present application;

[0063] Figure 3 is a photo of an embodiment of the asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate of the present application, wherein (a) is a 24-bit photo before conversion, (b) is an 8-bit photo converted from (a), and (c) is an 8-bit photo with the background removed from (b);

[0064] Figure 4 is the image appearance under different threshold values of an embodiment of the asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate of the present application, wherein the threshold value of (a) is 230, the threshold value of (b) is 205, the threshold value of (c) is 180, the threshold value of (d) is 155, and the threshold value of (e) is 130. DETAILED DESCRIPTION

[0065] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0066] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those with ordinary skills in the art to which the present application belongs.

[0067] As shown in Figure 1 , an asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate, comprising the following steps:

[0068] S1, preparing asphalt-coated aggregate, specifically comprising the following steps:

[0069] S11, randomly selecting an aggregate sample, tying the aggregate with a fine line in the middle, and placing it in a preheated oven at 105℃±5℃ for 1h; during the drying process, the oven door can be opened for 1-2 times, each time for 1-2min, to promote air circulation in the oven and ensure uniform drying of the aggregate; after drying, the aggregate is taken out using a high-temperature-resistant glove and placed on a clean, dry tray to avoid secondary pollution.

[0070] S12, lifting the dried aggregate with a fine line and immersing it in molten asphalt, so that the aggregate is completely coated with asphalt; if the asphalt is base asphalt (the heating temperature is generally controlled at 140-160℃), the immersion time is strictly controlled at 45s; if the asphalt is modified asphalt (the heating temperature is usually at 160-180℃), the immersion time is 30s. During the immersion process, the aggregate can be slightly shaken to make the asphalt more evenly coated on the surface of the aggregate.

[0071] S13, quickly hang the asphalt-coated aggregate on the test rack, adjust the position of the aggregate to be in a natural state of drooping, and the excess asphalt will naturally flow away under the action of gravity; place the test rack in a well-ventilated, dust-free environment, and cool it at room temperature 20-25℃ for 15min, so that the asphalt gradually solidifies to form a stable coating; after cooling, check whether the asphalt coating is uniform, if there is local over-thickness or over-thin, appropriate trimming or re-preparation can be carried out.

[0072] S14, use a fine line to lift the cooled asphalt-coated aggregate, slowly immerse it in a beaker containing pure water at a temperature of 90-94℃ for 3min, and ensure that the aggregate is completely immersed in water. This temperature range simulates the working conditions of the actual pavement in high temperature environment, and is used to test the adhesion between asphalt and aggregate. During the immersion process, observe whether there is peeling, blistering or other phenomena between the asphalt and the aggregate. If there is an abnormal situation, record and analyze the cause in time. At the same time, keep the water temperature stable to avoid affecting the accuracy of the test results due to water temperature fluctuations.

[0073] S15, after immersion, use a fine line to take out the immersed aggregate from the water, try to reduce the residual water, and hang the taken-out aggregate on the test rack again to cool for 15min at the same room temperature, so that the water on the surface of the aggregate is completely evaporated, and the asphalt coating is further stabilized. The cooled asphalt-coated aggregate is used for subsequent adhesion test, water damage resistance test and other related research. After preparation, clean and arrange the test equipment, and properly store the remaining materials for subsequent test use.

[0074] S2, obtain three photos of the aggregate from different angles by camera equipment, the specific process is: place the cooled aggregate on a clean, flat and non-reflective white hard board; at the same time, prepare several lighting equipment such as ring-shaped fill light, soft light, etc., to ensure that the light for shooting is sufficient and uniform. Take three aggregate photos with pixel density not less than 240dpi in the range of-90°-0°, 0°(i.e. vertical shooting), 0°-90° around the vertical direction as the center line.

[0075] Specific shooting: first, select an appropriate angle in the range of-90°-0°, fix the camera equipment on the tripod, adjust the height of the tripod and the angle of the equipment, so that the lens is aimed at the center of the aggregate, and ensure that the shooting picture completely contains the aggregate; then, take the 0° vertical shooting, adjust the equipment so that the lens is perpendicular to the surface of the white hard board, and ensure that the aggregate in the shooting picture is imaged correctly and without distortion; finally, select another angle in the range of 0°-90°, and complete the shooting by adjusting the tripod and the angle of the equipment; before each shooting, adjust the angle and position through the equipment viewfinder or screen preview picture, to ensure that the aggregate photo clearly and completely shows the surface features of the aggregate.

[0076] S3. Obtain the peeling area of ​​the asphalt film on the aggregate surface using image processing software, specifically including the following steps:

[0077] S31. Input the photo into the image processing software and set the photo's image bit depth to 8-bit. This invention uses the "ImageJ1.51j8" image processing software. Before importing the photo, ensure that the photo file format (such as JPEG, PNG, etc.) is compatible with the software. After importing, use the "Type / 8-bit" command to set the photo's image bit depth to 8-bit. Image bit depth determines the number of colors that each pixel in the image can represent. An 8-bit bit depth means that each pixel can represent 2^32 colors. 8 = 256 different grayscale values, from 0 (pure black) to 255 (pure white).

[0078] Therefore, choosing an 8-bit bit depth can meet the need to distinguish the grayscale differences between the asphalt peeling area and the non-peeled area in the photo, while balancing the amount of image data and processing efficiency. It avoids the large data processing burden caused by excessively high bit depth, and at the same time prevents the loss of image details due to excessively low bit depth, which would affect the accuracy of subsequent analysis.

[0079] S32. Use image processing software to calculate the area of ​​the aggregate in each photo, and sum the aggregate areas of the three photos to obtain the total aggregate area S. The specific operation is as follows:

[0080] Using the region selection tools in ImageJ software, such as the Free Selection Tool or the Polygonal Selection Tool, manually outline the aggregate along its edges. During the outlining process, carefully observe image details, striving to closely match the actual boundaries of the aggregate, avoiding mistakenly selecting background or asphalt spalling areas within the aggregate area, and ensuring no aggregate areas are missed. After outlining, use the area calculation function of the image processing software. The software will calculate the area of ​​the aggregate in the image based on the number of pixels within the selected area and image resolution. Repeat the above steps to calculate the area of ​​the aggregate in three separate images, then add these three area values ​​together to obtain the total aggregate area S.

[0081] S33, using pixel grayscale value t i The image is binarized using a threshold value. After binarization, the white areas in the image represent areas where asphalt has peeled off, and the black areas represent areas where asphalt has not peeled off.

[0082] By calculating the average aspect ratio of the aggregate in the three photos Determine the binarization threshold t i :

[0083]

[0084] Then the pixel grayscale value t iThe calculation formula is as follows:

[0085]

[0086] Obtained:

[0087]

[0088] wherein i is a natural number greater than 0, LD1, LD2, and LD3 are the aspect ratios of the aggregate in the three photos, the aspect ratio being the ratio of the longest dimension to the shortest dimension of the aggregate particles, and used to reflect the shape characteristics of the aggregate.

[0089] By considering the aspect ratio of the aggregate, the threshold value of binarization can be more accurately determined, so as to better distinguish the asphalt peeling area and the non-peeling area.

[0090] The binarization processing formula is as follows:

[0091]

[0092] wherein x and y are the horizontal and vertical coordinates of the pixel points in the photo; B(x, y) is the gray value of the pixel point with coordinates (x, y) in the image after binarization processing; and f(x, y) is the gray value of the pixel point with coordinates (x, y) in the original image.

[0093] S34, with t i and t i+1 as the threshold values, the three aggregate photos are respectively binarized through Image macro commands or plug-in batch processing, the image processing software is used to count the white area of each photo, and the sum of the white areas of the three photos is obtained to obtain the total white area;

[0094] S35, the difference between the total white areas under the thresholds t i and t i+1 is calculated until the difference between the total white areas is greater than 5% of the total aggregate area, and the total white area under the threshold t i is recorded.

[0095] The calculation formula of the white area of a single photo is as follows:

[0096]

[0097] wherein A k,i represents the white area of the kth photo under the threshold t i , k = 1, 2, 3, corresponding to three different photos; i represents the threshold number used; B k,i(x, y) is the value of the pixel point with coordinate (x, y) in the kth photo after binarization processing. According to the binarization processing formula (2) in S33, when the gray value f(x, y) of the pixel point in the original image is greater than or equal to t i , B k,i (x, y) = 255 (white, asphalt stripping area); when f(x, y) is less than or equal to t i , B k,i (x, y) = 0 (black, asphalt non-stripping area); W and H are the width and height of the photo respectively.

[0098] The total area of the white area of the three photos is calculated as follows:

[0099]

[0100] Where S i is the total area of the white area of the three photos under the threshold t i .

[0101] The difference ΔS i between the total areas of the white areas under adjacent thresholds t i and t i+1 is:

[0102] ΔS i = |S i+1 -S i | (7);

[0103] Where S i+1 is the total area of the white area of the three photos under the threshold t i+1 , and S i is the total area of the white area under the threshold t i ; whether the difference between the total areas of the white areas under adjacent thresholds is greater than 5% of the total area of the aggregate, that is, when ΔS i > 0.05 × S, the threshold iteration is stopped; the total area of the white area S i under the current threshold t i is recorded, which is used for subsequent calculation of the asphalt stripping area ratio.

[0104] S4, dividing the adhesion grade according to the asphalt stripping area ratio.

[0105] The calculation formula of the asphalt stripping area ratio P is as follows:

[0106]

[0107] Where m is the mass of the aggregate, ρ is the apparent density of the aggregate, d is the maximum nominal size of the aggregate, S i is the total area of the white area under the threshold t i , and S is the total area of the aggregate.

[0108] When classifying adhesion levels:

[0109] When the asphalt spalling area ratio P is less than 5%, the adhesion grade is 5, indicating that the asphalt has excellent adhesion to the aggregate.

[0110] When the asphalt spalling area ratio P is between 5% and 10%, the adhesion grade is 4, indicating that the asphalt has good adhesion to the aggregate.

[0111] When the asphalt spalling area ratio P is between 10% and 20%, the adhesion grade is 3, indicating that the adhesion between asphalt and aggregate is average.

[0112] When the asphalt spalling area ratio P is between 20% and 30%, the adhesion grade is 2, indicating that the adhesion between asphalt and aggregate is poor.

[0113] When the asphalt spalling area ratio P is greater than 30%, the adhesion grade is 1, indicating that the adhesion between asphalt and aggregate is extremely poor, and the asphalt or aggregate needs to be improved and optimized.

[0114] To demonstrate the effectiveness of the proposed method, the adhesion evaluation method comprises two parts: laboratory testing and result analysis. Considering usability and generalizability, the laboratory testing was optimized and implemented based on a boiling water test. Furthermore, based on existing research, image processing techniques were used to process the experimental results to assess adhesion.

[0115] Example 1

[0116] Laboratory test (boiling test):

[0117] The existing boiling water test mainly judges the adhesion level between aggregate and asphalt binder by the degree of peeling of the asphalt film on the surface of a coarse aggregate in boiling water. During the test, the factors affecting the test results are boiling time and boiling temperature.

[0118] In the boiling water test standard, the immersion time is set at 3 minutes, but the boiling water temperature is not specified. The test standard only describes that the water should be in a state of slight boiling, but without producing bubbles; however, the slight boiling state is difficult to judge, which is not conducive to test standardization and leads to large errors in the adhesion evaluation results.

[0119] Therefore, in this embodiment, the micro-boiling temperature will be determined by a boiling water test.

[0120] The specific experimental steps are as follows:

[0121] 1. Aggregate preparation: Select a piece of basalt aggregate and complete the asphalt coating and pre-treatment by boiling according to steps S11 to S15 (use No. 70 base asphalt and immersion time 45s).

[0122] 2. Water temperature control experiment: Pure water was heated to the target temperature (85℃, 90℃, 92℃, 94℃, 96℃, 98℃); when the boiling water test was carried out, the asphalt-coated aggregate was immersed in water at different temperatures for 3 min, and the bubble generation and asphalt film peeling degree were observed, as shown in Table 1, to determine the micro-boiling temperature; at the same time, the heating rate was controlled at 10℃ / min to ensure the linear correspondence of temperature-bubble characteristics.

[0123] Table 1 Temperature-bubble occurrence rate control table

[0124] Water boiling temperature (°C) Bubble generation Asphalt film stripping 85 No No 90 No (steam only) No 92 No (steam only) No 94 Few surface bubbles Slight edge stripping 96 Large amount of bubbles + rolling Large area stripping 98 Intense boiling Complete stripping

[0125] From Table 1, it can be found that there is no bubble and steam at 85℃; when the temperature reaches 90℃ and 92℃, steam can be observed and gradually increases, while there is still no bubble; when the temperature reaches 94℃, bubbles begin to generate, although the dissociated asphalt film does not appear in the water, although the dissociated asphalt film does not appear in the water, but many bubbles have been generated on the surface of the aggregate; when the temperature exceeds 96℃, a large amount of dissociated asphalt film can be observed, accompanied by a large amount of bubbles and steam, which is not allowed in the existing boiling water test.

[0126] At the same time, it can be concluded that when the water temperature is ≤92℃, no bubbles are generated, the peeling area ratio of the asphalt film is <5%, and the adhesion level is 5, which meets the requirements of "micro-boiling" state.

[0127] When the water temperature is ≥94℃, the bubbles increase significantly, and the peeling area ratio exceeds 5%, indicating that the water has entered the "vigorous boiling" state, resulting in a biased evaluation result.

[0128] Therefore, this embodiment takes 92±1℃ as the critical interval between micro-boiling and vigorous boiling, breaks through the fuzziness of the traditional "visual judgment of micro-boiling", and takes no bubbles + stable steam as the necessary condition for micro-boiling, and realizes standardization through the temperature threshold (92±1℃).

[0129] Example Two

[0130] Multi-view image acquisition and threshold optimization:

[0131] In this embodiment, the image processing software based on "ImageJ1.51j8" is used to obtain the peeling area of the asphalt film on the aggregate surface, and the process of this method is as follows:

[0132] 1) Place the aggregate after the boiling water test on a white plate, as shown in Figure 2 . Considering that the aggregate is not fully expanded in the boiling water test, due to the fluidity of the asphalt film at high temperature, there is no peeling area on the bottom surface of the aggregate.

[0133] Therefore, the aggregate bottom surface is in contact with the white plate. It should be explained that, due to its high fluidity at high temperature, the soft asphalt binder will not meet the assumption that there is no peeling area at the bottom of the aggregate. Therefore, the method proposed in this embodiment may not be applicable to asphalt binders with a low softening point. In fact, soft asphalt is rarely used in pavement engineering because the softening point of the asphalt used must meet the minimum standard.

[0134] 2) Use a stable light source to illuminate the aggregate. In order to reduce shadows, avoid misjudging shadow areas as asphalt peeling areas, and preferably apply light sources from three directions. If conditions are limited, the light source should be perpendicular to ensure the greatest degree of uniform illumination, laying the foundation for accurate image feature recognition later.

[0135] 3) Obtain three images of the aggregate from different angles of -45°, 0°, and +45° respectively through the camera equipment, to prevent partial peeling areas from being missed due to a single viewing angle, and to ensure that the image data obtained is complete. The image should be greater than 96 dpi (the pixel density of this embodiment is 300 dpi) to ensure image clarity and meet the needs of subsequent accurate image processing.

[0136] 4) As shown in (a) of Figure 3 , due to the images obtained using traditional camera equipment, they are usually 24-bit depth, making it difficult to process using "Image J". Therefore, these images should be converted to 8-bit grayscale depth using the "Image J" command "Type / 8-bit", as shown in (b) of Figure 3 . At the same time, a rough white paper can be placed on the white plate, and the aggregate is placed on the white paper. The rough texture on the paper can adjust the intensity of light reflection, thereby reducing glare as much as possible. In addition, the color of the area where the asphalt peels off from the aggregate is different from the area where glare occurs. The former is mainly black and blue, and the latter is white, and they can be distinguished by adjusting the threshold value of the image.

[0137] 5) Background interference will affect the identification of asphalt peeling areas. The background of the 8-bit depth image can be eliminated by the "Image J" command "Process / Subtract Background / Rolling ball radius 20% pixels". The threshold value is very important for the effect of eliminating the background. As shown in (c) of Figure 3 , the image after using the threshold value to eliminate the background is drawn. At the same time, through software statistics, the aspect ratios of the aggregate in the three photos are 1.02, 0.98, and 1.00, with an average of 1. As shown in (a) to (e) of Figure 4 , the black area represents the peeling area of the asphalt film; by comparing the image effects under different threshold values, it can be found that the area of the black area decreases with the increase of the threshold value, and when the threshold value exceeds 205, the recognizability of the black area will be greatly reduced.

[0138] However, this does not mean that the smaller the threshold value is, the better the sensitivity of the black area increases with the decrease of the threshold value; when the threshold value is lower than 180, many useless messages are contained in the black area. Therefore, by comparing the area of the black area and the actual peeling area of the asphalt film, the optimal threshold value is selected as 190.

[0139] 6) The aggregate profile can be automatically identified by "ImageJ".

[0140] 7) Finally, the area of the black area (peeling area of the asphalt film) and the area of the aggregate with an average aspect ratio of 1 can be obtained using the "ImageJ" command "Analyze / Measure". In addition, according to the peeling area ratio calculation formula of the aggregate and Table 2, the peeling area ratio R P Equation (9) can be used to calculate:

[0141]

[0142] where A P is the area of the black area (peeling area of the asphalt film), A A is the area of the aggregate.

[0143] The peeling area ratio calculated by formula (7) corresponds to Table 2, which can quantitatively evaluate the asphalt-aggregate adhesion grade.

[0144] Table 2 Adhesion grade division

[0145]

[0146] Example Three

[0147] Comparison of adhesion of different aggregate types

[0148] Test purposes:

[0149] Verify the applicability of the method of the present application to different lithology aggregates (basalt, limestone, granite), and analyze the influence of the geometric characteristics (aspect ratio, surface roughness) of the aggregate on the adhesion.

[0150] Test steps:

[0151] 1. Aggregate grouping:

[0152] Group A: Basalt (aspect ratio 1.3, surface rough);

[0153] Group B: Limestone (aspect ratio 1.0, smooth surface);

[0154] Group C: Granite (aspect ratio 1.6, medium rough surface);

[0155] 2. Adhesion test:

[0156] The asphalt stripping area ratio P of each group of aggregate was determined by the method of the present application, and the asphalt was SBS modified asphalt.

[0157] Table 3: Asphalt stripping area ratio and adhesion grade of aggregates of different lithology

[0158] Aggregate type Aspect ratio Surface characteristics Spalling area ratio P (%) Adhesion rating Basalt 1.3 Rough 4.2 5th Limestone 1.0 Smooth 12.5 3rd Granite 1.6 Medium 8.7 4th

[0159] The following conclusions were drawn from Table 3:

[0160] Aspect ratio effect: The greater the aspect ratio (e.g. granite LD = 1.6), the stronger the aggregate angularity, and the more significant the mechanical interlocking effect after asphalt coating, and the stripping area ratio decreases.

[0161] Surface roughness effect: The rough surface (e.g. basalt) has a larger physical adsorption area with asphalt, and the adhesion is better than that of the smooth surface of limestone.

[0162] Therefore, the method of the present application can objectively reflect the influence of aggregate geometric characteristics on adhesion by quantifying the stripping area ratio, and makes up for the shortcomings of traditional methods which rely only on subjective experience.

[0163] Example Four (Adhesion Evaluation of Different Asphalt Types)

[0164] Test purpose:

[0165] To compare the adhesion difference of the same aggregate (basalt, particle size 16 mm) between base asphalt and modified asphalt, and verify the adaptability of the method to different asphalt types.

[0166] Test steps:

[0167] 1. Asphalt grouping:

[0168] Group D: 70# base asphalt (immersion time 45s)

[0169] Group E: SBS modified asphalt (immersion time 30s)

[0170] 2. Adhesion test:

[0171] The stripping area ratio P of the two groups of asphalt was determined according to steps S1-S4, and the test results are shown in Table 4.

[0172] Table 4: Adhesion difference of basalt between base asphalt and modified asphalt

[0173] Asphalt type Immersion time (s) Spalling area ratio P (%) Adhesion rating Matrix asphalt 45 18.3 3rd Modified asphalt 30 6.1 4th

[0174] The following conclusions were drawn from Table 4:

[0175] The modified asphalt is stronger in chemical adsorption and physical adhesion with aggregate due to the addition of high molecular polymer, and the peeling area ratio is significantly lower than that of base asphalt.

[0176] It can be seen that the method of the present application can accurately reflect the difference in adhesion performance of different asphalts by setting different immersion times (45s for base asphalt and 30s for modified asphalt) according to the type of asphalt, and improve the scientificity of the evaluation results.

[0177] Therefore, the asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregate is adopted, the objective and quantitative evaluation of asphalt-aggregate adhesion is realized by introducing the asphalt peeling area ratio, and the geometric characteristics such as the aspect ratio of aggregate are integrated into the threshold calculation, so that the influence of the shape and surface characteristics of aggregate on adhesion can be comprehensively reflected, and a scientific basis for engineering material selection is provided.

[0178] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for evaluating asphalt-aggregate adhesion taking into account the geometric characteristics of aggregates, characterized by, It comprises the following steps: S1, preparing asphalt-coated aggregate; S2, obtaining three photos of the aggregate from different angles by a camera device; S3, obtaining the peeling area of the asphalt film on the aggregate surface by using image processing software; S4, dividing the adhesion grade according to the asphalt peeling area ratio; S1 specifically comprises the following steps: S11, tying the aggregate in the middle with a fine line and placing it in an oven at 105℃±5℃ for drying for 1h; S12, lifting the dried aggregate with a fine line and immersing it in asphalt heated to a molten state so that the aggregate is completely coated with asphalt; S13, hanging the asphalt-coated aggregate on a test rack to let the excess asphalt flow off and cooling it at room temperature for 15min; S14, lifting the cooled aggregate with a fine line and immersing it in a beaker containing pure water at a temperature of 90℃-94℃ for boiling for 3min; S15, taking out the boiled aggregate from the water, hanging it on a test rack to cool for 15min, and obtaining the asphalt-coated aggregate; S3 specifically comprises the following steps: S31, inputting the photos into the image processing software and setting the photo image bit depth to 8-bit; S32, using the image processing software to count the length-diameter ratio and the aggregate area in each photo and summing up the aggregate areas of the three photos to obtain the total aggregate area S; S33, binarize the photo with the pixel gray value t as the threshold value i Binarize the photo with the pixel gray value t as the threshold value, and after the binarization, the white region of the photo is the asphalt peeling region, and the black region is the asphalt non-peeling region. Calculate the average of the aspect ratio of the aggregate in the three photos Determine the binarization threshold t i : The pixel gray value t i The calculation formula is as follows: obtained: wherein i is a natural number greater than 0, LD1, LD2 and LD3 are the length-diameter ratios of the aggregate in the three photos; The binarization processing formula is as follows: wherein x and y are the horizontal and vertical coordinates of the pixel points in the photo; B(x, y) is the gray value of the pixel point with coordinates (x, y) in the image after binarization processing; f(x, y) is the gray value of the pixel point with coordinates (x, y) in the original image; S34, with t i and t i+1 The three aggregate photos are respectively binarized with the threshold value, the white area of each photo is counted by using the image processing software, and the total white area is obtained by summing the white areas of the three photos. S35, calculate threshold t i and t i+1 The total area of white regions under t until the total area of white regions under t is greater than 5% of the total area of aggregates, record the threshold t i The total area of white regions under t In S34, the area calculation formula of the white area in a single photo is as follows: wherein A k,i represents the white area of the kth photo under the threshold t i , k = 1, 2, 3, corresponding to three different photos; i represents the number of the threshold used; B k,i (x, y) is the value of the pixel point with coordinates (x, y) in the kth photo after binarization processing; W and H are the width and height of the photo, respectively. Then the total area calculation formula of the white area in the three photos is as follows: where S i is a threshold t i the total white area of the next three photos; Adjacent threshold value t i And t i+1 The total area difference ΔS of white regions under i Is: ΔS i = |S i+1 -S i | (7); where S i+1 is the total area of white regions under threshold t i+1 The total area of white regions under threshold t i is S i . If the difference of total area of white region under adjacent threshold is greater than 5% of total aggregate area, i.e. when ΔS>0.05×S is satisfied, the iteration of threshold is stopped, and the current threshold t is recorded, and the total area of white region S under the threshold is recorded for subsequent calculation of asphalt stripping area ratio. i If the difference of total area of white region under adjacent threshold is greater than 5% of total aggregate area, i.e. when ΔS>0.05×S is satisfied, the iteration of threshold is stopped, and the current threshold t is recorded, and the total area of white region S under the threshold is recorded for subsequent calculation of asphalt stripping area ratio. In S4, the calculation formula of the asphalt peeling area ratio P is as follows: where m is the mass of aggregate, p is the apparent density of aggregate, d is the maximum nominal size of aggregate, S i is the total area of white region under threshold t i S is the total area of aggregate.

2. The method for evaluating asphalt-aggregate adhesion considering aggregate geometric characteristics according to claim 1, characterized by, In S12, if the asphalt is base asphalt, the immersion time is 45s; if the asphalt is modified asphalt, the immersion time is 30s.

3. The method for evaluating asphalt-aggregate adhesion considering aggregate geometric characteristics according to claim 1, characterized by, In S2, the cooled aggregate is placed on a white hard board, sufficient light is ensured, and three aggregate photos with a pixel density of not less than 240dpi are taken in the range of -90°-0°, 0° and 0°-90° with the vertical direction as the center line.

4. The method for evaluating asphalt-aggregate adhesion considering aggregate geometric characteristics according to claim 1, characterized in that, The adhesion grade is divided according to the asphalt peeling area ratio P: When the asphalt peeling area ratio P is less than 5%, the adhesion grade is 5; When the asphalt peeling area ratio P is between 5% and 10%, the adhesion grade is 4; When the asphalt peeling area ratio P is between 10% and 20%, the adhesion grade is 3; When the asphalt peeling area ratio P is between 20% and 30%, the adhesion grade is 2; When the asphalt peeling area ratio P is greater than 30%, the adhesion grade is 1.

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