Asphalt-aggregate adhesiveness evaluation method considering geometric characteristics of aggregate

Abstract

The invention discloses an asphalt-aggregate adhesiveness evaluation method considering aggregate geometric characteristics. The asphalt-aggregate adhesiveness evaluation method comprises the following steps: S1, preparing asphalt-coated aggregate; s2, acquiring three photos of the aggregate from different angles through camera equipment; s3, the stripping area of the asphalt film on the surface of the aggregate is obtained through image processing software; and S4, dividing adhesiveness grades according to the asphalt stripping area ratio. According to the asphalt-aggregate adhesiveness evaluation method considering the aggregate geometrical characteristics, the defects that a traditional water boiling method depends on subjective experience and does not consider the aggregate geometrical characteristics are overcome, objective quantitative evaluation of the asphalt-aggregate adhesiveness is achieved, the influence of the aggregate geometrical characteristics on the adhesiveness can be reflected, and the method has the advantages of being high in operability, high in repeatability and the like. The method is suitable for different types of asphalt and aggregate, and provides scientific basis for engineering material selection.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt aggregate determination, and in particular to an asphalt-aggregate adhesion evaluation method taking into account aggregate geometric characteristics. Background Art

[0002] Asphalt-aggregate adhesion is one of the most important basic technical properties of asphalt and a core indicator for ensuring the water stability of asphalt mixtures. Existing standards primarily evaluate asphalt-aggregate adhesion using the boiling method: ① Tie the aggregate securely in the middle with a thin string and dry it in an oven at 105°C ± 5°C for 1 hour. ② Lift the dried aggregate with a thin string and immerse it in preheated asphalt for 45 seconds, completely coating it with asphalt. ③ Hang the asphalt-coated aggregate on a test stand to allow excess asphalt to drain off, then cool it at room temperature for 15 minutes. ④ Lift the cooled aggregate with a thin string and immerse it in a beaker of hot water for 3 minutes, keeping the water slightly boiling but preventing any foaming. ⑤ Remove the boiled aggregate from the water and, after cooling, observe the degree of asphalt flaking from the aggregate. The asphalt-aggregate adhesion grade (1 to 5) is determined based on the subjective experience of the tester.

[0003] However, the existing asphalt-aggregate adhesion evaluation methods have the following shortcomings:

[0004] (1) Strong subjective dependence: Currently, the determination of adhesion grade is highly dependent 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 features: Traditional methods do not take into account the influence of key geometric parameters such as aggregate shape and surface texture; existing methods simply classify aggregate into "coarse aggregate" and "fine aggregate", and are unable to quantify the contribution of characteristics such as angularity and surface porosity to adhesion, resulting in the evaluation results being unable to reflect the differences in aggregate microstructure.

[0006] (3) Ambiguous test conditions: The current regulations lack a quantitative standard for the description of "water slightly boiling but no boiling foam allowed." In practice, water temperatures between 85°C and 98°C may be considered "slightly boiling." However, for every 2°C increase in water temperature, the risk of thermal damage to the asphalt film increases by approximately 7%. This can result in fluctuations of up to two levels in the evaluation results for the same aggregate at different temperatures, severely impacting test repeatability.

[0007] The above defects make it difficult for traditional methods to meet the demand for accurate evaluation in the design of high-performance asphalt mixtures. Therefore, there is an urgent need to introduce a new evaluation system that is objectively quantified and multi-factor coupled. Summary of the Invention

[0008] The purpose of the present invention is to provide an asphalt-aggregate adhesion evaluation method that takes into account the geometric characteristics of aggregate. Unlike the existing technology that relies on the subjective judgment of testers on asphalt-aggregate adhesion, the present invention conducts quantitative evaluation through asphalt stripping rate and takes into account geometric characteristics such as aggregate aspect ratio, thereby solving the defect that traditional methods do not consider the influence of aggregate geometric characteristics.

[0009] To achieve the above object, the present invention provides an asphalt-aggregate adhesion evaluation method taking into account aggregate geometric characteristics, comprising the following steps:

[0010] S1. preparing asphalt-coated aggregate;

[0011] S2, obtain three photos of the aggregate from different angles using a camera;

[0012] S3. Obtain the peeling area of the asphalt film on the aggregate surface using image processing software;

[0013] S4. Adhesion grades are divided according to the asphalt peeling area ratio.

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

[0015] S11. Tie the aggregate in the middle with a thin thread and dry it in an oven at 105℃±5℃ for 1 hour;

[0016] S12, using a thin wire to lift the dried aggregate, and immerse it in asphalt heated to a molten state, so that the aggregate is completely coated with the asphalt;

[0017] S13. Hang the asphalt-coated aggregate on a test stand to allow excess asphalt to flow off, and cool at room temperature for 15 minutes.

[0018] S14. Lift the cooled aggregate with a thin wire and immerse it in a beaker filled with purified water at a temperature of 90°C to 94°C for 3 minutes.

[0019] S15. Take the boiled aggregate out of the water, hang it on a test stand and cool it for 15 minutes to obtain asphalt-coated aggregate.

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

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

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

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

[0024] S32. Count the aspect ratio and aggregate area of the aggregate in each photo using image processing software, and sum the aggregate areas of the three photos to obtain the total aggregate area S;

[0025] S33, taking the pixel gray value t i The photo is binarized using the threshold. After binarization, 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 aspect ratio of the aggregates in the three photos Determine the binarization threshold t i :

[0027]

[0028] Then the pixel gray value t i The calculation formula is as follows:

[0029]

[0030] get:

[0031]

[0032] Where i is a natural number greater than 0, LD1, LD2, and LD3 are the aspect ratios of the aggregates in the three photos respectively;

[0033] The binarization formula is as follows:

[0034]

[0035] Where x, y are the horizontal and vertical coordinates of the pixel in the photo; B(x, y) is the grayscale value of the pixel with coordinates (x, y) in the binarized image; f(x, y) is the grayscale value of the pixel with coordinates (x, y) in the original image;

[0036] S34, with t i and t i+1 The three aggregate photos were binarized for thresholding, and the white area of each photo was counted using image processing software. The white area of the three photos was summed to obtain the total white area.

[0037] S35. Calculate threshold t i and t i+1 The total area difference of the white area under the aggregate is calculated until the total area difference of the white area is greater than 5% of the total area of the aggregate, and the threshold value t is recorded. i The total area of the white area below.

[0038] Preferably, in S34, the white area calculation formula of a single photo is as follows:

[0039]

[0040] Among them, A k,i Indicates that the kth photo is at the threshold t i The white area under the image, k = 1, 2, 3, corresponds to three different photos; i represents the threshold number used; B k,i (x, y) is the value of the pixel with coordinates (x, y) in the kth photo after binarization; W and H are the width and height of the photo respectively;

[0041] The total area of the white areas in the three photos is calculated as follows:

[0042]

[0043] Among them, S i is the threshold t i The total area of white areas in the next three photos;

[0044] Adjacent threshold t i and t i+1 The total area difference of the white area under ΔS i for:

[0045] ΔS i =|S i+1 -S i | (7);

[0046] Among them, S i+1 is the threshold t i+1 The total area of the white areas in the next three photos, S i is the threshold t i The total area of the white area below;

[0047] Determine whether the total area difference of the white areas under adjacent thresholds is greater than 5% of the total area of the aggregate, that is, when ΔS i When it is >0.05×S, stop the threshold iteration and record the current threshold t i The total area of the white area below is S i , used for subsequent calculation of asphalt stripping area ratio.

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

[0049]

[0050] Where m is the aggregate mass, ρ is the aggregate apparent density, d is the maximum nominal particle size of the aggregate, S i is the threshold t iThe total area of the white area under is , and S is the total area of 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 level 5;

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

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

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

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

[0057] Therefore, the present invention adopts the above-mentioned asphalt-aggregate adhesion evaluation method considering the geometric characteristics of aggregates, and the beneficial effects are as follows:

[0058] (1) The introduction of asphalt spalling area ratio can objectively and quantitatively evaluate the asphalt-aggregate adhesion level: The present invention uses image processing technology to accurately count the spalling area of the asphalt film on the aggregate surface and calculate the asphalt spalling area ratio, which is used as a quantitative indicator for evaluating the adhesion level. Compared with the traditional method that relies on the subjective judgment of the test personnel on the degree of asphalt spalling, the present invention divides the adhesion level into 5 levels based on a clear calculation formula and grading standard, avoiding the evaluation bias caused by cognitive differences between different personnel, and significantly improving the objectivity, accuracy and repeatability of the evaluation results. Whether in laboratory testing or on-site evaluation, this method can provide reliable and consistent evaluation data, providing a solid basis for the quality control of asphalt mixtures.

[0059] (2) Considering the influence of aggregate geometric characteristics on asphalt-aggregate adhesion: The present invention fully incorporates the geometric characteristics of aggregates into the evaluation process, integrating them into key steps such as threshold calculation in image processing. Aggregates of different shapes and surface characteristics have different interlocking and physical adsorption effects with asphalt, which can more comprehensively and accurately reflect the adhesion performance between asphalt and aggregate, providing more scientific guidance for the rational selection of aggregate types and the optimization of asphalt mixture proportions.

[0060] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0062] Figure 2 The aggregate after the boiling water test on a white plate according to an embodiment of the asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics of the present invention;

[0063] Figure 3 The following are photos of an embodiment of an asphalt-aggregate adhesion evaluation method that takes into account aggregate geometric characteristics according to the present invention, wherein (a) is a 24-bit photo before conversion, (b) is an 8-bit photo after conversion of (a), and (c) is an 8-bit photo of (b) with the background removed.

[0064] Figure 4 These are the images displayed at different thresholds of an embodiment of the asphalt-aggregate adhesion evaluation method taking into account the geometric characteristics of aggregates according to the present invention, 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 solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0066] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0067] like Figure 1 As shown in FIG, a method for evaluating asphalt-aggregate adhesion considering aggregate geometric characteristics includes the following steps:

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

[0069] S11. Randomly select aggregate samples, tie the aggregate in the middle with a thin wire, and place it in an oven preheated to 105℃±5℃ for 1 hour. During the drying process, the oven door can be opened 1-2 times, each time for 1-2 minutes, to promote air circulation in the oven and ensure uniform drying of the aggregate. After drying, use high-temperature resistant gloves to take out the aggregate and place it on a clean, dry tray to avoid secondary contamination.

[0070] S12. Lift the dried aggregate with a thin wire and immerse it in molten asphalt until the aggregate is completely coated. If the asphalt is base asphalt (generally heated to 140-160°C), the immersion time is strictly controlled to 45 seconds. If the asphalt is modified asphalt (usually heated to 160-180°C), the immersion time is 30 seconds. During the immersion process, the aggregate can be gently shaken to ensure that the asphalt is more evenly coated on the aggregate surface.

[0071] S13. Quickly hang the asphalt-coated aggregate on the test frame and adjust the position of the aggregate so that it is in a natural drooping state. The excess asphalt will flow away naturally under the action of gravity. Place the test frame in a well-ventilated, dust-free environment and cool it at room temperature of 20℃-25℃ for 15 minutes to allow the asphalt to gradually solidify and form a stable coating. After cooling, check whether the asphalt coating is uniform. If it is partially too thick or too thin, it can be properly trimmed or re-prepared.

[0072] S14. Lift the cooled asphalt-coated aggregate with a thin wire and slowly immerse it in a beaker of purified water at 90°C to 94°C for 3 minutes, ensuring the aggregate is completely submerged. This temperature range simulates the high-temperature conditions of actual pavement and is used to test the adhesion between the asphalt and the aggregate. During the immersion process, observe for any peeling or blistering between the asphalt and the aggregate. If any abnormalities occur, record and analyze the cause promptly. Maintain a stable water temperature to prevent temperature fluctuations from affecting the accuracy of the test results.

[0073] S15. After the soaking is completed, use a thin wire to remove the soaked aggregate from the water to minimize the residual moisture. The removed aggregate is hung on the test frame again and cooled at the same room temperature for 15 minutes to allow the moisture on the aggregate surface to completely evaporate and the asphalt coating to be further stabilized. After cooling, the asphalt-coated aggregate is obtained for subsequent adhesion tests, water damage resistance tests and other related studies. After preparation, the test equipment is cleaned and sorted, and the remaining materials are properly stored for subsequent tests.

[0074] S2. Use a camera to obtain three photographs of the aggregate from different angles. The specific process is as follows: Place the cooled aggregate on a clean, flat, non-reflective white hardboard. Simultaneously, prepare lighting equipment, such as ring lights and soft lights, to ensure sufficient and even lighting. With the vertical axis as the centerline, take three photographs of the aggregate at an inclination range of -90° to 0°, at 0° (i.e., vertically), and at a pixel density of at least 240 dpi.

[0075] When shooting: first select a suitable angle within the inclination range of -90° to 0°, fix the camera equipment on the tripod, adjust the tripod height and the equipment angle, aim the lens at the center of the aggregate, and ensure that the shooting picture completely includes the aggregate; then shoot vertically at 0°, adjust the equipment so that its lens is perpendicular to the surface of the white hard board, and ensure that the aggregate image in the shooting picture is straight and without deformation; finally, select another angle within the range of 0° to 90°, and complete the shooting by adjusting the tripod and equipment angle; before each shooting, preview the picture through the equipment viewfinder or screen, fine-tune the angle and position, and ensure that the aggregate photo is clear and fully displays the surface characteristics of the aggregate.

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

[0077] S31. Input the photo into the image processing software and set the photo image bit depth to 8-bit. The present invention uses "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 image bit depth to 8-bit. The image bit depth determines the number of colors that each pixel in the image can represent. 8-bit bit depth means that each pixel can represent 2 8 = 256 different grayscale values, from 0 (pure black) to 255 (pure white).

[0078] Therefore, choosing an 8-bit bit depth can not only meet the need to distinguish the grayscale differences between the asphalt peeling area and the non-peeling area in the photo, but also balance the image data volume and processing efficiency, avoiding the large data processing burden caused by too high a bit depth, and preventing the loss of image details due to too low a bit depth, which affects the accuracy of subsequent analysis.

[0079] S32. Use image processing software to count the area of 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] Use the ImageJ software's region selection tools, such as the Free Selection tool or the Polygon Selection tool, to manually outline the aggregate along its edges. During the outline process, carefully observe the image details and try to fit the actual aggregate boundaries closely. Avoid mistakenly selecting background or asphalt spalling areas as part of the aggregate, and do not miss any areas of the aggregate. After the outline is complete, use the image processing software's area counting function. The software calculates the area of the aggregate in that photo based on information such as the number of pixels within the selected area and the image resolution. Repeat this process to count the areas of the aggregate in each of the three photos. Then, add these three area values to obtain the total aggregate area, S.

[0081] S33, taking the pixel gray value t i The photo is binarized using the threshold. After binarization, the white area in the photo is the asphalt peeling area, and the black area is the asphalt non-peeling area.

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

[0083]

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

[0085]

[0086] get:

[0087]

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

[0089] By considering the aspect ratio of aggregates, the threshold for binarization can be determined more accurately, leading to a better distinction between asphalt stripping and non-stripping areas.

[0090] The binarization formula is as follows:

[0091]

[0092] Where x and y are the horizontal and vertical coordinates of the pixel in the photo; B(x,y) is the grayscale value of the pixel with coordinates (x,y) in the binarized image; and f(x,y) is the grayscale value of the pixel with coordinates (x,y) in the original image.

[0093] S34, with t i and t i+1 For thresholding, the three aggregate photos were binarized by using the Image macro command or plug-in batch processing. The white area of each photo was counted using image processing software, and the white area of the three photos was summed to obtain the total white area.

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

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

[0096]

[0097] Among them, A k,i Indicates that the kth photo is at the threshold t i The white area under the image, k = 1, 2, 3, corresponds to three different photos; i represents the threshold number used; B k,i(x, y) is the value of the pixel with coordinates (x, y) in the k-th photo after binarization. According to the binarization formula (2) in S33, when the grayscale value of the pixel in the original image f(x, y) ≥ t i When B k,i (x,y)=255 (white, asphalt peeling area); when f(x,y)≤t i When B k,i (x, y) = 0 (black, asphalt unpeeled area); W and H are the width and height of the photo, respectively.

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

[0099]

[0100] Among them, S i is the threshold t i The total area of white areas in the next three photos.

[0101] Adjacent threshold t i and t i+1 The total area difference of the white area under ΔS i for:

[0102] ΔS i =|S i+1 -S i | (7);

[0103] Among them, S i+1 is the threshold t i+1 The total area of the white areas in the next three photos, S i is the threshold t i The total area of the white area under the adjacent threshold is determined to be greater than 5% of the total area of the aggregate. i When >0.05×S, stop the threshold iteration; record the current threshold t i The total area of the white area below is S i , used for subsequent calculation of asphalt stripping area ratio.

[0104] S4. Adhesion grades are divided according to the asphalt peeling area ratio.

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

[0106]

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

[0108] When grading adhesion:

[0109] When the asphalt stripping area ratio P is less than 5%, the adhesion grade is 5, indicating that the adhesion between asphalt and aggregate is excellent;

[0110] When the asphalt stripping area ratio P is between 5% and 10%, the adhesion grade is 4, indicating that the adhesion between asphalt and aggregate is good;

[0111] When the asphalt stripping 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 stripping 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 stripping area ratio P is greater than 30%, the adhesion grade is level 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 process consists of two parts: laboratory testing and results analysis. Considering usability and scalability, the laboratory test was optimized and implemented based on the boiling water test. Furthermore, based on existing research, image processing techniques were used to process the experimental results to evaluate adhesion.

[0115] Example 1

[0116] Laboratory test (boiling test):

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

[0118] The boiling water test standard sets the immersion time at 3 minutes, but does not specify the boiling water temperature. The standard only states that the water should be slightly boiling but not bubbling. However, determining the slightly boiling state is difficult, hindering test standardization and leading to significant errors in adhesion evaluation results.

[0119] Therefore, this embodiment will determine the micro-boiling temperature through 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 soaking pre-treatment according to steps S11 to S15 (the asphalt is No. 70 base asphalt, and the soaking time is 45 seconds).

[0122] 2. Water Temperature Control Experiment: Pure water was heated to target temperatures (85°C, 90°C, 92°C, 94°C, 96°C, and 98°C). During the boiling water test, the asphalt-coated aggregate was immersed in water at different temperatures for 3 minutes. The bubble generation and the degree of asphalt film peeling were observed, as shown in Table 1, to determine the micro-boiling temperature. The heating rate was controlled at 10°C / min to ensure a linear relationship between temperature and bubble characteristics.

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

[0124] Boiling temperature (℃) Bubble generation Asphalt membrane peeling 85 none none 90 None (steam only) none 92 None (steam only) none 94 A small amount of surface bubbles Slight peeling at the edges 96 Lots of bubbles + rolling Large area peeling 98 Violent boiling Completely peeled off

[0125] From Table 1, it can be found that there are no bubbles and steam at 85°C; when the temperature reaches 90°C and 92°C, steam can be observed and gradually increases, while there are still no bubbles; when the temperature reaches 94°C, bubbles begin to appear, although the dissociated asphalt film does not appear in the water, and although the dissociated asphalt film does not appear in the water, many bubbles have been generated on the aggregate surface; when the temperature exceeds 96°C, a large amount of dissociated asphalt film can be observed, accompanied by a large number 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 asphalt film peeling area ratio is <5%, and the corresponding adhesion level is level 5, which meets the "slightly boiling" state requirements.

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

[0128] Therefore, this embodiment uses 92±1°C as the critical interval between slight boiling and violent boiling, breaking through the ambiguity of the traditional "visual judgment of slight boiling", and uses no bubbles + stable steam as the necessary and sufficient conditions for slight boiling, and achieves standardization through the temperature threshold (92±1°C).

[0129] Example 2

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

[0131] This example uses image processing software based on "ImageJ1.51j8" to obtain the peeling area of the asphalt film on the aggregate surface. 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 the following example: Figure 2 Considering that the aggregate did not expand sufficiently in the boiling water test, there was no spalling area on the bottom surface of the aggregate due to the fluidity of the asphalt film at high temperature.

[0133] Therefore, the bottom surface of the aggregate was placed in contact with the white plate. It should be noted that due to its high fluidity at high temperatures, soft asphalt binders will not conform to the assumption of a lack of a debonded zone at the bottom of the aggregate. Therefore, the method proposed in this example may not be suitable for asphalt binders with low softening points. In fact, soft asphalt is rarely used in pavement engineering because the softening point of the asphalt used must meet minimum standards.

[0134] 2) Use a stable light source to illuminate the aggregate. In order to reduce shadows and avoid the shadow area being misjudged as asphalt spalling area, it is best to apply light sources from three directions. If conditions are limited, the light source should be vertical to ensure the greatest possible uniformity of lighting, laying the foundation for subsequent accurate recognition of image features.

[0135] 3) Use a camera to obtain three images of the aggregate at different angles of -45°, 0°, and +45° to prevent the omission of some peeling areas due to a single viewing angle and ensure that the acquired image data is complete. The image should be larger than 96dpi (the pixel density in this embodiment is 300dpi) to ensure image clarity and meet the requirements of subsequent precise image processing.

[0136] 4) If Figure 3 As shown in (a) in the figure, since the images are obtained using traditional camera equipment, they are usually 24-bit in depth and difficult to process using "ImageJ". Therefore, these images should be converted to 8-bit grayscale depth using the "ImageJ" command "Type / 8-bit", as shown in Figure 3 (b) in the figure. Alternatively, a rough white paper can be placed on a white surface before the aggregate is placed on top. The rough texture of the paper can adjust the intensity of light reflection, minimizing glare. Furthermore, the color of the areas where the asphalt has peeled off the aggregate differs from the areas where glare occurs. The former is primarily black and cyan, while the latter is white. These two areas can be distinguished by adjusting the image threshold.

[0137] 5) Background interference will affect the identification of asphalt peeling areas. The background of 8-bit depth images can be eliminated by using the "ImageJ" command "Process / SubtractBackground / Rollingballradius20% pixels". The threshold is very important for eliminating the background effect. Figure 3 (c) in the figure shows the image after removing the background by using the threshold. At the same time, the software statistics show that the aspect ratios of the aggregates in the three photos are 1.02, 0.98, and 1.00, respectively, with an average value of 1. Figure 4 As shown in (a) to (e) in the figure, the black area represents the peeling area of the asphalt film; by comparing the image effects under different thresholds, it can be found that the area of the black area decreases with the increase of the threshold, and when the threshold exceeds 205, the recognizability of the black area will be greatly reduced.

[0138] However, this does not mean that the smaller the threshold, the better. The sensitivity of the black area increases as the threshold decreases. When the threshold is lower than 180, the black area contains many useless messages. Therefore, by comparing the area of the black area and the actual peeling area of the asphalt film, the optimal threshold is selected as 190.

[0139] 6) Aggregate contours can be automatically identified using “ImageJ”.

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

[0141]

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

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

[0144] Table 2 Adhesion grade classification

[0145]

[0146] Example 3

[0147] Comparison of adhesion of different aggregate types

[0148] Purpose of the test:

[0149] The applicability of the method of the present invention to different lithologic aggregates (basalt, limestone, granite) was verified, and the effects of aggregate geometric characteristics (aspect ratio, surface roughness) on adhesion were analyzed.

[0150] Test steps:

[0151] 1. Aggregate grouping:

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

[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] As shown in Table 3, the asphalt stripping area ratio P of each group of aggregates was measured according to the method of the present invention, and SBS modified asphalt was selected as the asphalt.

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

[0158] Aggregate type Aspect ratio Surface characteristics Peeling area ratio P (%) Adhesion level basalt 1.3 Rough 4.2 Level 5 limestone 1.0 smooth 12.5 Level 3 granite 1.6 medium 8.7 Level 4

[0159] The following conclusions are drawn from the analysis of Table 3:

[0160] Influence of aspect ratio: The larger the aspect ratio (such as granite LD = 1.6), the stronger the angularity of the aggregate, the more significant the mechanical interlocking effect after asphalt coating, and the lower the spalling area ratio.

[0161] Influence of surface roughness: Rough surfaces (such as basalt) have a larger physical adsorption area with asphalt and better adhesion than limestone with a smooth surface.

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

[0163] Example 4 (Evaluation of Adhesion of Different Asphalt Types)

[0164] Purpose of the test:

[0165] The differences in adhesion between base asphalt and modified asphalt to the same aggregate (basalt, particle size 16 mm) were compared to verify the adaptability of the method to different asphalt types.

[0166] Test steps:

[0167] 1. Asphalt grouping:

[0168] Group D: No. 70 base asphalt (immersion time 45s)

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

[0170] 2. Adhesion test:

[0171] The peeling area ratio P of the two groups of asphalt was measured according to steps S1 to S4. The test results are shown in Figure 4.

[0172] Table 4 Differences in adhesion between base asphalt and modified asphalt to basalt

[0173] Asphalt type Immersion time (s) Peeling area ratio P (%) Adhesion level Base asphalt 45 18.3 Level 3 Modified asphalt 30 6.1 Level 4

[0174] The following conclusions are drawn from the analysis of Table 4:

[0175] Due to the addition of high molecular weight polymers, modified asphalt has stronger chemical adsorption and physical bonding with aggregates, and its spalling area ratio is significantly lower than that of base asphalt.

[0176] It can be seen that the method of the present invention can accurately reflect the differences in adhesion performance of different asphalts by distinguishing the asphalt types and setting different immersion times (45s for base asphalt and 30s for modified asphalt), thereby improving the scientific nature of the evaluation results.

[0177] Therefore, the present invention adopts the above-mentioned asphalt-aggregate adhesion evaluation method that takes into account the geometric characteristics of aggregates. By introducing the asphalt spalling area ratio, an objective quantitative evaluation of asphalt-aggregate adhesion is achieved. At the same time, geometric characteristics such as the aggregate aspect ratio are incorporated into the threshold calculation, which can comprehensively reflect the influence of aggregate shape and surface characteristics on adhesion, and provide a scientific basis for engineering material selection.

[0178] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for evaluating asphalt-aggregate adhesion considering aggregate geometric characteristics, characterized in that: The following steps are involved: S1. preparing asphalt-coated aggregate; S2, obtain three photos of the aggregate from different angles using a camera; S3. Obtain the peeling area of the asphalt film on the aggregate surface using image processing software; S4. Adhesion grades are divided according to the asphalt peeling area ratio.

2. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 1, characterized in that: S1 specifically includes the following steps: S11. Tie the aggregate in the middle with a thin thread and dry it in an oven at 105℃±5℃ for 1 hour; S12, using a thin wire to lift the dried aggregate, and immerse it in asphalt heated to a molten state, so that the aggregate is completely coated with the asphalt; S13. Hang the asphalt-coated aggregate on a test stand to allow excess asphalt to flow off, and cool at room temperature for 15 minutes. S14. Lift the cooled aggregate with a thin wire and immerse it in a beaker filled with purified water at a temperature of 90°C to 94°C for 3 minutes. S15. Take the boiled aggregate out of the water, hang it on a test stand and cool it for 15 minutes to obtain asphalt-coated aggregate.

3. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 2, characterized in that: In S12, if the asphalt is base asphalt, the immersion time is 45 seconds; if the asphalt is modified asphalt, the immersion time is 30 seconds.

4. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 1, characterized in that: In S2, the cooled aggregate was placed on a white hard board to ensure sufficient light. With the vertical direction as the center line, three photos of the aggregate with a pixel density of not less than 240 dpi were taken at inclination angles within the range of -90° to 0°, 0°, and 0° to 90°.

5. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 1, characterized in that: S3 specifically includes the following steps: S31, input the photo into the image processing software, and set the photo image bit depth to 8-bit; S32. Count the aspect ratio and aggregate area of the aggregate in each photo using image processing software, and sum the aggregate areas of the three photos to obtain the total aggregate area S; S33, taking the pixel gray value t i The photo is binarized using the threshold. After binarization, the white area of the photo is the asphalt peeling area, and the black area is the asphalt non-peeling area; Calculate the average aspect ratio of the aggregates in the three photos Determine the binarization threshold t i : Then the pixel gray value t i The calculation formula is as follows: get: Where i is a natural number greater than 0, LD1, LD2, and LD3 are the aspect ratios of the aggregates in the three photos respectively; The binarization formula is as follows: Where x, y are the horizontal and vertical coordinates of the pixel in the photo; B(x, y) is the grayscale value of the pixel with coordinates (x, y) in the binarized image; f(x, y) is the grayscale value of the pixel with coordinates (x, y) in the original image; S34, with t i and t i+1 The three aggregate photos were binarized for thresholding, and the white area of each photo was counted using image processing software. The white area of the three photos was summed to obtain the total white area. S35. Calculate threshold t i and t i+1 The total area difference of the white area under the aggregate is calculated until the total area difference of the white area is greater than 5% of the total area of the aggregate, and the threshold value t is recorded. i The total area of the white area below.

6. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 5, characterized in that: In S34, the formula for calculating the white area of a single photo is as follows: Among them, A k,i Indicates that the kth photo is at the threshold t i The white area under the image, k = 1, 2, 3, corresponds to three different photos; i represents the threshold number used; B k,i (x,u) is the value of the pixel with coordinates (x,y) in the kth photo after binarization; W and H are the width and height of the photo respectively; The total area of the white areas in the three photos is calculated as follows: Among them, S i is the threshold t i The total area of white areas in the next three photos; Adjacent threshold t i and t i+1 The total area difference of the white area under ΔS i for: ΔS i =|S i+1 -S i | (7); Among them, S i+1 is the threshold t i+1 The total area of the white areas in the next three photos, S i is the threshold t i The total area of the white area below; Determine whether the total area difference of the white areas under adjacent thresholds is greater than 5% of the total area of the aggregate, that is, when ΔS i When it is >0.05×S, stop the threshold iteration and record the current threshold t i The total area of the white area below is S i , used for subsequent calculation of asphalt stripping area ratio.

7. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 1, characterized in that: In S4, the calculation formula for the asphalt stripping area ratio P is as follows: Where m is the aggregate mass, ρ is the aggregate apparent density, d is the maximum nominal particle size of the aggregate, S i is the threshold t i The total area of the white area under is , and S is the total area of aggregate.

8. The asphalt-aggregate adhesion evaluation method considering aggregate geometric characteristics according to claim 7, characterized in that: Adhesion grades are divided according to the asphalt peeling area ratio P: When the asphalt peeling area ratio P is less than 5%, the adhesion level is level 5; When the asphalt stripping area ratio P is between 5% and 10%, the adhesion level is 4; When the asphalt stripping area ratio P is between 10% and 20%, the adhesion level is level 3; When the asphalt stripping area ratio P is between 20% and 30%, the adhesion level is level 2; When the asphalt peeling area ratio P is greater than 30%, the adhesion level is level 1.

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