Asphalt foaming performance evaluation method based on binocular distance measuring technology

Abstract

The application discloses a kind of based on binocular ranging technology's asphalt foaming performance evaluation method, belong to highway asphalt mixture test technical field.It includes using two micro cameras to simultaneously continuously shoot foam asphalt image;Image recognition is carried out to two photos at the same time;Division foam asphalt barrel wall adhesion area and effective inflation area;Obtain foam asphalt image pixel parallax value;Calculate the height confidence interval limit value of foam asphalt in different regions;Calculate the representative value of foam asphalt height;Obtain foam asphalt space index and time index;The foaming performance of asphalt is evaluated.The application obtains the height data of multiple points on the surface of foam asphalt according to the characteristics of foam asphalt using binocular ranging technology, and comprehensively considers the inflation height of foam asphalt in different regions, evaluates the foaming performance of asphalt from the angles of asphalt inflation capacity and foam stability, which is rigorous, scientific and highly reliable.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of bitumen foaming performance evaluation method based on binocular ranging technology, belong to highway asphalt mixture test technical field. BACKGROUND

[0002] Foamed asphalt is a special state of asphalt material, which is formed by injecting an appropriate amount of water into high-temperature asphalt, and the water vaporizes when heated, causing the asphalt to expand in volume. In this state, the viscosity of asphalt is significantly reduced, allowing it to be fully mixed with cold wet aggregate. Foamed asphalt is suitable for road cold recycling technology and warm mixing technology, which can reduce road maintenance costs, save energy and reduce carbon emissions.

[0003] Using foaming technology can foam asphalt, and the road performance of foamed asphalt mixture directly depends on its foaming effect. Currently, the maximum expansion rate and half-life are the main technical indicators for evaluating the foaming effect of asphalt. During the asphalt foaming test, visual method, high-speed camera, laser and ultrasonic wave are commonly used to measure the change of asphalt expansion rate over time.

[0004] The visual method estimates the expansion rate of foamed asphalt by manually observing the change of scale readings on the measuring barrel, and determines the half-life of foamed asphalt by using a stopwatch. This testing method relies too much on experience and is too subjective, with large experimental errors. High-speed cameras determine the expansion multiples at different times by observing the changes in pixel size and position of foamed asphalt in the image, and then calculate the expansion rate and half-life. However, the change range of foamed asphalt in the measuring barrel is usually small, and the barrel wall is often covered with a large amount of asphalt, making it difficult to accurately identify its position in the barrel, which raises questions about the accuracy of the measurement. Other measurement methods such as laser and ultrasonic wave often measure a random point on the surface of foamed asphalt, which is obviously inaccurate for foamed asphalt with extremely uneven surface.

[0005] Binocular ranging technology can accurately measure the distance from each pixel point on the high-definition image to the camera optical center based on the principle of parallax, and obtain the spatial three-dimensional coordinate information of any point in the high-definition image, which provides the possibility for accurate measurement of the change of foamed asphalt expansion height over time. Therefore, binocular ranging technology can provide a reliable technical means for studying the foaming characteristics of asphalt. SUMMARY

[0006] The present application provides a bitumen foaming performance evaluation method that is more advanced in test equipment, more reliable in data, and more reasonable in evaluation indicators.

[0007] The present application achieves the above-mentioned purposes by adopting the following technical solutions:

[0008] Firstly, two micro-cameras were fixed horizontally at a distance of 10 cm from each other and 150 cm above the center of the asphalt barrel. They were connected to a computer using data transmission lines and set to take 5 pictures per second.

[0009] Secondly, the asphalt foaming tester was started and the asphalt foaming test was conducted. The generated foamed asphalt was sprayed into the circular asphalt barrel.

[0010] Thirdly, the two micro-cameras were controlled by the computer to take pictures simultaneously. The shooting time lasted from the start of the asphalt foaming tester until the height of the foamed asphalt in the barrel no longer changed.

[0011] Fourthly, the two pictures taken by the two cameras at the same time were imported into OpenCV software.

[0012] Fifthly, the Canny edge detection algorithm was run to identify the circular boundary of the asphalt barrel in the pictures. A concentric circle was determined at half the radius of the asphalt barrel, and the foam asphalt barrel wall adhesion area and effective expansion area were further divided using a cropping function.

[0013] Sixthly, the pixel parallax value was calculated based on the different positions of the foam asphalt image in the two pictures. The vertical distance from the foam asphalt to the micro-camera at each pixel block was calculated using the principle of similar triangles.

[0014] Seventhly, based on the height set for the micro-camera, the height value of the foam asphalt from the bottom of the asphalt barrel at each pixel block was further calculated.

[0015] Eighthly, the average height of the foam asphalt was calculated, and a screening function was used to remove invalid data that differed from the average value by more than twice due to light reasons and foam asphalt splashing.

[0016] Ninthly, the upper confidence limit value of the foam asphalt height in the barrel wall adhesion area and the lower confidence limit value of the foam asphalt height in the effective expansion area were calculated with a confidence interval of 95%, and the representative value of the foam asphalt height at that moment was further calculated.

[0017]

[0018]

[0019]

[0020]

[0021] where: Z ijk is the height of the foam asphalt at the i-th pixel block in the k area at time j, cm.

[0022] n jkNjk is the number of pixel blocks in the k region at time j;

[0023] Hjk is the average height of foamed asphalt in the k region at time j, cm;

[0024] S jk Sjk is the standard deviation of foamed asphalt height in the k region at time j, cm;

[0025] t a t is the t-test coefficient at 95% confidence interval when the sample size is greater than 100;

[0026] H Lj Hj is the representative value of foamed asphalt height at time j, cm;

[0027] Step 10, aggregate the representative value of foamed asphalt height at different times, and according to the change of the representative value of foamed asphalt height with time, take the maximum value as the quasi-limitation expansion force E of foamed asphalt Hm , take the time when the representative value of foamed asphalt height decays from the maximum value to half of it as the quasi-decay period, and evaluate the foaming performance of asphalt from the aspects of asphalt expansion capacity and foam stability;

[0028] DP L = t 1 / 2m -t m

[0029] In the formula: t m is the time corresponding to H Lj-max (H Lj-max is the maximum representative value of foamed asphalt height, cm), s;

[0030] t 1 / 2m is the time corresponding to 1 / 2H Lj-max ;

[0031] DP L is the quasi-decay period, s.

[0032] Preferably, in the first step, the lenses of the two micro cameras are directed at the asphalt barrel, and are equipped with RGB three-color combined point light sources.

[0033] Further, in the third step, the criterion for the height of foamed asphalt in the barrel no longer changing is that the representative value of foamed asphalt height calculated continuously for ten seconds is the same.

[0034] Further, in the fifth step, the effective expansion region is the region within a concentric circle with a radius of one-half of the asphalt barrel, and the barrel wall adhesion region is the region outside the concentric circle and within the boundary of the asphalt barrel.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] 1. The present application proposes a method for simultaneously and accurately measuring the height of multiple points on the foamed asphalt surface by using binocular ranging technology, achieving accurate and efficient testing of the expansion height of foamed asphalt.

[0037] 2. The present application proposes to divide the free expansion area and the barrel wall adhesion area of foamed asphalt, and calculate the representative value of foamed asphalt height according to the limit value of the height confidence interval of foamed asphalt in the two areas.

[0038] 3. The present application obtains the spatial index and time index of foamed asphalt by the change of the representative value of foamed asphalt height, and evaluates the foaming performance of asphalt. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The present application is a schematic diagram of the device.

[0040] Figure 2 The present application is a schematic diagram of the device. DETAILED DESCRIPTION

[0041] The present application is further illustrated by combining the drawings and specific examples.

[0042] The technical solution adopted in this embodiment includes conducting asphalt foaming test, collecting 5 high-definition images of foamed asphalt expansion process per second, dividing the barrel wall adhesion area and the free expansion area, obtaining the pixel parallax value of foamed asphalt image, calculating the representative value of foamed asphalt height, and evaluating the foaming performance of asphalt by using the spatial index and time index of foamed asphalt.

[0043] Figure 1 The present application is a schematic diagram of the device.

[0044] Step 1, fix two miniature cameras horizontally on a support 150 cm above the center of the asphalt barrel at a distance of 10 cm, connect them to the electronic computer using data transmission lines, and set the photographing frequency to 5 pictures per second. The lenses of the two miniature cameras are directed at the asphalt barrel and are equipped with RGB three-color combined point light sources.

[0045] Step 2, start the asphalt foaming tester, set the asphalt foaming temperature to 160℃, and use 2.0% of water. According to the “Foamed Asphalt Cold Recycled Pavement Construction Technical Specification” (DB32 / T 2676-2014), conduct asphalt foaming test on South Korean Shuanglong 70# asphalt, Sinopec 70# asphalt, and PetroChina 70# asphalt, and perform five parallel tests for each type of asphalt. Spray the generated foamed asphalt into the circular asphalt barrel.

[0046] Step 3, use the electronic computer to control the two miniature cameras to take pictures simultaneously, and the photographing time lasts from starting the asphalt foaming tester to the height of foamed asphalt in the barrel no longer changing.

[0047] Fourthly, two photos taken by two cameras at the same time were imported into OpenCV software.

[0048] Fifthly, Canny edge detection algorithm was run to identify the circular boundary of asphalt bucket in the photos, and a concentric circle was determined with half of the radius of asphalt bucket. The foam asphalt bucket wall adhesion area and effective expansion area were further divided by using the clipping function. The effective expansion area was the area within the concentric circle with half of the radius of asphalt bucket, and the bucket wall adhesion area was the area outside the concentric circle and within the boundary of asphalt bucket.

[0049] Sixthly, pixel parallax value was calculated according to the different positions of foam asphalt image in two photos, and the vertical distance from foam asphalt to miniature camera at each pixel block was calculated by similar triangle principle.

[0050] Seventhly, the height value of foam asphalt from the bottom of asphalt bucket at each pixel block was further calculated according to the height of miniature camera.

[0051] Eighthly, the average height of foam asphalt was calculated, and the invalid data with more than twice difference from the average value due to light and foam asphalt splashing was removed by using the screening function.

[0052] Ninthly, the upper confidence limit value of foam asphalt height in the bucket wall adhesion area and the lower confidence limit value of foam asphalt height in the effective expansion area were calculated respectively with 95% confidence interval, and the representative value of foam asphalt height at this moment was further calculated.

[0053]

[0054]

[0055]

[0056]

[0057] In the formula: Z ijk is the height of foam asphalt at the i-th pixel block in the k area at j moment, cm;

[0058] n jk is the number of pixel blocks in the k area at j moment, pieces;

[0059] is the average height of foam asphalt in the k area at j moment, cm;

[0060] S jk is the standard deviation of foam asphalt height in the k area at j moment;

[0061] t a is the t-test coefficient under 95% confidence interval, and the sample number is greater than 100.

[0062] H Lj H

[0063] Table 1 Test data of Korea Shuanglong 70# asphalt

[0064]

[0065] Step 10, aggregate the representative value data of foamed asphalt height at different times, according to the change of the representative value of foamed asphalt height with time, take its maximum value as the quasi-limiting expansion force E Hm of foamed asphalt, take the time when the representative value of foamed asphalt height decays from the maximum value to half of it as the quasi-decay period, respectively evaluate the foaming performance of asphalt from the aspects of asphalt expansion ability and foamed stability;

[0066] DP L = t 1 / 2m -t m

[0067] In the formula: t m , the time corresponding to H Lj-max , s; H Lj-max , the maximum representative value of foamed asphalt height, cm.

[0068] t 1 / 2m , the time corresponding to 1 / 2 H Lj-max , s.

[0069] DP L , quasi-decay period, s.

[0070] As Figure 2 shown in an embodiment is a fitting curve diagram of the representative value of foamed asphalt height of three types of foamed asphalt in the barrel with time, combined with the image, the quasi-limiting expansion force E Hm of foamed asphalt and the quasi-decay period DP L can be further calculated.

[0071] The coefficient of variation (CV) is a commonly used repeatability parameter in the field of mathematics. CV is defined as the standard deviation (SD) divided by the average value, and the result is usually expressed in percentage form. This is one of the most commonly used statistical methods by researchers when evaluating experimental accuracy. The smaller the CV, the smaller the dispersion of the results relative to the measured target value. Therefore, a smaller CV is associated with high repeatability. Generally, for a set of repeated measurements, a CV less than 10% indicates highly repeatable measurements. From 10% to 20%, the CV is considered moderate, meaning good repeatability. From 20% to 30% is considered high, meaning low repeatability. Finally, if it exceeds 30%, it is considered very high, indicating very low repeatability. The CV of the foamed asphalt properties measured using the binocular distance measuring system and the traditional visual method is shown in the following table.

[0072] Table 2 test data coefficient of variation

[0073]

[0074] From the above table, the variability of the evaluation index of the foaming performance of asphalt calculated by using the binocular distance measuring technology is lower than that of the visual method, which proves that the test method has strong repeatability, the measurement data is reliable, and the test result is reliable.

[0075] As can be known from the above, the evaluation method for the foaming performance of asphalt based on the binocular distance measuring technology divides the foamed asphalt image into a barrel wall adhesion area and a free expansion area, calculates the height value of each point of the foamed asphalt by using pixel disparity data, calculates the representative value of the height of the foamed asphalt according to the height confidence interval limit value of the foamed asphalt in different areas, and evaluates the foaming performance of asphalt from the angles of the expansion capacity and the foam stability of asphalt, thereby providing a solid foundation for subsequent optimization of the mix proportion design and research on the relationship between the foaming characteristics and the pavement performance of the mixture.

[0076] In addition to the above embodiments, the present application can have other implementation manners. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present application.

Claims

1. A method for evaluating the foaming performance of asphalt based on binocular ranging technology, characterized in that, The method comprises the following steps: Firstly, two micro-cameras are fixed horizontally at a distance of 10 cm apart on a support (1) located 150 cm above the center of the asphalt barrel (5), and are connected to an electronic computer (3) using a data transmission line (2), and the photographing frequency is set to 5 pictures per second; Secondly, the asphalt foaming tester (4) is started, and an asphalt foaming test is performed, and the generated foamed asphalt is sprayed into the asphalt barrel (5); Thirdly, the two micro-cameras are controlled by the electronic computer (3) to take pictures at the same time, and the photographing time lasts from the start of the asphalt foaming tester to the time when the height of the foamed asphalt in the barrel no longer changes; Fourthly, the two pictures taken by the two cameras at the same time are imported into OpenCV software; Fifthly, a Canny edge detection algorithm is run to identify the circular boundary of the asphalt barrel in the pictures, and a concentric circle is determined at half the radius of the asphalt barrel, and then a clipping function is used to divide the foam asphalt barrel wall adhesion area and the effective expansion area, wherein the effective expansion area is the area within the concentric circle at half the radius of the asphalt barrel, and the barrel wall adhesion area is the area outside the concentric circle and within the boundary of the asphalt barrel; Sixthly, the pixel parallax value is calculated according to the different positions of the foamed asphalt image in the two pictures, and the vertical distance of the foamed asphalt to the micro-camera at each pixel block is calculated by the principle of similar triangles; Seventhly, the height value of the foamed asphalt at each pixel block from the bottom of the asphalt barrel is calculated according to the height set by the micro-camera and the vertical distance of the foamed asphalt to the micro-camera; Eighthly, the average height of the foamed asphalt is calculated, and a screening function is used to remove invalid data that is more than twice different from the average value due to light reasons and foamed asphalt splashing; Ninthly, the upper confidence limit value of the foamed asphalt height in the barrel wall adhesion area and the lower confidence limit value of the foamed asphalt height in the effective expansion area are calculated respectively at a confidence interval of 95%, and then the average value of the two limit values is calculated as the representative value of the foamed asphalt height at this moment; wherein: Z ijk hi is the height of the foam asphalt at the i-th pixel block in the k-th region at the j-th moment, cm. n jk Nk(j) is the number of pixel blocks in region k at time j. Hk is the average height of the foamed asphalt in the region at time j and k, cm; S jk Sj is the standard deviation of the height of the region of foamed bitumen at time j for time k. t a t-test coefficient for 95% confidence interval with sample size greater than 100; H Lj H is the height of the foamed bitumen at time j, cm. The tenth step is to summarize the representative value data of the foamed asphalt height at different times, and according to the change of the representative value of the foamed asphalt height with time, the maximum value is taken as the quasi-limit expansion force E of the foamed asphalt Hm The time when the representative value of the foamed asphalt height decays from the maximum value to half of it is taken as the quasi-decay period, and the foaming performance of the asphalt is evaluated from the aspects of the expansion capacity of the asphalt and the stability of the foam respectively. DP L = t 1 / 2m -t m wherein: t m - H Lj-max corresponding time, s; H Lj-max Maximum foamed asphalt height representative value, cm; t 1 / 2m - Attenuation to 1 / 2 H Lj-max Corresponding time, s; DP L - the quasi-decay period, s.

2. The bitumen foaming performance evaluation method based on binocular distance measurement technology according to claim 1, characterized in that, In the first step, the two micro-cameras are opposite to the asphalt barrel and are equipped with RGB three-color combined point light sources.

3. The bitumen foaming performance evaluation method based on binocular distance measurement technology according to claim 1, characterized in that, In the third step, the standard for the height of the foamed asphalt in the barrel not changing is that the representative values of the foamed asphalt height calculated for ten consecutive seconds are the same.

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