An asphalt pavement void ratio evaluation method based on three-dimensional ground penetrating radar images

Abstract

The application discloses a kind of asphalt pavement void ratio evaluation methods based on three-dimensional ground penetrating radar image, by preparing different void ratio's asphalt mixture rutting plate test piece in laboratory, using small three-dimensional ground penetrating radar to detect, using the relationship between the improved common center point method builds test piece thickness and electromagnetic wave in test piece inside propagation speed and test piece dielectric constant, simultaneously measured to obtain the void ratio of test piece, the dielectric constant of test piece and void ratio are fitted again.In actual pavement detection, the image obtained by three-dimensional ground penetrating radar detection, then using Canny edge detection image processing obtains asphalt surface layer thickness, and then obtains the void ratio of actual asphalt pavement surface layer according to the above relationship.

Description

TECHNICAL FIELD

[0001] The present application relates to a road non-destructive testing method, in particular to a three-dimensional ground penetrating radar detection method for evaluating the porosity of asphalt pavement. BACKGROUND

[0002] As the main stress layer of the pavement, the compaction quality of the asphalt surface layer has an important influence on the road performance and service life of the newly built road. The evaluation index of the compaction quality of the asphalt surface layer is the compaction porosity. For dense graded asphalt mixture, the compaction porosity range should be controlled between 3% and 8%, and for each 1% exceeding the upper limit, the service life of the pavement is reduced by about 10%. In the construction process, the compaction porosity is mainly affected by the compaction parameters of the road roller and the compaction temperature, and both insufficient compaction and over-compaction can lead to the compaction porosity of the asphalt mixture exceeding the control range. Therefore, the field porosity should be strictly controlled during the construction process to ensure the service quality of the asphalt pavement during the whole service life.

[0003] The traditional pavement porosity detection mainly includes the core drilling method and the nuclear density gauge: the core drilling method not only destroys the integrity of the pavement structure but also replaces the whole road with a point, which cannot well represent the performance of the whole road; the method of detecting the pavement porosity by the nuclear density gauge or the non-nuclear density gauge, although the integrity of the pavement is preserved, the instrument is expensive and requires high skilled operators, and also has the problem of replacing the whole road with a point. The non-nuclear density gauge can perform non-destructive testing, but this method can only detect discrete points, the detection efficiency is low, and the detection value is affected by the pavement temperature and humidity, the detection precision and stability are poor, and it is also not suitable for real-time monitoring of the compaction quality of the asphalt surface layer.

[0004] In addition, there is an existing domestic invention patent which uses ground penetrating radar to detect the porosity of the asphalt pavement. An asphalt concrete pavement porosity detection method based on ground penetrating radar (published on July 27, 2018, patent number: CN108333096A) discloses an asphalt concrete pavement porosity detection method based on ground penetrating radar, which measures the porosity of the asphalt mixture specimen prepared in the laboratory by using the ground penetrating radar equipment and then fits the dielectric constant obtained by the ground penetrating radar. This method has defects in the actual pavement rapid detection, needs to take core samples from the pavement for testing, has destructive and weak representativeness, and cannot directly obtain the porosity of the asphalt pavement from the ground penetrating radar detection image. SUMMARY

[0005] The purpose of the present application is to provide a three-dimensional ground penetrating radar detection method for evaluating the porosity of the asphalt pavement, which can rapidly and non-destructively detect the porosity of the asphalt pavement surface layer and the base layer.

[0006] Technical solution: The asphalt pavement porosity evaluation method of the present application comprises the following steps:

[0007] S1, prepare several pieces of asphalt mixture rutting plate test pieces with different void ratios and thicknesses, measure the thickness h of the test piece from four vertices, midpoints of the edges and the center point, and test the dielectric constant ε of the rutting plate test piece at the same position by a dielectric constant test system;

[0008] S2, calculate the theoretical density G of the test piece according to the asphalt mixture mix design mm , measure the dry density G of the test piece mb , and calculate the void ratio V of the test piece according to the above a ;

[0009] S3, obtain the relationship between the thickness h of the test piece and the radar wave propagation speed v and dielectric constant in the pavement interior according to the improved common center point method;

[0010] S4, fit the dielectric constant ε of the test piece with the void ratio V of the test piece a , obtain the regression relationship model of the two, combine the relationship between the thickness h of the test piece and the dielectric constant ε established in S3, and obtain the fitting relationship between the thickness h of the test piece and the void ratio V a ;

[0011] S5, in the actual newly built or operated road, use a large vehicle-mounted three-dimensional ground penetrating radar to obtain the radar image of the asphalt pavement surface layer, extract the surface layer thickness from the ground penetrating radar detection image through Canny edge detection, and realize the automatic detection of the surface layer void ratio by using the fitting relationship established in step S4.

[0012] Further, in step S1, 3 to 5 pieces of asphalt mixture rutting plate test pieces with different void ratios are prepared;

[0013] The dielectric constant ε of the asphalt mixture rutting plate test piece at different points is obtained by a dielectric constant test system:

[0014]

[0015] Wherein, A max is the maximum resonance value of the measuring point.

[0016] Further, in step S2, the void ratio V a is calculated according to the following formula:

[0017]

[0018] Further, in step S3, the detailed implementation steps of obtaining the relationship between the thickness h of the test piece and the radar wave propagation speed v and dielectric constant ε in the pavement interior by using the improved common center point method are as follows:

[0019] S31, set the distance between the three-dimensional ground penetrating radar and the road surface as h0, the depth of the first reflection layer (surface layer) from the ground as h1, the distance between the transmitter and the receiver of the ground penetrating radar as l0, and the dielectric constant of the air medium as 1; the electromagnetic wave propagation in the air satisfies the formula as follows:

[0020]

[0021] The propagation in the asphalt pavement satisfies the formula as follows:

[0022]

[0023] Wherein, c and v are the propagation speeds of the electromagnetic wave in the air and the asphalt mixture respectively, t1 and t2 are the propagation times of the electromagnetic wave in the air and the asphalt mixture respectively, and l1 is the distance between the incident point and the exit point of the electromagnetic wave of the ground penetrating radar transmitting antenna in the asphalt mixture;

[0024] S32, set the radar wave of the ground penetrating radar transmitter to enter the asphalt mixture at an angle of α1 and to be refracted at an angle of α2; the angle of the electromagnetic wave entering the asphalt mixture satisfies the formula as follows:

[0025]

[0026] The angle of the electromagnetic wave reflecting out of the asphalt mixture satisfies the formula as follows:

[0027]

[0028] The dielectric constant of the asphalt mixture satisfies the formula as follows:

[0029]

[0030] S33, according to the propagation of the electromagnetic wave of the ground penetrating radar in the asphalt mixture, the following formula is satisfied:

[0031]

[0032] The relationship between the thickness h of the test piece, the propagation speed v of the radar wave in the pavement and the dielectric constant ε is obtained:

[0033]

[0034] Wherein, T=t1+t2, which can be directly obtained from the radar map.

[0035] Further, in step S5, the detailed implementation steps of extracting the surface layer thickness from the ground penetrating radar detection image through Canny edge detection are as follows:

[0036] S51, perform gray scale conversion on the original ground penetrating radar detection image;

[0037] S52, select threshold values T1 and T2, wherein T1 is a high threshold value capable of distinguishing the extracted thickness edge feature from the background, and T2 is a low threshold value capable of smoothing the profile of the edge; the edge function is used to process the gray-scale image to detect all edges in the image, wherein the threshold values T1 and T2 are automatically calculated by the edge function;

[0038] S53, in the processed radar image, the interface between the asphalt surface layer and the base layer appears as two continuous and parallel edge lines in the horizontal direction, and the two edges are extracted;

[0039] S54, the thickness of the asphalt surface layer is finally obtained by subtracting the mean value of the longitudinal coordinates of the two extracted edges from the longitudinal coordinates of the road surface and multiplying a set proportion, wherein the proportion is the proportion of the longitudinal coordinates to the actual depth of the road surface.

[0040] Compared with the prior art, the present application has the following remarkable effects:

[0041] 1. The three-dimensional ground penetrating radar detection method of the present application is a non-destructive detection method for the void ratio of the asphalt pavement, which does not damage the pavement structure and does not affect the quality of the pavement;

[0042] 2. The present application is simple to operate, and in the process of pavement acceptance, it does not need to take core samples and conduct indoor test tests, the detection and evaluation method is non-destructive and comprehensive, and has very important practical value;

[0043] 3. The present application can greatly improve the detection speed of the void ratio of the asphalt pavement through rapid identification of the ground penetrating radar detection image, and provide accurate, efficient and non-destructive data source for pavement detection and evaluation and maintenance decision-making;

[0044] 4. When detecting the void ratio of the pavement, the present application can obtain a large number of continuous data points instead of discrete points, which can reduce the contingency of data collection and improve the rationality of the data. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a flowchart of the present application;

[0046] Figure 2 is a schematic diagram of the size and test point of the asphalt mixture rutting plate test piece;

[0047] Figure 3 is a road internal ground penetrating radar electromagnetic wave propagation calculation model improved from the common center point method;

[0048] Figure 4 is a fitting relationship diagram of the void ratio and the dielectric constant of the asphalt mixture rutting plate test piece in the embodiment;

[0049] Figure 5The Canny edge detection is used to extract the surface layer thickness result map of the actual road surface ground penetrating radar image in the embodiment. DETAILED DESCRIPTION

[0050] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0051] Ground penetrating radar (GPR) is a non-destructive testing technology based on the principle of electromagnetic wave propagation. Compared with traditional detection methods, ground penetrating radar has the characteristics of rapidity, non-destructivity and large number of data points in the detection of road surface void ratio. The detection principle of ground penetrating radar is to obtain the dielectric constant of the surface layer through the pulse waveform characteristics and propagation time, and then calculate the volume parameters of the asphalt pavement by using the corresponding mathematical physical model. Therefore, the application proposes a three-dimensional ground penetrating radar detection method for evaluating the void ratio of the asphalt pavement, so as to realize the rapid and non-destructive detection of the void ratio of the asphalt surface layer.

[0052] As shown in Figure 1 , the three-dimensional ground penetrating radar detection method of the application comprises the following steps:

[0053] S1, several asphalt mixture rut plate test pieces with different void ratios and thicknesses are prepared, the thickness h of the test piece is measured from four vertices, midpoints of the edges and the center point, and the dielectric constant ε of the same position of the rut plate test piece is tested by using a dielectric constant testing system;

[0054] The size of the asphalt mixture rut plate test piece is 300mm in length, 300mm in width and 50-100mm in thickness, which is convenient for indoor testing. 3 to 5 asphalt mixture rut plate test pieces with different void ratios are prepared to ensure that enough data points are provided for curve fitting.

[0055] The calculation formula of the dielectric constant ε of different points of the asphalt mixture rut plate test piece obtained by using the dielectric constant testing system is as follows:

[0056]

[0057] Wherein, A max is the maximum resonance value of the measuring point.

[0058] S2, the theoretical density G mm of the test piece is calculated according to the asphalt mixture mix design, the dry density (bulk density) G mb of the test piece is measured, and the void ratio V a of the test piece is calculated according to the above, the calculation formula of the void ratio V a is as follows:

[0059]

[0060] S3, the relationship between the specimen thickness h, the radar wave propagation speed v and the dielectric constant in the pavement interior is obtained according to the improved common center point method; the detailed implementation steps are as follows:

[0061] S31, assuming that the distance between the three-dimensional ground penetrating radar and the pavement is h0, the depth of the ground first reflection layer (surface layer) from the ground is h1, the distance between the transmitter and the receiver of the ground penetrating radar is l0, and the dielectric constant of the air medium is 1. Then the electromagnetic wave propagation in the air satisfies the formula:

[0062]

[0063] The propagation in the asphalt pavement satisfies the formula:

[0064]

[0065] Wherein, c and v are the propagation speeds of electromagnetic waves in air and asphalt mixture respectively, t1 and t2 are the propagation times of electromagnetic waves in air and asphalt mixture respectively, the total time T = t1 + t2 of the two parts of propagation can be directly obtained from the radar map; l1 is the distance between the electromagnetic wave incident point and the exit point of the ground penetrating radar transmitting antenna in the asphalt mixture.

[0066] S32, assuming that the radar wave of the ground penetrating radar transmitter enters the asphalt mixture at an angle of α1 and is refracted at an angle of α2, then the angle of the electromagnetic wave entering the asphalt mixture satisfies the formula:

[0067]

[0068] The angle of the electromagnetic wave reflecting out of the asphalt mixture satisfies the formula:

[0069]

[0070] The dielectric constant of the asphalt mixture satisfies the formula:

[0071]

[0072] S33, the electromagnetic wave propagation in the asphalt mixture satisfies the formula:

[0073]

[0074] Finally, the formulas (4)-(7) in steps S31 and S32 are combined to obtain the relationship between the specimen thickness h, the radar wave propagation speed v and the dielectric constant ε in the pavement interior:

[0075]

[0076] S4, the dielectric constant ε of the specimen and the void ratio V aThe fitting is performed to obtain the regression relationship model of both, and the fitting relationship between the specimen thickness h and the void ratio V is obtained by combining the relationship between the specimen thickness h and the dielectric constant ε established in step S3. a

[0077] S5, in the actual newly-built or operated road, the radar image of the asphalt pavement surface layer is acquired by using a large vehicle-mounted three-dimensional ground penetrating radar, the surface layer thickness is extracted from the ground penetrating radar detection image through Canny edge detection, and the automatic detection of the surface layer void ratio is realized through the fitting relationship established in S4.

[0078] The detailed implementation steps of extracting the surface layer thickness from the ground penetrating radar detection image through Canny edge detection are as follows:

[0079] S51, the original ground penetrating radar detection image is subjected to gray scale conversion, that is, if the original image is a color image, it is first converted into a gray scale image;

[0080] S52, appropriate threshold values T1 and T2 are selected, wherein T1 is a high threshold value (which can distinguish the extracted thickness edge features from the background), and T2 is a low threshold value (which can smooth the edge profile), the gray scale image is processed by using an edge function, and all edges in the image are detected, wherein the threshold values T1 and T2 are automatically calculated by the edge function;

[0081] S53, in the processed radar image, the interface between the asphalt surface layer and the base layer presents two continuous and mutually parallel edge lines in the horizontal direction, and the two edges are extracted according to this feature;

[0082] S54, the mean value of the longitudinal coordinates of the two extracted edges is subtracted from the longitudinal coordinate of the road surface, and then multiplied by the corresponding proportion (the proportion is the ratio of the coordinate value of the image longitudinal coordinate to the actual depth of the road surface, which realizes the conversion from the image length to the actual road surface depth), and finally the thickness of the asphalt surface layer is obtained.

[0083] The embodiment in the application uses asphalt mixture rutting plates with different thicknesses as test pieces, and the detailed implementation steps are as follows:

[0084] Step one, four asphalt mixture rutting plate test pieces with different void ratios and thicknesses of 50mm, 60mm, 70mm and 80mm are prepared, such as Figure 2 The thickness h of the test piece is measured from the four vertices, the midpoint of the side line and the center point, and the dielectric constant ε of the rutting plate test piece at the same position is tested by using a dielectric constant testing system;

[0085] Step two, the theoretical density G of the test piece is calculated according to the asphalt mixture mixing ratio design mm , and the dry density (bulk density) G of the test piece is measured mb ​According to the calculation, the porosity V of the test piece is obtained a ;

[0086] According to steps one and two, the thickness, porosity and dielectric constant of the asphalt mixture rutting plate test piece are obtained, and the data are shown in Table 1 below:

[0087] Table 1 Thickness, porosity and dielectric constant test values of the asphalt mixture rutting plate test piece

[0088]

[0089]

[0090] Step three, according to the improved common center point method, the relationship between the thickness h of the test piece, the radar wave propagation speed v in the pavement interior and the dielectric constant is obtained, as shown in Figure 3 ;

[0091] Step four, the dielectric constant ε of the test piece and the porosity V a of the test piece are fitted to obtain the regression relationship model of the two, as shown in Figure 4 The fitting relationship between the dielectric constant and the porosity is y = -97.82x + 12.312 (R 2 = 0.9456), wherein x is the porosity and y is the dielectric constant. Combined with the relationship between the thickness h of the test piece and the dielectric constant ε established in (3), the fitting relationship between the thickness h of the test piece and the porosity V a is further obtained:

[0092]

[0093] Step five, in actual asphalt pavement detection, the radar image of the asphalt pavement surface layer is obtained by using a large vehicle-mounted three-dimensional ground penetrating radar, and the porosity of the surface layer material is measured by extracting 10 detection positions. At the same time, the surface layer thickness is extracted by Canny edge detection of the ground penetrating radar image of these positions, and the test results are shown in Figure 5 According to the relationship in step four, the predicted porosity is obtained, and the average error of the predicted porosity and the measured porosity of the 10 groups is 2.31%.

[0094] Table 2 Canny extraction of three-dimensional ground penetrating radar measured pavement surface layer thickness, predicted porosity and measured porosity

[0095]

[0096]

[0097] Finally, it should be noted that the above-described embodiments are merely specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit the same. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that any person skilled in the art can still modify or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features, within the technical scope disclosed by the present application. The modifications, changes or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for evaluating void ratio of an asphalt pavement based on a three-dimensional ground penetrating radar image, characterized by, The method comprises the following steps: S1, prepare several pieces of asphalt mixture rutting plate test pieces with different porosities and thicknesses, measure the thickness of the test pieces from four vertices, midpoints of the edges and the center point h Test the dielectric constant of the same position of the rutting plate test piece with the dielectric constant test system ; S2, according to the asphalt mixture mix design to calculate the theoretical density of the test piece G mm , measure the dry density of the test piece G mb , according to the calculation of the test piece void ratio V a ; S3, obtaining the thickness of the test piece according to the improved common center point method h relationship between the radar wave propagation speed inside the road surface v and the dielectric constant; the detailed implementation steps are as follows: S31, the distance between the three-dimensional ground penetrating radar and the road surface is h 0, the depth of the first ground reflection layer from the ground is h 1, the distance between the transmitter and the receiver of the ground penetrating radar is l 0, the dielectric constant of the air medium is 1; the propagation of electromagnetic waves in the air satisfies the formula as follows: The electromagnetic wave propagation in the asphalt pavement satisfies the formula as follows: wherein, c and v V1and V2are the propagation velocities of electromagnetic waves in air and asphalt mixture, respectively, t 1and t 2are the propagation times of electromagnetic waves in air and asphalt mixture, respectively, l 1is the distance of the electromagnetic wave emitted by the ground penetrating radar transmitting antenna between the point of incidence and the point of emergence of the asphalt mixture. S32, the radar wave of the ground penetrating radar transmitter is emitted at an angle into the asphalt mixture, which is refracted at an angle, then the angle at which the electromagnetic wave enters the asphalt mixture satisfies the formula as follows: which is refracted at an angle, then the angle at which the electromagnetic wave enters the asphalt mixture satisfies the formula as follows: The angle of the electromagnetic wave reflection from the asphalt mixture satisfies the formula as follows: The dielectric constant of the asphalt mixture satisfies the formula as follows: ； S33, according to the electromagnetic wave propagation in the asphalt mixture, the following formula is satisfied: The thickness of the test piece is determined h The relationship between the radar wave propagation speed inside the road surface v and the dielectric constant is in, T = t 1+ t 2. It can be directly obtained from radar images; S4, the dielectric constant of the test piece and the porosity of the test piece V a The fitting is performed to obtain the regression relationship model of the two, and the relationship between the thickness of the test piece h and the dielectric constant is obtained by combining the relationship between the thickness of the test piece h and the porosity V a between the fitting relationship; S5, in the actual newly-built or operated road, the radar image of the asphalt pavement surface layer is acquired by using the large vehicle-mounted three-dimensional ground penetrating radar, the surface layer thickness is extracted from the ground penetrating radar detection image by Canny edge detection, and the automatic detection of the surface layer air void is realized by using the fitting relationship established in step S4.

2. The asphalt pavement void ratio evaluation method based on a three-dimensional ground-penetrating radar image according to claim 1, characterized by, In step S1, 3 to 5 asphalt mixture rutting plate test pieces with different air voids are prepared; Obtain the dielectric constant of different points of the asphalt mixture rutting plate test piece by the dielectric constant test system : wherein, A max is the maximum resonance value for the measurement point.

3. The asphalt pavement void ratio evaluation method based on a three-dimensional ground-penetrating radar image according to claim 1, characterized by, In step S2, the porosity V a The calculation formula is as follows: 。 4. The asphalt pavement void ratio evaluation method based on a three-dimensional ground-penetrating radar image according to claim 1, characterized by, In step S5, the detailed implementation steps of extracting the surface layer thickness from the ground penetrating radar detection image by Canny edge detection are as follows: S51, the original ground penetrating radar detection image is subjected to gray scale conversion; S52, selected threshold T 1、 T 2, wherein T 1 is a high threshold value, which can distinguish the extracted thickness edge feature from the background; T 2 is a low threshold value, which can smooth the profile of the edge; the edge function is used to process the gray image to detect all edges in the image, wherein the threshold T 1、 T 2 is automatically calculated by the edge function; S53, in the processed radar image, the interface between the asphalt surface layer and the base layer presents two continuous and through edge lines in the horizontal direction, and the two edges are extracted; S54, the thickness of the asphalt surface layer is finally obtained by subtracting the mean value of the longitudinal coordinates of the extracted two edges from the longitudinal coordinates of the road surface and multiplying a set proportion, and the proportion is the proportion of the longitudinal coordinates and the actual depth of the road surface.

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