A method for characterizing the development of void structure in cold recycled emulsified asphalt mixtures during the curing period

Abstract

This invention discloses a method for characterizing the void structure development of emulsified asphalt cold recycled mixtures during the curing period, comprising the following steps: S1, preparing emulsified asphalt cold recycled mixture samples and subjecting them to single-channel evaporation curing; S2, acquiring continuous tomographic grayscale images of the emulsified asphalt cold recycled mixture samples at the initial and final curing stages using industrial-grade X-ray CT scanning technology; S3, identifying void regions in the depth direction of the samples at the initial and final curing stages using digital image processing technology, and performing three-dimensional model calculations to obtain the overall porosity, number of voids, and volume of each void in the emulsified asphalt cold recycled mixture samples at the initial and final curing stages; S4, quantifying the void structure development status of the emulsified asphalt cold recycled mixture during the curing period by comparing the changes in void parameters at the initial and final curing stages. This invention enables a refined evaluation of the void structure development process of emulsified asphalt cold recycled mixtures during the curing period.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and more specifically to a method for characterizing the development of void structure in cold recycled emulsified asphalt mixtures during the curing period. Background Technology

[0002] Emulsified asphalt cold recycling technology can recycle 100% of old asphalt pavement materials, making it a green major and minor repair technology for asphalt pavements. Unlike traditional hot-mix asphalt pavements, cold-recycled pavements, due to the addition of emulsified asphalt and water, require a longer curing time to develop strength. During the curing process, the moisture inside the material continuously migrates and evaporates, leading to the continuous development of its internal void structure. Numerous experiments and engineering practices have shown that the strength characteristics of emulsified asphalt cold-recycled mixtures are closely related to their road performance and the development of their internal void structure. Therefore, it is necessary to quantitatively characterize the development process of void structure in emulsified asphalt cold-recycled mixtures during the curing period. Currently, traditional characterization methods mainly quantify the overall change in the internal void structure of the material through macroscopic void ratio testing. However, considering the non-uniformity of the material, a single void ratio value cannot accurately represent the trend of void structure change. It is necessary to delve deeper into the development of void structure characteristics from a microscopic perspective. Summary of the Invention

[0003] The purpose of this invention is to disclose a method for characterizing the development of void structure in cold recycled emulsified asphalt mixtures during the curing period. By combining two X-ray CT scans, continuous tomographic images of the cold recycled emulsified asphalt mixtures before and after curing are captured. The distribution changes of void structure during the curing period are identified through image processing, and the development characteristics of void structure are quantitatively characterized, providing technical support for the microscopic characterization of void structure development in cold recycled emulsified asphalt mixtures during the curing period.

[0004] To achieve the above objectives, this invention provides a method for characterizing the development of void structure in emulsified asphalt cold recycled mixtures during the curing period, comprising the following steps:

[0005] S1, Prepare emulsified asphalt cold recycled mixture samples and perform single-channel evaporation curing;

[0006] S2, using industrial-grade X-ray CT scanning technology to acquire continuous tomographic grayscale images of emulsified asphalt cold recycled mixture samples at the early and late curing stages;

[0007] S3 uses digital image processing technology to identify the void regions in the depth direction of the samples in the early and late curing stages, and performs three-dimensional model calculations to obtain the overall porosity, number of voids, and volume of each void in the emulsified asphalt cold recycled mixture samples in the early and late curing stages.

[0008] S4 quantifies the development of void structure in cold recycled emulsified asphalt mixtures during the curing period by comparing changes in void parameters at the beginning and end of the curing process.

[0009] As a further improvement of the present invention, in step S4, all gaps are statistically summarized according to their volume size, and the percentage of the number of gaps in different volume size intervals of the samples in the early stage and the late stage of health preservation, as well as the volume and percentage of gaps in the corresponding intervals are statistically summarized.

[0010] The development of pore structures during the restorative period is characterized by comparing the percentage changes in different volume ranges.

[0011] As a further improvement of the present invention, the three-dimensional model calculation in step S3 includes the following steps:

[0012] The interval statistical method requires first determining the maximum calculated void volume as V. max The three gap sizes are defined from smallest to largest as follows: micro-gap V1: 0-1mm 3 V2 gap: 1-200mm 3 Large gap interval V3: 200-V max mm 3 ;

[0013] Calculate the change in porosity A between the initial and final stages of the health regimen. e Change in the number of voids N e and the average void volume change value V e The calculation methods are shown in formulas 1 to 3;

[0014] A e =A t -A o (1)

[0015] N e =N t -N o (2)

[0016]

[0017] In the formula: A e —Change in porosity;

[0018] N e —Change in the number of voids;

[0019] V e —The average change in pore volume;

[0020] A t N t —The porosity and number of pores in the final stage of health preservation;

[0021] A o A o —The porosity and number of pores in the early stages of health preservation;

[0022] V tk —The volume of each gap in the final stage of health preservation;

[0023] V ok —The volume of each gap in the early stages of health preservation;

[0024] The development of pore structure during the conditioning period is expressed as the percentage change in the number of pores, P. i N and percentage change in void volume P i V To characterize it, the calculation method is shown in formulas 4 to 5;

[0025]

[0026]

[0027] In the formula: —Percentage change in the number of voids;

[0028] —Percentage change in void volume;

[0029] N ti —The number of pores within the Vi volume range at the end of the health preservation period;

[0030] N oi —The number of gaps within the Vi volume range during the initial stage of health preservation;

[0031] V ti —The volume of a single void within the Vi volume range at the end of the health preservation period;

[0032] V oi —The volume of a single void within the Vi volume range during the early stages of health maintenance;

[0033] i – takes values ​​of 1, 2, and 3, which respectively represent different gap intervals V1, V2, and V3.

[0034] As a further improvement of the present invention, in step S1, the emulsified asphalt cold recycling sample is wrapped with a waterproof cloth, leaving the upper surface of the specimen in contact with the air.

[0035] As a further improvement of the present invention, the digital image processing technology in step S3 includes image enhancement, filtering and segmentation algorithms to eliminate image noise and identify gap regions in the image.

[0036] As a further improvement of the present invention, the waterproof fabric is made of Teflon.

[0037] As a further improvement of the present invention, the accuracy of the planar and vertical images obtained by the X-ray CT scan test in step S2 should be less than 0.1 mm / pixel, the duration of the initial health preservation should be less than 1 hour, and the duration of the final health preservation should be greater than 14 days.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: A method for characterizing the development of void structure in emulsified asphalt cold recycled mixture during the curing period. Compared with the traditional indoor curing method for emulsified asphalt cold recycled samples, the single-channel evaporation curing method adopted in the present invention can better simulate the on-site curing process, providing technical support for obtaining the void structure development process of emulsified asphalt cold recycled mixture under on-site environmental conditions.

[0039] Compared with traditional X-ray CT scans that obtain the internal void structure of materials at a single time point, this invention obtains continuous tomographic images of emulsified asphalt cold recycled mixture before and after curing through two X-ray CT scans. By using digital image processing and morphological operation methods, the distribution of void structure before and after curing is identified, the microscopic morphology of voids is quantified, void structure indicators before and after curing are compared, and the development characteristics of void structure during curing are digitally characterized, thus achieving the goal of fine characterization of the void structure development process at the microscopic scale.

[0040] Compared with traditional methods for calculating the internal porosity of materials, this invention proposes a set of digital characterization index systems that can quantify changes in the morphology of porosity structures by analyzing the microscopic parameters of the internal porosity structure of emulsified asphalt cold recycled mixtures before and after curing. This enables a refined evaluation of the porosity structure development process of emulsified asphalt cold recycled mixtures during the curing period. Attached Figure Description

[0041] Figure 1 This invention provides an image analysis and void identification process for a method to characterize the void structure development of cold recycled emulsified asphalt mixtures during the curing period.

[0042] Figure 2 This is a schematic diagram showing the distribution of the proportion of voids in different intervals during the early and late stages of curing of a method for characterizing the void structure development of emulsified asphalt cold recycled mixture during the curing period, according to the present invention.

[0043] Figure 3 This is a schematic diagram showing the distribution of void volume ratio in different intervals during the early and late stages of curing of a method for characterizing the void structure development of emulsified asphalt cold recycled mixture during the curing period, according to the present invention. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0045] Please refer to Figures 1 to 3 The present invention illustrates a specific embodiment of a method for characterizing the void structure development of emulsified asphalt cold recycled mixtures during the curing period.

[0046] A method for characterizing the void structure development of emulsified asphalt cold recycled mixtures during the curing period, characterized by the following steps: 1) Based on the mix design, cylindrical samples of emulsified asphalt cold recycled mixtures with a diameter of 100 mm are formed using a rotary compactor. The emulsified asphalt cold recycled samples are wrapped with waterproof cloth, ensuring the upper surface of the specimen remains in contact with air, and guaranteeing a seal around the specimen and at the bottom, achieving single-channel evaporative curing. In this case, the curing temperature is set to 40℃.

[0047] 2) Continuous tomographic grayscale images of emulsified asphalt cold recycled mixture samples after 0 days and 7 days of curing were acquired using industrial-grade X-ray CT scanning technology; various image enhancement, filtering and segmentation algorithms were used to eliminate image noise and identify gap regions in the images.

[0048] 3) Based on the void slice images, a three-dimensional model calculation method was used to calculate the overall porosity, void quantity, and average void volume in the three-dimensional model of the emulsified asphalt cold recycled mixture samples at the initial and final curing stages, respectively. Figure 1 As shown. The change in porosity A before and after the sample's conditioning period was calculated based on parameters at different times. e The change in the number of voids, N, is 2.73%. e The average void volume change value V is 129985. e -0.3323mm 3 The results showed that after conditioning, the porosity increased and the number of pores increased, but the average pore volume decreased.

[0049] 4) Further, all voids are statistically summarized according to their volume, resulting in a micro-void interval V1, with a void volume range of 0-1mm. 3 V2 is a medium-void region with a void volume ranging from 1 to 200 mm. 3 Large void region V3, void volume range >200mm 3The percentage of voids in different volume ranges and the percentage of the total void volume in each range before and after the health regimen were statistically analyzed, as shown in Tables 1 and 2. It can be seen that the void quantity in range V1 is relatively high, exceeding 95%, but its total volume only accounts for 6.66%. In contrast, although the void quantity in range V3 is less than 1%, its volume accounts for over 50%. Looking at the trend, after 7 days of health regimen, the number of voids (microvoids) in range V1 increased from 96.24% to 98.89%, with a corresponding increase in volume percentage of 0.61%. The void quantity percentage in range V3 decreased slightly, but its corresponding void volume percentage increased by 6.45%. The void quantity and void volume percentage in range V2 both decreased during the health regimen.

[0050] In summary, this curing process shows that the number and volume of micropores increase significantly, while the number and volume of mesopores decrease to some extent. Although the number of large pores decreases, their volume proportion increases. The results of this case study accurately quantify the development pattern of the microstructure of pores of different sizes within emulsified asphalt cold recycled mixtures during curing, providing technical support for the refined design of the internal pore structure of emulsified asphalt cold recycled mixtures, thereby controlling their macroscopic properties.

[0051] Table 1. Parameters obtained from 3D reconstruction calculations before and after health maintenance.

[0052] parameter Initial stage of health maintenance (0 days) End of health regimen (7 days) porosity 4.93％ 7.66％ Number of gaps 57860 187845 Average void volume <![CDATA[0.6377mm 3 ]]> <![CDATA[0.3054mm 3 ]]>

[0053] Table 2. Proportion and Variation of the Number of Gaps in Different Intersections

[0054]

[0055] Table 3. Proportion and Variation of Void Volume in Different Zones

[0056]

[0057] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for characterizing the development of void structure in cold recycled emulsified asphalt mixtures during the curing period, characterized in that, Includes the following steps: S1, Prepare emulsified asphalt cold recycled mixture samples and perform single-channel evaporation curing; wherein, the emulsified asphalt cold recycled mixture is wrapped with waterproof cloth, leaving the upper surface of the specimen in contact with air, ensuring that the specimen is sealed around the sides and bottom, and realizing single-channel evaporation curing; S2, using industrial-grade X-ray CT scanning technology to acquire continuous tomographic grayscale images of emulsified asphalt cold recycled mixture samples at the initial curing stage (0 days) and the final curing stage (7 days); S3 uses digital image processing technology to identify the void regions in the depth direction of the samples at the initial curing stage (0 days) and the final curing stage (7 days), and performs three-dimensional model calculations to obtain the overall porosity, number of voids, and volume of each void in the emulsified asphalt cold recycled mixture samples at the initial and final curing stages. The void regions along the depth direction of the sample include: The micro-void region V1 has a void volume range of 0-1 mm. 3 ; V2 is a medium-void region with a void volume ranging from 1 to 100 mm. 3 ; Large void region V3, void volume range >100mm 3 ; After calculation using the three-dimensional model, the percentage of voids in each of the three sub-intervals (micro-void interval V1, medium-void interval V2, and large-void interval V3) of the emulsified asphalt cold recycled mixture sample in the early and late curing stages, as well as the percentage of void volume in the corresponding interval, can be obtained. S4, by comparing the percentage changes in the number of voids and the percentage changes in the volume of voids in the micro-void intervals V1, V2, and V3 during the early and late curing stages, quantifies the development of void structure during the curing period and the development law of the microstructure of voids of different sizes inside, which facilitates the refined design of the internal void structure of emulsified asphalt cold recycled mixture.

2. The method for characterizing the development of void structure in emulsified asphalt cold recycled mixture during the curing period according to claim 1, characterized in that, The three-dimensional model calculation in step S3 includes the following steps: Calculate the change in porosity A between the initial and final stages of the health regimen. e Change in the number of voids N e and the average void volume change value V e The calculation method is shown in formulas (1) to (3); A e =A t -A o (1) N e =N t -N o (2) In the formula: A e —Change in porosity; N e —Change in the number of voids; V e —The average change in pore volume; A t N t —The porosity and number of pores in the final stage of health preservation; A o N o —The porosity and number of pores in the early stages of health preservation; V tk —The volume of each gap in the final stage of health preservation; V ok —The volume of each gap in the early stages of health preservation; The development of pore structure during the conditioning period is expressed as the percentage change in the number of pores, P. i N and percentage change in void volume P i V The calculation method is shown in formulas (4) to (5); In the formula: —Percentage change in the number of voids; —Percentage change in void volume; N ti —The number of pores within the Vi volume range at the end of the health preservation period; N oi —The number of gaps within the Vi volume range during the initial stage of health preservation; V ti —The volume of a single void within the Vi volume range at the end of the health preservation period; V oi —The volume of a single void within the Vi volume range during the early stages of health maintenance; i – takes values ​​of 1, 2, and 3, which respectively represent different gap intervals V1, V2, and V3.

3. The method for characterizing the development of void structure in emulsified asphalt cold recycled mixtures during the curing period according to claim 1, characterized in that, The digital image processing techniques in step S3 include image enhancement, filtering, and segmentation algorithms to eliminate image noise and identify gap regions in the image.

4. The method for characterizing the development of void structure in emulsified asphalt cold recycled mixture during the curing period according to claim 1, characterized in that, The waterproof fabric is made of Teflon.

5. The method for characterizing the development of void structure in emulsified asphalt cold recycled mixtures during the curing period according to claim 1, characterized in that, The accuracy of the planar and vertical images obtained by the X-ray CT scan test in step S2 should be less than 0.1 mm / pixel.

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