Method for testing internal temperature of asphalt mixture under microwave response penetration heating condition

Abstract

The invention relates to a method for testing the internal temperature of an asphalt mixture under a microwave response penetration heating condition. The method comprises the following steps: S1, forming a sample; s2, drilling and coring; s3, performing microwave penetration isolation treatment on the periphery of the sample; s4, interface heat insulation treatment; and S5, testing data and temperature gradient indexes. Compared with the prior art, the device and the method can provide technical support for accurately simulating and researching the material internal temperature change of the asphalt mixture pavement structure under the microwave response heating condition.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave heating of asphalt mixtures, and relates to a method for testing the internal temperature of asphalt mixtures under microwave response penetration heating conditions. Background Art

[0002] The key principle of microwave response heating of asphalt mixture is to absorb microwaves through the microwave absorption capacity of asphalt mixture, generate a large amount of heat, and heat the asphalt mixture. Among them, the temperature change of asphalt mixture before and after microwave heating is the most intuitive indicator to observe the microwave absorption capacity of the material. In order to evaluate the quality of the microwave absorption capacity of asphalt mixture, researchers often use temperature guns or infrared thermal imagers to measure the temperature of the surface of asphalt mixture specimens before and after heating. However, studies have shown that the temperature measured in this way is only the temperature of the surface of the material, and the temperature increase brought by the microwave response heating method will be lost as the thickness of the material deepens. There is a large difference between the internal temperature and the surface temperature of the asphalt mixture. The conventional temperature measurement method is relatively backward and inaccurate; using the temperature index of the mixture surface to evaluate the asphalt mixture for engineering applications is not accurate enough.

[0003] Therefore, it is necessary to propose a temperature testing method that can simulate actual engineering application scenarios and accurately measure the internal temperature of the asphalt mixture heated by microwave response, so as to better propose temperature indicators that are more appropriate to the actual engineering. Summary of the invention

[0004] The purpose of the present invention is to provide a method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions, which can simulate the actual asphalt pavement structure to test the internal temperature of the asphalt mixture, solve the problem that the current temperature test of asphalt mixture under microwave response heating is limited to the surface of the material, and provide technical support for the accurate simulation and research of various properties of asphalt mixture under microwave response heating.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] In one aspect, a method for testing the internal temperature of an asphalt mixture under microwave response penetration heating conditions comprises the following steps:

[0007] S1, take asphalt mixture with the same proportion as the object to be tested, use a rotary compactor to prepare a rotary compaction specimen, after demoulding the specimen, cut the upper and lower surfaces to obtain the sample to be tested;

[0008] S2, coring the middle area of ​​the sample to be tested to obtain a drilled sample and a core column, which are then cleaned and dried for later use;

[0009] S3, taking another rotary compaction specimen formed with the same mix ratio as the sample to be tested, bonding it to the drilled sample to obtain a bonded sample, with the middle surface with holes as the top surface and the other corresponding surface as the bottom surface, and then wrapping the bottom surface and side surfaces of the bonded sample with aluminum foil;

[0010] S4, insert the core column into the hole on the top surface of the bonding sample, and then seal the gap between the core column and the bonding sample on the top surface with aluminum foil to cover it, so as to obtain a test piece sample;

[0011] S5, place the test specimen in a microwave oven for heating, take out the core column after heating, read the longitudinal temperature gradient on the side of the core column, and calculate the average interface temperature as the internal temperature index of the asphalt mixture.

[0012] Furthermore, the ratio of the diameter to the height of the sample to be tested is (2.5-3.5):1. Preferably, the diameter of the rotary compaction specimen can be set to 150 mm, and the height is not less than 70 mm, so that after cutting the upper and lower surfaces with a thickness of about 10 mm respectively, the thickness (i.e., height) of the sample to be tested can be ensured to be about 50 mm. In addition, the specific height can be adjusted according to the actual number of samples required.

[0013] Furthermore, in S1, the cutting thickness of the upper and lower surfaces of the specimen is 8 to 12 mm, and may be 10 mm.

[0014] Furthermore, in S2, the core column coincides with the central axis of the sample to be measured, and the diameter ratio of the core column to the sample to be measured is 1:(2.5-3.5).

[0015] Furthermore, in S3, the thickness of the rotary compaction specimen used for bonding is not less than the thickness of the sample being tested. If the thickness of the bonding specimen is too low, the isolation effect on the microwave penetration from the bottom will be weak, which will have a certain impact on the simulation of microwave penetration from top to bottom. When the thickness of the bonding specimen is higher than the sample thickness, the impact is small and can be ignored. In addition, the diameter of the rotary compaction specimen used for bonding is the same as that of the sample being tested, and the mix ratio is consistent.

[0016] Furthermore, in S3, the aluminum foil covering the bottom and sides of the bonded sample is also reinforced by surrounding with a high temperature resistant rubber band. In addition, the aluminum foil should be tightly wrapped without leaving any gaps to isolate the microwave penetration.

[0017] Furthermore, in S4, the aluminum foil paper that seals the gap between the core column and the bonded sample is in the shape of a ring, and the ratio of the gap to the difference in inner and outer diameters of the ring-shaped aluminum foil paper should be controlled at 1: (1.05-1.1), wherein the inner diameter of the ring-shaped aluminum foil paper and the core column diameter should be controlled at (0.9-0.95): 1. Here, the role of the aluminum foil paper is to cover the gap between the core column and the sample due to the core loss. At the same time, it should be noted that the surface of the core column needs to be exposed as much as possible and must not be covered. Therefore, the ring-shaped aluminum foil paper only needs to cover the gap, and can be slightly larger, such as about 1-3 mm.

[0018] Furthermore, in S4, the microwave heating time should not be too short or too long. If it is too short, the temperature rise of the material will be limited. If it is too long, the temperature rise will be too high and the core column may melt. Specifically, the microwave heating time can be 80 to 100 seconds, preferably about 1 minute and 30 seconds, and can be adjusted according to the heating characteristics of the material itself.

[0019] Furthermore, in S4, the calculation formula for the average interface temperature is:

[0020]

[0021] Where, T is the average interface temperature on the side of the core column, unit, °C;

[0022] T i is the temperature of the ith temperature gradient calibration point from top to bottom, unit, °C;

[0023] b is the number of temperature gradient calibration points divided according to the core column height.

[0024] Among them, the spacing between temperature gradient calibration points should be controlled at 5 to 10 mm, and the specific spacing should be divided according to the actual core column height. The denser the calibration points, the more accurate the obtained temperature gradient and average interface temperature.

[0025] On the other hand, the present invention provides a method for evaluating the microwave response penetration heating capability of asphalt mixture, firstly measuring the internal temperature index of the asphalt mixture of the tested mix ratio according to the test method as described above, thereby evaluating the best mix ratio with the best heating effect.

[0026] The temperature testing method proposed in the present invention physically isolates the side and bottom of the sample so that the resonant cavity can approximately achieve one-way penetration from top to bottom. Under such conditions, the external microwave frequency is kept unchanged. The stronger the microwave response heating ability of the material, the higher the internal temperature index obtained by the test. According to the test results, if the average temperature of the side interface of the core column is high, and the temperature gradient is not too large and relatively uniformly distributed, it can be determined that the microwave response heating ability of this material is good.

[0027] The traditional microwave response heating mixture temperature test method is limited to the determination of the surface temperature of the material, and the temperature sensor is usually used to test the internal temperature of the material. However, whether it is a thermocouple or a thermistor sensor, it will be affected by microwaves, and the response time is not accurate and timely enough. The present invention proposes a method of extracting an asphalt mixture core column, placing the core column in the original test piece for microwave heating as a whole, and then measuring the side temperature of the core column to characterize the temperature of the material under microwave response heating. Compared with the traditional cutting temperature measurement method, this method omits the step of cutting after heating. On the one hand, it can observe the temperature when the heating is completed in the first time, and on the other hand, it can ensure that the integrity of the sample is not destroyed, and the temperature measurement can be reused after the sample is cooled. In addition, the temperature test method proposed in the present invention, through physical isolation, approximately realizes the one-way penetration of microwaves in the resonant cavity, that is, only penetration heating is performed from top to bottom, which is more in line with the microwave penetration heating method in actual engineering applications. Through this test method, the change of the internal temperature of asphalt mixture under microwave response heating in actual engineering applications can be simulated more accurately, opening up the key link of microwave response heating, and providing technical support for subsequent research. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram for selecting temperature gradient calibration points;

[0029] Figure 2 Schematic diagram of the unit structure that makes up the specimen. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0031] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0032] Embodiment 1:

[0033] Please refer to Figure 2 The test sample of the microwave response heating asphalt mixture internal temperature test method of the present invention shown in the figure specifically includes a bonding sample 1 in which a drilled sample is bonded to another rotary compaction specimen, an aluminum foil shell 2 wrapping the bottom and side surfaces of the bonding sample, a core column 3 placed in the middle drilled position of the bonding sample 1, and an aluminum foil ring 4 covering the gap between the core column 3 and the bonding sample 1.

[0034] In addition, this embodiment also provides a method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions, which is characterized by comprising the following steps:

[0035] 1) Sample molding: A rotary compactor was used to prepare the rotary compaction specimens. The asphalt mixture gradation was shown in Table 1. The number of compactions was set to 100 times. The diameter of the rotary compaction specimens was 150 mm and the thickness was 180 mm. After demoulding, the asphalt portions of the upper and lower surfaces of the specimens were cut, and then a 50 mm thick specimen and a 60 mm thick specimen were cut for subsequent tests.

[0036] Table 1 Gyratory compaction specimen gradation design (mass ratio)

[0037]

[0038] 2) Drilling and coring: Use a 50mm thick specimen as the coring sample, select a 50mm diameter coring tube, and use a coring machine to coring the sample. When coring, pay attention to controlling the core column in the center of the specimen. After coring, rinse the core column and the drilled sample with clean water and dry them for later use.

[0039] 3) Microwave penetration isolation treatment around the sample: The 60 mm thick rotary compaction specimen prepared in step 1) is used as a bonding sample, and the core sample and the bonding sample are bonded with AB glue. After the glue solidifies, the lower surface and side of the entire sample are wrapped with aluminum foil. In order to prevent the wrapping from being loose, a high-temperature resistant rubber band can be used to surround the specimen for reinforcement.

[0040] 4) Interface thermal insulation treatment: Insert the core column into the sample hole treated in step 3), cut out an aluminum foil ring according to the gap between the core column and the hole, and cover it on the upper surface of the specimen to cover the gap, while ensuring that as much area as possible on the upper surface of the core column is exposed.

[0041] 5) Test data and temperature gradient index: The processed samples were placed in a microwave oven for heating. In this case, the Galanz microwave oven G90F25CN3LN-C2 (T1) was used, and the microwave output power was 900W. After heating for 1 minute and 30 seconds, the core column was immediately taken out and photographed with an infrared thermal imaging camera. The infrared thermal imaging camera was the Hikvision Micro-Imager HM-TPK20-3AQF / W. The temperature gradient calibration point was selected as the visible Figure 1 The temperature test results and temperature gradient analysis are shown in Table 2. According to the data in Table 2, the average temperature T of the core column side interface is calculated.

[0042]

[0043] It can be seen that the temperature on the side of the core column as a whole shows a gradient downward trend with increasing depth, which is consistent with the situation in engineering practice that the microwave heating capacity decreases with the depth of the asphalt pavement structure. The average interface temperature on the side of the core column is 33.06℃.

[0044] Table 2 Temperature values ​​of temperature gradient calibration points

[0045] Temperature gradient calibration point Temperature(℃) <![CDATA[T1]]> 35.6 <![CDATA[T2]]> 33.9 <![CDATA[T3]]> 31.4 <![CDATA[T4]]> 31.5 <![CDATA[T5]]> 32.9

[0046] In summary, the results of this case analysis are aimed at deepening the basic process of the internal temperature test method of microwave response heating asphalt mixture. The present invention provides a new path for testing the internal temperature of asphalt mixture under microwave response heating conditions, and provides technical support for accurate simulation and research on various properties of asphalt mixture under microwave response heating. This material internal temperature test method can not only be used to test the internal temperature of microwave response heating asphalt mixture, but also can be used for other tests that need to study the internal temperature index of the material for more accurate testing and research.

[0047] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions, characterized in that: The following steps are involved: S1, take asphalt mixture with the same proportion as the object to be tested, use a rotary compactor to prepare a rotary compaction specimen, after demoulding the specimen, cut the upper and lower surfaces to obtain the sample to be tested; S2, coring the middle area of ​​the sample to be tested to obtain a drilled sample and a core column, which are then cleaned and dried for later use; S3, taking another rotary compaction specimen formed with the same mix ratio as the sample to be tested, bonding it to the drilled sample to obtain a bonded sample, with the middle surface with holes as the top surface and the other corresponding surface as the bottom surface, and then wrapping the bottom surface and side surfaces of the bonded sample with aluminum foil; S4, insert the core column into the hole on the top surface of the bonding sample, and then seal the gap between the core column and the bonding sample on the top surface with aluminum foil to cover it, so as to obtain a test piece sample; S5, place the test specimen in a microwave oven for heating, take out the core column after heating, read the longitudinal temperature gradient on the side of the core column, and calculate the average interface temperature as the internal temperature index of the asphalt mixture.

2. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: The ratio of the diameter to the height of the sample to be tested is (2.5-3.5):

1.

3. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S1, the cutting thickness of the upper and lower surfaces of the specimen is 8 to 12 mm.

4. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S2, the core column coincides with the central axis of the sample to be measured, and the diameter ratio of the core column to the sample to be measured is 1:(2.5-3.5).

5. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S3, the thickness of the rotary compaction specimen used for bonding is not less than the thickness of the sample being tested.

6. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S3, the aluminum foil covering the bottom and sides of the bonded sample is also reinforced by surrounding it with a high temperature resistant rubber band.

7. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S4, the aluminum foil paper covering the gap between the core column and the adhesive sample is in a circular shape, and the ratio of the difference between the inner and outer diameters of the gap and the circular aluminum foil paper is controlled at 1:(1.05-1.1), wherein the ratio of the inner diameter of the circular aluminum foil paper and the diameter of the core column is controlled at (0.9-0.95):

1.

8. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S4, the microwave heating time is 80 to 100 seconds.

9. The method for testing the internal temperature of asphalt mixture under microwave response penetration heating conditions according to claim 1, characterized in that: In S4, the calculation formula for the average interface temperature is: Where, T is the average interface temperature on the side of the core column, unit, °C; T i is the temperature of the ith temperature gradient calibration point from top to bottom, unit, °C; b is the number of temperature gradient calibration points divided according to the core column height.

10. A method for evaluating the microwave response penetration heating capability of asphalt mixture, characterized in that: First, the internal temperature index of the asphalt mixture of the tested mix ratio is measured according to the test method as described in any one of claims 1 to 9, so as to evaluate and obtain the best mix ratio with the best heating effect.

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