A device for detecting the cumulative permanent deformation and permeability of porous asphalt mixture

Abstract

This utility model relates to the field of porous asphalt mixture design and maintenance, specifically disclosing a device for detecting the cumulative permanent deformation and permeability of porous asphalt mixtures. The device includes a universal triaxial chamber, a radial displacement sensor, an axial displacement sensor, a pressure sensor, a water pressure sensor, a Hall effect flow meter, and a control terminal. The universal triaxial chamber is placed in the environmental chamber of a multifunctional asphalt mixture testing machine, and each sensor is installed in its corresponding position and wired to the control terminal. This device can accurately and promptly measure the cumulative permanent deformation and permeability coefficient of porous asphalt mixtures during stress-strain processes, thereby detecting the cumulative permanent deformation and permeability degradation after mixture deformation. Using this device in the mix design stage can yield the optimal deformation-resistant and high-permeability mixture gradation type, guiding the design and construction of drainage asphalt pavements.

Description

Technical Field

[0001] This utility model relates to the field of road engineering technology, specifically to a device for detecting the cumulative permanent deformation and permeability of porous asphalt mixtures. Background Technology

[0002] In road engineering, the permeability coefficient is one of the key functional indicators of drainage asphalt pavement, closely related to its permeability and durability. The cumulative permanent deformation and the magnitude of the permeability coefficient directly affect the pavement's porosity, strength, anti-clogging performance of the porous structure, noise reduction, and drainage function. Therefore, ensuring the permeability coefficient of porous asphalt mixtures is a crucial measure to improve their permeability.

[0003] Currently, the main methods for testing the permeability of porous asphalt mixtures are the traditional variable head permeability test and the constant head permeability test. The instrument used for the variable head permeability test (pavement permeability meter) is only suitable for determining the permeability coefficient of asphalt mixtures with small pores or for on-site measurement of dense-graded asphalt pavements. For porous asphalt mixtures with larger pores, the permeability coefficient usually needs to be measured using a constant head permeability test device. However, there is currently a lack of standard equipment for testing the constant head permeability coefficient. The equipment developed by different companies varies significantly, and the testing procedures, conditions, and evaluation indicators are inconsistent, leading to a lack of comparability and representativeness in the results. Furthermore, most existing testing methods are based on static porous asphalt mixture specimens, and for the dynamic permeation of porous asphalt mixtures under stress-strain processes, existing testing methods still lack effective testing devices.

[0004] Chinese patent CN202322390895.1 discloses a device for measuring the permeability coefficient of a constant-head drainage pavement. This device can maintain a constant-head condition for measuring the permeability coefficient of drainage pavements. It uses a controller to automatically time and control a switching valve to collect the amount of water seeping through the specimen within a certain time. The maintained constant-head condition is more suitable for structures with high permeability coefficients in permeable pavements. Automatic timing and automatic collection of seepage volume can reduce errors and improve test accuracy. The collected seepage water flows in from the top surface of the specimen and out through the gaps on the side, more closely reflecting the actual working conditions of drainage pavements. However, its applicability is limited when used to test the permeability performance of porous asphalt mixtures during stress-strain processes.

[0005] Therefore, there is an urgent need for a testing device to accurately, effectively, and promptly detect the declining permeability of porous asphalt mixtures as deformation increases. Utility Model Content

[0006] The purpose of this invention is to solve the problems of the inability to effectively test the dynamic seepage process and the lack of comparability of test results in the existing technology, and to propose a device for detecting the cumulative permanent deformation and permeability of porous asphalt mixtures.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows: A device for detecting the cumulative permanent deformation and permeability of porous asphalt mixtures includes a control terminal, a press electrically connected to the control terminal, a water supply system, a permeability weighing system, and a universal triaxial chamber placed in the environmental chamber of an asphalt mixture multifunctional testing machine. The universal triaxial chamber forms a sealed testing cavity through a base, a top cover, and a pressure hood. The main shaft of the universal triaxial chamber extends into the testing cavity and is fixedly connected to the pressure plate. A space for placing the specimen is formed between the pressure plate and the base. A radial displacement sensor is provided on the pressure hood, an axial displacement sensor is installed on the top of the universal triaxial chamber, and two air inlets are provided on the top cover. One air inlet is connected to the press pipeline, and a pressure sensor is installed in the other air inlet. The water supply system is connected to the inlet pipe, and the outlet of the inlet pipe is located on the base; the seepage weighing system is connected to the outlet pipe, and the inlet of the outlet pipe is located below the pressure plate; both the inlet and outlet pipes are equipped with shut-off valves and water pressure sensors, and the outlet pipe is also equipped with a Hall flow meter. The water pressure sensor, Hall effect flow meter, radial displacement sensor, axial displacement sensor, pressure sensor, and main shaft are all electrically connected to the control terminal.

[0008] To investigate the seepage state of porous asphalt mixtures during deformation and to study the evolution of permeability within the porous structure of the mixture during stress-strain processes, pre-formed rotary compacted specimens were sealed with rubber sleeves and placed on the base of a universal triaxial chamber, forming a closed seepage channel between the specimen and the base. After the universal triaxial chamber was placed in the environmental chamber of a multi-functional asphalt mixture testing machine and temperature controlled for 3 hours, the spindle was started, driving the pressure plate downwards. The control terminal collected deformation and permeability data in real time during the spindle loading process. Radial displacement sensors transmitted the detected radial displacement signals to the control terminal; pressure sensors detected the pressure inside the triaxial chamber and fed it back to the control terminal, which then controlled the press operation based on the pressure signals; axial displacement sensors (accuracy ±0.06 mm) detected the spindle's movement distance and fed it back to the control terminal. The control terminal calculated the cumulative permanent deformation and permeability coefficient of the specimen based on the received radial displacement, axial displacement, pressure, and the water flow rate and quality from the outlet pipe.

[0009] As a further description of the above technical solution, perforated plates are fixed to the bottom of the pressure plate and the top of the base, and the specimen is placed between the two perforated plates; the outlet of the water inlet pipe is located below the lower perforated plate, and the inlet of the water outlet pipe is located above the upper perforated plate. To ensure test accuracy and avoid errors caused by gravity and water flow impact at the inlet, the outlet of the water inlet pipe is located on the top surface of the base, and a method of saturated water seepage is adopted from the bottom up. A perforated plate is set above the outlet to resist water flow impact. By adjusting the shut-off valve on the water inlet pipe, the flow rate of the inlet is controlled, allowing water to slowly enter the specimen, so as to ensure that the air medium inside the specimen's pores is completely displaced by water and the walls of the seepage channel are completely wetted by water.

[0010] As a further description of the above technical solution, the specimen is cylindrical in shape and its height does not exceed 150 mm. The specimen can be a road surface core sample or a specimen formed by indoor rotational compaction. During testing, the specimen is sealed in a rubber sleeve and placed on the base of the triaxial chamber to ensure that water only seeps out from the top of the specimen, which facilitates the collection and weighing of the seepage water.

[0011] As a further description of the above technical solution, the seepage weighing system includes a water-holding container and an electronic scale. The water-holding container is placed on the electronic scale, and the outlet of the water pipe is connected to the water-holding container. It is used to collect and weigh seepage water.

[0012] As a further description of the above technical solution, a through hole is opened on the top cover through which the water supply pipe passes, and a sealing element is provided between the water supply pipe and the through hole to ensure that the detection chamber is sealed.

[0013] As a further description of the above technical solution, the control terminal adopts the IMACS main controller. Each sensor corresponds to a calibration file (containing information such as sensor model, serial number, and range), and the calibration file corresponds to the interface of the IMACS main controller. When connecting the sensor to the IMACS main controller, it is necessary to confirm that the input port of the IMACS main controller, the calibration file of the sensor, and the serial number of the sensor all match.

[0014] The universal triaxial chamber, axial displacement sensor, radial displacement sensor, pressure sensor, water pressure sensor, Hall effect flow meter, etc., described in this utility model can all be commercially available. The axial displacement sensor is used to detect the cumulative permanent deformation of the specimen during the loading process of the main shaft of the asphalt mixture multi-functional testing machine, and the Hall effect flow meter is used to measure the water flow rate from the outlet pipe and transmit the detection signal to the control terminal in real time.

[0015] Compared with the prior art, the beneficial effects of this utility model are: The detection device of this invention can accurately and promptly measure the cumulative permanent deformation and permeability coefficient of porous asphalt mixtures. Through the coordinated operation of various sensors, it can accurately detect the cumulative permanent deformation and the decline in permeability performance of the mixture after deformation occurs. When used in the mix design stage, it can also obtain the optimal gradation type of the mixture with the best deformation resistance and high permeability, thereby guiding the design and construction of subsequent drainage asphalt pavements and improving the performance and durability of the pavement.

[0016] This invention addresses the lack of effective testing devices for the dynamic seepage of porous asphalt mixtures under stress-strain processes in existing technologies. It enables permeability testing under dynamic conditions, resulting in test results that more closely reflect actual engineering scenarios. Furthermore, all components of the device are commercially available, its structure is rationally designed, and its connection methods are clearly defined, exhibiting strong engineering applicability and stability, thus facilitating its widespread application. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 The curve representing the relationship between the permeability coefficient and the vertical permanent deformation is obtained by fitting a scatter plot of experimental statistical data.

[0018] Figure label: 1-Control terminal; 2-Pressure machine; 3-Water supply system; 4-Water container; 5-Electronic scale; 6-Stop valve; 7-Water pressure sensor; 8-Hall flow meter; 10-Universal triaxial chamber; 101-Base; 102-Top cover; 103-Pressure cover; 104-Radial displacement sensor; 105-Main shaft; 106-Pressure plate; 107-Perforated plate; 108-Axial displacement sensor; 109-Pressure sensor; 20-Specimen; 21-Rubber sleeve. Detailed Implementation

[0019] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0020] This embodiment provides a device for detecting the cumulative permanent deformation and permeability of porous asphalt mixtures, including a control terminal 1, a pressure machine 2, a water supply system 3, a permeation weighing system, and a universal triaxial chamber 10 placed in the environmental chamber of an asphalt mixture multifunctional testing machine. The control terminal 1 adopts an IMACS main controller, the pressure machine 2 is electrically connected to the control terminal 1, the water supply system 3 is connected to the universal triaxial chamber 10 through an inlet pipe, and the permeation weighing system is connected to the universal triaxial chamber 10 through an outlet pipe.

[0021] The general-purpose triaxial chamber 10 comprises a base 101, a cover plate 102, a pressure shroud 103, a main shaft 105, and a pressure plate 106. The base 101, cover 102, and pressure shroud 103 together form a sealed detection chamber. The top of the base 101 has a boss for placing the specimen 20. The main shaft 105 extends through the cover 102 into the detection chamber and is fixedly connected to the pressure plate 106 inside the detection chamber. The pressure plate 106 is located directly above the boss. Perforated plates 107 are fixed to the bottom of the pressure plate 106 and the top of the boss. A space for placing the specimen 20 is formed between the two perforated plates 107. During testing, the specimen 20 is fitted inside the rubber sleeve 21 and placed on the boss of the base 101, forming a closed seepage channel. The pressure shroud 103 has a radial displacement sensor interface for installing a radial displacement sensor 104. The radial displacement sensor 104 is electrically connected to the control terminal 1 and transmits the radial deformation displacement signal of the specimen 20 under pressure to the control terminal 1. An axial displacement sensor 108 (accuracy ±0.06 mm) is installed on the disc at the top of the general-purpose triaxial chamber 10. The axial displacement sensor 108 is electrically connected to the control terminal 1 and is used to detect the cumulative permanent deformation of the specimen 20 during the spindle loading process. Two air inlets are opened on the top cover 102. One air inlet serves as a servo air inlet and is connected to the air outlet pipe of the press 2. A pressure sensor 109 is installed in the other air inlet to collect the pressure signal in the detection chamber and transmit it to the control terminal 1.

[0022] In the indoor test simulating a water environment, a constant head water tank was used as the water supply system. Considering that the head height is the main factor affecting the seepage rate of porous asphalt mixture, and referring to the average daily rainfall (above 150 mm) corresponding to the common summer rainstorm levels in southern my country, the constant head height was set to 170 mm when conducting the seepage coefficient test. To ensure test accuracy and avoid errors caused by gravity and water flow impact at the inlet, the outlet of the water supply system's inlet pipe was placed on the base. A method of saturated seepage from the bottom up was adopted, and the water flow impact was further buffered by the porous plate 107. A shut-off valve 6 and a water pressure sensor 7 were installed on the inlet pipe. By adjusting the shut-off valve 6 on the inlet pipe, the flow rate at the inlet was controlled to prevent it from being too fast, allowing water to slowly enter the specimen 20, ensuring that the air medium inside the pores of the specimen 20 was completely displaced by water and the walls of the seepage channel were completely wetted by water. The seepage weighing system is used to collect and weigh seepage from the specimens. It includes a water container 4 (a beaker is used in this embodiment) and an electronic scale 5. The water container 4 is placed on the electronic scale 5. The inlet of the outlet pipe connected to the seepage weighing system is located on the lower surface of the pressure plate 106 and above the perforated plate 107. The seepage passes through the perforated plate 107 and is collected in the water container 4 through the outlet pipe for weighing. The outlet pipe is equipped with a shut-off valve 6, a water pressure sensor 7, and a Hall effect flow meter 8. Both the water pressure sensor 7 and the Hall effect flow meter 8 are electrically connected to the control terminal 1 and are used to collect the water pressure signals of the inlet and outlet pipes and the water flow rate of the outlet pipe in real time and transmit them to the main controller IMACS of the control terminal 1.

[0023] Cumulative permanent deformation and permeability coefficient are used to characterize the deformation state of porous asphalt mixtures and their permeability during stress-strain processes. For porous asphalt mixtures, both the initial permeability after specimen molding and the permeability during stress-strain processes are generally affected by the material composition and the degree of specimen compaction. In this invention, the cumulative permanent deformation of the mixture is calculated using the stress-strain signal measured by an axial displacement sensor, and the permeability coefficient of the deformed mixture is calculated using the flow signal from a Hall effect flowmeter. During the mix design stage of porous asphalt mixtures, if the deformation resistance and permeability of the mixture are both good, frequent maintenance of the paved drainage asphalt pavement is not required. Therefore, using the device and method described in this invention, the cumulative permanent deformation and permeability coefficient of porous asphalt mixtures can be measured accurately and promptly, and the optimal deformation-resistant and high-permeability mixture gradation type obtained can be used to guide the design and construction of subsequent drainage asphalt pavements.

[0024] The deformation-permeability coupling test of porous asphalt mixtures is a water-mechanical coupled transient stress-strain-permeability test process under repeated loading of dynamic water flow in the porous structure of the mixture and the semi-sinusoidal principal axis stress acting on the mixture matrix. The indoor test used five types of porous asphalt mixtures: PAC-13 (design porosity of 16%, 20%, and 24%), PAC-16 (design porosity of 20%), and PAC-20 (design porosity of 20%), with specimen dimensions of 100 mm diameter and 150 mm height. Before testing, the specimens were sealed in a rubber sleeve 21 and placed in a general triaxial chamber 10. The specimen dimensions were 100 mm (…). ) × 150 mm ( The triaxial chamber was placed in the environmental chamber of the multifunctional asphalt mixture testing machine and the temperature was controlled for 3 hours. The principal shaft loading frequencies were 5 Hz, 10 Hz and 15 Hz, and the peak load of the half-sine principal shaft stress was 0.7 MPa. The deformation and permeability performance data during the principal shaft loading process were collected in real time. The triaxial repeated loading stress-strain law of porous asphalt mixtures with different gradations and the permeability performance decay law during the deformation process were investigated. The permeability performance inversion method of porous asphalt mixtures based on the loading frequency under deformation-permeability coupling conditions was studied, and a characterization method of porous asphalt mixture permeability performance under deformation conditions was proposed.

[0025] The cumulative micro-strain of porous asphalt mixtures under triaxial repeated loading was plotted as a scatter plot, and the relationship between permanent deformation and the number of loading cycles was obtained by fitting. It can be seen that the permanent deformation of porous asphalt mixtures generally exhibits a three-stage growth trend with the increase of the number of loading cycles. Taking three porous asphalt mixtures (PAC-13, PAC-16, and PAC-20) with the same initial porosity (20%) as examples, under a temperature of 50℃, the number of loading cycles to reach the critical points of the second and third stages of deformation were 1300, 500, and 2300, respectively. At this time, the corresponding permeability coefficients decreased to 64%, 52%, and 69% of the initial permeability coefficient of the specimens, respectively. Similarly, under the same nominal maximum particle size, the number of loading cycles to reach the deformation critical point for PAC-13 porous asphalt mixture specimens with three different initial porosities (16%, 20%, and 24%, respectively) were 1800, 500, and 300, respectively. At this point, the corresponding permeability coefficients decreased to 75%, 52%, and 61% of the initial permeability coefficients of the specimens, respectively. In summary, during the deformation process of porous asphalt mixtures under triaxial repeated loading, the design void ratio and nominal maximum particle size are the main factors leading to the differences in mixture deformation and permeability degradation. By fitting the permanent deformation curves of mixtures with different gradations, it can be seen that the variation law of permanent deformation with the number of load applications can be expressed as a polynomial. The relationship between the permeability coefficient and permanent deformation can be represented by... It can be represented by a linear formula.

[0026] Test results and evaluation of the attenuation of permeability of porous asphalt mixture based on permanent deformation: By combining the measured permanent deformation data in the laboratory, the permeability of specimens with different amounts of permanent deformation can be obtained. Figure 2 This is the permeability coefficient-vertical permanent deformation relationship curve obtained by fitting a scatter plot based on experimental statistical data. From... Figure 2 It can be seen that there is a relatively obvious linear relationship between the permeability coefficient and permanent deformation; the greater the permanent deformation, the smaller the permeability coefficient. Under the same permanent deformation conditions, the porous asphalt mixtures with the best to worst permeability are PAC-20, PAC-13, and PAC-16. This permeability coefficient decay model helps to solve the problem of selecting the maintenance timing for drainage asphalt pavements and provides a theoretical basis for pavement condition assessment.

[0027] Inversion calculation based on the cumulative permanent deformation of porous asphalt mixtures.

[0028] According to literature reports, the permanent deformation of porous asphalt mixtures under triaxial loading increases with the number of load cycles, with the fastest growth in the early stage, a relatively stable growth rate in the middle stage, and a faster growth rate in the later stage. Therefore, it is possible to establish a relationship between the cumulative micro-strain of porous asphalt mixtures and the loading cycle during repeated triaxial loading, and obtain a regression relationship between the cumulative micro-strain and the number of load cycles. It can be found that the two have a good correlation, resulting in the following three-stage permanent deformation expression.

[0029] Phase 1: , ; Phase Two: , ; Phase Three: , ; In the formula, For loading cycle; For accumulated micro-strain (με); The first stage is the accumulated micro-strain (με); The cumulative load period corresponding to the end of the first stage; The second stage is the accumulated micro-strain (με); The cumulative load period corresponding to the end of the second stage; and These are the model coefficients.

[0030] The detection device of this invention includes a displacement sensor and a Hall effect flow meter. The stress-strain signal measured by the axial displacement sensor is used to evaluate the resistance to permanent deformation of porous asphalt mixtures, while the water permeability coefficient signal of the porous asphalt mixture measured by the Hall effect flow meter can be used to evaluate the permeability of the material during deformation. Therefore, the detection device of this invention can timely and accurately measure the cumulative permanent deformation and water permeability coefficient of porous asphalt mixtures, and can accurately detect the cumulative permanent deformation and water permeability degradation of the mixture after deformation.

[0031] The above description is merely the preferred embodiment of this utility model. It should be noted that, for those skilled in the art, various modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from its principles, and these modifications or substitutions can also achieve the technical effects of this utility model, and should also be considered within the protection scope of this utility model.

Claims

1. An apparatus for detecting the cumulative permanent deformation and permeability of porous asphalt mixtures, comprising a control terminal (1), a press (2) electrically connected to the control terminal (1), a water supply system (3), a permeability weighing system, and a universal triaxial chamber (10) placed in an environmental chamber of a multifunctional asphalt mixture testing machine. The universal triaxial chamber (10) forms a sealed testing chamber through a base (101), a top cover (102), and a pressure hood (103). The main shaft (105) of the universal triaxial chamber (10) extends into the testing chamber and is fixedly connected to a pressure plate (106). A space for placing a specimen (20) is formed between the pressure plate (106) and the base (101). A radial displacement sensor (104) is provided on the pressure hood (103), an axial displacement sensor (108) is installed on the top of the universal triaxial chamber (10), and two air inlets are provided on the top cover (102). One air inlet is connected to the press (2) pipe, and a pressure sensor (109) is installed in the other air inlet. Its features are: The water supply system (3) is connected to the inlet pipe, and the outlet of the inlet pipe is located on the top surface of the base (101); the seepage weighing system is connected to the outlet pipe, and the inlet of the outlet pipe is located on the bottom surface of the pressure plate (106); both the inlet pipe and the outlet pipe are equipped with a shut-off valve (6) and a water pressure sensor (7), and the outlet pipe is also equipped with a Hall flow meter (8). The water pressure sensor (7), Hall flow meter (8), radial displacement sensor (104), axial displacement sensor (108), pressure sensor (109) and main shaft (105) are all electrically connected to the control terminal (1).

2. The apparatus according to claim 1, characterized in that: A perforated plate (107) is fixed to the bottom of the pressure plate (106) and the top of the base (101), and the specimen (20) is placed between the two perforated plates (107).

3. The apparatus according to claim 2, characterized in that: The outlet of the water inlet pipe is located below the lower perforated plate (107), and the inlet of the water outlet pipe is located above the upper perforated plate (107).

4. The apparatus according to claim 2, characterized in that: The specimen (20) is cylindrical in shape and its height does not exceed 150 mm.

5. The apparatus according to claim 1, characterized in that: The water seepage weighing system includes a water container (4) and an electronic scale (5). The water container (4) is placed on the electronic scale (5), and the outlet of the water pipe is connected to the water container (4).

6. The apparatus according to claim 1, characterized in that: A through hole is provided on the top cover (102) through which the water supply pipe passes, and a sealing element is provided between the water supply pipe and the through hole.

7. The apparatus according to claim 1, characterized in that: The control terminal (1) adopts the IMACS main controller.

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