Apparatus and method for testing duration of black ice and coagulation strength on phase change asphalt pavement

Abstract

The application provides a device and method for testing the duration and coagulation strength of black ice on a phase change asphalt pavement, and belongs to the technical field of road surface anti-icing performance testing technology. The device comprises a pressure head unit, a water tank unit and a collection unit. The pressure head unit comprises a hollow circular tube, a concentric variable-diameter special-shaped tube, a circular sheet, a steel ball, a circular rod, a cylinder and a spring. The water tank unit comprises a fan-shaped water tank, a plastic film, a screw, a level and a horizontal adjustment foot with a screw rod. The collection unit comprises an electric conductivity meter and a pressure gauge. The test method of the application is as follows: a freeze-thaw test is carried out on the phase change asphalt mixture with different thicknesses of water film on the bottom surface, the coagulation time, melting time and duration of black ice with different thicknesses are tested from the electric conductivity-time curve, and the coagulation strength of black ice with different thicknesses is tested by pressing the black ice with different thicknesses to break.

Description

Technical Field

[0001] This invention belongs to the field of road surface anti-icing performance testing technology, specifically relating to a testing device for determining the icing state of black ice on phase change asphalt road surfaces. Background Technology

[0002] Black ice is highly susceptible to formation on mountain roads, roads in damp areas, paved sections of bridges, shaded areas, and low-lying sections of roads during autumn and winter. Black ice significantly reduces the coefficient of friction between vehicle tires and the road surface, making vehicles prone to skidding and difficult to control, thus greatly increasing driving hazards. Furthermore, because black ice is very thin, the black color of the asphalt can show through it, resulting in very low visibility and making it difficult to detect and provide effective warnings. Therefore, delaying the formation of black ice and accelerating its melting are ongoing challenges for road workers.

[0003] To achieve delayed setting and accelerated melting of pavements, researchers have developed low-freezing-point technologies, exemplified by salt-retaining asphalt pavements. This technology involves incorporating chloride-containing admixtures into the pavement surface layer; typical products include imported MFL and domestically produced LX. Through the continuous release of chloride during rain and snow, the freezing point of the pavement is lowered, delaying icing. Currently, the production of salt-retaining admixtures, the design of salt-retaining asphalt concrete compositions, and the construction technology of salt-retaining asphalt pavements are mature. Numerous test sections of salt-retaining asphalt pavements have been laid both domestically and internationally, demonstrating good retarding performance during icy and snowy weather. However, engineering practice has shown that the retarding function of salt-retaining asphalt pavements only lasts for 2–4 years. The main reason is that chloride continues to precipitate and release from the pavement during spring and summer, causing the chloride content of the pavement to decrease over time.

[0004] To address the short duration of the retarding effect in salt-retaining pavement technology, technologies such as phase change pavement have emerged in recent years. This technology incorporates low-temperature phase change materials (with a phase change temperature between 0℃ and 5℃) into the pavement. By storing heat during the phase transition, it slows down the rate of temperature drop in the pavement as the air temperature decreases, thus achieving the goal of retarding the pavement surface. Currently, this technology has achieved a series of results in the screening of low-temperature phase change materials, the evaluation of the mechanical properties and road performance of phase change asphalt concrete. However, the influence of the type and dosage of phase change materials on the freezing time, melting time, and setting strength of thin ice in low-temperature phase change asphalt concrete is still unclear. This makes it difficult to determine the appropriate type and dosage of low-temperature phase change materials for different climatic regions, which greatly hinders the application of low-temperature phase change asphalt concrete in road sections prone to black ice.

[0005] The fundamental reason why the influence of the type and dosage of phase change materials on the freezing time, melting time and freezing strength of black ice is unclear is that there is currently a lack of devices and methods for quantitatively testing the freezing time, melting time and freezing strength of black ice. This is mainly manifested in the following ways: (1) For black ice with a thickness of 1-4 mm, it is difficult to determine freezing and melting by measuring the temperature with a thermometer; the method of adding "ice crystal catalyst" and judging the freezing time by observing the color change is also highly subjective. It is necessary to adopt a high-precision method to determine the freezing time of water and the melting time of ice. (2) The relatively small thickness of black ice makes it difficult to test the strength of black ice or the bond strength between black ice and asphalt concrete by conventional test methods such as compression and pull-out. It is necessary to invent new methods to comprehensively evaluate the freezing strength of black ice. Summary of the Invention

[0006] To address the aforementioned shortcomings in existing technologies, this invention provides a testing device and method for measuring the duration and freezing intensity of black ice on phase change asphalt pavements. Utilizing the characteristic that the electrical conductivity of solid ice is much lower than that of liquid water, a conductivity meter is used to accurately determine the timing of water freezing and ice melting. Simultaneously, a novel method for testing the freezing intensity of black ice is proposed.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A testing device for the duration and solidification strength of black ice on phase change asphalt pavement includes: an indenter unit, a water reservoir unit, and a data acquisition unit. The indenter unit comprises a hollow circular tube, a concentric reducing tube, a disc, steel balls, a rod, a cylinder, and a spring; the water reservoir unit comprises a fan-shaped water reservoir, a plastic film, screws, a spirit level, and a leveling foot with a screw; the data acquisition unit comprises a conductivity meter and a pressure gauge.

[0009] Furthermore, the pressure head unit has an upper part consisting of a hollow cylindrical tube with a length of 6cm and an outer diameter of 1.95cm. A 5mm diameter through hole is located on the side 1cm from the top, and the inner wall of the tube is threaded within 1cm of the bottom. The lower part of the pressure head is a concentric reducing-diameter shaped tube. The outer side of the smaller diameter cylindrical tube is threaded, extending into the hollow cylindrical tube and screwed onto the inner wall of the hollow cylindrical tube. The outer diameter of the larger diameter cylindrical tube is the same as that of the hollow cylindrical tube, and the side is threaded along the height direction. Eight cuts of equal depth are provided. The inner wall of the large-diameter circular tube is threaded within 1 cm from the upper edge of the cut. A circular plate is provided to be screwed onto it. The side and bottom of the circular plate are respectively engraved with threads and "+" shaped grooves. After tightening, the bottom of the circular plate is flush with the upper edge of the cut. The inside of the pressure head is equipped with a conductivity probe. The probe enters the pressure head through the through hole on the hollow circular tube and is fixed from top to bottom to the inner wall of the hollow circular tube and the inner wall of the concentric variable diameter special tube. The bottom of the probe is flush with the lower edge of the cut.

[0010] Furthermore, the steel ball has a through hole through its center and is fitted onto a round rod, the two ends of which are fixed to the inner wall of the cylinder. Two cylinders form a group and are connected by a spring. The two ends of the spring are fixed to the bottom surfaces of the two cylinders, and after fixing, the two round rods in the two cylinders are parallel to each other.

[0011] Furthermore, the pressure head unit consists of 4 groups, with 2 pressure heads in each group, and the depth of the side cut of the large-diameter circular tube in each group of pressure heads is 1mm, 2mm, 3mm, and 4mm, respectively.

[0012] Furthermore, the water tank unit consists of four open fan-shaped water tanks with equal horizontal area. The depths of the fan-shaped water tanks are 1mm, 2mm, 3mm, and 4mm, respectively. The bottom plate of each fan-shaped water tank is 2cm thick and has two through holes with a diameter of 2cm. The inner wall of the hole is threaded, and each hole is equipped with a screw that can be screwed in. After tightening, the top surface of the screw is flush with the bottom surface of the water tank.

[0013] Furthermore, the water tank is made of stainless steel, and the outer surface is covered with glass wool with low thermal conductivity.

[0014] Furthermore, the distance between the center of each of the two through holes on the bottom plate of the fan-shaped water tank and the vertex of the fan is 4.36cm, and the vertical distance between each hole and the nearest fan radius is 1.67cm.

[0015] Furthermore, the number of spirit levels installed is 2, which simultaneously detect whether the surface is horizontal in two vertical directions.

[0016] Furthermore, the screw-type leveling foot provides an integrated screw and ball head. The screw can adjust the overall length of the leveling foot, and the ball head can adjust the angle of the screw.

[0017] Furthermore, the acquisition unit consists of a pressure gauge and a conductivity meter. The pressure gauge must have a range greater than 2 MPa and an accuracy greater than 0.1 MPa. The conductivity meter must have at least 8 channels, a range greater than 200 μS / cm, an accuracy greater than 1 μS / cm, and an applicable temperature range of -10℃ to 60℃.

[0018] Furthermore, the test method steps of the present invention are as follows:

[0019] S1. For the large Marshall specimen of phase change asphalt mixture, cut radially to obtain a disc specimen with a thickness of 4 cm. Mark 8 points 4.5 cm from the center of the top surface of the specimen and distribute them symmetrically. Drill 8 through holes with a diameter of 2 cm along the thickness direction of the specimen, using the 8 points as the centers. Immerse the specimen in water and place it in a constant temperature chamber at 20°C for 6 hours along with the testing device.

[0020] S2. Screw the eight screws from bottom to top into the eight round holes in the bottom plate of the fan-shaped water tank, ensuring the top surface of the screws is flush with the bottom surface of the fan-shaped water tank and fits tightly. Adjust the angle and length of the four screw-type leveling feet to keep the fan-shaped water tank level. Cut eight circular plastic films with a diameter of 1.5cm, align the center of the film with the center of the top surface of the screw, and attach the film to the top surface of the screw, fixing the part of the film extending beyond the edge of the screw to the fan-shaped water tank. Remove the test device and disc sample from the constant temperature chamber, and inject water samples with an initial conductivity greater than 50μS / cm at 20℃ into the four leveled water tanks, making the upper surface of the water film flush with the upper edge of the water tank, forming water films with thicknesses of 1mm, 2mm, 3mm, and 4mm respectively. Align the 8 sample through holes with the 8 water tank through holes, place the disc sample on the water tank, insert the pressure head unit into the sample through holes, and make the depth of each pressure head cut consistent with the thickness of the water film below it. Rotate the pressure head so that the conductivity probe faces the center of the sample.

[0021] S3. Transfer the assembled sample and apparatus to a -5℃ refrigerator, connect the conductivity meter, and after 12 hours, plot the conductivity versus time curves for the four water film thicknesses. Take the end of the conductivity drop segment as the time t when black ice begins to condense. 0i (min), where i = 1, 2, 3, 4; the device was placed back into a constant temperature chamber at 20℃, and after 3 hours, the water film conductivity versus time curves in the four water chambers were plotted. The end of the conductivity surge segment was taken as the time t when the black ice completely melted. 1i (min); by (t) 11 -t 01 min、(t) 12 -t 02 min、(t) 13 -t 03 min、(t) 14 -t 04 The duration of black ice with thicknesses of 1 mm, 2 mm, 3 mm, and 4 mm on phase change asphalt mixtures was obtained by measuring 1 min.

[0022] S4. Place the sample and apparatus back into the -5℃ refrigerator. For black ice with thicknesses of 1mm, 2mm, 3mm, and 4mm, respectively, at (t 01 +30)min、(t 02 +30)min、(t 03 +30)min、(t 04 At +30 min, unscrew the screw inside one through hole of each sector-shaped water tank by 1 cm, and press the pressure head on it with a pressure gauge until the black ice breaks, thus obtaining the freezing strength S of the black ice. 0i After 12 hours, unscrew the screw inside the other through hole of each fan-shaped water tank by 1 cm, and use a pressure gauge to measure the freezing strength S of the four thicknesses of black ice. 1i .

[0023] Beneficial effects of the present invention

[0024] (1) The present invention proposes a test device for the duration and solidification strength of black ice on phase change asphalt pavement, which can accurately simulate water film of different thicknesses on the surface of the mixture.

[0025] (2) The present invention proposes a test method for the duration and solidification intensity of black ice on phase change asphalt pavement, which can accurately determine the time of water freezing and ice melting.

[0026] (3) The present invention proposes a test method for the duration and solidification strength of black ice on phase change asphalt pavement, and proposes a new mechanical index to more effectively characterize the solidification strength of black ice. Attached Figure Description

[0027] Figure 1 This is a flowchart of the test method of the present invention.

[0028] Figure 2 This is a schematic diagram of the device of the present invention.

[0029] Figure 3 The conductivity changes of a 1 mm water film with 0%, 1.0%, 1.5%, and 2.0% phase change material doping.

[0030] Figure 4 The solidification strength of 1 mm black ice at phase change material dosages of 0%, 1.0%, 1.5%, and 2.0%. Detailed Implementation

[0031] The present invention is described in detail with reference to specific embodiments to enable those skilled in the art to understand the invention. However, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0032] Example

[0033] In this embodiment, the hollow cylindrical tube in the pressure head unit has dimensions of 6cm in length, 1.95cm in outer diameter, and 5mm in wall thickness, and is made of stainless steel. A 5mm diameter through hole is drilled on the side of the tube 1cm from the top using a high-precision drilling machine, and two symmetrical 10mm diameter through holes are drilled on the side of the tube at 2.5cm and 4.5cm from the top, respectively. Threads are then etched on the inner wall of the tube within 1cm from the bottom using a straight flute tap.

[0034] In this embodiment, a 10mm long, 2mm diameter round rod is threaded through a 6mm diameter steel ball with a 2mm diameter through-hole. The two ends of the round rod with the steel ball are welded to the inner wall of a 10mm diameter, 7mm high cylinder, with the steel ball extending beyond the top surface of the cylinder. A 10mm long spring is fixed to the bottom surfaces of the two cylinders, with the two round rods parallel to each other after fixing. The two connected cylinders are then passed through symmetrical through-holes in a hollow tube, with both cylinders located within the two through-holes, and both round rods parallel to the top surface of the hollow tube.

[0035] In this embodiment, the small-diameter round tube in the concentric variable-diameter shaped tube has a height of 1cm, an outer diameter of 1.9cm, and a wall thickness of 5mm; the large-diameter round tube has a height of 2cm, an outer diameter of 1.95cm, and a wall thickness of 5mm; and the disc has a thickness of 1cm and a diameter of 1.9cm. All materials are stainless steel. A cutting machine is used to make eight equal-depth cuts along the height direction on the side of the large-diameter round tube. A thread cutter is used to engrave threads on the outer side of the small-diameter round tube, and a straight-flute tap is used to engrave threads on the inner wall of the large-diameter round tube within 1cm of the top edge of the cuts and on the side of the disc. A 3mm long, 3mm wide, and 1mm deep "+" shaped groove and a 4mm diameter through hole are engraved on the bottom surface of the disc using a laser engraving machine and a drilling machine. Finally, a Phillips screwdriver is used to screw the disc into the large-diameter round tube, ensuring that the bottom of the disc is flush with the top edge of the cuts after tightening.

[0036] In this embodiment, the conductivity meter used is a DDS-307 conductivity testing instrument, with a testing range of 0.0 μS / cm-299.9 μS / cm, an applicable temperature range of -10℃ to 60℃, and 8 channels. The conductivity probe is inserted into the pressure head through a circular hole 1 cm from the top of the hollow cylindrical tube. After ensuring the bottom of the probe is flush with the lower edge of the cut in the large-diameter cylindrical tube, the probe is glued to the inner walls of the hollow cylindrical tube and the concentric reducing-diameter shaped tube from top to bottom.

[0037] In this embodiment, a stainless steel cylinder with a diameter of 15cm and a height of 6cm is laser-engraved to form four 90° fan-shaped water tanks with a radius of 7.2cm within the water tank unit. A cross-shaped frame with a length of 14.6cm, a width of 14.6cm, and a thickness of 2mm is formed between the water tanks, along with a circular frame with a thickness of 2mm on the outer side of the water tanks. The depths of the four water tanks are 1mm, 2mm, 3mm, and 4mm, respectively. A cutting machine is used to remove four fan-shaped columns from the middle of the cylinder. The top surfaces of these columns are fan-shaped sections 2cm from the bottom of the four water tanks, and the bottom surfaces are four fan-shaped sections 1cm from the bottom of the cylinder. This ultimately forms the top water tank base plate, the middle cross-shaped frame, and the bottom cylindrical base plate.

[0038] In this embodiment, on the surface of each sector-shaped water tank, two points are marked, each 4.36 cm away from the apex of the sector and 1.67 cm perpendicularly to the radius of the nearest sector. Two through holes with a diameter of 2 cm, centered at these two points, are drilled using a drilling machine. Each through hole is fitted with a screw with a length of 2 cm. On the surface of the cylindrical base plate, on each sector, a point is marked, located on the bisector of the sector angle and 5 cm away from the apex of the sector. A through hole with a diameter of 1 cm, centered at this point, is drilled using a drilling machine. Each through hole is fitted with a screw-type leveling foot.

[0039] In this embodiment, 2cm thick glass wool is glued to the side of the top plate of the fan-shaped water tank.

[0040] In this embodiment, a pair of mutually perpendicular horizontal rulers are installed on two adjacent sector-shaped surfaces of the cylindrical base plate.

[0041] In this embodiment, the phase change material used is tetradecane, and the wall material is silicon dioxide (SiO2). The properties of the prepared composite phase change material tetradecane / SiO2 are shown in Table 1, where T start T end ΔH m These represent the phase change initiation temperature, phase change termination temperature, and enthalpy value during the cooling process, respectively. Large Marshall specimens of phase change asphalt mixtures with tetradecane / SiO2 contents of 0%, 1%, 1.5%, and 2% were prepared by direct external admixture method. The mixture type was SMA-13, and the designed gradation is shown in Table 2. A 4cm high disc sample was cut from the center of the specimen using a cutting machine along its radial direction. Eight 2cm diameter holes were drilled into the sample using a drilling machine. The center of each hole was 4.5cm from the center of the specimen's cross-section and was centrally symmetrically distributed. The sample was then immersed in Nanjing tap water for 6 hours.

[0042] Table 1 Technical properties of the composite phase change material tetradecane / SiO2

[0043]

[0044] Table 2 SMA-13 ​​Design Grading

[0045]

[0046] In this embodiment, an Allen wrench is used to screw eight screws into the eight round holes of the fan-shaped water tank from bottom to top, so that the top surface of the screws is flush with the bottom surface of the water tank. The fan-shaped water tank is kept level by adjusting four screw-type leveling feet. Eight pieces of plastic wrap with a diameter of 2.5cm are cut into circular plastic films. The center of the film is aligned with the center of the top surface of the screw and the film is attached to the top surface of the screw. Then, the part of the film that extends beyond the edge of the screw is glued to the bottom surface of the water tank with 502 glue.

[0047] In this embodiment, the initial conductivity of local tap water in Nanjing was 120±10 μS / cm. The curing box and refrigerator used were a YH-40B type curing box and a BD-100DTEC refrigerator, respectively. This embodiment also tested the conductivity changes of water films of different thicknesses on the surface of phase change asphalt mixtures with tetradecane / SiO2 contents of 0%, 1%, 1.5%, and 2% in an environment of -5℃. Figure 3 The figure shows the conductivity variation curves of a 1 mm thick water film on the surface of phase change asphalt mixture samples with different phase change material (PCM) dosages. As shown in the figure, the termination times of the sudden drop and sudden rise in conductivity of the water film on the surface of the 0%, 1%, 1.5%, and 2% PCM mixture samples are 60 min, 95 min, 125 min, 145 min and 805 min, 790 min, 765 min, 745 min, respectively. This indicates that the addition of PCM to the specimens at -5℃ can effectively delay the freezing time of the surface water film, accelerate the melting of black ice, and significantly reduce the duration of black ice.

[0048] In this embodiment, an NK-200 pressure gauge with a range of 2.5 MPa and an accuracy of 0.02 MPa was used to test the solidification strength of a 1 mm thick water film on the surface of phase change asphalt mixtures with phase change material contents of 0%, 1%, 1.5%, and 2% after freezing for 30 minutes and 12 hours, respectively. As mentioned earlier, the freezing times of the water film for the four mixtures after 30 minutes were 90 min, 125 min, 155 min, and 175 min, respectively. Figure 4 The figure shows the setting strength of 1 mm thick black ice on the surface of asphalt mixtures at two time points under four different dosages of phase change material (PCM). As shown in the figure, the longer the freezing time, the greater the setting strength of the black ice. PCM can effectively reduce the setting strength of black ice, and the higher the PCM dosage in the asphalt mixture, the lower the setting strength of the black ice on the mixture surface.

Claims

1. A testing device for the duration and solidification strength of black ice on phase change asphalt pavement, comprising: The unit comprises a pressure head unit, a water tank unit, and a collection unit. The pressure head unit has an upper section consisting of a 6cm long, 1.95cm outer diameter hollow cylindrical tube with a 5mm diameter through hole on its side, 1cm from the top. The inner wall of the cylindrical tube is threaded within 1cm of the bottom. The lower section is a concentric reducing-diameter shaped tube. The smaller diameter cylindrical tube has threads on its outer side, extends into the hollow cylindrical tube, and is screwed onto the inner wall of the hollow cylindrical tube. The larger diameter cylindrical tube has the same outer diameter as the hollow cylindrical tube. The side section extends along the height... Eight equal-depth cuts are made in the direction of the tube. The inner wall of the large-diameter circular tube has threads within 1 cm of the top edge of the cuts, and a circular plate is fitted to it for screwing. The side and bottom surfaces of the circular plate are respectively engraved with external threads and a cross-shaped groove, and when tightened, the bottom surface of the circular plate is flush with the top edge of the cuts. The pressure head has an internal structure for adjusting and fixing the probe position. This structure includes a steel ball, a circular rod, a cylinder, and a spring. The steel ball has a through hole with its center and is fitted onto the circular rod, which is fixed at both ends. On the inner wall of the cylinder, two cylinders are grouped together and connected by the spring. The two ends of the spring are fixed to the bottom surfaces of the two cylinders, and after fixing, the two cylindrical rods in the two cylinders are parallel to each other. The inside of the pressure head is equipped with a conductivity probe. The probe enters the pressure head through a through hole 1 cm from the top of the hollow cylindrical tube, and the bottom of the probe is flush with the lower edge of the cut. The water tank unit consists of four open fan-shaped water tanks with equal horizontal areas. The depths of the fan-shaped water tanks are 1 mm, 2 mm, 3 mm, and 4 mm, respectively. The bottom plate of each fan-shaped water tank is 2 cm thick, and each bottom plate is provided with two through holes with a diameter of 2 cm. The inner wall of the hole is threaded, and each hole is equipped with a screw that can be screwed in. After tightening, the top surface of the screw is flush with the bottom surface of the water tank. The acquisition unit includes a conductivity meter and a pressure meter, which are used to acquire conductivity signals and pressure signals respectively to determine the duration of black ice and characterize the condensation intensity of black ice. The water tank is made of stainless steel, and the outer surface is pasted with glass wool with low thermal conductivity.

2. The testing device for the duration and solidification strength of black ice on phase change asphalt pavement according to claim 1, characterized in that, The pressure head unit consists of 4 groups, with 2 pressure heads in each group. The depth of the side cut of the large-diameter circular tube in each group of pressure heads is 1mm, 2mm, 3mm, and 4mm, respectively.

3. The testing device for the duration and solidification strength of black ice on phase change asphalt pavement according to claim 1, characterized in that, The distance between the center of each of the two through holes on the bottom plate of the fan-shaped water tank and the vertex of the fan is 4.36cm, and the vertical distance between each hole and the nearest fan radius is 1.67cm.

4. A test method for the duration and solidification strength of black ice on phase change asphalt pavement, characterized in that, The test is conducted using the testing apparatus for the duration and solidification strength of black ice on phase change asphalt pavement as described in any one of claims 1 to 3, and includes the following steps: S1. For the phase change asphalt mixture Marshall specimen, cut radially to obtain a disc specimen with a thickness of 4 cm. Mark 8 points 4.5 cm from the center of the top surface of the specimen and distribute them centrally symmetrically. Drill 8 through holes with a diameter of 2 cm along the thickness direction of the specimen with the 8 points as the center. Immerse the specimen in water and place it in a constant temperature chamber at 20℃ for 6 hours together with the testing device. S2. Remove the testing device and disc sample from the constant temperature chamber. Inject a 20℃ water sample with an initial conductivity greater than 50μS / cm into the four leveled water chambers, making the upper surface of the water film flush with the upper edge of the water chamber, forming water films with thicknesses of 1mm, 2mm, 3mm, and 4mm in the four water chambers respectively. Place the phase change asphalt mixture disc sample on the water chambers and align the 8 sample through holes with the 8 water chamber through holes. Insert the indenter unit into the sample through hole and make the depth of each indenter cut consistent with the thickness of the water film below it. Rotate the indenter so that the conductivity probe faces the center of the sample. S3. Transfer the assembled sample and apparatus to a -5℃ refrigerator, connect the conductivity meter, and after 12 hours, plot the conductivity versus time curves for the four water film thicknesses. Take the end of the conductivity drop segment as the time t when black ice begins to condense. 0i (min), where i = 1, 2, 3, 4; the device was placed back into a constant temperature chamber at 20℃, and after 3 hours, the water film conductivity versus time curves in the four water chambers were plotted. The end of the conductivity surge segment was taken as the time t when the black ice completely melted. 1i (min); by (t) 11 -t 01 min、(t) 12 -t 02 min、(t) 13 -t 03 min、(t) 14 -t 04 The duration of black ice with thicknesses of 1 mm, 2 mm, 3 mm, and 4 mm on phase change asphalt mixtures was obtained by measuring 1 min. S4. Place the sample and apparatus back into the -5℃ refrigerator. For black ice with thicknesses of 1mm, 2mm, 3mm, and 4mm, respectively, at (t 01 +30)min、(t 02 +30)min、(t 03 +30)min、(t 04 At +30 min, loosen the screw inside one through hole of each sector-shaped water tank by 0.5 cm to 1 cm, and press the pressure head on it with a pressure gauge until the black ice breaks, thus obtaining the freezing strength S of the black ice. 0i After 12 hours, unscrew the screw inside the other through hole of each fan-shaped water tank, and use a pressure gauge to measure the freezing strength S of the four thicknesses of black ice. 1i .

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