A contact-type asphalt pavement area water film thickness measuring device and method

Abstract

This application discloses a contact-type device and method for measuring the water film thickness of asphalt pavement, belonging to the technical field of asphalt pavement water film thickness testing. The measuring device provided by this invention includes a conductivity detection unit, a drive unit, and a data acquisition and processing unit. The conductivity detection unit employs multiple combinable conductivity probes, and the drive unit controls the probes to move vertically and uniformly via a stepper motor and a ball screw. During measurement, insulating silicone is first applied to the pavement to form a thin layer. The water film thickness is obtained by monitoring the two voltage signal abrupt changes generated when the probe passes through the air-water film interface and the water film-insulating silicone interface, calculating the time difference, and combining it with the moving speed. This invention effectively eliminates interference from environmental factors such as temperature and salinity, requires no pre-embedded sensors, does not damage the pavement, and enables simultaneous measurement at multiple points in a region, significantly improving the accuracy and efficiency of water film thickness measurement.

Description

Technical Field

[0001] This application belongs to the technical field of asphalt pavement water film thickness testing, specifically relating to a contact-type asphalt pavement area water film thickness measuring device and measurement method. Background Technology

[0002] While a well-developed highway network provides convenience for transportation and travel services, it also brings significant safety hazards. Water film thickness, as a crucial indicator affecting road safety and assessing road surface conditions, is vitally essential for road safety monitoring. Under adverse weather conditions such as rainfall, the water film formed by accumulated water on the road surface can affect visibility, reduce road surface skid resistance, and even trigger hydroplaning accidents. However, the contact critical surface for effective water film thickness is not clearly defined, and traditional measurement methods have significant shortcomings.

[0003] Currently, water film thickness measurement methods are divided into two categories: contact and non-contact. Contact methods include fiber optic detection, conductivity detection, and echo detection, which can directly identify road surface conditions. Non-contact methods include spectral intensity measurement, optical image analysis, and capacitance sensor measurement, some of which can achieve high-precision or area-specific measurements. All existing methods have shortcomings. In contact methods, fiber optic detection requires embedded sensors and has low accuracy under complex road conditions; conductivity detection is greatly affected by environmental factors; and echo detection requires pre-embedded sensors and has poor anti-interference capabilities. In non-contact methods, spectral measurement is easily affected by field-of-view interference; optical image analysis equipment is expensive and complex to install; and capacitance sensors are not suitable for road surfaces. Overall, these methods suffer from inconvenient installation and maintenance, insufficient detection accuracy, and high equipment costs. Therefore, this invention addresses these problems by developing a water film thickness detection device based on conductivity. Summary of the Invention

[0004] To address the problems of existing water film thickness measurement methods, which require burying sensors in the road, making installation and maintenance difficult, and the test results being greatly affected by the environment, thus failing to guarantee the accuracy of continuous detection, this application provides a contact-type asphalt pavement area water film thickness measurement device and method.

[0005] To achieve the above objectives, this application adopts the following technical solution: The first aspect of this application provides a contact-type asphalt pavement area water film thickness measuring device, comprising: A conductivity detection unit includes at least one conductivity probe. The conductivity probe includes an insulating probe body, a wire, and a resistor. One end of the insulating probe body is aligned with one end of the wire as the positive electrode of the conductivity probe. A resistor is connected in series on the wire, and the other end of the wire serves as the negative electrode of the conductivity probe. The driving unit includes a stepper motor and a guiding mechanism. The guiding mechanism is driven by the stepper motor, and the conductivity probe is fixedly connected to the guiding mechanism. The stepper motor is used to drive the ball screw to move the conductivity probe in the vertical direction. The data acquisition and processing unit is electrically connected to the conductivity detection unit and the stepper motor, respectively. It is used to control the vertical movement of the conductivity probe, acquire the voltage signal of the conductivity circuit in real time, and obtain the water film thickness at the test point based on the voltage signal.

[0006] Furthermore, the insulating probe body has an L-shaped structure, consisting of orthogonally fixed horizontal and vertical supports. The vertical support is 15-25cm long, and the top of the vertical support has a spring buffer section of 2-4cm in length to adapt to different road surface heights.

[0007] Furthermore, the horizontal support of the insulating probe body is provided with a fixing hole, through which the conductivity probe is fixedly connected to the slider of the ball screw.

[0008] Furthermore, the conductivity detection unit includes multiple conductivity probes, which are fixed in parallel to the slider of the ball screw through their respective fixing holes. The spacing between the conductivity probes can be adjusted according to the needs of the measurement area, so as to realize the simultaneous measurement of the water film thickness at multiple measurement points in the area.

[0009] Furthermore, the lower end of the insulating probe body is provided with a tapered tip, and the wire is fixed on the surface of the insulating probe body, with one end of the wire aligned with the tip of the insulating probe body.

[0010] Furthermore, it also includes an insulating housing, inside which both the stepper motor and the ball screw are housed; a limiting groove is formed on the side of the insulating housing, which is arranged vertically for the vertical movement of the conductivity probe.

[0011] A second aspect of this application provides a method for measuring the thickness of a water film in a contact-type asphalt pavement area, using the aforementioned contact-type asphalt pavement area water film thickness measuring device, comprising the following steps: Apply plastic insulating silicone to the surface of the asphalt pavement to be tested to form a thin insulating layer; Fully immerse the negative electrode of the conductivity probe in the water on the road surface, and vertically align the positive tip of the conductivity probe directly above the point to be measured. Start the data acquisition and processing unit to control the stepper motor to drive the ball screw and move the conductivity probe vertically downward; The voltage signal between the positive and negative electrodes of the conductivity probe is monitored in real time by the data acquisition and processing unit. The first voltage signal change generated when the positive electrode tip of the conductivity probe passes through the air-water film interface and the second voltage signal change generated when it passes through the water film-insulating silicone thin layer interface are identified and recorded. The time difference between the two signal changes is calculated. The thickness of the water film at the test point is calculated based on the vertical moving speed and time difference of the conductivity probe. After the measurement point is completed, the stepper motor is controlled to drive the conductivity probe to reset and the data acquisition and processing unit is turned off.

[0012] Furthermore, the specific calculation of the water film thickness at the measurement point based on the vertical moving speed of the conductivity probe and the time difference is as follows: WFT=T×V Where WFT is the water film thickness, T is the time difference between the two signal abrupt changes, and V is the vertical movement speed of the conductivity probe.

[0013] Furthermore, the coating thickness of the plastic insulating silicone is 0.1-0.5 mm.

[0014] Furthermore, according to the contact-type asphalt pavement area water film thickness measurement method according to claim 7, the conductivity probe needs to move downward at a constant speed when it descends vertically.

[0015] Compared with the prior art, this application has the following beneficial effects: The measuring device of this invention adopts a non-pre-embedded design, which can be directly placed on the road surface to be tested for detection. There is no need to pre-embed sensors during the road construction or maintenance stage, avoiding damage to the road structure. The position of the measuring point can be flexibly adjusted according to actual needs, making it suitable for on-site detection of various existing roads. By setting up a conductivity detection unit, the thickness of the water film is measured based on the change of relative conductivity, eliminating the influence of environmental factors on the measurement results and ensuring the accuracy of the measurement results. The drive unit can meet the high-precision measurement requirements of thin water films and also cope with situations where the road surface is deeply flooded. The measurement range covers most actual road conditions.

[0016] Furthermore, by setting up multiple sets of conductivity detection units, the water film thickness at any interval within any region can be measured simultaneously, overcoming the shortcomings of traditional water film thickness measuring devices that only measure at a single point and are not easy to move, thus greatly improving the efficiency of water film thickness measurement.

[0017] This invention provides a measurement method that leverages the excellent conductivity of electrolyte water, fully utilizing the significant conductivity difference between water and insulators. By monitoring two characteristic abrupt changes in the conductivity of the medium during the vertical penetration of the conductivity probe through the surface water to the asphalt layer, it effectively eliminates the interference of environmental factors such as road surface temperature and salinity on the measurement results in traditional direct measurement methods, significantly improving measurement accuracy and repeatability. This method eliminates the need for burying sensors inside the road, simplifying deployment without damaging the road structure. The measurement points can be flexibly adjusted, solving the problems of inconvenient maintenance and fixed measurement points in traditional contact measurements. Simultaneously, it enables simultaneous measurement at multiple points within a region, overcoming the shortcomings of traditional methods that only allow single-point measurements and are inefficient. It combines practicality and economy, and is suitable for various asphalt pavement water film thickness detection scenarios. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the water film thickness measuring device provided in this application; Figure 2 This is a schematic diagram of the structure of the conductivity probe provided in this application; Figure 3 This is a schematic diagram of the structure of the drive unit provided in this application; Figure 4 This is a schematic diagram of the ball screw structure provided in this application; Figure 5 This is a voltage change diagram of detection point A in an embodiment of this application; Figure 6 This is a voltage change diagram of detection point B in the embodiment of this application; Figure 7 This is a voltage change diagram at detection point C in the embodiments of this application; In the diagram, 1. Insulating probe body; 2. Wire; 3. Resistor; 4. Negative electrode; 5. Fixing hole; 6. Ball screw; 7. Slider; 8. Guide rail; 9. Stepper motor; 10. Insulating shell. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] This invention provides a contact-type asphalt pavement area water film thickness measurement device and method, aiming to solve the problems of existing water film thickness measurement technologies, such as the need for pre-embedded sensors, significant susceptibility to environmental factors, single-point measurement capability, high equipment cost, and low measurement accuracy. This invention utilizes the significant difference in conductivity between water, air, and insulating materials. It calculates the water film thickness by monitoring two characteristic voltage signal abrupt changes during the vertical penetration of a conductivity probe through surface water on the pavement. This effectively eliminates interference from environmental factors such as temperature and salinity, while also offering the technical advantages of simple device deployment, no need to damage the pavement structure, and the ability to perform simultaneous multi-point measurements across a region.

[0022] Existing technologies for measuring pavement water film thickness generally suffer from three major drawbacks, severely restricting their large-scale application in practical engineering. First, installation and maintenance costs are high. Mainstream contact methods such as fiber optic detection and microwave echo detection require sensors to be pre-embedded during road construction, which not only damages the original pavement structure but also limits the flexibility of measurement point placement, necessitating road excavation for later maintenance, resulting in extremely poor economic efficiency. Second, environmental adaptability is poor. Traditional conductivity detection directly measures the resistivity of accumulated water, which is significantly affected by environmental factors such as temperature, salinity, and impurity content, leading to large fluctuations in test results. Optical non-contact methods are easily affected by light, rain, snow, and water mist, causing a sharp drop in measurement accuracy in adverse weather conditions. Finally, measurement efficiency is low. Most existing equipment can only achieve single-point measurements and cannot simultaneously acquire the water film thickness distribution within a pavement area, failing to meet the demands of road safety monitoring for large-scale, high-density data.

[0023] Based on this, such as Figure 1 As shown, the contact-type asphalt pavement area water film thickness measuring device of this invention comprises three parts: a conductivity detection unit, a drive unit, and a data acquisition and processing unit, and also includes an insulating shell 10. The conductivity detection unit detects changes in the conductivity of the medium and converts them into a voltage signal; the drive unit drives the conductivity probe to move vertically; the data acquisition and processing unit controls the movement of the drive unit, acquires the voltage signal, and calculates the water film thickness at the measurement point; the insulating shell 10 protects the internal drive unit and electrical components, and also provides insulation.

[0024] like Figure 1 and Figure 2 As shown, the conductivity detection unit includes at least one conductivity probe. The conductivity probe includes an insulating probe body 1, a wire 2, and a resistor 3.

[0025] The insulating probe body 1 has an L-shaped structure, integrally formed from orthogonally fixed horizontal and vertical supports, and is manufactured using 3D printing technology. The length of the vertical support is 15-25cm, preferably 20cm; the top of the vertical support has a spring buffer section of 2-4cm in length, preferably 3cm, to adapt to different road surface heights, providing a buffer stage for the probe on low-lying surfaces, allowing the probe to descend fully. The lower end of the vertical support has a tapered tip, facilitating penetration of the water film and precise contact with the insulating silicone layer. The cross-section of the insulating probe body is a rectangle of 0.5mm × 0.3mm, ensuring sufficient structural strength while minimizing disturbance to the water film.

[0026] Wire 2 is uniformly adhered to the surface of the vertical support of the insulating probe body using hot melt adhesive. The lower end of wire 2 is aligned with the tapered tip of the insulating probe body, serving as the positive electrode of the conductivity probe. A resistor 3 is connected in series with wire 2, and the other end of wire 2 serves as the negative electrode 4 of the conductivity probe. When the positive electrode of the conductivity probe contacts the conductive medium, the positive electrode, the conductive medium, the negative electrode 4, and the resistor 3 together form a complete conductivity circuit. The data acquisition and processing unit detects the voltage change across the resistor 3 to reflect the change in conductivity in the circuit.

[0027] like Figure 1 , Figure 3 , Figure 4 and Figure 5 As shown, the drive unit includes a stepper motor 9 and a guide mechanism. The guide mechanism includes a ball screw 6, a slider 7, and a guide rail 8.

[0028] Stepper motor 9 is fixedly mounted on top of guide rail 9. The output shaft of stepper motor 9 is coaxially and fixedly connected to the upper end of ball screw 9 via a coupling. The lower end of ball screw 6 is rotatably mounted on the bottom of guide rail 8 via a bearing. Slider 7 is threadedly connected to ball screw 10, and slider 7 is also slidably engaged with guide rail 8. When stepper motor 9 drives ball screw 6 to rotate, slider 7 will move vertically along guide rail 8.

[0029] The horizontal support of the insulating probe body is provided with a fixing hole 5, through which the conductivity probe is fixedly connected to the slider 7. Specifically, the conductivity probe can be fastened to the slider 7 by passing a bolt through the fixing hole 5. This detachable connection method makes it easy to replace conductivity probes of different specifications or adjust the number and spacing of probes according to measurement requirements.

[0030] In a preferred embodiment, the conductivity detection unit includes multiple conductivity probes, which are fixed parallel to the slider 7 of the ball screw through their respective fixing holes 5. The spacing between the conductivity probes can be adjusted according to the requirements of the measurement area, thereby enabling simultaneous measurement of the water film thickness at multiple measurement points within the area, greatly improving measurement efficiency.

[0031] In one specific embodiment, stepper motor 8 is a two-phase stepper motor, and the compatible driver is the DM542 stepper driver from the Times Supergroup. The driver is used to receive pulse signals, direction signals, and enable signals sent by the data acquisition and processing unit. The driver 7 operates at DC 20-50V and is compatible with various models of two-phase stepper motors with a current of less than 3.0A (peak 4.2A) and an outer diameter of 42-60mm.

[0032] The data acquisition and processing unit is electrically connected to the conductivity detection unit and the stepper motor 8, respectively. In one specific embodiment, the data acquisition and processing unit uses the Arduino Uno development board, which has the advantages of small size, low cost, and ease of programming and expansion.

[0033] The data acquisition and processing unit is used to send control signals to the driver, controlling the stepper motor 8 to drive the ball screw at a set constant speed to move the conductivity probe vertically up and down; to acquire the voltage signal across the resistor 3 in the conductivity circuit in real time and convert it into a digital signal; to identify the two voltage signal abrupt changes generated when the conductivity probe passes through the air-water film interface and the water film-insulating silicone interface, and to record the time of the two abrupt changes; to calculate the time difference between the two signal abrupt changes, and to calculate the water film thickness at the test point based on the vertical moving speed of the conductivity probe; and to transmit the measurement data to the computer in real time for storage, display and subsequent analysis and processing.

[0034] like Figure 1 As shown, both the stepper motor 8 and the data acquisition and processing unit are housed inside the insulating housing 10. The insulating housing 10 is manufactured using 3D printing technology and is made of insulating plastic. This protects the internal mechanical structure and electrical components from damage caused by the external environment and prevents electric shock to operators, thus improving the safety of the device. Limiting slots are provided on the side of the insulating housing 10, arranged vertically for the vertical movement of the conductivity probe.

[0035] This invention also provides a method for measuring the thickness of a water film in a contact-type asphalt pavement area, using the aforementioned contact-type asphalt pavement area water film thickness measuring device, and includes the following steps: S1. Apply plastic insulating silicone to the surface of the asphalt pavement to be tested to form a thin insulating layer; S2. Fully immerse the negative electrode of the conductivity probe in the water on the road surface, and vertically align the positive tip of the conductivity probe directly above the point to be measured. S3. Start the data acquisition and processing unit, and control the stepper motor to drive the ball screw to move the conductivity probe vertically downward. S4. The voltage signal between the positive and negative electrodes of the conductivity probe is monitored in real time through the data acquisition and processing unit. The first voltage signal change generated when the positive electrode tip of the conductivity probe passes through the air-water film interface and the second voltage signal change generated when it passes through the water film-insulating silicone thin layer interface are identified and recorded. The time difference between the two signal changes is calculated. S5. Calculate the water film thickness at the test point based on the vertical moving speed and time difference of the conductivity probe. S6. After completing the measurement at the measuring point, control the stepper motor to drive the conductivity probe to reset and shut down the data acquisition and processing unit.

[0036] S1. Apply a plastic insulating silicone coating to the surface of the asphalt pavement to be tested, forming a uniform insulating thin layer. The coating thickness of the plastic insulating silicone is 0.1-0.5 mm, preferably 0.2 mm. Because asphalt pavement is hard and has a rough surface, it is difficult for conductivity probes to penetrate directly, and the conductivity of asphalt pavement is unstable, which may lead to an indistinct second voltage signal abrupt change. By applying plastic insulating silicone to the pavement surface to form a uniform insulating layer, it is ensured that when the positive tip of the conductivity probe contacts the insulating silicone, the conductivity circuit will be clearly broken, generating a clear second voltage signal abrupt change, thereby improving the accuracy of the measurement.

[0037] S2. Place the measuring device vertically on the road surface to be measured, and adjust the level of the measuring device to ensure that the conductivity probe can move vertically. Fully immerse the negative electrode 4 of the conductivity probe in the water on the road surface, ensuring that the negative electrode 4 is in full contact with the water; align the positive electrode tip of the conductivity probe vertically above the point to be measured, and adjust the initial distance between the positive electrode tip and the surface of the water film to ensure sufficient measurement stroke.

[0038] S3. Start the data acquisition and processing unit and set the operating parameters of the stepper motor 8, including the moving speed, pulse count, and sampling rate. In a specific embodiment, the pulse count of the driver 7 is set to 400, the step displacement is controlled to be 0.01mm, the controller frequency is 10Hz, the step displacement speed V is 0.1mm / s, and the sampling rate is 10Hz. Then, the stepper motor 8 is controlled to drive the ball screw to move the conductivity probe vertically downward at a set constant speed.

[0039] S4. During the descent of the conductivity probe, the voltage signal between the positive and negative terminals 4 of the conductivity probe is monitored in real time by the data acquisition and processing unit. The probe descent process is divided into three stages: Phase 1: The positive terminal of the conductivity probe has not yet come into contact with the water on the road surface, the conductivity circuit is in an open state, and the voltage signal across resistor 3 remains at a stable high level. Stage 2: When the positive tip of the conductivity probe comes into contact with the water on the road surface, the conductivity circuit is turned on, the voltage signal across resistor 3 drops sharply and remains at a stable low level. This is the first voltage signal change. The data acquisition and processing unit records the time T1 when this change occurs. Stage 3: The positive tip of the conductivity probe continues to descend and contacts the thin layer of insulating silicone on the road surface. The conductivity circuit is broken again, and the voltage signal across resistor 3 rises sharply and returns to a high level. This is the second voltage signal mutation. The data acquisition and processing unit records the time T2 when this mutation occurs.

[0040] The data acquisition and processing unit calculates the time difference T = T2 - T1 between the two signal abrupt changes. Then, based on the vertical moving speed V of the conductivity probe and the time difference T, it calculates the water film thickness WFT at the measurement point. The specific calculation formula is as follows: WFT=T×V Where WFT is the water film thickness in mm; T is the time difference between two signal abrupt changes in s; and V is the vertical moving speed of the conductivity probe in mm / s.

[0041] S6. After the measurement of the measuring point is completed, the data acquisition and processing unit controls the stepper motor 8 to reverse, driving the conductivity probe to rise and reset to the initial position. Then, the data acquisition and processing unit and the power supply are turned off, thus completing the measurement of the water film thickness at that point.

[0042] When simultaneous multi-point measurements are required, simply install multiple conductivity probes on slider 7, adjust the spacing between the probes, and then follow the steps described above. The data acquisition and processing unit will simultaneously acquire the voltage signals of each conductivity probe and calculate the water film thickness at each measurement point, thereby obtaining the water film thickness distribution within the measurement area.

[0043] Example 1 The surface water film thickness of an actual asphalt pavement section was measured and verified using the contact-type asphalt pavement area water film thickness measuring device of this invention. The experimental steps are as follows: Step 1: Connect the wiring of each component of the measuring device, check that the wiring contacts are good, and ensure that each component is working properly; Step 2: Select a test point every 30cm on the asphalt pavement to be tested. A total of 3 test points were selected along the driving direction and marked as A, B and C respectively. Step 3: Apply a plastic insulating silicone coating with a thickness of approximately 0.2 mm evenly to the road surface at the three test points to form an insulating thin layer; Step 4: Spray pure water evenly on the road surface to simulate rainfall, so that a water film of a certain thickness is formed on the road surface; immerse the negative electrode 4 of the 3 conductivity probes completely into the water on the road surface and measure at the same time; Step 5: Start the data acquisition and processing unit and set the parameters as follows: pulse count is 400, control step displacement is 0.01mm, controller frequency is 10Hz, step displacement speed V is 0.1mm / s, and sampling rate is 10Hz; record voltage changes. Step 6: Control the stepper motor 8 to drive the conductivity probe to descend vertically at a constant speed of 0.1 mm / s. When all probes have entered the insulating material, the voltage signal acquisition is completed. Step 7: After completing the measurement of the measuring point, control the stepper motor to drive the conductivity probe to reset and shut down the data acquisition and processing unit.

[0044] Experimental results are as follows Figure 5-7 As shown, the voltage signals detected at all three points during the test exhibited two distinct fluctuations. The time difference T between the two signal abrupt changes at point A was 53.5 s, at point B it was 53.0 s, and at point C it was 52.8 s. Using the formula WFT=T×V, the water film thicknesses at points A, B, and C were calculated to be 5.35 mm, 5.30 mm, and 5.28 mm, respectively. The experimental results demonstrate that the device of this invention can accurately and stably measure the water film thickness of asphalt pavement, and can achieve simultaneous measurement at multiple points with high measurement efficiency.

[0045] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this application, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A contact-type asphalt pavement area water film thickness measuring device, characterized in that, include: The conductivity detection unit includes at least one conductivity probe, which includes an insulating probe body (1), a wire (2) and a resistor (3). One end of the insulating probe body (1) is aligned with one end of the wire (2) as the positive electrode of the conductivity probe. The resistor (3) is connected in series on the wire (2), and the other end of the wire (2) serves as the negative electrode (4) of the conductivity probe. The driving unit includes a stepper motor (9) and a guide mechanism. The guide mechanism is connected to the stepper motor (9) in a transmission manner. The conductivity probe is fixedly connected to the guide mechanism. The stepper motor (9) is used to drive the ball screw (6) to move the conductivity probe in the vertical direction. The data acquisition and processing unit is electrically connected to the conductivity detection unit and the stepper motor (9) respectively. It is used to control the vertical movement of the conductivity probe, acquire the voltage signal of the conductivity circuit in real time, and obtain the water film thickness of the test point based on the voltage signal.

2. The contact-type asphalt pavement area water film thickness measuring device according to claim 1, characterized in that, The insulating probe body (1) is an L-shaped structure, consisting of a horizontally fixed support and a vertical support. The length of the vertical support is 15-25cm, and the top of the vertical support is provided with a spring buffer section with a length of 2-4cm to adapt to different road surfaces.

3. The contact-type asphalt pavement area water film thickness measuring device according to claim 2, characterized in that, The insulating probe body (1) has a fixing hole (5) on its horizontal support, and the conductivity probe is fixedly connected to the slider (7) of the ball screw (6) through the fixing hole (5).

4. The contact-type asphalt pavement area water film thickness measuring device according to claim 3, characterized in that, The conductivity detection unit includes multiple conductivity probes, which are fixed in parallel to the slider (7) of the ball screw (6) through their respective fixing holes (5). The spacing between each conductivity probe can be adjusted according to the needs of the measurement area, so as to realize the simultaneous measurement of the water film thickness at multiple measurement points in the area.

5. The contact-type asphalt pavement area water film thickness measuring device according to claim 1, characterized in that, The lower end of the insulating probe body (1) is provided with a tapered tip, and the wire (2) is fixed on the surface of the insulating probe body (1), with one end of the wire (2) aligned with the tip of the insulating probe body (1).

6. The contact-type asphalt pavement area water film thickness measuring device according to claim 1, characterized in that, It also includes an insulating shell (10), in which the stepper motor (9) and the ball screw (6) are both located inside the insulating shell (10); a limiting groove is opened on the side of the insulating shell (10), which is arranged in the vertical direction for the conductivity probe to move in the vertical direction.

7. A method for measuring the thickness of water film in a contact-type asphalt pavement area, characterized in that, The contact-type asphalt pavement area water film thickness measuring device according to claims 1-6 includes the following steps: Apply plastic insulating silicone to the surface of the asphalt pavement to be tested to form a thin insulating layer; The negative electrode (4) of the conductivity probe is completely immersed in the water on the road surface, and the positive electrode tip of the conductivity probe is vertically aligned with the top of the test point. Start the data acquisition and processing unit, control the stepper motor (9) to drive the ball screw (6) to drive the conductivity probe to descend vertically; The voltage signal between the positive and negative electrodes (4) of the conductivity probe is monitored in real time by the data acquisition and processing unit. The first voltage signal change generated when the positive tip of the conductivity probe passes through the air-water film interface and the second voltage signal change generated when it passes through the water film-insulating silicone thin layer interface are identified and recorded. The time difference between the two signal changes is calculated. The thickness of the water film at the test point is calculated based on the vertical moving speed and time difference of the conductivity probe. After the measurement point is completed, the stepper motor (9) is controlled to drive the conductivity probe to reset and the data acquisition and processing unit is turned off.

8. The method for measuring the thickness of water film in contact-type asphalt pavement areas according to claim 7, characterized in that, The specific calculation of the water film thickness at the measurement point, based on the vertical moving speed of the conductivity probe and the time difference, is as follows: WFT=T×V Where WFT is the water film thickness, T is the time difference between the two signal abrupt changes, and V is the vertical movement speed of the conductivity probe.

9. The method for measuring the thickness of water film in contact-type asphalt pavement areas according to claim 7, characterized in that, The coating thickness of the plastic insulating silicone is 0.1-0.5 mm.

10. The method for measuring the thickness of water film in a contact-type asphalt pavement area according to claim 7, characterized in that, The conductivity probe needs to move downwards at a constant speed when it descends vertically.

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