Multi-dimensional evaluation method for wheel non-sticking performance of emulsified asphalt

Abstract

The invention relates to a multi-dimensional evaluation method for the non-sticking performance of emulsified asphalt, which comprises the following steps: (1) substrate treatment: selecting a fiberboard as a base material, drying, polishing with abrasive paper to form a test surface with the roughness deviation of + / -0.5 mu m, and spraying a 0.08-0.12 mm silicone oil film to simulate a pavement demolding layer; (2) preparing a test piece: spraying emulsified asphalt at the precision of 480-520g / m, and maintaining at constant temperature and constant humidity until demulsification is completed; (3) simulating a rolling test: dynamically rolling the colored rubber strip-emulsified asphalt interface at the speed of 20-26 times / min by adopting a 590-610N load test wheel; and (4) detecting the adhesion amount: uncovering the rubber strip at a constant speed at an included angle of 55-65 degrees, and calculating the wheel adhesion rate through the mass difference. The method can comprehensively and accurately evaluate the non-sticking performance of the emulsified asphalt, has the characteristics of simple operation steps and capability of highly simulating the real condition of a road surface, not only ensures that the test result is reliable, but also is low in cost and short in time consumption, and has a great significance for research and development, quality control and reasonable application in practical engineering of the emulsified asphalt. And reliable technical support and data reference are provided.

Description

Technical Field

[0001] The present invention relates to the technical field of road material performance evaluation, and in particular to a multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt. Background Art

[0002] Asphalt pavement, the primary structural form of modern road engineering, typically utilizes a multi-layer paving system to achieve load transfer and durability assurance. Among these, interlayer bonding performance is a core factor determining the overall service quality of the pavement. As the key medium connecting the various structural layers, the bond strength of the adhesive layer directly affects the pavement's shear resistance, drainage efficiency, and fatigue resistance. Studies have shown that a 10% decrease in interlayer bond strength will directly lead to a 50% to 75% decrease in the fatigue life of the pavement structure and induce typical defects such as interlayer slippage, reflective cracking, and water damage. Actual engineering cases have shown that such defects can reduce the design life of asphalt pavements from 15 to 20 years to 7 to 8 years, causing huge economic losses and safety hazards.

[0003] In asphalt pavement construction, emulsified asphalt is the most widely used interlayer bonding material. By evenly spreading it between adjacent structural layers, it significantly enhances the pavement's overall bonding properties, effectively improving its durability and load-bearing capacity. However, conventional asphalt is highly temperature-sensitive, softening and significantly increasing its viscosity at high temperatures, making summer the peak season for asphalt pavement construction. During this period, after the emulsified asphalt is spread and cured, construction vehicles paving the upper mixture layer will compact the emulsified asphalt bonding layer as they drive. Due to the combined effects of asphalt viscosity and vehicle load, emulsified asphalt easily adheres to wheels, resulting in significant removal of the bonding layer material in the wheel track, causing a loss of the pavement bonding layer and subsequently leading to a series of pavement problems.

[0004] To address the issue of wheel sticking with emulsified asphalt, non-stick emulsified asphalt technology has been developed. However, accurately evaluating the non-stick properties of emulsified asphalt has become a key issue in the industry. Currently, testing methods for the non-stick properties of emulsified asphalt are primarily categorized into qualitative and quantitative approaches, both of which present significant drawbacks. Regarding qualitative evaluation, the traditional finger pressure method relies on tactile sensation to determine asphalt adhesion, which is subject to subjectivity, uncontrollable loading pressure, and inability to simulate the dynamic rolling conditions of construction vehicles. While the cohesimeter method can achieve quantitative measurement, the friction characteristics of the metal loading interface differ significantly from those of an actual tire (rubber material), and the method lacks the ability to simulate temperature environments, making it difficult to reflect the adhesion behavior under real-world construction scenarios. Regarding quantitative evaluation, the asphalt mixture rutting plate-based testing method, while capable of simulating wheel loads, is significantly affected by factors such as mixture gradation and molding process. Furthermore, specimen preparation requires a complex process involving mixing, molding, and curing, with a single test cycle lasting over 72 hours. The common defect of the above methods is that the test conditions deviate from the actual construction environment, the test results are highly discrete and have poor comparability, which makes it impossible to accurately guide the optimization of emulsified asphalt formula and construction quality control.

[0005] In this context, the industry urgently needs to develop a test method that can simultaneously meet the following core requirements: (1) realistically simulate the rubber material contact characteristics and dynamic rolling load of construction vehicle tires; (2) establish a standardized specimen preparation process to shorten the test cycle; and (3) achieve quantifiable multi-parameter testing under temperature-controlled conditions. The establishment of such a method will not only provide a scientific evaluation system for the non-stick performance of emulsified asphalt, but will also promote the research and development of tack layer materials, which has important engineering significance for extending the service life of pavement and reducing the maintenance cost throughout the entire life cycle.

[0006] The information disclosed in this background technology section is only used to deepen the understanding of the background technology of the present disclosure and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0007] In view of the technical problems existing in the prior art, the present disclosure provides a multi-dimensional evaluation method for the performance of emulsified asphalt non-stick wheels, which includes the following steps: (1) Substrate treatment: Use fiberboard as the substrate, divide at least one test area on its surface, dry and polish it to form a test surface with a roughness deviation of ±0.5μm, spray silicone oil to form a 0.08~0.12mm film and air dry it; (2) Specimen preparation: Spread the emulsified asphalt evenly on the test area, with the spreading amount controlled at 480-520 g / m², and maintain under constant temperature and humidity conditions until the emulsion breaks; (3) Simulated rolling test: After the pretreated rubber strip is placed in the wheel tracker and cured simultaneously with the specimen, the rubber strip is placed on the test area where the emulsified asphalt is spread. The test wheel with a load of 590~610N is used to roll back and forth at a rate of 20~26 times / min. (4) Adhesion detection: peel off the rubber strip at an angle of 55-65° and a speed of 50-70 mm / s, and calculate the adhesion rate based on the mass difference before and after rolling.

[0008] In some embodiments of the present disclosure, the fiberboard is any one of a glass fiber reinforced plastic board, a basalt fiberboard and a high-density fiberboard, and the pretreatment step includes: a) Divide the 300×300mm substrate into three 80×300mm test areas, leaving a 20mm gap between the two areas and an 8~12mm margin on the sides; b) Drying at 50-80°C until the mass change rate is less than 0.1%; c) Use sandpaper to grind the test surface at a constant pressure perpendicular to the test surface; d) After spraying silicone oil, air dry in an environment of 20-45°C and 40-60% relative humidity.

[0009] In some embodiments of the present disclosure, in step (1), the surface roughness is detected using a contact profilometer with a sampling length of 0.8 mm, an evaluation length of 4 mm, and an Ra value controlled within the range of 2.5 to 3.5 μm.

[0010] In some embodiments of the present disclosure, in step (2), the criteria for determining whether demulsification is complete are that the color and glossiness of the surface of the test piece differ from those of the standard sample by a color difference value ΔE ≤ 3, and the surface hardness reaches a Shore D hardness value of 35±2.

[0011] In some embodiments of the present disclosure, the rubber strip is any one of a colored natural rubber strip, a styrene-butadiene rubber strip and a nitrile-butadiene rubber strip, with a thickness of 1-3 mm and a surface hardness of 55-65 Shore A.

[0012] In some embodiments of the present disclosure, in step (2), the emulsified asphalt is first filtered through a 1.10-1.20 mm filter sieve and then spread; the spreading amount in each test area is precisely controlled to be 11.5-12.5 g; and the emulsion is cured and monitored for demulsification at 22-26°C and 45-55% humidity.

[0013] In some embodiments of the present disclosure, in step (3), the wheel tracking instrument parameter setting includes: a) Before testing, the temperature is set to 50~80℃ and the curing time is 3.5~4.5h; b) The test wheel shall be a solid rubber wheel with a rubber wheel surface hardness of 65~75 Shore A.

[0014] In some embodiments of the present disclosure, in step (4), the wheel sticking rate is calculated according to the following formula: , Among them, A is the wheel adhesion rate; B is the mass of the rubber strip before the test; C is the mass of the rubber strip after the test, and D is the total mass of the emulsified asphalt spread; S1 is the area of the test area where the emulsified asphalt is spread, and S2 is the area of the rubber strip.

[0015] According to another aspect of the present disclosure, a multi-area test mode is further included in step (5), wherein the three test areas divided on the front side of the substrate are tested in sequence by moving the test wheel of the wheel tracker or the position of the substrate, and then three test areas are divided on the back side of the same substrate and steps (2) to (4) are repeated, while the front side is covered at the same time to avoid detection errors.

[0016] One or more technical solutions provided in the embodiments of this application have at least any of the following technical effects or advantages: 1. Test Substrate Innovation and Performance Optimization: Fiberboard is used as the substrate for emulsified asphalt dispensing, boasting over 30% improved physical stability compared to traditional materials. After sandpaper polishing, the surface roughness can be adjusted from Ra 0.2 to 2.5 μm, enabling accurate simulation of various pavement structures, including asphalt concrete and open-air concrete concrete (OGFC). FTIR verification of the chemical compatibility of fiberboard with emulsified asphalt revealed no characteristic peak shift and a difference in interfacial contact angle of less than 5°, ensuring zero interference with material performance. The test substrate cost is 65% lower than stainless steel substrates, processing efficiency is 40% higher, and the test substrate can be reused over six times.

[0017] 2. Multi-Zone Integrated Testing System: The innovative multi-zone design (e.g., three zones, each 30 x 8 cm²) enables three parallel tests on the same sample, increasing testing density by 300%. The double-sided design allows a single plate to handle six different emulsified asphalt tests, significantly improving testing efficiency and reducing costs. Comparative testing has shown that this structure reduces inter-batch error from ±15% with traditional methods to within ±5%.

[0018] 3. Highly realistic tire simulator: Utilizing colored rubber strips (yellow / red / blue) with a Shore hardness of 55±3, the device boasts a strain recovery rate of >98%, resulting in a 200% improvement in contrast compared to traditional black rubber strips. A constant pressure roller system (0.7MPa±5%) simulates actual tire loads, achieving a 92% contact area match. The colored rubber strips increase asphalt residue detection sensitivity to 0.1g / m².

[0019] 4. Improved Engineering Suitability: The test cycle is shortened from the traditional minimum of 72 hours to less than 12 hours, reducing energy consumption by 70%. Actual engineering verification data shows that the emulsified asphalt selected by this method can reduce the adhesion rate of construction vehicle tires by 82%.

[0020] 5. Through material system reform and structural innovation, a rapid, accurate, and low-cost emulsified asphalt performance evaluation system has been established, providing key data support for the research and development of new tack coat materials. Authoritative organizations have verified that it can reduce the road construction quality accident rate by more than 45%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flowchart for evaluating the non-stick wheel performance of emulsified asphalt, wherein a is scratching, b is spreading, c is keeping warm, and d is rolling.

[0022] Figure 2 This is a real picture of the rubber strip adhering to asphalt after the test, with Example 1 on the left and Example 2 on the right. DETAILED DESCRIPTION

[0023] In order to better understand the technical solution of the present application, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0024] Unless otherwise specified, the instruments and equipment involved in the following examples are all conventional instruments and equipment; the preparation and detection methods involved are all conventional methods unless otherwise specified.

[0025] Example 1: Multi-dimensional evaluation of the performance of emulsified asphalt non-stick wheels Test object: non-stick wheel emulsified asphalt Testing equipment: basalt fiber substrate (300 mm × 300 mm), yellow rubber strip (300 mm × 50 mm), constant temperature and humidity chamber, wheel tracking instrument, electronic scale (accuracy 0.01 g), surface roughness meter, constant pressure sandpaper polishing device.

[0026] The specific implementation steps mainly include (see Figure 1 ): 1. Basalt fiber substrate pretreatment (1) Zoning design: Divide the 300mm×300mm basalt fiberboard into three test areas along the length direction. The size of a single area is 300mm (length) × 80mm (width). The interval between adjacent areas is 20mm, and the left and right areas are 10mm away from the edge of the board (see Figure 1 a); (2) Constant weight treatment: The substrate is placed in a 70°C forced air drying oven and weighed every hour until the mass difference between two consecutive times is ≤0.1% (to eliminate moisture interference); (3) Surface roughening: Use 80-grit sandpaper at a pressure of 0.2 MPa and a speed of 50 mm / s along the perpendicular fiber direction to control the roughness to Ra 1.2 ± 0.5 μm (corresponding to AC-13 asphalt pavement); (4) Formation of isolation layer: Evenly spray silicone oil (viscosity 350 cP) to form a 0.1 mm thick film (to block the direct interaction between emulsified asphalt and fiberboard and prevent its penetration), and ventilate and dry at room temperature.

[0027] 2. Precise spreading of emulsified asphalt (1) Sample filtration: Filter the emulsified asphalt through a 1.18 mm square hole sieve and let it stand for 15 minutes to defoam; (2) Quantitative spreading: Use a precision brush to evenly spread a total of 36.0 g (12.0 g per area) of emulsified asphalt on three test areas at a standard spreading rate of 500 g / m² in three times. The spreading area error is ±2%. (3) Demulsification determination: Place the sprayed substrate in a constant temperature and humidity chamber at 25°C / 50%RH, and compare it with a standard demulsification sample (grey-mat color, no fingerprint residue when touched) every hour until an equivalent demulsification state is reached.

[0028] 3. Preparation of colored rubber strips (1) Material cutting: Use yellow styrene-butadiene rubber strips with a Shore hardness of 55±3 and cut them into 300mm×50mm specifications; (2) Initial weighing: Use an electronic scale with an accuracy of 0.01g to record the mass B of a single piece. The data repeatability error is ≤0.05%.

[0029] 4. Environmental simulation and maintenance (1) Place the substrate and rubber strip in a wheel tracking chamber at 60°C for 4 hours (simulating high-temperature paving in summer); (2) Temperature control accuracy is ±0.5℃, and humidity is maintained at ≤30%.

[0030] 5. Dynamic rolling simulation (1) Set the test wheel parameters: linear speed 0.5 m / s (corresponding to a round trip frequency of 25 times / min), load 600 N (equivalent to 1 / 2 of the standard double-wheel load); (2) Place the rubber strip precisely on the test area and start the test wheel to roll it 10 times (simulating the number of rolls in the initial rolling stage); (3) After rolling, remove the rubber strip at an angle of 60° and a constant speed of 60 mm / s, and simultaneously observe or photograph the adhesion status.

[0031] 6. Quantitative Analysis of Adhesion Amount (1) Weigh the mass C of the rubber strip twice; (2) Calculate the wheel sticking rate according to the formula: , Among them, A is the wheel adhesion rate; B is the mass of the rubber strip before the test; C is the mass of the rubber strip after the test, and D is the total mass of the emulsified asphalt spread; S1 is the area of the test area where the emulsified asphalt is spread, and S2 is the area of the rubber strip.

[0032] (3) Repeat the test three times and take the average value. When the single deviation is greater than 5%, the data review mechanism is triggered.

[0033] The experimental test structure is shown in Table 1.

[0034] Multi-area continuous testing (1) The test wheel is automatically translated by 80 mm (single zone width + interval) through the wheel tracking instrument displacement module to switch to the adjacent test zone; (2) A total of 6 types of emulsified asphalt tests were completed on the front and back of the single board (a single board can be tested for 3 types at a time. In the second test, the surface where the emulsified asphalt was first spread was covered with newspaper, and then the emulsified asphalt was spread again for the test). The test efficiency is greatly improved compared with the traditional single-point method.

[0035] Technical effect verification: The dispersion of the three-zone test data is ≤3.2%, proving that the homogenization treatment of the fiberboard surface is effective; the yellow rubber strip makes the 0.1g adhesion level visible to the naked eye ( Figure 2 Left), the detection sensitivity is greatly improved compared to the black rubber strip; the efficiency is increased by 400% compared to the traditional single-sample single test.

[0036] As can be seen from the above, this embodiment successfully achieves high-throughput and high-precision evaluation of the non-stick wheel performance of emulsified asphalt, providing a reliable basis for engineering material selection.

[0037] Example 2: Multi-dimensional evaluation of the performance of emulsified asphalt non-stick wheels Test object: Ordinary emulsified asphalt Testing equipment: basalt fiber substrate (300 mm × 300 mm), yellow rubber strip (300 mm × 50 mm), constant temperature and humidity chamber, wheel tracking instrument, electronic scale (accuracy 0.01 g), surface roughness meter, constant pressure sandpaper polishing device.

[0038] The specific implementation steps mainly include (see Figure 1 ): 1. Basalt fiber substrate pretreatment (1) Partition design: Use the three-zone division standard of Example 1 (single zone 300mm×80mm, interval 20mm, margin 10mm) to ensure consistency of test conditions; (2) Constant weight treatment: The substrate is dried at 70°C with forced air until the mass fluctuation is ≤ 0.1% (eliminating the influence of the substrate's water absorption on the emulsified asphalt demulsification rate); (3) Surface roughening: Use 80-grit sandpaper at a pressure of 0.2 MPa and a speed of 50 mm / s to grind the surface to a roughness of R a =1.2±0.5μm (maintaining the road surface simulation consistency with Example 1); (4) Formation of isolation layer: Spray silicone oil film (thickness 0.1mm±5%) and ventilate and dry at room temperature.

[0039] 2. Precise spreading of emulsified asphalt (1) Sample filtration: Ordinary emulsified asphalt was filtered through a 1.18 mm sieve and allowed to stand for 15 minutes to defoam; (2) Quantitative coating: Use a precision brush to apply the coating in three times at a standard spreading rate of 500 g / m², with a total mass of 12.0 g per area (error ± 2%); (3) Demulsification determination: In a 25°C / 50%RH environment, compare the demulsification standard sample (gray-brown, matte surface and no plastic deformation when pressed) every hour until an equivalent demulsification state is reached.

[0040] 3. Preparation of colored rubber strips (1) Material cutting: Use yellow styrene-butadiene rubber strips (Shore hardness 55±3) from the same batch as in the example, with a specification of 300 mm × 50 mm; (2) Initial weighing: Use an electronic scale with an accuracy of 0.01g to record the mass B. The range of repeated weighing should be ≤0.03g.

[0041] 4. Environmental simulation and maintenance (1) The substrate and rubber strips were cured in a wheel rutting machine at 60°C for 4 h (simulating high-temperature paving conditions); (2) Humidity should be controlled at ≤30% to avoid water vapor affecting the adhesion of the asphalt-rubber interface.

[0042] 5. Dynamic rolling simulation (1) Test wheel parameters: linear speed 0.5 m / s (25 times / min round trip), load 600 N (equivalent to 1 / 2 standard axle load); (2) After rolling 10 times, remove the rubber strip at a 60° angle and a constant speed of 60 mm / s, and simultaneously collect adhesion images ( Figure 2 The middle right picture shows a typical adhesion morphology).

[0043] 6. Quantitative Analysis of Adhesion Amount (1) Weigh the mass C of the rubber strip twice; (2) Calculate the wheel sticking rate according to the formula in Example 1: (3) The allowable deviation of three parallel tests is ≤8% (the adhesion amount of ordinary asphalt fluctuates greatly).

[0044] The test results are shown in Table 1.

[0045] 7. Multi-area continuous testing (1) Automatically switch the test area through the wheel tracking instrument displacement module (single translation 80mm); (2) Complete three sets of ordinary asphalt tests on one side of the single board (conducted simultaneously with the non-stick wheel asphalt comparison test).

[0046] Table 1 Emulsified asphalt wheel adhesion test results Note: The visual grade is divided according to JTG E20-2011, from Grade I (no adhesion) to Grade V (severe adhesion).

[0047] Technical effect verification: The average wheel sticking rate of ordinary emulsified asphalt reached 18.9%, which was significantly higher than the 1.7% of the non-sticking asphalt in Example 1, proving that the method can effectively distinguish the performance differences of emulsified asphalt; the dispersion of the three-zone test data is ≤6.5%, reflecting the test volatility characteristics of ordinary emulsified asphalt due to the low material homogeneity; the yellow emulsified rubber strip clearly shows the large area of asphalt adhesion ( Figure 2 The color-coded image (right) contrasts sharply with the sporadic adhesion of the non-stick emulsified asphalt, validating the engineering practicality of the color-coded detection method. Combining qualitative and quantitative analysis results, the proposed method can comprehensively and accurately assess the non-stick properties of emulsified asphalt, providing reliable technical support and data reference for the research and development, quality control, and practical application of emulsified asphalt in practical engineering projects.

Claims

1. A multi-dimensional evaluation method for the performance of emulsified asphalt non-stick wheels, comprising the following steps: (1) Substrate treatment: Use fiberboard as the substrate, divide at least one test area on its surface, and after drying and polishing, form a test surface with a roughness deviation of -0.5~0.5μm. Spray silicone oil to form a 0.08~0.12mm film and air dry it; (2) Specimen preparation: Spread the emulsified asphalt evenly on the test area, with the spreading amount controlled at 480-520 g / m², and maintain under constant temperature and humidity conditions until the emulsion breaks; (3) Simulated rolling test: After the pretreated rubber strip is placed in the wheel tracker and cured simultaneously with the specimen, the rubber strip is placed on the test area where the emulsified asphalt is spread. The test wheel with a load of 590~610N is used to roll back and forth at a rate of 20~26 times / min. (4) Adhesion detection: peel off the rubber strip at an angle of 55-65° and a speed of 50-70 mm / s, and calculate the adhesion rate based on the mass difference before and after rolling.

2. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: In the step (1), the fiberboard is any one of glass fiber reinforced plastic board, basalt fiberboard and high-density fiberboard, and the pretreatment steps include: a) Divide the 300×300mm substrate into three 80×300mm test areas, leaving a 20mm gap between the two areas and an 8~12mm margin on the sides; b) Drying at 50-80°C until the mass change rate is less than 0.1%; c) Use sandpaper to grind the test surface at a constant pressure perpendicular to the test surface; d) After spraying silicone oil, air dry in an environment of 20-45°C and 40-60% relative humidity.

3. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: In the step (1), the surface roughness is detected by using a contact profilometer, with a sampling length of 0.8 mm, an evaluation length of 4 mm, and an Ra value controlled in the range of 2.5 to 3.5 μm.

4. The multi-dimensional evaluation method for the non-stick performance of emulsified asphalt wheels according to claim 1, characterized in that: In step (2), the demulsification completion judgment standard is that the color difference value ΔE between the surface color and glossiness of the test piece and the standard sample is ≤3, and the surface hardness reaches the Shore D hardness test value of 33~37.

5. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: The rubber strip is any one of a colored natural rubber strip, a styrene-butadiene rubber strip and a nitrile-butadiene rubber strip, has a thickness of 1-3 mm and a surface hardness of 55-65 Shore A.

6. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: In step (2), the emulsified asphalt is first filtered through a 1.10-1.20 mm filter sieve and then spread; the spreading amount in each test area is precisely controlled to be 11.5-12.5 g; and the emulsion is cured and monitored for demulsification at an environment of 22-26°C and 45-55% humidity.

7. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: In step (3), the wheel tracking instrument parameter setting includes: a) Before testing, the temperature is set to 50~80℃ and the curing time is 3.5~4.5h; b) The test wheel shall be a solid rubber wheel with a rubber wheel surface hardness of 65~75 Shore A.

8. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: In step (4), the wheel sticking rate is calculated according to the following formula: ， Among them, A is the wheel adhesion rate; B is the mass of the rubber strip before the test; C is the mass of the rubber strip after the test, and D is the total mass of the emulsified asphalt spread; S1 is the area of the test area where the emulsified asphalt is spread, and S2 is the area of the rubber strip.

9. The multi-dimensional evaluation method for the non-stick wheel performance of emulsified asphalt according to claim 1, characterized in that: The method further includes step (5) a multi-area test mode, wherein the three test areas divided on the front side of the substrate are tested in sequence by moving the test wheel of the wheel tracker or the position of the substrate, and then three test areas are divided on the back side of the same substrate and steps (2) to (4) are repeated, while the front side is covered at the same time to avoid detection errors.

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