An optical microscope-based in-situ characterization method of calcium sulfate whiskers in bitumen

Abstract

The application provides an optical microscope-based in-situ characterization method for calcium sulfate whiskers in asphalt, and relates to the technical field of material microscopic analysis, and comprises the following steps: S1: placing calcium sulfate whiskers in asphalt heated to a flow state, stirring, and obtaining an asphalt sample; S2: pretreating the asphalt sample; S3: placing a heated glass slide on the surface of the pretreated asphalt sample, and extracting a light-transmissive asphalt film; and S4: placing the glass slide with the asphalt film adhered thereon under an optical microscope for observation, and obtaining in-situ characterization results of the calcium sulfate whiskers in the asphalt. The glass slide is heated, the asphalt sample to be measured is extracted onto the glass slide, and a light-transmissive film is formed under the microscope, so that the purpose of observing the morphology of the calcium sulfate whiskers or other additives in the asphalt under the microscope is achieved.

Description

Technical Field

[0001] This invention relates to the field of materials microanalysis technology, and in particular to an in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy. Background Technology

[0002] In existing technologies, calcium sulfate whiskers are typically added to asphalt to improve its high-temperature stability, crack resistance, durability, and workability. The state of the calcium sulfate whiskers, such as their length, can affect the performance of the asphalt. When calcium sulfate whiskers are mixed into asphalt through mechanical stirring, the intensity or duration of the stirring can cause varying degrees of damage to the whiskers. Therefore, it is necessary to observe the state of the calcium sulfate whiskers in the asphalt after stirring under an optical microscope or electron microscope in order to adjust the appropriate mechanical stirring parameters.

[0003] In modern materials microstructure analysis, optical microscopy and electron microscopy are commonly used and efficient tools. For rigid materials, clear microstructural images can be obtained by preparing optical sections or thin sections. However, difficulties arise when observing viscous materials such as asphalt.

[0004] Existing techniques for characterizing the distribution of calcium sulfate whiskers in bitumen-based composites have the following limitations:

[0005] 1. When calcium sulfate whiskers are added to asphalt, they need to be melted by heat. During cooling, due to surface tension, the added calcium sulfate whiskers are encapsulated by the asphalt, and few whiskers are exposed on the surface. When observed with an electron microscope, only the morphological features of the asphalt surface can be observed. An optical microscope can observe the internal features of the object under test through its transmitted light. However, due to the opacity of asphalt, it is difficult to observe it with an optical microscope. Therefore, neither electron microscopes nor optical microscopes can observe the morphological features and distribution of calcium sulfate whiskers in asphalt.

[0006] As shown in patent CN 107037239 A, a molten asphalt sample is poured out and dropped onto the center of a preheated glass slide and spread evenly into a circle. The calcium sulfate whiskers in the asphalt are basically encapsulated. Due to the poor light transmittance of the asphalt, it cannot be observed under an optical microscope. Only the local surface features of the circular asphalt can be observed through an electron microscope, but the morphology and distribution of the calcium sulfate whiskers inside the asphalt cannot be obtained.

[0007] 2. Viscous materials like asphalt cannot be ground or polished like rigid materials, so they cannot be made into light slides or thin sections suitable for observation under optical or electron microscopes.

[0008] Currently, there is no effective method to clearly characterize the distribution of calcium sulfate whiskers inside asphalt while preserving the matrix structure. Therefore, there is an urgent need for an in-situ characterization method that can observe calcium sulfate whiskers in asphalt, requiring the sample to have an appropriate thickness to reflect the internal structure of the material, while minimizing structural disturbance during sample preparation. Summary of the Invention

[0009] The purpose of this invention is to provide an in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy. By heating a glass slide, the asphalt sample to be tested is extracted onto the glass slide to form a thin film that is transparent under a microscope, thereby achieving the purpose of observing the morphology of calcium sulfate whiskers or other additives in asphalt under a microscope.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention provides an in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy, comprising the following steps:

[0012] S1: Place calcium sulfate whiskers into asphalt heated to a fluid state, stir, and obtain an asphalt sample;

[0013] S2: Pretreatment of asphalt samples;

[0014] S3: Place the heated glass slide flat on the surface of the pretreated asphalt sample and extract the light-transmitting asphalt film.

[0015] S4: Place the glass slide with the asphalt film attached under an optical microscope for observation to obtain the in-situ characterization results of calcium sulfate whiskers in the asphalt.

[0016] Furthermore, based on the above technical solution, the temperature of the flowing asphalt is ≥130℃.

[0017] Furthermore, based on the above technical solution, the stirring speed in step S1 is 2000-3000 rpm, and the stirring time is 20-30 min.

[0018] Furthermore, based on the above technical solution, step S2 includes the following preprocessing steps:

[0019] The asphalt sample is dropped onto a flat carrier to form a circular raised spot with a diameter that matches the size of the glass slide.

[0020] Furthermore, based on the above technical solution, step S3 specifically includes the following steps:

[0021] Place the heated glass slide flat on the cooled circular raised spot and lift it up quickly within 0.5-1 second so that a layer of asphalt film adheres to one side of the glass slide.

[0022] Furthermore, based on the above technical solution, the asphalt film is a light-transmitting asphalt film with a thickness of 40-60μm.

[0023] Furthermore, based on the above technical solution, in step S3, the heated slide is obtained by holding the edge of a clean slide with tweezers and heating it at a temperature of 400-600℃ for 15-25 seconds.

[0024] Furthermore, based on the above technical solution, the temperature of the heated glass slide is 150-200℃.

[0025] Furthermore, based on the above technical solution, step S4 also includes:

[0026] Place the glass slide with the asphalt film adhered to it facing upwards on filter paper, cool it at room temperature, and then observe it under an optical microscope.

[0027] Furthermore, based on the above technical solution, observations are performed under an optical microscope using single-polarized light and / or cross-polarized light modes.

[0028] The present invention provides an in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy, which has the following advantages:

[0029] 1. This invention innovatively proposes a hot glass extraction technique, which enables in-situ observation of calcium sulfate whiskers in asphalt using an optical microscope. This technique causes minimal disturbance to the material structure, produces clear images, and meets the requirements for microscopic observation.

[0030] 2. This invention features a short process, simple operation, and low equipment requirements. It has a wide range of applications for characterizing the distribution of fillers such as calcium sulfate whiskers in asphalt. It can effectively solve the problem that currently, we can only rely on expensive instruments such as SEM and the observation results are not good. The entire detection process is simple, convenient and easy to implement, and has good feasibility. It has broad prospects in the application of calcium sulfate whisker products. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1This is a schematic diagram of the asphalt film provided by the present invention;

[0033] Figure 2 The image shows the morphology of calcium sulfate whiskers in asphalt as observed under an optical microscope in Embodiment 1 of the present invention.

[0034] Figure 3 The image shows the morphology of the original calcium sulfate whiskers observed under an optical microscope in Example 1.

[0035] Figure 4 The image shows the morphology of calcium sulfate whiskers observed under an optical microscope on the asphalt film prepared in Application Example 1.

[0036] Figure 5 The image shows the morphology of calcium sulfate whiskers observed under an optical microscope on the asphalt film prepared in Comparative Example 1.

[0037] Figure 6 A photograph of the finished asphalt film prepared in Example 1 of this invention;

[0038] Figure label:

[0039] 1. Glass slide; 2. Asphalt film. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0041] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0042] According to a first aspect of the present invention, an in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy is provided, comprising the following steps:

[0043] S1: Place calcium sulfate whiskers into asphalt heated to a fluid state, stir, and obtain an asphalt sample;

[0044] S2: Pretreatment of asphalt samples;

[0045] S3: Place the heated glass slide flat on the surface of the pretreated asphalt sample and extract the light-transmitting asphalt film.

[0046] S4: Place the glass slide with the asphalt film attached under an optical microscope for observation to obtain the in-situ characterization results of calcium sulfate whiskers in the asphalt.

[0047] Specifically, when the heated glass slide comes into contact with the surface of the asphalt sample, a layer of asphalt on the surface of the asphalt sample can be quickly melted and adhered to the heated glass slide to form an asphalt film. After the layer of asphalt on the surface of the asphalt sample melts, the calcium sulfate whiskers that were wrapped up due to the cooling of the asphalt can be exposed. Some of the calcium sulfate whiskers can adhere to the heated glass slide at the same time as the surface asphalt melts. The asphalt film formed has excellent light transmittance and can be observed under an optical microscope. The morphological characteristics and distribution of calcium sulfate whiskers in the asphalt film can be observed through transmitted light.

[0048] As an optional embodiment of the present invention, the temperature of the flowing asphalt is ≥130℃ (e.g., 150℃, 170℃, 200℃, etc.).

[0049] As an optional embodiment of the present invention, the stirring speed in step S1 is 2000-3000 rpm (e.g., 2300 rpm, 2500 rpm, 2700 rpm, etc.), and the stirring time is 20-30 min (e.g., 23 min, 25 min, 27 min, etc.).

[0050] Specifically, after visual inspection and preliminary instrument testing, the asphalt sample showed a highly homogeneous state in all parts; without limitation, the calcium sulfate whiskers were calcium sulfate whiskers prepared from metallurgical desulfurization gypsum, calcium sulfate whiskers prepared from power plant gypsum, or calcium sulfate whiskers prepared from rare earth white mud gypsum, etc.

[0051] In an optional embodiment of the present invention, step S2, the preprocessing includes the following steps:

[0052] After heating the asphalt sample to a fluid state, it is dripped onto a flat carrier such as a ceramic tile or glass plate, forming a circular raised spot with a diameter adapted to the size of the glass slide; after the circular raised spot cools, its surface is nearly flat; typically, without limitation, the standard glass slide width is usually 25 mm, then the diameter of the circular raised spot is ≤25 mm, such as 20 mm.

[0053] As an optional embodiment of the present invention, step S3 specifically includes the following steps:

[0054] Place the heated slide flat on the cooled circular raised spot and lift it quickly within 0.5-1 s (e.g., 0.6 s, 0.7 s, 0.8 s, 0.9 s, etc.). Figure 1 As shown, a layer of asphalt film 2 is adhered to one side of the glass slide 1.

[0055] As an optional embodiment of the present invention, the asphalt film is a light-transmitting asphalt film with a thickness of 40-60μm (e.g., 45μm, 50μm, 55μm, 57μm, etc.). This film has good light transmittance under an optical microscope and can be used to observe the morphology and distribution of calcium sulfate whiskers or other additives in asphalt.

[0056] As an optional embodiment of the present invention, in step S3, the heated slide is obtained by holding the edge of a clean slide with tweezers (avoiding contact with the central area) and heating it at a temperature of 400-600℃ (e.g., 450℃, 500℃, 550℃, 570℃, etc.) for 15-25s (e.g., 17s, 19s, 20s, 22s, 24s, etc.); typically, but not limited to, in the laboratory, the slide can be heated on the outer flame of an alcohol lamp, the temperature of which is 400-600℃.

[0057] As an optional embodiment of the present invention, the temperature of the heated glass slide is 150-200℃ (e.g., 160℃, 170℃, 180℃, 190℃, etc.).

[0058] Specifically, step S3 is crucial for successful sample preparation. It requires ensuring the heated glass slide is accurately placed flat on the smooth, raised, or circularly raised surface of the pretreated asphalt sample to facilitate the extraction of the thin film. Simultaneously, the heating temperature of the glass slide needs proper control. Too low a temperature may result in an excessively thick film, affecting observation clarity, while too high a temperature may cause oxidation of the asphalt and the generation of volatiles. It is recommended to conduct multiple practical training sessions before formal sample preparation to optimize the operating technique and ensure the film is translucent and of uniform thickness.

[0059] As an optional embodiment of the present invention, step S4 further includes:

[0060] Place the glass slide with the asphalt film adhered to it facing upwards on clean filter paper, allow it to cool at room temperature, and then observe it under an optical microscope. To ensure the quality of observation, avoid contamination of the film after sample preparation; do not touch it with your hands or allow it to come into contact with any object.

[0061] As an optional embodiment of the present invention, observation is performed under an optical microscope using single-polarized light and / or cross-polarized light modes.

[0062] Specifically, the asphalt film prepared by this invention is similar to a rock thin section and can be analyzed under an optical microscope using conventional thin section observation methods. It is suitable for both single-polarized and crossed-polarized light modes. To avoid missing calcium sulfate whiskers at the extinction position, it is recommended to combine single-polarized and crossed-polarized light for observation. When taking microscopic images, it is recommended to use the crossed-polarized light mode to effectively eliminate color unevenness caused by differences in film thickness.

[0063] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0064] Example 1

[0065] In this embodiment, the asphalt selected is 90# base asphalt, and the calcium sulfate whiskers are calcium sulfate whiskers prepared from metallurgical desulfurization gypsum.

[0066] S1: Heat the asphalt to a molten state, and then add calcium sulfate whiskers to the asphalt using a mechanical stirring method at a speed of 3000 rpm for 30 minutes to obtain an asphalt sample;

[0067] S2: Pretreatment of asphalt samples:

[0068] After heating the asphalt sample to a fluid state, it is dropped onto a flat glass plate to form a circular raised spot with a diameter of 20 mm that is adapted to the size of the glass slide (40 mm × 25 mm). After cooling, the surface of the circular raised spot is nearly flat.

[0069] S3: Hold the clean slide by its edges with tweezers (avoiding contact with the central area), heat it over the outer flame of an alcohol lamp (400-600℃) for 20 seconds, and while still hot, place the heated slide flat on the cooled circular raised spot, and quickly lift it within 0.5-1 second, so that a 40μm thick transparent bitumen film adheres to one side of the slide. Figure 6 As shown, it has excellent light transmittance;

[0070] S4: Place the glass slide with the asphalt film adhering to it facing upwards on clean filter paper, cool it at room temperature, and then place it under an optical microscope. Observe it using orthogonal polarization mode to obtain the in-situ characterization results of calcium sulfate whiskers in asphalt.

[0071] A typical observation result is as follows Figure 2 As shown (where the matte part is bitumen; the needle-like part is calcium sulfate whiskers), the calcium sulfate whiskers in bitumen are randomly distributed, with a length of 100-150 μm, a diameter of 1-2 μm, and an aspect ratio between 50:1 and 100:1.

[0072] Application Example 1: Observation of the effect of stirring on the destruction of calcium sulfate whiskers in asphalt

[0073] Calcium sulfate whiskers prepared from metallurgical desulfurization gypsum were observed under crossed polarized light. The results showed that the original whiskers were approximately 230-280 μm long, 1-3 μm in diameter, and had an aspect ratio of approximately 100:1 to 300:1. Their morphology is shown in the micrographs. Figure 3 As shown.

[0074] Using the in-situ characterization method of calcium sulfate whiskers in asphalt based on optical microscopy provided by this invention, calcium sulfate whiskers were added to 90# matrix asphalt and stirred at 3000 rpm for 50 min to prepare an asphalt sample. An asphalt film was then prepared according to the steps in Example 1. The film was observed under an optical microscope in single-polarized light mode. It was found that the calcium sulfate whiskers in the asphalt sample were uniformly and disorderedly distributed, with a significantly reduced length to below 50 μm, as shown in the photomicrograph. Figure 4 As shown.

[0075] The method provided by this invention allows for direct observation of whether calcium sulfate whiskers are destroyed during mechanical stirring:

[0076] The results showed that stirring at 3000 rpm for 50 minutes significantly damaged the length of calcium sulfate whiskers, making them less effective and reducing their performance. Therefore, it is recommended to optimize the process to shorten the stirring time.

[0077] Comparative Example 1

[0078] The main difference between this comparative example and Example 1 is that in step S3, the heating time is 10 seconds, while the remaining steps and technical parameters are the same as in Example 1.

[0079] In this comparative example, the heating time was too short, resulting in insufficient temperature of the glass slide. This led to a bitumen film thickness exceeding 100 μm during preparation. The excessive thickness of the film negatively impacted the clarity of the observations. Figure 5 As shown.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for in-situ characterization of calcium sulfate whiskers in asphalt based on optical microscopy, characterized in that, Includes the following steps: S1: Place calcium sulfate whiskers into asphalt heated to a fluid state, stir, and obtain an asphalt sample; S2: Pretreatment of asphalt samples; The pretreatment includes the following steps: dripping the asphalt sample onto a flat carrier to form a circular raised spot with a diameter adapted to the size of the glass slide; S3: Place the heated glass slide flat on the surface of the pretreated asphalt sample and extract the light-transmitting asphalt film. Specifically, the process involves placing a heated glass slide flat on a cooled circular raised spot and lifting it quickly within 0.5-1 second, so that a layer of asphalt film adheres to one side of the glass slide; the asphalt film is a light-transmitting asphalt film with a thickness of 40-60 μm. S4: Place the glass slide with the asphalt film attached under an optical microscope for observation to obtain the in-situ characterization results of calcium sulfate whiskers in the asphalt.

2. The method for in-situ characterization of calcium sulfate whiskers in asphalt based on optical microscopy according to claim 1, characterized in that, The temperature of the flowing asphalt is ≥130℃.

3. The in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy according to claim 2, characterized in that, The stirring speed in step S1 is 2000-3000 rpm, and the stirring time is 20-30 min.

4. The method for in-situ characterization of calcium sulfate whiskers in asphalt based on optical microscopy according to claim 1, characterized in that, In step S3, the heated slide is obtained by holding the edge of a clean slide with tweezers and heating it at a temperature of 400-600℃ for 15-25 seconds.

5. The in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy according to claim 4, characterized in that, The temperature of the heated glass slide is 150-200℃.

6. The method for in-situ characterization of calcium sulfate whiskers in asphalt based on optical microscopy according to claim 1, characterized in that, Step S4 also includes: Place the glass slide with the asphalt film adhered to it facing upwards on filter paper, cool it at room temperature, and then observe it under an optical microscope.

7. The in-situ characterization method for calcium sulfate whiskers in asphalt based on optical microscopy according to claim 6, characterized in that, Observations were performed under an optical microscope using single-polarized light and / or crossed-polarized light modes.

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