A method for measuring the contact angle of porous steel slag

Abstract

The present invention belongs to the technical field of adhesion performance evaluation of road construction materials, and relates to a method for measuring the contact angle of porous steel slag. The method for measuring the contact angle of porous steel slag described in the present invention includes: making, polishing, and testing a steel slag section; wherein the making of the steel slag section includes: first mixing the porous steel slag with an additive, using a Marshall compactor to make a cylindrical specimen similar to a Marshall specimen, and cutting it after conditional curing. The method for making the contact angle specimen described in the present invention has the characteristics of being more convenient and safer to operate, having a larger specimen output, and being easier to conduct multiple parallel samples. This method can solve the problem of the difficulty in measuring the contact angle when waste steel slag replaces natural stone as aggregate, thereby helping to more accurately evaluate the asphalt-aggregate interface adhesion performance of asphalt mixtures using construction waste as aggregate, and is more conducive to its promotion and application.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesion performance evaluation of road construction materials and relates to a method for measuring the contact angle of porous steel slag. Background Art

[0002] Asphalt mixture, a road construction material, is made by mixing aggregate and asphalt binder. Due to low drying temperatures, moisture in the aggregate may not be completely removed, accumulating at the interface between the aggregate and asphalt, affecting the bond between the aggregate and asphalt. This can lead to loosening and flaking of the asphalt pavement, a phenomenon known as water damage.

[0003] The main basis for the mechanism of water damage is adhesion theory. Existing technologies have proposed a variety of methods for testing the adhesion performance between asphalt and aggregate, but their accuracy is poor.

[0004] To this end, CN105806747A discloses a method for measuring asphalt-aggregate interfacial adhesion, comprising: A. selecting three test liquids insoluble in asphalt and with known surface energies; B. heating the asphalt, or, and warm mix agent, until fluid, and pouring them onto a flat plate, cooling them to form smooth surfaces, and polishing the aggregate into two parallel, smooth surfaces; C. dropping the three liquids onto the smooth surfaces formed by the asphalt, warm mix agent, or aggregate in step B, and measuring the contact angles of the three test liquids on the asphalt, aggregate, or, warm mix agent surfaces; D. calculating the surface energies of the asphalt, aggregate, or, warm mix agent; E. constructing adhesion models for different systems and calculating their adhesion work; and F. establishing energy parameters to evaluate the effects of additives on asphalt-aggregate adhesion. The steps are performed in the order of A, B, CF or B, A, CF. Test results show that this method significantly improves the accuracy of asphalt-aggregate adhesion work evaluation.

[0005] It is worth noting that the aggregates mentioned in the above methods are all natural stones such as limestone and basalt. Such natural stones can usually be cut and polished by conventional cutting machines to obtain a smooth surface that meets the requirements of the contact angle test. However, the road industry is currently constantly exploring the use of low-carbon and environmentally friendly materials, such as the use of recycled aggregates, waste steel slag and other construction waste instead of natural base materials. As for waste steel slag, since it is steelmaking residue that is cooled and precipitated after high-temperature forging (molten state), it contains a variety of elemental components with large differences, so most of them have porous structures and various shapes. When this type of waste steel slag is cut and polished using a conventional cutting machine, the steel slag is difficult to fix, the cutting is more dangerous, the processing takes a long time, and the porous holes make it difficult to polish out the smooth plane test surface required for the contact angle test.

[0006] Based on this, the present invention is proposed. Summary of the Invention

[0007] To address the difficulty of fabricating scrap steel slag into test specimens that meet contact angle testing requirements, the present invention proposes a method for measuring the contact angle of porous steel slag. By processing the porous steel slag, the present invention creates a test surface that meets the requirements of the contact angle test. This allows for accurate measurement of the contact angle of porous steel slag, thereby facilitating more accurate evaluation of the asphalt-aggregate interface adhesion performance of asphalt mixtures using construction waste as aggregate, further facilitating their widespread application.

[0008] The contact angle measurement method of porous steel slag described in the present invention includes: making, polishing and testing a steel slag cross-section; wherein the making of the steel slag cross-section includes: first mixing the porous steel slag with an additive, using a Marshall compactor to make a cylindrical specimen similar to a Marshall specimen, and then cutting it after conditional curing.

[0009] The present invention is based on the inspiration of the Marshall specimen. The waste porous steel slag is mixed with additives, and a cylindrical specimen similar to the Marshall specimen is made using a Marshall compactor. The steel slag of different sizes and shapes can be effectively fixed to prevent it from loosening; then a large-scale cutting machine (equipped with a safety cover) dedicated to the Marshall specimen is used to cut it. This not only makes the cutting process safer, but also can cut out more and more uniform thin slices compared to the traditional contact angle specimen production method, reduces the difficulty of later grinding, and is more conducive to later grinding of its roughness. In addition, the use of this specimen production method also increases the output of specimens, making it easier to conduct multiple parallel tests. In short, the present invention obtains the steel slag cross-section in the above-mentioned more convenient and efficient way, effectively solving the problem that the existing waste steel slag is difficult to conduct contact angle tests as aggregate.

[0010] As is well known, the Marshall test is used to determine the optimal asphalt-to-aggregate ratio in asphalt mixtures. Compared to the adhesion performance evaluation method and contact angle test described in this invention, the Marshall test differs in purpose, detection criteria, and testing methods. Prior to this application, the prior art did not provide any technical guidance or inspiration regarding the interchangeability or reference between the two test specimens. Therefore, the present invention's application of the Marshall test specimen preparation method to the production of contact angle specimens for scrap steel slag is a first in the field.

[0011] On the premise of obtaining the above-mentioned steel slag cross-section, the present invention has no special requirements for the binder (such as polyurethane, asphalt) selected when preparing the mixture, and has no special requirements for the gradation of the mixture. It is only necessary to ensure that the prepared cylindrical specimens meet the minimum use requirements of Marshall specimens (such as the oil-stone ratio / binder-stone ratio meets the use requirements).

[0012] However, considering the convenience of preparing and curing at room temperature, the present invention uses polyurethane as the binder. This not only eliminates the need for preheating the asphalt, but also shortens the time required to achieve the required strength for testing the physical and mechanical properties of the mixture (i.e., ensuring that the specimen does not fall apart). Generally speaking, normal natural curing takes one week, while accelerated curing only takes about four days, significantly saving time.

[0013] As one of the specific embodiments of the present invention, polyurethane is used as the binder, and the mass of the polyurethane accounts for 6-7% of the mass of the porous steel slag. The mass of the Marshall test piece is controlled to be 1200-1250g.

[0014] The additive also includes a catalyst, which is liquid phenylmercuric acetate. The mass of the catalyst accounts for 1% of the mass of the polyurethane. The catalyst accelerates the reaction of the polyurethane under the influence of external factors, thereby shortening the curing time.

[0015] The size (specification) of the cylindrical specimen is the standard Marshall specimen size, such as a cylinder of φ101.6mm×63.5mm, and its gross volume density is 2.85g / cm 3 about.

[0016] Furthermore, for cylindrical specimens containing porous steel slag, conventional curing methods in the field can be used. This involves curing the cylindrical specimen at room temperature, either indoors or outdoors, away from rain. Curing typically takes about a week, ensuring the specimen does not fall apart during cutting.

[0017] The present invention can also adopt an accelerated curing method, that is, the cylindrical specimen is first cured indoors for one day, then placed in an oven at 80°C for curing on the second and third days, and then taken out on the fourth day and cured indoors at room temperature.

[0018] The present invention enables the cylindrical specimen to reach a certain strength through curing, and can be used for physical and mechanical property tests (such as indirect tensile test, etc.).

[0019] Furthermore, the cutting process utilizes a conventional Marshall specimen cutter, producing slices with a thickness of 4-6 mm. For larger coarse aggregates, specimen slices of approximately 5 mm allow for the utilization of both the front and back sides, facilitating parallel testing of the same aggregate. Due to the high cutting precision of the conventional Marshall specimen cutter, the protective cover can be lowered after securing the fixture without manual intervention, ensuring high safety. Furthermore, the cut roughness and surface integrity can be controlled, resulting in high-quality specimens.

[0020] Furthermore, the polishing is achieved by sandpaper of different mesh sizes, and sandpaper of different mesh sizes has an impact on the roughness of the cross-section of the slag. Generally, the larger the mesh size, the finer the surface of the specimen after sandpaper polishing, and the more types of mesh sizes used for sandpaper polishing, the better the effect. However, improper grading of sandpaper mesh will affect the polishing effect or cause the polishing time to be too long. For this reason, the present application controls the mesh size grading of the sandpaper to be: 120, 400, 600, 1000, 1500, 2000, 4000 mesh; during specific operations, use sandpaper of 120, 400, 600, 1000, 1500, 2000, 4000 mesh to polish and polish it respectively, so that the surface roughness of the specimen meets the test requirements.

[0021] The contact angle test is to drop the reagent on the surface of the object to be tested, so there are certain requirements for the surface roughness of the object to be tested. If the object to be tested is absolutely flat, its surface energy and each component can be calculated using the formula; if the object to be tested is hydrophilic (the contact angle is less than 90°), the greater the roughness, the smaller the contact angle. Therefore, in order to ensure that the contact angle of multi-porous steel slag can be accurately measured, the roughness of the object is usually polished as small as possible, but this also increases the difficulty of polishing. Taking all factors into consideration, the present invention limits the roughness value Ra of the steel slag section to less than 0.1μm.

[0022] Preferably, for small aggregates that are not flat after cutting, you can consider using plasticine to level them. Figure 3 shown.

[0023] Preferably, after the polishing is completed, the surface of the specimen is first cleaned with distilled water to remove residues such as slag and then cleaned with anhydrous ethanol. The specimen is then placed in a (105±5)°C constant temperature drying oven and dried for 24 hours before being cooled to room temperature for use.

[0024] The contact angle test described in this invention uses the sessile drop method to measure the static contact angle of the aggregate. The standard reagents used in the test are distilled water, formamide, and ethylene glycol. Compared to other standard solutions, these three reagents offer greater stability at room temperature, exhibit significantly different liquid surface free energy values, and exhibit no physical or chemical reactions with the scrap slag aggregate, thus enhancing the accuracy of subsequent calculations of the aggregate's surface energy and component values.

[0025] By substituting the contact angle obtained from the test into the asphalt-aggregate interface adhesion performance determination method described in CN105806747A, the asphalt-aggregate interface adhesion performance when waste steel slag is used instead of natural stone as aggregate can be evaluated.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The method for making the contact angle specimen of the present invention is more convenient. The Marshall compactor and the large cutting machine for cutting the Marshall specimen are conventional equipment in the road or building materials fields and are easily available.

[0028] 2. The contact angle test specimen fabrication method described in the present invention is safer. Previously, smaller steel slag specimens placed directly on a cutting machine for cutting and grinding were difficult to secure due to their porous structure and diverse shapes, posing a certain risk. However, by preparing them into cylindrical Marshall test specimens, the steel slag aggregate within them can be effectively secured, preventing it from loosening. The presence of a safety shield during cutting also makes the steel slag section safer, better securing the waste slag for cutting more uniform slices and facilitating subsequent grinding to achieve a smoother surface.

[0029] 3. The contact angle test specimen production method of the present invention has a large test specimen output, making it easier to conduct multiple parallel tests. The cylindrical specimen is cut into specimen slices of approximately 5 mm. The flatness and roughness of the slices obtained by the same knife are highly consistent. At the same time, because the slices are thin, both the front and back sides can be used, facilitating parallel testing of the same aggregate.

[0030] 4. For other small pieces of aggregate that are uneven after cutting, you can also consider using plasticine to level them, which is simple and easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a photo of the specimen slice.

[0032] Figure 2 This is a photo of unprocessed waste steel slag.

[0033] Figure 3 For cylindrical specimens.

[0034] Figure 4 This is a cross-sectional photo of the specimen after cutting.

[0035] Figure 5 Schematic diagram of leveling small pieces of aggregate that are uneven after cutting. DETAILED DESCRIPTION

[0036] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0037] Example 1

[0038] This embodiment provides a method for measuring the contact angle of porous steel slag, comprising:

[0039] (1) Production of slag cross section:

[0040] Since the morphology of steel slag is very different and the surface is loose and porous, the steel slag particles with larger particle size (such as Figure 2), first mix it with polyurethane, and use Marshall compaction instrument to make a cylindrical specimen similar to Marshall specimen, such as Figure 3 As shown; the mass of the polyurethane accounts for 7% of the mass of the porous steel slag.

[0041] The cylindrical specimen is subjected to conditional curing, which can be conventional curing or accelerated curing. Through curing, the strength of the cylindrical specimen can meet the requirements of physical and mechanical property testing.

[0042] Then, the cylindrical specimen after conditional oxidation is cut using a Marshall specimen cutting machine to obtain slices of about 5 mm. Figure 4 shown.

[0043] (2) Polishing:

[0044] The obtained slices were ground and polished using 120, 400, 600, 1000, 1500, and 2000 grit sandpaper, respectively, to ensure that the surface roughness of the aggregate met the test requirements.

[0045] After polishing, the surface of the slice was cleaned with distilled water to remove slag and other residues, and then cleaned with anhydrous ethanol. Then, it was placed in a constant temperature drying oven at (105±5)℃ and dried for 24 hours, and then cooled to room temperature for use.

[0046] The obtained thin-film specimens Figure 1 As shown, the area inside the box meets the requirements of the contact angle test.

[0047] For other small pieces of aggregate that are uneven after cutting, you can also consider using plasticine to level them, such as Figure 5 shown.

[0048] (3) Testing;

[0049] The DSA100 contact angle measuring instrument produced by KRUSS Company of Germany was used. The test temperature was 25℃ and the sessile drop method was used to measure the static contact angle of the aggregate.

[0050] Standard reagents used in contact angle testing: Distilled water, formamide, and ethylene glycol were selected as standard reagents for contact angle measurement to facilitate subsequent calculation of the aggregate's surface energy and component values. Three contact angle measurements were performed for each standard reagent, and four parallel tests were conducted for each aggregate.

[0051] The surface free energy parameters of the three standard solutions are shown in Table 1, and the surface free energy parameters of the aggregates are shown in Table 2.

[0052] Table 1 Surface free energy parameters of test liquids at 25°C Unit: mJ·m -2

[0053] Test Reagents <![CDATA[γ L ]]> γLW L γAB L γ+L γ-L distilled water 72.80 21.80 51.00 25.50 25.50 Formamide 58.00 39.00 19.00 1.92 39.60 Ethylene glycol 48.00 29.00 19.00 1.92 47.00

[0054] Note: γ L is the total surface free energy of the test liquid; γLW L is the dispersion component of the test liquid; γAB L is the polar component of the test liquid; γ+L is the Lewis acid component of the test liquid; γ-L is the Lewis base component of the test liquid.

[0055] Table 2 Surface free energy parameters of aggregates Unit: mJ·m -2

[0056] contact angle γ <![CDATA[γ d ]]> <![CDATA[γ p ]]> <![CDATA[γ + ]]> <![CDATA[γ - ]]> limestone 56.28° 43.2 12.55 30.65 8.42 25.32 scrap steel slag 41.08° 46.48 15.05 31.43 5.29 27.95

[0057] Note: γ is the total surface free energy of aggregate; γ d is the aggregate dispersion component; γ p is the polar component of aggregate; γ + is the Lewis acid content of aggregate; γ - is the Lewis base content of aggregate.

[0058] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for measuring the contact angle of porous steel slag, comprising: Preparation, polishing, and testing of steel slag cross-sections; characterized in that the preparation of the steel slag cross-sections comprises: first mixing porous steel slag with additives, forming a cylindrical specimen similar to a Marshall specimen using a Marshall compactor, and then cutting the cylindrical specimen after conditioning; The additive includes a binder, and the binder is polyurethane.

2. The method for measuring the contact angle of porous steel slag according to claim 1, wherein: Polyurethane is used as a binder, and the mass of the polyurethane accounts for 6-7% of the mass of the porous steel slag.

3. The method for measuring the contact angle of porous steel slag according to claim 2, wherein: The additive further includes a catalyst, which is liquid phenylmercuric acetate. The mass of the catalyst accounts for 1% of the mass of the polyurethane.

4. The method for measuring the contact angle of porous steel slag according to claim 3, wherein: The maintenance includes conventional maintenance and accelerated maintenance; The conventional curing is as follows: curing the cylindrical specimen at room temperature for one week; The accelerated curing is as follows: on the first day, conventional indoor curing; on the second and third days, curing at 80°C; and on the fourth day, curing at room temperature indoors.

5. The method for measuring the contact angle of porous steel slag according to claim 4, wherein: The cutting was performed using a conventional Marshall specimen cutting machine; slices with a thickness of 4-6 mm were obtained by cutting.

6. The method for measuring the contact angle of porous steel slag according to claim 5, characterized in that: The polishing is achieved by using sandpaper of different mesh sizes to achieve the roughness required by the contact angle specimen; The mesh number grading of the sandpaper is: 120, 400, 600, 1000, 1500, 2000, 4000 mesh.

7. The method for measuring the contact angle of porous steel slag according to claim 6, wherein: For small pieces of aggregate that are uneven after cutting, use plasticine to level them.

8. The method for measuring the contact angle of porous steel slag according to claim 7, characterized in that: After the polishing is completed, the surface of the specimen is first cleaned with distilled water to remove the residue and then cleaned with anhydrous ethanol. Then, the specimen is placed in a constant temperature drying oven at (105±5)°C for drying and then cooled to room temperature for use.

9. The method for measuring the contact angle of porous steel slag according to claim 8, wherein: The contact angle measurement method adopts the sessile drop method to measure the static contact angle of the steel slag slice; the standard reagents used in the test are distilled water, formamide and ethylene glycol.

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