A preparation method of gradient carbonization-silane coupling synergistically modified steel slag and ultra-thin wearing layer

Abstract

This invention discloses a method for preparing ultrathin wearing course layers of steel slag synergistically modified by gradient carbonization and silane coupling, belonging to the fields of solid waste resource utilization and road paving engineering. This invention aims to solve the problems of insufficient volume stability and poor interfacial adhesion with asphalt caused by the dense calcium carbonate layer on the surface of carbonized steel slag aggregate hindering internal reactions. First, the steel slag undergoes gradient pressure carbonization. High-pressure carbonization rapidly forms a dense calcium carbonate layer on the surface of the steel slag, while low-pressure carbonization promotes the continued reaction of free calcium oxide and other substances within the steel slag. Subsequently, a silane coupling agent is used to treat the carbonized steel slag, relying on its chemical bonding to improve the volume stability and asphalt adhesion of the carbonized steel slag. Finally, the composite modified steel slag is applied to ultrathin asphalt wearing course layers to improve the overall road performance of asphalt mixtures. This method can synergistically solve problems such as the utilization of solid waste steel slag, the shortage of natural aggregates, and insufficient pavement performance, possessing both environmental benefits and engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and road paving engineering. Specifically, it relates to a method for preparing steel slag and ultrathin wear layer by gradient carbonization-silane coupling synergistic modification. Background Technology

[0002] Steel slag, a solid waste generated during the steelmaking process, is widely used in asphalt pavement mixtures due to its high hardness and strong wear resistance. However, its alkaline mineral components, such as free calcium oxide, easily expand in volume under moisture and carbon dioxide conditions, thus limiting its long-term durability in asphalt pavements. Although current carbonization methods can significantly reduce the free calcium oxide content in steel slag based on the reaction of carbon dioxide with the alkaline mineral components, this method often forms a dense layer of carbonization products on the surface of the steel slag aggregate, hindering the diffusion of carbon dioxide into the aggregate and resulting in incomplete carbonization reaction inside the steel slag, leading to insufficient volume stability. Furthermore, the bonding between carbonized steel slag aggregate and asphalt binder in asphalt mixtures relies on physical adsorption, making it susceptible to damage under moisture erosion, and failing to meet the high service performance requirements of ultra-thin wearing courses, such as resistance to water damage, skid resistance, and high-temperature stability. Although current research has utilized the chemical bonding of silane coupling agents to improve the interfacial adhesion between aggregates and asphalt, single surface modification techniques are insufficient to address the lack of volume stability in steel slag aggregates. Summary of the Invention

[0003] This invention addresses the issues of insufficient volume stability and poor adhesion to asphalt in carbonized steel slag aggregates due to the dense calcium carbonate layer on the surface hindering internal reactions. It proposes a gradient pressure carbonization-silane coupling agent synergistic modification method to treat steel slag aggregates and applies it to ultra-thin asphalt wearing courses to achieve efficient resource utilization of solid waste steel slag and comprehensive improvement of pavement service performance.

[0004] This invention first involves gradient pressure carbonization of steel slag. High-pressure carbonization rapidly forms a dense calcium carbonate layer on the surface of the slag, while low-pressure carbonization promotes the continued reaction of free calcium oxide and other substances within the slag. Subsequently, a silane coupling agent is used to treat the carbonized steel slag, improving its volume stability and asphalt adhesion through chemical bonding. Finally, the composite-modified steel slag is applied to ultra-thin asphalt wearing courses to improve the overall road performance of asphalt mixtures. This method synergistically addresses issues such as the utilization of solid waste steel slag, the shortage of natural aggregates, and insufficient pavement performance, offering both environmental benefits and engineering application value.

[0005] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0006] The purpose of this invention is to provide a method for preparing steel slag with gradient carbide-silane coupling synergistic modification, comprising the following steps:

[0007] Step 1: Rinse the steel slag coarse aggregate of 2.36mm to 9.50mm to remove surface dust, dry it, and obtain steel slag coarse aggregate of constant weight;

[0008] Step 2: Then place it in a high-pressure reactor and carbonize for 1 to 2 hours under the conditions of pressure 2.5 MPa to 4.0 MPa, CO2 volume concentration 90% to 98%, temperature 40℃ to 60℃, and liquid-solid ratio 5 mL:1 g to 20 mL:1 g. Subsequently, continue carbonizing for 2 to 4 hours under the conditions of pressure 0.8 MPa to 1.5 MPa, CO2 volume concentration 90% to 98%, temperature 40℃ to 60℃, and liquid-solid ratio 5 mL:1 g to 20 mL:1 g. Filter, dry, and obtain carbonized steel slag aggregate.

[0009] Step 3: Then soak the slag in a silane coupling agent solution, filter, and dry it to obtain the composite modified steel slag.

[0010] Further specifying, in step 1, the steel slag is one or more of the following: alkaline oxygen furnace slag, electric arc furnace slag, and ladle refining furnace slag.

[0011] Further specifying, in step 1, the steel slag is crushed, magnetically separated, and screened to obtain coarse steel slag aggregate with a particle size of 2.36mm to 9.50mm.

[0012] Further specifying, in step 1, high-pressure water can be used to wash the steel slag coarse aggregate to remove surface dust.

[0013] Further specifying, in step 1, the steel slag coarse aggregate is placed in an oven at 100℃~120℃ and dried for 16~28 hours.

[0014] Further specifying, in step 2, the product is dried in an oven at 100℃~120℃ for 16~28 hours.

[0015] Further specifying, in step 3, the soaking time is 0.5 to 1.5 hours at room temperature.

[0016] Further specifying, in step 3, the product is cured and dried in an oven at 100℃~160℃ for 4~6 hours.

[0017] Further specifying, in step 3, the silane coupling agent is one or more of γ-methacryloyloxysilane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane.

[0018] Furthermore, the preparation method of the γ-methacryloyloxysilane is as follows: First, sodium methacrylate and γ-chloropropyltrimethoxysilane are sequentially added to anhydrous ethanol for mixing, with the mass ratio of sodium methacrylate to γ-chloropropyltrimethoxysilane being 1:(1-2), and the mass of anhydrous ethanol being 1.5 to 2.5 times the total mass of sodium methacrylate and γ-chloropropyltrimethoxysilane; then, the mixture is stirred at a temperature of 50℃ to 80℃ and a stirring rate of 600 r / min to 1000 r / min for 0.5 h to 1.0 h; finally, the mixture is allowed to stand at 20℃ to 30℃ for 0.5 h to 1.0 h.

[0019] Further specifying, in step 3, the mass fraction of the silane coupling agent solution is 3% to 6%.

[0020] Another objective of this invention is to provide a method for preparing an ultrathin abrasion layer of steel slag with gradient carbonization-silane coupling synergistic modification, comprising the following steps: First, asphalt binder, composite modified steel slag prepared by any of the methods described above, natural coarse and fine aggregates, mineral powder, lignin fiber, steel slag fiber and initiator are mixed according to the asphalt mixture gradation; then, the mixture is sequentially treated with a heating temperature of 155℃~175℃, a mixing temperature of 165℃~185℃, and a compaction temperature of 140℃~155℃ to obtain an ultrathin asphalt abrasion layer.

[0021] Further specifying, the mass of the composite modified steel slag added is 40% to 50% of the mass of the asphalt mixture.

[0022] Further specified, the asphalt binder is one or more of rubber-modified asphalt, SBS-modified asphalt, PE-modified SBS composite modified asphalt, and PE-modified rubber composite modified asphalt, and the mass of the asphalt binder added is 4% to 6% of the mass of the asphalt mixture.

[0023] Further specifying, the natural coarse and fine aggregates are basalt coarse and fine aggregates, and the mass of natural coarse and fine aggregates added is 40% to 50% of the mass of the asphalt mixture.

[0024] Further specifying, the mineral powder is limestone mineral powder, and the added mineral powder mass is 4% to 8% of the mass of the asphalt mixture.

[0025] Further specifying, the mass of the added lignin fiber is 0.3% to 1.2% of the mass of the asphalt mixture.

[0026] Further specified, the steel slag fiber has a length of 3mm to 8mm and a diameter of 0.1mm to 0.3mm, and the mass of steel slag fiber added is 0.3% to 0.6% of the mass of the asphalt mixture.

[0027] Further specifying, the initiator is dicumyl peroxide, and the mass of dicumyl peroxide added is 0.025% to 0.075% of the mass of the asphalt mixture.

[0028] Further specifying, the asphalt mixture gradation is one or more of the SMA-10 type, OGFC-10 type, and AC-10 type gradation.

[0029] Furthermore, the preparation method of the PE-modified SBS composite modified asphalt is as follows:

[0030] First, preheated polyethylene (PE) particles (particle size < 1 mm) are slowly added to molten SBS modified asphalt for mixing. The mass of PE particles added is 3% to 6% of the mass of SBS modified asphalt binder. Then, the mixture is stirred and reacted for 20 to 40 minutes at 170℃ to 190℃ and a shear rate of 2000 to 5000 r / min using a high-speed shear mixer.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] This invention utilizes a gradient pressure carbonization process to treat steel slag coarse aggregate. Based on the pressure gradient, it achieves staged control of the steel slag carbonization reaction kinetics, improving the uniformity of carbonization both inside and outside the steel slag aggregate, thus overcoming the limitations of a single carbonization process. Simultaneously, after the steel slag aggregate undergoes wet carbonization with carbon dioxide, this invention modifies the surface of the carbonized steel slag using a silane coupling agent. This not only achieves good volume stability of the steel slag aggregate based on the carbonization process but also further improves the compatibility and adhesion between the carbonized steel slag and asphalt through the chemical bonding effect of the silane coupling agent. Furthermore, the silane coupling agent coated on the surface of the carbonized steel slag also possesses oleophilic and hydrophobic properties, indirectly improving the volume stability of the steel slag aggregate. The gradient pressure carbonization and silane coupling agent synergistic modification process proposed in this invention achieves efficient resource utilization of solid waste steel slag, reduces the dependence of road engineering on natural aggregates, and meets the requirements of green, low-carbon, and sustainable development.

[0033] This invention utilizes a gradient pressure carbonization process to impart excellent internal structural stability to steel slag coarse aggregates. This not only improves the volume stability of steel slag in ultra-thin asphalt wearing course mixtures but also indirectly enhances its reliability in asphalt mixture applications. Simultaneously, this invention employs a silane coupling agent to treat the carbonized steel slag, forming covalent bonds with it through its own chemical bonding, creating a coupling layer on the surface of the carbonized steel slag aggregate to further improve the adhesion between the steel slag aggregate and asphalt. The proposed gradient pressure carbonization and silane coupling agent synergistic modification process significantly improves the adhesion between steel slag aggregate and asphalt, enhancing the comprehensive performance of asphalt mixtures, including volume stability, water stability, and high-temperature stability. This meets the dual requirements of ultra-thin wearing courses for driving safety and durability, providing crucial technical support for green road construction. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, while not limiting the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0036] Example 1: Performance Testing of Gradient Pressure Carburized Steel Slag Aggregate

[0037] (1) Preparation of gradient pressure carburized steel slag aggregate

[0038] Example 1 describes the preparation of gradient pressure carbonized steel slag aggregate through the following pretreatment and gradient pressure carbonization treatment.

[0039] 1) Pretreatment: First, the alkaline oxygen furnace steel slag is crushed, magnetically separated, and screened to obtain steel slag coarse aggregate with a particle size of 2.36mm to 9.50mm; then, the steel slag coarse aggregate is washed with high-pressure water to remove surface dust; finally, the steel slag coarse aggregate is placed in an oven at 105℃ and dried until a constant weight of steel slag coarse aggregate is obtained.

[0040] 2) Gradient pressure carbonization treatment: First, the above-mentioned steel slag coarse aggregate is placed in a high-pressure reactor; then, it is carbonized for 1.5 hours under the process conditions of 4.0 MPa pressure, 98% CO2 volume concentration, 50℃ temperature, and 8 mL:1g liquid-solid ratio; subsequently, carbonization is continued for 3 hours under the process conditions of 1.5 MPa pressure, 98% CO2 volume concentration, 50℃ temperature, and 8 mL:1g liquid-solid ratio; finally, the carbonized steel slag mixture is filtered, and the steel slag coarse aggregate is placed in an oven at 105℃ and dried for 24 hours to obtain gradient pressure carbonized steel slag aggregate.

[0041] (2) Preparation of constant pressure carburized steel slag aggregate

[0042] Example 1 describes the preparation of constant pressure carbonized steel slag aggregate through the following pretreatment and constant pressure carbonization treatment.

[0043] 1) Pretreatment: First, the alkaline oxygen furnace steel slag is crushed, magnetically separated, and screened to obtain steel slag coarse aggregate with a particle size of 2.36mm to 9.50mm; then, the steel slag coarse aggregate is washed with high-pressure water to remove surface dust; finally, the steel slag coarse aggregate is placed in an oven at 105℃ and dried until a constant weight of steel slag coarse aggregate is obtained.

[0044] 2) Constant pressure carbonization treatment: First, the above-mentioned steel slag coarse aggregate is placed in a high-pressure reactor; then, it is carbonized for 4.5 hours under the process conditions of pressure 4.0 MPa, CO2 volume concentration 98%, temperature 50℃, and liquid-solid ratio 8 mL:1 g; finally, the carbonized steel slag mixture is filtered, and the steel slag coarse aggregate is placed in an oven at 105℃ and dried for 24 hours to obtain constant pressure carbonized steel slag aggregate.

[0045] (3) Gradient pressure carburized steel slag aggregate performance test

[0046] The effects of gradient pressure and constant pressure on the properties of carbide steel slag aggregate were studied by measuring the calcium oxide conversion rate on the surface, the internal calcium oxide conversion rate, and the porosity of the product layer. The results are shown in Table 1. Table 1 shows that, compared to gradient pressure, constant pressure resulted in a dense product layer on the surface of the carbide steel slag aggregate, severely limiting the internal reaction. While the lower pressure setting in the later stages of gradient pressure reduced the calcium oxide conversion rate on the surface of the carbide steel slag aggregate (due to reduced carbon dioxide solubility in liquids), the lower pressure allowed carbon dioxide to penetrate the interior of the carbide steel slag aggregate, promoting an increase in the internal calcium oxide conversion rate and significantly reducing the difference in carbonization between the inside and outside of the steel slag aggregate.

[0047] Table 1 Performance Test of Steel Carbide Slag Aggregate

[0048] Performance indicators Gradient pressure carburized steel slag aggregate Constant pressure carburized steel slag aggregate Surface calcium oxide conversion rate 92％ 97％ Internal calcium oxide conversion rate 84％ 37％ Product layer porosity 19％ 11％

[0049] Example 2: Performance Testing of Composite Modified Steel Slag Aggregate

[0050] (1) Preparation of composite modified steel slag aggregate

[0051] In conjunction with the gradient pressure carbonized steel slag aggregate prepared in Example 1, Example 2 prepares composite modified steel slag aggregate through the following preparation of γ-methacryloyloxysilane and surface modification treatment with silane coupling agent.

[0052] 1) Preparation of γ-methacryloyloxysilane: Sodium methacrylate and γ-chloropropyltrimethoxysilane were added sequentially to anhydrous ethanol for mixing. The mass ratio of sodium methacrylate to γ-chloropropyltrimethoxysilane was 1:1.5, and the mass of anhydrous ethanol was twice the sum of the masses of the two. Subsequently, the mixture was stirred at 60°C for 0.6 hours using an electric stirrer at a stirring rate of 800 r / min. Finally, the mixture was left to stand in a 25°C incubator for 0.5 hours.

[0053] 2) Surface modification treatment with silane coupling agent: First, the carbide steel slag aggregate is mixed with a 5% (w / w) silane coupling agent solution and soaked at room temperature for 0.5 hours; then, the steel slag is filtered and cured and dried in an oven at 140℃ for 5 hours.

[0054] (2) Comparison of steel slag aggregate preparation

[0055] Example 2 prepared comparative carburized steel slag aggregate only through pretreatment and gradient pressure carburization treatment, without surface modification treatment of the carburized steel slag aggregate. The pretreatment and gradient pressure carburization treatment process is the same as steps 1 and 2 in the gradient pressure carburized steel slag aggregate preparation in Example 1.

[0056] (3) Performance testing of modified steel slag aggregate

[0057] The volume stability and adhesion properties of the prepared composite modified steel slag aggregate and the comparative carbide steel slag aggregate were tested by volume expansion test and pull-out strength test.

[0058] 1) Test methods

[0059] Volumetric expansion test: Volumetric expansion tests were conducted on composite modified steel slag aggregate and comparative carbide steel slag aggregate according to GB / T 24175 standard. First, the two types of steel slag aggregate were respectively placed into two identical cylindrical molds and compacted using a compactor (the height of the specimens was 120 mm). Then, a 5 kg semi-circular load plate was placed on top of the two molded specimens. Next, the specimens were immersed in a 90℃ water bath for 6 hours in one cycle (one day), and then heating was stopped and the specimens were allowed to cool naturally. Finally, the above operation steps were repeated for 3 days, and the dial gauge readings on the 1st and 3rd days were recorded to calculate the volumetric expansion rate of the two types of steel slag aggregate.

[0060] Pull-out strength test: The adhesion strength between the two types of steel slag aggregates and asphalt was analyzed using a pull-out adhesion tester. First, the two types of steel slag aggregates were cut, surface-polished, and cleaned to obtain pull-out substrates with the same adhesion area. Then, molten asphalt binder was dripped onto the surface of the two types of steel slag aggregates, and a circular pull-out ingot with a diameter of 20 mm was used to statically press the asphalt binder to ensure that the thickness of the asphalt film adhering to the surface of the two types of steel slag aggregates was 1000 μm. Then, the prepared specimens were placed in a room temperature curing chamber for 24 hours. Finally, the pull-out tester was used at 25℃ with a pull-out rate of 10 mm / min to test and obtain the pull-out strength of the two types of steel slag aggregates.

[0061] 2) Analysis of aggregate performance test results

[0062] The volume stability and adhesion performance test results of the above-mentioned composite modified steel slag aggregate and the comparative carbide steel slag aggregate are shown in Table 2. As can be seen from Table 2, compared with the comparative carbide steel slag aggregate, the volume expansion rate of the composite modified steel slag aggregate is reduced by 81.6%, indicating that the composite modification method proposed in this invention can significantly improve the volume stability of steel slag aggregate; compared with the comparative carbide steel slag aggregate, the pull-out strength of the composite modified steel slag aggregate is increased by 100%, indicating that the composite modification method proposed in this invention can significantly improve the adhesion between steel slag and asphalt.

[0063] Table 2 Performance Test of Steel Slag Aggregates

[0064] Performance indicators Composite modified steel slag aggregate Comparison of steel slag aggregate Volume expansion rate (%) 0.07 0.38 Pull-out strength (MPa) 4.20 2.10

[0065] Example 3: Performance Testing of Ultra-Thin Wearing Layer Asphalt Mixture Containing Composite Modified Steel Slag

[0066] In combination with the composite modified steel slag coarse aggregate prepared in Example 2 and the comparative carbide steel slag, Example 3 prepared an ultra-thin wear-resistant asphalt mixture containing composite modified steel slag and comparative carbide steel slag through the following measures.

[0067] (1) Preparation of ultrathin abrasive layer asphalt mixture containing composite modified steel slag

[0068] 1) Preparation of PE-modified SBS composite modified asphalt: Preheated polyethylene (PE) particles (particle size < 1 mm) are slowly added to molten SBS modified asphalt for mixing. The mass of PE particles added is 4% of the mass of SBS modified asphalt binder. Then, the mixture is stirred and reacted for 30 minutes at 180°C and a shear rate of 3500 r / min using a high-speed shear mixer.

[0069] 2) Preparation of asphalt mixture: PE-modified SBS composite modified asphalt binder (5%), composite modified steel slag coarse aggregate (45%), basalt coarse and fine aggregate (45%), limestone mineral powder, lignin fiber (0.4%), steel slag fiber (0.3%), and dicumyl peroxide (0.05%) are mixed according to the SMA-10 type asphalt mixture gradation; then, the above mixture is subjected to a heating temperature of 155℃~175℃, a mixing temperature of 165℃~185℃, and a compaction temperature of 140℃~155℃ in sequence to obtain an ultra-thin wearing course asphalt mixture containing composite modified steel slag.

[0070] (2) Preparation of ultrathin wearing course asphalt mixture containing comparative steel slag

[0071] Asphalt mixture preparation: PE-modified SBS composite modified asphalt binder (5%), comparative carbonized steel slag coarse aggregate (45%), basalt coarse and fine aggregate (45%), limestone mineral powder, lignin fiber (0.4%), and steel slag fiber (0.3%) are mixed according to the SMA-10 type asphalt mixture gradation; then, the above mixture is subjected to a heating temperature of 155℃~175℃, a mixing temperature of 165℃~185℃, and a compaction temperature of 140℃~155℃ in sequence to obtain an ultra-thin wearing course asphalt mixture containing comparative carbonized steel slag.

[0072] (3) Performance testing of modified steel slag ultrathin wearing course asphalt mixture

[0073] The high-temperature stability, water stability, and skid resistance of asphalt mixtures containing composite modified steel slag aggregate and comparative carbonized steel slag aggregate were tested using high-temperature rutting test, immersion Marshall test, and pendulum friction test.

[0074] 1) Test methods

[0075] High-temperature rutting test: The two steel slag asphalt mixtures were subjected to a high-temperature rutting test using a rutting apparatus according to the JTG E20-2011 standard. First, the two steel slag asphalt mixtures were kept in a constant temperature chamber at 60℃ for 5 hours. Then, the two steel slag asphalt mixtures were placed in the testing machine and the specimens were rolled at a speed of 42 times / min. The deformation of the specimens was recorded at 45 min and 60 min. Finally, the dynamic stability was calculated to evaluate the high-temperature stability of the two steel slag asphalt mixtures.

[0076] Immersion Marshall Test: Immersion Marshall tests were conducted on the two steel slag asphalt mixtures according to the JTG E20-2011 standard using an asphalt mixture stability tester. First, the two steel slag asphalt mixtures were immersed in a 60℃ water bath for 30 minutes to test their stability. Simultaneously, the two steel slag asphalt mixtures were immersed in a 60℃ water bath for 48 hours to test their stability. Finally, the residual strength of the two steel slag asphalt mixtures after immersion was calculated to evaluate their water stability.

[0077] Pendulum friction test: According to the JTG E20-2011 standard, the pendulum friction test was conducted on the two steel slag asphalt mixtures mentioned above. First, the two steel slag asphalt mixtures were placed in wet conditions. Then, the pendulum friction tester was adjusted to meet the requirement of 126 mm. Finally, the pendulum values ​​of the two steel slag asphalt mixtures in the wet condition were tested to evaluate their skid resistance.

[0078] 2) Analysis of Asphalt Mixture Performance Test Results

[0079] The high-temperature stability, water stability, and skid resistance test results of the asphalt mixtures containing composite modified steel slag aggregate and comparative carbonized steel slag aggregate are shown in Table 3. As can be seen from Table 3, compared with the asphalt mixture containing comparative carbonized steel slag aggregate, the asphalt mixture containing composite modified steel slag aggregate has higher dynamic stability, water-immersed residual strength, and BPN value. This indicates that the gradient pressure carbonization and silane coupling agent synergistic modification method proposed in this invention significantly improves the high-temperature stability, water damage resistance, and skid resistance of steel slag asphalt mixtures. This fully demonstrates the advantages of this invention in the resource utilization of steel slag and the improvement of the performance of ultra-thin asphalt wearing courses.

[0080] Table 3 Asphalt Mixture Performance Tests

[0081]

[0082]

[0083] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing steel slag with gradient carburization-silane coupling synergistic modification, characterized in that, Includes the following steps: Step 1: Rinse the steel slag from 2.36mm to 9.50mm to remove surface dust, dry it, and obtain steel slag coarse aggregate of constant weight; Step 2: Then place it in a high-pressure reactor and carbonize for 1-2 hours under the conditions of pressure 2.5MPa~4.0MPa, CO2 volume concentration 90%~98%, temperature 40℃~60℃, and liquid-solid ratio 5mL:1g~20mL:1g; subsequently, continue carbonizing for 2-4 hours under the conditions of pressure 0.8MPa~1.5MPa, CO2 volume concentration 90%~98%, temperature 40℃~60℃, and liquid-solid ratio 5mL:1g~20mL:1g; filter, dry, and obtain carbonized steel slag aggregate; Step 3: Then soak the slag in a silane coupling agent solution, filter, and dry it to obtain the composite modified steel slag.

2. The method according to claim 1, characterized in that, The steel slag is one or more of the following: alkaline oxygen furnace slag, electric arc furnace slag, and ladle refining furnace slag.

3. The method according to claim 1, characterized in that, The silane coupling agent is one or more of γ-methacryloyloxysilane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane.

4. The method according to claim 3, characterized in that, The preparation method of the γ-methacryloyloxysilane is as follows: First, sodium methacrylate and γ-chloropropyltrimethoxysilane are added sequentially to anhydrous ethanol for mixing. The mass ratio of sodium methacrylate to γ-chloropropyltrimethoxysilane is 1:(1~2), and the mass of anhydrous ethanol is 1.5 to 2.5 times the total mass of sodium methacrylate and γ-chloropropyltrimethoxysilane. Then, the mixture is stirred at a temperature of 50℃ to 80℃ and a stirring rate of 600 r / min to 1000 r / min for 0.5 h to 1.0 h. Finally, the mixture is left to stand at 20℃ to 30℃ for 0.5 h to 1.0 h.

5. The method according to claim 1, characterized in that, The mass fraction of the silane coupling agent solution is 3% to 6%.

6. A method for preparing an ultrathin wear layer of steel slag synergistically modified by gradient carbide-silane coupling, characterized in that, The process includes the following steps: First, asphalt binder, composite modified steel slag prepared by the method described in any one of claims 1-5, natural coarse and fine aggregates, mineral powder, lignin fiber, steel slag fiber, and initiator are mixed according to the asphalt mixture gradation; then, the mixture is sequentially treated with a heating temperature of 155℃~175℃, a mixing temperature of 165℃~185℃, and a compaction temperature of 140℃~155℃ to obtain an ultra-thin asphalt wearing course.

7. The method according to claim 6, characterized in that, The mass of the composite modified steel slag added is 40% to 50% of the mass of the asphalt mixture; The asphalt binder is one or more of rubber-modified asphalt, SBS-modified asphalt, PE-modified SBS composite modified asphalt, and PE-modified rubber composite modified asphalt, and the mass of the asphalt binder added is 4% to 6% of the mass of the asphalt mixture; The natural coarse and fine aggregates are basalt coarse and fine aggregates, and the mass of natural coarse and fine aggregates added is 40% to 50% of the mass of the asphalt mixture. The mineral powder is limestone mineral powder, and the mineral powder is added at a mass of 4% to 8% of the asphalt mixture mass. The lignin fiber added is 0.3% to 1.2% of the mass of the asphalt mixture. The steel slag fibers have a length of 3mm to 8mm and a diameter of 0.1mm to 0.3mm, and the mass of steel slag fibers added is 0.3% to 0.6% of the mass of the asphalt mixture.

8. The method according to claim 6, characterized in that, The initiator is dicumyl peroxide, and the mass of dicumyl peroxide added is 0.025% to 0.075% of the mass of the asphalt mixture.

9. The method according to claim 6, characterized in that, The asphalt mixture gradation is one or more of the following: SMA-10, OGFC-10, and AC-10.

10. The method according to claim 7, characterized in that, The preparation method of the PE-modified SBS composite modified asphalt is as follows: First, preheated polyethylene (PE) particles with a particle size of less than 1 mm are slowly added to molten SBS modified asphalt for mixing. The mass of PE particles added is 3% to 6% of the mass of the SBS modified asphalt binder. Then, the mixture is stirred and reacted for 20 to 40 minutes at 170℃ to 190℃ and a shear rate of 2000 to 5000 r / min using a high-speed shear mixer.

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