Gradient carbonization-silane coupling synergistically modified steel slag and ultrathin wearing layer preparation method

Abstract

The invention discloses a gradient carbonization-silane coupling synergistically modified steel slag and an ultrathin wearing layer preparation method, and belongs to the field of solid waste recycling and road pavement engineering. The invention aims to solve the problems of insufficient volume stability and poor adhesion with an asphalt interface caused by the fact that a compact calcium carbonate layer on the surface of the carbonized steel slag aggregate hinders an internal reaction. The method comprises the following steps: firstly, carrying out gradient pressure carbonization on the steel slag, rapidly forming a compact calcium carbonate layer on the surface of the steel slag through high-pressure carbonization, and promoting substances such as free calcium oxide in the steel slag to continuously react through low-pressure carbonization; then, treating the carbonized steel slag by adopting a silane coupling agent, and improving the volume stability of the carbonized steel slag and the adhesion of the carbonized steel slag to asphalt by virtue of the chemical bonding effect of the silane coupling agent; finally, the composite modified steel slag is applied to the ultrathin asphalt wearing layer, so that the comprehensive pavement performance of the asphalt mixture can be improved. The method provided by the invention can synergistically solve the problems of utilization of solid waste steel slag, shortage of natural aggregate, insufficient pavement performance and the like, and has environmental protection benefits and engineering application values.

Description

Technical Field

[0001] The present invention belongs to the fields of solid waste resource utilization and road paving engineering. Specifically, it relates to a method for preparing steel slag and an ultra-thin wearing course by gradient carbonization-silane coupling synergistic modification. Background Art

[0002] As a solid waste generated in the steelmaking industrial process, steel slag is widely used in pavement asphalt mixtures due to its high hardness, strong wear resistance and other characteristics. However, due to the alkaline mineral components such as free calcium oxide contained in it, it is prone to volume expansion under the conditions of moisture and carbon dioxide, thus restricting its long-term durable application in asphalt pavements. Although the current carbonization method can significantly reduce the content of free calcium oxide in steel slag based on the reaction between carbon dioxide and alkaline mineral components in steel slag, this method often forms a dense carbonized product layer on the surface of steel slag aggregates, hindering the diffusion of carbon dioxide into the interior of steel slag aggregates, resulting in incomplete carbonization reaction inside the steel slag, and further causing insufficient volume stability of steel slag aggregates. In addition, the combination of carbonized steel slag aggregates applied to asphalt mixtures and asphalt binder depends on physical adsorption, resulting in easy occurrence of diseases such as breakage under the action of moisture erosion, and it is difficult to meet the high service performance requirements of ultra-thin wearing courses for water damage resistance, skid resistance, high-temperature stability, etc. Although current research has utilized the chemical bonding action of silane coupling agents themselves to improve the interfacial adhesion performance between aggregates and asphalt, a single surface modification technology is difficult to solve the defect of insufficient volume stability of steel slag aggregates. Summary of the Invention

[0003] Aiming at the problems of insufficient volume stability of carbonized steel slag aggregates caused by the dense calcium carbonate layer on the surface hindering the internal reaction and poor interfacial adhesion with asphalt, the present invention proposes a method of gradient pressure carbonization-silane coupling agent synergistic modification to treat steel slag aggregates and apply them to ultra-thin asphalt wearing courses to achieve efficient resource utilization of solid waste steel slag and comprehensive improvement of pavement service performance.

[0004] The present invention first performs gradient pressure carbonization on steel slag. Through high-pressure carbonization, a dense calcium carbonate layer is rapidly formed on the surface of the steel slag, and through low-pressure carbonization, substances such as free calcium oxide inside the steel slag are promoted to continue reacting; subsequently, the carbonized steel slag is treated with a silane coupling agent, and its chemical bonding action is relied on to improve the volume stability of the carbonized steel slag and its adhesion with asphalt; finally, the composite modified steel slag applied to the ultra-thin asphalt wearing course can improve the comprehensive road performance of the asphalt mixture. The above method can synergistically solve problems such as the utilization of solid waste steel slag, shortage of natural aggregates and insufficient pavement performance, and has both environmental benefits and engineering application value.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The object of the present invention is to provide a preparation method of steel slag modified by gradient carbonization-silane coupling, comprising the following steps:

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

[0008] Step 2: Then place it in a high-pressure reactor, and carry out carbonization for 1 h to 2 h under the conditions of a pressure of 2.5 MPa to 4.0 MPa, a CO2 volume concentration of 90% to 98%, a temperature of 40 °C to 60 °C, and a liquid-solid ratio of 5 mL:1 g to 20 mL:1 g; subsequently, continue carbonization for 2 h to 4 h under the conditions of a pressure of 0.8 MPa to 1.5 MPa, a CO2 volume concentration of 90% to 98%, a temperature of 40 °C to 60 °C, and a liquid-solid ratio of 5 mL:1 g to 20 mL:1 g, filter, and dry to obtain carbonized steel slag aggregate.

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

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

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

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

[0013] Further defined, in step 1, the steel slag coarse aggregate is placed in an oven at 100 °C to 120 °C and dried for 16 to 28 hours.

[0014] Further defined, in step 2, it is dried in an oven at 100 °C to 120 °C for 16 to 28 hours.

[0015] Further defined, in step 3, it is soaked at room temperature for 0.5 to 1.5 hours.

[0016] Further defined, in step 3, it is cured and dried in an oven at 100 °C to 160 °C for 4 to 6 hours

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

[0018] Further defined, the preparation method of the γ-methacryloyloxy silane is as follows: First, sodium methacrylate and γ-chloropropyltrimethoxysilane are successively added to absolute ethanol for mixing. The mass ratio of sodium methacrylate to γ-chloropropyltrimethoxysilane is 1:(1-2), and the mass of absolute ethanol is 1.5 to 2.5 times the total mass of sodium methacrylate and γ-chloropropyltrimethoxysilane. Subsequently, it is stirred at a temperature of 50°C to 80°C and a stirring rate of 600 r / min to 1000 r / min for 0.5 h to 1.0 h. Finally, it is allowed to stand at 20°C to 30°C for 0.5 h to 1.0 h.

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

[0020] Another object of the present invention is to provide a preparation method of a gradient carbonization-silane coupling synergistic modified steel slag ultra-thin wearing course, including the following steps: First, asphalt binder, the composite modified steel slag prepared by any of the above methods, natural coarse and fine aggregates, mineral powder, lignin fiber, steel slag fiber and initiator are mixed according to the asphalt mixture gradation. Subsequently, it is successively treated at a heating temperature of 155°C to 175°C, a mixing temperature of 165°C to 185°C, and a compaction temperature of 140°C to 155°C to obtain an ultra-thin asphalt wearing course.

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

[0022] Further defined, 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 added mass of the asphalt binder is 4% to 6% of the mass of the asphalt mixture.

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

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

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

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

[0027] Further limitation: The initiator is dicumyl peroxide, and the added mass of dicumyl peroxide is 0.025% - 0.075% of the mass of the asphalt mixture.

[0028] Further limitation: The asphalt mixture gradation is one or more of SMA-10 type, OGFC-10 type, and AC-10 type gradations.

[0029] Even further limitation: The preparation method of the PE-modified SBS composite modified asphalt is as follows:

[0030] First, slowly add preheated polyethylene (PE) particles (particle size < 1 mm) to the molten SBS modified asphalt for mixing, and the added mass of PE particles is 3% - 6% of the mass of the SBS modified asphalt binder; then, use a high-speed shear mixer to stir and react at 170°C - 190°C and a shear rate of 2000 - 5000 r / min for 20 - 40 minutes.

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

[0032] The present invention uses a gradient pressure carbonization process to treat steel slag coarse aggregates, and based on the pressure gradient, it realizes the staged regulation of the steel slag carbonization reaction kinetic process to improve the uniform carbonization degree inside and outside the steel slag aggregates, breaking through the limitations of a single carbonization process; at the same time, after the steel slag aggregates are treated by wet carbon dioxide carbonization, the present invention uses a silane coupling agent to modify the surface of the carbonized steel slag. This can not only achieve good volume stability of the steel slag aggregates based on the carbonization process, but also further improve the compatibility and adhesion between the carbonized steel slag and asphalt through the chemical bonding action of the silane coupling agent; in addition, the silane coupling agent wrapped on the surface of the carbonized steel slag also has lipophilic and hydrophobic properties, which can indirectly improve the volume stability of the steel slag aggregates. The gradient pressure carbonization and silane coupling agent synergistic modification process proposed by the present invention realizes the 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] Through the gradient pressure carbonization process, the steel slag coarse aggregate of the present invention has good internal structural stability, which not only improves the volume stability of the steel slag applied in the ultra-thin asphalt wearing course mixture, but also indirectly improves its application reliability in the asphalt mixture. At the same time, the present invention uses a silane coupling agent to treat the carbonized steel slag, and forms a covalent bond with the carbonized steel slag by virtue of its own chemical bonding action, forming a coupling layer on the surface of the carbonized steel slag aggregate to further improve the adhesion between the steel slag aggregate and the asphalt. The synergistic modification process of gradient pressure carbonization and silane coupling agent proposed by the present invention greatly improves the adhesion performance between the steel slag aggregate and the asphalt, improves the comprehensive performance of the asphalt mixture such as volume stability, water stability, and high-temperature stability, meets the dual requirements of the ultra-thin wearing course for driving safety and durability, and provides key technical support for green road construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention. These all belong to the protection scope of the present invention.

[0036] Example 1: Performance Test of Gradient Pressure Carbonized Steel Slag Aggregate

[0037] (1) Preparation of Gradient Pressure Carbonized Steel Slag Aggregate

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

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

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

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

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

[0043] (1) Pretreatment: First, obtain coarse steel slag aggregate with a particle size of 2.36 mm to 9.50 mm from basic oxygen furnace steel slag through crushing, magnetic separation, and screening; subsequently, use high-pressure water to wash the coarse steel slag aggregate to remove the dust on its surface; finally, place the coarse steel slag aggregate in an oven at 105 °C and dry it until a constant weight of coarse steel slag aggregate is obtained.

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

[0045] (3) Performance test of gradient pressure carbonized steel slag aggregate

[0046] The differences in the effects of gradient pressure and constant pressure on the performance of carbonized steel slag aggregate are studied through the calcium oxide conversion rate on the surface layer of the steel slag aggregate, the calcium oxide conversion rate inside, and the porosity of the product layer. The results are shown in Table 1. It can be seen from Table 1 that compared with gradient pressure, constant pressure makes the surface of the carbonized steel slag aggregate covered with a dense product layer, resulting in serious limitation of the internal reaction of the carbonized steel slag aggregate; compared with constant pressure, although the low-pressure setting in the later stage of gradient pressure will make the calcium oxide conversion rate on the surface of the carbonized steel slag aggregate lower because the low pressure will reduce the solubility of carbon dioxide in the liquid, the low-pressure condition will allow carbon dioxide to enter the inside of the carbonized steel slag aggregate, promoting the increase of the calcium oxide conversion rate inside the carbonized steel slag aggregate, resulting in a significant reduction in the carbonization difference inside and outside the steel slag aggregate.

[0047] Table 1 Performance test of carbonized steel slag aggregate

[0048] Performance index Gradient pressure carbonized steel slag aggregate Constant pressure carbonized 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 Test of Composite Modified Steel Slag Aggregate

[0050] (1) Preparation of Composite Modified Steel Slag Aggregate

[0051] Combined with the gradient pressure carbonized steel slag aggregate prepared in Example 1, in Example 2, the composite modified steel slag aggregate is prepared by the following preparation of γ-methacryloxy silane and surface modification treatment with silane coupling agent.

[0052] 1) Preparation of γ-methacryloxy silane: Sodium methacrylate and γ-chloropropyltrimethoxysilane are successively added to anhydrous ethanol for mixing. The mass ratio of sodium methacrylate to γ-chloropropyltrimethoxysilane is 1:1.5, and the mass of anhydrous ethanol is 2 times the sum of the masses of the above two; subsequently, at 60 °C, the above mixed solution is stirred with an electric stirrer for 0.6 hours, and the stirring rate is 800 r / min; finally, the above mixed solution is left standing in an incubator at 25 °C for 0.5 hours.

[0053] 2) Surface modification treatment with silane coupling agent: First, the carbonized steel slag aggregate is mixed with a 5% mass fraction silane coupling agent solution and soaked at room temperature for 0.5 hours; subsequently, the steel slag is filtered and cured and dried in an oven at 140 °C for 5 hours.

[0054] (2) Preparation of Comparative Carbonized Steel Slag Aggregate

[0055] In Example 2, the comparative carbonized steel slag aggregate is prepared only by pretreatment and gradient pressure carbonization treatment, and the carbonized steel slag aggregate at this place is not subjected to surface modification treatment. The pretreatment and gradient pressure carbonization treatment processes are the same as Steps 1 and 2 in the preparation of the gradient pressure carbonized steel slag aggregate in Example 1.

[0056] (3) Performance Test of Modified Steel Slag Aggregate

[0057] The volume stability and adhesion performance of the prepared composite modified steel slag aggregate and the comparative carbonized steel slag aggregate are tested by volume expansibility test and pull-out strength test.

[0058] 1) Test Methods

[0059] Volume expansion test: According to the GB / T 24175 standard, the volume expansion test was carried out on the composite modified steel slag aggregate and the comparative carbonized steel slag aggregate. First, the above two kinds of steel slag aggregates were respectively loaded into two identical cylindrical molds and compacted by a compactor (the height of the specimens was 120 mm); Subsequently, a semi-circular load plate with a mass of 5 kg was placed on the top of each of the two formed specimens; Then, the above specimens were first immersed in a 90 °C water bath environment for 6 h within one cycle (one day), and then the 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 reading data on the 1st day and the 3rd day were recorded, and the volume expansion rates of the two kinds of steel slag aggregates were calculated accordingly.

[0060] Pull-out strength test: A pull-out adhesion tester was used to analyze the adhesion strength between the above two kinds of steel slag aggregates and asphalt. First, the above two kinds of steel slag aggregates were cut, surface polished and cleaned to obtain pull-out bases with the same adhesion area; Subsequently, the molten asphalt binder was dropped onto the surfaces of the above two kinds 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 attached to the surfaces of the two kinds of steel slag aggregates was 1000 μm; Then, the above-prepared specimens were cured in a room temperature curing box for 24 h; Finally, a pull-out tester was used to test at a pull-out rate of 10 mm / min at 25 °C, and the pull-out strengths of the two kinds of steel slag aggregates were obtained.

[0061] 2) Analysis of aggregate performance test results

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

[0063] Table 2 Performance test of steel slag aggregate

[0064] Performance index Compound modified steel slag aggregate Comparative carbonized steel slag aggregate Volume expansion rate (%) 0.07 0.38 Pull-out strength (MPa) 4.20 2.10

[0065] Example 3: Performance test of ultra-thin wearing course asphalt mixture containing composite modified steel slag

[0066] Combined with the composite modified and comparative carbonized steel slag coarse aggregates prepared in Example 2, Example 3 prepared an ultra-thin wearing course asphalt mixture containing composite modified steel slag and comparative carbonized steel slag through the following measures.

[0067] (1) Preparation of ultra-thin wearing course asphalt mixture containing composite modified steel slag

[0068] 1) Preparation of PE-modified SBS composite modified asphalt: Slowly add preheated polyethylene (PE) particles (particle size < 1 mm) into molten SBS modified asphalt for mixing. The added mass of PE particles is 4% of the mass of SBS modified asphalt binder. Then, use a high-speed shear mixer to stir and react at 180 °C and a shear rate of 3500 r / min for 30 minutes.

[0069] 2) Preparation of asphalt mixture: Mix PE-modified SBS composite modified asphalt binder (dosage 5%), composite modified steel slag coarse aggregate (dosage 45%), basalt coarse and fine aggregate (dosage 45%), limestone powder, lignin fiber (dosage 0.4%), steel slag fiber (dosage 0.3%) and dicumyl peroxide (dosage 0.05%) according to the SMA-10 type asphalt mixture gradation. Subsequently, subject the above mixture to a treatment process with heating temperatures of 155 °C to 175 °C, mixing temperatures of 165 °C to 185 °C, and compaction temperatures of 140 °C to 155 °C to obtain an ultra-thin wearing course asphalt mixture containing composite modified steel slag.

[0070] (2) Preparation of ultra-thin wearing course asphalt mixture containing comparative carbonized steel slag

[0071] Preparation of asphalt mixture: Mix PE-modified SBS composite modified asphalt binder (dosage 5%), comparative carbonized steel slag coarse aggregate (dosage 45%), basalt coarse and fine aggregate (dosage 45%), limestone powder, lignin fiber (dosage 0.4%) and steel slag fiber (dosage 0.3%) according to the SMA-10 type asphalt mixture gradation. Subsequently, subject the above mixture to a treatment process with heating temperatures of 155 °C to 175 °C, mixing temperatures of 165 °C to 185 °C, and compaction temperatures of 140 °C to 155 °C to obtain an ultra-thin wearing course asphalt mixture containing comparative carbonized steel slag.

[0072] (3) Performance test of modified steel slag ultra-thin wearing course asphalt mixture

[0073] Use the high-temperature rutting test, immersion Marshall test and pendulum friction test to test the high-temperature stability, water stability and anti-skid performance of the prepared asphalt mixtures containing composite modified steel slag aggregate and comparative carbonized steel slag aggregate.

[0074] 1) Test methods

[0075] High-temperature rutting test: According to the JTG E20-2011 standard, a rutting meter was used to conduct a high-temperature rutting test on the above two kinds of steel slag asphalt mixtures. First, the above two kinds of steel slag asphalt mixtures were kept in a constant-temperature oven at 60°C for 5 hours. Subsequently, the above two kinds of steel slag asphalt mixtures were placed in the testing machine, and the specimens were rolled at a speed of 42 times / min, and the deformation of the specimens at 45 min and 60 min was recorded. Finally, the dynamic stability was calculated to evaluate the high-temperature stability of the two kinds of steel slag asphalt mixtures.

[0076] Immersion Marshall test: According to the JTG E20-2011 standard, an asphalt mixture stability meter was used to conduct an immersion Marshall test on the above two kinds of steel slag asphalt mixtures. First, the above two kinds of steel slag asphalt mixtures were immersed in a 60°C water bath for 30 min to test their stability. At the same time, the above two kinds of steel slag asphalt mixtures were immersed in a 60°C water bath for 48 hours to test their stability. Finally, the immersion residual strength of the two kinds of steel slag asphalt mixtures was calculated to evaluate the water stability of the two kinds of steel slag asphalt mixtures.

[0077] Pendulum friction test: According to the JTG E20-2011 standard, a pendulum friction tester was used to conduct a pendulum friction test on the above two kinds of steel slag asphalt mixtures. First, the above two kinds of steel slag asphalt mixtures were in two wet states. Subsequently, the pendulum friction tester was adjusted to meet the requirement of 126 mm. Finally, the pendulum value of the above two kinds of steel slag asphalt mixtures in the wet state was tested to evaluate the anti-skid performance of the two kinds of steel slag asphalt mixtures.

[0078] 2) Analysis of test results of asphalt mixture performance

[0079] The test results of the high-temperature stability, water stability and anti-skid performance of the above asphalt mixtures containing composite modified steel slag aggregates and comparative carbonized steel slag aggregates are shown in Table 3. It can be seen from Table 3 that compared with the asphalt mixture containing comparative carbonized steel slag aggregates, the dynamic stability, immersion residual strength and BPN value of the asphalt mixture containing composite modified steel slag aggregates are all larger, which indicates that the synergistic modification method of gradient pressure carbonization and silane coupling agent proposed by the present invention significantly improves the high-temperature stability, water damage resistance and anti-skid performance of steel slag asphalt mixtures. This fully reflects the advantages of the present invention in the resource utilization of steel slag and the improvement of the performance of ultra-thin asphalt wearing courses.

[0080] Table 3 Test of asphalt mixture performance

[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 above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A preparation method of steel slag co-modified by gradient carbonization and silane coupling, characterized in that, It includes the following steps: Step 1: Rinse the steel slag with a particle size of 2.36 mm to 9.50 mm to remove the surface dust, and then dry it to obtain steel slag coarse aggregate with a constant weight. Step 2: Then place it in a high-pressure reactor and carbonize it for 1 h to 2 h under the conditions of a pressure of 2.5 MPa to 4.0 MPa, a CO2 volume concentration of 90% to 98%, a temperature of 40 °C to 60 °C, and a liquid-solid ratio of 5 mL:1 g to 20 mL:1 g. Subsequently, continue to carbonize it for 2 h to 4 h under the conditions of a pressure of 0.8 MPa to 1.5 MPa, a CO2 volume concentration of 90% to 98%, a temperature of 40 °C to 60 °C, and a liquid-solid ratio of 5 mL:1 g to 20 mL:1 g. Filter and dry to obtain carbonized steel slag aggregate. Step 3: Then soak it in a silane coupling agent solution, filter, and dry to obtain composite modified steel slag.

2. The method according to claim 1, wherein The steel slag is one or more of basic oxygen furnace slag, electric arc furnace slag, and ladle refining furnace slag.

3. The method according to claim 1, wherein The silane coupling agent is one or more of γ-methacryloyloxy silane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltrimethoxysilane.

4. The method according to claim 3, wherein The preparation method of the γ-methacryloyloxy silane is as follows: First, add sodium methacrylate and γ-chloropropyltrimethoxysilane to anhydrous ethanol in sequence for mixing. The mass ratio of sodium methacrylate to γ-chloropropyltrimethoxysilane is 1:(1 - 2), and the mass of anhydrous ethanol is 1.5 times to 2.5 times the total mass of sodium methacrylate and γ-chloropropyltrimethoxysilane. Subsequently, stir at a temperature of 50 °C to 80 °C and a stirring rate of 600 r / min to 1000 r / min for 0.5 h to 1.0 h. Finally, let it stand at 20 °C to 30 °C for 0.5 h to 1.0 h.

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

6. A preparation method for a steel slag ultra-thin wearing course modified by gradient carbonization-silane coupling, characterized in that, It includes the following steps: First, mix asphalt binder, the composite modified steel slag prepared by the method according to any one of claims 1 - 5, natural coarse and fine aggregates, mineral powder, lignin fiber, steel slag fiber, and initiator according to the asphalt mixture gradation. Subsequently, process it successively through a heating temperature of 155 °C to 175 °C, a mixing temperature of 165 °C to 185 °C, and a compaction temperature of 140 °C to 155 °C to obtain an ultra-thin asphalt wearing course.

7. According to the method described in claim 6, The added mass of the composite modified steel slag 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. The added mass of the asphalt binder is 4% to 6% of the mass of the asphalt mixture. The natural coarse and fine aggregates are basalt coarse and fine aggregates. The added mass of the natural coarse and fine aggregates is 40% to 50% of the mass of the asphalt mixture. The mineral powder is limestone mineral powder. The added mass of the mineral powder is 4% to 8% of the mass of the asphalt mixture. The added mass of the lignin fiber is 0.3% to 1.2% of the mass of the asphalt mixture. The length of the steel slag fiber is 3 mm to 8 mm, and the diameter is 0.1 mm to 0.3 mm. The added mass of the steel slag fiber 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 added mass of dicumyl peroxide is 0.025% to 0.075% of the mass of the asphalt mixture.

9. The method according to claim 6, wherein The asphalt mixture gradation is one or more of SMA-10 type, OGFC-10 type, and AC-10 type gradations.

10. The method according to claim 7, wherein The preparation method of the PE-modified SBS composite modified asphalt is as follows: First, slowly add preheated polyethylene (PE) particles (particle size < 1 mm) to the molten SBS modified asphalt for mixing. The added mass of the PE particles is 3% to 6% of the mass of the SBS modified asphalt binder. Then, use a high-speed shear mixer to stir and react at 170 °C to 190 °C and a shear rate of 2000 to 5000 r / min for 20 to 40 minutes.

Images