Graphitized carbon layer modification-based high microwave thermal response aggregate as well as preparation method and application thereof

Abstract

The invention relates to a graphitized carbon layer modification-based high microwave thermal response aggregate as well as a preparation method and application thereof. The surface of a to-be-modified aggregate is coated with wood biomass; through a high-temperature pyrolysis carbonization process, biomass is directionally converted into a graphitized carbonization layer with a high heat conduction characteristic; and after annealing and screening treatment, the functionalized aggregate with the surface coated with a continuous carbonization layer is obtained. In the application process, the carbonized layer can efficiently absorb microwave energy and convert the microwave energy into heat energy, the aggregate-asphalt interface is induced to be rapidly heated, asphalt fluidity recovery is promoted, microcracks are filled, and self-healing repair of the pavement is achieved. Compared with the prior art, the graphitized carbon layer is generated on the surface of the aggregate in situ, so that the problems of local overheating, electromagnetic shielding effect and asphalt aging caused by non-uniform dispersion of a conductive phase in the prior art are solved in a breakthrough manner; and a solution with engineering feasibility is provided for intelligent repair of road micro-cracks, and meanwhile, the maintenance cost of the asphalt pavement is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering, and particularly to a highly microwave thermoresponsive aggregate modified by graphitized carbon layers, and a preparation method and application thereof. Background Art

[0002] Asphalt mixtures are widely used in the paving of highways and urban roads due to their excellent mechanical properties and durability. However, during long-term use, due to the repeated action of traffic loads, changes in environmental temperature and humidity, and the influence of ultraviolet aging and other factors, microcracks are likely to occur on asphalt pavements. The formation of these microcracks not only reduces the overall strength of the asphalt mixture but also exacerbates water penetration, causing the asphalt film to peel off, leading to further aging and structural damage. If the microcracks are not repaired in time, they will expand into macro-cracks, ultimately affecting the service life of the road and increasing maintenance costs. Therefore, an efficient repair technology for asphalt microcracks has become an important research direction in the field of road engineering.

[0003] Currently, the repair methods for asphalt microcracks mainly include physical repair, chemical repair, and microwave heating repair based on conductive fillers. Physical repair methods such as crack filling and heat repair usually require high-temperature construction, which not only consumes a large amount of energy but also has a greater impact on traffic (such as CN119432004A). Chemical repair mainly relies on polymer modifiers or tackifiers to improve the adhesion of asphalt, but the construction is complex, and it may cause secondary aging after being exposed to the environment for a long time (such as CN106810102A).

[0004] In recent years, microwave heating repair has been considered a promising intelligent road maintenance technology due to its non-contact heating characteristics and efficient energy transfer advantages. Microwave heating acts on polar molecules in the material, causing it to rapidly heat up, thereby promoting the restoration of the fluidity of asphalt and filling microcracks. However, due to the limited microwave absorption capacity of asphalt itself, existing microwave repair technologies generally need to add conductive fillers such as graphite, carbon nanotubes, and metal powders to asphalt mixtures to enhance the absorption and conversion of microwave energy. However, there are still many problems in the application of these traditional conductive fillers, such as easy agglomeration and uneven dispersion of the fillers, resulting in local overheating; in addition, some conductive fillers will produce an electromagnetic shielding effect, affecting the uniform transmission of microwave energy, thereby reducing the repair efficiency. The use of traditional conductive fillers may also cause excessive aging of asphalt and accelerate the deterioration of road performance. Summary of the Invention

[0005] The object of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a highly microwave thermoresponsive aggregate modified by a graphitized carbon layer, its preparation method and application, which breaks through the problems of local overheating, electromagnetic shielding and asphalt aging caused by uneven dispersion of fillers in the traditional conductive filler method. At the same time, the microwave energy utilization rate is significantly improved, making the repair of pavement microcracks more efficient and uniform, and providing a new idea for improving road durability and reducing maintenance costs.

[0006] In the conception process of the present invention, it is considered that in-situ growth of a graphitized carbon layer on the surface of the aggregate by high-temperature carbonization technology can effectively enhance the microwave absorption ability and thermal conductivity of the aggregate, thereby optimizing the efficiency of microwave repair of asphalt cracks. Traditional microwave repair technologies often rely on externally added conductive fillers such as metal powders, graphite, and carbon nanotubes. These materials have poor dispersibility in asphalt mixtures, easily leading to local overheating, low energy utilization rate, and even affecting the aging performance of asphalt. In contrast, the present invention constructs a stable conductive-thermal network by in-situ growth of a continuous carbonized layer on the surface of the aggregate, which can not only uniformly absorb microwave energy and improve the heat transfer efficiency, but also avoid the performance deterioration problems brought by additional fillers. In addition, the use of renewable biomass (such as bamboo powder, bagasse, wood chips, etc.) as the carbonization precursor conforms to the green and low-carbon development strategy, reduces carbon emissions during road construction and maintenance, and is of great significance for sustainable road engineering construction.

[0007] Therefore, the present invention proposes a highly microwave thermoresponsive aggregate modified by a graphitized carbon layer. By in-situ growth of a conductive carbonized layer on the surface of the aggregate through a high-temperature carbonization process, the microwave absorption ability and thermal conductivity of the aggregate are enhanced. Under the action of microwaves, this carbonized layer can efficiently absorb electromagnetic energy and convert it into heat energy, thereby inducing rapid heating of the aggregate-asphalt interface, improving the fluidity of the asphalt, and enabling self-healing of microcracks. This method makes microwave heating more uniform, avoids asphalt aging problems caused by poor filler dispersion, and further improves road durability and repair effects.

[0008] The object of the present invention can be achieved by the following technical solutions:

[0009] The first aspect of the present invention provides a preparation method of a highly microwave thermoresponsive aggregate modified by a graphitized carbon layer, which is characterized by including the following steps:

[0010] S1. Biomass loading: Mix natural mineral aggregates with a particle size of 2.36 - 31.5 mm and woody biomass with a mesh size of 50 - 300 in a volume ratio of 1:10 - 1:20, and uniformly wrap the woody biomass on the surface of the natural mineral aggregates by mechanical stirring to obtain biomass-loaded aggregates;

[0011] S2. High-temperature pyrolysis carbonization: Under nitrogen protection, heat the aggregate loaded with biomass to 800 - 1100 °C and keep it warm for 30 - 120 minutes to generate an in-situ graphitized carbon layer;

[0012] S3. Annealing treatment: Keep the pyrolyzed aggregate at a constant temperature of 600 - 800 °C for 10 - 60 minutes, and then perform particle size screening to obtain high microwave thermal response aggregates.

[0013] Further, in S1, the lignocellulosic biomass is selected from at least one of bamboo powder, wood chips, bagasse, cotton fiber or coconut shell fiber, and the carbon content of the lignocellulosic biomass is ≥ 40 wt%.

[0014] Further, in S1, the natural mineral aggregate is selected from at least one of basalt, granite, limestone, and siliceous sandstone, and the surface roughness Ra of the natural mineral aggregate is ≥ 50 μm.

[0015] Further, in S2, the microstructure of the graphitized carbon layer includes 3 - 10 graphene sheets, the interlayer spacing is 0.335 - 0.340 nm, and the ID / IG value is ≤ 0.25.

[0016] Further, in S2, the thickness of the graphitized carbon layer is 10 - 200 μm, the thermal conductivity of the graphitized carbon layer is ≥ 120 W / (m·K), and the resistivity is ≤ 1×10 -3 Ω·m;

[0017] In S2, the heating method is: heat the aggregate loaded with biomass to 800 - 1100 °C at a heating rate of 5 - 10 °C / min.

[0018] Further, in S3, the annealing treatment adopts a gradient cooling process, specifically including:

[0019] Cool from the pyrolysis temperature in S2 to the 600 °C constant temperature platform at a rate of 5 °C / min, keep it for 30 minutes and then cool naturally to room temperature;

[0020] During the gradient cooling process, the oxygen content is controlled at ≤ 50 ppm.

[0021] The second aspect of the present invention provides a high microwave thermal response aggregate prepared by the above method.

[0022] The third aspect of the present invention is an application of the above high microwave thermal response aggregate, including the following steps:

[0023] Prepare the road structure with high microwave thermal response aggregates according to the asphalt mixture gradation requirements. When microcracks appear on the road, use microwave energy to heat the road structure. The carbonized layer in it efficiently absorbs microwave energy and converts it into heat energy, inducing the rapid temperature rise at the aggregate-asphalt interface, restoring the fluidity of the asphalt and filling the microcracks, thereby achieving self-healing repair of the road surface.

[0024] Furthermore, during the microwave-activated repair process, when cracks of 10 μm - 1 cm appear, irradiate with microwaves of 2.45 - 5.80 GHz at a power of 300 - 1200 W for 1 - 10 minutes to raise the temperature of the carbon layer on the aggregate surface to 80 - 180 °C to induce asphalt flow, and let it stand for 12 - 24 hours to complete self-healing.

[0025] Furthermore, in S4, the dosage of the high microwave thermal response aggregates in the asphalt mixture is 20 - 60% of the total mass of the aggregates, and the particle size distribution meets the requirements of continuous gradation;

[0026] The microwave-activated repair process also includes a self-healing efficiency evaluation step: real-time monitor the temperature field distribution in the crack area through infrared thermal imaging, and terminate the irradiation when the temperature gradient ΔT ≤ 5 °C.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] Based on the high-temperature carbonization technology, the present invention realizes the intelligent repair of asphalt mixtures by in-situ constructing a high microwave response carbonized layer on the aggregate surface, and has the following outstanding advantages: (1) Compared with traditional asphalt concrete, its self-healing ability is improved by 2 times; (2) Optimize the energy transfer at the asphalt-aggregate interface, avoid local overheating, and make the repair of microcracks more uniform and efficient; (3) Reduce maintenance costs, improve road durability, and extend the service life of the road; (4) Use renewable biomass, meet the carbon neutral development goal, and provide a new solution for green road construction. This technology can be widely applied to high-grade highways, roads in cold regions and intelligent road repair projects, which has important value for improving the intelligence and sustainable development of road engineering, and has no environmental pollution, and has broad engineering application prospects. Description of the Drawings

[0029] Figure 1 It is an infrared photo taken after 30S of microwave heating;

[0030] Figure 1 Marking description in

[0031] (a) - unmodified aggregate, (b) - modified aggregate

[0032] Figure 2 It is an infrared photo taken after 1 minute of microwave heating;

[0033] Figure 2Marking Explanation:

[0034] (a) - Unmodified semi - circular specimen, (b) - Modified semi - circular specimen.

[0035] Figure 3 It is a bar chart of the maximum failure load in the splitting test of asphalt mixture. Specific Implementation Manner

[0036] Overall, in the method for preparing asphalt concrete for realizing the self - healing ability of pavement cracks in the present invention, part of the aggregates in the asphalt concrete are high - microwave - thermal - response aggregates. The surface of the modified aggregates is covered with a graphitized carbon layer. The modified aggregates have a high efficiency in converting electromagnetic waves into heat energy, which can improve the heating rate of asphalt concrete under the action of microwaves, make the asphalt have fluidity again, and realize the active healing of cracks in the asphalt concrete pavement. The method includes the following steps: covering biomass on the surface of the aggregates to be modified, in - situ growing a graphitized carbon layer on the surface of the aggregates through high - temperature treatment, and preparing asphalt concrete using the modified aggregates. The modified asphalt concrete has self - healing ability.

[0037] The specific process includes:

[0038] Biomass Loading: Wrapping woody biomass on the surface of the aggregates to be modified;

[0039] High - temperature Pyrolysis Carbonization: Performing high - temperature pyrolysis treatment on the aggregates loaded with biomass to in - situ convert the biomass on the surface of the aggregates into a graphitized carbonized layer with high thermal conductivity;

[0040] Annealing and Screening: Performing annealing treatment on the pyrolyzed aggregates to improve the structural stability of the carbonized layer, and screening to obtain functionalized aggregates with a continuous carbonized layer on the surface;

[0041] Microwave - activated Self - Healing: Using the functionalized aggregates in the road structure for preparing asphalt mixture, and when micro - cracks appear on the road surface, heating the carbonized layer on the surface of the aggregates by microwave energy to restore the fluidity of the asphalt and fill the micro - cracks, thereby realizing the self - healing repair of the road surface.

[0042] Specifically, the woody biomass is selected from natural high - carbon - content materials such as bamboo powder, wood chips, bagasse, cotton fiber, coconut shell fiber, etc.

[0043] Specifically, the aggregates are selected from natural mineral aggregates such as basalt, granite, limestone, siliceous sandstone or other aggregates suitable for asphalt mixture.

[0044] Specifically, the specific temperature range of the high - temperature pyrolysis treatment is 800 - 1100 °C to optimize the graphitization degree and thermal conductivity of the carbonized layer on the surface of the aggregates.

[0045] During specific implementation, the high-temperature pyrolysis time is controlled within 30 to 120 minutes to ensure that the biomass is fully carbonized and a continuous and uniform graphene-like carbonized layer is formed.

[0046] During specific implementation, the annealing treatment is carried out by constant-temperature treatment at a temperature of 600 to 800 °C for 10 to 60 minutes to reduce the structural defects in the carbonized layer and improve the thermal stability.

[0047] During specific implementation, the screening treatment uses particle size screening with a specification of 2.36 to 31.5 mm to ensure that the aggregate particle size meets the grading requirements of the asphalt mixture.

[0048] During specific implementation, the unmodified aggregate is immersed in distilled water and cleaned by an ultrasonic cleaner in water at a temperature of 20 to 30 °C for 5 to 10 minutes to remove surface dust and stains. After cleaning, it is dried in an oven at 80 to 120 °C for 1 to 3 hours to remove the excess water in the aggregate until the weight of the aggregate to be modified no longer changes to obtain the aggregate to be modified. The aggregate to be modified after preliminary treatment is left standing in a forced-air oven at 20 to 30 °C for 24 hours and stored in a dark and dry place for standby.

[0049] During specific implementation, the biomass waste is placed in a shady place and naturally air-dried for 24 to 48 hours. The air-dried biomass waste is sieved to remove the dust mixed in it, and further dried at 60 to 150 °C for 3 to 30 hours. After the preliminary-treated waste biomass is cooled to room temperature, it is stored in a dark and dry place for standby.

[0050] During specific implementation, the reserved biomass waste is crushed to a fineness of 50 to 300 meshes. After the crushed particles are sieved, the mixture of biomass waste particles with a fineness of 50 to 300 meshes and the aggregate to be modified is mechanically stirred at a low speed of 20 to 50 r / min so that the biomass waste particles wrap around the surface of the aggregate to be modified.

[0051] During specific implementation, according to the above, the volume ratio of the aggregate to be modified to the biomass waste is 1:10 to 1:20. The volume of the aggregate to be modified is measured by the drainage method, and the volume of the biomass waste powder is measured by the vibrating funnel method.

[0052] The pyrolysis temperature is 800 - 1100 °C, and the heating rate during the pyrolysis process is 5 °C / min to 10 °C / min. The temperature increase process in the pyrolysis stage is: starting from room temperature as the starting point of temperature increase, the temperature is increased to the pyrolysis temperature at a heating rate of 5 °C / min to 10 °C / min.

[0053] During specific implementation, the temperature of the functionalized aggregate can rise to 80 - 180 °C within 40 to 120 seconds of microwave irradiation, thereby inducing the asphalt to regain fluidity and fill the microcracks.

[0054] During specific implementation, the carbonization process is to keep the temperature at 800 - 1100°C for 50 - 70 minutes.

[0055] During specific implementation, the modified aggregate replaces the ordinary aggregate, and the self-healing asphalt concrete is prepared according to JTG E20 - 2011 "Test Procedures for Bitumen and Bituminous Mixtures in Highway Engineering".

[0056] During specific implementation, the microwave-activated self-healing process includes the following steps:

[0057] 1) Pre-open the microwave heating equipment and make it run stably for 10 - 15 minutes to ensure that the equipment outputs power in a stable state. The working frequency of the microwave heating equipment is set in the range of 2.45 GHz - 5.80 GHz, and an appropriate excitation frequency is selected within this range to ensure uniform heating of the modified asphalt concrete material. During the equipment preheating process, monitor that the microwave power is between 300 W and 1200 W.

[0058] 2) According to JTG E - 20 - 2011 "Test Procedures for Bitumen and Bituminous Mixtures in Highway Engineering", make the self-healing asphalt concrete into standard test specimens.

[0059] 3) According to JTG E - 20 - 2011 "Test Procedures for Bitumen and Bituminous Mixtures in Highway Engineering", induce cracks by simulating traffic loads, temperature alternation, or low-temperature freeze-thaw cycles, etc. The width of the microcracks is 10 microns - 1 centimeter.

[0060] 4) The microwave activation time is 1 - 10 minutes. After the heat is transferred to the edge of the crack area, the asphalt matrix softens and becomes fluid.

[0061] 5) After microwave heating, the modified asphalt concrete is left to stand at 20 - 25°C for 12 - 24 hours to stabilize the microstructure and macroscopic properties.

[0062] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Features such as preparation means, materials, structures, or composition ratios that are not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0063] Example 1

[0064] 1. Select basalt aggregates with a particle size greater than or equal to 2.36. Further, use an ultrasonic cleaner to clean the aggregates to be modified in a 27°C water bath environment for 20 minutes to obtain aggregates with no sand and stains on the surface. The surface roughness Ra = 85 μm (tested with a white light interferometer). Further, dry the cleaned aggregates in an oven at 100°C for 24 hours until the weight of the aggregates no longer changes.

[0065] 2. Select Chinese fir as the biomass source. Place the Chinese fir segments in a 27°C water bath and clean the Chinese fir segments with an ultrasonic machine for 5 minutes to obtain biomass with no sand and stains on the surface. Place the biomass in a 30°C forced-air oven and dry for 12 hours to remove the moisture in the biomass. Crush the Chinese fir segments into 200-mesh particles for standby. After testing, the carbon content of Chinese fir is ≥40 wt%.

[0066] 3. Mechanically stir 1 volume of aggregate and 15 volumes of Chinese fir particles for 5 minutes to disperse the aggregate in the biomass particles. Microscopic observation shows that the biomass coverage rate ≥95%. Pour the mixture into a crucible and mechanically compact it, then cover the crucible lid and place it in a muffle furnace.

[0067] 4. Pass nitrogen into the muffle furnace at a flow rate of 60 ml / min and pass nitrogen for 30 min before the reaction starts. Set the pyrolysis heating rate of the muffle furnace to 10°C / min, heat up to 800°C and then hold for 60 min for carbonization. The annealing treatment adopts a gradient cooling process, specifically including: cooling from the pyrolysis temperature to a 600°C constant temperature platform at a rate of 5°C / min, maintaining for 30 minutes and then naturally cooling to room temperature; controlling the oxygen content ≤50 ppm during the gradient cooling process. After carbonization, naturally cool to 25°C room temperature and take out the mixture in the crucible. Sieve to obtain the modified aggregate.

[0068] Raman spectroscopy proves that the ID / IG of the graphene carbonization layer ≤0.25, TEM shows 4 - 6 layers of graphene sheets with an interlayer spacing of 0.337 nm. The thermal conductivity is 135 W / (m·K) (LFA 467 laser thermal conductivity meter), and the resistivity is 0.7×10-3 Ω·m (four-probe method).

[0069] Figure 1 Photos taken by infrared after 30S of microwave heating: (a) - unmodified aggregate, (b) - modified aggregate. Figure 1 It can be seen that after heating the basalt aggregate and the modified aggregate in the microwave oven for 30 seconds, the average surface temperature of the ordinary aggregate under the infrared camera is 47.6°C, and the average surface temperature of the modified aggregate under the infrared camera is 141.2°C. The heat conduction ability of the modified aggregate far exceeds that of ordinary basalt.

[0070] 5. According to the JTG E-20-2011 "Test Procedures for Bitumen and Bituminous Mixtures in Highway Engineering" specification, use the Marshall standard compaction molding method to mold cylindrical Marshall specimens with a diameter of 101 mm and a height of 63 mm. Among them, 4 parallel control specimens W1 - W4 are prepared with unmodified aggregate, and 4 specimens G1 - G4 are prepared with modified aggregate. Among them, the bitumen used for the unmodified specimens and the modified specimens is SK-70 matrix bitumen produced in South Korea.

[0071] 6. And pre-treat all specimens according to the T 0716-2011 asphalt mixture splitting test in this specification.

[0072] 7. The loading rate of the press head is 50 mm / min. Record the maximum load at which the specimen fails.

[0073] The maximum loads at which the specimens fail are shown in the following table:

[0074] Table 2 Details of the maximum failure loads in the asphalt mixture splitting test

[0075]

[0076]

[0077] 8. Remove the failed specimen from the UTM machine and align the cracks on the ceramic tray for splicing.

[0078] 9. Pre-start the microwave heating equipment and run it stably for 10 minutes to ensure that the equipment outputs power in a stable state. Among them, the microwave power is 1200 W. Place the failed specimen and the ceramic tray in the microwave equipment and heat and activate for 3 minutes.

[0079] Figure 2 Infrared photos taken 1 minute after microwave heating: (a) - unmodified semi-circular specimen, (b) - modified semi-circular specimen. From Figure 2 It can be seen that the average surface temperature of the unmodified semi-circular specimen prepared with ordinary basalt aggregate under the infrared camera is 31 °C, and the average surface temperature of the modified semi-circular specimen prepared with modified aggregate under the infrared camera is 69.8 °C, and the surface thermal difference of the modified semi-circular specimen is much smaller than that of the unmodified semi-circular specimen.

[0080] 10. Place the specimen and the ceramic tray after heating and activation in a ventilated and shaded place at 25 °C - 30 °C and let it stand for 18 hours (during the standing process, the laboratory temperature may change).

[0081] 11. Repeat the asphalt mixture splitting test on the healed specimen until the specimen is completely damaged and the cracks cannot be healed under the action of microwaves. Record the number of times the specimen is healed.

[0082] The number of times the specimens are healed is shown in the following table:

[0083] Table 2 Details of the number of times the specimens are healed after the asphalt mixture splitting test

[0084] Test object Number Number of healing times Unmodified specimen W1 3 Unmodified specimen W2 3 Unmodified specimen W3 3 Unmodified specimen W4 4 Specimen modified with graphitized aggregate G1 5 Specimen modified with graphitized aggregate G2 7 Specimen modified with graphitized aggregate G3 6 Specimen modified with graphitized aggregate G4 6

[0085] Figure 3 It is a bar chart of the maximum failure loads in the asphalt mixture splitting test.

[0086] As can be seen from the above conclusions, the self-healing ability of the modified asphalt concrete specimens prepared from the modified aggregates of Chinese fir has been enhanced. The self-healing ability of the modified asphalt concrete has been increased by 2 times compared with that of the unmodified asphalt concrete.

[0087] Example 2

[0088] The following process is different from Example 1:

[0089] In this example, the aggregate is selected as 31.5 mm limestone aggregate (Ra = 120 μm).

[0090] Bamboo powder with a carbon content of 43 wt% (tested according to the standard of GB / T 28734-2012) is used and pulverized to 50 mesh.

[0091] The aggregate and bamboo powder are mixed in a volume ratio of 1:10 and strongly stirred by a planetary mixer for 15 minutes to form a pre-coating with a thickness of 2-3 mm.

[0092] It is heated to 1100 °C at a rate of 5 °C / min and held for 30 minutes, and the carbon layer thickness reaches 200 μm.

[0093] It is cooled down to 600 °C at a gradient and held at a constant temperature for 60 minutes (oxygen content ≤ 20 ppm), and the 26.5-31.5 mm aggregate is obtained by sieving.

[0094] Raman ID / IG = 0.08 (highly graphitized), interlayer spacing 0.335 nm (calculated by XRD).

[0095] Thermal conductivity 148 W / (m·K), resistivity 0.3×10-3 Ω·m.

[0096] Microwave response test: A 1 cm crack is completely healed after being irradiated with 5.8 GHz / 1200 W for 5 minutes.

[0097] Example 3

[0098] The following process is different from Example 1:

[0099] In this example, the aggregate is selected as 2.36 mm siliceous sandstone (Ra = 55 μm).

[0100] Coconut shell fiber with a carbon content of 68 wt% (GB / T 28734-2012) is used and pulverized to 300 mesh to form a nano-scale powder.

[0101] The aggregate and coconut shell powder are mixed in a volume ratio of 1:20.

[0102] It is heated to 800 °C at a rate of 10 °C / min in a vacuum furnace and held for 120 minutes, and the carbon layer thickness is 10 μm.

[0103] Directly cool down to 800 °C and keep it at a constant temperature for 10 minutes (oxygen content ≤ 10 ppm) to obtain fine aggregates with a size of 0.6 - 2.36 mm.

[0104] Raman ID / IG = 0.24, and TEM shows a three-layer graphene structure.

[0105] Thermal conductivity is 122 W / (m·K), and resistivity is 0.9×10-3 Ω·m.

[0106] A 10-μm microcrack heals after being irradiated at 3 GHz / 300 W for 1 minute, and the infrared thermal image shows ΔT = 3.2 °C.

[0107] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a highly microwave thermally responsive aggregate based on graphitized carbon layer modification, characterized in that: The following steps are involved: S1. Biomass loading: natural mineral aggregate with a particle size of 2.36-31.5 mm and woody biomass with a particle size of 50-300 mesh are mixed at a volume ratio of 1:10-1:20, and the woody biomass is evenly coated on the surface of the natural mineral aggregate by mechanical stirring to obtain a biomass-loaded aggregate; S2. High temperature pyrolysis carbonization: under nitrogen protection, the biomass-loaded aggregate is heated to 800-1100°C and kept at this temperature for 30-120 minutes to generate an in-situ graphitized carbon layer; S3. Annealing treatment: The pyrolyzed aggregate is treated at a constant temperature of 600-800°C for 10-60 minutes, and then the particle size is screened to obtain high microwave thermal response aggregate.

2. The method for preparing a highly microwave thermally responsive aggregate based on graphitized carbon layer modification according to claim 1, characterized in that: In S1, the woody biomass is selected from at least one of bamboo powder, wood chips, bagasse, cotton fiber or coconut shell fiber, and the carbon content of the woody biomass is ≥40wt%.

3. The method for preparing a highly microwave thermally responsive aggregate based on graphitized carbon layer modification according to claim 1, characterized in that: In S1, the natural mineral aggregate is selected from at least one of basalt, granite, limestone, and siliceous sandstone, and the surface roughness Ra of the natural mineral aggregate is ≥50 μm.

4. The method for preparing a highly microwave thermally responsive aggregate based on graphitized carbon layer modification according to claim 1, characterized in that: In S2, the microstructure of the graphitized carbon layer comprises 3-10 graphene sheets, the interlayer spacing is 0.335-0.340 nm, and the ID / IG value is ≤0.

25.

5. The method for preparing a highly microwave thermally responsive aggregate based on graphitized carbon layer modification according to claim 1, characterized in that: In S2, the thickness of the graphitized carbon layer is 10-200 μm, the thermal conductivity of the graphitized carbon layer is ≥120 W / (m·K), and the resistivity is ≤1×10 -3 Ω·m; In S2, the heating method is: heating the biomass-loaded aggregate to 800-1100°C at a heating rate of 5-10°C / min.

6. The method for preparing a highly microwave thermally responsive aggregate based on graphitized carbon layer modification according to claim 1, characterized in that: In S3, the annealing treatment adopts a gradient cooling process, which specifically includes: The temperature of S2 was lowered from the pyrolysis temperature to a constant temperature platform of 600 °C at a rate of 5 °C / min, maintained for 30 min, and then naturally cooled to room temperature; The oxygen content is controlled at ≤50 ppm during the gradient cooling process.

7. A high microwave thermal response aggregate prepared by the method as described in any one of claims 1 to 6.

8. An application of the high microwave thermal response aggregate as claimed in claim 7, comprising the following steps: The road structure is prepared with high microwave thermal response aggregate according to the asphalt mixture grading requirements. When microcracks appear on the road, microwave energy is used to heat the road structure. The carbonized layer efficiently absorbs microwave energy and converts it into heat energy, inducing rapid heating of the aggregate-asphalt interface, restoring the fluidity of the asphalt and filling the microcracks, thereby achieving self-healing repair of the road surface.

9. The use of a high microwave thermal response aggregate according to claim 8, characterized in that: During the microwave activated repair process, when cracks of 10μm-1cm appear, 2.45-5.80GHz microwaves are used at a power of 300-1200W for 1-10 minutes to heat the carbon layer on the aggregate surface to 80-180℃ to induce asphalt flow, and then the mixture is left to stand for 12-24 hours to complete self-healing.

10. The use of a high microwave thermal response aggregate according to claim 8, characterized in that: In S4, the amount of the high microwave thermal response aggregate in the asphalt mixture is 20-60% of the total mass of the aggregate, and the particle size distribution meets the continuous grading requirements; The microwave-activated repair process also includes a self-healing performance evaluation step: real-time monitoring of the temperature field distribution in the crack area through infrared thermal imaging, and terminating irradiation when the temperature gradient ΔT≤5°C.

Images