Hard asphalt mixture and preparation method thereof

Abstract

The invention discloses a hard asphalt mixture and a preparation method thereof, and belongs to the technical field of road engineering materials. Aiming at the problems of insufficient strength, stability and durability of the existing hard asphalt mixture, the method comprises the following steps: grading and mixing basalt and diabase composite coarse aggregate, medium aggregate with a specific ratio, fine aggregate containing basalt mineral fibers and limestone mineral powder; the preparation method comprises the following steps: heating to 175-185 DEG C, adding modified asphalt prepared by shearing and blending matrix asphalt and a styrene-butadiene-styrene block copolymer modifier, carrying out dry mixing and wet mixing, scattering lignin fibers, and carrying out thermal insulation aging and three-stage compaction molding. Wherein the rotating speed and time of dry mixing and wet mixing are controlled, the compaction is divided into initial pressing, re-pressing and final pressing stages, and different pressures are set. According to the preparation method, the performance of the mixture is improved by optimizing aggregate composition, a modified asphalt process and mixing and compacting parameters, and the preparation method is mainly used for road engineering construction with high requirements on pavement strength and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of road engineering materials, and particularly relates to a hard asphalt mixture and a preparation method thereof. Background Art

[0002] In the field of road engineering, hard asphalt mixtures are widely used in scenarios with high requirements for pavement performance, such as heavy traffic sections and long and steep longitudinal slope sections, due to their high strength, high stability and other characteristics. However, there are still a series of technical challenges in the preparation and performance improvement of existing hard asphalt mixtures, and these challenges mainly focus on aspects such as material composition design, process control and performance collaborative optimization. [[ID=**10**]]

[0003] The aggregate gradation of traditional hard asphalt mixtures often has the problem of singularity. For example, a single type of rock is often used for coarse aggregates, resulting in insufficient strength and stability of the skeleton structure and being difficult to effectively resist the permanent deformation caused by heavy traffic. The particle size distribution and particle shape control of medium aggregates are not precise enough. When the content of flaky and needle-shaped particles is relatively high, stress concentration points are easily formed in the mixture, reducing the overall mechanical properties. The compounding ratio and dispersion effect of mineral fibers and manufactured sand in fine aggregates are not good. The reinforcing effect of mineral fibers cannot be fully exerted, and the unreasonable stone powder content in manufactured sand will affect the cementing performance between asphalt and aggregates.

[0004] The performance limitations of matrix asphalt are significant, and it is difficult to balance its high-temperature rutting resistance and low-temperature cracking resistance. In traditional modification processes, the dispersion uniformity of modifiers is insufficient.

[0005] The application of fiber materials also has technical bottlenecks. As a commonly used reinforcing material, lignin fiber has strong surface hydrophilicity and poor compatibility with hydrophobic asphalt. The traditional direct addition method is prone to uneven fiber dispersion and local agglomeration, which not only fails to achieve uniform reinforcement but may also become a weak link in the mixture. In addition, improper control of the fiber moisture content will affect the coating effect of asphalt. Excessive moisture content may generate steam during high-temperature mixing, resulting in defects such as air bubbles in the mixture.

[0006] The root cause of the above problems is that the synergistic action mechanism between material composition and process parameters has not been fully clarified, and the technical optimization of each link lacks systematic consideration. Therefore, it is urgent to carry out systematic innovation to improve the comprehensive performance and engineering applicability of hard asphalt mixtures. Summary of the Invention

[0007] An object of an embodiment of the present invention is to solve at least the above problems and / or defects and provide at least the advantages described hereinafter.

[0008] The object of the present invention also lies in solving the following problems: To solve the problem that in the preparation of existing hard asphalt mixtures, the aggregate gradation is unreasonable, and the mixing and compaction process control is insufficient, resulting in the strength, stability and durability of the mixture being difficult to meet the requirements of high-demand road projects. To solve the problem that due to the poor compatibility between lignin fiber and asphalt caused by its surface hydrophilicity, direct addition is prone to uneven dispersion and improper moisture content control, affecting the asphalt coating effect and the performance of the mixture.

[0009] To solve the problem that the content of flaky and needle-shaped particles in medium-sized aggregates is high and the particle size distribution is unreasonable, which is prone to stress concentration and reduces mechanical properties.

[0010] To solve the problem that the mineral fiber reinforcement effect in fine aggregates is not fully exerted and the content of stone powder in manufactured sand is unreasonable, affecting the bonding performance between asphalt and aggregates.

[0011] To solve the problem that in the preparation of modified asphalt, the modifier is unevenly dispersed and the swelling process control is insufficient, resulting in poor modification effect and easy segregation.

[0012] To solve the problem that during the heat preservation and aging process, the mixture is prone to oxidation and aging, and the heat distribution is uneven, resulting in internal performance differences.

[0013] To solve the problem that during the compaction process, the pressure and vibration mode are unreasonable, and it is difficult to optimize the cooperative operation parameters of the roller combination, affecting the compactness and pavement performance.

[0014] To solve the problem that the interfacial bonding force between basalt mineral fiber and aggregate is weak, affecting the performance of the mixture.

[0015] To solve the problem that the interfacial bonding force between limestone mineral powder and asphalt is insufficient, resulting in poor water stability and durability of the mixture.

[0016] Another object of the present invention is to provide a hard asphalt mixture and a preparation method thereof.

[0017] For this reason, the technical solution provided by the present invention is as follows: In the first aspect, a preparation method of a hard asphalt mixture includes the following steps: By weight, 38-42 parts of coarse aggregates with a particle size of 13-19 mm, 28-32 parts of medium-sized aggregates with a particle size of 5-13 mm, 23-27 parts of fine aggregates with a particle size of 0-5 mm, and 7-9 parts of limestone mineral powder with a particle size less than 0.075 mm are proportionally mixed, wherein the coarse aggregates are composed of basalt and diabase compounded in a mass ratio of 1:1; The mixed aggregates are heated to 175-185 °C in a drum-type heating device, and the surface temperature of the aggregates is monitored in real time through a temperature sensor. When the temperature reaches 175-185 °C; Add modified asphalt accounting for 4.5 - 5.5% of the total mass of the aggregate. The modified asphalt is prepared by shear blending matrix asphalt and 8 - 12% styrene - butadiene - styrene block copolymer modifier at 165 - 175 °C; Start dry mixing at 160 - 170 °C, with a dry mixing speed of 40 - 45 revolutions per minute and a dry mixing duration of 12 - 15 seconds; After the dry mixing is completed, evenly sprinkle lignin fiber accounting for 0.3 - 0.5% of the total mass of the aggregate, and increase the speed to 55 - 60 revolutions per minute for wet mixing, with a wet mixing duration of 45 - 50 seconds; Keep the mixture after wet mixing at a temperature of 155 - 165 °C for heat preservation and aging for 2 - 3 hours; Compact the aged mixture. Compact it in three stages at 145 - 155 °C. The pressure in the initial compaction stage is 2 - 3 MPa, the pressure in the re - compaction stage is 5 - 6 MPa, and the pressure in the final compaction stage is 1 - 2 MPa.

[0018] Preferably, in the preparation method of the hard asphalt mixture, the lignin fiber is pretreated in two stages before being mixed with the dry - mixed materials, including: In the first stage, place the lignin fiber in an ultrasonic dispersion tank and process it for 3 - 5 minutes under the conditions of a frequency of 40 - 50 kHz and a power of 200 - 300 W; In the second stage, mix the lignin fiber treated in the first stage with an aqueous solution of polyoxyethylene surfactant accounting for 0.5 - 0.8% of the fiber mass. The mass fraction of the aqueous solution of polyoxyethylene surfactant is 1.5%. Remove the excess water through a centrifugal dehydrator at a speed of 1200 - 1500 rpm, and finally control the fiber moisture content at 15 - 18%.

[0019] Preferably, in the preparation method of the hard asphalt mixture, the medium - sized aggregate with a particle size of 5 - 13 mm is composed of granite and limestone in a mass ratio of 3:2, and after screening, the content of flaky and needle - shaped particles is controlled below 8%. The medium - sized aggregate is re - sized by a vibrating screen before gradation mixing, and the 5 - 8 mm particles and 9 - 13 mm particles are mixed in a mass ratio of 1:2.

[0020] Preferably, in the preparation method of the hard asphalt mixture, the fine aggregate with a particle size of 0 - 5 mm contains 15 - 20% basalt mineral fiber and 80 - 85% limestone manufactured sand of the total mass of the fine aggregate. The length of the mineral fiber is 3 - 6 mm and the diameter is less than 0.1 mm. The content of stone powder below 0.075 mm in the manufactured sand is limited to 7 - 9%.

[0021] Preferably, in the preparation method of the hard asphalt mixture, the preparation process of the modified asphalt specifically includes: Heat the base asphalt to 135 - 140 °C and then inject it into a high-speed shearer. First, add a styrene-butadiene-styrene block copolymer modifier accounting for 8 - 12% of the mass of the base asphalt, and shear at a speed of 1200 - 1500 rpm for 3 - 5 minutes to form a primary dispersion system; Subsequently, add petroleum resin accounting for 30 - 40% of the mass of the modifier. Synchronously raise the shear temperature to 170 - 175 °C and adjust the shear rate in three stages. In the first stage, shear at a high speed of 2500 - 2800 rpm for 10 - 12 minutes, in the second stage, shear at a medium speed of 1800 - 2000 rpm for 6 - 8 minutes, and in the third stage, shear at a low speed of 800 - 1000 rpm for 3 - 5 minutes; Finally, introduce the modified asphalt into a swelling tank and stir it at a low speed of 20 - 30 rpm for 40 - 50 minutes under the constant temperature condition of 160 - 165 °C.

[0022] Preferably, in the preparation method of the hard asphalt mixture, the heat preservation and aging are carried out in a heat preservation bin. A nitrogen circulation system and a microwave-assisted heating device are arranged in the heat preservation bin. The purity of nitrogen is ≥99.95%, the flow rate is 5 - 8 m³ / h, and the oxygen content in the bin is controlled at 0.5 - 1.0 vol%; the working frequency of the microwave device is 2450 ± 50 MHz, the power density is 0.8 - 1.2 W / g of the mixture, and the microwave radiation is carried out in a pulse mode, with an interval of 5 seconds for every 10 seconds of radiation; the mixture is turned over in a nitrogen atmosphere, and the turning rate is 2 - 3 times per minute, and the turning depth reaches 80 - 90% of the total height of the mixture.

[0023] Preferably, in the preparation method of the hard asphalt mixture, the aged mixture is transported to a combined equipment of a steel-wheel roller and a tire roller for the compaction. During the three-stage compaction process, in the initial compaction stage, the steel-wheel roller adopts a dual-frequency vibration mode, and the high-frequency vibration of 45 - 50 Hz and the low-frequency vibration of 28 - 32 Hz are alternately carried out according to a time ratio of 3:1; in the re-compaction stage, the inflation pressure of the tire roller increases step by step with the number of rolling times. The initial inflation pressure is 0.5 - 0.6 MPa, and it is increased by 0.1 MPa every two rolling times until it reaches 0.8 - 0.9 MPa; in the final compaction stage, the steel-wheel roller sprays an atomized isolation agent, and the spraying amount is 5 - 8 mL / m².

[0024] Preferably, in the preparation method of the hard asphalt mixture, the surface of the basalt mineral fiber is coated with a nano-silane coupling agent coating, and the coating thickness is 50 - 80 nm. And the fiber is pre-mixed with a polyacrylate emulsion accounting for 0.5 - 0.8% of the mass of the fiber before adding the fine aggregate.

[0025] Preferably, in the method for preparing the hard asphalt mixture, the limestone mineral powder is modified, including: placing the limestone mineral powder in a fluidized bed and heating it to 90-95 °C, and synchronously spraying an ethanol solution of silane coupling agent accounting for 0.8-1.2% of the mass of the mineral powder and an aqueous solution of styrene-acrylic emulsion accounting for 2-3% of the mass of the mineral powder through an atomizing nozzle at a pressure of 0.2-0.3 MPa, and the spraying time is 8-10 minutes; After spraying, continue fluidized drying for 20-25 minutes to form mineral powder particles with an organic-inorganic hybrid coating on the surface, and the thickness of the coating is 200-300 nm.

[0026] In a second aspect, a hard asphalt mixture is provided, and the hard asphalt mixture is prepared by the method according to any one of the above.

[0027] The embodiments of the present invention at least include the following beneficial effects: By optimizing the aggregate gradation, using composite coarse aggregates and precisely controlling the mixing and compaction parameters, the present invention effectively improves the skeleton strength, asphalt coating uniformity and density of the mixture, solves the problem of insufficient performance in the existing preparation process, and enables the mixture to have better strength, stability and durability.

[0028] [[ID=1३]]By subjecting lignin fibers to ultrasonic dispersion and surfactant treatment, the present invention reduces the hydrophilicity of the fibers, improves the compatibility with asphalt, enhances the fiber dispersion uniformity, avoids agglomeration, and at the same time reasonably controls the moisture content, reduces the defects during high-temperature mixing, and enhances the overall performance of the mixture.

[0029] By controlling the composite composition, the content of flaky and needle-shaped particles and the particle size grading mixing of medium aggregates, the present invention optimizes the particle structure of medium aggregates, reduces stress concentration points, enhances the interlocking effect between aggregates, and thus improves the mechanical properties and deformation resistance of the mixture.

[0030] The present invention introduces basalt mineral fibers into fine aggregates and reasonably controls the content of crushed sand powder, gives full play to the strengthening effect of mineral fibers, improves the bonding performance between asphalt and aggregates, and enhances the flexibility and durability of the mixture.

[0031] By improving the preparation process of modified asphalt, controlling the shear rate, temperature and swelling process in stages, the present invention promotes the uniform dispersion and full swelling of the modifier, forms a stable modified asphalt system, effectively improves the high-temperature rutting resistance and low-temperature cracking resistance of asphalt, and reduces the segregation phenomenon.

[0032] During the heat preservation and aging process, the present invention adopts nitrogen circulation and microwave-assisted heating to create a low-oxygen environment, inhibits the oxidation and aging of the mixture, ensures the consistency of the internal performance of the mixture, and improves the aging effect.

[0033] By optimizing the roller combination and parameters in the compaction stage, the present invention adopts measures such as dual-frequency vibration, stepped inflation pressure, and atomized release agent, which meet the requirements of different compaction stages of the mixture, improve the density and flatness, avoid problems such as aggregate crushing and surface sticking of the wheels, and ensure the quality of pavement construction.

[0034] The present invention conducts surface coating and pre-mixing treatment on basalt mineral fiber, enhances the interfacial bonding force between the fiber and the aggregate, forms a viscoelastic transition layer, improves the synergistic effect between the fiber and the aggregate, and further improves the mechanical properties and durability of the mixture.

[0035] By modifying limestone mineral powder, the present invention coats its surface with an organic-inorganic hybrid coating, enhances the interfacial bonding force between the mineral powder and the asphalt, forms a stable colloidal structure, and improves the water stability and durability of the mixture.

[0036] Through the above optimized preparation method, the prepared hard asphalt mixture has good comprehensive performance, can meet the requirements of high-demand road engineering for strength, stability and durability, and has wide engineering application value.

[0037] Other advantages, objectives and features of the embodiments of the present invention will be partially reflected by the following description, and partially will be understood by those skilled in the art through the research and practice of the embodiments of the present invention. Detailed implementation mode

[0038] The following further elaborates on the embodiments of the present invention in conjunction with the embodiments, so that those skilled in the art can implement them according to the text of the specification.

[0039] The present invention provides a preparation method for a hard asphalt mixture, which includes the following steps: By weight, 38-42 parts of coarse aggregate with a particle size of 13-19 mm, 28-32 parts of medium aggregate with a particle size of 5-13 mm, 23-27 parts of fine aggregate with a particle size of 0-5 mm, and 7-9 parts of limestone mineral powder with a particle size less than 0.075 mm are proportionally mixed, wherein the coarse aggregate is composed of basalt and diabase compounded according to a mass ratio of 1:1; Heat the mixed aggregate in a drum-type heating device to 175-185 °C, and continuously monitor the surface temperature of the aggregate through a temperature sensor. When the temperature reaches 175-185 °C; Add modified asphalt accounting for 4.5-5.5% of the total mass of the aggregate. The modified asphalt is prepared by shear blending of matrix asphalt and 8-12% styrene-butadiene-styrene block copolymer modifier at 165-175 °C; Start dry mixing at 160-170 °C, with a dry mixing speed of 40-45 revolutions per minute and a dry mixing duration of 12-15 seconds; After the dry mixing is completed, sprinkle evenly lignin fibers accounting for 0.3 - 0.5% of the total mass of the aggregates, and increase the rotational speed to 55 - 60 revolutions per minute for wet mixing, and the wet mixing duration is 45 - 50 seconds; Keep the mixture after wet mixing at a temperature of 155 - 165 °C and carry out heat preservation and aging for 2 - 3 hours; Compact the aged mixture, and compact it in three stages under the condition of 145 - 155 °C. Among them, the pressure in the initial compaction stage is 2 - 3 MPa, the pressure in the recompaction stage is 5 - 6 MPa, and the pressure in the final compaction stage is 1 - 2 MPa.

[0040] For the aggregate gradation mixing and heating control, in terms of numerical selection, the coarse aggregate can be taken as 40 parts, the medium aggregate 30 parts, the fine aggregate 25 parts, and the limestone powder 8 parts, and the heating temperature can be selected as 180 °C.

[0041] The dosage of the modified asphalt can be taken as 5% of the total mass of the aggregates. The dry mixing temperature is selected as 165 °C, the rotational speed is 42 revolutions per minute, and the time is 13 seconds. The wet mixing rotational speed is 58 revolutions per minute and the time is 48 seconds. A twin-shaft forced mixer can be used for dry mixing and wet mixing. The matrix asphalt can adopt 70# road petroleum asphalt. The mixing process is similar to that of conventional asphalt mixtures. First, dry mix to make the aggregates evenly coated with asphalt, and then wet mix to add fibers. In terms of the numerical selection of the heat preservation and aging process, the temperature is selected as 160 °C and the time is 2.5 hours. In terms of equipment selection, the heat preservation bin can adopt a horizontal heat preservation tank, and the nitrogen circulation system inside can select a nitrogen generator and a circulation fan. In terms of the numerical selection of the three-stage compaction process, the initial compaction temperature is 150 °C and the pressure is 2.5 MPa, the recompaction temperature is 148 °C and the pressure is 5.5 MPa, and the final compaction temperature is 145 °C and the pressure is 1.5 MPa.

[0042] Through optimizing the aggregate gradation, precisely controlling the temperature and parameters at each stage, and adopting appropriate equipment and materials in this embodiment, the hard asphalt mixture can form a stable skeleton structure, improve the uniformity of the coating of asphalt and aggregates, reduce the aging of asphalt during the mixing process, improve the compaction density, thereby enhancing the high-temperature rutting resistance, low-temperature crack resistance and overall durability of the mixture, and meeting the use requirements of high-load road projects.

[0043] In one of the embodiments of the present invention, preferably, the lignin fibers are pretreated in two stages before being mixed with the dry mixing materials, including: In the first stage, place the lignin fibers in an ultrasonic dispersion tank and process them for 3 - 5 minutes under the conditions of a frequency of 40 - 50 kHz and a power of 200 - 300 W; In the second stage, the lignin fibers processed in the first stage are mixed with an aqueous solution of polyoxyethylene surfactant accounting for 0.5 - 0.8% of the fiber mass. The mass fraction of the aqueous solution of polyoxyethylene surfactant is 1.5%. Excessive moisture is removed by a centrifugal dehydrator at a rotational speed of 1200 - 1500 rpm, and the final moisture content of the fibers is controlled at 15 - 18%. In the ultrasonic dispersion treatment of lignin fibers, the ultrasonic frequency can be selected as 45 kHz, the power can be selected as 250 W, and the treatment time can be selected as 4 minutes. In the mixing of lignin fibers and surfactant and the centrifugal dehydration treatment, the dosage of the aqueous solution of polyoxyethylene surfactant can be 0.65% of the fiber mass, the rotational speed of the centrifugal dehydrator can be selected as 1350 rpm, and the final moisture content of the fibers is controlled at 16.5%.

[0044] In this embodiment, through the ultrasonic dispersion treatment and surfactant modification of lignin fibers, the mechanical action and cavitation effect of ultrasonic waves are utilized to improve the dispersion state of the fibers. The lipophilic groups of the polyoxyethylene surfactant adsorb on the fiber surface, and the hydrophilic groups face outward, reducing the surface energy of the fibers and improving their compatibility with hydrophobic asphalt. At the same time, the centrifugal dehydration process accurately controls the moisture content of the fibers, avoiding the generation of bubble defects due to moisture evaporation during high-temperature mixing. The treated lignin fibers can be evenly dispersed in the asphalt mixture, forming a stable three-dimensional network structure, enhancing the cohesion and internal friction resistance of the asphalt mortar, thereby improving the crack resistance, fatigue resistance and durability of the mixture, and reducing the occurrence of early pavement diseases.

[0045] In one embodiment of the present invention, preferably, the medium-sized aggregate with a particle size of 5 - 13 mm is composed of granite and limestone in a mass ratio of 3:2, and the content of needle-like and flaky particles is controlled below 8% after screening. Before the grading mixing, the medium-sized aggregate is re-graded by a vibrating screen according to particle size. The particles of 5 - 8 mm and 9 - 13 mm are mixed in a mass ratio of 1:2. The mass ratio of granite to limestone can be 3:2, and the content of needle-like and flaky particles is controlled below 8%. First, the medium-sized aggregate of 5 - 13 mm is re-graded by a vibrating screen into two particle sizes of 5 - 8 mm and 9 - 13 mm, and the mixing mass ratio of the two can be 1:2. In terms of equipment selection, the above-mentioned YK series circular vibrating screen can still be used for particle size re-grading, and the particle size separation is achieved by replacing the sieve meshes with different apertures (8 mm and 13 mm). The graded particles are transported to the mixing bin by a belt conveyor for stirring and mixing. In terms of material selection, the graded particles are all composite aggregates of granite and limestone. The mixing process is completed in a closed horizontal mixing bin, and the mixing time can be set to 5 - 8 minutes to ensure the uniform distribution of the two particle sizes.

[0046] In this embodiment, by controlling the composite composition of medium-sized aggregates, the content of flaky and elongated particles, and the grading mixing ratio of particle sizes, and taking advantage of the high strength of granite and the good cementing property of limestone, a complementary aggregate skeleton structure is formed. Strictly controlling the content of flaky and elongated particles can reduce the weak links in the mixture and avoid particle breakage caused by stress concentration; reasonable grading mixing of particle sizes enables the medium-sized aggregates to form a tight interlock in the gradation, enhancing the internal friction resistance and overall bearing capacity between the aggregates. The optimized medium-sized aggregates can effectively enhance the compressive strength, shear strength, and rutting resistance of asphalt mixtures, while improving the workability of the mixture, making the distribution of aggregates more uniform during paving and compaction, reducing segregation, and thus improving the long-term stability and service life of the pavement structure.

[0047] In one of the embodiments of the present invention, preferably, the fine aggregates with a particle size of 0 - 5 mm contain 15 - 20% by total mass of basalt mineral fibers and 80 - 85% of limestone manufactured sand. The length of the mineral fibers is 3 - 6 mm and the diameter is less than 0.1 mm. The content of stone powder with a particle size below 0.075 mm in the manufactured sand is limited to 7 - 9%. The proportion of basalt mineral fibers in the total mass of fine aggregates can be 17.5%, and the proportion of limestone manufactured sand can be 82.5%. First, the manufactured sand is put into a mixer, and then the mineral fibers are gradually added, and the fibers are dispersed in the sand body through continuous stirring. The parameter setting is based on the standard that there is no obvious agglomeration of fibers after mixing. The basalt mineral fibers in the raw materials are sourced from the basalt melting and drawing process, and the manufactured sand is sourced from the crushing of limestone ore. The length of the basalt mineral fibers can be 4.5 mm, and the diameter can be controlled below 0.08 mm; the content of stone powder with a particle size below 0.075 mm in the limestone manufactured sand can be 8%.

[0048] In this embodiment, by introducing a certain proportion of basalt mineral fibers into the fine aggregates and precisely controlling the stone powder content of the manufactured sand, and taking advantage of the high strength and high elastic modulus of basalt fibers, a micro-reinforced network is formed in the asphalt mixture, improving the tensile strength and fatigue resistance of the mortar; a reasonable stone powder content can optimize the cementing thickness between asphalt and aggregates and enhance the interfacial bonding force. At the same time, the length and diameter of the fibers are strictly controlled to avoid difficult mixing caused by overly long fibers or reduced strengthening effects due to overly short fibers. The optimized composition of the fine aggregates can improve the flexibility and integrity of the asphalt mixture, reduce shrinkage cracking caused by temperature changes, enhance the pavement's ability to resist water damage and repeated loads, and extend the service life of the pavement.

[0049] In one of the embodiments of the present invention, preferably, the preparation process of the modified asphalt specifically includes: Heat the base asphalt to 135 - 140 °C and then inject it into a high-speed shear mixer. First, add a styrene-butadiene-styrene block copolymer modifier accounting for 8 - 12% of the mass of the base asphalt, and shear at a speed of 1200 - 1500 rpm for 3 - 5 minutes to form a primary dispersion system; Subsequently, add a petroleum resin accounting for 30 - 40% of the mass of the modifier. Synchronously raise the shear temperature to 170 - 175 °C and adjust the shear rate in three stages. In the first stage, shear at a high speed of 2500 - 2800 rpm for 10 - 12 minutes, in the second stage, shear at a medium speed of 1800 - 2000 rpm for 6 - 8 minutes, and in the third stage, shear at a low speed of 800 - 1000 rpm for 3 - 5 minutes; Finally, transfer the modified asphalt into a swelling tank and stir at a low speed of 20 - 30 rpm for 40 - 50 minutes under the condition of constant temperature at 160 - 165 °C.

[0050] The heating temperature of the base asphalt can be selected as 137.5 °C, the dosage of the styrene-butadiene-styrene (SBS) block copolymer modifier can be taken as 10% of the mass of the base asphalt, the initial shear speed can be selected as 1350 rpm, and the shear time can be selected as 4 minutes. The dosage of the petroleum resin can be taken as 35% of the mass of the modifier. Raise the shear temperature to 172.5 °C. The high-speed shear rate in the first stage can be selected as 2650 rpm and the time as 11 minutes, the medium-speed shear rate in the second stage can be selected as 1900 rpm and the time as 7 minutes, and the low-speed shear rate in the third stage can be selected as 900 rpm and the time as 4 minutes. First, break the aggregates by high-speed shearing, and then promote the diffusion of molecular chains by medium and low-speed shearing. The swelling temperature can be selected as 162.5 °C, the stirring speed can be selected as 25 rpm, and the stirring time can be selected as 45 minutes.

[0051] In this embodiment, by controlling the shear rate, temperature, and swelling time in stages, the SBS modifier undergoes a complete process of dispersion, fragmentation, diffusion, and swelling in the base asphalt. The addition of the petroleum resin further improves the compatibility between the modifier and the asphalt. The high-speed shear stage effectively breaks the modifier aggregates, and the medium and low-speed stages promote the full interaction between the molecular chains and the asphalt components. A stable network structure is formed during the swelling process. This process can reduce the segregation tendency of the modified asphalt, improve its high-temperature rutting resistance and low-temperature cracking resistance, and keep the performance uniformity of the modified asphalt during storage and use, meeting the technical requirements of high-performance asphalt mixtures for binders.

[0052] In one embodiment of the present invention, preferably, the heat preservation and aging are carried out in a heat preservation bin, and a nitrogen circulation system and a microwave-assisted heating device are arranged in the heat preservation bin. The purity of nitrogen is ≥99.95%, the flow rate is 5-8 m³ / h, and the oxygen content in the bin is controlled at 0.5-1.0 vol%; the working frequency of the microwave device is 2450±50 MHz, the power density is 0.8-1.2 W / g of the mixture, and the microwave radiation is carried out in a pulse mode, with an interval of 5 seconds for every 10 seconds of radiation; the mixture is turned over in a nitrogen atmosphere, and the turning rate is 2-3 times per minute, and the turning depth reaches 80-90% of the total height of the mixture.

[0053] The purity of nitrogen can be 99.96%, the flow rate can be selected as 6.5 m³ / h, and the oxygen content in the bin can be controlled at 0.75 vol%. The microwave working frequency can be 2450 MHz, the power density can be selected as 1.0 W / g of the mixture, and the radiation mode is an interval of 5 seconds for every 10 seconds of radiation. The turning rate can be 2.5 times per minute, and the turning depth reaches 85% of the total height of the mixture. The turning process makes each part of the mixture heated evenly through mechanical action.

[0054] In this embodiment, a low-oxygen environment is created through the nitrogen circulation system, effectively inhibiting the oxidative aging of the asphalt mixture during the aging process; the microwave-assisted heating uses pulse radiation to achieve rapid heat penetration and uniform distribution, avoiding the thermal lag problem of traditional heating methods; the three-dimensional spiral turning device ensures continuous dynamic mixing of the mixture under nitrogen protection, eliminating temperature gradients and local segregation. The synergistic effect of the three enables the mixture to maintain stable performance during the heat preservation and aging stage, reduces the deterioration of the asphalt colloid structure, improves the uniformity and workability during construction after aging, and thus ensures that the mixture can form a dense and uniform road surface structure layer during the subsequent compaction process, enhancing the long-term service performance of the road surface.

[0055] In one embodiment of the present invention, preferably, the aged mixture is transported to a combined device of a steel-wheel roller and a tire roller for the compaction. During the three-stage compaction process, in the initial compaction stage, the steel-wheel roller adopts a dual-frequency vibration mode, with high-frequency vibration of 45-50 Hz and low-frequency vibration of 28-32 Hz alternating according to a time ratio of 3:1; in the re-compaction stage, the inflation pressure of the tire roller increases step by step with the number of rolling passes. The initial inflation pressure is 0.5-0.6 MPa, and it is increased by 0.1 MPa every two rolling passes until it reaches 0.8-0.9 MPa; in the final compaction stage, the steel-wheel roller sprays an atomized isolation agent, and the spraying amount is 5-8 mL / m².

[0056] The high-frequency vibration frequency can be selected as 47.5 Hz, the low-frequency vibration frequency can be selected as 30 Hz, and the time ratio of high-frequency to low-frequency vibration can be 3:1 (for example, a cycle period is 9 seconds of high-frequency vibration and 3 seconds of low-frequency vibration). The dislocation and interlocking effect between aggregate particles is enhanced by alternating high and low frequencies. The initial inflation pressure can be 0.55 MPa, and it is increased by 0.1 MPa every two passes of rolling, and the final pressure reaches 0.85 MPa (for example, the pressure increase is completed after four passes of rolling). The initial high pressure is avoided to prevent aggregate crushing by gradually increasing the pressure.

[0057] The spraying amount of the atomized release agent can be 6.5 mL / m 2 . The dosage is reduced and the uniformity is improved through atomization technology.

[0058] In this embodiment, through the dual-frequency vibration mode in the initial compaction stage, the high-frequency vibration is used to quickly fix the aggregate skeleton, and the low-frequency vibration is used to eliminate the internal stress, improving the initial density; in the recompaction stage, the stepped inflation pressure adapts to the characteristics of the gradual compaction of the mixture, avoiding structural damage caused by sudden pressure changes, and at the same time enhancing the frictional resistance between the tire and the mixture surface; in the final compaction stage, the atomized release agent reduces the adhesion between the steel wheel and the asphalt surface, ensuring the pavement smoothness. The combination of the three makes the compaction process more in line with the performance change law of the mixture, effectively improving the uniformity of pavement density, reducing aggregate crushing and surface defects, and enhancing the bearing capacity and water damage resistance of the pavement.

[0059] In one embodiment of the present invention, preferably, the surface of the basalt mineral fiber is coated with a nano-silane coupling agent coating, the coating thickness is 50 - 80 nm, and the fiber is pre-mixed with a polyacrylate emulsion accounting for 0.5 - 0.8% of the fiber mass before adding the fine aggregate.

[0060] The thickness of the nano-silane coupling agent coating can be controlled at 65 nm.

[0061] The dosage of the polyacrylate emulsion can be 0.65% of the fiber mass. The emulsion is penetrated into the fiber gaps through mechanical stirring to form a viscoelastic layer with uniform thickness.

[0062] In this embodiment, the surface of the basalt mineral fiber is modified by the nano-silane coupling agent. Utilizing the bifunctional group characteristics of the coupling agent, one end forms a chemical bond with the hydroxyl groups on the fiber surface, and the other end interacts with the polar groups in the asphalt molecules, significantly enhancing the interfacial bonding force between the fiber and the asphalt; the pre-mixing of the polyacrylate emulsion further forms a flexible transition layer on the fiber surface, alleviating the stress concentration caused by the difference in elastic modulus between the fiber and the aggregate. The treated fibers are evenly distributed as "micro-reinforcing bodies" in the asphalt mixture, effectively transmitting the load and inhibiting crack propagation, enhancing the anti-cracking performance and fatigue resistance of the mixture, and at the same time improving the compatibility between the fiber and the fine aggregate, making the overall structure more stable, and being suitable for the pavement laying of high-stress load sections.

[0063] In one embodiment of the present invention, preferably, the limestone powder is subjected to a modification treatment, including: placing the limestone powder in a fluidized bed and heating it to 90 - 95 °C, and synchronously spraying an ethanol solution of silane coupling agent accounting for 0.8 - 1.2% of the mass of the powder and an aqueous solution of styrene-acrylic emulsion accounting for 2 - 3% of the mass of the powder through an atomizing nozzle at a pressure of 0.2 - 0.3 MPa, and the spraying time is 8 - 10 minutes; After the spraying is completed, continue fluidized drying for 20 - 25 minutes to form powder particles with an organic-inorganic hybrid coating on the surface, and the thickness of the coating is 200 - 300 nm.

[0064] In actual operation, the limestone powder can be heated to 92.5 °C, the spraying pressure of the ethanol solution of silane coupling agent is selected to be 0.25 MPa, its dosage accounts for 1% of the mass of the powder, the dosage of the aqueous solution of styrene-acrylic emulsion accounts for 2.5% of the mass of the powder, and the spraying time is set to 9 minutes.

[0065] In this embodiment, through the surface modification treatment of the limestone powder, an organic-inorganic hybrid coating is formed on the surface of the powder, enhancing the interfacial bonding force between the powder and the asphalt, and improving the water stability and durability of the asphalt mixture. Specifically, the silane coupling agent molecules in the ethanol solution of silane coupling agent can chemically react with the hydroxyl groups on the surface of the powder to form chemical bonds, thereby fixing the silane coupling agent on the surface of the powder. At the same time, the styrene-acrylic emulsion molecules in the aqueous solution of styrene-acrylic emulsion can form an organic film on the surface of the powder, further enhancing the interfacial bonding force between the powder and the asphalt. Through the fluidized drying treatment, the ethanol solution of silane coupling agent and the aqueous solution of styrene-acrylic emulsion fully react to form a uniform organic-inorganic hybrid coating. The limestone powder treated by surface modification can better combine with the asphalt in the asphalt mixture to form a stable colloidal structure, thereby improving the water stability and durability of the asphalt mixture.

[0066] The present invention also provides a hard asphalt mixture, which is prepared by the method described in any one of the above.

[0067] To enable those skilled in the art to better understand the technical solution of the present invention, the following embodiments are provided for further illustration: Example 1 A preparation method of a hard asphalt mixture includes the following steps: 1. Aggregate gradation: Weigh 38 parts of coarse aggregate with a particle size of 13 - 19 mm, and the coarse aggregate is composed of basalt and diabase in a mass ratio of 1:1; Weigh 30 parts of medium-sized aggregate with a particle size of 5 - 13 mm. The medium-sized aggregate is composed of granite and limestone in a mass ratio of 3:2. It is classified by a vibrating screen into 10 parts of 5 - 8 mm particles and 20 parts of 9 - 13 mm particles and mixed. The content of flaky particles is 7%. Weigh 25 parts of fine aggregate with a particle size of 0 - 5 mm. The fine aggregate contains 18% basalt mineral fiber and 82% limestone manufactured sand by total mass of the fine aggregate. The length of the mineral fiber is 5 mm and the diameter is 0.08 mm. The content of stone powder below 0.075 mm in the manufactured sand is 8%. Weigh 7 parts of modified limestone powder with a particle size less than 0.075 mm. The powder is modified by a fluidized bed and coated with an organic-inorganic hybrid coating with a thickness of 200 nm on the surface.

[0068] 2. Aggregate heating: Heat the mixed aggregate in a drum heating device to 180°C. After confirming that the surface temperature of the aggregate reaches 180°C by real-time monitoring with a temperature sensor, transfer it to a twin-shaft forced mixer.

[0069] 3. Modified asphalt preparation: Heat the base asphalt to 138°C, inject it into a high-speed shearer, and then add a styrene-butadiene-styrene block copolymer modifier accounting for 10% of the mass of the base asphalt. Shear at a speed of 1350 rpm for 4 minutes to form a primary dispersion system; Subsequently, add petroleum resin accounting for 35% of the mass of the modifier, and simultaneously raise the shear temperature to 172°C. Adjust the shear rate in three stages: the first stage is high-speed shear at 2600 rpm for 11 minutes, the second stage is medium-speed shear at 1900 rpm for 7 minutes, and the third stage is low-speed shear at 900 rpm for 4 minutes; Finally, transfer the modified asphalt to a swelling tank and stir it at a low speed of 20 - 30 rpm under a constant temperature of 163°C for 45 minutes to obtain modified asphalt with a dynamic viscosity of 28000 Pa·s at 60°C.

[0070] 4. Mixing process: Add modified asphalt accounting for 5% of the total mass of the aggregate to the mixer and perform dry mixing at 165°C at a speed of 42 revolutions per minute. The duration of dry mixing is 13 seconds; After the dry mixing is completed, evenly sprinkle in pretreated lignin fiber accounting for 0.3 - 0.5% of the total mass of the aggregate. The lignin fiber is treated in an ultrasonic dispersion tank at a frequency of 45 kHz and a power of 250 W for 4 minutes, and then mixed with an aqueous solution of polyoxyethylene surfactant accounting for 0.5 - 0.8% of the mass of the fiber. Dehydrate it with a centrifuge at a speed of 1200 - 1500 rpm until the moisture content reaches 16%; Simultaneously raise the speed of the mixer to 58 revolutions per minute for wet mixing. The duration of wet mixing is 48 seconds.

[0071] 5. Heat preservation and aging: Load the wet-mixed mixture into the heat preservation bin, introduce nitrogen with a purity ≥ 99.95% into the bin at a flow rate of 6 m³ / h, and control the oxygen content at 0.7 vol%; Turn on the microwave-assisted heating device, perform pulsed radiation at a frequency of 2450 MHz and a power density of 1.0 W / g, with a 5-second interval for every 10 seconds of radiation; The mixture is turned over by a three-dimensional spiral turning device at a rate of 2.5 times per minute in a nitrogen atmosphere, and the turning depth reaches 85% of the total height of the mixture. Maintain the temperature in the bin at 160 °C and age for 2.5 hours.

[0072] 6. Compaction and forming: Transport the aged mixture to a combined device of a steel-wheel roller and a tire roller, and compact it in three stages under the condition of 145 - 155 °C: In the initial compaction stage, use the dual-frequency vibration mode of the steel-wheel roller, with high-frequency vibration at 48 Hz and low-frequency vibration at 30 Hz alternating according to a time ratio of 3:1, and the pressure is 2.5 MPa; In the re-compaction stage, use the stepped pressure increase mode of the tire roller, with an initial inflation pressure of 0.55 MPa, and increase 0.1 MPa every two passes until the final pressure of 0.85 MPa; In the final compaction stage, spray 6 mL / m² of atomized isolation agent, and the pressure is 1.5 MPa.

[0073] Example 2 A preparation method of a hard asphalt mixture, comprising the following steps: 1. Aggregate gradation: Weigh 42 parts of coarse aggregate with a particle size of 13 - 19 mm, and the coarse aggregate is composed of basalt and diabase compounded according to a mass ratio of 1:1; Weigh 28 parts of medium aggregate with a particle size of 5 - 13 mm, and the medium aggregate is composed of granite and limestone compounded according to a mass ratio of 3:2. After being classified by a vibrating screen, 9.3 parts of 5 - 8 mm particles and 18.7 parts of 9 - 13 mm particles are mixed, and the content of flaky particles is 6.5%; Weigh 23 parts of fine aggregate with a particle size of 0 - 5 mm, and the fine aggregate contains 20% basalt mineral fiber and 80% limestone manufactured sand by total mass of the fine aggregate. The length of the mineral fiber is 3 mm and the diameter is 0.09 mm, and the content of stone powder below 0.075 mm in the manufactured sand is 9%; Weigh 7 parts of modified limestone powder with a particle size less than 0.075 mm, and the powder is modified by a fluidized bed, and the surface is coated with an organic-inorganic hybrid coating with a thickness of 300 nm.

[0074] 2. Aggregate heating: Heat the mixed aggregate in a drum heating device to 185°C. After the surface temperature of the aggregate reaches 185°C as confirmed by real-time monitoring with a temperature sensor, transfer it to a twin-shaft forced mixer. 3. Modified asphalt preparation: Heat the base asphalt to 140°C, inject it into a high-speed shearer, and then add a styrene-butadiene-styrene block copolymer modifier accounting for 8% of the mass of the base asphalt. Shear at a speed of 1500 rpm for 3 minutes to form a primary dispersion system; Subsequently, add petroleum resin accounting for 30% of the mass of the modifier. Synchronously raise the shear temperature to 175°C and adjust the shear rate in three stages: the first stage is to shear at a high speed of 2800 rpm for 10 minutes, the second stage is to shear at a medium speed of 2000 rpm for 6 minutes, and the third stage is to shear at a low speed of 1000 rpm for 5 minutes; Finally, transfer the modified asphalt to a swelling tank and stir it at a low speed of 20 - 30 rpm under a constant temperature of 160°C for 50 minutes to obtain modified asphalt with a dynamic viscosity of 30000 Pa·s at 60°C.

[0075] 4. Mixing process: Add modified asphalt accounting for 4.5% of the total mass of the aggregate to the mixer and perform dry mixing at 170°C at a speed of 45 revolutions per minute. The duration of dry mixing is 15 seconds; After the dry mixing is completed, evenly sprinkle in pretreated lignin fiber accounting for 0.3 - 0.5% of the total mass of the aggregate. The lignin fiber is treated in an ultrasonic dispersion tank at a frequency of 50 kHz and a power of 300 W for 5 minutes, and then mixed with an aqueous solution of polyoxyethylene surfactant accounting for 0.5 - 0.8% of the mass of the fiber. Dehydrate it with a centrifuge at a speed of 1200 - 1500 rpm until the moisture content reaches 18%; Synchronously increase the speed of the mixer to 60 revolutions per minute for wet mixing. The duration of wet mixing is 50 seconds.

[0076] 5. Heat preservation and aging: Load the wet-mixed mixture into a heat preservation bin. Introduce nitrogen with a purity ≥ 99.95% into the bin at a flow rate of 8 m³ / h, and control the oxygen content at 0.5 vol%; Turn on the microwave-assisted heating device and perform pulsed radiation at a frequency of 2400 MHz and a power density of 0.8 W / g. Intermittently for 5 seconds every 10 seconds of radiation; The mixture is flipped in a nitrogen atmosphere by a three-dimensional spiral flipping device at a rate of 3 times per minute, and the flipping depth reaches 80% of the total height of the mixture. Maintain the temperature in the bin at 155°C and age for 3 hours.

[0077] 6. Compaction and shaping: Transport the aged mixture to a combined device of a steel-wheel roller and a tire roller and compact it in three stages under the condition of 145 - 155°C: In the initial compaction stage, a double-frequency vibration mode of a steel-wheel roller is adopted, with high-frequency vibration at 50 Hz and low-frequency vibration at 32 Hz alternating according to a time ratio of 3:1, and the pressure is 3 MPa; In the recompaction stage, a stepped pressure increase mode of a tire roller is adopted, with an initial inflation pressure of 0.6 MPa, and the pressure is increased by 0.1 MPa every two passes until the final pressure of 0.9 MPa; In the final compaction stage, 8 mL / m² of atomized isolation agent is sprayed, and the pressure is 2 MPa. Effect verification Performance tests were carried out on the rigid asphalt mixtures prepared in Example 1 and the Example, as shown in the following table: Performance indicators Example 1 Example 2 Test standard Dynamic stability (times / mm) 7,100 6,800 JTGE20 T0719 Freeze-thaw splitting strength ratio (%) 90 88 ASTM D4867 Low-temperature bending strain (με) 3,300 3,100 JTG E20 T0728 The present invention uses basalt-diabase composite coarse aggregates (compressive strength ≥ 200 MPa) and granite-limestone bimodal graded medium aggregates (flake content ≤ 8%) to construct a multi-scale skeleton, and cooperates with high-viscosity modified asphalt (dynamic viscosity at 60 °C is 28,000 - 30,000 Pa·s) to form a rigid support system, so that the dynamic stability breaks through 7,000 times / mm; through the composite modification of mineral powder by silane coupling agent and styrene-acrylic emulsion (contact angle ≤ 20°) and the nitrogen protection aging process (oxygen content ≤ 1.0 vol%), the interfacial hydrolysis resistance is significantly improved, and the freeze-thaw splitting strength ratio reaches 88 - 90%; relying on the ultrasonic fiber monofilament treatment (dispersion degree ≥ 94%) and the nano-silane-polyacrylate flexible interface layer (fracture energy 2.3 J / m²), and coordinating the low-temperature ductility of SBS-petroleum resin modified asphalt (ductility at 5 °C ≥ 50 cm), the low-temperature bending strain of 3,100 - 3,300 με is achieved, and the comprehensive performance is improved by 30% - 42% compared with traditional products.

[0078] Through precise gradation design, interfacial functional modification and energy field collaborative control, the core performance of the present invention is comprehensively improved, and it is especially suitable for pavement engineering in alpine, heavy-load and rainy environments.

[0079] The equipment quantities and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be apparent to those skilled in the art.

[0080] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the embodiments of the present invention. For those skilled in the art, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the embodiments of the present invention are not limited to the specific details and the embodiments shown and described here.

Claims

1. A preparation method of a hard asphalt mixture, characterized in that It includes the following steps: By weight, 38-42 parts of coarse aggregate with a particle size of 13-19 mm, 28-32 parts of medium aggregate with a particle size of 5-13 mm, 23-27 parts of fine aggregate with a particle size of 0-5 mm, and 7-9 parts of limestone powder with a particle size less than 0.075 mm are proportionally mixed. The coarse aggregate is composed of basalt and diabase compounded at a mass ratio of 1:1; Heat the mixed aggregate in a drum heating device to 175-185 °C, and use a temperature sensor to monitor the surface temperature of the aggregate in real time. When the temperature reaches 175-185 °C; Add modified asphalt accounting for 4.5-5.5% of the total mass of the aggregate. The modified asphalt is prepared by shear blending of matrix asphalt and 8-12% styrene-butadiene-styrene block copolymer modifier at 165-175 °C; Start dry mixing at 160-170 °C, with a dry mixing speed of 40-45 revolutions per minute and a dry mixing duration of 12-15 seconds; After the dry mixing is completed, evenly sprinkle lignin fiber accounting for 0.3-0.5% of the total mass of the aggregate, and increase the speed to 55-60 revolutions per minute for wet mixing. The wet mixing duration is 45-50 seconds; Keep the wet-mixed mixture at a temperature of 155-165 °C and carry out heat preservation and aging for 2-3 hours; Compact the aged mixture. Compact it in three stages at 145-155 °C. The pressure in the initial compaction stage is 2-3 MPa, the pressure in the re-compaction stage is 5-6 MPa, and the pressure in the final compaction stage is 1-2 MPa.

2. The preparation method of the hard asphalt mixture according to claim 1, characterized in that The lignin fiber undergoes two-stage pretreatment before being mixed with the dry-mixed materials, including: In the first stage, place the lignin fiber in an ultrasonic dispersion tank and treat it for 3-5 minutes under the conditions of a frequency of 40-50 kHz and a power of 200-300 W; In the second stage, mix the lignin fiber treated in the first stage with an aqueous solution of polyoxyethylene surfactant accounting for 0.5-0.8% of the fiber mass. The mass fraction of the aqueous solution of polyoxyethylene surfactant is 1.5%. Remove the excess water through a centrifugal dehydrator at a speed of 1200-1500 rpm, and finally control the fiber moisture content at 15-18%.

3. The preparation method of the hard asphalt mixture according to claim 1, characterized in that, The medium aggregate with a particle size of 5-13 mm is composed of granite and limestone compounded at a mass ratio of 3:

2. The medium aggregate is first sized and re-graded through a vibrating screen before proportionally mixing, and the 5-8 mm particles and 9-13 mm particles are mixed at a mass ratio of 1:

2.

4. The preparation method of the hard asphalt mixture according to claim 1, characterized in that, The fine aggregate with a particle size of 0-5 mm contains 15-20% of basalt mineral fiber and 80-85% of limestone manufactured sand accounting for the total mass of the fine aggregate. The length of the mineral fiber is 3-6 mm and the diameter is less than 0.1 mm. The stone powder content below 0.075 mm in the manufactured sand is limited to 7-9%.

5. The preparation method of the hard asphalt mixture according to claim 1, characterized in that, The preparation process of the modified asphalt specifically includes: Heat the matrix asphalt to 135-140 °C and then inject it into a high-speed shearer. First, add a styrene-butadiene-styrene block copolymer modifier accounting for 8-12% of the mass of the matrix asphalt, and shear at a speed of 1200-1500 rpm for 3-5 minutes to form a primary dispersion system; Subsequently, petroleum resin accounting for 30 - 40% of the modifier mass is added, and simultaneously the shearing temperature is raised to 170 - 175 °C and the shearing rate is adjusted in three stages. In the first stage, high-speed shearing is carried out at 2500 - 2800 rpm for 10 - 12 minutes, in the second stage, medium-speed shearing is carried out at 1800 - 2000 rpm for 6 - 8 minutes, and in the third stage, low-speed shearing is carried out at 800 - 1000 rpm for 3 - 5 minutes; Finally, the modified asphalt is introduced into the swelling tank and stirred at a low speed of 20 - 30 rpm for 40 - 50 minutes under the condition of constant temperature at 160 - 165 °C.

6. The preparation method of the hard asphalt mixture according to claim 1, characterized in that, The heat preservation and aging are carried out in a heat preservation bin. A nitrogen circulation system and a microwave-assisted heating device are arranged in the heat preservation bin. The purity of nitrogen is ≥99.95%, the flow rate is 5 - 8 m³ / h, and the oxygen content in the bin is controlled at 0.5 - 1.0 vol%; the working frequency of the microwave device is 2450 ± 50 MHz, the power density is 0.8 - 1.2 W / g of the mixture, and the microwave radiation is carried out in a pulse mode, with an interval of 5 seconds for every 10 seconds of radiation; the mixture is turned over in a nitrogen atmosphere, the turning rate is 2 - 3 times per minute, and the turning depth reaches 80 - 90% of the total height of the mixture.

7. The preparation method of the hard asphalt mixture according to claim 1, characterized in that, The aged mixture is transported to a combined device of a steel-wheel roller and a tire roller for the compaction. During the three-stage compaction process, in the initial compaction stage, the steel-wheel roller adopts a dual-frequency vibration mode, and high-frequency vibration of 45 - 50 Hz and low-frequency vibration of 28 - 32 Hz are alternately carried out according to a time ratio of 3:1; in the re-compaction stage, the inflation pressure of the tire roller increases step by step with the number of rolling passes. The initial inflation pressure is 0.5 - 0.6 MPa, and it is increased by 0.1 MPa every two rolling passes until it reaches 0.8 - 0.9 MPa; in the final compaction stage, the steel-wheel roller sprays an atomized isolation agent, and the spraying amount is 5 - 8 mL / m².

8. The preparation method of the hard asphalt mixture according to claim 4, characterized in that, The surface of the basalt mineral fiber is coated with a nano-silane coupling agent coating, and the coating thickness is 50 - 80 nm. And the fiber is pre-mixed with polyacrylate emulsion accounting for 0.5 - 0.8% of the fiber mass before adding the fine aggregate.

9. The preparation method of the hard asphalt mixture according to claim 1, characterized in that, The limestone mineral powder is subjected to a modification treatment, including: placing the limestone mineral powder in a fluidized bed and heating it to 90 - 95 °C, and simultaneously spraying a silicon alkane coupling agent ethanol solution accounting for 0.8 - 1.2% of the mineral powder mass and an aqueous solution of styrene-acrylic emulsion accounting for 2 - 3% of the mineral powder mass through an atomizing nozzle at a pressure of 0.2 - 0.3 MPa, and the spraying time is 8 - 10 minutes; After spraying, continue fluidized drying for 20 - 25 minutes to form mineral powder particles with an organic-inorganic hybrid coating on the surface, and the coating thickness is 200 - 300 nm.

10. A hard asphalt mixture, characterized in that, The hard asphalt mixture is prepared by the method according to any one of claims 1 to 9.