A directly-dosable granular asphalt toughening agent, a preparation method and application thereof

Abstract

The application discloses a directly-dumpable granular asphalt toughening agent and a preparation method and application thereof, and belongs to the technical field of asphalt modification materials. The application solves the problems of poor processing fluidity, slow melting and dispersing rate, the need for a pre-modification process, insufficient toughening effect and difficulty in adapting to on-site rapid construction of the existing modifier. The application is a solid granular substance, and the preparation raw materials include, in mass fractions, waste rubber powder 50-70 parts, low-density polyethylene 20-30 parts, styrene-butadiene-styrene block copolymer 8-12 parts, thermoplastic polyurethane elastomer 8-12 parts, aromatic oil 2-5 parts, antioxidant 1-2 parts and compatibilizer 1-5 parts. In the processing process, the application is not prone to agglomeration, has good storage stability and processing adaptability, and is smooth in the extrusion granulation process without obvious plugging phenomenon, is suitable for continuous and large-scale production, and can meet the demand for efficient and convenient construction in engineering applications.

Description

Technical Field

[0001] This invention belongs to the field of asphalt modification materials technology, specifically relating to a directly applicable granular asphalt toughening agent, its preparation method, and its application. Background Technology

[0002] Base asphalt itself has poor low-temperature toughness and insufficient high-temperature stability, making it difficult to meet the high-performance requirements of heavy-duty traffic roads, ultra-thin overlays, and roads in low-temperature areas. Therefore, by adding external modifying materials, the low-temperature toughness and comprehensive performance of base asphalt can be improved, so that it has good deformation coordination and damage resistance under different temperature conditions.

[0003] Currently, polymer modification and rubber modification are widely used in engineering to improve the performance of asphalt. However, these modified materials still have the following shortcomings in practical applications: First, in terms of application methods, existing modified materials mostly rely on pre-modification or wet processing techniques, which require pretreatment or long-term shear mixing of asphalt in specialized equipment. This not only involves complex processes but also places high demands on construction conditions and equipment, making it difficult to meet the needs for convenience and flexibility in on-site construction. These methods are less adaptable when it is necessary to adjust the dosage or perform rapid modification according to the actual project conditions. Second, in terms of material form, some existing modified materials are added to the asphalt system in powder or irregular block form. During actual mixing, agglomeration or uneven dispersion can easily occur, making it difficult for the material to exert its effects promptly and uniformly, thus affecting the stability and consistency of the modification effect. Third, in terms of performance, single-component materials usually cannot simultaneously achieve the low-temperature crack resistance, high-temperature stability, and anti-aging properties of asphalt. In simple multi-component compound systems, insufficient interfacial compatibility makes it difficult to fully realize the synergistic effect. In particular, waste rubber powder has a dense surface, low activity, and poor compatibility with polyolefins and elastomers. Direct blending can easily lead to problems such as phase separation, uneven dispersion, and high processing viscosity, which greatly reduces the modification effect. Summary of the Invention

[0004] To address the problems of existing modifiers, such as poor processing fluidity, slow melting and dispersion rates, the need for pre-modification processes, insufficient toughening effects, and difficulty in adapting to rapid on-site construction, this invention provides a directly applicable granular asphalt toughening agent, its preparation method, and its application. This toughening agent, upon addition, can rapidly disperse and form a stable structure. Through the synergistic effect of multiple components, it improves the mechanical properties of asphalt under both low and high temperature conditions, while also enhancing its anti-aging ability. Furthermore, this toughening agent should possess good ease of use and construction adaptability to meet the demands for efficient and rapid modification in engineering applications. The toughening agent is a solid granular agent at room temperature, possessing excellent storage stability and convenient on-site application. It can be added during asphalt mixing, rapidly melting and dispersing to modify the base asphalt. It achieves efficient toughening modification of the base asphalt in situ without factory pre-modification, prolonged shearing, or stirring, thus overcoming the technical bottlenecks of existing modifiers, such as poor processing fluidity, slow melting and dispersion rates, the need for pre-modification processes, insufficient toughening effects, and difficulty in adapting to rapid on-site construction.

[0005] The technical solution adopted in this invention is as follows:

[0006] A directly applicable granular asphalt toughening agent, which is in solid granular form, and whose raw materials, by mass parts, include:

[0007] Waste rubber powder: 50-70 parts;

[0008] Low-density polyethylene: 20-30 parts;

[0009] Styrene-butadiene-styrene block copolymer: 8-12 parts;

[0010] Thermoplastic polyurethane elastomer: 8-12 parts;

[0011] Aromatic oil: 2-5 parts;

[0012] Antioxidant: 1-2 parts;

[0013] Compatibilizer: 1-5 parts.

[0014] The granular toughening agent using this technical solution comprises waste rubber powder, low-density polyethylene (LDPE), thermoplastic elastomer, aromatic oil, compatibilizer, and antioxidant. The thermoplastic elastomer is a compound system of styrene-butadiene-styrene block copolymer (SBS) and thermoplastic polyurethane (TPU). This invention first softens and swells the waste rubber powder with aromatic oil, then uses LDPE and a compatibilizer to achieve surface coating and interface activation pretreatment of the rubber powder. Through physical blending and synergistic effects, the toughening agent possesses a low melting temperature, excellent processing fluidity, and good storage stability. The toughening agent is a solid granule at room temperature and can be directly added during asphalt mixture mixing without factory pre-modification or prolonged high-shear stirring. It quickly melts and uniformly disperses in the asphalt matrix, completing the toughening modification of the base asphalt in situ, thereby significantly improving the low-temperature crack resistance, high-temperature stability, and elastic recovery performance of the modified asphalt.

[0015] Preferably, the aromatic oil is a high aromatic oil for rubber processing.

[0016] After adopting this technical solution, high aromatic oil for rubber processing is used to swell and soften waste rubber powder, assist in pretreatment, and improve processing fluidity.

[0017] Preferably, the low-density polyethylene is a low-density polyethylene with a melt index of 0.5~5 g / 10 min and a density of 0.91~0.93 g / cm³.

[0018] Preferably, the waste rubber powder is desulfurized waste tire rubber powder with a mesh size of 40-80.

[0019] As a preferred option, the waste rubber powder is tire pyrolysis waste rubber powder.

[0020] Preferably, the antioxidant is hindered phenolic antioxidant 1010.

[0021] Preferably, the compatibilizer is a polyolefin compatibilizer grafted with polar groups, preferably maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene.

[0022] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0023] S1: Heat the mixture of low-density polyethylene, compatibilizer and aromatic oil to 140-160℃ for 1-3 minutes to pre-melt. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, add waste rubber powder and mix at a temperature not higher than 160℃ for 8-12 minutes.

[0024] S2: Add styrene-butadiene-styrene block copolymer and thermoplastic polyurethane elastomer to the system obtained in S1, and mix them evenly at a temperature of 150-180℃.

[0025] S3: Add antioxidants to the system obtained from S2 and mix thoroughly;

[0026] S4: Granulate the product obtained from S3 to obtain a granular asphalt toughening agent that can be directly applied.

[0027] After adopting this technical solution, the waste rubber powder is first pretreated. Aromatic oil can deeply swell and soften the waste rubber powder particles, destroy the dense structure of the rubber powder surface, reduce the agglomeration force between particles, and improve the surface activity of the rubber powder. The waste rubber powder, as a dispersed elastic phase, provides basic toughening and crack resistance, and inhibits crack propagation through energy dissipation during the stress process. LDPE has a low melting point and excellent processing fluidity, and melts preferentially under heating conditions. Combined with aromatic oil and compatibilizer, it performs interface pretreatment and coating modification on the waste rubber powder, reducing the surface energy of the rubber powder, improving polarity matching, and eliminating agglomeration tendency. As a continuous phase, it improves the fluidity of the system and promotes the dispersion of each component. SBS and TPU are compounded to form a thermoplastic elastomer system. SBS constructs a continuous elastic skeleton structure, improving the material's elastic recovery ability and high-temperature stability. TPU, due to the polar groups in its molecular structure, can enhance the interfacial bonding with waste rubber powder under the action of compatibilizer and improve its compatibility with LDPE, thereby promoting the stability of the multiphase system structure. After the components are mixed and homogenized in the specified proportions, a stable multiphase elastic network structure can be formed, giving the granular toughening agent a lower melting temperature and better processing fluidity. During the mixing of asphalt mixtures, it can melt rapidly and disperse uniformly, achieving in-situ toughening modification of the base asphalt. This differs from traditional additives, which need to be added during asphalt production to complete the modification. In addition, the combination with antioxidants can effectively inhibit the thermo-oxidative aging of each component during high-temperature processing and mixing, improving the stability of the material in use. At the same time, the synergistic pretreatment effect of aromatic oil, compatibilizer and LDPE further improves the interfacial compatibility between waste rubber powder and elastomer, reduces the processing viscosity of the system, and improves the mixing uniformity of the system and the processing performance of twin-screw extrusion granulation.

[0028] Preferably, in step S4, the product obtained in step S3 is extruded and granulated using a twin-screw extruder at 140-170°C, and then cooled and pelletized to obtain the granular asphalt toughening agent that can be directly applied as described in any one of claims 1-5. The twin-screw extruder uses a segmented gradient temperature control of 140-170°C, and the screw speed is controlled at 100-300 r / min.

[0029] As a preferred method, the extrusion process preferably adopts a segmented temperature control method, with the temperature of each zone controlled in a gradient of 140-170℃.

[0030] As a preferred embodiment, in S1, the speed of the internal mixer during internal mixing is 30-60 r / min, and the filling coefficient is 0.6-0.8; in S2, a high-speed shearing machine is used to ensure uniform mixing, and the speed of the high-speed shearing machine is 2000-3000 r / min, and the shearing time is 20-40 min.

[0031] Preferably, the directly applicable granular asphalt toughening agent is a particle with a diameter of 2-5 mm.

[0032] The application of a direct-addition granular asphalt toughening agent as an asphalt modifier. The direct-addition granular asphalt toughening agent is added directly during the asphalt mixture mixing process by dry mixing, and the dosage of the granular asphalt toughening agent is 5-11 wt% of the asphalt mass.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] This invention utilizes a pretreatment process for waste rubber powder using aromatic oil in conjunction with LDPE and a compatibilizer. Combined with a compound system of waste rubber powder, LDPE, SBS, and TPU, and the interfacial regulation effect of the compatibilizer, a stable multiphase elastic network structure is constructed within the material. The aromatic oil effectively swells and softens the rubber powder, and the pretreatment steps thoroughly solve the problems of poor compatibility, easy agglomeration, and high processing viscosity of rubber powder with polyolefins and elastomers. Specifically, SBS forms a continuous elastic skeleton structure, improving the material's high-temperature stability and elastic recovery capability; TPU enhances the interfacial compatibility and low-temperature flexibility of the system; and the waste rubber powder, as a dispersed phase, participates in the energy dissipation process, thereby achieving a synergistic improvement in both high-temperature deformation resistance and low-temperature crack resistance.

[0035] Meanwhile, LDPE, acting as a melt carrier, softens preferentially under heating conditions, effectively improving the processing fluidity of the system and enabling the granular toughening agent to melt rapidly and disperse uniformly during asphalt mixture mixing. Compared to traditional methods that require pre-modification or prolonged high-shear treatment during asphalt production, the toughening agent of this invention can be directly added to the asphalt mixture via dry mixing, achieving in-situ modification of the base asphalt under the specified mixing temperature and time conditions.

[0036] Furthermore, the granular asphalt toughening agent of the present invention is not prone to agglomeration during processing, has good storage stability and processing adaptability, and the extrusion granulation process is smooth with no obvious material blockage. It is suitable for continuous and large-scale production and can meet the needs of efficient and convenient construction in engineering applications. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] It should be noted that the main raw materials used in the following embodiments and comparative examples are from:

[0039] 70 Base Asphalt: 70 Grade A asphalt produced by Sinopec Jinling Petrochemical;

[0040] Waste rubber powder: 40-80 mesh desulfurized waste tire rubber powder produced by Gaoneng Nanjing Environmental Protection Technology Co., Ltd.

[0041] Low-density polyethylene (LDPE): Low-density polyethylene M1840 produced by Sinopec Yanshan Petrochemical Co., Ltd.

[0042] Styrene-butadiene-styrene block copolymer (SBS): YH-791 produced by Sinopec Baling Petrochemical Company;

[0043] Thermoplastic polyurethane (TPU): 185ASM manufactured by Shanghai Lianjing Polymer Materials Co., Ltd.

[0044] Aromatic oil: TX-02 aromatic oil produced by Shandong Tianxu Chemical Co., Ltd.;

[0045] Compatibilizer: Maleic anhydride grafted polyethylene (PE-g-MAH) M226LL produced by Shanghai Puzhen Biotechnology Co., Ltd.

[0046] Antioxidant: Antioxidant 1010 manufactured by Merck Life Sciences.

[0047] Example 1

[0048] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0049] S1: By mass, a mixture of 30 parts low-density polyethylene, 3 parts compatibilizer, and 2 parts aromatic oil is added to a mixer and heated to 150°C for 2 minutes for pre-melting. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, 50 parts waste rubber powder is added and the mixture is mixed at 150°C for 10 minutes. The rubber powder is swollen and softened by the aromatic oil, and then the waste rubber powder is surface-coated and pre-treated with molten LDPE and compatibilizer to reduce the agglomeration force between rubber powder particles and improve interfacial compatibility. The rotor speed is maintained at 50 r / min, and the waste rubber powder is coated and pre-dispersed by molten LDPE until the torque of the mixer tends to stabilize, thus obtaining the LDPE modified rubber composite.

[0050] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled at 160℃. Then, 12 parts of styrene-butadiene-styrene block copolymer were added for pre-shear dispersion for 2 minutes to form a preliminary continuous elastic phase in the system. Subsequently, 12 parts of thermoplastic polyurethane elastomer were added for further shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0051] S3: Add 2 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0052] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material's direction of travel, with each section's temperature controlled at 140℃, 155℃, 170℃, and 165℃ respectively; the feeding section is controlled at 140℃ to prevent solid materials from sticking together and bridging prematurely, ensuring stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, the highest temperature control zone of the system, to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200 r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of 2-5 mm that can be directly applied is obtained.

[0053] Example 2

[0054] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0055] S1: By mass, a mixture of 25 parts low-density polyethylene, 3 parts compatibilizer, and 3 parts aromatic oil is added to a mixer and heated to 150°C for 2 minutes for pre-melting. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, 60 parts waste rubber powder is added and the mixture is mixed at 150°C for 10 minutes. The rubber powder is swollen and softened by the aromatic oil, and then the waste rubber powder is surface-coated and pre-treated by the molten LDPE and compatibilizer to reduce the agglomeration force between rubber powder particles and improve interfacial compatibility. The rotor speed is maintained at 50 r / min, and the waste rubber powder is coated and pre-dispersed by the molten LDPE until the torque of the mixer tends to stabilize, thus obtaining the LDPE modified rubber composite.

[0056] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled at 160℃. Then, 10 parts of styrene-butadiene-styrene block copolymer were added for pre-shear dispersion for 2 minutes to form a preliminary continuous elastic phase in the system. Subsequently, 10 parts of thermoplastic polyurethane elastomer were added for further shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0057] S3: Add 1.5 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0058] S4: The mixed material is conveyed to a twin-screw extruder, and the temperature is controlled in stages from 140 to 170°C. The screw speed is controlled at 200 r / min. After melt extrusion, air cooling and pelletizing, a granular asphalt toughening agent with uniform particle size of about 3 mm is produced that can be directly applied.

[0059] Example 3

[0060] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0061] S1: By mass, a mixture of 20 parts low-density polyethylene, 3 parts compatibilizer, and 5 parts aromatic oil is added to a mixer and heated to 150°C for 2 minutes for pre-melting. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, 70 parts waste rubber powder is added and the mixture is mixed at 150°C for 10 minutes. The rubber powder is swollen and softened by the aromatic oil, and then the waste rubber powder is surface-coated and pre-treated with molten LDPE and compatibilizer to reduce the agglomeration force between rubber powder particles and improve interfacial compatibility. The rotor speed is maintained at 50 r / min, and the waste rubber powder is coated and pre-dispersed by molten LDPE until the torque of the mixer tends to stabilize, thus obtaining the LDPE modified rubber composite.

[0062] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled at 160℃. Then, 8 parts of styrene-butadiene-styrene block copolymer were added for pre-shear dispersion for 2 minutes to form a preliminary continuous elastic phase in the system. Subsequently, 8 parts of thermoplastic polyurethane elastomer were added for further shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0063] S3: Add 1 part antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0064] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system, to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200 r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0065] Example 4

[0066] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0067] S1: By mass, a mixture of 30 parts low-density polyethylene, 3 parts compatibilizer, and 2 parts aromatic oil is added to a mixer and heated to 150°C for 2 minutes for pre-melting. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, 50 parts waste rubber powder is added and the mixture is mixed at 150°C for 10 minutes. The rubber powder is swollen and softened by the aromatic oil, and then the waste rubber powder is surface-coated and pre-treated with molten LDPE and compatibilizer to reduce the agglomeration force between rubber powder particles and improve interfacial compatibility. The rotor speed is maintained at 50 r / min, and the waste rubber powder is coated and pre-dispersed by molten LDPE until the torque of the mixer tends to stabilize, thus obtaining the LDPE modified rubber composite.

[0068] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled to 160℃. Then, 12 parts of styrene-butadiene-styrene block copolymer and 12 parts of thermoplastic polyurethane elastomer were added simultaneously for shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0069] S3: Add 2 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0070] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system, to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0071] Comparative Example 1

[0072] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0073] S1: By mass, a mixture of 25 parts low-density polyethylene, 3 parts compatibilizer, and 3 parts aromatic oil is added to a mixer and heated to 150°C for 2 minutes for pre-melting. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, 60 parts waste rubber powder is added and the mixture is mixed at 150°C for 10 minutes. The rubber powder is swollen and softened by the aromatic oil, and then the waste rubber powder is surface-coated and pre-treated by the molten LDPE and compatibilizer to reduce the agglomeration force between rubber powder particles and improve interfacial compatibility. The rotor speed is maintained at 50 r / min, and the waste rubber powder is coated and pre-dispersed by the molten LDPE until the torque of the mixer tends to stabilize, thus obtaining the LDPE modified rubber composite.

[0074] S2: Add the LDPE modified rubber composite obtained in S1 to a high-speed shear mill, control the temperature to 160℃, and then add 10 parts of thermoplastic polyurethane elastomer for pre-shear dispersion; during shearing, set the shearing speed to 2000 r / min and the total shearing time to 30 min to make the system uniformly mixed.

[0075] S3: Add 1.5 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0076] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0077] Comparative Example 2

[0078] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0079] S1: By mass, a mixture of 25 parts low-density polyethylene, 3 parts compatibilizer, and 3 parts aromatic oil is added to a mixer and heated to 150°C for 2 minutes for pre-melting. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, 60 parts waste rubber powder is added and the mixture is mixed at 150°C for 10 minutes. The rubber powder is swollen and softened by the aromatic oil, and then the waste rubber powder is surface-coated and pre-treated by the molten LDPE and compatibilizer to reduce the agglomeration force between rubber powder particles and improve interfacial compatibility. The rotor speed is maintained at 50 r / min, and the waste rubber powder is coated and pre-dispersed by the molten LDPE until the torque of the mixer tends to stabilize, thus obtaining the LDPE modified rubber composite.

[0080] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled at 160℃. Then, 10 parts of styrene-butadiene-styrene block copolymer were added for pre-shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0081] S3: Add 1.5 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0082] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system, to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0083] Comparative Example 3

[0084] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0085] S1: By mass, 25 parts of low-density polyethylene and 3 parts of compatibilizer were added to a mixer and heated to 150°C for 2 minutes to pre-melt. After the LDPE was completely melted, 60 parts of waste rubber powder were added and the mixture was mixed at 150°C for 10 minutes (maintaining a rotor speed of 50 r / min) to obtain the LDPE modified rubber composite.

[0086] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled at 160℃. Then, 10 parts of styrene-butadiene-styrene block copolymer were added for pre-shear dispersion for 2 minutes to form a preliminary continuous elastic phase in the system. Subsequently, 10 parts of thermoplastic polyurethane elastomer were added for further shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0087] S3: Add 1.5 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0088] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0089] Comparative Example 4

[0090] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0091] S1: By mass, a mixture of 25 parts low-density polyethylene, 3 parts compatibilizer, 3 parts aromatic oil and 60 parts waste rubber powder is added to a mixer and heated to 150°C and mixed for 10 minutes (maintaining a rotor speed of 50 r / min) to obtain LDPE modified rubber composite.

[0092] S2: The LDPE modified rubber composite obtained in S1 was added to a high-speed shear mill and the temperature was controlled at 160℃. Then, 10 parts of styrene-butadiene-styrene block copolymer were added for pre-shear dispersion for 2 minutes to form a preliminary continuous elastic phase in the system. Subsequently, 10 parts of thermoplastic polyurethane elastomer were added for further shear dispersion. During shearing, the shearing speed was set to 2000 r / min and the total shearing time was 30 min to ensure that the system was mixed evenly.

[0093] S3: Add 1.5 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0094] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0095] Comparative Example 5

[0096] A method for preparing a directly applicable granular asphalt toughening agent includes the following steps:

[0097] S1: By mass, add a mixture of 25 parts low-density polyethylene, 3 parts compatibilizer, 3 parts aromatic oil, 60 parts waste rubber powder, 10 parts styrene-butadiene-styrene block copolymer, and 10 parts thermoplastic polyurethane elastomer into a mixer, heat to 150℃ and mix for 10 minutes;

[0098] S2: Add the product obtained in S1 to a high-speed shearing machine and control the temperature to 160℃ for shearing and dispersion; during shearing, set the shearing speed to 2000 r / min and the total shearing time to 30 min to ensure that the system is mixed evenly.

[0099] S3: Add 2 parts of antioxidant to the system obtained in S2 and mix well (mix and shear for 2 minutes).

[0100] S4: The mixed material is conveyed to a twin-screw extruder, where a segmented gradient temperature control of 140-170℃ is adopted (the material is divided into feeding section, plasticizing section, mixing section, and die section along the material travel direction, with the temperature of each zone controlled in a gradient of 140℃, 155℃, 170℃, and 165℃; the feeding section is controlled at 140℃ to avoid premature adhesion and bridging of solid materials and ensure stable feeding; the plasticizing section is raised to 155℃ to allow LDPE and pretreated waste rubber powder to initially melt and plasticize; the mixing section is raised to 170℃, which is the highest temperature control zone of the system, to ensure that SBS and TPU are completely melted and uniformly blended with each component; the die section is slightly lowered to 165℃). The screw speed is controlled at 200r / min. After melt extrusion, air cooling, and pelletizing, a granular asphalt toughening agent with a uniform particle size of about 3mm is obtained that can be directly applied.

[0101] The variables for the various embodiments and comparative examples described above are shown in Table 1:

[0102] Table 1

[0103]

[0104] The granular asphalt toughening agent from the examples and comparative examples was added to the No. 70 Grade A base asphalt at a mass fraction of 8 wt% for modification treatment. The addition process was as follows: the No. 70 Grade A base asphalt was heated to 150°C, the granular asphalt toughening agent from one of the examples or comparative examples was added, and the asphalt was sheared for 3 minutes at a speed of 2000 r / min using a high-speed shearing machine to obtain the corresponding modified toughened asphalt.

[0105] It should be noted that the above shearing process is only used to evaluate material performance under laboratory conditions. In practical engineering applications, the granular asphalt toughening agent of this invention can be directly added during the asphalt mixture mixing process via dry mixing, without the need for pre-modification of the asphalt binder, and still achieves good dispersion effect (meaning: the conventional method is to first modify the base asphalt to obtain modified asphalt (such as PG 76-22 modified asphalt), and then transport the modified asphalt to the mixing plant to mix with aggregates to form asphalt mixtures. In this invention, the granular direct-addition toughening agent of this invention can be directly added during the mixing process of the base asphalt and aggregates at the mixing plant, hence the term "direct addition").

[0106] Modified toughened asphalt 1-4 corresponds to the granular asphalt toughening agent in Examples 1-4, and modified toughened asphalt 5-9 corresponds to the granular asphalt toughening agent in Examples 1-5.

[0107] The modified and toughened asphalt was subjected to performance testing, as detailed below:

[0108] The modified toughened asphalt 1-5 was tested according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG 3410-2025), and the relevant test methods were carried out according to the following standards:

[0109] Ductility test of asphalt at 5℃: T 0605-2011;

[0110] Asphalt softening point test: T 0606-2011;

[0111] Asphalt elastic recovery test: T 0662-2000;

[0112] Asphalt -12℃ flexural creep test: T 0627-2011;

[0113] The performance test results are shown in Table 2:

[0114] Table 2

[0115]

[0116] As shown in Table 2, compared with the base asphalt, the modified toughened asphalt obtained in the embodiments of the present invention exhibits significant improvements in low-temperature performance, high-temperature performance, and elastic recovery ability. Specifically, the softening point of the modified toughened asphalt is significantly higher than that of the base asphalt, indicating an improved high-temperature deformation resistance. Simultaneously, the ductility at 5℃ is significantly increased, and the flexural creep stiffness S-value at -12℃ is significantly reduced while the m-value is increased, indicating an effective improvement in the material's low-temperature crack resistance. Furthermore, the elastic recovery rate is significantly improved, indicating enhanced elastic properties of the system. Further comparison of the various embodiments reveals that different component ratios have a significant impact on performance. Among them, modified toughened asphalt 1 has a high content of LDPE and SBS, which gives the system a high softening point and elastic recovery ability under high temperature conditions; modified toughened asphalt 3 has a high content of waste rubber powder and TPU, which gives the material a lower flexural creep stiffness and higher ductility under low temperature conditions, exhibiting excellent crack resistance; while modified toughened asphalt 2 has a relatively balanced proportion of each component, which achieves a good match between the elastic skeleton constructed by SBS, the interface structure regulated by TPU and the energy dissipation effect of waste rubber powder, thus achieving a good balance between high temperature stability, low temperature crack resistance and elastic recovery performance, resulting in the best overall performance.

[0117] For modified toughened asphalt 4 (where SBS was not pre-sheared and dispersed before being directly mixed and sheared with TPU), the SBS, without pre-shearing to form a continuous elastic skeleton, easily leads to phase separation and uneven dispersion when directly blended with TPU. This prevents the construction of a stable multiphase elastic network, resulting in the failure of the system's high-temperature support and elastic recovery capabilities, and simultaneous damage to its low-temperature crack resistance. Compared to modified toughened asphalt 2, the elastic recovery rate decreased, the softening point decreased, the ductility at 5℃ decreased slightly, and the creep stiffness S at -12℃ increased while the m value decreased.

[0118] The results of the modified toughened asphalt experiments (5-6) show that the overall performance of the modified asphalt significantly decreases when SBS or TPU is absent from the system. Specifically, the lack of SBS significantly reduces the material's elastic recovery ability; the lack of TPU affects the system's dispersibility and high-temperature performance, indicating that each component plays an irreplaceable role in the system.

[0119] For modified toughened asphalt 7 (without aromatic oil), the lack of aromatic oil's swelling, softening, plasticizing, and fluxing effects on waste rubber powder resulted in dense, severely agglomerated rubber powder particles with poor processing fluidity, making uniform dispersion impossible. This ultimately led to a significant deterioration in low-temperature crack resistance, and a simultaneous decrease in high-temperature stability and elastic properties. Compared to modified toughened asphalt 2, ductility was significantly reduced, creep stiffness (S) at -12℃ was significantly increased, and the m value was significantly decreased, while the elastic recovery rate and softening point decreased simultaneously.

[0120] For modified toughened asphalt 8 (without pre-melting LDPE), the waste rubber powder cannot be pre-treated by pre-melting LDPE, resulting in uneven dispersion and obvious agglomeration of the rubber powder. The interfacial bonding force between the components is insufficient, and the synergistic effect cannot be exerted. The system has poor fluidity and disordered phase structure, which cannot effectively improve the performance of modified asphalt.

[0121] For modified toughened asphalt 9 (where all materials are first melted in an internal mixer and then sheared using a high-speed shearing machine), the internal mixer's shearing force is insufficient. When all materials are added to the internal mixer for melting, not only is it impossible to fully disperse SBS and TPU and form a continuous elastic network, but it also affects the dispersion of the rubber powder, resulting in uneven mixing of the rubber powder and the polymer phase. Subsequently, when using the high-speed shearing machine, it is difficult to obtain well-fused and uniform toughening agent particles. Therefore, the overall performance of modified toughened asphalt 9 is relatively low.

[0122] The above results demonstrate that this invention utilizes an aromatic oil-assisted waste rubber powder pretreatment process to composite waste rubber powder, LDPE, SBS, and TPU, and introduces a compatibilizer to regulate interfacial interactions. Specifically, SBS forms a continuous elastic network structure, providing primary high-temperature support and elastic recovery; TPU enhances interfacial compatibility and improves system flexibility; waste rubber powder acts as a dispersed phase participating in energy dissipation; and LDPE acts as a melt carrier, improving system fluidity and promoting uniform dispersion of all components, thereby achieving a synergistic improvement in the high-temperature stability and low-temperature crack resistance of asphalt.

[0123] Furthermore, the granular asphalt toughening agent of the present invention is a stable solid particle at room temperature. During use, it can be directly added to the asphalt mixture mixing system without pre-modification of the base asphalt or prolonged high shearing. It can quickly melt and disperse uniformly at the mixing temperature, significantly improving the convenience and adaptability of construction.

[0124] To verify the improved mixture performance of the granular asphalt toughening agent, AC-20 continuously graded asphalt mixtures with an asphalt content of 4.3% were used. One of the granular asphalt toughening agents from Examples 1-4 and Comparative Examples 1-5 was incorporated at 8 wt% of the asphalt mass, and the mixtures were prepared using a dry-mix direct-injection process. The specific process was as follows: aggregates of each grade were heated to 165°C and added to a mixing tank for dry mixing for 90 seconds. The granular asphalt toughening agent was then added and mixed for another 90 seconds to allow it to soften initially under high temperature and adhere to the aggregate surface. Subsequently, No. 70 Grade A base asphalt was added and mixed for 90 seconds. Finally, mineral powder was added and mixed for 90 seconds to obtain toughened asphalt mixtures 1-9. Corresponding Marshall specimens and rutting plate specimens were then formed. Performance tests were performed on the obtained specimens according to the following standards:

[0125] Marshall stability test of asphalt mixtures T 0709-2025;

[0126] Rutting test of asphalt mixture T0719-2025;

[0127] Low-temperature bending test of asphalt mixtures T 0715-2025;

[0128] The obtained performance test data are shown in Table 3:

[0129] Table 3

[0130]

[0131] Analysis of the mixture test data in Table 3 shows that, compared with the base asphalt mixture, the high-temperature stability, low-temperature crack resistance, and Marshall stability of the mixtures in each embodiment after adding the granular toughening agent of this invention are all improved, indicating that the toughening agent can effectively play a modifying role under dry-mix direct-injection conditions. Regarding high-temperature performance, the dynamic stability of the mixtures in each embodiment is significantly improved, indicating that the material's resistance to high-temperature rutting deformation is enhanced. This is mainly attributed to the continuous elastic skeleton structure formed by SBS and the effect of LDPE on improving the system stiffness. Regarding low-temperature performance, the low-temperature flexural strain of the mixtures in each embodiment is significantly increased, indicating that the material's low-temperature deformation capacity is enhanced. This is closely related to the improvement of interfacial flexibility by TPU and the participation of waste rubber powder in energy dissipation. Regarding strength indicators, the Marshall stability of the mixtures in each embodiment is improved, with toughened asphalt mixture 2 showing the highest value, indicating that when the proportions of each component are coordinated, the mixture can achieve superior overall mechanical properties. The results of toughened asphalt mixtures 5-6 show that the performance of the mixtures decreased when SBS or TPU was absent, indicating that the components have a synergistic reinforcing effect. Specifically, the high-temperature stability decreased significantly when SBS was absent, while the low-temperature crack resistance decreased when TPU was absent, demonstrating that the two elastomers work together in the system and neither can be omitted. Furthermore, without pre-modification of the base asphalt, the granular toughening agent of this invention can still achieve good dispersion and significantly improve the performance of the mixture by dry mixing, demonstrating good construction adaptability.

[0132] The toughened asphalt mixtures 4, 7, 8, and 9 demonstrate the necessity of the multi-process collaborative design of this invention through four key steps: thermoplastic elastomer dispersion, rubber powder pretreatment, LDPE coating, and high-speed shear mixing. The absence of any one of these steps will cause microstructural defects, leading to a significant deterioration in the performance of the asphalt and mixture.

[0133] For toughened asphalt mixture 4 (where SBS was not pre-sheared and dispersed before being directly mixed and sheared with TPU), direct blending resulted in phase separation, failing to form a uniform and continuous elastic phase. The elastomer was unevenly dispersed, with SBS agglomerating in some areas and TPU distributed separately in others, failing to form a synergistic three-dimensional elastic network. This led to a decrease in the high-temperature performance of the asphalt mixture. The discontinuous elastomer network resulted in an inability to effectively resist aggregate shear deformation at high temperatures, with the Marshall stability dropping to 13.33 kN. Low-temperature flexural strain also decreased slightly, and the unevenly dispersed elastomer could not effectively transfer and dissipate low-temperature stress.

[0134] For toughened asphalt mixture 7 (without aromatic oil), the rubber powder surface is dense and highly cross-linked, with severe particle agglomeration. It does not integrate well with LDPE and is merely dispersed as inert particles in the system, unable to effectively dissipate energy. This results in a significant deterioration in the low-temperature performance of the asphalt mixture. The agglomerated rubber powder cannot effectively transfer and dissipate low-temperature cracking energy; the low-temperature flexural strain decreases, the dynamic stability slightly decreases, and the insufficient interfacial bonding indirectly affects the high-temperature stability.

[0135] For toughened asphalt mixture 8 (without LDPE pre-melting treatment), LDPE cannot effectively coat the rubber powder, resulting in severe agglomeration of the rubber powder particles. This leads to insufficient contact with the elastomer and compatibilizer, weak interfacial bonding, and an inability to form a stable multiphase structure among the components. Consequently, the overall performance of the asphalt mixture is significantly reduced, with insufficient cohesion, making it prone to deformation at high temperatures and cracking at low temperatures.

[0136] For toughened asphalt mixture 9 (all materials are first melted in an internal mixer and then sheared using a high-speed shearing machine), the internal mixer's shearing force is insufficient, making it impossible to fully melt SBS and TPU, resulting in uneven dispersion of elastomer particles and failure to form a continuous elastic network. Due to the excessive amount of added materials, the rubber powder is also difficult to disperse evenly, and the interfacial bonding with the polymer is insufficient, causing the high and low temperature performance of the corresponding asphalt mixture to decline simultaneously.

[0137] The results show that the key innovations of this invention are the SBS pre-shearing, aromatic oil pretreatment, LDPE pre-melting, and high-speed shearing processes. The absence of any one of these processes will lead to microstructural defects, which in turn will cause a significant decline in the performance of asphalt and the mixture. This verifies the creativity and necessity of the multi-process collaborative design of this invention.

[0138] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A directly applicable granular asphalt toughening agent, characterized in that: The raw materials are in solid granular form and, by mass parts, include: Waste rubber powder: 50-70 parts; Low-density polyethylene: 20-30 parts; Styrene-butadiene-styrene block copolymer: 8-12 parts; Thermoplastic polyurethane elastomer: 8-12 parts; Aromatic oil: 2-5 parts; Antioxidant: 1-2 parts; Compatibilizer: 1-5 parts.

2. The directly applicable granular asphalt toughening agent according to claim 1, characterized in that: The aromatic oil is a high aromatic oil used in rubber processing.

3. The directly applicable granular asphalt toughening agent according to claim 1, characterized in that: The low-density polyethylene is a low-density polyethylene with a melt index of 0.5~5 g / 10 min and a density of 0.91~0.93 g / cm³.

4. The directly applicable granular asphalt toughening agent according to claim 1, characterized in that: The waste rubber powder mentioned is desulfurized waste tire rubber powder with a mesh size of 40-80.

5. The directly applicable granular asphalt toughening agent according to claim 1, characterized in that: The antioxidant mentioned is hindered phenolic antioxidant 1010.

6. A method for preparing a directly applicable granular asphalt toughening agent according to any one of claims 1-5, characterized in that: Includes the following steps: S1: Heat the mixture of low-density polyethylene, compatibilizer and aromatic oil to 140-160℃ for 1-3 minutes to pre-melt. After the LDPE is completely melted and the aromatic oil is fully impregnated and dispersed, add waste rubber powder and mix at a temperature not higher than 160℃ for 8-12 minutes. S2: Add styrene-butadiene-styrene block copolymer and thermoplastic polyurethane elastomer to the system obtained in S1, and mix them evenly at a temperature of 150-180℃. S3: Add antioxidants to the system obtained from S2 and mix thoroughly; S4: Granulate the product obtained in S3 to obtain the directly applicable granular asphalt toughening agent as described in any one of claims 1-5.

7. The method for preparing a directly applicable granular asphalt toughening agent according to claim 6, characterized in that: In S4, the product obtained in S3 is extruded and granulated by a twin-screw extruder at 140-170°C. After cooling and pelletizing, the granular asphalt toughening agent that can be directly applied according to any one of claims 1-5 is obtained. The twin-screw extruder adopts a segmented gradient temperature control of 140-170°C, and the screw speed is controlled at 100-300 r / min.

8. The method for preparing a directly applicable granular asphalt toughening agent according to claim 6, characterized in that: In S1, the speed of the internal mixer during mixing is 30-60 r / min, and the filling coefficient is 0.6-0.8; in S2, a high-speed shearing machine is used to ensure uniform mixing, and the speed of the high-speed shearing machine is 2000-3000 r / min, and the shearing time is 20-40 min.

9. The method for preparing a directly applicable granular asphalt toughening agent according to claim 6, characterized in that: The directly applicable granular asphalt toughening agent consists of particles with a particle size of 2-5 mm.

10. The application of a directly-applied granular asphalt toughening agent prepared by any one of claims 1-5 or by the preparation method of a directly-applied granular asphalt toughening agent according to claims 6-9 as an asphalt modifier, characterized in that: The directly-added granular asphalt toughening agent is added directly during the asphalt mixture mixing process by dry mixing, and the dosage of the granular asphalt toughening agent is 5-11 wt% of the asphalt mass.

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