Coarse grain type recycled asphalt mixture and preparation method thereof

Abstract

The invention relates to the technical field of waste asphalt regeneration, in particular to preparation of a coarse grain type regenerated asphalt mixture. The invention discloses a coarse grain type recycled asphalt mixture and a preparation method thereof, and the coarse grain type recycled asphalt mixture comprises the following components in parts by mass: 100 parts of the total mass of the mixture, the recycled asphalt pavement material comprises the following components in parts by weight: 50-70 parts of a recycled asphalt pavement material, 28-36 parts of a new aggregate, 2.5-3.2 parts of new asphalt, 0.2-0.6 part of an A-phase recycling agent formed by compounding waste vegetable oil and an antioxidant, 0.05-0.3 part of a B-phase recycling agent formed by compounding environment-friendly rubber oil and natural rock asphalt, 1.5-2.5 parts of fine-grained calcium oxide powder, 0.4-0.8 part of a dry premixing reinforcing agent and 0.8-1.5 parts of a warm mixing agent. According to the invention, the problem that the performance of the high-proportion regenerated mixture is degraded is solved, and high-performance resource utilization of the waste asphalt pavement material is realized.

Description

Technical Field

[0001] This invention relates to the field of waste asphalt recycling technology, specifically to the preparation of a coarse-grained recycled asphalt mixture. Background Technology

[0002] Plant-mixed hot recycling technology, currently the most widely used method for asphalt pavement recycling, typically involves transporting recycled asphalt pavement material (RAP) to a mixing plant, where it is crushed, screened, and then remixed with new aggregates, new asphalt, and recycling agents in a specific ratio to form a mixture. However, the existing mainstream plant-mixed hot recycling technology faces significant technical bottlenecks in its practical promotion and application, especially in the preparation of coarse-grained recycled asphalt mixtures for load-bearing layers. First, there is a contradiction between the RAP content limit and performance. Due to concerns about the road performance of the mixture, current technical specifications and engineering practices typically limit the RAP content to below 30%. Once this limit is exceeded, the performance of the mixture, especially its low-temperature crack resistance and water stability, will significantly deteriorate. This is mainly because the asphalt in the RAP has undergone long-term aging, its lightweight components volatilize, and the asphaltene content increases, leading to asphalt hardening, decreased ductility, and weakened bond properties. The introduction of a high proportion of RAP means that a large amount of aged and brittle asphalt exists in the mixture. Even with the addition of new asphalt and conventional recycling agents, it is difficult to fully restore its overall performance, resulting in recycled mixtures with acceptable high-temperature performance but increased low-temperature brittleness and insufficient durability. This prevents coarse-grained mixtures from absorbing the advantages of more RAP.

[0003] Secondly, there are inherent defects in the production process. Traditional intermittent mixing plants, when producing recycled asphalt mixtures, typically involve directly exchanging heat between cold RAP and hot new aggregate in the mixing drum, or, even more outdatedly, directly immersing the RAP in a drying drum for heating with a flame. The former, due to the short heat exchange time, easily leads to uneven RAP temperature and internal "under-cooked" material, while the latter subjectes the aged asphalt in the RAP to secondary high-temperature baking, causing further "secondary aging" and worsening its performance.

[0004] Third, the materials are not fully integrated. Most existing mixing processes spray the recycling agent and new asphalt into the mixing drum simultaneously. The recycling agent needs time to penetrate into the aged asphalt to achieve its softening and restorative effects. This simultaneous addition means that the recycling agent is diluted and encapsulated by a large amount of new asphalt before it can fully act on the old asphalt, resulting in a significant reduction in its effectiveness, insufficient integration of old and new asphalt, and poor homogeneity of the mixture.

[0005] Finally, the gradation control precision is insufficient. RAP itself has a large variability, especially coarse-grained RAP. If a single-grade RAP is used directly without fine multi-stage crushing, screening and modification pretreatment, it is difficult to accurately control the final gradation of the recycled mixture, which affects the strength and stability of the structural layer.

[0006] Based on the research of recycled asphalt mixtures, the core of existing technologies not only focuses on the component design of asphalt mixtures, but also pays attention to the pretreatment of RAP and the preparation of rejuvenating agents. For example, CN117887276A discloses an acylated silane coupling agent-modified asphalt with active bundled fibers and its preparation method. It uses 1-10% by mass of acylated silane coupling agent to modify asphalt with active bundled fibers, which solves the problem that the surface of bundled fibers used in traditional asphalt modification is chemically inert and cannot be modified, and improves the dispersion and uniformity of fibers in asphalt. CN120248625A discloses an asphalt rejuvenating agent and its preparation method and application. Its asphalt modifier includes an oil phase, a polymer phase, a nano-reinforcing phase and a functional additive phase. The asphalt rejuvenating agent provided by the invention is suitable for various types of aged asphalt, especially for aged polymer-modified asphalt. Through a multi-phase synergistic mechanism, it can accurately repair each failed phase of aged polymer-modified asphalt. While existing technologies attempt to prepare modifiers and regenerators by designing components and their proportions, they cannot simultaneously achieve high dosage ratios and synergistic effects of regenerators and modifiers during high-temperature regeneration.

[0007] In summary, how to increase the amount of recycled material while ensuring road performance, optimize pretreatment and mixing processes to prevent old asphalt aging, and improve material compatibility through composite recycling agents have become urgent technical problems to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a coarse-grained recycled asphalt mixture with high RAP content, excellent road performance, especially excellent low-temperature crack resistance and water stability, and to provide a preparation method that can avoid secondary aging of RAP and promote uniform fusion of new and old materials.

[0009] The specific technical solution is as follows: A coarse-grained recycled asphalt mixture and its preparation method are disclosed. The preparation method involves plasma-activating and silane-coupled interfacial modification of recycled asphalt pavement material (RAP), mixing it with new and old aggregates according to a specific gradation, and sequentially adding vegetable oil-based regenerator, fiber-nano composite reinforcing agent, warm mix agent and rock asphalt-based high viscosity modifier during the precisely temperature-controlled mixing process to finally prepare a high-performance recycled asphalt mixture.

[0010] Furthermore, the recycled asphalt mixture comprises, based on 100 parts by weight of the total mixture, 50-70 parts of RAP, 28-36 parts of new aggregate, 2.5-3.5 parts of new asphalt, 0.2-0.6 parts of A-phase regenerator composed of waste vegetable oil and antioxidant, 0.05-0.3 parts of B-phase regenerator composed of environmentally friendly rubber oil and natural rock asphalt, 1.5-2.5 parts of fine-grained calcium oxide powder, 0.4-0.8 parts of dry premixed reinforcing agent, and 0.8-1.5 parts of Sasobit warm mix agent; and the dry premixed reinforcing agent is premixed from polypropylene fiber and nano-wollastonite at a mass ratio of 1-3.

[0011] Furthermore, the plasma activation refers to treating the RAP with a low-temperature plasma with a power of 10~50kW for 10~60 seconds to clean and activate its surface and generate oxygen-containing polar functional groups.

[0012] Furthermore, the precise temperature control refers to sequentially controlling the following key temperature points during the mixing process: adding the fine-grained calcium oxide powder when the aggregate temperature is 115°C; adding the dry premixed reinforcing agent and the A-phase regenerator when the aggregate temperature is 130~145°C; adding the new asphalt and Sasobit warm mix additive when the material temperature is 150~155°C; and adding the B-phase regenerator and maintaining mixing for 50 seconds when the mixture temperature is 158~165°C.

[0013] The preparation of a coarse-grained recycled asphalt mixture includes the following steps: S1: Take waste catering vegetable oil, and after sedimentation, filtration, degumming, decolorization and refining treatment, obtain refined recycled base oil; under 60℃ and stirring conditions, add 1.0% antioxidant to the refined recycled base oil, react at a constant temperature for 60 minutes, mix evenly and cool to obtain the A phase regenerator; take environmentally friendly rubber oil, melt it at 180℃ and add it to natural rock asphalt, the natural rock asphalt needs to be crushed to below 0.15mm, bake and stir for 30 minutes to obtain a modified high viscosity agent as the B phase regenerator.

[0014] S2: Polypropylene fiber and nano-wollastonite powder are used as reinforcing materials. Weigh the polypropylene fiber and nano-wollastonite, place them in a dry mixer and stir to prepare a dry premixed reinforcing agent, seal it to prevent moisture and keep it for later use; S3: The recovered RAP is processed by crushing equipment and then screened to separate it into two gradation zones with a particle size of 10mm: coarse and fine. The coarse and fine particles are combined at a mass ratio of 2:1 to meet the target gradation requirements and mixed to form RAP. The mixed RAP is then subjected to low-temperature plasma activation treatment. After treatment, it is sprayed with an aqueous silane coupling agent solution and then dried in a 60°C hot air circulating chamber to complete the surface chemical modification of the RAP. It is then removed and set aside for later use.

[0015] S4: Add the treated RAP and new aggregate to the forced twin-shaft low-temperature asphalt mixing plant, start the combustion heating dry mixing, and when the aggregate temperature rises to 115℃, add fine-grained calcium oxide powder. Then continue heating, and add dry premixed reinforcing agent, A-phase waste vegetable oil recycler, and Sasobit warm mix agent in sequence for dry mixing. Immediately afterwards, add new asphalt for wet mixing to initially and evenly coat the aggregate with asphalt. Then add B-phase recycler, mix thoroughly, and discharge to obtain coarse-grained recycled asphalt mixture.

[0016] Furthermore, the mass ratio of the polypropylene fiber and nano-wollastonite in S2 is 1~3.

[0017] Further, in S3, the RAP formed by mixing is 50-70 parts by weight, based on 100 parts by weight of the total recycled asphalt mixture; the low-temperature plasma activation treatment has a treatment time of 10-60 seconds and a power of 10-30 kW; the silane coupling agent solution is sprayed at a rate of 0.05-2% of the RAP mass. Further, the new aggregate in S4 has a mass of 28-36 parts; the fine-grained calcium oxide powder has a mass of 1.5-2.5 parts; the A-phase waste vegetable oil regenerator has a mass of 0.3-0.6 parts; the B-phase regenerator has an added mass of 0.08-0.15 parts, with an addition temperature window of 158-165℃; the dry premixed reinforcing agent has an added mass of 0.4-0.8 parts, with an addition temperature window of 130-140℃; the Sasobit warm mix agent has an added mass of 0.8-1.5 parts, with an addition temperature window of 150-155℃; and the new asphalt has an added mass of 2.5-3.5 parts.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) Technical performance: By introducing a two-phase regenerator and adopting a phased release functional zone, the performance of aged asphalt is effectively restored, and the fusion of new and old asphalt is promoted. It has excellent water damage resistance, which solves the technical problem that high-proportion RAP mixtures are susceptible to water damage and ensures the long-term durability of the pavement.

[0019] (2) Economic cost: Due to the high RAP content, the amount of new asphalt and new aggregates used is greatly reduced, which can significantly reduce the production cost of the mixture of the present invention and the economic benefits are extremely significant. At the same time, the method realizes the on-site conversion and utilization of waste pavement materials, saves the cost of transporting and disposing of RAP and the cost of long-distance transportation of new materials, and reduces the overall project cost.

[0020] (3) Resource utilization: This invention realizes the high-value and high-volume resource utilization of waste asphalt pavement materials, greatly reducing the mining of natural stone resources and the occupation of land resources. Through the optimized low-temperature mixing process, the energy consumption and carbon dioxide emissions in the production process are reduced compared with traditional hot-mix asphalt mixtures.

[0021] (4) Process and implementation: The preparation method of the present invention has a clear process and precise parameter control. It is easy to modify and implement the equipment in the existing mixing plant. It has good prospects for industrial production and promotion value. Through strict process control, it solves the problems of uneven mixing and high temperature sensitivity that are easy to occur in high-content RAP mixtures. The product quality is stable and reliable. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of a coarse-grained recycled asphalt mixture according to the present invention.

[0023] Figure 2 This is a comparison chart of the experimental results for Marshall stability, flow value, dynamic stability, bending strain at -10℃, and freeze-thaw splitting strength ratio in Experiment Example 1. Detailed Implementation

[0024] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0025] The technical solution designed by this invention to solve the existing problems includes the following key points: 1. Plasma-silane interface activation modification process Traditional processes simply crush and screen waste asphalt (RAP) as inert aggregate, relying on the limited high-temperature physical diffusion between new and old asphalt, resulting in weak interfacial bonding. This invention first uses low-temperature plasma technology to bombard the RAP surface. High-energy particles remove surface contaminants through physical sputtering and chemical etching, increasing the specific surface area. Simultaneously, by breaking molecular bonds, a large number of oxygen-containing active functional groups are introduced to the surface, achieving deep cleaning and activation. Subsequently, a KH-550 solution is uniformly applied to the activated surface. The silane coupling agent undergoes hydrolysis, and the highly active silanol groups produced after hydrolysis undergo dehydration condensation reactions with the active functional groups on the RAP surface, forming strong Si-OC covalent bonds, thereby achieving the chemical grafting of silane molecules onto the RAP surface. One end of the successfully grafted silane molecule is covalently anchored to the RAP, while the polar amino functional group at the other end interacts with the acidic components in the subsequently added new asphalt through acid-base interactions and forms strong hydrogen bonds with polar molecules in the asphalt. These two strong intermolecular forces are far stronger than traditional van der Waals forces, enabling high-intensity chemical adsorption and directional spreading of nascent asphalt on the RAP surface.

[0026] 2. Dual-phase composite regenerant system Traditional processes typically use light oil components to restore asphalt fluidity, often at the expense of high-temperature performance and lacking a long-term stabilization mechanism. This invention, however, achieves synergistic restoration and enhancement of aged asphalt performance through the sequential addition of complementary A and B phase regenerators at different process stages. Specifically, the main function of the A phase regenerator is to penetrate, soften, and stabilize the aged asphalt over a long period. This phase uses refined waste vegetable oil as a base carrier and is compounded with high-molecular-weight hindered phenolic antioxidants. When the mixture reaches 130-140°C, the A phase regenerator is uniformly sprayed into the mixing system. Within this temperature range, the viscosity of the aged asphalt on the RAP surface decreases to a suitable penetration range. The vegetable oil component, with its moderate molecular weight and polarity, can effectively penetrate the microstructure of the aged asphalt, replenishing the lost soft asphaltenes and thus improving the plasticity and flow properties of the asphalt. Simultaneously added antioxidant molecules diffuse throughout the asphalt phase, effectively interrupting the thermo-oxidative aging chain reaction of the asphalt by capturing oxidative free radicals during subsequent service, achieving long-term performance stability of the regenerated asphalt.

[0027] The core function of the B-phase regenerator is to enhance the high-temperature strength and durability of asphalt binders. This phase is composed of environmentally friendly rubber oil and ultrafine-pulverized natural rock asphalt. The B-phase regenerator is added to the mixing system when the mixture temperature reaches 158℃. Under these temperature conditions, the natural rock asphalt particles fully melt, and the abundant natural asphaltenes and high-density condensed aromatic ring structures act as reinforcing phases, uniformly dispersed throughout the binder system, significantly improving the asphalt's softening point, high-temperature viscosity, and elastic recovery properties. The timing of the B-phase regenerator's addition ensures optimal dispersion of the modified natural rock asphalt phase at suitable asphalt viscosity; adding it too early hinders the penetration of the A-phase, while adding it too late results in uneven dispersion.

[0028] 3. Fiber-Nano Synergistic Reinforcement In traditional processes, polypropylene fibers, nanomaterials, and mineral anti-stripping agents are typically added individually or in simple blends, leading to problems such as uneven dispersion and functional attrition. Therefore, this invention designs a dry-premixed, staged feeding composite reinforcement technology system in the material reinforcement stage. This system comprises: polypropylene fibers as a macroscopic toughening phase to improve the tensile and crack resistance of the mixture; nano-wollastonite as a microscopic reinforcing and interface-modifying phase to improve the properties of asphalt mastic and the fiber-asphalt interface; and fine-grained calcium oxide as a mineral activating and anti-stripping phase, which reacts with trace amounts of moisture to generate calcium hydroxide, exerting chemical thickening and physical water absorption effects, significantly improving the adhesion between asphalt and aggregates. To achieve efficient synergy among the three phases, this invention first mechanically premixes polypropylene fibers and nano-wollastonite powder at a 2:1 mass ratio in a dry state. This ratio was optimized to ensure that the nanoparticles are fully loaded onto the fiber carrier while avoiding free agglomeration due to excessive powder. During mechanical stirring, nano-wollastonite powder effectively adheres to the surface of polypropylene fibers and the gaps between their monofilaments due to the electrostatic interaction generated by the friction between the polar groups on their surface and the fibers. This forms a functionalized composite reinforcing unit with fibers as a three-dimensional framework and nanoparticles anchored on the surface. This structure not only solves the problem of nanoparticle agglomeration but also creates a composite that can be simultaneously added and dispersed.

[0029] In the mixing process, when the dry-mixing temperature of the aggregate reaches 115℃, fine-grained calcium oxide powder is added first. At this time, the aggregate still contains trace amounts of moisture, which provides initial hydration conditions for the calcium oxide, allowing it to fully disperse and adhere to the aggregate surface, completing the activation pretreatment of the aggregate interface. Subsequently, the composite reinforcement unit is added during the hot aggregate dry-mixing stage before the addition of asphalt, when the aggregate temperature is 130~140℃. At this process node, the dry aggregate moves at high speed in the mixing tank, generating strong collision, friction, and shearing effects. After the composite reinforcement unit is added, its fiber skeleton is fully disintegrated and dispersed under the mechanical force of the aggregate, achieving initial dispersion at the macroscopic scale; simultaneously, the nanoparticles attached to the fibers are further peeled off and diffused into the aggregate gaps under continuous collision and impact, achieving secondary dispersion at the microscopic scale. This stage fully utilizes the powerful mechanical dispersion energy of the dry-mixing process, creating optimal conditions for the uniform distribution of the two different scale reinforcement materials. If added during the wet mixing stage, the high viscosity of the asphalt medium will severely weaken the mechanical dispersing force; if added too early, the aggregate temperature and kinetic energy will be insufficient, resulting in limited dispersion effect.

[0030] After the dry-mixing and dispersion process is completed, when the aggregate temperature continues to rise to 150-155℃, new asphalt is sprayed into the mixing tank. At this time, the fibers and nanoparticles, which are already evenly distributed in the gaps between the hot aggregates, are immediately surrounded and coated by the asphalt in a well-flowing state. The pre-dispersed fibers and nanoparticles provide a significantly increased specific surface area, allowing the asphalt to quickly contact and adsorb onto them. The fibers are firmly bonded to the asphalt through surface wetting, forming a three-dimensional reinforced network; the nanoparticles are fully integrated into the asphalt mastic, playing a role in thickening, strengthening, and improving the interfacial transition zone. The aggregate surface activated by calcium oxide also forms a stronger chemical and physical bond with the asphalt at this stage. This sequential process of first dry mechanical dispersion and then wet asphalt coating ensures that the reinforcing material can achieve optimal spatial distribution in a dry state and be effectively combined with the asphalt at the optimal time, thereby achieving efficient introduction and maximization of the reinforcing effect.

[0031] 4. Sequential addition process This invention utilizes a sequential addition process to enable each functional material to function at its optimal temperature and material state: firstly, calcium oxide is used to form an activation layer on the aggregate surface; then, reinforcing fibers and nanomaterials are dispersed within the optimal kinetic energy window, while simultaneously allowing the regenerator to penetrate into the aged asphalt; next, new asphalt is introduced with the assistance of a warm mix agent to complete the initial coating; finally, a high-performance modifier is incorporated under high temperature and high fluidity conditions to achieve ultimate reinforcement.

[0032] Example 1: A method for preparing coarse-grained recycled asphalt mixture, comprising the following steps: S1: Take waste vegetable oil from catering, and after sedimentation, filtration, degumming, decolorization and refining treatment, obtain refined recycled base oil; under 60℃ and stirring conditions, add 1.0% antioxidant 1010 to the refined recycled base oil, react at a constant temperature for 60 minutes, mix evenly and cool to obtain the A phase regenerator; take environmentally friendly rubber oil, melt it at 180℃ and add it to natural rock asphalt, the natural rock asphalt needs to be crushed to below 0.15mm, bake and stir for 30 minutes to obtain a modified high viscosity agent as the B phase regenerator.

[0033] S2: Polypropylene fiber and nano-wollastonite powder are used as reinforcing materials. Weigh polypropylene fiber and nano-wollastonite at a mass ratio of 2:1, place them in a dry mixer and stir for 10 minutes to prepare a dry premixed reinforcing agent. Seal and protect from moisture for later use. S3: The recycled RAP is processed by crushing equipment and then screened to separate it into two gradation zones based on a particle size of 10mm: coarse and fine aggregates. The coarse and fine aggregates are combined at a mass ratio of 2:1 to meet the target gradation requirements, forming a mixed RAP of 60 parts (based on a total recycled asphalt mixture mass of 100 parts by mass). The mixed RAP undergoes low-temperature plasma activation treatment for 30 seconds at a power of 20kW. After treatment, a 2% aqueous KH-550 silane coupling agent solution is sprayed on, at a rate of 0.1% of the RAP mass. Subsequently, it is dried in a 60℃ hot air circulating chamber for 30 minutes to complete the surface chemical modification of the RAP, which is then removed for later use.

[0034] S4: Add treated RAP and 31.7 parts of new aggregate (a mixture of basalt crushed stone and limestone manufactured sand) to a forced twin-shaft low-temperature asphalt mixing plant. The aggregate gradation meets the AC-25 coarse-grained requirement. Start combustion heating and dry mixing. When the aggregate temperature reaches 115℃, add 2.1 parts of fine-grained calcium oxide powder and continue dry mixing for 20 seconds. Then continue heating. When the aggregate temperature reaches 135℃, add 0.6 parts of dry premixed reinforcing agent evenly to the mixing drum and continue dry mixing with the hot aggregate for 20 seconds. Immediately afterward, spray in 0.4 parts of phase A waste vegetable oil regeneration agent and dry mix for 15 seconds. Continue heating and mixing until the RAP gradually becomes dark and shiny. When the temperature reaches 153℃, first add 1.1 parts of Sasobit warm mix agent to the mixing drum and dry mix for 10 seconds. Then immediately add 2.9 parts of new asphalt and wet mix for 20 seconds to initially and evenly coat the aggregate with asphalt. Subsequently, when the overall temperature of the mixture reaches 160℃, 0.1 parts of B-phase recycling agent are added, and mixing continues for 50 seconds. Utilizing the high-speed agitation of the mixing blades and the high temperature, the B-phase recycling agent rapidly softens and integrates into the asphalt binder phase, forming a homogeneous binder together with the softened asphalt. After thorough mixing and discharge, a coarse-grained recycled asphalt mixture with a maximum nominal particle size of 26.5mm is obtained.

[0035] Example 2: The preparation method is the same as in Example 1, except that: S2: Weigh polypropylene fiber and nano-wollastonite at a mass ratio of 2:1 instead of weighing polypropylene fiber and nano-wollastonite at a mass ratio of 1:1. S3: The dosage of 60 parts of the mixed RAP is replaced with 50 parts of the mixed RAP; the treatment time of 30 seconds and the power of 20kW are replaced with a treatment time of 10 seconds and a power of 10kW; the spraying amount of 0.1% of the RAP mass is replaced with a spraying amount of 0.05% of the RAP mass. S4: 31.7 parts new aggregate are replaced with 28 parts new aggregate; 2.1 parts fine-grained calcium oxide powder are replaced with 1.5 parts fine-grained calcium oxide powder; 0.4 parts A-phase waste vegetable oil regenerator are replaced with 0.3 parts A-phase waste vegetable oil regenerator; when the overall temperature of the mixture reaches 160℃, 0.1 parts B-phase regenerator are added instead of 0.08 parts B-phase regenerator when the overall temperature of the mixture reaches 158℃; when the aggregate temperature rises to 135℃, 0.6 parts dry premixed reinforcing agent are evenly added to the mixing drum instead of 0.4 parts dry premixed reinforcing agent when the aggregate temperature rises to 130℃; when the temperature reaches 153℃, 1.1 parts Sasobit warm mix additive are added to the mixing drum first instead of 0.8 parts Sasobit warm mix additive when the temperature reaches 150℃; 2.9 parts new asphalt are replaced with 2.5 parts new asphalt. All other steps are the same.

[0036] Example 3: The preparation method is the same as in Example 1, except that: S2: Weigh polypropylene fiber and nano-wollastonite at a mass ratio of 2:1 instead of weighing polypropylene fiber and nano-wollastonite at a mass ratio of 3:1. S3: The dosage of 60 parts of the mixed RAP is replaced with 70 parts of the mixed RAP; the treatment time of 30 seconds and the power of 20kW are replaced with a treatment time of 60 seconds and a power of 30kW; the spraying amount of 0.1% of the RAP mass is replaced with a spraying amount of 0.2% of the RAP mass. S4: 31.7 parts new aggregate are replaced with 36 parts new aggregate; 2.1 parts fine-grained calcium oxide powder are replaced with 3.5 parts fine-grained calcium oxide powder; 0.4 parts A-phase waste vegetable oil regenerator are replaced with 0.6 parts A-phase waste vegetable oil regenerator; when the overall temperature of the mixture reaches 160℃, 0.1 parts B-phase regenerator are added instead of 0.15 parts B-phase regenerator when the overall temperature of the mixture reaches 165℃; when the aggregate temperature rises to 135℃, 0.6 parts dry premixed reinforcing agent are evenly added to the mixing drum instead of 0.8 parts dry premixed reinforcing agent when the aggregate temperature rises to 140℃; when the temperature reaches 153℃, 1.1 parts Sasobit warm mix additive are added to the mixing drum first instead of 1.5 parts Sasobit warm mix additive when the temperature reaches 155℃; 2.9 parts new asphalt are replaced with 3.5 parts new asphalt. All other steps are the same.

[0037] Comparative Example 1 The preparation method is the same as in Example 1, except that: S3: The step of pretreating RAP with low-temperature plasma and 2% aqueous KH-550 silane coupling agent solution is omitted; All other steps are the same.

[0038] Comparative Example 2 The preparation method is the same as in Example 1, except that: S1: Replace the preparation of the biphase regenerator with a single-phase regenerator. The preparation method of the single-phase regenerator is as follows: filter and purify the waste vegetable oil to remove impurities. Add aromatic oil to the waste vegetable oil at 50°C and stir evenly. Add plasticizer (dioctyl phthalate), anti-aging agent (2,6-di-tert-butyl-4-methylphenol), and stabilizer (polyisobutylene) in sequence, and continue stirring until uniform to obtain the single-phase regenerator. S4: The step of adding phase A regenerator is omitted and replaced with adding single phase regenerator when heating to 130°C. At the same time, the step of adding phase B regenerator is omitted. All other steps are the same.

[0039] Comparative Example 3 The preparation method is the same as in Example 1, except that: S2: The preparation step of the dry premixed reinforcing agent is omitted. No dry premixed reinforcing agent is added to the warm mix asphalt; All other steps are the same.

[0040] Comparative Example 4 The preparation method is the same as in Example 1, except that: S4: Omit the step of adding warming agent and mixing; All other steps are the same.

[0041] Experimental Example 1 The mixtures prepared in Examples 1-3 and Comparative Examples 1-4 were tested according to the standard "Technical Specification for Recycling Asphalt Pavement of Highway" (JTG / T 5521-2019): (1) Marshall stability (MS) and flow value (FL): After the Marshall specimen was kept in a constant temperature water bath at 60℃ for 30 min, it was loaded at a rate of 50 mm / min on the Marshall stability tester until failure, and the stability and flow value were recorded. The higher the overall level of stability and flow value, the stronger its ability to resist load and plastic deformation.

[0042] (2) Dynamic stability (DS): The dynamic stability is evaluated by rutting test. The rutting specimen is kept in a constant temperature chamber at 60℃ for 5 hours, and then tested on a rutting tester with a wheel pressure of 0.7MPa and a rate of 42 times / min. The deformation is recorded to calculate the dynamic stability and evaluate the high temperature stability test. The larger the dynamic stability value, the better the rutting resistance.

[0043] (3) Bending strain at -10℃ (TSR (-10℃)): The low-temperature crack resistance of the mixture is evaluated by low-temperature bending test. The specimen is kept in a low-temperature chamber at -10℃ for 4 hours, and then it is loaded as a simply supported beam on a universal testing machine at a rate of 50 mm / min. The maximum load and mid-span deflection are recorded, the bending strain at -10℃ is calculated, and the low-temperature crack resistance is evaluated. The larger the bending strain at -10℃, the stronger its ability to bend without cracking at cold temperatures.

[0044] (4) Freeze-thaw splitting strength ratio (TSR): The splitting strength of standard Marshall specimens after freezing and thawing and those without freezing and thawing were determined by freeze-thaw splitting test, and the freeze-thaw splitting tensile strength ratio (TSR) was calculated. The higher the ratio, the better the water stability.

[0045] Table 1 Comparison of Experimental Results of Examples 1-3 Serial Number Testing items unit Example 1 Example 2 Example 3 Standard indicators 1 Marshall stability kN 15.2±0.4 14.2±0.3 13.6±0.4 ≥8.0 2 Stream value 0.1mm 31±1.5 30±1.4 34±1.6 20~40 3 Dynamic stability times / mm 8117±637 7846±548 7958±612 ≥6000 4 -10℃ Bending Strain με 2915±205 2836±198 2767±193 ≥2500 5 Freeze-thaw splitting strength ratio % 88.7±3.2 86.4±3.5 84.9±3.6 ≥80 Table 2 Comparison of experimental results for Examples 1-4 Serial Number Testing items unit Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Standard indicators 1 Marshall stability kN 14.0±0.3 12.0±0.4 8.2±0.2 13.3±0.4 ≥8.0 2 Stream value 0.1mm 30.5±2.0 23.2±2.1 36.4±2.4 30.1±2.0 20~40 3 Dynamic stability times / mm 5327±425 6583±526 7246±580 7785±638 ≥6000 4 -10℃ Bending Strain με 2218±188 2563±200 2734±195 2756±210 ≥2500 5 Freeze-thaw splitting strength ratio % 65.2±4.8 78.5±4.1 82.3±3.8 83.4±3.3 ≥80 The results of Examples 1-3 and Comparative Examples 1-4 are shown in Tables 1 and 2. Figure 2 As shown in Table 1, the comprehensive technical solution provided by this invention has achieved breakthrough results with a 60% RAP content, exhibiting a dynamic stability of 8817 cycles / mm, a bending strain of 2915 με at -10℃, and a freeze-thaw splitting strength ratio of 88.7%, all at the highest levels among all embodiments. Therefore, Example 1 was determined as the optimal implementation point of this invention, taking into account core indicators such as high content and low-temperature construction, and all performance characteristics exceed the technical limits for the lower layer in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40-2004).

[0046] The results of Comparative Examples 1-4 are shown in Table 2. The comparative examples are, in order, samples without plasma-silane interface modification, samples with one-time addition of single-phase regenerator, samples without dry premixed reinforcing agents, and blank samples without warm-mix additives, with the RAP content remaining at 60%. Comparative Example 1 shows the lowest values ​​for all three indicators, and its freeze-thaw splitting strength ratio is far below the standard indicator, demonstrating a critical weak point at the bonding interface between the untreated RAP and the new asphalt. This interface provides a channel for water penetration, severely affecting the water damage resistance of the mixture. Comparative Example 2 shows a significant decrease in all three indicators, proving that a single recycling approach cannot achieve high-performance recycling. The penetration and anti-aging properties of phase A and the strengthening and thickening properties of phase B are both indispensable, exhibiting a sequential effect. After the absence of the binder, the overall performance of the binder is insufficient, lacking high-performance reserves. In Comparative Example 3, the decrease was in the order of dynamic stability > flexural strain ≈ freeze-thaw splitting strength ratio, proving that the fiber-nano composite reinforcement system has the most significant effect on improving the high-temperature deformation resistance of the mixture, and also has a clear improvement effect on improving low-temperature crack resistance and reinforcing the interface transition zone. The performance data of Comparative Example 4 show that there is no necessary correlation between the warm mixing process and the mechanical properties of the mixture, proving that the core advantage of this invention lies in its unique material system and interface structure design. The warm mixing agent is only an optional process adaptation to meet the needs of energy-saving and environmentally friendly construction, and has no significant impact on the intrinsic mechanical properties of the final product.

[0047] This invention achieves simultaneous improvement in both high and low temperature performance, avoiding the shortcomings caused by one-sided optimization. Specifically, the combination of surface activation pretreatment and a two-phase regenerator restores the properties of aged asphalt while preventing excessive softening, achieving a balance between high-temperature enhancement and low-temperature toughening. The fiber-nano reinforcement network effectively improves toughness and crack resistance, and the temperature-adaptive warm mixing measures ensure mixing and construction quality and energy efficiency. These innovative elements work synergistically to ultimately produce a coarse-grained recycled asphalt mixture with RAP comprising 60% of the mix.

Claims

1. A method for preparing coarse-grained recycled asphalt mixture, comprising activation treatment and mixing, characterized in that, The activation treatment is carried out through a combination of physical sputtering and chemical modification. The physical sputtering is low-temperature plasma treatment, and the chemical modification is surface modification using a silane coupling agent. The mixing process involves adding different raw materials in sequence according to a gradually increasing temperature: fine-grained calcium oxide powder is added at 115°C; dry premixed reinforcing agent and A-phase regenerator are added at 130-140°C; new asphalt and warm mix agent are added at 150-155°C; and B-phase regenerator is added at 158-165°C.

2. The method for preparing coarse-grained recycled asphalt mixture as described in claim 1, characterized in that, Includes the following steps: S1: Refining waste catering vegetable oil and reacting it with antioxidants at 60°C to produce phase A regenerator; melting and mixing environmentally friendly rubber oil with natural rock asphalt at 180°C to obtain a modified high-viscosity agent as phase B regenerator; S2: Polypropylene fibers are dry-mixed with nano-wollastonite to form a sealed and moisture-proof dry premixed reinforcing agent; S3: The recycled asphalt pavement material is crushed and screened into coarse and fine materials, which are then mixed to form recycled asphalt pavement material. The mixed recycled asphalt pavement material is subjected to low-temperature plasma activation treatment, and after treatment, it is sprayed with water-based silane coupling agent solution, and then dried at 60°C for later use. S4: The recycled asphalt pavement material and new aggregate are dry-mixed by combustion heating. When the aggregate temperature rises to 115℃, fine-grained calcium oxide powder is added. Then heating continues, and dry premixed reinforcing agent, A-phase recycling agent and warm mix agent are added in sequence for dry mixing. After dry mixing, new asphalt is added immediately for wet mixing. Then B-phase recycling agent is added, and the mixture is fully mixed and discharged to obtain coarse-grained recycled asphalt mixture.

3. The method for preparing a coarse-grained recycled asphalt mixture as described in claim 2, characterized in that, S1 The A-phase regenerator, wherein the amount of antioxidant added is 1.0% of the mass of the waste catering vegetable oil; the B-phase regenerator, wherein the particle size of the natural rock asphalt should be less than 0.15mm.

4. The method for preparing a coarse-grained recycled asphalt mixture as described in claim 2, characterized in that, The mass ratio of polypropylene fiber to nano-wollastonite in S2 ranges from 1 to 3.

5. The method for preparing a coarse-grained recycled asphalt mixture as described in claim 2, characterized in that, S3 describes the mixing to form recycled asphalt pavement material, wherein particles with a diameter greater than 10 mm are coarse materials, and particles with a diameter less than or equal to 10 mm are fine materials, and the mass mixing ratio of the coarse materials and fine materials is 2:

1.

6. The method for preparing a coarse-grained recycled asphalt mixture as described in claim 2, characterized in that, The low-temperature plasma activation treatment described in S3 has a treatment time of 10-60 seconds and a power of 10-30kW; the silane coupling agent solution is sprayed at a rate of 0.05-2% of the recycled asphalt pavement material.

7. The method for preparing coarse-grained recycled asphalt mixture as described in claim 2, characterized in that, S4 describes adding fine-grained calcium oxide powder and dry mixing for 20 seconds; adding dry premixed reinforcing agent, A-phase regenerator, and warm mix agent sequentially and dry mixing for 45 seconds; adding new asphalt and wet mixing for 20 seconds; and adding B-phase regenerator and mixing for 50 seconds.

8. A coarse-grained recycled asphalt mixture prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The recycled asphalt mixture comprises, by weight, 50-70 parts of recycled asphalt pavement material, 28-36 parts of new aggregate, 2.5-3.2 parts of new asphalt, 0.2-0.6 parts of phase A recycling agent, 0.05-0.3 parts of phase B recycling agent, 1.5-2.5 parts of fine-grained calcium oxide powder, 0.4-0.8 parts of dry premixed reinforcing agent, and 0.8-1.5 parts of warm mix agent.

9. The coarse-grained recycled asphalt mixture as described in claim 8, characterized in that, The nominal maximum particle size of the recycled asphalt mixture is 26.5 mm.

10. The coarse-grained recycled asphalt mixture as described in claim 8, characterized in that, The recycled asphalt mixture has a Marshall stability ≥13.6kN, a flow value of 3.0~3.5mm, a dynamic stability ≥7846 cycles / mm, a flexural strain of -10℃ ≥2767με, and a freeze-thaw splitting strength ratio ≥84.9%.

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