Direct vat set asphalt modifier, dry modified asphalt mixture and preparation method of dry modified asphalt mixture

Abstract

The invention provides a direct vat set asphalt modifier, a dry modified asphalt mixture and a preparation method of the dry modified asphalt mixture, belongs to the technical field of new road materials, and aims to solve the problems of dust pollution, material segregation, poor stability and the like caused by a mineral powder post-adding process in the application process of the conventional direct vat set asphalt modifier. And the problems of poor uniformity of the mixture and damaged pavement performance are solved. The direct vat set asphalt modifier is granular and comprises the following components in parts by weight: 10-20 parts of polyurethane, 1-5 parts of asphalt and 50-80 parts of mineral powder, the polyurethane is obtained by mixing and reacting a polyurethane prepolymer and a polyol component, and the molar ratio of an NCO group to an OH group in the polyurethane is (1.01-1.1): 1. According to the direct vat set asphalt modifier, the polymer component (polyurethane) playing a role in modification and the mineral powder component playing a role in filling are combined, the dual functions of asphalt modification and mineral powder filling can be achieved at the same time, and the step of later addition of mineral powder is avoided.

Description

Technical Field

[0001] This invention relates to the field of new road materials technology, specifically to a direct-injection asphalt modifier, a dry-process modified asphalt mixture, and their preparation methods. Background Technology

[0002] Asphalt mixtures are the most widely used paving materials in modern road engineering, and their performance directly affects the service life, driving safety, and comfort of the road surface. Traditional asphalt modification processes mainly employ a "wet process," which involves pre-blending, swelling, and developing the base asphalt with polymer modifiers (such as SBS and SBR) under high temperature and high shear conditions to produce modified asphalt. This modified asphalt is then transported to a mixing plant for mixing with aggregates and mineral powder. While the wet process is technically mature and provides stable modification results, it has several inherent drawbacks: First, the production of modified asphalt requires specialized colloid mills or high-speed shear equipment, resulting in high investment costs and energy consumption. Second, the finished modified asphalt faces the risk of modifier segregation and degradation during high-temperature storage and transportation, affecting the stability of the modification effect. Third, modified asphalt typically has a higher viscosity, requiring stricter mixing and construction temperatures, increasing energy consumption and the risk of asphalt aging.

[0003] To overcome the aforementioned drawbacks of wet asphalt processing, "dry" modified asphalt technology has emerged and gradually become one of the mainstream development directions in the field of asphalt pavement technology. The dry modification process uses granular or powdered asphalt modifiers, which are directly added to the mixing drum during the asphalt mixture mixing process, mixing simultaneously with the aggregates and asphalt or in a specific sequence. Utilizing the high temperature of the aggregates and the kinetic energy of the mixing, the modifiers rapidly melt, disperse, and combine with the asphalt, thereby achieving the modification purpose. This process has significant advantages:

[0004] (1) Dry modification does not require the pre-preparation of modified asphalt, saving the special modified asphalt production equipment and high operation and maintenance costs. Ordinary asphalt mixing plants can directly apply it, which greatly reduces the technical threshold and application cost.

[0005] (2) The modifier is "modified on the spot", which avoids the performance degradation of the finished modified asphalt during storage and transportation, and ensures the stability and consistency of the modification effect.

[0006] (3) The type and dosage of direct-injection modifier can be flexibly adjusted according to specific engineering needs (such as heavy traffic, high and low temperatures, fatigue resistance, etc.) to achieve "customization" of asphalt mixture performance and meet diverse engineering scenarios.

[0007] (4) Unlike wet processes, it does not usually require excessively high storage and mixing temperatures to maintain the stability of modified asphalt, which helps to reduce energy consumption and emissions of asphalt fumes.

[0008] While dry modification technology offers significant advantages, its core lies in the "direct-injection asphalt modifier" itself. An ideal direct-injection modifier should possess characteristics such as rapid melting, uniform dispersion, good compatibility with asphalt, and significant improvement in the road performance of asphalt mixtures. However, many existing direct-injection modifier products and their application processes still reveal some shortcomings that urgently need to be addressed in practical engineering applications.

[0009] For example, CN118638428A discloses a direct-injection, fast-melting, high-viscosity, high-elasticity, fatigue-resistant asphalt modifier, its preparation method, and its application. This asphalt modifier incorporates phenol-terminated isocyanates or polyurethane prepolymers, exhibiting characteristics such as rapid direct-injection melting, high viscosity and elasticity, high fatigue resistance, and balanced performance at both high and low temperatures. The asphalt mixture is obtained by mixing this modifier with aggregates for 90 seconds, followed by adding mineral powder and mixing for another 90 seconds. However, in this process, aggregates and the modifier are first dry-mixed in a high-speed rotating mixing drum, followed by the addition of dry, fine mineral powder. At this point, the temperature inside the mixing drum is high, and the airflow is turbulent. The extremely light mineral powder is easily lifted by the immense centrifugal force and airflow, generating significant dust pollution. This not only causes loss of mineral powder materials and leads to uncontrolled mix proportions but also severely deteriorates the working environment of the mixing plant, posing a threat to the respiratory health of operators and placing high demands on the environmental dust removal system. Furthermore, this "post-addition process" easily leads to uneven material distribution. Mineral powder, as an important component of asphalt mixtures, primarily serves to fill the gaps between aggregates and form a structurally stable asphalt binder with the asphalt. When added late, due to significant differences in particle size, shape, density, and surface properties between mineral powder and aggregates, it is difficult to achieve uniform distribution within the aggregates, which have already been preliminarily coated with asphalt and modifiers, within the limited mixing time. This inhomogeneity leads to "weak points" within the asphalt mixture. Localized areas may become more brittle due to excessive mineral powder, or have reduced bonding strength due to insufficient mineral powder. Under long-term traffic loads and environmental factors, this can easily cause localized damage, such as loosening and potholes, severely affecting the overall durability and service life of the pavement.

[0010] For example, CN117447813A discloses a reactive direct-injection modifier for long-durability road surfaces. This modifier consists of epoxy resin, blocked isocyanate, and a curing agent. It modifies asphalt by forming an adhesive network structure through a cross-linking reaction between phenolic resin and epoxy resin. Simultaneously, the NCO release activity of the blocked isocyanate reacts with the active hydrogen in the phenolic resin and asphalt mixture to form polyurethane groups, effectively improving the high and low temperature performance of asphalt. Its reaction mechanism is advanced and theoretically helpful in improving the high and low temperature performance of asphalt. However, unfortunately, this technology also fails to overcome the constraints of the aforementioned mixing process, and may even be more pronounced because reactive modifiers require higher mixing uniformity. Uneven distribution of mineral powder not only affects the density of the physical structure but may also hinder or interfere with the uniformity of the chemical cross-linking reaction, resulting in a significant reduction in the modification effect and failing to achieve its expected "long-durability" goal.

[0011] In summary, dry modification technology represents the mainstream direction of asphalt pavement material development. However, existing technologies, especially many direct-injection modifiers based on complex chemical reaction systems, suffer from common defects in application processes. The core contradiction lies in the conflict between the complex components and mixing processes designed to achieve superior modification effects and the fundamental requirements of ensuring mixture uniformity, environmentally friendly construction, and ease of operation. While the "post-addition of mineral powder" process may protect the reactivity of the modifier to some extent, the resulting dust pollution and material segregation risks hinder the large-scale promotion of these advanced modification technologies and the stable performance of their effects in actual engineering projects. Summary of the Invention

[0012] This invention provides a direct-injection asphalt modifier, a dry-process modified asphalt mixture, and a method for preparing the same, in order to solve the problems of dust pollution, material segregation, and poor mixture uniformity and impaired road performance caused by the "post-addition of mineral powder" process in the application of existing direct-injection asphalt modifiers.

[0013] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0014] In a first aspect, the present invention provides a direct-injection asphalt modifier, wherein the direct-injection asphalt modifier is in granular form and comprises the following components in parts by weight: 10-20 parts polyurethane, 1-5 parts asphalt and 50-80 parts mineral powder.

[0015] The polyurethane is obtained by mixing and reacting polyurethane prepolymer and polyol components, and the molar ratio of NCO groups to OH groups in the polyurethane is 1.01-1.1:1.

[0016] Optionally, the particle size of the direct-injection asphalt modifier is 0.1~1mm.

[0017] Optionally, the NCO group content in the polyurethane prepolymer is 5%-25% by mass, and the polyurethane prepolymer is obtained by reacting aromatic diisocyanate with polyether polyol.

[0018] Optionally, the polyol component is obtained by mixing and reacting a polyether polyol with a chain extender, wherein the molecular weight of the polyether polyol is 1000-6000.

[0019] Optionally, the polyol component further includes a coupling agent.

[0020] Optionally, the mineral powder has a particle size of less than or equal to 0.075 mm and a moisture content of less than or equal to 0.2%.

[0021] Secondly, the present invention also provides a method for preparing the above-mentioned direct-injection asphalt modifier, comprising the following steps:

[0022] Step S1, preparation of polyol component: In a dry reaction vessel, add polyether polyol, chain extender and coupling agent, and vacuum dehydrate for 1-2 hours at 100-110℃ and -0.095MPa to -0.098MPa. Then cool down to 45-55℃, add catalyst, and continue stirring for 10-30 minutes to obtain polyol component;

[0023] Step S2, preparation of polyurethane prepolymer: In a dry reactor, aromatic diisocyanate is added, and under nitrogen protection, the temperature is slowly raised to 70℃-85℃; then, under stirring at 400-600 rpm, dehydrated polyether polyol is slowly and uniformly added dropwise; the dropping rate is controlled to maintain the reaction temperature at 80℃±5℃; after the addition is complete, the reaction is continued at this temperature for 2-4 hours, during which the NCO content of the system is periodically sampled and measured until it reaches 98% of the theoretical design value, at which point heating is stopped to obtain the polyurethane prepolymer;

[0024] Step S3, preparing polyurethane composite slurry: heat the polyurethane prepolymer prepared in step S2 to 90℃±5℃, add asphalt, and then shear and stir at 1000-1500rpm for 5-15 minutes. Then add the polyol component prepared in step S1 and continue stirring at 400-600rpm for 1-2 minutes to obtain polyurethane composite slurry.

[0025] Step S4, Granulation and Curing: Using a fluidized bed granulation device, mineral powder is placed in the bed as the initial crystal nucleus. Hot air at 70-90℃ is introduced for fluidization. The polyurethane composite slurry is atomized through the top nozzle and evenly sprayed onto the fluidized mineral powder. The atomized slurry collides and adheres to the mineral powder particles. After multiple coatings, the particles gradually increase in size and become regularized. Granulation and preliminary drying and curing are achieved simultaneously, and finally, dense composite particles are formed, which is the direct-injection asphalt modifier.

[0026] Optionally, in step S4, the temperature of the polyurethane composite slurry is 50-80°C.

[0027] Thirdly, the present invention also provides a dry-process modified asphalt mixture, the dry-process modified asphalt mixture comprising aggregates, asphalt, and the above-mentioned direct-injection asphalt modifier or the direct-injection asphalt modifier prepared by the above-mentioned preparation method.

[0028] Fourthly, the present invention also provides a method for preparing the above-mentioned dry-process modified asphalt mixture, comprising the following steps:

[0029] Step A1, heating aggregate: heat the graded aggregate to 165-185℃ in the asphalt mixing plant;

[0030] Step A2, simultaneous feeding and mixing: The heated aggregate is fed into the mixing tank, and then all the required hot asphalt and the above-mentioned direct-injection asphalt modifier or the direct-injection asphalt modifier prepared by the above preparation method are fed into the tank at the same time.

[0031] Step A3, wet mixing: turn off the mixing tank and mix for 45-90 seconds to obtain dry modified asphalt mixture.

[0032] The above-described solution of the present invention has at least the following beneficial effects:

[0033] (1) The direct-injection asphalt modifier of the present invention is a composite direct-injection asphalt modifier with mineral powder function. Through unique formula design and preparation process, the modifier organically combines the polymer component (polyurethane) that plays a modifying role with the mineral powder component that plays a filling role at the microscale to form a homogeneous composite particle. During the asphalt mixture mixing process, this particle can simultaneously perform the dual functions of "asphalt modification" and "mineral powder filling". The mineral powder is "pre-dispersed" in the modifier particles, ensuring that it is evenly distributed in the mixture, avoiding local weak points caused by segregation, and significantly improving the homogeneity and long-term durability of the pavement structure. Moreover, since the step of adding mineral powder after the process is eliminated, the problem of mineral powder dust is eliminated from the source, which greatly improves the working environment, protects the health of operators, and reduces the requirements for environmental protection facilities. Finally, the two steps of "modifier addition" and "mineral powder addition" are combined into one, which simplifies the mixing operation, improves the production efficiency of the mixing plant, and reduces the risk of human error.

[0034] (2) The asphalt component in the direct-injection asphalt modifier particles of the present invention acts as a "melt inducer," which accelerates the uniform dispersion of the polymer. The excess NCO groups achieve chemical anchoring, and the coupling agent strengthens the interfacial bonding. These factors work synergistically to enable the direct-injection asphalt modifier to achieve rapid and uniform modification effects in a short mixing time. The resulting mixture exhibits significantly improved high-temperature rutting resistance, low-temperature cracking resistance, water damage resistance, and fatigue resistance. Detailed Implementation

[0035] Exemplary embodiments of this disclosure will now be described in more detail. However, it should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0036] To address the shortcomings of existing technologies, there is an urgent need to develop a novel direct-application asphalt modifier, its preparation method, and supporting application technologies. This new modifier not only needs to possess advantages such as rapid melting speed and significant modification effects (e.g., high viscoelasticity, fatigue resistance, and long durability), but more importantly, its application process should fundamentally eliminate dust pollution and material segregation problems. This requires the modifier itself to have good physical properties (e.g., appropriate particle size) to facilitate uniform dispersion, and the modifier itself to function as mineral powder, eliminating the need for subsequent addition of mineral powder. This would further enhance the potential of dry modification technology and promote the development of high-performance, environmentally friendly asphalt pavements.

[0037] Based on this, the present invention proposes a direct-injection asphalt modifier, wherein the direct-injection asphalt modifier is in granular form and comprises the following components in parts by weight: 10-20 parts polyurethane, 1-5 parts asphalt and 50-80 parts mineral powder.

[0038] The polyurethane is obtained by mixing and reacting polyurethane prepolymer and polyol components, wherein the molar ratio of NCO groups to OH groups in the polyurethane is 1.01-1.1:1. A slight excess of NCO groups can react with the active hydrogen components (such as carboxyl and amino groups) in the asphalt to form a stable "asphalt-polymer-aggregate" chemical bonding interface, thereby improving the adhesion and cohesion of the mixture.

[0039] For example, the direct-injection asphalt modifier is a dense, uniform granular material with a particle size of 0.1-1 mm, preferably 0.2-0.5 mm. This particle size range is the optimal range verified by numerous experiments. If the particle size is too small (e.g., less than 0.1 mm), the particle surface area is too large, posing a risk of dust being stirred up by airflow; if the particle size is too large (e.g., greater than 1 mm), it is not conducive to its rapid melting and uniform dispersion into the asphalt binder within a short mixing time, affecting the modification effect.

[0040] For example, the NCO group content in the polyurethane prepolymer is 5%-25%, preferably 10%-20%, and the polyurethane prepolymer is obtained by reacting an aromatic diisocyanate with a polyether polyol. The amount of aromatic diisocyanate and polyether polyol can be determined according to the NCO group content and the molar ratio of NCO groups to OH groups.

[0041] For example, the aromatic diisocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate and their modifiers; the polyether polyol has a molecular weight of 500-2500, and the polyether polyol is one or more of polytetrahydrofuran polyether and polypropylene oxide polyether.

[0042] For example, the polyol component is obtained by mixing and reacting polyether polyol and chain extender, wherein the molecular weight of the polyether polyol is 1000-6000.

[0043] For example, the mass ratio of polyether polyol to chain extender is 8-20:1.

[0044] For example, the polyether polyol is one or more of polytetrahydrofuran polyether and polypropylene oxide polyether; the chain extender is one or more of 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and dipropylene glycol.

[0045] For example, the polyol component further includes a coupling agent, the amount of which is 0.5%-2% of the total mass of the polyol component.

[0046] For example, the coupling agent is at least one of titanate and aluminate.

[0047] For example, the asphalt is a base asphalt, preferably at least one of 70# and 90# base asphalt.

[0048] For example, the mineral powder is at least one of rock mineral powder and industrial waste powder, and the particle size of the mineral powder is less than or equal to 0.075 mm and the moisture content is less than or equal to 0.2%.

[0049] Secondly, the present invention provides a method for preparing the above-mentioned direct-injection asphalt modifier, characterized by comprising the following steps:

[0050] Step S1, preparation of polyol component: In a dry reaction vessel, add polyether polyol, chain extender and coupling agent, and vacuum dehydrate for 1-2 hours at 100-110℃ and -0.095MPa to -0.098MPa. Then cool to 45-55℃, add catalyst, and continue stirring for 10-30 minutes to obtain polyol component; the catalyst is dibutyltin dilaurate.

[0051] Step S2, preparation of polyurethane prepolymer: In a dry reactor, aromatic diisocyanate is added, and under nitrogen protection, the temperature is slowly raised to 70℃-85℃; then, under stirring at 400-600 rpm, dehydrated polyether polyol is slowly and uniformly added dropwise; the dropping rate is controlled to maintain the reaction temperature at 80℃±5℃; after the addition is complete, the reaction is continued at this temperature for 2-4 hours, during which the NCO content of the system is periodically sampled and measured until it reaches 98% of the theoretical design value, at which point heating is stopped to obtain the polyurethane prepolymer;

[0052] Step S3, preparing polyurethane composite slurry: heat the polyurethane prepolymer prepared in step S2 to 90℃±5℃, add asphalt, and then shear and stir at 1000-1500rpm for 5-15 minutes. Then add the polyol component prepared in step S1 and continue stirring at 400-600rpm for 1-2 minutes to obtain polyurethane composite slurry.

[0053] Step S4, Granulation and Curing: A fluidized bed granulation device is used. Mineral powder is placed in the bed as the initial crystal nucleus, and hot air at 70-90℃ is introduced for fluidization. The polyurethane composite slurry is atomized through the top nozzle and evenly sprayed onto the fluidized mineral powder. The atomized slurry collides and adheres to the mineral powder particles. Through multiple coatings, the particles gradually increase in size and become regularized, eventually forming dense composite particles, i.e., direct-injection asphalt modifier. This process simultaneously achieves granulation and preliminary drying and curing.

[0054] This method is simple and easy to industrialize, ensuring good compatibility and bonding between the components, ultimately forming a stable granular product.

[0055] For example, in step S4, the temperature of the polyurethane composite slurry is 50-80°C.

[0056] Thirdly, the present invention provides a dry-process modified asphalt mixture, the dry-process modified asphalt mixture comprising aggregates, asphalt, and the above-mentioned direct-injection asphalt modifier or the direct-injection asphalt modifier prepared by the above-mentioned preparation method.

[0057] For example, in dry modified asphalt mixtures, the amount of aggregate (95-105 parts by weight), asphalt (1-5 parts by weight), and direct-injection asphalt modifier is calculated based on the polyurethane component accounting for 0.5%-3% of the total mass of the dry modified asphalt mixture. At the same time, the mineral powder component it contains has fully met the total mineral powder requirements of the mixture, and no additional mineral powder needs to be added.

[0058] Fourthly, the present invention provides a method for preparing the above-mentioned dry-process modified asphalt mixture, comprising the following steps:

[0059] Step A1, heating aggregate: heat the graded aggregate to 165-185℃ in the asphalt mixing plant;

[0060] Step A2, simultaneous feeding and mixing: The heated aggregate is fed into the mixing tank, followed by the simultaneous feeding of all the required 155-165℃ hot asphalt and the above-mentioned direct-injection asphalt modifier or the direct-injection asphalt modifier prepared by the above preparation method; no additional mineral powder is required.

[0061] Step A3, wet mixing: Turn off the mixing tank and mix for 45-90 seconds. During this period, the heat of the aggregate causes the asphalt component in the modifier particles to melt rapidly and promotes the softening and dispersion of polyurethane. At the same time, the excess NCO groups in the polyurethane react with the active components on the aggregate surface and in the asphalt, ultimately resulting in a uniform, high-performance modified asphalt mixture.

[0062] For example, the method for preparing dry modified asphalt mixture further includes: step A4, discharge and subsequent construction: discharge the mixed dry modified asphalt mixture, and then carry out standard construction procedures such as transportation, paving and compaction.

[0063] The preparation method of this dry-process modified asphalt mixture is highly compatible with the existing dry-process modification process, but the steps are more simplified, the environmental friendliness and the uniformity of the mixture are significantly improved, and it can produce high-performance asphalt mixtures.

[0064] The following specific embodiments further illustrate the direct-injection asphalt modifier, dry-process modified asphalt mixture, and their preparation methods of the present invention.

[0065] Example 1

[0066] (1) Preparation of direct-injection asphalt modifier:

[0067] S1, Preparation of polyol component: In a dry reaction vessel, add 100 parts of polypropylene oxide polyether 2000 (purchased from Sinochem Dongda (Zibo) Co., Ltd., brand name DL-2000D), 12 parts of 1,4-butanediol and 1 part of titanate, and vacuum dehydrate at 110℃ and -0.098MPa for 1 hour. Then cool to 50℃, add 0.2 parts of dibutyltin dilaurate, and continue stirring for 15 minutes to obtain the polyol component.

[0068] S2, Preparation of polyurethane prepolymer: In a dry reactor, add 100 parts of diphenylmethane diisocyanate (purchased from Wanhua Chemical Group Co., Ltd., brand name WANNATE® MDI-50), heat to 80℃ under nitrogen protection, and uniformly add 100 parts of dehydrated polypropylene oxide polyether 1000 (purchased from Sinochem Dongda (Zibo) Co., Ltd., brand name DL-1000D) dropwise while stirring at 400 rpm; control the dropping rate to maintain the reaction temperature at 80℃±5℃; after the addition is complete, react for 2-3 hours until 98% of the theoretical design value is reached, then stop heating to obtain a polyurethane prepolymer with an NCO content of 12.6%.

[0069] S3, Preparation of composite slurry: Take 100 parts of polyurethane prepolymer and heat it to 95℃, add 15 parts of 70# base bitumen, then shear and stir at 1500rpm for 10 minutes, then add 85 parts of the polyol component prepared in S1, and continue stirring at 400rpm for 2 minutes to obtain composite slurry.

[0070] S4, Granulation and Curing: 100 parts of mineral powder (particle size 0.075 mm, moisture content 0.2%) are added to a fluidized bed, and hot air at 80°C is introduced for fluidization. 40 parts of composite slurry at 65°C are atomized through a top nozzle and evenly sprayed onto the fluidized mineral powder to obtain asphalt modifier particles with an average particle size of about 0.2 mm. The particles contain 18.5 parts polyurethane, 1.5 parts asphalt, and 50 parts mineral powder. The molar ratio of NCO groups to OH groups in the polyurethane is 1.09:1.

[0071] (2) Preparation of dry-process modified asphalt mixture:

[0072] A1: Aggregate heating: Except for mineral powder, the other aggregates of AC-13 gradation are heated to 175℃ in the asphalt mixing plant.

[0073] A2: Synchronous feeding and mixing: The heated aggregate is fed into the mixing drum, and 7.2% of the direct-injection asphalt modifier particles prepared in step (1) and 4.7% of 70# base asphalt are added. The polyurethane accounts for 1.90% of the total mass of the asphalt mixture.

[0074] A3: Wet mixing: The mixing time is 60 seconds to obtain dry modified asphalt mixture.

[0075] Example 2

[0076] (1) Preparation of direct-injection asphalt modifier:

[0077] S1, Preparation of polyol component: In a dry reaction vessel, add 100 parts of polypropylene oxide polyether 2000 (purchased from Sinochem Dongda (Zibo) Co., Ltd., brand name DL-2000D), 12 parts of 1,4-butanediol and 1 part of titanate, and vacuum dehydrate at 110℃ and -0.098MPa for 1 hour. Then cool to 50℃, add 0.2 parts of dibutyltin dilaurate, and continue stirring for 15 minutes to obtain the polyol component.

[0078] S2, Preparation of polyurethane prepolymer: In a dry reactor, add 100 parts of toluene diisocyanate (purchased from Wanhua Chemical Group Co., Ltd., brand name WANNATE® TDI-65), heat to 80℃ under nitrogen protection, and uniformly add 100 parts of dehydrated polypropylene oxide polyether 1000 (purchased from Sinochem Dongda (Zibo) Co., Ltd., brand name DL-1000D) dropwise while stirring at 400 rpm; control the dropping rate to maintain the reaction temperature at 80℃±5℃; after the addition is complete, react for 2-3 hours until 98% of the theoretical design value is reached, then stop heating to obtain a polyurethane prepolymer with an NCO content of 19.9%.

[0079] S3, preparation of composite slurry: Take 100 parts of polyurethane prepolymer and heat it to 90℃, add 15 parts of 70# base bitumen, then shear and stir at 1500rpm for 10 minutes, then add 140 parts of polyol component prepared in S1, and continue stirring at 400rpm for 2 minutes to obtain composite slurry.

[0080] S4, Granulation and Curing: 100 parts of mineral powder (particle size 0.075 mm, moisture content 0.2%) are added to a fluidized bed, and hot air at 80°C is introduced for fluidization. 40 parts of composite slurry at 65°C are atomized through a top nozzle and evenly sprayed onto the fluidized mineral powder to obtain asphalt modifier particles with an average particle size of about 0.2 mm. The particles contain 18.8 parts of polyurethane, 1.2 parts of asphalt, and 50 parts of mineral powder. The molar ratio of NCO groups to OH groups in the polyurethane is 1.05:1.

[0081] (2) Preparation of dry-process modified asphalt mixture:

[0082] A1: Aggregate heating: Except for mineral powder, the other aggregates of AC-13 gradation are heated to 175℃ in the asphalt mixing plant.

[0083] A2: Synchronous feeding and mixing: The heated aggregate is fed into the mixing drum, and 7.2% of the direct-injection asphalt modifier particles prepared in step (1) and 4.7% of 70# base asphalt are added. The polyurethane accounts for 1.94% of the total mass of the asphalt mixture.

[0084] A3: Wet mixing: The mixing time is 60 seconds to obtain dry modified asphalt mixture.

[0085] Example 3

[0086] (1) Preparation of direct-injection asphalt modifier:

[0087] S1, Preparation of polyol component: In a dry reaction vessel, add 100 parts of polypropylene oxide polyether 1000 (purchased from Sinochem Dongda (Zibo) Co., Ltd., brand name DL-1000D), 15 parts of neopentyl glycol and 1 part of titanate, and dehydrate under vacuum at 110℃ and -0.098MPa for 1 hour. Then cool down to 50℃, add 0.2 parts of dibutyltin dilaurate, and continue stirring for 15 minutes to obtain the polyol component.

[0088] S2, Preparation of polyurethane prepolymer: In a dry reactor, add 100 parts of toluene diisocyanate (purchased from Wanhua Chemical Group Co., Ltd., brand name WANNATE® TDI-65), heat to 80℃ under nitrogen protection, and uniformly add 135 parts of dehydrated polytetrahydrofuran polyether 2000 (purchased from BASF, brand name PolyTHF® 1000) dropwise while stirring at 400 rpm; control the dropping rate to maintain the reaction temperature at 80℃±5℃; after the addition is complete, react for 2-3 hours until 98% of the theoretical design value is reached, then stop heating to obtain a polyurethane prepolymer with an NCO content of 18.1%.

[0089] S3, preparation of composite slurry: Take 100 parts of polyurethane prepolymer and heat it to 95℃, add 40 parts of 90# base bitumen, then shear and stir at 1500rpm for 10 minutes, then add 100 parts of polyol component prepared in S1, and continue stirring at 400rpm for 2 minutes to obtain composite slurry.

[0090] S4, Granulation and Curing: 100 parts of mineral powder (particle size 0.075 mm, moisture content 0.2%) are added to a fluidized bed and hot air at 80°C is introduced for fluidization. 45 parts of composite slurry at 75°C are atomized through a top nozzle and evenly sprayed onto the fluidized mineral powder to obtain asphalt modifier particles with an average particle size of about 0.3 mm. The particles contain 18.75 parts polyurethane, 3.75 parts asphalt, and 50 parts mineral powder. The molar ratio of NCO groups to OH groups in the polyurethane is 1.03:1.

[0091] (2) Preparation of dry-process modified asphalt mixture:

[0092] A1: Aggregate heating: Except for mineral powder, the other aggregates of AC-13 gradation are heated to 175℃ in the asphalt mixing plant.

[0093] A2: Synchronous feeding and mixing: The heated aggregate is fed into the mixing drum, and 7.9% of the direct-injection asphalt modifier particles prepared in step (1) and 4.4% of 90# base asphalt are added. The polyurethane accounts for 2.04% of the total mass of the asphalt mixture.

[0094] A3: Wet mixing: The mixing time is 60 seconds to obtain dry modified asphalt mixture.

[0095] Comparative Example 1

[0096] Asphalt mixtures were prepared by adding 70# asphalt using AC-13 gradation and an asphalt-aggregate ratio of 5.0%, following the method of adding mineral powder later.

[0097] Comparative Example 2

[0098] Asphalt mixtures were prepared by adding SBS modified asphalt using AC-13 gradation and an asphalt-aggregate ratio of 5.0%, following the method of adding mineral powder later.

[0099] Comparative Example 3

[0100] The preparation process of Example 2 is adopted, except that mineral powder is not added in step S4, and the composite slurry is directly granulated. Mineral powder is added in step A1.

[0101] Comparative Example 4

[0102] The preparation process of Example 3 is adopted, except that 40 parts of 70# base asphalt are not added in step S3.

[0103] Comparative Example 5

[0104] The preparation process of Example 3 was used, except that the molar ratio of NCO groups to OH groups in the polyurethane was 0.95:1.

[0105] The Marshall stability, dynamic stability, flexural tensile strength, maximum flexural tensile strain, and freeze-thaw splitting strength of the asphalt mixtures in Examples 1-3 and Comparative Examples 1-4 were determined using the methods in JTG E20-2011 "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". Specifically, the Marshall stability was tested according to the Marshall stability test for asphalt mixtures (T 0709-2011) in JTG E20-2011; the dynamic stability was tested according to the rutting test for asphalt mixtures (T 0719-2011) in JTG E20-2011; the flexural tensile strength and maximum flexural tensile strain were tested according to the bending test for asphalt mixtures (T 0715-2011) in JTG E20-2011; and the freeze-thaw splitting strength was tested according to the freeze-thaw splitting test for asphalt mixtures (T 0729-2000) in JTG E20-2011. The results are shown in Table 1.

[0106] Table 1 Performance test results of the examples and comparative examples

[0107]

[0108] As shown in Table 1, compared to the comparative example, the dry-process asphalt mixture prepared using the direct-injection asphalt modifier provided by this invention exhibits higher Marshall stability, dynamic stability, flexural tensile strength, maximum flexural tensile strain, and freeze-thaw splitting strength. The high Marshall stability and dynamic stability indicate superior rutting resistance, the high flexural tensile strength and maximum flexural tensile strain indicate superior low-temperature cracking resistance, and the high freeze-thaw splitting strength indicates better resistance to water damage.

[0109] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A direct-application asphalt modifier, characterized in that, The direct-injection asphalt modifier is in granular form and comprises the following components by weight: 10-20 parts polyurethane, 1-5 parts asphalt, and 50-80 parts mineral powder. The polyurethane is obtained by mixing and reacting polyurethane prepolymer and polyol components, and the molar ratio of NCO groups to OH groups in the polyurethane is 1.01-1.1:

1.

2. The direct-injection asphalt modifier according to claim 1, characterized in that, The particle size of the direct-injection asphalt modifier is 0.1-1 mm.

3. The direct-injection asphalt modifier according to claim 1, characterized in that, The polyurethane prepolymer contains 5%-25% NCO groups by mass, and the polyurethane prepolymer is obtained by reacting aromatic diisocyanate with polyether polyol.

4. The direct-injection asphalt modifier according to claim 3, characterized in that, The polyol component is obtained by mixing and reacting polyether polyol and chain extender, and the molecular weight of the polyether polyol is 1000-6000.

5. The direct-injection asphalt modifier according to claim 4, characterized in that, The polyol component also includes a coupling agent.

6. The direct-injection asphalt modifier according to claim 1, characterized in that, The mineral powder has a particle size of less than or equal to 0.075 mm and a moisture content of less than or equal to 0.2%.

7. A method for preparing a direct-injection asphalt modifier according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step S1, preparation of polyol component: In a dry reaction vessel, add polyether polyol, chain extender and coupling agent, and vacuum dehydrate for 1-2 hours at 100-110℃ and -0.095MPa to -0.098MPa. Then cool down to 45-55℃, add catalyst, and continue stirring for 10-30 minutes to obtain polyol component; Step S2, preparation of polyurethane prepolymer: In a dry reactor, aromatic diisocyanate is added, and under nitrogen protection, the temperature is slowly raised to 70℃-85℃; then, under stirring at 400-600 rpm, dehydrated polyether polyol is slowly and uniformly added dropwise; the dropping rate is controlled to maintain the reaction temperature at 80℃±5℃; after the addition is complete, the reaction is continued at this temperature for 2-4 hours, during which the NCO content of the system is periodically sampled and measured until it reaches 98% of the theoretical design value, at which point heating is stopped to obtain the polyurethane prepolymer; Step S3, preparing polyurethane composite slurry: heat the polyurethane prepolymer prepared in step S2 to 90℃±5℃, add asphalt, and then shear and stir at 1000-1500rpm for 5-15 minutes. Then add the polyol component prepared in step S1 and continue stirring at 400-600rpm for 1-2 minutes to obtain polyurethane composite slurry. Step S4, Granulation and Curing: Using a fluidized bed granulation device, mineral powder is placed in the bed as the initial crystal nucleus. Hot air at 70-90℃ is introduced for fluidization. The polyurethane composite slurry is atomized through the top nozzle and evenly sprayed onto the fluidized mineral powder. The atomized slurry collides and adheres to the mineral powder particles. After multiple coatings, the particles gradually increase in size and become regularized. Granulation and preliminary drying and curing are achieved simultaneously, and finally, dense composite particles are formed, which is the direct-injection asphalt modifier.

8. The preparation method according to claim 7, characterized in that, In step S4, the temperature of the polyurethane composite slurry is 50-80℃.

9. A dry-process modified asphalt mixture, characterized in that, The dry-process modified asphalt mixture includes aggregates, asphalt, and the direct-injection asphalt modifier as described in any one of claims 1 to 6 or the direct-injection asphalt modifier prepared by the preparation method described in any one of claims 7 to 8.

10. The method for preparing dry-process modified asphalt mixture according to claim 9, characterized in that, Includes the following steps: Step A1, heating aggregate: heat the graded aggregate to 165-185℃ in the asphalt mixing plant; Step A2, simultaneous feeding and mixing: The heated aggregate is fed into the mixing tank, and then all the required hot asphalt and the direct-injection asphalt modifier as described in any one of claims 1 to 6 or the direct-injection asphalt modifier prepared by the preparation method described in any one of claims 7 to 8 are fed simultaneously. Step A3, wet mixing: turn off the mixing tank and mix for 45-90 seconds to obtain dry modified asphalt mixture.

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