A modified filler for asphalt mixtures and its preparation method

Abstract

This invention belongs to the field of road asphalt technology and discloses a modified filler for asphalt mixtures and its preparation method. It is characterized by comprising the following raw materials in parts by weight: 30-40 parts limestone powder, 25-35 parts hydrated lime, 15-20 parts steel slag powder, 10-15 parts phosphogypsum, 5-8 parts bauxite, 0.5-0.8 parts composite interface modifier, and 0.3-0.5 parts dispersant. Through the mechanochemical effect, the composite interface modifier and dispersant uniformly coat the filler, micronizing the interface of the modified filler, constructing interface properties, promoting good compatibility between the modified filler and asphalt, significantly reducing the surface potential of the aggregate, facilitating uniform adhesion of the aggregate, and preventing segregation between the filler and the aggregate. This significantly improves the water stability of the asphalt mixture. The application of the modified filler will broaden the range of aggregates that can be selected for asphalt mixtures, allowing for the use of locally sourced materials and promoting the application of more types of aggregates in asphalt mixtures.

Description

Technical Field

[0001] This invention relates to the field of road asphalt technology, specifically to asphalt mixtures, and particularly to a modified filler for asphalt mixtures and its preparation method. Background Technology

[0002] Asphalt mixtures are road materials made by mixing aggregates, asphalt, mineral powder, and other materials in a certain proportion. Due to their excellent elasticity, wear resistance, and skid resistance, asphalt mixtures are highly effective in reducing driving noise and improving driving comfort and safety. Currently, asphalt mixtures are widely used in highways, urban roads, bridges, tunnels, and other applications.

[0003] Based on existing engineering practices, asphalt mixtures utilize a wide variety of aggregates. For example, high-quality basalt and diabase aggregates are alkaline and have good adhesion to asphalt, but these are relatively scarce. In actual engineering applications, the majority of aggregates used are locally sourced. The most abundant and widely distributed aggregates are primarily acidic or neutral aggregates such as granite, slate, andesite, and quartzite. These aggregates have poor adhesion to asphalt, easily leading to deterioration of the asphalt pavement's performance, thus limiting their use. Furthermore, the aggregate gradation in asphalt mixtures used in actual engineering projects fluctuates significantly. Even within the gradation range specified in the standards, the complexity of the aggregates themselves makes it difficult to achieve the optimal gradation. Ultimately, this results in difficulty controlling the porosity of the asphalt pavement, hindering compaction, and ultimately affecting the asphalt pavement's permeability and durability. Currently, water damage to asphalt pavement layers is the main factor affecting pavement life. Due to insufficient adhesion strength between asphalt and aggregate, the aggregate surface separates from the asphalt under the penetration of external rainwater, thereby reducing the mechanical strength of the pavement and causing pavement defects such as loose gravel, ruts, and potholes.

[0004] Aggregates are the most abundant material in asphalt mixtures, typically accounting for around 90%, so they are usually sourced locally. The mineral composition, morphology, and specific surface area of ​​aggregates significantly affect the performance of asphalt mixtures. For example, andesite, a neutral aggregate, has a low content of high-valence cations, resulting in unstable chemical adsorption with asphalt and poor adhesion, thus affecting the water stability and durability of the asphalt mixture. Aggregates with high silica content are particularly hydrophilic and oleophobic, exhibiting poor adhesion to asphalt and readily absorbing water. This allows water to easily penetrate the asphalt film and be adsorbed by the aggregate, leading to separation and detachment of the aggregate from the base asphalt, causing pavement cracking and reducing pavement service life. Granite, abundant in various regions, is a primary aggregate for asphalt pavement due to its hardness, wear resistance, and skid resistance. However, since granite is an acidic rock with a high surface negative charge potential, its adhesion to asphalt is limited. When it is used to pave roads and is subjected to water erosion, the asphalt and aggregate are prone to falling off, which manifests as a significant decrease in water immersion stability, cracking, pitting, unevenness, and even stone falling off the road surface.

[0005] Existing technologies have disclosed the use of limestone powder as a filler to improve the stability of asphalt mixtures. Limestone powder is an alkaline mineral that can provide a good thickening effect to asphalt mixtures, increase the cohesiveness of the mixture, and improve its stability. By filling voids and micro-cracks, it can significantly enhance the load-bearing capacity and durability of pavements. However, for aggregates with poor adhesion, complex varieties, and unstable gradations, the effect of limestone powder or hydrated lime alone on improving the adhesion between asphalt and aggregates is limited.

[0006] The root cause of water damage to asphalt pavements is the poor adhesion between asphalt and aggregates. To promote the local use of aggregates and expand their applicability, it is necessary to further enhance the adhesion between asphalt and aggregates, thereby ensuring the compactness, water stability, spalling resistance, and high-temperature stability of asphalt mixtures. Therefore, this invention proposes a modified filler for asphalt mixtures. Summary of the Invention

[0007] To broaden the application of aggregates in asphalt mixtures, enhance the adhesion between aggregates and asphalt, and improve the compactness, water stability, anti-stripping properties, and high-temperature stability of asphalt mixtures, this invention proposes a modified filler for asphalt mixtures. This modified filler possesses excellent dispersibility and interfacial properties, exhibits good compatibility with asphalt, and can uniformly adhere to aggregates, reducing the surface potential of aggregates, thereby improving the bonding between aggregates with poor adhesion and asphalt. Specifically, by modifying the filler through mechanochemical dispersion, the dispersibility and interfacial properties of the filler can be enhanced, allowing for uniform dispersion and encapsulation with the aggregates, preventing segregation, improving the adhesion between asphalt and aggregates, and promoting the self-compacting properties and strength of the asphalt mixture, thereby improving the water stability of the asphalt mixture. Furthermore, a method for preparing the modified filler for asphalt mixtures is proposed.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The primary objective of this invention is to provide a modified filler for asphalt mixtures, characterized by comprising the following raw materials in parts by weight: 30-40 parts limestone powder, 25-35 parts hydrated lime, 15-20 parts steel slag powder, 10-15 parts phosphogypsum, 5-8 parts bauxite, 0.5-0.8 parts composite interface modifier, and 0.3-0.5 parts dispersant; wherein:

[0010] The composite interface modifier is a compound of titanate coupling agent and / or aluminate coupling agent with sodium oleate in a mass ratio of 1-3:1.

[0011] The dispersant is at least one of sodium tripolyphosphate and sodium hexametaphosphate;

[0012] The modified filler for the asphalt mixture is prepared by the following method:

[0013] (1) Add limestone powder, hydrated lime, steel slag powder, phosphogypsum and bauxite to No. 1 high-speed mixer and mix evenly; transport to microwave drying tunnel box through fully enclosed pipeline system and dry at 120-130℃ to obtain premixed material;

[0014] (2) The premix, composite interface modifier, and dispersant are added to the No. 2 high-speed mixer and mixed evenly. The mixture is then transported to the continuous airflow micro-mill through a fully enclosed pipeline system. The speed of the continuous airflow micro-mill is controlled to generate a high-speed airflow through high-speed rotation, which forms a vortex in the crushing chamber. The premix enters the crushing chamber quantitatively through the feed inlet. Under the action of the vortex, the premix particles collide, rub, and shear. At the same time as crushing, the mechanochemical effect causes the composite interface modifier and dispersant to modify the micro-powder, thereby achieving continuous dispersion modification. The mixture is then collected in a filter bag and fed into the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 10μm.

[0015] Preferably, the limestone ore powder D50 has a particle size of <50μm.

[0016] Preferably, the hydrated lime D50 particle size is <50μm. Hydrated lime has extremely high activity; through refining and interface modification treatment, the calcium ions in the modified hydrated lime, when added to asphalt, promote the deposition of a film of asphalt on the aggregate surface. The calcium ions accumulate on the aggregate surface and combine with acids in the asphalt to form water-insoluble salts, promoting the anti-stripping ability of asphalt and aggregate. It not only improves the bonding strength of the asphalt mixture but also fills the micro-voids in the asphalt mixture in powder form, increasing the compactness of the aggregate, thereby improving the adhesion between the aggregate and asphalt, and ultimately enhancing the self-compacting properties of the asphalt pavement.

[0017] Preferably, the steel slag powder has a D50 particle size < 50 μm; a basicity greater than 2.0; and an apparent density of 2.56-2.75 g / cm³. 3 Steel slag powder has a high specific surface area and alkalinity, which makes it easier for asphalt to aggregate in the steel slag powder, thus enhancing the adhesion performance of asphalt. At the same time, steel slag powder can promote the density and wear resistance of asphalt pavement.

[0018] Preferably, the phosphogypsum D50 particle size is <50μm; phosphogypsum is a by-product of phosphate fertilizer production, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). Phosphogypsum can help increase the melting point and viscosity of asphalt, thereby improving the high-temperature stability of asphalt mixtures.

[0019] Preferably, the bauxite D50 particle size is <50μm; the bauxite is composed of aluminum hydroxide, which exhibits a positive charge under alkaline conditions. When used in aggregates, it can significantly reduce the surface potential of negatively charged aggregates and has good adhesion to the aggregates. The aggregates with adhered ultrafine bauxite come into contact with the carboxylic acid anions in the asphalt, thereby firmly bonding the asphalt to the aggregate surface.

[0020] Preferably, the composite interface modifier is a combination of a titanate coupling agent and sodium oleate in a mass ratio of 2:1.

[0021] Preferably, the composite interface modifier is a composite of an aluminate coupling agent and sodium oleate in a mass ratio of 3:1.

[0022] Preferably, the composite interface modifier is composed of titanate coupling agent, aluminate coupling agent and sodium oleate in a mass ratio of 2:1:1.

[0023] More preferably, the titanate coupling agent is a chelating titanate coupling agent. The chelating titanate coupling agent readily binds to the hydroxyl groups on the filler surface, making the filler hydrophobic; the other end can wrap around the asphalt, thereby improving the interfacial compatibility with the asphalt and used to modify the filler to ensure stability in a wet environment; such as at least one of the grades YB-301, JN-201, and T3-1.

[0024] More preferably, the titanate coupling agent is selected from at least one of monooxyalkyl titanate coupling agents, such as YB-203, YB-201, NDZ-101, HY-102, and JTW-101.

[0025] More preferably, the aluminate coupling agent is selected from the F series, such as at least one of F-1, F-2, F-3, and F-4.

[0026] Titanate and aluminate coupling agents exhibit good chemisorption with alkaline minerals, thus imparting excellent interfacial compatibility to the filler. Sodium oleate-modified fillers possess excellent hydrophobic properties, which helps promote uniform dispersion of the filler in the asphalt matrix and improves its adhesion to asphalt. Through composite interfacial modifiers, efficient coating and composite modification are achieved under mechanochemical action.

[0027] Modified fillers obtained through interface modification and ultra-dispersion treatment have an ultra-fine interface effect. The modified fillers not only have good compatibility with asphalt, but also impart surface activity to the aggregates, promoting the reaction between the asphalt and the active components on the aggregate surface, effectively enhancing the adhesion between the asphalt and the aggregates.

[0028] Another object of the present invention is to provide a method for preparing the above-mentioned modified filler for asphalt mixtures, characterized in that the specific preparation method is as follows:

[0029] (1) Add limestone powder, hydrated lime, steel slag powder, phosphogypsum and bauxite to No. 1 high-speed mixer and mix evenly; transport to microwave drying tunnel box through fully enclosed pipeline system and dry at 120-130℃ to obtain premixed material;

[0030] (2) The premix, composite interface modifier, and dispersant are added to the No. 2 high-speed mixer and mixed evenly. The mixture is then transported to the continuous airflow micro-mill through a fully enclosed pipeline system. The speed of the continuous airflow micro-mill is controlled to generate a high-speed airflow through high-speed rotation, which forms a vortex in the crushing chamber. The premix enters the crushing chamber quantitatively through the feed inlet. Under the action of the vortex, the premix particles collide, rub, and shear. At the same time as crushing, the mechanochemical effect causes the composite interface modifier and dispersant to modify the micro-powder, thereby achieving continuous dispersion modification. The mixture is then collected in a filter bag and fed into the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 10μm.

[0031] Preferably, in step (1), the microwave drying tunnel box controls the free water content of the material to be less than 1% by adjusting the residence time of the material in the tunnel box; more preferably, the free water content of the material is controlled to be less than 0.5%; the microwave drying tunnel box is a non-stirring and non-contact drying method, which has a fast drying speed and can effectively prevent the powder material from scattering, and prevent possible agglomeration, clumping and adhesion, thus ensuring the looseness and flowability of the powder.

[0032] Preferably, the continuous airflow micro-milling process in step (2) is selected from gas vortex pulverizers or SLG type continuous powder surface modifiers.

[0033] The gas vortex pulverizer mainly consists of a feed inlet, a pulverizing chamber, a classifying wheel, a discharge outlet, and a drive system. During operation, high-speed rotation generates a high-speed airflow, forming a strong vortex within the pulverizing chamber. A measured amount of material enters the pulverizing chamber through the feed inlet. Under the action of the vortex, the material particles undergo intense collisions, friction, and shearing, thus achieving particle refinement. Simultaneously, the mechanochemical effect allows the composite interface modifier and dispersant to fully coat the filler, achieving continuous and efficient dispersion modification.

[0034] The SLG type continuous powder surface modifier mainly consists of a feed inlet, three continuous crushing chambers, a discharge outlet, and a classifying wheel. It forces the powder material to disperse and refine through the high-speed rotation of the rotor. The powder material continuously passes through three crushing chambers to form a secondary vortex, which allows the composite interface modifier and dispersant to act efficiently on the filler surface. It combines refining, deagglomeration and dispersion, and surface coating in one process.

[0035] More preferably, the classifier wheel speed of the continuous airflow micronizer is controlled at 1500-2000 rpm. The higher the classifier wheel speed, the smaller the modified filler particle size obtained at the end. Controlling the classifier wheel speed at 1500-2000 rpm allows the D80 particle size to be less than 5 μm. The powder is discharged through the outlet, while larger particles continue to be circulated and pulverized in the grinding chamber. When the micronized and dispersed modified filler is used in the production of asphalt mixtures, the increased surface area of ​​the modified filler enhances the interfacial bonding ability between asphalt and aggregates, easily forming asphalt cementitious substances with high adhesion.

[0036] The adhesion between asphalt and aggregate is mainly due to the polar adsorption of aggregate surface molecules by polar molecules such as carboxylic acids contained in asphalt. Since water molecules are highly polar and readily combine with acidic aggregates with negative surface charge potentials, when asphalt and acidic aggregates bond, water molecules compete with asphalt for aggregate adsorption, leading to the asphalt film peeling off the acidic aggregate surface. Therefore, the modified filler of this invention uses limestone powder as the main component, synergistically modified with hydrated lime, steel slag powder, phosphogypsum, and bauxite. Through the use of composite interface modifiers and dispersants under mechanochemical effects, the resulting modified filler exhibits good compatibility with asphalt, significantly reduces the surface potential of the aggregate, facilitates uniform adhesion to the aggregate, avoids segregation between the filler and aggregate, increases the wettability of asphalt on the aggregate, effectively coats the aggregate surface, enhances the adhesion between asphalt and aggregate, and resists water erosion.

[0037] According to a typical embodiment, the modified filler adheres positively to the aggregate, eliminating the negative charge of the acidic aggregate, thereby resulting in a stronger bond between the aggregate with the modified filler and the asphalt. This is mainly because the negatively charged aggregate readily combines with the negatively charged carboxylic acid in the asphalt, thus firmly bonding the asphalt to the aggregate surface. As the negative charge potential of the aggregate decreases, the adsorption of water by the aggregate is significantly reduced, making it difficult for water to penetrate the asphalt film barrier, thereby improving the asphalt's resistance to water loss.

[0038] The modified filler described in this invention is added in proportions adjusted according to the type of asphalt mixture. For AC type asphalt mixtures in the middle and lower layers, it is added at 2-4% of the total mass of the asphalt mixture. For SMA type asphalt mixtures in the upper and surface layers, it is added at 9-10% of the total mass of the asphalt mixture. Clearly, the amount of modified filler used is relatively small, allowing for long-distance transportation in bags or cans, which is of great significance in promoting the local sourcing of aggregates.

[0039] In summary, compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] (1) The modified filler of this invention combines limestone mineral powder, hydrated lime, steel slag powder, phosphogypsum and bauxite. Compared with using limestone mineral powder alone, it can significantly improve the adhesion performance between aggregate and asphalt, and significantly improve the compactness, water stability, anti-stripping and high temperature stability of asphalt mixture.

[0041] (2) Under the action of mechanochemical effect, the composite interface modifier and dispersant uniformly coat the filler, which promotes good compatibility between the modified filler and asphalt, greatly reduces the surface potential of the aggregate, makes it easy to uniformly adhere to the aggregate, and avoids the segregation of the filler and the aggregate.

[0042] (3) The raw materials for the modified filler of this invention are readily available and low in cost. The modified production equipment is mature and easy to scale up.

[0043] (4) The application of the modified filler of this invention will broaden the range of aggregates that can be selected for asphalt mixtures, allowing for the use of locally sourced materials and promoting the application of more types of aggregates in asphalt mixtures. Detailed Implementation

[0044] To enable those skilled in the art to further understand the technical means, objectives, and effects of this invention, the invention will be described in detail below with reference to embodiments. However, this does not limit the invention in any way. It should be noted that those skilled in the art can make various adjustments and improvements without departing from the concept of this invention. These all fall within the scope of protection of this invention.

[0045] The technical parameters of the raw materials used are as follows (raw materials for which no specific parameters are given are all conventional raw materials that are understandable in this field):

[0046] Limestone powder: D50 powder particle size <50μm.

[0047] Slaked lime: D50 particle size <50μm.

[0048] Phosphogypsum: D50 particle size < 50 μm.

[0049] Bauxite: D50 particle size < 50 μm.

[0050] Steel slag powder: D50 particle size < 50 μm, basicity 2.2; apparent density 2.63 g / cm³ 3 The ingredients are shown in Table 1:

[0051] Table 1: Composition of Steel Slag Powder

[0052] Element CaO MgO <![CDATA[AL2O3]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> <![CDATA[P2O5]]> other Loss on ignition content(%) 37.65 9.22 4.62 15.28 19.96 2.8 9.78 0.69

[0053] Titanium ester coupling agent: JTW-101 type monoalkoxy titanate coupling agent, provided by Nanjing Jingtianwei Chemical Co., Ltd.

[0054] Gas Vortex Pulverizer: ACM-60 type airflow vortex pulverizer, made in Shengzhou, Zhejiang.

[0055] SLG type continuous powder surface modification machine: provided by Jiangyin Qitai Nonmetallic Engineering Co., Ltd.

[0056] Example 1

[0057] (1) All raw materials are inspected and qualified, and are loaded into each raw material warehouse in advance according to the batch requirements; 35 parts limestone ore powder, 30 parts hydrated lime, 18 parts steel slag powder, 12 parts phosphogypsum and 8 parts bauxite are automatically metered and added to No. 1 high-speed mixer according to the weight parts, and mixed at 700 rpm for 10 minutes. The mixture is then transported to the microwave drying tunnel box through a fully enclosed pipeline system, and the temperature is controlled at 120℃. The mixture is continuously dried until the free water content of the material is less than 0.5%; thus, a premix is ​​obtained.

[0058] (2) The premix obtained in step (1), 0.8 parts of composite interface modifier, and 0.3 parts of dispersant sodium tripolyphosphate are added to the No. 2 high-speed mixer and dispersed at 1000 rpm for 20 min. The mixture is then transported to the ACM-60 airflow vortex pulverizer through a fully enclosed pipeline system. This equipment is a single pulverizing chamber. The continuous airflow micro-fine milling speed is controlled at 2000 rpm. High-speed airflow is generated by high-speed rotation, forming a vortex in the pulverizing chamber. The premix enters the pulverizing chamber quantitatively through the feed inlet. Under the action of the vortex, the premix particles collide, rub, and shear. At the same time as pulverizing, the mechanochemical effect causes the composite interface modifier and dispersant to modify the fine powder, achieving continuous dispersion modification. The mixture is collected in a filter bag and connected to the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 3 μm. The composite interface modifier is composed of aluminate coupling agent F-1 and sodium oleate in a mass ratio of 3:1.

[0059] Example 2

[0060] (1) All raw materials are inspected and qualified, and are loaded into each raw material warehouse in advance according to the batch requirements; 40 parts limestone ore powder, 25 parts hydrated lime, 19 parts steel slag powder, 15 parts phosphogypsum and 8 parts bauxite are automatically metered and added to No. 1 high-speed mixer according to the weight parts, and mixed at 700 rpm for 10 minutes. The mixture is then transported to the microwave drying tunnel box through a fully enclosed pipeline system, and the temperature is controlled at 120℃. The mixture is continuously dried until the free water content of the material is less than 0.5%; thus, a premix is ​​obtained.

[0061] (2) The premix obtained in step (1), 0.6 parts of composite interface modifier, and 0.5 parts of dispersant sodium hexametaphosphate were added to the No. 2 high-speed mixer and dispersed at 800 rpm for 20 min. The mixture was then transported to the ACM-60 airflow vortex pulverizer through a fully enclosed pipeline system. This equipment is a single pulverizing chamber, and the continuous airflow micro-fine grading speed is controlled at 1800 rpm. High-speed airflow is generated by high-speed rotation, forming a vortex in the pulverizing chamber. The premix is ​​quantitatively fed into the pulverizing chamber through the feed inlet. Under the action of the vortex, the premix particles collide, rub, and shear each other. At the same time as pulverizing, the mechanochemical effect causes the composite interface modifier and dispersant to modify the fine powder, achieving continuous dispersion modification. The mixture is collected in a filter bag and fed into the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 4 μm. The composite interface modifier is a composite of JTW-101 type monoalkoxy titanate coupling agent and sodium oleate in a mass ratio of 2:1.

[0062] Example 3

[0063] (1) All raw materials are inspected and qualified, and are loaded into each raw material warehouse in advance according to the batch requirements; 30 parts limestone ore powder, 25 parts hydrated lime, 20 parts steel slag powder, 15 parts phosphogypsum and 7 parts bauxite are automatically metered and added to No. 1 high-speed mixer according to the weight parts, and mixed at 700 rpm for 10 minutes. The mixture is then transported to the microwave drying tunnel box through a fully enclosed pipeline system, and the temperature is controlled at 120℃. The mixture is continuously dried until the free water content of the material is less than 0.5%; thus, a premix is ​​obtained.

[0064] (2) The premix obtained in step (1), 0.8 parts of composite interface modifier, and 0.3 parts of dispersant sodium hexametaphosphate were added to No. 2 high-speed mixer and dispersed at 800 rpm for 20 min. The mixture was then transported to SLG type continuous powder surface modifier through a fully enclosed pipeline system. This equipment has three continuous crushing chambers and controls the continuous airflow micro-classification speed at 1500 rpm. High-speed airflow is generated by high-speed rotation and a vortex two-phase flow is formed. The mixture passes through three crushing chambers so that the composite interface modifier and dispersant can act efficiently on the surface of the filler. It has the functions of refining, deagglomeration and dispersion, and surface coating. The filler is collected in a collection bag and connected to the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 4 μm. The composite interface modifier is composed of JTW-101 type monoalkoxy titanate coupling agent, aluminate coupling agent F-3, and sodium oleate in a mass ratio of 2:1:1.

[0065] Example 4

[0066] (1) All raw materials are inspected and qualified, and are loaded into each raw material warehouse in advance according to the batch requirements; 40 parts limestone ore powder, 30 parts hydrated lime, 20 parts steel slag powder, 10 parts phosphogypsum and 5 parts bauxite are automatically metered and added to No. 1 high-speed mixer according to the weight parts, and mixed at 700 rpm for 10 minutes. The mixture is then transported to the microwave drying tunnel box through a fully enclosed pipeline system, and the temperature is controlled at 120℃. The mixture is continuously dried until the free water content of the material is less than 0.5%; thus, a premix is ​​obtained.

[0067] (2) The premix obtained in step (1), 0.5 parts of composite interface modifier, and 0.4 parts of dispersant sodium tripolyphosphate are added to No. 2 high-speed mixer and dispersed at 800 rpm for 20 min. The mixture is then transported to SLG type continuous powder surface modifier through a fully enclosed pipeline system. This equipment has three continuous crushing chambers and controls the continuous airflow micro-classification speed at 1800 rpm. High-speed airflow is generated through high-speed rotation and a vortex two-phase flow is formed. The mixture passes through three crushing chambers, so that the composite interface modifier and dispersant can act efficiently on the surface of the filler. It has the functions of refining, depolymerization and dispersion, and surface coating. The filler is collected in a collection bag and connected to the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 3 μm. The composite interface modifier is a composite of JTW-101 type monoalkoxy titanate coupling agent and sodium oleate in a mass ratio of 2:1.

[0068] Comparative Example 1

[0069] The material ratio and method of Example 1 were modified, except that the use of steel slag powder was eliminated and replaced with limestone ore powder.

[0070] Comparative Example 2

[0071] The material ratio and method of Example 1 were used for modification, except that the dispersant was omitted.

[0072] Comparative Example 3

[0073] The material ratio and method of Example 1 were modified, except that the use of bauxite was eliminated and replaced with limestone powder.

[0074] Comparative Example 4

[0075] The material ratio and method of Example 1 were modified, except that the use of quicklime was eliminated and replaced with limestone powder.

[0076] Comparative Example 5

[0077] The material ratio and method of Example 1 were modified, except that the use of phosphogypsum was eliminated and replaced with limestone mineral powder.

[0078] Comparative Example 6

[0079] (1) All raw materials are inspected and qualified, and are loaded into each raw material warehouse in advance according to the batch requirements; 35 parts limestone ore powder, 30 parts hydrated lime, 18 parts steel slag powder, 12 parts phosphogypsum and 8 parts bauxite are automatically metered and added to No. 1 high-speed mixer according to the weight parts, and mixed at 700 rpm for 10 minutes. The mixture is then transported to the microwave drying tunnel box through a fully enclosed pipeline system, and the temperature is controlled at 120℃. The mixture is continuously dried until the free water content of the material is less than 0.5%; thus, a premix is ​​obtained.

[0080] (2) Add the premix obtained in step (1), 0.8 parts of composite interface modifier, and 0.3 parts of dispersant sodium tripolyphosphate to No. 2 high-speed mixer and mix and disperse at 1000 rpm for 20 min to obtain modified filler for asphalt mixture; wherein the composite interface modifier is composed of aluminate coupling agent F-1 and sodium oleate in a mass ratio of 3:1.

[0081] Comparative Example 6 did not use an air jet mill for mechanochemical treatment of the filler. The filler particles were coarser and had poor dispersibility. The interfacial effect between the filler and the asphalt and aggregates was affected, which was reflected in the reduced adhesion of the modified filler when it was used in asphalt mixtures.

[0082] Comparative Example 7

[0083] The material ratio and method of Example 1 were used for modification, except that no composite interface modifier was added.

[0084] Comparative Example 8

[0085] The modification was carried out according to the raw material ratio and method of Example 1, except that sodium oleate was not used in the composite interface modifier.

[0086] Comparative verification of the effect of modified fillers on improving the performance of asphalt mixtures: The modified fillers in Examples 1-4 and Comparative Examples 1-8 were used to improve the bonding ability between asphalt and granite aggregates in asphalt mixtures. 13# is an asphalt mixture without any mineral powder or fillers; 14# is an asphalt mixture with only limestone mineral powder. Marshall test specimens were prepared and subjected to comprehensive testing, including residual stability after immersion, freeze-thaw splitting strength ratio, Kentaburg immersion spillage loss rate, and rutting dynamic stability, to measure the bonding performance and water stability between asphalt and aggregates. Specific specimen preparation and testing are as follows:

[0087] (I) Basic asphalt raw materials: 70# Grade A asphalt, performance parameters are shown in Table 2.

[0088] Table 2 Performance parameters of 70# Grade A asphalt

[0089] Testing items Test data Test methods Penetration (25℃) / 0.1mm 74 T0604 "Asphalt Penetration Test" Softening point / °C 47 T0606 "Asphalt Softening Point Test (Ring and Ball Method)" Ductility (10℃) / cm 40 T0605 Asphalt Ductility Test Ductility (15℃) / cm 132 T0605 Asphalt Ductility Test

[0090] (ii) Coarse aggregate: Select acidic coarse aggregate of granite. The aggregate gradation ratio is designed with reference to the AC-20 target mix design, as shown in Table 3.

[0091] Table 3 Coarse aggregate gradation ratio

[0092] Granite acid coarse aggregate particle size range Grading ratio 16-19mm 14.3％ 13.2-16mm 21.6％ 9.5-13.2mm 14.1％ 4.75-9.5mm 27.7％ 2.36-4.75mm 22.3％

[0093] (III) Fine aggregate: Select acidic fine aggregate of granite. The aggregate gradation ratio is designed with reference to the AC-20 target mix design, as shown in Table 4.

[0094] Table 4 Fine aggregate gradation ratio

[0095]

[0096]

[0097] (iv) Asphalt mixture formulation, as shown in Table 5.

[0098] Table 5 Asphalt Mixture Formulation

[0099]

[0100]

[0101] (V) Marshall specimen preparation: Mix the modified filler or limestone powder with the granite acid coarse aggregate and fine aggregate evenly. Preheat the aggregate to 180°C and the asphalt material to 158°C. Then mix evenly at 160°C. Next, put the mixture into the Marshall mold and compact it 50 times on both sides at 145°C according to the Marshall compaction molding method to form a specimen of standard size.

[0102] (vi) Immersion Marshall stability test:

[0103] In accordance with the provisions of the "Technical Specification for Construction of Asphalt Pavement of Highway" (JTG F40-2023), the residual Marshall stability of each group of test specimens was tested. The specimens were kept in a 60℃ water bath for 30 min, and the Marshall stability was measured as the standard Marshall stability (MS0). The specimens were kept in a 60℃ water bath for 48 h, and the stability was measured as the immersion Marshall stability (MS1). The ratio of the immersion Marshall stability to the standard Marshall stability (MS1 / MS0) × 100% was the residual stability. A residual stability greater than 80% was considered to indicate good water stability. The test results are shown in Table 6.

[0104] (vii) Freeze-thaw splitting strength ratio test:

[0105] One set of specimens was immersed in a constant temperature water bath at 25℃ for 2 hours, and its basic splitting strength was recorded as R0. Another set of specimens was immersed in a constant temperature water bath at 25℃ for 2 hours, then immersed in water and vacuumed for 15 minutes to ensure full water absorption. The specimens were then frozen in a -18℃ freezer for 16 hours, and immediately placed in a 60℃ constant temperature water bath for 24 hours. Subsequently, they were immersed in 20℃ water for 0.5 hours, and their splitting strength was recorded as R1. The water stability of the asphalt mixture in harsh high and low temperature environments was evaluated by the ratio of splitting strength before and after the freeze-thaw splitting test (R1 / R0) × 100%. A freeze-thaw splitting strength ratio greater than 75% indicates good water stability. The test results are shown in Table 6.

[0106] Table 6. Results of Marshall specimen water immersion residual stability and freeze-thaw splitting strength ratio of asphalt mixtures.

[0107]

[0108]

[0109] (VIII) Kentucky Immersion Spread Test:

[0110] The test was conducted according to T0733-2011 of JTG E20-2011 "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". Specimens were immersed in a water tank at 60℃ for 48 hours, then left at room temperature for 24 hours, and their weight was recorded as m0. Subsequently, the specimens were placed in a Los Angeles testing machine and subjected to the required number of rotational impacts. The remaining specimen mass after the test, m1, was recorded. The loss due to scattering was expressed as the percentage of mass of the asphalt mixture specimen scattered. This method effectively simulates the degree of separation and scattering of asphalt mixture from aggregates under the erosive action of water. The test results are shown in Table 7.

[0111] (ix) Rutting resistance test:

[0112] Under high temperature conditions, the specimens deformed when subjected to a standard axle load. The number of standard axle load compactions for every 1 mm of deformation was taken as the dynamic stability. This was used to evaluate the asphalt mixture's resistance to rutting. The rutting test specimens were 300 mm x 300 mm x 50 mm. During the test, a wheel load of 0.7 MPa was applied at 60°C for 1 hour. The test results are shown in Table 7.

[0113] Table 7. Test results of Kentucky immersion dispersion rate and rutting dynamic stability of asphalt mixtures.

[0114]

[0115]

[0116] The Marshall test described above comprehensively evaluates the high-temperature stability, water stability, and rutting resistance of asphalt mixtures through the specimen's residual stability after immersion, freeze-thaw splitting strength ratio, and Kentucky immersion scattering test. The modified filler of this invention is clearly excellent in improving the bond between granite aggregate and asphalt, maintaining a residual stability after immersion above 94% and a freeze-thaw splitting strength ratio above 92%, fully meeting the technical requirements for road asphalt mixtures. In particular, the Kentucky immersion scattering test, by simulating the degree of asphalt peeling and scattering from aggregate under the erosion of water, can effectively reflect the bond strength and water resistance of asphalt mixtures.

[0117] Compared with the control group (6#-14#), the modified fillers (1#-4#) of this invention show that the synergistic assistance and mechanochemical modification of each raw material significantly improve the water stability of the modified fillers used in aggregates. This is because the modified fillers are uniformly dispersed, have improved compatibility, and adhere evenly to the aggregate surface, reducing the surface potential of negatively charged aggregates and constructing good interfacial properties. This improves the adhesion between aggregates and asphalt, and is obviously beneficial to promoting the high-temperature stability, water stability, and rutting resistance of asphalt mixtures.

[0118] It should be understood that any technical solution that can be obtained by those skilled in the art based on the concept of this invention through logical analysis, reasoning, or limited experimentation on the basis of the prior art should be within the scope of protection defined by the claims.

Claims

1. A modified filler for asphalt mixtures, characterized in that, The modified filler is composed of the following raw materials in parts by weight: 30-40 parts limestone powder, 25-35 parts hydrated lime, 15-20 parts steel slag powder, 10-15 parts phosphogypsum, 5-8 parts bauxite, 0.5-0.8 parts composite interface modifier, and 0.3-0.5 parts dispersant; wherein: The composite interface modifier is a compound of titanate coupling agent and / or aluminate coupling agent with sodium oleate in a mass ratio of 1-3:

1. The dispersant is at least one of sodium tripolyphosphate and sodium hexametaphosphate; The modified filler for the asphalt mixture is prepared by the following method: (1) Add limestone powder, hydrated lime, steel slag powder, phosphogypsum and bauxite to No. 1 high-speed mixer and mix evenly; transport to microwave drying tunnel box through fully enclosed pipeline system and dry at 120-130℃ to obtain premixed material; (2) The premix, composite interface modifier, and dispersant are added to the No. 2 high-speed mixer and mixed evenly. The mixture is then transported to the continuous airflow micro-mill through a fully enclosed pipeline system. The grading speed of the continuous airflow micro-mill is controlled. High-speed airflow is generated by high-speed rotation, which forms a vortex in the crushing chamber. The premix is ​​quantitatively fed into the crushing chamber through the feed inlet. Under the action of the vortex, the mechanochemical effect causes the composite interface modifier and dispersant to modify the micro-powder, thereby achieving continuous dispersion modification. The mixture is then collected in a filter bag and fed into the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 10μm.

2. The modified filler for asphalt mixtures according to claim 1, characterized in that, The limestone ore powder D50 has a particle size of <50μm; the hydrated lime D50 has a particle size of <50μm; the steel slag powder D50 has a particle size of <50μm; the phosphogypsum D50 has a particle size of <50μm; and the bauxite D50 has a particle size of <50μm.

3. The modified filler for asphalt mixtures according to claim 1, characterized in that, The composite interface modifier is a combination of a titanate coupling agent and sodium oleate in a mass ratio of 2:

1.

4. The modified filler for asphalt mixtures according to claim 1, characterized in that, The composite interface modifier is composed of an aluminate coupling agent and sodium oleate in a mass ratio of 3:

1.

5. The modified filler for asphalt mixtures according to claim 1, characterized in that, The composite interface modifier is composed of titanate coupling agent, aluminate coupling agent, and sodium oleate in a mass ratio of 2:1:

1.

6. The modified filler for asphalt mixtures according to claim 1, characterized in that, The titanate coupling agent is selected as a chelating titanate coupling agent.

7. The modified filler for asphalt mixtures according to claim 1, characterized in that, The titanate coupling agent is selected from monooxyalkyl titanate coupling agents.

8. A method for preparing a modified filler for asphalt mixtures according to any one of claims 1-7, characterized in that, The specific preparation method is as follows: (1) Add limestone powder, hydrated lime, steel slag powder, phosphogypsum and bauxite to No. 1 high-speed mixer and mix evenly; transport to microwave drying tunnel box through fully enclosed pipeline system and dry at 120-130℃ to obtain premixed material; (2) The premix, composite interface modifier, and dispersant are added to the No. 2 high-speed mixer and mixed evenly. The mixture is then transported to the continuous airflow micro-mill through a fully enclosed pipeline system. The grading speed of the continuous airflow micro-mill is controlled. High-speed airflow is generated by high-speed rotation, which forms a vortex in the crushing chamber. The premix is ​​quantitatively fed into the crushing chamber through the feed inlet. Under the action of the vortex, the mechanochemical effect causes the composite interface modifier and dispersant to modify the micro-powder, thereby achieving continuous dispersion modification. The mixture is then collected in a filter bag and fed into the finished product silo to obtain modified filler for asphalt mixture with a D80 particle size of less than 10μm.

9. The method for preparing a modified filler for asphalt mixtures according to claim 8, characterized in that, The microwave drying tunnel box described in step (1) controls the free water content of the material to be less than 1%.

10. The method for preparing a modified filler for asphalt mixtures according to claim 8, characterized in that, The speed of the classifier wheel in the continuous airflow micro-machine described in step (2) is controlled at 1500-2000 rpm.

Images