Preparation process of special mineral powder for asphalt mixture

Abstract

The invention discloses a preparation process of special mineral powder for an asphalt mixture, and relates to the technical field of building materials, and the preparation process comprises the following steps: S1, raw material pretreatment: carrying out preliminary crushing on limestone, silicate minerals and fly ash according to a mass ratio of 3: 1: 2, and controlling the particle size of the crushed materials to be 5-10 mm; and S2, high-temperature calcination: feeding the crushed material into a rotary kiln, and calcining at 1100-1250 DEG C for 2-3 hours. According to the preparation process of the special mineral powder for the asphalt mixture, the basic performance of the mineral powder is ensured through careful selection and scientific proportioning of the raw materials, the crystal structure of the raw materials is effectively improved, the activity and the stability of the mineral powder are improved by utilizing high-temperature calcination and quenching treatment technologies, and meanwhile, the mineral powder has the advantages that the production cost is reduced; the vertical roller mill is matched with the airflow classifier for use, so that fine grinding and granularity control of mineral powder are realized, and the specific surface area of the mineral powder is greatly increased, so that the combining capacity of the mineral powder and asphalt is improved, and the hydrophobicity and the ageing resistance of the mineral powder are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and specifically relates to a preparation process for special mineral powder for asphalt mixture. Background Technique

[0002] As a key filling material for asphalt concrete, the performance of special mineral powder for asphalt mixture directly affects the high-temperature stability, low-temperature crack resistance and durability of the road surface. Traditional mineral powder mostly uses limestone or industrial waste residue as raw materials and is prepared through processes such as crushing and grinding. However, due to problems such as insufficient raw material activity, uneven particle size distribution, and weak interfacial bonding force, asphalt mixture often exhibits defects such as segregation and accelerated aging. With the development of technologies such as high-modulus asphalt concrete and long-life road surfaces, the market has put forward higher requirements for the specific surface area, mineral composition and surface modification effect of mineral powder. In recent years, researchers have improved the performance of mineral powder by introducing composite mineral raw materials, optimizing the calcination process, developing functional modifiers, etc. However, there are still technical bottlenecks in the synergistic effect of raw materials, precise process control and long-term stability, which restrict the large-scale application of high-performance mineral powder.

[0003] In the existing technology, the preparation of mineral powder mostly uses a single limestone raw material, with large fluctuations in CaO content and easy introduction of MgO impurities. During calcination, due to rough temperature control, incomplete transformation of mineral crystal phases occurs, and the generated free calcium oxide will cause volume expansion problems. The grinding process generally relies on ordinary ball mills, with a wide particle size distribution range (D50 is often > 30 μm) and a low proportion of ultrafine powder, making it difficult to meet the adsorption requirements of asphalt for mineral fillers. The surface modification technology mostly uses mechanical mixing of single modifiers such as stearic acid, with uneven dispersion and easy shedding of the modified layer. The hydrophilicity index of the mineral powder is relatively low (contact angle < 90°), which increases the risk of interfacial peeling between asphalt and aggregate. In addition, the traditional process lacks key pretreatment steps such as magnetic separation and iron removal of fly ash and pre-roasting of silicate minerals. The residual impurity phases and crystal water directly affect the chemical stability of the mineral powder; in the storage link, ordinary packaging is mostly used, and the mineral powder is easy to absorb moisture and agglomerate, and the shelf life is usually less than 6 months. For this reason, we propose a preparation process for special mineral powder for asphalt mixture. Summary of the Invention

[0004] To solve the above technical problems and provide a preparation process for special mineral powder for asphalt mixture, this technical solution solves the above problems.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A preparation process for special mineral powder for asphalt mixture includes the following steps:

[0007] S1. Raw material pretreatment: preliminarily crush limestone, silicate minerals, and fly ash according to a mass ratio of 3:1:2, and control the particle size of the crushed material within 5 - 10 mm;

[0008] S2. High-temperature calcination: Feed the crushed materials into a rotary kiln and calcine them at 1100 - 1250 °C for 2 - 3 hours. After calcination, the materials are rapidly cooled to a temperature below 100 °C;

[0009] S3. Grinding and classification: Use a vertical roller mill to dry-grind the calcined materials, control the grinding pressure at 6 - 8 MPa, and the specific surface area of the ground ore powder reaches 400 - 600 m 2 / kg, and separate the fine powder with a particle size ≤ 75 μm through an air classifier;

[0010] S4. Surface modification: Mix the fine powder with a modifier at a mass ratio of 100:1 - 3. The modifier is composed of calcium stearate, silane coupling agent KH-550, and nano-titanium dioxide at a mass ratio of 2:1:0.5. Keep the temperature at 60 - 80 °C during mixing, the stirring speed at 300 - 500 r / min, and the time at 30 - 60 minutes;

[0011] S5. Homogenization treatment: Place the modified ore powder in a double-screw conical mixer and homogenize it at a rotation speed of 20 - 30 r / min for 2 - 4 hours, and introduce dry nitrogen to keep the humidity ≤ 5%;

[0012] S6. Performance detection: Detect the density, oil absorption value, hydrophilicity index, and mineral composition of the ore powder, and package and store it after passing the inspection.

[0013] Preferably, the raw material ratio is 45 - 55% limestone, 15 - 25% silicate minerals, and 20 - 30% fly ash, where the CaO content of the limestone is ≥ 85%, the SiO2 content of the silicate minerals is ≥ 70%, and the loss on ignition of the fly ash is ≤ 5%.

[0014] Preferably, in step S2, the inclination angle of the rotary kiln is 2.5 - 3.5°, and the rotation speed is 0.5 - 1.5 r / min;

[0015] The rapid cooling treatment uses an atomized water spray system, the water spray amount is 10 - 15% of the material mass, and the moisture content of the material after spraying is ≤ 0.5%;

[0016] The calcination process requires segmented temperature control. Heat up to 800 °C in the initial 30 minutes, and then rise to the target temperature at a rate of 10 °C / min. Control the oxygen concentration in the kiln at 8 - 12% at the end of calcination.

[0017] Preferably, in step S3, the gap between the grinding table and the grinding roller of the vertical roller mill is 2 - 3 mm, and the rotation speed of the grinding table is 80 - 120 r / min;

[0018] The inlet air velocity of the air classifier is 18 - 25 m / s, the rotation speed of the classification wheel is 2000 - 3000 r / min, and the classification efficiency is ≥ 90%;

[0019] After grinding, the particle size distribution requirements of the ore powder are as follows: D50 ≤ 15 μm, D90 ≤ 45 μm, and the proportion of particles with a particle size > 75 μm is < 0.1%.

[0020] Preferably, in step S4, the addition process of the modifier is carried out in three stages:

[0021] The first stage: adding calcium stearate, with a temperature of 60 - 65 °C, a stirring speed of 300 - 350 r / min, and a time of 10 - 15 minutes;

[0022] The second stage: adding silane coupling agent KH-550, heating up to 70 - 75 °C, a stirring speed of 400 - 450 r / min, and a time of 20 - 30 minutes;

[0023] The third stage: adding nano-titanium dioxide, maintaining the temperature at 75 - 80 °C, a stirring speed of 500 r / min, and a time of 10 - 15 minutes; ultrasonic-assisted dispersion is adopted throughout the process, with an ultrasonic frequency of 28 - 40 kHz and a power density of 0.5 - 1.0 W / cm 3 .

[0024] Preferably, in step S5, the gap between the spiral blade and the cylinder wall of the double-screw conical mixer is 3 - 5 mm, and the inner wall of the mixer is lined with a polytetrafluoroethylene coating;

[0025] During homogenization, samples are taken for detection every 30 minutes. If the coefficient of variation of the powder homogeneity > 5%, the homogenization time is extended by 1 hour;

[0026] The purity of nitrogen ≥ 99.99%, the flow rate is 0.5 - 1.0 m 3 / h, and the inlet temperature ≤ 30 °C.

[0027] Preferably, the specific requirements for the performance detection in step S6 are as follows:

[0028] The density detection is carried out by the helium pycnometry method, with a standard value of 2.6 - 2.8 g / cm 3 ;

[0029] The oil absorption value test is carried out according to GB / T5211.15 - 2014, and the requirement is ≤ 100 g / 100 g;

[0030] The hydrophilicity index is determined by the contact angle. A water contact angle ≥ 120° is qualified;

[0031] The mineral composition is analyzed by XRD. The requirements are that the calcite phase content ≥ 60%, the quartz phase ≤ 15%, and there is no free calcium oxide residue.

[0032] Preferably, the fly ash needs to be subjected to magnetic separation for iron removal, with a magnetic field intensity of 0.8 - 1.2 T, and the Fe2O3 content after iron removal ≤ 1.5%;

[0033] Silicate minerals need to be pre-calcined at 500 - 600 °C for 1 - 2 hours to remove crystal water;

[0034] Before limestone is crushed, it needs to be detected by XRF. If the MgO content > 3%, an additional pickling step is required, and it is soaked in 5% dilute hydrochloric acid for 30 minutes.

[0035] Preferably, in step S3, the grinding system is equipped with an on-line laser particle size analyzer for real-time monitoring. If the D50 value deviates from the set range by ±2 μm, the roller pressure is automatically adjusted by ±0.5 MPa;

[0036] After each batch of grinding is completed, the inside of the mill is purged in the reverse direction with compressed air at a pressure of 0.4 - 0.6 MPa for a purging time of ≥5 minutes to ensure no accumulated material.

[0037] Preferably, the finished mineral powder is packaged in a three-layer composite aluminum foil bag, with a polyethylene film on the inner layer, an aluminum foil barrier layer in the middle layer, and a polyester reinforcement layer on the outer layer;

[0038] During packaging, nitrogen is filled to displace oxygen, and the residual oxygen content ≤0.5%. A desiccant is added, and the mass ratio of silica gel to molecular sieve in the desiccant is 1:1. The addition amount of the desiccant is 0.1 - 0.3% of the mass of the mineral powder; the storage environment temperature ≤30 °C, the relative humidity ≤40%, and the shelf life ≥12 months.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The preparation process of the special mineral powder for asphalt mixture proposed by the present invention ensures the basic performance of the mineral powder through careful selection and scientific proportioning of raw materials. By using high-temperature calcination and rapid cooling treatment technologies, the crystal structure of the raw materials is effectively improved, and the activity and stability of the mineral powder are enhanced. At the same time, through the combined use of a vertical roller mill and an air classifier, fine grinding and particle size control of the mineral powder are achieved, resulting in a significant increase in its specific surface area and a more uniform particle size distribution, thereby improving the binding ability between the mineral powder and asphalt. This process introduces a composite modifier to modify the surface of the mineral powder, significantly enhancing the hydrophobicity and anti-aging performance of the mineral powder and strengthening its adhesion to asphalt, which helps to extend the service life of the road. During the homogenization process, by introducing dry nitrogen and strictly controlling the homogenization time, the consistency and stability of the mineral powder quality are further ensured. Packaging with a three-layer composite aluminum foil bag effectively prevents the mineral powder from being affected by moisture and oxidation during storage, ensuring the long-term storage quality of the mineral powder. Description of the Drawings

[0041] Figure 1 For. Detailed Embodiments

[0042] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and other obvious variations can be conceived by those skilled in the art.

[0043] Referring to Figure 1 As shown, a preparation process for special mineral powder for asphalt mixture includes the following steps:

[0044] S1. Raw material pretreatment: The primary task of preparing high-quality mineral powder is to carefully select raw materials. As the main component, the CaO content of limestone must be ≥ 85%, which is the key to ensuring the basic performance of the mineral powder. The SiO2 content of silicate minerals should be ≥ 70%, and the loss on ignition of fly ash should be ≤ 5%. When determining the raw material ratio, through a large number of experiments and engineering practices, it is most suitable to mix limestone, silicate minerals, and fly ash in a mass ratio of 3:1:2. Converted to percentages, limestone accounts for 45 - 55%, silicate minerals account for 15 - 25%, and fly ash accounts for 20 - 30%. Such a ratio enables each raw material to fully play a synergistic role in the subsequent processing, laying a good foundation for the performance of the mineral powder. Strict requirements for the raw material composition, such as the CaO content of limestone ≥ 85%, the SiO2 content of silicate minerals ≥ 70%, and the loss on ignition of fly ash ≤ 5%, ensure the stability of the basic performance of the mineral powder and guarantee the quality from the source. Secondly, the mass ratio of limestone, silicate minerals, and fly ash of 3:1:2 obtained through experiments and practices is scientific and reasonable. Within this ratio range (limestone 45 - 55%, silicate minerals 15 - 25%, fly ash 20 - 30%), each raw material can fully play a synergistic role, promote each other in the subsequent processing, improve the comprehensive performance of the mineral powder, lay a good foundation for producing high-quality mineral powder, and is conducive to improving the quality and production efficiency of the mineral powder.

[0045] In the raw material pretreatment stage, it is necessary to detect limestone first. If its MgO content > 3%, an additional pickling step is required, soaking it in 5% dilute hydrochloric acid for 30 minutes to remove impurities that may affect the performance of the ore powder. Silicate minerals need to be pre-roasted at 500 - 600 °C for 1 - 2 hours to remove crystal water and ensure their chemical activity in subsequent reactions. Fly ash needs to be treated by magnetic separation to remove iron. Under the condition of a magnetic field intensity of 0.8 - 1.2 T, the Fe2O3 content after iron removal should be ≤ 1.5%. After the above treatments, the raw materials are preliminarily crushed, and the particle size of the crushed materials is strictly controlled within 5 - 10 mm to prepare for the subsequent high-temperature calcination process. Deciding whether to pickle limestone according to its MgO content can specifically remove impurities that affect the performance of the ore powder and ensure the quality of the ore powder. Pre-roasting silicate minerals to remove crystal water can enhance their chemical activity, facilitate the full progress of subsequent reactions, and optimize the performance of the ore powder. Magnetic separation of fly ash to remove iron and strictly controlling the Fe2O3 content can reduce the interference of iron impurities. Preliminary crushing of the raw materials and controlling the particle size within 5 - 10 mm can make the materials heat more evenly and react more fully during subsequent high-temperature calcination, improve the calcination efficiency and quality, lay a solid foundation for the smooth progress of subsequent processes and the final acquisition of high-quality ore powder, and enhance the overall production efficiency.

[0046] S2. High-temperature calcination: The pretreated crushed materials are fed into a rotary kiln for high-temperature calcination. The inclination angle of the rotary kiln is set at 2.5 - 3.5°, and the rotation speed is 0.5 - 1.5 r / min. Such parameter settings help the materials heat evenly and tumble in the kiln. The calcination process adopts a segmented temperature control strategy. The temperature is rapidly increased to 800 °C within the initial 30 minutes, and then steadily increased to the target temperature of 1100 - 1250 °C at a rate of 10 °C / min and continuously calcined at this temperature for 2 - 3 hours. At the end of the calcination, the oxygen concentration in the kiln needs to be precisely controlled at 8 - 12% to ensure the full progress of the chemical reaction. After the calcination is completed, a spray water quenching system is used for rapid cooling treatment, and the water spray amount is 10 - 15% of the material mass to ensure that the material temperature rapidly drops below 100 °C. At this time, the moisture content of the material ≤ 0.5%, effectively preventing the material from agglomerating or undergoing other adverse chemical reactions during subsequent processing.

[0047] The reasonable setting of the inclination angle and rotation speed of the rotary kiln can make the materials heat evenly and tumble fully in the kiln, ensuring the uniformity and adequacy of calcination. The segmented temperature control strategy allows the materials to be heated gradually, avoiding damage to the material structure due to sudden temperature changes. The continuous calcination at the target temperature ensures the completion of the chemical reaction. Precisely controlling the oxygen concentration in the kiln provides a suitable environment for the reaction and guarantees the full progress of the reaction. The spray water quenching rapid cooling treatment can rapidly reduce the temperature, prevent material agglomeration and the occurrence of adverse chemical reactions, and control the moisture content at a low level, creating good conditions for subsequent processing, stabilizing the quality of the ore powder, improving production efficiency, and reducing the defective rate.

[0048] S3. Grinding and classification: The calcined materials enter a vertical roller mill for dry grinding. The gap between the grinding table and the grinding rollers is maintained at 2 - 3 mm, the rotational speed of the grinding table is 80 - 120 r / min, and the grinding pressure is controlled at 6 - 8 MPa. Through the precise control of these parameters, the specific surface area of the ground ore powder reaches 400 - 600 m 2 / kg. To ensure that the particle size of the ore powder meets the requirements, the grinding system is equipped with an on-line laser particle size analyzer for real-time monitoring. Once the D50 value deviates from the set range by ±2 μm, the system will automatically adjust the grinding roller pressure by ±0.5 MPa. The ground ore powder is separated by an air classifier. The inlet air velocity of the air classifier is 18 - 25 m / s, the rotational speed of the classification wheel is 2000 - 3000 r / min, and the classification efficiency is ≥90%. Thus, fine powder with a particle size ≤75 μm is accurately separated, and the particle size distribution requirements are: D50 ≤ 15 μm, D90 ≤ 45 μm, and the proportion of particles with a particle size > 75 μm is <0.1%. After each batch of grinding is completed, the inside of the mill is purged reversely with compressed air at 0.4 - 0.6 MPa for a purge time of ≥5 minutes to ensure that there is no residual accumulated material, guarantee the normal operation of the equipment and the stability of the product quality.

[0049] The precise control of the gap, rotational speed, and grinding pressure between the grinding table and the grinding rollers in the vertical roller mill can make the specific surface area of the ore powder reach the ideal range and ensure the activity of the ore powder. The on-line laser particle size analyzer for real-time monitoring can adjust the grinding roller pressure in a timely manner according to the D50 value to ensure that the particle size meets the requirements. The air classifier achieves efficient and accurate separation by reasonably setting the inlet air velocity and the rotational speed of the classification wheel, ensuring that the particle size distribution of the fine powder meets the standards and improving the quality of the ore powder. After each batch of grinding, reverse purging with compressed air can effectively remove the residual accumulated material, avoid equipment blockage, maintain the normal operation of the equipment, ensure the stability of the product quality, reduce equipment failures and maintenance costs, and improve production efficiency and economic benefits.

[0050] S4. Surface modification: The separated fine powder is mixed and modified with a modifier at a mass ratio of 100:1 - 3. The modifier is composed of calcium stearate, silane coupling agent KH-550, and nano-titanium dioxide at a mass ratio of 2:1:0.5. This composite modifier can significantly improve the performance of the mineral powder. The modification process is carried out in three stages: In the first stage, calcium stearate is added at 60 - 65°C and stirred at a speed of 300 - 350 r / min for 10 - 15 minutes to uniformly disperse calcium stearate and initially react with the surface of the mineral powder; in the second stage, silane coupling agent KH-550 is added, and at the same time the temperature is raised to 70 - 75°C, the stirring speed is increased to 400 - 450 r / min, and stirred for 20 - 30 minutes to promote the chemical bonding between the silane coupling agent and the mineral powder; in the third stage, nano-titanium dioxide is added, the temperature is maintained at 75 - 80°C, and stirred at a speed of 500 r / min for 10 - 15 minutes to further optimize the surface properties of the mineral powder by virtue of the special properties of nano-titanium dioxide. Ultrasonic-assisted dispersion is adopted throughout the process, with an ultrasonic frequency of 28 - 40 kHz and a power density of 0.5 - 1.0 W / cm 3 , ensuring the uniform dispersion of the modifier in the mineral powder and fully exerting the modification effect.

[0051] S5. Homogenization treatment: The modified mineral powder enters a double-helix conical mixer for homogenization treatment. The clearance between the spiral blades of the mixer and the cylinder wall is 3 - 5 mm, and the inner wall is lined with a polytetrafluoroethylene coating, effectively preventing material adhesion and equipment wear. Homogenize at a speed of 20 - 30 r / min for 2 - 4 hours, and introduce dry nitrogen with a purity ≥ 99.99%, with a flow rate of 0.5 - 1.0 m 3 / h, the inlet temperature ≤ 30°C, and the humidity ≤ 5%. During the homogenization process, samples are taken every 30 minutes to detect the uniformity of the mineral powder. If the coefficient of variation of the uniformity > 5%, the homogenization time is extended by 1 hour until the uniformity of the mineral powder meets the standard requirements, ensuring the consistency and stability of the product quality.

[0052] S6. Performance testing: The mineral powder is tested for density, oil absorption value, hydrophilicity index, and mineral composition. After passing the test, it is packaged and stored.

[0053] Density testing: The density of the mineral powder is tested using the helium pycnometry method because the helium pycnometry method has the characteristics of high precision and high accuracy. The standard value is required to be between 2.6 - 2.8 g / cm 3 If the test result deviates from this range, it is necessary to trace back and check the production process to find factors that may affect the density, such as fluctuations in raw material composition, abnormal processing parameters, etc., and adjust and optimize in a timely manner.

[0054] Oil absorption value test: The oil absorption value test is carried out in accordance with the standard of GB / T5211.15-2014, and the oil absorption value of the mineral powder is required to be ≤100g / 100g. The oil absorption value is an important index to measure the binding performance of the mineral powder and asphalt. If the oil absorption value is too high, it may cause problems such as excessive asphalt exudation during the use of the asphalt mixture, affecting the pavement performance. Therefore, once the oil absorption value is detected to exceed the standard, the reasons need to be analyzed, which may involve aspects such as the particle size distribution and surface properties of the mineral powder, and then the production process is improved accordingly.

[0055] Hydrophilicity index determination: The hydrophilicity index of the mineral powder is detected by the contact angle measurement method, and the water contact angle ≥120° is qualified. The hydrophilicity index reflects the affinity between the mineral powder and water. In the asphalt mixture, a lower hydrophilicity helps to improve the adhesion between the mineral powder and asphalt and enhance the water stability of the mixture. If the hydrophilicity index does not meet the standard, it is necessary to consider whether there are problems with the surface modification process, such as the type, dosage or dispersion effect of the modifier, so as to make adjustments and optimizations.

[0056] Mineral composition analysis: The mineral composition of the mineral powder is detected by using XRD analysis technology. The content of calcite phase is required to be ≥60%, the quartz phase ≤15%, and there is no residual free calcium oxide. The mineral composition directly affects the chemical activity and physical properties of the mineral powder. If the mineral composition does not meet the requirements, it may be due to deviations in raw material selection or calcination process. It is necessary to re-examine the raw material sources and parameters such as temperature and time during the processing to ensure that the mineral composition of the mineral powder meets the standards and guarantee the product quality.

[0057] Packaging materials and methods: The finished mineral powder is packaged in a three-layer composite aluminum foil bag. The inner layer is a polyethylene film with good moisture-proof performance; the middle layer is an aluminum foil barrier layer, which can effectively block the intrusion of external factors such as oxygen and moisture; the outer layer is a polyester reinforcement layer, which provides the strength and toughness of the packaging. During packaging, nitrogen is first filled into the bag to replace oxygen so that the residual oxygen content ≤0.5%, and then a desiccant (the mass ratio of silica gel to molecular sieve is 1:1) is added. The desiccant addition amount is 0.1-0.3% of the mass of the mineral powder to further ensure the dryness of the packaging environment and prevent the mineral powder from getting damp and deteriorating.

[0058] Storage environment requirements: The packaged mineral powder should be stored in an environment with a temperature ≤30°C and a relative humidity ≤40%, and the shelf life ≥12 months. During storage, it is necessary to regularly check the packaging integrity and the quality status of the mineral powder to avoid the decline of the mineral powder performance due to improper storage environment, and ensure that the mineral powder always maintains good quality during the storage period and can meet the use requirements of road construction at any time.

[0059] The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation process for special mineral powder for asphalt mixture, characterized in that, It includes the following steps: S1. Raw material pretreatment: preliminarily crush limestone, silicate minerals, and fly ash according to a mass ratio of 3:1:2, and control the particle size of the crushed material within 5 - 10 mm; S2. High-temperature calcination: Feed the crushed material into a rotary kiln, calcine it at 1100 - 1250 °C for 2 - 3 hours, and rapidly cool the calcined material to a temperature below 100 °C; S3. Grinding and classification: Use a vertical roller mill to dry-grind the calcined material, control the grinding pressure at 6 - 8 MPa, and ensure that the specific surface area of the ground ore powder reaches 400 - 600 m 2 / kg, and separate the fine powder with a particle size ≤ 75 μm through an air classifier; S4. Surface modification: Mix the fine powder and the modifier according to a mass ratio of 100:1 - 3. The modifier is composed of calcium stearate, silane coupling agent KH-550, and nano-titanium dioxide according to a mass ratio of 2:1:0.

5. Keep the temperature at 60 - 80 °C during mixing, with a stirring speed of 300 - 500 r / min and a time of 30 - 60 minutes; S5. Homogenization treatment: Place the modified mineral powder in a double-helix conical mixer, homogenize it at a rotation speed of 20 - 30 r / min for 2 - 4 hours, and introduce dry nitrogen to keep the humidity ≤ 5%; S6. Performance testing: Test the density, oil absorption value, hydrophilicity index, and mineral composition of the mineral powder. After passing the test, package and store it.

2. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: The raw material ratio is 45 - 55% limestone, 15 - 25% silicate minerals, and 20 - 30% fly ash. Among them, the CaO content of limestone ≥ 85%, the SiO2 content of silicate minerals ≥ 70%, and the loss on ignition of fly ash ≤ 5%.

3. The preparation process of a special mineral powder for asphalt mixture according to claim 1 is characterized in that: In step S2, the inclination angle of the rotary kiln is 2.5 - 3.5°, and the rotation speed is 0.5 - 1.5 r / min; The rapid cooling treatment uses an atomized water spraying system, with the water spraying amount being 10 - 15% of the material mass, and the moisture content of the sprayed material ≤ 0.5%; The calcination process requires segmented temperature control. Heat up to 800 °C in the initial 30 minutes, and then rise to the target temperature at a rate of 10 °C / min. Control the oxygen concentration in the kiln at 8 - 12% at the end of calcination.

4. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: In step S3, the gap between the grinding table and the grinding roller of the vertical roller mill is 2 - 3 mm, and the grinding table rotation speed is 80 - 120 r / min; The inlet air velocity of the air classifier is 18 - 25 m / s, the rotation speed of the classification wheel is 2000 - 3000 r / min, and the classification efficiency ≥ 90%; The particle size distribution requirements of the ground mineral powder are: D50 ≤ 15 μm, D90 ≤ 45 μm, and the proportion of particles with a particle size > 75 μm < 0.1%.

5. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: In step S4, the addition process of the modifier is carried out in three stages: The first stage: Add calcium stearate, with a temperature of 60 - 65 °C, a stirring speed of 300 - 350 r / min, and a time of 10 - 15 minutes; The second stage: Add silane coupling agent KH-550, raise the temperature to 70 - 75 °C, a stirring speed of 400 - 450 r / min, and a time of 20 - 30 minutes; The third stage: Add nano-titanium dioxide, maintain the temperature at 75 - 80 °C, the stirring speed at 500 r / min, and the time for 10 - 15 minutes; ultrasonic-assisted dispersion is adopted throughout the process, with an ultrasonic frequency of 28 - 40 kHz and a power density of 0.5 - 1.0 W / cm 3 .

6. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: In step S5, the gap between the spiral blade and the cylinder wall of the double-helix conical mixer is 3 - 5 mm, and the inner wall of the mixer is lined with a polytetrafluoroethylene coating; During homogenization, take samples for testing every 30 minutes. If the coefficient of variation of the powder homogeneity > 5%, extend the homogenization time by 1 hour; The purity of nitrogen gas is ≥99.99%, and the flow rate is 0.5 - 1.0 m 3 / h, and the inlet temperature is ≤30°C.

7. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: The specific requirements for S6 performance testing are as follows: Density detection is carried out by the helium pycnometry method, and the standard value is 2.6 - 2.8 g / cm 3 ; The oil absorption value test is carried out according to GB / T5211.15 - 2014, and the requirement is ≤ 100 g / 100 g; The hydrophilicity index is determined by the contact angle, and the water contact angle ≥ 120° is qualified; The mineral composition is analyzed by XRD. It is required that the calcite phase content ≥ 60%, the quartz phase ≤ 15%, and there is no residual free calcium oxide.

8. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: The fly ash needs to be treated by magnetic separation to remove iron. The magnetic field strength is 0.8 - 1.2 T, and the Fe2O3 content after iron removal ≤ 1.5%; The silicate minerals need to be calcined at 500 - 600 °C for 1 - 2 hours to remove the crystal water; Before the limestone is crushed, it needs to be detected by XRF. If the MgO content > 3%, an additional pickling step is required, and it is soaked in 5% dilute hydrochloric acid for 30 minutes.

9. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: In step S3, the grinding system is equipped with an on-line laser particle size analyzer for real-time monitoring. If the D50 value deviates from the set range by ±2 μm, the roller pressure is automatically adjusted by ±0.5 MPa; After each batch of grinding is completed, the inside of the mill is purged in the reverse direction with compressed air. The pressure is 0.4 - 0.6 MPa, and the purging time ≥ 5 minutes to ensure no accumulated materials.

10. The preparation process of a special mineral powder for asphalt mixture according to claim 1, characterized in that: The finished mineral powder is packaged in a three-layer composite aluminum foil bag. The inner layer is a polyethylene film, the middle layer is an aluminum foil barrier layer, and the outer layer is a polyester reinforcement layer; During packaging, nitrogen is filled to replace oxygen, and the residual oxygen content ≤ 0.5%. A desiccant is added. The mass ratio of silica gel to molecular sieve in the desiccant is 1:1, and the addition amount of the desiccant is 0.1 - 0.3% of the mass of the mineral powder; the storage environment temperature ≤ 30 °C, the relative humidity ≤ 40%, and the shelf life ≥ 12 months.

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