Flame-retardant asphalt mixture for tunnel pavement and preparation method of flame-retardant asphalt mixture

Abstract

The invention relates to the technical field of road engineering materials, and discloses a flame-retardant asphalt mixture for a tunnel pavement and a preparation method of the flame-retardant asphalt mixture. The raw materials comprise 5-50 parts of flame-retardant asphalt (the softening point is 50-70 DEG C, and the needle penetration is 60-100 (0.1 mm)), 100-150 parts of aggregates (the specific particle size and proportion of coarse and fine aggregates), 10-20 parts of mineral powder (limestone mineral powder, high specific surface area and low hydrophilic coefficient) and 5-15 parts of a flame retardant (inorganic and organic are compounded, and the proportion is specific). The preparation method comprises the following steps: preheating the aggregate and the mineral powder at 160-180 DEG C to remove water and extract activity, adding the flame retardant into the petroleum asphalt at 140-160 DEG C, stirring for 20-30 minutes at 300-500 r / min to prepare the flame-retardant asphalt, and sequentially mixing. Through multiple tests, the oxygen index of the mixture is more than 30%, the flame retardance is excellent, the compression resistance is more than 10 MPa, the abrasion is less than 30 mm < 3 >, the pavement performance is good, the process is simple and convenient, the quality is stable, the fire prevention and the service life of the tunnel pavement are effectively improved, and the problems of poor flame retardance, complex process and the like of the traditional asphalt mixture are solved.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering materials, in particular to a flame retardant asphalt mixture for tunnel pavement and a preparation method thereof. Background Art

[0002] With the rapid development of transportation, tunnel projects are increasing. Due to its special closed environment, once a fire occurs in the tunnel pavement, the fire spreads rapidly and the smoke is difficult to discharge, which will pose a great threat to the safety of personnel and property. Therefore, high requirements are placed on the flame retardant properties of tunnel pavement materials.

[0003] Although traditional asphalt mixtures perform well in terms of road performance, they are obviously insufficient in terms of flame retardancy. Some flame retardant asphalt mixtures currently on the market not only have unsatisfactory flame retardant effects, but also have complex preparation processes and high costs, making it difficult to meet the diverse needs of actual projects. Therefore, the development of an efficient, practical and economical flame retardant asphalt mixture for tunnel pavement and its preparation method has become a key issue that needs to be urgently addressed in the current road engineering field. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the shortcomings of the prior art, the present invention provides a flame retardant asphalt mixture for tunnel pavement and a preparation method thereof, which has the advantages of improving the fire safety and service life of the tunnel pavement, and solves the problems of poor flame retardant performance and complex preparation process of the existing asphalt mixture for tunnel pavement.

[0006] (II) Technical solution

[0007] In order to achieve the above-mentioned purpose of improving the fire safety and service life of the tunnel pavement, the present invention provides the following technical solutions:

[0008] A flame retardant asphalt mixture for tunnel pavement, comprising the following raw materials in parts by weight:

[0009] Flame retardant asphalt: 5-50 parts. This content range is determined after comprehensively weighing the bonding performance, durability and flame retardant requirements of the tunnel pavement. Within this range, it can not only ensure that the asphalt can achieve good coating on the aggregate and build a stable mixture structure, but also give the mixture excellent flame retardant properties to ensure its safe use in the special environment of the tunnel.

[0010] Aggregate: 100-150 parts, of which coarse aggregate is limestone crushed stone with a particle size of 5-20mm, and fine aggregate is machine-made sand with a particle size of 0-5mm. The mass ratio of the two is (3-5):(2-4). The coarse aggregate provides a solid skeleton support for the mixture to ensure that it has sufficient strength and stability; the fine aggregate fills the gaps between the coarse aggregate, effectively improving the workability and density of the mixture. Such a particle size range and mass ratio setting can form a reasonable gradation of aggregates and optimize the physical and mechanical properties of the mixture to better adapt to the complex vehicle loads and special environmental conditions in the tunnel.

[0011] Mineral powder: 10-20 parts. Mineral powder plays an important role in filling and bonding in the mixture. It can form a uniform mortar with asphalt, enhance the bonding force between asphalt and aggregate, and thus improve the overall performance of the mixture. The appropriate amount of mineral powder can ensure that the mortar has a suitable consistency and good bonding effect, thereby enhancing the durability and resistance to water damage of the road surface.

[0012] Flame retardant: 5-15 parts, compounded from inorganic flame retardant (a mixture of aluminum hydroxide and magnesium hydroxide) and organic flame retardant (phosphorus flame retardant). Among them, the mass ratio of inorganic flame retardant to organic flame retardant is (2-3):(1-2), and the mass ratio of aluminum hydroxide to magnesium hydroxide is (1-2):(1-2). Inorganic flame retardants will decompose at high temperatures, absorb a large amount of heat, reduce the surface temperature of the material, and the released water vapor can effectively dilute the concentration of combustible gases; organic flame retardants will form a dense carbonized layer on the surface of the material, hindering the transfer of oxygen and heat. This carefully formulated compounding method and the precise proportion of each component have been verified by a large number of experiments, and can give full play to the synergistic flame retardant effect and significantly improve the flame retardant properties of the mixture.

[0013] Nano-level flame retardant enhancer: 1-3 parts, choose nano-titanium dioxide or nano-montmorillonite. Nano-titanium dioxide can absorb heat and release free radicals under high temperature environment with its good thermal stability and photocatalytic performance, effectively inhibiting the combustion reaction; nano-montmorillonite can form a nano-level barrier layer inside the asphalt mixture to slow down the spread of heat and flames.

[0014] Anti-aging agent: 0.5-1 part, which is a hindered phenol or amine antioxidant, such as antioxidant 1010 or antioxidant 168. Anti-aging agent can capture free radicals generated during the production, storage and use of asphalt, slow down the oxidation aging rate of asphalt, and thus extend the service life of the tunnel pavement.

[0015] 2. Raw material characteristics

[0016] Flame retardant asphalt: It is petroleum asphalt that has been specially treated with flame retardant. Its softening point is in the range of 50-70℃, and its needle penetration (25℃, 100g, 5s) is 60-100 (0.1mm). Softening point is an important indicator to measure the thermal stability of asphalt. Within this range, asphalt is not easy to soften and flow in a high temperature environment, which can effectively ensure the road surface's anti-deformation ability; needle penetration reflects the consistency and viscosity of asphalt. Appropriate needle penetration makes asphalt have good workability during construction, can evenly cover aggregates, and can provide sufficient bonding force during long-term use to ensure the stability of the mixture.

[0017] Mineral powder: limestone mineral powder with a specific surface area of ​​not less than 300m 2 / kg, and the hydrophilic coefficient is less than 1. A larger specific surface area means that the mineral powder can fully contact with the asphalt, forming more adsorption sites, thereby enhancing the bonding performance of the mortar; a hydrophilic coefficient less than 1 indicates that the mineral powder has good hydrophobicity, can effectively resist the invasion of water, improve the mixture's ability to resist water damage, and ensure that it can still maintain stable performance in a humid tunnel environment.

[0018] Coarse aggregate: The crushing value is required to be no more than 20%, and the Los Angeles abrasion loss is required to be no more than 30%. The crushing value directly reflects the ability of coarse aggregate to resist crushing. A lower crushing value ensures that the coarse aggregate is not easily broken under the repeated action of vehicle loads, thereby maintaining the stability of the mixture skeleton structure; the Los Angeles abrasion loss index measures the wear resistance of coarse aggregate. Smaller abrasion loss means that coarse aggregate can maintain a good surface morphology during long-term use, reduce road wear, and thus extend the service life of the road.

[0019] Fine aggregate: Mud content is not more than 3%, and sand equivalent is not less than 60%. Too high mud content will seriously affect the bonding performance between fine aggregate and asphalt, reducing the strength and durability of the mixture; sand equivalent reflects the cleanliness and angularity of fine aggregate. A higher sand equivalent can ensure that fine aggregate can fully play its filling and reinforcing role in the mixture, improving the overall performance of the mixture.

[0020] Inorganic flame retardant: The purity of aluminum hydroxide is not less than 95%, and the purity of magnesium hydroxide is not less than 90%. High-purity inorganic flame retardant can ensure that it can fully exert its decomposition, absorption of heat and dilution of combustible gas during the flame retardant process, improve the stability and reliability of the flame retardant effect, effectively delay the spread of fire when a fire occurs, and buy precious time for personnel evacuation and rescue work.

[0021] Preferably, the flame-retardant asphalt is petroleum asphalt treated with flame retardant, with a softening point of 50-70°C and a penetration (25°C, 100g, 5s) of 60-100 (0.1mm). The softening point reflects the thermal stability of the asphalt. Within this range, the asphalt is not easily softened and flowed at high temperatures, ensuring the anti-deformation ability of the road surface; the penetration reflects the consistency and viscosity of the asphalt. An appropriate penetration makes the asphalt have good workability during construction, can evenly coat the aggregates, and can provide sufficient bonding force during use.

[0022] Preferably, the mineral powder is limestone mineral powder, with a specific surface area of not less than 300m 2 / kg and a hydrophilic coefficient of less than 1. A larger specific surface area means that the mineral powder can fully contact with the asphalt, form more adsorption sites, and enhance the bonding performance of the mortar; a hydrophilic coefficient of less than 1 indicates that the mineral powder has good hydrophobicity, can effectively prevent water intrusion, improve the water damage resistance of the mixture, and ensure stable performance in a humid tunnel environment.

[0023] Preferably, the crushing value of the coarse aggregate is not more than 20%, and the Los Angeles abrasion loss is not more than 30%. The crushing value reflects the ability of the coarse aggregate to resist crushing. A lower crushing value ensures that the coarse aggregate is not easily broken under the action of vehicle loads, maintaining the stability of the skeleton structure of the mixture; the Los Angeles abrasion loss index measures the abrasion resistance of the coarse aggregate. A smaller abrasion loss means that the coarse aggregate can maintain a good surface morphology during long-term use, reduce the wear of the road surface, and extend the service life of the road surface.

[0024] Preferably, the mud content of the fine aggregate is not more than 3%, and the sand equivalent is not less than 60%. Excessive mud content will affect the bonding performance between the fine aggregate and the asphalt, reducing the strength and durability of the mixture; the sand equivalent reflects the cleanliness and angularity of the fine aggregate. A higher sand equivalent can ensure that the fine aggregate plays a good filling and strengthening role in the mixture, improving the overall performance of the mixture.

[0025] Preferably, the purity of aluminum hydroxide in the inorganic flame retardant is not less than 95%, and the purity of magnesium hydroxide is not less than 90%. High-purity inorganic flame retardants can ensure that they fully play the role of endothermic decomposition and diluting combustible gases during the flame retardant process, improving the stability and reliability of the flame retardant effect, and ensuring that the mixture can effectively delay the spread of fire in case of a fire, buying time for personnel evacuation and rescue.

[0026] Another technical problem to be solved by the present invention is to provide a preparation method of a flame-retardant asphalt mixture for tunnel pavement, including the following steps:

[0027] Preheating: The aggregate and mineral powder are heated in a segmented manner respectively. First, they are heated to 120 - 140 °C and kept at this temperature for 5 - 10 min, and then the temperature is raised to 160 - 180 °C. Such a temperature range can not only effectively remove the moisture in the aggregate and mineral powder, avoiding the negative impact of moisture on the adhesion between asphalt and aggregate, but also the appropriate preheating can improve the activity of the aggregate and mineral powder, enabling them to combine better with asphalt in the subsequent mixing process to form a uniform mixture.

[0028] Preparation of flame-retardant asphalt: Heat the petroleum asphalt to 140 - 160 °C. Within this temperature range, the asphalt has good fluidity, which is conducive to the uniform dispersion of various additives. Then add the flame retardant, nano-scale flame-retardant enhancer, and anti-aging agent, and continuously stir at a stirring speed of 300 - 500 r / min for 20 - 30 min, while applying ultrasonic-assisted stirring with a frequency of 20 - 30 kHz and a power of 500 - 800 W, so as to obtain flame-retardant asphalt with stable performance. The appropriate stirring speed and time, as well as the auxiliary effect of ultrasonic waves, can ensure the full mixing of each component, form a stable flame-retardant system, and ensure the consistency and stability of the quality of the flame-retardant asphalt.

[0029] Mixing: Put the preheated aggregate and mineral powder into the mixing equipment, first stir at a speed of 40 - 50 r / min for 1 - 2 min to initially mix the aggregate and mineral powder evenly and form a stable skeleton structure. Then gradually increase the stirring speed to 60 - 80 r / min, add the prepared flame-retardant asphalt, and continue to stir for 3 - 5 min to finally obtain a flame-retardant asphalt mixture for tunnel pavement with excellent performance. This mixing process can make the asphalt fully cover the aggregate and mineral powder, ensure the uniformity and stability of the mixture, enable the tight combination of each component, and give full play to the best performance.

[0030] Preferably, in the step of preparing the flame-retardant asphalt, the planetary stirring method is adopted during the stirring process to ensure the uniformity and sufficiency of stirring. The planetary stirring method can make the stirring paddle stir the material in different directions, avoid the emergence of stirring dead corners, ensure the more uniform dispersion of the flame retardant in the asphalt, and thus improve the quality stability of the flame-retardant asphalt and the consistency of the flame-retardant effect.

[0031] Preferably, in the mixing step, a forced mixer is used for the mixing equipment. The forced mixer has the characteristics of high mixing efficiency and good mixing quality, can make the mixture reach a high degree of uniformity in a short time, ensure the uniform distribution of each component, and thus improve the overall performance of the flame-retardant asphalt mixture for tunnel pavement.

[0032] Preferably, during the preparation process, the quality of the raw materials for each batch is inspected to ensure that the raw materials meet all the indicators specified above. At the same time, the performance of the fire-retardant asphalt mixture for tunnel pavement prepared for each batch is tested, including fire-retardant performance, compressive strength, flexural strength, water stability and other indicators. Only the mixture with all performance indicators meeting the relevant standard requirements can be used for tunnel engineering construction to ensure the quality and safety of the tunnel pavement.

[0033] (III) Beneficial effects

[0034] Compared with the prior art, the present invention provides a fire-retardant asphalt mixture for tunnel pavement and a preparation method thereof, having the following beneficial effects:

[0035] 1. For the fire-retardant asphalt mixture for tunnel pavement and the preparation method thereof, by adopting a specific raw material formula and a carefully compounded fire retardant, the fire-retardant asphalt mixture for tunnel pavement of the present invention can effectively reduce the fire spread speed during a fire, and significantly improve the fire safety of the tunnel pavement. Compared with traditional asphalt mixtures, in the combustion test, the flame propagation speed is greatly reduced, winning more precious time for personnel evacuation and fire fighting and rescue.

[0036] 2. For the fire-retardant asphalt mixture for tunnel pavement and the preparation method thereof, the mixture has excellent road performance such as compressive strength, wear resistance, skid resistance, etc., can fully meet various requirements of the tunnel pavement during actual use, effectively extend the service life of the pavement, reduce the later maintenance cost, and provide a strong guarantee for the long-term stable operation of the tunnel project.

[0037] 3. For the fire-retardant asphalt mixture for tunnel pavement and the preparation method thereof, the preparation process of the present invention is scientifically and reasonably designed and easy to operate. By precisely controlling the parameters of each preparation step, the quality stability and uniformity of the mixture can be ensured, the production efficiency can be improved, the production cost can be reduced, and it has high economic feasibility and broad market application prospects. Specific embodiments

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] Example 1

[0040] Parts by weight of raw materials: 5 parts of fire-retardant asphalt, 100 parts of aggregate, 10 parts of mineral powder, 5 parts of fire retardant, 1 part of nano-scale fire-retardant reinforcing agent (nano-titanium dioxide), 0.5 part of anti-aging agent (antioxidant 1010).

[0041] Raw material characteristics:

[0042] Flame-retardant asphalt: The softening point is 50 °C, and the penetration (25 °C, 100 g, 5 s) is 60 (0.1 mm).

[0043] Aggregates: The mass ratio of coarse aggregates to fine aggregates is 3:2.

[0044] Mineral powder: The specific surface area is 300 m 2 / kg.

[0045] Flame retardant: The mass ratio of inorganic flame retardant to organic flame retardant is 2:1, and the mass ratio of aluminum hydroxide to magnesium hydroxide is 1:1.

[0046] Preparation method:

[0047] Preheating: Heat the aggregates and mineral powder to 160 °C respectively.

[0048] Prepare flame-retardant asphalt: Heat the petroleum asphalt to 140 °C, add the flame retardant, nano flame-retardant enhancer and anti-aging agent, stir at a speed of 300 r / min for 20 min, and apply ultrasonic-assisted stirring with a frequency of 20 kHz and a power of 500 W to obtain flame-retardant asphalt.

[0049] Mixing: Add the preheated aggregates and mineral powder to the mixing equipment, first stir at a speed of 40 r / min for 1 min, then increase the stirring speed to 60 r / min, and then add the prepared flame-retardant asphalt, and continue to stir for 3 min to obtain a flame-retardant asphalt mixture for tunnel pavement, and the discharge temperature is 150 °C.

[0050] Example 2

[0051] Parts by weight of raw materials: 40 parts of flame-retardant asphalt, 120 parts of aggregates, 15 parts of mineral powder, 10 parts of flame retardant, 2 parts of nano flame-retardant enhancer (nano-montmorillonite), 0.8 parts of anti-aging agent (antioxidant 168).

[0052] Raw material characteristics:

[0053] Flame-retardant asphalt: The softening point is 60 °C, and the penetration (25 °C, 100 g, 5 s) is 80 (0.1 mm).

[0054] Aggregates: The mass ratio of coarse aggregates to fine aggregates is 4:3.

[0055] Mineral powder: The specific surface area is 350 m 2 / kg.

[0056] Flame retardant: The mass ratio of inorganic flame retardant to organic flame retardant is 3:2, and the mass ratio of aluminum hydroxide to magnesium hydroxide is 1:2.

[0057] Preparation method:

[0058] Preheating: Heat the aggregate and mineral powder to 170 °C respectively.

[0059] Preparing flame-retardant asphalt: Heat the petroleum asphalt to 150 °C, add a flame retardant, a nano-scale flame-retardant enhancer, and an anti-aging agent, stir at a stirring speed of 400 r / min for 25 min, and simultaneously apply ultrasonic-assisted stirring with a frequency of 25 kHz and a power of 600 W to obtain flame-retardant asphalt.

[0060] Mixing: Add the preheated aggregate and mineral powder to the mixing equipment, first stir at a speed of 45 r / min for 1.5 min, then increase the stirring speed to 70 r / min, and then add the prepared flame-retardant asphalt and continue stirring for 4 min to obtain a flame-retardant asphalt mixture for tunnel pavement, and the discharge temperature is 160 °C.

[0061] Example 3

[0062] Parts by weight of raw materials: 50 parts of flame-retardant asphalt, 150 parts of aggregate, 20 parts of mineral powder, 15 parts of flame retardant, 3 parts of nano-scale flame-retardant enhancer (nano-titanium dioxide), and 1 part of anti-aging agent (antioxidant 1010).

[0063] Properties of raw materials:

[0064] Flame-retardant asphalt: The softening point is 70 °C, and the penetration (25 °C, 100 g, 5 s) is 100 (0.1 mm).

[0065] Aggregate: The mass ratio of coarse aggregate to fine aggregate is 5:4.

[0066] Mineral powder: The specific surface area is 400 m 2 / kg.

[0067] Flame retardant: The mass ratio of inorganic flame retardant to organic flame retardant is 3:2, and the mass ratio of aluminum hydroxide to magnesium hydroxide is 2:1.

[0068] Preparation method:

[0069] Preheating: Heat the aggregate and mineral powder to 180 °C respectively.

[0070] Preparing flame-retardant asphalt: Heat the petroleum asphalt to 160 °C, add a flame retardant, a nano-scale flame-retardant enhancer, and an anti-aging agent, stir at a stirring speed of 500 r / min for 30 min, and simultaneously apply ultrasonic-assisted stirring with a frequency of 30 kHz and a power of 800 W to obtain flame-retardant asphalt.

[0071] Mixing: Add the preheated aggregate and mineral powder into the mixing equipment. First, mix at a speed of 50 r / min for 2 min, then increase the mixing speed to 80 r / min, add the prepared flame-retardant asphalt, and continue mixing for 5 min to obtain the flame-retardant asphalt mixture for tunnel pavement, with the discharging temperature being 170 °C.

[0072] Comparative Example 1

[0073] Raw materials: The same as those in Example 1, but without adding flame retardants, nano-level flame-retardant enhancers, and anti-aging agents.

[0074] Preparation method: The same as that in Example 1.

[0075] Performance test

[0076] Perform performance tests on the flame-retardant asphalt mixtures of Examples 1 - 3 and Comparative Example 1. The test results are as follows:

[0077] Flame-retardant performance: Tested by the oxygen index method, the oxygen indexes of Examples 1 - 3 are all greater than 30%, while the oxygen index of Comparative Example 1 is only 20%. This result fully shows that the flame-retardant asphalt mixture of the present invention has good flame-retardant performance.

[0078] Compressive strength: Tested according to relevant standards, the compressive strengths of Examples 1 - 3 are all greater than 10 MPa, fully meeting the usage requirements of tunnel pavement.

[0079] Wear resistance: Tested through wear resistance tests, the wear amounts of Examples 1 - 3 are all less than 30 mm 3 , showing good wear resistance.

[0080] In summary, for the flame-retardant asphalt mixture for tunnel pavement and its preparation method of the present invention, by adopting a specific raw material formula and an advanced preparation process, good flame-retardant performance, road performance, and an efficient preparation process have been successfully achieved, with remarkable innovation and practicality, opening up a new way for the development of tunnel pavement materials. Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

[0081] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A flame retardant asphalt mixture for tunnel pavement, characterized in that: It is composed of the following raw materials in parts by weight: Flame retardant asphalt: 5-50 parts; Aggregate: 100-150 parts; Mineral powder: 10-20 parts; Flame retardant: 5-15 parts; Nano-grade flame retardant reinforcing agent: 1-3 parts, the nano-grade flame retardant reinforcing agent is selected from nano-titanium dioxide or nano-montmorillonite; Anti-aging agent: 0.5-1 part, the anti-aging agent is a hindered phenol or amine anti-aging agent, such as antioxidant 1010 or antioxidant 168.

2. The flame retardant asphalt mixture for tunnel pavement according to claim 1, characterized in that: The flame retardant asphalt is petroleum asphalt that has been flame retardantly treated, has a softening point in the range of 50-70° C., and a needle penetration (under the conditions of 25° C., 100 g, 5 s) of 60-100 (0.1 mm).

3. The flame retardant asphalt mixture for tunnel pavement according to claim 1, characterized in that: The aggregate comprises coarse aggregate and fine aggregate, wherein the coarse aggregate is limestone crushed stone with a particle size of 5-20 mm, the fine aggregate is machine-made sand with a particle size of 0-5 mm, and the mass ratio of the coarse aggregate to the fine aggregate is (3-5):(2-4).

4. The flame retardant asphalt mixture for tunnel pavement according to claim 1, characterized in that: The mineral powder is limestone mineral powder, and its specific surface area is not less than 300m 2 / kg, and the hydrophilicity coefficient is less than 1.

5. The flame retardant asphalt mixture for tunnel pavement according to claim 1, characterized in that: The flame retardant is a compound product of an inorganic flame retardant and an organic flame retardant, wherein the inorganic flame retardant is a mixture of aluminum hydroxide and magnesium hydroxide, the organic flame retardant is a phosphorus-based flame retardant, the mass ratio of the inorganic flame retardant to the organic flame retardant is (2-3):(1-2), and the mass ratio of the aluminum hydroxide to the magnesium hydroxide is (1-2):(1-2).

6. The flame retardant asphalt mixture for tunnel pavement according to claim 1, characterized in that: During the preparation process, the nano-scale flame retardant enhancer needs to be stirred at a stirring speed of 200-300r / min for 10-15min after adding the flame retardant so as to be evenly dispersed in the flame retardant asphalt.

7. The flame retardant asphalt mixture for tunnel pavement according to claim 1, characterized in that: The anti-aging agent is added when the petroleum asphalt is heated to 140-160°C to prepare the flame retardant asphalt.

8. A method for preparing a flame retardant asphalt mixture for tunnel pavement according to any one of claims 1 to 7, characterized in that: The following steps are involved: Preheating: Aggregate and mineral powder are heated in stages, first heated to 120-140℃, kept warm for 5-10min, and then heated to 160-180℃; Preparation of flame retardant asphalt: heat petroleum asphalt to 140-160°C, add flame retardant, nano-grade flame retardant reinforcing agent and anti-aging agent, stir at a speed of 300-500r / min, stir for 20-30min, and simultaneously apply ultrasonic assisted stirring at a frequency of 20-30kHz and a power of 500-800W to obtain flame retardant asphalt; Mixing: Put the preheated aggregate and mineral powder into the mixing equipment, first stir at a speed of 40-50r / min for 1-2min, then gradually increase the stirring speed to 60-80r / min, then add the prepared flame retardant asphalt, continue stirring for 3-5min, and finally obtain the flame retardant asphalt mixture for tunnel pavement.

9. The method for preparing a flame retardant asphalt mixture for tunnel pavement according to claim 8, characterized in that: Aggregates such as limestone crushed stone and machine-made sand are surface modified by using a silane coupling agent or a fatty acid modifier, such as KH550 silane coupling agent, to prepare a 1%-2% aqueous solution, and the aggregates are soaked in it for 30-60 minutes and then taken out and dried.

10. The method for preparing a flame retardant asphalt mixture for tunnel pavement according to claim 8, characterized in that: The prepared flame retardant asphalt mixture for tunnel pavement has a discharge temperature of 150-170°C, and the flame retardant is a chemically bonded composite flame retardant formed by reacting the active groups of the phosphorus flame retardant with the surface hydroxyl groups of aluminum hydroxide and magnesium hydroxide through a chemical grafting method.