Flame-retardant asphalt for tunnel pavement and preparation method thereof

Abstract

The application discloses a kind of tunnel pavement with flame-retardant asphalt and preparation method thereof.Flame-retardant asphalt is based on matrix asphalt, carbon nanotube, fly ash and lignin are added as flame-retardant component.The best flame-retardant proportion of flame-retardant asphalt can be further obtained by central composite design model and comprehensive evaluation method.The preparation method includes matrix asphalt heating, flame-retardant component preheating, matrix asphalt and flame-retardant component step-by-step mixing, high-speed shearing and degassing processes, which can adapt to indoor test preparation process and industrial scale preparation process, with good adaptability and practicality.The application introduces carbon nanotube, fly ash and lignin to form a composite flame-retardant system, and the three components synergistically build a stable multi-scale flame-retardant structure, which significantly improves the flame-retardant performance of asphalt material, while considering environmental protection, economy and engineering adaptability, with significant engineering application value and promotion prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road engineering materials, in particular to a kind of tunnel pavement fire-retardant asphalt and preparation method thereof, relate to road paving material and fire-retardant functional material cross. BACKGROUND

[0002] Tunnel engineering as an important means of crossing mountainous areas, crossing rivers, connecting islands occupies a crucial position in China's comprehensive transportation system. In recent years, a large number of regional connectivity projects have been implemented, driving China's tunnel engineering construction into a stage of rapid development. Especially in the economically developed eastern coastal areas, to expand urban space and strengthen intercity traffic links, major projects such as undersea tunnels and cross-sea tunnels are increasing. In the past, tunnel pavement design took fuel-powered motor vehicles as the design vehicle. However, in recent years, with the rapid development of new energy vehicles in China, the actual driving vehicles in tunnels are gradually changing. Due to the relatively closed space of tunnels, limited ventilation capacity, and limited evacuation channels, once an electric vehicle has a traffic accident or catches fire, the fire and toxic smoke can easily spread rapidly in a short time, seriously threatening the safety of passengers, affecting emergency rescue efficiency, and even causing long-term traffic disruption and significant economic losses.

[0003] The existing tunnel pavement in China generally uses traditional asphalt mixture paving. Although this type of material has good mechanical properties and durability, it is essentially a highly flammable organic material. In the event of an extreme situation such as a fire, it can easily melt, carbonize, or even burn intensely, which not only exacerbates the spread of fire but also releases a large amount of toxic and harmful smoke, significantly reducing the visibility and oxygen concentration inside the tunnel. Therefore, improving the fire-retardant properties of asphalt pavement materials has become a key link in improving the overall fire safety level of tunnels.

[0004] At present, the asphalt flame-retardant modification technology mainly includes adding inorganic flame retardants, organic phosphorus flame retardants, intumescent flame-retardant systems and the like. Although these technologies improve the fire resistance of asphalt to some extent, there are still many deficiencies. The inorganic flame retardants need to be added in large amounts, which easily affects the mechanical properties and construction performance of asphalt. The organic flame retardants may bring environmental pollution and volatility problems, and the problems such as high cost, poor thermal stability and secondary pollution also limit their large-scale application in engineering. The intumescent flame-retardant systems usually have poor compatibility with asphalt, which easily leads to asphalt segregation or delamination, affecting the basic properties of asphalt; at the same time, a large amount of dosage is needed to play its flame-retardant performance, which increases the production cost of the material; some intumescent flame-retardant systems produce irritating gas at high temperature, which has adverse effects on the tunnel environment. Therefore, it is urgent to develop a new type of flame-retardant asphalt material specially used for tunnel pavement, which has high flame retardancy, green environmental protection and controllable cost, can effectively inhibit the spread of fire and prolong the safe evacuation time, and meets the dual requirements of safety and environmental protection of tunnel pavement. SUMMARY

[0005] In view of the problems of flammability, high smoke density and the like of the existing asphalt for tunnel pavement under extreme conditions such as fire, the present application aims to provide a flame-retardant asphalt for tunnel pavement and a preparation method thereof, so as to improve the flame-retardant performance and safety of asphalt material in high-risk environments such as tunnels.

[0006] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0007] In a first aspect, the present application provides a flame-retardant asphalt for tunnel pavement, the main material of which is base asphalt, and the flame-retardant asphalt further comprises 0wt%-2wt% of carbon nanotubes, 8wt%-10wt% of fly ash and 5wt%-7wt% of lignin, calculated in terms of mass percentage.

[0008] As a preferred embodiment, the optimal flame-retardant ratio of the flame-retardant asphalt is determined by the following method:

[0009] 1) A central composite design model is used to input the dosage ranges of carbon nanotubes, fly ash and lignin, and a plurality of flame-retardant asphalt ratio schemes are generated;

[0010] 2) The basic performance indicators and flame-retardant performance indicators of asphalt are used as the evaluation indicators of the flame-retardant asphalt, and the evaluation indicator values of each ratio scheme are determined by indoor test; wherein the basic performance indicators of asphalt are ductility, softening point and penetration, and the flame-retardant performance indicators are flash point and limiting oxygen index;

[0011] 3) A comprehensive evaluation method is used to calculate the scores of the basic performance indicators and the flame-retardant performance indicators of asphalt, to obtain the comprehensive scores of each ratio scheme, and then the optimal flame-retardant ratio is obtained.

[0012] Preferably, the comprehensive evaluation method adopts entropy method.

[0013] Preferably, the optimal flame-retardant ratio of the flame-retardant asphalt is that the carbon nanotube is 1wt%, the fly ash is 10wt%, and the lignin is 5wt%.

[0014] In the second aspect, the application further provides a preparation method of the flame-retardant asphalt for tunnel pavement, which is an indoor test preparation method, comprising the following steps:

[0015] S1: heating the base asphalt to a fluid state;

[0016] S2: preheating the carbon nanotube, the fly ash and the lignin;

[0017] S3: weighing the base asphalt fluid and the carbon nanotube, adding the carbon nanotube into the base asphalt fluid for heating and stirring to obtain a preliminary mixture;

[0018] S4: using a high-speed shearing machine to perform high-speed shearing on the preliminary mixture in a heat preservation mode;

[0019] S5: weighing the fly ash and the lignin, adding the fly ash and the lignin into the preliminary mixture after shearing in multiple times and performing heating and stirring to obtain a secondary mixture;

[0020] S6: using a small high-speed shearing machine to perform high-speed shearing on the secondary mixture in a heat preservation mode;

[0021] S7: using a small high-speed shearing machine to perform low-speed shearing on the secondary mixture to remove bubbles therein, thereby obtaining the flame-retardant asphalt.

[0022] Preferably, the heating temperature, the preheating temperature and the heat preservation temperature are 155-175℃, and preferably 165℃.

[0023] Preferably, in the S3, the stirring speed is 150-250r / min, and preferably 200r / min, and the stirring time is 5-15min, and preferably 10min; in the S5, the stirring speed is 150-250r / min, and preferably 200r / min, and the stirring time is 5-15min, and preferably 10min.

[0024] As preferred, in the S4, the shearing speed is 3000-4000 r / min, preferably 3500 r / min, and the shearing time is 30-50 min, preferably 45 min; in the S6, the shearing speed is 3000-4000 r / min, preferably 3500 r / min, and the shearing time is 20-40 min, preferably 30 min; in the S7, the shearing speed is 300-700 r / min, preferably 500 r / min, and the shearing time is 5-10 min, preferably 5 min.

[0025] In a third aspect, the present application further provides another preparation method of the flame-retardant asphalt for tunnel pavement, which is an industrial preparation method, comprising the following steps:

[0026] T1: heating the base asphalt to a fluid state;

[0027] T2: preheating the carbon nanotubes, fly ash and lignin;

[0028] T3: weighing the base asphalt fluid and the carbon nanotubes, adding the carbon nanotubes into the base asphalt fluid, and performing heat preservation dispersion by using a high-speed disperser to obtain a preliminary mixture;

[0029] T4: performing heat preservation high-speed shearing on the preliminary mixture by using a large high-speed shearing machine;

[0030] T5: weighing the fly ash and the lignin, adding the fly ash and the lignin into the preliminary mixture, and performing heat preservation dispersion by using a high-speed disperser to obtain a secondary mixture;

[0031] T6: performing heat preservation high-speed shearing on the secondary mixture by using a large high-speed shearing machine;

[0032] T7: performing low-speed shearing on the secondary mixture by using a large high-speed shearing machine to remove bubbles therein, and obtaining the flame-retardant asphalt.

[0033] As preferred, the heating temperature, the preheating temperature and the heat preservation temperature are all 155-175℃, preferably 165℃.

[0034] As preferred, in the T3, the dispersion speed is 150-250 r / min, preferably 200 r / min, and the dispersion time is 5-15 min, preferably 10 min; in the T5, the dispersion speed is 150-250 r / min, preferably 200 r / min, and the dispersion time is 5-15 min, preferably 10 min.

[0035] Preferably, in T4, the shearing speed is 1500-2500 r / min, preferably 2000 r / min, and the shearing time is 20-40 min, preferably 30 min; in T6, the shearing speed is 1000-2000 r / min, preferably 1500 r / min, and the shearing time is 20-40 min, preferably 30 min; in T7, the shearing speed is 100-300 r / min, preferably 200 r / min, and the shearing time is 5-15 min, preferably 10 min.

[0036] Compared with the prior art, the flame-retardant asphalt of the present invention has the following outstanding advantages:

[0037] This invention provides a novel flame-retardant asphalt for tunnel pavements. By introducing carbon nanotubes, fly ash, and lignin to form a composite flame-retardant system, it significantly improves the flame-retardant performance of asphalt materials while also considering environmental friendliness, economy, and engineering adaptability. Carbon nanotubes endow the material with excellent carbonization and heat insulation capabilities, fly ash provides an inorganic mineral barrier effect, and lignin, as a natural biomass, has good coking and synergistic flame-retardant effects. The three components exert a synergistic flame-retardant effect in the matrix asphalt through carbonization, coking, and ceramization mechanisms, respectively, constructing a stable multi-scale flame-retardant structure and forming a three-stage linked flame-retardant mode of "low-temperature coking - medium-temperature carbonization - high-temperature ceramization." The three components work together to significantly reduce the heat release rate of the flame-retardant asphalt, increase the carbon residue rate, delay the ignition time, and inhibit the release of toxic fumes, comprehensively improving the flame-retardant performance of the material in tunnel fire environments.

[0038] (1) Significantly enhanced flame retardant performance: The composite additive system can delay flame propagation, improve fire resistance limit, effectively suppress dripping and heat release, and meet the tunnel's adaptation requirements for extreme high temperature environment;

[0039] (2) Green and environmentally friendly: All flame-retardant components are derived from renewable resources or industrial solid waste, avoiding the use of toxic chemical flame retardants such as halogens and organophosphorus compounds. There is no secondary pollution during the combustion process, which is in line with the development direction of green building materials.

[0040] (3) Good cost control, suitable for engineering promotion: the raw materials are widely available and inexpensive, making them suitable for large-scale and engineering applications in tunnel engineering;

[0041] (4) Strong adaptability: This flame retardant system can be modified without significantly changing the conventional asphalt preparation process and construction process, and has good engineering adaptability and replicability. Attached Figure Description

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0043] Figure 1 The response surface schematic diagram of the penetration of asphalt with different contents of fire-retardant components is shown in the figure, wherein, Figure 1 (a) represents the relationship between fly ash and regenerated carbon tube (carbon nanotube), Figure 1 (b) represents the relationship between fly ash and lignin, Figure 1 (c) represents the relationship between regenerated carbon tube and lignin;

[0044] Figure 2 The response surface schematic diagram of the ductility of asphalt with different contents of fire-retardant components is shown in the figure, wherein, Figure 2 (a) represents the relationship between fly ash and regenerated carbon tube (carbon nanotube), Figure 2 (b) represents the relationship between fly ash and lignin, Figure 2 (c) represents the relationship between regenerated carbon tube and lignin;

[0045] Figure 3 The response surface schematic diagram of the flash point of asphalt with different contents of fire-retardant components is shown in the figure, wherein, Figure 3 (a) represents the relationship between fly ash and regenerated carbon tube (carbon nanotube), Figure 3 (b) represents the relationship between fly ash and lignin, Figure 3 (c) represents the relationship between regenerated carbon tube and lignin;

[0046] Figure 4 The response surface schematic diagram of the oxygen index of asphalt with different contents of fire-retardant components is shown in the figure, wherein, Figure 4 (a) represents the relationship between fly ash and regenerated carbon tube (carbon nanotube), Figure 4 (b) represents the relationship between fly ash and lignin, Figure 4 (c) represents the relationship between regenerated carbon tube and lignin;

[0047] Figure 5 The response surface schematic diagram of the entropy value method with different contents of fire-retardant components is shown in the figure, wherein, Figure 5 (a) represents the relationship between fly ash and regenerated carbon tube (carbon nanotube), Figure 5 (b) represents the relationship between fly ash and lignin, Figure 5 (c) represents the relationship between regenerated carbon tube and lignin;

[0048] Figure 6 The schematic diagram of the thermal gravimetric analysis of SBS asphalt is shown in the figure,

[0049] Figure 7 Schematic diagram of thermal gravimetric analysis of flame-retardant asphalt;

[0050] Figure 8 Schematic diagram of heat release comparison of SBS asphalt and flame-retardant asphalt in cone calorimeter test; Figure 8 (a) represents the peak value of heat release rate, Figure 8 (b) represents the total heat release amount;

[0051] Figure 9 Schematic diagram of mass change comparison of SBS asphalt and flame-retardant asphalt in cone calorimeter test;

[0052] Figure 10 Schematic diagram of smoke release amount comparison of SBS asphalt and flame-retardant asphalt in cone calorimeter test;

[0053] Figure 11 Schematic diagram of complex shear modulus and phase angle comparison of SBS asphalt and flame-retardant asphalt in DSR;

[0054] Figure 12 Schematic diagram of rutting factor comparison of SBS asphalt and flame-retardant asphalt;

[0055] Figure 13 Schematic diagram of combustion at the end of cone calorimeter test of SBS asphalt and flame-retardant asphalt; wherein, Figure 13 (a) represents SBS asphalt, Figure 13 (b) represents the flame-retardant asphalt product. DETAILED DESCRIPTION

[0056] In order to more clearly understand the technical solutions of the present application, further description will be made in combination with the accompanying drawings and embodiments. It should be understood that, under the premise of no technical conflicts, the technical features of each embodiment in the present specification can be combined and replaced with each other. In addition, unless specifically stated, the technical terms and scientific terms used in the present application should be understood as the conventional understanding of the ordinary skilled in the art. The terms such as "include" or "contain" in the present specification should be understood as indicating that the listed content is not an exhaustive list, and also includes other elements or equivalent alternatives that are not explicitly stated but belong to the same or similar technical field, and should not be understood as excluding other unlisted technical solutions.

[0057] There are various existing flame-retardant modified materials. In order to make asphalt have high flame retardancy, green environmental protection and cost controllability, the present application selects carbon nanotubes, lignin and fly ash as three materials to meet the above three performance requirements.

[0058] Carbon nanotubes, as a kind of nanomaterial with excellent thermal stability and structural rigidity, have been used in some studies to improve the high-temperature stability, anti-aging performance and mechanical modulus of asphalt. However, such studies mostly use carbon nanotubes as structural reinforcing agents or functional additives, and do not systematically design and verify their flame-retardant effect, nor do they consider the renewability of the material source. The carbon nanotubes selected in the present invention are derived from waste plastic pyrolysis residues, have typical lamellar and high-carbon structural characteristics, and can quickly form a heat-insulating carbon layer under heat, effectively blocking the transfer of oxygen and heat required for combustion, significantly inhibiting the spread of fire and the heat release process, and embodying their core functional positioning as a "carbonized skeleton" in the asphalt flame-retardant system.

[0059] Lignin, as a natural biomass polymer material, has been used in some applications such as polymer and concrete systems to enhance or assist in combustion and flame retardation. However, there are few applications of lignin as an independent flame-retardant component in road asphalt materials in current domestic and foreign literature, especially lacking of synergistic analysis and optimization research of its ratio with other components. In the present invention, lignin is systematically introduced into the asphalt flame-retardant system, and its easy coking property in the pyrolysis process is utilized to improve the carbon residue rate of the material and inhibit the release of smoke. At the same time, the addition of lignin also improves the flexibility and structural stability of asphalt, enabling the material to still have good mechanical properties under high-temperature combustion conditions, and demonstrating its application potential in the dual demands of road safety and green environmental performance.

[0060] Fly ash, as an industrial byproduct, is mainly used as a filler or stabilizer in road engineering. In the direction of flame retardation, although fly ash itself has certain thermal stability and ceramicization characteristics, it is often used as an auxiliary material in previous studies, and its flame-retardant performance is limited when used alone. In the present invention, fly ash is redefined as an "inorganic thermal inertia flame-retardant barrier material", and its silicon and aluminum components form a stable skeleton at high temperatures, enabling it to play an important role in physical heat insulation and smoke suppression in asphalt. Especially when combined with carbon nanotubes and lignin, it exhibits good synergistic effect, significantly improving the overall thermal stability and flame-retardant performance of the material, and the cost of the material is controllable.

[0061] Embodiment one:

[0062] The present invention provides a kind of tunnel pavement with flame-retardant asphalt, main material is base asphalt, with mass percentage calculation, further include 0wt%~2wt% carbon nanotubes, 8wt%~10wt% fly ash, 5wt%~7wt% lignin.

[0063] The application adopts carbon nanotubes, lignin and fly ash as three kinds of flame-retardant components to construct a composite flame-retardant system, which plays a synergistic flame-retardant effect through carbonization, charring and ceramicization mechanisms in the matrix asphalt matrix, thereby effectively improving the thermal stability and safety performance of the material in high fire risk environments such as tunnels.

[0064] Firstly, carbon nanotubes have extremely high thermal stability, and their decomposition temperature is usually higher than 600 DEG C. In the process of asphalt combustion, carbon nanotubes can remain stable in the early stage and gradually carbonize under high temperature to form a continuous and dense carbon layer. This carbon layer effectively blocks the diffusion of heat and oxygen to the inside of the asphalt, significantly delaying the pyrolysis reaction process. In addition, carbon nanotubes can also enhance the viscosity and structural integrity of the asphalt system, inhibit the dripping phenomenon at high temperature, and help slow down the flame spread speed. At the same time, carbon nanotubes have adsorption effect on free radicals, which can capture active groups in the combustion chain reaction, and have chemical synergistic effect on inhibiting combustion.

[0065] Secondly, lignin is a complex natural aromatic biopolymer, and its main decomposition interval is concentrated in 250-400 DEG C. After decomposition, it can produce intermediate products such as phenols and aldehydes, and generate a large amount of carbon residue. Under the condition of heating, lignin is easy to dehydrate, condense and aromatize, and finally form a stable carbon structure, thereby constructing a primary charring layer on the surface of asphalt. This carbon layer not only enhances the heat insulation and structural stability of the material, but also cooperates with carbon nanotubes to build a more complete carbonization barrier. In addition, the intermediates generated during the pyrolysis of lignin have certain free radical neutralization ability, which can effectively inhibit the persistence of combustion reaction. Lignin as a flexible biomass can also improve the ductility of the flame-retardant asphalt, so that the carbon layer maintains better toughness and integrity at high temperature.

[0066] Thirdly, fly ash is an industrial by-product produced under high temperature conditions, which itself does not burn and has extremely high thermal stability, with a melting onset temperature of 800-1300 DEG C. Fly ash is rich in inorganic components such as SiO2 and Al2O3, which can undergo glass phase transition or ceramicization reaction when heated, forming a rigid and inert protective layer on the surface of the burning asphalt, effectively isolating the heat conduction and oxygen diffusion between the external heat source and the internal combustible components. At the same time, the addition of fly ash can reduce the concentration of combustible components in the asphalt system, and play a dilution effect; its microporous structure can also adsorb smoke and combustible volatile substances, and play a smoke suppression effect. Fly ash also has good dispersibility, which helps to improve the distribution of lignin and carbon nanotubes in the asphalt matrix, and enhance the synergism and uniformity of the overall flame-retardant system.

[0067] The synergistic mechanism of the three flame-retardant components during heating can be summarized as a three-stage linkage mode of "low-temperature carbonization, medium-temperature carbonization and high-temperature ceramicization": lignin is pyrolyzed first in the range of 250-400°C to provide an initial carbon layer and free radical inhibition; carbon nanotubes are carbonized above 600°C to enhance the carbon layer structure and form a high-density heat shield; and fly ash builds an inorganic ceramic skeleton above 800°C to improve the thermal stability of the residual asphalt structure. The three components cooperate with each other to significantly reduce the heat release rate of the flame-retardant asphalt, improve the carbon residue rate, delay the ignition time, inhibit the release of toxic smoke, and comprehensively improve the flame-retardant performance of the material in a tunnel fire environment.

[0068] It should be noted that, in addition to the carbon nanotubes selected for plastic pyrolysis in this embodiment, other carbon nanotubes are also suitable for use in the present application.

[0069] The determination process of the flame-retardant asphalt ratio is as follows: after determining that carbon nanotubes, fly ash and lignin are used as flame-retardant components, the existing research literature (including journal articles related to flame-retardant asphalt, tunnel pavement flame-retardant materials, intumescent flame-retardant systems, carbon nanomaterial flame-retardant effects, and composite flame-retardant systems, as well as patents related to flame-retardant asphalt, modified asphalt flame-retardant formulations, and nanofiller synergistic flame retardation) is investigated to determine the maximum amount of carbon nanotubes, fly ash and lignin when used alone. The present application first uses the maximum amount of the three to form an initial ratio for single-factor pre-testing, and conducts tests of ductility, softening point, penetration, flash point and limiting oxygen index to preliminarily determine the effective range of each component. Obviously, the flame-retardant asphalt at the initial ratio is difficult to meet the basic performance requirements of asphalt. Then, the next group of ratios is determined by means of bisection or reducing the amount, and the test results are observed to see if they meet the requirements. In this way, when a group meets the basic performance requirements of asphalt, further reduction of the ratio scheme that meets the basic performance requirements of asphalt is carried out according to the central composite design model and the test results of the flame-retardant asphalt, and finally the carbon nanotubes are determined to be 0wt%-2wt%, the fly ash is determined to be 8wt%-10wt%, and the lignin is determined to be 5wt%-7wt%. This trial-adjustment method can greatly reduce the number of tests required, save test time and test cost. The flame-retardant effect and material performance are most coordinated, and have engineering application feasibility. Alternatively, orthogonal test design can be used to test multiple groups of ratios of the three components, and the formation effect of the carbon layer, thermal stability, oxygen index and changes in the road performance of the asphalt are comprehensively analyzed, and then the amount of carbon nanotubes, fly ash and lignin is determined. However, the orthogonal test will increase the number of experiments.

[0070] It should be noted that the ductility, softening point, penetration reference "Highway asphalt pavement construction technical specification" JTGF40-2017 test, flash point and limiting oxygen index reference specification "Determination of petroleum products flash point and ignition Cleveland open cup method" GB / T3536-2008 and "Determination of asphalt combustion performance oxygen index method" NB / SH / T0815-2010 test, the ductility test of the flame-retardant asphalt in the present application is measured at 5 degrees Celsius. Specific embodiment one:

[0072] The present embodiment is found from the relevant research literature that the maximum content of carbon nanotubes is 2wt%, the maximum content of fly ash is 10wt%, and the maximum content of lignin is 7wt%. Based on the method in embodiment one, this embodiment first tries to prepare scheme B2, but the test finds that the obtained flame-retardant asphalt does not meet the basic performance requirements. Therefore, other trial preparation and deployment processes are continued. Specifically, the ratio test scheme of different flame-retardant components mixed in the matrix asphalt is as shown in Table 1.

[0073] ;

[0074] It should be noted that scheme B1 in the table is only matrix asphalt without mixing any flame-retardant components, which is used as a control group for other mixing ratio test schemes with flame-retardant components.

[0075] In each flame-retardant asphalt ratio test scheme, the results of the ductility, softening point, penetration, flash point and limiting oxygen index of the flame-retardant asphalt measured by indoor test are as shown in Table 2. The specific process of indoor test is described in embodiment three and specific embodiment three.

[0076] ;

[0077] "Highway asphalt pavement construction technical specification" JTGF40-2017 stipulates that the minimum requirement of modified asphalt ductility at 5 degrees Celsius (evaluating the ductility and toughness of modified asphalt at low temperature) is 20cm.

[0078] "Highway asphalt pavement construction technical specification" JTGF40-2017 stipulates that the penetration of modified asphalt (25°C, 100g, 5s) is 30-60 (0.1mm) in the requirement of heavy traffic, high temperature or high performance road.

[0079] "Highway asphalt pavement construction technical specification" JTGF40-2017 stipulates that the softening point of modified asphalt is greater than 65℃, and the softening point of matrix asphalt is greater than 45℃.

[0080] The national standard "Flame-retardant asphalt concrete for road" GB / T29051-2012 stipulates that the oxygen index (an index evaluating the degree of difficulty of material ignition) of asphalt used in tunnel road should not be less than 23%.

[0081] The flash point of base asphalt is greater than 230℃ and the flash point of modified asphalt is greater than 240℃ according to Technical Specification for Construction of Highway Asphalt Pavement (JTGF40-2004).

[0082] The elongation of the ratio scheme B2 does not meet the requirements. The oxygen index of the ratio scheme B1 does not meet the requirements.

[0083] Figures 1-4 The influence of each flame-retardant component on the penetration, ductility, flash point and limiting oxygen index of the flame-retardant asphalt in the above ratio test scheme is respectively shown.

[0084] Figure 1 The influence of each flame-retardant component on the penetration of the flame-retardant asphalt is shown. With the increase of the content of the recycled carbon nanotube, the penetration shows a trend of first decreasing and then increasing. The appropriate amount of recycled carbon nanotube can enhance the structural rigidity of the asphalt, so that the material shows stronger anti-deformation ability at high temperature, and the penetration decreases. However, when the content is too high, the internal structure of the material may become too brittle, resulting in the rebound of the penetration. As a natural polymer, the lignin can moderately improve the consistency and structural stability of the asphalt, but its strengthening effect is not as significant as that of the recycled carbon nanotube and fly ash. The fine mineral matter in the fly ash can fill the pores in the asphalt, enhance the skeleton structure, and significantly improve the compactness and rigidity of the flame-retardant asphalt, thereby greatly reducing the penetration.

[0085] Figure 2 The influence of each flame-retardant component on the ductility of the flame-retardant asphalt is shown. With the increase of the content of the recycled carbon nanotube, the ductility shows a trend of first increasing and then decreasing. The appropriate amount of recycled carbon nanotube can improve the elasticity and toughness of the asphalt, so that the ductility increases. However, when the content exceeds a certain range, the rigidity of the system increases and the brittleness increases, resulting in the decrease of the ductility. The addition of lignin helps to improve the flexibility of the material and form a certain compatible structure with the base asphalt, thereby improving the tensile properties. However, if the content is too high, it may lead to a decrease in compatibility, thereby affecting the ductility. The ductility shows a fluctuating trend with the change of the content of fly ash, i.e. it shows a trend of first increasing, then decreasing and then increasing, with strong non-linear characteristics. When the content is too high, the filler effect leads to the hardening of the structure and the decrease of the ductility.

[0086] Figure 3 The influence of each flame-retardant component on the flash point of the flame-retardant asphalt is shown. The recycled carbon nanotube and lignin show a positive correlation with the flash point of the asphalt. After being added, they help to improve the thermal decomposition temperature of the system, thereby increasing the flash point. The influence of the increase of the content of fly ash on the flash point is relatively complex, showing a trend of first decreasing and then slightly rising, with large overall fluctuations. The appropriate amount of fly ash can block heat conduction and dilute combustible components, thereby indirectly increasing the flash point. When the content is too high, the uneven distribution of particles or poor interface may weaken the thermal stability.

[0087] Figure 4The effects of each flame-retardant component on the limiting oxygen index of the flame-retardant asphalt are shown. With the increase of the content of the recycled carbon nanotubes, the limiting oxygen index increases first and then decreases slightly, and there is a peak interval, indicating that there is an optimal dosage. The effect of lignin on the limiting oxygen index is more significant, and the effect of fly ash on the limiting oxygen index is relatively small, and the overall surface is flat.

[0088] According to the above results, the content of carbon nanotubes is 0wt%-2wt%, the content of fly ash is 8wt%-10wt%, and the content of lignin is 5wt%-7wt%.

[0089] When the content of carbon nanotubes exceeds 2wt%, the performance of the asphalt material will change obviously. First, carbon nanotubes have a large specific surface area and high surface energy, and are prone to agglomeration. Excessive addition of carbon nanotubes will lead to uneven dispersion in the asphalt matrix, forming a large number of agglomerates, and then producing local stress concentration in the material, reducing the uniformity and mechanical stability of the overall material. In addition, excessive carbon nanotubes significantly improve the rigidity of the asphalt system, resulting in a significant decrease in high-temperature fluidity and a decrease in low-temperature ductility, making the material more fragile and prone to cracking, reducing the service life and reliability.

[0090] Because the polarity of lignin molecules is strong, and the main component of asphalt is non-polar component, excessive lignin will easily cause phase separation, resulting in uneven organization structure of the mixture, thereby affecting the long-term stability and durability of the material. At the same time, excessive lignin will significantly increase the rigidity of the asphalt system, reduce the ductility and toughness at low temperature, make the asphalt material hard and brittle, and significantly weaken the crack resistance. Lignin will produce a large amount of carbonized residue during combustion, which may destroy the continuity of the carbon layer of the material, reduce the structural integrity of the material, and even have an adverse effect on the microstructure of the asphalt material under non-combustion conditions. When the content of lignin is too low, it cannot fully participate in the construction of the carbon layer during the combustion process as a natural carbon source and an expanding carbon layer forming material, making it difficult to form a dense and continuous heat-insulating and oxygen-blocking barrier, thereby significantly reducing the heat-insulating and flame-retardant properties of the material.

[0091] When the fly ash content exceeds 10wt%, its adverse effects on the performance of asphalt begin to appear. Excessive fly ash can dilute the effective binding components in asphalt, leading to a decrease in the bonding force between asphalt and aggregate, and reducing the overall durability and mechanical properties of the mixture. At the same time, the incorporation of fly ash increases the rigidity of the asphalt system, resulting in a decrease in ductility and flexibility, and a decrease in penetration, which weakens the adaptability of the material in low temperature environments or under dynamic load. Too much fly ash can also lead to uneven internal mixing of the mixture, a loose skeleton structure, and quality problems such as spalling and potholes, which seriously affect the service life and safety performance of the road. When the fly ash content is low, the softening point and flash point of the flame-retardant asphalt are low, and the fly ash cannot build an effective inorganic skeleton structure in the system. Under heat conditions, the asphalt pyrolysis reaction is intensified, and the release of flammable volatiles increases, thereby reducing the overall flame-retardant performance.

[0092] Comparing schemes A1 and A2, the fly ash and lignin contents are the same, and the carbon nanotube content is increased from 0% (A1) to 2% (A2). The ductility is increased from 22.6 cm to 27.0 cm, the softening point is increased from 90.4°C to 91.5°C, the flash point is increased by 6°C, and the oxygen index is significantly increased from 26.20% to 27.90%. The introduction of carbon nanotubes forms a high thermal conductivity channel structure in the asphalt, which helps to quickly conduct heat and induce the formation of a carbon layer, thereby enhancing the flame-retardant performance and thermal stability of the material, verifying the synergistic effect between it and the basic flame-retardant components.

[0093] Comparing schemes A2 and A8, the carbon nanotube and lignin contents are the same, and the fly ash content is increased from 8% (A2) to 10% (A8). The increase in fly ash content increases the softening point of the flame-retardant asphalt to 91.8°C, the flash point to 439°C, and the oxygen index to only 28.10%, but the ductility decreases to 25.0 cm. It is found by comparison that fly ash can help to build a porous "skeleton" structure, effectively blocking heat conduction and oxygen diffusion, but the synergistic effect of its increase has a saturation value, and excessive content may reduce the flexibility and ductility of the composite system, inhibiting the increase in ductility.

[0094] Comparing schemes A4 and A5, the carbon nanotube and fly ash contents are the same, and the lignin content is increased from 5% (A4) to 7% (A5). Although the softening point of A5 is 95.5°C, its flash point is 442°C, lower than the 452°C of A4, and the oxygen index is reduced from 30.20% of A4 to 28.70%. This shows that the lignin content in A4 is more optimal, ensuring the formation of a dense and expanded carbon layer without causing the carbon layer structure to be loose due to excessive filling. Test scheme A4 performs excellently in key indicators such as ductility, penetration, flash point, and oxygen index, confirming that it is the most balanced and has the most significant synergistic effect among the flame-retardant asphalt schemes.

[0095] Embodiment Two:

[0096] Although the present application can determine the proportioning range of the flame-retardant asphalt by the above-mentioned way, the performances of the flame-retardant asphalt with different proportions are different, so the following method can be used to further determine the optimal flame-retardant proportion of the flame-retardant asphalt:

[0097] 1) using the central composite design model of Design Expert software, inputting the mixing amount ranges of the three components of carbon nanotubes, fly ash and lignin, generating various asphalt flame-retardant proportioning schemes;

[0098] 2) taking the basic performance indicators and the flame-retardant performance indicators of the asphalt as the evaluation indicators of the flame-retardant asphalt, determining the evaluation indicator values of each proportioning scheme by indoor test; wherein the basic performance indicators of the asphalt are ductility, softening point and penetration, and the flame-retardant performance indicators are flash point and limiting oxygen index;

[0099] 3) using the comprehensive evaluation method to calculate the scores of the basic performance indicators and the flame-retardant performance indicators of the asphalt in each proportioning scheme, obtaining the comprehensive scores of each proportioning scheme, and then obtaining the optimal flame-retardant proportion. Specific embodiment two:

[0101] In this embodiment, according to the flame-retardant asphalt proportioning test schemes in specific embodiment one, the entropy value method is used as the comprehensive evaluation method to evaluate the basic performance indicators and the flame-retardant performance indicators of the asphalt, and the scoring results are shown in Table 3. It should be noted that the mixing amount ranges of the flame-retardant components in the present application are only used in the present application; 17 test schemes are generated by using Design Expert software. In addition to the entropy value method preferred in this embodiment, other evaluation and analysis methods can also be applicable to the present application, such as independent weight coefficient method, CRITIC method, etc.

[0102] ;

[0103] Figure 5The response surface graph of using entropy method to screen the amount of each flame retardant component is shown. The recycled carbon nanotubes show a slight positive correlation with the comprehensive score value, showing a moderate upward trend, indicating that it helps to optimize the material structure and improve the flame retardant efficiency within a certain dosage range. Lignin shows a significant nonlinear effect, with a negative linear coefficient and a positive quadratic coefficient, indicating that it can significantly enhance the comprehensive score value (OD value) in the medium dosage range and has good synergistic flame retardant potential. There is a positive synergistic effect between recycled carbon nanotubes and lignin, which can alleviate the performance fluctuations caused by single flame retardant component to some extent; while the synergistic incorporation of fly ash and lignin may have a negative interference effect, which is not conducive to the improvement of the comprehensive score value (OD value). According to the response surface analysis, the best formula of the flame retardant is scheme A4, with recycled carbon nanotube dosage of 1wt%, fly ash dosage of 10wt%, and lignin dosage of 5wt%. If the dosage of each flame retardant component in the ratio test scheme is divided more carefully (increasing the precision), a more accurate best ratio scheme can be obtained, but limited by the number of tests, this example will not be described in more detail.

[0104] The following analyzes the differences between the flame-retardant asphalt obtained by the flame-retardant components according to test scheme A4 and SBS asphalt in terms of thermogravimetry, total heat release, mass change, smoke release characteristics, dynamic shear rheological properties, and rutting factor.

[0105] The thermogravimetric analyzer is used to test the flame-retardant asphalt and SBS asphalt of the above ratio scheme A4, Figure 6 is the thermogravimetric analysis result of SBS asphalt, Figure 7 is the thermogravimetric analysis result of the product flame-retardant asphalt. In an embodiment, the thermal decomposition behavior of conventional SBS modified asphalt and composite flame-retardant asphalt samples is tested by thermogravimetric analysis method to evaluate their thermal stability and pyrolysis characteristics. The test temperature range is from room temperature to 800℃, and the mass change rate and mass derivative change of the sample during the heating process are recorded.

[0106] As shown in Figure 6 , the SBS modified asphalt shows typical thermogravimetric weight loss characteristics during the heating process, and the mass change curve shows that a significant pyrolysis reaction begins to occur when the temperature rises to about 325℃, entering the stage of rapid decomposition. Within the temperature range of 325℃ to 560℃, the main components of the SBS modified asphalt decompose rapidly, showing a significant mass loss. The pyrolysis rate curve shows that the maximum decomposition rate is reached at about 520℃, corresponding to a mass derivative peak value close to -2.0%, reflecting the greater reaction intensity at this stage. After 560℃, the mass tends to be stable, and the pyrolysis process is basically complete, with an ultimate residual mass of less than 6%, indicating that the SBS modified asphalt has poor thermal stability at high temperatures, low carbonization residual rate, limited resistance to thermal decomposition, and is prone to secondary combustion, making it difficult to meet the requirements of high-temperature use or fire safety.

[0107] As shown in Figure 7 Compared with the SBS modified asphalt, the flame-retardant asphalt provided by the present application shows more excellent thermal stability and flame-retardant properties during the whole heating process. Before the temperature reaches 369℃, the sample basically does not have obvious mass loss, the thermogravimetric curve shows a smooth trend, and the initial pyrolysis reaction is effectively delayed, indicating that the material has good initial thermal stability. Between 369℃ and 640℃, the flame-retardant asphalt undergoes a slower multi-stage pyrolysis process, which can be divided into three stages: preliminary cracking, main pyrolysis and residual stability. The peak value of the main pyrolysis stage is significantly lower than that of the SBS modified asphalt, which does not exceed -1.2%, indicating that the thermal decomposition reaction is weaker and the decomposition process is more controllable. The final residual mass is about 10%, which is higher than that of the SBS modified asphalt.

[0108] The cone calorimeter instrument is used to test the product of the above ratio scheme A4 and the SBS asphalt, Figure 8 The total heat release of the product of the present application and the SBS asphalt is shown in the figure, Figure 9 The mass change comparison diagram, Figure 10 The smoke release amount comparison diagram. In the cone calorimeter test, the product of the present application and the SBS asphalt show significant differences in heat release performance.

[0109] Figure 8 In (a), the peak value of the heat release rate of the SBS asphalt reaches 892.39kW / m², which is much higher than the 653.6kW / m² of the product of the present application, indicating that the former releases heat more intensely and the fire develops more rapidly in a fire. Figure 8 In (b), the total heat release of the SBS asphalt is as high as 217.267MJ / m², while the total heat release of the product of the present application is 188.972MJ / m², which is reduced by about 13%, effectively inhibiting the heat release and thus delaying the fire development speed.

[0110] As shown in Figure 9 In the pyrolysis process, the mass loss rate per unit time of the flame-retardant asphalt sample of the present application and the SBS modified asphalt sample shows significant difference. The mass change trend of the two materials is consistent with the corresponding heat release rate curve, that is, the mass loss process is accompanied by heat release, and the two are obviously coupled. After the SBS modified asphalt sample is heated to a certain temperature, the mass loss rate rises rapidly, and the peak rate reaches 0.227g / s, which is much higher than the peak value 0.064g / s of the product of the present application, and the maximum rate difference is 0.163g / s. This difference quantitatively reflects the difference in pyrolysis intensity of the two materials, indicating that the SBS sample has a more intense and rapid thermal decomposition reaction in the combustion process. The pyrolysis initiation time of the flame-retardant asphalt of the present application is 103 seconds later than that of the SBS modified asphalt, which significantly improves the stable lagging property of the flame-retardant asphalt of the present application in high temperature environment.

[0111] like Figure 10 In terms of smoke release characteristics, the product of this invention also exhibits superior smoke suppression capabilities. The total smoke volume generated by SBS asphalt during combustion is 50.86 m², significantly higher than the 40.83 m² total smoke volume of the product of this invention, and the smoke release rate increases rapidly in the initial stage. In contrast, the smoke release rate of flame-retardant asphalt is generally lower, with a 150-second delay in activation time, and the total release volume is significantly reduced.

[0112] The product of this invention with the above-mentioned proportioning scheme A4 and SBS asphalt were tested using a dynamic shear rheometer. Figure 11 This diagram illustrates the comparison of the complex shear modulus and phase angle of SBS asphalt and the product of this invention using dynamic shear rheology (DSR). In the DSR test, the complex shear modulus of the flame-retardant asphalt provided by this invention and existing SBS modified asphalt were compared and analyzed under different temperature conditions. Phase angle (δ) and rutting factor The pattern of temperature variation. For example... Figure 11 As shown, the complex modulus of the two types of asphalt increases with increasing temperature. All showed a downward trend, but flame-retardant asphalt remained within the entire test temperature range. The value is significantly higher than that of SBS modified asphalt, indicating that it has better resistance to deformation. Correspondingly, the phase angle of flame-retardant asphalt is slightly higher than that of SBS asphalt, indicating that its elasticity is slightly lower, but it still maintains good viscoelastic properties overall.

[0113] The product of this invention with the above-mentioned mix proportion A4 and SBS asphalt were tested using a rutting tester. Figure 12 This diagram illustrates the comparison of rutting factors between SBS asphalt and flame-retardant asphalt. Further analysis using rutting factors... The high-temperature rutting resistance of two types of asphalt was evaluated. The results showed that the rutting factor of the flame-retardant asphalt was consistently higher than that of the SBS-modified asphalt in the 50–90°C range, and it met the failure criteria. The temperature of the asphalt was 94°C, while that of the SBS modified asphalt was 90°C, an increase of approximately 4°C. This indicates that the flame-retardant asphalt of the present invention exhibits superior structural stability and rutting resistance under high-temperature conditions, making it suitable for tunnel pavements with high requirements in high-temperature environments.

[0114] To further evaluate the combustion behavior of the flame-retardant asphalt of this invention, this embodiment also provides a comparative diagram of the combustion after the conical calorimetry test of SBS asphalt and the product of this invention, as shown in the figure. Figure 13 Cone calorimetry tests were conducted on it and traditional SBS modified asphalt, and the residues after combustion were compared and analyzed. Figure 13 As shown, traditional SBS modified bitumen (left) Figure 13(a) In the combustion process, the surface is carbonized with large area black coking area, and the residue is very little, which shows that a large amount of thermal decomposition reaction occurs in the combustion process and releases more combustible gas, which has serious fire hazard. In contrast, the flame-retardant asphalt provided by the present application (right Figure 13 (b) After combustion, a foam-shaped carbon layer with complete structure, full volume and uniform color is formed, and the residue is significantly more than that of SBS modified asphalt. The carbon layer has a good expansion structure, and the surface is covered with dense micropores, effectively isolating the further transmission of heat and oxygen, thereby inhibiting the sustained combustion of the substrate and playing a significant flame-retardant protection role.

[0115] The present application provides a new type of flame-retardant asphalt material suitable for tunnel environment, which introduces a composite flame-retardant system composed of carbon nanotubes, fly ash and lignin, significantly improving the flame-retardant performance of asphalt material while considering environmental protection, economy and engineering adaptability. Carbon nanotubes give the material excellent carbonization and heat insulation capacity, fly ash provides inorganic mineral barrier effect, and lignin as a natural biomass has good coking and synergistic flame-retardant effect, and the three work together to build a stable multi-scale flame-retardant structure.

[0116] The material has low smoke density, long ignition delay time and low heat release rate in the combustion process, which can effectively delay the spread of fire and inhibit the release of toxic smoke, significantly enhancing the fire safety performance of the tunnel pavement. At the same time, the flame retardant has wide sources, is renewable and has no toxic side effects, meeting the requirements of green and low-carbon development, and the preparation process is simple and suitable for popularization and application.

[0117] Embodiment three:

[0118] The present application also provides a preparation method of flame-retardant asphalt for tunnel pavement, which is an indoor test preparation method, comprising the following steps:

[0119] S1: heating the base asphalt to a fluid state;

[0120] S2: preheating carbon nanotubes, fly ash and lignin;

[0121] S3: weighing the base asphalt fluid and the carbon nanotubes, adding the carbon nanotubes to the base asphalt fluid for heating and stirring to obtain a preliminary mixture;

[0122] S4: using a high-speed shearing machine to perform high-speed shearing on the preliminary mixture while keeping warm;

[0123] S5: weighing the fly ash and lignin, adding the fly ash and lignin to the sheared preliminary mixture in multiple times and heating and stirring to obtain a secondary mixture;

[0124] S6: using a high-speed shearing machine to perform high-speed shearing on the secondary mixture while keeping warm;

[0125] S7: low speed shearing of the secondary mixture by using a high speed shearing machine to remove bubbles therein, and obtaining the flame-retardant asphalt.

[0126] The main difference of the present embodiment from the prior art is that the carbon nanotubes, fly ash and lignin and their adding sequence, heating, preheating and heat preservation are all determined according to the melting characteristics of the base asphalt, and the stirring and shearing rate and time are also determined according to the flow characteristics of the base asphalt fluid itself. By using the above preparation method, the flame-retardant asphalt of the present application can be prepared in the laboratory.

[0127] The carbon nanotubes should be added first and subjected to high speed shearing treatment under low viscosity conditions to realize their sufficient dispersion and uniform distribution in the base asphalt and to construct a stable carbonized skeleton structure. The fly ash and lignin have high dispersibility and thermal stability and will not significantly affect the initial rheological properties of the system, so they are added later. Specific embodiment three:

[0129] The present embodiment provides a preparation method of flame-retardant asphalt for tunnel pavement, comprising the following steps:

[0130] S1: placing the base asphalt into an oven for heating, and heating for 2h until the base asphalt is in a fluid state.

[0131] The heating temperature is 165℃.

[0132] S2: placing the carbon nanotubes, fly ash and lignin into an oven for preheating for 20min.

[0133] The carbon nanotubes are derived from waste plastic pyrolysis residues, the fly ash is an inorganic mineral filler produced industrially, and the lignin is derived from the papermaking industry. The preheating temperature is 165℃.

[0134] It should be noted that other types of carbon nanotubes, fly ash and lignin are also suitable for the present application.

[0135] S3: weighing the base asphalt fluid and the carbon nanotubes, adding the carbon nanotubes first into the base asphalt fluid and stirring, the stirring time being 5min, the stirring speed being 200r / min, and the container being heated during the stirring process; obtaining a preliminary mixture.

[0136] The stirring instrument is a small high-speed disperser, and the container is heated at 165℃.

[0137] It should be noted that the preparation container of the laboratory flame-retardant asphalt in the present embodiment is 500ml, and the power of the small high-speed disperser is 500W.

[0138] S4: using a small high-speed shearing machine to shear the preliminary mixture (matrix asphalt fluid added with carbon nanotubes), the shearing time is 45 min, the shearing rotation speed is 3500 r / min, and the matrix asphalt fluid is heated at the same time.

[0139] It should be noted that the power of the laboratory small high-speed shearing machine in the application is 1000W, and the asphalt is heated using an electric heating constant temperature jacket. The heating temperature is 165℃.

[0140] S5: weighing fly ash and lignin, adding the fly ash and lignin into the sheared preliminary mixture in multiple times and stirring, the stirring time is 10 min, the stirring rotation speed is 200 r / min, and the container is heated during the stirring process; obtaining a secondary mixture.

[0141] The stirring instrument is a small dispersing machine, and the container is heated at 165℃.

[0142] S6: using a small high-speed shearing machine to shear the secondary mixture (matrix asphalt fluid added with three kinds of flame retardants), the shearing time is 30 min, the shearing rotation speed is 3500 r / min, and the asphalt is heated at the same time.

[0143] It should be noted that the power of the laboratory small high-speed shearing machine in the application is 1000W, and the asphalt is heated using an electric heating constant temperature jacket. The heating temperature is 165℃.

[0144] S7: adjusting the shearing speed of the high-speed shearing instrument to 500 r / min, the shearing time is 5 min, using the high-speed shearing machine to shear the secondary mixture at low speed to remove the bubbles therein, and obtaining the flame-retardant asphalt.

[0145] The small high-speed dispersing machine and the small high-speed shearing machine refer to the dispersing machine and the shearing machine commonly used in the laboratory, which correspond to the indoor preparation method. The difference from the industrial preparation method lies in the difference in rotation speed and time length. However, the specific dispersing or shearing parameters are determined according to the characteristics of the matrix asphalt itself.

[0146] Embodiment four

[0147] The application also provides another preparation method of the flame-retardant asphalt for tunnel pavement, which is an industrial preparation method, comprising the following steps:

[0148] T1: heating the matrix asphalt to a fluid state;

[0149] T2: preheating the carbon nanotubes, fly ash and lignin;

[0150] T3: weighing the matrix asphalt fluid and the carbon nanotubes, adding the carbon nanotubes into the matrix asphalt fluid, and using a high-speed dispersing machine to heat and disperse, to obtain a preliminary mixture;

[0151] T4: using a large high-speed shearing machine to heat and high-speed shear the primary mixture;

[0152] T5: weighing fly ash and lignin, adding the fly ash and lignin to the primary mixture, and using a high-speed dispersion machine to heat and disperse, to obtain a secondary mixture;

[0153] T6: using a large high-speed shearing machine to heat and high-speed shear the secondary mixture;

[0154] T7: using a large high-speed shearing machine to low-speed shear the secondary mixture to remove bubbles therein, to obtain the flame-retardant asphalt.

[0155] The main difference of the present embodiment from the prior art is the carbon nanotubes, fly ash and lignin and their adding order, heating, preheating and heat preservation are all determined according to the melting characteristics of the base asphalt, and the stirring and shearing rate and time are also determined according to the flow characteristics of the base asphalt itself. By using the above preparation method, the flame-retardant asphalt of the present application can be quickly prepared on an industrial scale.

[0156] Current domestic and foreign research on flame-retardant asphalt mostly focuses on the laboratory stage, using small batches, high-shear mixers and intermittent heating equipment for batching and shearing, which has problems such as uneven component dispersion, unstable heat control, limited production capacity, inability to scale up, etc., and is difficult to directly convert into engineering applications. Based on the needs of engineering application scenarios, the present application specially designs a preparation process suitable for industrial conditions, and clearly gives the key process parameters, equipment requirements and operation sequence, to ensure that the material can still maintain stable performance and consistent quality under large-scale production. The present embodiment can make the present application have significant engineering application value and promotion prospects. Specific embodiment four:

[0158] The present embodiment also provides an industrial preparation method of flame-retardant asphalt for tunnel pavement, comprising the following steps:

[0159] T1: placing the base asphalt into an oven for heating, heating for 2h until the asphalt is in a fluid state.

[0160] The heating temperature is 165℃.

[0161] T2: placing the carbon nanotubes, fly ash and lignin into an oven for preheating for 20min.

[0162] The carbon nanotubes are derived from waste plastic pyrolysis residues, the fly ash is an inorganic mineral filler produced industrially, and the lignin is derived from the papermaking industry. The preheating temperature is 165℃.

[0163] T3: 20 kg of base asphalt fluid is weighed into a preparation container; 0.24 kg of carbon nanotubes is weighed and added to the base asphalt fluid, and a large high-speed dispersing machine is used for dispersion, the dispersion time is 10 minutes, the rotation speed of the dispersing machine is 200 r / min, and the container is kept warm during the dispersion process; a preliminary mixture is obtained.

[0164] The container is a stainless steel material with a diameter of 30 cm and a height of 50 cm. The volume of asphalt used in industrial production needs to be greater than two-thirds of the volume of the container and less than four-fifths of the volume of the container. An electric heating constant temperature jacket is used to keep the asphalt warm. The temperature of the constant temperature jacket is 165°C.

[0165] It should be noted that the large high-speed dispersing machine used in the industrial production of the flame-retardant asphalt has a power of 5 kW, and other high-speed dispersing machines with different powers are also suitable for the present application.

[0166] T4: A large high-speed shearing machine is used to shear the preliminary mixture, the shearing time is 30 minutes, the shearing rotation speed is 2000 r / min, and the asphalt is kept warm at the same time; the temperature of the constant temperature jacket is 165°C.

[0167] In a specific embodiment, an electric heating constant temperature jacket is used to keep the asphalt warm.

[0168] It should be noted that the large high-speed shearing machine used in the industrial production of the flame-retardant asphalt has a power of 25 kW, and other high-speed shearing machines with different powers are also suitable for the present application.

[0169] T5: 2.38 kg of fly ash and 1.19 kg of lignin are weighed and added to the preliminary mixture after shearing, and a high-speed dispersing machine is used for dispersion, the dispersion time is 10 minutes, the stirring rotation speed is 200 r / min, and the container is kept warm during the stirring process; a secondary mixture is obtained.

[0170] An electric heating constant temperature jacket is used to keep the asphalt warm. The temperature of the constant temperature jacket is 165°C.

[0171] It should be noted that the large high-speed dispersing machine used in the industrial production of the flame-retardant asphalt has a power of 5 kW, and other high-speed dispersing machines with different powers are also suitable for the present application.

[0172] T6: A large high-speed shearing machine is used to shear the secondary mixture (liquid asphalt added with three flame-retardant components), the shearing time is 30 minutes, the shearing rotation speed is 1500 r / min, and the asphalt is kept warm at the same time.

[0173] An electric heating constant temperature jacket is used to keep the asphalt warm. The temperature of the constant temperature jacket is 165°C.

[0174] It should be noted that the large high-speed shearing instrument used in the industrial preparation of the flame-retardant asphalt has a power of 25kW, and other large high-speed shearing instruments with other powers are also suitable for the present application.

[0175] T7: adjust the speed of the large high-speed shearing machine to 200r / min, the shearing time is 5min, remove the bubbles in the asphalt, and obtain the flame-retardant asphalt.

[0176] The large high-speed dispersing machine and the large high-speed shearing machine refer to the dispersing machine and the shearing machine commonly used in the laboratory, corresponding to the industrial preparation method. "Large" and "small" do not need to be specifically distinguished.

[0177] Specifically, the present application constructs a complete set of industrial process flow from substrate asphalt heating, flame-retardant component preheating, step-by-step addition of substrate asphalt and flame-retardant component, high-power shearing dispersion, whole-process temperature control to terminal degassing and shaping. Among them, the addition of carbon nanotubes adopts a high-speed dispersion + high-shear composite processing strategy, which makes the nano components quickly depolymerize under high temperature and high shear conditions to form a preliminary dispersion network; then by adding fly ash and lignin in stages and continuing to shear, combined with industrial-grade high-power equipment (such as 5kW dispersing machine, 25kW shearing machine) to ensure the synergistic distribution of the three components in the asphalt. In addition, in order to adapt to the requirements of continuity and batch stability of industrial production, a low-speed shearing defoaming process is specially introduced to solve the problems of material bubble inclusion, stratification and unevenness commonly encountered in large-scale preparation.

[0178] In terms of temperature control, the present embodiment uniformly sets the processing temperature of the asphalt and each component to 165℃, and uses an electric heating constant temperature sleeve to link with a stainless steel sandwich container for temperature control, to ensure stable processing conditions at each stage and adapt to the temperature control requirements under different production scales. The process has fully considered the flowability, safety and component reaction behavior of the asphalt material, and has good generalizability and process compatibility.

[0179] The present application not only solves the safety short board of traditional asphalt in high-risk tunnel environment, but also provides a new technical path for the high-value utilization of renewable resources and the development of road functional materials, which has important engineering popularization significance and industrial transformation prospect.

[0180] The above examples are only used to illustrate the technical solutions of the present application and do not constitute a limitation on the protection scope of the present application. For ordinary skilled persons in the art, various equivalent replacements, modifications, improvements or changes made based on the disclosed content without departing from the technical essence and spirit of the present application shall be considered as falling within the scope of the present application.

Claims

1. A flame-retardant asphalt for tunnel pavement, the main material of which is base asphalt, characterized by the following features (calculated by weight percentage): Further comprising 1wt%-2wt% of carbon nanotubes, 8wt%-10wt% of fly ash and 5wt%-7wt% of lignin; the carbon nanotubes, fly ash and lignin play a synergistic role in flame retardation through carbonization, coking and ceramization mechanisms in the matrix asphalt base, forming a three-stage linkage flame retardation mode of "low-temperature coking-moderate-temperature carbonization-high-temperature ceramization".

2. The flame-retardant asphalt for a tunnel pavement according to claim 1, characterized by: The optimal flame-retardant ratio of the flame-retardant asphalt is determined by the following method: 1) using a central composite design model, inputting the content range of carbon nanotubes, fly ash and lignin, generating multiple flame-retardant asphalt ratio schemes; 2) taking the basic performance indicators and flame-retardant performance indicators of asphalt as the evaluation indicators of the flame-retardant asphalt, determining the evaluation indicator values of each ratio scheme through indoor tests; wherein the basic performance indicators of asphalt are ductility, softening point and penetration, and the flame-retardant performance indicators are flash point and limiting oxygen index; 3) using a comprehensive evaluation method to calculate the scores of the basic performance indicators and the flame-retardant performance indicators of asphalt, obtaining the comprehensive scores of each ratio scheme, and then obtaining the optimal flame-retardant ratio.

3. The flame-retardant asphalt for tunnel pavement according to claim 2, characterized by: The comprehensive evaluation method adopts the entropy method.

4. The flame-retardant asphalt for a tunnel pavement according to claim 3, characterized by: The optimal flame-retardant ratio of the flame-retardant asphalt is: 1wt% of carbon nanotubes, 10wt% of fly ash and 5wt% of lignin.

5. The process for the preparation of a flame-retardant bitumen for tunnel pavements according to any one of claims 1-4, which is a process for the preparation in the laboratory, characterized in that: The method comprises the following steps: S1: heating the matrix asphalt to a fluid state; S2: preheating the carbon nanotubes, fly ash and lignin; S3: weighing the matrix asphalt fluid and the carbon nanotubes, adding the carbon nanotubes into the matrix asphalt fluid for heating and stirring to obtain a preliminary mixture; S4: performing high-speed shearing on the preliminary mixture under insulation; S5: weighing the fly ash and lignin, adding the fly ash and lignin into the sheared preliminary mixture for heating and stirring to obtain a secondary mixture; S6: performing high-speed shearing on the secondary mixture under insulation; S7: performing low-speed shearing on the secondary mixture to remove bubbles therein, and obtaining the flame-retardant asphalt.

6. The method of preparing a flame-retardant asphalt for tunnel pavements according to claim 5, characterized in that: The heating temperature, preheating temperature and insulation temperature are 155-175℃.

7. The preparation method of the flame-retardant asphalt for tunnel pavement according to claim 5, characterized in that: in the S3, the stirring speed is 150-250r / min, and the stirring time is 5-15min; in the S5, the stirring speed is 150-250r / min, and the stirring time is 5-15min; in the S4, the shearing speed is 3000-4000r / min, and the shearing time is 30-50min; in the S6, the shearing speed is 3000-4000r / min, and the shearing time is 20-40min; in the S7, the shearing speed is 300-700r / min, and the shearing time is 5-10min.

8. The process for the preparation of a flame-retardant bitumen for tunnel pavements according to any one of claims 1-4, which is an industrial preparation process, characterized by the fact that: The method comprises the following steps: T1: heating the matrix asphalt to a fluid state; T2: preheating the carbon nanotubes, fly ash and lignin; T3: weighing the matrix asphalt fluid and the carbon nanotubes, adding the carbon nanotubes into the matrix asphalt fluid for insulation and dispersion to obtain a preliminary mixture; T4: performing high-speed shearing on the preliminary mixture under insulation; T5: weighing the fly ash and lignin, adding the fly ash and lignin into the preliminary mixture for insulation and dispersion to obtain a secondary mixture; T6: the secondary mixture is subjected to high-speed shearing under insulation; T7: the secondary mixture is subjected to low-speed shearing to remove bubbles therein, and the flame-retardant asphalt is obtained.

9. The method of preparing a flame-retardant asphalt for tunnel pavements according to claim 8, characterized in that: The heating temperature, the preheating temperature and the insulation temperature are 155-175°C.

10. The preparation method of the flame-retardant asphalt for tunnel pavement according to claim 8, characterized in that: in the T3, the dispersion rotation speed is 150-250 r / min, and the dispersion time is 5-15 min; in the T5, the dispersion rotation speed is 150-250 r / min, and the dispersion time is 5-15 min; in the T4, the shearing rotation speed is 1500-2500 r / min, and the shearing time is 20-40 min; in the T6, the shearing rotation speed is 1000-2000 r / min, and the shearing time is 20-40 min; in the T7, the shearing rotation speed is 100-300 r / min, and the shearing time is 5-15 min.

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