An asphalt flame retardant and its preparation method

Abstract

The present invention belongs to the field of asphalt flame retardants, and provides an asphalt flame retardant, which comprises the following components in parts by weight: 10-30 parts of metal organic phosphate, 20-60 parts of magnesium hydroxide, 2-5 parts of titanate coupling agent, and 10-30 parts of expandable graphite; its preparation method comprises the following steps: dissolving phenol in an organic solvent, adding phosphorus oxychloride and triethylamine, reacting for a period of time to generate organic phosphoryl chloride, and then carrying out a hydrolysis reaction to obtain an organic phosphate ester; sequentially adding the above-mentioned organic phosphate ester and an alkaline substance containing metal ions into the organic solvent to obtain a metal organic phosphate; mixing the titanate coupling agent and the organic solvent to prepare an organic solution, sequentially adding the above-mentioned metal organic phosphate, expandable graphite and magnesium hydroxide into the organic solution, soaking for a period of time, filtering the organic solution, and drying and cooling the obtained filter body to obtain the asphalt flame retardant; the present invention can improve the flame retardancy and smoke suppression performance of asphalt, reduce the fire hazard of asphalt pavement, and at the same time improve the high-temperature performance of asphalt.

Description

Technical Field

[0001] The present invention relates to the field of asphalt flame retardants, and particularly to an asphalt flame retardant and a preparation method thereof. Background Art

[0002] China has a vast territory, and in some areas the terrain is steep. In recent years, the high-grade highways built have a relatively high bridge-tunnel ratio. Especially for the newly built expressways in some central and western provinces, the bridge-tunnel ratio can exceed 80%. In mountainous expressways, tunnel structures are widely used, which greatly reduces the driving mileage. Asphalt pavement has become the main pavement structure type for tunnel paving due to its advantages such as comfortable driving, good anti-skid performance, low noise, short construction period, and convenient maintenance. However, there are unique fire hazards in tunnel asphalt paving. Different from general fire accidents, the consequences caused by tunnel fire accidents are very serious. When a fire occurs on the tunnel pavement, since asphalt has the functions of flammability and combustion support, the combustion will decompose into flammable gases such as H2, CO, and short-chain alkanes. The combustion exothermic reaction of these flammable gases will further promote the pyrolysis and combustion of asphalt, causing the fire to spread, thus triggering more serious fire accidents. And due to the special characteristics of the tunnel itself, such as "small space, complex structure, and strong closure", the toxic thick smoke generated during a tunnel fire is very difficult to discharge, spreads rapidly, causing channel blockage, suffocation of trapped personnel, and increased rescue difficulty, etc.

[0003] At the present stage, improving the flame retardant performance of asphalt is mostly achieved by adding flame retardants. There are various types of flame retardants. According to the usage method, they are divided into additive flame retardants and reactive flame retardants. Due to some disadvantages of reactive flame retardants, such as high cost and few types, additive flame retardants are currently commonly used. Additive flame retardants are added to polymers by mechanical mixing methods to make the polymers flame retardant. Additive flame retardants mainly include: organic flame retardants, inorganic flame retardants, halogen-based flame retardants (organic chlorides and organic bromides), and non-halogen flame retardants. Organic flame retardants are some flame retardants represented by bromine-based, phosphorus-nitrogen-based, nitrogen-based, red phosphorus and its compounds. Inorganic flame retardants are mainly antimony trioxide, magnesium hydroxide, aluminum hydroxide, and silicon-based flame retardant systems.

[0004] The combustion of asphalt requires three conditions: heat, oxygen, and combustible materials. Therefore, for asphalt, in order to achieve the purpose of flame retardancy, it is necessary to interrupt the combustion cycle composed of heat, oxygen, and combustible materials by physical or chemical methods. However, existing flame retardants either have poor flame retardant ability and are prone to reignition; or in order to achieve the flame retardant effect, they often ignore the compatibility with the asphalt matrix, resulting in insufficient elasticity and poor anti-deformation ability of the asphalt. Summary of the Invention

[0005] The object of the present invention is to provide an asphalt flame retardant and its preparation method, which can improve the flame retardancy and smoke suppression performance of asphalt, reduce the fire hazard of asphalt pavement, enhance the high-temperature performance of asphalt, improve the compatibility between the flame retardant and asphalt components, and enhance the elasticity and anti-deformation ability of asphalt.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An asphalt flame retardant, comprising the following components in parts by weight: 10-20 parts of metal organic phosphate, 30-60 parts of magnesium hydroxide, 4-5 parts of titanate coupling agent, and 10-20 parts of expandable graphite; preferably, it comprises: 10-20 parts of metal organic phosphate, 20-60 parts of magnesium hydroxide, 40-60 parts of ethanol, 4-5 parts of titanate coupling agent, and 10-20 parts of expandable graphite; the molecular weight of the metal organic phosphate is 200-500, and the molecular weight of the expandable graphite is 10,000-30,000.

[0008] The flame retardant of the present invention realizes the directional flame retardancy of asphalt components by controlling the molecular weight ratio of the flame retardant. It mainly involves a metal organic phosphate with a molecular weight of about 300, which has a similar molecular weight to the small molecules in the saturate and aromatic components of asphalt, can improve the interfacial adhesion between the metal organic phosphate and asphalt, achieve the flame retardant effect on the saturate and aromatic components of asphalt, and further improve the thermodynamic stability of asphalt; it also includes expandable graphite with a molecular weight of about 10,000-30,000, which is close to the molecular weight of asphaltene. On the one hand, it can make the expandable graphite fuse well with asphaltene, so that the expandable graphite can be evenly distributed in asphalt. On the other hand, the expandable graphite can wrap the asphaltene well and achieve the flame retardant effect on the asphaltene component. Moreover, the compatibility between the flame retardant of the present invention and asphalt components is improved, enabling the flame retardant to exhibit better flame retardant performance and achieving the flame retardant and smoke suppression effects at the same time.

[0009] The preparation method of the above asphalt flame retardant comprises the following steps:

[0010] S1. Esterification reaction: Dissolve phenol in an organic solvent, such as ethanol (the present invention does not make restrictions, and those skilled in the art can select a suitable organic solvent according to actual needs), then add phosphorus oxychloride and triethylamine, keep the test temperature at 20-30 °C, react for 8-12 hours to generate organic phosphoryl chloride. Then add 100-120 parts of water to the product and raise the temperature to 30-40 °C, stir for 1 hour and then stop the test. Filter the product, wash the filtered solid with water until it is neutral and then dry it to obtain an organic phosphate ester. The reaction process is as follows:

[0011]

[0012] S2. Salt formation reaction: The above-mentioned organic phosphate ester and a basic substance containing metal ions, such as sodium hydroxide or aluminum hydroxide (hereinafter taking sodium hydroxide as an example), are successively added to an organic solvent. The test temperature is 60 - 80 °C, and the reaction time is 1.5 - 2 h. After the reaction, the product is distilled, filtered, washed with water until neutral, and then dried to obtain a metal organic phosphate salt. The reaction process is as follows:

[0013]

[0014] The metal organic phosphate salt is a substance with high thermal stability and high boiling point. The addition of the metal organic phosphate salt increases the ignition temperature of the asphalt. The metal organic phosphate salt burns and decomposes into phosphoric acid or polyphosphoric acid. The molecular weight of the metal organic phosphate salt is about 300, which is similar to the molecular weights of small molecules in saturates and aromatics, playing a certain volume-increasing role and being able to improve the interfacial adhesion between the metal organic phosphate salt and the asphalt, further enhancing the thermodynamic stability of the asphalt. At the same time, the metal organic phosphate salt itself has excellent high-temperature performance, and its thermal decomposition temperature range is 462 °C - 540 °C, having good flame retardancy, which can effectively act on saturates and aromatics for flame retardancy. When the metal organic phosphate salt is heated, it can generate a more stable carbonized layer. The formed carbonized layer adheres to the surface of the asphalt. The carbon layer is incombustible and can isolate oxygen, making the asphalt unable to burn. The carbon layer covering the surface of the asphalt has poor thermal conductivity, reducing the heat conduction from the flame to the asphalt, effectively reducing the heat transferred from the flame zone to the asphalt pavement, being able to prevent the further pyrolysis of the asphalt, thereby reducing the mass loss rate of the asphalt and the generation amount of combustible gases. At the same time, the carbonized layer can prevent the pyrolysis products of the asphalt from participating in combustion through the solid-phase flame retardancy mechanism, reducing the pyrolysis of the asphalt and playing a flame retardant role in the initial stage of asphalt combustion.

[0015] S3. Surface modification: A titanate coupling agent and an organic solvent (such as ethanol, which is not restricted in this invention and those skilled in the art can select a suitable organic solvent according to actual needs) are mixed to prepare an organic solution with an organic solvent:titanate coupling agent = 8 - 12:1. The above-mentioned metal organic phosphate salt, expandable graphite, and magnesium hydroxide are successively added to the organic solution, and it is soaked at room temperature for about 3 hours. Then the organic solution is filtered, and the obtained filter cake is put into a vacuum drying oven. The drying temperature is set at 100 - 110 °C, and the vacuum degree is set at 90 - 95 kPa. After drying for 1 - 2 hours, it is taken out and cooled to room temperature in a desiccator, thus obtaining the asphalt flame retardant.

[0016] There are a large number of alkanes in asphalt. When asphalt burns, chemical reactions occur with oxygen, generating a large amount of OH· and H· free radicals. These free radicals will accelerate the combustion of asphalt. The P=O double bond in organophosphoric acid metal salts can capture and consume free radicals such as OH· and H·. After these free radicals are consumed and replaced, they cannot trigger the next combustion of the asphalt pavement. The thermal decomposition reaction of magnesium hydroxide is an endothermic reaction, which will release a large amount of water, reduce the surface temperature of asphalt, slow down the pyrolysis rate of asphalt, reduce the generation of combustible gases, and at the same time the generated water vapor can dilute the concentration of combustible gases and oxygen, having a good smoke suppression effect. The titanate coupling agent is used to modify the surface of organophosphoric acid metal salts and magnesium hydroxide, enhancing their compatibility with asphalt and further improving the flame retardant effect. Expandable graphite is a graphite intercalation compound. Expandable graphite with a molecular weight of about 10,000 - 30,000 is selected to make the molecular weight of expandable graphite close to that of asphaltene. On the one hand, this can make expandable graphite fuse well with asphaltene, enabling expandable graphite to be evenly distributed in asphalt. On the other hand, expandable graphite can wrap asphaltene well, achieving a flame retardant effect for the asphaltene component. When expandable graphite is heated during combustion, it can quickly expand to form a "worm"-shaped fluffy expanded graphite carbon layer barrier, which can delay and prevent the flame from approaching the asphalt, effectively prevent the combustion of asphalt and the dripping of asphalt droplets after combustion, effectively prevent the heat conduction from the flame to the asphalt, and at the same time expandable graphite absorbs a large amount of heat during combustion, which can effectively reduce the surface temperature of the asphalt material, making the asphalt difficult to burn, thus achieving the purpose of flame retardancy. In addition, expandable graphite generates a large amount of carbon dioxide during combustion, which can dilute the concentration of combustible gases and achieve the purpose of flame retardancy through the gas-phase flame retardant mechanism.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. The preparation process of the flame retardant of the present invention is simple, has low requirements for equipment, has good applicability, is easy to be industrially mass-produced, has good economic value, and this asphalt flame retardant can be directly added to asphalt binder, and the modified asphalt preparation process is simple and easy to promote.

[0019] 2. The flame retardant of the present invention starts to play a flame retardant role from the asphalt pyrolysis process, and conducts flame retardancy through the synergistic action of the gas-phase flame retardant mechanism and the solid-phase fixation mechanism. The flame retardant of the present invention can achieve excellent flame retardant effects throughout the whole process of asphalt combustion, enabling the asphalt combustion pavement to reach the self-extinguishing effect; and it has relatively excellent flame retardant effects on the saturate, aromatic fraction and asphaltene of asphalt.

[0020] 3. The flame retardant of the present invention is added with expandable graphite, has a fast expansion speed, good heat insulation performance and certain smoke suppression performance, can achieve excellent flame retardant and smoke suppression effects, and this flame retardant of the present invention is in powder form and can act as a filler when added to asphalt, and also has a certain degree of improvement on the road performance of asphalt.

[0021] 4. The flame retardant of the present invention has polar groups, which can adhere to the surface of asphalt wax crystals, prompting the asphalt wax crystals to form an interlaced, perfect and dense network structure. This network structure has strong stability and is not easily deformed under the action of loads, which can greatly improve the bearing capacity of asphalt pavements.

[0022] 5. The organophosphoric acid metal salt and magnesium hydroxide in the flame retardant of the present invention have strong high-temperature stability. Adding them to asphalt can greatly improve the high-temperature performance of asphalt pavements. Therefore, the asphalt flame retardant of the present invention can be used for asphalt pavements in hot regions. Detailed implementation mode

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not indicated by the manufacturer can be obtained as conventional products through commercial purchase. All features disclosed in this specification, except for mutually exclusive features or / and steps, can be combined in any way.

[0024] Example 1

[0025] An asphalt flame retardant, comprising the following components in parts by weight: 15 parts of an organophosphoric acid metal salt with a molecular weight of 300, 40 parts of magnesium hydroxide, 5 parts of a titanate coupling agent, and 15 parts of expandable graphite with a molecular weight of 20,000.

[0026] Its preparation method includes the following steps:

[0027] Step 1: Add 50 parts of phenol to a beaker containing 50 parts of ethanol, dissolve the phenol in the ethanol, then add 25 parts of phosphorus oxychloride and 25 parts of triethylamine, keep the test temperature at 25 °C, and react for 10 hours to generate organophosphoryl chloride. Then add 110 parts of water to the product and raise the temperature to 35 °C, stir for 1 hour and then stop the test. Filter the product, wash the filtered solid with water until neutral and then dry it to obtain an organophosphoric acid ester;

[0028] Step 2: Add 25 parts of the organophosphoric acid ester and 10 parts of sodium hydroxide to an organic solution of ethanol: water = 1:1 in sequence, the test temperature is 60 °C, the reaction time is 1.5 h, after the reaction is completed, distill, filter and wash the product with water until neutral and then dry it to obtain an organophosphoric acid metal salt;

[0029] Step 3: Using ethanol as an organic solvent, add a titanate coupling agent to prepare an organic solution with ethanol:titanate coupling agent = 10:1. Sequentially add 15 parts of an organic metal phosphate salt, 15 parts of expandable graphite, and 40 parts of magnesium hydroxide to the organic solution, and soak for 3 hours at room temperature (25°C). Filter the organic solution, place the obtained filter cake in a vacuum drying oven, set the drying temperature to 105°C, set the vacuum degree to 93 kPa, take it out after drying for 2 hours, and cool it to room temperature in a desiccator to obtain an asphalt flame retardant.

[0030] Example 2

[0031] The difference between the flame retardant of this example and that of Example 1 lies in: it includes the following components in parts by weight: 10 parts of an organic metal phosphate salt with a molecular weight of 300, 30 parts of magnesium hydroxide, 4 parts of a titanate coupling agent, and 10 parts of expandable graphite with a molecular weight of 20000.

[0032] Example 3

[0033] The difference between the flame retardant of this example and that of Example 1 lies in: it includes the following components in parts by weight: 20 parts of an organic metal phosphate salt with a molecular weight of 300, 60 parts of magnesium hydroxide, 5 parts of a titanate coupling agent, and 20 parts of expandable graphite with a molecular weight of 15000.

[0034] Example 4

[0035] The difference between the flame retardant of this example and that of Example 1 lies in: it includes the following components in parts by weight: 15 parts of an organic metal phosphate salt with a molecular weight of 300, 20 parts of magnesium hydroxide, 4 parts of a titanate coupling agent, and 15 parts of expandable graphite with a molecular weight of 25000.

[0036] Examples for preparing high-performance asphalt doped with the flame retardants prepared in the above examples.

[0037] Example 5

[0038] Keep the base asphalt at 160°C for 30 min and take it out (SBS asphalt at 175°C for 30 min), respectively add the asphalt flame retardant prepared in Example 1, use a high-speed shearer to shear at a rate of 3000 r / min at 175°C for 40 min, and after stirring, put it into an oven at 175°C to swell and develop for 20 min to respectively obtain different modified asphalts doped with asphalt flame retardants, denoted as A~F. The ratio of the base asphalt to the flame retardant is shown in Table 1:

[0039] Table 1 Compositions of different modified asphalts A~F

[0040]

[0041] Experimental Example

[0042] 1. Flame retardant performance test

[0043] (1) The modified asphalts prepared in Example 5 were subjected to asphalt flash point and ignition point tests (Cleveland open cup method) in accordance with the Test Procedures for Asphalt and Asphalt Mixtures for Highway Engineering (JTG E20-2011) T0611-2011;

[0044] (2) Each modified asphalt obtained in Example 5 was made into a standard sample with a length of 110-120 mm and a width of 6.5 mm ± 0.5 mm according to the specification of "Determination of Oxygen Index of Combustion Performance of Asphalt" (NB / SH / T0815-2010), and a limiting oxygen index test was performed. The results are shown in Table 2:

[0045] Table 2 Asphalt flame retardant performance test data

[0046]

[0047] From the test data in Table 2, it can be seen that the asphalt flame retardant can improve the three asphalt flame retardant performance indicators of asphalt flash point, ignition point and limiting oxygen index, and the improvement effect increases with the increase of flame retardant dosage. Because the asphalt flame retardant contains organic phosphate metal salts, magnesium hydroxide and expandable graphite, they can all play a good flame retardant effect when asphalt burns, and achieve a synergistic flame retardant effect through gas phase flame retardant mechanism and solid phase flame retardant mechanism.

[0048] 2. Smoke suppression performance test

[0049] The modified asphalts prepared in Example 5 were subjected to asphalt smoke density test according to the "Test Method for Smoke Density of Combustion or Decomposition of Building Materials" (GB / T8627-2007). The smoke density test is to calculate the optical density by the change of the absorbance of the parallel light beams on both sides of the smoke box passing through the unit path length in the smoke, reflecting the amount of smoke generated by a sample with a certain exposure area in a smoke box of a specified volume. The smoke density grade SDR is used to evaluate the smoke suppression function of asphalt. The results are shown in Table 3:

[0050] Table 3 Technical indicators of asphalt smoke suppression test

[0051]

[0052] From the asphalt smoke suppression test data in Table 3, it can be seen that the addition of asphalt flame retardant makes the asphalt combustion grade SDR significantly reduced, and the degree of reduction increases with the increase of asphalt flame retardant dosage, and it is observed that the asphalt sample added with asphalt flame retardant has obvious self-extinguishing phenomenon during the test. The asphalt flame retardant is added with expandable graphite, which can rapidly expand to form a "worm"-shaped fluffy expanded graphite carbon layer barrier when burned and heated, which can delay and organize the flame to approach the asphalt, reduce the concentration of combustible gas, thereby achieving the purpose of smoke suppression and self-extinguishing. The asphalt flame retardant can take into account both flame retardant and smoke suppression properties.

[0053] 3. Flame Retardant Performance of Flame Retardant Modified Asphalt Mixture

[0054] 3.1. Conduct the rutting plate combustion test on the modified asphalt prepared in Example 5. Using gasoline as an ignition improver, carry out the combustion test on the formed specimens of asphalt mixture respectively. The asphalt-aggregate ratio in this test example is set at 5%, and the asphalt mixture gradation is OGFC-13. The specific mineral aggregate gradation is shown in Table 4. Evaluate the flame retardant effect of the flame retardant from the change in dynamic stability before and after combustion. The test data are shown in Table 5:

[0055] Table 4 Mineral Aggregate Gradation of OGFC-13

[0056]

[0057] Table 5 Change in Dynamic Stability before and after Combustion of Rutting Plate

[0058]

[0059] From Tables 4-5, it can be seen from the data of the change in dynamic stability before and after the combustion of the rutting plate that the addition of this asphalt flame retardant has greatly improved the dynamic stability of the asphalt mixture before and after combustion. Before combustion, this asphalt flame retardant acts as a filler in the asphalt mixture, improving the dynamic stability of the asphalt mixture; during combustion, this asphalt flame retardant exerts its flame retardant effect, greatly increasing the residual stability of the asphalt mixture. This asphalt flame retardant has strong practical engineering significance.

[0060] 3.2. Conduct the cone calorimeter test on the modified asphalt prepared in Example 5 according to the test procedure ISO5660-1-2015. The cone calorimeter test can measure the ignition time, average heat release rate, CO production, total smoke emission, etc. during the aerobic combustion process of the material. The combustion parameters of the asphalt mixture are shown in Table 6:

[0061] Table 6 Cone Calorimeter Test Data

[0062]

[0063] It can be seen from the test data of the asphalt cone calorimeter in Table 6 that the addition of the asphalt flame retardant increases the ignition time of the asphalt, reduces the average heat release rate, and decreases the production of combustible gas CO, indicating that the addition of this asphalt flame retardant has an obvious improvement effect on the flame retardant performance of the asphalt and preventing the secondary combustion of the asphalt. This asphalt flame retardant contains organophosphorus metal salts, magnesium hydroxide, and expandable graphite. The three act synergistically to greatly improve the flame retardant performance of the asphalt. When this asphalt flame retardant is heated, a more stable carbonized layer can be generated, and the formed carbonized layer adheres to the surface of the asphalt. The carbon layer is incombustible and can isolate oxygen, making it impossible for the asphalt to burn. Acting synergistically from the gas-phase flame retardant mechanism and the solid-phase flame retardant mechanism, the flame retardant performance of the asphalt is improved.

[0064] 4. Rheological Property Test of Flame Retardant Modified Asphalt

[0065] 4.1. Conduct a temperature scan on the modified asphalt prepared in Example 5 to test its storage modulus (G´). G´ reflects the elastic properties of the asphalt. The larger its value, the stronger the ability of the asphalt to resist deformation at high temperatures. The results are shown in Table 7:

[0066] Table 7 Technical Indexes of Storage Modulus G´

[0067]

[0068] It can be seen from the technical indexes of the storage modulus G´ in Table 7 that the addition of the asphalt flame retardant significantly increases the storage modulus of the asphalt. The storage modulus characterizes the elastic properties of the asphalt. Since this asphalt flame retardant is in powder form, it can act as a filler in the asphalt, making the asphalt show stronger elasticity, increasing the ability to resist deformation, and within a certain dosage range, the elastic improvement performance is proportional to the dosage of the asphalt flame retardant.

[0069] 4.2. Refer to the rutting factor G* / sinδ proposed in the SHRP specification as the evaluation index for the high-temperature stability of asphalt binder, and conduct a high-temperature stability test on the modified asphalt prepared in Example 5. The results are shown in Table 8:

[0070] Table 8 Technical Indexes of Rutting Factor G* / sinδ

[0071]

[0072] It can be seen from the technical indexes of the rutting factor G* / sinδ in Table 8 that as the temperature increases, the rutting factor gradually decreases; however, the asphalt with the asphalt flame retardant has a larger rutting factor than the original asphalt, and the trend of the rutting factor decreasing with temperature is slower. Since this asphalt flame retardant contains organophosphorus metal salts, magnesium hydroxide, and expandable graphite, all three have good high-temperature properties. Their addition can significantly improve the high-temperature performance of the asphalt and reduce the temperature sensitivity of the asphalt.

[0073] 4.3. The modified asphalt prepared in Example 2 was subjected to a Multiple Stress Creep Recovery (MSCR) test according to AASHTO TP-70. R3.2 and Jnr3.2, which are more in line with the true loading conditions of the asphalt, were selected for analysis. The results are shown in Table 9:

[0074] Table 9 MSCR Creep Technical Indexes

[0075]

[0076] It can be seen from the MSCR creep technical indexes in Table 9 that the asphalt doped with the asphalt flame retardant has a higher creep recovery rate than the original asphalt under the same stress conditions. This shows that the addition of this asphalt flame retardant can act as a filler in the asphalt, enhance the elastic properties of the asphalt, improve the creep recovery performance of the asphalt, and enhance the ability of the asphalt to resist deformation.

[0077] 4.4. The modified asphalt prepared in Example 5 was subjected to a Linear Amplitude Sweep (LAS) test, and the S-VECD analysis method was used to analyze the test data. The maximum strain level was selected as the failure index to determine the LAS test fatigue life of each modified asphalt. The fatigue life results at 5%, 10%, and 15% stress levels are shown in Table 10:

[0078] Table 10 LAS Fatigue Life Technical Indexes

[0079]

[0080] It can be seen from the LAS fatigue technical indexes in Table 10 that the asphalt doped with the asphalt flame retardant has a higher fatigue life than the original asphalt at 5%, 10%, and 15% stress levels, and the fatigue life is proportional to the dosage of the flame retardant. This shows that the modified asphalt prepared with this asphalt flame retardant can increase the fatigue life of the original asphalt and reduce the stress sensitivity of the original asphalt.

[0081] The present invention is not limited to the above embodiments. Any person should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, shall fall within the protection scope of the present invention.

Claims

1. A preparation method of an asphalt flame retardant, characterized in that, It includes the following steps: S1. Esterification reaction: Dissolve phenol in an organic solvent, then add phosphorus oxychloride and triethylamine. After reacting for a period of time, organophosphorus acyl chloride is formed; then the organophosphorus acyl chloride is subjected to a hydrolysis reaction to obtain an organic phosphate ester; S2. Salt formation reaction: Add the above-mentioned organic phosphate ester and a basic substance containing metal ions to the organic solvent in sequence to obtain a metal organic phosphate salt; S3. Surface modification: Mix a titanate coupling agent and an organic solvent to prepare an organic solution. Add the above-mentioned metal organic phosphate salt, expandable graphite and magnesium hydroxide to the organic solution in sequence, and soak for a period of time at room temperature. Then filter the organic solution, and dry and cool the obtained filter body to obtain an asphalt flame retardant; wherein, the molecular weight of the metal organic phosphate salt is 200-500, and the molecular weight of the expandable graphite is 10,000-30,000.

2. The preparation method of the asphalt flame retardant according to claim 1, characterized in that, In S1, during the esterification reaction, it reacts at 20-30 °C for 8-12 hours; when the organophosphorus acyl chloride is subjected to a hydrolysis reaction: add water to the organophosphorus acyl chloride and heat it to 30-40 °C, and stir for 1-2 hours.

3. The preparation method of the asphalt flame retardant according to claim 1, wherein, In S2, it reacts at 60-80 °C for 1.5-2 h.

4. The preparation method of the asphalt flame retardant according to claim 1, characterized in that, In S3, during drying: the drying temperature is 100-110 °C, the vacuum degree is 90-95 kPa, and the drying time is 1-2 hours.

5. The preparation method of the asphalt flame retardant according to claim 1, wherein In S1, the volume ratio of phenol, ethanol, phosphorus oxychloride and triethylamine is 1.5-2:1.5-2:1-1.5:

1.

6. The preparation method of the asphalt flame retardant according to claim 1, wherein In S2, the volume ratio of the organic phosphate ester and the basic substance containing metal ions is 2-6:

1.

7. The preparation method of the asphalt flame retardant according to claim 1, characterized in that, In S3, the volume ratio of the titanate coupling agent and the organic solvent is 1:8-12; the volume ratio of the metal organic phosphate salt, expandable graphite and magnesium hydroxide is 1:1-2:2-6.

8. An asphalt flame retardant, characterized in that, Prepared by the preparation method according to any one of claims 1-7.

9. The asphalt flame retardant according to claim 8, wherein, It includes the following components in parts by weight: 10-30 parts of metal organic phosphate salt, 20-60 parts of magnesium hydroxide, 2-5 parts of titanate coupling agent, and 10-30 parts of expandable graphite.

10. The asphalt flame retardant according to claim 8, wherein It includes the following components in parts by weight: 10-20 parts of metal organic phosphate salt, 30-60 parts of magnesium hydroxide, 4-5 parts of titanate coupling agent, and 10-20 parts of expandable graphite.

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