A salt spray resistant asphalt waterproof membrane and its preparation method

Abstract

This invention provides a salt spray resistant asphalt waterproof membrane and its preparation method, belonging to the field of building materials technology. It includes: a base layer; a modified asphalt layer comprising asphalt, polyurethane prepolymer, chain extender, and organo-montmorillonite, wherein the modified asphalt layer is coated on both the upper and lower surfaces of the base layer; the polyurethane prepolymer is prepared from hydroxyl-terminated polybutadiene and 4,4'-diphenylmethane diisocyanate; and the organo-montmorillonite is stearic acid-modified montmorillonite; a protective layer comprising ceramic sintered sand, fine sand, and asphalt binder, covering the outer side of the modified asphalt layer on the upper surface of the base layer; and a protective layer covering the outer side of the modified asphalt layer on the lower surface of the base layer. This invention significantly improves the salt spray resistance of the asphalt waterproof membrane through the synergistic effect of the polyurethane prepolymer and organo-montmorillonite.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a salt spray resistant asphalt waterproof membrane and its preparation method. Background Technology

[0002] Asphalt waterproof membranes have become the mainstream waterproofing material for building roofs, underground projects, and transportation infrastructure due to their reliable waterproofing and sealing properties, strong construction adaptability, and controllable costs. In high-salt-fog environments such as coastal areas and industrial zones, the membranes need to resist chloride ion erosion, thermal stress, and mechanical loads for extended periods, placing stringent requirements on corrosion resistance, temperature stability, and interface durability.

[0003] In the prior art, polymers are used to modify asphalt in order to improve the performance of asphalt waterproof membranes. Common polymers include polyethylene, ethylene-vinyl acetate copolymer, styrene-butadiene rubber and rubber powder. Although these polymers can improve the high-temperature deformation resistance and low-temperature crack resistance of asphalt binders to a certain extent, the salt spray resistance of modified asphalt needs to be further improved. Summary of the Invention

[0004] In view of the above situation and to overcome the defects of the prior art, the purpose of this invention is to provide a salt spray resistant asphalt waterproof membrane and its preparation method, so as to at least partially solve the problems mentioned in the background art.

[0005] The technical solution adopted in this invention is as follows:

[0006] The first aspect of this invention provides a salt spray resistant bitumen waterproof membrane, comprising:

[0007] Tire base layer;

[0008] The modified asphalt layer includes asphalt, polyurethane prepolymer, chain extender and organomontmorillonite. The modified asphalt layer is coated on both the upper and lower sides of the base course. The polyurethane prepolymer is prepared from hydroxyl-terminated polybutadiene and 4,4'-diphenylmethane diisocyanate. The organomontmorillonite is stearic acid-modified montmorillonite.

[0009] A protective layer, comprising ceramic sintered sand, fine sand and asphalt binder, is applied to the outside of the modified asphalt layer on the upper surface of the base course.

[0010] A protective layer, covering the outer side of the modified asphalt layer beneath the base course.

[0011] In some embodiments of the present invention, the mass ratio of asphalt, polyurethane prepolymer, chain extender and organomontmorillonite in the modified asphalt layer is 100:(15-25):(1-2):(5-10).

[0012] In some embodiments of the present invention, the thickness of the modified asphalt layer is between 2 mm and 4 mm.

[0013] In some embodiments of the present invention, the base layer is a polyester tire or a glass fiber reinforced polyester tire, and the protective layer is a polyethylene plastic film.

[0014] A second aspect of this invention provides a method for preparing an asphalt-waterproof membrane, comprising the following steps:

[0015] Heat the asphalt to 120-130℃, add organomontmorillonite, and stir for 20-30 minutes;

[0016] Maintain the temperature at 120-130℃, add polyurethane prepolymer and stir for 20-30 minutes, add chain extender preheated to 70-80℃, stir for 40-60 minutes, cool down to 100-105℃ and stop stirring, let stand and react for 2-3 hours to obtain modified asphalt.

[0017] The modified asphalt is simultaneously coated on both sides of the base layer, and then a protective layer and a protective layer are applied in sequence. After calendering and cooling, an asphalt waterproof membrane is obtained.

[0018] In some embodiments of the present invention, the method for applying the protective layer is as follows:

[0019] The asphalt surface is sprayed with compressed air, and asphalt binder is sprayed on. Before the asphalt binder sets, ceramic sintered sand is spread and statically pressed. Then, fine sand is evenly spread and statically pressed to obtain a protective layer.

[0020] In some embodiments of the present invention, the method for preparing the polyurethane prepolymer includes the following steps:

[0021] Under a nitrogen atmosphere, hydroxyl-terminated polybutadiene is heated to 80-90°C in an oil bath, and then 4,4'-diphenylmethane diisocyanate is heated to melt and added dropwise to the hydroxyl-terminated polybutadiene. The mixture is kept at this temperature and stirred for 2-3 hours to obtain a polyurethane prepolymer.

[0022] In some embodiments of the present invention, the mass ratio of the hydroxyl-terminated polybutadiene to 4,4'-diphenylmethane diisocyanate is 10:(1-3).

[0023] In some embodiments of the present invention, the method for preparing the organomontmorillonite includes the following steps:

[0024] Dimethyl sulfoxide and water were mixed at a mass ratio of 10:(1-2), montmorillonite was added, and the mixture was stirred at 60°C for 8 hours before centrifugation. The solid product obtained by centrifugation was added to methanol, stirred at room temperature for 50-70 hours, and dried to obtain modified montmorillonite.

[0025] Stearic acid was added to methanol under water bath heating at 60-65℃, followed by the modified montmorillonite. After stirring for 20-30 hours, the mixture was centrifuged, washed, and dried to obtain organomontmorillonite.

[0026] In some embodiments of the present invention, the mass ratio of stearic acid to modified montmorillonite is 1:(2-3).

[0027] The beneficial effects achieved by this invention are as follows:

[0028] This invention significantly improves the salt spray resistance of asphalt waterproof membranes through the synergistic effect of polyurethane prepolymer and organomontmorillonite. The polyurethane prepolymer is synthesized from hydroxyl-terminated polybutadiene and 4,4'-diphenylmethane diisocyanate. Its soft segment structure exhibits excellent compatibility with asphalt, and under the action of chain extenders, it forms a self-assembled network with alternating hard and soft segments, greatly enhancing the temperature resistance and adhesion of the asphalt. The organomontmorillonite, after stearic acid intercalation modification, expands the interlayer spacing, and the hydrophobic alkyl chains form a physical barrier, effectively blocking the penetration of chloride ions and moisture. The carboxyl groups (-COOH) of stearic acid chemically bond with the isocyanate groups (-NCO) of the polyurethane prepolymer, constructing a ternary cross-linked network. This covalent bridging further blocks the migration channels of corrosive media, enabling the membrane to possess excellent long-term protective performance in salt spray environments. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0031] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] To address the shortcomings of the prior art mentioned in the background section, the first aspect of this invention provides a salt spray resistant bitumen waterproof membrane, comprising:

[0033] Tire base layer;

[0034] The modified asphalt layer includes asphalt, polyurethane prepolymer, chain extender and organomontmorillonite. The modified asphalt layer is coated on both the upper and lower sides of the base course. The polyurethane prepolymer is prepared from hydroxyl-terminated polybutadiene and 4,4'-diphenylmethane diisocyanate. The organomontmorillonite is stearic acid-modified montmorillonite.

[0035] A protective layer, comprising ceramic sintered sand, fine sand and asphalt binder, is applied to the outside of the modified asphalt layer on the upper surface of the base course.

[0036] A protective layer, covering the outer side of the modified asphalt layer beneath the base course.

[0037] First, the polyurethane prepolymer is synthesized from hydroxyl-terminated polybutadiene and 4,4'-diphenylmethane diisocyanate. The hydroxyl-terminated polybutadiene, as a soft segment (containing polybutadiene segments in its molecular structure), has a similar low-polarity molecular structure to the asphalt components (aliphatic / aromatic compounds), which can improve the compatibility between the polyurethane prepolymer and asphalt. After the hydroxyl-terminated polybutadiene reacts with 4,4'-diphenylmethane diisocyanate to form the prepolymer, it undergoes in-situ polymerization in asphalt with a chain extender (such as 1,4-butanediol) to form a block structure with alternating hard segments (urethane bonds) and soft segments. This structure self-assembles into a continuous phase network through hydrogen bonds and van der Waals forces, significantly improving the temperature resistance and adhesion of the asphalt.

[0038] Secondly, organo-montmorillonite is prepared by stearic acid intercalation modification of montmorillonite. In organo-montmorillonite, stearic acid molecules combine with the silica-oxygen surface of montmorillonite through ion-dipole interactions and anchor between montmorillonite layers, which can significantly increase the interlayer spacing of montmorillonite. The expanded interlayer spacing and hydrophobic chains (stearic acid alkyl chains) can form a physical barrier to prevent chloride ions and water penetration, thereby enhancing the salt spray resistance of asphalt.

[0039] In addition, organomontmorillonite can also participate in the polymerization reaction of polyurethane prepolymer. The carboxyl group (-COOH) of stearic acid in organomontmorillonite can react with the isocyanate group (-NCO) in polyurethane prepolymer to form a chemical bond bridge, thereby enabling asphalt-polyurethane prepolymer-organomontmorillonite to form a ternary chemical cross-linking network, blocking the migration of corrosive media and further improving the salt spray resistance of asphalt.

[0040] In summary, this invention significantly improves the salt spray resistance of asphalt waterproof membranes through the synergistic effect of polyurethane prepolymer and organomontmorillonite.

[0041] In some embodiments, the mass ratio of asphalt, polyurethane prepolymer, chain extender, and organomontmorillonite in the modified asphalt layer is 100:(15-25):(1-2):(5-10). The polyurethane prepolymer content must reach the critical value for continuous phase (>15 parts). Below the critical value, the prepolymer is a dispersed phase in the asphalt and cannot form a through-network; above 25 parts, excessive crosslinking leads to excessively high system viscosity, hindering the wetting of the towing base. Insufficient chain extender addition results in incomplete NCO reaction, compromising the coating's density; excessive chain extender addition leads to excess -OH ions consuming hard segment crosslinking points, weakening the network's elastic recovery ability. Insufficient organomontmorillonite addition prevents the formation of a stable ternary chemical crosslinking network, reducing the asphalt's salt spray resistance; excessive organomontmorillonite addition causes agglomeration, reducing the asphalt's mechanical properties.

[0042] In some embodiments, the thickness of the modified asphalt layer is between 2 mm and 4 mm. If the thickness of the modified asphalt layer is too small, the modified asphalt layer will not completely cover the surface of the base material, resulting in an unprotected "weak interface zone"; if the thickness of the modified asphalt layer is too large, the interlayer stress will increase, and the interface will be prone to peeling during low-temperature bending.

[0043] In some embodiments, the base layer is a polyester base or a glass fiber reinforced polyester base, and the protective layer is a polyethylene plastic film. Choosing the base layer as the core skeleton of the roll material satisfies the tensile strength and dimensional stability requirements of the waterproof roll material. In the glass fiber reinforced polyester base, glass fibers are interwoven with the polyester network to form a composite structure, inhibiting thermal creep of the base layer and further improving dimensional stability. The polyethylene film covering the bottom surface of the roll material is easy to peel off and can resist wear and tear during transportation.

[0044] A second aspect of this invention provides a method for preparing an asphalt-waterproof membrane, comprising the following steps:

[0045] Heat the asphalt to 120-130℃, add organomontmorillonite, and stir for 20-30 minutes;

[0046] Maintain the temperature at 120-130℃, add polyurethane prepolymer and stir for 20-30 minutes, add chain extender preheated to 70-80℃, stir for 40-60 minutes, cool down to 100-105℃ and stop stirring, let stand and react for 2-3 hours to obtain modified asphalt.

[0047] Modified bitumen is simultaneously coated on both sides of the base layer, followed by a protective layer and a protective layer. After calendering and cooling, the bitumen waterproof membrane is obtained.

[0048] Organomontmorillonite is first added to viscous asphalt at 120–130℃. The organomontmorillonite is fully dispersed by high-temperature shear force, while exposing carboxyl active sites. Subsequently, polyurethane prepolymer is added and pre-reacts with organomontmorillonite. Then, chain extender is added for further reaction. Cooling and standing at 100–105℃ can promote the complete reaction of residual -NCO and form a continuous cross-linked network.

[0049] In some embodiments, the method for applying the protective layer is as follows: compressed air is used to spray the asphalt surface, an asphalt binder is sprayed, ceramic sintered sand is spread before the asphalt binder initially sets, static pressure is applied, and then fine sand is evenly spread and static pressure is applied again to obtain the protective layer. The asphalt binder allows the ceramic sintered sand and fine sand to adhere to the asphalt surface. The microporous structure of the ceramic sintered sand can adsorb salts, reduce the activity of corrosive media, and enhance the salt spray resistance of the roll material. The fine sand can block the gaps between the ceramic sand particles, improve surface smoothness, and reduce water accumulation and dust adhesion.

[0050] In some embodiments, the preparation method of polyurethane prepolymer includes the following steps: under a nitrogen atmosphere, hydroxyl-terminated polybutadiene is heated to 80-90°C in an oil bath, and then 4,4'-diphenylmethane diisocyanate is heated to melt and added dropwise to hydroxyl-terminated polybutadiene. The mixture is kept warm and stirred for 2-3 hours to obtain polyurethane prepolymer.

[0051] The hydroxyl groups (-OH) at both ends of hydroxyl-terminated polybutadiene undergo addition condensation polymerization with the isocyanate groups (-NCO) of 4,4'-diphenylmethane diisocyanate to generate a prepolymer with a block structure consisting of alternating soft segments of HTPB and hard segments of urethane. At the same time, unreacted -NCO groups are retained at both ends of the prepolymer.

[0052] In some embodiments, the mass ratio of hydroxyl-terminated polybutadiene to 4,4'-diphenylmethane diisocyanate is 10:(1-3). Insufficient addition of 4,4'-diphenylmethane diisocyanate will prevent the polyurethane prepolymer from reacting sufficiently, while excessive addition will cause the prepolymer to crosslink. Therefore, the mass ratio of hydroxyl-terminated polybutadiene to 4,4'-diphenylmethane diisocyanate is 10:(1-3).

[0053] In some embodiments, the preparation method of organomontmorillonite includes the following steps:

[0054] Dimethyl sulfoxide and water were mixed at a mass ratio of 10:(1-2), montmorillonite was added, and the mixture was stirred at 60°C for 8 hours before centrifugation. The solid product obtained by centrifugation was added to methanol, stirred at room temperature for 50-70 hours, and dried to obtain modified montmorillonite.

[0055] Stearic acid was added to methanol under water bath heating at 60-65℃, followed by modified montmorillonite. After stirring for 20-30 hours, the mixture was centrifuged, washed, and dried to obtain organomontmorillonite.

[0056] In this process, the sulfoxide group of dimethyl sulfoxide can disrupt the interlayer hydrogen bond network of montmorillonite, increasing the interlayer spacing of montmorillonite. The stearate carboxylate group is anchored to the cation site of montmorillonite by electrostatic force, thereby preparing organomontmorillonite.

[0057] In some embodiments, the mass ratio of stearic acid to modified montmorillonite is 1:(2-3). If there is too little stearic acid, its interlayer coverage of montmorillonite will be insufficient, forming a local monolayer. However, if there is too much stearic acid coating montmorillonite, it will hinder the contact between the polyurethane-NCO groups and the carboxyl groups. Therefore, the mass ratio of stearic acid to modified montmorillonite is 1:(2-3).

[0058] The present invention will be further described below by way of specific embodiments.

[0059] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods already existing in the art; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0060] Example 1:

[0061] Under a nitrogen atmosphere, hydroxyl-terminated polybutadiene was heated to 80°C in an oil bath, and then 4,4'-diphenylmethane diisocyanate was heated to melt and added dropwise to the hydroxyl-terminated polybutadiene. The mass ratio of hydroxyl-terminated polybutadiene to 4,4'-diphenylmethane diisocyanate was 10:1. The mixture was kept at the temperature and stirred for 2 hours to obtain a polyurethane prepolymer.

[0062] Dimethyl sulfoxide and water were mixed at a mass ratio of 10:1, montmorillonite was added, and the mixture was stirred at 60°C for 8 hours before centrifugation. The solid product obtained by centrifugation was added to methanol, stirred at room temperature for 50 hours, and dried to obtain modified montmorillonite.

[0063] Stearic acid was added to methanol under a water bath heating condition of 60℃, and then the modified montmorillonite was added. The mass ratio of stearic acid to modified montmorillonite was 1:2. After stirring at the temperature for 20 hours, the mixture was centrifuged, washed, and dried to obtain organomontmorillonite.

[0064] Heat the asphalt to 120°C, add organomontmorillonite (the mass ratio of asphalt to organomontmorillonite is 100:5), and stir for 20 minutes.

[0065] Maintain the temperature at 120℃, add polyurethane prepolymer and stir for 20 minutes, then add chain extender preheated to 70℃. The mass ratio of asphalt, polyurethane prepolymer and chain extender is 100:15:1. Stir for 40 minutes, cool down to 100℃ and stop stirring. Let it stand for 2 hours to obtain modified asphalt.

[0066] The modified asphalt is simultaneously coated on both sides of the base layer, with a thickness of 2mm on each side. The asphalt surface is then sprayed with compressed air, followed by the application of asphalt binder. Before the asphalt binder sets, ceramic sintered sand is sprinkled on top, and the mixture is statically pressed. Then, fine sand is evenly spread and statically pressed again to obtain a protective layer. A protective layer is then applied to the back of the asphalt. After calendering and cooling, the asphalt waterproof membrane is obtained.

[0067] Example 2:

[0068] Under a nitrogen atmosphere, hydroxyl-terminated polybutadiene was heated to 90°C in an oil bath, and then 4,4'-diphenylmethane diisocyanate was heated to melt and added dropwise to the hydroxyl-terminated polybutadiene. The mass ratio of hydroxyl-terminated polybutadiene to 4,4'-diphenylmethane diisocyanate was 10:3. The mixture was kept at the temperature and stirred for 3 hours to obtain a polyurethane prepolymer.

[0069] Dimethyl sulfoxide and water were mixed at a mass ratio of 10:2, montmorillonite was added, and the mixture was stirred at 60°C for 8 hours before centrifugation. The solid product obtained by centrifugation was added to methanol, stirred at room temperature for 70 hours, and dried to obtain modified montmorillonite.

[0070] Stearic acid was added to methanol under a water bath heating condition of 65℃, and then the modified montmorillonite was added. The mass ratio of stearic acid to modified montmorillonite was 1:3. After stirring at the temperature for 30 hours, the mixture was centrifuged, washed, and dried to obtain organomontmorillonite.

[0071] Heat the asphalt to 130°C, add organomontmorillonite (the mass ratio of asphalt to organomontmorillonite is 100:10), and stir for 30 minutes.

[0072] Maintain the temperature at 130℃, add polyurethane prepolymer and stir for 30 minutes, then add chain extender preheated to 80℃. The mass ratio of asphalt, polyurethane prepolymer and chain extender is 100:25:2. Stir for 60 minutes, cool down to 105℃ and stop stirring. Let the mixture stand for 3 hours to obtain modified asphalt.

[0073] The modified asphalt is simultaneously coated on both sides of the base layer, with a thickness of 4mm on each side. The asphalt surface is then sprayed with compressed air, followed by the application of asphalt binder. Before the asphalt binder sets, ceramic sintered sand is sprinkled on top, and the mixture is statically pressed. Then, fine sand is evenly spread and statically pressed again to obtain a protective layer. A protective layer is then applied to the back of the asphalt. After calendering and cooling, the asphalt waterproof membrane is obtained.

[0074] Example 3:

[0075] Consistent with Example 1, except that in the modified asphalt layer, the mass ratio of asphalt, polyurethane prepolymer and organomontmorillonite is 100:15:10.

[0076] Example 4:

[0077] Consistent with Example 1, except that in the modified asphalt layer, the mass ratio of asphalt, polyurethane prepolymer and organomontmorillonite is 100:25:5.

[0078] Example 5:

[0079] Consistent with Example 1, except that in the modified asphalt layer, the mass ratio of asphalt, polyurethane prepolymer and organomontmorillonite is 100:20:8.

[0080] Comparative Example 1:

[0081] Consistent with Example 1, except that montmorillonite is used instead of organomontmorillonite in the modified bitumen layer.

[0082] Comparative Example 2:

[0083] Consistent with Example 1, except that no organomontmorillonite is added to the modified asphalt layer.

[0084] Tests were conducted on Examples 1-5 and Comparative Examples 1 and 2. The specific test contents are as follows:

[0085] Salt spray resistance test: The asphalt waterproof membrane was cut into standard 100mm × 100mm samples, ensuring the surface was free of scratches or contamination. The samples were vertically suspended inside a salt spray test chamber, where a 5% sodium chloride solution was continuously sprayed. The temperature was kept constant at 35℃ ± 1℃, and the relative humidity ≥ 95%, simulating a high-salt-spray coastal environment for 500 hours. The silver nitrate colorimetric method was used; the sample cross-section was immersed in a 0.1mol / L AgNO3 solution, and the Cl- content was determined by the width of the brown precipitate (colorimetric reaction). - The diffusion depth and test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] Referring to the salt spray resistance test results in Table 1, the salt spray resistance of Comparative Example 1 decreased, indicating that the addition of organic montmorillonite can construct a ternary cross-linked network and improve the salt spray resistance of asphalt rolls. The salt spray resistance of Comparative Example 2 decreased significantly compared to Example 1 and Comparative Example 1, indicating that the addition of montmorillonite itself can also improve the salt spray resistance of asphalt rolls.

[0089] Mechanical property testing: The tensile strength of the specimens was tested using a universal testing machine with a clamping distance of 80 mm and a tensile rate of 100 mm / min. The load-displacement curve was continuously recorded until the specimen broke, and the peak force was used to calculate the tensile strength. The peel strength was tested using a PosiTest AT-A adhesion tester. The test results are shown in Table 2.

[0090] Table 2

[0091]

[0092] Referring to the test results in Table 2, the tensile strength and peel strength of Comparative Examples 1 and 2 decreased significantly compared to Example 1, indicating that organomontmorillonite can improve its tensile strength and peel strength by forming a ternary chemical crosslinking network with asphalt and polyurethane prepolymer.

[0093] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A salt-fog resistant bituminous waterproofing sheet, characterized by, The application relates to a modified asphalt waterproofing membrane, which comprises the following parts: a base layer; a modified asphalt layer, which is prepared from asphalt, polyurethane prepolymer, chain extender and organic montmorillonite, coats the upper and lower surfaces of the base layer, and is prepared from hydroxyl-terminated polybutadiene and 4,4'-diphenyl methane diisocyanate; a protective layer, which is prepared from ceramic sintered sand, fine sand and asphalt binder, covers the outer side of the modified asphalt layer on the upper surface of the base layer; and a protective layer, which covers the outer side of the modified asphalt layer on the lower surface of the base layer. The mass ratio of the asphalt, polyurethane prepolymer, chain extender and organic montmorillonite in the modified asphalt layer is 100:(15-25):(1-2):(5-10). The thickness of the modified asphalt layer is 2-4 mm. The base layer is a polyester base or a glass fiber reinforced polyester base, and the protective layer is a polyethylene plastic film. The application further discloses a preparation method of the modified asphalt waterproofing membrane, which comprises the following steps:

2. The bitumen sheet according to claim 1, characterized in that The asphalt is heated to 120-130 DEG C, the organic montmorillonite is added, and stirring is conducted for 20-30 min; the temperature is kept at 120-130 DEG C, the polyurethane prepolymer is added, stirring is conducted for 20-30 min, the chain extender preheated to 70-80 DEG C is added, stirring is conducted for 40-60 min, the temperature is lowered to 100-105 DEG C and stirring is stopped, and standing is conducted for 2-3 h, so that the modified asphalt is obtained; 3. The bitumen sheet according to claim 1, characterized in that The modified asphalt is synchronously coated on the two surfaces of the base layer, the protective layer and the protective layer are sequentially coated, calendering and cooling are conducted, and the asphalt waterproofing membrane is obtained.

4. The bitumen sheet according to claim 1, characterized in that The coating method of the protective layer is as follows:

5. A process for the production of bituminous waterproofing membranes according to any one of claims 1 to 4, characterized in that, The asphalt surface is sprayed by compressed air, the asphalt binder is sprayed, the ceramic sintered sand is scattered before the asphalt binder is initially solidified, static pressure is conducted, the fine sand is uniformly scattered, static pressure is conducted, and the protective layer is obtained. The preparation method of the polyurethane prepolymer comprises the following steps: The hydroxyl-terminated polybutadiene is heated to 80-90 DEG C under a nitrogen atmosphere, the 4,4'-diphenyl methane diisocyanate is heated to melt, is added dropwise into the hydroxyl-terminated polybutadiene, and standing stirring is conducted for 2-3 h, so that the polyurethane prepolymer is obtained. The mass ratio of the hydroxyl-terminated polybutadiene and the 4,4'-diphenyl methane diisocyanate is 10:(1-3).

6. The preparation method according to claim 5, characterized in that, The preparation method of the organic montmorillonite comprises the following steps: The dimethyl sulfoxide and water are mixed according to the mass ratio of 10:(1-2), the montmorillonite is added, stirring is conducted at 60 DEG C for 8 h, centrifugal separation is conducted, the solid product obtained through centrifugal separation is added into methanol, stirring is conducted at room temperature for 50-70 h, and drying is conducted, so that the modified montmorillonite is obtained; 7. The preparation method according to claim 5, characterized in that, The stearic acid is added into methanol under the condition of water bath heating at 60-65 DEG C, then the modified montmorillonite is added, centrifugal separation is conducted after standing stirring for 20-30 h, washing and drying are conducted, and the organic montmorillonite is obtained. The mass ratio of the stearic acid and the modified montmorillonite is 1:(2-3).

8. The preparation method according to claim 7, characterized in that, ​ 9. The preparation method according to claim 5, characterized in that, ​ ​ ​ 10. The method of claim 9, wherein, ​

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