Cement-based repairing mortar material for bridge expansion joints and preparation process of cement-based repairing mortar material

Abstract

The invention relates to the technical field of building materials, and particularly discloses a bridge expansion joint cement-based repairing mortar material and a preparation process thereof. The invention discloses a cement-based repair mortar material for bridge expansion joints. The cement-based repair mortar material is prepared from the following raw materials in parts by weight: 20-30 parts of Portland cement, 1-5 parts of benzoxazine resin, 30-40 parts of sandstone, 0.5-2 parts of nano silicon dioxide, 0.5-2 parts of a water reducing agent, 1-3 parts of hydrated calcium silicate, 15-25 parts of water and 10-15 parts of modified polyurethane, the preparation method comprises the following steps: dispersing the nano silicon dioxide in water, carrying out ultrasonic treatment, uniformly stirring to form a stable suspension, respectively adding the hydrated calcium silicate and the modified polyurethane, uniformly stirring, sequentially adding the Portland cement, the benzoxazine resin and the gravel, and stirring and mixing until the slurry is uniform to obtain the repair mortar material. The composition can be used for repairing bridge expansion joints, and has the advantages of good durability, high compressive strength and the like.

Description

Technical Field

[0001] This application relates to the technical field of building materials. More specifically, it relates to a cement-based repair mortar material for bridge expansion joints and its preparation process. Background Art

[0002] As an important part of the transportation network, the stability and durability of the bridge structure are crucial for traffic safety. However, during the use of the bridge, the expansion joint, as a key part of the bridge structure, is prone to damage and wear due to the long-term influence of various factors such as vehicle loads, temperature changes, and humidity changes. These damages not only affect the aesthetics of the bridge, but more importantly, they may reduce the overall structural safety of the bridge and even lead to traffic accidents.

[0003] To repair these damaged expansion joints, a high-performance repair material is needed. Traditional repair materials, such as ordinary cement mortar, although having a certain repair effect, often cannot meet the requirements of durability and mechanical properties under long-term loads and harsh environmental conditions. Therefore, it is particularly important to develop a new type of high-performance cement-based repair mortar material for bridge expansion joints. Summary of the Invention

[0004] In order to improve the durability of the repair mortar material, this application provides a cement-based repair mortar material for bridge expansion joints and its preparation method.

[0005] In the first aspect, a cement-based repair mortar material for bridge expansion joints provided by this application adopts the following technical scheme: A cement-based repair mortar material for bridge expansion joints includes the following raw materials in parts by weight: 20 - 30 parts of portland cement, 1 - 5 parts of benzoxazine resin, 30 - 40 parts of sand and gravel, 0.5 - 2 parts of nano-silica, 0.5 - 2 parts of water reducer, 1 - 3 parts of calcium silicate hydrate, 15 - 25 parts of water, and 10 - 15 parts of modified polyurethane.

[0006] By adopting the above technical scheme, the high strength, high toughness, and durability of the material are achieved, which is particularly suitable for the long-term service requirements of bridge expansion joints under dynamic loads. The composite cementitious system formed by portland cement and benzoxazine resin not only provides the strength basis of the material in the early stage, but also promotes the densification of cement hydration products through the high-temperature resistance and acid-base corrosion resistance characteristics of benzoxazine resin, significantly reducing the porosity, thereby improving the compressive strength of the material. In addition, the combination of benzoxazine resin and polyurethane further enhances the high-temperature resistance of the material, enabling it to withstand extreme conditions such as sunlight, rain, and temperature changes required for bridge expansion joint repair materials.

[0007] The addition of calcium silicate hydrate fills the microcracks through permeation crystallization, forming a barrier with "self-healing" function and effectively extending the service life of the material. The application of nano-silica enhances the interfacial adhesion force through its close combination with the cement paste. Meanwhile, the secondary hydration of nano-calcium silicate hydrate sol in the pores further forms a dense protective layer, improving the overall performance of the material.

[0008] The addition of modified polyurethane endows the material with high elastic modulus and low-temperature ductility, enabling it to compensate for the thermal expansion and contraction deformation of the concrete matrix, thus ensuring the dynamic stability of the bridge expansion joint. The interaction and synergistic effect among these multiphase composite systems achieve the unity of high strength, high toughness and durability of the material, while maintaining the convenience of construction.

[0009] Optionally, the modified polyurethane comprises the following raw materials in parts by weight: 30-40 parts of polyether polyol, 5-8 parts of bisphenol fluorene, 80-120 parts of N-methylpyrrolidone, 25-35 parts of 4,4'-methylenebis(phenyl isocyanate), 0.5-1.0 part of catalyst, 10-15 parts of chain extender, 10-20 parts of polyetherimide.

[0010] Optionally, the preparation of the modified polyurethane comprises the following steps: The preparation of the modified polyurethane comprises the following steps: (1) Add polyether polyol and bisphenol fluorene into N-methylpyrrolidone, heat to 55-65 °C, stir while introducing nitrogen until completely dissolved, add 4,4'-methylenebis(phenyl isocyanate) and catalyst, stir evenly, then heat to 70-80 °C and continue to react. Keep this temperature for 1-2 h, add the chain extender, raise the temperature to 85-90 °C and continue to react for 2-3 h. Cool to 35-45 °C, add water dropwise and stir, and dry to remove the solvent to obtain the preliminarily modified polyurethane; (2) Dissolve polyetherimide in N-methylpyrrolidone, ultrasonically disperse for 20-30 min, and then mix and stir evenly with the above preliminarily modified polyurethane to obtain the modified polyurethane.

[0011] By adopting the above technical scheme, the introduction of the rigid fluorene group increases the intermolecular force between polymer chains, forms a more compact and ordered network structure, improves the mechanical properties and thermal stability of the polyurethane material, and enables the polyester material to play a better role in improving the performance of the repair mortar material; the synergistic enhancement effect formed by the flexible ether bond on the polyetherimide and the polyurethane chain significantly improves the compressive strength of the material. Meanwhile, the polyetherimide also has good moisture resistance, which can improve the water resistance of the material and further improve the durability of the material.

[0012] Optionally, the chain extender is octafluoro-1,6-hexanediol.

[0013] By adopting the above technical solution, the electronegativity of fluorine atoms forms a strong induced dipole with the carbonyl group, enhancing the intermolecular force; at high temperatures, it can provide sufficient energy for the material to overcome the segmental motion barrier, achieve an ordered arrangement, maintain a good morphology of the material, and improve the high-temperature resistance of the material.

[0014] Optionally, the catalyst is bismuth naphthenate.

[0015] By adopting the above technical solution, the polycondensation reaction of isocyanate and hydroxyl is promoted. Bismuth naphthenate has good catalytic activity, can reduce the generation of side reactions, and has high selectivity for the activation of isocyanate groups, regulating the polymerization reaction rate, making the hard segments and soft segments uniformly dispersed, and improving the mechanical properties and thermal stability of the material.

[0016] Optionally, the sand and gravel has a continuous gradation of 8 - 12 mm.

[0017] By adopting the above technical solution, the repair mortar can obtain a denser pore structure, significantly reduce the risk of shrinkage cracking and improve the compressive strength; its moderate particle size can not only disperse the dynamic load stress, but also form an elastic complement with the cement matrix and modified polyurethane, enhancing the flexibility of the material to adapt to the thermal expansion and contraction deformation of the bridge expansion joint, and improving the durability of the material.

[0018] Optionally, the raw materials further include 0.1 - 0.5 parts of magnesium fluorosilicate.

[0019] By adopting the above technical solution, adding magnesium fluorosilicate can significantly improve the performance of the cement-based repair mortar: firstly, its active components such as fluoride ions can accelerate cement hydration, promote the formation of C-S-H gel and ettringite, improve the early compressive strength and optimize the pore structure, enhancing impermeability and frost resistance; secondly, it can inhibit the alkali-aggregate reaction by consuming free lime, reducing the risk of expansion and cracking of alkali-silica gel; thirdly, the formed dense composite gel can block the penetration of sulfate ions and chloride ions, significantly enhancing the resistance to sulfate erosion and chloride ion corrosion; in addition, appropriate addition can also adjust the setting time, improve the fluidity, and form a "double network structure" synergistically with calcium silicate nanowhiskers, enhancing the flexibility and high-temperature stability of the material, especially suitable for the long-term service requirements of bridge expansion joints in high-corrosion and large-temperature-difference environments.

[0020] In a second aspect, the present application provides a preparation method of a cement-based repair mortar material for a bridge expansion joint, adopting the following technical solution: A preparation method of a cement-based repair mortar material for a bridge expansion joint, comprising the following steps: Disperse nano-silica in water, and after ultrasonic treatment and stirring to form a stable suspension, successively add calcium silicate hydrate and modified polyurethane, stir well, then add Portland cement, benzoxazine resin and sand and gravel, and continue stirring until the slurry is completely uniform, thereby obtaining a repair mortar material.

[0021] In summary, the present application has the following beneficial effects: 1. In the present application, through the composite cementitious system of Portland cement and benzoxazine resin, combined with the permeation crystallization effect of calcium silicate hydrate and the interface enhancement effect of nano-silica, the compressive strength and impermeability of the material are significantly improved, while the porosity and the risk of shrinkage cracking are reduced, realizing long-term durability. The introduction of magnesium fluorosilicate further inhibits the alkali-aggregate reaction and chloride ion erosion, and prolongs the service life of the material.

[0022] 2. In the present application, a rigid-flexible synergistic network structure formed by modified polyurethane through an octafluoro-1,6-hexanediol chain extender is preferably adopted, endowing the material with high elastic modulus and low-temperature ductility, effectively compensating for the deformation caused by thermal expansion and contraction of the bridge expansion joint; the synergistic enhancement effect of polyetherimide and polyurethane significantly improves the compressive strength and ensures the stability of the material under dynamic loads.

[0023] 3. In the method of the present application, calcium silicate hydrate forms a "self-repair" barrier by permeation crystallization to fill microcracks, and nano-silica and calcium silicate hydrate sol undergo secondary hydration to form a dense protective layer, reducing the penetration of external erosion media; benzoxazine resin and magnesium fluorosilicate jointly block the penetration of sulfates and chloride ions, combined with the moisture resistance and high-temperature resistance of modified polyurethane, realizing multiple protection of the material in extreme environments. Specific Embodiments

[0024] The following further details the present application in conjunction with embodiments.

[0025] For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0026] The sand and gravel is ISO standard sand, purchased from Xiamen Aiso Co., Ltd.; the nano-silica is purchased from Hubei Huifu Nano Materials Co., Ltd., model: HB-132; the polyetherimide is purchased from Suzhou Hongkaiyuan Plastic Raw Materials Co., Ltd., grade: 2100; the Portland cement is purchased from Sanhe Yanhong Trading Co., Ltd., product number ZP-001; the polyether polyol is purchased from Jiangsu Haian Petrochemical Factory, model HSH-210; the benzoxazine resin is purchased from Jining Ribiluo Biotechnology Co., Ltd., model BZ-1201.

[0027] Preparation Examples of Raw Materials and / or Intermediates Preparation Example 1 A modified polyurethane, the preparation of which comprises the following steps: (1) Add 30 kg of polyether polyol and 5 kg of bisphenol fluorene to 60 kg of N-methylpyrrolidone, heat to 55 °C, stir while introducing nitrogen until completely dissolved, add 25 kg of 4,4'-methylenebis(phenyl isocyanate) and 0.5 kg of bismuth naphthenate (catalyst), stir evenly, then heat to 70 °C and continue the reaction. Maintain this temperature for 1.5 h, add 10 kg of octafluoro-1,6-hexanediol (chain extender), raise the temperature to 85 °C and continue the reaction for 2.5 h. Cool to 40 °C, dropwise add 10 kg of deionized water, stir for 10 min, then perform vacuum treatment at 80 °C and 0.01 MPa for 12 h to remove the solvent to obtain a preliminarily modified polyurethane; (2) Dissolve 10 kg of polyetherimide in 20 kg of N-methylpyrrolidone, ultrasonically disperse for 20 min, then mix and stir evenly with the above preliminarily modified polyurethane to obtain the modified polyurethane.

[0028] Preparation Example 2 A modified polyurethane, the preparation of which comprises the following steps: (1) Add 35 kg of polyether polyol and 6.5 kg of bisphenol fluorene to 70 kg of N-methylpyrrolidone, heat to 60 °C, stir while introducing nitrogen until completely dissolved, add 30 kg of 4,4'-methylenebis(phenyl isocyanate) and 0.75 kg of bismuth naphthenate, stir evenly, then heat to 75 °C and continue the reaction. Maintain this temperature for 1.5 h, add 12.5 kg of octafluoro-1,6-hexanediol, raise the temperature to 85 °C and continue the reaction for 2.5 h. Cool to 45 °C, dropwise add 10 kg of deionized water, stir for 10 min, then perform vacuum treatment at 80 °C and 0.01 MPa for 12 h to remove the solvent to obtain a preliminarily modified polyurethane; (2) Dissolve 15 kg of polyetherimide in 30 kg of N-methylpyrrolidone, ultrasonically disperse for 25 min, then mix and stir evenly with the above preliminarily modified polyurethane to obtain the modified polyurethane.

[0029] Preparation Example 3 A modified polyurethane, the preparation of which comprises the following steps: (1) Add 40 kg of polyether polyol and 8 kg of bisphenol fluorene to 80 kg of N-methylpyrrolidone, heat to 65 °C, stir while introducing nitrogen until completely dissolved, add 35 kg of 4,4'-methylenebis(phenyl isocyanate) and 1 kg of bismuth naphthenate, stir evenly, then heat to 80 °C and continue the reaction. Maintain this temperature for 2 h, add 15 kg of octafluoro-1,6-hexanediol, raise the temperature to 90 °C and continue the reaction for 3 h. Cool to 40 °C, dropwise add 10 kg of deionized water, stir for 10 min, then perform vacuum treatment at 80 °C and 0.01 MPa for 12 h to remove the solvent to obtain a preliminarily modified polyurethane; (2) Dissolve 20 kg of polyetherimide in 40 kg of N-methylpyrrolidone, ultrasonically disperse it for 30 min, and then mix it with the above preliminarily modified polyurethane and stir evenly to obtain the modified polyurethane.

[0030] Preparation Example 4 A modified polyurethane, different from Preparation Example 1 in that the catalyst added in this preparation example is dibutyltin dilaurate.

[0031] Preparation Example 5 A modified polyurethane, different from Preparation Example 1 in that the chain extender added in this preparation example is polyethylene glycol (PEG-400).

[0032] Comparative Preparation Example 1 A modified polyurethane, different from Preparation Example 1 in that bisphenol fluorene is not added in this preparation example.

[0033] Comparative Preparation Example 2 A modified polyurethane, different from Preparation Example 1 in that polyetherimide is not added in this preparation example. Examples

[0034] Example 1 A cement-based repair mortar material for bridge expansion joints, the preparation comprises the following steps: Take 1 kg of nano-silica and disperse it in 12.5 kg of water, ultrasonically treat it at 300 W for 20 min, stir it at a speed of 600 r / min for 15 min to form a stable suspension, add 3 kg of calcium silicate hydrate and stir evenly, then add 12.5 kg of the modified polyurethane prepared in Preparation Example 1 and continue to stir at the same speed for 10 min. Then add 25 kg of portland cement, 5 kg of benzoxazine resin, 35 kg of sand and gravel, and 1 kg of polycarboxylate superplasticizer PC-303 and stir and mix until the slurry is uniform to obtain the repair mortar material; the sand and gravel is a continuous gradation of 8-12 mm.

[0035] Example 2 A cement-based repair mortar material for bridge expansion joints, the preparation comprises the following steps: Take 0.5 kg of nano-silica and disperse it in 10 kg of water, ultrasonically treat it at 300 W for 20 min, stir it at a speed of 600 r / min for 15 min to form a stable suspension, add 1 kg of calcium silicate hydrate and stir evenly, then add 10 kg of the modified polyurethane prepared in Preparation Example 1 and continue to stir at the same speed for 10 min. Then add 20 kg of portland cement, 2.5 kg of benzoxazine resin, 30 kg of sand and gravel, and 2 kg of polycarboxylate superplasticizer PC-303 and stir and mix until the slurry is uniform to obtain the repair mortar material; the sand and gravel is a continuous gradation of 8-12 mm.

[0036] Example 3 A cement-based repair mortar material for bridge expansion joints, and its preparation includes the following steps: Disperse 2 kg of nano-silica in 15 kg of water, perform ultrasonic treatment at 300 W for 20 min, stir at a speed of 600 r / min for 15 min to form a stable suspension, add 2 kg of calcium silicate hydrate and stir evenly, then add 15 kg of the modified polyurethane prepared in Preparation Example 1 and continue to stir at the same speed for 10 min. Sequentially add 30 kg of portland cement, 1 kg of benzoxazine resin, 40 kg of sand and gravel, 0.5 kg of polycarboxylate water reducer PC-303 and stir and mix until the slurry is uniform to obtain the repair mortar material; the sand and gravel is a continuous gradation of 8-12 mm.

[0037] Example 4 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 2.

[0038] Example 5 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 3.

[0039] Example 6 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 4.

[0040] Example 7 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 5.

[0041] Example 8 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that 0.1 kg of magnesium fluorosilicate is further added in this example, and its preparation includes the following steps: Disperse 1 kg of nano-silica in 12.5 kg of water, perform ultrasonic treatment at 300 W for 20 min, stir at a speed of 600 r / min for 15 min to form a stable suspension, add 3 kg of calcium silicate hydrate and stir evenly, then add 12.5 kg of the modified polyurethane prepared in Preparation Example 1 and continue to stir at the same speed for 10 min. Sequentially add 25 kg of portland cement, 5 kg of benzoxazine resin, 35 kg of sand and gravel, 0.1 kg of magnesium fluorosilicate, 1 kg of polycarboxylate water reducer PC-303 and stir and mix until the slurry is uniform to obtain the repair mortar material; the sand and gravel is a continuous gradation of 8-12 mm.

[0042] Example 9 A cement-based repair mortar material for bridge expansion joints, which is different from Example 8 in that 0.25 kg of magnesium fluorosilicate is added in this example.

[0043] Example 10 A cement-based repair mortar material for bridge expansion joints, which is different from Example 8 in that 0.5 kg of magnesium fluorosilicate is added in this example.

[0044] Comparative example Comparative example 1 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that modified polyurethane is not added in this comparative example.

[0045] Comparative example 2 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the added polyurethane is unmodified. The preparation of the polyurethane includes the following steps: (1) Add 30 kg of polyether polyol to 60 kg of N-methylpyrrolidone and heat to 55 °C. Stir while introducing nitrogen until completely dissolved. Add 25 kg of 4,4'-methylenebis(phenyl isocyanate) and 0.5 kg of bismuth naphthenate (catalyst), stir evenly, then heat to 70 °C and continue to react. Keep this temperature for 1.5 h. Add 10 kg of octafluoro-1,6-hexanediol (chain extender), raise the temperature to 85 °C and continue to react for 2.5 h. Cool to 40 °C, dropwise add 10 kg of deionized water and stir for 10 min. Then, under vacuum at 80 °C and 0.01 MPa for 12 h to remove the solvent to obtain polyurethane.

[0046] Comparative example 3 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the modified polyurethane prepared in Comparative Preparation Example 1 is used in this comparative example.

[0047] Comparative example 4 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that the modified polyurethane prepared in Comparative Preparation Example 2 is used in this comparative example.

[0048] Comparative example 5 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that benzoxazine resin is not added in this comparative example.

[0049] Comparative example 6 A cement-based repair mortar material for bridge expansion joints, which is different from Example 1 in that calcium hydrosilicate is not added in this comparative example.

[0050] Performance detection test Detection method Compressive strength test: Use 100mm×100mm×100mm cube specimens, with a loading rate of 1 Mpa / s. According to GB / T 17671-2021 "Test Method for Strength of Cement Mortar", test the compressive strength of the specimens at 25°C, 200°C, and 500°C respectively.

[0051] Durability test: (1) Chloride ion penetration coefficient: Make specimens according to GB / T 50082-2009 "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete", and test the Cl - diffusion coefficient; (2) Freeze-thaw cycle test: According to the rapid freeze-thaw method in GB / T 50082-2009 "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete", test the frost resistance of the specimens. When the freeze-thaw cycle is carried out, the freezing temperature and melting temperature of the specimens are -20°C to -15°C and 6°C - 8°C respectively. The time for one freeze-thaw cycle is 4h, and the specimens are subjected to 200 freeze-thaw cycles. Test the mass of the specimens before and after the test, and calculate the mass loss rate. Table 1 Test and detection results Combined with Examples 1-3 and Comparative Examples 1-2 and Table 1, it can be seen that the test data of Examples 1-3 are better than those of Comparative Examples 1-2 in all aspects, indicating that using the method of this application to modify polyurethane and then adding it can obtain mortar materials with better durability and higher compressive strength; combined with the test data of Example 1 and Comparative Examples 1-2, the compressive strength of the specimens added with modified polyurethane has increased significantly, and the strength retention rate at different temperatures is also higher. The addition of modified polyurethane significantly enhances the mechanical properties and thermal stability of the materials.

[0052] Combined with Examples 1-3 and Comparative Examples 3-4 and Table 1, it can be seen that the test data of Examples 1-3 are better than those of Comparative Examples 3-4 in all aspects, indicating that the modified polyurethane prepared by the method of this application has a good performance improvement effect, improving the mechanical properties and durability of the materials.

[0053] Combined with Example 1 and Comparative Example 5 and Table 1, it can be seen that the test data of Examples 1-3 are better than those of Comparative Example 5 in all aspects, indicating that benzoxazine resin has good thermal stability and anti-shrinkage properties, and can help the mortar material maintain a better original form under extreme conditions, improving the durability of the materials.

[0054] Combined with Example 1 and Comparative Example 6 and Table 1, it can be seen that the test data of Examples 1-3 are better than those of Comparative Example 6 in all aspects, indicating that calcium silicate hydrate can fill microcracks and form a "self-healing" barrier, improving the mechanical properties and durability of the materials.

[0055] Combined with Examples 1-6 and Table 1, it can be seen that the test data of Examples 1-5 are all better than those of Example 6, indicating that the choice of catalyst affects the modification process of modified polyurethane. Selecting bismuth naphthenate has a better catalytic effect than other catalysts, reduces the generation of side reactions, and improves the mechanical properties and stability of the final product.

[0056] Combined with Example 1 and Example 7 and Table 1, it can be seen that the test data of Example 1 are all better than those of Example 7, indicating that the chain extender octafluoro-1,6-hexanediol can provide enough energy for the material to overcome the chain segment movement barrier, achieve an orderly arrangement, maintain a better morphology of the material, and improve the high-temperature resistance of the material.

[0057] Combined with Example 1 and Examples 8-10 and Table 1, it can be seen that the test data of Examples 8-10 are all better than those of Example 1, indicating that the addition of magnesium fluorosilicate can interact with the raw materials in the material, enhance the mechanical properties of the material, and at the same time prevent the entry of corrosive substances, improving the durability of the material.

[0058] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A cement-based repair mortar material for bridge expansion joints, characterized in that, The invention comprises the following raw materials in parts by weight: 20-30 parts of silicate cement, 1-5 parts of benzoxazine resin, 30-40 parts of sand and gravel, 0.5-2 parts of nano silicon dioxide, 0.5-2 parts of water reducing agent, 1-3 parts of hydrated calcium silicate, 10-15 parts of water and 10-15 parts of modified polyurethane.

2. The cement-based repair mortar material for bridge expansion joints according to claim 1, characterized in that: The modified polyurethane comprises the following raw materials in parts by weight: 30-40 parts of polyether polyol, 5-8 parts of bisphenol fluorene, 80-120 parts of N-methyl pyrrolidone, 25-35 parts of 4,4'-methylenebis(phenyl isocyanate), 0.5-1.0 parts of catalyst, 10-15 parts of chain extender, and 10-20 parts of polyetherimide.

3. A cement-based repair mortar material for bridge expansion joints according to claim 1, characterized in that: The modified polyurethane preparation comprises the following steps: (1) Add polyether polyol and bisphenol fluorene to N-methylpyrrolidone and heat to 55-65°C, introduce nitrogen while stirring until completely dissolved, add 4,4'-methylenebis(phenyl isocyanate) and catalyst and stir evenly, heat to 70-80°C to continue the reaction, keep the temperature for 1-2h, add chain extender and heat to 85-90°C to continue the reaction for 2-3h, cool to 35-45°C, add water dropwise and stir, dry and remove the solvent to obtain a preliminarily modified polyurethane; (2) Dissolve polyetherimide in N-methylpyrrolidone and disperse it ultrasonically for 20-30 minutes, then mix and stir with the above-mentioned preliminarily modified polyurethane to obtain modified polyurethane.

4. A cement-based repair mortar material for bridge expansion joints according to claim 2, characterized in that: The chain extender is octafluoro-1,6-hexanediol.

5. The cement-based repair mortar material for bridge expansion joints according to claim 3, characterized in that: The catalyst is bismuth naphthenate.

6. The cement-based repair mortar material for bridge expansion joints according to claim 1, characterized in that: The sand and gravel are continuously graded in the range of 8-12 mm.

7. A cement-based repair mortar material for bridge expansion joints according to claim 1, characterized in that: The raw materials also include 0.1-0.5 parts of magnesium fluorosilicate.

8. A method for preparing a cement-based repair mortar material for bridge expansion joints according to any one of claims 1 to 7, comprising the following steps: Nano-silicon dioxide is dispersed in water, and after ultrasonic treatment and stirring to form a stable suspension, calcium silicate hydrate and modified polyurethane are added in sequence and stirred thoroughly, and then silicate cement, benzoxazine resin and sand and gravel are added and stirred continuously until the slurry is completely uniform, thereby obtaining a repair mortar material.

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