A cement-based repair mortar material for bridge expansion joints and its preparation process

Abstract

This application relates to the field of building materials technology, specifically disclosing a cement-based repair mortar material for bridge expansion joints and its preparation process. The cement-based repair mortar material for bridge expansion joints comprises the following raw materials in parts by weight: 20-30 parts silicate cement, 1-5 parts benzoxazine resin, 30-40 parts sand and gravel, 0.5-2 parts nano-silica, 0.5-2 parts water-reducing agent, 1-3 parts hydrated calcium silicate, 15-25 parts water, and 10-15 parts modified polyurethane. The preparation method is as follows: nano-silica is dispersed in water, ultrasonically treated, and stirred until a stable suspension is formed. Hydrated calcium silicate and modified polyurethane are added separately and stirred until homogeneous. Then, silicate cement, benzoxazine resin, and sand and gravel are added sequentially and stirred until the slurry is homogeneous, thus obtaining the repair mortar material. The composition of this application can be used for repairing bridge expansion joints, and it has advantages such as good durability and high compressive strength.

Description

Technical Field

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

[0002] As a crucial component of transportation networks, the stability and durability of bridge structures are vital for traffic safety. However, during bridge use, expansion joints, being critical parts of the bridge structure, are prone to damage and wear due to the long-term effects of vehicle loads, temperature variations, humidity changes, and other factors. This damage not only affects the aesthetics of the bridge but, more importantly, can reduce its overall structural safety 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, while offering some repair effect, often fail to meet the requirements for durability and mechanical properties under long-term loads and harsh environmental conditions. Therefore, developing a new, high-performance cement-based repair mortar material for bridge expansion joints is particularly important. Summary of the Invention

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

[0005] Firstly, this application provides a cement-based repair mortar material for bridge expansion joints, which adopts the following technical solution:

[0006] A cement-based repair mortar material for bridge expansion joints comprises the following raw materials in parts by weight: 20-30 parts silicate cement, 1-5 parts benzoxazine resin, 30-40 parts sand and gravel, 0.5-2 parts nano silica, 0.5-2 parts water-reducing agent, 1-3 parts hydrated calcium silicate, 15-25 parts water, and 10-15 parts modified polyurethane.

[0007] By adopting the above technical solutions, high strength, high toughness, and durability of the material are achieved, making it particularly suitable for the long-term service requirements of bridge expansion joints under dynamic loads. The composite cementitious system formed by silicate cement and benzoxazine resin not only provides the material's early strength foundation but also promotes the densification of cement hydration products through the high-temperature resistance and acid and alkali corrosion resistance of benzoxazine resin, significantly reducing porosity and thus improving the material's compressive strength. Furthermore, the combination of benzoxazine resin and polyurethane further enhances the material's high-temperature resistance, enabling it to withstand the extreme conditions such as sunlight, rain, and temperature changes encountered by bridge expansion joint repair materials.

[0008] The addition of hydrated calcium silicate fills microcracks through penetration and crystallization, forming a barrier with "self-healing" function, effectively extending the service life of the material. The application of nano-silica enhances interfacial adhesion through its tight bonding with cement paste. At the same time, the secondary hydration of nano-hydrated calcium silicate sol in the pores further forms a dense protective layer, improving the overall performance of the material.

[0009] 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, thereby ensuring the dynamic stability of bridge expansion joints. The interaction and synergistic effect among these multiphase composite systems achieve a balance between high strength, high toughness, and durability in the material, while maintaining ease of construction.

[0010] Optionally, the modified polyurethane comprises the following raw materials in parts by weight:

[0011] 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 parts of catalyst, 10-15 parts of chain extender, and 10-20 parts of polyether imide.

[0012] Optionally, the preparation of the modified polyurethane includes the following steps:

[0013] The preparation of the modified polyurethane includes the following steps:

[0014] (1) Add polyether polyol and bisphenol fluorene to N-methylpyrrolidone and heat to 55-65°C. Stir while passing nitrogen gas through until completely dissolved. Add 4,4'-methylenebis(phenyl isocyanate) and catalyst and stir evenly. Heat to 70-80°C and continue the reaction. Maintain this temperature for 1-2 hours. Add chain extender and heat to 85-90°C and continue the reaction for 2-3 hours. Cool to 35-45°C and add water dropwise while stirring. Dry and remove solvent to obtain preliminarily modified polyurethane.

[0015] (2) After dissolving polyetherimide in N-methylpyrrolidone, ultrasonically disperse it for 20-30 min and then mix it with the preliminarily modified polyurethane to obtain the modified polyurethane.

[0016] By adopting the above technical solution, the introduction of fluorene groups with rigid structures increases the interaction force between polymer chains, forming a more compact and ordered network structure, which improves the mechanical properties and thermal stability of polyurethane materials, enabling polyester materials to play a better role in performance enhancement in repair mortar materials; the synergistic reinforcement effect formed by polyetherimide and the flexible ether bonds on the polyurethane chain significantly improves the compressive strength of the material, while polyetherimide also has good moisture resistance, which can improve the water resistance of the material, thereby improving the durability of the material.

[0017] Optionally, the chain extender is octafluoro-1,6-hexanediol.

[0018] By adopting the above technical solution, the electronegativity of fluorine atoms forms a strong induced dipole with carbonyl groups, enhancing intramolecular forces; at high temperatures, it can provide sufficient energy to overcome the potential barrier of chain segment movement, achieve orderly arrangement, maintain the material's good morphology, and improve the material's high-temperature resistance.

[0019] Optionally, the catalyst is bismuth naphthenate.

[0020] By adopting the above technical solution, the polycondensation reaction between isocyanate and hydroxyl groups is promoted. Bismuth naphthenate has good catalytic activity, which can reduce the generation of side reactions. In addition, it has high selectivity for the activation of isocyanate groups, regulates the polymerization reaction rate, makes hard segments and soft segments uniformly dispersed, and improves the mechanical properties and thermal stability of the material.

[0021] Optionally, the sand and gravel are 8-12mm continuously graded.

[0022] By adopting the above technical solutions, the repair mortar can obtain a denser pore structure, significantly reducing the risk of shrinkage cracking and improving compressive strength. Its moderate particle size can not only disperse dynamic load stress, but also form elastic complementarity with cement matrix and modified polyurethane, enhancing the material's flexibility to adapt to the thermal expansion and contraction deformation of bridge expansion joints and improving the material's durability.

[0023] Optionally, the raw material may also include 0.1-0.5 parts of magnesium fluorosilicate.

[0024] By adopting the above technical solution, the addition of magnesium fluorosilicate can significantly improve the performance of cement-based repair mortar: Firstly, its active components, such as fluoride ions, can accelerate cement hydration, promote the formation of CSH gel and ettringite, improve early compressive strength, optimize pore structure, and enhance impermeability and freeze-thaw resistance; Secondly, by consuming free lime, it inhibits alkali-aggregate reaction and reduces the risk of alkali-silicic acid gel expansion and cracking; Thirdly, the formed dense composite gel can block the penetration of sulfate and chloride ions, significantly improving the resistance to sulfate attack and chloride ion corrosion; In addition, appropriate addition can also adjust the setting time, improve fluidity, and synergistically form a "dual network structure" with nano-calcium silicate, enhancing the material's flexibility and high-temperature stability, making it particularly suitable for the long-term service requirements of bridge expansion joints in highly corrosive and large temperature difference environments.

[0025] Secondly, this application provides a method for preparing a cement-based repair mortar material for bridge expansion joints, using the following technical solution:

[0026] A method for preparing a cement-based repair mortar material for bridge expansion joints includes the following steps:

[0027] Nano-silica is dispersed in water, and after ultrasonic treatment and stirring, a stable suspension is formed. Then, hydrated calcium silicate and modified polyurethane are added in sequence and stirred thoroughly. Silicate cement, benzoxazine resin and sand are added and stirring is continued until the slurry is completely homogeneous, thus obtaining the repair mortar material.

[0028] In summary, this application has the following beneficial effects:

[0029] 1. This application utilizes a composite cementitious system of silicate cement and benzoxazine resin, combining the penetrating crystallization effect of hydrated calcium silicate with the interfacial reinforcement effect of nano-silica, to significantly improve the compressive strength and impermeability of the material, while reducing porosity and the risk of shrinkage cracking, thus achieving long-term durability. The introduction of magnesium fluorosilicate further inhibits alkali-aggregate reaction and chloride ion attack, extending the service life of the material.

[0030] 2. In this application, a rigid-flexible synergistic network structure formed by modified polyurethane through octafluoro-1,6-hexanediol chain extender is preferred, which endows the material with high elastic modulus and low-temperature ductility, effectively compensating for the deformation of bridge expansion joints caused by thermal expansion and contraction; the synergistic reinforcement effect of polyetherimide and polyurethane significantly improves compressive strength and ensures the stability of the material under dynamic loads.

[0031] 3. The method of this application involves hydrated calcium silicate filling microcracks through infiltration crystallization to form a "self-healing" barrier, and nano-silica and hydrated calcium silicate sol undergoing secondary hydration to form a dense protective layer, reducing the penetration of external corrosive media; benzoxazine resin and magnesium fluorosilicate jointly block the penetration of sulfate and chloride ions, and combined with the moisture resistance and high temperature resistance of modified polyurethane, the material achieves multiple protections in extreme environments. Detailed Implementation

[0032] The present application will be further described in detail below with reference to the embodiments.

[0033] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] The sand and gravel were ISO standard sand, purchased from Xiamen Aisiou Co., Ltd.; nano silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., model: HB-132; polyetherimide was purchased from Suzhou Hongkaiyuan Plastic Raw Materials Co., Ltd., grade: 2100; silicate cement was purchased from Sanhe Yanhong Trading Co., Ltd., item number ZP-001; polyether polyol was purchased from Jiangsu Haian Petrochemical Plant, model: HSH-210; benzoxazine resin was purchased from Jining Ribuluo Biotechnology Co., Ltd., model: BZ-1201.

[0035] Preparation examples of raw materials and / or intermediates

[0036] Preparation Example 1

[0037] A modified polyurethane, prepared by the following steps:

[0038] (1) Add 30 kg of polyether polyol and 5 kg of bisphenol fluorene to 60 kg of N-methylpyrrolidone and heat to 55 °C while stirring with nitrogen gas until completely dissolved. Add 25 kg of 4,4'-methylenebis(phenyl isocyanate) and 0.5 kg of bismuth naphthenate (catalyst) and stir evenly. 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) and heat to 85 °C and continue the reaction for 2.5 h. Cool to 40 °C and add 10 kg of deionized water dropwise. Stir for 10 min and then vacuum treat at 80 °C and 0.01 MPa for 12 h to remove solvent and obtain preliminarily modified polyurethane.

[0039] (2) Dissolve 10 kg of polyetherimide in 20 kg of N-methylpyrrolidone, then ultrasonically disperse for 20 min, and then mix and stir evenly with the preliminarily modified polyurethane to obtain the modified polyurethane.

[0040] Preparation Example 2

[0041] A modified polyurethane, prepared by the following steps:

[0042] (1) Add 35 kg of polyether polyol and 6.5 kg of bisphenol fluorene to 70 kg of N-methylpyrrolidone and heat to 60 °C while stirring with nitrogen gas until completely dissolved. Add 30 kg of 4,4'-methylenebis(phenyl isocyanate) and 0.75 kg of bismuth naphthenate and stir evenly. Heat to 75 °C and continue the reaction. Maintain this temperature for 1.5 h. Add 12.5 kg of octafluoro-1,6-hexanediol and heat to 85 °C and continue the reaction for 2.5 h. Cool to 45 °C and add 10 kg of deionized water dropwise. Stir for 10 min and then vacuum treat at 80 °C and 0.01 MPa for 12 h to remove the solvent and obtain the preliminarily modified polyurethane.

[0043] (2) Dissolve 15 kg of polyetherimide in 30 kg of N-methylpyrrolidone, then ultrasonically disperse for 25 min, and then mix and stir evenly with the above-mentioned pre-modified polyurethane to obtain modified polyurethane.

[0044] Preparation Example 3

[0045] A modified polyurethane, prepared by the following steps:

[0046] (1) Add 40 kg of polyether polyol and 8 kg of bisphenol fluorene to 80 kg of N-methylpyrrolidone and heat to 65 °C. Stir while passing nitrogen gas through until completely dissolved. Add 35 kg of 4,4'-methylenebis(phenyl isocyanate) and 1 kg of bismuth naphthenate and stir evenly. Heat to 80 °C and continue the reaction. Maintain this temperature for 2 h. Add 15 kg of octafluoro-1,6-hexanediol and heat to 90 °C and continue the reaction for 3 h. Cool to 40 °C and add 10 kg of deionized water dropwise. Stir for 10 min. Then, vacuum treat at 80 °C and 0.01 MPa for 12 h to remove the solvent and obtain the preliminarily modified polyurethane.

[0047] (2) Dissolve 20 kg of polyetherimide in 40 kg of N-methylpyrrolidone, then ultrasonically disperse for 30 min, and then mix and stir evenly with the preliminarily modified polyurethane to obtain modified polyurethane.

[0048] Preparation Example 4

[0049] A modified polyurethane, which differs from Preparation Example 1 in that the catalyst added in this preparation example is dibutyltin dilaurate.

[0050] Preparation Example 5

[0051] A modified polyurethane, which differs from Preparation Example 1 in that the chain extender added in this preparation example is polyethylene glycol (PEG-400).

[0052] Comparative Preparation Example 1

[0053] A modified polyurethane, which differs from Preparation Example 1 in that bisphenol fluorene was not added in this preparation example.

[0054] Comparative Preparation Example 2

[0055] A modified polyurethane, which differs from Preparation Example 1 in that no polyetherimide was added in this preparation example.

[0056] Example

[0057] Example 1

[0058] A cement-based repair mortar material for bridge expansion joints is prepared by the following steps:

[0059] 1 kg of nano-silica was dispersed in 12.5 kg of water and ultrasonically treated at 300 W for 20 min. After stirring at 600 r / min for 15 min, a stable suspension was formed. 3 kg of hydrated calcium silicate was added and stirred evenly. Then, 12.5 kg of the modified polyurethane prepared in Preparation Example 1 was added and stirred at the same speed for 10 min. 25 kg of silicate cement, 5 kg of benzoxazine resin, 35 kg of sand and gravel, and 1 kg of polycarboxylate superplasticizer PC-303 were added in sequence and stirred until the slurry was uniform to obtain the repair mortar material. The sand and gravel were of 8-12 mm continuous gradation.

[0060] Example 2

[0061] A cement-based repair mortar material for bridge expansion joints is prepared by the following steps:

[0062] 0.5 kg of nano-silica was dispersed in 10 kg of water and ultrasonically treated at 300 W for 20 min. After stirring at 600 r / min for 15 min, a stable suspension was formed. 1 kg of hydrated calcium silicate was added and stirred evenly. Then, 10 kg of the modified polyurethane prepared in Preparation Example 1 was added and stirred at the same speed for 10 min. 20 kg of silicate cement, 2.5 kg of benzoxazine resin, 30 kg of sand and gravel, and 2 kg of polycarboxylate superplasticizer PC-303 were added in sequence and stirred until the slurry was uniform to obtain the repair mortar material. The sand and gravel were of 8-12 mm continuous gradation.

[0063] Example 3

[0064] A cement-based repair mortar material for bridge expansion joints is prepared by the following steps:

[0065] 2 kg of nano-silica was dispersed in 15 kg of water and ultrasonically treated at 300 W for 20 min. After stirring at 600 r / min for 15 min, a stable suspension was formed. 2 kg of hydrated calcium silicate was added and stirred evenly. Then, 15 kg of the modified polyurethane prepared in Preparation Example 1 was added and stirred at the same speed for 10 min. 30 kg of silicate cement, 1 kg of benzoxazine resin, 40 kg of sand and gravel, and 0.5 kg of polycarboxylate superplasticizer PC-303 were added in sequence and stirred until the slurry was uniform to obtain the repair mortar material. The sand and gravel were 8-12 mm continuously graded.

[0066] Example 4

[0067] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 2.

[0068] Example 5

[0069] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 3.

[0070] Example 6

[0071] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 4.

[0072] Example 7

[0073] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that the modified polyurethane used in this example is the one prepared in Preparation Example 5.

[0074] Example 8

[0075] A cement-based repair mortar material for bridge expansion joints, differing from Example 1 in that 0.1 kg of magnesium fluorosilicate is added in this example, and its preparation includes the following steps:

[0076] 1 kg of nano-silica was dispersed in 12.5 kg of water and ultrasonically treated at 300 W for 20 min. After stirring at 600 r / min for 15 min, a stable suspension was formed. 3 kg of hydrated calcium silicate was added and stirred evenly. Then, 12.5 kg of the modified polyurethane prepared in Preparation Example 1 was added and stirred at the same speed for 10 min. 25 kg of silicate cement, 5 kg of benzoxazine resin, 35 kg of sand and gravel, 0.1 kg of magnesium fluorosilicate, and 1 kg of polycarboxylate superplasticizer PC-303 were added in sequence and stirred until the slurry was uniform to obtain the repair mortar material. The sand and gravel were of 8-12 mm continuous gradation.

[0077] Example 9

[0078] A cement-based repair mortar material for bridge expansion joints, which differs from Example 8 in that 0.25 kg of magnesium fluorosilicate is added in this example.

[0079] Example 10

[0080] A cement-based repair mortar material for bridge expansion joints, which differs from Example 8 in that 0.5 kg of magnesium fluorosilicate is added in this example.

[0081] Comparative Example

[0082] Comparative Example 1

[0083] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that no modified polyurethane is added in this comparative example.

[0084] Comparative Example 2

[0085] A cement-based repair mortar material for bridge expansion joints, differing from Example 1 in that the polyurethane added in this comparative example is unmodified, and the preparation of the polyurethane includes the following steps:

[0086] (1) Add 30 kg of polyether polyol to 60 kg of N-methylpyrrolidone and heat to 55 °C. Stir while introducing nitrogen gas until completely dissolved. Add 25 kg of 4,4'-methylenebis(phenyl isocyanate) and 0.5 kg of bismuth naphthenate (catalyst) and stir evenly. 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) and heat to 85 °C and continue the reaction for 2.5 h. Cool to 40 °C and add 10 kg of deionized water dropwise. Stir for 10 min and then vacuum treat at 80 °C and 0.01 MPa for 12 h to remove solvent and obtain polyurethane.

[0087] Comparative Example 3

[0088] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that this comparative example uses the modified polyurethane prepared in Comparative Preparation Example 1.

[0089] Comparative Example 4

[0090] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that this comparative example uses the modified polyurethane prepared in Comparative Preparation Example 2.

[0091] Comparative Example 5

[0092] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that benzoxazine resin is not added in this comparative example.

[0093] Comparative Example 6

[0094] A cement-based repair mortar material for bridge expansion joints, which differs from Example 1 in that calcium silicate hydrate is not added in this comparative example.

[0095] Performance testing

[0096] Detection methods

[0097] Compressive strength test: 100mm×100mm×100mm cubic specimens were used, and the loading rate was 1Mpa / s. The compressive strength of the specimens was tested at 25℃, 200℃ and 500℃ respectively according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar".

[0098] Durability testing: (1) Chloride ion permeability coefficient: Specimens were prepared according to GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", and the chloride ion permeability of the specimens was tested. - Diffusion coefficient;

[0099] (2) Freeze-thaw cycle test: The freeze resistance of the specimens was tested by the rapid freezing method in GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". During the freeze-thaw cycle, the freezing temperature and thawing temperature of the specimens were -20℃~-15℃ and 6℃-8℃, respectively. The time for one freeze-thaw cycle was 4 hours. After 200 freeze-thaw cycles, the mass of the specimens before and after the test was tested and the mass loss rate was calculated.

[0100] Table 1 Test Results

[0101]

[0102] Based on Examples 1-3 and Comparative Examples 1-2, and in conjunction with Table 1, it can be seen that the test data of Examples 1-3 are all superior to those of Comparative Examples 1-2, indicating that modifying polyurethane using the method of this application can result in mortar materials with better durability and higher compressive strength. Based on the test data of Examples 1 and Comparative Examples 1-2, the compressive strength of the specimens with modified polyurethane is significantly improved, 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 material.

[0103] As can be seen from Examples 1-3 and Comparative Examples 3-4, and Table 1, the test data of Examples 1-3 are all better than those of Comparative Examples 3-4, indicating that the modified polyurethane prepared by the method of this application has a better performance improvement effect, and improves the mechanical properties and durability of the material.

[0104] Combining Example 1 and Comparative Example 5 with Table 1, it can be seen that the test data of Examples 1-3 are all better than those of Comparative Example 5, indicating that benzoxazine resin has better thermal stability and shrinkage resistance, and can help mortar materials maintain a better original shape and improve the durability of materials under extreme conditions.

[0105] Combining Example 1 and Comparative Example 6 with Table 1, it can be seen that the test data of Examples 1-3 are all better than those of Comparative Example 6, indicating that calcium silicate hydrate can fill microcracks, form a "self-healing" barrier, and improve the mechanical properties and durability of the material.

[0106] As can be seen from Examples 1-6 and Table 1, the experimental 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. 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.

[0107] Combining Examples 1 and 7 with Table 1, it can be seen that the experimental data of Example 1 are all better than those of Example 7, indicating that the chain extender octafluoro-1,6-hexanediol can provide sufficient energy for the material to overcome the potential barrier of chain segment movement, achieve orderly arrangement, maintain the material's good morphology, and improve the material's high-temperature resistance.

[0108] Combining Examples 1 and 8-10 with 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, prevent the entry of corrosive substances, and improve the durability of the material.

[0109] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A cement-based repair mortar material for bridge expansion joints, characterized in that, The raw materials include the following parts by weight: 20-30 parts silicate cement, 1-5 parts benzoxazine resin, 30-40 parts sand and gravel, 0.5-2 parts nano-silica, 0.5-2 parts water-reducing agent, 1-3 parts hydrated calcium silicate, 10-15 parts water, and 10-15 parts modified polyurethane; the modified polyurethane comprises the following 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 parts of catalyst, 10-15 parts of chain extender, and 10-20 parts of polyether imide; The preparation of the modified polyurethane includes the following steps: (1) Add polyether polyol and bisphenol fluorene to N-methylpyrrolidone and heat to 55-65°C. Stir while passing nitrogen gas through until completely dissolved. Add 4,4'-methylenebis(phenyl isocyanate) and catalyst and stir evenly. Heat to 70-80°C and continue the reaction. Maintain this temperature for 1-2 hours. Add chain extender and heat to 85-90°C and continue the reaction for 2-3 hours. Cool to 35-45°C and add water dropwise while stirring. Dry and remove solvent to obtain preliminarily modified polyurethane. (2) After dissolving polyetherimide in N-methylpyrrolidone, ultrasonically disperse it for 20-30 min and then mix it with the preliminarily modified polyurethane to obtain the modified polyurethane.

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

3. The cement-based repair mortar material for bridge expansion joints according to claim 1, characterized in that: The catalyst is bismuth naphthenate.

4. The cement-based repair mortar material for bridge expansion joints according to claim 1, characterized in that: The sand and gravel have a continuous gradation of 8-12mm.

5. The 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.

6. A method for preparing a cement-based repair mortar material for bridge expansion joints according to any one of claims 1-4, comprising the following steps: Nano-silica is dispersed in water, and after ultrasonic treatment and stirring, a stable suspension is formed. Then, hydrated calcium silicate and modified polyurethane are added in sequence and stirred thoroughly. Silicate cement, benzoxazine resin and sand are added and stirring is continued until the slurry is completely homogeneous, thus obtaining the repair mortar material.

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