Polyurethane composite material for prestressed high-strength steel wire reinforcement and preparation method thereof

Abstract

This invention discloses a polyurethane composite material for prestressed high-strength steel wire reinforcement and its preparation method, belonging to the field of polyurethane composite material technology. This invention synergistically introduces halloysite nanotubes and hydroxyl-terminated polysilsesquioxane into the polyurethane composite system. Halloysite nanotubes function as crack bridging, micropore filling, and stress transfer agents, while hydroxyl-terminated polysilsesquioxane participates in polyurethane crosslinking to form a cage-like rigid network. Simultaneously, metakaolinite, as an active aluminosilicate mineral filler, improves the compactness of the composite system, the structure of the interfacial transition zone, and its synergistic effect with cement-based components, thereby enhancing the compressive strength, crack resistance, interfacial bonding performance, and durability of the composite material. The polyurethane composite material of this invention is particularly suitable for prestressed high-strength steel wire reinforcement of concrete beams.

Description

Technical Field

[0001] This invention relates to the field of polyurethane composite materials technology, specifically to polyurethane composite materials for prestressed high-strength steel wire reinforcement and their preparation methods. Background Technology

[0002] Prestressed high-strength steel wire reinforcement technology, with its advantages of clear stress distribution, convenient construction, and minimal damage to the original structure, has become the mainstream technique for strengthening and repairing reinforced concrete beams, bridge flexural members, and similar civil engineering structures. The load-bearing performance of this reinforcement system depends not only on the mechanical properties of the prestressed high-strength steel wire itself, but also on the composite material reinforcement layer that wraps around the wire, transmits tensile stress, and forms an integral working synergy with the original concrete matrix. As the key interface medium connecting the prestressed high-strength steel wire and the concrete structure, the mechanical strength, toughness, interfacial bonding performance, and long-term durability of the composite material reinforcement layer directly determine the force transmission efficiency, deformation coordination, and service life of the reinforcement system.

[0003] Currently, the commonly used prestressed high-strength steel wire reinforcement materials in engineering are mainly ordinary polymer mortar, epoxy repair materials, and conventional polyurethane composites. However, these materials have several technical shortcomings in practical applications: Inorganic mortar materials, although having high compressive strength, are brittle and have poor toughness. Under the coupled effects of repeated vehicle loads, temperature stress, and freeze-thaw cycles, they are prone to the initiation and continuous propagation of microcracks, leading to cracking and peeling of the reinforcement layer and loss of its load-bearing protective function. Epoxy materials have good toughness and adhesion, but lack rigidity and have poor dimensional stability. They also have limited resistance to damp heat aging and weathering, and are prone to softening, yellowing, and interface debonding during long-term service. Conventional polyurethane composites, although possessing good flexibility and workability, have relatively low strength and poor compatibility with inorganic matrices, making it difficult to meet the high load-bearing and high adhesion requirements of prestressed reinforcement systems.

[0004] More significantly, existing reinforcement materials generally suffer from insufficient interfacial compatibility: the interfacial bond strength between the material and the concrete matrix, as well as the prestressed high-strength steel wire, is low, and the interfacial transition zone is loose and porous. Under long-term loads, humid heat corrosion, or salt spray environments, interfacial debonding, slippage, or even peeling can easily occur, resulting in ineffective prestress transfer and a lack of coordinated stress distribution between the steel wire and concrete, significantly reducing the reinforcement effect. Furthermore, existing high-strength polyurethane modifications mostly employ single nanofillers or conventional coupling agents, failing to be specifically optimized for the unique service scenarios of prestressed high-strength steel wires characterized by "high stress, long cycles, and strong interfaces." This makes it difficult to simultaneously improve strength, toughness, interfacial performance, and durability, thus failing to meet the long-term safe service requirements of important structures such as bridges and industrial buildings.

[0005] Therefore, developing a special composite material that combines high mechanical strength, excellent crack resistance and toughness, superior interfacial bonding performance, good water and weather resistance, and construction adaptability is of great engineering value in solving the technical problems of existing materials in prestressed high-strength steel wire reinforcement systems, such as difficulty in balancing strength and toughness, unreliable interfacial force transmission, and insufficient long-term durability. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a polyurethane composite material for prestressed high-strength steel wire reinforcement and its preparation method. By synergistically introducing halloysite nanotubes and hydroxyl-terminated polysilsesquioxane into the polyurethane composite material, an organic-inorganic synergistic reinforcement structure of "nanotube bridging toughening + cage-type organosilicon cross-linking and densification" is constructed, thereby solving the problem that existing structural reinforcement materials are difficult to balance in terms of strength, toughness, interfacial bonding and durability.

[0007] The technical solution of this invention is as follows: On the one hand, the present invention provides a polyurethane composite material for prestressed high-strength steel wire reinforcement, which is composed of component A and component B, with a mass ratio of component A to component B of 120:180. By weight, component A comprises the following raw materials: 28-34 parts of polyisocyanate; 28-34 parts of polyether polyol; Parts 4-8 of metakaolin; Halloysite nanotubes, 0.5-2 parts; 0.2-1 parts of hydroxyl-terminated polysilsesquioxane; 2-3 parts catalyst; The mass ratio of halloysite nanotubes to hydroxyl-terminated polysilsesquioxane is (1.5-3):1. Component B consists of 100 parts of P·O42.5 silicate cement; The polyisocyanate is polymeric diphenylmethane diisocyanate (PMDI) to ensure that the system has high reactivity and good post-curing strength; the polyether polyol is PEG-1000. In this invention, the polyether polyol serves as both a polyurethane matrix forming component and a good dispersion environment for halloysite nanotubes and hydroxyl-terminated polysilsesquioxane. Furthermore, due to the unique tubular structure and high aspect ratio of halloysite nanotubes, they can form crack bridging channels in the cured composite system, hindering crack initiation and propagation, and filling micropores and interface defects. The hydroxyl-terminated polysilsesquioxane is a trisilyl isobutyl cage-type polysilsesquioxane (CAS: 307531-92-6) with a hydroxyl functionality of 3. After the trisilyl isobutyl cage-type polysilsesquioxane is added to component A, its hydroxyl groups react with polyisocyanate. While participating in the construction of the polyurethane crosslinking network, the cage-type rigid silica skeleton of the trisilyl isobutyl cage-type polysilsesquioxane improves the density, rigidity and dimensional stability of the crosslinking network, and improves the material's water resistance, heat resistance and weather resistance.

[0008] In this invention, the synergistic effect of halloysite nanotubes and hydroxyl-terminated polysilsesquioxane exhibits a significant range-dependent characteristic. When the mass ratio of halloysite nanotubes to hydroxyl-terminated polysilsesquioxane is less than 1.5:1, the bridging and crack deflection effects of halloysite nanotubes in the system are insufficient, making it difficult to form an effective multi-scale reinforcing network. When the mass ratio is greater than 3:1, the degree to which hydroxyl-terminated polysilsesquioxane participates in the polyurethane crosslinking reaction is insufficient, making it difficult to form a dense and stable organosilicon cage-like network structure, thus limiting the improvement in the material's water resistance and long-term stability. Only within the mass ratio range defined in this invention can the two form a synergistic reinforcement mechanism at the microstructure level, thereby achieving comprehensive optimization of the material's strength, toughness, and durability.

[0009] It should be noted that the polyurethane composite material of the present invention is not designed for ordinary plastering or repair mortar systems, but is specifically optimized for the synergistic stress system of "prestressed high-strength steel wire-polyurethane composite layer-concrete matrix", and its performance improvement has obvious application scenario targeting.

[0010] Preferably, the catalyst is CUCAT-YR11.

[0011] Preferably, its compressive strength is >92MPa and its pull-out bond strength with the concrete matrix is ​​>4MPa.

[0012] On the other hand, the present invention provides a method for preparing the above-mentioned polyurethane composite material for prestressed high-strength steel wire reinforcement, comprising the following steps: S1: Dry halloysite nanotubes and metakaolin for later use; S2: Polyether polyol, hydroxyl-terminated polysilsesquioxane, dried halloysite nanotubes and dried metakaolin are mixed and pre-dispersed to obtain a premixed component; Halloysite nanotubes are pre-dispersed with polyether polyol, hydroxyl-terminated polysilsesquioxane and metakaolin before being added to polyisocyanate so that they form a uniformly distributed nano-bridged reinforcing phase in component A; S3: Add polyisocyanate and catalyst to the premixed components, stir evenly, and obtain component A; S4: Mix and stir component A and component B to obtain a polyurethane composite material for prestressed high-strength steel wire reinforcement.

[0013] In this invention, the order in which raw materials are added has a significant impact on the performance of the final material. If halloysite nanotubes are directly added to a system containing polyisocyanate, the viscosity can rise rapidly due to the high reactivity of the system, resulting in uneven dispersion of the halloysite nanotubes and weakening their bridging and reinforcing effects. Therefore, in this invention, halloysite nanotubes are pre-dispersed with polyether polyol and hydroxyl-terminated polysilsesquioxane before adding polyisocyanate to ensure their uniform distribution in the system.

[0014] Preferably, in step S1, halloysite nanotubes are dried at 80-110℃ for 2-6 hours, and metakaolin is dried at 100-110℃ for 2-4 hours.

[0015] Preferably, in step S2, the pre-dispersion temperature is 20-40℃ and the pre-dispersion time is 2-5 min.

[0016] Preferably, in step S4, the mixing time of component A and component B is 2-4 minutes.

[0017] Compared with the prior art, the present invention has the following advantages: (1) Balancing strength and toughness Halloysite nanotubes act as bridges, deflect cracks, and disperse stress in the system; hydroxyl-terminated polysilsesquioxane participates in cross-linking to construct a rigid cage network. The synergistic effect of these two components improves the material's strength and stiffness while maintaining good fracture toughness.

[0018] (2) Enhanced force transmission capability at the interface Halloysite nanotubes and metakaolin work together in the transition zone of polyurethane interface, which is beneficial for filling micro-defects and reducing interfacial porosity; hydroxyl-terminated polysilsesquioxane improves the synergistic effect between organic and inorganic phases, and enhances the bonding and force transfer stability between polyurethane composites and concrete matrix as well as between polyurethane composites and prestressed high-strength steel wires.

[0019] (3) Significant improvement in durability The cage-like organosilicon structure of hydroxyl-terminated polysilsesquioxane helps improve the stability and hydrophobicity of the crosslinking network and reduce the material's tendency to soften due to water absorption. The filling effect of halloysite nanotubes and metakaolinite can reduce micropore connectivity, thereby improving the material's service performance under humid heat, freeze-thaw, wet-dry cycles and salt spray environments.

[0020] (4) Suitable for prestressed high-strength steel wire reinforcement scenarios The polyurethane composite material of the present invention has good workability, covering properties, adhesion and early strength development ability, and is suitable for use as an outer covering or embedding layer of prestressed high-strength steel wire, which can improve the cracking load, bending stiffness and overall stress stability of reinforced components.

[0021] (5) This invention does not simply replace conventional fillers, but introduces halloysite nanotubes and hydroxyl-terminated polysilsesquioxane into the polyurethane composite system for prestressed high-strength steel wire simultaneously, forming differentiated technical characteristics through the synergistic effect of the two components. Halloysite nanotubes and hydroxyl-terminated polysilsesquioxane are synergistically introduced into the polyurethane composite system for prestressed high-strength steel wire reinforcement, and by limiting the ratio range, addition order and application structure of the two, a nonlinear synergistic reinforcement effect is formed in specific application scenarios.

[0022] In summary, this invention does not employ the single-filler modification scheme commonly used in existing technologies, nor does it simply combine different modifying components side by side. Instead, it focuses on targeted material design around the synergistic stress-bearing structure of "prestressed high-strength steel wire - polyurethane composite layer - concrete matrix": on the one hand, halloysite nanotubes are used to achieve crack bridging, stress transfer, and micropore filling; on the other hand, hydroxyl-terminated polysilsesquioxanes are used to participate in polyurethane crosslinking and construct a cage-like rigid network; at the same time, metakaolin filler is combined to form a multi-scale graded filling structure, thereby establishing a reinforcement system that is progressively coupled from the molecular scale, nanoscale to microscale within the material. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the layers of the polyurethane composite material of the present invention in a prestressed high-strength steel wire reinforced structure.

[0024] In the diagram: 1. Concrete beam base; 2. Existing reinforcing steel; 3. Prestressed high-strength steel wire; 4. Anchorage end; 5. Polyurethane composite material layer; 6. Beam bottom interface area; 7. Tensioning direction. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0026] 1. Raw Material Description Polyisocyanate: PMDI, Lupranate® M20S, BASF.

[0027] Polyether polyol: PEG-1000.

[0028] Metakaolin: Amorphous aluminosilicate powder obtained through calcination and activation, with an average particle size of 1-10 μm and a specific surface area of ​​10-30 m². 2 / g. Metakaolin has high pozzolanic activity and filling effect, which can improve the microstructure of the interfacial region, reduce porosity, and improve the compactness, dimensional stability and compatibility with inorganic matrices of composite materials.

[0029] Halloysite nanotubes: with an average length of 0.5-5μm and an outer diameter of 30-120nm. They should be dried before use to reduce the moisture content to ≤0.5wt.% in order to minimize the adverse effects of moisture on the polyisocyanate reaction.

[0030] Catalyst: CUCAT-YR11, Guangzhou Yourun Synthetic Materials Co., Ltd.

[0031] 2. Preparation method The preparation method of the prestressed high-strength steel wire reinforcement polyurethane composite material of the present invention includes the following steps: S1: Inorganic filler pretreatment Halloysite nanotubes were dried in an oven at 80-110℃ for 2-6 hours, cooled, and then sealed for later use. Simultaneously, metakaolin was dried at 100-110℃ for 2-4 hours, cooled, and then stored for later use. Pre-drying halloysite nanotubes and metakaolin effectively reduces the surface water content, minimizes side reactions between water and polyisocyanate, and reduces the adverse effects of water on the reactivity of polyisocyanate, the curing process, and the uniformity of dispersion.

[0032] S2: Functional component predispersion At 20-40℃, polyether polyol is added to a stirring device, followed by hydroxyl-terminated polysilsesquioxane, and stirred to disperse it evenly; then dried halloysite nanotubes and metakaolin are added, and dispersed by high-speed shearing for 2-5 minutes to obtain a uniformly dispersed premixed system.

[0033] S3: Preparation of Component A Add polyisocyanate and catalyst to the premixed system and continue stirring at 20-30℃ for 1-3 minutes to obtain component A.

[0034] S4: Composite Material Preparation Mix component A and component B at a mass ratio of 120:180 and stir for 2-4 minutes to obtain a polyurethane composite material in an application-ready state, which can be used for scraping, injection, coating or filling.

[0035] Example 1 The polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment is composed of component A and component B, in parts by weight: Component A includes: 31 parts PMDI, 31 parts PEG-1000, 5 parts metakaolin, 1 part halloysite nanotubes, 0.5 parts trisilyl isobutyl cage polysilsesquioxane, and 2.5 parts catalyst CUCAT-YR11.

[0036] Component B consists of 100 parts of P·O42.5 silicate cement.

[0037] Component A and component B are mixed at a mass ratio of 120:180.

[0038] The preparation method of the polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment includes the following steps: S1: Inorganic filler pretreatment Halloysite nanotubes were dried in a 90°C oven for 4 hours, cooled, and then sealed for later use. Meanwhile, metakaolin was dried at 100°C for 3 hours, cooled, and then for later use.

[0039] S2: Functional component predispersion At 30°C, PEG-1000 was added to a stirring device, followed by the addition of trisilyl isobutyl cage-type polysilsesquioxane, and the mixture was stirred to disperse it evenly. Then, dried halloysite nanotubes and metakaolin were added, and the mixture was dispersed by high-speed shearing for 4 minutes to obtain a uniformly dispersed premixed system.

[0040] S3: Preparation of Component A PMDI and catalyst CUCAT-YR11 were added to the premixed system, and the mixture was stirred for 2 minutes at 30°C to obtain component A.

[0041] S4: Composite Material Preparation Mix component A and component B at a mass ratio of 120:180 and stir for 3 minutes to obtain a polyurethane composite material in an application-ready state.

[0042] Example 2 The polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment is composed of component A and component B, in parts by weight: Component A includes: 30 parts PMDI, 32 parts PEG-1000, 6 parts metakaolin, 0.8 parts halloysite nanotubes, 0.3 parts trisilyl isobutyl cage polysilsesquioxane, and 2 parts catalyst CUCAT-YR11.

[0043] Component B consists of 100 parts of P·O42.5 silicate cement.

[0044] Component A and component B are mixed at a mass ratio of 120:180.

[0045] The preparation method of the polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment includes the following steps: S1: Inorganic filler pretreatment Halloysite nanotubes were dried in an oven at 80°C for 2 hours, cooled, and then sealed for later use. Meanwhile, metakaolin was dried at 100°C for 2 hours, cooled, and then for later use.

[0046] S2: Functional component predispersion At 20°C, PEG-1000 was added to a stirring device, followed by the addition of trisilyl isobutyl cage-type polysilsesquioxane, and the mixture was stirred to disperse it evenly. Then, dried halloysite nanotubes and metakaolin were added, and the mixture was dispersed using a high-speed shearing method for 2 minutes to obtain a uniformly dispersed premixed system.

[0047] S3: Preparation of Component A PMDI and catalyst CUCAT-YR11 were added to the premixed system, and the mixture was stirred for 2 minutes at 20°C to obtain component A.

[0048] S4: Composite Material Preparation Mix component A and component B at a mass ratio of 120:180 and stir for 3 minutes to obtain a polyurethane composite material in an application-ready state.

[0049] Example 3 The polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment is composed of component A and component B, in parts by weight: Component A includes: 32 parts PMDI, 30 parts PEG-1000, 4.5 parts metakaolin, 1.5 parts halloysite nanotubes, 0.8 parts trisilyl isobutyl cage polysilsesquioxane, and 3 parts catalyst CUCAT-YR11.

[0050] Component B consists of 100 parts of P·O42.5 silicate cement.

[0051] Component A and component B are mixed at a mass ratio of 120:180.

[0052] The preparation method of the polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment includes the following steps: S1: Inorganic filler pretreatment Halloysite nanotubes were dried in an oven at 100°C for 3 hours, cooled, and then sealed for later use. Meanwhile, metakaolin was dried at 105°C for 4 hours, cooled, and then for later use.

[0053] S2: Functional component predispersion At 40°C, PEG-1000 was added to a stirring device, followed by the addition of trisilyl isobutyl cage-type polysilsesquioxane, and the mixture was stirred to disperse it evenly. Then, dried halloysite nanotubes and metakaolin were added, and the mixture was dispersed by high-speed shearing for 3 minutes to obtain a uniformly dispersed premixed system.

[0054] S3: Preparation of Component A PMDI and catalyst CUCAT-YR11 were added to the premixed system, and the mixture was stirred for 3 minutes at 25°C to obtain component A.

[0055] S4: Composite Material Preparation Mix component A and component B at a mass ratio of 120:180 and stir for 4 minutes to obtain a polyurethane composite material in an application-ready state.

[0056] Example 4 The polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment is composed of component A and component B, in parts by weight: Component A includes: 29 parts PMDI, 33 parts PEG-1000, 7 parts metakaolin, 0.6 parts halloysite nanotubes, 0.4 parts trisilyl isobutyl cage polysilsesquioxane, and 2.2 parts catalyst CUCAT-YR11.

[0057] Component B consists of 100 parts of P·O42.5 silicate cement.

[0058] Component A and component B are mixed at a mass ratio of 120:180.

[0059] The preparation method of the polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment includes the following steps: S1: Inorganic filler pretreatment Halloysite nanotubes were dried in an oven at 110°C for 5 hours, cooled, and then sealed for later use. Meanwhile, metakaolin was dried at 110°C for 4 hours and then cooled for later use.

[0060] S2: Functional component predispersion At 40°C, PEG-1000 was added to a stirring device, followed by the addition of trisilyl isobutyl cage-type polysilsesquioxane, and the mixture was stirred to disperse it evenly. Then, dried halloysite nanotubes and metakaolin were added, and the mixture was dispersed for 5 minutes using a high-speed shearing method to obtain a uniformly dispersed premixed system.

[0061] S3: Preparation of Component A PMDI and catalyst CUCAT-YR11 were added to the premixed system, and the mixture was stirred for 3 minutes at 30°C to obtain component A.

[0062] S4: Composite Material Preparation Mix component A and component B at a mass ratio of 120:180 and stir for 3 minutes to obtain a polyurethane composite material in an application-ready state.

[0063] Example 5 The polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment is composed of component A and component B, in parts by weight: Component A includes: 34 parts PMDI, 28 parts PEG-1000, 8 parts metakaolin, 1.2 parts halloysite nanotubes, 0.6 parts trisilyl isobutyl cage polysilsesquioxane, and 2.8 parts catalyst CUCAT-YR11.

[0064] Component B consists of 100 parts of P·O42.5 silicate cement.

[0065] Component A and component B are mixed at a mass ratio of 120:180.

[0066] The preparation method of the polyurethane composite material for prestressed high-strength steel wire reinforcement in this embodiment includes the following steps: S1: Inorganic filler pretreatment Halloysite nanotubes were dried in an oven at 90°C for 6 hours, cooled, and then sealed for later use. Meanwhile, metakaolin was dried at 110°C for 4 hours, cooled, and then for later use.

[0067] S2: Functional component predispersion At 40°C, PEG-1000 was added to a stirring device, followed by the addition of trisilyl isobutyl cage-type polysilsesquioxane, and the mixture was stirred to disperse it evenly. Then, dried halloysite nanotubes and metakaolin were added, and the mixture was dispersed using a high-speed shearing method for 2 minutes to obtain a uniformly dispersed premixed system.

[0068] S3: Preparation of Component A PMDI and catalyst CUCAT-YR11 were added to the premixed system, and the mixture was stirred for 1 min at 20 °C to obtain component A.

[0069] S4: Composite Material Preparation Mix component A and component B at a mass ratio of 120:180 and stir for 2 minutes to obtain a polyurethane composite material in an application-ready state.

[0070] Comparative Example 1 The difference from Example 1 is that halloysite nanotubes and trisilyl isobutyl cage polysilsesquioxane are not added to component A.

[0071] Comparative Example 2 The difference from Example 1 is that no trisilyl isobutyl cage polysilsesquioxane is added to component A.

[0072] Comparative Example 3 The difference from Example 1 is that halloysite nanotubes are not added to component A.

[0073] When the polyurethane composite materials of Examples 1-5 and Comparative Examples 1-3 are used in concrete beams, the following construction steps are adopted: (1) Base surface treatment The surface of the concrete beam base 1 is ground, roughened, dusted and cleaned. The original steel bars 2 are installed inside the concrete beam base 1 to make the base surface firm, rough and free of laitance and oil stains.

[0074] (2) Prestressed high-strength steel wire layout According to the design requirements, prestressed high-strength steel wires 3 are laid in the tension zone of the component, and anchor ends 4 are set.

[0075] (3) Tensioning The prestressed high-strength steel wire 3 is tensioned along the tensioning direction 7 to 30-55% of its standard tensile strength value and kept stable.

[0076] (4) Polyurethane composite material coating or embedding molding Polyurethane composite material is coated or filled around the prestressed high-strength steel wire 3 and between it and the concrete beam substrate 1 to form a continuous, dense polyurethane composite material layer 5 with a thickness of 20 mm. A beam bottom interface zone 6 is formed between the concrete beam substrate 1 and the polyurethane composite material layer 5.

[0077] (5) Maintenance After construction, the material is cured at 25℃ for 24 hours to form a composite reinforcement layer that works in synergy with the concrete beam substrate 1 and the prestressed high-strength steel wire 3.

[0078] Ultimately, polyurethane composite materials in prestressed high-strength steel wire reinforced structures, such as Figure 1 As shown.

[0079] Comparative Example 4 The reinforcement steps for prestressed high-strength steel wire reinforced beams using composite mortar as the reinforcement layer are as follows: (1) Anchorages are positioned and installed on the surface of the reinforced concrete beam by drilling; (2) Use a reaction frame and tensioning device to tension the prestressed high-strength steel wire to achieve the set tension stress; (3) Erect the formwork after the prestressed high-strength steel wires are tensioned in place; (4) Pour composite mortar to form a reinforcement layer; (5) Reinforcement shall be completed after the curing reaches the design strength.

[0080] The composite mortar used is polymer-modified cement-based reinforcing mortar produced by Jiangsu Subote New Material Co., Ltd., which is commonly used in engineering. Its thickness, tensile stress and concrete beam size parameters are consistent with those in Example 1.

[0081] Comparative Example 5 Concrete beams are reinforced using prestressed high-strength steel wires without a reinforcement layer. The reinforcement steps are as follows: (1) Anchorages are positioned and installed on the surface of the reinforced concrete beam by drilling; (2) Use a reaction frame and tensioning device to tension the prestressed high-strength steel wire to achieve the set tension stress; (3) After tensioning, no reinforcement layer material is poured, and the component reinforcement is completed directly.

[0082] Comparative Example 6 Comparative Example 6 uses a foundation reinforced concrete beam without any reinforcement treatment.

[0083] To verify the bulk properties, interfacial properties, environmental durability properties, and component reinforcement effects of the polyurethane composite material of the present invention, the following tests were conducted on the polyurethane composite materials obtained in Examples 1-5 and Comparative Examples 1-3, as well as the reinforced concrete beams in Examples 1-5 and Comparative Examples 4-6.

[0084] (1) The compressive strength and flexural strength shall be tested in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)"; (2) The splitting tensile strength shall be tested in accordance with the corresponding mechanical property test methods in JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar"; (3) The pull-out bond strength with the concrete matrix shall be tested according to the corresponding tensile bond strength test method in JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar"; (4) The 24h water absorption rate shall be tested in accordance with the corresponding water absorption rate test method in JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar"; (5) The interfacial shear strength was tested in accordance with the shear bond test principle of GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)" and ASTM C882 / C882M-23 "Standard test method for determining the bond strength of concrete bonded systems by inclined shear method". A composite interface specimen was prepared by using a roughened concrete matrix and a polyurethane composite material. The specimen was loaded until the interface failed or the specimen failed as a whole. The interfacial shear strength was calculated according to the ratio of the maximum failure load to the effective shear bond area. (5) The test method for the retention rate of compressive strength and pull-out bond strength after damp heat aging is as follows: the specimen is first aged at 60℃ and 95%RH for 7 days. After aging, the compressive strength and pull-out bond strength are tested according to the above test methods. The retention rate is calculated as the ratio of the test value after aging to the test value before aging. (6) The test method for the pull-out bond strength retention rate after chloride salt wet-dry cycle is as follows: the specimen is first subjected to 10 cycles of alternating immersion in 5wt.% NaCl solution and drying at room temperature. After the cycle, the pull-out bond strength test method is performed as described above. The retention rate is calculated as the ratio of the test value after the cycle to the initial test value. (7) The increase in crack stiffness of the reinforced beam was determined by referring to GB / T 50152-2012 "Standard for Test Methods of Concrete Structures" to conduct static bending load tests on simply supported beams, record the cracking load and corresponding deflection, and calculate the relative change in crack stiffness between the reinforced beam and the unreinforced control beam. (8) The maximum slip of the reinforced layer-concrete interface was determined by referring to GB / T 50152-2012 "Standard for Test Methods of Concrete Structures". Static loading tests were conducted on the components, and displacement gauges were placed at key locations on the reinforced layer-concrete interface to record the maximum relative slip of the interface during the entire loading process.

[0085] The bulk properties, interfacial properties, and environmental durability test results of the polyurethane composite materials of Examples 1-5 and Comparative Examples 1-3 are shown in Tables 1-3: Table 1. Test results of the bulk properties of polyurethane composites in Examples 1-5 and Comparative Examples 1-3

[0086] As shown in Table 1, the polyurethane composite material of the examples incorporating both halloysite nanotubes and trisilyl isobutyl cage-type polysilsesquioxane exhibits superior compressive, flexural, and splitting tensile strength properties compared to the comparative example. Specifically, Example 1 shows an increase of approximately 33.7% in compressive strength, approximately 57.1% in flexural strength, and approximately 65.5% in splitting tensile strength compared to Comparative Example 1. This indicates that the combined introduction of halloysite nanotubes and trisilyl isobutyl cage-type polysilsesquioxane not only improves the compressive strength of the polyurethane composite material but also significantly enhances its crack resistance and tensile properties.

[0087] Table 2. Test results of interfacial properties and water resistance of polyurethane composite materials in Examples 1-5 and Comparative Examples 1-3.

[0088] As shown in Table 2, the pull-out bond strength and interfacial shear strength of the polyurethane composite material in the examples are higher than those in Comparative Examples 1-3, and the 24-hour water absorption rate is lower than that in Comparative Examples 1-3. This indicates that there is a significant synergistic effect between the micropore filling and bridging effect of halloysite nanotubes and the crosslinking densification and hydrophobic effect of trisilyl isobutyl cage-type polysilsesquioxane, which can simultaneously improve interfacial force transmission capacity and water resistance.

[0089] Table 3. Environmental durability test results of polyurethane composite materials in Examples 1-5 and Comparative Examples 1-3

[0090] As shown in Table 3, the polyurethane composite material of the embodiment still maintains a high compressive strength and interfacial pull-out bond strength retention rate after humid heat aging and chloride salt wet-dry cycle, indicating that the composite system has better durability and stability in the common humid heat and salt corrosion environment of bridges.

[0091] The stress performance of concrete beams reinforced with polyurethane composite materials from Examples 1-5 and concrete beams from Comparative Examples 4-6 was tested. The cracking load, ultimate load, increase in cracking stiffness, and decrease in mid-span deflection were all measured in accordance with GB / T 50152-2012 "Standard for Test Methods of Concrete Structures".

[0092] The test results are shown in Table 4: Table 4. Test results of the stress performance of concrete beams in Examples 1-5 and Comparative Examples 4-6

[0093] As shown in Table 4, when the polyurethane composite materials of Examples 1-5 are used as composite reinforcement layers, the cracking load, ultimate load and cracking stiffness of the concrete beams are significantly better than those of concrete beams reinforced with conventional composite mortar and concrete beams reinforced only with prestressed high-strength steel wire. This indicates that the polyurethane composite material of the present invention can form a more effective synergistic working system with the prestressed high-strength steel wire and the concrete matrix.

[0094] Environmental durability tests were conducted on concrete beams reinforced with polyurethane composite materials from Examples 1-5 and concrete beams from Comparative Examples 4-5. Interface slip tests were performed for DH1, DH2, DH3, DH4, and the maximum slip, all in accordance with GB / T 50152-2012 "Standard Test Methods for Concrete Structures". The test results are shown in Table 5. Table 5. Environmental durability test results of concrete beams in Examples 1-5 and Comparative Examples 4-5

[0095] As shown in Table 5, the interfacial slip of the concrete beam in the embodiment during the entire loading process is significantly lower than that of the conventional composite mortar reinforcement system and the system using only prestressed high-strength steel wire reinforcement. This indicates that the polyurethane composite material of the present invention has higher interfacial bonding strength and more stable synergistic stress performance with the concrete beam.

[0096] The above results show that the polyurethane composite material of the present invention has significantly higher improvement in compressive strength, flexural strength and interfacial bonding performance than the sum of the improvement effects of adding only halloysite nanotubes or only trisilyl isobutyl cage polysilsesquioxane. This indicates that the relationship between the two is not a simple linear superposition, but rather a significant synergistic reinforcement effect.

[0097] Therefore, in the polyurethane composite system for reinforcing prestressed high-strength steel wire, the simultaneous addition of halloysite nanotubes and trisilyl isobutyl cage-type polysilsesquioxane can produce synergistic reinforcement effects in the following aspects: 1) Improve the compressive, flexural, and tensile properties of the material itself; 2) Improve the interfacial bonding and shear force transfer capacity with the concrete matrix; 3) Reduce water absorption rate and improve durability in humid and hot environments and chloride-salt environments; 4) Reduce interface slip after component reinforcement, and improve crack stiffness and ultimate bearing capacity.

[0098] The reason for this lies in the fact that halloysite nanotubes act as crack bridging, crack deflection, and micropore filling agents within the material, while trisilyl isobutyl cage-like polysilsesquioxane participates in the high-strength polyurethane crosslinking reaction to form a cage-like rigid network, improving the density, water resistance, and dimensional stability of the crosslinked structure. Together with metakaolin, these two components construct a multi-scale synergistically reinforced high-strength polyurethane structure, thereby comprehensively improving the material's strength, toughness, interfacial properties, and durability.

[0099] Further analysis shows that the performance improvement of the polyurethane composite material of the present invention originates from a multi-scale synergistic mechanism: 1) Nanoscale: Halloysite nanotubes provide crack bridging and stress transmission paths, and play a role in inhibiting, deflecting and passivating the propagation of microcracks; 2) Molecular scale: Trisilyl isobutyl cage-like polysilsesquioxane participates in the crosslinking reaction of high-strength polyurethane to form a cage-like network structure with high rigidity and stability, thereby improving the crosslinking density, dimensional stability and water and weather resistance of the system. 3) Micron scale: Metakaolin filler and halloysite nanotubes form a graded filling structure to fill and optimize the pores, interface defects and local loose areas in the high-strength polyurethane composite system in multiple levels.

[0100] The synergistic effect of the aforementioned multi-scale structure significantly improves the material's strength, toughness, interfacial properties, and durability. This improvement does not stem from the independent action of a single component, but rather from a synergistic reinforcement system formed under specific proportions, addition sequences, and processing conditions. Therefore, this invention is not a simple material superposition or conventional parallel modification, but rather a composite reinforcement mechanism with a clear structural foundation and action path in the specific application scenario of prestressed high-strength steel wire reinforcement.

Claims

1. A polyurethane composite material for reinforcing prestressed high-strength steel wire, characterized in that, It consists of component A and component B, with a mass ratio of component A to component B of 120:180; By weight, component A comprises the following raw materials: 28-34 parts of polyisocyanate; 28-34 parts of polyether polyol; Parts 4-8 of metakaolin; Halloysite nanotubes, 0.5-2 parts; 0.2-1 parts of hydroxyl-terminated polysilsesquioxane; 2-3 parts catalyst; The mass ratio of halloysite nanotubes to hydroxyl-terminated polysilsesquioxane is (1.5-3):

1. Component B consists of 100 parts of P·O42.5 silicate cement; Among them, the polyisocyanate is polymerized diphenylmethane diisocyanate; the polyether polyol is PEG-1000; and the hydroxyl-terminated polysilsesquioxane is trisilol isobutyl cage-type polysilsesquioxane with a hydroxyl functionality of 3.

2. The polyurethane composite material for prestressed high-strength steel wire reinforcement as described in claim 1, characterized in that, The catalyst is CUCAT-YR11.

3. The polyurethane composite material for prestressed high-strength steel wire reinforcement as described in claim 1, characterized in that, Its compressive strength is >92MPa, and its pull-out bond strength with the concrete matrix is ​​>4MPa.

4. The method for preparing polyurethane composite material for prestressed high-strength steel wire reinforcement as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Dry halloysite nanotubes and metakaolin for later use; S2: Polyether polyol, hydroxyl-terminated polysilsesquioxane, dried halloysite nanotubes and dried metakaolin are mixed and pre-dispersed to obtain a premixed component; S3: Add polyisocyanate and catalyst to the premixed components, stir evenly, and obtain component A; S4: Mix and stir component A and component B to obtain a polyurethane composite material for prestressed high-strength steel wire reinforcement.

5. The method for preparing polyurethane composite material for prestressed high-strength steel wire reinforcement as described in claim 4, characterized in that, In step S1, halloysite nanotubes are dried at 80-110℃ for 2-6 hours, and metakaolin is dried at 100-110℃ for 2-4 hours.

6. The method for preparing polyurethane composite material for prestressed high-strength steel wire reinforcement as described in claim 4, characterized in that, In step S2, the pre-dispersion temperature is 20-40℃ and the pre-dispersion time is 2-5 min.

7. The method for preparing polyurethane composite material for prestressed high-strength steel wire reinforcement as described in claim 4, characterized in that, In step S4, the mixing time for component A and component B is 2-4 minutes.

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