A method for reinforcing an rc beam with high toughness frcm
Patent Information
- Application Number
- CN202611282417.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-24
- Publication Date
- 2026-09-22
AI Technical Summary
[0005]FRCM加固体系的核心失效模式之一是纤维织物与水泥基基质之间的界面脱粘，作为外粘加固系统，FRCM的性能很大程度上取决于其与混凝土基材界面维持复合作用并有效传递力的能力，无锚固FRCM体系普遍存在过早界面滑移、端部剥离或局部界面损伤等问题，当采用脆性水泥基材料作为基体时，开裂后裂缝宽度较大，导致CFRP网格的强度无法充分发挥，为此，针对上述描述中提出的问题，本发明提出一种高韧性FRCM加固RC梁的方法
1.本发明采用ECC作为基体，本身具有多缝开裂和应变硬化的特性，在此基础上，改性CFRP网格与改性ECC之间的强界面结合确保了裂缝出现后应力能够有效传递至CFRP网格，由高韧性纤维网格承担拉应力，从而控制裂缝宽度在较小范围内，实现ECC分散开裂与CFRP网格承载的协同工作机制，强化的界面结合使FRCM加固层在受力过程中更不易发生界面剥离，加固层与RC梁本体能够作为一个整体协同工作，同时，化学键合界面层对水分和侵蚀性离子的侵入具有更好的阻隔效果，有利于提升加固体系在恶劣环境下的长期耐久性。
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Figure CN122792003A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of cement-based composite materials technology, and specifically to a method for reinforcing RC beams with high-toughness FRCM. Background Technology
[0002] An RC beam (Reinforced Concrete Beam) is a beam composed of steel bars and concrete. It is one of the most basic load-bearing components in building structures and is widely used in housing, bridges and other projects. There are various design and construction methods for RC beams to meet different engineering needs. According to their cross-sectional shape, RC beams can be divided into rectangular beams, T-beams, I-beams, channel beams and box beams, etc.
[0003] Carbon fiber reinforced polymer (CFRP) composites are composite materials formed with carbon fiber or carbon fiber fabric as reinforcement and resin, ceramics, metals, cement, carbonaceous materials or rubber as matrix. Among many lightweight materials, it has high specific strength and specific stiffness, and the lightweight effect is very obvious. However, the epoxy resin-based external CFRP reinforcement method has limitations in terms of fire resistance and UV radiation resistance. Furthermore, the compatibility between epoxy resin and concrete is low under temperature changes and moisture erosion. Due to the discontinuity of CFRP at the cut position and the incompatibility between the continuity of CFRP material and the discontinuity of concrete substrate (i.e. cracks), debonding failure between external CFRP and concrete substrate is also a key problem in CFRP-reinforced RC systems. This will lead to significant local stress concentration at the CFRP / concrete interface.
[0004] To address the aforementioned challenges of epoxy resin-bonded CFRP reinforcement methods, a fiber-reinforced cementitious matrix (FRCM) reinforcement method is proposed as an alternative. This reinforcement system uses cement mortar as the bonding medium, embedding CFRP within it to form a composite reinforcement system. The reinforcing fiber fabric in FRCM can be in the form of unimpregnated fibers (such as unidirectional dry fiber cloth and bidirectional fiber fabric / mesh) or resin-impregnated fibers. Simultaneously, its cement-based matrix can be made of various cement-based materials, including ordinary Portland cement (with short fibers and / or polymer additives), polymer-modified cement, and cement mortar with added silicate particles. When fiber fabric is used as the reinforcing material, the resulting composite material is usually called fabric-reinforced mortar or fabric-reinforced concrete. Benefiting from the non-combustible properties of the cement-based matrix, FRCM naturally possesses superior fire resistance compared to CFRP and exhibits better compatibility with concrete substrates in humid environments.
[0005] One of the core failure modes of FRCM reinforcement systems is the debonding of the interface between the fiber fabric and the cement-based matrix. As an externally bonded reinforcement system, the performance of FRCM largely depends on its ability to maintain a composite interaction with the concrete substrate interface and effectively transfer forces. Unanchored FRCM systems generally suffer from problems such as premature interface slippage, end peeling, or local interface damage. When brittle cement-based materials are used as the matrix, the crack width is large after cracking, which prevents the strength of the CFRP mesh from being fully utilized. Therefore, in response to the problems mentioned above, this invention proposes a method for reinforcing RC beams with high-toughness FRCM. Summary of the Invention
[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for reinforcing RC beams with high-toughness FRCM to solve the problems mentioned in the background art.
[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for reinforcing RC beams with high-toughness FRCM includes the following steps: S1. Cut the modified CFRP mesh according to the design dimensions, apply carbon fiber adhesive to the surface of the modified CFRP mesh, cure for 72-84 hours, and then assemble the cured modified CFRP mesh with the wooden template to make a composite template. S2. Clean and roughen the reinforcement area around the existing RC beam, then apply a layer of carbon fiber adhesive to the surface of the reinforcement area around the existing RC beam, and attach the composite template to the reinforcement area of the existing RC beam after applying the adhesive. S3. The ECC is poured into the cavity between the composite template and the existing RC beam in three layers to form a high-toughness FRCM layer. Each layer corresponds to a modified CFRP mesh. After each layer is poured, it is vibrated for 15-20 seconds. After the pouring is completed, the exposed surface is scraped and smoothed, and then placed in a standard concrete curing room for 28-32 days to obtain an RC beam reinforced with high-toughness FRCM. The modified CFRP mesh is prepared through the following steps: S11. Immerse the CFRP mesh in anhydrous ethanol and sonicate for 1-2 hours. Remove and dry to obtain desizing CFRP mesh. Immerse the desizing CFRP mesh in concentrated nitric acid and treat at 60-80℃ for 4-6 hours. Rinse with deionized water until the pH of the washing solution is 6-8. Dry to obtain oxidized CFRP mesh. S12. Place the oxidized CFRP mesh in tetrahydrofuran, add lithium aluminum hydride, stir at 40-60℃ for 1-2 hours, add hydrochloric acid, continue stirring for 1-2 hours, filter out the oxidized CFRP mesh, soak and wash in tetrahydrofuran for 20-24 hours, and dry to obtain the treated CFRP mesh. S13, ethanol and deionized water are mixed, pH is adjusted to 3-4 with acetic acid, KH550 is added, and the mixture is stirred at 40-50℃ for 20-30 min to obtain a hydrolysate. The treated CFRP grid is immersed in the hydrolysate and ultrasonically treated for 30-50 min. After drying, the modified CFRP grid is obtained. The ECC is formulated with 550-650 parts by weight of cement, 550-650 parts by weight of fly ash, 380-480 parts by weight of quartz sand, 18-22 parts by weight of polyethylene fiber, 2.5-4.5 parts by weight of polycarboxylate ether high-efficiency water-reducing agent, 0.8-1.8 parts by weight of modified thickener, 0.8-1.8 parts by weight of non-silicone high carbon alcohol polyether ester defoamer and 300-380 parts by weight of water.
[0008] Furthermore, the modified thickener is prepared through the following steps: A1. Dissolve hydroxypropyl methylcellulose in anhydrous dimethyl sulfoxide and stir at 50-60℃ for 2-3 hours. Then add 4-dimethylaminopyridine and triethylamine and stir under nitrogen protection for 30-40 minutes to obtain the reaction system. A2. Dissolve N-isopropylacrylamide and methacrylic acid in anhydrous ethanol to obtain a monomer solution. Add the monomer solution dropwise to the reaction system, add azobisisobutyronitrile, and stir the reaction under nitrogen protection at 60-70℃ for 8-10 hours. After the reaction is completed, add anhydrous ethanol to precipitate the product, and collect the precipitate by filtration. A3. Dissolve the precipitate in deionized water, dialyze for 40-48 hours, and dry after dialyzing to obtain the modified thickener.
[0009] Furthermore, in S1, the CFRP mesh is a woven 12K carbon fiber mesh with a mesh size of 20mm × 20mm, and the cross-sectional area of a single CFRP fiber bundle in the mesh is 1mm². 2 .
[0010] Furthermore, in S1, the mass ratio of A glue to B glue is (2-3):1, and the mass ratio of the modified CFRP mesh surface to carbon fiber glue is 1:(0.8-1.5).
[0011] Furthermore, in S11, the mass ratio of CFRP mesh to anhydrous ethanol is 1:(5-15), and the mass ratio of desizing CFRP mesh to concentrated nitric acid is 1:(10-20).
[0012] Furthermore, in S12, the mass ratio of oxidized CFRP mesh, tetrahydrofuran, lithium aluminum hydride and hydrochloric acid is 1:(15-30):(0.05-0.15):(0.5-1.5).
[0013] Furthermore, in S13, the mass ratio of ethanol, deionized water and KH550 is 1:(0.3-0.5):(0.08-0.15), and the mass ratio of the CFRP mesh to the hydrolysate is 1:(5-15).
[0014] Furthermore, the mass ratio of hydroxypropyl methylcellulose, anhydrous dimethyl sulfoxide, 4-dimethylaminopyridine and triethylamine in A1 is 1:(15-25):(0.03-0.08):(0.2-0.5).
[0015] Furthermore, in A2, the mass ratio of N-isopropylacrylamide, methacrylic acid and anhydrous ethanol is 1:(0.2-0.4):(5-10), and the mass ratio of monomer solution, reaction system and azobisisobutyronitrile is 1:(2-4):(0.01-0.02).
[0016] Furthermore, the mass ratio of the precipitate to deionized water in A3 is 1:(5-15).
[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses ECC as the matrix, which inherently possesses the characteristics of multi-crack propagation and strain hardening. Based on this, the strong interfacial bonding between the modified CFRP mesh and the modified ECC ensures that stress can be effectively transferred to the CFRP mesh after cracks appear. The high-toughness fiber mesh bears the tensile stress, thereby controlling the crack width within a small range. This achieves a synergistic working mechanism of ECC dispersed cracking and CFRP mesh load bearing. The strengthened interfacial bonding makes the FRCM reinforcement layer less prone to interfacial delamination during stress. The reinforcement layer and the RC beam body can work together as a whole. At the same time, the chemically bonded interfacial layer has a better barrier effect against the intrusion of moisture and corrosive ions, which is beneficial to improving the long-term durability of the reinforcement system in harsh environments.
[0018] 2. This invention involves casting ECC in three layers, with a modified CFRP mesh corresponding to each layer after casting. This ensures that the position of each mesh layer in the reinforcement layer is precisely controllable, forming a multi-layer parallel mesh reinforcement system. At the same time, the modified thickener endows ECC with thermosensitive and thixotropic dual-functional properties. After casting, the viscosity recovers under static conditions, effectively preventing the mesh from shifting or settling in the matrix. This ensures that each mesh layer maintains its designed position after curing. The three layers of modified CFRP mesh and the ECC matrix construct a multi-level interface transition zone in the interface region through chemical bonding and strong intermolecular interactions. This allows each mesh layer to form an effective stress transfer channel with the surrounding ECC matrix, enabling the FRCM reinforcement layer to work collaboratively with the RC beam body as a whole to the ultimate state, significantly improving the yield load and ultimate load of the reinforced beam. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the fabrication process of the high-toughness FRCM-reinforced RC beam in this invention; Figure 2 This is a schematic diagram of the preparation process of the modified CFRP mesh in this invention; Figure 3 This is a schematic diagram of the preparation process of the modified thickener in this invention; Figure 4 This is a schematic diagram of the RC beam structure reinforced with high-toughness FRCM according to the present invention (the areas at both ends not covered by the high-toughness FRCM layer are only for illustrative purposes in the attached diagram). Figure 5 The failure morphology diagram of the CFRP mesh specimen using 0 layers in Comparative Example 4 is shown. Figure 6 The failure morphology diagram of the specimen using a single layer of modified CFRP mesh in Comparative Example 4 is shown. Figure 7 The failure morphology diagram of the specimen using a 2-layer modified CFRP mesh in Comparative Example 4 is shown. Figure 8 This is a diagram showing the failure morphology of the specimen in Example 1.
[0020] In the figure: 10, existing RC beam; 20, reinforced area around the perimeter; 30, high-toughness FRCM layer; 40, reinforced RC beam. Detailed Implementation
[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0022] Please see Figures 1-8 The present invention provides a technical solution: Example 1: A method for reinforcing RC beams with high-toughness FRCM includes the following steps: I. Preparation of modified CFRP mesh: S11. Take 100g of CFRP mesh (12K twisted type, mesh size 20mm×20mm, cross-sectional area of a single fiber bundle 1mm²). 2 The CFRP mesh was immersed in 500g of anhydrous ethanol and ultrasonically treated for 1h. After being removed and dried, the desized CFRP mesh was obtained. 100g of the desized CFRP mesh was immersed in 1000g of concentrated nitric acid (68% by mass) and treated at 60℃ for 4h. It was then rinsed with deionized water until the pH of the washing solution was 6. After drying, the oxidized CFRP mesh was obtained.
[0023] S12. Place 100g of oxidized CFRP mesh in 1500g of tetrahydrofuran, add 5g of lithium aluminum hydride, stir at 40℃ for 1h, add 50g of hydrochloric acid (concentration 2mol / L), continue stirring for 1h, filter out the oxidized CFRP mesh, soak and wash in tetrahydrofuran for 20h, and dry to obtain the treated CFRP mesh.
[0024] S13. Mix 500g of ethanol with 150g of deionized water, adjust the pH to 3 with acetic acid, add 40g of KH550, stir at 40℃ for 20min to obtain hydrolysate, immerse 100g of treated CFRP mesh in 500g of hydrolysate, sonicate for 30min, remove and dry to obtain modified CFRP mesh.
[0025] II. Preparation of Modified Thickeners: A1. Dissolve 10g of hydroxypropyl methylcellulose in 150g of anhydrous dimethyl sulfoxide and stir at 50℃ for 2h. Then add 0.3g of 4-dimethylaminopyridine and 2g of triethylamine and stir for 30min under nitrogen protection to obtain the reaction system.
[0026] A2. Take 10g of N-isopropylacrylamide and 2g of methacrylic acid, dissolve them in 50g of anhydrous ethanol to obtain a monomer solution, add 50g of monomer solution dropwise to 100g of reaction system, add 0.5g of azobisisobutyronitrile, stir and react for 8h under nitrogen protection at 60℃. After the reaction is completed, add anhydrous ethanol to precipitate, and collect the precipitate by filtration.
[0027] A3. Dissolve 20g of the precipitate in 100g of deionized water, dialyze for 40h, and dry after dialyzing to obtain the modified thickener.
[0028] III. Preparation of High-Toughness FRCM-Reinforced RC Beams: S1. Cut the modified CFRP mesh according to the design dimensions, apply carbon fiber adhesive (two-component epoxy resin type carbon fiber impregnation adhesive) to the surface of the modified CFRP mesh, cure for 72 hours, and then assemble the cured modified CFRP mesh with the wooden template to make a composite template. S2. Clean and roughen the reinforcement area 20 around the existing RC beam 10, then apply a layer of carbon fiber adhesive (two-component epoxy resin type carbon fiber impregnation adhesive) to the surface of the reinforcement area 20 around the existing RC beam 10, and attach the composite template to the reinforcement area of the existing RC beam 10 after applying the adhesive. S3. The ECC is poured into the cavity between the composite template and the existing RC beam 10 in three layers to form a high-toughness FRCM layer 30. Each layer corresponds to a modified CFRP mesh. After each layer is poured, it is vibrated for 15 seconds. After the pouring is completed, the exposed surface is scraped and smoothed, and then placed in a standard concrete curing room for 28 days to obtain the RC beam 40 reinforced with high-toughness FRCM.
[0029] ECC weighs each raw material according to the following quantities: 5500g cement, 5500g fly ash, 3800g quartz sand, 3000g water, 180g polyethylene fiber, 25g polycarboxylate ether high-efficiency water-reducing agent, 8g modified thickener, 8g non-silicone high-carbon alcohol polyether ester defoamer: Premix the dry powder materials (cement, fly ash, and quartz sand) for 2 minutes, add an aqueous solution of polycarboxylate ether high-efficiency water-reducing agent, modified thickener, and non-silicone high carbon alcohol polyether ester defoamer, stir for 3 minutes, and finally add polyethylene fiber and continue stirring for 2 minutes until uniformly dispersed.
[0030] Example 2: A method for reinforcing RC beams with high-toughness FRCM includes the following steps: I. Preparation of modified CFRP mesh: S11. Take 100g of CFRP mesh (12K twisted type, mesh size 20mm×20mm, cross-sectional area of a single fiber bundle 1mm²). 2 The CFRP mesh was immersed in 1000g of anhydrous ethanol and ultrasonically treated for 1.5h. After being removed and dried, the desized CFRP mesh was obtained. 100g of the desized CFRP mesh was immersed in 1500g of concentrated nitric acid (68% by mass) and treated at 70℃ for 5h. It was then rinsed with deionized water until the pH of the washing solution was 7. After drying, the oxidized CFRP mesh was obtained.
[0031] S12. Place 100g of oxidized CFRP mesh in 2300g of tetrahydrofuran, add 10g of lithium aluminum hydride, stir at 50℃ for 1.5h, add 100g of hydrochloric acid (concentration 2mol / L), continue stirring for 1.5h, filter out the oxidized CFRP mesh, soak and wash in tetrahydrofuran for 22h, and dry to obtain the treated CFRP mesh.
[0032] S13. Mix 500g of ethanol with 200g of deionized water, adjust the pH to 3.5 with acetic acid, add 60g of KH550, stir at 45℃ for 25min to obtain hydrolysate, immerse 100g of treated CFRP mesh in 1000g of hydrolysate, sonicate for 40min, remove and dry to obtain modified CFRP mesh.
[0033] II. Preparation of Modified Thickeners: A1. Dissolve 10g of hydroxypropyl methylcellulose in 200g of anhydrous dimethyl sulfoxide and stir at 55℃ for 2.5h. Then add 0.5g of 4-dimethylaminopyridine and 3.5g of triethylamine and stir under nitrogen protection for 35min to obtain the reaction system.
[0034] A2. Take 10g of N-isopropylacrylamide and 3g of methacrylic acid, dissolve them in 80g of anhydrous ethanol to obtain a monomer solution, add 50g of the monomer solution dropwise to 150g of the reaction system, add 0.75g of azobisisobutyronitrile, stir and react for 9h under nitrogen protection at 65℃. After the reaction is completed, add anhydrous ethanol to precipitate, and collect the precipitate by filtration.
[0035] A3. Dissolve 20g of the precipitate in 200g of deionized water, dialyze for 44h, and dry after dialyzing to obtain the modified thickener.
[0036] III. Preparation of High-Toughness FRCM-Reinforced RC Beams: S1. Cut the modified CFRP mesh according to the design dimensions, apply carbon fiber (two-component epoxy resin type carbon fiber impregnation adhesive) to the surface of the modified CFRP mesh, cure for 78 hours, and then assemble the cured modified CFRP mesh with the wooden template to make a composite template. S2. Clean and roughen the reinforcement area 20 around the existing RC beam 10, then apply a layer of carbon fiber adhesive (two-component epoxy resin type carbon fiber impregnation adhesive) to the surface of the reinforcement area 20 around the existing RC beam 10, and attach the composite template to the reinforcement area of the existing RC beam 10 after applying the adhesive. S3. The ECC is poured into the cavity between the composite template and the existing RC beam 10 in three layers to form a high-toughness FRCM layer 30. Each layer corresponds to a modified CFRP mesh. After each layer is poured, it is vibrated for 18 seconds. After the pouring is completed, the exposed surface is scraped and smoothed, and then placed in a standard concrete curing room for 30 days to obtain the RC beam 40 reinforced with high-toughness FRCM.
[0037] ECC weighs each raw material according to the following quantities: 6000g cement, 6000g fly ash, 4300g quartz sand, 3400g water, 200g polyethylene fiber, 35g polycarboxylate ether high-efficiency water-reducing agent, 13g modified thickener, 13g non-silicone high-carbon alcohol polyether ester defoamer: Premix the dry powder materials (cement, fly ash, and quartz sand) for 2 minutes, add an aqueous solution of polycarboxylate ether high-efficiency water-reducing agent, modified thickener, and non-silicone high carbon alcohol polyether ester defoamer, stir for 3 minutes, and finally add polyethylene fiber and continue stirring for 2 minutes until uniformly dispersed.
[0038] Example 3: A method for reinforcing RC beams with high-toughness FRCM includes the following steps: I. Preparation of modified CFRP mesh: S11. Take 100g of CFRP mesh (12K twisted type, mesh size 20mm×20mm, cross-sectional area of a single fiber bundle 1mm²). 2 The CFRP mesh was immersed in 1500g of anhydrous ethanol and ultrasonically treated for 2h. After being removed and dried, the desized CFRP mesh was obtained. 100g of the desized CFRP mesh was immersed in 2000g of concentrated nitric acid (68% by mass) and treated at 80℃ for 6h. It was then rinsed with deionized water until the pH of the washing solution was 8. After drying, the oxidized CFRP mesh was obtained.
[0039] S12. Place 100g of oxidized CFRP mesh in 3000g of tetrahydrofuran, add 15g of lithium aluminum hydride, stir at 60℃ for 2h, add 150g of hydrochloric acid (concentration 2mol / L), continue stirring for 2h, filter out the oxidized CFRP mesh, soak and wash in tetrahydrofuran for 24h, and dry to obtain the treated CFRP mesh.
[0040] S13. Mix 500g of ethanol with 250g of deionized water, adjust the pH to 4 with acetic acid, add 75g of KH550, stir at 50℃ for 30min to obtain hydrolysate, immerse 100g of treated CFRP mesh in 1500g of hydrolysate, sonicate for 50min, remove and dry to obtain modified CFRP mesh.
[0041] II. Preparation of Modified Thickeners: A1. Dissolve 10g of hydroxypropyl methylcellulose in 250g of anhydrous dimethyl sulfoxide and stir at 60℃ for 3h. Then add 0.8g of 4-dimethylaminopyridine and 50g of triethylamine and stir under nitrogen protection for 40min to obtain the reaction system.
[0042] A2. Take 10g of N-isopropylacrylamide and 4g of methacrylic acid, dissolve them in 100g of anhydrous ethanol to obtain a monomer solution, add 50g of the monomer solution dropwise to 200g of the reaction system, add 1g of azobisisobutyronitrile, stir and react for 10h under nitrogen protection at 70℃. After the reaction is completed, add anhydrous ethanol to precipitate, and collect the precipitate by filtration.
[0043] A3. Dissolve 20g of the precipitate in 300g of deionized water, dialyze for 48h, and dry after dialysis to obtain the modified thickener.
[0044] III. Preparation of High-Toughness FRCM-Reinforced RC Beams: S1. Cut the modified CFRP mesh according to the design dimensions, apply carbon fiber adhesive (two-component epoxy resin type carbon fiber impregnation adhesive) to the surface of the modified CFRP mesh, cure for 84 hours, and then assemble the cured modified CFRP mesh with the wooden template to make a composite template. S2. Clean and roughen the reinforcement area 20 around the existing RC beam 10, then apply a layer of carbon fiber adhesive (two-component epoxy resin type carbon fiber impregnation adhesive) to the surface of the reinforcement area 20 around the existing RC beam 10, and attach the composite template to the reinforcement area of the existing RC beam 10 after applying the adhesive. S3. The ECC is poured into the cavity between the composite template and the existing RC beam 10 in three layers to form a high-toughness FRCM layer 30. Each layer corresponds to a modified CFRP mesh. After each layer is poured, it is vibrated for 20 seconds. After the pouring is completed, the exposed surface is scraped and smoothed, and then placed in a standard concrete curing room for 32 days to obtain the RC beam 40 reinforced with high-toughness FRCM.
[0045] ECC weighs each raw material according to the following quantities: 6500g cement, 6500g fly ash, 4800g quartz sand, 3800g water, 220g polyethylene fiber, 45g polycarboxylate ether high-efficiency water-reducing agent, 18g modified thickener, 18g non-silicone high-carbon alcohol polyether ester defoamer: Premix the dry powder materials (cement, fly ash, and quartz sand) for 2 minutes, add an aqueous solution of polycarboxylate ether high-efficiency water-reducing agent, modified thickener, and non-silicone high carbon alcohol polyether ester defoamer, stir for 3 minutes, and finally add polyethylene fiber and continue stirring for 2 minutes until uniformly dispersed.
[0046] Comparative Example 1: Comparative Example 1 differs from Example 1 in that the modified thickener is replaced with an equal mass of hydroxypropyl methylcellulose, and the remaining steps are exactly the same as in Example 1.
[0047] Comparative Example 2: Comparative Example 2 differs from Example 1 in that the modified CFRP mesh is replaced with a CFRP mesh of equal quality, while the remaining steps are exactly the same as in Example 1.
[0048] Comparative Example 3: Comparative Example 3 differs from Example 1 in that the modified thickener is replaced with an equal mass of hydroxypropyl methylcellulose, and the modified CFRP mesh is replaced with an equal mass of CFRP mesh. The remaining steps are exactly the same as in Example 1.
[0049] Comparative Example 4: Comparative Example 4, compared to Example 1, uses 0-layer, 1-layer, and 2-layer modified CFRP meshes for assembly, with the remaining steps being exactly the same as in Example 1.
[0050] The aforementioned existing RC beam is a simply supported rectangular beam with a cross-sectional dimension of 120mm (width) × 200mm (height) and a total beam length of 1900mm, and is cast with C30 concrete.
[0051] The reinforced RC beams prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to the following performance tests: The test beam was placed on an electro-hydraulic servo universal testing machine with a support span of 1650 mm and a distance of 500 mm between the two loading points. The loading method adopted displacement control, and the loading rate was 0.5 mm / min. An LVDT displacement sensor with a range of 50 mm was placed at the bottom of the mid-span of the test beam to monitor the vertical displacement of the test beam during the entire loading process. Strain gauges were attached to the tensile longitudinal reinforcement and the concrete surface of the compression zone at the mid-span section of the test beam. Load, displacement, and strain data were collected in real time using a TDS-540 static data acquisition instrument. During the loading process, the cracking load, yield load, and ultimate load of the test beam were determined by the load-displacement curve. The yield load was the load value corresponding to the yielding of the tensile longitudinal reinforcement, the ultimate load was the load value corresponding to the peak point of the load-displacement curve, and the mid-span deflection was the displacement gauge reading at the time corresponding to the ultimate load. The average value of the yield load, ultimate load, and ultimate deflection of each specimen was taken as the final test result, and its failure mode was recorded. The specific test results are shown in Table 1.
[0052] Table 1: Performance Test Table for High-Toughness FRCM-Reinforced RC Beams As shown in Table 1, the yield load (65.0 kN) and ultimate load (83.9 kN) of Example 1 were increased by 94.6% and 63.9% respectively compared to the unreinforced beam (0th floor in Comparative Example 4). In Comparative Example 1, after replacing the modified thickener with ordinary HPMC, the yield load and ultimate load decreased to 53.2 kN and 67.8 kN respectively, representing reductions of 18.2% and 19.2%. In Comparative Example 2, after replacing the modified CFRP mesh with the original CFRP mesh, the yield load and ultimate load decreased to 57.5 kN and 72.4 kN respectively, representing a reduction of 11.5%. The yield load and ultimate load in Comparative Example 3 were reduced by 13.7% after simultaneous replacement; the yield load and ultimate load in Comparative Example 3 were further reduced to 47.1 kN and 58.3 kN, respectively, representing a decrease of 27.5% and 30.5% compared to Example 1. The above comparison shows that the effect of using modified CFRP mesh alone or modified thickener alone on improving load-bearing capacity is limited, while the synergistic effect of the two can increase the ultimate load by 70.0% compared to Comparative Example 3. This proves the effectiveness of the oxidized-grafted modified CFRP mesh and the polar groups such as carboxyl and amide groups on the molecular chain of the modified thickener in constructing a multi-level interface transition region through chemical bonding and strong intermolecular interactions.
[0053] This invention effectively suppresses the end-peeling failure mode through interface reinforcement, allowing the tensile strength of the CFRP mesh to be fully utilized. The failure modes of Examples 1-3 are all characterized by a decrease in load-bearing capacity after CFRP mesh fracture, while Comparative Examples 1-3 all show end-peeling failure of the reinforcement layer. This indicates that the stress concentration points caused by abrupt changes in material properties at the fiber-matrix interface in the traditional FRCM system are effectively eliminated by the construction of multi-level interface transition zones. Stress is gradient-transferred and smoothly transitioned between the fiber and the matrix. As the number of modified CFRP mesh layers increases from 1 to 3, the yield load increases from 65.0 kN to 76.9 kN, and the ultimate load increases from 83.9 kN to 99.1 kN, representing increases of 94.6%-130.2% and 63.9%-93.6% respectively compared to the unreinforced beam. This shows that increasing the number of mesh layers can further improve the reinforcement effect, and because no peeling failure occurs at the interface, the tensile performance of the CFRP mesh is fully utilized.
[0054] Figure 5 To compare the failure mode of the 0-layer modified CFRP mesh specimen in Example 4, the specimen exhibits typical bending failure characteristics of a properly reinforced beam, that is, after the tensile longitudinal reinforcement yields, the concrete in the compression zone reaches the ultimate compressive strain and is crushed. The number of cracks on the beam surface is small and the width is large, which is the benchmark failure mode of an unreinforced RC beam.
[0055] Figure 6 To compare the failure mode of the specimen using a single layer of modified CFRP mesh in Example 4, obvious interfacial peeling cracks appeared at the end of the reinforcement layer when the specimen failed. The cracks rapidly propagated along the interface between the reinforcement layer and the RC beam matrix, eventually leading to the separation of the reinforcement layer from the beam and the failure of the FRCM reinforcement system. The modified CFRP mesh did not fracture at the time of failure, and its tensile strength was not fully utilized.
[0056] Figure 7 To compare the failure modes of the specimen using two layers of modified CFRP mesh in Example 4, the failure mode of the specimen changed to fracture of the modified CFRP mesh. Dense fine cracks were visible on the surface of the reinforcement layer in the mid-span pure bending section. The cracks were small in width and uniformly distributed, indicating that the multi-crack cracking characteristics of the ECC matrix were effectively utilized. No peeling phenomenon occurred at the end of the reinforcement layer at the time of failure. The bearing capacity decreased after the modified CFRP mesh was broken.
[0057] Figure 8 The failure mode of the specimen in Example 1 is the same as that of the modified CFRP mesh fracture failure, but it is similar to... Figure 7 In comparison, the mid-span pure bending section has more cracks, smaller crack spacing, and more uniform distribution, and the end interface remains intact. This indicates that the synergistic effect of the modified CFRP mesh and the modified thickener further strengthens the interfacial bonding, enabling the FRCM reinforcement layer to work together with the RC beam body as a whole to the ultimate state.
[0058] comprehensive Figures 5 to 8 The evolution of the failure modes shows that as the number of modified CFRP mesh layers increases from 0 to 3, the failure mode of the specimen changes from concrete crushing to modified CFRP mesh fracture. End peeling failure is effectively suppressed, and the tensile strength of the modified CFRP mesh is fully utilized. This verifies the effectiveness of the present invention in suppressing interface peeling, realizing the synergistic working mechanism of ECC dispersion cracking and modified CFRP mesh load bearing by constructing a multi-level interface transition zone through oxidation-grafted modified CFRP mesh and modified thickener.
[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for reinforcing RC beams with high-toughness FRCM, characterized in that, Includes the following steps: S1. Cut the modified CFRP mesh according to the design dimensions, apply carbon fiber adhesive to the surface of the modified CFRP mesh, cure for 72-84 hours, and then assemble the cured modified CFRP mesh with the wooden template to make a composite template. S2. Clean and roughen the reinforcement area around the existing RC beam, then apply a layer of carbon fiber adhesive to the surface of the reinforcement area around the existing RC beam, and attach the composite template to the reinforcement area of the existing RC beam after applying the adhesive. S3. The ECC is poured into the cavity between the composite template and the existing RC beam in three layers to form a high-toughness FRCM layer. Each layer corresponds to a modified CFRP mesh. After each layer is poured, it is vibrated for 15-20 seconds. After the pouring is completed, the exposed surface is scraped and smoothed, and then placed in a standard concrete curing room for 28-32 days to obtain an RC beam reinforced with high-toughness FRCM. The modified CFRP mesh is prepared through the following steps: S11. Immerse the CFRP mesh in anhydrous ethanol and sonicate for 1-2 hours. Remove and dry to obtain desizing CFRP mesh. Immerse the desizing CFRP mesh in concentrated nitric acid and treat at 60-80℃ for 4-6 hours. Rinse with deionized water until the pH of the washing solution is 6-8. Dry to obtain oxidized CFRP mesh. S12. Place the oxidized CFRP mesh in tetrahydrofuran, add lithium aluminum hydride, stir at 40-60℃ for 1-2 hours, add hydrochloric acid, continue stirring for 1-2 hours, filter out the oxidized CFRP mesh, soak and wash in tetrahydrofuran for 20-24 hours, and dry to obtain the treated CFRP mesh. S13, ethanol and deionized water are mixed, pH is adjusted to 3-4 with acetic acid, KH550 is added, and the mixture is stirred at 40-50℃ for 20-30 min to obtain a hydrolysate. The treated CFRP grid is immersed in the hydrolysate and ultrasonically treated for 30-50 min. After drying, the modified CFRP grid is obtained. The ECC is formulated with 550-650 parts by weight of cement, 550-650 parts by weight of fly ash, 380-480 parts by weight of quartz sand, 18-22 parts by weight of polyethylene fiber, 2.5-4.5 parts by weight of polycarboxylate ether high-efficiency water-reducing agent, 0.8-1.8 parts by weight of modified thickener, 0.8-1.8 parts by weight of non-silicone high carbon alcohol polyether ester defoamer and 300-380 parts by weight of water.
2. The method for reinforcing RC beams with high-toughness FRCM according to claim 1, characterized in that, The modified thickener is prepared through the following steps: A1. Dissolve hydroxypropyl methylcellulose in anhydrous dimethyl sulfoxide and stir at 50-60℃ for 2-3 hours. Then add 4-dimethylaminopyridine and triethylamine and stir under nitrogen protection for 30-40 minutes to obtain the reaction system. A2. Dissolve N-isopropylacrylamide and methacrylic acid in anhydrous ethanol to obtain a monomer solution. Add the monomer solution dropwise to the reaction system, add azobisisobutyronitrile, and stir the reaction under nitrogen protection at 60-70℃ for 8-10 hours. After the reaction is completed, add anhydrous ethanol to precipitate the product, and collect the precipitate by filtration. A3. Dissolve the precipitate in deionized water, dialyze for 40-48 hours, and dry after dialyzing to obtain the modified thickener.
3. The method for reinforcing RC beams with high-toughness FRCM according to claim 1, characterized in that, The CFRP mesh in S1 is a woven 12K carbon fiber mesh with a mesh size of 20mm × 20mm, and the cross-sectional area of a single CFRP fiber bundle in the mesh is 1mm². 2 .
4. The method for reinforcing RC beams with high-toughness FRCM according to claim 1, characterized in that, The mass ratio of A glue to B glue in S1 is (2-3):1, and the mass ratio of the modified CFRP mesh surface to carbon fiber glue is 1:(0.8-1.5).
5. The method for reinforcing RC beams with high-toughness FRCM according to claim 1, characterized in that, In S11, the mass ratio of CFRP mesh to anhydrous ethanol is 1:(5-15), and the mass ratio of desizing CFRP mesh to concentrated nitric acid is 1:(10-20).
6. The method for reinforcing RC beams with high-toughness FRCM according to claim 1, characterized in that, The mass ratio of CFRP mesh oxide, tetrahydrofuran, lithium aluminum hydride and hydrochloric acid in S12 is 1:(15-30):(0.05-0.15):(0.5-1.5).
7. The method for reinforcing RC beams with high-toughness FRCM according to claim 1, characterized in that, The mass ratio of ethanol, deionized water and KH550 in S13 is 1:(0.3-0.5):(0.08-0.15), and the mass ratio of the CFRP mesh to the hydrolysate is 1:(5-15).
8. The method for reinforcing RC beams with high-toughness FRCM according to claim 2, characterized in that, The mass ratio of hydroxypropyl methylcellulose, anhydrous dimethyl sulfoxide, 4-dimethylaminopyridine and triethylamine in A1 is 1:(15-25):(0.03-0.08):(0.2-0.5).
9. The method for reinforcing RC beams with high-toughness FRCM according to claim 2, characterized in that, The mass ratio of N-isopropylacrylamide, methacrylic acid and anhydrous ethanol in A2 is 1:(0.2-0.4):(5-10), and the mass ratio of monomer solution, reaction system and azobisisobutyronitrile is 1:(2-4):(0.01-0.02).
10. A method for reinforcing RC beams with high-toughness FRCM according to claim 2, characterized in that, The mass ratio of the precipitate to deionized water in A3 is 1:(5-15).