Cementitious Materials with Structural Reinforcement and Health Monitoring Functions, Preparation Method and Application

Abstract

The present invention discloses a cement-based material with both structural reinforcement and health monitoring functions, a preparation method and an application thereof. The cement-based material with both structural reinforcement and health monitoring functions includes a hybrid fiber cement matrix and a continuous carbon fiber grid. The continuous carbon fiber grid is disposed inside the hybrid fiber cement matrix. The hybrid fiber cement matrix comprises the following components in parts by weight: 1000 parts of cement, 300 parts of silica fume, 390 parts of fine aggregate, 390 parts of water, 8.75 - 13.13 parts of carbon fiber, 12.13 - 14.55 parts of polyethylene fiber, 6 - 7 parts of water reducing agent, and 0.3 - 0.4 parts of thickening agent. The cement-based material with both structural reinforcement and health monitoring functions proposed by the present invention can simultaneously achieve two functions of structural reinforcement and structural health monitoring on a damaged concrete structure by using only this one material, reducing the construction process, saving building materials, improving construction efficiency, and making full use of the self-attributes of the cement-based material of the present invention, thus having remarkable economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of cement-based materials, and particularly to a cement-based material with both structural reinforcement and health monitoring functions, a preparation method thereof, and an application thereof. Background Art

[0002] The urban construction in China is shifting from a large-scale new construction stage to a stage that emphasizes both new construction and repair and renovation. The scale of new construction is tending to be stable, and the focus of the construction market is on the reinforcement and renovation of existing building structures. Reinforcing and renovating existing building structures can not only improve the strength, stiffness, stability, and durability of existing structures, meet the service functions and safety of the structures, but also achieve the purpose of extending the service life of building structures, saving building resources, reducing carbon emissions, and promoting the sustainable development of buildings. The existing structural reinforcement methods mainly include: increasing cross-section reinforcement method, bonding steel reinforcement method, bonding fiber composite material reinforcement method, etc. It should be noted that the reinforced reinforced concrete structure also needs to be monitored for structural health to ensure the safety and reliability of the reinforced structure. However, the traditional structural health monitoring system is time-consuming, laborious, costly, and has low durability.

[0003] Therefore, it is necessary to develop and invent a dual-functional composite material with both structural reinforcement and health monitoring functions to meet the purposes of easy installation, cost savings, and strong durability. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, the present invention provides a cement-based material with both structural reinforcement and health monitoring functions, a preparation method thereof, and an application thereof, so as to solve the problem that the existing cement-based materials cannot simultaneously achieve structural reinforcement and health monitoring.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] In the first aspect of the present invention, there is provided a cement-based material with both structural reinforcement and health monitoring functions. The cement-based material with both structural reinforcement and health monitoring functions includes a hybrid fiber cement matrix and a continuous carbon fiber grid. The continuous carbon fiber grid is disposed inside the hybrid fiber cement matrix. The hybrid fiber cement matrix includes the following components in parts by weight: 1000 parts of cement, 300 parts of silica fume, 390 parts of fine aggregate, 390 parts of water, 8.75 - 13.13 parts of carbon fiber, 12.13 - 14.55 parts of polyethylene fiber, 6 - 7 parts of water reducer, and 0.3 - 0.4 parts of thickener.

[0007] Preferably, the dosage of the carbon fiber is 0.50% - 0.75% of the volume of the cement-based material with both structural reinforcement and health monitoring functions.

[0008] Preferably, the dosage of the polyethylene fiber is 1.25% - 1.50% of the volume of the cement-based material with both structural reinforcement and health monitoring functions.

[0009] Preferably, the diameter of the carbon fiber is 7 - 10 μm, the length is 3 - 6 mm, the resistivity is 1.0 - 1.6 Ω·cm, and the tensile modulus is 230 - 250 GPa.

[0010] Preferably, the diameter of the polyethylene fiber is 20 - 50 μm, the length is 18 - 30 mm, the elongation at break is 1% - 3%, and the tensile modulus is 110 - 130 GPa.

[0011] Preferably, the tensile strength of the continuous carbon fiber grid is 2700 - 3700 MPa, the tensile modulus is 230 - 250 GPa, the elongation rate is 1.2% - 1.5%, and the carbon content is 93% - 96%.

[0012] In the second aspect of the present invention, a preparation method of the above-mentioned cement-based material with both structural reinforcement and health monitoring functions is provided. The preparation method includes the following steps:

[0013] Mix the cement, silica fume, fine aggregate, water, carbon fiber, polyethylene fiber, water reducer, and thickening agent according to weight parts to obtain a hybrid fiber cement matrix slurry;

[0014] Place the continuous carbon fiber grid inside the hybrid fiber cement matrix slurry to obtain a cement-based precursor material;

[0015] Carry out curing and maintenance treatments on the cement-based precursor material in sequence to obtain the cement-based material with both structural reinforcement and health monitoring functions, which contains a hybrid fiber cement matrix and a continuous carbon fiber grid.

[0016] Preferably, the step of mixing the cement, silica fume, fine aggregate, water, carbon fiber, polyethylene fiber, water reducer, and thickening agent according to weight parts to obtain a hybrid fiber cement matrix slurry specifically includes:

[0017] Mix the cement, silica fume, and fine aggregate, and stir at a speed of 135 - 145 revolutions per minute for 3 - 5 minutes to obtain a mixed dry material;

[0018] Add water and 50% by weight of the water reducer to the mixed dry material, first stir at a speed of 135 - 145 revolutions per minute for 3 - 5 minutes, and then stir at a speed of 275 - 295 revolutions per minute for 3 - 5 minutes to obtain a first mixed material;

[0019] Stir the first mixed material at a rotation speed of 135 - 145 revolutions per minute, and add polyethylene fibers to the first mixed material. After all the polyethylene fibers are added to the first mixed material, continue to stir at a rotation speed of 275 - 295 revolutions per minute for 5 - 8 minutes to obtain a second mixed material;

[0020] Stir the second mixed material at a rotation speed of 135 - 145 revolutions per minute, and add a thickening agent, carbon fibers, and the remaining water reducing agent to the second mixed material. After all the thickening agent, carbon fibers, and the remaining water reducing agent are added to the second mixed material, continue to stir at a rotation speed of 275 - 295 revolutions per minute for 3 - 5 minutes to obtain the hybrid fiber cement matrix slurry.

[0021] Preferably, the step of disposing the continuous carbon fiber grid inside the hybrid fiber cement matrix slurry to obtain the cement - based precursor material specifically includes:

[0022] Pour a layer of hybrid fiber cement matrix slurry;

[0023] Place the continuous carbon fiber grid on the surface of the hybrid fiber cement matrix slurry, and apply a certain pressure to make the hybrid fiber cement matrix slurry infiltrate with the continuous carbon fiber grid;

[0024] Pour another layer of hybrid fiber cement matrix slurry on the continuous carbon fiber grid to obtain the cement - based precursor material.

[0025] In the third aspect of the present invention, there is provided the application of the above - mentioned cement - based material with both structural reinforcement and health monitoring or the cement - based material with both structural reinforcement and health monitoring prepared by the above - mentioned preparation method in the field of structural health monitoring.

[0026] Beneficial effects:

[0027] The present invention breaks through the limitations of the existing fiber - grid - reinforced cement - based composite material (FRCM) structural reinforcement technology, proposes a design idea based on fiber hybridization, and takes the optimized design of the cement mortar matrix as a means to invent a cement - based material with both structural reinforcement and health monitoring, providing an economical, effective, reliable reinforcement and health monitoring scheme for the existing FRCM reinforcement method to ensure the safety and reliability of the reinforced concrete structure. The added carbon fibers and polyethylene fibers make the cement - based composite material have good electrical conductivity and self - sensing function, and the toughness and crack - resistance performance of the cement matrix material are significantly enhanced, which can reduce the fracture and failure of the self - sensing conductive network, enabling the continuous carbon fiber grid in the present invention to have a composite failure mode of tensile fracture and slip, and further improving the utilization efficiency of the mechanical strength of the continuous carbon fiber grid, so that the FRCM of the present invention shows better mechanical properties in structural reinforcement. Description of the Drawings

[0028] Figure 1 Schematic structural diagram of the cement-based material provided by the present invention that combines structural reinforcement and health monitoring;

[0029] Figure 2 Schematic diagram showing the relationship between the resistivity change rate and the tensile strain of the cement-based material in Application Example 1 under tensile state;

[0030] Figure 3 Schematic diagram showing the relationship between the resistivity change rate and the tensile strain of the cement-based material in Application Example 2 under tensile state;

[0031] Figure 4 Schematic diagram showing the relationship between the resistivity change rate and the tensile strain of the cement-based material in Application Example 3 under tensile state. Detailed Embodiments

[0032] The present invention provides a cement-based material that combines structural reinforcement and health monitoring, as well as a preparation method and application thereof. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] Fabric Reinforced Cementitious Mortar (FRCM) is a new type of structural reinforcement material. Compared with the traditional FRP reinforcement method, the FRCM reinforcement method uses cement mortar as the bonding cementitious material to replace the organic epoxy resin glue in the FRP reinforcement method, making FRCM have advantages such as good durability, convenient construction, good reinforcement effect, and good compatibility with the original concrete structure. FRCM has been widely used in the repair and reinforcement projects of concrete and masonry structures, and industry standards and certification specifications have been established. FRCM provides a new technical means and option for the reinforcement industry.

[0034] The material properties of FRCM mainly depend on the design of the continuous fiber grid (cloth) as the reinforcement phase and the cement mortar matrix as the binder. Currently, FRCM is only used as a structural reinforcement material in the repair and reinforcement projects of building structures, with single material functionality and unable to be used as a structural health monitoring sensor to evaluate the health status of the reinforced structure, detect damage location, and identify damage types, etc. Therefore, it is necessary to optimize the design of the cement mortar matrix, invent a cement-based composite material that combines structural reinforcement and health monitoring, and propose an effective monitoring implementation method, which has important engineering significance for improving the safety and reliability of existing concrete structures.

[0035] Based on this, the present invention provides a cementitious material that combines structural reinforcement and health monitoring. The cementitious material that combines structural reinforcement and health monitoring includes a hybrid fiber cement matrix and a continuous carbon fiber grid. The continuous carbon fiber grid is disposed inside the hybrid fiber cement matrix. The hybrid fiber cement matrix includes the following components in parts by weight: 1000 parts of cement, 300 parts of silica fume, 390 parts of fine aggregate, 390 parts of water, 8.75 - 13.13 parts of carbon fiber, 12.13 - 14.55 parts of polyethylene fiber, 6 - 7 parts of water reducing agent, and 0.3 - 0.4 parts of thickening agent.

[0036] Hybrid Fiber Reinforced Cementitious Composites (HyFRCC) is a new type of building engineering material formed by mutually coordinating and mixing a variety of short-cut fibers in a cement matrix, which can make up for the deficiencies of single fiber doping and has good comprehensive properties. The cementitious material that combines structural reinforcement and health monitoring provided by the present invention includes carbon fiber and polyethylene fiber. As a conductive phase material, carbon fiber can be evenly dispersed in the cement matrix under effective dispersion and mixing techniques, and then form a wide conductive network inside it. By inputting a constant current into the cementitious material through an electrode, it can form a current conduction similar to the percolation property through the conductive network and the quantum electron tunneling effect, so that the cementitious material has a self-sensing function. At the same time, when the cementitious material of the present invention reinforces a concrete structure, the cementitious material is in a tensile state, and the hybrid fiber cement matrix therein is also stretched and deformed and cracked. However, due to the fiber bridging effect between the polyethylene fiber and the continuous fiber grid and the hybrid fiber cement matrix, the hybrid fiber cement matrix shows a multi-crack cracking form, and the average crack width is less than 0.1 mm. Under the working state with cracks, there is still an effective conductive network inside the cementitious material, and its resistivity also changes with the change of the tensile force received by the cementitious material. By analyzing the resistivity change curve of the hybrid fiber cement matrix, the tensile force and deformation size received by the cementitious material can be measured.

[0037] At the same time, as the continuous carbon fiber grid of the reinforcing phase not only has high mechanical strength and good durability, the cementitious material formed by combining it with the hybrid fiber cement matrix shows good crack resistance. Also, due to the excellent conductive characteristics of the continuous carbon fiber grid, the connectivity of the conductive network can be maintained even when the cementitious material cracks.

[0038] Specifically, the hybrid fiber cement matrix of the present invention serves as both the matrix of the FRCM composite material and the binder between the continuous carbon fiber grid and the concrete. The cement-based material and the concrete belong to the same type of cement-based inorganic materials, and the two have good compatibility, so the bonding strength between them is relatively high, and effective stress transfer can be carried out. There are chemical bonding forces, frictional forces and grid anchoring effects between the continuous carbon fiber grid and the hybrid fiber cement matrix, so effective stress transfer can also occur between the two. In addition, both the continuous carbon fiber grid reinforcement phase and the carbon fiber / polyethylene hybrid fiber hybrid fiber cement matrix phase in the present invention have relatively high tensile strength and tensile strain. Therefore, externally bonded FRCM can effectively improve the bearing capacity of the reinforced concrete structure.

[0039] Moreover, the hybrid fiber cement matrix in the present invention is a hybrid fiber cement-based (HyFRCC) formed by the coordinated mixing of carbon fibers and polyethylene fibers in the hybrid fiber cement matrix, which can make up for the deficiencies of fiber-free or single-fiber doping and has good comprehensive performance. The cement-based material formed by the combination of HyFRCC and the continuous carbon fiber grid has higher tensile strength and tensile deformation. Especially when the cement-based material is used to reinforce the concrete structure, the cement-based material is in a tensile state. HyFRCC and the continuous carbon fiber grid work together. HyFRCC shows a multi-crack cracking form under tensile action, and the average crack width is less than 0.1 mm. For the traditional FRCM formed by an ordinary cement matrix or a single-fiber doped cement matrix, the brittle fracture of the matrix causes the continuous carbon fiber grid to slip and fail, and the mechanical strength utilization efficiency of the continuous carbon fiber grid is not high. However, the continuous carbon fiber grid in the HyFRCC of the present invention undergoes a composite failure mode of tensile fracture and slip, and the mechanical strength utilization efficiency of the continuous carbon fiber grid is further improved. Therefore, the FRCM of the present invention shows better mechanical properties in structural reinforcement.

[0040] In some embodiments, the dosage of the carbon fiber is 0.50% - 0.75% of the volume of the cement-based material with both structural reinforcement and health monitoring functions.

[0041] In some preferred embodiments, the dosage of the carbon fiber is 0.5% of the volume of the cement-based material with both structural reinforcement and health monitoring functions.

[0042] When the volume fraction of carbon fiber is less than 0.50%, an effective conductive network cannot be formed inside the cement-based material. Under tensile or bending loads, the increased spacing between carbon fibers causes the conductive path to be interrupted, resulting in a sudden increase in the resistivity of the cement-based material and the failure of the self-sensing function of tensile or flexural resistance. When the volume fraction of carbon fiber is greater than 0.75%, a complete conductive path is formed inside the cement-based material. Under tensile or bending loads, although the spacing between carbon fibers increases, the carbon fibers still maintain a good conductive path, and the change in the resistivity of the cement-based material is small, and the sensitivity of the cement-based material is low.

[0043] In some embodiments, the content of the polyethylene fiber is 1.25% - 1.50% of the volume of the cement-based material with both structural reinforcement and health monitoring functions.

[0044] In some preferred embodiments, the content of the polyethylene fiber is 1.25% of the volume of the cement-based material with both structural reinforcement and health monitoring functions.

[0045] When the volume fraction of the polyethylene fiber is less than 1.25%, sufficient fiber bridging strength cannot be formed inside the cement-based material. Under tensile or bending loads, it is difficult for the cement-based material to form a multi-crack cracking pattern, and the crack width is large, which easily causes the fracture and failure of the self-sensing conductive network. When the volume fraction of the polyethylene fiber is greater than 1.50%, the total fiber content inside the hybrid fiber cement-based material is large. During the mixing and pouring preparation process of the cement paste, it is easy to cause poor fiber dispersion, which not only affects the formation of the conductive network of the cement-based material but also affects the mechanical properties of the cement-based material.

[0046] In some embodiments, the diameter of the carbon fiber is 7 - 10 μm, the length is 3 - 6 mm, the resistivity is 1.0 - 1.6 Ω·cm, and the tensile modulus is 230 - 250 GPa.

[0047] In some preferred embodiments, the diameter of the carbon fiber is 7 μm, the length is 6 mm, the resistivity is 1.0 Ω·cm, and the tensile modulus is 230 GPa.

[0048] In some embodiments, the diameter of the polyethylene fiber is 20 - 50 μm, the length is 18 - 30 mm, the elongation at break is 1% - 3%, and the tensile modulus is 110 - 130 GPa.

[0049] In some preferred embodiments, the diameter of the polyethylene fiber is 24 μm, the length is 18 mm, the elongation at break is 3%, and the tensile modulus is 120 GPa.

[0050] In some embodiments, the continuous carbon fiber grid has a tensile strength of 2700 - 3700 MPa, a tensile modulus of 230 - 250 GPa, an elongation at break of 1.2 - 1.5%, and a carbon content of 93 - 96%.

[0051] In some preferred embodiments, the continuous carbon fiber grid has a tensile strength of 3500 MPa, a tensile modulus of 230 GPa, an elongation at break of 1.5%, and a carbon content of 93%.

[0052] In some embodiments, there is also provided a method for preparing the above cement-based material with both structural reinforcement and health monitoring functions. The preparation method includes the following steps:

[0053] Mix the cement, silica fume, fine aggregate, water, carbon fiber, polyethylene fiber, water reducer, and thickener according to parts by weight to obtain a hybrid fiber cement matrix slurry;

[0054] Dispose the continuous carbon fiber grid inside the hybrid fiber cement matrix slurry to obtain a cement-based precursor material;

[0055] Cure and maintain the cement-based precursor material in sequence to obtain the cement-based material with both structural reinforcement and health monitoring functions, which includes a hybrid fiber cement matrix and a continuous carbon fiber grid.

[0056] In some embodiments, the step of mixing the cement, silica fume, fine aggregate, water, carbon fiber, polyethylene fiber, water reducer, and thickener according to parts by weight to obtain a hybrid fiber cement matrix slurry specifically includes:

[0057] Mix the cement, silica fume, and fine aggregate, and stir at a rotation speed of 135 - 145 revolutions per minute for 3 - 5 minutes to obtain a mixed dry material;

[0058] Add water and 50% parts by weight of the water reducer to the mixed dry material, first stir at a rotation speed of 135 - 145 revolutions per minute for 3 - 5 minutes, and then stir at a rotation speed of 275 - 295 revolutions per minute for 3 - 5 minutes to obtain a first mixed material;

[0059] Stir the first mixed material at a rotation speed of 135 - 145 revolutions per minute, and add polyethylene fiber to the first mixed material. After all the polyethylene fiber is added to the first mixed material, continue to stir at a rotation speed of 275 - 295 revolutions per minute for 5 - 8 minutes to obtain a second mixed material;

[0060] Stir the second mixed material at a rotation speed of 135 - 145 revolutions per minute, and add a thickening agent, carbon fiber, and the remaining water reducing agent to the second mixed material. After all of the thickening agent, carbon fiber, and the remaining water reducing agent are added to the second mixed material, continue to stir at a rotation speed of 275 - 295 revolutions per minute for 3 - 5 minutes to obtain the hybrid fiber cement matrix slurry.

[0061] In the present invention, first, cement, silica fume, and fine aggregate are mixed, which can make the mixed dry material uniform and is beneficial to the cement hydration process of the subsequent cement-based material. Water and 50% by weight of the water reducing agent are added to the mixed dry material, and a cement paste with good workability can be obtained under sufficient stirring, which is beneficial to the subsequent dispersion of fibers. The water absorption rate of polyethylene fiber is less than that of carbon fiber. Adding polyethylene fiber to the first mixed material can form a polyethylene fiber cement paste with strong fiber bridging effect. Adding a thickening agent, carbon fiber, and the remaining water reducing agent to the second mixed material can re-adjust the workability of the cement paste. The addition of the thickening agent and the water reducing agent is beneficial to the dispersion of the hybrid fibers. After sufficient stirring, a cement-based material with good functional and mechanical properties can be formed.

[0062] In some embodiments, the step of disposing the continuous carbon fiber grid inside the hybrid fiber cement matrix slurry to obtain the cement-based precursor material specifically includes:

[0063] Pour a layer of hybrid fiber cement matrix slurry;

[0064] Place the continuous carbon fiber grid on the surface of the hybrid fiber cement matrix slurry, and apply a certain pressure to make the hybrid fiber cement matrix slurry infiltrate with the continuous carbon fiber grid;

[0065] Pour another layer of hybrid fiber cement matrix slurry on the continuous carbon fiber grid to obtain the cement-based precursor material.

[0066] In some embodiments, there is also provided the application of the above cement-based material with both structural reinforcement and health monitoring or the cement-based material with both structural reinforcement and health monitoring prepared by the above preparation method in the field of structural health monitoring.

[0067] The continuous carbon fiber grid in the cement-based material of the present invention has good electrical conductivity. A constant current is input to the cement-based material at both ends of the continuous carbon fiber grid electrode. At the same time, when the cement-based material reinforces the concrete structure, the cement-based material composite is in a tensile state, and the continuous carbon fiber grid therein is also stretched and elongated or partially broken, and the material resistivity of the continuous carbon fiber grid also changes accordingly. Finally, the tensile force and deformation size of the cement-based material are measured by analyzing the resistivity change curve of the continuous carbon fiber grid.

[0068] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments, and are only used to illustrate the present invention without any limitation to the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0069] Example 1

[0070] The preparation of a cement-based material with both structural reinforcement and health monitoring includes the following steps:

[0071] (1) Add 1000 g of cement, 300 g of silica fume, and 390 g of quartz sand into a mixer in sequence, and dry mix at a speed of 140 revolutions per minute for 3 minutes to ensure uniform dispersion of the materials and obtain a mixed dry material;

[0072] (2) Slowly add 390 g of water and 3 g of polycarboxylate superplasticizer to the above mixed dry material, stir at a speed of 140 revolutions per minute for 3 minutes, and then stir at a speed of 285 revolutions per minute for 5 minutes;

[0073] (3) Set the mixer to a speed of 140 revolutions per minute and stir. During this process, slowly add 12.13 g of polyethylene fibers. After all the polyethylene fibers are added, stir at a speed of 285 revolutions per minute for 3 minutes to make them evenly dispersed; among them, the dosage of polyethylene fibers is 1.25%;

[0074] (4) Set the mixer to a speed of 140 revolutions per minute and stir. During this process, add 3 g of polycarboxylate superplasticizer and 0.3 g of hydroxypropyl methylcellulose with a viscosity of 200,000, and slowly add 8.75 g of carbon fibers into it. After all the carbon fibers are added, stir at a speed of 285 revolutions per minute for 2 minutes to obtain a cement-based slurry; among them, the dosage of carbon fibers is 0.50%;

[0075] (5) Nail 5-mm-thick wooden strips around the bottom template, leaving a pourable area in the middle, which is the actual size of the specimen. Pour a layer of cement-based slurry into it. The height of the cement-based slurry is slightly higher than the thickness of the wooden strips. Then place a continuous carbon fiber grid on the surface of the cement-based slurry and gently press it to make the cement-based slurry fully infiltrate the continuous carbon fiber grid. Then nail a 5-mm-thick wooden strip on top of the first layer of wooden strips and clamp the continuous carbon fiber grid. Continue to pour cement-based slurry on the continuous carbon fiber grid. In this process, it is required that the height of the cement-based slurry is the same as the thickness of the wooden strips;

[0076] (6) Cover the surface of the cement-based paste with a plastic film after the initial setting is completed, demold after 24 hours, and cure in a standard curing room at a temperature of 20°C and a relative humidity of 95% for 28 days to obtain a cement-based material with both structural reinforcement and health monitoring capabilities, as shown in Figure 1 .

[0077] Application Example 1

[0078] Prepare the electrodes: Cut 4 copper sheets with a size of 20 mm × 60 mm, and evenly apply highly viscous conductive silicone on one side surface of each sheet; Use two copper sheets to clamp the carbon fiber bundles on both sides of the specimen to act as electrodes respectively; After the conductive silicone is completely dry, use a spring clip to clamp the copper sheets to enhance the reliability of the electrodes.

[0079] Test the cement-based material prepared in Example 1: Paste steel plates with holes at the ends and a size of 200 mm × 60 mm × 2 mm on both sides at both ends of the cement-based material as reinforcement sheets to transfer the load, and use a 10 kg heavy object to press and hold for 48 hours to ensure firm adhesion; Use an electronic universal testing machine to perform uniaxial tensile loading on the above specimen, and use two clip-on extensometers with a gauge length of 100 mm to measure the tensile deformation of the specimen; Load is controlled by displacement, and the loading rate is 0.2 mm / min until the specimen fails. During the loading process, collect and record the tensile load, tensile deformation, and the resistance change data of the cement-based material.

[0080] Self-sensing ability evaluation: The resistivity change rate (Fractional Change In Electric Resistance, FCER) caused by unit tensile strain (Strain, ε) serves as the self-sensing sensitivity coefficient, and the calculation formula for the resistivity change rate is as follows:

[0081]

[0082] In the formula, ρ L and ρ 0 respectively represent the resistivity of the continuous carbon fiber grid during the loading process and in the initial state; S 网格布 and L represent the cross-sectional area of the test section of the grid cloth and the distance between the two end electrode plates respectively; U L and U 0 respectively represent the voltage values of the continuous carbon fiber grid test section during the loading process and in the initial state; I represents the current value applied to the electrodes during the loading process;

[0083] Establish the model relationship between strain and resistivity change rate.

[0084] Application Example 2

[0085] Preparing the electrode: Determine the arrangement position of the surrounding electrode on the cement-based material prepared in Example 1, and coat the surface of the electrode with conductive silver paste; after the conductive silver paste dries, fix the signal transmission wire at the electrode position to serve as the electrode current access wire; press the wire on the surface with a carbon fiber bundle and wind it tightly. After winding, soak the carbon fiber bundle with silver paste to make it closely adhere to the cement-based material, so that the signal transmission wire is well bonded to the cement-based material; after the silver paste is completely dry, coat the electrode with epoxy resin glue to enhance the stability of the electrode.

[0086] The methods for testing the cement-based material prepared in Example 1 and evaluating its self-sensing ability are exactly the same as those in Application Example 1. The calculation formula for the resistivity change rate is as follows:

[0087]

[0088] In the formula, ρ L and ρ 0 respectively represent the resistivity of HyFRCC during the loading process and in the initial state; S FRCM and L respectively represent the cross-sectional area of the FRCM and the distance between the two electrodes at both ends; U L and U 0 respectively represent the voltage values of the test section during the loading process and in the initial state; I represents the current value applied to the electrode during the loading process.

[0089] Application Example 3

[0090] Preparing the electrode: Determine the arrangement position of the surface electrode on the cement-based material prepared in Example 1, and coat the surface of the electrode with conductive silver paste to reduce the surface resistance; after the conductive silver paste dries, fix the signal transmission wire at the electrode position to serve as the electrode current access wire; press the wire on the surface with a carbon fiber bundle and, after winding, soak the carbon fiber bundle with silver paste to make it closely adhere to the cement-based material, so that the signal transmission wire is well bonded to the cement-based material; after the silver paste is completely dry, coat the electrode with epoxy resin glue to enhance the stability of the electrode.

[0091] The methods for testing the cement-based material prepared in Example 1 and evaluating its self-sensing ability are exactly the same as those in Application Example 1. The calculation formula for the resistivity change rate is as follows:

[0092]

[0093] In the formula, ρ L and ρ 0 respectively represent the resistivity of the cement-based material during the loading process and in the initial state; d and L respectively represent the length segment cross-sectional area of the electrode sheet and the distance between the two electrode sheets at both ends; U L and U 0They respectively represent the voltage values during the loading process and in the test section in the initial state; I represents the current value applied to the electrode during the loading process.

[0094] The model relationships of the above self-sensing sensitivity coefficient and strain-resistivity change rate are shown in Table 1 and Table 2 respectively.

[0095]

[0096] Table 1

[0097]

[0098] Note: ε represents the tensile strain generated by FRCM under tensile force, and FCER represents the resistivity change rate of FRCM.

[0099] Table 2

[0100] Such as Figures 2-4 For the relationship between the resistivity change rate and tensile strain of the cement-based materials in Application Examples 1-3 under tensile state, from the above results, it can be seen that the cement-based materials with both structural reinforcement and health monitoring adopted in the present invention, as inorganic cementitious binding materials, show more excellent self-sensing functionality and mechanical properties compared with FRCM formed by fiber-free and single-fiber cement mortar matrix. Among them, for the tensile performance, compared with FRCM formed by single-fiber cement mortar matrix with 0.50% carbon fiber, the tensile strength, tensile strain, and energy dissipation of FRCM with a mixed volume content of 1.25% - 1.50% polyethylene fiber and 0.50% carbon fiber are increased by 37%, 1.3%, and 55% respectively, improving the reinforcement and strengthening effect of damaged concrete structures.

[0101] The cement-based materials with both structural reinforcement and health monitoring prepared by the present invention can monitor the change of its own resistivity to reflect the stress state of the concrete structure strengthened by FRCM. Among them, the monitoring method of arranging electrodes on the surface of the HyFRCC matrix has a high self-sensing sensitivity, and the relative change rate of resistivity at the limit state exceeds 100%. Therefore, this high-contrast, non-contact, non-destructive structural health monitoring method has broad engineering application prospects.

[0102] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, it can be improved or transformed according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A cement-based material with both structural reinforcement and health monitoring functions, characterized in that, the cement-based material with both structural reinforcement and health monitoring functions includes a hybrid fiber cement matrix and a continuous carbon fiber grid. The continuous carbon fiber grid is arranged inside the hybrid fiber cement matrix. The hybrid fiber cement matrix includes the following components in parts by weight: 1000 parts of cement, 300 parts of silica fume, 390 parts of fine aggregate, 390 parts of water, 6-7 parts of water reducer, 0.3-0.4 parts of thickener, and carbon fiber and polyethylene fiber; the dosage of the carbon fiber is 0.50%-0.75% of the volume of the cement-based material with both structural reinforcement and health monitoring functions; the dosage of the polyethylene fiber is 1.25%-1.50% of the volume of the cement-based material with both structural reinforcement and health monitoring functions; the diameter of the carbon fiber is 7-10 μm, the length is 3-6 mm, the resistivity is 1.0-1.6 Ω·cm, and the tensile modulus is 230-250 Gpa; the diameter of the polyethylene fiber is 20-50 μm, the length is 18-30 mm, the elongation at break is 1%-3%, and the tensile modulus is 110-130 Gpa; the tensile strength of the continuous carbon fiber grid is 2700-3700 MPa, the tensile modulus is 230-250 GPa, the elongation rate is 1.2-1.5%, and the carbon content is 93-96%; in the cement-based material with both structural reinforcement and health monitoring functions, the continuous carbon fiber grid has a composite failure mode of tensile fracture and slip; there are chemical bonding force, friction force and grid anchoring effect between the continuous carbon fiber grid and the hybrid fiber cement matrix.

2. A preparation method of the cement-based material with both structural reinforcement and health monitoring functions according to claim 1, characterized in that, the preparation method includes the following steps: mix the cement, silica fume, fine aggregate, water, carbon fiber, polyethylene fiber, water reducer and thickener according to the parts by weight to obtain a hybrid fiber cement matrix slurry; arrange the continuous carbon fiber grid inside the hybrid fiber cement matrix slurry to obtain a cement-based precursor material; carry out curing and maintenance treatments on the cement-based precursor material in sequence to obtain the cement-based material with both structural reinforcement and health monitoring functions containing a hybrid fiber cement matrix and a continuous carbon fiber grid.

3. According to the preparation method of the cement-based material with both structural reinforcement and health monitoring functions according to claim 2, characterized in that, the step of mixing the cement, silica fume, fine aggregate, water, carbon fiber, polyethylene fiber, water reducer and thickener according to the parts by weight to obtain a hybrid fiber cement matrix slurry specifically includes: mix the cement, silica fume and fine aggregate, and stir at a speed of 135-145 revolutions per minute for 3-5 minutes to obtain a mixed dry material; add water and 50% by weight of the water reducer to the mixed dry material, first stir at a speed of 135-145 revolutions per minute for 3-5 minutes, and then stir at a speed of 275-295 revolutions per minute for 3-5 minutes to obtain a first mixed material; Stir the first mixed material at a rotation speed of 135 - 145 revolutions per minute, and add polyethylene fibers to the first mixed material. After all the polyethylene fibers are added to the first mixed material, continue to stir at a rotation speed of 275 - 295 revolutions per minute for 5 - 8 minutes to obtain a second mixed material; Stir the second mixed material at a rotation speed of 135 - 145 revolutions per minute, and add a thickening agent, carbon fibers, and the remaining water reducing agent to the second mixed material. After all the thickening agent, carbon fibers, and the remaining water reducing agent are added to the second mixed material, continue to stir at a rotation speed of 275 - 295 revolutions per minute for 3 - 5 minutes to obtain the hybrid fiber cement matrix slurry.

4. The preparation method of the cement - based material with both structural reinforcement and health monitoring according to claim 2, characterized in that, the step of disposing the continuous carbon fiber grid inside the hybrid fiber cement matrix slurry to obtain the cement - based precursor material specifically includes: Pour a layer of hybrid fiber cement matrix slurry; Place the continuous carbon fiber grid on the surface of the hybrid fiber cement matrix slurry, and apply a certain pressure to make the hybrid fiber cement matrix slurry infiltrate with the continuous carbon fiber grid; Pour another layer of hybrid fiber cement matrix slurry on the continuous carbon fiber grid to obtain the cement - based precursor material.

5. The application of the cement - based material with both structural reinforcement and health monitoring according to claim 1 or the cement - based material with both structural reinforcement and health monitoring prepared by the preparation method according to any one of claims 2 - 4 in the field of structural health monitoring.

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