A mineral impregnated modified carbon fiber fabric joule heating element and cementitious matrix composite and methods of making and using the same

Abstract

This invention belongs to the technical field of concrete components, specifically relating to a mineral-impregnated modified carbon fiber fabric Joule heating element and a cementitious composite material, its preparation method, and its application. The mineral-impregnated modified carbon fiber fabric Joule heating element provided by this invention includes a carbon fiber fabric layer, a carbon nanotube layer sequentially coated on the surface of the carbon fiber fabric layer, and an impregnation slurry layer; the impregnation slurry layer comprises calcined kaolin, an alkali activator, and a superplasticizer. The impregnation slurry layer on the surface of the mineral-impregnated modified carbon fiber fabric Joule heating element provided by this invention belongs to the same inorganic silicate system as the matrix, resulting in better interface compatibility and more reliable adhesion; furthermore, the impregnation slurry layer has high density, making it less prone to slippage and deterioration in humid, freeze-thaw, and de-icing salt environments, thus exhibiting better long-term stability. The impregnation slurry layer improves roughness and stiffness to strengthen mechanical interlocking, thereby enhancing tensile strength, damage resistance, and durability.

Description

Technical Field

[0001] This invention belongs to the field of concrete component technology, specifically relating to a mineral-impregnated modified carbon fiber fabric Joule heating element and a cementitious composite material, as well as their preparation method and application. Background Technology

[0002] In infrastructure construction in cold regions, concrete projects often face risks of freezing damage and slow early-age strength development during the construction phase, requiring effective insulation and heating to ensure setting, hardening, and structural formation. During the maintenance phase, functions such as snow melting and de-icing are often needed to ensure the normal use of the concrete structure. Therefore, electric heating technology, which can provide a uniform and stable heat source within the concrete material, is gradually becoming an important means of engineering in cold regions. Current technologies mainly utilize the Joule heating effect of electrically energized heating elements (such as metal cables, metal wire mesh, and carbon fiber cables) embedded in structural components to indirectly achieve internal heating; or they incorporate conductive fillers such as carbon fiber, carbon black, graphite, and steel fiber into the concrete material to prepare conductive concrete materials, utilizing the Joule heating effect after energization to directly generate internal heat for low-temperature pouring and curing, and road snow melting and de-icing scenarios.

[0003] Compared to direct Joule heating of concrete, the indirect Joule heating method using pre-embedded heating elements solves the problems of complex preparation processes, high costs, and significant differences in material resistivity between construction and maintenance stages of conductive concrete, making it suitable for large-scale application in practical engineering. Compared to traditional metal cables and wire mesh, carbon fiber cables, as heating elements, have significant advantages such as high low-voltage heating efficiency, uniform heating, alkali and corrosion resistance, lightweight, and the ability to integrate structural reinforcement and electrothermal functions. However, the interfacial bonding performance between existing carbon fiber cables and concrete materials is often insufficient. The surface of carbon-based materials is inert and has poor wettability, easily forming pores and loose interfacial transition zones at the interface, resulting in low bond strength and insufficient load transfer efficiency. Under the temperature gradient and repeated thermal cycling of energized heating, interfacial thermal stress concentration is more likely to cause cracking, slippage, and debonding. Interfacial damage, in turn, can alter the conductive path and exacerbate resistance fluctuations and hot spot formation. The cold-region service environment is compounded by humidity, freeze-thaw cycles, and snow-melting salt erosion. Water and ions seep in and accumulate along interface defects, which accelerates interface deterioration and electrothermal drift, making it difficult to guarantee long-term snow melting and ice removal as well as durability and reliability. Summary of the Invention

[0004] In view of this, the present invention provides a mineral-impregnated modified carbon fiber fabric Joule heating element and a cementitious composite material, as well as the preparation method and application thereof. The Joule heating element provided by the present invention has good interfacial bonding performance with cementitious materials such as cement or geopolymers, thereby improving the application effect of carbon fiber-based Joule heating elements in cementitious materials.

[0005] To solve the above-mentioned technical problems, the present invention provides a mineral impregnated modified carbon fiber fabric Joule heating element, comprising a carbon fiber fabric layer, a carbon nanotube layer sequentially coated on the surface of the carbon fiber fabric layer, and an impregnation slurry layer. The components of the impregnating slurry layer include calcined kaolin, alkali activator, and superplasticizer.

[0006] Preferably, the alkaline activator comprises potassium silicate; The mass ratio of the superplasticizer to calcined kaolin is 1.2~1.4:1, and the mass ratio of the total mass of calcined kaolin and alkali activator to the mass of the superplasticizer is 100:1.6~1.8.

[0007] Preferably, the carbon fiber fabric used for the carbon fiber fabric layer includes unidirectional carbon fiber cloth; the thickness of the carbon fiber fabric layer is 0.8~1.2mm; The thickness of the carbon nanotube layer is 0.05~0.15 mm; The thickness of the impregnating slurry layer is 2~4mm.

[0008] This invention also provides a method for preparing the mineral-impregnated modified carbon fiber fabric Joule heating element described in the above technical solution, comprising the following steps: Carbon nanotubes, organic solvents and perfluorosulfonic acid resins are first mixed to obtain a carbon nanotube dispersion. Carbon fiber fabric is first immersed in the carbon nanotube dispersion for deposition, and a carbon nanotube layer is formed on the surface of the carbon fiber fabric to obtain carbon nanotube modified carbon fiber fabric. After calcining kaolin, alkali activator, superplasticizer and water are mixed and defoamed to obtain impregnation slurry; The carbon nanotube-modified carbon fiber fabric is second-impregnated with the impregnation slurry and then precipitated. After scraping and surface trimming, the slurry is cured on the surface of the carbon nanotube-modified carbon fiber fabric to form an impregnation slurry layer, thereby obtaining the mineral-impregnated modified carbon fiber fabric Joule heating element.

[0009] Preferably, the second mixing includes the following steps: calcined kaolin, alkali activator, a portion of superplasticizer and water are mixed in a third mixing to obtain a primary impregnation slurry; the third mixing is carried out under stirring conditions, the stirring speed is 6000~7000 r / min, and the stirring time is 4~6 min; The remaining superplasticizer is added to the primary impregnation slurry for a fourth mixing to obtain the impregnation slurry; the fourth mixing is carried out under stirring conditions, the stirring speed is 6500~7500 r / min, and the stirring time is 4~6 min.

[0010] Preferably, the defoaming is performed by vibrating the second mixed material at a frequency of 40-50 kHz for a duration of 8-12 min. The second immersion time is 4-6 minutes, and the settling time is 10-15 minutes; The curing temperature is 65~80℃ and the time is 5.5~9h.

[0011] The present invention also provides a gel-based composite material, comprising a matrix, a plurality of heating elements connected in parallel within the matrix, a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode are respectively connected to the two ends of the plurality of heating elements connected in parallel, and the spacing between two adjacent heating elements is 75~85mm. The heating element is the mineral-impregnated modified carbon fiber fabric Joule heating element described in the above technical solution or the mineral-impregnated modified carbon fiber fabric Joule heating element prepared by the preparation method described in the above technical solution.

[0012] Preferably, the matrix comprises cementitious materials and / or geopolymer materials.

[0013] The present invention also provides a method for preparing the gel-based composite material described in the above technical solution, comprising the following steps: After laying a portion of the matrix material flat, a heating element is placed on it. After pouring the remaining portion of the matrix material, an electric current is applied for electrothermal curing to obtain the gel-based composite material.

[0014] The present invention also provides the application of the gel-based composite material described in the above technical solution or the gel-based composite material prepared by the preparation method described in the above technical solution in the preparation of heating materials, wherein the heating materials include road panels, bridge panels, building walls or roofs.

[0015] This invention provides a mineral-impregnated modified carbon fiber fabric Joule heating element, comprising a carbon fiber fabric layer, a carbon nanotube layer sequentially coated on the surface of the carbon fiber fabric layer, and an impregnation slurry layer; the impregnation slurry layer comprises calcined kaolin, an alkali activator, and a superplasticizer. The impregnation slurry layer on the surface of the Joule heating element provided by this invention belongs to the same inorganic silicate system as the matrix (cement or geopolymer), possessing similar temperature and chemical resistance to minerals, resulting in better interface compatibility and more reliable adhesion. Simultaneously, the carbon fiber fabric can bear part of the tensile stress when the element is under tension or cracking, inhibiting crack propagation through fiber bridging. The carbon nanotube interface transition layer improves the adhesion and interfacial shear transfer efficiency of the carbon fiber surface, while forming a bridging network between adjacent fibers, maintaining good stress and electrical continuity even after localized damage. The impregnation slurry layer increases roughness and stiffness to strengthen mechanical interlocking, thereby improving crack resistance, damage resistance, and durability. Meanwhile, the carbon nanotube layer can also reduce interfacial thermal resistance, making heating more uniform and reducing hot spots, and suppressing resistance fluctuations, thereby improving output stability under cyclic power-on. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the mineral-impregnated modified unidirectional carbon fiber cloth Joule heating element unit prepared in Example 1; Figure 2 These are schematic diagrams of the cementitious composite material specimens used for strength testing in Examples 1 and 2; Figure 3 The images show a schematic diagram and a physical image of the crosslinked heating element in Example 2, where (a) is a schematic diagram and (b) is a physical image. Figure 4 The images show physical photos and temperature distribution diagrams of the snow melting process using the gel-based composite material plates prepared in Example 2. Detailed Implementation

[0017] The present invention provides a mineral-impregnated modified carbon fiber fabric Joule heating element, comprising a carbon fiber fabric layer, a carbon nanotube layer sequentially coated on the surface of the carbon fiber fabric layer, and an impregnation slurry layer.

[0018] In this invention, the components of the impregnation slurry layer include calcined kaolin, an alkali activator, and a superplasticizer; the alkali activator may include potassium silicate; the molar ratio of SiO2 to K2O in the potassium silicate is 2.1~2.5:1, specifically 2.2:1, 2.3:1, or 2.4:1; in this invention, the potassium silicate is liquid, and its solid content can be 39.9%; the potassium silicate, as an alkali activator, can promote the dissolution and condensation of aluminosilicates, and provide reactive silicate and silanol groups, which is beneficial for the subsequent formation of a dense impregnation slurry layer.

[0019] The potassium silicate used in this embodiment of the invention is from Jiashan Yourui Refractory Materials Co., Ltd. The product is a colorless or slightly colored transparent viscous liquid, and its detailed specifications are shown in Table 1.

[0020] Table 1 Performance indicators of the potassium silicate used in the examples

[0021] In this invention, the superplasticizer can be a polycarboxylate superplasticizer. The superplasticizer used in the embodiments of this invention is a polycarboxylate superplasticizer from Zhaojia Technology Co., Ltd., which is a white powder and sourced from Hubei Zhaojia Materials Co., Ltd. Its performance indicators are shown in Table 2.

[0022] Table 2 Performance indicators of the superplasticizers used in the examples

[0023] In this invention, the mass ratio of the superplasticizer to calcined kaolin can be 1.2~1.4:1, specifically 1.3:1, and the mass ratio of the total mass of calcined kaolin and alkali activator to the mass of the superplasticizer can be 100:1.6~1.8, specifically 100:1.7. In this invention, the calcined kaolin, when combined with alkali activation, allows for rapid molding and high strength. Simultaneously, the low carbon content in calcined kaolin reduces carbon dioxide generation, making it environmentally friendly. This invention limits the dosage ratio of the superplasticizer and calcined kaolin to provide a reasonable soluble silicon source, promoting rapid activation of the calcined kaolin and avoiding excessively high alkalinity that could lead to overly vigorous reactions or excessive exothermic reactions in the slurry system. Furthermore, it better meets the dispersion requirements of the calcined kaolin particles, reducing particle flocculation and agglomeration, and improving the system's fluidity and workability. This invention controls the mass ratio of calcined kaolin and alkali activator to superplasticizer within the range of 100:1.6~1.8, which allows the superplasticizer dosage to be adapted to the overall cementitious system. While improving workability, it avoids the adverse effects of improper admixture dosage on setting time, structure formation and later strength, thereby improving the comprehensive performance and preparation stability of the material system.

[0024] In this invention, the carbon fiber fabric used for the carbon fiber fabric layer may include unidirectional carbon fiber cloth (UCFF); the thickness of the carbon fiber fabric layer may be 0.8~1.2mm, specifically 1mm; the thickness of the carbon nanotube layer may be 0.05~0.15mm, specifically 0.1mm; and the thickness of the impregnation slurry layer may be 2~4mm, specifically 3mm.

[0025] The heating element provided by the present invention can be rectangular. In the embodiments of the present invention, the width of the rectangle can be 10mm and the length of the rectangle can be 250~470mm, specifically 300mm, 350mm or 400mm.

[0026] The heating element provided by this invention has advantages under humid, alkaline, and high-temperature conditions. For example, the pore solution of geopolymer mortar is usually alkaline and contains ions. If bare carbon fibers or organic coating systems are used, problems such as interface degradation, electrothermal drift due to water absorption, and even insufficient fire resistance are likely to occur. However, the impregnated slurry layer can, to a certain extent, prevent the pore solution from directly penetrating into the fiber bundle, and improves fire resistance and heat resistance safety by virtue of the thermal stability of the mineral matrix. Therefore, pre-embedding the heating element provided by this invention in geopolymer mortar is not only beneficial for long-term service stability, but also facilitates the realization of functional integrated applications such as winter curing, de-icing and snow melting, or internal heating to promote setting.

[0027] This invention also provides a method for preparing the mineral-impregnated modified carbon fiber fabric Joule heating element described in the above technical solution, comprising the following steps: Carbon nanotubes, organic solvents and perfluorosulfonic acid resins are first mixed to obtain a carbon nanotube dispersion. Carbon fiber fabric is first immersed in the carbon nanotube dispersion for deposition, and a nanotube layer is formed on the surface of the carbon fiber fabric to obtain carbon nanotube modified carbon fiber fabric. After calcining kaolin, alkali activator, superplasticizer and water are mixed and defoamed to obtain impregnation slurry; The carbon nanotube-modified carbon fiber fabric is second-impregnated with the impregnation slurry and then precipitated. After scraping and surface trimming, the slurry is cured on the surface of the carbon nanotube-modified carbon fiber fabric to form an impregnation slurry layer, thereby obtaining the mineral-impregnated modified carbon fiber fabric Joule heating element.

[0028] This invention involves first mixing carbon nanotubes, an organic solvent, and a perfluorosulfonic acid resin to obtain a carbon nanotube dispersion. In this invention, the carbon nanotubes (CNTs) can be multi-walled carbon nanotubes; the organic solvent can be isopropanol; the mass ratio of the carbon nanotubes to the organic solvent is 95-105 mg:100 mL, specifically 100 mg:100 mL; and the volume ratio of the organic solvent to the perfluorosulfonic acid resin (Nafion) is 95-105:2, specifically 100:2. In this invention, the perfluorosulfonic acid resin promotes good dispersion of the carbon nanotubes in the organic solvent and provides a certain degree of adhesion, thereby providing conditions for the subsequent stable adhesion and continuous spreading of carbon nanotubes on the carbon fiber surface.

[0029] In this invention, the first mixing process may further include: subjecting the first mixed system to ultrasonic treatment, wherein the ultrasonic treatment power can be 40~50kHz, specifically 45kHz; and the ultrasonic treatment time can be 55~65min, specifically 60min. This invention uses ultrasonic treatment to break down carbon nanotube aggregates, obtaining a uniform carbon nanotube dispersion, thus avoiding localized enrichment, discontinuous conductive pathways, or concentrated interface defects during subsequent impregnation.

[0030] After obtaining the carbon nanotube dispersion, the present invention first immerses a carbon fiber fabric in the carbon nanotube dispersion for deposition, forming a carbon nanotube layer on the surface of the carbon fiber fabric, thus obtaining a carbon nanotube-modified carbon fiber fabric. In this invention, before the first immersion, the process may further include: washing and drying the carbon fiber fabric; the washing solvent may include isopropanol; the drying temperature may be 65~75℃, specifically 70℃; the drying time may be 10~20 min, specifically 15 min. In this invention, after drying, the dried product can be cooled to room temperature, which may be 20~35℃, or even 25~30℃; the present invention does not have a particular limitation on the cooling method, and conventional methods in the art can be used. This invention, through washing, can remove impurities and weak adhesion layers from the fiber surface, increasing the effective surface contact area, making the subsequent carbon nanotube suspension easier to spread and firmly adhere, and reducing the risk of subsequent detachment.

[0031] In this invention, the first impregnation time can be 100-140 minutes, specifically 110 minutes, 120 minutes, or 130 minutes. The first impregnation process enables carbon nanotubes to be gradually deposited on the surface of the carbon fiber fabric, forming a continuous conductive pathway.

[0032] In this invention, the process after the first impregnation may further include: drying the first impregnated product; the drying temperature may be 60~75℃, specifically 65℃ or 70℃; the drying time may be 2~3 hours; the drying may be carried out in an oven. This invention, through drying, allows the solvent to evaporate and promotes the adhesion of carbon nanotubes to the fiber surface under the action of Nafion, thus preparing a carbon nanotube-modified carbon fiber fabric composite material. The modified carbon fiber fabric (MUCFF) reduces resistivity, improves electrical heating efficiency and uniformity under the action of the carbon nanotube network, and simultaneously provides more anchoring sites through nano-coarsening and increased specific surface area, laying the foundation for the adhesion and interfacial stability of the subsequent impregnation slurry layer.

[0033] This invention involves mixing calcined kaolin, an alkali activator, a superplasticizer, and water, followed by defoaming to obtain an impregnation slurry. In this invention, the alkali activator may include potassium silicate; the molar ratio of SiO2 to K2O in the potassium silicate is 2.1~2.5:1, specifically 2.2:1, 2.2:1, or 2.4:1; the mass ratio of the superplasticizer to calcined kaolin can be 1.2~1.4:1, specifically 1.3:1; and the mass ratio of the total mass of calcined kaolin and the alkali activator to the mass of the superplasticizer can be 100:1.6~1.8, specifically 100:1.7.

[0034] In this invention, the calcined kaolin provides an active aluminum-silicon source; the potassium silicate provides alkali and silicon sources to achieve rapid solidification and molding; and the superplasticizer is used to inhibit flocculation, improve particle dispersion and flowability, thereby ensuring that the subsequent impregnation slurry can penetrate into the fiber bundle gaps and form a continuous shell on the surface.

[0035] In this invention, the average particle size of the calcined kaolin can be 3~5µm, specifically 4µm. This invention achieves complete penetration of the carbon fiber bundle by controlling the particle size (calcined kaolin) of the impregnation slurry to match the diameter of the carbon fiber monofilaments in the carbon fiber fabric, resulting in uniformly wrapped monofilaments.

[0036] In this invention, the second mixing may include the following steps: a third mixing of calcined kaolin, an alkali activator, a portion of the superplasticizer, and water to obtain a primary impregnation slurry; and a fourth mixing of the remaining superplasticizer into the primary impregnation slurry to obtain the impregnation slurry. In this invention, the mass of the portion of the superplasticizer can be 45-55% of the total mass of the superplasticizer, specifically 50%; the water can be deionized water; the third mixing can be carried out under stirring conditions, the stirring speed can be 6000-7000 r / min, specifically 6500 r / min, and the stirring time can be 4-6 min, specifically 5 min; the fourth mixing can be carried out under stirring conditions, the stirring speed can be 6500-7500 r / min, specifically 7000 r / min, and the stirring time can be 4-6 min, specifically 5 min.

[0037] The present invention provides sufficient high shear force and promotes full dispersion of fine particles through the third mixing and stirring; the subsequent addition of the remaining superplasticizer can adjust the consistency of the slurry to meet the impregnation requirements; the fourth mixing and stirring can obtain a uniform and stable mineral-based impregnation slurry, thereby reducing the weak adhesion caused by interfacial porosity and component inhomogeneity.

[0038] In this invention, defoaming can be achieved by vibrating the second mixed material. The vibration frequency can be 40-50 kHz, specifically 45 kHz, and the vibration time can be 8-12 minutes, specifically 10 minutes. This invention removes entrained air through vibration, preventing air bubbles from forming pores at the impregnation slurry layer (shell) and interface, thereby increasing the density of the impregnation slurry layer and the effective contact area at the interface, and enhancing the continuity of subsequent load transfer.

[0039] After obtaining the carbon nanotube-modified carbon fiber fabric and the impregnation slurry, the present invention further impregnates the carbon nanotube-modified carbon fiber fabric in the impregnation slurry for a second time, followed by precipitation. After scraping and surface trimming, the slurry is then cured to form an impregnation slurry layer on the surface of the carbon nanotube-modified carbon fiber fabric, thus obtaining the mineral-impregnated modified carbon fiber fabric Joule heating element. In this invention, the second impregnation of the carbon nanotube-modified carbon fiber fabric into the impregnation slurry followed by precipitation can be performed in stages. Specifically, the carbon nanotube-modified carbon fiber fabric can be thirdly impregnated into the impregnation slurry followed by a first precipitation, and the third impregnation and the first precipitation can be repeated. The third impregnation time can be 2 minutes, the first precipitation time can be 5 minutes, and the number of repetitions can be 2 to 3 times. In this invention, the total time for the second impregnation can be 4 to 6 minutes, and the total time for precipitation can be 10 to 15 minutes.

[0040] In this invention, the curing temperature can be 65~80℃, specifically 70℃ or 75℃, and the curing time can be 5.5~9h, specifically 6h, 7h, 8h or 8.5h; the drying can be carried out in an oven. During the curing process, alkali-activated calcination of kaolin generates a three-dimensional network of potassium-based aluminosilicate (KASH) gel. This gel forms a chemical bond with the carbon fiber surface and is cured in situ, achieving rigid coating and interfacial anchoring of the fiber. After curing, it forms a tight mechanical interlock with the carbon fiber, effectively dispersing stress, inhibiting crack propagation, and filling fiber surface defects, thus strengthening the carbon fiber fabric from both interfacial bonding and structural compaction aspects.

[0041] This invention enables the impregnation slurry to gradually deposit on the surface and interstices of carbon fiber bundles, forming a continuous mineral shell through impregnation and precipitation. Multiple impregnations allow the impregnating slurry to form a continuous shell on the surface of carbon nanotube-modified carbon fiber fabrics, filling the fiber bundle pores and reducing interfacial voids and weak areas. After curing, the surface roughness and stiffness of the impregnating slurry layer (shell) are improved, resulting in stronger mechanical bonding within the cementitious material (cement or geopolymer) matrix. Simultaneously, the impregnating slurry layer transforms the originally inert and difficult-to-wet carbon fiber surface into a more hydrophilic inorganic surface, making the cementitious material easier to spread and reducing loose and porous weak areas at the interface. Furthermore, the impregnating slurry has better chemical compatibility with cement-based materials, facilitating the continuous generation of reaction products at the interface and filling pores, thus forming a denser transition layer. The carbon nanotube nanolayer can act as a bridge and buffer when microcracks appear, synergistically inhibiting crack propagation with the impregnating slurry layer, thereby improving bond strength and durability.

[0042] This invention also provides a gel-based composite material, comprising a matrix, a plurality of heating elements connected in parallel within the matrix, a positive electrode, and a negative electrode. The positive electrode and the negative electrode are respectively connected to the two ends of the plurality of heating elements connected in parallel. The spacing between two adjacent heating elements is 75-85 mm, specifically 80 mm. The heating elements are the mineral-impregnated modified carbon fiber fabric Joule heating elements described in the above-mentioned technical solutions or the mineral-impregnated modified carbon fiber fabric Joule heating elements prepared by the preparation method described in the above-mentioned technical solutions. In this invention, the number of heating elements should be comprehensively determined based on the ambient temperature, the geometric dimensions of the component being heated, the electrothermal power and the target temperature, as well as the arrangement of the heating elements.

[0043] In this invention, the matrix comprises cementitious materials and / or geopolymer materials, specifically cement-based materials or cement-based materials doped with geopolymer materials; the doping mass of the geopolymer material in the cement-based material doped with geopolymer materials can be 5-15%, specifically 8%, 10%, or 13%. In this invention, the parallel-connected heating elements are in a grid configuration. The parallel connection in this invention ensures consistent voltage across each heating unit (mineral-impregnated modified carbon fiber fabric Joule heating element), resulting in more uniform overall heating. Simultaneously, the parallel connection provides redundancy; local failure of one unit does not affect the operation of other branches, which is beneficial for improving the stability and engineering applicability of electrothermal curing.

[0044] This invention can use copper plates connected in parallel, and thermally conductive graphite adhesive can be used to fix the copper plates to the heating element. In this invention, the positive electrode and negative electrode can be copper plates.

[0045] The copper plate has high conductivity, enabling uniform current distribution among multiple parallel branches. Thermally conductive graphite adhesive fills the contact gaps and increases the contact area, thereby reducing contact resistance, minimizing localized heat sources, preventing overheating of the electrodes, and improving current-carrying stability.

[0046] This invention connects each copper plate with a cable at the middle position and insulates the entire copper plate with silicone to avoid the risk of short circuits or leakage caused by the conductivity of the grout after pouring, and improves construction safety and durability.

[0047] In this invention, the surface of the cementitious composite material can also be provided with a basalt fiber mesh, the mesh diameter of which can be 18~22mm, specifically 20mm; the basalt fiber mesh can reinforce the cementitious composite material.

[0048] The present invention also provides a method for preparing the gel-based composite material described in the above technical solution, comprising the following steps: After laying a portion of the matrix material flat, the mineral-impregnated modified carbon fiber fabric Joule heating element is placed on it. After pouring the remaining portion of the matrix material, it is electrically heated for curing to obtain the gel-based composite material.

[0049] In this invention, the thickness of the first laid base material can be 20-25 mm, and the thickness of the remaining base material can be 25-35 mm, specifically 30 mm.

[0050] The present invention places the heating element on the surface of the first part of the substrate material, which enables the heating element to achieve stable positioning and make full contact with the substrate, ensuring that there is enough slurry to cover the heating element during subsequent pouring, thereby improving the efficiency of heat transfer to the interior of the mortar.

[0051] In this invention, the material is smoothed and shaped after casting; the power source for electrothermal curing can be alternating current (AC). After being energized, this invention utilizes Joule heating generated by a grid-type (parallel-connected grid) heating element to heat and cure the matrix material. AC power avoids the electrochemical side reactions and polarization effects that may result from long-term direct current operation, leading to more stable temperature rise. The uniformly distributed parallel electrothermal grid creates a relatively uniform temperature field within the matrix material, thereby shortening the setting and hardening time and improving early strength. This invention can determine specific energizing parameters based on the actual required heating heat, specifically by adjusting parameters such as power density, voltage, and energizing time.

[0052] In this invention, the process before smoothing may further include laying a basalt fiber mesh on the surface of the remaining matrix material.

[0053] This invention also provides the application of the gel-based composite material described in the above-described technical solutions or the gel-based composite material prepared by the preparation method described in the above-described technical solutions in the preparation of heating materials, including applications in road slabs, bridge slabs, building walls, or roofs. The gel-based composite material provided by this invention can melt snow and ice on road or bridge surfaces when used in road or bridge surfaces, can provide indoor heating when used in building walls, and can melt snow on roofs when used in roofs.

[0054] This invention constructs a modified carbon fiber Joule heating element using carbon fiber fabric as the load-bearing skeleton (bearing tensile loads and providing overall mechanical strength and stiffness), a carbon nanotube layer as the interface transition layer (some carbon nanotubes bridge with adjacent fibers to form a micro-network, thus firmly fixing the carbon nanotubes to the carbon fiber surface), and calcined kaolin + potassium silicate as the outer coating layer. Uniform energization and engineered arrangement are achieved through parallel networking and electrode current convergence. This invention utilizes carbon nanotubes to construct continuous conductive pathways to reduce resistivity, improve heating efficiency and uniformity, and reduce resistance fluctuations and localized overheating. Furthermore, by impregnating the slurry to form an inorganic mineral shell, the original inert carbon-based interface is transformed into an inorganic interface more compatible with the matrix material, improving wetting, spreading, and mechanical bonding, reducing interfacial voids and weak areas, and enhancing bonding reliability and structural stability in humid, freeze-thaw, and de-icing salt environments. Meanwhile, the continuous contact interface between the impregnated slurry layer and the substrate can reduce the interfacial thermal resistance, allowing Joule heat to be conducted to the interior of the substrate more efficiently, forming a stable heat source. This enables low-temperature electrothermal curing, promotes early strength and shortens the curing cycle during the construction phase, and can also serve as a heating layer under the cover layer for snow melting and ice removal during the maintenance phase. This achieves integrated and long-term reliable service for the construction and maintenance phases of concrete engineering in cold regions.

[0055] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] The potassium silicate used in the examples was purchased from Jiashan Yourui Refractory Materials Co., Ltd., and its specifications are shown in Table 1. The superplasticizer used in the examples was Zhaojia polycarboxylate superplasticizer, and its performance indicators are shown in Table 2.

[0057] Example 1: Preparation of cement mortar specimens with built-in heating elements 1. Raw material formula (1) Heating element 100 mg of multi-walled carbon nanotubes were added to 100 mL of isopropanol to form a carbon nanotube suspension with a concentration of 1 mg / mL. After adding 2 mL of perfluorosulfonic acid resin solution, the suspension was ultrasonically treated for 60 min at a power of 45 kHz to obtain a carbon nanotube dispersion.

[0058] After washing a 1 mm thick unidirectional carbon fiber cloth (UCFF) with isopropanol, it was placed in an oven and heated at 70 °C for 15 min, and then cooled to room temperature (25 °C). The cooled UCFF was then immersed in a carbon nanotube suspension for 120 min. After immersion, it was placed in an oven at 70 °C for 2.5 h to dry, forming a carbon nanotube layer with a thickness of about 0.1 mm on the surface of the unidirectional carbon fiber cloth, thus obtaining carbon nanotube modified unidirectional carbon fiber cloth (MUCFF).

[0059] A primary impregnation slurry was prepared by mixing potassium silicate (SiO2 and K2O molar ratio 2.4), calcined kaolin with an average particle size of 4µm, a portion of polycarboxylate superplasticizer (50% of all superplasticizers), and deionized water. The remaining superplasticizer was then added to the primary impregnation slurry and mixed to obtain the final impregnation slurry. The mass ratio of all superplasticizers to calcined kaolin was 1.3:1, and the mass ratio of the total mass of calcined kaolin and potassium silicate to the total mass of all superplasticizers was 100:1.7. The specific preparation process was as follows: calcined kaolin, potassium silicate, and 50% by mass of superplasticizer were added to a mixer and stirred at 6500 r / min for 5 min. Subsequently, the remaining superplasticizer was added, and the mixture was stirred at 7000 r / min for 5 min, followed by vibration at 45 kHz for 10 min to remove bubbles, thus obtaining the final impregnation slurry.

[0060] MUCFF was impregnated in impregnation slurry for 2 minutes and then settled for 5 minutes. The impregnation and settling steps were repeated twice. After scraping and surface correction, the product was placed in a drying oven and cured at 75°C for 6.5 hours to form an impregnation slurry layer with a thickness of 2-3 mm on the surface of MUCFF, thus obtaining mineral impregnated modified unidirectional carbon fiber cloth Joule heating element unit (MMUCFF).

[0061] The heating element unit has a rectangular planar shape, with a width of 10mm and a length that can be adjusted as needed. The specific lengths used for testing are 250mm and 470mm. Figure 1 This is a schematic diagram of the structure of the mineral-impregnated modified unidirectional carbon fiber cloth Joule heating element unit prepared in Example 1.

[0062] (2) Cement mortar matrix Anhui Conch brand P·O 42.5 ordinary Portland cement, Chinese ISO standard sand, and tap water from Zhangjiakou city were used as raw materials. Cement and water (water-cement ratio of 0.5) were placed in a JJ-5 type mortar mixer and stirred at low speed (140±5 r / min) for 30 seconds; then the speed was switched to high speed (285±10 r / min) and stirred for 30 seconds, with the addition of standard sand (cement to standard sand mass ratio of 1:3); finally, stirring was continued at high speed for 60 seconds to ensure uniformity of the mixture, resulting in a cement mortar mixture.

[0063] 2. Preparation of cement mortar (cement cementitious composite material) specimens with built-in heating elements Under ambient temperature conditions (20±2℃, relative humidity not less than 60%), with dimensions of 40×40×160mm... 3 The aforementioned cement mortar mixture was poured into a plastic mold (with holes cut into the side walls according to the size of the heating element, allowing the heating element to extend out of the mold and connect to the power source). To simulate winter construction, 50mm thick extruded polystyrene (XPS) boards were installed on the four sides and bottom of the plastic mold, and the top was covered with a glass cover. First, two 3mm × 10mm rectangular holes were drilled on each of the two sides of the mold. Then, a 250mm long heating element unit was directly passed through the holes, and power electrodes were connected to both ends. To avoid uneven contact between the copper clamp and the heating element unit, which could lead to overheating or combustion at the joint, the joint was wrapped with a small piece of copper mesh. The electrothermal curing power density was set to 360 W / m². 2 (Actual measurement: 363~367 W / m) 2 The energizing time is 24 hours. Immediately after the electrothermal curing is completed, the molded specimens are placed in the standard curing room until the specified age. Figure 2 Cement mortar specimens with built-in heating elements.

[0064] 3. Mechanical Property Testing: Based on the Chinese standard—Test Method for Strength of Cement Mortar (ISO Method) (GB / T 17671-2021), the compressive and flexural strengths of cement mortar with built-in heating elements were tested at 1d, 7d, and 28d. The testing apparatus was a WHY-300 kN / 10 kN microcomputer-controlled electronic compressive and flexural strength testing machine manufactured by Shanghai Hualong Testing Instruments Co., Ltd.

[0065] Comparative Example 1 1. Raw material formula: completely consistent with the cement mortar matrix of Example 1, without heating element.

[0066] 2. Specimen preparation method: Except for the absence of embedded heating elements, the stirring and molding processes are completely consistent with those in Example 1. Immediately after molding, the molded specimens are placed in a standard curing chamber until the specified curing age.

[0067] 3. Mechanical performance testing: The testing methods and contents are the same as those in Example 1.

[0068] Example 2 1. Raw Material Formulation: The cementitious composite material was prepared according to the method in Example 1, except that cement mortar was replaced with geopolymer mortar. The geopolymer mortar used was potassium silicate (WG) with a Baume degree of 1.7Be. 1.7 The preparation process involves metakaolin, standard sand, and polycarboxylate superplasticizer. The specific preparation process is as follows: WG 1.7The mixture was mixed with metakaolin at a mass ratio of 1.18 and stirred for 30 seconds at low speed (140±5 r / min) using a JJ-5 type mortar mixer. Then, the mixture was switched to high speed (285±10 r / min) and stirred for 60 seconds, while standard sand was slowly added (the mass ratio of geopolymer to standard sand was 1:1.03). Finally, the mixture was stirred at high speed for another 60 seconds and a polycarboxylate superplasticizer (mass ratio 0.48%) was added to ensure uniformity and obtain a geopolymer mortar mixture.

[0069] 2. Preparation of Geopolymer Mortar Specimens with Built-in Heating Elements: Geopolymer mortar specimens were prepared using the same casting method and built-in heating element method as in Example 1. The electrical curing parameters were adjusted to: power density 510 W / m³. 2 (Actual measurement: 512W / m) 2 The electrical maintenance time remains 24 hours.

[0070] 3. Mechanical property testing: The same testing methods and contents as in Example 1 were used to conduct compressive strength and flexural strength tests on the geopolymer mortar specimens.

[0071] 4. Snow melting performance test: Six heating element units are connected in parallel using copper plates, with an 80mm spacing between adjacent units to form a grid-like heating element. Thermally conductive graphite adhesive is used to fix the two ends of the grid-like heating element to the copper plate, and the copper plate is used as the electrode. The power cable is connected in the middle of each copper plate, and the entire copper plate is insulated with silicone. Figure 3 The diagrams and physical images of the mesh heating element are shown, where (a) is a schematic diagram and (b) is a physical image.

[0072] Under the same room temperature conditions, at a size of 600×600×80mm 3 Geopolymer mortar was poured into a plastic mold. The pouring process was done in three layers. First, a 20mm thick layer of geopolymer mortar was poured and vibrated for 120 seconds as the base layer. The treated mesh heating elements were then placed on the base layer (40mm from the mold edge). Next, a 30mm thick layer of geopolymer mortar was poured, and a layer of basalt fiber mesh coated with geopolymer impregnation solution was placed for reinforcement. Finally, the mortar was poured to the top of the mold and smoothed. After compaction, electrothermal curing was performed by applying alternating current to the copper plate electrodes, resulting in a cementitious composite material plate. The plate dimensions were 550×500×70mm. 3 .

[0073] At room temperature, using a voltage of 5V, the total power is 34.68W (power density 115W / m²). 2The sheet metal was electrothermally cured at a frequency of 50Hz for 24 hours. Once 95% of the design strength was achieved, the sheet metal was demolded and moved to a negative-temperature environment chamber for snow melting performance testing. During the snow melting test, a layer of tin foil was laid at the bottom of the sheet metal as a heat insulation barrier, and the ambient temperature was -5±2℃. Natural snow was laid on the surface of the sheet metal and compacted to a thickness of 45~50 mm to simulate the snow melting and de-icing process under snowfall conditions. The power density for the snow melting test was set to 300W / m². 2 (Measured value: 298 W / m) 2 ) After the snow melting test begins, thermal imaging is performed on the surface of the plate at intervals of 70-80 minutes to obtain a temperature distribution map. The snow melting rate is calculated by measuring the change in snow thickness at different melting times. Figure 4 This diagram shows the snow melting situation and temperature distribution of the plates during the snow melting test. The specific results are as follows: after 230 minutes of snow melting, the snow melting rate is approximately 65-75%, and after 300 minutes, the snow is completely melted.

[0074] Comparative Example 2 Geopolymer mortar mixture was prepared according to the method in Example 2. The obtained geopolymer mortar mixture was poured into a 40×40×160mm area. 3 The specimens were placed in a standard mold and vibrated on a vibrating table for 120 seconds to ensure compaction and uniformity. After vibration, the specimens were covered with a film to protect them and then cured in an environment with a temperature of 20±1℃ and a relative humidity of ≥90% for 1 to 28 days.

[0075] For the specimens of Examples 1-2 and Comparative Examples 1-2, their compressive strength and flexural strength at different ages were tested, and the specific results are listed in Tables 3-4.

[0076] Table 3. Strength of specimens from Example 1 and Comparative Example 1 at different ages.

[0077] Table 4. Strength of specimens from Example 2 and Comparative Example 2 at different ages.

[0078] As shown in Table 3, in cement mortar, compared with the standard-cured specimens (Comparative Example 1), the compressive strength changes of the specimens with built-in heating elements at 1d, 7d, and 28d were +271%, +2.9%, and -5.7%, respectively. The corresponding changes in flexural strength were +147%, +1.7%, and -2.3%. This indicates that electric curing with built-in heating elements significantly improves both the compressive and flexural strength of cement mortar specimens at early ages, with only a slight decrease in later stages.

[0079] As shown in Table 4, in geopolymer mortar, compared with specimens without heating elements, the compressive strength changes of specimens with built-in heating elements at 1d, 7d, and 28d were +113.8%, +2.7%, and -4.4%, respectively. The corresponding changes in flexural strength at these ages were +188.7%, +27.6%, and +6.5%. This indicates that electric curing with built-in heating elements significantly improves the strength of geopolymer mortar not only in the early stages but also in later stages.

[0080] Heating elements are embedded in geopolymers to create geopolymer composite materials. Utilizing Joule heating and heat transfer after energization, these materials can be used for electro-curing during construction in cold environments; and for snow and ice melting during maintenance. Figure 4 The snow melting test results show that the Joule heating element of mineral-impregnated carbon nanotube modified unidirectional carbon fiber fabric can be pre-embedded in the geopolymer mortar component. After being energized, the element generates Joule heat to form a stable built-in heat source, which can rapidly heat up under low temperature conditions. It is suitable as a heating layer under the overlay of road surfaces, bridge decks, or sidewalks for snow melting and ice removal; the heat is effectively conducted to the surface through the mortar layer, which can inhibit icing and accelerate the melting of snow and thin ice.

[0081] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A mineral-impregnated modified carbon fiber fabric Joule heating element, characterized in that, It includes a carbon fiber fabric layer, a carbon nanotube layer sequentially covering the surface of the carbon fiber fabric layer, and an impregnation slurry layer; The components of the impregnating slurry layer include calcined kaolin, alkali activator, and superplasticizer.

2. The mineral-impregnated modified carbon fiber fabric Joule heating element according to claim 1, characterized in that, The alkaline activator includes potassium silicate; The mass ratio of the superplasticizer to calcined kaolin is 1.2~1.4:1, and the mass ratio of the total mass of calcined kaolin and alkali activator to the mass of the superplasticizer is 100:1.6~1.

8.

3. The mineral-impregnated modified carbon fiber fabric Joule heating element according to claim 1 or 2, characterized in that, The carbon fiber fabric used in the carbon fiber fabric layer includes unidirectional carbon fiber cloth; the thickness of the carbon fiber fabric layer is 0.8~1.2mm; The thickness of the carbon nanotube layer is 0.05~0.15 mm; The thickness of the impregnating slurry layer is 2~4mm.

4. The method for preparing the mineral-impregnated modified carbon fiber fabric Joule heating element according to any one of claims 1 to 3, characterized in that, Includes the following steps: Carbon nanotubes, organic solvents and perfluorosulfonic acid resins are first mixed to obtain a carbon nanotube dispersion. Carbon fiber fabric is first immersed in the carbon nanotube dispersion for deposition, and a carbon nanotube layer is formed on the surface of the carbon fiber fabric to obtain carbon nanotube modified carbon fiber fabric. After calcining kaolin, alkali activator, superplasticizer and water are mixed and defoamed to obtain impregnation slurry; The carbon nanotube-modified carbon fiber fabric is second-impregnated with the impregnation slurry and then precipitated. After scraping and surface trimming, the slurry is cured on the surface of the carbon nanotube-modified carbon fiber fabric to form an impregnation slurry layer, thereby obtaining the mineral-impregnated modified carbon fiber fabric Joule heating element.

5. The preparation method according to claim 4, characterized in that, The second mixing includes the following steps: calcined kaolin, alkali activator, part of superplasticizer and water are mixed in a third mixing to obtain a primary impregnation slurry; the third mixing is carried out under stirring conditions, the stirring speed is 6000~7000 r / min, and the stirring time is 4~6 min; The remaining superplasticizer is added to the primary impregnation slurry for a fourth mixing to obtain the impregnation slurry; the fourth mixing is carried out under stirring conditions, the stirring speed is 6500~7500 r / min, and the stirring time is 4~6 min.

6. The preparation method according to claim 4, characterized in that, The defoaming process involves vibrating the second mixed material at a frequency of 40-50 kHz for a duration of 8-12 minutes. The second immersion time is 4-6 minutes, and the settling time is 10-15 minutes; The curing temperature is 65~80℃ and the time is 5.5~9h.

7. A gel-based composite material, characterized in that, It includes a substrate, a plurality of heating elements connected in parallel within the substrate, a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode are respectively connected to the two ends of the plurality of heating elements connected in parallel, and the spacing between two adjacent heating elements is 75~85mm; The heating element is the Joule heating element of mineral impregnated modified carbon fiber fabric as described in any one of claims 1 to 3, or the Joule heating element of mineral impregnated modified carbon fiber fabric prepared by the preparation method described in any one of claims 4 to 6.

8. The gel-based composite material according to claim 7, characterized in that, The matrix includes cementitious materials and / or geopolymer materials.

9. The method for preparing the gel-based composite material according to claim 7 or 8, characterized in that, Includes the following steps: After laying a portion of the matrix material flat, a heating element is placed on it. After pouring the remaining portion of the matrix material, an electric current is applied for electrothermal curing to obtain the gel-based composite material.

10. The application of the gel-based composite material of claim 7 or 8 or the gel-based composite material prepared by the preparation method of claim 9 in the preparation of heating materials, wherein the heating materials include road panels, bridge panels, building walls or roofs.

Images