Fe-doped biochar field-oriented enhanced conductive cement-based composite material and preparation method thereof

Abstract

The invention discloses a Fe-doped biochar field-oriented enhanced conductive cement-based composite material and a preparation method thereof. The preparation method comprises the following steps: firstly, performing high-temperature pyrolysis on a biomass raw material, an iron-containing compound and potassium hydroxide under the protection of inert gas to obtain Fe-doped porous biochar with a hierarchical pore structure and ferromagnetism; then doping the biochar into cement-based slurry, applying a static or dynamic gradient magnetic field in a forming stage, so that the biochar is directionally arranged in the direction of the magnetic field before cement is coagulated, and constructing a three-dimensional conductive network penetrating through a matrix; and performing standard curing to obtain the cement-based composite material with stable conductivity. According to the invention, efficient conductive network construction under the condition of low mixing amount is realized, and the composite material has the advantages of strong conductivity, high sensitivity and good stability, is suitable for the fields of concrete structure health monitoring, electrothermal deicing, electromagnetic shielding and the like, and has good engineering application prospects.

Description

Technical Field

[0001] This invention relates to an Fe-doped biochar magnetic field-oriented enhanced conductive cement-based composite material and its preparation method, belonging to the field of materials science and engineering technology. Background Technology

[0002] With the increasing demand for intelligent infrastructure, the requirements for early online monitoring of cracks in concrete structures are constantly rising. Critical concrete structures such as long-distance water conveyance tunnels are prone to cracking during service. Traditional monitoring methods based on manual inspections and distributed sensors have problems such as large monitoring blind spots and slow response.

[0003] The emerging field of self-sensing concrete incorporates conductive fillers into concrete, enabling measurable changes in resistance when the structure is under load or cracks appear, thus achieving spontaneous damage detection. Commonly used conductive fillers such as carbon nanotubes, graphene, and nano-carbon black effectively improve conductivity, but they often suffer from drawbacks such as high cost, tendency to agglomerate, and difficulty in large-scale production. Nano-carbon black is inexpensive and has excellent conductivity, but because it requires a high dosage to form a continuous conductive path, it can absorb moisture, hindering cement hydration, reducing paste fluidity, and ultimately weakening the mechanical properties of the concrete.

[0004] Conductive concrete is an important carrier for realizing intelligent civil engineering structures. Current mainstream technologies impart conductivity by incorporating carbon-based materials (such as carbon fibers, carbon nanotubes, and graphene) or metal particles into the cement matrix. However, these methods have inherent bottlenecks: 1) High dosage and performance contradiction: In order to achieve effective conductivity, carbon fiber and other materials often need to be added at a volume fraction of 0.5% to 1.5%. While graphene and other nanomaterials are highly efficient, they are prone to agglomeration. Furthermore, high dosage increases costs significantly and seriously impairs the workability and mechanical strength of concrete.

[0005] 2) Low efficiency of conductive network: Traditional mechanical stirring leads to random and disordered distribution of conductive filler, requiring higher doping levels (i.e., high percolation threshold) to form conductive pathways. Moreover, the pathways are tortuous, with high interfacial resistance, low and unstable conductivity.

[0006] 3) Limited functional mechanism: Existing conductive concrete mainly relies on electron conduction and does not make sufficient use of ion conduction, which limits its application in emerging fields such as energy storage and conversion.

[0007] Therefore, developing a method for preparing conductive concrete with low admixture, high efficiency, multiple functions, and controllable structure is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] To overcome the problem of insufficient conductivity of biochar in existing technologies, the purpose of this invention is to provide a conductive cement-based composite material with magnetic field-oriented enhancement by Fe-doped biochar. The prepared conductive cement-based composite material not only has excellent conductivity and high sensitivity, but is also low in cost, environmentally friendly and renewable, and is suitable for applications such as health monitoring of concrete structures.

[0009] Another objective of this invention is to provide a method for preparing a conductive smart concrete composite material that can significantly reduce the amount of conductive filler, greatly improve conductivity, and achieve active design of the conductive network.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0011] A conductive cement-based composite material with magnetic field-oriented enhancement by Fe-doped biochar, wherein the composite material has a three-dimensional interconnected conductive network formed by Fe-doped hierarchical porous biochar oriented along the magnetic field direction, and the conductivity of the conductive network along the magnetic field direction is higher than that in the vertical direction.

[0012] Furthermore, the Fe-doped hierarchical porous biochar is prepared through the following steps: Biomass raw materials, iron-containing compounds, and potassium hydroxide (KOH) are pyrolyzed at high temperature under inert gas protection. The resulting product is then washed and dried. The iron-containing compound is selected from ferric chloride (FeCl3·6H2O), ferric nitrate (Fe(NO3)3·9H2O), or ferrous sulfate; the pyrolysis temperature is 600℃ to 900℃, and the pyrolysis time is 1 to 3 hours.

[0013] Furthermore, the Fe-doped hierarchical porous biochar is added at a rate of 0.5% to 5.0% of the cement mass.

[0014] In addition, the present invention also discloses a method for preparing the above-mentioned conductive cement-based composite material, comprising the following steps: a) Biomass raw materials, iron-containing compounds and KOH are pyrolyzed at high temperature in an inert gas environment at a mass ratio of 1:(0.05~0.3):(1~4) to obtain Fe-doped hierarchical porous biochar; b) Mix cement, aggregates, admixtures and water to prepare cement paste; c) Add the Fe-doped biochar obtained in step a) to the cement paste, stir evenly, and immediately perform directional treatment in a gradient magnetic field with a magnetic field strength of 0.1T to 2.0T for 10 minutes until the cement paste initially sets. d) Perform curing to obtain conductive cement-based composite materials.

[0015] Furthermore, in step a), the biomass is pulverized to 80-200 mesh, dried at 105℃, and then mixed with Fe compound, KOH and deionized water, and soaked in a water bath at 60-80℃ for 6-12 hours. The impregnation mixture was heated to 600-900℃ at a rate of 5-10℃ / min under inert gas protection and kept at the temperature for 1-3h for pyrolysis activation. After cooling, the pyrolysis product was soaked in 1-3mol / L HCl, washed with deionized water until neutral, and then vacuum dried at 100-120℃ for 6-12h. FBC powder was then obtained by grinding.

[0016] Furthermore, in step b), ordinary silicate cement, fine aggregate and FBC powder (accounting for 0.5%-5.0% of the cement mass) are dry-mixed in a mixer for 2-5 minutes.

[0017] Furthermore, in step c), the dry mixture is mixed with water and 0.2-1.0% water-reducing agent, and then stirred at low speed for 1 minute followed by high speed for 2-4 minutes; after the slurry is poured into the mold, it is oriented in a magnetic field of 0.1-2.0T for 30 minutes to 2 hours. In step d), after magnetic field treatment, the specimen is in (20 + After standing in the mold for 24 hours under conditions of 1℃ and RH>90%, the molded material is removed and transferred to a standard curing room (20℃). + Continue maintenance at 2℃ until the specified age.

[0018] Furthermore, the electrical conductivity of the composite material is at least 10 times greater along the magnetic field direction than along the perpendicular direction; the magnetic field strength of the gradient magnetic field is 100mT to 2T, and the magnetic field treatment time is 10 minutes until the cement paste initially sets; the gradient magnetic field is a static gradient magnetic field or a dynamic rotating magnetic field.

[0019] Furthermore, the composite material also has the functions of stress / strain self-sensing, electrothermal conversion, or electromagnetic shielding.

[0020] Furthermore, the present invention also discloses an application of the above-mentioned conductive cement-based composite material for health monitoring, stress / strain self-sensing, electrothermal de-icing, or electromagnetic shielding of concrete structures.

[0021] By employing the above technical solution, the present invention has the following beneficial technical effects: 1) By using Fe-doped biochar to impart magnetism, combined with an external gradient magnetic field, the directional arrangement of conductive fillers can be effectively controlled; 2) The hierarchical porous structure provides high specific surface area and excellent conductive channels; 3) Reduce filler usage, improve conductivity, and enhance the stability and durability of the conductive network; 4) Achieving anisotropic conductivity provides a foundation for intelligent sensing and energy transmission. Attached Figure Description

[0022] Figure 1 This is a process flow diagram for preparing the composite material of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the Fe-doped hierarchical porous biochar (FBC) prepared in Example 1; Figure 3 This is the X-ray diffraction (XRD) pattern of the FBC; Figure 4 The diagrams show a comparison of the conductive network structure of the concrete samples after random dispersion (a) and magnetic field-directed dispersion (b). Figure 5 This is a graph showing the changes in resistivity-filler dosage relationship between Example 1 and Comparative Example 1. Detailed Implementation

[0023] To better illustrate the present invention, the following detailed description is provided in conjunction with specific embodiments. However, these specific embodiments are merely for illustrative purposes and are not intended to limit the scope of the invention.

[0024] This invention belongs to the field of functional building materials technology, specifically relating to a cement-based composite material with high conductivity and good mechanical properties. In particular, it relates to a smart concrete and its preparation method that constructs a three-dimensional interconnected conductive network through Fe doping modification and magnetic field directional alignment technology. The prepared conductive cement-based composite material not only has excellent conductivity and high sensitivity, but is also low in cost, environmentally friendly and renewable, and is suitable for applications such as health monitoring of concrete structures.

[0025] This invention relates to an Fe-doped biochar magnetic field-enhanced conductive cement-based composite material and its preparation method. The method involves constructing Fe-doped hierarchical porous biochar with both high conductivity and magnetic responsiveness, and then oriented it using an applied gradient magnetic field to obtain a three-dimensionally connected cement-based composite material with anisotropic conductivity.

[0026] This invention first involves the high-temperature pyrolysis of biomass raw materials, iron-containing compounds, and potassium hydroxide under an inert gas atmosphere to obtain Fe-doped porous biochar with a hierarchical pore structure and ferromagnetism. Subsequently, this biochar is incorporated into a cement-based slurry, and a static or dynamic gradient magnetic field is applied during the molding stage to orient it along the magnetic field direction at the cement setting front, constructing a three-dimensional conductive network penetrating the matrix. After standard curing, a cement-based composite material with stable electrical conductivity is obtained. The composite material of this invention exhibits significantly higher conductivity along the magnetic field direction than in the vertical direction and possesses multiple functions including piezoresistive self-sensing, electrothermal conversion, and electromagnetic shielding.

[0027] This invention utilizes Fe doping to enhance the intrinsic conductivity and magnetism of biochar, and combines this with magnetic field orientation to significantly reduce the percolation threshold of conductive fillers, achieving efficient conductive network construction under low doping conditions. This composite material exhibits strong conductivity, high sensitivity, and good stability, making it suitable for applications such as concrete structure health monitoring, electrothermal de-icing, and electromagnetic shielding, demonstrating promising engineering prospects.

[0028] The core concept of this invention lies in the combination of "precursor modification" and "process external field control".

[0029] First, a biochar functional filler with high intrinsic conductivity, hierarchical porous structure, and ferromagnetism was prepared through a synergistic process of KOH activation and Fe doping. Then, an external gradient magnetic field was used to oriented the magnetic filler before the cement paste solidified, thereby constructing a three-dimensional, highly efficient conductive network that penetrates the matrix.

[0030] To achieve the above objectives, the present invention adopts the following specific technical solution: I. Preparation of Fe-doped hierarchical porous biochar (FBC) functional filler Precursor processing: Crush biomass raw materials (such as rice husks and sawdust) to 80-200 mesh and dry them at 105℃ to constant weight.

[0031] Impregnation and mixing: The dried biomass, iron-containing compound, and potassium hydroxide (KOH) are mixed in deionized water at a mass ratio of 1:(0.05~0.3):(1~4). The iron-containing compound is preferably ferric chloride (FeCl3·6H2O) or ferric nitrate (Fe(NO3)3·9H2O); the mixture is stirred and impregnated in a water bath at 60-80℃ for 6-12 hours.

[0032] Pyrolysis activation: The impregnation mixture is transferred to a tube furnace and heated to 600-900°C at a heating rate of 5-10°C / min under the protection of an inert gas (such as N2 or Ar), and held at the same temperature for 1-3 hours.

[0033] Post-processing: After the pyrolysis product is naturally cooled to room temperature, it is first soaked in 1-3 mol / L hydrochloric acid solution to remove unstable iron species and residual KOH, then repeatedly washed with deionized water until the filtrate is neutral, and finally vacuum dried at 100-120℃ for 6-12 hours. After grinding, black powdery Fe-doped hierarchical porous biochar is obtained.

[0034] II. Preparation Method of Conductive Smart Concrete Dry mixing: Dry mix ordinary Portland cement, fine aggregate (such as standard sand), and the FBC powder prepared above in a mixer for 2-5 minutes to ensure that the FBC is initially and evenly dispersed in the dry material. The FBC content is 0.5%-5.0% of the cement mass, preferably 1%-3%.

[0035] Wet mixing: Add mixing water and high-efficiency polycarboxylate superplasticizer (dosage is 0.2%-1.0% of the mass of cementitious material) to the above dry mixture, stir at low speed for 1 minute, then stir at high speed for 2-4 minutes to form a uniform slurry with good fluidity.

[0036] Magnetic Orientation: The well-stirred slurry is rapidly injected into the molding mold, and the mold is immediately placed in a gradient magnetic field generator. The magnetic field strength is 0.1-2.0 T (Tesla), preferably 0.3-1.0 T. The magnetic field treatment time starts from the time the slurry enters the mold and continues until it initially sets, typically from 30 minutes to 2 hours.

[0037] Curing: After magnetic field treatment, the specimens were placed in the mold under standard curing conditions (20±1℃, RH>90%) for 24 hours before being demolded. They were then transferred to a standard curing room (20±2℃, in water or RH>95%) for continued curing until the specified age.

[0038] The mechanism and beneficial effects of this invention are as follows: 1. Material Innovation: Fe / KOH Synergistic Modification for Constructing Multifunctional Packing Material KOH activation: KOH reacts with carbon at high temperature, causing intense etching and generating numerous micropores. Simultaneously, some metallic K embeds into the carbon layer, contributing to pore formation, thus constructing a hierarchical pore structure with micropores, mesopores, and macropores. This structure not only provides a large specific surface area but also facilitates the release of Ca from the cement hydration environment. 2+ Na + K + Plasma provides fast transport channels and storage sites, enabling a cooperative ion / electron conduction mechanism.

[0039] Fe doping: Fe species play a dual role in the pyrolysis process. First, as a graphitization catalyst, it significantly reduces the energy barrier for the transformation of biochar from amorphous carbon to graphite lattice, greatly improving its intrinsic conductivity. Second, it is reduced to iron nanoparticles (Fe, Fe3C) and embedded in the carbon matrix, endowing biochar with strong ferromagnetism and providing the necessary conditions for subsequent magnetic field driving.

[0040] 2. Technological Innovation: Magnetic Field-Induced Construction of Three-Dimensional Directional Conductive Network This invention innovatively utilizes a gradient magnetic field to apply a magnetizing force (F=μ0*M·) to magnetic FBC particles. H) drives the particles to overcome the viscous resistance of the slurry, migrate directionally along the direction of the magnetic field lines and connect end to end to form a one-dimensional linear conductive chain.

[0041] By controlling the magnetic field configuration (such as using a rotating or alternating magnetic field), these one-dimensional chains can be induced to approach and overlap each other, ultimately forming a three-dimensional, interpenetrating, and highly interconnected conductive network within the cement matrix. Compared to a random, dispersed mode, this network can achieve extremely high conductivity with very low filler content (significantly reducing the seepage threshold) and possesses excellent conductive durability due to the stability of the network structure.

[0042] 3. Excellent performance and functionality Low dosage and high efficiency: With only 1-2% FBC content, the electrical conductivity of the concrete of this invention can be increased by 1-2 orders of magnitude compared with the random dispersion system of the same dosage.

[0043] Anisotropic conductivity: The material exhibits significant anisotropy in conductivity, with conductivity along the magnetic field orientation direction being much higher than that in the perpendicular direction, making it suitable for directional sensing and energy transmission.

[0044] Multifunctional integration: This material simultaneously possesses excellent piezoresistive effect (for stress / strain self-sensing), electrothermal effect (for road / bridge de-icing), and electromagnetic interference shielding capabilities. Its hierarchical porous structure also shows potential for application in structural supercapacitors.

[0045] like Figure 1 As shown, Figure 1 This is a process flow diagram of the preparation method of the present invention.

[0046] A method for preparing an Fe-doped biochar magnetic field-oriented reinforced conductive cement-based composite material includes the following steps: S101: Preparation of Fe-doped hierarchical porous biochar: Biomass raw materials, iron-containing compounds and potassium hydroxide (KOH) activator are mixed; S102: High-temperature pyrolysis was carried out under an inert atmosphere. After the reaction was completed, it was washed and dried to obtain Fe-doped hierarchical porous biochar. S103: Preparation of cement-based composite paste: Mix cement, aggregate, admixture and water, and stir evenly; S104: Magnetic directional dispersion: The obtained Fe-doped hierarchical porous biochar was incorporated into the cement-based slurry and stirred; S105: After stirring evenly, immediately place the slurry in an external gradient magnetic field for treatment to orient the biochar particles. S106: Curing and molding: After completing the magnetic field treatment, the cement-based slurry is cured to obtain the conductive cement-based composite material.

[0047] In step S101 above, the biomass raw material is rice husk, straw or sawdust; the iron-containing compound is ferric chloride, ferric nitrate or ferrous sulfate; the mass ratio of biomass, iron-containing compound and KOH is 1:(0.05~0.3):(1~4); the pyrolysis temperature is 600~900℃ and the holding time is 1~3 hours.

[0048] In step S103 above, the Fe-doped hierarchical porous biochar content is 0.5% to 5% of the cement mass; the magnetic field strength of the gradient magnetic field is 100 mT to 2 T, and the magnetic field treatment time is 10 minutes until the cement paste initially sets. The gradient magnetic field is a static gradient magnetic field or a dynamic rotating magnetic field.

[0049] A Fe-doped biochar magnetic field-oriented reinforced conductive cement-based composite material prepared by the method described above. The composite material contains a three-dimensional interconnected conductive network formed by Fe-doped hierarchical porous biochar oriented along the magnetic field direction. The composite material exhibits anisotropic conductivity, with higher conductivity along the magnetic field direction than in the perpendicular direction. The composite material possesses at least one of the following functions: stress / strain self-sensing, electrothermal conversion, electromagnetic shielding, or energy storage.

[0050] The present invention will be described in detail below through preferred embodiments, but the scope of protection of the present invention is not limited thereto.

[0051] Example 1 FBC preparation: Take 100g of dried rice husk powder, 15g of FeCl3·6H2O and 200g of KOH, and impregnate, pyrolyze (800℃, 2h), acid wash and dry according to the above method to obtain FBC.

[0052] Concrete preparation: 450g P·O 42.5 cement, 1350g standard sand, FBC (2% of cement mass, i.e., 9g), 225g water (water-cement ratio 0.5), and 1.35g polycarboxylate superplasticizer. Prepare the slurry according to the dry-wet mixing process.

[0053] Magnetic orientation: After the slurry is injected into a 40mm×40mm×160mm mold, it is immediately placed in a static gradient magnetic field with a magnetic field strength of 0.5T and treated for 90 minutes.

[0054] Maintenance: Maintain for 28 days under standard conditions.

[0055] Figure 2 This is a scanning electron microscope (SEM) image of the Fe-doped hierarchical porous biochar (FBC) prepared in Example 1; Figure 2The image clearly demonstrates the microstructure of Fe-doped hierarchical porous biochar (FBC): the FBC exhibits a typical hierarchical porous structure, with macropores, mesopores, and micropores interwoven and well-connected. This multi-level porous system provides abundant pathways for the transport of ions and electrons and endows the material with a high specific surface area. The fine particles in the red circle area are Fe-based nanoparticles successfully embedded in the carbon matrix. They are uniformly dispersed in the carbon matrix without obvious agglomeration, indicating that the Fe component is stably loaded in the biochar framework.

[0056] The aforementioned microstructural features are the core structural basis for FBC's excellent mass transfer performance and the activity of its functional components. Figure 3 This is the X-ray diffraction (XRD) pattern of the FBC; Figure 3 The differences in phase composition of biochar before and after Fe doping modification are presented: For undoped original biochar (BC, red curve), only broadened and low-intensity carbon-based diffraction peaks appear near 2θ≈20°, indicating that its carbon matrix is ​​mainly amorphous carbon with a weak degree of graphitization; while the Fe-doped FBC (black curve) shows significantly sharper carbon-based diffraction peaks and greatly increased intensity at the same 2θ position, indicating that Fe doping effectively promotes the graphitization crystal transformation of the carbon matrix. This structural change can directly enhance the intrinsic electron transport capability of the material.

[0057] Example 2 The FBC content is 1% of the cement mass, and the mixture is treated with a rotating magnetic field (intensity 0.3T) for 60 minutes to construct an in-plane isotropic conductive network, suitable for uniform heating of plate components. Other processes and methods are the same as in Example 1.

[0058] Figure 4 Comparison of conductive network structures of concrete samples after random dispersion and magnetic field-directed dispersion.

[0059] Figure 4 This study demonstrates the effect of gradient magnetic field on the distribution of conductive filler (Fe-doped hierarchical porous biochar, FBC) in self-sensing concrete: The left side shows the "random distribution" state without magnetic field intervention, where FBCs are randomly dispersed in the concrete matrix with local agglomeration. Due to the low overlap probability between FBC particles, only isolated local conductive pathways can be formed, resulting in a discontinuous conductive network that makes efficient electron transport difficult. The right side shows the "directional distribution" state induced by the gradient magnetic field. With the help of the magnetic response characteristics of the Fe-based components in FBCs, they are arranged in an orderly manner along the gradient magnetic field lines, overlapping to form a one-dimensional linear conductive chain that runs through the concrete matrix. Multiple sets of conductive chains further intertwine to construct a three-dimensional interconnected conductive network.

[0060] Example 3 The FBC content is 3% of the cement mass, and it is treated with a high-intensity static magnetic field (1.2T) for 120 minutes to obtain excellent conductivity in a single direction, which is suitable for axial stress monitoring of beam and column members. Other processes and methods are the same as in Example 1.

[0061] Example 4 Materials preparation: Take 100g of dried rice husk powder, 15g of FeCl3·6H2O, and 200g of KOH.

[0062] Fe-doped porous biochar was obtained by impregnation, pyrolysis (800°C, 2 hours), acid washing, and drying according to the process described in Example 1 above.

[0063] The concrete preparation formula composition is as follows: Cement: 450g; Sand: 1350g; FBC powder: 9g (2% of cement); Water: 225g (water-cement ratio 0.5) Polycarboxylate superplasticizer: 1.35g; Magnetic orientation: Inject the slurry into a 40×40×160mm mold and immediately place it in a 0.5T gradient magnetic field for 90 minutes.

[0064] Maintenance: Standard maintenance for 28 days, then test conductivity.

[0065] Comparative Example 1 Except for not applying a magnetic field, which allows the FBCs to be randomly dispersed in the slurry, the other conditions are exactly the same as in Example 1.

[0066] Performance comparison test: Electrical conductivity: tested using the four-electrode method. The conductivity of the sample in Example 1 along the magnetic field direction was 1.2 × 10⁻⁶. -2 The conductivity of the sample in Comparative Example 1 was only 2.5 × 10⁻⁶ S / m, while the conductivity of the sample in Comparative Example 1 was only 2.5 × 10⁻⁶ S / m. -4 S / m, the former is nearly 50 times that of the latter.

[0067] Piezoresistive properties: Under 5 MPa compressive stress, the resistance change rate of the sample in Example 1 reached 18%, which is much higher than that of Comparative Example 1 (5%), showing superior self-sensing sensitivity.

[0068] Figure 5 The curves showing the resistivity-filler dosage relationship between Example 1 and Comparative Example 1 demonstrate the significant effect of magnetic field orientation on reducing the seepage threshold.

[0069] Figure 5The effect of biochar content on the resistivity of self-sensing concrete was demonstrated, with light-colored columns corresponding to the "non-oriented" group and green columns corresponding to the "field-oriented" group. The overall trend shows that the resistivity of both groups of concrete decreases with increasing biochar content. Furthermore, at the same biochar content, the resistivity of the "field-oriented" group is consistently significantly lower than that of the "non-oriented" group, and the decrease in resistivity with increasing biochar content is more pronounced.

[0070] Performance Testing and Analysis Part 1: Electrical performance tests were performed on the samples from Examples 1 and 2. The volume resistivity was measured using the four-probe method. The results showed that the bulk conductivity of the sample in Example 1 was approximately 3.6 × 10⁻⁶. -5 S / cm, volume resistivity approximately 2.8 × 10⁻⁶ 4 Ω·cm.

[0071] In Example 2, the bulk conductivity was further increased to approximately 1.0 × 10⁻⁶ after the addition of nano-carbon black to the sample. -4 S / cm, volume resistivity approximately 1.0 × 10⁻⁶ 4 The resistivity of this composite material is significantly reduced to Ω·cm. Due to this substantial decrease in resistivity, the resistivity change rate under 10 MPa cyclic compressive stress can reach over 20%, sensitively reflecting stress and crack initiation. The resistivity of conventional cement slurry is typically on the order of 10^6 Ω·cm; the resistivity of the material in this invention is reduced by two to three orders of magnitude, demonstrating the effectiveness of the synergistic effect of biochar and nano-carbon black in constructing a highly efficient conductive network.

[0072] Performance Testing and Analysis II: The performance of the conductive material in Example 4 was verified as follows: Test results show that the conductivity along the magnetic field direction is 1.2 × 10⁻⁶. -2 S / m, the comparative sample (without magnetic field orientation) is only 2.5 × 10 -4 S / m, an increase of approximately 50 times.

[0073] Piezoresistive test: At a stress of 5 MPa, the resistance change rate reached 18%, which is significantly better than the 5% of the unoriented sample.

[0074] Technical effects and advantages: Significantly improves conductivity: High conductivity can be achieved with low filler content, reducing costs.

[0075] Stable conductive network: The conductive path formed by the magnetic field has good stability and durability.

[0076] Anisotropic conductivity: meets special requirements such as directional sensing and energy transmission.

[0077] Multifunctional integration: It has properties such as piezoresistive, thermal effect, and electromagnetic shielding, expanding the range of applications.

[0078] Through the above embodiments and performance tests, the significant advantages of the present invention in terms of conductivity, material cost, structural stability and multifunctionality have been verified, fully demonstrating its innovation and practicality in the field of intelligent building materials.

[0079] The Fe-doped biochar magnetic field-oriented reinforced conductive cement-based composite material provided by this invention, combined with cutting-edge magnetron-controlled conductive network construction technology, effectively improves conductivity, reduces filler usage, and enhances material stability and multifunctionality, thus possessing broad application prospects and promotional value.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A conductive cement-based composite material with Fe-doped biochar magnetic field-oriented enhancement, characterized in that: The composite material contains a three-dimensional interconnected conductive network formed by Fe-doped hierarchical porous biochar oriented along the magnetic field direction. The conductivity of the conductive network along the magnetic field direction is higher than that in the vertical direction.

2. The conductive cement-based composite material according to claim 1, characterized in that: The Fe-doped hierarchical porous biochar was prepared through the following steps: Biomass raw materials, iron-containing compounds, and potassium hydroxide (KOH) are pyrolyzed at high temperature under inert gas protection. The resulting product is then washed and dried. The iron-containing compound is selected from ferric chloride (FeCl3·6H2O), ferric nitrate (Fe(NO3)3·9H2O), or ferrous sulfate; the pyrolysis temperature is 600℃ to 900℃, and the pyrolysis time is 1 to 3 hours.

3. The conductive cement-based composite material according to claim 2, characterized in that: The Fe-doped hierarchical porous biochar is added at a concentration of 0.5% to 5.0% of the cement mass.

4. The method for preparing the conductive cement-based composite material according to any one of claims 1-3, characterized in that: Includes the following steps: a) Biomass raw materials, iron-containing compounds and KOH are pyrolyzed at high temperature in an inert gas environment at a mass ratio of 1:(0.05~0.3):(1~4) to obtain Fe-doped hierarchical porous biochar; b) Mix cement, aggregates, admixtures and water to prepare cement paste; c) Add the Fe-doped biochar obtained in step a) to the cement paste, stir evenly, and immediately perform directional treatment in a gradient magnetic field with a magnetic field strength of 0.1T to 2.0T for 10 minutes until the cement paste initially sets. d) Perform curing to obtain conductive cement-based composite materials.

5. The method for preparing the conductive cement-based composite material according to claim 4, characterized in that: In step a), the biomass is pulverized to 80-200 mesh, dried at 105℃, and then mixed with Fe compound, KOH and deionized water, and soaked in a water bath at 60-80℃ for 6-12 hours. The impregnation mixture was heated to 600-900℃ at a rate of 5-10℃ / min under inert gas protection and kept at the temperature for 1-3h for pyrolysis activation. After cooling, the pyrolysis product was soaked in 1-3mol / L HCl, washed with deionized water until neutral, and then vacuum dried at 100-120℃ for 6-12h. FBC powder was then obtained by grinding.

6. The method for preparing the conductive cement-based composite material according to claim 5, characterized in that: In step b), ordinary silicate cement, fine aggregate and FBC powder (0.5%-5.0% of the cement mass) are dry-mixed in a mixer for 2-5 minutes.

7. The method for preparing the conductive cement-based composite material according to claim 6, characterized in that: In step c), the dry mixture is mixed with water and 0.2-1.0% water-reducing agent, and stirred at low speed for 1 minute and then at high speed for 2-4 minutes. After the slurry is poured into the mold, it is oriented in a magnetic field of 0.1-2.0T for 30 minutes to 2 hours. In step d), after magnetic field treatment, the specimen is in (20 + After standing in the mold for 24 hours under conditions of 1℃ and RH>90%, the molded material is removed and transferred to a standard curing room (20℃). + Continue maintenance at 2℃ until the specified age.

8. The method for preparing the conductive cement-based composite material according to claim 7, characterized in that: The electrical conductivity of the composite material is at least 10 times greater along the magnetic field direction than along the perpendicular direction; the magnetic field strength of the gradient magnetic field is 100mT to 2T, and the magnetic field treatment time is 10 minutes until the cement paste initially sets; the gradient magnetic field is a static gradient magnetic field or a dynamic rotating magnetic field.

9. The method for preparing the conductive cement-based composite material according to claim 7, characterized in that: The composite material also has the functions of stress / strain self-sensing, electrothermal conversion, or electromagnetic shielding.

10. An application based on the conductive cement-based composite material of claim 9, characterized in that: Used for health monitoring, stress / strain self-sensing, electrothermal de-icing, or electromagnetic shielding of concrete structures.

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