A red mud-based supercapacitor energy storage structure for road engineering applications

Abstract

The application provides a red mud-based supercapacitor energy storage structure for road engineering application, and belongs to the technical field of road engineering and advanced building materials. The red mud-based supercapacitor comprises, from bottom to top, a first red mud-based composite electrode, a diaphragm and a second red mud-based composite electrode. The components of the first red mud-based composite electrode and the second red mud-based composite electrode comprise, by mass fraction, 40-60 parts of red mud, 10-15 parts of fly ash, 25-35 parts of cement, 5-15 parts of fine aggregate, 0.5-2 parts of Na2SO4 activator, 0.5-2 parts of conductive reinforcing material and 0.2-1 parts of reinforcing fiber. The first and second red mud-based composite electrodes are soaked in an electrolyte after initial setting, and the surface free liquid is removed after soaking and draining. The application adopts an electrode pore liquid absorption ion guiding mechanism, cancels the independent liquid electrolyte filling cavity in the existing road surface energy storage structure, and realizes the engineering configuration without free liquid electrolyte.

Description

Technical Field

[0001] This application belongs to the field of road engineering and advanced building materials technology, specifically relating to a red mud-based supercapacitor energy storage structure for road engineering applications. Background Technology

[0002] The core design principles of traditional asphalt concrete or cement concrete pavement are to bear traffic loads, provide a smooth driving surface, and ensure long-term durability; they do not inherently possess energy harvesting, storage, or conversion capabilities. With the development of smart city and green transportation concepts, upgrading road infrastructure into distributed energy nodes has become an important research direction. Existing technologies have attempted to embed photovoltaic cells, piezoelectric materials, or independent energy storage elements into the pavement structure, but these solutions generally suffer from poor integration with the pavement structure, high additional costs, insufficient long-term reliability, or limited energy density.

[0003] On the other hand, red mud is a highly alkaline solid waste generated after alumina extraction in the alumina industry, with a huge global stockpile and severe environmental pressure. Currently, the resource utilization of red mud is mostly concentrated in low-value-added areas such as roadbed fillers and cement admixtures, with consumption rates far lower than production rates, failing to achieve its high-value utilization. Red mud is rich in metal oxides such as iron, aluminum, and silicon, and possesses certain potential cementing activity and ionic conductivity. If it can be developed into a composite material with both structural load-bearing and electrical energy storage functions, it will provide a revolutionary solution for the large-scale, high-value-added disposal of red mud and the construction of smart roads. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a red mud-based supercapacitor energy storage structure for road engineering applications, comprising a red mud-based supercapacitor, wherein the red mud-based supercapacitor comprises, from bottom to top, a first red mud-based composite electrode, a diaphragm, and a second red mud-based composite electrode. The components of the first red mud-based composite electrode and the second red mud-based composite electrode, by mass parts, include: 40-60 parts red mud, 10-15 parts fly ash, 25-35 parts cement, 5-15 parts fine aggregate, 0.5-2 parts Na2SO4 activator, 0.5-2 parts conductive reinforcing material, and 0.2-1 parts reinforcing fiber; After the first and second red mud-based composite electrodes were cured to initial set, they were immersed in the electrolyte and then drained to remove the free liquid on the surface.

[0005] Among them, Na2SO4 activator, as a sulfate activator, accelerates the hydration reaction of aluminosilicate minerals in red mud and fly ash, generating more high-strength hydration products, while improving the migration efficiency of conductive ions and helping to improve energy storage performance.

[0006] The diaphragm serves to insulate against electrons and conduct ions, ensuring that there is no short circuit between the positive and negative electrodes, while allowing ions in the electrolyte to migrate freely, thus enabling charging and discharging.

[0007] Preferably, the preparation method of the first and second red mud-based composite electrodes is as follows: Mixing and slurry preparation: Red mud, fly ash, cement, fine aggregate, Na2SO4 activator, conductive reinforcing material, reinforcing fiber, water-reducing agent, and water are uniformly mixed to prepare a red mud-based conductive slurry. The ratio of water to the total mass of "red mud + cement + fly ash" is (0.25-0.45):1, and the water-reducing agent accounts for 0.5%-1.5% of the total mass of "red mud + cement + fly ash". Shaping and curing: Pour the red mud-based conductive slurry into a mold, vibrate, shape and cure for 3-5 days until initial setting, then soak in electrolyte and drain to complete the preparation of the red mud-based composite electrode.

[0008] Preferably, the red mud, cement, fine aggregate, fly ash, conductive reinforcing material, and reinforcing fiber are first dry-mixed evenly for 5-10 minutes. Then, water and water-reducing agent are added, and the mixture is stirred at a speed of 500-700 r / min for 25-35 minutes. After standing for 5-10 minutes to remove foam, it is poured.

[0009] Preferably, the red mud-based composite electrode has a connected porosity of 18%-22%, an electrolyte soaking absorption rate of ≥15% (mass fraction), and is naturally drained for 2-4 hours after soaking to remove free electrolyte from the surface.

[0010] Preferably, the water-reducing agent is a polycarboxylate-based water-reducing agent or a naphthalene-based water-reducing agent. The water-reducing agent can reduce the amount of water used for mixing, improve the density and mechanical strength of the electrode, and simultaneously improve the workability of the conductive slurry, ensuring uniform dispersion and compaction of the slurry during construction.

[0011] Preferably, the fly ash is Class F fly ash with a specific surface area ≥350m². 2 / kg, loss on ignition ≤8%. It works synergistically with red mud and cement to generate hydrated calcium silicate gel, which strengthens mechanical strength and optimizes electrode pore structure.

[0012] Preferably, the red mud is a byproduct of the alumina industry (Bayer process, sintering process, or combined process are all acceptable), dried to a moisture content of ≤5%, pulverized, and passed through a 0.075mm sieve. Its natural porous structure (connected porosity 18%-22%) is used to adsorb electrolyte, while simultaneously working synergistically with cement, fly ash, and fine aggregates to form mechanical strength.

[0013] Furthermore, the diaphragm is a red mud-based modified diaphragm, which is made by mixing red mud, cement and sodium carboxymethyl cellulose in a mass ratio of 1:(0.3-0.5):(0.02-0.05).

[0014] Furthermore, the electrolyte is a potassium chloride solution with a concentration of 1-2 mol / L or a sodium chloride solution with a concentration of 1.5-2.0 mol / L. This electrolyte is neutral (pH=6.5-7.5), has stable ionic conductivity (100-150 mS / cm), can fully fill the electrode pores to form ion channels, and does not corrode the electrodes, diaphragm, or sealing layer, ensuring safe construction and low environmental risk.

[0015] Furthermore, the conductive reinforcing material is one or more of reduced graphene oxide and nano-carbon black; the conductive reinforcing material forms a continuous conductive network inside the electrode, adsorbs charged ions to form an electric double layer, and improves the energy storage density.

[0016] Preferably, the reduced graphene oxide has a particle size of 1-5 μm and a specific surface area ≥1000 m². 2 For products per g, the preferred nano carbon black particle size is 15-40 nm and the specific surface area is ≥400 m². 2 / g of products.

[0017] The reinforcing fibers are short carbon fiber filaments with a diameter of 5μm-20μm and a length of 3mm-12mm.

[0018] Furthermore, the carbon fiber chopped strands undergo plasma surface activation treatment, the treatment steps of which include: drying the carbon fiber chopped strands at 60-80°C for 1-2 hours, placing them in a low-temperature plasma treatment chamber, and evacuating them to 20-60 Pa; then introducing a mixture of argon and oxygen, wherein the argon flow rate is 30-50 sccm and the oxygen flow rate is 5-15 sccm, and treating them at 80-150 W radio frequency power for 3-8 minutes.

[0019] Furthermore, the thickness of the first red mud-based composite electrode and the second red mud-based composite electrode is 5cm-12cm, and the thickness of the diaphragm is 0.1mm-2mm.

[0020] Furthermore, it also includes a first current collector and a second current collector; the first current collector is disposed on the side of the first red mud-based composite electrode away from the diaphragm, and the second current collector is disposed on the side of the second red mud-based composite electrode away from the diaphragm.

[0021] Furthermore, the first current collector and the second current collector are carbon fiber mesh or carbon fiber felt.

[0022] Furthermore, the first and second current collectors are carbon fiber meshes, wherein the carbon fibers in the mesh have a diameter of 2mm-3mm and the mesh pore size is 10mm-20mm. Carbon fiber meshes possess advantages such as high strength, high conductivity, and corrosion resistance, avoiding the problems of metal current collectors being prone to rusting and having poor durability.

[0023] Preferably, the first and second current collectors are tightly bonded to the outer surfaces of the corresponding red mud-based composite electrodes, covering the effective working area of ​​the electrodes and having leads for connection to external circuits. By maintaining stable contact between the current collectors and the electrode surfaces, the interfacial contact resistance is reduced, thereby improving electron collection and transport efficiency.

[0024] Furthermore, the fine aggregate is quartz sand with a particle size of 0.15mm-0.6mm. Utilizing the fine aggregate optimizes the particle size distribution of the red mud-based material, fills some ineffective pores, improves density and mechanical strength, while retaining effective interconnected pores for energy storage. The red mud has a particle size less than 0.075mm; the fly ash has a particle size of 5μm-30μm, preferably 10μm-25μm; the cement has a particle size of 8μm-25μm, preferably 10μm-20μm; the conductive reinforcing material has a particle size of 15nm-5μm; and the Na2SO4 activator has a particle size less than 0.15mm.

[0025] The particle size mentioned above refers to the median particle size D50.

[0026] Furthermore, it also includes a waterproof layer, which wraps around the red mud-based supercapacitor; It also includes a cushion layer and an asphalt surface layer. The red mud-based supercapacitor energy storage structure consists of, from bottom to top, a cushion layer, a first waterproof layer, a red mud-based supercapacitor (first red mud-based composite electrode, diaphragm, second red mud-based composite electrode), a second waterproof layer, and an asphalt surface layer. The thickness of the subbase layer is 10cm-20cm, and the thickness of the asphalt surface layer is 5cm-8cm.

[0027] Preferably, the subbase is a mixture of cement and crushed stone, consisting of 8-10% cement and 90-92% crushed stone by mass, wherein the particle size of the crushed stone is 10mm-32mm.

[0028] Preferably, the subbase is laid and compacted in layers, with each layer having a thickness of 5-10 cm; it is compacted to a compaction degree of ≥96% using a vibratory roller (tested according to GB / T 50123-2019); before laying the subbase, the roadbed needs to be compacted to a compaction degree of ≥93% and a rebound modulus of ≥200 MPa; the subbase is cured by covering it with geotextile and sprinkling water for 7 days, during which time vehicles are prohibited from passing.

[0029] Preferably, the first waterproof layer is an SBS modified bitumen waterproof membrane with a thickness of 3-10mm, the second waterproof layer is a polyurethane waterproof layer with a thickness of 3-5mm, and the overlap width between the first and second waterproof layers is ≥10cm, with the overlap sealed with polysulfide sealant.

[0030] This application provides a construction method for a red mud-based supercapacitor energy storage structure: Subbase construction: Lay a cement-aggregate mixture on the roadbed, spreading and compacting it in layers, each layer 5-10cm thick, with a compaction degree ≥96% (tested according to GB / T 50123-2019). After curing for 7 days, the subbase is formed. Clean the surface of the subbase, removing slag, dust, and debris, and repair surface cracks and potholes to ensure the subbase surface is flat, firm, and has a moisture content ≤9% (tested according to GB / T 50123-2019).

[0031] Substrate preparation: Clean the surface of the subbase, removing scum, dust and debris, repair surface cracks and pits, and ensure that the subbase surface is flat, firm and has a moisture content of ≤9%.

[0032] Apply primer: Apply asphalt-specific primer evenly to the surface of the subbase, at a rate of 0.3-0.5 kg / m². 2 After the primer has completely dried (usually 2-4 hours), the waterproof membrane can be laid.

[0033] First waterproof layer laying: Lay SBS modified bitumen waterproof membrane with a long side overlap width ≥10cm and a short side overlap width ≥15cm. The joints are welded using a hot-melt welding process with a welding temperature ≥180°C. After welding, compact with a roller to ensure that there are no air bubbles or curling edges at the joints, forming a continuous and sealed first waterproof layer.

[0034] Preparation and laying of red mud-based supercapacitor layers: Erecting the formwork: Erect steel formwork on the first waterproof layer according to the design dimensions. The height of the formwork should be consistent with the total thickness of the red mud-based supercapacitor layer. Apply release agent to the inside of the formwork so that the steel formwork can be removed after the red mud-based supercapacitor layer is formed. Laying and fixing the first manifold: After the first waterproof layer is constructed, the first manifold is pre-laid on the first waterproof layer, i.e., the SBS modified bitumen waterproof membrane. The first manifold is flattened and fixed to avoid wrinkles, warping, or local suspension, and an outlet end of the manifold is reserved. Subsequently, red mud-based conductive slurry is poured on-site above the first manifold and compacted by vibration to ensure that the slurry is densely formed, thereby ensuring that the first manifold and the side of the first red mud-based composite electrode facing away from the diaphragm are in close contact and form a stable electrical contact.

[0035] In-situ wetting of the first red mud-based composite electrode with electrolyte: After the first red mud-based composite electrode has initially solidified, electrolyte is introduced into the area enclosed by the template for in-situ wetting, allowing the electrolyte to penetrate into the internal pores of the first red mud-based composite electrode; after wetting, excess electrolyte is drained and allowed to air dry naturally for 2-4 hours to remove free electrolyte from the surface. During this process, the first red mud-based composite electrode remains within the area enclosed by the template and is not disassembled or removed for soaking.

[0036] Laying the diaphragm: Then lay the diaphragm, ensuring that it completely covers the surface of the lower electrode, and that the edges are tightly fitted to the inner wall of the template without wrinkles or damage. Press to make the diaphragm fit tightly against the lower electrode.

[0037] Casting the second red mud-based composite electrode: Prepare and pour red mud-based conductive slurry on-site above the diaphragm, vibrate and level it to ensure that the second red mud-based composite electrode is in close contact with the diaphragm, cover with a curing film and cure until initial setting.

[0038] In-situ wetting of the second red mud-based composite electrode with electrolyte: After the second red mud-based composite electrode has initially solidified, electrolyte is introduced into the area enclosed by the template so that the second red mud-based composite electrode is wetted and absorbs the liquid in in-situ. After wetting is completed, the electrolyte is discharged and allowed to drain naturally for 2-4 hours to remove the free electrolyte on the surface.

[0039] Laying the second current collector: After the second red mud-based composite electrode is in situ wetted with electrolyte and naturally drained, lay the second current collector on the exposed surface of the side away from the diaphragm, flatten it, press it and fix it so that the second current collector is in full contact with the surface of the second red mud-based composite electrode, and at the same time reserve the current collector lead-out end.

[0040] Curing and encapsulation preparation: After laying the second current collector, cover it with a curing film and cure it for 28 days in an environment with a temperature of 20±2°C and a relative humidity of ≥90% to ensure that the electrode is fully cured. During the curing period, check the electrode status regularly to avoid surface cracking. After curing, clean the dust, debris and excess electrolyte from the surface of the red mud-based supercapacitor layer and ensure that the surface is dry and clean before proceeding with encapsulation preparation.

[0041] Construction of the second waterproof layer: Apply a 3-5mm thick, continuous, and pinhole-free polyurethane waterproof coating evenly to the upper surface and sides of the red mud-based supercapacitor layer using spraying or scraping. After the coating has dried to the touch (usually 4-6 hours), overlap the second waterproof layer with the first waterproof layer (width ≥ 10cm), apply polysulfide sealant to the overlap, and compact it with a compaction roller to ensure the formation of a completely sealed cavity.

[0042] Asphalt surface layer laying: After uniformly applying asphalt tack coat to the surface of the second waterproof layer, a modified asphalt mixture is laid using a paver, with a paving thickness of 5-8 cm, and the paving temperature is controlled at 140-160°C. A double-drum roller is used for segmented compaction. The initial compaction stage involves static compaction at a temperature controlled at 130-150°C; the intermediate compaction stage involves vibratory compaction at a temperature controlled at 110-130°C; and the final compaction stage involves static compaction again at a temperature controlled at 60-80°C, until the pavement compaction degree is ≥98% and the smoothness error is ≤3mm / 3m. After the asphalt surface layer temperature drops to ambient temperature, subsequent drainage channel installation is carried out. The core performance indicators of the energy storage pavement of this invention, after optimization design, are as follows: Red mud-based supercapacitor layer: after 28 days of curing, the compressive strength is not less than 30 MPa, and the volumetric capacitance is not less than 7 F / m. 3 After 5000 charge-discharge cycles, the capacitance retention rate is ≥85%; Overall load-bearing capacity of the road surface: resilient modulus ≥3000MPa, splitting tensile strength ≥1.0MPa, meeting the design requirements of highways and urban arterial roads; Sealing performance: After immersion in water for 30 days, the capacitance performance of the supercapacitor layer decreases by ≤5%; Durability: After freeze-thaw cycle test (-20°C to 20°C, 50 cycles), the compressive strength loss of the red mud-based composite electrode is ≤10%, and the capacitance performance decay is ≤10%.

[0043] Key electrode parameters: interconnected porosity 18%-22%, electrolyte absorption rate ≥15% (mass fraction), soaking uniformity ≤2% (content difference in different areas).

[0044] The beneficial effects of this application are as follows: 1. The red mud-based supercapacitor is based on a sandwich energy storage configuration with direct bonding of red mud-based composite electrodes and diaphragms. It adopts an electrode pore liquid absorption and ion conduction mechanism, eliminating the independent liquid electrolyte filling cavity in the existing road surface energy storage structure, and realizing an engineering configuration without free liquid electrolyte.

[0045] The porous framework of the red mud-based composite electrode does not serve as a reservoir for the free electrolyte. Instead, it binds the electrolyte through capillary pores, gelation product channels, and conductive filler interfaces, allowing K... + Na + Cl - Plasma migrates and completes charge compensation within confined, interconnected pores. Compared to structures with independent liquid electrolyte chambers, this free liquid electrolyte design reduces the risk of electrolyte leakage and internal short circuits under repeated vehicle traffic. Even if microcracks appear locally, the electrolyte remains primarily within the electrode pores, which helps maintain electrochemical stability. This structure can be directly used as a base course for conventional road surfaces, reducing construction complexity and costs.

[0046] 2. The red mud-based modified diaphragm is an interface-adaptive diaphragm designed for direct bonding of red mud-based composite electrodes and diaphragms in a sandwich structure. Its innovation lies in the homogeneity of the material system, compatibility with alkaline environments, and adaptability to integrated road engineering construction. The red mud-based modified diaphragm can form a contact interface with the upper and lower layers of red mud-based composite electrodes, exhibiting similar material composition and continuous pore structure. During hydration curing, the hydrated calcium silicate gel at the diaphragm layer and electrode interface interweaves and grows, forming a continuous solid-solid interface. This reduces the interfacial contact resistance that may arise from traditional polymer diaphragms and improves interfacial stability under the shearing action of heavy-duty vehicles.

[0047] Rigid inorganic framework has stronger puncture resistance: PP and PE, as flexible polymers, are inferior to red mud-based modified membranes in terms of compressive strength and other parameters.

[0048] Sodium carboxymethyl cellulose exhibits a synergistic effect of "pore formation and ion conduction." It is not only a binder but also opens up nanoscale ion transport channels in the rigid red mud / cement skeleton. In liquid-free / quasi-solid systems, it utilizes its abundant oxygen-containing functional groups to promote the rapid hopping transport of cations.

[0049] 3. High-value utilization of solid waste: Red mud is added in a high amount to the composite electrode, and when combined with fly ash, it can simultaneously dispose of two kinds of industrial solid waste, effectively alleviating environmental pressure and achieving outstanding environmental benefits.

[0050] 4. Construction safety and environmental protection: The electrolyte is not highly corrosive, there are no safety hazards during construction, and the electrolyte can be directly neutralized during the dismantling of old roads, resulting in low environmental risk.

[0051] 5. Controllable cost: Red mud and fly ash replace part of the cement, Na2SO4 activator is inexpensive, construction process is based on traditional technology optimization, no special equipment is required, and it has economic, social and environmental benefits, which are suitable for the needs of green transportation construction. Attached Figure Description

[0052] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram of the structure of a red mud-based supercapacitor energy storage road surface; Among them: 1. Subbase, 2. First waterproof layer, 3. First current collector, 4. First red mud-based composite electrode, 5. Diaphragm, 6. Second red mud-based composite electrode, 7. Second current collector, 8. Second waterproof layer, 9. Asphalt surface layer.

[0053] Figure 2 Compaction curve of Bayer process red mud; Figure 3 The XRD pattern of the red mud sample; Figure 4 The images show the microstructure of red mud after pretreatment using the Bayer process, including (a) a cross-sectional SEM image of the red mud sample at 2000x magnification; (b) a cross-sectional SEM image of the red mud sample at 4000x magnification; (c) a cross-sectional SEM image of the red mud sample at 8000x magnification; and (d) a cross-sectional SEM-EDS image of the red mud sample. Figure 5 Microstructure diagram of red mud-based composite electrode; Figure 6 The constant current charge-discharge curves of the electrode under different current densities are shown. Figure 7 The test curves for the cyclic stability of red mud-based supercapacitors are shown. Detailed Implementation

[0054] Unless otherwise specified, the reagents and instruments used in the following examples are all commercially available products.

[0055] The specific performance test items and methods involved in the implementation are as follows: (1) pH measurement Place the sample in a 105°C oven to dry, and collect for later use. Weigh 10g of the air-dried sample that has passed through a 1mm sieve, place it in a stoppered wide-mouth bottle, add 50mL of water (soil-to-water ratio 1:5), and shake on a shaker for 3 minutes. Let stand for 30 minutes, and then determine the pH of the soil suspension.

[0056] (2) Compaction test The purpose of the compaction test is to obtain the maximum dry density and optimum moisture content of red mud. The test procedure is as follows: After drying the red mud, pulverize it using a pulverizer. Take five 2500g samples of dried Bayer process red mud powder, and add the corresponding amount of water at 2% intervals around the liquid limit. Calculate the required water and red mud for five different moisture contents. After thoroughly mixing the water and red mud, seal and let it sit for 24 hours. Before the compaction test, add the required curing agent to the red mud, stir, and sieve. Place the compaction cylinder on a firm ground, evenly coat the cylinder wall with Vaseline, and place permeable paper on the bottom of the cylinder. Pour the prepared modified red mud into the cylinder in five separate layers, 400-500g each, with a height equal to or slightly higher than 1 / 5 of the cylinder height. After 27 compactions, measure the soil height in the compaction cylinder and adjust the amount of soil added for the next layer. Roughen the surface of the compacted layer with a scraper. When completing the final compaction, the sample should not exceed 6mm above the top of the cylinder, and the top of the cylinder should be leveled with a scraper. Weigh and calculate the net soil mass and wet density of the sample after compaction. After the sample is removed using a demolding machine and crushed, a soil sample from the center of the sample is taken to measure the moisture content. Based on this, the dry density and moisture content of the five soil samples were calculated. Figure 2 As shown, draw on rectangular coordinate paper. The relationship curve shows that the extreme point of the curve represents the optimum moisture content.

[0057] (3) Electrochemical test Electrochemical performance characterization was performed using a CHI760F electrochemical workstation. The red mud-based supercapacitor was connected as a two-electrode test system according to its actual assembly state, with the first and second current collectors serving as the positive and negative leads, respectively. Before testing, the sample was thoroughly immersed in the electrolyte and drained until there was no free liquid on the surface. After standing at room temperature until the open-circuit voltage stabilized, cyclic voltammetry, constant current charge-discharge, AC impedance, and cycle stability tests were conducted. All electrochemical performance values ​​were taken as the average of at least three parallel measurements.

[0058] Cyclic voltammetry tests were first conducted to measure voltage curves at different voltage ranges of 0-0.6V, 0-0.8V, and 0-1.0V. Based on curve distortion, gas evolution, and polarization, 0.7V was determined as the stable operating voltage window for the device. Within this window, voltages of 50, 300, 500, and 1000 mV·s were set. -1 Curve tests were performed at different scan rates to analyze the material's capacitive behavior, rate response, and reversibility. The effects of different red mud dosages, carbon fiber meshes, and single and compound carbon black additives on electrochemical performance were also tested.

[0059] The evaluation was based on the integral area of ​​the cyclic voltammetry curve, the degree of rectangularity retention, and the retention rate at high scan rates. Table 1 shows that as the red mud content increased from 30 parts to 50 parts, the number of active sites on the electrode surface that could participate in ion adsorption and pseudocapacitive reactions increased, and the area enclosed by the curve gradually increased. When a carbon fiber mesh was combined with 2% nano-carbon black, the curve exhibited the best rectangularity and the weakest polarization, indicating a good match between the electron transport channel and the ion migration channel. When the carbon black content continued to increase to 3%, local agglomeration blocked some pores and increased ion diffusion resistance, leading to a decrease in rate retention.

[0060] Table 1 Cyclic Voltammetry Tests with Different Red Mud Content and Conductivity Configurations

[0061] The constant current charge-discharge test also used a voltage window of 0.7V, with settings of 0.10, 0.12, and 0.14 mA·g. -1 Multiple current density test curves were generated, and the volumetric current density was converted to the effective energy storage unit volume in the evaluation of engineering specimens. Key parameters such as discharge current, discharge time, effective discharge voltage, and initial IR drop were recorded. Based on the formulas, the volumetric specific capacitance, volumetric energy density, and volumetric power density were calculated, and the rate decay law of the material was analyzed. Simultaneously, curves were tested for different conductive skeleton ratios of 2% carbon black (carbon black content refers to the mass percentage of carbon black in red mud) to verify the charge storage and ion transport capabilities of the optimal ratio, providing measured data for material ratio optimization.

[0062] The results are shown in Table 2. The constant current charge-discharge results indicate that while single-doped carbon black improves electrode conductivity, the continuity of the electron collection path is insufficient, resulting in significant polarization of the charge-discharge curve. The carbon fiber mesh can reduce the current-collecting contact resistance, but its energy storage active sites are limited when used alone. When the carbon fiber mesh is combined with 2% nano-carbon black, the discharge time, volumetric specific capacitance, and energy density all reach optimal levels. The charge-discharge curve exhibits an approximately symmetrical triangular shape, indicating that this composite structure can form a continuous electron pathway within the red mud-based porous framework and maintain a good ion transport space.

[0063] AC impedance testing was conducted near the open-circuit potential with a perturbation voltage of 5 mV and a frequency range of 100 kHz–10 mHz. The electrolyte ohmic impedance, interfacial charge transfer impedance, and ion diffusion resistance were evaluated using the high-frequency intercept, semi-circular diameter, and low-frequency slope of the curve. This was used to verify the improvement effects of red mud-based modified membranes, carbon fiber meshes, and conductive reinforcing materials on interfacial impedance and pore ion transport.

[0064] Cyclic stability testing was conducted using a constant current charge-discharge method with a voltage window of 0-0.7V. The current density was consistent with that used in the volumetric capacitance test. The volumetric capacitance from the first cycle was used as the initial value, and the ratio of the volumetric capacitance after a specified number of cycles to the initial volumetric capacitance was used as the capacitance retention rate. Coulomb efficiency and curve morphology changes were recorded simultaneously to evaluate the long-term reversibility of the energy storage structure under road load service conditions.

[0065] Table 2 Constant current charge-discharge test of conductive framework under different carbon black contents

[0066] The formula is as follows, where V is the effective volume of the red mud-based supercapacitor participating in energy storage:

[0067] Where: Pv—volume power density (W / m³) 3 ) P — Total power (W) V — Volume (m³) 3 )

[0068] Where: Ev—volume energy density (Wh / m³) 3 ) E—Total Energy (Wh) V — Volume (m³) 3 )

[0069] Where: Cv—volume capacitance (F / m) 3 ) C — Measured capacitance (F) V — Volume (m³) 3 ) (4) Microscopic experiments To analyze the mineral composition and crystal structure of red mud-based electrode materials, X-ray diffraction (XRD) was used to perform phase analysis on the samples. Before the experiment, the samples were first dried in an oven to remove free moisture and prevent it from affecting the test results. After drying, the samples were thoroughly ground in a mortar to form a uniform fine powder, which was then passed through a 0.075 mm sieve. The powdered sample was then evenly spread into the XRD sample cell, compacted, and the surface was leveled to ensure a smooth surface flush with the edge of the sample cell. Figure 3 As shown, the sample exhibits several distinct diffraction peaks in the approximately 20°–40° range, some of which are sharp and have high intensity, indicating the presence of relatively highly crystalline mineral components. The characteristic peaks of quartz, hematite, and aluminum-bearing minerals are prominent, suggesting that these phases are important components of the sample. Simultaneously, some regions in the spectrum show broad, diffuse peaks or raised backgrounds, indicating that in addition to crystalline minerals, the sample may also contain a certain proportion of amorphous or low-crystallinity substances.

[0070] To observe the microstructure, pore distribution, and reaction product morphology within the red mud-based electrode, scanning electron microscopy was used for microscopic characterization of the electrode samples. Before the experiment, representative samples were selected from the interior of the red mud-based electrode after curing or electrochemical testing, avoiding selection only from the surface area, which is more susceptible to external influences. For electrodes containing cement or alkali-activated cementitious components, the samples were immersed in anhydrous ethanol for approximately 24 hours to terminate the hydration reaction. Residual moisture was then removed using low-temperature vacuum drying or freeze-drying methods to minimize damage to the microstructure during the drying process. Figure 4 As shown, with increasing magnification, numerous needle-like, rod-like, or fibrous structures can be clearly observed. These slender structures intersect and overlap, attaching to the surface of the bulk matrix to form a relatively complex network framework. At higher magnifications, the needle-like structures are tightly bonded to the gel-like material, with some fine particles filling the spaces between larger particles, creating a composite system of interconnected particles, gel, and needle-like structures within the material. This multi-scale structure helps increase the interfacial contact area within the electrode and provides channels for electrolyte penetration and ion migration.

[0071] Example 1 Preparation of red mud-based composite electrodes: Raw material proportions (by mass): 50 parts ordinary industrial red mud (Bayer process red mud, basic physical properties as shown in Table 3, chemical composition and content as shown in Table 4, dried and passed through a 0.075mm sieve), 12 parts fly ash (Class F, particle size 5μm), 30 parts 42.5 grade silicate cement (particle size 8μm), 5 parts fine aggregate (quartz sand, particle size 0.15mm), 1 part Na2SO4 activator (particle size 0.05mm), 1.2 parts reduced graphene oxide (particle size 2μm), 0.8 parts nano carbon black (particle size 25nm), 0.6 parts carbon fiber short chopped filaments (diameter 10μm, length 8mm), 1.0 part polycarboxylate superplasticizer, and 35 parts water. Dry material mixing: Put red mud, fly ash, cement, quartz sand, Na2SO4 activator, rGO, nano carbon black, and carbon fiber short filaments into a mixer and dry mix until uniform; Wet material mixing: Add water and water-reducing agent, stir at 650 r / min for 30 min, and let stand to defoam for 8 min; Pouring and shaping: Pour the grout into a 100 mm × 100 mm × 100 mm cubic mold and vibrate it for 30 seconds using high-frequency vibration to make the grout uniform and dense. Then, shape and cure it. Curing and solidification: The red mud-based composite electrode sample was obtained by curing in a curing chamber at 20°C and 95% relative humidity for 28 days.

[0072] Table 3 Basic physical properties of Bayer process red mud

[0073] Table 4 Chemical composition and content of Bayer red mud

[0074] Example 2 Preparation of red mud-based composite electrodes: Raw material proportions (by weight): 40 parts ordinary industrial red mud (Bayer process red mud, dried and sieved through a 0.075mm sieve), 10 parts fly ash (Class F, particle size 30μm), 25 parts 42.5 grade silicate cement (particle size 25μm), 10 parts fine aggregate (quartz sand, particle size 0.6mm), 0.5 parts Na2SO4 activator (particle size 150μm), 0.5 parts reduced graphene oxide (particle size 5μm), 0.2 parts carbon fiber short filaments (diameter 5μm, length 12mm), 0.8 parts naphthalene-based water-reducing agent, and 32 parts water; Dry material mixing: Put red mud, fly ash, cement, quartz sand, Na2SO4 activator, rGO, and carbon fiber short shreds into a mixer and dry mix until uniform; Wet material mixing: Add water and water-reducing agent, stir at 650 r / min for 30 min, and let stand to defoam for 8 min; Pouring and shaping: Pour the grout into a 100 mm × 100 mm × 100 mm cubic mold and vibrate it for 30 seconds using high-frequency vibration to make the grout uniform and dense. Then, shape and cure it. Curing and solidification: The red mud-based composite electrode sample was obtained by curing in a curing chamber at 20°C and 95% relative humidity for 28 days.

[0075] Example 3 Preparation of red mud-based composite electrodes: Raw material ratio (by mass): 60 parts ordinary industrial red mud (Bayer process red mud, pH=12.3, dried and passed through a 0.075mm sieve), 15 parts fly ash (Class C, particle size 15μm), 35 parts 42.5 grade silicate cement (particle size 15μm), 15 parts fine aggregate (quartz sand, particle size 0.3mm), 2 parts Na2SO4 activator (particle size 100μm), 1.2 parts nano carbon black (particle size 30nm), 1 part chopped carbon fiber (diameter 20μm, length 3mm), 1.2 parts polycarboxylate superplasticizer, and 38 parts water. Dry material mixing: Put red mud, fly ash, cement, quartz sand, Na2SO4 activator, nano carbon black, and carbon fiber short shreds into a mixer and dry mix until uniform; Wet material mixing: Add water and water-reducing agent, stir at 650 r / min for 30 min, and let stand to defoam for 8 min; Pouring and shaping: Pour the grout into a 100mm×100mm×100mm cubic mold, vibrate it at high frequency for 30 seconds to make the grout uniform and dense, and then shape and cure it. Curing and solidification: The red mud-based composite electrode sample was obtained by curing in a curing chamber at 20°C and 95% relative humidity for 28 days.

[0076] Example 4 The only difference from Example 3 is that the carbon fiber chopped filaments undergo plasma surface activation treatment. The specific treatment steps are as follows: the carbon fiber chopped filaments are first dried in a 70°C oven for 1.5 hours to remove surface adsorbed water; then, the dried carbon fiber chopped filaments are evenly spread on the sample tray of a low-temperature plasma treatment device, and a vacuum of 40 Pa is applied; a mixture of argon and oxygen is introduced into the treatment chamber, with an argon flow rate of 40 sccm and an oxygen flow rate of 10 sccm; the radio frequency power is set to 100 W, and the treatment time is 5 minutes; after treatment, the filaments are allowed to cool statically in the chamber for 5 minutes, then removed, sealed, and stored, and put into use within 24 hours. After plasma surface activation treatment, the surface roughness of the carbon fiber chopped filaments increases, and the number of oxygen-containing functional groups on the surface increases, which is beneficial to improving its interfacial bonding ability and dispersion uniformity with the red mud-based conductive slurry.

[0077] Comparative Example 1 The only difference from Example 1 is that the red mud mass fraction is 30 parts.

[0078] Example 5 Fabrication of red mud-based supercapacitors: Erecting the formwork: Erect a 20m×3m×0.25m (length×width×height) steel formwork, and apply a release agent to the inside of the formwork so that the steel formwork can be removed after the red mud-based supercapacitor layer is formed; Laying the first current collector and casting the first red mud-based composite electrode: Laying the first current collector with carbon fiber mesh (carbon fiber diameter is 2mm, mesh aperture is 10mm) in the lower area of ​​the template, flattening and fixing it and reserving the current collector lead-out end; pouring the wet material prepared in Example 4 onto the first current collector, casting to a thickness of 10cm, and using a high-frequency vibrator to compact it, ensuring that the slurry is free of honeycomb and pitting, and making the first current collector and the surface of the first red mud-based composite electrode facing away from the diaphragm closely adhere to each other and form a stable electrical contact; In-situ wetting of the first red mud-based composite electrode with electrolyte: After the first red mud-based composite electrode has initially solidified, electrolyte (1.5 mol / L KCl solution) is injected into the area enclosed by the template, allowing the electrolyte to penetrate into the internal pores of the first red mud-based composite electrode; after wetting for 20 hours, excess electrolyte is drained, and the electrode is allowed to stand and drain naturally for 3 hours to remove free electrolyte from the surface. During this process, the first red mud-based composite electrode remains within the area enclosed by the template and is not disassembled or removed for soaking. The first current collector remains on its surface facing away from the diaphragm. Laying the diaphragm: A polypropylene diaphragm (0.5 mm thick) is laid on the upper end of the first red mud-based composite electrode to ensure that the diaphragm completely covers the surface of the first red mud-based composite electrode, and that the edges are tightly attached to the inner wall of the template without wrinkles or damage. Press the diaphragm to make it tightly attached to the first red mud-based composite electrode. Casting the second red mud-based composite electrode: Prepare and pour the wet material prepared in Example 4 above the diaphragm, with a casting thickness of 10cm. Vibrate to compact and level, so that the second red mud-based composite electrode is closely attached to the diaphragm. Cover with a curing film and cure for 3-5 days until initial setting. In-situ wetting of the second red mud-based composite electrode with electrolyte: After the second red mud-based composite electrode has initially solidified, electrolyte (1.5 mol / L KCl solution) is injected into the area enclosed by the template to allow the second red mud-based composite electrode to be in-situ wetted for 20 hours. Then the electrolyte is discharged and the electrode is allowed to drain naturally for 3 hours. Laying the second current collector: After the second red mud-based composite electrode is in situ wetted with electrolyte and naturally drained, the second current collector is laid and pressed onto its exposed surface on the side away from the diaphragm, while reserving the current collector lead-out end. Curing and encapsulation preparation: After laying the second current collector, cover it with a curing film and cure it for 28 days in an environment with a temperature of 20±2℃ and a relative humidity of ≥90% to ensure that the electrode is fully cured. During the curing period, check the electrode status regularly to avoid surface cracking. After curing, prepare for encapsulation and proceed to the waterproof layer construction process to prepare the red mud-based supercapacitor.

[0079] Example 6 The only difference from Example 5 is that the diaphragm in this example is a red mud-based modified diaphragm. The specific preparation method is as follows: First, ordinary industrial red mud is dried to a moisture content of ≤5%, crushed, and passed through a 0.075mm sieve; 42.5 grade cement and sodium carboxymethyl cellulose are weighed separately and dry-mixed for 5 minutes; then, red mud:cement:CMC = 1:0.4:0.03 is added to the mixture and dry-mixed for 10 minutes; then, deionized water is added to control the solid-liquid ratio of the slurry at 1:0.4, and the mixture is stirred at 400r / min for 20 minutes to form a uniform diaphragm slurry; the slurry is formed on a flat template surface by scraping, casting, or thin-layer coating, and after standing in an environment of 20±2°C and relative humidity ≥90% for 18 hours, it is demolded and then cured for 5 days to obtain a red mud-based modified diaphragm with a thickness of 0.5mm.

[0080] The above-mentioned red mud-based modified diaphragm has a liquid absorption rate of ≥20%; a thickness retention rate of ≥85% after compression; no visible cracks after soaking in 1.5mol / L KCl or 2.0mol / L NaCl solution for 7 days; and an intact interface with no obvious delamination after assembly with the red mud-based composite electrode.

[0081] Example 7 The only difference from Example 6 is that the electrolyte used is a 1.5 mol / L NaCl solution.

[0082] Performance testing: 1. Slump: To evaluate the workability and flowability of the red mud-based conductive slurry, slump tests were conducted on the wet materials prepared in Examples 1-4 and Comparative Example 1. The tests were conducted in accordance with GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures".

[0083] During testing, the red mud-based conductive slurry, after being thoroughly mixed and allowed to stand to defoam, was layered into a slump cone. Each layer was tamped down, and after filling, the cone opening was leveled. The cone was then lifted vertically, and the height difference between the cone height and the highest point of the slurry after slump was measured as the slump value for that group of slurries. Each group of samples was tested in parallel three times, and the average value was taken as the final result.

[0084] During the testing process, the presence of obvious bleeding, segregation, fiber agglomeration, or sedimentation of conductive components in the slurry was observed simultaneously. Slump tests determined whether the red mud-based conductive slurry possessed suitable casting fluidity and molding stability, providing a basis for controlling the subsequent casting density, surface smoothness, current collector adhesion, and pore structure of the red mud-based composite electrode.

[0085] 2. Compressive strength: The red mud-based composite electrode samples obtained in Examples 1-4 and Comparative Example 1 were tested using a microcomputer-controlled electro-hydraulic servo pressure testing machine (HCT206A); The test was conducted in accordance with the "Specifications for Geotechnical Testing of Highways". The specimen preparation adopted the static pressure method, and the test steps are as follows: (1) Based on the optimum moisture content, maximum dry density and compaction degree obtained from the compaction test, calculate the mass of red mud and solidifying agent required for each sample. After mixing and sieving, put the sample into the custom-made model in multiple batches to form a cylinder of 39.1mm*80mm and use a jack to apply static pressure for 2-3 minutes.

[0086] (2) After the sample is demolded, measure the weight and height of the sample and record its appearance. Then put it into a plastic bag and place it in a curing box. Curing is carried out at a constant temperature and humidity of 20°C and ≥95%.

[0087] (3) Place the specimen into the universal testing machine at a loading rate of 0.12 mm / min. After the force reaches its peak value, the test can be stopped when the strain value drops by 3%.

[0088] To evaluate the structural stability and electrochemical performance retention of red mud-based supercapacitors under vehicle loads, a vehicle wheel-load pressure test was conducted. Molded and cured red mud-based supercapacitor specimens were placed horizontally on a flat road surface, and vehicle tires were slowly driven over them, pressing down on the specimens to simulate the vertical loads borne by supercapacitors when applied to road structures. Before the test, the specimens' appearance, dimensions, mass, initial capacitance, and internal resistance were recorded. During loading, the specimens were observed for cracking, breakage, edge peeling, and significant deformation. After loading, their appearance and electrochemical performance were re-tested and compared with the data before loading. The red mud-based supercapacitor specimens maintained a basically intact block shape after being directly crushed by vehicle tires, without significant crushing, through cracks, or large-area peeling, indicating that the specimens possess good load-bearing capacity and compressive stability.

[0089] 3. Connected porosity: Tested using the vacuum saturation method according to ASTM C642-21. The sample is dried to constant weight at 105±5°C, and the dried mass m1 is recorded. After vacuum saturation to constant weight, the saturated surface dry mass m2 is recorded, and the apparent mass in water m3 is determined according to the formula. Calculate the interconnected porosity.

[0090] This capacitor uses red mud-based composite materials as the core active material, compounded with cement, fine aggregates, conductive reinforcing materials, and carbon fiber mesh, and is cast to prepare the red mud-based energy storage electrode. The iron and aluminum oxides in the red mud provide electrochemical active sites, while the conductive reinforcing materials and carbon fiber mesh form an electron transport framework, and the KCl or NaCl electrolyte held in the pores provides ion migration channels. In terms of device assembly, the red mud-based supercapacitor adopts a "sandwich" structure: two layers of red mud-based composite electrodes serve as energy storage electrodes, with a red mud-based modified diaphragm in the middle and a carbon fiber mesh attached to the outside to reduce contact resistance and improve electron collection efficiency. Multiple individual units can be packaged and connected in series and parallel to form a modular energy storage system. Figure 5 As shown, the material forms a relatively continuous interconnected pore structure, cementation products, and conductive framework, which is conducive to ion migration, charge accumulation, and stress transfer, thus balancing energy storage performance and mechanical load-bearing capacity.

[0091] 4. Freeze-thaw cycles: The required specimen size, preparation method, and curing method are the same as those for unconfined compressive strength specimens. Five freeze-thaw cycles are set up, with three parallel specimens for each cycle. The specimen curing period is 28 days, and the specimens are soaked in water for one day on the last day of the curing period. The test procedure is based on the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering".

[0092] After 28 days of soaking, wipe the surface of the specimen with a damp cloth, weigh the specimen, and measure its dimensions.

[0093] Take a group of specimens to be frozen and thawed, and place them in the freezer according to their serial numbers for the freeze-thaw test. Set the freezer temperature to -18°C and place them for 16 hours. The spacing between each specimen is 20 mm to facilitate the circulation of cold air and ensure that the temperature around the specimen is consistent. After the low-temperature freezing is completed, take out the specimens and weigh them for mass and height. Then place them in a constant temperature water bath at 20°C for 8 hours to thaw. Ensure that the water level in the water bath is 20 mm higher than the specimens. After the specimens are thawed, wipe them dry and weigh them for mass and height. At this time, one freeze-thaw cycle is completed. Then repeat the previous steps for the next freeze-thaw cycle. When the specimens have completed the number of freeze-thaw cycles, take out the standard curing group specimens of the same time at the same time. Weigh and record the mass and height of the two groups of specimens and then conduct the strength test together. Equation (4) is the calculation method for the compressive strength loss rate of the freeze-thaw cycle of the modified red mud specimens. The test result is the average value of the results of the three specimens:

[0094] In the formula: —The rate of loss of compressive strength of the sample after N freeze-thaw cycles (%); —The compressive strength (MPa) of the 28-day-old specimen after immersion in water, accurate to 0.01 MPa; — Compressive strength (MPa) of the sample after N freeze-thaw cycles, accurate to 0.01 MPa.

[0095] The method for calculating the mass loss rate of modified red mud samples is as follows:

[0096] In the formula: —The rate of change in sample mass after N freeze-thaw cycles (%); —The mass (g) of the 28-day immersion group sample, accurate to 0.01g; —The mass (g) of the sample after N freeze-thaw cycles, accurate to 0.01g; Wet and dry cycle test method The specimen dimensions, sample preparation method, and curing method for the wet-dry cycle test were the same as those for the unconfined compressive strength test. To share a standard control group, the wet-dry cycle group and the freeze-thaw cycle group used the same test sampling time. The low-temperature oven temperature was 45°C, and three parallel samples were set up for each group.

[0097] The specific experimental steps are as follows: After curing the specimens for 27 days and then immersing them in water for 1 day, they were weighed, their dimensions were measured, and the wet-dry cycle was initiated. The specimens were then placed in an oven at 45°C for 16 hours. After removal, the specimens were placed in a cup, and water was added until the water level was 20 mm above the specimen. The cups were then left to stand for 8 hours. This constitutes one cycle. After the cycle was completed, all parameters were measured. The operation was repeated until the required number of cycles was reached.

[0098]

[0099] In the formula: SDI —Strength reduction rate (%) of the sample after N wet-dry cycles; —The compressive strength (MPa) of the 28-day-old specimen after immersion in water, accurate to 0.01 MPa; — Compressive strength (MPa) of the sample after N cycles of wet and dry treatment, accurate to 0.01 MPa.

[0100] The method for calculating the mass loss rate of modified red mud samples is as follows:

[0101] In the formula: —Sample mass change rate (%) after N wet-dry cycles; —The mass (g) of the 28-day immersion group sample, accurate to 0.01g; —The mass (g) of the sample after N cycles of wet and dry treatment, accurate to 0.01g; 5. Volumetric Capacitance: The red mud-based supercapacitors obtained in Examples 5, 6, and 7 were subjected to constant current charge-discharge tests using a CHI760F electrochemical workstation within a voltage window of 0-0.7V. Small-scale samples were tested at a current density of 0.10 mA·g⁻¹, and for engineering evaluation, the effective energy storage unit volume was converted to 100 A / m². 3 Volume current density. The volumetric capacitance was calculated based on the effective discharge time after deducting the IR drop in the discharge section, and the average value of three parallel tests was taken.

[0102] This device primarily relies on the electrochemical double-layer capacitance of the porous surface of the red mud-based composite electrode and the Faraday pseudocapacitance induced by transition metal oxides in the red mud for synergistic energy storage. In laboratory tests, K+ and Cl- ions in the KCl system or Na+ and Cl- ions in the NaCl system act as the main migrating ions, undergoing adsorption, desorption, and charge compensation along the electrode interconnect pores and membrane channels under the drive of an electric field. Figure 6 As shown, the constant current charge-discharge curves exhibit an approximately symmetrical triangle pattern within the 0-0.7V range, indicating that the device possesses good electrochemical reversibility. The combination of carbon fiber mesh and nano-carbon black can reduce electron transport resistance, decrease polarization, and reduce initial IR drop.

[0103] 6. Cyclic Stability: The red mud-based supercapacitor was subjected to constant current charge-discharge cycle tests according to IEC 62391-1:2022 and IEC 62391-2:2025. The test voltage window was 0-0.7V, and the current density was consistent with the volumetric capacitance test conditions. After 5000 consecutive charge-discharge cycles, the cycle stability was characterized by the ratio of the volumetric capacitance after the 5000th cycle to that after the 1st cycle.

[0104] like Figure 7 As shown, with the increase of charge-discharge cycles, the capacitance retention rate of the supercapacitor decreases slowly, while the coulombic efficiency remains stable overall. This indicates that the interfacial contact between the red mud-based composite electrode, the red mud-based modified separator, and the carbon fiber current collector is relatively stable, and the device's charge-discharge process has good reversibility. The capacitance retention rate is calculated using the formula.

[0105] 7. Alkali Resistance Stability: Referring to the evaluation of appearance changes of samples after immersion in chemical media in ASTM C267 / C267M-20, the "simulated alkali immersion-electrochemical retest" method was adopted. The specific steps are as follows: First, the initial volumetric capacitance of the sample was measured according to the volumetric capacitance test method of this application and recorded as C0; then, the sample was completely immersed in an alkaline solution with pH=13.0±0.2 and continuously immersed for 30 days at 20±2℃, with the alkali solution being replaced every 7 days during the immersion period; after the immersion was completed, the sample was taken out, the surface of the alkali solution was quickly rinsed with deionized water, the surface moisture was wiped off, and the sample was placed at room temperature for 2 hours to observe whether there was obvious corrosion, cracking, peeling, powdering or delamination; then, the volumetric capacitance after immersion was retested according to the aforementioned volumetric capacitance test conditions of this application and recorded as C30. The capacitance decay rate is calculated using the following formula: D = (C0 - C30) / C0 × 100%, where D is the capacitance decay rate after alkali immersion, in percentage terms; C0 is the volumetric capacitance before immersion; and C30 is the volumetric capacitance after immersion for 30 days. The retesting conditions for the volumetric capacitance are consistent with the aforementioned constant current charge-discharge test conditions of this application.

[0106] As shown in Table 5, different proportions and construction methods significantly affect the overall performance of the red mud-based composite electrode and supercapacitor. Among Examples 1-4, Example 4 exhibits the best overall performance, with a compressive strength of 31.2 MPa, representing increases of 3.4 MPa and 16.5 MPa compared to Example 3 and Comparative Example 1, respectively, representing increases of approximately 12.2% and 112.2%. Its interconnected porosity reaches 21.6%, an increase of 0.8 percentage points compared to Example 3 and 5.1 percentage points compared to Comparative Example 1. Furthermore, the slurry slump of Example 4 is 116 mm, maintaining good workability. The main difference between Example 4 and Example 3 lies in the plasma surface activation treatment of the chopped carbon fibers. This treatment increases the surface roughness and oxygen-containing functional groups of the carbon fibers, improving the interfacial bonding and dispersion effect between the carbon fibers and the red mud-based slurry. Therefore, while maintaining the interconnected pore structure, it significantly improves the compressive strength of the material. Comparative Example 1, due to its low red mud content, exhibits the lowest compressive strength and interconnected porosity, indicating that appropriately increasing the red mud content and optimizing the conductive material and fiber structure can facilitate the synergistic improvement of mechanical properties and pore structure.

[0107] Regarding the performance of supercapacitors, Example 6 exhibits the best overall energy storage and durability, with a volumetric capacitance of 7.4 F / m. 3 This represents an improvement of 1.0 F / m compared to Example 5, which uses a polypropylene diaphragm. 3The increase was approximately 15.6%; the capacitance retention rate after 5000 cycles reached 90.2%, an increase of 7.3 percentage points compared to Example 5; the capacitance decay rate after alkali impregnation was only 2.6%, a decrease of 2.5 percentage points compared to Example 5, a reduction of approximately 49.0%. This indicates that the red mud-based modified diaphragm and the red mud-based composite electrode have better material homology and interface compatibility, which can reduce interfacial impedance and improve ion transport. In Example 7, after using NaCl electrolyte, the volumetric specific capacitance and cycle stability were 6.9 F / m. 3 The capacitance decay rate was 85.6%, both lower than that of Example 6 using KCl electrolyte, and the capacitance decay rate increased to 3.9% after alkali impregnation, indicating that under the experimental conditions, KCl electrolyte is more beneficial for improving the energy storage performance and cycle stability of the device. No obvious dissolution, cracking, or delamination was observed in any of the examples after alkali impregnation, indicating that the constructed red mud-based supercapacitor has good alkali resistance stability.

[0108] Table 5. Comprehensive performance test results of red mud-based composite electrodes and supercapacitors in different embodiments.

[0109] The red mud-based supercapacitor prepared in Example 7 was further fabricated into an energy storage pavement structure, such as... Figure 1 As shown, the road structure from bottom to top consists of: subbase 1 (15cm thick, 9% cement + 91% crushed stone), first waterproof layer 2 (5mm thick, SBS modified bitumen waterproof membrane), first current collector 3, first red mud-based composite electrode 4, diaphragm 5, second red mud-based composite electrode 6, second current collector 7, second waterproof layer 8 (4mm thick, polyurethane waterproof coating), and asphalt surface layer 9 (6cm thick).

[0110] The construction method for energy storage pavement structures is as follows: Subbase construction: Lay a cement-aggregate mixture on the roadbed, spreading and compacting it in layers, each layer being 5cm thick with a compaction degree ≥96%. After curing for 7 days, the subbase is formed. Clean the surface of the subbase, removing loose slag, dust, and debris, and repair surface cracks and potholes to ensure a smooth, firm surface with a moisture content ≤9%. Apply primer: Apply asphalt-specific primer evenly to the surface of the subbase, at a rate of 0.4 kg / m². 2 After the primer has completely dried (usually 2-4 hours), the waterproof membrane can be laid. Roll installation: Lay SBS modified bitumen waterproof membrane with a 12cm overlap at the joints. The joints are welded using a hot-melt welding process at a temperature of 190°C. After welding, compact the membrane with a roller to ensure that there are no air bubbles or curling edges at the joints, forming a continuous and sealed first waterproof layer (SBS modified bitumen waterproof membrane).

[0111] Construction of red mud-based supercapacitor layer: A template is set up on the first waterproof layer (SBS modified bitumen waterproof membrane) and prepared according to the method in Example 7; Construction of the second waterproof layer (polyurethane waterproof layer): Apply polyurethane waterproof coating to the upper surface and sides of the red mud-based supercapacitor layer, overlap it with the first waterproof layer (SBS modified bitumen waterproof membrane) by 12cm, and seal it with polysulfide sealant. Asphalt surface layer laying: After uniformly applying asphalt tack coat to the surface of the second waterproof layer (polyurethane waterproof layer), the modified asphalt mixture is laid using a paver, with the paving temperature controlled at 150°C. Double-drum rollers are used for segmented compaction. The initial compaction stage involves static compaction at 140°C; the intermediate compaction stage involves vibratory compaction at 120°C; and the final compaction stage involves static compaction again at 70°C, until the pavement compaction degree is ≥98% and the smoothness error is ≤3mm / 3m.

[0112] Performance tests were conducted on the aforementioned energy storage pavement structure: Load-bearing capacity: Tested using a falling weight deflectometer, the pavement resilient modulus is 3250 MPa and the splitting strength is 1.2 MPa, meeting the design requirements for highways; Energy storage performance: The total capacitance of the test road surface (20m×3m) is 828kF, and the charge and discharge response speed is ≤0.3s, indicating good charge and discharge performance; Sealing performance: After immersion in water for 30 days, no electrolyte leakage was detected, and the capacitance performance of the supercapacitor layer decreased by 3.5%. Durability: After 50 freeze-thaw cycles (-20°C to 20°C), the compressive strength of the red mud-based composite electrode decreased by 8.5%, and the capacitance performance decreased by 9.1%.

[0113] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0114] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A red mud-based supercapacitor energy storage structure for road engineering applications, characterized in that, The invention includes a red mud-based supercapacitor, which, from bottom to top, comprises a first red mud-based composite electrode, a diaphragm, and a second red mud-based composite electrode. The components of the first red mud-based composite electrode and the second red mud-based composite electrode, by mass parts, include: 40-60 parts red mud, 10-15 parts fly ash, 25-35 parts cement, 5-15 parts fine aggregate, 0.5-2 parts Na2SO4 activator, 0.5-2 parts conductive reinforcing material, and 0.2-1 parts reinforcing fiber; After the first and second red mud-based composite electrodes were cured to initial set, they were immersed in the electrolyte and then drained to remove the free liquid on the surface.

2. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, The diaphragm is a red mud-based modified diaphragm, which is made by mixing red mud, cement and sodium carboxymethyl cellulose in a mass ratio of 1:(0.3-0.5):(0.02-0.05).

3. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, The electrolyte is a potassium chloride solution with a concentration of 1-2 mol / L or a sodium chloride solution with a concentration of 1.5-2.0 mol / L.

4. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, The conductive reinforcing material is one or more of reduced graphene oxide and nano carbon black; the reinforcing fiber is a short carbon fiber filament with a diameter of 5μm-20μm and a length of 3mm-12mm.

5. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 4, characterized in that, The carbon fiber chopped strands are subjected to plasma surface activation treatment, the treatment steps of which include: drying the carbon fiber chopped strands at 60-80°C for 1-2 hours, placing them in a low-temperature plasma treatment chamber, and evacuating them to 20-60 Pa; then introducing a mixture of argon and oxygen, wherein the argon flow rate is 30-50 sccm and the oxygen flow rate is 5-15 sccm, and treating them at 80-150 W radio frequency power for 3-8 minutes.

6. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, The thickness of the first red mud-based composite electrode and the second red mud-based composite electrode is 5cm-12cm, and the thickness of the diaphragm is 0.1mm-2mm.

7. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, It also includes a first current collector and a second current collector; the first current collector is disposed on the side of the first red mud-based composite electrode away from the diaphragm, and the second current collector is disposed on the side of the second red mud-based composite electrode away from the diaphragm.

8. The red mud-based supercapacitor energy storage structure for road engineering applications according to claim 7, characterized in that, The first current collector and the second current collector are carbon fiber meshes, wherein the carbon fiber diameter in the carbon fiber mesh is 2mm-3mm and the pore size of the carbon fiber mesh is 10mm-20mm.

9. A red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, The fine aggregate is quartz sand with a particle size of 0.15 mm to 0.6 mm; the red mud has a particle size of less than 0.075 mm; the fly ash has a particle size of 5 μm to 30 μm; the cement has a particle size of 8 μm to 25 μm; the conductive reinforcing material has a particle size of 15 nm to 5 μm; and the Na2SO4 activator has a particle size of less than 0.15 mm.

10. A red mud-based supercapacitor energy storage structure for road engineering applications according to claim 1, characterized in that, It also includes a waterproof layer, which is wrapped around the red mud-based supercapacitor; It also includes a cushion layer and an asphalt surface layer. The red mud-based supercapacitor energy storage structure consists of, from bottom to top, a cushion layer, a first waterproof layer, a red mud-based supercapacitor, a second waterproof layer, and an asphalt surface layer. The thickness of the subbase layer is 10cm-20cm, and the thickness of the asphalt surface layer is 5cm-8cm.

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