Phase change functional agent, preparation method and solid waste pavement containing phase change functional agent

Abstract

This invention relates to the field of road engineering materials and solid waste resource utilization technology, specifically to a phase change functional agent, its preparation method, and a solid waste pavement containing the phase change functional agent. The phase change functional agent is a paraffin-coal-based activated carbon-porous carrier composite phase change material, comprising: paraffin wax with a phase change temperature of 44-48℃, accounting for 30-40% of the total mass of the phase change functional agent; coal-based activated carbon, accounting for 5-10% of the total mass of the phase change functional agent; and porous carrier material, accounting for 50-65% of the total mass of the phase change functional agent. The porous carrier material has a pore structure suitable for paraffin wax impregnation and loading. The coal-based activated carbon and the porous carrier material form a synergistic thermal conductivity-adsorption network. The paraffin wax is loaded into the pores of the porous carrier material through vacuum impregnation. This invention's phase change functional agent simultaneously achieves three integrated functions: "phase change energy storage and temperature regulation - enhanced thermal conductivity - chemical alkali locking," and can be widely applied to pavement engineering using industrial solid waste such as red mud and fly ash, offering significant environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of road engineering materials and solid waste resource utilization technology, specifically to a phase change functional agent, a preparation method, and a solid waste pavement containing the phase change functional agent. Background Technology

[0002] The resource utilization of industrial solid waste is an important direction for current environmental protection and the circular economy. Industrial waste, represented by red mud, is generated in enormous quantities annually, and its resource utilization is of great significance for reducing environmental pollution and conserving land resources. Using red mud in road base materials is one of the effective ways to achieve large-scale disposal.

[0003] However, existing red mud pavement technology has the following technical bottlenecks: (1) Alkali release risk: Red mud contains a large amount of free alkali (NaOH, Na2CO3, etc.) and structural alkali (sodium silicate slag), which may be slowly released under the action of rainwater infiltration and freeze-thaw cycles, causing environmental pollution. How to achieve long-term stable solidification of alkali in red mud is the core problem of red mud road application.

[0004] (2) Temperature sensitivity: Road base courses are prone to freeze-thaw damage in cold regions, especially red mud materials, which are sensitive to temperature changes. Freeze-thaw cycles can cause the expansion of microcracks inside the material, accelerating alkali release and structural deterioration.

[0005] (3) Insufficient thermal conductivity: Traditional red mud pavement materials have low thermal conductivity (0.2-0.3 W / (m·K)), resulting in uneven pavement temperature distribution and exacerbated freeze-thaw damage. Studies have shown that paraffin wax, as a phase change material, has low thermal conductivity, which limits its heat charging and releasing rate in thermal storage systems.

[0006] (4) Paraffin leakage problem: Paraffin is prone to leakage when it is molten, and a porous carrier is needed for encapsulation and stability.

[0007] (5) Single function: Existing technologies mostly use single-function additives - either focusing only on curing strength or only on waterproof performance, lacking multi-functional integrated materials that can simultaneously achieve energy storage and temperature regulation, thermal conductivity enhancement and chemical alkali locking.

[0008] (6) Lack of concept of phase change functional agent: At present, there is no clear technical category of "phase change functional agent" in the field of road engineering. Traditional modifiers only focus on improving mechanical properties and have failed to recognize the possibility of endowing the road surface with "active temperature regulation" through phase change materials.

[0009] Existing technologies either use a single solid alkali agent (such as phosphoric acid) to treat red mud alkali damage, but cannot improve its thermal properties; or try to add common phase change materials (such as paraffin / expanded perlite) to improve freeze-thaw resistance, but face problems such as leakage, poor thermal conductivity, and no benefit to alkali damage. Summary of the Invention

[0010] To address the shortcomings of existing red mud pavement technologies, such as high alkali release risk, poor freeze-thaw stability, insufficient thermal conductivity, and easy paraffin leakage, this invention provides a phase change functional agent and its preparation method, and applies it to solid waste pavement. Through a specific ternary synergistic system of "paraffin / coal-based activated carbon / porous carrier", it achieves integrated synergy of phase change energy storage and temperature regulation, enhanced thermal conductivity, and chemical alkali locking.

[0011] This invention is achieved through the following technical solution: A phase change functional agent is provided, which is a paraffin-coal-based activated carbon-porous carrier composite phase change material, comprising the following components: Paraffin wax, as a phase change energy storage medium, has a phase change temperature of 44~48℃ and accounts for 30~40% of the total mass of phase change functional agents; Coal-based activated carbon, as a thermal conductivity enhancer and auxiliary adsorbent, accounts for 5-10% of the total mass of phase change functional agents; Porous carrier materials, serving as the main encapsulation framework and functional enhancer, account for 50-65% of the total mass of phase change functional agents; Among them, the porous carrier material has a pore structure that allows for paraffin impregnation and loading. Coal-based activated carbon and the porous carrier material form a synergistic thermally conductive-adsorption network. Paraffin is loaded into the pores of the porous carrier material through vacuum impregnation.

[0012] In one embodiment of the present invention, the porous carrier material is selected from artificially synthesized porous carbon materials or foam metal materials, so that the thermal conductivity of the phase change functional agent reaches 0.5 W / (m·K) or higher.

[0013] By selecting artificially synthesized porous carbon materials or foamed metal materials, the thermal conductivity of the phase change functional agent can reach above 0.5 W / (m•K), thus obtaining a phase change agent with high thermal conductivity.

[0014] Furthermore, the artificially synthesized porous carbon material is selected from at least one of expanded graphite, graphene aerogel, carbon nanotubes, carbon fibers, and ordered mesoporous carbon; its specific surface area is greater than 500 m² / g.

[0015] Furthermore, the foamed metal material is selected from at least one of foamed nickel, foamed copper, and foamed aluminum; its porosity is greater than 85% and its pore size is 50~500μm.

[0016] In one embodiment of the present invention, the porous carrier material is a mineral material or polymer microcapsule material with a hierarchical pore structure, so that the encapsulation rate of the phase change functional agent reaches more than 70% and the phase change enthalpy reaches more than 150 J / g.

[0017] By selecting hierarchical porous mineral materials or polymer microcapsule materials, the phase change enthalpy of the phase change functional agent can reach more than 150 J / g, resulting in a phase change agent with high encapsulation efficiency and high heat storage density.

[0018] Furthermore, the mineral material with a hierarchical porous structure is at least one of attapulgite, diatomite, or zeolite that has been modified by acid treatment, alkali treatment, or high-temperature activation.

[0019] Furthermore, the polymer microcapsule material is selected from at least one of urea-formaldehyde resin microcapsules, melamine resin microcapsules, polyurethane foam, and polystyrene foam, with an average particle size of 5-50 μm and a coverage rate of greater than 70%.

[0020] In one embodiment of the present invention, the porous carrier material is a natural porous mineral, which is selected from at least one of expanded vermiculite, attapulgite, diatomite, zeolite, expanded perlite, kaolinite, montmorillonite, and sepiolite, and is modified by acid treatment, alkali treatment, or high-temperature activation.

[0021] By selecting natural porous mineral materials, the cost of raw materials can be reduced by more than 30%, resulting in a low-cost phase change agent.

[0022] In one embodiment of the present invention, the porous carrier material is carbonized melamine foam or MOF-derived carbon material, so that the photothermal conversion efficiency of the phase change functional agent reaches more than 90%.

[0023] By selecting carbonized melamine foam or MOF-derived carbon materials, the photothermal conversion efficiency can reach over 90%, thus obtaining a phase change agent with photothermal conversion function.

[0024] By changing the type of porous carrier, a series of products such as high thermal conductivity type, high thermal storage type, photothermal type, and low cost type can be developed in a targeted manner.

[0025] A method for preparing a phase change functional agent includes the following steps: S1: Porous carrier pretreatment, which involves acid treatment, alkali treatment, high-temperature activation or surface modification of the porous carrier material to increase its specific surface area and pore volume; S2: Paraffin wax and coal-based activated carbon are mixed. The paraffin wax is heated to 80~90℃ to melt. Coal-based activated carbon is added at a mass ratio of paraffin wax to coal-based activated carbon of (80~85): (15~20). The mixture is stirred for 60~90 minutes under a vacuum of -0.08~-0.1 MPa to allow the paraffin wax to fully enter the micropores of the activated carbon, thus obtaining a primary paraffin wax-activated carbon composite. S3: Combine with a porous carrier. Add the pretreated porous carrier material in the specified proportion to the paraffin-activated carbon primary composite and stir under vacuum at 80~90℃ for 60~90 minutes. S4: Post-processing, natural cooling, and crushing to a particle size of less than 0.5mm.

[0026] A solid waste-based pavement material containing a phase change functional agent, comprising the following components: Industrial solid waste: selected from at least one of red mud, fly ash, coal gangue, and slag, accounting for 80-85 parts by weight; Hardener: Selected from at least one of cement, lime, and phosphogypsum, accounting for 8 to 12 parts by weight; Phase change functional agent: 3-5 parts by weight; Water: as needed.

[0027] By selecting different types of phase change functional agents, the performance of solid waste pavement materials can be controlled in a targeted manner: When natural porous mineral-based phase change functional agents are selected, the road surface material has both structural reinforcement and chemical alkali-locking functions. When artificially synthesized carbon-based phase change functional agents are selected, the thermal conductivity of road materials is improved by more than 40%, and the strength retention rate after 25 freeze-thaw cycles is improved by more than 12%. When polymer microcapsule-based phase change functional agents are selected, the road surface material exhibits long-lasting leak-proof performance.

[0028] The beneficial effects of this invention are: I. Phase Change Energy Storage and Active Temperature Regulation: Giving Road Surfaces "Thermal Buffering" Capability Using paraffin wax (phase change temperature 44~48℃) as its core, and leveraging its ability to absorb / release a large amount of latent heat during the solid-liquid phase change, phase change functional agents are no longer traditional passive materials, but rather "heat buffers" with active temperature regulation capabilities. When applied to road surfaces, they can effectively mitigate diurnal temperature differences: during the day, they absorb excess solar radiation heat, slowing down the road surface temperature rise and reducing temperature gradients; at night / during low-temperature periods, they release the stored heat, delaying or inhibiting road surface icing.

[0029] II. Construction of Heat Conduction Networks and Optimization of Thermal Management: Solving the Response Speed ​​Challenge By introducing coal-based activated carbon, the key lies not only in its adsorption properties but also in the interconnection of its highly graphitized carbon skeleton with a porous carrier, forming a three-dimensional continuous thermally conductive network. This network structure fundamentally alters the heat transfer mode of the composite material, significantly improving the overall thermal conductivity of the functional agent. This thermally conductive network greatly accelerates the heat charging and releasing rates of the phase change material layer, making road surface temperature regulation more timely and efficient. This effect is deeply synergistic with the phase change energy storage function.

[0030] III. Synergistic Alkali Locking Mechanisms: Radically Eliminating the Environmental Risks of Red Mud By selecting and modifying porous carrier materials, a synergistic effect of physical shielding and chemical alkali fixation was achieved. Natural minerals (such as attapulgite and diatomaceous earth) were modified with NaOH solution, activating the silicon and aluminum active sites on their surfaces. These sites react with free Na in the red mud. +A chemical reaction occurs, generating stable minerals such as sodium-based chalcogenide that are insoluble in water, thus "permanently solidifying" the free alkali (the active SiO2 and Al2O3 provided by the natural porous minerals react with the free Na in the red mud). + The reaction produces insoluble sodium-based chalcogenide (Na₂Al₂Si₄O₂). 12 •6H2O), achieving chemical solidification of alkali. The surface functional groups of coal-based activated carbon adsorb Na through ion exchange and surface complexation-assisted adsorption. + This forms a multi-layered alkali-locking mechanism. The large specific surface area of ​​coal-based activated carbon provides auxiliary adsorption; the nanofibers of the porous carrier fill the pores of the red mud, improving its impermeability by 20-30%, and physically preventing water molecules from carrying alkali out. This synergistic mechanism, with chemical reaction as the main method and physical barrier adsorption as a supplement, achieves long-term and fundamental treatment of red mud alkali damage.

[0031] IV. Structural reinforcement and passive self-healing: extending the service life of materials Porous carriers (especially fibrous attapulgite and mineral skeletons) serve as reinforcing phases in composite materials, improving overall mechanical properties. Paraffin wax undergoes approximately 10% volume change during phase transformation, allowing it to periodically compress and fill microcracks caused by temperature stress. This not only compensates for the slight strength loss that may result from adding paraffin wax but also endows the material with intelligent repair properties, helping to extend the service life of pavements.

[0032] V. Adjustable Functions and Universal Processes: Possesses high application flexibility Porous carriers are broadly categorized into four types: natural minerals, artificial carbon materials, polymer microcapsules, and foamed metals, each with different dominant properties.

[0033] Performance can be designed: By selecting the carrier, phase change agents with different functions can be directionally prepared, such as high thermal conductivity (>0.5 W / (m·K)), high heat storage (phase change enthalpy >150 J / g), photothermal conversion (efficiency >90%), and low cost, to meet various needs from special engineering to large-scale application. The two-step vacuum impregnation composite process uses readily available raw materials, is simple in steps, requires no complex equipment, is suitable for industrial production, and has controllable costs. Porous carrier materials (natural porous minerals, artificially synthesized porous carbon materials, polymer-based porous materials, and foamed metal materials) all have pore structures that can be used for paraffin impregnation and loading, and can physically adsorb paraffin through capillary force and surface tension, preventing melt leakage. The pore size, geometry, and surface chemical properties of different carrier materials directly affect the performance of composite materials, providing a basis for performance tunability. Carriers with hierarchical porous structures (such as carbonized melamine foam and chitosan-modified wood charcoal) can form a hierarchical network of macroscopic and microscopic channels, which enhances the adsorption of paraffin and provides a heat conduction path. The hierarchical network structure can divide the originally large channels into small porous structural units, which significantly improves the leak-proof performance.

[0034] This invention, through meticulous material design and composite processes, innovatively integrates three previously isolated functions—phase change temperature regulation, enhanced thermal conductivity, and chemical alkali locking—into a single composite material, creating a synergistic effect of "1+1+1>3". It not only introduces the concept of a new material suitable for road surfaces—a "phase change functional agent"—for the first time, but also provides a complete, efficient, and customizable solution. This systematically addresses the three major bottlenecks in the resource utilization of industrial solid waste (red mud) in road engineering: freeze-thaw damage, alkali damage risk, and poor thermal performance. It boasts significant environmental, economic, and technological advantages. Attached Figure Description

[0035] Figure 1 The scanning electron microscope (SEM) image of the expanded vermiculite-based phase change functional agent prepared in Example 1 of the present invention shows a thermally conductive network formed by the interweaving of coal-based activated carbon particles and vermiculite layered structure.

[0036] Figure 2 The SEM image of the diatomite-based phase change functional agent prepared in Example 2 of this invention shows the paraffin loading on the porous diatomite framework.

[0037] Figure 3 SEM image of the zeolite-based phase change functional agent prepared in Example 3 of the present invention.

[0038] Figure 4 The image shows an SEM image of the expanded graphite-based phase change functional agent prepared in Example 4 of this invention, revealing a highly thermally conductive network structure.

[0039] Figure 5 The image shows a three-dimensional carbon skeleton structure of the carbonized melamine foam-based phase change functional agent prepared in Example 5 of this invention.

[0040] Figure 6 The image shows the SEM image of the urea-formaldehyde resin microcapsule-based phase change functional agent prepared in Example 6 of this invention, displaying the morphology of the microcapsules.

[0041] Figure 7 The SEM image of the nickel-based phase change functional agent foam prepared in Example 7 of the present invention shows the metal skeleton structure.

[0042] Figure 8 This is a comparison chart of the thermal conductivity of the phase change functional agents in Examples 1-7 of this invention.

[0043] Figure 9 This is a comparison diagram of the phase change enthalpy of the phase change functional agents in Examples 1-7 of this invention.

[0044] Figure 10 This is the pH curve of the leachate solution after red mud was incorporated into the pavement in Example 1 of the present invention, showing the change in pH over the curing period.

[0045] Figure 11 This is a curve showing the relationship between the number of freeze-thaw cycles and the strength retention rate after red mud was incorporated into the pavement in Example 1 of the present invention. Detailed Implementation

[0046] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0047] Material description: Paraffin wax: No. 50 industrial paraffin wax, phase transition temperature 44-46℃, phase transition enthalpy 200 J / g, purchased from China Petroleum & Chemical Corporation.

[0048] Coal-based activated carbon: prepared from bituminous coal, with a particle size of 10-30μm, a specific surface area of ​​950 m² / g, an iodine adsorption value of 900mg / g, and an ash content of <8%.

[0049] Natural porous minerals: expanded vermiculite, attapulgite, diatomite, zeolite, etc., which are modified by alkali treatment or high-temperature activation before use.

[0050] Artificial synthetic materials: expanded graphite (expansion ratio 200 times, particle size 100 μm), carbonized melamine foam (laboratory-made, using melamine foam as a precursor, carbonized at 800℃ for 2h), nickel foam (porosity 95%, pore size 200-500 μm), etc.

[0051] Polymer material: Urea-formaldehyde resin microcapsules (laboratory-made, core material is paraffin wax, wall material is urea-formaldehyde resin).

[0052] Solid waste and solidifying agents: Bayer process red mud (main components: Al2O3 22-25%, SiO2 18-22%, Fe2O3 8-12%, Na2O 8-10%, pH 11.5-12.5), PO 42.5 ordinary silicate cement, quicklime (CaO>85%), phosphogypsum (CaSO4·2H2O>80%).

[0053] Example 1: Expanded vermiculite-based phase change functional agent (high encapsulation efficiency, low cost) Pretreatment: Expanded vermiculite was treated with 1.5 mol / L NaOH solution at 70℃ for 3 hours, then washed and dried.

[0054] preparation: 36g of paraffin wax (melted at 85℃) was vacuum-stirred and compounded with 6.4g of coal-based activated carbon (paraffin: activated carbon = 85:15) at 85℃ under a vacuum of -0.095 MPa for 60 minutes to obtain 42.4g of paraffin-activated carbon primary composite melt.

[0055] Add 57.6g of pretreated expanded vermiculite, stir at 85℃ for 90 minutes under a vacuum of -0.095 MPa; cool naturally, and pulverize to <0.5mm to obtain 100g of expanded vermiculite-based phase change functional agent powder.

[0056] Functional agent properties: phase change temperature 45.2℃, phase change enthalpy 118.5 J / g, thermal conductivity 0.38 W / (m·K), encapsulation efficiency 71.2%.

[0057] Phase change functional agent performance characterization Phase transition temperature DSC 45.2℃ Phase transition enthalpy DSC 118.5 J / g Thermal conductivity (25℃) Laser flash method 0.38 W / (m•K) Thermal conductivity (50℃) Laser flash method 0.41 W / (m•K) Packaging ratio TG 71.2% thermal stability TG (weight loss at 200℃) ＜1.5% Leakage 80℃ oven for 24 hours No obvious leakage Preparation and properties of red mud-based pavement materials Formula (total mass 1000g): 850g red mud; 50g cement; 20g lime; 20g phosphogypsum; 40g expanded vermiculite-based phase change functional agent (4%); 150g water.

[0058] Road surface performance test: The microstructure of the phase change functional agent prepared in Example 1 of this invention, as observed by scanning electron microscopy, is as follows: Figure 1 As shown, it can be clearly seen that the coal-based activated carbon particles (dark spheres) are uniformly dispersed and embedded between the layered structures of expanded vermiculite. This interwoven structure effectively constructs a continuous thermal conductivity-adsorption network, providing a physical basis for subsequent thermal conductivity enhancement and ion adsorption.

[0059] To address the issue of road surface alkali damage, a long-term leaching test was conducted on the functional agent in this embodiment. For example... Figure 10 As shown, the pH value of the leaching solution in the control group without the added functional agent remained at a strongly alkaline level above 11.5; while the pH value of the leaching solution in the experimental group with 4% of the functional agent of Example 1 of this invention decreased significantly with the extension of the maintenance period, and stabilized at a weakly alkaline environment of about 9.3 after 28 days, proving that the functional agent has excellent long-term chemical alkali-locking ability.

[0060] like Figure 11 As shown, in freeze-thaw cycle tests in frigid regions, the red mud pavement material incorporating the phase change functional agent of this invention exhibits excellent freeze-thaw durability. With increasing freeze-thaw cycle count, its compressive strength retention rate decreases extremely slowly, effectively solving the problem of early damage caused by frost heave cracking in traditional red mud pavements.

[0061] Example 2: Diatomaceous earth-based phase change functional agent Take 100g of diatomaceous earth, add 1000mL of 2.0 mol / L NaOH solution, stir in an 80℃ water bath for 4 hours; filter, wash until neutral; dry at 105℃, and pulverize for later use.

[0062] By replacing the expanded vermiculite with pretreated diatomaceous earth and following the same steps as in Example 1, a diatomaceous earth-based phase change functional agent was obtained.

[0063] Performance: Phase change enthalpy 115.2 J / g, thermal conductivity 0.35 W / (m·K), encapsulation efficiency 69.3%.

[0064] like Figure 2 As shown, the abundant micron-sized pores inside the diatomaceous earth carrier provide ample storage space for paraffin, and the white, translucent phase change material is fully filled in the pores, verifying that this embodiment has a high latent heat encapsulation rate for phase change.

[0065] Example 3: Zeolite-based phase change functional agent Take 100g of zeolite and perform high-temperature activation treatment: calcine it in a muffle furnace at 400℃ for 3 hours; cool it naturally and then crush it for later use.

[0066] By replacing expanded vermiculite with activated zeolite and following the same steps as in Example 1, a zeolite-based phase change functional agent was obtained.

[0067] Performance: Phase change enthalpy 108.6 J / g, thermal conductivity 0.33 W / (m·K), good cycle stability.

[0068] The microstructure of the product in Example 3 is shown below. Figure 3 The unique regular cage-like pore structure of zeolite is clearly visible, and this structure is very conducive to the physical exchange and chemical locking of alkaline ions.

[0069] Example 4: Expanded graphite-based phase change functional agent (high thermal conductivity type) Primary composite of paraffin and activated carbon: Same as in Example 1.

[0070] Composite with expanded graphite: Take 55g of expanded graphite; add 45g of paraffin-activated carbon primary composite melt (adjust the ratio to make the total paraffin content about 36%); stir at 85℃ for 60 minutes under a vacuum of -0.095 MPa; cool naturally and pulverize to <0.5mm.

[0071] Performance: Phase change enthalpy 112.5 J / g, thermal conductivity up to 0.62 W / (m·K), melting time reduced by 65% ​​compared to Example 1.

[0072] like Figure 4 As shown, the expanded graphite forms a highly oriented, stacked lamellar structure, which endows the material with extremely high axial thermal conductivity, providing microscopic evidence that the thermal conductivity of this embodiment is optimal.

[0073] Example 5: Carbonized melamine foam-based phase change functional agent (high heat storage, photothermal type) Preparation of carbonized melamine foam (CMF): Melamine foam is placed in a tube furnace and heated to 800°C at 5°C / min under nitrogen protection, held at that temperature for 2 hours, and then allowed to cool naturally.

[0074] Primary composite of paraffin and activated carbon: Same as in Example 1.

[0075] Composite with CMF: Take 50g of CMF; add 50g of paraffin-activated carbon primary composite melt (adjust the ratio to make the total paraffin content about 40%); stir at 85℃ for 90 minutes under a vacuum of -0.095 MPa; cool naturally and pulverize to <0.5mm.

[0076] Performance: Phase change enthalpy up to 156.3 J / g, thermal conductivity 0.48 W / (m·K), photothermal conversion efficiency 91.5%.

[0077] Figure 5 The three-dimensional interconnected carbon skeleton of carbonized melamine foam is shown. Its open-cell structure not only greatly increases the specific surface area and ensures a high paraffin loading, but also provides a channel for rapid heat transfer during the photothermal conversion process.

[0078] Example 6: Urea-formaldehyde resin microcapsule-based phase change functional agent (high encapsulation, leak-proof type) Preparation of urea-formaldehyde resin microcapsules: Microcapsule powder with an average particle size of 18 μm was prepared by in-situ polymerization using paraffin as the core material and urea-formaldehyde resin as the wall material.

[0079] Primary composite of paraffin and activated carbon: Same as in Example 1.

[0080] Composite with microcapsules: Take 60g of urea-formaldehyde resin microcapsules; add 40g of paraffin-activated carbon primary composite melt; stir at 80℃ and normal pressure for 60 minutes; cool naturally and pulverize.

[0081] Performance: Phase change enthalpy 135.8 J / g, no leakage after 48 hours in an 80℃ oven.

[0082] like Figure 6 As shown, the microcapsule particles prepared in this embodiment have regular morphology, relatively smooth surface and no obvious adhesion. This core-shell structure can effectively encapsulate the paraffin core material and prevent it from leaking during road compaction.

[0083] Example 7: Nickel-based foamed phase change functional agent (ultra-high thermal conductivity type) The carrier is nickel foam, which is composited by vacuum impregnation.

[0084] Primary composite of paraffin and activated carbon: Same as in Example 1, prepare paraffin-activated carbon composite melt.

[0085] Composite with nickel foam: Nickel foam is immersed in a paraffin-activated carbon composite melt and impregnated at 85°C for 60 minutes under a vacuum of -0.095 MPa; after removal and cooling, nickel foam-based phase change functional agent is obtained.

[0086] Performance: Thermal conductivity up to 1.25 W / (m·K), photothermal conversion efficiency 89.5%.

[0087] like Figure 7 As shown, this embodiment introduces nickel foam as a metal skeleton. Its robust three-dimensional network structure not only supports the phase change material, but also forms an efficient heat conduction path, significantly improving the overall thermal response speed.

[0088] To further verify the thermal conductivity enhancement effect of different carriers, the thermal conductivity of the functional agents in the above embodiments was tested, and the results are as follows: Figure 8 As shown in the data, Examples 4 (expanded graphite-based) and 7 (nickel foam-based), which employ high thermal conductivity frameworks, exhibit the best performance, with thermal conductivity reaching 1.25 W / (m·K) and 0.62 W / (m·K), respectively, significantly superior to traditional mineral carriers. Meanwhile, the composite mineral carriers of Examples 1-3 also show substantial improvements compared to the blank sample, demonstrating the universal advantages of the system of this invention in terms of thermal conductivity.

[0089] Figure 9 The phase change enthalpy data for each embodiment are presented. It can be seen that, due to the use of optimized encapsulation processes or porous structures, embodiments 5-7 of the present invention all maintain a high phase change enthalpy above 145 J / g, with embodiment 7 reaching 156.3 J / g. This indicates that the present invention achieves a good balance between thermal conductivity and heat storage without sacrificing the material's heat storage density while pursuing high thermal conductivity.

[0090] Example 8: Composite carrier (diatomaceous earth + expanded graphite) Diatomaceous earth was pretreated according to Example 2; expanded graphite was used directly.

[0091] Primary composite of paraffin and activated carbon: Same as in Example 1.

[0092] Composite with a carrier: Take 40g of pretreated diatomaceous earth and 20g of expanded graphite; add 40g of paraffin-activated carbon primary composite melt; stir at 85℃ for 90 minutes under a vacuum of -0.095 MPa; cool naturally and pulverize.

[0093] Performance: While maintaining a high encapsulation efficiency (70.5%), the thermal conductivity (0.48 W / (m·K)) is 37.1% higher than that of pure diatomaceous earth carrier.

[0094] Example 9: Effect of Functional Agent Dosage Using the functional agent from Example 1, the effects of different dosages (2%-8%) in red mud pavement were investigated. Conclusion: Considering strength, thermal conductivity, and alkali retention effect, the optimal dosage range is 3-5%. Comparative Example 1: Coal-free activated carbon Formula: Only paraffin wax and expanded vermiculite are combined, with expanded vermiculite: wax = 64:36, and no activated carbon is included.

[0095] By comparison with Example 1: thermal conductivity of phase change functional agents 0.26 W / (m•K) 0.38 W / (m·K) -46% Road surface thermal conductivity 0.25 W / (m•K) 0.36 W / (m·K) -44% pH of the leaching solution 9.9 9.3 Poor alkali-locking effect Results: The thermal conductivity of the functional agent decreased to 0.26 W / (m·K), and the pH of the road surface leachate increased to 9.9. This demonstrates that coal-based activated carbon is irreplaceable in its thermal conductivity and alkali-locking effects. It indicates that "paraffin + coal-based activated carbon + porous carrier" is a specific combination that produces a synergistic effect, rather than a simple mixture. Coal-based activated carbon is a key component in constructing the "thermal conductivity-adsorption network" and achieving enhanced thermal conductivity and alkali-locking. This comparison proves that coal-based activated carbon is a key component in constructing the "thermal conductivity-adsorption network" and achieving a synergistic effect of thermal conductivity and alkali-locking; without this component, the core advantages of this invention are lost.

[0096] Comparative Example 2: Wood-based activated carbon (non-coal-based) The coal-based activated carbon was replaced with wood-based activated carbon (coconut shell activated carbon), and the rest was the same as in Example 1.

[0097] By comparison with Example 1: thermal conductivity of phase change functional agents 0.31 W / (m•K) 0.38 W / (m•K) -22% pH of the leaching solution 9.6 9.3 Slightly worse Results: The thermal conductivity (0.31 W / (m·K)) and alkali retention effect (pH 9.6) of the functional agent were both inferior to those of Example 1 using coal-based activated carbon. This demonstrates that coal-based activated carbon has superior thermal conductivity due to its higher degree of graphitization. It indicates that the present invention does not use any particular activated carbon, but rather a specific and preferred choice based on the higher degree of graphitization and superior thermal conductivity of coal-based activated carbon. This comparison proves that the choice of activated carbon type has a significant impact on the effectiveness of the present invention; coal-based activated carbon, due to its higher degree of graphitization, is a specific choice for achieving better performance, rather than a conventional or obvious choice in the art.

[0098] Detailed experimental data demonstrate that the phase change functional agent and its application method of this invention can significantly improve the thermal conductivity and freeze-thaw stability of solid waste pavement in an integrated manner, and effectively solidify alkali metal ions. Furthermore, the performance can be directionally regulated by replacing the porous carrier.

[0099] Of course, the above description is not limited to the examples above. Technical features not described in this invention can be implemented by or using existing technology, and will not be repeated here. The above embodiments and drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. A phase change functional agent, characterized in that: The phase change functional agent is a paraffin-coal-based activated carbon-porous carrier composite phase change material, comprising the following components: Paraffin wax, as a phase change energy storage medium, has a phase change temperature of 44~48℃ and accounts for 30~40% of the total mass of phase change functional agents; Coal-based activated carbon, as a thermal conductivity enhancer and auxiliary adsorbent, accounts for 5-10% of the total mass of phase change functional agents; Porous carrier materials, serving as the main encapsulation framework and functional enhancer, account for 50-65% of the total mass of phase change functional agents; Among them, the porous carrier material has a pore structure that allows for paraffin impregnation and loading. Coal-based activated carbon and the porous carrier material form a synergistic thermally conductive-adsorption network. Paraffin is loaded into the pores of the porous carrier material through vacuum impregnation.

2. The phase change functional agent according to claim 1, characterized in that: The porous carrier material is selected from artificially synthesized porous carbon materials or foam metal materials, so that the thermal conductivity of the phase change functional agent reaches more than 0.5 W / (m·K).

3. The phase change functional agent according to claim 2, characterized in that: The artificially synthesized porous carbon material is selected from at least one of expanded graphite, graphene aerogel, carbon nanotubes, carbon fibers, and ordered mesoporous carbon; its specific surface area is greater than 500 m². 2 / g; the foamed metal material is selected from at least one of foamed nickel, foamed copper, and foamed aluminum; its porosity is greater than 85% and its pore size is 50~500μm.

4. The phase change functional agent according to claim 1, characterized in that: The porous carrier material is a mineral material or polymer microcapsule material with a hierarchical pore structure, which enables the encapsulation rate of the phase change functional agent to reach more than 70% and the phase change enthalpy to reach more than 150 J / g.

5. The phase change functional agent according to claim 4, characterized in that: The mineral material with a hierarchical porous structure is at least one of attapulgite, diatomite, or zeolite that has been modified by acid treatment, alkali treatment, or high-temperature activation.

6. The phase change functional agent according to claim 4, characterized in that: The polymer microcapsule material is selected from at least one of urea-formaldehyde resin microcapsules, melamine resin microcapsules, polyurethane foam, and polystyrene foam, with an average particle size of 5-50 μm and a coverage rate of more than 70%.

7. The phase change functional agent according to claim 1, characterized in that: The porous carrier material is a natural porous mineral, which is selected from at least one of expanded vermiculite, attapulgite, diatomite, zeolite, expanded perlite, kaolinite, montmorillonite, and sepiolite, and is modified by acid treatment, alkali treatment, or high-temperature activation.

8. The phase change functional agent according to claim 1, characterized in that: The porous carrier material is carbonized melamine foam or MOF-derived carbon material, which enables the photothermal conversion efficiency of the phase change functional agent to reach more than 90%.

9. A method for preparing the phase change functional agent according to any one of claims 1 to 8, characterized in that: Includes the following steps: S1: Porous carrier pretreatment, which involves acid treatment, alkali treatment, high-temperature activation or surface modification of the porous carrier material to increase its specific surface area and pore volume; S2: Paraffin wax and coal-based activated carbon are mixed. The paraffin wax is heated to 80~90℃ to melt. Coal-based activated carbon is added at a mass ratio of paraffin wax to coal-based activated carbon of (80~85): (15~20). The mixture is stirred for 60~90 minutes under a vacuum of -0.08~-0.1 MPa to allow the paraffin wax to fully enter the micropores of the activated carbon, thus obtaining a primary paraffin wax-activated carbon composite. S3: Combine with a porous carrier. Add the pretreated porous carrier material in the specified proportion to the paraffin-activated carbon primary composite and stir under vacuum at 80~90℃ for 60~90 minutes. S4: Post-processing, natural cooling, and crushing to a particle size of less than 0.5mm.

10. A solid waste-based pavement material comprising the phase change functional agent according to any one of claims 1 to 8, characterized in that: It consists of the following components: Industrial solid waste: selected from at least one of red mud, fly ash, coal gangue, and slag, accounting for 80-85 parts by weight; Hardener: Selected from at least one of cement, lime, and phosphogypsum, accounting for 8 to 12 parts by weight; Phase change functional agent: 3-5 parts by weight; Water: as needed.

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