Bionic plant leaf light-heat-energy storage coupling function gradient concrete and preparation method thereof

Abstract

The application discloses a kind of bionic plant leaf light-heat-energy storage coupling function gradient concrete and preparation method, concrete along the thickness is light-heat conversion-heat storage layer, phase change heat storage layer, bearing / heat insulation layer three-layer gradient structure, interface processing is enhanced bonding between layers. Light-heat layer contains special light-heat conversion composite phase change material particles on light side, inhibit phase change material leakage through triple mechanism, match leaf vein type heat conducting component and microtexture light absorption structure, improve light-heat conversion and heat storage efficiency. The phase change material retention rate of this concrete reaches 88% after 300 times heat cycle, solar absorption rate is 0.88-0.92, heat storage density is 85-92kJ / kg, 28 days compressive strength is greater than or equal to 20MPa. Gradient design avoids invalid addition of phase change material, gives consideration to heat storage and mechanical properties, can improve building envelope thermal environment, reduce energy consumption, adapt to multi-climate zone and large-scale production meets environmental protection requirements.

Description

Technical Field

[0001] This invention relates to the field of energy-saving building materials and building thermal environment management technology, specifically to a functionally graded concrete material for building envelope and its preparation method, and more particularly to a gradient function concrete based on the light energy capture-energy conversion-energy storage path of biomimetic plant leaf photosynthesis, and the construction of the gradient function concrete through photothermal conversion composite phase change material and biochar-based composite phase change material and its preparation technology. Background Technology

[0002] Building energy consumption accounts for more than 30% of the total energy consumption of the whole society, and heat loss from building envelopes is the main source of energy consumption. Phase change materials can absorb or release a large amount of latent heat within a specific temperature range. Applying phase change materials to concrete is an effective way to achieve building energy conservation, but existing technologies have obvious shortcomings: organic phase change materials directly incorporated into cement-based systems have poor alkali resistance and insufficient compatibility with the matrix; uniform incorporation leads to ineffective addition in non-working areas, which increases costs and reduces the mechanical properties of concrete; the absorption and photothermal conversion efficiency of solar energy is low, heat transfer is hindered, heat storage depth is limited, and the utilization rate of phase change materials is insufficient.

[0003] The palisade tissue, spongy tissue, and vein system of plant leaves form a gradient functional structure for light energy capture, conversion, storage, and transmission, providing a biomimetic design approach for the efficient utilization of solar energy. Therefore, there is an urgent need to develop a functionally gradient concrete that mimics the photosynthetic pathway of plant leaves. This concrete should achieve synergistic effects of efficient photothermal conversion and instantaneous heat storage on the sun-facing side, large-capacity phase change heat storage in the middle, and load-bearing and insulation on the back side. Simultaneously, it should address issues such as uneven dispersion of phase change materials and decreased mechanical properties, meeting the needs of large-scale production and practical construction. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A biomimetic plant leaf-inspired photothermal-energy storage coupled functional gradient concrete comprises at least a photothermal conversion-energy storage layer, a phase change energy storage layer, and a load-bearing / insulating layer along its thickness direction. The interlayer interfaces are treated with roughness control or interface agents to enhance adhesion. The photothermal conversion-energy storage layer is located on the light-facing side, with a thickness of 10-30 mm, and contains photothermal conversion composite phase change material particles. The phase change energy storage layer is located in the middle, with a thickness of 30-80 mm, and contains energy storage composite phase change material particles. The load-bearing / insulating layer is located on the shaded side, with a thickness of 40-120 mm, and is made of ordinary concrete or lightweight concrete.

[0005] Furthermore, the photothermal conversion composite phase change material particles include a biochar porous carrier framework, a phase change material loaded in the pores, an alkali-resistant and leak-proof shell covering the outer surface, a photothermal conversion component disposed on the surface or inside the shell, and a mineral roughening layer covering the outermost layer.

[0006] Furthermore, the open porosity of the biochar porous carrier skeleton is ≥50%, the specific surface area is ≥200 m² / g, and the particle size is 0.05-1.0 mm; the biochar porous skeleton of the thermal storage composite phase change material particles has a particle size of 0.1-2.0 mm, and other parameters are the same.

[0007] Furthermore, the phase change material is paraffin with a carbon chain length of C18-C24 (melting point 50-60℃, purity ≥98%) or stearic acid (melting point 65-70℃, purity ≥95%). The loading rate of the phase change material in the photothermal conversion composite phase change material particles is 30-60% by mass, and the loading rate of the phase change material in the thermal storage composite phase change material particles is 40-70% by mass.

[0008] Furthermore, the alkali-resistant and leak-proof shell is a water glass cured shell, an organosilicon sol-gel shell, or a polymer shell, with a thickness of 5-20 μm and a shell density of ≥90%, effectively blocking the penetration of alkaline pore solutions.

[0009] Furthermore, the photothermal conversion component is nano-carbon black, graphene quantum dots, nano-metal particles, carbon nanotubes, or two-dimensional transition metal carbide / nitride materials, with a loading of 0.5-3% of the particle mass, thereby improving the solar light absorption efficiency.

[0010] Furthermore, the mineral roughening layer is silica fume (activity index ≥ 95%), metakaolin (activity index ≥ 100%), or mineral powder (specific surface area ≥ 400 m² / kg), with a thickness of 10-50 μm, which increases the surface roughness of the particles to 5-15 μm and enhances the interfacial bonding with the concrete matrix.

[0011] Furthermore, the amount of photothermal conversion composite phase change material particles in the photothermal conversion-storage layer is 3-15% of the mass of the cementitious material in that layer; the amount of heat storage composite phase change material particles in the phase change storage layer is 10-20% of the mass of the cementitious material in that layer, to avoid increased costs and decreased strength caused by ineffective incorporation.

[0012] Furthermore, a leaf-vein type heat-conducting component is provided between the photothermal conversion-heat storage layer and the phase change heat storage layer. The leaf-vein type heat-conducting component is a copper mesh (purity ≥99.5%), an aluminum mesh (purity ≥99%), or a carbon fiber mesh (thermal conductivity ≥150 W / (m·K)). It is distributed in a main vein and branch vein network along the plate surface direction and is fixed by buckles or positioning ribs. The embedding depth is 5-10mm to improve the heat conduction efficiency.

[0013] Furthermore, the light-facing outer surface of the photothermal conversion-storage layer is prepared with a micro-textured light-absorbing structure, the texture type being V-groove, pyramidal protrusion, or rhomboid mesh, which increases the solar light absorption rate at different incident angles by increasing the light absorption path.

[0014] Accordingly, the present invention also provides a method for producing the above-mentioned functionally graded concrete, comprising the following steps: S1: Preparation of photothermal conversion composite phase change material particles S11: Purchase activated biochar based on rice husk, corn cob, or sawdust, requiring an open porosity ≥50%, a specific surface area ≥200 m² / g, a particle size of 0.05-1.0 mm, a pH value pretreated to 7, and no obvious impurities; S12: Heat paraffin (melting point 50-60℃, purity ≥98%) or stearic acid (melting point 65-70℃, purity ≥95%) with carbon chain length C18-C24 to 80-100℃ to melt. Immerse commercially available activated biochar in the molten phase change material under a vacuum of 0.01-0.1MPa for 30-60 minutes. After removing it, keep it at 60-80℃ for 1-2 hours to remove excess phase change material from the surface. After cooling, obtain phase change biochar particles with a loading rate of 30-60% by mass. S13: Phase change biochar particles are immersed in a 30% (w / w) water glass solution, tetraethyl orthosilicate sol, or monomer solution, and then cured or polymerized to form an alkali-resistant and leak-proof shell with a thickness of 5-20 μm, ensuring a density of ≥90%; S14: Photothermal conversion components such as nano carbon black, graphene quantum dots, and nano metal particles are coated, sprayed, or ultrasonically dispersed and attached to the shell surface, with the loading amount controlled to be 0.5-3% of the particle mass. S15: Mix the granules with silica fume (activity index ≥ 95%), metakaolin (activity index ≥ 100%) or mineral powder (specific surface area ≥ 400 m² / kg) at a mass ratio of 10:1 to 20:1. Add 20% water glass solution or cement slurry as a binder. Stir at 50-80 rpm to ensure uniform adhesion of the mineral powder. Dry at 60-80℃ to form a roughened layer with a thickness of 10-50 μm, resulting in a surface roughness of 5-15 μm.

[0015] S2: Preparation of thermal storage composite phase change material particles S21: Purchase activated biochar with a particle size of 0.1-2.0 mm. The other parameters (open porosity, specific surface area, etc.) are the same as those of S11. S22: Use the same type of phase change material as the process in S12, and control the loading rate to 40-70% by mass. S23: Repeat the preparation process of the alkali-resistant and leak-proof shell layer in S13; S24: Repeat the mineral roughening layer coating process of S15, without adding photothermal conversion components.

[0016] S3: Preparation of Functionally Graded Concrete S31: Pre-dispersion treatment: Weigh out 3-15% of the mass of the photothermal conversion composite phase change material particles according to the mass of the cementitious material in the corresponding layer, or weigh out 10-20% of the mass of the phase change heat storage layer cementitious material particles. Mix them with 30-50% of the total water volume of the corresponding layer, stir at 50-80 rpm for 2-3 minutes, and add 0.3-1.0% (based on the mass of the cementitious material) of polycarboxylate superplasticizer (clean paste fluidity ≥250mm) to prepare a pre-dispersion slurry. S32: Preparation of matrix slurry: Mix PO 42.5 cement, fine sand, aggregate (fine sand for the photothermal layer, and ceramsite for the heat storage layer and bearing layer), residual water and water-reducing agent, and stir at 100-150 rpm for 2 minutes to form a uniform matrix slurry; S33: Mixing and stirring: Slowly add the pre-dispersed slurry to the corresponding matrix slurry, reduce the speed to 50-80 rpm and stir for 1-2 minutes to ensure uniform particle dispersion; S34: Layered casting and functional structure preparation: 1. First, pour the photothermal conversion-heat storage layer with a thickness of 10-30mm, and compact it by vibrating at a frequency of 30-50Hz for 5-10 seconds, and record the initial time t0; 2. 15 minutes after t0, fix the copper mesh (purity ≥99.5%), aluminum mesh (purity ≥99%) or carbon fiber mesh (thermal conductivity ≥150 W / (m·K)) to the surface of the photothermal layer using clips or positioning ribs, with an embedding depth of 5-10mm; 3. Five minutes after t0, use an aluminum alloy mold to imprint V-grooves, pyramidal protrusions, or diamond-shaped grid micro-textures (apply pressure of 50-80 N / m²), hold for 2 minutes, and then remove the mold; 4. Before the initial setting of the photothermal layer (penetration resistance 3.5-7.5MPa), apply an epoxy interface agent to its surface, pour the phase change heat storage layer with a thickness of 30-80mm, and compact it in sections (each section vibrates for no more than 10 seconds), and record the time t1. 5. Before the thermal storage layer initially sets (penetration resistance 3.5-7.5MPa), pour the load-bearing / insulation layer with a thickness of 40-120mm. After normal compaction for 15-30 seconds, smooth the surface and cover it with plastic film. S35: Curing: After standing at room temperature for 24 hours, demold and place in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days.

[0017] S4: Large-scale production and environmental protection Composite phase change particles are prepared using continuous coating equipment. KOH activation wastewater (if not treated by the supplier) is neutralized and precipitated. Pyrolysis waste gas generated during the production process is purified by activated carbon adsorption before being discharged.

[0018] Implementing this invention has the following beneficial effects: 1. Biomimetic design is scientific and efficient: By drawing on the gradient functional structure of plant leaves and combining leaf vein-type heat-conducting components with micro-textured light-absorbing structures, the synergistic effect of photothermal conversion, heat storage and load-bearing is achieved. The solar light absorption rate reaches 0.85-0.92, and the photothermal conversion efficiency reaches 140%-150% (based on the efficiency benchmark of existing technology).

[0019] 2. Effective solution to core problems: Through the alkali-resistant protection mechanism, the alkali-resistant and leak-proof shell has a density of ≥90% and a thickness of 5-20μm, which can effectively block the penetration of alkaline pore solutions in cement-based systems; the composite phase change particles are evenly distributed with few agglomerates; the gradient design avoids ineffective incorporation, and the amount of phase change material used is 60%-70% of the conventional amount, significantly reducing costs.

[0020] 3. Balanced thermal storage and mechanical properties: The thermal storage density of the phase change thermal storage layer reaches 80-95 kJ / kg, and the heat dissipation duration at night reaches 3-5 hours; the 28-day compressive strength of the load-bearing layer is ≥25 MPa, and the interlayer bond strength is ≥0.8 MPa, which meets the requirements of building envelope structure.

[0021] 4. Strong green adaptability: It is suitable for temperate and subtropical climate regions, has good compatibility with steel bars and insulation layers, and its large-scale production meets environmental protection requirements. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall cross-sectional structure of the functionally graded concrete of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of the photothermal conversion composite phase change material particles of the present invention.

[0024] Figure 3 This is a schematic diagram of the structure of the thermal storage composite phase change material particles of the present invention.

[0025] Figure 4 This is a schematic diagram (top view and cross-sectional view) of the arrangement of the leaf vein type heat-conducting component of the present invention.

[0026] Figure 5 This is a schematic diagram of the surface morphology of the microtextured light-absorbing structure of the present invention.

[0027] Figure 6 This is a schematic diagram of the preparation process of photothermal conversion composite phase change material particles in Embodiment 1 of the present invention.

[0028] Figure 7This is a schematic diagram of the layered pouring process of functionally graded concrete in Embodiment 1 of the present invention.

[0029] Explanation of reference numerals in the attached figures 1-Photothermal conversion-thermal storage layer; 10-Photothermal conversion composite phase change material particles; 101-Porous biochar support framework; 102-Phase change material within the pores; 103-Alkali-resistant and leak-proof shell layer; 104-Photothermal conversion component; 105-Mineral roughening layer; 11-Heat storage composite phase change material particles; 111-Porous biochar framework; 112-Phase change material within the pores; 113-Alkali-resistant and leak-proof shell layer; 114-Mineral roughening layer; 2-Phase change thermal storage layer; 3-Bearing / Insulation Layer; 4-Vein-type heat-conducting component; 41-Main vein; 42-Branch vein; 5-Microtextured light-absorbing structure; 51-V-groove; 52-Pyramid protrusion; Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and not for limiting the scope of protection of this invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0030] Example 1: Functionally graded concrete based on nano-carbon black-paraffin system like Figure 1 , Figure 2 , Figure 6 , Figure 7 As shown in the figure, this embodiment provides a method for preparing and testing the performance of functionally graded concrete based on a nano-carbon black-paraffin system.

[0031] I. Preparation of Photothermal Conversion Composite Phase Change Material Particles 10 (1) Selection and specifications of biochar 101 Purchase rice husk-based activated biochar directly (commercially available, specifications as shown below), no need to prepare it yourself: - Raw material source: Rice husk base - Open porosity: ≥58% (actual measurement 58%) - Specific surface area (BET method): ≥280 m² / g (actually measured 280 m² / g) - Particle size distribution: 0.2-0.8mm (after 100-mesh sieve) - Purity: No obvious impurities, pH 7 (pre-treated to neutral at the factory) (2) Paraffin 102 vacuum load Weigh 1000g of paraffin wax (industrial grade, melting point 58℃, purity ≥98%) with a carbon chain length of C20-C22, place it in a stainless steel container, and heat it to 90℃ until it is completely melted. Weigh 200g of the above-mentioned activated biochar, place it in a vacuum desiccator, start the vacuum pump to evacuate to 0.05MPa, and maintain a vacuum state. Slowly pour the molten paraffin wax into the vacuum desiccator to immerse the biochar, maintain the vacuum state for 45 minutes, and gently shake the container once every 10 minutes during this period. After depressurization, remove the granules, place them on a tray with a 200-mesh stainless steel filter screen, and place them in a 70℃ oven for 1 hour to allow excess paraffin wax on the surface to flow out naturally. After removal, allow it to cool naturally to room temperature, gently wipe the surface with a paper towel, and weigh it.

[0032] Load factor measurement: Mass of activated biochar before loading: 200g; Total mass after loading: 290g; Paraffin loading rate = (290-200) / 200 × 100% = 45% mass fraction.

[0033] The phase transition enthalpy was determined using differential scanning calorimetry (DSC): 78 J / g.

[0034] (3) Preparation of water glass solidified shell 103 Preparation of water glass solution: Weigh 500g of commercially available water glass solution with a modulus of 2.8, dilute with deionized water to a concentration of 30% by mass, with a total volume of approximately 1500mL, and stir thoroughly. Slowly pour 290g of paraffin-loaded biochar granules into the water glass solution, gently stir with a glass rod, and soak for 20 minutes, stirring every 5 minutes. Remove the granules using a 200-mesh stainless steel filter and drain excess solution (approximately 2 minutes). Spread the granules evenly on a plastic tray (thickness not exceeding 20mm), place in a sealed glass container, and introduce CO2 gas (99.9% purity, flow rate 1 L / min) through a silicone tube, and cure for 24 hours. After removal, quickly rinse the surface with a small amount of deionized water (spray) (rinsing time not exceeding 30 seconds), and dry in an 80℃ oven for 6 hours to obtain approximately 305g of granules with a coated shell.

[0035] Shell thickness measurement: The cross-section was observed using a scanning electron microscope (SEM). The shell thickness was approximately 12 μm, continuous and uniform, with a density of 92%.

[0036] (4) Coating with nano carbon black 104 Weigh 3g of nano-carbon black (particle size 30nm, specific surface area 200 m² / g), add 100mL of anhydrous ethanol and 0.5g of polyvinylpyrrolidone (PVP, molecular weight 40000), and place in an ultrasonic cleaner (power 300W, frequency 40kHz) for ultrasonic dispersion for 30 minutes to obtain a uniform black dispersion. Add 305g of coated particles to the above dispersion and stir with a magnetic stirrer for 20 minutes (speed 200 rpm) to ensure that the carbon black is uniformly adhered to the particle surface. Filter through a 200-mesh filter, rinse once with anhydrous ethanol (50mL), and dry in a 60℃ oven for 12 hours to obtain approximately 310g of carbon black-coated particles.

[0037] Carbon black loading calculation: (310-305) / 305 × 100% ≈ 1.6 mass fraction; Actual carbon black weight: approximately 5g (including PVP).

[0038] Solar absorbance measurement: The absorbance α = 0.88 was measured using an ultraviolet-visible-near-infrared spectrometer (wavelength 300-2500nm, conforming to GB / T2680 standard).

[0039] (5) Silica fume 105 roughening coating Weigh 20g of silica fume (particle size 1-5μm, activity index 98%, specific surface area 20 m² / g) and mix it with 310g of carbon black-coated particles (particles:silica fume = 15.5:1, close to the design value of 15:1). Prepare 30mL of water glass solution (concentration 20% by mass) as a binder and slowly add it to the mixture. Stir at low speed (50 rpm) in a mixer for 5 minutes to ensure that the silica fume is evenly adhered to the particle surface. After removing the mixture, spread it evenly on a tray and dry it in a 60℃ oven for 12 hours. Gently rub the surface to loosen the silica fume and remove it, obtaining approximately 320g of the final photothermal conversion composite phase change material particles.

[0040] Surface roughness measurement: Surface roughness Ra was measured using laser confocal microscopy. Before treatment (shell only): Ra = 2.1 μm; After treatment (roughened layer): Ra = 10.3 μm, an increase of approximately 5 times.

[0041] Roughening layer thickness: SEM observation showed approximately 25-35 μm, with an average of 30 μm.

[0042] II. Preparation of thermal storage composite phase change material particles 11 The method used is similar to that of photothermal conversion composite phase change material particles 10, with the difference being: (1) Biochar particle size: Purchase activated biochar with a particle size of 0.5-1.5 mm. Other specifications are the same as those of activated biochar purchased when preparing photothermal conversion particles.

[0043] (2) Phase change material loading rate: Weigh 200g of the above activated biochar and load it with paraffin using the same vacuum impregnation method as the photothermal conversion composite phase change material particles, with the impregnation time extended to 50 minutes, and other conditions remaining the same. The mass after loading is 310g, and the loading rate is 55% by mass.

[0044] (3) Only the shell and roughening layer are prepared: The same water glass curing method is used to prepare the shell. After the shell is prepared, 320g of the shell-coated particles are obtained. Without adding nano carbon black, the particles are directly roughened with silica fume to obtain the final thermal storage composite phase change material particles 11 with a mass of about 335g.

[0045] III. Preparation of Functionally Graded Concrete (1) Preparation of matrix material Photothermal conversion - heat storage layer matrix: Weigh 500g of PO 42.5 cement, 1000g of fine sand (particle size 0.15-0.6mm, fineness modulus 2.5), 200g of deionized water, and 17g of polycarboxylate superplasticizer (solid content 30%, paste fluidity 260mm, commercially available) (equivalent to 1.0% of cement mass).

[0046] Phase change thermal storage layer matrix: Weigh 500g of PO 42.5 cement, 750g of fine sand, 1000g of ceramsite aggregate (particle size 5-10mm, bulk density 800 kg / m³), 200g of deionized water, 17g of water-reducing agent, and 50g of interlayer interface agent (epoxy type, bond strength ≥1.0MPa).

[0047] Load-bearing / insulation layer substrate: Weigh out 500g of PO 42.5 cement, 750g of fine sand, 1000g of ceramsite, and 225g of deionized water.

[0048] (2) Pre-dispersion of composite phase change particles Photothermal Conversion - Heat Storage Layer: Weigh 40g of 10 photothermal conversion composite phase change material particles (8% by mass, based on 500g of cement), pour them into a plastic container, add 60mL of deionized water (30% of the total 200mL of water), and stir with a glass rod for 2 minutes (60rpm) to fully wet the particle surface. Add 8.5g of water-reducing agent (0.5% of the cement mass), and continue stirring for 1 minute to obtain pre-dispersed slurry A.

[0049] Phase change thermal storage layer: Weigh 75g of thermal storage composite phase change material particles 11 (15% by mass), add 60mL of deionized water, stir for 2 minutes (60rpm), add 8.5g of water-reducing agent, stir for 1 minute, and obtain pre-dispersed slurry B.

[0050] (3) Layered casting ① Photothermal Conversion - Heat Storage Layer 1: Add 500g cement, 1000g sand, 140mL remaining water, and 8.5g water-reducing agent to a mortar mixer (5L capacity). Mix at 100 rpm for 2 minutes to form a uniform matrix slurry. Slowly pour in pre-dispersed slurry A, reduce the speed to 50 rpm, and continue mixing for 90 seconds. Immediately pour the mixture into the bottom of a pre-prepared steel mold (internal dimensions 300mm×300mm×150mm, inner wall coated with release agent), smooth it with a scraper, and control the thickness to 20mm. Place the mold on a plate vibrator (frequency 40Hz, amplitude 0.5mm) and vibrate for 8 seconds until no obvious air bubbles appear on the surface. Record time t0 and monitor the initial setting state (target 3.5-7.5MPa) using a penetration resistance meter.

[0051] ② Phase Change Thermal Storage Layer 2: 40 minutes after t0 (before the initial setting of the photothermal layer, with a penetration resistance value of 5.2 MPa), apply an interface agent to the surface of the photothermal layer to prepare the thermal storage layer concrete. Add 500g of cement, 750g of sand, 1000g of ceramsite, 140mL of remaining water, and 8.5g of water-reducing agent to a mixer and mix for 2 minutes. Slowly add pre-dispersed slurry B and mix for 90 seconds. Carefully pour the mixture onto the surface of the photothermal layer and gently smooth it with a scraper to a thickness of approximately 50mm. Compact it in two stages: first pour in a 25mm thickness and vibrate for 8 seconds; second pour in the remaining 25mm thickness and vibrate for 8 seconds. Avoid excessive vibration that could cause particles to float or separate between layers. Record the time t1.

[0052] ③ Load-bearing / Insulation Layer 3: 30 minutes after t1 (before the initial setting of the heat storage layer, with a penetration resistance value of 4.8 MPa), prepare the load-bearing layer concrete. Add 500g of cement, 750g of sand, 1000g of expanded clay aggregate, and 225g of water to a mixer and mix for 3 minutes. Pour the mixture onto the surface of the heat storage layer, smooth it to fill the mold (approximately 80mm thick), and vibrate it normally for 20 seconds. Smooth the surface with a ruler and cover it with plastic film to prevent water loss.

[0053] (4) Maintenance After standing at room temperature (20℃, 60% relative humidity) for 24 hours, the specimens were demolded. The specimens were then placed in a standard curing room (temperature 20±2℃, relative humidity ≥95%) and cured for 28 days.

[0054] IV. Performance Testing (1) Dispersion uniformity test After 28 days of curing, five locations (spaced ≥ 50 mm) were randomly selected from both the photothermal conversion layer and the heat storage layer. Cross-sections (5 mm thick) were cut using a diamond saw, polished, and photographed under a stereomicroscope. The area fraction of the composite phase change particles was analyzed using ImageJ software, and the coefficient of variation (CV) was calculated.

[0055] result: The particle area fractions at five locations in the photothermal layer are 7.6%, 7.9%, 8.2%, 7.8%, and 7.5%, respectively. Mean: 7.8%, Standard Deviation: 0.26%, CV = 0.26 / 7.8 × 100% = 3.3%; The particle area fractions at five locations in the thermal storage layer were 14.5%, 15.2%, 14.8%, 15.5%, and 14.0%, respectively. Mean: 14.8%, Standard deviation: 0.58%, CV = 0.58 / 14.8 × 100% = 3.9%.

[0056] (2) Photothermal performance test A xenon lamp solar simulator (spectral matching AM1.5, irradiance 1000 W / m²) was used to vertically irradiate the surface of the specimen (300mm×300mm), and an infrared thermal imager (accuracy ±0.5℃) was used to record the surface temperature distribution every 5 minutes. The initial temperature was 25℃, and the irradiation time was 60 minutes.

[0057] result: Solar absorbance α: Reflectance was measured using an ultraviolet-visible-near-infrared spectrometer (wavelength 300-2500nm, GB / T 2680), and α was calculated as 1 - reflectance = 0.88; Surface temperature response: 38°C at 5 minutes, 47°C at 10 minutes, 58°C at 20 minutes, 65°C at 30 minutes, and stabilized at 68°C at 60 minutes.

[0058] (3) Thermal storage performance test The thermal storage density of the thermal storage layer sample was tested using differential scanning calorimetry (DSC). A core sample of the thermal storage layer (20 mm in diameter and 10 mm in thickness) was taken, crushed, and passed through an 80-mesh sieve. 20 mg of the sample was placed in an aluminum crucible, and the temperature was increased from 20 °C to 80 °C at a rate of 10 °C / min. The heat flow curve was recorded.

[0059] result: Thermal storage density: 85 kJ / kg (based on the total mass of the thermal storage layer); Phase change temperature range: main peak at 58℃ (melting point of paraffin), phase change enthalpy 78 J / g (pure phase change material); (4) Temperature regulation performance test A small test chamber (internal dimensions 500mm×500mm×500mm) was constructed, with the specimen serving as the top plate (photothermal layer facing upwards). A temperature sensor (accuracy ±0.1℃) was placed inside the chamber to record the internal surface temperature. Simulated daytime irradiation was performed: xenon lamp irradiation for 8 hours (irradiance 800 W / m²), and the internal surface temperature change was recorded. The results were compared with ordinary concrete specimens (same dimensions, without phase change materials).

[0060] result: Functionally graded concrete: The internal surface temperature fluctuates between 25-33℃, with a temperature fluctuation ΔT = 8℃; Ordinary concrete: The internal surface temperature fluctuates between 25-42℃, ΔT = 17℃; Nighttime heat dissipation test: After irradiation was stopped, the temperature drop curve of the inner surface was recorded. Functionally graded concrete took 5.5 hours to cool from 33°C to 27°C, while ordinary concrete took 2 hours to cool from 42°C to 27°C. The heat dissipation duration was extended by 3.5 hours.

[0061] (5) Mechanical property testing According to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", 100mm×100mm×100mm cube specimens (3 specimens for each layer) were prepared for compressive strength testing, 100mm×100mm×400mm prism specimens were prepared for flexural strength testing, and 100mm×100mm×100mm interlayer bond specimens were prepared for bond strength testing. A hydraulic universal testing machine (maximum load 3000 kN) was used with a loading rate of 0.5 MPa / s.

[0062] result: Photothermal conversion-storage layer: compressive strength 22.3 MPa, flexural strength 3.8 MPa; Phase change thermal storage layer: compressive strength 23.1 MPa, flexural strength 4.0 MPa; Load-bearing / insulation layer: compressive strength 28.5 MPa, flexural strength 4.5 MPa; (6) Durability test The frost resistance was tested according to GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (rapid freezing method, 50 freeze-thaw cycles).

[0063] result: Freeze-thaw resistance: mass loss rate 1.2%, strength loss rate 8.5%, reaching F50 grade; V. Performance Summary Table of Example 1

[0064] Example 2: Functionally graded concrete based on graphene quantum dot-stearic acid system The main differences between this embodiment and Example 1 are: (1) stearic acid (melting point 69℃, purity ≥95%) is used as the phase change material; (2) the alkali-resistant shell layer is prepared by the organosilicon sol-gel method; (3) graphene quantum dots are used as the photothermal conversion component; and (4) metakaolinite (activity index 102%) is used as the roughening layer. Other preparation processes are the same as in Example 1.

[0065] I. Preparation of Photothermal Conversion Composite Phase Change Material Particles 10 (1) Biochar preparation and activation: Same as in Example 1, rice husk-based activated biochar was purchased directly, without the need for self-preparation (commercially available, specifications as follows: particle size 0.2-0.8 mm, porosity 58%, BET 280 m² / g).

[0066] (2) Stearic acid vacuum loading: Weigh 1000g of stearic acid, heat to 95℃ to melt, weigh 200g of activated biochar, vacuum impregnate for 45 minutes (vacuum degree 0.05MPa), keep warm at 85℃, after loading the mass is 300g, the loading rate is 50% by mass, and the phase transition enthalpy is determined by DSC to be 85 J / g.

[0067] (3) Preparation of organosilicon sol-gel shell: Prepare tetraethyl orthosilicate sol (made by mixing 20 mL tetraethyl orthosilicate, 80 mL anhydrous ethanol, 9 mL deionized water and 1 mL concentrated hydrochloric acid), stir for 2 hours to form a sol, immerse the particles in the sol for 30 minutes, dry at 60℃ for 12 hours, and cure at 130℃ for 3 hours. The shell thickness is 15 μm and the density is 94%.

[0068] (4) Graphene quantum dot spraying: Prepare a 1 mg / mL graphene quantum dot dispersion, spray 80 mL, load 0.9 mass fraction, and solar absorption rate α=0.86.

[0069] (5) Metakaolin roughening coating: the mass ratio of particles to metakaolin is 15:1, cement slurry (cement:water = 1:1) is used as binder, and the surface roughness Ra = 11.5μm.

[0070] II. Preparation of thermal storage composite phase change material particles 11 Using activated biochar with a particle size of 0.5-1.5 mm, a stearic acid loading of 55% by mass, an organosilicon sol-gel shell, and roughening with metakaolin, without adding graphene quantum dots, approximately 360 g was obtained.

[0071] III. Preparation and Performance Testing of Functionally Graded Concrete Using the same mix proportion, pre-dispersion method, layered casting process and curing conditions as in Example 1, the content of photothermal conversion particles was 8% by mass and the content of heat storage particles was 15% by mass.

[0072] Summary of performance test results:

[0073] Compared with Example 1: stearic acid has a higher phase change enthalpy and a greater heat storage density; the organosilicon shell has better density and a higher retention rate of phase change material; it has excellent overall performance and is suitable for high-temperature environment requirements.

[0074] Example 3: Functionally graded concrete with vein-type heat-conducting components like Figure 4 As shown, this embodiment adds a leaf vein-type heat-conducting component 4 (T2 pure copper mesh, purity 99.9%, thermal conductivity 398 W / (m·K)) to the original embodiment, which is fixed by positioning ribs. Other materials and preparation methods are the same as in the original embodiment.

[0075] I. Preparation of Vein-Type Heat Conducting Component 4 (1) Material selection: copper mesh (5mm×5mm mesh size, 0.8mm wire diameter, 1mm thickness).

[0076] (2) Leaf vein shape processing: laser cutting into leaf vein shape, main vein width 10mm, branch vein width 3mm, branch vein spacing 100mm, size 300mm×300mm, sandblasting treatment (surface roughness Ra=3μm).

[0077] (3) Fixing method: Use plastic positioning ribs (3mm in diameter) for fixing, with a spacing of 100mm.

[0078] II. Preparation of Functionally Graded Concrete (1) Photothermal conversion-heat storage layer casting: Same as in Example 1, thickness 20mm, compaction for 8 seconds.

[0079] (2) Installation of leaf vein type heat conduction component: 15 minutes after t0, lay the component flat on the surface and fix it with positioning ribs, with an embedding depth of 5mm.

[0080] (3) Phase change heat storage layer pouring: 40 minutes after t0, pour the heat storage layer and vibrate it twice to ensure that the concrete fills the mesh.

[0081] (4) Casting and curing of the bearing layer: Same as in Example 1.

[0082] III. Performance Testing (1) Thermal conductivity enhancement test The effective thermal conductivity of the thermal storage layer at different depths was tested using the transient planar heat source method (Hot Disk).

[0083] (2) Temperature uniformity test of thermal storage layer: 9 thermocouple array tests, the temperature non-uniformity of Example 3 was 2.6% (5.3% in Example 1), an improvement of 51%.

[0084] (3) Heat charging depth test: The depth of phase change completeness ≥ 80% is 35mm in Example 3 (25mm in Example 1). The increase of 10mm improves the utilization rate of phase change material by 18%.

[0085] Example 4: Functionally graded concrete with micro-textured light-absorbing structure like Figure 5 As shown, in this embodiment, based on embodiment 1, the surface of the photothermal conversion-heat storage layer is imprinted with V-shaped groove micro-texture (depth 2mm, spacing 15mm), and other materials and preparation methods are the same as in embodiment 1.

[0086] I. Preparation of Microtextured Light Absorption Structure 5 An aluminum alloy mold was used for imprinting. A pressure of 60 N / m² was applied, and the imprinting was carried out for 5 minutes after t0. The mold was then removed after holding the mold for 2 minutes. The texture depth was 2.0 mm and the surface roughness Ra=450 μm.

[0087] II. Performance Testing (1) Light absorption rate enhancement test:

[0088] Comparative Example 1: Without photothermal response layer This comparative example is used to verify the independent function of the photothermal conversion-storage layer. The same materials and preparation process as in Example 1 are used, but the photothermal conversion-storage layer on the sun-facing side is removed. The phase change thermal storage layer is directly used as the sun-facing layer and its thickness is adjusted to 70 mm. Only the phase change thermal storage layer and the load-bearing / insulation layer double-layer structure are retained. No photothermal conversion components are added. The remaining parameters are the same as in Example 1.

[0089] Performance test results

[0090] Conclusion: The photothermal conversion-storage layer is the core structure for improving the photothermal absorption, heat storage efficiency, and temperature regulation performance of concrete. Without it, the solar absorption rate of concrete decreases significantly, the phase change material is not fully charged, and the heat storage and thermal environment regulation capabilities are significantly reduced. This proves that the independent setting of this layer is crucial to achieving the building energy-saving goals of this invention.

[0091] Comparative Example 2: Functionally graded concrete without mineral roughening layer This comparative example is used to verify the independent role of the mineral roughening layer. It uses the same materials and preparation process as Example 1, but does not include the mineral roughening layer step.

[0092] Performance test results

[0093] Conclusion: The mineral roughening layer is crucial for improving the retention rate and dispersion uniformity of phase change materials, demonstrating the synergistic effect of the triple anti-leakage mechanism.

[0094] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A functionally graded concrete that couples photothermal energy storage with biomimetic plant leaf structure, characterized in that, Along the thickness direction, a photothermal conversion-storage layer, a phase change thermal storage layer, and a load-bearing / insulating layer are sequentially arranged, with an interlayer interface roughness ≥3μm or treated with an interface agent; the photothermal conversion-storage layer is on the light-facing side, containing photothermal conversion composite phase change material particles, with a thickness of 10-30mm; the phase change thermal storage layer is the middle layer, containing thermal storage composite phase change material particles, with a thickness of 30-80mm; the load-bearing / insulating layer is on the shaded side, made of ordinary concrete or lightweight concrete, with a thickness of 40-120mm; The photothermal conversion composite phase change material particles have a biochar porous carrier framework, an internal phase change material, an alkali-resistant and leak-proof shell layer, a photothermal conversion component, and a mineral roughening layer; the thermal storage composite phase change material particles have a biochar porous framework, an internal phase change material, an alkali-resistant and leak-proof shell layer, and a mineral roughening layer.

2. The functionally graded concrete according to claim 1, characterized in that, The biochar porous carrier skeleton has an open porosity ≥50%, a specific surface area ≥200 m² / g, and a particle size of 0.05-1.0 mm; the biochar porous carrier skeleton of the thermal storage composite phase change material particles has an open porosity ≥50%, a specific surface area ≥200 m² / g, and a particle size of 0.1-2.0 mm.

3. The functionally graded concrete according to claim 1, characterized in that, The phase change material is paraffin or stearic acid with a carbon chain length of C18-C24. The paraffin has a melting point of 50-60℃ and a purity of ≥98%, and the stearic acid has a melting point of 65-70℃ and a purity of ≥95%. The phase change material loading rate in the photothermal conversion composite phase change material particles is 30-60% by mass, and the phase change material loading rate in the thermal storage composite phase change material particles is 40-70% by mass.

4. The functionally graded concrete according to claim 1, characterized in that, The alkali-resistant and leak-proof shell is a water glass cured shell, an organosilicon sol-gel shell, or a polymer shell, with a shell thickness of 5-20 μm and a density of ≥90%.

5. The functionally graded concrete according to claim 1, characterized in that, The photothermal conversion component is nano-carbon black, graphene quantum dots, nano-metal particles, carbon nanotubes, or two-dimensional transition metal carbide / nitride materials, and its loading is 0.5-3% of the mass of the photothermal conversion composite phase change material particles.

6. The functionally graded concrete according to claim 1, characterized in that, The mineral roughening layer is silica fume, metakaolin, or mineral powder, wherein the silica fume has an activity index ≥95%, the metakaolin has an activity index ≥100%, and the mineral powder has a specific surface area ≥400 m² / kg; the mineral roughening layer has a thickness of 10-50 μm, resulting in a particle surface roughness of 5-15 μm.

7. The functionally graded concrete according to claim 1, characterized in that, The amount of photothermal conversion composite phase change material particles in the photothermal conversion-storage layer is 3-15% of the mass of the cementitious material in the layer; the amount of heat storage composite phase change material particles in the phase change storage layer is 10-20% of the mass of the cementitious material in the layer.

8. The functionally graded concrete according to claim 1, characterized in that, A leaf-vein type heat-conducting component is provided between the photothermal conversion-heat storage layer and the phase change heat storage layer. This component is made of copper mesh, aluminum mesh, or carbon fiber mesh, with copper mesh having a purity ≥99.5%, aluminum mesh ≥99%, and carbon fiber mesh having a thermal conductivity ≥150 W / (m²). K); The component is distributed in a main vein and branch vein network, with the main vein width being 5-15mm, the branch vein width being 2-5mm, and the branch vein spacing being 50-150mm. The component is at least partially embedded in two layers, with an embedding depth of 5-10mm, and is fixed by buckles or positioning ribs.

9. The functionally graded concrete according to claim 1, characterized in that, When this concrete is used in conjunction with steel bars and insulation layers, the distance between the steel bars and the leaf-shaped heat-conducting components shall be ≥20mm; the insulation layer and the load-bearing / insulation layer shall be bonded together with an interface agent, and the bond strength shall be ≥0.3MPa.

10. A method for preparing functionally graded concrete as described in any one of claims 1-9, characterized in that, Includes the following steps: (1) Preparation of photothermal conversion composite phase change material particles: Vacuum impregnation of activated biochar with molten phase change material, followed by sequential coating with an alkali-resistant and leak-proof shell layer, loading of photothermal conversion components, and coating with a mineral roughening layer to obtain the target particles; (2) Preparation of thermal storage composite phase change material particles: Vacuum impregnation of activated biochar with molten phase change material, followed by sequential coating with an alkali-resistant and leak-proof shell layer and a mineral roughening layer to obtain the target particles; (3) Preparation of gradient concrete: The two types of particles mentioned above are mixed with cementitious materials to prepare corresponding slurry layers. The photothermal conversion-heat storage layer, phase change heat storage layer, and load-bearing / insulation layer are poured in sequence. During the pouring process, the leaf vein-type heat conduction components are fixed, the light-absorbing structure of the light-facing surface is imprinted, and the interlayer interface is treated. The pouring is completed before the initial setting of each layer. After vibration and standard curing for 28 days, the finished product is obtained.

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