A radiation-cooled paving brick and its preparation method

Abstract

This invention belongs to the field of building materials technology and relates to a radiation-cooled paving brick and its preparation method. The radiation-cooled paving brick comprises, from bottom to top, a base layer, a functional layer, and a surface layer. The functional layer comprises, by weight, the following raw material components: 20-50 parts cement-based binder, 20-50 parts radiation-cooling functional filler, 0-30 parts aggregate, 0.5-2.5 parts admixture, and 0.1-0.5 parts reinforcing fiber. Both the functional layer and the base layer of this invention are cement-based materials, resulting in strong bonding. Through the synergistic effect of the functional filler in the functional layer and the cement hydration products with radiation-cooling function, and with the surface coated with an inorganic nano-high-hardness self-cleaning surface layer, a highly efficient and long-lasting radiation-cooling effect can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and relates to a radiation-cooled paving brick and its preparation method, and more specifically to a cement-based paving brick with passive radiation cooling function and its preparation method. Background Technology

[0002] With the acceleration of urbanization, the urban heat island effect is becoming increasingly serious. Traditional asphalt, cement concrete, and natural stone pavements absorb a large amount of heat under solar radiation, causing the surface temperature to rise sharply (reaching 60-70℃ in summer). This not only exacerbates urban high temperatures and affects pedestrian comfort, but may also accelerate the aging of pavement materials and increase building energy consumption.

[0003] Existing cooling pavement technologies, such as light-colored pavements, permeable pavements, and phase change material pavements, suffer from drawbacks such as incomplete reflectance spectrum, dependence on water resources, high cost, or poor durability. Passive radiative cooling technology (achieving cooling through high solar reflectivity and high infrared emissivity) offers a new approach to solving this problem. However, directly applying radiative cooling coatings to pavements results in poor adhesion, low mechanical strength, and easy wear and detachment. Therefore, the key to applying this technology to paving bricks lies in creating a functional layer that can bond firmly to the cement matrix, possess excellent and durable radiative cooling properties, and simultaneously meet mechanical, wear-resistant, and anti-slip requirements.

[0004] In view of this, it is of great significance to develop a radiation-cooling in-situ composite functional layer with a cement-based material that has a certain radiation-cooling function as the binder, so as to realize the integration of function and structure in radiation-cooling paving bricks. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a radiation-cooled paving brick and its preparation method. This radiation-cooled paving brick inherits the excellent mechanical properties, wear resistance, and fire resistance of cement materials, while also possessing a highly efficient and long-lasting radiation cooling effect.

[0006] The purpose of this invention is to provide a radiation-cooled paving brick, which comprises, from bottom to top, a base layer, a functional layer, and a topcoat layer; the functional layer comprises, by weight, the following raw material components: 20-50 parts of cement-based cementitious material, 20-50 parts of radiation-cooled functional filler, 0-30 parts of aggregate, 0.5-2.5 parts of admixture, and 0.1-0.5 parts of reinforcing fiber.

[0007] This invention is a gel composite material with cement-based cementitious material as the functional layer. It serves as both a functional phase and a binder, and can be combined with the cement-based matrix layer with strong adhesion. At the same time, it is combined with a radiative cooling filler that can reflect sunlight in the mid- and far-infrared bands, enhancing the radiative capacity of the functional layer in the atmospheric window band and significantly reducing temperature. Through the design of the matrix layer, functional layer and topcoat layer, it achieves a highly efficient and long-lasting radiative cooling effect, while also possessing the excellent mechanical properties, wear resistance, fire resistance and long service life of cement materials.

[0008] Preferably, in the above technical solution, the cement-based cementitious material is white sulfoaluminate cement with a Heinz whiteness ≥92, a bluish whiteness ≥87, and a specific surface area ≥500 m². 2 / kg.

[0009] Preferably, in the above technical solution, the radiation cooling functional filler is a composition of high solar reflectance filler and high infrared emission filler in a mass ratio of 2-3:1.

[0010] Preferably, in the above technical solution, the high solar reflectance filler is a mixture of rutile titanium dioxide (TiO2) and hollow titanium dioxide in a mass ratio of 3-4:1, with a particle size of 0.1-10 μm. Rutile titanium dioxide has a tetragonal crystal structure, composed of six-coordinated titanium and oxygen atoms, exhibiting high refractive index and strong optical stability. Hollow titanium dioxide has a hollow internal structure, possessing not only high refractive index but also lightweight and high strength, along with thermal insulation and controllable optical properties. This invention, by mixing two different specifications of titanium dioxide, yields a high solar reflectance filler that can reflect sunlight in the 0.3-2.5 μm wavelength range. By controlling its particle size, its scattering effect on visible and near-infrared light can be optimized, enhancing reflectivity and improving thermal insulation.

[0011] Preferably, in the above technical solution, the high infrared emission filler is a mixture of porous silica and metal oxide in a mass ratio of 4-5:1, with a particle size of 1-20 μm; the metal oxide is alumina or iron oxide. Porous silica has the characteristics of high surface area and high porosity. This structure provides a large number of surface active sites, which is beneficial to the absorption and emission of infrared radiation. It has multiple absorption peaks in the 8-13 μm band and has high emissivity. At the same time, its infrared emission characteristics can be adjusted by doping with metal oxide to better match the atmospheric window. In addition, by controlling its particle size, its phonon excitation and radiation capabilities in this band can be enhanced.

[0012] Preferably, in the above technical solution, the aggregate is quartz sand; the admixture includes a water-reducing agent and a dispersant, wherein the water-reducing agent is a polycarboxylate-based water-reducing agent and the dispersant is sodium hexametaphosphate; and the reinforcing fiber is polypropylene fiber or PVA fiber. This technical solution uses fine quartz sand as aggregate, which can adjust the fluidity of the slurry, reduce shrinkage, and lower costs; the use of an admixture containing a dispersant ensures the uniform dispersion of functional fillers in the cement slurry; and the addition of reinforcing fibers improves the crack resistance of the functional fillers.

[0013] Preferably, in the above technical solution, the matrix layer comprises the following raw material components by weight: 15-25 parts ordinary cement, 75-85 parts coarse / fine aggregate, 0.1-0.2 parts water-reducing agent, and water, with a water-cement ratio of 0.35-0.45 after adding water. The matrix layer provides the main structural strength and volume for the paving bricks, and C30 concrete paving material can be used. Specifically, the ratio of coarse aggregate to fine aggregate is 2:1, and the water-reducing agent is a conventional concrete water-reducing agent.

[0014] Preferably, in the above technical solution, the coating layer is an inorganic nano-titanium dioxide coating agent, and its preparation method includes the following steps: (1) Under inert gas protection and continuous stirring, the titanate precursor is slowly added to anhydrous ethanol containing hydrolysis inhibitor, and a small amount of silane coupling agent is added at the same time to form solution A. (2) Dissolve deionized water, acid catalyst and dopant source in anhydrous ethanol to form solution B; (3) At a constant temperature, solution B is slowly added dropwise to solution A, and the reaction is continuously stirred for 2-24 hours to obtain an inorganic nano-titanium dioxide coating agent. In this technical solution, a doping source is introduced into the coating layer, which can expand the light response range of the material to the visible light region, further improving the reflection effect of sunlight. At the same time, after the functional layer is sprayed and dried, a dense and hard paint film can be formed on the surface, which not only improves the hardness but also has a hydrophobic and self-cleaning effect.

[0015] Preferably, in the above technical solution, in step (1), the molar ratio of the hydrolysis inhibitor to the titanate is 0.5-2:1; the hydrolysis inhibitor is acetylacetone, the titanate precursor is tetrabutyl titanate, and the silane coupling agent is heptadecafluorodecyltrimethoxysilane, with an addition amount of 2-5% of the titanate. In step (2), the amounts of deionized water, acid catalyst, and dopant source are 50-60%, 1-2%, and 2-4% of the mass of the titanate precursor, respectively; the acid catalyst is nitric acid; and the dopant source is a nitrogen-containing compound or ammonium fluoride. In step (3), the reaction temperature is 25℃-60℃.

[0016] The present invention also provides a method for preparing the above-mentioned radiation-cooled paving brick, the method comprising the following steps: S1. After measuring, mixing and stirring the raw materials of the base layer evenly according to the proportion, pour the mixture into the mold, vibrate and press lightly to form the base layer. S2. After measuring, mixing, and stirring the raw materials according to the functional layer ratio into a slurry, pour it onto the base layer of the mold, vibrate and lightly press it to form the paving brick blank after curing. S3. Apply the topcoat agent online to the surface of the functional layer of the obtained paving brick blank, cure, demold, and obtain the finished radiation-cooled paving brick; In the finished radiant cooling paving brick, the thickness of the base layer is 50-55mm, the thickness of the functional layer is 3-5mm, and the thickness of the overlay layer is 15-20μm.

[0017] Advantages compared to existing technologies: The paving bricks of this invention achieve efficient and long-lasting radiative cooling effect through the design of a base layer, a functional layer and a topcoat layer, while also possessing the excellent mechanical properties, wear resistance, fire resistance and long service life of cement materials.

[0018] The functional layer of this invention is a gel composite material using cement-based cementitious material as the functional layer. It is a "homogeneous material" with the cement-based matrix layer, and its interfacial bonding strength is far superior to that of organic coatings and cement matrix. It has excellent mechanical strength, durability, peel resistance and aging resistance. At the same time, it is combined with high solar reflectance filler and high infrared emission filler with radiative cooling function. The two work together to reflect sunlight in the mid- and far-infrared bands, improve the radiation capability of the functional layer in the atmospheric window band and significantly reduce temperature. In addition, the high whiteness cement used has the same reflectivity in the solar light band, further improving the radiative cooling effect of the functional layer.

[0019] The present invention adds a dopant layer to the surface of the functional layer, which not only protects the functional layer, but also further improves the reflection effect and self-cleaning effect of sunlight.

[0020] The secondary material feeding process used in this invention is highly compatible with production lines commonly used in the brick-making industry, requires no major equipment modifications, and is easy to industrialize. Attached Figure Description

[0021] Figure 1 A schematic diagram of the structure for inventing a radiation-cooled paving brick; Figure 2 This is a flowchart of the preparation process of the present invention; Figure 3 The solar spectral reflectance and mid-infrared emissivity curves of the functional layer in Embodiment 1 of the present invention are shown. Figure 4The images show the cooling effect of the radiation-cooled paving bricks of Embodiment 1 of the present invention and ordinary paving bricks under direct sunlight outdoors. A is a normal mode photo, B is an infrared mode photo, the left side is an ordinary paving brick, and the right side is a paving brick prepared in Embodiment 1. Detailed Implementation

[0022] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products that can be purchased from the market.

[0024] The present invention will be further described in detail below with reference to embodiments: Example 1 A type of radiant cooling paving brick, comprising, from bottom to top, a base layer, a functional layer, and a surface layer; wherein... The matrix layer comprises the following raw material components by weight: 20 parts ordinary cement, 80 parts coarse / fine aggregate (coarse aggregate to fine aggregate ratio of 2:1), 0.2 parts polycarboxylate superplasticizer and a certain amount of water, with a water-cement ratio of 0.4 after adding water.

[0025] The functional layer comprises the following raw material components by weight: white sulfoaluminate cement (Henness whiteness ≥ 92, bluish whiteness ≥ 87, specific surface area ≥ 500 m²). 2 40 parts of rutile titanium dioxide (0.3μm), 20 parts of hollow titanium dioxide (0.5μm), 7 parts of porous silica (3μm), 1.4 parts of alumina, 14 parts of quartz sand (80 mesh), 0.3 parts of polycarboxylate superplasticizer, 0.5 parts of sodium hexametaphosphate, 0.2 parts of polypropylene fiber, and water as needed (water-binder ratio is 0.28).

[0026] The topcoat layer is an inorganic nano-silica topcoat agent, and the preparation method includes the following steps: (1) Under the protection of inert gas and continuous stirring, tetrabutyl titanate is slowly added to anhydrous ethanol containing acetylacetone, wherein the molar ratio of acetylacetone to tetrabutyl titanate is 1:1, and 2% by mass of heptadecafluorodecyltrimethoxysilane is added to form solution A. (2) Dissolve 50% of the mass of tetrabutyl titanate in deionized water, 1% in nitric acid and 3% in ammonium fluoride in anhydrous ethanol to form solution B; (3) At a constant temperature of 40°C, liquid B is slowly added dropwise to liquid A, and the reaction is continuously stirred for 12 hours to obtain an inorganic nano self-cleaning surface agent.

[0027] The preparation method of radiation-cooled paving bricks consists of a 50mm base layer, a 3mm functional layer, and a 20μm topcoat layer, from bottom to top. A schematic diagram of its structure is shown below. Figure 1 As shown, the preparation process flow chart is as follows: Figure 2 As shown, it includes the following steps: S1. Mix and stir the raw materials of the base layer according to the ratio, then pour the mixture into the mold, vibrate and gently press to form the base layer. S2. Mix the raw materials of the functional layer evenly according to the ratio, then add water (water-binder ratio of 0.28) and stir to form a slurry. Pour the slurry onto the base layer of the mold, vibrate and lightly press to form the paving brick blank after curing. S3. Apply the topcoat agent online to the surface of the functional layer of the obtained paving brick blank, cure for 28 days, demold, and obtain the finished radiation-cooled paving brick.

[0028] Example 2 A type of radiant cooling paving brick, comprising, from bottom to top, a base layer, a functional layer, and a surface layer; wherein... The matrix layer comprises the following raw material components by weight: 25 parts ordinary cement, 75 parts coarse / fine aggregate (coarse aggregate to fine aggregate ratio of 2:1), 0.1 parts polycarboxylate superplasticizer and a certain amount of water, with a water-cement ratio of 0.35 after adding water.

[0029] The functional layer comprises the following raw material components by weight: white sulfoaluminate cement (Henness whiteness ≥ 92, bluish whiteness ≥ 87, specific surface area ≥ 500 m²). 2 30 parts ( / kg) of rutile titanium dioxide (0.1μm), 15 parts of hollow titanium dioxide (0.6μm), 8 parts of porous silica (5μm), 2 parts of alumina, 23 parts of quartz sand (80 mesh), 1 part of polycarboxylate superplasticizer, 0.5 parts of sodium hexametaphosphate, 0.3 parts of PVA fiber, and water as needed (water-binder ratio is 0.28).

[0030] The topcoat layer is an inorganic nano-silica topcoat agent, and the preparation method includes the following steps: (1) Under the protection of inert gas and continuous stirring, tetrabutyl titanate is slowly added to anhydrous ethanol containing acetylacetone, wherein the molar ratio of acetylacetone to tetrabutyl titanate is 0.5:1, and 3% by mass of heptadecafluorodecyltrimethoxysilane is added to form solution A. (2) Dissolve 55% of tetrabutyl titanate in deionized water, 2% in nitric acid and 1% in ammonium fluoride in anhydrous ethanol to form solution B; (3) At a constant temperature of 60℃, liquid B is slowly added dropwise to liquid A, and the reaction is continuously stirred for 5 hours to obtain an inorganic nano self-cleaning surface agent.

[0031] The preparation method of radiation-cooled paving bricks, consisting of a 52mm base layer, a 4mm functional layer, and a 15μm topcoat layer from bottom to top, includes the following steps: S1. Mix and stir the raw materials of the base layer according to the ratio, then pour the mixture into the mold, vibrate and gently press to form the base layer. S2. Mix the raw materials of the functional layer evenly according to the ratio, then add water (water-binder ratio of 0.28) and stir to form a slurry. Pour the slurry onto the base layer of the mold, vibrate and lightly press to form the paving brick blank after curing. S3. Apply the topcoat agent online to the surface of the functional layer of the obtained paving brick blank, cure for 28 days, demold, and obtain the finished radiation-cooled paving brick.

[0032] Example 3 A type of radiant cooling paving brick, comprising, from bottom to top, a base layer, a functional layer, and a surface layer; wherein... The matrix layer comprises the following raw material components by weight: 15 parts ordinary cement, 85 parts coarse / fine aggregate (the ratio of coarse aggregate to fine aggregate is 2:1), 0.2 parts polycarboxylate superplasticizer, and a certain amount of water. The water-cement ratio after adding water is 0.45.

[0033] The functional layer comprises the following raw material components by weight: white sulfoaluminate cement (Henness whiteness ≥ 92, bluish whiteness ≥ 87, specific surface area ≥ 500 m²). 2 45 parts ( / kg) of rutile titanium dioxide (0.3μm), 24 parts of hollow titanium dioxide (0.5μm), 8 parts of porous silica (3μm), 12 parts of alumina, 3 parts of quartz sand (80 mesh), 0.3 parts of polycarboxylate superplasticizer, 0.5 parts of sodium hexametaphosphate, 0.2 parts of polypropylene fiber, and water as needed (water-binder ratio is 0.28).

[0034] The topcoat layer is an inorganic nano-silica topcoat agent, and the preparation method includes the following steps: (1) Under the protection of inert gas and continuous stirring, tetrabutyl titanate is slowly added to anhydrous ethanol containing acetylacetone, wherein the molar ratio of acetylacetone to tetrabutyl titanate is 2:1, and 5% by mass of heptadecafluorodecyltrimethoxysilane is added to form solution A. (2) Dissolve 60% of the mass of tetrabutyl titanate in deionized water, 2% in nitric acid and 4% in ammonium fluoride in anhydrous ethanol to form solution B; (3) At a constant temperature of 25°C, liquid B is slowly added dropwise to liquid A, and the reaction is continuously stirred for 24 hours to obtain an inorganic nano self-cleaning surface agent.

[0035] The preparation method of radiation-cooled paving bricks, consisting of a 55mm base layer, a 5mm functional layer, and a 20μm topcoat layer from bottom to top, includes the following steps: S1. Mix and stir the raw materials of the base layer according to the ratio, then pour the mixture into the mold, vibrate and gently press to form the base layer. S2. Mix the raw materials of the functional layer evenly according to the ratio, then add water (water-binder ratio of 0.28) and stir to form a slurry. Pour the slurry onto the base layer of the mold, vibrate and lightly press to form the paving brick blank after curing. S3. Apply the topcoat agent online to the surface of the functional layer of the obtained paving brick blank, cure for 28 days, demold, and obtain the finished radiation-cooled paving brick.

[0036] Comparative Example 1 A type of radiant cooling paving brick differs from Example 1 in that it does not have a topcoat layer, but is otherwise the same as Example 1.

[0037] Comparative Example 2 A radiation-cooled paving brick differs from Example 1 in that no doping source is introduced into the cover layer, i.e., no ammonium fluoride is used in step (2) of its preparation method, while the rest is the same as Example 1.

[0038] Comparative Example 3 A radiation-cooled paving brick differs from Example 1 in that the filler in the functional layer is a single high solar reflectance filler, while the rest is the same as Example 1.

[0039] Comparative Example 4 A type of radiation-cooled paving brick differs from Example 1 in that the high solar reflectance filler is a single rutile titanium dioxide, while the rest is the same as in Example 1.

[0040] Comparative Example 5 A radiation-cooled paving brick differs from Example 1 in that the filler in the functional layer is a single high-infrared-emitting filler, while the rest is the same as in Example 1.

[0041] Comparative Example 6 A radiation-cooled paving brick differs from Example 1 in that the high infrared emitting filler is a single ordinary silica, while the rest is the same as Example 1.

[0042] Comparative Example 7 A common gray cement paving brick, without a functional layer and a surface layer, is prepared using the same method as in Example 1.

[0043] Test case 1. Take 40mm×40mm test blocks from the paving bricks prepared in Examples 1-3 and Comparative Examples 1-7 according to the specifications. These blocks are used to test the solar reflectance (SR, referring to JC / T 235-2014 standard) and atmospheric window emissivity (referring to T / CECS 10378-2023 standard) of the functional layer in the paving bricks. At the same time, the compressive strength, frost resistance, weather resistance, wear resistance and anti-slip performance of the paving bricks are also tested (referring to the relevant standards of TC / T446-2000). The test results are shown in Table 1-2.

[0044] Table 1 Test results of Examples 1-3

[0045] Table 2 Test results of Comparative Examples 1-7

[0046] As can be seen from the results in Table 1, the paving bricks prepared by the method of the present invention have an average solar reflectivity of over 0.89 and an emissivity of over 0.9 in the atmospheric window band (8-13μm), which can achieve a highly efficient radiative cooling effect. In addition, the paving bricks have excellent compressive strength, frost resistance, weather resistance, good adhesion between layers, and are not easily worn.

[0047] In Table 2, the paving bricks prepared in Comparative Example 1, lacking a cover layer, experienced some impact on reflectivity, emissivity, and mechanical strength, but the most significant reduction was in weather resistance. In Comparative Example 2, the cover layer lacked a nitrogen source; while the overall mechanical properties remained unaffected, the solar reflectivity decreased, indicating that introducing a nitrogen source into the cover layer could expand the light response range of the paving bricks. In Comparative Example 3, the functional layer used a single high solar reflectance filler; although the solar reflectivity was not significantly affected, the average emissivity of the atmospheric window decreased severely, directly impacting the cooling effect. In Comparative Example 4, the high solar reflectance filler used only rutile titanium dioxide; although its reflectivity was relatively high, it was inferior to Example 1, and its heat insulation effect was worse. In Comparative Example 5, the functional layer used a single high infrared emission filler; although the average emissivity of the atmospheric window was unaffected, its solar reflectivity decreased severely, also affecting the cooling effect. In Comparative Example 6, the high infrared emission filler was ordinary silica, with a low refractive index and poor covering power; although the emissivity was good, the reflectivity decreased sharply. In Comparative Example 7, ordinary gray cement paving bricks had virtually no cooling effect.

[0048] 2. The solar spectral reflectance and mid-infrared emissivity of the functional layer of the floor tiles obtained in Example 1 were measured using a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer. The results are as follows: Figure 3As shown. Simultaneously, the floor tile prepared in Example 1 (right) and the floor tile prepared with ordinary cement in Comparative Example 7 (left) were placed under direct sunlight outdoors under the same conditions, and their surface temperature difference was measured. The test results are as follows. Figure 4 As shown.

[0049] from Figure 3 The results show that the paving bricks prepared by the method of the present invention in Example 1 have a solar spectral reflectance of 0.91 and a mid-infrared emissivity of 0.95, exhibiting efficient radiative cooling. After outdoor direct sunlight testing, the paving bricks prepared in Example 1 have a surface temperature 15.1℃ lower than ordinary paving bricks, demonstrating a significant cooling effect.

[0050] In summary, by designing the paving bricks into a structure consisting of a base layer, a functional layer, and a surface layer, and optimizing the composition of the functional layer and the surface layer, this invention not only achieves efficient and long-lasting radiative cooling effects, but also possesses the excellent mechanical properties, wear resistance, fire resistance, and long service life of cement materials, thus having broad application prospects.

[0051] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of radiant cooling paving brick, characterized in that, The radiation-cooled paving brick comprises, from bottom to top, a base layer, a functional layer, and a surface layer; the functional layer comprises, by weight, the following raw material components: 20-50 parts of cement-based cementitious material, 20-50 parts of radiation-cooled functional filler, 0-30 parts of aggregate, 0.5-2.5 parts of admixture, and 0.1-0.5 parts of reinforcing fiber.

2. The radiant cooling paving brick according to claim 1, characterized in that, The cementitious material is white sulfoaluminate cement with a Heinz whiteness ≥92, a bluish whiteness ≥87, and a specific surface area ≥500 m². 2 / kg.

3. The radiant cooling paving brick according to claim 1, characterized in that, The radiation cooling functional filler is a composition of high solar reflectance filler and high infrared emission filler in a mass ratio of 2-3:

1.

4. The radiant cooling paving brick according to claim 3, characterized in that, The high solar reflectance filler is a mixture of rutile titanium dioxide and hollow titanium dioxide in a mass ratio of 3-4:1, with a particle size of 0.1-10 μm.

5. A radiant cooling paving brick according to claim 3, characterized in that, The high infrared emission filler is a mixture of porous silica and metal oxide in a mass ratio of 4-5:1, with a particle size of 1-20 μm; the metal oxide is aluminum oxide or iron oxide.

6. The radiant cooling paving brick according to claim 1, characterized in that, The aggregate is quartz sand; the admixture includes a water-reducing agent and a dispersant, the water-reducing agent is a polycarboxylate-based water-reducing agent, and the dispersant is sodium hexametaphosphate; the reinforcing fiber is polypropylene fiber or PVA fiber.

7. The radiant cooling paving brick according to claim 1, characterized in that, The matrix layer comprises the following raw material components in parts by weight: 15-25 parts of ordinary cement, 75-85 parts of coarse / fine aggregate, 0.1-0.2 parts of water-reducing agent, and water, with a water-cement ratio of 0.35-0.45 after adding water.

8. The radiant cooling paving brick according to claim 1, characterized in that, The coating layer is an inorganic nano-titanium dioxide coating agent, and its preparation method includes the following steps: (1) Under inert gas protection and continuous stirring, titanate precursors are slowly added to anhydrous alcohol containing hydrolysis inhibitors, and a small amount of silane coupling agent is added at the same time to form solution A. (2) Dissolve deionized water, acid catalyst and dopant source in anhydrous ethanol to form solution B; (3) At a constant temperature, slowly add liquid B to liquid A and stir continuously for 2-24 hours to obtain inorganic nano titanium dioxide coating agent.

9. A radiant cooling paving brick according to claim 8, characterized in that, In step (1), the molar ratio of the hydrolysis inhibitor to the titanate is 0.5-2:1; the hydrolysis inhibitor is acetylacetone, the titanate precursor is tetrabutyl titanate, and the silane coupling agent is heptadecafluorodecyltrimethoxysilane, with an addition amount of 2-5% of the titanate. In step (2), the amounts of deionized water, acid catalyst, and dopant source are 50-60%, 1-2%, and 2-4% of the mass of the titanate precursor, respectively; the acid catalyst is nitric acid; and the dopant source is a nitrogen-containing compound or ammonium fluoride. In step (3), the reaction temperature is 25℃-60℃.

10. A method for preparing a radiation-cooled paving brick as described in any one of claims 1-9, characterized in that, The preparation method includes the following steps: S1. After measuring, mixing and stirring the raw materials of the base layer according to the proportion, inject the mixture into the mold, vibrate and press lightly to form the base layer. S2. After measuring, mixing, and stirring the raw materials according to the functional layer ratio into a slurry, pour it onto the base layer of the mold, vibrate and lightly press it to form the paving brick blank after curing. S3. Apply the topcoat agent online to the surface of the functional layer of the obtained paving brick blank, cure, demold, and obtain the finished radiation-cooled paving brick; In the finished radiant cooling paving brick, the thickness of the base layer is 50-55mm, the thickness of the functional layer is 3-5mm, and the thickness of the overlay layer is 15-20μm.

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