Boron-reinforced cement-based radiation refrigeration composite material and preparation method thereof

Abstract

The invention discloses a boron-reinforced cement-based radiation refrigeration composite material and a preparation method thereof, and belongs to the technical field of building materials.During preparation, Portland cement, ceramic micro powder and other powder are evenly mixed to obtain mixed powder; uniformly mixing the mixing water with the mixed powder, and fully stirring to obtain slurry; hardened cement paste with directional pores is obtained through an ice template method, and the boron-reinforced cement-based radiation refrigeration composite material is obtained after the hardened paste is subjected to high-temperature treatment. According to the preparation method, freezing forming and high-temperature treatment of an ice template method are combined, so that the radiation refrigeration capacity is obviously improved, the problem of insufficient material strength caused by freezing forming is avoided, and the prepared composite material has relatively high radiation refrigeration capacity and compressive strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and specifically relates to a boron-reinforced cement-based radiant cooling composite material and a preparation method thereof, which can improve the radiant cooling capacity of the cement-based material while enhancing its compressive strength and high-temperature resistance. Background Art

[0002] Passive radiative cooling technology primarily uses the 8-13 μm atmospheric window to transfer an object's own heat into the deep cold of space via radiation, achieving cooling without consuming additional energy. Therefore, passive radiative cooling performance requires adjusting the material's properties, optimizing its infrared thermal radiation emissivity in the atmospheric window band while minimizing its absorption of incident sunlight.

[0003] Cement-based materials are the most widely used building materials in the world, offering advantages such as easy access and low cost. Furthermore, hardened cement itself has a certain ability to radiate infrared light. Current literature reports on methods for enhancing the radiative cooling capacity of cement-based materials primarily include adding white mineral admixtures and whitening agent particles to increase solar reflectivity, or applying organic or inorganic radiative cooling coatings to building surfaces to achieve high solar reflectivity. The patent "A Cement-Based Passive Cooling Composite Material and Its Preparation Method" (CN115466086A) indicates that while the addition of admixtures and white minerals and an increase in the water-cement ratio can improve the solar reflectivity of hardened cement in the short term, these methods present challenges such as limited optical performance, reduced mechanical strength, and excessive cost. The patent "Polymer Cement Radiant Cooling Paint and Coating" (CN113563779B) shows that applying a polymer coating to a hardened cement surface can achieve a full-band reflectivity of sunlight greater than or equal to 90%. However, the addition of large amounts of functional fillers (such as rutile titanium dioxide and alumina powder) increases material costs and poses risks of weathering and peeling. The patent "Cement-based Radiant Cooling Dry Powder Paint, Building Coating, and Coating Preparation Method" (CN110105798A) shows that inorganic pigment particles have excellent radiant cooling properties. However, the interface between the coating and the building is held together only by fragile van der Waals forces, making it susceptible to wear and damage in extreme wind and rain, significantly reducing its optical performance.

[0004] As can be seen from the above, effectively improving the radiative cooling performance of cementitious materials remains a challenging problem. Existing research reports have mostly focused on using white fillers and other methods to increase the reflectivity of hardened cementitious materials in the solar spectrum. However, this approach fails to eliminate the influence of the hydroxyl absorption peaks located near 1.43 μm and 1.95 μm in the near-infrared spectrum on the solar reflectivity spectrum. Few reports have considered designing the material's pore structure to modify the emissivity in the near-infrared band, thereby enhancing radiative cooling efficiency by increasing the infrared radiation efficiency of the atmospheric window region. Summary of the Invention

[0005] To address the above technical issues, the present invention provides a boron-reinforced cement-based radiative cooling composite material and its preparation method. The cement composite material prepared by the present invention is subjected to an ice-templating method to form a directional microporous structure. After high temperature exposure, the radiative cooling capacity of the hardened cement specimen is further enhanced. More importantly, the preparation method provided by the present invention significantly improves the mechanical properties of the cement-based material prepared by the ice-templating method, effectively compensating for the inherent drawback of the ice-templating method, which severely degrades the mechanical properties of cement-based materials.

[0006] To achieve high-temperature enhanced radiative cooling performance of cement, the present invention utilizes Portland cement, ceramic micropowder, and water to form a gelling system. The performance of the fresh slurry is adjusted by adding a viscosity modifier. The present invention utilizes an ice-template method to prepare hardened cement specimens. Low-temperature, rapid freezing causes ice crystals in the cement slurry to grow directional along the temperature gradient, forming a microporous structure on the cement surface and enhancing the hardened specimens' ability to scatter sunlight. Furthermore, leveraging the high-temperature oxidative activity of the ceramic micropowder, high-temperature treatment of the cement specimens yields a product with excellent solar reflectivity, further enhancing the hardened cement specimens' radiative cooling capacity and high-temperature resistance. The ceramic micropowder selected in this invention undergoes oxidation reactions within a temperature range of 400°C to 1000°C, generating corresponding oxidation products that contribute to enhanced radiative cooling performance of cement. Calcium hydroxide, a cement hydration product, begins decomposing at approximately 460°C to form calcium oxide. With continued high temperatures, the hydration product, CSH gel, decomposes to form calcium silicate. The high-temperature decomposition products of the hydration products can further chemically react with the high-temperature oxidation products of the ceramic powder to form eutectic mixtures with dense structures, such as perovskite, rutile phase, and calcium borate. These eutectic mixtures inherently possess high strength and high-temperature resistance. On the one hand, they increase the compressive strength of the cement specimens after exposure to high temperatures. On the other hand, these eutectic mixtures can effectively reflect sunlight, further enhancing the radiant cooling effect of the cement specimens.

[0007] To achieve the above object, the present invention provides the following technical solutions: In one aspect, the present invention provides a method for preparing a boron-reinforced cement-based radiant cooling composite material, comprising the following steps: Step 1: uniformly mixing silicate cement, ceramic micropowder and admixture to obtain a dry powder mixture; Step 2: Mix the admixture and mixing water evenly and then stir evenly with the dry powder mixture to obtain a uniform slurry; Step 3: pouring the slurry into a mold and preparing a hardened cement-based specimen using the ice template method; Step 4, drying the hardened cement-based specimen to a constant weight; Step 5: The dried hardened cement-based specimen is subjected to high-temperature treatment at a temperature of 400 to 1000° C., and then cooled to obtain a boron-reinforced cement-based radiant cooling composite material.

[0008] As a preferred solution, the ceramic micropowder is any one or more micropowders of zirconium boride, vanadium boride, titanium boride, chromium boride, boron carbide, hafnium boride, and tantalum boride.

[0009] As a preferred solution, the D50 of the particle size distribution of the ceramic micropowder is less than 50 microns.

[0010] As a preferred solution, 40 to 80 parts by mass of ceramic powder are added to every 100 parts by mass of Portland cement.

[0011] As a preferred embodiment, the water-to-binder ratio of the obtained slurry is 0.5 to 1.0.

[0012] As a preferred solution, the admixture is one or a mixture of micron silicon dioxide, micron titanium dioxide, montmorillonite powder, halloysite nanotubes, micron alumina and the like.

[0013] As a preferred embodiment, the additive is a viscosity regulator, which is one or a mixture of hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, etc.

[0014] As a preferred solution, the viscosity value of the viscosity modifier is about 200,000 mPa·s, and the dosage is less than 2.0% of the mass of the Portland cement, and the optimal dosage is 0.6-1% of the mass of the Portland cement.

[0015] As a preferred embodiment, in step 2, the step of uniformly mixing the admixture with the mixing water and then uniformly stirring the admixture with the dry powder mixture comprises the following steps: Step 2.1, dispersing the admixture in mixing water, and magnetically stirring to obtain an admixture dispersion; Step 2.2, adding the dry powder mixture to the admixture dispersion and stirring to obtain a slurry; As a preferred embodiment, in step 2.2, the dry powder mixture is added to the admixture dispersion, first stirred at a low speed in a stirring pot for 60 to 120 seconds, and then stirred at a high speed for 180 to 210 seconds to obtain a uniform slurry.

[0016] As a preferred solution, in step 3, preparing a hardened cement-based specimen using the ice template method includes the following steps: Step 3.1, pouring the slurry into a mold and freezing it below freezing point, and then demolding to obtain a freeze-formed specimen; Step 3.2, placing the frozen specimen in a constant temperature box at a constant temperature above freezing point for drying and thawing; Step 3.3: Curing the thawed specimen to obtain a hardened cement-based specimen.

[0017] As a preferred solution, in step 3.1, the freeze molding temperature is -100 to -50°C, and the freeze molding is unidirectional freezing, so that the ice crystals in the slurry grow directionally along the temperature gradient direction.

[0018] As a preferred solution, in step 3.1, during the freezing process, liquid nitrogen (-196°C) is used as a cold source, a copper plate is used as a cold plate, and the mold is placed on the copper plate; a copper column is used to connect the copper plate to the cold source, and by controlling the current of the electric heating plate on the lower surface of the cold plate, the temperature of the copper plate is adjusted as the freezing temperature of the sample to achieve directional freezing preparation.

[0019] As a preferred embodiment, in step 3.1, the freezing time is 10 to 30 minutes.

[0020] As a preferred embodiment, in step 3.2, the constant temperature drying and thawing temperature is 2 to 10°C, and the thawing time is 48 to 72 hours.

[0021] As a preferred solution, in step 3.3, the specimens after thawing are cured under standard curing conditions, and the temperature of the standard curing box is 20±1°C and the relative humidity is 95-100%.

[0022] As a preferred solution, in step 3.3, standard curing is performed to the age of 7 days, that is, the constant temperature drying and thawing time in step 3.2 plus the curing time in step 3.3 is 7 days.

[0023] As a preferred solution, in step 4, the hardened cement-based specimen is placed in a forced air drying oven and dried to a constant weight at a drying temperature of 40 to 60°C.

[0024] As a preferred solution, in step 4, the hardened cement-based specimen is dried to a constant weight so that the mass difference between two consecutive weighings is less than 2%.

[0025] As a preferred solution, in step 5, the high-temperature treatment equipment is a muffle furnace, the heating rate is 8 to 15°C / min, and the temperature is kept constant for 1 to 5 hours before naturally cooling to room temperature.

[0026] It should be noted that the amount of water used is determined after determining the proportion of the cementitious material and the water-cement ratio.

[0027] It should be noted that the amount of powder added to the water is determined by the degree of dispersion in the water.

[0028] It should be noted that the types of ceramic micropowders are not limited to the above-mentioned types. They only need to be able to undergo oxidation reaction in the temperature range of 400 ~ 1000 ℃ to form oxides, and the generated oxides can react with the products of high-temperature decomposition of cement hydration products to form new mineral phases, and at the same time, a physical phase that can reflect sunlight due to its own physical properties is generated.

[0029] Compared with the prior art, the technical method and product provided by the present invention have the following beneficial effects: The present invention achieves light scattering through the use of directional pore-forming technology using an ice formwork. However, existing ice formwork techniques can reduce the compressive strength of cementitious materials. To address this issue, the present invention adds ceramic micropowder, which undergoes an oxidation reaction at high temperatures to generate new crystalline phases. The high-temperature decomposition products of the cement hydration products also react chemically with the high-temperature oxidation products of the ceramic micropowder at high temperatures, forming a new material structure that improves the compressive strength, thereby reducing the impact of the ice formwork process on the compressive strength of the cementitious material. Furthermore, the presence of specific elements in the ceramic micropowder, such as titanium, boron, zirconium, and silicon, can chelate with hydrates containing hydroxyl groups, reducing the vibration of the hydroxyl groups and nearly eliminating the influence of the absorption peaks near 1.43μm and 1.95μm in the near-infrared spectrum. Surprisingly, compared to the condition without high temperature exposure, these new crystalline phases and materials not only increase the compressive strength but also enhance the radiative cooling capacity of the cement.

[0030] The high-temperature enhanced cement radiant cooling composite material prepared by the present invention can be used to protect buildings in extremely high temperature weather, etc., while reducing the demand for cooling energy consumption, it also reduces the maintenance cost of the building. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 The present invention provides a flow chart for preparing a boron-reinforced cement-based radiant cooling composite material.

[0033] Figure 2 It is a three-dimensional diagram of a one-way freezing molding device.

[0034] Figure 3 This is a cross-sectional view of a one-way freezing molding device.

[0035] Figure 4 These are appearance pictures of the test blocks prepared in Examples 1-4 and Comparative Examples 1-4.

[0036] Figure 5 These are the UV-visible-near-infrared reflection spectra of the test blocks prepared in Examples 1-4 and Comparative Examples 1-4.

[0037] 110-insulation box, 120-cold plate, 130-electric heating plate, 140-thermal column, 150-liquid nitrogen, 160-ice template mold. DETAILED DESCRIPTION

[0038] The following is a clear and complete description of the technical solutions in the examples of implementation of the present invention. The examples of implementation described are merely further detailed descriptions of the present invention and are not intended to limit the present invention. All other examples of implementation obtained by persons of ordinary skill in the art based on the examples of implementation of the present invention fall within the scope of protection of the present invention.

[0039] like Figure 1 As shown, the present invention provides a method for preparing a boron-reinforced cement-based radiant cooling composite material, comprising the following steps: Step 1: uniformly mixing silicate cement, ceramic micropowder and admixture to obtain a dry powder mixture; Step 2: Mix the admixture and mixing water evenly and then stir evenly with the dry powder mixture to obtain a uniform slurry; Step 3: pouring the slurry into a mold and preparing a hardened cement-based specimen using the ice template method; Step 4, drying the hardened cement-based specimen to a constant weight; Step 5: The dried hardened cement-based specimen is subjected to high-temperature treatment at a temperature of 400 to 1000° C., and then cooled to obtain a boron-reinforced cement-based radiant cooling composite material.

[0040] like Figure 2 and Figure 3As shown, in order to achieve one-way freezing by the ice template method, the present invention provides a one-way freezing forming device, including an insulation box 110 (with an openable box cover on the top, not shown in the figure), a cold plate 120, an electric heating plate 130 and a plurality of heat-conducting columns 140. The cold plate 120 can be a copper plate made of copper, and the heat-conducting columns 140 can be copper columns. For example, four copper columns are fixed to the bottom of the insulation box 110, the cold plate 120 is fixed to the top of the four copper columns, and the electric heating plate 130 is located at the bottom of the cold plate 120. When in use, the cast ice template mold 160 is placed on the cold plate 120, and low-temperature liquid nitrogen 150 (-196 ℃) is injected into the bottom of the insulation box 110 as a cold source. The cold source is transferred to the copper plate through the copper column, and the temperature of the copper plate is adjusted to the required freezing temperature, such as -70 ℃, by heating with the electric heating plate.

[0041] Example 1: The specific ratios provided in this example are as follows: 100 parts of PW-1 52.5 Portland cement Ceramic micropowder: 20 parts of titanium boride micropowder Additive: 0.66 parts of hydroxypropyl methylcellulose Admixture: 1 part of halloysite nanotubes 65 parts water The preparation of the boron-reinforced cement-based radiant cooling composite material comprises the following steps: (1) Mixing silicate cement, titanium boride powder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture; (2) Adding halloysite nanotubes to water and dispersing them using a magnetic stirrer at a speed of 540 r / min for 40 minutes to obtain an admixture dispersion; (3) The admixture dispersion obtained in step (2) is slowly added to the dry mixture obtained in step (1), stirred at a low speed for 60 to 120 seconds in a stirring pot, and then stirred at a high speed for 180 to 210 seconds to obtain a uniform slurry.

[0042] (4) Prepare an ice template mold according to the desired specimen shape, pour the slurry into the ice template mold and place it on a copper plate, freeze-form it at -60°C for 30 minutes, and then demold it to obtain a frozen specimen; (5) Place the frozen specimen in a constant temperature box at 5°C and dry and thaw for 48 hours; (6) The thawed specimens were cured for 5 days to obtain hardened cement-based specimens. The temperature of the standard curing box was 20±1°C and the relative humidity was 95~100%.

[0043] (7) After curing, the hardened cement-based specimens were placed in a forced air drying oven and dried at 60 °C to constant weight.

[0044] (8) The dried and constant-weight hardened cement-based specimens were placed in a muffle furnace for high-temperature treatment, with the temperature rising from room temperature to 750 °C at a heating rate of 10 °C / min. After being kept constant at 750 °C for 2 hours, they were naturally cooled to room temperature to obtain test blocks.

[0045] Example 2: The specific ratios provided in this example are as follows: 100 parts of PW-1 52.5 Portland cement Ceramic micropowder: 20 parts of titanium boride micropowder Additive: 0.66 parts of hydroxypropyl methylcellulose Admixture: 1 part of halloysite nanotubes 65 parts water The preparation of the boron-reinforced cement-based radiant cooling composite material comprises the following steps: (1) Mixing silicate cement, titanium boride powder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture; (2) Adding halloysite nanotubes to water and dispersing them using a magnetic stirrer at a speed of 540 r / min for 40 min to obtain an admixture dispersion; (3) The admixture dispersion obtained in step (2) is slowly added to the dry mixture obtained in step (1), stirred at a low speed for 60 to 120 seconds in a stirring pot, and then stirred at a high speed for 180 to 210 seconds to obtain a uniform slurry.

[0046] (4) Prepare an ice template mold according to the desired specimen shape, pour the slurry into the ice template mold and place it on a copper plate, freeze-form it at -70°C for 30 minutes, and then demold it to obtain a frozen specimen; (5) Place the frozen specimen in a constant temperature box at 5°C and dry and thaw for 48 hours; (6) The thawed specimens were cured for 5 days to obtain hardened cement-based specimens. The temperature of the standard curing box was 20±1°C and the relative humidity was 95~100%.

[0047] (7) After curing, the hardened cement-based specimens were placed in a forced air drying oven and dried at 60 °C to constant weight.

[0048] (8) The dried and constant-weight hardened cement-based specimens were placed in a muffle furnace for high-temperature treatment, with the temperature rising from room temperature to 750 °C at a heating rate of 10 °C / min. After being kept constant at 750 °C for 2 hours, they were naturally cooled to room temperature to obtain test blocks.

[0049] Example 3: The specific ratios provided in this example are as follows: 100 parts of PW-1 52.5 Portland cement Ceramic micropowder: 20 parts of titanium boride micropowder Additive: 0.66 parts of hydroxypropyl methylcellulose Admixture: 1 part of halloysite nanotubes 65 parts water The preparation of the boron-reinforced cement-based radiant cooling composite material comprises the following steps: (1) Mixing silicate cement, titanium boride powder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture; (2) Adding halloysite nanotubes to water and dispersing them using a magnetic stirrer at a speed of 540 r / min for 40 min to obtain an admixture dispersion; (3) The admixture dispersion obtained in step (2) is slowly added to the dry mixture obtained in step (1), stirred at a low speed for 60 to 120 seconds in a stirring pot, and then stirred at a high speed for 180 to 210 seconds to obtain a uniform slurry.

[0050] (4) Prepare an ice template mold according to the desired specimen shape, pour the slurry into the ice template mold and place it on a copper plate, freeze it at -80°C for 30 minutes, and then demold it to obtain a frozen specimen; (5) Place the frozen specimen in a constant temperature box at 5°C and dry and thaw for 48 hours; (6) The thawed specimens were cured for 5 days to obtain hardened cement-based specimens. The temperature of the standard curing box was 20±1°C and the relative humidity was 95~100%.

[0051] (7) After curing, the hardened cement-based specimens were placed in a forced air drying oven and dried at 60 °C to constant weight.

[0052] (8) The dried and constant-weight hardened cement-based specimens were placed in a muffle furnace for high-temperature treatment, with the temperature rising from room temperature to 750 °C at a heating rate of 10 °C / min. After being kept constant at 750 °C for 2 hours, they were naturally cooled to room temperature to obtain test blocks.

[0053] On the basis of Examples 1-3, after the hardened cement-based specimens were dried to constant weight, no high-temperature treatment was performed to form Comparative Examples 1, 2, and 3.

[0054] Comparative Example 4: The specific ratios provided in this example are as follows: 100 parts of PI 42.5 Portland cement Ceramic powder: 60 parts zirconium boride powder Additive: Hydroxypropyl methylcellulose 0.4 parts Admixture: 0.5 parts of halloysite nanotubes 55 parts water The preparation of cement-based materials includes the following steps: (1) Mixing silicate cement, zirconium boride powder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture; (2) Adding halloysite nanotubes to water and dispersing them using a magnetic stirrer at a speed of 540 r / min for 40 minutes to obtain an admixture dispersion; (3) The admixture dispersion obtained in step (2) is slowly added to the dry mixture obtained in step (1), stirred at a low speed for 60 to 120 seconds in a stirring pot, and then stirred at a high speed for 180 to 210 seconds to obtain a uniform slurry.

[0055] (4) Prepare a plastic mold according to the desired specimen shape, pour the slurry into the plastic mold, remove the mold after 1 day, and then place it in a standard curing box for curing to 28 days to obtain a test block.

[0056] Example 4: The specific ratios provided in this example are as follows: 100 parts of PI 42.5 Portland cement Ceramic powder: 60 parts zirconium boride powder Additive: Hydroxypropyl methylcellulose 0.4 parts Admixture: 0.5 parts of halloysite nanotubes 55 parts water The preparation of cement-based materials includes the following steps: (1) Mixing silicate cement, zirconium boride powder and hydroxypropyl methylcellulose uniformly to obtain a dry mixture; (2) Adding halloysite nanotubes to water and dispersing them using a magnetic stirrer at a speed of 540 r / min for 40 minutes to obtain an admixture dispersion; (3) The admixture dispersion obtained in step (2) is slowly added to the dry mixture obtained in step (1), stirred at a low speed for 60 to 120 seconds in a stirring pot, and then stirred at a high speed for 180 to 210 seconds to obtain a uniform slurry.

[0057] (4) Prepare a plastic mold according to the desired specimen shape, pour the slurry into the plastic mold, remove the mold after 1 day, and then place it in a standard curing box for curing to 28 days to obtain a cement specimen.

[0058] (5) After curing, the cement specimens were placed in a forced air drying oven and dried at 60 °C to constant weight.

[0059] (6) The dried and constant-weight hardened cement-based specimens were placed in a muffle furnace for high-temperature treatment, with the temperature rising from room temperature to 900 °C at a heating rate of 10 °C / min. After being kept constant at 900 °C for 2 hours, they were naturally cooled to room temperature to obtain test blocks.

[0060] Performance testing method: (1) The reflectivity of the test piece in the sunlight band of 0.2~2.5 μm was measured using a UV-visible-near infrared spectrophotometer (Lambda1050+). The test piece size was 30 mm×30 mm×3 mm. The average of three groups of measurements was taken. The results are as follows: Figure 5 shown.

[0061] (2) The infrared emissivity of the test piece at 5-7 μm and 8-13 μm was measured using a Fourier transform infrared spectrometer (Thermo) model NICOLETIS20. The test piece size was 30 mm × 30 mm × 3 mm. The average of three groups of measurements was taken.

[0062] (3) The compression test of the 20 mm × 20 mm × 20 mm test block was carried out using the UTM5105X universal testing machine. The measurement parameters were based on the “Test Method for Basic Properties of Building Mortar” (JGJ / T70-2009).

[0063] The relevant performance test results of the embodiments of the present invention are shown in Table 1 and Table 2.

[0064] The appearance of the embodiment of the present invention changes as follows Figure 4 As shown, Figure 5 is the reflectivity map.

[0065] Table 1 Optical performance test results of each group of test blocks

[0066] As can be seen from the average sunlight reflectivity in Table 1, compared with Comparative Examples 1, 2, and 3, respectively, after high temperature treatment, the average sunlight reflectivity of Examples 1, 2, and 3 was significantly improved, and the average emissivity in the long-wave spectrum atmospheric window range of 8 to 13 μm was not significantly affected; in the mid-wave spectrum end atmospheric window range of 5 to 7 μm, after high temperature treatment, the average emissivity in this range decreased, reducing the influence of some atmospheric back radiation, thereby further improving its radiative cooling capacity. Compared with Comparative Example 4, the average sunlight reflectivity of Example 4 was significantly improved after high temperature treatment, and the average emissivity in the two atmospheric windows range of 5 to 7 μm and 8 to 13 μm was not significantly affected. This also indirectly shows that compared with the freeze-molded sample, the cast-molded sample had no significant effect on the average sunlight emissivity in the infrared band, and failed to improve the radiative cooling effect. Therefore, the combination of high temperature treatment and freeze molding can achieve the technical effect of the present invention.

[0067] Figure 4 The following are the actual pictures of the test blocks of Examples 1-4 and Comparative Examples 1-4. Figure 4 As can be seen, the surface color of the test pieces in the examples changes significantly, from dark gray to off-white or yellow. This is because the high temperature creates a new mineral phase, whose physical properties change the appearance of the sample, thereby achieving high reflectivity to sunlight.

[0068] Figure 5 The UV-Vis-NIR reflectance spectra of each test block group are shown. The spectra of the four experimental groups show no absorption peaks near 1.43 μm and 1.95 μm in the near-infrared spectrum. This demonstrates that the method for preparing the cement-based composite material proposed in the present invention virtually eliminates the influence of the absorption peaks near 1.43 μm and 1.95 μm in the near-infrared spectrum of traditional cement-based materials on their solar reflectance. Therefore, the method for preparing the boron-enhanced cement-based radiative cooling composite material proposed in the present invention can improve the radiative cooling capacity of cement-based materials. A comparison of Examples 1, 2, 3, and 4 in Table 1 shows that varying the freeze-molding temperature can improve the sample's solar reflectance. Lower molding temperatures increase the average solar reflectance after firing, and the sample's average reflectance in the 8-13 μm range also gradually increases. Samples cast at room temperature have a lower average solar reflectance before high-temperature exposure. After high-temperature exposure, their average solar reflectance improves, but still significantly lower than the solar reflectance of freeze-cast samples.

[0069] Therefore, it can be seen from Table 1 that when the appropriate freezing molding temperature is selected, the radiation cooling capacity of the cement-based material can be further improved after the high temperature action.

[0070] Table 2 Compressive strength values ​​of test blocks in each group

[0071] As can be seen from the compressive strength test in Table 2, the compressive strength of the test blocks in each embodiment has been improved, which to a certain extent reduces the impact of ice formwork technology on the compressive strength of cement-based materials. As the molding temperature decreases, the pore channels formed by the ice formwork become smaller, and its compressive strength increases to a certain extent. From the comparison of Comparative Examples 1 and 2, it can be seen that the lower the molding temperature, the higher the compressive strength; from Comparative Examples 2 and 3, it can be seen that when the temperature is reduced to a certain level, its compressive strength is actually affected. This is because the ice crystals grow too quickly, which may form irregular crystals. Therefore, choosing the appropriate molding temperature can further improve its compressive strength.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a boron-reinforced cement-based radiant cooling composite material, characterized in that: The following steps are involved: Mixing silicate cement, ceramic micropowder and admixtures uniformly to obtain a dry powder mixture; Mix the admixture and mixing water evenly and then stir evenly with the dry powder mixture to obtain a uniform slurry; The slurry is poured into a mold and then frozen below freezing point to form a test piece after demoulding; Place the frozen specimen in a constant temperature box and dry and thaw at a constant temperature above freezing point; The thawed specimens are cured to obtain hardened cement-based specimens; The hardened cement-based specimens were dried to constant weight; The dried hardened cement-based specimens were subjected to high-temperature treatment at 400-1000°C and then cooled to obtain boron-reinforced cement-based radiant cooling composite materials.

2. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, characterized in that: The ceramic micropowder is any one or more of zirconium boride, vanadium boride, titanium boride, chromium boride, boron carbide, hafnium boride, and tantalum boride.

3. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, characterized in that: According to the mass ratio, add 40 to 80 parts of ceramic micropowder for every 100 parts of Portland cement.

4. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, wherein: The water-to-binder ratio of the obtained slurry is 0.5 to 1.

0.

5. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, characterized in that: The admixture is one or a mixture of micron silicon dioxide, micron titanium dioxide, montmorillonite powder, halloysite nanotubes, and micron alumina.

6. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, characterized in that: The admixture is a viscosity regulator, and its dosage is less than 2.0% of the mass of Portland cement.

7. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, characterized in that: The freeze forming temperature is -100 to -50°C, and the freeze forming is unidirectional freezing, so that the ice crystals in the slurry grow directionally along the temperature gradient direction.

8. The method for preparing the boron-reinforced cement-based radiant cooling composite material according to claim 1, characterized in that: The constant temperature drying and thawing temperature is 2 to 10°C, and the thawing time is 48 to 72 hours.

9. A boron-reinforced cement-based radiant cooling composite material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

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