Low thermal conductivity concrete and method for producing same

Abstract

The application belongs to the technical field of building materials, and relates to low-thermal-conductivity concrete and a preparation method thereof. The application provides a preparation method of low-thermal-conductivity concrete, which comprises the following steps: modifying polypropylene fibers in a tannic acid solution and then modifying the polypropylene fibers in a polydimethylsiloxane solution to obtain modified polypropylene fibers; mixing a foaming agent and water to prepare a foaming solution; uniformly mixing cement, fly ash, the modified polypropylene fibers, an additive and water to obtain a mixture; foaming the foaming solution to generate foam, and then adding the foam into the mixture; and uniformly mixing to obtain the low-thermal-conductivity concrete. The application aims to solve the following technical problem: in the preparation process of foam concrete, although the addition of polypropylene fibers can effectively reduce the thermal conductivity of the foam concrete (to meet the low-thermal-conductivity requirement), the strength of the foam concrete is significantly reduced, and finally the low-thermal-conductivity performance and the high-strength performance of the concrete are difficult to be simultaneously considered.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology and relates to a low thermal conductivity concrete and its preparation method. Background Technology

[0002] Green building has become a core direction for the transformation and upgrading of the construction industry, and it places stringent requirements on the energy efficiency, environmental protection, and structural performance of building materials. Among these, foamed concrete, as a lightweight thermal insulation material, is widely used in the walls and roof insulation layers of green buildings due to its excellent thermal insulation performance, lightweight and high-strength characteristics, and environmental friendliness. The thermal conductivity of foamed concrete is a key indicator for evaluating its insulation performance and directly affects the building's energy consumption level. To reduce the thermal conductivity of foamed concrete, existing technologies often employ methods such as incorporating lightweight aggregates, optimizing the foam pore size distribution, or introducing fiber materials. Polypropylene fibers, due to their low density, strong chemical corrosion resistance, moderate cost, and low thermal conductivity, are widely used in the modification research of foamed concrete. Studies have shown that the incorporation of polypropylene fibers can form a three-dimensional randomized support system in the concrete matrix, which has a certain barrier effect on heat transfer and may reduce the thermal conductivity to some extent; at the same time, the fibers can also inhibit the generation and propagation of internal cracks in concrete, improving its toughness and crack resistance. However, in practical applications, it has been found that the interfacial bonding between polypropylene fibers and the foamed concrete matrix is ​​poor. When the fiber content exceeds a certain proportion, it leads to an increase in the internal porosity of the concrete and an increase in defects in the interfacial transition zone, resulting in a significant decrease in the compressive strength and other mechanical properties of the foamed concrete. To balance the thermal conductivity and mechanical properties of polypropylene fiber-modified foamed concrete, researchers have attempted to improve it by adjusting the fiber content, optimizing the fiber length, or improving the mixing process. For example, controlling the polypropylene fiber content within a small range can reduce the negative impact on strength, but this method limits the reduction in thermal conductivity, making it difficult to meet the requirements of ultra-low thermal conductivity for high-star green buildings. Another example is using surface coating with silane coupling agents to improve the interfacial bonding between the fibers and the matrix, but silane coupling agents have poor hydrolytic stability and are prone to failure in alkaline cementitious matrices, leading to unstable modification effects. In addition, some studies have used steel fibers and glass fibers to replace polypropylene fibers. Although this can improve mechanical properties to some extent, these fibers themselves have high thermal conductivity, which will offset the thermal insulation advantages of foamed concrete and significantly increase costs, hindering large-scale application. Summary of the Invention

[0003] This invention aims to address the technical problem that the incorporation of polypropylene fibers into foamed concrete significantly reduces its compressive strength, making it difficult to simultaneously achieve low thermal conductivity and high strength. To this end, this invention provides a low thermal conductivity concrete and its preparation method to meet this need in the art.

[0004] In the technical solution provided by this invention, the total weight of the cementitious material is the sum of the weight of the concrete and the concrete substitute (fly ash); the amount of concrete substitute is calculated based on the total weight of the cementitious material, and the calculation formula is: amount of concrete substitute = total weight of cementitious material × percentage of substitution; the amount of concrete admixture is calculated based on the total weight of the cementitious material, and the calculation formula is: amount of admixture = total weight of cementitious material × percentage of dosage; the water-cement ratio of concrete is calculated based on the total weight of the cementitious material, and the calculation formula is: water-cement ratio = weight of water / total weight of cementitious material.

[0005] On one hand, the present invention relates to a method for preparing low thermal conductivity concrete, which includes: modifying polypropylene fibers with tannic acid solution and then modifying them with polydimethylsiloxane solution to obtain modified polypropylene fibers.

[0006] A foaming agent and water are mixed to form a foaming liquid; cement, fly ash, the modified polypropylene fiber, additives and water are mixed evenly to obtain a mixture;

[0007] The foaming liquid is foamed to generate foam, which is then added to the mixture and mixed evenly to obtain the final product.

[0008] Furthermore, in the method for preparing low thermal conductivity concrete provided by the present invention, the concentration of the tannic acid solution is 2~5 mg / mL, and the concentration of the polydimethylsiloxane solution is 5~10 mg / mL.

[0009] Furthermore, the method for preparing low thermal conductivity concrete provided by the present invention includes: immersing polypropylene fibers in the tannic acid solution, reacting with shaking at 25~35°C for 12~24h, removing the fibers after the reaction, and washing away the unadsorbed tannic acid molecules with deionized water to complete the tannic acid modification.

[0010] Furthermore, in the preparation method of low thermal conductivity concrete provided by the present invention, the method includes: after polypropylene fibers are modified with tannic acid, they are immersed in the polydimethylsiloxane solution and reacted at 60~80°C for 6~12 hours. After the reaction is completed, the polypropylene fibers are taken out and washed alternately with ethanol and deionized water.

[0011] Furthermore, the method for preparing low thermal conductivity concrete provided by the present invention includes: after modification with polydimethylsiloxane, vacuum drying is performed at 50~60°C for at least 6 hours.

[0012] On the other hand, the present invention relates to a low thermal conductivity concrete, which is prepared by the aforementioned method for preparing low thermal conductivity concrete.

[0013] Furthermore, in the low thermal conductivity concrete provided by the present invention, the admixture is an early-strength agent, a water-reducing agent, and a quick-setting agent.

[0014] Furthermore, in the low thermal conductivity concrete provided by the present invention, the dosage of the early strength agent is 0.1-0.3% by mass percentage, the dosage of the water-reducing agent is 0.1-0.3%, and the dosage of the quick-setting agent is 1-3%.

[0015] Furthermore, in the low thermal conductivity concrete provided by the present invention, the water-cement ratio of the low thermal conductivity concrete is 0.45~0.50.

[0016] Furthermore, in the low thermal conductivity concrete provided by this invention, the replacement amount of fly ash with cement is 4-6% by mass percentage;

[0017] The modified polypropylene fiber content is 0.3~0.5%;

[0018] The amount of the foaming agent used is 0.5-1%.

[0019] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0020] This invention effectively solves the technical challenge of achieving both significant strength reduction and low thermal conductivity in traditional foamed concrete by synergistically modifying polypropylene fibers with tannic acid and polydimethylsiloxane. Tannic acid modification forms a physical adsorption layer on the surface of the polypropylene fibers through its polyphenolic structure, enhancing the fibers' polarity and hydrophilicity and providing active sites for subsequent modification. Polydimethylsiloxane modification introduces a hydrophobic and flexible coating on the surface, improving the interfacial adhesion between the fibers and the concrete matrix, reducing interfacial defects, and thus enhancing overall mechanical properties. The synergistic effect of these two modification steps optimizes fiber dispersion and interfacial bonding in concrete, both blocking heat conduction paths to reduce thermal conductivity and maintaining concrete strength through the fiber's reinforcing effect, ultimately achieving a balance between low thermal conductivity and high strength. The modified polypropylene fibers in concrete not only further reduce thermal conductivity but also significantly increase compressive strength, achieving a synergistic optimization of high strength and low thermal conductivity. In addition, this concrete meets relevant performance indicators in practical applications, has low dry density, high construction efficiency, and reduces cement usage, thus exhibiting good economic and environmental benefits. Detailed Implementation

[0021] The technical solution of the present invention will be described below with reference to embodiments; however, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentage content. Unless otherwise specified, all ratios in the following embodiments refer to mass ratios.

[0022] In the following examples, the cement is ordinary Portland cement with P·O 42.5; the fly ash is Grade II fly ash.

[0023] Example 1

[0024] This embodiment provides a process for preparing foamed concrete.

[0025] Calculated by weight, based on 1000 parts of cementitious material;

[0026] Take 450-500 parts water for a water-cement ratio of 0.45-0.50;

[0027] For a dosage of 0.5-1%, take 5-10 parts of foaming agent (LG-2258 anionic cement foaming agent).

[0028] For a substitution rate of 4-6%, use 940-960 parts of cement (P·O 42.5 ordinary Portland cement) and 40-60 parts of fly ash (Grade II).

[0029] The above is the basic formula: 940-960 parts cement, 40-60 parts fly ash, 5-10 parts foaming agent, and 450-500 parts water, with a total of 1000 parts cementitious materials.

[0030] For the corresponding basic formula, the dosage of early strength agent (triethylamine alcohol liquid early strength agent) is 0.1~0.3%, the dosage of water-reducing agent (polycarboxylate water-reducing agent) is 0.1~0.3%, and the dosage of quick-setting agent (sulfoaluminate cement quick-setting agent) is 1~3%; that is, the amount of admixture is 1~3 parts of early strength agent, 1~3 parts of water-reducing agent, and 10~30 parts of quick-setting agent;

[0031] The corresponding basic formulation uses polypropylene fiber (fiber specifications: 15mm, fiber diameter: 33μm, tensile strength: 530MPa, elastic modulus: 3.5GPa, density: 0.91g / cm³). 3 The dosage of polypropylene fiber (which has extremely low thermal conductivity, strong low-temperature resistance, and extremely high acid and alkali resistance) is 0.3~0.5%; that is, the dosage of polypropylene fiber is 3~5 parts.

[0032] By weight, the formula for conventional foamed concrete is: 940-960 parts cement, 40-60 parts fly ash, 5-10 parts foaming agent, 450-500 parts water, 1-3 parts early strength agent, 1-3 parts water-reducing agent, 10-30 parts quick-setting agent, and 3-5 parts polypropylene fiber.

[0033] The preparation process is as follows, based on parts by weight:

[0034] Step 1: Mix 5-10 parts of foaming agent with 100-150 parts of water and dilute to prepare foaming liquid;

[0035] Step 2: Mix 940-960 parts of cement, 40-60 parts of fly ash, 1-3 parts of early strength agent, 1-3 parts of water-reducing agent, 10-30 parts of quick-setting agent, 3-5 parts of polypropylene fiber and the remaining water to obtain a mixture.

[0036] Step 3: The foaming liquid is foamed in a foaming machine and then added to the mixture. After stirring evenly, foamed concrete is obtained.

[0037] Based on the above experimental scheme, the optimal water-cement ratio was determined to be 0.45 through orthogonal experiments; the optimal admixture dosage was 0.3% water-reducing agent, 1% quick-setting agent, and 0.2% early-strength agent; and the optimal foaming agent dosage was 0.8%.

[0038] Example 2

[0039] This embodiment provides a process for preparing modified polypropylene fibers.

[0040] Step 1, Pretreatment to remove spinning oil and contaminants from the fiber surface: Immerse the polypropylene fiber in anhydrous ethanol at 60°C and sonicate for 30 minutes; after removal, rinse with plenty of deionized water until the rinsing solution is clear; place the washed fiber in a vacuum drying oven at 60°C until completely dry.

[0041] Step 2, prepare the modified solution: Prepare a tannic acid solution with a concentration of 2 mg / mL using Tris-HCl buffer (pH=8.5); weigh a certain amount of polydimethylsiloxane (NH2-PDMS) and dissolve it in an ethanol / water mixed solvent (volume ratio 1:1) to prepare a polydimethylsiloxane solution with a concentration of 5 mg / mL.

[0042] Step 3, sequential soaking modification: The pretreated polypropylene fiber is completely immersed in tannic acid solution. The container is placed in a constant temperature water bath shaker and reacted at 25°C with low-speed shaking (50 rpm) for 12 hours to ensure that the fiber is fully wetted. After the reaction, the fiber is removed and gently rinsed with deionized water to wash away the unadsorbed tannic acid, thus completing the tannic acid modification. The tannic acid-modified fiber is immediately immersed in the prepared polydimethylsiloxane solution and placed in a constant temperature water bath shaker. It is reacted at 60°C for 6 hours. After the reaction, the polypropylene fiber is removed and washed three times alternately with ethanol and deionized water to remove unreacted PDMS monomers and physical adsorbates.

[0043] Step 4, Post-treatment and drying: Place the soaked and modified fibers into a vacuum drying oven and dry at 50°C for 6 hours to obtain modified polypropylene fibers; pay attention to the drying temperature to prevent fiber shrinkage or deformation.

[0044] Example 3

[0045] This embodiment provides a process for preparing modified polypropylene fibers.

[0046] Step 1, Pretreatment to remove spinning oil and contaminants from the fiber surface: Immerse the polypropylene fiber in anhydrous ethanol at 60°C and sonicate for 30 minutes; after removal, rinse with plenty of deionized water until the rinsing solution is clear; place the washed fiber in a vacuum drying oven at 60°C until completely dry.

[0047] Step 2, prepare the modified solution: Prepare a tannic acid solution with a concentration of 3.5 mg / mL using Tris-HCl buffer (pH=8.5); weigh a certain amount of polydimethylsiloxane (NH2-PDMS) and dissolve it in an ethanol / water mixed solvent (volume ratio 1:1) to prepare a polydimethylsiloxane solution with a concentration of 7.5 mg / mL.

[0048] Step 3, sequential soaking modification: The pretreated polypropylene fiber is completely immersed in tannic acid solution. The container is placed in a constant temperature water bath shaker and reacted at 30°C with low-speed shaking (50 rpm) for 18 hours to ensure that the fiber is fully wetted. After the reaction, the fiber is removed and gently rinsed with deionized water to wash away the unadsorbed tannic acid, thus completing the tannic acid modification. The tannic acid-modified fiber is immediately immersed in the prepared polydimethylsiloxane solution and placed in a constant temperature water bath shaker. It is reacted at 70°C for 9 hours. After the reaction, the polypropylene fiber is removed and washed three times alternately with ethanol and deionized water to remove unreacted PDMS monomers and physical adsorbates.

[0049] Step 4, Post-treatment and drying: Place the soaked and modified fibers into a vacuum drying oven and dry at 55°C for 6 hours to obtain modified polypropylene fibers.

[0050] Example 4

[0051] This embodiment provides a process for preparing modified polypropylene fibers.

[0052] Step 1, Pretreatment to remove spinning oil and contaminants from the fiber surface: Immerse the polypropylene fiber in anhydrous ethanol at 60°C and sonicate for 30 minutes; after removal, rinse with plenty of deionized water until the rinsing solution is clear; place the washed fiber in a vacuum drying oven at 60°C until completely dry.

[0053] Step 2, prepare the modified solution: Prepare a tannic acid solution with a concentration of 5 mg / mL using Tris-HCl buffer (pH=8.5); weigh a certain amount of polydimethylsiloxane (NH2-PDMS) and dissolve it in an ethanol / water mixed solvent (volume ratio 1:1) to prepare a polydimethylsiloxane solution with a concentration of 10 mg / mL.

[0054] Step 3, sequential soaking modification: The pretreated polypropylene fiber is completely immersed in tannic acid solution. The container is placed in a constant temperature water bath shaker and reacted at 35°C with low-speed shaking (50 rpm) for 24 hours to ensure that the fiber is fully wetted. After the reaction, the fiber is removed and gently rinsed with deionized water to wash away the unadsorbed tannic acid, thus completing the tannic acid modification. The tannic acid-modified fiber is immediately immersed in the prepared polydimethylsiloxane solution and placed in a constant temperature water bath shaker. It is reacted at 80°C for 12 hours. After the reaction, the polypropylene fiber is removed and washed three times alternately with ethanol and deionized water to remove unreacted PDMS monomers and physical adsorbates.

[0055] Step 4, Post-treatment and drying: Place the soaked and modified fibers into a vacuum drying oven and dry at 60°C for 6 hours to obtain modified polypropylene fibers.

[0056] Example 5

[0057] This embodiment provides a process for preparing modified polypropylene fibers.

[0058] Step 1, Pretreatment to remove spinning oil and contaminants from the fiber surface: Immerse the polypropylene fiber in anhydrous ethanol at 60°C and sonicate for 30 minutes; after removal, rinse with plenty of deionized water until the rinsing solution is clear; place the washed fiber in a vacuum drying oven at 60°C until completely dry.

[0059] Step 2, prepare the modified solution: Prepare a tannic acid solution with a concentration of 3.5 mg / mL using Tris-HCl buffer (pH=8.5).

[0060] Step 3, sequential soaking modification: The pretreated polypropylene fiber is completely immersed in the tannic acid solution. The container is placed in a constant temperature water bath shaker and reacted at a low speed (50 rpm) at 30°C for 18 hours to ensure that the fiber is fully wetted. After the reaction is completed, the fiber is removed and gently rinsed with deionized water to wash away the unadsorbed tannic acid, thus completing the tannic acid modification.

[0061] Step 4, Post-treatment and drying: Place the soaked and modified fibers into a vacuum drying oven and dry at 55°C for 6 hours to obtain modified polypropylene fibers.

[0062] Example 6

[0063] This embodiment provides a process for preparing modified polypropylene fibers.

[0064] Step 1, Pretreatment to remove spinning oil and contaminants from the fiber surface: Immerse the polypropylene fiber in anhydrous ethanol at 60°C and sonicate for 30 minutes; after removal, rinse with plenty of deionized water until the rinsing solution is clear; place the washed fiber in a vacuum drying oven at 60°C until completely dry.

[0065] Step 2, prepare the modified solution: Weigh a certain amount of polydimethylsiloxane (NH2-PDMS) and dissolve it in an ethanol / water mixed solvent (volume ratio 1:1) to prepare a polydimethylsiloxane solution with a concentration of 7.5 mg / mL.

[0066] Step 3, sequential soaking modification: Immerse the pretreated polypropylene fiber in the prepared polydimethylsiloxane solution and place it in a constant temperature water bath shaker. React at 70°C for 9 hours. After the reaction is complete, take out the polypropylene fiber and wash it three times alternately with ethanol and deionized water to remove unreacted PDMS monomers and physical adsorbents.

[0067] Step 4, Post-treatment and drying: Place the soaked and modified fibers into a vacuum drying oven and dry at 55°C for 6 hours to obtain modified polypropylene fibers.

[0068] Example 7

[0069] This embodiment provides the performance of foamed concrete prepared with different formulations.

[0070] By weight, the formula for conventional foamed concrete 0 is: 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 0 parts polypropylene fiber.

[0071] By weight, the formula for conventional foamed concrete 1 is: 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 3 parts polypropylene fiber.

[0072] By weight, the formula for conventional foamed concrete 2 is as follows: 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 4 parts polypropylene fiber.

[0073] By weight, the formula for conventional foamed concrete is as follows: 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 5 parts polypropylene fiber.

[0074] The modified foamed concrete 1 formula, by weight, consists of 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 3 parts modified polypropylene fiber prepared in Example 2.

[0075] The modified foamed concrete 2 formula, by weight, consists of 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 4 parts modified polypropylene fiber prepared in Example 3.

[0076] The modified foamed concrete formula 3, by weight, consists of 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 5 parts modified polypropylene fiber prepared in Example 4.

[0077] The modified foamed concrete formula 4, by weight, consists of 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 5 parts modified polypropylene fiber prepared in Example 5.

[0078] The modified foamed concrete 5 formula, by weight, consists of 950 parts cement, 50 parts fly ash, 8 parts foaming agent, 450 parts water, 2 parts early strength agent, 3 parts water-reducing agent, 10 parts quick-setting agent, and 5 parts modified polypropylene fiber prepared in Example 6.

[0079] Following the preparation method of Example 1, conventional foamed concrete 1-3 and modified foamed concrete 1-5 were prepared. After conventional curing for 28 days, the 28-day compressive strength was measured according to "JG / T 266-2011 Foamed Concrete", and the thermal conductivity was measured according to "GB / T 1024-2008 Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method". The test results are shown in Table 1.

[0080] Table 1 28d compressive strength and thermal conductivity

[0081]

[0082] Table 1 shows that as the amount of conventional polypropylene fiber increased from 0 to 5 parts, the thermal conductivity of the foamed concrete decreased slightly from 0.1221 W / (m·K) to 0.1144 W / (m·K) (a decrease of 6.3%), but the 28-day compressive strength plummeted from 3.0 MPa to 1.1 MPa (a loss of 63.3%), confirming that the incorporation of polypropylene fiber reduces the thermal conductivity of foamed concrete while also negatively impacting its strength. This application uses tannic acid and polydimethylsiloxane for synergistic modification. The 28-day compressive strength of modified foamed concrete 1-3 increased by 40.0%-53.3% compared to the fiber-free reference sample, while the thermal conductivity decreased to 0.0938-0.0971 W / (m·K), achieving a synergistic optimization of high strength and low thermal conductivity. The single-step modification schemes, with only tannic acid modification achieving the same strength as the benchmark sample and limited reduction in thermal conductivity, and only polydimethylsiloxane modification resulting in lower strength and insignificant improvement in thermal conductivity, fail to achieve the synergistic effect of the two-step modification.

[0083] Based on the optimized formula, modified foamed concrete 2 was used to complete the sample construction of Building 17. The implementation effect was checked according to the set objectives. According to the technical specification for foamed concrete application (JGJ / T 341-2014), areas that had been poured for 72 hours were selected. Three cylindrical core samples with a diameter of 100mm were drilled, penetrating a 50mm thick foamed concrete layer. These core samples were numbered S-01 to S-03, sealed, and sent to the laboratory for testing. The test results are shown in Table 2.

[0084] Table 2 Application Test Results

[0085]

[0086] As shown in Table 2, the tested items of the foamed concrete meet the performance index requirements. After the modified lightweight high-strength foamed concrete was implemented in the project, it significantly improved the construction efficiency of the workers, significantly improved the strength of the roof foamed concrete, and reduced the amount of cement used.

[0087] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing low thermal conductivity concrete, characterized in that, include: Polypropylene fibers are immersed in a tannic acid solution and reacted with shaking at 25-35°C for 12-24 hours. After the reaction, the fibers are removed and washed with deionized water to remove unadsorbed tannic acid molecules, thus completing the tannic acid modification. After tannic acid modification, the polypropylene fibers are then immersed in a polydimethylsiloxane solution and reacted at 60-80°C for 6-12 hours. After the reaction, the polypropylene fibers are removed and washed alternately with ethanol and deionized water. After polydimethylsiloxane modification, the fibers are vacuum dried at 50-60°C for at least 6 hours to obtain modified polypropylene fibers. A foaming agent and water are mixed to prepare a foaming liquid. Cement, fly ash, the modified polypropylene fibers, additives, and water are mixed evenly to obtain a mixture. The foaming liquid is foamed to generate foam, which is then added to the mixture and mixed evenly to obtain the final product. The concentration of the tannic acid solution is 2~5 mg / mL, and the polydimethylsiloxane solution is 5~10 mg / mL of NH2-PDMS solution.

2. A low thermal conductivity concrete, characterized in that, The low thermal conductivity concrete was prepared using the method described in claim 1.

3. The low thermal conductivity concrete according to claim 2, characterized in that, The admixtures are early strength agents, water-reducing agents, and quick-setting agents.

4. The low thermal conductivity concrete according to claim 3, characterized in that, By mass percentage, the dosage of early strength agent is 0.1-0.3%, the dosage of water-reducing agent is 0.1-0.3%, and the dosage of quick-setting agent is 1-3%.

5. The low thermal conductivity concrete according to claim 2, characterized in that, The water-cement ratio of the low thermal conductivity concrete is 0.45~0.

50.

6. The low thermal conductivity concrete according to claim 2, characterized in that, The amount of fly ash replacing cement is 4-6% by mass percentage; the amount of modified polypropylene fiber is 0.3-0.5%; and the amount of foaming agent is 0.5-1%.

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