Ardealite artificial sand, preparation method thereof and application of ardealite artificial sand in lightweight low-shrinkage ultra-high performance concrete

Abstract

The invention discloses ardealite artificial sand, a preparation method of the ardealite artificial sand and application of the ardealite artificial sand in light low-shrinkage ultra-high performance concrete. The ardealite artificial sand is prepared from, by weight, 45-60 parts of carbide slag modified ardealite, 25-35 parts of slag powder, 8-12 parts of cement, 2.5-3.5 parts of lithium slag and 1.5-2.5 parts of hydrophobic powder, the water-binder ratio is 0.21-0.25, and the hydrophobic powder is obtained by modifying thermal activated metakaolin through a silane coupling agent. The preparation method comprises four steps of dry mixing, wet mixing, granulation and maintenance. The ardealite artificial sand has good physical properties. The invention also discloses lightweight low-shrinkage ultra-high performance concrete using the ardealite artificial sand and a preparation method thereof. The concrete is composed of cement, silica fume, slag powder, the ardealite artificial sand, river sand, carbon fibers, a polycarboxylate superplasticizer and water. According to the invention, high-valued utilization of ardealite resources is realized, and the prepared artificial sand can replace natural sand to be used for high-performance concrete production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building materials, in particular to a kind of phosphogypsum artificial sand prepared by industrial solid waste and its application in light low shrinkage ultra-high performance concrete. BACKGROUND

[0002] With the development of building industry, ultra-high performance concrete is widely used in engineering field due to its excellent mechanical properties and durability. However, traditional ultra-high performance concrete has problems such as high self-weight, high shrinkage rate and large resource consumption, which limits its application in large-scale engineering. At the same time, the treatment and resource utilization of industrial solid waste such as phosphogypsum and calcium carbide slag are also current environmental problems to be solved.

[0003] Phosphogypsum, as the main solid waste produced in the process of phosphate fertilizer production, has a huge annual output, but the comprehensive utilization rate is low. Currently, phosphogypsum is mainly used in the fields of cement retarder, building gypsum, gypsum board and other fields, but the application research in the field of high-performance concrete is relatively less. CN114890762B discloses a composite admixture for improving the durability of shotcrete, which contains 10% to 20% modified phosphogypsum. The modified phosphogypsum is prepared by mixing raw phosphogypsum with sodium silicate at a mass ratio of 9:1, then baking at a temperature of 400°C to 500°C for 20 to 26 hours, and then mixing with calcium hydroxide at a mass ratio of 9:1 to grind into a powder with a specific surface area of 350 to 450 m² / kg. Although this technology improves the durability of concrete, the preparation process is complex, the energy consumption is high, and the problem of high self-weight of concrete is not solved.

[0004] In the field of phosphogypsum lightweight materials, CN108706944B discloses a kind of phosphogypsum lightweight board prepared by barium slag, which has a bulk density in the range of 600-1000 Kg / m³, a thermal conductivity coefficient less than 0.15 W / (m·K), and no obvious delamination cracking. This technology is mainly aimed at board application and does not involve the field of concrete, and the stability problem of phosphogypsum in concrete is not solved.

[0005] To improve the engineering application performance of phosphogypsum, CN114230301A provides a kind of phosphogypsum hardening agent, which includes phosphogypsum, modifier, active mineral admixture, cement, metakaolin and other components, which can effectively enhance the early strength of phosphogypsum and reduce the initial setting and final setting time of hardened phosphogypsum. However, this technology mainly aims at improving the performance of phosphogypsum itself and does not solve the application problem of phosphogypsum in concrete, especially the shrinkage problem of ultra-high performance concrete.

[0006] CN109574614B discloses a method for preparing concrete by using quartz stone mud modified phosphogypsum based cementitious material, in which the phosphogypsum content can reach 80%, greatly improving the comprehensive utilization rate of industrial solid waste. However, this technology does not solve the problem of lightweight of concrete, and is not designed for the special needs of ultra-high performance concrete.

[0007] In terms of lightweight concrete, CN116041026A provides a phosphogypsum lightweight aggregate concrete, which includes phosphogypsum cement, phosphogypsum lightweight aggregate and machine-made sand. Although this technology realizes the lightweight of concrete, it does not optimize the high strength, low shrinkage and other characteristics of ultra-high performance concrete, and does not solve the problem of easy corrosion of steel fiber in the phosphogypsum environment.

[0008] In summary, the existing ultra-high performance concrete in the prior art has the following problems: 1) heavy weight, not suitable for large-scale engineering applications; 2) high shrinkage rate, prone to cracking risk; 3) high consumption of natural resources, not environmentally friendly; 4) steel fiber is prone to corrosion in the phosphogypsum environment. At the same time, the existing phosphogypsum resource utilization technology has not effectively solved the problem of application of phosphogypsum in ultra-high performance concrete, especially how to use phosphogypsum to prepare lightweight, low shrinkage ultra-high performance concrete, and how to solve the stability problem of fiber reinforced materials in the phosphogypsum environment. Therefore, it is of great engineering application value and environmental protection significance to develop a lightweight low shrinkage ultra-high performance concrete prepared from phosphogypsum. SUMMARY

[0009] In order to solve the technical problems of existing ultra-high performance concrete, such as heavy weight, high shrinkage rate, high resource consumption and easy corrosion of steel fiber in the phosphogypsum environment, and to achieve the technical effects of lightweight, low shrinkage, high strength, environmental protection and durability, the present application provides a phosphogypsum artificial sand and a lightweight low shrinkage ultra-high performance concrete based on the phosphogypsum artificial sand and a preparation method thereof.

[0010] The present application is achieved by the following technical solutions: In a first aspect, the present application provides a phosphogypsum artificial sand, the preparation raw materials of which include the following components by weight: modified phosphogypsum from carbide slag 45-60 parts, slag powder 25-35 parts, cement 8-12 parts, lithium slag 2.5-3.5 parts, and hydrophobic powder 1.5-2.5 parts, wherein the hydrophobic powder is obtained by modifying the heat-activated metakaolin with a silane coupling agent; and the water-binder ratio is 0.21-0.25.

[0011] Preferably, the particle size of the phosphogypsum artificial sand is 2.36-0.075mm, the cylinder compressive strength is ≥8.9MPa, the bulk density is 1050-1100kg / m 3 , and the apparent density is 2150-2300kg / m 3Saturation surface dry water absorption 7.1-7.9%. Preferably, the modified phosphogypsum with carbide slag has less than 25% attached water and more than 80% calcium sulfate dihydrate. The modified phosphogypsum is obtained by adding carbide slag to phosphogypsum, uniformly mixing and crushing, and then aging.

[0012] Preferably, the preparation method of the hydrophobic powder comprises the following steps: (1) placing metakaolin in a crucible and heating at 105-115℃ for 45-50h to completely dry the metakaolin; (2) placing the dried metakaolin in a negative pressure screening machine to obtain metakaolin powder with a diameter less than 80μm; (3) mixing the metakaolin powder with polydimethylsiloxane and γ-aminopropyltriethoxysilane at a mass ratio of 1:0.01-0.02:0.01-0.02, and modifying at 115-125℃ for 30min to obtain the hydrophobic powder.

[0013] The hydrophobic powder prepared by this method has excellent hydrophobicity and stability: PDMS provides long-chain alkyl groups to form a low-surface-energy layer, and the amino functional groups of APTES can be firmly bonded to the surface of metakaolin and enhance the compatibility with PDMS, and the two work together to give the powder persistent and stable hydrophobicity.

[0014] Precise particle size control and good dispersibility: the particle size of the raw material powder is accurately controlled to be less than 80μm by pre-screening under negative pressure, ensuring the uniformity and completeness of the subsequent modification reaction, and the final hydrophobic powder has fine particles, concentrated distribution, excellent flowability and dispersibility, and is easy to uniformly disperse and composite in subsequent applications.

[0015] High-efficiency and reliable process: the long-time low-temperature drying (105-115℃, 45-50h) in step (1) completely removes water, avoiding possible water vapor interference during subsequent high-temperature modification, and ensuring the modification effect. The entire process steps are clear, the parameter (temperature, time, ratio) range is reasonably set, and the operation is strong, easy to implement in industrialization, and the modification time is short (30 minutes), and the efficiency is high.

[0016] Full utilization of raw materials and significant performance improvement: this method uses resource-rich metakaolin as the basic raw material, and through fine pretreatment (drying, screening) and efficient surface modification, the added value and functionality of metakaolin are significantly improved, making it suitable for composite materials and other fields that require hydrophobicity, moisture resistance, and enhanced interfacial properties.

[0017] In a second aspect, the present application provides a preparation method of the phosphogypsum artificial sand, comprising the following steps: (a) stirring: mixing all solid components for 3-5min to uniformity; adding water and stirring for 5-8min to form a slurry; (b) forming: pouring the slurry into a mold and hardening to form; (c) crushing: crushing and sieving the shaped artificial stone into a desired particle size.

[0018] Preferably, the water binder ratio in step (a) is 0.21-0.25.

[0019] In a third aspect, the present application provides the application of the phosphogypsum artificial sand in the preparation of light low-shrinkage ultra-high performance concrete.

[0020] In a fourth aspect, the present application provides a light low-shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, which comprises 780-900 kg of cement, 130-175 kg of silica fume, 100-170 kg of slag powder, 600-800 kg of phosphogypsum artificial sand, 150-450 kg of river sand, 900-1050 kg of total aggregate, 10-12 kg of carbon fiber, 20-28 kg of polycarboxylate superplasticizer, and 182-216 kg of water per cubic meter.

[0021] In a fifth aspect, the present application provides a preparation method of the light low-shrinkage ultra-high performance concrete, comprising the following steps: (1) mixing and stirring the phosphogypsum artificial sand, cement, silica fume, slag powder, and river sand for 2-3 min; (2) adding the polycarboxylate superplasticizer and water to the mixture of step (1) and stirring for 5-7 min; (3) adding the carbon fiber and mixing uniformly to obtain a concrete mixture; (4) pouring and shaping, and then standard curing for 28 days to obtain the finished product.

[0022] Preferably, the amount of river sand added in step (1) needs to meet the requirement that the total mass of the phosphogypsum artificial sand and the river sand is in the range of 900-1050 kg / m³.

[0023] The present application has the following beneficial effects: 1. Significant lightness effect: the apparent density of the phosphogypsum artificial sand is only 2150-2300 kg / m³, which is significantly lower than that of ordinary sand; the apparent density of the ultra-high performance concrete prepared based on the phosphogypsum artificial sand is 2270-2356 kg / m³, which is significantly lower than that of ordinary ultra-high performance concrete, effectively reducing the self-weight of the concrete structure and expanding the application range of the ultra-high performance concrete in large-scale engineering. 3

[0024] 2. Excellent low-shrinkage performance: the phosphogypsum artificial sand is slightly expanded under alkaline conditions, which can compensate for the shrinkage caused by the hydration of cementitious materials; at the same time, the phosphogypsum artificial sand contains a large number of capillary pores, which can slowly release internal water, so that the concrete can be fully internally cured, greatly reducing the autogenous shrinkage (less than 633 µɛ) and the drying shrinkage (less than 220 µɛ), and effectively solving the problem of easy cracking of traditional ultra-high performance concrete. ​

[0025] 3. Maintaining high strength performance: Despite the use of lightweight materials, the concrete of the present application can reach a 28d compressive strength level of C100 or above, with good workability and high flexural strength, meeting the strength requirements of ultra-high performance concrete.

[0026] 4. Significant environmental benefits: By utilizing industrial solid wastes such as phosphogypsum, slag powder, and silica fume, the consumption of natural resources is reduced, and the utilization rate of solid waste resources is improved, effectively contributing to the goal of zero discharge of industrial solid waste and carbon neutralization.

[0027] 5. Improved durability: The use of carbon fiber instead of steel fiber solves the problem of steel fiber corrosion caused by phosphogypsum environment, and a low dosage of carbon fiber can enhance the tensile properties of UHPC, effectively reducing the risk of UHPC cracking and prolonging the service life of concrete structures. Specific embodiments The technical solutions of the present application will be further illustrated by specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0029] The process, conditions, reagents, experimental methods, etc. for implementing the present application, except for the following specifically mentioned contents, are the general knowledge and common sense in the art, and the present application has no special limitations. The experimental methods not specified in the specific conditions in each embodiment are usually carried out according to the conventional conditions or according to the conditions recommended by the manufacturer.

[0030] Unless otherwise stated, the meanings of all professional terms and scientific terms used in this specification are the same as those generally understood by the skilled person in the technical field to which the present application belongs. However, if there is a conflict, the present specification including the definition shall prevail.

[0031] Example 1 A phosphogypsum artificial sand is made from the following components by weight: modified phosphogypsum from carbide slag 50 parts, slag powder 30 parts, cement 10 parts, lithium slag 3 parts, hydrophobic powder 2 parts, the hydrophobic powder is obtained by modifying the heat-activated metakaolin with a silane coupling agent.

[0032] The hydrophobic powder is prepared by the following steps: (1) Put the metakaolin into a crucible and heat it at 110℃ for 48h to completely dry it; (2) Put the dried metakaolin into a negative pressure screening machine and take the metakaolin powder with a diameter less than 80μm; (3) Mix the metakaolin powder with polydimethylsiloxane and γ-aminopropyltriethoxysilane at a mass ratio of 1:0.015:0.015, modify at 120℃ for 30min to obtain the hydrophobic powder.

[0033] The modified phosphogypsum of carbide slag has 20% attached water and 85% calcium sulfate dihydrate content.

[0034] The preparation method of the phosphogypsum artificial sand comprises the following steps: (a) stirring: mixing 50 parts of modified phosphogypsum of carbide slag, 30 parts of slag powder, 10 parts of cement, 3 parts of lithium slag and 2 parts of hydrophobic powder for 4 min until uniform; (b) adding water and stirring for 6 min to form a slurry; (b) molding: pouring the slurry into a mold and hardening to form a molded product; (c) crushing: crushing and sieving the molded product into a desired particle size.

[0035] Example 2 A phosphogypsum artificial sand is prepared from the following components by weight parts: 45 parts of modified phosphogypsum of carbide slag, 35 parts of slag powder, 12 parts of cement, 3.5 parts of lithium slag and 2.5 parts of hydrophobic powder, wherein the hydrophobic powder is obtained by modifying heat-activated metakaolin with a silane coupling agent.

[0036] The hydrophobic powder is prepared by the following steps: (1) Put the metakaolin into a crucible and heat it at 105°C for 50 h to completely dry it; (2) Put the dried metakaolin into a negative pressure screening machine to obtain metakaolin powder with a diameter less than 80 μm; (3) Mix the metakaolin powder with polydimethylsiloxane and γ-aminopropyltriethoxysilane at a mass ratio of 1:0.02:0.02, and modify it at 115°C for 30 min to obtain the hydrophobic powder.

[0037] The modified phosphogypsum of carbide slag has 25% attached water and 80% calcium sulfate dihydrate content.

[0038] The preparation method of the phosphogypsum artificial sand comprises the following steps: (a) stirring: mixing 45 parts of modified phosphogypsum of carbide slag, 35 parts of slag powder, 12 parts of cement, 3.5 parts of lithium slag and 2.5 parts of hydrophobic powder for 3 min until uniform; (b) adding water and stirring for 5 min to form a slurry; (b) molding: pouring the slurry into a mold and hardening to form a molded product; (c) crushing: crushing and sieving the molded product into a desired particle size.

[0039] Example 3 A phosphogypsum artificial sand is prepared from the following components by weight parts: 60 parts of modified phosphogypsum of carbide slag, 25 parts of slag powder, 8 parts of cement, 2.5 parts of lithium slag and 1.5 parts of hydrophobic powder, wherein the hydrophobic powder is obtained by modifying heat-activated metakaolin with a silane coupling agent.

[0040] The hydrophobic powder is prepared by the following steps: (1) Put the metakaolin into a crucible and heat it at 115℃ for 45h to completely dry it; (2) Put the dried metakaolin into a negative pressure screening machine to take metakaolin powder with a diameter less than 80μm; (3) Mix the metakaolin powder with polydimethylsiloxane and γ-aminopropyltriethoxysilane at a mass ratio of 1:0.01:0.01, modify it at 125℃ for 30min, and obtain the hydrophobic powder.

[0041] The modified phosphogypsum with carbide slag has an attached water of 15% and a calcium sulfate dihydrate content of 90%.

[0042] The preparation method of the phosphogypsum artificial sand comprises the following steps: (a) Stirring: mix 60 parts of the modified phosphogypsum with carbide slag, 25 parts of slag powder, 8 parts of cement, 2.5 parts of lithium slag, and 1.5 parts of hydrophobic powder for 5min until uniform; (b) Water stirring for 8min to form a slurry; (b) Molding: pour the slurry into a mold and harden to form a molding; (c) Breaking: break and screen the molding into a desired particle size.

[0043] Comparative Example 1 The difference between this comparative example and Example 1 is that no hydrophobic powder is added (the rest is the same as the phosphogypsum artificial sand of Example 1).

[0044] The performance of the phosphogypsum artificial sand prepared in Examples 1-3 and Comparative Examples 1-2 is detected according to the standards “Lightweight Aggregate and Test Methods for Lightweight Aggregate – Part 2: Test Methods for Lightweight Aggregate” GB / T 17431.2-2010 and “Sand for Construction” GB / T 14684-2022, and the results are shown in Table 1.

[0045] Table 1 Physical properties of phosphogypsum artificial sand of Examples 1-3

[0046] The above results of the examples show that the particle size of the phosphogypsum artificial sand is 2.36-0.075mm, the cylinder compressive strength is ≥8.9MPa, the bulk density is 1050-1100kg / m 3 , the apparent density is 2150-2300kg / m 3 , and the saturated surface dry water absorption is 7.1-7.9%. The apparent density, compressive strength, and saturated surface dry water absorption of the phosphogypsum artificial sand are significantly improved. Compared with Examples 1-3, Comparative Example 1 shows that the modification of the hydrophobic powder has a significant effect on the performance of the phosphogypsum artificial sand, especially the saturated surface dry water absorption.

[0047] Example 4 A lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, each cubic meter of concrete comprising the following components: cement 780 kg, silica fume 130 kg, slag powder 100 kg, phosphogypsum artificial sand 600 kg, river sand 450 kg, carbon fiber 10 kg, polycarboxylate superplasticizer 20 kg, water 182 kg; wherein the total amount of aggregate is 1050 kg, and the aggregate is composed of phosphogypsum artificial sand and river sand.

[0048] The preparation method of the lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand comprises the following steps: (1) Mix and stir phosphogypsum artificial sand 600 kg, cement 780 kg, silica fume 130 kg, slag powder 100 kg, and river sand 450 kg for 2 min; (2) Add polycarboxylate superplasticizer 20 kg and water 182 kg to the mixture of step (2) and stir for 5 min; (3) Add carbon fiber 10 kg and mix evenly to obtain a concrete mixture; (4) After casting and forming, standard curing for 28 days to obtain the finished product.

[0049] Example 5 A lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, each cubic meter of concrete comprising the following components: cement 900 kg, silica fume 150 kg, slag powder 130 kg, phosphogypsum artificial sand 700 kg, river sand 200 kg, carbon fiber 11 kg, polycarboxylate superplasticizer 24 kg, water 212 kg; wherein the total amount of aggregate is 900 kg, and the aggregate is composed of phosphogypsum artificial sand and river sand.

[0050] The preparation method of the lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand comprises the following steps: (1) Mix and stir phosphogypsum artificial sand 700 kg, cement 900 kg, silica fume 150 kg, slag powder 130 kg, and river sand 200 kg for 3 min; (2) Add polycarboxylate superplasticizer 24 kg and water 212 kg to the mixture of step (1) and stir for 7 min; (3) Add carbon fiber 11 kg and mix evenly to obtain a concrete mixture; (4) After casting and forming, standard curing for 28 days to obtain the finished product.

[0051] Example 6 A lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, each cubic meter of concrete comprising the following components: cement 805 kg, silica fume 175 kg, slag powder 170 kg, phosphogypsum artificial sand of Example Two 800 kg, river sand 150 kg, carbon fiber 12 kg, polycarboxylate superplasticizer 28 kg, water 216 kg; wherein the total amount of aggregate is 950 kg, and the aggregate is composed of phosphogypsum artificial sand and river sand.

[0052] A method for preparing a lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, comprising the following steps: (1) mixing and stirring phosphogypsum artificial sand 800 kg, cement 805 kg, silica fume 175 kg, slag powder 170 kg, and river sand 150 kg for 2.5 min; (2) adding polycarboxylate superplasticizer 28 kg and water 216 kg to the mixture of step (1) and stirring for 6 min; (3) adding carbon fiber 12 kg and mixing uniformly to obtain a concrete mixture; (4) pouring and forming, and then standard curing for 28 days to obtain a finished product.

[0053] Example 7 A lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, each cubic meter of concrete comprising the following components: cement 820 kg, silica fume 140 kg, slag powder 140 kg, phosphogypsum artificial sand of Example Three 650 kg, river sand 350 kg, carbon fiber 10.5 kg, polycarboxylate superplasticizer 22 kg, water 198 kg; wherein the total amount of aggregate is 1000 kg, and the aggregate is composed of phosphogypsum artificial sand and river sand.

[0054] A method for preparing a lightweight low shrinkage ultra-high performance concrete based on phosphogypsum artificial sand, comprising the following steps: (1) mixing and stirring phosphogypsum artificial sand 650 kg, cement 820 kg, silica fume 140 kg, slag powder 140 kg, and river sand 350 kg for 2.5 min; (2) adding polycarboxylate superplasticizer 22 kg and water 198 kg to the mixture of step (1) and stirring for 6 min; (3) adding carbon fiber 10.5 kg and mixing uniformly to obtain a concrete mixture; (4) pouring and forming, and then standard curing for 28 days to obtain a finished product.

[0055] Comparative Example 2 differs from Example 4 in that the phosphogypsum artificial sand used is that prepared in Comparative Example 1.

[0056] Comparative Example 3 differs from Example 4 in that an equal amount of steel fiber is used to replace the carbon fiber.

[0057] The difference between Comparative Example 4 and Example 4 is that ceramsite sand (apparent density 800 kg / m³) of equal mass is used to replace the phosphogypsum artificial sand.

[0058] According to the standard "Basic Properties and Test Methods of Ultra-High Performance Concrete" T / CBMF37-2019, the properties of the concrete prepared in Examples 4-7 and Comparative Examples 3-6 were tested, and the results are shown in Table 2.

[0059] Table 2 Properties of concrete prepared in Examples 4-7 and Comparative Examples 2-4

[0060] The results of Examples 4-7 show that the lightweight, low-shrinkage, ultra-high performance concrete based on phosphogypsum artificial sand obtained in the present invention has the advantages of simple preparation, high strength, light weight, and low shrinkage. The obtained lightweight ultra-high performance concrete has a 28d compressive strength grade of C100 or above and an apparent density of only 2270-2356 kg / m 3 Ultra-high performance concrete (UHPC) is significantly lighter than ordinary UHPC and offers excellent workability, high flexural strength, and volume stability. When used in large-scale projects such as bridges and high-rise buildings, it can effectively reduce the weight of concrete structures, improving the load-bearing capacity and durability of bridges. It also improves the utilization rate of solid waste and reduces the exploitation of natural sand and gravel resources, resulting in significant economic and environmental benefits.

[0061] The applicant declares that the above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, it is not intended to limit the present application. Any technical personnel familiar with this profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A phosphogypsum artificial sand, wherein the raw materials for its preparation comprise the following components, by weight: 45-60 parts of carbide slag-modified phosphogypsum, 25-35 parts of slag powder, 8-12 parts of cement, 2.5-3.5 parts of lithium slag, and 1.5-2.5 parts of hydrophobic powder, wherein the hydrophobic powder is obtained by modifying heat-activated metakaolin with a silane coupling agent.

2. The phosphogypsum artificial sand according to claim 1, characterized in that: The particle size of the phosphogypsum artificial sand is 2.36-0.075 mm, the cylinder pressure strength is ≥8.9 MPa, and the bulk density is 1050-1100 kg / m 3 , apparent density 2150~2300kg / m 3 , saturated surface dry water absorption rate is 7.1~7.9%.

3. The phosphogypsum artificial sand according to claim 1-2, characterized in that: The hydrophobic powder is prepared by the following steps: (1) placing metakaolin in a crucible and heating it at 105-115° C. for 45-50 hours to completely dry it; (2) placing the dried metakaolin in a negative pressure screening machine to obtain metakaolin powder with a diameter of less than 80 μm; and (3) mixing the metakaolin powder with polydimethylsiloxane and γ-aminopropyltriethoxysilane in a mass ratio of 1:0.01-0.02:0.01-0.02, and modifying the mixture at 115-125° C. for 30 minutes to obtain the hydrophobic powder.

4. The phosphogypsum artificial sand according to any one of claims 1-2 or claim 3, characterized in that: The carbide slag modified phosphogypsum has an attached water content of less than 25% and a calcium sulfate dihydrate content of more than 80%.

5. A method for preparing phosphogypsum artificial sand according to any one of claims 1 to 2, claim 3 or claim 4, comprising the following steps: (a) Stirring: Mix all solid components for 3-5 minutes until uniform; add water and stir for 5-8 minutes to form a slurry; (b) Molding: pouring the slurry into a mold and hardening it into shape; (c) Crushing: Crushing and screening the formed artificial stone into the required particle size.

6. Use of the artificial phosphogypsum sand according to any one of claims 1 to 2, claim 3 or claim 4, or the artificial phosphogypsum sand prepared by the preparation method according to claim 5 in preparing lightweight, low-shrinkage, ultra-high performance concrete.

7. A lightweight, low-shrinkage, ultra-high performance concrete according to claim 6, characterized in that: Each cubic meter of concrete contains the following components: 780-900 kg of cement, 130-175 kg of silica fume, 100-170 kg of slag powder, 600-800 kg of the phosphogypsum artificial sand according to claim 1, 150-450 kg of river sand, 10-12 kg of carbon fiber, 20-28 kg of polycarboxylic acid water reducer, and 182-216 kg of water; the total amount of aggregate is 900-1050 kg, and the aggregate is composed of phosphogypsum artificial sand and river sand.

8. A method for preparing the lightweight, low-shrinkage, ultra-high performance concrete according to claim 7, characterized in that: The following steps are involved: (1) Mix phosphogypsum artificial sand, cement, silica fume, slag powder and river sand for 2-3 minutes; (2) adding polycarboxylate water-reducing agent and water to the mixture of step (1) and stirring for 5-7 minutes; (3) adding carbon fiber and mixing uniformly to obtain a concrete mixture; (4) After pouring and forming, the finished product is cured for 28 days.

9. The method for preparing lightweight, low shrinkage, ultra-high performance concrete according to claim 8, characterized in that: The amount of river sand added in step (1) must satisfy the following requirement: the total mass of phosphogypsum artificial sand and river sand is within the range of 900-1050 kg / m³.

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