A phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete and its preparation method

Abstract

This invention belongs to the field of building materials technology and discloses a phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete and its preparation method. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete includes the following raw materials: cement 600-750 kg / m³. 3 Fly ash microspheres 150-200 kg / m³ 3 Silica fume 150-200 kg / m³ 3 550-700 kg / m³ of phosphogypsum micro-expansion lightweight aggregate 3 Quartz sand aggregate 300-350 kg / m³ 3 Temperature-sensitive fibers: 3-6 kg / m 3 Micro-coated copper short steel fibers 20-30 kg / m 3 Water-reducing agent 20-30 kg / m³ 3 Water 150-200 kg / m 3 This invention not only realizes the high-value application of phosphogypsum in ultra-high performance concrete, but also solves the problem of decreased mechanical properties and structural stability while achieving lightweight ultra-high performance concrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete and its preparation method. Background Technology

[0002] Phosphogypsum is an industrial byproduct of the wet process production of phosphoric acid in phosphate chemical enterprises. Its main component is calcium sulfate dihydrate, and it also contains characteristic pollutants such as phosphorus, fluoride, cadmium, mercury, arsenic, lead, chromium, copper, zinc, nickel, and thallium. Therefore, achieving high-value and harmless utilization of phosphogypsum is particularly urgent.

[0003] Ultra-high performance concrete (UHPC) refers to concrete with a compressive strength exceeding 120 MPa and excellent overall performance, possessing numerous advantages such as high strength and good durability. However, UHPC still faces some challenges, including high weight, high shrinkage, and high manufacturing costs. In recent years, to reduce the cost of UHPC materials, researchers both domestically and internationally have conducted research on using low-quality aggregates or industrial solid waste to replace quartz sand in UHPC preparation. Currently, some researchers are using aeolian sand, waste glass, and iron tailings powder to replace quartz sand in UHPC preparation. Therefore, it is of great significance to fully utilize phosphogypsum resources to prepare a new type of green, lightweight, high-strength, and low-shrinkage UHPC material.

[0004] Therefore, some studies have shown that phosphogypsum can be made into aggregate and directly added to concrete to reduce solid waste and lower concrete costs. However, directly adding ordinary phosphogypsum aggregate can easily alter the internal ionic environment of concrete, promoting the growth of Ca in the phosphogypsum. 2+ and SO4 2- The dissolution of phosphogypsum and the formation of ettringite (AFt) cause internal expansion of concrete, resulting in microcracks and affecting structural safety. This poses a technical challenge to the high-value and stable utilization of phosphogypsum in concrete. Furthermore, while using lightweight aggregates can simultaneously reduce the self-weight and shrinkage of UHPC, the strength and density of phosphogypsum lightweight aggregates are lower than those of high-quality quartz sand aggregates used in traditional UHPC. Therefore, how to maximize the utilization of phosphogypsum solid waste while ensuring the high strength performance of UHPC is also a technical challenge in the preparation of ultra-high performance concrete using phosphogypsum aggregates. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete and its preparation method. This invention not only realizes the high-value application of phosphogypsum in ultra-high performance concrete, but also solves the problem of decreased mechanical properties and structural stability while achieving the lightweighting of ultra-high performance concrete.

[0006] To address the technical problem proposed in this invention, this invention provides a phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete, comprising the following raw materials: cement 600-750 kg / m³ 3 Fly ash microspheres 150-200 kg / m³ 3 Silica fume 150-200 kg / m³ 3 550-700 kg / m³ of phosphogypsum micro-expansion lightweight aggregate 3 Quartz sand aggregate 300-350 kg / m³ 3 Temperature-sensitive fibers: 3-6 kg / m 3 Micro-coated copper short steel fibers 20-30 kg / m 3 Water-reducing agent 20-30 kg / m³ 3 Water 150-200 kg / m 3 .

[0007] In the above scheme, the cement is ordinary Portland cement with a specific surface area ≥340m². 2 / kg, 28d compressive strength ≥50.0MPa.

[0008] In the above scheme, the phosphogypsum micro-expanded lightweight aggregate consists of a lightweight phosphogypsum core and a polyurea elastomer shell; wherein, the lightweight phosphogypsum core comprises the following raw materials in weight percentage: phosphogypsum 60-75%, silica fume 4-10%, fly ash microspheres 4-10%, foaming agent A 3-6%, alkali activator 3-8%, and water 10-13%; the polyurea elastomer shell comprises the following raw materials in weight percentage: isocyanate 30-40%, amino-terminated polyether 45-55%, amino chain extender 7-10%, and foaming agent B 2-6%.

[0009] Furthermore, the particle size of the phosphogypsum micro-expanded lightweight aggregate is 3-6 mm, wherein the particle size of the lightweight phosphogypsum core is 2-4 mm, and the thickness of the polyurea elastomer shell is 1-2 mm.

[0010] Furthermore, the phosphogypsum is quicklime-modified phosphogypsum, with CaSO4·2H2O as its main component, a content of ≥95%, a pH value of 4-6, and a particle size of ≤80μm.

[0011] Furthermore, the foaming agent A is hydrogen peroxide solid powder with a hydrogen peroxide content ≥9.3%.

[0012] Furthermore, the alkali activator is modified water glass obtained by mixing water glass with alkali, and has a modulus of 1.5 to 2.

[0013] Furthermore, the alkali is sodium hydroxide or potassium hydroxide.

[0014] Furthermore, the mass ratio of water glass to alkali is 100:(15-40).

[0015] Furthermore, the temperature of the water used in the lightweight phosphogypsum core is 25–45°C.

[0016] Furthermore, the isocyanate is one or a combination of two of isophorone diisocyanate, diphenylmethane diisocyanate, and 1,6-hexanediisocyanate.

[0017] Furthermore, the terminal amino polyether is one or a combination of two of JEFFAMINE D-2000 and JEFFAMINE T-5000.

[0018] Furthermore, the amino chain extender is one or a combination of two of diethyltoluenediamine and WANALINK 6200.

[0019] Furthermore, the foaming agent B is a hydrogen peroxide solution with a concentration of 8-10%.

[0020] The preparation method of the phosphogypsum micro-expanded lightweight aggregate in the above scheme includes the following steps:

[0021] 1) After uniformly mixing phosphogypsum, silica fume, fly ash microspheres and foaming agent A, the mixture is fed into a disc granulator, sprayed with a mixed solution of alkali activator and water and granulated. After the particles coagulate, they are vacuum dried to obtain a lightweight phosphogypsum core.

[0022] 2) Isocyanate, amino-terminated polyether, amino chain extender and foaming agent B are put into a high-pressure sprayer, the lightweight phosphogypsum core is placed on a vibrating table and vibrated and sprayed, and cured to obtain phosphogypsum micro-expansion lightweight aggregate.

[0023] Furthermore, the disc granulator has an inclination angle of 40–55°, a rotation speed of 20–30 r / min, and a granulation time of ≥20 min.

[0024] Furthermore, the vacuum drying temperature is 30–40°C, and the drying time is ≥6 hours.

[0025] Furthermore, the high-pressure sprayer has a spraying temperature of 70-80℃, a spraying pressure of 650-700Pa, a vibration table frequency of 100-150Hz, and a spraying time of 15-55s.

[0026] Furthermore, the curing conditions for the phosphogypsum micro-expansion lightweight aggregate are as follows: first, cure at 20±2℃ for 20 to 24 hours, and then place it in a standard concrete curing room for 21 to 28 days.

[0027] In the above scheme, the specific surface area of ​​the fly ash microspheres is ≥1200m². 2 / kg, apparent density ≤2600kg / m³ 3 The activity index is ≥95% after 28 days.

[0028] In the above scheme, the specific surface area of ​​the silica fume is ≥18.5m². 2 / g, apparent density ≤2400kg / m³ 3 The SiO2 content is ≥92%, and the 28-day activity index is ≥110%.

[0029] In the above scheme, the fineness modulus of the quartz sand aggregate is 2.3 to 2.6, and the SiO2 content is 99.0 to 99.6%.

[0030] In the above scheme, the temperature-sensitive fiber is made from the following raw materials in the following mass percentages: 85-90% high-shrinkage polyester polymer, 5-10% modifier, and 2-6% antioxidant.

[0031] Furthermore, the temperature-sensitive fiber has a diameter of 0.1–1 mm and a length of 9–15 mm.

[0032] Furthermore, the initial shrinkage temperature of the temperature-sensitive fiber is 75–85°C.

[0033] Furthermore, the high-shrinkage polyester polymer is prepared by mixing polyethylene terephthalate, polyethylene terephthalate, dipropylene glycol monobutyl ether, and succinic anhydride in a mass ratio of 100:(30-90):(1-3):(2-4) and reacting the mixture at 130-150°C for 2-4 hours.

[0034] Furthermore, the modifier is one of silicon carbide whiskers and carbon nanotubes.

[0035] Furthermore, the antioxidant is one or more of 2,6-di-tert-butyl-p-methylphenol (BHT), phosphite antioxidants, and 3,3-thiodipropionate antioxidants.

[0036] In the above scheme, the method for preparing the temperature-sensitive fiber includes the following steps:

[0037] 1) After mixing the high-shrinkage polyester polymer, modifier, and antioxidant evenly, vacuum dry the mixture and then grind it to obtain a mixed powder;

[0038] 2) The mixed powder is fed into a twin-screw extruder and the nascent fibers are extruded through blending and melting. Then, the fibers are drawn and stretched twice to obtain temperature-sensitive fibers.

[0039] Furthermore, the specific process of the two traction stretching operations is as follows: the nascent fibers extruded by the twin-screw extruder are first subjected to traction stretching at a temperature of 90–120°C, with a stretching ratio of 4–7 times and a stretching rate of 0.3–0.4 m / s, and then cooled at a temperature of 10–20°C; then, a second traction stretching operation is performed at a temperature of 120–140°C, with a stretching ratio of 2.5–3.5 times and a stretching rate of 0.1–0.2 m / s, and then cooled at a temperature of 15–25°C.

[0040] In the above scheme, the diameter of the micro-copper-plated short steel fiber is 0.2-0.3 mm, the length is 10-13 mm, the aspect ratio is 50-65, and the tensile strength is ≥2000 MPa.

[0041] In the above scheme, the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with an effective water reduction rate of 40-60%.

[0042] This invention also provides a method for preparing ultra-high performance concrete using phosphogypsum micro-expansion lightweight aggregate, comprising the following steps:

[0043] S1, Soak the phosphogypsum micro-expanded lightweight aggregate in water until it is saturated, take it out, wipe off the surface moisture and let it stand to obtain the pre-wetted phosphogypsum micro-expanded lightweight aggregate;

[0044] S2, after mixing cement, fly ash microspheres and silica fume, add pre-wetted phosphogypsum micro-expansion lightweight aggregate and quartz sand aggregate and mix to obtain dry mix;

[0045] S3. After the water-reducing agent and water are mixed evenly, add them to the dry mixture and stir. Then add copper-plated short steel fibers and temperature-sensitive fibers in small amounts several times until they are completely mixed evenly to obtain the mixture.

[0046] S4 involves filling the mold, vibrating, and molding the mixture, followed by steam curing, then standard curing, and finally demolding to obtain phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete.

[0047] In the above scheme, the soaking water in step S1 is additional water, and the water volume is not included in the water volume of the concrete formula.

[0048] In the above scheme, the soaking time is 20-28 hours and the standing time is 2-3 hours.

[0049] In the above scheme, the steam curing conditions are: temperature 90-95℃, relative humidity ≥95%, and curing time 20-28h.

[0050] In the above scheme, the standard maintenance time is 28 to 56 days.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] This invention not only realizes the application of phosphogypsum in ultra-high performance concrete, but also solves the problem of decreased mechanical properties and structural stability while achieving lightweight ultra-high performance concrete. The resulting ultra-high performance concrete exhibits excellent performance and broad application prospects, specifically as follows:

[0053] 1. During hydration and hardening, the sulfate ions in the lightweight phosphogypsum core react with cement through the micropores of the polyurea elastomer shell to produce ettringite, causing a certain degree of expansion stress in the phosphogypsum micro-expansion lightweight aggregate. At the same time, the steam curing temperature of the concrete is higher than the initial shrinkage temperature of the temperature-sensitive fiber. The temperature-sensitive fiber shrinks and does not rebound after returning to room temperature. Thus, the temperature-sensitive fiber effectively limits the further expansion of the phosphogypsum micro-expansion lightweight aggregate. Through the composition design of this invention, a balance between expansion and shrinkage in ultra-high performance concrete is achieved, forming a suitable internal prestress field, which ensures the mechanical properties and crack resistance of the phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete material.

[0054] 2. This invention designs a core-shell structure for phosphogypsum micro-expansion lightweight aggregate: the lightweight phosphogypsum core contains a foaming agent, achieving lightweighting of the aggregate through foaming while ensuring strength; a polyurea elastomer is used as the outer shell, creating a buffer between the expansion of the lightweight phosphogypsum core and the cement paste, avoiding microcracks caused by excessive internal prestress; the polyurea elastomer outer shell uses a foaming agent to ensure that the phosphogypsum in the lightweight phosphogypsum core can react with the cement outside the phosphogypsum micro-expansion lightweight aggregate through the micropores of the polyurea elastomer outer shell, and the release of internal moisture forms an internal curing effect, reducing concrete shrinkage; in addition, the polyurea elastomer outer shell is prepared by high-pressure spraying, effectively reducing the particle size of the phosphogypsum micro-expansion lightweight aggregate, achieving equal volume replacement of quartz sand without affecting the compact packing structure of ultra-high performance concrete particles, and ensuring the stability of the phosphogypsum aggregate itself by utilizing the excellent bonding ability of the polyurea elastomer, achieving high-quality utilization.

[0055] 3. This invention, while ensuring mechanical properties and structural stability, eliminates solid waste, reduces material costs, and lowers material weight. It not only effectively solves the problems of high density and large shrinkage in ultra-high performance concrete, but also provides a new approach to phosphogypsum curing, resulting in significant economic and environmental benefits. The phosphogypsum-based micro-expansion lightweight aggregate ultra-high performance concrete prepared by this invention has a wide range of applications and can be used in various large-scale projects, especially bridge engineering, effectively solving the problem of heavy bridge weight. Detailed Implementation

[0056] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0057] In the following embodiments, the cement used is P·O52.5, with a specific surface area of ​​371 m². 2 / kg, 28-day compressive strength is 58.0 MPa; specific surface area of ​​fly ash microspheres is 1250 m² / kg. 2 / kg, apparent density 2513kg / m³ 3 The activity index after 28 days is 97%; the specific surface area of ​​the silica fume is 19.5 m². 2 / g, apparent density 2200kg / m³ 3 The silica sand aggregate has a SiO2 content of 92.22% and a 28-day activity index of 113%. The fineness modulus of the silica sand aggregate is 2.4, and the SiO2 content is 99.2%. The micro-fine copper-plated short steel fibers have a diameter of 0.2 mm, a length of 13 mm, an aspect ratio of 65, and a tensile strength of 2850 MPa. The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with an effective water reduction rate of 50%.

[0058] In the following examples, the selected phosphogypsum is quicklime-modified phosphogypsum, with the main component being CaSO4·2H2O, a content of 97%, a pH value of 5, and a particle size of 70 μm; foaming agent A is hydrogen peroxide solid powder with a hydrogen peroxide content of 10%; foaming agent B is hydrogen peroxide solution with a concentration of 10%; the alkali activator is modified water glass obtained by mixing water glass and alkali at a mass ratio of 100:15, with a modulus of 1.5; the isocyanate is isophorone diisocyanate; the amino-terminated polyether is a mixture of JEFFAMINE D-2000 and EFFAMINE T-5000; and the amino chain extender is a mixture of diethyltoluene diamine and WANALINK 6200.

[0059] In the following examples, the high-shrinkage polyester polymer used was prepared by mixing polyethylene terephthalate, polyethylene terephthalate, dipropylene glycol monobutyl ether, and succinic anhydride in a mass ratio of 100:60:2:3 and reacting them at 140°C for 4 hours; the modifier was silicon carbide whiskers; and the antioxidant was 2,6-di-tert-butyl-p-methylphenol.

[0060] Example 1

[0061] A phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete comprises the following raw materials: cement 600 kg / m³ 3 200kg / m³ of fly ash microspheres 3 Silica fume 200kg / m 3 550 kg / m³ of phosphogypsum micro-expanded lightweight aggregate with a particle size of 3 mm. 3 Quartz sand aggregate 350kg / m 3 Temperature-sensitive fiber 5kg / m 3 Micro-coated copper short steel fibers 20kg / m 3 Water-reducing agent 25kg / m 3 Water 180kg / m3 .

[0062] The preparation method of the above-mentioned phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete includes the following steps:

[0063] S1. Soak the phosphogypsum micro-expanded lightweight aggregate in water for 24 hours until it is saturated (additional water is used, and the amount of water is not included in the water content of the concrete formula). Take it out, wipe off the surface moisture and let it stand for 2 hours to obtain the pre-wetted phosphogypsum micro-expanded lightweight aggregate.

[0064] S2, after mixing cement, fly ash microspheres and silica fume for 3-5 minutes, add pre-wetted phosphogypsum micro-expansion lightweight aggregate and quartz sand aggregate and mix for 3-5 minutes to obtain dry mix;

[0065] S3, after mixing the water-reducing agent and water evenly, add it to the dry mixture and stir for 3-5 minutes. Then add copper-plated short steel fibers and temperature-sensitive fibers in small amounts several times, and stir for 3-5 minutes until the mixture is evenly mixed to obtain the mixture.

[0066] S4. After the mixture is molded, vibrated and shaped, it is first steam cured at 92℃ and 95% relative humidity for 24 hours, and then standard cured for 28 days. After demolding, ultra-high performance concrete with phosphogypsum micro-expansion lightweight aggregate is obtained.

[0067] In this embodiment, the phosphogypsum micro-expanded lightweight aggregate consists of a lightweight phosphogypsum core with a particle size of 2 mm and a polyurea elastomer shell with a thickness of 1 mm. The lightweight phosphogypsum core comprises the following raw materials in weight percentage: phosphogypsum 60%, silica fume 10%, fly ash microspheres 10%, foaming agent A 5%, alkali activator 5%, and water at 25°C 10%. The polyurea elastomer shell comprises the following raw materials in weight percentage: isocyanate 30%, amino-terminated polyether 54%, amino chain extender 10%, and foaming agent B 6%.

[0068] The preparation method of the above-mentioned phosphogypsum micro-expanded lightweight aggregate includes the following steps:

[0069] 1) After uniformly mixing phosphogypsum, silica fume, fly ash microspheres and foaming agent A, feed them into a disc granulator. Set the disc granulator tilt angle to 40° and the rotation speed to 25 r / min. Start the disc granulator and spray a mixed solution of alkali activator and water into the disc granulator for granulation. The granulation time is 20 min. After the particles coagulate, vacuum dry them at 30°C for 12 h to obtain a lightweight phosphogypsum core.

[0070] 2) Isocyanate, amino-terminated polyether, amino chain extender and foaming agent B were put into a two-component high-pressure sprayer. The spraying temperature (i.e. the two-component heating temperature) was set to 70℃ and the spray gun pressure was 650Pa. The lightweight phosphogypsum core was placed on a vibrating table and sprayed. The vibration frequency of the vibrating table was 100Hz and the spraying time was 20s. After spraying, it was first cured at 20±2℃ for 20h and then placed in a standard concrete curing room for 28d to obtain phosphogypsum micro-expansion lightweight aggregate.

[0071] In this embodiment, the temperature-sensitive fiber is made from the following raw materials by weight percentage: 85% high-shrinkage polyester polymer, 10% modifier, and 5% antioxidant; the preparation method includes the following steps:

[0072] 1) After mixing the high-shrinkage polyester polymer, modifier, and antioxidant evenly, vacuum dry the mixture and then grind it to obtain a mixed powder;

[0073] 2) The mixed powder is fed into a twin-screw extruder and melt-extruded into nascent fibers. The nascent fibers are first stretched at 100°C for the first time, stretched 6 times, with a stretching rate of 0.3 m / s, and then cooled at 15°C. Then, they are stretched a second time at 130°C for the second time, stretched 3 times, with a stretching rate of 0.1 m / s, and then cooled at 20°C. The fibers are then cut into short fibers with a length of 10 mm to obtain temperature-sensitive fibers.

[0074] The obtained temperature-sensitive fiber had a diameter of 0.2 mm and a density of 1130 kg / m³. 3 The tensile breaking strength is 120 MPa, the initial shrinkage temperature is 80℃, the shrinkage rate at 80℃ is 1.0%, and the shrinkage rate in boiling water is 6%.

[0075] Example 2

[0076] A phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete comprises the following raw materials: cement 700 kg / m³ 3 150kg / m³ of fly ash microspheres 3 Silica fume 150kg / m 3 600 kg / m³ of phosphogypsum micro-expanded lightweight aggregate with a particle size of 6 mm. 3 Quartz sand aggregate 300kg / m 3 Temperature-sensitive fiber 6kg / m 3 Micro-fine copper-plated short steel fibers 25kg / m 3 Water-reducing agent 25kg / m 3 Water 180kg / m 3 .

[0077] The preparation method of the above-mentioned phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete includes the following steps:

[0078] S1. Soak the phosphogypsum micro-expanded lightweight aggregate in water for 24 hours until it is saturated (additional water is used, and the amount of water is not included in the water content of the concrete formula). Take it out, wipe off the surface moisture and let it stand for 2 hours to obtain the pre-wetted phosphogypsum micro-expanded lightweight aggregate.

[0079] S2, after mixing cement, fly ash microspheres and silica fume for 3-5 minutes, add pre-wetted phosphogypsum micro-expansion lightweight aggregate and quartz sand aggregate and mix for 3-5 minutes to obtain dry mix;

[0080] S3, after mixing the water-reducing agent and water evenly, add it to the dry mixture and stir for 3-5 minutes. Then add copper-plated short steel fibers and temperature-sensitive fibers in small amounts several times, and stir for 3-5 minutes until the mixture is evenly mixed to obtain the mixture.

[0081] S4. After the mixture is molded, vibrated and shaped, it is first steam cured at 93℃ and 96% relative humidity for 24 hours, and then standard cured for 28 days. After demolding, ultra-high performance concrete with phosphogypsum micro-expansion lightweight aggregate is obtained.

[0082] In this embodiment, the phosphogypsum micro-expanded lightweight aggregate consists of a lightweight phosphogypsum core with a particle size of 4 mm and a polyurea elastomer shell with a thickness of 2 mm. The lightweight phosphogypsum core comprises the following raw materials in weight percentage: phosphogypsum 70%, silica fume 5%, fly ash microspheres 5%, foaming agent A 5%, alkali activator 5%, and water at 30°C 10%. The polyurea elastomer shell comprises the following raw materials in weight percentage: isocyanate 35%, amino-terminated polyether 52%, amino chain extender 8%, and foaming agent B 5%.

[0083] The preparation method of the above-mentioned phosphogypsum micro-expanded lightweight aggregate includes the following steps:

[0084] 1) After uniformly mixing phosphogypsum, silica fume, fly ash microspheres and foaming agent A, feed them into a disc granulator. Set the disc granulator tilt angle to 40° and the rotation speed to 30 r / min. Start the disc granulator and spray a mixed solution of alkali activator and water into the disc granulator for granulation. The granulation time is 25 min. After the particles coagulate, vacuum dry them at 40°C for 12 h to obtain a lightweight phosphogypsum core.

[0085] 2) Isocyanate, amino-terminated polyether, amino chain extender and foaming agent B were put into a two-component high-pressure sprayer. The spraying temperature (i.e. the two-component heating temperature) was set to 80℃ and the spray gun pressure was 700Pa. The lightweight phosphogypsum core was placed on a vibrating table and sprayed. The vibration frequency of the vibrating table was 120Hz and the spraying time was 50s. After spraying, it was first cured at 20±2℃ for 24h and then placed in a standard concrete curing room for 28d to obtain phosphogypsum micro-expansion lightweight aggregate.

[0086] In this embodiment, the temperature-sensitive fiber is made from the following raw materials by weight percentage: 90% high-shrinkage polyester polymer, 5% modifier, and 5% antioxidant; the preparation method includes the following steps:

[0087] 1) After mixing the high-shrinkage polyester polymer, modifier, and antioxidant evenly, vacuum dry the mixture and then grind it to obtain a mixed powder;

[0088] 2) The mixed powder is fed into a twin-screw extruder and melt-extruded into nascent fibers. The nascent fibers are first stretched at 110°C for the first time, stretched 7 times, with a stretching rate of 0.3 m / s, and then cooled at 15°C. Then, they are stretched a second time at 140°C for the second time, stretched 3.5 times, with a stretching rate of 0.1 m / s, and then cooled at 25°C. The fibers are then cut into short fibers with a length of 10 mm to obtain temperature-sensitive fibers.

[0089] The obtained temperature-sensitive fiber had a diameter of 0.1 mm and a density of 1095 kg / m³. 3 The tensile breaking strength is 125 MPa, the initial shrinkage temperature is 80℃, the shrinkage rate at 80℃ is 1.1%, and the shrinkage rate in boiling water is 6%.

[0090] Example 3

[0091] A phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete comprises the following raw materials: cement 750kg / m³ 3 150kg / m³ of fly ash microspheres 3 Silica fume 150kg / m 3 650 kg / m³ of phosphogypsum micro-expanded lightweight aggregate with a particle size of 5 mm. 3 Quartz sand aggregate 300kg / m 3 Temperature-sensitive fiber 4kg / m 3 Micro-coated copper short steel fiber 21kg / m 3 Water-reducing agent 30kg / m 3 Water 189kg / m 3 .

[0092] The preparation method of the above-mentioned phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete includes the following steps:

[0093] S1. Soak the phosphogypsum micro-expanded lightweight aggregate in water for 24 hours until it is saturated (additional water is used, and the amount of water is not included in the water content of the concrete formula). Take it out, wipe off the surface moisture and let it stand for 2 hours to obtain the pre-wetted phosphogypsum micro-expanded lightweight aggregate.

[0094] S2, after mixing cement, fly ash microspheres and silica fume for 3-5 minutes, add pre-wetted phosphogypsum micro-expansion lightweight aggregate and quartz sand aggregate and mix for 3-5 minutes to obtain dry mix;

[0095] S3, after mixing the water-reducing agent and water evenly, add it to the dry mixture and stir for 3-5 minutes. Then add copper-plated short steel fibers and temperature-sensitive fibers in small amounts several times, and stir for 3-5 minutes until the mixture is evenly mixed to obtain the mixture.

[0096] S4. After the mixture is molded, vibrated and shaped, it is first steam cured at 95℃ and 95% relative humidity for 24 hours, and then standard cured for 28 days. After demolding, ultra-high performance concrete with phosphogypsum micro-expansion lightweight aggregate is obtained.

[0097] In this embodiment, the phosphogypsum micro-expanded lightweight aggregate consists of a lightweight phosphogypsum core with a particle size of 4 mm and a polyurea elastomer shell with a thickness of 1 mm. The lightweight phosphogypsum core comprises the following raw materials in weight percentage: phosphogypsum 75%, silica fume 4%, fly ash microspheres 4%, foaming agent A 4%, alkali activator 3%, and water at 45°C 10%. The polyurea elastomer shell comprises the following raw materials in weight percentage: isocyanate 40%, amino-terminated polyether 50%, amino chain extender 7%, and foaming agent B 3%.

[0098] The preparation method of the above-mentioned phosphogypsum micro-expanded lightweight aggregate includes the following steps:

[0099] 1) After mixing phosphogypsum, silica fume, fly ash microspheres and foaming agent A evenly, put them into a disc granulator. Set the disc granulator tilt angle to 50° and the rotation speed to 30 r / min. Start the disc granulator and spray a mixed solution of alkali activator and water into the disc granulator and granulate. The granulation time is 30 min. After the particles coagulate, vacuum dry them at 35°C for 10 h to obtain a lightweight phosphogypsum core.

[0100] 2) Isocyanate, amino-terminated polyether, amino chain extender and foaming agent B were put into a two-component high-pressure sprayer. The spraying temperature (i.e. the two-component heating temperature) was set to 80℃ and the spray gun pressure was 670Pa. The lightweight phosphogypsum core was placed on a vibrating table and sprayed. The vibration frequency of the vibrating table was 150Hz and the spraying time was 30s. After spraying, it was first cured at 20±2℃ for 21h and then placed in a standard concrete curing room for 28d to obtain phosphogypsum micro-expansion lightweight aggregate.

[0101] In this embodiment, the temperature-sensitive fiber is made from the following raw materials by weight percentage: 90% high-shrinkage polyester polymer, 7% modifier, and 3% antioxidant; the preparation method includes the following steps:

[0102] 1) After mixing the high-shrinkage polyester polymer, modifier, and antioxidant evenly, vacuum dry the mixture and then grind it to obtain a mixed powder;

[0103] 2) The mixed powder is fed into a twin-screw extruder and melt-extruded into nascent fibers. The nascent fibers are first stretched at 115°C for the first time, stretched 4 times, with a stretching rate of 0.3 m / s, and then cooled at 10°C. Then, they are stretched a second time at 135°C for the second time, stretched 2.5 times, with a stretching rate of 0.1 m / s, and then cooled at 15°C. The fibers are then cut into short fibers with a length of 10 mm to obtain temperature-sensitive fibers.

[0104] The obtained temperature-sensitive fiber had a diameter of 0.15 mm and a density of 1053 kg / m³. 3 The tensile breaking strength is 118 MPa, the initial shrinkage temperature is 80℃, the shrinkage rate at 80℃ is 1.0%, and the shrinkage rate in boiling water is 6%.

[0105] Comparative Example 1

[0106] The only difference between Comparative Example 1 and Example 2 is that: no phosphogypsum micro-expanded lightweight aggregate and temperature-sensitive fiber are added, and the amount of quartz sand aggregate is adjusted to 900 kg / m³. 3 .

[0107] Comparative Example 2

[0108] The only difference between Comparative Example 2 and Example 2 is that no temperature-sensitive fibers are added.

[0109] Comparative Example 3

[0110] The only difference between Comparative Example 3 and Example 2 is that the phosphogypsum micro-expanded lightweight aggregate is replaced with a lightweight phosphogypsum core, that is, the lightweight phosphogypsum core is used directly as lightweight aggregate without being encased in a shell.

[0111] The performance of the ultra-high performance concrete obtained in each embodiment and comparative example was tested, and the results are shown in Table 1.

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, the phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete obtained in the various embodiments of the present invention has the advantages of being lightweight, high-strength, and low-shrinkage, with a density of 2083–2275 kg / m³. 3 56-day drying shrinkage ≤295×10 -6 With a compressive strength of over 120 MPa, it not only realizes the application of phosphogypsum in ultra-high performance concrete, but also solves the problem of decreased mechanical properties and structural stability while achieving the lightweighting of ultra-high performance concrete.

[0115] Compared to Comparative Example 1, which did not use phosphogypsum micro-expanded lightweight aggregate and temperature-sensitive fibers, Example 2 showed no decrease in strength and a significant reduction in shrinkage, indicating that a suitable level of internal prestress was generated, ensuring the mechanical properties and structural stability of the material. Comparative Example 2 used phosphogypsum micro-expanded lightweight aggregate without temperature-sensitive fibers, achieving the goal of lightweighting, but the strength decreased and the drying shrinkage rate was still unsatisfactory, indicating that phosphogypsum micro-expanded lightweight aggregate alone could not generate a suitable level of internal prestress, and the mechanical properties and structural stability of the material could not be guaranteed. Comparative Example 3 used temperature-sensitive fibers, but the phosphogypsum lightweight aggregate only contained a core and lacked an outer shell, resulting in insufficient strength. In addition, the microcracks caused by excessive internal prestress due to the expansion of phosphogypsum led to a significant decrease in the strength of the material.

[0116] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete, characterized in that, Including the following raw materials: cement 600~750 kg / m³ 3 Fly ash microspheres 150~200 kg / m 3 Silica fume 150~200 kg / m³ 3 550~700 kg / m³ of phosphogypsum micro-expansion lightweight aggregate 3 Quartz sand aggregate 300~350 kg / m³ 3 Temperature-sensitive fibers: 3~6 kg / m 3 Micro-coated copper short steel fibers 20~30kg / m 3 Water-reducing agent 20~30 kg / m 3 Water 150~200 kg / m 3 The phosphogypsum micro-expanded lightweight aggregate consists of a lightweight phosphogypsum core and a polyurea elastomer shell; the initial shrinkage temperature of the temperature-sensitive fiber is 75~85℃; after the phosphogypsum micro-expanded lightweight aggregate ultra-high performance concrete is formed, it is first steam-cured at a temperature of 90~95℃, and then converted to standard curing.

2. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that, The lightweight phosphogypsum core comprises the following raw materials in weight percentage: phosphogypsum 60-75%, silica fume 4-10%, fly ash microspheres 4-10%, foaming agent A 3-6%, alkali activator 3-8%, and water 10-13%; the polyurea elastomer shell comprises the following raw materials in weight percentage: isocyanate 30-40%, amino-terminated polyether 45-55%, amino chain extender 7-10%, and foaming agent B 2-6%.

3. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 2, characterized in that, The phosphogypsum is quicklime-modified phosphogypsum, with CaSO4·2H2O as its main component, a content ≥95%, a pH value of 4~6, and a particle size ≤80μm; the foaming agent A is hydrogen peroxide solid powder with a hydrogen peroxide content ≥9.3%; the alkali activator is modified water glass after mixing with alkali, with a modulus of 1.5~2; and the foaming agent B is a hydrogen peroxide solution with a concentration of 8~10%.

4. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 2, characterized in that, The preparation method of the phosphogypsum micro-expanded lightweight aggregate includes the following steps: 1) After uniformly mixing phosphogypsum, silica fume, fly ash microspheres and foaming agent A, the mixture is fed into a disc granulator, sprayed with a mixed solution of alkali activator and water and granulated. The granules are dried to obtain a lightweight phosphogypsum core. 2) Add isocyanate, amino-terminated polyether, amino chain extender and foaming agent into a high-pressure sprayer, place the lightweight phosphogypsum core on a vibrating table and spray it, then cure it to obtain phosphogypsum micro-expansion lightweight aggregate.

5. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that, The particle size of the phosphogypsum micro-expanded lightweight aggregate is 3-6 mm, wherein the particle size of the lightweight phosphogypsum core is 2-4 mm, and the thickness of the polyurea elastomer shell is 1-2 mm.

6. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that, The temperature-sensitive fiber has a diameter of 0.1~1mm and a length of 9~15mm; the temperature-sensitive fiber is made from the following raw materials in the following mass percentages: 85~90% high-shrinkage polyester polymer, 5~10% modifier, and 2~6% antioxidant.

7. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 6, characterized in that, The high-shrinkage polyester polymer is prepared by mixing polyethylene terephthalate, polypropylene terephthalate, dipropylene glycol monobutyl ether, and succinic anhydride in a mass ratio of 100:(30~90):(1~3):(2~4) and reacting them at 130~150℃ for 2~4 hours; the modifier is one of silicon carbide whiskers and carbon nanotubes; the antioxidant is one or more of 2,6-di-tert-butyl-p-methylphenol, phosphite antioxidants, and 3,3-thiodipropionate antioxidants.

8. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 6, characterized in that, The method for preparing the temperature-sensitive fiber includes the following steps: 1) After mixing the high-shrinkage polyester polymer, modifier, and antioxidant evenly, vacuum dry the mixture and then grind it to obtain a mixed powder; 2) The mixed powder is fed into a twin-screw extruder and the nascent fibers are extruded through blending and melting. Then, after two traction stretching processes, temperature-sensitive fibers are obtained.

9. The phosphogypsum micro-expansion lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that, The cement is ordinary Portland cement with a 28-day compressive strength ≥ 50.0 MPa; the fly ash microspheres have a 28-day activity index ≥ 95%; the silica fume has a SiO2 content ≥ 92% and a 28-day activity index ≥ 110%; the quartz sand aggregate has a fineness modulus of 2.3~2.6 and a SiO2 content of 99.0~99.6%; the micro-copper-plated short steel fibers have a diameter of 0.2~0.3 mm, a length of 10~13 mm, an aspect ratio of 50~65, and a tensile strength ≥ 2000 MPa; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with an effective water reduction rate of 40~60%.

10. A method for preparing ultra-high performance concrete with phosphogypsum micro-expansion lightweight aggregate as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1, Soak the phosphogypsum micro-expanded lightweight aggregate in water until it is saturated, take it out, wipe off the surface moisture and let it stand to obtain the pre-wetted phosphogypsum micro-expanded lightweight aggregate; S2, after mixing cement, fly ash microspheres and silica fume, add pre-wetted phosphogypsum micro-expansion lightweight aggregate and quartz sand aggregate and mix to obtain dry mix; S3. After the water-reducing agent and water are mixed evenly, add them to the dry mixture and stir. Then add copper-plated short steel fibers and temperature-sensitive fibers in small amounts several times until they are completely mixed evenly to obtain the mixture. S4 involves molding, vibrating, and shaping the mixture, then steam curing it at 90-95℃, followed by standard curing and demolding to obtain ultra-high performance concrete with phosphogypsum micro-expansion lightweight aggregate.

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