A functionally graded ultra-high performance concrete and a preparation method and application thereof

Abstract

The application provides a functionally graded ultra-high performance concrete, which comprises the following raw materials in parts by weight: cementing material 700-1300 parts, density gradient aggregate 700-1000 parts, micro-scale continuous agent 5-10 parts, functionally graded layering agent 2-5 parts, nano functional material 0.1-0.5 parts, water reducing agent 7-15 parts, water 190-235 parts, polymer fiber 0.5-1 part and steel fiber 50-250 parts. The micro-scale continuous agent and the functionally graded layering agent are compounded to realize the ordered regulation of the steel fiber and the light aggregate, so that the mechanical property and the thermal property of the concrete are continuously changed in the one-dimensional thickness direction. The functionally graded ultra-high performance concrete of the application does not have the cold joint connection between the conventional gradient concrete components, has better integrity, simplifies the construction process, has a wide application prospect, and is especially suitable for the application occasions where the fireproofing / heat preservation is required on one side of the concrete component and the structural load is required on the other side, and can truly realize the structure-fireproofing / heat preservation integration.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a functionally graded ultra-high performance concrete, its preparation method, and its application. Background Technology

[0002] Traditional buildings typically use concrete as the main material, which limits their use to structural functions. Additional functional requirements, such as insulation and fire protection, require additional enclosure measures, which undoubtedly increases the complexity and inconvenience of construction.

[0003] In recent years, the concept of functionally graded materials (FJTs) has received considerable attention in the field of civil engineering, providing insights into simultaneously addressing structural and functional requirements of buildings. FJTs are heterogeneous composite materials created by selecting two or more materials with different properties based on specific application requirements. Through continuous alteration of the composition and structure of these materials, the internal surfaces are reduced or even eliminated, resulting in a material whose properties and functions exhibit continuous and stable changes. Introducing the concept of gradients into cement concrete, using component variations to improve its performance and adapt it to complex and specialized engineering environments, is a goal that many concrete materials researchers are constantly pursuing and exploring.

[0004] Patent CN 113501686 discloses a radiation-resistant functional gradient concrete slab, composed of two types of concrete: a deceleration functional layer and an absorption functional layer connected sequentially from the near-radiation surface. Patent CN 109293299 discloses a functional gradient concrete for green roofs, composed of an upper root-barrier concrete layer and a lower self-healing, crack-resistant, and waterproof concrete layer. However, the design concepts of the above two inventions are closer to "functional gradient structures" than "functional gradient materials," that is, both require the second layer of concrete to be poured after the first layer of concrete has hardened to form a functional gradient concrete structure. This not only increases the construction process and time, but also the formation of cold joints between the two types of concrete is very detrimental to the overall performance of the functional and structural materials.

[0005] In view of this, the present invention is based on the concept of functionally graded materials and aims to provide a functionally graded ultra-high performance concrete, that is, the concrete material itself directly forms graded functions, thereby satisfying the structural stress and functional requirements of the building in the most convenient way. Summary of the Invention

[0006] To address the issues of "cold joints" in traditional concrete gradient components and the need for additional protective measures on the concrete surface to meet the structural stress and functional requirements of buildings, this invention provides a functionally gradient ultra-high performance concrete, its preparation method, and its application. It cleverly reverses the traditional notions of "steel fibers easily settling" and "lightweight aggregates easily floating," and achieves orderly control of steel fibers and lightweight aggregates through microscale continuous agents and functionally gradient stratification agents, thereby realizing continuous gradient changes in the mechanical and thermal properties of concrete in the one-dimensional thickness direction.

[0007] A functionally graded ultra-high performance concrete comprises the following raw materials in parts by weight: 700-1300 parts of cementitious material, 700-1000 parts of density graded aggregate, 5-10 parts of microscale continuous agent, 2-5 parts of functionally graded stratification agent, 0.1-0.5 parts of nano-functional material, 7-15 parts of water-reducing agent, 190-235 parts of water, 0.5-1 part of polymer fiber, and 50-250 parts of steel fiber;

[0008] The aforementioned density gradient aggregates are a blend of various materials including river sand, quartz sand, manufactured sand, artificially calcined heavy aggregates, artificially calcined lightweight aggregates, and recycled concrete aggregates, with an apparent density ranging from 100 to 5000 kg / m³. 3 The particle size is no greater than 2.36 mm. The proportion of artificially calcined lightweight aggregate in density gradient aggregates is 5%–50%. Artificially calcined lightweight aggregates include low-density aggregates such as fly ash ceramsite, clay ceramsite, perlite, vitrified microspheres, or shale ceramsite sand.

[0009] The aforementioned microscale continuous agent comprises whisker-like substances and nanofibers in a mass ratio of 1:(1-2). The whisker-like substances include one or more combinations of calcium silicate whiskers, calcium carbonate whiskers, wollastonite whiskers, mullite whiskers, and gypsum whiskers, with an aspect ratio of not less than 10. The nanofibers include one or more combinations of α-alumina nanofibers, zirconia nanofibers, and graphene oxide nanofibers, with an aspect ratio of not less than 1000. Excessive use of the microscale continuous agent will affect the workability of concrete, while insufficient use will make the concrete prone to localized weak areas, thus affecting the final mechanical properties.

[0010] The aforementioned functional gradient stratification agent is composed of 10–50 parts of ethylene glycol monovinyl polyethylene glycol ether, 10–50 parts of hydroxybutylvinyl polyethylene glycol ether, 5–15 parts of triethanolamine oleate and / or polymethyl methacrylate, 5–15 parts of acrylic acid, 5–15 parts of methacrylic acid tartaric acid, 0.05–0.15 parts of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone, 0.4–0.7 parts of hydrogen peroxide, 0.3–0.6 parts of mercaptopropanol and / or mercaptopropionic acid, 0.4–1.5 parts of 2,5-di-tert-butylhydroquinone, and 0.5–2 parts of sodium hydroxide. The amount of functional gradient stratification agent used can be determined according to the functional requirements of the gradient material.

[0011] Among them, the average molecular weight of ethylene glycol monovinyl polyethylene glycol ether is not less than 3200, and the average molecular weight of hydroxybutyl vinyl polyethylene glycol ether is not less than 3000.

[0012] The preparation method of the above-mentioned functional gradient stratification agent includes the following steps:

[0013] (1) Mix ethylene glycol monovinyl polyethylene glycol ether, hydroxybutyl vinyl polyethylene glycol ether, triethanolamine oleate and / or polymethyl methacrylate, add 4 to 5 times the mass of water to the mixture in a mixer to dissolve, and control the dissolution temperature to 35 to 40°C;

[0014] (2) After the solid in step (1) has dissolved for 5 to 8 minutes, add hydrogen peroxide and control the temperature at 35 to 40°C;

[0015] (3) After the reaction in step (2) has been going on for 5-8 minutes, 2,5-di-tert-butylhydroquinone is added. Then, acrylic acid and methacrylic acid, 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone and mercaptopropanol and / or mercaptopropionic acid are added dropwise simultaneously.

[0016] (4) Keep the reaction at a constant temperature for 2 to 2.5 hours, and add an appropriate amount of water and sodium hydroxide solution to adjust the solid content of the above solution to 40% to obtain the functional gradient stratification agent.

[0017] In step (2) above, the concentration of hydrogen peroxide is 50%, in step (3) the concentration of acrylic acid solution is 50-60%, the concentration of methacrylic acid is 50-60%, the concentration of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone is 10%, the concentration of mercaptopropanol and / or mercaptopropionic acid is 10%, and in step (4) the concentration of sodium hydroxide solution is 30%. The amount of sodium hydroxide added is just enough to adjust the pH to neutral.

[0018] In step (3) above, acrylic acid and methacrylic acid are added dropwise within 100 to 150 minutes; the dropwise addition time of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone and mercaptopropanol and / or mercaptopropionic acid is extended by 15 minutes compared to the dropwise addition time of acrylic acid and methacrylic acid.

[0019] The aforementioned cementitious materials are a blend of various silicate cement, silica fume, ultrafine mineral powder, ultrafine fly ash, fly ash microspheres, metakaolin, ultrafine calcium carbonate, and rice husk ash.

[0020] The aforementioned nanomaterials include one or more combinations of buckytubes, nano-calcium carbonate, nano-alumina, nano-silica, and nano-titanium dioxide; the particle size of the nanomaterials is no greater than 100 nm.

[0021] The polymer fibers mentioned above have a length of 6 to 19 mm and a diameter of 30 to 200 μm, and include one or more combinations of polypropylene fibers, polyoxymethylene fibers, polyvinyl alcohol fibers, and polyethylene fibers.

[0022] The aforementioned steel fibers are copper-plated steel fibers and / or stainless steel fibers.

[0023] The aforementioned water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of not less than 40%.

[0024] A method for preparing functionally graded ultra-high performance concrete includes the following steps: dry mixing cementitious materials, density gradient aggregates, microscale continuous agents and nano-functional materials in a mixer for 30-40 seconds; adding water, water-reducing agent and functionally graded stratification agent, and continuing to mix for 4-5 minutes; uniformly adding polymer fibers and steel fibers, and continuing to mix for 3-5 minutes; pouring the freshly mixed concrete into a mold and vibrating it to obtain functionally graded ultra-high performance concrete.

[0025] The vibration frequency is 50-100Hz, and the vibration time is 0-60s.

[0026] This functionally graded ultra-high performance concrete is suitable for applications where one side of the concrete requires thermal insulation / fireproofing, while the other side requires structural load-bearing capacity, such as tunnel flue slabs and thermal insulation wall panels.

[0027] This application has the following advantages over the prior art:

[0028] (1) This application cleverly reverses the traditional concept of “steel fibers are easy to settle” and “lightweight aggregates are easy to float”, and achieves orderly control of steel fibers and lightweight aggregates by compounding microscale continuous agents and functional gradient stratification agents. That is, the functional gradient stratification agent realizes the separation of function and structure of ultra-high performance concrete on a macro scale, while the microscale continuous agent can ensure the continuity of the overall phase of concrete, thereby realizing the continuous gradient change of the mechanical properties and thermal properties of concrete in one-dimensional thickness direction.

[0029] (2) This application differs from traditional concrete gradient structural members. The functional gradient ultra-high performance concrete of this application does not have cold joint connections between concretes, has better integrity, and simplifies the construction process. It has a wide range of application prospects, especially suitable for applications where one side of the concrete member requires fireproofing / insulation and the other side requires structural load. It avoids the traditional practice of needing to make additional protective measures on the concrete surface and can truly realize the integration of structure-fireproofing / insulation. Attached Figure Description

[0030] Figure 1 This is a comparison diagram of functionally graded ultra-high performance concrete and conventional graded concrete in Embodiment 1 of this application;

[0031] Figure 2 This application describes the variation of thermal conductivity at different heights in the functionally graded ultra-high performance concrete.

[0032] Figure 3 This application describes the variation of compressive strength at different heights in the functionally graded ultra-high performance concrete.

[0033] Figure 4 This is a comparison diagram of the single-sided fire test of concrete components in Example 3 and Comparative Example 5 of this application;

[0034] Figure 5 The deflection curves of the concrete components after high temperature in Example 3 and Comparative Example 4 of this application are shown.

[0035] Figure 6 This is a schematic diagram of the functionally graded ultra-high performance concrete of this application. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] The materials used in each embodiment and comparative example are as follows:

[0038] The cementitious materials include silicate cement, silica fume, and fly ash in a mass ratio of 4:1:1; the silicate cement is Conch brand P·II 52.5, the average particle size of the silica fume is 0.2μm, and the fly ash is Grade I fly ash;

[0039] Density gradient aggregate M1 contains quartz sand, river sand and shale ceramsite sand in a mass ratio of 2:1:1;

[0040] Density gradient aggregate M2 contains quartz sand, river sand and shale ceramsite sand in a mass ratio of 3:1:1;

[0041] Density gradient aggregate M3 contains quartz sand, river sand, and shale ceramsite sand in a mass ratio of 1:1:2;

[0042] Density gradient aggregate M4 contains quartz sand, river sand, and shale ceramsite sand in a mass ratio of 10:9:1;

[0043] Density gradient aggregate M5 contains quartz sand and river sand in a mass ratio of 3:1;

[0044] In the above density gradient aggregates, the particle size of quartz sand is no greater than 300 mesh, the particle size of river sand is no greater than 2.36 mm, and the particle size of shale ceramic sand is no greater than 2.36 mm.

[0045] The microscale continuum W1 contains whisker-like substances and nanofibers in a mass ratio of 1:1;

[0046] The microscale continuum W2 contains whisker-like substances and nanofibers in a mass ratio of 1:2;

[0047] The whisker-like material in the above-mentioned microscale continuum contains equal proportions of wollastonite whiskers and mullite whiskers, wherein the aspect ratio of wollastonite whiskers is 11 and the aspect ratio of mullite whiskers is 12; the nanofibers contain equal proportions of α-alumina nanofibers and zirconium oxide nanofibers, wherein the aspect ratio of α-alumina nanofibers is 1100 and the aspect ratio of zirconium oxide nanofibers is 1200.

[0048] The functional gradient stratification agent is made from 35 parts of ethylene glycol monovinyl polyethylene glycol ether with an average molecular weight of 3300, 15 parts of hydroxybutylvinyl polyethylene glycol ether with an average molecular weight of 3100, 8 parts of triethanolamine oleate, 12 parts of acrylic acid, 8 parts of methacrylic acid tartaric acid, 0.1 parts of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone, 0.5 parts of hydrogen peroxide, 0.5 parts of mercaptopropanol, 0.8 parts of 2,5-di-tert-butylhydroquinone, and 1 part of sodium hydroxide.

[0049] The preparation method of functionally graded stratifying agents includes the following steps:

[0050] (1) Prepare a 55% acrylic acid solution, a 50% methacrylic acid solution, a 10% 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone solution, a 50% hydrogen peroxide solution, a 10% mercaptopropanol solution, and / or mercaptopropionic acid by mass fraction.

[0051] (2) Mix ethylene glycol monovinyl polyethylene glycol ether, hydroxybutyl vinyl polyethylene glycol ether and triethanolamine oleate, add 5 times the mass of water to the mixture and dissolve in a mixer, and control the dissolution temperature to 37±2℃.

[0052] (3) After the solid in step (2) has dissolved for 5 minutes, add hydrogen peroxide and control the temperature at 37±2℃;

[0053] (4) After the reaction in step (3) has been going on for 5 minutes, 2,5-di-tert-butylhydroquinone is added, followed by the addition of acrylic acid and methacrylic acid, which is completed within 135 minutes. At the same time as the addition of acrylic acid and methacrylic acid, 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone and mercaptopropanol are added, and the addition time is extended by 15 minutes compared to the addition time of acrylic acid and methacrylic acid.

[0054] (5) Keep the reaction at a constant temperature for 2 hours, and add an appropriate amount of water and 30% sodium hydroxide solution to adjust the solid content of the above solution to 40% to obtain the functional gradient stratification agent.

[0055] The nanomaterials are equal proportions of nano-calcium carbonate and nano-titanium dioxide, wherein the average particle size of nano-calcium carbonate is 80 nm and the average particle size of nano-titanium dioxide is 75 nm.

[0056] The polymer fiber is a polypropylene fiber with a length of 6 mm and a diameter of 50 μm;

[0057] Steel fiber G1 is a straight, copper-plated steel fiber with a length of 13mm and a diameter of 0.2mm;

[0058] Steel fiber G2 is a straight stainless steel fiber with a length of 13mm and a diameter of 0.2mm;

[0059] The water-reducing agent was selected from PCA high-performance polycarboxylate water-reducing agent of Subote New Materials Co., Ltd., with a measured water reduction rate of 45%.

[0060] The proportions of raw materials used in each embodiment and comparative example are shown in Table 1.

[0061] Table 1

[0062]

[0063]

[0064] A method for preparing functionally graded ultra-high performance concrete includes the following steps:

[0065] According to the proportions in Table 1, dry mix the cementitious materials, density gradient aggregates, microscale continuous agents, and nano-functional materials in a mixer for 30 seconds; add water, water-reducing agent, and functional gradient stratification agent, and continue mixing for 4 minutes; uniformly add polymer fibers and steel fibers, and continue mixing for 3 minutes; pour the mixed concrete into a mold with a height of 20 cm (bottom area of ​​10*10 cm), then vibrate the concrete, controlling the vibration frequency to 50 Hz and the vibration time to 45 seconds; then, before the concrete sets and hardens, perform surface finishing on the concrete; finally, place the concrete in a standard curing room for 28 days of curing.

[0066] This application's embodiment 1, a functionally graded ultra-high performance concrete monolithic structure, and a conventional graded concrete structure are as follows: Figure 1 As shown. Conventional gradient structure: first pour lightweight aggregate concrete, then pour ultra-high performance concrete 24 hours later. According to... Figure 1 It can be seen that the functionally graded ultra-high performance concrete of this application does not have cold joint connections between conventional graded structural concrete, and has better overall integrity.

[0067] Test Example 1: Determination of Compressive Strength and Thermal Conductivity

[0068] After the concrete has cured to the specified age, specimens at different distances were cut from the top surface of the poured concrete as the origin for compressive strength and thermal conductivity testing. Compressive strength testing was performed according to GB / T 50081-2019 "Test Methods for Physical and Mechanical Properties of Concrete", and thermal conductivity testing was performed according to ISO-22007 "Standard Test Method for Thermal Conductivity". The test results are shown in […]. Figure 2 and Figure 3 .

[0069] The changes in thermal conductivity and compressive strength at different heights can be referenced respectively. Figure 2 and Figure 3 It can be seen that Examples 1, 7, and 8 all successfully achieved a continuous gradient change in the thermal and mechanical properties of concrete in one dimension, indicating that the present invention can successfully prepare functionally graded ultra-high performance concrete, which is a truly graded functional material.

[0070] Although Comparative Example 1 incorporated a functionally graded stratifying agent, the lack of a microscale continuum agent resulted in discontinuous performance changes and the presence of abrupt and abrupt regions.

[0071] In comparison, Comparative Examples 2 and 3, due to the lack of functional gradient layering agents, did not show a trend of change in compressive strength and thermal conductivity in the thickness direction.

[0072] Comparative Example 4, due to the lack of steel fiber reinforcement, has a significantly lower overall compressive strength compared to the other examples, making it unsuitable for applications requiring high mechanical performance.

[0073] Comparative Example 5, lacking the heat-insulating effect of lightweight aggregate, has a significantly increased thermal conductivity compared to the other examples, making it unsuitable for applications with high thermal insulation requirements.

[0074] Test Example 2: Single-sided fire test

[0075] Compared with Example 3 and Comparative Examples 4 and 5, flat plate specimens with dimensions of 3.7*0.9*1m were prepared according to the molding method described in this invention, and after natural curing for 6 months, a single-sided fire test was conducted.

[0076] In both Example 3 and Comparative Example 5, the molded surface faced the fire during the fire test. The fire temperature rise curve was based on the ISO-834 standard temperature rise curve, and the fire duration was set to 2 hours. The results are as follows: Figure 4 As shown.

[0077] According to Figure 4 After observing the appearance of Example 3 and Comparative Example 5 after the fire, it can be found that Example 3 can maintain the high integrity of the fire-exposed surface when facing the fire condition, while Comparative Example 3 exhibits high-temperature cracking behavior. In Example 3, as a functionally graded material, the combination of microscale continuation agent and functionally graded layering agent achieves orderly control of lightweight aggregate, resulting in a large number of orderly arranged shale ceramsite sands on its fire-exposed surface. This effectively reduces the thermal conductivity of the concrete (by more than 60% compared to the bottom layer concrete), ensuring that external heat cannot penetrate into the concrete and effectively protecting the safety load of the ultra-high performance concrete in the bottom structural load-bearing layer, thereby mitigating high-temperature damage to concrete components to a greater extent. In addition, the shale lightweight sands accumulated on the fire-exposed surface can act as pressure relief grids for vapor pressure, forming a three-dimensional pressure relief network with a small amount of polymer fibers (which melt at high temperatures to form channels). This alleviates the vapor pressure accumulated inside the ultra-high performance concrete when facing a fire, preventing high-temperature cracking. In contrast, the density gradient aggregate used in Comparative Example 5 lacks lightweight aggregates, resulting in an increased thermal conductivity on its fire-exposed surface, which cannot effectively isolate the transfer of external heat. More importantly, the lack of porous lightweight aggregates on the fire-exposed surface of the concrete means that the small amount of polymer fibers added cannot effectively release the large amount of water vapor generated when the concrete is heated, ultimately leading to high-temperature cracking of the concrete surface, which is very detrimental to concrete components.

[0078] In Comparative Example 4, although density gradient aggregates were added and the density gradient aggregates were controlled through a combination of microscale continuation agents and functionally graded stratification agents, the lack of steel fibers led to a significant decrease in its mechanical properties, particularly in its flexural tensile strength. Compared to Example 3, its deflection after firing decreased considerably. (See [link to example 3]). Figure 5 .

[0079] The functionally graded ultra-high performance concrete described in this invention is a graded functional material whose thermal and mechanical properties can continuously vary along a one-dimensional thickness direction. This effectively avoids the cold joint connection problem present in conventional concrete graded components and better leverages the overall advantages of graded materials. The functionally graded ultra-high performance concrete of this invention has a simple preparation process, uses widely available materials, and can be widely applied in the construction field. It is particularly suitable for applications where one side of the concrete requires thermal insulation / fireproofing, while the other side requires structural load-bearing capacity, such as tunnel flue slabs and insulated wall panels.

[0080] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A functionally graded ultra-high performance concrete, characterized in that, The raw materials include the following parts by weight: 700-1300 parts of cementitious material, 700-1000 parts of density gradient aggregate, 5-10 parts of microscale continuous agent, 2-5 parts of functional gradient stratification agent, 0.1-0.5 parts of nano-functional material, 7-15 parts of water-reducing agent, 190-235 parts of water, 0.5-1 part of polymer fiber, and 50-250 parts of steel fiber; The density gradient aggregate is a blend of various aggregates including river sand, quartz sand, manufactured sand, artificially calcined heavy aggregate, artificially calcined lightweight aggregate, and recycled concrete aggregate. The apparent density of the density gradient aggregate is 100–5000 kg / m³, and the particle size is no greater than 2.36 mm. The proportion of artificially calcined lightweight aggregate in the density gradient aggregate is 5%–50%. The microscale continuum comprises whisker-like substances and nanofibers in a mass ratio of 1:(1-2); The functional gradient stratification agent is composed of 10-50 parts of ethylene glycol monovinyl polyethylene glycol ether, 10-50 parts of hydroxybutylvinyl polyethylene glycol ether, 5-15 parts of triethanolamine oleate and / or polymethyl methacrylate, 5-15 parts of acrylic acid, 5-15 parts of methacrylic acid tartaric acid, 0.05-0.15 parts of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone, 0.4-0.7 parts of hydrogen peroxide, 0.3-0.6 parts of mercaptopropanol and / or mercaptopropionic acid, 0.4-1.5 parts of 2,5-di-tert-butylhydroquinone, and 0.5-2 parts of sodium hydroxide. The preparation method of the functionally graded stratifying agent includes the following steps: (1) Mix ethylene glycol monovinyl polyethylene glycol ether, hydroxybutyl vinyl polyethylene glycol ether, triethanolamine oleate and / or polymethyl methacrylate, add 4 to 5 times the mass of water to the mixture in a mixer to dissolve, and control the dissolution temperature to 35 to 40°C; (2) After the solid in step (1) has dissolved for 5 to 8 minutes, add hydrogen peroxide and control the temperature at 35 to 40°C; (3) After the reaction in step (2) has lasted for 5 to 8 minutes, 2,5-di-tert-butylhydroquinone is added. Then, acrylic acid and methacrylic acid, 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone and mercaptopropanol and / or mercaptopropionic acid are added dropwise simultaneously. (4) Keep the reaction at a constant temperature for 2 to 2.5 hours, and add an appropriate amount of water and sodium hydroxide solution to adjust the solid content of the above solution to 40% to obtain the functional gradient stratification agent.

2. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: The whisker-like material includes one or more combinations of calcium silicate whiskers, calcium carbonate whiskers, wollastonite whiskers, mullite whiskers, and gypsum whiskers, and its aspect ratio is not less than 10; the nanofiber includes one or more combinations of α-alumina nanofibers, zirconium oxide nanofibers, and graphene oxide nanofibers, and its aspect ratio is not less than 1000.

3. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: In step (2), the concentration of hydrogen peroxide is 50%; in step (3), the concentration of acrylic acid solution is 50-60%; the concentration of methacrylic acid is 50-60%; the concentration of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone is 10%; the concentration of mercaptopropanol and / or mercaptopropionic acid is 10%; and in step (4), the concentration of sodium hydroxide solution is 30%.

4. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: In step (3), acrylic acid and methacrylic acid are added dropwise within 100-150 minutes; the dropwise addition time of 2,3,5,6-tetrahydroxy-2-hexenoic acid-4-lactone and mercaptopropanol and / or mercaptopropionic acid is extended by 15 minutes compared to the dropwise addition time of acrylic acid and methacrylic acid.

5. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: The cementing material is a mixture of various silicate cement, silica fume, ultrafine mineral powder, ultrafine fly ash, fly ash microspheres, metakaolin, ultrafine calcium carbonate, and rice husk ash.

6. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: The nanomaterials include one or more combinations of buckytubes, nano-calcium carbonate, nano-alumina, nano-silica, and nano-titanium dioxide; the particle size of the nanomaterials is no greater than 100 nm.

7. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: The polymer fibers have a length of 6–19 mm and a diameter of 30–200 μm, and include one or more combinations of polypropylene fibers, polyoxymethylene fibers, polyvinyl alcohol fibers, and polyethylene fibers.

8. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: The steel fibers are copper-plated steel fibers and / or stainless steel fibers.

9. The functionally graded ultra-high performance concrete according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of not less than 40%.

10. A method for preparing functionally graded ultra-high performance concrete according to any one of claims 1-9, characterized in that, The process includes the following steps: dry mixing cementitious materials, density gradient aggregates, microscale continuous agents, and nano-functional materials in a mixer for 30-40 seconds; adding water, water-reducing agents, and functional gradient stratification agents, and continuing to mix for 4-5 minutes; uniformly adding polymer fibers and steel fibers, and continuing to mix for 3-5 minutes; pouring the freshly mixed concrete into a mold and vibrating it to obtain functional gradient ultra-high performance concrete.

11. The method for preparing functionally graded ultra-high performance concrete according to claim 10, characterized in that: The vibration frequency is 50-100Hz, and the vibration time is 0-60s.

12. The application of the functionally graded ultra-high performance concrete according to any one of claims 1-9, characterized in that: This functionally graded ultra-high performance concrete is suitable for applications where one side of the concrete requires thermal insulation / fireproofing, while the other side requires structural load-bearing capacity.

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