High-strength UHPC panel and preparation method thereof

Abstract

The invention provides a high-strength UHPC panel and a preparation method, and belongs to the field of building materials. The high-strength UHPC panel is prepared from the following components in parts by mass: 700 to 1000 parts of Portland cement, 8 to 12 parts of high-alumina cement, 300 to 400 parts of spherical fly ash, 120 to 180 parts of silica fume, 900 to 1000 parts of 0.075 to 3mm graded quartz sand, 45 to 75 parts of a water reducing agent, 18 to 25 parts of an expanding agent, 8 to 12 parts of metakaolin powder, 35 to 80 parts of steel fiber, 15 to 35 parts of polymer fiber and 0.5 to 5 parts of a water-retaining agent. And the end of the polymer fiber is in an expanded form. The problem of poor binding force between the polymer fibers in the UHPC material and the UHPC material is solved, the compressive strength and tensile strength of the UHPC panel are improved, and meanwhile, the UHPC panel material provided by the invention is good in flowability and easy to process and form.

Description

Technical Field

[0001] The present invention belongs to the field of building materials, and more particularly to a high-strength UHPC panel and a preparation method thereof. Background Art

[0002] Ultra-High Performance Concrete (UHPC) is a new type of cement-based composite material with excellent properties such as high strength, high durability, and high toughness, and has broad application prospects in many fields such as buildings, bridges, and tunnels.

[0003] The excellent properties of UHPC materials are largely due to their fine internal microstructure and reasonable composition design. In the development process of UHPC materials, in order to further improve their mechanical properties, especially in terms of strength, steel fibers are often added. The addition of steel fibers can effectively prevent the expansion and extension of internal cracks in concrete, and transfer external forces to a wider area by bridging the concrete matrix on both sides of the crack, thus significantly improving the tensile, flexural and other strength properties of UHPC materials. However, the application of steel fibers also brings a series of problems that cannot be ignored.

[0004] First of all, the price of steel fibers is relatively high, which to a certain extent restricts the large-scale promotion and application of UHPC materials. In engineering construction, cost is an important consideration. The high price of steel fibers significantly increases the production cost of UHPC materials, thereby reducing their competitiveness in the market.

[0005] Secondly, the presence of steel fibers will cause UHPC materials to have problems of easy penetration. Due to the existence of certain gaps at the interface between steel fibers and the UHPC matrix, under the action of the external environment, water, chemical substances, etc. are easily permeated into the material through these gaps, thereby triggering a series of durability problems such as steel bar corrosion and chemical erosion, seriously affecting the service life and safety of UHPC structures.

[0006] In addition, the density of steel fibers is relatively large, which makes the overall density of UHPC materials after adding steel fibers increase. In some engineering fields with strict requirements on structural self-weight, such as long-span structures in bridge engineering and top structures of high-rise buildings, the large self-weight will increase the burden on the structure, and additional structural design and construction measures may be required to ensure the stability and safety of the structure, which undoubtedly increases the engineering cost and construction difficulty.

[0007] To address the above problems caused by steel fibers, researchers have attempted to replace some steel fibers with polymer fibers. For example, the Chinese invention patent application with the application number 201911317857.5 discloses a hybrid fiber ultra-high performance concrete (UHPC) pole and its manufacturing method. The ultra-high performance concrete used in this pole is composed of cement, silica fume, quartz sand with different gradations, gravel, high-range water reducer, water, polypropylene fibers, and basalt fibers in a certain proportion. This technology demonstrates the application potential of UHPC in specific components, but its formulation and performance characteristics are not fully applicable to application scenarios such as formwork-free formwork.

[0008] Polymer fibers have advantages such as low density and relatively low price. It is expected that while reducing the material cost and self-weight of UHPC, they can maintain certain mechanical properties. However, there is a problem of poor compatibility between polymer fibers and UHPC materials. Due to the relatively smooth surface of polymer fibers, the adhesion force between them and the UHPC matrix is weak, and relative slippage is likely to occur under stress, resulting in a decrease in the strength of UHPC materials. In particular, key performance indicators such as tensile strength are difficult to meet the actual engineering requirements.

[0009] To improve the compatibility between polymer fibers and UHPC materials and enhance the strength performance of UHPC materials, the prior art has carried out surface roughening treatment on polymer fibers. By physical, chemical, and other methods, the surface of polymer fibers is modified to make it rough, increasing the frictional force and mechanical interlocking force between polymer fibers and UHPC substrates. This surface roughening treatment can effectively improve the bonding performance between polymer fibers and the UHPC matrix, enabling polymer fibers to work better with the matrix under stress, thereby increasing the tensile strength of UHPC materials.

[0010] Although the existing surface roughening treatment methods have improved the compatibility between polymer fibers and UHPC materials to a certain extent, there are still some deficiencies. For example, the chemical etching method may have a certain impact on the mechanical properties of the fibers, and the use of chemical reagents may cause environmental pollution problems; the physical etching method requires special equipment and processes, with high costs; in the coating method, the selection of coating materials and the control of coating processes are relatively complex, and the bonding stability between the coating and the fibers and concrete matrix needs to be further improved. Therefore, how to further optimize polymer fibers and improve their compatibility and bonding performance with UHPC materials remains an important topic in current research. Summary of the Invention

[0011] The present invention aims to provide a high-strength UHPC panel and a preparation method, which solves the problem of poor bonding force between polymer fibers and UHPC materials in UHPC materials, improves the compressive strength and tensile strength of the UHPC panel, and at the same time, the UHPC panel material provided by the present invention has good fluidity and is easy to process and form.

[0012] The high-strength UHPC panel described above, by mass fraction, comprises the following components: 700-1000 parts of portland cement, 8-12 parts of high-alumina cement, 300-400 parts of spherical fly ash, 120-180 parts of silica fume, 900-1000 parts of 0.075-3 mm graded quartz sand, 45-75 parts of water reducer, 18-25 parts of expansive agent, 8-12 parts of metakaolin powder, 35-80 parts of steel fiber, 15-35 parts of polymer fiber, and 0.5-5 parts of water retention agent.

[0013] Preferably, the polymer fiber includes aramid fiber or polypropylene fiber.

[0014] Preferably, the aramid fiber is a modified aramid fiber with hydroxyl or carboxyl groups introduced into the main chain by copolymer modification.

[0015] More preferably, the modified aramid fiber is specifically a third monomer with hydroxyl or carboxyl groups replacing the reaction monomer, and the molar ratio of the third monomer with hydroxyl or carboxyl groups to the replaced reaction monomer is 1:9-3:7.

[0016] Preferably, the end of the polymer fiber is in an enlarged shape.

[0017] Preferably, the diameter of the end of the polymer fiber is enlarged by 1.5-4 times.

[0018] More preferably, the enlarged shape of the end of the polypropylene fiber is achieved by heating.

[0019] More preferably, the enlarged shape of the end of the aramid fiber is achieved through the following steps: soaking the end of the aramid fiber in a DMSO solution dissolved with strong alkali, swelling, washing with deionized water until the washing solution is neutral, and freeze-drying or supercritical CO2 drying to obtain aramid fiber with an enlarged end state.

[0020] Even more preferably, the aramid fiber is ultrasonically cleaned with acetone or ethanol for 1-5 min before soaking to remove surface impurities.

[0021] Even more preferably, the strong alkali includes at least one of a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 5wt%-15wt%.

[0022] Even more preferably, the volume ratio of the strong alkali to DMSO is 1:9-3:7.

[0023] More preferably, the soaking is specifically carried out at a temperature of 40 to 90 °C and a stirring rate of 100 to 300 rpm for 2 to 6 h.

[0024] More preferably, the soaking is carried out under the protection of an inert atmosphere to reduce side oxidation reactions.

[0025] Preferably, the 0.075 - 3 mm graded quartz sand is specifically quartz sand of 0.075 - 0.2 mm, quartz sand of 0.2 - 0.35 mm, quartz sand of 0.35 - 1.5 mm, and quartz sand of 1.5 - 3 mm, and their mass ratio is 2 - 4:3 - 5:6 - 8:5 - 7.

[0026] Preferably, the expansive agent is composed of magnesium oxide and modified phosphogypsum in a mass ratio of 0.8 - 1.2; the modified phosphogypsum is α - gypsum and / or β - gypsum after calcination of phosphogypsum. The combination of magnesium oxide and modified phosphogypsum is used as the expansive agent, where magnesium oxide is used for early - stage expansion and modified phosphogypsum is used for late - stage expansion.

[0027] Preferably, when the modified gypsum is a composite of α - gypsum and β - gypsum after calcination of phosphogypsum, the mass ratio of α - gypsum to β - gypsum is 7:3 - 9:1.

[0028] This invention uses Portland cement and high-alumina cement as cementing materials, with Portland cement providing early strength and high-alumina cement accelerating hardening. During the hydration process, a water-retaining agent continuously provides water for the later hydration reactions of the Portland and high-alumina cements, enabling more complete hydration reactions and producing more hydration products such as ettringite and CSH gel, which contributes to the material's strength. Furthermore, the water-retaining agent allows active admixtures such as silica fume and metakaolin powder to better participate in the pozzolanic reaction, further optimizing the structure of the hydration products and improving the material's density and durability. Spherical fly ash improves the flow properties of the mixture. The high activity of silica fume fills the pores of the cement paste, increasing density and enhancing interfacial adhesion, further enhancing strength and durability. Quartz sand graded from 0.075 to 3 mm, formulated according to the performance requirements of this invention, forms a tightly packed structure, reduces porosity, and improves the density, strength, and impermeability of the UHPC panel. Quartz sand of different particle sizes interpenetrates each other, optimizing the aggregate gradation and making the overall system more uniform and stable. Steel fibers, with their high strength and elastic modulus, effectively carry loads and improve the tensile and flexural strength of the panel. Polymer fibers inhibit premature shrinkage cracking, enhancing toughness and impact resistance. Through copolymerization, hydroxyl or carboxyl groups are introduced into the backbone, forming hydrogen bonds with cement hydration products and strengthening the interfacial adhesion between the polymer fibers and the matrix. Furthermore, the expanded morphology of the ends, which expands by 1.5 to 4 times, allows the polymer fibers to form a stronger mechanical interlocking effect within the matrix, significantly enhancing interfacial bonding strength. Under load, the polymer fibers, leveraging their inherent strength, effectively disperse stress and prevent crack propagation, significantly increasing the material's flexural strength and making it less susceptible to brittle fracture under bending loads. They also synergize with the steel fibers and other components to improve the overall compressive strength of the material, playing an indispensable role in toughening and reinforcing the entire UHPC panel system, significantly enhancing its mechanical properties and crack resistance. Metakaolin powder, a mineral admixture, enhances the mixture's plasticity and post-hardening strength, while also improving durability and chemical resistance.

[0029] The method for preparing the high-strength UHPC panel comprises the following steps: S1. Add Portland cement, high alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the proportions, and dry mix until the materials are fully mixed; S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material; S3, adding steel fiber and polymer fiber, stirring to evenly disperse the fibers in the material; S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed; S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1. The high-strength UHPC panel provided by the present invention improves the bonding strength between the polymer fiber and the UHPC substrate by structurally and molecularly modifying the polymer fiber. Specifically, the end of the polymer fiber is expanded to enhance the mechanical bite force between the polymer fiber and the UHPC substrate. The introduction of hydroxyl or carboxyl groups on the main chain of the polymer fiber can form hydrogen bonds with cement hydration products, thereby enhancing the interfacial bonding strength between the polymer fiber and the matrix. This enables the panel to effectively disperse stress and prevent crack expansion when subjected to bending stress, thereby greatly improving the bending resistance of the structure. The rigid-flexible composite system formed with steel fibers provides rigid support when the material is stressed; when cracks appear in the material, the aramid fibers can effectively prevent further crack expansion, absorb energy, and avoid brittle failure of the structure, thereby enhancing the safety and reliability of the structure under complex stress conditions.

[0031] 2. The high-strength UHPC panel provided by the present invention is a non-disassembly panel. Through the synergistic hydration of silicate cement and high-alumina cement, the pozzolanic reaction of active admixtures such as silica fume and metakaolin, and the skeleton support of 0.075-3 mm graded quartz sand, the UHPC panel has ultra-high compressive strength and can withstand huge pressure loads.

[0032] 3. The high-strength UHPC panel provided by the present invention incorporates a small amount of water-retaining agent. This continuously provides moisture to the subsequent hydration reactions of Portland cement and high-alumina cement, enabling a more complete hydration reaction and generating more hydration products such as ettringite and CSH gel, thereby improving the material's strength. Furthermore, the water-retaining agent allows active admixtures such as silica fume and metakaolin powder to better participate in the pozzolanic reaction, further optimizing the structure of the hydration products and improving the material's density and durability.

[0033] 4. The high-strength UHPC panel provided by the present invention ensures good fluidity and formability of the UHPC mixture in the application of non-removal formwork by precisely controlling the particle size and ratio of raw materials and a reasonable mixing process, thereby improving construction efficiency and quality.

[0034] 5. Due to its excellent performance, the high-strength UHPC panel provided by the present invention is suitable for construction in various complex environments, such as coastal buildings, bridges, tunnels, marine engineering, etc., and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The reaction formula for modified aramid fiber is to introduce hydroxyl groups into the aramid main chain through copolymerization modification. Detailed implementation mode

[0036] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples can be purchased commercially or prepared by conventional methods.

[0037] Example 1 A high-strength UHPC panel is composed of the following raw materials according to mass parts: 800 parts of portland cement, 10 parts of high-alumina cement, 350 parts of spherical fly ash (particle size of 12 - 38 μm, sphericity not less than 0.9), 150 parts of silica fume (particle size not greater than 25 μm), 950 parts of 0.075 - 3 mm graded quartz sand (specific ratio of quartz sand of 0.075 - 0.2 mm, quartz sand of 0.2 - 0.35 mm, quartz sand of 0.35 - 1.5 mm, and quartz sand of 1.5 - 3 mm is 3:4:6:5), 60 parts of water reducer, 20 parts of expansive agent (composed of magnesia and modified gypsum in a mass ratio of 1:1, the modified gypsum is a complex of α-gypsum and β-gypsum after calcination of phosphogypsum, mass ratio is 8:2), 10 parts of metakaolin powder (particle size not greater than 25 μm), 50 parts of steel fiber, 25 parts of modified aramid fiber with enlarged ends, and 4 parts of water retention agent; Among them, the aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain by copolymerization modification, using p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, and the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 8:2; first react at -10 °C for 20 min, then react at room temperature until the product solidifies to obtain APPTA-x copolymer, and finally react at 190 °C for 6 h to carry out Claisen rearrangement reaction to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (the reaction formula is as Figure 1 shown); The end diameter of the modified aramid fiber is enlarged by 1.5 - 4 times, which is achieved through the following steps: The aramid fiber is ultrasonically cleaned with acetone or ethanol for 2 min to remove surface impurities. After drying, the end of the aramid fiber is immersed in a mixed solution prepared by mixing a 5wt% sodium hydroxide solution and DMSO with a purity of 99.9% in a volume ratio of 1 - 9, at a temperature of 90 °C, a stirring rate of 200 rpm, and under the protection of a nitrogen atmosphere, soak for 6 h. After swelling, it is washed with deionized water until the washing liquid is neutral, and freeze-dried or supercritically CO2 dried to obtain the modified aramid fiber with enlarged ends.

[0038] The above-mentioned high-strength UHPC panel is prepared by the following steps: S1. Add portland cement, high alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the ratio, and perform dry mixing to make the materials fully and evenly mixed. S2. Add a water reducing agent and an expansive agent, and continue dry mixing to evenly disperse the additives in the materials. S3. Add steel fibers and modified aramid fibers with enlarged ends, and stir to evenly disperse the fibers in the materials. S4. According to the requirements of the water-binder ratio, add water and stir until a uniform UHPC mixture with good fluidity is formed. S5. Pour the UHPC mixture into a mold for shaping and curing to obtain the described high-strength UHPC panel.

[0039] Example 2 A high-strength UHPC panel is composed of the following raw materials by mass fraction: 740 parts of portland cement, 12 parts of high alumina cement, 400 parts of spherical fly ash (particle size 12 - 38 μm, sphericity not less than 0.9), 180 parts of silica fume (particle size not greater than 25 μm), 1000 parts of 0.075 - 3 mm graded quartz sand (specific ratio: the mass ratio of quartz sand of 0.075 - 0.2 mm, 0.2 - 0.35 mm, 0.35 - 1.5 mm, and 1.5 - 3 mm is 4:5:7:6), 80 parts of water reducing agent, 25 parts of expansive agent (composed of magnesia and modified gypsum in a mass ratio of 0.9:1, the modified gypsum is a complex of α-gypsum and β-gypsum after calcination of phosphogypsum, mass ratio 9:1), 12 parts of metakaolin powder (particle size not greater than 25 μm), 80 parts of steel fibers, 30 parts of modified aramid fibers with enlarged ends, and 1 part of water retaining agent. Among them, the aramid fiber is a copolymer-modified aramid fiber with hydroxyl groups introduced into the main chain, using p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, and the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 8:2; first react at -10 °C for 20 min, then react at room temperature until the product solidifies to obtain the APPTA-x copolymer, and finally react at 190 °C for 6 h to carry out the Claisen rearrangement reaction to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (the reaction formula is as Figure 1 shown). The end diameter of the modified aramid fiber expands by 1.5 to 4 times, which is achieved through the following steps: The aramid fiber is ultrasonically cleaned with acetone or ethanol for 5 min to remove surface impurities. After drying, the end of the aramid fiber is immersed in a mixed solution prepared by mixing a 5wt% sodium hydroxide solution and DMSO with a purity of 99.9% at a volume ratio of 3 to 7. Under the condition of nitrogen atmosphere protection, the mixture is stirred at a rate of 200 rpm at 90 °C for 2 h. After swelling, it is washed with deionized water until the washing liquid is neutral, and then freeze-dried or supercritically CO2 dried to obtain the modified aramid fiber with enlarged ends.

[0040] The described high-strength UHPC panel is prepared through the following steps: S1. Add portland cement, high-alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the ratio, and dry-mix to make the materials fully and evenly mixed. S2. Add a water reducer and an expansive agent, and continue dry-mixing to evenly disperse the additives in the materials. S3. Add steel fibers and modified aramid fibers with enlarged ends, and stir to evenly disperse the fibers in the materials. S4. According to the requirements of the water-binder ratio, add water and stir until a uniform UHPC mixture with good fluidity is formed. S5. Pour the UHPC mixture into a mold for molding and curing to obtain the described high-strength UHPC panel.

[0041] Example 3 A high-strength UHPC panel, by mass, consists of the following raw materials: 850 parts of portland cement, 8 parts of high-alumina cement, 300 parts of spherical fly ash (particle size 12 - 38 μm, sphericity not less than 0.9), 120 parts of silica fume (particle size not greater than 25 μm), 900 parts of 0.075 - 3 mm graded quartz sand (specific ratio: the mass ratio of quartz sand with particle size 0.075 - 0.2 mm, 0.2 - 0.35 mm, 0.35 - 1.5 mm, and 1.5 - 3 mm is 2:3:6:5), 45 parts of water reducer, 18 parts of expansive agent (composed of magnesia and modified gypsum at a mass ratio of 0.8:1, the modified gypsum is a complex of α-gypsum and β-gypsum after calcination of phosphogypsum, mass ratio 7:3), 8 parts of metakaolin powder (particle size not greater than 25 μm), 35 parts of steel fibers, 20 parts of modified aramid fibers with enlarged ends, and 5 parts of water retention agent; Among them, the aramid fiber is a modified aramid fiber with a copolymerization modification to introduce hydroxyl groups into the main chain. Using p-phenylenediamine, p-phthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, the molar ratio of p-phthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 7:3. First, react at -10 °C for 20 min, then react at room temperature until the product solidifies to obtain the APPTA-x copolymer. Finally, react at 190 °C for 6 h to carry out the Claisen rearrangement reaction to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (the reaction formula is as Figure 1 shown); The end diameter of the modified aramid fiber expands by 1.5 to 4 times, which is achieved through the following steps: Ultrasonically clean the aramid fiber with acetone or ethanol for 1 to 5 min to remove surface impurities. After drying, immerse the end of the aramid fiber in a mixed solution prepared by mixing a 10wt% sodium hydroxide solution and DMSO with a purity of 99.9% at a volume ratio of 2:8. At a temperature of 70 °C, a stirring rate of 100 rpm, and under the protection of a nitrogen atmosphere, soak for 5 h. After swelling, wash with deionized water until the washing liquid is neutral, and freeze-dry or supercritically dry with CO2 to obtain a modified aramid fiber with an enlarged end.

[0042] The high-strength UHPC panel is prepared by the following steps: S1. Add portland cement, high-alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the ratio, and dry-mix to make the materials fully and evenly mixed; S2. Add a water reducer and an expansion agent, and continue dry-mixing to make the additives evenly dispersed in the materials; S3. Add steel fibers and modified aramid fibers with enlarged ends, and stir to make the fibers evenly dispersed in the materials; S4. According to the water-binder ratio requirement, add water and stir until a uniform UHPC mixture with good fluidity is formed; S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0043] Example 4 A high-strength UHPC panel consists of the following raw materials by mass parts: 1000 parts of portland cement, 12 parts of high-alumina cement, 400 parts of spherical fly ash (particle size 12 - 38 μm, sphericity not less than 0.9), 180 parts of silica fume (particle size not greater than 25 μm), 1000 parts of 0.075 - 3 mm graded quartz sand (specific ratio: the mass ratio of quartz sand of 0.075 - 0.2 mm, quartz sand of 0.2 - 0.35 mm, quartz sand of 0.35 - 1.5 mm, and quartz sand of 1.5 - 3 mm is 4:5:7:6), 80 parts of water reducer, 25 parts of expansive agent (composed of magnesia and modified gypsum in a mass ratio of 1.2:1, the modified gypsum is a complex of α-gypsum and β-gypsum after calcining phosphogypsum, mass ratio 9:1), 12 parts of metakaolin powder (particle size not greater than 25 μm), 80 parts of steel fiber, 30 parts of modified aramid fiber with enlarged ends, and 0.5 part of water retention agent; Among them, the aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain by copolymerization modification, using p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, and the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 9:1; first react at -10 °C for 20 min, then react at room temperature until the product solidifies to obtain the APPTA-x copolymer, and finally react at 190 °C for 6 h to carry out the Claisen rearrangement reaction to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (the reaction formula is as Figure 1 shown); The diameter of the ends of the modified aramid fiber is enlarged by 1.5 - 4 times, which is achieved through the following steps: ultrasonically clean the aramid fiber with acetone or ethanol for 1 - 5 min to remove surface impurities, and after drying, immerse the ends of the aramid fiber in a mixed solution prepared by mixing a 15wt% sodium hydroxide solution and DMSO with a purity of 99.9% in a volume ratio of 3:7, at a temperature of 40 °C, with a stirring rate of 300 rpm, under the protection of a nitrogen atmosphere, soak for 6 h, and after swelling, wash with deionized water until the washing solution is neutral, and obtain the modified aramid fiber with enlarged ends by freeze-drying or supercritical CO2 drying.

[0044] The above-mentioned high-strength UHPC panel is prepared by the following steps: S1. Add portland cement, high-alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the ratio, and dry-mix to make the materials fully and evenly mixed; S2. Add the water reducer and the expansive agent, and continue dry-mixing to make the additives evenly dispersed in the materials; S3. Add the steel fiber and the modified aramid fiber with enlarged ends, and stir to make the fibers evenly dispersed in the materials; S4. According to the requirements of the water-cement ratio, add water and stir until a uniform UHPC mixture with good fluidity is formed; S5. Pour the UHPC mixture into a mold for shaping and curing to obtain the high-strength UHPC panel.

[0045] Example 5 A high-strength UHPC panel is composed of the following raw materials by mass parts: 700 parts of portland cement, 10 parts of high-alumina cement, 3750 parts of spherical fly ash (particle size of 12 - 38 μm, sphericity not less than 0.9), 165 parts of silica fume (particle size not greater than 25 μm), 987.5 parts of 0.075 - 3 mm graded quartz sand (specific ratio: the mass ratio of quartz sand of 0.075 - 0.2 mm, 0.2 - 0.35 mm, 0.35 - 1.5 mm, and 1.5 - 3 mm is 3.5:4.5:6.5:6), 72.5 parts of water reducer, 22.5 parts of expansive agent (composed of magnesia and modified gypsum in a mass ratio of 1:1, the modified gypsum is a complex of α-gypsum and β-gypsum after calcination of phosphogypsum, mass ratio of 8:2), 11.25 parts of metakaolin powder (particle size not greater than 25 μm), 62.5 parts of steel fiber, 28.75 parts of modified aramid fiber with enlarged ends, and 1 part of water retention agent; Among them, the aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain by copolymerization modification, using p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, and the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 7:3; first react at -10 °C for 20 min, then react at room temperature until the product solidifies to obtain the APPTA-x copolymer, and finally react at 190 °C for 6 h to carry out the Claisen rearrangement reaction to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (the reaction formula is as Figure 1 shown); The ends of the modified aramid fiber are enlarged by 1.5 - 4 times, which is achieved through the following steps: The aramid fiber is ultrasonically cleaned with acetone or ethanol for 1 - 5 min to remove surface impurities. After drying, the ends of the aramid fiber are immersed in a mixed solution prepared by mixing a 10wt% sodium hydroxide solution and DMSO with a purity of 99.9% in a volume ratio of 2:8. At a temperature of 40 °C and a stirring rate of 300 rpm, under the protection of a nitrogen atmosphere, soak for 5 h. After swelling, wash with deionized water until the washing solution is neutral, and obtain the modified aramid fiber with enlarged ends by freeze-drying or supercritical CO2 drying.

[0046] The above-mentioned high-strength UHPC panel is prepared by the following steps: S1. Add portland cement, high alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the ratio, and dry mix to make the materials fully and evenly mixed. S2. Add a water reducer and an expansive agent, and continue dry mixing to evenly disperse the additives in the materials. S3. Add steel fibers and modified aramid fibers with enlarged ends, and stir to evenly disperse the fibers in the materials. S4. According to the requirements of the water-binder ratio, add water and stir until a uniform UHPC mixture with good fluidity is formed. S5. Pour the UHPC mixture into a mold for molding and curing to obtain the described high-strength UHPC panel.

[0047] Experimental Tests and Data Analysis 1. Fluidity Test The fluidity was measured according to the static mortar fluidity method. The specific operation is as follows: The UHPC mixtures in Steps S4 of Examples 1 to 5 were filled into a truncated cone mold for cement mortar fluidity with specified dimensions (height 60 ± 0.5 mm, upper inner diameter 70 ± 0.5 mm, lower inner diameter 100 ± 0.5 mm, lower outer diameter 120 mm. This instrument complies with the regulations of GB / T 2419-2016 Test Method for Fluidity of Cement Mortar). After scraping flat, lift the test mold, and take the average value of the longitudinal and transverse diameters of the mixture as the fluidity value. The results are shown in Table 1.

[0048] Table 1 Fluidity Data Table of UHPC Mixtures in Examples 1 to 5

[0049] 2. Compressive Strength, Flexural Strength, and Tensile Strength Tests According to the standard of GB17671-2021 Test Method for Strength of Cement Mortar, the compressive strength and flexural strength were tested. The test block size was a prism of 40 mm × 40 mm × 160 mm. According to the standard of GB / T 28900-2022 Test Methods for Steel Products for Reinforced Concrete, the tensile strength was tested. The results are shown in Table 2.

[0050] Table 2 Compressive Strength and Flexural Strength Data Table of UHPC Materials in Examples 1 to 5

[0051] Compared with the UHPC panel materials prepared from ordinary polymer fibers (for example, the 28-day compressive strength of the materials disclosed in the Chinese invention patent with the application number 201911317857.5 is 106 - 128 MPa), the 28-day compressive strength of the high-strength UHPC panel provided by the present invention is increased to 166 - 192 MPa. The reasons are as follows: (1) A small amount of water retention agent is added in the present invention, which continuously provides moisture for the hydration reactions of portland cement and high-alumina cement in the later stage, making the hydration reactions more sufficient, generating more hydration products such as ettringite and C-S-H gel, contributing to the improvement of the material strength. At the same time, the water retention agent enables active admixtures such as silica fume and metakaolin powder to better participate in the pozzolanic reaction, further optimizing the structure of the hydration products and improving the density of the material, thereby enhancing its strength; (2) By precisely controlling the particle size and particle size distribution of the raw materials, on the premise of ensuring fluidity, the density and strength of the material are further improved; (3) Through the structural and molecular modification of the polymer fibers, including the end swelling treatment to enhance the mechanical bite force and the introduction of hydroxyl or carboxyl groups into the main chain to form hydrogen bonds to strengthen the interfacial bonding force, the relative slippage of each component of the panel during the stress process can be effectively inhibited, further enhancing the strength of the material.

[0052] Meanwhile, the 28-day flexural strength of the material of the present invention reaches 27.8 - 29.0 MPa and the tensile strength reaches 12.5 - 15.5 MPa. Compared with the UHPC material disclosed in the Chinese patent application with the application number 202411085592.1, whose flexural strength is 18.5 - 25.2 MPa and tensile strength is 8.2 - 12.1 MPa, the flexural strength and tensile strength of the present invention have been improved to a certain extent. The increase in tensile strength can effectively resist the generation of microcracks, block the penetration path of erosion media, and enhance the structural durability; the increase in flexural strength solves the contradiction between structural thinning and strength guarantee, promoting the development of UHPC panels towards the direction of being thinner and lighter.

[0053] Although the present application has been described in combination with specific features and their embodiments, it is obvious that various modifications and combinations can be made without departing from the spirit and scope of the present application. Accordingly, the present specification and the drawings are merely exemplary descriptions of the present application defined by the appended claims, and are considered to have covered any and all modifications, variations, combinations, or equivalents within the scope of the present application. Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these changes and modifications.

Claims

1. A high-strength UHPC panel, characterized in that: By mass fraction, it includes the following components: 700 - 1000 parts of portland cement, 8 - 12 parts of high alumina cement, 300 - 400 parts of spherical fly ash, 120 - 180 parts of silica fume, 900 - 1000 parts of 0.075 - 3 mm graded quartz sand, 45 - 75 parts of water reducing agent, 18 - 25 parts of expansive agent, 8 - 12 parts of metakaolin powder, 35 - 80 parts of steel fiber, 15 - 35 parts of polymer fiber, and 0.5 - 5 parts of water retaining agent; the end of the polymer fiber is in an enlarged shape.

2. The high-strength UHPC panel according to claim 1, wherein: The polymer fiber described above includes aramid fiber or polypropylene fiber.

3. The high-strength UHPC panel according to claim 2, characterized in that: The aramid fiber is a modified aramid fiber with hydroxyl or carboxyl groups introduced into the main chain by copolymer modification.

4. The high-strength UHPC panel according to claim 3, characterized in that: The modified aramid fiber is specifically a third monomer with hydroxyl or carboxyl groups replacing the reaction monomer, and the molar ratio of the third monomer with hydroxyl or carboxyl groups to the replaced reaction monomer is 1:9 - 3:

7.

5. The high-strength UHPC panel according to claim 1, wherein: The diameter of the end of the polymer fiber is enlarged by 1.5 - 4 times.

6. The high-strength UHPC panel according to claim 5, characterized in that: The enlarged shape of the end of the aramid fiber is achieved through the following steps: soaking the end of the aramid fiber in a DMSO solution dissolved with strong base, swelling, washing with deionized water until the washing liquid is neutral, and freeze - drying or supercritical CO2 drying to obtain aramid fiber with an enlarged end state.

7. The high-strength UHPC panel according to claim 6, characterized in that: The aramid fiber is ultrasonically cleaned with acetone or ethanol for 1 - 5 min before soaking.

8. The high-strength UHPC panel according to claim 6, characterized in that: The strong base at least includes one of a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 5wt% - 15wt%; the volume ratio of the strong base to DMSO is 1:9 - 3:7; the soaking is specifically carried out at a temperature of 40 - 90 °C and a stirring rate of 100 - 300 rpm for 2 - 6 h.

9. The high-strength UHPC panel according to claim 5, characterized in that: The enlarged shape of the end of the polypropylene fiber is achieved by heating.

10. A method for preparing a high-strength UHPC panel as described in any one of claims 1 to 9, characterized in that: It includes the following steps: S1. Add portland cement, high alumina cement, spherical fly ash, silica fume, metakaolin, and quartz sand into a mixer according to the ratio, and dry - mix to make the materials fully and evenly mixed. S2. Add the water reducing agent and the expansive agent, and continue dry - mixing to make the additives evenly dispersed in the materials. S3. Add the steel fiber and the polymer fiber, and stir to make the fibers evenly dispersed in the materials. S4. According to the water - binder ratio requirement, add water and stir until a uniform UHPC mixture with good fluidity is formed. S5. Pour the UHPC mixture into a mold for shaping and curing to obtain the high - strength UHPC panel described above.

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