A high-strength UHPC panel and preparation method

Abstract

The present invention provides a high-strength UHPC panel and a preparation method, belonging to the field of building materials. The high-strength UHPC panel comprises the following components, calculated by weight: 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 a water reducer, 18-25 parts of an expansion 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 a water-retaining agent; the ends of the polymer fibers are in an expanded state. The present invention solves the problem of poor bonding between polymer fibers and UHPC materials in UHPC materials, improves the compressive strength and tensile strength of the UHPC panel, and the UHPC panel material provided by the present invention has good fluidity and is easy to process and form.

Description

Technical Field

[0001] The present invention belongs to the field of building materials, and in particular relates 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. It has broad application prospects in many fields such as construction, bridges, tunnels, etc.

[0003] The exceptional performance of UHPC materials is largely due to their refined internal microstructure and rational composition design. Throughout the development of UHPC, steel fibers have been frequently added to further enhance its mechanical properties, particularly its strength. The addition of steel fibers effectively prevents the propagation and extension of cracks within the concrete. By bridging the cracks within the concrete matrix, external forces are distributed over a wider area, significantly improving the tensile and flexural strength properties of UHPC. However, the use of steel fibers also presents a number of challenges that should not be overlooked.

[0004] First, the relatively high price of steel fiber has limited the widespread promotion and application of UHPC materials. Cost is a key consideration in engineering construction, and the high price of steel fiber significantly increases the production cost of UHPC materials, thereby reducing its competitiveness in the market.

[0005] Secondly, the presence of steel fibers can make UHPC materials susceptible to permeability. Because gaps exist at the interface between the steel fibers and the UHPC matrix, moisture and chemicals can easily penetrate the material under the influence of the external environment. This can lead to a series of durability issues, such as steel corrosion and chemical attack, seriously affecting the service life and safety of UHPC structures.

[0006] Furthermore, the high density of steel fibers increases the overall density of UHPC materials after adding them. In engineering fields with strict requirements on structural deadweight, such as long-span structures in bridge engineering and the roof structures of high-rise buildings, the high deadweight increases the structural burden and may require additional structural design and construction measures to ensure structural stability and safety, which undoubtedly increases project costs and construction difficulty.

[0007] To address the aforementioned issues with steel fibers, researchers are attempting to partially replace steel fibers with polymer fibers. For example, Chinese invention patent 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 a specific combination of cement, silica fume, quartz sand of varying grades, crushed stone, a high-efficiency water reducer, water, polypropylene fibers, and basalt fibers. This technology demonstrates the potential for UHPC applications in specific components, but its formulation and performance characteristics are not fully suitable for applications such as formwork removal.

[0008] Polymer fibers offer advantages such as low density and relatively low price, promising to reduce the cost and weight of UHPC materials while maintaining their mechanical properties. However, there is a problem of poor compatibility between polymer fibers and UHPC. Due to their relatively smooth surface, polymer fibers have a weak bond with the UHPC matrix, making them prone to relative slippage when subjected to stress. This results in a decrease in the strength of the UHPC material, particularly key performance indicators such as tensile strength, which are difficult to meet actual engineering requirements.

[0009] To improve the compatibility of polymer fibers with UHPC materials and enhance their strength, existing technologies use surface roughening treatments on polymer fibers. Physical and chemical methods are used to modify the polymer fiber surface, creating a rough surface that increases friction and mechanical engagement between the polymer fiber and the UHPC substrate. This surface roughening effectively enhances the bonding between the polymer fiber and the UHPC matrix, allowing the polymer fiber to better cooperate with the matrix under load, thereby increasing the tensile strength of the UHPC material.

[0010] Although existing surface roughening methods have improved the compatibility between polymer fibers and UHPC materials to a certain extent, some shortcomings still exist. For example, chemical etching may have a certain impact on the mechanical properties of the fiber, and the use of chemical reagents may cause environmental pollution problems; physical etching methods require special equipment and processes, which are relatively expensive; and the selection of coating materials and the control of the coating process in coating methods are relatively complex, and the bonding stability between the coating and the fiber and concrete matrix needs to be further improved. Therefore, how to further optimize polymer fibers and improve their compatibility and bonding properties with UHPC materials remains an important research topic. 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 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 shape.

[0012] The high-strength UHPC panel includes the following components, calculated by weight: 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 expansion 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.

[0013] Preferably, the polymer fibers include aramid fibers.

[0014] Preferably, the aramid fiber is a modified aramid fiber in which hydroxyl groups or carboxyl groups are introduced into the main chain through copolymerization modification.

[0015] Preferably, the ends of the polymer fibers are in an expanded state.

[0016] Preferably, the diameter of the end of the polymer fiber is expanded by 1.5 to 4 times.

[0017] Further preferably, the expanded shape of the end of the aramid fiber is achieved by the following steps: soaking the end of the aramid fiber in a DMSO solution dissolved with a strong base, washing with deionized water after swelling until the washing solution is neutral, and freeze-drying or supercritical CO2 drying to obtain the aramid fiber with the end in an expanded state.

[0018] More preferably, the aramid fiber is ultrasonically cleaned with acetone or ethanol for 1 to 5 minutes before soaking to remove surface impurities.

[0019] More preferably, the strong base comprises at least one of a sodium hydroxide solution or a potassium hydroxide solution with a solubility of 5 wt % to 15 wt %.

[0020] More preferably, the volume ratio of the strong base to DMSO is 1:9 to 3:7.

[0021] More preferably, the soaking is specifically: soaking at a temperature of 40-90° C. and a stirring rate of 100-300 rpm for 2-6 hours.

[0022] More preferably, the immersion is carried out under the protection of an inert atmosphere to reduce oxidation side reactions.

[0023] Preferably, the mass ratio of the 0.075-3 mm graded quartz sand, specifically 0.075-0.2 mm quartz sand, 0.2-0.35 mm quartz sand, 0.35-1.5 mm quartz sand, and 1.5-3 mm quartz sand is 2-4:3-5:6-8:5-7.

[0024] Preferably, the expansion agent comprises magnesium oxide and modified phosphogypsum in a mass ratio of 0.8 to 1.2; the modified phosphogypsum is α-gypsum and / or β-gypsum obtained by calcining phosphogypsum. The expansion agent is a combination of magnesium oxide and modified phosphogypsum, with the magnesium oxide used for initial expansion and the modified phosphogypsum used for later expansion.

[0025] Preferably, when the modified gypsum is a complex of α-gypsum and β-gypsum obtained by calcining phosphogypsum, the mass ratio of α-gypsum to β-gypsum is 7:3 to 9:1.

[0026] 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.

[0027] The method for preparing the high-strength UHPC panel comprises the following steps:

[0028] 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;

[0029] S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material;

[0030] S3, adding steel fiber and polymer fiber, stirring to evenly disperse the fibers in the material;

[0031] S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed;

[0032] S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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

[0039] Figure 1 The reaction formula for modified aramid fiber is to introduce hydroxyl groups into the aramid main chain through copolymerization modification. DETAILED DESCRIPTION

[0040] The technical scheme of the present invention is further described below through examples. The raw materials used in the examples can be purchased from the market or prepared by conventional methods.

[0041] Example 1

[0042] A high-strength UHPC panel is composed of the following raw materials, measured by mass: 800 parts of Portland cement, 10 parts of high-alumina cement, 350 parts of spherical fly ash (particle size of 12-38 μm, sphericity of not less than 0.9), 150 parts of silica fume (particle size of not more than 25 μm), 950 parts of 0.075-3 mm graded quartz sand (specifically, the mass ratio of 0.075-0.2 mm quartz sand, 0.2-0.35 mm quartz sand, 0.35-1.5 mm quartz sand, and 1.5-3 mm quartz sand is 3:4:6:5), 60 parts of a water reducer, 20 parts of an expansive agent (composed of magnesium oxide and modified gypsum in a mass ratio of 1:1, the modified gypsum being a composite of α-gypsum and β-gypsum obtained by calcining phosphogypsum, in a mass ratio of 8:2), and 150 parts of quartz fume (particle size of not more than 25 μm). μm), 10 parts of steel fiber, 50 parts of modified aramid fiber with expanded ends, and 4 parts of water-retaining agent;

[0043] The aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain through copolymerization modification, and is prepared with p-phenylenediamine, terephthaloyl chloride and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, wherein the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 8:2; the reaction is first carried out at -10°C for 20 minutes, and then at room temperature until the product solidifies to obtain an APPTA-x copolymer; finally, the reaction is carried out at 190°C for 6 hours, and a Claisen rearrangement reaction is carried out to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (reaction formula as shown in FIG. 1 ). Figure 1 shown);

[0044] The end diameter of the modified aramid fiber is expanded by 1.5 to 4 times, which is achieved by the following steps: the aramid fiber is ultrasonically cleaned with acetone or ethanol for 2 minutes to remove surface impurities, and after drying, the end of the aramid fiber is immersed in a mixed solution of a 5wt% sodium hydroxide solution and 99.9% pure DMSO in a volume ratio of 1 to 9, and the mixture is stirred at a temperature of 90°C and a speed of 200 rpm under a nitrogen atmosphere for 6 hours. After swelling, the modified aramid fiber is washed with deionized water until the washing solution is neutral, and freeze-dried or supercritical CO2 dried to obtain the modified aramid fiber with expanded end.

[0045] The high-strength UHPC panel is prepared by the following steps:

[0046] 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;

[0047] S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material;

[0048] S3, adding steel fiber and modified aramid fiber with expanded ends, stirring to evenly disperse the fibers in the material;

[0049] S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed;

[0050] S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0051] Example 2

[0052] A high-strength UHPC panel is composed of the following raw materials, measured by mass: 740 parts of Portland cement, 12 parts of high-alumina cement, 400 parts of spherical fly ash (particle size of 12-38 μm, sphericity of not less than 0.9), 180 parts of silica fume (particle size of not more than 25 μm), 1000 parts of 0.075-3 mm graded quartz sand (specifically, the mass ratio of 0.075-0.2 mm quartz sand, 0.2-0.35 mm quartz sand, 0.35-1.5 mm quartz sand, and 1.5-3 mm quartz sand is 4:5:7:6), 80 parts of a water reducer, 25 parts of an expansive agent (composed of magnesium oxide and modified gypsum in a mass ratio of 0.9:1, the modified gypsum being a composite of α-gypsum and β-gypsum obtained by calcining phosphogypsum, in a mass ratio of 9:1), and metakaolin powder (particle size of not more than 25 μm), 12 parts of steel fiber, 80 parts of modified aramid fiber with expanded ends, and 1 part of water-retaining agent;

[0053] The aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain through copolymerization modification, and is prepared with p-phenylenediamine, terephthaloyl chloride and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, wherein the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 8:2; the reaction is first carried out at -10°C for 20 minutes, and then at room temperature until the product solidifies to obtain an APPTA-x copolymer; finally, the reaction is carried out at 190°C for 6 hours, and a Claisen rearrangement reaction is carried out to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (reaction formula as shown in FIG. 1 ). Figure 1 shown);

[0054] The end diameter of the modified aramid fiber is expanded by 1.5 to 4 times, which is achieved by the following steps: the aramid fiber is ultrasonically cleaned with acetone or ethanol for 5 minutes to remove surface impurities, and after drying, the end of the aramid fiber is immersed in a mixed solution of a 5wt% sodium hydroxide solution and 99.9% pure DMSO in a volume ratio of 3 to 7, and the mixture is stirred at a temperature of 90°C and a speed of 200 rpm under a nitrogen atmosphere for 2 hours. After swelling, the modified aramid fiber is washed with deionized water until the washing solution is neutral, and freeze-dried or supercritical CO2 dried to obtain the modified aramid fiber with expanded end.

[0055] The high-strength UHPC panel is prepared by the following steps:

[0056] 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;

[0057] S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material;

[0058] S3, adding steel fiber and modified aramid fiber with expanded ends, stirring to evenly disperse the fibers in the material;

[0059] S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed;

[0060] S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0061] Example 3

[0062] A high-strength UHPC panel is composed of the following raw materials, measured by weight: 850 parts of silicate cement, 8 parts of high-alumina cement, 300 parts of spherical fly ash (particle size of 12-38 μm, sphericity of not less than 0.9), 120 parts of silica fume (particle size of not more than 25 μm), 900 parts of 0.075-3 mm graded quartz sand (specifically, the mass ratio of 0.075-0.2 mm quartz sand, 0.2-0.35 mm quartz sand, 0.35-1.5 mm quartz sand, and 1.5-3 mm quartz sand is 2:3:6:5), 45 parts of a water reducer, 18 parts of an expansive agent (composed of magnesium oxide and modified gypsum in a mass ratio of 0.8:1, the modified gypsum being a composite of α-gypsum and β-gypsum obtained by calcining phosphogypsum, in a mass ratio of 7:3), and 18 parts of metakaolin powder (particle size of not more than 25 μm), 8 parts of steel fiber, 35 parts of steel fiber, 20 parts of modified aramid fiber with expanded ends and 5 parts of water retaining agent;

[0063] The aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain through copolymerization modification, and is prepared with p-phenylenediamine, terephthaloyl chloride and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, wherein the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 7:3; the reaction is first carried out at -10°C for 20 minutes, and then at room temperature until the product solidifies to obtain an APPTA-x copolymer; finally, the reaction is carried out at 190°C for 6 hours, and a Claisen rearrangement reaction is performed to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (reaction formula as shown in FIG. 1 ). Figure 1 shown);

[0064] The end diameter of the modified aramid fiber is expanded by 1.5 to 4 times, which is achieved by the following steps: the aramid fiber is ultrasonically cleaned with acetone or ethanol for 1 to 5 minutes to remove surface impurities, and after drying, the end of the aramid fiber is immersed in a mixed solution of a 10wt% sodium hydroxide solution and 99.9% pure DMSO in a volume ratio of 2:8, and the mixture is stirred at a temperature of 70°C and a speed of 100 rpm under a nitrogen atmosphere for 5 hours. After swelling, the modified aramid fiber is washed with deionized water until the washing solution is neutral, and freeze-dried or supercritical CO2 dried to obtain the modified aramid fiber with expanded ends.

[0065] The high-strength UHPC panel is prepared by the following steps:

[0066] 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;

[0067] S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material;

[0068] S3, adding steel fiber and modified aramid fiber with expanded ends, stirring to evenly disperse the fibers in the material;

[0069] S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed;

[0070] S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0071] Example 4

[0072] A high-strength UHPC panel is composed of the following raw materials, calculated by weight: 1000 parts of Portland cement, 12 parts of high-alumina cement, 400 parts of spherical fly ash (particle size of 12-38 μm, sphericity of not less than 0.9), 180 parts of silica fume (particle size of not more than 25 μm), 0.075-3 mm graded quartz sand (specific proportions are (specifically 0.075-0.2 mm quartz sand, 0.2-0.35 mm quartz sand, 0.35-1.5 mm quartz sand, 1.5-3 1000 parts of quartz sand (with a mass ratio of 4:5:7:6 for 0.1 mm), 80 parts of water reducer, 25 parts of expansion agent (composed of magnesium oxide and modified gypsum in a mass ratio of 1.2:1, where the modified gypsum is a composite of α-gypsum and β-gypsum after calcining phosphogypsum, with a mass ratio of 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 expanded ends, and 0.5 parts of water retaining agent;

[0073] The aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain through copolymerization modification, and is prepared with p-phenylenediamine, terephthaloyl chloride and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, wherein the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 9:1; the reaction is first carried out at -10°C for 20 minutes, and then at room temperature until the product solidifies to obtain an APPTA-x copolymer; finally, the reaction is carried out at 190°C for 6 hours, and a Claisen rearrangement reaction is performed to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (reaction formula as shown in FIG. 1 ). Figure 1 shown);

[0074] The end diameter of the modified aramid fiber is expanded by 1.5 to 4 times, which is achieved by the following steps: the aramid fiber is ultrasonically cleaned with acetone or ethanol for 1 to 5 minutes to remove surface impurities, and after drying, the end of the aramid fiber is immersed in a mixed solution of a 15wt% sodium hydroxide solution and 99.9% pure DMSO in a volume ratio of 3:7, and the mixture is stirred at a temperature of 40°C and a speed of 300 rpm under nitrogen atmosphere protection for 6 hours. After swelling, the modified aramid fiber is washed with deionized water until the washing solution is neutral, and freeze-dried or supercritical CO2 dried to obtain the modified aramid fiber with expanded end.

[0075] The high-strength UHPC panel is prepared by the following steps:

[0076] 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;

[0077] S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material;

[0078] S3, adding steel fiber and modified aramid fiber with expanded ends, stirring to evenly disperse the fibers in the material;

[0079] S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed;

[0080] S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0081] Example 5

[0082] A high-strength UHPC panel is composed of the following raw materials, calculated by weight: 700 parts of Portland cement, 10 parts of high-alumina cement, 3750 parts of spherical fly ash (particle size of 12-38 μm, sphericity of not less than 0.9), 165 parts of silica fume (particle size of not more than 25 μm), 0.075-3 mm graded quartz sand (specific proportions are (specifically 0.075-0.2 mm quartz sand, 0.2-0.35 mm quartz sand, 0.35-1.5 mm quartz sand, 1.5-3 987.5 parts of quartz sand (with a mass ratio of 3.5:4.5:6.5:6), 72.5 parts of water reducer, 22.5 parts of expansion agent (composed of magnesium oxide and modified gypsum in a mass ratio of 1:1, where the modified gypsum is a composite of α-gypsum and β-gypsum after calcining phosphogypsum, with a 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 expanded ends, and 1 part of water retaining agent;

[0083] The aramid fiber is a modified aramid fiber with hydroxyl groups introduced into the main chain through copolymerization modification, and is prepared with p-phenylenediamine, terephthaloyl chloride and 2,5-bis(allyloxy)terephthaloyl chloride as raw materials, wherein the molar ratio of terephthaloyl chloride to 2,5-bis(allyloxy)terephthaloyl chloride is 7:3; the reaction is first carried out at -10°C for 20 minutes, and then at room temperature until the product solidifies to obtain an APPTA-x copolymer; finally, the reaction is carried out at 190°C for 6 hours, and a Claisen rearrangement reaction is performed to convert the product APPTA-x into a modified aramid fiber with hydroxyl groups introduced into the main chain (reaction formula as shown in FIG. 1 ). Figure 1 shown);

[0084] The end diameter of the modified aramid fiber is expanded by 1.5 to 4 times, which is achieved by the following steps: the aramid fiber is ultrasonically cleaned with acetone or ethanol for 1 to 5 minutes to remove surface impurities, and after drying, the end of the aramid fiber is immersed in a mixed solution of a 10wt% sodium hydroxide solution and 99.9% pure DMSO in a volume ratio of 2:8, and the mixture is stirred at a temperature of 40°C and a speed of 300 rpm under a nitrogen atmosphere for 5 hours. After swelling, the modified aramid fiber is washed with deionized water until the washing solution is neutral, and freeze-dried or supercritical CO2 dried to obtain the modified aramid fiber with expanded ends.

[0085] The high-strength UHPC panel is prepared by the following steps:

[0086] 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;

[0087] S2. Add water reducer and expansion agent, and continue dry mixing to make the additives evenly dispersed in the material;

[0088] S3, adding steel fiber and modified aramid fiber with expanded ends, stirring to evenly disperse the fibers in the material;

[0089] S4. Add water according to the water-binder ratio requirements and stir until a uniform UHPC mixture with good fluidity is formed;

[0090] S5. Pour the UHPC mixture into a mold for molding and curing to obtain the high-strength UHPC panel.

[0091] Experimental testing and data analysis

[0092] 1. Fluidity test

[0093] The fluidity was measured using the static mortar fluidity method. The specific procedure was as follows: The UHPC mixture from step S4 of Examples 1-5 was placed in a cement mortar fluidity truncated cone mold of 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 requirements of GB / T 2419-2016, Cement Mortar Fluidity Determination Method). After leveling, the mold was lifted and the average of the longitudinal and transverse diameters of the mixture was taken as the fluidity value. The results are shown in Table 1.

[0094] Table 1 Fluidity data of UHPC mixtures in Examples 1 to 5

[0095]

[0096] 2. Compressive strength, flexural strength and tensile strength tests

[0097] According to the standard GB17671-2021 "Test method for strength of cement mortar", the compressive strength and flexural strength were tested. The test block size was 40 mm × 40 mm × 160 mm prism. According to the standard GB / T 28900-2022 "Test method for steel for reinforced concrete", the tensile strength was tested. The results are shown in Table 2.

[0098] Table 2 Compressive strength and flexural strength data of UHPC materials in Examples 1 to 5

[0099]

[0100] Compared with UHPC panel materials made of ordinary polymer fibers (such as the material disclosed in Chinese invention patent application number 201911317857.5, which has a 28-day compressive strength of 106~128 MPa), the high-strength UHPC panel provided by the present invention has a 28-day compressive strength increased to 166~192 MPa. This is because: (1) the present invention adds a small amount of water-retaining agent to continuously provide water for the later hydration reaction of silicate cement and high-alumina cement, making the hydration reaction more complete and generating more hydration products such as calcium sulfonite and CSH gel, which helps to improve the strength of the material. At the same time, the water-retaining agent allows active admixtures such as silica fume and kaolin powder to better participate in the pozzolanic reaction, further optimize the structure of the hydration products, improve the density of the material, and thus improve its strength; (2) by precisely controlling the particle size and particle size grading of the raw materials, the density and strength of the material can be further improved while ensuring fluidity; (3) by structural and molecular modification of the polymer fibers, including end expansion treatment to enhance mechanical bite force, and the introduction of hydroxyl or carboxyl groups in the main chain to form hydrogen bonds to strengthen interfacial bonding force, the relative slip of the various components of the panel during the stress process can be effectively suppressed, further improving the strength of the material.

[0101] The material of the present invention also achieves a 28-day flexural strength of 27.8-29.0 MPa and a tensile strength of 12.5-15.5 MPa. Compared to the UHPC material disclosed in Chinese patent application number 202411085592.1, which has a flexural strength of 18.5-25.2 MPa and a tensile strength of 8.2-12.1 MPa, the present invention achieves significant improvements in both flexural and tensile strength. This increase in tensile strength effectively resists microcracks, blocks the penetration path of corrosive media, and enhances structural durability. The increase in flexural strength resolves the conflict between structural thinning and strength assurance, driving the development of thinner and lighter UHPC panels.

[0102] Although the present application has been described with reference to specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present application. Accordingly, this specification and the drawings are merely illustrative of the present application as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present application. Obviously, those skilled in the art may make various modifications and variations to the present application without departing from the scope of the present application. Thus, the present application is intended to include such modifications and variations if they fall within the scope of the claims of the present application and their equivalents.

Claims

1. A high-strength UHPC panel, characterized by: According to the weight percentage, it includes the following components: 700~1000 parts of silicate cement, 8~12 parts of high alumina cement, 300~400 parts of spherical fly ash, 120~180 parts of silica fume, 0.075~3 900-1000 parts of mm-graded quartz sand, 45-75 parts of water-reducing agent, 18-25 parts of expansion 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 ends of the polymer fibers are in an expanded state; the polymer fibers include aramid fibers; the aramid fibers are modified aramid fibers with hydroxyl or carboxyl groups introduced into the main chain through copolymerization; the expanded state of the ends of the aramid fibers is achieved by the following steps: immersing the ends of the aramid fibers in a DMSO solution dissolved with a strong base, washing with deionized water after swelling until the washing solution is neutral, and freeze-drying or supercritical CO2 drying to obtain the aramid fibers with expanded ends.

2. The high-strength UHPC panel according to claim 1, characterized in that: The diameter of the end of the polymer fiber is expanded by 1.5 to 4 times.

3. The high-strength UHPC panel according to claim 1, wherein: Aramid fibers were ultrasonically cleaned with acetone or ethanol for 1–5 min before immersion.

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

5. A method for preparing the high-strength UHPC panel according to any one of claims 1 to 4, characterized in that: The following steps are involved: 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.

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