A high-strength UHPC special aggregate and its preparation method and application

Abstract

The present invention discloses a high-strength UHPC special aggregate and its preparation method and application, and the present invention relates to the field of nano-modification technology. The aggregate is based on high-strength basalt or quartz sand, and forms continuously graded particles through a multi-stage crushing process, optimizing the particle morphology and size distribution. Its surface is modified using a nano-composite system, and the interface bonding performance between the aggregate and the UHPC matrix is ​​significantly improved by forming a gradient nano-composite coating. The process parameters are optimized to ensure the uniformity of the coating and the stability of the performance. The aggregate can significantly improve the compressive strength, flexural strength and durability of UHPC. In the wet joints of prefabricated bridges, the aggregate exhibits excellent construction performance and rapid maintenance characteristics, which can effectively shorten the construction period and increase the life of the structure. The present invention provides a high-performance special aggregate for UHPC through nano-modification technology, which promotes the development of ultra-high performance concrete in engineering applications.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-modification, and in particular to a high-strength UHPC special aggregate, a preparation method and an application thereof. Background Art

[0002] Ultra-High Performance Concrete (UHPC) has been widely used in modern construction due to its excellent mechanical properties and durability. Typical characteristics of UHPC include high compressive strength (typically exceeding 150 MPa), high flexural strength, excellent durability, and impermeability. These properties make it valuable for applications in demanding applications such as bridges, tunnels, high-rise buildings, and military facilities. The performance of UHPC depends significantly on the quality and proportions of its component materials. Aggregates, as a crucial component of UHPC, play a crucial role in its mechanical properties and durability.

[0003] Traditional UHPC aggregates typically utilize high-strength quartz sand or hard rock particles. While these aggregates can provide a certain level of strength, they still have some shortcomings. First, the surface properties of traditional aggregates limit their interfacial bonding strength with cement-based binders, making it difficult to further enhance the overall strength and durability of UHPC. Second, the particle size distribution and shape of traditional aggregates significantly impact the fluidity and density of UHPC, which in turn affects its mechanical properties and construction performance. Furthermore, with the increasing demand for UHPC applications in extreme environments (such as highly corrosive and abrasive environments), the durability and stability of traditional aggregates are also facing challenges.

[0004] In recent years, the application of nano-modification technology in materials science has provided a new approach to improving the performance of traditional materials. Nanomaterials, due to their high specific surface area, excellent mechanical properties, and chemical activity, can improve the structure and properties of materials at the microscopic level. In the field of concrete, the introduction of nanomaterials has been shown to significantly improve the strength, durability, and crack resistance of concrete. For example, nano-silica (Nano-SiO2), due to its high activity, can react with cement hydration products to produce more CSH gel, thereby enhancing the mechanical properties of concrete. Materials such as nano-alumina (Nano-Al2O3) and carbon nanotubes (CNTs) have also been widely studied due to their excellent mechanical properties and reinforcement effects.

[0005] Some prior research has attempted to incorporate nanomaterials into the preparation of UHPC to enhance its performance. For example, Chinese patent CN108585679A discloses a method for preparing high-strength UHPC, which improves the mechanical properties and durability of UHPC by adding nanosilica and nanocalcium carbonate. This method successfully enhances the compressive and flexural strengths of UHPC through the introduction of nanomaterials. However, this patent primarily focuses on the application of nanomaterials in cementitious materials and does not involve direct modification of aggregates. Another Chinese patent, CN110467389A, proposes a method for preparing UHPC-specific aggregates by surface treating the aggregates to improve their interfacial bonding strength with cementitious materials. This treatment involves modifying the aggregate surface with a silane coupling agent, thereby enhancing the bond between the aggregate and cement-based materials. While this method improves UHPC performance to some extent, its effectiveness is limited by the type of coupling agent and the treatment process, and it does not involve nanoscale modification techniques.

[0006] Internationally, U.S. Patent US20170226011A1 discloses a method for preparing nano-modified aggregate for UHPC. This method involves coating the aggregate surface with a thin layer of nano-silica film to enhance the interfacial bonding strength between the aggregate and the cementitious material. Experimental results show that the modified aggregate significantly improves the compressive strength and durability of UHPC. However, the nano-coating produced by this method exhibits poor stability and is prone to detachment during the UHPC production process, resulting in a short-lived modification effect.

[0007] Furthermore, European Patent EP3250531B1 proposes a method for preparing UHPC aggregates reinforced with carbon nanotubes. This method disperses carbon nanotubes on the aggregate surface to form a composite structure, thereby improving the aggregate's mechanical properties and its bonding strength with the cementitious material. While this method has theoretical potential, technical challenges remain regarding the dispersion of carbon nanotubes and their stable bonding with the aggregate. In practical applications, this method presents challenges such as complex preparation processes and high costs.

[0008] In summary, although attempts have been made to modify UHPC aggregates in the existing technology, the following problems still exist: Limited modification effect: Although traditional surface treatment methods such as coupling agent modification can improve the interfacial bonding strength, the improvement is limited and it is difficult to meet the performance requirements of UHPC in extreme environments. Poor stability of nano-coating: The existing nano-coating technology is not stable enough in the UHPC preparation process, which can easily lead to a weakening of the modification effect. Complex preparation process: The dispersion of nanomaterials and the technical requirements for combining with aggregates are high, resulting in a complex preparation process, high cost, and difficulty in large-scale application. Lack of systematic research: Existing research mostly focuses on the modification effect of a single nanomaterial, and lacks systematic research on the composite modification of UHPC aggregates with multiple nanomaterials. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to propose a high-strength UHPC special aggregate, a preparation method and an application, so as to overcome the shortcomings of traditional UHPC aggregate in terms of interface bonding strength, durability and construction performance, thereby improving the application effect of ultra-high performance concrete (UHPC) in high-demand engineering scenarios.

[0010] The technical solution adopted is: a high-strength UHPC special aggregate, wherein the aggregate includes a matrix material and a nanocomposite system; the matrix material is high-strength basalt or quartz sand with a Mohs hardness of ≥7, which is crushed into 0.15-1.18mm continuous graded particles through multi-stage crushing and has a bulk density of ≥1.85g / cm 3 , porosity ≤18%; the nano-composite system is composed of nano-silica with a particle size of 20-50nm and nano-alumina with a particle size of 30-80nm in a mass ratio of 3:1, with a total loading of 1.5-2.5% of the mass of the aggregate, prepared by a sol-gel method and uniformly dispersed by ultrasound; a gradient nano-composite coating is formed on the surface of the aggregate, including: a micron-scale rough substrate: the base material is etched with 5% hydrofluoric acid by mass for 2h, and the surface roughness Ra=5.2-6.8μm; a nano-penetration layer: formed by vacuum impregnation of a nano-SiO2-Al2O3 composite sol with a solid content of 30%, with a penetration depth of ≥200μm, a vacuum degree of 0.01-0.05MPa, and an impregnation time of 1-2h; a crystallization strengthening layer: 800℃, a heating rate of 5℃·min -1 Gradient sintering, keeping warm for 2-3h, forms eutectic structure of α-Al2O3 and cristobalite, Vickers hardness ≥12GPa.

[0011] Preferably, the preparation of the nano-SiO2-Al2O3 composite sol: During the preparation process, 0.5-1.2 wt% of polyvinyl pyrrolidone is added as a dispersant, the pH value of the sol is controlled within the range of 4.5-5.5, and the reaction temperature is maintained at 60±2°C. Subsequently, ultrasonic dispersion is performed at 40 kHz for 30-45 minutes to form a uniform colloid.

[0012] Preferably, the vacuum impregnation process is as follows: three-stage gradient pressure control is adopted: the first stage: the pressure is -0.05MPa, maintained for 20 minutes, to achieve surface penetration of the aggregate; the second stage: the pressure is -0.08MPa, continued for 40 minutes, to complete the deep penetration of the sol; the third stage: restore normal pressure, stand for 10 minutes, to promote the stable filling of the sol in the aggregate.

[0013] Preferably, the gradient sintering process is as follows: in the temperature range of 600-800° C., a carbon dioxide atmosphere is introduced for protection with a gas flow rate of 0.5 L / min to form a carbon-doped α-Al 2 O 3 grain boundary structure.

[0014] Preferably, the α-Al2O3 grain boundary structure is nano whiskers with a size of 50-80nm, an aspect ratio of 15-20, radial distribution, a whisker spacing of 100-300nm, and a grain boundary energy reduced to 0.8J / m 2 the following.

[0015] Preferably, 1-3wt% of silicon carbide nanowires with a diameter of 20-50nm and a length of 5-10μm are additionally added to the nanocomposite system, and are oriented along the tangential direction of the aggregate surface through electrostatic self-assembly technology to form a conductive network; the surface of the nanowires is coated with an amorphous silicon dioxide layer with a thickness of 2-5nm, forming a chemical bond with the nanocomposite coating.

[0016] The method for preparing high-strength UHPC special aggregate as described above includes the following steps: (1) providing a matrix material: selecting high-strength basalt or quartz sand as the matrix material, and forming continuously graded particles through multi-stage crushing processing; (2) surface etching treatment: etching the matrix material with hydrofluoric acid to form a micron-scale rough base on the surface of the matrix material; (3) preparing a nano-SiO2-Al2O3 composite sol: mixing nano-silicon dioxide and nano-alumina; adding polyvinyl pyrrolidone as a dispersant; controlling the pH value of the sol and dispersing it by ultrasonication to form a uniform composite sol; (4) vacuum impregnation to form a nano-permeable layer: placing the etched matrix material in the nano-SiO2-Al2O3 composite sol, and forming a nano-permeable layer by vacuum impregnation; (5) gradient sintering to form a crystallization strengthening layer: gradient sintering the impregnated aggregate to form a crystallization strengthening layer; introducing a carbon dioxide atmosphere for protection to form a carbon-doped α-Al2O3 grain boundary structure.

[0017] Preferably, the aggregate is used to prepare ultra-high performance concrete (UHPC), wherein the mass of the aggregate accounts for 30-50% of the total mass of the UHPC.

[0018] Preferably, in the connection of prefabricated bridge components, when the UHPC with the aggregate is used as the wet joint material: process parameters: fluidity ≥ 650 mm, initial setting time ≥ 120 min, and steam curing at 60° C. for 6 h to reach the design strength.

[0019] The optimization mechanism of matrix material is as follows: High hardness skeleton construction: Basalt / quartz sand with Mohs hardness ≥7 is used as the matrix, and 0.15-1.18mm continuous graded particles are formed through multi-stage crushing. This design makes the bulk density ≥1.85g / cm 3, porosity ≤ 18%, forming a dense skeleton structure. Mechanical support: The high hardness matrix can withstand >150MPa compressive stress without breaking. Stress transfer: Continuous grading optimizes stress distribution and reduces local stress concentration. Surface etching enhancement: 5% hydrofluoric acid etching for 2h forms a micron-level rough surface with Ra=5.2-6.8μm: Where S0 is the original surface area, and roughness increases the interface contact area by 42-68%.

[0020] The mechanism of action of the nanocomposite system is shown in Table 1 below:

[0021] Table 1

[0022]

[0023] The formation mechanism of the crystallization strengthening layer is as follows: α-Al2O3 / cristobalite eutectic structure is generated by gradient sintering at 800℃: Phase transformation strengthening: the cristobalite phase content reaches 35-40%, and the Vickers hardness is ≥12GPa. Grain boundary engineering: Carbon doped grain boundaries are formed in a CO2 atmosphere, and the grain boundary energy is reduced to 0.8J / m 2 The interface enhancement mechanism is as follows: mechanical interlocking, the rough surface forms a barb effect, and the interface shear strength is increased to 18.7MPa. Chemical bonding: SiO2-Al2O3 forms Si-O-Si and Al-O-Si bonds with CSH gel, with a bond energy of 460kJ / mol. Stress buffering: Gradient coating achieves elastic modulus transition: , the stress concentration factor is reduced by 57%. Rapid curing mechanism: Nano-Al2O3 accelerates early hydration, so that the design strength can be reached after curing at 60℃ for 6 hours: The reaction rate constant k0 increased by 2.3 times. Through multi-scale innovations in materials, structure, and process, this technology has enabled UHPC compressive strength to exceed 160 MPa and reduced the thickness of the interface transition zone from 50 μm to 15 μm, providing a breakthrough solution for ultra-high performance concrete engineering applications.

[0024] In summary, the beneficial effects of the present invention are: (1) Significantly improve the mechanical properties of UHPC: By introducing high-strength matrix materials and nanocomposite systems, the present invention greatly improves the hardness and durability of aggregates, thereby enhancing the compressive strength (>150MPa), flexural strength and overall stability of ultra-high performance concrete (UHPC). These performance improvements enable it to meet the needs of high-demand engineering scenarios such as bridges and tunnels. (2) Optimize interface bonding strength: The use of gradient nanocomposite coatings, through the design of micron-level rough substrates and nano-permeable layers, significantly enhances the mechanical bite and chemical bonding between aggregates and UHPC matrix. This optimization not only improves the interface bonding performance, but also reduces the generation of microcracks, thereby improving the material's crack resistance and durability. (3) Improve the construction performance of UHPC: Continuously graded particles and optimized surface properties improve the fluidity and density of UHPC, making it easier to pump and pour during construction. This feature enables it to adapt to the needs of complex engineering scenarios and improves the convenience of construction operations. (4) Achieve rapid curing and efficient construction: In applications such as prefabricated bridge wet joints, the aggregate gives UHPC excellent rapid hardening properties, with a fluidity of ≥650mm and an initial setting time of ≥120min. It only needs 6 hours of steam curing at 60°C to reach the design strength. This rapid curing property significantly shortens the construction period and improves engineering efficiency. (5) Enhance the durability and stability of UHPC: The α-Al2O3 and cristobalite eutectic structure formed by the crystallized strengthening layer and the carbon-doped grain boundary design enable the aggregate to maintain excellent stability in extreme environments (such as high corrosion and high wear). This feature significantly extends the service life of UHPC. (6) Promote the application of nano-modification technology in building materials: The present invention provides innovative ideas for the research and development of UHPC-specific aggregates through a systematic nano-composite system and process optimization. This technological breakthrough not only improves material properties, but also promotes the widespread application and development of nanotechnology in the field of high-performance concrete. These beneficial effects together constitute the core advantage of the present invention and provide strong technical support for the widespread application of ultra-high performance concrete in high-demand engineering scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a microscopic image of the material after application of Example 7 (the scale bar in the figure is 20 μm). DETAILED DESCRIPTION

[0026] The present invention is described in detail below through specific examples. However, the use and purpose of these exemplary embodiments are merely illustrative of the present invention and are not intended to limit the actual scope of protection of the present invention in any form, nor are they intended to limit the scope of protection of the present invention to these embodiments. The technical solutions described in the claims are used as a reference, and for parameter ranges not mentioned, intermediate values ​​are selected.

[0027] Example 1

[0028] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.90g / cm 3 , porosity 17%.

[0029] Nanocomposite system: 30nm nano-silica and 50nm nano-alumina are composited in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.5μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.03MPa for 1.5 hours, with a penetration depth of 220μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold time of 2.5 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.5GPa.

[0030] Example 2

[0031] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.88g / cm 3 , porosity 18%.

[0032] Nanocomposite system: Nano-silica with a particle size of 20 nm and nano-alumina with a particle size of 30 nm are compounded in a mass ratio of 3:1, and the total loading amount is 1.5% of the aggregate mass.

[0033] Gradient Nanocomposite Coating: Micron-level roughness substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.2μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at 0.01MPa for 1 hour, penetration depth 200μm. Crystallization Strengthening Layer: Gradient sintering at 800°C, heating rate 5°C / min, hold for 2 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.0GPa.

[0034] Example 3

[0035] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.92g / cm 3 , porosity 16%.

[0036] Nanocomposite system: Nano-silica with a particle size of 50nm and nano-alumina with a particle size of 80nm are compounded in a mass ratio of 3:1, and the total loading amount is 2.5% of the aggregate mass.

[0037] Gradient Nanocomposite Coating: Micron-level roughness substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.8μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.05MPa for 2 hours, penetration depth 250μm. Crystallization Strengthening Layer: Gradient sintering at 800°C, heating rate 5°C / min, hold temperature 3 hours, forming an α-Al2O3 and cristobalite eutectic structure, Vickers hardness 13.0GPa.

[0038] Example 4

[0039] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.85g / cm 3 , porosity 18%.

[0040] Nanocomposite system: Nano-silica (40nm) and nano-alumina (60nm) in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.0μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.04MPa for 1.5 hours, with a penetration depth of 230μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold time of 2.5 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.8GPa.

[0041] Example 5

[0042] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.90g / cm 3 , porosity 17%.

[0043] Nanocomposite system: 30nm nano-silica and 50nm nano-alumina are composited in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.5μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.03MPa for 1.5 hours, with a penetration depth of 220μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold time of 2.5 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.5GPa.

[0044] Additional addition: 2 wt% silicon carbide nanowires (30 nm in diameter, 8 μm in length) were added to the nanocomposite system, aligned by electrostatic self-assembly technology, and coated with a 3 nm amorphous silicon dioxide layer on the surface.

[0045] Example 6

[0046] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.88g / cm 3 , porosity 18%.

[0047] Nanocomposite system: 20nm nano-silica and 30nm nano-alumina are composited in a 3:1 mass ratio, with a total loading of 1.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.2μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.01MPa for 1 hour, with a penetration depth of 200μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold for 2 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.0GPa.

[0048] Additional addition: 1wt% silicon carbide nanowires (20nm in diameter, 5μm in length) were added to the nanocomposite system, aligned by electrostatic self-assembly technology, and coated with a 2nm amorphous silicon dioxide layer on the surface.

[0049] Example 7

[0050] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.92g / cm 3 , porosity 16%.

[0051] Nanocomposite system: Nano-silica (50nm particle size) and nano-alumina (80nm particle size) are combined in a 3:1 mass ratio, with a total loading of 2.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.8μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.05MPa for 2 hours, with a penetration depth of 250μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold temperature for 3 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 13.0GPa.

[0052] Additional addition: 3wt% silicon carbide nanowires (50nm in diameter, 10μm in length) were added to the nanocomposite system, aligned by electrostatic self-assembly technology, and coated with a 5nm amorphous silicon dioxide layer on the surface.

[0053] Example 8

[0054] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.85g / cm 3 , porosity 18%.

[0055] Nanocomposite system: Nano-silica (40nm) and nano-alumina (60nm) in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.0μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.04MPa for 1.5 hours, with a penetration depth of 230μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold time of 2.5 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.8GPa.

[0056] Additional addition: 2 wt% silicon carbide nanowires (40 nm in diameter, 7 μm in length) were added to the nanocomposite system, aligned by electrostatic self-assembly technology, and coated with a 4 nm amorphous silicon dioxide layer on the surface.

[0057] Example 9

[0058] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.90g / cm 3 , porosity 17%.

[0059] Nanocomposite system: 30nm nano-silica and 50nm nano-alumina are composited in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.5μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.03MPa for 1.5 hours, with a penetration depth of 220μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold time of 2.5 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.5GPa.

[0060] Preparation of nano-SiO2-Al2O3 composite sol: adding 0.8wt% polyvinyl pyrrolidone, pH=5.0, temperature 60℃, 40kHz ultrasonic dispersion for 40min.

[0061] Example 10

[0062] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.88g / cm 3 , porosity 18%.

[0063] Nanocomposite system: 20nm nano-silica and 30nm nano-alumina are composited in a 3:1 mass ratio, with a total loading of 1.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.2μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.01MPa for 1 hour, with a penetration depth of 200μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold for 2 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.0GPa.

[0064] Preparation of nano-SiO2-Al2O3 composite sol: adding 0.5wt% polyvinyl pyrrolidone, pH = 4.5, temperature 58℃, 40kHz ultrasonic dispersion for 30min.

[0065] Example 11

[0066] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.92g / cm 3 , porosity 16%.

[0067] Nanocomposite system: Nano-silica (50nm particle size) and nano-alumina (80nm particle size) are combined in a 3:1 mass ratio, with a total loading of 2.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.8μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.05MPa for 2 hours, with a penetration depth of 250μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold temperature for 3 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 13.0GPa.

[0068] Preparation of nano-SiO2-Al2O3 composite sol: adding 1.2wt% polyvinyl pyrrolidone, pH=5.5, temperature 62℃, 40kHz ultrasonic dispersion for 45min.

[0069] Example 12

[0070] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.85g / cm 3 , porosity 18%.

[0071] Nanocomposite system: Nano-silica (40nm) and nano-alumina (60nm) in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.0μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.04MPa for 1.5 hours, with a penetration depth of 230μm. Crystallization strengthening layer: Gradient sintering at 800°C, heating rate of 5°C / min, hold time of 2.5 hours, forming a eutectic structure of α-Al2O3 and cristobalite, with a Vickers hardness of 12.8GPa.

[0072] Preparation of nano-SiO2-Al2O3 composite sol: adding 1.0wt% polyvinyl pyrrolidone, pH=5.0, temperature 60℃, 40kHz ultrasonic dispersion for 40min.

[0073] Example 13

[0074] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.90g / cm 3 , porosity 17%.

[0075] Nanocomposite system: 30nm nano-silica and 50nm nano-alumina are composited in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.5μm. Nano-penetration layer: Utilizes a three-stage gradient pressure control: First stage: -0.05MPa, 20 minutes; Second stage: -0.08MPa, 40 minutes; Third stage: Return to normal pressure, let stand for 10 minutes. Penetration depth: 220μm.

[0076] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding time 2.5h, forming eutectic structure of α-Al2O3 and cristobalite, Vickers hardness 12.5GPa.

[0077] Example 14

[0078] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.88g / cm 3 , porosity 18%.

[0079] Nanocomposite system: 20nm nano-silica and 30nm nano-alumina are combined in a 3:1 mass ratio, with a total loading of 1.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.2μm. Nano-penetration layer: Utilizes a three-stage gradient pressure control: First stage: -0.05MPa, 20 minutes; Second stage: -0.08MPa, 40 minutes; Third stage: Return to normal pressure, let stand for 10 minutes. Penetration depth: 200μm.

[0080] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding for 2h, forming eutectic structure of α-Al2O3 and cristobalite, Vickers hardness 12.0GPa.

[0081] Example 15

[0082] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.92g / cm 3 , porosity 16%.

[0083] Nanocomposite system: Nano-silica (50 nm) and nano-alumina (80 nm) are combined in a 3:1 mass ratio, with a total loading of 2.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.8 μm. Nano-penetration layer: Utilizes a three-stage gradient pressure control: First stage: -0.05 MPa, 20 minutes; Second stage: -0.08 MPa, 40 minutes; Third stage: Return to normal pressure, let stand for 10 minutes. Penetration depth: 250 μm.

[0084] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding for 3h, forming eutectic structure of α-Al2O3 and cristobalite, Vickers hardness 13.0GPa.

[0085] Example 16

[0086] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.85g / cm 3 , porosity 18%.

[0087] Nanocomposite system: Nano-silica (40 nm) and nano-alumina (60 nm) in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.0 μm. Nano-penetration layer: Utilizes a three-stage gradient pressure control: First stage: -0.05 MPa, 20 minutes; Second stage: -0.08 MPa, 40 minutes; Third stage: Return to normal pressure, let stand for 10 minutes. Penetration depth: 230 μm.

[0088] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding time 2.5h, forming eutectic structure of α-Al2O3 and cristobalite, Vickers hardness 12.8GPa.

[0089] Example 17

[0090] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.90g / cm 3 , porosity 17%.

[0091] Nanocomposite system: 30nm nano-silica and 50nm nano-alumina are combined in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.5μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.03MPa for 1.5 hours, penetration depth 220μm.

[0092] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding temperature for 2.5h, introduction of carbon dioxide atmosphere protection (0.5L / min), forming a carbon-doped α-Al2O3 grain boundary structure, Vickers hardness 12.5GPa.

[0093] Example 18

[0094] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.88g / cm 3 , porosity 18%.

[0095] Nanocomposite system: 20nm nano-silica and 30nm nano-alumina are combined in a 3:1 mass ratio, with a total loading of 1.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 5.2μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.01MPa for 1 hour, penetration depth 200μm.

[0096] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding for 2h, introduction of carbon dioxide atmosphere protection (0.5L / min), forming a carbon-doped α-Al2O3 grain boundary structure, Vickers hardness 12.0GPa.

[0097] Example 19

[0098] Matrix material: High-strength basalt with a Mohs hardness of 7.5 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.92g / cm 3 , porosity 16%.

[0099] Nanocomposite system: 50nm nano-silica and 80nm nano-alumina are combined in a 3:1 mass ratio, with a total loading of 2.5% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.8μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.05MPa for 2 hours, with a penetration depth of 250μm.

[0100] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding for 3h, introduction of carbon dioxide atmosphere protection (0.5L / min), forming a carbon-doped α-Al2O3 grain boundary structure, Vickers hardness 13.0GPa.

[0101] Example 20

[0102] Matrix material: Quartz sand with a Mohs hardness of 7.0 is crushed into 0.15-1.18mm continuous graded particles through multiple stages, with a bulk density of 1.85g / cm 3 , porosity 18%.

[0103] Nanocomposite system: Nano-silica (40 nm) and nano-alumina (60 nm) in a 3:1 mass ratio, with a total loading of 2.0% of the aggregate mass. Gradient nanocomposite coating: Micron-rough substrate: Etched with 5% hydrofluoric acid for 2 hours, surface roughness Ra = 6.0 μm. Nano-penetration layer: Vacuum impregnation of a 30% solid content nano-SiO2-Al2O3 composite sol at a vacuum of 0.04 MPa for 1.5 hours, penetration depth 230 μm.

[0104] Crystallization strengthening layer: gradient sintering at 800℃, heating rate 5℃ / min, holding temperature for 2.5h, introduction of carbon dioxide atmosphere protection (0.5L / min), forming a carbon-doped α-Al2O3 grain boundary structure, Vickers hardness 12.8GPa.

[0105] Comparative Example 1

[0106] Traditional quartz sand aggregate is used without any modification.

[0107] Comparative Example 2

[0108] Use high strength basalt aggregate without nano modification.

[0109] Comparative Example 3

[0110] Quartz sand aggregate was used and only hydrofluoric acid etching was performed without nano-modification.

[0111] Comparative Example 4

[0112] High-strength basalt aggregate was used, and only nano-SiO2 modification was performed without Al2O3 composite and gradient coating treatment.

[0113] Comparative Example 5

[0114] Quartz sand aggregate was used for nano-SiO2-Al2O3 composite modification, but no gradient sintering treatment was performed.

[0115] Comparative Example 6

[0116] High-strength basalt aggregate was used for nano-SiO2-Al2O3 composite modification and gradient sintering, but no silicon carbide nanowires were added.

[0117] Comparative Example 7

[0118] Quartz sand aggregate was used for nano-SiO2-Al2O3 composite modification, gradient sintering and silicon carbide nanowire addition, but no vacuum impregnation treatment was performed.

[0119] Comparative Example 8

[0120] High-strength basalt aggregate was used for nano-SiO2-Al2O3 composite modification, vacuum impregnation and gradient sintering, but no carbon dioxide atmosphere protection was introduced.

[0121] Comparative Example 9

[0122] Quartz sand aggregate was used for nano-SiO2-Al2O3 composite modification, vacuum impregnation, gradient sintering and carbon dioxide atmosphere protection, but no polyvinyl pyrrolidone dispersant was added.

[0123] Comparative Example 10

[0124] High-strength basalt aggregate was used, and nano-SiO2-Al2O3 composite modification, vacuum impregnation, gradient sintering, carbon dioxide atmosphere protection and polyvinyl pyrrolidone dispersant were carried out, but three-stage gradient pressure control was not performed.

[0125] The following is a test plan for Examples 1-20 and Comparative Examples 1-10 designed for high-strength UHPC aggregates, intended to evaluate their performance.

[0126] The test methods are as follows: Compressive strength: Tested in accordance with GB / T17671-1999, "Test Method for Cement Mortar Strength." Flexural strength: Tested in accordance with GB / T17671-1999, "Test Method for Cement Mortar Strength." Fluidity: Tested in accordance with GB / T2419-2005, "Test Method for Fluidity of Cement Mortar." Initial setting time: Tested in accordance with GB / T1346-2011, "Test Method for Water Consumption, Setting Time, and Stability of Cement at Standard Consistency." Post-curing strength: Compressive strength is tested after the sample has been cured in a 60°C steam curing chamber for 6 hours.

[0127] Testing Equipment: Press: Used for compressive and flexural strength testing. Flow tester: Used for flow testing. Vicat apparatus: Used for initial setting time testing. Steam curing chamber: Used for post-curing strength testing. Electronic balance: Used for weighing materials. Mixer: Used for mixing UHPC.

[0128] The testing procedures are as follows: Sample Preparation: Aggregate Preparation: Prepare the corresponding aggregates according to the descriptions in Examples 1-20 and Comparative Examples 1-10. UHPC Preparation: Mix the aggregates with cement, silica fume, and a water reducer in the specified proportions to produce UHPC. The final mass ratio is as follows: Aggregate: 45%, Cement: 39%, Silica fume: 6%, Water reducer: 1%, and Water: 9%. Compressive Strength Test: The UHPC mixture was poured into a 40 mm × 40 mm × 160 mm test mold. After vibration molding, the mixture was placed in a standard curing chamber (temperature 20 ± 2°C, humidity ≥ 95%) for 24 hours. After demolding, the mixture was cured in the standard curing chamber for 28 days. Compressive strength testing was performed using a press at a loading rate of 0.5 MPa / s. The failure load was recorded and the compressive strength was calculated. Flexural Strength Testing: The same specimens used for the compressive strength test were used. A three-point bending test was performed on a press at a loading rate of 0.05 MPa / s. Record the failure load and calculate the flexural strength. Flowability Test: Pour the UHPC mixture into the cone of the flow tester. Lift the cone to allow the mixture to flow freely. Measure the flow spread diameter and calculate the flowability. Initial Setting Time Test: Pour the UHPC mixture into the circular mold of a Vicat apparatus. Use the Vicat apparatus to measure the initial setting time. Record the initial setting time. Post-Curation Strength Test: Cure the UHPC specimens in a 60°C steam curing chamber for 6 hours. Remove the specimens and cool them to room temperature. Test the compressive strength using a press. Data Analysis: For each test item, record the test data from at least three specimens and average them. Perform analysis of variance using SPSS statistical software to assess data significance. Testing Environment: Temperature: 20±2°C, Humidity: 60±5%. Sample Size: 40mm×40mm×160mm specimens were used for the compressive and flexural strength tests. Number of Tests: Each test item was repeated at least three times. Data recording: Detailed record of the date, time, operator, test results, etc. of each test.

[0129] The following are the test results for Examples 1 to 20. Example 1: Compressive Strength (28d): 158.2±2.5 MPa, Flexural Strength (28d): 22.4±0.8 MPa, Flow: 670±10 mm, Initial Setting Time: 130±5 min, Cured Strength (60°C, 6 h): 155.0±3.0 MPa. Example 2: Compressive Strength (28d): 152.6±2.8 MPa, Flexural Strength (28d): 21.0±0.7 MPa, Flow: 665±12 mm, Initial Setting Time: 135±6 min, Cured Strength (60°C, 6 h): 150.5±3.2 MPa. Example 3: Compressive strength (28d): 162.5±2.4MPa, flexural strength (28d): 23.8±0.9MPa, fluidity: 675±11mm, initial setting time: 128±4min, strength after curing (60℃, 6h): 159.0±2.8MPa. Example 4: Compressive strength (28d): 155.3±2.6MPa, flexural strength (28d): 21.8±0.8MPa, fluidity: 668±10mm, initial setting time: 132±5min, strength after curing (60℃, 6h): 153.2±3.1MPa. Example 5: Compressive strength (28d): 160.0±2.5MPa, flexural strength (28d): 23.0±0.9MPa, fluidity: 672±11mm, initial setting time: 130±5min, strength after curing (60℃, 6h): 157.5±2.9MPa. Example 6: Compressive strength (28d): 153.8±2.7MPa, flexural strength (28d): 21.5±0.8MPa, fluidity: 666±12mm, initial setting time: 134±6min, strength after curing (60℃, 6h): 151.0±3.3MPa. Example 7: Compressive strength (28d): 163.2±2.4MPa, flexural strength (28d): 24.0±0.9MPa, fluidity: 676±10mm, initial setting time: 129±4min, strength after curing (60℃, 6h): 160.0±2.7MPa. In addition, the prepared material is shown in Figure 1. Figure 1Example 8: Compressive strength (28d): 156.5±2.6MPa, flexural strength (28d): 22.2±0.8MPa, fluidity: 669±11mm, initial setting time: 133±5min, strength after curing (60℃, 6h): 154.0±3.0MPa. Example 9: Compressive strength (28d): 158.8±2.5MPa, flexural strength (28d): 22.6±0.8MPa, fluidity: 671±10mm, initial setting time: 131±5min, strength after curing (60℃, 6h): 156.0±2.9MPa. Example 10: Compressive strength (28d): 152.0±2.8 MPa, flexural strength (28d): 20.8±0.7 MPa, fluidity: 664±12 mm, initial setting time: 136±6 min, strength after curing (60°C, 6 h): 149.5±3.2 MPa. Example 11: Compressive strength (28d): 161.8±2.4 MPa, flexural strength (28d): 23.5±0.9 MPa, fluidity: 674±11 mm, initial setting time: 127±4 min, strength after curing (60°C, 6 h): 158.5±2.8 MPa. Example 12: Compressive strength (28d): 154.9±2.6MPa, flexural strength (28d): 21.6±0.8MPa, fluidity: 667±10mm, initial setting time: 132±5min, strength after curing (60℃, 6h): 152.5±3.1MPa. Example 13: Compressive strength (28d): 159.5±2.5MPa, flexural strength (28d): 22.8±0.8MPa, fluidity: 672±11mm, initial setting time: 130±5min, strength after curing (60℃, 6h): 157.0±2.9MPa. Example 14: Compressive strength (28d): 153.2±2.7 MPa, flexural strength (28d): 21.2±0.8 MPa, fluidity: 665±12 mm, initial setting time: 134±6 min, strength after curing (60°C, 6 h): 150.8±3.3 MPa. Example 15: Compressive strength (28d): 162.8±2.4 MPa, flexural strength (28d): 23.9±0.9 MPa, fluidity: 675±10 mm, initial setting time: 128±4 min, strength after curing (60°C, 6 h): 159.5±2.7 MPa. Example 16: compressive strength (28d): 155.7±2.6MPa, flexural strength (28d): 22.0±0.8MPa, fluidity: 668±11mm, initial setting time: 133±5min, strength after curing (60℃, 6h): 153.5±3.0MPa.Example 17: Compressive strength (28d): 159.0±2.5 MPa, flexural strength (28d): 22.7±0.8 MPa, fluidity: 670±10 mm, initial setting time: 131±5 min, strength after curing (60°C, 6 h): 156.5±2.9 MPa. Example 18: Compressive strength (28d): 152.4±2.8 MPa, flexural strength (28d): 20.9±0.7 MPa, fluidity: 663±12 mm, initial setting time: 135±6 min, strength after curing (60°C, 6 h): 149.8±3.2 MPa. Example 19: Compressive strength (28d): 161.5±2.4 MPa, flexural strength (28d): 23.6±0.9 MPa, fluidity: 673±11 mm, initial setting time: 129±4 min, strength after curing (60°C, 6 h): 158.0±2.8 MPa. Example 20: Compressive strength (28d): 154.5±2.6 MPa, flexural strength (28d): 21.4±0.8 MPa, fluidity: 666±10 mm, initial setting time: 132±5 min, strength after curing (60°C, 6 h): 152.0±3.1 MPa.

[0130] The following are the test results for Comparative Examples 1 to 10. Comparative Example 1: Compressive Strength (28 days): 120.0±3.5 MPa, Flexural Strength (28 days): 15.0±1.0 MPa, Flow: 600±15 mm, Initial Setting Time: 150±8 min, Cured Strength (60°C, 6 hours): 115.0±4.0 MPa. Comparative Example 2: Compressive Strength (28 days): 125.5±3.2 MPa, Flexural Strength (28 days): 16.2±0.9 MPa, Flow: 610±14 mm, Initial Setting Time: 145±7 min, Cured Strength (60°C, 6 hours): 120.0±3.8 MPa. Comparative Example 3: Compressive strength (28d): 130.8±3.0MPa, flexural strength (28d): 17.5±0.8MPa, fluidity: 620±13mm, initial setting time: 140±6min, strength after curing (60℃, 6h): 125.5±3.5MPa. Comparative Example 4: Compressive strength (28d): 135.2±2.8MPa, flexural strength (28d): 18.0±0.7MPa, fluidity: 625±12mm, initial setting time: 138±5min, strength after curing (60℃, 6h): 130.0±3.2MPa. Comparative Example 5: Compressive strength (28d): 140.0±2.6MPa, flexural strength (28d): 19.2±0.6MPa, fluidity: 630±11mm, initial setting time: 135±5min, strength after curing (60℃, 6h): 135.5±3.0MPa. Comparative Example 6: Compressive strength (28d): 142.5±2.5MPa, flexural strength (28d): 20.0±0.5MPa, fluidity: 635±10mm, initial setting time: 132±4min, strength after curing (60℃, 6h): 138.0±2.8MPa. Comparative Example 7: Compressive strength (28d): 145.0±2.4MPa, flexural strength (28d): 20.5±0.5MPa, fluidity: 640±9mm, initial setting time: 130±4min, strength after curing (60℃, 6h): 140.5±2.7MPa. Comparative Example 8: Compressive strength (28d): 147.8±2.3MPa, flexural strength (28d): 21.0±0.4MPa, fluidity: 645±8mm, initial setting time: 128±3min, strength after curing (60℃, 6h): 143.0±2.6MPa. Comparative Example 9: compressive strength (28d): 150.2±2.2MPa, flexural strength (28d): 21.5±0.4MPa, fluidity: 650±7mm, initial setting time: 126±3min, strength after curing (60℃, 6h): 145.5±2.5MPa.Comparative Example 10: compressive strength (28d): 152.0±2.1MPa, flexural strength (28d): 22.0±0.3MPa, fluidity: 655±6mm, initial setting time: 124±2min, strength after curing (60℃, 6h): 148.0±2.4MPa.

[0131] Selection and optimization of matrix materials: Aggregate serves as the skeleton of UHPC, and its performance directly affects the strength and durability of the overall material. Selection of high-hardness aggregate: Use high-strength basalt or quartz sand (Mohs hardness ≥7) as the matrix material. High-hardness aggregate can withstand the stress of UHPC under high loads, reduce the damage of the aggregate itself, and thus improve the overall compressive strength of the material. In addition, high-hardness aggregate can also reduce shrinkage and cracking, providing stable structural support for UHPC. Continuous grading design: Use continuously graded particles with a particle size range of 0.15-1.18mm. This design optimizes the particle size distribution, reduces the gaps between particles, and achieves a packing density of ≥1.85g / cm 3, reducing the porosity to ≤18%. The high packing density enhances the compactness of UHPC and reduces internal defects, significantly improving mechanical properties and durability. The role of the nanocomposite system: The nanocomposite system optimizes the microstructure of UHPC through chemical reactions and physical interactions. The mechanism of nano-SiO2: Nano-SiO2 has a high specific surface area and high reactivity, reacting with calcium hydroxide produced by cement hydration to form more calcium silicate hydrate (CSH gel). CSH gel is the primary cementing agent in UHPC. Increasing its content significantly improves the material's strength and density, playing a particularly critical role in later strength growth. The mechanism of nano-Al2O3: Nano-Al2O3 reacts with tricalcium aluminate in cement to form hydration products such as calcite, which enhances the strength of the interfacial zone. Furthermore, nano-Al2O3 particles act as crystal nuclei, promoting cement hydration, accelerating early strength development, and supporting rapid curing. Synergistic Effect of SiO2 and Al2O3: Nano-SiO2 and Al2O3 are combined in a 3:1 ratio to create a synergistic effect. SiO2 primarily contributes to later-stage strength improvement, while Al2O3 accelerates early hydration. The combination of these two enables UHPC to achieve both rapid hardening and high strength. Furthermore, the composite system optimizes the composition and distribution of hydration products, further enhancing the material's overall performance. Mechanism of the Gradient Nanocomposite Coating: The gradient coating utilizes a multi-layered structure to enhance the interface between the aggregate and the UHPC matrix. Micron-Scale Rough Base: Hydrofluoric acid etching creates a base with a roughness of Ra = 5.2-6.8μm on the aggregate surface. This rough surface increases the contact area between the aggregate and the matrix, providing mechanical engagement points and significantly strengthening interfacial adhesion. Nano-Permeation Layer: A vacuum impregnation process allows the nano-SiO2-Al2O3 sol to penetrate the aggregate (penetration depth ≥ 200μm). This layer functions through two mechanisms: Chemical bonding: Nano-SiO2 and Al2O3 form chemical bonds with silicates or aluminates on the aggregate surface, enhancing bonding strength. Physical filling: Nanoparticles fill micropores and cracks on the aggregate surface, reducing defects, forming a transition layer, smoothing the physical property differences between the aggregate and the matrix, and reducing stress concentration. Crystallization strengthening layer: Through gradient sintering at 800°C, a eutectic structure of α-Al2O3 and cristobalite is formed. This layer has the following characteristics: Phase transformation strengthening: α-Al2O3 and cristobalite are high-hardness and highly stable crystalline phases, providing excellent wear resistance and durability. Eutectic structure: The fine grains and uniformly distributed eutectic structure enhance the coating's toughness and strength, protecting the aggregate surface from damage during UHPC fabrication and use. Function of silicon carbide nanowires: In certain embodiments, the introduction of silicon carbide nanowires further enhances performance. Conductive network: Through electrostatic self-assembly, silicon carbide nanowires are oriented and aligned along the aggregate surface, forming conductive paths. This structure not only improves the toughness of the material, but may also be used in the development of smart concrete.Surface coating: The nanowire surface is coated with an amorphous SiO2 layer, forming a chemical bond with the nanocomposite coating, strengthening the integrity of the nanowire and coating and improving the stability of the overall structure. Carbon doping grain boundary strengthening: The introduction of CO2 atmosphere during the sintering process forms carbon-doped α-Al2O3 grain boundaries. The mechanism is as follows: Grain boundary strengthening: Carbon atom doping reduces the grain boundary energy (≤0.8J / m). 2 ), inhibiting grain growth and refining grains. Nanowhiskers: forming radial nanowhiskers of 50-80nm to enhance the crack resistance and toughness of the coating. This design improves the stability and durability of the coating and prevents interface damage. Comprehensive mechanism of improved interface performance: The gradient coating significantly improves the interface performance between the aggregate and the matrix through the following three mechanisms: Mechanical bite: The rough base and nano-permeable layer increase the contact area and bite force. Chemical bonding: Nano-SiO2 and Al2O3 form chemical bonds with the hydration products of the matrix. Stress dispersion: The gradient design smoothes the changes in physical properties, reduces stress concentration, and avoids interface cracking. Overall mechanism of improved UHPC performance: The present invention comprehensively improves the performance of UHPC through the synergistic effect of the above mechanisms: Improved strength: High-hardness aggregate and optimized interface properties enable UHPC to withstand higher loads. Enhanced durability: The crystallized strengthening layer and carbon-doped grain boundaries provide corrosion resistance and wear resistance. Improved construction performance: Continuous grading and surface modification improve fluidity and density. Rapid Curing: Nano-alumina accelerates early hydration and shortens curing time. This invention's mechanism, based on multiple interactions including physical filling, chemical reaction, phase transformation strengthening, and grain boundary engineering, systematically enhances the mechanical properties, durability, and construction efficiency of UHPC, from optimizing aggregate microstructure to improving interfacial properties. This technology provides innovative insights into the application of nanotechnology in building materials and holds significant engineering value.

[0132] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-strength UHPC special aggregate, characterized in that: The aggregate includes a matrix material and a nanocomposite system; the matrix material is high-strength basalt or quartz sand with a Mohs hardness of ≥7, which is crushed into 0.15-1.18mm continuous graded particles through multi-stage crushing and has a bulk density of ≥1.85g / cm 3 , porosity ≤18%; the nano-composite system is composed of nano-silica with a particle size of 20-50nm and nano-alumina with a particle size of 30-80nm in a mass ratio of 3:1, with a total loading of 1.5-2.5% of the mass of the aggregate, prepared by a sol-gel method and uniformly dispersed by ultrasound; a gradient nano-composite coating is formed on the surface of the aggregate, including: a micron-scale rough substrate: the base material is etched with 5% hydrofluoric acid by mass for 2h, and the surface roughness Ra=5.2-6.8μm; a nano-penetration layer: formed by vacuum impregnation of a nano-SiO2-Al2O3 composite sol with a solid content of 30%, with a penetration depth of ≥200μm, a vacuum degree of 0.01-0.05MPa, and an impregnation time of 1-2h; a crystallization strengthening layer: 800℃, a heating rate of 5℃·min -1 Gradient sintering, keeping warm for 2-3h, forms eutectic structure of α-Al2O3 and cristobalite, Vickers hardness ≥12GPa.

2. The high-strength UHPC special aggregate according to claim 1, characterized in that: The preparation of nano-SiO2-Al2O3 composite sol: During the preparation process, 0.5-1.2wt% polyvinyl pyrrolidone is added as a dispersant, the pH value of the sol is controlled in the range of 4.5-5.5, and the reaction temperature is maintained at 60±2°C; then, 40kHz ultrasonic dispersion is performed for 30-45 minutes to form a uniform colloid.

3. The high-strength UHPC special aggregate according to claim 1, characterized in that: The vacuum impregnation process is as follows: three-stage gradient pressure control is adopted: the first stage: the pressure is -0.05MPa, maintained for 20 minutes, to achieve surface penetration of the aggregate; the second stage: the pressure is -0.08MPa, continued for 40 minutes, to complete the deep penetration of the sol; the third stage: restore normal pressure, stand for 10 minutes, to promote the stable filling of the sol in the aggregate.

4. The high-strength UHPC special aggregate according to claim 1, characterized in that: The gradient sintering process is as follows: in the temperature range of 600-800°C, a carbon dioxide atmosphere protection is introduced with a gas flow rate of 0.5L / min to form a carbon-doped α-Al2O3 grain boundary structure.

5. The high-strength UHPC special aggregate according to claim 4, characterized in that: The α-Al2O3 grain boundary structure is nano whiskers with a size of 50-80nm, an aspect ratio of 15-20, radial distribution, and a whisker spacing of 100-300nm. The grain boundary energy can be reduced to 0.8J / m 2 the following.

6. The high-strength UHPC special aggregate according to claim 1, characterized in that: 1-3wt% of silicon carbide nanowires with a diameter of 20-50nm and a length of 5-10μm are additionally added to the nanocomposite system. They are oriented and arranged along the tangential direction of the aggregate surface through electrostatic self-assembly technology to form a conductive network. The surface of the nanowires is coated with an amorphous silicon dioxide layer with a thickness of 2-5nm, forming a chemical bond with the nanocomposite coating.

7. The method for preparing high-strength UHPC special aggregate according to claim 1, characterized in that: The method comprises the following steps: (1) providing a matrix material: selecting high-strength basalt or quartz sand as the matrix material, and forming continuously graded particles through multi-stage crushing processing; (2) surface etching treatment: etching the matrix material with hydrofluoric acid to form a micron-scale rough base on the surface of the matrix material; (3) preparing a nano-SiO2-Al2O3 composite sol: mixing nano-silicon dioxide and nano-alumina; adding polyvinyl pyrrolidone as a dispersant; controlling the pH value of the sol and dispersing it by ultrasonication to form a uniform composite sol; (4) vacuum impregnation to form a nano-permeable layer: placing the etched matrix material in the nano-SiO2-Al2O3 composite sol, and forming a nano-permeable layer by vacuum impregnation; (5) gradient sintering to form a crystallization strengthening layer: gradient sintering the impregnated aggregate to form a crystallization strengthening layer; introducing a carbon dioxide atmosphere for protection to form a carbon-doped α-Al2O3 grain boundary structure.

8. The use of the high-strength UHPC special aggregate according to claim 1, characterized in that: Aggregates are used to prepare ultra-high performance concrete (UHPC), and the mass of aggregates accounts for 30-50% of the total mass of UHPC.

9. The use of high-strength UHPC special aggregate according to claim 8, characterized in that: In the connection of prefabricated bridge components, when the UHPC with the aggregate is used as the wet joint material: process parameters: fluidity ≥ 650mm, initial setting time ≥ 120min, and steam curing at 60°C for 6h to reach the design strength.

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