Graphene oxide modified brown corundum aggregate, UHPC, and preparation method and application thereof

Abstract

The present invention relates to a graphene oxide-modified brown corundum aggregate, UHPC, and their preparation method and application, belonging to the technical field of building materials. The modified aggregate preparation method comprises: etching brown corundum, cleaning it, mixing it with an acidic alumina sol, evaporating it to dryness, and then calcining it; hydrothermally reacting the graphene oxide to obtain rGO; mixing the rGO and brown corundum, maintaining the mixture in a reducing atmosphere at 1400-1450°C for 1.5-2.5 hours, and then cooling and annealing it. The UHPC comprises the following components by weight: 1124-1224 parts of cement, 398-448 parts of the modified brown corundum aggregate, 105-135 parts of silica fume, 35-43 parts of steel fiber, 310-410 parts of water, and 8-14 parts of a water reducer. Modifying the aggregate indirectly reduces the proportion of the relatively weak interface transition zone, thereby improving the integrity and overall mechanical properties of the cement-based cementitious material.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a graphene oxide modified brown corundum aggregate, UHPC, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Ultra-High Performance Concrete (UHPC) is a new cement-based composite material with ultra-high strength, high toughness, and high durability. It offers significant advantages in penetration and blast resistance: under the same penetration conditions, UHPC exhibits far less penetration depth and crater damage than conventional concrete. However, after UHPC's compressive strength reaches a certain threshold, its penetration resistance fails to continue to improve, resulting in a plateau effect.

[0004] The bottlenecks in improving the penetration resistance of UHPC can be attributed to the following aspects: Although the aggregate in UHPC improves the penetration resistance of ultra-high performance concrete to a certain extent, the transition zone between the aggregate and the matrix interface is relatively weak, which is inconsistent with the performance of other components of UHPC, limiting the further improvement of the penetration resistance. Previous concrete performance improvement plans focused on static mechanical properties such as compressive strength. However, with the increasing differentiation between static mechanical properties and penetration resistance, the micromorphology and chemical properties of some common components used to improve static mechanical properties will have an adverse effect on the penetration resistance, and therefore need to be re-evaluated and screened. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a graphene oxide-modified brown corundum aggregate, UHPC and its preparation method and application. Graphene oxide is bonded with brown corundum aggregate to prepare a modified aggregate, thereby improving the performance of the aggregate-matrix interface transition zone and thereby improving its anti-penetration performance under the action of high-speed projectiles.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, a method for preparing graphene oxide modified brown corundum aggregate comprises the following steps:

[0008] S1, brown corundum of a set particle size is etched with HF solution and then cleaned, mixed with acidic γ-Al2O3 sol with a concentration of 3-10wt% at a solid-liquid mass ratio of (0.5-2):10, evaporated to dryness and then calcined to obtain pretreated brown corundum;

[0009] S2, hydrothermally reacting the graphene oxide at 180-220° C. for 10-14 hours to obtain partially reduced defective graphene oxide;

[0010] S3. After mixing the partially reduced defective graphene oxide and pretreated brown corundum in a mass ratio of (0.5-1.5):100, the mixture is kept in an inert atmosphere at 550-650°C for 0.5-2 h, then kept in a reducing atmosphere at 1400-1450°C for 1.5-2.5 h, and then kept under pressure at 1600-1700°C for 0.5-1 h, and then cooled and annealed to obtain graphene oxide modified brown corundum aggregate.

[0011] In the second aspect, a graphene oxide modified brown corundum aggregate is prepared based on the above preparation method.

[0012] In a third aspect, a UHPC comprises the following components in parts by mass: 1124-1224 parts of cement, 398-448 parts of the above-mentioned graphene oxide-modified brown corundum aggregate, 105-135 parts of silica fume, 35-43 parts of steel fiber, 310-410 parts of water, and 8-14 parts of a water reducer.

[0013] In a fourth aspect, the method for preparing the UHPC comprises the steps of:

[0014] S4, mixing cement and silica fume to obtain a first mixture, adding graphene oxide modified brown corundum aggregate, water and a water reducer to the first mixture, and mixing to obtain a second mixture;

[0015] S5. Add steel fiber to the second mixture, stir, cast and shape it, and cure it to a specified age.

[0016] Fifthly, the application of the above-mentioned UHPC includes its application in military protection engineering or civil structural engineering.

[0017] The beneficial effects of the present invention are:

[0018] 1. The present invention uses brown corundum to prepare modified aggregate. The surface of brown corundum has the characteristics of high roughness, low porosity and chemical inertness, which can significantly improve the interface bonding strength and durability between it and concrete. The present invention treats the surface of brown corundum so that the surface of brown corundum has more adhesion sites for graphene oxide to attach. After the brown corundum is modified, the Al attached to the surface 3+At high temperatures, the ions in the rGO (partially reduced defective graphene oxide) bond with defective carbon atoms, forming strong covalent bonds between Al and C atoms (bond energy ≈318 kJ / mol). This replaces the weak van der Waals forces between the traditional aggregate and the cementitious base. The Al-OC bond more than doubles the interfacial bonding strength (greater than 25 MPa) and reduces the thickness of the interfacial transition zone from 40 μm to 15 μm. Aggregate modification indirectly reduces the proportion of this relatively weak interfacial transition zone, improving the integrity and overall mechanical properties of the cementitious material.

[0019] 2. For inorganic materials like graphene oxide, achieving good dispersion in solutions has always been a major challenge in the preparation of cement-based composites. Aggregation of the material significantly reduces its gain. This invention bonds graphene oxide to brown corundum aggregate and then uses a stepped temperature bonding method to attach the graphene oxide to the surface of the brown corundum aggregate. This allows for uniform dispersion during concrete preparation, maximizing the effectiveness of the graphene oxide.

[0020] 3. This invention utilizes a high-temperature-induced chemical bonding mechanism and a multi-scale synergistic enhancement mechanism to jointly improve the penetration resistance and impact performance of ultra-high performance concrete. The modified brown corundum aggregate has a high hardness and can directly crush warheads, consuming a large amount of kinetic energy. rGO acts as a toughening and crack-resistance agent, suppressing radial cracking caused by shock waves by bridging microcracks at the nanoscale. The destruction between rGO layers also requires more impact energy. The Al-OC bond not only strengthens the bond between the aggregate and the UHPC matrix, but also strengthens the relatively weak interface transition zone, reducing aggregate debonding and improving the overall performance of ultra-high performance concrete. Although the aggregate cost increases, the thinning of the structure and the extension of its lifespan brought about by the performance improvement have significantly reduced the full-cycle cost, providing an irreplaceable material solution for extreme environment structures such as military engineering and nuclear power containment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 Schematic diagram of the preparation process of graphene oxide modified brown corundum aggregate in Example 1 of the present invention.

[0023] Figure 2 Schematic diagram of the preparation process of graphene oxide in Example 1 of the present invention.

[0024] Figure 3Schematic diagram of the reaction principle in Example 2 of the present invention.

[0025] Figure 4 1 is a graph showing the relationship between the compressive strength and the flexural strength of the examples and the comparative examples in the specific implementation manner of the present invention.

[0026] Figure 5 1 is a graph showing the relationship between the penetration depth and the pit diameter of the embodiment and the comparative example in the specific implementation manner of the present invention. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] One or more embodiments of the present invention provide a method for preparing graphene oxide modified brown corundum aggregate, comprising the following steps:

[0030] S1, brown corundum of a set particle size is etched with HF solution and then cleaned, mixed with acidic γ-Al Al2O3 sol with a concentration of 3-10wt% at a solid-liquid mass ratio of (0.5-2):10, evaporated to dryness and then calcined to obtain pretreated brown corundum;

[0031] S2, hydrothermally reacting graphene oxide at 180-220°C for 10-14 hours to obtain partially reduced defective graphene oxide (rGO);

[0032] S3. Partially reduced defective graphene oxide is mixed in the form of a powdered solid with pretreated brown corundum in a mass ratio of (0.5-1.5):100, and then kept warm in an inert atmosphere at 550-650°C for 0.5-2 h, then kept warm in a reducing atmosphere at 1400-1450°C for 1.5-2.5 h, and then kept under pressure at 1600-1700°C for 0.5-1 h, and then cooled and annealed to obtain graphene oxide modified brown corundum aggregate.

[0033] In the above process, the etching method is first used to increase the specific surface area of ​​brown corundum, that is, to increase the surface active sites, providing a stable interface guarantee for the subsequent bonding of rGO and reinforcement of UHPC; after the hydrothermal reaction, the thermal stability of graphene oxide is improved and the reaction sites are retained, providing a guarantee for the bonding process with brown corundum; the step-by-step temperature sintering method can maximize the activity and bonding efficiency of rGO to form a stable Al-OC bond.

[0034] Optionally, in S1, the brown corundum is an α-Al2O3 (corundum type) structure, has a Mohs hardness of 9.0, a compressive strength greater than 2000 MPa, an elastic modulus of 380-400 GPa, and a density of 3.95-4.0 g / cm 3 .

[0035] Optionally, in S1, the concentration of the HF solution is 10-20 wt%, which is used to remove surface Fe2O3 and SiO2 impurities and prevent rust from spreading.

[0036] Optionally, in S1, after cleaning, the residual water is replaced with anhydrous ethanol; the anhydrous ethanol is easily removed by heating and evaporation, thereby ensuring the treatment effect of the acidic γ-Al2O3 sol.

[0037] Optionally, in S1, the preparation method of the acidic γ-Al2O3 sol includes: adding dilute nitric acid to the γ-Al2O3 sol, adjusting the pH to 3-5, and then ultrasonically dispersing it for 0.5-1h; utilizing the high activity and convertibility of γ-Al2O3, under set process conditions, forming a strong physical connection and chemical bond on the surface of or between brown corundum particles, ultimately manifesting as a combination of α-Al2O3 of brown corundum and α-Al2O3 converted from γ-Al2O3, or forming a new reaction bonding phase to increase the active sites on the surface of brown corundum, thereby improving its bonding effect in UHPC.

[0038] Optionally, in S1, the evaporation drying method includes: stirring at 50-60° C. until evaporation into a paste, and then vacuum drying at 100-120° C. for 2-3 hours; this is a pretreatment step of the calcination process.

[0039] Optionally, in S1, the calcination method includes: heating to 500-550°C and then calcining at a constant temperature for 1-1.5 hours; combining the γ-Al2O3 in the sol with the γ-Al2O3 in the brown corundum to increase the active sites on the surface of the brown corundum, thereby enhancing the interfacial reaction activity.

[0040] Optionally, in S2, the typical molecular structure of graphene oxide is:

[0041] .

[0042] Optionally, in S2, the graphene oxide is pre-treated by ultrasonic exfoliation to improve dispersibility and binding ability.

[0043] Optionally, in S3, the inert atmosphere includes an argon atmosphere, which is used to completely remove residual oxygen-containing groups in GO and avoid high-temperature explosion; the reducing atmosphere includes hydrogen with a volume concentration of 3~5%, which is used to promote the formation of oxygen vacancies on the Al2O3 surface and accelerate Al-OC bonding. During this period, the temperature needs to be strictly controlled below 1450°C, and the optimal bonding temperature is 1420~1450°C. Too high a temperature (exceeding 1450°C) will cause the defective graphene structure to collapse, and too low a temperature will lead to incomplete reaction; pressurization and insulation are carried out after removing the reducing atmosphere, and the method includes: vacuuming to remove the reducing atmosphere containing hydrogen, and then pressurizing with an inert atmosphere to promote the molten Al2O3 to fill the interlayer gaps of rGO and improve the bonding degree.

[0044] Optionally, in S3, the cooling annealing method includes: cooling to 1200°C at a rate of 2-5°C / min in an inert atmosphere; so as to release internal stress, stabilize the Al-OC structure, and thereby effectively improve the performance of UHPC.

[0045] One or more embodiments of the present invention provide a graphene oxide modified brown corundum aggregate prepared based on the above preparation method.

[0046] Optionally, the particle size of the brown corundum raw material is 5~8 mm. After etching, pretreatment and modification, the particle size does not change much and remains 5~8 mm, and can be added to UHPC as an aggregate component.

[0047] One or more embodiments of the present invention provide a UHPC comprising the following components in parts by mass: 1124-1224 parts of cement, 398-448 parts of the above-mentioned graphene oxide-modified brown corundum aggregate, 105-135 parts of silica fume, 35-43 parts of steel fiber, 310-410 parts of water, and 8-14 parts of a water reducer.

[0048] The Al-OC bonds contained in graphene oxide-modified brown corundum aggregate not only strengthen the bond between the aggregate and the UHPC matrix, but also enhance the relatively weak interfacial transition zone and reduce aggregate peeling. The rGO component has oxygen-containing functional groups (such as carboxyl, hydroxyl, and epoxy groups) that can promote the formation of strong covalently bonded calcium silicate hydrate (CSH) gel, thereby replacing the weak van der Waals forces in the original CSH, forming a denser microstructure and a denser hydration product network around the rGO. The active sites represented by oxygen-containing functional groups can promote the nucleation and crystal growth of calcium hydroxide in the hydration product and inhibit the production of corrosive compounds (ettringite), thereby improving the early strength and hydration rate of the cement matrix. rGO can also form a regular and dense microstructure with columnar and flower-shaped hydrated crystals, further improving the penetration resistance of cement-based composites. The penetration resistance of ultra-high performance concrete based on graphene oxide modification has been greatly improved. Avoid adding ingredients that undergo a high-temperature melting process to other components, such as steel slag, slag powder, etc. The microstructure of these components that undergo a high-temperature melting process is relatively smooth and can only play the role of filling the hydration product network; although this structure has a positive effect on compressive properties, it will cause it to loosely bond with the matrix in situations where the anti-penetration performance needs to be improved, and it will not be able to strengthen the mechanical interlocking effect in the hydration product network, thereby making the internal structure of the ultra-high performance concrete more conducive to improving the anti-penetration performance.

[0049] Optionally, the cement is ordinary Portland cement of grade 52.5 or grade 52.5R, which has good compatibility with polycarboxylic acid-based high-efficiency water reducer.

[0050] Optionally, the amorphous silicon dioxide content in the silica fume is greater than 95wt%, and the silica fume is an ultrafine dry powder that is not fully densified; the specific surface area is greater than 21.0 m 2 / g, specific density greater than 2.2.

[0051] Optionally, the steel fiber is an ordinary straight steel fiber or a copper-plated straight steel fiber; the steel fiber has an average length of 13 mm, an average diameter of 0.16 mm, a tensile strength greater than 2500 MPa, an elastic modulus of 200 GPa, and a density of 7800 kg / m 3 .

[0052] One or more embodiments of the present invention provide a method for preparing the above-mentioned UHPC, comprising the steps of:

[0053] S4, mixing cement and silica fume to obtain a first mixture, adding graphene oxide modified brown corundum aggregate, water and a water reducer to the first mixture, and mixing to obtain a second mixture;

[0054] S5. Add steel fiber to the second mixture, stir, cast and shape it, and cure it to a specified age.

[0055] Optionally, in S4, cement and silica fume are mixed and stirred at a speed of 75-85 rpm for 2-3 minutes; and graphene oxide modified brown corundum aggregate, water and water reducing agent are added and stirred at a speed of 75-85 rpm for 2-3 minutes.

[0056] Optionally, in S5, after adding the steel fiber, stirring is performed at a speed of 155-165 rpm for 3-5 minutes.

[0057] Optionally, in S5, the curing method is to perform curing under standard curing conditions (temperature of 20±2°C and relative humidity of >95%RH).

[0058] One or more embodiments of the present invention provide applications of the above-mentioned UHPC, including applications in military protection engineering or civil structural engineering.

[0059] Optional, specifically including: application in fortifications, missile launch sites, nuclear waste storage facilities, war-ready roads or main structures of large-span bridges.

[0060] Example 1

[0061] A graphene oxide modified brown corundum aggregate, the preparation method comprising:

[0062] S1. Brown corundum with a particle size of 5-8 mm was used as raw material. The raw material aggregate of brown corundum was placed in a PTFE reactor, and a 10 wt% HF solution was injected. The raw material aggregate was etched at a speed of 300 rpm and a constant temperature of 60 ° C for 30 min. After the etching was completed, it was centrifuged at 8000 rpm for 5 min for separation. The supernatant was poured out and the solid was collected. The collected solid was washed with deionized water for 5 times until the pH was 7.0, and then anhydrous ethanol was added to replace the residual water. A 5 wt% γ-Al2O3 sol was prepared, and 0.1 M dilute nitric acid was added thereto to adjust the pH to 4.0. The sol was then ultrasonically treated for 30 min to uniformly disperse it. The treated brown corundum and acidic γ- The Al2O3 sol was mixed and ultrasonically treated for 20 min at 800 W power and 40 kHz frequency to obtain a mixture. The mixture was slowly stirred at 50 rpm at 60 ° C until it evaporated into a paste; then vacuum dried at 120 ° C for 2 h, and then kept in a vacuum environment and heated to 550 ° C at a rate of 5 ° C / min and calcined at a constant temperature for 1 h to complete the process. Figure 1 As shown, pretreated brown corundum is obtained by exposing high active sites through a high temperature activation process.

[0063] S2, such as Figure 2As shown, a three-necked round-bottom flask is used as a container, 2g of graphite powder and 2g of NaNO3 powder are added to 96mL of 98% concentrated sulfuric acid, and stirred in an ice bath (<5°C); while maintaining the stirring state, 4g of KMnO4 is added to the container three times, with an interval of 15min between each addition; the obtained mixture is reacted within two hours and cooled to room temperature. During this process, KMnO4 inserts oxygen-containing functional groups into graphene to form hydrophilic oxides; the container is removed from the ice bath, 80ml of deionized water is added and the temperature is raised to 90°C, and then 200mL of deionized water and 10mL of H2O2 are added to terminate the reaction, as shown in FIG. Figure 1 As shown, through sp 2 The orbital electron hybridization process exposes highly active sites. The contents of the container are purified by vacuum filtration and repeatedly washed with deionized water until the solution pH is close to 7. Then, it is treated with 35W ultrasound for 4 hours to remove dead skin cells. Finally, the graphene oxide is placed in a freeze dryer and dried for 36 hours to complete the preparation of graphene oxide. The graphene oxide is hydrothermally reacted at 200°C for 12 hours to obtain partially reduced defective graphene oxide (rGO) that retains 10-15% oxygen-containing groups.

[0064] S3, such as Figure 1 As shown, the obtained partially reduced defective graphene oxide (rGO) was mixed with pretreated brown corundum in a mass ratio of 1:100, placed in a heating furnace, and kept warm at 600℃ in an argon environment for 1 hour to complete the pre-sintering process. Then the temperature was raised to 1450℃, and hydrogen with a volume concentration of 2% was introduced into the heating furnace. The bonding process was completed in this reducing atmosphere. Then the temperature was raised to 1600℃, and the heating furnace was vacuumed to remove the reducing atmosphere. After the reducing atmosphere was removed, argon was filled and pressurized to 20MPa, and the temperature was kept warm for 30 minutes to complete the densification process; the temperature was cooled to 1200℃ at a rate of 2℃ / min for 200 minutes to complete the annealing process, and graphene oxide modified brown corundum aggregate was obtained; the realization of Al-OC bond provides a basis for introducing Al-OC bond into UHPC.

[0065] After testing, it was found that in step S1, the etching operation can reduce the specific surface area of ​​brown corundum from the original 1~2 m 2 / g increased to 8~10 m 2 / g, which increases the attachment sites of oxidation products; after mixing and calcining with γ-Al2O3 sol, the surface active site density increases by 5 to 8 times.

[0066] Comparative Example 1

[0067] A modified brown corundum aggregate is prepared using graphene oxide and brown corundum with a particle size of 5 to 8 mm as raw materials. The preparation method includes:

[0068] The brown corundum was immersed in a graphene oxide dispersion solution, that is, the brown corundum aggregate was modified by physical attachment, and the mass ratio of graphene oxide to brown corundum aggregate was 1:100.

[0069] The difference from Example 1 is that: no γ-Al2O3 sol is added; the graphene oxide is not subjected to hydrothermal treatment, and no rGO is generated; and the graphene oxide and brown corundum are not heated after being mixed.

[0070] Example 2

[0071] Currently, the primary hydration product of the ultra-high performance concrete (UHPC) matrix is ​​calcium silicate hydrate gel (CSH). Approximately one-third of this CSH gel is held together by weak van der Waals forces, requiring only minimal energy to degrade. Furthermore, during the CSH gel formation process, the material expands and contracts. This volume change, when constrained by other matrix components, can generate stress concentrations, leading to the formation of microcracks and thus limiting the UHPC matrix's penetration resistance. In recent years, high-strength and high-hardness coarse aggregates (such as sintered bauxite coarse aggregate) have been successfully incorporated into UHPC to improve its penetration resistance, particularly penetration depth. However, due to the limitations of van der Waals forces and microcracks within the material's pores, effective improvements in the UHPC matrix's penetration resistance remain difficult, limiting its widespread application in protective engineering.

[0072] This embodiment provides a UHPC, comprising the following components in parts by mass: 1174 parts of cement, 423 parts of graphene oxide-modified brown corundum aggregate prepared in Example 1, 120 parts of silica fume, 39 parts of steel fiber, 360 parts of water, and 14 parts of a water reducer.

[0073] Among them, the cement is 52.5 grade ordinary Portland cement.

[0074] Silica fume is an ultra-fine dry powder that is not fully densified and has a specific surface area greater than 21.0 m 2 / g, a specific density greater than 2.2, and an amorphous silicon dioxide content greater than 95wt%.

[0075] The steel fibers are copper-plated straight steel fibers with an average length of 13 mm and an average diameter of 0.16 mm.

[0076] The water reducer is a polycarboxylic acid-based high-efficiency water reducer.

[0077] The preparation method comprises:

[0078] S4. Mix the cement and silica fume, and stir at a speed of 80 rpm (stir at a low speed to prevent splashing) for 3 minutes to obtain a first mixture; add graphene oxide-modified brown corundum aggregate, 270 parts of water (accounting for 75% of the total water), and a water reducer to the first mixture, and stir at a speed of 80 rpm (stir at a low speed) for 1 minute. Then, add the remaining 90 parts of water and continue stirring for 2 minutes to obtain a second mixture;

[0079] S5. After the cementitious material of the second mixture can be mixed well and no obvious unhydrated material emerges on the surface of the fresh concrete, indicating that it has good fluidity, slowly add steel fiber through a square mesh sieve and stir at 160 rpm (medium speed) for 5 minutes to obtain UHPC slurry. After stirring the UHPC slurry at 360 rpm (high speed) for 3 minutes, cast it into shape and cure it to the specified age under the following curing conditions: temperature 20±2°C and relative humidity >95%RH.

[0080] During the pouring process in S5, a vibrating table was used to lightly vibrate for 2 minutes to expel bubbles and improve its density; after pouring, it was covered with plastic film to prevent surface moisture loss and demoulding was carried out after 24 hours.

[0081] Example 3

[0082] A UHPC comprises the following components in parts by mass: 1124 parts of cement, 398 parts of graphene oxide-modified brown corundum aggregate prepared in Example 1, 105 parts of silica fume, 39 parts of steel fiber, 310 parts of water, and 8 parts of a water reducer.

[0083] The requirements for raw materials and preparation methods are the same as those in Example 2.

[0084] Example 4

[0085] A UHPC comprises the following components in parts by mass: 1224 parts of cement, 448 parts of graphene oxide-modified brown corundum aggregate prepared in Example 1, 135 parts of silica fume, 43 parts of steel fiber, 410 parts of water, and 14 parts of a water reducer.

[0086] The requirements for raw materials and preparation methods are the same as those in Example 2.

[0087] Comparative Example 2

[0088] A UHPC comprises the following components in parts by mass: 1174 parts of cement, 423 parts of modified brown corundum aggregate prepared in Comparative Example 1, 120 parts of silica fume, 39 parts of steel fiber, 360 parts of water, and 12 parts of a water reducer.

[0089] The difference from Example 2 is that the aggregate prepared in Comparative Example 1 is used to replace the aggregate prepared in Example 1.

[0090] Other raw material requirements and preparation methods are the same as those in Example 1.

[0091] Comparative Example 3

[0092] A UHPC comprises the following components in parts by mass: 1174 parts of cement, 423 parts of brown corundum aggregate, 120 parts of silica fume, 39 parts of steel fiber, 360 parts of water, and 12 parts of a water reducing agent.

[0093] The difference from Example 2 is that brown corundum is used to replace the aggregate prepared in Example 1.

[0094] Other raw material requirements and preparation methods are the same as those in Example 1.

[0095] Comparative Example 4

[0096] A UHPC comprises the following components in parts by mass: 1174 parts of cement, 423 parts of calcined bauxite aggregate, 120 parts of silica fume, 39 parts of steel fiber, 360 parts of water, and 12 parts of a water reducing agent.

[0097] The particle size of the calcined bauxite aggregate is 5~8mm, and its physical properties include: aggregate crushing index of 8.0%, elastic modulus of 240GPa, and density of 3.2g / cm 3 .

[0098] The difference from Example 2 is that calcined bauxite aggregate is used to replace the aggregate prepared in Example 1.

[0099] Other raw material requirements and preparation methods are the same as those in Example 1.

[0100] Performance Testing

[0101] Conventional mechanical tests and high-speed projectile penetration resistance tests were conducted on each example and comparative example. Conventional mechanical tests measured compressive strength, elastic modulus, and flexural strength. The high-speed projectile penetration resistance testing followed the same procedures as those described in Chinese patent application No. 2023117815297, "A Penetration-Resistant Ultra-High Performance Concrete, Preparation Method, and Application," except that the impact velocity was increased from 400 m / s to 650 m / s. Penetration depth, crater diameter, and projectile mass loss rate were measured. The performance test results are shown in Table 1.

[0102] Table 1 Performance test results of various embodiments and comparative examples

[0103]

[0104] According to the compressive strength and elastic modulus values ​​in Table 1, Figure 4 , through Table 1 and Figure 4From the comparison of the numerical values, it can be found that the compressive strength, elastic modulus and flexural strength of the embodiment are improved to varying degrees compared with those of comparative example 2. Specifically, compared with comparative example 2, the aggregate of comparative example 3 is replaced by brown corundum aggregate instead of calcined bauxite. Brown corundum has higher hardness and less surface impurities than calcined bauxite, and its interface bonding area is also denser, so the mechanical properties are also greatly improved. Compared with comparative example 3, the significant improvement in compressive strength in comparative example 2 is mainly attributed to: the nanoscale of graphene oxide enables it to effectively fill the micropores in the cement matrix, significantly improve the density of concrete, and reduce porosity; at the same time, graphene oxide has an extremely high specific surface area, and its surface contains oxygen-containing functional groups such as carboxyl, hydroxyl and epoxy groups, such as Figure 3 As shown, these functional groups can react with calcium ions (Ca 2+ ) produces a complexation effect, promoting the formation of CSH gel and the growth of hydrated crystals, forming a denser microstructure.

[0105] This significant improvement in elastic modulus is primarily attributed to the ability of graphene oxide's oxygen-containing functional groups to form complexes with calcium ions in the cement matrix, significantly enhancing the interfacial strength between the cement matrix and aggregate. Graphene oxide strengthens the interfacial transition zone (ITZ), the most vulnerable region in concrete, thereby increasing the material's elastic modulus. Furthermore, graphene oxide promotes the formation of CSH gels, the primary binder during cement hydration, significantly enhancing the mechanical properties of concrete. Graphene oxide's catalytic effect leads to the formation of more CSH gels, further increasing the material's rigidity.

[0106] This significant improvement in flexural strength is primarily attributed to the two-dimensional nanosheet structure of graphene oxide acting as a bridge during microcrack propagation, preventing further crack growth and thereby increasing the material's flexural strength. This effect is particularly important for preventing fracture caused by bending. As a reinforcing material, graphene oxide interweaves with hydration products in the cement matrix, forming a tight network structure that improves the concrete's ductility and toughness under stress and reduces the occurrence of cracks.

[0107] According to the numerical arrangement of penetration depth and crater diameter in Table 1, Figure 5 , through Table 1 and Figure 5From the comparison of the numerical values, it can be found that the penetration depth and the pit diameter of each embodiment are reduced to varying degrees compared with those of each comparative example; that is, compared with each comparative example, the anti-penetration performance of each embodiment is significantly improved. The significant improvement in the anti-penetration performance of ultra-high performance concrete is mainly attributed to: 1) Graphene oxide greatly improves the impact resistance and penetration resistance of concrete. By improving the pore structure and enhancing the density of the microstructure, graphene oxide effectively resists the invasion of external impact loads, reduces the penetration depth, and significantly improves the performance of concrete under impact loads. 2) The reduction in the pit diameter shows the effectiveness of graphene oxide in resisting impact damage. Graphene oxide can reduce surface damage caused by impact through filling and reinforcement effects. The expansion of cracks caused by impact loads is organized through bridging action, reducing the surface damage area. At the same time, the dense and uniform distribution of the material improves the toughness of the material and reduces material damage caused by stress concentration.

[0108] Comparative Example 2 significantly improved the compressive strength, elastic modulus, flexural strength, and penetration resistance of Comparative Example 3. However, because the graphene oxide was physically attached to the brown corundum using an attachment method, its dispersion in the matrix was poor, which to some extent affected the hydration reaction of the graphene oxide. To overcome these deficiencies, Example 2 used modified graphene oxide bonded to brown corundum aggregate via gradient sintering. After chemical bonding, Al-OC bonds with higher bond energy were formed between the graphene oxide and the brown corundum aggregate, which more than doubled the interfacial bonding strength (greater than 25 MPa) and simultaneously reduced the thickness of the interfacial transition zone from 40 μm to 15 μm. Modifying the aggregate indirectly reduced the proportion of the relatively weak interfacial transition zone, thereby improving the integrity and overall mechanical properties of the cementitious material.

[0109] Therefore, the present invention provides an ultra-high performance concrete with excellent resistance to high-speed projectile penetration and mechanical properties, and its penetration resistance is significantly higher than that of the ultra-high performance concrete in Comparative Example 4 that does not contain a graphene oxide modifier. It can be seen that the CSH gel and hydrate crystals formed by the addition of the graphene oxide modifier are beneficial to improving the penetration resistance of the ultra-high performance concrete. At the same time, the introduction of Al-OC bonds improves the integrity of the matrix, compensates for the defect of the large number of weak interface transition zones in the ultra-high performance concrete, and greatly improves the penetration resistance of the ultra-high performance concrete. On the one hand, the graphene oxide modifier can promote the production of CSH gel and hydrate crystals in the ultra-high performance concrete, forming a denser microstructure and improving the mechanical properties of the material. On the other hand, the graphene oxide modifier can provide more attachment sites that are conducive to the generation and expansion of hydrate crystals, repairing the pores and cracks in the matrix and the interface transition zone, and greatly improving the material's penetration resistance. The optimization of the penetration resistance and mechanical properties of the ultra-high performance concrete by the graphene oxide modifier enables it to be used as a modern new protective material.

[0110] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing graphene oxide modified brown corundum aggregate, characterized in that: The following steps are involved: S1, brown corundum of a set particle size is etched with HF solution and then cleaned, mixed with acidic γ-Al2O3 sol with a concentration of 3-10wt% at a solid-liquid mass ratio of (0.5-2):10, evaporated to dryness and then calcined to obtain pretreated brown corundum; S2, hydrothermally reacting the graphene oxide at 180-220° C. for 10-14 hours to obtain partially reduced defective graphene oxide; S3. After mixing the partially reduced defective graphene oxide and pretreated brown corundum in a mass ratio of (0.5-1.5):100, the mixture is kept in an inert atmosphere at 550-650°C for 0.5-2 h, then kept in a reducing atmosphere at 1400-1500°C for 1.5-2.5 h, and then kept under pressure at 1600-1700°C for 0.5-1 h, and then cooled and annealed to obtain graphene oxide modified brown corundum aggregate.

2. The preparation method of graphene oxide modified brown corundum aggregate as claimed in claim 1, wherein In S1, the concentration of HF solution is 10~20wt%; Alternatively, in S1, after washing, the residual water is replaced with anhydrous ethanol; Alternatively, in S1, the preparation method of the acidic γ-Al2O3 sol comprises: adding dilute nitric acid to the γ-Al2O3 sol, adjusting the pH to 3-5, and then ultrasonically dispersing for 0.5-1 h; Alternatively, in S1, the evaporation drying method comprises: stirring at 50-60°C until the mixture evaporates into a paste, and then vacuum drying at 100-120°C for 2-3 hours; Alternatively, in S1, the calcination method comprises: heating to 500-550° C. and then calcining at a constant temperature for 1-1.5 hours.

3. The preparation method of graphene oxide modified brown corundum aggregate as claimed in claim 1, wherein In S2, graphene oxide was pre-treated by ultrasonic exfoliation.

4. The preparation method of graphene oxide modified brown corundum aggregate as claimed in claim 1, wherein In S3, the inert atmosphere includes an argon atmosphere; the reducing atmosphere includes hydrogen with a volume concentration of 3 to 10%; The pressurization and heat preservation is carried out after the reducing atmosphere is removed, and the method includes: vacuuming to remove the reducing atmosphere containing hydrogen, and then pressurizing with an inert atmosphere; Alternatively, in S3, the temperature reduction annealing method comprises: cooling to 1200° C. at a rate of 2-5° C. / min in an inert atmosphere.

5. A graphene oxide modified brown corundum aggregate prepared by the preparation method according to any one of claims 1 to 4.

6. A UHPC, characterized in that: The invention comprises the following components in parts by mass: 1124-1224 parts of cement, 398-448 parts of the graphene oxide modified brown corundum aggregate according to claim 5, 105-135 parts of silica fume, 35-43 parts of steel fiber, 310-410 parts of water and 8-14 parts of a water reducer.

7. The UHPC according to claim 6, wherein The cement is ordinary Portland cement of grade 52.5 or grade 52.5R; Alternatively, the silica fume has an amorphous silicon dioxide content greater than 95 wt %, and is an ultrafine dry powder that is not fully densified; Alternatively, the steel fiber is an ordinary straight steel fiber or a copper-plated straight steel fiber.

8. A method for preparing UHPC according to any one of claims 6 to 7, characterized in that: Including steps: S4, mixing cement and silica fume to obtain a first mixture, adding graphene oxide modified brown corundum aggregate, water and a water reducer to the first mixture, and mixing to obtain a second mixture; S5. Add steel fiber to the second mixture, stir, cast and shape it, and cure it to a specified age.

9. The method for preparing UHPC according to claim 8, wherein: In S4, cement and silica fume are mixed and stirred at a speed of 75-85 rpm for 2-3 min; graphene oxide modified brown corundum aggregate, water and water reducer are added and stirred at a speed of 75-85 rpm for 2-3 min; Alternatively, in S5, after adding the steel fiber, stir at 155–165 rpm for 3–5 min; Alternatively, in S5, the curing method is curing under standard curing conditions.

10. A use of the UHPC according to any one of claims 6-7, characterized in that: Including applications in military protection engineering or civil structural engineering.

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