Ultra-high performance concrete as well as preparation method and application thereof

Abstract

The invention relates to ultra-high performance concrete and a preparation method and application thereof, the preparation method comprises the following steps: (1) uniformly paving short fine steel fibers and long thick steel fibers at the bottom of a mold, and vibrating to form a fiber layer; wherein the feeding mass ratio of the long thick steel fibers to the short thin steel fibers is controlled to be 1.1-2.5; (2) preparing nano silicon dioxide, cement, silica fume, microbeads, fly ash, quartz sand, a water reducing agent and water into slurry; wherein the feeding mass of the nano silicon dioxide is controlled to be 10%-23% of the feeding mass of the silica fume; (3) adding the slurry into the mold and enabling the slurry to slowly permeate into the fiber layer until the fiber layer is completely wrapped by the slurry, and demolding after the concrete is formed; and (4) carrying out standard curing on the demolded concrete for 24-48 hours, and then carrying out steam curing for 48-72 hours to obtain the ultra-high performance concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to ultra-high performance concrete and a preparation method and application thereof. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the invention that are recited in the claims. No statement herein is admitted to be prior art by virtue of its inclusion in this section.

[0003] As modern architecture develops towards lightweight, large span, super-high-rise and special engineering, such as the main load-bearing structures of large bridges, key components of offshore platforms, and nuclear power plant containment, extremely high requirements are placed on the tensile strength of concrete materials. In large-span bridges, the structure is subjected to huge tensile stresses. The tensile strength of conventional concrete is generally only between 1-5MPa. When used in special components, it is prone to cracking, which not only affects the appearance, but also causes steel corrosion, greatly shortening the service life of the bridge. Ultra-high Performance Concrete (UHPC), designed under the close stacking theory, has become an important demand point for special projects such as the national nuclear industry, marine development, and military construction due to its high strength and lightweight.

[0004] UHPC, through rational material usage and tightly packed mix design, combines high strength, high durability, and excellent workability. Through the synergistic reinforcement of multi-scale materials, it achieves high toughness and strain-hardening properties. It is typically made from cement, mineral admixtures (silica fume, microspheres, mineral powder, fly ash), fine aggregate, steel fiber, and a water-reducing agent. Ultra-high performance concrete (UHPC) typically boasts a compressive strength exceeding 120 MPa and a tensile strength exceeding 5 MPa. Its exceptional mechanical properties and durability give UHPC components advantages such as high strength, low weight, and low lifecycle costs. Consequently, it is widely used in engineering construction projects such as bridges, tunnels, wind turbine towers, and nuclear power plants, demonstrating promising development and application prospects. Furthermore, specialized structures such as long-span cantilever structures and deep-sea platforms require UHPC to exhibit the properties of "multi-crack propagation" and "strain hardening" under load, thereby avoiding the risk of brittle fracture and significantly improving the seismic and impact resistance of critical structures such as bridges and high-rise buildings. Therefore, the mechanical properties of UHPC, such as tensile strength, need to be continuously improved to meet the needs of economic and social development. Summary of the Invention

[0005] The purpose of the present invention is to provide an improved ultra-high performance concrete and its preparation method and application. The ultra-high performance concrete has high tensile strength and can meet the high requirements of special building materials. The preparation method is simple and can significantly improve the tensile strength and compressive strength of the ultra-high performance concrete material.

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

[0007] A first aspect of the present invention provides a method for preparing ultra-high performance concrete, comprising the following steps:

[0008] (1) short thin steel fibers and long thick steel fibers are evenly spread on the bottom of a mold and vibrated to form a fiber layer; wherein the mass ratio of the long thick steel fibers to the short thin steel fibers is controlled to be 1.1-2.5;

[0009] (2) preparing a slurry of nano-silicon dioxide, cement, silica fume, microbeads, fly ash, quartz sand, a water reducer, and water; wherein the mass of the nano-silicon dioxide is controlled to be 10% to 23% of the mass of the silica fume;

[0010] (3) adding the slurry into the mold and allowing the slurry to slowly penetrate into the fiber layer until the fiber layer is completely wrapped by the slurry, and then demolding after the concrete is formed;

[0011] (4) The demoulding concrete is first subjected to standard curing for 24-48 hours and then subjected to steam curing for 48-72 hours to obtain the ultra-high performance concrete.

[0012] According to some embodiments, the feed mass ratio of the long thick steel fiber to the short thin steel fiber is 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc. Further, the feed mass ratio of the long thick steel fiber to the short thin steel fiber is 1.5-2.

[0013] According to some embodiments, the mass of the nano-silicon dioxide feed is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, etc. of the mass of the silica ash feed. Furthermore, the mass of the nano-silicon dioxide feed is 10%-15% of the mass of the silica ash feed.

[0014] According to some embodiments, in step (1), the vibration is performed at 1500-2500 times / minute using a concrete vibration platform.

[0015] According to some embodiments, in step (3), during the process of the slurry slowly infiltrating into the fiber layer, a concrete vibration platform is used to vibrate at 4500-5500 times / minute.

[0016] According to some embodiments, the specific method of step (2) includes: first dry-mixing the nano-silica, the cement, the silica fume, the microbeads and the fly ash to obtain a premix, then dry-mixing the premix with the quartz sand, and then adding part of the water and the water reducer, stirring, and then adding the remaining water, and stirring to obtain the slurry.

[0017] Furthermore, the mass of the partial water is 70%-90% of the mass of the total water, for example, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, etc.

[0018] Further, after adding part of the water and the water reducing agent and stirring and mixing for 2-3 minutes, the remaining part of the water is added and stirring is continued for 1-5 minutes.

[0019] According to some embodiments, in step (3), the slurry is added to the mold in 2-4 batches.

[0020] According to some embodiments, in step (3), the slurry is slowly added into the mold from the top of the mold.

[0021] According to some embodiments, in step (3), the demoulding is performed 20 to 28 hours after the concrete is formed.

[0022] According to some embodiments, in step (4), the temperature of the standard curing is controlled to be 18-22°C and the humidity is controlled to be 95% or above; and the temperature of the steam curing is controlled to be 80-100°C.

[0023] According to some embodiments, based on the total feed mass of the cement, the silica fume, the microbeads, and the fly ash as 100%, the feed mass of the fly ash is 5%-12%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc.

[0024] According to some embodiments, based on the total mass of the cement, the silica fume, the microbeads, and the fly ash being 100%, the mass of the microbeads is 5%-12%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc.

[0025] According to some embodiments, based on the total feed mass of the cement, the silica fume, the microbeads, and the fly ash as 100%, the feed mass of the silica fume is 10%-20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0026] According to some embodiments, based on the total mass of the cement, the silica fume, the microbeads, and the fly ash being 100%, the mass of the nano-silicon dioxide is 2%-3%.

[0027] According to some embodiments, based on the total feed mass of the cement, the silica fume, the microbeads, and the fly ash as 100%, the feed mass of the quartz sand is 110%-125%, for example, 110%, 111%, 112%, 113%, 114%, 115%, 116%, 117%, 118%, 119%, 120%, 121%, 122%, 123%, 124%, 125%, etc.

[0028] According to some embodiments, based on the total feed mass of the cement, the silica fume, the microbeads, and the fly ash as 100%, the total feed mass of the short fine steel fibers and the long thick steel fibers is 70%-80%, for example, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, etc.

[0029] According to some embodiments, based on the total mass of the cement, the silica fume, the microbeads, and the fly ash as 100%, the mass of the water is 10%-20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0030] According to some embodiments, based on the total mass of the cement, the silica fume, the microbeads, and the fly ash being 100%, the mass of the water reducer is 2%-3%.

[0031] According to some embodiments, the raw materials of the ultra-high performance concrete include, by weight: 600-700 parts of cement, 100-200 parts of silica fume, 50-100 parts of microspheres, 50-100 parts of fly ash, 15-30 parts of nano-silicon dioxide, 1000-1200 parts of quartz sand, 250-300 parts of short and fine steel fibers, 500-600 parts of long and thick steel fibers, 25-35 parts of water reducer, and 160-180 parts of water.

[0032] According to some embodiments, the cement is silicate cement or ordinary silicate cement, and the strength of the cement is not less than 52.5 MPa.

[0033] According to some embodiments, the water requirement ratio of the microbeads is 98% or less. Further, the water requirement ratio of the microbeads is 90%-98%.

[0034] According to some embodiments, the water requirement ratio of the fly ash is 95% or less. Further, the water requirement ratio of the fly ash is 90%-95%.

[0035] According to some embodiments, the silica content of the silica fume is 95% or more.

[0036] According to some embodiments, the silica fume has a particle size of 0.2-200 μm.

[0037] According to some embodiments, the nano-silica is hydrophilic fumed nano-silica, and the particle size of the nano-silica is 0.01-0.2 μm.

[0038] According to some embodiments, the quartz sand is a mixture of quartz sands of different mesh sizes ranging from 30 to 120 mesh. Furthermore, the quartz sand comprises, by weight percentage, 30% to 35% of 30-35 mesh quartz sand, 30% to 35% of 50-55 mesh quartz sand, 15% to 20% of 60-65 mesh quartz sand, and 15% to 20% of 115-120 mesh quartz sand.

[0039] According to some embodiments, the short thin steel fibers and the long thick steel fibers are both copper-plated hook-ended steel fibers.

[0040] According to some embodiments, the length of the short steel fibers is 10-20 mm, further 13-20 mm.

[0041] According to some embodiments, the diameter of the short steel fibers is 0.1-0.4 mm, further 0.25-0.4 mm.

[0042] According to some embodiments, the length of the long thick steel fiber is 20-35 mm, further 25-30 mm.

[0043] According to some embodiments, the diameter of the long thick steel fiber is 0.3-0.9 mm, further 0.4-0.8 mm.

[0044] According to some embodiments, the water reducer is a polycarboxylate water reducer.

[0045] According to some embodiments, the solid content of the water reducing agent is greater than 25%.

[0046] According to some embodiments, the water reducing agent has a water reducing rate of 30% or more.

[0047] A second aspect of the present invention provides an ultra-high performance concrete produced by the above-described preparation method.

[0048] According to some embodiments, the ultra-high performance concrete has a tensile strength of 25 MPa or above.

[0049] A third aspect of the present invention provides an ultra-high performance concrete prepared by the preparation method described above, or the use of the ultra-high performance concrete described above in special engineering.

[0050] Furthermore, the special projects include but are not limited to large-span bridges, offshore platforms, nuclear power plants, etc.

[0051] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0052] This invention utilizes a fiber mesh-like fiber layer and slurrying process, nano-silica to refine the pore structure, and optimized slurry workability to address the dispersion challenges of high-content steel fibers, significantly improving matrix density and interfacial adhesion. The resulting UHPC achieves a tensile strength exceeding 25 MPa, combining high strength, high toughness, and durability. It is suitable for specialized projects such as long-span bridges, offshore platforms, and nuclear power plants, meeting the needs of developing low-carbon, green building materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is the particle size distribution and close packing curve of each raw material;

[0054] Figure 2 These are photos of the failure process of the specimens prepared using the combined curing method in Example 1. DETAILED DESCRIPTION

[0055] Common UHPC uses high dosages of cement, mineral admixtures, and appropriately graded fine aggregate to achieve the densest packing design. By incorporating highly fine and reactive silica fume, a high-density, high-strength matrix is ​​achieved. However, excessive silica fume content not only prevents it from fully participating in the hydration reaction but also leads to decreased system performance and increased shrinkage later in the process. The addition of nano-silica to UHPC, with its high specific surface area, helps promote the formation of hydration products, thereby optimizing the pore structure and reducing porosity. However, its dosage must be carefully considered to avoid negative impacts on the matrix caused by excessive additions.

[0056] Through a large number of experimental studies, the inventors of this application found that by adding high-activity, high-water-demand silica fume and nano-silica and low-water-demand fly ash and microbeads to UHPC materials, and controlling the amount of each admixture within a specific range, the filling effect and volcanic ash effect of the admixture can be fully utilized, improving the matrix density while ensuring working performance, which is in line with the current "dual carbon" policy.

[0057] The present invention pre-lays a large amount of steel fibers in a mold and compacts them, then infiltrates a high-workability and high-density slurry composed of cement, mineral admixtures, nano-silica, and fine aggregate and assists in compaction. This method improves the problems of difficult stirring and poor workability of UHPC slurry when a large amount of fiber is used, while also avoiding the problem of uneven distribution of steel fibers, promoting the formation of a steel fiber skeleton, and improving the tensile strength of concrete.

[0058] The present invention adopts steam curing. Since the UHPC microstructure is very dense, the heat released by the hydration reaction causes the water or air inside the closed pores to expand due to heat, increasing the pressure in the pores. At this time, the synergistic steam curing keeps the UHPC under a high-temperature, high-pressure state, which promotes the formation of tobermorite and xonotlite crystals. The hydration products fit tightly with the densely distributed fibers, resulting in a rapid development of tensile strength.

[0059] The beneficial effects of the present invention are mainly manifested in: 1) The present invention can overcome the situation that a large amount of steel fibers cannot be stirred in the slurry and formed into test pieces through infiltration pouring. 2) The present invention can give full play to the activity effect and ball effect of the admixtures by reasonably adjusting the composition ratio of mineral admixtures (fly ash, microbeads, silica fume) and reasonably adjusting the amount of nano-silicon dioxide, so as to obtain a high-strength and high-workability infiltration slurry that meets the requirements of UHPC. 3) The present invention can control the distribution and orientation of the fibers, and can obtain a high-mechanical performance matrix after infiltration on the surface of the flattened steel fibers, which significantly improves the tensile strength of UHPC. The tensile strength of the ultra-high performance concrete material of the present invention can be as high as 25MPa or more, which can meet the high requirements of special building materials.

[0060] definition:

[0061] In the present invention, the water demand ratio refers to the ratio of the water consumption when the fluidity of the mineral admixture mortar reaches the same fluidity as the reference mortar to the water consumption of the reference mortar.

[0062] In the present invention, the sand-to-cement ratio is the mass percentage of quartz sand to cementitious material, wherein the cementitious material is composed of cement, silica fume, fly ash and microbeads.

[0063] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the embodiments of the present invention. Therefore, the description is to be regarded as illustrative in nature and not restrictive.

[0064] The present invention is further described below with reference to the following examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples may be further adjusted according to the specific requirements of the application. Unspecified implementation conditions are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0065] Unless otherwise specified herein, the preparation methods and detection methods involved in the following examples or comparative examples refer to the prior art. Unless otherwise specified in the following examples, all raw materials were purchased from commercial sources or prepared by conventional methods in the art.

[0066] In the following examples and comparative examples, the raw materials used can be purchased commercially or prepared by themselves. The specific raw materials are as follows:

[0067] The silica fume is fully encrypted silica fume with a silicon dioxide content of ≥95%, a D50 of 6.10μm, and a specific surface area of ​​19800m 2 / kg.

[0068] The fly ash is Class I fly ash, with a water requirement ratio of 94%, a D50 of 45.00 μm, and a specific surface area of ​​400 m 2 / kg.

[0069] The water demand ratio of the microbeads is 95%, D50 is 36.11 μm, and the specific surface area is 483 m 2 / kg.

[0070] Nano-silica, D50 is 0.20μm.

[0071] The short thin steel fiber is a copper-plated end hook steel fiber with a length of 13mm and a diameter of 0.25mm.

[0072] The long thick steel fiber is a copper-plated end hook steel fiber with a length of 26mm and a diameter of 0.5mm.

[0073] The quartz sand is a mixture of four types according to weight percentage, including 35% of 30 mesh, 35% of 50 mesh, 15% of 60 mesh, and 15% of 120 mesh.

[0074] The water reducer is a polycarboxylic acid water reducer with a solid content of 30% and a water reduction rate of 35%.

[0075] The cement is silicate cement that complies with GB175-2023 "General silicate cement" and has a strength grade of 52.5MPa.

[0076] Example 1

[0077] This embodiment provides an ultra-high performance concrete, the raw material formula (weight parts) of which is shown in Table 1, which is prepared by the following steps:

[0078] (1) Weigh each component according to weight percentage;

[0079] (2) Short and thin steel fibers and long and thick steel fibers are evenly spread on the bottom of the mold and vibrated on a vibration table at 2000 times / min for 30 seconds to form a three-dimensional staggered network structure;

[0080] (3) Dry mixing nano-silica with cement, silica fume, microbeads, and fly ash for 2 minutes to obtain a premix;

[0081] (4) dry-mix the premix with quartz sand for 2 min, add 80% water (4.56 parts) and all the water reducer, stir for 3 min, then add the remaining 20% ​​water (1.14 parts), stir for 5 min to obtain a slurry;

[0082] (5) Slowly infiltrate the slurry into the fiber layer from the top of the mold three times. After each infiltration, vibrate at 5000 times / min for 1 minute until the fiber is completely wrapped by the slurry. Demold 24 hours after the infiltration.

[0083] (6) The demoulded specimens were placed in a temperature of 20±2°C and a humidity of ≥95% for 48 h, and then placed in a steam curing box at 90°C for 72 h.

[0084] The particle size distribution and close packing curves of the raw materials in Example 1 are as follows: Figure 1 As shown, Figure 1 The curve of Example 1 is the actual curve of Example 1. It can be seen that the stacking method of Example 1 is basically close to the target dense stacking method, that is, close to the ideal curve.

[0085] Examples 2-4

[0086] This embodiment provides an ultra-high performance concrete, which is basically the same as Example 1, with the only differences being: a different raw material formula, a different fiber gradation, and a different curing process time. See Table 1 for details.

[0087] Comparative Example 1

[0088] This comparative example provides a concrete, which is basically the same as Example 1, except that the concrete mixing and molding method is different and the amount of water reducer is different. Specifically, the concrete preparation method is as follows:

[0089] (1) Weigh each component according to weight percentage;

[0090] (2) Dry mixing nano-silica with cement, silica fume, microbeads, and fly ash for 2 minutes to obtain a premix;

[0091] (3) Add the premix and quartz sand to the mixer and dry mix for 2 minutes, then add 80% of the water and all the water reducer and stir for 4 minutes;

[0092] (4) Add the remaining 20% ​​of water and continue stirring for 2 minutes;

[0093] (5) Add short fine steel fibers and long thick steel fibers and stir for 2 minutes to obtain a mixture;

[0094] (6) Pour the mixture into the mold in two steps and vibrate to form the mixture. Demold the mixture after 24 hours.

[0095] (7) The demoulded specimens were placed in a temperature of 20±2°C and a humidity of ≥95% for 48 h, and then placed in a steam curing box at 90°C for 72 h.

[0096] Comparative Example 2

[0097] This comparative example provides a concrete, which is basically the same as Example 1, except that the mass of nano-silica used in this comparative example is 30% of the mass of silica fume, and the amount of water reducer added is different.

[0098] Comparative Example 3

[0099] This comparative example provides a concrete, which is basically the same as Example 1, except that the ratio of long thick steel fibers to short thin steel fibers used in this comparative example is 1:1.

[0100] Comparative Example 4

[0101] This comparative example provides a concrete, which is basically the same as Example 1, except that: after demolding, the comparative example specimen is placed under conditions of temperature of 20±2°C and humidity ≥95% for curing for 96 hours, and then placed in a steam curing box at 90°C for steam curing for 24 hours.

[0102] Table 1

[0103]

[0104]

[0105] Performance testing

[0106] The compressive and tensile strengths of the ultra-high performance concrete specimens from each example and comparative example were tested according to the methods specified in "Ultra-High Performance Concrete (UHPC) Technical Requirements," T / CECS 10107-2020. The test results are shown in Table 2. The standard curing for 28 days refers to curing the specimens for each example and comparative example for 28 days, with the final curing step being replaced by the standard curing method. This serves as the basis for strength comparison.

[0107] Table 2

[0108]

[0109] The results in Table 2 show that the tensile strength of the UHPC prepared by pre-laying steel fibers and then slurrying after containing about 0.7% nano-silica reached 28.7 MPa after combined curing (Example 1). Compared with the standard curing for 28 days, the tensile strength increased by 54.3%. The failure process of the specimen prepared by the combined curing method in Example 1 was multi-crack failure. After failure, some steel fibers still bridged the two ends of the cracks, such as Figure 2 As shown. With the increase of silica fume and microbead content and the decrease of cement and fly ash content (Example 2), the tensile strength of UHPC after standard curing and combined curing decreased, and decreased by 5.9% and 10.8% respectively compared with Example 1. With the reduction of the ratio of long coarse steel fiber to short fine steel fiber (Example 3), the tensile strength of the specimen after standard curing for 28 days and combined curing decreased by 1.6% and 3.8% respectively compared with Example 1. When the sand-binder ratio was changed to 1.15:1 (Example 4), the tensile strength of the specimen decreased compared with Example 1. However, the tensile strength after combined curing of each example was higher than 25MPa.

[0110] When the non-slurrying method is adopted and the fibers are stirred together with the slurry (Comparative Example 1), the slurry is difficult to stir and difficult to shape, resulting in the tensile strength of the specimens after standard curing and combined curing decreased by 47.3% and 56.8% respectively compared with Example 1; when the amount of nano-silica added is too much (Comparative Example 2), the tensile strength of the specimens after standard curing and combined curing decreased by 43% and 52.6% respectively compared with Example 1; when the ratio of long thick steel fiber to short fine steel fiber is changed to 1:1 (Comparative Example 3), the tensile strength of the specimens after standard curing and combined curing decreased by 32.8% and 37.6% respectively compared with Example 1; when the curing method is changed to standard curing for 96 hours and then steam curing for 24 hours (Comparative Example 4), the tensile strength of the specimens after standard curing and combined curing decreased by 49.5% and 63.4% respectively compared with Example 1.

[0111] The strength test results above demonstrate that the synergistic effects of raw material composition design, controlled nano-silica dosage, pre-laying steel fibers followed by slurry infiltration, and combined curing conditions result in excellent homogeneity and high tensile strength in the prepared UHPC. Specifically, by pre-laying steel fibers in the mold and then infiltrating the UHPC slurry into the mold, the high-density slurry effectively encapsulates the three-dimensional mesh fiber structure, effectively avoiding uneven and erratic fiber distribution, improving fiber utilization efficiency, reducing the interface transition zone area and internal defects, and significantly improving the tensile strength of the structure.

[0112] The combined curing process in Example 1 includes 48 hours of standard curing and 72 hours of steam curing. Because the initial hydration reaction of UHPC is relatively intense, often occurring within the first three days, during which hydration products such as CSH gel and ettringite are generated and polymerized in large quantities, the 2-day standard curing period ensures sufficient early hydration of the UHPC, achieving a certain level of early strength. When the UHPC hydration reaction enters its decline phase, the hydration reaction rate decreases. The high temperature of steam curing facilitates the continued hydration of unreacted raw material particles in the system, allowing the hydration products to continuously fill the system's pores, thereby improving the mechanical properties and density of the UHPC.

[0113] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

[0114] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

Claims

1. A method for preparing ultra-high performance concrete, characterized by: It includes the following steps: (1) short thin steel fibers and long thick steel fibers are evenly spread on the bottom of a mold and vibrated to form a fiber layer; wherein the mass ratio of the long thick steel fibers to the short thin steel fibers is controlled to be 1.1-2.5; (2) preparing a slurry of nano-silicon dioxide, cement, silica fume, microbeads, fly ash, quartz sand, a water reducer, and water; wherein the mass of the nano-silicon dioxide is controlled to be 10% to 23% of the mass of the silica fume; (3) adding the slurry into the mold and allowing the slurry to slowly penetrate into the fiber layer until the fiber layer is completely wrapped by the slurry, and then demolding after the concrete is formed; (4) The demoulding concrete is first subjected to standard curing for 24-48 hours and then subjected to steam curing for 48-72 hours to obtain the ultra-high performance concrete.

2. The method for preparing ultra-high performance concrete according to claim 1, wherein: In step (1), the vibration is performed at 1500-2500 times / minute using a concrete vibration platform; and / or, In step (3), while the slurry slowly infiltrates into the fiber layer, a concrete vibration platform is used to vibrate at 4500-5500 times / minute.

3. The method for preparing ultra-high performance concrete according to claim 1, wherein: The specific method of step (2) includes: first dry-mixing the nano-silica, the cement, the silica fume, the microbeads and the fly ash to obtain a premix, then dry-mixing the premix with the quartz sand, adding part of the water and the water reducer, stirring, adding the remaining water, and stirring to obtain the slurry.

4. The method for preparing ultra-high performance concrete according to claim 3, wherein: The mass of the partial water is 70%-90% of the mass of the whole water.

5. The method for preparing ultra-high performance concrete according to claim 1, wherein: In step (3), the slurry is added to the mold in 2-4 times, and / or the slurry is slowly added to the mold from the top of the mold, and / or the demoulding is performed 20 to 28 hours after the concrete is formed.

6. The method for preparing ultra-high performance concrete according to claim 1, wherein: In step (4), the temperature of the standard curing is controlled to be 18-22°C and the humidity is controlled to be 95% or above; the temperature of the steam curing is controlled to be 80-100°C.

7. The method for preparing ultra-high performance concrete according to claim 1, wherein: Taking the total feed weight of the cement, the silica fume, the microbeads, and the fly ash as 100%, the feed weight of the fly ash is 5%-12%, and / or the feed weight of the microbeads is 5%-12%, and / or the feed weight of the silica fume is 10%-20%, and / or the feed weight of the nano-silicon dioxide is 2%-3%, and / or the feed weight of the quartz sand is 110%-125%, and / or the total feed weight of the short and fine steel fibers and the long and thick steel fibers is 70%-80%, and / or the feed weight of the water is 10%-20%, and / or the feed weight of the water reducer is 2%-3%.

8. The method for preparing ultra-high performance concrete according to claim 1, wherein: The cement is silicate cement or ordinary silicate cement, and the strength of the cement is not less than 52.5 MPa; and / or, The water demand ratio of the microbeads is 98% or less; and / or, The water demand ratio of the fly ash is 95% or less; and / or, The silica content of the silica fume is 95% or above; and / or, The particle size of the silica fume is 0.2-200 μm; and / or, The nano-silica is hydrophilic fumed nano-silica, and the particle size of the nano-silica is 0.01-0.2 μm; and / or, The quartz sand is a mixture of quartz sands of different mesh sizes ranging from 30 to 120 meshes; and / or, The short thin steel fibers and the long thick steel fibers are both copper-plated end hook steel fibers; and / or, The short steel fibers have a length of 10-20 mm and a diameter of 0.1-0.4 mm; and / or The long steel fiber has a length of 20-35 mm and a diameter of 0.3-0.9 mm; and / or The water reducer is a polycarboxylate water reducer; and / or, The solid content of the water reducing agent is above 25%; and / or, The water reducing agent has a water reducing rate of more than 30%.

9. The method for preparing ultra-high performance concrete according to claim 8, wherein: The water requirement ratio of the microbeads is 90%-98%; and / or, The water requirement ratio of the fly ash is 90%-95%; and / or, In terms of weight percentage, the quartz sand includes 30%-35% of 30-35 mesh quartz sand, 30%-35% of 50-55 mesh quartz sand, 15%-20% of 60-65 mesh quartz sand and 15%-20% of 115-120 mesh quartz sand.

10. An ultra-high performance concrete produced by the preparation method according to any one of claims 1 to 9.

11. The ultra-high performance concrete according to claim 10, characterized in that: The tensile strength of the ultra-high performance concrete is 25 MPa or above.

12. An ultra-high performance concrete produced by the preparation method according to any one of claims 1 to 9, or use of the ultra-high performance concrete according to claim 10 or 11 in special engineering.

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