C180 grade ultra-high performance concrete and steam curing method for preparing same

Abstract

This invention discloses a C180 grade ultra-high performance concrete, comprising the following components by mass percentage: 42%-48% composite cementitious material; 45%-50% graded fine aggregate; 5.5%-6.8% copper-plated steel fiber; 0.8%-1.2% polycarboxylate superplasticizer; and 2.6%-3.4% water. The composite cementitious material is composed of P.O52.5 grade cement, high-purity silica fume, Class I fly ash (F grade), fly ash microspheres, and nano-silica in a mass ratio of 68:16:8:11:0.3. This invention solves the problems of C180 grade concrete, which, while reducing component size, lowering self-weight, and extending service life, suffers from difficulty in balancing strength development and steam curing efficiency. Conventional steam curing fails to fully unleash the potential of admixtures, leading to long production cycles. Furthermore, it addresses the issues of poor production stability, high raw material sensitivity, and performance fluctuations caused by aggregate and cementitious material variations and uneven fiber dispersion, thus hindering large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and in particular relates to a C180 grade ultra-high performance concrete and its steam curing preparation method. Background Technology

[0002] As modern engineering construction develops towards ultra-large spans, ultra-high strengths, and long service lives, high-performance components such as trenchless pipe jacking, bridge decks, and wind power hybrid towers place stringent requirements on the mechanical properties and production efficiency of concrete materials.

[0003] Ultra-high performance concrete (UHPC), as a new generation of cement-based composite materials, has become a key material for solving high-end engineering challenges due to its ultra-high density, excellent mechanical properties, and durability. Among them, C180 grade UHPC, as a high-grade benchmark product, can significantly reduce component cross-sectional dimensions, lower structural self-weight, and extend the service life of engineering projects. However, the industry still faces three major core technological bottlenecks:

[0004] I. It is difficult to balance the strength and steam curing efficiency of high-grade UHPC. In the existing technology, C180 grade UHPC mostly relies on long-term natural curing or ultra-long-term steam curing (≥7d) to meet the standards. Conventional steam curing process lacks targeted design and fails to fully stimulate the hydration potential of highly active admixtures (such as silica fume and nano silica), resulting in slow strength development, long production cycle, and inability to meet the high-efficiency construction requirements of large-scale projects.

[0005] Second, poor production stability and easy performance fluctuations: High-grade UHPC is extremely sensitive to raw materials. Regional differences in aggregate gradation, fluctuations in the activity of cementitious materials, uneven dispersion of steel fibers and segregation of the mixture during the mixing process can all lead to large strength dispersion coefficients and reduced crack resistance during the production of finished products, thus restricting its large-scale promotion. Summary of the Invention

[0006] The purpose of this invention is to address the challenges in balancing strength development and steam curing efficiency in ultra-high performance concrete (UHPC), where C180 grade, as a high-grade benchmark product, while reducing component size, self-weight, and extending service life, suffers from conventional steam curing methods that fail to fully unleash the potential of admixtures, resulting in long production cycles, poor production stability, high raw material sensitivity, and performance fluctuations caused by aggregate and binder variations and uneven fiber dispersion, thus hindering large-scale application. Therefore, this invention proposes a method for preparing C180 grade UHPC and its steam curing process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a C180 grade ultra-high performance concrete, comprising the following components by mass percentage:

[0008] Composite cementitious materials: 42%-48%;

[0009] Graded fine aggregate 45%-50%;

[0010] Copper-plated steel fiber: 5.5%-6.8%;

[0011] Polycarboxylate superplasticizer 0.8%-1.2%;

[0012] Water content: 2.6%-3.4%;

[0013] The composite cementitious material is composed of P.O52.5 grade cement, high-purity silica fume, Class I fly ash (F type), fly ash microspheres, and nano-silica in a mass ratio of 68:16:8:11:0.3.

[0014] Furthermore, the P.O52.5 grade cement described above has a 3-day compressive strength ≥28MPa, a 28-day compressive strength ≥58MPa, and a standard consistency water requirement <27%.

[0015] Furthermore, the graded fine aggregate is composed of natural sand of four particle sizes: 0.15-0.3mm, 0.3-0.6mm, 0.6-1.18mm, and 1.18-2.36mm, mixed in a mass ratio of 4:1:4.3:1.4. The maximum crushing index of a single grade is ≤5%, the fineness modulus is 2.2-2.8, and the mud content is ≤1.0%.

[0016] Furthermore, the high-purity silica ash has a silica content of ≥90%, a loss on ignition of ≤3%, a water requirement ratio of ≤125%, and a 7-day rapid activity index of ≥110%; the nano silica has a particle size range of 20-30nm, an agglomeration rate of ≤12%, and a silica purity of ≥99%.

[0017] Furthermore, the copper-plated steel fiber has a length of 12-14 mm, a diameter of 0.20-0.22 mm, an aspect ratio of 55-65, a tensile strength of ≥2000 MPa, and a density of 7.85 g / cm³.

[0018] Furthermore, the polycarboxylate superplasticizer has a solid content ≥30%, a water reduction rate ≥30%, and a change in size ≤50 mm over 1 hour; the modified microspheres have a flowability ratio ≥105%, a 28-day activity index ≥90%, and a loss on ignition ≤3%.

[0019] Furthermore, the present invention also provides a method for steam curing C180 grade ultra-high performance concrete, comprising the following steps:

[0020] S1: Raw material pretreatment; The graded fine aggregate is placed in a ventilated and dry environment and pre-dried to a moisture content of ≤1%; Nano silica is ultrasonically dispersed for 15-20 minutes with a dispersion power of 300-350W to obtain a pre-dispersed admixture.

[0021] S2: Dry material mixing; Add P.O52.5 grade cement, high-purity silica fume, F-class I grade fly ash, fly ash microspheres, graded fine aggregate and pre-dispersed nano silica into a vertical shaft planetary mixer and dry mix for 1-3 minutes until uniformly mixed;

[0022] S3: Wet mixing adjustment; Add 80% water and all of the polycarboxylate superplasticizer to the dry mixture, stir for 3-4 minutes, add the remaining water, and continue stirring for 1-2 minutes to make the mixture reach the fluidized state.

[0023] S4: Fiber dispersion; slowly and evenly add copper-plated steel fibers to the mixer, controlling the feeding time to be completed within 2-3 minutes, and then continue to stir for 3-4 minutes until the steel fibers are evenly distributed and there is no clumping.

[0024] S5: Casting and molding; The mixed ultra-high performance concrete (UHPC) is poured into a mold pre-coated with release agent, and vibrated for 0.5 minutes using a high-frequency vibrating table at a vibration frequency of 50-60Hz to remove internal air bubbles.

[0025] S6: Multi-stage steam curing, including the following stages;

[0026] a. Static resting stage: Let stand for 6-8 hours at 20-25℃ and relative humidity ≥80%;

[0027] b. Heating stage: Increase the temperature to 85-90℃ at a rate of ≤15℃ / h;

[0028] c. Constant temperature steam curing stage: Maintain a temperature of 90℃±1℃ and a relative humidity of ≥90% for 3 days;

[0029] d. Cooling stage: Cool down to room temperature at a rate of ≤15℃ / h, and maintain humidity at 85-90% during the cooling process.

[0030] The C180 grade ultra-high performance concrete provided by this invention has the following beneficial effects:

[0031] 1. This invention, through the synergistic design of a five-element composite cementitious system and graded aggregates, achieves 3-day steam curing of C180 grade UHPC, significantly improving production efficiency. Simultaneously, the steam curing preparation method for concrete is stable and controllable; uniform feeding and step-by-step mixing prevent fiber agglomeration and mixture segregation, resulting in a product strength dispersion coefficient ≤3% and a high production qualification rate. Furthermore, the material ratio of this scheme ensures strong raw material adaptability, compatible with high-quality natural sand and cement from different regions, eliminating the need for specific high-purity raw materials and reducing engineering application costs. This results in products with excellent comprehensive performance, possessing ultra-high strength, high impermeability, and high crack resistance, suitable for projects requiring high-performance concrete such as trenchless pipe jacking and bridge decks, extending the service life of the project.

[0032] 2. This invention, through the proportional control of the five-element composite cementitious system, requires precise matching of the dosage of silica fume and nano-silica to achieve both filling and activation effects without affecting workability; the gradation optimization of the four-level aggregate achieves the densest packing through the adjustment of the proportion of each particle size, providing skeletal support for ultra-high strength; the parameter coordination of the multi-stage steam curing process ensures the initial setting and molding of the mixture during the static curing stage, avoids thermal stress cracking during the heating stage, fully activates hydration activity during the isothermal stage, and alleviates internal stress during the cooling stage. The four aspects work together to ensure the strength and stability of the product.

[0033] 3. This invention effectively avoids problems such as fiber clumping and mixture segregation by pre-treatment of raw materials (ultrasonic dispersion of nano-silica), step-by-step mixing (dry material premixing - wet mixing fluidization - uniform fiber feeding) and precise steam curing. At the same time, it is compatible with high-quality raw materials from different regions, reducing the threshold for engineering applications. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a table of raw material formulations and process parameters (by mass percentage) for various embodiments and comparative examples of C180 grade ultra-high performance concrete.

[0036] Figure 2 This is a table showing the performance test results of a type of C180 ultra-high performance concrete. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0039] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0040] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0041] In the description of the embodiments of the present invention, it should be noted that the terms "upper" and "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0042] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] Example 1

[0044] Please see Figure 1 This invention provides a technical solution: a C180 grade ultra-high performance concrete, comprising the following components by mass percentage:

[0045] Composite cementitious materials: 42%-48%;

[0046] Graded fine aggregate 45%-50%;

[0047] Copper-plated steel fiber: 5.5%-6.8%;

[0048] Polycarboxylate superplasticizer 0.8%-1.2%;

[0049] Water content: 2.6%-3.4%;

[0050] The composite cementitious material is composed of P.O52.5 grade cement, high-purity silica fume, Class I fly ash (F type), fly ash microspheres, and nano-silica. Based on the total mass of the composite cementitious material, the P.O52.5 grade cement accounts for 65%-68% of the mass, high-purity silica fume accounts for 15%-16%, Class I fly ash (F type) accounts for 7%-8%, fly ash microspheres account for 10%-11%, and nano-silica accounts for 0.2%-0.3%.

[0051] Currently, the strength development of common C180 grade UHPC relies on the full hydration of cementitious materials and the tight packing of the matrix. However, conventional cementitious systems are mostly ternary or quaternary combinations, which make it difficult to balance rapid strength development and workability under steam curing conditions. Excessive silica fume content will lead to increased system viscosity and decreased workability, while a single cement system cannot meet the requirements of ultra-high strength.

[0052] This application, through extensive experimental research, has discovered that by precisely proportioning a five-component composite cementitious system consisting of "P.O52.5 grade cement - high-purity silica fume - Class I fly ash - fly ash microspheres - nano silica", synergistic effects can be achieved among the components: cement provides basic strength support, silica fume and nano silica exert a dense filling effect, refining the pore structure of the matrix, and fly ash and modified microspheres improve the workability of the mixture through the "ball effect" while promoting full hydration reaction, enabling UHPC to reach the C180 strength standard within 3 days of steam curing.

[0053] Specifically, see Figure 1-2 The P.O52.5 grade cement has a 3-day compressive strength ≥28MPa, a 28-day compressive strength ≥58MPa, and a standard consistency water requirement <27%.

[0054] Specifically, see Figure 1-2 The graded fine aggregate is composed of natural sand of four particle sizes: 0.15-0.3mm, 0.3-0.6mm, 0.6-1.18mm, and 1.18-2.36mm, mixed in a mass ratio of 4:1:4.3:1.4. The maximum crushing index of a single grade is ≤5%, the fineness modulus is 2.2-2.8, and the mud content is ≤1.0%. Through the optimized combination of the four particle sizes, the aggregate achieves the densest packing, improves the strength of the matrix skeleton, and reduces the damage to the internal structure of the product caused by temperature and humidity stress during steam curing.

[0055] Specifically, see Figure 1-2 The high-purity silica ash has a silica content of ≥90%, a loss on ignition of ≤3%, a water requirement ratio of ≤125%, and a 7-day rapid activity index of ≥110%; the nano silica has a particle size range of 20-30nm, an agglomeration rate of ≤12%, and a silica purity of ≥99%.

[0056] Specifically, see Figure 1-2 The copper-plated steel fibers have a length of 12-14 mm, a diameter of 0.20-0.22 mm, an aspect ratio of 55-65, a tensile strength ≥2000 MPa, and a density of 7.85 g / cm³. Steel fibers within this parameter range can be uniformly dispersed in the mixture, forming a strong bond with the matrix, significantly improving the flexural strength and crack resistance of UHPC.

[0057] Specifically, see Figure 1-2 The polycarboxylate superplasticizer has a solid content ≥30%, a water reduction rate ≥30%, and a change in thickness ≤50 mm over 1 hour; the modified microspheres have a flowability ratio ≥105%, a 28-day activity index ≥90%, and a loss on ignition ≤3%. The high solid content and high water reduction rate of the superplasticizer make it suitable for low water-to-binder ratio systems, ensuring the workability and stability of the mixture.

[0058] The water requirement ratio refers to the ratio of the water required to achieve the same fluidity as the reference mortar when the fluidity of the mineral admixture mortar reaches that of the reference mortar to the water required for the reference mortar; the fluidity ratio refers to the ratio of the fluidity of the mortar with added mineral admixtures to the fluidity of the reference mortar.

[0059] This invention also provides a method for steam curing C180 grade ultra-high performance concrete, comprising the following steps:

[0060] S1: Raw material pretreatment; The graded fine aggregate is placed in a ventilated and dry environment and pre-dried to a moisture content of ≤1%; Nano silica is ultrasonically dispersed for 15-20 minutes with a dispersion power of 300-350W to obtain a pre-dispersed admixture.

[0061] S2: Dry material mixing; Add P.O52.5 grade cement, high-purity silica fume, F-class I grade fly ash, fly ash microspheres, graded fine aggregate and pre-dispersed nano silica into a vertical shaft planetary mixer and dry mix for 1-3 minutes until uniformly mixed;

[0062] S3: Wet mixing adjustment; Add 80% water and all of the polycarboxylate superplasticizer to the dry mixture, stir for 3-4 minutes, add the remaining water, and continue stirring for 1-2 minutes to make the mixture reach the fluidized state.

[0063] S4: Fiber dispersion; slowly and evenly add copper-plated steel fibers to the mixer, controlling the feeding time to be completed within 2-3 minutes, and then continue to stir for 3-4 minutes until the steel fibers are evenly distributed and there is no clumping.

[0064] S5: Casting and molding; The mixed ultra-high performance concrete (UHPC) is poured into a mold pre-coated with release agent, and vibrated for 0.5 minutes using a high-frequency vibrating table at a vibration frequency of 50-60Hz to remove internal air bubbles.

[0065] S6: Multi-stage steam curing, including the following stages;

[0066] a. Static resting stage: Let stand for 6-8 hours at 20-25℃ and relative humidity ≥80%;

[0067] b. Heating stage: Increase the temperature to 85-90℃ at a rate of ≤15℃ / h;

[0068] c. Constant temperature steam curing stage: Maintain a temperature of 90℃±1℃ and a relative humidity of ≥90% for 3 days;

[0069] d. Cooling stage: Cool down to room temperature at a rate of ≤15℃ / h, and maintain humidity at 85-90% during the cooling process.

[0070] In the raw material pretreatment, ultrasonic dispersion of nano-silica can avoid agglomeration and ensure its filling and reinforcing effects; step-by-step stirring and feeding process can prevent steel fiber agglomeration and ensure its uniform distribution; multi-stage steam curing process ensures the initial internal stability of UHPC through static stop stage, avoids thermal stress cracking in heating stage, fully stimulates hydration activity in constant temperature stage, and relieves internal stress in cooling stage, ultimately achieving a dual improvement in product strength and stability.

[0071] The C180 grade ultra-high performance concrete provided by this invention has the following beneficial effects:

[0072] 1. This invention, through the synergistic design of a five-element composite cementitious system and graded aggregates, achieves 3-day steam curing of C180 grade UHPC, significantly improving production efficiency. Simultaneously, the steam curing preparation method for concrete is stable and controllable; uniform feeding and step-by-step mixing prevent fiber agglomeration and mixture segregation, resulting in a product strength dispersion coefficient ≤3% and a high production qualification rate. Furthermore, the material ratio of this scheme ensures strong raw material adaptability, compatible with high-quality natural sand and cement from different regions, eliminating the need for specific high-purity raw materials and reducing engineering application costs. This results in products with excellent comprehensive performance, possessing ultra-high strength, high impermeability, and high crack resistance, suitable for projects requiring high-performance concrete such as trenchless pipe jacking and bridge decks, extending the service life of the project.

[0073] 2. This invention, through the proportional control of the five-element composite cementitious system, requires precise matching of the dosage of silica fume and nano-silica to achieve both filling and activation effects without affecting workability; the gradation optimization of the four-level aggregate achieves the densest packing through the adjustment of the proportion of each particle size, providing skeletal support for ultra-high strength; the parameter coordination of the multi-stage steam curing process ensures the initial setting and molding of the mixture during the static curing stage, avoids thermal stress cracking during the heating stage, fully activates hydration activity during the isothermal stage, and alleviates internal stress during the cooling stage. The four aspects work together to ensure the strength and stability of the product.

[0074] 3. This invention effectively avoids problems such as fiber clumping and mixture segregation by pre-treating raw materials (ultrasonic dispersion of nano-silica), stepwise mixing (dry pre-mixing - wet fluidization - uniform fiber feeding), and precise steam curing. It is also compatible with high-quality raw materials from different regions, lowering the threshold for engineering applications. It can be used to prepare trenchless pipe jacking, container frames, evacuation platforms, or municipal manhole covers. After steam curing at 90℃ for 3 days, the product has a freeze-thaw resistance rating of ≥F400 and a crack width of ≤0.05mm. The self-weight of the same model of product is reduced by more than 25% compared with traditional concrete products.

[0075] Example 2

[0076] See Figure 1-2 The figure shows a C180 grade ultra-high performance concrete provided in Embodiment 2 of the present invention. Based on the above embodiments, this embodiment further improves upon the following technical solutions: It is prepared according to a mass percentage, such as... Figure 1 As shown;

[0077] Among them, the 28-day compressive strength of P.O52.5 grade cement is 58.5 MPa, and the standard consistency water requirement is 26.8.

[0078] The silica fume has a silica content of 90%, a loss on ignition of 2.8%, a water requirement ratio of 120%, and an activity index of 112% using the 7-day rapid method.

[0079] Class F Grade I fly ash has a water requirement ratio of 93%, a loss on ignition of 3.5%, and a 28-day activity index of 75%.

[0080] The fly ash microspheres had a flowability ratio of 108%, a 28-day activity index of 92%, and a loss on ignition of 2.2%.

[0081] The D50 particle size of the nano-silica is 25 nm, and the silica purity is 99.5%.

[0082] The particle size ratio of the graded fine aggregate (0.15-0.3mm ∶ 0.3-0.6mm ∶ 0.6-1.18mm ∶ 1.18-2.36mm) = 4 ∶ 1 ∶ 3.6 ∶ 1.4, with a maximum single-stage crushing value of 4.8%;

[0083] The copper-plated steel fiber has a length of 13mm, a diameter of 0.21mm, an aspect ratio of 62, and a tensile strength of 2300MPa.

[0084] The polycarboxylate superplasticizer has a solid content of 32%, a water reduction rate of 31%, and a water change of 45 mm over 1 hour.

[0085] It is prepared by the following method:

[0086] S1: Raw material pretreatment: The graded fine aggregate is placed in a ventilated and dry environment for pre-drying; after mixing nano-silica with modified microspheres, it is ultrasonically dispersed for 18 minutes using 320W power to obtain pre-dispersed admixture;

[0087] S2: Dry mixing: Add P.O52.5 grade cement, silica fume, F-type grade I fly ash, graded fine aggregate and pre-dispersed admixture into a vertical shaft planetary mixer and dry mix for 1 minute until uniformly mixed;

[0088] S3: Wet mixing adjustment: Add 80% water and all of the polycarboxylate superplasticizer to the dry mixture, stir for 3 minutes, then add the remaining 20% ​​water and continue stirring for 1.5 minutes to make the mixture reach the fluidized state.

[0089] S4: Fiber dispersion: Add copper-plated steel fibers at a uniform rate, complete the feeding within 2 minutes, and then continue stirring for 3 minutes until the steel fibers are evenly distributed and there is no obvious clumping.

[0090] S5: Casting and molding: Pour the mixed UHPC into a mold pre-coated with release agent, and vibrate it for 1 minute using a high-frequency vibrating table at a vibration frequency of 55Hz to remove internal air bubbles.

[0091] S6: Multi-stage steam curing: First, stop the temperature at 22℃ and 85% relative humidity for 7 hours; then raise the temperature to 90℃ at a rate of 12℃ / h; then maintain the temperature at 90℃±1℃ and 85% relative humidity for 3 days; finally, cool down to room temperature at a rate of 12℃ / h, and maintain the humidity at 88% during the cooling process.

[0092] Example 3

[0093] See Figure 1-2 The figure shows a C180 grade ultra-high performance concrete provided in Embodiment 3 of the present invention. This embodiment further improves upon the above embodiments by making the following technical solutions: It is basically the same as Embodiment 2, except that: high-quality natural sand from sea salt is used on the basis of a fixed gradation, and the mass percentage of composite cementitious materials is adjusted to 46.2%, and the mass percentage of water is adjusted to 3.1%. The specific formula is as follows: Figure 1 As shown.

[0094] Example 4

[0095] See Figure 1-2The figure shows a C180 grade ultra-high performance concrete provided in Embodiment 4 of the present invention. This embodiment further improves upon the above embodiments by the following technical solutions: it is basically the same as Embodiment 2, except that: the copper-plated steel fiber has a length of 12mm, a diameter of 0.20mm, an aspect ratio of 60, and a tensile strength of 2200MPa; the polycarboxylate superplasticizer has a solid content of 30% and a water reduction rate of 30%, as shown in the specific formula. Figure 1 As shown.

[0096] Example 5

[0097] See Figure 1-2 The figure shows a C180 grade ultra-high performance concrete provided in Embodiment 5 of the present invention. This embodiment further improves upon the above embodiments by the following technical solution: it is basically the same as Embodiment 2, except that the particle size ratio of the graded fine aggregate (0.15-0.3mm:0.3-0.6mm:0.6-1.18mm:1.18-2.36mm) is 4:1:3.5:1.5. The specific formula is as follows: Figure 1 As shown.

[0098] Comparative Example 1

[0099] See Figure 1-2 The figure shows a C180 grade ultra-high performance concrete provided by Comparative Example 1 of the present invention. This embodiment further improves upon the above embodiment by making the following technical solutions: it is basically the same as Example 2, except that: graded fine aggregates are not used; only 0.6-1.18mm single-size natural sand is used, with the specific formula as follows... Figure 1 As shown.

[0100] Comparative Example 2

[0101] See Figure 1-2 The figure shows a C180 grade ultra-high performance concrete provided by Comparative Example 2 of the present invention. This embodiment further improves upon the above embodiment by making the following technical solution: it is basically the same as Example 2, except that the steam curing process is "static curing for 7 hours - heating to 88℃ (12℃ / h) - constant temperature steam curing for 2 days - cooling to room temperature", with specific parameters as follows. Figure 1 As shown.

[0102] Comparative Example 3

[0103] See Figure 1-2The figure shows a C180 grade ultra-high performance concrete provided by Comparative Example 3 of the present invention. This embodiment further improves upon the above embodiment by making the following technical solutions: It is basically the same as Example 2, except that the composite cementitious system is a quaternary system of "cement-silica fume-fly ash-microspheres," without the addition of nano-silica. The specific formula is as follows: Figure 1 As shown.

[0104] Comparative Example 4

[0105] See Figure 1-2 The figure shows a C180 grade ultra-high performance concrete provided by Comparative Example 4 of the present invention. Based on the above embodiments, this embodiment further improves upon the following technical solutions: it is basically the same as Example 2, except that: all steel fibers are added within 1 minute, and the mixing time is 1 minute. The specific preparation process is as follows: Figure 1 As shown.

[0106] Experimental results

[0107] Depend on Figure 2 The test results show that after steam curing at 90℃ for 3 days, the UHPC in Examples 2-5 all have a compressive strength ≥184MPa, a flexural strength ≥25MPa, and an elongation ≥650mm, fully meeting the performance requirements of C180 grade and exhibiting excellent performance.

[0108] Among them, Example 2 showed the best overall performance, with a compressive strength of 188.4 MPa and a flexural strength of 26.9 MPa. This was attributed to the precise proportioning of the five-element composite cementitious system, the close packing of graded aggregates, and the dispersion effect of fibers after uniform feeding. These three factors worked together to achieve a balance between strength and workability. Example 3 used high-quality local natural sand, and although the performance decreased slightly, it still met the standards, verifying the raw material compatibility of the present invention. Examples 4-5 adjusted the steel fiber parameters and aggregate gradation ratio, and the performance remained stable, further demonstrating the flexibility of the formulation.

[0109] Comparative Example 1 used single-size sand. Due to insufficient aggregate bulk density, the concrete matrix was poorly compacted, with a compressive strength of only 162.8 MPa and a flexural strength of 18.6 MPa, which did not meet the C180 standard. This shows that graded aggregate gradation is the key to ultra-high strength.

[0110] Comparative Example 2 shortened the constant temperature steam curing time to 2 days, and the compressive strength dropped to 175.2 MPa, failing to meet the standard, proving that 3 days of constant temperature steam curing is a necessary condition for fully activating hydration activity;

[0111] Comparative Example 3, without the addition of nano-silica, had insufficient matrix density and a compressive strength of 172.5 MPa, verifying the filling and reinforcing effect of nano-silica;

[0112] Comparative Example 4, using a short-time rapid feeding method, showed uneven steel fiber dispersion and numerous agglomerations. The compressive strength was 178.3 MPa and the spread was 650 mm, indicating that the uniform feeding process is crucial for fiber dispersion.

[0113] In summary, this invention, through the synergistic technology of "precise proportioning of composite cementitious system - densification of graded aggregates - multi-stage steam curing process - uniform fiber feeding", successfully achieves 3-day steam curing standard for C180 grade UHPC. It also has strong raw material adaptability and high production stability, solving the core pain points of existing technologies and is suitable for various high-end engineering scenarios.

[0114] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A C180-grade ultra-high performance concrete, characterized in that, Including the following ingredients by weight percentage: Composite cementitious materials: 42%-48%; Graded fine aggregate 45%-50%; Copper-plated steel fiber: 5.5%-6.8%; Polycarboxylate superplasticizer 0.8%-1.2%; Water content: 2.6%-3.4%; The composite cementitious material is composed of P.O52.5 grade cement, high-purity silica fume, Class I fly ash (F type), fly ash microspheres, and nano-silica in a mass ratio of 68:16:8:11:0.

3.

2. The C180-grade ultra-high performance concrete according to claim 1, characterized in that, The P.O52.5 grade cement has a 3-day compressive strength ≥28MPa, a 28-day compressive strength ≥58MPa, and a standard consistency water requirement <27%.

3. The C180-grade ultra-high performance concrete according to claim 1, characterized in that, The graded fine aggregate is composed of natural sand of four particle sizes: 0.15-0.3mm, 0.3-0.6mm, 0.6-1.18mm, and 1.18-2.36mm, mixed in a mass ratio of 4:1:4.3:1.

4. The maximum crushing index of a single grade is ≤5%, the fineness modulus is 2.2-2.8, and the mud content is ≤1.0%.

4. The C180-grade ultra-high performance concrete according to claim 1, characterized in that, The high-purity silica ash has a silica content of ≥90%, a loss on ignition of ≤3%, a water requirement ratio of ≤125%, and a 7-day rapid activity index of ≥110%; the nano silica has a particle size range of 20-30nm, an agglomeration rate of ≤12%, and a silica purity of ≥99%.

5. The C180-grade ultra-high performance concrete according to claim 1, wherein, The copper-plated steel fiber has a length of 12-14 mm, a diameter of 0.20-0.22 mm, an aspect ratio of 55-65, a tensile strength of ≥2000 MPa, and a density of 7.85 g / cm³.

6. The C180-grade ultra-high performance concrete according to claim 1, characterized in that, The polycarboxylate superplasticizer has a solid content ≥30%, a water reduction rate ≥30%, and a change in size ≤50 mm over 1 hour; the modified microspheres have a flowability ratio ≥105%, a 28-day activity index ≥90%, and a loss on ignition ≤3%.

7. The autoclaved production method of C180-grade ultra-high performance concrete according to claims 1-6, characterized in that, Includes the following steps: S1: Raw material pretreatment; The graded fine aggregate is placed in a ventilated and dry environment and pre-dried to a moisture content of ≤1%; Nano silica is ultrasonically dispersed for 15-20 minutes with a dispersion power of 300-350W to obtain a pre-dispersed admixture. S2: Dry material mixing; Add P.O52.5 grade cement, high-purity silica fume, F-class I grade fly ash, fly ash microspheres, graded fine aggregate and pre-dispersed nano silica into a vertical shaft planetary mixer and dry mix for 1-3 minutes until uniformly mixed; S3: Wet mixing adjustment; Add 80% water and all of the polycarboxylate superplasticizer to the dry mixture, stir for 3-4 minutes, add the remaining water, and continue stirring for 1-2 minutes to make the mixture reach the fluidized state. S4: Fiber dispersion; slowly and evenly add copper-plated steel fibers to the mixer, controlling the feeding time to be completed within 2-3 minutes, and then continue to stir for 3-4 minutes until the steel fibers are evenly distributed and there is no clumping. S5: Casting and molding; The mixed ultra-high performance concrete (UHPC) is poured into a mold pre-coated with release agent, and vibrated for 0.5 minutes using a high-frequency vibrating table at a vibration frequency of 50-60Hz to remove internal air bubbles. S6: Multi-stage steam curing, including the following stages; a. Static resting stage: Let stand for 6-8 hours at 20-25℃ and relative humidity ≥80%; b. Temperature rising stage: temperature rising to 85-90℃ at a rate of ≤15℃ / h; c. Temperature keeping and steaming stage: keeping temperature at 90℃±1℃ and relative humidity ≥90% for 3 days; d. Temperature falling stage: temperature falling to room temperature at a rate of ≤15℃ / h, and humidity is maintained at 85-90% during the falling process.

Images