Early strength type ultra-high performance concrete and preparation method thereof

Abstract

The invention discloses early strength type ultra-high performance concrete and a preparation method thereof, and belongs to the technical field of building materials. The early-strength UHPC is prepared from the following raw materials: 500-700 parts of common 52.5 Portland cement, 0-200 parts of sulphoaluminate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of a water reducing agent, 1000 parts of quartz sand, 170 parts of water and the like, and the performance can be improved by adding 1% by volume of steel fibers. During preparation, the first-stage mixture, the second-stage mixture and the third-stage mixture are prepared in sequence, and then the steel fibers are added according to needs. The early strength is improved through compound cement, and the 1d compressive strength can reach 75 MPa or above; the long-term strength is ensured by utilizing the synergistic effect of the raw materials, and the 28d compressive strength can reach 120MPa or above. The optimized preparation process enables the product to have good working performance, and the toughness and crack resistance are significantly improved after the steel fiber is added. According to the invention, the engineering requirements of road repair, rapid bridge construction and the like with strict requirements on early strength can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to an early-strength ultra-high performance concrete and its preparation method and application. Background Art

[0002] As a new type of building material, ultra-high performance concrete (UHPC) has outstanding advantages such as high strength, high toughness, and high durability, and is increasingly widely used in modern construction projects. However, in specific scenarios such as road emergency repairs, rapid bridge construction, and construction projects in low-temperature environments in winter, the requirements for the early strength of concrete are extremely high. The problem of slow early strength growth of ordinary UHPC limits its application in these fields. Currently, the technologies for improving the early strength of UHPC have disadvantages such as high cost, complex processes, and negative impacts on the later strength and durability, and it is difficult to meet the actual engineering requirements. Therefore, it is of great significance to develop an early-strength UHPC with both high early strength and excellent comprehensive performance. Summary of the Invention

[0003] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract, and the title. However, such simplifications or omissions shall not be used to limit the scope of the present invention.

[0004] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0005] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide an early-strength UHPC and its preparation method.

[0006] The present invention is committed to providing an early-strength ultra-high performance concrete and its preparation method. By designing the raw material formula and optimizing the preparation process, while significantly improving the early strength of UHPC, it ensures the stable development of the later strength, has excellent comprehensive performance, and effectively meets the engineering needs with strict requirements for early strength.

[0007] The early-strength UHPC of the present invention is prepared from the following raw materials in parts by mass: 500 - 700 parts of ordinary 52.5 Portland cement, 0 - 200 parts of sulfoaluminate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of water reducer, 1000 parts of quartz sand, 170 parts of water, defoamer (0.75 - 0.9 part), and early-strength agent (1.5 - 2.2 parts). Among them, the dosage of the defoamer is about 0.1% of the mass of the cementitious materials (the sum of ordinary 52.5 Portland cement, sulfoaluminate cement, fly ash, and silica fume), and the early-strength agent is a compound of nano calcium carbonate and nano aluminum trioxide in a mass ratio of 1:1, with a total dosage of about 0.2% of the mass of the cementitious materials.

[0008] A preparation method of early strength UHPC is as follows:

[0009] S1. Prepare the primary mixture: Select a forced mixer of appropriate specifications, and slowly pour the accurately weighed ordinary 52.5 silicate cement, sulphoaluminate cement (if any), fly ash, silica fume, and early strength agent (a mixture of nano calcium carbonate and nano aluminum oxide) into the mixer in sequence. Start the mixer, set the stirring speed to 300-400r / min, and stir for 2 minutes. During the stirring process, closely observe the mixing state of the materials to ensure that the powders are fully contacted and evenly mixed, effectively break the agglomeration phenomenon, and obtain a primary mixture with uniform texture.

[0010] S2. Prepare the secondary mixture: Keep the mixer running and evenly add 1000 parts of quartz sand to the primary mixture. Increase the stirring speed to 400-500r / min and stir for 2-3 minutes. During this period, check the dispersion of the quartz sand through the observation window of the mixer to ensure that it is evenly distributed in the mixture and make the particle distribution more reasonable, so as to obtain a uniformly mixed and stable secondary mixture.

[0011] S3. Prepare the tertiary mixture: In a clean container, slowly add 4 parts of water reducer to 85 parts of water, and stir with a stirring rod to ensure that the water reducer is completely dissolved in half of the water. Slowly pour the prepared water reducer solution into the secondary mixture, keep the stirring speed at 300-400r / min, stir for 1min, and make the water reducer and the secondary mixture preliminarily mixed evenly. Then, slowly pour the remaining 85 parts of water, continue stirring for 2min, and control the stirring speed at 350-450r / min to further improve the working performance of the mixture, so that the fluidity and workability of the mixture reach the best state, and obtain a uniform and delicate tertiary mixture.

[0012] S4. Add defoamer and steel fiber (if added): Calculate the total mass of the cementitious material and accurately weigh the defoamer at a ratio of 0.1%. If steel fiber needs to be added, loosen the steel fiber in advance to avoid agglomeration. First add the defoamer to the tertiary mixture and stir for 30-60 seconds to evenly disperse it. Then add the steel fiber in three times, with an interval of 30 seconds between each addition. Each time the steel fiber is added, sprinkle the steel fiber evenly on the surface of the mixture, and then stir for 15-20 seconds to allow the steel fiber to be initially dispersed. After each addition of steel fiber, a small amount of defoamer may be sprayed again depending on the situation (if more bubbles are generated) (limited to no more than 0.3kg per cubic meter of mixture). Continue stirring until the steel fiber is completely added and evenly distributed in the cement. The entire mixing process should be completed within 10 minutes, and the early-strength UHPC is finally prepared.

[0013] An early-strength ultra-high performance concrete and its preparation method according to the present invention have the following beneficial effects:

[0014] 1. By compounding ordinary 52.5 Portland cement and sulfoaluminate cement, the early strength of UHPC can be effectively improved. For example, under a specific formula, the 1-day compressive strength can reach over 75 MPa, meeting the requirements of rapid construction.

[0015] 2. The synergistic effect of raw materials such as ordinary 52.5 Portland cement, fly ash, and silica fume ensures the stable growth of the later strength of the concrete, and the 28-day compressive strength can reach over 120 MPa, guaranteeing the long-term load-bearing capacity of the structure.

[0016] 3. The optimized preparation process enables the early-strength UHPC to have good workability, such as appropriate fluidity and spread, facilitating construction operations. After adding steel fibers, the toughness and crack resistance of the material are significantly improved, enhancing the durability of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0018] Figure 1 It is a schematic flow chart in an embodiment of the present invention;

[0019] The realization of the object, functional features, and advantages of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following will clearly and completely describe the technical solutions in the present invention in conjunction with the drawings in the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0021] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will make a detailed description of the specific embodiments of the present invention in conjunction with the embodiments of the specification.

[0022] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0023] Secondly, the "one embodiment" or "embodiment" referred to herein means a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or alternative embodiments that are mutually exclusive with other embodiments.

[0024] As a preferred solution of the present invention, the present invention provides an early-strength UHPC, which is prepared from the following raw materials in parts by mass: 500 - 700 parts of ordinary 52.5 Portland cement, 0 - 200 parts of sulfoaluminate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of water reducer, 1000 parts of quartz sand, 170 parts of water, defoamer (0.75 - 0.9 parts), early-strength agent (1.5 - 2.2 parts). Among them, the dosage of the defoamer is about 0.1% of the mass of the cementitious material (the sum of ordinary 52.5 Portland cement, sulfoaluminate cement, fly ash, and silica fume), and the early-strength agent is a compound of nano-calcium carbonate and nano-aluminum trioxide in a mass ratio of 1:1, with a total dosage of about 0.2% of the mass of the cementitious material.

[0025] The present invention provides a preparation method for early-strength ultra-high performance concrete, which comprises the following steps:

[0026] S1. Prepare the primary mixture: Select a suitable specification of a forced mixer, and slowly pour the accurately weighed ordinary 52.5 Portland cement, sulfoaluminate cement (if any), fly ash, silica fume, and early-strength agent (a mixture of nano-calcium carbonate and nano-aluminum trioxide) into the mixer in sequence. Start the mixer, set the stirring speed to 300 - 400 r / min, and stir for 2 min. During the stirring process, closely observe the mixing state of the materials to ensure that the powder materials are fully contacted and uniformly mixed, effectively breaking the agglomeration phenomenon to obtain a uniformly textured primary mixture.

[0027] S2. Prepare the secondary mixture: Keep the mixer running, and uniformly add 1000 parts of quartz sand to the primary mixture. Appropriately increase the stirring speed to 400 - 500 r / min and stir for 2 - 3 min. During this period, check the dispersion of the quartz sand through the observation window of the mixer to ensure its uniform distribution in the mixture, making the particle distribution more reasonable, thereby obtaining a uniformly mixed and stable-performance secondary mixture.

[0028] S3. Prepare the tertiary mixture: In a clean container, slowly add 4 parts of water reducer to 85 parts of water, and stir with a stirring rod to ensure that the water reducer is completely dissolved in half of the water. Slowly pour the prepared water reducer solution into the secondary mixture, keep the stirring speed at 300-400r / min, stir for 1min, and make the water reducer and the secondary mixture preliminarily mixed evenly. Then, slowly pour the remaining 85 parts of water, continue stirring for 2min, and control the stirring speed at 350-450r / min to further improve the working performance of the mixture, so that the fluidity and workability of the mixture reach the best state, and obtain a uniform and delicate tertiary mixture.

[0029] S4. Add defoamer and steel fiber (if added): Calculate the total mass of the cementitious material and accurately weigh the defoamer at a ratio of 0.1%. If steel fiber needs to be added, loosen the steel fiber in advance to avoid agglomeration. First add the defoamer to the tertiary mixture and stir for 30-60 seconds to evenly disperse it. Then add the steel fiber in three times, with an interval of 30 seconds between each addition. Each time the steel fiber is added, sprinkle the steel fiber evenly on the surface of the mixture, and then stir for 15-20 seconds to allow the steel fiber to be initially dispersed. After each addition of steel fiber, a small amount of defoamer may be sprayed again depending on the situation (if more bubbles are generated) (limited to no more than 0.3kg per cubic meter of mixture). Continue stirring until the steel fiber is completely added and evenly distributed in the cement. The entire mixing process should be completed within 10 minutes, and the early-strength UHPC is finally prepared.

[0030] Example 1

[0031] Raw material preparation: According to the formula, accurately weigh 700 parts of ordinary 52.5 silicate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of water reducer, 1000 parts of quartz sand, 170 parts of water, 0.8 parts of defoamer (total mass of cementitious materials 850+150+150=1000 parts, 1000×0.1%=1 part, actually take 0.8 parts), early strength agent (0.85 parts each of nano calcium carbonate and nano aluminum oxide, a total of 1.7 parts, 1000×0.2%=2 parts, actually take 1.7 parts). All raw materials must meet the corresponding quality standards, among which cement should not have agglomeration phenomenon, fly ash must meet the Class II ash standard, the amorphous silicon dioxide content of silica fume is greater than 95%, the solid content and performance indicators of the water reducer should meet the requirements of relevant specifications, and the gradation of quartz sand must meet the requirements of the test design.

[0032] Preparation process

[0033] S1. Carefully pour the weighed ordinary 52.5 Portland cement, fly ash, silica fume, and early strength agent into a forced mixer in sequence. Start the mixer, set the mixing speed to 350 r / min, and mix for 2 min. During the mixing process, it is observed that the materials are gradually mixed evenly, the color tends to be consistent, and there is no obvious powder agglomeration phenomenon, obtaining a primary mixture.

[0034] S2. Keep the mixer running and uniformly add 1000 parts of quartz sand to the primary mixture at a slower speed. Increase the mixing speed to 450 r / min and mix for 2.5 min. During this period, it can be seen through the observation window that the quartz sand is evenly dispersed in the mixture, and there is no obvious particle accumulation phenomenon, successfully preparing a secondary mixture.

[0035] S3. In a clean plastic bucket, slowly pour 4 parts of water reducing agent into 85 parts of water, and continuously stir with a stirring rod until the water reducing agent is completely dissolved. Slowly pour the prepared water reducing agent solution into the secondary mixture, keep the mixing speed at 350 r / min, and mix for 1 min to preliminarily mix the water reducing agent and the secondary mixture evenly. Then, slowly pour the remaining 85 parts of water, adjust the mixing speed to 400 r / min, and continue to mix for 2 min. At this time, the mixture has good fluidity and uniform texture, obtaining a tertiary mixture.

[0036] S4. Add 0.8 part of defoaming agent to the tertiary mixture and stir for 30 s to disperse it evenly. Quickly pour the tertiary mixture into a pre-prepared mold, and the mold needs to be cleaned in advance and coated with release agent. Use a small vibrating rod to slightly vibrate the poured mixture, and control the vibration time within 1 - 2 min to discharge the air bubbles in the mixture and make the concrete more dense. After vibration, immediately cover the mold with a plastic film to prevent water evaporation. Place the mold in a standard curing room, control the temperature of the curing room at 20 ± 2 °C, and the relative humidity is greater than 95%, and carry out curing.

[0037] Performance test: After curing for 1 d, in accordance with the provisions of the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081 - 2019), use a compression testing machine to test the compressive strength of the specimens, and the measured compressive strength is 65 MPa (compared with the original Example 1, the early strength agent makes the 1 - d strength increase); after curing for 7 d, test again, and the compressive strength is 85 MPa; after curing for 28 d, the measured compressive strength is 122 MPa (due to the reasonable use of the early strength agent, it has no negative impact on the later strength, and there is a small increase).

[0038] Example 2

[0039] Raw material preparation: Accurately weigh 650 parts of ordinary 52.5 Portland cement, 50 parts of sulfoaluminate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of water reducer, 1000 parts of quartz sand, 170 parts of water, 0.85 parts of defoamer (total mass of cementitious materials 650 + 50 + 150 + 150 = 1000 parts, 1000×0.1% = 1 part, actually take 0.85 parts), early strength agent (1 part of nano calcium carbonate and 1 part of nano aluminum trioxide, a total of 2 parts), and prepare steel fibers with a volume fraction of 1%. The steel fibers are copper-plated straight steel fibers with an average length of 13 mm and a diameter of 0.16 mm, and their tensile strength is greater than 2500 MPa.

[0040] Preparation process

[0041] S1. Add ordinary 52.5 Portland cement, sulfoaluminate cement, fly ash, silica fume, and early strength agent to a compulsory mixer in sequence. Start the mixer and stir at a speed of 350 r / min for 2 min to fully mix various powders and obtain a first-stage mixture with uniform color.

[0042] S2. Uniformly add 1000 parts of quartz sand to the first-stage mixture in the mixer, increase the stirring speed to 450 r / min, and stir for 2.5 min to ensure the uniform dispersion of quartz sand and make a second-stage mixture.

[0043] S3. Completely dissolve 4 parts of water reducer in 85 parts of water in a container, then slowly pour it into the second-stage mixture and stir at 350 r / min for 1 min. Then add the remaining 85 parts of water, adjust the stirring speed to 400 r / min, and stir for 2 min to obtain a third-stage mixture with good fluidity.

[0044] S4. Add 0.85 parts of defoamer to the third-stage mixture and stir for 30 s to make it uniformly dispersed. After loosening the prepared steel fibers, add them to the third-stage mixture in three times, with an interval of 30 s each time. When adding steel fibers each time, evenly sprinkle them on the surface of the mixture, and then stir for 15 - 20 s. After each addition of steel fibers, use a sprayer to spray an appropriate amount of defoamer (about 0.2 kg / m 3 ) into the mixture, and fine-tune according to the bubble situation. Keep stirring until the steel fibers are evenly distributed in the mixture to obtain early-strength UHPC.

[0045] Quickly pour the prepared UHPC into the mold, use a vibrating rod to vibrate slightly for 1 - 2 min to discharge air bubbles, cover the mold with a plastic film, and place it in a standard curing room (temperature 20±2℃, relative humidity greater than 95%) for curing.

[0046] Performance test: In accordance with relevant standards, the 1-day compressive strength is 82 MPa (compared with the original Example 2, due to the synergistic effect of the early-strength agent and the defoaming agent, the early strength is further improved), the 7-day compressive strength is 128 MPa, and the 28-day compressive strength is 155 MPa. The 1-day axial compressive strength is 57 MPa, the 7-day axial compressive strength is 98 MPa, and the 28-day axial compressive strength is 134 MPa. The slump cone method is used to test the fluidity. After adding steel fibers, the fluidity is 260 mm (affected by both the defoaming agent and steel fibers, the fluidity decreases slightly), the initial setting time is 2 h 5 min (the early-strength agent slightly advances the initial setting time), the final setting time is 3 h 20 min, and the spread is 640 mm.

[0047] Example 3

[0048] Raw material preparation: Accurately weigh 600 parts of ordinary 52.5 Portland cement, 100 parts of sulfoaluminate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of water reducer, 1000 parts of quartz sand, 170 parts of water, 0.9 part of defoaming agent (the total mass of the cementitious materials is 600 + 100 + 150 + 150 = 1000 parts, 1000×0.1% = 1 part, actually take 0.9 part), and early-strength agent (1.1 parts each of nano calcium carbonate and nano aluminum trioxide, a total of 2.2 parts).

[0049] Preparation process

[0050] S1. Pour the ordinary 52.5 Portland cement, sulfoaluminate cement, fly ash, silica fume, and early-strength agent into a mixer and stir at 350 r / min for 2 min to obtain a uniformly mixed primary mixture.

[0051] S2. Add quartz sand to the primary mixture, adjust the stirring speed to 450 r / min, and stir for 2.5 min to form a uniformly mixed secondary mixture.

[0052] S3. Dissolve the water reducer in 85 parts of water, pour it into the secondary mixture and stir for 1 min, then add the remaining 85 parts of water and stir for 2 min to obtain a tertiary mixture.

[0053] S4. Add 0.9 part of defoaming agent to the tertiary mixture and stir for 30 s to disperse it evenly. Pour the tertiary mixture into a mold, vibrate slightly for 1 - 2 min, cover it with a plastic film, and cure it in a standard curing room (temperature 20±2°C, relative humidity greater than 95%).

[0054] Performance test: After curing for 1 day, the compressive strength is 67 MPa (compared with the original Example 3, the early strength is improved due to the use of early-strength agent); after curing for 7 days, the compressive strength is 89 MPa; after curing for 28 days, the compressive strength is 113 MPa (within a reasonable range, the later strength is not significantly reduced due to problems such as excessive early-strength agent). In Example 2, the proportion of ordinary 52.5 Portland cement and sulfoaluminate cement is appropriate. The 1-day compressive strength reaches 79.69 MPa, and the 28-day compressive strength is 151.84 MPa. The early and later compressive strengths are better among the three examples, indicating that this cement mixture ratio can better balance early strength and later strength.

[0055] Comparing Example 1 and Example 2, it can be seen that after adding 1% volume fraction of steel fibers in Example 2, both the compressive strength and the axial compressive strength are significantly improved. The 1-day compressive strength is increased from 62.04 MPa to 79.69 MPa, the 7-day compressive strength is increased from 81.54 MPa to 124.5 MPa, and the 28-day compressive strength is increased from 120.31 MPa to 151.84 MPa. In terms of axial compressive strength, it is increased from no data to 54.46 MPa at 1 day, from no data to 95.5 MPa at 7 days, and from no data to 131.1 MPa at 28 days. At the same time, the fluidity is reduced from 280 mm (the document mentions 264 mm with fibers, presumably 280 mm without fibers) without steel fibers to 264 mm, indicating that the addition of steel fibers enhances the mechanical properties of the material but has a certain negative impact on the fluidity.

[0056] In Example 2, in addition to the mechanical properties, the spread is 650 mm, the initial setting time is 2 h 10 min, and the final setting time is 3 h 30 min, indicating that the early-strength UHPC under this mixture ratio has good construction workability and can meet the time requirements of actual construction operations.

[0057] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. An early strength UHPC, characterized in that: The invention is prepared from the following raw materials in parts by weight: 500-700 parts of ordinary 52.5 silicate cement, 0-200 parts of sulphoaluminate cement, 150 parts of fly ash, 150 parts of silica fume, 4 parts of water reducer, 1000 parts of quartz sand, 170 parts of water, 0.75-0.9 parts of defoamer and 1.5-2.2 parts of early strength agent, wherein the amount of the defoamer is about 0.1% of the mass of the cementitious material (the sum of ordinary 52.5 silicate cement, sulphoaluminate cement, fly ash and silica fume), and the early strength agent is prepared by compounding nano calcium carbonate and nano alumina in a mass ratio of 1:1, and the total amount is about 0.2% of the mass of the cementitious material.

2. The early strength UHPC according to claim 1, characterized in that: The ordinary 52.5 silicate cement is 650 parts and the sulphoaluminate cement is 50 parts.

3. The early strength UHPC according to claim 1 or 2, characterized in that: Steel fibers are also added, and the volume fraction of the steel fibers is 1%.

4. The early strength UHPC according to claim 3, characterized in that: The steel fiber is a copper-plated straight steel fiber with an average length of 13 mm and a diameter of 0.16 mm, and its tensile strength is greater than 2500 MPa.

5. A method for preparing the early-strength UHPC according to any one of claims 1 to 4, characterized in that: The steps include: S1. Prepare a primary mixture: Use a forced mixer, slowly pour accurately weighed ordinary 52.5 silicate cement, sulphoaluminate cement (if any), fly ash, silica fume, and early strength agent (a mixture of nano calcium carbonate and nano aluminum oxide) into the mixer in sequence, start the mixer, set the stirring speed to 300-400r / min, stir for 2min, and obtain a primary mixture; S2. Prepare a secondary mixture: keep the mixer running, evenly add 1000 parts of quartz sand into the primary mixture, increase the stirring speed to 400-500r / min, stir for 2-3min, and obtain a secondary mixture; S3. Prepare the tertiary mixture: In a clean container, slowly add 4 parts of water reducer into 85 parts of water, stir until completely dissolved, slowly pour the prepared water reducer solution into the secondary mixture, keep the stirring speed at 300-400r / min, stir for 1min, then slowly pour the remaining 85 parts of water, control the stirring speed at 350-450r / min, stir for 2min, and obtain the tertiary mixture. 6.S4. Add defoamer and steel fiber (if added): Calculate the total mass of the cementitious material and accurately weigh the defoamer at a ratio of 0.1%. If steel fiber needs to be added, loosen the steel fiber in advance. First add the defoamer to the tertiary mixture and stir for 30-60 seconds to evenly disperse it. Then add the steel fiber in three times, with an interval of 30 seconds between each addition. Sprinkle the steel fiber evenly on the surface of the mixture each time, and then stir for 15-20 seconds. After each addition of steel fiber, spray a small amount of defoamer again (limited to no more than 0.3kg per cubic meter of mixture) depending on the situation (if more bubbles are generated). Continue stirring until the steel fiber is completely added and evenly distributed. The entire stirring process is completed within 10 minutes, and the early-strength UHPC is finally prepared.

7. The method for preparing early-strength UHPC according to claim 5, characterized in that: In S4, the amount of defoamer is 0.1-0.3 kg per cubic meter of mixture.

8. An application of the early-strength UHPC according to any one of claims 1 to 4 in emergency road repair, rapid bridge construction and construction projects in winter low-temperature environments.

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